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The confining trailing string
We extend the holographic trailing string picture of a heavy quark to the
case of a bulk geometry dual to a confining gauge theory. We compute the
classical trailing confining string solution for a static as well as a
uniformly moving quark. The trailing string is infinitely extended and
approaches a confining horizon, situated at a critical value of the radial
coordinate, along one of the space-time directions, breaking boundary
rotational invariance. We compute the equations for the fluctuations around the
classical solutions, which are used to obtain boundary force correlators
controlling the Langevin dynamics of the quark. The imaginary part of the
correlators has a non-trivial low-frequency limit, which gives rise to a
viscous friction coefficient induced by the confining vacuum. The vacuum
correlators are used to define finite-temperature dressed Langevin correlators
with an appropriate high-frequency behavior.Comment: 63 pages plus appendices, 19 figures; version accepted for
publication in JHE
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Formalising Engineering Judgement on Software Dependability via Belief Networks
Low-dimensional weakly interacting Bose gases: non-universal equations of state
The zero-temperature equation of state is analyzed in low-dimensional bosonic
systems. In the dilute regime the equation of state is universal in terms of
the gas parameter, i.e. it is the same for different potentials with the same
value of the s-wave scattering length. Series expansions of the universal
equation of state are reported for one- and two- dimensional systems. We
propose to use the concept of energy-dependent s-wave scattering length for
obtaining estimations of non-universal terms in the energy expansion. We test
this approach by making a comparison to exactly solvable one-dimensional
problems and find that the generated terms have the correct structure. The
applicability to two-dimensional systems is analyzed by comparing with results
of Monte Carlo simulations. The prediction for the non-universal behavior is
qualitatively correct and the densities, at which the deviations from the
universal equation of state become visible, are estimated properly. Finally,
the possibility of observing the non-universal terms in experiments with
trapped gases is also discussed.Comment: 11 pages, 4 figure
Conformational Studies by Dynamic NMR. 64. Stereomutations of Atropisomers and of Conformational Enantiomers in Ethers of Hindered Naphthylcarbinols.
Conformational Studies by Dynamic NMR. Part 62. Stereomutations of Rotamers and of Conformational Enantiomers in 1,2-Diacylbenzenes.
Conformational Studies by Dynamic NMR. 65.1 Interconversion of Stereolabile Meso and Racemic Diastereoisomers of Hindered 1,4-Diacylnaphthalenes.
Steric Effects which Determine the Conformational Preferences and Stereodynamic Processes of Aryl Fluorenyl Ketones.
The stereodynamic processes and conformational preferences of two classes of aryl fluorenyl ketones have been investigated by means of dynamic NMR spectroscopy, DFT calculations and X-ray diffraction. When the aryl substituent has two hydrogens in the ortho positions, its rotation is independent of that of the fluorene ring. On the contrary, if the two ortho hydrogens are replaced by the bulkier methyl groups (e.g. mesityl fluorenyl ketones), the motion of the aryl ring interacts with the fluorene, and the two rings rotate in a correlated manner
Gating of L-type Ca2+ channels in embryonic chick ventricle cells: dependence on voltage, current and channel density
1. L-type calcium channels in embryonic chick heart ventricle have voltage-dependent, time-variant kinetics when they conduct inward currents carried by 20 mM-Ba2+. Depolarizing the membrane from -20 to 20 mV increases mean open time from 1.4 to 4.2 ms. Mean open time increases monotonically with voltage. The single-channel conductance, 18 +/- 2 pS, is approximately linear over this voltage range, and the extrapolated reversal potential is 38 +/- 5 mV. 2. In cell-attached patches with five or more L-type Ca2+ channels in the patch, the currents elicited by 500 ms depolarizing steps, from a -80 mV holding potential, inactivate rapidly and have large tail currents. In the same patch, currents from a -40 mV holding potential are smaller, inactivate more slowly, and have practically no tail currents. 3. In cell-attached patches containing one of two L-type Ca2+ channels, currents from -80 or -40 mV are virtually identical, and they are similar to the currents from multichannel patches held at -40 mV. 4. The voltage-dependent, time-variant kinetics of individual L-type Ca2+ channels are unaltered if the patch is removed from the cell and forms an inside-out configuration. In these experiments the internal membrane was bathed with an artificial, intracellular-like solution containing no phosphorylating enzymes or substrates. 5. Cells bathed in 20 mM-Ba2+ solutions and held at -80 mV have currents with an early phase that inactivates in tens of milliseconds, a late phase that inactivates in hundreds of milliseconds, and a large, slow tail current. Currents from -40 mV have only the late phase and practically no tails. However, if the maximum current is less than 0.1 pA pF-1, records from either -80 or -40 mV are virtually identical, and they are similar to currents from cells with higher channel density held at -40 mV. Furthermore, if cells are stimulated before full recovery from inactivation, the reduced current is accompanied by slower inactivation. 6. Whole-cell currents in 1.5 mM-Ca2+ solutions are entirely abolished by addition of 20 microM-nifedipine, and they are enhanced 2-3 times by addition of 30 microM-cyclic AMP and 3 mM-ATP to the whole-cell recording electrode. The whole-cell currents in 20 mM-Ba2+ solutions are also completely blocked by 20 microM-nifedipine, regardless of kinetics or holding potential. Thus, by definition, the cells we are studying contain only L-type channels
Conformational Studies by Dynamic NMR. 80. Cog-Wheel Effect in the Stereolabile Helical Enantiomers of Dimesityl Sulfoxide and Sulfone.
The 1H NMR solution spectra of the title compounds display anisochronous lines for the o-methyl substituents below -170 °C, due to the existence of two propeller-like M and P conformational enantiomers. The free energies of activation for the interconversion were determined to be 4.5 and 5.0 kcal mol -1, respectively, for dimesityl sulfoxide and dimesityl sulfone. Molecular mechanics calculations indicate that the enantiomerization process occurs via a correlated rotation (cog-wheel effect) entailing a one-ring flip (gear-meshing) pathway. 13C NMR (CP-MAS) spectra and X-ray diffraction show that these helical enantiomers are stable in the crystalline state
Experimental Investigation of the Effect of Transient Overvoltages on XLPE-insulated HVDC Cables
HVDC cables are subject to several types of impulses superimposed on the rated DC voltage during their service lifetime. Temporary Overvoltages (TOVs) and Superimposed Switching impulses (SSIs) are considered some of the most challenging due to the relatively long impulse duration. This paper aims at investigating experimentally the effect of TOVs and SSIs on XLPE insulation for extruded HVDC cables. 0.15-mm-thick DC-XLPE specimens, aged by applying TOVs and SSIs, are characterized using dielectric analyzer and Fourier Transform InfraRed spectroscopy (FTIR) to detect the aging effects on the insulation. Results show an increase in the imaginary part of permittivity, ε", accompanied with the appearance of additional dipolar polarization losses peaks. The amplitude and frequency of the aforementioned peaks vary with the amplitude and the number of applied TOVs and SSIs. An increase in electrical conductivity is also noticed with aging. FTIR results show absorbance peaks in the aged specimens likely due to the intramolecular bonds rupture accompanied with the formation of aging products. In summary, SSIs and TOVs cause a noticeable reduction of insulating properties in XLPE specimens. The higher the peak of the transient, the greater the aging effect
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