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排序方式: 共有1271条查询结果,搜索用时 15 毫秒
161.
Konrad Bergmeister Prof. Dr.Dr. Dipl.‐Ing. Walter Weis Dipl.‐Ing. Josef Taferner Dipl.‐Ing. Dr. Philipp Sicher Dipl.‐Ing. 《Beton- und Stahlbetonbau》2009,104(6):322-329
Internal unbounded Posttensioning in Wide Span Slabs for Building Constructions In order to comply with the needs of robustness and economy to be considered in design and construction, the internal, unbounded posttensioning has been optimized, in a way to install the cables with the minimum necessary amount of work. For this purpose a free system of posttensioning cables has been adopted, in which border uplift forces (in correspondence of the supports) and single or multiple midspan uplift forces are necessary. The deviation forces helps to limit the deflections and cracks. In this paper after some theoretical reflections two innovative practical applications are presented. On the basis of the mechanics of the load bearing behaviour and with three dimensional finite element calculations also the soil‐structure interaction have been taken into account. 相似文献
162.
Brunner TJ Wick P Manser P Spohn P Grass RN Limbach LK Bruinink A Stark WJ 《Environmental science & technology》2006,40(14):4374-4381
Early indicators for nanoparticle-derived adverse health effects should provide a relative measure for cytotoxicity of nanomaterials in comparison to existing toxicological data. We have therefore evaluated a human mesothelioma and a rodent fibroblast cell line for in vitro cytotoxicity tests using seven industrially important nanoparticles. Their response in terms of metabolic activity and cell proliferation of cultures exposed to 0-30 ppm nanoparticles (microg g(-1)) was compared to the effects of nontoxic amorphous silica and toxic crocidolite asbestos. Solubility was found to strongly influence the cytotoxic response. The results further revealed a nanoparticle-specific cytotoxic mechanism for uncoated iron oxide and partial detoxification or recovery after treatment with zirconia, ceria, or titania. While in vitro experiments may never replace in vivo studies, the relatively simple cytotoxic tests provide a readily available pre-screening method. 相似文献
163.
Gallic Acid Improves Health‐Associated Biochemical Parameters and Prevents Oxidative Damage of DNA in Type 2 Diabetes Patients: Results of a Placebo‐Controlled Pilot Study 下载免费PDF全文
164.
Chawla F Steinmann P Loizeau JL Hassouna M Froidevaux P 《Environmental science & technology》2010,44(22):8509-8514
Colloidal transport has been shown to enhance the migration of plutonium in groundwater downstream from contaminated sites, but little is known about the adsorption of ??Sr and plutonium onto colloids in the soil solution of natural soils. We sampled soil solutions using suction cups, and separated colloids using ultrafiltration to determine the distribution of 23?Pu and ??Sr between the truly dissolved fraction and the colloidal fraction of the solutions of three Alpine soils contaminated only by global fallout from the nuclear weapon tests. Plutonium was essentially found in the colloidal fraction (>80%) and probably associated with organic matter. A significant amount of colloidal ??Sr was detected in organic-rich soil solutions. Our results suggest that binding to organic colloids in the soil solutions plays a key role with respect to the mobility of plutonium in natural alpine soils and, to a lesser extent, to the mobility of ??Sr. 相似文献
165.
Adrian Körzendörfer Philipp Temme Eberhard Schlücker Jörg Hinrichs Stefan Nöbel 《Journal of dairy science》2018,101(5):3866-3877
Machinery such as pumps used for the commercial production of fermented milk products cause vibrations that can spread to the fermentation tanks. During fermentation, such vibrations can disturb the gelation of milk proteins by causing texture defects including lumpiness and syneresis. To study the effect of vibrations on yogurt structure systematically, an experimental setup was developed consisting of a vibration exciter to generate defined vibrational states and accelerometers for monitoring. During the fermentation of skim milk, vibrations (frequency sweep: 25 to 1,005 Hz) were introduced at different pH (5.7 to 5.1, step width 0.1 units) for 200 s. Physical properties of set gels (syneresis, firmness) and resultant stirred yogurts (visible particles, rheology, laser diffraction) were analyzed. Vibrational treatments at pH 5.5 to 5.2 increased syneresis, gel firmness, and the number of large particles (d > 0.9 mm); hence, this period was considered critical. The particle number increased from 34 ± 5 to 242 ± 16 particles per 100 g of yogurt due to vibrations at pH 5.4. In further experiments, yogurts were excited with fixed frequencies (30, 300, and 1,000 Hz). All treatments increased syneresis, firmness, and particle formation. As the strongest effect was observed by applying 30 Hz, the amplitude was set to vibration accelerations of a = 5, 10, 15, 20, and 25 m/s2 in the final experiments. The number of large particles was increased due to each treatment and a positive correlation with the amplitude was found. We concluded that vibrations during gelation increase the collision probability of aggregating milk proteins, resulting in a compressed set gel with syneresis. Resultant stirred yogurts exhibit large particles with a compact structure leading to a reduced water-holding capacity and product viscosity. 相似文献
166.
Ter Laak TL Mayer P Busser FJ Klamer HJ Hermens JL 《Environmental science & technology》2005,39(11):4220-4225
Sorption coefficients of hydrophobic organic chemicals (HOC) to sediments and soils can easily be underestimated in traditional batch experiments, especially because analysis of the aqueous concentration often includes compounds sorbed to colloidal organic matter. In this work, a "sediment dilution approach" has been combined with measurements of freely dissolved concentrations to determine sorption coefficients of five chlorobenzenes and two chloroanilines in spiked sediment and of two unknown chemicals in field-contaminated sediment. A range of sediment suspensions with different sediment-water ratios was made. Freely dissolved concentrations in these suspensions were measured by negligible depletion solid-phase microextraction (nd-SPME). Sediment-water sorption coefficients (KD) were derived from the decrease of the freely dissolved concentrations as a function of the "dilution factor" (DF = volume water/mass sediment). The determined sorption coefficients were very similar to literature values. The experimental setup provides sorption coefficients without the need for total extractions, and the negligible depletion SPME technique does not require phase separation. The proposed method might be an alternative for batch equilibrium experiments to determine sorption coefficients. 相似文献
167.
L. Antonio González-Grajales Laura Pieper Stefan Görner Philipp Görner Rudolf Staufenbiel 《Journal of dairy science》2019,102(4):3609-3614
Few studies have compared individual variability of an intravenous glucose tolerance test (ivGTT) obtained daily in young cattle. The objective of this study was to evaluate the repeatability of glucose traits and insulin responses derived from ivGTT during 3 consecutive days in Holstein-Friesian cattle (bulls: n = 4, steers: n = 3, heifers: n = 3). Blood collections were performed from min 0 (basal concentrations) to min 63 (last measurement). Additional estimates included maximal concentration for glucose and insulin, glucose half-life time (GHLT), and glucose and insulin area under the curve. Glucose traits showed higher repeatability when compared with insulin responses. On average, the glucose trait and insulin response with the lowest coefficient of variation was GHLT (0.7%) and insulin area under the curve (21.3%), respectively. In addition, a general linear model with repeated measures was used to test for significant differences in glucose and insulin concentrations over time at different trial days. Both glucose and insulin concentrations were influenced by time point but not by trial day or time point × trial day. The results from this study showed that individual insulin responses were more variable than glucose traits. The high repeatability of GHLT evidenced the strict regulatory glucose disposal mechanisms occurring in young Holstein-Friesian cattle, whereas insulin responses showed high variability despite controlled management and nutritional practices. 相似文献
168.
169.
In the current study the savings of CO2 emissions due to the use of ground source heat pump (GSHP) systems was investigated in comparison to conventional heating systems. Based on a subsidy program for GSHP systems in southwest Germany, the regional, average, and total CO2 savings of 1105 installed GSHP systems were determined on a regional scale. The emitted CO2 per kWh of heating demand for the studied scenario resulted in 149 g CO2/kWh for GSHP using the German electricity mix and 65 g CO2/kWh using the regional electricity mix, which results in CO2 savings of 35% or 72%, respectively. Similar CO2 avoidances of GSHP systems were found in American and European studies ranging between 15% and 77% strongly depending on the supplied energy for the heat pumps and the efficiency of installation. The resulting CO2 savings for one installed GSHP unit in the present study therefore range between 1800 and 4000 kg per year. Nevertheless, the minimum average total annual CO2 savings of all installed GSHP systems due to the subsidy program amounted to 2000 tons per year. The maximum regional avoided additional CO2 emissions are primarily associated with the affluent suburbs of the most densely populated area in the region. In 2006 the total contribution of CO2 savings due to GSHP systems in Germany was only about 3.4% of the total renewable energies. However, continuously rising numbers of installed GSHP units and the increasing use of renewable electricity demonstrate that there is a fine opportunity to substantially avoid additional CO2 emissions associated with the provision of heating (and cooling) of buildings and other facilities. 相似文献
170.