Improved Strategies for Radial basis Function Methods for Global Optimization

We propose some strategies that can be shown to improve the performance of the radial basis function (RBF) method by Gutmann [J. Global optim. 19(3), 201–227 (2001a)] (Gutmann-RBF) and the RBF method by Regis and Shoemaker [J. Global optim. 31, 153–171 (2005)] (CORS–RBF) on some test problems when they are initialized by symmetric Latin hypercube designs (SLHDs). Both methods are designed for the global optimization of computationally expensive functions with multiple local optima. We demonstrate how the original implementation of Gutmann-RBF can sometimes converge slowly to the global minimum on some test problems because of its failure to do local search. We then propose Controlled Gutmann-RBF (CG-RBF), which is a modification of Gutmann-RBF where the function evaluation point in each iteration is restricted to a subregion of the domain centered around a global minimizer of the current RBF model. By varying the size of this subregion in different iterations, we ensure a better balance between local and global search. Moreover, we propose a complete restart strategy for CG-RBF and CORS-RBF whenever the algorithm fails to make any substantial progress after some threshold number of consecutive iterations. Computational experiments on the seven Dixon and Szegö [Towards Global optimization, pp. 1–13. North-Holland, Amsterdam (1978)] test problems and on nine Schoen [J. Global optim. 3, 133–137 (1993)] test problems indicate that the proposed strategies yield significantly better performance on some problems. The results also indicate that, for some fixed setting of the restart parameters, the two modified RBF algorithms, namely CG-RBF-Restart and CORS-RBF-Restart, are comparable on the test problems considered. Finally, we examine the sensitivity of CG-RBF-Restart and CORS-RBF-Restart to the restart parameters.     

Synthesis and crystal structure of a novel Zn(II) 2-D coordination polymer containing 1,3-bis(4-pyridyl)propane ligand and Croconate Violet dianion

From the reaction between Zn(NO₃)₂ · 6H₂O and tetrabutylammonium croconate violet ((NBu₄)₂CV) in the presence of the flexible ligand 1,3-bis(4-pyridyl)propane (BPP) a novel neutral 2-D coordination polymer {[Zn(μ-BPP)(BPP)(CV)(H₂O)] · H₂O}_n (1) was obtained. Compound 1 was characterized by means of elemental analysis, thermogravimetric analysis and vibrational spectroscopy. The crystal structure of 1 reveals that each Zn(II) is coordinated by three nitrogen atoms from two different BPP ligands, two oxygen atoms from one Croconate Violet dianion and one aqua ligand, within a distorted octahedral geometry in a facial arrangement (ZnN₃O₃). One of the BPP ligands adopts a TG (trans–gauche) conformation bridging two zinc centers giving rise to a 1-D polymeric chain along the crystallographic a axis, and the other is coordinated to metal site in a monodentate fashion adopting a TT (trans–trans) conformation. Adjacent 1-D chains are extended into a 2-D coordination network of (4, 4) topology through cooperative hydrogen bonding involving N31, OW2 and OW1 atoms, in direction of the c axis. Two complementary 2-D sheets fit each other exhibiting an interdigitation phenomenon, giving rise to a bilayer supramolecular structure.     

Stereocontrol of intramolecular Diels-Alder reactions by an allylic diphenylcyclopropyl group

Intramolecular Diels-Alder reactions of ester-linked 1,3,8-nonatrienes carrying a diphenylcyclopropyl substituent attached to C1 proceed with high levels of stereoselectivity. The stereochemical outcomes of these reactions are explained by reference to B3LYP/6-31G(d) transition structures. Experimentally, the diphenylcyclopropane rings remain intact through these IMDA reactions, notwithstanding their predicted extremely high degree of asynchronicity (the B3LYP-computed lengths in the IMDA transition structures differ by as much as 1.1 angstroms), providing support to the notion that these reactions are concerted processes.     

Novel triazolyl derivatives for acidic release of amines

Triazolyl derivatives of amines were prepared using click chemistry and evaluated as releasing systems in mildly acidic environments. Triazolylcarbamates and alkylamines were obtained, depending on the reactivity of the propargylic intermediates used for the Huisgen cycloaddition. A fast hydrolysis of some derivatives in mildly acidic conditions was achieved. The relative rates were correlated to a proposed mechanism highlighting the complementary role of the triazole ring and carbocation reactivity/stability.     

The stepwise Diels-Alder reaction of 4-nitrobenzodifuroxan with Danishefsky's diene

The Diels–Alder reaction of 4‐nitrobenzodifuroxan (NBDF) with 1‐methoxy‐3‐trimethylsilyloxy‐1,3‐butadiene has been investigated experimentally and theoretically. Treatment of NBDF with excess diene in chloroform at room temperature was found to afford a single product that contained a carbonyl functionality. Based on an X‐ray structure and NMR spectroscopic data, the product appeared to be a result of the hydrolysis of the OSiMe₃ moiety of the thermodynamically more stable endo [2+4] cycloadduct, characterized by a cis arrangement of the MeO and NO₂ functionalities. In situ NMR investigations of the interaction were carried out at room temperature in CDCl₃ and at ?40 °C in deuterated acetonitrile. Calculations at the B3LYP/6‐31G* level in the gas phase and in acetonitrile were carried out under the assumption that the most stable cis conformation of the diene is also the most reactive in the interaction. The analysis revealed the NBDF/cis diene interaction involves the formation of a zwitterionic intermediate. Importantly, this intermediate is formed in two preferred conformations, which correspond to the endo and exo modes of approach of the reagents. Cyclization of these two identified conformations afforded the experimentally characterized endo and exo [2+4] cycloadducts. According to the calculations, the interconversion of the two conformers can either take place through a return to the pre‐reaction complexes or it can occur by rotation through an intermediate conformation of lesser stability. In view of the stepwise character of the interaction, the possibility that the intermediate zwitterion is the result of the interaction between NBDF and the trans diene could not be excluded. Calculations carried out with the most stable and more populated s‐trans conformer confirmed this idea and supported the role of the zwitterion in the overall interaction.     

Polyimide-silica sol–gel membranes from a novel alkoxysilane functionalized polyimide: preparation,characterization and gas separation properties

Novel polyimide-organosilicate hybrid films were prepared by sol–gel process from a novel functionalized polyimide with alkoxysilanes as pendant groups that increase the affinity between inorganic and organic phases. The synthesis of this functionalized polyimide was carried out by an esterification reaction of a copolyimide containing carboxylic acid groups with allyl alcohol and subsequent hydrosililation. Tetraethoxysilane was used as precursor of silica in different amounts to obtain hybrid membranes with a silica content of 5, 10 and 20 %. The polymers and hybrid membranes were structural, mechanical and thermally characterized. The ²⁹Si-NMR solid state spectroscopy confirmed that silica was covalently bonded to the polyimide. SEM pictures showed a good dispersion of the silica particles and an amorphous morphology was observed by WAXS. DSC analyses revealed an increase in rigidity with the increase in silica content. The mechanical strength of the hybrid membranes decreased with the silica amount, exhibiting a brittle behavior. The evaluation of the gas permeation properties revealed that the film with the lowest silica content showed the highest permeability coefficients for O₂, N₂, CH₄, and CO₂ with 34, 8, 6, and 128 barrers respectively, while all hybrid membranes showed similar permselectivities around 4 and 22 for O₂/N₂ and CO₂/CH₄ respectively. The fractional free volume of hybrid membranes determined by positron annihilation lifetime spectroscopy followed the same trend that permeability coefficients, confirming that the gas transport properties are mainly governed by the free volume elements.     

Systematic investigation and in vitro biocompatibility studies on mesoporous europium doped hydroxyapatite

This paper reports the systematic investigation of europium doped hydroxyapatite (Eu:HAp). A set of complementary techniques, namely Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) technique were used towards attaining a detailed understanding of Eu:HAp. The XPS analysis confirmed the substitution of Ca ions by Eu ions in the Eu:HAp samples. Secondly, Eu:HAp and pure HAp present type IV isotherms with a hysteresis loop at a relative pressure (P/P₀) between 0.4 and 1.0, indicating the presence of mesopores. Finally, the in vitro biological effects of Eu:HAp nanoparticles were evaluated by focusing on the F-actin filament pattern and heat shock proteins (Hsp) expression in HEK293 human kidney cell line. Fluorescence microscopy studies of the actin protein revealed no changes of the immunolabelling profile in the renal cells cultured in the presence of Eu:HAp nanoparticles. Hsp60, Hsp70 and Hsp90 expressions measured by Western blot analysis were not affected after 24 and 48 hours exposure. Taken together, these results confirmed the lack of toxicity and the biocompatibility of the Eu:HAp nanoparticles. Consequently, the possibility of using these nanoparticles for medical purposes without affecting the renal function can be envisaged.      

A comparison of three metaheuristics for the workover rig routing problem

The workover rig routing problem (WRRP) is a variant of the Vehicle Routing Problem with Time Windows (VRPTW) and arises in the operations of onshore oil fields. In this problem, a set of workover rigs located at different positions must service oil wells requesting maintenance as soon as possible. When a well requires maintenance, its production is reduced or stopped for safety reasons and some workover rig must service it within a given deadline. It is therefore important to service the wells in a timely fashion in order to minimize the production loss. Whereas for classical VRPTWs the objective is to minimize route length, in the WRRP the objective is to minimize the total lost production, equal to the sum of arrival times at the wells, multiplied by production loss rates. The WRRP generalizes the Delivery Man Problem with Time Windows by considering multiple open vehicle routes and multiple depots. This paper compares three metaheuristics for the WRRP: an iterated local search, a clustering search, and an Adaptive Large Neighborhood Search (ALNS). All approaches, in particular ALNS, have yielded good solutions for instances derived from a real-life setting.     

Measurement of atmospheric neutrino flux consistent with tau neutrino appearance

A search for the appearance of tau neutrinos from nu(mu) <--> nu(tau) oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutrino data from the Super-Kamiokande-I experiment. A best fit tau neutrino appearance signal of 138+/-48(stat)-32(+15)(syst) events is obtained with an expectation of 78+/-26(syst). The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.