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排序方式: 共有114条查询结果,搜索用时 15 毫秒
1.
Anthony Valenzuela Chase Munson Andrew Porwitzky Matthew Weidman Martin Richardson 《Applied physics. B, Lasers and optics》2014,116(2):485-491
Kerr self-focusing of high-power ultrashort laser pulses in atmosphere may result in a structure or structures of high intensity that can propagate over long distances with little divergence. Filamentation has garnered significant interest in the nonlinear optics community due to its unique properties. Salient features of filaments include a central region of intense laser power (greater than the ionization threshold of the propagation medium) and a low temperature plasma column that lasts up to nanoseconds in duration after the passage of the laser pulse. Steel and titanium samples are ablated by filaments and by sharply focused sub-picosecond laser pulses. We then performed metrology on the samples to compare the ablation features in addition to modeling of the plasma ablation process. Ablation with filaments leads to a wider range of material responses as compared to ablation with sharply focused pulse. This results in potential complications for applications of filament ablation that depends on the rate of material removal and spectroscopic analysis. 相似文献
2.
The high-pressure collisional activation mass spectra with methane as the reagent/collision gas are reported for five aromatic halides. The major decomposition of the protonated aromatic halides is hydrogen halide elimination. The energy-resolved mass spectra and the chemical reactivities of fragment ions with the methane collision gas are used to establish dissociation pathways and structures of fragment ions. The high-pressure collisional activation mass spectra are compared with conventional collisionally induced dissociation and chemical ionization mass spectra. 相似文献
3.
This note presents a variation of the well-known Silver–Meal heuristic to deal with lot sizing under a combination of a known, but time-varying, demand pattern along with an incremental quantity discount structure. The heuristic is shown to perform very well on a set of experiments presented in a recent paper in this journal. Additional experiments are performed to further explore the time horizon effects on the relative performance of the newly proposed heuristic compared to the two best performing ones from the previous paper. 相似文献
4.
H. K. Gersch J. D. Robertson A. G. Henderson D. Pollack C. A. Munson 《Journal of Radioanalytical and Nuclear Chemistry》1998,234(1-2):85-90
Particle-induced X-ray emission (PIXE) spectrometry is being used to nondestructively determine the elemental composition
of copper-based artifacts excavated from prehistoric/protohistoric sites in the Ohio River Valley. Copper objects from Caborn-Welborn
(C-W) and contemporary Fort Ancient sites are being studied so as to differentiate between native American and European copper.
The trace element analysis of metal artifacts enables archaeologists to more accurately assess the material culture and chronological
development of C-W society (A.D. 1400–1700) with particular reference to geological sources of copper and brass. 相似文献
5.
Yukio Shimizu Burnaby Munson 《Journal of polymer science. Part A, Polymer chemistry》1979,17(7):1991-2001
Pyrolysis/mass spectrometric studies have been made on polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) with electron ionization (EI) and chemical ionization (CI) mass spectrometry and a variable temperature probe for direct insertion into the source of the mass spectrometer. Similar results obtained with EI and CI mass spectrometry are in agreement with previous experiments. Advantages of the simplification of spectra in the CI made, as well as the advantages of using both techniques for identification of pyrolysis products, are discussed. 相似文献
6.
Multi-site organizations must balance conflicting forces to determine the appropriate degree of purchasing centralization for their respective supplies. The ability to garner quantity discounts represents one of the primary reasons that organizations centralize procurement. This paper provides methodologies to calculate optimal order quantities and compute total purchasing and inventory costs when products have quantity discount pricing. Procedures for both all-units and incremental quantity discount schedules are provided for four different strategic purchasing configurations (scenarios): complete decentralization, centralized pricing with decentralized purchasing, centralized purchasing with local distribution, and centralized purchasing and warehousing. For ordering decisions under local distribution, procedures to determine optimal order quantities and costs are presented in a precise form that could be easily implemented into spreadsheets by practicing managers. For the more complicated multi-echelon scenarios, we introduce a single-cycle policy with a tailored aggregation refinement step that performs very well under experimentation when compared to a conservative bound. 相似文献
7.
Charles Allgood Yi Lin Yee-Chung Ma Burnaby Munson 《Journal of mass spectrometry : JMS》1990,25(10):497-502
Dilute mixtures of C6H6 or C6D6 in He provide abundant [C6H6]+· or [C6D6]+· ions and small amounts of [C6H7]+ or [C6D7]+ ions as chemical ionization (CI) reagent ions. The C6H6 or C6D6 CI spectra of alkylbenzenes and alkylanilines contain predominantly M+· ions from reactions of [C6H6]+· or [C6D6]+· and small amounts of MH+ or MD+ ions from reactions of [C6H7]+ or [C6D7]+. Benzene CI spectra of aliphatic amines contain M+·, fragment ions and sample-size-dependent MH+ ions from sample ion-sample molecules reactions. The C6D6 CI spectra of substituted pyridines contain M+· and MD+ ions in different ratios depending on the substituent (which alters the ionization energy of the substituted pyridine), as well as sample-size-dependent MH+ ions from sample ion-sample molecule reactions. Two mechanisms are observed for the formation of MD+ ions: proton transfer from [C6D6]+· or charge transfer from [C6D6]+· to give M+·, followed by deuteron transfer from C6D6 to M+·. The mechanisms of reactions were established by ion cyclotron resonance (ICR) experiments. Proton transfer from [C6H6]+· or [C6D6]+· is rapid only for compounds for which proton transfer is exothermic and charge transfer is endothermic. For compounds for which both charge transfer and proton transfer are exothermic, charge transfer is the almost exclusive reaction. 相似文献
8.
Burnaby Munson Ta-Min Feng Harry D. Ward Roger K. Murray 《Journal of mass spectrometry : JMS》1987,22(9):606-609
Analysis of the isobutane chemical ionization mass spectra of hexenols, cyclohexenols and various syn/anti pairs of bicyclic and tricyclic homoallylic alcohols shows that: (i) the spectra of the allylic alcohols are dominated by [M + H – H2O]+ and [M + C4H9–H2O]+ ions and contain traces of [M + H]+ ions; (ii) [M + H]+ ions are prominent in the spectra of acyclic and certain cyclic homoallylic alcohols; and (iii) [M + H]+ ions dominate the spectra of other acyclic unsaturated alcohols. The [M + H]+ ions may result from either: (a) protonation of the hydroxyl group, followed by a very rapid intramolecular proton transfer from the protonated hydroxyl group to the carbon–carbon double bond or internal solvation of the protonated hydroxyl group by the carbon–carbon double bond; and/or (b) direct protonation of the carbon–carbon double bond with significant internal solvation of the resulting carbocation by the hydroxyl group, which may lead to carbon–oxygen bond formation to give a protonated cyclic ether. The consequences of placing various geometric constraints on the possible intramolecular interactions between the hydroxyl group and the carbon–carbon double bond in unsaturated alcohols are explored. 相似文献
9.
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