On the evolution of cooling cores in X-ray galaxy clusters

(Abridged) To define a framework for the formation and evolution of the cooling cores in X-ray galaxy clusters, we study how the physical properties change as function of the cosmic time in the inner regions of a 4 keV and 8 keV galaxy cluster under the action of radiative cooling and gravity only. The cooling radius, R_cool, defined as the radius at which the cooling time equals the Universe age at given redshift, evolves from ~0.01 R200 at z>2, where the structures begin their evolution, to ~0.05 R200 at z=0. The values measured at 0.01 R200 show an increase of about 15-20 per cent per Gyr in the gas density and surface brightness and a decrease with a mean rate of 10 per cent per Gyr in the gas temperature. The emission-weighted temperature diminishes by about 25 per cent and the bolometric X-ray luminosity rises by a factor ~2 after 10 Gyrs when all the cluster emission is considered in the computation. On the contrary, when the core region within 0.15 R500 is excluded, the gas temperature value does not change and the X-ray luminosity varies by 10-20 per cent only. The cooling time and gas entropy radial profiles are well represented by power-law functions. The behaviour of the inner slopes of the gas temperature and density profiles are the most sensitive and unambiguous tracers of an evolving cooling core. Their values after 10 Gyrs of radiative losses, T_gas ~ r^0.4 and n_gas ~ r^(-1.2) for the hot (cool) object, are remarkably in agreement with the observational constraints available for nearby X-ray luminous cooling core clusters. Because our simulations do not consider any AGN heating, they imply that the feedback process does not greatly alter the gas density and temperature profiles as generated by radiative cooling alone.Comment: 8 pages. MNRAS in pres

Testing Multi-Field Inflation: A Geometric Approach

We develop an approach for linking the power spectra, bispectrum, and trispectrum to the geometric and kinematical features of multifield inflationary Lagrangians. Our geometric approach can also be useful in determining when a complicated multifield model can be well approximated by a model with one, two, or a handful of fields. To arrive at these results, we focus on the mode interactions in the kinematical basis, starting with the case of no sourcing and showing that there is a series of mode conservation laws analogous to the conservation law for the adiabatic mode in single-field inflation. We then treat the special case of a quadratic potential with canonical kinetic terms, showing that it produces a series of mode sourcing relations identical in form to that for the adiabatic mode. We build on this result to show that the mode sourcing relations for general multifield inflation are extension of this special case but contain higher-order covariant derivatives of the potential and corrections from the field metric. In parallel, we show how these interactions depend on the geometry of the inflationary Lagrangian and on the kinematics of the associated field trajectory. Finally, we consider how the mode interactions and effective number of fields active during inflation are reflected in the spectra and introduce a multifield consistency relation, as well as a multifield observable that can potentially distinguish two-field scenarios from scenarios involving three or more effective fields.Comment: 21 pages, 4 figures + tables. Revised to clarify several points and reorganized Section III for pedagogical reasons. Error in one equation and typos were corrected, as well as additional references adde

Analytical review of passive mass transfer of water vapor in a space suit

Engineering study and analysis of water vapor mass transfer in space sui

On the soft X-ray spectrum of cooling flows

Strong evidence for cooling flows has been found in low resolution X-ray imaging and spectra of many clusters of galaxies. However high resolution X-ray spectra of several clusters from the Reflection Grating Spectrometer (RGS) on XMM-Newton now show a soft X-ray spectrum inconsistent with a simple cooling flow. The main problem is a lack of the emission lines expected from gas cooling below 1--2 keV. Lines from gas at about 2--3 keV are observed, even in a high temperature cluster such as A 1835, indicating that gas is cooling down to about 2--3 keV, but is not found at lower temperatures. Here we discuss several solutions to the problem; heating, mixing, differential absorption and inhomogeneous metallicity. Continuous or sporadic heating creates further problems, including the targetting of the heat at the cooler gas and also the high total energy required. So far there is no clear observational evidence for widespread heating, or shocks, in cluster cores, except in radio lobes which occupy only part of the volume. The implied ages of cooling flows are short, at about 1 Gyr. Mixing. or absorption, of the cooling gas are other possibilities. Alternatively, if the metals in the intracluster medium are not uniformly spread but are clumped, then little line emission is expected from the gas cooling below 1 keV. The low metallicity part cools without line emission whereas the strengths of the soft X-ray lines from the metal-rich gas depend on the mass fraction of that gas and not on the abundance, since soft X-ray line emission dominates the cooling function below 2 keV.Comment: 5 pages, with 2 figures, submitted to MNRA

Testing Two-Field Inflation

We derive semi-analytic formulae for the power spectra of two-field inflation assuming an arbitrary potential and non-canonical kinetic terms, and we use them both to build phenomenological intuition and to constrain classes of two-field models using WMAP data. Using covariant formalism, we first develop a framework for understanding the background field kinematics and introduce a "slow-turn" approximation. Next, we find covariant expressions for the evolution of the adiabatic/curvature and entropy/isocurvature modes, and we discuss how the mode evolution can be inferred directly from the background kinematics and the geometry of the field manifold. From these expressions, we derive semi-analytic formulae for the curvature, isocurvature, and cross spectra, and the spectral observables, all to second-order in the slow-roll and slow-turn approximations. In tandem, we show how our covariant formalism provides useful intuition into how the characteristics of the inflationary Lagrangian translate into distinct features in the power spectra. In particular, we find that key features of the power spectra can be directly read off of the nature of the roll path, the curve the field vector rolls along with respect to the field manifold. For example, models whose roll path makes a sharp turn 60 e-folds before inflation ends tend to be ruled out because they produce strong departures from scale invariance. Finally, we apply our formalism to confront four classes of two-field models with WMAP data, including doubly quadratic and quartic potentials and non-standard kinetic terms, showing how whether a model is ruled out depends not only on certain features of the inflationary Lagrangian, but also on the initial conditions. Ultimately, models must possess the right balance of kinematical and dynamical behaviors, which we capture in a set of functions that can be reconstructed from spectral observables.Comment: Revised to match accepted PRD version: Improved discussion of background kinematics and multi-field effects, added tables summarizing key quantities and their links to observables, more detailed figures, fixed typos in former equations (103) and (117). 49 PRD pages, 11 figure

An absorption spectrum amplifier for determining gas composition

Compositions of gas samples are frequently studied by laser absorption spectroscopy. Sensitivity is improved by two orders of magnitude when absorption cell is placed inside an organic-dye laser cavity

NASA metrology information system: A NEMS subsystem

the NASA Metrology Information Systems (NMIS) is being developed as a standardized tool in managing the NASA field Center's instrument calibration programs. This system, as defined by the NASA Metrology and Calibration Workshop, will function as a subsystem of the newly developed NASA Equipment Management System (NEMS). The Metrology Information System is designed to utilize and update applicable NEMS data fields for controlled property and to function as a stand alone system for noncontrolled property. The NMIS provides automatic instrument calibration recall control, instrument historical performance data storage and analysis, calibration and repair labor and parts cost data, and instrument user and location data. Nineteen standardized reports were developed to analyze calibration system operations

Active and passive multispectral scanner for earth resources applications: An advanced applications flight experiment

The development of an experimental airborne multispectral scanner to provide both active (laser illuminated) and passive (solar illuminated) data from a commonly registered surface scene is discussed. The system was constructed according to specifications derived in an initial programs design study. The system was installed in an aircraft and test flown to produce illustrative active and passive multi-spectral imagery. However, data was not collected nor analyzed for any specific application