Can the ischemic penumbra be identified on noncontrast CT of acute stroke?

<p><b>Background and Purpose:</b> Early ischemic changes on noncontrast CT in acute stroke include both hypoattenuation and brain swelling, which may have different pathophysiological significance.</p> <p><b>Methods:</b> Noncontrast CT and CT perfusion brain scans from patients with suspected acute stroke <6 hours after onset were reviewed. Five raters independently scored noncontrast CTs blind to clinical data using the Alberta Stroke Program Early CT Score (ASPECTS). Each ASPECTS region was scored as hypodense or swollen. A separate reviewer measured time to peak and cerebral blood volume in each ASPECTS region on CT perfusion. Time to peak and cerebral blood volume were compared for each region categorized as normal, hypodense, or isodense and swollen.</p> <p><b>Results:</b> Scans of 32 subjects a median 155 minutes after onset yielded 228 regions with both CT perfusion and noncontrast CT data. Isodense swelling was associated with significantly higher cerebral blood volume (P=0.016) and with penumbral perfusion (posttest:pretest likelihood ratio 1.44 [95% CI: 0.68 to 2.90]), whereas hypodensity was associated with more severe time to peak delay and with core perfusion (likelihood ratio 3.47 [95% CI: 1.87 to 6.34]). Neither isodense swelling nor hypodensity was sensitive for prediction of perfusion pattern, but appearances were highly specific (87.2% and 91.0% for penumbra and core, respectively). Intrarater agreement was good or excellent, but interrater agreement for both hypodensity and swelling was poor.</p> <p><b>Conclusions:</b> Regions exhibiting hypoattenuation are likely to represent the infarct core, whereas regions that are isodense and swollen have increased cerebral blood volume and are more likely to signify penumbral perfusion. Although noncontrast CT is not sensitive for detection of core and penumbra, appearances are specific. Some information on tissue viability can therefore be obtained from noncontrast CT.</p&gt

Recent advances in the ITO/InP solar cell

It was demonstrated that Indium Tin Oxide (ITO)/InP solar cells can now be made on as-received p(-) bulk substrates which are of nearly equal quality to those which could previously only be made on epitaxially grown p(-) InP base layers. Although this advancement is due in part to both increases in substrate quality and a better understanding of back contact formation, it appears that the passivation/compensation effects resulting from having H2 in the sputtering gas tends to reduce significantly the performance differences previously observed between these two substrates. It is shown that since high efficiency ITO/InP cells can be made from as-received substrates, and since the type conversion process is not highly spatially dependent, large area ITO/InP cells (4 sq cm) with efficiencies approaching 17 percent (Global) can be made. Furthermore, the measured open circuit voltages (V sub OC) and quantum efficiencies (QEs) from these large cells suggest that, when they are processed using optimum grid designs, the efficiencies will be nearly equal to that of the smaller cells thus far produced. It has been shown, through comparative experiments involving ITO/InP and IO/InP cells, that Sn may not be the major cause of type conversion of the InP surface and thus further implies that the ITO may not be an essential element in this type of device. Specifically, very efficient photovoltaic solar cells were made by sputtering (Sn free) In2O3 showing that type conversion and subsequent junction formation will occur even in the absence of the sputtered SN species. The result suggests that sputter damage may indeed be the important mechanism(s) of type conversion. Finally, an initial study of the stability of the ITO/InP cell done over the course of about one year has indicated that the J(sub SC) (short circuit current) and the fill factor (FF) are measurably stable within experimental certainty

High-efficiency heteroepitaxial InP solar cells

High-efficiency, thin-film InP solar cells grown heteroepitaxially on GaAs and Si single-crystal bulk substrates are being developed as a means of eliminating the problems associated with using single-crystal InP substrates. A novel device structure employing a compositionally graded Ga(x)In(1-x)As layer between the bulk substrate and the InP cell layers is used to reduce the dislocation density and improve the minority carrier properties in the InP. The structures are grown in a continuous sequence of steps using computer-controlled atmospheric pressure metalorganic vapor phase epitaxy (APMOVPE). Dislocation densities as low as 3 x 10(exp 7) sq cm and minority carrier lifetimes as high as 3.3 ns are achieved in the InP layers with this method using both GaAs or Si substrates. Structures prepared in this fashion are also completely free of microcracks. These results represent a substantial improvement in InP layer quality when compared to heteroepitaxial InP prepared using conventional techniques such as thermally cycled growth and post-growth annealing. The present work is is concerned with the fabrication and characterization of high-efficiency, thin-film InP solar cells. Both one-sun and concentrator cells were prepared for device structures grown on GaAs substrates. One-cell cells have efficiencies as high as 13.7 percent at 25 C. However, results for the concentrator cells are emphasized. The concentrator cell performance is characterized as a function of the air mass zero (AM0) solar concentration ratio and operating temperature. From these data, the temperature coefficients of the cell performance parameters are derived as a function of the concentration ratio. Under concentration, the cells exhibit a dramatic increase in efficiency and an improved temperature coefficient of efficiency. At 25 C, a peak conversion efficiency of 18.9 percent is reported. At 80 C, the peak AM0 efficiency is 15.7 percent at 75.6 suns. These are the highest efficiencies yet reported for InP heteroepitaxial cells. Approaches for further improving the cell performance are discussed

An empirical study of the performance of APMOVPE AM0 InP homojunction solar cells as a function of emitter thickness and doping, and base doping

Their excellent radiation resistance and conversion efficiencies greater than 20 percent, measured under global conditions, make InP shallow-homojunction solar cells very attractive for space or terrestrial application. In addition, modeling studies show that, for optimized design, efficiencies of these devices should exceed 20 percent even under AM0 conditions. However, a systematic experimental investigation of the influence of the various cell design parameters on cell performance has not as yet been made. For the n+/p/p+ structures investigated in the previous modeling study, the design parameters include the impurity concentrations and thicknesses of the emitter and base layers. In the work reported here, researchers discuss an experimental investigation of the effects on cell performance of varying the impurity concentrations of the emitter and base and thickness of the emitter

InP concentrator solar cells for space applications

The design, fabrication, and characterization of high-performance, n(+)/p InP shallow-homojunction (SHJ) concentrator solar cells is described. The InP device structures were grown by atmospheric-pressure metalorganic vapor phase epitaxy (APMOVPE). A preliminary assessment of the effects of grid collection distance and emitter sheet resistance on cell performance is presented. At concentration ratios of over 100, cells with AM0 efficiencies in excess of 21 percent at 25 C and 19 percent at 80 C are reported. These results indicate that high-efficiency InP concentrator cells can be fabricated using existing technologies. The performance of these cells as a function of temperature is discussed, and areas for future improvement are outlined

Curved Gratings as Plasmonic Lenses for Linearly Polarised Light

The ability of curved gratings as sectors of concentric circular gratings to couple linearly polarized light into focused surface plasmons is investigated by theory, simulation and experiment. Curved gratings, as sectors of concentric circular gratings with four different sector angles, are etched into a 30-nm thick gold layer on a glass coverslip and used to couple linearly-polarised free space light at nm into surface plasmons. The experimental and simulation results show that increasing the sector angle of the curved gratings decreases the lateral spotsize of the excited surface plasmons, resulting in focussing of surface plasmons which is analogous to the behaviour of classical optical lenses. We also show that two faced curved gratings, with their groove radius mismatched by half of the plasmon wavelength (asymmetric configuration), can couple linearly-polarised light into a single focal spot of concentrated surface plasmons with smaller depth of focus and higher intensity in comparison to single-sided curved gratings. The major advantage of these structures is the coupling of linearly-polarised light into focused surface plasmons with access to and control of the plasmon focal spot, which facilitates potential applications in sensing, detection and nonlinear plasmonics.Comment: 15 pages and 12 figure

The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET v1.0) : an efficient and user-friendly model of city cooling

The adverse impacts of urban heat and global climate change are leading policymakers to consider green and blue infrastructure (GBI) for heat mitigation benefits. Though many models exist to evaluate the cooling impacts of GBI, their complexity and computational demand leaves most of them largely inaccessible to those without specialist expertise and computing facilities. Here a new model called The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET) is presented. TARGET is designed to be efficient and easy to use, with fewer user-defined parameters and less model input data required than other urban climate models. TARGET can be used to model average street-level air temperature at canyon-to-block scales (e.g. 100 m resolution), meaning it can be used to assess temperature impacts of suburb-to-city-scale GBI proposals. The model aims to balance realistic representation of physical processes and computation efficiency. An evaluation against two different datasets shows that TARGET can reproduce the magnitude and patterns of both air temperature and surface temperature within suburban environments. To demonstrate the utility of the model for planners and policymakers, the results from two precinct-scale heat mitigation scenarios are presented. TARGET is available to the public, and ongoing development, including a graphical user interface, is planned for future work