The specific contribution of phosphorus in dendrimer chemistry

Besides properties commonly found for all types of dendrimers, phosphorus-containing dendrimers possess some specific properties seldom or never found for other types of dendrimers. Emphasis will be put on these specificities.     

List of subject

We report the high resolution emission (S₁ → S₀, T₁ → S₀) and laser single site singlet excitation (S₁ ← S₀) spectra for the various insertion sites of coronene in n-heptane cooled to 1.5 K. The observation of site splitting of doubly degenerate vibrations and weak electric dipole forbidden 0, 0 bands in the S₁ → S₀ and T₁ → S₀ spectra indicates that the ground state, the first excited singlet and lowest triplet states are all distorted. In these spectra, the intensity distribution of the various sites in the 0, 0 bands suggests that the distortion is different from site to site but similar in S₀, S₁ and T₁. Identical ordering of the sites in S₁ S₀ and S₁ S₀ spectra as well as the observation of weak shifts in the vibrational frequencies in the two states implies the absence of strong pseudo Jahn-Teller forces in the first excited singlet state. We propose, further, that this is also true for the triplet state. This conclusion is supported by the similarity in zero-field splitting parameters of coronene and deuterated coronene. Taken together, these results indicate strongly that the distortion of coronene in n-heptane is primarily crystal field induced and is not greatly changed upon excitation of the molecule to its lowest excited states.     

Anechoic chamber qualification: traverse method,inverse square law analysis method,and nature of test signal

Qualification of anechoic chambers is intended to demonstrate that the chamber supports the intended free-field environment within some permissible tolerance bounds. Key qualification issues include the method used to obtain traverse data, the analysis method for the data, and the use of pure tone or broadband noise as the chamber excitation signal. This paper evaluates the relative merits of continuous versus discrete traverses, of fixed versus optimal reference analysis of the traverse data, and of the use of pure tone versus broadband signals. The current practice of using widely space discrete sampling along a traverse is shown to inadequately sample the complexity of the sound field extant with pure tone traverses, but is suitable for broadband traverses. Continuous traverses, with spatial resolution on the order of 15% of the wavelength at the frequency of interest, are shown to be necessary to fully resolve the spatial complexity of pure tone qualifications. The use of an optimal reference method for computing the deviations from inverse square law is shown to significantly improve the apparent performance of the chamber for pure tone qualifications. Finally, the use of broadband noise as the test signal, as compared to pure tone traverses over the same span, is demonstrated to be a marginal indicator of chamber performance.     

On composite formal power series

Let be a holomorphic map from to defined in a neighborhood of such that . If the Jacobian determinant of is not identically zero, P. M. Eakin et G. A. Harris proved the following result: any formal power series such that is analytic is itself analytic. If the Jacobian determinant of is identically zero, they proved that the previous conclusion is no more true.

The authors get similar results in the case of formal power series satifying growth conditions, of Gevrey type for instance. Moreover, the proofs here give, in the analytic case, a control of the radius of convergence of by the radius of convergence of .

RÉSUMÉ. Soit une application holomorphe de dans définie dans un voisinage de et vérifiant . Si le jacobien de n'est pas identiquement nul au voisinage de , P.M. Eakin et G.A. Harris ont établi le résultat suivant: toute série formelle telle que est analytique est elle-même analytique. Si le jacobien de est identiquement nul, ils montrent que la conclusion précédente est fausse.

Les auteurs obtiennent des résultats analogues pour les séries formelles à croissance contrôlée, du type Gevrey par exemple. De plus, les preuves données ici permettent, dans le cas analytique, un contrôle du rayon de convergence de par celui de .

     

Shaping of gelling biopolymer drops in an elongation flow

Shaping, defined as deformation in combination with gel formation of gelatine and kappa-carrageenan drops in an elongation flow, was studied. The focus was to investigate the possibility of shaping and fixating small drops in the diameter range 20 to 229 mum. In the shaping progress and the influence of experimental properties, the viscosity, temperature, and flow of the deforming fluid were examined on the final drop shape. In the experiments a hot emulsion of an aqueous biopolymer solution in silicone oil was injected into cold silicone oil where a deforming elongation flow field existed. After injection, a temperature decrease in the drops resulted in a gel formation of the biopolymer and a fixation of the deformed drop in the flow. The shape was measured and the effect on the drop aspect ratio was determined by image analysis. Over the total drop diameter range, kappa-carrageenan was more ellipsoid-shaped than gelatine, with a maximum aspect ratio of 6 compared to 4 for gelatine. For small drops, around 22 mum, it is possible to shape kappa-carrageenan, but for gelatine small drops tend to be unaffected. An increase in viscosity, temperature, and flow resulted in an increase in the final fixated shape of the drops. The differences in drop deformation between the biopolymers were explained by drop-viscosity/oil differences and differences in the kinetics of gel formation. The different gel formation kinetics resulted in a short, well-defined, shaping process for kappa-carrageenan, while for gelatine the process was more complex, with both deformation and relaxation present at different stages.     

Predicting ion concentration polarization and analyte stacking/focusing at nanofluidic interfaces

We report on the investigation of electropreconcentration phenomena in micro-/nanofluidic devices integrating 100 μm long nanochannels using 2D COMSOL simulations based on the coupled Poisson–Nernst–Planck and Navier–Stokes system of equations. Our numerical model is used to demonstrate the influence of key governing parameters such as electrolyte concentration, surface charge density, and applied axial electric field on ion concentration polarization (ICP) dynamics in our system. Under sufficiently extreme surface-charge-governed transport conditions, ICP propagation is shown to enable various transient and stationary stacking and counter-flow gradient focusing mechanisms of anionic analytes. We resolve these spatiotemporal dynamics of analytes and electrolyte ICP over disparate time and length scales, and confirm previous findings that the greatest enhancement is observed when a system is tuned for analyte focusing at the charge, excluding microchannel, nanochannel electrical double layer (EDL) interface. Moreover, we demonstrate that such tuning can readily be achieved by including additional nanochannels oriented parallel to the electric field between two microchannels, effectively increasing the overall perm-selectivity and leading to enhanced focusing at the EDL interfaces. This approach shows promise in providing added control over the extent of ICP in electrokinetic systems, particularly under circumstances in which relatively weak ICP effects are observed using only a single channel.     

An economic theory of public facilities in space

This paper deals with the determination of the number and locations of facilities in which a public service is made available to consumers. The solutions obtained by planning and voting are characterized and compared for both a benefit taxation, based on consumers' locations, and an income taxation.     

Cyclic PNA-based compound directed against HIV-1 TAR RNA: modelling, liquid-phase synthesis and TAR binding

A cyclic molecule including a hexameric PNA sequence has been designed and synthesized in order to target the TAR RNA loop of HIV-1 through the formation of a "kissing complex". For comparison, its linear analogue has also been investigated. The synthesis of the cyclic and linear PNA has been accomplished following a liquid-phase strategy using mixed PNA and fully N-protected (aminoethylglycinamide) fragments. The interactions of this cyclic PNA and its linear analogue with TAR RNA have been studied and the results indicate clearly that no interaction occurs between the cyclic antisense PNA and TAR RNA, whereas a tenuous interaction has been detected with its linear PNA analogue.