398,807 research outputs found
Dirac point metamorphosis from third-neighbor couplings in graphene
We study the band structure and the density of states of graphene in the
presence of a next-to-nearest-neighbor coupling (N2) and a
third-nearest-neighbor coupling (N3). We show that for values of N3 larger or
equal to 1/3 of the value of the nearest-neighbor hopping (NN), extra Dirac
points appear in the spectrum. If N3 is exactly equal to 1/3 NN, the new Dirac
points are localized at the M points of the Brillouin zone and are hybrid: the
electrons have a linear dispersion along the GammaM direction and a quadratic
dispersion along the perpendicular direction MK. For larger values of N3 the
new points have a linear dispersion, and are situated along the MK line. For a
value of N3 equal to 1/2 NN, these points merge with the Dirac cones at the K
points, yielding a gapless quadratic dispersion around K, while for larger
values each quadratic point at K splits again into four Dirac points. The
effects of changing the N2 coupling are not so dramatic. We calculate the
density of states and we show that increasing the N3 coupling lowers the energy
of the Van Hove singularities, and when N3 is larger than 1/3 NN the Van Hove
singularities split in two, giving rise to extra singularities at low energies.Comment: 13 pages, 10 figure
Compound oxidized styrylphosphine
A process is described for preparing flame resistant, nontoxic vinyl polymers which contain phosphazene groups and which do not emit any toxic or corrosive products when they are oxidatively degraded. Homopolymers, copolymers, and terpolymers of a styrene based monomer are prepared by polymerizing at least one oxidized styrylphosphine monomer from a group of organic azides, or by polymerizing p-diphenylphosphinestyrene and then oxidizing that monomer with an organoazide from the group of (C6H5)2P(O)N3, (C6H5O)2P(O)N3, (C6H5)2C3N3(N3), and C6H5C3N3(N3)2. Copolymers can also be prepared by copolymerizing styrene with at least one oxidized styrylphosphine monomer
Effect of Intensity on Prevalence of N3 Potential in Ears with Severe to Profound Hearing Loss
Objective of the study: To look for the presence of N3 potential at two different intensities in children and in adults. Method: A total of 260 ears with severe to profound hearing loss were studied from the participants in the age range of 1 to 50 years, with 170 subjects in the age group below 10 years and remaining 90 subjects of more than 10 years. Auditory brainstem response (ABR) was recorded at two intensities, 90 and 99dBnHL, to look for the presence of N3 potential. Result: N3 potential was observed in 30% of the total ears taken in the study at 90dBnHL and 38.8% at 99dBnHL. Presence of N3 potential in children was 45%, which was higher than the age group of above 10 years. When the intensity was increased there was an increase in amplitude and a reduction in latency with better wave morphology. Conclusion: It is better to use higher intensity for the identification of the N3 potential while doing ABR and thus with the single recording, auditory assessment as well as saccular assessment can be done
Synthesis, characterisation and photochemistry of PtIV pyridyl azido acetato complexes
PtII azido complexes [Pt(bpy)(N3)2] (1), [Pt(phen)(N3)2] (2) and trans-[Pt(N3)2(py)2] (3) incorporating the bidentate diimine ligands 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) or the monodentate pyridine (py) respectively, have been synthesised from their chlorido precursors and characterised by X-ray crystallography; complex 3 shows significant deviation from square-planar geometry (N3–Pt–N3 angle 146.7°) as a result of steric congestion at the Pt centre. The novel PtIV complexes trans, cis-[Pt(bpy)(OAc)2(N3)2] (4), trans, cis-[Pt(phen)(OAc)2(N3)2] (5), trans, trans, trans-[Pt(OAc)2(N3)2(py)2] (6), were obtained from 1–3via oxidation with H2O2 in acetic acid followed by reaction of the intermediate with acetic anhydride. Complexes 4–6 exhibit interesting structural and photochemical properties that were studied by X-ray, NMR and UV-vis spectroscopy and TD-DFT (time-dependent density functional theory). These PtIV complexes exhibit greater absorption at longer wavelengths (ε = 9756 M−1 cm−1 at 315 nm for 4; ε = 796 M−1 cm−1 at 352 nm for 5; ε = 16900 M−1 cm−1 at 307 nm for 6, in aqueous solution) than previously reported PtIV azide complexes, due to the presence of aromatic amines, and 4–6 undergo photoactivation with both UVA (365 nm) and visible green light (514 nm). The UV-vis spectra of complexes 4–6 were calculated using TD-DFT; the nature of the transitions contributing to the UV-vis bands provide insight into the mechanism of production of the observed photoproducts. The UV-vis spectra of 1–3 were also simulated by computational methods and comparison between PtII and PtIV electronic and structural properties allowed further elucidation of the photochemistry of 4–6
CP Violation and the CKM Matrix: Assessing the Impact of the Asymmetric B Factories
We update the profile of the CKM matrix. The apex (rhobar,etabar) of the
Unitarity Triangle is given by means of a global fit. We propose to include
therein sin2alpha from the CP-violating asymmetries in B0->rho+rho-, using
isospin to discriminate the penguin contribution. The constraint from
epsilon'/epsilon is briefly discussed. We study the impact from the measurement
of the rare decay K+->pi+nunu-bar, and from a future observation of
KL->pi0nunubar. The B system is investigated in detail, beginning with
2beta+gamma and gamma from B0->D(*)+-pi-+ and B+->D(*)0K+. A significant part
of this paper is dedicated to B decays into pipi, Kpi, rhopi and rhorho.
Various phenomenological and theoretical approaches are studied. Within QCD
Factorization we find a remarkable agreement of the pipi and Kpi data with the
other UT constraints. A fit of QCD FA to all pipi and Kpi data leads to precise
predictions of the related observables. We analyze separately the B->Kpi
decays, and in particular the impact of electroweak penguins in response to
recent phenomenological discussions. We find no significant constraint on
electroweak nor hadronic parameters. We do not observe any unambiguous sign of
New Physics, whereas there is some evidence for potentially large rescattering
effects. Finally we use a model-independent description of a large class of New
Physics effects in both BBbar mixing and B decays, namely in the b->d and b->s
gluonic penguin amplitudes, to perform a new numerical analysis. Significant
non-standard corrections cannot be excluded yet, however standard solutions are
favored in most cases.Comment: Final version accepted for publication in EPJ C, updated results and
plots are available at: http://ckmfitter.in2p3.fr or
http://www.slac.stanford.edu/xorg/ckmfitter/ (mirror
Rarita-Schwinger-Weyl semimetal in Jeff=3/2 electron systems
We propose a relativistic Jeff=3/2 semimetal with 4d1 or 5d1 electrons on a
cubic lattice when the strong spin-orbital coupling takes over the Hunds'
coupling. A relativistic spinor with spin 3/2 is historically called
Rarita-Schwinger spinor. In the massless case, the right- and left-handed
chiral degrees of freedom of the Rarita-Schwinger spinors are independent. In
the lattice model that we propose, the right- and left- handed gapless points
in Brillouin zone are separated. We call this linearly dispersed semimetal
Rarita-Schwinger-Weyl semimetal, similar to Weyl semimetal for spin 1/2
systems. There is a network of gapless Fermi arcs in the surface Brillouin zone
if n1+n2+n3 is even for the normal vector (n1,n2,n3) of the surface while the
surface is insulator if n1+n2+n3 is odd.Comment: 5 pages, 4 figure
Orthogonal Linear Combinations of Gaussian Type Orbitals
The set of Gaussian Type Orbitals g(n1,n2,n3) of order (n+1)(n+2)/2, of
common n=n1+n2+n3<=7, common center and exponential, is customized to define a
set of 2n+1 linear combinations t(n,m) (-n<=m<=n) such that each t(n,m) depends
on the azimuthal and polar angle of the spherical coordinate system like the
real or imaginary part of the associated Spherical Harmonic. (Results cover
both Hermite and Cartesian Gaussian Type Orbitals.) Overlap, kinetic energy and
Coulomb energy matrix elements are presented for generalized basis functions of
the type r^s*t(n,m) (s=0,2,4,...). In addition, normalization integrals int
|g(n1,n2,n3)|d^3r are calculated up to n=7 and normalization integrals int
|r^s*t(n,m)|d^3r up to n=5.Comment: 13 pages, no figures, REVTeX4. Corrected eqs. (23) and (C4
Spin-transfer in diffusive ferromagnet-normal metal systems with spin-flip scattering
The spin-transfer in biased disordered ferromagnet (F) - normal metal (N)
systems is calculated by the diffusion equation. For F1-N2-F2 and
N1-F1-N2-F2-N3 spin valves, the effect of spin-flip processes in the normal
metal and ferromagnet parts are obtained analytically. Spin-flip in the center
metal N2 reduces the spin-transfer, whereas spin-flip in the outer normal
metals N1 and N3 can increase it by effectively enhancing the spin polarization
of the device.Comment: 9 pages, 3 figure
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