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1.
Rahul Sarpeshkar Richard F. Lyon Carver Mead 《Analog Integrated Circuits and Signal Processing》1998,16(3):245-274
Low-power wide-dynamic-range systems are extremely hard to build. The biological cochlea is one of the most awesome examples of such a system: It can sense sounds over 12 orders of magnitude in intensity, with an estimated power dissipation of only a few tens of microwatts. In this paper, we describe an analog electronic cochlea that processes sounds over 6 orders of magnitude in intensity, and that dissipates 0.5 mW. This 117-stage, 100 Hz to 10 KHz cochlea has the widest dynamic range of any artificial cochlea built to date. The wide dynamic range is attained through the use of a wide-linear-range transconductance amplifier, of a low-noise filter topology, of dynamic gain control (AGC) at each cochlear stage, and of an architecture that we refer to as overlapping cochlear cascades. The operation of the cochlea is made robust through the use of automatic offset-compensation circuitry. A BiCMOS circuit approach helps us to attain nearly scale-invariant behavior and good matching at all frequencies. The synthesis and analysis of our artificial cochlea yields insight into why the human cochlea uses an active traveling-wave mechanism to sense sounds, instead of using bandpass filters. The low power, wide dynamic range, and biological realism make our cochlea well suited as a front end for cochlear implants. 相似文献
2.
OBJECTIVE: Highly sulfated glycosaminoglycans (GAG) have been demonstrated in every form of amyloid examined to date. Based on temporal studies in murine amyloidogenesis heparan sulfate is deposited coincidentally with the amyloid protein. Our purpose was to follow in vivo GAG synthesis by monitoring 35SO4 incorporation during amyloidogenesis. Several necessary previously unexamined nonamyloidogenic controls were also examined. METHODS: Murine splenic amyloid was induced with lipopolysaccharide (LPS) and amyloid enhancing factor (AEF). Splenic GAG synthesis was monitored by 35SO4 incorporation. Corrections were made for alterations in SO4 metabolism which occur during inflammation. RESULTS: All animals with an inflammatory reaction had a marked increase in GAG synthesis. Those animals receiving AEF, or AEF+LPS, had a significant increase in heparan sulfate synthesis. This was particularly profound in the group developing amyloid (i.e., AEF+LPS). CONCLUSION: Our results indicate that critical factors in amyloid deposition include quantitative as well as qualitative changes that take place in tissue GAG synthesis. A distinct metabolic effect of AEF is demonstrated for the first time. 相似文献
3.
This article addresses several issues and trends relevant to the instruction of the learning disabled (LD). Although the concept of LD has received some support as a diagnostic category, limited data exist that demonstrate the effect of different instructional methods on the academic deficits of LD students. In this review, attempts to remediate LD are examined according to the adequacy of the theoretical context that guides the instruction and the efficacy and validity of the remediation procedures. Selected studies representative of medical, psychoeducational, neuropsychological, behavioral, linguistic, and cognitive treatment approaches are reviewed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
We have estimated the turnover and relative pool sizes of nascent-VLDL-TG and VLDL-remnants-TG in anesthetized rats. [1-14C]Palmitoyl- and [2-3H]glyceryl-labeled “VLDL”-TG (including nascent VLDL-TG and VLDL-remnants-TG) were prepared by injecting labeled palmitate and glycerol into donor rats. Labeled serum from these rats was then injected intravenously into nembutalized male rats and serial blood samples taken for 30 min. Special care was taken to define any early components in the labeled “VLDL”-TG disappearance curves. In other experiments, the donors were rendered functionally hepatectomized 30 min after injection of3H-glycerol and the endogenous labeled VLDL-TG was allowed to circulate 30–60 min before collection of the TG-labeled VLDL-remnants-containing serum. The latter was injected into 4 recipient nembutalized rats and the remnant-TG-turnover measured by serial sampling as above. In two cases,14C-“VLDL” and3H-VLDL-remnants were injected as a single bolus into ether-anesthetized rats. Despite its complex composition, “VLDL”-TG in most cases disappeared in a single exponential fashion for 30 min with an average half-life of 5.9 min in nembutalized and 2.8 in ether-anesthetized rats. VLDL-remnants-TG showed a more complex behavior, but contained a major rapid component with a mean t1/2 of ca. 1.5 min in both groups. The data, analyzed by multicompartmental analysis, were fitted to a simple model in which turnover of a larger nascent VLDL-TG pool with formation of a more rapidly turning over smaller pool of VLDL-remnant-TG is the rate-limiting step in overall TG removal from the d<1.006 fraction of rat serum. The data are consistent with our theoretical prediction that under these conditions the kinetics of the VLDL-remnants cannot be resolved from analysis of the total composite “VLDL” (nascent plus remnant) pool. 相似文献
5.
Characterisation of n-type GaAs, etched in a 5:1:1 mixture of H2SO4:H2O2:H2O, was performed using X-ray photoelectron spectroscopy (XPS) and electrochemical AC impedance. Quantitative XPS analysis of GaAs indicated that the as-received wafers had a gallium-rich native oxide which was not affected by solvent degreasing treatments. Subsequent, oxidative etching formed a thinner arsenic-rich oxide. It is suggested that etching causes initial thinning of the native oxide; subsequently, transport of Ga and As ions occurs through the film by high-field ionic conduction. Arsenic enrichment in the resultant oxide film arises from the greater mobility of Ga3+ ions compared with As3+ ions as well as the relative solubility of Ga2O3 compared with As2O3. The as-received oxide film thickness, determined from the ratio of the oxide to substrate XPS peaks, was approximately 1.1 nm. After etching this was reduced to about 0.7 nm. This thickness is consistent with the driving voltage for oxide formation being provided by the electrochemical potential difference between hydrogen peroxide and the GaAs wafer (i.e. between 0.4 V, for As, and 1.2 V, for Ga, at a nm V−1 ratio of 2). Capacitance measurements, derived from electrochemical impedance data, combined with film thickness data, gave a value of about 5 for the dielectric constant of As2O3. 相似文献
6.
This paper presents three projects involving the design and fabrication of architectural structures through the use of different
parametric software and digital manufacturing methods. The first project is a flexible partition composed of interlocking
elements shaped using a laser-cutter. The second project is a university exhibition unit made with various wooden panels manufactured
through a computer numerical controlled (CNC) system. The third project is a system of metal sheets folded by digital machines
to create urban circulation spaces. The three works develop a parametric programming of geometry based on certain technical
factors, enabling the recognition of patterns of interaction between formal and constructive issues involved in the definition
of shapes through parametric controls. Differences in materials and processes are contrasted by similarities of function and
conditions involved, creating a system of local, global, productive and environmental parameters that produces a repertoire
of self-similar dimensions and variations as well as multiple possibilities of initial setups and final configurations. It
suggests a specific field of design exploration focusing on the development of differentiated components and variable architectural
configurations, in a kind of open parametric system. 相似文献
7.
Inhibition of corrosion by a mixture of nonchromate pigments in organic coatings on galvanized steel 总被引:3,自引:0,他引:3
We consider several possible substitutes for toxic chromate pigments. Among the most promising compositions for the corrosion inhibition of galvanized steel with a protective organic coating, we should mention a mixture of phosphate- and calcium-containing pigments. As was shown earlier, such a mixture possesses a high efficiency under conditions of the corrosion of zinc and galvanized steel sheet; however, it is less efficient for the protection of carbon steels. This pigment mixture forms an adsorbed phosphate film on the metal and hinders the course of anodic and cathodic reactions. Zinc ions play an important role for obtaining a synergistic protective effect, increasing the coherence and decreasing the porosity of the deposited film. Traditional and local electrochemical methods (EIS and SVE) were used for studying the corrosion of galvanized steel with coatings in acid rain solution. The data obtained corroborated the high anticorrosive efficiency of a pigment mixture in an organic coating on galvanized steel. In addition, we established some specific features of its inhibiting action near defects in the coating.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 74–80, May–June, 2004. 相似文献
8.
9.
K. C. Lyon 《Journal of the American Ceramic Society》1944,27(6):186-189
Factors have been derived for the calculation of the surface tensions of glasses from their compositions at temperatures of 1200° and 1400°C. The nine oxides evaluated are those commonly found in significant amounts in glass compositions. The surface tension of a glass may be calculated with a fair degree of assurance from its composition to within about 4 dynes per cm. 相似文献
10.
Satellite study of oceanic eddy formation, propagation, interactions, and fate was first conducted by sea surface temperature derived at infrared wavelengths. For visible wavelength ocean color reflectances, it is shown that recent radiative transfer model inversions provide additional characteristics of eddies: their constituent absorption and backscattering inherent optical properties. The chromophoric dissolved organic matter absorption coefficient has the highest contrast and is therefore the most visually evident inherent optical property (while the phytoplankton absorption coefficient and backscattering coefficients are respectively less discernible). For use as an analytical tool, comparisons suggests that the chromophoric dissolved organic matter absorption coefficient has a ∼10× higher contrast (i.e., ∼5% vs. 50%) in the Middle Atlantic Bight making eddy events detectable over longer time periods than with SST imagery. Example imagery illustrates the application of chromophoric dissolved organic matter and phytoplankton absorption coefficient inherent optical properties to the visual injection of dissolved and particulate organic carbon into the deep ocean by a Gulf Stream ring. 相似文献