6,392 research outputs found
Numerical test of the damping time of layer-by-layer growth on stochastic models
We perform Monte Carlo simulations on stochastic models such as the
Wolf-Villain (WV) model and the Family model in a modified version to measure
mean separation between islands in submonolayer regime and damping time
of layer-by-layer growth oscillations on one dimension. The
stochastic models are modified, allowing diffusion within interval upon
deposited. It is found numerically that the mean separation and the damping
time depend on the diffusion interval , leading to that the damping time is
related to the mean separation as for the WV model
and for the Family model. The numerical results are in
excellent agreement with recent theoretical predictions.Comment: 4 pages, source LaTeX file and 5 PS figure
Gravitational Waves: Just Plane Symmetry
We present some remarkable properties of the symmetry group for gravitational
plane waves. Our main observation is that metrics with plane wave symmetry
satisfy every system of generally covariant vacuum field equations except the
Einstein equations. The proof uses the homothety admitted by metrics with plane
wave symmetry and the scaling behavior of generally covariant field equations.
We also discuss a mini-superspace description of spacetimes with plane wave
symmetry.Comment: 10 pages, TeX, uses IOP style file
The shape and erosion of pebbles
The shapes of flat pebbles may be characterized in terms of the statistical
distribution of curvatures measured along their contours. We illustrate this
new method for clay pebbles eroded in a controlled laboratory apparatus, and
also for naturally-occurring rip-up clasts formed and eroded in the Mont
St.-Michel bay. We find that the curvature distribution allows finer
discrimination than traditional measures of aspect ratios. Furthermore, it
connects to the microscopic action of erosion processes that are typically
faster at protruding regions of high curvature. We discuss in detail how the
curvature may be reliable deduced from digital photographs.Comment: 10 pages, 11 figure
Clinical and imaging considerations in primary immunodeficiency disorders: an update
Primary immunodeficiencies are a group of genetically determined disorders with diverse presentations. The purpose of this review is to provide a practical and brief description of a select number of these diseases and to discuss the important role the radiologist can have in making an early diagnosis and in detecting and following disease complications. The role of diagnostic imaging and informed performance and interpretation are vital in the diagnosis, surveillance and management of all primary immunodeficiency disorders
Unrestricted CTL recognition of HFE, an empty-peptide-groove MHC class I molecule controlling iron metabolism highlights its potential role as a major histocompatibility antigen in unrelated bone marrow tranplantation
Bungeâs Mathematical Structuralism Is Not a Fiction
In this paper, I explore Bungeâs fictionism in philosophy of mathematics. After an overview of Bungeâs views, in particular his mathematical structuralism, I argue that the comparison between mathematical objects and fictions ultimately fails. I then sketch a different ontology for mathematics, based on Thomassonâs metaphysical work. I conclude that mathematics deserves its own ontology, and that, in the end, much work remains to be done to clarify the various forms of dependence that are involved in mathematical knowledge, in particular its dependence on mental/brain states and material objects
Ultrahigh Vacuum Chamber for Synchrotron X-ray Diffraction from Films Adsorbed on Single-crystal Surfaces
An ultrahigh vacuum chamber has been developed for structural analysis of adsorbed films and singleâcrystal surfaces using synchrotron xâray diffraction. It is particularly well suited for investigations of physisorbed and other weakly bound films. The chamber is small enough to transport and mount directly on a standard fourâaxis diffractometer and can also be used independently of the xâray diffractometer. A lowâcurrent, pulseâcounting, lowâenergy electron diffraction/Auger spectroscopy system with a positionâsensitive detector enables in situ characterization of the film and substrate while the sample is located at the xâray scattering position. A closedâcycle He refrigerator and electron bombardment heater provide controlled substrate temperatures from 30 to 1300 K. The chamber is also equipped with an ion sputter gun, a quadrupole mass spectrometer, and a gas handling system. Details of the design and operation of the instrument are described. To demonstrate the performance of the instrument, we present some preliminary results of a study of Xe physisorbed on the Ag(111) surface
Rigid Singularity Theorem in Globally Hyperbolic Spacetimes
We show the rigid singularity theorem, that is, a globally hyperbolic
spacetime satisfying the strong energy condition and containing past trapped
sets, either is timelike geodesically incomplete or splits isometrically as
space time. This result is related to Yau's Lorentzian splitting
conjecture.Comment: 3 pages, uses revtex.sty, to appear in Physical Review
Molecular Dynamics Simulation of Semiflexible Polyampholyte Brushes - The Effect of Charged Monomers Sequence
Planar brushes formed by end-grafted semiflexible polyampholyte chains, each
chain containing equal number of positively and negatively charged monomers is
studied using molecular dynamics simulations. Keeping the length of the chains
fixed, dependence of the average brush thickness and equilibrium statistics of
the brush conformations on the grafting density and the salt concentration are
obtained with various sequences of charged monomers. When similarly charged
monomers of the chains are arranged in longer blocks, the average brush
thickness is smaller and dependence of brush properties on the grafting density
and the salt concentration is stronger. With such long blocks of similarly
charged monomers, the anchored chains bond to each other in the vicinity of the
grafting surface at low grafting densities and buckle toward the grafting
surface at high grafting densities.Comment: 8 pages,7 figure
Demanding stories: television coverage of sustainability, climate change and material demand
This paper explores the past, present and future role of broadcasting, above all via the medium of television, in shaping how societies talk, think about and act on climate change and sustainability issues. The paper explores these broad themes via a focus on the important but relatively neglected issue of material demand and opportunities for its reduction. It takes the outputs and decision-making of one of the worldâs most influential broadcasters, the BBC, as its primary focus. The paper considers these themes in terms of stories, touching on some of the broader societal frames of understanding into which they can be grouped. Media decision-makers and producers from a range of genres frequently return to the centrality of âstoryâ in the development, commissioning and production of an idea. With reference to specific examples of programming, and drawing on interviews with media practitioners, the paper considers the challenges of generating broadcast stories that can inspire engagement in issues around climate change, and specifically material demand. The concluding section proposes actions and approaches that might help to establish material demand reduction as a prominent way of thinking about climate change and environmental issues more widely.
This article is part of the themed issue âMaterial demand reductionâ
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