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Journal articles on the topic 'Neutron scattering theories'
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1
Mansuripur, Masud. "A Tutorial on the Classical Theories of Electromagnetic Scattering and Diffraction." Nanophotonics 10, no. 1 (2020): 315–42. http://dx.doi.org/10.1515/nanoph-2020-0348.
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AbstractStarting with Maxwell’s equations, we derive the fundamental results of the Huygens-Fresnel-Kirchhoff and Rayleigh-Sommerfeld theories of scalar diffraction and scattering. These results are then extended to cover the case of vector electromagnetic fields. The famous Sommerfeld solution to the problem of diffraction from a perfectly conducting half-plane is elaborated. Far-field scattering of plane waves from obstacles is treated in some detail, and the well-known optical cross-section theorem, which relates the scattering cross-section of an obstacle to its forward scattering amplitude, is derived. Also examined is the case of scattering from mild inhomogeneities within an otherwise homogeneous medium, where, in the first Born approximation, a fairly simple formula is found to relate the far-field scattering amplitude to the host medium’s optical properties. The related problem of neutron scattering from ferromagnetic materials is treated in the final section of the paper.
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DE BLASIO, F. V., and G. LAZZARI. "NUCLEAR EFFECTS ON SUPERFLUID NEUTRON STAR MATTER." Modern Physics Letters A 13, no. 17 (1998): 1383–92. http://dx.doi.org/10.1142/s0217732398001443.
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In the inner crust of a neutron star, the superfluid neutron liquid shares a fraction of the volume with neutron-rich nuclei and thus cannot be considered as uniform. We find that quasi-resonant states, due to elastic scattering with the effective nuclear potential wells, can enhance the neutron density of states at the Fermi surface for some values of the energy of the incident neutron. This may locally change the pairing energy gap of the superfluid neutrons up to a factor of three to four. We then discuss the smoother change of the neutron effective matrix element induced by the presence of the nuclei considering the case in which the superfluid coherence length is larger than the nuclear sizes. The results show that the value of the pairing gap as calculated for infinite systems is not directly the one that should be expected to exist in the crust of a neutron star and we work out an approximate formula for the gap taking into account both effects. The sudden change of the neutronic superfluid gap in localized crust shells due to the nuclear quasi-resonant states can have consequences for theories of the rotational and thermal evolution of neutron stars while the smooth, continuous variation of the effective matrix element can have implications for the cooling of the star.
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Bénard, Pierre, Liang Chen, and A. M. S. Tremblay. "Neutron-scattering measurements as a test of theories of high-temperature superconductivity." Physical Review B 47, no. 1 (1993): 589–92. http://dx.doi.org/10.1103/physrevb.47.589.
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Armstrong, Clare L., Laura Toppozini, Hannah Dies, Antonio Faraone, Michihiro Nagao, and Maikel C. Rheinstädter. "Incoherent Neutron Spin-Echo Spectroscopy as an Option to Study Long-Range Lipid Diffusion." ISRN Biophysics 2013 (March 31, 2013): 1–9. http://dx.doi.org/10.1155/2013/439758.
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Diffusion is the fundamental mechanism for lipids and other molecules to move in a membrane. It is an important process to consider in modelling the formation of membrane structures, such as rafts. Lipid diffusion is mainly studied by two different techniques: incoherent neutron scattering and fluorescence microscopy. Both techniques access distinctly different length scales. While neutron scattering measures diffusion over about 3 lipid diameters, microscopic techniques access motions of lipids over micrometer distances. The diffusion constants which are determined by these two methods often differ by about an order of magnitude, with the neutrons usually seeing a faster lipid diffusion. Different theories are used to describe lipid diffusion in the two experiments. In order to close the “gap” between these two techniques, we propose to study lipid diffusion at mesoscopic length scales using a neutron spin-echo (NSE) spectrometer. We have conducted an experiment in highly oriented, solid supported lipid bilayers to prove the feasibility of performing incoherent NSE on biological samples. Lateral lipid diffusion was measured in a fluid phase model membrane system at a length scale of 12 Å. Using the high-energy resolution of the NSE technique, we find evidence for two dynamic processes.
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Innerlohinger, Josef, Mario Villa, Matthias Baron, and Otto Glatter. "Ultra-small-angle neutron scattering from dense micrometre-sized colloidal systems: data evaluation and comparison with static light scattering." Journal of Applied Crystallography 39, no. 2 (2006): 202–8. http://dx.doi.org/10.1107/s0021889806001592.
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Ultra-small-angle neutron scattering (USANS) probes the sameqregime as static light scattering (LS), making USANS an additional tool for the study of structures between 100 nm and 10 µm. Dense oil-in-water emulsions, which have already been characterized intensively by light scattering, are investigated in this study as a model system using USANS. The two basic problems of such scattering studies are the following: on the one hand, one has to use different scattering theories for USANS and LS, and on the other hand, in both cases one has to deal not only with particle interactions but also with multiple-scattering effects. For neutron scattering it is always possible to use the simpler Rayleigh–Debye–Gans (RDG) theory instead of the Lorenz–Mie theory, which generally describes light scattering from micrometre-sized globular objects. The samples have different contrasts in neutron and light scattering, such that only low-contrast (close to index match) LS data can be interpreted by the RDG theory. The data evaluation is performed by means of the generalized indirect Fourier transformation (GIFT) method, which enables the simultaneous calculation of the form and structure factors. The results are discussed and compared with those from light scattering experiments, taking into account the advantages of both methods. The effect of multiple scattering and its influence on data evaluation is also examined. Data evaluation by applying the GIFT method works well for both neutron and light scattering data, with results of comparable quality. The advantages of light scattering are the fast data acquisition and the large number of data points. USANS, on the other hand, covers a widerqrange and the problem of multiple scattering is not as severe as for light scattering, but still must not be neglected.
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DOSTER, W. "THE GLASS TRANSITION ANOMALIES OF MYOGLOBIN IN THE LIGHT OF MODE COUPLING THEORY." Modern Physics Letters B 05, no. 21 (1991): 1407–14. http://dx.doi.org/10.1142/s0217984991001702.
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The physics and some predictions of recent mode coupling theories concerning the liquid to glass instability are reviewed with the scope to explore its potential to explain the dynamics of non-simple liquids. It is proposed that the dynamics scaling behaviour observed in the neutron scattering spectra of myoglobin reveal a critical temperature which is associated with the arrest of density fluctuations.
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Papoulias, D. K., and T. S. Kosmas. "Probing electromagnetic neutrino properties within the tensor non-standard neutrino-nucleus interactions." HNPS Proceedings 23 (March 8, 2019): 119. http://dx.doi.org/10.12681/hnps.1915.
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Non-standard coherent neutrino scattering off nuclei is extensively studied through realistic nuclear structure calculations performed within the framework of the quasi-particle random phase approximation (QRPA). More specifically, we focus on the accurate estimation of the number of events expected to be measured by the COHERENT experiment at the Spallation Neutron Source at Oak Ridge, as well as by the reactor neutrino experiments TEXONO and GEMMA. To this purpose our study concentrates on the relevant detector materials 20 Ne, 40 Ar, 76 Ge and 132 Xe. In this context, we obtain stringent constraints on the vector and tensor non-standard interaction parameters and examine their impact on various electromagnetic neutrino phenomena such as neutrino magnetic moments and neutrino milli-charges. Our results indicate that the aforementioned experiments offer significant prospects to probe neutrino properties predicted in theories beyond the Standard Model.
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Henning, Greg, Antoine Bacquias, Catalin Borcea та ін. "MEASUREMENT OF 182,184,186W (N, N’ γ) CROSS SECTIONS AND WHAT WE CAN LEARN FROM IT". EPJ Web of Conferences 247 (2021): 09003. http://dx.doi.org/10.1051/epjconf/202124709003.
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Today’s development of nuclear installations rely on numerical simulation for which the main input are evaluated nuclear data. Inelastic neutron scattering (n, xn) is a reaction of importance because it modifies the neutron population, the neutron energy distribution and may create new isotopes. The study of this reaction on tungsten isotopes is interesting because it is a common structural material. Additionally, tungsten isotopes are a good testing field for theories. The IPHC group started an experimental program with the GRAPhEME setup installed at the neutron beam facility GELINA to measure (n, xn γ) reaction cross sections using prompt gamma spectroscopy and neutron energy determination by time-of-flight. The obtained experimental data provide constraints on nuclear reaction mechanisms models for 182,184,186W. Indeed, to reproduce correctly the experimental (n, n’ γ) cross-sections, the reaction codes must include accurate models of the reaction mechanism, nuclear de-excitation process and use correct nuclear structure information.
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RANA, ANWAR MANZOOR, and M. IQBAL ANSARI. "PARTICLE COARSENING IN Fe(Cu) ALLOYS." Modern Physics Letters B 09, no. 06 (1995): 343–50. http://dx.doi.org/10.1142/s0217984995000322.
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Particle coarsening behavior in Fe(Cu) alloys has been studied by electrical resistivity measurements at different ageing temperatures. Measured resistivity data for these alloys were analyzed by discussing the electrical resistivity behavior during thermal ageing and theories of diffusion-controlled coarsening of precipitates. Some important parameters such as the precipitate radius r, solute concentration C, diffusivity D, etc. were calculated and compared with the previous results obtained with Transmission Electron Microscopy (TEM) and Small Angle Neutron Scattering (SANS) techniques.
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Bramwell, Steven T. "Generalized longitudinal susceptibility for magnetic monopoles in spin ice." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, no. 1981 (2012): 5738–66. http://dx.doi.org/10.1098/rsta.2011.0596.
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The generalized longitudinal susceptibility χ (q, ω ) affords a sensitive measure of the spatial and temporal correlations of magnetic monopoles in spin ice. Starting with the monopole model, a mean field expression for χ (q, ω ) is derived as well as expressions for the mean square longitudinal field and induction at a point. Monopole motion is shown to be strongly correlated, and both spatial and temporal correlations are controlled by the dimensionless monopole density x which defines the ratio of the magnetization relaxation rate and the monopole hop rate. Thermal effects and spin-lattice relaxation are also considered. The derived equations are applicable in the temperature range where the Wien effect for magnetic monopoles is negligible. They are discussed in the context of existing theories of spin ice and the following experimental techniques: DC and AC magnetization, neutron scattering, neutron spin echo and longitudinal and transverse field μ SR. The monopole theory is found to unify diverse experimental results, but several discrepancies between theory and experiment are identified. One of these, concerning the neutron scattering line shape, is explained by means of a phenomenological modification to the theory.
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Lynn, J. E., I. Tews, S. Gandolfi, and A. Lovato. "Quantum Monte Carlo Methods in Nuclear Physics: Recent Advances." Annual Review of Nuclear and Particle Science 69, no. 1 (2019): 279–305. http://dx.doi.org/10.1146/annurev-nucl-101918-023600.
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In recent years, the combination of precise quantum Monte Carlo (QMC) methods with realistic nuclear interactions and consistent electroweak currents, in particular those constructed within effective field theories (EFTs), has led to new insights in light and medium-mass nuclei, neutron matter, and electroweak reactions. For example, with the same chiral interactions, QMC calculations can reproduce binding energies and radii for light nuclei, n–α scattering phase shifts, and the neutron matter equation of state. This compelling new body of work has been made possible both by advances in QMC methods for nuclear physics, which push the bounds of applicability to heavier nuclei and to asymmetric nuclear matter, and by the development of local chiral EFT interactions up to next-to-next-to-leading order and minimally nonlocal interactions including Δ degrees of freedom. In this review, we discuss these recent developments and give an overview of the exciting results for nuclei, neutron matter and neutron stars, and electroweak reactions.
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Kerscher, Michael, Frederik Lipfert, and Henrich Frielinghaus. "Exploring Hidden Local Ordering in Microemulsions with a Weak Directive Second Order Parameter." Chemistry Africa 3, no. 3 (2020): 703–9. http://dx.doi.org/10.1007/s42250-020-00126-7.
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Abstract So far, the near-surface ordering of microemulsions was focused on lamellar ordering while the bulk microemulsion was bicontinuous. In a series of different non-ionic surfactants the near-surface ordering of microemulsions at a hydrophilic silicon surface was studied using grazing incidence small angle neutron scattering. For the surfactant C8E3, most likely a gyroid structure was found at the solid–liquid interface, while the more efficient surfactants find lamellar ordering up to lamellar capillary condensation. The ranges for near-surface ordering are deeper than the bulk correlation lengths. These findings point towards theories that use directional order parameters that would lead to deeper near-surface ordering than simple theories with a single scalar order parameter would predict. Rheology experiments display high viscosities at very low shear rates and, therefore, support the existence of a directional order parameter.
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Kunz, Werner, and Pierre Turq. "Structure and Dynamics of Nonaqueous Electrolyte Solutions by Small Angle Neutron Scattering, Brownian Dynamics and Primitive Model Theories." Berichte der Bunsengesellschaft für physikalische Chemie 94, no. 3 (1990): 321–25. http://dx.doi.org/10.1002/bbpc.19900940324.
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Li, Bao-An, and Lie-Wen Chen. "Neutron–proton effective mass splitting in neutron-rich matter and its impacts on nuclear reactions." Modern Physics Letters A 30, no. 13 (2015): 1530010. http://dx.doi.org/10.1142/s0217732315300104.
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The neutron–proton effective mass splitting in neutron-rich nucleonic matter reflects the spacetime nonlocality of the isovector nuclear interaction. It affects the neutron/proton ratio during the earlier evolution of the Universe, cooling of proto-neutron stars, structure of rare isotopes and dynamics of heavy-ion collisions. While there is still no consensus on whether the neutron–proton effective mass splitting is negative, zero or positive and how it depends on the density as well as the isospin-asymmetry of the medium, significant progress has been made in recent years in addressing these issues. There are different kinds of nucleon effective masses. In this mini-review, we focus on the total effective masses often used in the non-relativistic description of nuclear dynamics. We first recall the connections among the neutron–proton effective mass splitting, the momentum dependence of the isovector potential and the density dependence of the symmetry energy. We then make a few observations about the progress in calculating the neutron–proton effective mass splitting using various nuclear many-body theories and its effects on the isospin-dependence of in-medium nucleon–nucleon cross-sections. Perhaps, our most reliable knowledge so far about the neutron–proton effective mass splitting at saturation density of nuclear matter comes from optical model analyses of huge sets of nucleon–nucleus scattering data accumulated over the last five decades. The momentum dependence of the symmetry potential from these analyses provide a useful boundary condition at saturation density for calibrating nuclear many-body calculations. Several observables in heavy-ion collisions have been identified as sensitive probes of the neutron–proton effective mass splitting in dense neutron-rich matter based on transport model simulations. We review these observables and comment on the latest experimental findings.
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Radaelli, Paolo G., and James D. Jorgensen. "Neutron Diffraction from Novel Materials." MRS Bulletin 24, no. 12 (1999): 24–28. http://dx.doi.org/10.1557/s0883769400053689.
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The discovery and development of new materials is the foundation of the science and technology “food chains.” Examples of new materials with novel properties that have stimulated new scientific questions and/or led to new technologies include liquid crystals, advanced batteries, structural ceramics, dielectrics, ferroelectrics, catalysts, high-temperature superconductors, har dmagnets, and magnetoresistive devices. Establishing the crystal structure of a newly discovered Compound is a mandatory first step, but the most important contribution of diffraction techniques is to provide an understanding of the relationships among chemical composition, crystal structure, and physical behavior. In this way, diffraction experiments provide critical Information for testing theories that explain novel behavior and guide the optimization of new materials to meet the demands of emerging technologies.The first samples of newly discovered materials are often polycrystalline. With state-of-the-art neutron powder diffraction data and Rietveld refinement techniques, for structures of modest complexity, the precision for atom positions rivals that obtained by single-crystal diffraction. Rietveld refinement is a method of obtaining accurate values for atom positions and other structural parameters from powder diffraction data by least-squares fitting of a calculated model to the full diffraction pattern. As evidence of thi s success, the Inorganic Crystal Structure Database contains 6044 entries from neutron powder diffraction, 7096 from laboratory x-ray powder diffraction, an d 228 from Synchrotron x-ray powder diffraction. Other reasons for the rapidly growing impact of neutron diffraction include the favorable neutron-scattering cross sections for light elements, the sensitivity to magnetic moments, and the ability to penetrate special sample environments for in situ studies. These strengths are widely accepted and have been exploited for many years. Previous reviews have focused on these topics.
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Bartsch, E., F. Fujara, M. Kiebel, H. Sillescu, and W. Petry. "Inelastic Neutron Scattering Experiments on Van der Waals Glasses - A Test of Recent Microscopic Theories of the Glass Transition." Berichte der Bunsengesellschaft für physikalische Chemie 93, no. 11 (1989): 1252–59. http://dx.doi.org/10.1002/bbpc.19890931121.
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Bykovetz, N., A. Hoser, J. Klein, C. L. Lin, and M. S. Seehra. "Neutron scattering measurements in RbMnF3: A test of spin-wave-region theories at low temperatures and critical behavior near TN." Journal of Applied Physics 111, no. 7 (2012): 07E145. http://dx.doi.org/10.1063/1.3679410.
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Goldman, Maurice. "Anatole Abragam. 15 December 1914 — 8 June 2011." Biographical Memoirs of Fellows of the Royal Society 63 (January 2017): 7–21. http://dx.doi.org/10.1098/rsbm.2017.0026.
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Anatole Abragam, a French physicist of Russian origin, made a profound and lasting impact on the field of magnetic resonance, both electronic and nuclear, through his discoveries, contributions and his eminent educational role. In nuclear magnetic resonance (NMR) especially, he brought to the field theoretical rigour and clarity. Many of the most distinguished scientists in the field consider themselves to be his students, and he is known by many as a ‘giant of magnetic resonance’. Among his main contributions are: theories of the spin Hamiltonian and of core polarization in electron paramagnetic resonance (EPR); the theory of perturbed angular correlations of radioactive emissions in condensed matter; a new theoretical formalism of spin relaxation; the invention of an Earth magnetometer; basic studies of spin temperature; dynamic nuclear polarization in solids and production of polarized targets; nuclear dipolar magnetic ordering studied both by NMR and by neutron diffraction; the discovery of nuclear pseudo-magnetism and its use for measuring the spin-dependent neutron–nucleus scattering amplitudes; and a new spectroscopic technique for muon spin rotation ( μ SR).
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Han, Zehua, Guisheng Jiao, Changli Ma, Taisen Zuo, Charles C. Han, and He Cheng. "The Relationship between Free Volume and Cooperative Rearrangement: From the Temperature-Dependent Neutron Total Scattering Experiment of Polystyrene." Polymers 13, no. 18 (2021): 3042. http://dx.doi.org/10.3390/polym13183042.
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Although many theories have been proposed to describe the nature of glass formation, its microscopic picture is still missing. Here, by a combination of neutron scattering and molecular dynamics simulation, we present the temperature-dependent atomic structure variation of polystyrene at the glass formation, free volume and cooperative rearrangement. When it is close to glass formation, the polymer is confined in tubes, whose diameter is the main chain–main chain distance, in a “static cage” from its neighbors. This definition can not only account for the kinetic pathway dependence of Williams-Landel-Ferry (WLF) free volume, but also be testified in a set of six polymers. However, the free volume which allows a monomer to move cannot be found in any frame of its real-space image. Monomers, thus, have to move cooperatively to be out of the cage. During glass formation, dynamic heterogeneity develops, and string-like cooperative rearrangement region (CRR) grows over a long range of time and length scales. All of these CRRs tend to walk through loose “static cages”. Our observation unifies the concepts of free volume and cooperative rearrangement. The former is a statistical average leading to a polydisperse “static cage” formation; while a loose “static cage” provides the way that CRRs move.
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DJAJAPUTRA, DAVID, and JOHN RUVALDS. "SUSCEPTIBILITY AND VERTEX CORRECTIONS FOR A SQUARE FERMI SURFACE." International Journal of Modern Physics B 13, no. 01 (1999): 25–48. http://dx.doi.org/10.1142/s0217979299000035.
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We investigate the response of an electron system which exhibits ideal nesting features. Using the standard Matsubara formalism we derive analytic expressions for the imaginary and real parts of the bare particle–hole susceptibility. The imaginary part has sharp peaks whose maxima at the nesting momenta approximately scale with (ω/T). The peak lineshapes resemble neutron scattering data on chromium and some copper oxide superconductors. The real part of the bare susceptibility at the nesting vectors diverges logarithmically at low temperatures. Analytic formulas for the first vertex correction to the susceptibility are derived for a Hubbard interaction and its momentum and temperature variations are calculated numerically. This term detracts substantially from the ordinary RPA terms for intermediate values of the Coulomb repulsion. Exact cancellation of a certain class of diagrams at half filling is shown to result from particle–hole symmetry. We discuss the consequences of these results for spin fluctuation theories of high temperature superconductors and spin density wave instabilities.
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Takagi, R., J. S. White, S. Hayami, et al. "Multiple-q noncollinear magnetism in an itinerant hexagonal magnet." Science Advances 4, no. 11 (2018): eaau3402. http://dx.doi.org/10.1126/sciadv.aau3402.
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Multiple-q spin order, i.e., a spin texture characterized by a multiple number of coexisting magnetic modulation vectors q, has recently attracted attention as a source of nontrivial magnetic topology and associated emergent phenomena. One typical example is the triple-q skyrmion lattice state stabilized by Dzyaloshinskii-Moriya interactions in noncentrosymmetric magnets, while the emergence of various multiple-q states of different origins is expected according to the latest theories. Here, we investigated the magnetic structure of the itinerant polar hexagonal magnet Y3Co8Sn4, in which several distinctive mechanisms favoring multiple-q states are allowed to become active. Small-angle neutron-scattering experiments suggest the formation of incommensurate triple-q magnetic order with an in-plane vortex-like spin texture, which can be most consistently explained in terms of the novel four-spin interaction mechanism inherent to itinerant magnets. The present results suggest a new route to realizing exotic multiple-q orders and that itinerant hexagonal magnets, including the R3M8Sn4 family with wide chemical tunability, can be a unique material platform to explore their rich phase diagrams.
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Huberman, T., D. A. Tennant, R. A. Cowley, R. Coldea, and C. D. Frost. "A study of the quantum classical crossover in the spin dynamics of the 2DS= 5/2 antiferromagnet Rb2MnF4: neutron scattering, computer simulations and analytic theories." Journal of Statistical Mechanics: Theory and Experiment 2008, no. 05 (2008): P05017. http://dx.doi.org/10.1088/1742-5468/2008/05/p05017.
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Almásy, László, and Attila Bende. "Intermolecular Interaction in Methylene Halide (CH2F2, CH2Cl2, CH2Br2 and CH2I2) Dimers." Molecules 24, no. 9 (2019): 1810. http://dx.doi.org/10.3390/molecules24091810.
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The intermolecular interaction in difluoromethane, dichloromethane, dibromomethane, and diiodomethane dimers has been investigated using high level quantum chemical methods. The potential energy curve of intermolecular interaction along the C⋯C bond distance obtained using the coupled-cluster theory with singles, doubles, and perturbative triples excitations CCSD(T) were compared with values given by the same method, but applying the local (LCCSD(T)) and the explicitly correlated (CCSD(T)-F12) approximations. The accuracy of other theoretical methods—Hartree–Fock (HF), second order Møller–Plesset perturbation (MP2), and dispersion corrected DFT theory—were also presented. In the case of MP2 level, the canonical and the local-correlation cases combined with the density-fitting technique (DF-LMP2)theories were considered, while for the dispersion-corrected DFT, the empirically-corrected BLYP-D and the M06-2Xexchange-correlation functionals were applied. In all cases, the aug-cc-pVTZ basis set was used, and the results were corrected for the basis set superposition error (BSSE) using the counterpoise method. For each molecular system, several dimer geometries were found, and their mutual orientations were compared with the nearest neighbor orientations obtained in recent neutron scattering studies. The nature of the intermolecular interaction energy was discussed.
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Kramer, M., I. H. Stairs, V. Venkatraman Krishnan, et al. "The relativistic binary programme on MeerKAT: science objectives and first results." Monthly Notices of the Royal Astronomical Society 504, no. 2 (2021): 2094–114. http://dx.doi.org/10.1093/mnras/stab375.
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ABSTRACT We describe the ongoing Relativistic Binary programme (RelBin), a part of the MeerTime large survey project with the MeerKAT radio telescope. RelBin is primarily focused on observations of relativistic effects in binary pulsars to enable measurements of neutron star masses and tests of theories of gravity. We selected 25 pulsars as an initial high priority list of targets based on their characteristics and observational history with other telescopes. In this paper, we provide an outline of the programme, and present polarization calibrated pulse profiles for all selected pulsars as a reference catalogue along with updated dispersion measures. We report Faraday rotation measures for 24 pulsars, twelve of which have been measured for the first time. More than a third of our selected pulsars show a flat position angle swing confirming earlier observations. We demonstrate the ability of the Rotating Vector Model, fitted here to seven binary pulsars, including the Double Pulsar (PSR J0737–3039A), to obtain information about the orbital inclination angle. We present a high time resolution light curve of the eclipse of PSR J0737–3039A by the companion’s magnetosphere, a high-phase-resolution position angle swing for PSR J1141–6545, an improved detection of the Shapiro delay of PSR J1811–2405, and pulse scattering measurements for PSRs J1227–6208, J1757–1854, and J1811–1736. Finally, we demonstrate that timing observations with MeerKAT improve on existing data sets by a factor of, typically, 2–3, sometimes by an order of magnitude.
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Gvaramia, Manuchar, Gaetano Mangiapia, Vitaliy Pipich, et al. "Tunable viscosity modification with diluted particles: when particles decrease the viscosity of complex fluids." Colloid and Polymer Science 297, no. 11-12 (2019): 1507–17. http://dx.doi.org/10.1007/s00396-019-04567-6.
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Abstract While spherical particles are the most studied viscosity modifiers, they are well known only to increase viscosities, in particular at low concentrations of approx. 1%. Extended studies and theories on non-spherical particles in simple fluids find a more complicated behavior, but still a steady increase with increasing concentration. Involving platelets in combination with complex fluids—in our case, a bicontinuous microemulsion—displays an even more complex scenario that we analyze experimentally and theoretically as a function of platelet diameter using small angle neutron scattering, rheology, and the theory of the lubrication effect, to find the underlying concepts. The clay particles effectively form membranes in the medium that itself may have lamellar aligned domains and surfactant films in the case of the microemulsion. The two-stage structure of clay and surfactant membranes explains the findings using the theory of the lubrication effect. This confirms that layered domain structures serve for lowest viscosities. Starting from these findings and transferring the condition for low viscosities to other complex fluids, namely crude oils, even lowered viscosities with respect to the pure crude oil were observed. This strengthens our belief that also here layered domains are formed as well. This apparent contradiction of a viscosity reduction by solid particles could lead to a wider range of applications where low viscosities are desired. The same concepts of two-stage layered structures also explain the observed conditions for extremely enhanced viscosities at particle concentrations of 1% that may be interesting for the food industry.
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Li, Boyu, Joey Kim, and Julie Kornfield. "A Molecular Picture for the Thermo-Reversibility of Gels Formed by Isophthalic Acid-Ended Telechelic Polymers." MRS Proceedings 1794 (2015): 9–14. http://dx.doi.org/10.1557/opl.2015.638.
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ABSTRACTWe demonstrate that isophthalic acid-ended telechelic poly(1,5-cyclooctadiene)s (A-PCODs) form thermo-reversible gels in non-polar solvent with a unique molecular mechanism for their thermo-reversibility. Like other associative telechelic polymers, A-PCODs form “flower-like” micelles at low concentration and form gels through bridging at higher concentration which exhibit linear viscoelasticity. However, unlike the widely studied hydrophobically end-capped PEOs, A-PCODs show clear thermo-reversibility in viscosity and dynamic modulus around 30 °C due to the hydrogen-bonding end groups. In addition, they differ from other reported thermo-reversible gelators (eg. Pluronics, PNIPAm containing block copolymers, etc.): neither the end group nor the backbone in the present system has a critical solution temperature within the measured temperature range (0 °C to 60 °C), indicating that the present system has a unique mechanism for its thermo-reversibility. To obtain a molecular picture of the mechanism, rheology and small angle neutron scattering (SANS) studies were implemented. Topological changes above the transition temperature (30 °C) were observed in both oscillatory rheology and SANS. SANS reveals that the size of clusters, which are formed by interacting micelles, depends highly on temperature (T) but independent of polymer concentration. These results cannot be explained by current theories on associative telechelic polymers which assume constant and large aggregation number of end groups at all temperatures and concentrations. We hypothesize that the temperature-sensitive sol-gel transition is due to a decrease in aggregation number for T above the critical temperature in our system, and this temperature-dependence of aggregation number is further determined by the chemical structure and hydrogen-bonding property of isophthalic acid ends.
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CHHABRA, TARANJEET, and P. RAM BABU. "LIMITING LEPTONIC GAUGE BOSON COUPLING FROM NEUTRINO-ELECTRON SCATTERING." International Journal of Modern Physics A 09, no. 30 (1994): 5409–14. http://dx.doi.org/10.1142/s0217751x9400217x.
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The phenomenological consequences of the leptonic gauge boson (X-), predicted in certain unified theories, are pointed out. The new boson’s contribution in electronic neutrino-electron scattering is calculated. Combining the data on Z decay, electronic neutrino-electron scattering etc., we obtain the region of allowed coupling strengths of X-. The analysis is model-independent but assumes V, A Lorentz structure and μ-e universality.
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ADAMS, T., P. BATRA, L. BUGEL, et al. "TERASCALE PHYSICS OPPORTUNITIES AT A HIGH STATISTICS, HIGH ENERGY NEUTRINO SCATTERING EXPERIMENT: NuSOnG." International Journal of Modern Physics A 24, no. 04 (2009): 671–717. http://dx.doi.org/10.1142/s0217751x09043316.
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This paper presents the physics case for a new high-energy, ultra-high statistics neutrino scattering experiment, NuSOnG (Neutrino Scattering on Glass). This experiment uses a Tevatron-based neutrino beam to obtain over an order of magnitude higher statistics than presently available for the purely weak processes νμ + e- → νμ + e- and νμ + e- → νe + μ-. A sample of Deep Inelastic Scattering events which is over two orders of magnitude larger than past samples will also be obtained. As a result, NuSOnG will be unique among present and planned experiments for its ability to probe neutrino couplings to Beyond the Standard Model physics. Many Beyond Standard Model theories physics predict a rich hierarchy of TeV-scale new states that can correct neutrino cross-sections, through modifications of Zνν couplings, tree-level exchanges of new particles such as Z′'s, or through loop-level oblique corrections to gauge boson propagators. These corrections are generic in theories of extra dimensions, extended gauge symmetries, supersymmetry, and more. The sensitivity of NuSOnG to this new physics extends beyond 5 TeV mass scales. This paper reviews these physics opportunities.
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Batool, Sidra, Mehwish Nisar, Fabio Mangini, Fabrizio Frezza, and Eugenio Fazio. "Scattering of Light from the Systemic Circulatory System." Diagnostics 10, no. 12 (2020): 1026. http://dx.doi.org/10.3390/diagnostics10121026.
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There are many factors of methodological origin that influence the measurement of optical properties of the entire circulatory system which consists of blood as the basic component. The basic idea of this review article is to provide the optical properties of the circulatory system with all those factors of influence that have been employed in biomedical optics for different applications. We begin with the available optical properties, i.e., absorption, scattering and, reduced scattering coefficient, in general for any tissue inside the human body and prominent scattering theories (e.g., light, X-rays, neutrons) that are helpful in this regard. We have reviewed and compiled already available formulas and their respective available data for different human tissues for these optical properties. Then we have descended to the blood composition and to different scattering techniques available in the literature to study scattering and light propagation inside blood. We have reviewed both computational and theoretical scattering techniques.
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JOHNSON, GLENN ERIC. "INTERACTING QUANTUM FIELDS." Reviews in Mathematical Physics 11, no. 07 (1999): 881–928. http://dx.doi.org/10.1142/s0129055x99000271.
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A wide class of quantum field theories (QFTs) describing interacting neutral scalar bosons are constructed. It is shown that a redefinition of the vacuum expectation values (VEV) of quantum fields as generalized functions leads to constructions of interacting fields that are operators in a Hilbert space and satisfy the physical requirements for a field theory. The field operators are constructed directly, without perturbation expansion, and constructed in spacetime of any number of dimensions. The corresponding scattering theory is developed. The limited function class underlying the QFT imposes a direction to time.
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BASEILHAC, P., and V. A. FATEEV. "FERMION–BOSON DUALITY IN INTEGRABLE QUANTUM FIELD THEORY." Modern Physics Letters A 13, no. 35 (1998): 2807–18. http://dx.doi.org/10.1142/s0217732398002989.
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We introduce and study one-parameter family of integrable quantum field theories. This family has a Lagrangian description in terms of massive Thirring fermions ψ, ψ† and charged bosons χ, [Formula: see text] of complex sinh–Gordon model coupled with BCn affine Toda theory. Perturbative calculations, analysis of the factorized scattering theory and the Bethe ansatz technique are applied to show that under duality transformation, which relates weak and strong coupling regimes of the theory, the fermions ψ, ψ† transform to bosons and χ, [Formula: see text] and vice versa. The scattering amplitudes of neutral particles in this theory coincide exactly with S-matrix of particles in pure BCn Toda theory, i.e. the contribution of charged bosons and fermions to these amplitudes exactly cancel each other. We describe and discuss the symmetry responsible for this compensation property.
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Garat, Alcides. "Tetrads in low-energy weak interactions." International Journal of Modern Physics A 33, no. 33 (2018): 1850197. http://dx.doi.org/10.1142/s0217751x1850197x.
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Tetrads are introduced in order to study the relationship between tetrad gauge states of space–time and particle interactions, specially in weak processes at low energy. Through several examples like inverse muon decay, elastic neutrino–electron scattering, it is explicitly shown how to assign to each vertex of the corresponding low-order Feynman diagram in a weak interaction, a particular set of tetrad vectors. The relationship between the tetrads associated to different vertices is exhibited explicitly to be generated by a SU(2) local tetrad gauge transformation. We are establishing a direct link between standard gauge and tetrad gauge states of space–time using the quantum field theories perturbative formulations.
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Danylevsky, V. "Cosmic rays and aerosols in the terrestrial atmosphere." Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 57 (2018): 15–27. http://dx.doi.org/10.17721/btsnua.2018.57.15-27.
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Galactic cosmic rays are considered as one of the external force influencing the Earth’s climate change. The cosmic rays are the main cause of the troposphere ionization. Ions are considered as one of the factors that participates in producing of the aerosol particles and cloud condensation nuclei, when the super saturation level of the water vapor or/and other atmosphere constituents vapor is sufficient. Aerosols are present throughout the atmosphere and affect Earth’s climate directly through backscattering of sunlight and indirectly by altering cloud properties. Both effects are known with considerable uncertainty only, and translate into even bigger uncertainties in future climate predictions. Whereas disputable, the idea is discussed by the scientists that variations in galactic cosmic rays closely correlate with variations in atmospheric cloud cover and therefore constitute a driving force behind aerosol-cloud-climate interactions. A lot of studies were performed to validate or disprove the connection between cosmic ray’s variation (e.g. the Forbush events) and changes of the aerosol content and properties in the atmosphere, cloud cover and properties and other climate parameters, but results are controversial. The enhancement of atmospheric aerosol particle formation by ions generated from cosmic rays was proposed as a physical mechanism explaining this correlation. But the main problem is to find the appropriate physical model which allows to calculate correctly the ion concentrations, nucleation and aerosol particles rate and cosmic rays intensity. Aerosol particle formation occurs in two stages: nucleation to form a critical nucleus and subsequent growth of the critical nucleus to a larger size (>2 – 3 nm) that competes with removal of the freshly nucleated nanoparticles by coagulation with pre-existing aerosols. The most used nucleation and particle growth theories are reviewed and analyzed in the article. The base of the theories is follow. Nucleation is generally defined as creation of molecular embryos or clusters prior to formation of a new phase during the transformation of vapor liquid solid. This process is characterized by a decrease in both enthalpy and entropy of the nucleating system. A free energy barrier is often involved and needs to be surmounted before transformation to the new phase becomes spontaneous. Another limitation in the nucleation and growth of atmospheric nanoparticles lies in significantly elevated equilibrium vapor pressures above small clusters and nanoparticles, also known as the Kelvin (curvature) effect, which considerably restricts growth of freshly nucleated nanoparticles. Ions are capable, under certain conditions, of suppressing or even removing the barrier to nucleation in embryonic molecular clusters of water. But results of the theories are very uncertain so far. Results of the observations of the nucleation and particles formation as well as the special CLOUD experiment results are reviewed and analyzed in the article. The molecular clusters and nuclei can not be observed by remote sensing techniques like sun-photometers, lidars or satellite instruments. The in-situ measurements of the nucleation concentration and particles growth rate are performed in the certain sites only. The observations and experiments revealed the important influence of the trace gases and organic molecules on the nucleation and particle growth rate. Sulphuric acid, ammonia, amines, and oxidised organics play a crucial role in nanoparticle formation in the atmosphere competing with ionmediated mechanism. Saturation pressure of the sulphuric acid and organics vapors at the typical atmospheric conditions is much lower than for water vapor and at typical atmospheric concentration they are capable of suppressing the nucleation barrier. Nucleation with ions started earlier and run faster but the nucleus with sizes ≥ 3 nm more than 90 % of clusters are neutral. Ion-mediated mechanism can dominate when sulphuric asid and organic molecules concentration is low. But more observations in the different atmosphere layers and locations and experiments at different conditions is required to better understanding the ion-mediated nucleation in the atmosphere. Nucleation contribution to the aerosol content and properties in the terrestrial atmosphere is also simulated by the special modules included to the regional and global models of the atmosphere and climate, e.g. GEOS-Chem and CAM5. Comparison of the simulation and observations has showed that in general the averaged model results are in good agreement with observational data at some sites but same biases were revealed at some sites too. It requires the further analysis and models developments. Also ion-mediated mechanism contribution was also estimated by the simulation not more than 10%. Analysis of the observations and models results in the article showed that cosmic rays influencing the aerosol formation also influence the microphysical and optical properties of the particles. First of all particles size distribution is influenced by nucleation mechanism and relative content of the Aitken nuclei increases. Also sulphuric acid can influence the particle refractive index increasing the single-scattering albedo of the aerosols. Modern remote sense technique such as the AERONET sun-photometers can measure the spectral AOD and sky radiance with high accuracy and the reliable size distribution, refractive index and single-scattering albedo averaged over atmosphere column can be determined from that observations, but the AERONET inversion algorithm has to be developed to obtain the particles size finer than 50 nm.
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Borkowski, Mateusz, Alexei A. Buchachenko, Roman Ciuryło, et al. "Weakly bound molecules as sensors of new gravitylike forces." Scientific Reports 9, no. 1 (2019). http://dx.doi.org/10.1038/s41598-019-51346-y.
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Abstract Several extensions to the Standard Model of particle physics, including light dark matter candidates and unification theories predict deviations from Newton’s law of gravitation. For macroscopic distances, the inverse-square law of gravitation is well confirmed by astrophysical observations and laboratory experiments. At micrometer and shorter length scales, however, even the state-of-the-art constraints on deviations from gravitational interaction, whether provided by neutron scattering or precise measurements of forces between macroscopic bodies, are currently many orders of magnitude larger than gravity itself. Here we show that precision spectroscopy of weakly bound molecules can be used to constrain non-Newtonian interactions between atoms. A proof-of-principle demonstration using recent data from photoassociation spectroscopy of weakly bound Yb2 molecules yields constraints on these new interactions that are already close to state-of-the-art neutron scattering experiments. At the same time, with the development of the recently proposed optical molecular clocks, the neutron scattering constraints could be surpassed by at least two orders of magnitude.
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Nakatani, Alan I., Hongdoo Kim, and Charles C. Han. "Shear Induced Phase Behavior of Polymer Blends by Small Angle Neutron Scattering." MRS Proceedings 166 (1989). http://dx.doi.org/10.1557/proc-166-479.
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ABSTRACTThe phase behavior of polymer blends and solutions can be changed dramatically by a flow field using a variety of flow geometries. Unlike simple binary fluids which require extremely high shear rates to produce only small shifts in the phase boundary, polymer phase behavior may be influenced by as much as 10 degrees with the application of much lower shear rates. However, there is a large body of conflicting data concerning the nature of these shear effects in polymers.Here we report on the effects of shear on the phase behavior of polymer blends by small angle neutron scattering (SANS). Experiments were conducted using a specially constructed, concentric cylinder apparatus for in situ studies of concentrated polymer solutions and melts. Two separate systems will be discussed: 1) a blend of polystyrene and polybutadiene. 2) a blend of polystyrene and poly(vinylmethylether). Both systems exhibit shifts in the phase behavior which indicate shear induced mixing in agreement with previous results obtained by other techniques. These results will be interpreted within the context of existing theories of shear induced phase behavior.
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Sarte, P. M., K. Cruz-Kan, B. R. Ortiz, et al. "Dynamical ground state in the XY pyrochlore Yb2GaSbO7." npj Quantum Materials 6, no. 1 (2021). http://dx.doi.org/10.1038/s41535-021-00343-4.
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AbstractThe magnetic ground state of the pyrochlore Yb2GaSbO7 has not been established. The persistent spin fluctuations observed by muon spin-relaxation measurements at low temperatures have not been adequately explained for this material using existing theories for quantum magnetism. Here we report on the synthesis and characterisation of Yb2GaSbO7 to revisit the nature of the magnetic ground state. Through DC and AC magnetic susceptibility, heat capacity, and neutron scattering experiments, we observe evidence for a dynamical ground state that makes Yb2GaSbO7 a promising candidate for disorder-induced spin-liquid or spin-singlet behaviour. This state is quite fragile, being tuned to a splayed ferromagnet in a modest magnetic field μ0Hc ~ 1.5 T.
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Ullman, Robert. "Polymer Chain Deformation in Stretched and Swollen Elastomers." MRS Proceedings 79 (1986). http://dx.doi.org/10.1557/proc-79-225.
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AbstractIn the early theories of rubber elasticity, the retractive force and change in free energy of a stretched specimen were calculated from the deformation of the polymer chains of which the rubber network was formed. The mean chain deformation was presumed to be the same as that of the macroscopic specimen, an assumption which seemed reasonable, but could not be confirmed experimentally. Small angle neutron scattering (SANS) made measurement of chain dimensions possible, and it was soon discovered [1], [2] that the actual relation between dimensional changes of the polymer chain and deformation of the specimen was not at all what had been assumed.SANS studies of carefully prepared elastomeric networks provide the most direct experimental information required for a molecular theory of rubber elasticity, and have stimulated many new developments.
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Kampmann, R., H. Eckerlebe, and R. Wagner. "Precipitation Kinetics in Metastable Solid Solutions – Theoretical Considerations and Application to Cu-Ti Alloys." MRS Proceedings 57 (1985). http://dx.doi.org/10.1557/proc-57-525.
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AbstractCu-2.9 at.% Ti single crystals were homogenized at various temperatures (780 °C ≤ TH ≤ 960°C) and quenched. Subsequent isothermal aging at 350 °C led to phase separation, the kinetics of which have been followed by employing small-angle neutron scattering (SANS). According to comple-mentary transmission electron and analytical field ion microscopy studies, the resulting transformation products of this first order phase transition are stoichiometrically ordered ellipsoidal Cu4Ti particles, the aspect ratio of which changes with aging time (t) as revealed by two-dimensional SANS-detection. In the early stages of phase separation, the decomposition kinet-ics are strongly influenced by the quenching rate via quenched-in excess vacancies. During aging the structure factor S(K,t) develops a maximum, the height (Sm) of which increases and the position (Km) of which decreases with t. Neither Sm(t) nor Km(t) follow a power law as predicted by several recent theories on spinodal decomposition. On the other hand, the time evolution of the mean Ti-rich cluster size (R), their number density (Nv), and the supersaturation (Δc) as inferred from the SANS-data and the diffuse Laue-scattering, are well predicted by a precipitation model which describes nucleation, growth and coarsening as competing processes.
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Rollet, A. L., M. Jardat, J. F. Dufrêche, P. Turq, and D. Canet. "Transport Properties in Ionic Media." MRS Proceedings 651 (2000). http://dx.doi.org/10.1557/proc-651-t9.5.1.
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AbstractTransportcoe[ ]cients in charged media exhibit strong variations, according to the conditions of displacement of the particles. Electrical transport, characterized by the simultaneous displacement of positive and negative charges in opposite directions obeys Ohm's law, but its variation with concentration (non-ideality), depends on several types of interactions, whose time of establishment varies from picosecond to nanosecond. Several diffusion processes can occur: mutual diffusion, where ions move simultaneously in the same direction, keeping local elec- troneutrality, and self diffusion where individual ionic particles move separately. The variation of diffusion coefficients with concentration dependson non-ideality factors analogous to those occuring in conductance, and their experimental evidence is facilitated b y the availability of experimental tec hniquesowing different characteristic times of observation. This phenomenon is particularly noticeable for self-diffsuion coefficients, where the dynamical processes can be observed from the picosecond range (neutron quasi-elastic scattering), to millisecond (NMR) and to hour scale (radiactive tracers). The results are especially enhanced for porous charged media like ion exchanging membranes (nafions).Those results are be explained here theoretically in the framework of contin uous solv en t model theories (brownian dynamics) and experimentally in the study of self-diffusion in nafion membranes.
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Bell, Nicole F., James B. Dent, Jayden L. Newstead, Subir Sabharwal, and Thomas J. Weiler. "Migdal effect and photon bremsstrahlung in effective field theories of dark matter direct detection and coherent elastic neutrino-nucleus scattering." Physical Review D 101, no. 1 (2020). http://dx.doi.org/10.1103/physrevd.101.015012.
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