103 research outputs found
Quaking Aspen Ecology on Forest Service Lands North of Yellowstone National Park
Quaking aspen (Populus tremuloides) occupy a small area in the northern Rocky Mountains, but are highly valued as wildlife habitat. Aspen stands in and around Yellowstone National Park commonly consist of few, large, mature overstory stems and numerous root suckers that do not grow above the browsing reach (â 2 m) of most wild ungulates. Our primary objective was to determine if the recruitment or density of aspen stems \u3e 2 m tall had changed from 1991 to 2006 on a portion of the Gallatin National Forest. The same aspen stands were surveyed in 1991 and 2006 in the 560 kmÂČ study area (n = 316). Secondary objectives were to determine if aspen density was influenced by elk (Cervus elaphus) browsing, conifer establishment, and cattle (Bos spp.) grazing. Mean recruitment stem density did not change from 1991 to 2006 (P = 0.95). Density of stems \u3e 2 m declined 12 percent from 1991 to 2006 (P = 0.04), which indicates that recruitment stems are not being produced at a sufficient rate to replace aging overstories. Areas with the greatest elk densities had the lowest recruitment stem densities and contributed the most to the decline. Although elk browsing seemed to play the largest role, conifer establishment and cattle grazing have also negatively impacted overstory recruitment in aspen stands. Even though elk numbers on the Northern Yellowstone Winter Range have declined since wolf reintroduction, aspen recruitment has not increased at the landscape level on the Gallatin National Forest
Coherent generation of EPR-entangled light pulses mediated by a single trapped atom
We show that a single, trapped, laser-driven atom in a high-finesse optical
cavity allows for the quantum-coherent generation of entangled light pulses on
demand. Schemes for generating simultaneous and temporally separated pulse
pairs are proposed. The mechanical effect of the laser excitation on the
quantum motion of the cold trapped atom mediates the entangling interaction
between two cavity modes and between the two subsequent pulses, respectively.
The entanglement is of EPR-type, and its degree can be controlled through
external parameters. At the end of the generation process the atom is
decorrelated from the light field. Possible experimental implementations of the
proposals are discussed.Comment: 11 pages, 4 figure
Symmetric photon-photon coupling by atoms with Zeeman-split sublevels
We propose a simple scheme for highly efficient nonlinear interaction between
two weak optical fields. The scheme is based on the attainment of
electromagnetically induced transparency simultaneously for both fields via
transitions between magnetically split F=1 atomic sublevels, in the presence of
two driving fields. Thereby, equal slow group velocities and symmetric
cross-coupling of the weak fields over long distances are achieved. By simply
tuning the fields, this scheme can either yield giant cross-phase modulation or
ultrasensitive two-photon switching.Comment: Modified scheme, 4 pages, 1 figur
Photon-photon correlations and entanglement in doped photonic crystals
We consider a photonic crystal (PC) doped with four-level atoms whose
intermediate transition is coupled near-resonantly with a photonic band-gap
edge. We show that two photons, each coupled to a different atomic transition
in such atoms, can manifest strong phase or amplitude correlations: One photon
can induce a large phase shift on the other photon or trigger its absorption
and thus operate as an ultrasensitive nonlinear photon-switch. These features
allow the creation of entangled two-photon states and have unique advantages
over previously considered media: (i) no control lasers are needed; (ii) the
system parameters can be chosen to cause full two-photon entanglement via
absorption; (iii) a number of PCs can be combined in a network.Comment: Modified, expanded text; added reference
The Hubble Space Telescope Wide Field Camera 3 Early Release Science data: Panchromatic Faint Object Counts for 0.2-2 microns wavelength
We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR
filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter.
Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South
mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50
square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and
0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma})
for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy
separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26
mag from the UV to the near-IR, respectively.Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.2
The next detectors for gravitational wave astronomy
This paper focuses on the next detectors for gravitational wave astronomy
which will be required after the current ground based detectors have completed
their initial observations, and probably achieved the first direct detection of
gravitational waves. The next detectors will need to have greater sensitivity,
while also enabling the world array of detectors to have improved angular
resolution to allow localisation of signal sources. Sect. 1 of this paper
begins by reviewing proposals for the next ground based detectors, and presents
an analysis of the sensitivity of an 8 km armlength detector, which is proposed
as a safe and cost-effective means to attain a 4-fold improvement in
sensitivity. The scientific benefits of creating a pair of such detectors in
China and Australia is emphasised. Sect. 2 of this paper discusses the high
performance suspension systems for test masses that will be an essential
component for future detectors, while sect. 3 discusses solutions to the
problem of Newtonian noise which arise from fluctuations in gravity gradient
forces acting on test masses. Such gravitational perturbations cannot be
shielded, and set limits to low frequency sensitivity unless measured and
suppressed. Sects. 4 and 5 address critical operational technologies that will
be ongoing issues in future detectors. Sect. 4 addresses the design of thermal
compensation systems needed in all high optical power interferometers operating
at room temperature. Parametric instability control is addressed in sect. 5.
Only recently proven to occur in Advanced LIGO, parametric instability
phenomenon brings both risks and opportunities for future detectors. The path
to future enhancements of detectors will come from quantum measurement
technologies. Sect. 6 focuses on the use of optomechanical devices for
obtaining enhanced sensitivity, while sect. 7 reviews a range of quantum
measurement options
Assaying Environmental Nickel Toxicity Using Model Nematodes
Although nickel exposure results in allergic reactions, respiratory conditions, and cancer in humans and rodents, the ramifications of excess nickel in the environment for animal and human health remain largely undescribed. Nickel and other cationic metals travel through waterways and bind to soils and sediments. To evaluate the potential toxic effects of nickel at environmental contaminant levels (8.9-7,600 Ôg Ni/g dry weight of sediment and 50-800 Ôg NiCl2/L of water), we conducted assays using two cosmopolitan nematodes, Caenorhabditis elegans and Pristionchus pacificus. We assayed the effects of both sediment-bound and aqueous nickel upon animal growth, developmental survival, lifespan, and fecundity. Uncontaminated sediments were collected from sites in the Midwestern United States and spiked with a range of nickel concentrations. We found that nickel-spiked sediment substantially impairs both survival from larval to adult stages and adult longevity in a concentration-dependent manner. Further, while aqueous nickel showed no adverse effects on either survivorship or longevity, we observed a significant decrease in fecundity, indicating that aqueous nickel could have a negative impact on nematode physiology. Intriguingly, C. elegans and P. pacificus exhibit similar, but not identical, responses to nickel exposure. Moreover, P. pacificus could be tested successfully in sediments inhospitable to C. elegans. Our results add to a growing body of literature documenting the impact of nickel on animal physiology, and suggest that environmental toxicological studies could gain an advantage by widening their repertoire of nematode species
Returning Individual Research Results from Digital Phenotyping in Psychiatry
Psychiatry is rapidly adopting digital phenotyping and artificial intelligence/machine learning tools to study mental illness based on tracking participantsâ locations, online activity, phone and text message usage, heart rate, sleep, physical activity, and more. Existing ethical frameworks for return of individual research results (IRRs) are inadequate to guide researchers for when, if, and how to return this unprecedented number of potentially sensitive results about each participantâs real-world behavior. To address this gap, we convened an interdisciplinary expert working group, supported by a National Institute of Mental Health grant. Building on established guidelines and the emerging norm of returning results in participant-centered research, we present a novel framework specific to the ethical, legal, and social implications of returning IRRs in digital phenotyping research. Our framework offers researchers, clinicians, and Institutional Review Boards (IRBs) urgently needed guidance, and the principles developed here in the context of psychiatry will be readily adaptable to other therapeutic areas
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