51,180 research outputs found
The flares of August 1972
Analysis is made of observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra. In each flare the observations fit a model of particle acceleration in the chromosphere with emission produced by impart and by heating by the energetic electrons and protons. The region showed twisted flux and high gradients from birth, and flares appear due to strong magnetic shears and gradients across the neutral line produced by sunspot motions. Post flare loops show a strong change from sheared, force-free fields parallel to potential-field-like loops, perpendicular to the neutral line above the surface
Homogeneous SPC/E water nucleation in large molecular dynamics simulations
We perform direct large molecular dynamics simulations of homogeneous SPC/E
water nucleation, using up to molecules. Our large system
sizes allow us to measure extremely low and accurate nucleation rates, down to
, helping close the gap between
experimentally measured rates .
We are also able to precisely measure size distributions, sticking
efficiencies, cluster temperatures, and cluster internal densities. We
introduce a new functional form to implement the Yasuoka-Matsumoto nucleation
rate measurement technique (threshold method). Comparison to nucleation models
shows that classical nucleation theory over-estimates nucleation rates by a few
orders of magnitude. The semi-phenomenological nucleation model does better,
under-predicting rates by at worst, a factor of 24. Unlike what has been
observed in Lennard-Jones simulations, post-critical clusters have temperatures
consistent with the run average temperature. Also, we observe that
post-critical clusters have densities very slightly higher, , than
bulk liquid. We re-calibrate a Hale-type vs. scaling relation using
both experimental and simulation data, finding remarkable consistency in over
orders of magnitude in the nucleation rate range, and K in the
temperature range.Comment: Accepted for publication in the Journal of Chemical Physic
Effects of wear on structure-sensitive magnetic properties of ceramic ferrite in contact with magnetic tape
Wear experiments and electron microscopy and diffraction studies were conducted to examine the wear and deformed layers in single-crystal Mn-Zn (ceramic) ferrite magnetic head material in contact with magnetic tape and the effects of that contact on magnetic properties. The crystalline state of the single-crystal magnetic head was changed drastically during the sliding process. A nearly amorphous structure was produced on its wear surface. Deformation in the surficial layer of the magnetic head was a critical factor in readback signal loss above 2.5 dB. The signal output level was reduced as applied normal load was increased. Considerable plastic flow occurred on the magnetic tape surface with sliding, and the signal loss due to the tape wear was approximately 1 dB
Transversely Polarized Drell-Yan Process and Soft Gluon Resummation in QCD
We calculate the transverse-momentum spectrum of the dilepton in the
transversely polarized Drell-Yan process on the basis of the factorization
theorem in QCD. We take into account universal logarithmically enhanced
corrections in edge region of phase space by resumming multiple soft-gluon
emissions to all orders in the small region.Comment: 84 pages, 5 figures, Revised version published in Prog.Theor.Phy
Martian sample sites: Examples based on a global geologic perspective
Ten areas were selected that each include several rock units of varying lithology and age. These areas were chosen to optimize the geologic and chronologic data return from Mars. Geologic mapping and stratigraphic studies identify stratigraphic ages, rock types, and information on Martian geologic history that samples of a given site may yield. Volcanic rocks occur over much of the planet and in virtually all stratigraphic positions, and they are amenable to radioisotopic dating. Therefore, a reasonable and essential goal for a sample return mission is to return datable rocks from widely varying strata. Generally, about three or four major geologic units can be sampled at any of the given sites, most of which can probably be dated. The Mars Observer mission will aid greatly in interpreting lithology and defining contacts at the high resolution required to actually pinpoint good sample acquisition sites within these areas
Single-cycle THz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3
Using the tilted-pulse-intensity-front scheme, we generate single-cycle
terahertz (THz) pulses by optical rectification of femtosecond laser pulses in
LiNbO3. In the THz generation setup, the condition that the image of the
grating coincides with the tilted-optical-pulse front is fulfilled to obtain
optimal THz beam characteristics and pump-to-THz conversion efficiency. The
designed focusing geometry enables tight focus of the collimated THz beam with
a spot size close to the diffraction limit, and the maximum THz electric field
of 1.2 MV/cm is obtained
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