Transparent manganite films as hole injectors for organic light emitting diodes

Organic light-emitting diodes (OLEDs) are nowadays one of the most attractive devices based on organic semiconductors due to their successful application in the display technology. Electroluminescence in OLEDs is mainly governed by the fluorescence from excited singlet states, which have large transition probabilities providing the major radiative pathway. The “forbidden” triplet state emission can be activated by increasing spin–orbit coupling via dye doping. The singlet–triplet exciton formation statistics is usually given by 1:3 partition due to the quantum constrains.

Injection of carriers with finite spin polarisation should influence and modify the recombination statistics and can be used for tuning of the device efficiency. In this context, the development of a new class of electrodes able to guarantee both efficient charge and spin injection becomes of paramount importance. We show that strongly spin polarised colossal magnetoresistance manganite La_0.7Sr_0.3MnO₃ (LSMO) can successfully substitute conventional ITO electrodes in OLEDs. Highly transparent, metallic and ferromagnetic LSMO layers were used in combination with standard Al and spin polarised Co top electrodes. Electrical and optical characterisations of the OLEDs with spin polarised electrodes indicate the applicability of the new manganite electrodes for organic light-emitting devices.     

Covariant polarization bases for spin=12, 1, 32 particles and their use

A simple method is presented for evaluating transition amplitudes between massive states with $\text{spin}\text{=}\text{1}\text{2}\text{, 1}$ and definite polarization. The $\text{spin}\text{-}\text{3}\text{2}$ case is also briefly discussed. Applications to testing the decay and production of vector bosons are considered.     

Minimizing the Makespan in Nonpreemptive Parallel Machine Scheduling Problem

A new n log n algorithm for the scheduling problem of n independent jobs on m identical parallel machines with minimum makespan objective is proposed and its worst-case performance ratio is estimated. The algorithm iteratively combines partial solutions that are obtained by partitioning the set of jobs into suitable families of subsets. The computational behavior on three families of instances taken from the literature provided interesting results.     

Demystifying the three dimensional structure of G protein-coupled receptors (GPCRs) with the aid of molecular modeling

We review our recent work on adenosine receptors, a family of GPCRs; focusing our attention on A3 adenosine receptor, we have demonstrated that the reciprocal integration of different theoretical and experimental disciplines can be very useful for the successful protein-based design of new, potent and selective receptor ligands.     

Boundary terms for massless fermionic fields

Local supersymmetry leads to boundary conditions for fermionic fields in one-loop quantum cosmology involving the Euclidean normal _e n _A/A to the boundary and a pair of independent spinor fields ^A and . This paper studies the corresponding classical properties, i.e., the classical boundary-value problem and boundary terms in the variational problem. If is set to zero on a 3-sphere bounding flat Euclidean 4-space, the modes of the massless spin–1/2 field multiplying harmonics having positive eigenvalues for the intrinsic 3-dimensional Dirac operator onS ³ should vanish onS ³. Remarkably, this coincides with the property of the classical boundary-value problem when spectral boundary conditions are imposed onS ³ in the massless case. Moreover, the boundary term in the action functional is proportional to the integral on the boundary of ^A _e n _AA ^A .     

Synthesis of peptides containing 1,2,3,4-tetrahydroquinoline-2-carboxylic acid. Part 3. Cyclization of dipeptides and amides with acetic anhydride

Treatment of protected dipeptides containing 1,2,3,4-tetrahydroquinoline-2-carboxylic acid with acetic anhydride affords only 1H,3H,5H-oxazolo[3,4-a]quinolin-3-one derivatives. The formation of a-acylaminomethylketones, arising from the competitive Dakin-West reaction, was generally observed when the cyclization procedure was extended to some amides of the cyclic imino acid. The preferential stabilization of one of two probable mesoionic intermediates seems to determine the preferred pathway.     

Mathematical Structures of Space-Time

At first we introduce the space-time manifold and we compare some aspects of Riemannian and Lorentzian geometry such as the distance function and the relations between topology and curvature. We then define spinor structures in general relativity, and the conditions for their existence are discussed. The causality conditions are studied through an analysis of strong causality, stable causality and global hyperbolicity. In looking at the asymptotic structure of space-time, we focus on the asymptotic symmetry group of Bondi, Metzner and Sachs, and the b-boundary construction of Schmidt. The Hamiltonian structure of space-time is also analyzed, with emphasis on Ashtekar's spinorial variables. Finally, the question of a rigorous theory of singularities in space-times with torsion is addressed, describing in detail recent work by the author. We define geodesics as curves whose tangent vector moves by parallel transport. This is different from what other authors do, because their definition of geodesics only involves the Christofel symbols, though studying theories with torsion. We then prove how to extend Hawking's singularity theorem without causality assumptions to the space-time of the ECSK theory. This is achieved studying the generalized Raychauduri equation in the ECSK theory, the conditions for the existence of conjugate points and properties of maximal timelike geodesics. Our result can also be interpreted as a no-singularity theorem if the torsion tensor does not obey some additional conditions. Namely, it seems that the occurrence of singularities in closed cosmological models based on the ECSK theory is less generic than in general relativity. Our work is to be compared with important previous papers. There are some relevant differences, because we rely on a different definition of geodesics, we keep the field equations of the ECSK theory in their original form rather than casting them in a form similar to general relativity with a modified energy-momentum tensor, and we emphasize the role played by the full extrinsic curvature tensor and by the variation formulae.     

Some presentations for the special linear groups on finite fields

We simplify the Steinberg presentation of SL _n (F _d ), where n≥1 and F _d is any finite field with d elements. That presentation has the elementary matrices e _ij (r), with i,j∈{1,...,n}, i≠=j and r∈F _d , as generators, and (E1)–(E3), described at the opening of this work, as relations. The presentation that we shall obtain reduces the number of generators e _ij (r) and relations (E1)–(E3). In particular, relations (E3) are considerably reduced. Received: March 16, 1998; in final form: November 3, 2000?Published online: October 2, 2001