Reformulations and solution algorithms for the maximum leaf spanning tree problem

Given a graph G = (V, E), the maximum leaf spanning tree problem (MLSTP) is to find a spanning tree of G with as many leaves as possible. The problem is easy to solve when G is complete. However, for the general case, when the graph is sparse, it is proven to be NP-hard. In this paper, two reformulations are proposed for the problem. The first one is a reinforced directed graph version of a formulation found in the literature. The second recasts the problem as a Steiner arborescence problem over an associated directed graph. Branch-and-Cut algorithms are implemented for these two reformulations. Additionally, we also implemented an improved version of a MLSTP Branch-and-Bound algorithm, suggested in the literature. All of these algorithms benefit from pre-processing tests and a heuristic suggested in this paper. Computational comparisons between the three algorithms indicate that the one associated with the first reformulation is the overall best. It was shown to be faster than the other two algorithms and is capable of solving much larger MLSTP instances than previously attempted in the literature.     

The preparation and characterisation of ruthenium cyanovinylidene complexes

Reactions of half-sandwich ruthenium metal acetylide complexes with 1-cyano-4-dimethylaminopyridinium salts afford complexes containing mono- or di-cyanovinylidene ligands; the procedure can be adapted to permit the simple synthesis of a cyanoacetylide complex, via the in situ deprotonation of a primary cyanovinylidene complex.     

Evaluation of propolis polyphenols absorption in humans by liquid chromatography/tandem mass spectrometry

Propolis has various biological activities such as antibacterial, antiviral, antioxidant, immunostimulating and antiinflammatory, which are generally ascribed to the polyphenolic fraction. The aim of this study was to evaluate the absorption of the main polyphenols [caffeic acid (CA), pinobanksin-5methyl ether (P-5ME), pinobanksin (Pb), chrysin (C), pinocembrin (P), galangin (G), pinobanksin-3-acetate, pinobanksin esters and caffeic acid phenylethyl ester (CAPE)] from a dewaxed and standardized extract of propolis (EPID). Fifteen healthy volunteers consumed 5 mL EPID in water, corresponding to 125 mg of flavonoids. Blood samples were collected before, each hour for 8 h and 24 h after EPID intake. After deconjugation by beta-glucuronidase/sulfatase the plasma samples were analyzed by a selective liquid chromatography/tandem mass spectrometry (LC/MS/MS) method using morin as internal standard (I.S.). A kinetic profile characterized by two t(max), respectively at 1 h and about 5 h post-ingestion, was observed in all the subjects. The two peaks may be due to enterohepatic cycling. Among the various polyphenols ingested, only P-5ME, Pb, C, P and G were detected in plasma and C(max)t(1h) were 65.7 +/- 13.3, 46.5 +/- 12.7, 79.5 +/- 18.6, 168.1 +/- 16.3 and 113.7 +/- 16.8 ng/mL, respectively. These levels decreased significantly after 8 h and were no longer detectable 24 h after EPID intake. The recovery of the extraction for CA, Pb, C, P, G and I.S. from spiked plasma was 95.2 +/- 3.1, 93.1 +/- 3.6, 91 +/- 2.5, 96.4 +/- 4.2, 93.4 +/- 2.4 and 85.5 +/- 2.4%, respectively. The results of this study evidence that flavonoids from EPID are absorbed, metabolized and Pb-5ME and G seem to have apparent absorption, measured as (AUC/dose), higher than C, P and Pb.     

Harmonic IR spectra from empirical force fields and ab initio dipole-moment derivatives

Infrared spectra simulations require ab initio techniques to get reliable intensities. On the other hand, recent force fields can provide accurate molecular geometries and frequencies. Therefore, it is suggested that these new force fields could be used to simulate infrared spectra, dipole-moment surfaces being described at high levels of theory in order to get satisfactory intensities. As pointed out, for a system with N atoms, the cost of such a simulation would be reduced N-fold with respect to standard quantum approaches. Preliminary calculations based on this scheme are reported here. Encouraging results are obtained since no significant lost of accuracy is noted on going from the ab initio to the molecular mechanics potential energy surface. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 705–711, 1998     

Modeling of CN-functionalized silica as vehicle for delivery of the chemotherapeutic agent: cisplatin

The adsorption of cisplatin and its complexes, cis-[PtCl(NH₃)₂]⁺ and cis-[Pt(NH₃)₂]²⁺, on a CN-functionalized SiO₂(111) surface has been studied by the atom superposition and electron delocalization method. The adiabatic energy curves for the adsorption of the drug and its complexes on the delivery system were considered. Electronic structure and bonding analyses were also performed. The molecules are adsorbed on the functionalized surface resulting in a major absorption of the cis-[Pt(NH₃)₂]²⁺ complex. The molecule?Csurface interactions are strengthened due to the incorporation of the CN silane group. The most important bonds occur through Pt?CC, Pt?CN and Pt?CSi interactions. Despite the new interactions, the functionalized carrier maintains its matrix properties after adsorption. The remarkable properties may be attributed to the small electronic structure changes in the Si?CCN groups caused by the interaction with neighboring cisplatin molecules and the enhancement in Pt-bonding interactions due to the surface incorporation of the CN silane groups.     

Synthesis of the unique angular tricyclic chromone structure proposed for aspergillitine, and its relationship with alkaloid TMC-120B

The synthesis of the tricyclic angular chromone structure originally assigned to aspergillitine is reported. The synthesis was achieved in 11 steps and 15% overall yield from 2,4-dihydroxypropiophenone, through the intermediacy of 2,3-dimethyl-7-hydroxychromen-4-one. Construction of the nitrogen-bearing heterocyclic ring entailed a Stille cross-coupling reaction with n-Bu(3)SnCH(2)CH=CH(2), followed by double bond isomerization, oximation of the chromone carbonyl, and a final microwave-assisted electrocyclization of the thus formed 6π-electron aza-triene system.     

Extraction of the oxide thickness using a MOS structure quantum model for SiO2 oxide <5 nm thick films

In this paper, we present a full quantum model of metal oxide semiconductor capacitance based on a self-consistent resolution of Schrödinger and Poisson equations. The model is used in accumulation to extract the oxide thickness of N⁺ polycrystalline silicon–SiO₂–P silicon capacitors in the range 2–5 nm. The extraction results are in agreement with reference ellipsometric measurements to <±4%. We also show the necessity of a quantum computation of the gate capacitance for high substrate doping and low oxide thickness. The influence of the tunneling current is also discussed.     

Surface modification of iron oxide nanoparticles by a phosphate‐based macromonomer and further encapsulation into submicrometer polystyrene particles by miniemulsion polymerization

A new strategy relying on the use of a phosphate‐based macromonomer (PAM200) to modify the surface of iron oxide nanoparticles was developed for the synthesis of submicrometer polystyrene (PS) magnetic particles. First, iron oxide nanoparticles were synthesized using the coprecipitation of ferrous and ferric salts in alkaline medium. Besides the classical oleic acid (OA)/octane‐based ferrofluid, styrene‐based ferrofluids were elaborated with either OA or PAM200 as the stabilizer. In all cases, maghemite (γ‐Fe₂O₃) was clearly identified, with nanoparticles rather spherical in shape but exhibiting broad particle size distribution (PSD). Both OA and PAM200 led to stable maghemite‐based ferrofluids showing superparamagnetic properties. Further use of these ferrofluids in styrene miniemulsion polymerization resulted in inhomogeneous distribution of maghemite among and inside the polymer particles with OA‐based ferrofluids, whereas PAM200/styrene‐based ferrofluids led to magnetic particles with homogeneous distribution of maghemite inside PS particles. Broad PSD and small nonmagnetic particles were however observed. The true mechanisms operating in these systems are still to elucidate, but this study validates PAM200 as an efficient compatibilizing agent between hydrophilic maghemite and hydrophobic PS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 327–340, 2008