246 research outputs found
995-22 The Effect of Perioperative Storage Solutions on the Long Term Vein Graft Function and Morphology
It has been shown that suboptimal preparation of a vein graft prior to its insertion results in immediate morphological and functional damage to the endothelial cells but not to the underlying smooth muscle cells. However. little is known if such perioperative injury to the vein grafts may influence the subsequent development of intimal hyperplasia and smooth muscle cell contractility. This study examines the influence of storage in saline or Ringer's lactate on the development of intimal hyperplasia and vasomotor function in experimental vein grafts. Twenty-six NM rabbits had a carotid vein bypass graft performed after the veins had been immersed (15 minutes) in either heparinized saline (Sal; n=13) or Ringer's lactate (RL; n=13) and each group was harvested after 28 days for either histology (n=8) or functional studies (n=5; four 5 mm rings/graft). Saline storage of the vein graft resulted in a 38% increase in the thickness of the intimal hyperplasia (113±2 vs. 83±μm, Sal vs. RL; mean±SEM, p<0.05) without a change in medial thickness (87±5 vs. 86±8μm, Sal vs. RL; p>0.05). There was no difference in the sensitivity to norepinephrine, serotonin and bradykinin between the two sets of vein grafts. The maximal contractile forces to serotonin and bradykinin were increased in the saline compared to Ringer's lactate stored vein grafts.SalineRinger'sp-valueNorepinephrine0.88±0.121.57±020<0.05Serotonin1.23±0.150.37±013<0.01Bradykinin2.08±0.110.52±007<0.01Values are the standardized maximal contractile force (maximal contraction/contraction to 60 mM KCI) expressed as mean±SEM.Saline storage of the vein graft results in the increased development of intimal hyperplasia with an overall enhanced contractility but without changes in agonist sensitivity. This study places further emphasis on the need for good perioperative care of the vein bypass graft because it results not only in the previously documented short term problems but also in long term structural and contractile changes which may contribute to decreased graft patency
1030-13 Alterations in Endothelial Cell Adenosine Receptors Mediate Endothelium-Dependent Vasoconstriction in Experimental Vein Grafts
Adenosine is a potent endogenous vasodilator which mediates its action through A1 and A2 receptor subtypes located on both vascular endothelial and vascular smooth muscle cells (SMC). Adenosine-mediated relaxation in vein grafts has not been examined. This study assesses the in vitro isometric tension responses to specific adenosine receptor agonists (A1: R-phenyl-isopropyl-adenosine and A2: CSG-21680; 10–9 to 10–4 M) of common carotid external jugular vein bypass grafts (VG) in New Zealand White rabbits. These responses were compared to those obtained in the extemal jugular vein (JV) and in the common carotid artery (CA). All vessels were precontracted with prostaglandin F2a (10–5 M). Endothelialized and de-endothelialized vessels were examined. The A1 mediated relaxation in JV was endothelium-independent, whereas A2 mediated relaxation was endothelium-dependent. In CA, A1 mediated relaxation was partially endothelium-dependent, while A2 mediated relaxation was endotheliumindependent. In VG, Al activation induced endothelium-dependent vasoconstriction. Endothelial denudation restored Al mediated relaxation, but reduced compared to that of JV (max. 19±9%). A2 relaxation in VG was endothelium-independent (max. 39±4%). Primary cultures of arterial and vein graft SMC expressed both A1 and A2 receptors on northern blot analysis. There was, however, a marked reduction in the A1 affinity of the SMC from the VG compared to the arterial SMC (40.9±1.3% arterial binding). This study, therefore, demonstrates that there is a substantial change in the adenosine mediated vasoreactivity in VG compared to JV, due to a change in endothelial A1 receptor mediated response from relaxation to constriction, coupled with a decreased affinity of the A1 receptors on the VG SMC. The adenosine responses of the VG are also different from CA. Therefore, the endothelial celis of VG appear to be unique, in that functionally they neither maintain a venous phenotype nor acquire an arterial phenotype in response to adenosine
Three Super-Earths Orbiting HD 7924
We report the discovery of two super-Earth mass planets orbiting the nearby
K0.5 dwarf HD 7924 which was previously known to host one small planet. The new
companions have masses of 7.9 and 6.4 M, and orbital periods of 15.3
and 24.5 days. We perform a joint analysis of high-precision radial velocity
data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to
robustly detect three total planets in the system. We refine the ephemeris of
the previously known planet using five years of new Keck data and high-cadence
observations over the last 1.3 years with the APF. With this new ephemeris, we
show that a previous transit search for the inner-most planet would have
covered 70% of the predicted ingress or egress times. Photometric data
collected over the last eight years using the Automated Photometric Telescope
shows no evidence for transits of any of the planets, which would be detectable
if the planets transit and their compositions are hydrogen-dominated. We detect
a long-period signal that we interpret as the stellar magnetic activity cycle
since it is strongly correlated with the Ca II H and K activity index. We also
detect two additional short-period signals that we attribute to
rotationally-modulated starspots and a one month alias. The high-cadence APF
data help to distinguish between the true orbital periods and aliases caused by
the window function of the Keck data. The planets orbiting HD 7924 are a local
example of the compact, multi-planet systems that the Kepler Mission found in
great abundance.Comment: Accepted to ApJ on 4/7/201
Constraints on the Atmospheric Circulation and Variability of the Eccentric Hot Jupiter XO-3b
We report secondary eclipse photometry of the hot Jupiter XO-3b in the
4.5~m band taken with the Infrared Array Camera (IRAC) on the Spitzer
Space Telescope. We measure individual eclipse depths and center of eclipse
times for a total of twelve secondary eclipses. We fit these data
simultaneously with two transits observed in the same band in order to obtain a
global best-fit secondary eclipse depth of and a center of
eclipse phase of . We assess the relative magnitude of
variations in the dayside brightness of the planet by measuring the size of the
residuals during ingress and egress from fitting the combined eclipse light
curve with a uniform disk model and place an upper limit of 0.05. The new
secondary eclipse observations extend the total baseline from one and a half
years to nearly three years, allowing us to place an upper limit on the
periastron precession rate of degrees/day the tightest
constraint to date on the periastron precession rate of a hot Jupiter. We use
the new transit observations to calculate improved estimates for the system
properties, including an updated orbital ephemeris. We also use the large
number of secondary eclipses to obtain the most stringent limits to date on the
orbit-to-orbit variability of an eccentric hot Jupiter and demonstrate the
consistency of multiple-epoch Spitzer observations.Comment: 14 pages, 11 figures, published by Ap
3.6 and 4.5 m Phase Curves of the Highly-Irradiated Hot Jupiters WASP-19b and HAT-P-7b
We analyze full-orbit phase curve observations of the transiting hot Jupiters
WASP-19b and HAT-P-7b at 3.6 and 4.5 m obtained using the Spitzer Space
Telescope. For WASP-19b, we measure secondary eclipse depths of and at 3.6 and 4.5 m, which are consistent
with a single blackbody with effective temperature K. The
measured 3.6 and 4.5 m secondary eclipse depths for HAT-P-7b are
and , which are well-described by a
single blackbody with effective temperature K. Comparing the phase
curves to the predictions of one-dimensional and three-dimensional atmospheric
models, we find that WASP-19b's dayside emission is consistent with a model
atmosphere with no dayside thermal inversion and moderately efficient day-night
circulation. We also detect an eastward-shifted hotspot, suggesting the
presence of a superrotating equatorial jet. In contrast, HAT-P-7b's dayside
emission suggests a dayside thermal inversion and relatively inefficient
day-night circulation; no hotspot shift is detected. For both planets, these
same models do not agree with the measured nightside emission. The
discrepancies in the model-data comparisons for WASP-19b might be explained by
high-altitude silicate clouds on the nightside and/or high atmospheric
metallicity, while the very low 3.6 m nightside planetary brightness for
HAT-P-7b may be indicative of an enhanced global C/O ratio. We compute Bond
albedos of 0 ( at ) and for WASP-19b and
HAT-P-7b, respectively. In the context of other planets with thermal phase
curve measurements, we show that WASP-19b and HAT-P-7b fit the general trend of
decreasing day-night heat recirculation with increasing irradiation.Comment: 22 pages, 29 figures, accepted by Ap
Spitzer Secondary Eclipse Observations of Five Cool Gas Giant Planets and Empirical Trends in Cool Planet Emission Spectra
In this work we present Spitzer 3.6 and 4.5 micron secondary eclipse
observations of five new cool (<1200 K) transiting gas giant planets:
HAT-P-19b, WASP-6b, WASP-10b, WASP-39b, and WASP-67b. We compare our measured
eclipse depths to the predictions of a suite of atmosphere models and to
eclipse depths for planets with previously published observations in order to
constrain the temperature- and mass-dependent properties of gas giant planet
atmospheres. We find that the dayside emission spectra of planets less massive
than Jupiter require models with efficient circulation of energy to the night
side and/or increased albedos, while those with masses greater than that of
Jupiter are consistently best-matched by models with inefficient circulation
and low albedos. At these relatively low temperatures we expect the atmospheric
methane to CO ratio to vary as a function of metallicity, and we therefore use
our observations of these planets to constrain their atmospheric metallicities.
We find that the most massive planets have dayside emission spectra that are
best-matched by solar metallicity atmosphere models, but we are not able to
place strong constraints on metallicities of the smaller planets in our sample.
Interestingly, we find that the ratio of the 3.6 and 4.5 micron brightness
temperatures for these cool transiting planets is independent of planet
temperature, and instead exhibits a tentative correlation with planet mass. If
this trend can be confirmed, it would suggest that the shape of these planets'
emission spectra depends primarily on their masses, consistent with the
hypothesis that lower-mass planets are more likely to have metal-rich
atmospheres.Comment: 16 pages, 14 figures, accepted for publication in Ap
The First Direct Detection of Kirkwood Transitions in Concentrated Aqueous Electrolytes using Small Angle X-ray Scattering
Ion-ion correlations, screening, and equilibrium bulk structure in various
concentrated electrolytes are investigated using synchrotron small angle X-ray
scattering (SAXS), theory, and molecular simulation. Utilizing SAXS
measurements we provide estimates of the Kirkwood Transition (KT) for a variety
of aqueous electrolytes (NaCl, CaCl, SrCl, and ErCl). The KT may be
defined as the concentration above which the ion-ion correlations cease to
decay exponentially with a single length scale given by the Debye length
and develop an additional length scale, that
reflects the formation of local domains of charge. Theoretical models of the KT
have been known for decades for highly idealized models of electrolytes, but
experimental verification of KT in real electrolytes has yet to be confirmed.
Herein, we provide consistent theoretical and experimental estimates of both
the inverse screening lengths and inverse domain size, for the
aforementioned electrolyte systems. Taken together, and are known
descriptors of the KT and provide a view into the complexity of ion-ion
interaction beyond the well-accepted Debye-H\"{u}ckel limit. Our findings
suggest a picture of interaction for real electrolytes that is more general
than that found in idealized models that is manifest in the precise form of the
non-local response function that we estimate through the interpretation of the
experimental SAXS signal. Importantly, the additional complexity of describing
ion-ion interaction of real electrolytes will implicate the short-range ion-ion
interactions that can only be computed via molecular simulation and provide a
quantitative approach to describe electrolyte phenomena beyond Debye-H\"{u}ckel
theory.Comment: 3
Guide to Magellan image interpretation
An overview of Magellan Mission requirements, radar system characteristics, and methods of data collection is followed by a description of the image data, mosaic formats, areal coverage, resolution, and pixel DN-to-dB conversion. The availability and sources of image data are outlined. Applications of the altimeter data to estimate relief, Fresnel reflectivity, and surface slope, and the radiometer data to derive microwave emissivity are summarized and illustrated in conjunction with corresponding SAR image data. Same-side and opposite-side stereo images provide examples of parallax differences from which to measure relief with a lateral resolution many times greater than that of the altimeter. Basic radar interactions with geologic surfaces are discussed with respect to radar-imaging geometry, surface roughness, backscatter modeling, and dielectric constant. Techniques are described for interpreting the geomorphology and surface properties of surficial features, impact craters, tectonically deformed terrain, and volcanic landforms. The morphologic characteristics that distinguish impact craters from volcanic craters are defined. Criteria for discriminating extensional and compressional origins of tectonic features are discussed. Volcanic edifices, constructs, and lava channels are readily identified from their radar outlines in images. Geologic map units are identified on the basis of surface texture, image brightness, pattern, and morphology. Superposition, cross-cutting relations, and areal distribution of the units serve to elucidate the geologic history
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