An Active Acoustic Metamaterial With Tunable Effective Density

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Amr M. Baz
Keyword(s):  
Material Properties ◽  
Control Strategies ◽  
Natural Extension ◽  
Effective Density ◽  
Acoustic Metamaterials ◽  
Active Metamaterials ◽  
Theoretical Predictions ◽  
Material Volume ◽  
The Individual ◽  
Active Acoustic Metamaterials

Extensive efforts are being exerted to develop various types of acoustic metamaterials to effectively control the flow of acoustical energy through these materials. However, all these efforts are focused on passive metamaterials with fixed material properties. In this paper, the emphasis is placed on the development of a class of one-dimensional acoustic metamaterials with tunable effective densities in an attempt to enable the adaptation to varying external environment. More importantly, the active metamaterials can be tailored to have increasing or decreasing variation of the material properties along and across the material volume. With such unique capabilities, physically realizable acoustic cloaks can be achieved and objects treated with these active metamaterials can become acoustically invisible. The theoretical analysis of this class of active acoustic metamaterials is presented and the theoretical predictions are determined for an array of fluid cavities separated by piezoelectric boundaries. These boundaries control the stiffness of the individual cavity and in turn its dynamical density. Various control strategies are considered to achieve different spectral and spatial control of the density of this class of acoustic metamaterials. A natural extension of this work is to include active control capabilities to tailor the bulk modulus distribution of the metamaterial in order to build practical configurations of acoustic cloaks.

An Active Acoustic Metamaterial With Tunable Effective Density

2009 ◽  
Author(s):  
A. Baz
Keyword(s):  
Material Properties ◽  
Control Strategies ◽  
Natural Extension ◽  
Effective Density ◽  
Acoustic Metamaterials ◽  
New Class ◽  
Active Metamaterials ◽  
Theoretical Predictions ◽  
The Individual ◽  
Air Cavities

Extensive efforts are being exerted to develop various types of acoustic metamaterials to effectively control the flow of acoustical energy through these materials. However, all these efforts are focused on passive metamaterials with fixed material properties. In this paper, the emphasis is placed on the development of a new class of one-dimensional acoustic metamaterials with tunable effective densities in an attempt to enable the adaptation to varying external environment. More importantly, the active metamaterials can be tailored to have increasing or decreasing variation of the material properties along and across the material volume. With such unique capabilities, physically realizable acoustic cloaks can be achieved and objects treated with these active metamaterials can become acoustically invisible. The theoretical analysis of this class of active acoustic metamaterials is presented and the theoretical predictions are determined for an array of air cavities separated by piezoelectric boundaries. These boundaries control the stiffness of the individual cavity and in turn its dynamical density. Various control strategies are considered to achieve different spectral and spatial control of the density of this class of acoustic metamaterials. A natural extension of this work is to include active control capabilities to tailor the bulk modulus distribution of the metamaterial in order to build practical configurations of acoustic cloaks.

Recent Advances in Active Acoustic Metamaterials

2019 ◽  
Vol 11 (08) ◽  
pp. 1950081 ◽  
Author(s):  
Sanjay Kumar ◽  
Heow Pueh Lee
Keyword(s):  
Sound Wave ◽  
Dynamic Responses ◽  
Acoustic Metamaterials ◽  
Design Strategies ◽  
Acoustic Characteristics ◽  
Early 21St Century ◽  
Active Metamaterials ◽  
Potential Applications ◽  
Restricted Use ◽  
Active Acoustic Metamaterials

Since its first demonstration of an acoustic metamaterial in the early 21st century, it is widely used for sound wave manipulation purposes in many applications such as aerospace, automotive, defense, marine, etc. However, the traditional acoustic metamaterials display acoustic characteristics for restricted use because of their fixed structures. For real-world applications, the active sound wave manipulation is desirable. In recent years, active acoustic metamaterials (AAMs) have garnered attention owing to their unique design and material characteristics, which result in various dynamic responses against the incoming sound wave. This paper aims to provide an overview of the fundamental concept of active metamaterials, describing the multiple tuning mechanisms and design strategies, and highlighting their potential applications. The current fabrication challenges and future outlook in this promising field are also discussed.

Multicell Active Acoustic Metamaterial With Programmable Effective Densities

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
W. Akl ◽  
A. Baz
Keyword(s):  
Wave Propagation ◽  
Material Properties ◽  
Density Variation ◽  
Acoustic Metamaterials ◽  
One Dimensional ◽  
Periodic Cell ◽  
Theoretical Predictions ◽  
Pressure Feedback ◽  
Specific Material ◽  
Viable Approach

Considerable interest has been devoted to the development of various classes of acoustic metamaterials. Acoustic metamaterials are those structurally engineered materials that are composed of periodic cells designed in such a fashion to yield specific material properties (density and bulk modulus) that would affect the wave propagation pattern within in a specific way. All the currently exerted efforts are focused on studying passive metamaterials with fixed material properties. In this paper, the emphasis is placed on the development of a new class of composite one-dimensional acoustic metamaterials with effective densities that are programmed to vary according to any prescribed patterns along the volume of the metamaterial. The theoretical analysis of this class of multilayered composite active acoustic metamaterials (CAAMM) is presented and the theoretical predictions are determined for an array of fluid cavities separated by piezoelectric boundaries. These smart self-sensing and actuating boundaries are used to modulate the overall stiffness of the metamaterial periodic cell and in turn its dynamic density through direct acoustic pressure feedback. The interaction between the neighboring layers of the composite metamaterial is modeled using a lumped-parameter approach. One-dimensional wave propagation as well as long wavelength assumptions are adapted in the current analysis. Numerical examples are presented to demonstrate the performance characteristics of the proposed CAAMM and its potential for generating prescribed spatial and spectral patterns of density variation. The CAAMM presents a viable approach to the development of effective acoustic cloaks that can be used for treating critical objects in order to render them acoustically invisible.

Active Acoustic Metamaterials With Programmable Densities Using an H-∞ Controller

2018 ◽  
Author(s):  
Amr Baz
Keyword(s):  
Disturbance Rejection ◽  
Acoustic Metamaterials ◽  
Acoustic Wave Propagation ◽  
Robust Controller ◽  
One Dimensional ◽  
Response Characteristics ◽  
Acoustic Media ◽  
The Individual ◽  
Active Acoustic Metamaterials ◽  
Acoustical Energy

Various types of acoustic metamaterials have been developed to control the flow of acoustical energy through these materials. Most of these metamaterials are passive in nature with pre-tuned and fixed material properties. In this paper, the emphasis is placed on the development of a class of one-dimensional acoustic metamaterials with programmable densities in order to enable the control the acoustic wave propagation in these media. With such unique capabilities, the proposed active acoustic metamaterials (AAMM) can be utilized to physically realize, for example, acoustic cloaks, wave shifters and focusers, tunable acoustic absorbers and reflectors, as well as non-reciprocal acoustic media. The theoretical analysis of this class of AAMM with programmable effective dynamical densities is presented for an array of cavities separated by piezoelectric boundaries. These boundaries provide means for controlling the stiffness of the individual cavity and, in turn, its dynamical densities. In this regard, a disturbance rejection strategy is considered which is based on an H-∞ robust controller. The time and frequency response characteristics of a unit cell of the AAMM are investigated for various parameters of the controller in an attempt to optimize the performance characteristics. Extension of this study to include active control capabilities of the bulk modulus of the metamaterials would enable the development of wide classes of AAMM that are only limited by our imagination.

scholarly journals Secretion of Anti-Plasmodium Effector Proteins from a Natural Pantoea agglomerans Isolate by Using PelB and HlyA Secretion Signals

2011 ◽  
Vol 77 (13) ◽  
pp. 4669-4675 ◽  
Author(s):  
Dawn C. Bisi ◽  
David J. Lampe
Keyword(s):  
Control Strategies ◽  
Pectate Lyase ◽  
Erwinia Carotovora ◽  
Individual Characteristics ◽  
Pantoea Agglomerans ◽  
Effector Proteins ◽  
World Health ◽  
Content Type ◽  
E Coli ◽  
The Individual

ABSTRACTThe insect-vectored disease malaria is a major world health problem. New control strategies are needed to supplement the current use of insecticides and medications. A genetic approach can be used to inhibit development of malaria parasites (Plasmodiumspp.) in the mosquito host. We hypothesized thatPantoea agglomerans, a bacterial symbiont ofAnophelesmosquitoes, could be engineered to express and secrete anti-Plasmodiumeffector proteins, a strategy termed paratransgenesis. To this end, plasmids that include thepelBorhlyAsecretion signals from the genes of related species (pectate lyase fromErwinia carotovoraand hemolysin A fromEscherichia coli, respectively) were created and tested for their efficacy in secreting known anti-Plasmodiumeffector proteins (SM1, anti-Pbs21, and PLA2) inP. agglomeransandE. coli.P. agglomeranssuccessfully secreted HlyA fusions of anti-Pbs21 and PLA2, and these strains are under evaluation for anti-Plasmodiumactivity in infected mosquitoes. Varied expression and/or secretion of the effector proteins was observed, suggesting that the individual characteristics of a particular effector may require empirical testing of several secretion signals. Importantly, those strains that secreted efficiently grew as well as wild-type strains under laboratory conditions and, thus, may be expected to be competitive with the native microbiota in the environment of the mosquito midgut.

Study on a global control strategy for rotation speed with different work states in variable-speed constant-frequency wind turbines

2011 ◽  
Vol 225 (7) ◽  
pp. 968-976 ◽  
Author(s):  
G Zheng ◽  
H Xu ◽  
X Wang ◽  
J Zou
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Control Strategy ◽  
Control Strategies ◽  
Stable Operation ◽  
Constant Frequency ◽  
Global Control ◽  
Control Rules ◽  
The Individual ◽  
And Control

This paper studies the operation of wind turbines in terms of three phases: start-up phase, power-generation phase, and shutdown phase. Relationships between the operational phase and control rules for the speed of rotation are derived for each of these phases. Taking into account the characteristics of the control strategies in the different operational phases, a global control strategy is designed to ensure the stable operation of the wind turbine in all phases. The results of simulations are presented that indicate that the proposed algorithm can control the individual phases when considered in isolation and also when they are considered in combination. Thus, a global control strategy for a wind turbine that is based on a single algorithm is presented which could have significant implications on the control and use of wind turbines.

scholarly journals Indirectness in the Age of Globalization: A Social Network Analysis

2019 ◽  
Vol 23 (4) ◽  
pp. 930-949
Author(s):  
Marina Terkourafi
Keyword(s):  
African American ◽  
American English ◽  
Historical Context ◽  
Theory Building ◽  
Network Ties ◽  
British English ◽  
Theoretical Predictions ◽  
The Individual ◽  
Individual Self

Indirectness has traditionally been viewed as commensurate with politeness and attributed to the speaker’s wish to avoid imposition and/or otherwise strategically manipulate the addressee. Despite these theoretical predictions, a number of studies have documented the solidarity-building and identity-constituting functions of indirectness. Bringing these studies together, Terkourafi 2014 proposed an expanded view of the functions of indirect speech, which crucially emphasizes the role of the addressee and the importance of network ties. This article focuses on what happens when such network ties become loosened, as a result of processes of urbanization and globalization. Drawing on examples from African American English and Chinese, it is argued that these processes produce a need for increased explicitness, which drives speakers (and listeners) away from indirectness. This claim is further supported diachronically, by changes in British English politeness that coincide with the rise of the individual Self. These empirical findings have implications for im/politeness theorizing and theory-building more generally, calling attention to how the socio-historical context of our research necessarily influences the theories we end up building.

Does Aging and Disease Increase the Importance of Cognitive Strategies? Social and Temporal Comparisons in Healthy Younger and Older Adults and in Younger and Older Cancer Patients

2017 ◽  
Vol 88 (1) ◽  
pp. 60-81
Author(s):  
Mimi Mehlsen ◽  
Mai Bjørnskov Mikkelsen ◽  
Christina Maar Andersen ◽  
Chaitali Ollars
Keyword(s):  
Older Adults ◽  
Cancer Patients ◽  
Control Strategies ◽  
Cognitive Strategies ◽  
Well Being ◽  
Primary Control ◽  
Physical Decline ◽  
Age Related ◽  
Older Cancer Patients ◽  
The Individual

Social and temporal comparisons may help the individual anchor his or her self-image in a social and temporal context. In the Life-Span Theory of Control, comparisons are included in the repertoire of secondary control strategies individuals may apply when primary control strategies are obstructed, for example, by age-related losses or physical decline. The aim of this study was to explore differences in prevalence and effects of social and temporal comparisons in younger and older adults and healthy and diseased individuals ( n = 34). Semistructured interviews were conducted and analyzed using a mixed-methods approach combining qualitative and quantitative data analysis. The results revealed that older adults engaged in more comparisons than younger adults and that the outcomes of comparisons were more positive for older adults, particularly older cancer patients. The results indicate that comparisons may be applied more often by older and diseased individuals in the service of maintaining well-being.

Effect of Testing Conditions on Performance and Durability of Stabilisers in Plastics

2003 ◽  
Vol 11 (2) ◽  
pp. 81-90 ◽  
Author(s):  
J. Pospíšil ◽  
Z. Horák ◽  
J. Pilař ◽  
S. Nešpurek ◽  
N. C. Billingham ◽  
...  
Keyword(s):  
Thermal Aging ◽  
Material Properties ◽  
Activation Energies ◽  
Physical Processes ◽  
Factors Affecting ◽  
Testing Conditions ◽  
Testing Method ◽  
Principal Factors ◽  
The Individual ◽  
Accelerated Thermal Aging

The accelerated thermal aging and weathering of stabilised plastics provides information on stabiliser efficiency and polymer durability more quickly than natural testing. This allows the monitoring of the material properties of plastics in the foreseen application environment and the development of new stabilisation formulations. The harshness of the testing method affects the individual processes involved regarding their activation energies and mechanisms, the physical relations in the polymer – stabiliser system, and the chemical and physical processes accounting for the consumption of stabilisers. The principal factors affecting any comparison of accelerated results with natural testing are outlined.

Robust and Adaptive Resolved Motion Control of a Hydraulic Loader Crane

2003 ◽  
Author(s):  
Henrik C. Pedersen ◽  
Brian Nielsen ◽  
Torben O. Andersen ◽  
Michael R. Hansen
Keyword(s):  
Motion Control ◽  
Control Algorithm ◽  
Control Strategies ◽  
Robust Adaptive Control ◽  
Kinematic Redundancy ◽  
Control Loops ◽  
Mobile Crane ◽  
Robust Adaptive ◽  
The Individual ◽  
Adaptive Control Algorithm

The focus of this paper is the comparison of a robust and a robust adaptive control algorithm, in connection to a resolved motion control system for a mobile hydraulic loader crane with a telescopic arm. The compared control strategies are related to the inner control loops of the system, which are controlling the velocities of the individual actuators on the mobile crane. Along with the inner loops an outer loop in the form of an algorithm for solving the problem of kinematic redundancy is used. The considered control strategies are tested on a simulation model incorporating structural flexibility of the mechanical system. Results obtained with the robust inner control algorithm are verified experimentally and it is explored how accurate the crane may be maneuvered. A comparison of the two methods is made based on the obtained results.

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