12,964 research outputs found
Modelling and Optimising of a Light-Weight Rockfall Catch Fence System
Rockfall catch fence is a mechanical barrier system that is used at the foot of cliffs to stop and retain falling rocks from reaching nearby infrastructures. A typical system comprises of a high tensile strength wire mesh that is anchored to the ground by rigid posts and strengthened to the lateral and upslope sides by anchoring tension cables. Additional components, such as shock absorbers, might be added to improve the system capacity to dissipate energy. This multi-component system characterises by geometrical complexity and high nonlinear response to impact loads.
A light-weight catch fence system is a simple system that can be easily installed in a time efficient manner using manpower rather than heavy machinery, which makes it ideal for railways located in mountainous and difficult terrain regions where there is difficulty in accessing sites with limited workspaces and restricted installation times. However, this should be combined with a proper design to ensure that the system provides the required protection to impede falling rocks from reaching the train lines. In this paper, a parametric study based on finite element analysis is developed to optimise the design of a light-weight catch fence system that has an energy absorption capacity of up to 100 kJ
Sharp two-sided heat kernel estimates for critical Schr\"odinger operators on bounded domains
On a smooth bounded domain \Omega \subset R^N we consider the Schr\"odinger
operators -\Delta -V, with V being either the critical borderline potential
V(x)=(N-2)^2/4 |x|^{-2} or V(x)=(1/4) dist (x,\partial\Omega)^{-2}, under
Dirichlet boundary conditions. In this work we obtain sharp two-sided estimates
on the corresponding heat kernels. To this end we transform the Scr\"odinger
operators into suitable degenerate operators, for which we prove a new
parabolic Harnack inequality up to the boundary. To derive the Harnack
inequality we have established a serier of new inequalities such as improved
Hardy, logarithmic Hardy Sobolev, Hardy-Moser and weighted Poincar\'e. As a
byproduct of our technique we are able to answer positively to a conjecture of
E.B.Davies.Comment: 40 page
On the definition of a moist-air potential vorticity
A new potential vorticity is derived by using a specific entropy formulation
expressed in terms of a moist-air entropy potential temperature. The new
formulation is compared with Ertel's version and with others based on virtual
and equivalent potential temperatures. The new potential vorticity is subject
to conservative properties ensured by the Second Law applied to the moist-air
material derivatives. It is shown that the upper tropospheric and stratospheric
(dry) structures are nearly the same as those obtained with Ertel's component.
Moreover, new structures are observed in the low troposphere, with negative
values associated with moist frontal regions. The negative values are observed
in the frontal regions where slantwise convection instabilities may take place,
but they are smaller than those observed with the equivalent potential
vorticity. The main purpose of the article is to diagnose the behaviour of the
new potential vorticity from numerical output generated by the ARPEGE NWP
model, with the help of isobaric charts and vertical cross-sections. Two
inversion methods are suggested. The first method could be based on the
invertibility principle verified by the virtual potential vorticity, with a
possibility to control and modify separately potential vorticity components in
the (dry) upper and (moist) lower atmospheric levels. The other method may
consist of an inversion process directly applied to the new moist-air entropy
potential vorticity, because the negative values and the solenoidal term are
smaller than those observed with equivalent potential vorticity, as shown by
numerical evaluations.Comment: Submitted to the Q. J. R. Meteorol. Soc. in August 2012. Accepted in
April 2013. Early view on the QJRMS site
http://onlinelibrary.wiley.com/doi/10.1002/qj.2182/abstract. 24 pages, 10
color figures. V2: add the arXiv links of Marquet (2011), Geleyn and Marquet
(2012) and Marquet and Geleyn (2013
Construction of a Multiplex Promoter Reporter Platform to Monitor Staphylococcus aureus Virulence Gene Expression and the Identification of Usnic Acid as a Potent Suppressor of psm Gene Expression
As antibiotic resistance becomes phenomenal, alternative therapeutic strategies for bacterial infections such as anti-virulence treatments have been advocated. We have constructed a total of 20 gfp-luxABCDE dual-reporter plasmids with selected promoters from S. aureus virulence-associated genes. The plasmids were introduced into various S. aureus strains to establish a gfp-lux based multiplex promoter reporter platform for monitoring S. aureus virulence gene expressions in real time to identify factors or compounds that may perturb virulence of S. aureus. The gene expression profiles monitored by luminescence correlated well with qRT-PCR results and extrinsic factors including carbon dioxide and some antibiotics were shown to suppress or induce the expression of virulence factors in this platform. Using this platform, sub-inhibitory ampicillin was shown to be a potent inducer for the expression of many virulence factors in S. aureus. Bacterial adherence and invasion assays using mammalian cells were employed to measure S. aureus virulence induced by ampicillin. The platform was used for screening of natural extracts that perturb the virulence of S. aureus and usnic acid was identified to be a potent repressor for the expression of psm.published_or_final_versio
Causality Problem in a Holographic Dark Energy Model
In the model of holographic dark energy, there is a notorious problem of
circular reasoning between the introduction of future event horizon and the
accelerating expansion of the universe. We examine the problem after dividing
into two parts, the causality problem of the equation of motion and the
circular logic on the use of the future event horizon. We specify and isolate
the root of the problem from causal equation of motion as a boundary condition,
which can be determined from the initial data of the universe. We show that
there is no violation of causality if it is defined appropriately and the
circular logic problem can be reduced to an initial value problem.Comment: 5 page
Transverse Momentum Distribution Through Soft-Gluon Resummation in Effective Field Theory
We study resummation of transverse-momentum-related large logarithms
generated from soft-gluon radiations in soft-collinear effective field theory.
The anomalous dimensions of the effective quark and gluon currents, an
important ingredient for the resummation, are calculated to two-loop order. the
result at next-to-leading-log reproduces that obtained using the standard
method for deep-inelastic scattering, Drell-Yan process, and Higgs production
through gluon-gluon fusion. We comment on the extension of the calculation to
next-to-next-to-leading logarithms.Comment: 13 pages, one figur
On entropic gravity: the entropy postulate, entropy content of screens and relation to quantum mechanics
We consider the controversial hypothesis that gravity is an entropic force
that has its origin in the thermodynamics of holographic screens. Several key
aspects of entropic gravity are discussed. In particular, we revisit and
elaborate on our criticism of the recent claim that entropic gravity fails to
explain observations involving gravitationally-bound quantum states of neutrons
in the GRANIT experiment and gravitationally induced quantum interference. We
argue that the analysis leading to this claim is troubled by a
misinterpretation concerning the relation between the microstates of a
holographic screen and the state of a particle in the emergent space,
engendering inconsistencies. A point of view that could resolve the
inconsistencies is presented. We expound the general idea of the aforementioned
critical analysis of entropic gravity in such a consistent setting. This
enables us to clarify the problem and to identify a premise whose validity will
decide the faith of the criticism against entropic gravity. It is argued that
in order to reach a sensible conclusion we need more detailed knowledge on
entropic gravity. These arguments are relevant to any theory of emergent space,
where the entropy of the microscopic system depends on the distribution of
matter in the emergent space.Comment: 15 pages; v2: presentation and arguments improved, particularly in
section 5; accepted to Phys. Lett.
The evolution of the binary population in globular clusters: a full analytical computation
I present a simplified analytical model that simulates the evolution of the
binary population in a dynamically evolving globular cluster. A number of
simulations have been run spanning a wide range in initial cluster and
environmental conditions by taking into account the main mechanisms of
formation and destruction of binary systems. Following this approach, I
investigate the evolution of the fraction, the radial distribution, the
distribution of mass ratios and periods of the binary population. According to
these simulations, the fraction of surviving binaries appears to be dominated
by the processes of binary ionization and evaporation. In particular, the
frequency of binary systems changes by a factor 1-5 depending on the initial
conditions and on the assumed initial distribution of periods. The comparison
with the existing estimates of binary fractions in Galactic globular clusters
suggests that significant variations in the initial binary content could exist
among the analysed globular cluster. This model has been also used to explain
the observed discrepancy found between the most recent N-body and Monte Carlo
simulations in the literature.Comment: 18 pages, 12 figures, accepted for publication by MNRA
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