Energy conversion in isothermal nonlinear irreversible processes - struggling for higher efficiency

First we discuss some early work of Ulrike Feudel on structure formation in nonlinear reactions including ions and the efficiency of the conversion of chemical into electrical energy. Then we give some survey about energy conversion from chemical to higher forms of energy like mechanical, electrical and ecological energy. We consider examples of energy conversion in several natural processes and in some devices like fuel cells. Further, as an example, we study analytically the dynamics and efficiency of a simple "active circuit" converting chemical into electrical energy and driving currents which is roughly modeling fuel cells. Finally we investigate an analogous ecological system of Lotka - Volterra type consisting of an "active species" consuming some passive "chemical food". We show analytically for both these models that the efficiency increases with the load, reaches values higher then 50 percent in a narrow regime of optimal load and goes beyond some maximal load abrupt to zero.Comment: 25 pages, 4 figure

Thermodynamics of hot dense H-plasmas: Path integral Monte Carlo simulations and analytical approximations

This work is devoted to the thermodynamics of high-temperature dense hydrogen plasmas in the pressure region between $10^{-1}$ and $10^2$ Mbar. In particular we present for this region results of extensive calculations based on a recently developed path integral Monte Carlo scheme (direct PIMC). This method allows for a correct treatment of the thermodynamic properties of hot dense Coulomb systems. Calculations were performed in a broad region of the nonideality parameter $\Gamma \lesssim 3$ and degeneracy parameter $n_e \Lambda^3 \lesssim 10$. We give a comparison with a few available results from other path integral calculations (restricted PIMC) and with analytical calculations based on Pade approximations for strongly ionized plasmas. Good agreement between the results obtained from the three independent methods is found.Comment: RevTex file, 21 pages, 5 ps-figures include

The evolution of the cluster X-ray scaling relations in the WARPS sample at 0.6<z<1.0

The X-ray properties of a sample of 11 high-redshift (0.6<z<1.0) clusters observed with Chandra and/or XMM are used to investigate the evolution of the cluster scaling relations. The observed evolution of the L-T and M-L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the universe at their redshift of observation. When the systematic effect of assuming isothermality on the derived masses of the high-redshift clusters is taken into account, the high-redshift M-T and Mgas-T relations are also consistent with self-similar evolution. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L-T relation is consistent with the high-z clusters having formed at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L-T relation at high-redshift (B=3.29+/-0.38) is consistent with the local relation, and significantly steeper then the self-similar prediction of B=2. This suggests that the non-gravitational processes causing the steepening occurred at z>1 or in the early stages of the clusters' formation, prior to their observation. The properties of the intra-cluster medium at high-redshift are found to be similar to those in the local universe. The mean surface-brightness profile slope for the sample is 0.66+/-0.05, the mean gas mass fractions within R2500 and R200 are 0.073+/-0.010 and 0.12+/-0.02 respectively, and the mean metallicity of the sample is 0.28+/-0.16 solar.Comment: 23 pages, 17 figures. Accepted for publication in MNRAS. Revised to match accepted version: reanalysed data with latest calibrations, several minor changes. Conclusions unchange

A Lensed Arc in the Low Redshift Cluster Abell 2124

We report the discovery of an arc-like object 27" from the center of the cD galaxy in the redshift $z=0.066$ cluster A2124. Observations with the Keck II telescope reveal that the object is a background galaxy at $z=0.573$, apparently lensed into an arc of length \sim 8 \farcs5 and total R magnitude $m_R = 20.86\pm0.07$. The width of the arc is resolved; we estimate it to be $\sim$0\farcs6 after correcting for seeing. A lens model of the A2124 core mass distribution consistent with the cluster galaxy velocity dispersion reproduces the observed arc geometry and indicates a magnification factor \gta 9. With this magnification, the strength of the [OII] \lambda 3727 line implies a star-formation rate of SFR \sim 0.4 h^{-2}\msun yr^{-1}$. A2124 thus appears to be the lowest redshift cluster known to exhibit strong lensing of a distant background galaxy.Comment: 6 pages using emulateapj.sty; 4 Postscript figures; Figure 4 uses color. Accepted for publication, but ApJ Letters' new policy of counting data images makes the manuscript too long; will appear in main journal. This final version has minor correction

Numerical Simulation of Nano Scanning in Intermittent-Contact Mode AFM under Q control

We investigate nano scanning in tapping mode atomic force microscopy (AFM) under quality (Q) control via numerical simulations performed in SIMULINK. We focus on the simulation of whole scan process rather than the simulation of cantilever dynamics and the force interactions between the probe tip and the surface alone, as in most of the earlier numerical studies. This enables us to quantify the scan performance under Q control for different scan settings. Using the numerical simulations, we first investigate the effect of elastic modulus of sample (relative to the substrate surface) and probe stiffness on the scan results. Our numerical simulations show that scanning in attractive regime using soft cantilevers with high Qeff results in a better image quality. We, then demonstrate the trade-off in setting the effective Q factor (Qeff) of the probe in Q control: low values of Qeff cause an increase in tapping forces while higher ones limit the maximum achievable scan speed due to the slow response of the cantilever to the rapid changes in surface profile. Finally, we show that it is possible to achieve higher scan speeds without causing an increase in the tapping forces using adaptive Q control (AQC), in which the Q factor of the probe is changed instantaneously depending on the magnitude of the error signal in oscillation amplitude. The scan performance of AQC is quantitatively compared to that of standard Q control using iso-error curves obtained from numerical simulations first and then the results are validated through scan experiments performed using a physical set-up

The spatial distribution of galaxies of different spectral types in the massive intermediate-redshift cluster MACSJ0717.5+3745

We present the results of a wide-field spectroscopic analysis of the galaxy population of the massive cluster MACSJ0717.5+3745 and the surrounding filamentary structure (z=0.55), as part of our systematic study of the 12 most distant clusters in the MACS sample. Of 1368 galaxies spectroscopically observed in this field, 563 are identified as cluster members; of those, 203 are classified as emission-line galaxies, 260 as absorption-line galaxies, and 17 as E+A galaxies (defined by $\frac{H_{\delta}+H_{\gamma}}{2}>6$\AA and no detection of [OII] and $H_{\beta}$ in emission). The variation of the fraction of emission- and absorption-line galaxies as a function of local projected galaxy density confirms the well-known morphology-density relation, and becomes flat at projected galaxy densities less than $\sim 20Mpc^{-2}. Interestingly, 16 out of 17 E+A galaxies lie (in projection) within the ram-pressure stripping radius around the cluster core, which we take to be direct evidence of ram-pressure stripping being the primary mechanism that terminates star-formation in the E+A population of galaxy clusters. This conclusion is supported by the rarity of E+A galaxies in the filament which rules out galaxy mergers as the dominant driver of evolution for E+A galaxies in clusters. In addition, we find the 42 e(a) and 27 e(b) member galaxies, i.e., the dusty-starburst and starburst galaxies respectively, to be spread out across almost the entire study area. Their spatial distribution, which shows a strong preference for the filament region, suggests that starbursts are triggered in relatively low-density environments as galaxies are accreted from the field population.Comment: 16 pages, 15 figures, accepted by Ap

Statistical Mechanics of Canonical-Dissipative Systems and Applications to Swarm Dynamics

We develop the theory of canonical-dissipative systems, based on the assumption that both the conservative and the dissipative elements of the dynamics are determined by invariants of motion. In this case, known solutions for conservative systems can be used for an extension of the dynamics, which also includes elements such as the take-up/dissipation of energy. This way, a rather complex dynamics can be mapped to an analytically tractable model, while still covering important features of non-equilibrium systems. In our paper, this approach is used to derive a rather general swarm model that considers (a) the energetic conditions of swarming, i.e. for active motion, (b) interactions between the particles based on global couplings. We derive analytical expressions for the non-equilibrium velocity distribution and the mean squared displacement of the swarm. Further, we investigate the influence of different global couplings on the overall behavior of the swarm by means of particle-based computer simulations and compare them with the analytical estimations.Comment: 14 pages incl. 13 figures. v2: misprints in Eq. (40) corrected, ref. updated. For related work see also: http://summa.physik.hu-berlin.de/~frank/active.htm

Discovery of a very X-ray luminous galaxy cluster at z=0.89 in the WARPS survey

We report the discovery of the galaxy cluster ClJ1226.9+3332 in the Wide Angle ROSAT Pointed Survey (WARPS). At z=0.888 and L_X=1.1e45 erg/s (0.5-2.0 keV, h_0=0.5) ClJ1226.9+3332 is the most distant X-ray luminous cluster currently known. The mere existence of this system represents a huge problem for Omega_0=1 world models. At the modest (off-axis) resolution of the ROSAT PSPC observation in which the system was detected, ClJ1226.9+3332 appears relaxed; an off-axis HRI observation confirms this impression and rules out significant contamination from point sources. However, in moderately deep optical images (R and I band) the cluster exhibits signs of substructure in its apparent galaxy distribution. A first crude estimate of the velocity dispersion of the cluster galaxies based on six redshifts yields a high value of 1650 km/s, indicative of a very massive cluster and/or the presence of substructure along the line of sight. While a more accurate assessment of the dynamical state of this system requires much better data at both optical and X-ray wavelengths, the high mass of the cluster has already been unambiguously confirmed by a very strong detection of the Sunyaev-Zel'dovich effect in its direction (Joy et al. 2001). Using ClJ1226.9+3332 and ClJ0152.7-1357 (z=0.835), the second-most distant X-ray luminous cluster currently known and also a WARPS discovery, we obtain a first estimate of the cluster X-ray luminosity function at 0.8<z<1.4 and L_X>5e44 erg/s. Using the best currently available data, we find the comoving space density of very distant, massive clusters to be in excellent agreement with the value measured locally (z<0.3), and conclude that negative evolution is not required at these luminosities out to z~1. (truncated)Comment: accepted for publication in ApJ Letters, 6 pages, 2 figures, uses emulateapj.st