Biogenic 2‐methyl‐3‐buten‐2‐ol increases regional ozone and HO x sources

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95042/1/grl23505.pd

Dropping cold quantum gases on Earth over long times and large distances

We describe the non-relativistic time evolution of an ultra-cold degenerate quantum gas (bosons/fermions) falling in Earth's gravity during long times (10 sec) and over large distances (100 m). This models a drop tower experiment that is currently performed by the QUANTUS collaboration at ZARM (Bremen, Germany). Starting from the classical mechanics of the drop capsule and a single particle trapped within, we develop the quantum field theoretical description for this experimental situation in an inertial frame, the corotating frame of the Earth, as well as the comoving frame of the drop capsule. Suitable transformations eliminate non-inertial forces, provided all external potentials (trap, gravity) can be approximated with a second order Taylor expansion around the instantaneous trap center. This is an excellent assumption and the harmonic potential theorem applies. As an application, we study the quantum dynamics of a cigar-shaped Bose-Einstein condensate in the Gross-Pitaevskii mean-field approximation. Due to the instantaneous transformation to the rest-frame of the superfluid wave packet, the long-distance drop (100m) can be studied easily on a numerical grid.Comment: 18 pages latex, 5 eps figures, submitte

Free energy and configurational entropy of liquid silica: fragile-to-strong crossover and polyamorphism

Recent molecular dynamics (MD) simulations of liquid silica, using the ``BKS'' model [Van Beest, Kramer and van Santen, Phys. Rev. Lett. {\bf 64}, 1955 (1990)], have demonstrated that the liquid undergoes a dynamical crossover from super-Arrhenius, or ``fragile'' behavior, to Arrhenius, or ``strong'' behavior, as temperature $T$ is decreased. From extensive MD simulations, we show that this fragile-to-strong crossover (FSC) can be connected to changes in the properties of the potential energy landscape, or surface (PES), of the liquid. To achieve this, we use thermodynamic integration to evaluate the absolute free energy of the liquid over a wide range of density and $T$. We use this free energy data, along with the concept of ``inherent structures'' of the PES, to evaluate the absolute configurational entropy $S_c$ of the liquid. We find that the temperature dependence of the diffusion coefficient and of $S_c$ are consistent with the prediction of Adam and Gibbs, including in the region where we observe the FSC to occur. We find that the FSC is related to a change in the properties of the PES explored by the liquid, specifically an inflection in the $T$ dependence of the average inherent structure energy. In addition, we find that the high $T$ behavior of $S_c$ suggests that the liquid entropy might approach zero at finite $T$, behavior associated with the so-called Kauzmann paradox. However, we find that the change in the PES that underlies the FSC is associated with a change in the $T$ dependence of $S_c$ that elucidates how the Kauzmann paradox is avoided in this system. Finally, we also explore the relation of the observed PES changes to the recently discussed possibility that BKS silica exhibits a liquid-liquid phase transition, a behavior that has been proposed to underlie the observed polyamorphism of amorphous solid silica.Comment: 14 pages, 18 figure

Wetting and particle adsorption in nanoflows

Molecular dynamics simulations are used to study the behavior of closely-fitting spherical and ellipsoidal particles moving through a fluid-filled cylinder at nanometer scales. The particle, the cylinder wall and the fluid solvent are all treated as atomic systems, and special attention is given to the effects of varying the wetting properties of the fluid. Although the modification of the solid-fluid interaction leads to significant changes in the microstructure of the fluid, its transport properties are found to be the same as in bulk. Independently of the shape and relative size of the particle, we find two distinct regimes as a function of the degree of wetting, with a sharp transition between them. In the case of a highly-wetting suspending fluid, the particle moves through the cylinder with an average axial velocity in agreement with that obtained from the solution of the continuum Stokes equations. In contrast, in the case of less-wetting fluids, only the early-time motion of the particle is consistent with continuum dynamics. At later times, the particle is eventually adsorbed onto the wall and subsequently executes an intermittent stick-slip motion.We show that van der Walls forces are the dominant contribution to the particle adsorption phenomenon and that depletion forces are weak enough to allow, in the highly-wetting situation, an initially adsorbed particle to spontaneously desorb

Vacuum Ambiguity in de Sitter Space at Strong Coupling

It is well known that in the weak coupling regime, quantum field theories in de Sitter space do not have a unique vacuum, but a class of vacua parametrized by a complex parameter $\alpha$, i.e., the so-called $\alpha$-vacua. In this article, using gauge/gravity duality, we calculate the symmetric two-point function of strongly coupled ${\cal N}=4$ supersymmetric Yang-Mills theory on $dS_3$. We find that there is a class of de Sitter invariant vacua, parametrized by a set of complex parameters $\{\alpha_{\nu}\}$.Comment: 17 pages in JHEP style, references adde

Algorithm for numerical integration of the rigid-body equations of motion

A new algorithm for numerical integration of the rigid-body equations of motion is proposed. The algorithm uses the leapfrog scheme and the quantities involved are angular velocities and orientational variables which can be expressed in terms of either principal axes or quaternions. Due to specific features of the algorithm, orthonormality and unit norms of the orientational variables are integrals of motion, despite an approximate character of the produced trajectories. It is shown that the method presented appears to be the most efficient among all known algorithms of such a kind.Comment: 4 pages, 1 figur

Physics on the edge: contour dynamics, waves and solitons in the quantum Hall effect

We present a theoretical study of the excitations on the edge of a two-dimensional electron system in a perpendicular magnetic field in terms of a contour dynamics formalism. In particular, we focus on edge excitations in the quantum Hall effect. Beyond the usual linear approximation, a non-linear analysis of the shape deformations of an incompressible droplet yields soliton solutions which correspond to shapes that propagate without distortion. A perturbative analysis is used and the results are compared to analogous systems, like vortex patches in ideal hydrodynamics. Under a local induction approximation we find that the contour dynamics is described by a non-linear partial differential equation for the curvature: the modified Korteweg-de Vries equation. PACS number(s): 73.40.Hm, 02.40.Ma, 03.40.Gc, 11.10.LmComment: 15 pages, 12 embedded figures, submitted to Phys. Rev.

Lectures on string theory and cosmology

In these lectures I review recent attempts to apply string theory to cosmology, including string cosmology and various models of brane cosmology. In addition, the review includes an introduction to inflation as well as a discussion of transplanckian signatures. I also provide a critical discussion of the possible role of holography. The material is based on lectures given in January 2004 at the RTN String School in Barcelona, but also contain some additional material.Comment: Lectures given in January 2004 at the RTN Barcelona String School, 50 pages, 9 figure

Axiomatic geometrical optics, Abraham-Minkowski controversy, and photon properties derived classically

By restating geometrical optics within the field-theoretical approach, the classical concept of a photon (and, more generally, any elementary excitation) in arbitrary dispersive medium is introduced, and photon properties are calculated unambiguously. In particular, the canonical and kinetic momenta carried by a photon, as well as the two corresponding energy-momentum tensors of a wave, are derived from first principles of Lagrangian mechanics. As an example application of this formalism, the Abraham-Minkowski controversy pertaining to the definitions of these quantities is resolved for linear waves of arbitrary nature, and corrections to the traditional formulas for the photon kinetic energy-momentum are found. Several other applications of axiomatic geometrical optics to electromagnetic waves are also presented