1,012 research outputs found
Ch(k) grammars:A characterization of LL(k) languages
In this paper we introduce the class of so called Ch(k) grammars [pronounced "chain k grammars"]. This class of grammars is properly contained in the class of LR(k) grammars and it properly contains the LL(k) grammars. However, the family of Ch[k) languages coincides with the family of LL(k) languages. Nevertheless, the parsing properties of Ch(k) grammars are quite different from the parsing properties of LL(k) grammars. The class of Ch(k) grammars can be considered as a generalization of the class of simple chain grammars in the same sense as the class of LL(k) grammars is a generalization of the class of simple LL(1) grammars
Exciton spectroscopy of hexagonal boron nitride using non-resonant x-ray Raman scattering
We report non-resonant x-ray Raman scattering (XRS) measurements from
hexagonal boron nitride for transferred momentum from 2 to 9
along directions both in and out of the basal plane. A
symmetry-based argument, together with real-space full multiple scattering
calculations of the projected density of states in the spherical harmonics
basis, reveals that a strong pre-edge feature is a dominantly -type
Frenkel exciton with no other \textit{s}-, \textit{p}-, or \textit{d}-
components. This conclusion is supported by a second, independent calculation
of the \textbf{q}-dependent XRS cross-section based on the Bethe-Salpeter
equation
The Effects of Phase Separation in the Cuprate Superconductors
Phase separation has been observed by several different experiments and it is
believed to be closely related with the physics of cuprates but its exactly
role is not yet well known. We propose that the onset of pseudogap phenomenon
or the upper pseudogap temperature has its origin in a spontaneous phase
separation transition at the temperature . In order to perform
quantitative calculations, we use a Cahn-Hilliard (CH) differential equation
originally proposed to the studies of alloys and on a spinodal decomposition
mechanism. Solving numerically the CH equation it is possible to follow the
time evolution of a coarse-grained order parameter which satisfies a
Ginzburg-Landau free-energy functional commonly used to model superconductors.
In this approach, we follow the process of charge segregation into two main
equilibrium hole density branches and the energy gap normally attributed to the
upper pseudogap arises as the free-energy potential barrier between these two
equilibrium densities below . This simulation provides quantitative
results %on the hole doping and temperature %dependence of the degree of the
charge inhomogeneity in agreement with %some experiments and the simulations
reproduce the observed stripe and granular pattern of segregation. Furthermore,
with a Bogoliubov-deGennes (BdG) local superconducting critical temperature
calculation for the lower pseudogap or the onset of local superconductivity, it
yields novel interpretation of several non-conventional measurements on
cuprates.Comment: Published versio
Antibody responses to nasopharyngeal carriage of Streptococcus pneumoniae in adults: A longitudinal household study
Background. Natural immunity to Streptococcus pneumoniae is thought to be induced by exposure to S. pneumoniae or cross-reactive antigens. No longitudinal studies of carriage of and immune responses to S. pneumoniae have been conducted using sophisticated immunological laboratory techniques.Methods. We enrolled 121 families with young children into this study. Nasopharyngeal (NP) swabs were collected monthly for 10 months from all family members and were cultured in a standard fashion. Cultured S. pneumoniae isolates were serotyped. At the beginning (month 0) and end (month 10) of the study, venous blood was collected from family members 118 years old. Serotype-specific antipolysaccharide immunoglobulin G (IgG) and functional antibody and antibodies to pneumolysin, pneumococcal surface protein A (PspA), and pneumococcal surface antigen A (PsaA) were measured in paired serum samples.Results. Levels of anticapsular IgG increased significantly after carriage of serotypes 9V, 14, 18C, 19F, and 23F by an individual or family member. For serotype 14, a higher level of anticapsular IgG at the beginning of the study was associated with reduced odds of carriage (P = .0006). There was a small (similar to 20%) but significant increase in titers of antibodies to PsaA and pneumolysin but no change in titers of antibody to PspA.Conclusions. Adults respond to NP carriage by mounting anticapsular and weak antiprotein antibody responses, and naturally induced anticapsular IgG can prevent carriage
GINZBURG-LANDAU THEORY OF VORTICES IN -WAVE SUPERCONDUCTORS
Ginzburg-Landau theory is used to study the properties of single vortices and
of the Abrikosov vortex lattice in a superconductor. For a single
vortex, the -wave order parameter has the expected four-lobe structure in a
ring around the core and falls off like at large distances. The
topological structure of the -wave order parameter consists of one
counter-rotating unit vortex, centered at the core, surrounded by four
symmetrically placed positive unit vortices. The Abrikosov lattice is shown to
have a triangular structure close to and an oblique structure at lower
temperatures. Comparison is made to recent neutron scattering data.Comment: 4 pages, REVTeX, 3 figures available upon reques
Understanding the effect of cognitive/brain reserve and depression on regional atrophy in early Alzheimer’s disease
Introduction: Depression in patients with mild cognitive impairment (MCI) and dementia of the Alzheimer’s type (AD) is associated with worse prognosis. Indeed, depressed MCI patients have worse cognitive performance and greater loss of gray-matter volume in several brain areas. To date, knowledge of the factors that can mitigate this detrimental effect is still limited. The aim of the present study was to understand in what way cognitive reserve/brain reserve and depression interact and are linked to regional atrophy in early stage AD.
Methods: Depression was evaluated with the Patient Health Questionnaire-9 in 90 patients with early AD, and a cutoff of ≥ 5 was used to separate depressed (n = 44) from non-depressed (n = 46) patients. Each group was further stratified into high/low cognitive reserve/brain reserve. Cognitive reserve was calculated using years of education as proxy, while normalized parenchymal volumes were used to estimate brain reserve. Voxel-based morphometry was carried out to extract and analyze gray-matter maps. 2 × 2 ANCOVAs were run to test the effect of the reserve-by-depression interaction on gray matter. Age and hippocampal ratio were used as covariates. Composite indices of major cognitive domains were also analyzed with comparable models.
Results: No reserve-by-depression interaction was found in the analytical models of gray matter. Depression was associated with less gray matter volume in the cerebellum and parahippocampal gyrus. The brain reserve-by-depression interaction was a significant predictor of executive functioning. Among those with high brain reserve, depressed patients had poorer executive skills. No significant results were found in association with cognitive reserve.
Conclusion: These findings suggest that brain reserve may modulate the association between neurodegeneration and depression in patients with MCI and dementia of the AD type, influencing in particular executive functioning
- and -wave components induced around a vortex in -wave superconductors
Vortex structure of -wave superconductors is microscopically
analyzed in the framework of the quasi-classical Eilenberger equations. If the
pairing interaction contains an -wave (-wave) component in addition
to a -wave component, the -wave (-wave) component of
the order parameter is necessarily induced around a vortex in
-wave superconductors. The spatial distribution of the induced
-wave and -wave components is calculated. The -wave component has
opposite winding number around vortex near the -vortex core and
its amplitude has the shape of a four-lobe clover. The amplitude of
-component has the shape of an octofoil. These are consistent with
results based on the GL theory.Comment: RevTex,9 pages, 6 figures in a uuencoded fil
Ginzburg Landau theory for d-wave pairing and fourfold symmetric vortex core structure
The Ginzburg Landau theory for d_{x^2-y^2}-wave superconductors is
constructed, by starting from the Gor'kov equation with including correction
terms up to the next order of ln(T_c/T). Some of the non-local correction terms
are found to break the cylindrical symmetry and lead to the fourfold symmetric
core structure, reflecting the internal degree of freedom in the pair
potential. Using this extended Ginzburg Landau theory, we investigate the
fourfold symmetric structure of the pair potential, current and magnetic field
around an isolated single vortex, and clarify concretely how the vortex core
structure deviates from the cylindrical symmetry in the d_{x^2-y^2}-wave
superconductors.Comment: 12 pages including 8 eps figs, LaTeX with jpsj.sty & epsfi
Induction of non-d-wave order-parameter components by currents in d-wave superconductors
It is shown, within the framework of the Ginzburg-Landau theory for a
superconductor with d_{x^2-y^2} symmetry, that the passing of a supercurrent
through the sample results, in general, in the induction of order-parameter
components of distinct symmetry. The induction of s-wave and
d_{xy(x^2-y^2)-wave components are considered in detail. It is shown that in
both cases the order parameter remains gapless; however, the structure of the
lines of nodes and the lobes of the order parameter are modified in distinct
ways, and the magnitudes of these modifications differ in their dependence on
the (a-b plane) current direction. The magnitude of the induced s-wave
component is estimated using the results of the calculations of Ren et al.
[Phys. Rev. Lett. 74, 3680 (1995)], which are based on a microscopic approach.Comment: 15 pages, includes 2 figures. To appear in Phys. Rev.
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