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排序方式: 共有216条查询结果,搜索用时 31 毫秒
1.
Geraint Johnes Swati Virmani 《International Transactions in Operational Research》2020,27(4):1869-1885
Data from the Young Lives study are used to evaluate the efficiency of education systems in four low and middle income countries: Ethiopia, India, Peru and Vietnam. A meta‐frontier variant of data envelopment analysis is used to assess the relative performance of each country's system, and, within each country, to evaluate the impact of public and private schooling, and of urban and rural location. Comparisons are drawn between the four countries; the results indicate that in no country does the educational system perform uniformly badly or well. Conditioning on the inputs available, rural areas are often indicative of higher levels of efficiency, thus suggesting a number of implications for policy. 相似文献
2.
The stability of the reactive interface during the solid-state displacement reaction, Cu2O+Co1−X
Fe
X
=2Cu+(Co1−X
Fe
X
)O, is studied as a function of Co-Fe alloy composition at 1223 K. For X≤0.03, the reaction zone has a layered structure, and the cation diffusion in (Co, Fe)O is the rate-limiting step. The interface
is unstable in the early stages of the reaction; the instability decreases with time as the oxide thickness increases, and
the interface becomes planar at long times. The time required for the attainment of interface planarity increases with the
value of X. The reaction kinetics are consistent with the available cation-diffusion data in (Co, Fe)O. For X≥0.045, the product zone is a composite of Cu+(Co, Fe)O, and the rate is limited by the oxygen transport in copper. The transition
to interface instability occurs when the oxide can support a cation flux that exceeds the maximum possible oxygen flux in
copper. During the reaction, composition gradients develop in (Co, Fe)O because of higher diffusion rates for iron than for
cobalt. 相似文献
3.
PM Wiggins 《Canadian Metallurgical Quarterly》1996,20(6):429-435
Melanoma is prone to spread to the brain and is the third most common source of intracranial metastasis. Patients usually present with signs and symptoms of increased intracranial pressure, a new focal neurologic deficit, or seizures. Contrasted magnetic resonance imaging (MRI) is the single most valuable imaging modality. Surgical therapy is the appropriate choice for single lesions that are accessible, especially if they are causing significant mass effect or are located in the posterior fossa. Patients with several intracranial metastases who undergo resection of all lesions may have a similar prognosis to those with single resected lesion. Stereotactic radiosurgery appears to provide good local control of small lesions. External beam radiotherapy may provide some benefit to patients, and is often used in conjunction with surgery or stereotactic radiosurgery. To date, chemotherapy has been limited because of chemo-resistance and drug delivery issues. Future directions for treatment may include local sustained delivery of either chemotherapy or immunoregulatory molecules. 相似文献
4.
A method is described for releasing reactive dye adducts from wool fibres. The resulting solutions are amenable to analysis by thin layer chromatography. 相似文献
5.
Eernisse EP Ward RW Watts MH Wiggins RB Wood OL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1990,37(6):566-570
Experimental results are presented to support the hypothesis that the shape and location of the active region of vibration in a thickness shear mode quartz resonator are the dominant factors in determining the acceleration sensitivity of the resonator. The shape and location of the mode in a real world resonator vary sufficiently from unit to unit (due to material and processing variations) that all other considerations are overwhelmed. It is shown experimentally that the mode shape and/or location can be trimmed with energy trapping by judicious addition or subtraction of mass to produce resonators with improved acceleration sensitivity. 相似文献
6.
Ben W. Morrison Mark W. Wiggins Glenn Porter 《International journal of human-computer interaction》2013,29(4):297-316
This study examined trainee crime-scene investigators' preference for, and accuracy in using, four different computer-based decision support interface designs, each of which incorporated a different reduced processing information acquisition strategy. The interfaces differed on the basis of the number of options that could be considered simultaneously and the level of control that could be exercised over the number and sequence in which feature values were accessed. Forty trainee investigators completed six decision scenarios in which they were asked to acquire information and formulate a decision by selecting one of three options. The study comprised two phases, the first of which involved familiarizing participants with each of the four interface designs and collecting performance and subjective data. The second phase involved trainees selecting one of the four interfaces to engage in a fifth and sixth decision scenario involving high or low levels of time-pressure. The results indicated that the “all options, full control” interface was the preferred option in the low time-pressure condition. Although the strategy remained the most frequently selected in the high time-pressure condition, this preference was not significant. It was concluded that the perceptions of difficulty and the degree of user control over information acquisition were more important than perceived efficiency in the selection of computer-based interface designs. The outcomes have implications for the design of decision support systems. 相似文献
7.
John Wiggins 《Journal of Architectural Education》2013,67(4):6-8
Abstract Extending Deleuze's later writing on the cinema and engaging both film and built work, the article explores what I call the “close-up,” an immanent subjectivity of architectural encounter, whereby the architectural surface aggressively colonizes the subject at close range through a touch or by another mechanism I describe as the “withdrawn effect,” the surface assimilates the subject. 相似文献
8.
Ian Mabbett Jon Elvins Catherine Gowenlock Carol Glover Paul Jones Geraint Williams David Worsley 《Progress in Organic Coatings》2014
Near infrared (NIR) is becoming a popular option for rapid cure of coatings in the coil coating industry particularly where fast line speeds are required. The technology has the potential to reduce the cure time of a 20 μm polyester coating on a galvanised steel substrate from around 30 s via conventional heating methods down to <10 s under the lamps. Previous work suggested that the ideal situation in this case is to have a topcoat which is slightly transparent to NIR and an absorbing substrate to heat the coating from the substrate outwards in a two stage process which separates solvent removal from cross linking and film formation. This can be taken further by tinting the primer layer with a pigment that absorbs in the NIR region. In this study spectroscopy was used to show that a coated steel system could appear white in the visible region because of the reflectance of TiO2 but the NIR absorption could be altered by adding absorbing pigments such as carbon black. Lamp settings could be reduced by 20% to achieve equivalent cure with tinted primer systems. The potential degradation in corrosion protection afforded by carbon-black containing pigments at various loadings was assessed for model organic coatings applied to galvanised steel specimens. In situ scanning Kelvin probe studies showed that rates of corrosion-driven coating delamination by cathodic disbondment remained unchanged by pigment loadings of up to 3.5 wt%. 相似文献
9.
Jaime C. Auton Mark W. Wiggins Ben J. Searle Thomas Loveday Nan Xu Rattanasone 《The Journal of communication》2013,63(3):600-616
The readback/hearback protocol is a radio procedure intended to reduce communication errors in technical industries. It consists of the delivery of an instruction to a receiver, and the readback of that instruction by the receiver to confirm to the sender that it has been heard accurately. It does not, however, ensure that the receiver has understood the instruction. Using 2 samples within electricity transmission control, the present research explored whether the prosodic cues that listeners use to interpret uncertainty are also used to judge whether a receiver is perceived to have understood an instruction. Rising intonation and filled interturn delays were identified as prosodic cues that operators use to identify nonunderstandings. Theoretical and practical implications of the findings are considered. 相似文献
10.
A cognitive task can often be subdivided into several subprocesses, which follow a specific temporal order. Here, we report an event-related functional magnetic resonance imaging (fMRI) experiment on memory search, in which the temporal onset of search in primary memory was varied relative to retrieval from secondary memory. Furthermore, previous behavioral studies demonstrated that search times in primary memory depend on the number of items in a memory set, whereas retrieval from secondary memory is a set-size independent process. We analyzed the dependency of the blood oxygenation level dependent (BOLD)-response on the temporal onset of memory search on the one hand and on memory set size on the other hand to differentiate the contribution of retrieval from secondary memory, maintenance in primary memory, item search in primary memory, and response-related processes. The timing of activation followed cue presentation bilaterally in the middle frontal gyri (Brodmann area (BA) 9,46) and the inferior parts of the precentral gyri (BA6). In all other regions of interest (ROI), supplementary motor area (SMA), posterior parietal cortex, antero-superior insula, and primary motor cortex, the onset of activation was delayed with delayed probe presentation, ruling out participation in retrieval from secondary memory. The amplitude of the BOLD-response increased with increasing memory set size in all ROI except primary motor cortex and left posterior parietal cortex. All areas with cue-associated BOLD onset, suggesting involvement in retrieval, showed prolonged BOLD activation, suggesting that they also support maintenance of the retrieved information. 相似文献