5,054 research outputs found
Wage and Occupational Differences Between Black and White Men: Labor Market Discrimination in the Rural South
The existence of labor market discrimination based on race is well established.However, study continues into a variety of aspects of discrimination-among them the extent to which it exists in different regions. Gwartney has estimated the ratio of black to white earnings to be between .83 and .88 for the North and between .68 and .74 for the South. Masters, in a study of earnings differentials between black and white men, found a ratio of .79 for the non-South and .69 for the South. Although considerable literature has developed concerning earnings differentials, wage discrimination in rural areas is one topic which has received relatively little attention. In an attempt to eliminate this oversight this paper concentrates on the extent of wage differences between black and white men in the rural South attributable to labor market discrimination
One-dimensional time-dependent fluid model of a very high density low-pressure inductively coupled plasma
A time-dependent two-fluid model has been developed to understand axial variations in the plasma parameters in a very high density (peak n_e ≳5×10^(19)  m^(−3)) argon inductively coupled discharge in a long 1.1 cm radius tube. The model equations are written in 1D with radial losses to the tube walls accounted for by the inclusion of effective particle and energy sink terms. The ambipolar diffusion equation and electron energy equation are solved to find the electron density n_e (z,t) and temperature T_e (z,t), and the populations of the neutral argon 4s metastable, 4s resonant, and 4pexcited state manifolds are calculated to determine the stepwise ionization rate and calculate radiative energy losses. The model has been validated through comparisons with Langmuir probe ion saturation current measurements; close agreement between the simulated and measured axial plasma density profiles and the initial density rise rate at each location was obtained at pAr =30−60 mTorr. We present detailed results from calculations at 60 mTorr, including the time-dependent electron temperature, excited state populations, and energy budget within and downstream of the radiofrequency antenna
Battery-powered pulsed high density inductively coupled plasma source for pre-ionization in laboratory astrophysics experiments
An electrically floating radiofrequency (RF) pre-ionization plasma source has been developed to enable neutral gas breakdown at lower pressures and to access new experimental regimes in the Caltech laboratory astrophysics experiments. The source uses a customized 13.56 MHz class D RF power amplifier that is powered by AA batteries, allowing it to safely float at 3–6 kV with the electrodes of the high voltage pulsed power experiments. The amplifier, which is capable of 3 kW output power in pulsed (<1 ms) operation, couples electrical energy to the plasma through an antenna external to the 1.1 cm radius discharge tube. By comparing the predictions of a global equilibrium discharge model with the measured scalings of plasma density with RF power input and axial magnetic field strength, we demonstrate that inductive coupling (rather than capacitive coupling or wave damping) is the dominant energy transfer mechanism. Peak ion densities exceeding 5 × 10^(19) m^(−3) in argon gas at 30 mTorr have been achieved with and without a background field. Installation of the pre-ionization source on a magnetohydrodynamically driven jet experiment reduced the breakdown time and jitter and allowed for the creation of hotter, faster argon plasma jets than was previously possible
Emission and afterglow properties of an expanding RF plasma with nonuniform neutral gas density
We describe some notable aspects of the light emission and afterglow properties in pulsed, high-density (10^(18)–10^(20) m^(−3) argon inductively coupled discharges initiated following fast gas injection. The plasma was created in a long, narrow discharge tube and then expanded downstream of the radiofrequency (RF) antenna into a large chamber. Fast camera images of the expanding plasma revealed a multi-phase time-dependent emission pattern that did not follow the ion density distribution. Dramatic differences in visible brightness were observed between discharges with and without an externally applied magnetic field. These phenomena were studied by tracking excited state populations using passive emission spectroscopy and are discussed in terms of the distinction between ionizing and recombining phase plasmas. Additionally, a method is presented for inferring the unknown neutral gas pressure in the discharge tube from the time-dependent visible and infrared emission measured by a simple photodiode placed near the antenna. In magnetized discharges created with fast gas injection, the downstream ion density rose by Δn_i ∼10^(18) m^(−3) in the first ∼100 μs after the RF power was turned off. The conditions conducive to this afterglow density rise are investigated in detail, and the effect is tentatively attributed to pooling ionization
Higgs ID at the LHC
We make a complete catalog of extended Higgs sectors involving SU(2)_L
doublets and singlets, subject to natural flavor conservation. In each case we
present the couplings of a light neutral CP-even Higgs state h in terms of the
model parameters, and identify which models are distinguishable in principle
based on this information. We also give explicit expressions for the model
parameters in terms of h couplings and exhibit the behaviors of the couplings
in the limit where the deviations from the Standard Model Higgs couplings are
small. Finally we discuss prospects for differentiation of extended Higgs
models based on measurements at the LHC and ILC and identify the regions in
which these experiments could detect deviations from the SM Higgs predictions.Comment: 46 pages, 6 figures, 2 tables, PRD versio
Long Range Hops and the Pair Annihilation Reaction A+A->0: Renormalization Group and Simulation
A simple example of a non-equilibrium system for which fluctuations are
important is a system of particles which diffuse and may annihilate in pairs on
contact. The renormalization group can be used to calculate the time dependence
of the density of particles, and provides both an exact value for the exponent
governing the decay of particles and an epsilon-expansion for the amplitude of
this power law. When the diffusion is anomalous, as when the particles perform
Levy flights, the critical dimension depends continuously on the control
parameter for the Levy distribution. The epsilon-expansion can then become an
expansion in a small parameter. We present a renormalization group calculation
and compare these results with those of a simulation.Comment: As-published version; two significant errors fixed, two references
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Investigation of external refrigeration systems for long term cryogenic storage Final report
Data on external refrigeration systems for space storage of cryogens for long period
Investigation of external refrigeration systems for long-term cryogenic storage
Evaluation of cryogenic refrigeration systems for space application
LHC discovery potential for supersymmetry with \sqrt{s}=7 TeV and 5-30 fb^{-1}
We extend our earlier results delineating the supersymmetry (SUSY) reach of
the CERN Large Hadron Collider operating at a centre-of-mass energy \sqrt{s}=7
TeV to integrated luminosities in the range 5 - 30 fb^{-1}. Our results are
presented within the paradigm minimal supergravity model (mSUGRA or CMSSM).
Using a 6-dimensional grid of cuts for the optimization of signal to background
ratio -- including missing E_T-- we find for m(gluino) \sim m(squark) an LHC
5\sigma SUSY discovery reach of m(gluino) \sim 1.3,\ 1.4,\ 1.5 and 1.6 TeV for
5, 10, 20 and 30 fb^{-1}, respectively. For m(squark)>> m(gluino), the
corresponding reach is instead m(gluino)\sim 0.8,\ 0.9,\ 1.0 and 1.05 TeV, for
the same integrated luminosities.Comment: 7 pages with 2 .eps figure. In version 2, a new figure has been added
along with associated discussio
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