Fast DNA sequencing with a graphene-based nanochannel device

Devices in which a single strand of DNA is threaded through a nanopore could be used to efficiently sequence DNA. However, various issues will have to be resolved to make this approach practical, including controlling the DNA translocation rate, suppressing stochastic nucleobase motions, and resolving the signal overlap between different nucleobases. Here, we demonstrate theoretically the feasibility of DNA sequencing using a fluidic nanochannel functionalized with a graphene nanoribbon. This approach involves deciphering the changes that occur in the conductance of the nanoribbon as a result of its interactions with the nucleobases via π-π stacking. We show that as a DNA strand passes through the nanochannel, the distinct conductance characteristics of the nanoribbon (calculated using a method based on density functional theory coupled to non-equilibrium Green function theory) allow the different nucleobases to be distinguished using a data-mining technique and a two-dimensional transient autocorrelation analysis. This fast and reliable DNA sequencing device should be experimentally feasible in the near future.     

Performance degradation of solid oxide fuel cells due to sulfur poisoning of the electrochemical reaction and internal reforming reaction

Hydrogen sulfide is known to degrade the solid oxide fuel cell (SOFC) performance by adsorbing on the nickel anode catalyst. In this research, the mechanism underlying such SOFC degradation was evaluated based on a theoretical mathematical modeling approach and the sulfur coverage was calculated from a Temkin-like isotherm which is related to both temperature and hydrogen sulfide (H₂S) concentration. The influences of the cell temperature, H₂S concentration and electrochemical performance on both the sulfur coverage and cell polarization are studied in detail. Two specific models were considered to identify whether sulfur poisoning has a larger impact on cell performance through its effect on the electrochemical reaction or on the internal reforming reaction. It was found that sulfur poisoning has different effects on the hydrogen oxidation reaction and internal reforming reaction, leading to competing changes in cell performance with temperature and H₂S concentration.     

Estimation of void boundaries in flow field using expectation–maximization algorithm

Phase distribution in the flow field provides an insight into the hydrodynamics and heat transfer between the fluids. Void fraction, which is one of the key flow parameters, can be determined by estimating the phase boundaries. Electrical impedance tomography (EIT), which has high temporal characteristics, has been used as an imaging modality to estimate the void boundaries, using the prior knowledge of conductivities. The voids formed within the process vessel are not stable and their movement is random in nature, thus dynamic estimation schemes are necessary to track the fast changes. Kalman-type estimators like extended Kalman filter (EKF) assume the knowledge of model parameters, such as the initial states, state transition matrix and the covariance of process and measurement noise. In real situations, we do not have the prior information of the model parameters; therefore, in such circumstances the estimation performance of the Kalman-type filters is affected. In this paper, the expectation–maximization (EM) algorithm is used as an inverse algorithm to estimate the model parameters as well as non-stationary void boundary. The uncertainties caused in Kalman-type filters, due to the inaccurate selection of model parameters are overcome using an EM algorithm. The performance of the method is tested with numerical and experimental data. The results show that an EM has better estimation of the void boundary as compared to the conventional EKF.     

Drying characteristics of sewage sludge

To obtain the drying rate of sewage sludge for use in design of a conductive indirect-heating dryer with agitation, the drying characteristics of sewage sludge from three different wastewater treatment plants were investigated with a thermogravimetric analyzer (TGA) in isothermal conditions. Temperature and sample mass were considered as experimental variables. The drying mechanism agreed well with the shrinking core model dominated by the kinetic rate. The activation energy of drying was 17.30 kJ/g mol. A rate equation was proposed for drying of sewage sludge.     

A statistical characterization method for damping material properties and its application to structural-acoustic system design

The performance of surface damping treatments may vary once the surface is exposed to a wide range of temperatures, because the performance of viscoelastic damping material is highly dependent on operational temperature. In addition, experimental data for dynamic responses of viscoelastic material are inherently random, which makes it difficult to design a robust damping layout. In this paper a statistical modeling procedure with a statistical calibration method is suggested for the variability characterization of viscoelastic damping material in constrained-layer damping structures. First, the viscoelastic material property is decomposed into two sources: (i) a random complex modulus due to operational temperature variability, and (ii) experimental/model errors in the complex modulus. Next, the variability in the damping material property is obtained using the statistical calibration method by solving an unconstrained optimization problem with a likelihood function metric. Two case studies are considered to show the influence of the material variability on the acoustic performances in the structural-acoustic systems. It is shown that the variability of the damping material is propagated to that of the acoustic performances in the systems. Finally, robust and reliable damping layout designs of the two case studies are obtained through the reliability-based design optimization (RBDO) amidst severe variability in operational temperature and the damping material.     

Optimal combination of design parameters for improving the kinematics characteristics of a midsize truck through design of experiment

This paper optimizes the combination of design parameters for improving the kinematic characteristics of a midsize truck using both design of experiment and computer simulation. A computational model of the front suspension and steering system of a midsize truck is developed for analyzing kinematic and compliance characteristics. A taper leaf spring is modeled as a flexible body using finite elements. A bump mode test is performed to validate the reliability of the developed computational model. Mean absolute values of the toe angle and wheel base change are used as objective functions. Modifiable hard points are selected as design parameters. An optimal combination of design parameters for improving kinematic characteristics is suggested based on analyses of variance and factor effects using a table of orthogonal arrays.     

Investigation on variable shear modulus of magnetorheological elastomer based on natural rubber due to change of fabrication design

A magnetorheological elastomer (MRE) is a smart material that has a reversible and variable modulus in a magnetic field. Natural rubber (NR), which has better mechanical properties than other rubbers, was used as the matrix. Carbonyl iron powder (CIP) was selected for the generation of a magnetic field‐dependent modulus in the MREs. The MRE specimens were cured in an anisotropic mold, which was used to induce a magnetic field. SEM images validated the CIP orientation. The shear modulus of the MREs was evaluated under a magnetic field induced by a magnetic flux generator (MFG). An evaluation system was designed that includes an MFG, which is a device that generates a magnetic field via a continuously variable‐induced current to determine the magnetic field‐dependent shear modulus. The variations of the shear modulus were observed with increasing CIP volume fraction and induced current. The experimental results revealed that the maximum variation rate of the shear modulus was 76.3% for 40 vol% of CIP and an induced current of 4 A. Using these results, the appropriate CIP volume fraction and induced current can be proposed as the guidelines in fabrication design of MREs based on NR. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Estimation of Phase Currents from a DC-Link Current Sensor Using Space Vector PWM Method

The single-current sensor technique obtaining three phase currents from only a DC-link current sensor has been applied to reduce the cost and increase the reliability for various voltage-fed PWM inverters; however, in this technique there are some practical problems, such as unreliable detection of phase currents andphase shift. A new method that overcomes these problems by employing the estimation scheme with identified system parameters is proposed. The Space Vector PWM (SVPWM) strategy is modified to generate the switching pattern adequate for the proposed method. To obtain a good detection in spite of parameter uncertainties, system parameters used in the estimation method are identified using a recursive least square method (RLSM). Experimental results show that the proposed scheme not only provides a very good detection method for three phase currents without current sensors, but also identifies system parameters very well. This proposed method is very simple, has a small detection error, and gives the information on system parameters.     

Integral Variable Structure Controller for Current Control of PWM Inverter-Fed AC Drives

A new current control technique is presented for three-phase PWM inverterfed AC drives. The features of several existing approaches are analyzed and an integral variable structure control (IVSC) is proposed as an effective way of realizing the high-performance current control. The characteristics of the proposed IVSC are investigated and the design method is presented for the AC drives associated with a voltage-fed PWM inverter. By employing the proposed control, a robust control performance against the parameter uncertainties is obtained in both transient and steady states. The proposed control is applied to the three-phase induction motor drives and the performance improvement is well demonstrated through the simulations and experiments.