Effect of refilling time on microstructure and mechanical properties of friction spot welded LY12 aluminum alloy

Friction spot welding （FSpW） was successfully used to produce joints of LY12 aluminum alloy. The effects of refilling time on microstructure and mechanical properties of FSpW joints were systematically studied. Results show that the cross-section of FSpW joint presents a basin-like morphology. A white bonding ligament exists in the center of the joint. The stir zone can be clarified into sleeve affected zone and pin affected zone based on different grain sizes. With increasing the refilling time from 2. 0 s to 3.5 s, grains in the stir zone become coarser, microhardness of the joint decreases and tensile shear failure load of the joint firstly increases and then decreases. The maximum tensile shear failure load of 8 130 N is attained when the refilling time is 3.0 s. Shear-plug fracture mode and shear fracture mode can be observed in the tensile shear tests. The maximum hardness of 169. 7 HV is attained in the joint center when the refilling time is 2. 0 s.

Impacts of wind conditions on hydrogen leakage during refilling hydrogen-powered vehicles

Although hydrogen leakage at hydrogen refueling stations has been a concern,less efforts have been devoted to hydrogen leakage during the refueling of hydrogen-powered vehicles.In this study,hydrogen leakage and dilution from the hydrogen dispenser during the refueling of hydrogen-powered vehicles were numerically investigated under different wind configurations.The shape,size,and distribution of flammable gas clouds(FGC)during the leakage and dilution processes were analyzed.The results showed that the presence of hydrogen-powered vehicles resulted in irregular FGC shapes.Greater wind speeds(v wv)were associated with longer FGC propagation distances.At v_(wv)=2 m·s^(−1)and 10 m·s^(−1),the FGC lengths at the end of the leakage were 7.9 m and 20.4 m,respectively.Under downwind conditions,higher wind speeds corresponded to lower FGC heights.The FGC height was larger under upwind conditions and was slightly affected by the magnitude of the wind speed.In the dilution process,the existence of a region with a high hydrogen concentration led to the FGC volume first increasing and then gradually decreasing.Wind promoted the mixing of hydrogen and air,accelerated FGC dilution,inhibited hydrogen uplifting,and augmented the horizontal movement of the FGC.At higher wind speeds,the low-altitude FGC movements could induce potential safety hazards.

The Effect of Topologies and Refilling Short-chain PEG on Protein Adsorption

PEGylation is the gold standard for constructing protein resistance surfaces.Herein,grafting mPEG-SH and SH-PEG-SH with varied molecular weights(Mw=5K,10K,and 20K)on a gold chip,and the subsequent lysozyme adsorptions of the PEG layers are evaluated using quartzcrystal microbalance based on dissipation(QCM-D).The lysozyme resistance depends on the features of grafting density and chain conformation,i.e.,linear and looped conformation.However,long-chain PEG(Mw≥10K)is insufficient to form a dense layer to resist protein due to large steric hindrances.Short-chain PEG(Mw=1K)with linear and looped structures is used to refill onto the long-chain PEG layer to increase the grafting density of PEGs and improve protein resistance.The refilling process and the subsequent protein adsorption depend on conformation rather than the density of the long-chain PEG substrate.Notably,the long-chain PEG looped substrates significantly improve protein resistance,attributing to the high viscoelasticity of the looped substrate and an increase in grafting density after refilling.Thus,refilling short-chain PEG improves protein resistance and the substrate conformation-dependence gives insight into the impact of topology,providing new ideas for how to increase chain density and select suitable topology to resist protein adsorption and demonstrating a potential application in biomedical fields.

Effect of thermo-mechanical conditions during constrained friction processing on the particle refinement of AM50 Mg-alloy phases

Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In this study,the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material,in particular the eutecticβ-Mg_(17)Al_(12)and Al-Mn phases.For that purpose,as-cast and solution heat-treated base material and processed samples were analyzed.The Al_(8)Mn_(5) intermetallic phase was identified as the main secondary phase present in all samples before and after the processing.A notorious refinement of these particles was observed,starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing.The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution,where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces.As for the eutectic phase,the results indicate the presence of the partially divorcedβ-Mg_(17)Al_(12)particles exclusively in the as-cast base material,indicating that no further phase transformations regarding the eutectic phase,such as dynamic precipitation,occurred after the CFP.In the case of the processed as-cast material analyzed after the CFP,the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase,which associated with the mechanical breakage of the particles,enabled the complete dissolution of this phase.Therefore,CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects,in terms of grain sizes of theα-Mg phase and presence and morphology of the Al-Mn and eutecticβ-Mg_(17)Al_(12).

Hypoperfusion context as a predictor of 28-d all-cause mortality in septic shock patients:A comparative observational study

BACKGROUND As per the latest Surviving Sepsis Campaign guidelines,fluid resuscitation should be guided by repeated measurements of blood lactate levels until normalization.Nevertheless,raised lactate levels should be interpreted in the clinical context,as there may be other causes of elevated lactate levels.Thus,it may not be the best tool for real-time assessment of the effect of hemodynamic resuscitation,and exploring alternative resuscitation targets should be an essential research priority in sepsis.AIM To compare the 28-d mortality in two clinical patterns of septic shock:hyperlactatemic patients with hypoperfusion context and hyperlactatemic patients without hypoperfusion context.METHODS This prospective comparative observational study carried out on 135 adult patients with septic shock that met Sepsis-3 definitions compared patients with hyperlactatemia in a hypoperfusion context(Group 1,n=95)and patients with hyperlactatemia in a non-hypoperfusion context(Group 2,n=40).Hypoperfusion context was defined by a central venous saturation less than 70%,central venousarterial PCO_(2)gradient[P(cv-a)CO_(2)]≥6 mmHg,and capillary refilling time(CRT)≥4 s.The patients were observed for various macro and micro hemodynamic parameters at regular intervals of 0 h,3 h,and 6 h.All-cause 28-d mortality and all other secondary objective parameters were observed at specified intervals.Nominal categorical data were compared using theχ^(2)or Fisher’s exact test.Nonnormally distributed continuous variables were compared using the Mann-Whitney U test.Receiver operating characteristic curve analysis with the Youden index determined the cutoff values of lactate,CRT,and metabolic perfusion parameters to predict the 28-d all-cause mortality.A P value of<0.05 was considered significant.RESULTS Patient demographics,comorbidities,baseline laboratory,vital parameters,source of infection,baseline lactate levels,and lactate clearance at 3 h and 6 h,Sequential Organ Failure scores,need for invasive mechanical ventilation,days on mechanical ventilation,and renal replacement therapy-free days within 28 d,duration of intensive care unit stay,and hospital stay were comparable between the two groups.The stratification of patients into hypoperfusion and nonhypoperfusion context did not result in a significantly different 28-d mortality(24%vs 15%,respectively;P=0.234).However,the patients within the hypoperfusion context with high P(cva)CO_(2)and CRT(P=0.022)at baseline had significantly higher mortality than Group 2.The norepinephrine dose was higher in Group 1 but did not achieve statistical significance with a P>0.05 at all measured intervals.Group 1 had a higher proportion of patients requiring vasopressin and the mean vasopressor-free days out of the total 28 d were lower in patients with hypoperfusion(18.88±9.04 vs 21.08±8.76;P=0.011).The mean lactate levels and lactate clearance at 3 h and 6 h,CRT,P(cv-a)CO_(2)at 0 h,3 h,and 6 h were found to be associated with 28-d mortality in patients with septic shock,with lactate levels at 6 h having the best predictive value(area under the curve lactate at 6 h:0.845).CONCLUSION Septic shock patients fulfilling the hypoperfusion and non-hypoperfusion context exhibited similar 28-d all-cause hospital mortality,although patients with hypoperfusion displayed a more severe circulatory dysfunction.Lactate levels at 6 h had a better predictive value in predicting 28-d mortality than other parameters.Persistently high P(cv-a)CO_(2)(>6 mmHg)or increased CRT(>4 s)at 3 h and 6 h during early resuscitation can be a valuable additional aid for prognostication of septic shock patients.

减少TLB失效开销提高64位Linux系统性能的方法

针对64位的Linux提出了一个减少TLB失效开销的方法——FAST_TLB_REFILL（快速TLB重载入）。测试结果表明，这种方法可以将TLB失效处理时间减少30％以上，对TLB失效比较频繁的程序会有1％～7％的性能提高。

Some Issues on Cement Grouting of Hydraulic Tunnel

Based on the practices of construction supervision to cement grouting at the reservoir emptying and power tunnels of the TSQ stage Ⅰ Hydropower station, some issues on quality control of cement grouting of hydraulic tunnel are discussed, and corresponding suggestions are put forward for revision of current standard (SL62-94). It is regarded that the refilling grouting could not be used for remedying the thickness of concrete lining; the end sealing of refilling grouting section should not be neglected; higher grouting pressure would be used. For the consolidation grouting, grout return pipe should be placed at the grout hole top for pure pressure type grouting; five-grade water cement ratio of grout mix is suggested; a certain standard should be specified for changing the grout to thicker mix by skipping the intermediate grade; the standard for ending the grouting should be relaxed. In current grouting standard, some terms should be complemented for contact grouting of steel penstock and spiral case and for plug grouting of circular-anchor hole.

The effect of cavity density on the formation of electrostatic shock in the lunar wake: 1-D hybrid simulation

One-dimensional hybrid simulations are carried out to study the plasma refilling process in the lunar wake.Previous theoretical and simulation studies have shown that ion-ion acoustic(ⅡA)instability can be initiated and electrostatic shock can be formed under the condition Te>>Ti.We find that the time evolution ofⅡA instability and the formation of electrostatic shock strongly depend on initial cavity density.The initial position of the electrostatic shock is dependent on the ratio between initial cavity density and background solar wind density,i.e.,the farther away the initial position,the lower is the ratio.When the initial cavity density is low enough,the density and electric field profile across the wake become much complex.Meanwhile,the back-to-back electrostatic shock is unstable in the case of lower cavity densities;at the late evolution stage,a new shock-like structure can be formed at the central region of the lunar wake.

Effect of tool plunge depth on the microstructure and fracture behavior of refill friction stir spot welded AZ91 magnesium alloy joints

We used refill friction stir spot welding(RFSSW)to join 2-mm-thick AZ91D-H24 magnesium alloy sheets,and we investigated in detail the effect of tool plunge depth on the microstructure and fracture behavior of the joints.A sound joint surface can be obtained using plunge depths of 2.0 and 2.5 mm.Plunge depth was found to significantly affect the height of the hook,with greater plunge depths corresponding to more severe upward bending of the hook,which compromised the tensile-shear properties of the joints.The hardness reached a minimum at the thermo-mechanically affected zone due to the precipitation phases of this zone as it dissolved into theα-matrix during the welding process.The fracture modes of RFSSW joints can be divided into three types:shear fracture,plug fracture,and shear–plug fracture.Of these,the joint with a shear–plug fracture exhibited the best tensile-shear load of 6400 N.

Effect of connection processes on mechanical properties of 7B04 aluminum alloy structures

The static and fatigue properties of 7B04 aluminum alloy structures connected by riveting and refill friction stir spot welding(refill FSSW)were compared and analyzed.Results show that the static compression load of the typical structure connected by riveting and refill FSSW fluctuated in the range of 117-124 kN,and the shear load was in the range of 89-95 kN.Welds spacing had a small influence on the static load of the structures joined by refill FSSW.However,the fatigue life of riveted structures was lower than that joined by refill FSSW.For the welded structure,the heterogeneous microstructures of the welded joint led to the uneven microhardness,and the hook at the lap interface bent upwards at the same time.These factors made the welded structures during the fatigue test failure along the path of sleeve moving.

Sap flow characteristics of three afforestation species during the wet and dry seasons in a dry-hot valley in Southwest China

Assessing and using tree species （exotic or native） with superior tolerance to environmental stresses （such as drought and high temperature） play an important role in afforestation practices. In the present study, stem sap flow characteristics and responses to ambient meteo- rological factors of three tree species, Albizzia kalkora （native）, Azadirachta indica （exotic）, and Acacia auriculaeformis （exotic）, in a dry-hot valley （Yuanmou, Yunnan Province, China） were investigated using thermal dissipation probes. The diurnal dynamics of sap flow in three studied species displayed an obvious circadian rhythm during the wet and dry seasons, with the exception of A. indica during the dry season. The sap flow velocity （SFV） in A. kalkora and A. auriculaeformis was significantly positively correlated with photosynthetically active radiation （PAR）, air temperature, vapour pressure deficit （VPD） and wind speed, but negatively correlated with atmospheric relative humidity over the two seasons. The cross-corre- lation analysis also revealed that the SFV of the three species was significantly correlated with PAR and VPD （P 〈 0.001）. Additionally, stem sap flow lagged behind PAR but ahead of VPD, and the diurnal sap flow was more dependent on PAR than on VPD. However, we found that the dominant climatic factor influencing the stem sap flow differed between daytime and nighttime. PAR was more influential than other meteorological factors during the daytime, while VPD or other factors were more influential overnight. When the nighttime refilling ability of the three tree species was compared, our results suggest that A. indica has higher drought resistance and better for afforestation of the studied region.

Refill Friction Stir Spot Welding Al Alloy to Copper via Pure Metallurgical Joining Mechanism

The current investigation of refill friction stir spot welding(refill FSSW)Al alloy to copper primarily involved plunging the tool into bottom copper sheet to achieve both metallurgical and mechanical interfacial bonding.Compared to conventional FSSW and pinless FSSW,weld strength can be significantly improved by using this method.Nevertheless,tool wear is a critical issue during refill FSSW.In this study,defect-free Al/copper dissimilar welds were successfully fabricated using refill FSSW by only plunging the tool into top Al alloy sheet.Overall,two types of continuous and ultra-thin intermetallic compounds(IMCs)layers were identified at the whole Al/copper interface.Also,strong evidence of melting and resolidification was observed in the localized region.The peak temperature obtained at the center of Al/copper interface was 591℃,and the heating rate reached up to 916℃/s during the sleeve penetration phase.A softened weld region was produced via refill FSSW process,the hardness profile exhibited a W-shaped appearance along middle thickness of top Al alloy.The weld lap shear load was insensitive to the welding condition,whose scatter was rather small.The fracture path exclusively propagated along the IMCs layer of Cu_(9)Al_(4) under the external lap shear loadings,both CuAl_(2) and Cu_(9)Al_(4) were detected on the fractured surface on the copper side.This research indicated that acceptable weld strength can be achieved via pure metallurgical joining mechanism,which has significant potential for the industrial applications.

Optimal early refill rules for Danjiangkou Reservoir

Water levels in reservoirs are generally not allowed to exceed the flood-limited water level during the flood season, which means that huge amounts of water spill in order to provide adequate storage for flood prevention and that it is difficult to fill the reservoir fully at the end of year. Early reservoir refill is an effective method for addressing the contradiction between the needs of flood control and of comprehensive utilization. This study selected the Danjiangkou Reservoir, which is the water source for the middle route of the South-North Water Diversion Project （SNWDP） in China, as a case study, and analyzed the necessity and operational feasibility of early reservoir refill. An early reservoir refill model is proposed based on the maximum average storage ratio, optimized by the progressive optimality algorithm, and the optimal scheduling schemes were obtained. Results show that the best time of refill operation for the Danjiangkou Reservoir is September 15, and the upper limit water level during September is 166 m. The proposed early refill scheme, in stages, can increase the annual average storage ratio from 77.51% to 81.99%, and decrease spilled water from 2.439 × 109 m^3 to 1.692×109 m^3, in comparison to the original design scheme. The suggested early significant comprehensive benefits, which decision-making. reservoir refill scheme can be easily operated with may provide a good reference for scheduling

Coping with handover effects in video streaming over cellular networks

The 3rd generation partnership project (3GPP) has defined the protocols and codecs for implementing media streaming services over packet-switched 3G mobile networks. The specification is based on IETF RFCs on audio/video transport.It also adds new features to achieve better adaptation to the mobile network environment. In this paper, we propose an algorithm for handover detection and fast buffer refill that is based on the existing feedback and signaling mechanisms. The proposed algorithm refills the receiver buffer at a faster pace during a limited time frame after a hard handover is detected in order to achieve higher video quality.

Capillary refill time as a guide for operational decision-making process of autoimmune pancreatitis:Preliminary results

AIM: To investigate the efficacy of a novel intraoperative diagnostic technique for patients with preliminary diagnosis of autoimmune pancreatitis(AIP).METHODS: Patients with pancreatic surgery were reviewed to identify those who received a preliminary diagnosis of AIP between January 2010 and January 2014. The following data were collected prospectively for patients with a pathological diagnosis of AIP: clinical and demographic features, radiological and operative findings, treatment procedure, and intraoperative capillary refill time(CRT) in the pancreatic bed.RESULTS: Eight patients(six males, two females; mean age: 51.4 years) met the eligibility criteria of pathologically confirmed diagnosis. The most frequent presenting symptoms were epigastric pain and weight loss. The most commonly conducted preoperative imaging studies were computed tomography and endoscopic retrograde pancreaticodoudenography. The most common intraoperative macroscopic observations were mass formation in the pancreatic head and diffuse hypervascularization in the pancreatic bed. All patients showed decreased CRT(median value: 0.76 s, range: 0.58-1.35). One-half of the patients underwent surgical resection and the other half received medical treatment without any further surgical intervention. CONCLUSION: This preliminary study demonstrates a novel experience with measurement of CRT in the pancreatic bed during the intraoperative evaluation of patients with AIP.

Material flow behavior and microstructural evolution during refill friction stir spot welding of alclad 2A12-T4 aluminum alloy

In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot welding.There are two material flow components, i.e., the inward-or outward-directed spiral flow on the horizontal plane and the upward-or downward-directed flow on the vertical plane.In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer.In the refill stage, this is process reversed.As such, there is no obvious vertical plasticized metal flow between adjacent layers.Welding leads to the coarsening of S(Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone.Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.

Cryotherapy and ankle motion in chronic venous disorders

This study compared ankle range of motion (AROM) including dorsiflexion, plantar flexion, inversion and eversion, and venous refill time (VRT) in leg skin inflamed by venous disorders, before and after a new cryotherapy ulcer prevention treatment. Fifty-seven individuals participated in the randomized clinical trial;28 in the experimental group and 29 received usual care only. Results revealed no statistically significant differences between the experimental and usual care groups although AROM measures in the experimental group showed a consistent, non-clinically relevant decrease compared to the usual care group except for dorsiflexion. Within treatment group comparisons of VRT results showed a statistically significant increase in both dorsiflexion and plantar flexion for patients with severe VRT in the experimental group (6.9 ± 6.8;p = 0.002 and 5.8 ± 12.6;p = 0.02, respectively). Cryotherapy did not further restrict already compromised AROM, and in some cases, there were minor improvements.

Refill friction stir spot welding (RFSSW): a review of processing, similar/dissimilar materials joining, mechanical properties and fracture mechanism

Refill friction stir spot welding(RFSSW)provides a novel method to join similar and/or dissimilar metallic materials without a key-hole in the center of the joint.Having the key-hole free characterization,the similar/dissimilar RFSSW joint exhibits remarkable and endurable characteristics,including high shear strength,long fatigue life,and strong corrosion resistance.In the meanwhile,as the key-hole free joint has different microstructures compared with conventional friction stir spot welding,thus the RFSSW joint shall possess different shear and fatigue fracture mechanisms,which needs further investigation.To explore the underlying failure mechanism,the similar/dissimilar metallic material joining parameters and pre-treatment,mechanical properties,as well as fracture mechanisms under this novel technology will be discussed.In details,the welding tool design,welding parameters setting,and the influence of processing on the lap shear and fatigue properties,as well as the corrosion resistance will be mainly discussed.Moreover,the roadmap of RFFSW is also discussed.

How to integrate hemodynamic variables during resuscitation of septic shock?

Resuscitation of septic shock is a complex issue because the cardiovascular disturbances that characterize septic shock vary from one patient to another and can also change over time in the same patient. Therefore, different therapies (fluids, vasopressors, and inotropes) should be individually and carefully adapted to provide personalized and adequate treatment. Implementation of this scenario requires the collection and collation of all feasible information, including multiple hemodynamic variables. In this review article, we propose a logical stepwise approach to integrate relevant hemodynamic variables and provide the most appropriate treatment for septic shock.

Responses of nighttime sap flow to atmospheric and soil dryness and its potential roles for shrubs on the Loess Plateau of China

Aims Nocturnal sap flow(E_(night))has been observed in a variety of plant species and environmental conditions.In water-limited environ-ments,E_(night) is important in the regulation of plant water’s physi-ology.This study was designed to evaluate the way in which E_(night)(defined as sap flow from 20:30 to 06:00)responded to changes in the atmospheric vapor pressure deficit(VPD)and the soil water con-tent(SWC),and explored its potential physiological significance for different plant species in a semi-arid area.Methods We selected three shrub species:Vitex negundo L.(VN),Hippophae rhamnoides L.(HR)and Spiraea pubescens Turcz(SP)in the semi-arid Loess Plateau of China.The plots of the three communities dominated by each of three species were on the same hill slope.Half-hourly sap flow density was measured in six to seven sample stems for each species during the main grow-ing season(June to August 2015).VPD,SWC,leaf water potential(Ψleaf)and stomatal conductance(G_(s))were measured at the same time.Regression analyses were conducted to determine the rela-tionships between E_(night),E_(day),E_(night)/E_(daily),VPD and SWC at half-hourly and daily time scales,as well as between E_(night),E_(day) andΨleaf.Important Findings The mean values of E_(night) and E_(day) were higher,but E_(night)/E_(daily) val-ues were lower for VN compared to HR and SP.The responses of sap flow density to VPD and SWC varied at different temporal scales.VPD was the dominant factor that affected E_(night) and E_(day) at the half-hourly scale for all three species.In contrast,SWC was the key factor that influenced E_(day) at the daily time scale.The values of E_(day) and E_(night)/E_(daily) correlated negatively with SWC because the effect of SWC was stronger on E_(day) than on E_(night).Although the low fraction of E_(night)/E_(daily)(4%-7%)may indicate a minor short-term effect of E_(night) on the standing water balance,E_(night) had eco-physiologically significance to the plants.The discrepancy inΨleaf between sunset and the following day’s predawn(ΔΨ)indicated that stem refilling occurred during this period.SP had the higher fraction of recharge water among the three species,as it had the relatively higher value ofΔΨ/E_(night).E_(night) had positive relation-ship with predawn Gs.The increased Gs facilitated rapid onset of photosynthesis in the early morning.In addition,the positive correlation between E_(night) and E_(day) from 06:00 to 10:30 suggested that E_(night) was beneficial for transpiration in the following morning.The responses of E_(night) to VPD and SWC indicated differences in plant adaptation to drought stress,which provides important infor-mation for our understanding of the reactions to climate changes among species in semi-arid areas.