Dynamics and scaling of noise-induced domain growth

The domain growth processes originating from noise-induced nonequilibrium phase transitions are analyzed, both for non-conserved and conserved dynamics. The existence of a dynamical scaling regime is established in the two cases, and the corresponding growth laws are determined. The resulting universal dynamical scaling scenarios are those of Allen-Cahn and Lifshitz-Slyozov, respectively. Additionally, the effect of noise sources on the behaviour of the pair correlation function at short distances is studied. Received 28 June 2000 and Received in final form 29 September 2000     

The Memetic Tree-based Genetic Algorithm and its application to Portfolio Optimization

We introduce a Memetic system to solve the application problem of Financial Portfolio Optimization. This problem consists of selecting a number of assets from a market and their relative weights to form an investment strategy. These weights must be optimized against a utility function that considers the expected return of each asset, and their co-variance; which means that as the number of available assets increases, the search space increases exponentially. Our method introduces two new concepts that set it apart from previous evolutionary based approaches. The first is the Tree-based Genetic Algorithm (GA), a recursive representation for individuals which allows the genome to learn information regarding relationships between the assets, and the evaluation of intermediate nodes. The second is the hybridization with local search, which allows the system to fine-tune the weights of assets after the tree structure has been decided. These two innovations make our system superior than other representations used for multi-weight assignment of portfolios.     

Luminescent properties of Nd3+ in the NaxNdxM(1−2x)Ga2S4 thiogallates (M = Ca,Sr,Ba; x ≤ 0.5): A family of materials characterized by weak self-quenching and efficient band excitation

As a consequence of the weak phonon energies and the low crystal field, several excited states of Nd³⁺ are emitters in the Na_xNd_xM_1?2xGa₂G₄ thiogallates (x ≤ 0.5 for M = Ca or Sr and ≤0.2 for M = Ba). The infrared ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ emission is little affected by concentration quenching. NaNdGa₄S₈ is the first efficient stoichiometric sulfide so far reported. Unlike other sulfides previously investigated, the neodymium thiogallates show an intense excitation band, ascribed to electron transfer from the valence band to states constituted essentially by neodymium orbitals.     

Performance of gamma camera collimators used for single photon emission computed tomography imaging with 123I-isopropyl iodoamphetamine

123I Produced by 124Te(p, 2n)123I reaction is contaminated with 124I (less than 5%) and 126I (less than 0.3%). High energy photons from these mixed radioiodine compromise seriously image quality due to scattered photons and to septal penetration in the collimator. Four collimators of LEAP (for low energy all purpose), LEHR (for low energy high resolution), MESI (for medium energy made by Siemens) and MENU (for medium energy made by nuclear technology) mounted on a rotating gamma camera (Siemens, ZLC-7500), were examined in order to select a suitable collimator for 123I SPECT (single photon emission computed tomography) imaging. Sensitivities were measured with a plane source (5 X 5 X 0.5 cm) at the collimator face and distances from 2 to 30 cm in air. And, spatial resolutions in FWHM (full width at half maximum) and FWTM (full width at tenth maximum) were determined from line spread functions with planar and SPECT imaging. From the comparison of collimator performances with 99mTc and 123I, both collimators for low energy were not useful for 123I imaging. In other two collimators for medium energy, however, apparently the effect of septal penetration by the higher energy photons were also recognized, MENU with high geometrical resolution was more suitable for 123I SPECT imaging compared with MESI. And, it is important to perform the SPECT imaging with radius as short as possible.     

Double pion photoproduction from3He at low energies

A generalization of the Gauge-invariant OPE model to double pion photoproduction on³He is presented. Results for the total and differential cross-sections are shown. The relevance of double pion photoproduction in the nuclear shadowing of photons is remarked.     

A convenient route to the furopyran core of dysiherbaine

The bicyclic core, furo[3,2-b]pyran, of the dysiherbaines has been synthesized via two routes involving the imino 1,2-Wittig rearrangement of allyl furohydroximate and the asymmetric dihydroxylation of furylpropenol derivative.     

A Study of the Hydrolysis Pathway in Oxalic Acid Catalyzed Reacting TMOS-Water Mixtures Under Ultrasound Stimulation

The hydrolysis of TMOS in oxalic acid catalyzed reacting TMOS-water mixtures, under ultrasound stimulation, was studied by fitting a simplified dissolution and reaction modeling for samples, the hydrolysis rate of which had been measured in a previous work. The reaction pathway represented in a ternary diagram shows a heterogeneous step for the reaction which gradually progresses until complete homogenization of the system. Besides the water dissolved due to the homogenizing effect of the alcohol, ultrasound maintains a virtual and additional dissolution of water located at the interface between the TMOS and water during the heterogeneous step of the reaction. The mean radius of the heterogeneity represented by water dispersed in TMOS was evaluated as around 150 Å. The oxalic acid concentration accordingly increases the hydrolysis rate constant but its fundamental role on the solubility of water in TMOS could not unequivocally be established.     

From linear to nonlinear PGD-based parametric structural dynamics

The present paper analyzes different integration schemes of solid dynamics in the frequency domain involving the so-called Proper Generalized Decomposition – PGD. The last framework assumes for the solution a parametric dependency with respect to frequency. This procedure allowed introducing other parametric dependences related to loading, geometry, and material properties. However, in these cases, affine decompositions are required for an efficient computation of separated representations. A possibility for circumventing such difficulty consists in combining modal and harmonic analysis for defining an hybrid integration scheme. Moreover, such a procedure, as proved in the present work, can be easily generalized to address nonlinear parametric dynamics, as well as to solve problems with non-symmetric stiffness matrices, always operating in the domain of low frequencies.