Consolidation and mechanical properties of nanostructured MoSi2-SiC-Si3N4 from mechanically activated powder by high frequency induction heated sintering

A dense nanostructured MoSi₂-SiC-Si₃N₄ composite was sintered by the high frequency induction heating method within 2 min from mechanically activated powder of Mo₂N, Mo₂C and Si. Highly dense MoSi₂-SiC-Si₃N₄ composite was produced under simultaneous application of a 80 MPa pressure and the induced current. Mechanical properties and grain size of the composite were investigated. The average hardness and fracture toughness values obtained were 1420 kg/mm² and 4.5 MPa m^1/2, respectively.     

Toward Advanced Mobile Cloud Computing for the Internet of Things: Current Issues and Future Direction

Cloud computing is the coming new era of information processing and has proved its benefits in high scalability and functional diversity. However, almost all cloud-computing architectures including SaaS, PaaS, and IaaS are vulnerable to serious security issues. Similarly, Mobile Cloud Computing (MCC) is vital to overcoming mobile limited storage and computing capabilities. MCC authentication and authorization issues must be provided on two levels: login password control and the environment from where the cloud is accessed. MCC has overcome the barrier of limited storage by providing remote storage but requires a strict security system that is responsible for retrievability, integrity, and seamless storage access. Elasticity and connectivity are also of major concern in MCC because delays and jitters cause degradation in the user experience. Cloud-computing architecture creates more challenges in maintaining security because of the liberty of users to choose any MCC architecture. Thus in this paper we discuss current cloud computing issues and future directions.     

弹脆性损伤理论与破坏过程的计算机模拟

本文提出了一种增量形式的受损弹脆性材料的本构关系,此关系考虑了材料与损伤两者的各向异性.而且,导出了损伤模量、有效弹性模量以及动态弹性模量等张量表达式.根据本文提出的理论和方法,给出了考虑局部损伤的结构有限元方法,并应用于模拟复合材料板的损伤一破坏过程.最后,受拉伸的带中心圆孔的玻璃纤维布/环氧树脂复合材料板损伤过程的计算结果用等损伤线图形显示出来.     

Simultaneous Synthesis and Densification of MoSi2 by Field-Activated Combustion

A method to simultaneously synthesize and consolidate MoSi₂ from powders of Mo and Si was investigated. Combustion synthesis was carried out under the combined effect of an electric field and mechanical pressure. Highly dense molybdenum silicide up to (99.2%) was produced from elemental powders in one step. Minor amounts of Mo₅Si₃ were present at the boundaries of MoSi₂ grains in the interior of samples made from stoichiometric reactants. The addition of 2.5 mol% Si excess, however, resulted in Mo₅Si₃-free, dense MoSi₂ products.     

Effect of Fe2O3 addition on consolidation and properties of 8 mol% yttria-stabilized zirconia by high-frequency induction heated sintering (HFIHS)

Dense nanophase 8 mol% yttria-stabilized zirconia was sintered by high-frequency induction heated sintering (HFIHS) within 6 min from 8YSZ nanopowder prepared by co-precipitation method. Sintering was accomplished under the combined effects of an induced current and mechanical pressure. Highly dense 8YSZ with relative density of up to 96% was produced under simultaneous application of a 60-MPa pressure and the induced current. The effects of Fe₂O₃ additions on the sintering behavior, mechanical properties and ionic conductivities of the 8YSZ were investigated.     

Effect of processing conditions on functional properties of collagen powder from skate (<Emphasis Type="Italic">Raja kenojei</Emphasis>) skins

Optimum conditions for collagen extraction from skate (Raja kenojei) skins with various liming concentrations, extraction solution pH, extraction temperature and time, and functional properties were investigated. The optimum conditions for collagen extraction are as combination of place the skins in a lime solution of 0.15 N of NaOH, extract with 5 volumes water (pH 4.0) for 4 hr at 40°C, filter, centrifuge, and lyophilize to obtain collagen powder. The characteristics of skate skin collagen obtained under optimum extraction conditions were: solubility 82.7%, turbidity 0.28, and Hunter color L, a, and b values were 88.4, 0.92, and 11.2, respectively. On the other hand, the acidic pH values (3.0 and 5.0) of collagen were more resistant to precipitation upon extended heating.     

Synthesis of dense MoSi2 by high-frequency induction heated combustion and its mechanical properties

Dense MoSi₂ compound was synthesized with the high-frequency induction heated combustion synthesis method in one step from elemental powders of Mo and Si within 2 min. Simultaneous combustion synthesis and densification were carried out under the combined effects of induced current and mechanical pressure. A highly dense MoSi₂ with a relative density of up to 98% was produced with simultaneous application of 60 MPa pressure and induced current. The percentages of the total shrinkage occurring before and during the synthesis reaction were 16% and 53%, respectively. The average grain size was about 15 μm and a slight amount of Mo₅Si₃ was observed at the boundaries of the MoSi₂ grains. The fracture toughness and hardness values obtained were 3.5 MPa·m^1/2 and 1050 kg/mm², respectively. These values were similar to those of commercial ones.     

An effective authentication mechanism for ubiquitous collaboration in heterogeneous computing environment

With the advent of new generation of mobile access devices such as smartphone and tablet PC, there is coming a need for ubiquitous collaboration which allows people to access information systems with their disparate access devices and to communicate with others in anytime and in anywhere. As the number of collaborators with a large number of disparate access devices increases in ubiquitous collaboration environment, the difficulties for protecting secured resources from unauthorized users as well as unsecured access devices will increase since the resources can be compromised by inadequately secured human and devices. Therfore, authentication mechanism for access of legitimate participants is essential in ubiquitous collaboration environment. In this paper we present an efficient authentication mechanism in ubiquitous collaboration environment. We show that proposed scheme is secure through security analysis and is efficient through the experimental results obtained from the practical evaluation of the scheme in ubiquitous collaboration environment.     

Synthesis of TiC, TiC-Cu Composites, and TiC-Cu Functionally Graded Materials by Electrothermal Combustion

Titanium carbide and composites and functionally graded materials (FGMs) of TiC– x Cu were synthesized by an electrothermal combustion (ETC) method. TiC synthesized by ETC showed small amounts of porosity relative to those synthesized by ignition using radiative heating. Composites and FGMs with higher copper content can be synthesized by ETC. In the FGM products a nearly linear change in composition in the graded region was observed in samples with 0 ≤ x (wt%) ≤ 75.