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排序方式: 共有685条查询结果,搜索用时 156 毫秒
61.
John R. Kucklick Michele M. Schantz Rebecca S. Pugh Barbara J. Porter Dianne L. Poster Paul R. Becker Teri K. Rowles Stefan Leigh Stephen A. Wise 《Analytical and bioanalytical chemistry》2010,397(2):423-432
The National Institute of Standards and Technology (NIST) has a diverse collection of control materials derived from marine
mammal blubber, fat, and serum. Standard Reference Material (SRM) 1945 Organics in Whale Blubber was recertified for polychlorinated
biphenyl (PCB) congeners, organochlorine pesticides, and polybrominated diphenyl ether (PBDE) congeners. SRM 1945 has also
been assigned mass fraction values for compounds not frequently determined in marine samples including toxaphene congeners,
coplanar PCBs, and methoxylated PBDE congeners which are natural products. NIST also has assigned mass fraction values, as
a result of interlaboratory comparison exercises, for PCB congeners, organochlorine pesticides, PBDE congeners, and fatty
acids in six homogenate materials produced from marine mammal blubber or serum. The materials are available from NIST upon
request; however, the supply is very limited for some of the materials. The materials include those obtained from pilot whale
blubber (Homogenates III and IV), Blainville’s beaked whale blubber (Homogenate VII), polar bear fat (Homogenate VI), and
California sea lion serum (Marine Mammal Control Material-1 Serum) and blubber (Homogenate V). 相似文献
62.
Filippo Cammaroto Andrei Catalioto Jack Porter 《Central European Journal of Mathematics》2011,9(6):1242-1251
In this article, we extend the work on minimal Hausdorff functions initiated by Cammaroto, Fedorchuk and Porter in a 1998
paper. Also, minimal Urysohn functions are introduced and developed. The properties of heredity and productivity are examined
and developed for both minimal Hausdorff and minimal Urysohn functions. 相似文献
63.
M. Gharebaghi K.J. Hughes R.T.J. Porter M. Pourkashanian A. Williams 《Proceedings of the Combustion Institute》2011,33(2):1779-1786
In this study, a mechanism for mercury chlorination in flue gases resulting from the combustion of pulverised coal has been presented. Arrhenius parameters of the gas-phase elementary reactions in the Hg–Cl sub-mechanism have been updated and are mainly based on recent experimental and quantum mechanical rate determinations. The mechanism is validated by comparison to accurate experimental data that is unbiased by Hg oxidation in the impinger solutions of aqueous chemistry methods. Solid-phase retention of Hg0 has been studied in parallel to char combustion; the heterogeneous model describes condensation of mercury on fly ash particles. The combined homogeneous–heterogeneous model predictions show comparable trends to those of power plant data. This approach aims to provide an improved prediction of mercury speciation from coal-fired power plants and to shed light on the chemical kinetic changes encountered during oxy-coal operation. 相似文献
64.
65.
Li Hui Wang Stefano Ottani Roger S. Porter 《Journal of Polymer Science.Polymer Physics》1991,29(10):1189-1192
The lamellar thickness of polyethylene virgin reactor powder has been successfully measured using the Raman longitudinal acoustic mode (LAM). Relatively high lamellar thicknesses have been found. These values change with polymerization temperature in an unusual way, with lamellar thickness being larger for lower polymerization temperature, i.e., at higher undercooling for crystallization. Agreement within an experimental error of 10% has been obtained between values from LAM and those calculated by the Thompson—Gibbs equation from the melting point measured by differential scanning calorimetry. 相似文献
66.
Richard L. Liboff Nils Weimann Mason A. Porter 《International Journal of Theoretical Physics》2002,41(7):1389-1395
We construct a prime symmetry relation for integers that is equivalent to Goldbach's conjecture and show that numerical computations of this prime symmetry property strongly resemble a chaotic sequence. We define and examine the notions of global and local prime quasientropies. Finally, we employ the fact that the prime number sequence satisfies the property of deterministic randomness to consider its utility for the field of quantum computation. 相似文献
67.
Based on the free volume concept and the equation by Doolittle, an empirical equation is offered for the flow activation energy, E
*, for polymer melts for the range of over 150°C above glass transition temperature, T
g. This E
* represents the temperature coefficient of viscosity for the Newtonian region which is also equal to the value measured at constant shear stress for non-Newtonian flow. Data show that the E
* of linear polymers approaches a constant value for a temperature range above T
g+150°C. Data on 17 polymers are correlated. The proposed equation for this region predicts the E
* of polymer melts from the volume expansion coefficient, l, above T
g and also from the T
g.Correlations have also been developed between E
* and
l
and between E
* and T
g by simplifying the equation by use of the Simha-Boyer expression. A polymer having a lower
l
or higher T
g generally has a higher E
*. However, more satisfactory results are obtained by calculating E
* from both
l
and T
g. The E
* calculated is found to agree with measurements within the experimental precision of about ±1 Kcal/mole.The effects of polymer composition, molecular weight, branching and microstructure on E
* are also discussed. These factors influence E
* in the way in which they effect
l
and T
g. 相似文献
68.
M. J. R. Cantow T. Y. Ting E. M. Barrall II R. S. Porter E. R. George 《Rheologica Acta》1986,25(1):69-71
The shear dependence of the bulk viscosities of two structurally different types of perfluoropolyether fluids was determined by two different techniques. The first involved direct measurement in a high shear Couette viscometer, the second utilized the time-temperature superposition principle to establish master curves from viscosity determinations at low shear rates and temperature; the results are comparable. Both fluids begin to show non-Newtonian behavior at shear rates above 10,000 s–1. 相似文献
69.
Summary Pressure effects in the capillary flow of a single sample of poly(methyl methacrylate),M
v = 1.33 · 105, were evaluated. The length/diameter ratios of the different capillaries used varied from 4 to 100. The tests were made with an Instron rheometer in the range 160–250 °C. The pressure-viscosity model, derived from the free volume-WLF equation, was used to pressure correct the capillary data. The corrected data agreed well with data obtained at atmospheric pressure using aWeissenberg rheogoniometer. A derived expression to calculate an increase in the flow activation energy with increasing stress predicts the observed increase in activation energy.
On leave from Montecatini Edison, Milan (Italy). 相似文献
Zusammenfassung Druckeffekte bei der Kapillarströmung einer einzelnen Polymethylmethacrylat-ProbeM v = 1,33 · 105 werden abgeschätzt. Die Längen/Durchmesserverhältnisse der verschiedenen verwendeten Kapillaren variierten zwischen 4 und 100. Im Temperaturbereich zwischen 160 und 250 °C wurden die Versuche mit einem Instron-Rheometer durchgeführt. Das Druck-Viskositätsmodell, das aus der WLF-Gleichung abgeleitet war, wurde zur Druckkorrektur der Kapillardaten verwendet. Die korrigierten Werte zeigten eine gute Übereinstimmung mit den Werten, die bei Atmosphärendruck mit Hilfe einesWeissenberg-Rheogoniometers gewonnen worden waren. Ein abgeleiteter Ausdruck zur Berechnung des Anstiegs der Strömungs-Aktivierungsenergie mit steigender Spannung sagt den beobachteten Anstieg in der Aktivierungsenergie voraus.
On leave from Montecatini Edison, Milan (Italy). 相似文献
70.
Quan Z Luo Z Loc WS Zhang J Wang Y Yang K Porter N Lin J Wang H Fang J 《Journal of the American Chemical Society》2011,133(44):17590-17593
We report a robust method for synthesis of monodisperse PbSeTe single ternary alloy and core/shell heterostructured nanocubes, respectively. The key synthetic strategy to produce such different classes of nanocubes is to precisely control the time of reaction and successive growth. The crystallinity, shape/size distributions, structural characteristics, and compositions of as-prepared nanocubes, both ternary alloy and core/shell, were carefully studied. A plausible growth mechanism for developing each type of lead chalcogenide nanocubes is proposed. These delicately designed PbSeTe nanoscale architectures offer tunable compositions in PbSeTe ternary alloy and nano-interfaces in core/shell nanocubes, which are the critical factors in controlling thermal conductivity for applications in thermoelectrics. 相似文献