1,948 research outputs found
Xcompact3D: An open-source framework for solving turbulence problems on a Cartesian mesh
Xcompact3D is a Fortran 90â95 open-source framework designed for fast and accurate simulations of turbulent flows, targeting CPU-based supercomputers. It is an evolution of the flow solver Incompact3D which was initially designed in France in the mid-90âs for serial processors to solve the incompressible NavierâStokes equations. Incompact3D was then ported to parallel High Performance Computing (HPC) systems in the early 2010âs. Very recently the capabilities of Incompact3D have been extended so that it can now tackle more flow regimes (from incompressible flows to compressible flows at low Mach numbers), resulting in the design of a new user-friendly framework called Xcompact3D. The present manuscript presents an overview of Xcompact3D with a particular focus on its functionalities, its ready-to-run simulations and a few case studies to demonstrate its impact
Enhanced radiative strength in the quasi-continuum of 117Sn
Radiative strength functions of 117Sn has been measured below the neutron
separation energy using the (3He,3He'gamma) reactions. An increase in the slope
of the strength functions around E_gamma= 4.5 MeV indicates the onset of a
resonance-like structure, giving a significant enhancement of the radiative
strength function compared to standard models in the energy region 4.5 <=
E_gamma <= 8.0 MeV. For the first time, the functional form of this
resonance-like structure has been measured in an odd tin nucleus below neutron
threshold in the quasi-continuum region.Comment: 4 pages, 3 figure
Hummingbirds Budget Energy Flexibly in Response to Changing Resources
A key component of individual fitness is the ability to manage energy stores in response to variable resource availability, but because directly measuring energy budgets is difficult, daily energy management is rarely measured. Hummingbirds\u27 energy management is relatively simple to model compared to other endotherms because they have high massâspecific metabolic rates and store little fat. We determined which aspects of the hummingbird daily energy budget (i.e. thermoregulation, daytime activity costs, nightâtime costs) change at the individual level in response to environmental variation. We found that daily energy expenditure varied threefold in two populations of broadâbilled hummingbirds (Cynanthus latirostris). Our model indicated the energy budget was distributed in the following proportions: daytime activity, 59% (range 22%â84%); thermoregulation, 23% (11%â32%); basal metabolism, 7% (3%â16%); and nightâtime energy, 17% (6%â37%). Activity costs were higher at the hotter, homogeneous site and during the earlyâwet season at both sites. Increased daily energy expenditure was related to decreased nectar availability and not significantly related to temperature or bird mass. With climate change, the indirect energetic costs of shifting resources could have greater impacts on endotherm energy budgets than direct costs such as thermoregulation. Increased foraging and activity costs could decrease the energy available to birds for somatic repair and reproduction, potentially causing differential fitness across seasons and sites
Effects of activity and temperature on aerobic and anaerobic metabolism in the Galapagos marine iguana
1 Standard and maximal levels of oxygen consumption, and lactate production during burst activity were determined in the Galapagos marine iguana, Amblyrhynchus cristatus . This semiaquatic lizard sustains vigorous activity at relatively low body temperatures during underwater feeding (<25°C).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47117/1/360_2004_Article_BF00691052.pd
Critical Behavior of the Meissner Transition in the Lattice London Superconductor
We carry out Monte Carlo simulations of the three dimensional (3D) lattice
London superconductor in zero applied magnetic field, making a detailed finite
size scaling analysis of the Meissner transition. We find that the magnetic
penetration length \lambda, and the correlation length \xi, scale as \lambda ~
\xi ~ |t|^{-\nu}, with \nu = 0.66 \pm 0.03, consistent with ordinary 3D XY
universality, \nu_XY ~ 2/3. Our results confirm the anomalous scaling dimension
of magnetic field correlations at T_c.Comment: 4 pages, 5 ps figure
Dynamical stability criterion for inhomogeneous quasi-stationary states in long-range systems
We derive a necessary and sufficient condition of linear dynamical stability
for inhomogeneous Vlasov stationary states of the Hamiltonian Mean Field (HMF)
model. The condition is expressed by an explicit disequality that has to be
satisfied by the stationary state, and it generalizes the known disequality for
homogeneous stationary states. In addition, we derive analogous disequalities
that express necessary and sufficient conditions of formal stability for the
stationary states. Their usefulness, from the point of view of linear dynamical
stability, is that they are simpler, although they provide only sufficient
criteria of linear stability. We show that for homogeneous stationary states
the relations become equal, and therefore linear dynamical stability and formal
stability become equivalent.Comment: Submitted to Journal of Statistical Mechanics: Theory and Experimen
Dual superfluid-Bose glass critical point in two dimensions and the universal conductivity
We study the continuum version of the dual theory for a system of
two-dimensional, zero temperature, disordered bosons, interacting with short
range repulsion and at a commensurate density. The dual theory, which describes
vortices in the bosonic ground state, and has a form of 3D classical scalar
electrodynamics in random, correlated magnetic field, admits a new disordered
critical point within RG calculation at fixed dimension. The universal
conductivity and the critical exponents at the superfluid-Bose glass critical
point are calculated as series in fixed-point values of the dual coupling
constants, to the lowest non-trivial order: ,
and . The comparison with numerical results and experiments
is discussed.Comment: 8 pages, LaTex, some clarifications and references adde
Facilitation Differentially Affects Competitive Responses of Aspen and Subalpine Fir Through Stages of Stand Development
Spatial interactions between trees influence forest community succession. The objective of this study was to investigate how shifts in forest composition and proximity between tree species affect stand development over time in mixed forest systems. At six locations across the Fishlake National Forest, Utah, USA, in stands where facilitation has been documented previously, tree-ring samples were collected from aspen and subalpine fir trees. Basal area increment was calculated to characterize the effects of the proximity of overstory trees on multidecadal growth responses of aspen and subalpine fir in aspen-dominant and mixed aspenâconifer stands. Subalpine fir seedlings were established next to aspen (within 10 cm) when aspen was between 15 and 120 years old with a mean age of 60 years. Aspen and subalpine fir growth rates were reduced with increasing conifer abundance. Aspen trees growing next to a proximate subalpine fir tree had slower growth rates over time than aspen trees growing independently. Growth rates of subalpine fir in aspen-dominated stands were similar when growing independently or near aspen trees. However, subalpine fir in conifer-dominated stands maintained higher growth rates when growing next to an aspen tree than when growing independently. The data suggest that as stand competition increases with conifer abundance, the proximity of overstory trees increases competitive exclusion of aspen while having a beneficial growth effect on subalpine fir. These results underscore the importance of maintaining natural fire regimes in forest systems that keep competitive interactions in balance
Charge Delocalization in Self-Assembled Mixed-Valence Aromatic Cation Radicals
The spontaneous assembly of aromatic cation radicals (D+âą) with their neutral counterpart (D) affords dimer cation radicals (D2+âą). The intermolecular dimeric cation radicals are readily characterized by the appearance of an intervalence charge-resonance transition in the NIR region of their electronic spectra and by ESR spectroscopy. The X-ray crystal structure analysis and DFT calculations of a representative dimer cation radical (i.e., the octamethylbiphenylene dimer cation radical) have established that a hole (or single positive charge) is completely delocalized over both aromatic moieties. The energetics and the geometrical considerations for the formation of dimer cation radicals is deliberated with the aid of a series of cyclophane-like bichromophoric donors with drastically varied interplanar angles between the cofacially arranged aryl moieties. X-ray crystallography of a number of mixed-valence cation radicals derived from monochromophoric benzenoid donors established that they generally assemble in 1D stacks in the solid state. However, the use of polychromophoric intervalence cation radicals, where a single charge is effectively delocalized among all of the chromophores, can lead to higher-order assemblies with potential applications in long-range charge transport. As a proof of concept, we show that a single charge in the cation radical of a triptycene derivative is evenly distributed on all three benzenoid rings and this triptycene cation radical forms a 2D electronically coupled assembly, as established by X-ray crystallography
Dual theory of the superfluid-Bose glass transition in disordered Bose-Hubbard model in one and two dimensions
I study the zero temperature phase transition between superfluid and
insulating ground states of the Bose-Hubbard model in a random chemical
potential and at large integer average number of particles per site. Duality
transformation maps the pure Bose-Hubbard model onto the sine-Gordon theory in
one dimension (1D), and onto the three dimensional Higgs electrodynamics in two
dimensions (2D). In 1D the random chemical potential in dual theory couples to
the space derivative of the dual field, and appears as a random magnetic field
along the imaginary time direction in 2D. I show that the transition from the
superfluid state in both 1D and 2D is always controlled by the random critical
point. This arises due to a coupling constant in the dual theory with replicas
which becomes generated at large distances by the random chemical potential,
and represents a relevant perturbation at the pure superfluid-Mott insulator
fixed point. At large distances the dual theory in 1D becomes equivalent to the
Haldane's macroscopic representation of disordered quantum fluid, where the
generated term is identified with random backscattering. In 2D the generated
coupling corresponds to the random mass of the complex field which represents
vortex loops. I calculate the critical exponents at the superfluid-Bose glass
fixed point in 2D to be \nu=1.38 and z=1.93, and the universal conductivity at
the transition \sigma_c = 0.26 e_{*}^2 /h, using the one-loop field-theoretic
renormalization group in fixed dimension.Comment: 25 pages, 6 Postscript figures, LaTex, references updated, typos
corrected, final version to appear in Phys. Rev. B, June 1, 199
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