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Acta Metallurgica Sinica(English Letters) 2005年第3期18卷 254-260页

作者： p.w.shum M.Escursell T.H.wong K.Y.Li Z.F.Zhou Y.G.Shen Advanced Coatings Applied Research Laboratory(ACARL) Department of Manufacturi ng Engineering and Engineering ManagementCity University of Hong KongKowloonHong KongChina

Titanium-aluminium-nitride(Ti_(1-x)Al_(x)N)coatings were deposited by close-field un balanced magnetron sputtering on M42 steel substrates and wC-6wt%Co inserts at 450℃.The tribological behavior was analyzed by sliding against steel and wC-6wt%Co balls,while the turning performance was evaluated by a conventional tu rning machine at high cutting speeds without using *** the tribological tests,the formation of transfer layer and the variations of hardness of the co atings played an important role for sliding against steel *** the coating s sliding against wC-6wt%Co balls,the Ti-Al-N coatings showed a similar frictio n coefficient,but the TiN coating exhibited a lower *** difference could be explained by the tri-oxidation wear *** the turning tests,a super ior cutting performance of the coating was found at x=0.45,which endured 38 min utes before the tool flank wear reached the maximum value of 0.3mm,whereas only 20 minutes were endured for the TiN *** excellent performance of the c oatings in the turning tests could be explained by the enhanced mechanical prope rties and oxidation/diffusion resistance of the coatings.

关键词： hardness Ti-Al-N coating tribology turning test wear test

Mechanical Behaviors of Ti-Si-N Coatings Deposited by Bias Sputtering

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稀有金属材料与工程 2012年第S1期41卷 18-23页

作者： p.w.shum Advanced Coatings Applied Research Laboratory(ACARL) Department of Mechanical and Biomedical Engineering(MBE)City University of Hong KongHong KongChina

Ti-Si-N hard coatings were deposited on steel substrates by reactive unbalanced magnetron sputtering from Ti and Si elemental targets in a mixture of Ar and N2 *** influences of negative bias voltage(in the range of-30 to-80 V)on the mechanical properties of the coatings were *** particular,the critical cycle during dynamic impact tests was employed to indicate the bonding strength of the *** was found that the Ti-Si-N coatings prepared at lower constant bias voltages could effectively improve the adhesion and the cyclic impact performance,but their hardness was dropped significantly to 13 Gpa at a bias of-30 *** bias voltage values induced greater hardness.A maximum hardness of 47 Gpa was obtained at a bias of-60 ***,the coating adhesion was worse in this case,and the number of impact cycles(～8×10 3)that the coatings could endure was much shorter than that of TiN binary coatings(～2×104).On the other hand,the bias voltage was varied linearly from-40 to-60 V during Ti-Si-N *** this circumstance,the hardness of the coatings deposited with the bias-graded configuration remained very high(42 Gpa),and the adhesion strength was improved ***,the critical impact cycle could reach as high as 1.8×***,bias-graded deposition can provide an effective processing route to prepare Ti-Si-N superhard coatings with high adhesion strength and impact resistance.

关键词： Ti-Si-N coatings magnetron sputtering bias voltage mechanical properties impact test

Feasibility Study of Using DLC Coating in Conjunction with Laser Ablation process to Improve the Tribological performance of an Engineering Surface

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稀有金属材料与工程 2012年第S1期41卷 52-56页

作者： shum p w Department of Manufacturing Engineering and Engineering Management(MEEM) City University of Hong KongHong KongChina

Increasing demands such as low friction,low wear rate,and long life-time have reached the limits of single DLC *** order to meet the requirements,we propose to use an integrated approach to improve the wear property of an engineering ***,dimples are introduced perpendicular to an engineering surface by a Nd:YAG laser emitting at 1064 ***,solid lubricant DLC is prepared on the patterned surface by magnetron sputtering *** effect of dimple densities from 7%to 45 %on tribological properties of the coating surface was *** wear performance of the textured DLC surfaces was studied by a pin-on-disk reciprocating sliding wear tester under boundary lubrication and dry *** results showed that the DLC coatings with appropriate dimple densities have an obvious improvement on wear performance in term of friction coefficient,wear rate and wear life,as compared to un-textured DLC *** boundary lubrication conditions,the improved wear performance can be explained by the promotion of reservoirs to enhance lubricant retention during *** dry condition,the dimples trap wear particles and leave a free interface between pin and sliding contact surface,and avoid the surface worn by abrasive manner,thereby improving the wear performance of the DLC coating.

关键词： laser wear DLC

The structure of superabundant semigroups

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Science China Mathematics 2004年第5期47卷 756-771页

作者： K.p.shum 2.Faculty of Science The Chinese University of Hong KongHong KongChina structure theorem for superabundant semigroups in terms of semilattices of normalized Rees matrix semigroups over some cancellative monoids is obtained. This result not only provides a construction method for superabundant semigroups but also generalizes the well-known result of Petrich on completely regular semigroups. Some results obtained by Fountain on abundant semigroups are also extended and strengthened.

A structure theorem for superabundant semigroups in terms of semilattices of normalized Rees matrix semigroups over some cancellative monoids is obtained. This result not only provides a construction method for superabundant semigroups but also generalizes the well-known result of petrich on completely regular semigroups. Some results obtained by Fountain on abundant semigroups are also extended and strengthened.

关键词： superabundant semigroups completely regular semigroups normalized Rees matrix semigroups

Storage and repair bandwidth tradeoff for heterogeneous cluster distributed storage systems

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Science China(Information Sciences) 2020年第2期63卷 131-145页

作者： Jingzhao wANG Yuan LUO Kenneth w.shum Department of Computer Science and Engineering Shanghai Jiao Tong University Institute of Network Coding The Chinese University of Hong Kong

The storage and repair bandwidth tradeoff is an important issue in distributed storage systems(DSSs) where large scale data are stored in multiple nodes with erasure coding to ensure reliability. There are lots of studies on the DSS model with multiple clusters where the repair bandwidths from intra-cluster and cross-cluster nodes are differentiated to improve repair efficiency based on the realistic network topological structures. At the same time, separate nodes are also prevalent due to the variety of practical networks, but the work on the cluster DSS model with multiple separate nodes is insufficient, which is a main motivation of this paper. we formulate the tradeoff bound between storage repair bandwidth for a heterogeneous DSS model consisting of clusters and separate nodes by analyzing the min-cuts of heterogeneous information flow graphs corresponding to the orders of failed nodes. Additionally, the tradeoff bounds are investigated in multiple aspects when the repair bandwidth constraints and the amount of separate nodes vary, ***, a class of regenerating codes are illustrated to achieve the tradeoff in the heterogeneous cases.

关键词： distributed storage system cluster separate node repair bandwidth information flow graph

SOME REMARKS ON (L)-GREEN’S RELATIONS AND STRONGLY Rpp SEMIGROUpS

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Acta Mathematica Scientia 2011年第4期31卷 1591-1599页

作者：杜兰郭聿琦 K.p. shum Department of Mathematics Ningxia University Department of Mathematics Southwest University Department of Mathematics Hong Kong University

In order to study rpp semigroups, in particular, some special cases, several facts on （l）-Green’s relations and strongly rpp semigroups are given as some remarks.

关键词： (l)-Green’s relations strongly rpp semigroups semilattice congruences Dprimitive idempotents

Correction of CT Burst Array Errors in the Generalized-Lee-RT Spaces

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Acta Mathematica Sinica,English Series 2010年第8期26卷 1475-1484页

作者： Sapna JAIN K.p.shum Department of Mathematics University of Delhi Department of Mathematics The University of Hong Kong

In [Jain, S.： Array codes in the generalized-Lee-RT-pseudo-metric （the GLRTp-metric）, to appear in Algebra Colloq.], Jain introduced a new pseudo-metric on the space Matm×s（Zq）, the module space of all m × s matrices with entries from the finite ring Zq, generalized the classical Lee metric [Lee, C. Y.： Some properties of non-binary error correcting codes. IEEE Trans. Inform. Theory, IT-4, 77- 82 （1958）] and array RT-metric [Rosenbloom, M. Y., Tsfasman, M. A.： Codes for m-metric. prob. Inf. Transm., 33, 45-52 （1997）] and named this pseudo-metric as the Generalized-Lee-RT-pseudo-Metric （or the GLRTp-Metric）. In this paper, we obtain some lower bounds for two-dimensional array codes correcting CT burst array errors [Jain, S.： CT bursts from classical to array coding. Discrete Math., 308-309, 1489-1499 （2008）] with weight constraints under the GLRTp-metric.

关键词： Linear array codes Lee metric RT metric CT burst array errors

On p-nilpotency and minimal subgroups of finite groups

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Science China Mathematics 2003年第2期46卷 176-186页

作者：郭秀云 K.p.shum Department of Mathematics Shanxi University Department of Mathematics The Chinese University of Hong Kong

we call a subgroup H of a finite group G c-supplemented in G if there exists a subgroup K ofG such that G = HK and H ∩K ≤ core(H). In this paper it is proved that a finite group G is p-nilpotentif G is S4-free and every minimal subgroup of p ∩ GN is c-supplemented in NG(p), and when p = 2 p isquaternion-free, where p is the smallest prime number dividing the order of G, p a Sylow p-subgroup of *** some applications of this result, some known results are generalized.

关键词： p-nilpotent groups, minimal subgroups, formation.

On Almost Armendariz Ring

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Algebra Colloquium 2020年第2期27卷 199-212页

作者： Om prakash Sushma Singh K.p.shum Department of Mathematics Indian Institute of Technology Patna PatnaBihar 801106India Department of Mathematics John Fulton Center The Chinese University of Hong KongShatinN.T.Hong KongChina

In this paper,we introduce the notion of an almost Armendariz ring,which is a generalization of an Armendariz ring,and discuss some of its *** has been found that every almost Armendariz ring is weak Armendariz but the converse is not *** prove that a ring R is almost Armendariz if and only if R[x]is almost *** is also shown th at if R/I is an almost Armendariz ring and I is a semicommutative ideal,then H is an almost Armendariz ***,the class of minimal non-commutative almost Armendariz rings is completely determined,up to isomorphism(minimal means having smallest cardinality).

关键词： Armendariz ring almost Armendariz ring weak Armendariz ring lower nil radical reduced ring semicommutative ring

On f-Disjunctive Languages, f-Disjunctive Domains and Solid Codes(Dedicated to the late professor Xu Yonghua (1932-2019))

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Algebra Colloquium 2020年第2期27卷 331-342页

作者： Jing Leng Yuqi Guo K.p.shum School of Mathematics and Statistics Lanzhou University Lanzhou 730000China Institute of Mathematics Yunnan University Kunming 650091China

Every language is either the disjoint union or the intersection of two disjunctive *** family of f-disjunctive languages is a natural generalization of the family of disjunctive *** domains(f-disjunctive domains)are defined as the languages which can be checked whether a given language is disjunctive(f-disjunctive)or *** f-disjunctive domains were first studied by Guo et *** *** continue their study on f-disjunctive *** new results for f-disjunctive domains,containing a relation between disjunctive domains and f-disjunctive domains,are *** this respect,we also make an appropriate opening for the completely dense languages and solid codes.

关键词： f-disjunctive languages f-disjunctive domains completely dense languages solid codes