Mobile applications and services relying on mobility prediction have recently spurred lots of interest. In this paper, we propose mobility prediction based on cellular traces as an infrastructural level service of telecom cloud. Mobility Prediction as a Service (MPaaS) embeds mobility mining and forecasting algorithms into a cloud-based user location tracking framework. By empowering MPaaS, the hosted 3rd-party and value-added services can benefit from online mobility prediction. Particularly we took Mobility-aware Personalization and Predictive Resource Allocation as key features to elaborate how MPaaS drives new fashion of mobile cloud applications. Due to the randomness of human mobility patterns, mobility predicting remains a very challenging task in MPaaS research. Our preliminary study observed collective behavioral patterns (CBP) in mobility of crowds, and proposed a CBP-based mobility predictor. MPaaS system equips a hybrid predictor fusing both CBP-based scheme and Markov-based predictor to provide telecom cloud with large-scale mobility prediction capacity. 相似文献
Virtualization is the cornerstone of the developing third-party compute industry, allowing cloud providers to instantiate multiple virtual machines (VMs) on a single set of physical resources. Customers utilize cloud resources alongside unknown and untrusted parties, creating the co-resident threat—unless perfect isolation is provided by the virtual hypervisor, there exists the possibility for unauthorized access to sensitive customer information through the exploitation of covert side channels. This paper presents co-resident watermarking, a traffic analysis attack that allows a malicious co-resident VM to inject a watermark signature into the network flow of a target instance. This watermark can be used to exfiltrate and broadcast co-residency data from the physical machine, compromising isolation without reliance on internal side channels. As a result, our approach is difficult to defend against without costly underutilization of the physical machine. We evaluate co-resident watermarkingunder a large variety of conditions, system loads and hardware configurations, from a local laboratory environment to production cloud environments (Futuregrid and the University of Oregon’s ACISS). We demonstrate the ability to initiate a covert channel of 4 bits per second, and we can confirm co-residency with a target VM instance in $<$10 s. We also show that passive load measurement of the target and subsequent behavior profiling is possible with this attack. We go on to consider the detectability of co-resident watermarking, extending our scheme to create a subtler watermarking attack by imitating legitimate cloud customer behavior. Our investigation demonstrates the need for the careful design of hardware to be used in the cloud. 相似文献
DNA family shuffling was used to create chimeric lipase B proteins with improved activity toward the hydrolysis of diethyl 3-(3',4'-dichlorophenyl)glutarate (DDG). Three homologous lipases from Candida antarctica ATCC 32657, Hyphozyma sp. CBS 648.91 and Crytococcus tsukubaensis ATCC 24555 were cloned and shuffled to generate a diverse gene library. A high-throughput screening assay was developed and used successfully to identify chimeric lipase B proteins having a 20-fold higher activity toward DDG than lipase B from C.antarctica ATCC 32657 and a 13-fold higher activity than the most active parent derived from C.tsukubaensis ATCC 24555. In addition, the stability characteristics of several highly active chimeric proteins were also improved as a result of family shuffling. For example, the half-life at 45 degrees C and melting point (T(m)) of one chimera exceeded those of lipase B from C.antarctica ATCC 32657 by 11-fold and 6.4 degrees C, respectively, which closely approached the stability characteristics of the most thermostable parent derived from Hyphozyma sp. CBS 648.91. 相似文献
Ambient-pressure thermogravimetric characterization of four different coals and their chars was performed to obtain fundamental information on pyrolysis and coal and char reactivity for these materials. Using a Perkin-Elmer TGS-1 thermobalance, weight loss as a function of temperature was systematically determined for each coal heated in helium at 40 and 160 °C/min under various experimental conditions, and for its derived char heated in air over a temperature range of 20 to 1000 °C. The results indicate that the temperature of maximum rate of devolatilization increases with increasing heating rate for all four coals. However, heating rate does not have a significant effect on the ultimate yield of total volatiles upon heating in helium to 1000 °C; furthermore, coupled with previous data9 for identical coal samples, this conclusion extends over a wide range of heating rate from 0.7 to 1.5 × 104 °C/s. Using the temperature of maximum rate of devolatilization as an indication of relative reactivity, the devolatilization reactivity differences among the four coals tested that were suggested by this criterion are not large. For combustion in air, the overall coal/char reactivity sequence as determined by comparison of sample ignition temperature is: N. Dakota lignite coal ≈ Montana lignite coal > North Dakota lignite char > III. No. 6 bituminous coal ≈ Pittsburgh Seam bituminous coal > Montana lignite char > III. No. 6 bituminous char > Pittsburgh Seam bituminous char. The reactivity differences are significantly larger than those for devolatilization. The reactivity results obtained suggest that coal type appears to be the most important determinant of coal and char reactivity in air. The weight loss data were fitted to a distributed-activation-energy model for coal pyrolysis; the kinetic parameters so computed are consistent with the view that coal pyrolysis involves numerous parallel first-order organic decomposition reactions. 相似文献
Scratch durability of polymer surfaces and coatings is becoming critical for the increasing use of these materials in new applications, replacing other materials with harder surfaces.
Scratch resistance of polymers has been the subject of numerous studies, which have led to specific definitions for plastic deformation characterization and fracture resistance during scratch testing. Viscoelastic and viscoplastic behavior during a scratch process have been related to dynamic mechanical properties that can be measured via dynamic nano-indentation testing. Yet, the understanding of the origin of the fracture process of a polymer during scratch remains approximate. Parameters like tip shape and size, scratch velocity and loading rate, applied strain and strain rates, have been considered critical parameters for the fracture process, but no correlation has been clearly established.
The goal of this work is to define and analyze scratch parameters that relate to mechanical properties. The evolution of scratch resistance parameters as a function of temperature and strain rate, compared to the evolution of dynamic mechanical properties obtained from indentation and uniaxial tensile tests over a range of temperature for poly(methyl methacrylate) (PMMA) helped in identifying a correlation between the tensile stress–strain behavior and scratch fracture toughness.
This correlation brings a new understanding of the origin of the fracture mechanisms during a scratch process. In particular, it is demonstrated that the characteristic strain applied by the indenter is a most relevant parameter to describe the fracture resistance during a scratch process, independently of the indenter geometry. 相似文献
The role of the C-terminal Leu300 in maintaining thermal stabilityof the neutral protease of Bacillus subtilis was investigated.From model building studies based on the three dimensional structureof thermolysin, the neutral protease of B.thermoproteolyticus,it was conduded that this residue is located in a hydrophobicpocket composed of residues located in the C-terminal and themiddle domain. To test the hypothesis that Leu300, by contributingto a stabilizing interaction between these domains, is importantfor enzyme stability, several neutral protease mutants wereconstructed and characterized. The thermostability of the enzymewas lowered by deleting Leu300 or by replacing this residueby a smaller (Ala), a polar (Asn) or a sterically unfavourable(He) amino acid. Thermostabiity was increased upon replacingLeu300 by Phe. These results are in agreement with model-buildingstudies. The effects on thermostability observed after mutatingthe corresponding Val318 in the thermostable neutral proteaseof B.stearothermophilus were less pronounced. 相似文献
Methods of improving seismic event locations were investigated as part of a research study aimed at reducing ground control safety hazards. Seismic event waveforms collected with a 23-station three-dimensional sensor array during longwall coal mining provide the data set used in the analyses. A spatially variable seismic velocity model is constructed using seismic event sources in a passive tomographic method. The resulting three-dimensional velocity model is used to relocate seismic event positions. An evolutionary optimization algorithm is implemented and used in both the velocity model development and in seeking improved event location solutions. Results obtained using the different velocity models are compared. The combination of the tomographic velocity model development and evolutionary search algorithm provides improvement to the event locations. 相似文献
The glass-forming region in a GeSe2–As2Se3–CdSe system and the dependence of properties on glass compositions as a formula of 70GeSe2–(30− x )As2Se3– x CdSe ( x =0–25) were investigated. Measurements included density, micro-hardness, differential scanning calorimetry (DSC), X-ray diffraction, and IR transmission spectra. A large glass-forming region was shown while addition of Cd increases the crystallization trend of the system. Besides, the Cd content accommodated by the system to form glass is found to be lower in the As2Se3-rich region than in the GeSe2-rich region. With the introduction of CdSe, density, micro-hardness, and T g of glasses increase whereas an exothermal peak in the DSC curve appears and thermal stability (Δ T ) decreases. The activation energy of crystallization and the Avrami exponent were also obtained using the modified Ozawa equation. 相似文献
Following our previous papers on mechanism of cyclic esters' polymerization coinitiated by tin(II) octoate [tin(II) bis-(2-ethylhexanoate), (Sn(Oct)2)] in the presence of either the low molar mass coinitiator (an alcohol, hydroxy acid, or H2O) or a macromolecule fitted with a hydroxy end group (ROH), the present work deals with ?-caprolactone (CL) and l,l-lactide (LA) polymerizations coinitiated with zinc octoate (Zn(Oct)2) or aluminum acetylacetonate (Al(Acac)3). A series of kinetic measurements revealed that similarly as in the Sn(Oct)2 coinitiated process, these polymerizations proceed by simple monomer insertion into the …Mt-OR bond, reversibly formed in the reaction -Mt-L + ROH ? …-Mt-OR + LH (where Mt = Sn, Zn or Al; L = Oct or Acac), taking place throughout the whole polymerization process. MtLn itself does not play an active role in the polymerization. Applicability of the commercially available Zn(Oct)2 or Al(Acac)3 for the aliphatic polyester (103 ≤ Mn ≤ 4 × 105) synthesis is also discussed. 相似文献