4,766 research outputs found
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
A Kinetic Contribution to the Knowledge of Carbon-rings
A mechanism involving a cyclic intermediate has been suggested by Welsh and Fodor independently. To obtain a deeper insight acyl shifts with (1) 2-acylamidocyclopentanol-cis (2) 2-benzamidocyclohexanol-cis
and (3) trans have been -investigated kinetically with hydrochloric acid in dry dioxan
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
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
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
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
Phase Fluctuations near the Chiral Critical Point
The Helmholtz free energy density is parametrized as a function of
temperature and baryon density near the chiral critical point of QCD. The
parametrization incorporates the expected critical exponents and amplitudes. An
expansion away from equilibrium states is achieved with Landau theory. This is
used to calculate the probability that the system is found at a density other
than the equilibrium one. Such fluctuations are predicted to be very large in
heavy ion collisions.Comment: 7 pages, 8 figures, Winter Workshop on Nuclear Dynamics 201
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