33,507 research outputs found
Dynamical Inequality in Growth Models
A recent exponent inequality is applied to a number of dynamical growth
models. Many of the known exponents for models such as the Kardar-Parisi-Zhang
(KPZ) equation are shown to be consistent with the inequality. In some cases,
such as the Molecular Beam Equation, the situation is more interesting, where
the exponents saturate the inequality. As the acid test for the relative
strength of four popular approximation schemes we apply the inequality to the
exponents obtained for two Non Local KPZ systems. We find that all methods but
one, the Self Consistent Expansion, violate the inequality in some regions of
parameter space. To further demonstrate the usefulness of the inequality, we
apply it to a specific model, which belongs to a family of models in which the
inequality becomes an equality. We thus show that the inequality can easily
yield results, which otherwise have to rely either on approximations or general
beliefs.Comment: 6 pages, 4 figure
Substituent effects on the nitrogen-15 and carbon-13 shieldings of some N-arylguanidinium chlorides
The 13C and 15N chemical shifts of five N-arylguanidinium chlorides carrying polar substituents, ranging in character from 4-methoxy to 4-nitro groups, have been determined by NMR spectroscopy at the natural-abundance level of 13C and 15N in dimethyl sulfoxide solution. Comparison of the 13C shifts of these salts with those of monosubstituted benzenes shows that the guanidinium group induces an average downfield shift of -5.8 ppm of the resonance of the aryl carbon to which it is attached (C1), an average upfield shift of +4.2 ppm for C2 and C6, and a small upfield shift of +1.9 ppm for C4. The shifts of C3 and C5 are small and erratic relative to the corresponding carbons in monosubstituted benzenes. The 15N resonances of the guanidinium nitrogens are quite sensitive to electric effects resulting from substitution of polar groups at C4. The 15N shift of the ==NAr nitrogen relative to that of the salts suggests that the predominant tautomer for N-arylguanidines is (H2N)2C==NAr. The 15N shifts of the (NH2) 2 nitrogens correlate rather well with σp- parameters, whereas the shifts of the -NHAr nitrogens seem to correlate only with R values derived from the σp- substituent constants
Upper critical dimension of the KPZ equation
Numerical results for the Directed Polymer model in 1+4 dimensions in various
types of disorder are presented. The results are obtained for system size
considerably larger than that considered previously. For the extreme strong
disorder case (Min-Max system), associated with the Directed Percolation model,
the expected value of the meandering exponent, zeta = 0.5 is clearly revealed,
with very week finite size effects. For the week disorder case, associated with
the KPZ equation, finite size effects are stronger, but the value of seta is
clearly seen in the vicinity of 0.57. In systems with "strong disorder" it is
expected that the system will cross over sharply from Min-Max behavior at short
chains to weak disorder behavior at long chains. This is indeed what we find.
These results indicate that 1+4 is not the Upper Critical Dimension (UCD) in
the week disorder case, and thus 4+1 does not seem to be the upper critical
dimension for the KPZ equation
A characterization of quasi-rational polygons
The aim of this paper is to study quasi-rational polygons related to the
outer billiard. We compare different notions introduced, and make a synthesis
of those.Comment: 15 pages, 9 figure
Determinisitic Writing and Control of the Dark Exciton Spin using Short Single Optical Pulses
We demonstrate that the quantum dot-confined dark exciton forms a long-lived
integer spin solid state qubit which can be deterministically on-demand
initiated in a pure state by one optical pulse. Moreover, we show that this
qubit can be fully controlled using short optical pulses, which are several
orders of magnitude shorter than the life and coherence times of the qubit. Our
demonstrations do not require an externally applied magnetic field and they
establish that the quantum dot-confined dark exciton forms an excellent solid
state matter qubit with some advantages over the half-integer spin qubits such
as the confined electron and hole, separately. Since quantum dots are
semiconductor nanostructures that allow integration of electronic and photonic
components, the dark exciton may have important implications on implementations
of quantum technologies consisting of semiconductor qubits.Comment: Added two authors, minor edits to figure captions, expanded
discussion of dark exciton eigenstate
The Upper Limit Solar Gamma-ray Spectrum to 10 Mev
Balloon flight data on upper limit solar gamma ray spectrum from quiet su
Preliminary results of the University of California X-ray experiment on the OSO-3
Cosmic and solar X ray data obtained by Orbiting Solar Observatory /OSO-3
Franklin D. Roosevelt\u27s Psychological Contribution To The United Nations
FDR promoted U.S. participation in the United Nations in several ways. In this article I focus on his use of mass communication to reach individuals and families in the U.S. In his \u27\u27fireside chats, he empathically addressed widely experienced problems and then proposed solutions requiring publicly supported governmental actions. In his first term, that technique gained Roosevelt popular support for the New Deal programs. In his second term, FDR turned the nation\u27s attention to the international situation, drawing on the motivations he had earlier tapped. In the 1940 election, both major parties chose internationalist candidates, and Roosevelt was able in his third term (and brief fourth term) to develop the internationalist idea embodied in the United Nations
All-Optical Depletion of Dark Excitons from a Semiconductor Quantum Dot
Semiconductor quantum dots are considered to be the leading venue for
fabricating on-demand sources of single photons. However, the generation of
long-lived dark excitons imposes significant limits on the efficiency of these
sources. We demonstrate a technique that optically pumps the dark exciton
population and converts it to a bright exciton population, using intermediate
excited biexciton states. We show experimentally that our method considerably
reduces the DE population while doubling the triggered bright exciton emission,
approaching thereby near-unit fidelity of quantum dot depletion.Comment: 5 pages, 3 figure
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