34,848 research outputs found
The Complex Links Between Governance and Biodiversity
We argue that two problems weaken the claims of those who link corruption and the exploitation of natural resources. The first is conceptual. Studies that use national level indicators of corruption fail to note that corruption comes in many forms, at multiple levels, and may or may not affect resource use. Without a clear causal model of the mechanism by which corruption affects resources, one should treat with caution any estimated relationship between corruption and the state of natural resources. The second problem is methodological: Simple models linking corruption measures and natural resource use typically do not account for other important causes and control variables pivotal to the relationship between humans and natural resources. By way of illustration of these two general concerns, we demonstrate that the findings of a well known recent study that posits a link between corruption and decreases in forests, elephants, and rhinoceros are fragile to simple conceptual and methodological refinements
Simulating a White Dwarf-dominated Galactic Halo
Observational evidence has suggested the possibility of a Galactic halo which
is dominated by white dwarfs (WDs). While debate continues concerning the
interpretation of this evidence, it is clear that an initial mass function
(IMF) biased heavily toward WD precursors (1 < m/Msol < 8), at least in the
early Universe, would be necessary in generating such a halo. Within the
framework of homogeneous, closed-box models of Galaxy formation, such biased
IMFs lead to an unavoidable overproduction of carbon and nitrogen relative to
oxygen (as measured against the abundance patterns in the oldest stars of the
Milky Way). Using a three-dimensional Tree N-body smoothed particle
hydrodynamics code, we study the dynamics and chemical evolution of a galaxy
with different IMFs. Both invariant and metallicity-dependent IMFs are
considered. Our variable IMF model invokes a WD-precursor-dominated IMF for
metallicities less than 5% solar (primarily the Galactic halo), and the
canonical Salpeter IMF otherwise (primarily the disk). Halo WD density
distributions and C,N/O abundance patterns are presented. While Galactic haloes
comprised of ~5% (by mass) of WDs are not supported by our simulations, mass
fractions of ~1-2% cannot be ruled out. This conclusion is consistent with the
present-day observational constraints.Comment: accepted for publication in MNRA
Nanodiamond arrays on glass for quantification and fluorescence characterisation
Quantifying the variation in emission properties of fluorescent nanodiamonds
is important for developing their wide-ranging applicability. Directed
self-assembly techniques show promise for positioning nanodiamonds precisely
enabling such quantification. Here we show an approach for depositing
nanodiamonds in pre-determined arrays which are used to gather statistical
information about fluorescent lifetimes. The arrays were created via a layer of
photoresist patterned with grids of apertures using electron beam lithography
and then drop-cast with nanodiamonds. Electron microscopy revealed a 90%
average deposition yield across 3,376 populated array sites, with an average of
20 nanodiamonds per site. Confocal microscopy, optimised for nitrogen vacancy
fluorescence collection, revealed a broad distribution of fluorescent lifetimes
in agreement with literature. This method for statistically quantifying
fluorescent nanoparticles provides a step towards fabrication of hybrid
photonic devices for applications from quantum cryptography to sensing
Transportation noise pollution - Control and abatement
Control and abatement of transportation noise pollutio
Brayton heat exchanger unit development program (alternate design)
A Brayton Heat Exchanger Unit Alternate Design (BHXU-Alternate) consisting of a recuperator, a heat sink heat exchanger, and a gas ducting system, was designed and fabricated. The design was formulated to provide a high performance unit suitable for use in a long-life Brayton-cycle powerplant. Emphasis was on double containment against external leakage and leakage of the organic coolant into the gas stream. A parametric analysis and design study was performed to establish the optimum component configurations to achieve low weight and size and high reliability, while meeting the requirements of high effectiveness and low pressure drop. Layout studies and detailed mechanical and structural design were performed to obtain a flight-type packaging arrangement, including the close-coupled integration of the BHXU-Alternate with the Brayton Rotating Unit (BRU)
The complex links between governance and biodiversity
We argue that two problems weaken the claims of those who link corruption and the exploitation of natural resources. The first is conceptual. Studies that use national level indicators of corruption fail to note that corruption comes in many forms, at multiple levels, and may or may not affect resource use. Without a clear causal model of the mechanism by which corruption affects resources, one should treat with caution any estimated relationship between corruption and the state of natural resources. The second problem is methodological: Simple models linking corruption measures and natural resource use typically do not account for other important causes and control variables pivotal to the relationship between humans and natural resources. By way of illustration of these two general concerns, we demonstrate that the findings of a well known recent study that posits a link between corruption and decreases in forests, elephants, and rhinoceros are fragile to simple conceptual and methodological refinements.Environmental Economics and Policy,
FUSE Observations of Outflowing OVI in the Dwarf Starburst Galaxy NGC1705
We report FUSE far-UV spectroscopy of the prototypical dwarf starburst galaxy
NGC 1705. These data allow us for the first time to probe the coronal-phase gas
(T = 10E5 to 10E6 K) that may dominate the radiative cooling of the
supernova-heated ISM and thereby determine the dynamical evolution of
starburst-driven outflows. We detect a broad (100 km/s) and blueshifted (by 80
km/s) OVI absorption-line arising in the previously-known galactic outflow. The
properties of the OVI absorption are inconsistent with the standard superbubble
model in which this gas arises in a conductive interface inside the outer
shell. We show that the superbubble in NGC 1705 is blowing out of the galaxy
ISM. During blow-out, coronal-phase gas can be created by hydrodynamical mixing
as hot gas rushes out through fissures in the fragmenting shell of cool gas. As
the coronal gas cools radiatively, it can naturally produce the observed OVI
column density and outflow speed. The OVI data show that the cooling rate in
the coronal-phase gas is less than about 10% of the supernova heating rate.
Since the X-ray luminosity from hotter gas is even smaller, we conclude that
radiative losses are insignificant. The outflow should be able to vent its
metals and kinetic energy out of the galaxy. This process has potentially
important implications for the evolution of dwarf galaxies and the IGM.Comment: ApJ (in press
Gravitational hydrodynamics of large scale structure formation
The gravitational hydrodynamics of the primordial plasma with neutrino hot
dark matter is considered as a challenge to the bottom-up cold dark matter
paradigm. Viscosity and turbulence induce a top-down fragmentation scenario
before and at decoupling. The first step is the creation of voids in the
plasma, which expand to 37 Mpc on the average now. The remaining matter clumps
turn into galaxy clusters. Turbulence produced at expanding void boundaries
causes a linear morphology of 3 kpc fragmenting protogalaxies along vortex
lines. At decoupling galaxies and proto-globular star clusters arise; the
latter constitute the galactic dark matter halos and consist themselves of
earth-mass H-He planets. Frozen planets are observed in microlensing and
white-dwarf-heated ones in planetary nebulae. The approach also explains the
Tully-Fisher and Faber-Jackson relations, and cosmic microwave temperature
fluctuations of micro-Kelvins.Comment: 6 pages, no figure
Shuttle STS-2 mission communication systems RF coverage and performance predictions. Volume 1: Ascent
The RF communications capabilities and nominally expected performance for the ascent phase of the second orbital flight of the shuttle are provided. Predicted performance is given mainly in the form of plots of signal strength versus elapsed mission time for the STDN (downlink) and shuttle orbiter (uplink) receivers for the S-band PM and FM, and UHF systems. Performance of the NAV and landing RF systems is treated for RTLS abort, since in this case the spacecraft will loop around and return to the launch site. NAV and landing RF systems include TACAN, MSBLS, and C-band altimeter. Signal strength plots were produced by a computer program which combines the spacecraft trajectory, antenna patterns, transmit and receive performance characteristics, and system mathematical models. When available, measured spacecraft parameters were used in the predictions; otherwise, specified values were used. Specified ground station parameter values were also used. Thresholds and other criteria on the graphs are explained
- …