29,166 research outputs found
Optically nonlinear energy transfer in light-harvesting dendrimers
Dendrimeric polymers are the subject of intense research activity geared towards their implementation in nanodevice applications such as energy harvesting systems,organic light-emitting diodes, photosensitizers, low-threshold lasers, and quantum logic elements, etc. A recent development in this area has been the construction of dendrimers specifically designed to exhibit novel forms of optical nonlinearity, exploiting the unique properties of these materials at high levels of photon flux. Starting from a thorough treatment of the underlying theory based on the principles of molecular quantum electrodynamics, it is possible to identify and characterize several optically nonlinear mechanisms for directed energy transfer and energy pooling in multichromophore dendrimers. Such mechanisms fall into two classes: first, those where two-photon absorption by individual donors is followed by transfer of the net energy to an acceptor; second, those where the excitation of two electronically distinct but neighboring donor groups is followed by a collective migration of their energy to a suitable acceptor. Each transfer process is subject to minor dissipative losses. In this paper we describe in detail the balance of factors and the constraints that determines the favored mechanism, which include the excitation statistics, structure of the energy levels, laser coherence factors, chromophore selection rules and architecture, possibilities for the formation of delocalized excitons, spectral overlap, and the overall distribution of donors and acceptors. Furthermore, it transpires that quantum interference between different mechanisms can play an important role. Thus, as the relative importance of each mechanism determines the relevant nanophotonic characteristics, the results reported here afford the means for optimizing highly efficient light-harvesting dendrimer devices
Dynamics of Macroscopic Wave Packet Passing through Double Slits: Role of Gravity and Nonlinearity
Using the nonlinear Schroedinger equation (Gross-Pitaevskii equation), the
dynamics of a macroscopic wave packet for Bose-Einstein condensates falling
through double slits is analyzed. This problem is identified with a search for
the fate of a soliton showing a head-on collision with a hard-walled obstacle
of finite size. We explore the splitting of the wave packet and its
reorganization to form an interference pattern. Particular attention is paid to
the role of gravity (g) and repulsive nonlinearity (u_0) in the fringe pattern.
The peak-to-peak distance in the fringe pattern and the number of interference
peaks are found to be proportional to g^(-1/2) and u_0^(1/2)g^(1/4),
respectively. We suggest a way of designing an experiment under controlled
gravity and nonlinearity.Comment: 10 pages, 4 figures and 1 tabl
A double bounded key identity for Goellnitz's (big) partition theorem
Given integers i,j,k,L,M, we establish a new double bounded q-series identity
from which the three parameter (i,j,k) key identity of Alladi-Andrews-Gordon
for Goellnitz's (big) theorem follows if L, M tend to infinity. When L = M, the
identity yields a strong refinement of Goellnitz's theorem with a bound on the
parts given by L. This is the first time a bounded version of Goellnitz's (big)
theorem has been proved. This leads to new bounded versions of Jacobi's triple
product identity for theta functions and other fundamental identities.Comment: 17 pages, to appear in Proceedings of Gainesville 1999 Conference on
Symbolic Computation
First order phase transition in the quark matter
We investigate chiral phase transition of the first order in the quark
matter. Using the Nambu-Jona-Lasinio model, an equation of state of the quark
matter which is similar to the van der Waals' one is obtained. Moreover the
specific heat and the compressibility are calculated. It is shown that they are
enhanced in the symmetry broken phase, in particular diverge near the
tricritical point.Comment: 6 pages, 7 figure
Interparticle interactions:Energy potentials, energy transfer, and nanoscale mechanical motion in response to optical radiation
In the interactions between particles of material with slightly different electronic levels, unusually large shifts in the pair potential can result from photoexcitation, and on subsequent electronic excitation transfer. To elicit these phenomena, it is necessary to understand the fundamental differences between a variety of optical properties deriving from dispersion interactions, and processes such as resonance energy transfer that occur under laser irradiance. This helps dispel some confusion in the recent literature. By developing and interpreting the theory at a deeper level, one can anticipate that in suitable systems, light absorption and energy transfer will be accompanied by significant displacements in interparticle separation, leading to nanoscale mechanical motion
Real-world comparison of probe vehicle emissions and fuel consumption using diesel and 5 % biodiesel (B5) blend.
An instrumented EURO I Ford Mondeo was used to perform a real-world comparison of vehicle exhaust (carbon dioxide, carbon monoxide, hydrocarbons and oxides of nitrogen) emissions and fuel consumption for diesel and 5% biodiesel in diesel blend (B5) fuels. Data were collected on multiple replicates of three standardised on-road journeys: (1) A simple urban route; (2) A combined urban/inter-urban route; and, (3) An urban route subject to significant traffic management. At the total journey measurement level, data collected here indicate that replacing diesel with a B5 substitute could result in significant increases in both NOx emissions (8-13%) and fuel consumption (7-8%). However, statistical analysis of probe vehicle data demonstrated the limitations of comparisons based on such total journey measurements, i.e., methods analogous to those used in conventional dynamometer/drive cycle fuel comparison studies. Here, methods based on the comparison of speed/acceleration emissions and fuel consumption maps are presented. Significant variations across the speed/acceleration surface indicated that direct emission and fuel consumption impacts were highly dependent on the journey/drive cycle employed. The emission and fuel consumption maps were used both as descriptive tools to characterise impacts and predictive tools to estimate journey-specific emission and fuel consumption effects
Coal Resources of the Springfield Coal Bed in Western Kentucky
Historically, the Springfield (Western Kentucky No. 9) coal bed has been the leading source of production in the Western Kentucky Coal Field. The Springfield coal is known for its lateral continuity in terms of both thickness and coal quality. It is estimated to have the largest original and remaining resource in the Western Kentucky Coal Field (Greb and others, 1992)
A model for conservative chaos constructed from multi-component Bose-Einstein condensates with a trap in 2 dimensions
To show a mechanism leading to the breakdown of a particle picture for the
multi-component Bose-Einstein condensates(BECs) with a harmonic trap in high
dimensions, we investigate the corresponding 2- nonlinear Schr{\"o}dinger
equation (Gross-Pitaevskii equation) with use of a modified variational
principle. A molecule of two identical Gaussian wavepackets has two degrees of
freedom(DFs), the separation of center-of-masses and the wavepacket width.
Without the inter-component interaction(ICI) these DFs show independent regular
oscillations with the degenerate eigen-frequencies. The inclusion of ICI
strongly mixes these DFs, generating a fat mode that breaks a particle picture,
which however can be recovered by introducing a time-periodic ICI with zero
average. In case of the molecule of three wavepackets for a three-component
BEC, the increase of amplitude of ICI yields a transition from regular to
chaotic oscillations in the wavepacket breathing.Comment: 5 pages, 4 figure
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