Tribological behavior of metal matrix composites

The wear and friction behavior of continuous graphite fiber reinforced metal matrix composites was investigated. Composite materials were tested against 4620 steel at 54 m s^?1 at room temperature in air without lubricant. The graphite fibers studied included rayon-, pitch- and polyacrilonitrile (PAN)-based fibers. Both high modulus and high strength PAN-based fibers were examined. The fibers were incorporated into copper- and silver-based alloys by means of a liquid metal infiltration technique. The results of this study indicate that the type of graphite fiber in the composite is the most significant factor in the wear and friction behavior of metal matrix composites. In some high modulus fiber tin-bronze composites the fiber fraction influences the wear rate but not the coefficient of friction. Neither the matrix alloy nor the composite tensile strength per se correlate with the friction and wear properties; however, there are specific trends for the various matrix alloys.     

Remote sensing the radionuclide contaminated Belarusian landscape: a potential for imaging spectrometry?

The 1986 Chernobyl accident resulted in radionuclide contamination (dominated by ¹³⁷Cs) across large areas of Belarus. Consequences of this accident continue to affect Belarus long after initial contamination, which in turn has placed strain upon social, economic and political infrastructures. One method to reduce this strain and remediate contamination is to return areas of land no longer posing a risk, back to an appropriate use. As a method of remediation, this requires regular and accurate monitoring of the landscape at which existing ground based techniques have not been entirely well‐suited. Remote sensing, specifically the use of imaging spectrometry offers the potential to monitor the Belarusian landscape at opportune spatial and temporal resolutions. Vegetation has been shown to be an important agent in the cycling of radioactive isotopes in the environment and therefore a useful indicator of radionuclide contamination. This pilot research has focused on assessing the spectral response from Pinus sylvestris (dominant on the Belarusian landscape) at differing ages and with varying levels of ¹³⁷Cs contamination. Continuum removal was applied to the spectra showing that for older forests (c. 35 years) significant spectral differences between low and high contaminated sites exist at wavelengths that are causally related to foliar biochemicals. This was not the case for young forests (c. 15 years) where no significant differences were found. The results signify the potential to infer contamination levels from spectra of forests, partitioned by age, thus indicating the possibility of using imaging spectrometry to monitor radionuclide contamination, a possibility warranting further investigation.     

Supracutaneous vibrotactile perception threshold at various non-glabrous body loci

Researchers at the University of Nebraska-Lincoln are currently designing a wearable/portable neutron detector. As an alerting mechanism, the device will transmit vibration to the wearer's skin in the presence of hazardous levels of neutron radiation. The present study was designed to help in the ergonomically correct body placement of the neutron detection device while providing numerical values for vibratory thresholds at the surface of various non-glabrous body loci. The aim of the study was to investigate the underlying effects of locus stimulated, amount of subcutaneous fat around a specific body site and gender on low frequency vibration thresholds. Thirty-six participants, who were categorised by both dichotomous body fat group (high or low) and gender, were tested at 24 loci orthogonally located around six body sites: head; neck; upper arm; wrist; waist; ankle. The results indicated that frequency threshold depends significantly on the locus stimulated (p=0.001). The nape of the neck had the greatest sensitivity to low frequency stimulations, while the loci around the waist were least sensitive. Also, body fat significantly affected ability to perceive vibratory stimuli (p=0.048), with the mean frequency threshold of the low body fat group lower than that of the high body fat group. There was no statistical difference in thresholds with gender.     

Variable path length transmittance cell for ultraviolet, visible, and infrared spectroscopy and spectroelectrochemistry

The design and characteristics of a transmittance cell for ultraviolet, visible, and infrared spectroscopy and spectroelectrochemistry are described. Through modification of a previously reported design, this cell employs threaded glass connectors as insertion ports for either quartz- or silicon-windowed tubes, thus permitting essentially continuous variation of the optical path length from ～0.050 to 200 mm. Though the initial fabrication requires skillful glassblowing, once constructed, the cell's simple design allows for rapid and reproducible disassembly/reassembly between experiments. The utility of the cell for a diversity of fluid samples is demonstrated through applications to water, aqueous ferricyanide, ferrocene in methylene chloride, and acetone vapor.     

Unavoidable low level aflatoxin contamination of peanuts

A major portion of aflatoxin contamination of peanuts probably occurs when decayed or discolored peanuts are incompletely removed by sorting. Quality control measures have been instituted in the United States to insure that unavoidable aflatoxins in consumer peanuts and peanut products do not exceed 20 μg/kg. However, low level aflatoxin contamination, from trace amounts to about 50 μg/kg in sound mature unblemished peanuts, can occur before peanuts are dug. This low level contamination is not related to high levels of Aspergillus flavus infection or to current production practices. Low level aflatoxin contamination of peanuts may be endemic, and current sorting procedures may not be effective in removing unblemished contaminated peanuts.     

Surface recording of His-Purkinje activity on an every-beat basis without digital averaging

Efforts to record evidence of electrical activity from the body surface originating in the His bundle or bundle branches have been reported since 1973. Almost exclusively, these techniques have required digital averaging of 50-100 sequential cardiac cycles. For immediate diagnostic, therapeutic and prognostic application, recording on an every-beat basis is highly desirable. This is especially important in instances of changing atrioventricular conduction, arrhythmias or less-than-constant RR intervals. Our object has been to develop a system for more nearly optimal noise reduction, to avoid the disadvantages of serial signal averaging, and to be able to record His-Purkinje activity in man on an every-beat basis. Using multiple parallel inputs wih linear amplification, additional logarithmic amplification, some bandpass filtering, and a logic circuit that ultimately examines and accepts or rejects a deflection as "true" signal, we can record, in most instances, on a beat-by-beat basis, this very valuable component of the cardiac electrical cycle.     

Modeling and analysis of radio frequency connector degradation using time domain reflectometry technique

Radio frequency (RF) connectors play an important role in electronic and communication systems. Their reliability behavior directly affects the integrity of transmitted signals and degradation in the contact surface reduces reliability. In this work, a combination of experimental and theoretical analysis was used to investigate the effects of contact interface degradation in RF connectors using time domain reflectometry (TDR), and the TDR analysis technique had been employed to identify the faulty position. A series of experiments was conducted to measure the reflected voltages using a network analyzer for time domain analysis and the position of the degraded contact surface was identified. An equivalent circuit model was developed, and the failure mechanism analyzed. It was found that when the connector initially degrades, the inductive characteristics increase. As further degradation occurs, the inductive characteristic will decrease, and the resistance characteristics will become more significant. The simulation and experimental results show good consistency each other. The contact degradation process of RF connector and TDR variations under different degradation levels were performed from the perspective of the time domain.     

Study of PAH dissipation and phytoremediation in soils: comparing freshly spiked with weathered soil from a former coking works

A comparison was made between the dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil freshly spiked with pure PAHs, soil spiked with a coal tar mixture and a contaminated soil from a former coking works where the PAHs had been present for more than a century. The potential of five selected plant species for phytoremediation was investigated. The levels of all 7 PAHs in chemically amended soil, both planted and unplanted, fell significantly (>80% reduction) over the 12 weeks of the growing trial. In the coal tar treated soils all PAHs were significantly reduced. In both the planted and unplanted soils the 2-3 ringed compounds demonstrated much greater loss (>77%) than the 4-6 ringed (16-39%). The 3-4 ringed compounds demonstrated strong evidence of phytoremediation but not the 5-6 ringed. The coking soil showed limited reduction (7-24%) of all 12 PAHs present. There was little difference in dissipation between the PAHs and little evidence of a phytoremediation effect in coking soil. The results demonstrated that the form in which PAHs were added to soil influenced their susceptibility to dissipation. Therefore, predictions of PAH dissipation from laboratory amended soil do not reflect the true situation in the field.     

Health Assessment of Polycyclic Aromatic Hydrocarbon Mixtures: Current Practices and Future Directions

The U.S. EPA's Integrated Risk Information System (IRIS) program has initiated a health assessment for polycyclic aromatic hydrocarbon (PAH) mixtures. The IRIS program develops EPA consensus scientific positions on potential human health effects from chronic exposure to chemicals. Currently, the IRIS database contains health assessments for the toxic effects of exposure to coke oven emissions, creosote, diesel emissions, and 15 individual PAH compounds. As a whole, these assessments do not consider issues related to the environmental occurrence of PAH compounds as complex mixtures. Risk assessment of PAH mixtures has been hindered by a lack of information on the composition and toxicity of specific mixtures, the components that contribute most to toxicity, and the interactions and differences in mode of action between components. The state-of-the-science has advanced considerably in the past decade and will play a key role in the development of the health assessment. Consideration of these issues led to an EPA-sponsored Workshop on Approaches to PAH Health Assessment in October 2001. The current practices of the EPA regarding the health assessment of PAH compounds and future directions of the agency are discussed in this article.