1,767 research outputs found
BRS symmetry versus supersymmetry in Yang-Mills-Chern-Simons theory
We prove that three-dimensional supersymmetric Yang-Mills-Chern-Simons
theory is finite to all loop orders. In general this leaves open the
possibility that different regularization methods lead to different finite
effective actions. We show that in this model dimensional regularization and
regularization by dimensional reduction yield the same effective action.
Consequently, the superfield approach preserves BRS invariance for this model.Comment: 27 pages, 2 figures, latex2e, uses epsfi
myCopter: Enabling Technologies for Personal Aerial Transportation Systems: Project status after 2.5 years
Current means of transportation for daily commuting are reaching their limits during peak travel times, which results in waste of fuel and loss of time and money. A recent study commissioned by the European Union considers a personal aerial transportation system (PATS) as a viable alternative for transportation to and from work. It also acknowledges that developing such a transportation system should not focus on designing a new flying vehicle for personal use, but instead on investigating issues surrounding the implementation of the transportation system itself. This is the aim of European project myCopter: to determine the social and technological aspects needed to set up a transportation system based on personal aerial vehicles (PAVs). The project focuses on three research areas: human-machine interfaces and training, automation technologies, and social acceptance. Our extended abstract for inclusion in the conference proceedings and our presentation will focus on the achievements during the first 2.5 years of the 4-year project. These include the development of an augmented dynamic model of a PAV with excellent handling qualities that are suitable for training purposes. The training requirements for novice pilots are currently under development. Experimental evaluations on haptic guidance and human-in-the-loop control tasks have allowed us to start implementing a haptic Highway-in-the-Sky display to support novice pilots and to investigate metrics for objectively determining workload using psychophysiological measurements. Within the project, developments for automation technologies have focused on vision-based algorithms. We have integrated such algorithms in the control and navigation architecture of unmanned aerial vehicles (UAVs). Detecting suitable landing spots from monocular camera images recorded in flight has proven to reliably work off-line, but further work is required to be able to use this approach in real time. Furthermore, we have built multiple low-cost UAVs and equipped them with radar sensors to test collision avoidance strategies in real flight. Such algorithms are currently under development and will take inspiration from crowd simulations. Finally, using technology assessment methodologies, we have assessed potential markets for PAVs and challenges for its integration into the current transportation system. This will lead to structured discussions on expectations and requirements of potential PAV users
Inflammatory Dendritic Cells, Regulated by IL-4 Receptor Alpha Signaling, Control Replication, and Dissemination of Leishmania major in Mice
Ehrenfest relations at the glass transition: solution to an old paradox
In order to find out whether there exists a thermodynamic description of the
glass phase, the Ehrenfest relations along the glass transition line are
reconsidered. It is explained that the one involving the compressibility is
always satisfied, and that the one involving the specific heat is principally
incorrect.
Thermodynamical relations are presented for non-ergodic systems with a
one-level tree in phase space. They are derived for a spin glass model, checked
for other models, and expected to apply, e.g., to glass forming liquids. The
second Ehrenfest relation gets a contribution from the configurational entropy.Comment: 4 pages revtex, to appear in Phys. Rev. Let
Thermodynamics of the glassy state: effective temperature as an additional system parameter
A system is glassy when the observation time is much smaller than the
equilibration time. A unifying thermodynamic picture of the glassy state is
presented. Slow configurational modes are in quasi-equilibrium at an effective
temperature. It enters thermodynamic relations with the configurational entropy
as conjugate variable. Slow fluctuations contribute to susceptibilities via
quasi-equilibrium relations, while there is also a configurational term.
Fluctuation-dissipation relations also involve the effective temperature.
Fluctuations in the energy are non-universal, however. The picture is supported
by analytically solving the dynamics of a toy model.Comment: 5 pages, REVTEX. Phys. Rev. Lett, to appea
Third Cumulant of the total Transmission of diffuse Waves
The probability distribution of the total transmission is studied for waves
multiple scattered from a random, static configuration of scatterers. A
theoretical study of the second and third cumulant of this distribution is
presented. Within a diagrammatic approach a theory is developed which relates
the third cumulant normalized to the average, , to the normalized second cumulant . For a broad Gaussian beam profile it is found that .
This is in good agreement with data of optical experiments.Comment: 16 pages revtex, 8 separate postscript figure
Thermodynamic picture of the glassy state
A picture for thermodynamics of the glassy state is introduced. It assumes
that one extra parameter, the effective temperature, is needed to describe the
glassy state. This explains the classical paradoxes concerning the Ehrenfest
relations and the Prigogine-Defay ratio. As a second part, the approach
connects the response of macroscopic observables to a field change with their
temporal fluctuations, and with the fluctuation-dissipation relation, in a
generalized non-equilibrium way.Comment: Proceedings of the Conference "Unifying Concepts in Glass Physics",
ICTP, Trieste, 15 - 18 September 199
Do the Herschel cold clouds in the Galactic halo embody its dark matter?
Recent Herschel/SPIRE maps of the Small and Large Magellanic Clouds (SMC,
LMC) exhibit in each thousands of clouds. Observed at 250 microns, they must be
cold, T ~ 15 K, hence the name "Herschel cold clouds" (HCCs). From the observed
rotational velocity profile and the assumption of spherical symmetry, the
Galactic mass density is modeled in a form close to that of an isothermal
sphere. If the HCCs constitute a certain fraction of it, their angular size
distribution has a specified shape. A fit to the data deduced from the SMC/LMC
maps supports this and yields for their radius 2.5 pc, with a small change when
allowing for a spread in HCC radii. There are so many HCCs that they will make
up all the missing Halo mass density if there is spherical symmetry and their
average mass is of order 15,000 Mo. This compares well with the Jeans mass of
circa 40,000 Mo and puts forward that the HCCs are in fact Jeans clusters,
constituting all the Galactic dark matter and much of its missing baryons, a
conclusion deduced before from a different field of the sky (Nieuwenhuizen,
Schild and Gibson 2011). A preliminary analysis of the intensities yields that
the Jeans clusters themselves may consist of some billion MACHOs of a few dozen
Earth masses. With a size of dozens of solar radii, they would mostly obscure
stars in the LMC, SMC and towards the Galactic center, and may thus have been
overlooked in microlensing.Comment: Revised and corrected version, matches published version. Conclusions
unchange
Changes in Pilot Control Behaviour across Stewart Platform Motion Systems
Low-cost motion systems have been proposed for certain training tasks that would otherwise be performed on high-performance full flight simulators. These systems have shorter stroke actuators, lower bandwidth, and higher noise. The influence of these characteristics on pilot perception and control behaviour is unknown, and can be investigated by simulating a model of a simulator with limited capabilities on a high-end simulator. The platform limitations, such as a platform filter, time delay, and simulator noise characteristics, can then be removed one by one and their effect on control behaviour studied in isolation. By applying a cybernetic approach, human behaviour can be measured objectively in target-following disturbance-rejection control tasks. Experimental results show that small changes in time delay and simulator noise characteristics do not negatively affect human behaviour in these tasks. However, the motion system bandwidth has a significant effect on performance and control behaviour. Participants barely use motion cues when these have a low bandwidth, and instead rely on visual cues to generate lead to perform the control task. Therefore, simulator motion cues must be considered carefully in piloted control tasks in simulators and measured results depend on simulator characteristics as pilots adapt their control behaviour to the available cues
- …