633 research outputs found
Permittivity enhancement of aluminum oxide thin films with the addition of silver nanoparticles
doi:10.1063/1.2425010Multilayer reactive electron-beam evaporation of thin aluminum oxide layers with embedded silver nanoparticles (Ag-nps) has been used to create a dielectric thin film with an enhanced permittivity. The results show a frequency dependent increase of the dielectric constant κ. Overall stack κ of the control sample was found to be 7.7-7.4 in the 1 kHz-1 MHz range. This is in comparison with κ = 16.7-13.0 over the same frequency range in the sample with Ag-nps. Capacitance-voltage and conductance-voltage measurements indicate the presence of charge capture resulting from the Ag-nps. The authors attribute this dielectric constant enhancement to dipole and space charge polarization mechanisms.The authors thank M. Othman for ellipsometry measurements. They are also grateful for the funding provided by the National Science Foundation Grant No. ECS0223
Transport properties of one-dimensional Kronig-Penney models with correlated disorder
Transport properties of one-dimensional Kronig-Penney models with binary
correlated disorder are analyzed using an approach based on classical
Hamiltonian maps. In this method, extended states correspond to bound
trajectories in the phase space of a parametrically excited linear oscillator,
while the on site-potential of the original model is transformed to an external
force. We show that in this representation the two probe conductance takes a
simple geometrical form in terms of evolution areas in phase-space. We also
analyze the case of a general N-mer model.Comment: 16 pages in Latex, 12 Postscript figures include
Formulation, Interpretation and Application of non-Commutative Quantum Mechanics
In analogy with conventional quantum mechanics, non-commutative quantum
mechanics is formulated as a quantum system on the Hilbert space of
Hilbert-Schmidt operators acting on non-commutative configuration space. It is
argued that the standard quantum mechanical interpretation based on Positive
Operator Valued Measures, provides a sufficient framework for the consistent
interpretation of this quantum system. The implications of this formalism for
rotational and time reversal symmetry are discussed. The formalism is applied
to the free particle and harmonic oscillator in two dimensions and the physical
signatures of non commutativity are identified.Comment: 11 page
One-loop effects in a self-dual planar noncommutative theory
We study the UV properties, and derive the explicit form of the one-loop
effective action, for a noncommutative complex scalar field theory in 2+1
dimensions with a Grosse-Wulkenhaar term, at the self-dual point. We also
consider quantum effects around non-trivial minima of the classical action
which appear when the potential allows for the spontaneous breaking of the U(1)
symmetry. For those solutions, we show that the one-loop correction to the
vacuum energy is a function of a special combination of the amplitude of the
classical solution and the coupling constant.Comment: Version to appear in JHE
Hawking radiation, W-infinity algebra and trace anomalies
We apply the "trace anomaly method" to the calculation of moments of the
Hawking radiation of a Schwarzschild black hole. We show that they can be
explained as the fluxes of chiral currents forming a W-infinity algebra. Then
we construct the covariant version of these currents and verify that up to
order 6 they are not affected by any trace anomaly. Using cohomological methods
we show that actually, for the fourth order current, no trace anomalies can
exist. The results reported here are strictly valid in two dimensions.Comment: 22 pages, typos correcte
Outcome of pterygium surgery: analysis over 14 years
Aim: To report the outcome of pterygium surgery performed at a tertiary eye care centre in South India. Methods: Retrospective analysis of medical records of 920 patients (989 eyes) with primary and recurrent pterygia operated between January 1988 and December 2001. The demographic variables, surgical technique (bare sclera, primary closure, amniotic membrane transplantation (AMT), conjunctival autograft (CAG), conjunctival-limbal autograft (CLAG), or surgical adjuvants), recurrences and postoperative complications were analysed. Results: A total of 496 (53.9%) were male and 69 (7.5%) had bilateral pterygia. Bare sclera technique was performed in 267 (27.0%) eyes, primary conjunctival closure in 32 (3.2%), AMG in 123 (12.4%), CAG in 429 (43.4%), and CLAG in 70 (7.1%). Adjuvant mitomycin C was used in 44 (4.4%) cases. The mean duration of follow-up was 8.917.0 and 5.98.8 months for unilateral primary and recurrent pterygia, respectively. The overall recurrence rate was 178 (18.0%). Following primary and recurrent unilateral pterygium excision respectively, recurrences were noted in 46 (19.4%) and 1 (33.3%) eyes after bare sclera technique, five (16.7%) and 0 after primary closure, 28 (26.7%) and 0 with AMG, 42 (12.2%) and five (31.3%) with CAG, and nine (17.3%) and two (40%) with CLAG. Recurrences were significantly more in males with primary (23.3 vs10.7%, P<0.0001) and recurrent (26.7 vs0%, P=0.034) pterygia, and in those below 40 years (25.2 vs14.8%, P=0.003). Conclusion: CAG appears to be an effective modality for primary and recurrent pterygia. Males and patients below 40 years face greater risk of recurrence. Bare sclera technique has an unacceptably high recurrence. Prospective studies comparing CAG, CLAG, and AMG for primary and recurrent pterygia are needed
Noncommutativity In The Mechanics Of A Free Massless Relativistic Particle
We show the existence of a noncommutative spacetime structure in the context
of a complete discussion on the underlying spacetime symmetries for the
physical system of a free massless relativistic particle. The above spacetime
symmetry transformations are discussed for the first-order Lagrangian of the
system where the transformations on the coordinates, velocities and momenta
play very important roles. We discuss the dynamics of this system in a
systematic manner by exploiting the symplectic structures associated with the
four dimensional (non-)commutative cotangent (i.e. momentum phase) space
corresponding to a two dimensional (non-)commutative configuration (i.e.
target) space. A simple connection of the above noncommutativity (NC) is
established with the NC associated with the subject of quantum groups where
transformations play a decisive role.Comment: LaTeX file, 19 page
Delocalization in Continuous Disordered Systems
Continuous One-dimensional models supporting extended states are studied.
These delocalized statesoccur at well defined values of the energy and are
consequences of simple statistical correlation rules. We explicitly study
alloys of delta-barrier potentials as well as alloys and liquids of quantum
well as.The divergence of the localization length is studied and a critical
exponent 2/3 is found for the delta-barrier case, whereas for the quantum wells
we find an exponent of 2 or 2/3 depending on the well's parameters. These
results support the idea that correlations between random scattering sequences
break Anderson localization. We further calculate the conductance of disordered
superlattices. At the peak transmission the relative fluctuations of the
transmission coefficient are vanishing.Comment: 8 page
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