45,118 research outputs found
Spin-polarized states of nuclear matter
The equations of state of spin-polarized nuclear matter and pure neutron
matter are studied in the framework of the Brueckner-Hartree-Fock theory
including a three-body force. The energy per nucleon calculated
in the full range of spin polarization for symmetric nuclear matter
and pure neutron matter fulfills a parabolic law. In both cases the
spin-symmetry energy is calculated as a function of the baryonic density along
with the related quantities such as the magnetic susceptibility and the Landau
parameter . The main effect of the three-body force is to strongly reduce
the degenerate Fermi gas magnetic susceptibility even more than the value with
only two body force. The EOS is monotonically increasing with the density for
all spin-aligned configurations studied here so that no any signature is found
for a spontaneous transition to a ferromagnetic state.Comment: Contribution to GISELDA Meeting, 14-18 January, 2002 (Frascati), to
appear in World Scientific (Singapore
Optimization of Dimples in Microchannel Heat Sink with Impinging Jets—Part B: the Influences of Dimple Height and Arrangement
The combination of a microchannel heat sink with impinging jets and dimples (MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design
Stratospheric circulation studies based on Tiros 7, 15-micron data Final report
Stratospheric temperature distribution data based on Tiros 7 radiometer dat
NIMBUS-5 sounder data processing system. Part 2: Results
The Nimbus-5 spacecraft carries infrared and microwave radiometers for sensing the temperature distribution of the atmosphere. Methods developed for obtaining temperature profiles from the combined set of infrared and microwave radiation measurements are described. Algorithms used to determine (a) vertical temperature and water vapor profiles, (b) cloud height, fractional coverage, and liquid water content, (c) surface temperature, and (d) total outgoing longwave radiation flux are described. Various meteorological results obtained from the application of the Nimbus-5 sounding data processing system during 1973 and 1974 are presented
Acoustic waves and heating due to molecular energy transfer in an electric discharge CO laser
This paper summarizes analytical studies and the interpretation of experimental results for the compression and rarefaction waves generated in the cavity of a pulsed CO electric discharge laser. A one-dimensional analysis of acoustic waves is applied to a transversely excited laser. The influences of heating in the cathode fall, heat transfer to the cathode, flow through both the anode and cathode, and bulk heating of the plasma are included. The analysis is used to relate the bulk heating rate to observable features of the pressure and density waves. Data obtained from interferograms and reported elsewhere are used to infer the bulk heating rates in a pulsed CO laser. Results are presented for CO/Ar, CO/N2, and N2 plasmas. Comparison of the data with recent theoretical results for the heating due to electron/ neutral collisions and the anharmonic defect associated with V-V energy transfer shows substantial differences at lower values of total energy deposition. The change of heating with E/N is in fairly good agreement with predicted values
Resonant Clumping and Substructure in Galactic Discs
We describe a method to extract resonant orbits from N-body simulations
exploiting the fact that they close in a frame rotating with a constant pattern
speed. Our method is applied to the N-body simulation of the Milky Way by Shen
et al. (2010). This simulation hosts a massive bar, which drives strong
resonances and persistent angular momentum exchange. Resonant orbits are found
throughout the disc, both close to the bar itself and out to the very edges of
the disc. Using Fourier spectrograms, we demonstrate that the bar is driving
kinematic substructure even in the very outer parts of the disc. We identify
two major orbit families in the outskirts of the disc that make significant
contributions to the kinematic landscape, namely the m:l = 3:-2 and 1:-1
families resonating with the pattern speed of the bar. A mechanism is described
that produces bimodal distributions of Galactocentric radial velocities at
selected azimuths in the outer disc. It occurs as a result of the temporal
coherence of particles on the 3:-2 resonant orbits, which causes them to arrive
simultaneously at pericentre or apocentre. This resonant clumping, due to the
in-phase motion of the particles through their epicycle, leads to both inward
and outward moving groups which belong to the same orbital family and
consequently produce bimodal radial velocity distributions. This is a possible
explanation of the bimodal velocity distributions observed towards the Galactic
anti-Centre by Liu et al. (2012). Another consequence is that transient
overdensities appear and dissipate (in a symmetric fashion) on timescales equal
to the their epicyclic period resulting in a periodic pulsing of the disc's
surface density.Comment: 11 Figures, 1 Table. Accepted for publication in ApJ. Version 2
reflects minor changes to the text. Animation referenced in Figure 7 is
available at http://hubble.shao.ac.cn/~shen/resonantclumping/DensMovie.mp
Data acquisition and path selection decision making for an autonomous roving vehicle
Problems related to the guidance of an autonomous rover for unmanned planetary exploration were investigated. Topics included in these studies were: simulation on an interactive graphics computer system of the Rapid Estimation Technique for detection of discrete obstacles; incorporation of a simultaneous Bayesian estimate of states and inputs in the Rapid Estimation Scheme; development of methods for estimating actual laser rangefinder errors and their application to date provided by Jet Propulsion Laboratory; and modification of a path selection system simulation computer code for evaluation of a hazard detection system based on laser rangefinder data
Pulsed THz radiation due to phonon-polariton effect in [110] ZnTe crystal
Pulsed terahertz (THz) radiation, generated through optical rectification
(OR) by exciting [110] ZnTe crystal with ultrafast optical pulses, typically
consists of only a few cycles of electromagnetic field oscillations with a
duration about a couple of picoseconds. However, it is possible, under
appropriate conditions, to generate a long damped oscillation tail (LDOT)
following the main cycles. The LDOT can last tens of picoseconds and its
Fourier transform shows a higher and narrower frequency peak than that of the
main pulse. We have demonstrated that the generation of the LDOT depends on
both the duration of the optical pulse and its central wavelength. Furthermore,
we have also performed theoretical calculations based upon the OR effect
coupled with the phonon-polariton mode of ZnTe and obtained theoretical THz
waveforms in good agreement with our experimental observation.Comment: 9 pages, 5 figure
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