1,418 research outputs found
Transverse flow of nuclear matter in collisions of heavy nuclei at intermediate energies
The Quantum Molecular Dynamics Model (IQMD) is used to investigate the origin
of the collective transverse velocity observed in heavy ion experiments. We
find that there are three contributions to this effect: initial-final state
correlations, potential interactions and collisions. For a given nuclear
equation of state (eos) the increase of the transverse velocity with increasing
beam energy is caused by the potential part. For a given beam energy the
collective transverse velocity is independent of the nuclear eos but the
relative contributions of potential and collisions differ. In view of the
importance of the potential interactions between the nucleons it is not evident
that the similarity of the radial velocities measured for fragments at beam
energies below 1 AGeV and that for mesons at beam energies above 2 AGeV is more
than accidental.Comment: 5 pages, 5 figures, revtex, OASIS ref PLB1700
Using reciprocity for relating the simulation of transcranial current stimulation to the EEG forward problem
To explore the relationship between transcranial current stimulation (tCS) and the electroencephalography (EEG) forward problem, we investigate and compare accuracy and efficiency of a reciprocal and a direct EEG forward approach for dipolar primary current sources both based on the finite element method (FEM), namely the adjoint approach (AA) and the partial integration approach in conjunction with a transfer matrix concept (PI). By analyzing numerical results, comparing to analytically derived EEG forward potentials and estimating computational complexity in spherical shell models, AA turns out to be essentially identical to PI. It is then proven that AA and PI are also algebraically identical even for general head models. This relation offers a direct link between the EEG forward problem and tCS. We then demonstrate how the quasi-analytical EEG forward solutions in sphere models can be used to validate the numerical accuracies of FEM-based tCS simulation approaches. These approaches differ with respect to the ease with which they can be employed for realistic head modeling based on MRI-derived segmentations. We show that while the accuracy of the most easy to realize approach based on regular hexahedral elements is already quite high, it can be significantly improved if a geometry-adaptation of the elements is employed in conjunction with an isoparametric FEM approach. While the latter approach does not involve any additional difficulties for the user, it reaches the high accuracies of surface-segmentation based tetrahedral FEM, which is considerably more difficult to implement and topologically less flexible in practice. Finally, in a highly realistic head volume conductor model and when compared to the regular alternative, the geometry-adapted hexahedral FEM is shown to result in significant changes in tCS current flow orientation and magnitude up to 45° and a factor of 1.66, respectively
Room temperature high frequency transport of Dirac fermions in epitaxially grown Sb_2Te_3 based topological insulators
We report on the observation of photogalvanic effects in epitaxially grown
Sb_2Te_3 three-dimensional (3D) topological insulators (TI). We show that
asymmetric scattering of Dirac electrons driven back and forth by the terahertz
electric field results in a dc electric current. Due to the "symmetry
filtration" the dc current is generated in the surface electrons only and
provides an opto-electronic access to probe the electric transport in TI,
surface domains orientation and details of electron scattering even in 3D TI at
room temperature where conventional surface electron transport is usually
hindered by the high carrier density in the bulk
Fluorescence Blinking and Photobleaching of Single Terrylenediimide Molecules Studied with a Confocal Microscope
Single terrylenediimide molecules diluted in a 20-nm-thick polyvinylbutyral polymer film were localized and observed by scanning confocal fluorescence microscopy. A modular and compact confocal microscope and the high optical stability of the molecules allowed a repeated imaging and observation over >5 h at room temperature. Most of the molecules showed several “on-off-on” transitions (blinking) on a time scale from seconds to hours, before permanent bleaching occurred. We determined that >1.5 × 10^7 fluorescence photons are emitted from the most-stable molecules before the final bleaching step occurs. Despite the “on-off-on” transitions, however, the overall change in fluorescence intensity, either integrated over each image of a time series or summed for several individual molecules, resembled an exponential-like decay, familiar from measurements of many-molecule ensembles. We also observed the polarization of the fluorescence from single molecules during excitation with circular polarized light. From these measurements, possible rotations of the molecular dipoles were studied. Over a span of 5 h, the polarization angle in most cases did not change by >15-20°. This may explain the slow and small intensity changes but excludes molecular rotation as a reason for the blinking behavior
Mapping heterogeneities through avalanche statistics
Avalanche statistics of various threshold activated dynamical systems are known to depend on the magnitude of the drive, or stress, on the system. Such dependencies exist for earthquake size distributions, in sheared granular avalanches, laboratory scale fracture and also in the outage statistics of power grids. In this work we model threshold-activated avalanche dynamics and investigate the time required to detect local variations in the ability of model elements to bear stress. We show that the detection time follows a scaling law where the scaling exponents depend on whether the feature that is sought is either weaker, or stronger, than its surroundings. We then look at earthquake data from Sumatra and California, demonstrate the trade-off between the spatial resolution of a map of earthquake exponents (i.e. the b-values of the Gutenberg-Richter law) and the accuracy of those exponents, and suggest a means to maximise both
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Mini-Cog for the diagnosis of Alzheimer's disease dementia and other dementias within a primary care setting.
BACKGROUND: Alzheimer's disease and other forms of dementia are becoming increasingly common with the aging of most populations. The majority of individuals with dementia will first present for care and assessment in primary care settings. There is a need for brief dementia screening instruments that can accurately diagnose dementia in primary care settings. The Mini-Cog is a brief, cognitive screening test that is frequently used to evaluate cognition in older adults in various settings. OBJECTIVES: To determine the diagnostic accuracy of the Mini-Cog for diagnosing Alzheimer's disease dementia and related dementias in a primary care setting. SEARCH METHODS: We searched the Cochrane Dementia and Cognitive Improvement Register of Diagnostic Test Accuracy Studies, MEDLINE, Embase and four other databases, initially to September 2012. Since then, four updates to the search were performed using the same search methods, and the most recent was January 2017. We used citation tracking (using the databases' 'related articles' feature, where available) as an additional search method and contacted authors of eligible studies for unpublished data. SELECTION CRITERIA: We only included studies that evaluated the Mini-Cog as an index test for the diagnosis of Alzheimer's disease dementia or related forms of dementia when compared to a reference standard using validated criteria for dementia. We only included studies that were conducted in primary care populations. DATA COLLECTION AND ANALYSIS: We extracted and described information on the characteristics of the study participants and study setting. Using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) criteria we evaluated the quality of studies, and we assessed risk of bias and applicability of each study for each domain in QUADAS-2. Two review authors independently extracted information on the true positives, true negatives, false positives, and false negatives and entered the data into Review Manager 5 (RevMan 5). We then used RevMan 5 to determine the sensitivity, specificity, and 95% confidence intervals. We summarized the sensitivity and specificity of the Mini-Cog in the individual studies in forest plots and also plotted them in a receiver operating characteristic plot. We also created a 'Risk of bias' and applicability concerns graph to summarize information related to the quality of included studies. MAIN RESULTS: There were a total of four studies that met our inclusion criteria, including a total of 1517 total participants. The sensitivity of the Mini-Cog varied between 0.76 to 1.00 in studies while the specificity varied between 0.27 to 0.85. The included studies displayed significant heterogeneity in both methodologies and clinical populations, which did not allow for a meta-analysis to be completed. Only one study (Holsinger 2012) was found to be at low risk of bias on all methodological domains. The results of this study reported that the sensitivity of the Mini-Cog was 0.76 and the specificity was 0.73. We found the quality of all other included studies to be low due to a high risk of bias with methodological limitations primarily in their selection of participants. AUTHORS' CONCLUSIONS: There is a limited number of studies evaluating the accuracy of the Mini-Cog for the diagnosis of dementia in primary care settings. Given the small number of studies, the wide range in estimates of the accuracy of the Mini-Cog, and methodological limitations identified in most of the studies, at the present time there is insufficient evidence to recommend that the Mini-Cog be used as a screening test for dementia in primary care. Further studies are required to determine the accuracy of Mini-Cog in primary care and whether this tool has sufficient diagnostic test accuracy to be useful as a screening test in this setting
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