445 research outputs found
Patterns of sea otter haul-out behavior of California tidal estuary in relation to environmental variables
This study provides the first in depth assessment of Sea Otter haul-out patterns in Elkhorn Slough, California and their relationship to environmental variables. Seasonal and daily water and air temperature fluctuations are a good predictor of Sea Otter haul-out patterns but are affected by the availability of haul-out sites at different tide levels. The cost effectiveness of this choice may be maximal at night because of lack of human disturbance. Southern Sea Otters (Enhydra lutris nereis) were observed during 50 bimonthly 24-h periods between August 2007 and July 2009 (n = 1187 h) from a shore-based observation site located above a non-territorial male resting area on the north side of Moss Landing Harbor. We counted the number of Sea Otters in the area (both in the water and on land) at 30-min intervals. We also recorded tide height, and air and water temperature. Thirty-minute counts averaged 42 Sea Otters using the area (land and water) during the day and 66 at night. The average number of Sea Otters hauled out in the study area during the same haul-out event was 22, and the maximum number was 93. Sea Otters were observed hauled out on 70% of the days surveyed, and the proportion of Sea Otters hauled out was significantly higher at night. Higher numbers of Sea Otters on land was significantly correlated with lower air and water temperature, and with mid-range tide-heights. We speculate that haul-out behavior could play an important role in energy conservation; however, human-related traffic patterns in the area may negatively affect this energy conservation strategy
Photoreceptor Inner Segment Morphology in Best Vitelliform Macular Dystrophy
PURPOSE
To characterize outer retina structure in best vitelliform macular dystrophy (BVMD) and to determine the effect of macular lesions on overlying and adjacent photoreceptors.
METHODS
Five individuals with BVMD were followed prospectively with spectral domain optical coherence tomography and confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO). The AOSLO cone photoreceptor mosaic images were obtained within and around retinal lesions. Cone density was measured inside and outside lesions. In 2 subjects, densities were compared with published measurements acquired ∼2.5 years before. One subject was imaged 3 times over a 5-month period.
RESULTS
The AOSLO imaging demonstrated that photoreceptor morphology within BVMD retinal lesions was highly variable depending on the disease stage, with photoreceptor structure present even in advanced disease. The AOSLO imaging was repeatable even in severe disease over short-time and long-time intervals. Photoreceptor density was normal in retinal areas immediately adjacent to lesions and stable over ∼2.5 years. Mobile disk-like structures possibly representing subretinal macrophages were also observed.
CONCLUSION
Combined confocal and nonconfocal split-detector AOSLO imaging reveals substantial variability within clinical lesions in all stages of BVMD. Longitudinal cellular photoreceptor imaging could prove a powerful tool for understanding disease progression and monitoring emerging therapeutic treatment response in inherited degenerations such as BVMD
Enhanced selectivity towards O2 and H2 dissociation on ultrathin Cu films on Ru(0001)
The following article appeared in Journal of Chemical Physics 137.7 (2012): 074706 and may be found at http://scitation.aip.org/content/aip/journal/jcp/137/7/10.1063/1.4746942The reactivity of Cu monolayer (ML) and bilayer films grown on Ru(0001) towards O2 and H2 has been investigated. O2 initial sticking coefficients were determined using the King and Wells method in the incident energy range 40-450 meV, and compared to the corresponding values measured on clean Ru(0001) and Cu(111) surfaces. A relative large O2 sticking coefficient (∼0.5-0.8) was measured for 1 ML Cu and even 2 ML Cu/Ru(0001). At low incident energies, this is one order of magnitude larger than the value observed on Cu(111). In contrast, the corresponding reactivity to H2 was near zero on both Cu monolayer and bilayer films, for incident energies up to 175 meV. Water adsorption on 2 ML Cu/Ru(0001) was found to behave quite differently than on the Ru(0001) and Cu(111) surfaces. Our study shows that Cu/Ru(0001) is a highly selective system, which presents a quite different chemical reactivity towards different species in the same range of collision energiesThe authors gratefully acknowledge the financial support by the Ministerio de Educación y Ciencia through projects CONSOLIDER-INGENIO 2010 on Molecular Nanoscience and FIS2007-61114 and Comunidad de Madrid through the program NANOMAGNET S-0505/MAT/0194. P.P. acknowledges support through the Marie Curie AMAROUT EU action and the Spanish MICINN “Juan de la Cierva” contrac
Velocity-selected molecular pulses produced by an electric guide
Electrostatic velocity filtering is a technique for the production of
continuous guided beams of slow polar molecules from a thermal gas. We extended
this technique to produce pulses of slow molecules with a narrow velocity
distribution around a tunable velocity. The pulses are generated by
sequentially switching the voltages on adjacent segments of an electric
quadrupole guide synchronously with the molecules propagating at the desired
velocity. This technique is demonstrated for deuterated ammonia (ND),
delivering pulses with a velocity in the range of and a
relative velocity spread of at FWHM. At velocities around
, the pulses contain up to molecules each. The data are
well reproduced by Monte-Carlo simulations, which provide useful insight into
the mechanisms of velocity selection.Comment: 8 pages, 6 figure
High-energy-resolution molecular beams for cold collision studies
Stark deceleration allows for precise control over the velocity of a pulsed
molecular beam and, by the nature of its limited phase-space acceptance,
reduces the energy width of the decelerated packet. We describe an alternate
method of operating a Stark decelerator that further reduces the energy spread
over the standard method of operation. In this alternate mode of operation, we
aggressively decelerate the molecular packet using a high phase angle. This
technique brings the molecular packet to the desired velocity before it reaches
the end of the decelerator; the remaining stages are then used to
longitudinally and transversely guide the packet to the detection/interaction
region. The result of the initial aggressive slowing is a reduction in the
phase-space acceptance of the decelerator and thus a narrowing of the velocity
spread of the molecular packet. In addition to the narrower energy spread, this
method also results in a velocity spread that is nearly independent of the
final velocity. Using the alternate deceleration technique, the energy
resolution of molecular collision measurements can be improved considerably.Comment: 12 pages, 9 figure
Photoionization Broadening of the 1S-2S Transition in a Beam of Atomic Hydrogen
We consider the excitation dynamics of the two-photon \sts transition in a
beam of atomic hydrogen by 243 nm laser radiation. Specifically, we study the
impact of ionization damping on the transition line shape, caused by the
possibility of ionization of the 2S level by the same laser field. Using a
Monte-Carlo simulation, we calculate the line shape of the \sts transition for
the experimental geometry used in the two latest absolute frequency
measurements (M. Niering {\it et al.}, PRL 84, 5496 (2000) and M. Fischer {\it
et al.}, PRL 92, 230802 (2004)). The calculated line shift and line width are
in excellent agreement with the experimentally observed values. From this
comparison we can verify the values of the dynamic Stark shift coefficient for
the \sts transition for the first time on a level of 15%. We show that the
ionization modifies the velocity distribution of the metastable atoms, the line
shape of the \sts transition, and has an influence on the derivation of its
absolute frequency.Comment: 10 pages, 5 figure
An ellipsoidal mirror for focusing neutral atomic and molecular beams
Manipulation of atomic and molecular beams is essential to atom optics applications including atom lasers, atom lithography, atom interferometry and neutral atom microscopy. The manipulation of charge-neutral beams of limited polarizability, spin or excitation states remains problematic, but may be overcome by the development of novel diffractive or reflective optical elements. In this paper, we present the first experimental demonstration of atom focusing using an ellipsoidal mirror. The ellipsoidal mirror enables stigmatic off-axis focusing for the first time and we demonstrate focusing of a beam of neutral, ground-state helium atoms down to an approximately circular spot, (26.8±0.5) μm×(31.4±0.8) μm in size. The spot area is two orders of magnitude smaller than previous reflective focusing of atomic beams and is a critical milestone towards the construction of a high-intensity scanning helium microscope
Assessment of bacterial diversity in the cattle tick Rhipicephalus (Boophilus) microplus through tag-encoded pyrosequencing
<p>Abstract</p> <p>Background</p> <p>Ticks are regarded as the most relevant vectors of disease-causing pathogens in domestic and wild animals. The cattle tick, <it>Rhipicephalus </it>(<it>Boophilus</it>) <it>microplus</it>, hinders livestock production in tropical and subtropical parts of the world where it is endemic. Tick microbiomes remain largely unexplored. The objective of this study was to explore the <it>R. microplus </it>microbiome by applying the bacterial 16S tag-encoded FLX-titanium amplicon pyrosequencing (bTEFAP) technique to characterize its bacterial diversity. Pyrosequencing was performed on adult males and females, eggs, and gut and ovary tissues from adult females derived from samples of <it>R. microplus </it>collected during outbreaks in southern Texas.</p> <p>Results</p> <p>Raw data from bTEFAP were screened and trimmed based upon quality scores and binned into individual sample collections. Bacteria identified to the species level include <it>Staphylococcus aureus, Staphylococcus chromogenes, Streptococcus dysgalactiae, Staphylococcus sciuri, Serratia marcescens, Corynebacterium glutamicum</it>, and <it>Finegoldia magna</it>. One hundred twenty-one bacterial genera were detected in all the life stages and tissues sampled. The total number of genera identified by tick sample comprised: 53 in adult males, 61 in adult females, 11 in gut tissue, 7 in ovarian tissue, and 54 in the eggs. Notable genera detected in the cattle tick include <it>Wolbachia</it>, <it>Coxiella</it>, and <it>Borrelia</it>. The molecular approach applied in this study allowed us to assess the relative abundance of the microbiota associated with <it>R. microplus</it>.</p> <p>Conclusions</p> <p>This report represents the first survey of the bacteriome in the cattle tick using non-culture based molecular approaches. Comparisons of our results with previous bacterial surveys provide an indication of geographic variation in the assemblages of bacteria associated with <it>R. microplus</it>. Additional reports on the identification of new bacterial species maintained in nature by <it>R. microplus </it>that may be pathogenic to its vertebrate hosts are expected as our understanding of its microbiota expands. Increased awareness of the role <it>R. microplus </it>can play in the transmission of pathogenic bacteria will enhance our ability to mitigate its economic impact on animal agriculture globally. This recognition should be included as part of analyses to assess the risk for re-invasion of areas like the United States of America where <it>R. microplus </it>was eradicated.</p
An ellipsoidal mirror for focusing neutral atomic and molecular beams
Manipulation of atomic and molecular beams is essential to atom optics applications including atom lasers, atom lithography, atom interferometry and neutral atom microscopy. The manipulation of charge-neutral beams of limited polarizability, spin or excitation states remains problematic, but may be overcome by the development of novel diffractive or reflective optical elements. In this paper, we present the first experimental demonstration of atom focusing using an ellipsoidal mirror. The ellipsoidal mirror enables stigmatic off-axis focusing for the first time and we demonstrate focusing of a beam of neutral, ground-state helium atoms down to an approximately circular spot, (26.8±0.5) μm×(31.4±0.8) μm in size. The spot area is two orders of magnitude smaller than previous reflective focusing of atomic beams and is a critical milestone towards the construction of a high-intensity scanning helium microscope
Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film
Environmental molecular beam experiments are used to examine water
interactions with liquid methanol films at temperatures from 170 K to 190 K. We
find that water molecules with 0.32 eV incident kinetic energy are efficiently
trapped by the liquid methanol. The scattering process is characterized by an
efficient loss of energy to surface modes with a minor component of the
incident beam that is inelastically scattered. Thermal desorption of water
molecules has a well characterized Arrhenius form with an activation energy of
0.47{\pm}0.11 eV and pre-exponential factor of 4.6 {\times} 10^(15{\pm}3)
s^(-1). We also observe a temperature dependent incorporation of incident water
into the methanol layer. The implication for fundamental studies and
environmental applications is that even an alcohol as simple as methanol can
exhibit complex and temperature dependent surfactant behavior.Comment: 8 pages, 5 figure
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