Search

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jss.2006.06.029 Byline: Letian Jiang, Guozhi Xu Keywords: Software faults; Software aging; Software failure; Reliability; Robust locally weighted regression (Loess) Abstract: Many studies reported that system suffered from outages more due to software faults than hardware faults. Recently, the phenomenon of "software aging", which was caused by aging-related faults, is observed in many software systems. Software aging, characterized by progressive performance degradation, is mainly caused by exhaustion of the operating system resources, such as memory leaking, unreleased-file locks, data corruption, etc. This paper mainly focuses on the modeling and analysis of software aging and software failure. A stochastic time series decomposition algorithm based on robust locally weighted regression (Loess) is presented to separate the exhaustion of system resource from the resource usage, from which aging trend is estimated. Then the model of software aging and software failure process is constructed. Experiments on a practical server system verify the effectiveness of the algorithm presented in this paper, and the two-stage failure process is also confirmed for the first time in the history of research on software aging. The conclusions drawn from this paper will greatly benefit the application of software rejuvenation technique, that is, it makes it easy to determine when to perform software rejuvenation, which is a key issue in implementation of software rejuvenation. The results for the server system employing different rejuvenation policies show that software performance can be effectively improved. Author Affiliation: Electronic Engineering Department, EE Building No. 1, Shanghai Jiaotong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China Article History: Received 10 October 2005; Revised 19 May 2006; Accepted 24 June 2006

Extracting thermal energy from medium-deep ground layer for building heating is a promising means for pushing forward cleaner heating initiative. There is no available analytical model that can provide fast, accurate and effective simulation of both fluid and soil temperature field of deep borehole heat exchanger (DBHE) under complex geothermal gradient and subsurface stratifications. In this study, a stratified segmented finite line source method (SS-FLS) is proposed as an main contribution and novelty. The proposed model is validated by comparing with finite element method, model degradation example, and actual engineering project data of DBHE. The accuracy and robustness of the SS-FLS is fully checked. Then the effects of stratification on soil temperature field and fluid temperature field are investigated. It is found that the shape of temperature contour and temperature distribution have direct link with stratification as well as heat extraction rate on the heat pump side. Moreover, two critical model parameters are discussed in details which poses an important guide for both model application and system analysis. [Display omitted] • Stratified segmented finite line source (SS-FLS) method is proposed. • SS-FLS model is accurate, fast and easy-implemented for DBHE applications. • Impacts radius of DBHE is enlarging from shallow to deeper layers. • The fluid in the coaxial tube of DBHE is cooled down at the same pace. [ABSTRACT FROM AUTHOR]

The geothermal heat pump system based on deep borehole heat exchanger (DBHE) is one of the important systems to realize cleaner heating. It is key to ensure that DBHE can make full use of the dynamic characteristics of deep heat extraction and recovery (HER) in a long period of time to maintain the stability of geothermal field as well as sustainable development of DBHE and geothermal energy. This study mainly has made contributions in the following four aspects: (1) Through numerical analysis with a "stratified segmented finite line source method" (S2-FLS) and its model analytical expression, the impacts of heating duration and heating load distribution on the long-term operation performance of DBHE is revealed, which provides a theoretical basis for the optimal operation of DBHE. (2) The numerical analysis explained how complex geological conditions affect the dynamic heat extraction and heat recovery of DBHE in intermittent operation mode, which provides a theoretical basis for DBHE drilling site selection. (3) The model robustness is fully checked and an initial investigation on DBHE array with HER is presented, which may lead to massive application of deep geothermal systems. • A robust, efficient and easy implemented model is proposed for deep borehole heat exchanger. • The long-term heat extraction/recovery ability of deep borehole heat exchanger is verified. • Analysis on geological conditions can provide guides for drilling site selection. • The deep borehole array with heat extraction and recover is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The present work prepared a series of soy protein isolate/agar blend films containing 33% glycerol as plasticizer by solution casting and thermo-molding methods. The microstructure and mechanical properties of the blend films were evaluated in relation to the agar/protein ratio as well as the processing methods. Experimental results revealed that hydrogen bonding interactions existed between soy protein and agar. The casting films possessed more homogeneous interfaces compared with the molding films, leading to the superior mechanical properties than those molding films. Owing to the rigid three-dimensional network formed by the agar, the tensile strength of casting blend films was enhanced. With the increase of agar in the casting blend films, the crosslinking density increased and was responsible for the variations in tensile strength. [Copyright &y& Elsevier]

• A new analytical model is proposed for deep geothermal systems. • New observations in non-uniform insulated system in cooling mode. • Turning points are identified when non-uniformity of insulation is investigated. • Multi-factor based evaluation is performed based on orthogonal test design. Deep borehole heat exchanger (DBHE) based ground source heat pump (GSHP) is a promising system for geothermal energy application in medium-deep layer. In this study, DBHE with non-uniform pipe insulation is proposed and numerically investigated. An effective analytical model is built based on segmented finite line-source method and a newly derived water heat transfer model. The year-round field test data are used for model verification. In-depth analyses are given to a comparison between the uniform and non-uniform insulation cases in both heating and cooling modes, and sensitivity analysis on non-uniformity of insulation. A orthogonal test is conducted for energy performance evaluation and optimization. It is found that DBHE with non-uniform insulation can outperform the one with full insulation in cooling mode, which offers new insights. In addition, an optimum insulation length can be identified through the non-uniformity analysis on insulation. It shows that the order of influence factor is heating season duration ratio, flow rate of working fluid, material thermal resistance non-uniformity of the center pipe, pipe sizing ratio, borehole depth, and insulation length non-uniformity of the center pipe. By choosing the proper system design parameters, the system energy saving could be up to 21.8%. [ABSTRACT FROM AUTHOR]

Abstract The concentrations, variations and distribution of molybdenum (Mo) in catchment outlet sediments from China were studied in this contribution based on the results of recently-finished, continental-scale, China Geochemical Baselines (CGB) project. The data from CGB were combined with other published data-sets with the purpose of understanding the spatial distribution of Mo in China and, in addition, relating the observed geochemical features to natural and/or anthropogenic processes. This geochemical mapping with a density of ca. 3000 km2 per site involves catchment sediments in two horizons at each site: a top sample (TOS) at a depth of 0–25 cm and a bottom sample (BOS) at a depth greater than 100 cm. In total, 3382 TOS and 3380 BOS samples were collected. The analytical results show that the concentrations of Mo in the catchment outlet sediments of China range from 0.07 to 57.86 μg/g for the TOS and 0.09–32.43 μg/g for the BOS. The median and mean values of the TOS data are 0.73 and 1.01 μg/g respectively, and those of the BOS data are 0.71 and 0.94 μg/g. The variations of both the TOS and BOS are high at this continental scale. The Mo concentrations vary greatly from one geological and/or geographic unit to another. For instance, from the Cathaysia Block with the TOS and BOS median values of 1.22 and 1.46 μg/g to the North China craton with those of approximately 0.61 and 0.58 μg/g. Various processes govern the spatial distribution of Mo in the catchment sediments of China but regional-scale natural sources (e.g. lithologies) predominate. Sedimentary sandstones and carbonate rocks, alluvium in plain terrain and aeolian materials (e.g. loess) account for the extensive low concentrations (<0.5 μg/g) at such regions as the Songpan-Ganzi orogen and Songliao Basin; whereas shales, basalts and granitoids like granodiorite, plagiogranite and granite porphyry are taken to be responsible for the high concentrations (>1.2 μg/g) in the Yangtze and Cathaysia blocks. Simultaneously, some local mineralized areas can be also identified at this scale because the sampled sites just happened to fall on sediments derived from mineralized rocks or anthropogenic addition by mining activities. Furthermore, the TOS share the similar patterns with the BOS indicating relatively stable inheritance and no apparent extensive secondary enrichment or depletion in the catchment sediments of China. The CGB demonstrates that a series of baseline levels of Mo are needed at different regions and scales and ultra-low density mapping can still deliver robust geochemical patterns. Highlights • Concentrations and distribution of Mo in catchment sediments of China were studied. • The spatial distribution patterns of Mo are dominated by lithologies. • Local mineralized regions can be identified due to proper sampled sites. • Ultra-low density geochemistry can still deliver robust geochemical patterns. • A series of baselines at different scales would be required for various purposes. [ABSTRACT FROM AUTHOR]

This article reports on the fabrication of modified high-density polyethylene (HDPE) foams with complex cellular structure (CCS) using supercritical CO 2 as a physical blowing agent by a cooling and two-step depressurization method. HDPE was modified by dicumyl peroxide (DCP) and carbon nanotubes (CNTs) to improve its viscoelasticity and foaming behavior. The gel content test demonstrated that the cross-linking structure formed in the modified HDPE samples. Compared with that of neat HDPE, the viscoelasticity of modified HDPE was improved largely, which was characterized by rotational rheometer and torque rheometer. The introduction of DCP and CNTs had a slightly effect on the thermal behaviors of HDPE. The foaming properties of various HDPE samples showed that the cross-linking structure caused by DCP improved the foamability of HDPE and CNTs acted as a nucleating agent for cell nucleation. The degree of the first-step depressurization was critical to control the CCS evolution in HDPE foam. [ABSTRACT FROM AUTHOR]

The solvent-coordinated metal cations as templates affecting the architectures of anionic heterothiometallic Mo(W)/S/Ag polymeric clusters was investigated. Four W/S/Ag polymeric clusters {[Tb(DMSO) 8 ][W 3 S 12 Ag 3 ]} n ( 1 , DMSO = dimethyl sulfoxide), {[Tb(DMF) 8 ][W 3 S 12 Ag 3 ]} n ( 2 , DMF = N,N′-dimethylformamide), {[Tb(NMP) 8 ][W 4 S 16 Ag 5 ]} n ( 3 , NMP = N-methyl-2-pyrrolidone) and {[Mg(NMP) 6 ][W 2 S 8 Ag 2 ]·2NMP} n ( 4 ) with distinct 1-D anionic structures were obtained by the reactions of (NH 4 ) 2 WS 4 , AgI and M(NO 3 ) x (M = Tb, x = 3; M = Mg, x = 2) in corresponding solvents (DMSO, DMF or NMP). 1 – 4 were determined by elemental analysis, IR, UV–Vis, thermogravimetric analysis, X-ray powder and single crystal diffractions. Directed by different solvent-coordinated trivalent terbium metal cations, 1 shows a 1-D anionic helical chain architecture; 2 exhibits a 1-D anionic zigzag chain with hexanuclear [W 3 S 12 Ag 3 ] 3 − repeated units; 3 possesses another kind of 1-D anionic zigzag chain with the unique nonanuclear planar square-like [W 4 S 16 Ag 5 ] 3 − repeated units. While induced by NMP-coordinated bivalent magnesium metal cation, 4 exhibits a 1-D anionic linear chain structure. [ABSTRACT FROM AUTHOR]

A novel flame retardant TGIC-DOPO, which was constructed by phosphaphenanthrene and triazine-trione groups, was synthesized via a controllable ring-opening addition reaction between 1,3,5-triglycidyl isocyanurate (TGIC) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The flame-retardant effect of TGIC-DOPO on an epoxy resin, diglycidyl ether of bisphenol-A (DGEBA), cured with 4,4'-diamino-diphenyl sulfone was investigated. The results of the limited oxygen index (LOI), UL94 vertical burning test, and cone calorimeter test indicated that the TGIC-DOPO imparted flame-retardant properties to DGEBA thermosets. When the mass fraction of TGIC-DOPO reached 12wt.%, the DGEBA thermoset acquired a LOI value of 33.3%, UL94 V-0 rating, and the lower peak of heat release rate (pk-HRR) at 481 kW/m². Specifically, the DGEBA thermoset with 6wt.% TGIC-DOPO had an LOI value of 33.3%, whereas the DGEBA thermoset with 10wt.% TGIC-DOPO had the highest LOI value of 35.2% among the specimens. Meanwhile, the time to ignition, pk-HRR, average of effective heat of combustion (av-EHC), and total heat release of the DGEBA thermoset were all negatively correlated with the mass fraction of TGIC-DOPO. Moreover, the average CO2 and CO yields exhibited a downtrend with increasing mass fraction of TGIC-DOPO from 6wt.%. The reduction of av-EHC with increase of TGIC-DOPO content in thermosets confirmed the free radical quenching effect of TGIC-DOPO in gaseous phase during combustion. The macromorphology, micromorphology and element content of the residues from the cone calorimeter test revealed the bi-phase flame-retardant effect of TGIC-DOPO. Furthermore, the pyrolysis route of TGIC-DOPO were investigated via Py-GC/MS, which disclosed that the decomposed TGIC-DOPO with double flame-retardant groups released various fragments with quenching effect on free radical chain reaction of combustion. The fragments enhanced the flame-retardant performance of DGEBA thermosets both in gaseous and condensed phases. The flame-retardant performance of TGIC-DOPO was resulted by the quenching effect of TGIC-DOPO and the synergistic effect of phosphaphenanthrene and triazine-trione groups. [ABSTRACT FROM AUTHOR]