showing 36 of ~574560 from 574555 documents
Structure of 5,17-dimethyl-11,23-dioctylcalix[4]arene
1991
The title compound C46O4H60 crystallizes in the triclinic space group, P¯1, witha=11.584(2),b=16.261(2),c=11.172(1) A,α=103.15(8),β=95.68(1),γ=96.85(1)°. The structure was solved by direct methods, and refined by weighted full-matrix least squares toR=0.097. This is the second calix[4]arene with two different alkyl substituents atpara positions of the phenolic rings. The macrocycle adopts the cone conformation. Interactions CH3-π are established between two calixarenes related by a center of symmetry. Comparisons are made between the conformation of this molecule and that of symmetrically substituted calix[4]arenes.
Fluctuating food supply affects the clutch size of Tengmalm's owl independent of laying date.
1991
In western Finland, yearly median laying dates of Tengmalm's owls varied from 14 March to 27 April during 1973–1989 and were negatively correlated with the winter densities of voles. Yearly mean clutch sizes varied from 4.0 to 6.7 and were more closely related to the spring than to the winter densities of voles. The yearly mean clutch size decreased with yearly median laying date. The 3-year vole population cycle is typical of the study area. The start of egg-laying was earliest in the peak phase of the cycle (median laying date 22 March), when vole numbers are high during egg-laying, but decline rapidly to low numbers in the next autumn or winter. In the increase phase (1 April) vole abund…
Thermoanalytical studies on sodium 1,2-naphthoqoinone oximesolfonates
1991
Abstract Five sodium 1,2-nitrosonaphtholsulfonatea were prepared or purified and their thermal behaviour studied by TG, DTG and DSC. Pyrolysis MS technique was used to identify evolved gases and FTIR to characterize residuals. The water contents depended on preparation and conservation. The decomposition was analysed in three stages which can be formed by one or more steps. The final product was sodium sulfate in air at 530 °C and the mixture of carbon and sodium sulfide at 950 °C in nitrogen. The structure effects on decomposition is discussed.
Analysis of high-frequency rotational angioplasty-induced echo contrast.
1991
During high-frequency rotational angioplasty (HFRA), myocardial contrast enhancement (echo contrast) was observed by means of two-dimensional echocardiography. In order to evaluate the echo contrast produced by HFRA, an in vitro experimental model was built using a cylinder with the HFRA catheter scanned in a water bath. The cylinder was filled with blood, mineral water, and distilled water. With a 2.5-MHz transducer, echograms were recorded and analyzed by video intensitometer, and the maximum intensity IUmax and persistence time P were calculated. Rotation frequencies of 20,000-200,000 rpm with 2.0--mm burrs and times of 10 s were tested. In another model, hyperbaric conditions for the sa…
Effects of ovariectomy and steroid replacement on GABAA receptor binding in female rat brain.
1991
Abstract The specific binding of tritiated muscimol to γ-aminobutyric acid (GABA) receptor sites was studied in distinct brain areas of female rats during different endocrine states. In diestrous rats with intact ovaries the highest receptor densities were found in the cortex (10.24 pmol/mg protein) and the lowest concentrations in the mediobasal hypothalamus (3.29 pmol/mg protein). Four weeks after removal of the ovaries, the number of binding sites was enhanced up to 2.4-fold in all brain areas investigated: the preoptic brain area, mediobasal hypothalamus, corticomedial amygdala, and cerebral cortex. The affinity of the binding sites remained unchanged. Substitution of estradiol and prog…
A late Precambrian (∼ 710 Ma) high volcanicity rift in the southern Eastern Desert of Egypt
1991
The late Precambrian Shadli Metavolcanics of SE Egypt constitute a slightly metamorphosed bimodal sequence that has been previously interpreted as manifesting volcanic activity at an island arc. We report the first Rb-Sr geochronologic, trace element (including REE), and Nd isotopic data for these rocks. Two types of basalt are recognized, the stratigraphically lower suite having compositions like N-MORB ferrobasalt while the overlying basalt is similar to slightly fractionated E-MORB. The two basalt types were derived from melting of a strongly depleted source, most likely within the upper 60–75 km of the upper mantle. The origin of the felsic melts is problematic, and these could either h…
QRPA estimate for the Δ (1232) contribution to the Gamow-Teller decay of heavy nuclei
1991
Abstract The contribution of the Δ (1232) isobars to the nuclear beta decay strength function is estimated in the framework of the charge-changing form of the QRPA. This procedure is applied to neutron-deficient tin isotopes. The results imply that the quenching of the low-energy Gamow-Teller decay strength cannot attributed to the presence of delta admixtures in the nuclear wave function.
The role of arginine-vasopressin for pineal melatonin synthesis in the rat: involvement of vasopressinergic receptors.
1991
Abstract The endogenously synthesized nonapeptide arginine vasopressin (AVP) is thought to be involved in transduction of photic information to the pineal gland. The enhancement of circulating AVP leads to a suppression of the nocturnal melatonin surge the mechanisms of which are unknown so far. We therefore studied the effect of dDAVP, an AVP analog with antidiuretic but without vasopressor activity, on pineal melatonin synthesis in Sprague-Dawley and AVP-deficient Brattleboro rats. The nocturnal intra-arterial application of dDAVP mimicked the inhibitory effect of AVP on the activity of the rate-limiting enzyme for pineal melatonin synthesis, N-acetyltransferase (NAT), in both rat strains…
Relativistic SU(6) wave functions as the basis of modern approaches to hadronic wave functions
1991
The connections between various models of hadrons and the relativistic SU(6) wave functions are established. In formal terms and by concrete example it is shown how the Bargman-Wigner fields of freely moving quarks and antiquarks of equal velocity form the basis of the above approaches. This places modern attempts in their historical setting and allows for a more unified analysis of the various schemes.
Distributions of oxygen, nutrient, and metabolic waste concentrations in multicellular spheroids and their dependence on spheroid parameters.
1991
The distribution of oxygen, nutrients and metabolic wastes in multicellular tumor spheroids and its dependence on the parameters characterizing the spheroid (i.e., spheroid geometry, diffusivity, and consumption/production rates of biological substances) have been investigated by a theoretical analysis: 1. Parameter dependence is qualitatively demonstrated and visualized. 2. Reduction of the number of variables by specific coordinate transformations made it possible to generate nomograms from which concentration distributions for any choice of parameter values may easily be obtained. In particular, these nomograms may also be used for estimating concentration profiles of metabolic waste pro…
Effects of triiodothyronine (T3) on differentiation of rat cortical neurons in primary cultures.
1991
Some of the events which characterize neuronal terminal differentiation have been studied in rat cortical neurons cultured in a selective synthetic medium for a period which corresponds to terminal brain maturation in vivo. In particular, we have studied the effect of T3 on the synthesis of nuclear proteins and the expression of the mRNAs which encode different variants of T3 nuclear receptors (c erb A proteins). We have shown that: a) T3 stimulates the turnover of nuclear proteins, with a more evident effect on the non-histone component; b) for the whole lifespan of cultures the predominant form of c erb Aα mRNA is the α2 variant (which encodes a protein unable to bind T3); whatever the fu…
Bone mineral density and physical activity in 50–60-year-old women
1991
Abstract The bone mineral density (BMD) of the calcaneus was measured utilizing a single energy photon absorption method in 108 women, aged 50–60 years. The women who participated in vigorous exercise two or more times a week or whose total physical activity amounted to 4 h a week had significantly higher BMD values than those who exercised less than two times a week or did less than 4 h physical activity a week. The physically active women also showed higher values for leg extension force and maximal oxygen uptake. BMD and leg extension force were positively correlated, whereas correlations between BMD and body mass, and the width of the calcaneus were negative. When other life-style varia…
Structural fluctuations in glass-forming liquids: Mössbauer spectroscopy on iron in glycerol.
1991
M\"ossbauer absorption spectra of $^{57}\mathrm{Fe}^{2+}$ dissolved in a glycerol-water mixture have been measured over a wide temperature range (80--275 K). In the supercooled liquid state the shapes of the spectra depend strongly on temperature. The M\"ossbauer spectra can be fit with jump diffusion with a Cole-Davidson distribution of fluctuation times. The results are in agreement with those obtained from dielectric and ultrasonic volume relaxations, proving that the \ensuremath{\alpha} relaxation of viscous liquids is responsible for the line broadening of the spectra. From the temperature dependence of the integrated area of the M\"ossbauer spectrum a second dynamic process is inferre…
Diffusive energy growth in classical and quantum driven oscillators
1991
We study the long-time stability of oscillators driven by time-dependent forces originating from dynamical systems with varying degrees of randomness. The asymptotic energy growth is related to ergodic properties of the dynamical system: when the autocorrelation of the force decays sufficiently fast one typically obtains linear diffusive growth of the energy. For a system with good mixing properties we obtain a stronger result in the form of a central limit theorem. If the autocorrelation decays slowly or does not decay, the behavior can depend on subtle properties of the particular model. We study this dependence in detail for a family of quasiperiodic forces. The solution involves the ana…
Deformation of current algebras in 3+1 dimensions
1991
It was shown in an earlier paper that there is an Abelian extension \(\widehat{{\text{gl}}}_2 \) of the general linear algebra gl2, that contains the current algebra with anomaly in 3+1 dimensions. We construct a three-parameter family of deformations \(\widetilde{{\text{gl}}}_2 (t)\) of \(\widehat{{\text{gl}}}_2 \). For certain choices of the deformation parameters, we can construct unitary representations. We also construct highest-weight nonunitary representations for all choices of the parameters.
Forensics of birds of prey by DNA fingerprinting with 32P-labeled oligonucleotide probes.
1991
Paternity tests on confiscated families of eight species of birds of prey were carried out successfully by DNA fingerprinting with 32P-labeled oligonucleotide probes. Variations in the number of hybridized fragments, depending on the species of birds, are observed using the same probe, as well as differences of polymorphism by hybridizing the DNA samples with several oligonucleotide probes.
Ergebnisse der chirurgischen Therapie von Pankreaspseudozysten
1991
Pankreaspseudozysten werden zunehmend haufiger beobachtet. Zwischen dem 1. 1. 1978 und 31. 12. 1987 wurden an der Chirurgischen Klinik der Johannes Gutenberg-Universitat Mainz 145 Patienten wegen Pankreaspseudozysten operiert. In 93 Fallen erfolgte eine innere Zystendrainage, die mit einer Komplikationsrate von 11,8% und mit einer Letalitat von 1,1% belastet war. Nach resezierenden Verfahren stieg die Letalitat auf 4,7% und nach auserer Drainage auf 6,5% an. Nach einer mittleren Beobachtungszeit von 7,3 Jahren zeigte sich, das die nichtresezierenden Verfahren einen gunstigeren Einflus auf die endokrine Funktion und die resezierenden Verfahren auf die Schmerzfreiheit hatten. Zystenrezidive e…
Conformational relaxation of a low-temperature protein as probed by photochemical hole burning. Horseradish peroxidase
1991
For the first time, conformational relaxation processes have been measured in a small protein, mesoporphyrin-horseradish peroxidase via their influence on spectral diffusion broadening of holes burnt in the fluorescence excitation spectrum of free base mesoporphyrin. Holes were burnt in three 0----0 bands of different tautomeric forms of the chromophore at 1.5 and 4 K, and the spectral diffusion broadening was measured in temperature cycling experiments between 4 and 30 K. The inhomogeneous linewidth for the tautomeric 0----0 bands was estimated to be 60-70 cm-1; the hole width was found narrow, being in the order of 350 MHz (10(-2) cm-1) at 1.5 K what allowed for an extremely sensitive det…
On a theorem of Sobczyk
1991
In this paper the result of Sobczyk about complemented copies of c0 is extended to a class of Banach spaces X such that the unit ball of their dual endowed with the weak* topology has a certain topological property satisfied by every Corson-compact space. By means of a simple example it is shown that if Corson-compact is replaced by Rosenthal-compact, this extension does not hold. This example gives an easy proof of a result of Phillips and an easy solution to a question of Sobczyk about the existence of a Banach space E, c0 ⊂ E ⊂ l∞, such that E is not complemented in l∞ and c0 is not complemented in E. Assuming the continuum hypothesis, it is proved that there exists a Rosenthal-compact s…
MRI of transient osteoporosis of the hip.
1991
Among the available imaging techniques such as conventional radiography, radionuclide bone scan, and computed tomography (CT), magnetic resonance imaging (MRI) has made significant contributions to the diagnosis of acute hip joint disease in adults by enabling early differentiation between such conditions as idiopathic avascular femoral head necrosis, septic coxitis, degenerative disease, and tumors. In this study we investigated the use of MRI for evaluation of patients with transient osteoporosis (TO). MRI with T1- and T2-weighted sequences in coronal, transverse, and sagittal sections was performed in 12 patients with retrospectively confirmed TO, both at the onset of the disease and lat…
Diagnostik von Pleuraergüssen und Atelektasen: Sonographie und Radiologie im Vergleich
1991
In a prospective study it was shown that chest ultrasonography is superior to conventional x-ray diagnosis of recumbent patients in diagnosing pleural effusion and lung atelectasis. In 110 supine radiographs we found a sensitivity of 47% and a specificity of 71% for right pleural effusions and a sensitivity of 55% and a specificity of 93% for left pleural effusions in comparison to 110 sonographic examinations. The results of supine radiographs in detection of atelectasis were less efficient: sensitivity for the right side: 7%; sensitivity for the left side: 13.5%. Hence, the knowledge of chest ultrasonographic diagnosis can improve the interpretation of supine radiographs.
Cardiovascular Risk in Young Finns
1991
This report describes the general outline and progress of a multicentre study on risk factors of coronary heart disease and their determinants in children and adolescents. "Cardiovascular Risk in Young Finns" comprises a cross-sectional study of 3 to 18-year old subjects in 1980, and follow-up studies in 1983 and 1986 in various parts of Finland, and in 1989 in one of the study areas (Turku). The number of participants in 1980 was 3596 (83.1%) of those invited. In 1983 and 1986 83.2% and 77.8% of them, respectively, participated. The study programme has comprised questionnaire data on, for example, general health and living conditions, physical activity, eating habits, smoking, and psycholo…
Role of the fauna in soil processes: techniques using simulated forest floor
1991
Abstract Laboratory experiments were conducted to test the influence of soil animals on processes such as decomposition, nutrient cycling, and plant growth in northern coniferous forests. The techniques included simulation of a complex pattern of forest floor, controlled air flow through the systems, and automatic measurement of carbon flows. The soil fauna generally enhanced evolution of CO2 and mineralization of N and P from soil and litter, and increased considerably the biomass production and N content of birch seedlings. Significant results were also obtained on interactions between different faunal components.
Mesophase behaviour of 2,5-dibenzoyloxy-p-benzoquinone derivatives and tetrahydrobenzene tetraesters
1991
Abstract The synthesis of 2,5-dibenzoyloxy-p-benzoquinone derivatives, their products after reduction and tetraesters from tetrahydroxybenzene prepared from those products is described. Their phase behaviour was investigated by differential scanning calorimetry and polarizing microscopy and is discussed in terms of their detailed structure.
Evidence that neuronally released vasoactive intestinal polypeptide inhibits the release of serotonin from enterochromaffin cells of the guinea pig s…
1991
Abstract. Isolated small intestinal segments of the guinea pig were arterially perfused and the release of serotonin (5-hydroxytryptamine) and 5-hydroxyindoleacetic acid into the portal venous effluent was determined by HPLC with electrochemical detection. Test substances were intra-arterially applied. The muscarine receptor agonist oxotremorine (1 μmol/l inhibited the release of 5-hydroxytryptamine by about 50%. In the presence of the neurotoxin tetrodotoxin, oxotremorine enhanced the release of 5-hydroxytryptamine by 145%, indicating that the inhibitory effect of oxotremorine was mediated by the release of a neurotransmitter. Exogenous vasoactive intestinal polypeptide ( 1-100 pmol/l inhi…
Application of the slurry technique to biological materials: a survey of literature
1991
The literature on the application of the slurry technique to biological materials is reviewed. It is obvious from the various applications that the most frequently employed atomization method for slurry analysis in biological materials is electrothermal atomization using either graphite tube or platform atomizers. The slurry technique is particularly useful when certified reference materials are not available and when the standard addition method is to be avoided. The literature survey revealed that this technique compares favourably with other methods for the determination of trace metals in biological materials.
Spatial fluctuations of the chemical potential in case of nearly coherent transport along an ordered chain
1991
The Landauer-Buttiker approach is used to describe electron transport along a chain of scatterers which allow elastic as well as inelastic processes. The inelastic scattering takes place via side branches coupling the chain to electron reservoirs which serve as a heat bath. For small inelastic coupling of the scatterers to the heat bath strong interference effects lead to spatial fluctuations of the charge density. The corresponding oscillations of the chemical potential are discussed in view of phase-sensitive experiments measuring the four-probe resistance.
Conformational transitions of gramicidin A in phospholipid model membranes. A high-performance liquid chromatography assessment.
1991
We have investigated the conformation of gramicidin A reconstituted in different phospholipid environments, small unilamellar vesicles, extensive bilayers, and micelles by exploiting a recently proposed experimental approach based on high-performance liquid chromatography [Bano et al. (1988) J. Chromatogr. 458, 105; Bano et al. (1989) FEBS Lett. 250, 67]. The method allows the separation of conformational species of the peptide namely, antiparallel double-stranded (APDS) dimers and β 6.3 -helical monomers, and quantitation of their proportions in the lipid environment. Various experimental parameters (e.g., nature of organic solvent, time of incubation in organic solvent, lipid-to-peptide m…
CORRELATIONS BETWEEN ε′/ε AND HEAVY TOP
1991
The paper reviews new theoretical developments for the CP-parameter ε′/ε and its intimate connection with the mass of a heavy top quark. It presents an extensive list of results and their implications for experiments.
Effect of acidosis on lipid peroxidation in brain slices.
1991
Acidification of the incubation medium markedly increased lipid peroxidation of cortical brain slices. Lactic acidosis caused a more extensive lipid peroxidation than did phosphoric acidosis (+35% at pH 6 and +81% at pH 5), probably due to the rapid diffusion of the protonated form of lactic acid across cell membranes. These results support the hypothesis that free radical mechanisms may be involved in the cytotoxicity of acidosis.
Magnetic Disaccommodation in Manganese Ferrites in the Temperature Region IV
1991
The magnetic relaxation in polycrystalline, nonstoichiometric manganese ferrite samples MnxFe3−xO4 is investigated as a function of the Mn content (0 ≦ x ≦ 1). The analysis of the experimental results shows that in the temperature region IV two different relaxation processes at 285 (IV) and 220 K (IVa) can be distinguished. The process IV exhibits orientational relaxation characteristics and is composed by the superposition of two Debye processes with activation energies close to 0.75 and 0.80 eV whereas relaxation IV a could be associated with vacancy migration through the lattice, but future investigations are necessary to probe this. Es wird die magnetische Relaxation in polykristallinen…
Effect of Hydrostatic Pressure on the Phase Transitions of {N(CH3)4}2ZnCl4-xBrxMixed Crystals
1991
Single crystals of the solid solution system {N(CH 3 ) 4 } 2 ZnCl 4- x Br x have been prepared in a low x region, and the effect of hydrostatic pressure on the phase transitions were measured for x =0.2 and 0.3. The normal-to-incommensurate phase transition temperatures increase linearly with increasing pressure with the rates of 0.126 K/MPa and 0.129 K/MPa for x =0.2 and 0.3 crystals, respectively. The ferroelectric III phase disappears at about 60 MPa for x =0.2 crystal. On the other hand, phase III is not observed for the x =0.3 crystal both at 0 pressure and at high pressures. The II-IV or III-IV transition temperatures also increases with increasing pressure with the rates of 0.162 K/M…
Selective labelling of melittin with a fluorescent dansylcadaverine probe using guinea-pig liver transglutaminase
1991
Abstract Melittin, a C-terminal peptide, incorporated the fluorescent probe monodansylcadaverine (DNC) when catalysed by guinea-pig liver transglutaminase and Ca2+, as determined by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). A 1:1 adduct DNC-melittin was identified in which a single glutamine residue out of two, i.e. Gln25, acts as acyl donor. Incubation of melittin with transglutaminase in the absence of DNC originated high molecular mass complexes indicative that the peptide lysine residue can act as an acyl acceptor. The DNC-melittin was about 3 times more active in the lysis of red cell membranes than native melittin. Fluorescence study of the lab…
Anticonvulsants do not suppress long-term potentiation (LTP) in the rat hippocampus
1991
Long-term potentiation (LTP) of population spikes in the CA1 area of rat hippocampus was induced by tetanic stimulation of stratum radiatum in slices kept submerged in a perfusion chamber. Addition of the two antiepileptic drugs phenytoin or the diazepine midazolam to the medium did not significantly alter this phenomenon within 22 min after the tetanus. The early enhancement (post-tetanic potentiation, PTP) was reduced only by phenytoin. Therefore an interaction of these drugs with N-methyl-D-aspartate (NMDA) receptors and LTP induction is unlikely.
Thimerosal induces calcium mobilization, fructose 2,6-bisphosphate synthesis and cytoplasmic alkalinization in rat thymus lymphocytes
1991
The effect of thimerosal on intracellular calcium ([Ca2+]i), pH (pHi) and fructose 2,6-bisphosphate (Fru 2,6-P2) in thymus lymphocytes was investigated. The effect of thimerosal on cell growth was also examined. Thimerosal produced a dose-dependent increase in [Ca2+]i, pHi and in the level of fructose 2,6-bisphosphate. Thimerosal was, however, unable to produce cell proliferation and inhibited [3H]thymidine incorporation when cells were challenged with PHA and costimulator. In the absence of external calcium, thimerosal produced only a slight increase in [Ca2+]i. In Na(+)-containing buffer, thimerosal induced an initial acidification (0.05 +/- 0.01 pH units), followed by an alkalinization o…
Effects of endothelin-1 on the cerebrovascular bed of the goat.
1991
Abstract The aim of the present study was to analyze the effects of endothelin-1 (ET-1) in the cerebrovascular bed of the goat, the importance of endothelial integrity and the contribution of extracellular Ca2+ to these responses. We measured isometric tension and 45Ca2+ uptake in isolated middle cerebral arteries, and cerebral blood flow (CBF) in unanesthetized animals. ET-1 elicited concentration-dependent contractions which were potentiated in arteries without endothelium. Ca2+-free medium and nicardipine inhibited, and Bay K 8644 potentiated the ET-1-induced contractions. ET-1 enhanced 45Ca2+ uptake in isolated arteries. Injections of ET-1 directly into the cerebral circulation decrease…