Athermal character of the solid state amorphization of lactose induced by ball milling

In this paper, we report the possibility to reach pure glassy amorphous lactose by ball milling of crystalline α lactose under a dry nitrogen atmosphere. This route to the glassy state is found to be free of mutarotation towards the anomer β while this mutarotation is unavoidable using the usual thermal route, i.e. the quench of the liquid. This result definitely makes the ‘local quench melting’ hypothesis unsuitable to account for amorphization by ball milling.     

Efficient Sensing of Explosives by Using Fluorescent Nonporous Films of Oligophenyleneethynylene Derivatives Thanks to Optimal Structure Orientation and Exciton Migration

The fluorescence of thin films of a diimine‐substituted phenyleneethynylene compound can be efficiently quenched by nitroaromatic vapors, which is not the case for the unsubstituted parent compound. Thin‐film porosity is usually considered to be an essential factor for efficient quenching, but in the present case the origin of the quenching is completely different, as both films are nonporous and hermetic to 2,4‐dinitrotoluene (DNT) molecules. The molecular organization in the two crystallized thin films offers a low level of π stacking for both compounds, but the orientation of the phenylenethynylene fluorophore differs markedly with respect to the surface of the films. For the substituted compound, the fluorophore is almost parallel to the surface, thus making it readily available to molecules of a nitroaromatic quencher. This rationale is also observed in the case of a related compound bearing methoxy side chains instead of the long octyloxy moieties. Fluorescence‐lifetime experiments show that the efficient quenching process in the nonporous crystallized films of the substituted compound is due to a fast (<70 ps) diffusion of excitons from the bulk of the film toward the surface where they are quenched, thus providing evidence of antenna effects.     

Complexing capacity of low-level radioactive waste leachates for Co and Cd using an ion-exchange technique

Low-level radioactive wastes (LLRW) intended for disposal at Chalk River laboratories (CRL) are composed primarily (>90% by volume) of organic material (paper, used clothing, packaging material, mop heads, etc.). Upon contact with water, microbial degradation of this material will produce dissolved organic matter (DOM) which has the potential to change the speciation and mobility of radionuclides in soils. The determination of the aqueous speciation of nuclides will provide a tool that will enable a better prediction of the behaviour of nuclides and their potential to migrate in soils.

This work is one aspect of the characterisation of the DOM produced by the microbial degradation of LLRW. An ion-exchange technique was set up to demonstrate the applicability of the method to determine the complexing capacity of the DOM in a difficult matrix. Leachates from a LLRW degradation experiment were used with two radioisotopes (¹⁰⁹Cd and ⁶⁰Co). The method allows the determination of the free-ion content of a metal in a solution, which also leads to the determination of the complexed fraction.

The leachate matrix consisted of 0.1 M ionic strength of inorganic salts, with 4177 mg C/l of DOM. The complexing capacity of the DOM in the leachates was 50 μg/l for Co, and 0.54 μg/l for Cd. This represents 0.0028% and 0.000015% of the available DOM sites to Co and Cd, respectively. The conditional stability constant of the DOM with Cd was slightly higher (log β = 1.98) than that of acetic acid, whereas it was ambiguous for Co (log β = 2.02 or 2.54). DOM fouling did not constitute a problem, and the method could be used for other radionuclides and metals.     

Efficient Bayesian Inference for Generalized Bradley–Terry Models

The Bradley–Terry model is a popular approach to describe probabilities of the possible outcomes when elements of a set are repeatedly compared with one another in pairs. It has found many applications including animal behavior, chess ranking, and multiclass classification. Numerous extensions of the basic model have also been proposed in the literature including models with ties, multiple comparisons, group comparisons, and random graphs. From a computational point of view, Hunter has proposed efficient iterative minorization-maximization (MM) algorithms to perform maximum likelihood estimation for these generalized Bradley–Terry models whereas Bayesian inference is typically performed using Markov chain Monte Carlo algorithms based on tailored Metropolis–Hastings proposals. We show here that these MM algorithms can be reinterpreted as special instances of expectation-maximization algorithms associated with suitable sets of latent variables and propose some original extensions. These latent variables allow us to derive simple Gibbs samplers for Bayesian inference. We demonstrate experimentally the efficiency of these algorithms on a variety of applications.     

Causal coupling inference from multivariate time series based on ordinal partition transition networks

Nonlinear Dynamics - Identifying causal relationships is a challenging yet crucial problem in many fields of science like epidemiology, climatology, ecology, genomics, economics and neuroscience,...     

A modified simplex partition algorithm to test copositivity

Journal of Global Optimization - A real symmetric matrix A is copositive if $$x^\top Ax\ge 0$$ for all $$x\ge 0$$ . As A is copositive if and only if it is copositive on the standard simplex,...     

Interaction of Functionalized Naphthalenophanes with Abasic Sites in DNA: DNA Cleavage,DNA Cleavage Inhibition,and Formation of Ligand–DNA Adducts

Ligands interacting with abasic (AP) sites in DNA may generate roadblocks in base-excision DNA repair (BER) due to indirect inhibition of DNA repair enzymes (e.g., APE1) and/or formation of toxic byproducts, resulting from ligand-induced strand cleavage or covalent cross-links. Herein, a series of 12 putative AP-site ligands, sharing the common naphthalenophane scaffold, but endowed with a variety of substituents, have been prepared and systematically studied. The results demonstrate that most naphthalenophanes bind to AP sites in DNA and inhibit the APE1-induced hydrolysis of the latter in vitro. Remarkably, their APE1 inhibitory activity, as characterized by IC₅₀ and K_I values, can be directly related to their affinity and selectivity to AP sites, as assessed by means of fluorescence melting experiments. On the other hand, the molecular design of naphthalenophanes has a crucial influence on their intrinsic AP-site cleavage activity (i.e., ligand-catalyzed β- and β,δ-elimination reactions at the AP site), as illustrated by the compounds either having an exceptionally high AP-site cleavage activity (e.g., 2,7-BisNP-S , 125-fold more efficacious than spermine) or being totally devoid of this activity (four compounds). Finally, the unprecedented formation of a stable covalent DNA adduct upon reaction of one ligand ( 2,7-BisNP-NH ) with its own product of the AP-site cleavage is revealed.     

Electron-exciton complex formation in organic solids

Sharp structure in the doubly differentiated electron transmission spectra of thin (? 150 Å) benzene films is shown to result from electron-exciton complex formation. The large energy shift between the electronic energy levels of the molecule and the transmission maxima is related to the electron binding energy. This is due to the polarizability difference between the Frenkel exciton and the organic molecule. From a simple Wigner-Seitz model, we show that the captured electron is localized between the exciton and the sorrounding molecules.     

The energy-band parameters of cadmium arsenide and their variation with temperature and pressure

Using Kane's model for an HgTe-type inverted energy band structure along with available transport and optical data, various band parameters of Cd₃As₂ have been obtained at room and at low temperatures. Theoretical estimates of the variation of the energy gap at Γ as a function of temperature and pressure have also been obtained. These are found to be consistent with our band model and with our analysis of existing temperature and pressure data.