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Microstructure and mechanical properties of friction stir welded AA7075-t651 aluminum alloy thick plates

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transactions of Nonferrous Metals Society of China 2015年第6期25卷 1770-1778页

作者： t.SRINIVASA RAO g.MADHUSUDHAN REDDY S.R.KOtESWARA RAO Department of Mechanical Engineering Tagore Engineering College Metal Joining group Defense Metallurgical Research Laboratory Department of Mechanical Engineering SSN College of Engineering

Friction stir butt welding of AA7075-t651 plates with thicknesses of 10 and 16 mm was investigated. Defect-free, full- penetration welds were obtained after careful process parameter selection. While the nuggets in both welds exhibited very fine reerystallized grains, and finer grains were observed in welds made on 10 mm thick plates. Microhardness surveys revealed that significant loss in hardness occurs in the heat-affected zone. the reduction in hardness due to the welding process is higher in the case of welds made on 16 mm thick plates. Welds made on 10 mm thick plates exhibited superior tensile properties compared with those made on 16 mm thick plates. Fracture during tensile test occurred in the heat-affected zone in both cases. tEM images of specimens revealed that the heat-affected zone consisted of widened precipitate-free zones along grain boundaries and partial dissolution of precipitates in the grain interiors. It is concluded that defect-free single pass welds can be made on AA7075-t651 thick plates using friction stir welding and the welds made on 10 mm thick plates exhibit high joint efficiency.

关键词： AA7075-t651 aluminum alloy friction stir welding microstructure mechanical properties

titanate Nanorods Modified with Nanocrystalline ZnS Particles and their Photocatalytic Activity on Pollutant Removal

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Journal of Materials Science & technology 2016年第11期32卷 1122-1128页

作者： g.Naudin t.Entradas B.Barrocas O.C.Monteiro Faculte de Chimie Universite Pierre et Marie Curie (UPMC) Batiment F 3e etage 4 placeJussieu 75005 Paris France Centro de Quimica e Bioquimica Faculdade de Ciencias Universidade de Lisboa 1749-016 Lisboa Portugal

Aiming to produce materials with enhanced photocatalytic properties, the synthesis of new crystalline nanocomposites by combining titanate nanorods（tNR） with ZnS nanocrystallites is described in this *** tNR modification was accomplished by an in situ nucleation and growth process of ZnS *** diethyldithiocarbamate was used as the metal chalcogenide precursor. the prepared materials were structural, morphological and optical characterized by X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy, energy dispersive spectroscopy and powder diffuse reflectance spectra. Crystalline Zn S nanoparticles were obtained as a homogeneous and continuous layer, covering completely the tNR surface. the application of these new nanocomposite materials on photocatalytic degradation of pollutants was investigated. First, the evaluation of hydroxyl radical formation, using the terephthalic acid as probe, was studied. Afterwards, the adsorption and photodegradation of safranine-t, used here as a model pollutant molecule, was investigated. the obtained data indicate that the prepared nanocomposites have potential to be used as photocatalysts for organic pollutant *** best removal results（97% removal） were obtained using the 0.01 Zn S/HtNR sample as catalyst（0.2 g/L; 10 ppm safranin-t solution） with a combination of a low dye adsorption（20%） and a high dye photocatalytic degradation（77%）.

关键词： Nanocomposite materials Surface modification Photocatalysis Adsorption ability Optical properties

EFFECt OF PREDEFORMAtION MANNER ON SEMI-SOLID StRUCtURE OF AZ61 MAgNESIUM ALLOY IN SIMA PROCESS

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Acta Metallurgica Sinica(English Letters) 2008年第3期21卷 197-204页

作者： g.P. Chen t.R. Zhou H. Yan School of Mechanical and Electrical Engineering Nanchang University Nanchang 330000 China School of Mechanical Engineering Hunan Industrial University Zhuzhou 412008 China

the effect of predeformation manner, predeformation ratio and isothermal heat-treat parameter on the non-dendrite structure of AZ61 magnesium alloy in SIMA process was studied. Under coequal heat-treat condition, the impact of the hot upsetting pre- deformation on semi-solid microstructure in SIMA process was compared with that of the cold compressive predeformation. the results indicate that non-dendrite microstructure in AZ61 magnesium alloy billets can be obtained by hot or cold upsetting predeformation in SIMA process, although their mechanisms of evolution are different. Increasing hot or cold upsetting predeformation ratio can enhance the effect and quality of the non-dendrite microstructure formed before storage energy up to saturation, but the proper isothermal temperature and holding time should be selected.

关键词： AZ61 magnesium alloy Strain-induced melt activated (SIMA) Hot and cold upsetting Predeformation Non-dendrite structure

A striking confluence between theory and observations of high-mass X-ray binary pulsars

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Research in Astronomy and Astrophysics 2018年第10期18卷 117-122页

作者： Dimitris M.Christodoulou Silas g.t.Laycock Demosthenes Kazanas Lowell Center for Space Science and technology University of Massachusetts Lowell Dept.of Mathematical Sciences Univ.of Massachusetts Lowell Dept. of Physics & Applied Physics Univ. of Massachusetts Lowell NASA/gSFC Laboratory for High-Energy Astrophysics

We analyze the most powerful X-ray outbursts from neutron stars in eleven Magellanic high-mass X-ray binaries and three pulsating ultraluminous X-ray sources. Most of the outbursts rise to Lmax which is about the level of the Eddington luminosity, while the remaining more powerful outbursts also appear to recognize that limit when their emissions are assumed to be anisotropic and beamed toward our direction. We use the measurements of pulsar spin periods Ps and their derivatives Ps to calculate the X-ray luminosities Lp in their faintest accreting （＂propeller-line＂） states. In five cases with unknown Ps, we use the lowest observed X-ray luminosities, which only adds to the heterogeneity of the sample. then we calculate the ratios Lp/Lmax and we obtain an outstanding confluence of theory and observations from which we conclude that work done on both fronts is accurate and the results are trustworthy： sources known to reside on the lowest Magellanic propeller line are all located on/near that line, whereas other sources jump higher and reach higher-lying propeller lines. these jumps can be interpreted in only one way, higher-lying pulsars have stronger surface magnetic fields in agreement with previous empirical results in which Ps and Lp values were not used.

关键词： accretion accretion disks - stars magnetic fields - stars neutron - X-rays binaries

the influence of hydrogel soil amendment on the survival and growth of newly transplanted Pinus patula seedlings

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Journal of Forestry Research 2018年第1期29卷 103-109页

作者： Ada Mudhanganyi Hilton g.t.Ndagurwa Carlton Maravanyika Robert Mwase Department of Forest Resources and Wildlife Management Faculty of Applied Science National University of Science and Technology Forest Ecology Laboratory Faculty of Applied ScienceNational University of Science and Technology Stapleford Forest Allied Timbers Limited

Hydrogel amendments have been used to improve seedling survival and establishment particularly in dry environments. However, their effect on survival and growth of newly transplanted seedlings under varying water stress conditions is poorly known. In this regard, we examined the effects of Aqua Matrix Forestry~？, a potassium-based water-absorbent polymer, on the survival and early growth of Pinus patula seedlings planted in early-,mid-and late-dry season in the eastern highlands of Zimbabwe. the late-dry season was hotter and received more rainfall than the early-and mid-dry season. Hydrogel increased seedling survival by 34 and 22% in the mid-and late-dry season, respectively. Also, hydrogel-treated seedlings were significantly taller than untreated seedlings（P ／ 0.001）. the height to root collar diameter ratio of hydrogel-treated seedlings was greater than that of untreated seedlings only in the mid-dry season. In conclusion, increase in survival and early growth of hydrogel-treated seedlings suggests that hydrogels can be used to extend planting beyond the rainy season to include the dry months, a feat previously unattainable due to high seedling mortality. Further, these findings reflect similar findings with other hydrogels, suggesting that improved seedling survival and plant performance may be a general consequence of hydrogel amendments.

关键词： Hydrogel Pinus patula Reforestation Seedling Survival

RF and microwave characteristics of a 10 nm thick IngaN-channel gate recessed HEMt

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Journal of Semiconductors 2013年第11期34卷 36-41页

作者： t.R.Lenka g.N.Dash A.K.Panda Department of Electronics and Communication Engineering National Institute of Technology Silchar School of Physics Sambalpur University National Institute of Science and technology

A new depletion-mode gate recessed A1gaN/IngaN/gaN-high electron mobility transistor （HEMt） with 10 nm thickness of IngaN-channel is proposed. A growth of A1gaN over gaN leads to the formation of two- dimensional electron gas （2DEg） at the heterointerface. High 2DEg density （ns） is achieved at the heterointerface due to a strain induced piezoelectric effect between A1gaN and gaN layers. the electrons are confined in the IngaN-channel without spilling over into the buffer layer, which also reduces the buffer leakage current. From the input transfer characteristics the threshold voltage is obtained as -4.5 V and the device conducts a current of 2 A/mm at a drain voltage of 10 V. the device also shows a maximum output current density of 1.8 A/ram at Vds of 3 V. the microwave characteristics like transconductance, cut-off frequency, max frequency of oscillation and Mason＇s Unilateral gain of the device are studied by AC small-signal analysis using a two-port network. the stability and power performance of the device are analyzed by the Smith chart and polar plots respectively. to our knowledge this proposed IngaN-channel HEMt structure is the first of its kind.

关键词： 2DEg HEMt IngaN microwave

Space decomposition based parallelization solutions for the combined finiteediscrete element method in 2D

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Journal of Rock Mechanics and geotechnical Engineering 2014年第6期6卷 607-615页

作者： t.Lukas g.g.Schiava D'Albano A.Munjiza School of Engineering and Materials Science Queen Mary University of LondonUK

the combined finiteediscrete element method （FDEM） belongs to a family of methods of computationalmechanics of discontinua. the method is suitable for problems of discontinua, where particles aredeformable and can fracture or fragment. the applications of FDEM have spread over a number of disciplinesincluding rock mechanics, where problems like mining, mineral processing or rock blasting canbe solved by employing FDEM. In this work, a novel approach for the parallelization of two-dimensional（2D） FDEM aiming at clusters and desktop computers is developed. Dynamic domain decompositionbased parallelization solvers covering all aspects of FDEM have been developed. these have beenimplemented into the open source Y2D software package and have been tested on a PC cluster. theoverall performance and scalability of the parallel code have been studied using numerical examples. theresults obtained confirm the suitability of the parallel implementation for solving large scale problems. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

关键词： Parallelization Load balancing PC cluster Combined finiteediscrete element method(FDEM)

Effect of equal channel angular extrusion on Al-6063 bending fatigue characteristics

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International Journal of Minerals,Metallurgy and Materials 2015年第4期22卷 395-404页

作者： J.Nemati g.H.Majzoobi S.Sulaiman B.t.H.t.Baharudin M.A.Azmah Hanim Department of Mechanical and Manufacturing Engineering University Putra Malaysia Engineering Faculty Bu-Ali Sina University School of Mechanics Islamic Azad UniversityTakestan Branch

the purpose of this investigation was to refine the grains of annealed 6063 aluminum alloy and to improve its yield stress and ul- timate strength. this was accomplished via the equal channel angular extrusion （ECAE） process at a temperature of 200℃ using route A, with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels for as many as 6 passes. the experiments were conducted on an Avery universal testing machine. the results showed that the grain diameter decreased from 45 μm to 2.8 μm after 6 extru- sion passes. the results also indicated that the major improvement in fatigue resistance occurred after the first pass. the subsequent passes improved the fatigue life but at a considerably lower rate. A maximum increase of 1100% in the case of low applied stresses and an ap- proximately 2200% increase in fatigue resistance in the case of high applied stresses were observed after 5 passes. the improvement of fa- tigue resistance is presumed to be due to （1） a reduction in the size and the number of Si crystals with increasing number of ECAE passes, （2） the aggregation of Cu during the ECAE process, （3） the formation and growth of CuA12 grains, and （4） grain refinement of the A1--6063 alloy during the ECAE process.

关键词： aluminum alloys equal channel angular pressing bending fatigue life grain size microstructure

Fatty acids of erythrocyte membrane in acute pancreatitis patients

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World Journal of gastroenterology 2013年第34期19卷 5678-5684页

作者： Irma Kuliaviene Antanas gulbinas Johannes Cremers Juozas Pundzius Limas Kupcinskas Zilvinas Dambrauskas Eugene jansen Department of gastroenterology Medical AcademyLithuanian University of Health Sciences Department of Surgery Medical AcademyLithuanian University of Health Sciences Institute for Digestive Research Medical AcademyLithuanian University of Health Sciences Centre for Health Protection National Institute for Public Health and the Environment 3720 BA Bilthoven The Netherlands

AIM:to evaluate changes in the fatty acid composition of erythrocyte membrane phospholipids during severe and mild acute pancreatitis(AP)of alcoholic and nonalcoholic ***:All consecutive patients with a diagnosis of AP and onset of the disease within the last 72 h admitted to the Hospital of Lithuanian University of Health Sciences between June and December 2007 were *** to the Acute Physiology and ChronicHealth Evaluation(APACHEⅡ)scale,the patients were subdivided into the mild(APACHEⅡscoreted from patients on admission to the *** acids(FAs)were extracted from erythrocyte phospholipids and expressed as percentages of the total FAs present in the *** concentrations of superoxide dismutase and glutathione peroxidase were measured in ***:We found an increase in the percentages of saturated and monounsaturated FAs,a decrease in the percentages of total polyunsaturated FAs(PUFAs)and n-3 PUFAs in erythrocyte membrane phospholipids of AP patients compared with healthy ***(C16:0),palmitoleic(C16:1n7cis),arachidonic(C20:4n6),docosahexaenoic(DHA,C22:6n3),and docosapentaenoic(DPA,C22:5n3)acids were the major contributing factors.A decrease in the peroxidation and unsaturation indexes in AP patients as well as the severe and mild AP groups as compared with controls was *** concentrations of antioxidant enzymes in the mild AP group were lower than in the control *** severe AP of nonalcoholic etiology,the percentages of arachidic(C20:0)and arachidonic(C20:4n6)acids were decreased as compared with the control *** patients with mild AP of nonalcoholic etiology had the increased percentages of total saturated FAs and gama linoleic acid(C18:3n6)and the decreased percentages of elaidic(C18:1n9t),eicosapentaenoic acid(EPA,C20:5n3),DPA(C22:5n3),DHA(C22:6n3)as we

关键词： Acute pancreatitis Alcohol Fatty acids Oxidative stress Systemic inflammatory response syndrome