bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application and Description of a Portable Calibration System
Authors: Debbrecht FJ , Neel EM 
Published: March 2009

A newly introduced calibration system for air pollution monitors and its field use will be discussed. The system is based upon the Environmental Protection Agency's developed permeation tube technique and is fully portable, allowing intercalibration of monitors at different locations.
Two major requirements are necessary for accurate use of permeation tubes in the generation of primary standard quality calibration gas mixtures. The temperature of the permeation tube must be held within 0.1°C of the temperature at which it was calibrated to ensure accuracy within 1 percent. Also the flow rate of the gas across the permeation tube must be readable to within 1 percent accuracy.
The portable calibration system described controls the permeation tube at 35°C to well within 0.1°C. This temperature is fixed and is read out on the expanded scalemeter that is 0.4°C full scale to ensure that the permeation tube is within 0.1°C of the fixed 35°C.
The calibration system draws in ambient air through a particulate filter by an internal dual headed pump. One head provides a flow of 10 ml/min through a restriction, a charcoal scrubber, the permeation chamber, and a flow directional valve. The other head provides a diluent flow, settleable on the front panel, from 300 to 1500 ml/min. This flow is read out on a special dual ball rotameter, individually calibrated, with settleability to within 1 percent. This diluent flow can provide a fivefold change in concentration available for calibration, permitting calibration at a number of points. In addition the flow direction valve has a high concentration position in which all of the permeation effluent is mixed with the diluent air, a low concentration position in which only 20 percent of the permeation effluent is mixed with the diluent air, and a “zero” air position in which no permeation effluent is used. This last position provides only air that has passed the charcoal scrubber for the analyzer to be calibrated. The high/low concentration positions provide a 5 to 1 concentration range and when coupled with the diluent air flow range provide a 25 to 1 concentration range.
This calibration system can operate for at least 8 h from internal batteries, indefinitely from 110 V lines, while the batteries are recharging, or from an auto cigarette lighter adapter supplied as standard.
The present emphasis and concern on data correlation among the various locations and agencies involved in the air pollution effort requires the instrumentation used to be calibrated properly. A portable calibration system provides the necessary common demoninator between a number of remote monitoring systems. This common standardization is the first crucial step before data can be compared.
Interagency Comparison of lodometric Methods for Ozone Determination
Authors: DeMore WB , Romanovsky JC , Feldstein M , Hamming WJ , Mueller PK 
Published: March 2009

In 1973 it was learned that measurements of oxidants by the Los Angeles Air Pollution Control District (LAAPCD) were about 30 percent lower than measurements by the California Air Resources Board (ARB) and that the discrepancy was due to differences in the calibration methods of the two agencies. To resolve this problem, the ARB appointed an Oxidant Calibration Committee for the purpose of evaluating the accuracy of the different agency calibration procedures.
The committee selected ultraviolet absorption photometry as the reference method for ozone measurement. Interagency comparisons of the various iodometric methods were conducted relative to the ultraviolet standard. The tests included versions of the iodometric methods as employed by ARB, LAAPCD, and the Environmental Protection Agency (EPA). An alternative candidate reference method for ozone measurement, gas phase titration, was also included in the test series.
Under the conditions of these tests, which were considered to be representative of procedures employed by the California agencies, the ARB method read high by 25 to 30 percent, and the LAAPCD method read low by about 4 percent. The EPA method, which is similar to the ARB method, also read high. The gas phase titration results were about 9 percent higher than the reference ultraviolet standard.
Based on the results of these tests and other considerations, the committee has recommended that future ozone calibration procedures in the State of California be referenced to an ultraviolet standard.
Evaluation and Collaborative Testing of a Continuous Colorimetric Method for Measurement of Nitrogen Dioxide in Ambient Air
Authors: Margeson JH , Fuerst RG , Constant PC , Sharp MC , Scheil GW 
Published: March 2009

A continuous colorimetric method for measurement of nitrogen dioxide (NO2) in ambient air, which uses Saltzman type absorbing solutions, was evaluated and then subjected to a collaborative test.
The evaluation shows that dynamic calibration is required to obtain reliable results. Static calibration is not reliable. The method write-up specifies dynamic calibration.
The collaborative test was carried out by having ten collaborators sample ambient air and the same ambient air spiked with a reliable source of NO2 for four days at a common site in Kansas City, Missouri; NO2 concentrations of 50 to 370 μg/m3 were sampled.
The results show that, based on 1-h avg concentrations, the within-laboratory standard deviation is 6 percent of the concentration over the range 90 to 370-μg NO2/m3, and the between-laboratory standard deviation is 14 percent of the concentration over the same range. The results also show that the method has a significant positive bias. This bias cannot be accurately quantitated because different collaborators give widely different biases, that is, the bias is collaborator dependent. The “average” bias ranges from +3 to +15 percent of the NO2 concentration over the just mentioned range.
The lower detectable limit of the method is 19 μg/m3.
Use of the National Bureau of Standards Standard Reference Gases in Mobile Source Emissions Testing
Authors: Paulsell CD 
Published: March 2009

The Mobile Source Air Pollution Control (MSAPC) program has developed a system of primary gas standards which permits commercial gas blends to be named within 2 percent of true value and a computer program which documents the path and traceability relationship of each gas to the National Bureau of Standards (NBS) standard reference material (SRM).
The MSAPC program incorporates gravimetric gas blending as a primary means to verify and extrapolate the work of the NBS. These blends comprise the reference points for a two-point linear interpolation procedure for gas analysis and correlation. The advantages and limitations of this procedure are outlined and quantified.
Gas Standards, How Standard Are They?
Authors: Wechter SG , Grieco HA 
Published: March 2009

Not everyone who works with ultra-high purity gases is aware of the difficulties involved in establishing a primary gas standard. The problems associated with the necessary correlation procedures, the instability of certain gases, reaction of gas mixtures, etc., are complicated further by the fact that many firms maintain their own primary standards, with little or no effort given to correlate values with others. It is obvious, therefore, that the only remedy for this haphazard situation is to establish a single repository for primary standards. Because of its history and experience in such matters, the U.S. National Bureau of Standards (NBS) is the only likely choice to serve as this repository. As is commonly known, this is no panacea. All firms involved in the specialty gas business must work continuously to maintain the effectiveness of the primary standards established. An absolute, by definition, is impossible to attain. However, by diligent efforts in correlating gases, we, as an industry, can approach that absolute as closely as possible.
The use of by-weight mixtures is not always as accurate as one may think. This paper intends to point up, by way of specific examples, several correlation techniques we have found necessary in certifying a primary standard, and to point up our present and future needs for standard reference materials supplied by NBS.
Development of Synthetic Standard Samples for Trace Analysis of Air Particulates
Authors: Pradzynski AH , Rhodes JR 
Published: March 2009

Synthetic, “homogeneous,” and particulate standard samples in the form of deposits on filters have been developed for use in quality control of analytical methods and for calibration of X-ray emission spectrometers.
The standards for X-ray emission spectrometer calibration comprise membrane filters with single element or multielement solutions homogeneously deposited and dried, and membrane filters with known amounts of single mineral powders of well-defined particle size ranges deposited and fixed on them.
For quality control of analytical methods and laboratories, synthetic standards for sulfates, nitrates, and trace elements have been developed. The standards for sulfates, nitrates, and volatile trace elements were deposited in the form of solutions on glass fiber filters and dried. The standards for nonvolatile trace elements were prepared from -10-μm quartz powder spiked with compounds of the elements and deposited from air suspension.
Comparisons of the Ballistic Impact Response of Metals and Composites for Military Aircraft Applications
Authors: Avery JG , Porter TR 
Published: March 2009

This paper compares the ballistic impact response of advanced fiber composites and metals. These comparisons are made within the framework of a methodology that defines the necessary data and analysis requirements for evaluating the survivability of combat aircraft designs.
A side-by-side comparison was made of the available residual strength and damage size test data for metals and fiber composites damaged by small arms projectiles. In addition, the available composite data was used to extend a model for predicting the ultimate strength of composite tension panels damaged by bullets. This model was used in conjunction with an existing model for metals to extend the comparisons to equal strength, equal stiffness, or equal weight structural panels.
The results show that both metal and fiber composite panels lose a significant percent of their undamaged strength (50 percent or more) when impacted with small arms projectiles. For the cases considered, the percent reduction in the fiber composite panels was greater than in the metal panels. These results are considered to be preliminary for structural evaluations, however, because only simple panel data were used in the comparison.
Impact Damage Tolerance of Graphite/Epoxy Sandwich Panels
Authors: Oplinger DW , Slepetz JM 
Published: March 2009

The resistance of graphite/epoxy sandwich panels to low energy, foreign object impact damage was studied. Falling weight impact tests were performed on 104 rectangular sandwich panel specimens. The effect of several material, geometry, and loading parameters on damage susceptibility was explored. Damage observed visually was related to residual strength of specimens taken from the impact region, and in some cases, to static indentation tests carried out on companion specimens.
Sandwich test specimens were fabricated with face sheets of graphite or S-glass/epoxy with a 1-in. depth nomex honeycomb core. Fiber type, core density, and laminate orientation were fabrication variables. Drop weight tests were accomplished using a 2-in.-diameter steel ball. Initial and residual static shear strength were measured on notched, four-point bend specimens.
Impact tests showed that graphite sandwich panels are much more susceptible to foreign object damage than S-glass panels. The impact energy required to sustain the same relative damage level was an order of magnitude greater for the S-glass than for the graphite panels. The failure characteristics observed suggest that this is due primarily to the low strain to failure of graphite composites. Local core crushing occurred in all tests, and all but the S-glass panels suffered fiber fracture and permanent indentation at low energy levels. Core stiffness had an observable effect on impact resistance, but other parameters studied did not appear to significantly affect damage tolerance.
An analysis was carried out in which the sandwich panel was represented as an orthotropic sheet on an elastic foundation, and a classical, double Fourier series approach was taken. The load condition was approximated by an influence function technique to effect a constant radius of bending curvature, simulating the region around the drop weight ball. The capability exists to vary the material constants of the face sheet and core to investigate the nature of indentation failure, and to identify factors contributing to impact resistance. Numerical results were obtained for some of the material parameters employed in the impact tests.
Failure Mechanisms in Composite Plates Impacted by Blunt-Ended Penetrators
Authors: Cristescu N , Malvern LE , Sierakowski RL 
Published: March 2009

Tests of 0–90° ply fiberglass roving-epoxy plates, impacted by hard steel cylindrical penetrators, have revealed a sequential delamination mechanism, especially well developed in plates having more than one layer of fibers in each unidirectionally reinforced lamina. In these plates the sequential delamination mechanism was the principal mechanism of spreading the deformation to parts of the plate distant from the impact point.
In impacts by a cylinder of radius R, at moderate velocities such that the shear cut-out of a plug does not extend all the way through the plate, the sequential delamination is begun when a strip of width 2R of the first lamina is pushed forward by the penetrator, initiating two shear cracks through the thickness of the lamina parallel to the fibers of the first lamina. This strip in turn loads transversely the second lamina and initiates a separation between the first two laminas. This interlaminar crack spreads until it is stopped by the cutting-through of the loading strip by the penetrator. The process is then repeated by the second and third laminas, followed by the third and fourth, and continues through the thickness of the plate, with each subsequent delamination covering a larger area than the one before it.
Other failure mechanisms in composite-plate perforation are also discussed, especially fiber stretching and tensile breaking. Recommendations for further analytical and diagnostic testing are made.
Fatigue and Shakedown in Metal Matrix Composites
Authors: Dvorak GJ , Tarn JQ 
Published: March 2009

Simple mechanical models of unidirectional metal matrix composites are used to analyze elastoplastic deformation and shakedown in the matrix under cyclic composite loads. Both axial and off-axis loadings of a lamina are considered. It is shown that the fatigue limits of as-fabricated boron-aluminum, beryllium-aluminum, tungsten-copper, and other composites generally coincide with the composite shakedown limits because the matrix yield stresses and fatigue limits are equal.
In heat-treated composites, the matrix yield stress is usually much higher than the fatigue limit, and matrix fatigue failure can take place in the shakedown state. The residual microstresses caused by heat treatment are estimated, and their influence on fatigue is discussed. A method for improvement of the fatigue resistance of heat-treated composites is discussed.
The theoretical predictions of fatigue limits are verified by an extensive comparison with available experiments, and a very good agreement is obtained. It is concluded that, in principle, the composite fatigue failure can be avoided if each of the constituents is stressed within its particular fatigue limits during a cyclic loading program of the composite.
Reliability After Inspection
Authors: Davidson JR 
Published: March 2009

Because materials and structures cannot be made to always be perfect, they are inspected to determine if they contain flaws or defects large enough to influence their strength, reliability, or economic life. Inspection methods and procedures depend upon the part configuration, possible flaw type, orientation, location, and accessibility. The procedure will depend upon prior knowledge of possible defects and whether or not the inspector is to decide if a single flaw is at a specific location or if no significant flaws exist anywhere in some distributed area or volume.
Long-lived structures require that initial flaws be small so that the flaws will not grow to a critical size during the structure's life or between inspections. Consequently, nondestructive inspection methods are commonly pushed to their limits. For example, the size of a permitted flaw might be just less than the size flaw which will be detected 90 percent of the time. As a result, nondestructive engineering (NDE) methods are not infallible, and some flawed parts might pass inspection. The question, then, is how to calculate the reliability of a part or a structure that has passed inspection.
Three analyses have been developed to calculate this a posteriori reliability. Each handles an increasingly complex situation. The first and simplest gives the reliability based upon the efficiency of the detection method and the probability that the part was unflawed when it reached the inspector (a priori reliability).
The second deals with the problem where flaws are distributed over an area or throughout a volume. Here, the mean number of flaws per unit area or volume (a priori) is a parameter; the actual number in a part is assumed to be Poisson distributed.
The third analysis predicts the a posteriori reliability for a structure with distributed flaws but where some portions are inaccessible and cannot be inspected.
Definition, Functional Design, and Implementation of a Dedicated Computerized Laboratory System: The GC Computing Recorder
Authors: Zawadowicz ST , Kegg AL 
Published: March 2009

This paper describes the process employed in defining and creating an integrated instrument with computing and recording capability that generates a document containing a full chromatogram juxtaposed with its quantitative on-line analysis. This selfcontained system, called the GC Computing Recorder, operates from the raw gas chromatograph detector signal through appropriate signal conditioning, analog-to-digital conversion, microcomputer-based digital integration and postintegration calculation to generate the final analytical report, termed the integrated chromatogram.
The paper briefly reviews the historical development of gas chromatographic quantitation technology and it postulates the system requirements for single channel quantitation instrumentation. Then, it summarizes the specific design approaches considered for the computing recorder, the evolution of the system architecture from the point of view of its inputs and outputs, and the selection of the architectural approach adopted for the final design. Particular attention is devoted to man/machine interface considerations, signal conditioning design, digital filtering, analog-to-digital conversion techniques, and firmware integration treatments.
Criteria developed to enhance the integration portion of the system firmware are explored, and the algorithmic treatments of overlapping peaks, drifting baselines, area recovery, and multiple peak resolution are discussed. The detailed systems description also covers the areas of postintegration calculations including area normalization, response factors, and relative retention times, as well as the application of internal standard methods for precision determinations of component concentration levels.
Experience with the instrument under actual laboratory conditions is summarized, and observations are made concerning possible system extensions.
Feasibility Study and Functional Design for the Computerized Automation of the Central Regional Laboratory EPA Region V, Chicago
Authors: Frazer JW , Barton GW 
Published: March 2009

A feasibility study and functional design is presented for the computerized automation of the Central Regional Laboratory of Region V of the Environmental Protection Agency. The system recommended, which meets all the stated objectives, is built around a Data General Nova 840 computer operating in a time-share mode using the BASIC high-level language operating system for applications programs. Instruments to be automated include Technicon Auto Analyzers, atomic absorption spectrometers, and an electronic balance. The system will include file management programs to take care of the laboratory needs. Data will be transferred to STORET on magnetic tape.
This paper is divided into several sections. The first section includes (1) an overview of the functions selected by the laboratory for our consideration with a discussion of the benefits expected from automation of these functions, and (2) a detailed cost and benefit breakdown of ten alternatives, each meeting the same or all of the objectives. The final sections are functional designs for each of the instruments and the sample file control, detailing the desired interaction between the operators, instruments, and data.
The goals of this project are to: (1) increase instrument capacity, (2) improve the accuracy and precision of analytical results, (3) save analysts' time, (4) reduce clerical time and associated errors, and (5) provide ready access to the analytical data.
Performance of Portable Automatic Wastewater Composite Sample Collectors
Authors: Keffer WJ 
Published: March 2009

A summary of the reliability of eleven commercially available wastewater sample collectors is presented. Installation procedures are reported which resulted from about 90 000 h of operation with sampling equipment at municipal and industrial waste treatment facilities under summer and winter conditions.
Water chemistry data, primarily five-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and nonfilterable solids (NFS), for time and flow-proportional samples collected concurrently by piston pump, peristaltic pump, vacuum, and pressure operated compositors were compared to results obtained with manual sampling techniques.
Variations in nonfilterable solids levels exceed 100 percent in some instances for composite samples collected at the same point and over the same time span by different models of commercially available compositor equipment. Variations in five-day biochemical oxygen demand and chemical oxygen demand levels were also significant but ranged, generally, from 35 to 50 percent.
A proposal is presented for the development of a standardized test procedure for evaluation of sampler performance based on suspended solids recovery. Equipment features which the “ideal” sampler would incorporate are recommended.