2,574 research outputs found
Subtleties of witnessing quantum coherence in non-isolated systems
Identifying non-classicality unambiguously and inexpensively is a
long-standing open challenge in physics. The No-Signalling-In-Time protocol was
developed as an experimental test for macroscopic realism, and serves as a
witness of quantum coherence in isolated quantum systems by comparing the
quantum state to its completely dephased counterpart. We show that it provides
a lower bound on a certain resource-theoretic coherence monotone. We go on to
generalise the protocol to the case where the system of interest is coupled to
an environment. Depending on the manner of the generalisation, the resulting
witness either reports on system coherence alone, or on a disjunction of system
coherence with either (i) the existence of non-classical system-environment
correlations or (ii) non-negligible dynamics in the environment. These are
distinct failure modes of the Born approximation in non-isolated systems.Comment: 16pp, 2 figs, 5 thms. v2: typos corrected, references added and small
change to title to reflect that of published versio
Riparian trees and aridland streams of the southwestern United States: An assessment of the past, present, and future
Riparian ecosystems are vital components of aridlands within the southwestern United States. Historically, surface flows influenced population dynamics of native riparian trees. Many southwestern streams has been altered by regulation, however, and will be further affected by greenhouse warming. Our analysis of stream gage data revealed that decreases in volume of annual discharge and mean peak discharge and a shift to earlier peak discharge will occur in the Southern Rockies region of Colorado, New Mexico, and Utah. These changes will likely decrease rates of reproduction and survival of cottonwood (Populus fremontii and Populus deltoides ssp. wislizenii), Goodding\u27s willow (Salix gooddingii), and boxelder (Acer negundo), which rely on surface flows to stimulate germination and recharge groundwater aquifers. Streams in the Central Highlands of Arizona and New Mexico will likely see reductions in annual discharge volume, which could limit reproduction and survival of the above taxa and Arizona sycamore (Platanus wrightii). These effects may be exacerbated by demands of expanding urban areas and agricultural operations, but could also be ameliorated by increasing water use efficiency and environmental mitigation. These factors must be considered, along with climate projections, when planning for conservation of riparian trees and the animal communities they support
Riparian trees and aridland streams of the southwestern United States: An assessment of the past, present, and future
Riparian ecosystems are vital components of aridlands within the southwestern United States. Historically, surface flows influenced population dynamics of native riparian trees. Many southwestern streams has been altered by regulation, however, and will be further affected by greenhouse warming. Our analysis of stream gage data revealed that decreases in volume of annual discharge and mean peak discharge and a shift to earlier peak discharge will occur in the Southern Rockies region of Colorado, New Mexico, and Utah. These changes will likely decrease rates of reproduction and survival of cottonwood (Populus fremontii and Populus deltoides ssp. wislizenii), Goodding\u27s willow (Salix gooddingii), and boxelder (Acer negundo), which rely on surface flows to stimulate germination and recharge groundwater aquifers. Streams in the Central Highlands of Arizona and New Mexico will likely see reductions in annual discharge volume, which could limit reproduction and survival of the above taxa and Arizona sycamore (Platanus wrightii). These effects may be exacerbated by demands of expanding urban areas and agricultural operations, but could also be ameliorated by increasing water use efficiency and environmental mitigation. These factors must be considered, along with climate projections, when planning for conservation of riparian trees and the animal communities they support
Non-invasive Scanning Raman Spectroscopy and Tomography for Graphene Membrane Characterization
Graphene has extraordinary mechanical and electronic properties, making it a
promising material for membrane based nanoelectromechanical systems (NEMS).
Here, chemical-vapor-deposited graphene is transferred onto target substrates
to suspend it over cavities and trenches for pressure-sensor applications. The
development of such devices requires suitable metrology methods, i.e.,
large-scale characterization techniques, to confirm and analyze successful
graphene transfer with intact suspended graphene membranes. We propose fast and
noninvasive Raman spectroscopy mapping to distinguish between freestanding and
substrate-supported graphene, utilizing the different strain and doping levels.
The technique is expanded to combine two-dimensional area scans with
cross-sectional Raman spectroscopy, resulting in three-dimensional Raman
tomography of membrane-based graphene NEMS. The potential of Raman tomography
for in-line monitoring is further demonstrated with a methodology for automated
data analysis to spatially resolve the material composition in micrometer-scale
integrated devices, including free-standing and substrate-supported graphene.
Raman tomography may be applied to devices composed of other two-dimensional
materials as well as silicon micro- and nanoelectromechanical systems.Comment: 23 pages, 5 figure
A Graphene-based Hot Electron Transistor
We experimentally demonstrate DC functionality of graphene-based hot electron
transistors, which we call Graphene Base Transistors (GBT). The fabrication
scheme is potentially compatible with silicon technology and can be carried out
at the wafer scale with standard silicon technology. The state of the GBTs can
be switched by a potential applied to the transistor base, which is made of
graphene. Transfer characteristics of the GBTs show ON/OFF current ratios
exceeding 50.000.Comment: 18 pages, 6 figure
Quantifying Catch Rates, Shark Abundance and Depredation Rate at a Spearfishing Competition on the Great Barrier Reef, Australia
We developed and applied a method to quantify spearfisher effort and catch, shark interactions and shark depredation in a boat-based recreational spearfishing competition in the Great Barrier Reef Marine Park in Queensland. Survey questions were designed to collect targeted quantitative data whilst minimising the survey burden of spearfishers. We provide the first known scientific study of shark depredation during a recreational spearfishing competition and the first scientific study of shark depredation in the Great Barrier Reef region. During the two-day spearfishing competition, nine vessels with a total of 33 spearfishers reported a catch of 144 fish for 115 h of effort (1.25 fish per hour). A subset of the catch comprised nine eligible species under competition rules, of which 47 pelagic fish were weighed. The largest fish captured was a 34.4 kg Sailfish (Istiophorus platypterus). The most common species captured and weighed was Spanish Mackerel (Scomberomorus commerson). The total weight of eligible fish was 332 kg and the average weight of each fish was 7.1 kg. During the two-day event, spearfishers functioned as citizen scientists and counted 358 sharks (115 h effort), averaging 3.11 sharks per hour. Grey Reef Sharks (Carcharhinus amblyrhynchos) comprised 64% of sightings. Nine speared fish were fully depredated by sharks as spearfishers attempted to retrieve their catch, which equates to a depredation rate of 5.9%. The depredated fish included four pelagic fish and five reef fish. The shark species responsible were Grey Reef Shark (C. amblyrhynchos) (66%), Bull Shark (Carcharhinus leucas) (11%), Whitetip Reef Shark (Triaenodon obesus) (11%) and Great Hammerhead (Sphyrna mokarran) (11%). There were spatial differences in fish catch, shark sightings and rates of depredation. We developed a report card that compared average catch of fish, sightings of sharks per hour and depredation rate by survey area, which assists recreational fishers and marine park managers to assess spatio-temporal changes. The participating spearfishers can be regarded as experienced (average 18 days a year for average 13.4 years). Sixty percent of interviewees perceived that shark numbers have increased in the past 10 years, 33% indicated no change and 7% indicated shark numbers had decreased. Total fuel use of all vessels was 2819 L and was equivalent to 6.48 tons of greenhouse gas emissions for the competition
Adaptive Optics Imaging of QSOs with Double-Peaked Narrow Lines: Are they Dual AGNs?
Active galaxies hosting two accreting and merging super-massive black holes
(SMBHs) -- dual Active Galactic Nuclei (AGN) -- are predicted by many current
and popular models of black hole-galaxy co-evolution. We present here the
results of a program that has identified a set of probable dual AGN candidates
based on near Infra-red (NIR) Laser Guide-Star Adaptive Optics (LGS AO) imaging
with the Keck II telescope. These candidates are selected from a complete
sample of radio-quiet Quasi-stellar Objects (QSOs) drawn from the Sloan Digital
Sky Survey (SDSS), which show double-peaked narrow AGN emission lines. Of the
twelve AGNs imaged, we find six with double galaxy structure, of which four are
in galaxy mergers. We measure the ionization of the two velocity components in
the narrow AGN lines to test the hypothesis that both velocity components come
from an active nucleus. The combination of a well-defined parent sample and
high-quality imaging allows us to place constraints on the fraction of SDSS
QSOs that host dual accreting black holes separated on kiloparsec (kpc) scales:
~0.3%-0.65%. We derive from this fraction the time spent in a QSO phase during
a typical merger and find a value that is much lower than estimates that arise
from QSO space densities and galaxy merger statistics. We discuss possible
reasons for this difference. Finally, we compare the SMBH mass distributions of
single and dual AGN and find little difference between the two within the
limited statistics of our program, hinting that most SMBH growth happens in the
later stages of a merger process.Comment: 9 pages, 4 figures, 1 table; accepted to the Astrophysical Journa
Molecular Engineering of the Autographa californica Nuclear Polyhedrosis Virus Genome: Deletion Mutations Within the Polyhedrin Gene
We describe a method to introduce site-specific mutations into the genome of Autographa californica nuclear polyhedrosis virus. Specifically, the A. californica nuclear polyhedrosis virus gene for polyhedrin, the major protein that forms viral occlusions in infected cells, was mutagenized by introducing deletions into the cloned DNA fragment containing the gene. The mutagenized polyhedrin gene was transferred to the intact viral DNA by mixing fragment and viral DNAs, cotransfecting Spodoptera frugiperda cells, and screening for viral recombinants that had undergone allelic exchange. Recombinant viruses with mutant polyhedrin genes were obtained by selecting the progeny virus that did not produce viral occlusions in infected cells (occlusion-negative mutants). Analyses of occlusion-negative mutants demonstrated that the polyhedrin gene was not essential for the production of infectious virus and that deletion of certain sequences within the gene did not alter the control, or decrease the level of expression, of polyhedrin. An early viral protein of 25,000 molecular weight was apparently not essential for virus replication in vitro, as the synthesis of this protein was not detected in cells infected with a mutant virus
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