Random Walks in Rindler Spacetime and String Theory at the Tip of the Cigar

In this paper, we discuss Rindler space string thermodynamics from a thermal scalar point of view as an explicit example of the results obtained in JHEP 1402 (2014) 127. We discuss the critical behavior of the string gas and interpret this as a random walk near the black hole horizon. Combining field theory arguments with the random walk path integral picture, we realize (at genus one) the picture put forward by Susskind of a long string surrounding black hole horizons. We find that thermodynamics is dominated by a long string living at string-scale distance from the horizon whose redshifted temperature is the Rindler or Hawking temperature. We provide further evidence of the recent proposal for string theory at the tip of the cigar by comparing with the flat space orbifold approach to Rindler thermodynamics. We discuss all types of closed strings (bosonic, type II and heterotic strings).Comment: 54 pages, v2: version accepted for publication in JHE

Near-Hagedorn Thermodynamics and Random Walks: a General Formalism in Curved Backgrounds

In this paper we discuss near-Hagedorn string thermodynamics starting from the explicit path integral derivation recently found by JHEP 0607 (2006) 031. Their result is extended and the validity is checked by comparing with some known exact results. We compare this approach with the first-quantized one-loop result from the low energy effective field theory and establish correction terms to the above result.Comment: 38 pages, v2: version accepted for publication in JHE

Inhomogeneous soliton ratchets under two ac forces

We extend our previous work on soliton ratchet devices [L. Morales-Molina et al., Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac forces including non-harmonic drivings, as proposed for particle ratchets by Savele'v et al. [Europhys. Lett. 67}, 179 (2004); Phys. Rev. E {\bf 70} 066109 (2004)]. Current reversals due to the interplay between the phases, frequencies and amplitudes of the harmonics are obtained. An analysis of the effect of the damping coefficient on the dynamics is presented. We show that solitons give rise to non-trivial differences in the phenomenology reported for particle systems that arise from their extended character. A comparison with soliton ratchets in homogeneous systems with biharmonic forces is also presented. This ratchet device may be an ideal candidate for Josephson junction ratchets with intrinsic large damping

Vidarabin-monophosphate, BCNU, VM26--an in vitro comparative study of active agents in the treatment of malignant human brain tumours.

BCNU (carmustine), VM26 (teniposide) and ARA-A5'P (vidarabin-monophosphate) were compared in their activity against 30 cell lines of primary (N = 21) and metastatic (N = 9) human brain tumours, which were characterized in tissue culture by cytochemical, immunological and cytogenetic criteria. In vivo achievable concentration-time products c X t were correlated with in vitro pharmacokinetic data in order to evaluate in vitro drug sensitivity at relevant exposure doses. A microcytotoxicity assay was employed to screen for drug toxicity in individual tumour cell lines. Following drug exposure and 5 to 8 population doubling times of untreated controls, RNA-synthesis - as a parameter of cell metabolism and proliferation - was determined by incorporation of [5,6-3H]-uridine into cellular RNA (liquid scintillation counting protocol). The cytotoxic effect of each drug on individual cell lines was expressed in terms of a sensitivity index (SI); by these means effects of different drugs on individual tumour cell lines could be compared. Mean sensitivity indices of ARA-A5'P, BCNU and VM26 for primary brain tumour cell lines were 0.59, 0.82 and 0.54. ARA-A5'P and VM26 had almost similar activities against brain tumour cell lines, whereas BCNU was significantly (P less than 0.001) less active. High grade gliomas were less sensitive to all three agents than low grade and infratentorial gliomas. ARA-A5'P was also able to effectively reduce colony formation in brain tumour cell lines. A cross-resistance of ARA-A5'P to either BCNU or VM26 could not be observed. Clearly, ARA-A5'P is an effective drug in treatment of brain tumour cells in vitro

Switching between different vortex states in 2-dimensional easy-plane magnets due to an ac magnetic field

Using a discrete model of 2-dimensional easy-plane classical ferromagnets, we propose that a rotating magnetic field in the easy plane can switch a vortex from one polarization to the opposite one if the amplitude exceeds a threshold value, but the backward process does not occur. Such switches are indeed observed in computer simulations.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

Simplifying Random Satisfiability Problem by Removing Frustrating Interactions

How can we remove some interactions in a constraint satisfaction problem (CSP) such that it still remains satisfiable? In this paper we study a modified survey propagation algorithm that enables us to address this question for a prototypical CSP, i.e. random K-satisfiability problem. The average number of removed interactions is controlled by a tuning parameter in the algorithm. If the original problem is satisfiable then we are able to construct satisfiable subproblems ranging from the original one to a minimal one with minimum possible number of interactions. The minimal satisfiable subproblems will provide directly the solutions of the original problem.Comment: 21 pages, 16 figure

Number partitioning as random energy model

Number partitioning is a classical problem from combinatorial optimisation. In physical terms it corresponds to a long range anti-ferromagnetic Ising spin glass. It has been rigorously proven that the low lying energies of number partitioning behave like uncorrelated random variables. We claim that neighbouring energy levels are uncorrelated almost everywhere on the energy axis, and that energetically adjacent configurations are uncorrelated, too. Apparently there is no relation between geometry (configuration) and energy that could be exploited by an optimization algorithm. This ``local random energy'' picture of number partitioning is corroborated by numerical simulations and heuristic arguments.Comment: 8+2 pages, 9 figures, PDF onl

Vortices in the presence of a nonmagnetic atom impurity in 2D XY ferromagnets

Using a model of nonmagnetic impurity potential, we have examined the behavior of planar vortex solutions in the classical two-dimensional XY ferromagnets in the presence of a spin vacancy localized out of the vortex core. Our results show that a spinless atom impurity gives rise to an effective potential that repels the vortex structure.Comment: 6 pages, 2 figures, RevTex

Field momentum and gyroscopic dynamics of classical systems with topological defects

The standard relation between the field momentum and the force is generalized for the system with a field singularity: in addition to the regular force, there appear the singular one. This approach is applied to the description of the gyroscopic dynamics of the classical field with topological defects. The collective variable Lagrangian description is considered for gyroscopical systems with account of singularities. Using this method we describe the dynamics of two-dimensional magnetic solitons. We establish a relation between the gyroscopic force and the singular one. An effective Lagrangian description is discussed for the magnetic soliton dynamics.Comment: LaTeX, 19 page