12,372 research outputs found
Determining the luminosity function of Swift long gamma-ray bursts with pseudo-redshifts
The determination of luminosity function (LF) of gamma-ray bursts (GRBs) is
of an important role for the cosmological applications of the GRBs, which is
however hindered seriously by some selection effects due to redshift
measurements. In order to avoid these selection effects, we suggest to
calculate pseudo-redshifts for Swift GRBs according to the empirical L-E_p
relationship. Here, such a relationship is determined by reconciling
the distributions of pseudo- and real redshifts of redshift-known GRBs. The
values of E_p taken from Butler's GRB catalog are estimated with Bayesian
statistics rather than observed. Using the GRB sample with pseudo-redshifts of
a relatively large number, we fit the redshift-resolved luminosity
distributions of the GRBs with a broken-power-law LF. The fitting results
suggest that the LF could evolve with redshift by a redshift-dependent break
luminosity, e.g., L_b=1.2\times10^{51}(1+z)^2\rm erg s^{-1}. The low- and
high-luminosity indices are constrained to 0.8 and 2.0, respectively. It is
found that the proportional coefficient between GRB event rate and star
formation rate should correspondingly decrease with increasing redshifts.Comment: 5 pages, 5 figures, accepted for publication in ApJ
Fault Diagnosis Based on Optimized Wavelet Packet Transform and Time Domain Convolution Network
In the past, the method of combining signal processing and neural network was widely used in the fault diagnosis of mechanical rolling bearings to achieve the purpose of fault signal detection and identification. However, traditional methods cannot fully extract fault features. In this paper, taking mechanical rolling bearings as an example, a new rolling bearing fault diagnosis model is proposed by combining the improved wavelet packet transform with time domain convolution network. The improved Northern Goshawk algorithm is used to optimize the wavelet packet transform and analyse the fault signal; then, the time domain convolution network is used to establish a fault diagnosis model. When compared with the wavelet packet decomposition model optimized by the improved Northern Goshawk algorithm, the accuracy of the improved wavelet packet transform model in detecting inner ring faults and rolling element faults is found to be increased by 8.3% and 7.4%, respectively
Experimental demonstrations of high-Q superconducting coplanar waveguide resonators
We designed and successfully fabricated an absorption-type of superconducting
coplanar waveguide (CPW) resonators. The resonators are made from a Niobium
film (about 160 nm thick) on a high-resistance Si substrate, and each resonator
is fabricated as a meandered quarter-wavelength transmission line (one end
shorts to the ground and another end is capacitively coupled to a through
feedline). With a vector network analyzer we measured the transmissions of the
applied microwave through the resonators at ultra-low temperature (e.g., at 20
mK), and found that their loaded quality factors are significantly high, i.e.,
up to 10^6. With the temperature increases slowly from the base temperature
(i.e., 20 mK), we observed the resonance frequencies of the resonators are blue
shifted and the quality factors are lowered slightly. In principle, this type
of CPW-device can integrate a series of resonators with a common feedline,
making it a promising candidate of either the data bus for coupling the distant
solid-state qubits or the sensitive detector of single photons.Comment: Accepted by Chinese Science Bulleti
Joint constraint on the jet structure from the short GRB population and GRB 170817A
The nearest GRB 170817A provided an opportunity to probe the angular
structure of the jet of this short gamma-ray burst (SGRB), by using its
off-axis observed afterglow emission. It is investigated that whether the
afterglow-constrained jet structures can be consistent with the luminosity of
the prompt emission of GRB 170817A. Furthermore, by assuming that all SGRBs
including GRB 170817A have the same explosive mechanism and jet structure, we
apply the different jet structures into the calculation of the flux and
redshfit distributions of the SGRB population, in comparison with the
observational distributions of the Swift and Fermi sources. As a result, it is
found that the single-Gaussian structure can be basically ruled out, whereas
the power-law and two-Gaussian models can in principle survive.Comment: 9 pages,6 figure
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