54,217 research outputs found
Reply to [arXiv:1105.5147] "Are GRB 090423 and Similar Bursts due to Superconducting Cosmic Strings?"
The GRB outflow driven by superconducting cosmic strings is likely to be an
arc rather than a usually-considered spherical cap. In such a case, the
afterglows of the cosmic string GRBs could be basically consistent with the
observation of the high-redshift GRBs.Comment: 2 pages, 1 figure, to appear in Phys. Rev. Let
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TDLAS Detection of propane and butane gas over the near-infrared wavelength range from 1678nm to 1686nm
It is important in the petrochemical industry that there are high sensitivity, high accuracy, low-power consumption and intrinsically safe methods for the detection of propane, butane and their gas mixtures, to provide early warning of potential explosion hazards during both storage and transportation of oil and gas. This paper proposes a 'proof of principle' method for the detection of propane and butane using a Tunable Diode Laser Absorption Spectroscopy (TDLAS) technique over the near-infrared wavelength range from 1678nm to 1686nm. This method is relatively inexpensive to implement and is thus more practical, compared with detection methods using wavelengths further into the infra-red, near 3.3μm. The minimum detectable concentration was found to be low as 300ppm for propane or butane. Importantly, the relative measurement errors were all below 3% LEL, which meets the requirements from the petrochemical and oil-gas storage and transportation industries for a field-based system for monitoring of combustible gases
Diverse Temporal Properties of GRB Afterglow
The detection of delayed X-ray, optical and radio emission, "afterglow",
associated with -ray bursts (GRBs) is consistent with fireball models,
where the emission are produced by relativistic expanding blast wave, driven by
expanding fireball at cosmogical distances. The emission mechanisms of GRB
afterglow have been discussed by many authors and synchrotron radiation is
believed to be the main mechanism. The observations show that the optical light
curves of two observed gamma-ray bursts, GRB970228 and GRB GRB970508, can be
described by a simple power law, which seems to support the synchrotron
radiation explanation. However, here we shall show that under some
circumstances, the inverse Compton scattering (ICS) may play an important role
in emission spectrum and this may influence the temporal properties of GRB
afterglow. We expect that the light curves of GRB afterglow may consist of
multi-components, which depends on the fireball parameters.Comment: Latex, no figures, minor correctio
Is GRO J1744-28 a Strange Star?
The unusal hard x-ray burster GRO J1744-28 recently discovered by the Compton
Gamma-ray Observatory (GRO) can be modeled as a strange star with a dipolar
magnetic field Gauss. When the accreted mass of the star exceeds
some critical mass, its crust may break, resulting in conversion of the
accreted matter into strange matter and release of energy. Subsequently, a
fireball may form and expand relativistically outward. The expanding fireball
may interact with the surrounding interstellar medium, causing its kinetic
energy to be radiated in shock waves, producing a burst of x-ray radiation. The
burst energy, duration, interval and spectrum derived from such a model are
consistent with the observations of GRO J1744-28.Comment: Latex, has been published in SCIENCE, Vol. 280, 40
The topological glass in ring polymers
We study the dynamics of concentrated, long, semi-flexible, unknotted and unlinked ring polymers embedded in a gel by Monte Carlo simulation of a coarse-grained model. This involves the ansatz that the rings compactify into a duplex structure where they can be modelled as linear polymers. The classical polymer glass transition involves a rapid loss of microscopic freedom within the polymer molecule as the temperature is reduced toward Tg. Here we are interested in temperatures well above Tg where the polymers retain high microscopic mobility. We analyse the slowing of stress relaxation originating from inter-ring penetrations (threadings). For long polymers an extended network of quasi-topological penetrations forms. The longest relaxation time appears to depend exponentially on the ring polymer contour length, reminiscent of the usual exponential slowing (e.g., with temperature) in classical glasses. Finally, we discuss how this represents a universality class for glassy dynamics
Strong Pinning Enhancement in MgB2 Using Very Small Dy2O3 Additions
0.5 to 5.0 wt.% Dy2O3 was in-situ reacted with Mg + B to form pinned MgB2.
While Tc remained largely unchanged, Jc was strongly enhanced. The best sample
(only 0.5 wt.% Dy2O3) had a Jc of 6.5 x 10^5 A/cm^2 at 6K, 1T and 3.5 x 10^5
A/cm^2 at 20K, 1T, around a factor of 4 higher compared to the pure sample, and
equivalent to hot-pressed or nano-Si added MgB2 at below 1T. Even distributions
of nano-scale precipitates of DyB4 and MgO were observed within the grains. The
room temperature resistivity decreased with Dy2O3 indicative of improved grain
connectivity.Comment: 13 pages, 4 figures and 1 tabl
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Study of quasi-distributed optical fiber methane sensors based on laser absorption spectrometry
The coal industry plays an important role in the economic development of China. With the increase of coal mining year by year, coal mine accidents caused by gas explosion also occur frequently, which poses a serious threat to the life safety of absenteeism and national property safety. Therefore, high-precision methane fiber sensor is of great significance to ensure coal mine safety. This paper mainly introduces two kinds of quasi-distributed gas optical fiber sensing systems based on laser absorption spectroscopy. The gas fiber optic sensor based on absorption spectrum has high measurement accuracy, fast response and long service life. One is quasi-distributed optical fiber sensing system based on spatial division multiplexing (SDM) technology and the other is quasi-distributed optical fiber sensing system based on optical time domain reflection and time division multiplexing(TDM) technology
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