6,774 research outputs found
The ion motion in self-modulated plasma wakefield accelerators
The effects of plasma ion motion in self-modulated plasma based accelerators
is examined. An analytical model describing ion motion in the narrow beam limit
is developed, and confirmed through multi-dimensional particle-in-cell
simulations. It is shown that the ion motion can lead to the early saturation
of the self-modulation instability, and to the suppression of the accelerating
gradients. This can reduce the total energy that can be transformed into
kinetic energy of accelerated particles. For the parameters of future
proton-driven plasma accelerator experiments, the ion dynamics can have a
strong impact. Possible methods to mitigate the effects of the ion motion in
future experiments are demonstrated.Comment: 11 pages, 3 figures, accepted for publication in Phys. Rev. Let
FLOW PATTERNS OF THE ESTER OIL-REFRIGERANT R134A MIXTURE FLASHING FLOW THROUGH A SMALL DIAMETER TUBE
This work presents an experimental investigation of the ester oil ISO VG10-refrigerant R134a mixture flashing flow with foam formation through a straight horizontal 3.22 mm-diameter-6.0 m- long tube. An experimental apparatus was designed to allow the measurement of both pressure and temperature profiles along the tube as well as the visualization of the flow patterns. Tests were performed at different mass flow rates, several refrigerant mass fractions at the inlet of the flow, and inlet mixture temperatures around 28 and 39 °C. A liquid mixture flow with constant temperature and pressure gradient could be noticed at the inlet of the tube. As the flow proceeded towards the exit of the tube the pressure drop produced a reduction of the refrigerant solubility in the oil yielding to formation of the first bubbles. Initially, small and few bubbles could be noticed and the flow behaved as a conventional two-phase flow. Eventually, the bubble population increased and foam flow was observed at the exit of the tube. Due to the great formation of bubbles, both the temperature and pressure gradient of the mixture were greatly reduced in this region of the flow
Efeito do aumento simulado da radiação UV-B na expressão peroxidase na interação morangueiro X Botrytis cinerea X Clonostachys rosea em campo.
Com a diminuição da camada de ozônio espera-se um aumento da radiação UV- B (290-315 nm). Os estudos sobre o efeito da radiação UV-B em patossistemas são limitados principalmente em condições de campo. O objetivo deste trabalho foi estudar o efeito do aumento simulado da radiação UV-B na expressão da enzima peroxidase na interação morangueiro x Clonostachys rosea x Botrytis cinerea em condições de campo. O experimento foi conduzido durante 15 dias em parcelas subdivididas em três condições de radiação (1. Ambiente; 2.Ausência de radiação e 3. Aumento de radiação suplementada por lâmpadas) e quatros tratamentos (1. Testemunha, 2. Plantas inoculadas com C. rosea; 3. Plantas inoculadas com B. cinerea e 4. Plantas inoculadas com ambos microrganimos). A atividade da peroxidase foi determinada por espectrofotômetro a 470 nm. Os resultados expressos em unidades de PO. mg-1 tecido.min-1 demonstraram que a radiação UV-B natural e a suplementada por lâmpadas reduziram a atividade da peroxidase em plantas inoculadas com ambos microrganimos
Spin measurements for 147Sm+n resonances: Further evidence for non-statistical effects
We have determined the spins J of resonances in the 147Sm(n,gamma) reaction
by measuring multiplicities of gamma-ray cascades following neutron capture.
Using this technique, we were able to determine J values for all but 14 of the
140 known resonances below En = 1 keV, including 41 firm J assignments for
resonances whose spins previously were either unknown or tentative. These new
spin assignments, together with previously determined resonance parameters,
allowed us to extract separate level spacings and neutron strength functions
for J = 3 and 4 resonances. Furthermore, several statistical test of the data
indicate that very few resonances of either spin have been missed below En =
700eV. Because a non-statistical effect recently was reported near En = 350 eV
from an analysis of 147Sm(n,alpha) data, we divided the data into two regions;
0 < En < 350 eV and 350 < En < 700 eV. Using neutron widths from a previous
measurement and published techniques for correcting for missed resonances and
for testing whether data are consistent with a Porter-Thomas distribution, we
found that the reduced-neutron-width distribution for resonances below 350 eV
is consistent with the expected Porter-Thomas distribution. On the other hand,
we found that reduced-neutron-width data in the 350 < En < 700 eV region are
inconsistent with a Porter-Thomas distribution, but in good agreement with a
chi-squared distribution having two or more degrees of freedom. We discuss
possible explanations for these observed non-statistical effects and their
possible relation to similar effects previously observed in other nuclides.Comment: 40 pages, 13 figures, accepted by Phys. Rev.
Impact of continuous positive airway pressure treatment on left atrial volume and function in patients with obstructive sleep apnoea assessed by real-time three-dimensional echocardiography
Background: Obstructive sleep apnoea (OSA) has been reported as a predictor of left ventricle (LV) diastolic dysfunction and left atrium (LA) remodelling. the aim of this study is to evaluate the impact of OSA treatment with a continuous positive airway pressure device (CPAP) on the LA volume and function, as well as on the LV diastolic function.Methods: in total, 56 OSA patients were studied. All patients underwent real-time three-dimensional (RT3DE) and two-dimensional echocardiogram with tissue Doppler evaluation in order to estimate LA volumes, function and LV diastolic performance. A total of 30 patients with an apnoea-hypopnoea index greater than 20 were randomly selected to receive sham CPAP (n = 15) or effective CPAP (n = 15) for 24 weeks. They underwent echo examination on three different occasions: at baseline, after 12 weeks and 24 weeks of CPAP or sham CPAP.Results: in the effective CPAP group we observed the following changes from the baseline to the 24-week echo evaluation: (a) a reduction in the E/E' ratio (10.3 (1.9) to 7.9 (1.3), p = 0.03); (b) an increase in the LA passive emptying fraction (28.8% (11.9%) to 46.8% (9.3%), p = 0.01); and (c) a reduction in the LA active emptying fraction (42.7% (11.5%) to 25.7 (15.7), p<0.01). in the sham group, there were no changes from the baseline to the 24-week echo. We found a positive correlation between 24 week/baseline LA active emptying volume and 24 week/baseline E/E' ratios (r = 0.40, p<0.05) and a negative correlation between 24 week/baseline LA passive emptying volume and 24 week/baseline E/E' ratios (r = 20.53, p<0.05). No significant changes were found on LA total emptying fraction.Conclusion: CPAP improved LV diastolic function and LA passive emptying, but not LA structural variables in OSA patients.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CEPIDAFIPUniversidade Federal de São Paulo, Dept Psychobiol, Discipline Sleep Biol & Med, BR-05021010 São Paulo, BrazilAlbert Einstein Hosp, São Paulo, BrazilUniversidade Federal de São Paulo, Discipline Cardiol, BR-05021010 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Psychobiol, Discipline Sleep Biol & Med, BR-05021010 São Paulo, BrazilUniversidade Federal de São Paulo, Discipline Cardiol, BR-05021010 São Paulo, BrazilWeb of Scienc
Point-contact spectroscopy on URuSi
Tunnel and point contact experiments have been made in a URuSi single
crystal along the c-axis. The experiments were performed changing temperature
and contact size in a low temperature scanning tunneling microscope. A
resonance develops at the Fermi level at K. This resonance splits
and becomes asymmetric when the 17.5 K phase transition is crossed. These
results are consistent with the existence of Kondo like bound states of the
U ionic configurations and the conduction electrons. Below the
transition, these configurations are split by the development of quadrupolar
ordering. The peak separation can be interpreted as a direct measurement of the
order parameter. Measurements on a policrystalline UAu_2Si_2$ sample are also
reported, with a comparative study of the behavior of both materials.Comment: 4 pages (Latex) + 2 postscript figure
Star-Forming Brightest Cluster Galaxies at 0.25 < z < 1.25: A Transitioning Fuel Supply
We present a multi-wavelength study of 90 brightest cluster galaxies (BCGs)
in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by
the South Pole Telescope, utilizing data from various ground- and space-based
facilities. We infer the star formation rate (SFR) for the BCG in each cluster,
based on the UV and IR continuum luminosity, as well as the [O II] emission
line luminosity in cases where spectroscopy is available, finding 7 systems
with SFR > 100 Msun/yr. We find that the BCG SFR exceeds 10 Msun/yr in 31 of 90
(34%) cases at 0.25 < z < 1.25, compared to ~1-5% at z ~ 0 from the literature.
At z > 1, this fraction increases to 92(+6)(-31)%, implying a steady decrease
in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific star
formation rate in BCGs is declining more slowly with time than for field or
cluster galaxies, most likely due to the replenishing fuel from the cooling ICM
in relaxed, cool core clusters. At z > 0.6, the correlation between cluster
central entropy and BCG star formation - which is well established at z ~ 0 -
is not present. Instead, we find that the most star-forming BCGs at high-z are
found in the cores of dynamically unrelaxed clusters. We investigate the
rest-frame near-UV morphology of a subsample of the most star-forming BCGs
using data from the Hubble Space Telescope, finding complex, highly asymmetric
UV morphologies on scales as large as ~50-60 kpc. The high fraction of
star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times
suggests that the dominant mode of fueling star formation in BCGs may have
recently transitioned from galaxy-galaxy interactions to ICM cooling.Comment: 20 pages, 10 figures. Submitted for publication in ApJ. Comments
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Influence of realistic parameters on state-of-the-art LWFA experiments
We examine the influence of non-ideal plasma-density and non-Gaussian
transverse laser-intensity profiles in the laser wakefield accelerator
analytically and numerically. We find that the characteristic amplitude and
scale length of longitudinal density fluctuations impacts on the final energies
achieved by electron bunches. Conditions that minimize the role of the
longitudinal plasma density fluctuations are found. The influence of higher
order Laguerre-Gaussian laser pulses is also investigated. We find that higher
order laser modes typically lead to lower energy gains. Certain combinations of
higher order modes may, however, lead to higher electron energy gains.Comment: 16 pages, 6 figures; Accepted for publication in Plasma Physics and
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