2,576 research outputs found
Development of passive radiation detectors of improved sensitivity
The future development of a solid track high energy particle detector is discussed. The goal is to improve the sensitivity and lower the threshold of the detector. One most widely used material for such purpose is a plastic commercially known as CR-39. A scheme is presented which involves changing the formula of the monomer, diethylene glycol-bis-allyl carbonate. This is to be accomplished by substituting some heteroatoms for H and substituting sulfur atoms for oxygen in the ether linkages. Use of a new plasticizer to make the etched surface clearer than what has been accomplished as of today is suggested. Possible improvement in acquiring better tracks and increasing the ratio of V sub T/V sub B was planned. This is to be accomplished by changing the composition of the etchants, etching time, and etching temperature
X-Ray Spectroscopy of the Low-Mass X-ray Binaries 2S 0918-549 and 4U1543-624: Evidence for Neon-Rich Degenerate Donors
We present high-resolution spectroscopy of the neutron-star/low-mass X-ray
binaries 2S 0918-549 and 4U 1543-624 with the High Energy Transmission Grating
Spectrometer onboard the Chandra X-ray Observatory and the Reflection Grating
Spectrometer onboard XMM-Newton. Previous low-resolution spectra of both
sources showed a broad line-like feature at 0.7 keV that was originally
attributed to unresolved line emission. We recently showed that this feature
could also be due to excess neutral Ne absorption, and this is confirmed by the
new high-resolution Chandra spectra. The Chandra spectra are each well fit by
an absorbed power-law + blackbody model with a modified Ne/O number ratio of
0.52+/-0.12 for 2S 0918-549 and 1.5+/-0.3 for 4U 1543-624, compared to the
interstellar-medium value of 0.18. The XMM spectrum of 2S 0918-549 is best fit
by an absorbed power-law model with a Ne/O number ratio of 0.46+/-0.03,
consistent with the Chandra result. On the other hand, the XMM spectrum of 4U
1543-624 is softer and less luminous than the Chandra spectrum and has a
best-fit Ne/O number ratio of 0.54+/-0.03. The difference between the measured
abundances and the expected interstellar ratio, as well as the variation of the
column densities of O and Ne in 4U 1543-624, supports the suggestion that there
is absorption local to these binaries. We propose that the variations in the O
and Ne column densities of 4U 1543-624 are caused by changes in the ionization
structure of the local absorbing material. It is important to understand the
effect of ionization on the measured absorption columns before the abundance of
the local material can be determined. This work supports our earlier suggestion
that 2S 0918-549 and 4U 1543-624 are ultracompact binaries with Ne-rich
companions.Comment: 11 pages, 5 figures, major revisions including addition of XMM
spectral analysis, accepted for publication in the Astrophysical Journal,
vol. 59
Characterizations of the diurnal shapes of OI 630.0 nm dayglow intensity variations: inferences
International audienceMeasurements of OI 630.0 nm thermospheric dayglow emission by means of the Dayglow Photometer (DGP) at Mt. Abu (24.6° N, 73.7° E, dip lat 19.09° N), a station under the crest of Equatorial Ionization Anomaly (EIA), reveal day-to-day changes in the shapes of the diurnal profiles of dayglow intensity variations. These shapes have been characterized using the magnetometer data from equatorial and low-latitude stations. Substantial changes have been noticed in the shapes of the dayglow intensity variations between 10:00?15:00 IST (Indian Standard Time) during the days when normal and counter electrojet events are present over the equator. It is found that the width (the time span corresponding to 0.8 times the maximum dayglow intensity) of the diurnal profile has a linear relationship with the integrated electrojet strength. Occasional deviation from this linear relationship is attributed to the presence of substantial mean meridional wind
Instability of Quark Matter Core in a Compact Newborn Neutron Star With Moderately Strong Magnetic Field
It is explicitly shown that if phase transition occurs at the core of a
newborn neutron star with moderately strong magnetic field strength, which
populates only the electron's Landau levels, then in the -equilibrium
condition, the quark core is energetically much more unstable than the neutron
matter of identical physical condition.Comment: Six pages REVTEX file, one .eps file (included
Universality of modulation length (and time) exponents
We study systems with a crossover parameter lambda, such as the temperature
T, which has a threshold value lambda* across which the correlation function
changes from exhibiting fixed wavelength (or time period) modulations to
continuously varying modulation lengths (or times). We report on a new
exponent, nuL, characterizing the universal nature of this crossover. These
exponents, similar to standard correlation length exponents, are obtained from
motion of the poles of the momentum (or frequency) space correlation functions
in the complex k-plane (or omega-plane) as the parameter lambda is varied. Near
the crossover, the characteristic modulation wave-vector KR on the variable
modulation length "phase" is related to that on the fixed modulation length
side, q via |KR-q|\propto|T-T*|^{nuL}. We find, in general, that nuL=1/2. In
some special instances, nuL may attain other rational values. We extend this
result to general problems in which the eigenvalue of an operator or a pole
characterizing general response functions may attain a constant real (or
imaginary) part beyond a particular threshold value, lambda*. We discuss
extensions of this result to multiple other arenas. These include the ANNNI
model. By extending our considerations, we comment on relations pertaining not
only to the modulation lengths (or times) but also to the standard correlation
lengths (or times). We introduce the notion of a Josephson timescale. We
comment on the presence of "chaotic" modulations in "soft-spin" and other
systems. These relate to glass type features. We discuss applications to Fermi
systems - with particular application to metal to band insulator transitions,
change of Fermi surface topology, divergent effective masses, Dirac systems,
and topological insulators. Both regular periodic and glassy (and spatially
chaotic behavior) may be found in strongly correlated electronic systems.Comment: 22 pages, 15 figure
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