832 research outputs found
Ultrasonic cavity solitons
We report on a new type of localized structure, an ultrasonic cavity soliton,
supported by large aspect-ratio acoustic resonators containing viscous media.
The spatio-temporal dynamics of this system is analyzed on the basis of a
generalized Swift-Hohenberg equation, derived from the microscopic equations
under conditions close to nascent bistability. These states of the acoustic and
thermal fields are robust structures, existing whenever a spatially uniform
solution and a periodic pattern coexist. An analytical solution for the
ultrasonic cavity soliton is also presented
Influência de duas intensidades de exploração no crescimento da floresta residual.
bitstream/item/57816/1/CPATU-PA129.pd
Neoker Single Crystal Alumina Fibers as reinforcement in Al-based MMC: first steps
α-Al2O3 whiskers are good candidates for use as strengtheners in advanced composites, specifically, single crystal -Al2O3 whiskers grown with c-axis orientation, because of their favorable fracture strength, stiffness, and creep resistance, even at high temperatures are optimum reinforces. Very few methods are currently available to obtain single-crystal α-Al2O3 whiskers, and these methods were too complex and expensive for use on an industrial scale. A novel method for obtaining c-axis alumina single-crystal whiskers (developed at the Institute of Ceramic Materials of Galicia) has been scaled-up to industrial production by Neoker, a Spin-Off of the of the University of Santiago de Compostela, Spain. The technology for the production of the whiskers involves the reaction between aluminum and powdered silica in Ar atmospheres containing metal vapors. Aluminum is the most popular matrix for the metal matrix composites (MMCs). The Al alloys are quite attractive due to their low density, their capability to be strengthened by precipitation, their good corrosion resistance, high thermal and electrical conductivity, and their high damping capacity. The reinforcement in AMCs could be in the form of continuous/discontinuous whiskers, whisker or particulates, in volume fractions ranging from a few percent to 70%. Properties of AMCs can be tailored to the demands of different industrial applications by suitable combinations of matrix, reinforcement and processing route. The composites studied in the present work were prepared by infiltration processes where the reinforcements were pressed into a preform that was then infiltrated by the molten Al allo
Phase IV open-label study of the efficacy and safety of deferasirox after allogeneic stem cell transplantation
This is the first prospective study of deferasirox in adult allogeneic hematopoietic stem cell transplant recipients with transfusional iron overload in hematologic malignancies. Patients at least six months post transplant were treated with deferasirox at a starting dose of 10 mg/kg/day for 52 weeks or until serum ferritin was less than 400 ng/mL on two consecutive occasions. Thirty patients were enrolled and 22 completed the study. A significant reduction from baseline in median serum ferritin and in liver iron concentration at 52 weeks was observed in the overall population: from 1440 to 755.5 ng/mL (P=0.002) and from 14.5 to 4.6 mg Fe/g dw (P=0.0007), respectively. Reduction in serum ferritin in patients who did not discontinue deferasirox therapy was significantly greater than that found in those who prematurely discontinued the treatment (from 1541 to 581 ng/mL vs. from 1416 to 1486 ng/mL; P=0.008). Drug-related adverse events, reported in 17 patients (56.7%), were mostly mild to moderate in severity. There were no drug-related serious adverse events. Twelve patients (40.0%) showed an increase of over 33% in serum creatinine compared to baseline and greater than the upper limit of normal on two consecutive visits. Two patients (6.7%) with active graft-versus-host disease showed an increase in alanine aminotransferase exceeding 10 times upper limit of normal; both resolved. In this prospective study, deferasirox provided a significant reduction in serum ferritin and liver iron concentration over one year of treatment in allogeneic hematopoietic stem cell transplant recipients with iron overload. In addition, the majority of adverse events related to deferasirox were mild or moderate in severity. (clinicaltrials.gov identifier:01335035)
The number of transmission channels through a single-molecule junction
We calculate transmission eigenvalue distributions for Pt-benzene-Pt and
Pt-butadiene-Pt junctions using realistic state-of-the-art many-body
techniques. An effective field theory of interacting -electrons is used to
include screening and van der Waals interactions with the metal electrodes. We
find that the number of dominant transmission channels in a molecular junction
is equal to the degeneracy of the molecular orbital closest to the metal Fermi
level.Comment: 9 pages, 8 figure
VERITAS Observations of the gamma-Ray Binary LS I +61 303
LS I +61 303 is one of only a few high-mass X-ray binaries currently detected
at high significance in very high energy gamma-rays. The system was observed
over several orbital cycles (between September 2006 and February 2007) with the
VERITAS array of imaging air-Cherenkov telescopes. A signal of gamma-rays with
energies above 300 GeV is found with a statistical significance of 8.4 standard
deviations. The detected flux is measured to be strongly variable; the maximum
flux is found during most orbital cycles at apastron. The energy spectrum for
the period of maximum emission can be characterized by a power law with a
photon index of Gamma=2.40+-0.16_stat+-0.2_sys and a flux above 300 GeV
corresponding to 15-20% of the flux from the Crab Nebula.Comment: accepted for publication in The Astrophysical Journa
Stabilization of Spatial Solitons by Gain Diffusion
It is shown, that diffusion of saturated gain (e.g. diffusion of population
inversion in lasers) causes, and/or enhances a modulational instability of
generated light field. In case of a subcritical system (e.g. a laser with
saturable absorber) the enhancement of the modulational instability stabilizes
spatial solitons. These predictions are made for general nonlinear optical
systems, and are illustrated by numerical simulation of lasers with saturable
absorber.Comment: 10 pages, 4 figures, submitted to Phys.Rev.
VERITAS Observations of the BL Lac Object 1ES 1218+304
The VERITAS collaboration reports the detection of very-high-energy (VHE)
gamma-ray emission from the high-frequency-peaked BL Lac object 1ES 1218+304
located at a redshift of z=0.182. A gamma-ray signal was detected with high
statistical significance for the observations taken during several months in
the 2006-2007 observing season. The photon spectrum between ~160 GeV and ~1.8
TeV is well described by a power law with an index of Gamma = 3.08 +/-
0.34(stat) +/- 0.2(sys). The integral flux above 200 GeV corresponds to ~6% of
that of the Crab Nebula. The light curve does not show any evidence for VHE
flux variability. Using lower limits on the density of the extragalactic
background light (EBL) in the near-IR to mid-IR we are able to limit the range
of intrinsic energy spectra for 1ES 1218+304. We show that the intrinsic photon
spectrum is harder than a power law with an index of Gamma = 2.32 +/- 0.37.
When including constraints from the spectra of 1ES 1101-232 and 1ES 0229+200,
the spectrum of 1ES 1218+304 is likely to be harder than Gamma = 1.86 +/- 0.37.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Status of the VERITAS Observatory
VERITAS, an Imaging Atmospheric Cherenkov Telescope (IACT) system for
gammma-ray astronomy in the GeV-TeV range, has recently completed its first
season of observations with a full array of four telescopes. A number of
astrophysical gamma-ray sources have been detected, both galactic and
extragalactic, including sources previously unknown at TeV energies. We
describe the status of the array and some highlight results, and assess the
technical performance, sensitivity and shower reconstruction capabilities.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Phase-Locked Spatial Domains and Bloch Domain Walls in Type-II Optical Parametric Oscillators
We study the role of transverse spatial degrees of freedom in the dynamics of
signal-idler phase locked states in type-II Optical Parametric Oscillators.
Phase locking stems from signal-idler polarization coupling which arises if the
cavity birefringence and/or dichroism is not matched to the nonlinear crystal
birefringence. Spontaneous Bloch domain wall formation is theoretically
predicted and numerically studied. Bloch walls connect, by means of a
polarization transformation, homogeneous regions of self-phase locked
solutions. The parameter range for their existence is analytically found. The
polarization properties and the dynamics of walls in one- and two transverse
spatial dimensions is explained. Transition from Bloch to Ising walls is
characterized, the control parameter being the linear coupling strength. Wall
dynamics governs spatiotemporal dynamical states of the system, which include
transient curvature driven domain growth, persistent dynamics dominated by
spiraling defects for Bloch walls, and labyrinthine pattern formation for Ising
walls.Comment: 27 pages, 16 figure
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