Lévy exponents at critical excitation of nanostructured random amplifying media

2012 ◽  
Author(s):  
Ravitej Uppu ◽  
Sushil Mujumdar
Keyword(s):  
Random Amplifying Media ◽  
Critical Excitation

Investigation of Power Harvesting via Parametric Excitations

2008 ◽  
Vol 20 (5) ◽  
pp. 545-557 ◽  
Author(s):  
Mohammed F. Daqaq ◽  
Christopher Stabler ◽  
Yousef Qaroush ◽  
Thiago Seuaciuc-Osório
Keyword(s):  
Output Power ◽  
Coupling Coefficient ◽  
Electromechanical Coupling ◽  
Multiple Scales ◽  
Broad Band ◽  
Parametric Instability ◽  
Load Resistance ◽  
Resistive Load ◽  
Parametrically Excited ◽  
Critical Excitation

This article presents an analytical and experimental investigation of energy harvesting via parametrically excited cantilever beams. To that end, we consider a lumped-parameter non-linear model that describes the first-mode dynamics of a parametrically excited cantilever-type harvester. The model accounts for the beam's geometric and inertia non-linearities as well as non-linearities representing air drag. Using the method of multiple scales, we obtain approximate analytical expressions describing the beam response, voltage drop across a purely resistive load, and output power in the vicinity of the first principle parametric resonance. Using these expressions, we study the effect of the electromechanical coupling and load resistance on the output power. We show that these parameters play an imperative role in determining the magnitude of the output power and characterizing the broad-band properties of the harvester. Specifically, we show that the region of parametric instability wherein energy can be harvested shrinks as the coupling coefficient increases. Furthermore, we show that there exists a coupling coefficient beyond which the peak power decreases. We also demonstrate that there is a critical excitation level below which no energy can be harvested. The amplitude of this critical excitation increases with the coupling coefficient and is maximized for a given load resistance. Theoretical findings that were compared to experimental results show good agreement and reflect the general trends.

Physical Considerations in Low Energy Biological Analysis

1999 ◽  
Vol 5 (S2) ◽  
pp. 302-303 ◽  
Author(s):  
David C Joy
Keyword(s):  
Periodic Table ◽  
Incident Energy ◽  
Low Voltage ◽  
Energy Dispersive Spectrometer ◽  
Incident Beam ◽  
X Ray ◽  
Upper Limit ◽  
Physical Effects ◽  
Fundamental Physical ◽  
Critical Excitation

Biological scanning electron microscopy is increasingly performed at low beam energies in order to improve image contrast, reduce charging artifacts, and minimize beam induced damage to the sample. It is natural then to wish to also use these same low accelerating voltage for X-ray microanalysis using an energy dispersive spectrometer (EDS) but a variety of fundamental physical effects affect the performance that can be achieved. An X-ray photon can only be emitted when the incident beam Eo energy exceeds the critical excitation energy Ecrit for that line. As the beam energy is reduced the number of elements that can be excited falls and it is becomes necessary to use L- and M-lines rather than the K-lines accessible at higher energies. At 5keV, the upper limit of ‘low voltage’ microscopy, K-lines can be excited from elements up to calcium, L-lines can be detected up to cesium, and the rest of the periodic table is available using M-lines. The entire periodic table is therefore, in principle, available at an overvoltage U>2, where U = E0/Ecrit But at lower energies the number of accessible excitations falls and some elements cannot, with current technology, then be analyzed and for general purposes an incident energy lower than about 3keV is probably too limiting to be useful.

scholarly journals Critical excitation-inhibition balance in dense neural networks

2019 ◽  
Vol 100 (1) ◽  
Author(s):  
Lorenz Baumgarten ◽  
Stefan Bornholdt
Keyword(s):  
Neural Networks ◽  
Critical Excitation

Optimal Circumferential Placement of Cylindrical Thermocouple Probes for Reduction of Excitation Forces

1992 ◽  
Author(s):  
Eben C. Cobb ◽  
Tsu-Chien Cheu ◽  
Jay Hoffman
Keyword(s):  
Sensitivity Analysis ◽  
Linear Programming ◽  
Finite Difference ◽  
Design Methodology ◽  
Turbine Stage ◽  
Linear Programming Method ◽  
Optimization Scheme ◽  
Forcing Function ◽  
Finite Difference Formulation ◽  
Critical Excitation

This paper presents a design methodology to determine the optimal circumferential placement of cylindrical probes upstream of a turbine stage for reduced excitation forces. The potential flow forcing function generated by the probes is characterized by means of a Fourier analysis. A finite difference formulation is used to evaluate the sensitivity of the forcing function to the probe positions. An optimization scheme, based on the linear programming method, uses the sensitivity analysis results to reposition the probes such that the Fourier amplitudes of critical excitation orders are reduced. The results for an example design situation are presented.

Sign in / Sign up

Export Citation Format

Share Document