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A direct proof of Oka’s lemma on the relation of holomorphic convexity and the properties of the distance to the boundary function is provided. Some related problems for subharmonicity properties of this function are also studied. A new geometric property of pseudoconvex domains is described. [ABSTRACT FROM AUTHOR]

This work investigates the primary and secondary resonances of an electrostatically excited double-clamped microbeam and its feasibility to be used for sensing applications. The sensor design can be excited directly in the vicinity of the primary and secondary resonances. This excitation mechanism would portray certain nonlinear phenomena and it would certainly lead in increasing the sensitivity of the device. To achieve this, a nonlinear beam model describing transverse deflection based on the Euler–Bernoulli beam theory was utilized. Then, a reduced-order model (ROM) considering all geometric and electrical nonlinearities was derived. Three different techniques involving time domain, fast Fourier transforms (FFTs), and frequency domain (FRCs) were used to examine the appearance of subharmonic resonance of order of one-half under various excitation waveforms. The results show that higher forcing levels and lower damping are required to activate this resonance. We note that as the forcing increases, the size of the instability region grows fast and the size of the unstable region increases rapidly. This, in fact, is an ideal place for designing bifurcation inertia MEMS sensors. [ABSTRACT FROM AUTHOR]

This paper deals with the modeling and theoretical study of an average-current-mode-controlled photovoltaic power conversion chain. It should be noted that current mode control is a superior scheme for controlling DC–DC power electronic converters for photovoltaic applications. Bifurcation diagrams, largest Lyapunov exponents, Floquet theory, and time series are used to study the dynamics of the system. The theoretical results show the existence of subharmonic oscillations and period-1 oscillations in the system. The results of the numerical simulations showed that when the battery voltage at the output of the converter is fixed and ramp amplitude is taken as a control parameter, the photovoltaic power system exhibits the phenomenon of period doubling leading to chaotic dynamics. Furthermore, bifurcation diagrams showed that both the critical value of ramp amplitude for the occurrence of border collision bifurcation and the critical value of ramp amplitude for the occurrence of period-1 in the proposed system increased with the value of the battery terminal voltage. The numerical results are in accordance with the theoretical ones. Finally, an external control based on a non-adaptive controller having a sinusoidal function as a target is applied to the overall system for the suppression of chaotic behavior. [ABSTRACT FROM AUTHOR]

Internal gravity waves are propagating disturbances in stably stratified fluids, and can transport momentum and energy over large spatial extents. From a fundamental viewpoint, internal waves are interesting due to the nature of their dispersion relation, and their linear dynamics are reasonably well-understood. From an oceanographic viewpoint, a qualitative and quantitative understanding of significant internal wave generation in the ocean is emerging, while their dissipation mechanisms are being debated. This paper reviews the current knowledge on instabilities in internal gravity waves, primarily focusing on the growth of small-amplitude disturbances. Historically, wave-wave interactions based on weakly nonlinear expansions have driven progress in this field, to investigate spontaneous energy transfer to various temporal and spatial scales. Recent advances in numerical/experimental modeling and field observations have further revealed noticeable differences between various internal wave spatial forms in terms of their instability characteristics; this in turn has motivated theoretical calculations on appropriately chosen internal wave fields in various settings. After a brief introduction, we present a pedagogical discussion on linear internal waves and their different two-dimensional spatial forms. The general ideas concerning triadic resonance in internal waves are then introduced, before proceeding towards instability characteristics of plane waves, wave beams and modes. Results from various theoretical, experimental and numerical studies are summarized to provide an overall picture of the gaps in our understanding. An ocean perspective is then given, both in terms of the relevant outstanding questions and the various additional factors at play. While the applications in this review are focused on the ocean, several ideas are relevant to atmospheric and astrophysical systems too. [ABSTRACT FROM AUTHOR]

This paper presents a 220‐GHz subharmonic downconverter with high conversion gain (CG) and low noise figure (NF) implemented in 28 nm bulk CMOS, including a core mixer and an intermediate frequency (IF) amplifier. Based on the traditional quasi‐subharmonic mixer, new gate‐shorted technology is presented to improve NF and CG by adding a source inductor to reduce the loss of radiofrequency signals. In addition, the impedance transformation network provides passive voltage gain to suppress the noise of the IF amplifier. The downconverter achieves a minimum single‐sidebandNF of 15.5 dB and a maximum CG of 21.3 dB when the IF frequency is 10 MHz. The 1 dB compression point of the downconverter is −30 dBm and consumes 8 mA current with an operating voltage of 0.9 V. The core area of the chip is 200 × 160 µm2 [ABSTRACT FROM AUTHOR]

Objectives: Subharmonic aided pressure estimation (SHAPE) has been shown effective for noninvasively measuring hydrostatic fluid pressures in a variety of clinical applications. The objective of this study was to explore potential improvements in SHAPE sensitivity using monodisperse microbubbles. Methods: Populations of monodisperse microbubbles were created using a commercially available microfluidics device (Solstice Pharmaceuticals). Size distributions were assessed using a Coulter Counter and stability of the distribution following fabrication was evaluated over 24 hours. Attenuation of the microbubble populations from 1 to 10 MHz was then quantified using single element transducers to identify each formulation's resonance frequency. Frequency spectra over increasing driving amplitudes were investigated to determine the nonlinear phases of subharmonic signal generation. SHAPE sensitivity was evaluated in a hydrostatic pressure‐controlled water bath using a Logiq E10 scanner (GE Healthcare). Results: Monodisperse lipid microbubble suspensions ranging from 2.4 to 5.3 μm in diameter were successfully created and they showed no discernable change in size distribution over 24 hours following activation. Calculated resonance frequencies ranged from 2.1 to 6.3 MHz and showed excellent correlation with microbubble diameter (R2 > 0.99). When investigating microbubble frequency response, subharmonic signal occurrence was shown to begin at 150 kPa peak negative pressure, grow up to 225 kPa, and saturate at approximately 250 kPa. Using the Logiq E10, monodisperse bubbles demonstrated a SHAPE sensitivity of −0.17 dB/mmHg, which was nearly twice the sensitivity of the commercial polydisperse microbubble currently being used in clinical trials. Conclusions: Monodisperse microbubbles have the potential to greatly improve the sensitivity of SHAPE for the noninvasive measurement of hydrostatic pressures. [ABSTRACT FROM AUTHOR]

In this paper, we are interested in giving sufficient conditions of a quaternionic plurisubharmonic function defined on a bounded quaternionic hyperconvex domain such that it can be approximated by a decreasing sequence of smooth functions. As an application, we study the geometric property of quaternionic B-regular domains. [ABSTRACT FROM AUTHOR]

A 27–44 GHz subharmonic up-conversion mixer using 65 nm CMOS technology is presented. For subharmonic scheme and wide RF/IF bandwidth, a dual-ring topology is developed in this mixer design. To increase the linearity and conversion gain (CG) without adding additional local oscillator (LO) power, a LO boosting linearization technique is adopted. The subharmonic up-conversion mixer achieves a measured CG of −12 dB ± 1.5 dB from a wide RF frequency of 27 to 44 GHz. The 3-dB IF bandwidth is from dc to 10 GHz. After adopting the linearization technique, the output 1-dB compression point (OP1 dB) of the subharmonic up-conversion mixer can be improved from −12 to −9 dBm at 38 GHz with zero addition dc consumption. [ABSTRACT FROM AUTHOR]

We present an analytical proof that certain natural metric universal covers are Hadamard metric spaces. If ρ d s induces a complete distance d on a plane domain Ω , and ρ = φ ∘ u where u is (locally Lipschitz and) subharmonic in Ω , φ is positive and increasing on an interval containing u (Ω) with log φ convex, then (Ω , d) has a universal cover (Ω ~ , d ~) which is a Hadamard metric space (with geodesics that have Lipschitz continuous first derivatives). [ABSTRACT FROM AUTHOR]

We present an analytical proof that certain natural metric universal covers are Hadamard metric spaces. If ρ d s induces a complete distance d on a plane domain Ω , and ρ = φ ∘ u where u is (locally Lipschitz and) subharmonic in Ω , φ is positive and increasing on an interval containing u (Ω) with log φ convex, then (Ω , d) has a universal cover (Ω ~ , d ~) which is a Hadamard metric space (with geodesics that have Lipschitz continuous first derivatives). [ABSTRACT FROM AUTHOR]

We present an analytical proof that certain natural metric universal covers are Hadamard metric spaces. If ρ d s induces a complete distance d on a plane domain Ω , and ρ = φ ∘ u where u is (locally Lipschitz and) subharmonic in Ω , φ is positive and increasing on an interval containing u (Ω) with log φ convex, then (Ω , d) has a universal cover (Ω ~ , d ~) which is a Hadamard metric space (with geodesics that have Lipschitz continuous first derivatives). [ABSTRACT FROM AUTHOR]

We present an analytical proof that certain natural metric universal covers are Hadamard metric spaces. If ρ d s induces a complete distance d on a plane domain Ω , and ρ = φ ∘ u where u is (locally Lipschitz and) subharmonic in Ω , φ is positive and increasing on an interval containing u (Ω) with log φ convex, then (Ω , d) has a universal cover (Ω ~ , d ~) which is a Hadamard metric space (with geodesics that have Lipschitz continuous first derivatives). [ABSTRACT FROM AUTHOR]

Harmonic distortions caused by non-linear loads (NLLs) affect the behavior of electrical systems, creating harmonics in the fundamental signal. As a result, this deteriorates the power quality. Therefore, this work proposes the implementation of a hybrid filter based on an artificial neural network (ANN) control system, focused on subharmonic, interharmonic and odd harmonic distortions generated by a three-pulse cycloconverter. In addition, a passive double tuned filter was implemented to damp even and odd harmonics. As a result, the simulation performed in MATLAB/SIMULINK showed that the responses produced by the ANN are approximate to the distortions present in the electrical system. Consequently, the levels of total voltage distortions (THDV) and total current distortions (THDI) are reduced. Therefore, the ANN control system improves the quality in the electrical network because the current and voltage harmonics comply with the electrical standards. [ABSTRACT FROM AUTHOR]

In this letter, we propose a novel wideband subharmonically pumped fully differential I–Q resistive mixer architecture, which eliminates the necessity for on-chip dc-blocking capacitors to integrate IF amplifiers. The proposed differential subharmonic mixer topology is verified by presenting a CMOS millimeter-wave monolithic integrated circuit (MMIC), which includes the mixer and two on-chip differential IF amplifiers at the mixer’s I- and Q-channels. The 3-dB IF frequency bandwidth is measured from 0.01 to 5 GHz with a peak conversion gain (CG) of −2 dB and an image rejection ratio (IRR) of more than 25 dB over the IF frequency range. The proposed mixer covers the input signal (RF) frequency from 170 to 185 GHz. The mixer has also been tested with an on-chip voltage-controlled oscillator (VCO) and shows −4.7-dB CG with a 3-dB IF bandwidth from 0.01 to 4.5 GHz. [ABSTRACT FROM AUTHOR]

We examine the stability of the elliptic solutions of the focusing nonlinear Schrödinger equation (NLS) with respect to subharmonic perturbations. Using the integrability of NLS, we discuss the spectral stability of the elliptic solutions, establishing that solutions of smaller amplitude are stable with respect to larger classes of perturbations. We show that spectrally stable solutions are orbitally stable by constructing a Lyapunov functional using higher-order conserved quantities of NLS. [ABSTRACT FROM AUTHOR]

This article presents a multi-subharmonic switching (SHS) digital power amplifier (PA) architecture for enhancing power back-off (PBO) efficiency while achieving watt-level output power. The proposed phase-interleaved architecture provides the inherent cancellation of the subharmonic components in the PBO region, alleviating the burden of the matching network. The proposed multi-SHS scheme can be further combined with a class-G operation to create a greater number of efficiency peaks in the PBO region. A transformer-based, three-way power combiner and a triple-stacking class-D driver are utilized to obtain watt-level output power. The proof-of-concept PA prototype is implemented with a switched-capacitor PA (SCPA) architecture in 65-nm CMOS and achieved 30-dBm peak power at 1.9 GHz, with 45.9%/41.3%/35.3%/32.2%/24.2% drain efficiency located at 0-, −3.5-, −7.0-, −9.5-, and −12-dB PBO, respectively. The average efficiency was 31.4% in real-time operation with a 7.2-dB peak-to-average power ratio (PAPR) modulated signal. [ABSTRACT FROM AUTHOR]

Time-delay displacement and velocity feedback of different types of active control in a cantilever beam carrying an lumped mass is investigated in this paper. Based on Euler–Bernoulli beam theory, the nonlinear governing equation is studied with damping, harmonic distribution, displacement delay, velocity delay and two time delays. The multiple scales perturbation method is applied to obtain the frequency response equations near primary, superharmonic and subharmonic resonances. A thorough study on the stability is proposed, with a particular emphasis on delay feedback. The results show that the hardening and softening behaviors of the system depend on the location of lumped mass. Furthermore, the displacement feedback gain coefficient only makes the peak amplitude move to the low frequency, yet velocity feedback coefficient and their time delays can be used to effectively enhance the stability and quench the nonlinear vibration of the cantilever beam. Thus, reasonable selection of the control system parameters can effectively improve the level of vibration control for the mechanical system. [ABSTRACT FROM AUTHOR]

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This paper presents a subharmonic switching (SHS) digital power amplifier (PA) architecture that enhances power efficiency in the power back-off (PBO) region. The proposed technique can be combined with the class-G operation. By using either SHS or dual-power supply switching, it can provide several peak efficiency points, located at 0, −3.5, −9.5, and, −13 dB PBO. By judiciously choosing the optimal operation mode between SHS and dual supplies for each PA cell at different output power levels, we can further improve the efficiency between peaks. The SHS PA prototype is implemented with a switched-capacitor PA (SCPA) architecture in 65-nm CMOS to validate the effectiveness of the proposed technique, which achieves a 26.8-dBm peak output power with a 49.3% peak drain efficiency (DE) at 2.25 GHz and a 27% DE at −13-dB PBO. [ABSTRACT FROM AUTHOR]

Summary: Noncumulative higher and subharmonic Lamb wave modes generated as a result of partial de‐bonding of piezoelectric wafer transducers (PWT) is numerically investigated and experimentally validated. The influence of excitation frequency on the extent of nonlinear interaction as a result of partially de‐bonded PWTs is discussed. A set of specific frequency ranges is arrived at based on the eigenvalue and harmonic analyses of PWTs used in this study. These are the frequency ranges in which resonant width direction modes of a square PWT or radial modes of a circular PWT are seen. In these frequency ranges, significantly high amplitudes of higher and subharmonics are observed. It is also seen that in these frequency ranges, subharmonic and higher harmonic amplitudes are dependent on de‐bond length and location. Signal processing is carried out using normalized fast Fourier transform for relative comparisons. [ABSTRACT FROM AUTHOR]

In this paper we establish that several maximal operators of convolution type, associated to elliptic and parabolic equations, are variation-diminishing. Our study considers maximal operators on the Euclidean space Rd, on the torus Td and on the sphere Sd. The crucial regularity property that these maximal functions share is that they are subharmonic in the corresponding detachment sets. [ABSTRACT FROM AUTHOR]

In this brief, a current ripple recovery (CRR) model is proposed for voltage-mode control converters. By adding a duty cycle sample-hold effect, the inductor current ripple can be recovered so that the high-frequency dynamical information in the inductor current compensates for a conventional averaged model. The CRR model can be used to judge the system stability and, more importantly, identify the subharmonic oscillation. These theoretical results are in good agreement with experimental ones, which demonstrates the validity of the CRR model. [ABSTRACT FROM AUTHOR]

Subharmonic-perturbed shear flow downstream of a two-dimensional backward-facing step was experimentally investigated. The Reynolds number was Re = 2.0 ×10, based on free-stream velocity and step height. Planar 2D-2C particle image velocimetry was employed to measure the separating and reattaching flow in the horizontal-vertical plane in the center position. The subharmonic perturbations were generated by an oscillating flap which was implemented over the step edge and driven by periodic Ampere force. The subharmonic frequency was 55 Hz as the half of the fundamental frequency of the turbulent shear layer. As a result of the subharmonic perturbations, the size of recirculation region behind the backward-facing step is reduced and the time-averaged reattachment length is 31.0% shorter than that of the natural flow. The evolution of vortices, including vortex roll-up, growth and breakdown process, is analyzed by using phase-averaging, cross-correlation function and proper orthogonal decomposition. It is found that Reynolds shear stress is considerably increased in which the vortices roll up and then break down further downstream. In particular, rapid growth of vortices based on the 'step mode' occurs at approximate half of the recirculation region, caused by in interaction between the shear layer and the recirculation region. Furthermore, the coherent structures, which are represented by a phase-correlated POD mode pair, are reconstructed in phases in order to show regular patterns of the subharmonic-perturbed coherent structures. [ABSTRACT FROM AUTHOR]

Bolted joint structures are prone to bolt loosening under environmental and operational vibrations, which may severely affect the structural integrity. This paper presents a bolt looseness recognition method based on the subharmonic resonance analysis. The bolted joint structure was simplified to a two-degree-of-freedom nonlinear model, and a multiple timescale method was used to explain the phenomenon of the subharmonic resonance and conditions for the generation of subharmonics. Numerical simulation predictions for the generation of the subharmonics and conditions for the subharmonics can be found with respect to the excitation frequency and the excitation amplitude. Experiments were performed on a bolt-joint aluminum beam, where the damage was simulated by loosening the bolts. Two surface-bonded piezoelectric transducers were utilized to generate continuous sinusoidal excitation and to receive corresponding sensing signals. The experimental results demonstrated that subharmonic components would appear in the response spectrum when the bolted structure was subjected to the excitation of twice its natural frequency. This subharmonic resonance method was found to be effective on bolt looseness detection. [ABSTRACT FROM AUTHOR]

The paper considers the degenerate parametric interaction of an intense acoustic pumping beam and a weak signal beam at the subharmonic. The use of a special emitter system with independent signal emission at the harmonic and subharmonic made it possible to study the features of nonlinear interaction both for different amplitude levels and arbitrary phase relations of the fields at these frequencies. Just as predicted in the theory, the experiment showed that signal amplification at the subharmonic hardly occurs at all. It is shown that the use of odd field harmonics, which are absent for a zero amplitude of the signal wave, makes it possible to substantially increase the efficiency of isolating a weak signal wave. The interaction of beams for large and small acoustic Reynolds numbers of the signal wave is studied. [ABSTRACT FROM AUTHOR]

We recall the definition of quasinearly subharmonic functions, point out that this function class includes, among others, subharmonic functions, quasisubharmonic functions, nearly subharmonic functions and essentially almost subharmonic functions. It is shown that the sum of two quasinearly subharmonic functions may not be quasinearly subharmonic. Moreover, we characterize the harmonicity via quasinearly subharmonicity. [ABSTRACT FROM AUTHOR]

The subharmonic threshold for ultrasound contrast agents has been defined as a 20–25 dB difference between the fundamental and subharmonic (2/1) spectral components of the backscatter signal. However, this Fourier-based criterion assumes a linear time-invariant signal. A more appropriate criterion for short cycle and frequency-modulated waveforms is proposed with an adaptive signal-processing approach based on the empirical mode decomposition (EMD) method. The signal is decomposed into an orthogonal basis known as intrinsic mode functions (IMFs) and a subharmonic threshold is defined with respect to the energy ratio of the subharmonic IMF component to that of the incident signal. The method is applied to backscatter data acquired from two polymer-shelled contrast agents, Philips (#38, mean diameter 2.0 \mu \textm ) and Point Biomedical (#12027, mean diameter 3.9 \mu \textm ). The acoustic backscatter signals are investigated for a single contrast agent subjected to monofrequency (20 MHz, 20 cycles) and chirp (15–25 MHz, 20 cycles) forcing for incident pressures ranging from 0.5 to 2.4 MPa. In comparison to the spectral peak difference (20 dB) criterion, the EMD method is more sensitive in determining subharmonic signals. [ABSTRACT FROM PUBLISHER]

ABSTRACT Harmonic suppression is an important study for microstrip patch antenna that radiates harmonic frequencies. In an active microstrip patch antenna, severe surface waves perturb the impedance parameters of the patch element, which cause pattern anomalies associated with the higher harmonics. In this study, the higher order modes including 1st harmonic and a subharmonic (which exist in between fundamental and 1st harmonic) have been removed by using open ended stubs. The subharmonic and the 1st harmonic have been suppressed by using a pair of quarter wave length stubs placed on either sides of the feed line. The introduction of stubs on the feed line does not affect antenna characteristics associated with the fundamental frequency. Simulated and measured results show that the harmonic components existing at 7.9 GHz (subharmonic) and 10.0 GHz (1st harmonic) of the fundamental frequency of 5.20 GHz have been successfully suppressed. The harmonic properties of microstrip antenna with and without stubs have been studied and the result indicates that the 1st and the subharmonic of the patch antenna have been well eliminated because of the effect of the tuning stubs. A parametric study has been done to optimize the stub dimensions. Finally, the influence of other antenna parameters at the presence of stubs in the antenna structure has been studied. Prototype antennas of different combination of stubs have been fabricated, measured and the idea has been verified. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1340-1345, 2016 [ABSTRACT FROM AUTHOR]

We discuss Chebyshev sets of Riemannian manifolds. These are closed sets characterized by the existence of a well-defined distance-realizing projection onto them. The results we establish relate analytical properties of the distance function to these sets to their geometrical properties. They are extensions of some theorems on Chebyshev sets in Euclidean space to the context of Riemannian manifolds. [ABSTRACT FROM AUTHOR]

Wiman–Valiron theory and the results of Macintyre about “flat regions” describe the asymptotic behaviour of entire functions in certain discs around maximum points. We use a technique of Bergweiler, Rippon and Stallard to describe the asymptotic behaviour of a certain type of subharmonic function, and a technique of Bergweiler to estimate the size of its Wiman–Valiron discs from above and below. The results are extended to-subharmonic functions. [ABSTRACT FROM PUBLISHER]

We prove estimates of a p-harmonic measure, p∈( n− m, ∞], for sets in R which are close to an m-dimensional hyperplane Λ⊂ R, m∈[0, n−1]. Using these estimates, we derive results of Phragmén-Lindelöf type in unbounded domains Ω⊂ R∖Λ for p-subharmonic functions. Moreover, we give local and global growth estimates for p-harmonic functions, vanishing on sets in R, which are close to an m-dimensional hyperplane. [ABSTRACT FROM AUTHOR]

This paper is a sequel to Choi (Math Ann 362(1-2):121-146, ) in Math. Ann. In that paper we studied the subharmonicity of Kähler-Einstein metrics on strongly pseudoconvex domains of dimension greater than or equal to 3. In this paper, we study the variations Kähler-Einstein metrics on bounded strongly pseudoconvex domains of dimension 2. In addition, we discuss the previous result with general bounded pseudoconvex domain and local triviality of a family of bounded strongly pseudoconvex domains. [ABSTRACT FROM AUTHOR]

This study presents the nonlinear vibrations of simply supported beams that are subjected to a subharmonic resonance excitation of order two. The applied axial force has a static component to buckle the beam and a dynamic component for parametric excitation. The equation governing the nonlinear transverse deformations is an integral partial differential equation. The static counter part of the governing equation represents the nonlinear buckling problem that is solved for the critical buckling loads and exact buckled configurations. A reduced-order model based on the Galerkin's discretization is obtained where a multi-mode discretization is assumed. The significance of the number of modes retained in the discretization is examined. It is found out that for simply supported beams, the second and higher modes have no contribution on either the static or the dynamic response of the beam. To study the nonlinear dynamics of the problem, a shooting method is used to locate periodic orbits and long-time numerical integration using fifth-order Runge-Kutta method is used to find the fast Fourier transforms of the response. A forward sweep, where the amplitude of the force is increased, while the frequency is kept fixed, is used to drive the beam. We find local attractors coexisting with snapthrough motion. Nonlinear instabilities such as period-doubling leading to chaos, symmetry-breaking, cyclic-fold, period-demultiplying, and jumping are reported. A bifurcation diagram showing all possible attractors near and far from the equilibrium positions is presented. This diagram is a helpful tool to design beams for a desired response especially for energy harvesting applications where high-amplitude vibration is needed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the properties on some classes of complex-valued functions which satisfy certain elliptic equations. First, we discuss the Lipschitz-type spaces and Hardy spaces on these functions, and then we show that for a class of complex-valued functions, if it admits some bounded Dirichlet-type energy integral, then it has a harmonic majorant in the unit disk. [ABSTRACT FROM AUTHOR]

Nonlinear bistable systems have been shown to provide improved efficiency for harvesting energy from random and broadband vibration sources. This article explores the distinct frequency response in the broadened spectrum of a particular nonlinear energy harvester, a piezoelectric cantilever with magnetic coupling. The cantilever response evolves dynamically with frequency around the main cantilever resonance. Both stochastic and multifrequency vibration responses are observed and account for some of the improved efficiency. In addition, subharmonics and ultraharmonics of the main resonance, along with various combinations of these, appear. An analytical model of the bistable dynamics produces results consistent with those observed experimentally. Overall, four distinct types of efficiency improvements appear, in which the signal is amplified above the noncoupled cantilever response: (a) ultraharmonic amplification below resonance frequency, (b) stochastic amplifications in multifrequency and multiamplitude oscillations, (c) ultrasubharmonic amplification, and (d) subharmonic amplification. Taken together, the stochastic, subharmonic, and ultraharmonic responses produce an average of threefold to fivefold increase in voltage production. [ABSTRACT FROM PUBLISHER]

LetAbe a complex semisimple Banach algebra with identity. We explore the situation whereby a portion of the elements ofAhave the same spectrum under multiplication bya ∈ A, as under multiplication byb ∈ A; and when this situation implies thataandbare the same. In particular we show that if the spectrum ofaxequals the spectrum ofbxfor allxwith a spectral radius away from the identity less than 1, thenaandbcoincide. By way of examples we show that this is the best situation possible in general. In another result we show that in the case where these spectra are finite, the assumption need only hold for an arbitrarily small open set inA, with the same conclusion. Additive versions of these results are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a new subharmonic analysis for buck converters with constant on-time control and ramp compensation. For constant on-time control, subharmonic oscillation can be eliminated by adding a compensation ramp with a fixed slope during the off time and a fixed level during the on time. Based on the inductor current information, the compensation ramp, and the charge variations of the output capacitor, the minimum amount of compensation ramp to avoid subharmonic is derived, and the effect of circuit propagation delay is quantified. A prototype of buck converter is built by using constant on-time control with ramp compensation. Experimental results demonstrate the detailed theoretical analysis. [ABSTRACT FROM PUBLISHER]

In the area of mechanics and electronics, the behaviors of mechanical systems under periodic loadings have been examined by many researchers. Vertical conveyors are effective examples observing various kinds of parameters of this problem. In this study, primary, subharmonic, and superharmonic responses have been investigated with multiple scales along with numerical methods for vertical conveyors. The change in the parameters of motion, stability condition, and jump phenomena has been shown graphically by Mathematica software for comparing the results. Both analytical and numerical results obtained had good agreement. [ABSTRACT FROM AUTHOR]

A simple optical method is proposed for performing in-plane experimental modal analysis of micromachined structures with a conventional charge-coupled device (CCD) camera. The motion of a micromechanical device actuated by high-frequency sinusoidal forces (kilohertz range) is recorded at the fixed sampling rate of a camera (typically, 28 frames/s) which is configured with a short shutter aperture time (1/5000 s). Provided a CCD sensor with sufficient sensitivity, much information is contained in the video on the dynamics of the vibrating system despite the limited frame rate. Taking advantage of the theory of undersampling, we show that the dynamics of the systems with several-kilohertz bandwidth can be retrieved very easily. For demonstration purposes, we first study a push–pull electrostatic comb-drive actuator, which is a well-known damped harmonic oscillator system. Then, we show that our measurement method also provides useful information on the behavior of nonlinear systems. In particular, we can characterize the systems' superharmonic and subharmonic resonances in a straightforward way. \hfill[2011-0281] [ABSTRACT FROM AUTHOR]

For functions u, subharmonic in the plane, let\begin{align*} A(r,u)&=\inf_{|z|=r}u(z), \\ B(r,u)&=\sup_{|z|=r}u(z) \end{align*}and let N(r,u) be the integrated counting function. Suppose that $\mathcal{N}\colon[0,\infty)\rightarrow\mathbb{R}$ is a non-negative non-decreasing convex function of log r for which $\mathcal{N}(r)=0$ for all small r and $\limsup_{r\to\infty}\log\mathcal{N}(r)/\4\log r=\rho$, where 1 < ρ < 2, and define\begin{align*} \mathcal{A}(r,\mathcal{N})&=\inf\{A(r,u)\colon N(r,u)=\mathcal{N}(r)\}, \\ \mathcal{B}(r,\mathcal{N})&=\sup\{B(r,u)\colon N(r,u)=\mathcal{N}(r)\}. \end{align*}A sharp upper bound is obtained for $\liminf_{r\to\infty}\mathcal{B}(r,\mathcal{N})/\mathcal{N}(r)$ and a sharp lower bound is obtained for $\limsup_{r\to\infty}\mathcal{A}(r,\mathcal{N})/\mathcal{N}(r)$. [ABSTRACT FROM AUTHOR]

We define nonnegative quasi-nearly subharmonic functions on so called locally uniformly homogeneous spaces. We point out that this function class is rather general. It includes quasi-nearly subharmonic (thus also subharmonic, quasisubharmonic and nearly subharmonic) functions on domains of Euclidean spaces $${{\mathbb{R}}^n}$$, n ≥ 2. In addition, quasi-nearly subharmonic functions with respect to various measures on domains of $${{\mathbb{R}}^n}$$, n ≥ 2, are included. As examples we list the cases of the hyperbolic measure on the unit ball B of $${{\mathbb{R}}^n}$$, the $${{\mathcal{M}}}$$-invariant measure on the unit ball B of $${{\mathbb{C}}^n}$$, n ≥ 1, and the quasihyperbolic measure on any domain $${D\subset {\mathbb{R}}^n}$$, $${D\ne {\mathbb{R}}^n}$$. Moreover, we show that if u is a quasi-nearly subharmonic function on a locally uniformly homogeneous space and the space satisfies a mild additional condition, then also u is quasi-nearly subharmonic for all p > 0. [ABSTRACT FROM AUTHOR]

A 1-V quadrature voltage-controlled oscillator (QVCO) using subharmonic and injection-locked techniques (SHIL-QVCO) is presented. Instead of using the traditional transformer-coupling LC tank with a large area to implement the quadrature output, we use a frequency-doubled differential pair with an injection-locked method. The proposed QVCO is implemented with a TSMC 0.18-\mu\m 1P6M CMOS process having a 1.4 \times 0.67\ \mm^2 chip area. This QVCO has the advantages of low phase noise and low power consumption. Experimental results show that the QVCO has a phase noise of - 126 dBc/Hz at an offset frequency of 1 MHz and a power consumption of 4.9 mW to achieve a 186 figure of merit. Moreover, a tuning frequency between 2.17 and 2.52 GHz can be obtained with a tuning voltage range of 0-1 V for the IEEE 802.15.4. [ABSTRACT FROM PUBLISHER]

In this article, a narrow band pass filter with reduced size using the λg/4 short stubs is presented.The filter size is reduced by realization of transmission line at the second harmonic while the power can be transferred to the output using the fundamental frequency band generated in the resonator and the transmission line in which the impedance mismatching technique is adopted. The experimental results show that the insertion loss is 2.0 dB and return loss is 11.1 dB, and the fractional bandwidth is 10% at the center frequency of 5.8 GHz. The filter size is 19.7 × 8.6 mm2. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2002–2005, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25419 [ABSTRACT FROM AUTHOR]