Comparative planetology: Significance for terrestrial geology

The crustal evolution of the terrestrial planets increase in complexity and duration with increasing size and mass of the planet. The lunar and mercurian surfaces are largely the result of intense, post-differentiation impact bombardment and subsequent volcanic filling of major impact basins. Mars, being larger, has evolved further: crustal uplifts, rifting, and shield volcanoes have begun to modify its largely Moon-like surface. The Earth is the large end-number of this sequence, where modern plate tectonic processes have erased the earlier lunar and martian type of surfaces. Fundamental problems of the origin of terrestrial continents, ocean basins, and plate tectonics are now addressed within the context of the evolutionary pattern of the terrestrial planets

Reliability analysis of an ultra-reliable fault tolerant control system

This report analyzes the reliability of NASA's Ultra-reliable Fault Tolerant Control System (UFTCS) architecture as it is currently envisioned for helicopter control. The analysis is extended to air transport and spacecraft control using the same computational and voter modules applied within the UFTCS architecture. The system reliability is calculated for several points in the helicopter, air transport, and space flight missions when there are initially 4, 5, and 6 operating channels. Sensitivity analyses are used to explore the effects of sensor failure rates and different system configurations at the 10 hour point of the helicopter mission. These analyses show that the primary limitation to system reliability is the number of flux windings on each flux summer (4 are assumed for the baseline case). Tables of system reliability at the 10 hour point are provided to allow designers to choose a configuration to meet specified reliability goals

Probing the Active Massive Black Hole Candidate in the Center of NGC 404 with VLBI

Recently Nyland et al. (2012) argued that the radio emission observed in the center of the dwarf galaxy NGC 404 originates in a low-luminosity active galactic nucleus (LLAGN) powered by a massive black hole ($M\sim<10^6$ M$_{\odot}$). High-resolution radio detections of MBHs are rare. Here we present sensitive, contemporaneous Chandra X-ray, and very long baseline interferometry (VLBI) radio observations with the European VLBI Network (EVN). The source is detected in the X-rays, and shows no long-term variability. If the hard X-ray source is powered by accretion, the apparent low accretion efficiency would be consistent with a black hole in the hard state. Hard state black holes are known to show radio emission compact on the milliarcsecond scales. However, the central region of NGC 404 is resolved out on 10 milliarcsecond (0.15-1.5 pc) scales. Our VLBI non-detection of a compact, partially self-absorbed radio core in NGC 404 implies that either the black hole mass is smaller than $3^{+5}_{-2}\times10^5$ M$_{\odot}$, or the source does not follow the fundamental plane of black hole activity relation. An alternative explanation is that the central black hole is not in the hard state. The radio emission observed on arcsecond (tens of pc) scales may originate in nuclear star formation or extended emission due to AGN activity, although the latter would not be typical considering the structural properties of low-ionization nuclear emission-line region galaxies (LINERs) with confirmed nuclear activity.Comment: Accepted for publication in the Astrophysical Journal. 7 pages, 2 figures, 1 tabl

Proposed satellite laser ranging and very long baseline interferometry sites for crustal dynamics investigations

Recommendations are presented for a global network of 125 sites for geodetic measurements by satellite laser ranging and very long baseline interferometry. The sites were proposed on the basis of existing facilities and scientific value for investigation of crustal dynamics as related to earthquake hazards. Tectonic problems are discussed for North America peripheral regions and for the world. The sites are presented in tables and maps, with bibliographic references

Psychological Issues in Online Adaptive Task Allocation

Adaptive aiding is an idea that offers potential for improvement over many current approaches to aiding in human-computer systems. The expected return of tailoring the system to fit the user could be in the form of improved system performance and/or increased user satisfaction. Issues such as the manner in which information is shared between human and computer, the appropriate division of labor between them, and the level of autonomy of the aid are explored. A simulated visual search task was developed. Subjects are required to identify targets in a moving display while performing a compensatory sub-critical tracking task. By manipulating characteristics of the situation such as imposed task-related workload and effort required to communicate with the computer, it is possible to create conditions in which interaction with the computer would be more or less desirable. The results of preliminary research using this experimental scenario are presented, and future directions for this research effort are discussed

Nonlinear ptychographic coherent diffractive imaging

Ptychographic Coherent diffractive imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions

The use of happiness research for public policy

Research on happiness tends to follow a "benevolent dictator" approach where politicians pursue people's happiness. This paper takes an antithetic approach based on the insights of public choice theory. First, we inquire how the results of happiness research may be used to improve the choice of institutions. Second, we show that the policy approach matters for the choice of research questions and the kind of knowledge happiness research aims to provide. Third, we emphasize that there is no shortcut to an optimal policy maximizing some happiness indicator or social welfare function since governments have an incentive to manipulate this indicator

Metastable dark matter mechanisms for INTEGRAL 511 keV γ\gamma rays and DAMA/CoGeNT events

We explore dark matter mechanisms that can simultaneously explain the galactic 511 keV gamma rays observed by INTEGRAL/SPI, the DAMA/LIBRA annual modulation, and the excess of low-recoil dark matter candidates observed by CoGeNT. It requires three nearly degenerate states of dark matter in the 4-7 GeV mass range, with splittings respectively of order an MeV and a few keV. The top two states have the small mass gap and transitions between them, either exothermic or endothermic, can account for direct detections. Decays from one of the top states to the ground state produce low-energy positrons in the galaxy whose associated 511 keV gamma rays are seen by INTEGRAL. This decay can happen spontaneously, if the excited state is metastable (longer-lived than the age of the universe), or it can be triggered by inelastic scattering of the metastable states into the shorter-lived ones. We focus on a simple model where the DM is a triplet of an SU(2) hidden sector gauge symmetry, broken at the scale of a few GeV, giving masses of order \lsim 1 GeV to the dark gauge bosons, which mix kinetically with the standard model hypercharge. The purely decaying scenario can give the observed angular dependence of the 511 keV signal with no positron diffusion, while the inelastic scattering mechanism requires transport of the positrons over distances \sim 1 kpc before annihilating. We note that an x-ray line of several keV in energy, due to single-photon decays involving the top DM states, could provide an additional component to the diffuse x-ray background. The model is testable by proposed low-energy fixed target experiments.Comment: 27 pp, 19 figures; v2. minor clarification, added refs; v3. corrected observed rate of positron production, added new section responding to criticisms of arXiv:0904.1025; v4. corrected typos in eqs. (6) and (40

Detection, attribution, and sensitivity of trends toward earlier streamflow in the Sierra Nevada

Observed changes in the timing of snowmelt dominated streamflow in the western United States are often linked to anthropogenic or other external causes. We assess whether observed streamflow timing changes can be statistically attributed to external forcing, or whether they still lie within the bounds of natural (internal) variability for four large Sierra Nevada (CA) basins, at inflow points to major reservoirs. Streamflow timing is measured by “center timing” (CT), the day when half the annual flow has passed a given point. We use a physically based hydrology model driven by meteorological input from a global climate model to quantify the natural variability in CT trends. Estimated 50-year trends in CT due to natural climate variability often exceed estimated actual CT trends from 1950 to 1999. Thus, although observed trends in CT to date may be statistically significant, they cannot yet be statistically attributed to external influences on climate. We estimate that projected CT changes at the four major reservoir inflows will, with 90% confidence, exceed those from natural variability within 1–4 decades or 4–8 decades, depending on rates of future greenhouse gas emissions. To identify areas most likely to exhibit CT changes in response to rising temperatures, we calculate changes in CT under temperature increases from 1 to 5°. We find that areas with average winter temperatures between −2°C and −4°C are most likely to respond with significant CT shifts. Correspondingly, elevations from 2000 to 2800 m are most sensitive to temperature increases, with CT changes exceeding 45 days (earlier) relative to 1961–1990