Modeling of maximum endurance time for one‐handed carrying tasks

The objective of this study was to establish models to predict maximum endurance time (MET) for one‐handed carrying tasks. A one‐handed carrying experiment, under three loads and two walking speeds, was performed. The participant carried a dumbbell on the side using either dominant or nondominant hand. His or her arm was straight‐down. The MET values were collected. Both power and exponential functions were adopted in establishing simplified MET models considering the relative force (f_MVC) applied. The simplified models were further expanded to full models where body weight and walking speed were also included. It was found that the power models provided better estimates than the exponential models when the f_MVC was lower than approximately 0.17 for both the simplified and full models. Considering the effects of the walking speed, the full models are recommended when the f_MVC is 0.3 or lower.     

Computational analysis of cutoff wavenumbers in rectangular waveguides filled with left‐handed material and/or right‐handed material

This paper investigates the cutoff wavenumbers and their geometric and dielectric dependence in rectangular waveguides filled with left‐handed material (LHM) and/or right‐handed material (RHM). A rigorous hybrid mode analysis of these structures produces the dispersion equations and the formulations of cutoff wavenumbers for the first three modes. It is shown how the geometric and dielectric parameters may influence the cutoff wavenumbers of the waveguides filled with LHM and/or RHM. The graphs of cutoff wavenumbers over a range of geometric and dielectric parameters sufficiently wide to cover most requirements of design and application have been plotted. The cutoff wavenumbers of waveguides with LHM increase as the thicknesses or the absolute values of permittivity of LHM increase. It is noted that the variation rules of cutoff wavenumbers in waveguides with LHM show different changing tendencies compared with the waveguides with RHM.     

Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.     

Cluster validation in clustering‐based one‐class classification

Reconstruction‐based one‐class classification has shown to be very effective in a number of domains. This approach works by attempting to capture the underlying structure of the normal class, typically, by means of clusters of objects. It has the main disadvantage, however, that one has to indicate the number of clusters in advance, for this yields an efficient way of computing a clustering. In this paper, we introduce a new algorithm, OCKRA++, which achieves a better performance, by enhancing a clustering‐based one‐class ensemble classifier (OCKRA) with a cluster validity index that is used to set the best number of clusters during the classifier's training process. We have thoroughly tested OCKRA++ in a particular domain, namely masquerade detection. For this purpose, we have used the Windows‐Users and ‐Intruder simulation Logs data set repository, which contains 70 different masquerade data sets. We have found that OCKRA++ is currently the algorithm that achieves the best area under the curve, with a significant difference, in masquerade detection using the file system navigation approach.     

A miniaturized planar nonbianisotropic left‐handed metamaterial

In this article, a miniaturized nonbianisotropic left‐handed metamaterial composed of spiral‐S‐shaped resonator and conducting wire is proposed. This symmetrical structure avoids bianisotropy and it shows a controllable low‐loss double negative (DNG) band. Its electrical size is less than half of the well‐known S‐shaped resonator, which makes it to be considered as a good homogenous effective media. Although the structure is not uniplanar, it is not vulnerable to fabrication errors stem from misalignment of both sides. Both the simulation and experiment results demonstrate left‐handed properties. Also, a circuit model is proposed which can accurately predict the magnetic resonant frequency. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Bandwidth improvement of rat‐race couplers having left‐handed transmission‐line sections

A novel broadband rat‐race coupler has been investigated. The coupler utilizes an artificial left‐handed transmission line section for broadband phase response realization. Moreover, a narrowband model of left‐handed section has been shown to prove the couplers equivalent circuit at the center frequency. To broaden the operational bandwidth multisection quarter‐wave transformers have been proposed. The exemplary rat‐race coupler with two‐section impedance transformers has been designed and manufactured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:341–347, 2014.     

Spatial dependency of shoulder muscle demands in horizontal pushing and pulling

Pushing and pulling account for nearly half of all manual material handling tasks. The purpose of this investigation was to develop a 3-D spatial muscle activity map for the right upper extremity during pushing and pulling tasks. Nineteen males performed 140 ramped directional hand exertions (70 push; 70 pull) at locations along three axes aligned with the anatomical planes. Electromyography (EMG) of 14 sites on the right upper extremity was recorded. Two directional 3-way repeated measures ANOVAs assessed the influence of hand position on EMG. Hand position and exertion direction influenced total and individual muscle demand. During pulling exertions, all three hand location parameters influenced total muscle activity (p < 0.001) and similarly in pushing exertions (p < 0.002), though less pronounced than in pulling. Data were used to create equations to predict the muscle activity of untested hand locations for novel work design scenarios.     

Two‐handed human reach prediction models for ergonomic evaluation

As an essential function of computerized ergonomic evaluation models based on digital human models, realistic simulation or prediction of human reach profiles is of great importance. Although several human‐modeling efforts have been made to provide the capability of reach simulation, most studies have been limited to the reach of a single extremity. A variety of activities of human operators, however, frequently involve simultaneous positioning of two or more extremities to different target positions. Such a multiple reach problem cannot be satisfactorily resolved by means of conventional single‐extremity reach models because formulation of the problem as a series of single reaches rarely yields accurate trajectory of human‐reach profiles due to interactions of multiple extremities. In this research, a two‐handed reach prediction model was developed. The human upper body was modeled as a seven‐link system with 13 degrees of freedom, being regarded as a redundant open kinematic chain with two end‐effectors. As a way of solving the two‐handed reach problem, the resolved motion method was adopted among several inverse kinematics methods as the technique is fit for real‐time redundancy control. The method is also capable of incorporating the joint range availability criterion as a cost function to minimize excessive deviations of body joints from their neutral positions. Real human‐reach profiles were compared to those obtained from the prediction model and were found to be statistically similar. The methodology is expected to be applicable to the reach simulation of both upper and lower extremities without algorithmic difficulties. © 2010 Wiley Periodicals, Inc.     

Band‐notched ultra‐wideband antennas using nonperiodic composite right/left‐handed resonators

This article investigates the characteristics of a single/double‐cell composite right/left‐handed (CRLH) resonator and its application on multiple band‐notched ultra‐wideband (UWB) antennas while suggesting an accurate design procedure. Periodicity assumption and calculating a dispersion diagram allow band‐notched frequencies to adequately predict prior to antenna design. Zeroth‐order resonance (ZOR) frequency due to the CRLH characteristics of a mushroom resonator and higher‐order resonance frequencies are predictable through the hypothetical dispersion diagram. To demonstrate this method, compact, printed, ultra‐wideband circular monopole antennas with four/five‐band notched characteristics using a single/double mushroom resonator are presented. The effects of mushroom cell size on ZOR and the other band notched resonant frequencies are also investigated. The numerical simulations show that the asymmetrical unit cell provides the capability to tune both ZOR and band notched frequencies. Comparison between the simulation and measurement results shows reasonable agreement.     

Design and optimization of CPW‐based composite right/left‐handed transmission line

This article presents a systematic design procedure of CPW‐based Composite Right/Left‐Handed Transmission Line (CRLH TL), including the initial design and optimization algorithm. A Graphical User Interface (GUI) is provided to help inexperienced users synthesize CRLH at any given transition frequency, without tedious tuning or iterative trial. An improved fitness function based on Genetic Algorithm (GA) is presented to reduce the return loss and diminish the bandgap. This design procedure is fast and available, and has been verified by both measurement and full‐wave simulation results. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Dual extended composite right/left‐handed transmission line metamaterial

The new concept of dual extended composite right/left‐handed transmission line (D‐ECRLH TL), with 2 right handed and 2 left handed frequency bands is presented. The D‐ECRLH TL and extended composite right/left handed transmission line are structurally dual. Therefore, the proposed TL shows the dual properties of the ECRLH TL. The D‐ECRLH indeed behaves as a dual‐band bandstop filter, in opposition to the ECRLH which is a dual‐band bandpass one. In contrast, the D‐ECRLH creates an unlimited LH bandwidth. In this article, the transmission parameters and the fundamental properties of the D‐ECRLH TL (dispersion and impedance diagrams) are investigated. The results show that the proposed structure is suitable to design the quad‐band microwave circuits and systems. A prototype of the proposed D‐ECRLH unit cell is realized by the microstrip technology. The good agreement between the measurement and simulation results confirms the realizability of the proposed structure.     

State‐constrained stabilization of beam‐balance systems

We present nonlinear control techniques to stabilize a beam‐balance system with state constraints. We consider two different actuator configurations: the first one is actuated by a cart moving on the beam, while in the second case, the actuation is by a single electromagnet. In the first case, the constrained stabilization problem is solved via an output feedback controller designed using feedback linearization, Luenberger‐like observer and linear matrix inequality based optimization. In the second case, a Lyapunov‐based controller is proposed that takes care of both the input and state constraints. Copyright © 2007 John Wiley & Sons, Ltd.     

Miniaturized low‐profile antenna based on uniplanar quasi‐composite right/left‐handed metamaterial

In this article, a metamaterial‐based broadband low‐profile antenna is presented. The proposed antenna employed an array of uniplanar quasi‐composite right/left‐hand (CRLH) metamaterial cells. This structure contributes to exciting the operating modes in lower frequencies. The antenna has an overall electrical size of 0.75 × 0.60 × 0.07 λ₀³ (λ₀ is the center operating wavelength in free space) and provides a 25% measured bandwidth with the center frequency of 5.1 GHz and maximum gain of 6.6 dB. The proposed antenna is an appropriate candidate for WLAN, WiMAX, and other wireless communication applications.     

Bandwidth and gain‐enhanced composite right/left‐handed antenna for ultra‐wideband applications

A coplanar waveguide‐fed metamaterial antenna is presented for ultra‐wideband (UWB) applications. The proposed antenna is designed with single unit‐cell composite right/left‐handed transmission line (CRLH‐TL) loaded with a split‐ring resonator (SRR). The UWB characteristic is obtained by merging the zeroth‐order resonance of CRLH‐TL with two additional resonances due to the ground plane and SRR respectively. Subsequently, a partial reactive impedance surface is embedded on the rear side of the proposed antenna to enhance the realized gain without affecting the UWB response. The overall size of the antenna is 0.241λ_o x 0.267λ_o x 0.013λ_o (28.8 x 32 x 1.6 mm³), where λ_o is the free space wavelength at 2.51 GHz. The measured results indicate –10 dB fractional bandwidth of 139.19% (2.51‐14 GHz) with realized gains of 2.3, 4.6, and 6 dBi at the resonant frequencies 4, 7.84, and 10.29 GHz respectively. The measured peak realized gain is 6.6 dBi at 10.6 GHz. The radiation efficiency is above 63.85% for the entire UWB range with a peak value of 86.84%. A fairly stable group delay with variation within 1 ns is obtained throughout the operating frequency band. A good agreement has been observed between the measured and simulated results.     

The area of glenoid asymmetry identified as important contributor to shoulder strength during pushing and pulling in the coronal plane

The geometrical dimensions of the bones that make up the glenohumeral joint could be a key factor in strength predictability. Understanding the mechanical influence of these dimensions (individually or in combination) on shoulder strength could help explain the mechanism of musculoskeletal disorders. The following study shows how a recently discovered geometric parameter, the area of glenoid asymmetry (AGA), is a good indicator of shoulder strength. A comprehensive study was conducted to test whether glenohumeral geometry, as measured through MRI scans, is correlated with upper arm strength. The isometric shoulder strength of 12 subjects during one-handed arm abduction and adduction in the coronal plane, in a range from 5 to 30 degrees , was correlated with the geometries of their glenoid fossae. All subjects were stronger during adduction than abduction for all arm positions. The results revealed a high correlation in the coronal plane between the AGA and mean maximum force and mean maximum moment when an arm was abducted and adducted in a range from 5 degrees to 30 degrees (0.80, p 相似文献   

Event‐triggered distributed constrained consensus

We consider a distributed consensus problem for continuous‐time multi‐agent systems with set constraints on the final states. To save communication costs, an event‐triggered communication‐based protocol is proposed. By comparing its own instantaneous state with the one previously broadcasted to neighbours, each agent determines the next communication time. Based on this event‐triggered communication, each agent is not required to continuously monitor its neighbours' state and the communication only happens at discrete time instants. We show that, under some mild conditions, the constrained consensus of the multi‐agent system with the proposed protocol can be achieved with an exponential convergence rate. A lower bound of the transmission time intervals is provided that can be adjusted by choosing different values of parameters. Numerical examples illustrate the results. Copyright © 2016 John Wiley & Sons, Ltd.     

A one‐step leapfrog HIE‐FDTD method for rotationally symmetric structures

In this work, they propose a one‐step leapfrog hybrid implicit‐explicit finite‐difference time‐domain (HIE‐FDTD) method for body‐of‐revolution (BOR). Meanwhile, its Convolutional Perfect Matched Layer (CPML) absorbing boundary condition is implemented. In this method, the implicit difference is applied in the angular direction. All the resultant updating equations are still explicit. However, the stability condition of the proposed method is relaxed. The analytical analysis shows that its time step is only determined by the smaller one of spatial increments Δρ and Δz. A scattering example is provided to demonstrate the new algorithm. At the same time, the relative of reflection error of the CPML is given with comparisons of Mur.     

Applications of anisotropic one‐step leapfrog HIE‐FDTD method in microwave circuit and antenna

To verify the effect of artificial anisotropy parameters in one‐step leapfrog hybrid implicit‐explicit finite‐difference time‐domain (FDTD) method, we calculated several microwave components with different characteristics. Introduced auxiliary field variable can reduce the program difficulty and improve the computational efficiency without additional computational time and memory cost. Analyses of the numerical results are proved that the calculation time is reduced to about one‐sixth compared to the traditional FDTD method for the same example simulated. The memory cost and relative error are remained at a good level. The numerical experiments for microwave circuit and antenna have been well demonstrated the method available.     

D‐type iterative learning control for one‐sided Lipschitz nonlinear systems

In this paper, the problem of iterative learning control for a class of nonlinear systems is studied. Here, the nonlinear functions satisfy the one‐sided Lipschitz and quadratically inner‐bounded conditions. For such nonlinear systems, open‐loop and closed‐loop D‐type learning algorithms are adopted, respectively, and furthermore, the convergence conditions of the D‐type learning algorithms are established. It is shown that both algorithms can ensure that the system output converges to the desired trajectory on the whole time interval. Finally, the validity of the presented D‐type learning algorithms is verified by a numerical example.