Numerical comparison of methods for solving second-order ordinary initial value problems

In this paper, we apply Adomian decomposition method (shortly, ADM) to develop a fast and accurate algorithm of a special second-order ordinary initial value problems. The ADM does not require discretization and consequently of massive computations. This paper is particularly concerned with the ADM and the results obtained are compared with previously known results using the Quintic C²-spline integration methods. The numerical results demonstrate that the ADM is relatively accurate and easily implemented.     

Parity violation in the 17/2−–17/2+ doublet in93Tc

The parity-violating mixing of the 17/2^– and 17/2⁺ levels in⁹³Tc nuclei, polarized by the tilted multifoil interaction, was measured by the observation of the forward-backward-ray asymmetry. The nuclear polarization, induced by the tilted multifoils, was measured directly for the neighboring^88,90Zr isomers. The forward to backward asymmetry was determined to be A=(2.5±2.1) 10^–3 which implies a parity violating matrix element ¦H _PV )¦=(4.0±3.7)meV.     

Solid-phase extraction and HPLC determination of 4-vinyl guaiacol and its precursor, ferulic acid, in orange juice.

This study is undertaken to develop a simplified, rapid method to determine both immediate and potential off odors due to 4-vinyl guaiacol and its odorless precursor, ferulic acid, from a single sample preparation and chromatographic analysis. Orange juice sample preparation consists of a simple, C18 solid phase extraction. Utilizing a 5-microns, 25-cm, C18 column, both compounds can be separated within 40 min using a one-step, linear gradient beginning with an aqueous 12% tetrahydrofuran (THF)-5% acetonitrile mixture and ending with 35% aqueous THF. Hesperidin and nariutin have been identified as the compounds that interfered with the ultraviolet (UV) determination of sinapic and caffeic acids. Fluorescence detection with wavelength programming offers optimal sensitivity and selectivity. Recoveries of 4-vinyl guaiacol and ferulic acid range from 90 to 103%. Detection limits are 1 ppm and 5 ppm for ferulic acid and 4-vinyl guaiacol, respectively. Other hydroxycinnamic acids such as coumaric, sinapic, and caffeic acids may also be determined from the same chromatogram.     

A longitudinal study of evolving networks in response to natural disaster

In this study, we present a longitudinal analysis of the evolution of interorganizational disaster coordination networks (IoDCNs) in response to natural disasters. There are very few systematic empirical studies which try to quantify the optimal functioning of emerging networks dealing with natural disasters. We suggest that social network analysis is a useful method for exploring this complex phenomenon from both theoretical and methodological perspective aiming to develop a quantitative assessment framework which could aid in developing a better understanding of the optimal functioning of these emerging IoDCN during natural disasters. This analysis highlights the importance of utilizing network metrics to investigate disaster response coordination networks. Results of our investigation suggest that in disasters the rate of communication increases and creates the conditions where organizational structures need to move at that same pace to exchange new information. Our analysis also shows that inter-organizational coordination network structures are not fixed and vary in each period during a disaster depending on the needs. This may serve the basis for developing preparedness among agencies with an improved perspective for gaining effectiveness and efficiency in responding to natural disasters.     

Exceptionally Plastic/Elastic Organic Crystals of a Naphthalidenimine-Boron Complex Show Flexible Optical Waveguide Properties

The design of molecular compounds that exhibit flexibility is an emerging area of research. Although a fair amount of success has been achieved in the design of plastic or elastic crystals, realizing multidimensional plastic and elastic bending remains challenging. We report herein a naphthalidenimine–boron complex that showed size-dependent dual mechanical bending behavior whereas its parent Schiff base was brittle. Detailed crystallographic and spectroscopic analysis revealed the importance of boron in imparting the interesting mechanical properties. Furthermore, the luminescence of the molecule was turned-on subsequent to boron complexation, thereby allowing it to be explored for multimode optical waveguide applications. Our in-depth study of the size-dependent plastic and elastic bending of the crystals thus provides important insights in molecular engineering and could act as a platform for the development of future smart flexible materials for optoelectronic applications.     

Exploring the Reactivity of α‐Lithiated Aryl Benzyl Ethers: Inhibition of the [1,2]‐Wittig Rearrangement and the Mechanistic Proposal Revisited

By carefully controlling the reaction temperature, treatment of aryl benzyl ethers with tBuLi selectively leads to α‐lithiation, generating stable organolithiums that can be directly trapped with a variety of selected electrophiles, before they can undergo the expected [1,2]‐Wittig rearrangement. This rearrangement has been deeply studied, both experimentally and computationally, with aryl α‐lithiated benzyl ethers bearing different substituents at the aryl ring. The obtained results support the competence of a concerted anionic intramolecular addition/elimination sequence and a radical dissociation/recombination sequence for explaining the tendency of migration for aryl groups. The more favored rearrangements are found for substrates with electron‐poor aryl groups that favor the anionic pathway.     

Synthesis of a C-2 Stapled Bis-Lexitropsin

Summary. A convenient synthesis method was developed for the preparation of C-stapled homodimeric bis-lexitropsins connected through the nitrogen atoms of the central pyrrole ring with a bis-methylene linker. This lexitropsin is designed as a standard for other bis-lexitropsins with longer chains in biological evaluation and NMR studies. The key step in this method is the treatment of ethyl 4-nitropyrrole-2-carboxylate with flame-dried potassium carbonate in DMF followed by the addition of 1,2-dibromoethane to form the 1,2-dipyrroloethane derivative.     

Detection of incipient gear failures using statistical techniques

Gears are important components in most power transmission mechanisms.Failures of gears can cause heavy losses in industry. Conditionmonitoring and fault diagnosis of gears is therefore importantto improve safety and reliability of gearbox operations andreduce losses caused by gear failures. This research proposesa new diagnostic approach based on the statistical analysisof data. It investigates the use of Principal Components Analysis(PCA) to detect growing local faults in a two-stage industrialhelical gearbox. In this research, the vibration signal is usedto monitor fault conditions and a broken tooth is simulatedas a local fault. Since the early detection of faults is a challenge,small fault conditions were tested first as well as severe faultconditions. In order to examine the ability of the PCA to detectfault conditions, first the PCA-based model was created fornormal operating conditions. Any unexpected event such as afault condition causes a significant deviation from the PCAmodel, which is obtained from the normal condition data of thegearbox. The Square Prediction Error (SPE) was calculated todetect the fault conditions. When the vibration signal fromthe gearbox is representative of normal operation, the valueof the SPE shows very little fluctuation and remains under acertain threshold value. However, in the presence of the faultthe SPE fluctuates considerably beyond the threshold value.It is shown that the PCA-based statistical approach cannot onlybe used to detect severe fault conditions, but that it alsoreveals small growing fault conditions at very early stage.The technique also provides information about the state of thefault such as the location of the fault as well as its severity. Received 5 March 2001. Revised 12 December 2001. Accepted 17 January 2002.     

Comparative properties of Amazonian oils obtained by different extraction methods

Pequi (Caryocar brasiliense Camb.), baba?u (Orbignya phalerata Mart.), buriti (Mauritia flexuosa), and passion fruit (Passiflora edulis) oils were studied to determine their antibacterial, antioxidant and cytotoxic activities, as well as their total phenol and carotenoid contents. The fatty acid contents were determined by GC-MS. The three types of passion fruit oils studied were refined, cold pressed or extracted from seeds in a Soxhlet apparatus. The oils thus obtained showed differences in antioxidant activity and carotenoid content, but were similar in regard to total phenols. Buriti and pequi had the highest carotenoid contents, while refined and cold pressed passion fruit oil displayed the highest antioxidant activity. Pequi oil was the only oil to display antibacterial and cytotoxic activity.     

Computational characterization of a complete palladium-catalyzed cross-coupling process: the associative transmetalation in the Stille reaction

[reaction: see text] The species presumably involved in the associative ligand substitution mechanism for the Stille cross coupling of vinyl bromide and trimethylvinyl stannane with Pd(PMe(3))(2)/PMe(3) as catalysts in DMF (as ligand and solvent) have been structurally and energetically characterized. The cyclic four-coordinate transition state for the rate-determining transmetalation step explains the retention of configuration in the Stille coupling of chiral nonracemic alkyl stannanes.