4,980 research outputs found
Three-way electrical gating characteristics of metallic Y-junction carbon nanotubes
Y-junction based carbon nanotube (CNT) transistors exhibit interesting switching behaviors, and have the structural advantage that the electrical gate for current modulation can be formed by any of the three constituent branches. In this letter, we report on the gating characteristics of metallic Y-CNT morphologies. By measuring the output conductance and transconductance we conclude that the efficiency and gain depend on the branch diameter and is electric field controlled. Based on these principles, we propose a design for a Y-junction based CNT switching device, with tunable electrical properties
Semileptonic Hyperon Decays and CKM Unitarity
Using a technique that is not subject to first-order SU(3) symmetry breaking
effects, we determine the element of the CKM matrix from data on
semileptonic hyperon decays. We obtain =0.2250(27). This value is of
similar precision to the one derived from , but higher and in better
agreement with the unitarity requirement, .Comment: 3 pages, 1 tabl
Gaugino Condensation with S-Duality and Field-Theoretical Threshold Corrections
We study gaugino condensation in the presence of an intermediate mass scale
in the hidden sector. S-duality is imposed as an approximate symmetry of the
effective supergravity theory. Furthermore, we include in the K\"ahler
potential the renormalization of the gauge coupling and the one-loop threshold
corrections at the intermediate scale. It is shown that confinement is indeed
achieved. Furthermore, a new running behaviour of the dilaton arises which we
attribute to S-duality. We also discuss the effects of the intermediate scale,
and possible phenomenological implications of this model.Comment: 19 pages, LaTeX, 3 postscript figures include
The Holographic Dual of 2+1 Dimensional QFTs with N=1 SUSY and Massive Fundamental Flavours
The Maldacena Nastase solution is generalised to include massive fundamental
matter through the addition of a flavour profile. This gives a holographic dual
to N=1 SYM-CS with massive fundamental matter with a singularity free IR. We
study this solution in some detail confirming confinement and asymptotic
freedom. A recently proposed solution generating technique is then applied
which results in a new type-IIA supergravity solution. In a certain limit the
geometry of this solution is asymptotically AdS_4X Y, where Y is the metric at
the base of the Bryant-Salamon G_2 cone, which has topology S^3XS^3.Comment: 31 pages plus appendices, 6 figures. v3: Typos corrected, version to
appear in JHE
1/N_c Corrections to the Hadronic Matrix Elements of Q_6 and Q_8 in K --> pi pi Decays
We calculate long-distance contributions to the amplitudes A(K^0 --> pi pi,
I) induced by the gluon and the electroweak penguin operators Q_6 and Q_8,
respectively. We use the 1/N_c expansion within the effective chiral lagrangian
for pseudoscalar mesons. In addition, we adopt a modified prescription for the
identification of meson momenta in the chiral loop corrections in order to
achieve a consistent matching to the short-distance part. Our approach leads to
an explicit classification of the loop diagrams into non-factorizable and
factorizable, the scale dependence of the latter being absorbed in the
low-energy coefficients of the effective theory. Along these lines we calculate
the one-loop corrections to the O(p^0) term in the chiral expansion of both
operators. In the numerical results, we obtain moderate corrections to
B_6^(1/2) and a substantial reduction of B_8^(3/2).Comment: 32 pages, LaTeX, 8 eps figures. One reference added, to appear in
Phys. Rev.
Inflation and flat directions in modular invariant superstring effective theories
The potential during inflation must be very flat in, at least, the direction
of the inflaton. In renormalizable global supersymmetry, flat directions are
ubiquitous, but they are not preserved in a generic supergravity theory. It is
known that at least some of them are preserved in no-scale supergravity, and
simple generalizations of it. We here study a more realistic generalization,
based on string-derived supergravity, using the linear supermultiplet formalism
for the dilaton. We consider a general class of hybrid inflation models, where
a Fayet-Illiopoulos term drives some fields to large values. The potential
is dominated by the term, but flatness is preserved in some directions.
This allows inflation, with the dilaton stabilized in its domain of attraction,
and some moduli stabilized at their vacuum values. Another modulus may be the
inflaton.Comment: 19 pages, REVTEX, further typos, refs fixe
``Non-factorizable'' terms in hadronic B-meson weak decays
The branching ratios for the hadronic B-meson weak decays B -> J/psi K and B
-> D pi are used to extract the size of the ``non-factorizable'' terms in the
decay amplitudes. It is pointed out that the solutions are not uniquely
determined. In the B -> J/psi K case, a 2-fold ambiguity can be removed by
analyzing the contribution of this decay to B -> K l+ l-. In the B -> D pi
case, a 4-fold ambiguity can only be removed if the ``non-factorizable'' terms
are assumed to be a small correction to the vacuum insertion result.Comment: 15 pages (and 1 figure, available upon request), TRIUMF report no.
TRI-PP-94-7
Reactivity of Gold Hydrides: O2 Insertion into the Au–H Bond
Dioxygen reacts with the gold(I) hydride (IPr)AuH under insertion to give the hydroperoxide, (IPr)AuOOH, a long-postulated reaction in gold catalysis and the first demonstration of O2 activation by Au-H in a well-defined system. Subsequent condensation gave the peroxide (IPr)Au-OO-Au(IPr) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The reaction kinetics are reported, as well as the reactivity of Au(I) hydrides with radical scavengers
Causes of regional change—land cover
Anthropogenic land-cover change (ALCC) is one of the few climate forcings for which the net direction of the climate response over the last two centuries is still not known. The uncertainty is due to the often counteracting temperature responses to the many biogeophysical effects and to the biogeochemical versus biogeophysical effects. Palaeoecological studies show that the major transformation of the landscape by anthropogenic activities in the southern zone of the Baltic Sea basin occurred between 6000 and 3000/2500 cal year BP. The only modelling study of the biogeophysical effects of past ALCCs on regional climate in north-western Europe suggests that deforestation between 6000 and 200 cal year BP may have caused significant change in winter and summer temperature. There is no indication that deforestation in the Baltic Sea area since AD 1850 would have been a major cause of the recent climate warming in the region through a positive biogeochemical feedback. Several model studies suggest that boreal reforestation might not be an effective climate warming mitigation tool as it might lead to increased warming through biogeophysical processes
Weak radiative hyperon decays, Hara's theorem and the diquark
Weak radiative hyperon decays are discussed in the diquark-level approach. It
is pointed out that in the general diquark formalism one may reproduce the
experimentally suggested pattern of asymmetries, while maintaining Hara's
theorem in the SU(3) limit. At present, however, no detailed quark-based model
of parity-violating diquark-photon coupling exists that would have the
necessary properties.Comment: 10 pages, LaTe
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