Polymerization of styrene to isotactic polymer with MAO-Ni(acac)2. Examination of the factors that influence activity and stereospecificity

The soluble catalyst system methylaluminoxane (MAO)-Ni(acac), (acac: acetylacetonate) gives polystyrene consisting of an amorphous (aPS) and a crystalline isotactic (ips) fraction. Al(CH₃)₃, which is always present in commercial samples of MAO, decreases both polymer yield and stereospecificity. The polymer yield increases with increasing the MAO/Ni ratio but, at the same time, the iPS/aPS ratio decreases. Addition of N(C₂H₅)₃ (mole ratio N/Ni = 1) increases the proportion of the isotactic fraction, while it decreases the polymer yield. A tentative interpretation of the stereospecificity is reported.     

LAA: a project using dedicated funding to develop technology for high-energy physics experiments

The European Physical Journal H - In the mid-1980s, the cost of investment in infrastructure for particle accelerators and colliders at the highest energy had risen to such level that the host...     

How graphene flexes and stretches under concomitant bending couples and tractions

We propose a geometrically and materially nonlinear discrete mechanical model of graphene that assigns an energetic cost to changes in bond lengths, bond angles, and dihedral angles. We formulate a variational equilibrium problem for a rectangular graphene sheet with assigned balanced forces and couples uniformly distributed over opposite side pairs. We show that the resulting combination of stretching and bending makes achiral graphene easier to bend and harder (easier) to stretch for small (large) traction loads. Our general developments hold for a wide class of REBO potentials; we illustrate them in detail by numerical calculations performed in the case of a widely used 2nd-generation Brenner potential.     

DNA interaction of platinum(II) complexes with 1,10-phenanthroline and extended phenanthrolines

The interaction with DNA of the platinum(II) square planar complexes [Pt(N-N)(py)(2)](2+) (N-N = 1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), dipyrido[3,2-a:2',3'-c]phenazine (dppz), benzodipyrido[b:3,2-h:2'3'-f]phenazine (bdppz)) has been investigated by means of absorption, circular and linear dichroism spectroscopy, DNA melting, and viscosity. In the presence of excess [DNA] all the complexes intercalate to the double helix. For those with the most extended phenanthrolines the binding mode depends on the [DNA]/[complex] ratio (q); at low q values the substances bind externally to DNA probably self-aggregating along the double helix. When the DNA concentration is large enough, the aggregate breaks up and the complex intercalates within the nucleobases. The complexes self-aggregate, without added DNA, in the presence of a large salt concentration.     

Laboratory tests addressed to realize customized restoration procedures of underwater archaeological ceramic finds

The present contribution is part of a biennial research project funded by the Italian Ministry of Education, Universities and Research (MIUR). This study, currently in progress, deals with innovative experimental approaches applied to the chemical, mineralogical and physical transformations occurring during the prolonged permanence of archaeological ceramic finds in seawater environments as well as to restoration and conservation issues of the same underwater artifacts. The experimental approach used in this research consisted in the manufacture of ceramic test-pieces (briquettes) and their successive placing in underwater environment. This work aims at assessing how textural and compositional parameters along with firing temperatures of a ceramic paste could affect total porosity, pore size distribution and kinetics of capillary water absorption. A further purpose is concerned with the study of the potential modification of porosity and pore size distribution in the same ceramic bodies after immersion in seawater (3 and 6 months). The study was carried out using a multi-technique approach including investigations through polarized light microscopy (PLM), capillary water absorption test, mercury intrusion porosimetry (MIP) analyses and theoretical calculation of salt crystallization pressures. The obtained results show a different behavior of the six experimental pastes as a function of their compositional and textural features as well as pore size distribution and firing temperatures. These parameters, in various extents, have been found significantly influencing the kinetics of water absorption and the susceptibility of ceramic artifacts to salt crystallization processes, with important implications on conservation procedures needed before the musealization.     

Interpretation of cw-ESR spectra of p-methyl-thio-phenyl-nitronyl nitroxide in a nematic liquid crystalline phase

In this paper we report on the characterization by continuous wave electron spin resonance spectroscopy (cw-ESR) of a nitronyl nitroxide radical in a nematic phase. A detailed analysis is performed by exploiting an innovative modeling strategy alternative to the usual spectral simulation approach: most of the molecular parameters needed to calculate the spectrum are evaluated a priori and the ESR spectrum is obtained by direct application of the stochastic Liouville equation. Allowing a limited set of fitting parameters it is possible to reproduce satisfactorily ESR spectra in the temperature range 260 K-340 K including the nematic-to-isotropic phase transition (325.1 K). Our results open the way to a more quantitative understanding of the ordering and mobility of nitronyl nitroxide radicals in nanostructured environments.     

Studying ancient crop provenance: implications from δ(13)C and δ(15)N values of charred barley in a Middle Bronze Age silo at Ebla(NW Syria)

The discovery of a storeroom full of barley and other cereals (L.9512) in the proto-historic site of Ebla has provided a unique opportunity to study the centralized storage system of the early city-state from a different perspective. Epigraphic evidence available within the site reveals a complex system of taxation which included gathering grain tributes from satellite sites and redistributing semi-finished products such as flour. In this paper, we intend to explore the possibilities of a combined approach to studying the storage system, based on estimated barley grain volumes and δ(13)C-δ(15)N analyses. This approach is used to distinguish between grain from different harvesting sites and to identify any grain cultivated using special agricultural practices (e.g. manuring or irrigation). The basic assumption for this kind of analysis is that the growth-site conditions, natural or anthropogenic, of harvested cereals are reflected in their grain size and δ(13)C-δ(15)N values. Since the remains found in the storeroom were charred, the first task was to evaluate the effect of carbonization on the δ(13)C-δ(15)N and the size of the grains. Thus, the effect of charring was tested on modern samples of Syrian barley landraces. Once it had been ascertained that fresh grains reduced to charred remains retain their original biometric and isotopic traits, the ancient material was examined. Thirteen groups were identified, each characterized by a specific average volume and specific carbon and nitrogen values. The analysis revealed that what had first appeared to be a homogeneous concentration of grain was in fact an assemblage of barley harvested from different sites.     

Synthesis, physicochemical properties and antioxidant activity of deferiprone-cyclodextrin conjugates and their iron(III) complexes

3-Hydroxy-1,2-dimethylpyridin-4(1H)-one (deferiprone) is a successful iron chelator, which has been widely investigated for its activity in mitigating iron overload and in protecting against oxidative stress due to Reactive Oxygen Species (ROS). Herein, we present the synthesis, characterisation, physicochemical properties and antioxidant activity of two novel bioconjugates of β-cyclodextrin bearing the deferiprone moiety either on the upper rim (1) or on the lower rim (2) of the cyclodextrin and their iron(III) complexes. Protonation and iron stability constants were measured by spectrophotometric titration for the two systems and antioxidant activity studied for both the ligands and the iron(III) complexes.     

Towards a Loop Quantum Gravity and Yang–Mills unification

We propose a new method of unifying gravity and the Standard Model by introducing a spin-foam model. We realize a unification between an SU(2)$\mathit{SU}(2)$ Yang–Mills interaction and 3D   general relativity by considering a constrained Spin(4)∼SO(4)$\mathrm{Spin}(4)\sim \mathit{SO}(4)$ Plebanski action. The theory is quantized à la   spin-foam by implementing the analogue of the simplicial constraints for the Spin(4)$\mathrm{Spin}(4)$ symmetry, providing a way to couple Yang–Mills fields to spin-foams. A natural 4D extension of the theory is introduced. We also present a way to recover 2-point correlation functions between the connections as a first way to implement scattering amplitudes between particle states, aiming to connect Loop Quantum Gravity to new physical predictions.     

Accusation probabilities in Tardos codes: beyond the Gaussian approximation

We study the probability distribution of user accusations in the q-ary Tardos fingerprinting system under the Marking Assumption, in the restricted digit model. In particular, we look at the applicability of the so-called Gaussian approximation, which states that accusation probabilities tend to the normal distribution when the fingerprinting code is long. We introduce a novel parametrization of the attack strategy which enables a significant speedup of numerical evaluations. We set up a method, based on power series expansions, to systematically compute the probability of accusing innocent users. The ‘small parameter’ in the power series is 1/m, where m is the code length. We use our method to semi-analytically study the performance of the Tardos code against majority voting and interleaving attacks. The bias function ‘shape’ parameter k{{\kappa}} strongly influences the distance between the actual probabilities and the asymptotic Gaussian curve. The impact on the collusion-resilience of the code is shown. For some realistic parameter values, the false accusation probability is even lower than the Gaussian approximation predicts.