149,446 research outputs found
Efficient iterative method for solving the Dirac-Kohn-Sham density functional theory
We present for the first time an efficient iterative method to directly solve
the four-component Dirac-Kohn-Sham (DKS) density functional theory. Due to the
existence of the negative energy continuum in the DKS operator, the existing
iterative techniques for solving the Kohn-Sham systems cannot be efficiently
applied to solve the DKS systems. The key component of our method is a novel
filtering step (F) which acts as a preconditioner in the framework of the
locally optimal block preconditioned conjugate gradient (LOBPCG) method. The
resulting method, dubbed the LOBPCG-F method, is able to compute the desired
eigenvalues and eigenvectors in the positive energy band without computing any
state in the negative energy band. The LOBPCG-F method introduces mild extra
cost compared to the standard LOBPCG method and can be easily implemented. We
demonstrate our method in the pseudopotential framework with a planewave basis
set which naturally satisfies the kinetic balance prescription. Numerical
results for Pt, Au, TlF, and BiSe indicate that the
LOBPCG-F method is a robust and efficient method for investigating the
relativistic effect in systems containing heavy elements.Comment: 31 pages, 5 figure
Telomere length as a predictor of response to Pioglitazone in patients with unremitted depression: a preliminary study.
We studied peripheral leukocyte telomere length (LTL) as a predictor of antidepressant response to PPAR-γ agonist in patients with unremitted depression. In addition we examined correlation between LTL and the insulin resistance (IR) status in these subjects. Forty-two medically stable men and women ages 23-71 with non-remitted depression participated in double-blind placebo-controlled add-on of Pioglitazone to treatment-as-usual. Oral glucose tolerance tests were administered at baseline and at 12 weeks. Diagnostic evaluation of psychiatric disorders was performed at baseline and mood severity was followed weekly throughout the duration of the trial. At baseline, no differences in LTL were detected by depression severity, duration or chronicity. LTL was also not significantly different between insulin-resistant and insulin-sensitive subjects at baseline. Subjects with longer telomeres exhibited greater declines in depression severity in the active arm, but not in a placebo arm, P=0.005, r=-0.63, 95% confidence interval (95% CI)=(-0.84,-0.21). In addition, LTL predicted improvement in insulin sensitivity in the group overall and did not differ between intervention arms, P=0.036, r=-0.44, 95% CI=(-0.74,0.02) for the active arm, and P=0.026, r=-0.50, 95% CI=(-0.78,-0.03) for the placebo arm. LTL may emerge as a viable predictor of antidepressant response. An association between insulin sensitization and LTL regardless of the baseline IR status points to potential role of LTL as a non-specific moderator of metabolic improvement in these patients
Preventing the Unnecessary Losses of Alzheimer\u27s Disease
Educational Objectives
1. To state the importance of early detection and diagnosis of Alzheimer\u27s disease.
2. To describe common concerns of people in the early stages of Alzheimer\u27s disease.
3. To describe interventions to help people who have recently been diagnosed with Alzheimer\u27s disease or other dementias
Saltless solar pond
A solar pond adapted for efficiently trapping and storing radiant solar energy without the use of a salt concentration gradient in the pond is disclosed. A body of water which may be fresh, saline, relatively clear or turbid, is substantially covered by a plurality of floating honeycomb panels. The honeycomb panels are made of a material such as glass which is pervious to short wave solar radiation but impervious to infrared radiation. Each honeycomb panel includes a multitude of honeycomb cells. The honeycomb panels are divided into the elongated honeycomb cells by a multitude of intermediate plates disposed between a bottom plate and top plate of the panel. The solar pond is well suited for providing hot water of approximately 85 to 90 C temperature for direct heating applications, and for electrical power generation
Magnetotunneling in a Two-Dimensional Electron-Hole System Near Equilibrium
We have measured the zero-bias differential tunneling conductance of
InAs/AlSb/GaS b/AlSb/InAs heterostructures at low temperatures (1.7K < T < 60K)
and unde r a magnetic field at various angles with the heterostructure's
interfaces. Shubni kov-de Haas oscillations in the magnetoconductance reveal
the two-dimensional (2D) character of the electrons accumulated at the InAs
interfaces and yield their num ber in each of them. The temperature dependence
of the oscillations suggests the f ormation of a field-induced energy gap at
the Fermi level, similar to that observe d before in simpler 2D-2D tunneling
systems. A calculation of the magnetoconductan ce that considers different 2D
densities in the two InAs electrodes agrees with th e main observations, but
fails to explain features that might be related to the pr esence of 2D holes in
the GaSb region.Comment: 4 papes, 3 eps figures. Submit to Phys. Rev.
Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins
Several pyridine-like ligands were found to improve Pd(OAc)2-catalyzed allylic oxidation of allylbenzene to cinnamyl acetate by p-benzoquinone in acetic acid. The best ligand examined, bipyrimidine, was used to identify the catalyst precursor for this system, (bipyrimidine)Pd(OAc)2, which was fully characterized. Mechanistic studies suggest the reaction takes place through disproportionation of (bipyrimidine)Pd(OAc)2 to form a bipyrimidine-bridged dimer, which reacts with olefin to form a Pd^II-olefin adduct, followed by allylic C–H activation to produce (η^3-allyl)Pd^II species. The (η^3-allyl)Pd^II intermediate undergoes a reversible acetate attack to generate a Pd^0-(allyl acetate) adduct, which subsequently reacts with p-benzoquinone to release allyl acetate and regenerate (bipyrimidine)Pd(OAc)2. No KIE is observed for the competition experiment between allylbenzene-d0 and allylbenzene-d5 (CD2=CDCD2C6H5), suggesting that allylic C–H activation is not rate-determining. Catalytic allylic acetoxylations of other terminal olefins as well as cyclohexene were also effected by (bipyrimidine)Pd(OAc)2
Prediction of a new potential high-pressure structure of FeSiO
We predict a new candidate high-temperature high-pressure structure of
FeSiO with space-group symmetry Cmmm by applying an evolutionary algorithm
within DFT+U that we call post-perovskite II (PPv-II). An exhaustive search
found no other competitive candidate structures with ABO composition. We
compared the X-ray diffraction (XRD) pattern of FeSiO PPv-II with
experimental results of the recently reported H-phase of (Fe,Mg)SiO. The
intensities and positions of two main X-ray diffraction peaks of PPv-II
FeSiO compare well with those of the H-phase. We also calculated the static
equation of state, the enthalpy and the bulk modulus of the PPv-II phase and
compared it with those of perovskite (Pv) and post-perovskite (PPv) phases of
FeSiO. According to the static DFT+U computations the PPv-II phase of
FeSiO is less stable than Pv and PPv phases under lower mantle pressure
conditions at 0 K and has a higher volume. PPv-II may be entropically
stabilized, and may be a stable phase in Earths lower mantle, coexisting
with -PbO (Columbite-structured) silica and perovskite, or with
magnesiowustite or ferropericlase, depending on bulk composition
Symplectic reduction and topology for applications in classical molecular dynamics
This paper aims to introduce readers with backgrounds in classical molecular dynamics to some ideas in geometric mechanics that may be useful. This is done through some simple but specific examples: (i) the separation of the rotational and internal energies in an arbitrarily floppy N-body system and (ii) the reduction of the phase space accompanying the change from the laboratory coordinate system to the center of mass coordinate system relevant to molecular collision dynamics. For the case of two-body molecular systems constrained to a plane, symplectic reduction is employed to demonstrate explicitly the separation of translational, rotational, and internal energies and the corresponding reductions of the phase space describing the dynamics for Hamiltonian systems with symmetry. Further, by examining the topology of the energy-momentum map, a unified treatment is presented of the reduction results for the description of (i) the classical dynamics of rotating and vibrating diatomic molecules, which correspond to bound trajectories and (ii) the classical dynamics of atom–atom collisions, which correspond to scattering trajectories. This provides a framework for the treatment of the dynamics of larger N-body systems, including the dynamics of larger rotating and vibrating polyatomic molecular systems and the dynamics of molecule–molecule collisions
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