47,660 research outputs found
Spin-resolved optical conductivity of two-dimensional group-VIB transition-metal dichalcogenides
We present an ab-initio study of the spin-resolved optical conductivity of
two-dimensional (2D) group-VIB transition-metal dichalcogenides (TMDs). We
carry out fully-relativistic density-functional-theory calculations combined
with maximally localized Wannier functions to obtain band manifolds at
extremely high resolutions and focus on the photo-response of 2D TMDs to
circularly-polarized light in a wide frequency range. We present extensive
numerical results for monolayer TMDs involving molybdenum and tungsten combined
with sulphur and selenium. Our numerical approach allows us to locate with a
high degree of accuracy the positions of the points in the Brillouin zone that
are responsible for van Hove singularities in the optical response.
Surprisingly, some of the saddle points do not occur exactly along
high-symmetry directions in the Brillouin zone, although they happen to be in
their close proximity.Comment: 9 pages, 5 figure
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Prostate Cancer Care Before and After Medicare Eligibility.
Prior studies suggest Medicare eligibility confers significant and substantial reductions in mortality and beneficial increases in health service utilization. We compared 13,882 patients diagnosed with prostate cancer at ages 63 to 64 years with 14,774 patients diagnosed at ages 65 to 66 (controls) in 2004 to 2007. Compared with controls, patients diagnosed with prostate cancer before Medicare eligibility had no statistically significant or meaningful differences in cancer stage, time to treatment, or type of treatment
Shilnikov problem in Filippov dynamical systems
In this paper we introduce the concept of sliding Shilnikov orbits for D
Filippov systems. In short, such an orbit is a piecewise smooth closed curve,
composed by Filippov trajectories, which slides on the switching surface and
connects a Filippov equilibrium to itself, namely a pseudo saddle-focus. A
version of the Shilnikov's Theorem is provided for such systems. Particularly,
we show that sliding Shilnikov orbits occur in generic one-parameter families
of Filippov systems, and that arbitrarily close to a sliding Shilnikov orbit
there exist countably infinitely many sliding periodic orbits. Here, no
additional Shilnikov-like assumption is needed in order to get this last
result. In addition, we show the existence of sliding Shilnikov orbits in
discontinuous piecewise linear differential systems. As far as we know, the
examples of Fillippov systems provided in this paper are the first exhibiting
such a sliding phenomenon
Evidences Behind Skype Outage
Skype is one of the most successful VoIP application in the current Internet spectrum. One of the most peculiar characteristics of Skype is that it relies on a P2P infrastructure for the exchange of signaling information amongst active peers. During August 2007, an unexpected outage hit the Skype overlay, yielding to a service blackout that lasted for more than two days: this paper aims at throwing light to this event. Leveraging on the use of an accurate Skype classification engine, we carry on an experimental study of Skype signaling during the outage. In particular, we focus on the signaling traffic before, during and after the outage, in the attempt to quantify interesting properties of the event. While it is very difficult to gather clear insights concerning the root causes of the breakdown itself, the collected measurement allow nevertheless to quantify several interesting aspects of the outage: for instance, measurements show that the outage caused, on average, a 3-fold increase of signaling traffic and a 10-fold increase of number of contacted peers, topping to more than 11 million connections for the most active node in our network - which immediately gives the feeling of the extent of the phenomeno
Rigorous derivation of nonlinear scalar conservation laws from follow-the-leader type models via many particle limit
We prove that the unique entropy solution to a scalar nonlinear conservation
law with strictly monotone velocity and nonnegative initial condition can be
rigorously obtained as the large particle limit of a microscopic
follow-the-leader type model, which is interpreted as the discrete Lagrangian
approximation of the nonlinear scalar conservation law. More precisely, we
prove that the empirical measure (respectively the discretised density)
obtained from the follow-the-leader system converges in the 1-Wasserstein
topology (respectively in ) to the unique Kruzkov entropy solution
of the conservation law. The initial data are taken in ,
nonnegative, and with compact support, hence we are able to handle densities
with vacuum. Our result holds for a reasonably general class of velocity maps
(including all the relevant examples in the applications, e.g. in the
Lighthill-Whitham-Richards model for traffic flow) with possible degenerate
slope near the vacuum state. The proof of the result is based on discrete BV
estimates and on a discrete version of the one-sided Oleinik-type condition. In
particular, we prove that the regularizing effect
for nonlinear scalar conservation laws is intrinsic of the discrete model
The Explosive Yields Produced by the First Generation of Core Collapse Supernovae and the Chemical Composition of Extremely Metal Poor Stars
We present a detailed comparison between an extended set of elemental
abundances observed in some of the most metal poor stars presently known and
the ejecta produced by a generation of primordial core collapse supernovae. We
used five stars which form our initial database and define a "template" ultra
metal poor star which is then compared to the theoretical predictions. Our main
findings are as follows: a) the fit to [Si/Mg] and [Ca/Mg] of these very metal
poor stars seems to favor the presence of a rather large C abundance at the end
of the central He burning; in a classical scenario in which the border of the
convective core is strictly determined by the Schwarzschild criterion, such a
large C abundance would imply a rather low C12(alpha,gamma)O16 reaction rate;
b) a low C abundance left by the central He burning would imply a low [Al/Mg]
(<-1.2 dex) independently on the initial mass of the exploding star while a
rather large C abundance would produce such a low [Al/Mg] only for the most
massive stellar model; c) at variance with current beliefs that it is difficult
to interpret the observed overabundance of [Co/Fe], we find that a mildly large
C abundance in the He exhausted core (well within the present range of
uncertainty) easily and naturally allows a very good fit to [Co/Fe]; d) our
yields allow a reasonable fit to 8 out of the 11 available elemental
abundances; e) within the present grid of models it is not possible to find a
good match of the remaining three elements, Ti, Cr and Ni (even for an
arbitrary choice of the mass cut); f) the adoption of other yields available in
the literature does not improve the fit; g) since no mass in our grid provides
a satisfactory fit to these three elements, even an arbitrary choice of the
initial mass function would not improve their fit.Comment: 30 pages, 8 figures, 8 tables. Accepted for publication on Ap
Improving building energy efficiency: case study
The main purpose of this study was to conduct a study for improving energy efficiency of an important building in Rome, the Headquarters of the Italian State Monopoly. The study was conducted by comparing conventional analysis tools with innovative ones, in order to evaluate the possible solutions, both structural and plant, aimed at the use of renewable sources and at energy saving. After making a thermo graphic survey, the first and useful step for a good energy audit, conduct building energy was simulated, at first in steady state by the use of a software widely used at the professional level, then in transient state by the use of TRNSYS, a finite difference method software which is able to simulate more accurately conduct building energy. The next step was to propose possible redevelopment of a structural and energy plant that promotes the building energy rating higher, finding the right balance between the energetic and economic aspect. Among the interventions plant, two possible workarounds have been proposed and designed in detail:
- installation of a photovoltaic system;
- installation of a solar cooling system.
Both solutions lead to a reduction of electricity consumption with a significant impact in economic and environmental term
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Lung Cancer Care Before and After Medicare Eligibility.
Uninsured and underinsured near-elderly may not have timely investigation, diagnosis, or care of cancer. Prior studies suggest Medicare eligibility confers significant and substantial reductions in mortality and increases in health service utilization. We compared 2245 patients diagnosed with lung cancer at ages 64.5 to 65 years and 2512 patients aged 65 to 65.5 years, with 2492 patients aged 65.5 to 66 years (controls) in 2000 to 2005. Compared with controls, patients diagnosed with lung cancer before Medicare eligibility had no statistically significant differences in cancer stage, time to treatment, type of treatment, and survival. Study power was sufficient to exclude mortality reductions and health service utilization changes of the magnitude found in prior work, suggesting that typically, appropriate lung cancer care may be sought and delivered regardless of insurance status
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