Search results for "composition"
showing 10 items of 2675 documents
Reduced scaling in electronic structure calculations using Cholesky decompositions
2003
The small numerical rank of the two-electron integral matrix for large molecular systems and large basis sets was demonstrated. Though, the current implementation still requires some improvements on the calculations done in the inner most loop of the decomposition do not exploit the parsity in the Cholesky vectors. With respect to the practical applicability of the presented method an efficient approach to geometrical derivatives was imperative. Such an approach was obtained including certain derivative product functions and decomposing an expanded integral matrix.
DIRECT EVIDENCE FOR CONDENSATION IN THE EARLY SOLAR SYSTEM AND IMPLICATIONS FOR NEBULAR COOLING RATES
2009
We have identified in an acid resistant residue of the carbonaceous chondrite Murchison a large number (458) of highly refractory metal nuggets (RMNs) that once were most likely hosted by Ca,Al-rich inclusions (CAIs). While osmium isotopic ratios of two randomly selected particles rule out a presolar origin, the bulk chemistry of 88 particles with sizes in the submicron range determined by energy dispersive X-ray (EDX) spectroscopy shows striking agreement with predictions of single-phase equilibrium condensation calculations. Both chemical composition and morphology strongly favor a condensation origin. Particularly important is the presence of structurally incompatible elements in particl…
Harmonic decomposition of two particle angular correlations in Pb–Pb collisions at sNN=2.76 TeV
2012
Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb-Pb collisions at root s(NN) = 2.76 TeV for transverse momenta 0.25 p(T)(a). The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval |eta| 0.8, and are referred to as "long-range correlations". Fourier components V-n Delta equivalent to are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, …
Sweeping the Space of Admissible Quark Mass Matrices
2002
We propose a new and efficient method of reconstructing quark mass matrices from their eigenvalues and a complete set of mixing observables. By a combination of the principle of NNI (nearest neighbour interaction) bases which are known to cover the general case, and of the polar decomposition theorem that allows to convert arbitrary nonsingular matrices to triangular form, we achieve a parameterization where the remaining freedom is reduced to one complex parameter. While this parameter runs through the domain bounded by a circle with radius R determined by the up-quark masses around the origin in the complex plane one sweeps the space of all mass matrices compatible with the given set of d…
Production of hypernuclei in peripheral relativistic ion collisions
2013
Within a dynamical and statistical approach we study the main regularities in production of hypernuclei coming from projectile and target residues in relativistic ion collisions. We demonstrate that yields of hypernuclei increase considerably above the energy threshold for Lambda hyperons, and there is a saturation for yields of single hypernuclei with increasing the beam energy up to few TeV. Production of specific hypernuclei depend very much on the isotopic composition of the projectile, and this gives a chance to obtain exotic hypernuclei that may be difficult to reach in traditional hypernuclear experiments. Possibilities for the detection of such hypernuclei with planned and available…
The performance of thin layers produced by molecular plating as α-particle sources
2013
Abstract Sources for α-spectroscopy studies were prepared. Constant current density molecular plating was used to produce layers containing the α-particle emitter 147 Sm. Different parameters of the molecular plating process were varied, namely the plating solvent (an isopropanol/isobutanol mixture, pyridine, and N , N -dimethylformamide), the applied deposition time (90, 180, and 360 min), and the surface roughness of the deposition substrate (ca. 10, 20, and 300 nm). Using different analytical techniques, Sm deposition yields, chemical composition of the produced surfaces, surface homogeneity, roughness and morphology were investigated. Alpha spectra were recorded with a Si solid-state de…
Modelling of Magnetic Resonance Spectra Using Mixtures for Binned and Truncated Data
2007
Magnetic Resonance Spectroscopy (MRS) provides the biochemical composition of a tissue under study. This information is useful for the in-vivo diagnosis of brain tumours. Prior knowledge of the relative position of the organic compound contributions in the MRS suggests the development of a probabilistic mixture model and its EM-based Maximum Likelihood Estimation for binned and truncated data. Experiments for characterizing and classifying Short Time Echo (STE) spectra from brain tumours are reported.
Phase Transitions in Polymeric Systems
1995
The study of collective phenomena in polymeric systems is a particular challenge,because there occurs structure simultaneously on many length scales. Restricting attention to neutral flexible linear macromolecules, we disregard here interesting problems like polyelectrolytes, stiff chains or chains with stiff parts, branched chains and polymer networks, and all combinations thereof including e.g. liquid crystalline polymers, and treat only the simplest case. But already then there occurs structure from the scale of a covalent bond along the backbone of a chain (~ 1 A) over the scale of the persistence length (~ 10 A) to the coil gyration radius R g (~ 102 A), in the description of a single …
Soft X-Ray Irradiation of Methanol Ice: Implication for H2CO Formation in Interstellar Regions
2010
We performed 0.3 keV soft X-ray irradiation of a methanol ice at 8 K under ultra-high vacuum conditions. To the best of our knowledge, this is the first time that soft X-rays are used to study photolysis of ice analogs. Despite the low irradiation dose of 10{sup -6} photons molecule{sup -1}, the formation of formaldehyde has been observed. The results of our experiments suggest that X-rays may be a promising candidate to the formation of complex molecules in regions where UV radiation is severely inhibited.
Method specific Cholesky decomposition : Coulomb and exchange energies
2008
We present a novel approach to the calculation of the Coulomb and exchange contributions to the total electronic energy in self consistent field and density functional theory. The numerical procedure is based on the Cholesky decomposition and involves decomposition of specific Hadamard product matrices that enter the energy expression. In this way, we determine an auxiliary basis and obtain a dramatic reduction in size as compared to the resolution of identity (RI) method. Although the auxiliary basis is determined from the energy expression, we have complete control of the errors in the gradient or Fock matrix. Another important advantage of this method specific Cholesky decomposition is t…