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 $L-E_p$ 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

Spin superconductor in ferromagnetic graphene

We show a spin superconductor (SSC) in ferromagnetic graphene as the counterpart to the charge superconductor, in which a spin-polarized electron-hole pair plays the role of the spin $2 (\hbar/2)$ `Cooper pair' with a neutral charge. We present a BCS-type theory for the SSC. With the `London-type equations' of the super-spin-current density, we show the existence of an electric `Meissner effect' against a spatial varying electric field. We further study a SSC/normal conductor/SSC junction and predict a spin-current Josephson effect.Comment: 6 pages, 4 figure

Flexible-body Dynamics Simulation of Crankshaft Torsional Vibration System

Abstract:The crankshaft accidents due to vibration become severe with increasing number of rows of reciprocating compressors.The crankshaft vibration needs to be studied thoroughly to promote development of the reciprocating compressor.Early calculations of crankshaft torsional vibration was mainly with discretization method, the crankshaft is discretized into a series of lumped inertia and lumped stiffness,then calculate the swing angle of crankshaft in the gas force and inertia force,but because of the simplified calculation,which has low precision.The currently calculation method of crankshaft torsional vibration is simplified into an equivalent system model,the model is composed of a lumped mass disc,massless elastic shaft and a damping.In calculation the torsional natural frequency and forced vibration usually adopt the Holzer method and transfer matrix method,due to this method only calculation the crankshaft torsional direction, so it can only obtained the crankshaft natural frequency and vibration characteristics in the direction.To make the crankshaft torsional vibration calculation more accurately,we proposed a new calculation model based on the flexible multibody dynamics theory.The process of the model establishment and solving by ADAMS was introduced.The torsional vibration of a crankshaft, which often suffers from the crankpin fracture,was calculated before and after the structure change.Results show that before the structure change,the crankshaft natural frequency was closed to the excitation frequency,so that the tortional vibration amplitude of the crankshaft is very large.The stress of piston pins in the first and second row increase so rapidly along the directionof the cylinder center line that the impact factor ofthe crank pin bearing reache the upper limit,thus the oil film of it is damaged.After the structure change,the natural frequency of crankshaft is away from the excitation frequency,the vibration amplitude of the crankshaft torsional vibration decrease substantially,and the crankpin fracture does not happen anymore.This is a successful validation of the proposed calculation method

Physico-mechanical properties of particleboard made from seaweed adhesive and tapioca starch flo

Flour acted as filler was added into adhesive formulations in industry and it affects the performance of adhesive. Seaweed was chosen to act as adhesive as seaweed produces glue that can attach very strongly to the rocks despite the presence of contaminants. This study was conducted on physical and mechanical properties of particleboard by adding different percentages of tapioca starch flour (0%, 25%, 50%, and 75% based on solid basis) into seaweed adhesive formulation. 100% urea formaldehyde was used as control in the production of particleboard. The particleboards were cut and tested based on JIS A5908. The moisture content was lowered from 11.00 to 8.45% when 25% tapioca starch flour rose to 75% when added into seaweed adhesive. Thickness swelling declined from 40.18 to 26.55% and water absorption from 192.25 to 96.21% when 75% tapioca starch flour was added. Hence, it improved the physical properties of particleboard. Meanwhile, the mixing of higher percentage of tapioca starch flour into seaweed adhesive contributed a higher value of modulus of rupture, modulus of elasticity and internal bonding. In a nutshell, mixing higher percentage of tapioca starch flour in seaweed adhesive improved the physical and mechanical properties of seaweed adhesive in particleboard

Pressure Loss Analysis of the Perforated Tube Attenuator

Gas pulsation produces excessive noise in the piping system of the reciprocating compressor and even causes damage in the piping and the machine. Therefore, it is very important for reasonable analysis and proper control of pressure pulsation. The perforated tube attenuator is widely applied in the compressor because of its favourable performance of acoustic attenuation. For the attenuator design, pressure loss and transmission loss are the two equally significant parameters characterizing its performance. Even if an attenuator can greatly reduce the compressor pressure pulsation, but cause large pressure loss, it will not be used yet. So it’s necessary to pursue the attenuator with low pressure loss as well as low pressure pulsation. The traditional method of calculating pressure loss of the attenuator is according to empirical formulas, which only fit for simple structures. But for the perforated tube attenuator, the flow is complex, and the empirical formulas are not available to calculate the pressure loss. Presently, CFD method is used to calculate pressure loss of the attenuator with complex structure. Most perforated attenuators could consist of hundreds of small holes distributed on the pipe, so three-dimensional flow models ensure the accurate solution. This paper predicts pressure loss of the perforated tube attenuator with various geometry parameters using CFD. A three-dimensional CFD model of the attenuator was established under the following assumptions: (1) The physical parameters of the solid and fluid domain of the attenuator are constant; (2) The flow is steady turbulent flow; (3) The influence of the gravity is ignored; (4) The inlet velocity of the attenuator is homogeneous without impulse effect. The standard - model is used in this paper. The flow through the attenuator follows the law of conservation of mass, law of conservation of momentum and the law of conservation of energy. The solution of the model was implemented with the FVM method of the commercial CFD code fluent. According to the CFD model, the following three aspects were analyzed: (1) The influence of the hole diameter on the pressure loss (2) The influence of porosities on the pressure loss (3) The influence of the inlet velocity on the pressure loss Based on analysis of the above three aspects, an attenuator with low pressure loss as well as low pressure pulsation was designed

Directed evolution of glycosyltransferase for the artificial biosynthesis of natural product glycosides

Over one fifth natural product drugs (including protein biopharmaceuticals), cosmetics, and nutraceuticals have a diverse set of sugars in their structures. These glycosylations dramatically influence the physicochemical and pharmacological properties of these compounds. Glycosyltransferases (GTs) offer very attractive approaches to the biosynthesis of complex glycosylated natural products. However, the limited number of available GTs, together with their instability and strict substrate specificity, have severely hampered the broad application of these enzymes. In the past few years, we have used directed evolution as a tool to tailor the GTs with desired substrate specificity and higher catalytic activity. Here I will introduce some of our efforts in 1) the semi-rational design of a glucosyltransferase UGT51 from S. cerevisiae to repurposing its promiscuous activity towards the biosynthesis of rare ginsenoside Rh2; and 2) the directed evolution of an α1,3-fucosyltransferase using a single-cell ultrahigh-throughput screening method. I will also discuss the development of new tools for the high-throughput screening method for GTs and the mechanistic insight we found during the evolution of these enzymes

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