5,199 research outputs found
Nernst and Seebeck effect in a graphene nanoribbon
The thermoelectric power, including the Nernst and Seebeck effects, in
graphene nanoribbon is studied. By using the non-equilibrium Green function
combining with the tight-binding Hamiltonian, the Nernst and Seebeck
coefficients are obtained. Due to the electron-hole symmetry, the Nernst
coefficient is an even function of the Fermi energy while the Seebeck
coefficient is an odd function regardless of the magnetic field. In the
presence of a strong magnetic field, the Nernst and Seebeck coefficients are
almost independent of the chirality and width of the nanoribbon, and they show
peaks when the Fermi energy crosses the Landau levels. The height of -th
(excluding ) peak is for the Nernst effect and is
for the Seebeck effect. For the zeroth peak, it is abnormal with height
for the Nernst effect and the peak disappears for the Seebeck effect.
When the magnetic field is turned off, however, the Nernst effect is absent and
only Seebeck effect exists. In this case, the Seebeck coefficient strongly
depends on the chirality of the nanoribbon. The peaks are equidistant for the
nanoribbons with zigzag edge but are irregularly distributed for the armchair
edge. In particular, for the insulating armchair ribbon, the Seebeck
coefficient can be very large near the Dirac point. When the magnetic field
varies from zero to large values, the differences among the Seebeck
coefficients for different chiral ribbons gradually vanish and the nonzero
value of Nernst coefficient appears first near the Dirac point then gradually
extents to the whole energy region.Comment: 8 pages, 7 figure
The double charm decays of B Mesons in the mSUGRA model
Based on the low energy effective Hamiltonian with naive factorization, we
calculate the branching ratios(BRs) and CP asymmetries (CPAs) for the twenty
three double charm decays in both the
standard model (SM) and the minimal supergravity (mSUGRA) model. Within the
considered parameter space, we find that (a) the theoretical predictions for
the BRs, CPAs and the polarization fractions in the SM and the mSUGRA model are
all consistent with the currently available data within errors;
(b) For all the considered decays, the supersymmetric contributions in the
mSUGRA model are very small, less than numerically. It may be difficult
to observe so small SUSY contributions even at LHC.Comment: 15 pages, 5tables, no figure
Photoproduction of the charged top-pions at the LHeC
The top triangle moose model, which can be seen as the deconstructed
version of the topcolor-assisted technicolor () model, predicts the
existence of the charged top-pions in low energy spectrum. In
the context of this model, we consider photoproduction of via
the subprocesses and at the large hadron-electron collider (), in which high
energy photon beams are generated by using the Compton backscatting method. We
find that, as long as the charged top-pions are not too heavy, they can be
abundantly produced via collision.Comment: 16 pages, 5 figure
Growth factor in f(T) gravity
We derive the evolution equation of growth factor for the matter over-dense
perturbation in gravity. For instance, we investigate its behavior in
power law model at small redshift and compare it to the prediction of
CDM and dark energy with the same equation of state in the framework
of Einstein general relativity. We find that the perturbation in gravity
grows slower than that in Einstein general relativity if \p f/\p T>0 due to
the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added,
accepted by JCA
Organoaluminium complexes derived from Anilines or Schiff bases for ring opening polymerization of epsilon-caprolactone, delta-valerolactone and rac-lactide
Reaction of R¹R²CHN=CH(3,5-tBu₂C₆H₂-OH-2) (R¹ = R² = Me L¹H; R¹ = Me, R² = Ph L²H; R¹ = R2 = Ph L³H) with one equivalent of R³3Al (R³ = Me, Et) afforded [(L¹-³)AlR³₂] (L¹, R³ = Me 1, R³ = Et 2; L², R³ = Me 3, R³ = Et 4; L³ R³ = Me 5, R³ = Et 6); complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2/-diphenylglycine afforded either 5 or a by-product [Ph₂NCH₂(3,5-tBu₂C₆H₂-O-2)AlMe₂] (7). The known Schiff base complex [2-Ph₂PC₆H4CH₂(3,5-tBu₂C₃H₂-O-2)AlMe₂] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH₂,2-PPh₂C₆H4 with Me3Al, namely {Ph₂PC₆H4N[(Me₂Al)₂mu-Me](mu-Me₂Al)} (9) were also isolated. For structural and catalytic comparisons, complexes resulting from interaction of Me₃Al with diphenylamine or benzhydrylamine, namely {Ph₂N[(Me₂Al)2mu-Me]} (10) and [Ph₂CHNH(mu-Me₂Al)]₂·MeCN (11), were prepared. The molecular structures of the Schiff pro-ligands derived from Ph₂CHNH₂ and 2,2/-Ph2C(CO₂H)(NH₂), together with complexes 5, 7 and 9 - 11·MeCN were determined. All complexes have been screened for their ability to ring opening polymerization (ROP) epsilon-caprolactone, delta-valerolactone or rac-lactide, in the presence of benzyl alcohol, with or without solvent present. The co-polymerization of epsilon-caprolactone with rac-lactide has also been studied
Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2
75As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) measurements are performed on CaFe2As2 under pressure. At P =
4.7 and 10.8 kbar, the temperature dependences of nuclear-spin-lattice
relaxation rate (1/T1) measured in the tetragonal phase show no coherence peak
just below Tc(P) and decrease with decreasing temperature. The
superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple
gaps at P = 10.8 kbar. We find that the superconductivity appears near a
quantum critical point under pressures in the range 4.7 kbar < P < 10.8 kbar.
Both electron correlation and superconductivity disappear in the collapsed
tetragonal phase. A systematic study under pressure indicates that electron
correlations play a vital role in forming Cooper pairs in this compound.Comment: 5pages, 5figure
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