Journal articles on the topic 'Optique relativiste'
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Alarcon, W. "De Devereux à Nathan : une lecture ethnopsychiatrique de la schizophrénie." European Psychiatry 30, S2 (November 2015): S93. http://dx.doi.org/10.1016/j.eurpsy.2015.09.397.
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Au milieu du 19e siècle, en rupture avec les théories des aliénistes tels que Pinel et Esquirol, a émergé l’idée que la folie serait le signe de la décadence d’une civilisation corrompue par la modernité. Certaines théories ethnopsychiatriques, étudiant les troubles mentaux au sein d’un milieu culturel donné, s’opposent à la conception hippocratique d’une folie endogène (Folie-Maladie) en réaffirmant les conceptions exogènes (Folie-Sacré), décrites de façon similaire sous nos latitudes au Moyen-Âge chrétien. À l’image de Devereux, certaines figures de l’ethnopsychiatrie, sous l’influence conjointe de la psychanalyse et du structuralisme, prendront comme acquis fondamental l’idée relativiste selon laquelle l’interprétation du symptôme serait plus importante que le symptôme lui-même, la culture et le symbolique occultant quasiment le biologique. Devereux élaborera dans cette optique une théorie socioculturelle de la schizophrénie qu’il considérera comme le désordre ethnique caractéristique de la société occidentale dysfonctionnelle. Pour lui, ce trouble mental serait absent des sociétés authentiquement primitives et n’apparaîtrait en leur sein que suite aux processus d’acculturation qu’elles subissent [1]. Dans le sillage de cette pensée, Tobie Nathan développera quant à lui une théorie sociale et culturelle de la Folie [2]. Faisant fi des connaissances scientifiques au profit de la cosmogonie traditionnelle, il suppose que les populations étrangères n’auraient pas la même façon de penser le sujet et l’inconscient psychique, rendant toute théorie psychiatrique, neurodéveloppementale comme psychanalytique, inutilisable. En cherchant systématiquement des symboliques différentes à toute anomalie clinique, ce courant de l’ethnopsychiatrie tombe souvent dans la surinterprétation culturaliste. Nous questionnerons enfin l’idée que cet aspect de la pensée ethnopsychiatrique, en s’appuyant sur la culpabilité occidentale issue de la colonisation, répondrait au besoin de l’« Homme blanc » de réparer la faute dont on l’accuse, celle d’avoir souillé de façon indélébile la pureté originelle fantasmée des sociétés traditionnelles et d’y avoir importé jusqu’aux pathologies psychiatriques les plus graves
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Antoine, Jean-Pierre. "Symétries en physique." Revue des questions scientifiques 190, no. 1-2 (January 1, 2019): 7–26. http://dx.doi.org/10.14428/qs.v190i1-2.69423.
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Cet article passe en revue les multiples applications de la théorie des groupes aux problèmes de symétrie en physique. En physique classique, il s’agit surtout de la relativité : euclidienne, galiléenne, einsteinienne (relativité restreinte). Passant à la mécanique quantique, on remarque d’abord que les principes de base impliquent que l’espace des états d’un système quantique a une structure intrinsèque d’espace préhilbertien, que l’on complète ensuite en un espace de Hilbert. Dans ce contexte, la description de l’invariance sous un groupe G se base sur une représentation unitaire de G. On parcourt ensuite les différents domaines d’application : physique atomique et moléculaire, matière condensée, optique quantique, ondelettes, symétries internes, symétries approchées. On discute ensuite l’extension aux théories de jauge, en particulier au Modèle Standard des interactions fondamentales. On conclut par quelques indications sur des développements récents. * * * The present article reviews the multiple applications of group theory to the symmetry problems in physics. In classical physics, this concerns primarily relativity : Euclidean, Galilean, Einsteinian (special). Going over to quantum mechanics, we first note that the basic principles imply that the state space of a quantum system has an intrinsic structure of pre-Hilbert space, that one completes into a genuine Hilbert space. In this framework, the description of the invariance under a group G is based on a unitary representation of G. Next we survey the various domains of application : atomic and molecular physics, condensed matter physics, quantum optics, wavelets, internal symmetries, approximate symmetries. Next we discuss the extension to gauge theories, in particular to the Standard Model of fundamental interactions. We conclude with some remarks about recent developments.
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Jaccard, Jean-Philippe. "Voir – connaître : Optique, représentation, voyance." Modernités Russes 11, no. 1 (2010): 323–44. http://dx.doi.org/10.3406/modru.2010.936.
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On the margin of the general problematic of the «synthesis of Arts» , the problem of vision definitely deserves particular attention in the framework of Silver Age studies. It is certainly possible to relate the painter Mixail Matjušin’s works on the «enlarged vision» to those by Jules Romain on the «extra-retinian vision» , and their further elaboration in the works by René Daumal. This constant interest, in France as well as in Russia (and certainly elsewhere) towards the functioning of the eye and its impact on the artistic creation is to be placed in a larger context of the 19th century scientific discoveries in optics, the works on the 4th dimension, and, finally, the theory of relativity. The objective of this article is to show how these purely scientific discoveries influenced artistic research and provided, at least partially, the theoretical foundation for it, even when the resulting theory itself gradually became fanciful, or at least unscientific. In a similar fashion, it is possible to relate the physiological notion of «peripheral vision» (Helmholtz) to the «enlarged vision» (Matjušin) and, a posteriori, to the discovery of abstraction. Furthermore, this problematic does not concern exclusively painting : vision theories have also had an important impact on poetry, which can be demonstrated by the experiments of Aleksandr Tufanov in the 1920s which followed the works by Matjušin or by the research of Daumal in the same years, which followed the works by Romain. All these elements allow to establish, in line with Arthur Rimbaud’s famous «Letter of the Clairvoyant» , a certain rapprochement of this problematic with the enthusiasm of certain representatives of the Silver Age for the phenomenon of clairvoyance.
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Kuramitsu, Yasuhiro, Yosuke Matsumoto, and Takanobu Amano. "Nonlinear evolution of the Weibel instability with relativistic laser pulses." Physics of Plasmas 30, no. 3 (March 2023): 032109. http://dx.doi.org/10.1063/5.0138855.
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The Weibel instability is investigated using relativistic intense short laser pulses. A relativistic short laser pulse can generate a sub-relativistic high-density collisionless plasma. By irradiating double parallel planar targets with two relativistic laser pulses, sub-relativistic collisionless counterstreaming plasmas are created. Since the growth rate of the Weibel instability is proportional to the plasma density and velocity, the spatial and temporal scales of the Weibel instability can be much smaller than that from nanosecond large laser facilities. Recent theoretical and numerical studies have revealed that astrophysical collisionless shocks in sub-relativistic regimes in the absence and presence of an ambient magnetic field play essential roles in cosmic ray acceleration. With experimental verification in mind, we discuss the possible experimental models on the Weibel instability with intense short laser pulses. In order to show the experimental feasibility, we perform 2D particle-in-cell simulations in the absence of an external magnetic field as the first step and discuss the optimum conditions to realize the nonlinear evolutions of the Weibel instability in laboratories.
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Moshkelgosha, M., and R. Sadighi-Bonabi. "Generating the Optimum Self-Focusing in the Relativistic Laser-Plasma Interaction." IEEE Transactions on Plasma Science 41, no. 5 (May 2013): 1570–74. http://dx.doi.org/10.1109/tps.2013.2255888.
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Alhassan, Jibrin A., Augustine A. Ubachukwu, Finbar C. Odo, and Chika C. Onuchukwu. "RELATIVISTIC BEAMING EFFECTS AND STRUCTURAL ASYMMETRIES IN HIGHLY ASYMMETRIC DOUBLE RADIO SOURCES." Revista Mexicana de Astronomía y Astrofísica 55, no. 2 (September 13, 2019): 151–59. http://dx.doi.org/10.22201/ia.01851101p.2019.55.02.03.
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We have studied the comparative importance of the relativistic beaming model (RBM) and the density variation model (DVM) in our understanding of asymmetries in double radio sources, using their lobe separation ratio (Q) and flux density ratio (F). Our result shows an F − Q correlation in the sense expected for the RBM but contrary to the DVM. We attributed the result for the DVM to varying beam power, as its efficiency is density profile-dependent. From the coredominant parameter-linear size R − D relation for the RBM subsample, we found that sources in this subsample are beamed within an optimum cone angle Phi_c≈8°. We posit that relativistic beaming is largely accountable for the observed structural asymmetries in radio sources, though other effects cannot be ruled out.
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Jung, D., B. J. Albright, L. Yin, D. C. Gautier, B. Dromey, R. Shah, S. Palaniyappan, et al. "Scaling of ion energies in the relativistic-induced transparency regime." Laser and Particle Beams 33, no. 4 (October 14, 2015): 695–703. http://dx.doi.org/10.1017/s0263034615000828.
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AbstractExperimental data are presented showing maximum carbon C6+ ion energies obtained from nm-scaled targets in the relativistic transparent regime for laser intensities between 9 × 1019 and 2 × 1021 W/cm2. When combined with two-dimensional particle-in-cell simulations, these results show a steep linear scaling for carbon ions with the normalized laser amplitude a0 ($a_0 \propto \sqrt ( I)$). The results are in good agreement with a semi-analytic model that allows one to calculate the optimum thickness and the maximum ion energies as functions of a0 and the laser pulse duration τλ for ion acceleration in the relativistic-induced transparency regime. Following our results, ion energies exceeding 100 MeV/amu may be accessible with currently available laser systems.
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Xie, B. S., and N. C. Wang. "Optimum Effect of Asymmetric Laser Pulse Shape on Relativistic Laser-Plasma Wake Field." Physica Scripta 65, no. 5 (January 1, 2002): 444–46. http://dx.doi.org/10.1238/physica.regular.065a00444.
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de Bruijne, Jos, Hassan Siddiqui, Uwe Lammers, John Hoar, William O'Mullane, and Timo Prusti. "Optimising the Gaia scanning law for relativity experiments." Proceedings of the International Astronomical Union 5, S261 (April 2009): 331–33. http://dx.doi.org/10.1017/s1743921309990597.
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AbstractGaia is ESA's upcoming astrometry mission, building on the heritage of its predecessor, Hipparcos. The Gaia nominal scanning law (NSL) prescribes the ideal attitude of the spacecraft over the operational phase of the mission. As such, it precisely determines when certain areas of the sky are observed. From theoretical considerations on sky-sampling uniformity, it is easy to show that the optimum scanning law for a space astrometry experiment like Gaia is a revolving scan with uniform rotation around the instrument symmetry axis. Since thermal stability requirements for Gaia's payload require the solar aspect angle to be fixed, the optimum parallax resolving power is obtained by letting the spin axis precess around the solar direction. The precession speed has been selected as compromise, limiting the across-scan smearing of images when they transit the focal plane, providing sufficient overlap between successive “great-circle” scans of the fields of view, and guaranteeing overlap of successive precession loops. With this scanning law, with fixed solar-aspect angle, spin rate, and precession speed, only two free parameters remain: the initial spin phase and the initial precession angle, at the start of science operations. Both angles, and in particular the initial precession angle, can be initialized following various (programmatic) criteria. Examples are optimization/fine-tuning of the Earth-pointing angle, of the number and total duration of Galactic-plane scans, or of the ground-station scheduling. This paper explores various criteria, with particular emphasis on the opportunity to optimise the scanning-law initial conditions to “observe” the most favorable passages of bright stars very close to Jupiter's limb. This would allow a unique determination of the light deflection due to the quadrupole component of the gravitational field of this planet.
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Li, Wei, and Yong-gui Liu. "Choosing optimum method for the efficient design of a relativistic magnetron with diffraction output." Journal of Applied Physics 108, no. 11 (December 2010): 113303. http://dx.doi.org/10.1063/1.3520219.
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Léna, Pierre, and Guy Perrin. "Du flou des images astronomiques à un prix Nobel de physique." Reflets de la physique, no. 69 (June 2021): 21–27. http://dx.doi.org/10.1051/refdp/202169021.
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Deux des lauréats du prix Nobel de physique 2020 sont primés pour leurs observations 1, qui ont confirmé l’existence d’un trou noir supermassif au centre de notre Galaxie. En améliorant considérablement, jusqu’à un facteur de plus de cent-mille parfois, la résolution spatiale des télescopes utilisés, ils ont exploré un véritable laboratoire de relativité générale, au plus près de cette singularité de l’espace-temps. Ces gains en résolution résultent d’un franchissement de la limitation imposée par l’atmosphère terrestre, grâce à l’interférométrie des tavelures (1970), puis l’optique adaptative (1989), enfin la mise en service de télescopes optiques géants (ca. 2000), et du réseau interférométrique du Very Large Telescope européen.
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Kargarian, A., and K. Hajisharifi. "Self-magnetic field effects on laser-driven wakefield electron acceleration in axially magnetized ion channel." Laser and Particle Beams 38, no. 4 (October 5, 2020): 222–28. http://dx.doi.org/10.1017/s0263034620000324.
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AbstractIn this paper, we have investigated the relativistic electron acceleration by plasma wave in an axially magnetized plasma by considering the self-magnetic field effects. We show that the optimum value of an external axial magnetic field could increase the electron energy gain more than 40% than that obtained in the absence of the magnetic field. Moreover, results demonstrate that the self-magnetic field produced by the electric current of the energetic electrons plays a significant role in the plasma wakefield acceleration of electron. In this regard, it will be shown that taking into account the self-magnetic field can increase the electron energy gain up to 36% for the case with self-magnetic field amplitude Ωs = 0.3 and even up to higher energies for the systems containing stronger self-magnetic field. The effects of plasma wave amplitude and phase, the ion channel field magnitude, and the electron initial kinetic energy on the acceleration of relativistic electron have also been investigated. A scaling law for the optimization of the electron energy is eventually proposed.
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Domanski, Jaroslaw, and Jan Badziak. "Numerical studies of acceleration of thorium ions by a laser pulse of ultra-relativistic intensity." EPJ Web of Conferences 167 (2018): 01004. http://dx.doi.org/10.1051/epjconf/201816701004.
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One of the key scientific projects of ELI-Nuclear Physics is to study the production of extremely neutron-rich nuclides by a new reaction mechanism called fission-fusion using laser-accelerated thorium (232Th) ions. This research is of crucial importance for understanding the nature of the creation of heavy elements in the Universe; however, they require Th ion beams of very high beam fluencies and intensities which are inaccessible in conventional accelerators. This contribution is a first attempt to investigate the possibility of the generation of intense Th ion beams by a fs laser pulse of ultra-relativistic intensity. The investigation was performed with the use of fully electromagnetic relativistic particle-in-cell code. A sub-μm thorium target was irradiated by a circularly polarized 20-fs laser pulse of intensity up to 1023 W/cm2, predicted to be attainable at ELI-NP. At the laser intensity ~ 1023 W/cm2 and an optimum target thickness, the maximum energies of Th ions approach 9.3 GeV, the ion beam intensity is > 1020 W/cm2 and the total ion fluence reaches values ~ 1019 ions/cm2. The last two values are much higher than attainable in conventional accelerators and are fairly promising for the planned ELI-NP experiment.
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Burinskaya, T. M. "Ray tracing model of the auroral kilometric radiation generation in the 3-D plasma cavity." Annales Geophysicae 31, no. 10 (October 7, 2013): 1645–52. http://dx.doi.org/10.5194/angeo-31-1645-2013.
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Abstract. Propagation and amplification of the auroral kilometric radiation (AKR) in a three-dimensional plasma cavity is investigated using the approximation of the geometrical optics, and taking into account both the slightly relativistic electrons propagating inside a cavity and the background cold electrons. It is shown that the global magnetic field inhomogeneity plays a key role in a wave escape from a thin plasma cavity. The main contribution to the AKR spectrum is made by waves initially generated with the component of group velocity directed to the Earth and with the optimum relationship between the wave vector components, controlling the value of the linear grow rate and duration of the ray lifetime inside a source.
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Scheffel, Chr, R. J. Stening, H. Hora, R. Höpfl, J. M. Martinez-Val, S. Eliezer, G. Kasotakis, M. Piera, and E. Sarris. "Analysis of the retrograde hydrogen boron fusion gains at inertial confinement fusion with volume ignition." Laser and Particle Beams 15, no. 4 (December 1997): 565–74. http://dx.doi.org/10.1017/s0263034600011149.
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The very clean nuclear fusion reaction of hydrogen and boron-11 by inertial confinement arrives at conditions for power stations by volume ignition only at compressions to 100,000 times the solid state. The earlier (numerically) observed anomaly of decreasing gain at increasing density (retrograde behavior) is analyzed and the reason clarified: the strong stopping power mechanism, based on Gabor's collective model, is reaching its limit of too small Debye lengths at the extremely high densities because of the optimum temperature in the range of 30 keV due to the reabsorption of the bremsstrahlung. The relativistic correction of the bremsstrahlung for the always much higher temperatures after volume ignition is included from Maxon's model.
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Rötheli, Tobias F. "A Theory of Relativity of Cultures, Incomes and Happiness." Journal of Interdisciplinary Economics 33, no. 1 (January 2021): 54–73. http://dx.doi.org/10.1177/0260107921989905.
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The concepts of cultural relativism (introduced by Franz Boas) and hedonic relativism (introduced by Richard Easterlin) are reference points of a theory that addresses international differences in per capita incomes and variations in the contribution of income to happiness. The pivotal concept in this study is diligence. Painstaking effort, that is, diligence, is needed to produce high quality goods and services. The downside of such efforts lies in the psychological burden that comes with the necessary high level of self-control of the individual worker and the required organisational feedback mechanisms in firms. We present two competing views concerning the determination of diligence. The first, anthropologically inspired, hypothesis states that a society’s cultural forces such as cognitive styles, organisational traditions and religion determine the level of diligence. One implication of this perspective is that societies can have income levels that are either too high or too low relative to the welfare optimum. The second view holds that diligence is determined in a maximising way, balancing the gains and pains of diligence in the economic realm. Cross-country data are studied in order to assess the two competing views. The econometric evidence indicates that it is the maximising view that can explain key aspects of the data. JEL: D63, P5, Z1
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Mishra, Gaurav, Amol R. Holkundkar, and N. K. Gupta. "Effect of laser pulse time profile on its absorption by argon clusters." Laser and Particle Beams 29, no. 3 (July 13, 2011): 305–13. http://dx.doi.org/10.1017/s0263034611000346.
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AbstractThe interaction of medium sized Argon clusters (30 Å) with high-intensity femtosecond laser pulses (806 nm, 8 × 1016 W/cm2) of durations ranging from 10 fs to 120 fs have been studied using a three-dimensional relativistic time dependent molecular dynamic approach. The dynamics of cluster expansion is explained in terms of temporal evolution of electron population in the cluster and snapshots of particle positions at various times. The effects of inter-cluster distance on ionization dynamics are presented. It is observed that the collisional ionization increases with decreasing inter-cluster distance. The effect of pulse duration on laser energy absorption is also studied. For a laser pulse of gaussian time profile, there exists an optimum pulse duration for maximum absorption. No such optimum exists for a nearly flat top (super-gaussian) laser pulse. Results indicate the existence of resonance absorption inside the cluster. It is also observed that the high energy component of ion emission from cluster is anisotropic, showing a preferential direction of emission along laser polarization while the low energy ions emerge almost isotropically.
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Turi Nagy, Ladislav, Marek Liška, and Daniel Tunega. "Parametrization of the Scaling Factor in the Quasi-Relativistic INDO Method Based on the Equilibrium Geometries and Vibrational Frequencies of Electroneutral Closed-Shell XY4 Molecules Possessing the Td Symmetry." Collection of Czechoslovak Chemical Communications 59, no. 9 (1994): 1901–10. http://dx.doi.org/10.1135/cccc19941901.
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The parameter K in the quasi-relativistic INDO (QR-INDO) relation hiAjBcore = 1/2 K Si,j (βiA + βjB) was optimized by applying the QR-INDO method to the optimization of the geometries and calculation of vibrational wavenumbers of 36 molecules of the XY4 type with X = C, Si, Ti, Ge, Zr, Sn, Hf and Pb, and Y = H, F, Cl, Br and I. The calculations were performed for 10 values of K uniformly spaced across the region of 1.1 to 2.0. The optimum value with which the best fit of the bond lengths and vibrational frequencies was achieved was K = 1.5. This is very close to the value of 1.4 recommended in the literature. The study was performed using recent tabulated gas-phase data. The application of the variable scaling approximation approach was found generally unsuitable.
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Wang, X. L., Z. Y. Tan, W. Luo, Z. C. Zhu, X. D. Wang, and Y. M. Song. "Photo-transmutation of long-lived radionuclide 135Cs by laser–plasma driven electron source." Laser and Particle Beams 34, no. 3 (June 20, 2016): 433–39. http://dx.doi.org/10.1017/s0263034616000318.
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AbstractLaser-driven relativistic electrons can be focused onto a high-Z convertor for generating high-brightness γ-rays, which in turn can be used to induce photonuclear reactions. In this work, photo-transmutation of long-lived radionuclide 135Cs induced by laser–plasma–interaction-driven electron source is demonstrated using Geant4 simulation (Agostinelli et al., 2003 Nucl. Instrum. Meth. A506, 250). High-energy electron generation, bremsstrahlung, as well as photonuclear reaction are observed at four different laser intensities: 1020, 5 × 1020, 1021, and 5 × 1021 W/cm2. The transmutation efficiency depends on the laser intensity and target size. An optimum laser intensity, namely 1021 W/cm2, was found, with the corresponding photonuclear reaction yield reaching 108 J−1 of the laser energy. Laser-generated electrons can therefore be a promising tool for transmutation reactions. Potential application in nuclear waste management is suggested.
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Limpouch, J., J. Psikal, A. A. Andreev, K. YU Platonov, and S. Kawata. "Enhanced laser ion acceleration from mass-limited targets." Laser and Particle Beams 26, no. 2 (May 6, 2008): 225–34. http://dx.doi.org/10.1017/s0263034608000268.
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AbstractLaser interactions with mass-limited targets are studied here via numerical simulations using our relativistic electromagnetic two-dimensional particle-in cell code including all three-velocity components. Analytical estimates are derived to clarify the simulation results. Mass-limited targets preclude the undesirable spread of the absorbed laser energy out of the interaction zone. Mass-limited targets, such as droplets, are shown here to enhance the achievable fast ion energy significantly due to an increase in the hot electron concentration. For given target dimensions, the existence is demonstrated for an optimum laser beam diameter when ion acceleration is efficient and geometrical energy losses are still acceptable. Ion energy also depends on the target geometrical form and rounded targets are found to enhance the energy of accelerated ions. The acceleration process is accompanied by generation of the dipole radiation in addition to the ordinary scattering of the electromagnetic wave.
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Amid, Mehrnoush, Mohd Yazid ABD Manap, and Nor Khanani Zohdi. "Purification and Characterization of Alkaline-Thermostable Protease Enzyme from Pitaya (Hylocereus polyrhizus) Waste: A Potential Low Cost of the Enzyme." BioMed Research International 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/259238.
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The thermoalkaline protease enzyme from pitaya (Hylocereus polyrhizus) waste was purified by a factor of 221.2 with 71.3% recovery using ammonium sulphate precipitation, gel filtration, and cation exchange chromatography. Gel filtration chromatography together with sodium dodecyl sulphate gel electrophoresis (SDS-PAGE) revealed that the enzyme is monomeric with a molecular weight of 26.7 kDa. The apparentKmandVmaxof the protease were 2.8 mg/mL and 31.20 u/min, respectively. The optimum pH and temperature were 8.0 and 70°C. The enzyme was highly active and stable over a wide pH range (from pH 3.0 to pH 11.0 with the optimum activity at pH 8.0). The protease has broad specificity toward azocasein, casein, hemoglobin, and gelatine. Activity of the enzyme was inhibited by Fe2+and Zn2+, while protease activity was increased in the presence of Ca2+and Mg2+and Cu2+by factors of 125%, 110%, and 105%, respectively. The alkaline protease showed extreme stability toward surfactants and oxidizing agent. The purified protease exhibited extreme stability in the presence of organic solvents and inhibitors. In addition, the enzyme was relativity stable toward organic solvents and chelating agents, such as ethylenediaminetetraacetic acid (EDTA). The enzyme, derived from pitaya peel, possesses unique characteristics and could be used in various industrial and biotechnological applications.
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VALIN, P., B. GOULARD, and M. SANIELEVICI. "TOPOLOGY DEPENDENCE IN LATTICE SIMULATIONS OF NON-LINEAR PDES ON A MIMD COMPUTER." International Journal of Modern Physics C 05, no. 06 (December 1994): 957–71. http://dx.doi.org/10.1142/s0129183194001070.
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We tested the parallelization of explicit schemes for the solution of non-linear classical field theories of complex scalar fields which are capable of simulating hadronic collisions. Our attention focused on collisions in a fractional model with a particularly rich inelastic spectrum of final states. Relativistic collisions of all types were performed by computer on large lattices (64 to 256 sites per dimension). The stability and accuracy of the objects were tested by the use of two other methods of solutions: Pseudo-spectral and semi-implicit. Parallelization of the Fortran code on a 64-transputer MIMD Volvox machine revealed, for certain topologies, communication deadlock and less-than-optimum routing strategies when the number of transputers used was less than the maximum. The observed speedup, for N transputers in an appropriate topology, is shown to scale approximately as N, but the overall gain in execution speed, for physically interesting problems, is a modest 2–3 when compared to state-of-the-art workstations.
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Sharma, Vinay, Vishal Thakur, Arvinder Singh, and Niti Kant. "Third harmonic generation of a relativistic self-focusing laser in plasma under exponential density ramp." Zeitschrift für Naturforschung A 77, no. 4 (December 17, 2021): 323–28. http://dx.doi.org/10.1515/zna-2021-0266.
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Abstract Present study focuses on self-focusing and its effect on third harmonic generation (THG) of a Gaussian laser beam in plasma under the influence of exponential density ramp. Relativistic nonlinearity has been taken into account which is aroused due the modification of electron’s mass in the presence of high intensity laser. Under strong ponderomotive force, electrons acquire very high quiver velocity and mass variation takes place. Equations for beam width parameter of incident laser and the amplitude of THG have been derived under WKB and paraxial ray approximation, and solved them numerically. It is found that the presence of exponential plasma density ramp results strong self-focusing of laser which further leads to enhance the efficiency of THG. Wiggler magnetic field adds an additional momentum to the photons of third harmonic due to which appreciable gain is observed in the normalized amplitude of THG. Significant enhancement in the THG amplitude has been reported in the presence of exponential density ramp for optimum values of intensity of incident laser, wiggler magnetic field and plasma frequency.
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Wang, Chun Sheng, Xu Wang, Qiu Ying Du, Bin Dong, and Gui Ling Chen. "Optimizing Structure about Strong Base ASP Flooding Molecule Weight Adjusting Mechanism." Advanced Materials Research 868 (December 2013): 614–17. http://dx.doi.org/10.4028/www.scientific.net/amr.868.614.
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Daqing oilfield ASP flooding drive target gradually changes from the first reservoir to the second and third reservoir,which leads to the unequal of the reservoirs producing extent, and seriously affects the developing for ASP flooding molecule weight. On the basis of that, we optimum the Molecule Weight Adjusting Mechanism of low permeability reservoir, and use the method of control variables to change the nozzle angle of diffuser section, cylinder length, diffuser angle, nozzle angle to establish 81 models. At the same time, we simulate flow field characteristics of these models with the help of Fluent. Ultimately, the models of low pressure drop and high stick loss rate could be found. Through analyzing and contrasting large of models, we found that shrinkage angle is 30 degree models under the same pressure drop condition the stick loss rate relativity high. Simultaneously, these models are suitable for the field requirements, and can provide theoretical basis for molecular weight adjusting and optimizing structure.
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Jarocha, Andrzej. "Egzekucja sądowa z kilku nieruchomości dłużnika stanowiących całość gospodarczą." Przegląd Prawa Egzekucyjnego 2024, no. 1 (March 29, 2024): 9–28. http://dx.doi.org/10.62627/ppe.2024.001.
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Specific rules, relevant only for enforcement proceedings, are applied in enforcement proceedings, such as the rule of applying enforcement measures that are least onerous for a debtor, while ensuring protection of creditor’s rights (so-called principle of relativity). The compliance with this rule in the practice of enforcement proceedings results in the necessity to look for the maximum efficiency of enforcement by its execution in such a manner, for example, that optimum effects are obtained in enforcement against cash benefits by obtaining funds to repay a creditor and cover costs of proceedings, while keeping factual, legal and financial burdens to the minimum. An example of adhering to the principle of relativity that is aimed at maximising the efficiency of enforcement is the combination of several enforcement proceedings that concern several real properties into single proceedings, in order to optimise effects of enforcement activities undertaken during proceedings pending separately beforehand. Achieving the objectives of combining proceedings is beneficial for the creditor, the bailiff and for the debtor as well. The analysis focuses on the development of the concept of ‘economic whole’ of several real properties as well as on the identification of conditions for admissibility of combining proceedings pending against several real properties developed based on regulations of the Code of Civil Proceedings. The analysis conducted in the article leads to the conclusion that if there is a combination of several proceedings, because real properties being subject to separate enforcement proceedings constitute an economic whole, the whole as well as each real property are to be described and estimated, and next, if this is not contrary to the objective of enforcement understood as the optimization of effectiveness and efficiency of enforcement and if this may lead to better results than the sales of individual real properties separately, the should be sold jointly.
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Yazdani, E., R. Sadighi-Bonabi, H. Afarideh, J. Yazdanpanah, and H. Hora. "Enhanced laser ion acceleration with a multi-layer foam target assembly." Laser and Particle Beams 32, no. 4 (August 22, 2014): 509–15. http://dx.doi.org/10.1017/s0263034614000342.
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AbstractInteraction of a linearly polarized Gaussian laser pulse (at relativistic intensity of 2.0 × 1020 Wcm−2) with a multi-layer foam (as a near critical density target) attached to a solid layer is investigated by using two-dimensional particle-in-cell simulation. It is found that electrons with longitudinal momentum exceeding the free electrons limit of meca02/2 so-called super-hot electrons can be produced when the direct laser acceleration regime is fulfilled and benefited from self-focusing inside of the subcritical plasma. These electrons penetrate easily through the target and can enhance greatly the sheath field at the rear, resulting in a significant increase in the maximum energy of protons in target normal sheath acceleration regime. The results indicate that the maximum proton energy is enhanced by 2.7 times via using an assembled target arrangement compared to a bare solid target. Furthermore, by demonstration of this assembly, the maximum proton energy is improved beyond the optimum amount achieved by a two-layer target proposed by Sgattoni et al. (2012).
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Mbhiza, Hlamulo. "Witchcraft and Mathematics Learning in South African Rural Schools." Interdisciplinary Journal of Education Research 3, no. 1 (March 9, 2021): 27–36. http://dx.doi.org/10.51986/ijer-2021.vol3.01.03.
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In South Africa, there is no adequate research that explored mathematics learning and teaching within rural schools and classrooms. Various literature posits that mathematics education research has virtually over-concentrated on urban and township schools and consistently ignored rural contexts and schools. Arguments exist that rural education and rural education research have been understudied in South Africa. Presumably, this would include mathematics education research as well. This paper explores the relationship between witchcraft beliefs, which is considered as an entrenched cultural phenomenon, and learners' mathematics learning within rural classrooms. In this paper, the local influences include that the learners end up not demonstrating their full understanding of mathematics contents because of the beliefs that if they exhibit their knowledge of the subject, they may be bewitched. Cultural Relativism was used to theorise the study within qualitative critical phenomenology as a methodology for the study. The study comprises 12 mathematics learners from a rural Acornhoek region in Mpumalanga Province, and data were collected using individual semi-structured interviews while the collected data were analysed using Critical Discourse Analysis. Findings from this study illuminated that local beliefs and knowledge such as witchcraft exert significant influence on schools and learners' learning, including learners' not demonstrating their optimum understanding of mathematics.
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SÁNCHEZ DEL RÍO, J., M. J. G. BORGE, E. NÁCHER, A. PEREA, G. RIBEIRO, O. TENGBLAD, M. MÅRTENSSON, T. NILSSON, and H. T. JOHANSSON. "CEPA: A LaBr3(Ce)/LaCl3(Ce) PHOSWICH ARRAY FOR SIMULTANEOUS DETECTION OF PROTONS AND GAMMA RADIATION EMITTED IN REACTIONS AT RELATIVISTIC ENERGIES." International Journal of Modern Physics: Conference Series 27 (January 2014): 1460143. http://dx.doi.org/10.1142/s2010194514601434.
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A sophisticated design of 750 LaBr3(Ce):LaCl3(Ce) phoswich crystals (CEPA10) with a segmentation determined by the Doppler correction and an energy resolution of 5% at 1 MeV is presented. Monte Carlo simulations have been performed for high energy protons (50–500 MeV) and gamma radiation (0.5–30 MeV) to determine the length and shape of the crystals for optimum performance of the detector. In the case of protons, the two-layer detector can be used as a ΔELaBr3 − ETot telescope or, for very high energies, as a double energy loss detector (ΔELaBr3 + ΔELaCl3), in order to determine the initial energy. In addition, an experimental test with high energy protons (70–230 MeV) was performed at the cyclotron center in Krakow, Poland with a first prototype of 2 x 2 phoswich rectangular crystals (CEPA4) packed in an aluminum can (0.5 mm case). To simulate CEPA10 efficiencies and resolutions, optical pulses detected in CEPA4 by photomultiplier tubes with a DAQ system were used as energy input functions in Monte Carlo simulations.
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Kiladze, A. B. "Evaluation of the effectiveness of cryptic coloration of the Carolina anole’s skin." Regulatory Mechanisms in Biosystems 10, no. 3 (August 21, 2019): 320–26. http://dx.doi.org/10.15421/021950.
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Cryptic coloration of animals’ integument is one of the effective adaptations that allow them to lead an active lifestyle while being protected from natural enemies due to visual disguise. This is achieved by the similarity of body color of a particular individual to the background of various substrates in its environment. The morphological and functional basis of cryptic coloration in vertebrates, including reptiles, is ensured by the skin pigmentation. Using bioinformatic methods, we calculated the skin camouflage index of the Carolina anole (Anolis carolinensis Voigt, 1832) in various conditions of its habitat. The skin camouflage index (Ic) is the ratio of the sum of the average values of rgb coordinates of the skin color to the sum of the average values of rgb coordinates of the color of the external substrate. Ic satisfies the effective level of adaptation to habitat conditions if it falls within the range of 0.80–1.20. It has been shown that rgb-values of the dominant color of the dorsal skin of green anoles slightly differ from the similar parameters characteristic of the deciduous habitat, which is reflected by Ic of its skin (0.94). In the brown anoles on a background of woody substrate, the Ic value of its skin (0.88) is also optimal, since it exceeds the lower limit (0.80), which indicates close values of the sums of the rgb coordinates of the skin color and the color of the external background. In the mixed green-brown anoles, the deciduous habitat is preferable to the woody one. In the first case, Ic (1.11) is in the optimum zone, and in the second case, Ic (0.70) goes beyond the lower limit of the optimum, which indicates a greater vulnerability of the animal to external threats. We have confirmed the relativity of visual hiding of the skin that is effective only in the habitat conditions in which the camouflage abilities of the skin manifest as fully as possible.
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Şenol, Mehmet Burak. "A new optimization model for design of traditional cockpit interfaces." Aircraft Engineering and Aerospace Technology 92, no. 3 (January 20, 2020): 404–17. http://dx.doi.org/10.1108/aeat-04-2019-0068.
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Purpose Real flight is cognitively demanding; accordingly, both indicators and display panel layout should be user-friendly to improve pilot-aircraft interaction. Poor pilot-interface interactions in aircrafts could result in accidents. Although a general reason of accidents is improper displays, relatively few studies were conducted on interfaces. This study aims to present an optimization model to create intuitively integrated user-friendly cockpit interfaces. Design/methodology/approach Subjectivity within most usability evaluation techniques could bring about interface design problems. A priori information about indicator’s possible locations may be available or unavailable. Thus different analytical approaches must be applied for modifications and new interface designs. Relative layout design (RLD) model was developed and used in new interface designs to optimize locations of indicators. This model was based on layout optimization and constructed in accordance with design requirements, ergonomic considerations with the pilot preferences. RLD model optimizes interface design by deploying indicators to the best locations to improve usability of display panel, pilot-aircraft interaction and flight safety. Findings Optimum interfaces for two problem instances were gathered by RLD model in 15.77 CPU(s) with 10 indicators and 542.51 CPU(s) with 19 indicators. A comparison between relative and existing cockpit interfaces reveals that locations of six navigation and four mechanical system indicators are different. The differences may stem from pilots’ preferences and relativity constraints. Both interfaces are more similar for the central part of the display panel. The objective function value of relative interface design (Opt: 527938) is far better than existing interface (737100). The RLD model improved usability of existing interface (28.61 per cent considering decrease in the objective function values from 737100 to 527938. Practical implications Future cockpit and new helicopter interface designs may involve RLD model as an alternative interface design tool. Furthermore, other layout optimization problems, e.g. circuit boards, microchips and engines, etc. could be handled in a more realistic manner by RLD model. Originality/value Originality and impact of this study related to development and employment of a new optimization model (RLD) on cockpit interface design for the first time. Engineering requirements, human factors, ergonomics and pilots’ preferences are simultaneously considered in the RLD model. The subjectivity within usability evaluation techniques could be diminished in this way. The contributions of RLD model to classical facility layout models are relativity constraints with the physical constrictions and ergonomic objective function weights. Novelty of this paper is the development and employment of a new optimization model (RLD) to locate indicators.
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Buranok, Sergey Olegovich. "War, Imperialism, and colonies: a view of the US press." Samara Journal of Science 8, no. 1 (February 28, 2019): 219–22. http://dx.doi.org/10.17816/snv201981216.
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Questions about the perspectives of the European empires colonial system after the Great War, forms and ways of its transition to postcolonial age, relativity of the colonial powers experience to the US foreign policy, were very popular and quite debating for the American public opinion during and after the end of the World War I. colonial system research cannot be complete without studying the press of the powers that signed the Versailles Treaty. In order to give a detailed analysis of international relationships in terms of the global transformations from the American point of view relevant newspaper articles published after the Great War should be analyzed. The results have shown changes in priority in schemes of colonial system transformation as it was viewed in American public discourse during 1919-1922. Woodrow Wilson plan for the colonial powers dismantle was gradually replaced by the less radical plans, which presupposed the use of the colonial experience in the US foreign policy. Materials of the American press for the 1919-1922 reveals that there was a search of the most effective and optimum strategy of the relations with the European empires as well as with its dependent territories. Analysis of American press reveals its steady interest in negative and positive experience of colonial empires in search of the lessons of history. In 1919-1922 most prominent journalists were focused on Europe, which was represented as the cornerstone for the US foreign policy by the White House, the US State Department and the media. And we can clearly see another factor affecting approaches to the colonial issue in American press. It was the Soviet Russia attention and support to the national liberation movements in Asia and Africa. The Red Menace had become one of the factors that forced American media to redefine the colonial issue in light of the new world order which had been created after the end of the Great War on the base of the Versailles Treaty.
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De Martini, Francesco. "The Higgs field and the resolution of the Cosmological Constant Paradox in the Weyl-geometrical Universe." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2106 (October 2, 2017): 20160388. http://dx.doi.org/10.1098/rsta.2016.0388.
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The nature of the scalar field responsible for the cosmological inflation is found to be rooted in the most fundamental concept of Weyl's differential geometry: the parallel displacement of vectors in curved space–time. Within this novel geometrical scenario, the standard electroweak theory of leptons based on the SU (2) L ⊗ U (1) Y as well as on the conformal groups of space–time Weyl's transformations is analysed within the framework of a general-relativistic, conformally covariant scalar-tensor theory that includes the electromagnetic and the Yang–Mills fields. A Higgs mechanism within a spontaneous symmetry breaking process is identified and this offers formal connections between some relevant properties of the elementary particles and the dark energy content of the Universe. An ‘effective cosmological potential’: V eff is expressed in terms of the dark energy potential: via the ‘mass reduction parameter’: , a general property of the Universe. The mass of the Higgs boson, which is considered a ‘free parameter’ by the standard electroweak theory, by our theory is found to be proportional to the mass which accounts for the measured cosmological constant, i.e. the measured content of vacuum-energy in the Universe. The non-integrable application of Weyl's geometry leads to a Proca equation accounting for the dynamics of a ϕ ρ -particle, a vector-meson proposed as an an optimum candidate for dark matter. On the basis of previous cosmic microwave background results our theory leads, in the condition of cosmological ‘critical density’, to the assessment of the average energy content of the ϕ ρ -excitation. The peculiar mathematical structure of V eff offers a clue towards a very general resolution of a most intriguing puzzle of modern quantum field theory, the ‘Cosmological Constant Paradox’ (here referred to as the ‘ Λ -Paradox’). Indeed, our ‘universal’ theory offers a resolution of the Λ -Paradox for all exponential inflationary potentials: V Λ ( T , ϕ )∝ e − nϕ , and for all linear superpositions of these potentials, where n belongs to the mathematical set of the ‘real numbers’. An explicit solution of the Λ -Paradox is reported for n =2. The resolution of the Λ -Paradox cannot be achieved in the context of Riemann's differential geometry. This article is part of the themed issue ‘Second quantum revolution: foundational questions’.
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De Martini, Francesco. "The quantum Higgs field and the resolution of the cosmological constant paradox in the Weyl-geometrical Universe." International Journal of Quantum Information 15, no. 08 (December 2017): 1740025. http://dx.doi.org/10.1142/s0219749917400251.
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The nature of the scalar field responsible for the cosmological inflation is found to be rooted in the most fundamental concept of the Weyl’s differential geometry: the parallel displacement of vectors in curved spacetime. Within this novel geometrical scenario, the standard electroweak theory of leptons based on the [Formula: see text] as well as on the conformal groups of spacetime Weyl’s transformations is analyzed within the framework of a general-relativistic, conformally-covariant scalar–tensor theory that includes the electromagnetic and the Yang–Mills fields. A Higgs mechanism within a spontaneous symmetry breaking process is identified and this offers formal connections between some relevant properties of the elementary particles and the dark energy content of the Universe. An “effective cosmological potential”: [Formula: see text] is expressed in terms of the dark energy potential: [Formula: see text] via the “mass reduction parameter”: [Formula: see text], a general property of the Universe. The mass of the Higgs boson, which is considered a “free parameter” by the standard electroweak theory, by our theory is found to be proportional to the mass [Formula: see text] which contributes to the measured Cosmological Constant, i.e. the measured content of vacuum-energy in the Universe. The nonintegrable application of the Weyl’s geometry leads to a Proca equation accounting for the dynamics of a [Formula: see text]-particle, a vector-meson proposed as an optimum candidate for Dark Matter. The peculiar mathematical structure of [Formula: see text] offers a clue towards a very general resolution in 4-D of a most intriguing puzzle of modern quantum field theory, the “cosmological constant paradox”(here referred to as: “[Formula: see text]-paradox”). Indeed, our “universal” theory offers a resolution of the “[Formula: see text]-paradox” for all exponential inflationary potentials: [Formula: see text], and for all linear superpositions of these potentials, where [Formula: see text] belongs to the mathematical set of the “real numbers”. An explicit solution of the [Formula: see text]-Paradox is reported for [Formula: see text]. The results of the theory are analyzed in the framework of the recent experimental data of the PLANCK Mission. The average vacuum-energy density in the Universe is found: [Formula: see text], the mass-reduction parameter: [Formula: see text] and the value of the “cosmological constant”: [Formula: see text](eV/c[Formula: see text]. A quite remarkable result of the theory consists of the complete formulation of the Einstein equation including in its structure the “cosmological constant”, [Formula: see text]. This was the term that Einstein added “by hand” to his famous equation. The critical stability of the Universe is also discussed.
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Fizer, M. M., and V. I. Sidey V.I. "TESTING OF THE OPTIMUM BASIS SET FOR MODELING THE HEXABROMOTELURATE ANION." Scientific Bulletin of the Uzhhorod University. Series «Chemistry» 45, no. 1 (June 30, 2021). http://dx.doi.org/10.24144/2414-0260.2021.1.53-57.
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Using the PRIRODA 19 program, the bond lengths Te–Br have been calculated for the hexabromotelurate anion [TeBr6]2– within the frameworks of the GGA PBE density functional theory and the Møller–Plesset second order perturbation theory. In order to find the optimum basis set, the λXa (where X = 1-4) basis sets developed by D. Laikov, with diffusion functions, were tested. It must be noticed that in the case of the λXa (where X = 1-4) basis sets, the anion [TeBr6]2– is described by different numbers of basis functions: 261 for the double-zeta basic set λ1a, 422 for the triple-zeta basic set λ2a, 660 and 989 for the basis sets λ3a and λ4a, respectively. As the system under investigation contains relatively heavy atoms, the relativistic effects were taken into account using the four-component scalar-relativistic Hamiltonian by Dirac and using the new two-component AAA Hamiltonian by Laikov.
The optimization of the geometric parameters of the hexabromotelurate anion was carried out with no symmetry restrictions. In all cases, the optimized [TeBr6]2– geometry corresponds to the nearly perfect octahedral symmetry; so the average Te–Br bond lengths have been considered. In the case of the PBE/λXa method (where X = 1-4), an increase in the size of the basis set results in a shortening of the Te–Br bond lengths. It has been shown that the difference between the four-component and two-component relativistic approximations increases with an increase of the basic set used. In turn, in the case of the MP2 method, the difference between the four-component and two-component relativistic approximations decreases with an increase of the basic set, and goes through the minimum for the quadruple-zeta λ3a basis set. Thus, in the post-Hartree–Fock approach, such as the Møller–Plesset perturbation theory and the coupled clusters theory, the agreement between the above relativistic approximations is reasonably good, and the two-component scalar-relativistic AAA Hamiltonian by Laikov (which is characterized by much lesser recourse demands) is more optimal for a variety of «heavy» and time-consuming calculations at the higher levels of theory. For modeling the geometric parameters of hexabromotelurate anion with an accuracy of 0.01 Å, we recommend the use of the triple-zeta basis set with the scalar-relativistic Hamiltonian.
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Hadad, M., and M. Torkiha-Esfhani. "Optimum point of acceleration of an electron inside the collisional plasma-filled elliptical waveguide." Journal of Plasma Physics 81, no. 2 (September 5, 2014). http://dx.doi.org/10.1017/s0022377814000646.
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In this paper, the effect of the electron collision frequency with background ions on TMmr mode field components, the trajectory and the electron energy gain is studied. The field components of the TMmr mode in the elliptical waveguides are calculated. The ohmic heating for three different value of collision frequency calculated and the power losses is obtained. The deflection angle and acceleration gradient of an electron in the fields associated with a transverse magnetic (TM) wave propagating inside a elliptical waveguide for TMmr mode is studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the microwave. The results for TMmr mode are graphically represented. Finally, the optimum point of acceleration for the even mode TM11 is obtained and it is shown that in a cross section of elliptical waveguide optimum point is center of ellipse.
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Watanabe, C., K. Yanase, and N. Yoshinaga. "Searching optimum equations of state of neutron star matter in strong magnetic fields with rotation." Progress of Theoretical and Experimental Physics 2020, no. 10 (September 2, 2020). http://dx.doi.org/10.1093/ptep/ptaa134.
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Abstract Masses and radii of neutron stars are obtained in the presence of strong magnetic fields together with rotation. Mass-radius relations are calculated using 11 equations of state (EoSs: GM1, TM1-a, TM1-b, TM2$\omega\rho$-a, TM2$\omega\rho$-b, NL3-a, NL3-b, NL3$\omega\rho$-a, NL3$\omega\rho$-b, DDME2-a and DDME2-b) in relativistic mean field (RMF) theory. Obtained masses are over and around twice the solar mass ($M_\odot$) for all EoSs in the presence of strong magnetic fields of $3 \times 10^{18}$ G at the center. For NL3$\omega\rho$-a and NL3$\omega\rho$-b EoSs, masses are more than $M=2.17\,M_\odot$(observed maximum mass: $2.14\,M_\odot$) even without magnetic fields. Rotational effects are found to be insignificant in any case, at least up to the Kepler frequency. Suitable EoSs are also selected concerning the constraint on the radius of a neutron star.
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Hata, Masayasu, Takayoshi Sano, Natsumi Iwata, and Yasuhiko Sentoku. "Optimum design of double-layer target for proton acceleration by ultrahigh intense femtosecond lasers considering relativistic rising edge." Physical Review E 108, no. 3 (September 6, 2023). http://dx.doi.org/10.1103/physreve.108.035205.
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Fasano, Nicholas M., Matthew R. Edwards, and Julia M. Mikhailova. "Electron bunch dynamics and emission in particle-in-cell simulations of relativistic laser–solid interactions: On density artifacts, collisions, and numerical dispersion." Physics of Plasmas 30, no. 6 (June 1, 2023). http://dx.doi.org/10.1063/5.0140028.
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Sub-optical-cycle dynamics of dense electron bunches in relativistic-intensity laser–solid interactions lead to the emission of high-order harmonics and attosecond light pulses. The capacity of particle-in-cell simulations to accurately model these dynamics is essential for the prediction of emission properties because the attosecond pulse intensity depends on the electron density distribution at the time of emission and on the temporal distribution of individual electron Lorentz-factors in an emitting electron bunch. Here, we show that in one-dimensional collisionless simulations, the peak density of the emitting electron bunch increases with the increase in the spatial resolution of the simulation grid. When collisions are added to the model, the peak electron density becomes independent of the spatial resolution. Collisions are shown to increase the spread of the peaks of Lorentz-factors of emitting electrons in time, especially in the regimes far from optimum generation conditions, thus leading to lower intensities of attosecond pulses as compared to those obtained in collisionless simulations.
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Ferri, J., E. Siminos, L. Gremillet, and T. Fülöp. "Effects of oblique incidence and colliding pulses on laser-driven proton acceleration from relativistically transparent ultrathin targets." Journal of Plasma Physics 86, no. 5 (September 29, 2020). http://dx.doi.org/10.1017/s0022377820000847.
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The use of ultrathin solid foils offers optimal conditions for accelerating protons to high energies from laser–matter interactions. When the target is thin enough that relativistic self-induced transparency sets in, all of the target electrons get heated to high energies by the laser, which maximizes the accelerating electric field and therefore the final ion energy. In this work, we first investigate how ion acceleration by ultraintense femtosecond laser pulses in transparent CH $_2$ solid foils is modified when turning from normal to oblique ( $45^\circ$ ) incidence. Due to stronger electron heating, we find that higher proton energies can be obtained at oblique incidence but in thinner optimum targets. We then show that proton acceleration can be further improved by splitting the laser pulse into two half-pulses focused at opposite incidence angles. An increase by ${\sim }30\,\%$ in the maximum proton energy and by a factor of ${\sim }4$ in the high-energy proton charge is reported compared to the reference case of a single normally incident pulse.
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van Leeuwen, K. A. H. (Ton), Walter Jouke Schaap, Bart Buijsse, Simona Borrelli, Stefan Kempers, Wouter Verhoeven, and O. Jom Luiten. "Feasibility of a Pulsed Ponderomotive Phase Plate for Electron Beams." New Journal of Physics, February 15, 2023. http://dx.doi.org/10.1088/1367-2630/acbc44.
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Abstract We propose a scheme for constructing a phase plate for use in an ultrafast Zernike-type phase contrast electron microscope, based on the interaction of the electron beam with a strongly focused, high-power femtosecond laser pulse and a pulsed electron beam. Analytical expressions for the phase shift using the time-averaged ponderomotive potential and a paraxial approximation for the focused laser beam are presented, as well as more rigorous quasiclassical simulations based on the quantum phase integral along classical, relativistic electron trajectories in an accurate, non-paraxial description of the laser beam. The results are shown to agree well unless the laser beam is focused to a waist size below a wavelength. For realistic (off-the-shelf) laser parameters the optimum phase shift of -π/2 is shown to be achievable. When combined with RF-cavity based electron chopping and compression techniques to produce electron pulses, a femtosecond regime pulsed phase contrast microscope can be constructed. The feasibility and robustness of the scheme are further investigated using the simulations, leading to motivated choices for design parameters such as wavelength, focus size and polarization.
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Dover, Nicholas P., Tim Ziegler, Stefan Assenbaum, Constantin Bernert, Stefan Bock, Florian-Emanuel Brack, Thomas E. Cowan, et al. "Enhanced ion acceleration from transparency-driven foils demonstrated at two ultraintense laser facilities." Light: Science & Applications 12, no. 1 (March 13, 2023). http://dx.doi.org/10.1038/s41377-023-01083-9.
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AbstractLaser-driven ion sources are a rapidly developing technology producing high energy, high peak current beams. Their suitability for applications, such as compact medical accelerators, motivates development of robust acceleration schemes using widely available repetitive ultraintense femtosecond lasers. These applications not only require high beam energy, but also place demanding requirements on the source stability and controllability. This can be seriously affected by the laser temporal contrast, precluding the replication of ion acceleration performance on independent laser systems with otherwise similar parameters. Here, we present the experimental generation of >60 MeV protons and >30 MeV u−1 carbon ions from sub-micrometre thickness Formvar foils irradiated with laser intensities >1021 Wcm2. Ions are accelerated by an extreme localised space charge field ≳30 TVm−1, over a million times higher than used in conventional accelerators. The field is formed by a rapid expulsion of electrons from the target bulk due to relativistically induced transparency, in which relativistic corrections to the refractive index enables laser transmission through normally opaque plasma. We replicate the mechanism on two different laser facilities and show that the optimum target thickness decreases with improved laser contrast due to reduced pre-expansion. Our demonstration that energetic ions can be accelerated by this mechanism at different contrast levels relaxes laser requirements and indicates interaction parameters for realising application-specific beam delivery.
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Järvinen, A. E., T. Fülöp, E. Hirvijoki, M. Hoppe, A. Kit, and J. Åström. "Bayesian approach for validation of runaway electron simulations." Journal of Plasma Physics 88, no. 6 (December 2022). http://dx.doi.org/10.1017/s0022377822001210.
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Plasma-terminating disruptions in future fusion reactors may result in conversion of the initial current to a relativistic runaway electron beam. Validated predictive tools are required to optimise the scenarios and mitigation actuators to avoid the excessive damage that can be caused by such events. Many of the simulation tools applied in fusion energy research require the user to specify input parameters that are not constrained by the available experimental information. The conventional approach, where an expert modeller calibrates these input parameters based on domain knowledge, is prone to lead to an intractable validation challenge without systematic uncertainty quantification. Bayesian inference algorithms offer a promising alternative approach that naturally includes uncertainty quantification and is less subject to user bias in choosing the input parameters. The main challenge in using these methods is the computational cost of simulating enough samples to construct the posterior distributions for the uncertain input parameters. This challenge can be overcome by combining probabilistic surrogate modelling, such as Gaussian process regression, with Bayesian optimisation, which can reduce the number of required simulations by several orders of magnitude. Here, we implement this type of Bayesian optimisation framework for a model for analysis of disruption runaway electrons, and explore for simulations of current quench in a JET plasma discharge with an argon induced disruption. We use this proof-of-principle framework to explore the optimum input parameters with uncertainties in optimisation tasks ranging from one to seven dimensions. The relevant Python codes that are used in the analysis are available via https://github.com/aejarvin/BO_FOR_RE_SIMULATIONS/.