923 research outputs found
Inelastic electron tunneling via molecular vibrations in single-molecule transistors
In single-molecule transistors, we observe inelastic cotunneling features
that correspond energetically to vibrational excitations of the molecule, as
determined by Raman and infrared spectroscopy. This is a form of inelastic
electron tunneling spectroscopy of single molecules, with the transistor
geometry allowing in-situ tuning of the electronic states via a gate electrode.
The vibrational features shift and change shape as the electronic levels are
tuned near resonance, indicating significant modification of the vibrational
states. When the molecule contains an unpaired electron, we also observe
vibrational satellite features around the Kondo resonance.Comment: 5 pages, 4 figures. Supplementary information available upon reques
Experimental and theoretical characterization of microbial bioanodes formed in pulp and paper mill effluent in electrochemically controlled conditions
Microbial bioanodes were formed in pulp and paper effluent on graphite plate electrodes under constant polarization at -0.3 V/SCE, without any addition of nutriment or substrate. The bioanodes were characterized in 3-electrode set-ups, in continuous mode, with hydraulic retention times from 6 to 48 h and inlet COD from 500 to 5200 mg/L. Current densities around 4 A/m2 were obtained and voltammetry curves indicated that 6 A/m2 could be reached at +0.1 V/SCE. A theoretical model was designed, which allowed the effects of HRT and COD to be distinguished in the complex experimental data obtained with concomitant variations of the two parameters. COD removal due to the electrochemical process was proportional to the hydraulic retention time and obeyed a MichaelisâMenten law with respect to the COD of the outlet flow, with a Michaelis constant KCOD of 400 mg/L. An inhibition effect occurred above inlet COD of around 3000 mg/L
On the basis property for the root vectors of some nonselfadjoint operators
When does the root system of a nonselfadjoint operator form a Riesz basis of a Hilbert space? This question is discussed in the paper.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24433/1/0000706.pd
N=4 Twisted Superspace from Dirac-Kahler Twist and Off-shell SUSY Invariant Actions in Four Dimensions
We propose N=4 twisted superspace formalism in four dimensions by introducing
Dirac-Kahler twist. In addition to the BRST charge as a scalar counter part of
twisted supercharge we find vector and tensor twisted supercharges. By
introducing twisted chiral superfield we explicitly construct off-shell twisted
N=4 SUSY invariant action. We can propose variety of supergauge invariant
actions by introducing twisted vector superfield. We may, however, need to find
further constraints to identify twisted N=4 super Yang-Mills action. We propose
a superconnection formalism of twisted superspace where constraints play a
crucial role. It turns out that N=4 superalgebra of Dirac-Kahler twist can be
decomposed into N=2 sectors. We can then construct twisted N=2 super Yang-Mills
actions by the superconnection formalism of twisted superspace in two and four
dimensions.Comment: 62page
Current Exchanges and Unconstrained Higher Spins
The (Fang-)Fronsdal formulation for free fully symmetric (spinor-) tensors
rests on (gamma-)trace constraints on gauge fields and parameters. When these
are relaxed, glimpses of the underlying geometry emerge: the field equations
extend to non-local expressions involving the higher-spin curvatures, and with
only a pair of additional fields an equivalent ``minimal'' local formulation is
also possible. In this paper we complete the discussion of the ``minimal''
formulation for fully symmetric (spinor-) tensors, constructing one-parameter
families of Lagrangians and extending them to (A)dS backgrounds. We then turn
on external currents, that in this setting are subject to conventional
conservation laws and, by a close scrutiny of current exchanges in the various
formulations, we clarify the precise link between the local and non-local
versions of the theory. To this end, we first show the equivalence of the
constrained and unconstrained local formulations, and then identify a unique
set of non-local Lagrangian equations which behave in exactly the same fashion
in current exchanges.Comment: 37 pages, Latex. Typos corrected, note and references added. Final
version to appear in Nucl. Phys.
Lingual Lymphangioma Ablation With High Power Diode Laser: A Case Report
Introduction: Lymphangioma is a rare vascular anomaly that affects the lymphatic vessels. Its etiology is not yet clear and it usually occurs in the head and neck region. This pathology is commonly diagnosed in childhood and there is no consensus about the most effective treatment of it.Case Report: We report a case of lymphangioma located on the dorsum of the tongue in a 9-year-old boy, with the clinical appearance of small transparent vesicles similar to âfrog-eggsâ. The diagnosis was defined according to the clinical aspect and ultrasound images. The treatment performed consisted of two sessions of ablation with a high-power diode laser.Conclusion: High-intensity diode laser ablation was a safe and effective tool for the treatment of this lesion in the tongue, which provided the patient with a faster, efficient transoperative period and a more comfortable postoperative period.
Branes: from free fields to general backgrounds
Motivated by recent developments in string theory, we study the structure of
boundary conditions in arbitrary conformal field theories. A boundary condition
is specified by two types of data: first, a consistent collection of reflection
coefficients for bulk fields on the disk; and second, a choice of an
automorphism of the fusion rules that preserves conformal weights.
Non-trivial automorphisms correspond to D-brane configurations for
arbitrary conformal field theories. The choice of the fusion rule automorphism
amounts to fixing the dimension and certain global topological
features of the D-brane world volume and the background gauge field on it. We
present evidence that for fixed choice of the boundary conditions are
classified as the irreducible representations of some commutative associative
algebra, a generalization of the fusion rule algebra. Each of these irreducible
representations corresponds to a choice of the moduli for the world volume of
the D-brane and the moduli of the flat connection on it.Comment: 56 pages, LaTeX2e. Typos corrected; two references adde
One-dimensional metallic behavior of the stripe phase in LaSrCuO
Using an exact diagonalization method within the dynamical mean-field theory
we study stripe phases in the two-dimensional Hubbard model. We find a
crossover at doping from diagonal stripes to vertical
site-centered stripes with populated domain walls, stable in a broad range of
doping, . The calculated chemical potential shift and the doping dependence of the magnetic incommensurability are in
quantitative agreement with the experimental results for doped
LaSrCuO. The electronic structure shows one-dimensional
metallic behavior along the domain walls, and explains the suppression of
spectral weight along the Brillouin zone diagonal.Comment: 4 pages, 4 figure
Gauge Equivalence in Two--Dimensional Gravity
Two-dimensional quantum gravity is identified as a second-class system which
we convert into a first-class system via the Batalin-Fradkin (BF) procedure.
Using the extended phase space method, we then formulate the theory in most
general class of gauges. The conformal gauge action suggested by David, Distler
and Kawai is derived from a first principle. We find a local, light-cone gauge
action whose Becchi-Rouet-Stora-Tyutin invariance implies Polyakov's curvature
equation , revealing the origin of the
Kac-Moody symmetry. The BF degree of freedom turns out be dynamically
active as the Liouville mode in the conformal gauge, while in the light-cone
gauge the conformal degree of freedom plays that r{\^o}le. The inclusion of the
cosmological constant term in both gauges and the harmonic gauge-fixing are
also considered.Comment: 30 pages, KANAZAWA 93-
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