Dynamics and mechanism of light harvesting in UV photoreceptor UVR8

Photosynthetic pigments form light-harvesting networks to enable nearly perfect quantum efficiency in photosynthesis via excitation energy transfer. However, similar light-harvesting mechanisms have not been reported in light sensing processes in other classes of photoreceptors during light-mediated signaling. Here, based on our earlier report, we mapped out a striking energy-transfer network composed of 26 structural tryptophan residues in the plant UV-B photoreceptor UVR8. The spectra of the tryptophan chromophores are tuned by the protein environments, funneling all excitation energy to a cluster of four tryptophan residues, a pyramid center, where the excitation-induced monomerization is initiated for cell signaling. With extensive site-directed mutagenesis, various time-resolved fluorescence techniques, and combined QM/MM simulations, we determined the energy-transfer rates for all donor–acceptor pairs, revealing the time scales from tens of picoseconds to nanoseconds. The overall light harvesting quantum efficiency by the pyramid center is significantly increased to 73%, compared to a direct excitation probability of 35%. UVR8 is the only photoreceptor discovered so far using a natural amino-acid tryptophan without utilizing extrinsic chromophores to form a network to carry out both light harvesting and light perception for biological functions.

The light-harvesting network from distal and peripheral to central tryptophans with transfer efficiencies determined from measured energy-transfer rates.     

Inspection of interfaces between corroded steel bars and concrete using the combination of a piezoelectric zirconate-titanate transducer and an electromagnetic acoustic transducer

We have conducted an inspection of the interface between a steel bar and concrete using the combination of a piezoelectric zirconate-titanate transducer (PZT) and an electromagnetic acoustic transducer (EMAT). The PZT is used for generating elastic waves by mechanical vibration and then the EMAT is used for receiving the transmitted ultrasonic guided waves. This arrangement is made in order to overcome the major shortcomings of the PZT, i.e., the requirement of a couplant, and of the EMAT, i.e., relatively low transmitted ultrasonic energy. To investigate the applicability of this technique in the field, outside the laboratory environment, the experiments are conducted on different types of steel bars: corrosion-free, naturally corroded, and zinc-coated as well as corroded bars. It is shown that the PZT-EMAT combination is very effective for inspecting the steel bar-concrete interface. Using this technique, small separation at the steel bar-concrete interface can be effectively detected for corroded as well as corrosion-free specimens. This method can be applied in the field to pre-stressed tendons and soil nails, where one side of the reinforcement is exposed.     

Exact likelihood inference based on Type-I and Type-II hybrid censored samples from the exponential distribution

Chen and Bhattacharyya (1988,Comm. Statist. Theory Methods,17, 1857–1870) derived the exact distribution of the maximum likelihood estimator of the mean of an exponential distribution and an exact lower confidence bound for the mean based on a hybrid censored sample. In this paper, an alternative simple form for the distribution is obtained and is shown to be equivalent to that of Chen and Bhattacharyya (1988). Noting that this scheme, which would guarantee the experiment to terminate by a fixed timeT, may result in few failures, we propose a new hybrid censoring scheme which guarantees at least a fixed number of failures in a life testing experiment. The exact distribution of the MLE as well as an exact lower confidence bound for the mean is also obtained for this case. Finally, three examples are presented to illustrate all the results developed here.     

Ba-Zr codoped sodium bismuth titanate by novel alkoxyless wet chemical route: processing and electromechanical behavior

Sodium bismuth titanate (NBT) based ceramics have been shown to be a promising lead-free alternative to commercial piezoelectrics and high capacitance materials. This article reports a novel aqueous citrate gel route for the synthesis of (Na_0.5Bi_0.5)_xBa_1-xTi_yZr_1-yO₃ powders. Instead of alkoxides, usually used in citrate gel route, aqueous citrate solutions of titanium and bismuth were prepared from their respective inorganic salts. These solutions were used to prepare powder of (Na_0.5Bi_0.5)_0.88Ba_0.12Ti_0.96Zr_0.04O₃. The process produced an amorphous xerogel that was readily crystallized to a pseudocubic perovskite phase when calcined at temperatures as low as 500 °C. The decomposition and oxidation of the xerogel was studied using TG-DTA, which showed complete removal of volatile components by 580 °C. The formation of crystalline phases was studied using XRD. SEM was used to evaluate the sintering behavior of the powder. The powder exhibits significant sintering at temperatures 800–900 °C. The polarization behavior of the sintered material was similar to one prepared by conventional solid state route. A maximum polarization of ∼24 μC/cm² and peak bipolar strain ∼0.095% at 44 kV/cm was achieved in the sintered material. PACS 77.22.Ej; 77.84.Dy     

The role of power law nonlinearity in the discrete nonlinear Schrödinger equation on the formation of stationary localized states in the Cayley tree

We study the formation of stationary localized states using the discrete nonlinear Schr?dinger equation in a Cayley tree with connectivity K. Two cases, namely, a dimeric power law nonlinear impurity and a fully nonlinear system are considered. We introduce a transformation which reduces the Cayley tree into an one dimensional chain with a bond defect. The hopping matrix element between the impurity sites is reduced by . The transformed system is also shown to yield tight binding Green's function of the Cayley tree. The dimeric ansatz is used to find the reduced Hamiltonian of the system. Stationary localized states are found from the fixed point equations of the Hamiltonian of the reduced dynamical system. We discuss the existence of different kinds of localized states. We have also analyzed the formation of localized states in one dimensional system with a bond defect and nonlinearity which does not correspond to a Cayley tree. Stability of the states is discussed and stability diagram is presented for few cases. In all cases the total phase diagram for localized states have been presented. Received: 18 September 1997 / Revised: 31 October and 17 november 1997 / Accepted: 19 November 1997     

Elastic waves in a multilayered solid due to a dislocation source

A modified version of the wave number integral approach is applied to the calculation of the motion produced in a multilayered solid by dynamic sources. A new method of pole removal is introduced to facilitate separation of the continuous and the discrete spectral responses of the medium. The well-known numerical difficulties associated with the calculation of the integrands of the continuous spectra and the mode shapes of the discrete spectra are avoided through the use of delta matrices. Special numerical integration schemes are used to calculate the body wave integrals accurately at smaller distances and higher frequencies.     

Laser diode to monomode elliptic core fiber excitation via hemispherical lens on the fiber tip: Efficiency computation by ABCD matrix with consideration for allowable aperture

Employing Gaussian field distributions for both the source and the fiber, we report a simple theoretical prediction of the coupling efficiency of a laser diode to a single-mode elliptic core fiber via hemispherical lens on the fiber tip. The analysis is based on ABCD matrix for hemispherical lens under paraxial approximation. Our formalism takes care of the allowable aperture of the hemispherical lens. The present analysis prescribes analytical expressions for the coupling efficiency and the concerned calculations are executable by pocket calculator.     

Quality of potential harmonics expansion method for dilute Bose-Einstein condensate

We present and examine an approximate but ab initio many-body approach, viz., potential harmonics expansion method (PHEM), which includes two-body correlations for dilute Bose-Einstein condensates. Comparing the total ground state energy for three trapped interacting bosons calculated in PHEM with the exact energy, the new method is shown to be very good in the low density limit which is necessary for achieving Bose-Einstein condensation experimentally.      

Dielectric spectroscopy of an antiferroelectric liquid crystal showing an antiferroelectric-ferrielectric transition

We report the dielectric relaxation behaviour in the antiferroelectric SmC_A* and ferrielectric SmC_γ* phases of the antiferroelectric liquid crystal 4-[5-(4-octloxyphenyl)-2-pyrimidinyl]phenyl 4,4,4-trifluoro-3-(methoxyphenyl)butanoate which shows an antiferroelectric transition at around 88±0.1°C. In the SmC_A* phase, two dielectric relaxation modes have been found, namely the usual antiferroelectric Goldstone mode and another arising from molecular rotation around its short axis. In the SmC_γ* phase, one dielectric relaxation mode has been observed due to the ferrielectric Goldstone mode. Dielectric increments and relaxation frequencies of the antiferroelectric and ferrielectric phases are estimated from the fits of the Cole-Cole function of the dielectric spectrum. The dependence of the bias field in the ferrielectric phase is also discussed.