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排序方式: 共有805条查询结果,搜索用时 15 毫秒
21.
Professional order‐picking in deep cold‐storage depots (i.e., storing, picking, and dispatching of frozen groceries) requires employees to remain working at temperatures of approximately ?24°C for a whole workday. Actually, a well‐regulated organization of working times and breaks has not been established, and no competent knowledge exists as to whether an additional age‐differentiated organization is necessary. To assess the physiological effects while working in deep cold, 30 male subjects (Ss) were classified into two age groups (20‐ to 35‐year‐olds and 40‐ to 65‐year‐olds). In whole workday tests, possible age‐dependent effects on the strain were measured to guarantee the preservation of the subjects' ability to work in the long run. For the objectification of the physiological strain, heart rate and skin surface temperature were registered continuously, and blood pressure and body core temperature were measured and recorded discretely during cold exposures of 80, 100, and 120 min, separated by 20‐min warming‐up breaks. Systematic differences of blood pressure could not be found. The heart rate values indicated a high physiological strain for both younger and older Ss, with work‐related increases above the resting level of 30 bpm and more. Due to increases over time, endurance level sometimes was exceeded. Age‐related differences in skin temperature could not be recorded, but the ability to generate heat deteriorated with advancing age, which is shown by more substantial decreases of body core temperature in the group of 40‐ to 65‐year‐olds taken at the tympanum. Regarding physiological strain brought about by maximum heart rate decreasing with age and declined heat generation, correspondingly adapted workday break regimes have to be provided for older employees to ensure their ability to work in the long run. © 2011 Wiley Periodicals, Inc. 相似文献
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Flame-assisted spray pyrolysis (FASP) is a versatile process for synthesis of nanoparticles from a broad choice of precursors and solvents. Water is an attractive solvent particularly for inexpensive inorganic precursors (e.g. metal nitrates) as it can effectively reduce the process cost. Furthermore when water usage is combined with a carbon-free fuel (e.g. H2), nanoparticles can be made without forming CO2. Here such a FASP process is explored for synthesis of Bi2O3 and other oxide nanoparticles from aqueous precursor solutions. The flame temperature was measured by FTIR emission–transmission spectroscopy while powders were characterized by X-ray diffraction and N2 adsorption. At low FASP fuel gas (H2 or C2H2) flow rates or process temperatures, product powders had a bimodal crystal size distribution. Its large and small modes were made by droplet- and gas-to-particle conversion, respectively. Homogeneous Bi2O3 and CeO2 powders were obtained for sufficiently high flow rates of either C2H2 or H2. Prolonged high temperature residence times promoted precursor evaporation from the spray droplets and yielded homogeneous nanostructured powders by gas-to-particle conversion. In contrast, FASP of aqueous solutions of aluminum nitrate yielded rather large particles by droplet-to-particle conversion at all fuel flows investigated. 相似文献
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Forschung im Ingenieurwesen - Nasslaufende Lamellenkupplungen weisen zu Betriebsbeginn eine Phase des Einlaufens auf, in der sich das Reibungsverhalten durch Anpassung der Reibflächen... 相似文献
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Norgauer Philipp Grunewald Laura Priester Lena Heilemann Jens Hein Michael Stahl Karsten 《Forschung im Ingenieurwesen》2020,84(2):141-150
Forschung im Ingenieurwesen - Schneckengetriebe finden sich in verschiedenen Anwendungen als Stell- und Leistungsgetriebe. Aufgrund der Realisierbarkeit einer hohen Übersetzung bei kleinem... 相似文献
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Hydrogenation of liquid organic hydrogen carriers is usually carried out in liquid phase. To measure the kinetics of this hydrogenation, an experimental setup using in situ Raman spectroscopy for analysis of the reaction mixture is proposed. With this setup it is possible to perform hydrogenation reactions at temperatures of up to 573 K and pressures up to 25 MPa. For validation of the experimental setup the hydrogenation of 1‐octene was measured in liquid phase. The reaction progress can be monitored in detail by Raman spectroscopy. To determine kinetic parameters from the experimental data, two modeling approaches were applied: a classic kinetic model and a thermodynamic kinetic model. The results were compared to literature data. 相似文献
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Bertram Boehrer Lars Golmen Jarl Eivind Løvik Karsten Rahn Dag Klaveness 《Journal of Great Lakes research》2013
Thermobaric stratification was investigated in very deep lakes of elongated shape. We considered the spring time configuration when large freshwater lakes may have their deepest recirculation. In five very deep freshwater lakes in Norway, profiles were measured in spring 2006 with multiparameter probes. Temperature profiles confirmed thermobaric stratification in all of these lakes, i.e. the temperature profiles crossed the 4 °C line and thus were affected by pressure effects on the temperature of maximum density. Electrical conductance was low in all of the investigated lakes, and vertical gradients were too small to play a role in the density stratification. In all lakes, deep water was well supplied with oxygen. Three out of five lakes showed a temperature gradient close to Eklund's stability theorem. However, the remaining two lakes clearly opposed the theorem. Bottom temperatures were more closely related to lake length than their maximum depths. Oxygen saturation profiles documented recent intensive gas exchange with the atmosphere. They agree well with the possible formation of deep water from density driven flows at horizontal temperature gradients close to 4 °C. 相似文献
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Molecular Heterojunctions of Oligo(phenylene ethynylene)s with Linear to Cruciform Framework 下载免费PDF全文
Zhongming Wei Tim Hansen Marco Santella Xintai Wang Christian R. Parker Xingbin Jiang Tao Li Magni Glyvradal Karsten Jennum Emil Glibstrup Nicolas Bovet Xiaowei Wang Wenping Hu Gemma C. Solomon Mogens Brøndsted Nielsen Xiaohui Qiu Thomas Bjørnholm Kasper Nørgaard Bo W. Laursen 《Advanced functional materials》2015,25(11):1700-1708
Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO–LUMO energy gaps. OPE3, OPE3–DTF, and OPE3–tetrathiafulvalene (TTF) can form good self‐assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe–atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3–TTF > OPE3–DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero‐bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes. 相似文献
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