Showing papers by "Saarland University published in 1975"

Dielectric function and plasma resonances of small metal particles

Abstract: Using the simple model of electrons in a box, a dielectric function is derived which should be appropriate for small metal particles. This dielectric function is used to examine quantum size effects in the optical absorption spectra. For very small particles of uniform size and shape, the plasma resonance absorption should shift and broaden and should show fine structure corresponding to transitions between discrete conduction band energy levels. The size dependence of the shift and broadening was measured and found to be in quantitative agreement with theory.

Is potassium conductance of cardiac Purkinje fibres controlled by [Ca 2+ ] i ?

Abstract: ELEVATED extracellular Ca2+ concentration1, prolonged treatment with high doses of cardiac glycosides2, and metabolic inhibition3 shorten the action potential of cardiac muscle. In these conditions the intracellular free Ca2+ may be increased and an increase in intracellular Ca2+ could produce shortening of the action potential either by affecting the Ca2+ inward current or by increasing the potassium permeability4. The latter mechanism has been observed in red blood cells5 and in the neurones of some species6–8. Here I give the results of studying the effect of iontophoretically injected Ca2+ in cardiac Purkinje cells. Such injection led to membrane hyperpolarisation and considerable shortening of the action potential, suggesting that the level of intracellular free Ca2+ can affect the potassium permeability in cardiac muscle.

Calcium conductance and tension in mammalian ventricular muscle.

Abstract: Voltage, membrane current and contraction were simultaneously measured in voltage clamp experiments (single sucrose gap) on cat ventricular trabeculae The pulse programs allowed the determination of the potential dependence of the steady state activation and inactivation as well as the restoration of the calcium-carrying system (slow inward current)

Nearly optimal binary search trees

Abstract: We discuss two simple strategies for constructing binary search trees: "Place the most frequently occurring name at the root of the tree, then proceed similary on the subtrees "and" choose the root so as to equalize the total weight of the left and right subtrees as much as possible, then proceed similarly on the subtres." While the former rule may yield extremely inefficient search trees, the latter rule always produces nearly optimal trees.

Über die punktweise Konvergenz Finiter Elemente

Abstract: The solution of the Dirichlet problem for Poissons equation ??u=f in a two dimensional convex polyhedral domain Ω is approximated by the simplest finite element method, where the trial functions are linear in triangles of maximal diameterh. The convergence rate in certain weighted Sobolev spaces is established. It follows that for everyx?Ω, the rate of convergence inx ish 2?? with arbitrary small ?>0, iff?L 2(Ω) andf bounded in a neighbourhood ofx. This estimate is close to theh 2-accuracy observed in practical calculations.

Displacement currents in the node of Ranvier. Voltage and time dependence.

Abstract: The time course of the membrane currents in the node of Ranvier in which the sodium and potassium conductances have been blocked reveals asymmetries during and after the application of depolarizing and hyperpolarizing voltage-clamp pulses of identical size. Since, 1. the integrals of the “on” and “off” current transients were found to be equal and opposite, 2. the charge displaced reached saturation (about 140·10−15 C/node) when the internal potential was taken to a sufficiently positive value during the depolarizing pulses and, 3. the size of the charge transferred was unaffected by temperature although its time constant had a large temperature coefficient (Q10=2.4), these currents to our opinoon must result from charge movements confined to the membrane and, therefore, can be considered as non-linear displacement currents.

On the structure of non-equilibrium high-angle grain boundaries

Abstract: The incorporation of lattice dislocations into high-angle grain boundaries either with small radii of curvature or absorbing lattice defects is observed by the in situ heating of thin foils in a transmission electron microscope. At a given temperature, the rate of incorporation is higher than for equilibrium boundaries. The observations indicate that the forces acting on the types of boundaries studied have displaced some of the atoms in them from their equilibrium sites.

Violation of Dynamical Scaling for Randomly Dilute Ising Ferromagnets near Percolation Threshold

Abstract: Strongly anisotropic magnets at low temperatures with many (quenched) nonmagnetic impurities are shown to deviate from usual dynamical scaling assumptions near the critical concentration; instead of the time, the logarithm of the time is the basic variable. Analysis of previous Monte Carlo data confirms the static droplet picture used here, which fulfills for the first time the homogeneity, analyticity, and symmetry requirements of static scaling.

Acetylcholine receptor: modification of synaptic gating mechanism after treatment with a disulfide bond reducing agent.

Abstract: Reduction of a ‘reactive’ disulfide bond in the postsynaptic membrane of the frog neuromuscular junction by dithiothreitol (DTT) decreases both the sensitivity of the membrane to applied acetylcholine (ACh) and the amplitude of the single ‘shot effect’. Analysis of ACh induced conductance fluctuations in voltage clamped frog endplates indicates that DTT reduces both the amplitude γ and duration τ of the elementary conductance events. The mean control value of γ was 18.5·10−12 Ω−1 with no significant dependence on temperature. The mean control values of τ were 2.3 msec at 7–9°C and 0.94 msec at 20–22°C. At 7–9°C 1 mM DTT (20–50 min after application) reduced γ to 61% of the control value and at 20–22°C to 39%, while τ was reduced to 70% at both temperature ranges. The dose-response curve for iontophoretically applied ACh indicates that neither the total number of ionic channels nor the cooperativity within the receptors are changed. However, the affinity of ACh for the receptor sites was reduced. All effects of DTT were fully reversed by the oxidizing agent 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB).

Effect of vanadium on growth, chlorophyll formation and iron metabolism in unicellular green algae.

Abstract: In the presence of vanadium, growth of Scenedesmus obliquus and Chlorella pyrenoidosa was increased five to sixfold as determined by dry weight, when cultured under autotrophic conditions for 7 days. The stimulation by vanadium decreased with increasing stability towards hydrolysis of the iron(III)-compounds added. Pentavalent vanadium (20 mug V/1 as NH4VO3) was able to overcome completely a limited iron-deficiency in the algae following growth in presence of 1.8 - 10(-5) m ferric chloride. Vanadium did not alter the iron uptake into the algal cells. 90% of offered 48V was taken up by Scenedesmus obliquus during 5 days of growth, and 21% thereof were found in the chloroplast fraction. In presence of vanadium, the chlorophyll formation was stimulated in Scenedesmus obliquus. This stimulation by vanadium was found to be light-dependent but occurred to a certain extent in the dark also. The main porphyrin of the yellow mutant 211-11h/20 of Chlorella vulgaris was identified as protoporphyrin-IX. The formation of this compound was stimulated by vanadium within 10 days up to 83%. The role of vanadium in the biosynthesis of chlorophylls is discussed.

Density and dose-response curve of acetylcholine receptors in frog neuromuscular junction

Abstract: THE description of the reaction between acetylcholine (ACh) and receptors in the end-plate membrane requires determination of the dose-response curve. The most appropriate response to measure is the conductance change of the voltage clamped end-plate1,2. Recent improvements of the microiontophoretic method3,4, as well as direct visual control of the ACh-pipette in relation to the nerve terminal5, enabled us to use the focal application method in a reasonably quantitative way. Only end-plates with a sole, straight running terminal were chosen for the experiments3–5, and ACh was always applied at the end of a terminal. The known geometrical arrangement allowed us to calculate the local ACh concentration in amplitude and time course at each point of the terminal by the diffusion law, and to compare it with the measured response of the voltage clamped end-plate. Our results indicate that at least three molecules of ACh react with one receptor unit.

Crossover scaling, correlation function and connectivity in dilute low temperature ferromagnets

Abstract: For quenched dilute ferromagnets with a fractionp of spins (nearest neighbor exchange energyJ) and a fraction 1 —p of randomly distributed nonmagnetic atoms, a crossover assumption similar to tricritical scaling theory relates the critical exponents of zero temperature percolation theory to the low temperature critical amplitudes and exponents near the critical lineT c (p)>0. For example, the specific heat amplitude nearT c (p) is found to vanish, the susceptibility amplitude is found to diverge forT c (p →p c ) → 0. (Typically,p c =20%.) AtT=0 the spin-spin correlation function is argued from a droplet picture to obey scaling homogeneity but (at fixed distance) not to vary like the energy; instead it varies as const + (p c —p)2β +⋯ for fixed small distances. A generalization of the correlation function to finite temperatures nearT c (p) allows to estimate the number of effective percolation channels connecting two sites in the infinite (percolating) network forp>p c ; this in turn gives, via a dynamical scaling argument, a good approximation for theT=0 percolation exponent 1.6 in the conductivity of random three-dimensional resistor networks. This channel approximation also givesΦ=2 for the crossover exponent; i.e. exp(−2J/kT c (p)) is an analytic function ofp nearp=p c . An appendix shows that cluster-cluster correlations atT=0 (excluded volume effects) are responsible for the difference between percolation exponents and the (pure) Ising exponents atT c (p=1).

Molecular structure, quadrupole splitting, and magnetic susceptibility of iron in deoxygenated myoglobin and hemoglobin

Abstract: For three stereo-structural models of deoxymyoglobin (Mb) and deoxyhemoglobin (Hb) we derive electronic configurations and their mutual spin-orbit coupling. From the temperature dependent molecular electric field gradient (EFG) tensor we calculate temperature dependent quadrupole splittings, ΔE q(T), asymmetry parameters, η(T), and orientations of the EFG component V zz(T) with respect to the heme group. Comparing theoretical and experimental data we find a molecular electronic structure, which then is used to compute temperature dependent magnetic susceptibilities, χ(T). Theoretical and experimental χ(T) data are in reasonable agreement. From the consistency of our model calculations with experimental results we conclude that iron in Mb and Hb probably is pentacoordinated and considerably out of the heme plane by 0.4–0.8 A.

Relativistic electron densities and isomer shifts of Fe57 in iron-oxygen and iron-fluorine clusters and of iron in solid noble gases

Abstract: Relativistic calculations of various electronic configurations of the iron atom are used in conjunction with Huckel-type molecular-orbital and limited-configuration-interaction calculations of iron-containing clusters to determine electron densities at the iron nucleus. The calculations include all effects of the overlap of iron core and ligand orbitals, and the effect of potential distortion of iron-core orbitals due to molecular configurations $3{d}^{m}4{s}^{n}$. Using the calculated electron densities and experimental isomer shifts, the relative change in the $^{57}\mathrm{Fe}$ nuclear-charge radius is deduced from studies of Fe$\mathrm{O}_{6}^{\ensuremath{-}9}$ and Fe$\mathrm{O}_{6}^{\ensuremath{-}10}$ as (-8.72 \ifmmode\pm\else\textpm\fi{} 1.02) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, from studies of Fe$\mathrm{F}_{6}^{\ensuremath{-}3}$ and Fe$\mathrm{F}_{6}^{\ensuremath{-}4}$ as (-9.18 \ifmmode\pm\else\textpm\fi{} 0.56) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, and from iron monomers and dimers dissolved in solid noble gases as (-7.12 \ifmmode\pm\else\textpm\fi{} 0.59) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ or (-8.65 \ifmmode\pm\else\textpm\fi{} 0.71) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, depending upon the assumed dimer geometry. From all these studies we obtain for the relative change in charge-radius value an average of (-8.85 \ifmmode\pm\else\textpm\fi{} 0.9) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$, in reasonable agreement with the work of several other investigators.

Gating currents in the node of Ranvier: voltage and time dependence.

Abstract: Like the axolemma of the giant nerve fibre of the squid, the nodal membrane of frog myelinated nerve fibres after blocking transmembrane ionic currents exhibits asymmetrical displacement currents during and after hyperpolarizing and depolarizing voltage clamp pulses of equal size. The steady-state distribution of charges as a function of membrane potential is consistent with Boltzmanns law (midpoint potential minus 33.7 mV; saturation value 17200 charges/mum-2). The time course of the asymmetry current and the voltage dependence of its time constant are consistent with the notion that due to a sudden change in membrane potential the charges undergo a first order transition between two configurations. Size and voltage dependence of the time constant are similar to those of the activation of the sodium conductance assuming m-2h kinetics. The results suggest that the presence of ten times more sodium channels (5000/mum-2) in the node of Ranvier than in the squid giant axon with similar sodium conductance per channel (2-3 pS).

Correlations between aerodynamic output, electrical activity in the indirect flight muscles and wing positions of bees flying in a servomechanically controlled wind tunnel

Abstract: 1) Bees hanging on an aerodynamic two component balance were placed in front of a laminar wind tunnel. They controlled the wind velocity in the tunnel through a servo-mechanism that held the wind velocity to exactly the opposite of the flight speed, thus selecting lift and thrust freely. The parameters lift, wind velocity, occurrence of action potentials in the indirect dorsoventral flight muscles (DV) and indirect dorsolongitudinal flight muscles (DL) and body temperature were measured. The correlations were analysed (Fig. 1). 2) The lift is positively correlated to the body angle (angle between body length axis and wind tunnel length axis), the flight speed is negatively correlated to the body angle (Fig. 2). 3) Action potential frequencies in both muscle groups exhibit a strong positive correlation to the lift (Fig. 3). Changes in action potential frequencies and lift run parallel with a delay of less than 200 msec (limitation imposed by measuring system). Different motor units in a given muscle have different absolute discharge frequencies (Fig. 4). 4) A pronounced synchronization between wingbeats and action potentials in the indirect dorsoventral muscles can always be found. 5) Randomly triggered photographic pictures show the wings most frequently at the lower turning point. Exposures that were triggered by action potentials in the dorsoventral indirect flight muscles display this wing position significantly more frequently (Fig. 5).

Recent observations on ependyma and subependymal basement membranes.

Abstract: Directly under the ependyma, and between the ependymal cells, there are basement membranes which form labyrinths connecting with the perivascular basement membranes of the subependymal vessels. The basement membranes exhibit differences in form, position, and distribution, and they can be distended by fluid absorption into large lacunae. The membranes can be identified as glycoprotein and glylcolipid substances. Electron microscopic studies have shown the differences between the basement membrane labyrinths of the human, the rabbit and the rat. In the human, the labyrinths contain isolated collagen fibrils. Basement membranes generally line all connective tissue spaces and form their interstitial borders. From this point of view, the subependymal basement membrane labyrinths can be seen as interstitial spaces near the ventricles, forming pathways between the ependyma and the subependymal capillaries or postcapillary veins.

Temperature sensitivity of outward current in cardiac Purkinje fibers. Evidence of electrogenicity of active transport.

Abstract: 1. In cardiac Purkinje fibers the temperature sensitivity of the membrane current flowing after 2 sec in response to depolarizing clamp steps was recorded. When the temperature was quickly lowered (30 sec) from 37°C to 20°C for a period of 2 min the outward current was markedly reduced. The effect was immediately reversed upon rewarming. The reduction in outward current on cooling was most pronounced between 30°C and 20°C. 2. In the range of anomalous rectification cooling to 20°C shifted the i.v. relation in a negative direction by a constant amount of 20 nA. Outside this potential range (negative to −80 mV and positive to −45 mV) the slope conductance was reduced with a Q10 of about 1.3. 3. In the presence of dihydroouabain cooling did not further reduce the outward current in the potential range of anomalous rectification. However, negative to −80 mV and positive to −40 mV the slope conductance was reduced.

Pt(CN)2-4 and Au(CN)-2: potential general probes for anion-binding sites of proteins. 35Cl and 81Br nuclear-magnetic-resonance studies.

Abstract: Nuclear magnetic quadrupole relaxation appears to be a general method for studying the binding of anions to proteins. This is shown by the increase in transverse quadrupole relaxation rate of 35Cl− and 81Br− in the presence of horse liver alcohal dehydrogenase, lysozyme, trypsin, α-chymotrypsin, human carbonic anhydrase, fructose-1,6-bisphosphate aldolase and human serum albumin. Of the many possible binding sites at the surface of a protein (e.g. positively charged amino acid side-chains) only a few account for the main part of the relaxation enhancement. This is shown by the decrease in 35Cl− and 81Br− relaxation rate on addition of functional ligands. Large, kinetically inert, complex anions like Pt(CN)2-4 and Au(CN)−2 are found to act as strong competitors towards halogen ions for the high-affinity anion binding sites of a number of proteins. Titrations with complex anions following the 35Cl− or 81Br− relaxation rates are found to be helpful in attempts to elucidate binding mechanisms. Especially, the complex anions may be useful probes for the discrimination between general and metallic anion binding sites in proteins and they also permit correlation of information from X-ray investigations of crystals with that from physical measurements in solution. From the change in halide ion quadrupole relaxation rate on addition of strongly binding ligands the quadrupole coupling constants of the high affinity Cl− and Br− binding sites are estimated using certain assumptions. It is found that for several proteins, comprising the metal-free proteins but also alcohol dehydrogenase and Escherichia coli alkaline phosphatase, the 35Cl quadrupole coupling constants have approximately the same values. For some other metallo-proteins like carbonic anhydrase and a zinc · serum-albumin complex considerably greater quadrupole coupling constants were obtained. The estimated quadrupole coupling constants are used as a basis for a discussion of the interactions involved in anion-protein interactions.

A language over a one symbol alphabet requiring only O (log log n) space

Abstract: A language over a one symbol alphabe t requiring only 0(log log n) spac e It is well known that the minimal growth function for th e tape complexity of Turing machines is log log n (21. In th e literature, one can find essentially one example of a language requiring only 0(log log n) space, namel y Lo ={ bin(1) $ bin(2) bin(3)-if. .. # bin(n)* ; n E IN } where bin(i) is the binary representation of the integer i. In this note we describe a language over a one symbo l alphabet having space complexity 0(log log n). Let L 1 = { an ; the smallest number q which does not divid e n is a power of two } For every natural number n let q(n) be the smallest numbe r which does not divide n. Lemma : 3c > 0 : q(n) S c log n Proof :. Let n be any natural number and let m = q(n). The n all primes less than m divide n and hence their product P divides them. By the prime number theorem of Gauss there ar e about m/ log m primes less than m and hence P is larger than