19,324 research outputs found
Introducing the Spatial Conflict Dynamics indicator of political violence
Modern armed conflicts have a tendency to cluster together and spread
geographically. However, the geography of most conflicts remains under-studied.
To fill this gap, this article presents a new indicator that measures two key
geographical properties of subnational political violence: the conflict
intensity within a region on the one hand, and the spatial distribution of
conflict within a region on the other. We demonstrate the indicator in North
and West Africa between 1997 to 2019 to show that it can clarify how conflicts
can spread from place to place and how the geography of conflict changes over
time
Nutritional status and nutritional treatment are related to outcomes and mortality in older adults with hip fracture
Malnutrition is very prevalent in geriatric patients with hip fracture. Nevertheless, its importance is not fully recognized. The objective of this paper is to review the impact of malnutrition and of nutritional treatment upon outcomes and mortality in older people with hip fracture. We searched the PubMed database for studies evaluating nutritional aspects in people aged 70 years and over with hip fracture. The total number of studies included in the review was 44, which analyzed 26,281 subjects (73.5% women, 83.6 ± 7.2 years old). Older people with hip fracture presented an inadequate nutrient intake for their requirements, which caused deterioration in their already compromised nutritional status. The prevalence of malnutrition was approximately 18.7% using the Mini-Nutritional Assessment (MNA) (large or short form) as a diagnostic tool, but the prevalence was greater (45.7%) if different criteria were used (such as Body Mass Index (BMI), weight loss, or albumin concentration). Low scores in anthropometric indices were associated with a higher prevalence of complications during hospitalization and with a worse functional recovery. Despite improvements in the treatment of geriatric patients with hip fracture, mortality was still unacceptably high (30% within 1 year and up to 40% within 3 years). Malnutrition was associated with an increase in mortality. Nutritional intervention was cost effective and was associated with an improvement in nutritional status and a greater functional recovery. To conclude, in older people, the prevention of malnutrition and an early nutritional intervention can improve recovery following a hip fracture
Mode mixing in asymmetric double trench photonic crystal waveguides
e investigate both experimentally and theoretically the waveguiding
properties of a novel double trench waveguide where a conventional single-mode
strip waveguide is embedded in a two dimensional photonic crystal (PhC) slab
formed in silicon on insulator (SOI) wafers. We demonstrate that the bandwidth
for relatively low-loss (50dB/cm) waveguiding is significantly expanded to
250nm covering almost all the photonic band gap owing to nearly linear
dispersion of the TE-like waveguiding mode. The flat transmission spectrum
however is interrupted by numerous narrow stop bands. We found that these stop
bands can be attributed to anti-crossing between TE-like (positive parity) and
TM-like (negative parity) modes. This effect is a direct result of the strong
asymmetry of the waveguides that have an upper cladding of air and lower
cladding of oxide. To our knowledge this is the first demonstration of the
effects of cladding asymmetry on the transmission characteristics of the PhC
slab waveguides.Comment: 7 pages, 6 figure
A model problem for the initial-boundary value formulation of Einstein's field equations
In many numerical implementations of the Cauchy formulation of Einstein's
field equations one encounters artificial boundaries which raises the issue of
specifying boundary conditions. Such conditions have to be chosen carefully. In
particular, they should be compatible with the constraints, yield a well posed
initial-boundary value formulation and incorporate some physically desirable
properties like, for instance, minimizing reflections of gravitational
radiation.
Motivated by the problem in General Relativity, we analyze a model problem,
consisting of a formulation of Maxwell's equations on a spatially compact
region of spacetime with timelike boundaries. The form in which the equations
are written is such that their structure is very similar to the
Einstein-Christoffel symmetric hyperbolic formulations of Einstein's field
equations. For this model problem, we specify a family of Sommerfeld-type
constraint-preserving boundary conditions and show that the resulting
initial-boundary value formulations are well posed. We expect that these
results can be generalized to the Einstein-Christoffel formulations of General
Relativity, at least in the case of linearizations about a stationary
background.Comment: 25 page
Factorization of finite temperature graphs in thermal QED
We extend our previous analysis of gauge and Dirac fields in the presence of
a chemical potential. We consider an alternate thermal operator which relates
in a simple way the Feynman graphs in QED at finite temperature and charge
density to those at zero temperature but non-zero chemical potential. Several
interesting features of such a factorization are discussed in the context of
the thermal photon and fermion self-energies.Comment: 4 page
Stability of Monitoring Weak Changes in Multiply Scattering Media with Ambient Noise Correlation: Laboratory Experiments
Previous studies have shown that small changes can be monitored in a
scattering medium by observing phase shifts in the coda. Passive monitoring of
weak changes through ambient noise correlation has already been applied to
seismology, acoustics and engineering. Usually, this is done under the
assumption that a properly reconstructed Green function as well as stable
background noise sources are necessary. In order to further develop this
monitoring technique, a laboratory experiment was performed in the 2.5MHz range
in a gel with scattering inclusions, comparing an active (pulse-echo) form of
monitoring to a passive (correlation) one. Present results show that
temperature changes in the medium can be observed even if the Green function
(GF) of the medium is not reconstructed. Moreover, this article establishes
that the GF reconstruction in the correlations is not a necessary condition:
the only condition to monitoring with correlation (passive experiment) is the
relative stability of the background noise structure
Statistics of eigenfunctions in open chaotic systems: a perturbative approach
We investigate the statistical properties of the complexness parameter which
characterizes uniquely complexness (biorthogonality) of resonance eigenstates
of open chaotic systems. Specifying to the regime of isolated resonances, we
apply the random matrix theory to the effective Hamiltonian formalism and
derive analytically the probability distribution of the complexness parameter
for two statistical ensembles describing the systems invariant under time
reversal. For those with rigid spectra, we consider a Hamiltonian characterized
by a picket-fence spectrum without spectral fluctuations. Then, in the more
realistic case of a Hamiltonian described by the Gaussian Orthogonal Ensemble,
we reveal and discuss the r\^ole of spectral fluctuations
Contrasted role of disorder for magnetic properties in an original mixed valency iron Phosphate
We have measured the magnetic properties of a mixed valency iron phosphate.
It presents an original structure with crossed chains containing Fe II and
orthogonal to the longest direction of the crystallites. Microstructural
investigations using electron microscopy show the presence of random
nano-twinning. The ac susceptibility measurements demonstrate similarities with
the kinetics of a disordered magnetic, spin-glass like, state but are shown to
be essentially due to this peculiar disorder. Scaling properties are
characteristics of 3D second order transition implying that this disorder at a
small scale does not influence significantly long range magnetic ordering. At
low temperature, a decrease of the spontaneous magnetization and an
irreversible metamagnetic transition is observed, and is attributed to a
canting of the spins in the iron chain.Comment: accepted for publication in PR
Exactly solvable models of adaptive networks
A satisfiability (SAT-UNSAT) transition takes place for many optimization
problems when the number of constraints, graphically represented by links
between variables nodes, is brought above some threshold. If the network of
constraints is allowed to adapt by redistributing its links, the SAT-UNSAT
transition may be delayed and preceded by an intermediate phase where the
structure self-organizes to satisfy the constraints. We present an analytic
approach, based on the recently introduced cavity method for large deviations,
which exactly describes the two phase transitions delimiting this adaptive
intermediate phase. We give explicit results for random bond models subject to
the connectivity or rigidity percolation transitions, and compare them with
numerical simulations.Comment: 4 pages, 4 figure
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