Explore the vast range of titles available.

As data centers proliferate, their energy intensity deserves close attention. Always-on operations and growing usage for cloud and other backend processes make servers the fundamental driver of data center energy use. Yet servers’ power draw under real-world conditions is poorly understood. This paper explores characteristics of volume servers that affect energy use, quantifying differences in power draw between higher-performing Standard Performance Evaluation Corporation (SPEC) and ENERGY STAR servers and that of a typical server. First, we establish general characteristics of the US installed base, before reporting hardware configurations from a major online retail website. We then compare idle power across three datasets (one unique to this paper) and explain their differences via the hardware characteristics to which power draw is most sensitive. We find idle server power demand to be significantly higher than benchmarks from ENERGY STAR and the industry-released SPEC database, and SPEC server configurations—and likely their power scaling—to be atypical of volume servers. Next, we examine power draw trends among high-performing servers across their load range to consider whether these trends are representative of volume servers, before inputting average idle power load values into a recent national server energy use model. Lastly, results from two surveys of IT professionals illustrate the incidence of more efficient equipment and operational practices in server rooms/closets. Future work should include server power field measurements in data centers of different sizes, accounting for variations in configurations and setting changes post-purchase, as well as investigating the linkage between time and server energy efficiency.

Energy researchers need data on residential appliances to make effective recommendations for reducing energy consumption. For some products, however, traditional data sources do not have sufficient detail. Online surveys can provide a less expensive alternative for data collection, but the accuracy of these surveys is still unclear. Here, we compare the results of Amazon Mechanical Turk online surveys of refrigerators, freezers, televisions, and ceiling fans to the nationwide Residential Energy Consumption Survey (RECS) deployed by the US Energy Information Administration. To account for differences in demographic distributions between the online survey results and the general population, we weighted the results using standard cell weighting and raking techniques, as well as a combination of these, termed “hybrid.” The weighted results gave a distribution of product ownership that was reasonably close to RECS, albeit with small, statistically significant differences in some cases. The cell weighting method provided a slightly better agreement with RECS than the other two approaches. We recommend online surveys as an efficient and cost-effective way of gathering in-home use data on appliances that are not adequately covered by existing data sources.

There has been an increased in attention placed on the energy consumption of miscellaneous electronic loads in buildings by energy analysts and policymakers in recent years. The share of electricity consumed by consumer electronics in US households has increased in the last decade. Many devices, however, lack robust energy use data, making energy consumption estimates difficult and uncertain. Video game consoles are high-performance machines present in approximately half of all households and can consume a considerable amount of power. The precise usage of game consoles has significant uncertainty, however, leading to a wide range of recent national energy consumption estimates. We present here an analysis based on field-metered usage data, collected as part of a larger field metering study in the USA. This larger study collected data from 880 households in 2012 on a variety of devices, including 113 game consoles (the majority of which are Generation 7 consoles). From our metering, we find that although some consoles are left on nearly 24 h/day, the overall average usage is lower than many other studies have assumed, leading to a US national energy consumption estimate of 7.1 TWh in 2012. Nevertheless, there is an opportunity to reduce energy use with proper game console power management, as a substantial amount of game console usage occurs with the television turned off. The emergence of Generation 8 consoles may increase national energy consumption.

In order to project the potential energy savings from implementing energy efficiency policy, realistic usage profiles are essential. In the case of televisions (TVs), these usage profiles can be complex due to the range of functions TVs provide, the increasing number of TVs per household, the increasing hours of TV viewing, and the changing usage of a TV over its lifetime. Calculating the energy use of a TV over its lifetime is a challenge because, when a new TV is purchased, the old TV is often maintained and used less frequently in another room in the home, rather than being disposed of. Due to limited access to comprehensive usage data, previous analyses have either assumed a single static usage value, based on either metered or survey data, or estimated a usage profile adjusted from measured values to account for possible increases in future viewing. In this analysis, we investigate detailed TV usage over time using historical metered TV use data from more than 12,000 U.S. households, collected by The Nielsen Company. We found that the main TV in a household is used for 7.2 h per day, while other TVs are used for 2.5 h per day or less. We also found that 65 % of TVs in the total stock are considered the “main” TV. Combining this information, we determined the mean hours per day per TV to be 5.5.

We present X-ray properties of optically-selected intermediate-mass (~10^5--10^6 M_Sun) black holes (BHs) in active galaxies (AGNs), using data from the Chandra X-Ray Observatory. Our observations are a continuation of a pilot study by Greene & Ho (2007). Of the 8 objects observed, 5 are detected with X-ray luminosities in the range L_0.5-2 keV = 10^41--10^43 erg s^-1, consistent with the previously observed sample. Objects with enough counts to extract a spectrum are well fit by an absorbed power law. We continue to find a range of soft photon indices 1 < \\Gamma_s < 2.7, where N(E) \\propto E^-\\Gamma_s, consistent with previous AGN studies, but generally flatter than other narrow-line Seyfert 1 active nuclei (NLS1s). The soft photon index correlates strongly with X-ray luminosity and Eddington ratio, but does not depend on BH mass. There is no justification for the inclusion of any additional components, such as a soft excess, although this may be a function of the relative inefficiency of detecting counts above 2 keV in these relatively shallow observations. As a whole, the X-ray-to-optical spectral slope \\alpha_ox is flatter than in more massive systems, even other NLS1s. Only X-ray-selected NLS1s with very high Eddington ratios share a similar \\alpha_ox. This is suggestive of a physical change in the accretion structure at low masses and at very high accretion rates, possibly due to the onset of slim disks. Although the detailed physical explanation for the X-ray loudness of these intermediate-mass BHs is not certain, it is very striking that targets selected on the basis of optical properties should be so distinctly offset in their broader spectral energy distributions.

In this first paper in a series we present 1298 low-redshift (z\\leq0.2) optical spectra of 582 Type Ia supernovae (SNe Ia) observed from 1989 through 2008 as part of the Berkeley SN Ia Program (BSNIP). 584 spectra of 199 SNe Ia have well-calibrated light curves with measured distance moduli, and many of the spectra have been corrected for host-galaxy contamination. Most of the data were obtained using the Kast double spectrograph mounted on the Shane 3 m telescope at Lick Observatory and have a typical wavelength range of 3300-10,400 Ang., roughly twice as wide as spectra from most previously published datasets. We present our observing and reduction procedures, and we describe the resulting SN Database (SNDB), which will be an online, public, searchable database containing all of our fully reduced spectra and companion photometry. In addition, we discuss our spectral classification scheme (using the SuperNova IDentification code, SNID; Blondin & Tonry 2007), utilising our newly constructed set of SNID spectral templates. These templates allow us to accurately classify our entire dataset, and by doing so we are able to reclassify a handful of objects as bona fide SNe Ia and a few other objects as members of some of the peculiar SN Ia subtypes. In fact, our dataset includes spectra of nearly 90 spectroscopically peculiar SNe Ia. We also present spectroscopic host-galaxy redshifts of some SNe Ia where these values were previously unknown. [Abridged]

Recent detections of massive black holes (BHs), with masses of roughly 106–109 [special characters omitted], in both our own Milky Way and in other galaxies suggest that central galactic BHs are common. In this work, we attempt to shed some light on the relatively new population of local intermediate-mass BHs (103–10 6 [special characters omitted]) that reside at the low-mass end of the central BH mass distribution. This population is important because it represents the closest analogue of primordial galactic BHs, not far removed from the first \"seed\" BHs. Understanding the characteristics of this population will help constrain any seed BH formation model. We begin in Chapter 2 by looking at the properties of elliptical galaxies, nearly all of which likely host a massive BH. Although elliptical galaxies were thought to be a very homogeneous class, whose properties scaled simply with increasing mass, we show with the large sample available from the Sloan Digital Sky Survey (SDSS) that important deviations exist between low-mass and high-mass elliptical galaxies. Such differences arise due to slightly varied formation histories, predominantly involving the fraction of baryonic mass in gas (as opposed to stars) during merger events that build up elliptical galaxies. The gas fraction, higher in low-mass ellipticals, alters the structure of the remnant elliptical because gas is collisional and dissipative, whereas stars are dissipationless. Carefully understanding these host-galaxy properties will be key in future studies. In Chapter 3, we present multiwavelength observations of NGC 4395, the least luminous Seyfert AGN known. NGC 4395 is special for two reasons: (a) the AGN resides in an essentially bulgeless host spiral, challenging the deep connection that is prevalent between massive BHs and host bulges; and (b) the central BH is thought to have a mass of only ∼105 [special characters omitted], placing it squarely in the intermediate-mass BH regime. We present results from reverberation mapping, a technique that is used to estimate the mass of the central BH (MBH). We estimate MBH ≈ 3 × 105 [special characters omitted], consistent with another reverberation result based on simultaneous UV observations. In Chapter 4, we present an archival study of Chandra X-ray Telescope data, in which we search for AGN signatures in a population of bulgeless or nearly-bulgeless late-type spiral galaxies. Motivated by the case of NGC 4395, it is unclear how many BHs exist in bulgeless systems. Optical studies are notoriously poorly suited for this task, since BHs in such late-type spirals are likely of low mass (since the host galaxy is equally of low mass) and thus have very weak AGN signatures. In addition, late-type spirals have relatively large amounts of circumnuclear gas and dust, which easily obscures optical radiation. X-ray photons are largely unaffected (excluding exceptionally large columns of gas) and are therefore a more reliable indicator of central AGN activity (even weak, radiatively inefficient accretion). Unfortunately, stellar-mass BH binaries are equally capable of producing such X-ray emission, and we lack the depth, spacial resolution, and sensitivity to make a definitive identification. Based on nuclear stellar densities and the probability of finding an X-ray binary, we still conclude that roughly ∼20–25% of bulgeless galaxies host an AGN, implying that objects such as NGC 4395 are not as rare as once thought. Finally, in Chapter 5, we present a comprehensive X-ray study of a large sample of intermediate-mass BHs discovered in SDSS via optical identification of broad emission lines. Such BHs, while sampling a mass regime that is poorly understood, are biased toward high accretion rates to make them optically identifiable. Interestingly, such high-accretion, low-mass BHs behave in many ways like narrow-line Seyfert 1 nuclei (a higher-mass cousin), except that in general the low-mass sample is X-ray bright. This result is surprising, and we suggest it may arise from a slim disk, an accretion-disk structure which differs from the usual geometrically thin and optically thick disk normally associated with high accretion rates. Slim disks are thought to arise in systems with Eddington or super-Eddington accretion. Although the precise physical explanation is still elusive, it is surprising that optically selected AGNs should exhibit such differing broader spectral energy distributions. (Abstract shortened by UMI.)

We have assembled a sample of 64 late-type spiral galaxies (T types 6.0-9.0, corresponding to Hubble types Scd-Sm) with archival Chandra data. At a signal-to-noise (S/N) threshold of 3, we find 12 objects with X-ray point-source detections in close proximity with the optical or near-infrared position of the nucleus (median offset \\delta = 1.6\"), suggestive of possible low-luminosity active galactic nuclei (AGNs). Including measurements with 3 > S/N > 1.5, our detections increase to 18. These X-ray sources range in luminosity from L_X(2-10 keV) = 10^{37.1} to 10^{39.6} ergs s^-1. Considering possible contamination from low-mass X-ray binaries (LMXBs), we estimate that ~5 detections are possible LMXBs instead of true AGNs, based on the probability of observing a LMXB in a nuclear star cluster typically found in these late-type spiral galaxies. Given the typical ages of nuclear star clusters, contamination by high-mass X-ray binaries is unlikely. This AGN fraction is higher than that observed in optical surveys, indicating that active nuclei, and hence central black holes, are more common than previously suggested. The incidence of AGN activity in such late-type spiral galaxies also suggests that nuclear massive black holes can form and grow in galaxies with little or no evidence for bulges. Follow-up multiwavelength observations will be necessary to confirm the true nature of these sources.

We analyze the fundamental plane projections of elliptical galaxies as a function of luminosity, using a sample of approximately 80,000 galaxies drawn from Data Release 4 (DR4) of the Sloan Digital Sky Survey (SDSS). We separate brightest cluster galaxies (BCGs) from our main sample and reanalyze their photometry due to a problem with the default pipeline sky subtraction for BCGs. The observables we consider are effective radius (R_e), velocity dispersion (sigma), dynamical mass (M_dyn ~ R_e sigma2), effective density (sigma2/R_e2), and effective surface brightness (mu_e). With the exception of the L-M_dyn correlation, we find evidence of variations in the slope (i.e. the power-law index) of the fundamental plane projections with luminosity for our normal elliptical galaxy population. In particular, the radius-luminosity and Faber-Jackson relations are steeper at high luminosity relative to low luminosity, and the more luminous ellipticals become progressively less dense and have lower surface brightnesses than lower luminosity ellipticals. These variations can be understood as arising from differing formation histories, with more luminous galaxies having less dissipation. Data from the literature and our reanalysis of BCGs show that BCGs have radius-luminosity and Faber-Jackson relations steeper than the brightest non-BCG ellipticals in our sample, consistent with significant growth of BCGs via dissipationless mergers. The variations in slope we find in the Faber-Jackson relation of non-BCGs are qualitatively similar to that reported in the black hole mass-velocity dispersion (M_BH-sigma) correlation. This similarity is consistent with a roughly constant value of M_BH/M_star over a wide range of early type galaxies, where M_star is the stellar mass.

We report on two Chandra observations, and a simultaneous Hubble Space Telescope ultraviolet observation, of the dwarf Seyfert 1 galaxy NGC 4395. Each Chandra observation had a duration of ~30 ks, with a separation of ~50 ks. The spectrum was observed to harden between these observations via a scaling down of the soft-band flux. The inter-observation variability is in a different sense to the observed variability within each observation and is most likely the result of increased absorption. Spectral variations were seen during the first observation suggesting that the X-ray emission is produced in more than one disconnected region. We have also re-analyzed a ~17 ks Chandra observation conducted in 2000. During the three Chandra observations the 2-10 keV flux is about a factor of 2 lower than seen during an XMM-Newton observation conducted in 2003. Moreover, the fractional variability amplitude exhibited during the XMM-Newton observation is significantly softer than seen during the Chandra observations. A power-spectral analysis of the first of the two new Chandra observations revealed a peak at 341s with a formal detection significance of 99%. A similar peak was seen previously in the 2000 Chandra data. However, the detection of this feature is tentative given that it was found in neither the second of our two new Chandra observations nor the XMM-Newton data, and it is much narrower than expected. The Hubble Space Telescope observation was conducted during part of the second Chandra visit. A zero-lag correlation between the ultraviolet and X-ray fluxes was detected with a significance of about 99.5%, consistent with the predictions of the two-phase model for the X-ray emission from active galactic nuclei.