终止浪涌的简单高效浪涌电流限制器

通常为200W或200W以上负载供电的离线电源,都需要采用浪涌电流限制器.毫无限制的浪涌电流可达数百安培.这样大的电流会损坏线路整流器,融断保险、使输入滤波电感器开路、或损坏PFC(功率因数校正)滤波器电容.     

Ultrasound elastography: a dynamic programming approach

This paper introduces a 2-D strain imaging technique based on minimizing a cost function using dynamic programming (DP). The cost function incorporates similarity of echo amplitudes and displacement continuity. Since tissue deformations are smooth, the incorporation of the smoothness into the cost function results in reduced decorrelation noise. As a result, the method generates high-quality strain images of freehand palpation elastography with up to 10% compression, showing that the method is more robust to signal decorrelation (caused by scatterer motion in high axial compression and nonaxial motions of the probe) in comparison to the standard correlation techniques. The method operates in less than 1 s and is thus also potentially suitable for real time elastography.      

Disruptive Technologies,Services, or Business Models?

Convergence in the realm of media, consumer electronics, computer technologies, and telecommunications has contributed to societal changes in terms of individual expectations and behavior leading to the re-appraisal of traditional market segments. Key innovations like the internet create a global platform that provides for new means in product and services configuration. This expands opportunities and threats in the business environment contributing to increased competition in a dynamic environment where traditional boundaries are shifting. In a world of converging technologies, increasing marketplace dynamics and rapid technological advances, new upcoming “disruptive technologies” such as Voice-over-IP (VoIP) pose threats to traditional telecommunications companies. Business leaders in order to succeed need to be “thinking outside the box”. We introduce the concept of a business model as a tool in crafting strategy for the purpose of achieving sustainable innovation in the face of the reshaping of the industry and the market. We apply this model to the VoIP market and in particular the Skype technology and service. The significance of this contribution is that it highlights the importance of developing an innovative business model to take advantage of disruptive technologies. Our analysis of the dimensions of innovations shows that the more dimensions the greater the impact. ICT convergence is leading to a paradigm shift with innovation effects that are both effective and disruptive. Thus, leading to equally disruptive business models reshaping innovation strategy.

TEM characterization of super-hydrophilic Ni-Ti thin film

A super-hydrophilic Ni-Ti thin film is evaluated using cross-sectional transmission electron microscopy (TEM). Following sputter deposition and annealing, the Ni-Ti thin films are chemically treated with buffered oxide etchant, nitric acid and 30% hydrogen peroxide solution to produce a 100-nm-thick surface oxide layer. The fabricated Ni-Ti thin films show a 10- to 15-nm TiO₂ thick layer on its surface with a ~ 67° wetting angle. For the surface treated sample, a porous oxide 100 nm TiO layer is found with a < 5°. It is believed that TiOOH(H₂O)_n complex forms on the surface to produce the observed super-hydrophilic behavior.     

Nanochannel electroporation delivers precise amounts of biomolecules into living cells

Many transfection techniques can deliver biomolecules into cells, but the dose cannot be controlled precisely. Delivering well-defined amounts of materials into cells is important for various biological studies and therapeutic applications. Here, we show that nanochannel electroporation can deliver precise amounts of a variety of transfection agents into living cells. The device consists of two microchannels connected by a nanochannel. The cell to be transfected is positioned in one microchannel using optical tweezers, and the transfection agent is located in the second microchannel. Delivering a voltage pulse between the microchannels produces an intense electric field over a very small area on the cell membrane, allowing a precise amount of transfection agent to be electrophoretically driven through the nanochannel, the cell membrane and into the cell cytoplasm, without affecting cell viability. Dose control is achieved by adjusting the duration and number of pulses. The nanochannel electroporation device is expected to have high-throughput delivery applications.     

Partial biochemical characterization of tetrazolium red‐reactive Lactobacillus plantarum mutants

One thousand colonies derived from Lactobacillus plantarum ATCC 8014 cells that survived 34–43 × 10³ ergs cm^‐2 ultraviolet irradiation were screened on media containing tetrazolium red to detect fermentative mutants. Fermentation end‐products formed from pyruvate, glucose, or lactose catabolism were determined. All 37 stable tetrazolium red‐reactive mutants had increased pyruvate utilization compared to the wild‐type strain. Only two did not produce lactate from exogenous pyruvate. When glucose or lactose were substrates, these two mutants and six other representative mutants produced lactate at levels similar to the parent strain. Although the average lactate and acetoin production from pyruvate by the mutants and wild‐type strains were similar, 25% of the mutants had increased acetoin production.     

On the sources of methane to the los angeles atmosphere

We use historical and new atmospheric trace gas observations to refine the estimated source of methane (CH(4)) emitted into California's South Coast Air Basin (the larger Los Angeles metropolitan region). Referenced to the California Air Resources Board (CARB) CO emissions inventory, total CH(4) emissions are 0.44 ± 0.15 Tg each year. To investigate the possible contribution of fossil fuel emissions, we use ambient air observations of methane (CH(4)), ethane (C(2)H(6)), and carbon monoxide (CO), together with measured C(2)H(6) to CH(4) enhancement ratios in the Los Angeles natural gas supply. The observed atmospheric C(2)H(6) to CH(4) ratio during the ARCTAS (2008) and CalNex (2010) aircraft campaigns is similar to the ratio of these gases in the natural gas supplied to the basin during both these campaigns. Thus, at the upper limit (assuming that the only major source of atmospheric C(2)H(6) is fugitive emissions from the natural gas infrastructure) these data are consistent with the attribution of most (0.39 ± 0.15 Tg yr(-1)) of the excess CH(4) in the basin to uncombusted losses from the natural gas system (approximately 2.5-6% of natural gas delivered to basin customers). However, there are other sources of C(2)H(6) in the region. In particular, emissions of C(2)H(6) (and CH(4)) from natural gas seeps as well as those associated with petroleum production, both of which are poorly known, will reduce the inferred contribution of the natural gas infrastructure to the total CH(4) emissions, potentially significantly. This study highlights both the value and challenges associated with the use of ethane as a tracer for fugitive emissions from the natural gas production and distribution system.     

Excessive ovarian production of nerve growth factor elicits granulosa cell apoptosis by setting in motion a tumor necrosis factor α/stathmin-mediated death signaling pathway

Excessive nerve growth factor (NGF) production by the ovary, achieved via a transgenic approach, results in arrested antral follicle growth, reduced ovulatory capacity, and a predisposition to cyst formation in response to mildly elevated LH levels. Two salient features in these mutant mice (termed 17NF) are an elevated production of 17α-hydroxyprogesterone (17-OHP(4)), testosterone, and estradiol (E(2)) in response to gonadotropins, and an increased frequency of granulosa cell (GC) apoptosis. In this study, we show that the increase in steroidal response is associated with enhanced expression of Cyp17a1, Hsd17b, and Cyp19a1, which encode the enzymes catalyzing the synthesis of 17-OHP(4), testosterone, and E(2) respectively. Using a proteomic approach, we identified stathmin (STMN1), as a protein that is overproduced in 17NF ovaries. In its phosphorylated state, STMN1 mediates a cell death signal initiated by tumor necrosis factor α (TNF). STMN1 is expressed in GCs and excessive NGF increases its abundance as well as that of its forms phosphorylated at serine (Ser) 16, 25, and 38. TNF synthesis is also increased in 17NF ovaries, and this change is abolished by blocking neurotrophic tyrosine kinase receptors. Inhibiting TNF actions in vivo by administering a soluble TNF receptor prevented the increase in total and phosphorylated STMN1 production, as well as GC apoptosis in NGF-overproducing ovaries. These results indicate that an excess of NGF in the ovary promotes steroidogenesis by enhancing the expression of enzyme genes involved in 17-OHP(4), testosterone, and E(2) synthesis, and causes GC apoptosis by activating a TNF/ STMN1-mediated cell death pathway.     

Effect of TCE concentration and dissolved groundwater solutes on NZVI-promoted TCE dechlorination and H2 evolution

Nanoscale zero-valent iron (NZVI) is used to remediate contaminated groundwater plumes and contaminant source zones. The target contaminant concentration and groundwater solutes (NO3-, Cl-, HCO3-, SO4(2-), and HPO4(2-)) should affect the NZVI longevity and reactivity with target contaminants, but these effects are not well understood. This study evaluates the effect of trichloroethylene (TCE) concentration and common dissolved groundwater solutes on the rates of NZVI-promoted TCE dechlorination and H2 evolution in batch reactors. Both model systems and real groundwater are evaluated. The TCE reaction rate constant was unaffected by TCE concentration for [TCE] < or = 0.46 mM and decreased by less than a factor of 2 for further increases in TCE concentration up to water saturation (8.4 mM). For [TCE] > or = 0.46 mM, acetylene formation increased, and the total amount of H2 evolved at the end of the particle reactive lifetime decreased with increasing [TCE], indicating a higher Fe0 utilization efficiency for TCE dechlorination. Common groundwater anions (5mN) had a minor effect on H2 evolution but inhibited TCE reduction up to 7-fold in increasing order of Cl- < SO4(2-) < HCO3- < HPO4(2). This order is consistent with their affinity to form complexes with iron oxide. Nitrate, a NZVI-reducible groundwater solute, present at 0.2 and 1 mN did not affect the rate of TCE reduction but increased acetylene production and decreased H2 evolution. NO3- present at > 3 mM slowed TCE dechlorination due to surface passivation. NO3- present at 5 mM stopped TCE dechlorination and H2 evolution after 3 days. Dissolved solutes accounted for the observed decrease of NZVI reactivity for TCE dechlorination in natural groundwater when the total organic content was small (< 1 mg/L).