17,966 research outputs found
HOUSEHOLD DEMAND FOR PET FOOD AND THE OWNERSHIP OF CATS AND DOGS: AN ANALYSIS OF A NEGLECTED COMPONENT OF U.S. FOOD USE
Demand and Price Analysis,
Force chain splitting in granular materials: a mechanism for large scale pseudo-elastic behaviour
We investigate both numerically and analytically the effect of strong
disorder on the large scale properties of the hyperbolic equations for stresses
proposed in \protect\cite{bcc,wcc}. The physical mechanism that we model is the
local splitting of the force chains (the characteristics of the hyperbolic
equation) by packing defects. In analogy with the theory of light diffusion in
a turbid medium, we propose a Boltzmann-like equation to describe these
processes. We show that, for isotropic packings, the resulting large scale
effective equations for the stresses have exactly the same structure as those
of an elastic body, despite the fact that no displacement field needs to be
introduced at all. Correspondingly, the response function evolves from a two
peak structure at short scales to a broad hump at large scales. We find,
however, that the Poisson ratio is anomalously large and incompatible with
classical elasticity theory that requires the reference state to be
thermodynamically stable.Comment: 7 pages, 6 figures, An incorrect definition of the Poisson ratio in
dimensions not equal to 3 was amended. The conclusions are unchange
MAMA: An Algebraic Map for the Secular Dynamics of Planetesimals in Tight Binary Systems
We present an algebraic map (MAMA) for the dynamical and collisional
evolution of a planetesimal swarm orbiting the main star of a tight binary
system (TBS). The orbital evolution of each planetesimal is dictated by the
secular perturbations of the secondary star and gas drag due to interactions
with a protoplanetary disk. The gas disk is assumed eccentric with a constant
precession rate. Gravitational interactions between the planetesimals are
ignored. All bodies are assumed coplanar. A comparison with full N-body
simulations shows that the map is of the order of 100 times faster, while
preserving all the main characteristics of the full system.
In a second part of the work, we apply MAMA to the \gamma-Cephei, searching
for friendly scenarios that may explain the formation of the giant planet
detected in this system. For low-mass protoplanetary disks, we find that a
low-eccentricity static disk aligned with the binary yields impact velocities
between planetesimals below the disruption threshold. All other scenarios
appear hostile to planetary formation
A study of event traffic during the shared manipulation of objects within a collaborative virtual environment
Event management must balance consistency and responsiveness above the requirements of shared object interaction within a Collaborative Virtual Environment
(CVE) system. An understanding of the event traffic during collaborative tasks helps in the design of all aspects of a CVE system. The application, user activity, the display
interface, and the network resources, all play a part in determining the characteristics of event management.
Linked cubic displays lend themselves well to supporting natural social human communication between remote users. To allow users to communicate naturally and subconsciously, continuous and detailed tracking is necessary. This, however, is hard to balance with the real-time consistency constraints of general shared object interaction.
This paper aims to explain these issues through a detailed examination of event traffic produced by a typical CVE, using both immersive and desktop displays, while supporting a variety of collaborative activities. We analyze event traffic during a highly collaborative task requiring various forms of shared object manipulation, including the concurrent manipulation of a shared object. Event sources are categorized and the influence of the form of object sharing as well as the display device
interface are detailed. With the presented findings the paper wishes to aid the design of future systems
Nuclear fusion induced by X-rays in a crystal
The nuclei that constitute a crystalline lattice, oscillate relative to each
other with a very low energy that is not sufficient to penetrate through the
Coulomb barriers separating them. An additional energy, which is needed to
tunnel through the barrier and fuse, can be supplied by external
electromagnetic waves (X-rays or the synchrotron radiation). Exposing to the
X-rays the solid compound LiD (lithium-deuteride) for the duration of 111
hours, we have detected 88 events of the nuclear fusion d+Li6 ---> Be8*. Our
theoretical estimate agrees with what we observed. One of possible applications
of the phenomenon we found, could be the measurements of the rates of various
nuclear reactions (not necessarily fusion) at extremely low energies
inaccessible in accelerator experiments.Comment: 27 pages, 12 figures; submitted to Phys. Rev. C on 28 October 201
Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature
We investigate the transport properties of double-gated bilayer graphene
nanoribbons at room temperature. The devices were fabricated using conventional
CMOS-compatible processes. By analyzing the dependence of the resistance at the
charge neutrality point as a function of the electric field applied
perpendicular to the graphene surface, we show that a band gap in the density
of states opens, reaching an effective value of ~sim50 meV. This demonstrates
the potential of bilayer graphene as FET channel material in a conventional
CMOS environment.Comment: 3 pages, 3 figure
Finite-size effects in dynamics of zero-range processes
The finite-size effects prominent in zero-range processes exhibiting a
condensation transition are studied by using continuous-time Monte Carlo
simulations. We observe that, well above the thermodynamic critical point, both
static and dynamic properties display fluid-like behavior up to a density
{\rho}c (L), which is the finite-size counterpart of the critical density
{\rho}c = {\rho}c (L \rightarrow \infty). We determine this density from the
cross-over behavior of the average size of the largest cluster. We then show
that several dynamical characteristics undergo a qualitative change at this
density. In particular, the size distribution of the largest cluster at the
moment of relocation, the persistence properties of the largest cluster and
correlations in its motion are studied.Comment: http://pre.aps.org/abstract/PRE/v82/i3/e03111
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Do we (need to) care about canopy radiation schemes in DGVMs? Caveats and potential impacts
Dynamic global vegetation models (DGVMs) are an essential part of current state-of-the-art Earth system models. In recent years, the complexity of DGVMs has increased by incorporating new important processes like, e.g., nutrient cycling and land cover dynamics, while biogeophysical processes like surface radiation have not been developed much further. Canopy radiation models are however very important for the estimation of absorption and reflected fluxes and are essential for a proper estimation of surface carbon, energy and water fluxes.
The present study provides an overview of current implementations of canopy radiation schemes in a couple of state-of-the-art DGVMs and assesses their accuracy in simulating canopy absorption and reflection for a variety of different surface conditions. Systematic deviations in surface albedo and fractions of absorbed photosynthetic active radiation (faPAR) are identified and potential impacts are assessed.
The results show clear deviations for both, absorbed and reflected, surface solar radiation fluxes. FaPAR is typically underestimated, which results in an underestimation of gross primary productivity (GPP) for the investigated cases. The deviation can be as large as 25% in extreme cases. Deviations in surface albedo range between â0.15 †Îα †0.36, with a slight positive bias on the order of Îα â 0.04. Potential radiative forcing caused by albedo deviations is estimated at â1.25 †RF †â0.8 (W mâ2), caused by neglect of the diurnal cycle of surface albedo.
The present study is the first one that provides an assessment of canopy RT schemes in different currently used DGVMs together with an assessment of the potential impact of the identified deviations. The paper illustrates that there is a general need to improve the canopy radiation schemes in DGVMs and provides different perspectives for their improvement
Effect of Growth Hormone (hGH) Replacement Therapy on Physical Work Capacity and Cardiac and Pulmonary Function in Patients with hGH Deficiency Acquired in Adulthood.
The effects of 6 months of replacement therapy with recombinant human GH (hGH) on physical work capacity and cardiac structure and function were investigated in 20 patients with hGH deficiency of adult onset in a double blind, placebo-controlled trial. The GH dose of 12.5 micrograms/kg BW was self-administered daily sc. Oxygen consumption (VO2), CO2 production, and ventilatory volumes were measured during exercise on a bicycle spiroergometer. M-Mode echocardiography was performed using standard techniques. The VO2 max data, expressed per kg BW (mL/min.kg BW) showed a significant increase from 23.2 +/- 2.4 to 30.0 +/- 2.3 (P < 0.01) in the hGH-treated group, whereas the VO2 max data, expressed per lean body mass (milliliters per min/kg lean body mass) did not change significantly in either group. Maximal O2 pulse (milliliters per beat) increased significantly from 15.2 +/- 5.6 to 19.6 +/- 3.3 mL/beat (P < 0.01), but remained constant in the placebo group. The maximal power output (watts +/- SE) increased significantly (P < 0.01) from 192.5 +/- 13.5 to 227.5 +/- 11.5 in the hGH-treated group, but remained constant in the placebo group. Cardiac structure (left ventricular posterior wall, interventricular septum thickness, left ventricular mass, left ventricular end-systolic dimension, and left ventricular end-diastolic dimension) as well as echocardiographically assessed cardiac function did not change significantly after 6 months of treatment in either group. We conclude that hGH replacement in hGH-deficient adults improves oxygen uptake and exercise capacity. These improvements in pulmonary parameters might be due to an increase in respiratory muscle strength and partly to the changes in muscle volume per se observed during hGH replacement therapy. Furthermore, an increased cardiac output might contribute to the improvement in exercise performance during hGH treatment. According to our data, hGH replacement therapy leads to an improvement of exercise capacity and maximal oxygen uptake, but has no significant effect on cardiac structure
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