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K Keil

Publications and source records attributed to K Keil.

17 recordsLinked to original sources
PubMed2000

Large-scale thermal events in the solar nebula: evidence from Fe,Ni metal grains in primitive meteorites

Chemical zoning patterns in some iron, nickel metal grains from CH carbonaceous chondrites imply formation at temperatures from 1370 to 1270 kelvin by condensation from a solar nebular gas cooling at a rate of approximately 0.2 kelvin per hour. This cooling rate requires a large-scale thermal event in the nebula, in contrast to the localized, transient heating events inferred for chondrule formation. In our model, mass accretion through the protoplanetary disk caused large-scale evaporation of precursor dust near its midplane inside of a few astronomical units. Gas convectively moved from the midplane to cooler regions above it, and the metal grains condensed in these parcels of rising gas.

Journal Article↗
PubMed1999

Local and global stereopsis in the horse.

Although horses have laterally-placed eyes, there is substantial binocular overlap, allowing for the possibility that these animals have stereopsis. In the first experiment of the present study we measured local stereopsis by obtaining monocular and binocular depth thresholds for renal depth stimuli. On all measures, the horses' binocular performance was superior to their monocular. When depth thresholds were obtained, binocular thresholds were several times superior to those obtained monocularly, suggesting that the animals could use stereoscopic information when it was available. The binocular thresholds averaged about 15 min arc. In the second experiment we obtained evidence for the presence of global stereopsis by testing the animals' ability to discriminate between random-dot stereograms with and without consistent disparity information. When presented with such stimuli they showed a strong preference for the cyclopean equivalent of the positive stimulus with the real depth. These results provide the first behavioral demonstration of a full range of stereoscopic skills in a lateral-eyed mammal.

Animals↗
PubMed1998

53Mn-53Cr dating of fayalite formation in the CV3 chondrite Mokoia: evidence for asteroidal alteration.

Fayalite grains in chondrules in the oxidized, aqueously altered CV3 chondrite Mokoia have large excesses of radiogenic chromium-53. These excesses indicate the in situ decay of short-lived manganese-53 (half-life = 3.7 million years) and define an initial 53Mn/55Mn ratio of 2.32 (+/-0.18) x 10(-6). This ratio is comparable to values for carbonates in CI and CM chondrites and for several classes of differentiated meteorites. Mokoia fayalites formed 7 to 16 million years after Allende calcium-aluminum-rich inclusions, during hydrothermal activity on a geologically active asteroid after chondritic components had ceased forming in the solar nebula.

Chromium Isotopes↗
PubMed1998

Going Nondispersive.

: The energy-dispersive Si(Li) X-ray spectrometer, introduced 30 years ago into electron probe microanalysis (EPMA) by R. Fitzgerald et al., has profoundly affected the development of microanalysis. It offers many advantages over the wavelength-dispersive crystal spectrometer. It has no moving parts and covers the full energy range of interest in EPMA. There is no defocusing over large distances on the specimen, the efficiency of the device is high, varies slowly and continuously with atomic number, and can be predicted fairly accurately, and, most importantly, all emission lines are detected and can be observed simultaneously. The one remaining disadvantage of the Si(Li) spectrometer is its poorer energy resolution. Solid-state detection devices now under development promise to achieve resolution comparable to that of the crystal spectrometer.

Journal Article↗
PubMed1997

Transient and sustained activity in a distributed neural system for human working memory.

Working memory involves the short-term maintenance of an active representation of information so that it is available for further processing. Visual working memory tasks, in which subjects retain the memory of a stimulus over brief delays, require both the perceptual encoding of the stimulus and the subsequent maintenance of its representation after the stimulus is removed from view. Such tasks activate multiple areas in visual and prefrontal cortices. To delineate the roles these areas play in perception and working memory maintenance, we used functional magnetic resonance imaging (fMRI) to obtain dynamic measures of neural activity related to different components of a face working memory task-non-selective transient responses to visual stimuli, selective transient responses to faces, and sustained responses over memory delays. Three occipitotemporal areas in the ventral object vision pathway had mostly transient responses to stimuli, indicating their predominant role in perceptual processing, whereas three prefrontal areas demonstrated sustained activity over memory delays, indicating their predominant role in working memory. This distinction, however, was not absolute. Additionally, the visual areas demonstrated different degrees of selectivity, and the prefrontal areas demonstrated different strengths of sustained activity, revealing a continuum of functional specialization, from occipital through multiple prefrontal areas, regarding each area's relative contribution to perceptual and mnemonic processing.

Adult↗
PubMed1996

Functional magnetic resonance imaging of human visual cortex during face matching: a comparison with positron emission tomography.

Cortical areas associated with the perception of faces were identified using functional magnetic resonance imaging (fMRI). T2*-weighted gradient echo, echo-planar MR images were obtained using a modified 1.5-T GE Signa MRI. In all nine subjects studied, performance of a face-matching task was associated with a region of significantly increased MR signal in the ventral occipitotemporal cortex, extending from the inferior occipital sulcus to the lateral occipitotemporal sulcus and fusiform gyrus. Smaller and more variable signal increases were found in dorsolateral occipitoparietal cortex near the intraparietal sulcus. Signal decreases were found in the angular gyrus and posterior cingulate cortex. Single-subject fMRI analyses revealed discrete areas of activation with well-defined borders. Group analyses of spatially smoothed fMRI data produced results that replicated most aspects of previous studies of face processing using positron emission tomography (PET). These results show that PET and fMRI identify functional areas with similar anatomical locations. In addition, fMRI reveals interindividual variation in the anatomical location of higher-level processing areas with greater anatomical precision.

Adult↗
PubMed1996

Horses are sensitive to pictorial depth cues.

In an attempt to demonstrate whether horses could make use of pictorial cues to depth, two were trained initially to make a relative-line-length discrimination between two lines placed one above the other. Psychophysical measurement of their discrimination thresholds showed that from a viewing distance of approximately 160 cm they could reliably distinguish a lower line of 10 cm from an upper one of 14 cm. In the second phase of the experiment, two lines of equal length were superimposed on a photograph of a set of railway tracks with many pictorial cues to depth, or a photograph of a pastoral scene with fewer obvious depth cues. To humans, the railway tracks created a Ponzo illusion, making the upper line-appear longer. When the horses were allowed to choose between the photographs, they overwhelmingly chose the display containing the converging railway tracks. Control experiments ruled out alternative explanations, leading to the conclusion that horses are susceptible to a Ponzo illusion created by depth cues in photographs.

Animals↗
PubMed1995

Signatures of the martian atmosphere in glass of the Zagami meteorite.

Isotopic signatures of nitrogen, argon, and xenon have been determined in separated millimeter-sized pockets of shock-melted glass in a recently identified lithology of the meteorite Zagami, a shergottite. The ratio of nitrogen-15 to nitrogen-14, which is at least 282 per mil larger than the terrestrial value, the ratio of xenon-129 to xenon-132 = 2.40, and the argon isotopic abundances match the signatures previously observed in the glassy lithology of the Antarctic shergottite EETA 79001. These results show that the signatures in EETA 79001 are not unique but characterize the trapped gas component in shock-melted glass of shergottites. The isotopic and elemental ratios of nitrogen, argon, and xenon closely resemble the Viking spacecraft data for the martian atmosphere and provide compelling evidence for a martian origin of the two shergottites and, by extension, of the meteorites in the shergottites-nakhlites-chassignites (SNC) group.

Argon↗
PubMed1994

Expectant management of placenta previa: cost-benefit analysis of outpatient treatment.

OBJECTIVE: In this study outpatient and inpatient expectant management for complete placenta previa were compared in terms of maternal and neonatal outcome and overall cost. STUDY DESIGN: We reviewed the outcomes and hospital costs of 72 mother-infant pairs where the pregnancy was complicated by second- or third-trimester placenta previa and was managed expectantly either with hospitalization or outpatient bed rest. The data were analyzed with the two-sided unpaired t test, chi 2, and simple correlation analysis. RESULTS: There were no differences in maternal morbidity as measured by estimated total blood loss, number of blood transfusions, nadir hematocrit, or need for emergency delivery. Fetal mortality was comparable in both groups, and there were no significant differences in neonatal morbidity as measured by gestational age, birth weight, 5-minute Apgar score, or occurrence of fetal distress. Among outpatients the number of maternal hospital days was reduced by 50% (p < 0.01). Outpatient management achieved a hospital cost reduction of 48.5% for mothers (p < 0.001) and 39.4% for mother-infant pairs (p < 0.05). CONCLUSION: In selected patients outpatient management of complete placenta previa can be cost-effective and safe.

Adult↗
PubMed1992

Visual acuity in the horse.

We assessed the ease with which horses could learn visual discriminations and measured their resolution acuity. We trained three horses to press their noses against one of two large wooden panels to receive a small food reward. Following training on a series of two-choice discrimination tasks, resolution acuity was measured. Although there was some variability between animals, the best acuity obtained was 23.3 c deg-1. Within the margin of error imposed by limited anatomical data, the obtained values are consistent with predictions based on retinal ganglion cell density estimates and posterior nodal distance/axial length ratios. They suggest that the resolution acuity of the horse is limited by ganglion cell density in the temporal portion of the narrow visual streak.

Animals↗
PubMed1991

[Drug and non-drug tumor pain therapy in ENT medicine].

The basic of analgesic therapy in patients with advanced cancer of the head and neck is the regular application of analgesics and adjuvant analgesics. Radiotherapy is the treatment of choice in patients suffering from severe pain by bone metastases. Analgesic-resistant pain of dura in patients with tumour infiltration of the skull base is an indication for intraventricularly application of opioids by neurosurgeon.

Analgesics↗
PubMed1989

Oxidation of polyethylene glycols by alcohol dehydrogenase.

The present studies were undertaken to investigate the enzymology of a fatal toxic syndrome that resulted from the absorption and subsequent oxidation of polyethylene glycol (PEG). The presence of organic acids of PEG in the blood of poisoned patients and in an animal model suggested that the metabolism of PEG involved sequential oxidations by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase. A key question concerned the ability of ADH to initiate this pathway for oxidation of PEG. In the present studies the oxidation of PEG homologues by ADH was characterized. The polymer homologues of ethylene glycol from n = 1 to n = 8 were used as substrates. ADH catalyzed the oxidation of each of these PEGs. The oxidation of PEG was inhibited by the ADH inhibitor 4-methylpyrazole. With the exception of diethylene glycol, the Km decreased as the homologue number increased, and the Vmax decreased progressively through the series. The concentrations of PEG in the blood of poisoned humans and animals were 0.06 to 0.8 Km of ADH for all the PEG homologues above the triethylene glycol. These investigations establish ADH as a candidate enzyme for mammalian metabolism of PEG and thus suggest that specific inhibitors of ADH may prove to be useful as tools to treat PEG poisoning.

Alcohol Oxidoreductases↗
PubMed1987

A method for the characterization of aldehyde dehydrogenase with use of alcohol dehydrogenase.

The metabolism of alcohols and glycols is catalyzed sequentially by alcohol and aldehyde dehydrogenases to toxic oxidation products. The study of aldehyde dehydrogenase (ALDH) is complicated by instability and limited availability of aldehyde substrates. We have synthesized aldehydes by use of alcohol dehydrogenase (ADH)-catalyzed oxidation of alcohols; aldehydes produced were immediately used as substrates for ALDH measurements on a centrifugal analyzer. The accuracy of the ADH-ALDH assay was investigated by comparison of the reaction kinetics determined by this method with those obtained using commercially available aliphatic aldehydes as substrates. The mean Michaelis constants determined by the two methods were identical for butyraldehyde and propionaldehyde (3.7 and 4.6 mumol/L, respectively). For glycoaldehyde, values agreed within experimental error: 670 +/- 50 mumol/L and 720 +/- 20 mumol/L using commercial substrate and the proposed method, respectively. This technique allows kinetic studies of the oxidation of a wide variety of toxic aldehydes.

Alcohol Dehydrogenase↗
PubMed1968

Solid-state energy-dispersion spectrometer for electron-microprobe x-ray analysis.

Improved lithium-drifted silicon solid-state detectors allow detection and energy dispersion of x-rays of about 3 to 30 kiloelectron volts in the electron-microprobe x-ray analyzer. Energy resolution is sufficient to separate peaks of characteristic x-rays of elements adjacent in the periodic system at atomic number 20 and higher. The detected x-ray spectrum emitted from an unknown sample can be recorded with a multichannel analyzer in approximately 60 seconds.

Electron Probe Microanalysis↗
PubMedDate not supplied

Object and spatial visual working memory activate separate neural systems in human cortex.

Human and nonhuman primate visual systems are divided into object and spatial information processing pathways. In the macaque, it has been shown that these pathways project to separate areas in the frontal lobe and that the ventral and dorsal frontal areas are, respectively, involved in working memory for objects and spatial locations. A positron emission tomography (PET) study was done to determine if a similar anatomical segregation exists in humans for object and spatial visual working memory. Face working memory demonstrated significant increases in regional cerebral blood flow (rCBF), relative to location working memory, in fusiform, parahippocampal, inferior frontal, and anterior cingulate cortices, and in right thalamus and midline cerebellum. Location working memory demonstrated significant increases in cRBF, relative to face working memory, in superior and inferior parietal cortex, and in the superior frontal sulcus. Our results show that the neural systems involved in working memory for faces and for spatial location are functionally segregated, with different areas recruited in both extrastriate and frontal cortices for processing the two types of visual information.

Adult↗