嗜碱耐盐奇异变形杆菌病原学实验研究

为了解嗜碱耐盐性奇异变形杆菌的生物学特征及致病力 ,用生化试验、ELISA、动物试验等方法进行病原学鉴定及毒力试验。该奇异变形杆菌除能在pH1 0和 10 %Nacl的培养基上生长外 ,其余生理生化特征无特殊表现。内毒素检出率为 10 0 % ,2株检出ST ;对小白鼠的致病力很强 ,能产生耐热性溶血素 ,80 %以上菌株产生超广谱 β -内酰胺酶 ,3重以上耐药株发生率 10 0 %。本组奇异变形杆菌具有嗜碱耐盐性 ,其生物学特征与变形杆菌标准菌株无特殊区别 。

多种类沥青及复合改性材料常规-流变性能相关性分析

通过试验研究胶粉改性沥青、SBS改性沥青及混合改性沥青微观组织结构、高温环境与低温环境对其流变性能影响。测试结果表明:胶粉改性沥青、SBS改性剂与沥青相容性较好,但橡胶粉改性沥青与石材之间界面附着力高于SBS改性沥青。DSR试验表明:橡胶粉改性沥青温度具备低温耐裂性及高温耐变形性。综上对混合改性沥青流变性能研究,旨在为我国研发新型高性能沥青提供有效技术支持。

多种类沥青及复合改性材料常规-流变性能相关性分析

通过试验研究胶粉改性沥青、SBS改性沥青及混合改性沥青微观组织结构、高温环境与低温环境对其流变性能影响。测试结果表明:胶粉改性沥青、SBS改性剂与沥青相容性较好,但橡胶粉改性沥青与石材之间界面附着力高于SBS改性沥青。DSR试验表明:橡胶粉改性沥青温度具备低温耐裂性及高温耐变形性。综上对混合改性沥青流变性能研究,旨在为我国研发新型高性能沥青提供有效技术支持。

Properties and microstructure of Ti6Al4V by deformation accelerated low temperature plasma nitriding

An integrated low-temperature nitriding process was carried out for Ti6Al4V to investigateitseffect on microstructure and properties.The process was designed to enhance the nitriding kinetics in low-temperature（500℃） nitriding by deformation, and to strengthen Ti6Al4V alloybydispersionat the same time. Specimens of Ti6Al4V alloyweretreated through the process of solid solutionstrengthening-cold deformation-nitriding at 500℃. The white nitriding layeris formed after some time and then kept stable, changing little withthedeformationdegreeand time. The effect of aging on substrate is significant. Surface hardness and substrate hardnessincrease with deformation increasing. The construction was investigated by XRD.The surface nitridesare TiN, Ti2N, Ti4N3-Xand Ti3N1.29,and thenitridesin cross-section are Ti3N1.29and TiN0.3. The wear tests of specimens after nitriding, aging and deformation were carried out,andthetest data show that the nitrided pieces have the best wear resistance.

Corrosion properties of plastically deformed AZ80 magnesium alloy

AZ80 magnesium alloys were deformed at 200,250,300,350 and 400℃ with different deformation degree of 50%,75%, 83%,87%and 90%,respectively.The corrosion properties of different deformed AZ80 samples were studied by galvanic test in 3.5%NaCl solution.The results show that plastic deformation could improve the corrosion resistance of AZ80 alloy;and the corrosion rate of AZ80 deformed at 250℃ with the deformation degree of 83%was the lowest,which was 33%of the as-cast AZ80 alloy.Further studies of the microstructure show that the refined grain size and continuously distribution ofβphase around the grain boundary did have a positive effect on the improvement of corrosion resistance of AZ80 alloys.For AZ80 alloys,the smaller the grain size is,the more homogeneous the structure is,and the better the corrosion resistance is.

Wear resistance of TC4 by deformation accelerated plasma nitriding at 400 °C

An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400℃, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti3N（2-X）. The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.

Efficient energy absorption of functionally-graded metallic foam-filled tubes under impact loading

The deformation behavior and crashworthiness of functionally-graded foam-filled tubes(FGFTs)under drop-weight impact loading were investigated.Closed cell aluminum,A356 alloy and zinc foams fabricated by the liquid state processing were used as axial grading fillers for the manufacture of single-layer and multilayer structures with different configurations.The results indicate that the deformation of multilayer foam filled tubes initiates from the low-strength components,and then propagates in the high-strength components through the gradual increment of stress.The use of more A356 alloy and aluminum foam layers provides greater specific energy absorption(SEA)for the graded structures,whereas the high-strength zinc foam has no positive effect on the crash performance.The progressive collapse of graded structures consisting of the aluminum and A356 alloy foams occurs in a symmetric mode under quasi-static and drop-weight impact conditions.However,the zinc foam causes a combination of symmetric and extension modes as well as greater localized deformation under dynamic loading and greater local rupture in quasi-static loading condition.The Al−A356 foam-filled tubes with a combination of the highest SEA(10 J/g)and the lowest initial peak stress(σmax of 10.2 MPa)are considered as the best lightweight crashworthy structures.

Enhancing mechanical properties and corrosion performance of AA6063 aluminum alloys through constrained groove pressing technique

The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity is considerably decreased after the first pass, while subsequent passes result in better hardness behavior for the processed material. Also, the elongated grains formed in the first pass of the CGP are gradually converted to the equiaxed counterparts by adding pass numbers. Eventually, higher corrosion resistance of the sample by imposing the CGP process is related to the quick formation of passivation film and the change in the morphology of the second phase and precipitates which hinder their electrochemical reactions and decrease the potential localized attack sites.

Construction and Verification of LuxS-negative Mutants of Streptococcus Mutans and the Effect of the Absence of LuxS Gene on the Acid Tolerance

Objective: To knock out the entire Luxs gene of Streptococcus mutans(S.mutans) UA159 strain via homologous recombination and construct a Luxs-deleted mutant strain of S. mutans. To study the difference between the acid resistance of S. mutans Ingbritt C international standard strain and the acid resistance of LuxS mutant strain. Methods: Two DNA fragments locating in the upper and downstream of Luxs gene were amplified and a erythromycin resistance gene of PJT10 between them were engineered into PUC19 plasmid for constructing the recombination plasmid pUCluxKO. Electrotransformation of S.mutans cells with pUCluxKO-mutant resulted in isolation of erythromycin resistant S. mutans transformants, which was identified by polymerase chain reaction, V.harveyi BB170 luminescence bioassay and sequencing analysis. Solutions of S. mutans standard strain and LuxS mutant strain with same density were made and cultured at pH 3.5 to 7.0 BHI liquid for the same period.Terminal growth situation was compared.Firstly acidized in pH 5.5 BHI liquid,the two strains were cultured at pH 3.0 BHI liquid. The acid tolerance responses of the two strains were compared.Results:Restriction endonuclease analyses showed that pUCluxKO-mutant vector had been successfully recombined. The Luxs-deleted status of S.mutans mutants was confirmed by PCR with primers which were specific for the genes of Luxs and Erythromycin resistance. S.mutans mutant can not induce bioluminescence, indiating the mutant had been successfully recombined. After twenty generations of culture, the constructed Chinese S.mutans mutants were confirmed to be stable. Significant difference of aciduricity was observed between S.mutans standard strain and LuxS mutant strain.The acid resistance of standard strain was stronger than that of LuxS mutant strain.The two strains both displayed the capability of acid tolerance responses. Conclusion:The S.mutans gene allelic exchange plasmid is constructed correctively and a Luxs-negative mutants of S.mutans is constructed, which can help to further study the role of Luxs in the pathogenesis of S.mutans. LuxS mutant strain is more sensitive to acid inactivation,but the capability of acid tolerance responses exist still.