5,577 research outputs found
Impulsive Spin-Motion Entanglement for Fast Quantum Computation and Sensing
We perform entanglement of spin and motional degrees of freedom of a single,
ground-state trapped ion through the application of a ps laser pulse. The
duration of the interaction is significantly shorter than both the motional
timescale ( s) and spin precession timescale (
ns), demonstrating that neither sets a fundamental speed limit on this
operation for quantum information processing. Entanglement is demonstrated
through the collapse and revival of spin coherence as the spin components of
the wavefunction separate and recombine in phase space. We infer the fidelity
of these single qubit operations to be .Comment: 5 pages, 4 figure
Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles
We propose angle-resolved photoelectron spectroscopy of aerosol particles as
an alternative way to determine the electron mean free path of low energy
electrons in solid and liquid materials. The mean free path is obtained from
fits of simulated photoemission images to experimental ones over a broad range
of different aerosol particle sizes. The principal advantage of the aerosol
approach is twofold. Firstly, aerosol photoemission studies can be performed
for many different materials, including liquids. Secondly, the size-dependent
anisotropy of the photoelectrons can be exploited in addition to size-dependent
changes in their kinetic energy. These finite size effects depend in different
ways on the mean free path and thus provide more information on the mean free
path than corresponding liquid jet, thin film, or bulk data. The present
contribution is a proof of principle employing a simple model for the
photoemission of electrons and preliminary experimental data for potassium
chloride aerosol particles
Gut content metabarcoding of specialized feeders is not a replacement for environmental DNA assays of seawater in reef environments
In tropical marine ecosystems, the coral-based diet of benthic-feeding reef fishes provides a window into the composition and health of coral reefs. In this study, for the first time, we compare multi-assay metabarcoding sequences of environmental DNA (eDNA) isolated from seawater and partially digested gut items from an obligate corallivore butterflyfish (Chaetodon lunulatus) resident to coral reef sites in the South China Sea. We specifically tested the proportional and statistical overlap of the different approaches (seawater vs gut content metabarcoding) in characterizing eukaryotic community composition on coral reefs. Based on 18S and ITS2 sequence data, which differed in their taxonomic sensitivity, we found that gut content detections were only partially representative of the eukaryotic communities detected in the seawater based on low levels of taxonomic overlap (3 to 21%) and significant differences between the sampling approaches. Overall, our results indicate that dietary metabarcoding of specialized feeders can be complimentary to, but is no replacement for, more comprehensive environmental DNA assays of reef environments that might include the processing of different substrates (seawater, sediment, plankton) or traditional observational surveys. These molecular assays, in tandem, might be best suited to highly productive but cryptic oceanic environments (kelp forests, seagrass meadows) that contain an abundance of organisms that are often small, epiphytic, symbiotic, or cryptic.</p
Manipulating ultracold atoms with a reconfigurable nanomagnetic system of domain walls
The divide between the realms of atomic-scale quantum particles and
lithographically-defined nanostructures is rapidly being bridged. Hybrid
quantum systems comprising ultracold gas-phase atoms and substrate-bound
devices already offer exciting prospects for quantum sensors, quantum
information and quantum control. Ideally, such devices should be scalable,
versatile and support quantum interactions with long coherence times.
Fulfilling these criteria is extremely challenging as it demands a stable and
tractable interface between two disparate regimes. Here we demonstrate an
architecture for atomic control based on domain walls (DWs) in planar magnetic
nanowires that provides a tunable atomic interaction, manifested experimentally
as the reflection of ultracold atoms from a nanowire array. We exploit the
magnetic reconfigurability of the nanowires to quickly and remotely tune the
interaction with high reliability. This proof-of-principle study shows the
practicability of more elaborate atom chips based on magnetic nanowires being
used to perform atom optics on the nanometre scale.Comment: 4 pages, 4 figure
Albedo and Reflection Spectra of Extrasolar Giant Planets
We generate theoretical albedo and reflection spectra for a full range of
extrasolar giant planet (EGP) models, from Jovian to 51-Pegasi class objects.
Our albedo modeling utilizes the latest atomic and molecular cross sections, a
Mie theory treatment of extinction by condensates, a variety of particle size
distributions, and an extension of the Feautrier radiative transfer method
which allows for a general treatment of the scattering phase function. We find
that due to qualitative similarities in the compositions and spectra of objects
within each of five broad effective temperature ranges, it is natural to
establish five representative EGP albedo classes: a ``Jovian'' class (T K; Class I) with tropospheric ammonia clouds, a ``water
cloud'' class (T K; Class II) primarily affected by
condensed HO, a ``clear'' class (T K; Class III)
which lacks clouds, and two high-temperature classes: Class IV (900 K
T 1500 K) for which alkali metal absorption
predominates, and Class V (T 1500 K and/or low surface
gravity ( 10 cm s)) for which a high silicate layer
shields a significant fraction of the incident radiation from alkali metal and
molecular absorption. The resonance lines of sodium and potassium are expected
to be salient features in the reflection spectra of Class III, IV, and V
objects. We derive Bond albedos and effective temperatures for the full set of
known EGPs and explore the possible effects of non-equilibrium condensed
products of photolysis above or within principal cloud decks. As in Jupiter,
such species can lower the UV/blue albedo substantially, even if present in
relatively small mixing ratios.Comment: revised LaTeX manuscript accepted to Ap.J.; also available at
http://jupiter.as.arizona.edu/~burrows/paper
VEZF1 elements mediate protection from DNA methylation
There is growing consensus that genome organization and long-range gene regulation involves partitioning of the genome into domains of distinct epigenetic chromatin states. Chromatin insulator or barrier elements are key components of these processes as they can establish boundaries between chromatin states. The ability of elements such as the paradigm β-globin HS4 insulator to block the range of enhancers or the spread of repressive histone modifications is well established. Here we have addressed the hypothesis that a barrier element in vertebrates should be capable of defending a gene from silencing by DNA methylation. Using an established stable reporter gene system, we find that HS4 acts specifically to protect a gene promoter from de novo DNA methylation. Notably, protection from methylation can occur in the absence of histone acetylation or transcription. There is a division of labor at HS4; the sequences that mediate protection from methylation are separable from those that mediate CTCF-dependent enhancer blocking and USF-dependent histone modification recruitment. The zinc finger protein VEZF1 was purified as the factor that specifically interacts with the methylation protection elements. VEZF1 is a candidate CpG island protection factor as the G-rich sequences bound by VEZF1 are frequently found at CpG island promoters. Indeed, we show that VEZF1 elements are sufficient to mediate demethylation and protection of the APRT CpG island promoter from DNA methylation. We propose that many barrier elements in vertebrates will prevent DNA methylation in addition to blocking the propagation of repressive histone modifications, as either process is sufficient to direct the establishment of an epigenetically stable silent chromatin stat
Selective improvement of pulmonary arterial hypertension with a dual ETA/ETB receptors antagonist in the apolipoprotein E−/− model of PAH and atherosclerosis
Idiopathic pulmonary arterial hypertension (IPAH) is increasingly diagnosed in elderly
patients who also have an increased risk of comorbid atherosclerosis. Apolipoprotein E
deficient (ApoE-/-) mice develop atherosclerosis with severe PAH when fed a high-fat diet
(HFD), and have increased levels of endothelin (ET)-1. ET-1 receptor antagonists (ERAs) are
used for the treatment of PAH but less is known about whether ERAs are beneficial in
atherosclerosis. We therefore examined whether treatment of HFD-ApoE-/- mice with
macitentan, a dual ETA/ETB receptor antagonist, would have any effect on both
atherosclerosis and PAH. ApoE-/- mice were fed chow or HFD for 8 weeks. After 4 weeks of
HFD, mice were randomised to a 4-week treatment of macitentan by food (30mg/kg/day dual
ETA/ETB antagonist), or placebo groups. Echocardiography and closed-chest right heart
catheterisation were used to determine PAH phenotype and serum samples were collected for
cytokine analysis. Thoracic aortas were harvested to assess vascular reactivity using wire
myography, and histological analyses were performed on the brachiocephalic artery and
aortic root to assess atherosclerotic burden. Macitentan treatment of HFD-fed ApoE-/- mice
was associated with a beneficial effect on the PAH phenotype and led to an increase in
endothelial-dependent relaxation in thoracic aortae. Macitentan treatment was also
associated with a significant reduction in interleukin 6 (IL-6) concentration but there was no
significant effect on atherosclerotic burden. Dual blockade of ETA/ETB receptors improves
endothelial function and improves experimental PAH but had no significant effect on
atherosclerosis
CARMA Survey Toward Infrared-bright Nearby Galaxies (STING) II: Molecular Gas Star Formation Law and Depletion Time Across the Blue Sequence
We present an analysis of the relationship between molecular gas and current
star formation rate surface density at sub-kpc and kpc scales in a sample of 14
nearby star-forming galaxies. Measuring the relationship in the bright, high
molecular gas surface density (\Shtwo\gtrsim20 \msunpc) regions of the disks
to minimize the contribution from diffuse extended emission, we find an
approximately linear relation between molecular gas and star formation rate
surface density, \nmol\sim0.96\pm0.16, with a molecular gas depletion time
\tdep\sim2.30\pm1.32 Gyr. We show that, in the molecular regions of our
galaxies there are no clear correlations between \tdep\ and the free-fall and
effective Jeans dynamical times throughout the sample. We do not find strong
trends in the power-law index of the spatially resolved molecular gas star
formation law or the molecular gas depletion time across the range of galactic
stellar masses sampled (\mstar \msun). There is a
trend, however, in global measurements that is particularly marked for low mass
galaxies. We suggest this trend is probably due to the low surface brightness
CO, and it is likely associated with changes in CO-to-H2 conversion factor.Comment: To appear in ApJ, December 2011; 17 pages; 8 figure
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