368 research outputs found
Nondielectric long-range solvation of polar liquids in cubic symmetry
Long-range solvation properties of strongly coupled dipolar systems simulated using the Ewald and reaction field methods are assessed by using electric fluctuation formulas for a dielectric medium. Some components of the fluctuating electric multipole moments are suppressed, whereas other components are favored as the boundary of the simulation box is approached. An analysis of electrostatic interactions in a periodic cubic system suggests that these structural effects are due to the periodicity embedded in the Ewald method. Furthermore, the results obtained using the reaction field method are very similar to those obtained using the Ewald method, an effect which we attribute to the use of toroidal boundary conditions in the former case. Thus, the long-range solvation properties of polar liquids simulated using either of the two methods are nondielectric in their character. (C) 2009 American Institute of Physics. [doi:10.1063/1.3250941
Heat dissipation in atomic-scale junctions
Atomic and single-molecule junctions represent the ultimate limit to the
miniaturization of electrical circuits. They are also ideal platforms to test
quantum transport theories that are required to describe charge and energy
transfer in novel functional nanodevices. Recent work has successfully probed
electric and thermoelectric phenomena in atomic-scale junctions. However, heat
dissipation and transport in atomic-scale devices remain poorly characterized
due to experimental challenges. Here, using custom-fabricated scanning probes
with integrated nanoscale thermocouples, we show that heat dissipation in the
electrodes of molecular junctions, whose transmission characteristics are
strongly dependent on energy, is asymmetric, i.e. unequal and dependent on both
the bias polarity and the identity of majority charge carriers (electrons vs.
holes). In contrast, atomic junctions whose transmission characteristics show
weak energy dependence do not exhibit appreciable asymmetry. Our results
unambiguously relate the electronic transmission characteristics of
atomic-scale junctions to their heat dissipation properties establishing a
framework for understanding heat dissipation in a range of mesoscopic systems
where transport is elastic. We anticipate that the techniques established here
will enable the study of Peltier effects at the atomic scale, a field that has
been barely explored experimentally despite interesting theoretical
predictions. Furthermore, the experimental advances described here are also
expected to enable the study of heat transport in atomic and molecular
junctions, which is an important and challenging scientific and technological
goal that has remained elusive.Comment: supporting information available in the journal web site or upon
reques
Trajectories in New York Heart Association functional class in heart failure across the ejection fraction spectrum: data from the Swedish Heart Failure Registry.
AIMS: To investigate incidence, predictors and prognostic implications of longitudinal New York Heart Association (NYHA) class changes (i.e. improving or worsening vs. stable NYHA class) in heart failure (HF) across the ejection fraction (EF) spectrum. METHODS AND RESULTS: From the Swedish HF Registry, 13 535 patients with EF and ≥2 NYHA class assessments were considered. Multivariable multinomial regressions were fitted to identify the independent predictors of NYHA change. Over a 1-year follow-up, 69% of patients had stable, 17% improved, and 14% worsened NYHA class. Follow-up in specialty care predicted improving NYHA class, whereas an in-hospital patient registration, lower EF, renal disease, lower mean arterial pressure, older age, and longer HF duration predicted worsening. The association between NYHA change and subsequent outcomes was assessed with multivariable Cox models. When adjusting for the NYHA class at baseline, improving NYHA class was independently associated with lower while worsening with higher risk of all-cause and cardiovascular mortality, and first HF hospitalization. After adjustment for the NYHA class at follow-up, NYHA class change did not predict morbidity/mortality. NYHA class assessment at baseline and follow-up predicted morbidity/mortality on top of the changes. Results were consistent across the EF spectrum. CONCLUSION: In a large real-world HF population, NYHA class trajectories predicted morbidity/mortality after extensive adjustments. However, the prognostic role was entirely explained by the resulting NYHA class, i.e. the follow-up value. Our results highlight that considering one-time NYHA class assessment, rather than trajectories, might be the preferable approach in clinical practice and for clinical trial design
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Identification of novel genetic regions associated with resistance to European canker in apple
Background: European canker, caused by the fungal pathogen Neonectria ditissima, is an economically damaging
disease in apple producing regions of the world – especially in areas with moderate temperatures and high rainfall.
The pathogen has a wide host range of hardwood perennial species, causing trunk cankers, dieback and branch
lesions in its hosts. Although apple scion germplasm carrying partial resistance to the disease has been described, little is still known of the genetic basis for this quantitative resistance.
Results: Resistance to Neonectria ditissima was studied in a multiparental population of apple scions using several
phenotyping methods. The studied population consists of individuals from multiple families connected through a
common pedigree. The degree of disease of each individual in the population was assessed in three experiments: artificial
inoculations of detached dormant shoots, potted trees in a glasshouse and in a replicated field experiment. The
genetic basis of the differences in disease was studied using a pedigree-based analysis (PBA). Three quantitative trait loci (QTL), on linkage groups (LG) 6, 8 and 10 were identified in more than one of the phenotyping strategies. An additional four QTL, on LG 2, 5, 15 and 16 were only identified in the field experiment. The QTL on LG2 and 16 were further validated in a biparental population. QTL effect sizes were small to moderate with 4.3 to 19% of variance explained by a single QTL. A subsequent analysis of QTL haplotypes revealed a dynamic response to this disease, in which the estimated effect of a haplotype varied over the field time-points.
Conclusions: This study describes the first identified QTL associated with resistance to N. ditissima in apple scion
germplasm. The results from this study show that QTL present in germplasm commonly used in apple breeding have a low to medium effect on resistance to N. ditissima. Hence, multiple QTL will need to be considered to improve resistance through breeding
A linear nonequilibrium thermodynamics approach to optimization of thermoelectric devices
Improvement of thermoelectric systems in terms of performance and range of
applications relies on progress in materials science and optimization of device
operation. In this chapter, we focuse on optimization by taking into account
the interaction of the system with its environment. For this purpose, we
consider the illustrative case of a thermoelectric generator coupled to two
temperature baths via heat exchangers characterized by a thermal resistance,
and we analyze its working conditions. Our main message is that both electrical
and thermal impedance matching conditions must be met for optimal device
performance. Our analysis is fundamentally based on linear nonequilibrium
thermodynamics using the force-flux formalism. An outlook on mesoscopic systems
is also given.Comment: Chapter 14 in "Thermoelectric Nanomaterials", Editors Kunihito
Koumoto and Takao Mori, Springer Series in Materials Science Volume 182
(2013
On the possibility of magneto-structural correlations: detailed studies of di-nickel carboxylate complexes
A series of water-bridged dinickel complexes of the general formula [Ni<sub>2</sub>(ÎĽ<sub>2</sub>-OH<sub>2</sub>)(ÎĽ2-
O<sub>2</sub>C<sup>t</sup>Bu)<sub>2</sub>(O<sub>2</sub>C<sup>t</sup>Bu)2(L)(L0)] (L = HO<sub>2</sub>C<sup>t</sup>Bu, L0 = HO<sub>2</sub>C<sup>t</sup>Bu (1), pyridine (2),
3-methylpyridine (4); L = L0 = pyridine (3), 3-methylpyridine (5)) has been synthesized
and structurally characterized by X-ray crystallography. The magnetic properties
have been probed by magnetometry and EPR spectroscopy, and detailed measurements
show that the axial zero-field splitting, D, of the nickel(ii) ions is on the same order as
the isotropic exchange interaction, J, between the nickel sites. The isotropic exchange
interaction can be related to the angle between the nickel centers and the bridging
water molecule, while the magnitude of D can be related to the coordination sphere at
the nickel sites
On the Adsorption of Two-State Polymers
Monte Carlo(MC) simulations produce evidence that annealed copolymers
incorporating two interconverting monomers, P and H, adsorb as homopolymers
with an effective adsorption energy per monomer, , that depends
on the PH equilibrium constants in the bulk and at the surface. The cross-over
exponent, is unmodified. The MC results on the overall PH ratio, the PH
ratio at the surface and in the bulk as well as the number of adsorbed monomers
are in quantitative agreement with this hypothesis and the theoretically
derived . The evidence suggests that the form of surface
potential does not affect but does influence the PH equilibrium.Comment: 22 pages, 10 figure
Structural Anisotropy in Polar Fluids Subjected to Periodic Boundary Conditions
A heuristic model based on dielectric continuum theory for the long-range solvation free energy of a dipolar system possessing periodic boundary conditions (PBCs) is presented. The predictions of the model are compared to simulation results for Stockmayer fluids simulated using three different cell geometries. The boundary effects induced by the PBCs are shown to lead to anisotropies in the apparent dielectric constant and the long-range solvation free energy of as much as 50%. However, the sum of all of the anisotropic energy contributions yields a value that is very close to the isotropic one derived from dielectric continuum theory, leading to a total system energy close to the dielectric value. It is finally shown that the leading-order contribution to the energetic and structural anisotropy is significantly smaller in the noncubic simulation cell geometries compared to when using a cubic simulation cell
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