Synthesis and photoluminescence properties of Yb doped Ba5(PO4)3Cl phosphor for white light-emitting diodes

Yb²⁺ ion doped Ba₅(PO₄)₃Cl phosphor was synthesized by solid state reaction. Four distinct absorption bands were observed in the Ultraviolet (UV) light region due to the electronic transitions of Yb²⁺ ion from ¹S₀ ground state to ²F_5/2(t_2g), ²F_5/2(e_g), ²F_7/2(t_2g), and ²F_7/2(e_g) excited states. The main emission wavelength of the phosphor was around 630 nm. The optimized Yb²⁺ ion concentration was 0.2 mol% (λ_exc. = 400 nm). The calculated critical distance was about 8.729 Å and the concentration quenching was observed above 0.2 mol% due to the electric dipole–dipole interaction.     

A novel tetanus neurotoxin-insensitive vesicle-associated membrane protein in SNARE complexes of the apical plasma membrane of epithelial cells

The importance of soluble N-ethyl maleimide (NEM)-sensitive fusion protein (NSF) attachment protein (SNAP) receptors (SNAREs) in synaptic vesicle exocytosis is well established because it has been demonstrated that clostridial neurotoxins (NTs) proteolyze the vesicle SNAREs (v-SNAREs) vesicle-associated membrane protein (VAMP)/brevins and their partners, the target SNAREs (t-SNAREs) syntaxin 1 and SNAP25. Yet, several exocytotic events, including apical exocytosis in epithelial cells, are insensitive to numerous clostridial NTs, suggesting the presence of SNARE-independent mechanisms of exocytosis. In this study we found that syntaxin 3, SNAP23, and a newly identified VAMP/brevin, tetanus neurotoxin (TeNT)-insensitive VAMP (TI-VAMP), are insensitive to clostridial NTs. In epithelial cells, TI-VAMP-containing vesicles were concentrated in the apical domain, and the protein was detected at the apical plasma membrane by immunogold labeling on ultrathin cryosections. Syntaxin 3 and SNAP23 were codistributed at the apical plasma membrane where they formed NEM-dependent SNARE complexes with TI-VAMP and cellubrevin. We suggest that TI-VAMP, SNAP23, and syntaxin 3 can participate in exocytotic processes at the apical plasma membrane of epithelial cells and, more generally, domain-specific exocytosis in clostridial NT-resistant pathways.     

Finite element method for mixed elastohydrodynamic lubrication of journal‐bearing systems

A finite element model is presented for mixed lubrication of journal‐bearing systems operating in adverse conditions. The asperity effects on contact and lubrication at large eccentricity ratios are modelled. The elastic deformation due to both hydrodynamic and contact pressure, and the cavitation of the lubricant film are considered in the model system. Two verification problems with both theoretical and experimental comparisons are given to show the effectiveness of this model. Finally, a new example is presented which discusses the influence of waviness depth, secondary roughness, external force and shaft speed on the mixed lubrication. Copyright © 2004 John Wiley & Sons, Ltd.     

A comprehensive model for software rejuvenation

Recently, the phenomenon of software aging, one in which the state of the software system degrades with time, has been reported. This phenomenon, which may eventually lead to system performance degradation and/or crash/hang failure, is the result of exhaustion of operating system resources, data corruption, and numerical error accumulation. To counteract software aging, a technique called software rejuvenation has been proposed, which essentially involves occasionally terminating an application or a system, cleaning its internal state and/or its environment, and restarting it. Since rejuvenation incurs an overhead, an important research issue is to determine optimal times to initiate this action. In this paper, we first describe how to include faults attributed to software aging in the framework of Gray's software fault classification (deterministic and transient), and study the treatment and recovery strategies for each of the fault classes. We then construct a semi-Markov reward model based on workload and resource usage data collected from the UNIX operating system. We identify different workload states using statistical cluster analysis, estimate transition probabilities, and sojourn time distributions from the data. Corresponding to each resource, a reward function is then defined for the model based on the rate of resource depletion in each state. The model is then solved to obtain estimated times to exhaustion for each resource. The result from the semi-Markov reward model are then fed into a higher-level availability model that accounts for failure followed by reactive recovery, as well as proactive recovery. This comprehensive model is then used to derive optimal rejuvenation schedules that maximize availability or minimize downtime cost.     

Optimization of fermentation parameters for enhanced production of naringinase by soil isolate Aspergillus niger VB07

Aspergillus niger VB07 was isolated from the soil of citrus fruit market used to produce extracellular naringinase in a liquid medium. Various parameters of fermentation have been examined in order to improve overall enzyme yield. Naringinase yield of 17.28 IU/mL in an optimized medium containing naringin (0.1%), rhamnose (0.5%), peptone (0.25%), glycine (10 mM), and pH 4.5 at 28°C for 7 days has been obtained at shake flask level. Compared to the initial medium, the highest naringinase yield observed is approximately increased by 1.8 times under the optimized conditions. Amino acids mediated naringinase synthesis was reported.     

碳纳米管增强的陶瓷基复合材料

利用聚合物前驱体热裂解工艺制备了碳纳米管增强的陶瓷基复合材料.制备了含1.3%和6.4%(体积分数)碳纳米管的硅碳氮复合材料.SEM和HRTEM微观结构表明碳纳米管被均匀地分布在陶瓷基体中.采用纳米压痕测量了材料的力学性能,结果表明碳纳米管增强陶瓷复合材料的力学性能明显提高.     

Desorption Kinetics of Polyether Lubricants from Surfaces

Desorption or evaporation is one of the mechanisms for loss of perfluoropolyalkylether (PFPE) lubricants from the surfaces of data storage media. One approach to minimizing PFPE loss to desorption is the use of lubricants with increasing molecular weight or increasing average chain length. In order to understand the effects of chain length on the lubricant evaporation kinetics we have studied the desorption kinetics of monolayer films of oligomeric ethers with varying chain length adsorbed on the surface of graphite. The desorption pre-exponents, v, and desorption barriers, E _des , have been measured for poly(ethylene glycol) dimethyl ethers, CH₃O(CH₂CH₂O) _m CH₃, with m=1,2,3,4,8 and 10. These are models for the PFPE known as Fomblin Z, which has a structure CF₃O(CF₂CF₂O) _x (CF₂O) _y CF₃. The results show that the desorption pre-exponents are independent of chain length and have an average value of v=10^18.7±0.3 s^–1. The E _des for the poly(ethylene glycol) dimethyl ethers vary non-linearly with chain length and can be fit with a power law expression of the form E _des =a+bN , where N is the total number of atoms in the oligomer backbone (N=3m+3) and the scaling exponent has a value of 1/2. This non-linear dependence of E _des on chain length has also been observed in recent studies of the desorption kinetics of straight chain alkanes from graphite. A desorption mechanism is described that explains the non-linearity of E _des for the poly(ethylene glycol) dimethyl ethers. The implication for the lifetime of lubricants on data storage media is that the long chain PFPE lubricants desorb more rapidly than one might expect based on simple linear scaling of the E _des of lower molecular weight PFPEs.     

Multidimensional multirate filters and filter banks derived fromone-dimensional filters

A method by which every multidimensional (M-D) filter with an arbitrary parallelepiped-shaped passband support can be designed and implemented efficiently is presented. It is shown that all such filters can be designed starting from an appropriate one-dimensional prototype filter and performing a simple transformation. With D denoting the number of dimensions, the complexity of design and implementation of the M-D filter are reduced from O(N^D) to O(N). Using the polyphase technique, an implementation with complexity of only 2N is obtained in the two-dimensional. Even though the filters designed are in general nonseparable, they have separable polyphase components. One special application of this method is in M-D multirate signal processing, where filters with parallelepiped-shaped passbands are used in decimation, interpolation, and filter banks. Some generalizations and other applications of this approach, including M-D uniform discrete Fourier transform (DFT) quadrature mirror filter banks that achieve perfect reconstruction, are studied. Several design example are given     

Interactive effects of resin composition and ambient temperature of light curing on the percentage conversion,molar heat of cure and hardness of dental composite resins

The interactive effects of ambient temperature of cure and resin composition on the extent of cure are evaluated by the measurement of percentage conversion of double bonds, heat of cure and microhardness of visible light cure dental resin systems. Three bonding agents, including two BisGMA-based resins (Command Bond, Pentron Bond) and one urethane-dimethacrylate-based resin (Coe Bond), were evaluated. The results indicate a significant effect of ambient temperature of cure and resin composition on percentage conversion, molar heat of cure and microhardness. In the temperature range of 25–60 °C, thermal activation appears to be a promising approach to improve conversion and crosslinking in dental resins. At lower ambient temperatures of cure (25 °C), urethane dimethacrylate resin undergoes higher levels of conversion than BisGMA-based resins. At higher temperatures, the percentage conversion increases with temperature in all resins. However, the molar heat of cure and hardness values show a significant increase with temperature only in BisGMA-based resins, but not in the urethane dimethacrylate resin. The difference in percentage conversion and heat of cure variation with temperature and the similarity of the latter variation with that of microhardness, probably indicates that the heat of cure is a better predictor of the extent of cure in these thermoset resins. It appears that enhanced crosslinking due to thermal activation may significantly influence the extent of cure at higher ambient temperatures.