6,935 research outputs found
Theoretical studies of solar-pumped lasers
The power output of a black body solar-pumped laser as a function of time (computer graphic solutions) and under steady state conditions (analytic conditions); computer analyses of polymerization using lasers; and metallic sodium as a laser medium were studied
Theoretcial studies of solar-pumped lasers
A method of pumping a COhZ laser by a hot cavity was demonstrated. The cavity, heated by solar radiation, should increase the efficiency of solar pumped lasers used for energy conversion. Kinetic modeling is used to examine the behavior of such a COhZ laser. The kinetic equations are solved numerically vs. time and, in addition, steady state solutions are obtained analytically. The effect of gas heating filling the lower laser level is included. The output power and laser efficiency are obtained as functions of black body temperature and gas ratios (COhZ-He-Ar) and pressures. The values are compared with experimental results
Theoretical studies of solar-pumped lasers
In any lasing medium the emission wavelength should be chosen where there is little self absorption. As emission and absorption spectra for metallic vapors did not seem available, therefore, estimates were made of these cross sections for sodium vapor as functions of wavelength. Although absolute values were not obtained, information on where the emission wavelength should occur became evident. The method of obtaining quantities proportional to the cross sections versus wavelength is outlined. A further comparison based on alternative expressions for the absorption and emission cross sections over a limited wavelength range is made
Supercritical multicomponent solvent coal extraction
The yield of organic extract from the supercritical extraction of coal with larger diameter organic solvents such as toluene is increased by use of a minor amount of from 0.1 to 10% by weight of a second solvent such as methanol having a molecular diameter significantly smaller than the average pore diameter of the coal
A "kilonova" associated with short-duration gamma-ray burst 130603B
Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic
gamma-rays, lasting less than ~2 s, whose origin is one of the great unsolved
questions of astrophysics today. While the favoured hypothesis for their
production, a relativistic jet created by the merger of two compact stellar
objects (specifically, two neutron stars, NS-NS, or a neutron star and a black
hole, NS-BH), is supported by indirect evidence such as their host galaxy
properties, unambiguous confirmation of the model is still lacking. Mergers of
this kind are also expected to create significant quantities of neutron-rich
radioactive species, whose decay should result in a faint transient in the days
following the burst, a so-called "kilonova". Indeed, it is speculated that this
mechanism may be the predominant source of stable r-process elements in the
Universe. Recent calculations suggest much of the kilonova energy should appear
in the near-infrared (nIR) due to the high optical opacity created by these
heavy r-process elements. Here we report strong evidence for such an event
accompanying SGRB 130603B. If this simplest interpretation of the data is
correct, it provides (i) support for the compact object merger hypothesis of
SGRBs, (ii) confirmation that such mergers are likely sites of significant
r-process production and (iii) quite possibly an alternative, un-beamed
electromagnetic signature of the most promising sources for direct detection of
gravitational waves.Comment: preprint of paper appearing in Nature (3 Aug 2013
Leptogenesis from Soft Supersymmetry Breaking (Soft Leptogenesis)
Soft leptogenesis is a scenario in which the cosmic baryon asymmetry is
produced from a lepton asymmetry generated in the decays of heavy sneutrinos
(the partners of the singlet neutrinos of the seesaw) and where the relevant
sources of CP violation are the complex phases of soft supersymmetry-breaking
terms. We explain the motivations for soft leptogenesis, and review its basic
ingredients: the different CP-violating contributions, the crucial role played
by thermal corrections, and the enhancement of the efficiency from lepton
flavour effects. We also discuss the high temperature regime GeV in
which the cosmic baryon asymmetry originates from an initial asymmetry of an
anomalous -charge, and soft leptogenesis reembodies in -genesis.Comment: References updated. Some minor corrections to match the published
versio
Repetitive Segmental Structure of the Transducin β Subunit: Homology with the CDC4 Gene and Identification of Related mRNAs
Retinal transducin, a guanine nucleotide regulatory protein (referred to as a G protein) that activates a cGMP phosphodiesterase in photoreceptor cells, is comprised of three subunits. We have identified and analyzed cDNA clones of the bovine transducin β subunit that may be highly conserved or identical to that in other G proteins. From the cDNA nucleotide sequence of the entire coding region, the primary structure of a 340-amino acid protein was deduced. The encoded β subunit has a Mr of 37,375 and is comprised of repetitive homologous segments arranged in tandem. Furthermore, significant homology in primary structure and segmental sequence exists between the β subunit and the yeast CDC4 gene product. The Mr 37,375 β subunit polypeptide is encoded by a 2.9-kilobase (kb) mRNA. However, there exists in retina other β-related mRNAs that are divergent from the 2.9-kb mRNA on the basis of oligonucleotide and primer-extended probe hybridizations. All mammalian tissues and clonal cell lines that have been examined contain at least two β-related mRNAs, usually 1.8 and 2.9 kb in length. These results suggest that the mRNAs are the processed products of a small number of closely related genes or of a single highly complex β gene
The Afterglow and Environment of the Short GRB111117A
We present multi-wavelength observations of the afterglow of the short
GRB111117A, and follow-up observations of its host galaxy. From rapid optical
and radio observations we place limits of r \gtrsim 25.5 mag at \deltat \approx
0.55 d and F_nu(5.8 GHz) < 18 \muJy at \deltat \approx 0.50 d, respectively.
However, using a Chandra observation at t~3.0 d we locate the absolute position
of the X-ray afterglow to an accuracy of 0.22" (1 sigma), a factor of about 6
times better than the Swift-XRT position. This allows us to robustly identify
the host galaxy and to locate the burst at a projected offset of 1.25 +/- 0.20"
from the host centroid. Using optical and near-IR observations of the host
galaxy we determine a photometric redshift of z=1.3 (+0.3,-0.2), one of the
highest for any short GRB, and leading to a projected physical offset for the
burst of 10.5 +/- 1.7 kpc, typical of previous short GRBs. At this redshift,
the isotropic gamma-ray energy is E_{gamma,iso} \approx 3\times10^51 erg
(rest-frame 23-2300 keV) with a peak energy of E_{pk} \approx 850-2300 keV
(rest-frame). In conjunction with the isotropic X-ray energy, GRB111117A
appears to follow our recently-reported E_x,iso-E_gamma,iso-E_pk universal
scaling. Using the X-ray data along with the optical and radio non-detections
we find that for a blastwave kinetic energy of E_{K,iso} \approx E_{gamma,iso},
the circumburst density is n_0 \sim 3x10^(-4)-1 cm^-3 (for a range of
epsilon_B=0.001-0.1). Similarly, from the non-detection of a break in the X-ray
light curve at t<3 d, we infer a minimum opening angle for the outflow of
theta_j> 3-10 degrees (depending on the circumburst density). We conclude that
Chandra observations of short GRBs are effective at determining precise
positions and robust host galaxy associations in the absence of optical and
radio detections.Comment: ApJ accepted versio
On graded polynomial identities with an antiautomorphism
AbstractLet G be a commutative monoid with cancellation and let R be a strongly G-graded associative algebra with finite G-grading and with antiautomorphism. Suppose that R satisfies a graded polynomial identity with antiautomorphism. We show that R is a PI algebra
Antarctic polar stratospheric aerosols: The roles of nitrates, chlorides and sulfates
Nitric and hydrochloric acids have been postulated to condense in the winter polar stratosphere to become an important component of polar stratospheric clouds. One implication is that the removal of NO(y) from the gas phase by this mechanism allows high Cl(x) concentrations to react with O3, because the formation of ClNO3 is inhibited. Contributions of NO3 and Cl to the stratospheric aerosol were determined during the 1987 Airborne Antarctic Ozone Experiment by testing for the presence of nitrates and chlorides in the condensed phase. Aerosol particles were collected on four 500 micron diameter gold wires, each pretreated differently to give results that were specific to certain physical and chemical aerosol properties. One wire was carbon-coated for concentration and size analyses by scanning electron microscopy; X-ray energy dispersive analyses permitted the detection of S and Cl in individual particles. Three more wires were coated with Nitron, barium chloride and silver nitrate, respectively, to detect nitrate, sulfate and chloride in aerosol particles. All three ions, viz., sulfates, nitrates and chlorides were detected in the Antarctic stratospheric aerosol. In terms of number concentrations, the aerosol was dominated by sulfates, followed by chlorides and nitrates. An inverse linear regression can be established between nitrate concentrations and ozone mixing ratio, and between temperature and nitrates
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