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D J Gibson

Publications and source records attributed to D J Gibson.

12 recordsLinked to original sources
PubMed2006

Stream insect occupancy-frequency patterns and metapopulation structure.

An understanding of the distribution patterns of organisms and the underlying factors is a fundamental goal of ecology. One commonly applied approach to visualize these is the analysis of occupancy-frequency patterns. We used data sets describing stream insect distributions from different regions of North America to analyze occupancy-frequency patterns and assess the effects of spatial scale, sampling intensity, and taxonomic resolution on these patterns. Distributions were dominated by satellite taxa (those occurring in or=90% of sites) determined the overall modality of occupancy-frequency patterns. The proportions of satellite taxa increased with spatial scale and showed positive relationships with sampling intensity (r2=0.74-0.96). Furthermore, analyses of data sets from New York (USA) showed that generic-level assessments underestimated the satellite class and occasionally shifted occupancy-frequency distributions from unimodal to bimodal. Our results indicate that, regardless of species- or generic-level taxonomy, stream insect communities are characterized by satellite species and that the proportion of satellite species increases with spatial scale and sampling intensity. Thus, niche-based models of occupancy-frequency patterns better characterize stream insect communities than metapopulation models such as the core-satellite species hypothesis.

Animals↗
PubMed2005

Classical theory of Compton scattering: assessing the validity of the Dirac-Lorentz equation.

The Dirac-Lorentz equation describes the dynamics of a classical point charge in an electromagnetic field, accounting for radiative effects in a manifestly covariant and gauge-invariant manner. The validity of this equation is assessed by direct comparison between the Dirac-Lorentz dynamics of an electron subjected to a plane wave in vacuum and the well-known recoil associated with Compton scattering. In the small recoil limit, the classical Dirac-Lorentz is shown to yield the correct momentum transfer. For larger values of the recoil, the quantum scale appears explicitly, and the classical Dirac-Lorentz equation does not properly model this situation, as shown by deriving an exact analytical solution for a monochromatic plane wave of wave number k0 to any order in k0r0, where r0 is the classical electron radius.

Journal Article↗
PubMed1998

Randomized prospective trial of early versus delayed feeding after percutaneous endoscopic gastrostomy placement.

OBJECTIVE: By convention, most clinicians delay feeding through the gastrostomy tube until 24 h after placement. However, evidence is lacking to support the rationale for such a delay in PEG use. This randomized, prospective study was designed to assess the safety of early feeding after PEG placement. METHODS: One hundred-twelve patients referred for PEG were randomized to begin tube feedings at 4 h (group A) or at 24 h (group B) after placement. All patients received prophylactic antibiotics. Full-strength Isocal was administered with the following schedule: day 1, 100 ml every 4 h for six feedings; day 2, 200 ml every 4 h for six feedings. Immediately before each scheduled feeding, gastric residual volume was recorded and the next feeding was withheld if the residual volume was > 50 percent (gastric retention). Patients were evaluated on day 1, day 2, day 7, and day 30 for major and minor complications. RESULTS: The two groups were similar with regard to age, gender, baseline nutritional status, and indications for PEG placement. On the first day of feeding, 14 of 57 patients (25%) in group A, but only five of 55 patients (9%) in group B, had evidence of gastric retention, p = 0.029. The proportion of patients with high gastric residual volumes was not significantly different on day two. In group B, one death occurred because of aspiration of gastric contents on day 2. All other complications were minor and did not differ significantly between the two groups. CONCLUSIONS: Early initiation of PEG feedings is safe, well tolerated, and reduces cost by decreasing hospital stay.

Adult↗
PubMed1994

Eugene W. Caldwell Lecture. Technology: the key to controlling health care costs in the future.

The American health care financing system is in a state of crisis. The rising cost of health care and the progressive difficulty Americans are experiencing in accessing the system have produced a great national debate concerning the future of medicine in America. Current health care cost trends, which are not sustainable, are projected to consume 37% of the gross national product by the year 2030. The financing system that supports the health care system is failing. The number of uninsured residents is growing more than twice as fast as the number with health insurance. The legitimate concern about the spiraling cost for medicine has focused attention on seeking root causes. Critics have focused on technology as the single most important factor in driving the cost trends in medicine upward. They have concluded that "long-term control of the rate of increase in expenditures requires that we curb the development and diffusion of clinically useful technology." These critics have not made their case, because they base their conclusions on hospital-derived data. These data are inaccurate because of the phenomenon of "cost-shifting." The critics do not examine the important issue of productivity and do not have reliable data on the costs and benefits of new technologies. Finally, the critics do not take into account the issue of use and abuse of technology. This is particularly important in the ambulatory environment. To break the health care cost spiral, radiologists, as the keepers of new technology, must commit themselves to at least four fundamental initiatives. The current American hospital-based health system must be replaced with an ambulatory system; productivity must be the primary business goal for radiologists; pricing of new services should reflect actual resources consumed, not the in-patient services displaced; and radiologists must reassert their role as doctors' doctors. The health care cost spiral is a real national crisis. The mission for radiology is to introduce the minimally invasive, ambulatory system of the future. The costs for delivering care within the new system will be a fraction of former costs. My assignment is to present a perspective on the role radiology must play in introducing new imaging technology to medicine. One of the distinguishing features of American society is its fascination with technology. It is only natural that the American health care system reflects this orientation.

Cost Control↗
PubMed1985

Similarity of dynamic range adjustment in auditory nerve and cochlear nuclei.

Rate versus level functions were recorded for responses to best-frequency (BF) tones of 116 cochlear nucleus units and 53 auditory-nerve fibers in the presence of interrupted tone backgrounds and continuous noise backgrounds of various intensities. The backgrounds shifted the dynamic ranges of rate-level functions to higher test intensities, so in the presence of backgrounds, rate saturation occurred at higher intensities than in quiet. The shift in saturation intensity evoked by each background was measured by comparing the rate-level function recorded with the background to one recorded without. The relation between change in saturation intensity and background intensity could be approximated by the formula (formula: see text) delta Isat is the shift in saturation intensity, I is the background intensity, theta is the threshold for evoking shift, and A is the ratio of shift to background intensity re theta. In the appendix, it is shown that A is a measure of a unit's ability to avoid saturation by the background stimulus. The optimal value of A is unity, at which point a unit's operating range is infinite. The value of A depended on BF for interrupted tone backgrounds, but not for continuous noise backgrounds. For BF less than 10 kHz, the mean value of A for tone backgrounds was 0.33 in the auditory nerve, 0.37 in the ventral cochlear nuclei (VCN), and 0.47 in the dorsal cochlear nucleus (DCN). The difference between auditory nerve and VCN was not statistically significant. For BF greater than 10 kHz, the mean A was 0.16 in auditory nerve and 0.30 in VCN. The mean value of A for noise backgrounds was 0.79 in auditory nerve, 0.86 in VCN, 0.86 in DCN units of response types II and III, and 1.04 in DCN type IV units. Only the differences between DCN type IV and the non-DCN unit groups were statistically significant. The qualitative changes produced in rate-level functions by tone and noise backgrounds were similar in auditory nerve and cochlear nuclei except for DCN type IV units. The shifts in rate functions produced by interrupted tone backgrounds did not prevent saturation of the rate response at background intensities above the dynamic range of the unit as recorded in quiet. However, the rate response to test tones was preserved in the presence of all noise background levels used (up to a 30-dB spectrum level). The shift in rate function produced by the noise was almost sufficient to allow the unit to encode test intensity relative to noise background intensity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Effects of continuous noise backgrounds on rate response of auditory nerve fibers in cat.

This study describes the effects of broadband background noise on the average discharge rate to best-frequency (BF) tones of auditory nerve fibers in the cat. The effects of exposure to long-term continuous noise are compared to the effects of noise gated on and off simultaneously with test tones. Addition of background noise causes a shift of the dynamic portion of tone-evoked rate versus level functions to higher tone intensities. The shift occurs at a mean rate of 0.61 dB of shift for each 1-dB increment in noise level. The rate of shift is independent of best frequency and spontaneous discharge rate. The noise level at which the shift begins is frequency dependent and is consistent with the frequency-dependent bandwidths of auditory nerve fiber tuning curves. The adjustment of the dynamic range shows many similarities to two-tone suppression. Therefore, it is most likely that it is caused by suppression of the response to the BF test tone by energy present in the noise at surrounding frequencies. At high noise levels, the ability of auditory nerve fibers to respond to test tones is limited by the rate response to the noise. As noise level increases, the discharge rate it evokes approaches a fiber's saturation rate and ultimately eliminates the fiber's ability to respond to test tones. Low spontaneous rate fibers, which have been shown to have higher thresholds and wider dynamic range (17,29), are significantly more resistant to saturation by high noise levels. Exposure to broadband noise prior to onset of test tones produces an overall decrement in response rate. This phenomenon is similar to the effects of short-term adaptation (32) and seems to develop independently of the shift of dynamic range. At high noise levels, previous exposure to the noise produces a small dynamic range shift. This effect is similar to that produced by suppression but is smaller. The effect is occluded in continuous noise backgrounds by the adjustment of sensitivity produced by suppression.

Animals↗
PubMed1982

Interaural crosstalk in the cat.

The physiologically effective interaural acoustic crosstalk in cat was measured by means of binaural threshold differences for single auditory-nerve fibers and for cochlear microphonics. There were generally two maxima, at about 800 Hz and 3 kHz, attaining values as high as -25 dB (transmission to cochlea via contralateral ear re transmission via ipsilateral ear) in some cats. This figure could be reduced to -50 dB by mechanically isolating the acoustic drivers from each other and from the stereotaxic head frame.

Animals↗
PubMed1976

Hereditary C2 deficiency: diagnosis and HLA gene complex associations.

Nine families with genetically controlled C2 deficiency have been described where the propositii and family members are heterozygous C2 deficient. The diagnosis of hereditary C2 heterozygous deficiency was suspected on the basis of analysis for CH50, C2 protein, and C2 function, and then confirmed by family studies. Analysis of HLA antigens in these families supported the close association of C2 defiency and HLA-A10 and/or B18, particularly the latter. Analysis by MLC studies revealed recombination in one family between the HLA and B and D loci and in another family probable recombination between the D and C2 complement loci. Therefore, the order of the loci on the sixth chromosome is likely to be C2 complement, HLA-D, HLA-B, HLA-A.

Chromosome Mapping↗
PubMed1975

Re-examination of histocompatibility antigens found in patients with juvenile rheumatoid arthritis.

One hundred and twenty-three patients with juvenile rheumatoid arthritis and a similar number of controls were tissue typed for 30 HL-A antigens to determine if there were any associations between particular HL-A antigens and the disease. None were found. However, HL-A7 was found more frequently in patients with juvenile rheumatoid arthritis demonstrating tenosynovitis than in the population with juvenile rheumatoid arthritis as a whole. These observations fail to support the contention of others that HL-A-W27 is found more frequently than expected in such patients.

Adolescent↗