A Scalable Asynchronous Cache Consistency Scheme (SACCS) for mobile environments

In the literature, there exit two types of cache consistency maintenance algorithms for mobile computing environments: stateless and stateful. In a stateless approach, the server is unaware of the cache contents at a mobile user (MU). Even though stateless approaches employ simple database management schemes, they lack scalability and ability to support user disconnectedness and mobility. On the other hand, a stateful approach is scalable for large database systems at the cost of nontrivial overhead due to server database management. We propose a novel algorithm, called Scalable Asynchronous Cache Consistency Scheme (SACCS), which inherits the positive features of both stateless and stateful approaches. SACCS provides a weak cache consistency for unreliable communication (e.g., wireless mobile) environments with small stale cache hit probability. It is also a highly scalable algorithm with minimum database management overhead. The properties are accomplished through the use of flag bits at the server cache (SC) and MU cache (MUC), an identifier (ID) in MUC for each entry after its invalidation, and estimated time-to-live (TTL) for each cached entry, as well as rendering of all valid entries of MUC to uncertain state when an MU wakes up. The stale cache hit probability is analyzed and also simulated under the Rayleigh fading model of error-prone wireless channels. Comprehensive simulation results show that the performance of SACCS is superior to those of other existing stateful and stateless algorithms in both single and multicell mobile environments.     

Surface behaviour of as-Cast Al–Fe intermetallic composites

In order to produce energy-efficient material for tribological applications, Al–Fe inter-metallic composites have been produced by liquid metallurgy route. Iron content of the composites varies from 1.67 to 11.2 wt.%. These composites have been tested for their wear properties at different parameters. Debris and wear tracks have been studied in detail to see the surface effects during dry sliding and have been correlated to wear properties. Observations show that low loads and sliding velocities are dominated by oxidative debris and largely covered wear track surface with smooth oxide layer is observed. Whereas metallic debris dominates at higher loads and sliding velocities and highly deformed wear track surface with deep grooves and gross delamination were observed. Further, wear rate is seen to increase continuously with load whereas with sliding velocity it attains a minima after initial decrease and then increases continuously. Low solubility of iron supports the formation of FeAl₃ and an increase in hardness from 95 to 179 VHN continuously improves the wear resistance with increase in percentage iron.     

寒地大学校园环境要素与冬季体力活动相关性

为探究促进冬季体力活动的寒地大学校园环境设计依据,基于循证设计理论和社会生态学模型在中国东北地区9座大学校园年内进行了问卷调查,用实证方法探究了寒地大学校园的建成、气候及感知环境要素对学生冬季体力活动频率和水平的影响.通过描述性统计横向对比了学生冬季与非冬季月份的体力活动模式及各个校园的主观评价得分;并通过多重线性回归分析探求了校园环境要素对冬季体力活动的影响.统计结果表明:学生在冬季月份进行体力活动的频率和总量低于非冬季月份;校园冬季环境质量低于非冬季月份,且设施防寒、步行可达性、交通安全性、冬季活动安全性得分较低;在冬季,目的地多样性、公共交通选择多样性、道路交通网络连通性、步行道路环境品质、辅助设施存在性、犯罪安全性与交通性体力活动正相关,冰雪危害和空气污染与交通性体力活动负相关;校园环境与冬季休闲性活动无相关关系.利用上述数据可以初步推测促进体力活动的寒地大学校园环境设计倾向并对各个环境要素的重要程度进行评级,重要程度较高的要素是校内目的地、步行道路、犯罪安全性、步行辅助设施和校园公共交通服务.     

A review on solar still: a simple desalination technology to obtain potable water

Present review paper presents an overall summarised presentational view of the research work to be discussed on the solar still. The current review paper also includes the infused crisis and struggle for obtaining fresh water for drinking purpose and consumption for other household activities which are a result of the ecological imbalance that has prevailed and is in continuation for past many centuries. It also shows the various tested and applied techniques for freshwater production and their suitability in the usability context in the present scenario of the scarcity of clean water. The use of solar desalination technology is discussed elaborately for a broader consumption to be employed in the current and future works.     

An investigation of the electrical transport properties of graphene-oxide thin films

The electrical transport properties of graphene-oxide (GO) thin films were investigated. The GO was synthesized by a modified Hummers method and was characterized by X-ray diffraction and UV-visible spectroscopy. The thin film of GO was made on a Si/SiO₂ substrate by drop-casting. The surface morphology of the GO film was analyzed by using scanning electron microscopy and atomic force microscopy techniques. Temperature dependent resistance and current-voltage measurements were studied using four-terminal method at various temperatures (120, 150, 175, 200, 250 and 300 K) and their charge transport followed the 3D variable range hopping mechanism which was well supported by Raman spectra analysis. The presence of various functional groups in GO were identified by using high resolution X-ray photo electron (XPS) and Fourier transform infra red (FT-IR) spectroscopic techniques. Graphene-oxide thin film field effect transistor devices show p-type semiconducting behavior with a hole mobility of 0.25 cm² V⁻¹ s⁻¹ and 0.59 cm² V⁻¹ s⁻¹ when measured in air and vacuum respectively.