9,501 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&
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The Diderot meteorite: The second chassignite
The Diderot meteorite is a dunite discovered in Sahara. The martian origin is unambiguous and Diderot shares strong petrographical similarities with Chassigny
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
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
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
A biodegradable polyurethane dermal matrix in reconstruction of free flap donor sites: a pilot study
We have developed a biodegradable temporizing matrix (BTM) capable of supporting secondary split-skin graft-take in animal studies. We report its first long-term implantation and use as a dermal scaffold in humans. This preliminary study assesses its ability to integrate, its ease of delamination, its ability to sustain split-skin graft in complex wounds, the degree of wound contraction, and ultimately the quality of the scar at 1 year postimplantation. Ten patients were recruited, each requiring elective free flap reconstruction. Free flap donor sites created were anterolateral thigh flaps, fibular osseocutaneous flaps, or radial/ulnar forearm (RF/UF) flaps. The BTM was implanted when the flap was detached from its donor site. Dressing changes were performed twice weekly. The time elapsed between implantation and delamination depended on the type of flap and thus the wound bed left. Once integrated, the BTMs were delaminated in theatre, and the surface of the "neodermis" was refreshed by dermabrasion, prior to application of a split-skin graft. The BTM integration occurred in all patients (100% in 6 patients, with 90%, 84%, 76%, and 60% integration in the remainder). Integrated BTM sustained successful graft-take in all patients. Complete take was marred in 2 patients, over areas of BTM that had not integrated and graft application was performed too early. The BTM can be applied into wounds in humans and can integrate, persist in the presence of infection, and sustain split-skin overgrafting, despite the trial group presenting with significant comorbidities.Marcus J.D. Wagstaff, Bradley J. Schmitt, Patrick Coghlan, James P. Finkemeyer, Yugesh Caplash and John E. Greenwoo
Performance of an Operating High Energy Physics Data Grid: D0SAR-Grid
The D0 experiment at Fermilab's Tevatron will record several petabytes of
data over the next five years in pursuing the goals of understanding nature and
searching for the origin of mass. Computing resources required to analyze these
data far exceed capabilities of any one institution. Moreover, the widely
scattered geographical distribution of D0 collaborators poses further serious
difficulties for optimal use of human and computing resources. These
difficulties will exacerbate in future high energy physics experiments, like
the LHC. The computing grid has long been recognized as a solution to these
problems. This technology is being made a more immediate reality to end users
in D0 by developing a grid in the D0 Southern Analysis Region (D0SAR),
D0SAR-Grid, using all available resources within it and a home-grown local task
manager, McFarm. We will present the architecture in which the D0SAR-Grid is
implemented, the use of technology and the functionality of the grid, and the
experience from operating the grid in simulation, reprocessing and data
analyses for a currently running HEP experiment.Comment: 3 pages, no figures, conference proceedings of DPF04 tal
Elastic contact between self-affine surfaces: Comparison of numerical stress and contact correlation functions with analytic predictions
Contact between an elastic manifold and a rigid substrate with a self-affine
fractal surface is reinvestigated with Green's function molecular dynamics.
Stress and contact autocorrelation functions (ACFs) are found to decrease
algebraically. A rationale is provided for the observed similarity in the
exponents for stress and contact ACFs. Both exponents differ substantially from
analytic predictions over the range of Hurst roughness exponents studied. The
effect of increasing the range of interactions from a hard sphere repulsion to
exponential decay is analyzed. Results for exponential interactions are
accurately described by recent systematic corrections to Persson's contact
mechanics theory. The relation between the area of simply connected contact
patches and the normal force is also studied. Below a threshold size the
contact area and force are consistent with Hertzian contact mechanics, while
area and force are linearly related in larger contact patches.Comment: 12 pages, 9 figure
Adhesive Contact to a Coated Elastic Substrate
We show how the quasi-analytic method developed to solve linear elastic
contacts to coated substrates (Perriot A. and Barthel E. {\em J. Mat. Res.},
{\bf 2004}, {\em 19}, 600) may be extended to adhesive contacts. Substrate
inhomogeneity lifts accidental degeneracies and highlights the general
structure of the adhesive contact theory. We explicit the variation of the
contact variables due to substrate inhomogeneity. The relation to other
approaches based on Finite Element analysis is discussed
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
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