Showing papers by "University of Bordeaux published in 1978"

Analysis of the alternating current properties of ionic conductors

Abstract: A method of analysis of inclined semicircular complex impedance (Z) diagrams for ionic conductors has been developed on the basis of the concept of “non-Debye” behaviour of solid dielectrics. This approach replaces the rather arbitrary distribution of relaxation times by the physically much simpler concept of a frequency-independent ratio of energy lost per cycle to energy stored. This criterion of dielectric behaviour leads directly to complex admittance (Y) plots in the form of straight lines inclined to the vertical which then transform to inclined semicircles in Z. The use of Y diagrams gives better accuracy of representation and it is shown how this can be further enhanced by plotting log Yi − log Yr instead of the usual linear representation. Different parts of the graphs are assigned to “bulk” and “barrier” regions on the basis of the value of the dielectric permittivity and it is shown that a hitherto unrecognized physical process can manifest itself as a strong dispersion at frequencies intermediate between the high-frequency bulk response and the low-frequency barrier-dominated behaviour.

Increased spontaneous activity following substance P infusion into A10 dopaminergic area.

Abstract: THE polypeptide, substance P, has a discrete regional distribution in mammalian CNS; particularly high concentrations are found in the mesencephalon, close to the origin of the two major ascending dopaminergic pathways1,2 Two further observations which may reflect functional neurotransmission are, first, that substance P is released from spinal cord and hypothalamus3,4, and second, that it has been localised using fragmentation techniques in nerve ending particles of bovine hypothalamus and substantia nigra5,6 Further support for this hypothesis comes from iontophoretic studies in which application of substance P into the medial nucleus of amygdala and substantia nigra induced a strong neuronal activation7,8 It has also been shown biochemically that the activity of dopaminergic systems may be modulated by substance P neurones9,0 The ventral tegmental area (VTA), which contains the cell bodies of the dopaminergic A10 neurones (DA-A10), receives a substance P innervation mainly from substance P cell bodies localised in the medial habenular nucleus11,12 DA-A10 neurones give rise to the mesolimbic DA system and also to the mesocortical DA axons innervating cerebral cortical area13,14 We have studied the behavioural effects of local application of substance P into the VTA, to try to elucidate the physiological role of substance P innervation of this area A strong enhancement of spontaneous activity was observed following bilateral infusion of substance P A major feature of this enhancement was increased exploratory behaviour Moreover d-amphetamine-induced behavioural arousal was potentiated by previous infusion (1 h) of substance P into the VTA

Van der corput’s difference theorem

Abstract: We obtain a sufficient condition for a subsetH of positive integers to satisfy that the equidistribution (mod 1) of the sequences (u n+h − u n; n=1, 2, ···) for allh ∈H implies the equidistribution of (u n). Our condition is satisfied, for example, for the following sets: (1)H={n − m; n ∈ I, m ∈ I, n>m}, whereI is any infinite subset of integers; (2)H={| ψ (n)|; ψ(n)≠0,n ∈ Z}, where ψ is a nonconstant polynomial with integral coefficients having at least one integral zero (modq) for allq=2, 3, ···; (3)H={p+1;p is a prime} andH={p − 1;p is a prime}.

New antibiotics from the fungus Epicoccum nigrum. I. Fermentation, isolation and antibacterial properties.

Abstract: An atmosphere isolate of the fungus Epicoccum nigrum was found to exhibit an activity against Staphylococcus aureus. A more active, non-sporulating variant of this strain was selected. From its fermentation broth, two novel compounds, epicorazines A and B, were isolated by preparative TLC and tested against a series of bacteria.

Analysis of the complex impedance data for ?-PbF2

Abstract: Previously published complex impedance plots for the ionic conductor β-PbF2 show the familiar depressed circular arcs with an angle 07 π/2 and an activation energy for the volume conductivity Wv=045 eV A detailed analysis of this behaviour in terms of the recently developed “non-Debye” model shows the real part of the relative dielectric permittivity to have a frequency dependence ω07−1, with a high frequency limit of 50 Hz and with only weak dependence on temperature The low-frequency “spurs” on the impedance plots are shown to indicate an interfacial barrier at each electrode having a similar “non-Debye” frequency characteristic to the bulk but showing a strong temperature dependence with an activation energy equal to Wv/2 This suggests the presence of low Debye-screened barriers of about k T height, resulting from depletion and accumulation of ionic carriers at incompletely transmitting electrodes There is no visible effect of inter-grain boundaries on the flow of direct current

Model-Potential Calculations on the Molecular System NaNe

Abstract: Calculations for the $X^{2}\ensuremath{\Sigma}$, $A^{2}\ensuremath{\Pi}$, and $B^{2}\ensuremath{\Sigma}$ states of the NaNe molecular system are reported. The electron-neon interaction is represented by a local potential together with an explicit orthogonality condition to the neon orbitals. The well depth and location are $D=7.8$ ${\mathrm{cm}}^{\ensuremath{-}1}$ at ${\mathcal{r}}_{m}=10$ a.u. for the $X^{2}\ensuremath{\Sigma}$ state and $D=132$ ${\mathrm{cm}}^{\ensuremath{-}1}$ at ${\mathcal{r}}_{m}=5$ a.u. for the $A^{2}\ensuremath{\Pi}$ state, in excellent agreement with the laser-spectroscopy results of Ahmad-Bitar et al.

Influence of Magnesium on the Steady-State-Derived Order of Substrate Addition and Product Release in tRNA Trp Aminoacylation by Beef Pancreas Tryptophan: tRNA Ligase

Abstract: The order of the partial reactions in the aminoacylation of tRNATrpbeef by tryptophan : tRNA ligase from beef pancreas has been explored by measurements of intial velocity and product inhibition according to the analytical framework described by Cleland [Biochim. Biophys. Acta. 67, 104– 137, 173– 187, 188– 196 (1963)]. The kinetic patterns are suggestive of a ping-pong mechanism (bi-uni uni-bi). The oreder of addition of tryptophan and ATP that one can derive is crucially dependent on the conditions of magnesium concentration used. Random fixation of tryptophan and ATP is observed in studies performed at catalytically optimal magnesium concentration. Linear-ordered fixation of the two substrates, ATP binding first, is observed under conditions where magnesium concentration is in excess, which are not catalytically optimal. The analysis of the inhibition patterns taking into account the calculated concentrations of teh main active species Mg · ATP2− and Mg · P2O2−7 favors the random substrate-binding mechanism derived under optimal magnesium conditions. Under both conditions, adjusted and fixed magnesium, the release of products, AMP and tryptophanyl-tRNATrpbeef is, ordered, AMP released first. The change in the product nhibition patterns of aminoacylation of tRNATrpbeef by beef pancreas tryptophan: tRNA ligase under different magnesium concentration conditions casts some doubt on the significance of the comparison of mechanisms derived for amino-acid: tRNA ligases of different sources.