Search

A review of flow modulation techniques is presented with a particular emphasis put on the EHD impedance. Due to the general formalism of impedances, a close relation is demonstrated between this EHD and the usual ac impedance. An analysis is hence presented about the general procedure for considering the effect of interfacial kinetics of finite rate. The technique is also demonstrated to be especially powerful when the interface is coated by a porous layer or is non-uniformly reactive (partial blocking). Finally, the concept of EHD impedance is also shown to be linked to the frequency response of microelectrodes used for investigating the properties of hydrodynamic fluctuations close to a wall.

The objective was to analyse relationships between inspiratory and expiratory static and dynamic elastic pressure-volume (P(el)/V) curves in healthy pigs.The modulated low flow method was developed to allow studies also of the expiratory P(el)/V curves. Static P(el)/V (P(el,st)/V) and dynamic P(el)/V (P(el,dyn)/V) loops were studied in healthy pigs.Animal research laboratory in a university hospital.Ten healthy anaesthetised and paralysed pigs.A computer controlled a Servo Ventilator 900C with respect to respiratory rate, inspiratory flow and expiratory pressure to achieve a sinusoidal modulation of inspiration and expiration for determination of P(el,dyn)/V loops from zero end-expiratory pressure (ZEEP) and from a positive end-expiratory pressure (PEEP) of 6 cmH(2)O to 20, 35 and 50 cmH(2)O. The same system was used for studies of P(el,st)/V loops with the flow-interruption method from ZEEP and PEEP to 35 cmH(2)O. Recordings were analysed with an iterative technique.The feasibility of automated determination of P(el,dyn)/V loops was demonstrated. Differences between P(el,dyn)/V and P(el,st)/V loops were explained by viscoelastic behaviour. P(el,st)/V loops recorded from PEEP to 35 cmH(2)O showed no significant hysteresis, indicating a non-significant surface tension hysteresis. P(el,dyn)/V loops from PEEP and both P(el,st)/V and P(el,dyn)/V loops from ZEEP to 35 cmH(2)O showed hysteresis. This indicates that lung collapse/re-expansion caused P(el)/V loop hysteresis which, in P(el,dyn)/V loops, was augmented by viscoelastic behaviour.Viscoelasticity influences P(el,dyn)/V curves. Hysteresis caused by surface tension merits re-evaluation. Lung collapse and re-expansion may be indicated by hysteresis of P(el)/V loops.

This is certainly the most important book dealing with gas and liquid chromatography that has appeared for many years. Two-dimensional (2D) chromatography dates back almost to the beginnings of the modern era of chromatography, and 2D GC systems have been used since the 1960s. Indeed, Deans who was the first to publish pneumatic switching, believed that all GC problems at that time could be solved by multiple column combinations. The idea of comprehensive 2D chromatography (where all peaks from one column pass to a second, different column) dates back 20 years, but it is only within the last 10 years that it has been taken up by a few enthusiasts most of whom appear as contributors to this book. In particular the editor, Mondello, appears as a co-author in no less than six of the 12 chapters. The potential advantages of comprehensive 2D chromatography are clear, but the practical problems are formidable and this book does not disguise this fact. After a short introductory chapter to set the scene, the book properly starts with a chapter on theoretical aspects of multidimensional gas chromatography by Blumberg. This chapter reminded me of my student course on thermodynamics—after a year of lectures and some 230 equations I was little the wiser. The author manages 91 equations in 46 pages, but in fairness he does try hard to stress the conclusions of his work by inserting paragraphs in italics that outline the practical significance of his theoretical analysis. It is worth quoting a slightly condensed version of his concluding italic paragraph—‘‘GC x GC has the potential to provide at least one order of magnitude larger peak capacity than 1D GC. When the hardware problems are solved the separation performance will be out of reach of any known alternative GC technique. Further significant increase in peak capacity can be obtained by improved data analysis’’. The next chapter deals with the theoretical aspects of multidimensional LC, but fortunately this is considerably simpler than the preceding chapter (a mere 27 equations in 26 pages!). Chapter 4 deals with more practical aspects of comprehensive 2D GC, in particular with the various ‘‘modulators’’ that have been developed. The modulator is the device that samples at short time intervals the peaks emerging from the first column and sends them to the second column. To get reliable determination of peak area at least ten data points per peak should be collected and this places severe demands on the modulator (and also on the detector and data handling system). Indeed the performance of the modulator is the most important of the ‘‘hardware problems’’ touched on in Blumberg’s summary quoted above. Chapter 5 by Seeley describes what seems to me to be possibly the best solution of the modulator problem using flow modulation, since it is by far the least demanding of equipment and operating costs although as always there are E. R. Adlard (&) Burton, South Wirral, UK e-mail: chromatographia@springer.com

Flow modulation epitaxy (FME) has been employed previously to synthesize III-V arsenides and phosphides. However, the ability of FME to extend growth to lower temperatures than those required for conventional organometallic vapor phase epitaxy (OMVPE) has only recently been explored for the synthesis of nitride based semiconductors. Because, in part, of the importance of low temperature growth to the synthesis of indium-containing group III-nitrides, this growth technique should be explored further. In this paper we report on the FME of group III-nitride compounds on sapphire and silicon carbide substrates.

Two fixed-ratio in-line direct-injection units and a throttling-valve bypass in parallel were investigated for pressure, flow, and chemical discharge transients at measurement sampling intervals of 0.6, 1.0, and 0.6 s, respectively. Flow modulation through each branch of the circuit was hypothesized as a means of varying chemical concentration and applied rates. Test condition factors included flow partitioning through branches, flow rates, in-line unit ratios, chemical sample locations, and pressure dampening with hose length. Flow partitioning through parallel in-line injection units exhibited preferential flow through some in-line units even though units were subjected to equal pressure potentials. Flow rates differed between in-line units up to a factor of 4.58 for two inline units, and up to 10.2 for two units and the bypass. The bypass operating alone had pressure fluctuations up to a CV of 2.6%, and may have been due to the pressure relief valve and/or the throttling valve. Flow and pressure cycles had a frequencies of ~0.3 Hz. However, the bypass tended to dampen flow and pressure fluctuations introduced by in-line units. Single in-line units and dual in-line units usually increased upstream and downstream pressure fluctuations that typically had a frequency of 0.5 Hz. CV in pressure for single units ranged from 1.4 to 18.2%. CV in pressure for dual units ranged from 5.8 to 32.4%. Increased flow rates through in-line units and increased hose lengths downstream from in-line units generally resulted in dampened pressure fluctuations. CV in Br- concentration ranged from 1.3 to 14.5% and metering error ranged from –44 to +57%.

Cerebral hemodynamics were evaluated in 7 patients with large high-flow arteriovenous malformations (AVMs) using an intra-operative thermo-gradient flowmeter. The maximum post-excision/ pre-excision blood flow ratio was determined. Special clamps made from silicone tubes with absorbable threads were applied on the proximal feeding arteries.

The second of two methods for reducing oxide interferences in inductively coupled plasma mass spectrometry is outlined. In both methods, manipulation of the central-channel gas flow generates unique behavior from analytes and interfering oxides that can subsequently be used to isolate signal contributions from both species superimposed at a given mass. Here, mathematical correlation between an interferent-compromised analyte response and an internal standard allows errors from troublesome interferences to be effectively eliminated. This correction method is capable of addressing multiple analyte-oxide interferences without sacrificing analyte sensitivity. A time-of-flight mass analyzer was used in this work to provide multi-elemental capabilities; however, the method is amenable to implementation on other simultaneous or scan-based mass analyzers.

The first of two new methods for reducing oxide interferences in inductively coupled plasma mass spectrometry is described. This method utilizes careful manipulation of the central-channel gas flow to impart distinguishable frequency-specific behavior to analyte and oxide species. Subsequently, application of a Fourier transform (FT) permits contributions from the analyte and oxide superimposed at a given mass to be unraveled. Through application of this correction method, a greater than ten-fold error at m/z 156 caused by the interference of 140Ce16O+ on 156Gd+ has been effectively eliminated. This correction method is well suited for overcoming multiple analyte–oxide interferences (most notably where monoisotopic elements have been compromised) in a simultaneous manner. Although a time-of-flight mass analyzer was utilized here, this correction method is well suited also for implementation with scan-based systems (e.g. quadrupoles and sector-field mass spectrometers).

Chemical vapor deposition titanium nitride (CVD-TiN) films were deposited from TiCl4 and NH3 at 410°C, that was sufficiently low for making ULSI multi-level interconnections. We investigated the Cl content and resistivity of CVD-TiN films as a function of TiCl4 and NH3 partial pressure (P TiCl4 , P NH3 ). We found that Ti/(Ti+N) ratio was almost constant against different P TiCl4 and P NH3 conditions, while the resistivity and residual chlorine concentration were sensitive to these conditions. The lowest resistivity of 480 µΩ·cm and the lowest Cl concentration of 2% were achieved in the condition of the step coverage of 96% and the throughput of 16 nm/min when P TiCl4 = 0.01 Torr, and P NH3 = 0.25 Torr, respectively. These values may be further improved by using flow modulation method.

In this article, we report on the low temperature growth of HgTe, CdTe, and HgCdTe by flow modulation epitaxy (FME). Dimethylmercury, dimethylcadmium, and methylallyltelluride were used as the precursors in this ‘‘layer‐by‐layer’’ growth approach. Growth of CdTe at one monolayer per cycle was obtained at temperatures above 250 °C. The growth rate was invariant with temperature and reactant pressures. HgTe growth was carried out by FME at 140 °C at atmospheric pressure by precracking the Hg and Te alkyls at 350 °C. HgCdTe layers were grown by interdiffusing sequential layers of CdTe and HgTe.

This article presents a guide to the popular value types and how they are automated for remote on-off control and flow modulation.

Effective domestic wastewater treatment is a significant problem of the construction industry. To solve this problem, one has to design and operate a chain of successive constructions. Biological treatment is the final link in this chain. The method is based on a degradation process that affects dissolved organic waste in the water. As urban population is rapidly growing, and households use more and more appliances that utilize water, engineers face a number of issues in relation to making biological treatment more efficient. It is due to the fact that such issues are the most long-lasting and energy-intensive problems in the above-mentioned chain. The solution we propose is arotary machine with flow modulation. This approach allows to activate protozoa and effectively saturate the treated medium with oxygen. The device presented herein allows to optimize the hydrodynamic and acoustic pulse impact on the milieu of these microorganisms. Thanks to the extended interface area, the device enables effective control over the regeneration of such microorganisms as well as oxygen saturation of the medium.

The urodynamic parameters during voiding are tabulated for a group of women with voiding dysfunction. These patients have consistently lower flow rates than a normal population and the cross-sectional area of the voided stream is statistically less in the patient group. The parameters measured can behave as they do only if there is a zone of active neuromuscular control of the urinary stream localized within the urethra. Surgical intervention in this flow modulation zone tends to compromise voiding function and to affect flow rate adversely.

Vortex valve for hot gas flow modulation in secondary injection thrust vector control system

The report summarizes the development of a fluidic vortex valve controlled servoactuator for a UH-1B helicopter stability augmentation system (pitch, roll, and yaw control). Alternate fluidic approaches for hydraulic actuator control were studied, and an approach utilizing two vortex valves was selected. Vortex valves were developed to meet the specified performance requirements. A circuit was designed to incorporate the vortex valves for second-stage flow modulation.

The stability of time‐dependent flows is analyzed by the energy theory. Lower bounds as well as optimal results are obtained for modulated Benard and Taylor problems. It is found that the region of certain stability is reduced because of the basic flow modulation.