Strongly coupled ruthenium-polypyridyl complexes for efficient electron injection in dye-sensitized semiconductor nanoparticles

Dynamics of interfacial electron transfer (ET) in the ruthenium-polypyridyl complex [{bis(2,2'-bpy)-(4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol)} ruthenium(II) hexafluorophosphate] (Ru-cat)-sensitized TiO(2) nanoparticles has been investigated using femtosecond transient absorption spectroscopy detecting in the visible and near-infrared region. It has been observed that Ru-cat is coupled strongly with the TiO(2) nanoparticles through its pendant catechol moiety. Electron injection has been confirmed by direct detection of electrons in the conduction band, cation radical of the adsorbed dye, and a bleach of the dye in real time as monitored by transient absorption spectroscopy. A single-exponential and pulse width limited (<100 fs) electron injection has been observed, and the origin of it might have been from the nonthermalized excited states of the Ru-cat molecule. The result gave a strong indication that the electron injection competes with the thermalization of the photoexcited states due to large coupling elements for the forward ET reaction. Back-ET dynamics has been determined by monitoring the decay kinetics of the cation radical and injected electron and also from recovery kinetics of the bleach of the adsorbed dye. It has been fit with a multiexponential function, where approximately 30% of the injected electrons are recombined with a time constant of <2 ps, again indicating large coupling elements for the charge recombination reaction. However, our results have shown relatively long-lived charge separation in the Ru-cat/TiO(2) system as compared to other organic dye-sensitized TiO(2) nanoparticles with similar interactions.     

Migration phenomena of surfactants in polyethylene film

Migration diffusion coefficients of two surfactants (sorbitan laurate, SPAN‐20 and sorbitan palmitate, SPAN‐40) in polyethylene blend are calculated in the desorption process by means of Fourier transform infrared (FT‐IR) spectroscopy technique at 25°C. They are 2.31 and 2.24 × 10⁻¹¹ cm²/s, respectively, which show no significant dependency of molecular weights of the surfactants on diffusion. The composition of LLDPE (linear low‐density polyethylene) and LDPE (low‐density polyethylene) in LLDPE blend is a 7 : 3 ratio, and ethylene acrylic acid (EAA) copolymer is used to verify its role as a migration controller. The key factor affecting the diffusion of the surfactant is suggested to be the segmental mobility by the semicrystalline LLDPE blend. Incorporation of 20 wt% EAA in the LLDPE blend retards the migration rate of the surfactants by reducing the diffusion coefficients to be 9.6 and 7.7 × 10⁻¹² cm²/s and this is believed to be due to the blocking effect of EAA. Although the diffusion coefficient was varied from system to system, the migration kinetics of the surfactants in short times obeys the Fickian behavior if the experimental error is allowed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1387–1395, 1999     

Non-statistical fluctuations in 16O-AgBr interaction at 60A GeV in terms of factorial correlators

An analysis of ¹⁶O-AgBr interaction data at 60A GeV in terms of factorial correlators is presented. The correlated moments are found to increase with decreasing bin-bin separation D, following a power law within the region D 1. The data are also consistent with the dimension-independent scaling relation proposed by Seixas. Received: 5 October 1998 / Accepted: 20 April 2000     

Laser-induced changes in silver metal nanoparticles incorporated in viscous media

The effect of laser pulse irradiation on silver metal nanoparticles in ethylene glycol and glycerol is studied and compared with the parallel processes in aqueous solutions. The influence of 355 nm laser pulse irradiation at the surface plasmon frequency and on the size of the silver nanoparticles is examined by UV-Vis absorption spectroscopy and by transmission electron microscopy. It appears that viscosity of the medium plays a crucial role for the stabilization of the melted particles in the absence of the stabilizer. In ethylene glycol containing PVP, fragmentation of particles was observed. In neat glycerol, similar excitation led to morphological changes as the nanoparticles fused to produce particles of larger size. The changes in reduction of shape and size are considered to occur through melting and vaporization of the silver nanoparticles.     

Trimmed minimax estimator of a covariance matrix

Summary In the problem of estimating the covariance matrix of a multivariate normal population, James and Stein (Proc. Fourth Berkeley Symp. Math. Statist. Prob.,1, 361–380, Univ. of California Press) obtained a minimax estimator under a scale invariant loss. In this paper we propose an orthogonally invariant trimmed estimator by solving certain differential inequality involving the eigenvalues of the sample covariance matrix. The estimator obtained, truncates the extreme eigenvalues first and then shrinks the larger and expands the smaller sample eigenvalues. Adaptive version of the trimmed estimator is also discussed. Finally some numerical studies are performed using Monte Carlo simulation method and it is observed that the trimmed estimate shows a substantial improvement over the minimax estimator. The second author's research was supported by NSF Grant Number MCS 82-12968.     

A General Class of Change Point and Change Curve Modeling for Life Time Data

Change point hazard rate models arise in many life time data analysis, for example, in studying times until the undesirable side effects occur in clinical trials. In this paper we propose a general class of change point hazard model for survival data. This class includes and extends different types of change point models for survival data, e.g. cure rate model and lag model. Most classical approach develops estimates of model parameters, with particular interest in change point parameter and often the whole hazard function, but exclusively in terms of asymptotic properties. We propose a Bayesian approach, avoiding asymptotics and provide inference conditional upon the observed data. The proposed Bayesian models are fitted using Markov chain Monte Carlo method. We illustrate our proposed methodology with an application to modeling life times of the printed circuit board.     

Ultrasound and deep eutectic solvent (DES): A novel blend of techniques for rapid and energy efficient synthesis of oxazoles

The present work deals with the synthesis of novel oxazole compounds by using effective combination of ultrasound (US) and deep eutectic solvent (DES). The reaction was also conducted by thermal method (NUS) and the comparative studies are provided. It was observed that applying ultrasound not only improved yields and reduced reaction times but also saved more than 85% energy as shown by energy consumption calculations. The advantages of using DES as reaction medium is highlighted from the fact that it is bio-degradable, non-toxic, recyclable and could be easily prepared using inexpensive raw materials. The recyclability for DES was studied wherein it was found that ultrasound has no negative effects on DES even up to four runs. In addition, the present work is the first report on the combinative use of DES and US in organic synthesis.     

Interfacing High-Energy Charge-Transfer States to a Near-IR Sensitizer for Efficient Electron Transfer upon Near-IR Irradiation

Push–pull systems comprising of triphenylamine–tetracyanobutadiene (TPA-TCBD), a high-energy charge-transfer species, are linked to a near-IR sensitizer, azaBODIPY, for promoting excited-state CS. These systems revealed panchromatic absorption owing to intramolecular CT and near-IR absorbing azaBODIPY. Using electrochemical and computational studies, energy levels were established to visualize excited state events. Fs-TA studies were performed to monitor excited state CT events. From target analysis, the effect of solvent polarity, number of linked CT entities, and excitation wavelength dependence in governing the lifetime of CS states was established. Electron exchange between two TPA-TCBD entities in 3 seem to prolong lifetime of the CS state. We have been successful in demonstrating efficient CS upon both high-energy CT and low-energy near-IR excitations, signifying importance of these push–pull systems for optoelectronic applications operating in the wide optical window.     

Comparing symbolic powers of edge ideals of weighted oriented graphs

Journal of Algebraic Combinatorics - Let D be a weighted oriented graph and I(D) be its edge ideal. If D contains an induced odd cycle of length $$2n+1$$ , under certain condition, we show that $$...