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Zhao, Lu, Antoine Normand, Jonathan Houard, Ivan Blum, Fabien Delaroche, Olivier Latry, Blaise Ravelo, and Francois Vurpillot. "Optimizing Atom Probe Analysis with Synchronous Laser Pulsing and Voltage Pulsing." Microscopy and Microanalysis 23, no. 2 (February 8, 2017): 221–26. http://dx.doi.org/10.1017/s1431927616012666.
Повний текст джерелаАнотація:
AbstractAtom probe has been developed for investigating materials at the atomic scale and in three dimensions by using either high-voltage (HV) pulses or laser pulses to trigger the field evaporation of surface atoms. In this paper, we propose an atom probe setup with pulsed evaporation achieved by simultaneous application of both methods. This provides a simple way to improve mass resolution without degrading the intrinsic spatial resolution of the instrument. The basic principle of this setup is the combination of both modes, but with a precise control of the delay (at a femtosecond timescale) between voltage and laser pulses. A home-made voltage pulse generator and an air-to-vacuum transmission system are discussed. The shape of the HV pulse presented at the sample apex is experimentally measured. Optimizing the delay between the voltage and the laser pulse improves the mass spectrum quality.
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Liang, Zhen Guang, and Ming Yuan Yang. "Immunity Test of a Microcontroller by Using Transmission Line Pulse Generator." Advanced Materials Research 860-863 (December 2013): 2296–99. http://dx.doi.org/10.4028/www.scientific.net/amr.860-863.2296.
Повний текст джерелаАнотація:
Electrostatic discharge is a familiar interfere. Repeatability of discharge current is poor. Transmission line pulse (TLP) is used in study of immunity of a microcontroller. A TLP generator is first manufactured with the rise time of output pulse less than 1ns. Then couplings by electric field probe, magnetic field probe and direct injection are presented. And immunity test of a microcontroller is done by using the TLP generator and probes. Results show that the tested microcontroller is more sensitive to magnetic field interference; reset pin and crystal oscillator pin of the chip are more sensitive than other pins under action of direct injection interference.
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Currie, S. N., and P. S. Stein. "Electrical activation of the pocket scratch central pattern generator in the turtle." Journal of Neurophysiology 60, no. 6 (December 1, 1988): 2122–37. http://dx.doi.org/10.1152/jn.1988.60.6.2122.
Повний текст джерелаАнотація:
1. A low-spinal, immobilized turtle displays a fictive scratch reflex in hindlimb motor neurons in response to tactile stimulation of the shell (17, 19). Turtles exhibit three forms of the scratch reflex: rostral, pocket, and caudal. Each form is elicited by tactile stimulation of a different receptive field on the body surface. The ventral-posterior pocket (VPP) cutaneous nerve innervates the ventral-posterior portion of the pocket scratch receptive field (Fig. 1). Natural stimulation within the VPP nerve's receptive field evoked a pocket scratch reflex (Fig. 2A). Electrical stimulation of this nerve elicited robust pocket scratch reflexes (Fig. 2, B and C). 2. A single electrical pulse to the VPP nerve delivered at a voltage (greater than 5 V, 0.1 ms) that activated all the axons in the nerve was termed a "maximal" pulse. A single maximal pulse did not evoke a scratch motor response. It raised the excitability of the pocket scratch central pattern generator for several seconds, however. We revealed such excitability changes by applying maximal pulses to the VPP nerve at multisecond intervals (Figs. 5 and 6). When we delivered maximal pulses with interpulse intervals of less than or equal to 5 s, the first pulse produced no motor response and the second pulse evoked one or more cycles of pocket scratch. 3. A stimulus pulse applied to the VPP nerve was used as a probe for studying changes in the excitability of the pocket scratch CPG following scratch motor patterns. In a rested preparation, the stimulus pulse did not activate motor output. In contrast, the stimulus pulse evoked one or two cycles of pocket scratch activity if delivered within 2.5 s after the cessation of rhythmic pocket scratch motor activity (Figs. 7-9). These results are consistent with the hypothesis that the pocket scratch CPG has elevated excitability for seconds following the cessation of pocket scratch motor output. A single pulse applied to the VPP nerve evoked no response if delivered after the cessation of rostral scratch motor activity, however (Fig. 9D). 4. We used a train of maximal pulses to the VPP nerve to probe the form-specificity of the changes in the excitability following a rostral scratch motor pattern (Fig. 10). We set the stimulus parameters so that the train evoked one or two cycles of a pocket scratch motor pattern in a preparation that had rested for over 1 min.(ABSTRACT TRUNCATED AT 400 WORDS)
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Lee, Jeong Min, Nam Hun Kim, and Jeong Woo Park. "Possibility of Pulsed Electrochemical Processes to Nanofabrication Using Scanning Probe Oxidation." Advanced Materials Research 154-155 (October 2010): 862–66. http://dx.doi.org/10.4028/www.scientific.net/amr.154-155.862.
Повний текст джерелаАнотація:
This study demonstrates nano-scale lithography process on localized (100) silicon (p-type) surface using modified AFM apparatuses and controlling methods. AFM-based experimental apparatuses are connected the customized pulse generator that supplies electricity between conductive tip and silicon surface maintaining constant humidity during processes. Then pulse durations are controlled according to various experimental conditions. The pulsed electrochemical reaction within the gap between conductive tip and silicon surface induces the formation of oxide with nano-scale topographies. Various heights and widths of oxides can be created by AFM surface modification according to various pulse durations and applied electrical conditions under humidity environment. In addition, it can be known that oxides are completely removed after sample surface is etched in diluted HF solution, which shows micro/nano-scale grooves can be fabricated after predefined chemical treatment. They are wider than oxides widths and have several nanometer depths. Nano patterning technique from this experiment suggests that pulse electrochemical machining process has bright potential for advancing nano machining technologies.
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Lippincott, Margaret F., Silvia León, Yee-Ming Chan, Chrysanthi Fergani, Rajae Talbi, I. Sadaf Farooqi, Christopher M. Jones, et al. "Hypothalamic Reproductive Endocrine Pulse Generator Activity Independent of Neurokinin B and Dynorphin Signaling." Journal of Clinical Endocrinology & Metabolism 104, no. 10 (May 27, 2019): 4304–18. http://dx.doi.org/10.1210/jc.2019-00146.
Повний текст джерелаАнотація:
Abstract Context Kisspeptin–neurokinin B (NKB)–dynorphin neurons are critical regulators of the hypothalamic–pituitary–gonadal axis. NKB and dynorphin are hypothesized to influence the frequency of GnRH pulses, whereas kisspeptin is hypothesized to be a generator of the GnRH pulse. How these neuropeptides interact remains unclear. Objective To probe the role of NKB in GnRH pulse generation and to determine the interactions between NKB, kisspeptin, and dynorphin in humans and mice with a complete absence of NKB. Design Case/control. Setting Academic medical center. Participants Members of a consanguineous family bearing biallelic loss-of-function mutations in the gene encoding NKB and NKB-deficient mice. Interventions Frequent blood sampling to characterize neuroendocrine profile and administration of kisspeptin, GnRH, and naloxone, a nonspecific opioid receptor antagonist used to block dynorphin. Main Outcome Measures LH pulse characteristics. Results Humans lacking NKB demonstrate slow LH pulse frequency, which can be increased by opioid antagonism. Mice lacking NKB also demonstrate impaired LH secretion, which can be augmented with an identical pharmacologic manipulation. Both mice and humans with NKB deficiency respond to exogenous kisspeptin. Conclusion The preservation of LH pulses in the absence of NKB and dynorphin signaling suggests that both peptides are dispensable for GnRH pulse generation and kisspeptin responsiveness. However, NKB and dynorphin appear to have opposing roles in the modulation of GnRH pulse frequency.
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Sahoo, Gourishankar, Rita Paikaray, Subrata Samantaray, Dheeren Chandra Patra, Narayan Chandra Sasini, Joydeep Ghosh, Malay Bikash Chowdhuri, and Amulya Sanyasi. "A Compact Plasma System for Experimental Study." Applied Mechanics and Materials 278-280 (January 2013): 90–100. http://dx.doi.org/10.4028/www.scientific.net/amm.278-280.90.
Повний текст джерелаАнотація:
A compact plasma system is set up at Ravenshaw University, India. The plasma system consists of a curved vacuum chamber which is nothing but a part of a toroid (θ=700) having minor radius, r= 0.3 m and major radius, R= 0.5 m, vacuum system, electromagnet, gas injected washer stacked plasma gun to produce plasma blobs/filaments, pulse forming network to energise plasma gun, diagnostic tools like electric probes, magnetic probes, spectrometer, high speed CCD camera, digital pulse/delay generator to synchronise the diagnostic tools. A pair of copper coil is wound over the chamber and capacitive pulse is fed to the coil to produce non-uniform magnetic field inside the chamber. The gas injected washer stacked plasma gun is a mono-anode - multi cathode system having five cathodes made up of brass and an anode made up of copper. The gun impedance is ~ 15 Ω. The pulse forming network (PFN) is Guillemin E type which consists of capacitors having equal capacitance 5.5 μF and inductors having equal inductances 1.5 μH. The pulse width of the PFN is ~ 7.6 μs for a seven stage network, as tested with known resistive circuit. Magnetic probes are designed and calibrated using a Helmholtz coil to map the radial magnetic field profile of the plasma chamber. Electric probes like Langmuir triple probe, velocity probes are designed to measure plasma parameters like blob velocity, density, temperature etc. Emission spectroscopy method is used to identify charged species inside the plasma. High speed CCD camera is used to interpret the structure of the plasma. A digital pulse/trigger generator is used to synchronise the CCD, spectrometer and switching thyristor etc. Preliminary results are also reported.
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Lee, Jeong Ki, Dong Man Suh, and Seung Seok Lee. "Change of the Pulsed Eddy Current Signals by the Variation of the Thickness of an Aluminum Specimen." Key Engineering Materials 297-300 (November 2005): 2028–33. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2028.
Повний текст джерелаАнотація:
The conventional eddy current testing uses a sinusoidal signal with very narrow frequency bandwidth. Whereas, the pulsed eddy current method uses a pulse signal with a broad frequency bandwidth. This allows multi-frequency eddy current testing, and the penetration depth is greater than that of the conventional eddy current testing. In this work, the pulsed eddy current instrument was developed for evaluating the metal loss. The developed instrument was consist of the pulse generator generating the square pulse of maximum 40 V, the amplifier controlled to 52dB, the A/D converter of 16bit 20MHz, and the industrial personal computer for operating with Windows program. And, the probe for the pulsed eddy current was designed as the pancake type in which the sensing coil was located in the driving coil. The peak voltage did not linearly increase with the voltage of the step pulse. For the driving coil with inductance of 670µH, the peak voltage linearly increased with the step pulse voltage to 30V. But, for the other driving coils with the inductance of 1.7mH, 2.7mH, 3.6mH, 22mH, the peak voltage linearly increased with the step pulse voltage to 20V. The output signals of the sensing coil rapidly increased when the step pulse driving voltage was off, and the latter part of the sensing coil output voltage exponentially decreased with a time. The decrement value of the output signals of sensing coil increased with the thickness of the aluminum test piece.
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Cassabli, Salam Bussi EP Michel, G. M. Suchkov, S. Yu Plesnetsov, R. P. Mygushchenko, O. Yu Kropachek, and Yu O. Plesnetsov. "GENERATOR OF POWERFUL HIGH-FREQUENCY PACKAGE CURRENT PULSES FOR POWER SUPPLY OF ULTRASONIC ELECTROMAGNETIC-ACOUSTIC TRANSDUCERS." METHODS AND DEVICES OF QUALITY CONTROL, no. 2(43) (December 24, 2019): 88–95. http://dx.doi.org/10.31471/1993-9981-2019-2(43)-88-95.
Повний текст джерелаАнотація:
It is possible to increase the sensitivity of electromagnetic-acoustic transducers by three main methods: increasing the induction of a polarizing magnetic field; increase in strength of high-frequency current in the inductor of the converter; using modern methods of processing information packet pulses excited and received from the product. The increase in magnetic field induction of the converter is limited by the capabilities of modern powerful permanent magnets. In addition, there are significant difficulties in monitoring ferromagnetic control samples, due to the large pressing force between the sample and the transducer and sticking of scale to the transducer. Usage of modern processing methods significantly complicates and increases the cost of electromagnetic-acoustic testing devices. Of the selected sensitivityincreasingmethods, the most acceptable way is to increase the power of high-frequency current generators under the condition of excitation of packet pulses. Power supply process of the converter is carried out in two stages. Meander type powerful high-frequency current pulses are excited, which ensures operation of the output transistors in key mode. Isolation of a powerful sinusoidal high-frequency packet current pulse is carried out directly on the electromagnetic - acoustic transducer, the elements of which are included in the resonant circuit with low quality factor. Based on the transistors switched in the push-pull circuit in the key mode, a small-sized generator design has been created that excites a peak current of up to 800 A in the electromagnetic-acoustic transducer and a voltage of up to 3 kV in the transducer in the frequency range 0.3 ... 8 MHz. It was experimentally determined that the new design of the probe pulse generator made it possible to increase the amplitude of pulses reflected from a flat-bottom reflector with a diameter of 2 mm with respect to the interference amplitude by more than 2 times.
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Liang, Zhen Guang, and Xue Gu. "Waveform Analysis of a Transmission Line Pulse Generator by Use of Wavelet Transform." Applied Mechanics and Materials 668-669 (October 2014): 1166–69. http://dx.doi.org/10.4028/www.scientific.net/amm.668-669.1166.
Повний текст джерелаАнотація:
With good repeatability and simple structure, transmission line pulse (TLP) has been used in immunity test of integrated circuit and printed circuit board. A TLP generator is first manufactured and its output waveform is presented. By using wavelet transform, the waveform is denoised and discriminated to components inherent to system function and parasitic parameters. Frequency spectrum changed with time is also obtained by continuous wavelet transform of complex morlet. Decomposed damping oscillation component and high frequency component in instant frequency spectrum show influence of inductance in circuit on the waveform. Improvement of rising time and overshoot is achieved by change of probe connection with shorter grounding line.
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Golovkov, V. A., N. I. Potapova, P. N. Rudenko, B. G. Stradov, and S. V. Teliatnikov. "Receiving Unit of a Precision Pulsed Laser Range Finder." Journal of the Russian Universities. Radioelectronics 23, no. 2 (April 28, 2020): 73–81. http://dx.doi.org/10.32603/1993-8985-2020-23-2-73-81.
Повний текст джерелаАнотація:
Introduction. At present the most accurate estimate of ranges is specific to laser range finders using phase measuring techniques. Design of a pulsed laser range finder with short probe pulses enabling one to gain high resolution and accuracy of estimate of target range close to the phase range finders is the topical problem.Aim. Development of a receiving part of the pulsed laser rangefinder with precision characteristics; determination of the accuracy of the measurements; description of the hardware.Materials and methods. The construction of the receiving part of the precision pulsed laser rangefinder with a two-scale digital range estimation system implemented by counting clock generator pulses and an analog integrator that specifies the discrete range estimation was considered. Using the methods of mathematical statistics, the energy characteristics of the rangefinder were determined: the accuracy of the range estimation and the probability of false alarm were provided by the developed scheme. The hardware of the precision laser rangefinder was described.Results. The principles of implementation of the receiving part of the laser rangefinder with a two-scale digital system for estimating the distance to the object were given. The results of numerical simulation of rangefinder characteristics were obtained, confirming the accuracy of range estimation of the order of millimeters. In the implemented rangefinder scheme, the probability of false alarm was 10-4 during 200 s of observing signal and noise mixture. The hardware of the precision laser rangefinder with a digital two-scale range estimation was proposed.Conclusion. The implemented laser range finder approaches to the capabilities of phase laser rangefinders in terms of potential accuracy of distance up to millimeters, while implementing the specified parameter in rapidly changing phono-target environment. Using of short probing pulses with a duration of 10...20 ns allows one to achieve a resolution of up to 1.5 m. In contrast to the phase rangefinder the range can be estimated from a single probe pulse.
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Katkov, Alexander S., Viktor E. Lovtsyus, Andrey I. Bykov, Vladimir I. Shevtsov, Anastasia N. Petrovskaya, Ralf Behr, and Oliver F. Kieler. "Quantum Standard for Synthesis AC Voltage." Izmeritel`naya Tekhnika, no. 4 (April 2020): 39–43. http://dx.doi.org/10.32446/0368-1025it.2020-4-39-43.
Повний текст джерелаАнотація:
Prototype of quantum standard based on the Josephson effect for synthesis sine wave with low level harmonics and high accuracy was developed at VNIIM, which opens up new possibilities for metrological support in the field of АС voltage. The standard includes cryogenic probe with Josephson chips, delta-sigma modulator, pulse pattern generator, compensation circuit, spectrum analyzer, video control unit and software. The capability of synthesis sine wave with an output voltage up to 130 mV RMS over a wide frequency range from about 1 kHz to 100 kHz is shown. Higher harmonics are suppressed bellow the noise floor up to 100 dBc.
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Uchanin, Valentyn. "Enhanced Eddy Current Techniques for Detection of Surface-Breaking Cracks in Aircraft Structures." Transactions on Aerospace Research 2021, no. 1 (March 1, 2021): 1–14. http://dx.doi.org/10.2478/tar-2021-0001.
Повний текст джерелаАнотація:
Abstract Well-timed detection of the defects (e.g., fatigue cracks and corrosive damages) in aircraft structures is the question of vital importance. Periodic in-service non-destructive inspection (NDI) is necessary to prevent expensive aircraft breakdowns during in-service life. Eddy current (EC) NDI method have many advantages for in-service aircraft inspection due to high mobility and the possibility to detect fatigue cracks without direct contact with the inspected surface (even through a protective coating without removal). Last decades some enhanced EC techniques were developed for aircraft in-service inspection in the Karpenko Physico-Mechanical Institute of National Academy of Sciences (Lviv) in collaboration with Ukrainian and foreign aircraft companies. Proposed earlier EC efficiency coefficient was applied for the selection of the ferrite-core EC probe parameters. Investigations concerned with the crack detectability for single-coil EC probes of different sizes were carried out to improve the inspection procedures. The sensitivity of the developed single-coil EC probe was experimentally investigated. The possibility to distinguish the signals associated with detected defect and lift-off was shown. The new inspection procedure was proposed for full suppression of the noise concerned with the rivet edge influence. The high-frequency EC flaw detector of Leotest VD 3.03 type based on self-generator mode and miniature single-coil EC probes application was developed for detection of the surface-breaking fatigue cracks. The original scheme of double-circuit self-generator with intermittent oscillations was invented and investigated. The pulse-repetition frequency of high-frequency oscillations was used as an informative parameter. The important feature of the developed self-generating scheme is the effective suppression of the lift-off influence (the changes of the clearance between the EC probe and the inspected object surface during the scanning). Developed EC flaw detectors of Leotest VD 3.03 type and inspection procedures were successfully implemented into the maintenance practice for detection of the fatigue cracks initiated in the wing and the fuselage structures and aviation engines in many companies such as ANTONOV AIRCRAFT, Lviv State Aircraft Repair Plant, Konotop aircraft repair plant «AVIAKON», Ukrainian International Airlines, MOTOR-SICH, State Enterprise “IVCHENKO-PROGRESS”, etc.
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Mojid, M. A. "Technical Note:Practical considerations on the use of down-sized time-domain reflectometry (TDR) probes." Hydrology and Earth System Sciences 6, no. 5 (October 31, 2002): 949–55. http://dx.doi.org/10.5194/hess-6-949-2002.
Повний текст джерелаАнотація:
Abstract. Nine time-domain reflectometry (TDR) probes, 2 to 10 cm long, were evaluated by comparing their measurement accuracy of TDR-pulse travel time in a sand and sandy loam soil, and electrical conductivity in NaCl solutions. TDR probes <2.5 cm in length generated trough-haped TDR waveforms with rounded corners at the points of the pulse reflection from the probe ends. The sharpness of the pulse reflection on the waveforms increased with both the increasing probe length and soil-water content. The transition time for the propagation of TDR pulse at the probe entrance increased as the soil dried up. The increased transition time caused a rightward movement of the first peak of the waveform at the probe entrance. Because of such peak movement, TDR-support software algorithm determined travel path of TDR pulse through the probe that was smaller than the actual travel path. TDR-measured pulse travel time tTDR varied erratically with the predicted pulse travel time tg (from volumetric soil-water content) for the probes <2.5 cm in length. But, for all probes ³2.5 cm in length, tTDR varied linearly with tg and followed the 1:1 line. TDR could not measure tTDR <300 ps accurately. A minimum probe length Lmin and the lowest allowable soil-water content qmin that the probe can accurately measure govern this lowest pulse travel time tmin. The mean absolute deviation between tTDR and tg was 77 ps for the 2.3 cm long probe and 1.39 ps for all probes ≥2.5 cm in length. All probes ≥2.5 cm in length measured electrical conductivity of salt solutions sTDR that compared well with the electrical conductivity measured by a conductivity meter sm. The length of the probes did not exert any noticeable influence on the accuracy of electrical conductivity measurement. Keywords: TDR probe, pulse travel time, dielectric constant, electrical conductivity
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De Marco, Massimo, Jakub Cikhardt, Josef Krása, Andriy Velyhan, Miroslav Pfeifer, Eduard Krouský, Daniel Klír, et al. "Electromagnetic pulses produced by expanding laser-produced Au plasma." Nukleonika 60, no. 2 (June 1, 2015): 239–43. http://dx.doi.org/10.1515/nuka-2015-0043.
Повний текст джерелаАнотація:
Abstract The interaction of an intense laser pulse with a solid target produces large number of fast free electrons. This emission gives rise to two distinct sources of the electromagnetic pulse (EMP): the pulsed return current through the holder of the target and the outflow of electrons into the vacuum. A relation between the characteristics of laser-produced plasma, the target return current and the EMP emission are presented in the case of a massive Au target irradiated with the intensity of up to 3 × 1016 W/cm2. The emission of the EMP was recorded using a 12 cm diameter Moebius loop antennas, and the target return current was measured using a new type of inductive target probe (T-probe). The simultaneous use of the inductive target probe and the Moebius loop antenna represents a new useful way of diagnosing the laser–matter interaction, which was employed to distinguish between laser-generated ion sources driven by low and high contrast laser pulses.
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Myoung, Hyoun-Seok, and Kyoung-Joung Lee. "A Unique Electrical Thermal Stimulation System Comparable to Moxibustion of Subcutaneous Tissue." Evidence-Based Complementary and Alternative Medicine 2014 (2014): 1–6. http://dx.doi.org/10.1155/2014/518313.
Повний текст джерелаАнотація:
Moxibustion strengthens immunity and it is an effective treatment modality, but, depending on the material quantity, shape, and composition, the thermal strength and intensity can be difficult to control, which may cause pain or epidermal burns. To overcome these limitations, a heat stimulating system which is able to control the thermal intensity was developed. The temperature distributions on epidermis, at 5 mm and 10 mm of depth, in rabbit femoral tissue were compared between moxibustion and the electric thermal stimulation system. The stimulation system consists of a high radio frequency dielectric heating equipment (2 MHz frequency, maximum power 200 W), isolation probe, isolation plate, negative pressure generator, and a temperature assessment system. The temperature was modulated by controlling the stimulation pulse duty ratio, repetition number, and output. There were 95% and 91% temperature distribution correlations between moxibustion and the thermal stimulus at 5 mm and 10 mm of depth in tissue, respectively. Moreover, the epidermal temperature in thermal stimulation was lower than that in moxibustion. These results showed that heat loss by the electric thermal stimulation system is less than that by the traditional moxibustion method. Furthermore, the proposed electric thermal stimulation did not cause adverse effects, such as suppuration or blisters, and also provided subcutaneous stimulation comparable to moxibustion.
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Xue, Bing, Atsushi Yabushita, and Takayoshi Kobayashi. "Ultrafast dynamics of uracil and thymine studied using a sub-10 fs deep ultraviolet laser." Physical Chemistry Chemical Physics 18, no. 25 (2016): 17044–53. http://dx.doi.org/10.1039/c5cp07861j.
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Park, Byung Nam, and Sie Young Choi. "Copper Metalization Using Electroplating Process." International Journal of Modern Physics B 17, no. 08n09 (April 10, 2003): 1261–66. http://dx.doi.org/10.1142/s0217979203018843.
Повний текст джерелаАнотація:
Recently, electroplating method which deposits copper films by using cupric sulfate solution, has been proposed. The electroplating method has the advantages of simplicity, safety, low cost, low deposition temperature, high purity, low resistivity, and high capability of gap filling. In this method, an electrical contact is made to the seed layer and a current is passed such that the reaction ⌊ Cu 2++ 2e → Cu (0)⌋ occurs at the wafer surface (cathode). At the anode, an oxidation reaction occurs which balances the current flow at the cathode, thus maintaining electrical neutrality in the cupric sulfate solution. The seed layer used in this experiment was a copper thin film deposited using the sputtering method on p-type (100) silicon wafer using Ta thin film for barrier material. The thickness of seed and barrier layer were 400 and 600 Å respectively. The electroplating process was performed for 5min with a cathode current of 2A and a electrode distance of 4 cm. The intensity of magnetic field was about 200 – 400 Gauss. The pulse current generator was used for uniform surface and gap filling. The thickness and the sheet resistivity were measured using an α-step profiler and 4-point probe system, respectively. Scanning electron microscopy (SEM) was used to investigate the film morphology and the surface grdin size of the plated copper films. X-rdy diffraction(XRD) was performed for the crystal texture. The impurity levels and atomic composition were determined using Auger electron spectroscopy (AES).
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Fried, Daniel, Toshimoto Kushida, Gene P. Reck, and Erhard W. Rothe. "YO A2II1/2,3/2 Vibrational State Distributions Measured after the Excimer Laser Ablation of Y2O3 Using a Laser-Initiated Pulsed Discharge as a Probe." Applied Spectroscopy 48, no. 2 (February 1994): 248–51. http://dx.doi.org/10.1366/0003702944028380.
Повний текст джерелаАнотація:
The vibrational populations of the YO A2II- X2Σ system of YO were measured in the plasmas generated after the excimer laser ablation of Y2O3 in oxygen when both continuous and pulsed electric fields were applied. When an electric field is applied antiparallel to the direction of propagation of the ejected electrons, two luminous plumes appear, separated by several microseconds. The measured vibrational populations of the YO A2II- X2Σ system are different for each plume. The YO A2II populations were nonthermal in the first plume, representing emission from chemiluminescent reactive collisions in the plume after ablation. The second emission pulse, initiated by the discharge of a high-voltage capacitor, probes the ground-state YO in the plume via electron collisions. This pulsed electric field holds promise as a diagnostic probe of the ground-state species emitted in laser ablative processes.
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Feist, Armin, Katharina E. Priebe, Christopher Rathje, Nora Bach, Nara Rubiano da Silva, Thomas Danz, Marcel Moller, et al. "Generation and attosecond shaping of high coherence free-electron beams for ultrafast TEM." EPJ Web of Conferences 205 (2019): 08012. http://dx.doi.org/10.1051/epjconf/201920508012.
Повний текст джерелаАнотація:
We demonstrate the generation and optical control of ultrashort high-coherence electron pulses. The free-electron quantum state is phase-modulated in the longitudinal and transverse dimensions, and the formation of attosecond electron pulse trains is quantitatively probed.
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Towrie, Michael, David C. Grills, Joanne Dyer, Julia A. Weinstein, Pavel Matousek, Robin Barton, Philip D. Bailey, et al. "Development of a Broadband Picosecond Infrared Spectrometer and its Incorporation into an Existing Ultrafast Time-Resolved Resonance Raman, UV/Visible, and Fluorescence Spectroscopic Apparatus." Applied Spectroscopy 57, no. 4 (April 2003): 367–80. http://dx.doi.org/10.1366/00037020360625899.
Повний текст джерелаАнотація:
We have constructed a broadband ultrafast time-resolved infrared (TRIR) spectrometer and incorporated it into our existing time-resolved spectroscopy apparatus, thus creating a single instrument capable of performing the complementary techniques of femto-/picosecond time-resolved resonance Raman (TR3), fluorescence, and UV/visible/infrared transient absorption spectroscopy. The TRIR spectrometer employs broadband (150 fs, ∼150 cm−1 FWHM) mid-infrared probe and reference pulses (generated by difference frequency mixing of near-infrared pulses in type I AgGaS2), which are dispersed over two 64-element linear infrared array detectors (HgCdTe). These are coupled via custom-built data acquisition electronics to a personal computer for data processing. This data acquisition system performs signal handling on a shot-by-shot basis at the 1 kHz repetition rate of the pulsed laser system. The combination of real-time signal processing and the ability to normalize each probe and reference pulse has enabled us to achieve a high sensitivity on the order of ΔOD ∼ 10−4–10−5 with 1 min of acquisition time. We present preliminary picosecond TRIR studies using this spectrometer and also demonstrate how a combination of TRIR and TR3 spectroscopy can provide key information for the full elucidation of a photochemical process.
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Jiang, Shicheng, and Konstantin Dorfman. "Detecting electronic coherences by time-domain high-harmonic spectroscopy." Proceedings of the National Academy of Sciences 117, no. 18 (April 16, 2020): 9776–81. http://dx.doi.org/10.1073/pnas.1919360117.
Повний текст джерелаАнотація:
Ultrafast spectroscopy is capable of monitoring electronic and vibrational states. For electronic states a few eV apart, an X-ray laser source is required. We propose an alternative method based on the time-domain high-order harmonic spectroscopy where a coherent superposition of the electronic states is first prepared by the strong optical laser pulse. The coherent dynamics can then be probed by the higher-order harmonics generated by the delayed probe pulse. The high nonlinearity typically modeled by the three-step mechanism introduced by Lewenstein and Corkum can serve as a recipe for generation of the coherent excitation with broad bandwidth. The main advantage of the method is that only optical (non–X-ray) lasers are needed. A semiperturbative model based on the Liouville space superoperator approach is developed for the bookkeeping of the different orders of the nonlinear response for the high-order harmonic generation using multiple pulses. Coherence between bound electronic states is monitored in the harmonic spectra from both first- and second-order responses.
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Gong, Peng Wei, Zhe Ma, Hong Mei Ma, and Chun Tao Yang. "Experimental Investigation of Terahertz Temporal Response of a Photoconductive Switch." Advanced Materials Research 571 (September 2012): 491–95. http://dx.doi.org/10.4028/www.scientific.net/amr.571.491.
Повний текст джерелаАнотація:
Picosecond or subpicosecond electrical pulses can be generated from femtosecond laser excited photoconductive switches, and this technique is an effective method to characterize the rise time of the broadband oscilloscopes recently. In this paper, low temperature grown GaAs (LT-GaAs) is used as the substrate of the photoconductive switch which is excited by the femtosecond laser. After propagating along a coplanar waveguide, the generated terahertz pulses are transferred to a 1.85 mm coaxial cable through a microwave probe. The pulse width is measured in a 70 GHz sampling oscilloscope, the FWHM value is about 7.4 ps.
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HAZAMA, HISANAO, KATSUNORI ISHII, and KUNIO AWAZU. "LESS-INVASIVE LASER THERAPY AND DIAGNOSIS USING A TABLETOP MID-INFRARED TUNABLE LASER." Journal of Innovative Optical Health Sciences 03, no. 04 (October 2010): 285–92. http://dx.doi.org/10.1142/s179354581000109x.
Повний текст джерелаАнотація:
Since numerous characteristic absorption lines caused by molecular vibration exist in the mid-infrared (MIR) wavelength region, selective excitation or selective dissociation of molecules is possible by tuning the laser wavelength to the characteristic absorption lines of target molecules. By applying this feature to the medical fields, less-invasive treatment and non-destructive diagnosis with absorption spectroscopy are possible using tunable MIR lasers. A high-energy nanosecond pulsed MIR tunable laser was obtained with difference-frequency generation (DFG) between a Nd:YAG and a tunable Cr:forsterite lasers. The MIR-DFG laser was tunable in a wavelength range of 5.5–10 μm and generated laser pulses with energy of up to 1.4 mJ, a pulse width of 5 ns, and a pulse repetition rate of 10 Hz. Selective removal of atherosclerotic lesion was successfully demonstrated with the MIR-DFG laser tuned at a wavelength of 5.75 μm, which corresponds to the characteristic absorption of the ester bond in cholesterol esters in the atherosclerotic lesions. We have developed a non-destructive diagnostic probe with an attenuated total reflection (ATR) prism and two hollow optical fibers. An absorption spectrum of cholesterol was measured with the ATR probe by scanning the wavelength of the MIR-DFG laser, and the spectrum was in good agreement with that measured with a commercial Fourier transform infrared spectrometer.
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Jomtarak, Rangsan, Preecha P. Yupapin, and Jalil Ali. "Doppler shift velocimetry using two point probe nested-microring resonators." Journal of Nonlinear Optical Physics & Materials 24, no. 01 (March 2015): 1550003. http://dx.doi.org/10.1142/s0218863515500034.
Повний текст джерелаАнотація:
In this paper, a micro Doppler shift velocimeter using two nested-microring resonators incorporating two gratings is designed and simulated. Two wavelength light pulse can be generated by a single input wavelength source after travelling through the two defect grating. Whispering gallery mode of light pulses are localized within the nested-microring resonators, which can be used to form the two point probe Doppler shift velocimeter. The shifted frequency (velocity) can be obtained by the difference of optical path length between two point probes, where the relative velocity of Doppler frequency shift velocimeter can be obtained. The light absorption behaviors can also be investigated by the different light output spectrum. The obtained simulation results shows that the relative velocities of the reflection and transmission light intensities are ranged from 104 m/s to 105 m/s, which can be useful for Doppler frequency shift velocimeter and sensors, where the micro-optical device and multi-functions are the advantages.
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Opromolla, Michele, and Vittoria Petrillo. "Two-Color TeraHertz Radiation by a Multi-Pass FEL Oscillator." Applied Sciences 11, no. 14 (July 14, 2021): 6495. http://dx.doi.org/10.3390/app11146495.
Повний текст джерелаАнотація:
In this paper, we show that an electron beam produced by a super-conducting linac, driven in a sequence of two undulator modules of different periods, can generate two-color Terahertz radiation with wavelengths ranging from 100 μm to 2 μm. The generated pulses are synchronized, both MW-class, and highly coherent. Their specific properties and generation will be discussed in detail. Besides the single-spike pulse structure, usually observed in oscillators, we show that both the THz pump and probe can be modulated in a coherent comb of pulses, enabling periodic excitation and stroboscopic measurements.
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Luo, W., H. B. Zhuo, Y. Y. Ma, X. H. Yang, N. Zhao та M. Y. Yu. "Ultrashort-pulse MeV positron beam generation from intense Compton-scattering γ-ray source driven by laser wakefield acceleration". Laser and Particle Beams 31, № 1 (20 грудня 2012): 89–94. http://dx.doi.org/10.1017/s0263034612000948.
Повний текст джерелаАнотація:
AbstractIntense Compton-scattering γ-ray radiation driven by laser wakefield acceleration (LWFA) and generation of ultrashort positron beams are investigated by Monte Carlo simulation. Using an LWFA driven GeV electron bunch and a 45 femtosecond, 90 mJ/pulse, and 10 Hz Ti:Sapphire laser for driving the Compton scattering, fs γ-ray pulses were generated. The latter have a flux of ≥108/s, peak brightness of ≥1020 photons/(s mm2 mrad2 0.1% bandwidth), and photon energy of 5.9 to 23.2 MeV. The γ-ray pulses then impinge on a thin high-Z target. More than 107 positrons/s in the form of sub-100 fs pulses at several MeV can be produced. Such ultrashort positron pulses can be useful as the pump-probe type positron annihilation spectroscopy as well as in other applications.
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Amir, Samreen, B. S. Chowdhry, Manzoor Hashmani, and Musarrat Hasan. "The Analysis of the Artifacts due to the Simultaneous Use of Two Ultrasound Probes with Different/Similar Operating Frequencies." Computational and Mathematical Methods in Medicine 2013 (2013): 1–5. http://dx.doi.org/10.1155/2013/890170.
Повний текст джерелаАнотація:
The ultrasound imaging has the potential to become a dominant technique for noninvasive therapies and least invasive surgeries. Few cases may require using multiple probes of different units with different modes of ultrasound on the same patient. It generates imaging artifacts, which makes it complicated to gather information from the acquired image. This study was to identify and analyse the artifacts which are produced by simultaneous use of two probes with different/same operating frequencies. Six imaging studies were performed. First of all, the imaging artifacts of the 3.5 MHz and 6 MHz center frequencies with similar (longitudinal) positions of the probes. Secondly, with similar operating frequencies the 6 MHz probe changed from longitudinal to transverse placement to analyse the resulting artifacts. The third study was done with transverse placement of 3.5 MHz probe. The rest of the three cases were just the repetition with common pulse frequencies. Such artifacts in 3D ultrasound images are more obscure than the other artifacts associated and reported.
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Xue, Yinghong, Yueping Niu, and Shangqing Gong. "External Modulation Optical Coherent Domain Reflectometry with Long Measurement Range." Sensors 21, no. 16 (August 16, 2021): 5510. http://dx.doi.org/10.3390/s21165510.
Повний текст джерелаАнотація:
Optical coherent domain reflectometry (OCDR) can achieve a high spatial resolution that is independent of the bandwidth of the receiver, but the measurement range is usually very limited. Here we propose an external modulation OCDR system, in which a pair of linear frequency-modulated pulses generated by one modulator are employed as the probe pulse and the reference, respectively. The spatial resolution is determined by the frequency modulation range of the pulse, and the measurement speed is boosted by orders because the proposed technology can simultaneously diagnose a section of fiber with each pair of pulses, while only a single point can be accessed at a time in typical OCDR. In the demonstrational experiment, a measurement range of up to 50 km is achieved with a spatial resolution of 1.4 m and a measuring time of less than 30 s.
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Kaya, Gamze. "Field-free molecular alignment of carbon dioxide molecules measured with above-threshold ionization yields." Canadian Journal of Physics 98, no. 4 (April 2020): 390–94. http://dx.doi.org/10.1139/cjp-2019-0361.
Повний текст джерелаАнотація:
We present measurements of above-threshold ionization (ATI) of CO2 in a pump-probe experiment where the pump pulse creates a rotational wave packet and the linearly polarized probe pulse generates the ATI spectrum as a function of the pump-probe delay time, which sweeps over the revival time of field-free alignment and its quarter fractions. The observed alignment signals, which are the electron yields of ATI by a probe pulse as a function of a delay between the pump and probe pulse, are compared with the calculated alignment parameter [Formula: see text]. The results are explained by nuclear spin statistics and the wave packet evolution of the CO2 molecule in terms of the highest occupied molecular orbital.
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Gesuele, Felice. "Ultrafast Hyperspectral Transient Absorption Spectroscopy: Application to Single Layer Graphene." Photonics 6, no. 3 (August 29, 2019): 95. http://dx.doi.org/10.3390/photonics6030095.
Повний текст джерелаАнотація:
We describe the basic principles and the experimental implementation of the hyperspectral transient absorption technique, based on femtosecond laser sources. In this technique the samples were optically “pumped” using the femtosecond tunable pulse delivered by an Optical Parametric Amplifier, and “probed” for changes in transmission in a broad spectral range with a “white light” laser-generated supercontinuum. The spectra were collected by a pair of multichannel detectors which allowed retrieval of the absorbance change in a wide spectral range in one time. The use of the supercontinuum probe introduced artifacts in the measured 2D data set which could be corrected with a proper calibration of the chirp. The configuration with crossed polarization for pump and probe pulse extended the spectral measured range above and below the pump energy within the same experiment. We showed the versatility of the technique by applying it to the investigation of the charge carrier dynamics in two-dimensional single layer graphene.
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Oura, Masaki, Tatsuya Wagai, Ashish Chainani, Jun Miyawaki, Hiromi Sato, Masaharu Matsunami, Ritsuko Eguchi, et al. "Development of a single-shot CCD-based data acquisition system for time-resolved X-ray photoelectron spectroscopy at an X-ray free-electron laser facility." Journal of Synchrotron Radiation 21, no. 1 (December 10, 2013): 183–92. http://dx.doi.org/10.1107/s1600577513028233.
Повний текст джерелаАнотація:
In order to utilize high-brilliance photon sources, such as X-ray free-electron lasers (XFELs), for advanced time-resolved photoelectron spectroscopy (TR-PES), a single-shot CCD-based data acquisition system combined with a high-resolution hemispherical electron energy analyzer has been developed. The system's design enables it to be controlled by an external trigger signal for single-shot pump–probe-type TR-PES. The basic performance of the system is demonstrated with an offline test, followed by online core-level photoelectron and Auger electron spectroscopy in `single-shot image', `shot-to-shot image (image-to-image storage or block storage)' and `shot-to-shot sweep' modes at soft X-ray undulator beamline BL17SU of SPring-8. In the offline test the typical repetition rate for image-to-image storage mode has been confirmed to be about 15 Hz using a conventional pulse-generator. The function for correcting the shot-to-shot intensity fluctuations of the exciting photon beam, an important requirement for the TR-PES experiments at FEL sources, has been successfully tested at BL17SU by measuring Au 4fphotoelectrons with intentionally controlled photon flux. The system has also been applied to hard X-ray PES (HAXPES) in `ordinary sweep' mode as well as shot-to-shot image mode at the 27 m-long undulator beamline BL19LXU of SPring-8 and also at the SACLA XFEL facility. The XFEL-induced Ti 1score-level spectrum of La-doped SrTiO3is reported as a function of incident power density. The Ti 1score-level spectrum obtained at low power density is consistent with the spectrum obtained using the synchrotron source. At high power densities the Ti 1score-level spectra show space-charge effects which are analysed using a known mean-field model for ultrafast electron packet propagation. The results successfully confirm the capability of the present data acquisition system for carrying out the core-level HAXPES studies of condensed matter induced by the XFEL.
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ASLAN, BARBAROS, LESTER F. EASTMAN, and QUENTIN DIDUCK. "SIMULATION AND EXPERIMENTAL RESULTS ON GaN BASED ULTRA-SHORT PLANAR NEGATIVE DIFFERENTIAL CONDUCTIVITY DIODES FOR THz POWER GENERATION." International Journal of High Speed Electronics and Systems 19, no. 01 (March 2009): 1–6. http://dx.doi.org/10.1142/s0129156409006035.
Повний текст джерелаАнотація:
A GaN based negative differential conductivity diode utilizing transient ballistic transport effects is proposed and large-signal circuit simulations along with preliminary experimental results are presented. The diode is an n +- n - n + structure and transport is described by an empirical velocity-field relation which is derived directly from femtosecond pulse-probe measurements available in literature and incorporated into the simulations through curve fitting. Efficient THz generation is predicted as a result of ~2.8 peak-to-valley ratio. Pulsed current-voltage characteristics were measured and N -type dependence was observed.
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Zhao, Di, Pengxian You, Jing Yang, Junhong Yu, Hang Zhang, Min Liao, and Jianbo Hu. "A Highly Stable-Output Kilohertz Femtosecond Hard X-ray Pulse Source for Ultrafast X-ray Diffraction." Applied Sciences 12, no. 9 (May 7, 2022): 4723. http://dx.doi.org/10.3390/app12094723.
Повний текст джерелаАнотація:
Femtosecond hard X-ray pulses generated by laser-driven plasma sources are eminently suitable to probe structural dynamics due to the angstrom spatial resolution and sub-picosecond time resolution. However, the insufficient flux of X-ray photons and high pulse-to-pulse instability compared with the large-scale ultrashort X-ray source, such as X-ray free-electron laser and synchrotrons, largely restricts its applications. In this work, we have optimized automation control and mechanical designs to significantly enhance the reliability and photon flux in our femtosecond laser plasma-induced X-ray source. Specifically, the optimized source provides a reliable pulse-to-pulse stability with a fluctuation of less than 1% (root-mean-square) and a total flux of Cu-Kα X-ray photons above 1011 photons/s. To confirm its functionality, ultrafast X-ray diffraction experiments are conducted on two different samples and the high consistency with previous results verifies the system’s superior performance.
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Bandrauk, André D., and Hong Shon Nguyen. "Attosecond molecular spectroscopy The one-electron H2+ system." Canadian Journal of Chemistry 82, no. 6 (June 1, 2004): 831–36. http://dx.doi.org/10.1139/v04-080.
Повний текст джерелаАнотація:
Numerical solutions of the time-dependent Schrödinger equation for a 1-D model non-BornOppenheimer H2+ are used to illustrate the nonlinear, nonperturbative response of molecules to intense (I ≥ 1013 W/cm2), ultrashort (t < 10 fs) laser pulses. Molecular high-order harmonic generation (MHOHG) is shown to be an example of such response, and the resulting nonlinear photon emission spectrum is shown to lead to the synthesis of single attosecond (1018 s) pulses. Application of such ultrashort pulses to the H2+ system results in localized electron wave packets whose motion can be detected by asymmetry in the photoelectron spectrum generated by a subsequent probe attosecond pulse, thus leading to measurement of electron motion in molecules on an attosecond time scale. Key words: attosecond spectroscopy, attosecond photoionization.
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Engel, Robin Y., Piter S. Miedema, Diego Turenne, Igor Vaskivskyi, Günter Brenner, Siarhei Dziarzhytski, Marion Kuhlmann, et al. "Parallel Broadband Femtosecond Reflection Spectroscopy at a Soft X-Ray Free-Electron Laser." Applied Sciences 10, no. 19 (October 4, 2020): 6947. http://dx.doi.org/10.3390/app10196947.
Повний текст джерелаАнотація:
X-ray absorption spectroscopy (XAS) and the directly linked X-ray reflectivity near absorption edges yield a wealth of specific information on the electronic structure around the resonantly addressed element. Observing the dynamic response of complex materials to optical excitations in pump–probe experiments requires high sensitivity to small changes in the spectra which in turn necessitates the brilliance of free electron laser (FEL) pulses. However, due to the fluctuating spectral content of pulses generated by self-amplified spontaneous emission (SASE), FEL experiments often struggle to reach the full sensitivity and time-resolution that FELs can in principle enable. Here, we implement a setup which solves two common challenges in this type of spectroscopy using FELs: First, we achieve a high spectral resolution by using a spectrometer downstream of the sample instead of a monochromator upstream of the sample. Thus, the full FEL bandwidth contributes to the measurement at the same time, and the FEL pulse duration is not elongated by a monochromator. Second, the FEL beam is divided into identical copies by a transmission grating beam splitter so that two spectra from separate spots on the sample (or from the sample and known reference) can be recorded in-parallel with the same spectrometer, enabling a spectrally resolved intensity normalization of pulse fluctuations in pump–probe scenarios. We analyze the capabilities of this setup around the oxygen K- and nickel L-edges recorded with third harmonic radiation of the free electron laser in Hamburg (FLASH), demonstrating the capability for pump–probe measurements with sensitivity to reflectivity changes on the per mill level.
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Romagnani, L., M. Borghesi, C. A. Cecchetti, S. Kar, P. Antici, P. Audebert, S. Bandhoupadjay, et al. "Proton probing measurement of electric and magnetic fields generated by ns and ps laser-matter interactions." Laser and Particle Beams 26, no. 2 (May 6, 2008): 241–48. http://dx.doi.org/10.1017/s0263034608000281.
Повний текст джерелаАнотація:
AbstractThe use of laser-accelerated protons as a particle probe for the detection of electric fields in plasmas has led in recent years to a wealth of novel information regarding the ultrafast plasma dynamics following high intensity laser-matter interactions. The high spatial quality and short duration of these beams have been essential to this purpose. We will discuss some of the most recent results obtained with this diagnostic at the Rutherford Appleton Laboratory (UK) and at LULI - Ecole Polytechnique (France), also applied to conditions of interest to conventional Inertial Confinement Fusion. In particular, the technique has been used to measure electric fields responsible for proton acceleration from solid targets irradiated with ps pulses, magnetic fields formed by ns pulse irradiation of solid targets, and electric fields associated with the ponderomotive channelling of ps laser pulses in under-dense plasmas.
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Boháč, Vlastimil, Peter Dieška, Viliam Vretenár, Danica Opatt-Fidríková, Vladimír Štofanik, and Marian Markovič. "New Planar Disc Transient Method for the Measurement of Thermal Properties of Materials." Advanced Materials Research 1126 (October 2015): 16–21. http://dx.doi.org/10.4028/www.scientific.net/amr.1126.16.
Повний текст джерелаАнотація:
Recently the physical model for the temperature field generated by thermophysical single-probe sensor in a shape of planar disc has been derived. The model accounts cylindrical sample having final radius and infinite length. The prototype of measuring electronics RTA was build that operates with auto balancing bridge. For the measurements the single-transition method is used. While the measurement error of the temperature response measured by thermocouple was 1% at the height of temperature response 1°C, the sensitivity of the measurement with the automatically balanced bridge is better and the signal to noise ratio is improved about 10 times. The measuring electronics was tested for measuring the temperature response using a single-sensor. This sensor generates the heat pulse and sense the temperature response in the same time. The next advantage is that the temperature response to the generated step-wise pulse is much smaller and it can be reduced to the level of 1-8° C compared to stationary method like guarded hot plate method. The effect of the temperature field generated by the probe is much smaller, which in the case of measurement of porous materials at the presence of moisture is beneficial, as the resulting redistribution of moisture under the created temperature gradient is negligible. There were derived basic models for the evaluation of this type of experiment. The probe should be in form of full cylinder or an annulus. The derived temperature function counts the outer and inner diameter of annulus. Putting the inner radius to zero we get the solution for full circle probe, so the model is universal. The model counts also the heat losses from the outer surface of the sample, when the time of measurement exceed the time when the penetration depth of generated heat pulse rich the outer radius of sample. The estimated output parameters from single measurement are the thermal conductivity, thermal diffusivity and specific heat. The heat transfer coefficient is additional parameter fitted as free parameter of the model.
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Diederich, C. J., S. Clegg, and R. B. Roemer. "A Spherical Source Model for the Thermal Pulse Decay Method of Measuring Blood Perfusion: A Sensitivity Analysis." Journal of Biomechanical Engineering 111, no. 1 (February 1, 1989): 55–61. http://dx.doi.org/10.1115/1.3168340.
Повний текст джерелаАнотація:
The thermal pulse-decay method, as developed and analyzed by Chen et al. [1–6], is a thermal clearance technique that uses a small thermistor probe for determining the blood perfusion and thermal conductivity of the tissue immediately surrounding the probe. They described the energy transfer of the probe/tissue system mathematically with a simple analytical model, the point source model, which assumes that the heating source is infinitely small. This paper introduces a new, more accurate analytical description that assumes the heating source is spherically symmetric with a finite radius. A numerical study of these two alternative mathematical models is presented in which the solutions of each model are compared to transient temperature decay data generated from a detailed finite difference simulation of the probe/tissue system. The accuracy and sensitivity of the predictions of each of these models to variations in tissue thermal conductivity and perfusion, probe characteristics, and heating time are presented. In all cases, the accuracy of the spherical source model was better than the point source model. It is also shown that the spherical source model can accurately predict low rates of perfusion (on the order of 1 kg/m3s) unlike the point source model. The spherical source model also allows for the possibility of the measurement probes to be calibrated for an “effective bead radius” which accounts for the nonideal characteristics of the probe, thereby giving even more accurate determinations of perfusion.
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Lewis, T. J., H. Villinger, and E. E. Davis. "Thermal conductivity measurement of rock fragments using a pulsed needle probe." Canadian Journal of Earth Sciences 30, no. 3 (March 1, 1993): 480–85. http://dx.doi.org/10.1139/e93-036.
Повний текст джерелаАнотація:
A heat pulse generated inside a needle probe can be used to measure the thermal conductivity of surrounding rock fragments or drill cuttings. As the pulse of heat is conducted outwards into the surrounding aggregate of rock fragments and water, the decrease in temperature inside the probe is recorded as a function of time. An asymptotic relation between probe temperature, conductivity, and inverse time since the heat pulse is shown to be accurate for the range of times used. The relatively slow thermal response of the probe in samples with higher conductivities is accommodated by a delay in the origin time of the pulse. The combined correction for finite pulse length and slow probe response is shown to be small and predictable. The thermal conductivity of rock fragments is calculated from a model that is dependent on the water content of the sample, as in other methods. Results using this method and a divided bar apparatus are equivalent, given the expected accuracy of a divided bar. The measured thermal conductivities of water, fused quartz, and crystalline quartz compare closely with their accepted values.
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Kolpakhchyan, P. G., and D. V. Olkhovatov. "Sensorless control of the high-speed switched reluctance generator of the micro power plant." Vestnik of Don State Technical University 19, no. 4 (January 3, 2020): 357–65. http://dx.doi.org/10.23947/1992-5980-2019-19-4-357-365.
Повний текст джерелаАнотація:
Introduction. In the distributed and autonomous generation systems using renewable energy sources, low-power generating units (not more than 100-200 kW) based on microturbines function. Microturbines operate most efficiently at high rotational speeds. In this regard, the generator running with a microturbine must also be a high-speed one. A generator is a switched reluctance electric machine (EM) that needs information on the rotor position. It is difficult to use a position sensor in such mechanisms at high speeds. This paper discusses the issues of sensorless control of a high-speed switched reluctance electric generator in conjunction with a steam microturbine.Materials and Methods. So, it is required to evaluate the proof-of-principle developed to control a high-speed switched reluctance EM. For this purpose, a mathematical model has been created including models of the investigated EM, an electric power converter, and a control system. For the EM under consideration, the active resistance is determined, as well as the dependence of the phase flux linkage on the current flowing through it and the position of the moving element. The method used involves probing the idle phase of an electric machine with short voltage pulses of equal duration, and measuring the current in this phase. If the voltage pulse length is much shorter than the phase time constant, then the current pulse amplitude is inversely proportional to the inductance. Thus, registering the maximum current pulse amplitude, it is possible to determine the rotor passage through an uncoordinated position for the probed phase. This information is used to form control actions by other phases. Moreover, the length of the test voltage pulses, required to obtain current pulses sufficient for measuring the value, is of significance versus the duration of the pulsing time. Hence, with an increase in the rotational speed, the number of test pulses is insufficient for measuring the position with the accuracy required for the control goals. This reduces drastically the precision of determining the rotor position; therefore, at high speeds, the application of this method is limited without further refinement of the rotor position. In this case, to increase the precision of measurements, it is necessary to evaluate the rate of current rise when applying the basic voltage pulse or the voltage pulse rate forming the phase current before switching to a single-pulse control mode. Research Results. Two conclusions important for correcting the estimation of the rotor position in a single-pulse operation mode of a reluctance EM are proved. The first conclusion is on the efficiency of the proposed technique of filtering phase current measurement data, the second one concerns the applicability of the identified information criteria. The analysis results of the processes in the switched reluctance EM using sensorless control that implements the described principles for determining the rotor position are presented.Discussion and Conclusions. To correct the estimation of the rotor position, the following information criteria can be used: the presence of a pause between the excitation pulse and the start of the generation process; the decrease in current by the time the generation begins. To refine the estimate, the following fact can be used: on the generation interval, the current curve knee corresponding to the maximum phase inductance is observed at the same rotor position.
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Potma, Eric, Nicoletta Kahya, Wim P. de Boeij, and Douwe A. Wiersma. "A Multicolor Femtosecond Lightsource for (Multiphoton) Confocal Fluorescence Microscopy." Microscopy and Microanalysis 5, S2 (August 1999): 472–73. http://dx.doi.org/10.1017/s1431927600015683.
Повний текст джерелаАнотація:
Recent advances in fluorescence microscopy add to the versatility of this optical technique and intensify its significance as an indispensable tool in biological research. Especially the use of multiphoton excitation offers the microscopist many advantages like inherent optical sectioning, reduced out-of-focus bleaching and higher penetration depths into the sample. In this regard, the commercial availability of pulsed solid-state lightsources like the Ti:Sapphire laser, that provide short pulses needed in the nonlinear multiphoton process, have paved the way for the routine implementation of multiphoton microscopy in the biologists laboratory. Although the spectral range of the commonly used Ti:Sapphire laser allows the application of two-photon fluorescence microscopy on chromophores that absorb in the range of 350-450 nm, a lasersource that enables the two-photon excitation of molecular probes at even shorter wavelengths (<350nm) would be highly beneficial.In this contribution we present a visible femtosecond optical parametric oscillator (OPO, Figure 1) that is ideally suited to excite molecular species at 285-335 nm by means of a two-photon process. Femtosecond pulses with durations as short as 30 fs can be generated within a tuning range from 570 to 670 nm. A cavity dumper incorporated in the laser cavity provides variable pulse repetition rates (single shot to 82 MHz).
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Ding, Yingying, Liwei Song, Junyu Qian, Zhe Liu, Pengfei Wang, Yanyan Li, Yujie Peng, Ye Tian, and Yuxin Leng. "A compact platform for efficient generation and single-shot measurement of high-field terahertz wave with a broadband naturally synchronized mid-infrared source." European Physical Journal Applied Physics 93, no. 1 (January 2021): 10501. http://dx.doi.org/10.1051/epjap/2020200177.
Повний текст джерелаАнотація:
High-field terahertz (THz) wave is a powerful tool for investigating ultrafast dynamics such as the motion of electrons, the vibration of crystal lattices, the precession of spin, etc. In this letter, we demonstrate the generation of intense single-cycle THz pulses from an organic crystal DSTMS (4-N, N-dimethylamino-4'-N'-methyl–stilbazolium 2,4,6–trimethylbenzenesulfonate) via optical rectification. The generated THz field is characterized by single-shot electro-optic sampling with a linearly chirped probe beam. Meanwhile, the spectrum of the infrared pump is broadened to an octave which supports a 1.9-cycle pulse duration. The proposed scheme displays a sophisticated platform of efficient high-field THz generation, single-shot THz measurement, and a broadband mid-infrared source which is naturally synchronized with the THz pulses.
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Zaitsu, Shin-ichi, Takumi Tanabe, Kota Oshima, and Hiroyuki Hirata. "Theoretical Analysis of a Molecular Optical Modulator for a Continuous-Wave Laser Based on a Hollow-Core Photonic Crystal Fiber." Applied Sciences 8, no. 10 (October 12, 2018): 1895. http://dx.doi.org/10.3390/app8101895.
Повний текст джерелаАнотація:
A THz optical modulator for a continuous-wave laser using a hollow-core photonic crystal fiber (HC-PCF) was proposed and theoretically analyzed. Lightwaves traveling through the HC-PCF is modulated by interactions with coherently driven Raman-active molecules in the core. The coherent molecular motion is excited by a pulse train having an interval between successive pulses shorter than the molecular dephasing time. In principle, a rotational transition of molecular hydrogen (S 0 (1)) at a pressure of 1 atm has a long enough dephasing time to maintain molecular coherence during a 1 GHz commercially available mode-locked pulse train. Optimization of the waveguide dispersion would enable phase-matching between the probe beam and generated sidebands during optical modulation. The proposed scheme would be achievable with a reasonable pump beam power and HC-PCF length, and with a feasible pressure of molecules in the core.
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Crampton, Kevin T., Alan G. Joly, and Patrick Z. El-Khoury. "Uncovering surface plasmon optical resonances in nanohole arrays through interferometric photoemission electron microscopy." Applied Physics Letters 120, no. 8 (February 21, 2022): 081102. http://dx.doi.org/10.1063/5.0082481.
Повний текст джерелаАнотація:
The role of surface plasmon polaritons (SPPs) in nanohole array optical extinction spectra is explored using a time-resolved technique capable of isolating the air/metal interfacial SPP contribution to the typical Fano profile in optical transmission curves. A pair of interferometrically locked broad-band femtosecond pulses is used to launch SPPs from lithographically patterned plasmonic nanohole arrays. SPPs launched in the co- and counter-propagating directions are probed using a third probe pulse in a photoemission electron microscope. Using this approach, we record interferometric SPP–SPP linear autocorrelations that selectively report on the resonances of SPPs launched from arrays of varying pitches and hole diameters. Aside from advancing an approach to selective SPP spectroscopy, we illustrate that resonant coupling in the counter-propagating direction may be exploited to control the spatial, temporal, and spectral characteristics of SPPs. For the counter-propagating direction, we show that tuning the array pitch near the fundamental plasmon resonance generates color-tuned (∼770–820 nm), narrow bandwidth SPPs, and the bandwidth may be controlled by changing the ratio of pitch to hole diameter. The SPP resonances we recover through Fourier transforms of the interferometric autocorrelations shed light on the classical problem of Fano interference in nanohole array extinction spectra.
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Aoukili, Abdeslam, and Abdellatif Khamlichi. "Damage detection of cracks in carbon fibre reinforced composites by pulsed eddy-current testing." MATEC Web of Conferences 191 (2018): 00003. http://dx.doi.org/10.1051/matecconf/201819100003.
Повний текст джерелаАнотація:
Non-destructive evaluation techniques that are based on electromagnetic methods are commonly used for inspection of metallic and carbon fibre reinforced plastics parts. Some of these inspection methods are based on eddycurrents which are generated by the electromagnetic induction phenomenon occurring under variable magnetic induction field. In eddy-currents testing, the depth of penetration into the material is controlled by the conductivity of the tested material and also the work frequency. Transient eddy-currents, also called pulsed eddy-currents, is an emerging non destructive technique that employs a pulsed excitation to induce a transient electromagnetic response from defects lying deep within a conducting structure. Such defects are difficult to inspect by conventional techniques, such as harmonic eddy-currents or ultrasonics. A large number of recent scientific publications have dealt with the theoretical understanding of the pulsed eddy-currents phenomenon and have also undertaken the design feature of appropriate probes. Finite element solution of the governing equations has been used to simulate the output signals as function of the input electrical excitation signal. Considering a B-scan strategy, simulation of a pulsed eddy-currents based probe is performed in this work with the objective to assess detectability of small defects through monitoring impedance changes of a detection probe.
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Balerna, Antonella, Samanta Bartocci, Giovanni Batignani, Alessandro Cianchi, Enrica Chiadroni, Marcello Coreno, Antonio Cricenti, et al. "The Potential of EuPRAXIA@SPARC_LAB for Radiation Based Techniques." Condensed Matter 4, no. 1 (March 7, 2019): 30. http://dx.doi.org/10.3390/condmat4010030.
Повний текст джерелаАнотація:
A proposal for building a Free Electron Laser, EuPRAXIA@SPARC_LAB, at the Laboratori Nazionali di Frascati, is at present under consideration. This FEL facility will provide a unique combination of a high brightness GeV-range electron beam generated in a X-band RF linac, a 0.5 PW-class laser system and the first FEL source driven by a plasma accelerator. The FEL will produce ultra-bright pulses, with up to 10 12 photons/pulse, femtosecond timescale and wavelength down to 3 nm, which lies in the so called “water window”. The experimental activity will be focused on the realization of a plasma driven short wavelength FEL able to provide high-quality photons for a user beamline. In this paper, we describe the main classes of experiments that will be performed at the facility, including coherent diffraction imaging, soft X-ray absorption spectroscopy, Raman spectroscopy, Resonant Inelastic X-ray Scattering and photofragmentation measurements. These techniques will allow studying a variety of samples, both biological and inorganic, providing information about their structure and dynamical behavior. In this context, the possibility of inducing changes in samples via pump pulses leading to the stimulation of chemical reactions or the generation of coherent excitations would tremendously benefit from pulses in the soft X-ray region. High power synchronized optical lasers and a TeraHertz radiation source will indeed be made available for THz and pump–probe experiments and a split-and-delay station will allow performing XUV-XUV pump–probe experiments.
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Kim, Taehoon, Fabian Fool, Djalma Simoes dos Santos, Zu-Yao Chang, Emile Noothout, Hendrik J. Vos, Johan G. Bosch, Martin D. Verweij, Nico de Jong, and Michiel A. P. Pertijs. "Design of an Ultrasound Transceiver ASIC with a Switching-Artifact Reduction Technique for 3D Carotid Artery Imaging." Sensors 21, no. 1 (December 29, 2020): 150. http://dx.doi.org/10.3390/s21010150.
Повний текст джерелаАнотація:
This paper presents an ultrasound transceiver application-specific integrated circuit (ASIC) directly integrated with an array of 12 × 80 piezoelectric transducer elements to enable next-generation ultrasound probes for 3D carotid artery imaging. The ASIC, implemented in a 0.18 µm high-voltage Bipolar-CMOS-DMOS (HV BCD) process, adopted a programmable switch matrix that allowed selected transducer elements in each row to be connected to a transmit and receive channel of an imaging system. This made the probe operate like an electronically translatable linear array, allowing large-aperture matrix arrays to be interfaced with a manageable number of system channels. This paper presents a second-generation ASIC that employed an improved switch design to minimize clock feedthrough and charge-injection effects of high-voltage metal–oxide–semiconductor field-effect transistors (HV MOSFETs), which in the first-generation ASIC caused parasitic transmissions and associated imaging artifacts. The proposed switch controller, implemented with cascaded non-overlapping clock generators, generated control signals with improved timing to mitigate the effects of these non-idealities. Both simulation results and electrical measurements showed a 20 dB reduction of the switching artifacts. In addition, an acoustic pulse-echo measurement successfully demonstrated a 20 dB reduction of imaging artifacts.
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Yamaguchi, Masashi, Minfeng Wang, and Pablo Suarez. "TERAHERTZ PHONON-POLARITON IMAGING FOR THE APPLICATION OF CHEMICAL DETECTION." International Journal of High Speed Electronics and Systems 17, no. 02 (June 2007): 355–65. http://dx.doi.org/10.1142/s0129156407004552.
Повний текст джерелаАнотація:
A combination of Terahertz (THz) polariton spectroscopy and polariton imaging technique for the application to chemical sensing is presented. We use phonon-polaritons, a coupled oscillation of the lattice vibration and radiation field, as an intense radiation source for THz spectroscopy. The propagation process of the polaritons generated in one of the two LiNbO 3 transducer crystals through the sample sandwiched between the crystals is visualized using a polariton imaging technique. Partially reflected polaritons at the transducer-sample interface and polaritons partially transmitted through the sample are visualized simultaneously in a single frame of an image. The temporal profile of reflected and transmitted phonon-polaritons can be obtained without scanning the delay time between the pump and probe femtosecond laser pulses unlike THz time-domain spectroscopy which requires point-by-point acquisition of the temporal pulse profile using conventional pump-probe scheme. The results suggest possible application of this technique to the chemical sensing with fast acquisition rate. The technique has been successfully applied to the measurement of liquid and solid samples, and simultaneous measurement of multiple samples has also been achieved.
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TRITA, A., I. CRISTIANI, V. DEGIORGIO, M. DÖBELI, D. CHRASTINA, and H. VON KÄNEL. "MEASUREMENT OF THE LIFETIME OF PHOTO-GENERATED FREE CARRIERS IN SiGe WAVEGUIDES." Journal of Nonlinear Optical Physics & Materials 16, no. 02 (June 2007): 207–16. http://dx.doi.org/10.1142/s0218863507003718.
Повний текст джерелаАнотація:
The carrier lifetime in SiGe planar waveguides with Si cladding was measured with a pump-and-probe technique, using an ultrashort 810 nm laser pulse and a CW 1.55 μm probe, as a function of layer thickness d and Ge concentration x. The measured lifetimes are in the range of 20-90 ns. The obtained interface recombination velocity S is a growing function of both d and x, taking values in the range from 300 to 4000 cm/s.
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Zavadilová, Alena, Václav Kubeček, and David Vyhlídal. "Synchronously Intracavity-Pumped Picosecond Optical Parametric Oscillators for Sensors." Sensors 22, no. 9 (April 21, 2022): 3200. http://dx.doi.org/10.3390/s22093200.
Повний текст джерелаАнотація:
The research and development of laser systems for intracavity phase interferometry is described. These systems are based on an intracavity synchronously pumped optical parametric oscillator (OPO), enabling the generation of two trains of picosecond pulses inside a single cavity. In such a configuration, it is possible to measure the beat note frequency between two pulses and to very precisely determine the phase difference between them. The pump source is a diode-pumped passively mode-locked Nd:YVO4 laser. A periodically poled magnesium-doped lithium niobate crystal is used as the optical parametric oscillator crystal coupling the pump and the signal cavities. We designed a synchronously pumped OPO in a linear and ring cavity configuration allowing generation in a dual-pulse regime. By a mutual detuning of both cavity lengths, the quasi-synchronous regime of pumping was achieved and high harmonics of repetition rate frequencies were generated. Such a system can be useful for applications such as pump-probe spectroscopy or for testing telecommunication systems. We also realized the subharmonic OPO cavity as a source of two independent trains of picosecond pulses suitable for intracavity phase interferometry; we also measured the beat note signal.