Showing papers by "University of Konstanz published in 1981"

Magic Numbers for Sphere Packings: Experimental Verification in Free Xenon Clusters

Abstract: The existence of magic numbers for atomic microclusters has been found experimentally for the first time. The magic numbers ${n}^{*}$ manifest themselves in the mass spectra of free xenon clusters, nucleated in the gas phase. The observed numbers ${n}^{*}=13, 55, \mathrm{and} 147$ coincide with the numbers of spheres required for complete-shell icosahedra. The appearance of further magic numbers (19, 25, 71, and 87) is only partially explained by previous calculations.

The filtration apparatus of Cladocera: Filter mesh-sizes and their implications on food selectivity

Abstract: The filtering apparatus of eleven Cladoceran species was studied. The distances between the setulae, which act as filters, were measured. Among adult individuals, they vary from 0.2 μm in Diaphanosoma brachyurum to 4.7 μm in Sida crystallina. Species can be grouped according to the mesh-sizes, as “fine mesh filter-feeders”: Diaphanosoma brachyurum, Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia cucullata and Daphnia magna; “medium mesh filter-feeders”: Daphnia galeata, D. hyalina. D. pulicaria, Bosmina coregoni, and “coarse mesh filter-feeders”: Holopedium gibberum and Sida crystallina. In Daphnia hyalina, the distances between setulae increase from 0.3–0.4 μm in small juveniles, to 0.8–2.0 μm in adults. In Daphnia magna, the mesh-size of the filter does not increase significantly with growth. There is good evidence that the relative abundance of the filter-feeding types varies with the trophic state of the lake. In oligotrophic lakes the “coarse mesh filter-feeders” usually dominate throughout the year. The seasonal succession of zooplankton species in eutrophic lakes can be interpreted as a succession of feeding types; during winter “coarse mesh filter-feeders” dominate, while “fine mesh filter-feeders” are most abundant during summer phytoplankton blooms. Our results support the hypothesis that the species composition of filter-feeding zooplankton is strongly influenced by the amount of suspended bacteria which are available as food only for filter-feeding species with fine meshes.

Selective isolation of Acetobacterium woodii on methoxylated aromatic acids and determination of growth yields

Abstract: Anaerobic enrichments with methoxylated aromatic compounds as substrates (vanillate, syringate, trimethoxycinnamate) were inoculated from freshwater mud and sewage sludge samples. In 12 out of 16 cultures the same type of rod-shaped, motile bacteria was selectively enriched. Two strains, NZva16 and NZva24, were isolated in pure culture and recognized as Acetobacterium woodii by comparison with the type strain (DSM 1030).

Evidence for Coulomb Explosion of Doubly Charged Microclusters

Abstract: Mass spectra of Pb, NaI, and Xe microclusters show that below a critical number of atoms per cluster, ${n}^{**}$, doubly charged particles are not stable. These numbers are 30 for ${\mathrm{Pb}}_{n}$, 20 for ${(\mathrm{NaI})}_{n}$ and 52 for ${\mathrm{Xe}}_{n}$. The two positive charges generated at one atom by electron bombardment are likely to move to opposite sides of the cluster which then explodes into singly charged fragments as long as the Coulomb repulsion energy is greater than the binding energy.

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments.

Abstract: Colony counts of acetate-, propionate- and l-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers.

Relaxation studies of ion transport systems in lipid bilayer membranes.

Abstract: Relaxation techniques have been widely used in kinetic studies of chemical reactions in homogeneous solution (Eigen & DeMayer, 1963). The principle of this method is well known: an external variable such as temperature or pressure is suddenly changed and the time course of a state parameter of the system such as concentration is recorded as it approaches a new steady value. Relaxation techniques can also be used for studying the rate of elementary processes in membranes. This method has proved particularly useful for the investigation of ion transport systems (ion carriers, channels, pumps) in artificial planar bilayer membranes. In this review we describe different relaxation techniques which have been developed for this purpose during the last years, as well as applications to a number of ion transport systems.

Distribution and specific central projections of mechanoreceptors in the thorax and proximal leg joints of locusts

Abstract: The mechanoreceptive supply of ventral thoracic parts and proximal leg joints of the pro- and metathorax of two locust species has been studied with the help of a modification of the axonal infusion technique with cobaltous chloride, which permits staining of the peripheral nervous system of an entire segment. The number, location, and innervation of serially homologous chordotonal organs (CO), strand receptors (SR), multipolar sensilla (MS), hair plates (HP) and clustered campaniform sensilla (CS) are described, as well as population specific central projections of primary afferent fibers from internal receptors (CO, MS). CO projections tend to form intersegmental projections within the thoracic ganglia, the extent varying with the organ's location. Apart from dorso-lateral collaterals, they terminate mainly in the medioventral neuropile, where they also cross the longitudinal midline of the CNS. By contrast, MS projections stay ipsilateral and do not leave their ganglia, where they send collaterals into all levels of the neuropile.

Dirac Electron in Space-times With Torsion: Spinor Propagation, Spin Precession, and Nongeodesic Orbits

Abstract: The WKB limit of the noniterated Dirac equation in a Riemann-Cartan space-time is discussed It is shown that within this framework the behavior of a Dirac particle is dominated by the new connection ${{\ensuremath{\Gamma}}_{\ensuremath{\mu}\ensuremath{ u}}^{*}}^{\ensuremath{\lambda}}=\left\{{\ensuremath{\lambda}}{\ensuremath{\mu}\ensuremath{ u}}\right\}\ensuremath{-}3{K}_{[\ensuremath{\mu}\ensuremath{ u}\ensuremath{\epsilon}]}{g}^{\ensuremath{\epsilon}\ensuremath{\lambda}}$ formed from the Christoffel connection and the contortion The relevant effects are the following: (i) The normalized Dirac spinor is parallel propagated by ${{\ensuremath{\Gamma}}_{\ensuremath{\mu}\ensuremath{ u}}^{*}}^{\ensuremath{\lambda}}$ along the particle's orbit (ii) The same is true for the spin vector By this the gyrogravitational ratio is specified as well (iii) The particle orbit is nongeodesic The respective "force" is of the usual form with the spin coupled to the curvature tensor ${R}^{*\ensuremath{\alpha}\ensuremath{\beta}\ensuremath{\gamma}\ensuremath{\delta}}({\ensuremath{\Gamma}}^{*})$ of the connection ${{\ensuremath{\Gamma}}_{\ensuremath{\mu}\ensuremath{ u}}^{*}}^{\ensuremath{\lambda}}$ The orbit is thereby defined by the streamlines of the conserved convection four-current obtained from the Dirac current by a Gordon decomposition The cumulative effects (ii) and (iii) can in principle be used to detect torsion by measuring the spin precession of a massive spin-\textonehalf{} particle or by measuring its orbit in a Stern-Gerlach type of experiment

Photocurrent kinetics of purple-membrane sheets bound to planar bilayer membranes

Abstract: The kinetics of light-driven proton transport by bacteriorhodopsin has been studied in a model system consisting of a planar lipid bilayer membrane to which purple membrane fragments have been attached. After excitation with a 10-nsec laser flash a fast negative current-transient occurs, followed by a positive transient which decays to zero. The time course of the photocurrent may be represented by a sum of four exponentials with time constantsτ1= 1.2μsec,τ2= 17μsec,τ4= 57μsec,τ1= 950μsec (at 25°C). In a D2O mediumτ2 andτ3 are increased by a factor of 2.6 and 2.9, respectively, whereasτ1 remains unaffected. The observed components of the photocurrent can be correlated to photochemical reaction steps inferred from flash-photometric experiments on the basis of the observed time constants, the activation energies, and the effects of pH and D2O. From the photocurrent signals information may be obtained on the magnitude of the charge displacement associated with the elementary transitions of the bacteriorhodopsin molecule.

On the function of the common inhibitory neurone in the walking legs of the crab,Eriphia spinifrons

Abstract: 1 The activity of the motor axons innervating the closer and opener muscles in walking legs of the crabEriphia spinifrons was recorded on the trailing side during sideways walking on a treadmill 2 During walking the ‘slow’ excitatory axon (SCE) to the closer and the ‘specific’ inhibitory axon (OI) to the opener discharged at about the same time in rhythmic, fairly discrete bursts and approximately reciprocally with the discharge of the single excitatory axon (OE) to the opener muscle The ‘fast’ excitatory axon (FCE) to the closer was rarely active 3 The common inhibitory neurone (CI) innervating both the closer and opener muscles was identified as being the smallest and most slowly conducting unit in the closer and opener nerves 4 CI was active in walking crabs In individuals stepping at low rates CI usually discharged tonically at an irregularly, low frequency throughout the step cycle 5 The significance of CI activity for mechanical performance was investigated by stimulating the closer muscle of isolated recipient legs with artificial patterns or with naturally occurring activity in SCE and CI obtained from walking donor crabs 6 The effect of CI was to increase relaxation between SCE evoked contractions with a small or no reduction in the amplitude of individual contractions 7 The results suggest that one function of CI is to promote a phasic pattern of contractions in the limb muscle of walking crabs by eliminating the slow build up of tension in populations of tonic fibres

On the glass transition and the residual entropy of glasses

Abstract: A general statistical–mechanical description of the liquid–glass transition as a transition from ergodic to non-ergodic behaviour is presented. The description is based on the concept of the differ...

Sporulation and further nutritional characteristics of Desulfotomaculum acetoxidans

Abstract: Acetate-oxidizing sulfate-reducing bacteria of the Desulfotomaculum acetoxidans type have been enriched from animal manure, rumen content and dung contaminated freshwater habitats, indicating that they are primarily intestinal bacteria. Sporulation was observed only when acetate was the organic substrate; with butyrate, which allowed faster growth than acetate, spore formation never occurred. The cone-shaped highly refractile areas adjacent to the spores in spore-forming mother cells were shown to be gas vacuoles. Biotin was the only growth factor required by Desulfotomaculum acetoxidans strain 5575 in minimal media with sulfate and acetate or other organic substrates.

Sexual behavior of castrated sex offenders

Abstract: Data are reported on the sexual behavior of 39 released sex offenders who agreed voluntarily to surgical castration while imprisoned in West Germany. Findings indicated that frequency of coitus, masturbation, and sexual thoughts are seen as strongly reduced after castration. Sexual desire and sexual arousability are perceived by the subjects as having been considerably impaired by castration. In comparison with other studies, however, it was shown that male sexual capacity was not extinguished soon after castration. Particularly noteworthy is that 11 of 35 castrates (31%) stated they were still able to engage in sexual intercourse. Rapists proved to be sexually more active after castration than homosexuals or pedophiliacs. There seems to be a strong effect on sexual behavior only if castration is performed on males between the age of 46 and 59 years. In general, the findings do not justify recommending surgical castration as a reliable treatment for incarcerated sex offenders.

Vibration signal transmission in spider orb webs.

Abstract: Vibration transmission from the prey-catching region to the hub of the unloaded orb web of Nuctenea sclopetaria was measured by laser vibrometry. Compared to transverse or lateral vibrations, longitudinal vibration shows less attenuation and contains more directional information. It is transmitted well throughout the entire frequency range measured (1 to 10,000 hertz).

Microphotometric measurement of initial maximum reaction rates in quantitative enzyme histochemistry in situ.

Abstract: Final reaction product formation was recorded microphotometrically for succinate dehydrogenase in cross-sectioned muscle fibres at initial rate conditions and during prolonged incubations. Incubations with gel films and aqueous reaction medium both showed a decline of reaction rates. Maximum reaction rates could only be determined at initial rate conditions during the first minute of the incubation. Reaction rates recorded in different areas of the same tissue section were found to change with time to different degrees. From these results it was concluded that quantitative histochemical measurements of enzyme reactionsin situ can only be valid if measured under initial maximum velocity conditions.

Trajectories and spin motion of massive spin-1/2 particles in gravitational fields

Abstract: From covariant Dirac theory in curved space-time, dynamical equations for the motion of the spin and the spin-induced non-geodesic behaviour of the particle trajectories are deduced. This is done for arbitrary space-times in a generally covariant and observer- independent way. The procedure is thereby based on a WKB scheme and a Gordon decomposition of the Dirac probability four-current. A complete, correspondence between the quantum mechanical equations of motion and the classical equations for extended isolated bodies or pole-dipole particles is found. This can as well be taken as a confirmation that to the first order of a WKB approximation the gyro-gravitational factors of the classical angular nromentum and of the intrinsic quantum mechanical spin agree.

A preliminary note on a new optomotor response in crickets: Antennal tracking of moving targets

Abstract: Black disks moving horizontally in the visual field of a cricket (Gryllus campestris) induce an antennal tracking response. It consists of movements of the ipsilateral antenna following the target in a saccade-like fashion.

Eisenkomplexe als Modellverbindungen zur homogenen Hydrierung von Kohlenmonoxid

Abstract: Der μ-Distickstoffkomplex {Fe(CO)2[P(OCH3)3]2N2 (2) wird dargestellt und mit H2, CH2O und C2H4 zu Dihydrido-, Formaldehyd- und Ethylen-dicarbonylbis(trimethylphosphit)eisen-Komplexen 4,5 bzw. 6 umgesetzt. Die Strukturen von 2 und dem Dicarbonyltris(trimethylphosphit)-eisen-Komplex 3 wurden rontgenographisch bestimmt. Iron Complexes as Model Compounds for the Homogeneous Hydrogenation of Carbon Monoxide The μ-dinitrogen complex {Fe(CO)2[P(OCH3)3]2N2 (2) is prepared. Its reaction with H2, CH2O and C2H4 leads to dihydrido-, formaldehyde-, and ethylene-dicarbonylbis(trimethylphosphite)-iron complexes (4,5, and 6, respectively). The structures of 2 and of the dicarbonyltris(trimethylphosphite)iron complex 3 were determined by X-ray analyses.

Cryofixation of monolayer cell cultures for freeze-fracturing without chemical pre-treatments

Abstract: SUMMARY A cryofixation method is presented which gives excellent ultrastructural preservation of monolayer cell cultures without any chemical pretreatments. Rat hepatocytes in primary culture were used in this study. The equipment needed is inexpensive and easy to manufacture. Cells are grown on a usual tissue culture support material (Thermanox plastic sheets). For cryofixation, samples are prepared essentially by a combined sandwich-cryogen-jet technique. 3 mm large discs are punched out and sandwiched with Cu- or Au-object holders of little mass; a 15 μm spacer is put in between. The viability of the cells is not impaired by the manipulations before freezing. The sandwich sample is quickly frozen by shooting a propane jet from a simple pressure chamber on to the metal object holder. The relevant parameters were optimized by parallel freeze-fracture analyses of 5% glycerol as a model system and by thermocouple measurements. Sandwich samples are then mounted in an appropriate double replication specimen table for further analysis by freeze-fracturing. It is possible to obtain a certain selectivity of the fracture plane with regard to apical, lateral or basal aspects of the cell layer. Alternatively, disc samples can be processed by chemical fixation methods (including freeze substitution to determine the freeze-fracture plane), since the support material Thermanox is insensitive to organic solvents and easy to cut. In each case the cells remain attached to their substratum throughout the whole procedure. Thus, the ultrastructural data can be directly correlated with parallel functional analyses obtained from the same cell cultures.

Nucleotide. XIV. Substituierte β‐Phenyläthyl‐Gruppen. Neue Schutzgruppen für Oligonucleotid‐Synthesen nach dem Phosphorsäuretriester‐Verfahren

Abstract: XIV. Substituted β-Phenyl-ethyl Groups. New Blocking Groups for Oligonucleotide Syntheses by the Phosphotriester Approach Various o- and p-substituted β-phenylethanols (2–10) have been synthesized and investigated as blocking groups in the phosphotriester approach. A large number of 5′-O-tritylated thymidine-3′-phosphotriesters (13–36) with two different phosphate protecting groups have been prepared, characterized, and studied according to their chemical stability and usefullness for oligonucleotide syntheses. The combination of a 5′-O-monomethoxytrityl- and a 3′-(2,5-dichlorophenyl, p-nitrophenylethyl)-phosphate function as in 18 turned out to possess optimal properties as a monomeric nucleotide building block due to the fact that these blocking groups can be quantitatively and selectively be removed without harming each other by trifluoroacetic acid in chloroform to 41, by oximate to 42, and by DBU to 43. The base-catalyzed removal of the monosubstituted phenylethyl groups by DBU or DBN respectively as well as the disubstituted phenylethyl groups by triethylamine in aprotic solvents is a β-elimination process leading to phosphodiesters without attack on the P-center.

The Effects of Serial Order in Long Sequences of Auditory Stimuli on Event-Related Potentials

Abstract: The generalizability of the model relating P300 amplitudes to subjective probabilities, developed by Squires et al (1976) for random series of events, was examined with respect to long sequences of repetitions, which had been restricted in randomness, allowing only for sequences of between 4 and 12 frequent clicks Subjects were asked to silently count either the rarer of two clicks, presented with a probability of 10, or light stimuli occurring with the same temporal distribution Within these limits there was an increase in P300 amplitude not only to the rare clicks, but also—contrary to predictions from the model—to the frequent non-target clicks following longer series of repetitions, provided that clicks had to be counted A plausible interpretation might be that the longer the series of repetitions in long non-random sequences with low predictability, the more the subjects become involved in the “stimulus evaluation” of both kinds of events A similar increase across serial position was found for the N100 component to frequent clicks when the auditory modality was defined as task relevant, and was interpreted as progressive focusing of selective attention For the rare clicks there occurred a decrease in a slow Negative Shift with peak amplitude at 220 msec after long series of non-targets, possibly reflecting a facilitative effect of the focused attention on decision processes related to target detection There were no differences between normals and chronic alcoholics with respect to the above-mentioned effects