Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

Low-dispersion electrokinetic flows for expanded separation channels in microfluidic systems: multiple faceted interfaces

A novel methodology to design on-chip conduction channels is presented for expansion of low-dispersion separation channels. Designs are examined using two-dimensional numerical solutions of the Laplace equation with a Monte Carlo technique to model diffusion. The design technique relies on trigonometric relations that apply for ideal electrokinetic flows. Flows are rotated and stretched along the abrupt interface between adjacent regions having differing specific permeability. Multiple interfaces can be placed in series along a channel. The resulting channels can be expanded to extreme widths while minimizing dispersion of injected analyte bands. These channels can provide a long path length for line-of-sight optical absorption measurements. Expanded sections can be reduced to enable point detection at the exit section of the channel. Designed to be shallow, these channels have extreme aspect ratios in the wide section, greatly increasing the surface-to-volume ratio to increase heat removal and decrease unwanted pressure-driven flow. The use of multiple interfaces is demonstrated by considering several three-interface designs. Faceted flow splitters can be constructed to divide channels into any number of exit channels while minimizing dispersion. The resulting manifolds can be used to construct medians for structural support in wide, shallow channels.     

Inter-comparison among fast neutron dosimetric services using PADC material of different composition

A trial inter-comparison has been performed among four fast neutron dosimetric services: PSI(CH), ENEA (I), DRPS (UK), LANL (US). The PADC used for the tests has been produced by Intercast Europe S.p.A. Three sets of detectors have been employed: two of PADC standard material from two different batches, and one of PADC with the addition of 0.1% dioctylphthalate. Each set consisted of 50 detectors.

For each set of detectors, 20 have been irradiated free-in-air at 1 mSv of H^*(10) with an ²⁴¹Am–Be source at ENEA-IRP, whilst the other detectors have been used as background samples. For each batch the value of the average background signal, B, the average neutron sensitivity, S, and minimum detectable dose equivalent, MDDE, have been determined. Two identical tests have been completed and separated with a time of 4 months in order to evaluate the ageing effect on the material stored in different conditions. Each dosimetric service processed the detectors according to local routine procedures. Three laboratories used an Autoscan60 reader, whilst one laboratory has an in-house reading system. Therefore, the results of the tests allowed a comparison of either the performance PADC materials, of different batches and of different compositions, or to evaluate how different etching, reading and storage conditions affect the results.     

Electrochemical processes in electrospray ionization mass spectrometry

Editorial Comment Last month we presented, as a Special Feature, a set of five articles that constituted a Commentary on the fundamentals and mechanism of electrospray ionization (ESI). These articles produced some lively discussion among the authors on the role of electrochemistry in ESI. Six authors participated in a detailed exchange of views on this topic, the final results of which constitute this month's Special Feature. We particularly hope that younger scientists will find value in this month's Special Feature, not only for the science that it teaches but also what it reveals about the processes by which scientific conclusions are drawn. To a degree, the contributions part the curtains on these processes and show science in action. We sincerely thank the contributors to this discussion. The give and take of intellectual debate is not always easy, and to a remarkable extent this set of authors has maintained good humor and friendships, even when disagreeing strongly on substance. Graham Cooks and Richard Caprioli Copyright 2000 John Wiley & Sons, Ltd.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.     

Injection of single and multiple vortices in an opposed-jet burner

A thorough understanding of turbulent reacting flows is essential to the continued development of practical combustion systems. Combustor codes can be validated using data such as those generated in this study of a vortex interacting with a nonpremixed, opposed-jet hydrogen-air flame. When experimental results are compared with model predictions, the underlying flowfield must be matched carefully. Since the vortex-injection process used in the present experiments can result in many types of vortices, including multiple vortices, restrictions on the experimental operation of the burner are required as well as careful vortex characterization. Vortex-characterization data are acquired using digital, two-color particle-image velocimetry (PIV), and the hydroxyl (OH) layer produced by the flame is imaged using planar laser-induced fluorescence (PLIF). The PIV and OH PLIF measurements are performed simultaneously. Good agreement with previous numerical-modeling predictions is obtained when experiments and computations are performed using similar vortex conditions.