DNA-Based Asymmetric Inverse Electron-Demand Hetero-Diels–Alder

While artificial cyclases hold great promise in chemical synthesis, this work presents the first example of a DNA-catalyzed inverse electron-demand hetero-Diels–Alder (IEDHDA) between dihydrofuran and various α,β-unsaturated acyl imidazoles. The resulting fused bicyclic O,O-acetals containing three contiguous stereogenic centers are obtained in high yields (up to 99 %) and excellent diastereo- (up to >99:1 dr) and enantioselectivities (up to 95 % ee) using a low catalyst loading. Most importantly, these results show that the concept of DNA-based asymmetric catalysis can be expanded to new synthetic transformations offering an efficient, sustainable, and highly selective tool for the construction of chiral building blocks.     

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.     

Puzzle of bulk conformal field theories at central charge c = 0

Nontrivial critical models in 2D with a central charge c=0 are described by logarithmic conformal field theories (LCFTs), and exhibit, in particular, mixing of the stress-energy tensor with a "logarithmic" partner under a conformal transformation. This mixing is quantified by a parameter (usually denoted b), introduced in Gurarie [Nucl. Phys. B546, 765 (1999)]. The value of b has been determined over the last few years for the boundary versions of these models: b(perco)=-5/8 for percolation and b(poly)=5/6 for dilute polymers. Meanwhile, the existence and value of b for the bulk theory has remained an open problem. Using lattice regularization techniques we provide here an "experimental study" of this question. We show that, while the chiral stress tensor has indeed a single logarithmic partner in the chiral sector of the theory, the value of b is not the expected one; instead, b=-5 for both theories. We suggest a theoretical explanation of this result using operator product expansions and Coulomb gas arguments, and discuss the physical consequences on correlation functions. Our results imply that the relation between bulk LCFTs of physical interest and their boundary counterparts is considerably more involved than in the nonlogarithmic case.     

Natural Convection Induced by a Centrifugal Force Field in a Horizontal Annular Porous Layer Saturated with a Binary Fluid

The Darcy Model with the Boussinesq approximation is used to study natural convection in a horizontal annular porous layer filled with a binary fluid, under the influence of a centrifugal force field. Neumann boundary conditions for temperature and concentration are applied on the inner and outer boundary of the enclosure. The governing parameters for the problem are the Rayleigh number, Ra, the Lewis number, Le, the buoyancy ratio, j{\varphi } , the radius ratio of the cavity, R, the normalized porosity, e{\varepsilon } , and parameter a defining double-diffusive convection (a = 0) or Soret induced convection (a = 1). For convection in a thin annular layer (R → 1), analytical solutions for the stream function, temperature and concentration fields are obtained using a concentric flow approximation and an integral form of the energy equation. The critical Rayleigh number for the onset of supercritical convection is predicted explicitly by the present model. Also, results are obtained from the analytical model for finite amplitude convection for which the flow and heat and mass transfer are presented in terms of the governing parameters of the problem. Numerical solutions of the full governing equations are obtained for a wide range of the governing parameters. A good agreement is observed between the analytical model and the numerical simulations.     

Search with the ATLAS detector for new physics with significant missing transverse energy and two isolated leptons

Results of searches for supersymmetry in events with significant missing transverse energy and two isolated leptons with the ATLAS experiment at the LHC are presented. Three analyses are presented here, the first two are analyses with leptons of opposite charge and same charge, respectively. The third one is an analysis that searches for an excess of same-flavour opposite-charge lepton pairs over those of different-flavour. Data corresponding to an integrated luminosity of 1 fb^?1 are analysed.     

Probability Density Function of the Output Current of Cascaded Multiplexer/Demultiplexers in Transparent Optical Networks

The influence of the concatenation of arbitrary optical multiplexers/demultiplexers (MUX/DEMUXs) on the probability density function (PDF) of the output current of a transparent optical network is assessed. All PDF results obtained analytically are compared with estimates from Monte Carlo simulation and an excellent agreement is achieved.

The non-Gaussian behavior of the PDFs, previously reported by other authors for square-law detectors, is significantly enhanced with the number of nodes increase due to the noise accumulation along the cascade of MUX/DEMUXs. The increase of the MUX/DEMUXs bandwidth and detuning also enhances the PDFs non-Gaussian behavior. The PDF shape variation with the detuning depends strongly on the number of nodes.

Explanations for the Gaussian approximation (GA) accuracy on the assessment of the performance of a concatenation of optical MUX/DEMUXs are also provided. For infinite extinction ratio and tuned MUX/DEMUXs, the GA error probabilities are, in general, pessimistic, due to the inaccurate estimation of the error probability for both bits. For low extinction ratio, the GA is very accurate due to a balance between the error probabilities estimated for the bits “1” and “0.” With the detuning increase, the GA estimates can become optimistic.     

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.