An efficient implementation of a QM�CMM method in SIESTA

We present the major features of a new implementation of a QM?CMM method that uses the DFT code Siesta to treat the quantum mechanical subsystem and the AMBER force field to deal with the classical part. The computation of the electrostatic interaction has been completely revamped to treat periodic boundary conditions exactly, using a real-space grid that encompasses the whole system. Additionally, we present a new parallelization of the Siesta grid operations that provides near-perfect load balancing for all the relevant operations and achieves a much better scalability, which is important for efficient massive QM?CMM calculations in which the grid can potentially be very large.     

Crystallization in glasses monitored by thermomechanical analysis

Thermomechanical analysis (TMA) can be used as a sensitive tool to follow crystallization behavior in non-crystalline materials. Newly developed method is based on slowing down of sample deformation caused by viscous flow above the glass transition due to macroscopic crystal growth. It is shown that a typical TMA sigmoidal curve reasonably well corresponds to direct measurement of crystal growth kinetics by means of optical microscopy. The method has been used to study crystallization kinetics in Ge₃₈S₆₂ glass. The TMA measurement is able to detect earlier stages of crystallization than obtained by differential scanning calorimetry measurement. The activation energy obtained from the shift of extrapolated end of TMA curve with heating rate (E = 263 ± 7 kJ mol^?1) is similar to the activation energy of ??-GeS₂ crystal growth in Ge₃₈S₆₂ glass (E _G = 247 ± 23 kJ mol^?1) obtained from direct optical microscopy measurements.     

Thermodynamics of complexation of tauro- and glyco-conjugated bile salts with two modified ��-cyclodextrins

The interaction between two modified ??-cyclodextrins and bile salts, common for rat, dog and man, was studied using isothermal titration calorimetry. The structural differences in the interaction were investigated by ¹³C NMR. The two modified ??-cyclodextrins were chosen because of their frequent use as oral excipients in drug formulation and in marketed products. All the investigated bile salts had an affinity for the ??-cyclodextrins, although there were large variations in the stability constants. The variations in the enthalpic and entropic contributions to the overall Gibbs free energy revealed differences in the binding mode to the investigated bile salts, i.e. the bile salts with a hydroxyl group at C12 interacted differently than bile salts without this hydroxyl group. These observations were supported by ¹³C NMR, which suggested binding to the D-ring of the steroid structure for bile salts with a hydroxyl group at C12 and to the C-ring for the bile salts without this hydroxyl group. The type of substitution of ??-cyclodextrin had significant effects on the thermodynamics of the interaction where especially the entropic changed were affected.     

A functional equation involving comparable weighted quasi-arithmetic means

We discuss the functional equation $$f(M(x,y))=f(N(x,y)) \qquad (x,y\in I) $$ where I is a nonvoid open subinterval of the set of real numbers ?, f:?I??? is an unknown function, and M, N are weighted quasi-arithmetic means on?I. Our typical assumption will be that M and N are comparable. Complete solution will be presented under the additional supposition that f is the product of the generating functions of?M and?N, respectively.     

Formation of copper(I)-templated [2]rotaxanes using ��click�� methodology: influence of the base, the thread and the catalyst

Three new copper(I)-assembled [2]rotaxanes incorporating the same macrocycle and different axes containing a bipy, a phen or a terpy have been synthesized thanks to CuAAC reaction for attaching the stoppers. The influence of the nature of the base used for the stoppering reaction was investigated on the formation of the bipy-containing rotaxane. The yield of the [2]rotaxane synthesis was increased when using a phen as a coordinating unit in the thread with [Cu(CH₃CN)₄](PF₆) as catalyst. The strong influence of the nature of the catalyst was clearly evidenced for the formation of the terpy rotaxane, increasing the yield of the stoppering reaction from 0 to 95% by just substituting the Cu(I) catalyst. Finally, the best conditions found for our systems are the use of Na₂CO₃ as a base and Cu(tren??)Br as a catalyst.     

��Hypertractions and hyperstresses convey the same mechanical information Continuum Mech. Thermodyn. (2010) 22:163�C176�� by Prof. Podio Guidugli and Prof. Vianello and some related papers on higher gradient theories

In this commentary, we try to make clearer the state of the art concerning the relation between mechanical contact interactions and the different notions of stresses. We emphasize the importance of the concept of virtual displacements. Its role has been recognized in Mechanics and in Continuum Mechanics long ago (see e.g., Vailati in Il principio dei lavori virtuali da Aristotele a Erone d’Alessandria, 113–128, 1987; Russo in The forgotten revolution, Springer, Berlin, 2003, or Cosserat and Cosserat in Sur la Théorie des Corps Déformables, Herman, Paris, 1909; Cosserat and Cosserat in Note sur la théorie de l.action euclidienne, Gauthier-Villars, Paris, 1908), and it is central as well when starting with an expression of the power expended by internal stresses and deducing the form of contact interactions as when starting with some form of the contact interactions and developing a representation theorem for these contact interactions based on the Cauchy tetrahedron construction.     

On the birth of stall cells on airfoils

Critical point theory asserts that two-dimensional topologies are defined as degeneracies and any three-dimensional disturbance of a two-dimensional flow will lead to a new three-dimensional flowfield topology, regardless of the disturbance amplitude. Here, the topology of the composite flowfields reconstructed by linear superposition of the two-dimensional flow around a stalled airfoil and the leading stationary three-dimensional global eigenmode has been studied. In the conditions monitored the two-dimensional flow is steady and laminar and is separated over a fraction of the suction side, while the amplitudes considered in the linear superposition are small enough for the linearization assumption to be valid. The multiple topological bifurcations resulting have been analysed in detail; the surface streamlines generated by the leading stationary global mode of the separated flow have been found to be strongly reminiscent of the characteristic stall cells, observed experimentally on airfoils just beyond stall in both laminar and turbulent flow.     

Collimated-hole structures as efficient differential pumping barrier, one-way valve and tool for aligning Penning traps

A collimated-hole structure consists of a very large number of parallel channels which have each a very small diameter and are closely packed together. Such devices, installed in vacuum systems allow one to separate regions of very different gas pressures. A collimated-hole structure has high transmission for a directed ion beam with low emittance but a very low conductance for rest gas atoms or molecules exhibiting random walk. Therefore it is proposed to use such a structure as one-way valve and/or efficient differential pumping barrier in set-ups using Penning traps. Furthermore, these devices might be very useful to align the axis of a Penning trap with the direction of the magnetic field lines which is essential to avoid systematic uncertainties in high-accuracy mass spectroscopy.     

Projecting the Bethe�CSalpeter Equation onto the Light-Front and Back: A Short Review

The technique of projecting the four-dimensional two-body Bethe?CSalpeter equation onto the three-dimensional Light-Front hypersurface, combined with the quasi-potential approach, is briefly illustrated, by placing a particular emphasis on the relation between the projection method and the effective dynamics of the valence component of the Light-Front wave function. Some details on how to construct the Fock expansion of both (a) the Light-Front effective interaction and (b) the electromagnetic current operator, satisfying the proper Ward?CTakahashi identity, will be presented, addressing the relevance of the Fock content in the operators living onto the Light-Front hypersurface. Finally, the generalization of the formalism to the three-particle case will be outlined.