RESUMEN
A similarity decay law is proposed for enstrophy of a one-signed-vorticity fluid in a circular free-slip domain. It excludes the metastable equilibrium enstrophy which cannot drive turbulence, and approaches Batchelor's t(-2) law for strong turbulence. Measurements of the decay of a turbulent electron fluid agree well with the predictions of the decay law for a variety of initial conditions.
RESUMEN
Dynamical relaxation of a pure electron plasma in a Malmberg-Penning trap is studied, comparing experiments, numerical simulations and statistical theories of weakly dissipative two-dimensional (2D) turbulence. Simulations confirm that the dynamics are approximated well by a 2D hydrodynamic model. Statistical analysis favors a theoretical picture of relaxation to a near-maximum entropy state with constrained energy, circulation, and angular momentum. This provides evidence that 2D electron fluid relaxation in a turbulent regime is governed by principles of maximum entropy.
RESUMEN
A theory is presented of beat-wave resonant down scattering of two-dimensional diocotron (or Kelvin) modes, in which modes down scatter to lower azimuthal mode number. The phenomenon is a fluid analogue to nonlinear Landau damping. The principal new result is a quantitative prediction of the scattering rate. The predicted rates and scalings are close to those observed in experiments with magnetized electron columns.
RESUMEN
BACKGROUND: The clinical implementation and evaluation of heroin substitution programmes have been confounded by the lack of objective and validated biomarkers for illicit heroin use in patients prescribed pharmaceutical heroin. This study examined the capacity to detect illicit heroin use by gas chromatography-mass spectrometry (GC-MS) analysis of urine samples for the presence of opium impurities common to illicit, but not pharmaceutical heroin. AIMS: To characterize the diagnostic properties of the metabolites of noscapine and papaverine in comparison to morphine as a gold-standard marker of illicit heroin use; and to examine the relationships between the self-reported time since most recent heroin use and the detection of these opioids in urine. DESIGN: A cross-sectional study of 52 opioid-dependent patients in treatment (not prescribed heroin), who self-reported illicit heroin use within the preceding 2 weeks. Self-report data regarding recent drug use and a urine sample were collected. GC-MS analyses of urines were conducted and reported by laboratory staff blinded to self-report data. FINDINGS: The metabolites of papaverine (hydroxypapaverine and dihydroxypapeverine) were found to have high sensitivity, specificity and negative predictive values as markers for illicit heroin use compared to the 'gold-standard' morphine. Other opioids, including 6-mono-acetylmorphine (6-MAM), codeine and noscapine metabolites (e.g. meconine) were less adequate in detecting heroin use. CONCLUSIONS: GC-MS detection of papaverine metabolites in urine appears to be suitable method of identifying illicit heroin use for clinical and research purposes.
Asunto(s)
Dependencia de Heroína/rehabilitación , Heroína/orina , Detección de Abuso de Sustancias/métodos , Adulto , Estudios Transversales , Femenino , Cromatografía de Gases y Espectrometría de Masas/métodos , Heroína/uso terapéutico , Dependencia de Heroína/diagnóstico , Humanos , Masculino , Persona de Mediana Edad , Resultado del TratamientoRESUMEN
Locally excited plasma waves are generated in a Coulomb crystal by "pushing" with radiation pressure on a rotating cloud of laser-cooled 9Be+ ions. The waves form a stationary wake that is directly imaged through the dependence of the ion fluorescence on Doppler shifts, and theoretical calculations in a slab geometry are shown to accurately reproduce these images. The technique demonstrates a new method of exciting and studying waves in cold ion clouds.