Search results for "Neutron"
showing 10 items of 2330 documents
MATHEMATICAL MODEL FOR GLITCHES IN PULSARS
2010
Thermodynamic and Neutron-Diffraction Studies of H2 and D2 Multilayers Physisorbed on Graphite
1991
The evolution of physisorbed films from two-dimensional (2D) to bulk behavior is a topic of high current interest.1 In this context the behavior of the quantum systems H2, HD and D2 is of particular relevance because of the following reasons: 1. Due to the strong influence of the quantum zero-point energy the hydrogen isotopes are highly compressible. This leads to strongly compressed monolayers2,3 before further layer condensation occurs. This property makes these systems significant for the exploration of conditions of multilayer growth. It is generally believed,1,4–6 that the incompatibility between the adsorbate and bulk lattice structures gives rise to lateral strains between the overl…
Interpretation of the Solar 48Ca/46Ca Abundance Ratio and the Correlated Ca-Ti-Cr Isotopic Anomalies in Inclusions of the Allende Meteorite
1986
In the past, astrophysical models encountered severe difficulties in explaining the solar 46,48Ca abundances or the correlated Ca-Ti-Cr isotopic anomalies observed in inclusions of the Allende meteorite [1–3]. Among the various attempts. SANDLER et al. [4] suggested the production of neutron-rich stable Ca-Ti-Cr isotopes in a high neutron density environment of ~107 mol/cm3 with a neutron-exposure time of 10 s. Assuming the initial abundances to be solar and applying Hauser-Feshbach neutron-capture crosa sections, the above authors have calculated a 48Ca/46Ca abundance ratio which is only a factor of 2.6 smaller than the observed solar value of 56. However, the predicted isotopic anomalies …
Ab initiothermodynamics ofBacSr(1−c)TiO3solid solutions
2005
Based on ab initio calculations for a number of the ${\mathrm{Ba}}_{\mathrm{c}}{\mathrm{Sr}}_{(1\ensuremath{-}\mathrm{c})}\mathrm{Ti}{\mathrm{O}}_{3}$ (BST) superlattices, we developed a thermodynamic approach to these solid solutions. In particular, we calculate the BST phase diagram and show that at relatively low temperatures (below $400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $c=0.5$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $c=0.1$) the spinodal decomposition of the solid solution occurs. As a result, we predict for small Ba concentrations formation of $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_{3}$ nanoregions in a predominantly $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ matrix and …
Measuring Multiple Residual-Stress Components using the Contour Method and Multiple Cuts
2009
The conventional contour method determines one component of residual stress over the cross section of a part. The part is cut into two, the contour (topographic shape) of the exposed surface is measured, and Bueckner’s superposition principle is analytically applied to calculate stresses. In this paper, the contour method is extended to the measurement of multiple residual-stress components by making multiple cuts with subsequent applications of superposition. The theory and limitations are described. The theory is experimentally tested on a 316L stainless steel disk with residual stresses induced by plastically indenting the central portion of the disk. The multiple-cut contour method resu…
PHASE TRANSITIONS AT INTERFACES
1989
The interface between two phases may exhibit significant structural changes if one of them comes close to a phase transition in its bulk. Surface critical phenomena, critical adsorption, and wetting phenomena, like e.g. surface melting or surface induced disorder, can occur. The grazing incidence of X rays and neutrons is particularly well suited in order to obtain precise informations about these kind of critical phenomena which link the space dimensions two and three.
Constraining the surface properties of effective Skyrme interactions
2016
The purpose of this study is threefold: first, to identify a scheme for the determination of the surface energy coefficient a_surf that offers the best compromise between robustness, precision, and numerical efficiency; second, to analyze the correlation between values for a_surf and the characteristic energies of the fission barrier of Pu240; and third, to lay out a procedure how the deformation properties of the Skyrme energy density functional (EDF) can be constrained during the parameter fit. There are several frequently used possibilities to define and calculate the surface energy coefficient a_surf of effective interactions. The most direct access is provided by the model system of se…
A new liquid surface neutron reflectometer and its application to the study of DPPC in a monolayer at the air/water interface
1991
A constant wavelength neutron reflectometer is described. Using this reflectometer, the neutron reflectivities from phosphatidylcholine monolayers in the highly condensed LC phase on ultra pure H2O and D2O have been measured on a Wilhelmy film balance. The neutron reflectivities have been carefully compared with those obtained by the X-ray method applied to the same monolayer under similar conditions. A new approach to analyzing a combined set of data composed of X-ray and neutron reflectivities has been used. From the analysis it is concluded that despite their limited qz range neutron reflectivities are as essential as X-ray reflectivities for the unique determination of the monolayer str…
Optical counterpart to Swift J0243.6+6124
2020
Context. Swift J0243.6+6124 is a unique system. It is the first and only ultra-luminous X-ray source in our Galaxy. It is the first and only high-mass Be X-ray pulsar showing radio jet emission. It was discovered during a giant X-ray outburst in October 2017. While there are numerous studies in the X-ray band, very little is known about the optical counterpart. Aims. Our aim is to characterize the variability timescales in the optical and infrared bands in order to understand the nature of this intriguing system. Methods. We performed optical spectroscopic observations to determine the spectral type. Long-term photometric light curves together with the equivalent width of the Hα line were u…
A measurement of the antineutrino asymmetry B in free neutron decay
2005
Abstract We have measured the antineutrino asymmetry B in neutron beta decay, i.e., the correlation of the neutron spin and the antineutrino momentum, with a new method. Our result is B = 0.967 ± 0.006 stat ± 0.010 syst = 0.967 ± 0.012 . Statistical and systematic uncertainty can be considerably reduced in future experiments.