Determination of selected hydrocarbon concentrations in reformate using near infrared spectroscopy

Near infrared spectroscopy was used as a quantitative technique employing multiple linear regression and partial least squares regression for determining the concentration of hydrocarbon groups and individual hydrocarbons present in reformate, a refinery process stream. Models were generated for total aromatics, benzene, toluene, total xylenes and individual xylene isomers, ethylbenzene, total paraffins, n-hexane, n-heptane, total isoparaffins, isopentane, 2-methylhexane, total naphthenes, methylcyclopentane, and total olefins. Some models are being used with an on-line instrument to constantly monitor a reformate stream as it leaves the reforming unit, with a standard error of performance of 0.118 volume percent for the prediction of the benzene concentration for a six month period. This technique serves as a faster method which takes less than a minute to perform the operation, whereas the primary methods of gas chromatography can take in excess of three hours to perform. By providing reliable data, this faster analysis can lead to enhanced economics concerning analysis time and can be used on-line for better control of a refinery process

The use of kainic acid for studying the origins of scalp-recorded auditory brainstem responses in the guinea pig

Kainic acid was injected into the medial nucleus of the trapezoid body (MNTB) of guinea pigs to evaluate its use in studying generator loci of the scalp-recorded auditory brain stem response (ABR). Sound-evoked near-field potentials from the MNTB and far-field ABRs were recorded before, during and up to 2 h after the injections. Two hours post-injection, small amounts of kainic acid (0.25 nmol in 0.1 [mu]l of Ringer solution) resulted in neuronal destruction which histologically appeared confined to the MNTB. Larger amounts (10 nmol in 1.0 [mu]l) produced more extensive lesions. Regardless of the dose of kainic acid, near-field activity evoked by contralateral ear stimulation was almost totally abolished and ABR wave III amplitude was reduced by as much as 60%. In future studies, the use of excitotoxic amino acids to produce lesions within complex nuclear subdivisions of the auditory pathway may yield valuable information as to the relative contributions that brainstem structures make to the various waves comprising the ABR and about the behavioral effects that axon sparing lesions produce.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24227/1/0000487.pd

An energy-dependent step in aminoglycoside ototoxicity: Prevention of gentamicin ototoxicity during reduced endolymphatic potential

Guinea pigs received a bolus of gentamicin (10 mM for 5 min) by perilymphatic perfusion which normally led to an irreversible loss of the cochlear microphonic potential (CM). Various experimental conditions that reduced the endolymphatic potential (EP) were then superimposed on the gentamicin application. Reversible reductions in EP (and, concomitantly, in CM) were induced by asphyxia (3 min), intravenous furosemide (50 mg/kg), and perilymphatic perfusion of aminooxyacetic acid (10 mM). When the administration of gentamicin was initiated at the time of maximal EP reduction the usual irreversible gentamicin-induced decline of CM was prevented.The results indicate that a metabolic process is essential in the expression of gentamicin toxicity. The data are consistent with the inhibition of an energy-dependent transport of the aminoglycoside. Alternatively, the data are also compatible with the hypothesis that entry of gentamicin into hair cells is prevented by a reduction in their transmembrane electrical potential.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25874/1/0000437.pd

Analysis of histamine as a hair-cell transmitter in the lateral line of Xenopus laevis

The actions of histamine and histamine antagonists on afferent nerve activity were investigated in the lateral line of Xenopus laevis. Histamine (0.002-2.0 mM) had no effect on spontaneous activity or excitatory responses to water motion. In contrast, pyrilamine, an H1 receptor antagonist, suppressed spontaneous activity beginning at 0.01-0.05 mM. Below 0.3 mM the suppression was often preceded by a small excitatory response and responses to high (24-30 dB re threshold), but not low (0-18 dB) levels of water motion were selectively suppressed. Higher concentrations (0.3-2.0 mM) abolished spontaneous activity and suppressed responses at all levels of water motion. Cimetidine, an H2 receptor antagonist, had similar actions but was one-tenth as potent as pyrilamine. Tetrodotoxin (0.001-0.1 [mu]M), which blocks voltage-sensitive Na+ channels, mimicked the suppressive effects of the histamine antagonists. Histamine (2.0 mM) failed to block the actions of pyrilamine (0.1 mM) indicating its effects are mediated through a mechanism other than histamine receptors. In addition, pyrilamine (0.05-0.1 mM) non-selectively suppressed excitation to exogenously applied -glutamate (1.0-2.0 mM), -aspartate (1.0-2.0 mM), kainate (0.005-0.01 mM), and quisqualate (0.002-0.005 mM) and altered responses to (0.5-1.0 mM). The results are inconsistent with histamine being a transmitter in the Xenopus lateral line and reveal that the actions of histamine antagonists are nonspecific, possibly due, in part, to blockade of voltage-sensitive Na+ channels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28027/1/0000465.pd

Spatial representation of corticofugal input in the inferior colliculus: a multicontact silicon probe approach

The inferior colliculus (IC) is a well-established target of descending projections from the auditory cortex (AC). However, our understanding of these pathways has been limited by an incomplete picture of their functional influence within the three-dimensional space of the IC. Our goal was to study the properties and spatial representation of corticofugal input in the IC of guinea pigs with a high degree of spatial resolution. We systematically mapped neural activity in the IC using two types of silicon substrate probes that allow for simultaneous recording at multiple neural sites. One probe provided a high resolution in the dorsal-ventral plane and the other provided spatial resolution in the medial-lateral plane. Electrical stimulation of the ipsilateral AC produced excitatory responses in the IC with thresholds usually below 5–10 µA. First spike latencies were predominantly in the 6–20 ms range, although latencies from 3–5 ms were also observed. Broadly distributed unimodal spike patterns with modal latencies greater than 30 ms were occasionally seen. The excitatory responses to cortical stimulation were mostly unimodal and occasionally bimodal with a wide range of spike distribution patterns and response durations. Excitation was often followed by suppression of spontaneous activity. Suppression of acoustic responses was observed even when there was little or no response to electrical stimulation, suggesting spatial-temporal integration. A few of the responding neurons showed purely inhibitory responses to electrical stimulation, suggesting that there are disynaptic routes of corticocollicular inhibition. Detailed spatial mapping revealed that the response patterns and their durations had a characteristic spatial distribution in the IC.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46534/1/221_2003_Article_1671.pd

Summary of CPAS Gen II Parachute Analysis

The Orion spacecraft is currently under development by NASA and Lockheed Martin. Like Apollo, Orion will use a series of parachutes to slow its descent and splashdown safely. The Orion parachute system, known as the CEV Parachute Assembly System (CPAS), is being designed by NASA, the Engineering and Science Contract Group (ESCG), and Airborne Systems. The first generation (Gen I) of CPAS testing consisted of thirteen tests and was executed in the 2007-2008 timeframe. The Gen I tests provided an initial understanding of the CPAS parachutes. Knowledge gained from Gen I testing was used to plan the second generation of testing (Gen II). Gen II consisted of six tests: three singleparachute tests, designated as Main Development Tests, and three Cluster Development Tests. Gen II required a more thorough investigation into parachute performance than Gen I. Higher fidelity instrumentation, enhanced analysis methods and tools, and advanced test techniques were developed. The results of the Gen II test series are being incorporated into the CPAS design. Further testing and refinement of the design and model of parachute performance will occur during the upcoming third generation of testing (Gen III). This paper will provide an overview of the developments in CPAS analysis following the end of Gen I, including descriptions of new tools and techniques as well as overviews of the Gen II tests

Simulating New Drop Test Vehicles and Test Techniques for the Orion CEV Parachute Assembly System

The Crew Exploration Vehicle Parachute Assembly System (CPAS) project is engaged in a multi-year design and test campaign to qualify a parachute recovery system for human use on the Orion Spacecraft. Test and simulation techniques have evolved concurrently to keep up with the demands of a challenging and complex system. The primary simulations used for preflight predictions and post-test data reconstructions are Decelerator System Simulation (DSS), Decelerator System Simulation Application (DSSA), and Drop Test Vehicle Simulation (DTV-SIM). The goal of this paper is to provide a roadmap to future programs on the test technique challenges and obstacles involved in executing a large-scale, multi-year parachute test program. A focus on flight simulation modeling and correlation to test techniques executed to obtain parachute performance parameters are presented

Potassium-induced release of endogenous glutamate and two as yet unidentified substances from the lateral line of Xenopus laevis

The release of endogenous glutamate and other primary amines from the lateral line of Xenopus laevis was studied using an in vitro superfusion technique and high performance liquid chromatography. Potassium stimulation (50 mM KCl) applied to 60 or 120 lateral-line organs dissected from the skin and pooled in a perfusion chamber induced the release of glutamate and aspartate. The release of aspartate was smaller than that of glutamate and more variable. A variable release of two, as yet, unidentified substances was also detected. In low calcium (0.1 mM CaCl2), high magnesium (10 mM MgCl2) solution, 50 mM potassium failed to induce an increase in glutamate, aspartate and the two unknowns, suggesting they are released in a transmitter-like manner. The technique presents a new and simple method for studying transmitters in hair-cell systems. Although other interpretations are possible, the results are consistent with the hypothesis that glutamate is a hair-cell transmitter and suggest a potential role for other substances in the transduction process, perhaps as neuromodulators.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27844/1/0000254.pd