showing 36 of ~574560 from 574555 documents
Reply to Drs. Machin and Knisely
1992
Molecular surface area and hydrophobic effect.
1992
Detection of mammalian carcinogens with an immunological DNA synthesis-inhibition test.
1992
There is a close relationship between genotoxicity, mutagenicity and carcinogenicity. But the controversy of which short-term test system best recognizes human carcinogens is still going on. Currently, the Salmonella gene mutation assay ('Ames test') is the most widely used test for the screening of mutagens. However, many in vitro tests hold unsatisfactory validity data, presumably because of the inability of present short-term tests to detect non-genotoxic carcinogens, which are increasingly being brought into focus in the discussions of genesis of cancer. One principle often neglected in this context is the property of genotoxic agents to inhibit replicative DNA synthesis in (proliferati…
Measurement of the transverse Doppler shift using a stored relativistic7Li+ ion beam
1992
We have performed for the first time precision spectroscopy on a coasting fast7Li+ ion beam in a storage ring. The ion beam moving with 6.4% speed of light was first electron cooled and then merged with two counterpropagating laser beams acting on two different hyperfine transitions sharing a common upper level (λ-system). One laser was frequency locked to thea 3 127J2 hfs frequency component established as a secondary frequency standard at 514 nm. The second laser was tuned over theλ-resonance, which was recorded relative to127J2 hfs components. This experiment is sensitive to the time dilation in fast moving frames and will lead to new limits for the verification of special relatively. Th…
Stereoselective Nucleophilic Addition Reactions of Reactive Pseudopeptides
1992
Phenolic Compounds in Needles of Norway Spruce Trees in Relation to Novel Forest Decline I. Studies on Trees from a Site in the Northern Black Forest
1992
Summary Contents of selected phenolic compounds in needles of Norway spruce trees (Picea abies) from the Black Forest were measured using a HPLC-technique elaborated for serial studies in forest decline research. Measurements on needles that were harvested on several dates during two growing seasons gave no hint of seasonal variations in the concentrations of the studied phenolic compounds. Values for picein demonstrate an average decrease in the needles of severely damaged trees compared with the still undamaged ones, but the results are impaired by strong individual variations among the single trees. p-Hydroxyacetophenone was found in only very low amounts showing no constant differences …
The manipulation of ions using electromagnetic traps
1992
Electromagnetic traps, in addition to providing very clean and gentle confinement for very precise and sensitive observation of charged particles, are very versatile devices for collecting and preparing charged particles from outside sources for observation by devices which are also outside, devices which may in themselves be other electromagnetic traps. This paper introduces the basic principles of using electromagnetic traps for collecting and cooling and presents some preliminary test results from using Paul traps for these purposes. Specifically, in relatively modest Paul traps with 28 mm between end electrodes a collection efficiency of 0.2% was achieved for a 60 keV DC beam of 132Xe i…
Comparacion numerica de algoritmos para calcular distribuciones estacionarias de cadenas de Markov finitas
1992
En este trabajo se estudia la eficiencia de un conjunto de algoritmos, exactos e iterativos, para el problema de obtener la distribucion estacionaria de una cadena de Markov homogenea, irreducible y finita. Se presentan los resultados computacionales obtenidos al resolver problemas de diferentes tipos y tamanos, aleatoriamente generados, asi como el tratamiento estadistico realizado sobre los mismos. Se ha comparado la estabilidad de estos algoritmos frente a la perdida de irreducibilidad y la existencia de estados transitorios mediante su aplicacion a 26 problemas test. El trabajo concluye con una discusion del comportamiento de los diversos algoritmos.
Evaluation and elimination of the “blank bias error” using the H-point standard addition method
1992
Abstract The basis of the H-point standard addition method in the cases where the analyte determination requires the use of an absorbent reagent is considered. The method evaluates and eliminates the blank bias error present in such procedures by using the absorbance increment at two selected wavelengths as the analytical signal of the calibration graphs. Three different determinations were tested: the determination of proteins with the biuret method, thorium with thoron and of magnesium with Titan Yellow. These procedures are better described by the proposed method than by the traditional approach using absorbance values against reagent blank.
A small-bowel segment as a total extrahepatic bile duct replacement.
1992
• The effect of a small-bowel segment as a total extrahepatic bile duct replacement, with preservation of the bile passage through the papilla of Vater, was examined in 12 pigs followed up for 420 days. No complications during or after surgery were observed in any of the animals. The laboratory parameters were within normal range during the entire observation period. No anastomotic stenosis was evident on percutaneous transhepatic cholangiography in animals examined 2, 6, or 12 months after surgery. The intrahepatic biliary tract was not dilated. There was obvious peristalsis of the grafted small-bowel toward the papilla of Vater. Autopsies showed that the grafts had healed without any sign…
Schizoaffective disorder and affective disorders with mood-incongruent psychotic features: keep separate or combine? Evidence from a family study.
1992
Objective This study investigated whether the distinction between schizoaffective disorder and affective disorders with mood-incongruent psychotic features as described in DSM-III-R is reflected by aggregation of schizophrenia in the families of probands with the former disorder and aggregation of affective disorders mainly among the relatives of probands with the latter type of disorders. Method The probands were 118 inpatients with definite lifetime diagnoses of DSM-III-R schizoaffective disorder or a major mood disorder with incongruent psychotic features according to structured clinical interviews. Diagnostic information on 475 of the probands' first-degree relatives was gathered throug…
Lattice quantum hadrodynamics on a CRAY Y-MP
1992
Quantum corrections to the mean-field equation of state for nuclear matter are estimated in a lattice simulation of quantum hadrodynamics on a CRAY Y-MP. In contrast with lattice quantum chromodynamics, where coordinate space methods are the standard, the calculations are carried out in momentum space and on nonhypercubic (irregular) lattices. The quantum corrections to the known, mean-field equation of state were found to be considerable. The time frame of the project and the large computational needs of the program required the use of powerful supercomputers, like the CRAY Y-MP, which are capable of performing at a very high computing speed by using both vector and parallel hardware, the …
The Development of Visuo-spatial Memory: How to Remember Location
1992
Recent studies on developmental differences in spatial memory have reported equivocal results. Some found an age-dependent improvement of memory performance whereas others did not. The two studies reported here investigate age differences in memory for visual-spatial information. A picture reconstruction task with simultaneous presentation of scene-like visual-spatial arrangements was used. Subjects had to recognise objects and to reconstruct the initial spatial arrangement. The first study with 5to 10year-olds produced the typical age-dependent improvement in recognising visual material as well as in remembering the locations of specific objects. No effect for age was obtained in memory f…
Exclusive non-leptonic charm baryon decays
1992
We present a spectator quark model calculation of the Cabibbo-enhanced non-leptonic decays of the lowest lying charm baryons Λc, Ξc and Ωc decaying into non-charm ground state baryons and mesons. We employ covariant quark model wave functions to describe the ground state baryons and mesons. They are obtained by boosting rest frame wave functions to equal velocity frames. The non-leptonic decay amplitudes are then obtained in terms of two wave function overlap parameters which we fit to the experimental data. We discuss general features of the flavour and helicity composition of the final states in the quark model approach. We emphasize thatW-exchange contributions are of crucial importance …
Dipole surface plasmon in K+N clusters
1992
Abstract The technique of sum rules has been used to investigate the dipole surface plasmon for K + N clusters within a Density Functional Theory and the spherical jellium model. The role played by non-local effects is discussed comparing the results obtained from different functionals. Band-structure and core-polarization effects have been phenomenologically included in the calculation by means of an electron effective mass and a dielectric constant. Comparison with recent experimental data is presented.
Detection of DNA damage in stimulated human lymphocytes after enflurane exposure in vitro
1992
DNA damage was detected by nucleoid sedimentation in human lymphocytes stimulated with pokeweed mitogen after exposure to enflurane. Enflurane induces DNA damage at an exposure concentration of 0.2 vol%. Higher enflurane concentrations increase the rate of DNA damage. The DNA damage seen after exposure to enflurane concentrations of 0.2 and 3.0% vol is comparable to damage after X-radiation of 0.1 and 0.7 Gy. DNA single-strand breaks can be demonstrated by nucleoid sedimentation and can indicate damage before DNA repair begins. Therefore, detected DNA single-strand breaks may be reversible. However, DNA repair is not always successful and an increased number of DNA single-strand breaks coul…
Cytogenetics, flow cytometry, cytophotometry and morphometry of 22 cases of primary breast carcinoma. A comparative study.
1992
Cytogenetic, flow cytometric, cytophotometric and morphometric analyses were performed on 22 previously untreated, primary solid breast carcinomas. Although the cell nuclei as the primary object of these studies were the same in all the tumors, distinct features were evaluated in each case to determine to what degree the results obtained by these techniques are comparable. From the cytogenetic viewpoint, six tumors had a modal number in the diploid range, seven were in the triploid range, and two in the tetraploid range; seven tumors had no modal number. These data correlate with the flow cytometry and cytophotometry results obtained, with DNA values slightly higher than their respective ch…
Taxonomie der gattungchiropteridium gocht (dinophyceae) im rupelium des mainzer beckens (mitteloligozän, SW-Deutschland)
1992
Es werden funf Morphotypen der Dinoflagellaten-Zysten-GattungChiropteridium Gocht aus dem Mittleren Rupelton (mittl. Mitteloligozan) des Mainzer Beckens beschrieben. Zwei der Morphotypen werden den ArtenChiropteridium aspinatum undC. lohospinosum zugeordnet. Fur einen weiteren wird die neue ArtChiropteridium brevifolium aufgestellt.
Global extrapolation with a parallel splitting method
1992
Extrapolation with a parallel splitting method is discussed. The parallel splitting method reduces a multidimensional problem into independent one-dimensional problems and can improve the convergence order of space variables to an order as high as the regularity of the solution permits. Therefore, in order to match the convergence order of the space variables, a high order method should also be used for the time integration. Second and third order extrapolation methods are used to improve the time convergence and it was found that the higher order extrapolation method can produce a more accurate solution than the lower order extrapolation method, but the convergence order of high order extr…
Instantaneous diffusion in spin-echo dynamics: A frequency-domain experimental investigation.
1992
We report an experimental investigation on the spectral content of the echo radiation emitted by an electron spin system excited by a two-pulse sequence. The measurements are carried out at liquid-helium temperature in a sample of quartz containing a very low concentration of [${\mathrm{AlO}}_{4}$${]}^{0}$ centers, in which instantaneous diffusion mechanism makes the main contribution to the phase relaxation. The experimental spectral shapes reproduce the theoretical ones, as calculated for an ideal system of noninteracting spins. However, the agreement is only qualitative, as the experimental spectral widths are found to be less than expected by a factor that depends on the exciting sequen…
Patterns of Boys' Social Adjustment in Two Cultures and at Different Ages: A Longitudinal Perspective
1992
In the comparison of two longitudinal studies, patterns of boys' social adjustment were identified by using aggression, hyperactivity, inattentiveness, anxiety, and lack of prosocial behaviour as clustering variables. Eight comparable clusters were obtained across two cultures, French Canada and Finland; three age groups, 6, 8, and 10 years; and two decades, the 1960s and 1980s. The clusters confirmed three frequently used categories of behaviour: (1) normal (for no adjustment problems); (2) anxious; and (3) inattentive; two infrequently used categories: (1) passive; and (2) nervous; and the importance of subcategorising aggressive-hyperactive boys into three categories: (1) bully; (2) unc…
Anti-Idiotypic Antibodies Against the Kinin Receptor
1992
Three sets of monoclonal antibodies against bradykinin (MBK1, MBK2, and MBK3) were generated by somatic cell fusion, characterized by their peptide specificity, and compared with the known ligand specificity of the kinin receptor subtypes. By these criteria, the paratope of MBK3 resembled the B 2 receptor binding site, whereas MBK1 shared principal binding characteristics with the B 1 receptor. Anti-idiotypic antibodies against MBK1, MBK2, and MBK3 were raised in rabbit and sheep
Alignment processes in 119Cs, 121Cs and 123Cs
1992
Rotational band structures have been observed in the odd-A Cs isotopes 119Cs, 121Cs and 123Cs. The previously known bands have been extended to higher spin values and several new bands have been es ...
Acquired monocular elevation paresis. An asymmetric upgaze palsy.
1992
Five patients with acquired monocular elevation paresis were investigated using direct current electrooculography. With recovery, upward saccade velocities significantly increased in both eyes in all patients. The gain of upward-following eye movements significantly increased in the paretic eye of all patients and in the opposite eye of four patients. These findings are interpreted in terms of an asymmetric upgaze palsy which clinically presented as monocular elevation paresis in the more severely affected eye. A brainstem lesion contralateral to monocular elevation paresis was suggested in four patients by contralateral Horner's syndrome and contralateral abduction paresis, each in one pat…
One loop integrals revisited
1992
We present a new calculation of the well-known one-loop two-point scalar and tensor functions. We also present a systematic reduction to a certain class of functions which minimizes the effort for calculating tensor integrals drastically. We avoid standard techniques such as Feynman parametrization and Wick rotation.
A Frozen-Flow Approximation to the Evolution of Large-Scale Structures in the Universe
1992
A new approximation to the evolution of large-scale structures in the Universe is proposed which is based on neglecting the role of particle inertia compared to the damping implied by the Hubble drag. We call this approximation frozen flow because particles move by updating at each step their velocity to the local value of the peculiar velocity field, here approximated by its growing linear mode: stream-lines are then frozen to their initial shape. The situation is quite different from that of the Zel'dovich algorithm, where the velocity is kept constant along each particle trajectory
The stellate cell (Ito-cell, fat-storing cell, lipocyte, perisinusoidal cell) of the liver. New insights into pathophysiology of an intriguing cell.
1992
DC electrical resistivity of Nb-Doped BaTiO3 and EPR measurements
1992
DC electrical resistivity measurements along the c-axis of Nb-doped BaTiO3 single crystals are presented in a wide range of temperature, covering the four phases, with special attention to the rhomboedral one. The temperature dependence of the conductivity leads to convincing arguments in favour of a polaronic mechanism. Below the orthorhombic-rhomboedral transition point, a strong increase of the resistivity is observed. The correlation of this behavior with EPR analysis in the same temperature range, is consistent with a sharp trapping of the ''free'' electrons, when the temperature decreases.
Clavine alkaloids and derivatives as mutagens detected in the Ames test.
1992
Eight cytostatic clavines were investigated for mutagenicity in Salmonella typhimurium (reversion of the his-strains TA98, TA100, TA102 and TA1537), directly and in the presence of a mammalian xenobiotic metabolizing system, S9 (NADPH-fortified postmitochondrial fraction of liver homogenate from Aroclor 1254-treated rats). Four compounds (festuclavine, 17-bromofestuclavine, 1-allylelymoclavine and 1-methyllysergol methyl ether) were direct mutagens, whose activity was enhanced in the presence of S9. The other compounds (1-cyclopentylfestuclavine, 13-bromo-1-cyclopropylmethylfestuclavine, 6-cyano-1-propyl-6-norfestuclavine and 6-allyl-1-propyl-6-norfestuclavine) showed mutagenic effects only…
Beyond the audit expectations gap
1992
In seeking to encourage a broader, European dimension to research on auditing and audit expectations, this paper examines the recent history of auditing and its regulation in Spain within the context of international developments in the accounting profession. The more expansive role being assigned to the audit function in Spain following the implementation of the Fourth and Eighth European Company Law Directives is generally viewed by Spanish writers as a progressive step, with largely positive effects. Such views stand in some contrast to the history of auditing in Britain, where the prevalence of an ‘audit expectations gap’ suggests a rather more problematic state of affairs. In exploring…
Neuronal cell cultures: A tool for investigations in developmental neurobiology
1992
The aim of this review is to describe environmental requirements for survival of neuronal cells in culture, and secondly to survey the complex interplay between hormones, neurotrophic factors, transport- and extracellular matrix- proteins, which characterize the developmental program of differentiating neurons. An overall reconsideration of the literature in this vast field is above the limits of the present paper; since progress and refinement in the techniques of neuronal cell cultures have paralleled the advancement in Developmental Neurobiology, we will run instead through the main steps which form the conceptual framework of neuronal cell cultures. © 1992 Plenum Publishing Corporation.
A second-order sparse factorization method for Poisson's equation with mixed boundary conditions
1992
Abstract We propose an algorithm for solving Poisson's equation on general two-dimensional regions with an arbitrary distribution of Dirichlet and Neumann boundary conditions. The algebraic system, generated by the five-point star discretization of the Laplacian, is solved iteratively by repeated direct sparse inversion of an approximating system whose coefficient matrix — the preconditioner — is second-order both in the interior and on the boundary. The present algorithm for mixed boundary value problems generalizes a solver for pure Dirichlet problems (proposed earlier by one of the authors in this journal (1989)) which was found to converge very fast for problems with smooth solutions. T…
Retroaortic left renal vein: a report of six cases
1992
Six cases of retroaortic left renal vein have been studied, two in corpses and four by means of Computed Tomography. Any previous pathology has been rejected. The total number of dissected specimens was 116, whereas the patients with non-pathological retroperitoneum studied by CT numbered 170. In our six cases, the left renal vein formed a single trunk of considerable size, retroaortic position and directed obliquely towards the inferior vena cava.
Modelos de crecimiento economico endogeno e historia economica: ¿Una nueva perspectiva ante el debate protección-librecambio?
1992
La evidencia cuantitativa aportada en los últimos años en diferentes investigaciones ha permitido una interpretación sobre la trayectoria económica española para el período 1874–1936, en la cual se combina la constatación de tasas apreciables de crecimiento con el mantenimiento de un grado elevado de atraso. Y como señaló Lluch (1988), si el ámbito temporal se amplía hasta la actualidad, cualquier interpretación debería incluir la tardía recuperación de este último como un hecho clave a considerar.No resulta, por tanto, sorprendente que las razones de la persistencia durante un largo período histórico de esta distancia entre los logros de la economía española y los conseguidos por los denom…
Figures of equilibrium in close binary systems
1992
The equilibrium configurations of close binary systems are analyzed. The autogravitational, centrifugal and tidal potentials are expanded in Clairaut's coordinates. From the set of the total potential angular terms an integral equations system is derived. The reduction of them to ordinary differential equations and the determination of the boundary conditions allow a formulation of the problem in terms of a single variable.