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排序方式: 共有1156条查询结果,搜索用时 15 毫秒
931.
Flexible Low‐Voltage Organic Complementary Circuits: Finding the Optimum Combination of Semiconductors and Monolayer Gate Dielectrics 下载免费PDF全文
932.
Trond H. Hagen Tomas L. Jensen Erik Unneberg Yngve H. Stenstrm Tor E. Kristensen 《Propellants, Explosives, Pyrotechnics》2015,40(2):275-284
Glycidyl azide polymer (GAP) is an important energetic binder candidate for new minimum signature solid composite rocket propellants, but the mechanical properties of such GAP propellants are often limited. The mechanical characteristics of composite rocket propellants are mainly determined by the nature of the binder system and the binder‐filler interactions. In this work, we report a detailed investigation into curing systems for GAP diol with the objective of attaining the best possible mechanical characteristics as evaluated by uniaxial tensile testing of non‐plasticized polymer specimens. We started out by investigating isocyanate and isocyanate‐free curing systems, the latter by using the crystalline and easily soluble alkyne curing agent bispropargylhydroquinone (BPHQ). In the course of the presented study, we then assessed the feasibility of dual curing systems, either by using BPHQ and isophorone diisocyanate (IPDI) simultaneously (synchronous dual curing), or by applying propargyl alcohol and IPDI consecutively (sequential dual curing). The latter method, which employs propargyl alcohol as a readily available and adjustable hydroxyl‐telechelic branching agent for GAP through thermal triazole formation, gave rise to polymer specimens with mechanical characteristics that compared favorably with the best polymer specimens obtained from GAP diol and mixed isocyanate curatives. The glass transition temperature (Tg) of non‐plasticized samples was heightened when triazole‐based curing agents were included, but when plasticized with nitratoethylnitramine (NENA) plasticizer, Tg values were very similar, irrespective of the curing method. 相似文献
933.
Grosenick D Hagen A Steinkellner O Poellinger A Burock S Schlag PM Rinneberg H Macdonald R 《The Review of scientific instruments》2011,82(2):024302
We present a scanning time-domain fluorescence mammograph capable to image the distribution of a fluorescent contrast agent within a female breast, slightly compressed between two parallel glass plates, with high sensitivity. Fluorescence of the contrast agent is excited using a near infrared picosecond diode laser module. Four additional picosecond diode lasers with emission wavelengths between 660 and 1066 nm allow to measure the intrinsic optical properties of the breast tissue. By synchronously moving a source fiber and seven detection fiber bundles across the breast, distributions of times of flight of photons are recorded simultaneously for selected source-detector combinations in transmission and reflection geometry either at the fluorescence wavelength or at the selected laser wavelengths. To evaluate the performance of the mammograph, we used breastlike rectangular phantoms comprising fluorescent and absorbing objects using the fluorescent dye Omocyanine as contrast agent excited at 735 nm. We compare two-dimensional imaging of the phantom based on transmission and reflection data. Furthermore, we developed an improved tomosynthesis algorithm which permits three-dimensional reconstruction of fluorescence and absorption properties of lesions with good spatial resolution. For illustration, we present fluorescence mammograms of one patient recorded 30 min after administration of the contrast agent indocyanine green showing the carcinoma at high contrast originating from fluorescence of the extravasated dye, excited at 780 nm. 相似文献
934.
Delazer Margarete; H?gl Birgit; Zamarian Laura; Wenter Johanna; Gschliesser Viola; Ehrmann Laura; Brandauer Elisabeth; Cevikkol Zehra; Frauscher Birgit 《Canadian Metallurgical Quarterly》2011,25(4):477
Objective: Narcolepsy with cataplexy (NC) affects neurotransmitter systems regulating emotions and cognitive functions. This study aimed to assess executive functions, information sampling, reward processing, and decision making in NC. Method: Twenty-one NC patients and 58 healthy participants performed an extensive neuropsychological test battery. Results: NC patients scored as controls in executive function tasks assessing set shifting, reversal learning, working memory, and planning. Group differences appeared in a task measuring information sampling and reward sensitivity. NC patients gathered less information, tolerated a higher level of uncertainty, and were less influenced by reward contingencies than controls. NC patients also showed reduced learning in decision making and had significantly lower scores than controls in the fifth block of the IOWA gambling task. No correlations were found with measures of sleepiness. Conclusions: NC patients may achieve high performance in several neuropsychological domains, including executive functions. Specific differences between NC patients and controls highlight the importance of the hypocretin system in reward processing and decision making and are in line with previous neuroimaging and neurophysiological studies. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
935.
This paper presents the results of an experimental study on the transient strain of high strength concrete (HSC) under heating
up to 750°C and the impact of polypropylene (PP) fibers. Concerning this topic only few results are available in the literature
and systematic investigations are missing. However, basic knowledge is necessary for the understanding of the internal damage
processes in the material as well as for heated structures. The transient strain during heating can be separated in two basic
components: the free thermal strain and the mechanical strain. They were experimentally determined exemplarily for one HSC.
For the determination of the mechanisms of transient strain and particularly the influence of PP fibers different techniques
were applied. In this context the monitoring of the microcracking was done for the first time with acoustic emission analysis
in combination with ultrasonic measurements. This new approach helps fundamentally to explain the impact of PP fibers on free
thermal strain and mechanical strain during heating up. Furthermore weight loss measurements were carried out to characterize
the moisture transport. It was shown that the PP fibers cause an acceleration of the moisture transport in the temperature
range from 200 to 250°C which leads to drying shrinkage in opposite direction to the free thermal strain. Hence this paper
is a contribution to the general understanding of the impact of PP fibers in HSC at high temperatures and emphasizes the important
influence of PP fibers on the thermal and mechanical induced strain of HSC. 相似文献
936.
OBJECTIVE: To determine the rates of immediate survival and survival to discharge for adult patients undergoing in-hospital cardiopulmonary resuscitation, and to identify demographic and clinical variables associated with these outcomes. MEASUREMENTS AND MAIN RESULTS: The MEDLARS database of the National Library of Medicine was searched. In addition, the authors' extensive personal files and the bibliography of each identified study were searched for further studies. Two sets of inclusion criteria were used, minimal (any study of adults undergoing in-hospital cardiopulmonary resuscitation) and strict (included only patients from general ward and intensive care units, and adequately defined cardiopulmonary arrest and resuscitation). Each study was independently reviewed and abstracted in a nonblinded fashion by two reviewers. The data abstracted were compared, and any discrepancies were resolved by consensus discussion. For the subset of studies meeting the strict criteria, the overall rate of immediate survival was 40.7% and the rate of survival to discharge was 13.4%. The following variables were associated with failure to survive to discharge: sepsis on the day prior to resuscitation (odds ratio [OR] 31.3; 95% confidence interval [CI] 1.9, 515), metastatic cancer (OR 3.9; 95% CI 1.2, 12. 6), dementia (OR 3.1; 95% CI 1.1, 8.8), African-American race (OR 2. 8; 95% CI 1.4, 5.6), serum creatinine level at a cutpoint of 1.5 mg/dL (OR 2.2; 95% CI 1.2, 3.8), cancer (OR 1.9; 95% CI 1.2, 3.0), coronary artery disease (OR 0.55; 95% CI 0.4, 0.8), and location of resuscitation in the intensive care unit (OR 0.51; 95% CI 0.4, 0.8). CONCLUSIONS: When talking with patients, physicians can describe the overall likelihood of surviving discharge as 1 in 8 for patients who undergo cardiopulmonary resuscitation and 1 in 3 for patients who survive cardiopulmonary resuscitation. 相似文献
937.
Norman Tanner Birgit Lichtenberg‐Kraag 《European Journal of Lipid Science and Technology》2019,121(12)
Marketing of adulterated beeswax foundation has recently become a major economic problem for beekeepers. Paraffin contamination leads to collapse of combs, and stearic acid has a negative influence on the development of bee brood. The quality of beeswax for beekeeping has not been standardized in EU regulations. Recently, it was shown that attenuated total reflectance Fourier‐transform infrared spectroscopy (FTIR‐ATR) can be used to determine beeswax adulteration. Differences in the IR spectra of authentic beeswax can be identified and calculated through comparison with authentic beeswax. In this study, the method is further validated by employing a high number of samples of authentic beeswax from different origins. Low quantification and detection limits are achieved for paraffin, stearic acid, tallow, carnauba wax, and candelilla wax. Furthermore, the FTIR‐ATR analytical conditions are verified by analyzing 358 samples of commercial and beekeeper‐produced beeswax foundations. Multi‐adulterated samples with as many as five different additives in beeswax mixtures are identified with the same accuracy as single substances. Additionally, the spectra of a further 14 different natural and synthetic waxes and hardened fats are analyzed and are compared with beeswax. Finally, a spectral library is established that can be used for further studies. Practical Applications: FTIR‐ATR is a fast and cost‐efficient tool in beeswax analysis for accurately monitoring a high sample volume. Analysis of 358 beeswax foundations showed an adulteration of 21.8% of the samples with paraffin, stearic acid, tallow, and combinations. Based on the results of this study, it is possible to detect beeswax adulteration of less than 3% of these adulterants and their combinations by FTIR‐ATR spectroscopy. This method can be used for monitoring beeswax foundations to identify adulterated materials, exclude these materials from the recycling process, and produce high‐quality beeswax, which is essential for bee health. 相似文献
938.
The hydration behavior of aerosols, made up of various fluorescent dyes, when exposed to water saturation or supersaturated conditions has been studied. Critical supersaturation spectra are reported. The dyes are found to behave as high molecular weight ionic compounds that obey Kohler theory. Their relevant Kohler parameters are measured. This study makes use of and compares results from the isothermal haze, continuous-flow, and alternating-gradient thermal diffusion cloud chambers. The ability of the continuous-flow thermal diffusion chamber to operate correctly at high supersaturations is shown. 相似文献
939.
Anna Frey Diana Rose Birgit Wehner Thomas Müller Yafang Cheng Alfred Wiedensohler 《Aerosol science and technology》2013,47(10):817-828
A Volatility-Tandem-Differential-Mobility-Analyzer (VTDMA) and a Differential Mobility Particle Sizer (DMPS) were used to determine the number and mass concentration of externally mixed aerosol particles in urban background air. In the VTDMA the less-volatile (LV) particle fraction was measured at 300°C for particles in the size range 20–250 nm. The LV particle fraction was converted to the number concentration of LV particles (NLV) and the mass concentration (MLV). MLV was compared with the mass concentration of black carbon (MBC) measured by a Multi-Angle Absorption Photometer (MAAP). The DMPS and VTDMA data were used for calculating scattering and absorption coefficients (σSP and σ AP) with a Mie model and compared with σ SP and σ AP measured with a TSI nephelometer and the MAAP. The model was run by assuming external and internal mixing of absorbing and scattering aerosol. The best fit of measured and modeled σ SP and σ AP was sought by varying the refractive index. During periods dominated by local emissions LV particle fraction ??LV ? was high ( >0.2). In these cases, the MLV and the modeled σ AP assuming external mixing agreed well with the measured MBC and σ AP, respectively. For the long-range transported aerosol ??LV ? was small ( <0.1) and MBC was higher than MLV. For the whole period the average (± std) refractive index was 1.55 (± 0.09) – 0.04 (±0.02)i when internal mixing was assumed. When ??LV ? was >0.2 the average refractive index of LV particles was 1.96 – 0.8 (±0.18)i when σ AP was modeled assuming external mixing. 相似文献
940.
Gregor Beulertz Mirko Fritsch Gerhard Fischerauer Felix Herbst Jürgen Gieshoff Martin Votsmeier Gunter Hagen Ralf Moos 《Topics in Catalysis》2013,56(1-8):405-409
Three-way catalyst-based automotive exhaust gas aftertreatment is of high importance to meet today’s emission standards. To determine in situ the oxygen loading state of three-way catalysts, a microwave cavity perturbation method is used. In this study, it is investigated whether this measurement setup that had originally been described for full-sized catalysts can be transferred to a lab test bench using cores of 1″ diameter. The initial tests were successful and a high correlation between the oxygen loading degree dependent resonance frequency and the conversion was found. As an application example of the new in situ characterization technique, the steady state degree of oxidation of a three way catalyst was measured as a function of the exhaust stoichiometry. The experimental results are compared with the prediction of a recently published improved kinetic model that takes into account the oxidation of reduced ceria by H2O and CO2. It is shown that the experimental observations agree very well with this improved model. This result provides evidence that under typical operating conditions, the degree of oxidation of the three way catalyst is controlled by equilibrium effects. 相似文献