Interpreting the High Frequency QPO Power Spectra of Accreting Black Holes

In the context of a relativistic hot spot model, we investigate different physical mechanisms to explain the behavior of quasi-periodic oscillations (QPOs) from accreting black holes. The locations and amplitudes of the QPO peaks are determined by the ray-tracing calculations presented in Schnittman & Bertschinger (2004a): the black hole mass and angular momentum give the geodesic coordinate frequencies, while the disk inclination and the hot spot size, shape, and overbrightness give the amplitudes of the different peaks. In this paper additional features are added to the existing model to explain the broadening of the QPO peaks as well as the damping of higher frequency harmonics in the power spectrum. We present a number of analytic results that closely agree with more detailed numerical calculations. Four primary pieces are developed: the addition of multiple hot spots with random phases, a finite width in the distribution of geodesic orbits, Poisson sampling of the detected photons, and the scattering of photons from the hot spot through a corona of hot electrons around the black hole. Finally, the complete model is used to fit the observed power spectra of both type A and type B QPOs seen in XTE J1550-564, giving confidence limits on each of the model parameters.Comment: 30 pages, 5 figures, submitted to Ap

Українське музичне діаспорознавство як новий напрям сучасного мистецтвознавства (Ukrainian Music Diaspora Studies as a New Trend in Contemporary Art Criticism)

Стаття присвячена новому напряму сучасного мистецтвознавства – українському музичному діаспорознавству, яке утверджується в дослідженнях Ганни Карась, Віолетти Дутчак. Музична культура української західної діаспори ХХ ст. розглядається як соціокультурний феномен. Розробляється її структурна модель, накреслюються нові перспективні напрями подальших досліджень (The article is devoted to a new trend in contemporary art criticism, i.e. Ukrainian music Diaspora studies. It is stated that these studies have become the subject of scientific research for Hanna Karas and Violetta Dutchak. The musical culture of the Ukrainians of the Western Diaspora of XX century is considered to be a social and cultural phenomenon. The author devises its structural model and outlines the new perspectives for further research. The structural model of the Western Diaspora’s musical culture is a complex integral self-organized open system which consists of musical artefacts, all kinds of cultural and music activities, establishments, social institutions, etc. The author concludes that the musical culture of the Ukrainian Diaspora is a complex constituent part of the Ukrainian art in general and of the musical culture in particular

Non-linear resonance in nearly geodesic motion in low-mass X-ray binaries

We have explored the ideas that parametric resonance affects nearly geodesic motion around a black hole or a neutron star, and that it may be relevant to the high frequency (twin) quasi-periodic oscillations occurring in some low-mass X-ray binaries. We have assumed the particles or fluid elements of an accretion disc to be subject to an isotropic perturbation of a hypothetical but rather general form. We find that the parametric resonance is indeed excited close to the radius where epicyclic frequencies of radial and meridional oscillations are in a 2:3 ratio. The location and frequencies of the highest amplitude excitation vary with the strength of the perturbation. These results agree with actual frequency ratios of twin kHz QPOs that have been reported in some black hole candidates, and they may be consistent also with correlation of the twin peaks in Sco X-1.Comment: 5 pages; accepted for publication in PAS

Baseline and On-Treatment High-Density Lipoprotein Cholesterol and the Risk of Cancer in Randomized Controlled Trials of Lipid-Altering Therapy

ObjectivesWe sought to examine the relationship between high-density lipoprotein cholesterol (HDL-C) levels and the risk of the development of cancer in large randomized controlled trials (RCTs) of lipid-altering interventions.BackgroundEpidemiologic data demonstrate an inverse relationship between serum total cholesterol levels and incident cancer. We recently reported that lower levels of low-density lipoprotein cholesterol are associated with a significantly higher risk of incident cancer in a meta-analysis of large RCTs of statin therapy. However, little is known about the relationship between HDL-C levels and cancer risk.MethodsA systematic MEDLINE search identified lipid intervention RCTs with ≥1,000 person-years of follow-up, providing baseline HDL-C levels and rates of incident cancer. Using random-effects meta-regressions, we evaluated the relationship between baseline HDL-C and incident cancer in each RCT arm.ResultsA total of 24 eligible RCTs were identified (28 pharmacologic intervention arms and 23 control arms), with 625,477 person-years of follow-up and 8,185 incident cancers. There was a significant inverse association between baseline HDL-C levels and the rate of incident cancer (p = 0.018). The inverse association persisted after adjusting for baseline low-density lipoprotein cholesterol, age, body mass index (BMI), diabetes, sex, and smoking status, such that for every 10-mg/dl increment in HDL-C, there was a 36% (95% confidence interval: 24% to 47%) relatively lower rate of the development of cancer (p < 0.001).ConclusionsThere is a significant inverse association between HDL-C and the risk of incident cancer that is independent of LDL-C, age, BMI, diabetes, sex, and smoking

Global climate change and international security.

This report originates in a workshop held at Sandia National Laboratories, bringing together a variety of external experts with Sandia personnel to discuss 'The Implications of Global Climate Change for International Security.' Whatever the future of the current global warming trend, paleoclimatic history shows that climate change happens, sometimes abruptly. These changes can severely impact human water supplies, agriculture, migration patterns, infrastructure, financial flows, disease prevalence, and economic activity. Those impacts, in turn, can lead to national or international security problems stemming from aggravation of internal conflicts, increased poverty and inequality, exacerbation of existing international conflicts, diversion of national and international resources from international security programs (military or non-military), contribution to global economic decline or collapse, or international realignments based on climate change mitigation policies. After reviewing these potential problems, the report concludes with a brief listing of some research, technology, and policy measures that might mitigate them

Modelers and policymakers : improving the relationships.

On April 22 and 23, 2004, a diverse group of 14 policymakers, modelers, analysts, and scholars met with some 22 members of the Sandia National Laboratories staff to explores ways in which the relationships between modelers and policymakers in the energy and environment fields (with an emphasis on energy) could be made more productive for both. This report is not a transcription of that workshop, but draws very heavily on its proceedings. It first describes the concept of modeling, the varying ways in which models are used to support policymaking, and the institutional context for those uses. It then proposes that the goal of modelers and policymakers should be a relationship of mutual trust, built on a foundation of communication, supported by the twin pillars of policy relevance and technical credibility. The report suggests 20 guidelines to help modelers improve the relationship, followed by 10 guidelines to help policymakers toward the same goal

Energy and national security.

On May 19 and 20, 2003, thirty-some members of Sandia staff and management met to discuss the long-term connections between energy and national security. Three broad security topics were explored: I. Global and U.S. economic dependence on oil (and gas); II. Potential security implications of global climate change; and III. Vulnerabilities of the U.S. domestic energy infrastructure. This report, rather than being a transcript of the workshop, represents a synthesis of background information used in the workshop, ideas that emerged in the discussions, and ex post facto analysis of the discussions. Each of the three subjects discussed at this workshop has significant U.S. national security implications. Each has substantial technology components. Each appears a legitimate area of concern for a national security laboratory with relevant technology capabilities. For the laboratory to play a meaningful role in contributing to solutions to national problems such as these, it needs to understand the political, economic, and social environments in which it expects its work to be accepted and used. In addition, it should be noted that the problems of oil dependency and climate change are not amenable to solution by the policies of any one nation--even the one that is currently the largest single energy consumer. Therefore, views, concerns, policies, and plans of other countries will do much to determine which solutions might work and which might not

US Renewable Futures in the GCAM

This project examines renewable energy deployment in the United States using a version of the GCAM integrated assessment model with detailed a representation of renewables, the GCAM-RE. Electricity generation was modeled in four generation segments and 12-subregions. This level of regional and sectoral detail allows a more explicit representation of renewable energy generation. Wind, solar thermal power, and central solar PV plants are implemented in explicit resource classes with new intermittency parameterizations appropriate for each technology. A scenario analysis examines a range of assumptions for technology characteristics, climate policy, and long-distance transmission. We find that renewable generation levels grow over the century in all scenarios. As expected, renewable generation increases with lower renewable technology costs, more stringent climate policy, and if alternative low-carbon technology are not available. The availability of long distance transmission lowers policy costs and changes the renewable generation mix

Line Emission from an Accretion Disk around a Rotating Black Hole: Toward a Measurement of Frame Dragging

Line emission from an accretion disk and a corotating hot spot about a rotating black hole are considered for possible signatures of the frame-dragging effect. We explicitly compare integrated line profiles from a geometrically thin disk about a Schwarzschild and an extreme Kerr black hole, and show that the line profile differences are small if the inner radius of the disk is near or above the Schwarzschild stable-orbit limit of radius 6GM/c^2. However, if the inner disk radius extends below this limit, as is possible in the extreme Kerr spacetime, then differences can become significant, especially if the disk emissivity is stronger near the inner regions. We demonstrate that the first three moments of a line profile define a three-dimensional space in which the presence of material at small radii becomes quantitatively evident in broad classes of disk models. In the context of the simple, thin disk paradigm, this moment-mapping scheme suggests formally that the iron line detected by the Advanced Satellite for Cosmology and Astrophysics mission from MCG-6-30-15 (Tanaka et al. 1995) is 3 times more likely to originate from a disk about a rotating black hole than from a Schwarzschild system. A statistically significant detection of black hole rotation in this way may be achieved after only modest improvements in the quality of data. We also consider light curves and frequency shifts in line emission as a function of time for corotating hot spots in extreme Kerr and Schwarzschild geometries. Both the frequency-shift profile and the light curve from a hot spot are valuable measures of orbital parameters and might possibly be used to detect frame dragging even at radii approaching 6GM/c^2 if the inclination angle of the orbital plane is large.Comment: 15 pages (LaTex), 7 postscript figures; color plot (Figure 1) available at http://cfata2.harvard.edu/bromley/nu_nofun.html (This version contains a new subsection as well as minor corrections.