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991.
High purity GaxIn1-x As has been grown lattice matched on <111>B InP by liquid phase epitaxy. Silicon, the residual impurity, is purged from the
melt by long time baking in a hydrogen atmosphere with slight ambient water vapor concentration. Epitaxial layers with a net
electron concentration as low as 3.5 × 1014 cm-3 and a liquid nitrogen mobility of 70,000 cm2/Vsec have been grown. The room temperature mobility is shown to be significantly higher than GaAs over a wide range of net
electron concentrations useful for device applications, with the highest value of μ300 = 13,800 cm2/Vsec on a sample with n = 1.9 × I015 cm-3 相似文献
992.
Water soft paths begin from the vision that future water management has more to gain from reducing demand than from increasing supply. This article reviews three case studies of water soft path analysis in small urban areas in Canada, and one study of an urban planning process incorporating soft path concepts. The analytical studies indicate how communities can avoid the need for expansion of water infrastructure with negligible impacts on lifestyles or livelihoods. The planning study demonstrates that it is possible to introduce water soft paths early in a review, and that this will stimulate more ecologically sensitive thinking among citizens, officials and political leaders. Similar conclusions can be expected from soft path studies in urban areas elsewhere in the developed world. 相似文献
993.
Oliver Trepte 《Scanning》1995,17(3):171-174
An optical spectrometer for the visible range has been developed for the confocal scanning laser microscope (CSLM) Phoibos 1000. The spectrometer records information from a single point or a user-defined region within the microscope specimen. A prism disperses the spectral components of the recorded light over a linear CCD photodiode array with 256 elements. A regulated cooling unit cools the diode array, thereby reducing the detector dark current to a level, which allows integration times of up to 60 s. The spectral resolving power, λ/Δλ, ranges from 400 at λ = 375 nm to 100 at λ = 700 nm. Since the entrance aperture of the spectrometer has the same diameter as the detector aperture of the CSLM, the three-dimensional spatial resolution for spectrometer readings is equivalent to that of conventional confocal scanning, that is, down to 0.2 μm lateral and 0.8 μm axial resolution with an N.A.=1.3 objective. 相似文献
994.
To detect changes of cortical cytoarchitectonics, digital images of cortical laminations are analyzed. Cortical regions are transformed into a rectangular grid for subsequent evaluations. Transformations are realized by stepwise scanning using perpendicular testlines. 3D cytoarchitectonic data of the human brain at a histological resolution are not available and 2D sections deliver partial information only. The problem is to find an optimal scanning‐technique that introduces a minimum of distortions and noise by the transformation of the curvilinear cortex to a rectangular presentation. In the past this was solved by constructing testlines dependent on the outlined cortical contours only. An advanced approach was to model the contours as electrically charged surfaces and to use the resulting field lines as testlines. However, local information of cell distributions were not considered. Hence a novel hybrid approach was developed which is able to construct significantly better testlines in cortical images with mixtures of columnar rich (local orientation rich) and orientation poor parts of strongly curved and large regions of the cerebral cortex. The novel hybrid approach is based on the computer vision methods such as the structure tensor and constrained anisotropic diffusion. In addition, the introduction of projective transformations yields a significant improvement of cortical fingerprints, thereby offering the possibility for detecting weakly pronounced regions of cytoarchitectonic transitions. The statistical evaluation of the novel hybrid approach confirms robustness. This technique can be generalized and applied to different types of cerebral cortex with any kind and amount of local orientation information. Microsc. Res. Tech. 2010. © 2010 Wiley‐Liss, Inc. 相似文献
995.
Lee GS Miele LF Turhan A Lin M Hanidziar D Konerding MA Mentzer SJ 《Microscopy research and technique》2009,72(2):85-92
Quantitative assessment of microvascular structure is relevant to the investigations of ischemic injury, reparative angiogenesis and tumor revascularization. In light microscopy applications, thick tissue specimens are necessary to characterize microvascular networks; however, thick tissue leads to image distortions due to out-of-focus light. Structured illumination confocal microscopy is an optical sectioning technique that improves contrast and resolution by using a grid pattern to identify the plane-of-focus within the specimen. Because structured illumination can be applied to wide-field (nonscanning) microscopes, the microcirculation can be studied by sequential intravital and confocal microscopy. To assess the application of structured illumination confocal microscopy to microvessel imaging, we studied cell-sized microspheres and fused silica microcapillary tissue phantoms. As expected, structured illumination produced highly accurate images in the lateral (X-Y) plane, but demonstrated a loss of resolution in the Z-Y plane. Because the magnitude of Z-axis distortion was variable in complex tissues, the silica microcapillaries were used as spatial calibration standards. Morphometric parameters, such as shape factor, were used to empirically optimize Z-axis software compression. We conclude that the silica microcapillaries provide a useful tissue phantom for in vitro studies as well as spatial calibration standard for in vivo morphometry of the microcirculation. 相似文献
996.
997.
998.
M Moritz MB Braunfeld JW Sedat B Alberts DA Agard 《Canadian Metallurgical Quarterly》1995,378(6557):638-640
The microtubule cytoskeleton of animal cells does not assemble spontaneously, but instead requires the centrosome. This organelle consists of a pair of centrioles surrounded by a complex collection of proteins known as the pericentriolar material (PCM). The PCM is required for microtubule nucleation. The minus, or slow-growing, ends of microtubules are embedded in the PCM and the plus, or fast-growing, ends project outwards into the cytoplasm during interphase, or into the spindle apparatus during mitosis. gamma-Tubulin is the only component of the PCM that is so far implicated in microtubule nucleation. Here we use immuno-electron microscopic tomography to show that gamma-tubulin is localized in ring structures in the PCM of purified centrosomes without microtubules. When these centrosomes are used to nucleate microtubule growth, gamma-tubulin is localized at the minus ends of the microtubules. We conclude that microtubule-nucleating sites within the PCM are ring-shaped templates that contain multiple copies of gamma-tubulin. 相似文献
999.
A Oliver Bańuls 《Canadian Metallurgical Quarterly》1996,18(6):304-308
OBJECTIVE: To study the appropriateness of minimally invasive surgical treatment of primary hyperparathyroidism. DESIGN: Prospective. SETTING: University Hospital Utrecht, the Netherlands. METHOD: In patients with primary hyperparathyroidism, parathyroid adenomas were located preoperatively by means of Doppler assisted ultrasonography and spiral computer tomography. If the results were positive, minimally invasive surgery was performed. RESULTS: Minimally invasive surgery was carried out in 13 out of 15 successive patients with good results (the serum calcium and parathyroid hormone levels returned to normal). Two patients were subjected to conventional neck exploration, also with good results (preoperatively several adenomas were suspected in one, while no adenoma was seen in the other). CONCLUSION: It can be calculated that minimally invasive surgery will probably suffice in 60-70% of the patients with primary hyperparathyroidism, so that conventional neck exploration can be avoided. 相似文献
1000.
Oliver Stueker Van A. Ortega Greg G. Goss Maria Stepanova 《Small (Weinheim an der Bergstrasse, Germany)》2014,10(10):2006-2021
Nanomaterials in biological solutions are known to interact with proteins and have been documented to affect protein function, such as enzyme activity. Understanding the interactions of nanoparticles with biological components at the molecular level will allow for rational designs of nanomaterials for use in medical technologies. Here we present the first detailed molecular mechanics model of functionalized gold nanoparticle (NP) interacting with an enzyme (l ‐lactate dehydrogenase (LDH) enzyme). Molecular dynamics (MD) simulations of the response of LDH to the NP binding demonstrate that although atomic motions (dynamics) of the main chain exhibit only a minor response to the binding, the dynamics of side chains are significantly constrained in all four active sites that predict alteration in kinetic properties of the enzyme. It is also demonstrated that the 5 nm gold NPs cause a decrease in the maximal velocity of the enzyme reaction (Vmax) and a trend towards a reduced affinity (increased Km) for the β‐NAD binding site, while pyruvate enzyme kinetics (Km and Vmax) are not significantly altered in the presence of the gold NPs. These results demonstrate that modeling of NP:protein interactions can be used to understand alterations in protein function. 相似文献