553 research outputs found
Mechanisms of lipid extraction from skin lipid bilayers by sebum triglycerides
The skin surface, our first barrier against the external environment, is covered by the sebum oil, a lipid film composed of sebaceous and epidermal lipids, which is important in the regulation of the hydration level of our skin. Here, we investigate the pathways leading to the transfer of epidermal lipids from the skin lipid bilayer to the sebum. We show that the sebum triglycerides, a major component of sebum, interact strongly with the epidermal lipids and extract them from the bilayer. Using microsecond time scale molecular dynamics simulations, we identify and quantify the free energy associated with the skin lipid extraction process
Neutron Scattering and magnetization studies of BaCuCoOCl: A decorated two-dimensional antiferromagnet
BaCuOCl has two inter-penetrating square Cu sublattices, one
with square root 2 times the in-plane spacing of the other. Isotropic magnetic
interactions between the two sublattices are completely frustrated. Quantum
fluctuations resolve the intrinsic degeneracy in the ordering direction of the
more weakly coupled sublattice in favor of collinear ordering. We present
neutron scattering and magnetization studies of the magnetic structure when the
Cu ions are substituted with Co. The Co spins create new magnetic interactions
between the two sublattices. The ordering behavior of both Cu sublattices is
retained largely unmodified. Between the phase transitions of the two
sublattices spin-glass behavior is observed. Magnetization results show a
strong enhancement to the ferromagnetic aspect of the magnetic structure. The
combination of glassy behavior and large moments strongly suggest that the Co
moments induce the formation of local canted states.Comment: 4 figure
A trajetória do plano de gestão democrática do governo Antônio Britto e sua aceitação nas escolas de Santa Maria
Tight-binding parameters and exchange integrals of Ba_2Cu_3O_4Cl_2
Band structure calculations for Ba_2Cu_3O_4Cl_2 within the local density
approximation (LDA) are presented. The investigated compound is similar to the
antiferromagnetic parent compounds of cuprate superconductors but contains
additional Cu_B atoms in the planes. Within the LDA, metallic behavior is found
with two bands crossing the Fermi surface (FS). These bands are built mainly
from Cu 3d_{x^2-y^2} and O 2p_{x,y} orbitals, and a corresponding tight-binding
(TB) model has been parameterized. All orbitals can be subdivided in two sets
corresponding to the A- and B-subsystems, respectively, the coupling between
which is found to be small. To describe the experimentally observed
antiferromagnetic insulating state, we propose an extended Hubbard model with
the derived TB parameters and local correlation terms characteristic for
cuprates. Using the derived parameter set we calculate the exchange integrals
for the Cu_3O_4 plane. The results are in quite reasonable agreement with the
experimental values for the isostructural compound Sr_2Cu_3O_4Cl_2.Comment: 5 pages (2 tables included), 4 ps-figure
Relativistic predictions of spin observables for exclusive proton knockout reactions
Within the framework of the relativistic distorted wave impulse approximation
(DWIA), we investigate the sensitivity of complete sets of polarization
transfer observables for exclusive proton knockout from the 3s,
2d and 2d states in Pb, at an incident laboratory
kinetic energy of 202 MeV, and for coincident coplanar scattering angles
(, ), to different distorting optical potentials,
finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as
medium-modified meson-nucleon coupling constants and meson masses. Results are
also compared to the nonrelativistic DWIA predictions based on the
Schr\"{o}dinger equation.Comment: Submitted for publication to Physicical Review C, 23 pages, 7 figure
Anomalous Spin Dynamics observed by High Frequency ESR in Honeycomb Lattice Antiferromagnet InCu2/3V1/3O3
High-frequency ESR results on the S=1/2 Heisenberg hexagonal antiferromagnet
InCu2/3V1/3O3 are reported. This compound appears to be a rare model substance
for the honeycomb lattice antiferromagnet with very weak interlayer couplings.
The high-temperature magnetic susceptibility can be interpreted by the S=1/2
honeycomb lattice antiferromagnet, and it shows a magnetic-order-like anomaly
at TN=38 K. Although, the resonance field of our high-frequency ESR shows the
typical behavior of the antiferromagnetic resonance, the linewidth of our
high-frequency ESR continues to increase below TN, while it tends to decrease
as the temperature in a conventional three-dimensional antiferromagnet
decreases. In general, a honeycomb lattice antiferromagnet is expected to show
a simple antiferromagnetic order similar to that of a square lattice
antiferromagnet theoretically because both antiferromagnets are bipartite
lattices. However, we suggest that the observed anomalous spin dynamics below
TN is the peculiar feature of the honeycomb lattice antiferromagnet that is not
observed in the square lattice antiferromagnet.Comment: 5 pages, 5 figure
Valoración diagnóstica de enzimas hepáticas en perfiles bioquímicos sanguíneos de vacas lecheras
RESUMEN
Objetivo. El objetivo del estudio fue determinar la asociación, sensibilidad (Se) y especificidad (Es) de las enzimas glutamato deshidrogenasa (GDH, EC: 1.4.1.3), aspartato aminotransferasa (AST, EC: 2.6.1.1) y g-glutamil transpeptidasa (GGT, EC: 2.3.2.2) como indicadores de daño hepático en perfiles bioquímicos sanguíneos de vacas lecheras. Materiales y métodos. Se analizaron los valores de la actividad plasmática de GDH, AST y GGT, obtenidos de 1566 vacas correspondientes a 112 perfiles bioquímicos realizados en rebaños lecheros. Se determinó la asociación entre la actividad de las enzimas y el área bajo la curva (ABC) y la Se y la Es mediante curva ROC considerando la presencia de daño hepático cuando GDH>30 U/L o GGT>39 U/L. Resultados. La AST presentó mayor asociación con la GDH (r=0.55) que la GGT (r=0.44), así como una mayor ABC (p=0.01) al utilizar GDH>30 U/L para indicar daño hepático. El grado de asociación entre AST y GGT fue de r=0.42. La sensibilidad de la AST para detectar daño hepático, utilizando el punto de corte de referencia del laboratorio (>150 U/L), fue inferior que al emplear GGT (>39 U/L). El punto crítico de máxima Se y Es de la curva ROC para daño hepático se obtuvo con AST>110 U/L, valor que incrementó la concordancia diagnóstica con la GDH (Kappa >0.300), pero no con la GGT. Conclusiones. La actividad plasmática de AST en vacas lecheras se asocia mayormente con la de GDH que con la de GGT y su límite de referencia para predecir daño hepático correspondería a >110 U/L
Confirmation of Anomalous Dynamical Arrest in attractive colloids: a molecular dynamics study
Previous theoretical, along with early simulation and experimental, studies
have indicated that particles with a short-ranged attraction exhibit a range of
new dynamical arrest phenomena. These include very pronounced reentrance in the
dynamical arrest curve, a logarithmic singularity in the density correlation
functions, and the existence of `attractive' and `repulsive' glasses. Here we
carry out extensive molecular dynamics calculations on dense systems
interacting via a square-well potential. This is one of the simplest systems
with the required properties, and may be regarded as canonical for interpreting
the phase diagram, and now also the dynamical arrest. We confirm the
theoretical predictions for re-entrance, logarithmic singularity, and give the
first direct evidence of the coexistence, independent of theory, of the two
coexisting glasses. We now regard the previous predictions of these phenomena
as having been established.Comment: 15 pages,15 figures; submitted to Phys. Rev.
Supramolecular assemblies involving metal organic ring interactions: Heterometallic Cu(II)-Ln(III) two dimensional coordination polymers
Three isostructural two-dimensional coordination polymers of the general formula [Ln2(CuL)3(H2O)9]$5.5H2O, where Ln is La (1), Nd (2), and Gd (3), have been synthesized and isolated from aqueous solutions and their single-crystal structures determined by X-ray diffraction. The supramolecular interaction between the non-aromatic metallorings plays an important role in stabilizing the structure of these compounds. The thermal stability, reversible solvent uptake, electronic properties and magnetic studies of these compounds are also reported
Neutron Scattering study of Sr_2Cu_3O_4Cl_2
We report a neutron scattering study on the tetragonal compound
Sr_2Cu_3O_4Cl_2, which has two-dimensional (2D) interpenetrating Cu_I and
Cu_{II} subsystems, each forming a S=1/2 square lattice quantum Heisenberg
antiferromagnet (SLQHA). The mean-field ground state is degenerate, since the
inter-subsystem interactions are geometrically frustrated. Magnetic neutron
scattering experiments show that quantum fluctuations lift the degeneracy and
cause a 2D Ising ordering of the Cu_{II} subsystem. Due to quantum fluctuations
a dramatic increase of the Cu_I out-of-plane spin-wave gap is also observed.
The temperature dependence and the dispersion of the spin-wave energy are
quantitatively explained by spin-wave calculations which include quantum
fluctuations explicitly. The values for the nearest-neighbor superexchange
interactions between the Cu_I and Cu_{II} ions and between the Cu_{II} ions are
determined experimentally to be J_{I-II} = -10(2)meV and J_{II}= 10.5(5)meV,
respectively. Due to its small exchange interaction, J_{II}, the 2D dispersion
of the Cu_{II} SLQHA can be measured over the whole Brillouin zone with thermal
neutrons, and a novel dispersion at the zone boundary, predicted by theory, is
confirmed. The instantaneous magnetic correlation length of the Cu_{II} SLQHA
is obtained up to a very high temperature, T/J_{II}\approx 0.75. This result is
compared with several theoretical predictions as well as recent experiments on
the S=1/2 SLQHA.Comment: Figures and equations are rearrange
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