1,941 research outputs found
IUE spectra of a flare in HR 5110: A flaring RS CVn or Algol system?
Ultraviolet spectra of the RS CVn type binary system HR 5110 were obtained with IUE on May 31, 1979 during a period of intense radio flaring of this star. High temperature transition region lines are present, but are not enhanced above observed quiescent strengths. The similarities of HR 5110 to the Algol system, As Eri, suggest that the 1979 May to June flare may involve mass exchange rather than annihilation of coronal magnetic fields
Time Dependent Effects and Transport Evidence for Phase Separation in La_{0.5}Ca_{0.5}MnO_{3}
The ground state of La_{1-x}Ca_{x}MnO_{3} changes from a ferromagnetic
metallic to an antiferromagnetic charge-ordered state as a function of Ca
concentration at x ~ 0.50. We present evidence from transport measurements on a
sample with x = 0.50 that the two phases can coexist, in agreement with other
observations of phase separation in these materials. We also observe that, by
applying and then removing a magnetic field to the mainly charge-ordered state
at some temperatures, we can "magnetically anneal" the charge order, resulting
in a higher zero-field resistivity. We also observe logarithmic time dependence
in both resistivity and magnetization after a field sweep at low temperatures.Comment: 9 pages, LATEX, 3 postscript figure
Ultraviolet light curves of U Geminorum and VW Hydri
Ultraviolet light curves were obtained for the quiescent dwarf novae U Gem and VW Hyi. The amplitude of the hump associated with the accretion hot spot is much smaller in the UV than in the visible. This implies that the bright spot temperature is roughly 12000 K if it is optically thick. The flux distribution of U Gem in quiescence cannot be fitted by model spectra of steady state, viscous accretion disks. The absolute luminosity, the flux distribution, and the far UV spectrum suggest that the primary star is visible in the far UV. The optical UV flux distribution of VW Hyi can be matched roughly by the model accretion disks
Low Temperature Spin Freezing in Dy2Ti2O7 Spin Ice
We report a study of the low temperature bulk magnetic properties of the spin
ice compound Dy2Ti2O7 with particular attention to the (T < 4 K) spin freezing
transition. While this transition is superficially similar to that in a spin
glass, there are important qualitative differences from spin glass behavior:
the freezing temperature increases slightly with applied magnetic field, and
the distribution of spin relaxation times remains extremely narrow down to the
lowest temperatures. Furthermore, the characteristic spin relaxation time
increases faster than exponentially down to the lowest temperatures studied.
These results indicate that spin-freezing in spin ice materials represents a
novel form of magnetic glassiness associated with the unusual nature of
geometrical frustration in these materials.Comment: 24 pages, 8 figure
Coercive Field and Magnetization Deficit in Ga(1-x)Mn(x)As Epilayers
We have studied the field dependence of the magnetization in epilayers of the
diluted magnetic semiconductor Ga(1-x)Mn(x)As for 0.0135 < x < 0.083.
Measurements of the low temperature magnetization in fields up to 3 T show a
significant deficit in the total moment below that expected for full saturation
of all the Mn spins. These results suggest that the spin state of the
non-ferromagnetic Mn spins is energetically well separated from the
ferromagnetism of the bulk of the spins. We have also studied the coercive
field (Hc) as a function of temperature and Mn concentration, finding that Hc
decreases with increasing Mn concentration as predicted theoretically.Comment: 15 total pages -- 5 text, 1 table, 4 figues. Accepted for publication
in MMM 2002 conference proceedings (APL
Quantum Mechanics, Common Sense and the Black Hole Information Paradox
The purpose of this paper is to analyse, in the light of information theory
and with the arsenal of (elementary) quantum mechanics (EPR correlations,
copying machines, teleportation, mixing produced in sub-systems owing to a
trace operation, etc.) the scenarios available on the market to resolve the
so-called black-hole information paradox. We shall conclude that the only
plausible ones are those where either the unitary evolution of quantum
mechanics is given up, in which information leaks continuously in the course of
black-hole evaporation through non-local processes, or those in which the world
is polluted by an infinite number of meta-stable remnants.Comment: 15 pages, Latex, CERN-TH.6889/9
Performance of a GridPix detector based on the Timepix3 chip
A GridPix readout for a TPC based on the Timepix3 chip is developed for
future applications at a linear collider. The GridPix detector consists of a
gaseous drift volume read out by a single Timepix3 chip with an integrated
amplification grid. Its performance is studied in a test beam with 2.5 GeV
electrons. The GridPix detector detects single ionization electrons with high
efficiency. The Timepix3 chip allowed for high sample rates and time walk
corrections. Diffusion is found to be the dominating error on the track
position measurement both in the pixel plane and in the drift direction, and
systematic distortions in the pixel plane are below 10 m. Using a
truncated sum, an energy loss (dE/dx) resolution of 4.1% is found for an
effective track length of 1 m.Comment: To be published in Nuclear Instruments and Methods in Physics
Research Section
Flux through a hole from a shaken granular medium
We have measured the flux of grains from a hole in the bottom of a shaken
container of grains. We find that the peak velocity of the vibration, vmax,
controls the flux, i.e., the flux is nearly independent of the frequency and
acceleration amplitude for a given value of vmax. The flux decreases with
increasing peak velocity and then becomes almost constant for the largest
values of vmax. The data at low peak velocity can be quantitatively described
by a simple model, but the crossover to nearly constant flux at larger peak
velocity suggests a regime in which the granular density near the container
bottom is independent of the energy input to the system.Comment: 14 pages, 4 figures. to appear in Physical Review
Field induced transitions in a kagome antiferromagnet
The thermal order by disorder effect in magnetic field is studied for a
classical Heisenberg antiferromagnet on the kagome lattice. Using analytical
arguments we predict a unique H-T phase diagram for this strongly frustrated
magnet: states with a coplanar and a uniaxial triatic order parameters
respectively at low and high magnetic fields and an incompressible collinear
spin-liquid state at a one-third of the saturation field. We also present the
Monte Carlo data which confirm existence of these phases.Comment: 4 pages, 2 figures, accepted versio
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