Rod Network Research Articles

TensCERs: Tension-Constrained Elastic Rods

We study ensembles of elastic rods that are tensioned by a small set of inextensible cables. The cables induce forces that deform the initially straight, but flexible rods into 3D space curves at equilibrium. Rods can be open or closed, knotted, and arranged in arbitrary topologies. We specifically focus on equilibrium states with no contacts among rods. Our setup can thus be seen as a generalization of classical tensegrities that are composed of rigid rods and tensile cables, to also support rods that elastically deform. We show how this generalization leads to a rich design space, where complex target shapes can be achieved with a small set of elastic rods. To explore this space, we present an inverse design optimization algorithm that solves for the length and placement of cables such that the equilibrium state of the rod network best approximates a given set of input curves. We introduce appropriate sparsity terms to minimize the number of required cables, which significantly simplifies fabrication. Using our algorithm, we explore new classes of bending-active 3D structures, including elastic tensegrity knots that only require a few internal cables. We design and fabricate several physical models from basic materials that attain complex 3D shapes with unique structural properties.

Linear and Nonlinear Behaviors of the Photoreceptor Coupled Network.

Photoreceptors are electrically coupled to one another, and the spatiotemporal properties of electrical synapses in a two-dimensional retinal network are still not well studied, because of the limitation of the single electrode or pair recording techniques which do not allow simultaneously measuring responses of multiple photoreceptors at various locations in the retina. A multiple electrode recording system is needed. In this study, we investigate the network properties of the two-dimensional rod coupled array of the salamander retina (both sexes were used) by using the newly available multiple patch electrode system that allows simultaneous recordings from up to eight cells and to determine the electrical connectivity among multiple rods. We found direct evidence that voltage signal spread in the rod-rod coupling network in the absence of I h (mediated by HCN channels) is passive and follows the linear cable equation. Under physiological conditions, I h shapes the network signal by progressively shortening the response time-to-peak of distant rods, compensating the time loss of signal traveling from distant rods to bipolar cell somas and facilitating synchronization of rod output signals. Under voltage-clamp conditions, current flow within the coupled rods follows Ohm's law, supporting the idea that nonlinear behaviors of the rod network are dependent on membrane voltage. Rod-rod coupling is largely symmetrical in the 2D array, and voltage-clamp blocking the next neighboring rod largely suppresses rod signal spread into the second neighboring rod, suggesting that indirect coupling pathways play a minor role in rod-rod coupling.

A graph model to describe the network connectivity of trabecular plates and rods.

Introduction: The trabecular network is perceived as a collection of interconnected plate- (P) and rod-like (R) elements. Previous research has highlighted how these elements and their connectivity influence the mechanical properties of bone, yet further work is required to elucidate better the deeply interconnected nature of the trabecular network with distinct element formations conducting forces per their mechanical boundary conditions. Within this network, forces act through elements: a rod or plate with force applied to one end will transmit this force to a component connected to the other end, defining the boundary conditions for the loading of each element. To that end, this study has two aims: First, to investigate the connectivity of individually segmented elements of trabecular bone with respect to their local boundary conditions as defined by the surrounding trabecular network and linking them directly to the bone's overall mechanical response during loading using a mathematical graph model of the plate and rod (PR) Network. Second, we use this model to quantify side artifacts, a known artifact when testing an excised specimen of trabecular bone, where vertical trabeculae lose their load-bearing capacity due to a loss of connectivity, ultimately resulting in a change of the trabecular network topology. Resuts: Connected elements derived from our model predicted apparent elastic modulus by fitting a linear regression (R 2 = 0.81). In comparison, prediction using conventional bone volume fraction results in a lower accuracy (R 2 = 0.72), demonstrating the ability of the PR Network to estimate compressive elastic modulus independent of specimen size or loading boundary condition. Discussion: PR Network models are a novel approach to describing connectivity within the trabecular network and incorporating mechanical boundary conditions within the morphological analysis, thus enabling the study of intrinsic material properties of trabecular bone. Ultimately, PR Network models may be an early predictor or provide further insights into osteo-degenerative diseases.

Imprinting reversible deformations on a compressed soft rod network.

We present emergent behaviour of storing mechanical deformation in compressed soft cellular materials (a network of soft polymeric rods). Under an applied compressive strain field, the soft cellular material transits from an elastic regime to a 'pseudo-plastic' regime (not to be confused with pseudoplasticity in fluids). In the elastic phase, it is capable of forgetting (or relaxing) any applied indentation once the applied indentation is removed. This relaxation will be determined by the visco-elasticity and internal relaxation timescales in polymeric hyperelastic cellular materials. In the pseudo-plastic phase, however, the material is capable of storing local indentation (or deformation) indefinitely. This deformation can be erased via removal of the external strain field and is therefore reversible. We characterise this behaviour experimentally and present a simple model that makes use of friction for understanding this behavior.

Nonlinear dynamic modeling of a tether-net system for space debris capture

In this paper, a flexible tether-net system is applied to capture the space debris and a numerical framework is established to explore its nonlinear dynamic behaviors, which comprises four principal phases: folding, spreading, contacting, and closing. Based on the discretization of the whole structure into multiple nodes and connected edges, elastic force vectors and associated Jacobian matrix are derived analytically to solve a series of equations of motion. With a fully implicit method applied to analyze the nonlinear dynamics of a slender rod network, the involved mechanical responses are investigated numerically accounting for the interactions. Contact between the deformable net and a rigid body is handled implicitly through a cost-effective modified mass algorithm while the catenary theory is utilized to guide the folding process (from planar configuration to origami-like pattern). The dragging and spreading actions for the folded hexagon net could be realized by shooting six corner mass toward a specific direction; next, the six corners would be controlled to move along a prescribed path producing a closing gesture, when touch between the flying net and the target body is detected, so that for the space debris could be captured and removed successfully. We think the established discrete model could provide a novel insight in the design of active debris removal (ADR) techniques and promote further development of the model-based control of tether tugging systems.

Synthesis and Formation Mechanism of Limestone-Derived Porous Rod Hierarchical Ca-based Metal-Organic Framework for Efficient CO2 Capture.

Limestone is a relatively abundant and low-cost material used for producing calcium oxide as a CO2 adsorbent. However, the CO2 capture capacity of limestone decreases rapidly after multiple carbonation/calcination cycles. To improve the CO2 capture performance, we developed a process using limestone to transform the material into a rod Ca-based metal–organic framework (Ca-MOF) via a hydrothermal process with the assistance of acetic acid and terephthalic acid (H2BDC). The structural formation of rod Ca-MOF may result from the (200) face-oriented attachment growth of Ca-MOF sheets. Upon heat treatment, a highly stable porous rod network with a calcined Ca-MOF-O structure was generated with a pore distribution of 50–100 nm, which allowed the rapid diffusion of CO2 into the interior of the sorbent and enhanced the CO2 capture capacity with high multiple carbonation–calcination cycle stability compared to limestone alone at the intermediate temperature of 450 °C. The CO2 capture capacity of the calcined porous Ca-MOF-O network reached 52 wt% with a CO2 capture stability of 80% after 10 cycles. The above results demonstrated that rod Ca-MOF can be synthesized from a limestone precursor to form a porous network structure as a CO2 capture sorbent to improve CO2 capture performance at an intermediate temperature, thus suggesting its potential in environmental applications.

A versatile route to metal oxide nanoparticles impregnated in carbon matrix for electrochemical energy storage

Metal oxide/carbon (MO/C) composites with an intimate coupling MO/C interface structure are promising electrode materials for electrochemical energy storage devices because of their valuable synergistic effects and structural stability. However, the existing synthetic routes could not fully meet the needs of versatile design and synthesis of MO/C composites with controllable structure. Here we propose a general synthetic strategy for versatile synthesis of various MO/C composites composed of metal oxide nanoparticles tightly impregnated in the carbon matrix. The utilization of polydopamine with excellent adhesive and coating capability allows an in situ and confined reaction to form metal ion–polydopamine inorganic–organic hybrid on various substrates, which can be converted to MO nanoparticles intimately embedded in carbon framework after a carbonization treatment. The present synthetic strategy is highly versatile for incorporating various MO nanoparticles, such as Fe2O3, CoO, NiO, Mn3O4, MoO2, VOx, into the carbon matrix with diverse dimensions (e.g., 1D hollow rod, 2D sheet, and 3D network) through employing different substrates. Profiting from the well-organized structure, the resulting MO/C composites exhibit extraordinary potassium ion storage performance when used as anode materials of potassium ion battery. The proposed strategy provides a facile and versatile avenue for boosting the development of advanced carbon-based functional materials for catalysis and other energy storage fields besides potassium ion battery.

Electrical Conductivity Analysis for Networks of Conducting Rods Using a Block Matrix Approach: A Case Study under Junction Resistance Dominant Assumption

In recent years, numerous studies have reported that high-aspect-ratio and rod-shaped nanoparticles, including carbon nanotubes and metallic nanowires, are promising materials for the next-generation flexible and stretchable transparent conductive films. The functionality of the films is determined by their optoelectric performance, which is significantly affected by the microstructure inside the coated films. In this study, we derive closed-form equations for the electrical conductivity analysis of networks of conducting rods based on the block matrix, Kirchhoff’s laws, and junction resistance dominant assumption (JRDA) model. This simple model is used to reveal a linear algebraic structure underneath the proposed block matrix approach. The block matrix approach under JRDA allows mapping among the key parameters of the rod network system, for example, junction resistance, network structure, and conductivity. Based on numerical experiments, we report a range of parameters for a valid JRDA model. Finally, we apply the model to as-coated silver nanowire networks to demonstrate the extraction of information directly from the micrographs of the networks.

Image analysis for measuring rod network properties

In recent years, metallic nanowires have been attracting significant attention as next-generation flexible transparent conductive films. The performance of films depends on the network structure created by nanowires. Gaining an understanding of their structure, such as connectivity, coverage, and alignment of nanowires, requires the knowledge of individual nanowires inside the microscopic images taken from the film. Although nanowires are flexible up to a certain extent, they are usually depicted as rigid rods in many analysis and computational studies. Herein, we propose a simple and straightforward algorithm based on the filtering in the frequency domain for detecting the rod-shape objects inside binary images. The proposed algorithm uses a specially designed filter in the frequency domain to detect image segments, namely, the connected components aligned in a certain direction. Those components are post-processed to be combined under a given merging rule in a single rod object. In this study, the microscopic properties of the rod networks relevant to the analysis of nanowire networks were measured for investigating the opto-electric performance of transparent conductive films and their alignment distribution, length distribution, and area fraction. To verify and find the optimum parameters for the proposed algorithm, numerical experiments were performed on synthetic images with predefined properties. By selecting proper parameters, the algorithm was used to investigate silver nanowire transparent conductive films fabricated by the dip coating method.

The rheological properties of hydrogenated castor oil crystals

The present study focuses on the rheological performance of a surfactant-rich aqueous suspension containing hydrogenated castor oil (HCO) crystals. HCO can be typically crystallized in five distinct shapes: spherically shaped, irregularly shaped, star-shaped (also called rosettes), short needles, and thick or thin fibers. The effect of the differences in shape on the rheological performance is studied, and the rheological properties are compared to the behavior of other triacylglycerol’s (TAG) suspensions. A suspension of TAG crystals usually behaves as a colloidal gel wherein a colloidal gel is defined as a network of flocs, with each floc being an aggregate of smaller subunits. All of these surfactant-rich aqueous suspensions of HCO crystals behaved according to a colloidal gel in the transient regime, independent of the studied crystal shapes, except the long thin fibers at a concentration above 0.1 wt% HCO transitioning from a heterogeneous fractal rod network to a homogeneous rod network, shifting from a colloidal gel to a glass.

Improving TCP Throughput Using Modified Packet Reordering Technique (MPRT) Over Manets

at the beginning of development of network technology TCP transport agent were designed assuming that communication is using wired network, but recently there is huge demand and use of wireless networks for communication. Those TCP variants which are successful in wired networks are neither able to detect exact causes of packet losses nor unnecessary transmission delays over wireless networks. The biggest challenge over MANET is design of robust and reliable TCP variant which should give best performance in different network scenarios. Till date more than dozens of TCP variants designed and modified by researcher and scientist communities even though the level of TCP performance have to be optimum in different scenarios, Such as congestion, link failure, signal loss and interferences. Over rod, grid and bulk network model also. As some of TCP-variant performs well in particular network scenarios but degrades in other scenarios. The objective of this research work, to modify packet reordering technique based TCP variant, implement and compare its performance with other variants. Validation of basic and main network model done using network simulator (NS2) and calculated throughput, delay and packet drop by processing trace files. The simulated result shows that, proposed technique performs outstanding almost in all network scenarios with minimum packet losses and minimum delay.

Convection and radiation heat transfer in a tube with core rod and honeycomb network inserts at high temperature

Heat transfer and friction factor characteristics in a circular tube fitted with core rod and honeycomb network inserts at high temperature have been investigated experimentally. In the experiments, ambient air with Reynolds numbers ranging from 6000 to 20,000 is passed through a circular tube with uniform wall temperature. Convection and radiation heat transfer phenomena are studied. The experimental results show that at uniform wall temperatures of 373, 473, 553, and 633 K, the average shares of the radiation heat transfer coefficient to the total heat transfer coefficient are 13.9%, 18.3%, 24.7%, and 28.7% for core rod and 11.5%, 13.1%, 15.3%, and 17.8% for honeycomb network insert, respectively. In addition, the heat transfer coefficient increased by 227%, 299%, 327%, and 369% for core rod and 409%, 529%, 614%, and 679% for honeycomb network insert compared with the plain tube under the aforementioned temperatures.

Pretreatment of Bamboo Powder for Cellulose Nanocrystalline by Sulfuric Acid Hydrolysis

The pretreatment of bamboo fiber by the sulfuric acid was investigated by means of experiments. Effect of the sulfuric acid concentration, reaction temperature, hydrolysis time, and solid-liquid ratio on the yield of Cellulose Nanocrystalline (CNC) was studied by orthogonal experiments and single factor experiments. Pretreatment with 60% sulfuric acid and 1:8 solid-liquid ratio for 90 min at 45°Cwas found to be the most optimal condition for pretreatment of bamboo powder for CNC. After pretreatment at the optimal condition, 30.2% of theoretical yield was obtained. Meanwhile, the study of rheological properties showed that CNC had a shear thinning phenomenon, the viscosity of CNC varied in different temperature and different concentrations. We can draw the conclusion through Transmission electron microscopy (TEM) that CNC was mainly existed in two forms of rod and porous network, and had a basic chemical structure of cellulose, while the molecular internal hydrogen bonds were destroyed.

Polymer Chain Conformations in CNT/PS Nanocomposites from Small Angle Neutron Scattering

Chain conformations dictate many of the important physical properties of polymers including their dynamics. Using small angle neutron scattering, we probed chain conformations, specifically the radius of gyration (Rg), in both SWCNT/polystyrene (rSWCNT/Rg ∼ 0.4) and MWCNT/polystyrene (rMWCNT/Rg ∼ 1) nanocomposites. We fit the scattering data using a model that includes an ideal Gaussian chain to describe the polymer conformation and a rod network to describe the carbon nanotube (CNT) network. The scattering contribution from the rod network increases with the CNT concentration in both SWCNT and MWCNT nanocomposites, and the contribution is higher for SWCNT nanocomposites due to the smaller mesh size and higher mesh density. When the SWCNT and MWCNT concentrations are below 2 wt %, there is no significant change in Rg. Above 2 wt %, Rg in the MWCNT nanocomposites decreases slightly, while Rg in the SWCNT nanocomposites increases monotonically as a function of CNT concentration, showing a ∼30% increase at 1...

Stratified rod network model of electrical conductance in ultrathin polymer–carbon nanotube multilayers

The electronic conductance of polymer--carbon nanotube multilayered composite films assembled by the spin-spray layer-by-layer method is investigated. Our measurements show that the film conductance per bilayer ${\ensuremath{\sigma}}_{1}$ vanishes for film thickness below a critical value, and above this threshold it grows logarithmically with the number of polyelectrolyte bilayers ${k}_{\mathrm{l}}$. The results of our experiments are interpreted using a stratified quasi-two-dimensional conducting-network model, in which the junction resistance between nanotubes deposited in different bilayers is a function of the interlayer distance. Using scaling arguments and numerical simulations, we show that the linear dependence of the junction resistance on the layer separation leads to the logarithmic behavior ${\ensuremath{\sigma}}_{1}\ensuremath{\sim}\mathrm{log}{k}_{\mathrm{l}}$ for large ${k}_{\mathrm{l}}$, as observed in our experiments. Properties of our stratified-network model are investigated, and we show that with proper rescaling, different sets of experimental measurements can be collapsed onto a master curve. The overall shape of the master curve is determined by a single dimensionless parameter characterizing the slope of the junction-resistance function.

Probing Selected Morphological Models of Hydrated Nafion Using Large-Scale Molecular Dynamics Simulations

Atomistic molecular dynamics simulations were performed to study hydrated Nafion systems large enough (approximately 2 million atoms, approximately 30 nm box length) to directly observe several hydrophilic domains at the molecular level. These systems consisted of six of the most significant and relevant morphological models of Nafion to-date: (1) the cluster-channel model, (2) the parallel cylinder model, (3) the local order model, (4) the lamellar model, (5) the rod network model, and (6) a "random" model that does not directly assume any particular geometry, distribution, or morphology. Each system was initially built to closely approximate the proposed hydrophilic cluster structure in a given model. Molecular dynamics simulations were then used to observe resulting changes from and behavior of the assumed initial configurations. These simulations revealed fast intercluster "bridge" formation and network percolation in all models. Sulfonate groups were found inside these bridges and played a significant role in percolation. Sulfonates also strongly aggregated around and inside clusters. Cluster surfaces were analyzed to study the hydrophilic-hydrophobic interface. Interfacial area and cluster volume significantly increased during the simulations, and radial distribution functions and structure factors were also calculated. All nonrandom models clearly exhibited the characteristic experimental scattering peak, underscoring the insensitivity of this measurement to hydrophilic domain structure and highlighting the need for future work to clearly distinguish morphological models of Nafion.

Complementary conductance changes by Ikx and Ih contribute to membrane impedance stability during the rod light response

In addition to the HCN1 channels that mediate the h current, the kx current also performs signal filtering in rod photoreceptors. This current is known to be mediated by potassium channels and has similarities to the neuronal M current and EAG potassium channels. Although it is known that in filtering the light response of rods, Ih and Ikx undergo complementary conductance changes, the qualities and significance of these changes are not clear. Here we present an analysis demonstrating the filtering effect of HCN1 channels in salamander rods when Ikx is blocked, and a simulation of the rod light response demonstrating the magnitude and time course of the conductance changes by both currents. Finally, we propose that the purpose of opposing conductance changes by Ih and Ikx may be to optimize the propagation of signals in the rod network.

Simulation analysis of bandpass filtering properties of a rod photoreceptor network

The bandpass filtering properties of a rod network were studied via computer simulations. Sinusoidal current stimuli were applied to a single rod model to characterize its temporal filtering properties. The simulated frequency response revealed that a single rod behaves as a bandpass filter whose characteristics are affected by the stimulus strength and frequency. We analyzed the contribution of individual ionic currents to bandpass filtering and found that the filtering of small signals is largely regulated by the calcium-dependent currents I K(Ca) and I Cl(Ca), whereas the filtering of large signals is regulated by the hyperpolarization-activated current, I h . Furthermore, rod network modeling by electrically interconnecting the single rod models revealed that the acceleration of signals that spread laterally through the rod network is attributed to I K(Ca) and not I h .

Diffusion of spheres in isotropic and nematic networks of rods: Electrostatic interactions and hydrodynamic screening

Translational diffusion of a small charged tracer sphere in isotropic and nematic suspensions of long and thin charged rods is investigated as a function of ionic strength and rod concentration. A theory for the diffusive properties of a small sphere is developed, where both (screened) hydrodynamic interactions and charge interactions between the tracer sphere and the rod network are analyzed. Hydrodynamic interactions are formulated in terms of the hydrodynamic screening length. As yet, there are no independent theoretical predictions for the hydrodynamic screening length for rod networks. Experimental tracer-diffusion data are presented for various ionic strengths as a function of the rod concentration, both in the isotropic and nematic states. Orientational order parameters are measured for the same ionic strengths as a function of the rod concentration. The hydrodynamic screening length is determined from these experimental data and scaling relations obtained from the above mentioned theory. For the isotropic networks, a master curve is found for the hydrodynamic screening length as a function of the rod concentration. For the nematic networks the screening length turns out to be a very sensitive function of the orientational order parameter.

Dynamics and Transport of Molecules in Polymer and Colloidal-Rod Networks

ABSTRACTRe-orientational dynamics of liquid crystal molecules in a polymer network subjected to an electric field is studied by means of light diffraction [1]. When the optical pitch of the electric-field induced cholesteric phase is small compared to the optical wavelength of light, dynamic light scattering (DLS) can be performed to extract the relaxation dynamics of the chiral nematic molecules in the presence of the polymer network. Intriguingly, the reactive mesogenic type of polymer network exhibits a confinement effect, which can be probed within the limited range of scattering angles that comply with the structural correlation length in the system [2].Diffusive mass transport of molecules through a rod network can be studied via fluorescence correlation spectroscopy (FCS) and DLS. Long time self-diffusion of tracer spheres (silica and proteins) in isotropic and nematic colloidal-rod networks (fd-viruses) is systematically studied for various tracer-sphere sizes as compared to the mesh size of the network [3]. In addition, by varying the salt concentration, the relative contribution of electrostatic interactions can be varied. A theory is developed where the diffusion coefficient is expressed in terms of the hydrodynamic screening length of the highly entangled rod-network. The hydrodynamic screening length of rod networks is extracted from diffusion data as a function of the rod concentration both for isotropic and nematic networks [4-5].