Model for Triplet State Engineering in Organic Light Emitting Diodes

Engineering the position of the lowest triplet state (T1) relative to the first excited singlet state (S1) is of great importance in improving the efficiencies of organic light emitting diodes and organic photovoltaic cells. We have carried out model exact calculations of substituted polyene chains to understand the factors that affect the energy gap between S1 and T1. The factors studied are backbone dimerisation, different donor-acceptor substitutions and twisted geometry. The largest system studied is an eighteen carbon polyene which spans a Hilbert space of about 991 million. We show that for reverse intersystem crossing (RISC) process, the best system involves substituting all carbon sites on one half of the polyene with donors and the other half with acceptors.Comment: 7 Pages; 10 Figure

Static polarizability of molecular materials: environmental and vibrational contributions

Modeling the dielectric behavior of molecular materials made up of large pi-conjugated molecules is an interesting and complex task. Here we address linear polarizabilities, and the related dielectric constant, of molecular crystals and aggregates made up of closed-shell pi-conjugated molecules with either a non-polar or largely polar ground-state, and also examine the behavior of mixed-valence (or charge-transfer) organic salts. We recognize important collective phenomena due to supramolecular interactions in materials with large molecular polarizabilities, and underline large vibrational contributions to the polarizability in materials with largely delocalized electrons.Comment: 18 pages, including 9 figure

Disentangling Neutrino Oscillations

The theory underlying neutrino oscillations has been described at length in the literature. The neutrino state produced by a weak decay is usually portrayed as a linear superposition of mass eigenstates with, variously, equal energies or equal momenta. We point out that such a description is incomplete, that in fact, the neutrino is entangled with the other particle or particles emerging from the decay. We offer an analysis of oscillation phenomena involving neutrinos (applying equally well to neutral mesons) that takes entanglement into account. Thereby we present a theoretically sound proof of the universal validity of the oscillation formulae ordinarily used. In so doing, we show that the departures from exponential decay reported by the GSI experiment cannot be attributed to neutrino mixing. Furthermore, we demonstrate that the `Mossbauer' neutrino oscillation experiment proposed by Raghavan, while technically challenging, is correctly and unambiguously describable by means of the usual oscillation formalae.Comment: 16 page

Dielectric response of modified Hubbard models with neutral-ionic and Peierls transitions

The dipole P(F) of systems with periodic boundary conditions (PBC) in a static electric field F is applied to one-dimensional Peierls-Hubbard models for organic charge-transfer (CT) salts. Exact results for P(F) are obtained for finite systems of N = 14 and 16 sites that are almost converged to infinite chains in deformable lattices subject to a Peierls transition. The electronic polarizability per site, \alpha_{el} = (\partial P/\partial F)_0, of rigid stacks with alternating transfer integrals t(1 +/- \delta) diverges at the neutral-ionic transition for \delta = 0 but remains finite for \delta > 0 in dimerized chains. The Peierls or dimerization mode couples to charge fluctuations along the stack and results in large vibrational contributions, \alpha_{vib}, that are related to \partial P/\partial \delta and that peak sharply at the Peierls transition. The extension of P(F) to correlated electronic states yields the dielectric response \kappa of models with neutral-ionic or Peierls transitions, where \kappa peaks >100 are found with parameters used previously for variable ionicity \rho and vibrational spectra of CT salts. The calculated \kappa accounts for the dielectric response of CT salts based on substituted TTFs (tetrathiafulvalene) and substituted CAs (chloranil). The role of lattice stiffness appears clearly in models: soft systems have a Peierls instability at small \rho and continuous crossover to large \rho, while stiff stacks such as TTF-CA have a first-order transition with discontinuous \rho that is both a neutral-ionic and Peierls transition. The transitions are associated with tuning the electronic ground state of insulators via temperature or pressure in experiments, or via model parameters in calculations.Comment: 10 pages, 9 figures; J.Chem.Phys., in pres

The Choice of Marketing Cooperative in a Transition Agriculture

The agriculture in transition countries can be described by considerable uncertainties. In these countries public institutions are ineffective in ensuring contract enforcement. The absence of enforceable contract to set up any kind of vertical co-ordination has become difficult. In addition, this creates severe barriers for price discovery involving high transaction costs to co-ordinate market exchanges. Although there is a wealth of literature on marketing cooperative, but research on their role in transition agriculture is scarce. This paper tries to contribute to this gap. In this paper we have analysed the potential benefits and costs of the marketing cooperatives in Hungary employing transaction cost economics framework. The results presented add to a small literature on the marketing cooperatives in transition agriculture. We found that the quantity, the existence of contract, flexibility and trust are the most important factor for farmers to selling their product via cooperative. The cluster analysis provides some additional insights regarding farmers' choices. Namely, direct benefits including price, input finance extension services and speed of payments from cooperative membership have also important role. The most striking result is that the diversification and reputation has positive influences on the share of cooperative. Furthermore, large farmers have less willingness to sell their product to the cooperative. Surprisingly, asset specificity has rather negative effects on the share of cooperative.Agribusiness,

THE IMPACT OF TRUST ON COOPERATIVE MEMBERSHIP PERFORMANCE AND SATISFACTION IN THE HUNGARIAN HORTICULTURE

The paper investigates the impacts of trust on the relationships among members and between members and the management in an agricultural marketing cooperative in the Hungarian horticultural sector. We focus on the effects of trust on cooperative members performance and satisfaction and their commitment to remaining a part of cooperative. We analyse the trust along two dimensions: cognitive and affective. Our results suggest that trust among cooperative members and trust between cooperative and management have positive effects on group cohesions. In line with a priori hypotheses we found differences between cognitive and affective trust influencing the group cohesion and cooperative members satisfaction.trust, marketing cooperative, Hungary, Farm Management, Marketing,

Price transmission in the Hungarian vegetable sector

In this paper we analyse price transmission for the carrot, parsley, tomato, green pepper and potato markets. Although there is a dual farm structure dominated by small individual farms, our results imply that price information flows from the producer to the retail level for potatoes, parsley and carrots. Our results also suggest that farmers do not merely accept prices, but can actually influence market prices. Tomato and green pepper prices have large transmission elasticities, and causality runs from the retail to producer level. It therefore follows that tomato and green pepper producers tend to accept prices and that the sector’s prices are determined by upper market levels (processors, wholesalers, retailers). These results are reinforced by the fact that vegetable producers sell a large share of their production through procurement and processing, and therefore are more dependent on the upstream industries, and thus cannot influence prices. For all vegetables in this study the short-run price transmission is symmetric while on the tomato market the long-run price transmission is asymmetric. Results indicate that the tomato market is not competitive and efficient; therefore processors, wholesalers, and retailers are capable of exercising market power, and can instantly transmit producer price increases while just slowly and partially transmitting producer price decreases.Hungarian vegetable sector, producer prices, price transmission, Demand and Price Analysis, Crop Production/Industries,

Current and voltage based bit errors and their combined mitigation for the Kirchhoff-law-Johnson-noise secure key exchange

We classify and analyze bit errors in the current measurement mode of the Kirchhoff-law-Johnson-noise (KLJN) key distribution. The error probability decays exponentially with increasing bit exchange period and fixed bandwidth, which is similar to the error probability decay in the voltage measurement mode. We also analyze the combination of voltage and current modes for error removal. In this combination method, the error probability is still an exponential function that decays with the duration of the bit exchange period, but it has superior fidelity to the former schemes.Comment: 9 pages, accepted for publication in Journal of Computational Electronic

A coding problem for pairs of subsets

Let $X$ be an $n$--element finite set, $0<k\leq n/2$ an integer. Suppose that $\{A_1,A_2\}$ and $\{B_1,B_2\}$ are pairs of disjoint $k$-element subsets of $X$ (that is, $|A_1|=|A_2|=|B_1|=|B_2|=k$, $A_1\cap A_2=\emptyset$, $B_1\cap B_2=\emptyset$). Define the distance of these pairs by $d(\{A_1,A_2\} ,\{B_1,B_2\})=\min \{|A_1-B_1|+|A_2-B_2|, |A_1-B_2|+|A_2-B_1|\}$. This is the minimum number of elements of $A_1\cup A_2$ one has to move to obtain the other pair $\{B_1,B_2\}$. Let $C(n,k,d)$ be the maximum size of a family of pairs of disjoint subsets, such that the distance of any two pairs is at least $d$. Here we establish a conjecture of Brightwell and Katona concerning an asymptotic formula for $C(n,k,d)$ for $k,d$ are fixed and $n\to \infty$. Also, we find the exact value of $C(n,k,d)$ in an infinite number of cases, by using special difference sets of integers. Finally, the questions discussed above are put into a more general context and a number of coding theory type problems are proposed.Comment: 11 pages (minor changes, and new citations added