10,733 research outputs found
Tm3+/Ho3+ codoped tellurite fiber laser
Continuous-wave and Q-switched lasing from a Tm 3+ /Ho 3+ codoped tellurite fiber is reported. An Yb 3+ /Er 3+ -doped silica fiber laser operating at 1.6μm was used as an in-band pump source, exciting the Tm 3+ ions into the F 4 3 level. Energy is then nonradiatively transferred to the upper laser level, the I 7 5 state of Ho 3+ . The laser transition is from the I 7 5 level to the I 8 5 level, and the resulting emission is at 2.1μm . For continuous wave operation, the slope efficiency was 62% and the threshold 0.1W ; the maximum output demonstrated was 0.16W . Mechanical Q switching resulted in a pulse of 0.65μJ energy and 160ns duration at a repetition rate of 19.4kHz
Comparison of Canonical and Grand Canonical Models for selected multifragmentation data
Calculations for a set of nuclear multifragmentation data are made using a
Canonical and a Grand Canonical Model. The physics assumptions are identical
but the Canonical Model has an exact number of particles, whereas, the Grand
Canonical Model has a varying number of particles, hence, is less exact.
Interesting differences are found.Comment: 12 pages, Revtex, and 3 postscript figure
Electromagnetic Chirps from Neutron Star-Black Hole Mergers
We calculate the electromagnetic signal of a gamma-ray flare coming from the
surface of a neutron star shortly before merger with a black hole companion.
Using a new version of the Monte Carlo radiation transport code Pandurata that
incorporates dynamic spacetimes, we integrate photon geodesics from the neutron
star surface until they reach a distant observer or are captured by the black
hole. The gamma-ray light curve is modulated by a number of relativistic
effects, including Doppler beaming and gravitational lensing. Because the
photons originate from the inspiraling neutron star, the light curve closely
resembles the corresponding gravitational waveform: a chirp signal
characterized by a steadily increasing frequency and amplitude. We propose to
search for these electromagnetic chirps using matched filtering algorithms
similar to those used in LIGO data analysis.Comment: 13 pages, 5 figures, submitted to Ap
Endothelium-derived microparticles from chronically thromboembolic pulmonary hypertensive patients facilitate endothelial angiogenesis.
11 p.-4 fig.-1 tab.Background: Increased circulating levels of endoglin+ endothelial microparticles (EMPs) have been identified in several cardiovascular disorders, related to severity. Endoglin is an auxilary receptor for transforming growth factor β (TGF-β) important in the regulation of vascular structure.Results: We quantified the number of microparticles in plasma of six patients with chronic thromboembolic pulmonary hypertension (CTEPH) and age- and sex-matched pulmonary embolic (PE) and healthy controls and investigated the role of microparticle endoglin in the regulation of pulmonary endothelial function in vitro. Results show significantly increased levels of endoglin+ EMPs in CTEPH plasma, compared to healthy and disease controls. Co-culture of human pulmonary endothelial cells with CTEPH microparticles increased intracellular levels of endoglin and enhanced
TGF-β-induced angiogenesis and Smad1,5,8 phosphorylation in cells, without affecting BMPRII expression. In an in vitro model, we generated endothelium-derived MPs with enforced membrane localization of endoglin. Co-culture of these MPs with endothelial cells increased cellular endoglin content, improved cell survival and stimulated
angiogenesis in a manner similar to the effects induced by overexpressed protein.Conclusions: Increased generation of endoglin+ EMPs in CTEPH is likely to represent a protective mechanism supporting endothelial cell survival and angiogenesis, set to counteract the effects of vascular occlusion and endothelial damage.This research was supported by a project grant (PG 11/13/28765) from the British Heart Foundation and by grants from Ministerio de Economia y Competitividad of Spain (SAF2013-43421-R to CB)Peer reviewe
The Influence of in-medium NN cross-sections, symmetry potential and impact parameter on the isospin observables
We explore the influence of in-medium nucleon-nucleon cross section, symmetry
potential and impact parameter on isospin sensitive observables in
intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified
version of Quantum Molecular Dynamics model. At incident velocities above the
Fermi velocity, we find that the density dependence of symmetry potential plays
a more important role on the double neutron to proton ratio and the
isospin transport ratio than the in-medium nucleon-nucleon cross
sections, provided that the latter are constrained to a fixed total NN
collision rate. We also explore both and as a function of the
impact parameter. Since the copious production of intermediate mass fragments
is a distinguishing feature of intermediate-energy heavy-ion collisions, we
examine the isospin transport ratios constructed from different groups of
fragments. We find that the values of the isospin transport ratios for
projectile rapidity fragments with are greater than those constructed
from the entire projectile rapidity source. We believe experimental
investigations of this phenomenon can be performed. These may provide
significant tests of fragmentation time scales predicted by ImQMD calculations.Comment: 24 pages, 9 figures, to be published in Phys. Rev.
Neutron spectroscopic factors of Ni isotopes from transfer reactions
177 neutron spectroscopic factors for nickel isotopes have been extracted by
performing a systematic analysis of the angular distributions measured from
(d,p) transfer reactions. A subset of the extracted spectroscopic factors are
compared to predictions of large-basis shell models in the full pf model space
using the GXPF1A effective interaction, and the (f5/2, p3/2, p1/2, g9/2) model
space using the JJ4PNA interaction. For ground states, the predicted
spectroscopic factors using the GXPF1A effective interaction in the full pf
model space agree very well with the experimental values, while predictions
based on several other effective interactions and model spaces are about 30%
higher than the experimental values. For low-energy excited states (<3.5 MeV),
the agreement between the extracted spectroscopic factors and shell model
calculations is not better than a factor of two.Comment: 18 pages, 4 figures, 2 tables. accepted for publication in PR
Transport Model Simulations of Projectile Fragmentation Reactions at 140 MeV/nucleon
The collisions in four different reaction systems using Ca and
Ni isotope beams and a Be target have been simulated using the Heavy
Ion Phase Space Exploration and the Antisymmetrized Molecular Dynamics models.
The present study mainly focuses on the model predictions for the excitation
energies of the hot fragments and the cross sections of the final fragments
produced in these reactions. The effects of various factors influencing the
final fragment cross sections, such as the choice of the statistical decay code
and its parameters have been explored. The predicted fragment cross sections
are compared to the projectile fragmentation cross sections measured with the
A1900 mass separator. At MeV, reaction dynamics can significantly
modify the detection efficiencies for the fragments and make them different
from the efficiencies applied to the measured data reported in the previous
work. The effects of efficiency corrections on the validation of event
generator codes are discussed in the context of the two models.Comment: 28 pages, 13 figure
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