5,595 research outputs found
An inexpensive and rapid technique for obtaining current profiles in estuarine waters
A current indicator, consisting of a confined submerged biplane-shaped drag and a device for reading the angle made by the suspending wire with t he vertical, is introduced in t heory and practice. It was designed for rapid determination of current velocities and directions at any depth from a vessel an chored in shallow water. A number of calibration runs made with t he Drag and with a von Arx Current Meter indicate that the Drag is reliable and suffi ciently accurate for the purpose for wluch it was designed. The gear proved to be rugged, easy to use, and inexpensive. It requires little time to make a number of observations from the surface down to 50 feet
New Ekpyrotic Cosmology
In this paper, we present a new scenario of the early Universe that contains
a pre big bang Ekpyrotic phase. By combining this with a ghost condensate, the
theory explicitly violates the null energy condition without developing any
ghost-like instabilities. Thus the contracting universe goes through a
non-singular bounce and evolves smoothly into the expanding post big bang
phase. The curvature perturbation acquires a scale-invariant spectrum well
before the bounce in this scenario. It is sourced by the scale-invariant
entropy perturbation engendered by two ekpyrotic scalar fields, a mechanism
recently proposed by Lehners et al. Since the background geometry is
non-singular at all times, the curvature perturbation remains nearly constant
on super horizon scales. It emerges from the bounce unscathed and imprints a
scale-invariant spectrum of density fluctuations in the matter-radiation fluid
at the onset of the hot big bang phase. The ekpyrotic potential can be chosen
so that the spectrum has a ``red'' tilt, in accordance with the recent data
from WMAP. As in the original Ekpyrotic scenario, the model predicts a
negligible gravity wave signal on all observable scales. As such ``New
Ekpyrotic Cosmology" provides a consistent and distinguishable alternative to
inflation to account for the origin of the seeds of large scale structure.Comment: 41 pages, 4 figures. v2: minor corrections, references added. v3:
small modifications in bounce section, references added. v4: version
published in PR
Supersymmetric Galileons
Galileon theories are of considerable interest since they allow for stable
violations of the null energy condition. Since such violations could have
occurred during a high-energy regime in the history of our universe, we are
motivated to study supersymmetric extensions of these theories. This is carried
out in this paper, where we construct generic classes of N=1 supersymmetric
Galileon Lagrangians. They are shown to admit non-equivalent stress-energy
tensors and, hence, vacua manifesting differing conditions for violating the
null energy condition. The temporal and spatial fluctuations of all component
fields of the supermultiplet are analyzed and shown to be stable on a large
number of such backgrounds. In the process, we uncover a surprising connection
between conformal Galileon and ghost condensate theories, allowing for a deeper
understanding of both types of theories.Comment: 41 pages, v2: added a referenc
Time-Varying Potassium in High-Resolution Spectra of the Type Ia Supernova 2014J
We present a time series of the highest resolution spectra yet published for
the nearby Type Ia supernova (SN) 2014J in M82. They were obtained at 11 epochs
over 33 days around peak brightness with the Levy Spectrograph (resolution
R~110,000) on the 2.4m Automated Planet Finder telescope at Lick Observatory.
We identify multiple Na I D and K I absorption features, as well as absorption
by Ca I H & K and several of the more common diffuse interstellar bands (DIBs).
We see no evolution in any component of Na I D, Ca I, or in the DIBs, but do
establish the dissipation/weakening of the two most blueshifted components of K
I. We present several potential physical explanations, finding the most
plausible to be photoionization of circumstellar material, and discuss the
implications of our results with respect to the progenitor scenario of SN
2014J.Comment: 11 pages, 8 figures, 3 tables, submitted to Ap
Entangled Quantum Clocks for Measuring Proper-Time Difference
We report that entangled pairs of quantum clocks (non-degenerate quantum
bits) can be used as a specialized detector for precisely measuring difference
of proper-times that each constituent quantum clock experiences. We describe
why the proposed scheme would be more precise in the measurement of proper-time
difference than a scheme of two-separate-quantum-clocks. We consider
possibilities that the proposed scheme can be used in precision test of the
relativity theory.Comment: no correction, 4 pages, RevTe
Yukawa Couplings in Heterotic Standard Models
In this paper, we present a formalism for computing the Yukawa couplings in
heterotic standard models. This is accomplished by calculating the relevant
triple products of cohomology groups, leading to terms proportional to Q*H*u,
Q*Hbar*d, L*H*nu and L*Hbar*e in the low energy superpotential. These
interactions are subject to two very restrictive selection rules arising from
the geometry of the Calabi-Yau manifold. We apply our formalism to the
"minimal" heterotic standard model whose observable sector matter spectrum is
exactly that of the MSSM. The non-vanishing Yukawa interactions are explicitly
computed in this context. These interactions exhibit a texture rendering one
out of the three quark/lepton families naturally light.Comment: 21 pages, LaTe
Development of a chicken 5 K microarray targeted towards immune function
<p>Abstract</p> <p>Background</p> <p>The development of microarray resources for the chicken is an important step in being able to profile gene expression changes occurring in birds in response to different challenges and stimuli. The creation of an immune-related array is highly valuable in determining the host immune response in relation to infection with a wide variety of bacterial and viral diseases.</p> <p>Results</p> <p>Here we report the development of chicken immune-related cDNA libraries and the subsequent construction of a microarray containing 5190 elements (in duplicate). Clones on the array originate from tissues known to contain high levels of cells related to the immune system, namely Bursa, Peyers patch, thymus and spleen. Represented on the array are genes that are known to cluster with existing chicken ESTs as well as genes that are unique to our libraries. Some of these genes have no known homologies and represent novel genes in the chicken collection. A series of reference genes (ie. genes of known immune function) are also present on the array. Functional annotation data is also provided for as many of the genes on the array as is possible.</p> <p>Conclusion</p> <p>Six new chicken immune cDNA libraries have been created and nearly 10,000 sequences submitted to GenBank [GenBank: <ext-link ext-link-type="gen" ext-link-id="AM063043">AM063043</ext-link>-<ext-link ext-link-type="gen" ext-link-id="AM071350">AM071350</ext-link>; <ext-link ext-link-type="gen" ext-link-id="AM071520">AM071520</ext-link>-<ext-link ext-link-type="gen" ext-link-id="AM072286">AM072286</ext-link>; <ext-link ext-link-type="gen" ext-link-id="AM075249">AM075249</ext-link>-<ext-link ext-link-type="gen" ext-link-id="AM075607">AM075607</ext-link>]. A 5 K immune-related array has been developed from these libraries. Individual clones and arrays are available from the ARK-Genomics resource centre.</p
Electron and hole states in quantum-dot quantum wells within a spherical 8-band model
In order to study heterostructures composed both of materials with strongly
different parameters and of materials with narrow band gaps, we have developed
an approach, which combines the spherical 8-band effective-mass Hamiltonian and
the Burt's envelope function representation. Using this method, electron and
hole states are calculated in CdS/HgS/CdS/H_2O and CdTe/HgTe/CdTe/H_2O
quantum-dot quantum-well heterostructures. Radial components of the wave
functions of the lowest S and P electron and hole states in typical quantum-dot
quantum wells (QDQWs) are presented as a function of radius. The 6-band-hole
components of the radial wave functions of an electron in the 8-band model have
amplitudes comparable with the amplitude of the corresponding 2-band-electron
component. This is a consequence of the coupling between the conduction and
valence bands, which gives a strong nonparabolicity of the conduction band. At
the same time, the 2-band-electron component of the radial wave functions of a
hole in the 8-band model is small compared with the amplitudes of the
corresponding 6-band-hole components. It is shown that in the CdS/HgS/CdS/H_2O
QDQW holes in the lowest states are strongly localized in the well region
(HgS). On the contrary, electrons in this QDQW and both electron and holes in
the CdTe/HgTe/CdTe/H_2O QDQW are distributed through the entire dot. The
importance of the developed theory for QDQWs is proven by the fact that in
contrast to our rigorous 8-band model, there appear spurious states within the
commonly used symmetrized 8-band model.Comment: 15 pages, 5 figures, E-mail addresses: [email protected],
[email protected]
Helically corrugated waveguides for compression of frequency swept microwave pulses
Short pulse high power microwave radiation can be used for time of flight diagnostic measurements in plasmas, e.g. density profiles by reflectometry. A three-fold helical corrugation of the inner surface of a waveguide synthesises eigenwaves having useful dispersive properties by combining two distinct counter-rotating modes of a corresponding circular waveguide. The dispersion may be tailored to the requirements of an application by adjusting the amplitude and period of the corrugations. Such dispersive properties have proven useful in broadband radiation amplifiers, or to achieve passive compression of smoothly frequency modulated microwave pulses. The paper presents results of experiments using a solid state source to produce an optimised frequency-chirped input pulse and amplified by a high power Travelling Wave Tube Amplifier (TWTA). The waveforms of the input and output microwave signals were captured on a UHF Digital Storage Oscilloscope. The results demonstrated at 5.7kW input power levels that X-band radiation pulses of 67ns duration with 5% frequency modulation can be compressed into a 2.8ns pulse having 12 times higher peak power, whilst retaining 50% of the energy in the input signal. The technique offers great potential for scaling to higher frequencies and power levels
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