380 research outputs found
Symmetry of `molecular' configurations of interacting electrons in a quantum dot in strong magnetic fields
A molecular description for magic-number configurations of interacting
electrons in a quantum dot in high magnetic fields developed by one of the
authors has been elaborated for four, five and six electron dots. For four
electrons, the magic spin-singlet states are found to alternate between two
different resonating valence bond (RVB)-like states. For the five-electron
spin-polarized case, the molecular description is shown to work for the known
phenomenon of magic-number sequences that correspond to both the N-fold
symmetric ring configuration and a -fold symmetric one with a center
electron. A six-electron dot is shown here to have an additional feature in
which inclusion of quantum mechanical mixing between classical configurations,
which are deformed and degenerate, restores the N-fold symmetry and reproduces
the ground-state energy accurately.Comment: 4 pages, to be published in Physisca
Advanced optimization models for the location of charging stations in e-mobility
For a reduction in environmental pollution and dependency on petroleum,
electric vehicles (EV) present an advantageous alternative to traditionally
fossil-fuel powered automobiles. Rapid growth in the number of EVs requires an
urgent need to develop an adequate charging station infrastructure to stimulate
and facilitate their usage. Due to restricted investments in the development of
a sufficient infrastructure, locations have to be chosen deliberately.
In this paper, three extensions considering different objectives and various
constraints to the deterministic flow refuelling location problem (DFRLP),
described 2017 by de Vries and Duijzer, are introduced. In the first extension
we ask how many charging stations (CS) are necessary to cover a pre-specified
number of EVs and therefore exchange the original objective function for a
minimizing cost function. Secondly, our research shows that, when considering
location-dependent construction costs, results heavily depend on the relations
of said cost differences. Tests for different cost scenarios are carried out
and policy implications are discussed. In the last extension, we consider the
capacity of a CS to be limited. The DFRLP assumes an unlimited capacity,
meaning it is always possible to refuel all EVs at all CSs, where they stop. In
our model the capacity is put into relation to the total sum of demands
generated by all EVs, passing a particular CS, which means that our model
determines the placement and the sizes of all CSs simultaneously.
Finally, all extensions are evaluated using benchmarks instances based on
test instances from the literature
Effective Sample Size: Quick Estimation of the Effect of Related Samples in Genetic Case-Control Association Analyses
Correlated samples have been frequently avoided in case-control
genetic association
 studies in part because the methods for handling them are either not
easily implemented or not widely known. We
advocate one method for case-control association analysis of correlated
samples -- the effective sample size method -- as a simple and
accessible approach that does not require specialized computer programs.
The effective sample size method captures the variance inflation
of allele frequency estimation exactly, and can be used to modify the
chi-square test statistic, p-value, and 95% confidence interval of
odds-ratio simply by replacing the apparent number of allele counts with the
effective ones. For genotype frequency estimation, although a single
effective sample size is unable to completely characterize the variance inflation,
an averaged one can satisfactorily approximate the simulated result.
The effective sample size method is applied to the rheumatoid arthritis
siblings data collected from the North American Rheumatoid Arthritis Consortium (NARAC)
to establish a significant association with the interferon-induced
helicasel gene (IFIH1) previously being identified as a type 1 diabetes
susceptibility locus. Connections between the effective sample size
method and other methods, such as generalized estimation equation,
variance of eigenvalues for correlation matrices, and genomic controls,
are also discussed.

Equilibration of isolated macroscopic quantum systems
We investigate the equilibration of an isolated macroscopic quantum system in
the sense that deviations from a steady state become unmeasurably small for the
overwhelming majority of times within any sufficiently large time interval. The
main requirements are that the initial state, possibly far from equilibrium,
exhibits a macroscopic population of at most one energy level and that
degeneracies of energy eigenvalues and of energy gaps (differences of energy
eigenvalues) are not of exceedingly large multiplicities. Our approach closely
follows and extends recent works by Short and Farrelly [2012 New J. Phys. 14
013063], in particular going beyond the realm of finite-dimensional systems and
large effective dimensions.Comment: 19 page
Rapid quantification and validation of lipid concentrations within liposomes
Quantification of the lipid content in liposomal adjuvants for subunit vaccine formulation is of extreme importance, since this concentration impacts both efficacy and stability. In this paper, we outline a high performance liquid chromatography-evaporative light scattering detector (HPLC-ELSD) method that allows for the rapid and simultaneous quantification of lipid concentrations within liposomal systems prepared by three liposomal manufacturing techniques (lipid film hydration, high shear mixing, and microfluidics). The ELSD system was used to quantify four lipids: 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), cholesterol, dimethyldioctadecylammonium (DDA) bromide, and D-(+)-trehalose 6,6′-dibehenate (TDB). The developed method offers rapidity, high sensitivity, direct linearity, and a good consistency on the responses (R2 > 0.993 for the four lipids tested). The corresponding limit of detection (LOD) and limit of quantification (LOQ) were 0.11 and 0.36 mg/mL (DMPC), 0.02 and 0.80 mg/mL (cholesterol), 0.06 and 0.20 mg/mL (DDA), and 0.05 and 0.16 mg/mL (TDB), respectively. HPLC-ELSD was shown to be a rapid and effective method for the quantification of lipids within liposome formulations without the need for lipid extraction processes
The Herschel Planetary Nebula Survey (HerPlaNS) - a comprehensive dusty photoionization model of NGC6781
We perform a comprehensive analysis of the planetary nebula (PN) NGC6781 to
investigate the physical conditions of each of its ionized, atomic, and
molecular gas and dust components and the object's evolution, based on
panchromatic observational data ranging from UV to radio. Empirical nebular
elemental abundances, compared with theoretical predictions via nucleosynthesis
models of asymptotic giant branch (AGB) stars, indicate that the progenitor is
a solar-metallicity, 2.25-3.0 Msun initial-mass star. We derive the best-fit
distance of 0.46 kpc by fitting the stellar luminosity (as a function of the
distance and effective temperature of the central star) with the adopted
post-AGB evolutionary tracks. Our excitation energy diagram analysis indicate
high excitation temperatures in the photodissociation region (PDR) beyond the
ionized part of the nebula, suggesting extra heating by shock interactions
between the slow AGB wind and the fast PN wind. Through iterative fitting using
the Cloudy code with empirically-derived constraints, we find the best-fit
dusty photoionization model of the object that would inclusively reproduce all
of the adopted panchromatic observational data. The estimated total gas mass
(0.41 Msun) corresponds to the mass ejected during the last AGB thermal pulse
event predicted for a 2.5 Msun initial-mass star. A significant fraction of the
total mass (about 70 percent) is found to exist in the PDR, demonstrating the
critical importance of the PDR in PNe that are generally recognized as the
hallmark of ionized/H+ regions.Comment: 34 pages, 13 Figures and 16 Tables, accepted for publication in the
Astrophysical Journal Supplement Serie
- …