209 research outputs found
Vibronic enhancement of excitation energy transport : interplay between local and non-local exciton-phonon interaction
It has been reported in recent years that vibronic resonance between vibrational energy of the intramolecular nuclear mode and excitation-energy difference is crucial to enhance excitation energy transport in light harvesting proteins. Here we investigate how vibronic enhancement induced by vibronic resonance is influenced by the details of local and non-local exciton-phonon interaction. We study a heterodimer model with parameters relevant to the light-harvesting proteins with the surrogate Hamiltonian quantum dynamics method in a vibronic basis. In addition, the impact of field-driven excitation on the efficiency of population transfer is compared with the instantaneous excitation, and the effect of multi-mode vibronic coupling is presented in comparison with the coupling to a single effective vibrational mode. We find that vibronic enhancement of site population transfer is strongly suppressed with the increase of non-local exciton-phonon interaction and increasing the number of strongly coupled high-frequency vibrational modes leads to further decrease in vibronic enhancement. Our results indicate that vibronic enhancement is present but may be much smaller than previously thought and therefore care needs to be taken when interpreting its role in excitation energy transport. Our results also suggest that non-local exciton-phonon coupling, which is related to the fluctuation of the excitonic coupling, may be as important as local exciton-phonon coupling and should be included in any quantum dynamics model
Charge dynamics in organic photovoltaic materials : interplay between quantum diffusion and quantum relaxation
This paper discusses the mechanism of generation of free charges in organic photovoltaic cells (OPV) from electrostatically bound electronâhole pairs. The efficiency of this process is explained when interfacial charge-transfer (CT) states are generated by direct optical excitation. We used semiclassical quantum dynamics at a short time scale (âŒ100 fs) and Redfield theory at a relatively long time scale (âŒ10â100 ps) to cover both the process of dissociation and the relaxation to the lowest energy state. Our calculations suggest that a CT state with an intermediate electronâhole separation can evolve into a charge-separated (CS) state on ultrafast time scales (âŒ100 fs) as a result of quantum diffusion. On long time scales, however, the CS states ultimately relax to the low-energy CT states due to the interaction with the thermal bath, indicating that the yield of free charge carrier generation is determined by the interplay between ultrafast charge separation, due to quantum diffusion, and the much slower quantum relaxation process
Higgs Structures of Dyonic Instantons
We study Higgs field configurations of dyonic instantons in spontaneously
broken (4+1)-dimensional Yang-Mills theory. The adjoint scalar field solutions
to the covariant Laplace equation in the ADHM instanton background are
constructed in general noncanonical basis, and they are used to study
explicitly the Higgs field configurations of dyonic instantons when the gauge
fields are taken by Jackiw-Nohl-Rebbi instanton solutions. For these solutions
corresponding to small instanton number we then consider in some detail the
zero locus of the Higgs field, which describes the cross section of supertubes
connecting parallel D4-branes in string theory. Also the information on the
Higgs zeroes is used to discuss the residual gauge freedom concerning the
Jackiw-Nohl-Rebbi solutions.Comment: 1+27 pages, 6 figure
Microlensing Optical Depth Revisited with Recent Star Counts
More reliable constraints on the microlensing optical depth comes from a
better understanding of the Galactic model. Based on well-constrained Galactic
bulge and disk models constructed from survey observations, such as, HST,
2MASS, and SDSS, we calculate the microlensing optical depths toward the
Galactic bulge fields, and compare them with recent results of microlensing
surveys. We test chi^2 statistics of microlensing optical depths expected from
those models, as well as previously proposed models, using two types of data:
optical depth map in (l, b) and averaged optical depth over the Galactic
longitude l as a function of the latitude b. From this analysis, we find that
the Galactic bulge models of 2MASS, Han & Gould (2003), and G2 of Stanek et al.
(1997) show a good agreement with the microlensing optical depth profiles for
all the microlensing observations, compared with E2 of Stanek et al. (1997). We
find, on the other hand, that models involving an SDSS disk model produce
relatively higher chi^2 values. It should be noted that modeled microlensing
optical depths diverge in the low Galactic latitude, |b| < 2 arcdeg. Therefore,
we suggest the microlensing observation toward much closer to central regions
of the Galaxy to further test the proposed Galactic models, if it is more
technically feasible than waiting for large data set of microlensing events.Comment: 15 pages, 3 figures and 3 tables, accepted for publication in Ap
Vortex Dynamics in Selfdual Maxwell-Higgs Systems with Uniform Background Electric Charge Density
We introduce selfdual Maxwell-Higgs systems with uniform background electric
charge density and show that the selfdual equations satisfied by topological
vortices can be reduced to the original Bogomol'nyi equations without any
background. These vortices are shown to carry no spin but to feel the Magnus
force due to the shielding charge carried by the Higgs field. We also study the
dynamics of slowly moving vortices and show that the spin-statistics theorem
holds to our vortices.Comment: 24 pages + 2 figures ( not included), Cu-TP-611, IASSNS-HEP-93/33,
NSF-ITP-93-13
Chern-Simons Solitons, Chiral Model, and (affine) Toda Model on Noncommutative Space
We consider the Dunne-Jackiw-Pi-Trugenberger model of a U(N) Chern-Simons
gauge theory coupled to a nonrelativistic complex adjoint matter on
noncommutative space. Soliton configurations of this model are related the
solutions of the chiral model on noncommutative plane. A generalized
Uhlenbeck's uniton method for the chiral model on noncommutative space provides
explicit Chern-Simons solitons. Fundamental solitons in the U(1) gauge theory
are shaped as rings of charge `n' and spin `n' where the Chern-Simons level `n'
should be an integer upon quantization. Toda and Liouville models are
generalized to noncommutative plane and the solutions are provided by the
uniton method. We also define affine Toda and sine-Gordon models on
noncommutative plane. Finally the first order moduli space dynamics of
Chern-Simons solitons is shown to be trivial.Comment: latex, JHEP style, 23 pages, no figur
ULTRAFILTRATED FRACTION OF KOREAN RED GINSENG EXTRACT IMPROVES MEMORY IMPAIRMENT OF TG2576 MICE VIA INHIBITION OF SOLUBLE AĂâ PRODUCTION AND ACETYLCHOLINESTERASE ACTIVITY
Objective: The goal of this study was to research for an effective fraction on memory improvement of Korean red ginseng.Methods: In this study, 80 % ethanol red ginseng extract (RE) was divided into inner fluid (REUI) and outer fluid (REUO) by the ultrafiltration and then REUO was further separated into four fractions namely, REUO-00, REUO-30, REUO-50 and REUO-70, respectively, by Diaion HP-20 column chromatography.Results: REUO has protected more significantly the H2O2-induced SHSY-5Y cell death than REUI. Interestingly, the hydrophobic parts of the REUO (REUO-EtOHs) such as REUO-30,-50 and-70 decreased more significantly the H2O2-induced cell death than its hydrophilic part (REUO-00) in a dose-dependent manner. Then, we focused on the activity of a candidate for cholinergic functions, because memory deficits of neurodegenerative diseases are closely associated with cholinergic dysfunctions. The REUO-EtOHs (1.25 mg/ml) inhibited the activity of the acetylcholinesterase and its half maximal inhibitory concentration (IC50) was about 2.358 mg/ml. Additionally, we investigated whether the intake of the REUO (50 mg/kg/d) during 12 w could improve memory impairment of 12-month old Tg2576 mice and decrease total soluble amyloid-ĂÂČ (AĂÂČ) proteins in the mouse brain cortex. The REUO alleviated significantly the memory impairment and successfully reduced the levels of the soluble AĂÂČ proteins in the mouse cortex.Conclusion: We finally suggest that the REUO, including majorly its hydrophobic part that may be considered as more effective for memory improvement, will be highly considered as valuable candidate for the memory-enhancing ingredients against cholinergic dysfunctions and cognitive impairments of neurodegenerative diseases including Alzheimer's disease.Keywords: Ginseng, Alzheimer's disease, Acetylcholinesterase, Ultrafiltration, MemoryĂ
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