Sheldon I. Green

The discipline dependence of citation statistics

This study compares the citations characteristics of researchers in engineering disciplines with other major scientific disciplines, and investigates variations in citing patterns within subdisciplines in the field of engineering. Utilizing citations statistics including Hirsch’s (Proc Natl Acad Sci USA 102(46):16569–16572, 2005) h-index value, we find that significant differences in citing characteristics exist between engineering disciplines and other scientific fields. Our findings also reveal statistical differences in citing characteristics between subdisciplines found within the same engineering discipline.

Wing Tip Vortices

One of the most conspicuous features of an airplane flying at high altitude is its white contrails. These contrails, which are formed by the condensation of engine exhaust water vapour, clearly delineate the location of the wing tip vortices. The contrails are often the first — and perhaps the only — exposure most of us have to wing tip vortices (also referred to as “trailing vortices” or, imprecisely, as “wing wake vortices” or “tip wake vortices”). This chapter aims to explain the origin of tip vortices (§X.l) and review their technological relevance (§X.2). The chapter then summarizes lifting line theory, the simplest finite wing theory (§X.3), and synopsizes our knowledge of tip vortex behaviour (§X.4, §X.5).

Preventing Airborne Disease Transmission: Review of Methods for Ventilation Design in Health Care Facilities

Health care facility ventilation design greatly affects disease transmission by aerosols. The desire to control infection in hospitals and at the same time to reduce their carbon footprint motivates the use of unconventional solutions for building design and associated control measures. This paper considers indoor sources and types of infectious aerosols, and pathogen viability and infectivity behaviors in response to environmental conditions. Aerosol dispersion, heat and mass transfer, deposition in the respiratory tract, and infection mechanisms are discussed, with an emphasis on experimental and modeling approaches. Key building design parameters are described that include types of ventilation systems (mixing, displacement, natural and hybrid), air exchange rate, temperature and relative humidity, air flow distribution structure, occupancy, engineered disinfection of air (filtration and UV radiation), and architectural programming (source and activity management) for health care facilities. The paper describes major findings and suggests future research needs in methods for ventilation design of health care facilities to prevent airborne infection risk.

A 3D swallowing simulation using smoothed particle hydrodynamics

A three-dimensional (3D) computer simulation of swallowing is presented. The soft structures (i.e. pharyngeal wall, soft palate and tongue) are simulated using finite element models. Bony structures (e.g. mandible, hard palate and hyoid) are simulated as rigid bodies. A fluid bolus is simulated using smoothed particle hydrodynamics (SPH). A Newtonian viscosity model is validated by comparing a 3D SPH simulation of Hagen–Poiseuille flow with theoretical results. A previously unreported source of error is reported and discussed. In the swallowing simulation, fluid boundaries are determined by the rigid and deformable surfaces, and the coupling is in one direction only. Movement of solid boundaries was determined in previous work for a deformable solid bolus. Two swallowing simulations are presented with different bolus viscosities in order to demonstrate that SPH can be used to simulate and track the liquid phase of a bolus during swallow. We find that SPH robustly handles moving boundary conditions as well as changes in viscosity. SPH simulations of the bolus are therefore potentially a useful visual aid to understand the effects of solid boundary motion on swallowing.

Correlating Single Phase Flow Measurements With Observations of Trailing Vortex Cavitation

The single phase and caviting tip vortex shed by a NACA 66-209 rectangular planform, rounded tip hydrofoil has been studied. Single-phase measurements of instantaneous flow velocity were made by taking double-pulsed holograms of microbubbles moving in and around the vortex core. The tailored air bubble technique of Ooi and Acosta was employed to measure both the mean and fluctuating single phase vortex core static pressure. Cavitation inception was determined visually. The flow in the vortex core is highly unsteady; the r.m.s. axial velocity fluctuation can be as high as 0.2U ∞ .

Introduction to Vorticity

A fluid vortices text, even one replete with experimental and computational results, must, of necessity, include information on the mathematical and physical underpinnings of vorticity. The purpose of this chapter is to provide the reader with this information. Some advanced graduate level fluid mechanics courses cover the material in this chapter, but readers without this background would be well-advised to read the chapter carefully. Without this foundation of fluid vorticity understanding, subsequent chapters will be more abstruse.

Use of tracer gas for direct calibration of emission-factor measurements in a traffic tunnel

Pollutant measurements in traffic tunnels have been used to estimate motor-vehicle emissions for several decades. The objective in this type of study is to use the traffic tunnel as a tool for characterizing motor vehicles rather than seeking a tunnel design with acceptably low pollutant concentrations. In the past, very simple aerodynamic models have been used to relate measured concentrations to vehicle emissions. Typically, it is assumed that velocities and concentrations are uniform across the tunnel cross section. In the present work, a vehicle emitting a known amount of sulfur hexafluoride (SF6) was driven repeatedly through a 730-m-long traffic tunnel in Vancouver, Canada. Comparing the measured SF6 concentrations to the known emission rates, it is possible to directly assess the accuracy of the simple tunnel aerodynamic models typically used to interpret tunnel data. Correction factors derived from this procedure were then applied to measurements of carbon monoxide and other pollutants to obtain gram-per-kilometer emission factors for vehicles. Although the specific correction factors measured here are valid only for the tunnel tested, the magnitude of the factors (up to two or more) suggests that the phenomena observed here should be considered when interpreting data from other tunnels.

Impact of Relative Humidity on HVAC Filters Loaded with Hygroscopic and Non-Hygroscopic Particles

The key characteristics of an air filter—flow resistance and filtration efficiency—are strongly affected by captured particles. The impact of exposing loaded heating, ventilating, and air conditioning air filters to a relative humidity (RH) other than that experienced during loading is investigated to develop an understanding of the role of RH throughout filter operation. Flat sheets of commercial filter media were loaded with hygroscopic, non-hygroscopic, or a mixture of particles in a laboratory apparatus. When filters loaded with hygroscopic particles in dry air were exposed to an elevated RH of 40%, the flow resistance reduced by up to 47%, depending on the filter being tested. Investigation of filter efficiency before and after changes in RH in the same samples shows reductions of up to 11 percentage points in the 130-nm size range. Further increasing RH causes additional drops in flow resistance and efficiency whereas reverting back to a lower humidity does not change the filter characteristics. The irreversibility of the particle-loaded filter characteristics implies that the RH increases are associated with an irreversible change in the particle structure. The response to humidity was reduced if an aerosol mixture of hygroscopic and non-hygroscopic particles is used. Exposure of filters loaded with only non-hygroscopic particles does not show the same dependence on RH. Small increases in growth factor for RH changes below deliquescence, causing morphological changes in captured particle aggregates, is a potential explanation for the changes observed. Copyright 2015 American Association for Aerosol Research

Structural Change of Aerosol Particle Aggregates with Exposure to Elevated Relative Humidity

Structural changes of aggregates composed of inorganic salts exposed to relative humidity (RH) between 0 and 80% after formation at selected RH between 0 and 60% were investigated using a tandem differential mobility analyzer (TDMA) and fluorescence microscopy. The TDMA was used to measure a shift in peak mobility diameter for 100-700 nm aggregates of hygroscopic aerosol particles composed of NaCl, Na2SO4, (NH4)2SO4, and nonhygroscopic Al2O3 as the RH was increased. Aggregates of hygroscopic particles were found to shrink when exposed to RH greater than that during the aggregation process. The degree of aggregate restructuring is greater for larger aggregates and greater increases in RH. Growth factors (GF) calculated from mobility diameter measurements as low as 0.77 were seen for NaCl before deliquescence. The GF subsequently increased to 1.23 at 80% RH, indicating growth after deliquescence. Exposure to RH lower than that experienced during aggregation did not result in structural changes. Fluorescent microscopy confirmed that aggregates formed on wire surfaces undergo an irreversible change in structure when exposed to elevated RH. Analysis of 2D movement of aggregates shows a displacement of 5-13% compared to projected length of initial aggregate from a wire surface. Surface tension due to water adsorption within the aggregate structure is a potential cause of the structural changes.

Effect of ambient air on liquid jet impingement on a moving substrate

An experimental investigation into the effect of surrounding air pressure on liquid jet impingement on a moving substrate was performed. The study was carried out with Newtonian liquids impacting dry substrates. A variety of jet speeds, substrate speeds, and liquid viscosities were studied. It was observed that, as is the case for Newtonian droplet impact, the surrounding air pressure plays a crucial role in the splashing behaviour of jet impingement. There exists a threshold pressure below which splash does not occur. It is proposed that for certain impingement conditions lamella detachment from the substrate occurs due to aerodynamic forces acting on the leading edge of the lamella, which destabilizes the balance between surface tension and fluid pressure forces.