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11.
H. Pollaczek-Geiringer 《Mathematische Zeitschrift》1926,24(1):684-705
Ohne Zusammenfassung 相似文献
12.
The thermodynamic properties of a direct gap semiconducting system, under high intensity optical pumping are studied. The strong electromagnetic field of the pumping beam must have a frequency larger than the band gap. A Bose condensation of electron-hole pairs of zero momentum is found as the temperature goes to zero. This condensation persits even when the finite wavevector of the pump is taken into account. 相似文献
13.
Hilda A. Cerdeira 《Solid State Communications》1980,35(2):109-112
A simplified model of small metallic regions embedded in an insulator is presented, to explain the anomalous results found in CuCl by Brandt et al. We set up the Dyson equations for the model and outline a self-consistent procedure, which can be used to obtain detailed solutions. Without solving the equations, we find that the anomalous Green's function for the metallic region is a rapidly decaying function of the distance from the metal-insulator boundary. This indicates the existence of surface superconductivity, which could account for almost ideal diamagnetism as well as non zero resistivity. 相似文献
14.
We highlight the potentiality of a special Information Theory (IT) approach in order to unravel the intricacies of nonlinear dynamics, the methodology being illustrated with reference to the logistic map. A rather surprising dynamic feature→plane-topography map becomes available. 相似文献
15.
16.
Rex A. Palmer Hilda T. Palmer John N. Lisgarten Robert Lancaster 《Journal of chemical crystallography》1993,23(4):279-283
The crystal and molecular structure of 11-dimethylamino-2-ethoxy-3-hydroxy-5-pregnan-20-one (Dethoxyprone, formII) (C25H43NO3) has been determined by direct methods, and refined to a finalR of 0.067 for 4508 observed reflections. The compound crystallizes in space groupP212121 with cell dimensionsa=10.830 (2),b=12.703 (2),c=17.490 (1) Å;Z=4,D
x
=1.12 g cm–3, (CuK
)=5.28 cm–1. The rings of the steroid skeleton are trans connected. Rings A, B, and C have chair conformations, while ring D has a half-chair conformation. The molecules are hydrogen bonded in a head to tail fashion through the hydroxy and keto groups. 相似文献
17.
Hilda Marta Szabo Raghida Lepistö Tuula Tuhkanen 《International journal of environmental analytical chemistry》2016,96(3):257-270
This work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produced the best separation for all wastewater effluents tested at any detection. UV-254 absorbance was higher at neutral and basic eluent pH while tryptophan-like fluorescence depended on the sample composition rather than on the eluent pH or ionic strength. Tyrosine-like fluorescence decreased significantly with the increase of eluent ionic strength. Accurate molecular weight measurements could not be done, the separation being influenced by secondary interactions, but could be approximated using separate calibrations with sodium salts of polystyrene-sulfonates and protein standards. The results show that this method is suitable for determining DOM in wastewater at low eluent concentrations (up to 0.03 M), at neutral or slightly basic pH. 相似文献
18.
19.
Francisco Javier Guevara-Pantoja Flor Gómez-Galván Iván Eleazar Cipriano Hilda Mercado-Uribe Jesús Carlos Ruiz-Suárez 《Rheologica Acta》2014,53(2):159-164
We study on a suspension of poly(N-isopropylacrylamide) at a low concentration using particle-tracking microrheology in two modalities: at constant temperatures and during a heating ramp. The dilute suspensions do not present a glass state at low temperatures, and at high temperatures, the polymer particles collapse, giving rise to entropic forces that induce aggregation of the tracking colloids. The viscoelastic moduli of the system, which drastically change with temperature, allow us to follow this dynamics. Furthermore, the viscosity of the system remains approximately constant with temperature but suddenly increases as it passes the lower critical solution temperature (LCST). Such effect is probably associated to hydration before the collapse of the polymer, as verified by electrical conductivity measurements. 相似文献
20.
Sérgio L. C. Ferreira Marcus L. S. F. Bandeira Valfredo A. Lemos Hilda C. dos Santos A. C. Spinola Costa Djane S. de Jesus 《Analytical and bioanalytical chemistry》1997,357(8):1174-1178
A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic
acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP).
The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 105 l mole–1cm–1 and 5.69 × 104 l mole–1cm–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml–1, a calibration sensitivity of 0.744 ml μg–1 at 560 nm and 0.323 ml μg–1 at 748 nm, and a detection limit of 15 ng ml–1 and 44 ng ml–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations.
The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The
Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system.
Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996 相似文献