951 research outputs found
Geometrical and electronic structures of the (5, 3) single-walled gold nanotube from first-principles calculations
The geometrical and electronic structures of the 4 {\AA} diameter perfect and
deformed (5, 3) single-walled gold nanotube (SWGT) have been studied based upon
the density-functional theory in the local-density approximation (LDA). The
calculated relaxed geometries show clearly significant deviations from those of
the ideally rolled triangular gold sheet. It is found that the different
strains have different effects on the electronic structures and density of
states of the SWGTs. And the small shear strain can reduce the binding energy
per gold atom of the deformed SWGT, which is consistent with the experimentally
observed result. Finally, we found the finite SWGT can show the
metal-semiconductor transition.Comment: 11 pages, 4 figure
Mitophagy in the aging nervous system
Aging is characterised by the progressive accumulation of cellular dysfunction, stress, and inflammation. A large body of evidence implicates mitochondrial dysfunction as a cause or consequence of age-related diseases including metabolic disorders, neuropathies, various forms of cancer and neurodegenerative diseases. Because neurons have high metabolic demands and cannot divide, they are especially vulnerable to mitochondrial dysfunction which promotes cell dysfunction and cytotoxicity. Mitophagy neutralises mitochondrial dysfunction, providing an adaptive quality control strategy that sustains metabolic homeostasis. Mitophagy has been extensively studied as an inducible stress response in cultured cells and short-lived model organisms. In contrast, our understanding of physiological mitophagy in mammalian aging remains extremely limited, particularly in the nervous system. The recent profiling of mitophagy reporter mice has revealed variegated vistas of steady-state mitochondrial destruction across different tissues. The discovery of patients with congenital autophagy deficiency provokes further intrigue into the mechanisms that underpin neural integrity. These dimensions have considerable implications for targeting mitophagy and other degradative pathways in age-related neurological disease.Peer reviewe
Electronic Quantum Monte Carlo Calculations of Atomic Forces, Vibrations, and Anharmonicities
Atomic forces are calculated for first-row monohydrides and carbon monoxide
within electronic quantum Monte Carlo (QMC). Accurate and efficient forces are
achieved by using an improved method for moving variational parameters in
variational QMC. Newton's method with singular value decomposition (SVD) is
combined with steepest descent (SD) updates along directions rejected by the
SVD, after initial SD steps. Dissociation energies in variational and diffusion
QMC agree well with experiment. The atomic forces agree quantitatively with
potential energy surfaces, demonstrating the accuracy of this force procedure.
The harmonic vibrational frequencies and anharmonicity constants, derived from
the QMC energies and atomic forces, also agree well with experimental values.Comment: 6 pages, 2 figures; updated conten
Post density functional theoretical studies of highly polar semiconductive Pb(TiNi)O solid solutions: The effects of cation arrangement on band gap
We use a combination of conventional density functional theory (DFT) and
post-DFT methods, including the local density approximation plus Hubbard
(LDA+), PBE0, and self-consistent to study the electronic properties of
Ni-substituted PbTiO (Ni-PTO) solid solutions. We find that LDA
calculations yield unreasonable band structures, especially for Ni-PTO solid
solutions that contain an uninterrupted NiO layer. Accurate treatment of
localized states in transition-metal oxides like Ni-PTO requires post-DFT
methods. -site Ni/Ti cation ordering is also investigated. The -site
cation arrangement alters the bonding between Ni and O, and therefore strongly
affects the band gap () of Ni-PTO. We predict that Ni-PTO solid
solutions should have a direct band gap in the visible light energy range, with
polarization similar to the parent PbTiO. This combination of properties
make Ni-PTO solid solutions promising candidate materials for solar energy
conversion devices.Comment: 19 pages, 6 figure
Structural and electronic properties of the metal-metal intramolecular junctions of single-walled carbon nanotubes
Several intramolecular junctions (IMJs) connecting two metallic (11, 8) and
(9, 6) carbon nanotubes along their common axis have been realized by using a
layer-divided technique to the nanotubes and introducing the topological
defects. Atomic structure of each IMJ configuration is optimized with a
combination of density-functional theory (DFT) and the universal force field
(UFF) method, based upon which a four-orbital tight-binding calculation is made
on its electronic properties. Different topological defect structures and their
distributions on the IMJ interfaces have been found, showing decisive effects
on the localized density of states, while the sigma-pi coupling effect is
negligible near Fermi energy (EF). Finally, a new IMJ model has been proposed,
which probably reflects a real atomic structure of the M-M IMJ observed in the
experiment [Science 291, 97 (2001)].Comment: 11 pages and 3 figure
A mixed ultrasoft/normconserved pseudopotential scheme
A variant of the Vanderbilt ultrasoft pseudopotential scheme, where the
normconservation is released for only one or a few angular channels, is
presented. Within this scheme some difficulties of the truly ultrasoft
pseudopotentials are overcome without sacrificing the pseudopotential softness.
i) Ghost states are easily avoided without including semicore shells. ii) The
ultrasoft pseudo-charge-augmentation functions can be made more soft. iii) The
number of nonlocal operators is reduced. The scheme will be most useful for
transition metals, and the feasibility and accuracy of the scheme is
demonstrated for the 4d transition metal rhodium.Comment: 4 pages, 2 figure
Structure and Vibrations of the Vicinal Copper (211) Surface
We report a first principles theoretical study of the surface relaxation and
lattice dynamics of the Cu(211) surface using the plane wave pseudopotential
method. We find large atomic relaxations for the first several atomic layers
near the step edges on this surface, and a substantial step-induced
renormalization of the surface harmonic force constants. We use the results to
study the harmonic fluctuations around the equilibrium structure and find three
new step-derived features in the zone center vibrational spectrum. Comparison
of these results with previous theoretical work and weith experimental studies
using inelastic He scattering are reported.Comment: 6 Pages RevTex, 7 Figures in Postscrip
First-principles extrapolation method for accurate CO adsorption energies on metal surfaces
We show that a simple first-principles correction based on the difference
between the singlet-triplet CO excitation energy values obtained by DFT and
high-level quantum chemistry methods yields accurate CO adsorption properties
on a variety of metal surfaces.
We demonstrate a linear relationship between the CO adsorption energy and the
CO singlet-triplet splitting, similar to the linear dependence of CO adsorption
energy on the energy of the CO 2* orbital found recently {[Kresse {\em et
al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations
underestimate the CO singlet-triplet excitation energy ,
whereas coupled-cluster and CI calculations reproduce the experimental . The dependence of on is used
to extrapolate for the top, bridge and hollow sites for the
(100) and (111) surfaces of Pt, Rh, Pd and Cu to the values that correspond to
the coupled-cluster and CI value. The correction
reproduces experimental adsorption site preference for all cases and obtains
in excellent agreement with experimental results.Comment: Table sent as table1.eps. 3 figure
Ostaci polikloriranih-dibenzodioksina, -dibenzofurana i -bifenila u uzorcima humanog mlijeka sakupljenim u kontinentalnom gradu u Hrvatskoj, Jugoslavija
The levels of several polychlorinated-dibenzodioxins (PCDDs), poly-chlorinated-dibenzofurans (PCDFs) and total polychlorinated-biphenyls (PCBs) were determined in pooled human milk samples. The samples were collected in a continental town of Croatia, Yugoslavia, during the years 1981/82 and 1985. The concentrations of seven PCDDs and nine PCDFs were within the range < 0.2 - 116 ng/kg milk fat; the total PCBs were 0.47 and 0.32 mg/kg milk fat. The levels determined were about the same as those reported for the general population in other countries.Određene su koncentracije nekoliko PCDD i PCDF spojeva te ukupnih PCB spojeva u zajedničkim uzorcima humanog mlijeka. Uzorci su sakupljeni u kontinentalnom gradu Hrvatske, Jugoslavija, tokom 1981/82 i 1985. Koncentracije sedam PCDD spojeva bile su u rasponu < 0,2 - 116 ng/kg mliječne masti; ukupni PCB spojevi bili su 0,47 i 0,32 mg/kg mliječne masti. Koncentracije određivanih spojeva slične su koncentracijama istih spojeva objavljenih za opće populacije ostalih zemalja
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