23,093 research outputs found
Supersymmetric Reflection Matrices
We briefly review the general structure of integrable particle theories in
1+1 dimensions having N=1 supersymmetry. Examples are specific perturbed
superconformal field theories (of Yang-Lee type) and the N=1 supersymmetric
sine-Gordon theory. We comment on the modifications that are required when the
N=1 supersymmetry algebra contains non-trivial topological charges.Comment: 7 pages, Revtex, 2 figures, talk given at the International Seminar
on Supersymmetry and Quantum Field Theory, dedicated to the memory of
D.V.Volkov, Kharkov (Ukraine), January 5-7, 199
Charge carrier induced lattice strain and stress effects on As activation in Si
We studied lattice expansion coefficient due to As using density functional
theory with particular attention to separating the impact of electrons and
ions. Based on As deactivation mechanism under equilibrium conditions, the
effect of stress on As activation is predicted. We find that biaxial stress
results in minimal impact on As activation, which is consistent with
experimental observations by Sugii et al. [J. Appl. Phys. 96, 261 (2004)] and
Bennett et al.[J. Vac. Sci. Tech. B 26, 391 (2008)]
Characterization of Si/Si_(1-y)C_y superlattices grown by surfactant assisted molecular beam epitaxy
Si/Si_(0.97)C_(0.03) superlattices grown on Si(001) substrates by Sb surfactant assisted molecular beam epitaxy are characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy, transmission electron microscopy (TEM), and high resolution x‐ray diffraction. The RHEED shows that, in the absence of Sb, the growth front roughens during Si_(0.97)C_(0.03) growth and smooths during subsequent Si growth. In contrast, when Sb is present, the growth front remains smooth throughout the growth. This observation is confirmed by cross‐sectional TEM, which reveals that for samples grown without the use of Sb, the Si/Si_(0.97)C_(0.03) interfaces (Si_(0.97)C_(0.03) on Si) are much more abrupt than the Si_(0.97)C_(0.03)/Si interfaces. In the case of Sb assisted growth, there is no observable difference in abruptness between the two types of interfaces. Atomic force microscopy micrographs of the Si_(0.97)C_(0.03) surface reveal features that could be the source of the roughness observed by RHEED and TEM
Sb-surfactant-mediated growth of Si/Si1–yCy superlattices by molecular-beam epitaxy
Si/Si0.97C0.03 superlattices were grown on Si(001) substrates by molecular beam epitaxy (MBE) to study the use of Sb as a surfactant during Si1–yCy growth. In situ reflection high energy electron diffraction (RHEED) shows that while carbon easily disrupts the two-dimensional growth of homoepitaxial Si, such disruption is suppressed for layers grown on Sb-terminated Si(001) surfaces. Cross-sectional transmission electron microscopy (TEM) reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03 interfaces (Si0.97C0.03 on Si) were much more abrupt than Si0.97C0.03/Si interfaces. In the case of Sb-mediated growth, differences in abruptness between the two types of interfaces were not readily observable
Atomic scale lattice distortions and domain wall profiles
We present an atomic scale theory of lattice distortions using strain related
variables and their constraint equations. Our approach connects constrained
{\it atomic length} scale variations to {\it continuum} elasticity and
describes elasticity at several length scales. We apply the approach to a
two-dimensional square lattice with a monatomic basis, and find the elastic
deformations and hierarchical atomic relaxations in the vicinity of a domain
wall between two different homogeneous strain states. We clarify the
microscopic origin of gradient terms, some of which are included
phenomenologically in Ginzburg-Landau theory, by showing that they are
anisotropic.Comment: 6 figure
Nonlinear Bias of Cosmological Halo Formation in the Early Universe
We present estimates of the nonlinear bias of cosmological halo formation,
spanning a wide range in the halo mass from to , based upon both a suite of high-resolution cosmological
N-body simulations and theoretical predictions. The halo bias is expressed in
terms of the mean bias and stochasticity as a function of local overdensity
(), under different filtering scales, which is realized as the density
of individual cells in uniform grids. The sampled overdensities span a range
wide enough to provide the fully nonlinear bias effect on the formation of
haloes. A strong correlation between and halo population overdensity
is found, along with sizable stochasticity. We find that the
empirical mean halo bias matches, with good accuracy, the prediction by the
peak-background split method based on the excursion set formalism, as long as
the empirical, globally-averaged halo mass function is used. Consequently, this
bias formalism is insensitive to uncertainties caused by varying halo
identification schemes, and can be applied generically. We also find that the
probability distribution function of biased halo numbers has wider distribution
than the pure Poisson shot noise, which is attributed to the sub-cell scale
halo correlation. We explicitly calculate this correlation function and show
that both overdense and underdense regions have positive correlation, leading
to stochasticity larger than the Poisson shot noise in the range of haloes and
halo-collapse epochs we study.Comment: 18 pages, 8 figures, in press for publication in MNRAS; supplementary
material (additional 16 figures) separately supplied (supplement.pdf) as a
part of source file
Implications of WMAP 3 Year Data for the Sources of Reionization
New results on the anisotropy of the cosmic microwave background (CMB) and
its polarization based on the first 3 years of data from the Wilkinson
Microwave Anisotropy Probe (WMAP) have revised the electron scattering optical
depth downward from tau_es=0.17+0.08-0.07 to tau_es=0.09+/-0.03. This implies a
shift of the effective reionization redshift from z_r~17 to z_r~11. Previous
attempts to explain the high redshift of reionization inferred from the WMAP 1
year data have led to widespread speculation that the sources of reionization
must have been much more efficient than those associated with the star
formation observed at low redshift. This is consistent, for example, with the
suggestion that early star formation involved massive, Population III stars
that early on produced most of the ionizing radiation escaping from halos. It
is therefore tempting to interpret the new WMAP results as implying that we can
now relax those previous high demands on the efficiency of the sources of
reionization and perhaps even turn the argument around as evidence against such
high efficiency. We show that this is not the case, however. The new WMAP
results also find that the primordial density fluctuation power spectrum has a
lower amplitude, sigma_8, and departs substantially from the scale-invariant
spectrum. We show that these effects combine to cancel the impact of the later
reionization implied by the new value of tau_es on the required ionizing
efficiency per collapsed baryon. The delay of reionization is surprisingly well
matched by a comparable delay (by a factor of ~1.4 in scale factor) in the
formation of the halos responsible for reionization.Comment: 4 pages, 3 figures, Published in ApJ Letters, revised to match
published versio
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