Nonlinear optimisation using directional step lengths based on RPROP

A search method based on the backpropagation rule commonly used for training neural networks is proposed here for the optimisation of smooth nonlinear functions. The use of the Resilient backPROPagation (RPROP) heuristic rule for local minimisation is described. The details of employing the directional step length determined by RPROP along with a simple restarting scheme are provided. In the approach proposed here direct use of the directional step determined by the heuristic without using any line search conditions takes place. The overall algorithm has been tested on a number of benchmark functions found in the literature with very positive results. The test problems’ dimension ranges from 100 to 50,000. The results obtained show that the suggested search direction method results to a highly efficient algorithm suitable for large scale optimisation.     

Hydrodynamics in a Gas-Solids Fluidized Bed Using X-Ray Fluoroscopy and Pressure Fluctuation Measurements

In this work, non-intrusive techniques were used to characterize the hydrodynamics in a gas-solids bubbling fluidized bed using polyethylene powder and glass beads of comparable mean diameter (d_p = 360 µm) but different density. X-ray fluoroscopy measurements and pressure fluctuations were performed on a pseudo 2-dimensional gas-solids fluidized bed. Bubble properties were captured from X-ray fluoroscopy measurements. Similarities and differences of flow behavior of the two particle systems were revealed from comparison of bubble properties. Bubble properities normally varied similary with operating conditions for the two particle systems, while bubble sizes for the glass beads system are larger than those for the polyethylene system. Wavelet analysis of pressure fluctuations was applied to investigate the gas and solids phase flow behavior. Multi-scale flow behavior was extracted from the standard deviation of the decomposed coefficient series. Flow behavior due to particles and bubbles of different sizes were captured at different decomposition levels of pressure fluctuations, which is difficult to know from analysis of the original signal. Results extracted from X-ray fluoroscopy and pressure fluctuation measurements were consistent, suggesting that conventional pressure fluctuation measurements can be effectively used for investigation of the bubbling behavior.     

Water sorption characteristics of poly(2‐hydroxyethyl acrylate)/silica nanocomposite hydrogels

Water sorption in hydrogels based on nanocomposites of poly(2‐hydroxyethyl acrylate) (PHEA) and silica, prepared by simultaneous polymerization and sol‐gel process, were studied gravimetrically over wide ranges of silica content, both below and above the percolation threshold of about 15% wt for the formation of a continuous inorganic network interpenetrated with the organic network. Measurements were performed at room temperature from the vapor phase, both at equilibrium and dynamic, for selected values of water activity α_w between 0 and 0.95, and from the liquid phase. In the nanocomposite hydrogels, the overall water uptake from the vapor phase is practically the same as in pure PHEA below the percolation threshold, whereas it is reduced above the percolation threshold, in particular at high α_w values where swelling becomes significant. Water clustering sets in at around 14 vol % (10 wt %) of water independently of composition, whereas the mean value of water molecules in a cluster decreases at high silica contents. In immersion experiments water uptake decreases as silica content increases to the percolation threshold of about 15 wt % and is then almost independent of composition. A scheme is proposed, which explains these results in terms of the existence of micelles, where a number of hydrophilic hydroxy groups are linked together, and their disentaglement by immersion into water. Diffusion coefficients of water depend on water content and are reduced on addition of silica above the percolation threshold. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Strongly segregated cubic microdomain morphology consistent with the double gyroid phase in high molecular weight diblock copolymers of polystyrene and poly(dimethylsiloxane)

We report the observation of a cubic phase consistent with the double gyroid structure in strongly segregated diblock copolymers of PS‐b‐PDMS over a volume fraction (φ_PDMS) range of ～0.39 to 0.45. The samples have respective molecular weights of 127 kg/mol and 73 kg/mol and degree of segregation Nχ equal to 187 and 106, respectively, at annealing temperature of 130 °C. It is important to highlight that two out of the total four samples investigated, exhibited hexagonally close packed cylindrical domains of PDMS and alternating lamellae at φ_PDMS = 0.39 and 0.45, respectively, indicating the possible narrow range of the DG morphology for the specific diblock copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2419–2427, 2009     

Synthesis of dendritic terpolymers consisting of polystyrene,polybutadiene, and polyisoprene with different isomerisms

We report the synthesis of two 2nd generation dendritic terpolymers consisting of poly(butadiene) (PB) of 1,4 geometric isomerism, poly(isoprene) (PI) enriched in 3,4 geometric isomerism (at least 55% PI_3,4) and polystyrene (PS). The main focus of this work was the synthesis of well‐defined dendritic terpolymers exhibiting high levels of molecular and compositional homogeneity. The preparation of these materials was achieved via anionic polymerization techniques in combination with chlorosilane linking chemistry. The molecular characterization of the intermediate products and the final dendritic materials was accomplished via gel permeation chromatography, membrane osmometry, differential scanning calorimetry, and ¹H‐nuclear magnetic resonance spectroscopy, leading to the conclusion that they can be considered model polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1567–1574, 2009     

Priority option pricing in an M/M/m queue

We study a system where the service provider offers priority options. We identify the optimal option pricing policy, by deriving the optimal number a customer would buy and the customer’s exercise policy as a function of system congestion, options remaining, time to expiration and possibility of balking.     

CP violation in correlated production and decay of unstable particles

We study resonant CP-violating Einstein-Podolsky-Rosen correlations that may take place in the production and decay of unstable scalar particles at high-energy colliders. We show that as a consequence of unitarity and CPT invariance of the S-matrix, in 2→2 scatterings mediated by mixed scalar particles, at least three linearly independent decay matrices associated with the unstable scalar states are needed to obtain non-zero CP-odd observables that are also odd under C-conjugation. Instead, for the correlated production and decay of two unstable particle systems in 2→4 processes, we find that only two independent decay matrices are sufficient to induce a net non-vanishing CP-violating phenomenon. As an application of this theorem, we present numerical estimates of CP asymmetries for the correlated production and decay of supersymmetric scalar top-anti-top pairs at the LHC, and demonstrate that these could reach values of order one. As a byproduct of our analysis, we develop a novel spinorial trace technique, which enables us to efficiently evaluate lengthy expressions of squared amplitudes describing the resonant scalar transitions.     

The Crystal Structure of Human α(2) -Macroglobulin Reveals a Unique Molecular Cage

I'm your Venus: The crystal structure of the human methylamine-induced form of α(2) -macroglobulin (α(2) M) shows its large central cavity can accommodate two medium-sized proteinases (see structure, front part clipped off to better show central cavity). Twelve major entrances provide access for small substrates to the cavity and the still-active trapped "prey". The structure unveils the molecular basis of the unique "venus flytrap" mechanism of α(2) M.