3,814 research outputs found
Depletion potentials in highly size-asymmetric binary hard-sphere mixtures: Comparison of accurate simulation results with theory
We report a detailed study, using state-of-the-art simulation and theoretical
methods, of the depletion potential between a pair of big hard spheres immersed
in a reservoir of much smaller hard spheres, the size disparity being measured
by the ratio of diameters q=\sigma_s/\sigma_b. Small particles are treated
grand canonically, their influence being parameterized in terms of their
packing fraction in the reservoir, \eta_s^r. Two specialized Monte Carlo
simulation schemes --the geometrical cluster algorithm, and staged particle
insertion-- are deployed to obtain accurate depletion potentials for a number
of combinations of q\leq 0.1 and \eta_s^r. After applying corrections for
simulation finite-size effects, the depletion potentials are compared with the
prediction of new density functional theory (DFT) calculations based on the
insertion trick using the Rosenfeld functional and several subsequent
modifications. While agreement between the DFT and simulation is generally
good, significant discrepancies are evident at the largest reservoir packing
fraction accessible to our simulation methods, namely \eta_s^r=0.35. These
discrepancies are, however, small compared to those between simulation and the
much poorer predictions of the Derjaguin approximation at this \eta_s^r. The
recently proposed morphometric approximation performs better than Derjaguin but
is somewhat poorer than DFT for the size ratios and small sphere packing
fractions that we consider. The effective potentials from simulation, DFT and
the morphometric approximation were used to compute the second virial
coefficient B_2 as a function of \eta_s^r. Comparison of the results enables an
assessment of the extent to which DFT can be expected to correctly predict the
propensity towards fluid fluid phase separation in additive binary hard sphere
mixtures with q\leq 0.1.Comment: 16 pages, 9 figures, revised treatment of morphometric approximation
and reordered some materia
Plasma arginine vasopressin concentrations in epileptics under monotherapy
Plasma arginine vasopressin concentrations were determined by radio-immunoassay in 112 adult epileptics who were taking carbamazepine, phenytoin, primidone, or sodium valproate in long-term monotherapy, and in 19 controls. No significant difference was found between the groups, but some epileptics taking carbamazepine and primidone showed low values. Serum
concentrations of carbamazepine did not correlate with the concentrations of plasma arginine vasopressin.
In conclusion, there was no evidence of a stimulating
effect of chronic carbamazepine medication or a special inhibiting effect of phenytoin on the release of vasopressin arginine from the posterior pituitary
A Vehicular Traffic Flow Model Based on a Stochastic Acceleration Process
A new vehicular traffic flow model based on a stochastic jump process in
vehicle acceleration and braking is introduced. It is based on a master
equation for the single car probability density in space, velocity and
acceleration with an additional vehicular chaos assumption and is derived via a
Markovian ansatz for car pairs. This equation is analyzed using simple driver
interaction models in the spatial homogeneous case. Velocity distributions in
stochastic equilibrium, together with the car density dependence of their
moments, i.e. mean velocity and scattering and the fundamental diagram are
presented.Comment: 27 pages, 6 figure
Alterations in macrophage G proteins are associated with endotoxin tolerance
AbstractPrevious studies have suggested that endotoxin tolerance induces macrophage desensitization to endotoxin through altered guanine nucleotide regulatory (G) protein function. In the present study the binding characteristics of the nonhydrolyzable GTP analogue GTPγ[35S] to macrophage membranes from endotoxin tolerant and control rats were determined. Membranes were prepared from peritoneal macrophages harvested from rats 72 h after two sequential daily doses of vehicle or Salmonella enteritidis endotoxin (100 μg/kg on day 1 and 500 μg/kg on day 2). GTPγ[35S] bound to a single class of sites that were saturable and displaceable in control and endotoxin tolerant macrophage membranes. The maximum specific binding of GTPγ[35S] was significantly (P < 0.01) decreased in membranes from tolerant rats compared to control (Bmax = 39 ± 7 pmol/mg protein in control vs. 11 ± 2 pmol/mg protein in endotoxin tolerant; n = 5). There were no significant differences in the Kd values. To determine whether the reduced GTPγS binding was due to decreases in G proteins, macrophage membrane G protein content was determined by western blotting with specific antisera to Gi1,2 α, Gi3α, Gs α, and the β subunit of G. Scanning densitometric analysis demonstrated differential decreases in tolerant macrophage membrane G proteins. Gi3α was reduced the most to 48 ± 8% of controls (n = 3), and this reduction was significant compared to those of other G proteins. Gi1,2α and Gβ were reduced to 73 ± 5% (n = 3) and 65 ± 4% (n = 3) of control values, respectively. Gs α) (L) and Gs α(H) were reduced to 61 ± 5% (n = 3) and 68 ± 3% (n = 3) of control, respectively. These results demonstrate that endotoxin tolerant macrophages exhibit decreased membrane GTP binding capacity and differential reductions in the content of specific G proteins. The cellular mechanisms leading to such alterations in G proteins and their functional significance in the acquisition of endotoxin tolerance merit further investigation
The interaction between wheat roots and soil pores in structured field soil
Wheat (Triticum aestivum L.) root growth in the subsoil is usually constrained by soil strength, although roots can use macropores to elongate to deeper layers. The quantitative relationship between the elongation of wheat roots and the soil pore system, however, is still to be determined. We studied the depth distribution of roots of six wheat varieties and explored their relationship with soil macroporosity from samples with the field structure preserved. Undisturbed soil cores (to a depth of 100 cm) were collected from the field and then non-destructively imaged using X-ray computed tomography (at a spatial resolution of 90 µm) to quantify soil macropore structure and root number density (the number of roots cm–2 within a horizontal cross-section of a soil core). Soil macroporosity changed significantly with depth but not between the different wheat lines. There was no significant difference in root number density between wheat varieties. In the subsoil, wheat roots used macropores, especially biopores (i.e. former root or earthworm channels) to grow into deeper layers. Soil macroporosity explained 59% of the variance in root number density. Our data suggested that the development of the wheat root system in the field was more affected by the soil macropore system than by genotype. On this basis, management practices which enhance the porosity of the subsoil may therefore be an effective strategy to improve deep rooting of wheat
A comparison between water uptake and root length density in winter wheat: effects of root density and rhizosphere properties
© 2020, The Author(s). Background and aims: We aim to quantify the variation in root distribution in a set of 35 experimental wheat lines. We also compared the effect of variation in hydraulic properties of the rhizosphere on water uptake by roots. Methods: We measured the root length density and soil drying in 35 wheat lines in a field experiment. A 3D numerical model was used to predict soil drying profiles with the different root length distributions and compared with measured soil drying. The model was used to test different scenarios of the hydraulic properties of the rhizosphere. Results: We showed that wheat lines with no detectable differences in root length density can induce soil drying profiles with statistically significant differences. Our data confirmed that a root length density of at least 1cm/cm3 is needed to drain all the available water in soil. In surface layers where the root length density was far greater than 1cm/cm3 water uptake was independent of rooting density due to competition for water. However, in deeper layers where root length density was less than 1cm/cm3, water uptake by roots was proportional to root density. Conclusion: In a set of wheat lines with no detectable differences in the root length density we found significant differences in water uptake. This may be because small differences in root density at depth can result in larger differences in water uptake or that the hydraulic properties of the rhizosphere can greatly affect water uptake
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A preliminary analysis of US CO/sub 2/ emissions reduction potential from energy conservation and the substitution of natural gas for coal in the period to 2010
Carbon dioxide (CO/sub 2/) is a product of burning fossil fuels (oil, gas and coal) and fossil fuel burning is the dominant source of global CO/sub 2/ emissions amounting to 5.2 petagrams of carbon per year (PgC) in 1985. The control of CO/sub 2/ emissions would require control of energy production and use. US emissions were 1.25 PgC in 1985. National Energy Policy Plan (NEPP) projections show total US emissions rising 38% by 2010 to 1.7 PgC. The US Department of Energy (DOE) Carbon Dioxide Research Division (CDRD) has sponsored research at the Pacific Northwest Laboratory (PNL), Brookhaven National Laboratory (BNL), and at the Oak Ridge National Laboratory to do a preliminary assessment of the technical feasibility and consequences of reducing US CO/sub 2/ emissions from 1985 levels by 10, 25 or 50 percent by either the year 1995 and 2010. In addition, DOE/CDRD sponsored a day-long roundtable attended by nine experts in the field to discuss this issue. Two methods of CO/sub 2/ emissions reduction were considered: energy intensity reductions (conservation), and substitution of natural gas for coal. The study did not address the contribution of other energy supply options or the feasibility of pre- or post-combustion CO/sub 2/ removal. Furthermore, the study made no attempt to explore specific policies that might be employed to achieve technically feasible CO/sub 2/ emissions reductions. This is not a policy document
The Contribution of Water Radiolysis to Marine Sedimentary Life
Water radiolysis continuously produces H2 and oxidized chemicals in wet sediment and rock. Radiolytic H2 has been identified as the primary electron donor (food) for microorganisms in continental aquifers kilometers below Earth’s surface. Radiolytic products may also be significant for sustaining life in subseafloor sediment and subsurface environments of other planets. However, the extent to which most subsurface ecosystems rely on radiolytic products has been poorly constrained, due to incomplete understanding of radiolytic chemical yields in natural environments. Here we show that all common marine sediment types catalyse radiolytic H2 production, amplifying yields by up to 27X relative to pure water. In electron equivalents, the global rate of radiolytic H2 production in marine sediment appears to be 1-2% of the global organic flux to the seafloor. However, most organic matter is consumed at or near the seafloor, whereas radiolytic H2 is produced at all sediment depths. Comparison of radiolytic H2 consumption rates to organic oxidation rates suggests that water radiolysis is the principal source of biologically accessible energy for microbial communities in marine sediment older than a few million years. Where water permeates similarly catalytic material on other worlds, life may also be sustained by water radiolysis
Temperature as an external field for colloid-polymer mixtures : "quenching" by heating and "melting" by cooling
We investigate the response to temperature of a well-known colloid-polymer
mixture. At room temperature, the critical value of the second virial
coefficient of the effective interaction for the Asakura-Oosawa model predicts
the onset of gelation with remarkable accuracy. Upon cooling the system, the
effective attractions between colloids induced by polymer depletion are
reduced, because the polymer radius of gyration is decreases as the
theta-temperature is approached. Paradoxically, this raises the effective
temperature, leading to "melting" of colloidal gels. We find the Asakura-Oosawa
model of effective colloid interactions with a simple description of the
polymer temperature response provides a quantitative description of the
fluid-gel transition. Further we present evidence for enhancement of
crystallisation rates near the metastable critical point.Comment: 13 page
Biomarkers for tau pathology
The aggregation of fibrils of hyperphosphorylated and C-terminally truncated microtubule-associated tau protein characterizes 80% of all dementia disorders, the most common neurodegenerative disorders. These so-called tauopathies are hitherto not curable and their diagnosis, especially at early disease stages, has traditionally proven difficult. A keystone in the diagnosis of tauopathies was the development of methods to assess levels of tau protein in vivo in cerebrospinal fluid, which has significantly improved our knowledge about these conditions. Tau proteins have also been measured in blood, but the importance of tau-related changes in blood is still unclear. The recent addition of positron emission tomography ligands to visualize, map and quantify tau pathology has further contributed with information about the temporal and spatial characteristics of tau accumulation in the living brain. Together, the measurement of tau with fluid biomarkers and positron emission tomography constitutes the basis for a highly active field of research. This review describes the current state of biomarkers for tau biomarkers derived from neuroimaging and from the analysis of bodily fluids and their roles in the detection, diagnosis and prognosis of tau-associated neurodegenerative disorders, as well as their associations with neuropathological findings, and aims to provide a perspective on how these biomarkers might be employed prospectively in research and clinical settings
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