210 research outputs found
Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses
Flow patterns generated by medusan swimmers such as
jellyfish are known to differ according the morphology of
the various animal species. Oblate medusae have been
previously observed to generate vortex ring structures
during the propulsive cycle. Owing to the inherent
physical coupling between locomotor and feeding
structures in these animals, the dynamics of vortex ring
formation must be robustly tuned to facilitate effective
functioning of both systems. To understand how this is
achieved, we employed dye visualization techniques on
scyphomedusae (Aurelia aurita) observed swimming in
their natural marine habitat. The flow created during each
propulsive cycle consists of a toroidal starting vortex
formed during the power swimming stroke, followed by a
stopping vortex of opposite rotational sense generated
during the recovery stroke. These two vortices merge in a
laterally oriented vortex superstructure that induces flow
both toward the subumbrellar feeding surfaces and
downstream. The lateral vortex motif discovered here
appears to be critical to the dual function of the medusa
bell as a flow source for feeding and propulsion.
Furthermore, vortices in the animal wake have a greater
volume and closer spacing than predicted by prevailing
models of medusan swimming. These effects are shown to
be advantageous for feeding and swimming performance,
and are an important consequence of vortex interactions
that have been previously neglected
An intense, slow and cold beam of metastable Ne(3s) ^3P_2 atoms
We employ laser cooling to intensify and cool an atomic beam of metastable
Ne(3s) atoms. Using several collimators, a slower and a compressor we achieve a
^{20}Ne^* flux of 6 10^{10} atoms/s in an 0.7 mm diameter beam traveling at 100
m/s, and having longitudinal and transverse temperatures of 25mK and 300microK,
respectively. This constitutes the highest flux in a concentrated beam achieved
to date with metastable rare gas atoms. We characterize the action of the
various cooling stages in terms of their influence on the flux, diameter and
divergence of the atomic beam. The brightness and brilliance achieved are 2.1
10^{21} s^{-1} m^{-2} sr^{-1} and 5.0 10^{22} s^{-1} m^{-2} sr^{-1},
respectively, comparable to the highest values reported for alkali-metal beams.
Bright beams of the ^{21}Ne and ^{22}Ne isotopes have also been created.Comment: 18 pages, 9 figures, RevTe
Studying the Lunar-Solar Wind Interaction with the SARA Experiment aboard the Indian Lunar Mission Chandrayaan-1
The first Indian lunar mission Chandrayaan-1 was launched on 22 October 2008.
The Sub-keV Atom Reflecting Analyzer (SARA) instrument onboard Chandrayaan-1
consists of an energetic neutral atom (ENA) imaging mass analyzer called CENA
(Chandrayaan-1 Energetic Neutrals Analyzer), and an ion-mass analyzer called
SWIM (Solar wind Monitor). CENA performed the first ever experiment to study
the solar wind-planetary surface interaction via detection of sputtered neutral
atoms and neutralized backscattered solar wind protons in the energy range
~0.01-3.0 keV. SWIM measures solar wind ions, magnetosheath and magnetotail
ions, as well as ions scattered from lunar surface in the ~0.01-15 keV energy
range. The neutral atom sensor uses conversion of the incoming neutrals to
positive ions, which are then analyzed via surface interaction technique. The
ion mass analyzer is based on similar principle. This paper presents the SARA
instrument and the first results obtained by the SWIM and CENA sensors. SARA
observations suggest that about 20% of the incident solar wind protons are
backscattered as neutral hydrogen and ~1% as protons from the lunar surface.
These findings have important implications for other airless bodies in the
solar system.Comment: 4 pages, 6 figure
Heteronuclear ionizing collisions between laser-cooled metastable helium atoms
We have investigated cold ionizing heteronuclear collisions in dilute
mixtures of metastable (2 3S1) 3He and 4He atoms, extending our previous work
on the analogous homonuclear collisions [R. J. W. Stas et al., PRA 73, 032713
(2006)]. A simple theoretical model of such collisions enables us to calculate
the heteronuclear ionization rate coefficient, for our quasi-unpolarized gas,
in the absence of resonant light (T = 1.2 mK): K34(th) = 2.4*10^-10 cm^3/s.
This calculation is supported by a measurement of K34 using magneto-optically
trapped mixtures containing about 1*10^8 atoms of each species, K34(exp) =
2.5(8)*10^-10 cm^3/s. Theory and experiment show good agreement.Comment: 8 pages, 6 figure
Ultrastructural Islet Study of Early Fibrosis in the Ren2 Rat Model of Hypertension Emerging Role of the Islet Pancreatic Pericyte-Stellate Cell
Type 2 diabetes mellitus is a multifactorial disease with polygenic and environmental stressors resulting in multiple metabolic toxicities and islet oxidative stress. We have integrated the role of the islet renin-angiotensin system (RAS) in the pathogenesis of early islet fibrosis utilizing the transgenic (mRen2)27 rodent model of hypertension and tissue RAS overexpression. The Ren2 pancreatic islet tissue was evaluated with transmission electron microscopy to study both early cellular and extracellular matrix remodeling. Major remodeling differences in the Ren2 model were found to be located within the islet exocrine interface, including deposition of early fibrillar-banded collagen (fibrosis) and cellular remodeling of the pericyte suggesting proliferation, migration, hypertrophy and activation as compared to the Sprague Dawley controls.This research was supported by the investigator initiated grants NIH (R01 HL73101-01A1), the Veterans
Affairs Merit System (0018) grant and Novartis Pharmaceuticals. Male transgenic Ren2 rats and male Sprague-Dawley controls were kindly provided by Dr. Carlos M.
Ferrario, Wake Forest University School of Medicine, Winston-Salem, North Carolina through the Transgenic Core Facility supported in part by NIH grant HL-51952
Magneto-optical trap for metastable helium at 389 nm
We have constructed a magneto-optical trap (MOT) for metastable triplet
helium atoms utilizing the 2 3S1 -> 3 3P2 line at 389 nm as the trapping and
cooling transition. The far-red-detuned MOT (detuning Delta = -41 MHz)
typically contains few times 10^7 atoms at a relatively high (~10^9 cm^-3)
density, which is a consequence of the large momentum transfer per photon at
389 nm and a small two-body loss rate coefficient (2 * 10^-10 cm^3/s < beta <
1.0 * 10^-9 cm^3/s). The two-body loss rate is more than five times smaller
than in a MOT on the commonly used 2 3S1 -> 2 3P2 line at 1083 nm. Furthermore,
we measure a temperature of 0.46(1) mK, a factor 2.5 lower as compared to the
1083 nm case. Decreasing the detuning to Delta= -9 MHz results in a cloud
temperature as low as 0.25(1) mK, at small number of trapped atoms. The 389 nm
MOT exhibits small losses due to two-photon ionization, which have been
investigated as well.Comment: 11 page
Extremely high reflection of solar wind protons as neutral hydrogen atoms from regolith in space
We report on measurements of extremely high reflection rates of solar wind
particles from regolith-covered lunar surfaces. Measurements by the Sub-keV
Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1
spacecraft in orbit around the Moon show that up to 20% of the impinging solar
wind protons are reflected from the lunar surface back to space as neutral
hydrogen atoms. This finding, generally applicable to regolith-covered
atmosphereless bodies, invalidates the widely accepted assumption that regolith
almost completely absorbs the impinging solar wind.Comment: 2 figure
How Do Midwives View Their Professional Autonomy, Now and in Future?
Background: Internationally, midwives’ professional autonomy is being challenged, resulting in their inability to practice to their full scope of practice. This situation contrasts with the increasing international calls for strengthening the midwifery profession. The aim of this study therefore is to explore Belgian midwives’ views on their current and future autonomy. Methods: An online survey among Belgian midwives was performed. Data were collected and analyzed using a quantitative approach, while quotes from respondents were used to contextualize the quantitative data. Results: Three hundred and twelve midwives from different regions and professional settings in Belgium completed the questionnaire. Eighty-five percentage of respondents believe that they are mostly or completely autonomous. Brussels’ midwives feel the most autonomous, while those in Wallonia feel the least. Primary care midwives feel more autonomous than hospital-based midwives. Older midwives and primary care midwives feel less recognized and respected by other professionals in maternity care. The majority of our respondents believe that in future midwives should be able to work more autonomously in constructive collaboration with other professionals. Conclusion: While Belgian midwives generally rated their own professional autonomy as high, a significant majority of respondents desire more autonomy in future. In addition, our respondents want to be recognized and respected by society and other health professionals in maternity care. It is recommended to prioritize efforts in enhancing midwives’ autonomy, while also addressing the need for increased recognition and respect from society and other maternity care professionals
Mineralocorticoid Receptor Blockade Attenuates Chronic Overexpression of the Renin-Angiotensin- Aldosterone System Stimulation of Reduced Nicotinamide Adenine Dinucleotide Phosphate Oxidase and Cardiac Remodeling
doi: 10.1210/en.2006-1691The renin-angiotensin-aldosterone system contributes to cardiac remodeling, hypertrophy, and left ventricular dysfunction.
Angiotensin II and aldosterone (corticosterone in rodents) together generate reactive oxygen species (ROS) via reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which likely facilitate this hypertrophy and remodeling. This investigation sought to determine whether cardiac oxidative stress and cellular remodeling could be attenuated by in vivo mineralocorticoid receptor (MR) blockade in a rodent model of the chronically elevated
tissue renin-angiotensin-aldosterone system, the transgenic TG (mRen2) 27 rat (Ren2). The Ren2 overexpresses the mouse renin transgene with resultant hypertension, insulin resistance, proteinuria, and cardiovascular damage. Young (6- to 7-wk-old) male Ren2 and age-matched Sprague-Dawley rats were treated with spironolactone or placebo for 3 wk. Heart
tissue ROS, immunohistochemical analysis of 3-nitrotyrosine,and NADPH oxidase (NOX) subunits (gp91phox recently renamed
NOX2, p22phox, Rac1, NOX1, and NOX4) were measured. Structural changes were assessed with cine-magnetic resonance
imaging, transmission electron microscopy, and light microscopy. Significant increases in Ren2 septal wall thickness (cine-magnetic resonance imaging) were accompanied by perivascular fibrosis, increased mitochondria, and other ultrastructural changes visible by light microscopy and transmission electron microscopy. Although there was no significant
reduction in systolic blood pressure, significant improvements were seen with MR blockade on ROS formation and NOX subunits (each P < 0.05). Collectively, these data suggest that MR blockade, independent of systolic blood pressure reduction, improves cardiac oxidative stress-induced structural
and functional changes, which are driven, in part, by angiotensin type 1 receptor-mediated increases in NOX.This research was supported by National Institutes of Health (NIH) Grants R01 HL73101-01A1 (to J.R.S.) and P01 HL-51952 (to C.F.), the Veterans Affairs Merit System (0018) (to J.R.S.), and Advanced Research Career Development (to C.S.). Male transgenic Ren2 rats and male Sprague-Dawley controls were kindly provided by C.F. through the Transgenic Core Facility supported in part by NIH Grant HL-51952
Massive Black Hole Binary Inspirals: Results from the LISA Parameter Estimation Taskforce
The LISA Parameter Estimation (LISAPE) Taskforce was formed in September 2007
to provide the LISA Project with vetted codes, source distribution models, and
results related to parameter estimation. The Taskforce's goal is to be able to
quickly calculate the impact of any mission design changes on LISA's science
capabilities, based on reasonable estimates of the distribution of
astrophysical sources in the universe. This paper describes our Taskforce's
work on massive black-hole binaries (MBHBs). Given present uncertainties in the
formation history of MBHBs, we adopt four different population models, based on
(i) whether the initial black-hole seeds are small or large, and (ii) whether
accretion is efficient or inefficient at spinning up the holes. We compare four
largely independent codes for calculating LISA's parameter-estimation
capabilities. All codes are based on the Fisher-matrix approximation, but in
the past they used somewhat different signal models, source parametrizations
and noise curves. We show that once these differences are removed, the four
codes give results in extremely close agreement with each other. Using a code
that includes both spin precession and higher harmonics in the
gravitational-wave signal, we carry out Monte Carlo simulations and determine
the number of events that can be detected and accurately localized in our four
population models.Comment: 14 pages, 2 figures, 5 tables, minor changes to match version to be
published in the proceedings of the 7th LISA Symposium. For more information
see the Taskforce's wiki at http://www.tapir.caltech.edu/dokuwiki/lisape:hom
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