Impulse Function Research Articles

Modulating Energy Among Foot-Ankle Complex With an Unpowered Exoskeleton Improves Human Walking Economy.

Over the course of both evolution and development, the human musculoskeletal system has been well shaped for the cushion function of the foot during foot-strike and the impulsive function of the ankle joint during push-off. Nevertheless, an efficient energy interaction between foot structure and ankle joint is still lacking in the human body itself, which may limit the further potential of economical walking. Here we showed the metabolic expenditure of walking can be lessened by an unpowered exoskeleton robot that modulates energy among the foot-ankle complex towards a more effective direction. The unpowered exoskeleton recycles negative mechanical energy of the foot that is normally dissipated in heel-strike, retains the stored energy before mid-stance, and then transfers the energy to the ankle joint to assist the push-off. The modulation process of the exoskeleton consumes no input energy, yet reduces the metabolic cost of walking by 8.19 ± 0.96 % (mean ± s.e.m) for healthy subjects. The electromyography measurements demonstrate the activities of target ankle plantarflexors decreased significantly without added effort for the antagonistic muscle, suggesting the exoskeleton enhanced the subjects' energy efficiency of the foot-ankle complex in a natural manner. Furthermore, the exoskeleton also provides cushion assistance for walking, which leads to significantly decreased activity of the quadriceps muscle during heel-strike. Rather than strengthening the functions of existing biological structures, developing the complementary energy loop that does not exist in the human body itself also shows its potential for gait assistance.

Resolution-Oriented Weighted Stacking Algorithm

In this paper, we proposed a weighted stacking algorithm for obtaining high-resolution data and constructed an optimization objective function using the similarity of the stacked amplitude spectrum and constant (amplitude spectrum of impulse function). The optimization problem is solved to obtain the stacking weights involved in the common midpoint (CMP) gathers by using the alternating iterative method of gradient descent and subgradient descent. Then, the weighted stacking is performed to obtain resolution-enhanced data. A traditional post-stack deconvolution algorithm decomposes the data and performs frequency-weighted recombination, which alters the original frequency composition. Furthermore, most existing methods require wavelet estimation, which may be inaccurate. The amplitude-spectrum shape of CMP gather controls the resolution-enhanced data using the proposed method, which is a stacking scheme that does not require wavelet estimation. On the other hand, our proposed stacking algorithm can handle data containing white noise, and we introduce a penalty term to avoid the mutual offset between the effective signals caused by negative weight, which improves the stacked signal-to-noise ratio. Applications to synthetic and field seismic datasets demonstrate that data stacked using the proposed method have higher resolution and can be more easily interpretated compared to the traditional equal-weight stacking.

Asymptotic Properties of the Solutions to a Class of Perturbed Stochastic Impulsive Functional Differential Equations

The asymptotic properties of the solutions to a class of perturbed stochastic impulsive functional differential equations were investigated. Through comparison of the solution to the perturbed equation with the solution to the corresponding unperturbed one, the sufficient conditions for these solutions to be close in a finite time interval were derived. Then, when small perturbations approach zero and the length of the time interval approaches infinity, the 2 solutions will still be close to each other. Finally, an example illustrates the effectiveness of the results.

EXISTENCE AND UNIQUENESS OF DISCONTINUOUS PERIODIC ORBITS IN SECOND ORDER DIFFERENTIAL EQUATIONS WITH STATE-DEPENDENT IMPULSES

<abstract> In this paper, we are concerned with the existence and uniqueness of discontinuous periodic orbits for a class of second order impulsive differential equations with state-dependent jumps. we apply geometric method to estimate the time mapping of the equation, and then by using Poincaré-Bohl fixed point theorem to obtain some existence criteria under assumptions that the nonlinear term satisfies linear growth conditions. And, the uniqueness of the discontinuous periodic orbit is further proved. Finally, several specific impulsive functions are presented in examples to illustrate the obtained results. </abstract>

Non-instantaneous impulsive fractional-order delay differential systems with Mittag-Leffler kernel

&lt;abstract&gt;&lt;p&gt;The existence of fractional-order functional differential equations with non-instantaneous impulses within the Mittag-Leffler kernel is examined in this manuscript. Non-instantaneous impulses are involved in such equations and the solution semigroup is not compact in Banach spaces. We suppose that the nonlinear term fulfills a non-compactness measure criterion and a local growth constraint. We further assume that non-instantaneous impulsive functions satisfy specific Lipschitz criteria. Finally, an example is given to justify the theoretical results.&lt;/p&gt;&lt;/abstract&gt;

Pemodelan Suspensi Kendaraan Dalam Tinjauan Multi Derajat Kebebasan

The two most important parameters in vehicle vibration are the level of comfort and stability. To get the best value from that parameter, the vehicle suspension system is very important to reduce vibration due to road waves and keep the wheels attached to the road. This paper studied the effect of the type of suspension on the vibration of a one-wheeled vehicle in terms of comfort and stability. The type of suspension is related to the value of the spring stiffness and the damping. While the vehicle is modeled with one wheel in two degrees of freedom. The test is carried out by loading the vehicle including the mass of the vehicle and passengers for each type of suspension, namely soft, medium and hard. Vibration analysis was performed using Matlab Simulink to obtain the acceleration response and deflection response. The vibration response graph shows the comparison of the level of comfort and stability of the vehicle on the road profile modeled in step, impulse and sinusoidal functions. From the simulation results, it is found that the Soft and Medium Suspension can handle vibration very well, especially from the level of response speed for relatively flat roads. Meanwhile, the Hard type of suspension is very good at dampening vibrations for high bumpy roads.

Free vibrations of a thin-walled curvilinear section of an oil-trunk pipeline during ground laying

In this article authors obtained solutions to determine the ground curved sections free vibrations of thin-walled large-diameter pipelines with a liquid flow, based on a geometrically nonlinear version of the semi-momentless toroidal shells medium bending theory by V.Z. Vlasov and V.V. Novozhilov. The pipeline is a toroidal shell, the design scheme is presented in the form of a half torus. Angle β = 1800. The shell is laid on an elastic foundation and makes contact with the ground along a narrow strip. The problem of the soil pressure influence on the shell along a narrow strip is solved as a contact problem, using Fourier's series and an impulse function. The shell is exposed to the cooperative effect of the internal operating pressure, the liquid flowing pressure, the elastic soil foundation, and changes in the geometric characteristics. Motion equations of the middle shell surface are obtained taking into account the geometric and mechanical characteristics, and all the components of the shell material inertial forces. The hinged fastening of the shell ends is taken as the limiting condition. Using the semi-momentless shell theory assumptions, displacements in the longitudinal and circumferential directions are obtained. The solution to the problem of determining the free vibrations comes down to solving the problem of determining AB matrix values. The solutions obtained make it possible to determine the free vibrations frequencies at various wavenumbers values in the longitudinal and circumferential directions, and also make it possible to determine the internal operating pressure contribution, the soil bed coefficient, and geometric characteristics to the pipeline free vibrations frequencies.

Features of the Computational Implementation of the Algorithm for Estimating the Lyapunov Exponents of Systems with Delay

The computational implementation of the algorithm for estimating the spectrum of Lyapunov exponents for systems of differential equations with delayed arguments is considered. Taking into account that for such systems, as well as for boundary value problems, it is not possible to prove the well-known Oseledets theorem, which makes it possible to efficiently calculate the required values, we only have to talk about estimates of characteristic exponents, in a sense close to Lyapunov ones. In this paper, we propose two methods for processing solutions of systems linearized on an attractor, one of which is based on a set of impulse functions; the other one is based on a set of trigonometric functions. The flexibility of application of the indicated algorithms is demonstrated in the case of quasi-stable structures, when several Lyapunov exponents are close to zero. The developed methods are tested on the logistic equation with delay. The results illustrate the “closeness” of the estimated characteristics and Lyapunov exponents.

Dynamic analysis of a plankton–herbivore state-dependent impulsive model with action threshold depending on the density and its changing rate

A plankton–herbivore state-dependent impulsive model with nonlinear impulsive functions and action threshold including population density and rate of change is proposed. Since the use of action threshold makes the model have complex phase set and pulse set, we adopt the Poincar $$\acute{\text{ e }}$$ map as a tool to study its complex dynamics. The Poincar $$\acute{\text{ e }}$$ map is defined on the phase set and its properties in different situations are analyzed. Furthermore, the periodic solution of model is discussed, including the existence and stability conditions of the order-1 periodic solution and the existence of the order-k ( $$k\ge 2$$ ) periodic solutions. Compared with the fixed threshold in the existing literature, our results show that the use of action threshold is more practical, which is conducive to the sustainable development of population and makes people obtain more economic benefits. The analysis method used in this paper can study the complex dynamics of the model more comprehensively and deeply.

The addiction risk factor: A unitary genetic vulnerability characterizes substance use disorders and their associations with common correlates.

Substance use disorders commonly co-occur with one another and with other psychiatric disorders. They share common features including high impulsivity, negative affect, and lower executive function. We tested whether a common genetic factor undergirds liability to problematic alcohol use (PAU), problematic tobacco use (PTU), cannabis use disorder (CUD), and opioid use disorder (OUD) by applying genomic structural equation modeling to genome-wide association study summary statistics for individuals of European ancestry (Total N = 1,019,521; substance-specific Ns range: 82,707-435,563) while adjusting for the genetics of substance use (Ns = 184,765-632,802). We also tested whether shared liability across SUDs is associated with behavioral constructs (risk-taking, executive function, neuroticism; Ns = 328,339-427,037) and non-substance use psychopathology (psychotic, compulsive, and early neurodevelopmental disorders). Shared genetic liability to PAU, PTU, CUD, and OUD was characterized by a unidimensional addiction risk factor (termed The Addiction-Risk-Factor, independent of substance use. OUD and CUD demonstrated the largest loadings, while problematic tobacco use showed the lowest loading. The Addiction-Risk-Factor was associated with risk-taking, neuroticism, executive function, and non-substance psychopathology, but retained specific variance before and after accounting for the genetics of substance use. Thus, a common genetic factor partly explains susceptibility for alcohol, tobacco, cannabis, and opioid use disorder. The Addiction-Risk-Factor has a unique genetic architecture that is not shared with normative substance use or non-substance psychopathology, suggesting that addiction is not the linear combination of substance use and psychopathology.

Impulse functions applied to compute pressure change during injectivity tests

Analytical solutions to compute the pressure change during injectivity tests are desired, as they are useful to interpret pressure transient data. Currently, impulse functions (or Green’s functions) for single-phase flow are already known. However, these formulations are not applicable for injectivity tests, as they cannot handle two-phase flow. Instead, the existing analytical solutions for pressure change during injectivity tests assume that flow-rate within the swept region remains constant, which is not necessarily true for multilayer reservoirs. Therefore, the main novelty of this work is to obtain an impulse function for two-phase flow in single-layer reservoirs with vertical wells. The proposed formulation, which accounts for a flow-rate transient inside the flooded region, employs a radially composite reservoir approach to depict the waterfront propagation and assumes a piston-like fluid displacement. Then, we apply the proposed impulse function to determine pressure change in multilayer reservoirs with different layer properties and in single-layer reservoirs with horizontal wells. To the best of our knowledge, the solutions developed in this work have not been presented in literature before. This work also aims to estimate individual layer permeabilities based on the pressure and flow-rate data computed using the developed formulation. A computational implementation of the models proposed in this work was developed and compared to previously existing solutions and to a commercial flow simulator. Results showed a good agreement, and evidenced that a layer flow-rate transient occurs at the wellbore in multilayer reservoirs. Moreover, layer permeabilities were estimated with decent accuracy.

Discrete time domain analysis of radiation detector noise

In this paper, the analysis of radiation detector noise is carried out based on digital signal processing in the discrete time domain. To generate accurate noise models, detector noise sources are analyzed and modeled in the discrete region. Poisson noise generator was used for shot noise, and White Gaussian Noise Generator was used for Johnson Noise and Channel Thermal Noise. For flicker noise, White Gaussian Noise Generator with 1/f filter was applied. The output noise was calculated by convolution sum of the system impulse function and noise input. In order to improve the accuracy noise analysis, the time domain equation was derived based on the advanced model compared to the existing noise model. CSA model is based on a realistic limited-bandwidth OP-AMP. For the realistic detector model, Laplace transformed function of CSA and shaper out signal for parallel and series noise were derived and inversed for time domain signal. The results of the existing frequency domain analysis match well with the discrete time domain analysis. The discrete time domain analysis can increase the accuracy of noise investigation because it can visualize results of existing frequency domain models and provide different representation methods for the same results.

Performance Analysis of Multi-Branch Reconfigurable Intelligent Surfaces-Assisted Optical Wireless Communication System in Environment With Obstacles

Since optical links are easily blocked by obstacles in the environment, they have been considered difficult to directly perform wireless communications. However, reconfigurable intelligent surfaces (RISs), as a new type of digital coding meta-materials, can significantly improve the coverage of optical communication by establishing new links. We propose a controllable multi-branch wireless optical communication system based on optical RISs. By setting up multiple optical RISs in the environment, multiple artificial channels are built to improve the system performance and to reduce the outage probability. In this paper, we investigate three factors affecting channel coefficients, including beam jitter, RIS jitter, and obstruction probability. We derive closed-form probability density function of channel coefficients, asymptotic average bit-error rate (BER), and the outage probability for systems with multiple branches. Our analysis reveals that the probability density function contains an impulse function, which causes irreducible error rate and outage probability floors. Based on our numerical results, the BER and outage probability floor of the multi-branch system are significantly reduced compared with the single direct path system. Therefore, the optical RIS assisted multi-branch wireless communication is a promising solution against obstacles of optical channel.

A Rapid Approach for the Prediction of Seismic Ground Motion in Urban Areas

Rapid prediction of seismic ground motion can help with the assessment of seismic damage during earthquake emergencies. A numerical simulation is a powerful tool for achieving this end. However, existing methods for such simulations need a large number of seismic ground motion records. Moreover, their performance depends on large-scale computing resources, so they cannot meet the requirement of near real-time prediction of seismic ground motion. This paper proposes a rapid method for predicting seismic ground motion based on the 3D transfer function. This approach obtains the transfer function by solving the site seismic response under three impulse function excitations, calculated by different pre-event 3D physics-based numerical simulations. The approach only needs one seismic record in the study area and can quickly yield the seismic ground motion of the whole study area. The proposed approach is verified by modeling site response to an assumed earthquake, which was affected by the 2008 Wenchuan M7.9 event. The results confirm that the proposed method has sufficient accuracy in near real-time prediction of seismic ground motion.

A Note on Existence of Global Solutions for Impulsive Functional Integrodifferential Systems

In our manuscript, we research the existence of global solutions for a class of impulsive abstract functional integrodifferential systems with nonlocal conditions. We proved our outcomes by utilizing the Leray-Schauder's Alternative fixed point theorem. Lastly, a model is presented for illustration of theory.

Approximate controllability of nonlocal impulsive neutral integro‐differential equations with finite delay

In this paper, we apply the resolvent operator theory and an approximating technique to derive the existence and controllability results for nonlocal impulsive neutral integro‐differential equations with finite delay in a Hilbert space. To establish the results, we take the impulsive functions as a continuous function only, and we assume that the nonlocal initial condition is Lipschitz continuous function in the first case and continuous functions only in the second case. The main tools applied in our analysis are semigroup theory, the resolvent operator theory, an approximating technique, and fixed‐point theorems. Finally, we illustrate the main results with the help of two examples.

Investigations on using white noise as a test signal for performing frequency response measurements on transformers

White noise is a random signal mathematically analogous to an impulse function in time and flat spectrum in frequency. Naturally, the white noise may be used as an alternative test signal for determining the frequency response analysis (FRA) of transformers. Such an attempt not only enhances the power of FRA testing but also enable development of an online diagnostic test method. At present, the concept of using white noise is well-defined, but the crucial knowledge of applying the same on a real-time power transformer is currently not available or at least in the public domain. The study attempts to bridge this gap between theoretical contribution and practical requirement. The mathematical concept, experimental illustrations, and onsite / field validation altogether provides a complete insight into the identified problem. In this regard, an experimental study that investigates on using white noise as a test signal in determining the frequency response of a two-winding transformer is initiated. First, the possibilities of application of theoretical and mathematical concepts of using white noise as a test signal for measuring the frequency response of winding-core assembly is verified. Following this, the white noise signal applied to the circuit model and the corresponding response is recorded and the arbitrary choice of data samples measured from the circuit model is ensured using brute-force approach. In this procedure, the number of samples are manually increased until the magnitude and natural frequencies of resonant peaks matches atleast within 2 % accuracy with conventional FRA measurements. This is performed to ensure the repeatability of the method. Later, the time and frequency dependent statistical properties of the measured signals are computed and the respective transfer function is obtained. Subsequently, the transfer function obtained from the white noise method and the respective natural frequency (tabulated) are compared with the values measured using conventional FRA method. Once this is accomplished, these findings are experimentally validated on an actual high voltage transformer.

Effects of impulsive harvesting and an evolving domain in a diffusive logistic model*

In order to understand how the combination of the evolution of a domain and impulsive harvesting affect the dynamics of a population, we investigate a diffusive logistic population model with impulsive harvesting on a periodically evolving domain. Initially the ecological reproduction index of the impulsive problem is introduced and given by an explicit formula, which depends on the domain evolution rate and the impulsive function. Then the threshold dynamics of the population subject to monotone or nonmonotone impulsive harvesting are established based on this index. Finally numerical simulations are carried out to illustrate our theoretical results, and these reveal that a large domain evolution rate can improve the populations ability to survive, no matter which impulsive harvesting takes place. On the contrary, impulsive harvesting has a negative effect on the survival of the population, and can even lead to its extinction.

Rapid Prediction of Strong Ground Motions from Major Earthquakes: An Example in the Wudu Basin, Sichuan, China

ABSTRACT Rapid prediction of ground motions of major earthquakes can assist emergency response and postseismic damage assessment. Numerical simulations can perform such prediction. However, they need a large number of calculations based on real data and depend on large-scale computation resources, limiting practice of real-time prediction. To solve this problem, this article proposes a new prediction method based on a 3D transfer function, which is obtained by solving the site seismic response to three impulse function excitations that can be calculated by different pre-event 3D physics-based numerical simulations. This approach only needs one seismic record in the study area and can quickly (near-real time) predict ground motions in the whole study area. We verify the proposed approach with an Mw 5.7 aftershock of the 2008 Mw 7.9 Wenchuan earthquake in the Wudu basin, Sichuan Province, China. The results show that this method is feasible and has sufficient accuracy in nearly real-time prediction of seismic ground motions.

The Relationship Between Habitual Physical Activity, Sitting Time, and Cognitive Function in Young Adult Women.

There is evidence that physical activity (PA), sitting time, and obesity may impact cognition, but few studies have examined this in young women. Healthy women (18-35y), without conditions that impair cognition, were recruited for this cross-sectional study. Participants completed anthropometric and validated computerized cognitive assessments (IntegNeuro™). Performance on 5 cognitive domains (impulsivity, attention, information processing, memory, and executive function) was reported as z scores. Sitting hours and weekly PA calculated from time in low-, moderate-, and high-intensity activity were obtained via the International Physical Activity Questionnaire. Analysis of variance/analysis of covariance, chi-square, and linear regression were used. 299 (25.9 [5.1]y) women (low PA = 19%; moderate PA = 40%; high PA = 41%) participated. High PA women had lower body mass index (high PA = 26.1 [6.5]; moderate PA = 30.0 [8.7]; low PA = 31.0 [11.1]kg/m2; P < .001) and less sitting time (high PA = 6.6 [3.1]; moderate PA = 7.7 [2.8]; low PA = 9.3 [3.6]hr/weekday; P < .0001). Cognitive function was within normal ranges and did not differ between any PA groups (P = .42). Adjusting for body mass index, C-reactive protein, or sitting hours did not alter results. Weak correlations were found between time in high-intensity activity and impulsivity (b = 0.12, r2 = .015; P = .04), and between sitting hours and information processing efficiency (b = -0.18, r2 = .03; P = .002). Valuesare presented as mean (SD). Cognitive function was within the normal range, regardless of PA or sitting time.