在可逆过程中·d■不是外力对系统所作的功

本文首先论述了相对论热力学可逆过程,并证明它与惯性系无关.进而证明在可逆过程中,基本公式dR=dE+pdV-(?·d(?)中的(?)．d(?)不是外力对系统所作的功．在讨论中,我们对几种认为(?)·d(?)是外力对系统作功的观点作了分析.

从微观角度再看理想气体的绝热过程

在＂从微观角度看理想气体的绝热过程＂一文中提到了一种从微观角度来计算理想气体绝热公式的推导,这一推导中的物理本质为气体分子对活塞壁做功的集体效应,即气体压强的微观解释.基于这一思考,从气体分子对外做功的角度给出了相应的推导,同时发现该文结论在其给定模型下的一个更为直观的解,与热力学第一定律中的做功项可以更直接地对应,从而更直接地联系起微观过程和宏观的理想气体状态方程.

Effect of laser power on microstructure and mechanical properties of laser heat conduction lap welded joint between AZ31B magnesium alloy and DP780 galvanized steel

In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and mechanical properties of the joint were studied. The pros and cons of the joint were identified and evaluated by measuring the tensile shear strength, microhardness and microstructure observation. The formation mechanism of various phases at the Mg/steel interface was analyzed. The results indicated that the galvanized layer could promote the metallurgical bonding between magnesium alloy and steel by improving the diffusion ability of molten magnesium alloy at the steel interface and reacting with Mg, so as to enhance the strength of the joint. A continuous dense layered eutectic structure(α-Mg+MgZn) was formed at the interface of the joint, while MgZn_(2)and MgZn phase was formed at the weld edge zone and heat affective zone(HAZ), whereas no reaction layer was generated between the uncoated steel and magnesium alloy. A sound joint could be obtained at 2.5 kW, and the corresponding tensile shear strength reached the maximum value of 42.9 N/mm. The strength was slightly reduced at 2.6 kW due to the existence of microcracks in the eutectic reaction layer.

Impact of ultrasonic power on liquid fraction,microstructure and physical characteristics of A356 alloy molded through cooling slope

This study involves A356 alloy molded through ultrasonically vibrated cooling slope.The slope alongside ultrasonic power enables indispensable shear for engendering slurry from which the semisolid cast/heat treated billets got produced.An examination demonstrates ultrasonically vibrated cooling slope influencing the liquid fraction/microstructure/physical characteristics of stated billets.The investigation encompasses five diverse ultrasonic powers(0,75,150,200,250 W).The ultrasonic power of 150 W delivers finest/rounded microstructure with enhanced physical characteristics.Microstructural modifications reason physical transformations because of grain refinement and grain boundary/Hall-Petch strengthening.A smaller grain size reasons a higher strength/shape factor and an increased homogeneity reasons a higher ductility.Microstructural characteristics get improved by reheating.It is owing to coalescence throughout temperature homogenization.The physical characteristics is improved by reheating because of a reduced porosity and enhanced dissolution besides augmented homogeneity.A direct comparison remains impossible owing to unavailability of researches on ultrasonically vibrated cooling slope.

Effects of penehyclidine hydrochloride on rat intestinal barrier function during cardiopulmonary bypass

AIM:To test the ability of penehyclidine hydrochloride (PHC) to attenuate intestinal injury in a rat cardiopulmonary bypass (CPB) model.METHODS:Male Sprague-Dawley rats were randomly divided into six groups (eight each):sham-operated control;sham-operated low-dose PHC control (0.6 mg/kg);sham-operated high-dose PHC control (2.0 mg/kg);CPB vehicle control;CPB low-dose PHC (0.6 mg/kg);and CPB high-dose PHC (2.0 mg/kg).Blood samples were collected from the femoral artery 2 h after CPB for determination of plasma diamine oxidase (DAO),D-lactate and endotoxin levels.Spleen,liver,mesenteric lymph nodes and lung were removed for biochemical analyses.Intestinal tissue ultrastructure was examined by electron microscopy.RESULTS:In the sham-operated groups,high-and low-dose-PHC had no significant impact on the levels of DAO,D-lactate and endotoxin,or the incidence of intestinal bacterial translocation (BT).Serum levels of DAO,D-lactate,endotoxin and the incidence of intestinal BT were significantly increased in the surgical groups,compared with the sham-operated groups (0.543 ± 0.061,5.697 ± 0.272,14.75 ± 2.46,and 0/40 vs 1.038 ± 0.252,9.377 ± 0.769,60.37 ± 5.63,and 30/40,respectively,all P < 0.05).PHC alleviated the biochemical and histopathological changes in a dosedependent manner.Serum levels of DAO,D-lactate,and endotoxin and the incidence of intestinal BT in the high-dose PHC group were significantly lower than in the low-dose PHC group (0.637 ± 0.064,6.972 ± 0.349,29.64 ± 5.49,and 14/40 vs 0.998 ± 0.062,7.835 ± 0.330,38.56 ± 4.28,and 6/40,respectively,all P < 0.05).CONCLUSION:PHC protects the structure and function of the intestinal mucosa from injury after CPB in rats.

Effect of laser heating on the microstructure and hardness of TRIP590advanced high strength steel used for roll forming

TRIP590 advanced high strength steel sheets were heated by laser with different powers.Changes of the microstructure and the hardness of TRIP590 steel under laser heating with different powers were investigated by metallographic microscope,scanning electron microscope,and hardness tester.The purpose was to study the effect of laser power on microstructure and hardness of TRIP590 steel.It is shown that the power of laser plays an important role on the microstructure and hardness of heated steel sheets.The results are helpful to determine suitable power for the laser auxiliary forming of Trip590 steel in order to obtain uniform microstructure and high hardness.

Fabrication and characterization of high density LaB_(6) polycrystalline with(100) preferred orientation

High density lanthanum hexaboride(LaB_(6))polycrystalline with(100)preferred orientation was prepared by spark plasma sintering(SPS)using LaB_(6) nanocubes as raw materials in this work.Microstructure and thermionic electron emission property of LaB_(6) polycrystalline were investigated detailedly.The results show that the LaB_(6) polycrystalline had a relative density of 95.8%,and there was a(100)preferred orientation on its surface normal to SPS pressing direction.The work function of LaB_(6) polycrystalline normal surface was only 2.73 eV,which was almost close to the theoretical work function of LaB_(6)(100)single crystal surface.The reasons for preferential orientation of LaB_(6) polycrystalline were analyzed.