28,036 research outputs found
Newtonian limit of String-Dilaton Gravity
We study the weak-field limit of string-dilaton gravity and derive
corrections to the Newtonian potential which strength directly depends on the
self interaction potential and the nonminimal coupling of the dilaton scalar
field. We discuss also possible astrophysical applications of the results, in
particular the flat rotation curves of spiral galaxies.Comment: 11 pages, LATEX file, to appear in IJMP
Dynamic hysteresis from zigzag domain walls
We investigate dynamic hysteresis in ferromagnetic thin films with zigzag
domain walls. We introduce a discrete model describing the motion of a wall in
a disordered ferromagnet with in-plane magnetization, driven by an external
magnetic field, considering the effects of dipolar interactions and anisotropy.
We analyze the effects of external field frequency and temperature on the
coercive field by Monte Carlo simulations, and find a good agreement with the
experimental data reported in literature for Fe/GaAs films. This implies that
dynamic hysteresis in this case can be explained by a single propagating domain
wall model without invoking domain nucleation.Comment: 10 pages, 13 figures; minor modifications and two figures adde
Is dark matter an extra-dimensional effect?
We investigate the possibility that the observed behavior of test particles
outside galaxies, which is usually explained by assuming the presence of dark
matter, is the result of the dynamical evolution of particles in higher
dimensional space-times. Hence, dark matter may be a direct consequence of the
presence of an extra force, generated by the presence of extra-dimensions,
which modifies the dynamic law of motion, but does not change the intrinsic
properties of the particles, like, for example, the mass (inertia). We discuss
in some detail several possible particular forms for the extra force, and the
acceleration law of the particles is derived. Therefore, the constancy of the
galactic rotation curves may be considered as an empirical evidence for the
existence of the extra dimensions.Comment: 11 pages, no figures, accepted for publication in MPLA; references
adde
Implications of the first detection of coherent elastic neutrino-nucleus scattering (CEvNS) with Liquid Argon
The CENNS-10 experiment of the COHERENT collaboration has recently reported
the first detection of coherent-elastic neutrino-nucleus scattering (CEvNS) in
liquid Argon with more than significance. In this work, we exploit
the new data in order to probe various interesting parameters which are of key
importance to CEvNS within and beyond the Standard Model. A dedicated
statistical analysis of these data shows that the current constraints are
significantly improved in most cases. We derive a first measurement of the
neutron rms charge radius of Argon, and also an improved determination of the
weak mixing angle in the low energy regime. We also update the constraints on
neutrino non-standard interactions, electromagnetic properties and light
mediators with respect to those derived from the first COHERENT-CsI data.Comment: discussion expanded including light mediators and nuclear
uncertainties, figures added, references added. V3: Fig. 7 corrected,
conclusions unchange
Optimal states and almost optimal adaptive measurements for quantum interferometry
We derive the optimal N-photon two-mode input state for obtaining an estimate
\phi of the phase difference between two arms of an interferometer. For an
optimal measurement [B. C. Sanders and G. J. Milburn, Phys. Rev. Lett. 75, 2944
(1995)], it yields a variance (\Delta \phi)^2 \simeq \pi^2/N^2, compared to
O(N^{-1}) or O(N^{-1/2}) for states considered by previous authors. Such a
measurement cannot be realized by counting photons in the interferometer
outputs. However, we introduce an adaptive measurement scheme that can be thus
realized, and show that it yields a variance in \phi very close to that from an
optimal measurement.Comment: 4 pages, 4 figures, journal versio
Effects of arcing due to spacecraft charging on spacecraft survival
A quantitative assessment of the hazard associated with spacecraft charging and arcing on spacecraft systems is presented. A literature survey on arc discharge thresholds and characteristics was done and gaps in the data and requirements for additional experiments were identified. Calculations of coupling of arc discharges into typical spacecraft systems were made and the susceptibility of typical spacecraft to disruption by arc discharges was investigated. Design guidelines and recommended practices to reduce or eliminate the threat of malfunction and failures due to spacecraft charging/arcing were summarized
Low Temperature Drying With Air Dehumidified by Zeolite for Food Products: Energy Efficiency Aspect Analysis
Developments in low temperature drying of food products are still an interesting issue; especially with respect to the energy efficiency. This research studies the energy efficiency that can be achieved by a dryer using air which is dehumidified by zeolite. Experimental results are fitted to a dynamic model to find important variables for the drying operation. The results show that ambient air temperature as well as the ratio between air flow for drying and air flow for regeneration, affect the energy efficiency significantly. Relative humidity of used air, and shift time have a minor effect on the dryer performance. From the total work, it can be noted that the dryer efficiency operated at 50-60°C achieves 75 percent, which is attractive for drying of food products
Outflows in Infrared-Luminous Starbursts at z < 0.5. I. Sample, NaI D Spectra, and Profile Fitting
We have conducted a spectroscopic survey of 78 starbursting infrared-luminous
galaxies at redshifts up to z = 0.5. We use moderate-resolution spectroscopy of
the NaI D interstellar absorption feature to directly probe the neutral phase
of outflowing gas in these galaxies. Over half of our sample are ultraluminous
infrared galaxies that are classified as starbursts; the rest have infrared
luminosities in the range log(L_IR/L_sun) = 10.2 - 12.0. The sample selection,
observations, and data reduction are described here. The absorption-line
spectra of each galaxy are presented. We also discuss the theory behind
absorption-line fitting in the case of a partially-covered, blended absorption
doublet observed at moderate-to-high resolution, a topic neglected in the
literature. A detailed analysis of these data is presented in a companion
paper.Comment: 59 pages, 18 figures in AASTeX preprint style; to appear in September
issue of ApJ
Polynomial time algorithms for multicast network code construction
The famous max-flow min-cut theorem states that a source node s can send information through a network (V, E) to a sink node t at a rate determined by the min-cut separating s and t. Recently, it has been shown that this rate can also be achieved for multicasting to several sinks provided that the intermediate nodes are allowed to re-encode the information they receive. We demonstrate examples of networks where the achievable rates obtained by coding at intermediate nodes are arbitrarily larger than if coding is not allowed. We give deterministic polynomial time algorithms and even faster randomized algorithms for designing linear codes for directed acyclic graphs with edges of unit capacity. We extend these algorithms to integer capacities and to codes that are tolerant to edge failures
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