Method of determination of the mass composition of ring current ions

A method for individual registration of protons, and helium and oxygen ions, with energies E for a charge on the order of 100 kev/q in the ring currents of the Earth's magnetosphere was examined. The method is based on the various specific losses in energy by these ions in matter. The ion current, selected according to E/q, is passed through a solid target, after which identification of the masses is carried out, based on the energy losses in the possibly to reliably divide the flows of protons, and helium and oxygen ions

Crossing Statistic: Bayesian interpretation, model selection and resolving dark energy parametrization problem

By introducing Crossing functions and hyper-parameters I show that the Bayesian interpretation of the Crossing Statistics [1] can be used trivially for the purpose of model selection among cosmological models. In this approach to falsify a cosmological model there is no need to compare it with other models or assume any particular form of parametrization for the cosmological quantities like luminosity distance, Hubble parameter or equation of state of dark energy. Instead, hyper-parameters of Crossing functions perform as discriminators between correct and wrong models. Using this approach one can falsify any assumed cosmological model without putting priors on the underlying actual model of the universe and its parameters, hence the issue of dark energy parametrization is resolved. It will be also shown that the sensitivity of the method to the intrinsic dispersion of the data is small that is another important characteristic of the method in testing cosmological models dealing with data with high uncertainties.Comment: 14 pages, 4 figures, discussions extended, 1 figure and two references added, main results unchanged, matches the final version to be published in JCA

Transitions to palliative care in acute hospitals in England: qualitative study

Objective To explore how transitions to a palliative care approach are perceived to be managed in acute hospital settings in England

The Importance of Lens Galaxy Environments

While many strong gravitational lens galaxies are suspected to lie in groups or clusters of galaxies, environmental effects in lens models are often unconstrained and sometimes ignored. We show that this creates significant biases in a variety of lensing applications, by creating mock lenses associated with each of 13 galaxies in a realistic model group, and then analyzing them with standard techniques. We find that standard models of double lenses, which neglect environment, grossly overestimate the ellipticity of the lens galaxy (de/e~0.5) and the Hubble constant (dh/h~0.22). Standard models of quad lenses, which approximate the environment as a tidal shear, recover the ellipticity reasonably well (|de/e|<~0.24) but overestimate the Hubble constant (dh/h~0.15), and have significant (~30%) errors in the millilensing analyses used to constrain the amount of substructure in dark matter halos. For both doubles and quads, standard models slightly overestimate the velocity dispersion of the lens galaxy (d(sigma)/sigma~0.06), and underestimate the magnifications of the images (d(mu)/mu ~ -0.25). Standard analyses of lens statistics overestimate Omega_Lambda (by 0.05-0.14), and underestimate the ratio of quads to doubles (by a factor of 2). These biases help explain some long-standing puzzles (such as the high observed quad/double ratio), but aggravate others (such as the low value of H_0 inferred from lensing). Most of the biases are caused by neglect of the convergence from the mass associated with the environment, but additional uncertainty is introduced by neglect of higher-order terms. Fortunately, we show that directly observing and modeling lens environments should make it possible to remove the biases and reduce the uncertainties associated with environments to the few percent level. (Abridged)Comment: 14 emulateapj pages; accepted in Ap

Median Statistics, H_0, and the Accelerating Universe

(Abridged) We develop median statistics that provide powerful alternatives to chi-squared likelihood methods and require fewer assumptions about the data. Applying median statistics to Huchra's compilation of nearly all estimates of the Hubble constant, we find a median value H_0=67 km/s/Mpc. Median statistics assume only that the measurements are independent and free of systematic errors. This estimate is arguably the best summary of current knowledge because it uses all available data and, unlike other estimates, makes no assumption about the distribution of measurement errors. The 95% range of purely statistical errors is +/- 2 km/s/Mpc. The statistical precision of this result leads us to analyze the range of possible systematic errors in the median, which we estimate to be roughly +/- 5 km/s/Mpc (95% limits), dominating over the statistical errors. A Bayesian median statistics treatment of high-redshift Type Ia supernovae (SNe Ia) apparent magnitude versus redshift data from Riess et al. yields a posterior probability that the cosmological constant Lambda > 0 of 70 or 89%, depending on the prior information used. The posterior probability of an open universe is about 47%. Analysis of the Perlmutter et al. high-redshift SNe Ia data show the best-fit flat-Lambda model favored over the best-fit Lambda = 0 open model by odds of 366:1; corresponding Riess et al. odds are 3:1 (assuming prior odds of 1:1).Median statistics analyses of the SNe Ia data do not rule out a time-variable Lambda model, and may even favor it over a time-independent Lambda and a Lambda = 0 open model.Comment: Significant revisions include discussion of systematic errors in the median of H_0. Accepted for publication in The Astrophysical Journal, v548, February 20, 2001 issue. 47 pages incl. figures and table

Resonance Structure for Preheating with Massless Fields

We extend recent work on the resonance structure for post-inflation reheating, providing an analytic treatment for models in which both the inflaton and the fields into which it decays are massless. Solutions are derived which are valid for either a spatially-flat or spatially-open metric. Closed-form solutions are given for the characteristic exponent, which measures the rate of particle production during preheating. It is demonstrated that in certain regions of parameter space, the maximum values of the characteristic exponent in an open universe are several times greater than the maximum values in a spatially-flat universe. It is further demonstrated that the solutions found here by means of a simple algebraic construction match the two previously-known exact solutions, which were derived in terms of special functions.Comment: 13pp, revtex. Minor revisions. Forthcoming in Phys Rev

Preheating in an Expanding Universe: Analytic Results for the Massless Case

Analytic results are presented for preheating in both flat and open models of chaotic inflation, for the case of massless inflaton decay into further inflaton quanta. It is demonstrated that preheating in both these cases closely resembles that in Minkowski spacetime. Furthermore, quantitative differences between preheating in spatially-flat and open models of inflation remain of order $10^{-2}$ for the chaotic inflation initial conditions considered here.Comment: 15pp, revtex. No figures. Very minor revisions; forthcoming in Phys Rev

Dark matter and non-Newtonian gravity from General Relativity coupled to a fluid of strings

An exact solution of Einstein's field equations for a point mass surrounded by a static, spherically symmetric fluid of strings is presented. The solution is singular at the origin. Near the string cloud limit there is a $1/r$ correction to Newton's force law. It is noted that at large distances and small accelerations, this law coincides with the phenomenological force law invented by Milgrom in order to explain the flat rotation curves of galaxies without introducing dark matter. When interpreted in the context of a cosmological model with a string fluid, the new solution naturally explains why the critical acceleration of Milgrom is of the same order of magnitude as the Hubble parameter.Comment: 12 pages, REVTeX, no figure

Topologically massive gravito-electrodynamics: exact solutions

We construct two classes of exact solutions to the field equations of topologically massive electrodynamics coupled to topologically massive gravity in 2 + 1 dimensions. The self-dual stationary solutions of the first class are horizonless, asymptotic to the extreme BTZ black-hole metric, and regular for a suitable parameter domain. The diagonal solutions of the second class, which exist if the two Chern-Simons coupling constants exactly balance, include anisotropic cosmologies and static solutions with a pointlike horizon.Comment: 15 pages, LaTeX, no figure

Energy Production in the Formation of a Finite Thickness Cosmic String

The classical electromagnetic modes outside a long, straight, superconducting cosmic string are calculated, assuming the string to be surrounded by a superconducting cylindric surface of radius R. Thereafter, by use of a Bogoliubov-type argument, the electromagnetic energy W produced per unit length in the lowest two modes is calculated when the string is formed "suddenly". The essential new element in the present analysis as compared with prior work of Parker [Phys. Rev. Lett. {\bf 59}, 1369 (1987)] and Brevik and Toverud [Phys. Rev. D {\bf 51}, 691 (1995)], is that the radius {\it a} of the string is assumed finite, thus necessitating Neumann functions to be included in the fundamental modes. We find that the theory is changed significantly: W is now strongly concentrated in the lowest mode $(m,s)=(0,1)$, whereas the proportionality $W \propto (G\mu /t)^2$ that is characteristic for zero-width strings is found in the next mode (1,1). Here G is the gravitational constant, $\mu$ the string mass per unit length, and t the GUT time.Comment: 20 pages, LaTeX, no figure