160,018 research outputs found
Small asymmetric Brownian objects self-align in nanofluidic channels
No full textAlthough the self-alignment of asymmetric macro-sized objects of a few tens of microns in size have been studied extensively in experiments and theory, access to much smaller length scales is still hindered by technical challenges. We combine molecular dynamics and stochastic rotation dynamics techniques to investigate the self-orientation phenomenon at different length scales, ranging from the micron to the nano scale by progressively increasing the relative strength of diffusion over convection. To this end, we model an asymmetric dumbbell particle in Hele-Shaw flow and explore a wide range of Péclet numbers (Pe) and different particle shapes, as characterized by the size ratio of the two dumbbell spheres (R). By independently varying these two parameters we analyse the process of self-orientation and characterize the alignment of the dumbbell with the direction of the fluid flow. We identify three different regimes of strong, weak and no alignment and we map out a state diagram in Pe versus R plane. Based on these results, we estimate dimensional length scales and flow rates for which these findings would be applicable in experiments. Finally, we find that the characteristic reorientation time of the dumbbell is a monotonically decreasing function of the dumbbell anisotropy.Accepted Author ManuscriptComplex Fluid Processin
Semiclassical magnetotransport in strongly spin-orbit coupled Rashba two-dimensional electron systems
No full textSemiclassical magnetoelectric and magnetothermoelectric transport in strongly spin-orbit coupled Rashba two-dimensional electron systems is investigated. In the presence of a perpendicular classically weak magnetic field and short-range impurity scattering, we solve the linearized Boltzmann equation self-consistently. Using the solution, it is found that when Fermi energy EF locates below the band crossing point (BCP), the Hall coefficient is a nonmonotonic function of electron density ne and not inversely proportional to ne. While the magnetoresistance (MR) and Nernst coefficient vanish when EF locates above the BCP, non-zero MR and enhanced Nernst coefficient emerge when EF decreases below the BCP. Both of them are nonmonotonic functions of EF below the BCP. The different semiclassical magnetotransport behaviors between the two sides of the BCP can be helpful to experimental identifications of the band valley regime and topological change of Fermi surface in considered systems.National Natural Science Foundation of China [11274018]SCI(E)[email protected]
The clinical importance of white matter hyperintensities on brain magnetic resonance imaging: systematic review and meta-analysis.
No full textObjectives: To review the evidence for an association of white matter hyperintensities with risk of stroke, cognitive decline, dementia, and death.
Design: Systematic review and meta-analysis.
Data sources: PubMed from 1966 to 23 November 2009.
Study selection: Prospective longitudinal studies that used magnetic resonance imaging and assessed the impact of white matter hyperintensities on risk of incident stroke, cognitive decline, dementia, and death, and, for the meta-analysis, studies that provided risk estimates for a categorical measure of white matter hyperintensities, assessing the impact of these lesions on risk of stroke, dementia, and death.
Data extraction: Population studied, duration of follow-up, method used to measure white matter hyperintensities, definition of the outcome, and measure of the association of white matter hyperintensities with the outcome.
Data synthesis: 46 longitudinal studies evaluated the association of white matter hyperintensities with risk of stroke (n=12), cognitive decline (n=19), dementia (n=17), and death (n=10). 22 studies could be included in a meta-analysis (nine of stroke, nine of dementia, eight of death). White matter hyperintensities were associated with an increased risk of stroke (hazard ratio 3.3, 95% confidence interval 2.6 to 4.4), dementia (1.9, 1.3 to 2.8), and death (2.0, 1.6 to 2.7). An association of white matter hyperintensities with a faster decline in global cognitive performance, executive function, and processing speed was also suggested.
Conclusion: White matter hyperintensities predict an increased risk of stroke, dementia, and death. Therefore white matter hyperintensities indicate an increased risk of cerebrovascular events when identified as part of diagnostic investigations, and support their use as an intermediate marker in a research setting. Their discovery should prompt detailed screening for risk factors of stroke and dementia
Introduction: Condensed matter theory by computer simulation
No full textThe basic laws of physics that govern the phenomena on the scales of length and energy relevant for condensed matter systems, ranging from simple fluids and solids to complex multicomponent materials and even problems of chemical biology, are well known and understood: one just deals with the Schrödinger equation for the quantum many-body problem of the nuclei and electrons interacting with Coulomb potentials (for simplicity, we disregard, here throughout, the need for relativistic corrections in electronic structure calculations of matter containing heavy atoms). Statistical mechanics then supplies the framework to extend this quantum many-body theory to provide a statistical description in terms of averages taken at nonzero temperature. © 2006 Springer
NaYF4:Er3+,Yb3+/SiO2 Core/Shell Upconverting Nanocrystals for Luminescence Thermometry up to 900 K
No full textThe rapid development of nanomaterials with unique size-tunable properties forms the basis for a variety of new applications, including temperature sensing. Luminescent nanoparticles (NPs) have demonstrated potential as sensitive nanothermometers, especially in biological systems. Their small size offers the possibility of mapping temperature profiles with high spatial resolution. The temperature range is however limited, which prevents use in high-temperature applications such as, for example, nanoelectronics, thermal barrier coatings, and chemical reactors. In this work, we extend the temperature range for nanothermometry beyond 900 K using silica-coated NaYF4 nanoparticles doped with the lanthanide ions Yb3+ and Er3+. Monodisperse ∼20 nm NaYF4:Yb,Er nanocrystals were coated with a ∼10 nm silica shell. Upon excitation with infrared radiation, bright green upconversion (UC) emission is observed. From the intensity ratio between 2H11/2 and 4S3/2 UC emission lines at 520 and 550 nm, respectively, the temperature can be determined up to at least 900 K with an accuracy of 1–5 K for silica-coated NPs. For bare NaYF4:Yb,Er NPs, the particles degrade above 600 K. Repeated thermal cycling experiments demonstrate the high durability and reproducibility of the silica-coated nanocrystals as temperature probes without any loss of performance. The present results open avenues for the development of a new class of highly stable nanoprobes by applying a silica coating around a wide variety of lanthanide-doped NPs
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