A generalized expression for the ratio of the critical temperature to the critical pressure with the van der Waals surface area

Using an extensive database of experimental critical properties for heavy compounds, which have been compiled mostly from recent literature sources, it is shown that the ratio T_c: P_c (critical temperature over critical pressure) can be expressed in terms of the van der Waals surface area (Q_w), which is readily available for any compound from the group contributions of Bondi (given also in UNIFAC tables). The proposed correlation is based on the hole theory of Kurata and Isida for n-paraffin liquids, which is mathematically equivalent to Flory's theory of polymer solutions. The method is suitable for medium to high molecular weight compounds with unknown critical constants. For example, if only one of the two critical constants is available, then the proposed generalized equation offers a useful rapid procedure for the estimation of the other critical property for use in corresponding states, and other relevant applications where knowledge of the critical properties is required. Furthermore, the T_c: P_c method can be used in many cases for identifying the most suitable among the existing group contribution methods for estimating the critical properties of heavy and complex compounds for which experimental values are, very often, not available.     

Robust network design in telecommunications under polytope demand uncertainty

We consider a model for robust network design in telecommunications, in which we minimize the cost of the maximum mismatch between supply and demand. In the present study, the demand is uncertain and takes its values in a polytope defined by constraints. This problem is hardly tractable, so we limit ourselves to computing lower bounds (by a column-generation mechanism) and upper bounds (using an algorithm due to Falk and Soland for maximizing a separable convex function over a polytope). The experimental gap obtained turns out to be large, and this seems to be mainly due to poor upper bounds. Two possible solutions are suggested for further research aimed at improving them: dc optimization (to minimize the difference of two convex functions) and AARC modeling (affinely adjustable robust counterpart).     

A versatile and general one-pot method for synthesizing bis-spiroketal motifs

[reaction: see text] A versatile and general method for the biomimetic construction of [5,5,5]- and [6,5,6]-bis-spiroketals, starting from easily accessible furan nuclei, by means of a powerful one-pot singlet oxygen-mediated cascade sequence is reported.     

Ultrasound enhanced thrombolysis in acute arterial ischemia

In vitro and animal studies have shown that thrombolysis with intravenous tissue plasminogen activator (tPA) can be enhanced with ultrasound. Ultrasound delivers mechanical pressure waves to the clot, thus exposing more thrombus surface to circulating drug. Moreover, intravenous gaseous microspheres with ultrasound have been shown to be a potential alternative to fibrinolytic agents to recanalize discrete peripheral thrombotic arterial occlusions or acute arteriovenous graft thromboses. Small phase I-II randomized and non-randomized clinical trials have shown promising results concerning the potential applications of ultrasound-enhanced thrombolysis in the setting of acute cerebral ischemia. CLOTBUST was an international four-center phase II trial, which demonstrated that, in patients with acute ischemic stroke, transcranial Doppler (TCD) monitoring augments tPA-induced arterial recanalization (sustained complete recanalization rates: 38% vs. 13%) with a non-significant trend toward an increased rate of clinical recovery from stroke, as compared with placebo. The rates of symptomatic intracerebral hemorrhage (sICH) were similar in the active and placebo group (4.8% vs. 4.8%). Smaller single-center clinical trials using transcranial color-coded sonography (TCCD) reported recanalization rates ranging from 27% to 64% and sICH rates of 0-18%. A separate clinical trial evaluating the safety and efficacy of therapeutic low-frequency ultrasound was discontinued because of a concerning sICH rate of 36% in the active group. To further enhance the ability of tPA to break up thrombi, current ongoing clinical trials include phase II studies of a single beam 2 MHz TCD with perflutren-lipid microspheres. Moreover, potential enhancement of intra-arterial tPA delivery is being clinically tested with 1.7-2.1 MHz pulsed wave ultrasound (EKOS catheter) in ongoing phase II-III clinical trials. Intravenous platelet-targeted microbubbles with low-frequency ultrasound are currently investigated as a rapid noninvasive technique to identify thrombosed intracranial and peripheral vessels. Multi-national dose escalation studies of microspheres and the development of an operator independent ultrasound device are underway.     

Investigation of Catalytic Chain Transfer Copolymerization of Methacrylates

Batch experiments were carried out to investigate the kinetics of catalytic chain transfer copolymerization of methyl methacrylate and n‐butyl methacrylate. The Predici® model developed to represent the system describes the numerous experimental data measured at high concentrations of Co(II ) catalyst, taking into account the chain‐length dependencies of termination, propagation and catalytic chain transfer. The constants for catalytic chain transfer are determined as 2.3 × 10⁴ for both methyl methacrylate and n‐butyl methacrylate from fitting the experimental data. Two inhibition mechanisms are shown to describe the decrease of the polymerization rate in the presence of catalyst equally well, with an unknown impurity dissolved in initiator introduced to explain experimental profiles measured at high initiator concentrations.

     

Some physicochemical aspects of nanoparticulate magnetic iron oxide colloids in neat water and in the presence of poly(vinyl alcohol)

The preparation of magnetic iron oxide colloids directly from the coprecipitation of Fe (2+) and Fe (3+) species at different temperatures may lead to crystallites of higher size as the temperature of the reaction increases. On the other hand, dynamic light scattering investigations and dielectric measurements rather point to the similar colloidal size of the entities existing in their aqueous or solid-state dispersions, irrespective of the size of the primary nanocrystallites. Significant enhancement of the stability of the colloids, even in the presence of high electrolyte concentrations, is furnished after the addition of relatively small amounts of poly(vinyl alcohol), and the stabilization mechanism is discussed in terms of the various forces participating in the system. The experimental results suggest that the increased colloidal stability is triggered from the particles' decrease of velocity rather than from steric (entropic) effects originating from polymer absorption.     

Using singlet oxygen to synthesise a [6,6,5]-bis-spiroketal in one-pot from a simple 2,5-disubstituted furan

Singlet oxygen (1O2) proves to be a powerful tool in mediating the one-pot synthesis of a salinomycin-type [6,6,5]-bis-spiroketal unit starting from a suitably substituted furan nucleus.     

Exact X-wave solutions of the hyperbolic nonlinear Schrödinger equation with a supporting potential

We find exact solutions of the two- and three-dimensional nonlinear Schrödinger equation with a supporting potential. We focus in the case where the diffraction operator is of the hyperbolic type and both the potential and the solution have the form of an X-wave. Following similar arguments, several additional families of exact solutions can also can be found irrespectively of the type of the diffraction operator (hyperbolic or elliptic) or the dimensionality of the problem. In particular we present two such examples: The one-dimensional nonlinear Schrödinger equation with a stationary and a “breathing” potential and the two-dimensional nonlinear Schrödinger with a Bessel potential.     

Metal-dielectric-metal plasmonic waveguide devices for manipulating light at the nanoscale Invited Paper

We review some of the recent advances in the development of subwavelength plasmonic devices for ma- nipulating light at the nanoscale, drawing examples from our own work in metal-dielectric-metal (MDM) plasmonic waveguide devices. We introduce bends, splitters, and mode converters for MDM waveguides with no additional loss. We also demonstrate that optical gain provides a mechanism for on/off switch- ing in MDM plasmonie waveguides. Highly efficient compact couplers between dielectric waveguides and MDM waveguides are also introduced.