3,363 research outputs found
Thermal optical non-linearity of nematic mesophase enhanced by gold nanoparticles – an experimental and numerical investigation
In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n 2 , is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity
Maternal colonization with Staphylococcus aureus and Group B streptococcus is associated with colonization in newborns.
OBJECTIVES: Although Staphylococcus aureus and Group B streptococcus (GBS) are major causes of neonatal sepsis in sub-Saharan Africa, it is unclear how these bacteria are transmitted to the neonate. METHODS: In a cohort of 377 Gambian women and their newborns, nasopharyngeal swabs were collected at delivery (day 0), and 3, 6, 14 and 28 days later. Breast milk samples and vaginal swabs were collected from the mother. Staphylococcus aureus and GBS were isolated using conventional microbiological methods. RESULTS: Most women were carriers of S. aureus (264 out of 361 with all samples collected, 73.1%) at some point during follow up and many were carriers of GBS (114 out of 361, 31.6%). Carriage of S. aureus was common in all three maternal sites and GBS was common in the vaginal tract and breast milk. Among newborns, carriage of S. aureus peaked at day 6 (238 out of 377, 63.1%) and GBS at day 3 (39 out of 377, 10.3%). Neonatal carriage of S. aureus at day 6 was associated with maternal carriage in the breast milk adjusted OR 2.54; 95% CI 1.45-4.45, vaginal tract (aOR 2.55; 95% CI 1.32-4.92) and nasopharynx (aOR 2.49; 95% CI 1.56-3.97). Neonatal carriage of GBS at day 6 was associated with maternal carriage in the breast milk (aOR 3.75; 95% CI 1.32-10.65) and vaginal tract (aOR 3.42; 95% CI 1.27-9.22). CONCLUSIONS: Maternal colonization with S. aureus or GBS is a risk factor for bacterial colonization in newborns
Universal bifurcation property of two- or higher-dimensional dissipative systems in parameter space: Why does 1D symbolic dynamics work so well?
The universal bifurcation property of the H\'enon map in parameter space is
studied with symbolic dynamics. The universal- region is defined to
characterize the bifurcation universality. It is found that the universal-
region for relative small is not restricted to very small values. These
results show that it is also a universal phenomenon that universal sequences
with short period can be found in many nonlinear dissipative systems.Comment: 10 pages, figures can be obtained from the author, will appeared in
J. Phys.
On Quantum State Observability and Measurement
We consider the problem of determining the state of a quantum system given
one or more readings of the expectation value of an observable. The system is
assumed to be a finite dimensional quantum control system for which we can
influence the dynamics by generating all the unitary evolutions in a Lie group.
We investigate to what extent, by an appropriate sequence of evolutions and
measurements, we can obtain information on the initial state of the system. We
present a system theoretic viewpoint of this problem in that we study the {\it
observability} of the system. In this context, we characterize the equivalence
classes of indistinguishable states and propose algorithms for state
identification
Sulfur gas monitoring in volcanic/geothermal areas with passive samplers: human health implications
Volcanic and geothermal areas are one of the major natural sources of sulphur gases to the atmosphere. Hydrogen sulphide (H2S) is a toxic gas mainly associated to geothermal systems while sulphur dioxide (SO2) is released in huge quantities from volcanoes characterized by open conduit activity.
Apart from being one of the most impressive geodynamic expressions, volcanoes are also an important tourist attraction. During the summer season the number of tourists visiting the crateric areas each day is on average many tens at Stromboli, hundreds at Vulcano, Santorini and Nisyros and thousands at Etna. Touristic exploitation of active volcanic areas cannot exempt from warranting a reasonable security to the visiting persons. But while many risks in these areas have been since long time considered, gas hazard, a very subtle risk, is often disregarded.
The atmospheric concentrations and dispersion pattern of naturally emitted SO2 were measured at three volcanoes of southern Italy (Etna, Vulcano and Stromboli) while that of H2S at four volcanic/geothermal areas of Greece (Sousaki, Milos, Santorini and Nisyros). Measurements were made with a network of passive samplers positioned at about 1.5 m above the ground, which gave time-integrated values for periods from few days to 1 month. Samplers were placed in zones of the volcanoes with high tourist frequentation.
Measured concentrations and dispersion pattern depend on the strength of the source (craters, fumaroles), meteorological conditions and geomorphology of the area.
At Etna, Vulcano, Stromboli and Nisyros measured concentrations reach values that are absolutely dangerous to people affected by bronchial asthma or lung diseases. But considering that these are average values over periods from few days up to one month, concentrations could have reached much higher peak values dangerous also to healthy people.
The present study evidences a peculiar volcanic risk connected to the touristic exploitation of volcanic areas. Such risk is particularly enhanced at Etna where elderly and not perfectly healthy people can easily reach, with cableway and off-road vehicles, areas with dangerous SO2 concentrations
Control of electron spin decoherence caused by electron-nuclear spin dynamics in a quantum dot
Control of electron spin decoherence in contact with a mesoscopic bath of
many interacting nuclear spins in an InAs quantum dot is studied by solving the
coupled quantum dynamics. The nuclear spin bath, because of its bifurcated
evolution predicated on the electron spin up or down state, measures the
which-state information of the electron spin and hence diminishes its
coherence. The many-body dynamics of nuclear spin bath is solved with a
pair-correlation approximation. In the relevant timescale, nuclear pair-wise
flip-flops, as elementary excitations in the mesoscopic bath, can be mapped
into the precession of non-interacting pseudo-spins. Such mapping provides a
geometrical picture for understanding the decoherence and for devising control
schemes. A close examination of nuclear bath dynamics reveals a wealth of
phenomena and new possibilities of controlling the electron spin decoherence.
For example, when the electron spin is flipped by a -pulse at , its
coherence will partially recover at as a consequence of quantum
disentanglement from the mesoscopic bath. In contrast to the re-focusing of
inhomogeneously broadened phases by conventional spin-echoes, the
disentanglement is realized through shepherding quantum evolution of the bath
state via control of the quantum object. A concatenated construction of pulse
sequences can eliminate the decoherence with arbitrary accuracy, with the
nuclear-nuclear spin interaction strength acting as the controlling small
parameter
Measurement of forward photon production cross-section in proton-proton collisions at = 13 TeV with the LHCf detector
In this paper, we report the production cross-section of forward photons in
the pseudorapidity regions of and ,
measured by the LHCf experiment with proton--proton collisions at =
13 TeV. The results from the analysis of 0.191 of data
obtained in June 2015 are compared to the predictions of several hadronic
interaction models that are used in air-shower simulations for
ultra-high-energy cosmic rays. Although none of the models agree perfectly with
the data, EPOS-LHC shows the best agreement with the experimental data among
the models.Comment: 21 pages, 4 figure
Control landscapes for two-level open quantum systems
A quantum control landscape is defined as the physical objective as a
function of the control variables. In this paper the control landscapes for
two-level open quantum systems, whose evolution is described by general
completely positive trace preserving maps (i.e., Kraus maps), are investigated
in details. The objective function, which is the expectation value of a target
system operator, is defined on the Stiefel manifold representing the space of
Kraus maps. Three practically important properties of the objective function
are found: (a) the absence of local maxima or minima (i.e., false traps); (b)
the existence of multi-dimensional sub-manifolds of optimal solutions
corresponding to the global maximum and minimum; and (c) the connectivity of
each level set. All of the critical values and their associated critical
sub-manifolds are explicitly found for any initial system state. Away from the
absolute extrema there are no local maxima or minima, and only saddles may
exist, whose number and the explicit structure of the corresponding critical
sub-manifolds are determined by the initial system state. There are no saddles
for pure initial states, one saddle for a completely mixed initial state, and
two saddles for other initial states. In general, the landscape analysis of
critical points and optimal manifolds is relevant to the problem of explaining
the relative ease of obtaining good optimal control outcomes in the laboratory,
even in the presence of the environment.Comment: Minor editing and some references adde
Quark-Gluon Plasma - New Frontiers
As implied by organizers, this talk is not a conference summary but rather an
outline of progress/challenges/``frontiers'' of the theory. Some fundamental
questions addressed are:
Why is sQGP such a good liquid? Do we understand (de)confinement and what do
we know about ``magnetic'' objects creating it? Can we understand the AdS/CFT
predictions, from the gauge theory side? Can they be tested experimentally? Can
AdS/CFT duality help us understand rapid equilibration/entropy production? Can
we work out a complete dynamical ``gravity dual'' to heavy ion collisions?Comment: final talk at Quark Matter 2008, Jaipur, India, Feb.200
Symmetry Decomposition of Chaotic Dynamics
Discrete symmetries of dynamical flows give rise to relations between
periodic orbits, reduce the dynamics to a fundamental domain, and lead to
factorizations of zeta functions. These factorizations in turn reduce the labor
and improve the convergence of cycle expansions for classical and quantum
spectra associated with the flow. In this paper the general formalism is
developed, with the -disk pinball model used as a concrete example and a
series of physically interesting cases worked out in detail.Comment: CYCLER Paper 93mar01
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