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排序方式: 共有720条查询结果,搜索用时 187 毫秒
131.
Vurma M Chung YK Shellhammer TH Turek EJ Yousef AE 《International journal of food microbiology》2006,106(3):263-269
Three Listeria monocytogenes strains (Scott A, OSY-8578, and OSY-328) that differ considerably in barotolerance were grown to stationary phase and suspended individually in phosphate buffer (pH 7.0). Twelve phenolic compounds, including commercially used food additives, were screened for the ability to sensitize L. monocytogenes to high-pressure processing (HPP). Each L. monocytogenes strain was exposed to each of the 12 phenolic compounds (100 ppm each) for 60 min; this was followed by a pressure treatment at 400 MPa for 5 min. Six phenolic compounds increased the efficacy of HPP against L. monocytogenes but tert-butylhydroquinone (TBHQ) was the most effective. The additives alone at 100 ppm were not lethal for L. monocytogenes. Subsequently, the three L. monocytogenes strains were exposed to TBHQ before or after pressure treatments at 400 or 500 MPa for 5 min. When TBHQ was added after the pressure treatment, the combined treatment was more lethal than was pressure alone. However, the lethality attributable to TBHQ was greater when the additive was applied before rather than after pressure treatment. The inactivation kinetics of the L. monocytogenes strains at 300, 500, and 700 MPa, in the presence or absence of TBHQ, was investigated. All survivor plots showed non-linear inactivation kinetics, but tailing behavior was most pronounced when HPP was used alone. Combinations of TBHQ and HPP eliminated tailing behavior when survivors were monitored by direct plating or an enrichment procedure. Pressure and phenolic additives are apparently a potent bactericidal combination against L. monocytogenes. 相似文献
132.
Al-Assaf Y 《IEEE transactions on bio-medical engineering》2006,53(11):2248-2256
Toward the goal of elbow and wrist prostheses control by characterizing events in surface myoelectric signals, this paper presents a dynamic method to simultaneously detect and classify such events. Dynamic cumulative sum of local generalized likelihood ratios using wavelet decomposition of the myoelectric signal is used for on-line detection. Frequency as well as energy changes are detected with this hybrid approach. Classification is composed of using multiresolution wavelet analysis and autoregressive modeling to extract signal features while polynomial classifiers are used for pattern modeling and matching. The results of detecting and classifying four elbow and wrist movements show that, in average, 91% of the events are correctly detected and classified using features obtained from multiresolution wavelet analysis while 95% accuracy is achieved with AR modeling. The classification accuracy decreases, however, if short prostheses response delay is desired. This paper also shows that the performance of the polynomial classifiers is better than that of the commonly used neural networks since it gives higher classification accuracy and consistent classification outcomes. In comparison to the well known support vector machine classification, the polynomial classifier gives similar results without the need to optimize and search for classifier parameters. 相似文献
133.
Study of cell signaling often requires examination of the cellular dynamics under variation in the stimulant concentration. Such variation has typically been conducted by dispensing cell populations in a number of chambers or wells containing discrete concentrations. Such practice adds to the complexity associated with experimental or device design and requires substantial labor for implementation. Furthermore, there is also potential risk of missing important results due to the often arbitrary selection of discrete concentration values for testing. In this Letter, we study NF-κB activation and translocation at the single cell level using a microfluidic device that generates continuously varying concentration gradient. We use only three device settings to cover stimulant (interleukin-1β) concentrations of 4 orders of magnitude (0.001-10 ng/mL). Such device allows us to study temporal dynamics of NF-κB in single cells under different stimulant concentrations by real-time imaging. Interestingly, our results reveal that, while the percent of cells with NF-κB translocation decreases with lower stimulant concentration in the range of 0.1-0.001 ng/mL, the response time of such translocation remains constant, reflected by the single cell data. 相似文献
134.
Wren AW Coughlan A Hassanzadeh P Towler MR 《Journal of materials science. Materials in medicine》2012,23(5):1331-1341
Bioactive glass particles (0.42SiO2–0.15CaO–0.23Na2O–0.20ZnO) of varying size (<90 μm and 425–850 μm) were synthesized and coated with silver (Ag) to produce Ag coated particles
(PAg). These were compared against the uncoated analogous particles (Pcon.). Surface area analysis determined that Ag coating of the glass particles resulted in increased the surface area from 2.90
to 9.12 m2/g (90 μm) and 1.09–7.71 m2/g (425–850 μm). Scanning electron microscopy determined that the Ag coating remained at the surface and there was little
diffusion through the bulk. Antibacterial (Escherichia coli—13 mm and Staphylococcus epidermidis—12 mm) and antifungal testing (Candida albicans—7.7 mm) determined that small Ag-coated glass particles exhibited the largest inhibition zones compared to uncoated particles.
pH analysis determined an overall higher pH consider in the smaller particles, where after 24 h the large uncoated and Ag
coated particles were 8.27 and 8.74 respectively, while the smaller uncoated and Ag coated particles attained pH values of
9.63 and 9.35 respectively. 相似文献
135.
Saleh Alsayed Yousef Al-Salloum Tarek Almusallam Sherif El-Gamal Mohammed Aqel 《Composites Part B》2012,43(5):2265-2271
This paper investigates the residual tensile properties of newly developed glass fiber reinforced polymer (GFRP) bars after being subjected to elevated temperatures for different periods. A total of 120 GFRP specimens were tested in this study. Half of the samples were covered with concrete while the other half were bare bars. The specimens were subjected to three different controlled temperatures (100, 200 and 300 °C) for three different periods (1, 2, and 3 h). Test results showed that almost no losses were observed in the tensile modulus after all exposure periods and temperatures. Losses in the tensile strength, proportional to the level of temperature and exposure period, were recorded. The bars with concrete cover showed higher residual tensile strength compared to their counterparts without coating. The concrete cover was more effective at the lowest temperature level (100 °C) and at the shortest time period (1 h). Scanning Electronic Microscopy (SEM) technique was also used to investigate the effect of elevated temperature on the degradation mechanism of the GFRP bars. The results showed that increasing the temperature level affected the resin matrix surrounding the glass fibers and consequently affected the bond between the fibers and the matrix. 相似文献
136.
Analysis of the convective heat transfer and flow behavior around two counter‐rotating side‐by‐side cylinders
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This study presents details of the heat and fluid flow around two counter‐rotating cylinders. For this goal, three different nondimensional gap spaces such as G/D = 1.5, 2.0, and 3.0 are examined in the constant Reynolds number of 200 and Prandtl number of 7.0. In addition, computations are carried out at various nondimensional rotating speeds (R.S) in the range from 0 to 4. The obtained results are validated against the available data in the open literature for stationary cases. The results showed that the flow structure, vortex shedding process, and exerted forces on the cylinders strongly depended on the R.S and G/D. Reductions of the drag coefficients are observed for both cylinders with increasing the R.S due to suppression of the wake downstream of the cylinders at low R.S and eliminating the vortex shedding process at high R.S. Finally, it is demonstrated that, regardless of the G/D value, increasing the R.S diminishes dramatically the convective heat exchange rate between the cylinders and fluid flow. 相似文献
137.
Reduction of Escherichia coli O157:H7 population on baby spinach leaves by liquid sanitizers
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Taras Pyatkovskyy Mykola Shynkaryk Ahmed Yousef Sudhir K. Sastry 《Journal of food process engineering》2017,40(3)
The effectiveness of various liquid sanitizers and methods of application against Escherichia coli on baby spinach was investigated. Inoculated spinach was treated with (i) Pro‐San L (commercially prepared solution containing 0.66% citric acid, 0.036% sodium dodecyl sulfate (SDS); (ii) chlorine solution (200 ppm), alone or with addition of 0.036% SDS; and (iii) aqueous solution of 0.66% levulinic acid with 0.036% SDS. Population reduction in response to these treatments ranged between 2.1 and 2.8 log CFU/g. No significant difference (p > .05) was found among tested sanitizers in microbial count reduction. Spraying, dipping, and “dry” vacuum impregnation methods of Pro‐San L application were compared. Dipping was the most effective in reducing E. coli O157:H7 population (4.4 log CFU/g reduction). Dry vacuum impregnation was less effective (3.3 log CFU/g reduction) and caused damage to the produce. The effectiveness of spray Pro‐San L application and holding for prolonged time (up to 3 days) was also evaluated. However, increasing time of exposure to organic acid sanitizer did not increase sanitizing effectiveness and led to progressive damage of spinach leaves. 相似文献
138.
Ebrahim Elkhtab Mohamed El-Alfy Mohamed Shenana Abdelaty Mohamed Ahmed E. Yousef 《Journal of dairy science》2017,100(12):9508-9520
Compounds with the ability to inhibit angiotensin-converting enzyme (ACE) are used medically to treat human hypertension. The presence of such compounds naturally in food is potentially useful for treating the disease state. The goal of this study was to screen lactic acid bacteria, including species commonly used as dairy starter cultures, for the ability to produce new potent ACE-inhibiting peptides during milk fermentation. Strains of Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus helveticus, Lactobacillus paracasei, Lactococcus lactis, Leuconostoc mesenteroides, and Pediococcus acidilactici were tested in this study. Additionally, a symbiotic consortium of yeast and bacteria, used commercially to produce kombucha tea, was tested. Commercially sterile milk was inoculated with lactic acid bacteria strains and kombucha culture and incubated at 37°C for up to 72 h, and the liberation of ACE-inhibiting compounds during fermentation was monitored. Fermented milk was centrifuged and the supernatant (crude extract) was subjected to ultrafiltration using 3- and 10-kDa cut-off filters. Crude and ultrafiltered extracts were tested for ACE-inhibitory activity. The 10-kDa filtrate resulting from L. casei ATCC 7469 and kombucha culture fermentations (72 h) showed the highest ACE-inhibitory activity. Two-step purification of these filtrates was done using HPLC equipped with a reverse-phase column. Analysis of HPLC-purified fractions by liquid chromatography–mass spectrometry/mass spectrometry identified several new peptides with potent ACE-inhibitory activities. Some of these peptides were synthesized, and their ACE-inhibitory activities were confirmed. Use of organisms producing these unique peptides in food fermentations could contribute positively to human health. 相似文献
139.
In this paper, a detailed analysis of the solar radiation on horizontal and tilted surfaces for six locations in Oman is presented. The locations are (from North to South): Majis/Sohar, Sur, Fahud, Masira, Marmul, and Salalah. These locations spread over Oman and cover different types of landscape. The method is validated through the use of measured data. The effect of tilt angle and orientation on the incident solar radiation is presented along with optimum surface tilt angles and directions for maximum solar radiation collection in these six locations. The solar radiation models used in this paper show good agreement with measured data. The results presented in this paper are extremely useful for quick estimation of solar radiation for calculations of buildings’ cooling load and solar collector system performance. This can be easily extended for other locations with similar landscapes and geographical conditions. 相似文献
140.
In this research, a dynamometer was designed, constructed and calibrated to measure the forces and moments applied on tillage implements. This dynamometer is able to measure the three orthogonal forces acting on the implement and the three moments acting around the orthogonal axes, up to a maximum force of 20 kN and a maximum moment of 20 kN m. The dynamometer uses two extended octagonal ring transducers mounted in a back-to-back arrangement with their axes at right angles and has a tubular torque meter for torque measurement. For mechanical design of the dynamometer frame and its units, the finite element method and CATIA software were used. The device was machined from the solid part and high tensile steel. The forces and moments acting on the dynamometer were measured by using the strain gauge bridges on two extended octagonal ring transducers and on the torque meter tube. The results of data analysis, including forces applied on the dynamometer, the designing method of rings and torque meter tubes, the mounting arrangement of load cell parts on each other, the mounting method of load cell on frame and the position of strain gauge on load cell, in other words, the position of different parts of the dynamometer relative to each other has been explained in this paper. Calibration of the measurement unit was done by a calibration system which was designed for static calibration of the triaxial dynamometer. The results of calibration of the measurement unit showed that the designed and constructed dynamometer has appropriate precision, sensitivity and good repeatability for measuring the desired forces and moments. The results showed a high degree of linearity between output voltage of bridges and applied forces and moments. The interaction effects of the applied forces and moments were very negligible. 相似文献