Accurate Background Research Articles

Quantitative EPMA of nitrogen : A tricky element in the electron-probe microanalyzer

Among the ultra-light elements B, C, N, and O nitrogen is the most difficult element to deal with in the electron probe microanalyzer. This is mainly caused by the severe absorption that N-Kα radiation suffers in carbon which is abundantly present in the detection system (lead-stearate crystal, carbonaceous counter window). As a result the peak-to-background ratios for N-Kα measured with a conventional lead-stearate crystal can attain values well below unity in many binary nitrides . An additional complication can be caused by the presence of interfering higher-order reflections from the metal partner in the nitride specimen; notorious examples are elements such as Zr and Nb. In nitrides containing these elements is is virtually impossible to carry out an accurate background subtraction which becomes increasingly important with lower and lower peak-to-background ratios. The use of a synthetic multilayer crystal such as W/Si (2d-spacing 59.8 Å) can bring significant improvements in terms of both higher peak count rates as well as a strong suppression of higher-order reflections.

Quantitative electron probe microanalysis of nitrogen

AbstractQuantitative electron probe microanalysis of nitrogen has been performed on 18 nitride specimens in the voltage range of 4–30 kV. A conventional lead stearate and a new W/Si multilayer analyzer crystal (2d = 5.98 nm) were used simultaneously. The net peak count rates on the latter crystal were approximately 2.8 times higher than on the lead stearate crystal. In addition, significant improvements in the peak to background ratios were achieved, which proved critical when dealing with difficult nitrides such as ZrN, Nb2N, and Mo2N. A most conspicuous feature of the new crystal, however, is its effective suppression of higher‐order reflections in the wavelength range of N‐Kα. As a result, backgrounds are free of interfering lines and spectral artifacts, which facilitates accurate background determination. Two procedures for the analysis of nitrogen in the presence of titanium are also discussed. One procedure is based on the assumption that the area–peak factor (APF, integral k‐ratio/peak k‐ratio) of the N‐Kα peak in Ti–N compounds relative to a nitrogen standard (Cr2N) has a fixed value which can be used in order to separate the Ti‐ll peak from the N‐Kα peak. Extensive tests on a number of compositions in the Ti–N system have shown that it is possible to do quantitative analysis of nitrogen in Ti–N compounds with a relative accuracy of better than 5%. For very low levels of nitrogen (below 15 at%) the APF method was found unsuitable. In such cases, however, the well‐known multiple least‐squares digital‐fitting techniques appeared to do an excellent job. In order to account for the effects of peak shape alterations in the N‐Kα peak, all nitrogen spectra were recorded in integral fashion and compared with those of the Cr2N standard. The shape alterations for the N‐Kα peak were much smaller than for B‐Kα and C‐Kα radiations: The observed values for the area–peak factor relative to Cr2N differed less than 5% from unity. The present work has resulted in a database containing 144 integral k‐ratios for N‐Kα and 149 peak k‐ratios for the x‐ray lines of the metal partners in the nitrides. Our own Gaussian ϕ(pz) matrix correction procedure “PROZA,” used in conjunction with a set of improved mass absorption coefficients, yielded excellent results for the nitrogen data: An average value of kcalc/Kmeas of 1.0051 and a relative root mean square deviation of 3.99%.

The ROSAT diffuse X-ray background survey

The quality and capabilities of the ROSAT survey (0.1–2.0 keV) for the study of the diffuse X-ray background and the interstellar medium are discussed. All-sky maps created from data collected during the survey phase of ROSAT operations will greatly exceed previous surveys in spatial resolution (∼5 arc min pixels) and statistical significance (better than 25% for unbinned pixels). The spectral information of the survey will, in general, be greater as well. Finally, because of the survey geometry, very accurate contamination identification and background subtraction will be possible ensuring the reliability of the data.

A Tribute to Jan LaRue on the Publication of "A Catalogue of 18th-Century Symphonies. Vol. 1: Thematic Identifier"

A preoccupation of Jan LaRue's for more than three decades, this catalogue accounts for nearly sixteen thousand works dating from c. 1720 to c. 181o-essentially the entire repertoire 142 of one of the central genres of the eighteenth century. When LaRue began to study the symphony, he soon discovered that a large number of works existed with conflicting attributions and even more were without dates. Better bibliographic control became the necessary first step in order to answer the most basic of questions: who wrote what and when did they write it? Something of the depth of the problem was exposed in Major and Minor Mysteries of Thematic Identification in the Eighteenth-Century Symphony, (for this and other articles cited, see bibliography below, p. 147-49) where misattributions were shown to be the result of everything from innocent happenstance to outright fraud. As LaRue viewed it, the only way to assure an accurate background for any study of the symphony was to account not only for every work, but also for every copy, print, and eighteenth-century catalogue incipit. I estimate that LaRue and his assistants must have examined somewhere in the neighborhood of seventy to eighty thousand sources. Since there are only a dozen keys in the major and minor modes, it is virtually impossible to identify a given symphony from library catalogues, which often list it only by tonality. (One immediately realizes the severe limitations of RISM Series A/I, since both keys and ribute to Jan LaRue

A multiple regression analysis for accurate background subtraction in 99Tcm-DTPA renography.

A technique for accurate background subtraction in 99Tcm-DTPA renography is described. The technique is based on a multiple regression analysis of the renal curves and separate heart and soft tissue curves which together represent background activity. It is compared, in over 100 renograms, with a previously described linear regression technique. Results show that the method provides accurate background subtraction, even in very poorly functioning kidneys, thus enabling relative renal filtration and excretion to be accurately estimated.

A new LMS-based algorithm for rapid adaptive classification in dynamic environments: Theory and preliminary results: [formula omitted], [formula omitted] Boeing Electronics High Technology Center, P. O. Box 24969, MS 7J-24, Seattle, WA 98124-6269

To further enhance the small targets and suppress the heavy clutters simultaneously, a robust non-negative infrared patch-image model via partial sum minimization of singular values is proposed. First, the intrinsic reason behind the undesirable performance of the state-of-the-art infrared patch-image (IPI) model when facing extremely complex backgrounds is analyzed. We point out that it lies in the mismatching of IPI model’s implicit assumption of a large number of observations with the reality of deficient observations of strong edges. To fix this problem, instead of the nuclear norm, we adopt the partial sum of singular values to constrain the low-rank background patch-image, which could provide a more accurate background estimation and almost eliminate all the salient residuals in the decomposed target image. In addition, considering the fact that the infrared small target is always brighter than its adjacent background, we propose an additional non-negative constraint to the sparse target patch-image, which could not only wipe off more undesirable components ulteriorly but also accelerate the convergence rate. Finally, an algorithm based on inexact augmented Lagrange multiplier method is developed to solve the proposed model. A large number of experiments are conducted demonstrating that the proposed model has a significant improvement over the other nine competitive methods in terms of both clutter suppressing performance and convergence rate.

Three‐dimensional Born inversion with an arbitrary reference

Recent work of G. Beylkin helped set the stage for very general seismic inversions. We have combined these broad concepts for inversion with classical high‐frequency asymptotics and perturbation methods to bring them closer to practically implementable algorithms. Applications include inversion schemes for both stacked and unstacked seismic data. Basic assumptions are that the data have relative true amplitude, and that a reasonably accurate background velocity c(x, y, z) is available. The perturbation from this background is then sought. Since high‐frequency approximations are used throughout, the resulting algorithms essentially locate discontinuities in velocity. An expression for a full 3-D velocity inversion can be derived for a general data surface. In this degree of generality the formula does not represent a computationally feasible algorithm, primarily because a key Jacobian determinant is not expressed in practical terms. In several important cases, however, this shortcoming can be overcome and expressions can be obtained that lead to feasible computing schemes. Zero‐offsets, common‐sources, and common‐receivers are examples of such cases. Implementation of the final algorithms involves, first, processing the data by applying the FFT, making an amplitude adjustment and filtering, and applying an inverse FFT. Then, for each output point, a summation is performed over that portion of the processed data influencing the output point. This last summation involves an amplitude and traveltime along connecting rays. The resulting algorithms are computationally competitive with analogous migration schemes.

Enhancement of the ESDIAD method for imaging bond directionality in chemisorbed species

The ESDIAD method for imaging adsorbate bond directions by photographic observation of positive ion angular distributions during electron stimulated desorption suffers from inherent low contrast due to background effects. The use of a digital acquisition system designed to overcome this difficulty in ESDIAD measurement is presented. Measurements on a Ni(110) single crystal substrate show the presence of a significant background signal due to soft X-ray generation by electron impact. By subtraction of the background signal, a significant enhancement of positive ion signal-to-noise ratio is achieved in ESDIAD, converting the ESDIAD method into a high contrast, high resolution surface measurement technique. Quantitative studies of the soft X-ray background have shown it to be linearly dependent on electron current density and electron energy, with no change in angular shape. These properties permit an accurate background subtraction procedure to be employed to significant;y enhance the capability of the ESDIAD method.

Iterative codes for fitting complete spectra

An iterative method for fitting spectra reported on earlier has been modified to incorporate matrix methods of error estimation. Spectra up to 8192 channels are fitted as a single cosine series with up to 512 constants plus a sum of up to 512 peaks. These begin as a curvefit involving up to 34 constants to an experimental singlet. For highest accuracy this singlet should be a large well isolated peak in the spectrum of interest. The background begins as a fast Fourier transform of the experimental data. Peaks are added and the background refitted iteratively until the maximum residual is less than a specified cutoff. Along the way the full widths at half maximum are first fitted to the theoretical curve, them constrained to lie within two standard deviations of the curve. As a result of the accurate background and width determinations it is possible to locate peaks with areas only slightly larger than the background fluctuations and to separate closely spaced doublets. In test runs two artificial peaks introduced into a spectrum of Europium with widths of 5.5 channels could be separated accurately (areas > 4 σ) when separated by 3 channels and crudely (areas < 3 σ) when separated by 2 channels.

Crystal/liquid partitioning of REE in basaltic systems: Extreme fractionation of REE in olivine

Partition coefficients for Nd, Sm, Gd, and Yb between olivine and synthetic basaltic melts were determined using the percent level doping technique and special microprobe analytical techniques for REE in olivine. These techniques permit much more accurate background measurement and thus greater sensitivity than conventional techniques. Spurious results were obtained if REE contents were measured in olivine at locations closer than about 100 micrometers to crystal margins, because of detection of REE x-rays generated in surrounding glass. For results that avoid this “edge” effect, average olivine/liquid distribution coefficients are Nd, 0.00007 ± 3; Sm, 0.00058 ± 7; Gd, 0.00102 ± 8; and Yb, 0.0194 ± 3 for synthetic lunar mare basaltic melts; and Sm, 0.00079 ± 9; Gd, 0.00144 ± 13; Yb, 0.027 ± 3 for synthetic lunar highlands basaltic melts. These values for the light REE are much lower than those of previous experimental or phenocryst/matrix studies. The higher LREE values, and consequently flatter patterns obtained in earlier experimental studies probably resulted from measurement of spuriously high LREE contents in olivines, because of small crystal size. Flatter patterns from phenocryst/matrix studies probably result from small amounts of contamination in olivine mineral separates. The steep slope of the new olivine/liquid pattern is consistent with olivine/clinopyroxene patterns previously obtained from inclusion-free olivines separated from peridotite nodules.

Method of spectral background evaluation using higher energy peaks in x‐ray energy analysis

AbstractA method for spectral background evaluation in x‐ray energy analysis is proposed, based on a simple model of background generation in the detector. This model assumes that photons, of a given energy, interacting with the detector have probabilities of generating background counts within lower energy windows. The usefulness of the method resides in the fact that it allows a background evaluation with different levels of complexity and accuracy. The method also permits accurate background calculation with samples of variable mass and composition, such as biological and environmental materials.

A square-wave wavelength modulation system for automatic background correction in carbon furnace atomic emission spectrometry

A square-wave wavelength modulation system, based on a rotating quartz chopper with four quadrants of different thicknesses, has been developed and evaluated as a method for automatic background correction in carbon furnace atomic emission spectrometry. Accurate background correction is achieved for the residual black body radiation (Rayleigh scatter) from the tube wall and Mie scatter from particles generated by a sample matrix and formed by condensation of atoms in the optical path. Intensity modulation caused by overlap at the edges of the quartz plates and by the divergence of the optical beam at the position of the modulation chopper has been investigated and is likely to be small.

A microanalytical method for the analysis of gold in biological media by flameless atomic absorption spectroscopy.

A simple and sensitive method is presented for the determination of gold in various biological matrices by flameless atomic absorption spectrometry (FAAS). The effects of the biological media on the atomic absorption of gold and the application of some of the important fundamental principles in relation to the measurement of the analyte are also discussed. The results demonstrate that, in FAAS analysis, to obtain maximum peak height sensitivity the samples must be confined to the centre of the graphite atomiser, and for accurate background correction the light paths of the analyte and the continuum lamps through the atomised sample must be synchronised. for measurement of gold in the presence of sodium chloride, the concentration of the salt in the gold standards and the samples must be matched to neutralise the severe depression of the gold signal by sodium.

An Accurate Background Cross-Section Method for Reactor Cell Homogenization

An Accurate Background Cross-Section Method for Reactor Cell Homogenization

GIMMAP--An Interactive Computer Cartography System: ABSTRACT

Computer-produced contour maps with postings of data points and optional perspective views for surface representation are widely recognized as valuable tools in oil exploration, seismic studies, ground-water modeling, and other geologic applications. Few, in any, of the myriad contouring packages are designed to provide an accurate background of cartographic information to help the scientist, engineer, or politician relate contoured information to the real world of political boundaries, highways, and river beds. Additionally, there is much information of interest (e.g., geologic contacts) which cannot be contoured, but which must be treated as pure cartographic information. The GIMMAP (Geodata Interactive Management Map Analysis and Production) system, developed jointly b the Kansas Geological Survey and the Bureau de Recherches Geologiques et Minieres (France), is being used to produce such background maps as well as traditional multi-color geologic maps. The U.S. Geological Survey 7.5-minute topographic series is used as the primary input source for construction of a cartographic data base consisting of political boundaries, surface hydrology, the transportation network, and U.S. Land Survey information (township-range-section). Additional features may be digitized or projected from latitude-longitude coordinates as required for special projects. GIMMAP employs interactive techniques to assist graphical editing of linework; relative definition, editing, and coloring of areal features; placement and editing of symbology; and versatile, user-specified re rieval for producing plots or high-quality scribes for color separation. The modular FORTRAN package relies on physical and logical data segmentation and extensive use of random-access files to operate on a (64 K byte) minicomputer. End_of_Article - Last_Page 1707------------

Application of a Wavelength Modulation Inductively Coupled Plasma-Echelle Spectrometer to Cd and Pb Determinations in Marine Samples

The installation and performance of a wavelength modulation system in a custom-built inductively coupled plasma-echelle spectrometer is described. The system, based on a computer-controlled rotatable quartz plate mounted just behind the entrance slit, permits extremely reproducible short (∼0.1 nm) wavelength scans in the vicinity of any chosen wavelength, as well as automatic two-point background subtraction during analyses. Its effectiveness, both in facilitating the characterization of spectroscopic interferences and in enabling accurate background correction, is demonstrated by determinations of trace quantities of cadmium and lead in biological tissues and sediments. Its potential use for wavelength modulation plasma emission spectrometry is discussed.

Application of edta to direct graphite-furnace atomic absorption analysis for cadmium in sea water

A method is described for the direct determination of cadmium in undiluted sea water by graphite-furnace atomic absorption spectrometry. The addition of EDTA ( 1 mg ml -1) reduces the temperature of atomization of cadmium to far below that of volatilization of other matrix components. The need for very careful temperature control and accurate background compensation is thus minimized. Sea water was analyzed by the method of standard additions. A detection limit of 0.01 μg l -1, a sensitivity of 0.034 μg l -1 and a precision of ±10% at the 0.05 μg l -1 level were obtained for 20-μl injections.

GAS CHROMATOGRAPHIC ANALYSIS OF HALOGENATED HYDROCARBONS IN AIR OVER JAPAN

Abstract Preliminary measurements were conducted of atmospheric concentrations of CCl2F2, CCl3F, CCl2FCClF2, CH3CCl3, CCl4, CHCl=CCl2 and CCl2=CCl2 in remote and urban areas in Japan to determine accurate background levels as well as the profile of local pollution. Samples collected in all-metal canisters were analyzed with an extremely clean stainless steel high vacuum sampling and calibration system and an EC-GC.

Some Design Considerations in Background Corrected Atomic Absorption Instrumentation

Two recent papers have described modifications to single-beam Varian Techtron AA5 atomic absorption spectrometers which are purported to allow accurate background correction to be performed with that instrument. Unfortunately, the simple modifications described will not, generally, give an accurate atomic absorption signal under conditions often encountered in nonflame atomic absorption experiments. The reason for this is that emission light from either the atomizer or its contents cannot be accurately corrected for with the equipment described.

Computer-controlled programmable monochromator with repetitive optical scanner for accurate peak detection and background correction

A 0.5-m grating monochromator is controlled by a minicomputer for multi-element analysis of solutions with a microwave-induced argon plasma as light source. The monochromator slews at a rate of 3.4 nm s -1 between wavelengths of analytical interest and remains at a particular wavelength until the measurement is made. A vibrating quartz plate placed behind an entrance slit repetitively scans narrow wavelength regions around the spectral lines of interest. Data acquisition is synchronized with the vibration of the quartz plate so that the profile of each line can be obtained and accurate peak detection and background correction are possible.