12,623 research outputs found
Absence of synaptic regulation by phosducin in retinal slices.
Phosducin is an abundant photoreceptor protein that binds G-protein βγ subunits and plays a role in modulating synaptic transmission at photoreceptor synapses under both dark-adapted and light-adapted conditions in vivo. To examine the role of phosducin at the rod-to-rod bipolar cell (RBC) synapse, we used whole-cell voltage clamp recordings to measure the light-evoked currents from both wild-type (WT) and phosducin knockout (Pd(-/-)) RBCs, in dark- and light-adapted retinal slices. Pd(-/-) RBCs showed smaller dim flash responses and steeper intensity-response relationships than WT RBCs, consistent with the smaller rod responses being selectively filtered out by the non-linear threshold at the rod-to-rod bipolar synapse. In addition, Pd(-/-) RBCs showed a marked delay in the onset of the light-evoked currents, similar to that of a WT response to an effectively dimmer flash. Comparison of the changes in flash sensitivity in the presence of steady adapting light revealed that Pd(-/-) RBCs desensitized less than WT RBCs to the same intensity. These results are quantitatively consistent with the smaller single photon responses of Pd(-/-) rods, owing to the known reduction in rod G-protein expression levels in this line. The absence of an additional synaptic phenotype in these experiments suggests that the function of phosducin at the photoreceptor synapse is abolished by the conditions of retinal slice recordings
Approximations of thermoelastic and viscoelastic control systems
Well-posed models and computational algorithms are developed and analyzed for control of a class of partial differential equations that describe the motions of thermo-viscoelastic structures. An abstract (state space) framework and a general well-posedness result are presented that can be applied to a large class of thermo-elastic and thermo-viscoelastic models. This state space framework is used in the development of a computational scheme to be used in the solution of a linear quadratic regulator (LQR) control problem. A detailed convergence proof is provided for the viscoelastic model and several numerical results are presented to illustrate the theory and to analyze problems for which the theory is incomplete
A Prediction of Observable Rotation in the ICM of Abell 3266
We present a numerical Hydro+N-body model of A3266 whose X-ray surface
brightness, temperature distribution, and galaxy spatial and velocity
distribution data are consistent with the A3266 data. The model is an old (~3
Gyr), off-axis merger having a mass ratio of ~2.5:1. The less massive
subcluster in the model is moving on a trajectory from southwest to northeast
passing on the western side of the dominant cluster while moving into the plane
of the sky at ~45 degrees. Off-axis mergers such as this one are an effective
mechanism for transferring angular momentum to the intracluster medium (ICM),
making possible a large scale rotation of the ICM. We demonstrate here that the
ICM rotation predicted by our fully 3-dimensional model of A3266 is observable
with current technology. As an example, we present simulated observations
assuming the capabilities of the high resolution X-ray spectrometer (XRS) which
was to have flown on Astro-E.Comment: 9 pages, 7 postscript figures, Fig. 3 and 6 are color postscript,
Accepted for publication in the Astrophysical Journa
Cluster Structure in Cosmological Simulations I: Correlation to Observables, Mass Estimates, and Evolution
We use Enzo, a hybrid Eulerian AMR/N-body code including non-gravitational
heating and cooling, to explore the morphology of the X-ray gas in clusters of
galaxies and its evolution in current generation cosmological simulations. We
employ and compare two observationally motivated structure measures: power
ratios and centroid shift. Overall, the structure of our simulated clusters
compares remarkably well to low-redshift observations, although some
differences remain that may point to incomplete gas physics. We find no
dependence on cluster structure in the mass-observable scaling relations, T_X-M
and Y_X-M, when using the true cluster masses. However, estimates of the total
mass based on the assumption of hydrostatic equilibrium, as assumed in
observational studies, are systematically low. We show that the hydrostatic
mass bias strongly correlates with cluster structure and, more weakly, with
cluster mass. When the hydrostatic masses are used, the mass-observable scaling
relations and gas mass fractions depend significantly on cluster morphology,
and the true relations are not recovered even if the most relaxed clusters are
used. We show that cluster structure, via the power ratios, can be used to
effectively correct the hydrostatic mass estimates and mass-scaling relations,
suggesting that we can calibrate for this systematic effect in cosmological
studies. Similar to observational studies, we find that cluster structure,
particularly centroid shift, evolves with redshift. This evolution is mild but
will lead to additional errors at high redshift. Projection along the line of
sight leads to significant uncertainty in the structure of individual clusters:
less than 50% of clusters which appear relaxed in projection based on our
structure measures are truly relaxed.Comment: 57 pages, 18 figures, accepted to ApJ, updated definition of T_X and
M_gas but results unchanged, for version with full resolution figures, see
http://www.ociw.edu/~tesla/sims.ps.g
Oak pruning in the Missouri Ozarks
Cover title.Includes bibliographical references
Relationship of shortleaf pine growth to soil properties
A report on Department of Forestry research project number 103 entitled 'Forest Plantations'--P. [2].Digitized 2007 AES.Includes bibliographical references (page 11)
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The F220C and F45L rhodopsin mutations identified in retinitis pigmentosa patients do not cause pathology in mice.
Retinitis pigmentosa is a retinal degenerative disease that leads to blindness through photoreceptor loss. Rhodopsin is the most frequently mutated protein in this disease. While many rhodopsin mutations have well-understood consequences that lead to cell death, the disease association of several rhodopsin mutations identified in retinitis pigmentosa patients, including F220C and F45L, has been disputed. In this study, we generated two knockin mouse lines bearing each of these mutations. We did not observe any photoreceptor degeneration in either heterozygous or homozygous animals of either line. F220C mice exhibited minor disruptions of photoreceptor outer segment dimensions without any mislocalization of outer segment proteins, whereas photoreceptors of F45L mice were normal. Suction electrode recordings from individual photoreceptors of both mutant lines showed normal flash sensitivity and photoresponse kinetics. Taken together, these data suggest that neither the F220C nor F45L mutation has pathological consequences in mice and, therefore, may not be causative of retinitis pigmentosa in humans
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Phosducin regulates the expression of transducin betagamma subunits in rod photoreceptors and does not contribute to phototransduction adaptation.
For over a decade, phosducin's interaction with the betagamma subunits of the G protein, transducin, has been thought to contribute to light adaptation by dynamically controlling the amount of transducin heterotrimer available for activation by photoexcited rhodopsin. In this study we directly tested this hypothesis by characterizing the dark- and light-adapted response properties of phosducin knockout (Pd- / -) rods. Pd- / - rods were notably less sensitive to light than wild-type (WT) rods. The gain of transduction, as measured by the amplification constant using the Lamb-Pugh model of activation, was 32% lower in Pd- / - rods than in WT rods. This reduced amplification correlated with a 36% reduction in the level of transducin betagamma-subunit expression, and thus available heterotrimer in Pd- / - rods. However, commonly studied forms of light adaptation were normal in the absence of phosducin. Thus, phosducin does not appear to contribute to adaptation mechanisms of the outer segment by dynamically controlling heterotrimer availability, but rather is necessary for maintaining normal transducin expression and therefore normal flash sensitivity in rods
Tablet Use by Occupational Therapists for Preliteracy Learning with Preschool Children
Purpose: Tablet technologies are being used in pediatric occupational therapy (OT) despite a dearth of literature supporting their use. The purpose of this study was to investigate key strategies and decision-making considerations occupational therapists are using with tablet technologies to develop preliteracy skills with preschool aged children. Method: An ethnographic study of three pediatric occupational therapists (one school-based; one private clinic; and one school-based/private clinic) was conducted through semi-structured interviews and observations of the participants using the tablet. Results: One central theme, that tablets are “just a tool,” and three subthemes, that tablets are versatile, motivating, and fun, were identified. Results indicated that participants in this study are using tablets purposefully as a tool and as an alternative to traditional preliteracy activities. Conclusion: It is becoming more important for therapists to integrate the tablet and other mainstream technology into their practice in order to assist children in learning how to navigate an increasingly digital world. Further research regarding the efficacy of using tablet technology in pediatric occupational therapy is recommended
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