234 research outputs found
Fracture model with variable range of interaction
We introduce a fiber bundle model where the interaction among fibers is
modeled by an adjustable stress-transfer function which can interpolate between
the two limiting cases of load redistribution, the global and the local load
sharing schemes. By varying the range of interaction several features of the
model are numerically studied and a crossover from mean field to short range
behavior is obtained. The properties of the two regimes and the emergence of
the crossover in between are explored by numerically studying the dependence of
the ultimate strength of the material on the system size, the distribution of
avalanches of breakings, and of the cluster sizes of broken fibers. Finally, we
analyze the moments of the cluster size distributions to accurately determine
the value at which the crossover is observed.Comment: 8 pages, 8 figures. Two columns revtex format. Final version to be
published in Phys. Rev.
Time evolution of damage under variable ranges of load transfer
We study the time evolution of damage in a fiber bundle model in which the
range of interaction of fibers varies through an adjustable stress transfer
function recently introduced. We find that the lifetime of the material
exhibits a crossover from mean field to short range behavior as in the static
case. Numerical calculations showed that the value at which the transition
takes place depends on the system's disorder. Finally, we have performed a
microscopic analysis of the failure process. Our results confirm that the
growth dynamics of the largest crack is radically different in the two limiting
regimes of load transfer during the first stages of breaking.Comment: 8 pages, 7 figures, revtex4 styl
Faking like a woman? Towards an interpretative theorization of sexual pleasure.
This article explores the possibility of developing a feminist approach to gendered and sexual embodiment which is rooted in the pragmatist/interactionist tradition derived from G.H. Mead, but which in turn develops this perspective by inflecting it through more recent feminist thinking. In so doing we seek to rebalance some of the rather abstract work on gender and embodiment by focusing on an instance of 'heterosexual' everyday/night life - the production of the female orgasm. Through engaging with feminist and interactionist work, we develop an approach to embodied sexual pleasure that emphasizes the sociality of sexual practices and of reflexive sexual selves. We argue that sexual practices and experiences must be understood in social context, taking account of the situatedness of sex as well as wider socio-cultural processes the production of sexual desire and sexual pleasure (or their non-production) always entails interpretive, interactional processes
Roles of Fast-Cyclotron and Alfven-Cyclotron Waves for the Multi-Ion Solar Wind
Using linear Vlasov theory of plasma waves and quasi-linear theory of
resonant wave-particle interaction, the dispersion relations and the
electromagnetic field fluctuations of fast and Alfven waves are studied for a
low-beta multi-ion plasma in the inner corona. Their probable roles in heating
and accelerating the solar wind via Landau and cyclotron resonances are
quantified. We assume that (1) low-frequency Alfven and fast waves have the
same spectral shape and the same amplitude of power spectral density; (2) these
waves eventually reach ion cyclotron frequencies due to a turbulence cascade;
(3) kinetic wave-particle interaction powers the solar wind. The existence of
alpha particles in a dominant proton/electron plasma can trigger linear mode
conversion between oblique fast-whistler and hybrid alpha-proton cyclotron
waves. The fast-cyclotron waves undergo both alpha and proton cyclotron
resonances. The alpha cyclotron resonance in fast-cyclotron waves is much
stronger than that in Alfven-cyclotron waves. For alpha cyclotron resonance, an
oblique fast-cyclotron wave has a larger left-handed electric field
fluctuation, a smaller wave number, a larger local wave amplitude, and a
greater energization capability than a corresponding Alfven-cyclotron wave at
the same wave propagation angle \theta, particularly at < \theta <
. When Alfven-cyclotron or fast-cyclotron waves are present, alpha
particles are the chief energy recipient. The transition of preferential
energization from alpha particles to protons may be self-modulated by
differential speed and temperature anisotropy of alpha particles via the
self-consistently evolving wave-particle interaction. Therefore, fast-cyclotron
waves as a result of linear mode coupling is a potentially important mechanism
for preferential energization of minor ions in the main acceleration region of
the solar wind.Comment: 29 pages, 10 figures, 3 tables. Accepted for publication in Solar
Physic
An all-solid-state laser source at 671 nm for cold atom experiments with lithium
We present an all solid-state narrow line-width laser source emitting
output power at delivered in a
diffraction-limited beam. The \linebreak source is based on a
fre-quency-doubled diode-end-linebreak pumped ring laser operating on the
transition in Nd:YVO. By using
periodically-poled po-tassium titanyl phosphate (ppKTP) in an external build-up
cavity, doubling efficiencies of up to 86% are obtained. Tunability of the
source over is accomplished. We demonstrate the suitability of
this robust frequency-stabilized light source for laser cooling of lithium
atoms. Finally a simplified design based on intra-cavity doubling is described
and first results are presented
The Milky Way Bulge: Observed properties and a comparison to external galaxies
The Milky Way bulge offers a unique opportunity to investigate in detail the
role that different processes such as dynamical instabilities, hierarchical
merging, and dissipational collapse may have played in the history of the
Galaxy formation and evolution based on its resolved stellar population
properties. Large observation programmes and surveys of the bulge are providing
for the first time a look into the global view of the Milky Way bulge that can
be compared with the bulges of other galaxies, and be used as a template for
detailed comparison with models. The Milky Way has been shown to have a
box/peanut (B/P) bulge and recent evidence seems to suggest the presence of an
additional spheroidal component. In this review we summarise the global
chemical abundances, kinematics and structural properties that allow us to
disentangle these multiple components and provide constraints to understand
their origin. The investigation of both detailed and global properties of the
bulge now provide us with the opportunity to characterise the bulge as observed
in models, and to place the mixed component bulge scenario in the general
context of external galaxies. When writing this review, we considered the
perspectives of researchers working with the Milky Way and researchers working
with external galaxies. It is an attempt to approach both communities for a
fruitful exchange of ideas.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing. 36 pages, 10 figure
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Structural characterisation of neutrophil glycans by ultra sensitive mass spectrometric glycomics methodology
Neutrophils are the most abundant white blood cells in humans and play a vital role in several aspects of the immune response. Numerous reports have implicated neutrophil glycosylation as an important factor in mediating these interactions. We report here the application of high sensitivity glycomics methodologies, including matrix assisted laser desorption ionisation (MALDI-TOF) and MALDI-TOF/TOF analyses, to the structural analysis of N- and O-linked carbohydrates released from two samples of neutrophils, prepared by two separate and geographically remote laboratories. The data produced demonstrates that the cells display a diverse range of sialylated and fucosylated complex glycans, with a high level of similarity between the two preparations
ReïŹning and regaining skills in ïŹxation/diversiïŹcation stage performers: The Five-A Model
Technical change is one of many factors underpinning success in elite, fixation/diversification stage performers. Surprisingly, however, there is a dearth of research pertaining to this process or the most efficacious methods used to bring about such a change. In this paper we highlight the emergent processes, yet also the lack in mechanistic comprehension surrounding technical change, addressing issues within the motor control, sport psychology, coaching and choking literature. More importantly, we seek an understanding of how these changes can be made more secure to competitive pressure, and how this can be embedded within the process of technical change. Following this review, we propose The Five-A Model based on successful coaching techniques, psychosocial concomitants, the avoidance of choking and principles of effective behaviour change. Specific mechanisms for each stage are discussed, with a focus on the use of holistic rhythm-based cues as a possible way of internalising changes. Finally, we suggest the need for further research to examine these five stages, to aid a more comprehensive construction of the content and delivery of such a programme within the applied setting
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