A Decision Model for Selecting Energy Efficient Technologies for Low -Sloping Roof Tops Using Value-Focused Thinking

The Air Force has a large inventory of low-sloping built up roofs (BURs) and millions of dollars are spent each year retrofitting these systems. The DOD has been directed to reduce non-renewable energy consumption by using energy-efficient technologies. These two details present a great opportunity to use the open roof space to install energy-efficient roofing technologies. The purpose of this research is to provide Air Force decision makers with a tool to assist them in deciding what roofing technologies should be installed on facilities. Value Focused-Thinking is the methodology used to construct the model, in which values were used, instead of alternatives, to create the model. Data was collected from three different Air Force bases and values from three different Air Force Base Civil Engineers were used to evaluate the alternatives. The results show that based on current technologies these decision makers would be best served to retrofit BURs with standing seam metal roofs with some energy-efficient technologies added

Processing adjunct control: Evidence on the use of structural information and prediction in reference resolution

The comprehension of anaphoric relations may be guided not only by discourse, but also syntactic information. In the literature on online processing, however, the focus has been on audible pronouns and descriptions whose reference is resolved mainly on the former. This paper examines one relation that both lacks overt exponence, and relies almost exclusively on syntax for its resolution: adjunct control, or the dependency between the null subject of a non-finite adjunct and its antecedent in sentences such as Mickey talked to Minnie before ___ eating. Using visual world eyetracking, we compare the time course of interpreting this null subject and overt pronouns (Mickey talked to Minnie before he ate). We show that when control structures are highly frequent, listeners are just as quick to resolve reference in either case. When control structures are less frequent, reference resolution based on structural information still occurs upon hearing the non-finite verb, but more slowly, especially when unaided by structural and referential predictions. This may be due to increased difficulty in recognizing that a referential dependency is necessary. These results indicate that in at least some contexts, referential expressions whose resolution depends on very different sources of information can be resolved approximately equally rapidly, and that the speed of interpretation is largely independent of whether or not the dependency is cued by an overt referring expression

The Effects of Anisotropic Viscosity on Turbulence and Heat Transport in the Intracluster Medium

In the intracluster medium (ICM) of galaxy clusters, heat and momentum are transported almost entirely along (but not across) magnetic field lines. We perform the first fully self-consistent Braginskii-MHD simulations of galaxy clusters including both of these effects. Specifically, we perform local and global simulations of the magnetothermal instability (MTI) and the heat-flux-driven buoyancy instability (HBI) and assess the effects of viscosity on their saturation and astrophysical implications. We find that viscosity has only a modest effect on the saturation of the MTI. As in previous calculations, we find that the MTI can generate nearly sonic turbulent velocities in the outer parts of galaxy clusters, although viscosity somewhat suppresses the magnetic field amplification. At smaller radii in cool-core clusters, viscosity can decrease the linear growth rates of the HBI. However, it has less of an effect on the HBI's nonlinear saturation, in part because three-dimensional interchange motions (magnetic flux tubes slipping past each other) are not damped by anisotropic viscosity. In global simulations of cool core clusters, we show that the HBI robustly inhibits radial thermal conduction and thus precipitates a cooling catastrophe. The effects of viscosity are, however, more important for higher entropy clusters. We argue that viscosity can contribute to the global transition of cluster cores from cool-core to non cool-core states: additional sources of intracluster turbulence, such as can be produced by AGN feedback or galactic wakes, suppress the HBI, heating the cluster core by thermal conduction; this makes the ICM more viscous, which slows the growth of the HBI, allowing further conductive heating of the cluster core and a transition to a non cool-core state.Comment: Submitted to MNRAS. Comments are welcom

Can conduction induce convection? The non-linear saturation of buoyancy instabilities in dilute plasmas

We study the effects of anisotropic thermal conduction on low-collisionality, astrophysical plasmas using two and three-dimensional magnetohydrodynamic simulations. For weak magnetic fields, dilute plasmas are buoyantly unstable for either sign of the temperature gradient: the heat-flux-driven buoyancy instability (HBI) operates when the temperature increases with radius while the magnetothermal instability (MTI) operates in the opposite limit. In contrast to previous results, we show that, in the presence of a sustained temperature gradient, the MTI drives strong turbulence and operates as an efficient magnetic dynamo (akin to standard, adiabatic convection). Together, the turbulent and magnetic energies contribute up to ~10% of the pressure support in the plasma. In addition, the MTI drives a large convective heat flux, ~1.5% of rho c_s^3. These findings are robust even in the presence of an external source of strong turbulence. Our results on the nonlinear saturation of the HBI are consistent with previous studies but we explain physically why the HBI saturates quiescently by re-orienting the magnetic field (suppressing the conductive heat flux through the plasma), while the MTI saturates by generating sustained turbulence. We also systematically study how an external source of turbulence affects the saturation of the HBI: such turbulence can disrupt the HBI only on scales where the shearing rate of the turbulence is faster than the growth rate of the HBI. In particular, our results provide a simple mapping between the level of turbulence in a plasma and the effective isotropic thermal conductivity. We discuss the astrophysical implications of these findings, with a particular focus on the intracluster medium of galaxy clusters.Comment: 18 pages, 14 figures. Submitted to MNRA

Turbulent Pressure Support in the Outer Parts of Galaxy Clusters

We use three-dimensional MHD simulations with anisotropic thermal conduction to study turbulence due to the magnetothermal instability (MTI) in the intracluster medium (ICM) of galaxy clusters. The MTI grows on timescales of ~1 Gyr and is capable of driving vigorous, sustained turbulence in the outer parts of galaxy clusters if the temperature gradient is maintained in spite of the rapid thermal conduction. If this is the case, turbulence due to the MTI can provide up to 5-30% of the pressure support beyond r_500 in galaxy clusters, an effect that is strongest for hot, massive clusters. The turbulence driven by the MTI is generally additive to other sources of turbulence in the ICM, such as that produced by structure formation. This new source of non-thermal pressure support reduces the observed Sunyaev-Zel'dovich (SZ) signal and X-ray pressure gradient for a given cluster mass and introduces a cluster mass and temperature gradient-dependent bias in SZ and X-ray mass estimates of clusters. This additional physics may also need to be taken into account when estimating the matter power spectrum normalization, sigma-8, through simulation templates from the observed amplitude of the SZ power spectrum.Comment: Accepted to MNRAS Letters. In Pres

Thermal Instability in Gravitationally-Stratified Plasmas: Implications for Multi-Phase Structure in Clusters and Galaxy Halos

We study the interplay among cooling, heating, conduction, and magnetic fields in gravitationally stratified plasmas using simplified, plane-parallel numerical simulations. Since the physical heating mechanism remains uncertain in massive halos such as groups or clusters, we adopt a simple, observationally-motivated prescription which enforces global thermal equilibrium when averaged over large scales. The plasma remains susceptible to local thermal instability, however, and cooling drives an inward flow of material. In contrast to previous results, we argue that the thermal stability of the plasma is independent of its convective stability. We find that the ratio of the cooling timescale to the dynamical timescale t_cool/t_ff controls the saturation of the thermal instability: when t_cool/t_ff < 1, the plasma develops extended multi-phase structure, whereas when t_cool / t_ff > 1 it does not. (In a companion paper, we show that the criterion for thermal instability in a spherical potential is somewhat less stringent, t_cool / t_ff < 10.) When thermal conduction is anisotropic with respect to the magnetic field, the criterion for multi-phase structure is essentially independent of the thermal conductivity of the plasma. Our criterion for local thermal instability to produce multi-phase structure is an extension of the cold vs. hot accretion modes in galaxy formation that applies at all radii in hot halos, not just to the virial shock. We show that this criterion is consistent with data on multi-phase gas in the ACCEPT sample of clusters; in addition, when t_cool / t_ff > 1, the net cooling rate to low temperatures and the mass flux to small radii are suppressed enough relative to models without heating to be qualitatively consistent with star formation rates and x-ray line emission in groups and clusters.Comment: This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society, Volume 419, Issue 4, pp. 3319-333

Dark Matter and Baryons in the Most X-ray Luminous and Merging Galaxy Cluster RX J1347.5-1145

The galaxy cluster RX J1347-1145 is one of the most X-ray luminous and most massive clusters known. Its extreme mass makes it a prime target for studying issues addressing cluster formation and cosmology. In this paper we present new high-resolution HST/ACS and Chandra X-ray data. The high resolution and sensitivity of ACS enabled us to detect and quantify several new multiply imaged sources, we now use a total of eight for the strong lensing analysis. Combining this information with shape measurements of weak lensing sources in the central regions of the cluster, we derive a high-resolution, absolutely-calibrated mass map. This map provides the best available quantification of the total mass of the central part of the cluster to date. We compare the reconstructed mass with that inferred from the new Chandra X-ray data, and conclude that both mass estimates agree extremely well in the observed region, namely within 400 / h_70 kpc of the cluster center. In addition we study the major baryonic components (gas and stars) and hence derive the dark matter distribution in the center of the cluster. We find that the dark matter and baryons are both centered on the BCG within the uncertainties (alignment is better than <10 kpc). We measure the corresponding 1-D profiles and find that dark matter distribution is consistent with both NFW and cored profiles, indicating that a more extended radial analysis is needed to pinpoint the concentration parameter, and hence the inner slope of the dark matter profile.Comment: 12 pages, Accepted for publication in ApJ, full-res version http://www.physics.ucsb.edu/~marusa/RXJ1347.pd