Circuit macromodels and large-signal behaviour of fet-input operational amplifiers

The origin of the slew rate asymmetry found experimentally in FET-input LF355 op amps is analysed in order to explain why macromodels based on a strict build-up technique can fail when used to simulate the behaviour of amplifiers driven by out-of-band large voltage signals. These simulations may be very important in predicting the effects of electromagnetic interferences conveyed to the circuit input port. Other performances of op amp macromodels designed either by build-up techniques or by simplification/build-up techniques are also compared and discussed.     

Phenomenological study of saltating motion of individual particles in horizontal particle–gas systems

A comprehensive use of particle–fluid conveying systems for a wide range of industries requires a deep understanding in all interactions of the particular conveying process. One of the most common particle motions occurring in conveying systems is the saltating motion of particles. Although the literature abounds with theoretical, empirical and numerical studies that investigate the saltation phenomenon, there remain many questions and misunderstandings. Some of the recently solved issues are: which non-dimensional groups are introducing the particle saltating motion, how the saltation length might be predicted, how the pipe diameter and the coefficient of restitution influence the saltation velocity and length.The present work investigates the motion of individual saltating particles and presents a wide range of experimental measurements of the conveying length for a variety of particulate solids, sizes and shapes. The total conveying length was divided into three lengths: the first flight, the rebound and the rolling/sliding and each one of them is theoretically and empirically analyzed and compared. This phenomenological study presents the theoretical evidence to previously empirical findings. The theoretical analysis is further used to define the border conditions between various mechanisms. The results show that for coarse particles the rebound and rolling/sliding motions might be presented by a simple relationship between the Reynolds and Archimedes numbers. Additionally we find that the preferred saltation mode of fine powders depends on the conveying system length and diameter. For example for large pipe diameters and short length the first flight mode is the dominant; however, for small pipe diameters and long systems length the rebound mode is the dominant.     

ISSN Exercise & Sport Nutrition Review: Research & Recommendations

Sport nutrition is a constantly evolving field with literally thousands of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper presents a well-referenced overview of the current state of the science related to how to optimize training through nutrition. More specifically, this article discusses: 1.) how to evaluate the scientific merit of nutritional supplements; 2.) general nutritional strategies to optimize performance and enhance recovery; and, 3.) our current understanding of the available science behind weight gain, weight loss, and performance enhancement supplements. Our hope is that ISSN members find this review useful in their daily practice and consultation with their clients.     

Aerosol Sampling Efficiency in a Model Room

The sampling process of a model room with a suction nozzle in a calm or low movement environment was numerically simulated and experimentally analyzed. Computational fluid dynamics (CFD) software, Fluent (Fluent Inc.), was used for the numerical simulation. The flow was considered to be compressible and turbulent, and particles were considered to be spheres of constant density. A good agreement was found between the numerical and experimental results (maximum difference of 15% in the overlapping zone), and the numerical model was further extended and used for parametric analysis. The influence of sampling velocity and shape of the suction nozzle on sampling efficiency was investigated experimentally and numerically in a particle size range of 2-45 µm. It was found that sampling efficiency is smaller for V-shaped nozzles, mainly for lower velocities. Sampling efficiency was calculated for each particle diameter and for the whole particle size distribution as well. Sampling efficiency decreases as particle size increases. It is concluded that knowledge of sampling efficiency for each of the sampled particle sizes may indicate the concentration and size distribution in the sampled space.     

Numerical Model for Heat Transfer in Dilute Turbulent Gas-Particle Flows

The heat transfer between a vertical pipe wall and turbulent gas-particle flow is numerically investigated according to the Eulerian-Lagrangian approach and the k-ε turbulence model. The particles are introduced homogeneously into the simulation volume by a unique technique referred to as an artificial feeding volume. The numerical code using additional computer programs is validated with available experimental results for the constant heat flux boundary condition. An average deviation of about 4% and a maximum deviation of about 7% were attained from the numerical predictions for various particle and pipe diameters. The effect of the geometrical parameters and the flow parameters on the gas/particle temperature, the convection heat transfer coefficient between the wall and the gas-particle mixture, and the thermal entry length were studied. An increase in particle diameter (loading ratio ≈ 0.5) extended the thermal entry length and decreased the bulk mixed temperature, particle temperature, and convection heat transfer coefficient. Increasing the pipe diameter led to a significant reduction in bulk mixed temperature and thermal entry length, in addition to a decrease in particle temperature and Nusselt number. Increasing the loading ratio up to 2.36 led to a reduction in wall temperature and bulk mixed temperature, in addition to an increase in the convective heat transfer coefficient and thermal entry length.     

Flow-induced properties of nanotube-filled polymer materials

Carbon nanotubes (CNTs) are under intense investigation in materials science owing to their potential for modifying the electrical conductivity sigma, shear viscosity eta, and other transport properties of polymeric materials. These particles are hybrids of filler and nanoscale additives because their lengths are macroscopic whereas their cross-sectional dimensions are closer to molecular scales. The combination of extended shape, rigidity and deformability allows CNTs to be mechanically dispersed in polymer matrices in the form of disordered 'jammed' network structures. Our measurements on representative network-forming multiwall nanotube (MWNT) dispersions in polypropylene indicate that these materials exhibit extraordinary flow-induced property changes. Specifically, sigma and eta both decrease strongly with increasing shear rate, and these nanocomposites exhibit impressively large and negative normal stress differences, a rarely reported phenomenon in soft condensed matter. We illustrate the practical implications of these nonlinear transport properties by showing that MWNTs eliminate die swell in our nanocomposites, an effect crucial for their processing.     

Typical Fluidization Characteristics for Geldart's Classification Groups

This article describes a comprehensive experimental analysis that defines typical fluidization characteristic curve for Geldart's classification groups. Geldart defined four types of materials which differ by the cohesion forces between particles. An experimental apparatus containing fluidized beds of four pipe diameters and fully controlled by LabVIEW was used to perform the fluidization tests. All tests were performed automatically by gradually increasing the air velocity and measuring the pressure drop over the bed. For each test, the fluidization curve was recorded and the minimum fluidization, bubbling, and slugging velocities were defined. It was found that the fluidization curve of material define accurately the Geldart's group to which the material belongs. In addition, was reviewed the reason for those materials and under which conditions the pressure drop increases in the slugging state. Finally, the influence of height to bed diameter H/D ratio on the shape of characterization curve was found. The present study has significant interest for researchers and designers since it enables to predict the fluidization characteristics of two-phase (fluid-solids) flows.     

Does nicotine do what we think it does? A meta-analytic review of the subjective effects of nicotine in nasal spray and intravenous studies with smokers and nonsmokers.

We conducted a meta-analysis of placebo-controlled laboratory studies of the subjective effects of nicotine. A total of 15 studies (11 with nasal spray, four with intravenous administration) with smokers and six studies (all with nasal spray) with never-smokers were included. Studies of other routes of administration (e.g., smoked tobacco) were not included because of insufficient numbers of available effect sizes. Meta-analysis results indicated that nicotine increased vigor for smokers but increased fatigue for never-smokers. Nicotine increased head rush for both smokers and never-smokers. In studies of smokers only, nicotine also increased ratings of drug high and drug liking. Contrary to expectations, nicotine decreased relaxation and increased tension/jitteriness for both smokers and never-smokers. Dose-response relationships were most clearly observed for head rush and drug high. Considerable variability was found across studies for a given nicotine dose and route of administration. Implications of the current findings about the role of subjective effects in nicotine reinforcement and self-administration are discussed along with commentary on methodological issues and recommendations for future studies.     

Sarcomas in syrian hamster, induced by an oncorna virus and cellfree transmissible (author''s transl)]

A previous study had shown that in children with third degree protein-energy malnutrition, ultrafilterable or diffusible serum calcium concentrations remain normal, while the protein-bound fraction is low in those with hypoalbuminemia, accounting for over-all hypocalcemia. In order to retest those findings, a new series consisting of 20 small marasmic infants and 16 children with kwashiorkor was studied, using a membrane ultrafiltration procedure. Fifteen eutrophic children served as controls. At time of their admission into hospital, both groups of patients showed hypocalcemia, more so the cases of kwashiorkor. Diffusible calcium was normal, while the protein-bound moiety was significantly decreased in children with kwashiorkor. Upon recovery, protein-bound as well as total calcium concentrations returned to normal values.     

Frequency response of non-linear single degree-of-freedom systems

Simple linear Kelvin or Maxwell models cannot predict adequately the response of many practical systems to vibration excitation. A more realistic model consisting of a mass between two preloaded non-linear (cubic elasticity springs) and restrained by a Coulomb and viscous damper is proposed. A harmonic motion solution, satisfying “on the average” the non-linear differential equation of motion of the model is developed whereby equations for frequency response curves are obtained. Expressions for relative and absolute transmissibility as well as their values at resonance are developed, these are shown to properly reduce to the respective exact expressions of a Kelvin model and friction damped linear spring. Although the model is intended mainly for quantitative design in packaging engineering problems, it is suitable for studying general vibration isolation problems as well.