Variable - temperature scanning optical and force microscope

The implementation of a scanning microscope capable of working in confocal, atomic force and apertureless near field configurations is presented. The microscope is designed to operate in the temperature range 4 - 300 K, using conventional helium flow cryostats. In AFM mode, the distance between the sample and an etched tungsten tip is controlled by a self - sensing piezoelectric tuning fork. The vertical position of both the AFM head and microscope objective can be accurately controlled using piezoelectric coarse approach motors. The scanning is performed using a compact XYZ stage, while the AFM and optical head are kept fixed, allowing scanning probe and optical measurements to be acquired simultaneously and in concert. The free optical axis of the microscope enables both reflection and transmission experiments to be performed.Comment: 24 pages, 9 figures, submitted to the journal "Review of Scientific Instruments

Wilson Loops in string duals of Walking and Flavored Systems

We consider the VEV of Wilson loop operators by studying the behavior of string probes in solutions of Type IIB string theory generated by Nc D5 branes wrapped on an internal manifold. In particular, we focus on solutions to the background equations that are dual to field theories with a walking gauge coupling as well as for flavored systems. We present in detail our walking solution and emphasize various general aspects of the procedure to study Wilson loops using string duals. We discuss the special features that the strings show when probing the region associated with the walking of the field theory coupling.Comment: 28 pages. Various figures. Version to be published

Autonomous engines driven by active matter: Energetics and design principles

Because of its nonequilibrium character, active matter in a steady state can drive engines that autonomously deliver work against a constant mechanical force or torque. As a generic model for such an engine, we consider systems that contain one or several active components and a single passive one that is asymmetric in its geometrical shape or its interactions. Generally, one expects that such an asymmetry leads to a persistent, directed current in the passive component, which can be used for the extraction of work. We validate this expectation for a minimal model consisting of an active and a passive particle on a one-dimensional lattice. It leads us to identify thermodynamically consistent measures for the efficiency of the conversion of isotropic activity to directed work. For systems with continuous degrees of freedom, work cannot be extracted using a one-dimensional geometry under quite general conditions. In contrast, we put forward two-dimensional shapes of a movable passive obstacle that are best suited for the extraction of work, which we compare with analytical results for an idealised work-extraction mechanism. For a setting with many noninteracting active particles, we use a mean-field approach to calculate the power and the efficiency, which we validate by simulations. Surprisingly, this approach reveals that the interaction with the passive obstacle can mediate cooperativity between otherwise noninteracting active particles, which enhances the extracted power per active particle significantly.Comment: 21 pages, 8 figure

On World Problems. Facts and Implications - A Hungarian View

This volume of Hungarian studies was compiled as part of the UNESCO Major Programme I (Reflection on World Problems and Future-oriented Studies) within the framework of the contract concluded between UNESCO and IIASA. The subject of the contract was the preparation of a study entitled World Problems and their Perceptions. The study was compiled in coordination with the Hungarian National Member Organization of IIASA. The Report, in addition to the State of the Art part, contains information about the Task Force Meeting which UNESCO and IIASA organized in Budapest, February 1985, on a theme in accordance with the title of the report and the contributions of which will appear later in book form. This Collaborative Paper is part of the background material of the Report. It shows a possible perception and interpretation of a group of problems, and the implications arising therefrom. The Report sets out to show what concealed cultural or professional presuppositions there are behind the weight of the different conceptions of so-called global or world problems and how they differ in relation to each other. In this connection it reflects on the UNESCO Medium-Term Plan: "Whatever the approaches adopted, studies on world problems are inevitably linked, by the very nature of the field they cover -- which is none other than the present and future of societies -- to choices based on presuppositions regarding standards or on systems of values or even on ideological choices. They seem to require, as their necessary complement, an open-minded examination carried out in a context which promotes intellectual cooperation and within which all currents of thought can be freely expressed; and no organization seems to offer such a context more successfully than UNESCO." The Report tries to justify the hypothesis formulated in UNESCO's Medium-Term Plan and make clear the necessary existence of differing cultural and professional world views in this respect. It shows that there is no one correct point of view, that many rational conceptions of equal value to each other exist, and that in relation to these problems only the acceptance of plural rationality can lead to common solutions. While this conception seems trivial, practice shows that in seeking solutions this approach is not unique and not at all self-explanatory. The Report and the Collaborative Paper show how the economic, social and cultural conditions, as well as practice, determine the world view, how wide the differences are, and that they necessarily lead to various problem formulations and action plans. In actual fact these outlined differences and knowledge of their explanation can lead the international organizations to the formulation of fuller and, probably, more successful action programmes than previously. In the Collaborative Paper we offer a selection of Hungarian studies prepared recently in various specialized fields, we give an insight into the workshop debates and results of the Hungarian research teams, and last but not least, we try to show the options formed an different topics by Hungarian researchers. The volume is not a homogeneous-topic selection, but at the same time we endeavored, by examining the facts, to concentrate on different features of the unequal development taking place globally and to indicate the interconnection between the studies. The authors of the studies examine, in a complex way, the world economic. and world political changes of the past years, the present state and tendencies of world factors and draw conclusions as to the expected developments. Naturally, as with all selections, the content of our volume cannot cover the wide range of problems -- also formulated by UNESCO's programmes, even though we plan several selections during the programme period. With this initiative, while wishing to give a sample of the work and opinions of Hungarian researchers, we would also like to encourage other national research teams to make a similar statement of opinion, so that we can contribute directly to the dialogue in the range of topics of the world problems programme being discussed also in international organizations. The range of studies closes with a summary, in which in addition to a summing up of the contents and conclusions of the studies, a sharper formulation is made of those questions to which we want particularly to draw attention at the present stage of the World Problems Programme, covering an extremely wide range of topics

SU(2) chiral perturbation theory low-energy constants from 2+1 flavor staggered lattice simulations

We extract the next-to-leading-order low-energy constants \bar\ell_3 and \bar\ell_4 of SU(2) chiral perturbation theory, based on precise lattice data for the pion mass and decay constant on ensembles generated by the Wuppertal-Budapest Collaboration for QCD thermodynamics. These ensembles feature 2+1 flavors of two-fold stout-smeared dynamical staggered fermions combined with Symanzik glue, with pion masses varying from 135 to 435 MeV, lattice scales between 0.7 and 2.0 GeV, while m_s is kept fixed at its physical value. Moderate taste splittings and the scale being set through the pion decay constant allow us to restrict ourselves to the taste pseudoscalar state and to use formulas from continuum chiral perturbation theory. Finally, by dropping the data points near 135 MeV from the fits, we can explore the range of pion masses that is needed in SU(2) chiral perturbation theory to reliably extrapolate to the physical point.Comment: 40 pages, 22 figures, 3 tables; v2: expanded discussion, matches published versio

Screening of heavy quark free energies at finite temperature and non-zero baryon chemical potential

We analyze the dependence of heavy quark free energies on the baryon chemical potential (mu_b) in 2-flavour QCD using improved (p4) staggered fermions with a bare quark mass of m/T = 0.4. By performing a 6th order Taylor expansion in the chemical potential which circumvents the sign problem. The Taylor expansion coefficients of colour singlet and colour averaged free energies are calculated and from this the expansion coefficients for the corresponding screening masses are determined. We find that for small mu_b the free energies of a static quark anti-quark pair decrease in a medium with a net excess of quarks and that screening is well described by a screening mass which increases with increasing mu_b. The mu_b-dependent corrections to the screening masses are well described by perturbation theory for T > 2 T_c. In particular, we find for all temperatures above T_c that the expansion coefficients for singlet and colour averaged screening masses differ by a factor 2.Comment: 14 page

Four-dimensional Simulation of the Hot Electroweak Phase Transition with the SU(2) Gauge-Higgs Model

We study the finite-temperature phase transition of the four-dimensional SU(2) gauge-Higgs model for intermediate values of the Higgs boson mass in the range 50 \lsim m_H \lsim 100GeV on a lattice with the temporal lattice size $N_t=2$. The order of the transition is systematically examined using finite size scaling methods. Behavior of the interface tension and the latent heat for an increasing Higgs boson mass is also investigated.Comment: Talk presented at LATTICE96(electroweak), 3 pages of LaTeX, 4 PostScript figure

Modeling the dynamics of a tracer particle in an elastic active gel

The internal dynamics of active gels, both in artificial (in-vitro) model systems and inside the cytoskeleton of living cells, has been extensively studied by experiments of recent years. These dynamics are probed using tracer particles embedded in the network of biopolymers together with molecular motors, and distinct non-thermal behavior is observed. We present a theoretical model of the dynamics of a trapped active particle, which allows us to quantify the deviations from equilibrium behavior, using both analytic and numerical calculations. We map the different regimes of dynamics in this system, and highlight the different manifestations of activity: breakdown of the virial theorem and equipartition, different elasticity-dependent "effective temperatures" and distinct non-Gaussian distributions. Our results shed light on puzzling observations in active gel experiments, and provide physical interpretation of existing observations, as well as predictions for future studies.Comment: 11 pages, 6 figure

Technicolor and Beyond: Unification in Theory Space

The salient features of models of dynamical electroweak symmetry breaking are reviewed. The ideal walking idea is introduced according to which one should carefully take into account the effects of the extended technicolor dynamics on the technicolor dynamics itself. The effects amount at the enhancement of the anomalous dimension of the mass of the techniquarks allowing to decouple the Flavor Changing Neutral Currents problem from the one of the generation of the top mass. Precision data constraints are reviewed focussing on the latest crucial observation that the S-parameter can be computed exactly near the upper end of the conformal window (Conformal S-parameter) with relevant consequences on the selection of nature's next strong force. We will then introduce the Minimal Walking Technicolor (MWT) models. In the second part of this review we consider the interesting possibility to marry supersymmetry and technicolor. The reason is to provide a unification of different extensions of the standard model. For example, this means that one can recover, according to the parameters and spectrum of the theory distinct extensions of the standard model, from supersymmetry to technicolor and unparticle physiscs. A surprising result is that a minimal (in terms of the smallest number of fields) supersymmetrization of the MWT model leads to the maximal supersymmetry in four dimensions, i.e. N=4 SYM.Comment: Extended version of the PASCOS10 proceedings for the Plenary Tal