Efficacy and economic benefits of a modified Valsalva maneuver in patients with paroxysmal supraventricular tachycardia

BACKGROUND A modified Valsalva maneuver(VM)has been suggested to be superior to the standard VM for conversion of paroxysmal supraventricular tachycardia(PSVT).AIM To evaluate the efficacy and economic benefits of a modified VM in Chinese patients.METHODS Patients with PSVT admitted to our center between October 2017 and September 2019 were randomly assigned to the modified and standard VM groups.Conversion via VM was performed up to three times.The primary outcome of the study was the success rate of PSVT conversion to sinus rhythm.The secondary outcomes included the incidence of adverse events,economic cost during the visit,and the degree of patient acceptance of the treatment.RESULTS Overall,361 patients were enrolled,with 180 allocated to the modified VM group and 181 to the standard VM group.Baseline characteristics were well matched in the groups.Overall,the modified VM group had higher success rates of PSVT conversion after single(47.78%vs 15.38%,P<0.001)and multiple(62.22%vs 19.78%,P<0.001)VM sessions.No significant differences in the incidences of adverse events and rates of patient acceptance were detected between the two groups(both P>0.05).Moreover,the economic cost of the clinic visit was significantly lower for the modified VM group than for the standard VM group(P<0.05).CONCLUSION The modified VM may confer both therapeutic and economic benefits as compared with the standard VM for conversion of PSVT.

A unified model for ductile-to-brittle transition in body-centered cubic metals

Ductile-to-brittle transition(DBT)is a well-known phenomenon in body-centered-cubic(BCC)metals,in-termetallics and semiconductor materials.A quantitative prediction of the DBT temperature,however,has so far remained intractable.Here,we propose a unified model based on the efficacy of dislocation multi-plication as the controlling factor for DBT,with the dislocation source efficiency governed by the relative mobility of screw versus edge dislocations.The model successfully predicts the DBT temperature of iron,molybdenum and tungsten,and also covers the influence of grain size,initial dislocation density,and the multiplicity of dislocation sources.A comparison with experiments indicates that the model captures the key DBT features,providing new insight into the toughness of BCC metals.

Effect of ordered helium bubbles on deformation and fracture behavior of α-Zr

Radiation-induced helium bubbles are detrimental to the mechanical properties of metals, usually causing severe hardening and embrittlement. Hexagonal close-packed(HCP) α-Zr alloys are one of the primary structural materials for nuclear applications, however, the effect of helium bubbles on their deformation and fracture behaviors still remains unexplored. Here, we found that ordered helium bubbles prefer to align along the basal plane in HCP α-Zr. Micro-scale in situ tensile tests revealed that helium bubbles less than 8 nm in size can increase the critical resolved shear stress of the prismatic slip. However, once the helium bubbles are larger than 8 nm, a bubble-softening effect happens due to a decrease in number density of helium bubbles and an increase in porosity. Once the Schmid factor of basal slip is considerably higher than prismatic slip, bubble coalescence along the basal plane becomes the major failure mode in helium-irradiated α-Zr.

Transmission electron microscopy characterization of dislocation loops in irradiated zirconium

Characterization of irradiation defects is of great importanceto mitigate irradiation damage,reduce irradiation growth and tune mechanical properties in Zr alloys.Here,we describe a practical method to characterize the dislocation loops in irradiated Zr using conventional transmission electron microscopy(TEM).Vacancy or interstitial nature of dislocation loops is determined using the inside and outside contrast method.The habit plane of dislocation loops is determined by tilting the sample to multiple zone axes and judged based on the projected loop shape.The size ofloops is measured by tilting the sample to an edge-on position and the loop number is counted under a weak-beam dark-field TEM condition.<c>loops have a line contrast under viewing direction of a-axis and a circular shape under viewing direction of c-axis.In addition,a large number of triangle-shaped vacancy platelets(TVPs)were formed on the basal plane.With increasing the irradiation damage from 0.5 to 1.5 dpa,the number density ofloops keeps constant,while the number density of TVPs increased significantly,owing to the anisotropic diffusion and accumulation of point defects within basal plane.The methods introduced here are easy to follow and extend into other related investigations.