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Biomedical subjects

D Eichler

Publications and source records attributed to D Eichler.

At least 19 recordsLinked to original sources
PubMed2001

Slow proliferation as a survival advantage: an attempt to resolve a paradox.

A model is proposed for immunological high zone- and self-tolerance that is based on the concept of overstimulation of replication: It is demonstrated that if proliferation is hindered by delayed response to nutritional deficiency, then under competitive conditions slower proliferation can become a survival advantage. This offers a resolution of the paradox that self-antigens promote both positive and negative selection in the development of lymphocytes. It also suggests that maintaining nutrition and caloric intake at a minimal level can prolong the survival of cancer patients if the cancer cells replicate more rapidly than healthy ones.

Cell Division↗
PubMed2000

Nonthermal optical transients from relativistic fireballs

A general upper bound is derived on the total energy in incoherent nonthermal transients at frequency nu from relativistic fireballs with bulk Lorentz factors gamma and observed duration Deltat, and shown to be about 10(-2)[gammanuDeltat](3) ergs. It is suggested that detection in the optical can be achieved with the next generation of ground based gamma ray telescopes and/or small optical telescopes. Phenomena within the Galaxy such as accretion disk flares and neutron star magnetospheric discharges might be discovered in this way.

Journal Article↗
PubMed2000

Hydrodynamic collimation of gamma-ray-burst fireballs

Analytic solutions are presented for the hydrodynamic collimation of a relativistic fireball by a surrounding baryonic wind emanating from a torus. The opening angle is shown to be the ratio of the power output of the inner fireball to that of the exterior baryonic wind. The gamma ray burst 990123 might thus be interpreted as a baryon-poor jet (BPJ) with an energy output of order 10(50) erg or less, collimated by a baryonic wind from a torus with an energy output of order 10(52.5) erg, roughly the geometric mean of the BPJ and its isotropic equivalent.

Journal Article↗
PubMed2000

Landau excitation of spiral density waves in an inhomogeneous disk of stars

Drift-resonant Landau excitation of spiral density waves in a stellar disk of flat galaxies is proposed. This excitation of waves is suggested as a mechanism for the formation of structural features such as spiral arms and the slow dynamical relaxation of galaxies in a regime of hydrodynamical Jeans-type stability.

Journal Article↗
PubMed2000

Leptin binding activity (LBA) in plasma of nondiabetic and diabetic adolescents and obese children: relation to auxologic and hormonal data.

Leptin circulates in serum bound to high molecular weight proteins. Hypothesizing that leptin binding proteins may regulate the functional efficiency of leptin, we characterized auxologic and hormonal factors that influence leptin binding in three disparate groups: normal adolescents, obese children, and teenagers with type I diabetes mellitus (IDDM). Specific leptin binding activity (sLBA) was assessed by column chromatography after incubation of serum with 125I-leptin in the presence and absence of excess unlabeled leptin. Mean sLBA was 17.0 +/- 7% (SD) in the healthy adolescents (n=41), 6.6 +/-4.3% in the obese children (n=26), and 14.9 +/-7.3% in the diabetic teenagers (n=17). At any value of sLBA, obese children had higher serum leptin levels than non-obese adolescents or diabetic teenagers, consistent with "leptin resistance" in the obese group. sLBA was higher in males than in females only in those with diabetes (18.6 +/- 7.3 vs 10.9 +/- 5.1%, p<0.05). sLBA correlated inversely with serum insulin-like growth factor-I values in the normal group (r= -0.45, p<0.01) and with insulin in the obese children (r= -0.53, p<0.01). There was no correlation between sLBA or serum leptin values and HbA1c, in the diabetic group. The serum leptin concentration was the principal determinant explaining the total variability of sLBA in all three cohorts. However, body mass index (BMI = weight/ height2) accounted for more of the total variability of percent specific binding in the healthy adolescents than in the other groups. We conclude that sLBA reflects circulating leptin levels, body composition, and hormonal milieu. Thus, in addition to leptin, qualitative and quantitative characteristics of leptin binding may play a physiological role in the regulation of appetite and in the "leptin resistance" of obesity.

Adolescent↗
PubMed1992

[In-vitro research on the marginal adaptation of composites with the use of different dentin adhesives].

The aim of this investigation was the check and evaluation of 7 various dentin adhesives regarding their influence on the connection between dentin resp. enamel and composite filling. For that cylindrical cavities in dental crowns (enamel cavities) and roots (dentin cavities) were prepared and treated with dentin adhesives and composite materials. One part of the test teeth was subjected to loads storage in aqueous solution and thermocycling. The marginal adaptation of the composite filling was checked by means of the dye penetration test. The evaluation was made after cutting the teeth in the stereo microscope TECHNIVAL 2 (Carl Zeiss Jena) at 16-resp. 25 magnifications and defined criteria. The fillings in cavities bound by enamel exhibited a very good marginal adaptation of the composite. The location of the dentin cavity (crown or root dentin) had no significant influence on the fitting of the filling. A clear penetration of dye could be observed with the fillings in the dentin with and without adhesives, which considerably intensified after thermocycling. Best results with regard to the marginal adaptation were obtained with Scotchbond 2, Mirage-Bond and Cavex-Clearfil-Newbond. A restoration without a marginal gap was not possible.

Composite Resins↗
PubMed1990

[Experiences with material and clinical properties of the Ni/Cr-alloy Gisadent NCS1 under consideration of the Silicoating-procedure].

Investigations to the corrosive behavior in artificial saliva, to shear-bond-strengths and to the formation of gaps in composite-alloy-compounds produced by using the SILICOATING-PROCEDURE show the better properties of the alloy GISADENT NCS1 respectively to NCA. The clinical results are in agreement with these facts, but it is necessary to pay attention to the small changes in the technological process.

Chromium Alloys↗
PubMed1987

Distributed reacceleration of cosmic rays.

We develop a model in which cosmic rays, in addition to their initial acceleration by a strong shock, are continuously reaccelerated (e.g., by weak shocks) while propagating through the galaxy. The equations describing this acceleration scheme are solved analytically (approximating ionization losses by a cutoff) and numerically. Solutions for the spectra of primary and secondary cosmic rays are given in a closed analytic form, and they allow a rapid search in parameter space for viable propagation models with distributed reacceleration included. The observed boron-to-carbon ratio can be reproduced by the reacceleration theory over a range of escape parameters, some of them quite different from the standard "leaky box" model. It is also shown that even a very modest amount of reacceleration by strong shocks causes the boron-to carbon ratio to level off at sufficiently high energies, and this effect may be observed in the CRNE data. Several other curiosities in the data may be explained naturally if a modest amount of distributed reacceleration is invoked, including (a) the apparent truncation at low energy in the otherwise exponential pathlength distribution associated with the leaky box model, (b) the sub-iron isotopic anomalies and other effects noted by Silberberg et al., and (c) the discrepancy between the reported 10Be lifetime and the lifetime of cosmic rays in the dense strata of the galactic disk.

Acceleration↗
PubMed1986

[Isolation of antibodies against soy protein from the eggs of immunized laying hens].

The authors report on their experiences with immunization of laying hens with alpha-, alpha'- and beta-conglycinin, and on the isolation of specific antibodies from the yolks. Activity and specificity of the immunoglobulins were tested by an enzyme-linked immuno sorbent assay (ELISA). This method of antibody production proved to be very convenient, especially in regard to the high yield of antibodies and the easy handling of the animals. The necessity of using specific antisera for quantitative immunoassays is pointed out.

Animals↗
PubMed1983

Comparative study on the distribution of alpha- and gamma-hexachlorocyclohexane in the rat with particular reference to the problem of isomerization.

Blood levels and tissue distributions of alpha-, beta-, gamma- and delta-hexachlorocyclohexane (HCH) were studied following oral administration of alpha-HCH and gamma-HCH to rats. Following administration of alpha-HCH, there was no evidence of beta-HCH, gamma-HCH or delta-HCH, nor could transformation into alpha-HCH, beta-HCH or delta-HCH be detected after exposure to gamma-HCH. After eight weeks of administration, tissue retention of alpha-HCH was 10-20 times greater than that of gamma-HCH. gamma-HCH was eliminated to a much greater extent than alpha-HCH from the tissues, and in particular from fatty tissue. alpha-HCH accumulated in fat and brain, while gamma-HCH showed very low affinity for lipid.

Animals↗
PubMed1982

Chlorflurenol-methyl in soil: degradation, leaching, and effects on microbiological processes.

Tests were conducted with the synthetic growth regulator chlorflurenol-methyl to investigate its rate of degradation in soil, leaching behavior, and possible side-effects on the soil microflora and on soil physiological processes. With two sandy soils (Ct = 1.0 and 2.58%) which were treated with 11.35 mg kg-1 chlorflurenol-methyl (congruent to 2.8 kg a.i. ha-1), over 90% of the compound disappeared within 4 to 8 days. The degradation products were 2-chloro-9-hydroxyfluorene-9-carboxylic acid and 2-chlorofluorenone, which undergo further decomposition. In leaching tests with three sandy soils (Ct = 0.69, 1.0 and 2.58%), chlorflurenol-methyl was not washed from the soil; however, with one soil (0.69% C), very small residues were observed in the effluent identified as 2-chlorofluorenone. In side-effects experiments with a parabrown (Ct = 1.26%) and a chernozem soil (Ct = 2.3%), which were treated with 1 and 10 mg kg-1 chlorflurenolmethyl, no persistent inhibition of anaerobic or aerobic nitrogen fixation (C2H2-reduction) was detected. Ammonification, nitrification, and mineralization of soluble starch were also not influenced. The mineralization of cellulose in compost soil (Ct = 13.59%) was temporarily delayed; however, this delay was later compensated for by a higher mineralization rate. The colonization density of fungi on soil particles and the numbers of bacteria, actinomycetes, and fungi were not negatively influenced. Chlorflurenol-methyl does not significantly influence these microbiological processes and populations in the soil.

Actinomycetales↗