scholarly journals Dehydration-induced mechanical instabilities in active elastic spherical shells

2021 ◽  
Vol 477 (2254) ◽  
Author(s):  
M. Curatolo ◽  
G. Napoli ◽  
P. Nardinocchi ◽  
S. Turzi
Keyword(s):  
Analytical Model ◽  
Numerical Experiments ◽  
Water Concentration ◽  
Closed Shell ◽  
Natural World ◽  
Cavity Volume ◽  
Stress Diffusion ◽  
Elastic Instabilities ◽  
Simplifying Assumptions ◽  
Set Up

Active elastic instabilities are common phenomena in the natural world, where they have the character of sudden mechanical morphings. Frequently, the driving force of the instability mechanisms has a chemo-mechanical nature, which makes the instabilities very different from the standard elastic instabilities. In this paper, we describe and study the active elastic instability occurring in a swollen spherical closed shell, confining a water-filled cavity, during a dehydration process. We set up a few numerical experiments based on a stress-diffusion model to give an insight into the phenomenon. Then, we present a study that looks at the chemo-mechanical problem and, through a few simplifying assumptions, allows us to derive a semi-analytical model of the phenomenon. It takes into account both the stress state and the water concentration in the walls of the shell at the onset of the instability. Moreover, it considers the invariance of the cavity volume at the onset of instability, which is due to the impossibility of instantaneously changing the cavity volume filled with water. Eventually, it is shown that the semi-analytic model matches very well the outcomes of the numerical experiments far from the initial regime; the ranges of validity of the approximated analytical model are also discussed.

scholarly journals CONTRACTING-OUT OF HOUSEHOLD WASTE COLLECTION SERVICES IN JAPAN

2017 ◽  
Vol 65 (02) ◽  
pp. 443-455
Author(s):  
NORIMICHI MATSUEDA ◽  
JUN’ICHI MIKI
Keyword(s):  
Analytical Model ◽  
Inverse Relationship ◽  
Municipal Waste ◽  
Household Waste ◽  
Private Firms ◽  
Simple Analytical Model ◽  
Waste Collection ◽  
Contracting Out ◽  
Contract Price ◽  
Set Up

We first report three empirical findings from our survey on the contracting-out of municipal waste collection services in Japan: (1) the rate of contracting-out and the contract price are inversely related, (2) this inverse relationship tapers out as the contracting rate becomes sufficiently high, and the contract price even tends to go up as the contracting rate approaches 100% and (3) there is a significant disparity in the contracting rates between the eastern and western parts of Japan. In order to account for these observations, we then set up a simple analytical model and examine its implications. Also, we discuss the issues that a potential hold-up situation could give rise to when the services are completely contracted out to private firms.

PC-Based Computer Modeling of Combustion Processes

1999 ◽  
Author(s):  
Greg W. Gmurczyk ◽  
Ashwani K. Gupta
Keyword(s):  
Numerical Simulations ◽  
Computer Modeling ◽  
Numerical Experiments ◽  
Laboratory Experiments ◽  
Combustion Process ◽  
Numerical Algorithms ◽  
Computer Hardware ◽  
Simplifying Assumptions ◽  
High Level ◽  
Analytical Approaches

Abstract Constant and significant progress in both computer hardware and numerical algorithms, in recent years, have made it possible to investigate complex phenomena in engineering systems using computer modeling and simulations. Advanced numerical simulations can be treated as an extension of traditional analytical-theoretical analyses. In such cases, some of the simplifying assumptions can usually be dropped and the nonlinear interactions between various processes can be captured. One of the most complex engineering processes encountered in industry is a combustion process utilized either for power/thrust generation or incineration. However, even nowadays, because of the high level of complexity of the general problem of a combustion process in practical systems, it is not currently possible to simulate directly all the length and time scales of interest. Simplifying assumptions still need to be made, but they can be less drastic than in analytical approaches. Therefore, another view of numerical simulations is as a tool to simulate idealized systems and conduct numerical experiments. Such numerical experiments can be complementary to laboratory experiments and can also provide more detailed, nonintrusive diagnostics. Therefore, simulations, along with theory and laboratory experiments, can provide a more complete picture and better understanding of a combustion process. As an example of computer modeling of industrial combustion systems, an enclosed spray flame was considered. Such a flame can frequently be encountered in power generation units, turbine engines, and incinerators. Both the physical and mathematical models were formulated based on data from earlier laboratory studies and results obtained for open air spray flames. The purpose of this study was to use those data as model input to predict the characteristics of a confined flame and provide a means of optimizing the system design with a PC computer.

Numerical and Experimental Analysis of the Nonlinear Dynamics due to Impacts of a Continuous Overhung Rotor

1997 ◽  
Author(s):  
Mohammed F. Abdul Azeez ◽  
Alexander F. Vakakis
Keyword(s):  
Nonlinear Dynamics ◽  
Partial Differential Equations ◽  
Differential Equations ◽  
Numerical Experiments ◽  
The Other ◽  
Experimental Setup ◽  
Partial Differential ◽  
Qualitative Comparison ◽  
Set Up ◽  
Theory And Experiments

Abstract This work is aimed at obtaining the transient response of an overhung rotor when there are impacts occurring in the system. An overhung rotor clamped on one end, with a flywheel on the other and impacts occurring in between, due to a bearing with clearance, is considered. The system is modeled as a continuous rotor system and the governing partial differential equations are set up and solved. The method of assumed modes is used to discretize the system in order to solve the partial differential equations. Using this method numerical experiments are run and a few of the results are presented. The different numerical issues involved are also discussed. An experimental setup was built to run experiments and validate the results. Preliminary experimental observations are presented to show qualitative comparison of theory and experiments.

scholarly journals A Multivariate Model to Quantify and Mitigate Cybersecurity Risk

Risks ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 61 ◽  
Author(s):  
Mark Bentley ◽  
Alec Stephenson ◽  
Peter Toscas ◽  
Zili Zhu
Keyword(s):  
Numerical Experiments ◽  
Optimal Choice ◽  
Multivariate Model ◽  
Cyber Attacks ◽  
Mitigation Strategies ◽  
Cyber Attack ◽  
Simplifying Assumptions ◽  
Attack Data ◽  
The Cost ◽  
Support Decision Making

The cost of cybersecurity incidents is large and growing. However, conventional methods for measuring loss and choosing mitigation strategies use simplifying assumptions and are often not supported by cyber attack data. In this paper, we present a multivariate model for different, dependent types of attack and the effect of mitigation strategies on those attacks. Utilising collected cyber attack data and assumptions on mitigation approaches, we look at an example of using the model to optimise the choice of mitigations. We find that the optimal choice of mitigations will depend on the goal—to prevent extreme damages or damage on average. Numerical experiments suggest the dependence aspect is important and can alter final risk estimates by as much as 30%. The methodology can be used to quantify the cost of cyber attacks and support decision making on the choice of optimal mitigation strategies.

scholarly journals Analysis and Experimental Validation of a Piezoelectric Harvester with Enhanced Frequency Bandwidth

Materials ◽  
2018 ◽  
Vol 11 (7) ◽  
pp. 1243 ◽  
Author(s):  
Haim Abramovich ◽  
Idan Har-nes
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Vibrational Energy ◽  
Total Output ◽  
Frequency Bandwidth ◽  
Parametric Investigation ◽  
Two Factors ◽  
Set Up ◽  
Spring Constants ◽  
Advanced System

The use of a single bimorph as a harmonic oscillator aimed at harvesting vibrational energy is not effective due to its inherent narrow frequency bandwidth stemming from the need to adjust the natural frequency of the harvester to the platform excitation frequencies. Therefore, the present research focuses on the development, manufacturing, and testing of an advanced system based on three bimorphs, capable of adjusting their natural frequencies using tip end masses, and interconnected by springs, thus enlarging the system’s bandwidth. An analytical model was developed for three bimorphs interconnected by two springs with three end masses. The model can predict the output generated voltage from each bimorph, and then the total output power is measured on a given outside resistor as a function of the material properties, the geometric dimensions of the vibrating beams, the end-masses, and the spring constants. The analytical model was then compared with data in the literature, yielding a good correlation. To further increase the reliability of the model, a test set-up was designed and manufactured that included three bimorphs with three end-masses connected by two springs. The system was excited using a shaker, and the output voltage was measured for each bimorph for various configurations. Then, the analytical model was tuned based on the test results by introducing two factors, the quality and the stiffness factors, and the predictions of the calibrated analytical model were compared with the experimental results, yielding a good correlation. The calibrated analytical model was then used to perform a comprehensive parametric investigation for two and three bimorphs systems, in which the influences of various parameters—like spring constant, mass value, thickness, and width and length of the bimorph and the substrate beam—on the output generated power were investigated. The main conclusion from this parametric investigation was that by correctly choosing the geometric sizes of the cantilevers, the adequate tip end masses, and the ratio between constants of the springs, the frequency bandwidth is expanded yielding a higher harvested power. Typical harvested power of the present designed system can reach up to 20 mW at the first natural frequency and up to 5 mW for the second natural frequency.

Waiting for the Payday? The Market for Startups and the Timing of Entrepreneurial Exit

2020 ◽  
Author(s):  
Ashish Arora ◽  
Andrea Fosfuri ◽  
Thomas Rønde
Keyword(s):  
Analytical Model ◽  
Business Strategy ◽  
Exit Strategy ◽  
Trade Off ◽  
Early Exit ◽  
Early Acquisition ◽  
Set Up ◽  
Exclusive Choice ◽  
Early Market ◽  
Technology Startups

Most technology startups are set up for exit through acquisition by large corporations. In choosing when to sell, startups face a trade-off. Early acquisition reduces execution errors, but later acquisition both improves the likelihood of finding a better match and benefits from increased buyer competition. Startups’ exit strategies vary considerably: Some startups aim to sell early; others remain in stealth mode by developing the invention for a late sale. We develop an analytical model to study the timing of the exit strategy. We find that startups with more capable founding teams commit to a late exit, whereas those with less capable founding teams commit to an early exit. Finally, startups with founding teams of intermediate capabilities remain flexible: They seek early offers but eventually sell late. If trying the early market is so costly that startups have to make a mutually exclusive choice between an early and late sale, startups sell inefficiently late. Instead, if they can collect early offers at no cost before deciding on the timing of sale, there are too many early acquisitions. This paper was accepted by David Simchi-Levi, business strategy.

scholarly journals Analytic model of comet ionosphere chemistry

2018 ◽  
Vol 616 ◽  
pp. A59 ◽  
Author(s):  
Erik Vigren
Keyword(s):  
Analytical Model ◽  
Dissociative Recombination ◽  
Flow Speed ◽  
Rate Coefficients ◽  
Ion Composition ◽  
Free Electrons ◽  
Ion Removal ◽  
Simplifying Assumptions ◽  
Computational Simplicity ◽  
Insight Into

Context. We consider a weakly to moderately active comet and make the following simplifying assumptions: (i) The partial ionization frequencies are constant throughout the considered part of the coma. (ii) All species move radially outward with the same constant speed. (iii) Ion-neutral reactions affect the chemical composition of the ions, but ion removal through dissociative recombination with free electrons is negligible. Aims. We aim to derive an analytical model for the radial variation of the abundances of various cometary ions. Methods. We present two methods for retrieving the ion composition as a function of r. The first method, which has previously been used frequently, solves a series of coupled differential equations. The new method introduced here is based on probabilistic arguments and is analytical in nature. Results. For a pure H2O coma, the resulting closed-form expressions yield results that are identical to the standard method, but are computationally much less expensive. Conclusions. In addition to the computational simplicity, the analytical model provides insight into how the various abundances depend on parameters such as comet production rate, outflow speed, and reaction rate coefficients. It can also be used to investigate limiting cases. It cannot easily be extended to account for a radially varying flow speed or dissociative recombination in the way a code based on numerical integrations can.

Chiral effects in the scattering of electrons by molecules

1996 ◽  
Vol 74 (11-12) ◽  
pp. 920-924 ◽  
Author(s):  
D. G. Thompson
Keyword(s):  
Physical Mechanism ◽  
Closed Shell ◽  
Spin Orbit ◽  
Polarized Electrons ◽  
Invariance Properties ◽  
Inversion Time ◽  
Consistent Manner ◽  
Chiral Effects ◽  
Set Up ◽  
Considerable Discussion

There are a number of scattering phenomena that depend on the "handedness" of the scattering system. In this paper we concentrate on the elastic scattering of polarized electrons by closed-shell molecules and consider mainly the property of electron optic dichroism. The effects can be fully analysed using the general invariance properties of the scattering matrix under spatial inversion, time reversal, and rotations. However, there is still considerable discussion about the physical mechanism causing the effects. Among the models proposed are two involving the spin–orbit interaction; in one the bound orbitals are perturbed, and in the other the incident electron. In this paper we show how these two approaches can be combined in a unified treatment. We set up the scattering equation including exchange and spin–orbit in a consistent manner and identify which terms contribute to the chiral effects.

Modelling Friction Under Complex Motion Conditions

1989 ◽  
Vol 111 (3) ◽  
pp. 491-494 ◽  
Author(s):  
T. A. Stolarski
Keyword(s):  
Analytical Model ◽  
Contact Area ◽  
Complex Motion ◽  
Friction Process ◽  
Simplifying Assumptions ◽  
Characteristic Features ◽  
Model Of Friction

An analytical model of friction under combined linear sliding and spin of the contact area is presented. It is shown that the model, although based on simplifying assumptions, predicts reasonably well the characteristic features of the friction process.

scholarly journals Looking Thru the Nano Lens: Art, Science and Nature

2019 ◽  
Vol 27 (7) ◽  
Author(s):  
Chiara O’Reilly ◽  
Alice Motion ◽  
Chiara Neto
Keyword(s):  
Informal Learning ◽  
Pilot Project ◽  
Natural World ◽  
Postgraduate Students ◽  
The Public ◽  
The Arts ◽  
Set Up ◽  
New Research ◽  
The University ◽  
Opening Up

In 2018, an interdisciplinary team of researchers from the School of Chemistry, Sydney Nano and the Department of Art History at the University of Sydney set up a pilot project called the Nano Lens. Our project set out to examine and experiment with what it means to look closely at the natural world and inviting us, as colleagues, into a discussion and collaboration, drawing on our different perspectives. The Nano Lens also gave agency to a group of scientists in training (undergraduate and postgraduate students), and a sense of ownership of the science, which was then transmitted to the public. Taking inspiration from the artwork of the prominent Australian painter Margaret Preston (1875-1963) and the flora she depicted, the Nano Lens has opened up new research that intersects science and the arts; celebrating the value of collaboration and offering opportunities for staff and students to engage in and lead interdisciplinary discussions with the public. This paper will discuss our pilot project and the initial findings of our research together and discuss the benefits that our alliance has had in fostering collaboration and outreach activities where academics and students work together to share their research with the public. We seek to reflect on what we have learnt from the project and from opportunities to share our work and approaches. What does it mean to look like a scientist or to look like an artist and how has this enriched student learning? What value is there in opening up opportunities for informal learning about science and collaboration outside your disciplines?

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