Commutative POVMs and Fuzzy Observables

In this paper we review some properties of fuzzy observables, mainly as realized by commutative positive operator valued measures. In this context we discuss two representation theorems for commutative positive operator valued measures in terms of projection valued measures and describe, in some detail, the general notion of fuzzification. We also make some related observations on joint measurements. This article is dedicated to Pekka Lahti on the occasion of his 60th birthday.     

Nonsymmetric 2‐(v,k,λ) designs,with (r,λ) = 1, admitting a solvable flag‐transitive automorphism group of affine type

Nonsymmetric $2‐\left(v,k,\lambda \right)$ designs, with $\left(r,\lambda \right)=1$, admitting a solvable flag‐transitive automorphism group of affine type not contained in $A\mathrm{\Gamma }{L}_1\left(v\right)$ are classified.     

An Infrared-Finite Algorithm for Rayleigh Scattering Amplitudes,and Bohr's Frequency Condition

In this paper, we rigorously justify Bohr’s frequency condition in atomic spectroscopy. Moreover, we construct an algorithm enabling us to calculate the transition amplitudes for Rayleigh scattering of light at an atom, up to a remainder term of arbitrarily high order in the finestructure constant. Our algorithm is constructive and circumvents the infrared divergences that invalidate standard perturbation theory.     

Liquid fuel microcombustor using microfabricated multiplexed electrospray sources

The use of hydrocarbons is very appealing for the realization of high energy density power sources, so long as the fuel can be stored in the liquid phase. As a result, except for the most volatile hydrocarbons, a miniaturized combustor must rely on a good design of the fuel atomizer, which should yield small, rapidly evaporating droplets to generate the fuel vapor promptly, mix it with the oxidizer and subsequently burn it with the attending heat release. To achieve this goal, we relied on the use of multiplexed electrosprays and a catalytic reactor for fuel conversion consisting of a pack of catalyst impregnated meshes (Microliths^®). Fuel dispersion was achieved by microfabricating the fuel distributor in Si using deep reactive ion etching. Tests were performed using JP-8 as the liquid fuel. Preliminary experiments in a 0.8 cm³ optically accessible combustor, enabling the measurements of droplet size and velocity, revealed that the spreading of the electrospray by Coulombic repulsion is the phenomenon controlling the volume of the mixing/evaporation chamber. Droplet evaporation occurs in the thin (Peclet number dependent) thermal layer preceding the catalytic section of the combustor. Subsequent system optimization in a fully ceramic combustor yielded a volumetric heat release rate as large as 270 MW/m³, a value that is of the same order as that of conventional gas turbines. The small overall combustor volume, at only 0.22 cm³, suggests that the large volumetric energy density was achieved despite the device large surface-to-volume ratio and attending heat losses. The fuel was fully oxidized, with CO/CO₂ ratios well under 1% over a range of equivalence ratios. Inspection of the combustor inner walls after operating continuously for 10 h, revealed no traces of deposits. The design has the potential of being scaled either up or down, depending on power needs.     

Breakup and breakdown of bent kerosene jets in gas turbine conditions

Jet A-1 kerosene injection in air crossflow conditions has been studied for temperature up to 600 K and pressure up to 2 MPa. Thousand frames of jet shadowgraphs have been sampled for each of the 82 experimental conditions to determine statistical parameters characterizing the jet behavior. Among them the breakdown point, corresponding to the spatial position along the jet where the momentum jet looses its coherence, is the most relevant one. The axial coordinate of this point is strongly correlated with the liquid–gas momentum ratio while the breakdown position in gas stream direction mainly depends on the aerodynamic Weber number. This shows that the deformation of the liquid before and after its primary atomization is the most significant correction in respect to the ballistic, inviscid evolution of a bent cylindrical jet. The generalized profile equation, normalized to the breakdown coordinates, is invariant in respect of whatever external parameter and it predicts with high level of accuracy the measured profile upstream of the breakdown position.     

Bioactive peptides from libraries

New ligands for a variety of biological targets can be selected from biological or synthetic combinatorial peptide libraries. The use of different libraries to select novel peptides with potential therapeutic applications is reviewed. The possible combination of molecular diversity provided by combinatorial libraries and a rational approach derived from computational modeling is also considered. Advantages and disadvantages of different approaches are compared. Possible strategies to bypass loss of peptide bioactivity in the transition from ligand selection to in vivo use are discussed.     

Reconstructing the density of states by history-dependent metadynamics

We present a novel method for the calculation of the energy density of states D(E) for systems described by classical statistical mechanics. The method builds on an extension of a recently proposed strategy that allows the free-energy profile of a canonical system to be recovered within a preassigned accuracy [Proc. Natl. Acad. Sci. U.S.A. 99, 12562 (2002)]]. The method allows a good control over the error on the recovered system entropy. This fact is exploited to obtain D(E) more efficiently by combining measurements at different temperatures. The accuracy and efficiency of the method are tested for the two-dimensional Ising model (up to size 50 x 50) by comparison with both exact results and previous studies. This method is a general one and should be applicable to more realistic model systems.     

Velocity and hierarchical spread of epidemic outbreaks in scale-free networks

We study the effect of the connectivity pattern of complex networks on the propagation dynamics of epidemics. The growth time scale of outbreaks is inversely proportional to the network degree fluctuations, signaling that epidemics spread almost instantaneously in networks with scale-free degree distributions. This feature is associated with an epidemic propagation that follows a precise hierarchical dynamics. Once the highly connected hubs are reached, the infection pervades the network in a progressive cascade across smaller degree classes. The present results are relevant for the development of adaptive containment strategies.     

Detecting intermolecular NOEs by means of a novel DPFGSE pulse sequence. Application to the solvation of carbohydrates in binary mixtures

We present a pulse sequence based on solute-to-solvent NOE enhancement and aimed at the detection of intermolecular NOE's. Thus, a W3 pulse cluster is used to selectively filter the solvent signals in a DPFGSE sequence. The sequence has been tested on a sample of glucose dissolved in two binary aqueous mixtures (water-acetonitrile and water-DMSO). We show how the resulting enhancements may derive from intermolecular cross-relaxation or, in the water-DMSO sample, also from chemical exchange. In each case, a quantitative interpretation of the data is also supplied, both in terms of local enrichment in one specific solvent (preferential solvation), and by means of a kinetic model for a two-site chemical exchange.     

Microcavity polariton splitting of intersubband transitions

The optical response of the intersubband excitation of multiple two-dimensional electron gases within a semiconductor microcavity has been studied through angle-dependent reflectance measurements. Using a resonator based on total internal reflection, a clear splitting of about 14 meV of the coupled intersubband cavity modes is observed from 10 K to room temperature, with resulting polaritonlike dispersion. The experimental findings are in good agreement with theoretical calculations performed in a transfer-matrix formalism.