Physical arguments and comparisons with published experimental data suggest that in simple liquids: (i) single-molecule-scale viscous forces are produced by temperature-dependent London dispersion ...forces, (ii) viscosity decay with increasing temperature reflects electron cloud compression and attendant suppression of electron screening, produced by increased nuclear agitation, and (iii) temperature-dependent self-diffusion is driven by a narrow band of phonon frequencies lying at the low-frequency end of the solid-state-like phonon spectrum. The results suggest that collision-induced electron cloud distortion plays a decisive role in single molecule dynamics: (i) electron cloud compression produces short-lived repulsive states and single molecule, self-diffusive hops, while (ii) shear-induced distortion generates viscosity and single-molecule-scale viscous drag. The results provide new insight into nonequilibrium molecular dynamics in nonpolar, nonmetallic liquids.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Medical procedures that produce aerosolized particles are under great scrutiny due to the recent concerns surrounding the COVID-19 virus and increased risk for nosocomial infections. For example, ...thoracostomies, tracheotomies and intubations/extubations produce aerosols that can linger in the air. The lingering time is dependent on particle size where, e.g., 500 μm (0.5 mm) particles may quickly fall to the floor, while 1 μm particles may float for extended lengths of time. Here, a method is presented to characterize the size of <40 μm to >600 μm particles resulting from surgery in an operating room (OR). The particles are measured in-situ (next to a patient on an operating table) through a 75mm aperture in a ∼400 mm rectangular enclosure with minimal flow restriction. The particles and gasses exiting a patient are vented through an enclosed laser sheet while a camera captures images of the side-scattered light from the entrained particles. A similar optical configuration was described by Anfinrud et al.; however, we present here an extended method which provides a calibration method for determining particle size. The use of a laser sheet with side-scattered light provides a large FOV and bright image of the particles; however, the particle image dilation caused by scattering does not allow direct measurement of particle size. The calibration routine presented here is accomplished by measuring fixed particle distribution ranges with a calibrated shadow imaging system and mapping these measurements to the in-situ imaging system. The technique used for generating and measuring these particles is described. The result is a three-part process where 1) particles of varying sizes are produced and measured using a calibrated, high-resolution shadow imaging method, 2) the same particle generators are measured with the in-situ imaging system, and 3) a correlation mapping is made between the (dilated) laser image size and the measured particle size. Additionally, experimental and operational details of the imaging system are described such as requirements for the enclosure volume, light management, air filtration and control of various laser reflections. Details related to the OR environment and requirements for achieving close proximity to a patient are discussed as well.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper explores how undergraduate students understood the social relevance of their engineering course content knowledge and drew (or failed to draw) broader social and ethical implications from ...that knowledge. Based on a three-year qualitative study in a junior-level engineering class, we found that students had difficulty in acknowledging the social and ethical aspects of engineering as relevant topics in their coursework. Many students considered the immediate technical usability or improved efficiency of technical innovations as the noteworthy social and ethical implications of engineering. Findings suggest that highly-structured engineering programs leave little room for undergraduate students to explore the ethical dimension of engineering content knowledge and interact with other students/programs on campus to expand their “technically-minded” perspective. We discussed the issues of the “culture of disengagement” (Cech, Sci Technol Human Values 39(1):42–72, 2014) fueled by disciplinary elitism, spatial distance, and insulated curriculum prevalent in the current structure of engineering programs. We called for more conscious effort by engineering educators to offer meaningful interdisciplinary engagement opportunities and in-class conversations on ethics that support engineering students' holistic intellectual growth and well-rounded professional ethics.
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DOBA, EMUNI, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Confined, vibration-driven grain piles exhibit fluid-like properties, in particular, predictable, non-random flow patterns, hydrodynamic modal response to vibrational forcing, and a persistent, ...spatially uniform tendency toward local statistical mechanical equilibrium. This paper presents a technique that combines particle image velocimetry of vibration-driven grain flow over a submerged, instrumented cylinder and measurement of the flow-induced drag force on the cylinder to determine the grain flows effective kinematic viscosity. The fundamental basis of such measurements is provided by recent work showing that high-restitution grain piles subject to low-amplitude vibration are macroscopic dynamical analogs of liquid-state molecular hydrodynamic systems. Practically, the proposed viscometric method provides a key material property, the kinematic, or equivalently, dynamic viscosity, for use in computational fluid dynamic simulations of a variety of materials processing operations that utilize vibration-driven grain flows.
In this interpretative phenomenological study, the implicit cultural values and expectations embedded in faculty/staff's perceptions and how they functioned as a hidden curriculum against student ...veterans' smooth transition into higher education were analyzed based on in-depth interviews with 20 student veterans and 9 faculty/staff members. By clarifying faculty/staff's points of misunderstanding/misjudgment and the consequences of hidden curriculum as experienced by student veterans, we offer a culturally sensitive perspective on student veterans' challenges during transition. Practical implications for institutions and university employees seeking to support the civilian reintegration of military veterans are also provided.
Experimental evidence and theoretical modeling suggest that piles of confined, high-restitution grains, subject to low-amplitude vibration, can serve as experimentally-accessible analogs for studying ...a range of liquid-state molecular hydrodynamic processes. Experiments expose single-grain and multiple-grain, collective dynamic features that mimic those either observed or predicted in molecular-scale, liquid state systems, including: (i) near-collision-time-scale hydrodynamic organization of single-molecule dynamics, (ii) nonequilibrium, long-time-scale excitation of collective/hydrodynamic modes, and (iii) long-time-scale emergence of continuum, viscous flow. In order to connect directly observable macroscale granular dynamics to inaccessible and/or indirectly measured molecular hydrodynamic processes, we recast traditional microscale equilibrium and nonequilibrium statistical mechanics for dense, interacting microscale systems into self-consistent, macroscale form. The proposed macroscopic models, which appear to be new with respect to granular physics, and which differ significantly from traditional kinetic-theory-based, macroscale statistical mechanics models, are used to rigorously derive the continuum equations governing viscous, liquid-like granular flow. The models allow physically-consistent interpretation and prediction of observed equilibrium and non-equilibrium, single-grain, and collective, multiple-grain dynamics.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A long‐standing, though ill‐understood problem in rocket dynamics, rocket response to random, altitude‐dependent nozzle side‐loads, is investigated. Side loads arise during low altitude flight due to ...random, asymmetric, shock‐induced separation of in‐nozzle boundary layers. In this paper, stochastic evolution of the in‐nozzle boundary layer separation line, an essential feature underlying side load generation, is connected to random, altitude‐dependent rotational and translational rocket response via a set of simple analytical models. Separation line motion, extant on a fast boundary layer time scale, is modeled as an Ornstein‐Uhlenbeck process. Pitch and yaw responses, taking place on a long, rocket dynamics time scale, are shown to likewise evolve as OU processes. Stochastic, altitude‐dependent rocket translational motion follows from linear, asymptotic versions of the full nonlinear equations of motion; the model is valid in the practical limit where random pitch, yaw, and roll rates all remain small. Computed altitude‐dependent rotational and translational velocity and displacement statistics are compared against those obtained using recently reported high fidelity simulations Srivastava, Tkacik, and Keanini, J. Appl. Phys. 108, 044911 (2010); in every case, reasonable agreement is observed. As an important prelude, evidence indicating the physical consistency of the model introduced in the above article is first presented: it is shown that the study's separation line model allows direct derivation of experimentally observed side load amplitude and direction densities. Finally, it is found that the analytical models proposed in this paper allow straightforward identification of practical approaches for: i) reducing pitch/yaw response to side loads, and ii) enhancing pitch/yaw damping once side loads cease.
A long‐standing problem in rocket dynamics, rocket response to random, altitude‐dependent nozzle side‐loads, is investigated. It is found that the analytical models proposed in this paper allow straightforward identification of practical approaches for reducing pitch/yaw response to side loads, and enhancing pitch/yaw damping once side loads cease.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this qualitative study, we explored the experiences of 26 engineering student mentors and mentees in a peer mentoring program. We found that mentors and mentees exploited the mentoring program's ...fluid structure and situated social relationships to enact a specific type of academic/professional goal and identity conducive to their entry to one of two communities of practice, the on-campus engineering program community and the community of professional engineers. The mentoring program functioned as a social space in which identities of these students converged and diverged, creating a subtle tension and self-reflection in relation to the two different communities of practice that they pursued.
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BFBNIB, NUK, PILJ, SAZU, UL, UM, UPUK
High-fidelity numerical experiments and theoretical modelling are used to study the dynamics of a sounding-rocket-scale rocket, subject to altitude-dependent random wind and nozzle side loads and ...deterministic aerodynamic loading. This paper completes a series of studies that showed that Ornstein-Uhlenbeck (OU) rotational dynamics arise when random nozzle side loads dominate wind and aerodynamic loading. In contrast to the earlier work, this paper elucidates that under conditions where aerodynamic, wind and nozzle side loads are comparable, the rocket behaves as stochastic Brownian oscillator. The Brownian oscillator model allows straightforward interpretation of the complex rotational dynamics observed: three dynamical regimes-each characterized by differing balances between nozzle-side-load-induced torques, spring-like aerodynamic torques and mass flux damping torques-characterize rocket ascent. Further, the paper illuminates that in the limit where wind and aerodynamic loads are small, random mass flux variations exponentially amplify side-load-induced rotational stochasticity. In this practical limit, pitch/yaw dynamics are described by a randomly damped OU process; an exact solution of the associated Fokker-Planck equation can be obtained and used to compute, e.g. time-dependent pitch/yaw rate means and variances.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image ...velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.
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