12,043 research outputs found
Ge-substitutional defects and the r3xr3 <--> 3x3 transition in alpha--SnGe(111)
The structure and energetics of Ge substitutional defects on the
alpha-Sn/Ge(111) surface are analyzed using Density Functional Theory (DFT)
molecular dynamics (MD) simulations. An isolated Ge defect induces a very local
distortion of the 3x3 reconstruction, confined to a significant downwards
displacement (-0.31 A) at the defect site and a modest upward displacement
(0.05 A) of the three Sn nearest neighbours with partially occupied dangling
bonds. Dynamical fluctuations between the two degenerate ground states yield
the six-fold symmetry observed around a defect in the experiments at room
temperature. Defect-defect interactions are controlled by the energetics of the
deformation of the 3x3 structure: They are negligible for defects on the
honeycomb lattice and quite large for a third defect on the hexagonal lattice,
explaining the low temperature defect ordering.Comment: 4 pages, Revtex, 7 Encapsulated Postscript figures, uses epsf.sty.
Submitted to Phys. Rev. Let
Multifunctional Magnetoelectric Materials for Device Applications
Mutiferroics are a novel class of next generation multifunctional materials,
which display simultaneous magnetic spin, electric dipole, and ferroelastic
ordering, and have drawn increasing interest due to their multi-functionality
for a variety of device applications. Since single-phase materials exist rarely
in nature with such cross-coupling properties, an intensive research activity
is being pursued towards the discovery of new single-phase multiferroic
materials and the design of new engineered materials with strong
magneto-electric (ME) coupling. This review article summarizes the development
of different kinds of multiferroic material: single-phase and composite
ceramic, laminated composite, and nanostructured thin films. Thin-film
nanostructures have higher magnitude direct ME coupling values and clear
evidence of indirect ME coupling compared with bulk materials. Promising ME
coupling coefficients have been reported in laminated composite materials in
which signal to noise ratio is good for device fabrication. We describe the
possible applications of these materials
Narrativización y dialogicidad lingüística, literaria y cultural en La Celestina : el texto de Rojas en el contexto de Bajtín
Global Disk Oscillation Modes in Cataclysmic Variables and Other Newtonian Accretors
Diskoseismology, the theoretical study of small adiabatic hydrodynamical
global perturbations of geometrically thin, optically thick accretion disks
around black holes (and other compact objects), is a potentially powerful probe
of the gravitational field. For instance, the frequencies of the normal mode
oscillations can be used to determine the elusive angular momentum parameter of
the black hole. The general formalism developed by diskoseismologists for
relativistic systems can be readily applied to the Newtonian case of
cataclysmic variables (CVs). Some of these systems (e.g., the dwarf nova SS
Cygni) show rapid oscillations in the UV with periods of tens of seconds and
high coherence. In this paper, we assess the possibility that these dwarf nova
oscillations (DNOs) are diskoseismic modes. Besides its importance in
investigating the physical origin of DNOs, the present work could help us to
answer the following question. To what extent are the similarities in the
oscillation phenomenology of CVs and X-ray binaries (XRBs) indicative of a
common physical mechanism?Comment: 1 figur
12CO and 13CO J=3-2 observations toward N11 in the Large Magellanic Cloud
After 30 Doradus, N11 is the second largest and brightest nebula in the LMC.
This large nebula has several OB associations with bright nebulae at its
surroundings. N11 was previously mapped at the lowest rotational transitions of
CO (J=1--0 and 2--1), and in some particular regions pointings of the
CO J=1--0 and 2--1 lines were also performed. Using ASTE we mapped the
whole extension of the N11 nebula in the CO J=3--2 line, and three
sub-regions in the CO J=3--2 line. The regions mapped in the CO
J=3--2 were selected based on that they may be exposed to the radiation at
different ways: a region lying over the nebula related to the OB association
LH10 (N11B), another one that it is associated with the southern part of the
nebula related to the OB association LH13 (N11D), and finally a farther area at
the southwest without any embedded OB association (N11I). We found that the
morphology of the molecular clouds lying in each region shows some signatures
that could be explained by the expansion of the nebulae and the action of the
radiation. Fragmentation generated in a molecular shell due to the expansion of
the N11 nebula is suggested. The integrated line ratios CO/CO
show evidences of selective photodissociation of the CO, and probably
other mechanisms such as chemical fractionation. The CO contribution to the
continuum at 870 m was directly derived. The distribution of the
integrated line ratios CO J=3--2/2--1 show hints of stellar feedback in
N11B and N11D. The ratio between the virial and LTE mass (M/M) is higher than unity in all analyzed molecular clumps, which suggests
that the clumps are not gravitationally bounded and may be supported by
external pressure. A non-LTE analysis suggests that we are mapping gas with
densities about a few 10 cm.Comment: Accepted to be published in A&A. Figures were degrade
Spectroscopic investigation of a 'Virgin of Sorrows' canvas painting : a multi-method approach
Dietary elimination of children with food protein induced gastrointestinal allergy – micronutrient adequacy with and without a hypoallergenic formula?
Background:
The cornerstone for management of Food protein-induced gastrointestinal allergy (FPGIA) is dietary exclusion; however the micronutrient intake of this population has been poorly studied. We set out to determine the dietary intake of children on an elimination diet for this food allergy and hypothesised that the type of elimination diet and the presence of a hypoallergenic formula (HF) significantly impacts on micronutrient intake.
Method:
A prospective observational study was conducted on children diagnosed with FPIGA on an exclusion diet who completed a 3 day semi-quantitative food diary 4 weeks after commencing the diet. Nutritional intake where HF was used was compared to those without HF, with or without a vitamin and mineral supplement (VMS).
Results:
One-hundred-and-five food diaries were included in the data analysis: 70 boys (66.7%) with median age of 21.8 months [IQR: 10 - 67.7]. Fifty-three children (50.5%) consumed a HF and the volume of consumption was correlated to micronutrient intake. Significantly (p <0.05) more children reached their micronutrient requirements if a HF was consumed. In those without a HF, some continued not to achieve requirements in particular for vitamin D and zinc, in spite of VMS.
Conclusion:
This study points towards the important micronutrient contribution of a HF in children with FPIGA. Children, who are not on a HF and without a VMS, are at increased risk of low intakes in particular vitamin D and zinc. Further studies need to be performed, to assess whether dietary intake translates into actual biological deficiencies
Planning with Information-Processing Constraints and Model Uncertainty in Markov Decision Processes
Information-theoretic principles for learning and acting have been proposed
to solve particular classes of Markov Decision Problems. Mathematically, such
approaches are governed by a variational free energy principle and allow
solving MDP planning problems with information-processing constraints expressed
in terms of a Kullback-Leibler divergence with respect to a reference
distribution. Here we consider a generalization of such MDP planners by taking
model uncertainty into account. As model uncertainty can also be formalized as
an information-processing constraint, we can derive a unified solution from a
single generalized variational principle. We provide a generalized value
iteration scheme together with a convergence proof. As limit cases, this
generalized scheme includes standard value iteration with a known model,
Bayesian MDP planning, and robust planning. We demonstrate the benefits of this
approach in a grid world simulation.Comment: 16 pages, 3 figure
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