Minimal Surfaces, Screw Dislocations and Twist Grain Boundaries

Large twist-angle grain boundaries in layered structures are often described by Scherk's first surface whereas small twist-angle grain boundaries are usually described in terms of an array of screw dislocations. We show that there is no essential distinction between these two descriptions and that, in particular, their comparative energetics depends crucially on the core structure of their screw-dislocation topological defects.Comment: 10 pages, harvmac, 1 included postscript figure, final versio

Phase Transition between the Cholesteric and Twist Grain Boundary C Phases

The upper critical temperature Tc2 for the phase transition between the Cholesteric phase (N*) and the Twist Grain Boundary C phase with the layer inclination tilted to the pitch axis (TGBct) in thermotropic liquid crystals is determined by the mean field Chen-Lubensky approach. We show that the N*-TGBct phase transition is split in two with the appearance of either the TGBA or the TGB2q phase in a narrow temperature interval below Tc2. The latter phase is novel in being superposed from two degenerate TGBct phases with different (left and right) layers inclinations to the pitch axis.Comment: Phys. Rev. E, to be publ; 24 pages, RevTeX + 3 ps figure

Cannabinoids: an Effective Treatment for Chemotherapy-Induced Peripheral Neurotoxicity?

Chemotherapy-induced peripheral neurotoxicity (CIPN) is one of the most frequent side effects of antineoplastic treatment, particularly of lung, breast, prostate, gastrointestinal, and germinal cancers, as well as of different forms of leukemia, lymphoma, and multiple myeloma. Currently, no effective therapies are available for CIPN prevention, and symptomatic treatment is frequently ineffective; thus, several clinical trials are addressing this unmet clinical need. Among possible pharmacological treatments of CIPN, modulation of the endocannabinoid system might be particularly promising, especially in those CIPN types where analgesia and neuroinflammation modulation might be beneficial. In fact, several clinical trials are ongoing with the specific aim to better investigate the changes in endocannabinoid levels induced by systemic chemotherapy and the possible role of endocannabinoid system modulation to provide relief from CIPN symptoms, a hypothesis supported by preclinical evidence but never consistently demonstrated in patients. Interestingly, endocannabinoid system modulation might be one of the mechanisms at the basis of the reported efficacy of exercise and physical therapy in CIPN patients. This possible virtuous interplay will be discussed in this review

Boundary Effects in Chiral Polymer Hexatics

Boundary effects in liquid-crystalline phases can be large due to long-ranged orientational correlations. We show that the chiral hexatic phase can be locked into an apparent three-dimensional N+6 phase via such effects. Simple numerical estimates suggest that the recently discovered "polymer hexatic" may actually be this locked phase.Comment: 4 pages, RevTex, 3 included eps figure

Comment on "Quantum Phase Slips and Transport in Ultrathin Superconducting Wires"

In a recent Letter (Phys. Rev. Lett.78, 1552 (1997) ), Zaikin, Golubev, van Otterlo, and Zimanyi criticized the phenomenological time-dependent Ginzburg-Laudau model which I used to study the quantum phase-slippage rate for superconducting wires. They claimed that they developed a "microscopic" model, made qualitative improvement on my overestimate of the tunnelling barrier due to electromagnetic field. In this comment, I want to point out that, i), ZGVZ's result on EM barrier is expected in my paper; ii), their work is also phenomenological; iii), their renormalization scheme is fundamentally flawed; iv), they underestimated the barrier for ultrathin wires; v), their comparison with experiments is incorrect.Comment: Substantial changes made. Zaikin et al's main result was expected from my work. They underestimated tunneling barrier for ultrathin wires by one order of magnitude in the exponen

Band Gaps for Atoms in Light based Waveguides

The energy spectrum for a system of atoms in a periodic potential can exhibit a gap in the band structure. We describe a system in which a laser is used to produce a mechanical potential for the atoms, and a standing wave light field is used to shift the atomic levels using the Autler-Townes effect, which produces a periodic potential. The band structure for atoms guided by a hollow optical fiber waveguide is calculated in three dimensions with quantised external motion. The size of the band gap is controlled by the light guided by the fiber. This variable band structure may allow the construction of devices which can cool atoms. The major limitation on this device would be the spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through http://online.anu.edu.au/Physics/papers/atom.htm

Tunneling Between a Pair of Parallel Hall Droplets

In this paper, we examine interwell tunneling between a pair of fractional quantum Hall liquids in a double quantum well system in a tilted magnetic field. Using a variational Monte Carlo method, we calculate moments of the intra-Landau level tunneling spectrum as a function of in-plane field component $B_{\parallel}$ and interwell spacing $d$. This is done for variety of incompressible states including a pair of $\nu=1/3$ layers ([330]), pair of $\nu=1/5$ layers ([550]), and Halperin's [331] state. The results suggest a technique to extract interwell correlations from the tunneling spectral data.Comment: 21 pages and 8 figures (included), RevTeX, preprint no. UCSDCU

Resonant radiation pressure on neutral particles in a waveguide

A theoretical analysis of electromagnetic forces on neutral particles in an hollow waveguide is presented. We show that the effective scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induce a resonant enhanced backscattering state of the scatterer-guide system close to the onset of new modes. The particle effective cross section can then be as large as the wavelength even far from any transition resonance. As we will show, a small particle can be strongly accelerated along the guide axis while being highly confined in a narrow zone of the cross section of the guide.Comment: RevTeX,4 pages,3 PS figure

Shifting the quantum Hall plateau level in a double layer electron system

We study the plateaux of the integer quantum Hall resistance in a bilayer electron system in tilted magnetic fields. In a narrow range of tilt angles and at certain magnetic fields, the plateau level deviates appreciably from the quantized value with no dissipative transport emerging. A qualitative account of the effect is given in terms of decoupling of the edge states corresponding to different electron layers/Landau levels.Comment: 3 pages, 3 figures include

Analytical results for random walks in the presence of disorder and traps

In this paper, we study the dynamics of a random walker diffusing on a disordered one-dimensional lattice with random trappings. The distribution of escape probabilities is computed exactly for any strength of the disorder. These probabilities do not display any multifractal properties contrary to previous numerical claims. The explanation for this apparent multifractal behavior is given, and our conclusion are supported by numerical calculations. These exact results are exploited to compute the large time asymptotics of the survival probability (or the density) which is found to decay as $\exp [-Ct^{1/3}\log^{2/3}(t)]$. An exact lower bound for the density is found to decay in a similar way.Comment: 21 pages including 3 PS figures. Submitted to Phys. Rev.