9,237 research outputs found
The effects of dust evolution on disks in the mid-IR
In this paper, we couple together the dust evolution code two-pop-py with the
thermochemical disk modelling code ProDiMo. We create a series of
thermochemical disk models that simulate the evolution of dust over time from
0.018 Myr to 10 Myr, including the radial drift, growth, and settling of dust
grains. We examine the effects of this dust evolution on the mid-infrared gas
emission, focussing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3,
OH, and H2O that are readily observable with Spitzer and the upcoming E-ELT and
JWST.
The addition of dust evolution acts to increase line fluxes by reducing the
population of small dust grains. We find that the spectral lines of all species
except C2H2 respond strongly to dust evolution, with line fluxes increasing by
more than an order of magnitude across the model series as the density of small
dust grains decreases over time. The C2H2 line fluxes are extremely low due to
a lack of abundance in the infrared line-emitting regions, despite C2H2 being
commonly detected with Spitzer, suggesting that warm chemistry in the inner
disk may need further investigation. Finally, we find that the CO2 flux
densities increase more rapidly than the other species as the dust disk
evolves. This suggests that the flux ratios of CO2 to other species may be
lower in disks with less-evolved dust populations.Comment: 13 pages, 9 figures, accepted in A&
Using a Grid-Enabled Wireless Sensor Network for Flood Management
Flooding is becoming an increasing problem. As a result there is a need to deploy more sophisticated sensor networks to detect and react to flooding. This paper outlines a demonstration that illustrates our proposed solution to this problem involving embedded wireless hardware, component based middleware and overlay networks
Total scattering descriptions of local and cooperative distortions in the oxide spinel (Mg,Cu)Cr2O4 with dilute Jahn-Teller ions
The normal spinel oxide MgCr2O4 is cubic at room temperature while the normal
spinel CuCr2O4 is tetragonal as a consequence of the Jahn-Teller nature of Cu2+
on the tetrahedral sites. Despite different end-member structures, complete
solid solutions of Mg_{1-x}Cu_xCr2O4 can be prepared that display a first-order
structural transition with composition x = 0.43 at room temperature. Reverse
Monte Carlo analysis of total neutron scattering on data acquired between 300 K
and 15 K on samples with x = 0.10, 0.20, and 0.43 provides unbiased local and
average structure descriptions of the samples, including an understanding of
the transition from local Jahn-Teller distortions in the cubic phase to
cooperative distortions that result in a tetragonal structure. Distributions of
continuous symmetry measures help to understand and distinguish distorted and
undistorted coordination around the tetrahedral site in the solid solutions.
Magnetic exchange bias is observed in field-cooled hysteresis loops of samples
with dilute Cu2+ concentration and in samples with tetragonal--cubic phase
coexistence around 300 K.Comment: 10 pages, 14 figure
Static Versus Dynamic Friction: The Role of Coherence
A simple model for solid friction is analyzed. It is based on tangential
springs representing interlocked asperities of the surfaces in contact. Each
spring is given a maximal strain according to a probability distribution. At
their maximal strain the springs break irreversibly. Initially all springs are
assumed to have zero strain, because at static contact local elastic stresses
are expected to relax. Relative tangential motion of the two solids leads to a
loss of coherence of the initial state: The springs get out of phase due to
differences in their sizes. This mechanism alone is shown to lead to a
difference between static and dynamic friction forces already. We find that in
this case the ratio of the static and dynamic coefficients decreases with
increasing relative width of the probability distribution, and has a lower
bound of 1 and an upper bound of 2.Comment: 10 pages, 2 figures, revtex
Epigenetic control of the vasopressin promoter explains physiological ability to regulate vasopressin transcription in dehydration and salt loading states in the rat
The synthesis of arginine vasopressin (AVP) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus is sensitive to increased plasma osmolality and a decreased blood volume, and thus is robustly increased by both dehydration (increased plasma osmolality and decreased blood volume) and salt loading (increased plasma osmolality). Both stimuli result in functional remodelling of the SON and PVN, a process referred to as functionalârelated plasticity. Such plastic changes in the brain have recently been associated with altered patterns of DNA methylation at CpG (cytosineâphosphateâguanine) residues, a process considered to be important for the regulation of gene transcription. In this regard, the proximal Avp promoter contains a number of CpG sites and is recognised as one of four CpG islands for the Avp gene, suggesting that methylation may be regulating Avp transcription. In the present study, we show that, in an immortalised hypothalamic cell line 4B, the proximal Avp promoter is highly methylated, and treatment of these cells with the DNA methyltransferase inhibitor 5âAzaâ2âČâdeoxycytidine to demethylate DNA dramatically increases basal and stimulated Avp biosynthesis. We report no changes in the expression of DNA methyltransferases, Dnmt1 and Dnmt3a, whereas there is decreased expression of the demethylating enzyme tenâelevenâtranslocation 2, Tet2, in the SON by dehydration and salt loading. We found higher methylation of the SON Avp promoter in dehydrated but not saltâloaded rats. By analysis of individual CpG sites, we observed hypomethylation, hypermethylation and no change in methylation of specific CpGs in the SON Avp promoter of the dehydrated rat. Using reporter gene assays, we show that mutation of individual CpGs can result in altered Avp promoter activity. We propose that methylation of the SON Avp promoter is necessary to coâordinate the duel inputs of increased plasma osmolality and decreased blood volume on Avp transcription in the chronically dehydrated rat
Measurement of serum haptoglobin as an indicator of the efficacy of malaria intervention trials
Serum haptoglobin levels were measured by an enzyme-linked immunosorbent assay in Gambian children who participated in 3 malaria intervention trials with untreated or impregnated bed nets. In one study, in which a significant effect on clinical malaria was observed, the mean serum haptoglobin level was significantly higher in the intervention than in the control group. In the other 2 studies, in which no significant protection was observed, mean haptoglobin levels were similar in intervention and control groups. Measurement of serum haptoglobin may provide a useful indirect measure of the effectiveness of malaria control programme
Attosecond spectroscopy of bio-chemically relevant molecules
Understanding the role of the electron dynamics in the photochemistry of bio-chemically relevant molecules is key to getting access to the fundamental physical processes leading to damage, mutation and, more generally, to the alteration of the final biological functions. Sudden ionization of a large molecule has been proven to activate a sub-femtosecond charge flow throughout the molecular backbone, purely guided by electronic coherences, which could ultimately affect the photochemical response of the molecule at later times. We can follow this ultrafast charge flow in real time by exploiting the extreme time resolution provided by attosecond light sources. In this work recent advances in attosecond molecular physics are presented with particular focus on the investigation of bio-relevant molecules
Transcription factor CREB3L1 mediates cAMP and glucocorticoid regulation of arginine vasopressin gene transcription in the rat hypothalamus
BACKGROUND: Arginine vasopressin (AVP), a neuropeptide hormone that functions in the regulation of water homeostasis by controlling water re-absorption at kidneys, is synthesised in supraoptic nucleus and paraventricular nucleus of the hypothalamus. An increase in plasma osmolality stimulates secretion of AVP to blood circulation and induces AVP synthesis in these nuclei. Although studies on mechanism of AVP transcriptional regulation in hypothalamus proposed that cAMP and glucocorticoids positively and negatively regulate Avp expression, respectively, the molecular mechanisms have remained elusive. Recently, we identified CREB3L1 (cAMP-responsive element binding protein 3 like 1) as a putative transcription factor of Avp transcription in the rat hypothalamus. However the mechanism of how CREB3L1 is regulated in response of hyperosmotic stress in the neurons of hypothalamus has never been reported. This study aims to investigate effect of previously reported regulators (cAMP and glucocorticoid) of Avp transcription on transcription factor CREB3L1 in order to establish a molecular explanation for cAMP and glucocorticoids effect on AVP expression. RESULTS: The effect of cAMP and glucocorticoid treatment on Creb3l1 was investigated in both AtT20 cells and hypothalamic organotypic cultures. The expression of Creb3l1 was increased in both mRNA and protein level by treatment with forskolin, which raises intracellular cAMP levels. Activation of cAMP by forskolin also increased Avp promoter activity in AtT20 cells and this effect was blunted by shRNA mediated silencing of Creb3l1. The forskolin induced increase in Creb3l1 expression was diminished by combined treatment with dexamethasone, and, in vivo, intraperitoneal dexamethasone injection blunted the increase in Creb3l1 and Avp expression induced by hyperosmotic stress. CONCLUSION: Here we shows that cAMP and glucocorticoid positively and negatively regulate Creb3l1 expression in the rat hypothalamus, respectively, and regulation of cAMP on AVP expression is mediated through CREB3L1. This data provides the connection between CREB3L1, a newly identified transcription factor of AVP expression, with the previously proposed mechanism of Avp transcription which extends our understanding in transcription regulation of Avp in the hypothalamus
Rubber friction: role of the flash temperature
When a rubber block is sliding on a hard rough substrate, the substrate
asperities will exert time-dependent deformations of the rubber surface
resulting in viscoelastic energy dissipation in the rubber, which gives a
contribution to the sliding friction. Most surfaces of solids have roughness on
many different length scales, and when calculating the friction force it is
necessary to include the viscoelastic deformations on all length scales. The
energy dissipation will result in local heating of the rubber. Since the
viscoelastic properties of rubber-like materials are extremely strongly
temperature dependent, it is necessary to include the local temperature
increase in the analysis. At very low sliding velocity the temperature increase
is negligible because of heat diffusion, but already for velocities of order
0.01 m/s the local heating may be very important. Here I study the influence of
the local heating on the rubber friction, and I show that in a typical case the
temperature increase results in a decrease in rubber friction with increasing
sliding velocity for v > 0.01 m/s. This may result in stick-slip instabilities,
and is of crucial importance in many practical applications, e.g., for the
tire-road friction, and in particular for ABS-breaking systems.Comment: 22 pages, 27 figure
Contact and Friction of Nano-Asperities: Effects of Adsorbed Monolayers
Molecular dynamics simulations are used to study contact between a rigid,
nonadhesive, spherical tip with radius of order 30nm and a flat elastic
substrate covered with a fluid monolayer of adsorbed chain molecules. Previous
studies of bare surfaces showed that the atomic scale deviations from a sphere
that are present on any tip constructed from discrete atoms lead to significant
deviations from continuum theory and dramatic variability in friction forces.
Introducing an adsorbed monolayer leads to larger deviations from continuum
theory, but decreases the variations between tips with different atomic
structure. Although the film is fluid, it remains in the contact and behaves
qualitatively like a thin elastic coating except for certain tips at high
loads. Measures of the contact area based on the moments or outer limits of the
pressure distribution and on counting contacting atoms are compared. The number
of tip atoms making contact in a time interval grows as a power of the interval
when the film is present and logarithmically with the interval for bare
surfaces. Friction is measured by displacing the tip at a constant velocity or
pulling the tip with a spring. Both static and kinetic friction rise linearly
with load at small loads. Transitions in the state of the film lead to
nonlinear behavior at large loads. The friction is less clearly correlated with
contact area than load.Comment: RevTex4, 17 pages, 13 figure
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