Photonic tunneling between two wires

The tunneling of a well-defined propagating state from one wire to another, leaving all other neighbor states unaffected, is of great importance for photons, electrons and phonons. We present a simple coupling structure enabling such a transfer to be realized, for any given state energy and state width. We illustrate the analytic study of this structure by an application to the transmission of a telecommunication signal. We discuss then how such a structure could be realized with the help of current surface technologies.     

Indecomposability parameters in chiral logarithmic conformal field theory

Work of the last few years has shown that the key algebraic features of Logarithmic Conformal Field Theories (LCFTs) are already present in some finite lattice systems (such as the XXZ spin-1/2 chain) before the continuum limit is taken. This has provided a very convenient way to analyze the structure of indecomposable Virasoro modules and to obtain fusion rules for a variety of models such as (boundary) percolation etc.LCFTs allow for additional quantum numbers describing the fine structure of the indecomposable modules, and generalizing the ‘b-number’ introduced initially by Gurarie for the c=0 case. The determination of these indecomposability parameters (or logarithmic couplings) has given rise to a lot of algebraic work, but their physical meaning has remained somewhat elusive. In a recent paper, a way to measure b for boundary percolation and polymers was proposed. We generalize this work here by devising a general strategy to compute matrix elements of Virasoro generators from the numerical analysis of lattice models and their continuum limit. The method is applied to XXZ spin-1/2 and spin-1 chains with open (free) boundary conditions. They are related to gl(n+m|m) and osp(n+2m|2m)-invariant superspin chains and to non-linear sigma models with supercoset target spaces. These models can also be formulated in terms of dense and dilute loop gas.We check the method in many cases where the results were already known analytically. Furthermore, we also confront our findings with a construction generalizing Gurarie?s, where logarithms emerge naturally in operator product expansions to compensate for apparently divergent terms. This argument actually allows us to compute indecomposability parameters in any logarithmic theory. A central result of our study is the construction of a Kac table for the indecomposability parameters of the logarithmic minimal models LM(1,p) and LM(p,p+1).     

Synthesis and preliminary evaluation of pro-RNA 2'-O-masked with biolabile pivaloyloxymethyl groups in an RNA interference assay

The cellular delivery of bioactive nucleic acid-based drugs such as small interfering RNA (siRNA) represents a major technical hurdle for their pharmaceutical application. Prodrug-like approaches provide an attractive concept to address the delivery problem. With the aim to prepare RNA-based prodrugs bearing biolabile protections which facilitate cellular uptake and are prone to be removed enzymatically inside cells in order to release functional RNA, we synthesized pro-RNA totally or partially masked in 2'-OH position with pivaloyloxymethyl (PivOM) groups. A suitable strategy has been developed to synthesize and to purify base-sensitive mixed 2'-OH/2'-O-PivOM oligoribonucleotides, and to include them in siRNA. In this strategy, the fluoride labile [(triisopropylsilyl)oxy]-benzyloxycarbonyl group (tboc) as nucleobase protection (for A and C), the TBS group as 2'-OH protection and the Q-linker to solid-support were compatible with the PivOM groups masking some 2'-OH. We have taken advantage of the specific stability of the PivOM group to apply selected acidic, basic, and fluoride ions treatment for the deprotection and release of pro-RNA. This kind of pro-siRNA was studied in a human cell culture-based RNAi assay and preliminary promising data are discussed.     

ESI-MS studies of the dehydrogenative Heck reaction of furans with acrylates using benzoquinone as the reoxidant and DMSO as the solvent

Electrospray ionization mass spectrometry, subsequent MS/MS, and high-resolution mass spectrometry were used to study the dehydrogenative Heck reaction of 2-alkylfurans 1 with acrylates 2, using [Pd(OAc)(2)](3) as the precatalyst, benzoquinone (BQ) as the stoichiometric oxidant, and a mixture of DMSO and AcOH as the solvent. Complexation of [Pd(OAc)(2)](3) by DMSO afforded mononuclear and dinuclear Pd(II) species, which proved to be active catalysts for the C-H activation of 1. Mononuclear and dinuclear Pd(II) species seem also to be involved in the insertion of 2 into the furyl-Pd bond. The C-H activation of 2 and DMSO by mononuclear complexes was observed. The reaction leads to 5,5'-dialkyl-2,2'-bifuran 4 as a byproduct. Bifuryl-palladium, which is an intermediate in the formation of 4, showing the coordination of BQ, was obtained and characterized.     

Efficient guanidination of the phosphate linkage towards cationic phosphoramidate oligonucleotides

An efficient postsynthesis method of guanidination of oligonucleotides was employed to introduce several guanidinium groups into internucleotide phosphoramidate linkages. The amino functions of aminobutylphosphoramidate links were converted to guanidine butylphosphoramidates using a solution of O-methylisourea hemisulfate in aqueous ammonia, in a short reaction time. The synthesis of various fully guanidylated oligonucleotides was successfully performed to provide a new class of cationic phosphoramidate oligonucleotides.     

Delocalization due to correlations in two-dimensional disordered systems

We study the spectral statistics of interacting spin-less fermions in a two-dimensional disordered lattice. Within a full quantum treatment for small few-particle systems, we compute the low-energy many-body states numerically. While at weak disorder the interactions reduce spectral correlations and lead to localization, for the case of strong disorder we find that a moderate Coulomb interaction has a delocalizing effect. In addition, we observe a non-universal structure in the level-spacing distribution which we attribute to a mechanism reinforcing spectral correlations taking place in small systems at strong disorder.Received: 1 July 2004, Published online: 14 December 2004PACS: 71.27. + a Strongly correlated electron systems; heavy fermions - 73.20.Jc Delocalization processes - 72.15.Rn Localization effects (Anderson or weak localization)     

Microstubs resonators integrated to bent Y-branch waveguide

We report numerical simulations, based on a finite difference time domain (FDTD) method, of light propagation in two-dimensional semiconductor micro-optical waveguides coupled to one or several lateral stubs. It is shown that when the stub is covered with a perfectly metallic thin layer, the transmission spectrum contains several narrow dips. Such simulation of the metallic coating can be used in the far infrared frequency domain, far from the optical regime. We propose a selective filtering device based on the interaction between several stubs. Inserting an appropriate defect stub between a set of periodical stubs leads to a tunnelling transmission, with a narrow peak inside the gap. This filtering phenomenon is used to propose a demultiplexer based on a Y-shaped waveguide for separating signals with different frequencies. Finally, we show that the filtering effect of a stub can also be reproduced when the metal is described in the frame of a Drude model instead of being perfect, which makes plausible the realization of the above devices in the near optical regime.     

Evidence of fano-like interference phenomena in locally resonant materials

Sonic crystals consisting of three-dimensional arrays of units which exhibit localized resonances have been discovered recently. Here, it is shown that their two-dimensional counterparts behave in a similar manner. Particularly, it is observed that the transmittance spectra show very asymmetric peaks which are explained as a Fano-like interference phenomenon. A finite difference time domain method is employed to perform a comprehensive study of the resonance line shape as a function of the mass density of the structural units. Also, a simple analytical model is introduced to give an intuitive account of the origin of the interference phenomenon.