食品中大肠菌群检测三步发酵法检验步序和检出率的关系

大肠菌群是食品卫生检验的主要指标之一。国家标准检验方法为三步发酵法，本文作者对各检验步序和检出率之间的关系进行了分析。结果见（表1）。     

Real-time PCR quantification of Vibrio parahaemolyticus in oysters using an alternative matrix

This study examined the relationship between levels of total Vibrio parahaemolyticus found in oyster tissues and mantle fluid with the goal of using mantle fluid as a template matrix in a new quantitative real-time PCR assay targeting the thermolabile hemolysin (tlh) gene for the enumeration of total V. parahaemolyticus in oysters. Oysters were collected near Mobile Bay, Ala., in June, July, and September and tested immediately after collection and storage at 26 degrees C for 24 h. Initial experiments using DNA colony hybridization targeting tlh demonstrated that natural V. parahaemolyticus levels in the mantle fluid of individual oysters were strongly correlated (r = 0.85, P < 0.05) with the levels found in their tissues. When known quantities of cultured V. parahaemolyticus cells were added to real-time PCR reactions that contained mantle fluid and oyster tissue matrices separately pooled from multiple oysters, a strong linear correlation was observed between the real-time PCR cycle threshold and the log concentration of cells inoculated into each PCR reaction (mantle fluid: r = 0.98, P < 0.05; and oyster: r = 0.99, P < 0.05). However, the mantle fluid exhibited less inhibition of the PCR amplification than the homogenized oyster tissue. Analysis of natural V. parahaemolyticus populations in mantle fluids using both colony hybridization and real-time PCR demonstrated a significant (P < 0.05) but reduced correlation (r = -0.48) between the two methods. Reductions in the efficiency of the real-time PCR that resulted from low population densities of V. parahaemolyticus and PCR inhibitors present in the mantle fluid of some oysters (with significant oyster-to-oyster variation) contributed to the reduction in correlation between the methods that was observed when testing natural V. parahaemolyticus populations. The V. parahaemolyticus-specific real-time PCR assay used for this study could estimate elevated V. parahaemolyticus levels in oyster mantle fluid within 1 h from sampling time.     

基于样机型式试验的液压支架有限元分析

基于液压支架样机型式试验的思路,模拟不同型式试验的加载方式,对液压支架进行有限元分析;同时将常规设计的液压支架与支架型式试验不同加载方式下的液压支架有限元应力云图进行了分析比较,建立了该液压支架的虚拟型式试验平台。     

Review: functional properties of kefir

Kefir is a unique cultured dairy product due to combined lactic acid and alcoholic fermentation of lactose in milk. Kefir is produced by microbial activity of "kefir grains" which have a relatively stable and specific balance of lactic acid bacteria and yeast. Due to the claimed health benefits of kefir which include reduction of lactose intolerance symptoms, stimulation of the immune system, lowering cholesterol, and antimutagenic and anticarcinogenic properties, kefir has become an important functional dairy food and consequently, research on kefir has increased in the past decade. In the following review, recent studies on the functional properties of kefir are reviewed.     

Micrometer-scale ballistic transport in encapsulated graphene at room temperature

Devices made from graphene encapsulated in hexagonal boron-nitride exhibit pronounced negative bend resistance and an anomalous Hall effect, which are a direct consequence of room-temperature ballistic transport at a micrometer scale for a wide range of carrier concentrations. The encapsulation makes graphene practically insusceptible to the ambient atmosphere and, simultaneously, allows the use of boron nitride as an ultrathin top gate dielectric.     

Annealing effects on capacitance-voltage characteristics of a-Si/SiN(x) multilayer prepared using hot-wire chemical vapour deposition

Post-deposition annealing of a-Si/SiN(x) multilayer films at different temperature shows varying shift in high frequency (1 MHz) capacitance-voltage (HFCV) characteristics. Various a-Si/SiN(x) multilayer films were deposited using hot wire chemical vapor deposition (HWCVD) and annealed in the temperature range of 800 to 900 degrees C to precipitate Si quantum dots (Si-QD) in a-Si layers. HFCV measurements of the as-deposited and annealed films in metal-insulator-semiconductor (MIS) structures show hysterisis in C-V curves. The hysteresis in the as-deposited films and annealed films is attributed to charge trapping in Si-dangling bonds in a-Si layer and in Si-QD respectively. The charge trapping density in Si-QD increases with temperature while the interface defects density (D(it)) remains constant.     

Signalling of DNA damage and cytokines across cell barriers exposed to nanoparticles depends on barrier thickness

The use of nanoparticles in medicine is ever increasing, and it is important to understand their targeted and non-targeted effects. We have previously shown that nanoparticles can cause DNA damage to cells cultured below a cellular barrier without crossing this barrier. Here, we show that this indirect DNA damage depends on the thickness of the cellular barrier, and it is mediated by signalling through gap junction proteins following the generation of mitochondrial free radicals. Indirect damage was seen across both trophoblast and corneal barriers. Signalling, including cytokine release, occurred only across bilayer and multilayer barriers, but not across monolayer barriers. Indirect toxicity was also observed in mice and using ex vivo explants of the human placenta. If the importance of barrier thickness in signalling is a general feature for all types of barriers, our results may offer a principle with which to limit the adverse effects of nanoparticle exposure and offer new therapeutic approaches.     

Enhanced hydrogen storage by spillover on metal-doped carbon foam: an experimental and computational study

A lightweight, oxygen-rich carbon foam was prepared and doped with Pd/Hg alloy nanoparticles. The composite revealed high H2 sorption capacity (5 wt%) at room temperature and moderate pressure (2 MPa). The results were explained on the basis of the H2 spillover mechanism using Density Functional Theory.     

Nitrification and potential control mechanisms in simulated premises plumbing

Indigenous drinking water organisms were used to establish nitrification in glass reactors containing copper or polyvinyl chloride (PVC) surfaces. The reactors were fed soil-derived humics as the organic carbon source and ammonium sulfate as the nitrogen source in biologically treated tap water. Water in the reactors was stagnant for 8 h and then flowed for 5 min to simulate conditions in household plumbing. Following the establishment of complete nitrification (conversion of ammonia to nitrate) in both reactor types, various inhibitors of nitrification were tested followed by a period where recovery of nitrification was observed. In one PVC reactor, copper was gradually introduced up to 1.3 ppm. To ensure that most of the copper was in the ionic form, the pH of the influent was then gradually lowered to 6.6. No significant change in nitrification was observed in the presence of copper. Chlorite was introduced into copper and PVC reactors at doses increasing from 0.2 ppm to 20 ppm. There was limited effect on the PVC system and inhibition in the copper reactor only at 20 ppm. Chloramine was tested at chlorine to ammonia ratios ranging from 0.5:1 to 5:1. Nitrification activity was impacted significantly at a 5:1 ratio and ultimately stopped, with the fastest response being in the copper system. Whenever a control mechanism was tested, there was increased release of copper from the reactors with copper coupons. In all cases, nitrification recovered when inhibitors were removed but the rates of recovery differed depending on the treatment method and coupon surface.     

Effects of the transportation of beef cattle from the feedyard to the packing plant on prevalence levels of Escherichia coli O157 and Salmonella spp

Two hundred steers and heifers from a large feedyard (65,000-head capacity) were used to determine the prevalence levels of enterohemorrhagic Escherichia coli O157 (EHEC O157) and Salmonella spp. prior to and after shipping to a commercial packing facility. Two samples, a ventral midline hide swab and a fecal sample, were aseptically collected from each animal 2 weeks prior to the date of transportation and at the packing plant immediately after exsanguination. Samples were collected from all trailers (n = 46) before animals were loaded for transport to the packing facility. The average prevalence levels of EHEC O157 on hides (18%) and in feces (9.5%) at the feedyard decreased (P > 0.05) at the packing plant to 4.5 and 5.5%, respectively. The average prevalence levels of Salmonella spp. on hides (6%) and in feces (18%) at the feedyard increased to 89 and 46%, respectively, upon arrival at the packing plant. Average prevalence levels for EHEC O157 and Salmonella spp. on the trailers were 5.43 and 59%, respectively. The results of this study demonstrate that transportation may be a potential stressor for cattle, as evidenced by the increased shedding of Salmonella spp.