1,803 research outputs found

    Rheology of human blood plasma: Viscoelastic versus Newtonian behavior

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    We investigate the rheological characteristics of human blood plasma in shear and elongational flows. While we can confirm a Newtonian behavior in shear flow within experimental resolution, we find a viscoelastic behavior of blood plasma in the pure extensional flow of a capillary break-up rheometer. The influence of the viscoelasticity of blood plasma on capillary blood flow is tested in a microfluidic device with a contraction-expansion geometry. Differential pressure measurements revealed that the plasma has a pronounced flow resistance compared to that of pure water. Supplementary measurements indicate that the viscoelasticity of the plasma might even lead to viscoelastic instabilities under certain conditions. Our findings show that the viscoelastic properties of plasma should not be ignored in future studies on blood flow.Comment: 4 figures, 1 supplementary material Highlighted in http://physics.aps.org/articles/v6/1

    Anisotropic Assembly of Colloidal Nanoparticles: Exploiting Substrate Crystallinity

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    We show that the crystal structure of a substrate can be exploited to drive the anisotropic assembly of colloidal nanoparticles. Pentanethiol-passivated Au particles of approximately 2 nm diameter deposited from toluene onto hydrogen-passivated Si(111) surfaces form linear assemblies (rods) with a narrow width distribution. The rod orientations mirror the substrate symmetry, with a high degree of alignment along principal crystallographic axes of the Si(111) surface. There is a strong preference for anisotropic growth with rod widths substantially more tightly distributed than lengths. Entropic trapping of nanoparticles provides a plausible explanation for the formation of the anisotropic assemblies we observe

    Application of Fourier Analysis of Cerebral Glucose Metabolism in Color-Induced Long-Term Potentiation: A Novel Functional PET Spectroscopy (<em>f</em>PETS) Study in Mice

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    Fourier time-series analysis could be used to segregate changes in the ventral and dorsal streams of the visual system in male and female mice. Color memory processes of long-term potentiation and long-term depression could be identified through spectral analysis. We used small animal positron emission tomography and magnetic resonance imaging (PET/MRI) to measure the accumulation of [18F]fluorodeoxyglucose ([18F]FDG) in the mouse brain during light stimulation with blue and yellow filters compared to darkness condition. The mean standardized uptake values (SUV) of [18F]FDG for each stimulus condition was analyzed using standard Fourier analysis software to derive spectral density estimates for each condition. Spectral peaks were identified as originating from the subcortical region (S-peak) by subcortical long-term potentiation (SLTP) or depression (SLTD), and originating from the cortical region (C-peak) by cortical long-term potentiation (CLTP) or depression (CLTD). Luminance opponency occurred at S-peak by SLTP in the dorsal stream in the left visual cortex in male mice. On the other hand, chromatic opponency occurred by wavelength-differencing at C-peak by CLTP in the cortico-subcortical pathways in the ventral stream in the left visual cortex in male mice. In contrast in female mice, during luminance processing, there was resonance phenomenon at C-peak in the ventral stream in the right visual cortex. Chromatic opponency occurred at S-peak by SLTP in the dorsal stream in the right visual cortex in female mice. Application of Fourier analysis improved spatial and temporal resolutions of conventional fPET/MRI methods. Computation of color processing as a conscious experience has wide range applications in neuroscience and artificial intelligence

    Separating the effects of changes in land cover and climate: a hydro-meteorological analysis of the past 60 yr in Saxony, Germany

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    Understanding and quantifying the impact of changes in climate and land use/land cover on water availability is a prerequisite to adapt water management; yet, it can be difficult to separate the effects of these different impacts. In this paper we illustrate a separation and attribution method based on a Budyko framework. We assume that evapotranspiration (<i>E</i><sub>T</sub>) is limited by the climatic forcing of precipitation (<i>P</i>) and evaporative demand (<i>E</i><sub>0</sub>), but modified by land-surface properties. Impacts of changes in climate (i.e., <i>E</i><sub>0</sub>/<i>P</i>) or land-surface changes on <i>E</i><sub>T</sub> alter the two dimensionless measures describing relative water (<i>E</i><sub>T</sub>/<i>P</i>) and energy partitioning (<i>E</i><sub>T</sub>/<i>E</i><sub>0</sub>), which allows us to separate and quantify these impacts. We use the separation method to quantify the role of environmental factors on <i>E</i><sub>T</sub> using 68 small to medium range river basins covering the greatest part of the German Federal State of Saxony within the period of 1950‚Äď2009. The region can be considered as a typical central European landscape with considerable anthropogenic impacts. In the long term, most basins are found to follow the Budyko curve which we interpret as a result of the strong interactions of climate, soils and vegetation. However, two groups of basins deviate. Agriculturally dominated basins at lower altitudes exceed the Budyko curve while a set of high altitude, forested basins fall well below. When visualizing the decadal dynamics on the relative partitioning of water and energy the impacts of climatic and land-surface changes become apparent. After 1960 higher forested basins experienced large land-surface changes which show that the air pollution driven tree damages have led to a decline of annual <i>E</i><sub>T</sub> on the order of 38%. In contrast, lower, agricultural dominated areas show no significant changes during that time. However, since the 1990s effective mitigation measures on industrial pollution have been established and the apparent brightening and regrowth has resulted in a significant increase of <i>E</i><sub>T</sub> across most basins. In conclusion, data on both, the water and the energy balance is necessary to understand how long-term climate and land cover control evapotranspiration and thus water availability. Further, the detected land-surface change impacts are consistent in space and time with independent forest damage data and thus confirm the validity of the separation approach

    Humidity-Dependent Reversible Transitions in Gold Nanoparticle Superlattices

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    The changes in interparticle spacing upon hydration and dehydration of drop-cast films of hydrophilic gold nanoparticles (GNP) have been measured in situ with nanometer resolution using WetSTEM and ESEM. These subtle variations correlate well with the corresponding changes in the optical spectra and perceived color as well as changes in the electrical conductivity of the films. AC impedance analysis allows us to differentiate between resistive and capacitive components and to evaluate how these depend on average particle spacing and the water content of the matrix, respectively. Thin films of this type are well-known structures used for development of sensors and diagnostics

    Cyclophilin D links programmed cell death and organismal aging in Podospora anserina

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    This is the final version of the article. Available from Wiley via the DOI in this record.Cyclophilin D (CYPD) is a mitochondrial peptidyl prolyl-cis,trans-isomerase involved in opening of the mitochondrial permeability transition pore (mPTP). CYPD abundance increases during aging in mammalian tissues and in the aging model organism Podospora anserina. Here, we show that treatment of the P. anserina wild-type with low concentrations of the cyclophilin inhibitor cyclosporin A (CSA) extends lifespan. Transgenic strains overexpressing PaCypD are characterized by reduced stress tolerance, suffer from pronounced mitochondrial dysfunction and are characterized by accelerated aging and induction of cell death. Treatment with CSA leads to correction of mitochondrial function and lifespan to that of the wild-type. In contrast, PaCypD deletion strains are not affected by CSA within the investigated concentration range and show increased resistance against inducers of oxidative stress and cell death. Our data provide a mechanistic link between programmed cell death (PCD) and organismal aging and bear implications for the potential use of CSA to intervene into biologic aging.The research was supported by grants of the Deutsche Forschungsgemeinschaft (Os75/12-1) and by the European Commission via the Integrated Project with the acronym MiMage; (LSHM-CT-2004-512020)
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