Experimental and numerical investigations on flashing-induced instabilities in a single channel

During the start-up phase, natural circulation BWRs (NC-BWRs) need to be operated at low pressure conditions. Such conditions favor flashing-induced instabilities due to the large hydrostatic pressure drop induced by the tall chimney. Moreover, in novel NC-BWR designs the steam separation is performed in the steam separators which create large pressure drops at the chimney outlet, which effect on stability has not been investigated yet.In this work, flashing-induced oscillations occurring in a tall, bottom heated channel are numerically investigated by using a simple linear model with three regions and an accurate implementation for estimating the water properties. The model is used to investigate flashing-induced instabilities in a channel for different values of the core inlet friction value. The results are compared with experiments obtained by using the CIRCUS facility at the same conditions, showing a good agreement. In addition, the experiments on flashing-induced instabilities are presented in a novel manner allowing visualizing new details of the phenomenon numerical stability investigations on the effect of the friction distribution are also done. It is found that by increasing the total restriction in the channel the system is destabilized. In addition, the chimney outlet restriction has a stronger destabilizing effect than the core inlet restriction. A stable two-phase region is observed prior to the instabilities in the experiments and the numerical simulations which may help to pressurize the vessel of NC-BWRs and thus reducing the effects of flashing instabilities during start-up.     

Multivariate stochastic delay differential equations and CAR representations of CARMA processes

In this study we show how to represent a continuous time autoregressive moving average (CARMA) as a higher order stochastic delay differential equation, which may be thought of as a CAR($\infty$) representation. Furthermore, we show how the CAR($\infty$) representation gives rise to a prediction formula for CARMA processes. To be used in the above mentioned results we develop a general theory for multivariate stochastic delay differential equations, which will be of independent interest, and which will have particular focus on existence, uniqueness and representations.     

A non-oxidative approach toward chemically and electrochemically functionalizing Si(111)

A general method for the non-oxidative functionalization of single-crystal silicon(111) surfaces is described. The silicon surface is fully acetylenylated using two-step chlorination/alkylation chemistry. A benzoquinone-masked primary amine is attached to this surface via Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition ("click" chemistry). The benzoquinone is electrochemically reduced, resulting in quantitative cleavage of the molecule and exposing the amine terminus. Molecules presenting a carboxylic acid have been immobilized to the exposed amine sites. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and contact angle goniometry were utilized to characterize and quantitate each step in the functionalization process. This work represents a strategy for providing a general platform that can incorporate organic and biological molecules on Si(111) with minimal oxidation of the silicon surface.     

Enhanced surface-plasmon resonance absorption in metal-dielectric-metal layered microspheres

We present a theoretical study of the dispersion relation of surface-plasmon resonances of mesoscopic metal-dielectric-metal microspheres. By analyzing the solutions to Maxwell's equations, we obtain a simple geometric condition for which the system exhibits a band of surface-plasmon modes whose resonant frequencies are weakly dependent on the multipole number. Using a modified Mie calculation, we find that a large number of modes belonging to this flat-dispersion band can be excited simultaneously by a plane wave, thus enhancing the absorption cross section. We demonstrate that the enhanced absorption peak of the sphere is geometrically tunable over the entire visible range.     

Synthesis, crystal structures and magnetic behaviour of dimeric and tetrameric gadolinium carboxylates with trichloroacetic acid

The novel gadolinium(III) containing compounds (CH3NH3)2[Gd2(CCl3COO)6(H2O)6](CCl3COO)2.2CCl3COOH (1) and (NH3CH3)2[Gd4(OH)4(CCl3COO)10(H2O)6].2H2O (2) were synthesized and structurally characterized by X-ray crystallography. In the crystal structure of 1 the gadolinium ions are bridged by carboxylate groups to dimers with a Gd3+ -Gd3+ distance of 420.2(3) pm. The compound crystallizes in the triclinic space group P1. In the crystal structure of the Gd3+ ions are bridged by hydroxide ions and carboxylate groups to tetramers with Gd3+ -Gd3+ distances between 380.3(1) and 388.0(1) pm. The compound crystallizes in the triclinic space group P1. The magnetic behaviour of these two compounds as well as of Gd2(CCl3COO)6(bipy)2(H2O)2.4bipy (3) (bipy = 2,2'-bipyridyl) was investigated in the temperature range 1.77-300 K. The magnetic data for these compounds indicate weak antiferromagnetic interactions.     

Conformal Metrics on the Unit Ball in Euclidean Space

We study densities on the unit ball in euclidean space whichsatisfy a Harnack type inequality and a volume growth conditionfor the measure associated with . For these densities a geometrictheory can be developed which captures many features of thetheory of quasiconformal mappings. For example, we prove generalizationsof the Gehring-Hayman theorem, the radial limit theorem andfind analogues of compression and expansion phenomena on theboundary. 1991 Mathematics Subject Classification: 30C65.     

Synthesis of the potent immunostimulatory adjuvant QS-21A

QS-21A is one of the most promising new adjuvants for immune response potentiation and dose-sparing in vaccine therapy, given its exceedingly high level of potency and its favorable toxicity profile. Melanoma, breast cancer, small cell lung cancer, prostate cancer, HIV-1, and malaria are among the numerous maladies targeted in more than 80 recent and ongoing clinical trials involving QS-21A as a critical component for immune response augmentation in microgram doses. Herein is reported the first synthesis and structure verification of QS-21Aapi, applying novel glycosylation methodologies in the convergent modular construction of this rare and potent natural product immunostimulant.