Drugmart: Heroin epidemics as complex adaptive systems

Illicit drug epidemics are infamous for their unexpected arrival and their speed of onset. Based on ethnographic work with youthful heroin experimenters in the Baltimore metropolitan area, an explanation was constructed based on circulating stories of drug reputation. An agent‐based model was built in SWARM to evaluate the explanation with good and bad stories about the drug passed among agents, which changed their initial attitudes. On repeated runs with different initial attitudes the model shows wide variation in outcomes and a dampening effect of increased social connections, contrary to epidemiologic expectations. The conclusion spells out implications for drug intervention and social research that relies on single case studies. © 2002 Wiley Periodicals, Inc.     

Laser dye stability part 1. Flash frequency and fluid filtration effects

A commercial coaxial xenon flashlamp was used to measure laser dye stability. The output energy of each lasing pulse was recorded and periodic measurements were made of the untuned lasing wavelength, the temporal flashlamp output, and the temporal lasing output. The present study demonstrates that it is possible to have a number of different types of apparent dye laser system “half-lifes” through the use of filtration and frequency of flash parameters. The use of near-zero flash frequency and moderate pore size filters allows a determination of the lifetime that is more representative of the dye as opposed to the lifetime of the dye laser system.     

Cookbook asymptotics for spiral and scroll waves in excitable media

Algebraic formulas predicting the frequencies and shapes of waves in a reaction-diffusion model of excitable media are presented in the form of four recipes. The formulas themselves are based on a detailed asymptotic analysis (published elsewhere) of the model equations at leading order and first order in the asymptotic parameter. The importance of the first order contribution is stressed throughout, beginning with a discussion of the Fife limit, Fife scaling, and Fife regime. Recipes are given for spiral waves and detailed comparisons are presented between the asymptotic predictions and the solutions of the full reaction-diffusion equations. Recipes for twisted scroll waves with straight filaments are given and again comparisons are shown. The connection between the asymptotic results and filament dynamics is discussed, and one of the previously unknown coefficients in the theory of filament dynamics is evaluated in terms of its asymptotic expansion. (c) 2002 American Institute of Physics.     

Symmetry Breaking and Turbulence in Perturbed Plane Couette Flow

Perturbed plane Couette flow containing a thin spanwise-oriented ribbon undergoes a subcritical bifurcation at Re≈230 to a steady three-dimensional state containing streamwise vortices. This bifurcation is followed by several others giving rise to a fascinating series of stable and unstable steady states of different symmetries and wavelengths. First, the backwards-bifurcating branch reverses direction and becomes stable near Re≈200. Then the spanwise reflection symmetry is broken, leading to two asymmetric branches which are themselves destabilized at Re≈420. Above this Reynolds number, time evolution leads first to a metastable state whose spanwise wavelength is halved and then to complicated time-dependent behavior. These features are in agreement with experiments. Received 15 December 2001 and accepted 29 March 2002 Published online: 2 October 2002 Communicated by H.J.S. Fernando     

Magnetoresistance near the metal-insulator transition of Cd0.99Mn0.01Se

At 0.5 ≤ T ≤ 4.2 K samples of Cd_0.99Mn_0.01Se which are near the metal-insulator transition exhibit a large positive magnetoresistance (MR) in fields H ∽ 10 k0e. The effect is accompanied by an increase in the Hall coefficient and a decrease in the Hall mobility. At the lowest temperatures and for fields well above 10 k0e a small negative MR is observed. The positive MR is tentatively attributed to an increase in the screening radius r_s, which leads to enhanced Coulomb-potential fluctuations.     

Negative-ion liquid secondary ion mass spectrometry of antiparallel N-carbamoylmorpholine-linked nucleic acid oligomers: Evidence for fragmentation from molecular radical ion precursors

N-Carbamoylmorpholine-linked nucleic acid oiigomers were analyzed by negative-ion liquid secondary ion mass spectrometry. Cleavage of the carbamate backbone in repeating fashion on both sides of the carbonyl groups gives two sequence ion series. The main fragment arises from cleavage of the base-morpholine bond. Important fragment ions are postulated to arise from cleavage of an M^?· radical ion precursor.     

A study of the magnetic susceptibility of R3Au3Sb4 (R = Tb,Ho, Er,Tm)

The magnetic susceptibilities of the new cubic intermetallic compounds R₃Au₃Sb₄ (R = Tb, Ho, Er, and Tm) have been measured between 4 and 300 K. The compounds are paramagnetic down to 4 K. The experimental effective magnetic moment of the erbium compound is in agreement with the free-ion value, whereas the effective moments of the other three compounds are lower than the corresponding free-ion values. This discrepancy is interpreted in terms of quenching by the crystalline electric field.