4,819 research outputs found
How cold is cold dark matter? Small scales constraints from the flux power spectrum of the high-redshift Lyman-alpha forest
We present constraints on the mass of warm dark matter (WDM) particles
derived from the Lyman-alpha flux power spectrum of 55 high- resolution HIRES
spectra at 2.0 < z < 6.4. From the HIRES spectra, we obtain a lower limit of
mwdm > 1.2 keV 2 sigma if the WDM consists of early decoupled thermal relics
and mwdm > 5.6 keV (2 sigma) for sterile neutrinos. Adding the Sloan Digital
Sky Survey Lyman-alpha flux power spectrum, we get mwdm > 4 keV and mwdm > 28
keV (2 sigma) for thermal relics and sterile neutrinos. These results improve
previous constraints by a factor two.Comment: Some issues clarified (especially resolution related). Conclusions
unchanged. Accepted version by PR
Ultraslow light in inhomogeneously broadened media
We calculate the characteristics of ultraslow light in an inhomogeneously
broadened medium. We present analytical and numerical results for the group
delay as a function of power of the propagating pulse. We apply these results
to explain the recently reported saturation behavior [Baldit {\it et al.}, \prl
{\bf 95}, 143601 (2005)] of ultraslow light in rare earth ion doped crystal.Comment: 4 pages, 5 figure
Steady state entanglement in open and noisy quantum systems at high temperature
We show that quantum mechanical entanglement can prevail even in noisy open
quantum systems at high temperature and far from thermodynamical equilibrium,
despite the deteriorating effect of decoherence. The system consists of a
number N of interacting quantum particles, and it can interact and exchange
particles with some environment. The effect of decoherence is counteracted by a
simple mechanism, where system particles are randomly reset to some standard
initial state, e.g. by replacing them with particles from the environment. We
present a master equation that describes this process, which we can solve
analytically for small N. If we vary the interaction strength and the reset
against decoherence rate, we find a threshold below which the equilibrium state
is classically correlated, and above which there is a parameter region with
genuine entanglement.Comment: 5 pages, 3 figure
Constraining reionization using the thermal history of the baryons
The thermal evolution of the intergalactic medium (IGM) depends on the
reionization history of the universe. Numerical simulations indicate that the
low density IGM, which is responsible for the low column density Ly-alpha
forest, follows a well defined temperature-density relation. This results in a
cut-off in the distribution of line widths as a function of column density. We
use hydrodynamic simulations to calibrate the relation between the cut-off and
the temperature-density relation and apply this relation to Keck spectra
spanning a redshift range z=2-4.5. We find that the temperature peaks at z~3
and interpret this as evidence for reheating due to the reionization of helium.Comment: 4 pages, 2 figures, to appear in "Cosmic evolution and galaxy
formation: Structure, interactions, and feedback", eds. J. Franco et a
The circumbinary disk of HD 98800B: Evidence for disk warping
The quadruple young stellar system HD 98800 consists of two spectroscopic binary pairs with a circumbinary disk around the B component. Recent work by Boden and collaborators using infrared interferometry and radial velocity data resulted in a determination of the physical orbit for HD 98800B. We use the resulting inclination of the binary and the measured extinction toward the B component stars to constrain the distribution of circumbinary material. Although a standard optically and geometrically thick disk model can reproduce the spectral energy distribution, it cannot account for the observed extinction if the binary and the disk are coplanar. We next constructed a dynamical model to investigate the influence of the A component, which is not in the Ba‐Bb orbital plane, on the B disk. We find that these interactions have a substantial impact on the inclination of the B circumbinary disk with respect to the Ba‐Bb orbital plane. The resulting warp would be sufficient to place material into the line of sight and the noncoplanar disk orientation may also cause the upper layers of the disk to intersect the line of sight if the disk is geometrically thick. These simulations also support that the dynamics of the Ba‐Bb orbit clear the inner region to a radius of~3 AU. We then discuss whether the somewhat unusual properties of the HD 98800B disk are consistent with material remnant from the star formation process or with more recent creation by collisions from larger bodies
Nurse delivered lifestyle interventions in primary health care to treat chronic disease risk factors associated with obesity:
Nurses in primary health care (PHC) provide an increasing proportion of chronic disease management and preventive lifestyle advice. The databases MEDLINE, CINAHL, EMBASE and PsychINFO were searched and the articles were systematically reviewed for articles describing controlled adult lifestyle intervention studies delivered by a PHC nurse, in a PHC setting. Thirty-one articles describing 28 studies were analysed by comparison group which revealed: (i) no difference of effect when the same intervention was delivered by a PHC nurse compared to other health professionals in PHC (n = 2); (ii) the provision of counselling delivered by a PHC nurse was more effective than health screening (n = 10); (iii) counselling based on behaviour change theory was more effective than the same dose of non-behavioural counselling when at least three counselling sessions were delivered (n = 3). The evidence supports the effectiveness of lifestyle interventions delivered by nurses in PHC to affect positive changes on outcomes associated with the prevention of chronic disease including: weight, blood pressure, cholesterol, dietary and physical activity behaviours, patient satisfaction, readiness for change and quality of life. The strength of recommendations is limited by the small number of studies within each comparison group and the high risk of bias of the majority of studies
Laser theory in manifest Lindblad form
We discuss the laser theory for a single-mode laser with nonlinear gain. We
focus in particular on a micromaser which is pumped with a dilute beam of
excited atoms crossing the laser cavity. In the weak-coupling regime, an
expansion in the coupling strength is developed that preserves the Lindblad
form of the master equation, securing the positivity of the density matrix.
This expansion breaks rapidly down above threshold. This can be improved with
an alternative approach, not restricted to weak coupling: the Lindblad
operators are expanded in orthogonal polynomials adapted to the probability
distribution for the atom-laser interaction time. Results for the photon
statistics and the laser linewidth illustrate the theory.Comment: 13 pages, 8 figures, to be published in J Phys B (minor revision
One dimensional chain of quantum molecule motors as a mathematical physics model for muscle fibre
A quantum chain model of many molecule motors is proposed as a mathematical
physics theory on the microscopic modeling of classical force-velocity relation
and tension transients of muscle fibre. We proposed quantum many-particle
Hamiltonian to predict the force-velocity relation for the slow release of
muscle fibre which has no empirical relation yet, it is much more complicate
than hyperbolic relation. Using the same Hamiltonian, we predicted the
mathematical force-velocity relation when the muscle is stimulated by
alternative electric current. The discrepancy between input electric frequency
and the muscle oscillation frequency has a physical understanding by Doppler
effect in this quantum chain model. Further more, we apply quantum physics
phenomena to explore the tension time course of cardiac muscle and insect
flight muscle. Most of the experimental tension transients curves found their
correspondence in the theoretical output of quantum two-level and three-level
model. Mathematically modeling electric stimulus as photons exciting a quantum
three-level particle reproduced most tension transient curves of water bug
Lethocerus Maximus.Comment: 16 pages, 12 figures, Arguments are adde
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