203 research outputs found
The Role of Efficient Programming in Theoretical Chemistry and Physics Problems
Various aspects of efficient programming of high-performance computer systemsare discussed, using an example from modern electronic structure theory. It isshown that efficient programming is indispensable in today's theoretical studies byreducing drastically involved computer time. Timings from our quantum chemicalprogram CORREL are given for several platforms ranging from Cray Y-MP EL toPC/486.Pozna
HIGH-PERFORMANCE COMPUTINGON HETEROGENEOUS SYSTEMS
A model two-processor heterogeneous computer consisting of one scalar and one vector processoris analyzed in terms of its performance. It is demonstrated that on mixed-type (scalar-vector) applicationsit is much more effective than a homogeneous environment. Various models of the job distribution areintroduced. A working implementation in the field of quantum chemistry is presented.Pozna
Coupled anharmonic oscillators: the Rayleigh-Ritz approach versus the collocation approach
For a system of coupled anharmonic oscillators we compare the convergence
rate of the variational collocation approach presented recently by Amore and
Fernandez (2010 Phys.Scr.81 045011) with the one obtained using the optimized
Rayleigh-Ritz (RR) method. The monotonic convergence of the RR method allows us
to obtain more accurate results at a lower computational cost.Comment: 7 pages, 1 figur
On the acceleration of the convergence of singular operators in Gaussian basis sets
Gaussian type wave functions do not reproduce the interparticle cusps which result in a slow convergence of the expectation values of the operators involved in calculations of the relativistic and QED energy corrections. Methods correcting this deficiency are the main topic discussed in this paper. Benchmark expectation values of the singular operators for several few-electron systems are presented
Larval ascaridoid nematodes in horned and musky octopus (Eledone cirrhosa and E. moschata) and longfin inshore squid (Doryteuthis pealeii): Safety and quality implications for cephalopod products sold as fresh on the Italian market
The aim of this study was to evaluate the occurrence, infection level and distribution of ascaridoid larvae in cephalopod products sold in Italy. Data on the species most commonly commercialized as whole and fresh on the Italian market were collected. After comparing commercial and literature data, Eledone spp., comprising E. cirrhosa and E. moschata (horned octopus and musky octopus, respectively) and Doryteuthis pealeii (longfin inshore squid) were selected, as they had been rarely investigated. Overall, 75 Eledone spp. caught in the Mediterranean Sea (FAO area 37) and 70 D. pealeii from the Northwest Atlantic Ocean (FAO area 21) were examined by visual inspection and artificial digestion (viscera and mantle separately). Parasites were submitted to morphological and molecular analysis. Prevalence (P), mean intensity (MI) and mean abundance (MA) were calculated. In D. pealeii, 2 nematode larvae molecularly identified as Anisakis simplex s.s. were found in the viscera and in the mantle of two specimens (P: 2.9% 95% CI: 0–6.8%; MI: 1; MA: 0.028). In Eledone spp. 9 nematode larvae molecularly attributed to Hysterothylacium spp. were found in the mantle of 5 specimens (P: 6.7% 95% CI: 1–12.3%; MI: 1.8; MA: 0.12). This is the first report of A. simplex s.s. in D. pealeii. Considering the zoonotic and allergenic potential of these larvae and their localization also in the edible part (mantle), a potential public health issue exists
The prevalence of Echinococcus multilocularis in red foxes in Poland—current results (2009–2013)
The aim of the study was to determine the prevalence of Echinococcus multilocularis in red foxes (Vulpes vulpes) in Poland. Overall, 1,546 intestinal samples from 15 of the 16 provinces in Poland were examined by the sedimentation and counting technique (SCT). The mean prevalence of E. multilocularis in Poland was 16.5 % and was found in 14 of the 15 examined provinces. The mean intensity of infection was 2,807 tapeworms per intestine. Distinct differences in prevalence were observed between regions. In some provinces of eastern and southern Poland, the level of prevalence was 50.0 % (Warmińsko-Mazurskie), 47.2 % (Podkarpackie), 30.4 % (Podlaskie) and 28.6 % (Małopolskie), while in other provinces (west and south-west), only a few percent was found: 2.0 % (Dolnośląskie), 2.5 % (Wielkopolskie) and 0.0 % (in Opolskie). The border between areas with higher and lower prevalence seems to coincide with a north–south line running through the middle of Poland, with prevalence from 17.5 to 50.0 % in the eastern half and from 0.0 to 11.8 % in the western half. The dynamic situation observed in the prevalence of this tapeworm indicated the necessity of continuing to monitor the situation concerning E. multilocularis in red foxes in Poland
Deuterated hydrogen chemistry: Partition functions, Equilibrium constants and Transition intensities for the H3+ system
H3+ and the deuterated isotopomers are thought to play an important role in
interstellar chemistry. The partition functions of H3+, D2H+ and D3+ are
calculated to a temperature of 800 K by explicitly summing the ab initio
determined rotation-vibration energy levels of the respective species. These
partition functions are used to calculate the equilibrium constants for nine
important reactions in the interstellar medium involving H3+ and its deuterated
isotopomers. These equilibrium constants are compared to previously determined
experimental and theoretical values. The Einstein A coefficients for the
strongest dipole transitions are also calculated
The optimized Rayleigh-Ritz scheme for determining the quantum-mechanical spectrum
The convergence of the Rayleigh-Ritz method with nonlinear parameters
optimized through minimization of the trace of the truncated matrix is
demonstrated by a comparison with analytically known eigenstates of various
quasi-solvable systems. We show that the basis of the harmonic oscillator
eigenfunctions with optimized frequency ? enables determination of boundstate
energies of one-dimensional oscillators to an arbitrary accuracy, even in the
case of highly anharmonic multi-well potentials. The same is true in the
spherically symmetric case of V (r) = {\omega}2r2 2 + {\lambda}rk, if k > 0.
For spiked oscillators with k < -1, the basis of the pseudoharmonic oscillator
eigenfunctions with two parameters ? and {\gamma} is more suitable, and
optimization of the latter appears crucial for a precise determination of the
spectrum.Comment: 22 pages,8 figure
Second bound state of the positronium molecule and biexcitons
A new, hitherto unknown bound state of the positronium molecule, with orbital
angular momentum L=1 and negative parity is reported. This state is stable
against autodissociation even if the masses of the positive and negative
charges are not equal. The existence of a similar state in two-dimension has
also been investigated. The fact that the biexcitons have a second bound state
may help the better understanding of their binding mechanism.Comment: Latex, 8 pages, 2 Postscript figure
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