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961.
We find sufficient conditions for the absence of harmonic L 2 spinors on spin manifolds constructed as cone bundles over a compact Kähler base. These conditions are fulfilled for certain perturbations of the Euclidean metric, and also for the generalized Taub-NUT metrics of Iwai-Katayama, thus proving a conjecture of Vi?inescu and the second author. 相似文献
962.
Dobek K 《Journal of fluorescence》2011,21(4):1547-1557
The influence of temperature varied in the range 183 K–323 K on the fluorescence quantum yield, fluorescence lifetime, absorption
and emission transition moments and non-radiative deactivation rate was determined for the well known and largely used dye
Coumarin 153, dissolved in 1-chloropropane. The Kennard-Stepanov relation connecting the absorption and emission spectra was
used to check for the presence of more than one absorbing/emitting species and to investigate whether intramolecular vibrational
redistribution completes in the C153 excited S
1 state before the emission takes place. The emission spectrum corresponding to S
1→S
0 transition, was fitted at each temperature to the model function including the information on the dye vibrational modes coupling.
In this way the displacement in equilibrium distance for the most active vibrational mode was determined for C153 in S
1 and in S
0. Using the temperature dependence of the fluorescence decay time and quantum yield, the non-radiative deactivation rate was
determined. Its temperature dependence was compared to that calculated using the theoretical model with the most active vibrational
mode displacement values taken from steady-state spectra analysis. The somewhat surprising dependence of the fluorescence
decay time and quantum yield on temperature was related to non-trivial coupling between low-frequency vibrational modes of
C153 in the excited and ground states. 相似文献
963.
Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the
dispersion relation and the growth rate have been derived and analysed numerically for plasma-filled rippled wall rectangular
waveguide driven by sheet electron beam. To see the effect of plasma on the TM01 cold wave structure mode and on the generated frequency, the parameters used are: relativistic factor γ = 1.5 (i.e. v/c = 0.741), average waveguide height y
0 = 1.445 cm, axial corrugation period z
0 = 1.67 cm, and corrugation amplitude ε = 0.225 cm. The plasma density is varied from zero to 2 ×1012 cm − 3. The presence of plasma tends to raise the TM01 mode cut-off frequency (14 GHz at 2 ×1012 cm − 3 plasma density) relative to the vacuum cut-off frequency (5 GHz) which also causes a decrease in the group velocity everywhere,
resulting in a flattening of the dispersion relation. With the introduction of plasma, an enhancement in absolute instability
was observed. 相似文献
964.
A photo-induced radical pair of FADH· and Y8· and in BLUF protein SyPixD was studied by pulsed electron paramagnetic resonance (EPR) spectroscopy. Blue light illumination
at 150 K for 30 min followed by cooling to 50 K during illumination induced the stable radical pair. The EPR signal has been
characterized by a Pake doublet signal with complete S = 1 spin state. The radical pair was utilized as a probe to analyze the oligomer of SyPixD. The relative arrangement of PixD
proteins in the complex was investigated by pulsed electron–electron double resonance (PELDOR) with the orientation selection.
Based on the decameric structure in the crystal, the possible structure for the PELDOR results was discussed. 相似文献
965.
V. G. Arkhipkin V. A. Gunyakov S. A. Myslivets V. Ya. Zyryanov V. F. Shabanov Wei Lee 《Journal of Experimental and Theoretical Physics》2011,112(4):577-587
The transmission spectra of polarized light waves in a photonic crystal/liquid crystal (PC/LC) cell placed between crossed
polarizers and controlled by an electric or magnetic field have been studied experimentally and theoretically. Electro- and
magneto-optical switching based on the interference of polarized defect modes has been demonstrated. The transmission spectra
of the PC/LC cell have been calculated as a function of the voltage applied to the LC layer and the magnetic field strength.
The results of the calculations agree well with the experimental data. 相似文献
966.
Bert Schroer 《Foundations of Physics》2011,41(10):1543-1568
The standard formulation of quantum gauge theories results from the Lagrangian (functional integral) quantization of classical
gauge theories. A more intrinsic quantum theoretical access in the spirit of Wigner’s representation theory shows that there
is a fundamental clash between the pointlike localization of zero mass (vector, tensor) potentials and the Hilbert space (positivity,
unitarity) structure of QT. The quantization approach has no other way than to stay with pointlike localization and sacrifice
the Hilbert space whereas the approach built on the intrinsic quantum concept of modular localization keeps the Hilbert space
and trades the conflict creating pointlike generation with the tightest consistent localization: semiinfinite spacelike string
localization. Whereas these potentials in the presence of interactions stay quite close to associated pointlike field strengths,
the interacting matter fields to which they are coupled bear the brunt of the nonlocal aspect in that they are string-generated
in a way which cannot be undone by any differentiation. 相似文献
967.
The effect of resonant fluorescent enhancement from a photonic crystal surface upon the fluorescent photobleaching rate of
Cyanine-5 labeled protein has been investigated. We show that the enhanced excitation mechanism for photonic crystal enhanced
fluorescence, in which the device surface resonantly couples light from an excitation laser, accelerates photobleaching in
proportion to the coupling efficiency of the laser to the photonic crystal. We also show that the enhanced extraction mechanism,
in which the photonic crystal directs emitted photons approximately normal to the surface, does not play a role in the rate
of photobleaching. We show that the photobleaching rate of dye molecules on the photonic crystal surface is accelerated by
30x compared to an ordinary glass surface, but substantial signal gain is still evident, even after extended periods of continuous
illumination at the resonant condition. 相似文献
968.
Dipsikha Bhattacharya Sumanta K. Sahu Indranil Banerjee Manasmita Das Debashish Mishra Tapas K. Maiti Panchanan Pramanik 《Journal of nanoparticle research》2011,13(9):4173-4188
In this article, we report the design and synthesis of a series of well-dispersed superparamagnetic iron oxide nanoparticles
(SPIONs) using chitosan as a surface modifying agent to develop a potential T
2 contrast probe for magnetic resonance imaging (MRI). The amine, carboxyl, hydroxyl, and thiol functionalities were introduced
on chitosan-coated magnetic probe via simple reactions with small reactive organic molecules to afford a series of biofunctionalized
nanoparticles. Physico-chemical characterizations of these functionalized nanoparticles were performed by TEM, XRD, DLS, FTIR,
and VSM. The colloidal stability of these functionalized iron oxide nanoparticles was investigated in presence of phosphate
buffer saline, high salt concentrations and different cell media for 1 week. MRI analysis of human cervical carcinoma (HeLa)
cell lines treated with nanoparticles elucidated that the amine-functionalized nanoparticles exhibited higher amount of signal
darkening and lower T
2 relaxation in comparison to the others. The cellular internalization efficacy of these functionalized SPIONs was also investigated
with HeLa cancer cell line by magnetically activated cell sorting (MACS) and fluorescence microscopy and results established
selectively higher internalization efficacy of amine-functionalized nanoparticles to cancer cells. These positive attributes
demonstrated that these nanoconjugates can be used as a promising platform for further in vitro and in vivo biological evaluations. 相似文献
969.
The production of acoustic wave is one of the most important factors on the action of High Repetition Rate TEA-CO2 lasers. In this paper a three-dimensional mathematical modeling has been considered for investigation of temporal and spatial variations of acoustic waves in the laser cavity and its effect on the output of HRR lasers. By calculation of equations obtained from this model and plotting the pressure spectrum in different states, the effect of electrodes dimensions, cavity dimensions, gas flow velocity and repetition rate of laser in different times have been acquired. At last, optimum conditions for performance of laser action and having a good output have been arrived. 相似文献
970.
Ramón Herrera Eugenio San Martin 《The European Physical Journal C - Particles and Fields》2011,71(7):1701
Warm-intermediate inflationary universe models in the context of braneworld cosmologies are studied. This study is done in
the weak and strong dissipative regimes. We find that the scalar potentials and dissipation coefficients in terms of the scalar
field evolve as type-power-law and powers of logarithms, respectively. General conditions required for these models to be
realizable are derived and discussed. We also study the scalar and tensor perturbations for each regime. We use recent astronomical
observations to constrain the parameters appearing in the braneworld models. 相似文献