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Oxidation Mechanisms in MgO-C Refractories

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China's Refractories 2004年第2期13卷 13-20页

作者： b.hashemi Z.Ali Nemati S.K.Sadrnezhaad Department of Materials Science and Engineering Department of Materials Science and Engineering Department of Materials Science and Engineering Sharif University of Technology TehranIran11365-9466Sharif University of Technology TehranIran11365-9466Sharif University of Technology TehranIran11365-9466

An investigation on the oxidation mechanism of the graphite in the MgO-C refractory materials is helpful to improving both the quality of these materials and to preventing and/or lowering of the adverse effects of the high-temperature oxidation. In this research, the oxidation behavior of the MgO-C refractories containing 5～20 wt% graphite was studied via weight-loss method. Atmospheric air was used for oxidation at temperatures ranging from 900℃ to 1300°C and the experimental data were compared with those obtained from the dimensionless kinetic equations of the shrinking core model, in order to determine the oxidation mechanisms of the refractories. The best fit was achieved with the porous layer diffusion control regime. Oxidation mechanism tends, however, to slightly deviate from pure pore diffusion control to pore diffusion-external gas transfer regime in the samples having more graphite contents (e.g. 20%).

关键词： MgO Carbon Diffusion Refractories Oxidation

Analysis of the formation conditions and characteristics of interphase and random vanadium precipitation in a low-carbon steel during isothermal heat treatment

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International Journal of Minerals,Metallurgy and Materials 2018年第3期25卷 339-349页

作者： Sayed Ghafar hashemi b.Eghbali Department of Materials Engineering Sahand University of Technology

The characteristics of nanosized precipitates in steels depend on the heat-treatment parameters. The effects of characteristics of vanadium precipitates formed during isothermal heat treatment on the hardness of the ferrite matrix in low-carbon vanadium-alloyed steel were investigated through analysis of transmission electron microscopy images and microhardness measurements. The results show that, during isothermal holding in the temperature range from 675 to 750℃, only interphase precipitation occurs, whereas only random precipitation occurs in the ferrite matrix during holding at 600℃. Furthermore, during isothermal heat treatment between 600 and 675℃, both random and interphase precipitates occurred in the ferrite. Nanoscale vanadium carbides with different atomic ratios of vanadium(V) and carbon(C) were the dominant precipitates in the random and interphase precipitates. The sizes of random precipitation carbides were smaller than those of interphase ones. Also, the sample isothermally heat treated at 650℃ for 900s exhibited a higher hardness with a narrower hardness distribution.

关键词： low carbon steel vanadium carbide precipitation heat treatment microhardness

Attuned design of demand response program and M-FACTS for relieving congestion in a restructured market environment

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Frontiers in Energy 2015年第3期9卷 282-296页

作者： Y. hashemi H. SHAYEGHI b. hashemi Technical Engineering Department University of Mohaghegh Ardabili Ardabil *** Iran Network Studies Group Bakhtar Regional Electric Company Arak *** Iran

This paper addresses the attuned use of multi- converter flexible alternative current transmission systems （M-FACTS） devices and demand response （DR） to perform congestion management （CM） in the deregulated environment. The strong control capability of the M- FACTS offers a great potential in solving many of the problems facing electric utilities. besides, DR is a novel procedure that can be an effective tool for reduction of congestion. A market clearing procedure is conducted based on maximizing social welfare （SW） and congestion as network constraint is paid by using concurrently the DR and M-FACTS. A multi-objective problem （MOP） based on the sum of the payments received by the generators for changing their output, the total payment received by DR participants to reduce their load and M-FACTS cost is systematized. For the solution of this problem a nonlinear time-varying evolution （NTVE） based multi-objective particle swarm optimization （MOPSO） style is formed. Fuzzy decision-making （FDM） and technique for order preference by similarity to ideal solution （TOPSIS） approaches are employed for finding the best compromise solution from the set of Pareto-solutions obtained through multi-objective particle swarm optimization-nonlinear time-varying evolution （MOPSO-NTVE）. In a real power system, Azarbaijan regional power system of Iran, comparative analysis of the results obtained from the application of the DR ＆ unified power flow controller （UPFC） and the DR ＆ M-FACTS are presented.

关键词： multi-converter flexible alternative currenttransmission systems (M-FACTS) demand response,

Application of biocementation technique using bacillus sphaericus for stabilization of soil surface and dust storm control

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Journal of Arid Land 2022年第5期14卷 537-549页

作者： Davood NAMDAR-KHOJASTEH Masoud bAZGIR Seyed Abdollah hashemi bAbAHEIDARI Akwasi b ASUMADU-SAKYI Department of Soil Science Faculty of AgricultureShahed UniversityTehran ***Iran Department of Soil and Water Engineering Faculty of AgricultureIlam UniversityIlam ***Iran Department of Plant Protection Faculty of AgricultureShahed UniversityTehran ***Iran International Laboratory for Air Quality and Health School of ChemistryPhysics and Mechanical EngineeringQueensland University of TechnologyBrisbaneQueensland 4000Australia

Dust emission and wind erosion are widespread phenomena in arid and semi-arid regions,which have far-reaching harmful effects to the *** study aimed to use microbial induced carbonate precipitation(MICP)method with bacillus sphaericus to reduce soil losses that occur in a dust-producing area due to wind erosion in the Ilam Province,*** samples at the 0-30 cm depth were used and sterilized in an autoclave for 2 h at 121℃ and 103 *** 3 kg soils were weighed and poured in the 35 cm×35 cm×3 cm *** treatments included two levels of ***(0.0 and 0.5 OD),three levels of suspension volume(123,264,and 369 mL),two levels of urea-chloride cementation solution(0.0 and 0.5 M),and two levels of bacterial spray(once and twice spray).After 28 d,soil properties such as soil mass loss,penetration resistance,and aggregate stability were *** results showed a low soil mass loss(1 g)in F_(14)formulation(twice bacterial spray+264 mL suspension volume+without cementation solution)and a high soil mass loss(246 g)in F_(5) formulation(without bacteria+264 mL suspension volume+0.5 M cementation solution).The highest(42.55%)and the lowest(19.47%)aggregate stabilities were observed in F_(16)and F_(7)formulations,respectively,and the highest penetration resistance(3.328 kg/cm^(2))was observed in F_(18) *** to the final results,we recommended the formulation with twice bacterial spray,0.5 M cementation solution,and 269 mL suspension volume as the best combination for soil surface ***,this method is environmentally friendly because it has no adverse effects on soil,water,and plants,thus,it would be an efficient approach to stabilize soil surface.

关键词： soil stabilization microbial cementation calcium carbonate bacteria penetration resistance

Undirected Zero-Divisor Graphs and Unique Product Monoid Rings

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Algebra Colloquium 2019年第4期26卷 665-676页

作者： Ebrahim hashemi Abdollah Alhevaz LAbokut Faculty of Mathematical Sciences Shahrood University of Technology P.O.Box:316-***ShahroodIran 不详

Let R be an associative ring with identity and Z^*(K)be its set of non-zero *** undirected zero-divisor graph of R、denoted byΓ(R),is the graph whose vert ices are the non-zero zero-divisors of R、and where two distinct verticesγand s are adjacent if and only ifγs=0 or sγ=*** dist ance bet ween vertices a and b is the length of the shortest path connecting them,and the diameter of the graph,diam(Γ(R)),is the superimum of these *** this paper,first we prove some results aboutΓ(R)of a semi-commutative ring ***,for a reversible ring R and a unique product monoid M、we prove 0≦diam(Γ(R))be all the possibilities for the pair diam(Γ(R))and diam(Γ(R[M])),strictly in terms of the properties of a ring R,where K is a reversible ring and M is a unique product ***,an example showing the necessity of our assumptions is provided.

关键词： zero-divisor graph diameter semi-commutative ring unique product monoid monoid ring

INVESTIGATING SILVICULTURAL CHARACTERISTICS OF YEW （TAXUS bACCATA L.） STAND USING FULL-CALLIPERING IN NORTHERN FORESTS OF IRAN

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International Journal of biomathematics 2013年第1期6卷 105-114页

作者： MIR MOZAFFAR FALLAHCHAI SEYED ARMIN hashemi GASEM RAHANJAM Department of Forestry Lahijan Branch Islamic Azad University Lahijan Iran MS. c Forestry Department of Forestry Lahijan Branch Islamic Azad University Lahijan Iran

In this research, some of site and silvicultural characteristics of Yew stand in northern forests of Iran was studied. For this purpose, compartment number 16 of district 4 Shir-ghalaye was selected. According to research purposes, stands with an area of 20 ha were chosen in center of the compartment and was separated from map. Due to restricted area of region and according to few number of Yew trees in the stand, the full-callipering method was conducted for measuring quantitative and qualitative characteristics. In the stand diameter at breast height （D.b.H.）, height and canopy diameter of all Yew trees were measured. The results showed that the diameter distribution curve and height distribution curve of Yew trees were similar to even-age forests curve. but according to average annual increment, mixture type of Yew trees in stand, diameter distribution of other species and low rate regeneration of Yew, it can be concluded that the studied Yew stand, is an uneven-age stand and because of low rate regeneration in previous years the number of young Yew trees were reduced and even-age forest curve was formed subsequently. The maximum height and diameter of Yew trees were recorded 26.8 m and 112 cm, respectively. Also, the number of trees per hectare and basal area per hectare of Yew trees were calculated 14.55 and 3.23 m2 respectively.

关键词： Silviculture full-callipering Yew.

Voltage rise mitigation for solar PV integration at LV grids Studies from ***

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Journal of Modern Power Systems and Clean Energy 2015年第3期3卷 411-421页

作者： Guangya YANG Francesco MARRA Miguel JUAMPEREZ Søren bækhøj KJÆR Seyedmostafa hashemi JacobØSTERGAARD Hans Henrik IPSEN Kenn H.b.FREDERIKSEN Centre for Electric Power and Energy Department of Electrical EngineeringTechnical University of Denmark2800 Kgs.LyngbyDenmark Danfoss Solar Inverter A/S 6430 NordborgDenmark Østkraft 3700 RønneDenmark FREDERIKSEN Energimidt8600 SilkeborgDenmark

Solar energy from photovoltaic(PV)is among the fastest developing renewable energy systems *** by governmental subsidies and technological development,Europe has seen a fast expansion of solar PV in the last few *** the installed PV plants,most of them are situated at the distribution systems and bring various operational challenges such as power quality and power flow *** paper discusses the modelling requirements for PV system integration studies,as well as the possible techniques for voltage rise mitigation at low voltage(LV)grids for increasing PV *** solutions are listed and preliminary results are presented.

关键词： Solar photovoltaic(PV) Voltage rise Virtual power plants Ancillary services

Ultrafine and fine particle emission in turning titanium metal matrix composite(Ti-MMC)

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Journal of Central South University 2019年第6期26卷 1563-1572页

作者： Seyed Ali NIKNAM Masoud SAbERI Jules KOUAM Ramin hashemi Victor SONGMENE Marek bALAZINSKI School of Mechanical Engineering Iran University of Science and TechnologyHengam St.Resalat SquareFehran 13114-16846Iran Department of Mechanical Engineering Ecole de Technologie Superieure (ETS)MontrealQCH3C 1K3Canada Department of Mechanical Engineering Polytechnique MontrealMontrealQCH3T 1J4Canada

Titanium metal matrix composite(Ti-MMC)has excellent features and capabilities which can be considered a potential candidate to replace commercial titanium and superalloys within an extensive range of products and industrial *** of the superior features in Ti-MMC,however,referring to several factors including high unit cost and existence of rigid and abrasive ceramic particles in the generated matrices of the work part,the Ti-MMC is grouped as extremely difficult to cut with a poor level of ***,adequate process parameters for machining Ti-MMCs under several lubrication methods are rarely ***,adequate knowledge of this regard is strongly *** machinability attributes,ultrafine particles(UFPs)and fine particles(FPs)have been selected as the main machinability attributes and the factors leading to minimized emission have been *** to experimental observations,despite the type of coating used,the use of higher levels of flow rate led to less UFPs,while no significant effects were observed on *** similar cutting conditions,higher levels of FPs were recorded under the use of uncoated ***,cutting speed had no significant influence on UFPs;nevertheless,it significantly affects the FPs despite the type of insert used.

关键词： metal matrix composites(MMCs) particle emission dust emission turning lubrication mode

An AlGaN/GaN HEMT with a reduced surface electric field and an improved breakdown voltage

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Chinese Physics b 2012年第8期21卷 360-364页

作者：谢刚 Edward Xu Niloufar hashemi 张波 Fred Y.Fu Wai Tung Ng The Edward S.Rogers Sr.Electrical and Computer Engineering Department University of Toronto State key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of China Crosslight Software Inc.burnaby BCCanada

A reduced surface electric field in an AlGaN/GaN high electron mobility transistor （HEMT） is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas （2-DEG） channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional sourceconnected field plates and double field plates, the HEMT with a Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. by optimizing both the length of Mg-doped layer, Lm, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with VGS = -5 V, Lm 1.5 m, a peak Mg doping concentration of 8×10^17 cm-3 and a drift region length of 10 m, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.

关键词： AlGaN/GaN HEMT reduced surface electric field Mg-doped layer breakdown voltage