Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1?xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

Cirrus Logic公司新款音频系统处理器芯片集成功能强劲的32位DSP及CobraNetTM界面

Cirrus Logic公司新近推出名为“音频系统处理器”的CS496xxx系列集成电路产品,该系列芯片进一步降低了系统成本,减小了占板尺寸并增强了音频功能。     

Measurement of Torsion from Multitemporal Images of the Eye Using Digital Signal Processing Techniques

Two methods of measuring ocular torsion from digital images of the eyes were developed and tested. One method measures torsion from the translation of two landmarks using a rectilinear coordinate system. The second method measures torsion from the translation of two landmarks using a polar coordinate system. The center for the polar sampling is the center of the pupil. After thresholding and filtering the images, landmark translation is measured from the interpolated peak in the normalized cross correlation of the reference landmark with the image.     

Optical switching of a GaAs triangular barrier switch grown by MBE

A 100 ?m-diameter GaAs triangular barrier switch (TBS) has been optically switched using a GaAlAs laser diode. The resulting transient response has been measured to have a leading edge of ~ 295 ps.     

Visual Appearance of Chiral Nematic Cellulose‐Based Photonic Films: Angular and Polarization Independent Color Response with a Twist

Hydroxypropyl cellulose (HPC) is a biocompatible cellulose derivative capable of self‐assembling into a lyotropic chiral nematic phase in aqueous solution. This liquid crystalline phase reflects right‐handed circular polarized light of a specific color as a function of the HPC weight fraction. Here, it is demonstrated that, by introducing a crosslinking agent, it is possible to drastically alter the visual appearance of the HPC mesophase in terms of the reflected color, the scattering distribution, and the polarization response, resulting in an exceptional matte appearance in solid‐state films. By exploiting the interplay between order and disorder, a robust and simple methodology toward the preparation of polarization and angular independent color is developed, which constitutes an important step toward the development of real‐world photonic colorants.     

Large shift in source of fine sediment in the upper Mississippi river

Although sediment is a natural constituent of rivers, excess loading to rivers and streams is a leading cause of impairment and biodiversity loss. Remedial actions require identification of the sources and mechanisms of sediment supply. This task is complicated by the scale and complexity of large watersheds as well as changes in climate and land use that alter the drivers of sediment supply. Previous studies in Lake Pepin, a natural lake on the Mississippi River, indicate that sediment supply to the lake has increased 10-fold over the past 150 years. Herein we combine geochemical fingerprinting and a suite of geomorphic change detection techniques with a sediment mass balance for a tributary watershed to demonstrate that, although the sediment loading remains very large, the dominant source of sediment has shifted from agricultural soil erosion to accelerated erosion of stream banks and bluffs, driven by increased river discharge. Such hydrologic amplification of natural erosion processes calls for a new approach to watershed sediment modeling that explicitly accounts for channel and floodplain dynamics that amplify or dampen landscape processes. Further, this finding illustrates a new challenge in remediating nonpoint sediment pollution and indicates that management efforts must expand from soil erosion to factors contributing to increased water runoff.     

Internal pancreatic fistulas: pancreatic ascites and pleural effusions

Thirty-four patients seen over a 10-year period with internal pancreatic fistulas are reported. In 22 patients the fistula was into the peritoneal cavity and they presented with pancreatic ascits. In 7 patients the fistula tracked up through the mediastinum into a pleural cavity, and they presented with pancreatic pleural effusions. Five patients presented with both pancreatic ascites and pancreatic pleural effusions. Diagnosis was made by finding a markedly elevated amylase and protein content in the ascitic and pleural fluids. Serum amylase was usually, but not always, elevated. Over one half of the patients had no history of inflammatory pancreatic disease. Initial treatment was non-operative using nasogastric suction, diamox, atropine, and multiple paracenteses or thoracenteses. This was successful in 48% (12/25). If non-operative therapy failed, surgery was performed to drain or resect the internal fistula. Surgery was successful in 82% (14/17). The internal pancreatic fistula was successfully demontrated in most instances by preoperative, operative, or postmortem pancreatography, or by gross observation at the time of surgery.     

Effect of high amounts of dietary zinc and age upon tissue zinc in young chicks

Weight gains of younger broiler chicks were not reduced by up to 2400 p.p.m. added zinc fed to four weeks of age. Tissue zinc was not changed significantly by 600 or 1200 p.p.m. supplemental dietary zinc, but at 2400 p.p.m. added zinc, blood, kidney, and liver zinc were significantly elevated (P less than 0.05). In the heart, zinc was not affected by the added dietary zinc but increased over time with all diets. Unlike the calf and weanling pig, the metabolism of zinc in the young chick does not appear to change appreciably with increasing maturity. Thus, the homeostatic control mechanisms of the young chick are effective for up to 1200 p.p.m. dietary zinc, but are partially overcome by 2400 p.p.m. added dietary zinc.     

Acetylcholine hot spots: development on myotubes cultured from aneural limb buds

The hypothesis that neural induction plays a role in the development of acetylcholine hot spots (high-sensitivity regions) was tested by electrophysiological mapping of the distribution of acetylcholine sensitivity of myotubes derived from aneural hindlimb buds of chick embryos. Hot spots were found. Therefore, hot spot development is not dependent on prior contact with nerve processes.