A Neural Model of Coordinated Head and Eye Movement Control

Gaze shifts require the coordinated movement of both the eyes and the head in both animals and humanoid robots. To achieve this the brain and the robot control system needs to be able to perform complex non-linear sensory-motor transformations between many degrees of freedom and resolve the redundancy in such a system. In this article we propose a hierarchical neural network model for performing 3-D coordinated gaze shifts. The network is based on the PC/BC-DIM (Predictive Coding/Biased Competition with Divisive Input Modulation) basis function model. The proposed model consists of independent eyes and head controlled circuits with mutual interactions for the appropriate adjustment of coordination behaviour. Based on the initial eyes and head positions the network resolves redundancies involved in 3-D gaze shifts and produces accurate gaze control without any kinematic analysis or imposing any constraints. Furthermore the behaviour of the proposed model is consistent with coordinated eye and head movements observed in primates.     

Complexity control of HEVC encoders targeting real-time constraints

High Efficiency Video Coding (HEVC) encoders impose several challenges in computing constrained embedded applications, especially under real-time throughput constraints. This paper proposes an adaptive complexity control scheme (CCS) that dynamically adjusts the encoder to the varying computing capabilities of the hardware platform. To design an efficient scheme, an extensive complexity analysis of key HEVC encoding parameters is herein presented. For this analysis, we developed a parameterized complexity model called “arithmetic complexity,” which can be widely applied to any computing platform. Our results demonstrate that the proposed scheme provides time savings ranging from 10 up to 90 % with an average error (between target and effective complexity) of 1.2 %. Our adaptability and control performance analysis show that the scheme rapidly adapts to dynamic set-point adjustments. Compared to state of the art, our complexity control achieves more accurate results and extra features (such as dynamic set-point adjustment) at the cost of minor losses in coding efficiency.     

Viscoplastic fluid flow in irregular eccentric annuli due to axial motion of the inner pipe

Fully developed axial laminar flow of viscoplastic Herschel-Bulkley fluids in eccentric annuli between two pipes has been investigated numerically. The pipes are closed at one end and flow is due to the axial motion of the inner pipe. The annuli may be filly open or partially blocked. General non-orthogonal, boundary-fitted curvilinear coordinates have been used to accurately model the irregular annular geometry due to the presence of a flow blockage. A computer code has been developed using a second-order finite-difference scheme. An exponential model for the shear stress, valid for both yielded and unyielded regions of the flow, is used in the computation. The effects of generalized Bingham number, flow behavior index, eccentricity, and blockage height on the pressure gradient or the surge pressure have been studied and the results are presented in dimensionless form. The pressure gradient is found to decrease with increasing eccentricity. For a partially blocked eccentric annulus the pressure gradient is found to decrease with an increase in the blockage height.     

Reverse micelle facilitated synthesis of nanostructured polyaniline as the counter electrode materials in dye-sensitized solar cells

ABSTRACT

We report a reverse-micelle emulsion polymerization of nanostructured PANI using a nonionic surfactant Polyglyceryl-2-Dipolyhydroxystearate (PGPH) at various concentrations from 2% to 6% (v/v). SEM images show that the obtained morphologies are irregular agglomerates at low PGPH concentration and relatively regular granules at high PGPH concentration. FTIR and Raman spectra show that the synthesized PANI is in the form of Emeraldine salt (PANI ES) with electrical conductivity around 10^?3 S cm^?1. Photovoltaic current-voltage (J-V) measurements show the highest power conversion efficiency is achieved at 1.71% at 6% (v/v) of PGPH.     

Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g^-1 at pH 4.0 and 25 ℃. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl^-, SO₄^2- and PO₄^3- reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g^-1 after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

Zirconia Nanoparticles Made in Spray Flames at High Production Rates

Synthesis of zirconia nanoparticles by flame spray pyrolysis (FSP) at high production rates is investigated. Product powder is collected continuously in a baghouse filter unit that is cleaned periodically by air-pressure shocks. Nitrogen adsorption (BET), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) are used to characterize the product powder. The effect of powder production rate (up to 600 g/h), dispersion gas flow rate, and precursor concentration on product particle size, crystallinity, morphology, and purity is investigated. The primary particle size of zirconia is controlled from 6 to 35 nm, while the crystal structure consists of mostly tetragonal phase (80–95 wt%), with the balance monoclinic phase at all process conditions. The tetragonal crystal size is close to the primary particle size, which indicates weak agglomeration of single crystals.     

Synthesis and characterization of functionalized MWCNTs/PMMA composites: device fabrication for RH sensing

ABSTRACT

Functionalization of multiwalled carbon nanotubes (MWCNTs) with amine group using 4,4′-diaminodiphenyl sulfone (DDS) is achieved after carboxylation of pure MWCNTs (p-MWCNTs). p-MWCNTs, a-MWCNTs (acid functional MWCNTs) and f-MWCNTs (amine functional MWCNTs) were used to fabricate their nanocomposite with PMMA. A comparative study of the humidity characteristics of p-MWCNTs/PMMA, a-MWCNTs/PMMA and f-MWCNTs/PMMA-based capacitive humidity sensors was carried. f-MWCNTs/PMMA-based capacitive humidity sensor shows low hysteresis loss (5%), good response recovery behavior and highest sensitivity (S ~ 9736%) among all the studied composites. The maximum capacitance drift under different relative humidity was 1%RH.     

Evolution of ferroelectric and piezoelectric response by heat treatment in pseudocubic BiFeO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript> ceramics

Heat treatment of ceramics is an important process to tailor the fine electromechanical properties. To explore the criteria for optimized heat treatment in a perovskite structure of (1–x)Bi_1.05FeO₃–xBaTiO₃ (BF–BT100x) system, the structural phase relation, ferroelectric and piezoelectric response of BF–BT36 and BF–BT40 ceramics prepared by furnace cooling (FC) and quenching process were investigated. The X-ray diffraction examination showed single pseudocubic perovskite structure for all the ceramics. The homogenous microstructure was obtained for all ceramics with relatively large grain size in the furnace cooled samples. Well saturated ferroelectric hysteresis loops and enhanced piezoelectric constant (d₃₃?=?97 pC/N) were achieved by quenching process. Dielectric curve of BF–BT36 showed large dielectric constant at its Curie temperature, however, BF–BT40 showed diffused relaxor-like dielectric anomalies. Quenched BF–BT36 samples showed typical butterfly like field induced strain curves, however negative strain decreased in BF–BT40 ceramics. From these investigated study, it is observed that BF–BT ceramics are very sensitive to the heat treatment process (furnace cooling and quenching) on the dielectric, electromechanical properties.     

Optimal model‐free control for a generic MIMO nonlinear system with application to autonomous mobile robots

In this paper, the design procedure for optimal model‐free control algorithm is presented for the tracking problem of completely unknown nonlinear dynamic systems operating under unknown disturbances. The procedure includes a new structure in the context of model‐free control and data‐driven control algorithms. In the new structure, the unknown nonlinear functions are segmented into 1 unknown linear‐in‐states part and another unknown nonlinear part. The adaptive laws proposed for estimating the unknown system dynamics are regressor‐free estimation methods in which there is no need for regressor parameters and, consequently, the persistent excitation condition is not required anymore. Moreover, the main controller gains are updated online, incorporating the adapted values of linear terms in the system dynamics. A comparative study is presented to show that the proposed optimal model‐free control outperforms the state‐of‐the‐art model‐free control algorithms. In addition, the simulation results for the application of the algorithm on autonomous mobile robots are provided.     

Effects of Rheological Behavior of Viscoelastic Surfactants on Formation Damage in Carbonate Rocks

Viscoelastic surfactants (VES) are used in various oilfield applications such as matrix stimulation and enhanced oil recovery. The loss of surfactants during the propagation of VES could result in a significant reduction in the permeability of the rock (formation damage). The objective of the current work was to identify the effect of rheological behavior of the VES on the formation damage using core‐flooding experiments, nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) analysis. A combination of core‐flooding, NMR, and SEM techniques was used to quantify and identify the location of formation damage in carbonate core samples. The viscosity and storage modulus strongly depend on the nature and concentration of salts. The viscosity increased by increasing the salt concentration up to a specific point (15 wt% CaCl₂) and then starts decreasing. The VES formulations that displayed the maximum and minimum viscosities were used to identify the impact of rheological behavior on formation damage. Core‐flooding experiments were performed to assess the formation damage due to high‐viscosity and low‐viscosity VES formulations. The reduction in the permeability of carbonate rocks reaches more than 90% of the initial permeability. It was found that low‐viscosity VES caused more damage compared with high‐viscosity VES when they were used at constant concentrations. NMR and core‐flooding results revealed that the damage took place both in pore body and pore throat. However, most of the surfactant was retained at the pore throat.