Effective Flow And Force Areas Of Discharge Valve In A Rotary Compressor

In this paper, two fluid–structure interaction (FSI) models of the discharge valve are presented to study the effect of partly covering the discharge port by the cylinder and the roller on the effective flow and force areas. One is the full FSI model and another is the simplified FSI model in which the discharge port is not covered and the cylinder shape is simplified to be cylindrical. The pressure in the compression chamber, the displacement of the valve reed, the volumetric flow rate through the valve and the gas force acting on the valve reed head are obtained by the two FSI model. The results comparison between the two FSI models shows the effective flow and force area in the full FSI model are much different from those in the simplified FSI model. The factors which affect the covering area of the discharge port must be taken into consideration in the calculations of these two areas

The Power Spectra of Two Classes of Long-duration Gamma-ray Bursts

We have studied the averaged power density spectra (PDSs) of two classes of long-duration gamma-ray bursts in the recent classification by Balastegui et al.(2001) based on neural network analysis. Both PDSs follow a power law over a wide frequency range with approximately the same slope, which indicates that a process with a self-similar temporal property may underlie the emission mechanisms of both. The two classes of bursts are divided into groups according to their brightness and spectral hardness respectively and each group's PDS was calculated; For both classes, the PDS is found to flatten both with increasing burst brightness and with increasing hardness.Comment: 6 pages, 3 figures, a translated version from published in the Acta Astronomica Sinica, to appear in the Chinese Astronomy & Astrophysics Vol.27, Issue

Expanding CRISPR/Cas9 Genome Editing Capacity in Zebrafish Using SaCas9.

The type II CRISPR/Cas9 system has been used widely for genome editing in zebrafish. However, the requirement for the 5'-NGG-3' protospacer-adjacent motif (PAM) of Cas9 from Streptococcus pyogenes (SpCas9) limits its targeting sequences. Here, we report that a Cas9 ortholog from Staphylococcus aureus (SaCas9), and its KKH variant, successfully induced targeted mutagenesis with high frequency in zebrafish. Confirming previous findings, the SpCas9 variant, VQR, can also induce targeted mutations in zebrafish. Bioinformatics analysis of these new Cas targets suggests that the number of available target sites in the zebrafish genome can be greatly expanded. Collectively, the expanded target repertoire of Cas9 in zebrafish should further facilitate the utility of this organism for genetic studies of vertebrate biology

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

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

Antibody dependent enhancement infection of Enterovirus 71 in vitro and in vivo

BACKGROUND: Human enterovirus 71 (EV71) has emerged as a significant cause of acute encephalitis and deaths in young children. The clinical manifestations caused by EV71 varied from mild hand, foot and mouth disease to severe neurological complications and deaths, but its pathogenesis remains elusive. Antibody dependent enhancement (ADE) infection has been reported in various viruses and has been shown to contribute to disease severity. RESULTS: In this study, the presence of sub-neutralizing antibody was demonstrated to enhance EV71 infection in THP-1 cells and increase the mortality of EV71 infection in a suckling mouse model. Further, a secondary infection model was established to characterize the correlation between ADE and disease severity, and primary asymptomatic EV71 infection was shown to increase the mortality of the secondary EV71 infection in suckling mice. CONCLUSIONS: Together, these in vitro and in vivo experiments strongly supported the hypothesis of ADE infection of EV71. The present findings indicate ADE might contribute to the pathogenesis of severe EV71 infection, and raise practical issues of vaccine development and antibody-based therapy

Evolutionary Enhancement of Zika Virus Infectivity in Aedes aegypti Mosquitoes

Zika virus (ZIKV) remained obscure until the recent explosive outbreaks in French Polynesia (2013-2014) and South America (2015-2016). Phylogenetic studies have shown that ZIKV has evolved into African and Asian lineages. The Asian lineage of ZIKV was responsible for the recent epidemics in the Americas. However, the underlying mechanisms through which ZIKV rapidly and explosively spread from Asia to the Americas are unclear. Non-structural protein 1 (NS1) facilitates flavivirus acquisition by mosquitoes from an infected mammalian host and subsequently enhances viral prevalence in mosquitoes. Here we show that NS1 antigenaemia determines ZIKV infectivity in its mosquito vector Aedes aegypti, which acquires ZIKV via a blood meal. Clinical isolates from the most recent outbreak in the Americas were much more infectious in mosquitoes than the FSS13025 strain, which was isolated in Cambodia in 2010. Further analyses showed that these epidemic strains have higher NS1 antigenaemia than the FSS13025 strain because of an alanine-to-valine amino acid substitution at residue 188 in NS1. ZIKV infectivity was enhanced by this amino acid substitution in the ZIKV FSS13025 strain in mosquitoes that acquired ZIKV from a viraemic C57BL/6 mouse deficient in type I and II interferon (IFN) receptors (AG6 mouse). Our results reveal that ZIKV evolved to acquire a spontaneous mutation in its NS1 protein, resulting in increased NS1 antigenaemia. Enhancement of NS1 antigenaemia in infected hosts promotes ZIKV infectivity and prevalence in mosquitoes, which could have facilitated transmission during recent ZIKV epidemics