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排序方式: 共有414条查询结果,搜索用时 15 毫秒
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Zhao Donghui Wang Hua Chen Guorong Stefania Baccaro Angelica Cecilia Mauro Falconieri L. Pilloni 《Journal of the American Ceramic Society》2006,89(11):3582-3584
Gamma-ray irradiations induced various alterations in sulfur- and selenium-based chalcogenide glasses. The absorbed dose was in the range of 0.01–3.6 MGy. The glasses exhibit prominent sensitivity to γ-ray irradiation, characterized by changes in some of the physical properties of the glasses, e.g., optical transmission, optical band gap, density, and thermal expansion coefficient. The effects on glass structure and microscopic morphology were also studied by Raman spectra and scanning electron microscopic observations. 相似文献
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J Avorn M Monane DE Everitt MH Beers D Fields 《Canadian Metallurgical Quarterly》1994,154(10):1113-1117
BACKGROUND: We sought to quantify the relationship between antipsychotic drug use and clinical evidence of extrapyramidal dysfunction in a large population of elderly nursing home patients. METHODS: Subjects were 251 residents (mean age, 84.1 years; range, 65 to 105 years) who were taking psychoactive drugs in 12 long-term care facilities. Patient characteristics and all medication use (both scheduled and as needed) were measured during a 1-month observation period. We then performed neuropsychological and functional testing on residents who received any psychoactive medications during the study month. The presence of rigidity, bradykinesia, or masklike facies was assessed in each patient by a research assistant who was unaware of diagnoses and medication use. RESULTS: The parkinsonian signs studied were found in 127 (50.6%) of these residents. Using logistic regression modeling to adjust for potential confounding, we found this outcome to be increased more than threefold in patients who took low-potency neuroleptics (odds ratio [OR], 3.49 for > or = 50 mg/d of chlorpromazine-type drugs; 95% confidence interval [CI], 1.28 to 9.57) and more than sixfold for use of 1 mg/d or more of haloperidol (OR, 6.42; 95% CI, 2.16 to 19.04). Age, gender, and use of nonneuroleptic psychoactive drugs were not associated with an increase in parkinsonian signs. CONCLUSIONS: Clinical evidence of extrapyramidal dysfunction is three to six times more common in institutionalized elderly patients given antipsychotic medication than in comparable patients not using such drugs. Its risk is substantially increased even in patients given low-potency chlorpromazine-type drugs, as well as those taking haloperidol. The effect is not explained by age or mental status and is not seen with other psychoactive medications. The expected frequency of parkinsonian symptoms can help to inform the balancing of risks vs therapeutic effect when the use of all drugs in this class is considered. 相似文献
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Linear polyethers possess unusually high CO2 solubility and, hence, selectivity due to the presence of accessible ether linkages that can interact with the quadrupolar moment of CO2 molecules. In this work, membranes derived from crosslinked poly(propylene glycol) diacrylate (PPGda) oligomers differing in molecular weight (M), as well as PPGda nanocomposites containing either an organically-modified montmorillonite clay or a methacrylate-terminated fumed silica are investigated and compared with highly CO2-selective poly(ethylene glycol) diacrylate (PEGda) homopolymer and nanocomposite membranes previously reported. The rheological and permeation properties of PPGda depend sensitively on M, with the elastic modulus decreasing, but CO2 permeability and CO2/H2 selectivity increasing, with increasing M. Incorporation of either nanofiller into PPGda enhances the elastic modulus and reduces the gas permeability in the resultant nanocomposites without strongly affecting CO2/H2 selectivity. Blending PPGda and PEGda prior to chemical crosslinking yields binary membranes that exhibit intermediate gas-transport properties accurately described by a linear rule of mixtures. 相似文献
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The phenomenon of plasticizer acceptance by poly(vinyl chloride) (PVC) in hotprocess dry blending is examined via scanning electron microscopy, mercury intrusion porosimetry, and torque rheometer measurements. The effects of granule porosity, resin molecular weight, and synthesis recipe in PVC manufacture by the suspension process are related to the rate of plasticizer acceptance. For a PVC resin to dry blend, i.e., to become a free-flowing powder when mixed with plasticizer under hot-processing conditions, the resin granules must be porous. Porosity arises from interstices between primary PVC particles. At a given granule porosity, an increase in primary particle agglomeration adversely affects dry blend performance. At constant molecular weight and for resins manufactured by a given recipe, dry-blend performance is quantitatively described by granule porosity. With an increase in resin molecular weight, a greater granule porosity is required to maintain an equivalent dry-blend time (DBT). Accordingly, for most suspending agent recipes, DBT is dependent directly upon granule porosity and inversely upon molecular weight. However, if the suspending agent used in resin manufacture is an excessively rapid film former, dry-blend performance with molecular weight variation is dependent upon the suspending agent's concentration, not upon granule porosity, which must be adequate, nor upon the resin's molecular weight. An interfacial film-forming suspending agent enhances fusion of primary PVC particles at the suspension granule—water interface, increasing the granule's “pericellular membrane” thickness. This membrane, a PVC skin, does not significantly influence dry-blend performance with low- or intermediate-viscosity plasticizers. The particle skin does impede dry-blend rates with high-viscosity, poorly solvating plasticizers, but this effect can be negated in part by increasing the diameter of pore openings in the topographical skin. Dry blending occurs below the glass transition temperature (Tg) of PVC with low-viscosity plasticizers and above the Tg with high-viscosity, poorly solvating modifiers. The influence of resin and plasticizer variables indicates the dry-blend phenomenon to be a diffusion-controlled process. The rate of dry blending is dependent upon two mechanisms: (1) the rate of pore penetration—which exposes the plasticizer to a much greater surface area than if it remained exterior, encapsulating the granule—and (2) the rate of plasticizer diffusion into the PVC matrix. 相似文献
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Bob Fields Paola Amaldi William Wong Satinder Gill 《International journal of human-computer interaction》2013,29(4):359-360
This study used protocol analyses and user drawings of their models of the system to investigate the “getting lost” problem in hypertext navigation. The “getting lost” problem is viewed as occurring when routine expectations of naive users, concerning appropriate linear sequences, are violated. Several ways in which users persistently attempt to work within a linear model, despite its inapplicability, are examined. The transition to more hierarchical user models is described. 相似文献
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Andrea Caiti Vincenzo Calabrò Andrea Munafò Gianluca Dini Angelica Lo Duca 《野外机器人技术杂志》2013,30(2):237-253
The EU‐funded project UAN (Underwater Acoustic Network) was aimed at conceiving, developing, and testing at sea an innovative and operational concept for integrating underwater and above‐water sensors in a unique communication system to protect offshore and coastline critical infrastructures. This work gives details on the underwater part of the project. It introduces a set of original security features and gives details on the integration of autonomous underwater vehicles (AUVs) as mobile nodes of the network and as surveillance assets, acoustically controlled by the command and control center to respond against intrusions. Field results are given of the final UAN project sea trial, UAN11, held in May 2011 in Norway. During the experimental activities, a UAN composed of four fixed nodes, two AUVs, and one mobile node mounted on the supporting research vessel was operated continuously and integrated into a global protection system. In this article, the communication performance of the network is reported in terms of round‐trip time, packet loss, and average delivery ratio. The major results of the experiment can be thus summarized: the implemented network structure was successful in continuously operating over five days with nodes seamlessly entering and exiting the network; the performance of the network varied greatly with fluctuations in the acoustic channel; the addition of security features induced a minor degradation in network performance with respect to channel variation; the AUVs were successfully controlled from a remote station through acoustic signals routed by the network. © 2013 Wiley Periodicals, Inc. 相似文献
9.
We propose an experimental methodology to determine the secondary Bjerknes force between rigid particles. Measurements done for different particles sizes showed acoustical inter particles interactions. We use and extend the methodology presented in a previous work. The determination of this force will lead us a better understanding of the aggregation process in acoustic resonators. We report in this work, the results of two parabolic flights campaigns performed at the Airbus A300 ZERO-G (Novespace, France). 相似文献
10.
Garzón-Alvarado DA Martinez AM Segrera DL 《Computer methods and programs in biomedicine》2011,104(3):489-497
The cerebral cortex is a gray lamina formed by bodies of neurons covering the cerebral hemispheres, varying in thickness from 1.25 mm in the occipital lobe to 4 mm in the anterior lobe. The brain's surface is about 30 times greater that of the skull because of its many folds; such folds form the gyri, sulci and fissures and mark out areas having specific functions, divided into five lobes. Convolution formation may vary between individuals and is an important feature of brain formation; such patterns can be mathematically represented as Turing patterns. This article describes how a phenomenological model was developed by describing the formation pattern for the gyri occurring in the cerebral cortex by reaction diffusion equations with Turing space parameters. Numerical examples for simplified geometries of a brain were solved to study pattern formation. The finite element method was used for the numerical solution, in conjunction with the Newton–Raphson method. The numerical examples showed that the model can represent cerebral cortex fold formation and reproduce pathologies related to gyri formation, such as polymicrogyria and lissencephaly. 相似文献