Generation of simulation input scenarios using bootstrap methods

Simulation modellers frequently face a choice between fidelity and variety in their input scenarios. Using an historical trace provides only one realistic scenario. Using the input modelling facilities in commercial simulation software may provide any number of unrealistic scenarios. We ease this dilemma by developing a way to use the moving blocks bootstrap to convert a single trace into an unlimited number of realistic input scenarios. We do this by setting the bootstrap block size to make the bootstrap samples mimic independent realizations in terms of the distribution of distance between pairs of inputs. We measure distance using a new statistic computed from zero crossings. We estimate the best block size by scaling up an estimate computed by analysing subseries of the trace.     

Simple Functors of Admissible Linear Categories

Generalizing an idea used by Bouc, Thévenaz, Webb and others, we introduce the notion of an admissible R-linear category for a commutative unital ring R. Given an R-linear category \(\mathcal {L}\), we define an \(\mathcal {L}\)-functor to be a functor from \(\mathcal {L}\) to the category of R-modules. In the case where \(\mathcal {L}\) is admissible, we establish a bijective correspondence between the isomorphism classes of simple functors and the equivalence classes of pairs (G, V) where G is an object and V is a module of a certain quotient of the endomorphism algebra of G. Here, two pairs (F, U) and (G, V) are equivalent provided there exists an isomorphism F ← G effecting transport to U from V. We apply this to the category of finite abelian p-groups and to a class of subcategories of the biset category.     

Comparative mechanical property characterization of three indirect composite resin materials compared with two direct composites

Various new indirect composite materials have been developed with required advantages. In this study three indirect composite material (Artglass, Belleglass HP, Targis) were tested for flexural strength, fracture toughness, wear resistance and hardness against Filtek P60 and Z‐100. Five specimens of each material were fabricated according to the manufacturer's directions. The flexural strength and fracture toughness was measured using the bending test. The wear test was performed to accelerated wear in a toothbrushing apparatus. Vickers hardness was measured for each of the tested materials. The statistical tests used for flexural strength, fracture toughness, wear and hardness were One‐way ANOVA and Kruskal–Wallis test. The level of statistical significance chosen was p = 0.05. Results of the study showed that Filtek P60 was superior to the other composites in all tests. Significant differences were found among the materials. The differences in flexural strength, fracture toughnes, wear and hardness may have been due to differences in chemistry or method of polymerization of the composites. Copyright © 2003 John Wiley & Sons, Ltd.     

Spatially organized free-standing poly(p-xylylene) nanowires fabricated by vapor deposition

Thin films of poly(chloro-p-xylylene) (PPXC) grown by the pyrolysis and evaporation of chloro-[2.2]paracyclophane in an evacuated chamber contain free-standing, slanted, parallel columns that are 50 mum long and are assemblies of 50- to 100-nm-diameter nanowires, which thus can have an unprecedented aspect ratio as high as 1000:1. The nanostructured thin films organize spatially with a chemical structure similar to that of planar PPXC thin films, but the former also possess nanostructured morphology. Nanostructured thin films of poly(p-xylylene) (PPX) and its derivatives shall be useful as functionalized interfaces for antifouling coatings and biomedical devices.     

Controlling the wettability and adhesion of nanostructured poly-(p-xylylene) films

The hydrophobic surface properties of structured poly-(p-xylylene) (PPX) films, as measured by water wettability, are studied as functions of surface chemistry, film composition, and surface roughness. We demonstrate the fabrication of very hydrophobic surfaces and control over adhesion properties via nanoscale modulation of roughness, changes in composition, and alteration of the surface chemistry of PPX films. The formation of superhydrophobic surfaces through the chemisorption of fluoroalkylsiloxane coatings to hydroxyl sites created on the nanostructured PPX surface is also illustrated. The ability to control both hydrophobicity and adhesion using nanostructured PPX films is a promising development because it may lead to a new generation of coatings with applicability ranging from self-cleaning surfaces to robotics.     

Solid phase extractive preconcentration of trace metals using p-tert-butylcalix[4]arene-1,2-crown-4-anchored chloromethylated polymeric resin beads

5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,26-dihydroxy-27,28-crown-4-calix[4]arene in the cone conformation was synthesized. This p-tert-butylcalix[4]arene-1,2-crown-4 compound was then anchored with Merrifield chloromethylated resin beads. The modified polymeric resin was characterized by ¹H NMR, FT-IR and elemental analysis and used successfully for the separation and preconcentration of Cu(II), Cd(II), Co(II), Ni(II) and Zn(II) prior to their determination by FAAS. Effective extraction conditions were optimized in both batch and column methods. The resin exhibits good separating ability with maximum between pH 6.0-7.0 for Cu(II), pH 6.0 for Cd(II), pH 5.0 for Co(II), pH 4.0-4.5 for Ni(II), and pH 4.5 for Zn(II). The elution studies were carried out with 0.5 mol L⁻¹ HCl for Cu(II), Co(II) and Co(II), 1.0 mol L⁻¹ HCl for Cd(II) and Zn(II). The sorption capacity, preconcentration factor and distribution coefficient of each metal ion were determined. The detection limits were 1.10, 1.25, 1.83, 1.68 and 2.01 μg L⁻¹ for Cu(II), Cd(II), Co(II), Ni(II) and Zn(II). The influence of several ions on the resin performance was also investigated. The validity of the proposed method was checked for these metal ions in NIST standard reference material 2709 (San Joaquin Soil) and 2711 (Montana Soil).     

Raman lasing near 630 nm from stationary glycerol-water microdroplets on a superhydrophobic surface

We demonstrate, for the first time to our knowledge, Raman lasing from stationary microdroplets on a superhydrophobic surface. In the experiments, glycerol-water microdroplets with radii in the 11-15 microm range were pumped at 532 nm with a pulsed, frequency-doubled Nd:YAG laser. Two distinct operation regimes of the microdroplets were observed: cavity-enhanced Raman scattering and Raman lasing. In the latter case, the Raman lasing signal was higher than the background by more than 30 dB. Investigation of the Raman spectra of various glycerol-water mixtures indicates that lasing occurs within the glycerol Raman band. Raman lasing was not sustained; rather, oscillation would occur in temporally separated bursts. Increasing the rate of convective cooling by nitrogen purging improved the lasing performance and reduced the average interburst separation from 2.3 to 0.4 s.     

Salicylate Ion‐Selective Electrode Based on a Calix[4]arene as Ionophore

A salicylate‐selective electrode based on calix[4]arene derivative was developed and its response characteristics were investigated. The optimum membrane composition was 1 % ionophore, 30 % PVC, 69 % DOS. The electrode exhibited a Nernstian slope of 58.8±0.5 mV/pSal in the range of 1.0×10^?5–1.0×10^?1 M with a detection limit of 4.3×10^?6 M at pH 4.0, 20±1 °C. The potentiometric response of the electrode in the presence of different anions was investigated by the separate solution method. The lifetime was found at least 4 months, and its response time was 5–10 s. It was successfully used for the potentiometric determination of salicylate in pharmaceutical preparations.     

An efficient boundary element method for two-dimensional transient wave propagation problems

The boundary element method (BEM) has been recognized by its unique feature of requiring neither internal cells nor their associated domain integrals in the computation. The method preserves its elegance for transient problems by means of a certain time-stepping scheme that initiates the time integration always from the initial time. Unfortunately, this time-marching scheme becomes rather difficult to apply, because the computation time and storage requirement grow dramatically with the increasing number of time steps. This paper shows that a reduction of one half of the computation time as well as the storage requirement can be achieved by an efficient truncation scheme for two-dimensional transient wave propagation problems. In particular, a guiding parameter for the determination of the truncation limit is proposed, and the overall measure of the error with respect to the truncation guide parameter is established.     

Dynamical correlations in the one-dimensional electron gas with short-range interactions

We study the dynamical correlation effects in a one-dimensional Fermion gas with repulsive delta-function interaction within the quantum version of the self-consistent field approximation of Singwi, Tosi, Land, and Sj?lander [Phys. Rev. 176, 589 (1968)]. The dynamic correlation effects are described by a frequency dependent local-field correction . There is a corresponding local-field factor for the spin-density correlations. We investigate the structure factors, spin-dependent pair-correlation functions, the frequency dependences of and , and the plasmon dispersion relation within this formalism. We compare our results with other theoretical approaches, in particular the static version of the self-consistent field approximation to highlight the importance of dynamical correlations. Received 11 December 1998 and Received in final form 25 April 1999