Papers by Keyword: Lifetime

Abstract: Lifetime prediction of steam turbine components under biaxial thermo-mechanical fatigue (TMF) loading of modern high chromium steel is prerequisite for design optimization. In this paper a phenomenological method which envelopes the synthesis of stress strain hysteresis loops and damage assessment under considering creep fatigue interaction is extended to multiaxial loadings. It is proposed as a post processing step depending on the results of a preceding finite element analysis based on a constitutive material model. Recalculation of biaxial service-type experiments on cruciform specimen of modern high chromium rotor steel 10CrMoWVNbN shows satisfactory results for lifetime estimation.

Abstract: Clustering in wireless sensor networks is one of the crucial methods for increasing of network lifetime. There are many algorithms for clustering. One of the cluster based algorithm in wireless sensor networks is LEACH algorithm. In this paper we proposed a new clustering method for increasing of network lifetime. In proposed method Clustering is done symmetrically and the best node with respect to remained energy and distance of other nodes in comparing with each that selected as a cluster head. Although in this protocol we didn’t use GPS but we could find geographical position nodes so easily. However, failures in higher level of hierarchy e.g. cluster-head cause more damage to the system because they also limit accessibility to the nodes that are under their supervision. In this paper we propose an efficient mechanism to recover sensors from a failed cluster. In this performance of the proposed algorithm via computer simulation was evaluated and compared with other clustering algorithms. The simulation results show the high performance of the proposed clustering algorithm.

Abstract: With the coming rush of population aging and the termination of the demographic dividend, the question on the extension of the legal retirement age is becoming a hot topic in the community. This paper analyzes factors affecting retirement age，such　as demographic dividend, life expectancy, years of education per capita, supply and demand situation in labor market. From these factors, reasonable quantitative reference standards can be introduced.

Abstract: Description of crack initiation behavior under thermo-mechanical fatigue (TMF) of modern high chromium steel is prerequisite for design optimization of steam turbine components. In this paper a phenomenological method which envelopes the synthesis of stress-strain hysteresis loops according to cycle counting methods and the individual assessment of creep fatigue damage is extended to TMF with superimposed creep. Recalculation of such service-type experiments on specimen of rotor steel 10CrMoWVNbN shows acceptable results for deformation description and lifetime estimation.

Abstract: Transient and quasi-steady-state photoconductance methods were used to measure minority carrier lifetime in p-type Czochralski silicon processed in very clean conditions to contain oxide precipitates. Precipitation treatments were varied to produce a matrix of samples, which were then characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. The lifetime component associated with the precipitates was isolated by preventing or factoring out the effects of other known recombination mechanisms. The lifetime component due to unstrained precipitates could be extremely high (up to ~4.5ms). Recombination at unstrained precipitates was found to be weak, with a capture coefficient of ~8 x 10^-8cm³s^-1 at an injection level equal to half the doping level. Strained precipitates and defects associated with them (dislocations and stacking faults) act as much stronger recombination centres with a capture coefficient of ~3 x 10^-6cm³s^-1 at the same level of injection. The lifetime associated with strained precipitates increases with temperature with a ~0.18eV activation energy over the room temperature to 140°C range. The shape of the injection level dependence of lifetime was similar for all the specimens studied, with the magnitude of the lifetime being dependent on the precipitate density, strain state and temperature, but independent of precipitate size.

Abstract: Lifetime distribution of a multicrystalline silicon ingot of 250 mm diameter and 100 mm height, grown by unidirectional solidification has been modeled. The model computes the combined effect of interstitial iron and dislocation distribution on minority carrier lifetime of the ingot based on Shockley Read Hall (SRH) recombination model for iron point defects and Donolato’s model for recombination on dislocations. The iron distribution model was based on the solid state diffusion of iron from the crucible and coating to the ingot during its solidification and cooling, taking into account segregation of iron to the melt and back diffusion after the end of solidification. Dislocation density distribution is determined from experimental data obtained by PVScan analysis from a vertical cross section slice. Calculated lifetime is fitted to the measured one by fitting parameters relating the recombination strength and the local concentration of iron

Abstract: Product tolerance is one of the important factors which affect the quality and cost of product. However, influenced by many complicated factors, there are still many problems which need to be resolved compared with other research works in CAD field. How to determine tolerances of product effectively is still a big problem. Based on exponent model of tolerance-cost, the relationships between tolerance and other characteristics influencing processing cost are studied in this paper. A relational model of tolerance-cost is come up with based on the above relationships. And then, internal relation between tolerance and lifetime is discussed. Meanwhile, along with the lifetime converted into the cost, the compensated relational model of tolerance-lifetime is presented. Finally, the method on the decision of tolerance grade is analyzed. This paper realizes the organic combination of tolerance, lifetime and cost, and effectively decides how to generate tolerance grades.

Abstract: An environmentally friendly synthesis was developed to fabricate aqueous CdTe quantum dots (QDs) using thilglycolic acid (TGA) as a capping agent. Optimal preparation conditions including pH (11.2) and TGA/Cd molar ratio (1.5:1) resulted in CdTe QDs with high photoluminescence (PL) quantum yield up to 56%. The TGA-capped CdTe QDs exhibited tunable PL from green to red. Lifetime measurement indicated that the average lifetime of the TGA-capped QDs increased with increasing their sizes (27.5 and 37.2 ns for the QDs with PL peak wavelength of 607 and 636 nm, respectively). The PL of the QDs revealed the dependence of temperature, in which the QDs exhibited a red-shifted PL peak with increasing temperature. Such PL behavior depended strongly on the QD sizes.

Abstract: This paper describes a new electro-active actuator based on cellulose and poly(3-hydroxybutyrate) (PHB) blend film that can produce high bending displacement in room humidity condition. Cellulose based actuator has been reported as a smart material that has merits in terms of lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage. However, its actuator performance is very sensitive to humidity, which requires high humidity condition for the maximum actuator performance. To overcome this drawback, we introduce cellulose-PHB blend film based actuator. To fabricate this new actuator, cellulose and PHB were dissolved in trifluoroacetic acid. The solution was cast to form a film followed by depositing thin gold electrode on both sides of the film. The morphology of the blend was characterized by scanning electron microscopy. The actuator can be actuated under AC voltage. The bending performance was evaluated in terms of free bending displacement, electrical power consumption output with respect to voltage and frequency and lifetime test at ambient condition. Primary results show that this cellulose- PHB blend actuator is less sensitive to humidity and it shows much high bending displacement and long lifetime (more than 10 hours) at room humidity condition. These results indicate that this new cellulose-PHB blend actuator is promising for many biomimetic applications in foreseeable future.

Abstract: Our recent high resolution core level and valence level X-ray photoelectron spectra (XPS) of Natural-Styrene Butylene Rubber (NR/SBR) demonstrated much narrower linewidths than previously obtained on rubbers or other polymer coatings. This improvement is due to low-current, low-energy beam flood gun charge compensation on non-conductor rubbers. The different charging has compensated on the rough surface and in the bulk of sponge structure in depth 50 Å of rubber sample. Despite residual charging has occurred on the surface which is apparent in C1s and O1s shoulder on its right side of the peak shape. Carbon groups such as C-H, C-C, C=C cannot be easily differentiated by their principal C(1s) peak chemical shift. Carbon black fillers seem to behave quite differently in the rubber-curing reaction. The stability of vulcanized rubber with sulfur curing system was studied in components of C(1s), O(1s), S(2p) regions which represented appropriate estimation of changes of crosslinked with sulfide bonds on rubber surface. The connection between the Shore hardness of rubber and the presence of carbonyl and sulphonyl groups was apparent. A model has been proposed for the degradation of the crosslinking density of rubber after long term exposure.