Direction-dependent Responses Research Articles

Two-Dimensional Anisotropic Flexibility of Mechanically Responsive Crystalline Cadmium(II) Coordination Polymers.

Crystals of a family of six one-dimensional (1D) coordination polymers of cadmium(II) with cyanopyridines [[CdX2L2]n, where X = Cl, Br, or I and L = 3-cyanopyridine (3-CNpy) or 4-cyanopyridine (4-CNpy)] presented a variety of morphologies and mechanical responses with dominant two-dimensional (2D) anisotropic flexibility, which has not been previously reported. All mechanically adaptable crystals were 2D flexible and displayed a variety of direction-dependent responses; in addition to 2D isotropic flexibility observed for solely elastic materials, 2D anisotropic flexibility was noticed for both elastic and elastic → plastic crystals. The consequences of fine and controlled structural variations on mechanical behavior were additionally explored via microfocus single-crystal X-ray diffraction and complementary theoretical studies, revealing that the relative strength and direction of the hydrogen bonding interactions were the key parameters in delivering a specific mechanical response.

Bayesian inversion for anisotropic hydraulic phase-field fracture

In this work, we employ a Bayesian inversion framework to fluid-filled phase-field fracture. We develop a robust and efficient numerical algorithm for hydraulic phase-field fracture toward transversely isotropic and orthotropy anisotropic fracture. In the fluid-driven coupled problem, three primary fields for pressure, displacements, and the crack phase-field are solved while direction-dependent responses (due to the preferred fiber orientation) are enforced via penalty-like parameters. A new crack driving state function is introduced by avoiding the compressible part of anisotropic energy to be degraded. Next, we use a successful extension of the anisotropic hydraulic phase-field fracture as a departure point for Bayesian inversion to estimate material parameters. To this end, we employ the delayed rejection adaptive Metropolis–Hastings (DRAM) algorithm to identify the parameters. The focus is on uncertainties arising from different variables, including elasticity modulus, Biot’s coefficient, Biot’s modulus, dynamic fluid viscosity and Griffith’s energy release rate in the case of the isotopic hydraulic fracture while in the anisotropic setting, we will have additional penalty-like parameters to be identified. Several numerical examples substantiate our algorithmic developments.

Multidirectional mechanical properties and constitutive modeling of human adipose tissue under dynamic loading

The mechanical behavior of subcutaneous adipose tissue (SAT) affects the interaction between vehicle occupants and restraint systems in motor vehicle crashes (MVCs). To enhance future restraints, injury countermeasures, and other vehicle safety systems, computational simulations are often used to augment experiments because of their relative efficiency for parametric analysis. How well finite element human body models (FE-HBMs), which are often used in such simulations, predict human response has been limited by the absence of material models for human SAT that are applicable to the MVC environment. In this study, for the first time, dynamic multidirectional unconfined compression and simple shear loading tests were performed on human abdominal SAT specimens under conditions similar to MVCs. We also performed multiple ramp-hold tests to evaluate the quasilinear viscoelasticity (QLV) assumption and capture the stress relaxation behavior under both compression and shear. Our mechanical characterization was supplemented with scanning electron microscopy (SEM) performed in different orientations to investigate whether the macrostructural response can be related to the underlying microstructure. While the overall structure was shown to be visually different in different anatomical planes, a preferred orientation of any fibrous structures could not be identified. We showed that the nonlinear, viscoelastic, and direction-dependent responses under compression and shear tests could be captured by incorporating QLV in an Ogden-type hyperelastic model. Our comprehensive approach will lead to more accurate computational simulations and support the collective effort on the research of future occupant protection systems. Statement of significanceThere is an urgent need to characterize the mechanical behavior of human adipose tissue under multiple dynamic loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We performed the first series of experiments on human adipose tissue specimens to characterize the multi-directional compression and shear behavior at impact loading rates and obtained scanning electron microscope images to investigate whether the macrostructural response can be related to the underlying microstructure. The results showed that human adipose tissue is nonlinear, viscoelastic and direction dependent, and its mechanical response under compression and shear tests at different loading rates can be captured by incorporating quasi-linear viscoelasticity in an Ogden-type hyperelastic model.

Unidirectional sound manipulation with acoustic metamaterials

Abstract: Unidirectional sound propagation introduces strong direction-dependent responses. Such effect has drawn considerable attentions in acoustics. In this presentation, we introduce some of the interesting unidirectional sound manipulation phenomenon that is achieved by acoustic metamaterials. The experimentally observed phenomenon is associated with the enhanced wave-structure interactions. We can predict and tune the operating frequency by further trimming the material’s geometry. Our demonstration provides a new degree of freedom to the realization of unique wave dynamics for applications like noise control, acoustic sensing, and imaging. [This work was supported by the Early Career Scheme (ECS) of Hong Kong RGC (Grant No. 25208115).]

Rat thalamic neurons encode complex combinations of heading and movement directions and the trajectory route during translocation with sensory conflict.

It is unknown how thalamic head direction neurons extract meaningful information from multiple conflicting sensory information sources when animals run under conditions of sensory mismatch. In the present study, rats were placed on a treadmill on a stage that moved in a figure-8-shaped pathway. The anterodorsal and laterodorsal neurons were recorded under two conditions: (1) control sessions, in which both the stage and the treadmill moved forward, or (2) backward (mismatch) sessions, in which the stage was moved backward while the rats ran forward on the treadmill. Of the 222 thalamic neurons recorded, 55 showed differential responses to the directions to window (south) and door (north) sides, along which the animals were translocated in the long axis of the trajectory. Of these 55 direction-related neurons, 15 showed heading direction-dependent responses regardless of movement direction (forward or backward movements). Thirteen neurons displayed heading and movement direction-dependent responses, and, of these 13, activity of 6 neurons increased during forward movement to the window or door side, while activity of the remaining 7 neurons increased during backward movement to the window or door side. Eighteen neurons showed movement direction-related responses regardless of heading direction. Furthermore, activity of some direction-related neurons increased only in a specific trajectory. These results suggested that the activity of these neurons reflects complex combinations of facing direction (landmarks), movement direction (optic flow/vestibular information), motor/proprioceptive information, and the trajectory of the movement.

Visualization of Trunk Muscle Synergies During Sitting Perturbations Using Self-Organizing Maps (SOM)

The purpose of this study was to demonstrate the use of the self-organizing map (SOM) method for visualization, modeling, and comparison of trunk neuromuscular synergies during perturbed sitting. Thirteen participants were perturbed at the level of the sternum, in eight directions during sitting. Electromyographic (EMG) responses of ten trunk muscles involved in postural control were recorded. The SOM was used to encode the EMG responses on a 2-D projection (i.e., visualization). The result contains similar patterns mapped close together on the plot therefore forming clusters of data. Such visualization of ten EMG responses, following eight directional perturbations, allows for comparisons of direction-dependent postural synergies. Direction-dependent neuromuscular response models for each muscle were then constructed from the SOM visualization. The results demonstrated that the SOM was able to encode neuromuscular responses, and the SOM visualization showed direction-dependent differences in the postural synergies. Moreover, each muscle was modeled using the SOM-based method, and derived models showed that all muscles, except for one, produced a Gaussian fit for direction-dependent responses. Overall, SOM analysis offers a reverse engineering method for exploration and comparison of complex neuromuscular systems, which can describe postural synergies at a glance.

Direction-dependent systems — A survey

In this paper, a survey on systems which exhibit gains and/or dynamics depending on the input or output direction is presented. Several examples of such systems covering a wide range of application areas, and the causes of their direction-dependent responses, are given. Direction-dependent systems are mathematically classified into three classes, depending on their state-space representation and switching function. The related linear dynamic, transient, and steady-state characteristics of these systems are investigated. Approaches to model direction-dependent systems using Wiener models, piecewise linear models, bilinear models and recurrent neural networks are described. Three application examples are used to illustrate the usefulness of the direction-dependent description. The advantages and disadvantages of direction-dependent models, as well as possible directions for future work, are pointed out.

A VLSI-Based Model of Azimuthal Echolocation in the Big Brown Bat

The azimuthal localization of objects by echolocating bats is based on the difference of echo intensity received at the two ears, known as the interaural level difference (ILD). Mimicking the neural computation of ILD in bats, we have constructed a spike-based VLSI model of the lateral superior olive (LSO) that can successfully produce direction-dependent responses. This simple algorithm, while studied in the acoustic domain, is applicable to any localization based on direction-dependent signal attenuation differences.

Identification of processes having direction-dependent responses, with gas-turbine engine applications

Many processes have dynamic responses which are dependent on the direction in which the process variable is moving. The effects of such nonlinear behaviour on the weighting function model of a process obtained by cross-correlation and on the difference equation model obtained by a generalised least-squares procedure are determined theoretically for a process with first-order dynamics perturbed with pseudo-random binary signals. The theory is confirmed by results from a hybrid computer simulation, and computer-simulated results for processes with second-order dynamics are also presented. The theory is used to explain discontinuities in weighting-function models of a gas-turbine engine in which the input-transducer had direction-dependent dynamic responses. Experimental work on a pilot-scale process is reported, and further examples from the literature are examined.