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排序方式: 共有1726条查询结果,搜索用时 15 毫秒
51.
Susanne V. Hering Nathan M. Kreisberg Mark R. Stolzenburg Gregory S. Lewis 《Aerosol science and technology》2013,47(1):86-96
As part of the California Regional PM 2.5 and PM 10 Air Quality Study (CRPAQS) particle size distributions were measured simultaneously at two sites; the city of Fresno and the agricultural site of Angiola. Reported here are data obtained by scanning mobility analysis over the size range from 10 nm to 400 nm for the intensive study period from December 1, 2000 through February 6, 2001. These high time resolution data show variability in the character of the distributions, as well as the in the total number concentrations. The most pronounced feature of the data set is a consistent, nighttime maxima in particle number concentrations with a modal diameter near 80 nm during the evening hours at the urban Fresno site. Although these maxima are correlated with CO, NO, and black carbon, the particle size is larger than the 30–40 nm modal diameters observed for traffic aerosols during the commute hours, and is attributed to a non-vehicle source. At the agricultural site, the morning maxima particle number concentration coincides with the maxima in NO concentration, but often precedes the morning maxima in black carbon. Values for the geometric mean particle diameter varied from day to day, but are correlated between the two sites, with somewhat larger particle sizes at Angiola during periods of stagnation. 相似文献
52.
Bryan Harder Nathan Jacobson Dwight Myers 《Journal of the American Ceramic Society》2013,96(2):606-612
Oxidation of SiC can occur in a passive mode, where a protective film is generated, or in an active mode, where a volatile suboxide is generated. The transitions from active‐to‐passive and passive‐to‐active are particularly important to understand as they occur via different mechanisms. In Part II of this article, the passive‐to‐active transition is explored. Three different types of SiC are examined—Si‐rich SiC, stoichiometric SiC, and C‐rich SiC. In addition to an in situ transition from passive‐to‐active, the effect of a preformed film on all three types of SiC is explored. It appears that the passive‐to‐active transition occurs when the SiO2 scale begins to react with the SiC substrate. This reaction generates SiO(g) and CO(g), which build pressure beneath the SiO2 scale, eventually causing the oxide to rupture. In addition, the SiO(g) can oxidize a distance away from the surface leading to the formation of SiO2 needles and further promoting this SiO2/SiC reaction. Thermodynamic and kinetic data are used to predict transition pressures of oxygen, which show reasonable agreement with those measured. 相似文献
53.
Nathan D. Marsh Mary J. Wornat Lawrence T. Scott Atena Necula Arthur L. Lafleur Elaine F. Plummer 《Polycyclic Aromatic Compounds》2013,33(4):379-402
In order to investigate new aspects of polycyclic aromatic hydrocarbon (PAH) growth and soot formation, we have synthesized special reference standards of cyclopenta-fused PAH (CP-PAH) and ethynyl-substituted PAH. We have identified several of these CP-PAH and ethynyl-PAH in benzene droplet combustion products, using high pressure liquid chromatography (HPLC) and ultraviolet-visible (UV) absorption spectroscopy. Although one CP-PAH identified in these products - acenaphthylene - has previously been identified as a product of a variety of combustion systems, we have identified six additional CP-PAH and two ethynyl-PAH which have never before been unequivocally identified as the products of benzene pyrolysis or combustion: acephenanthrylene, aceanthrylene, cyclopent[hi]acephenanthrylene, cyclopenta[cd]fluoranthene, cyclopenta[cd] pyrene, dicyclopenta[cd, jk]pyrene, 2-ethynylnaphthalene, and 1-ethynylacenaphthylene. We present the corresponding UV absorption spectra obtained from the HPLC analysis of benzene droplet combustion products, and compare them to the UV absorption 相似文献
54.
Ockwig NW Delgado-Friedrichs O O'Keeffe M Yaghi OM 《Accounts of chemical research》2005,38(3):176-182
The structures of all 1127 three-periodic extended metal-organic frameworks (MOFs) reported in the Cambridge Structure Database have been analyzed, and their underlying topology has been determined. It is remarkable that among the almost infinite number of net topologies that are available for MOFs to adopt, only a handful of nets are actually observed. The discovery of this inversion between expected and observed nets led us to deduce a system of classification "taxonomy" for interpreting and rationalizing known MOF structures, as well as those that will be made in future. The origin of this inversion is attributed to the different modes with which MOF synthesis has been approached. Specifically, three levels of complexity are defined that embody rules "grammar" for the design of MOFs and other extended structures. This system accounts for the present proliferation of MOF structures of high symmetry nets, but more importantly, it provides the basis for designing a building block that "codes" for a specific structure and, indeed, only that structure. 相似文献
55.
The weak-link approach (WLA) to supramolecular assemblies allows for the design of multimetallic two- and three-dimensional arrays, host-guest architectures, sensors, catalysts, switches, and signal amplification devices. This Account describes the course of our investigations in this area beginning with the development of a chemical tool kit of building blocks consisting of multiple metals and ligands. These building blocks can be rationally mixed and matched to provide structures with a wide range of properties that have been used to develop functional supramolecular architectures, including chemical sensors and allosteric catalysts. 相似文献
56.
Nathan M. Korlesky Lucas J. Stolp Dharma R. Kodali Robert Goldschmidt William C. Byrdwell 《Journal of the American Oil Chemists' Society》2016,93(7):995-1005
Montmorency sour cherry (Prunus cerasus L.) pit oil (CPO) was extracted and characterized by various methods including: GC, LC–MS, NMR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X‐ray powder diffraction (XRD). The oil gave an acid value of 1.45 mg KOH/g, saponification value of 193 mg KOH/g and unsaponifiable matter content of 0.72 %. The oil contained oleic (O) and linoleic (l ) acids as the major components with small concentrations of α‐eleostearic acid (El, 9Z,11E,13E‐octadecatrienoic acid) and saturated fatty acid palmitic (P) acid. The CPO contained six major triacyglycerols (TAG), OOO (16.83 %), OLO (16.64 %), LLO (13.20 %), OLP (7.25 %), OOP (6.49 %) and LElL (6.16 %) plus a number of other minor TAG. The TAG containing at least one saturated fatty acid constitute 33 % of the total. The polymorphic behavior of CPO as studied by DSC and XRD confirmed the presence of α, β′ and β crystal forms. The oxidative induction time of CPO was 30.3 min at 130 °C and the thermal decomposition temperature was 352 °C. 相似文献
57.
We report the fabrication of gold/polycarbonate (Au/PC) hybrid nano resonators on plastic substrates through a nano-transfer
printing (nTP) technique, and the parametric studies of the resonant frequency of the resulting hybrid nano resonators. nTP
is a nanofabrication technique that involves an assembly process by which a printable layer can be transferred from a transfer
substrate to a device substrate. In this article, we applied nTP to fabricate Au/PC hybrid nano resonators on a PC substrate.
When an AC voltage is applied, the nano resonator can be mechanically excited when the AC frequency reaches the resonant frequency
of the nano resonator. We then performed systematic parametric studies to identify the parameters that govern the resonant
frequency of the nano resonators, using finite element method. The quantitative results for a wide range of materials and
geometries offer vital guidance to design hybrid nano resonators with a tunable resonant frequency in a range of more than
three orders of magnitude (e.g., 10 KHz-100 MHz). Such nano resonators could find their potential applications in nano electromechanical
devices. Fabricating hybrid nano resonators via nTP further demonstrates nTP as a potential fabrication technique to enable
a low-cost and scalable roll-to-roll printing process of nanodevices. 相似文献
58.
Jordan M. Anderson Jigna Patel Ajay S. Karakoti Nathan Greeneltch Diego J. Díaz Sudipta Seal 《Electrochimica acta》2011,56(5):2541
Nanocrystalline Pt/CeO2 composite electrodes were fabricated to study the electrochemical oxidation of methanol and ethanol. The performance of the electrodes was tested as the ceria solutions aged over time. It was observed that the performance oscillated with time, suggesting that the catalytic behavior towards alcohol oxidation was greatly dependent on the aging of the particles. These results point to a great dependence of the catalytic effect on the redox state of the ceria particles. 相似文献
59.
60.
Charles W. Bauschlicher Jr. Cameron J. Bodenschatz Dwight L. Myers Nathan S. Jacobson 《Journal of the American Ceramic Society》2020,103(10):5870-5880
Thermodynamic parameters are reported for gaseous hydroxides and oxyhydroxides of Al, Zr, and Y. The structures and vibrational frequencies are calculated using density functional theory with the B3LYP functional. This yields entropies at 298.15 K and heat capacities. The enthalpies are calculated from appropriate reactions and the CCSD(T) (Coupled Cluster, Singles, Doubles, and perturbative Triples) approach. The hydroxide groups are treated as hindered rotors for all species. The results are compared to the limited experimental and theoretical calculations for these species. Finally, the data are put into a database for a free-energy minimizer and the vapor pressures for each species are compared. 相似文献