286 research outputs found
Optical properties of 4 A single-walled carbon nanotubes inside the zeolite channels studied from first principles calculations
The structural, electronic, and optical properties of 4 A single-walled
carbon nanotubes (SWNTs) contained inside the zeolite channels have been
studied based upon the density-functional theory in the local-density
approximation (LDA). Our calculated results indicate that the relaxed
geometrical structures for the smallest SWNTs in the zeolite channels are much
different from those of the ideal isolated SWNTs, producing a great effect on
their physical properties. It is found that all three kinds of 4 A SWNTs can
possibly exist inside the Zeolite channels. Especially, as an example, we have
also studied the coupling effect between the ALPO_4-5 zeolite and the tube
(5,0) inside it, and found that the zeolite has real effects on the electronic
structure and optical properties of the inside (5,0) tube.Comment: 9 pages, 6figure
Quantum interference in deformed carbon nanotube waveguides
Quantum interference (QI) in two types of deformed carbon nanotubes (CNTs),
i.e., axially stretched and AFM tip-deformed CNTs, has been investigated by the
pi-electron only and four-orbital tight-binding (TB) method. It is found that
the rapid conductance oscillation (RCO) period is very sensitive to the applied
strains, and decreases in an inverse proportion to the deformation degree,
which could be used as a powerful experimental tool to detect precisely the
deformation degree of the deformed CNTs. Also, the sigma-pi coupling effect is
found to be negligible under axially stretched strain, while it works on the
transport properties of the tip-deformed CNTs.Comment: 14 pages and 5 figure
The electronic structures and magnetic properties of perovskite ruthenates from constrained orbital hybridization calculations
We introduce a method to analyze the effect of hybridization by shifting
corresponding atomic levels using external potentials. Based on this approach,
we study perovskite ruthenates,\ and unambiguously identify that the covalency
between the \textit{A}-site cation and O ion will modify the Ru-O hybridization
and change the density of state at Fermi level, consequently affect the
magnetic properties significantly. We also study the effect of pressure and
reveal that hydrostatic pressure has a small effect on the Ru-O-Ru bond angle
of SrRuO, while it will decrease the Ru-O length and increase the band
width significantly. Therefore, the magnetic ordering temperature will decrease
monotonically with pressure
Optical rotation of heavy hole spins by non-Abelian geometrical means
A non-Abelian geometric method is proposed for rotating of heavy hole spins
in a singly positive charged quantum dot in Voigt geometry. The key ingredient
is the delay-dependent non-Abelian geometric phase, which is produced by the
nonadiabatic transition between the two degenerate dark states. We demonstrate,
by controlling the pump, the Stokes and the driving fields, that the rotations
about - and -axes with arbitrary angles can be realized with high
fidelity. Fast initialization and heavy hole spin state readout are also
possible.Comment: 7 pages, 6 figure
First principles investigation of transition-metal doped group-IV semiconductors: RY (R=Cr, Mn, Fe; Y=Si, Ge)
A number of transition-metal (TM) doped group-IV semiconductors,
RY (R=Cr, Mn and Fe; Y=Si, Ge), have been studied by the first
principles calculations. The obtained results show that antiferromagnetic (AFM)
order is energetically more favored than ferromagnetic (FM) order in Cr-doped
Ge and Si with =0.03125 and 0.0625. In 6.25% Fe-doped Ge, FM interaction
dominates in all range of the R-R distances while for Fe-doped Ge at 3.125% and
Fe-doped Si at both concentrations of 3.125% and 6.25%, only in a short R-R
range can the FM states exist. In the Mn-doped case, the RKKY-like mechanism
seems to be suitable for the Ge host matrix, while for the Mn-doped Si, the
short-range AFM interaction competes with the long-range FM interaction. The
different origin of the magnetic orders in these diluted magnetic
semiconductors (DMSs) makes the microscopic mechanism of the ferromagnetism in
the DMSs more complex and attractive.Comment: 14 pages, 2 figures, 6 table
Mutations in hepatitis C virus E2 located outside the CD81 binding sites lead to escape from broadly neutralizing antibodies but compromise virus infectivity.
Broadly neutralizing antibodies are commonly present in the sera of patients with chronic hepatitis C virus (HCV) infection. To elucidate possible mechanisms of virus escape from these antibodies, retrovirus particles pseudotyped with HCV glycoproteins (HCVpp) isolated from sequential samples collected over a 26-year period from a chronically infected patient, H, were used to characterize the neutralization potential and binding affinity of a panel of anti-HCV E2 human monoclonal antibodies (HMAbs). Moreover, AP33, a neutralizing murine monoclonal antibody (MAb) to a linear epitope in E2, was also tested against selected variants. The HMAbs used were previously shown to broadly neutralize HCV and to recognize a cluster of highly immunogenic overlapping epitopes, designated domain B, containing residues that are also critical for binding of viral E2 glycoprotein to CD81, a receptor essential for virus entry. Escape variants were observed at different time points with some of the HMAbs. Other HMAbs neutralized all variants except for the isolate 02.E10, obtained in 2002, which was also resistant to MAb AP33. The 02.E10 HCVpp that have reduced binding affinities for all antibodies and for CD81 also showed reduced infectivity. Comparison of the 02.E10 nucleotide sequence with that of the strain H-derived consensus variant, H77c, revealed the former to have two mutations in E2, S501N and V506A, located outside the known CD81 binding sites. Substitution A506V in 02.E10 HCVpp restored binding to CD81, but its antibody neutralization sensitivity was only partially restored. Double substitutions comprising N501S and A506V synergistically restored 02.E10 HCVpp infectivity. Other mutations that are not part of the antibody binding epitope in the context of N501S and A506V were able to completely restore neutralization sensitivity. These findings showed that some nonlinear overlapping epitopes are more essential than others for viral fitness and consequently are more invariant during earlier years of chronic infection. Further, the ability of the 02.E10 consensus variant to escape neutralization by the tested antibodies could be a new mechanism of virus escape from immune containment. Mutations that are outside receptor binding sites resulted in structural changes leading to complete escape from domain B neutralizing antibodies, while simultaneously compromising viral fitness by reducing binding to CD81
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
Electronic Structure and Optical Properties of the Co-doped Anatase TiO Studied from First Principles
The Co-doped anatase TiO, a recently discovered room-temperature
ferromagnetic insulator, has been studied by the first-principles calculations
in the pseudo-potential plane-wave formalism within the local-spin-density
approximation (LSDA), supplemented by the full-potential linear augmented plane
wave (FP-LAPW) method. Emphasis is placed on the dependence of its electronic
structures and linear optical properties on the Co-doping concentration and
oxygen vacancy in the system in order to pursue the origin of its
ferromagnetism. In the case of substitutional doping of Co for Ti, our
calculated results are well consistent with the experimental data, showing that
Co is in its low spin state. Also, it is shown that the oxygen vacancy enhances
the ferromagnetism and has larger effect on both the electronic structure and
optical properties than the Co-doping concentration only.Comment: 12 pages, 4 figure
Fenitrothion: toxicokinetics and toxicologic evaluation in human volunteers.
An unblinded crossover study of fenitrothion 0.18 mg/kg/day [36 times the acceptable daily intake (ADI)] and 0.36 mg/kg/day (72 X ADI) administered as two daily divided doses for 4 days in 12 human volunteers was designed and undertaken after results from a pilot study. On days 1 and 4, blood and urine samples were collected for analysis of fenitrothion and its major metabolites, as well as plasma and red blood cell cholinesterase activities, and biochemistry and hematology examination. Pharmacokinetic parameters could only be determined at the higher dosage, as there were insufficient measurable fenitrothion blood levels at the lower dosage and the fenitrooxone metabolite could not be measured. There was a wide range of interindividual variability in blood levels, with peak levels achieved between 1 and 4 hr and a half-life for fenitrothion of 0.8-4.5 hr. Although based on the half-life, steady-state levels should have been achieved; the area under the curve (AUC)(0-12 hr) to AUC(0-(infinity) )ratio of 1:3 suggested accumulation of fenitrothion. There was no significant change in plasma or red blood cell cholinesterase activity with repeated dosing at either dosage level of fenitrothion, and there were no significant abnormalities detected on biochemical or hematologic monitoring
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