Search

Working temperature, internal pressure and the creep of bolted flange joints are the direct factors that influencing the gasket stress of bolted flange joints, the tightness of the whole system will be reduced because of these factors. thus the security level of bolted flange connection will be affected. In this paper, the deformation coordination equation of bolted flange connection system, the gasket compressive and resilient performance, as well as the gasket creep equation are combined to study the effect of internal pressure on bolted flange connections under a certain bolt preload and operating temperature, the equation about the relationship of the gasket force and internal pressure is simplified, and the main objective of the work is the calculation of the time-correlated gasket force, flange rotation and gasket unloading deformation under the different internal pressure. The results show that when the internal pressure is greater, the gasket force is smaller, on the contrary, the leakage rate are greater. Through the relevant conditions, in a period of the safe operation time, the maximum working internal pressure is got when reaching the condition of corresponding level of tightness.

Zika virus (ZIKV) has caused significant outbreaks and epidemics in the Americas recently, raising global concern due to its ability to cause microcephaly and other neurological complications. A stable and efficient infectious clone of ZIKV is urgently needed. However, the instability and toxicity of flavivirus cDNA clones in Escherichia coli hosts has hindered the development of ZIKV infectious clones. Here, using a novel self-splicing ribozyme-based strategy, we generated a stable infectious cDNA clone of a contemporary ZIKV strain imported from Venezuela to China in 2016. The constructed clone contained a modified version of the group II self-splicing intron P.li.LSUI2 near the junction between the E and NS1 genes, which were removed from the RNA transcripts by an easy-to-establish in vitro splicing reaction. Transfection of the spliced RNAs into BHK-21 cells led to the production of infectious progeny virus that resembled the parental virus. Finally, potential cis -acting RNA elements in ZIKV genomic RNA were identified based on this novel reverse genetics system, and the critical role of 5′-SLA promoter and 5′-3′ cyclization sequences were characterized by a combination of different assays. Our results provide another stable and reliable reverse genetics system for ZIKV that will help study ZIKV infection and pathogenesis, and the novel self-splicing intron-based strategy could be further expanded for the construction of infectious clones from other emerging and reemerging flaviviruses. IMPORTANCE The ongoing Zika virus (ZIKV) outbreaks have drawn global concern due to the unexpected causal link to fetus microcephaly and other severe neurological complications. The infectious cDNA clones of ZIKV are critical for the research community to study the virus, understand the disease, and inform vaccine design and antiviral screening. A panel of existing technologies have been utilized to develop ZIKV infectious clones. Here, we successfully generated a stable infectious clone of a 2016 ZIKV strain using a novel self-splicing ribozyme-based technology that abolished the potential toxicity of ZIKV cDNA clones to the E. coli host. Moreover, two crucial cis -acting replication elements (5′-SLA and 5′-CS) of ZIKV were first identified using this novel reverse genetics system. This novel self-splicing ribozyme-based reverse genetics platform will be widely utilized in future ZIKV studies and provide insight for the development of infectious clones of other emerging viruses.

The global spread of Zika virus (ZIKV) as well as its unexpected link to infant microcephaly have resulted in serious public health concerns. No antiviral drugs against ZIKV is currently available, and vaccine development is of high priority to prepare for potential ZIKV pandemic. In the present study, a truncated E protein with the N-terminal 90% region reserved (E90) from a contemporary ZIKV strain was cloned and expressed in Escherichia coli, purified by a Ni-NTA column, and characterized by Western blotting assays. Immunization with recombinant E90 induced robust ZIKV-specific humoral response in adult BALB/c mice. Passive transfer of the antisera from E90-immunized mice conferred full protection against lethal ZIKV challenge in a neonatal mice model. Our results indicate that recombinant ZIKV E90 described here represents as a promising ZIKV subunit vaccine that deserves further clinical development.

Zika virus (ZIKV) has caused significant outbreaks and epidemics in the Americas recently, raising global concern due to its ability to cause microcephaly and other neurological complications. A stable and efficient infectious clone of ZIKV is urgently needed. However, the instability and toxicity of flavivirus cDNA clones in Escherichia coli hosts has hindered the development of ZIKV infectious clones. Here, using a novel self-splicing ribozyme-based strategy, we generated a stable infectious cDNA clone of a contemporary ZIKV strain imported from Venezuela to China in 2016. The constructed clone contained a modified version of the group II self-splicing intron P.li.LSUI2 near the junction between the E and NS1 genes, which were removed from the RNA transcripts by an easy-to-establish in vitro splicing reaction. Transfection of the spliced RNAs into BHK-21 cells led to the production of infectious progeny virus that resembled the parental virus. Finally, potential cis-acting RNA elements in ZIKV genomic RNA were identified based on this novel reverse genetics system, and the critical role of 5′-SLA promoter and 5′-3′ cyclization sequences were characterized by a combination of different assays. Our results provide another stable and reliable reverse genetics system for ZIKV that will help study ZIKV infection and pathogenesis, and the novel self-splicing intron-based strategy could be further expanded for the construction of infectious clones from other emerging and reemerging flaviviruses.

Mutation for microcephaly Zika virus infections in humans have been known since 1947. Microcephaly and neuropathologies associated with Zika have only been reported recently, most prevalently in the Americas. Yuan et al. investigated recent stable mutations in the virus genome and engineered them into a low-virulence ancestral strain (see the Perspective by Screaton and Mongkolsapaya). A single amino acid substitution (serine to asparagine, S139N) in the viral precursor membrane protein exacerbated symptoms in pregnant mice. The reverse mutation (N139S) was less virulent. The S139N mutation arose in 2013 in French Polynesia before the virus jumped to Brazil in 2015. In vitro, this amino acid change made the virus more infectious for mouse and human neural progenitor cells and promoted apoptosis. The terrible sequelae of infection during pregnancy could thus be the result of a simple viral mutation. Science , this issue p. 933 ; see also p. 863

Two-dimensional numerical simulation is performed to understand the effect of flow pulsation on the flow and heat transfer from a heated square cylinder at Re = 100. Numerical calculations are carried out by using a finite volume method based on the pressure-implicit with splitting of operators algorithm in a collocated grid. The effects of flow pulsation amplitude (0.2 ≤ A ≤ 0.8) and frequency (0 ≤ f p ≤ 20 Hz) on the detailed kinematics of flow (streamlines, vorticity patterns), the macroscopic parameters (drag coefficient, vortex shedding frequency) and heat transfer enhancement are presented in detail. The Strouhal number of vortices shedding, drag coefficient for non-pulsating flow are compared with the previously published data, and good agreement is found. The lock-on phenomenon is observed for a square cylinder in the present flow pulsation. When the pulsating frequency is within the lock-on regime, time averaged drag coefficient and heat transfer from the square cylinder is substantially augmented, and when the pulsating frequency in about the natural vortex shedding frequency, the heat transfer is also substantially enhanced. In addition, the influence of the pulsating amplitude on the time averaged drag coefficient, heat transfer enhancement and lock-on occurrence is discussed in detail.

Vibration responses of the water wall of coal gasifier under impact loads were investigated. The influences of different diameters of water walls and impact loads on the effectiveness of ash removal were further considered. The results showed that the peak acceleration along the axial direction of the water wall is greater than 80% of the peak acceleration at the impact point when rapping devices are installed at the 1/4, 1/2 and 3/4 heights. Moreover, rapping devices should be staggered 30 degree in the hoop direction at different heights to avoid the dead zone of ash removal. Furthermore, vibration accelerations increase with increasing the diameter of water wall, while the impact time should be as short as possible for higher efficiency of ash removal.

The heat transfer properties of pulsating flow around the tube with simple harmonic vibration were analyzed. The effect of the angle θ between the flow direction and the tube vibrating direction, which changes from 0° to 150°, on heat transfer properties was numerically investigated by the dynamic mesh technology of FLUENT. The results showed that the transient surface heat transfer coefficient decreases with increasing θ when amplitudes of pulsating flow or vibrating tube increase. Comparing with the still tube, the angle between the temperature gradient and the velocity vector is smaller when the tube vibrates along different directions, hence the field synergy performance is better, and the heat transfer performance is more enhanced.

Viral replicase recruitment and long-range RNA interactions are essential for RNA virus replication, yet the mechanism of their interplay remains elusive. Flaviviruses include numerous important human pathogens, e.g., dengue virus (DENV) and Zika virus (ZIKV). Here, we revealed a highly conserved, conformation-tunable cis-acting element named 5′-UAR-flanking stem (UFS) in the flavivirus genomic 5′ terminus. We demonstrated that the UFS was critical for efficient NS5 recruitment and viral RNA synthesis in different flaviviruses. Interestingly, stabilization of the DENV UFS impaired both genome cyclization and vRNA replication. Moreover, the UFS unwound in response to genome cyclization, leading to the decreased affinity of NS5 for the viral 5′ end. Thus, we propose that the UFS is switched by genome cyclization to regulate dynamic RdRp binding for vRNA replication. This study demonstrates that the UFS enables communication between flavivirus genome cyclization and RdRp recruitment, highlighting the presence of switch-like mechanisms among RNA viruses. DOI: http://dx.doi.org/10.7554/eLife.17636.001, eLife digest Flaviviruses include a large family of viruses that are harmful to human health, such as dengue virus, West Nile virus and Zika virus. Understanding the details of the life cycle of these viruses is important for better controlling and treating the diseases that they cause. The genetic information of flaviviruses is stored in single-stranded molecules of RNA. To form new copies of a virus, the RNA must be replicated in a process that involves two critical steps. First, an enzyme called viral RNA polymerase NS5 must be recruited to a specific end of the RNA strand (known as the 5′ end). Then, the ends of the RNA strand bind together to form a circular loop. However, little is known about whether these two processes are linked, or how they are regulated. Using bioinformatics, biochemical and reverse genetics approaches, Liu et al. have now identified a new section of RNA in the 5′ end of the flavivirus RNA, named the 5′-UAR-flanking stem (or UFS for short), which is critical for viral replication. The UFS plays an important role in efficiently recruiting the NS5 viral RNA polymerase to the 5′ end of the flavivirus RNA. After the RNA forms a circle, the UFS unwinds. This makes the NS5 polymerase less likely to bind to the 5′ end of the RNA. Stabilizing the structure of the UFS impairs the ability of the RNA strand to form a circle, and hence reduces the ability of the RNA to replicate. Thus, the UFS links and enables communication between the processes that form the flavivirus RNA into a circle and that recruit the viral RNA polymerase to the RNA. The structural basis of the interaction between the flavivirus RNA 5′ end, including the UFS element, and the viral RNA polymerase now deserves further investigation. It will be also important to explore whether other types of viruses regulate their replication via a similar mechanism. DOI: http://dx.doi.org/10.7554/eLife.17636.002

The mechanism of heat transfer enhancement of pulsating flow in a spiral fluted tube was researched by CFD (computational fluid dynamics) software FLUENT. Numerical results showed that pulsating flow leads to cyclical fluctuation of outlet pressure and the extent of fluctuation increases with increasing the pulsating flow frequency. Moreover, the pulsating flowing causes whirlpools near the spiral flute and the vortices generate, drift, and fall off periodically. The optimum pulsating frequency in the spiral fluted tube is 6HZ and the optimum amplitude A is equal to 0.7 approximately when the Reynolds number is 1683.

The weld cracking mechanism of the entrance elbow of crude oil cracking furnace served at 490°C was investigated. The performance and microstructure of failed elbow were characterized by hardness testing, optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The results showed that cracks are caused by the combination of sulfide corrosion, embrittlement of weld metal and thermal stress.

The present paper focuses on the analysis of transient heat transfer and flow in a vibratory tube. The characteristics of flow and heat transfer are investigated by dynamic mesh of CFD (computational fluid dynamics) software FLUENT, the velocity and temperature distributions in a vibration cycle are analyzed by field synergy theory. The results indicate that the vibration parameters have great effect on heat transfer, and the tube vibration leads to heat transfer enhancement or reduction. Moreover, the optimum heat transfer performance inside tubes is obtained in a half-cycle when time phase is 90°.

Fluid flow and heat transfer characteristics of pulsating flow around the vibrating tube was numerically investigated by the dynamic meshing technique of FLUENT. The results showed the combined action of pulsating flow and vibration enhances the coefficient of heat transfer, and the surface heat transfer coefficient of vibrating tube increases with the increment of the tube vibration amplitude, frequency and pulsating flow amplitude, and pulsating flow frequency has less affected. The main reason that pulsating flow enhances heat transfer is the secondary flow, generated by the combined effect of pulsating flow and tube vibration, enhances momentum and energy transfer.

ANSYS was employed to build nonlinear finite element models of seal structure of double-Y and quad-ring between the piston and casing of rapping device respectively. The relationships of the contact stress versus fluid pressure and the Von-Mises equivalent stress versus working pressure of fluid were obtained. The comparison of the two calculated results presented the seal structure of double-Y was proper for rapping device between the piston and casing.

By numerical simulation computation, after passing the pulsating flow, enhanced heat transfer mechanism in spirally fluted tubes was researched. Numerical result shows that pulsating flow can cause the outlet pressure to fluctuate cyclical and the extent of fluctuation increases with the pulsating flow frequency. The pulse flowing can make the fluid generate the whirlpool nearby the spirally fluted tubes and the phenomenon of periodic production, drift, and fall-off appears. Because of the vortex, the fluid motion and relative motion are enhanced. The pulse flowing can improve the coordination level between velocity and temperature, thus has strengthened the heat transfer effect.

The performance of reciprocating seals in rapping device of gasifier was studied through finite element method. The contact stress, Von-Mises stress, and friction power loss of O-ring and Sliding-ring combined Seal-ring were obtained. Meanwhile, the experimental study in performance of seal structures of rapping device were carried out. The results show that both of the seal structures are satisfied seal requirement, but compared with the Sliding-ring combined Seal-ring, the O-ring is easier to be destroyed and power loss of O-ring is higher than Sliding-ring combined Seal-ring. The results also verify the superiority of Sliding-ring combined Seal-ring in rapping device of gasifier.

The present paper is concerned with the buckling of a thin spiral cylindrical shell constituted by a series of eccentric semicylinders. The spiral cylinder is the main pressurized element of the spiral cylinder heat exchanger. Since the configuration and boundary condition of the structure are very complex, it is impossible to solve the theoretical buckling pressure using the classical method. In this paper, the approximate solution is obtained by means of the finite element method. To verify the reliability of the results, experiments are performed. The experimental results show that the errors in manufacture will decrease the critical pressure dramatically.