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181.
E. Kamatani I. S. Teletow S. J. Bysstritzkaja C. Dreyspring C. W. Whittaker F. O. Lundstrom W. L. Hill J. Herzig J. Zák und G. S. Fraps 《Fresenius' Journal of Analytical Chemistry》1937,111(2-4):145-148
Ohne Zusammenfassung 相似文献
182.
A. Polimeni A. Patan M. Henini L. Eaves P. C. Main G. Hill 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
The optical properties of InAs/AlyGa1−yAs self-assembled quantum dots are studied as a function of temperature from 10 K to room temperature. The temperature dependence of carrier hopping between dots is discussed in terms of the depth of the dot confinement potential and the dispersion in dot size and composition. We show that carrier hopping between dots influences both the electrical and optical properties of laser devices having dots as active medium. 相似文献
183.
Bryan S. Holtzman Eric T. Roberts Nicholas S. Caminiti Jacob A. Fox Madison B. Goodstein Staci A. Hill Zitong B. Jia Isabelle N.-M. Leibler Michael L. Martini Gina M. Mendolia Sarah B. Nodder Molly S. Costanza-Robinson Richard C. Bunt 《Tetrahedron letters》2017,58(5):432-436
A nucleophile crossover experiment was used to monitor the reversibility of nucleophilic addition of benzylamine to π-allylpalladium complexes. Dppe, dppp, dppb, and PHOX showed more crossover than PPh3 and dppm in both DMF and dichloromethane. Crossover was inhibited by the addition of DBU or Cs2CO3, but much less elimination to diene side products was observed with Cs2CO3. Analysis of percent crossover vs. percent reaction completion using the PHOX ligand revealed that with added DBU or Cs2CO3 crossover only began occurring after 100% completion had been reached. 相似文献
184.
Ronald G. Hill 《Experimental Mechanics》1968,8(2):75-81
This paper investigates the elastic behavior of bilaminate-composite coupons segmented from a filament-wound rocket case and of a laboratory prepared flat panel for direct tension-compression and flexural loading under static and dynamic conditions. New methods of testing have been developed which are primarily applicable to composite constructions. The dynamic test consists of exciting the primary free-free resonant mode of a specimen. Flexure tests utilizing a unique pure-bend system are employed for the static evaluations. The composite moduli determined from the static and dynamic test are compared with analytic values. The analytic values for the composite are derived from tension-compression and flexure analytical models using the material properties of the constituents. The measured elastic moduli compared favorably with analytical prediction and are indicative of the history of loading effects as well as the crazed condition of the composite constructions. The moduli determined by the dynamic test showed the closest agreement with analytic values, with a difference of 0 to 16 percent. 相似文献
185.
The rolling contact problem involving circular cylinders is at the heart of numerous industrial processes, and critical to any elastohydrodynamic lubrication analysis is an accurate knowledge of the associated contact pressure for the static dry problem. In a recent article [1] the authors have obtained new horizontal pressure distributions, both exact and approximate for various problems involving the symmetrical contact of circular elastic cylinders. In [1] it is assumed that only the circumferential horizontal displacement is prescribed in the contact region while the vertical circumferential displacement is left arbitrary and is assumed to take on whatever value is predicted by the deformation. The advantage of this assumption is that the problem reduces to a single singular integral equation which by transformations can be simplified to an integral equation involving the standard finite Hilbert transform. Here we consider the more general displacement boundary value problem within the contact region, and to be specific we examine the problem with zero vertical circumferential displacement and prescribed horizontal circumferential displacement. The solution of this problem involves two coupled singular integral equations for the horizontal and vertical pressure distributions. Basic equations and some approximate analytical solutions are obtained for symmetrical contact of circular elastic cylinders by both parallel plates and circular cylinders which are either rigid or elastic. Numerical results for the approximate analytical solutions are given for contact by rigid parallel plates and rigid circular cylinders. 相似文献
186.
Detection limits and reduced mobilities for 12 ribonucleotides and 4 ribonucleosides were measured by ambient pressure electrospray ionization-ion mobility spectrometry (ESI-IMS). With the instrument used in this study it was possible to separate some of these compounds within mixtures. Detection limits reported for ribonucleotides and ribonucleosides ranged from 15 to 300 pmol and the reduced mobilities ranged from 41 to 56 suggesting that ambient pressure ESI-IMS may be used for their rapid and sensitive separation and detection. This report demonstrates that it was possible to use ion mobility spectrometry (IMS) to obtain a spectrum for the separation of nucleotides and nucleosides in less than 1 min. The application holds great promise for nucleotide analysis in the area of separating DNA fragments in genome sequencing and also for forensics DNA typing examinations used for the identification of blood stains in crime scenes and paternity testing. 相似文献
187.
Hill MP Carroll EC Vang MC Addington TA Toney MD Larsen DS 《Journal of the American Chemical Society》2010,132(47):16953-16961
The mechanisms of pyridoxal 5'-phosphate (PLP)-dependent enzymes require substrates to form covalent "external aldimine" intermediates, which absorb light strongly between 410 and 430 nm. Aspartate aminotransferase (AAT) is a prototypical PLP-dependent enzyme that catalyzes the reversible interconversion of aspartate and α-ketoglutarate with oxalacetate and glutamate. From kinetic isotope effects studies, it is known that deprotonation of the aspartate external aldimine C(α)-H bond to give a carbanionic quinonoid intermediate is partially rate limiting in the thermal AAT reaction. We show that excitation of the 430-nm external aldimine absorption band increases the steady-state catalytic activity of AAT, which is attributed to the photoenhancement of C(α)-H deprotonation on the basis of studies with Schiff bases in solution. Blue light (250 mW) illumination gives an observed 2.3-fold rate enhancement for WT AAT activity, a 530-fold enhancement for the inactive K258A mutant, and a 58600-fold enhancement for the PLP-Asp Schiff base in water. These different levels of enhancement correlate with the intrinsic reactivities of the C(α)-H bond in the different environments, with the less reactive Schiff bases exhibiting greater enhancement. Time-resolved spectroscopy, ranging from femtoseconds to minutes, was used to investigate the nature of the photoactivation of C(α)-H bond cleavage in PLP-amino acid Schiff bases both in water and bound to AAT. Unlike the thermal pathway, the photoactivation pathway involves a triplet state with a C(α)-H pK(a) that is estimated to be between 11 and 19 units lower than the ground state for the PLP-Val Schiff base in water. 相似文献
188.
Daniella Morgos Ivan Geroy Richard G. Sevier Molly M. Gribb Kevin P. Ryan Herbert H. Hill 《International Journal for Ion Mobility Spectrometry》2010,13(1):1-7
An ion mobility spectrometer (IMS) probe system for real-time, subsurface soil-gas sampling applications is presented. The
system includes an IMS and supporting electronics encased in a 51 mm diameter stainless steel probe housing. The IMS was challenged
in the laboratory with 2,6-di-tert-butylpyridine (DtBP) and tetrachloroethylene (PCE) in zero air yielding reduced ion mobility
constants (Ko) values of 1.42 cm2/Vs (n = 3) and 1.79 ± 0.01 cm2/Vs (n = 3), respectively. A resolving power of 38 and 31 was obtained for DtBP and PCE, respectively. The system was deployed at
a PCE-contaminated site to demonstrate its performance under field conditions. PCE was detected in the vapor samples as evidenced
by peaks with a Ko value of 1.80 ± 0.01 cm2/Vs for two measurements that were taken 6 min apart. The presence of PCE at the contaminated site was confirmed by GC-MS
analysis of a gas sample at an EPA-certified laboratory, suggesting that this IMS system can be used to detect PCE under field
conditions. 相似文献
189.
Grant J Rodgers CA Chickering CD Hill SJ Stry JJ 《Journal of AOAC International》2010,93(4):1293-1301
An analytical method is presented for the determination of chlorantraniliprole residues in crops. Chlorantraniliprole residues were extracted from crop matrixes with acetonitrile after a water soak. The extracts were passed through a strong anion-exchange (SAX) SPE cartridge stacked on top of a reversed-phase (RP) polymer cartridge. After both cartridges were rinsed and vacuum-dried, the SAX cartridge was removed, and chlorantraniliprole was eluted from the RP polymer cartridge with acetonitrile. The acetonitrile eluate was evaporated to dryness, reconstituted, and analyzed using an LC/MS/MS instrument equipped with an atmospheric pressure chemical ionization source. The method was successfully validated at 0.010, 0.10, and 10 mg/kg for the following crop matrixes: potatoes, sugar beets (tops), lettuce, broccoli, soybeans, soybean forage, tomatoes, cucumbers, oranges, apples, pears, peaches, almonds (nutmeat), rice grain, wheat grain, wheat hay, corn stover, alfalfa forage, cottonseed, grapes, and corn grain. The average recoveries from all crop samples fortified at the method LOQ ranged from 91 to 108%, with an overall average recovery of 97%. The average recoveries from all crop samples fortified at 10 times the method LOQ ranged from 89 to 115%, with an overall average recovery of 101%. For all of the fortified control samples analyzed in this study, the overall average recovery was 99%. 相似文献
190.
Kuznetsov AE Geletii YV Hill CL Musaev DG 《The journal of physical chemistry. A》2010,114(43):11417-11424
To probe photoinduced water oxidation catalyzed by the Mn?O?L? cubane clusters, we have computationally studied the mechanism and controlling factors of the O? formation from the [Mn?O?L?] catalyst, 6. It was demonstrated that dissociation of an L = H?PO?? ligand from 6 facilitates the direct O-O bond formation that proceeds with a 28.3 (33.4) kcal/mol rate-determining energy barrier at the transition state TS1. This step (the O-O single bond formation) of the reaction is a two-electron oxidation/reduction process, during which two oxo ligands are transformed into to μ2:η2-O?2? unit, and two ("distal") Mn centers are reduced from the 4+ to the 3+ oxidation state. Next two-electron oxidation/reduction occurs by "dancing" of the resulted O?2? fragment between the Mn1 and Mn2/Mn(2')-centers, keeping its strong coordination to the Mn(1')-center. As a result of this four-electron oxidation/reduction process Mn centers of the Mn?-core of I transform from {Mn1(III)-Mn(1')(III)-Mn2(IV)-Mn(2')(IV)} to {Mn1(II)-Mn(1')(II)-Mn2(III)-Mn(2')(III)} in IV. In other words, upon O? formation in cationic complex [Mn?O?L?](+), I, all four Mn-centers are reduced by one electron each. The overall reaction I → TS1 → II → III → TS2 → IV → TS3 → V → VI + O? is found to be exothermic by 15.4 (10.5) kcal/mol. We analyze the lowest spin states and geometries of all reactants, intermediates, transition states, and products of the targeted reaction. 相似文献