Tesi sul tema "Optical cycle"
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1
Kim, Jung-Won 1976. "Toward single-cycle optical pulses". Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32336.
Abstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 143-151).
Single-cycle optical pulses, the never-before-achieved regime, have a great potential for attosecond science and phase-sensitive nonlinear optics. To achieve single-cycle optical pulses by active synchronization, three major steps are required. Firstly, two very stable and broadband mode-locked lasers with overlapping spectra are necessary. Secondly, a tight timing synchronization with timing jitter under one-tenth of the synthesized pulsewidth has to be implemented. Finally, the carrier-envelope offset frequency lock between two lasers completes the coherent pulse synthesis process. In this thesis, the major ideas, techniques, and experimental results for single-cycle optical pulse synthesis are presented. A broadband Cr:forsterite laser mode-locked by a semiconductor saturable absorber is designed and implemented. The output spectrum spans from 1080 nm to 1500 nm range, and has a 3-dB bandwidth of 90 nm. This is the broadest spectrum from a prismless Cr:forsterite laser to our best knowledge, and corresponds to a sub-20 fs Fourier-transform limited pulsewidth. A new broadband output coupler is designed to optimize the output spectrum of an octavespanning Ti:sapphire laser. The resulting combined spectrum covers 1.5 octave from 600 nm to 1500 nm and has a strong overlap in 1100 to 1200 nm range, which enables a strong beat-note signal between the two lasers. A tight timing synchronization between the two lasers is achieved by balanced cross-correlation. The resulting timing jitter is 300 attoseconds, which is less than one-tenth of the synthesized pulsewidth.
(cont.) For a high-quality pulse synthesis, an ultra-broadband 50:50 beam splitter, a bandpass filter beam splitter, and a tapping beam splitter are designed with optical thin-film multilayer structures. A novel scheme for synchronization of an RF-signal to the pulse train of a mode-locked laser is proposed. Currently the isolation of cross-talk between two locking loops for repetition rate and carrier-envelope phase is under investigation, and it is expected to generate true single- cycle optical pulses in the near future. Future work will include full characterization of the synthesized pulses with SPIDER (spectral phase interferometry for direct electric-field reconstruction) and novel phase-sensitive nonlinear optic experiments.
by Jung-Won Kim.
S.M.
2
Ališauskas, Skirmantas. "Infrared Few-Cycle Pulse Optical Parametric Amplifier". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101001_145118-06284.
Abstract (sommario):
Main objective of this thesis is to generate and amplify few cycle pulses in the infrared region. In this thesis, two approaches were introduced for few cycle pulse parametric amplification at 800 nm and 1.5 μm. First approach is dedicated for prospects for increasing average power of OPCPA via multi-beam pumping; the second approach is dedicated for generation of carrier-envelope-phase (CEP) stable high energy (up to tens of millijoules) few-cycle pulses at 1.5 μm.
An experimental investigation of two or three beams-pumped OPCPA system based on type I BBO crystal is presented. The 2nd OPA stage was pumped by two or three pump beams derived from independent Nd:YAG laser amplifiers. The efficiency of interaction was shown to be comparable to that of single-beam pumped OPA and diminishes only slightly due to cascaded parametric diffraction of interacting waves. The effect was observed and its impact on efficiency of parametric amplification process was shown to decrease at larger intersecting angles of pump. In the prospect, the use of multiple lasers for OPA pumping has an appeal for increasing the repetition rate and consequently the average power of an ultrashort pulse laser system. Finally, the concept and realization of hybrid system based on type II KTP OPCPA and filamentation are described. A CEP-stable 1.5 μm OPCPA system with pulse energies up to 12.5 mJ after 4 OPA stages is demonstrated. Furthermore, self-compression of CEP-stable 2.2 mJ, 74.4 fs, 1.57 μm input... [to full text]Disertacijos darbo tikslas – suformuoti ir parametriškai stiprinti kelių optinių ciklų trukmės impulsus infraraudonojoje srityje Šioje disertacijoje buvo tirtos dvi moduliuotosios fazės („čirpuotų“) impulsų parametrinio stiprinimo sistemos, stiprinančios ypač plataus spektro impulsus 800 nm bei 1,5 μm srityse. Pirmoji sistema skirta tirti galimybę didinti lazerinės spinduliuotės vidutinę galią keliais pluoštais kaupinamame parametriniame stiprintuve; antroji sistema skirta kelių optinių ciklų trukmės stabilios fazės impulsų formavimui 1,5 μm srityje. Disertacijoje aprašomas I tipo parametrinis stiprintuvas, kurio 2-oji pakopa buvo kaupinama dviem arba trimis nepriklausomų lazerinių šaltinių pluoštais. Nustatyta, kad parametrinį stiprintuvą kaupinant keliais pluoštais stebimas naujų erdvinių komponentų atsiradimas, kuriuos sąlygoja parametrinė pakopinė difrakcija, o tai mažina bendrą sistemos energetinio keitimo efektyvumą.. Darbo metu pademonstruota galimybė mažinti parametrinės difrakcijos sąlygotus nuostolius parametriniame stiprintuve derinant kampus tarp kaupinimo pluoštų. Taip pat pristatomas alternatyvus būdas formuoti didelės energijos (kelių dešimčių milidžaulių) kelių optinių ciklų trukmės stabilios fazės impulsus 1,5 μm srityje. Būdas paremtas sąlyginai siauro spektro 1,5 μm srityje stiprinimu II tipo KTP kristale bei spektro plėtra inertinėse dujose po stiprinimo. 4 pakopų parametriniame stiprintuve pasiekta iki šiol didžiausia 12,5 mJ impulso energija 1,5 μm... [toliau žr. visą tekstą]
3
Huang, Shu-Wei Ph D. Massachusetts Institute of Technology. "High-energy sub-cycle optical waveform synthesizer". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75634.
Abstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-157).
Over the last decade, the control of atomic-scale electronic motion by optical fields strong enough to mitigate the atomic Coulomb potential, has broken tremendous new ground with the advent of phase controlled high-energy few-cycle pulse sources. In particular, broadband optical parametric chirped pulse amplifier (OPCPA) has been investigated intensively in recent years to enable studies of novel strong-field physics phenomena such as high-harmonic generation (HHG) and strong-field ionization. Further investigation and control of these physical processes ask for the capability of waveform shaping on sub-cycle time scales, which requires a fully phase-controlled multiple-octave-spanning spectrum. To date, no single laser source can support a bandwidth of more than an octave. Coherent synthesis of pulses with different spectra, or wavelength multiplexing, presents a route towards obtaining a multi-octave spanning laser spectrum. The benefit of this approach lies in its modular design and scalability in both bandwidth and pulse energy. However, it was only recently laser scientists were able to successfully demonstrate coherent synthesis of two lasers albeit at low energy and high repetition rate. Achieving high pulse energy requires synthesis of low repetition rate pulses, which is a challenge because of the environmental perturbations typifying high-energy amplifiers. The technological advancements towards the ideal source for study and control of such strong-field physics are the focus of this thesis. The background reviews on femtosecond Ti:sapphire oscillators, carrier-envelope phase stabilization, chirped pulse amplifier, broadband OPCPAs, and HHG are given in Chapter 1. Chapter 2 starts with a discussion on the various properties of OPCPA which lends itself to the ideal building module for high-energy pulse synthesis. Then it is followed by a comprehensive optimization study and experimental results of broadband OPCPAs at different spectral ranges. In chapter 3, the first high-energy sub-cycle waveform synthesizer is presented. It is the prototype of a class of novel optical tools for atto-second control of strong-field physics experiments. Novel technologies that enable such a waveform synthesizer are described in details. At the end of the chapter, work towards the construction of a large-scale waveform synthesizer is included. Finally, the thesis is concluded by introducing some possible future directions.
by Shu-Wei Huang.
Ph.D.
4
He, Dong. "Efficient cycle algorithms for capacitated optical network design". Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/26919.
Abstract (sommario):
This thesis studies the cycle-based protection schemes for DWDM (Dense Wavelength Division Multiplexing) networks. We first present the MSCC (Min-Sum Cycle Cover) Algorithm for simultaneous detection and protection using the Eulerian graph theory, and then analyze the performance of the algorithm through making comparison of it with other algorithms.
By extending the features of algorithm SLA (Straddling Link Algorithm) and initial ideas for p-cycle candidate generation (operations called Add and Join), we formulate more advanced cycle-generation algorithms: SP-Add, SP-Join and SP-Merge. We then use the developed heuristic spare capacity planning algorithms based on weighted or unity capacity efficiency of p-cycles, WCIDA, to test the fully restorable p-cycle network design. In addition, two capacitated algorithms will be presented and compared with each other.
5
Siddiqui, Aleem 1977. "Few-cycle and cavity-enhanced optical parametric amplification". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79494.
Abstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 179-185).
Optical parametric amplifiers have emerged as important optical sources by extending the properties of few-cycle laser sources, which exist only in materials with sufficiently large gain bandwidths, to wide array of spectral ranges. The work reported in this thesis relates to two areas for the continued development of optical parametric amplification based sources. First, we present a white light seeded, carrier-envelope stable, degenerately pumped OPA producing near tranform-limited sub 7 fs , 3 [mu]J pulses at the driver wavelength from a long pulse, non-CEP stable Ti:sapphire regenerative amplifier. Problems to the spectral phase jump at the driver wavelength, 800 nm, were avoided by using a near infrared OPA to produce white light continuum down to 800 nm where the spectral phase is smooth. Secondly, enhancement cavities are used in conjunction with parametric amplifiers resulting in a new technique entitled, cavity-enhanced optical parametric chirped-pulse amplification (C-OPCPA). C-OPCPA increases the capabilities of nonlinear crystals and can allow continued scaling of parametric amplifier systems to high repetition rate. This work contains the first theoretical and experimental investigation of C-OPCPA. Numerically, passive pump pulse shaping of the intracavity pump power is shown to enable octave spanning gain. Experimentally, a first proof-of-principle experiment demonstrates a 78 MHz C-OPCPA with more than 50% conversion with under 1 W of incident pump power. A comparison to a single pass system shows improvements in the C-OPCPA of orders of magnitude in conversion efficiency and 3 fold increase in phase matching bandwidth in 10 and 20 mm periodically poled lithium niobate phase matched for parametric amplification with 1030 nm pump wavelength and a 1550 nm signal wavelength. A Yb-fiber laser based CPA system producing up to 5 W of 500 fs pulses comprises the pump source, and a Er-fiber laser the signal.
by Aleem Mohammad Siddiqui.
Ph.D.
6
Laban, Dane Edward. "Highly Nonlinear Optical Phenomena with Few-Cycle Light Pulses". Thesis, Griffith University, 2014. http://hdl.handle.net/10072/365337.
Abstract (sommario):
This thesis details two investigations of highly nonlinear optical phenomena using few-cycle light pulses. Specifically, self-focusing in air with carrier-envelope phase locked pulses and high-order harmonic generation from successive sources. Producing few-cycle light pulses with a sufficient intensity to observe these phenomena has only become possible with the recent development of mode-locked lasers. By observing the behaviour of atoms in such an intense electromagnetic field, new conclusions can be drawn on the nature of nonlinear phenomena.
Intense electromagnetic fields propagate nonlinearly and one effect that plays an important role in determining the propagation is the Kerr effect. This effect makes it possible for an intense light pulse to undergo self-focusing, in which the light modifies the spatial refractive index of the medium such that the light is brought to a focus. The position of the self-focus is determined by the power of the light pulse relative to a critical power for self-focusing that is a property of the medium. When using a few-cycle pulse, shifting the carrier-envelope phase alters the peak value of the electric field within the pulse envelope that determines the maximum instantaneous power achieved. In this thesis, self-focusing
in air with a 6.3 fs, 800 nm pulse was investigated. The critical power of self-focusing was measured to be 18 ± 1 GW. A first-order theory was developed and predicted that altering the carrier-envelope phase would shift the focus by 790 µm. When the experiment was performed, no change in the focus position
was observed and a 3σ upper limit to a fit of the data gave a total shift of 180 µm.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical Sciences
Science, Environment, Engineering and Technology
Full Text
7
Bates, Philip Kevin. "Optical parametric chirped pulse amplification in the few-cycle regime". Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445345.
8
Krogen, Peter Ra. "A novel few-cycle optical source in the mid-infrared". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93067.
Abstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 43-45).
In this thesis, I designed, simulated, and implemented a novel optical pulse generation system which is shown to be able to generate exceptionally short optical pulses in the mid-infrared, tunable from 2-4[mu]m with pulse widths as low as 1.5 optical cycles at 3.5[mu]m (18fs). Energies as high a 1[mu]J were achieved, representing a peak power of roughly 100MW, at a 1kHz repetition rate, with excellent beam quality. The system was based on adiabatic difference frequency generation in an aperiodically polled lithium niobate crystal of an amplified, mode-locked Ti:Sapphire laser system.
by Peter Ra Krogen.
S.M.
9
Krogen, Peter Ra. "A novel single-cycle optical source in the mid-infrared". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105945.
Abstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 90-106).
In this thesis, I demonstrate the generation of single-optical-cycle pulses in the mid-infrared, which are generated using adiabatic difference frequency in an aperiodically polled lithium niobate crystal. The input pulses were generated in amplified Ti:Sapphire laser system, the construction of which is covered in detail, along with complete characterization of the generated pulses. The generated pulses have a bandwidth spanning (1.8-4.5[mu]m), energy in excess of 1[mu]J at a 1kHz repetition rate, and are compressed to within 15% of their Fourier transform limited duration of 10fs, which is 1.1 optical cycles at their central wavelength of 2.6[mu]m, and represents a peak power well in excess of 100MW. Furthermore, intrinsic to the design of the system is the ability to shape both the spectral amplitude and phase of the generated pulses, which makes this source immediately suitable for applications requiring shaped pulses.
by Peter Ra Krogen.
Ph. D.
10
Hallberg, Oskar. "Simulation and optimization of a multi-TW few-cycle optical parametric synthesizer". Thesis, Umeå universitet, Institutionen för fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-142100.
Abstract (sommario):
The Light Wave Synthesizer 20 (LWS20) is an Optical Parametric Synthesizer (OPS) system used for relativistic attosecond physics research. The LWS20 performs OPS through the means of multiple two-color pumped Noncollinear Optical Parametric Chirped Pulse Amplification (NOPCPA) stages. NOPCPA is basedon the nonlinear optical effect Optical Parametric Amplification (OPA) which is only described analytically through simplified expressions. A natural route around this difficulty is through the means of numerical models. In this thesis a (2+1) dimensional simulation software [1], [2] is used to simulate the four currently present NOPCPA stages of the LWS20, operated under two different options. The simulationwill be key to the planned upgrade of the LWS20, propelling the system fromthe current 16 TW power [3] to the wanted 100 TW power domain. It is shown that the used software is able to, with some caveats, emulate the results achieved in a laboratory environment and that the two operational options are optimized under slightly different settings. Furthermore, some barely documented, albeit crucial, features of the simulation software have been exposed, indicating that it is not very well optimized for simulating the OPA processes of the LWS20. By increasing the pump energy of the simulation beyond the realisticlevel it is still possible to attain relatively realistic amplification and thus the software ought to prove a valuable tool for the planned system upgrade. Some alternative approaches to the continuation of the simulations are presented which would further increase the software’s usefulness in the process of expanding theLWS20. Historically, the LWS20 has been operated successfully under the sameconditions under the two possible operational options, but the simulations clearly show that an optimized set-up for one option is far from optimal for the other option. Therefore, there is a possibility to further optimize the LWS20, an idea worth pursuing in future experiments.
11
Ripin, Daniel Jacob 1973. "A few-cycle Cr⁴⁺:YAG laser and optical studies of photonic crystals". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8291.
Abstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002.Includes bibliographical references (p. 261-279).
A prismless Cr4+:YAG laser was used to generate 20 fs pulses at 1450 nm with a bandwidth of 190 nm FWHM. Intracavity group velocity dispersion was compensated with double-chirped mirrors. Pulse spectrum was observable from 1140 to >1700 nm. Broadband saturable Bragg reflectors were designed and used to ensure self-starting of 35 fs pulses in the ultrafast Cr4+:YAG laser or to generate picosecond pulses tunable from 1400 to 1525 nm. The mirrors were a 7-pair GaAs/AlxOy quarter-wave dielectric stack, and the absorber consisted of a InGaAs quantum well centered in a half-wave InP layer. Transmission was measured through a photonic bandgap crystal microcavity resonant near 1550 nm. Cavity quality factors as high as 360 were observed for cavities with a modal volume of only 2([lambda]/2n)3. Photonic crystals were used to enhance the total emission of a light emitting diode at 980 nm by 8-fold. At particular wavelengths, collected photoluminescence enhancements larger than 100 were observed.
by Daniel Jacob Ripin.
Ph.D.
12
Wan, Hui [Verfasser], e Jörg [Akademischer Betreuer] Wrachtrup. "Nonlinear optical microspectroscopy with few-cycle laser pulses / Hui Wan ; Betreuer: Jörg Wrachtrup". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1156611520/34.
13
Ridente, Enrico [Verfasser], e Ferenc [Akademischer Betreuer] Krausz. "Few-cycle optical waveforms for transient molecular fingerprinting / Enrico Ridente ; Betreuer: Ferenc Krausz". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2021. http://nbn-resolving.de/urn:nbn:de:bvb:19-285410.
14
Vaupel, Andreas. "High Energy, High Average Power, Picosecond Laser Systems to Drive Few-Cycle OPCPA". Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5881.
Abstract (sommario):
The invention of chirped-pulse amplification (CPA) in 1985 led to a tremendous increase in obtainable laser pulse peak intensities. Since then, several table-top, Ti:sapphire-based CPA systems exceeding the 100 TW-level with more than 10 W average power have been developed and several systems are now commercially available. Over the last decade, the complementary technology of optical parametric chirped-pulse amplification (OPCPA) has improved in its performance to a competitive level. OPCPA allows direct amplification of an almost-octave spanning bandwidth supporting few-cycle pulse durations at center wavelengths ranging from the visible to the mid-IR. The current record in peak power from a table-top OPCPA is 16 TW and the current record average power is 22 W. High energy, few-cycle pulses with stabilized carrier-envelope phase (CEP) are desired for applications such as high-harmonic generation (HHG) enabling attoscience and the generation keV-photon bursts. This dissertation conceptually, numerically and experimentally describes essential aspects of few-cycle OPCPA, and the associated pump beam generation. The main part of the conducted research was directed towards the few-cycle OPCPA facility developed in the Laser Plasma Laboratory at CREOL (University of Central Florida, USA) termed HERACLES. This facility was designed to generate few-cycle pulses in the visible with mJ-level pulse energy, W-level average power and more than 100 GW peak power. Major parts of the implementation of the HERACLES facility are presented. The pump generation beam of the HERACLES system has been improved in terms of pulse energy, average power and stability over the last years. It is based on diode-pumped, solid-state amplifiers with picosecond duration and experimental investigations are presented in detail. A robust system has been implemented producing mJ-level pulse energies with ~100 ps pulse duration at kHz repetition rates. Scaling of this system to high power (>30 W) and high peak power (50-MW-level) as well as ultra-high pulse energy (>160 mJ) is presented. The latter investigation resulted in the design of an ultra-high energy system for OPCPA pumping. Following this, a new OPCPA facility was designed termed PhaSTHEUS, which is anticipated to reach ultra-high intensities. Another research effort was conducted at CELIA (Univerist&"233; de Bordeaux 1, France) and aimed towards a previously unexplored operational regime of OPCPA with ultra-high repetition rates (10 MHz) and high average power. A supercontinuum seed beam generation has been established with an output ranging from 1.3 to 1.9 ?m and few ps duration. The pump beam generation has been implemented based on rod-type fiber amplifiers producing more than 37 W average power and 370 kW peak power. The utility of this system as an OPCPA pump laser is presented along with the OPA design. The discussed systems operate in radically different regimes in terms of peak power, average power, and repetition rate. The anticipated OPCPA systems with few-cycle duration enable a wide range of novel experimental studies in attoscience, ultrafast materials processing, filamentation, LIBS and coherent control.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
15
Wall, Simon. "Photo-induced dynamics in complex materials probed with femtosecond x-rays and few cycle optical pulses". Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510258.
16
Culver, Mary Evans. "Applications of chlorophyll a fluorescence in bio-optical models of phytoplankton biomass and productivity / by Mary Evans Culver". Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10966.
17
Favier, Marine. "Vers un instrument commercial pour la mesure des rapports isotopiques par Optical Feedback Cavity Enhanced Absorption Spectroscopy". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY106.
Abstract (sommario):
Les isotopes stables ont permis de faire des découvertes majeures en science, comme, la datation de l'apparition de l'oxygène sur Terre à partir des isotopes du soufre [1] et l'analyse des échanges entre le carbone atmosphérique et celui des autres réservoirs (biosphère, océans) à partir du rapport isotopique 13C/12C [2].Traditionnellement, les rapports isotopiques sont mesurés avec des spectromètres de masse dédiés (IRMS : « isotope ratio mass spectrometer »). Depuis une dizaine d’années, ils sont également remplacés par des spectromètres commerciaux basés sur la spectroscopie infrarouge. Ces nouveaux instruments peuvent quantifier en temps réel et in-situ les rapports isotopiques des petites molécules d’intérêt environnemental en phase gazeuse (notamment l’eau et le dioxyde de carbone). Cependant, dans certains cas, ces instruments sont inadaptés. Ils utilisent soit trop d'échantillon, ou sont trop coûteux, ou ne mesurent pas certains isotopes. C'est en particulier le cas des isotopes du soufre.Nous montrons dans ce travail deux prototypes d’instruments qui mesurent des rapports isotopiques par Optical Feedback Cavity Enhanced Absorption Spectroscopy (OFCEAS). Le premier instrument détermine le rapport 13C/12C dans des échantillons d’air atmosphérique contenant entre 200 et 500 ppmv de CO2. Les concentrations les plus basses de cette gamme sont typiques de celles de l’air atmosphérique datant d’une dizaine de milliers d’années. On retrouve cet air dans les bulles emprisonnées dans les carottes de glace. Les concentrations les plus élevées correspondent à celles de l’air atmosphérique actuel. Pour cet instrument nous avons mis en évidence, grâce à une étude systématique des variables du système, l'impact de la pression, de la température et des franges optiques sur la mesure du rapport 13C/12C. En limitant ces sources de bruit, nous avons obtenu une précision de 0.2‰ en 2 minutes sur la mesure du rapport 13C/12C avec une concentration de CO2 autour de 280 ppmv. Nous avons obtenu une précision de 0.05‰ en référençant alternativement la mesure d'un échantillon à celle d'un gaz standard dans un cycle de mesure d'une durée de 2h par échantillon.Le deuxième prototype est le premier opérant dans le proche infrarouge capable d’analyser les rapports isotopiques 33S/32S et 34S/32S. Pour cela, il utilise la molécule H2S en phase gazeuse. Les composés de soufre, tels que les sulfates, sont en effet facilement convertis en H2S, contrairement au SF6 et au SO2, qui sont les gaz employés par la méthode IRMS conventionnelle. Les performances de l'instrument ont été examinées en réalisant des mesures statique sur trois mélanges de H2S et d'azote, présentant trois enrichissements en soufre différents. Ces trois mélanges ont été synthétisés au laboratoire. Les trois enrichissements relatifs en soufre-34 (0‰, 42.6‰ et 83.6‰) et en soufre-33 (0 ‰, 2.81‰, 5.39‰) ont été rigoureusement calibrés par IRMS. Nos mesures OFCEAS s'accordent à 1‰ près avec les valeurs obtenues par spectrométrie de masse. La précision obtenue en moyennant les résultats de 3 injections comportant 12 minutes de mesure est de 0.08‰ sur les deux rapports isotopiques 33S/32S et 34S/32SThe study of stable isotopes has led to many important advances in science, such as, for example, the determination of the timing of the oxygenation of Earth’s atmosphere using sulfur isotopes [1] and the quantification of the exchanges of carbon between the atmosphere and other reservoirs (biosphere, oceans) from the analysis of the 13C/12C isotope ratio [2].The conventional method to measure such isotopic ratios is by means of isotope ratio mass spectrometry (IRMS). About ten years ago, commercial instruments appeared that enabled the measurement of isotopic ratios using infrared spectroscopy of small molecules in the gas phase of interest for environmental studies (notably water and carbon dioxide). However, for some applications these instruments are not well adapted, for example, because they require too much material, or too expensive, or not able to measure isotopes in question. This is in particular the case for sulfur isotopes.During this work two prototype instruments were developed for the analysis of isotopic ratios by means of Optical Feedback Cavity Enhanced Absorption Spectroscopy (OFCEAS). The first targets the 13C/12C isotopic ratio in atmospheric air samples containing between 200 and 500 ppmv of CO2.The lowest concentration of this range is typical of paleo-air trapped in bubbles in ice cores, whereas the higher concentrations are encountered in modern air samples. For this instrument we have shown, through a detailed and systematic study, the effect of pressure, temperature, and optical interference fringes on the measurement of the isotopic ratio. Mitigating these sources of errors has led to a performance characterized by a precision of 0.2‰ in 2 minutes on measurements at a concentration of about 280 ppmv and a precision of 0.05‰ when alternatingly referencing the sample measurement to that of a standard material in a measurement cycle with duration of 2h for one sample.The second instrument is the first of its kind being able to analyze the 33S/32S and 34S/32S ratios through near-infrared spectroscopy on H2S gas. Sulfur compounds, such as sulfate, are easily converted to H2S, but this is not the case for SF6 or SO2, which are the common gases used in the conventional IRMS method. The instrument was demonstrated by performing static measurements on three isotopically different samples of H2S – nitrogen mixtures. These local standard materials were synthesized by us, and shown to have relative enrichment levels of 0‰, 42.6‰ and 83.6‰ for 34S/32S, and 0 ‰, 2.81‰, and 5.39‰ for 33S/32S by IRMS analyses. Our laser spectrometer measurements agree to within 1‰ with the calibrated IRMS values. The precision obtained after averaging three 12-minute measurements is 0.08‰ for both isotopic ratios
18
Wang, Yicheng [Verfasser]. "Passive mode-locking of 2-μm solid-state lasers : Towards sub-10 optical cycle pulse generation / Yicheng Wang". Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1147758271/34.
19
Brown, Andrew Gavin. "Measurement and modelling of combustion in a spark ignition engine". Thesis, Brunel University, 1991. http://bura.brunel.ac.uk/handle/2438/5143.
Abstract (sommario):
A study has been conducted into the causes of cycle by cycle variations in combustion within a spark ignition engine, the best measured engine parameter to use for its characterization, and the effects that: ignition timing, equivalence ratio, fuel type, throttle position and knock, have upon it. A Ricardo E6 single cylinder variable compression ratio research engine was instrumented to allow measurement of: cylinder pressure, temperatures, speed, load, fuel flow and air flow. The engine was also fitted with an optical slice that allowed optical access to the combustion chamber and enabled measurement of the early flame speed (up to 10 mm from spark plug gap) using a laser schileren system. Cylinder pressure data were collected on a dedicated HP1000 computer for every degree of crank angle rotation for up to 300 successive cycles. A phenomenological model was developed for turbulent combustion that split the combustion process into three phases: early laminar burn, turbulent combustion, and final burn. The model allowed the study of the physical phenomena occurring within the combustion chamber and enabled insights to be gained into their effects on combustion and cyclic variations. The study showed: The variation in mixture strength has a far greater effect on the average and Coefficient of Variation (COV) values of all the combustion performance parameters, than does changing the fuel type. Cycle by cycle variations in combustion are best characterized by COV of imep. The onset of knock has no discernible effect on the COVs of the measured parameters. The part throttle results show higher COVs than at Wide Open Throttle (WOT) due to slower burn, supporting the theory that faster initial flame speeds reduce cyclic variations. The combustion model was used to support the hypothesis that cycle by cycle variations are caused by movement of the flame kernel by turbulence within the combustion chamber.
20
Talisa, Noah Brodzik. "Laser-Induced Damage and Ablation of Dielectrics with Few-Cycle Laser Pulses". The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1609243476481238.
21
Bäcklund, Tomas. "Development and validation of a system for clinical assessment of gait cycle parameter in patients with idiopathic normal pressure hydocephalus". Thesis, Umeå universitet, Institutionen för tillämpad fysik och elektronik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-82891.
Abstract (sommario):
A number of parameters have been identified as characteristic of the walking pattern in patients with INPH. Most of these have been identified through qualitative surveys and manually conducted test batteries. In order to obtain quantitative, standardized and objective measures, which enable studies based on larger patient populations and comparable results, there is a need for a user-friendly system that can measure specific key parameters over time in a reliable manner in everyday clinical work. Step height, width and the variability in the gait cycle are such parameters which are interesting research areas for this group of patient. Problems with balance and gait are very common in other patient groups as well, particularly in neurological diseases such as Parkinson's disease, multiple sclerosis and stroke. This is the reason that the development of this gait analyzer is performed. Giving access to a simple and objective method for estimating gait and balance ability in clinical routine investigations would increase the ability to provide the right kind of treatment, confirm treatment results, and conducting larger research studies. Therefore, this equipment can contribute to the assessment of diseases which contain impaired gait. As a first test of the usability and for the validation of accuracy and repeatability of the equipment a group of healthy volunteers was used. Results from tests on healthy subjects show god repeatability between measurements, for step width at normal gait the difference was -0,2 ±0,34 cm (mean, ±SD) and step height 0,69 ±3,34 cm. The stride time variability in the healthy group where very small 0,00048 ±0,00028 s2 with a difference between test of 0,000019 ±0,00038 s2. Three pilot patients have been tested where we have clearly seen indications of increased stride time variability and reduced step height.
22
Jargot, Gaëtan. "High-repetition rate CEP-stable few-cycle OPCPA sources in the short wavelength infrared/mid-infrared". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLO020.
Abstract (sommario):
Résumé : La génération d’impulsions de quelques cycles optiques stabilisées en CEP dans le moyen infrarouge utilisant la technique d’amplification paramétrique optique à fort taux de répétition est d’un grand intérêt pour diverses études de dynamiques ultra-brèves. Les travaux de cette thèse sont directement inscrits dans ce cadre. Nous décrivons un système émettant des impulsions dont le spectre est centré à 2.1 µm avec une durée de 19.5 fs et une énergie de 31 µJ opérant à 10 kHz avec une stabilité RMS de 0.54 %. Ce système se distingue de l’état de l’art par la mise en œuvre d’une technique de différence de fréquence en ligne permettant d’obtenir une stabilité de la CEP tir-à-tir de 107 mrad pendant quatre heures. De plus cette thèse à permis le dévelopement d’un dispositf émettant des impulsions de quelques cycles optiques à 1.55 µm opérant à haut taux de répétition (125 kHz). Ce système est le résultat de l’assemblage d’un amplificateur paramétrique optique et d’un systéme de compression non-lineaire dans une cellule multi-passage. La propagation non linéaire périodique dans la cellule en régime de dispersion anormale permet une compression solitonique, tout en moyennant les effets spatiaux de la nonlinéarité sur le faisceau. Nous démontrons ainsi l’autocompression d’impulsions initiales de 19 µJ 63 fs vers des impulsions en sortie de 14 µJ 22 fsAbstract : The generation of carrier envelope phase (CEP) stable few-cycle pulses in the SWIR/Mid-IR using optical parametric chirped pulse amplification (OPCPA) at high repetition rate is of great interest for several applications in ultrafast dynamics. During this thesis the work was primarily focused on the development of OPCPA sources for attosecond science. We present an OPCPA operating at 2.1 µm delivering 19.5 fs pules duration with an energy of 31 µJ at 10 kHz with a RMS energy stability of 0.54 %. An original architecture using an all-inline difference frequency generation stage allows performances beyond the state of the art in terms of CEP stability. We report RMS CEP fluctuations of 107 mrad RMS measured shot-to-shot over four hours. On another hand, the development of a high repetition rate (125 kHz) OPCPA coupled with an innovative nonlinear compression scheme is described. The OPCPA provides pulses centered at 1.55 µm, with a pulse duration of 63 fs with an energy of 19 µJ after compression. Then a nonlinear compression stage based on a soliton dynamics in a multipass cell is implemented. The periodic propagation inside the cell allows to retain the temporal nonlinear effects, while the spatial nonlinear effects are washed out by the distributed nature of the nonlinearity over a large number of passes. We report the self-compression of 63 fs pulse at 1.5 µm down to 22 fs with an energy of 14 µJ
23
Schröder, Birgit Eva. "Spatial and temporal dynamics of the terrestrial carbon cycle : assimilation of two decades of optical satellite data into a process-based global vegetation model". Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1759/.
Abstract (sommario):
This PhD thesis presents the spatio-temporal distribution of terrestrial carbon fluxes for the time period of 1982 to 2002 simulated by a combination of the process-based dynamic global vegetation model LPJ and a 21-year time series of global AVHRR-fPAR data (fPAR – fraction of photosynthetically active radiation). Assimilation of the satellite data into the model allows improved simulations of carbon fluxes on global as well as on regional scales.
As it is based on observed data and includes agricultural regions, the model combined with satellite data produces more realistic carbon fluxes of net primary production (NPP), soil respiration, carbon released by fire and the net land-atmosphere flux than the potential vegetation model. It also produces a good fit to the interannual variability of the CO2 growth rate.
Compared to the original model, the model with satellite data constraint produces generally smaller carbon fluxes than the purely climate-based stand-alone simulation of potential natural vegetation, now comparing better to literature estimates. The lower net fluxes are a result of a combination of several effects: reduction in vegetation cover, consideration of human influence and agricultural areas, an improved seasonality, changes in vegetation distribution and species composition.
This study presents a way to assess terrestrial carbon fluxes and elucidates the processes contributing to interannual variability of the terrestrial carbon exchange. Process-based terrestrial modelling and satellite-observed vegetation data are successfully combined to improve estimates of vegetation carbon fluxes and stocks. As net ecosystem exchange is the most interesting and most sensitive factor in carbon cycle modelling and highly uncertain, the presented results complementary contribute to the current knowledge, supporting the understanding of the terrestrial carbon budget.In der vorliegenden Arbeit wird anhand der Kombination eines dynamischen globalen Vegetationsmodells mit einer Zeitreihe von 21 Jahren optischer Satellitendaten eine realistische Abschätzung der terrestrischen Quellen und Senken von CO2 ermöglicht. Grundlage des hier vorgestellten neuen Modells stellt das dynamische globale Vegetationsmodell LPJ dar, ein prozessorientiertes Vegetationsmodell, das basierend auf ökophysiologischen Grundlagen die Vegetationsverteilung und -dynamik, Störungen (z.B. Feuer) und den Kohlenstoff- sowie den Wasserkreislauf modelliert. Die Kopplung des LPJ-DGVM erfolgte mit einer Zeitreihe globaler AVHRR-fPAR Daten (fPAR – Anteil photosynthetisch aktiver Strahlung), für den Zeitraum 1982 bis 2002 in einer räumlichen Auflösung von 0.5°. Als Ergebnis liegt nun eine globale raum-zeitliche Verteilung aller relevanten Kohlenstoffflüsse vor: Nettoprimärproduktion, Bodenrespiration, Nettoökosystemproduktion, durch Feuer und Ernte emittierter Kohlenstoff, sowie der in Biomasse und Boden gespeicherte Kohlenstoff. Verglichen mit dem Originalmodell haben sich durch die Einspeisung der Satellitendaten alle relevanten Kohlenstoffkomponenten verringert und zeigen nun bessere Übereinstimmung mit Literaturwerten. Die geringeren Kohlenstoffflüsse resultieren aus einer Kombination verschiedener Effekte: geringere Vegetationsbedeckung, Berücksichtigung der landwirtschaftlichen Nutzfläche, realistischere Abbildung der Saisonalität, Veränderung der Vegetationsverteilung und Verschiebung der Artenzusammensetzung. Die globalen Kohlenstoffflüsse werden mit dem vorgestellten Modell realistischer abgebildet als mit Ansätzen, die nur die potentiell natürliche Vegetation simulieren. Insbesondere die Quellen- und Senkendynamik unterliegt vielfältigen Prozessen, die mit einem Modell, dass auch die Bodenrespiration prozessorientiert berücksichtigt, verlässlich geschätzt wird.
24
Wittmann, Emanuel [Verfasser], e Eberhard [Akademischer Betreuer] Riedle. "Taming optical parametric amplification : stable few cycle pulses at 210 to 10000 nm from Ti:Sapphire and Yb-based lasers / Emanuel Wittmann ; Betreuer: Eberhard Riedle". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1206877715/34.
25
Ouillé, Marie. "Génération d'impulsions laser proches du cycle optique en durée pour l'interaction laser-matière relativiste à haute cadence". Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. http://www.theses.fr/2022IPPAE007.
Abstract (sommario):
Cette thèse expérimentale s’est essentiellement déroulée au Laboratoire d’Optique Appliquée à Palaiseau (France), sur un système laser capable de générer des impulsions proches du cycle optique en durée avec des énergies de plusieurs mJ à une cadence de 1 kHz : la Salle Noire 2. Ce système laser Titane:Sapphire est double CPA avec un filtre non-linéaire entre les deux étages (basé sur la génération d’onde de polarisation croisée ou ‘XPW’) pour améliorer le contraste temporel, suivi d’un étage de post-compression dans une fibre flexible étirée à cœur creux. Grâce à ce système, nous étudions l’interaction laser-matière en régime relativiste à haute cadence. Nous parvenons, d’une part, dans des jets de gaz, à accélérer des électrons dans le sillage du laser jusqu’ à une énergie de quelques MeV; et d’autre part, par interaction avec des miroirs plasma, à générer des harmoniques d’ordres élevés qui sont associées dans le domaine temporel à des impulsions attosecondes. Malgré la prouesse technique de ces expériences, les propriétés des faisceaux XUV et d’électrons ainsi générés restent encore peu compatibles avec des applications phares en aval. À la suite de travaux précédents en Salle Noire 2, l’objectif de cette thèse était d’obtenir des faisceaux aux propriétés stables, ce qui a été accompli en rendant le système laser plus stable et fiable, ainsi qu’en implémentant une boucle de contrôle rapide de la phase enveloppe-porteuse des impulsions laser. En variant la phase enveloppe-porteuse, nous avons ainsi pu générer des impulsions attosecondes uniques en formant une porte temporelle d’intensité relativiste à la surface du miroir plasma, et aussi produire des faisceaux d’électrons stables en énergie et en direction, en contrôlant l’injection d’ électrons dans l’accélérateur laser-plasma. De plus, différents régime d’interaction avec les miroirs plasma ont été étudiés expérimentalement, tels que l’accélération d’électrons dans les longs gr adients de densité plasma, et l’accélération de protons en face avant de la cible (la face sur laquelle le laser est incident) le long de la direction normale à la cible, afin de mesurer de nouvelles observables (spectre d’énergie des électrons, divergence des faisceaux de protons) et ainsi mieux comprendre la dynamique d’interaction laser-plasmaThis experimental thesis was essentially conducted at Laboratoire d’Optique Appliquée in Palaiseau (France), on a laser system capable of delivering near-single-cycle duration pulses containing a few mJ of energy at 1kHz repetition rate: the Salle Noire 2. This laser is a Titanium:Sapphire double CPA system with a nonlinear filter in between (based on the crossed polarized wave generation effect) for temporal contrast enhancement, followed by a stretched-flexible hollow-core-fiber based post-compression stage. Using this system, we study laser-matter interaction in the relativistic regime at high repetition rate. We can, on one hand, in gas jets, accelerate electrons in the wakefield of the laser up to several MeVs; and on the other hand, by interacting with plasma mirrors, generate high order harmonics which are associated to bright attosecond pulses in the time domain. Despite the technological prowess in these experiments, the properties of the XUV and electron beams thus generated remain scarcely compatible with the main applications downstream. Following up on previous works in Salle Noire 2, the objective of this thesis was to obtain beams with stable properties, which was achieved by making the laser system more stable and reliable, as well as implementing a fast carrier-envelope phase control loop. By varying the carrier-envelope phase of the laser pulses, we could generate XUV continua/isolated attosecond pulses by forming a relativistic-intensity temporal gate at the surface of the plasma mirror, and also produce electron beams exhibiting stable energy and angle of emission, by controlling the electron injection within the plasma accelerator. Additionally, different regimes of interaction with plasma mirrors were experimentally investigated, such as wakefield acceleration of electrons in long plasma density gradients, and the acceleration of protons on the target’s front side (onto which the laser impinges) along the target no rmal direction, in order to measure new observables (electron energy spectra, proton beam divergence) and thus gain deeper insights into the laser-plasma dynamics
26
Gervais, Martin. "Housing and optimal taxation in life-cycle economies". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0006/NQ42520.pdf.
27
Wei, Yu-Feng 1970. "Concurrent design for optimal quality and cycle time". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8859.
Abstract (sommario):
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 113-116).
Product and manufacturing system design are the core issues in product development and dominate the profitability of a company. In order to assess and optimize the product and manufacturing system design, an objective evaluation framework is needed. Despite the many existing tools for product and manufacturing system design, there is a missing link between the product design and the production performances under system variability. The goal of the thesis is to explore and understand the interactions among part design and tolerancing, processes and system variability, and system control decision, then provide an integrated model to assess the total cost in a system. This model will be used to aid part design, tolerancing, batching, as well as strategy analysis in process improvement. A two-stage modeling approach is used to tackle the problem: quality prediction and production prediction. The quality prediction model projects the process variations into the output quality variations at each manufacturing stage, then predict the yield rate from the stochastic behavior of the variations and the tolerance. The production prediction model projects the demand rate and variability, processing times and variability, yield rates and batch-sizes into the manufacturing cycle time and inventories. After the performances are predicted through the previous two models, concurrent optimization of part design, tolerance, and batch-sizes are achieved by varying them to find the minimum cost. A case study at Boeing Tube shop is used to illustrate this approach. The result shows that the costless decisions in part design, tolerancing, and batch- sizes can significantly improve the system performance. In addition, conducting them separately or without using the system performance as the evaluation criteria may only lead to the local optima.
by Yu-Feng Wei.
Ph.D.
28
Kapp, Konrad Phillip. "Optimal cycle dating of large financial time series". Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/17767.
Abstract (sommario):
The study of cycles in the context of economic time series has been active for many decades, if not centuries; however, it was only in recent decades that more formal approaches for identifying cycles have been developed. Litvine and Bismans (2015) proposed a new approach for dating cycles in financial time series, for purposes of optimising buysell strategies. In this approach, cycle dating is presented as an optimisation problem. They also introduced a method for optimising this problem, known as the hierarchical method (using full evaluation 2, or HR-FE2). However, this method may be impractical for large data sets as it may require unacceptably long computation time. In this study, new procedures that date cycles using the approach proposed by Litvine and Bismans (2015), were introduced, and were speciffically developed to be feasible for large time series data sets. These procedures are the stochastic generation and adaptation (SGA), buy-sell adapted Extrema importance identity sequence retrieval (BSA-EIISR) and buysell adapted bottom-up (BSA-BU) methods. An existing optimisation technique, known as particle swarm optimisation (PSO), was also employed. A statistical comparison was then made between these methods, including HR-FE2. This involved evaluating, on simulated data, the performance of the algorithms in terms of objective function value and computation time on different time series lengths, Hurst exponent, and number of buy-sell points. The SRace methodology (T. Zhang, Georgiopoulos, and Anagnostopoulos 2013) was then applied to these results in order to determine the most effcient methods. It was determined that, statistically, SGA, BSA-EIISR and BSA-BU are the most effcient methods. Number of buysell points was found to have the largest effect on relative performance of these methods. In some cases, the Hurst exponent also has a small effect on relative performance.
29
Weber, Tom. "Optimal timing of phase resolved cell cycle progression". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2015. http://dx.doi.org/10.18452/17253.
Abstract (sommario):
Selbstreproduktion ist eines der Kennzeichen aller lebenden Organismen. Der Zellzyklus dient der Selbstreproduktion in einzelligen Organismen. In mehrzelligen Organismen ist der Zellzyklus darüber hinaus für andere lebenswichtige Prozesse, einschließlich Immunreaktionen, unerlässlich. In dieser Arbeit wird eine Methode entwickelt mit der die Dauer der Zellzyklus Phasen bestimmt werden kann. Kenntnis über die Zellzyklusphasendauer ermöglicht vorherzusagen, wie schnell eine Population von proliferierenden Zellen wachsen wird, oder wie viele neue Zellen pro Stunde in einem Gewebe geboren werden. Im Kapitel 1 dieser Arbeit wird ein Zellzyklusmodell aufgestellt und mit experimentellen Bromdesoxyuridin Daten verglichen. Die Analyse zeigt, dass das Modell gut die experimentelle Kinetik beschreibt, hebt jedoch auch hervor dass einige der Parameter nicht identifiziert werden können. Dieses Problem wird in Kapitel 2 bearbeitet, wo zwei Ansätze erforscht werden, um den Informationsgehalt der Experimente zu erhöhen. In einem ersten Ansatz wird die Theorie der Versuchsplanung angewendet, um optimale Versuchspläne zu bestimmen. In einem zweiten Ansatz wird das übliche Bromdesoxyuridin Protokoll durch ein zweites Nukleosid erweitert. Beide Methoden verbessern in silico erheblich die Genauigkeit und Präzision der Abschätzungen. Im dritten Kapitel wird die Methodik in der Analyse der Keimzentrumsreaktion angewendet. Ein erheblicher Zufluss von Zellen in die dunkle Zone von Keimzentren wird vorhergesagt, und die Ansicht einer extrem schellen Zellteilung im Keimzentrum erscheint in dem Modell als ein Artefakt der Zellmigration.Self-reproduction is one of the distinguishing marks of living organisms. The cell cycle is the underlying process by which self-reproduction is accomplished in single-celled organisms. In multi-cellular organisms, the cell cycle is in addition indispensable for other vital processes, including immune reactions. In this thesis a method is developed that allows to estimate the time it takes for a dividing cells to complete the CC phases. Knowledge of the CC phase durations allows to predict, for example, how fast a population of proliferating cells will grow in size, or how many new cells are born per hour in a given tissue. In Chapter 1 of this thesis, a cell cycle model with delays and variability in the completion times of each phase is developed. Analytical solutions are derived to describe a common experimental technique used for cell cycle analysis, namely pulse labeling with bromodeoxyuridine (BrdU). Comparison with data shows that the model reproduces closely measured cell cycle kinetics, however also reveals that some of the parameter values cannot be identified. This problem is addressed in Chapter 2. In a first approach, the framework of D-optimal experimental designs is employed, in order to choose optimal sampling schemes. In a second approach, the prevailing protocol with a single nucleoside is modified by adding a second nucleoside analog pulse. Both methods are tested and the results suggest that experimental design can significantly improve parameter estimation. In Chapter 3, the model is applied to the germinal center reaction. A substantial influx of cells into the dark zone of germinal centers is predicted. Moreover the wide-held view of rapid proliferation in germinal centers, appears, under this model, as an artifact of cell migration.
30
Ališauskas, Skirmantas. "Kelių optinių ciklų trukmės impulsų parametrinis stiprinimas infraraudonojoje srityje". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101001_145146-49682.
Abstract (sommario):
Disertacijos darbo tikslas – suformuoti ir parametriškai stiprinti kelių optinių ciklų trukmės impulsus infraraudonojoje srityje Šioje disertacijoje buvo tirtos dvi moduliuotosios fazės („čirpuotų“) impulsų parametrinio stiprinimo sistemos, stiprinančios ypač plataus spektro impulsus 800 nm bei 1,5 μm srityse. Pirmoji sistema skirta tirti galimybę didinti lazerinės spinduliuotės vidutinę galią keliais pluoštais kaupinamame parametriniame stiprintuve; antroji sistema skirta kelių optinių ciklų trukmės stabilios fazės impulsų formavimui 1,5 μm srityje.
Disertacijoje aprašomas I tipo parametrinis stiprintuvas, kurio 2-oji pakopa buvo kaupinama dviem arba trimis nepriklausomų lazerinių šaltinių pluoštais. Nustatyta, kad parametrinį stiprintuvą kaupinant keliais pluoštais stebimas naujų erdvinių komponentų atsiradimas, kuriuos sąlygoja parametrinė pakopinė difrakcija, o tai mažina bendrą sistemos energetinio keitimo efektyvumą.. Darbo metu pademonstruota galimybė mažinti parametrinės difrakcijos sąlygotus nuostolius parametriniame stiprintuve derinant kampus tarp kaupinimo pluoštų. Taip pat pristatomas alternatyvus būdas formuoti didelės energijos (kelių dešimčių milidžaulių) kelių optinių ciklų trukmės stabilios fazės impulsus 1,5 μm srityje. Būdas paremtas sąlyginai siauro spektro 1,5 μm srityje stiprinimu II tipo KTP kristale bei spektro plėtra inertinėse dujose po stiprinimo. 4 pakopų parametriniame stiprintuve pasiekta iki šiol didžiausia 12,5 mJ impulso energija 1,5 μm... [toliau žr. visą tekstą]Main objective of this thesis is to generate and amplify few cycle pulses in the infrared region. In this thesis, two approaches were introduced for few cycle pulse parametric amplification at 800 nm and 1.5 μm. First approach is dedicated for prospects for increasing average power of OPCPA via multi-beam pumping; the second approach is dedicated for generation of carrier-envelope-phase (CEP) stable high energy (up to tens of millijoules) few-cycle pulses at 1.5 μm. An experimental investigation of two or three beams-pumped OPCPA system based on type I BBO crystal is presented. The 2nd OPA stage was pumped by two or three pump beams derived from independent Nd:YAG laser amplifiers. The efficiency of interaction was shown to be comparable to that of single-beam pumped OPA and diminishes only slightly due to cascaded parametric diffraction of interacting waves. The effect was observed and its impact on efficiency of parametric amplification process was shown to decrease at larger intersecting angles of pump. In the prospect, the use of multiple lasers for OPA pumping has an appeal for increasing the repetition rate and consequently the average power of an ultrashort pulse laser system. Finally, the concept and realization of hybrid system based on type II KTP OPCPA and filamentation are described. A CEP-stable 1.5 μm OPCPA system with pulse energies up to 12.5 mJ after 4 OPA stages is demonstrated. Furthermore, self-compression of CEP-stable 2.2 mJ, 74.4 fs, 1.57 μm input... [to full text]
31
Marchesini, Camilo. "Optimal Monetary Policy, Macroprudential Instruments, and the Credit Cycle". Thesis, Uppsala universitet, Nationalekonomiska institutionen, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388488.
Abstract (sommario):
I study optimal monetary and macroprudential policies in a New Keynesian DSGE framework with leverageconstrainedbanks. In particular, I assess the desirability of alternative operational policy rules when theeconomy is hit by mortgage default shocks and show that their implications for inflation dynamics and policytrade-offs depend on whether the shocks originate in the household sector or in the entrepreneurial sector ofthe economy. Moreover, I find that the strategy of ‘leaning against the wind’ (LAW) of credit growth deliverssystematically poorer stabilization outcomes than standard flexible inflation-targeting when there exists anon-trivial trade-off between stabilizing output and inflation, but outperforms conventional monetary policyfor shocks that generate a comovement between the two, irrespective of the real or financial nature of theshock.I show that optimal macroprudential regulation that is as concerned with output as monetary policy candrastically reduce, and in many cases completely eliminate, the incentive to lean against the wind. I arguethat this is due to the ability of full-fledged optimal macroprudential policy to break the favourable complementaritybetween stabilizing credit growth and stabilizing output growth which underlies the incentive tolean against the wind. Macroprudential policy proves a superior substitute to LAW because it can achieve thesame financial stability objectives without systematically imposing costs in terms of price stability.
32
O'Loughlin, R. L. "Optimal design of organic refrigerant reverse cycle absorption air conditioning systems /". Title page, contents and abstract only, 1986. http://web4.library.adelaide.edu.au/theses/09ENS/09enso52.pdf.
33
Taylor, Tracy A. "Optimal Control and Its Application to the Life-Cycle Savings Problem". VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4288.
Abstract (sommario):
Throughout the course of this thesis, we give an introduction to optimal control theory and its necessary conditions, prove Pontryagin's Maximum Principle, and present the life-cycle saving under uncertain lifetime optimal control problem. We present a very involved sensitivity analysis that determines how a change in the initial wealth, discount factor, or relative risk aversion coefficient may affect the model the terminal depletion of wealth time, optimal consumption path, and optimal accumulation of wealth path. Through simulation of the life-cycle saving under uncertain lifetime model, we are not only able to present the model dynamics through time, but also to demonstrate the feasibility of the model.
34
Yekoladio, Peni Junior. "Thermodynamic optimization of sustainable energy system : application to the optimal design of heat exchangers for geothermal power systems". Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/31615.
Abstract (sommario):
The present work addresses the thermodynamic optimization of small binary-cycle geothermal power plants. The optimization process and entropy generation minimization analysis were performed to minimize the overall exergy loss of the power plant, and the irreversibilities associated with heat transfer and fluid friction caused by the system components. The effect of the geothermal resource temperature to impact on the cycle power output was studied, and it was found that the maximum cycle power output increases exponentially with the geothermal resource temperature. In addition, an optimal turbine inlet temperature was determined, and observed to increase almost linearly with the increase in the geothermal heat source. Furthermore, a coaxial geothermal heat exchanger was modeled and sized for minimum pumping power and maximum extracted heat energy. The geofluid circulation flow rate was also optimized, subject to a nearly linear increase in geothermal gradient. In both limits of the fully turbulent and laminar fully-developed flows, a nearly identical diameter ratio of the coaxial pipes was determined irrespective of the flow regime, whereas the optimal geofluid mass flow rate increased exponentially with the Reynolds number. SeveORCs were observed to yield maximum cycle power output. The addition of an IHE and/or an Oral organic Rankine Cycles were also considered as part of the study. The basic types of the FOH improved significantly the effectiveness of the conversion of the available geothermal energy into useful work, and increased the thermal efficiency of the geothermal power plant. Therefore, the regenerative ORCs were preferred for high-grade geothermal heat. In addition, a performance analysis of several organic fluids was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n-pentane, were recommended for the basic type of ORCs, whereas those with lower vapour specific heat capacity, such as butane, were more suitable for the regenerative ORCs.Dissertation (MEng)--University of Pretoria, 2013.
Mechanical and Aeronautical Engineering
unrestricted
35
Ju, Min. "Optimisation de la protection des réseaux optiques de nouvelle génération". Thesis, Avignon, 2018. http://www.theses.fr/2018AVIG0226/document.
Abstract (sommario):
La tolérance aux pannes est une propriété très importante des réseaux optiques de nouvelle génération. Cette thèse aborde la conception des mécanismes de protection contre des pannes liées à la défaillance d’une fibre optique ou à une catastrophe naturelle. Deux systèmes de protection classiques, à savoir la protection par des cycles préconfigurés(p-cycles) et la protection du chemin de secours, sont étudiés pour atteindre une efficacité de protection élevée, tout en considérant le coût de l’équipement optique,la consommation d’énergie et l’utilisation de la ressource spectrale. Ces problèmes de survivabilité sont d’abord formulés en utilisant la programmation linéaire en nombres entiers (PLNE), et ensuite résolus soit par algorithmes heuristiques, soit par une approche de décomposition.La panne d’une seule fibre optique est le scénario le plus courant. Nous allons donc considérer d’abord des pannes liées à la défaillance d’une fibre optique dans les réseaux optiques multi-débit. Pour réduire le coût des transpondeurs, un système de protection par p-cycles de longueur adaptable et peu coûteux est proposé. Spécifiquement, les p cycles de longueur limitée sont conçus pour utiliser un débit approprié en fonction du coût du transpondeur et de la portée de transmission. Un modèle de programmation linéaire en nombres entiers (PLNE) sans énumération des cycles candidats est formulé pour générer directement les p-cycles de coût dépenses d’investissement minimum. De plus, un algorithme GPA (Graph Partitioning in Average) et un algorithme d’estimation des nombres de cycles (EI) sont développés pour rendre le modèle PLNE plus efficace au niveau du temps de calcul. En ce qui concerne la consommation d’énergie des réseaux optiques élastiques résilients,nous proposons d’utiliser un schéma de p-cycles dirigés, efficaces en énergie,pour protéger le trafic asymétrique. En raison de l’avantage de distinguer du volume de trafic dans les deux directions, les p-cycles dirigés consomment peu d’énergie en attribuant de créneaux ou slots du spectre et des formats de modulation différents à chaque direction.Un modèle PLNE est formulé pour minimiser la consommation d’énergie totale sous contraintes de génération du cycle dirigée, d’allocation de spectre, d’adaptation de modulation et de capacité de protection. Pour le passage à l’échelle, le modèle PLNE est décomposé en deux sous-problèmes: une méthode d’énumération de cycles améliorée et un modèle PLNE simplifié pour la sélection des cycles. Nous avons montré que les p-cycles dirigés obtiennent une meilleure performance comparant les p-cyclesiii non-dirigés pour le trafic asymétrique en termes de la consommation d’énergie et de l’utilisation du spectre.Afin d’améliorer l’efficacité d’utilisation du spectre dans réseaux optiques élastiques, une protection par p-cycles (SS-p-cycle) à spectre partagé est proposée. Les SS-p-cycles permettent de réduire l’utilisation du spectre et le taux de fragmentation spectrale en exploitant un partage de spectre spécial entre plusieurs p-cycles ayant des liens communs.Les modèles PLNE est conçus dans les cas "sans" ou "avec" conversion spectrale afin de minimiser l’utilisation du spectre. Ces modèles peuvent obtenir la solution optimale pour un petit réseaux optiques élastiques, et une heuristique efficace est développée pour résoudre les instances à grande échelle. Les résultats de simulations montrent que les SS-p-cycles ont des avantages significatifs pour réduire l’utilisation de la ressource spectrale et la défragmentation des fréquence. De plus, la conversion du spectre aide les SS-p-cycles à acquérir une meilleure utilisation du spectreNetwork survivability is a critical issue for optical networks to maintain resilience against network failures. This dissertation addresses several survivability design issues against single link failure and large-scale disaster failure in optical networks. Twoclassic protection schemes, namely pre-configured Cycles (p-Cycle) protection and path protection, are studied to achieve high protection capacity efficiency while taking intoaccount the equipment cost, power consumption and resource usage. These survivable network design problems are first formulated by mathematical models and then offered scalable solutions by heuristic algorithms or a decomposition approach.We first consider single link failure scenario. To cut the multi-line rates transponderscost in survivable Mixed-Line-Rate (MLR) optical networks, a distance-adaptive andlow Capital Expenditures (CAPEX) cost p-cycle protection scheme is proposed withoutcandidate cycle enumeration. Specifically, path-length-limited p-cycles are designed touse appropriate line rate depending on the transponder cost and transmission reach.A Mixed Integer Linear Programming (MILP) model is formulated to directly generate the optimal p-cycles with the minimum CAPEX cost. Additionally, Graph Partitioning in Average (GPA) algorithm and Estimation of cycle numbers (EI) algorithm are developed to make the proposed MILP model scalable, which are shown to be efficient.Regarding the power consumption in survivable Elastic Optical Networks (EONs),power-efficient directed p-cycle protection scheme for asymmetric traffic is proposed.Owing to the advantage of distinguishing traffic amount in two directions, directedp-cycles consume low power by allocating different Frequency Slots (FSs) and modulation formats for each direction. An MILP model is formulated to minimize total power consumption under constraints of directed cycle generation, spectrum assignment,modulation adaptation and protection capacity allocation. To increase the scalability, the MILP model is decomposed into an improved cycle enumeration and a simplified Integer Linear Programming (ILP) model. We have shown that the directedp-cycles out perform the undirected p-cycles in terms of power consumption and spectrum usage.In order to improve the spectrum usage efficiency in p-cycle protection, a SpectrumShared p-cycle (SS-p-cycle) protection is proposed for survivable EONs with and without spectrum conversion. SS-p-cycles permit to reduce spectrum usage and Spectrum Fragmentation Ratio (SFR) by leveraging potential spectrum sharing among multiplep-cycles that have common link(s). The ILP formulations are designed in both cases of with and without spectrum conversion to minimize the spectrum usage of SS-p-cycleswhich can obtain the optimal solution in small instance, and a time-efficient heuristic algorithm is developed to solve large-scale instances. Simulation results show that SSp-cycles have significant advantages on both spectrum allocation and defragmentation efficiency, and the spectrum conversion does help SS-p-cycle design to acquire better spectrum utilization
36
Bodnar, Nathan. "Phase-locking Stability of a Quasi-single-cycle Pulse". Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5606.
Abstract (sommario):
There is increasing interest in the generation of very short laser pulses, even down to attosecond (10-18 s) durations. Laser systems with femtosecond pulse durations are needed for these applications. For many of these applications, positioning of the maximum electric field within the pulse envelope can affect the outcome. The peak of the electric field relative to the peak of the pulse is called the Carrier Envelope Phase (CEP). Controlling the position of the electric field becomes more important when pulse duration approaches single-cycle. This thesis focuses on the stabilization of a quasi-single-cycle laser facility. Improvements to this already-established laser facility, HERACLES (High Energy, Repetition rate Adjustable, Carrier-Locked-to-Envelope System) described in this thesis include a stabilized pump line and the improvement in CEP stabilization electronics. HERACLES is built upon an Optical Parametric Chirped Pulse Amplification (OPCPA) architecture. This architecture uses Optical Parametric Amplification (OPA) as the gain material to increase the output energy of the system. OPA relies on a nonlinear process to generate high gain (106) with ultra-wide bandwidth. Instabilities in the OPA driving pump energy can create dynamically fluctuations in the final OPCPA output energy. To reduce these fluctuations two key upgrades were implemented on the pump beam. Both were major improvements in the stability. Firstly, an improved regenerative amplifier design reduced beam pointing fluctuations. Secondly, the addition of a pump monitoring system with feedback-control eliminated long-term power drifts. Both enhanced the OPA pulse-to-pulse and long-term stability. To improve the stability in measuring CEP drifts, modification of the feedback electronics was needed. The modification consisted of integrating noise reduction electronics. This novel noise reducer uses a similar process to a super-heterodyne receiver. The noise reducer resulted in 60 dB reduction of out-of-band noise. This led to increased signal quality with cleaner amplification of weaker signals. The enhanced signal quality led to more reliable long-term locking. The synthetically increased signal-to-noise ratio allows locking of the CEP frequency below the typically requirements. This integration allows relaxed constraints on the laser systems. The optics and electronics of a high-power, quasi-single cycle laser facility were improved. This thesis included the stabilization of the pump line and the stabilization of the CEP. This work allows for new long-duration experiments.M.S.
Masters
Optics and Photonics
Optics and Photonics
Optics; International
37
El-khawas, Ihab N. "The optimal design of buildings : a life-cycle approach to energy efficiency /". The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487948158626783.
38
Zhang, Xiaoying. "Contrast improvement of few-cycle pulses". Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-165565.
Abstract (sommario):
The intense few-cycle laser pulses play an important role in the investigations of laser-plasma interaction. However, one of the biggest challenges in their generation is the reduction of temporal intensity contrast by introducing undesired pre-pulses and a long pedestal. Two techniques were investigated in this work to improve the contrast. First, the crossed-polarized wave (XPW) generation was optimized to get clean pulse. The conditions for XPW were optimized including crystal thickness and maximal background pressure in the vacuum cell. Second, the method of elliptical polarization rotation (EPR) in a gas-filled hollow-core fiber (HCF) was implemented to produce both broadened and cleaned pulse, since its setup is much simpler. For the tested EPR-based nonlinear filter, the spectral smoothening and broadening were obtained. The contrast of cleaned pulse was characterized providing 2 order of magnitude contrast enhancement, while it had a high average power of 80 mW. The EPR-based nonlinear filter is a promising simplified technique in the development of intense few-cycle lasers.
39
Parks, Geoffrey Thomas. "Optimal in-core nuclear fuel cycles under integral constraint". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304442.
40
SALMAN, RAMIZ. "Identification of common economic cycles using optimal multivariate filters". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/394321.
Abstract (sommario):
This thesis includes two essays that are focused on developing multivariate filter approaches to be used for extracting common cyclical components where the common components can be used as an estimator of a business cycle.
The first chapter aims to develop an optimal multivariate filter in order to extract common cyclical components of macroeconomic indicators. The filter allows macroeconomic series to be modeled as a phase shifted version of a coinciding business cycle (BC) while keeping other time series components such as the stochastic trend and idiosyncratic shocks intact (i.e. they are individually specified for each series). Earlier studies of Rünstler (2004), Valle e Azevedo et al. (2006) have applied phase shift in the form of a delay parameter when specifying lead-lag cycles. However, the lead-lag relationship is defined by rotating the baseline cycle which leads to loss of information. This deficiency is especially important if one considers working in continuous time. Therefore, this paper improves on the former technique by allowing a more flexible phase shift mechanism on the original BC. This in turn should lead to more realistic estimates and filters considering that the underlying data is generated through a continuous time framework. The study starts by presenting a structure for bi-variate time series system and then extends to model to incorporate a structure for three time series and beyond. Kalman filter and smoothing recursions are applied to compute the smoothed cycle estimates and to construct the likelihood function. Using simulated data, we test both model specifications by carrying out a grid search of the initial delay parameter to see the likelihood behavior as the parameter moves into fractional neighborhoods. Afterwards, applying the methodology to a set of EU countries and macroeconomic indicators; the study aims to shed light to the presence of cyclical heterogeneity at country level economic activity for major EU member states. A second empirical study provides analysis on how the model can be implemented for assigning a lead/lag ordering to three main economic indicators of a single country.
The second chapter implements a multivariate non-parametric filtering approach; the Vertical Multivariate Singular Spectrum Analysis (V-MSSA) of Hassani and Mahmoudvand (2013) and Golyandina et al.
(2013). to be applied for identifying a common economic cycle indicator. The methodology is a data-driven procedure that can decompose a time series into many sub components. By exploiting this ability of the SSA, the paper aims to first extract cyclical components based on frequency characteristics and then follow by choosing only common cyclical component pairs with-in the business cycle frequency spectrum. These components will then be aggregated for constructing an EU region wide Business cycle indicator. The chapter outlines each steps of the algorithm that will eventually identify the SSA filter to act as a band-pass filter. The study then proceeds with simulation based data where the common cycle can be controlled and extracted a priori as a benchmark to the SSA-based filter estimates. The study follows with an empirical analysis similar to the framework set in Valle e Azevedo et al. (2006) with the aim to identify a Euro region business cycle indicator. The SSA based filter estimate is compared with Euro region economic activity indicators; the EuroCoin and the quarterly GDP growth rate of the EU area. Our results presents evidence of a successful alternative for tracing the cyclical position of the EU economy from a much smaller data set. Moreover, the constructed indicator also could serve as an unobserved proxy for a monthly growth cycle. A further analysis is also conducted to reveal whether the SSA based approach can be considered as an alternative to parametric filtering methods by providing results of common cycle extraction using Unobserved component model alternatives.This thesis includes two essays that are focused on developing multivariate filter approaches to be used for extracting common cyclical components where the common components can be used as an estimator of a business cycle. The first chapter aims to develop an optimal multivariate filter in order to extract common cyclical components of macroeconomic indicators. The filter allows macroeconomic series to be modeled as a phase shifted version of a coinciding business cycle (BC) while keeping other time series components such as the stochastic trend and idiosyncratic shocks intact (i.e. they are individually specified for each series). Earlier studies of Rünstler (2004), Valle e Azevedo et al. (2006) have applied phase shift in the form of a delay parameter when specifying lead-lag cycles. However, the lead-lag relationship is defined by rotating the baseline cycle which leads to loss of information. This deficiency is especially important if one considers working in continuous time. Therefore, this paper improves on the former technique by allowing a more flexible phase shift mechanism on the original BC. This in turn should lead to more realistic estimates and filters considering that the underlying data is generated through a continuous time framework. The study starts by presenting a structure for bi-variate time series system and then extends to model to incorporate a structure for three time series and beyond. Kalman filter and smoothing recursions are applied to compute the smoothed cycle estimates and to construct the likelihood function. Using simulated data, we test both model specifications by carrying out a grid search of the initial delay parameter to see the likelihood behavior as the parameter moves into fractional neighborhoods. Afterwards, applying the methodology to a set of EU countries and macroeconomic indicators; the study aims to shed light to the presence of cyclical heterogeneity at country level economic activity for major EU member states. A second empirical study provides analysis on how the model can be implemented for assigning a lead/lag ordering to three main economic indicators of a single country. The second chapter implements a multivariate non-parametric filtering approach; the Vertical Multivariate Singular Spectrum Analysis (V-MSSA) of Hassani and Mahmoudvand (2013) and Golyandina et al. (2013). to be applied for identifying a common economic cycle indicator. The methodology is a data-driven procedure that can decompose a time series into many sub components. By exploiting this ability of the SSA, the paper aims to first extract cyclical components based on frequency characteristics and then follow by choosing only common cyclical component pairs with-in the business cycle frequency spectrum. These components will then be aggregated for constructing an EU region wide Business cycle indicator. The chapter outlines each steps of the algorithm that will eventually identify the SSA filter to act as a band-pass filter. The study then proceeds with simulation based data where the common cycle can be controlled and extracted a priori as a benchmark to the SSA-based filter estimates. The study follows with an empirical analysis similar to the framework set in Valle e Azevedo et al. (2006) with the aim to identify a Euro region business cycle indicator. The SSA based filter estimate is compared with Euro region economic activity indicators; the EuroCoin and the quarterly GDP growth rate of the EU area. Our results presents evidence of a successful alternative for tracing the cyclical position of the EU economy from a much smaller data set. Moreover, the constructed indicator also could serve as an unobserved proxy for a monthly growth cycle. A further analysis is also conducted to reveal whether the SSA based approach can be considered as an alternative to parametric filtering methods by providing results of common cycle extraction using Unobserved component model alternatives.
41
Jacquet, Maxime J. "Negative frequency at the horizon : scattering of light at a refractive index front". Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/11780.
Abstract (sommario):
This thesis considers the problem of calculating and observing the mixing of modes of positive and negative frequency in inhomogeneous, dispersive media. Scattering of vacuum modes of the electromagnetic field at a moving interface in the refractive index of a dielectric medium is discussed. Kinematics arguments are used to demonstrate that this interface may, in a regime of linear dispersion, act as the analogue of the event horizon of a black hole to modes of the field. Furthermore, a study of the dispersion of the dielectric shows that five distinct configurations of modes of the inhomogeneous medium at the interface exist as a function of frequency. Thus it is shown that the interface is simultaneously a black- and white-hole horizon-like and horizonless emitter. The role, and importance, of negative-frequency modes of the field in mode conversion at the horizon is established and yields a calculation of the spontaneous photonic flux at the interface. An algorithm to calculate the scattering of vacuum modes at the interface is introduced. Spectra of the photonic flux in the moving and laboratory frame, for all modes and all realisable increase in the refractive index at the interface are computed. As a result of the various mode configurations, the spectra are highly structured in intervals with black-hole, white-hole and no horizon. The spectra are dominated by a negative-frequency mode, which is the partner in any Hawking-type emission. An experiment in which an incoming positive-frequency wave is populated with photons is assembled to observe the transfer of energy to outgoing waves of positive and negative frequency at the horizon. The effect of mode conversion at the interface is clearly shown to be a feature of horizon physics. This is a classical version of the quantum experiment that aims at validating the mechanism of Hawking radiation.
42
Gong, Liying. "Optimal spatial sampling of infrastructure condition a life-cycle-based approach under uncertainty /". Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1155273960.
43
Shin, Hyun. "Life-Cycle Cost-Based Optimal Seismic Design of Structures with Energy Dissipation Devices". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/40399.
Abstract (sommario):
Seismic designs of building structures are currently made based on the design criterion
of life-safety and this requires that the structures do not collapse to compromise safety
of people in the structure, but they can be designed to experience some damage.
However, this design approach has allowed large economic losses primarily due to the
damage to the nonstructural components at relatively moderate levels of seismic
intensities. This led to a new thinking about design approach called performance-based
design approach that satisfies the life-safety objective at the same time, reduces the
economic loss to an acceptable level. The performance-based design approaches are
multi-level design that addresses several different levels of structural performances
under different levels of seismic intensities. In this study, we have investigated the use
of energy dissipating damping devices to achieve the performance of a building
structure in a desirable manner over all levels of seismic intensity. Since the initial
motivation of performance-based design was reducing economic loss, the life-cycle
cost-based optimization is considered in this study to obtain the optimal designs with
different damping devices. For the optimal design, three types of devices are used in this
study: fluid viscous dampers, solid visco-elastic dampers, and yielding metallic
dampers. The combinations of two different types of dampers are also examined in this
study. The genetic algorithm (GA) approach is adopted as an optimizer that searches for
the optimal solution in an iterative manner. Numerical results from the application of
the optimal design to the selected model building are presented to demonstrate the
iii
applicability of the developed approach and to estimate the effectiveness of the obtained
optimal design with each device. It is shown in the results that the optimal design with
each individual damping devices or the combination of two different types of damping
devices are very effective in reducing the expected failure cost as well as the
displacement response quantities and fragilities. The results also show that the optimal
designs focus relatively more on reducing economic losses for the lower but more
frequent excitation intensities as these intensities contribute most to the failure costs.Ph. D.
44
Kox, Stephan. "Remote sensing of the diurnal cycle of optically thin cirrus clouds". Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-151170.
45
Hemmer, Michaël. "Few-cycle pulses amplification for attosecond science applications modeling and experiments". Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4920.
Abstract (sommario):
The emergence of mode-locked oscillators providing pulses with durations as short as a few electric-field cycles in the near infra-red has paved the way toward electric-field sensitive physics experiments. In addition, the control of the relative phase between the carrier and the pulse envelope, developed in the early 2000's and rewarded by a Nobel price in 2005, now provides unprecedented control over the pulse behaviour. The amplification of such pulses to the millijoule level has been an on-going task in a few world-class laboratories and has triggered the dawn of attoscience, the science of events happening on an attosecond timescale. This work describes the theoretical aspects, modeling and experimental implementation of HERACLES, the Laser Plasma Laboratory optical parametric chirped pulse amplifier (OPCPA) designed to deliver amplified carrier-envelope phase stabilized 8-fs pulses with energy beyond 1 mJ at repetition rates up to 10 kHz at 800 nm central wavelength. The design of the hybrid fiber/solid-state amplifier line delivering 85-ps pulses with energy up to 10 mJ at repetition rates in the multi-kHz regime tailored for pumping the optical parametric amplifier stages is presented. The novel stretcher/compressor design of HERACLES, suitable for handling optical pulses with spectra exceeding 300 nm of bandwidth with unprecedented flexibility, is fully modeled and also presented in the frame of this thesis. Finally, a 3D model of the multi-stage non-collinear optical parametric amplifier is also reported. The current and foreseen overall performances of HERACLES are presented. This facility is designed to enable attosecond physics experiments, high-harmonic generation and physics of plasma studies.ID: 029809569; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 218-230).
Ph.D.
Doctorate
Optics and Photonics
46
Enes, Aaron R. "Shared control of hydraulic manipulators to decrease cycle time". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37251.
Abstract (sommario):
This thesis presents a technique termed Blended Shared Control, whereby a human operator's commands are merged with the commands of an electronic agent in real time to control a manipulator. A four degree-of-freedom hydraulic excavator is used as an application example, and two types of models are presented: a fully dynamic model incorporating the actuator and linkage systems suitable for high-fidelity user studies, and a reduced-order velocity-constrained kinematic model amenable for real-time optimization. Intended operator tasks are estimated with a recursive algorithm; the task is optimized in real time; and a command perturbation is computed which, when summed with the operator command, results in a lower task completion time. Experimental results compare Blended Shared Control to other types of controllers including manual control and haptic feedback. Trials indicate that Blended Shared Control decreases task completion time when compared to manual operation.
47
Duineveld, Sijmen [Verfasser], e Burkhard [Akademischer Betreuer] Heer. "Solving Life Cycle Models, Optimal Age-Dependent Unemployment Insurance, and Adaptive Beliefs in a Real Business Cycle Model / Sijmen Duineveld ; Betreuer: Burkhard Heer". Augsburg : Universität Augsburg, 2019. http://d-nb.info/1190564904/34.
48
Zeng, Shuo. "Understanding diatomic molecular dynamics triggered by a few-cycle pulse". Diss., Kansas State University, 2015. http://hdl.handle.net/2097/19165.
Abstract (sommario):
Doctor of PhilosophyPhysics
Brett D. Esry
In strong field physics, complex atomic and molecular motions can be triggered and steered by an ultrashort strong field. With a given pulse as an carrier-envelope form, E(t) = E₀(t) cos(ωt + φ), we established our photon-phase formalism to decompose the solution of a time-dependent Schrödinger equation in terms of photons. This formalism is further implemented into a general analysis scheme that allows extract photon information direct from the numerical solution. The φ-dependence of any observables then can be understood universally as an interference effect of different photon channels. With this established, we choose the benchmark system H₂⁺ to numerically study its response to an intense few-cycle pulse. This approach helps us identify electronic, rovibrational transitions in terms of photon channels, allowing one to discuss photons in the strong field phenomena quantitatively. Furthermore, the dissociation pathways are visualized in our numerical calculations, which help predicting the outcome of dissociation. Guided by this photon picture, we explored the dissociation in a linearly polarized pulse of longer wavelengths (compared to the 800 nm of standard Ti:Saphire laser). We successfully identified strong post-pulse alignment of the dissociative fragments and found out that such alignment exists even for heavy molecules. More significant spatial asymmetry is confirmed in the longer wavelength regime, because dissociation is no longer dominated by a single photon process and hence allowed for richer interference. Besides, quantitative comparison between theory and experiment have been conducted seeking beyond the qualitative features. The discrepancy caused by different experimental inputs allows us to examine the assumptions made in the experiment. We also extend numerical studies to the dissociative ionization of H₂ by modeling the ionization.
49
Hyyti, Janne Juhani. "Ultrafast Nonlinear Nano-Optics via Collinear Characterization of Few-Cycle Pulses". Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19410.
Abstract (sommario):
Die Methode „interferometric frequency-resolved optical gating“ (iFROG) zur Charakterisierung ultrakurzer Laserimpulse wurde erweitert. Als optische Nichtlinearität werden sowohl die Erzeugung der 2. als auch der 3. Harmonischen (THG) separat verwendet. Eine iFROG-Messung stellt ein inverses Problem dar, bei dem die Amplitude und Phase des elektrischen Feldes des Laserimpulses nur durch einen iterativen Algorithmus rekonstruiert werden kann. In dieser Arbeit wird ein mathematischer Formalismus entwickelt und mit einem evolutionären Optimierungsalgorithmus kombiniert, um einen neuartigen Impuls-Rekonstruktions-Algorithmus für iFROG zu erschaffen.
Während iFROG ursprünglich ausschließlich zur Charakterisierung von Laserimpulsen konzipiert wurde, kann die Technik gleichermaßen für spektroskopische Zwecke eingesetzt werden. Wird das nichtlineare Medium in iFROG durch ein Untersuchungsobjekt ersetzt und ein bekannter Laserimpuls erneut charakterisiert, so kann die Antwortfunktion des Untersuchungsobjekts mit einer sub-Femtosekunden-Auflösung entschlüsselt werden. Da für die THG-Variante bisher keine Lösung bekannt ist, ermöglicht der vorgestellte Rekonstruktion-Algorithmus die erstmalige Nutzung von iFROG zur Untersuchung ultraschneller nichtlinearer Effekte dritter Ordnung.
Die spektroskopische Fähigkeit von iFROG wird durch das Studium von drei unterschiedlichen physikalischen Systemen (Nanostrukturen) geprüft. In ZnO-Nanostäben wird die Leistungsabhängigkeit der durch Multiphotonenabsorption induzierten Lumineszenz gemessen, wobei nachgewiesen werden konnte, dass diese mit einer Lokalisierung des optischen Nahfelds verknüpft ist. Eine Dreiphotonenresonanz in einem dünnen Titandioxid Film und eine Oberflächenplasmonenresonanz in Au-Nanoantennen führen beide zu einer endlichen Lebensdauer der induzierten Materialpolarisation. Die iFROG-Methode wird verwendet, um die ultraschnelle zeitliche Dynamik dieser Systeme auf der Nanometer- und wenige Femtosekunden-Skala zu messen.The ultrashort laser pulse characterization method “interferometric frequency-resolved optical gating” (iFROG) is extended. Both second- and third harmonic generation (SHG and THG) are separately employed as the optical nonlinearity. An iFROG measurement represents an inverse problem, where the electric field amplitude and phase of the underlying laser pulse can only be reconstructed by an iterative algorithm. In this work, a mathematical formalism for both the SHG and THG variants of iFROG is developed and combined with an evolutionary optimization algorithm to create a novel pulse retrieval algorithm for iFROG. While iFROG was originally conceived solely for pulse characterization, the technique can equally well be applied for spectroscopic purposes. By replacing the nonlinear medium in iFROG with an object of study, say a nanostructure, and characterizing a known pulse again such that the sample affects the harmonic generation process, the response of the object can be deciphered with sub-femtosecond precision. As no previous solution for the THG variant exists, the presented retrieval algorithm allows iFROG to be exploited in the study of ultrafast third-order nonlinear effects for the first time. The spectroscopic capability of iFROG is put to test by studying three differing physical systems, each consisting of nanostructures resting on dielectric substrates. Subjecting these specimen to few-cycle near-infrared pulses, a rich variety of nonlinear optical phenomena is observed. In ZnO nanorods, the power dependence of multiphoton-absorption induced luminescence is measured and found to be connected to a localization of the optical near-field. A three-photon resonance in a thin film of titania and a localized surface plasmon resonance in Au nanoantennas both lead to a finite lifetime of the induced material polarization. The THG-iFROG method is harnessed to measure the ultrafast temporal dynamics of these systems at the nanometer and few-femtosecond scales.
50
de, Medeiros Rocha Caroline Thennecy. "Optimization of p-cycle protection schemes in optical networks". Thèse, 2009. http://hdl.handle.net/1866/3671.
Abstract (sommario):
La survie des réseaux est un domaine d'étude technique très intéressant ainsi qu'une préoccupation critique dans la conception des réseaux. Compte tenu du fait que de plus en plus de données sont transportées à travers des réseaux de communication, une simple panne peut interrompre des millions d'utilisateurs et engendrer des millions de dollars de pertes de revenu. Les techniques de protection des réseaux consistent à fournir une capacité supplémentaire dans un réseau et à réacheminer les flux automatiquement autour de la panne en utilisant cette disponibilité de capacité.
Cette thèse porte sur la conception de réseaux optiques intégrant des techniques de survie qui utilisent des schémas de protection basés sur les p-cycles. Plus précisément, les p-cycles de protection par chemin sont exploités dans le contexte de pannes sur les liens. Notre étude se concentre sur la mise en place de structures de protection par p-cycles, et ce, en supposant que les chemins d'opération pour l'ensemble des requêtes sont définis a priori. La majorité des travaux existants utilisent des heuristiques ou des méthodes de résolution ayant de la difficulté à résoudre des instances de grande taille. L'objectif de cette thèse est double. D'une part, nous proposons des modèles et des méthodes de résolution capables d'aborder des problèmes de plus grande taille que ceux déjà présentés dans la littérature. D'autre part, grâce aux nouveaux algorithmes, nous sommes en mesure de produire des solutions optimales ou quasi-optimales. Pour ce faire, nous nous appuyons sur la technique de génération de colonnes, celle-ci étant adéquate pour résoudre des problèmes de programmation linéaire de grande taille. Dans ce projet, la génération de colonnes est utilisée comme une façon intelligente d'énumérer implicitement des cycles prometteurs.
Nous proposons d'abord des formulations pour le problème maître et le problème auxiliaire ainsi qu'un premier algorithme de génération de colonnes pour la conception de réseaux protegées par des p-cycles de la protection par chemin. L'algorithme obtient de meilleures solutions, dans un temps raisonnable, que celles obtenues par les méthodes existantes. Par la suite, une formulation plus compacte est proposée pour le problème auxiliaire. De plus, nous présentons une nouvelle méthode de décomposition hiérarchique qui apporte une grande amélioration de l'efficacité globale de l'algorithme. En ce qui concerne les solutions en nombres entiers, nous proposons deux méthodes heurisiques qui arrivent à trouver des bonnes solutions.
Nous nous attardons aussi à une comparaison systématique entre les p-cycles et les schémas classiques de protection partagée. Nous effectuons donc une comparaison précise en utilisant des formulations unifiées et basées sur la génération de colonnes pour obtenir des résultats de bonne qualité. Par la suite, nous évaluons empiriquement les versions orientée et non-orientée des p-cycles pour la protection par lien ainsi que pour la protection par chemin, dans des scénarios de trafic asymétrique. Nous montrons quel est le coût de protection additionnel engendré lorsque des systèmes bidirectionnels sont employés dans de tels scénarios.
Finalement, nous étudions une formulation de génération de colonnes pour la conception de réseaux avec des p-cycles en présence d'exigences de disponibilité et nous obtenons des premières bornes inférieures pour ce problème.Network survivability is a very interesting area of technical study and a critical concern in network design. As more and more data are carried over communication networks, a single outage can disrupt millions of users and result in millions of dollars of lost revenue. Survivability techniques involve providing some redundant capacity within the network and automatically rerouting traffic around the failure using this redundant capacity. This thesis concerns the design of survivable optical networks using p-cycle based schemes, more particularly, path-protecting p-cycles, in link failure scenarios. Our study focuses on the placement of p-cycle protection structures assuming that the working routes for the set of connection requests are defined a priori. Most existing work carried out on p-cycles concerns heuristic algorithms or methods suffering from critical lack of scalability. Thus, the objective of this thesis is twofold: on the one hand, to propose scalable models and solution methods enabling to approach larger problem instances and on the other hand, to produce optimal or near optimal solutions with mathematically proven optimality gaps. For this, we rely on the column generation technique which is suitable to solve large scale linear programming problems. Here, column generation is used as an intelligent way of implicitly enumerating promising cycles to be part of p-cycle designs. At first, we propose mathematical formulations for the master and the pricing problems as well as the first column generation algorithm for the design of survivable networks based on path-protecting p-cycles. The resulting algorithm obtains better solutions within reasonable running time in comparison with existing methods. Then, a much more compact formulation of the pricing problem is obtained. In addition, we also propose a new hierarchical decomposition method which greatly improves the efficiency of the whole algorithm and allows us to solve larger problem instances. As for integer solutions, two heuristic approaches are proposed to obtain good solutions. Next, we dedicate our attention to a systematic comparison of p-cycles and classical shared protection schemes. We perform an accurate comparison by using a unified column generation framework to find provably good results. Afterwards, our study concerns an empirical evaluation of directed and undirected link- and path-protecting p-cycles under asymmetric traffic scenarios. We show how much additional protection cost results from employing bidirectional systems in such scenarios. Finally, we investigate a column generation formulation for the design of p-cycle networks under availability requirements and obtain the first lower bounds for the problem.