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11.
Frank C. De Lucia Jr. Jennifer L. Gottfried Chase A. Munson Andrzej W. Miziolek 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(12):1399-1404
Detecting trace explosive residues at standoff distances in real-time is a difficult problem. One method ideally suited for real-time standoff detection is laser-induced breakdown spectroscopy (LIBS). However, atmospheric oxygen and nitrogen contributes to the LIBS signal from the oxygen- and nitrogen-containing explosive compounds, complicating the discrimination of explosives from other organic materials. While bathing the sample in an inert gas will remove atmospheric oxygen and nitrogen interference, it cannot practically be applied for standoff LIBS. Alternatively, we have investigated the potential of double pulse LIBS to improve the discrimination of explosives by diminishing the contribution of atmospheric oxygen and nitrogen to the LIBS signal. These initial studies compare the close-contact (< 1 m) LIBS spectra of explosives using single pulse LIBS in argon with double pulse LIBS in atmosphere. We have demonstrated improved discrimination of an explosive and an organic interferent using double pulse LIBS to reduce the air entrained in the analytical plasma. 相似文献
12.
13.
Support vector machines can be posed as quadratic programming problems in a variety of ways. This paper investigates a formulation using the two-norm for the misclassification error that leads to a positive definite quadratic program with a single equality constraint under a duality construction. The quadratic term is a small rank update to a diagonal matrix with positive entries. The optimality conditions of the quadratic program are reformulated as a semismooth system of equations using the Fischer-Burmeister function and a damped Newton method is applied to solve the resulting problem. The algorithm is shown to converge from any starting point with a Q-quadratic rate of convergence. At each iteration, the Sherman-Morrison-Woodbury update formula is used to solve the key linear system. Results for a large problem with 60 million observations are presented demonstrating the scalability of the proposed method on a personal computer. Significant computational savings are realized as the inactive variables are identified and exploited during the solution process. Further results on a small problem separated by a nonlinear surface are given showing the gains in performance that can be made from restarting the algorithm as the data evolves.Accepted: December 8, 2003This work partially supported by NSF grant number CCR-9972372; AFOSR grant number F49620-01-1-0040; the Mathematical, Information, and Computational Sciences Division subprogram of the Office of Advanced Scientific Computing, U.S. Department of Energy, under Contract W-31-109-Eng-38; and Microsoft Corporation. 相似文献
14.
Acoustic imaging of objects buried in soil 总被引:4,自引:0,他引:4
Frazier CH Cadalli N Munson DC O'Brien WD 《The Journal of the Acoustical Society of America》2000,108(1):147-156
In this study, we demonstrate an acoustic system for high-resolution imaging of objects buried in soil. Our goal is to image cultural artifacts in order to assess in a rapid manner the historical significance of a potential construction site. We describe the imaging system and present preliminary images produced from data collected from a soil phantom. A mathematical model and associated computer software are developed in order to simulate the signals acquired by the system. We have built the imaging system, which incorporates a single element source transducer and a receiver array. The source and receiver array are moved together along a linear path to collect data. Using this system, we have obtained B-mode images of several targets by using delay-and-sum beamforming, and we have also applied synthetic aperture theory to this problem. 相似文献
15.
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
16.
Li F Munson B Edwards J Yoneyama K Hall K 《The Journal of the Acoustical Society of America》2011,129(2):999-1011
Both English and Japanese have two voiceless sibilant fricatives, an anterior fricative /s/ contrasting with a more posterior fricative /∫/. When children acquire sibilant fricatives, English children typically substitute [s] for /∫/, whereas Japanese children typically substitute [∫] for /s/. This study examined English- and Japanese-speaking adults' perception of children's productions of voiceless sibilant fricatives to investigate whether the apparent asymmetry in the acquisition of voiceless sibilant fricatives reported previously in the two languages was due in part to how adults perceive children's speech. The results of this study show that adult speakers of English and Japanese weighed acoustic parameters differently when identifying fricatives produced by children and that these differences explain, in part, the apparent cross-language asymmetry in fricative acquisition. This study shows that generalizations about universal and language-specific patterns in speech-sound development cannot be determined without considering all sources of variation including speech perception. 相似文献
17.
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
18.
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
19.
Sheth AR Lubach JW Munson EJ Muller FX Grant DJ 《Journal of the American Chemical Society》2005,127(18):6641-6651
Structural and solid-state changes of piroxicam in its crystalline form under mechanical stress were investigated using cryogenic grinding, powder X-ray diffractometry, diffuse-reflectance solid-state ultraviolet-visible spectroscopy, variable-temperature solid-state (13)C nuclear magnetic resonance spectroscopy, and solid-state diffuse-reflectance infrared Fourier transform spectroscopy. Crystalline piroxicam anhydrate exists as colorless single crystals irrespective of the polymorphic form and contains neutral piroxicam molecules. Under mechanical stress, these crystals become yellow amorphous piroxicam, which has a strong propensity to recrystallize to a colorless crystalline phase. The yellow color of amorphous piroxicam is attributed to charged piroxicam molecules. Variable-temperature solid-state (13)C NMR spectroscopy indicates that most of the amorphous piroxicam consists of neutral piroxicam molecules; the charged species comprise only about 8% of the amorphous phase. This ability to quantify the fractions of charged and neutral molecules of piroxicam in the amorphous phase highlights the unique capability of solid-state NMR to quantify mixtures in the absence of standards. Other compounds of piroxicam, which are yellow, are known to contain zwitterionic piroxicam molecules. The present work describes a system in which proton transfer accompanies both solid-state disorder and a change in color induced by mechanical stress, a phenomenon which may be termed mechanochromism of piroxicam. 相似文献
20.
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