Steady-state composition of a two-component gas bubble growing in a liquid solution: self-similar approach

The paper presents an analytical description of the growth of a two-component bubble in a binary liquid-gas solution. We obtain asymptotic self-similar time dependence of the bubble radius and analytical expressions for the non-steady profiles of dissolved gases around the bubble. We show that the necessary condition for the self-similar regime of bubble growth is the constant, steady-state composition of the bubble. The equation for the steady-state composition is obtained. We reveal the dependence of the steady-state composition on the solubility laws of the bubble components. Besides, the universal, independent from the solubility laws, expressions for the steady-state composition are obtained for the case of strong supersaturations, which are typical for the homogeneous nucleation of a bubble.Comment: 12 pages, 2 figure

Inquiry-based learning to explore the design of the built environment

Typically in introductory structural engineering courses with a lab component, the instructional approach is to present the underlying theory via pre-lab lecture/reading and subsequently have students conduct guided experiments that affirm that theory. The new Fall 2015 course offering described in this paper takes the reverse approach where students’ hands-on exploration of a concept occurs prior to formal instruction. As such, the course is based upon Da Vinci’s perspective that: “[i]n the examination of physical problems I begin by making a few experiments,…we must commence with experience, and strive by means of it to discover truth.” In the course, student exploration of fundamental structural engineering concepts was facilitated through the following activities: • Full-class physical demonstrations led by the instructor during lecture • Small-group experimentation in a laboratory setting • Case studies highlighting both failures and exemplary natural/engineered structures presented via instructor lectures and supplementary multi-media materials The paper describes the open-ended course framework where instructors posed targeted questions for students/teams to investigate based on the demonstrations, experiments and case studies. The students explored these questions in the manner they (individually or in teams) deem appropriate, while documenting relevant quantitative and qualitative observations in their lab notebooks. Reflecting on their gathered information, students developed evidence-based responses to the questions. These learning exercises were followed by instructor-facilitated discussion where students/teams share their observations and collaboratively draw conclusions that point towards related engineering theory. Finally, the instructor formally defined the associated theory. The objective of this paper is demonstrate how the “exploration before theory” approach can be implemented and what is required to accomplish the hands-on, inquiry, discussion, and formal teaching aspects that comprise this teaching style. Associated with this objective, the authors also share student feedback on the course that will be collected through mid- and end-of-semester surveys for about twenty undergraduate students. These surveys solicited student input on the inquiry-based learning atmosphere as well as individual course activities. The authors believe that a classroom environment that emphasizes discovery – where students act as researchers and play an active role in building their own knowledge – is a format that can be readily adapted to other engineering disciplines; furthermore, it can inspire higher-level thinking and lead to a more engaging learning experience

Gas bubble growth dynamics in a supersaturated solution: Henry's and Sievert's solubility laws

Theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution is presented. We study the influence of Laplace pressure on the bubble growth. We consider two different solubility laws: Henry's law, which is fulfilled for the systems where no gas molecules dissociation takes place and Sievert's law, which is fulfilled for the systems where gas molecules completely dissociate in the solvent into two parts. We show that the difference between Henry's and Sievert's laws for chemical equilibriumconditions causes the difference in bubble growth dynamics. Assuming that diffusion flux of dissolved gas molecules to the bubble is steady we obtain differential equations on bubble radius for both solubility laws. For the case of homogeneous nucleation of a bubble, which takes place at a significant pressure drop bubble dynamics equations for Henry's and Sievert's laws are solved analytically. For both solubility laws three characteristic stages of bubble growth are marked out. Intervals of bubble size change and time intervals of these stages are found. We also obtain conditions of diffusion flux steadiness corresponding to consecutive stages. The fulfillment of these conditions is discussed for the case of nucleation of water vapor bubbles in magmatic melts. For Sievert's law the analytical treatment of the problem of bubble dissolution in a pure solvent is also presented.http://deepblue.lib.umich.edu/bitstream/2027.42/84215/1/CAV2009-final167.pd

Dynamics of gas bubble growth in a supersaturated solution with Sievert's solubility law

This paper presents a theoretical description of diffusion growth of a gas bubble after its nucleation in supersaturated liquid solution. We study systems where gas molecules completely dissociate in the solvent into two parts, thus making Sievert's solubility law valid. We show that the difference between Henry's and Sievert's laws for chemical equilibrium conditions causes the difference in bubble growth dynamics. Assuming that diffusion flux is steady we obtain a differential equation on bubble radius. Bubble dynamics equation is solved analytically for the case of homogeneous nucleation of a bubble, which takes place at a significant pressure drop. We also obtain conditions of diffusion flux steadiness. The fulfillment of these conditions is studied for the case of nucleation of water vapor bubbles in magmatic melts.Comment: 22 pages, 3 figure

К вопросу о кризисе украинского образования

Стаття присвячена розгляду актуальних проблем сучасної української освіти. Наведено деякі характеристики, яких має набути вища школа України для подолання наслідків системної кризи. Досліджуються поняття «надлишкова освіта», «широка спеціалізація» та їх роль в освітній системі.The article is devoted to consideration of the modern Ukrainian education urgent problems. Some descriptions which ukrainian high school must acquire for overcoming of consequences of system crisis are resulted. Also in the article such concepts as "redundant education" and wide specialization and their role in the educational system are explored.Статья посвящена рассмотрению актуальных проблем современного украинского образования. Приведены некоторые характеристики, которые должна приобрести высшая школа Украины для преодоления следствий системного кризиса. Также в статье исследуются понятия "избыточное образование" и широкая специализация и их роль в образовательной системе

Minor Pilins of the Type IV Pilus System Participate in the Negative Regulation of Swarming Motility

Pseudomonas aeruginosa exhibits distinct surface-associated behaviors, including biofilm formation, flagellum-mediated swarming motility, and type IV pilus-driven twitching. Here, we report a role for the minor pilins, PilW and PilX, components of the type IV pilus assembly machinery, in the repression of swarming motility. Mutating either the pilW or pilX gene alleviates the inhibition of swarming motility observed for strains with elevated levels of the intracellular signaling molecule cyclic di-GMP (c-di-GMP) due to loss of BifA, a c-di-GMP-degrading phosphodiesterase. Blocking PilD peptidase-mediated processing of PilW and PilX renders the unprocessed proteins defective for pilus assembly but still functional in c-di-GMP-mediated swarming repression, indicating our ability to separate these functions. Strains with mutations in pilW or pilX also fail to exhibit the increase in c-di-GMP levels observed when wild-type (WT) or bifA mutant cells are grown on a surface. We also provide data showing that c-di-GMP levels are increased upon PilY1 overexpression in surface-grown cells and that this c-di-GMP increase does not occur in the absence of the SadC diguanylate cyclase. Increased levels of endogenous PilY1, PilX, and PilA are observed when cells are grown on a surface compared to liquid growth, linking surface growth and enhanced signaling via SadC. Our data support a model wherein PilW, PilX, and PilY1, in addition to their role(s) in type IV pilus biogenesis, function to repress swarming via modulation of intracellular c-di-GMP levels. By doing so, these pilus assembly proteins contribute to P. aeruginosa\u27s ability to coordinately regulate biofilm formation with its two surface motility systems

Seismic Performance of Slender C-Shaped Walls Subjected to UniI- and Bi-Directional Loading

Reinforced concrete structural walls are common as the primary lateral load resisting system in modern mid- and high-rise buildings constructed in seismic regions, yet few research programs have investigated the seismic performance of modern, slender walls with nonplanar cross-sectional geometries. Three large-scale, C-shaped wall specimens, designed per ACI 318-08, were tested under uni- and bi-directional loading at the University of Illinois at Urbana-Champaign (UIUC). This paper presents experimental results including the cyclic load-deformation response and measured versus nominal flexural/shear strengths as well as a description of damage sequence. Final failure occurs due to a flexure-tension failure of boundary elements where multiple previously buckled bars fracture. From these tests, it is possible to conclude that with respect to uni- versus bi-directionally loading C-shaped walls have similar strong-axis load-deformation response until 0.75% drift as well as effective flexure/shear stiffness; however, there is a notable reduction in strong-axis ductility due to bi-directional loading. When comparing C-shaped walls to planar walls, the C-shaped specimens exhibit a more ductile flexural-tension controlled response where wall flanges contribute significantly to carrying compressive loads. Additionally, wall flanges and boundary elements are noted to be critical to resisting shear demands after the lightly-reinforced wall web has deteriorated

Surface Attachment Induces Pseudomonas aeruginosa Virulence

Pseudomonas aeruginosa infects every type of host that has been examined by deploying multiple virulence factors. Previous studies of virulence regulation have largely focused on chemical cues, but P. aeruginosa may also respond to mechanical cues. Using a rapid imaging-based virulence assay, we demonstrate that P. aeruginosa activates virulence in response to attachment to a range of chemically distinct surfaces, suggesting that this bacterial species responds to mechanical properties of its substrates. Surface-activated virulence requires quorum sensing, but activating quorum sensing does not induce virulence without surface attachment. The activation of virulence by surfaces also requires the surface-exposed protein PilY1, which has a domain homologous to a eukaryotic mechanosensor. Specific mutation of the putative PilY1 mechanosensory domain is sufficient to induce virulence in non-surface-attached cells, suggesting that PilY1 mediates surface mechanotransduction. Triggering virulence only when cells are both at high density and attached to a surface—two host-nonspecific cues—explains how P. aeruginosa precisely regulates virulence while maintaining broad host specificity

Summary of large-scale nonplanar reinforced concrete wall tests

Nonplanar wall configurations are prevalent in engineering practice, yet relatively little research has addressed nonplanar walls and the earthquake response of these components remains poorly understood. A recent experimental test program conducted by the authors investigated the earthquake response of modern, ACI Code compliant C‐shaped walls subjected to unidirectional and bidirectional lateral loading. To compare the results of this study with previous experimental investigations conducted by others, this document examines laboratory tests of slender nonplanar walls available in the literature. Response histories, damage patterns, drift capacity and failure mechanisms are used to characterize the behavior of each nonplanar wall test specimen. The impact on behavior of various design parameters as well as unidirectional versus bidirectional load history is investigated. Results are synthesized to provide improved understanding of behavior and guidance for design of nonplanar walls. Section 2 provides an overview of the nonplanar wall test found in the literature. Section 3 provides a more in‐depth overview of C‐ and U‐shaped walls, including the C‐shaped wall tests conducted as part of this study. Section 4 presents failure and response mechanism observed during nonplanar wall tests. Section 5 summarizes observations and presents conclusions about nonplanar wall behavior