Synthesis and physico-chemical properties of a novel series of aromatic electron acceptors based on N-heterocycles

The synthesis of a novel series of N-based heterocyclic salts using a simple and efficient N-alkylation of 1,2-bis(4-pyridyl)ethane with reactive halides is reported. These compounds can be transformed into the corresponding pyridinium methylides by addition of a base. The former exhibit an unstable absorption bands at 395–410 nm. The structures of the salts were fully characterized by UV–vis, IR, NMR and MS spectroscopy and elemental analysis. The pK values of selected compounds were also determined and the acid–basic equilibrium was investigated by UV–vis spectrophotometry. The thermal stability of all species was determined by thermogravimetric analysis.     

Viability property for a backward stochastic differential equation and applications to partial differential equations

In the present paper, we study conditions under which the solutions of a backward stochastic differential equation remains in a given set of constraints. This property is the so-called “viability property”. In a separate section, this condition is translated to a class of partial differential equations. Received: 23 April 1998 / Published online: 14 February 2000     

Improved Estimation of Parameter Matrices in a One-Sample and Two-Sample Problems

In this paper, the problems of estimating the covariance matrix in a Wishart distribution (refer as one-sample problem) and the scale matrix in a multi-variate F distribution (which arise naturally from a two-sample setting) are considered. A new class of estimators which shrink the eigenvalues towards their harmonic mean is proposed. It is shown that the new estimator dominates the best linear estimator under two scale invariant loss functions.     

Effects of Y incorporation in TaON gate dielectric on electrical performance of GaAs metal–oxide–semiconductor capacitor

In this study, GaAs metal–oxide–semiconductor (MOS) capacitors using Y‐incorporated TaON as gate dielectric have been investigated. Experimental results show that the sample with a Y/(Y + Ta) atomic ratio of 27.6% exhibits the best device characteristics: high k value (22.9), low interfacestate density (9.0 × 10¹¹ cm^–2 eV^–1), small flatband voltage (1.05 V), small frequency dispersion and low gate leakage current (1.3 × 10^–5A/cm² at V_fb + 1 V). These merits should be attributed to the complementary properties of Y₂O₃ and Ta₂O₅:Y can effectively passivate the large amount of oxygen vacancies in Ta₂O₅, while the positively‐charged oxygen vacancies in Ta₂O₅ are capable of neutralizing the effects of the negative oxide charges in Y₂O₃. This work demonstrates that an appropriate doping of Y content in TaON gate dielectric can effectively improve the electrical performance for GaAs MOS devices.

Capacitance–voltage characteristic of the GaAs MOS capacitor with TaYON gate dielectric (Y content = 27.6%) proposed in this work with the cross sectional structure and dielectric surface morphology as insets.     

Temperature dependence of the single-particle spectrum in sodium clusters

We show that the electronic density of states of small sodium clusters is strongly affected by both thermal fluctuations about the ground state ionic configuration and transitions between different shape isomers as the temperature of the cluster is increased. Contrary to common expectations, the clusters undergo a sharp transition in the temperature range of 100K to 150 K, after which the single-particle level distributions become bimodal. At even higher temperatures the signature of the ground state configuration disappears, and the density of states is dominated by higher energy isomers. We also discuss the implications of these findings for the interpretation of the photoelectron spectra of these systems.     

Martin compactification for discrete potential theory and the mean value property

A converse of the well-known theorem on themean value property of harmonic functions is given. It is shown that a positive measurable function is harmonic if it possesses arestricted mean value property. Earlier proofs obtained using the probabilistic techniques were given by Veech, Heath and Baxter. Our approach is based on a Martin type compactification built up with the help of some quite elementarya priori inequalities foraveraging kernels.     

The effect of delayed feedback information on network performance

The performance of a network subject to either state dependent or state independent flow control is investigated. In the state dependent case, the flow control policy is a function of the total number of packets for which the controller has not yet received an acknowledgment. In this case it is shown that the optimal flow control is a sliding window mechanism. The effect of the delayed feedback on the network performance as well as the size of the window are studied. The state independent optimal rate is also derived. The performance of the state dependent and state independent flow control policies are compared. Conditions for employing one of the two types of flow control policies for superior end-to-end network performance are discussed. All the results obtained are demonstrated using simple examples.