13,327 research outputs found
Dietary assessment methods for micronutrient intake in elderly people: a systematic review
The European micronutrient recommendations aligned (EURRECA) Network of Excellence seeks to establish clear guidelines for assessing the validity of reported micronutrient intakes among vulnerable population groups. A systematic literature review identified studies validating the methodology used in elderly people for measuring usual dietary micronutrient intake. The quality of each validation study selected was assessed using a EURRECA-developed scoring system. The validation studies were categorised according to whether the reference method applied reflected short-term intake ( <7 d), long-term intake ( = 7 d) or used biomarkers (BM). A correlation coefficient for each micronutrient was calculated from the mean of the correlation coefficients from each study weighted by the quality of the study. Thirty-three papers were selected, which included the validation of twenty-five different FFQ, six diet histories (DH), one 24-h recall (24HR) and a videotaped dietary assessment method. A total of five publications analysed BM, which were used to validate four FFQ, and one 24HR, presenting very good correlations only for vitamin E. The analysis of weighted correlation coefficients classified by FFQ or DH showed that most of the micronutrients had higher correlations when the DH was used as the dietary method. Comparing only FFQ results showed very good correlations for measuring short-term intakes of riboflavin and thiamin and long-term intakes of P and Mg. When frequency methods are used for assessing micronutrient intake, the inclusion of dietary supplements improves their reliability for most micronutrients
Half-metallic ferromagnets: From band structure to many-body effects
A review of new developments in theoretical and experimental electronic
structure investigations of half-metallic ferromagnets (HMF) is presented.
Being semiconductors for one spin projection and metals for another ones, these
substances are promising magnetic materials for applications in spintronics
(i.e., spin-dependent electronics). Classification of HMF by the peculiarities
of their electronic structure and chemical bonding is discussed. Effects of
electron-magnon interaction in HMF and their manifestations in magnetic,
spectral, thermodynamic, and transport properties are considered. Especial
attention is paid to appearance of non-quasiparticle states in the energy gap,
which provide an instructive example of essentially many-body features in the
electronic structure. State-of-art electronic calculations for correlated
-systems is discussed, and results for specific HMF (Heusler alloys,
zinc-blende structure compounds, CrO FeO) are reviewed.Comment: to be published in Reviews of Modern Physics, vol 80, issue
Nonpolar resistive switching in Cu/SiC/Au non-volatile resistive memory devices
Amorphous silicon carbide (a-SiC) based resistive memory (RM) Cu/a-SiC/Au devices were fabricated and their resistive switching characteristics investigated. All four possible modes of nonpolar resistive switching were achieved with ON/OFF ratio in the range 10 6-10 8. Detailed current-voltage I-V characteristics analysis suggests that the conduction mechanism in low resistance state is due to the formation of metallic filaments. Schottky emission is proven to be the dominant conduction mechanism in high resistance state which results from the Schottky contacts between the metal electrodes and SiC. ON/OFF ratios exceeding 10 7 over 10 years were also predicted from state retention characterizations. These results suggest promising application potentials for Cu/a-SiC/Au RM
Interrelation of work function and surface stability: the case of BaAl4
The relationship between the work function (Phi) and the surface stability of
compounds is, to our knowledge, unknown, but very important for applications
such as organic light-emitting diodes. This relation is studied using
first-principles calculations on various surfaces of BaAl4. The most stable
surface [Ba terminated (001)] has the lowest Phi (1.95 eV), which is lower than
that of any elemental metal including Ba. Adding barium to this surface neither
increases its stability nor lowers its work function. BaAl4 is also strongly
bound. These results run counter to the common perception that stability and a
low Phi are incompatible. Furthermore, a large anisotropy and a stable
low-work-function surface are predicted for intermetallic compounds with polar
surfaces.Comment: 4 pages, 5 figures, to be published in Chem. Ma
Dissipative hydrodynamics in 2+1 dimension
In 2+1 dimension, we have simulated the hydrodynamic evolution of QGP fluid
with dissipation due to shear viscosity. Comparison of evolution of ideal and
viscous fluid, both initialised under the same conditions e.g. same
equilibration time, energy density and velocity profile, reveal that the
dissipative fluid evolves slowly, cooling at a slower rate. Cooling get still
slower for higher viscosity. The fluid velocities on the otherhand evolve
faster in a dissipative fluid than in an ideal fluid. The transverse expansion
is also enhanced in dissipative evolution. For the same decoupling temperature,
freeze-out surface for a dissipative fluid is more extended than an ideal
fluid. Dissipation produces entropy as a result of which particle production is
increased. Particle production is increased due to (i) extension of the
freeze-out surface and (ii) change of the equilibrium distribution function to
a non-equilibrium one, the last effect being prominent at large transverse
momentum. Compared to ideal fluid, transverse momentum distribution of pion
production is considerably enhanced. Enhancement is more at high than at
low . Pion production also increases with viscosity, larger the viscosity,
more is the pion production. Dissipation also modifies the elliptic flow.
Elliptic flow is reduced in viscous dynamics. Also, contrary to ideal dynamics
where elliptic flow continues to increase with transverse momentum, in viscous
dynamics, elliptic flow tends to saturate at large transverse momentum. The
analysis suggest that initial conditions of the hot, dense matter produced in
Au+Au collisions at RHIC, as extracted from ideal fluid analysis can be changed
significantly if the QGP fluid is viscous.Comment: 11 pages, 10 figures (revised). In the revised version, calculations
are redone with ADS/CFT and perurbative estimate of viscosity. Comments on
the unphysical effects like early reheating of the fluid, in 1st order
dissipative theories are added. The particle spectra calculations are redone
with modified programm
Improved drive current in RF vertical MOSFETS using hydrogen anneal
This letter reports a study on the effect of a hydrogen anneal after silicon pillar etch of surround-gate vertical MOSFETs intended for RF applications. A hydrogen anneal at 800 ?C is shown to give a 30% improvement in the drive current of 120-nm n-channel transistors compared with transistors without the hydrogen anneal. The value of drive current achieved is 250 ?A/?m, which is a record for thick pillar vertical MOSFETs. This improved performance is obtained even though a sacrificial oxidation was performed prior to the hydrogen anneal to smooth the pillar sidewall. The values of subthreshold slope and DIBL are 79 mV/decade and 45 mV/V, respectively, which are significantly better than most values reported in the literature for comparable devices. The H2 anneal is also shown to decrease the OFF-state leakage current by a factor of three
Collision Thermalization of Nucleons in Relativistic Heavy-Ion Collisions
We consider a possible mechanism of thermalization of nucleons in
relativistic heavy-ion collisions. Our model belongs, to a certain degree, to
the transport ones; we investigate the evolution of the system created in
nucleus-nucleus collision, but we parametrize this development by the number of
collisions of every particle during evolution rather than by the time variable.
We based on the assumption that the nucleon momentum transfer after several
nucleon-nucleon (-hadron) elastic and inelastic collisions becomes a random
quantity driven by a proper distribution. This randomization results in a
smearing of the nucleon momenta about their initial values and, as a
consequence, in their partial isotropization and thermalization. The trial
evaluation is made in the framework of a toy model. We show that the proposed
scheme can be used for extraction of the physical information from experimental
data on nucleon rapidity distribution.Comment: 13 pages, 8 figure
Onsager approach to 1D solidification problem and its relation to phase field description
We give a general phenomenological description of the steady state 1D front
propagation problem in two cases: the solidification of a pure material and the
isothermal solidification of two component dilute alloys.
The solidification of a pure material is controlled by the heat transport in
the bulk and the interface kinetics.
The isothermal solidification of two component alloys is controlled by the
diffusion in the bulk and the interface kinetics.
We find that the condition of positive-definiteness of the symmetric Onsager
matrix of interface kinetic coefficients still allows an arbitrary sign of the
slope of the velocity-concentration line near the solidus in the alloy problem
or of the velocity-temperature line in the case of solidification of a pure
material. This result offers a very simple and elegant way to describe the
interesting phenomenon of a possible non-single-value behavior of velocity
versus concentration which has previously been discussed by different
approaches. We also discuss the relation of this Onsager approach to the thin
interface limit of the phase field description.Comment: 5 pages, 1 figure, submitted to Physical Review
The Simple Non-degenerate Relativistic Gas: Statistical Properties and Brownian Motion
This paper shows a novel calculation of the mean square displacement of a
classical Brownian particle in a relativistic thermal bath. The result is
compared with the expressions obtained by other authors. Also, the
thermodynamic properties of a non-degenerate simple relativistic gas are
reviewed in terms of a treatment performed in velocity space.Comment: 6 pages, 2 figure
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