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

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

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

Analisi carpologiche per la Vasca dello Specchio (Ferrara, XIV-XV sec. d.C.): metodologie d’indagine e risultati

Lo scavo condotto tra Corso Porta Reno e Via Vaspergolo, nel centro storico di Ferrara, ha portato alla luce un vano sotterraneo rettangolare denominato “Vasca dello Specchio”, utilizzato per lo smaltimento dei rifiuti tra XIV e XV secolo. Il riempimento, in parte già analizzato e pubblicato, è stato oggetto di nuove analisi carpologiche. I semi e i frutti, conservati prevalentemente per sommersione e in ottimo stato, sono complessivamente oltre 400.000 e la lista floristica comprende 168 taxa. La maggior parte dei reperti appartiene a piante coltivate/coltivabili o spontanee correlate all’uomo, che forniscono nuove informazioni sulla dieta vegetale e sull’ambiente urbano della Ferrara basso-medievale/rinascimentale. I reperti evidenziano anche pratiche domestiche e culinarie talora curiose