Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves

Large-amplitude drift wave fluctuations are observed to cause severe ion temperature oscillations in plasmas of the Caltech Encore tokamak [J. M. McChesney, P. M. Bellan, and R. A. Stern, Phys. Fluids B 3, 3370 (1991)]. Experimental investigations of the complete ion dynamical behavior in these waves are presented. The wave electric field excites stochastic ion orbits in the plane normal (perpendicular to) to B, resulting in rapid perpendicular to heating. Ion-ion collisions impart energy along (parallel to) B, relaxing the perpendicular to-parallel to temperature anisotropy. Hot ions with large orbit radii escape confinement, reaching the chamber wall and cooling the distribution. Cold ions from the plasma edge convect back into the plasma (i.e., recycle), causing further cooling and significantly replenishing the density depleted by orbit losses. The ion-ion collision period tau(ii)similar to Tau(3/2)/n fluctuates strongly with the drift wave phase, due to intense (approximate to 50%) fluctuations in n and Tau. Evidence for particle recycling is given by observations of bimodal ion velocity distributions near the plasma edge, indicating the presence of cold ions (0.4 eV) superposed atop the hot (4-8 eV) plasma background. These appear periodically, synchronous with the drift wave phase at which ion fluid flow from the wall toward the plasma center peaks. Evidence is presented that such a periodic heat/loss/recycle/cool process is expected in plasmas with strong stochastic heating

Real-time phase-selective data acquisition system for measurement of wave phenomena in pulsed plasma discharges

A novel data acquisition system and methodology have been developed for the study of wave phenomena in pulsed plasma discharges. The method effectively reduces experimental uncertainty due to shot-to-shot fluctuations in high repetition rate experiments. Real-time analysis of each wave form allows classification of discharges by wave amplitude, phase, or other features. Measurements can then be constructed from subsets of discharges having similar wave properties. The method clarifies the trade-offs between experimental uncertainty reduction and increased demand for data storage capacity and acquisition time. Finally, this data acquisition system is simple to implement and requires relatively little equipment: only a wave form digitizer and a moderately fast computer

Newtonian limit of String-Dilaton Gravity

We study the weak-field limit of string-dilaton gravity and derive corrections to the Newtonian potential which strength directly depends on the self interaction potential and the nonminimal coupling of the dilaton scalar field. We discuss also possible astrophysical applications of the results, in particular the flat rotation curves of spiral galaxies.Comment: 11 pages, LATEX file, to appear in IJMP

Phylogenetic and functional analysis of the Cation Diffusion Facilitator (CDF) family: improved signature and prediction of substrate specificity

BACKGROUND The Cation Diffusion Facilitator (CDF) family is a ubiquitous family of heavy metal transporters. Much interest in this family has focused on implications for human health and bioremediation. In this work a broad phylogenetic study has been undertaken which, considered in the context of the functional characteristics of some fully characterised CDF transporters, has aimed at identifying molecular determinants of substrate selectivity and at suggesting metal specificity for newly identified CDF transporters. RESULTS Representative CDF members from all three kingdoms of life (Archaea, Eubacteria, Eukaryotes) were retrieved from genomic databases. Protein sequence alignment has allowed detection of a modified signature that can be used to identify new hypothetical CDF members. Phylogenetic reconstruction has classified the majority of CDF family members into three groups, each containing characterised members that share the same specificity towards the principally-transported metal, i.e. Zn, Fe/Zn or Mn. The metal selectivity of newly identified CDF transporters can be inferred by their position in one of these groups. The function of some conserved amino acids was assessed by site-directed mutagenesis in the poplar Zn2+ transporter PtdMTP1 and compared with similar experiments performed in prokaryotic members. An essential structural role can be assigned to a widely conserved glycine residue, while aspartate and histidine residues, highly conserved in putative transmembrane domains, might be involved in metal transport. The potential role of group-conserved amino acid residues in metal specificity is discussed. CONCLUSION In the present study phylogenetic and functional analyses have allowed the identification of three major substrate-specific CDF groups. The metal selectivity of newly identified CDF transporters can be inferred by their position in one of these groups. The modified signature sequence proposed in this work can be used to identify new hypothetical CDF members

Galactic metric, dark radiation, dark pressure and gravitational lensing in brane world models

In the braneworld scenario, the four dimensional effective Einstein equation has extra terms which arise from the embedding of the 3-brane in the bulk. These non-local effects, generated by the free gravitational field of the bulk, may provide an explanation for the dynamics of the neutral hydrogen clouds at large distances from the galactic center, which is usually explained by postulating the existence of the dark matter. We obtain the exact galactic metric, the dark radiation and the dark pressure in the flat rotation curves region in the brane world scenario. Due to the presence of the bulk effects, the flat rotation curves could extend several hundred kpc. The limiting radius for which bulk effects are important is estimated and compared with the numerical values of the truncation parameter of the dark matter halos, obtained from weak lensing observations. There is a relatively good agreement between the predictions of the model and observations. The deflection of photons is also considered and the bending angle of light is computed. The bending angle predicted by the brane world models is much larger than that predicted by standard general relativistic and dark matter models. The angular radii of the Einstein rings are obtained in the small angles approximation. The predictions of the brane world model for the tangential shear are compared with the observational data obtained in the weak lensing of galaxies in the Red-Sequence Cluster Survey. Therefore the study of the light deflection by galaxies and the gravitational lensing could discriminate between the different dynamical laws proposed to model the motion of particles at the galactic level and the standard dark matter models.Comment: 33 pages, 3 figures, accepted for publication in Ap

X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin

We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus cluster, for which van den Bosch et al. have recently claimed the presence of an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF of the stars in the stellar bulge is extremely bottom heavy. The X-rays originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded in a 1 keV thermal minicorona which has a half-light radius of about 360 pc, typical of many early-type galaxies in rich clusters of galaxies. If Bondi accretion operated onto the UMBH from the minicorona with a radiative efficiency of 10 per cent, then the object would appear as a quasar with luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The accretion flow must be highly radiatively inefficient, similar to past results on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any significant growth at the present epoch. We note that there are 3 UMBH candidates in the Perseus cluster and that the inferred present mean mass density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the estimated mean mass density of all black holes. We speculate on the implied growth of UMBH and their hosts, and discuss the possibiity that extreme AGN feedback could make all UMBH host galaxies have low stellar masses at redshifts around 3. Only those which end up at the centres of groups and clusters later accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277 and the other Perseus core UMBH, NGC1270, have not however been able to gather more stars or gas owing to their rapid orbital motion in the cluster core.Comment: 5 pages, 4 figures, MNRAS in pres

Modified gravity without dark matter

On an empirical level, the most successful alternative to dark matter in bound gravitational systems is the modified Newtonian dynamics, or MOND, proposed by Milgrom. Here I discuss the attempts to formulate MOND as a modification of General Relativity. I begin with a summary of the phenomenological successes of MOND and then discuss the various covariant theories that have been proposed as a basis for the idea. I show why these proposals have led inevitably to a multi-field theory. I describe in some detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and discuss its successes and shortcomings. This lecture is primarily pedagogical and directed to those with some, but not a deep, background in General RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School, The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected, references update

The virial theorem and the dynamics of clusters of galaxies in the brane world models

A version of the virial theorem, which takes into account the effects of the non-compact extra-dimensions, is derived in the framework of the brane world models. In the braneworld scenario, the four dimensional effective Einstein equation has some extra terms, called dark radiation and dark pressure, respectively, which arise from the embedding of the 3-brane in the bulk. To derive the generalized virial theorem we use a method based on the collisionless Boltzmann equation. The dark radiation term generates an equivalent mass term (the dark mass), which gives an effective contribution to the gravitational energy. This term may account for the well-known virial theorem mass discrepancy in actual clusters of galaxies. An approximate solution of the vacuum field equations on the brane, corresponding to weak gravitational fields, is also obtained, and the expressions for the dark radiation and dark mass are derived. The qualitative behavior of the dark mass is similar to that of the observed virial mass in clusters of galaxies. We compare our model with the observational data for galaxy clusters, and we express all the physical parameters of the model in terms of observable quantities. In particular, we predict that the dark mass must extend far beyond the presently considered virial radius. The behavior of the galaxy cluster velocity dispersion in brane world models is also considered. Therefore the study of the matter distribution and velocity dispersion at the extragalactic scales could provide an efficient method for testing the multi-dimensional physical models.Comment: 29 pages, no figures, accepted for publication in PR

Generalized virial theorem in Palatini f(R)f(R) gravity

We use the collision-free Boltzmann equation in Palatini $f({\mathcal{R}})$ gravity to derive the virial theorem within the context of the Palatini approach. It is shown that the virial mass is proportional to certain geometrical terms appearing in the Einstein field equations which contribute to gravitational energy and that such geometric mass can be attributed to the virial mass discrepancy in cluster of galaxies. We then derive the velocity dispersion relation for clusters followed by the metric tensor components inside the cluster as well as the $f({\mathcal{R}})$ lagrangian in terms of the observational parameters. Since these quantities may also be obtained experimentally, the $f({\mathcal{R}})$ virial theorem is a convenient tool to test the viability of $f({\mathcal{R}})$ theories in different models. Finally, we discuss the limitations of our approach in the light of the cosmological averaging used and questions that have been raised in the literature against such averaging procedures in the context of the present work.Comment: 16 pages, to appear in PR

Optimal states and almost optimal adaptive measurements for quantum interferometry

We derive the optimal N-photon two-mode input state for obtaining an estimate \phi of the phase difference between two arms of an interferometer. For an optimal measurement [B. C. Sanders and G. J. Milburn, Phys. Rev. Lett. 75, 2944 (1995)], it yields a variance (\Delta \phi)^2 \simeq \pi^2/N^2, compared to O(N^{-1}) or O(N^{-1/2}) for states considered by previous authors. Such a measurement cannot be realized by counting photons in the interferometer outputs. However, we introduce an adaptive measurement scheme that can be thus realized, and show that it yields a variance in \phi very close to that from an optimal measurement.Comment: 4 pages, 4 figures, journal versio