7,127 research outputs found
Hysteresis and competition between disorder and crystallization in sheared and vibrated granular flow
Experiments on spherical particles in a 3D Couette cell vibrated from below
and sheared from above show a hysteretic freezing/melting transition. Under
sufficient vibration a crystallized state is observed, which can be melted by
sufficient shear. The critical line for this transition coincides with equal
kinetic energies for vibration and shear. The force distribution is
double-peaked in the crystalline state and single-peaked with an approximately
exponential tail in the disordered state. A linear relation between pressure
and volume () exists for a continuum of partially and/or
intermittently melted states over a range of parameters
An explanation of the Newman-Janis Algorithm
After the original discovery of the Kerr metric, Newman and Janis showed that
this solution could be ``derived'' by making an elementary complex
transformation to the Schwarzschild solution. The same method was then used to
obtain a new stationary axisymmetric solution to Einstein's field equations now
known as the Kerr-newman metric, representing a rotating massive charged black
hole. However no clear reason has ever been given as to why the Newman-Janis
algorithm works, many physicist considering it to be an ad hoc procedure or
``fluke'' and not worthy of further investigation. Contrary to this belief this
paper shows why the Newman-Janis algorithm is successful in obtaining the
Kerr-Newman metric by removing some of the ambiguities present in the original
derivation. Finally we show that the only perfect fluid generated by the
Newman-Janis algorithm is the (vacuum) Kerr metric and that the only Petrov
typed D solution to the Einstein-Maxwell equations is the Kerr-Newman metric.Comment: 14 pages, no figures, submitted to Class. Quantum Gra
Calculations of polarizabilities and hyperpolarizabilities for the Be ion
The polarizabilities and hyperpolarizabilities of the Be ion in the
state and the state are determined. Calculations are performed
using two independent methods: i) variationally determined wave functions using
Hylleraas basis set expansions and ii) single electron calculations utilizing a
frozen-core Hamiltonian. The first few parameters in the long-range interaction
potential between a Be ion and a H, He, or Li atom, and the leading
parameters of the effective potential for the high- Rydberg states of
beryllium were also computed. All the values reported are the results of
calculations close to convergence. Comparisons are made with published results
where available.Comment: 18 pp; added details to Sec. I
Fine Structure of the 1s3p ^3P_J Level in Atomic ^4He: Theory and Experiment
We report on a theoretical calculation and a new experimental determination
of the 1s3p ^3P_J fine structure intervals in atomic ^4He. The values from the
theoretical calculation of 8113.730(6) MHz and 658.801(6) MHz for the nu_{01}
and nu_{12} intervals, respectively, disagree significantly with previous
experimental results. However, the new laser spectroscopic measurement reported
here yields values of 8113.714(28) MHz and 658.810(18) MHz for these intervals.
These results show an excellent agreement with the theoretical values and
resolve the apparent discrepancy between theory and experiment.Comment: 9 pages, 3 figure
The evolutionary state of short-period magnetic white dwarf binaries
We present phase-resolved spectroscopy of two new short-period low accretion rate magnetic binaries, SDSS J125044.42+154957.3 (Porb= 86 min) and SDSS J151415.65+074446.5 (Porb= 89 min). Both systems were previously identified as magnetic white dwarfs from the Zeeman splitting of the Balmer absorption lines in their optical spectra. Their spectral energy distributions exhibit a large near-infrared excess, which we interpret as a combination of cyclotron emission and possibly a late-type companion star. No absorption features from the companion are seen in our optical spectra. We derive the orbital periods from a narrow, variable Hα emission line which we show to originate on the companion star. The high radial velocity amplitude measured in both systems suggests a high orbital inclination, but we find no evidence for eclipses in our data. The two new systems resemble the polar EF Eri in its prolonged low state and also SDSS J121209.31+013627.7, a known magnetic white dwarf plus possible brown dwarf binary, which was also recovered by our method
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