1,724 research outputs found
The violation of the Hund's rule in semiconductor artificial atoms
The unrestricted Pople-Nesbet approach for real atoms is adapted to quantum
dots, the man-made artificial atoms, under applied magnetic field. Gaussian
basis sets are used instead of the exact single-particle orbitals in the
construction of the appropriated Slater determinants. Both system chemical
potential and charging energy are calculated, as also the expected values for
total and z-component in spin states. We have verified the validity of the
energy shell structure as well as the Hund's rule state population at zero
magnetic field. Above given fields, we have observed a violation of the Hund's
rule by the suppression of triplets and quartets states at the 1p energy shell,
taken as an example. We also compare our present results with those obtained
using the LS-coupling scheme for low electronic occupations. We have focused
our attention to ground-state properties for GaAs quantum dots populated up to
forty electrons.Comment: 5 pages, 2 figures, submitted to Semic. Sci. Techno
The Richardson's Law in Large-Eddy Simulations of Boundary Layer flows
Relative dispersion in a neutrally stratified planetary boundary layer (PBL)
is investigated by means of Large-Eddy Simulations (LES). Despite the small
extension of the inertial range of scales in the simulated PBL, our Lagrangian
statistics turns out to be compatible with the Richardson law for the
average of square particle separation. This emerges from the application of
nonstandard methods of analysis through which a precise measure of the
Richardson constant was also possible. Its values is estimated as
in close agreement with recent experiments and three-dimensional direct
numerical simulations.Comment: 15 LaTex pages, 4 PS figure
HYPOTHETICAL HUMAN IMMUNE GENOME COMPLEX GRADIENT MAY HELP TO EXPLAIN THE CONGENITAL ZIKA SYMDROME CATASTROPHE IN BRAZIL: A NEW THEORY
There are few data considering human genetics as an important risk factor for birth abnormalities related to ZIKV infection during pregnancy, even though sub-Saharan African populations are apparently more resistant to CZS as compared to populations in the Americas. We hypothesized that single nucleotide variants (SNVs), especially in innate immune genes, could make some populations more susceptible to Zika congenital complications than others. Differences in the SNV frequencies among continental populations provide great potential for Machine Learning techniques. We explored a key immune genomic gradient between individuals from Africa, Asia and Latin America, working with complex signatures, using 297 SNVs. We employed a two-step approach. In the first step, decision trees (DTs) were used to extract the most discriminating SNVs among populations. In the second step, machine learning algorithms were used to evaluate the quality of the SNV pool identified in step one for discriminating between individuals from sub-Saharan African and Latin-American populations. Our results suggest that 10 SNVs from 10 genes (CLEC4M, CD58, OAS2, CD80, VEPH1, CTLA4, CD274, CD209, PLAAT4, CREB3L1) were able to discriminate sub-Saharan Africans from Latin American populations using only immune genome data, with an accuracy close to 100%. Moreover, we found that these SNVs form a genome gradient across the three main continental populations. These SNVs are important elements of the innate immune system and in the response against viruses. Our data support the Human Immune Genome Complex Gradient hypothesis as a new theory that may help to explain the CZS catastrophe in Brazil
Degradation versus self-assembly of block copolymer micelles
The stability of micelles self-assembled from block copolymers can be altered
by the degradation of the blocks. Slow degradation shifts the equilibrium size
distribution of block copolymer micelles and change their properties.
Quasi-equilibrium scaling theory shows that the degradation of hydrophobic
blocks in the core of micelles destabilize the micelles reducing their size,
while the degradation of hydrophilic blocks forming coronas of micelles favors
larger micelles and may, at certain conditions, induce the formation of
micelles from individual chains.Comment: Published in Langmuir http://pubs.acs.org/doi/pdf/10.1021/la204625
Density functional calculations of nanoscale conductance
Density functional calculations for the electronic conductance of single
molecules are now common. We examine the methodology from a rigorous point of
view, discussing where it can be expected to work, and where it should fail.
When molecules are weakly coupled to leads, local and gradient-corrected
approximations fail, as the Kohn-Sham levels are misaligned. In the weak bias
regime, XC corrections to the current are missed by the standard methodology.
For finite bias, a new methodology for performing calculations can be
rigorously derived using an extension of time-dependent current density
functional theory from the Schroedinger equation to a Master equation.Comment: topical review, 28 pages, updated version with some revision
Tratamento medicamentoso de 1217 pacientes epilépticos. II: estudo em relação à idade de início, ao tempo de doença e à freqüência das crises
Self-Similar Interpolation in Quantum Mechanics
An approach is developed for constructing simple analytical formulae
accurately approximating solutions to eigenvalue problems of quantum mechanics.
This approach is based on self-similar approximation theory. In order to derive
interpolation formulae valid in the whole range of parameters of considered
physical quantities, the self-similar renormalization procedure is complimented
here by boundary conditions which define control functions guaranteeing correct
asymptotic behaviour in the vicinity of boundary points. To emphasize the
generality of the approach, it is illustrated by different problems that are
typical for quantum mechanics, such as anharmonic oscillators, double-well
potentials, and quasiresonance models with quasistationary states. In addition,
the nonlinear Schr\"odinger equation is considered, for which both eigenvalues
and wave functions are constructed.Comment: 1 file, 30 pages, RevTex, no figure
The non-equilibrium phase transition of the pair-contact process with diffusion
The pair-contact process 2A->3A, 2A->0 with diffusion of individual particles
is a simple branching-annihilation processes which exhibits a phase transition
from an active into an absorbing phase with an unusual type of critical
behaviour which had not been seen before. Although the model has attracted
considerable interest during the past few years it is not yet clear how its
critical behaviour can be characterized and to what extent the diffusive
pair-contact process represents an independent universality class. Recent
research is reviewed and some standing open questions are outlined.Comment: Latexe2e, 53 pp, with IOP macros, some details adde
Bioheterojunction Effect on Fluorescence Origin and Efficiency Improvement of Firefly Chromophores
We propose the heterojunction effect in the analysis of the fluorescence
mechanism of the firefly chromophore. Following this analysis, and with respect
to the HOMO-LUMO gap alignment between the chromophore's functional fragments,
three main heterojunction types (I, II, and I*) are identified. Time-dependent
density-functional theory optical absorption calculations for the firefly
chromophore show that the strongest excitation appears in the deprotonated
anion state of the keto form. This can be explained by its high HOMO-LUMO
overlap due to strong bio-heterojunction confinement. It is also found that the
nitrogen atom in the thiazolyl rings, due to its larger electronegativity,
plays a key role in the emission process, its importance growing when HOMO and
LUMO overlap at its location. This principle is applied to enhance the
chromophore's fluorescence efficiency and to guide the functionalization of
molecular optoelectronic devices.Comment: 7 pages, 6 figure
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