202 research outputs found
Standard clinical computed tomography fails to precisely visualise presence, course and branching points of deep cerebral perforators
Background: Standard computed tomography (CT) images have earned a well-established position in neuroimaging. Despite that, CT is somehow limited by its resolution, which does not enable to distinctively visualize structures smaller than 300 um in diameter. Perforating arteries, most of which measure 100-400 um in diameter, supply important subcortical structures (thalamus, basal ganglia, internal capsule). Consequently, pathologies affecting these vessels (e.g. lacunar strokes) can have a devastating clinical outcome. The aim of our study was to assess standard CT’s ability to visualize perforators and compare it with microscopical and micro-CT pictures. Materials and methods: We have obtained six brainstem and seventeen basal ganglia specimens. We infused them with barium sulphate contrast medium administered into either vertebral or internal cerebral artery. After that, the specimens were fixed in formalin and subsequently a series of CT, micro-CT and microscopical examinations were performed. Results: The median number of visualized perforators in brainstem and basal ganglia specimens was 8 and 3, respectively for CT and 18 and 7 for micro–CT (p < 0.05). Standard CT failed to clearly visualize branching points and vessels smaller than 0.25-0.5 mm (1-2 voxels) in diameter. Parallel vessels, like lenticulostriate arteries could not be differentiated in standard CT due to their proximity being smaller that the resolution. Conclusions: Basing on our results, we infer that CT is a poor modality for imaging of the perforators, presenting both quantitative and qualitative flaws in contrast with micro-CT
Results from a Low-Energy Analysis of the CDMS II Germanium Data
We report results from a reanalysis of data from the Cryogenic Dark Matter
Search (CDMS II) experiment at the Soudan Underground Laboratory. Data taken
between October 2006 and September 2008 using eight germanium detectors are
reanalyzed with a lowered, 2 keV recoil-energy threshold, to give increased
sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs)
with masses below ~10 GeV/c^2. This analysis provides stronger constraints than
previous CDMS II results for WIMP masses below 9 GeV/c^2 and excludes parameter
space associated with possible low-mass WIMP signals from the DAMA/LIBRA and
CoGeNT experiments.Comment: 9 pages, 8 figures. Supplemental material included as ancillary
files. v3) Added appendix with additional details regarding energy scale and
background
Search for inelastic dark matter with the CDMS II experiment
Results are presented from a reanalysis of the entire five-tower data set
acquired with the Cryogenic Dark Matter Search (CDMS II) experiment at the
Soudan Underground Laboratory, with an exposure of 969 kg-days. The analysis
window was extended to a recoil energy of 150 keV, and an improved
surface-event background-rejection cut was defined to increase the sensitivity
of the experiment to the inelastic dark matter (iDM) model. Three dark matter
candidates were found between 25 keV and 150 keV. The probability to observe
three or more background events in this energy range is 11%. Because of the
occurrence of these events the constraints on the iDM parameter space are
slightly less stringent than those from our previous analysis, which used an
energy window of 10-100 keV.Comment: 10 pages, 10 figures, minor changes to match published version,
conclusion unchange
Assessing Multivariate Constraints to Evolution across Ten Long-Term Avian Studies
Background
In a rapidly changing world, it is of fundamental importance to understand processes constraining or facilitating adaptation through microevolution. As different traits of an organism covary, genetic correlations are expected to affect evolutionary trajectories. However, only limited empirical data are available.
Methodology/Principal Findings
We investigate the extent to which multivariate constraints affect the rate of adaptation, focusing on four morphological traits often shown to harbour large amounts of genetic variance and considered to be subject to limited evolutionary constraints. Our data set includes unique long-term data for seven bird species and a total of 10 populations. We estimate population-specific matrices of genetic correlations and multivariate selection coefficients to predict evolutionary responses to selection. Using Bayesian methods that facilitate the propagation of errors in estimates, we compare (1) the rate of adaptation based on predicted response to selection when including genetic correlations with predictions from models where these genetic correlations were set to zero and (2) the multivariate evolvability in the direction of current selection to the average evolvability in random directions of the phenotypic space. We show that genetic correlations on average decrease the predicted rate of adaptation by 28%. Multivariate evolvability in the direction of current selection was systematically lower than average evolvability in random directions of space. These significant reductions in the rate of adaptation and reduced evolvability were due to a general nonalignment of selection and genetic variance, notably orthogonality of directional selection with the size axis along which most (60%) of the genetic variance is found.
Conclusions
These results suggest that genetic correlations can impose significant constraints on the evolution of avian morphology in wild populations. This could have important impacts on evolutionary dynamics and hence population persistence in the face of rapid environmental change
A Search for WIMPs with the First Five-Tower Data from CDMS
We report first results from the Cryogenic Dark Matter Search (CDMS II)
experiment running with its full complement of 30 cryogenic particle detectors
at the Soudan Underground Laboratory. This report is based on the analysis of
data acquired between October 2006 and July 2007 from 15 Ge detectors (3.75
kg), giving an effective exposure of 121.3 kg-d (averaged over recoil energies
10--100 keV, weighted for a weakly interacting massive particle (WIMP) mass of
60 \gev). A blind analysis, incorporating improved techniques for event
reconstruction and data quality monitoring, resulted in zero observed events.
This analysis sets an upper limit on the WIMP-nucleon spin-independent cross
section of 6.6 cm (4.6 cm when combined
with previous CDMS Soudan data) at the 90% confidence level for a WIMP mass of
60 \gev. By providing the best sensitivity for dark matter WIMPs with masses
above 42 GeV/c, this work significantly restricts the parameter space for
some of the favored supersymmetric models.Comment: 5 pages, 4 figures, submitted to PRL 28 March 200
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