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101.
Peña-Gomar MC González-González ML García-Valenzuela A Antó-Roca J Pérez E 《Applied optics》2004,43(32):5963-5970
We investigate the use of laser reflectometry near the critical angle to monitor particle adsorption onto a flat glass surface. Experimental results show that positive particles are adsorbed onto the glass surface and that their adsorption kinetics depend strongly on the volume fraction occupied by the particles in suspension but not appreciably on the particle size. The reflectance near the critical angle is dominated by the particles on the surface, with the contribution of the particles in suspension being very low. We compare the reflectance change near the critical angle with the change in reflectance near the Brewster angle when particles are adsorbed onto the glass surface. We find that reflectometry near the critical angle is 3000 times more sensitive than it is near the Brewster angle. Some optical images are presented to validate our results. 相似文献
102.
A new species of Hemicheyletia Volgin was found on Scottish farms and in a creamery. This mite falls into the bakeri group according to the arrangement of the dorso-median setae. A short key to some related species is given. 相似文献
103.
Recent experiments by Maynard et al on fourth sound in a Grafoil-filled4He cell show a periodic dependence of the resonant frequency on the average number of solid layers. We interpret their sharp minima as resulting from the inherent smoothness of complete layers, which inhibits the propagation of waves of melting and freezing, and reduces their damping and their coupling to fourth sound. Using a lattice-gas model, we study the roughness of incomplete surface layers, and suggest how this can lead to the observed broad maxima. We predict that the maxima of damping and of resonant frequency coincide. 相似文献
104.
Thompson Richard W.; Piroch Joan; Fallen Dave; Hatton Dan 《Canadian Metallurgical Quarterly》1974,87(3):507
4 experiments provided support for the hypothesis that tonic immobility (TI) in chickens, which may be analogous to response suppression in the rat, is a result of fear and is mediated by central cholinergic systems. A total of 124 experimental and 54 control, White Leghorn cockerel chicks were the Ss. Exp I established that scopolamine, a central and peripheral acting anticholinergic, will reduce the duration of TI, whereas methylscopolamine, which acts only peripherally, will not. Exp II established a dose-response curve for scopolamine and TI. Exp III demonstrated that scopolamine increased activity and that this increase may be a factor in reducing the duration of TI. Exp IV showed that physostigmine, which blocks acetylcholinesterase and allows longer action of acetylcholine at the synapse, increased the duration of TI. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
Combined scattering and absorption properties of suspended particles can be obtained as a function of wavelength by measuring the complete ultraviolet-visible (UV-vis) spectrum. This research reports on the quantitative interpretation of measured UV-vis spectra of Cryptosporidium parvum oocyst suspensions obtained from several commercial sources and evaluated using two different purification techniques. The reproducibility of the measured spectral data was assessed, and the quantitative interpretation of the oocyst spectra in terms of the particle size and the chemical composition of the particles are reported herein. The interpretation model of the spectra is based on light scattering theory, spectral deconvolution techniques, and on the approximation of the wavelength-dependent optical properties of the basic constituents of living organisms. A characteristic set of optical properties for C. parvum oocysts has been determined as a function of wavelength and used for the quantitative interpretation of UV-vis spectra. The results from the spectral deconvolution show quantitative differences among oocyst preparations. These results represent the first step in establishing a set of critical parameters (e.g., oocyst size and chemical composition) necessary for the detection and identification of C. parvum oocysts in water using spectroscopy. 相似文献
106.
Cortina JL Lagreca I De Pablo J Cama J Ayora C 《Environmental science & technology》2003,37(9):1971-1977
Passive remediation consists of a permeable system that enables the water to pass through while retaining metals by means of biogeochemical reactions. Conventional passive treatments are based on calcite dissolution. This increases the pH to values between 6 and 7, which are insufficiently high to precipitate divalent metals. Alternative treatments are based on sulfate reduction with organic matter in order to precipitate metal sulfides. However, redox reactions are usually too slow to treat large groundwater flows as currently found in gravel aquifers (>50 m/a). Caustic magnesia obtained from calcination of magnesium carbonate was tested as an alternative material to devising passive remediation systems. Caustic magnesia reacts with water to form magnesium hydroxide, which dissolves, increasing the pH to values higher than 8.5. Then zinc and lead are mainly precipitated as hydroxides, copper is precipitated as hydroxysulfate, and manganese(II) is oxidized and precipitated as manganese(III) oxides. Thus, metal concentrations as high as 75 mg/L in the inflowing water are depleted to values below 0.04 mg/L. Magnesia dissolution is sufficiently fast to treat flows as high as 100 m/a. The new precipitates may lead to a permeability drop in the porous treating system. Mixtures of caustic magnesia and an inert material such as silica sand (approximately 50% of each) have been shown to be as reactive as pure magnesia and permeable for a longer time (more than 10 months and 1000 pore vol). 相似文献
107.
Joan Waldvogel 《Journal of Computer-Mediated Communication》2007,12(2):456-477
This article reports on a study of the use and form of greetings and closings in the emails of two New Zealand workplaces: an educational organization and a manufacturing plant. Using discourse analytic techniques, 515 emails were analyzed and a number of differences were identified. In the educational organization, where restructuring has resulted in low staff morale and a mistrust of management, indirect and socially distant styles of communication prevailed and greetings and closings were not widely used. In the manufacturing plant, the more extensive use of greetings and closings reflected and constructed the open and positive relationships between staff and management and the direct, friendly, and familial workplace culture. The findings suggest that workplace culture is a more important factor accounting for the frequency and form of greetings and closings than are relative status, social distance, and gender. 相似文献
108.
Temperature and emissivity separation from ASTER data for low spectral contrast surfaces 总被引:1,自引:0,他引:1
César Coll Vicente Caselles Enric Valor Raquel Niclòs Juan M. Sánchez Joan M. Galve Maria Mira 《Remote sensing of environment》2007,110(2):162-175
The performance of Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) thermal infrared (TIR) data product algorithms was evaluated for low spectral contrast surfaces (such as vegetation and water) in a test site close to Valencia, Spain. Concurrent ground measurements of surface temperature, emissivity, and atmospheric radiosonde profiles were collected at the test site, which is a thermally homogeneous area of rice crops with nearly full vegetation cover in summer. Using the ground data and the local radiosonde profiles, at-sensor radiances were simulated for the ASTER TIR channels and compared with L1B data (calibrated at-sensor radiances) showing discrepancies up to 3% in radiance for channel 10 at 8.3 μm (equivalently, 2.5 °C in temperature or 7% in emissivity), whereas channel 13 (10.7 μm) yielded a closer agreement (maximum difference of 0.5% in radiance or 0.4 °C in temperature). We also tested the ASTER standard products of land surface temperature (LST) and spectral emissivity generated with the Temperature-Emissivity Separation (TES) algorithm with standard atmospheric correction from both global data assimilation system profiles and climatology profiles. These products showed anomalous emissivity spectra with lower emissivity values and larger spectral contrast (or maximum-minimum emissivity difference, MMD) than expected, and as a result, overestimated LSTs. In this work, a scene-based procedure is proposed to obtain more accurate MMD estimates for low spectral contrast materials (vegetation and water) and therefore a better retrieval of LST and emissivity with the TES algorithm. The method uses various gray-bodies or near gray-bodies with known emissivities and assumes that the calibration and atmospheric correction performed with local radiosonde data are accurate for channel 13. Taking the channel 13 temperature (atmospherically and emissivity corrected) as the true LST, the radiances for the other channels were simulated and used to derive linear relationships between ASTER digital numbers and at-ground radiances for each channel. The TES algorithm was applied to the adjusted radiances and the resulting products showed a closer agreement with the ground measurements (differences lower than 1% in channel 13 emissivities and within ± 0.3 °C in temperature for rice and sea pixels). 相似文献
109.
Oriol Gomis-Bellmunt Daniel Montesinos-Miracle Samuel Galceran-Arellano Joan Rull-Duran 《Electrical Engineering (Archiv fur Elektrotechnik)》2007,90(2):115-125
The present work deals with the development of a converter to drive piezoelectric actuators to be used in automotive and aerospace
applications and work under mechanical frequencies up to 2 kHz with rectangular, triangular and sinusoidal reference signals.
In order to maximize the field in the piezoelectric ceramic important voltages (up to 2,000 V) are needed. To fulfill such
requirements with a limited input voltage a bidirectional buck-boost converter is proposed. Such a converter shows voltage
reduction and elevation capability. This advantage overcomes its intrinsic control non-linearity and the drawbacks involved.
The converter is controlled by means of a sliding mode control strategy based on two different linked sliding surfaces which
are defined as the energy error of the converter for charging and discharging operation modes, so that each surface controls
one of the two switches employed. The state-space evolution of the voltage and current is investigated in order to analyze
the converter limitations. The proposed converter and control strategy have been simulated and have proved to be appropriate
and robust for different voltage references and values of the equivalent capacitance C
P
. 相似文献
110.
Joan Daniel Prades Albert Cirera Joan Ramon Morante Albert Cornet 《Thin solid films》2007,515(24):8670-8673
The luminescence spectrum of ZnO exhibits, besides a UV band-edge recombination line, a broad visible band around 2.2-2.4 eV whose origin has not been satisfactorily established. Recently, analysis of the luminescence of nanostructured materials with high surface-to-volume ratios has led some authors to suggest that the band could be related to surface states. This work presents a novel ab initio study of the most relevant ZnO surfaces and their intrinsic point defects. It reveals the existence of intragap surface states 0.5 eV above the valence band maximum. If additional bulk defect levels are considered, several bulk-to-surface transitions are compatible with the observed visible luminescence. 相似文献