40,153 research outputs found
The Small Observed Baryon Asymmetry from a Large Lepton Asymmetry
Primordial Big-Bang Nucleosynthesis (BBN) tightly constrains the existence of
any additional relativistic degrees of freedom at that epoch. However a large
asymmetry in electron neutrino number shifts the chemical equilibrium between
the neutron and proton at neutron freeze-out and allows such additional
particle species. Moreover, the BBN itself may also prefer such an asymmetry to
reconcile predicted element abundances and observations. However, such a large
asymmetry appears to be in conflict with the observed small baryon asymmetry if
they are in sphaleron mediated equilibrium. In this paper we point out the
surprising fact that in the Standard Model, if the asymmetries in the electron
number and the muon number are equal (and opposite) and of the size required to
reconcile BBN theory with observations, a baryon asymmetry of the Universe of
the correct magnitude and sign is automatically generated within a factor of
two. This small remaining discrepancy is naturally remedied in the
supersymmetric Standard Model.Comment: 14 page
Application of the scalar and vector potentials to the aerodynamics of jets
The applicability of a method based on the Stokes potentials (vector and scalar potentials) to computations associated with the aerodynamics of jets was examined. The aerodynamic field near the nozzle could be represented and that the influence of a nonuniform velocity profile at the nozzle exit plane could be determined. Also computations were made for an axisymmetric jet exhausting into a quiescient atmosphere. The velocity at the axis of the jet, and the location of the half-velocity points along the jet yield accurate aerodynamic field computations. Inconsistencies among the different theoretical characterizations of jet flowfields are shown
A Mathematical Model for Estimating Biological Damage Caused by Radiation
We propose a mathematical model for estimating biological damage caused by
low-dose irradiation. We understand that the Linear Non Threshold (LNT)
hypothesis is realized only in the case of no recovery effects. In order to
treat the realistic living objects, our model takes into account various types
of recovery as well as proliferation mechanism, which may change the resultant
damage, especially for the case of lower dose rate irradiation. It turns out
that the lower the radiation dose rate, the safer the irradiated system of
living object (which is called symbolically "tissue" hereafter) can have
chances to survive, which can reproduce the so-called dose and dose-rate
effectiveness factor (DDREF).Comment: 22 pages, 6 Figs, accepted in Journal of the Physical Society of
Japa
Semi-Classical Description of Antiproton Capture on Atomic Helium
A semi-classical, many-body atomic model incorporating a momentum-dependent
Heisenberg core to stabilize atomic electrons is used to study antiproton
capture on Helium. Details of the antiproton collisions leading to eventual
capture are presented, including the energy and angular momentum states of
incident antiprotons which result in capture via single or double electron
ionization, i.e. into [He or He], and the
distribution of energy and angular momentum states following the Auger cascade.
These final states are discussed in light of recently reported, anomalously
long-lived antiproton states observed in liquid He.Comment: 15 pages, 9 figures may be obtained from authors, Revte
ATMOS Spacelab 1 science investigation
Existing infrared spectra from high speed interferometer balloon flights were analyzed and experimental analysis techniques applicable to similar data from the ATMOS experiment (Spacelab 3) were investigated. Specific techniques under investigation included line-by-line simulation of the spectra to aid in the identification of absorbing gases, simultaneous retrieval of pressure and temperature profiles using carefully chosen pairs of CO2 absorption lines, and the use of these pressures and temperatures in the retrieval of gas concentration profiles for many absorbing species. A search for a new absorption features was also carried out, and special attention was given to identification of absorbing gases in spectral bandpass regions to be measured by the halogen occultation experiment
Effects of marine reserves in the context of spatial and temporal variation:an analysis using Bayesian zero-inflated mixed models
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Ecological relationships between marine microorganisms and hydrocarbons in the OEI study area, Louisiana
Supported by Gulf Universities Research Consortium, Project #OE73HJMCataloged from imperfect copy: all after leaf 20 wantingSeven cruise projects were conducted in association with the Louisiana Offshore Ecological Investigation (OEI) to determine the relationships between microorganisms and hydrocarbons in surface waters. Techniques were developed to take surface samples and to determine bacterial numbers, hydrocarbon content, and the response of indigenous microorganisms to various added hydrocarbon molecules. The numbers of heterotrophic bacteria as determined by dilution techniques varied from 10 to 10,000 per ml. The hydrocarbon oxidizing organisms varied from 10 to 100,000 per liter with maxima in the month of January. Hydrocarbon concentrations varied from 0.03 to 0.6 micrograms per liter. There was no correlation between the numbers of oil degraders and hydrocarbon concentration found. This may be the result of the in situ low concentrations of hydrocarbons which would limit microbial response. The numbers of bacteria and hydrocarbons were similar to control areas in the eastern and western parts of the Gulf. BOD experiments conducted to measure the response of the microorganisms to various low and high molecular weight paraffinic and aromatic hydrocarbons indicated that all hydrocarbons were oxidized by some of the mixed indigenous microorganisms. These data suggest that an adequate inoculum was naturally present to respond to oil contamination in nature. The high numbers of hydrocarbon oxidizing microorganisms associated with January hydrographic data may indicate that the upland leaching and other contamination of hydrocarbons in the Mississippi River produce the noted microbial response for that month. The dominant saturated hydrocarbons and isoprenoids ranged from C-15 to C-41. Water from Timbalier Bay generally contained higher concentrations than offshore samples and exhibited a more pronounced odd-even preference in the range C-24 to C-33. GC-MS analysis of the dominant paraffins revealed a characteristic biomodal distribution dominated by C-17 and pristane and C-25 to C-35 with an unresolved envelope. No buildup of specific n-paraffin molecules was found, which data corresponded to BOD results of added hydrocarbons to indigenous microflora.Marine Scienc
Retrieval of upper atmosphere pressure-temperature profiles from high resolution solar occultation spectra
Pressure-temperature profiles over the 18 to 75 km altitude range were retrieved from 0.01 cm(-1) resolution infrared solar absorption spectra recorded with the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer operating in the solar occultation mode during the Spacelab 3 shuttle mission (April 30 to May 1, 1985). The analysis method is described and preliminary results deduced for five occultation events are compared to correlative pressure-temperature measurments
Structural Estimation and Solution of International Trade Models with Heterogeneous Firms
We present an empirical implementation of a general-equilibrium model of international trade with heterogeneous manufacturing firms. The theory underlying our model is consistent with Melitz (2003). A nonlinear structural estimation procedure identifies a set of core parameters and unobserved firm-level trade frictions that best fit the geographic pattern of trade. Once the parameters are identified, we utilize a decomposition technique for computing general-equilibrium counterfactuals. We illustrate this technique using trade and protection data from the Global Trade Analysis Project (GTAP). We first assess the economic effects of reductions in measured tariffs. Taking the simple-average welfare change across regions the Melitz structure indicates welfare gains from liberalization that are nearly four times larger than in a standard policy simulation model. Furthermore, when we compare the economic impact of tariffs with reductions in estimated fixed trade costs we find that policy measures affecting the fixed costs of firmentry are of greater importance than conventional tariff barriers.
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