Exponential Gain Research Articles

Control of the non-linear static deflection experienced by a fluid-carrying double-walled carbon nanotube using an external distributed load

In this work, an external distributed line load is used to control the postbuckled static deflection of a double-walled carbon nanotube within which a continuous non-viscous fluid flows at a constant velocity. The non-linear equation of motion and boundary conditions are derived using the non-local Timoshenko beam model for the double-walled carbon nanotube, incorporating Von Karman-type geometric non-linear behavior and taking account of the Van der Waals interaction between adjacent layers. First, in the absence of the control force, an analytical approach is used to determine the buckling fluid flow velocities and steady state non-linear static deflection at velocities greater than the buckling velocity for both the cases of a simple-simple and a simple-clamped end support. Then, the control force participates as an indeterminate parameter in the equations. The control force is obtained by resolving equations in which the postbuckled configuration is considered to be an exponential function of time with a negative exponential gain and initial value of the time that is equal to a steady configuration before the control force is applied. The influences of the non-local parameter, aspect ratio and the end supports on the maximum value of control force are investigated.

Theoretical Study of High Repetition Rate Short Pulse Generation With Fiber Optical Parametric Amplification

In this paper, we study theoretically the generation of high repetition rate short pulses using fiber optical parametric amplification. We show that the pulse shape and duration depend on the signal location relatively to the pump frequency. We demonstrate that in order to get the shortest pulse width, the signal must be located at one of the extremities of the gain spectrum associated with the pump peak power. We derive the analytical expression of the pulse shape in this case and compare it to the exponential gain regime case. Using numerical simulations, we also analyze the impact of walk-off and pump phase modulation that is required to suppress Stimulated Brillouin Scattering and derive guidelines to design stable train of short and high repetition rate pulses.

Dynamics of the Himalayan singing bowl

The singing bowl, commonly known as the Tibetan or Himalayan singing bowl, is an idiophone indigenous to many Asian cultures. Singing bowls are usually made of brass, which is hammered into a nearly symmetrical hemispherical shell and then hand-turned on a lathe. A sound is produced by either striking the bowl or rubbing the surface with an excitation stick referred to as a puja. We report on an investigation of the sound generation mechanism of the singing bowl, with an emphasis on understanding the origin of the sound created by the stick-slip excitation mechanism that occurs while rubbing the bowl with the puja. It is shown that both the radial and tangential motion of the puja experience exponential gain during the excitation process, and the feedback mechanism required to produce this behavior is discussed. A slow oscillation in the sound produced by the bowl is explained by the dominance of a single vibrational mode that rotates at the angular speed of the puja.

Amplified spontaneous emission of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole molecule embedded in various polymer matrices

Results of studies on the amplified spontaneous emission (ASE) phenomenon in 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) molecules in four different polymeric matrices are reported. We have analyzed ASE spectra coming from thin films of DCNP-matrix samples when excited by the Nd:YAG nanosecond pulsed laser doubled in frequency (λ=532nm). We report on ASE characteristics in function of different excitation pulse energy densities evaluating ASE thresholds, exponential gain coefficients and reporting the influence of the specific matrix–dye interactions on the photo-degradation process of the dye.

A low power 48-dB/stage linear-in-dB variable gain amplifier for direct-conversion receivers

In this paper, a low power Variable Gain Amplifier (VGA) circuit with an approximation to exponential gain characteristic is presented. It is achieved using current mirrors to generate appropriate current signals to bias the input stage of the VGA circuit working in triode region, and the output stage working in saturation region, respectively. The VGA circuit presented herein comes with a 549μW maximum power consumption given a 1.8V supply. Most important of all, it has a linear-in-dB 48-dB dynamic gain range per stage. The effect of the input trasconductance and the output resistance on the linearity of gain control is also discussed. This circuit is fabricated using a 0.18μm standard CMOS process with a core area of 0.0045mm2.

Optimal working point of a Brillouin amplifier for a weak input signal in the transient regime

In order to improve the working performances of a transient Brillouin amplifier, the dependences of the signal-noise-ratio, sensitivity, energy extraction efficiency and signal amplification factor on exponential gain G are numerically studied based on the theoretical model of transient Brillouin amplification including distributed noise, and an optimal working point of a Brillouin amplifier is obtained. Experimental verifications are performed by choosing CS2 and FC-72 as nonlinear media. A frequency-doubled Nd:YAG pulse laser is used. Results show that when the pump pulse lags behind the Stokes signal pulse by an amount of time equal to half the pulse width, Gopt can be set to be above the SBS threshold exponential gain Gth. For a collinear Brillouin amplifier, Gopt is 1.1-1.3 times Gth; while for a non-collinear structure, Gopt can be set to be over 1.3 times Gth. Nearly saturated amplification is achieved.

Canonical- systematic form for codes in hierarchical poset metrics

In this work we present a canonical-systematic form of a generator matrix for linear codes whith respect to a hierarchical poset metric on the linear space $\mathbb F_q^n$. We show that up to a linear isometry any such code is equivalent to the direct sum of codes with smaller dimensions. The canonical-systematic form enables to exhibit simple expressions for the generalized minimal weights (in the sense defined by Wei), the packing radius of the code, characterization of perfect codes and also syndrome decoding algorithm that has (in general) exponential gain when compared to usual syndrome decoding.

Innovative Approaches to Congenital Heart Disease

In the last two decades, tremendous progress has been made in the diagnosis and treatment of even complex Congenital Heart Disease (CHD). These advances would not have been possible without the exponential gain of knowledge in the field of heart development, the pathophysiologic/hemodynamic delineation of structural cardiovascular lesions, and the discovery of many important basic mechanisms underlying disease development and progression. In this special issue of the Journal of Clinical and Experimental Cardiology (JCEC), internationally renowned experts from multiple disciplines comprehensively discuss and summarize the most impactful discoveries and innovations in the fascinating field of CHD that have emerged in the last 5 years.

Stability and Performance of SISO Control Systems With First-Order Reset Elements

We consider set-point regulation and L2 robust stability properties of a class of reset control systems consisting of a minimum-phase relative degree-one linear SISO plant controlled by a novel first-order reset element (FORE). These results rely on necessary and sufficient conditions for exponential and L2 finite gain stability of a class of planar reset systems consisting of a scalar linear plant controlled by the novel FORE. We show that the L2 gain of the planar reset system decreases to zero as the pole and/or the gain of the FORE are increased to infinity. A number of stability results, including Lyapunov conditions for Lp and exponential stability, for a larger class of reset and hybrid systems are presented and used to prove our main results.

All-Optical Highly Sensitive Chromatic Dispersion Monitoring Method Utilizing Phase-Matched Four-Wave Mixing

This letter represents a highly sensitive all-optical chromatic dispersion (CD) monitoring method utilizing phase-matched four-wave mixing (FWM) in highly nonlinear optical fibers (HNLFs). The monitoring ability arises from the exponential FWM gain which provides an exponential power transfer function (PTF) mapping the CD experienced by the signals onto the average power of the output idler wave. Our method is simple and much more sensitive compared to the other PTF-based monitoring methods proposed before. The sensitivity enhancement is important for highly accurate dispersion compensation and makes the method effective for signals with high duty cycles. Furthermore, by tailoring the phase-matched wavelength range our method can be used to monitor CD in a wavelength-division-multiplexing (WDM) network.

Dietary threonine requirement of Atlantic salmon smolts

This study was conducted to determine the threonine requirement of Atlantic salmon ( Salmo salar) smolts. Five diets containing 10.6, 11.7, 13.4, 14.9 and 16.6 g kg −1 threonine (presented in protein-bound form of threonine) were fed hourly to satiation to triplicate groups of smolts during the first 7 weeks in seawater. Average initial body weights were 79 ± 2 g per salmon (42 fish per tank). Feed intake was measured daily and growth rates were measured over the trial period. Body composition was analyzed in three groups of 10 fish at the start of the trial and in all of the fish in each group at the end of the trial. Based on the exponential threonine gain response to increasing dietary threonine concentrations, the minimum threonine requirement was found to be 13.1 g kg −1 dry matter (15.4 g kg −1 free form). The efficiency of digestible threonine utilization for growth in the deficient diets was 0.87.

Constant barrier strategies in a two-state Markov-modulated dual risk model

In this paper, we consider the dividend problem in a two-state Markov-modulated dual risk model, in which the gain arrivals, gain sizes and expenses are influenced by a Markov process. A system of integro-differential equations for the expected value of the discounted dividends until ruin is derived. In the case of exponential gain sizes, the equations are solved and the best barrier is obtained via numerical example. Finally, using numerical example, we compare the best barrier and the expected discounted dividends in the two-state Markov-modulated dual risk model with those in an associated averaged compound Poisson risk model. Numerical results suggest that one could use the results of the associated averaged compound Poisson risk model to approximate those for the two-state Markov-modulated dual risk model.

Amplified spontaneous emission in polymethyl methacrylate doped with 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP)

Luminescence and amplified spontaneous emission (ASE) phenomenon of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) dissolved in a polymethyl methacrylate (PMMA) matrix have been studied. We analyzed luminescence from thin films of DCNP–PMMA excited by the neodymium doped yttrium aluminum garnet (Nd:YAG) nanosecond pulsed laser doubled and tripled in frequency. We report on ASE in function of different excitation pulse energy densities (ASE threshold was estimated to be 10 and 13mJ/cm2 for pumping beams wavelengths of 532 and 355nm, respectively). We observed the photo-degradation process of a dye and performed exponential gain coefficient measurements (up to 10cm−1) in the system.

Self-amplified spontaneous emission for a single pass free-electron laser

SPARC (acronym of ‘‘Sorgente Pulsata ed Amplificata di Radiazione Coerente’’, i.e. Pulsed and Amplified Source of Coherent Radiation) is a single pass free-electron laser designed to obtain high gain amplification at a radiation wavelength of 500 nm. Self-amplified spontaneous emission has been observed driving the amplifier with the high-brightness beam of the SPARC linac. We report measurements of energy, spectra, and exponential gain. Experimental results are compared with simulations from several numerical codes.

Memory Reduction via Delayed Simulation

We address a central (and classical) issue in the theory of infinite games: the reduction of the memory size that is needed to implement winning strategies in regular infinite games (i.e., controllers that ensure correct behavior against actions of the environment, when the specification is a regular omega-language). We propose an approach which attacks this problem before the construction of a strategy, by first reducing the game graph that is obtained from the specification. For the cases of specifications represented by "request-response"-requirements and general "fairness" conditions, we show that an exponential gain in the size of memory is possible.

Particle swarm optimization on threshold exponential gain of stimulated Brillouin scattering in single mode fibers

We implement a particle swarm optimization (PSO) algorithm to characterize stimulated Brillouin scattering phenomena in optical fibers. The explicit and strong dependence of the threshold exponential gain on the numerical aperture, the pump laser wavelength and the optical loss coefficient are presented. The proposed PSO model is also evaluated with the localized, nonfluctuating source model and the distributed (non-localized) fluctuating source model. Using our model, for fiber lengths from 1 km to 29 km, the calculated threshold exponential gain of stimulated Brillouin scattering is gradually decreased from 17.4 to 14.6 respectively. The theoretical results of Brillouin threshold power predicted by the proposed PSO model show a good agreement with the experimental results for different fiber lengths from 1 km to 12 km.

The minimum dietary lysine requirement, maintenance requirement and efficiency of lysine utilization for growth of Atlantic salmon smolts

This study was conducted to evaluate and refine the dietary lysine requirement of Atlantic salmon (Salmo salar) smolts using both the dose–response technique to determine the minimum dietary requirement and different ration levels to determine the maintenance lysine requirement and the efficiency of lysine utilization for growth. Diets containing 1.97–3.16% lysine (presented in protein-bound form of lysine) were fed to satiation or at 25–75% ration levels to smolts during the last week in fresh water and the following 9 weeks in seawater. Based on the exponential lysine gain response to increasing dietary lysine concentrations, the minimum lysine requirement was found to be 2.67% of diet (dry matter basis; protein-bound form or 3.05% free form). The smolts fed the unsupplemented diet maximally utilized the digestible lysine intake for growth. The efficiency of digestible lysine utilization for growth was 0.85 in the diet containing 2.88% lysine and the maintenance requirement was 21.7 mg digestible lysine kg−0.7 day−1.

Two-beam energy exchange in a hybrid photorefractive-flexoelectric liquid-crystal cell

We develop a semiquantitative theory to describe the experimentally observed energy gain when two light beams intersect in hybrid organic-inorganic photorefractives. These systems consist of a nematic liquid-crystal (LC) layer placed between two photorefractive windows. A periodic space-charge field is induced by the interfering light beams in the photorefractive windows. The field penetrates into the LC, interacting with the nematic director and giving rise to a diffraction grating. LC flexoelectricity is the principal physical mechanism driving the grating structure. Each light beam diffracts from the induced grating, leading to an apparent energy gain and loss within each beam. The LC optics is described in the Bragg regime. In the theory the exponential gain coefficient is a product of a beam interference term, a flexoelectricity term and a space-charge term. The theory has been compared with results of an experimental study on hybrid cells filled with the LC mixture TL 205. Experimentally the energy gain is maximal at much lower grating wave numbers than is predicted by naïve theory. However, if the director reorientation is cubic rather than linear in the space-charge field term, then good agreement between theory and experiment can be achieved using only a single fitting parameter. We provide a semiquantitative argument to justify this nonlinearity in terms of electric-field-induced local phase separation between different components of the liquid crystal.

Measurement of stimulated Brillouin scattering threshold by the optical limiting of pump output energy

AbstractA new approach to measure stimulated Brillouin scattering threshold based on the output energy characteristic of stimulated Brillouin scattering optical limiting is proposed. The stimulated Brillouin scattering threshold or its exponential gain, Gth, can be accurately and conveniently determined by the intersection point of linear-fitting lines of the output energy below and above the threshold. The values of Gth in CS2 and FC-72 for different wavelengths and interaction lengths are measured in Continuum's Nd:YAG Q-switched laser and its frequency-doubled system. We show that Gth for transient regime is larger than that for steady state, and increases with the pump wavelength and the interaction length.

Robust Fault Diagnosis Based on Nonlinear Model of Hydraulic Gauge Control System on Rolling Mill

A nonlinear model of a hydraulic automatic gauge control (AGC) system is established for fault detection and isolation (FDI). By analyzing the relationship between faults and load uncertainties, a decoupling subsystem has been derived using a differential geometric approach. An exponential gain observer has been designed based on the observable decoupling subsystem. Diagnosis residual signal is sensitive to designated faults and robust to load uncertainty. Two real data examples verify that the observer is stable and asymptotically convergent. The correctness and superiority are testified by actual data examples.