3,165 research outputs found
A new scenario of dynamical heterogeneity in supercooled liquid and glassy states of 2D monatomic system
Via analysis of spatio-temporal arrangements of atoms based on their dynamics in supercooled liquid and glassy states of 2D monatomic system with a double-well Lennard-Jones-Gauss (LJG) interaction potential, we find a new scenario of dynamical heterogeneity. Atoms with the same or very close mobility have a tendency to aggregate into clusters. Number of atoms with high mobility (and size of their clusters) increases with decreasing temperature passing over a maximum before decreasing downto zero. Position of the peak moves toward a lower temperature if mobility of atoms in clusters is lower together with an enhancement of height of the peak. In contrast, number of atoms with very low mobility or solidlike atoms (and size of their clusters) has a tendency to increase with decreasing temperature and then it suddenly increases in the vicinity of glass transition temperature leading to the formation of a glassy state. A sudden increase in the number of strongly correlated solidlike atoms in the vicinity of a glass transition temperature ( ) may be an origin of a drastical increase in viscosity of the glass-forming systems approaching glass transition. The fact, we find that diffusion coefficient decays exponentially with fraction of solidlike atoms exhibiting a sudden decrease in the vicinity of glass transition region
Pade/renormalization-group improvement of inclusive semileptonic B decay rates
Renormalization Group (RG) and optimized Pade-approximant methods are used to
estimate the three-loop perturbative contributions to the inclusive
semileptonic b \to u and b \to c decay rates. It is noted that the \bar{MS}
scheme works favorably in the b \to u case whereas the pole mass scheme shows
better convergence in the b \to c case. Upon the inclusion of the estimated
three-loop contribution, we find the full perturbative decay rate to be
192\pi^3\Gamma(b\to u\bar\nu_\ell\ell^-)/(G_F^2| V_{ub}|^2) = 2065 \pm 290{\rm
GeV^5} and 192\pi^3\Gamma(b\to c\ell^-\bar\nu_\ell)/(G_F^2|V_{cb}|^2)= 992 \pm
198 {\rm GeV^5}, respectively. The errors are inclusive of theoretical
uncertainties and non-perturbative effects. Ultimately, these perturbative
contributions reduce the theoretical uncertainty in the extraction of the CKM
matrix elements |V_{ub}| and |V_{cb}| from their respective measured inclusive
semileptonic branching ratio(s).Comment: 3 pages, latex using espcrc2.sty. Write-up of talk given at BEACH
2002, UBC, Vancouve
Acceleration of small astrophysical grains due to charge fluctuations
We discuss a novel mechanism of dust acceleration which may dominate for
particles smaller than m. The acceleration is caused by their
direct electrostatic interactions arising from fluctuations of grain charges.
The energy source for the acceleration are the irreversible plasma processes
occurring on the grain surfaces. We show that this mechanism of
charge-fluctuation-induced acceleration likely affects the rate of grain
coagulation and shattering of the population of small grains.Comment: 8 pages, 2 figures, revised version, submitted to Astrophysical
Journa
Combined effects of a simulated marine heatwave and an algal toxin on a tropical marine aquaculture fish cobia (Rachycentron canadum)
Ongoing global warming is one of the major challenges for the development of aquaculture in the tropical regions where species are already cultured in the water temperature close to their upper physiological thresholds. Furthermore, warming can trigger blooms of toxic algae, yet we do not know how extreme warming such as a marine heatwave (MHW) and algal toxins may affect marine aquaculture species. To address this issue, we investigated the effects of a simulated MHW in combination with exposure to trans-4-trans-decadienal (PUA), a diatom-derived toxin, on survival, growth, development and biochemical composition of cobia larvae and juveniles. Cobia larvae were exposed for 48 hr to one of two temperatures (29 vs. 34°C) and two PUA treatments (0 vs. 0.5 µM). Surviving larvae from each treatment were divided into two subsets: three replicates were used for the feeding test and five replicates were used for the recovery test in a non-contaminated environment at the respective temperatures of 29 or 34°C. Survival of cobia larvae was reduced by 16% in either MHW or PUA, but it dropped by 60% when both stressors were present, indicating a synergistic effect. MHW, but not PUA, reduced the feeding of cobia larvae. PUA had no delayed effects on growth rate and biochemical composition of the fish. MHW strongly reduced specific growth rate, body protein and lipid contents in cobia. Our results provide the first empirical evidence of how MHW and toxic algae may interact and challenge cobia and marine aquaculture production in tropical countries.publishedVersio
Rhad: A program for the evaluation of the hadronic R-ratio in the perturbative regime of QCD
This paper describes the fortran program rhad which performs a numerical
evaluation of the photon-induced hadronic R-ratio, R(s), related to the cross
section for electron-positron annihilation, for a given center-of-mass energy
\sqrt{s}. In rhad the state-of-the-art perturbative corrections to R(s) are
implemented and the running and decoupling of the strong coupling constant and
the quark masses is automatically treated consistently. Several options allow
for a flexible use of the program.Comment: 40 pages, LaTeX. 18 ps-files included. Typos fixed, references
updated. The program and this paper are available from http://www.rhad.de
CAMELLIA QUYNHII (THEACEAE, SECT. STEREOCARPUS), A NEW YELLOW SPECIES FROM THE CENTRAL HIGHLANDS, VIETNAM
Camellia quynhii is described and illustrated as a new species of section Stereocarpus (Pierre) Sealy from 12th village, Vu Bon Commune, Krong Pak District, Dak Lak Province. C. quynhii resembles C. dormoyana (Pierre) Sealy but differs in several morphological characteristics: sepals 6–7; petals about 12–15; filaments tomentose at the base; style 3(–4), basally united; capsule 3(–4) locular, 2–6 seeds in each locule. Information on its phenology, distribution, ecology, and conservation status is also provided.Camellia quynhii is described and illustrated as a new species of section Stereocarpus (Pierre) Sealy from 12th village, Vu Bon Commune, Krong Pak District, Dak Lak Province. C. quynhii resembles C. dormoyana (Pierre) Sealy but differs in several morphological characteristics: sepals 6–7; petals about 12–15; filaments tomentose at the base; style 3(–4), basally united; capsule 3(–4) locular, 2–6 seeds in each locule. Information on its phenology, distribution, ecology, and conservation status is also provided
Skeleton-stabilized ImmersoGeometric Analysis for incompressible viscous flow problems
A Skeleton-stabilized ImmersoGeometric Analysis technique is proposed for
incompressible viscous flow problems with moderate Reynolds number. The
proposed formulation fits within the framework of the finite cell method, where
essential boundary conditions are imposed weakly using a Nitsche-type method.
The key idea of the proposed formulation is to stabilize the jumps of
high-order derivatives of variables over the skeleton of the background mesh.
The formulation allows the use of identical finite-dimensional spaces for the
approximation of the pressure and velocity fields in immersed domains. The
stability issues observed for inf-sup stable discretizations of immersed
incompressible flow problems are avoided with this formulation. For B-spline
basis functions of degree with highest regularity, only the derivative of
order has to be controlled, which requires specification of only a single
stabilization parameter for the pressure field. The Stokes and Navier-Stokes
equations are studied numerically in two and three dimensions using various
immersed test cases. Oscillation-free solutions and high-order optimal
convergence rates can be obtained. The formulation is shown to be stable even
in limit cases where almost every elements of the physical domain is cut, and
hence it does not require the existence of interior cells. In terms of the
sparsity pattern, the algebraic system has a considerably smaller stencil than
counterpart approaches based on Lagrange basis functions. This important
property makes the proposed skeleton-stabilized technique computationally
practical. To demonstrate the stability and robustness of the method, we
perform a simulation of fluid flow through a porous medium, of which the
geometry is directly extracted from 3D scan data
RG/Pade Estimate of the Three-Loop Contribution to the QCD Static Potential Function
The three renormalization-group-accessible three-loop coefficients of powers
of logarithms within the \bar{MS} series momentum-space for the QCD static
potential are calculated and compared to values obtained via asymptotic
Pad\'e-approximant methods. The leading and next-to-leading logarithmic
coefficients are both found to be in exact agreement with their asymptotic
Pad\'e-predictions. The predicted value for the third RG-accessible coefficient
is found to be within 7% relative |error| of its true value for n_f leq 6, and
is shown to be in exact agreement with its true value in the n_f \to \infty
limit. Asymptotic Pad\'e estimates are also obtained for the remaining
(RG-inaccessible) three-loop coefficient. Comparison is also made with recent
estimates of the three-loop contribution to the configuration-space
static-potential function.Comment: 13 pages, LaTeX, additional discussion on the result
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