Nonmonotone Algorithms for Pattern Search Methods

This work deals with the solution of ill-conditioned unconstrained minimization problems by means of pattern search methods. To this end, the usual requirement of monotonic reduction of the objective function is relaxed and nonmonotone pattern search methods are proposed, which maintain the convergence properties of their monotone counterparts. Numerical experimentation on several well-known ill-conditioned functions is reported. The results highlight a class of pattern search methods which benefit very much by the introduction of nonmonotone strategies.     

Can extensional viscosity be measured with opposed-nozzle devices?

Opposed-nozzle devices are widely used to try to measure the extensional viscosity of low-viscosity liquids. A thorough literature survey shows that there are still several unanswered questions on the relationship between the quantity measured in opposed-nozzle devices and the true extensional viscosity of the liquids. In addition to extensional stresses, opposed nozzle measurements are influenced by dynamic pressure, shear on the nozzles, and liquid inertia. Therefore the ratio of the apparent extensional viscosity that is measured to the shear viscosity that is independently measured is greater than three even for Newtonian liquids. The effect of inertia on the extensional measurements is analyzed by computer-aided solution of the Navier-Stokes system, and by experiments on low-viscosity Newtonian liquids(1 mPa sS 800 mPa s). The effect of nozzle separation-to-diameter ratio on the average residence time of the liquid is analyzed under the assumption of simple extensional flow kinematics. The average residence time of the liquid is independent of this ratio unless the radial inflow section of the extensional flow volume is related to the nozzle separation. Experiments indicate that in some cases widening the gap lowers the apparent extensional viscosity that is measured, whereas in other cases the opposite is true. In the light of these theoretical considerations and experimental observations, the use of systematic corrections to extensional viscosity measurements on non-Newtonian liquids is not recommended. Thus opposed nozzle devices should be considered as useful indexers rather than rheometers. Finally, measurements on a series of semi-dilute solutions of high molecular weight poly(ethylene oxide) in. water are also reported.Dedicated to the memory of Anastasios C. Papanastasiou     

“True” Hydrophilic-Lipophilic Balance of Polyoxyethylene Fatty Acid Esters Nonionic Surfactants

This article proposes a set of equations that allow the calculation of the hydrophilic-lipophilic balance (HLB) value of polyoxyethylene esters from quality control data of the raw materials (fatty acids and polyethylene glycol) and the finished product (surfactant). The quality control data required include the acid value of the fatty acid, the hydroxyl value of the polyethylene glycol, and the hydroxyl value of the surfactant. Moreover, these calculations allow the determination of the mean relative molecular masses of the fatty acids, polyethylene glycol, monoesters, and diesters, and to calculate the proportion of polyoxyethylene monoester and polyoxyethylene diester. Models such as this would be of great utility for the rational design of emulsified products.      

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C−N, C−O and C−S bond forming reactions, and later widely employed in C−C cross-coupling reactions with C(sp³), C(sp²) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.     

A highly selective, one-pot purification method for single-walled carbon nanotubes

We report on a one-pot, highly selective chemistry to remove residual catalysts from single-walled carbon nanotubes (SWNTs). The impurities, initially present at approximately 35 wt % and mostly as carbon-coated iron nanoparticles, can be driven below 5 wt % with nearly no loss of SWNTs. The carbon-coated iron impurities are dissolved simply by reacting with an aqueous mixture of H2O2 and HCl at 40-70 degrees C for 4-8 h. This purification combines two known reactions involving H2O2 and HCl, respectively; however, by combining these two typically inefficient reactions into a one-pot reaction, the new process is surprisingly selective toward the removal of the metal impurities. This high selectivity derives from the proximity effect of the iron-catalyzed Fenton chemistry. At pH approximately 1-3, iron is dissolved upon exposure, avoiding the otherwise aggressive iron-catalyzed digestion of SWNTs by H2O2. This extremely simple and selective chemistry offers a "green" and scalable process to purify carbon nanotube materials.     

Chemical Characterization of Plant Extracts and Evaluation of their Nematicidal and Phytotoxic Potential

Nacobbus aberrans ranks among the “top ten” plant-parasitic nematodes of phytosanitary importance. It causes significant losses in commercial interest crops in America and is a potential risk in the European Union. The nematicidal and phytotoxic activities of seven plant extracts against N. aberrans and Solanum lycopersicum were evaluated in vitro, respectively. The chemical nature of three nematicidal extracts (EC_50,48h ≤ 113 µg mL⁻¹) was studied through NMR analysis. Plant extracts showed nematicidal activity on second-stage juveniles (J2): (≥87%) at 1000 µg mL⁻¹ after 72 h, and their EC₅₀ values were 71.4–468.1 and 31.5–299.8 µg mL⁻¹ after 24 and 48 h, respectively. Extracts with the best nematicidal potential (EC_50,48h < 113 µg mL⁻¹) were those from Adenophyllum aurantium, Alloispermum integrifolium, and Tournefortia densiflora, which inhibited L. esculentum seed growth by 100% at 20 µg mL⁻¹. Stigmasterol (1), β-sitosterol (2), and α-terthienyl (3) were identified from A. aurantium, while 1, 2, lutein (4), centaurin (5), patuletin-7-β-O-glucoside (6), pendulin (7), and penduletin (8) were identified from A. integrifolium. From T. densiflora extract, allantoin (9), 9-O-angeloyl-retronecine (10), and its N-oxide (11) were identified. The present research is the first to report the effect of T. densiflora, A. integrifolium, and A. aurantium against N. aberrans and chemically characterized nematicidal extracts that may provide alternative sources of botanical nematicides.     

Su una classe di procedimenti iterativi per la risoluzione di equazioni funzionali e applicazioni

Summary In this paper, we study a class of iterative processes of the type z_n=T_nz_n, which approximate the iterative processes x_n+1=Tx_n, where T and T_n are more general operators than contractions in a metric space.

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Lavoro eseguito in relazione al Contratto N^o 115.3050.0.5189 del Comitato per la Matematica del C.N.R. nel corso dell'anno accademico 1968–69.

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Entrata in Redazione il 25 luglio 1969.     

Numerical solution of unstable two-point boundary-value problems by quasilinearization and orthonormalization

This paper reports on a method of numerical solution of sensitive nonlinear two-point boundary-value problems. The method consists of a modification of the continuation technique in quasilinearization obtained by combination with an orthogonalization procedure for linear boundary-value problems.This work was supported by CNR, Rome, Italy, within the framework of GNAFA.     

Thermal degradation and melting point determination of diclofenac

The thermal behaviour of Diclofenac was investigated using Differential Scanning Calorimetry, Hot Stage Microscopy, and Thermogravimetric Analysis. A discrepancy was observed between the melting point values recorded under dynamic flow of either dry nitrogen (180°C) or air (160°C). By means of High Performance Liquid Chromatography/Mass Spectrometric analyses, it has been possible to ascribe this difference in melting points to the formation of three degradation products as a result of intramolecular cyclization and condensation reactions during the heating process in an oxidative atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stable luminescence from individual carbon nanotubes in acidic, basic, and biological environments

Aqueous surfactant suspensions of single walled carbon nanotubes (SWNTs) are very sensitive to environmental conditions. For example, the photoluminescence of semiconducting SWNTs varies significantly with concentration, pH, or salinity. In most cases, these factors restrict the range of applicability of SWNT suspensions. Here, we report a simple strategy to obtain stable and highly luminescent individualized SWNTs at pH values ranging from 1 to 11, as well as in highly saline buffers. This strategy relies on combining SWNTs previously suspended in sodium dodecylbenzene sulfonate (SDBS) with biocompatible poly(vinyl pyrrolidone) (PVP), which can be polymerized in situ to entrap the SWNT-SDBS micelles. We present a model that accounts for the photoluminescence stability of these suspensions based on PVP morphological changes at different pH values. Moreover, we demonstrate the effectiveness of these highly stable suspensions by imaging individual luminescent SWNTs on the surface of live human embryonic kidney cells (HEK cells).