10,115 research outputs found
Golden Desert Speech and Debate
Health and well- being of kids.https://digitalscholarship.unlv.edu/educ_sys_202/1019/thumbnail.jp
Crystal-controlled multivibrator
Method is described for designing crystal oscillator which has frequency and symmetry stability suitable for system-clock-generators used in spacecraft data systems. Simple multivibrator is used in which timing capacitor is replaced by a crystal
Vibrations and Relaxations in a Soft Sphere Glass: Boson Peak and Structure Factors
The dynamics of a soft sphere model glass, studied by molecular dynamics, is
investigated. The vibrational density of states divided by shows a
pronounced boson peak. Its shape is in agreement with the universal form
derived for soft oscillators interacting with sound waves. The excess
vibrations forming the boson peak have mainly transverse character. From the
dynamic structure factor in the Brillouin regime pseudo dispersion curves are
calculated. Whereas the longitudinal phonons are well defined up to the pseudo
zone boundary the transverse ones rapidly get over-damped and go through the
Ioffe-Regel limit near the boson peak frequency. In the high regime
constant- scans of the dynamic structure factor for frequencies around
the boson peak are clearly distinct from those for zone boundary frequencies.
Above the Brillouin regime, the scans for the low frequency modes follow
closely the static structure factor. This still holds after a deconvolution of
the exact harmonic eigenmodes into local and extended m odes. Also the
structure factor for local relaxations at finite temperatures resembles the
static one. This semblance between the structure factors mirrors the collective
motion of chain like structures in both low frequency vibrations and atomic
hopping processes, observed in the earlier investigations
Diffusion of hydrogen in transition metals
The mobility of interstitial atoms is closely correlated with their vibrational behaviour. Not only can the classical (hopping) activation energy be evaluated with good accuracy from the vibrational spectrum, but also low temperature tunnelling rates are strongly related to vibrations. Because of their small mass interstitial hydrogen atoms constitute an ideal probe to study this correlation over a large temperature range (0 K < T < 300 K). Hydrogen atoms vibrate mainly with localized (optical) modes but also with strongly distorted lattice vibrations (short-wavelength acoustic modes). These vibrations lead to a "dressing" of the tunnelling element. More interesting, they determine the temperature dependence of the diffusion constant (at low temperatures together with electronic terms). Using a realistic description of the vibrations as input we calculate the diffusion constants quantitatively. We present results for hydrogen in niobium and in lutetium
Characteristic polyhedra of singularities without completion -- Part II
Hironaka's characteristic polyhedron is an important combinatorial object
reflecting the local nature of a singularity. We prove that it can be
determined without passing to the completion if the local ring is a G-ring and
if additionally either it is Henselian, or a certain polynomiality condition holds, or a mild condition on the singularity holds.
For example, the latter is fulfilled if the residue field is perfect.Comment: 46 pages; minor change
An irreducibility criterion for power series
We prove an irreducibility criterion for polynomials with power series
coefficients generalizing previous known results concerning quasi-ordinary
polynomials
No Vacuum Cerenkov Radiation Losses in the Timelike Lorentz-Violating Chern-Simons Theory
In a Lorentz- and CPT-violating modification of electrodynamics that includes
a timelike Chern-Simons term, there are no energy losss through vacuum Cerenkov
radiation. A charge moving with a constant velocity does not lose energy,
because of an unusual cancellation. Higher frequency modes of the
electromagnetic field carry away positive energy, but lower frequency modes
carry away a compensating negative amount of energy.Comment: 11 page
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