7,779 research outputs found
Preservation of in vivo Morphology of Blood Vessels for Morphometric Studies
Preservation of in vivo morphology of the blood vessels is important for morphometric studies. With each fixation method (e.g., immersion fixation, perfusion fixation), there are inherent pitfalls which can easily distort vessel wall morphology, thereby creating artifacts. Alteration of the vessel wall cell volume due to tissue preparation is another common source for errors. Selection of proper morphometric protocols for comparative studies is crucial. Lack of attention in these areas is a cause of confusion and contradiction in the literature. In this review, the merits of various commonly used methods for vessel wall preparation and measurements are discussed
Scanning Electron Microscopy of Vascular Smooth Muscle Cells from Rat Muscular Arteries
The use of scanning electron microscopy (SEM) for the examination of medial smooth muscle cells (SMC) is limited by the presence of connective tissue mass in the adventitia obscuring the detailed structure of the SMC. This study deals with the description of a method which selectively removes the connective tissue, allowing three dimensional observation of SMC using SEM. A number of methods were tried. One method involving post fixation with 2% Os04 used in conjunction with HCl proved most successful in removing the extracellular matrix of large mesenteric arteries from spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto normotensive rats (WKY). In both SHR and WKY, the spindle-shaped cells are circumferentially oriented, and ran parallel to one another and formed a continuous compact medial layer with a number of intercellular junctions being evident. Surface morphology of SMC changed between relaxed and contracted states. Relaxed SMC had a smooth regular surface with very fine longitudinal grooves or striations running parallel to the cell long axis. Contracted SMC possessed regular transverse folds on its surface giving a corrugated appearance. The nerve network possessed a fishnet appearance with many triangular bulges at nerve branch points. The internal elastic laminae showed longitudinal furrows and fenestrations, the number of which varied from vessel to vessel. In the superior mesenteric artery, the SMC were circular and helically arranged. Longitudinally and diagonally arranged SMC were evident at bifurcations. Mesenteric veins consisted of one layer of flattened circular SMC that ran parallel to one another and formed a compact and complete medial layer
Scanning Electron Microscopy of Vascular Smooth Muscle Cells from Spontaneously Hypertensive Rats
The fine structure of vascular smooth muscle cells from large mesenteric arteries of adult (28 weeks) spontaneously hypertensive rats and Wistar-Kyoto rats was studied using scanning electron microscopy (SEM). The effect of the digestion method for SEM on tissue size and smooth muscle cell size was also studied using morphometric analysis. A significant reduction in cell size (42-43%) was present after critical point drying, based on the reduction in volume to surface ratio of smooth muscle cells. However, percent change of volume density and volume to surface ratio of smooth muscle cells after digestion and after critical point drying, was similar between the hypertensives and normotensives. Most of the tissue shrinkage occurred during the digestion process to remove the connective tissue. Overall tissue shrinkage due to the digestion method involving OsO4/HCl and subsequent processing for SEM, based on changes in the thickness of the medial wall, was similar between arteries from hypertensive (34.7%) and normotensive (31.4%). After compensating for the shrinkage, vascular smooth muscle cells from hypertensive animals were found to have a wider soma! region (5.94 μm) than those from the normotensives (5.46 μm), suggesting cellular hypertrophy. We conclude that a significant reduction in size of tissue and smooth muscle cells took place when arteries were processed for SEM. For comparative study of vascular changes in hypertension involving SEM, cellular shrinkage due to processing should be included in the calculations in order to provide a reasonable estimate of the alterations
A disk census for the nearest group of young stars: Mid-infrared observations of the TW Hydrae Association
A group of young, active stars in the vicinity of TW Hydrae has recently been
identified as a possible physical association with a common origin. Given its
proximity (50 pc), age (10 Myr) and abundance of binary systems,
the TW Hya Association is ideally suited to studies of diversity and evolution
of circumstellar disks. Here we present mid-infrared observations of 15
candidate members of the group, 11 of which have no previous flux measurements
at wavelengths longer than 2m. We report the discovery of a possible
10m excess in CD -337795, which may be due to a circumstellar
disk or a faint, as yet undetected binary companion. Of the other stars, only
TW Hya, HD 98800, Hen 3-600A, and HR 4796A -- all of which were detected by
IRAS -- show excess thermal emission. Our 10m flux measurements for the
remaining members of the Association are consistent with photospheric emission,
allowing us to rule out dusty inner disks. In light of these findings, we
discuss the origin and age of the TW Hya Association as well as implications
for disk evolution timescales.Comment: 10 pages and 1 PostScript figure, accepted for publication in The
Astrophysical Journal Letter
Direct Measurement of Kirkwood-Rihaczek distribution for spatial properties of coherent light beam
We present direct measurement of Kirkwood-Rihaczek (KR) distribution for
spatial properties of coherent light beam in terms of position and momentum
(angle) coordinates. We employ a two-local oscillator (LO) balanced heterodyne
detection (BHD) to simultaneously extract distribution of transverse position
and momentum of a light beam. The two-LO BHD could measure KR distribution for
any complex wave field (including quantum mechanical wave function) without
applying tomography methods (inverse Radon transformation). Transformation of
KR distribution to Wigner, Glauber Sudarshan P- and Husimi or Q- distributions
in spatial coordinates are illustrated through experimental data. The direct
measurement of KR distribution could provide local information of wave field,
which is suitable for studying particle properties of a quantum system. While
Wigner function is suitable for studying wave properties such as interference,
and hence provides nonlocal information of the wave field. The method developed
here can be used for exploring spatial quantum state for quantum mapping and
computing, optical phase space imaging for biomedical applications.Comment: 27 pages, 14 figure
Mid-infrared imaging of the young binary star Hen 3-600: Evidence for a dust disk around the primary
We present high-resolution mid-infrared observations of the nearby late-type
young binary system Hen 3-600. The binary, at a distance of 50 pc, could
be a member of the TW Hydrae Association, the nearest known group of young
stars, with an age of a few million years. Our images make it possible for the
first time to determine which star in the pair, separated by 1.4'', harbors the
mid-infrared excess detected by IRAS. In the near-infrared, where the radiation
is primarily photospheric, Hen 3-600A (M3) and Hen 3-600B (M3.5) have a flux
ratio of 1.6. At 4.8m, 10.8m, and 18.2m, the primary becomes
increasingly dominant over the secondary, suggesting that most of the
circumstellar dust in the system resides around Hen 3-600A. Comparison of the
spectral energy distribution (SED) of Hen 3-600A to the median SED of classical
T Tauri stars suggests that its disk may be truncated by the secondary and
provides tentative evidence for a central disk hole. The distribution of dust
in the Hen 3-600 system may provide important clues to the formation and
evolution of protoplanetary disks in close binaries.Comment: 9 pages, 2 PostScript figures, accepted for publication in The
Astrophysical Journal Letter
Commensurate antiferromagnetic ordering in Ba(Fe{1-x}Co{x})2As2 determined by x-ray resonant magnetic scattering at the Fe K-edge
We describe x-ray resonant magnetic diffraction measurements at the Fe K-edge
of both the parent BaFe2As2 and superconducting Ba(Fe0.953Co0.047)2As2
compounds. From these high-resolution measurements we conclude that the
magnetic structure is commensurate for both compositions. The energy spectrum
of the resonant scattering is in reasonable agreement with theoretical
calculations using the full-potential linear augmented plane wave method with a
local density functional.Comment: 5 pages, 3 figures; accepted for publication in Phys. Rev. B Rapid
Com
Manipulating the ABCs of self-assembly via low-χ block polymer design
Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χ_ij). In this article, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χ_(AC) ≲ 0), promotes organization into a unique mixed-domain lamellar morphology, which we designate LAM_P. Transmission electron microscopy indicates that LAM_P exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM_3) with ABCB periods. Complementary small-angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations and predicts that LAM_P is thermodynamically stable below a critical χ_(AC), above which LAM_3 emerges. Both experiments and theory expose close analogies to ABA′ triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. These conclusions provide fresh opportunities for block polymer design with potential consequences spanning all self-assembling soft materials
Order via Nonlinearity in Randomly Confined Bose Gases
A Hartree-Fock mean-field theory of a weakly interacting Bose-gas in a
quenched white noise disorder potential is presented. A direct continuous
transition from the normal gas to a localized Bose-glass phase is found which
has localized short-lived excitations with a gapless density of states and
vanishing superfluid density. The critical temperature of this transition is as
for an ideal gas undergoing Bose-Einstein condensation. Increasing the
particle-number density a first-order transition from the localized state to a
superfluid phase perturbed by disorder is found. At intermediate number
densities both phases can coexist.Comment: Author Information under
http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir/. International Journal
of Bifurcation and Chaos (in press
- …