Y(P,V)O4:Dy phosphors for white light generation: Emission dynamics and host effect

The structural characteristics and optical spectra of Y(P,V)O₄:Dy³⁺phosphors obtained by solid state reaction, sol-gel and hydrothermal routes have been investigated and compared. The luminescence features of these materials show a complicate dependence on the composition, synthetic method and excitation conditions. The emission performance depends on different effects: host luminescence, energy transfer to the doping ions and host dependence of the Dy³⁺ emission properties. These effects have been rationalized in order to provide useful information for the development of a suitable material for the white light emitting phosphors technology.     

Comparison of mass transfer models for the numerical prediction of sheet cavitation around a hydrofoil

Cavitating flows, which can occur in a variety of practical cases, can be modelled with a wide range of methods. One strategy consists of using the RANS (Reynolds Averaged Navier Stokes) equations and an additional transport equation for the liquid volume fraction, where mass transfer rate due to cavitation is modelled by a mass transfer model. In this study, we compare three widespread mass transfer models available in literature for the prediction of sheet cavitation around a hydrofoil. These models share the common feature of employing empirical coefficients, to tune the models of condensation and evaporation processes, that can influence the accuracy and stability of the numerical predictions. In order to compare the different mass transfer models fairly and congruently, the empirical coefficients of the different models are first well tuned using an optimization strategy. The resulting well tuned mass transfer models are then compared considering the flow around the NACA66(MOD) and NACA009 hydrofoils. The numerical predictions based on the three different tuned mass transfer models are very close to each other and in agreement with the experimental data. Moreover, the optimization strategy seems to be stable and accurate, and could be extended to additional mass transfer models and further flow problems.     

Guest-controlled aggregation of cavitand gold nanoparticles and N-methyl pyridinium-terminated PEG

The introduction of a disulfide functionalized tetraphosphonate cavitand on Au nanoparticles promotes the reversible self-assembly of a hybrid network upon addition of a polymeric ditopic guest.     

Supramolecular assemblies tailored by dipyridyl-1,2-4-thiadiazoles: influence of the building blocks in the predictability of the final network

ABSTRACT

Coordinatively unsaturated dithiophosphato complex [Cd((MeO)₂PS₂)₂] (1) was reacted with the bifunctional ligands 3,5-di-(4-pyridyl)-1,2,4-thiadiazole (L1) and 3,5-di-(3-pyridyl)-1,2,4-thiadiazole (L2) to give the helicoidal coordination polymer (1·L1)_∞ and the paddle-wheel dimer (1·L2)₂, both characterised by single-crystal X-ray diffraction. A comparison of the structures with the different supramolecular constructs obtained by reacting L1 and L2 with differently P-substituted dithiophosphoric Ni^II complexes allowed to evaluate the role of the metal ion for the predictable assembly of this class of coordination polymers.     

Dye-Doped Silica Nanoparticles for Enhanced ECL-Based Immunoassay Analytical Performance

The combination of highly sensitive techniques such as electrochemiluminescence (ECL) with nanotechnology sparked new analytical applications, in particular for immunoassay-based detection systems. In this context, nanomaterials, particularly dye-doped silica nanoparticles (DDSNPs) are of high interest, since they can offer several advantages in terms of sensitivity and performance. In this work we synthesized two sets of monodispersed and biotinylated [Ru(bpy)₃]²⁺-doped silica nanoparticles, named bio-Triton@RuNP and bio-Igepal@RuNP, obtained following the reverse microemulsion method using two different types of nonionic surfactants. Controlling the synthetic procedures, we were able to obtain nanoparticles (NPs) offering highly intense signal, using tri-n-propylamine (TPrA) as coreactant, with bio-Triton@RuNps being more efficient than bio-Igepal@RuNP.     

Real-time manipulation of gold nanoparticles inside a scanning electron microscope

The forces needed to overcome static friction and move 150 nm diameter Au nanoparticles on an oxidized Si substrate were measured in Normal and Shear oscillation modes inside a scanning electron microscope (SEM) in real time. The experimental setup consisted of a quartz tuning fork (QTF) mounted onto a high-precision 3D nanomanipulator used with a glued silicon or tungsten tip as a force sensor. Static friction was found to range from tens of nN to several hundred nN. Large variations in static friction values were related to differences in particle shape. Kinetic friction tended to be close to the detection limit and in most cases did not exceed several nN. The influence of thermal treatment in reducing the static friction of nanoparticles was considered.     

An exact approach for the Vertex Coloring Problem

Given an undirected graph $G=(V,E)$, the Vertex Coloring Problem (VCP) requires to assign a color to each vertex in such a way that colors on adjacent vertices are different and the number of colors used is minimized. In this paper, we present an exact algorithm for the solution of VCP based on the well-known Set Covering formulation of the problem. We propose a Branch-and-Price algorithm embedding an effective heuristic from the literature and some methods for the solution of the slave problem, as well as two alternative branching schemes. Computational experiments on instances from the literature show the effectiveness of the algorithm, which is able to solve, for the first time to proven optimality, five of the benchmark instances in the literature, and reduce the optimality gap of many others.     

Multiplicity results for interfaces of Ginzburg-Landau-Allen-Cahn equations in periodic media

The Ginzburg-Landau-Allen-Cahn equation is a variational model for phase coexistence and for other physical problems. It contains a term given by a kinetic part of elliptic type plus a double-well potential. We assume that the functional depends on the space variables in a periodic way.We show that given a plane with rational normal, there are minimal solutions, satisfying the following properties. These solutions are asymptotic to the pure phases and are separated by an interface. The convergence to the pure phases is exponentially fast. The interface lies at a finite distance M from the chosen plane, where M is a universal constant. Furthermore, these solutions satisfy some monotonicity properties with respect to integer translations (namely, integer translations are always comparable to the function).We then show that all the interfaces of the global periodic minimizers satisfy similar monotonicity and plane-like properties.We also consider the case of possibly irrationally oriented planes. We show that either there is a one parameter family of minimizers whose graphs provide a field of extremals or there are at least two solutions, one which is a minimizer and another one which is not. These solutions also have interfaces bounded by a universal constant, they enjoy monotonicity properties with respect to integer translations and the nonminimal solutions are trapped inside a gap of the lamination induced by the minimizers.     

Sum Rules for the spin surface response of metal clusters within the time dependent local spin density approximation

We study surface spin collective modes of simple metallic clusters using a sum rule approach. We derive analytical expressions for the energy and cubic energy-weighted moments of the time-dependent local-spin-density approximation (TDLSDA) strength function. With these two moments we obtain a mean excitation energy of multipole spin modes and study its dispersion with cluster size up to very large sizes. The crucial roles played by the surface diffuseness and by correlation and kinetic energy effects on the resonance energies are stressed.