694 research outputs found
A Solid State \u3csup\u3e13\u3c/sup\u3eC-NMR Study of Diamonds and Graphites
The 13C-NMR spectra of gem quality and industrial diamonds show two resonances with the more intense resonance at high field. Two resonances are also shown in 13C-NMR spectra of various graphites; however, the low field resonance is of greater intensity than the high field resonance in the graphites. The resonances are very broad and they are assigned to graphite type (sp2) carbon and diamond type (sp3) carbon
Measuring the effect of airway pressure on pulmonary arterial diameter in the intact rat lung
To study the relationship between transpulomnary pressure (Ptp), intravascular pressure (Pv), and the pulmonary arterial tree structure, morphometric measurements of pulmonary arterial trees were made in intact lungs from Sprague-Dawley rats. Using cone beam micro-CT and techniques we developed for imaging small animal lungs, volumetric CT data were acquired for Ptp from 0 - 12 mmHg and Pv from 5 - 30 mmHg. The diameter, D (measured range approximately 0.08-2.0 mm), vs. pressure, P, relation can be described by D(P) = D(0)(1+ α P), where α is a distensibility coefficient. Unlike studies performed in larger animals, where changes in either Ptp or Pv had nearly identical effect on vessel distensibility, we found that there is only a small dependence of arterial diameter on Ptp in the rat. For example, using the above relation where P=Ptp and Pv is held constant at 12mmHg, alpha = 0.55±0.42(SE) %/mmHg, compared with when P=Pv and Ptp is held at 12mmHg, alpha = 2.59±0.17(SE) %/mmHg
Estimation of Pulmonary Arterial Volume Changes in the Normal and Hypertensive Fawn-Hooded Rat from 3D Micro-CT data
In the study of pulmonary vascular remodeling, much can be learned from observing the morphological changes undergone in the pulmonary arteries of the rat lung when exposed to chronic hypoxia or other challenges which elicit a remodeling response. Remodeling effects include thickening of vessel walls, and loss of wall compliance. Morphometric data can be used to localize the hemodynamic and functional consequences. We developed a CT imaging method for measuring the pulmonary arterial tree over a range of pressures in rat lungs. X-ray micro-focal isotropic volumetric imaging of the arterial tree in the intact rat lung provides detailed information on the size, shape and mechanical properties of the arterial network. In this study, we investigate the changes in arterial volume with step changes in pressure for both normoxic and hypoxic Fawn-Hooded (FH) rats. We show that FH rats exposed to hypoxia tend to have reduced arterial volume changes for the same preload when compared to FH controls. A secondary objective of this work is to quantify various phenotypes to better understand the genetic contribution of vascular remodeling in the lungs. This volume estimation method shows promise in high throughput phenotyping, distinguishing differences in the pulmonary hypertensive rat model
Electronic versus paper record keeping in scientific research: a case study for the Open Exeter project
In this case study the nature of record keeping for two different kinds of research in Physics, experiment and theory, is used to assess the potential value of keeping electronic instead of paper records. We find that, although there is already a range of positive aspects to electronic record keeping, the software currently available is not yet able to fulfill all of the requirements of a lab book and may be inappropriate in novel working environments. Given the rate at which the relevant hardware and software is developing and the option for researchers to try current note taking software for free, we suggest waiting at least another year and assessing the latest options before investing in support for electronic record keeping.JIS
Changes in Pulmonary Arterial Wall Mechanical Properties and Lumenal Architecture with Induced Vascular Remodeling
To explore and quantify pulmonary arterial remodeling we used various methods including micro-CT, high-resolution 3-dimensional x-ray imaging, to examine the structure and function of intact pulmonary vessels in isolated rat lungs. The rat is commonly used as an animal model for studies of pulmonary hypertension (PH) and the accompanying vascular remodeling, where vascular remodeling has been defined primarily by changes in the vessel wall composition in response to hypertension inducing stimuli such as chronic hypoxic exposure (CHE) or monocrotaline (MCT) injection. Little information has been provided as to how such changes affect the vessel wall mechanical properties or the lumenal architecture of the pulmonary arterial system that actually account for the hemodynamic consequences of the remodeling. In addition, although the link between primary forms of pulmonary hypertension and inherited genetics is well established, the role that genetic coding plays in hemodynamics and vascular remodeling is not. Therefore, we are utilizing Fawn-Hooded (FH), Sprague-Dawley (SD) and Brown Norway (BN)rat strains along with unique imaging methods to parameterize both vessel distensibility and lumenal morphometry using a principal pulmonary arterial pathway analysis based on self-consistency. We have found for the hypoxia model, in addition to decreased body weight, increased hematocrit, increased right ventricular hypertrophy, the distensibility of the pulmonary arteries is shown to decrease significantly in the presence of remodeling
Post-Acquisition Small-Animal Respiratory Gated Imaging Using Micro Cone-Beam CT
On many occasions, it is desirable to image lungs in vivo to perform a pulmonary physiology study. Since the lungs are moving, gating with respect to the ventilatory phase has to be performed in order to minimize motion artifacts. Gating can be done in real time, similar to cardiac imaging in clinical applications, however, there are technical problems that have lead us to investigate different approaches. The problems include breath-to-breath inconsistencies in tidal volume, which makes the precise detection of ventilatory phase difficult, and the relatively high ventilation rates seen in small animals (rats and mice have ventilation rates in the range of a hundred cycles per minute), which challenges the capture rate of many imaging systems (this is particularly true of our system which utilizes cone-beam geometry and a 2 dimensional detector). Instead of pre-capture ventilation gating we implemented a method of post-acquisition gating. We acquire a sequence of projections images at 30 frames per second for each of 360 viewing angles. During each capture sequence the rat undergoes multiple ventilation cycles. Using the sequence of projection images, an automated region of interest algorithm, based on integrated grayscale intensity, tracts the ventilatory phase of the lungs. In the processing of an image sequence, multiple projection images are identified at a particular phase and averaged to improve the signal-to-ratio. The resulting averaged projection images are input to a Feldkamp cone-beam algorithm reconstruction algorithm in order to obtain isotropic image volumes. Minimal motion artifact data sets improve qualitative and quantitative analysis techniques useful in physiologic studies of pulmonary structure and function
Semiautomated Skeletonization of the Pulmonary Arterial Tree in Micro-CT Images
We present a simple and robust approach that utilizes planar images at different angular rotations combined with unfiltered back-projection to locate the central axes of the pulmonary arterial tree. Three-dimensional points are selected interactively by the user. The computer calculates a sub- volume unfiltered back-projection orthogonal to the vector connecting the two points and centered on the first point. Because more x-rays are absorbed at the thickest portion of the vessel, in the unfiltered back-projection, the darkest pixel is assumed to be the center of the vessel. The computer replaces this point with the newly computer-calculated point. A second back-projection is calculated around the original point orthogonal to a vector connecting the newly-calculated first point and user-determined second point. The darkest pixel within the reconstruction is determined. The computer then replaces the second point with the XYZ coordinates of the darkest pixel within this second reconstruction. Following a vector based on a moving average of previously determined 3- dimensional points along the vessel\u27s axis, the computer continues this skeletonization process until stopped by the user. The computer estimates the vessel diameter along the set of previously determined points using a method similar to the full width-half max algorithm. On all subsequent vessels, the process works the same way except that at each point, distances between the current point and all previously determined points along different vessels are determined. If the difference is less than the previously estimated diameter, the vessels are assumed to branch. This user/computer interaction continues until the vascular tree has been skeletonized
Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field
We investigate the effect of including diffuse field radiation when modelling
the radiatively driven implosion of a Bonnor-Ebert sphere (BES).
Radiation-hydrodynamical calculations are performed by using operator splitting
to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics
that includes self-gravity. It is found that the diffuse field has a
significant effect on the nature of radiatively driven collapse which is
strongly coupled to the strength of the driving shock that is established
before impacting the BES. This can result in either slower or more rapid star
formation than expected using the on-the-spot approximation depending on the
distance of the BES from the source object. As well as directly compressing the
BES, stronger shocks increase the thickness and density in the shell of
accumulated material, which leads to short, strong, photo-evaporative ejections
that reinforce the compression whenever it slows. This happens particularly
effectively when the diffuse field is included as rocket motion is induced over
a larger area of the shell surface. The formation and evolution of 'elephant
trunks' via instability is also found to vary significantly when the diffuse
field is included. Since the perturbations that seed instabilities are smeared
out elephant trunks form less readily and, once formed, are exposed to enhanced
thermal compression.Comment: Accepted for publication in MNRAS. 19 pages, 14 figures, 8 table
The first multidimensional view of mass loss from externally FUV irradiated protoplanetary discs
Computing the flow from externally FUV irradiated protoplanetary discs
requires solving complicated and expensive photodissociation physics
iteratively in conjunction with hydrodynamics. Previous studies have therefore
been limited to 1D models of this process. In this paper we compare
2D-axisymmetric models of externally photoevaporating discs with their 1D
analogues, finding that mass loss rates are consistent to within a factor four.
The mass loss rates in 2D are higher, in part because half of the mass loss
comes from the disc surface (which 1D models neglect). 1D mass loss rates used
as the basis for disc viscous evolutionary calculations are hence expected to
be conservative. We study the anatomy of externally driven winds including the
streamline morphology, kinematic, thermal and chemical structure. A key
difference between the 1D and 2D models is in the chemical abundances. For
instance in the 2D models CO can be dissociated at smaller radial distances
from the disc outer edge than in 1D calculations because gas is
photodissociated by radiation along trajectories that are assumed infinitely
optically thick in 1D models. Multidimensional models will hence be critical
for predicting observable signatures of environmentally photoevaporating
protoplanetary discs.Comment: 15 pages, 12 figures. Accepted for publication in the MNRAS main
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Pulmonary arterial remodeling revealed by microfocal x-ray tomography
Animal models and micro-CT imaging are useful for understanding the functional consequences of, and identifying the genes involved in, the remodeling of vascular structures that accompanies pulmonary vascular disease. Using a micro-CT scanner to image contrast-enhanced arteries in excised lungs from fawn hooded rats (a strain genetically susceptible to hypoxia induced pulmonary hypertension), we found that portions of the pulmonary arterial tree downstream from a given diameter were morphometrically indistinguishable. This \u27self-consistency\u27 property provided a means for summarizing the pulmonary arterial tree architecture and mechanical properties using a parameter vector obtained from measurements of the contiguous set of vessel segments comprising the longest (principal) pathway and its branches over a range of vascular pressures. This parameter vector was used to characterize the pulmonary vascular remodeling that occurred in rats exposed to a hypoxic (11.5% oxygen) environment and provided the input to a hemodynamic model relating structure to function. The major effect of the remodeling was a longitudinally (pulmonary artery to arterioles) uniform decrease in vessel distensibility that resulted in a 90% increase in arterial resistance. Despite the almost uniform change in vessel distensibility, over 50% of the resistance increase was attributable to vessels with unstressed diameters less than 125 microns
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