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Artykuły w czasopismach na temat "Ionization bubbles"
1
Danehkar, A., M. S. Oey i W. J. Gray. "Numerical Modeling of Galactic Superwinds with Time-evolving Stellar Feedback". Proceedings of the International Astronomical Union 17, S370 (sierpień 2021): 217–22. http://dx.doi.org/10.1017/s1743921323000066.
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AbstractMass-loss and radiation feedback from evolving massive stars produce galactic-scale superwinds, sometimes surrounded by pressure-driven bubbles. Using the time-dependent stellar population typically seen in star-forming regions, we conduct hydrodynamic simulations of a starburst-driven superwind model coupled with radiative efficiency rates to investigate the formation of radiative cooling superwinds and bubbles. Our numerical simulations depict the parameter space where radiative cooling superwinds with or without bubbles occur. Moreover, we employ the physical properties and time-dependent ionization states to predict emission line profiles under the assumption of collisional ionization and non-equilibrium ionization caused by wind thermal feedback in addition to photoionization created by the radiation background. We see the dependence of non-equilibrium ionization structures on the time-evolving ionizing source, leading to a deviation from collisional ionization in radiative cooling wind regions over time.
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Dwarkadas, Vikram V. "On the Evolution of, and Hot Gas in, Wind-Blown Bubbles around Massive Stars - Wind Bubbles Are Not Energy-Conserving". Galaxies 11, nr 3 (19.06.2023): 78. http://dx.doi.org/10.3390/galaxies11030078.
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The structure and evolution of wind-blown bubbles (WBBs) around massive stars has primarilybeen investigated using an energy-conserving model of wind-blown bubbles. While this model is useful in explaining the general properties of the evolution, several problems remain, including inconsistencies between observed wind luminosities and those derived using this formulation. Major difficulties include the low X-ray temperature and X-ray luminosity, compared to the model. In this paper, we re-examine the evolution, dynamics, and kinematics of WBBs around massive stars, using published ionization gasdynamic simulations of wind-blown bubbles. We show that WBBs can cool efficiently due to the presence of various instabilities and turbulence within the bubble. The expansion of WBBs is more consistent with a momentum-conserving solution, rather than an energy-conserving solution. This compares well with the dynamics and kinematics of observed wind bubbles. Despite the cooling of the bubble, the shocked wind temperature is not reduced to the observed values. We argue that the X-ray emission arise mainly from clumps and filaments within the hot shocked wind region, with temperatures just above 106 K. The remainder of the plasma can contribute to a lesser extent.
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Soria, R., M. W. Pakull, C. Motch, J. C. A. Miller-Jones, A. D. Schwope, R. T. Urquhart i M. S. Ryan. "The ultraluminous X-ray source bubble in NGC 5585". Monthly Notices of the Royal Astronomical Society 501, nr 2 (9.12.2020): 1644–62. http://dx.doi.org/10.1093/mnras/staa3784.
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ABSTRACT Some ultraluminous X-ray sources (ULXs) are surrounded by collisionally ionized bubbles, larger and more energetic than supernova remnants: they are evidence of the powerful outflows associated with super-Eddington X-ray sources. We illustrate the most recent addition to this class: a huge (350 pc × 220 pc in diameter) bubble around a ULX in NGC 5585. We modelled the X-ray properties of the ULX (a broadened-disc source with LX ≈ 2–4 × 1039 erg s−1) from Chandra and XMM–Newton, and identified its likely optical counterpart in Hubble Space Telescope images. We used the Large Binocular Telescope to study the optical emission from the ionized bubble. We show that the line emission spectrum is indicative of collisional ionization. We refine the method for inferring the shock velocity from the width of the optical lines. We derive an average shock velocity ≈125 km s−1, which corresponds to a dynamical age of ∼600 000 yr for the bubble, and an average mechanical power Pw ∼ 1040 erg s−1; thus, the mechanical power is a few times higher than the current photon luminosity. With Very Large Array observations, we discovered and resolved a powerful radio bubble with the same size as the optical bubble, and a 1.4-GHz luminosity ∼1035 erg s−1, at the upper end of the luminosity range for this type of source. We explain why ULX bubbles tend to become more radio luminous as they expand while radio supernova remnants tend to fade.
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Xu, Yidong, Bin Yue i Xuelei Chen. "The Neutral Islands during the Late Epoch of Reionization". Proceedings of the International Astronomical Union 12, S333 (październik 2017): 64–67. http://dx.doi.org/10.1017/s174392131701153x.
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AbstractThe large-scale structure of the ionization field during the epoch of reionization (EoR) can be modeled by the excursion set theory. While the growth of ionized regions during the early stage are described by the “bubble model”, the shrinking process of neutral regions after the percolation of the ionized region calls for an “island model”. An excursion set based analytical model and a semi-numerical code (islandFAST) have been developed. The ionizing background and the bubbles inside the islands are also included in the treatment. With two kinds of absorbers of ionizing photons, i.e. the large-scale under-dense neutral islands and the small-scale over-dense clumps, the ionizing background are self-consistently evolved in the model.
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Bolotnova, R. Kh. "Wide-range equations of state for organic liquids". Proceedings of the Mavlyutov Institute of Mechanics 5 (2007): 113–20. http://dx.doi.org/10.21662/uim2007.1.011.
Pełny tekst źródłaStreszczenie:
The method of construction the wide-range equations of state for organic liquids, describing the gas and liquid phases including dissociation and ionization which occurs during an intense collapse of steam bubbles and accompanied by ultra-high pressures and temperatures, is proposed.
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Yasui, Kyuichi. "Multibubble Sonoluminescence from a Theoretical Perspective". Molecules 26, nr 15 (30.07.2021): 4624. http://dx.doi.org/10.3390/molecules26154624.
Pełny tekst źródłaStreszczenie:
In the present review, complexity in multibubble sonoluminescence (MBSL) is discussed. At relatively low ultrasonic frequency, a cavitation bubble is filled mostly with water vapor at relatively high acoustic amplitude which results in OH-line emission by chemiluminescence as well as emissions from weakly ionized plasma formed inside a bubble at the end of the violent bubble collapse. At relatively high ultrasonic frequency or at relatively low acoustic amplitude at relatively low ultrasonic frequency, a cavitation bubble is mostly filled with noncondensable gases such as air or argon at the end of the bubble collapse, which results in relatively high bubble temperature and light emissions from plasma formed inside a bubble. Ionization potential lowering for atoms and molecules occurs due to the extremely high density inside a bubble at the end of the violent bubble collapse, which is one of the main reasons for the plasma formation inside a bubble in addition to the high bubble temperature due to quasi-adiabatic compression of a bubble, where “quasi” means that appreciable thermal conduction takes place between the heated interior of a bubble and the surrounding liquid. Due to bubble–bubble interaction, liquid droplets enter bubbles at the bubble collapse, which results in sodium-line emission.
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Medling, Anne M., Lisa J. Kewley, Daniela Calzetti, George C. Privon, Kirsten Larson, Jeffrey A. Rich, Lee Armus i in. "Tracing the Ionization Structure of the Shocked Filaments of NGC 6240". Astrophysical Journal 923, nr 2 (1.12.2021): 160. http://dx.doi.org/10.3847/1538-4357/ac2ebb.
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Abstract We study the ionization and excitation structure of the interstellar medium in the late-stage gas-rich galaxy merger NGC 6240 using a suite of emission-line maps at ∼25 pc resolution from the Hubble Space Telescope, Keck/NIRC2 with Adaptive Optics, and the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 6240 hosts a superwind driven by intense star formation and/or one or both of two active nuclei; the outflows produce bubbles and filaments seen in shock tracers from warm molecular gas (H2 2.12 μm) to optical ionized gas ([O iii], [N ii], [S ii], and [O i]) and hot plasma (Fe XXV). In the most distinct bubble, we see a clear shock front traced by high [O iii]/Hβ and [O iii]/[O i]. Cool molecular gas (CO(2−1)) is only present near the base of the bubble, toward the nuclei launching the outflow. We interpret the lack of molecular gas outside the bubble to mean that the shock front is not responsible for dissociating molecular gas, and conclude that the molecular clouds are partly shielded and either entrained briefly in the outflow, or left undisturbed while the hot wind flows around them. Elsewhere in the galaxy, shock-excited H2 extends at least ∼4 kpc from the nuclei, tracing molecular gas even warmer than that between the nuclei, where the two galaxies’ interstellar media are colliding. A ridgeline of high [O iii]/Hβ emission along the eastern arm aligns with the southern nucleus’ stellar disk minor axis; optical integral field spectroscopy from WiFeS suggests this highly ionized gas is centered at systemic velocity and likely photoionized by direct line of sight to the southern active galactic nucleus.
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Dwarkadas, Vikram V. "Ionization-Gasdynamic Simulations of Wind-Blown Nebulae around Massive Stars". Galaxies 10, nr 1 (17.02.2022): 37. http://dx.doi.org/10.3390/galaxies10010037.
Pełny tekst źródłaStreszczenie:
Using a code that employs a self-consistent method for computing the effects of photo-ionization on circumstellar gas dynamics, we model the formation of wind-driven nebulae around massive stars. We take into account changes in stellar properties and mass-loss over the star’s evolution. Our simulations show how various properties, such as the density and ionization fraction, change throughout the evolution of the star. The multi-dimensional simulations reveal the presence of strong ionization front instabilities in the main-sequence phase, similar to those seen in galactic ionization fronts. Hydrodynamic instabilities at the interfaces lead to the formation of filaments and clumps that are continually being stripped off and mixed with the low density interior. Even though the winds start out as completely radial, the spherical symmetry is quickly destroyed, and the shocked wind region is manifestly asymmetrical. The simulations demonstrate that it is important to include the effects of the photoionizing photons from the star, and simulations that do not include this may fail to reproduce the observed density profile and ionization structure of wind-blown bubbles around massive stars.
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Gorce, Adélie, i Jonathan R. Pritchard. "Studying the morphology of reionization with the triangle correlation function of phases". Monthly Notices of the Royal Astronomical Society 489, nr 1 (9.08.2019): 1321–37. http://dx.doi.org/10.1093/mnras/stz2195.
Pełny tekst źródłaStreszczenie:
ABSTRACT We present a new statistical tool, called the triangle correlation function (TCF), inspired by the earlier work of Obreschkow et al. It is derived from the three-point correlation function and aims to probe the characteristic scale of ionized regions during the epoch of reionization from 21cm interferometric observations. Unlike most works, which focus on power spectrum, i.e. amplitude information, our statistic is based on the information we can extract from the phases of the Fourier transform of the ionization field. In this perspective, it may benefit from the well-known interferometric concept of closure phases. We find that this statistical estimator performs very well on simple ionization fields. For example, with well-defined fully ionized discs, there is a peaking scale, which we can relate to the radius of the ionized bubbles. We explore the robustness of the TCF when observational effects such as angular resolution and noise are considered. We also get interesting results on fields generated by more elaborate simulations such as 21CMFAST. Although the variety of sources and ionized morphologies in the early stages of the process make its interpretation more challenging, the nature of the signal can tell us about the stage of reionization. Finally, and in contrast to other bubble size distribution algorithms, we show that the TCF can resolve two different characteristic scales in a given map.
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Sönksen, Carsten P., Peter Roepstorff, Per-Olof Markgren, U. Helena Danielson, Markku D. Hämäläinen i Östen Jansson. "Capture and Analysis of Low Molecular Weight Ligands by Surface Plasmon Resonance Combined with Mass Spectrometry". European Journal of Mass Spectrometry 7, nr 4-5 (sierpień 2001): 385–91. http://dx.doi.org/10.1255/ejms.448.
Pełny tekst źródłaStreszczenie:
The combination of biomolecular interaction analysis (BIA)by surface plasmon resonance (SPR)and nano-electrospray ionization ion trap mass spectrometry (nanoESI-Ion Trap MS)as well as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS)is demonstrated for the binding of low molecular weight inhibitors (∼ 600 Da) to HIV-1 protease. Inhibitors were captured on sensor chips of a manual or an automated SPR biosensor, to which HIV-1 protease was immobilized. Compounds and buffer components that bound unspecifically to the sensor surface were removed and the inhibitors were eluted in a minimal volume (3 μL), between air bubbles, in order to prevent dispersion of analyte into buffer eluent. Molecular weights were subsequently determined by mass spectrometry, structural information was obtained by MALDI-ToF post-source decay as well as by electrospray ionization tandem mass spectrometry (MS/MS)analysis. Furthermore, competition experiments, using a mixture of different ligands, demonstrated that the peak intensities in the MALDI-ToF spectrum could be used for relative quantification of the amount of the different ligands bound to the immobilized target. Methodology for automated capture and elution of analytes was developed and evaluated.
Rozprawy doktorskie na temat "Ionization bubbles"
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Khadka, Sovit M. "Multi-diagnostic Investigations of the Equatorial and Low-latitude Ionospheric Electrodynamics and Their Impacts on Space-based Technologies". Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:108001.
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Thesis advisor: Prof. Michael J. NaughtonThesis advisor: Dr. Cesar E. Valladares
The equatorial and low-latitude ionosphere of the Earth exhibits unique features on its structuring, coupling, and electrodynamics that offer the possibility to forecast the dynamics and fluctuations of ionospheric plasma densities at later times. The scientific understanding and forecasting of ionospheric plasma are necessary for several practical applications, such as for mitigating the adverse effects of space weather on communication, navigation, power grids, space mission, and for various scientific experiments and applications. The daytime equatorial electrojet (EEJ), equatorial ionization anomaly (EIA), as well as nighttime equatorial plasma bubble (EPB) and plasma blobs are the most prominent low-latitude ionospheric phenomena. This dissertation focuses on the multi-diagnostic study of the mechanism, properties, abnormalities, and interrelationships of these phenomena to provide significant contributions to space weather communities from the ground- and space-based measurements. A strong longitudinal, seasonal, day-to-day variability and dependency between EEJ, ExB vertical plasma drift, and total electron content (TEC) in the EIA distribution are seen in the equatorial and low-latitude region. In general, the EEJ strength is stronger in the west coast of South America than in its east coast. The variability of the EEJ in the dayside ionosphere significantly affects the ionospheric electron density variation, dynamics of the peak height of F2-layer, and TEC distributions as the EEJ influences the vertical transport mechanism of the ionospheric plasma. The eastward electric field (EEF) and the neutral wind play a decisive role in controlling the actual configuration of the EIA. The trans-equatorial neutral wind profile calculated using data from the Second-generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator and a physics-based numerical model, LLIONS (Low-Latitude IONospheric Sector) give new perspectives on the effects of daytime meridional neutral winds on the consequent evolution of the asymmetry of the equatorial TEC anomalies during the afternoon onwards. The spatial configurations including the strength, shape, amplitude and latitudinal extension of the EIA crests are affected by the EEF associated with the EEJ under undisturbed conditions, whereas the meridional neutral winds play a significant role in the development of their asymmetric structure in the low-latitude ionosphere. Additionally, the SWARM satellite constellation and the ground-based LISN (Low-Latitude Ionospheric Sensor Network) data allow us to resolve the space-time ambiguity of past single-satellite studies and detect the drastic changes that EPBs and plasma blobs undergo on a short time scale. The coordinated quantitative analysis of a plasma density observation shows evidence of the association of plasma blobs with EPBs via an appropriate geomagnetic flux tube. Plasma blobs were initially associated with the EPBs and remained at the equatorial latitude right above the EPBs height, but later were pushed away from geomagnetic equator towards EIA latitudes by the EPB/ depleted flux tubes that grew in volume. Further, there exists a strong correlation between the noontime equatorial electrojet and the GPS-derived TEC distributions during the afternoon time period, caused by vertical E × B drift via the fountain effect. Nevertheless, only a minor correlation likely exists between the peak EEJ and the net postsunset ionospheric scintillation index (S4) greater than 0.2. This study not only searches for a mutual relationship between the midday, afternoon and nighttime ionospheric phenomena but also aims at providing a possible route to improve our space weather forecasting capability by predicting nighttime ionospheric irregularities based on midday measurements at the equatorial and low latitudes
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Raste, Janakee. "Analytical Formalism to Study the 21 cm Signal from Cosmic Dawn and Epoch of Reionization". Thesis, 2019. https://etd.iisc.ac.in/handle/2005/4746.
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The epoch of Cosmic Dawn and Reionization is one of the most important time periods of the
universe when first sources of radiation like stars and galaxies were formed, and they changed the
properties of their surrounding medium. 21 cm radiation emitted due to the hyperfine splitting of
ground state of neutral hydrogen is one of the most important probes to study the state and
dynamics of neutral medium during this epoch. I present an analytical formalism to compute the
fluctuating component of the 21 cm signal from CD/EoR.
I have used excursion set formalism to calculate the size distribution of randomly distributed selfionized
regions, and calculate the isotropic spin temperature profiles around them, taking into
account the effect of X‐rays and Ly‐alpha photons. I present an analytical formalism to compute the
two‐point correlation function for this topology, where small ionization bubbles are surrounded by
large and shallow spin temperature profiles, which can overlap with one another and merge with a
background value far away from any source. Using geometric and probabilistic arguments, I compute
the global 21 cm signal, its auto‐correlation and power spectrum in the redshift range 10 < z < 30.
Our results from this analytical formalism agree reasonably well with existing results in the literature
from N‐body simulations
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"Effects of ionization in a single sonoluminescing bubble". 2000. http://library.cuhk.edu.hk/record=b5890351.
Pełny tekst źródłaStreszczenie:
Ho Chun Yan = 電離對單泡聲致發光的影響 / 何俊恩.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references (leaves [90]-93).
Text in English; abstracts in English and Chinese.
Ho Chun Yan = Dian li dui dan pao sheng zhi fa guang de ying xiang / He Junen.
Abstract --- p.i
Acknowledgements --- p.ii
Contents --- p.iii
List of Figures --- p.vii
List of Tables --- p.xii
Chapter Chapter 1. --- Introduction --- p.1
Chapter Chapter 2. --- Hydro dynamical Framework --- p.7
Chapter 2.1 --- Bubble wall motion --- p.8
Chapter 2.2 --- Navier-Stokes equations --- p.10
Chapter 2.3 --- Energy equation in water --- p.11
Chapter 2.4 --- Boundary condition --- p.12
Chapter 2.5 --- Equation of state of the gas in the bubble --- p.13
Chapter 2.5.1 --- Hard-core van der Waals EOS --- p.13
Chapter 2.5.2 --- Young's EOS --- p.14
Chapter 2.6 --- Numerical method --- p.14
Chapter 2.7 --- Numerical results and discussion --- p.15
Chapter 2.8 --- Chapter summary --- p.19
Chapter Chapter 3. --- Equilibrium Approach --- p.20
Chapter 3.1 --- Saha equation --- p.21
Chapter 3.2 --- Equation of state (EOS) --- p.22
Chapter 3.3 --- Numerical method --- p.23
Chapter 3.4 --- Numerical results --- p.23
Chapter 3.5 --- Chapter summary --- p.28
Chapter Chapter 4. --- Reaction Rates Approach --- p.29
Chapter 4.1 --- Conservation equations --- p.30
Chapter 4.2 --- Ionization and recombination processes --- p.32
Chapter 4.2.1 --- Collisional ionization --- p.32
Chapter 4.2.2 --- Radiative recombination --- p.33
Chapter 4.2.3 --- Three-body recombination --- p.34
Chapter 4.2.4 --- Consistency with Saha equation --- p.34
Chapter 4.3 --- Equation of state --- p.35
Chapter 4.3.1 --- Modified Van der Waals EOS --- p.35
Chapter 4.3.2 --- Modified Young's EOS --- p.36
Chapter 4.4 --- Numerical method --- p.37
Chapter 4.5 --- Numerical results --- p.38
Chapter 4.5.1 --- Effect of ionization on hydrodynamic variables --- p.38
Chapter 4.5.2 --- Time variation of temperature --- p.40
Chapter 4.5.3 --- Near the upper threshold of SBSL --- p.41
Chapter 4.5.4 --- Onset of SBSL --- p.44
Chapter 4.5.5 --- Effect of EOS --- p.46
Chapter 4.5.6 --- Effect of physical parameters --- p.51
Chapter 4.6 --- Chapter summary --- p.56
Chapter Chapter 5. --- Emitted Radiation --- p.57
Chapter 5.1 --- Bremsstrahlung emission --- p.59
Chapter 5.1.1 --- Numerical results --- p.60
Chapter 5.2 --- Simple blackbody radiation model --- p.63
Chapter 5.2.1 --- Planck's law --- p.63
Chapter 5.2.2 --- Calculated pulse width and spectrum --- p.64
Chapter 5.3 --- Blackbody radiation with finite opacity --- p.68
Chapter 5.3.1 --- Photon absorption --- p.68
Chapter 5.3.2 --- Importance of photon absorption --- p.70
Chapter 5.3.3 --- The refined model --- p.72
Chapter 5.3.4 --- Pulse width and spectrum in the refined model --- p.73
Chapter 5.4 --- Chapter summary --- p.80
Chapter Chapter 6. --- Summary --- p.81
Appendix A. Hydrodynamics of an SL Bubble --- p.83
Chapter A.1 --- The normal viscous stress and heat conductivity --- p.83
Chapter A.2 --- Transformation of Navier-Stoke equations --- p.83
Chapter A.3 --- Transformation of the energy equation of liquid --- p.84
Appendix B. Numerical Scheme for the gas dynamics with ionization --- p.85
Chapter B.1 --- Finite difference equation --- p.85
Chapter B.2 --- The TVD scheme --- p.86
Bibliography --- p.90
Książki na temat "Ionization bubbles"
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Gravity wave seeding of equatorial plasma bubbles. [Washington, DC: National Aeronautics and Space Administration, 1997.
Znajdź pełny tekst źródłaCzęści książek na temat "Ionization bubbles"
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Jenkins, Edward B. "Pressure and Ionization Balances in the Circum-Heliospheric Interstellar Medium and the Local Bubble". W From the Outer Heliosphere to the Local Bubble, 205–16. New York, NY: Springer New York, 2008. http://dx.doi.org/10.1007/978-1-4419-0247-4_16.
Pełny tekst źródłaStreszczenia konferencji na temat "Ionization bubbles"
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Menchiari, Stefano, Giovanni Morlino, Elena Amato i Niccolò Bucciantini. "Cosmic ray induced ionization of molecular clouds embedded in the wind blown bubbles of massive star clusters". W 38th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2023. http://dx.doi.org/10.22323/1.444.0059.
Pełny tekst źródła
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Tabei, Katsuine, Shunji Mashiko i Hiroyuki Shirai. "Study of Cavitation Light Emission Generated by a Waterhammer". W ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45274.
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Cavitation light emission generated by a waterhammer is investigated experimentally and theoretically for water containing a small amount of rare gas (xenon and argon). In the experiment, the water is forced to flow upwards in an evacuated vertical circular tube by the rapid opening of a ball valve that is connected to the liquid reservoir. The liquid vaporizes until the flow reaches the top end of the tube, and many minute cavitation bubbles are generated in the liquid. When the water column collides with the end of the closed pipe, a waterhammer with a pressure of over 1 MPa is generated in the multi-phase liquid, and it progresses toward the reverse direction. In such a process, the cavitation bubble collapses, and emits an instantaneous flash of light. Physical quantities such as the propagation velocity of the pressure waves and the cavitation emission intensity are measured. In addition, the momentary patterns of the bubbly flow and the light emission are also visualized by using an image intensifier and a stroboscope. The theory is constituted for the multi-phase flow of the waterhammer, in which the Keller and Miksis’ equation for the collapse of a bubble includes the effect of the ionization reaction of rare gas in the bubble. From the study, the following features are shown: Light emission occurs only at the front of the shock wave of the waterhammer. The position of light emission moves exactly at the same speed as the propagation speed of the pressure wave. Changes of pressure and emission intensity in the waterhammer are both strongly dependent on a void fraction. The ratio of emission intensity for water dissolved with argon and water dissolved with xenon is nearly 1:5.
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Shkolnikov, P. L., i A. E. Kaplan. "Backward and multi-echo field ionization by intense non-envelope "superpulses"". W Applications of High Field and Short Wavelength Sources. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/hfsw.1997.the29.
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Recently, we have proposed two avenues to generating ultrashort (potentially, subfemtosecond) and intense (up to atomic fields) nonoscillating pulses: a high-repetition train of such pulses can be produced in multicomponent stimulated Raman scattering [1], and a single pulse ("electromagnetic bubble" -- EMB) or several of them can result [2,3] from the propagation of an initially broad unipolar pulse (half-cycle pulse -- HCP [4]) in an appropriate nonlinear medium. Such pulses could cause a substantial "shake-up" excitation or ionization of an atomic system within the time much smaller than any characteristic time of the system. These "superpulses" would open a new chapter in nonlinear optics and atomic and molecular physics, both as a new probing tool and a source of new effects. In the present paper, we consider one of them: backward and multi-echo field ionization [5].
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Vogel, Alfred, i Joachim Noack. "Numerical Simulation of Optical Breakdown for Cellular Surgery at Nanosecond to Femtosecond Time Scales". W European Conference on Biomedical Optics. Washington, D.C.: Optica Publishing Group, 2001. http://dx.doi.org/10.1364/ecbo.2001.4433_70.
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We have shown by experimental investigations that cellular surgery (microdissection, optoporation, and optoinjection) with Nd:YAG laser pulses of 1064 nm and 532 nm wavelength relies on nonlinear absorption leading to optical breakdown and plasma formation at the laser focus. The present study explores possibilities of refining the breakdown effects by employing shorter pulse durations and irradiances that generate plasmas below the threshold for shock wave and bubble formation. Optical breakdown in water at NA = 0.9 and NA = 1.3 was simulated numerically for wavelengths of 1064 nm, 532 nm and 355 nm, and pulse durations of 6 ns, 30 ps and 100 fs. We used a rate model that allows the calculation of the temporal evolution of the free electron density ρ during breakdown, ρ (t) could be followed separately for the free electrons generated by multiphoton ionization and avalanche ionization. We obtained excellent agreement between the calculated and measured threshold values for breakdown with 6-ns pulses. The simulations predict that the energy threshold for cellular surgery can be reduced by a factor of 350-2600 (depending on wavelength) when the pulse duration is reduced from 6 ns to 100 fs. The calculated breakdown energies for 100 fs pulses focused by an objective with NA = 1.3 are 0.6 nJ at 355 nm, 1.6 nJ at 532 nm, and 3.9 nJ at 1064 nm. With ns-pulses at 1064 nm, the breakdown threshold is very sharp, i. e. there is either no effect at all, or a dense plasma is formed causing a micro-explosion. With shorter wavelengths and pulse durations, the threshold is smoother, and electron densities may be produced that stay below the threshold for explosive vaporization and bubble formation. This creates the possibility of achieving highly localized plasma-mediated chemical or thermal changes in the cell. We conclude that both the reduced energy threshold and the smoother breakdown process with fs pulses bear a large potential for the refinement of intracellular surgery.