bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual-Fuel Diesel Engine Combustion With Hydrogen, Gasoline, and Ethanol as Fumigants: Effect of Diesel Injection Timing
Authors: Fang Wei , Huang Bin , Kittelson David B. , Northrop William F.
Published: February 2014

Premixed compression ignition (CI) combustion has attracted increasing research effort recently due to its potential to achieve both high thermal efficiency and low emissions. Dual-fuel strategies for enabling premixed CI have been a focus using a low-reactivity fumigant and direct diesel injection to control ignition. Alternative fuels like hydrogen and ethanol have been used as fumigants in the past but typically with diesel injection systems that did not allow the same degree of control or mixing enabled by modern common rail systems. In this work, we experimentally investigated hydrogen, ethanol, and gasoline as fumigants and examined three levels of fumigant energy fraction (FEF) using gasoline over a large, direct diesel injection timing range with a single-cylinder diesel engine. It was found that the operable diesel injection timing range at constant FEF was dependent on the fumigant's propensity for autoignition. Peak indicated gross cycle efficiency occurred with advanced diesel injection timing and aligned well with combustion phasing near top dead center (TDC), as we found in an earlier work. The use of hydrogen as a fumigant resulted in very low hydrocarbon (HC) emissions compared with ethanol and gasoline, establishing that they mainly result from incomplete combustion of the fumigated fuel. Hydrogen emissions were independent of diesel injection timing, and HC emissions were strongly linked to combustion phasing, giving further indication that squish and crevice flows are responsible for partially burned species from fumigation combustion.
Comparative Study of Flange-to-Seal Contact Couplings With Bolt Relaxation Under Creep Condition
Authors: Mao Jianfeng , Wang Weizhe , Liu Yingzheng , Zhang Junhui
Published: February 2014

Future coal-fired steam turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet steam temperatures and pressures leading to severe creep that significantly influences the sealing behavior and high temperature strength of bolted flange-seal couplings. Flanges with different thicknesses were employed for a comparative study. The important stress/creep values in the flanges and U-type seals had been obtained for variations in flange thickness and bolt relaxation while maintaining other leading parameters constant. The variation of contact stresses due to creep deformation plays an important role in achieving a leak proof sealing. In this paper, a two-dimensional finite element analysis of bolted flange-seal couplings has been carried out by taking the relaxation of bolt stress under full-loading turbine service. The creep strength of flanges and U-type seals are investigated by Cocks–Ashby (C–A) equivalent strain method. The multiaxial state of stresses is considered in this method by using C–A multiaxial coefficient. According to ASME allowable creep limit, the C–A equivalent strains of three flange-seal couplings are evaluated and compared. Furthermore, based on the results of contact stresses, the creep behavior of U-type seals is analyzed varying flange thickness. Finally, analysis shows that the thinner flange-seal coupling has larger long-term contact stress, while the U-type seal with the thicker flange has the least creep strength.
Research on Swing up Control Based on Energy for the Pendubot System
Authors: Ordaz Patricio , Espinoza Eduardo S. , Muñoz Filiberto
Published: February 2014

In this paper, we present a class of nonlinear control scheme for swinging up and stabilization of an underactuated two-link robot called as Pendubot. The main objective of this paper is to present a switched control that swing up and stabilize for almost all combination of initial states given on the four equilibrium points of the double underactuated pendulum. The proposed methodology is based on two control strategies to swing up and stabilize the Pendubot system. The first one is based on Lagrangian dynamics, energy analysis, and stability theory, while the second one is based on linear quadratic regulator. Moreover, here we present a stability analysis of the switched control algorithm. In order to verify the proposed control strategy, experimental results were performed.
A Control-Oriented Two-Zone Charge Mixing Model for HCCI Engines With Experimental Validation Using an Optical Engine
Authors: Yoon Yongsoon , Sun Zongxuan , Zhang Shupeng , Zhu Guoming G.
Published: February 2014

A control-oriented two-zone charge mixing model is developed to simplify, but to describe mixing of fresh charge and residual gas during the intake stroke. Engine valve timing has a strong influence on the realization of stable homogeneous charge compression ignition (HCCI), since it affects turbulent flow that promotes mixing of fresh charge and residual gas. Controlled auto-ignition of a HCCI engine is achieved by good mixing of fresh charge and residual gas. Therefore, it is useful to develop a mixing model that can be executed in real-time to help extend the operational range of HCCI. For model derivation, the cylinder volume is artificially divided into two zones with a fictitious divider between them. First, the mixed zone consists of fresh charge induced by opening intake valves and some residual gas transferred from the unmixed zone. They are assumed to have been mixed homogeneously so that cold fresh charge gains thermal energy from hot residual gas. Second, the unmixed zone contains the rest of hot residual gas. Mass transfer between them which is forced by a fluid jet is directed from the unmixed zone to the mixed one. Based on the definitions of two zones and interaction between them, a two-zone charge mixing model is derived. To investigate phasing effects of valve timing on charge mixing, comparative simulation was carried out with different valve timings. For experimental validation and calibration of the proposed model, optical engine tests were performed with an infrared (IR) camera, together with GT-power simulation. From good agreement between the model temperature and the estimated temperature from IR images, the model turns out to be useful to describe mixing of fresh charge and residual gas.
Analytical Modeling of Gaseous Slip Flow in Parabolic Microchannels
Authors: Tahmouresi Farzad , Das Samir K.
Published: February 2014

The paper presents an analytical solution of velocity, mass flow rate, and pressure distribution for fully developed gaseous slip flow in nonsymmetric and symmetric parabolic microchannels. The flow is considered to be steady, laminar, and incompressible with constant fluid properties. Fully developed gaseous slip flow in microchannels of parabolic cross section is solved analytically for various aspect ratios using a parabolic cylindrical coordinate system on applying the method of separation of variables. Prior to apply separation of variables, Arfken transform [Arfken, 1970, Mathematical Methods for Physicists, Academic Press, Orlando, FL, Ch. 2] was used on momentum equations and first-order slip boundary conditions at each channel wall were imposed. A simple model is proposed to predict the friction factor and Reynolds number product fRe for slip flow in parabolic microchannels. Through the selection of a characteristic length scale, the square root of cross-sectional area and the effect of duct shape have been minimized. The results of a normalized Poiseuille number for symmetric parabolic microchannels (ɛ=1) shows good agreement with the previous results [Morini et al., 2004, “The Rarefaction Effect on the Friction Factor of Gas Flow in Micro/Nano-Channels,” Superlattices Microstruct., 35(3–6), pp. 587–599; Khan and Yovanovich, 2008, “Analytical Modeling of Fluid Flow and Heat Transfer in Microchannel/Nanochannel Heat Sinks,” J. Thermophys. Heat Transf., 22(3), pp. 352–359] for rectangular microchannels. The developed model can be used to predict mass flow rate and pressure distribution of slip flow in parabolic microchannels.
Application of the Design For Control Approach for the Integrated Design and Control of Parallel Robots
Authors: Li Qing
Published: February 2014

To effectively control a complex mechanical structure for precise performance, a model-based type of controller is usually desired. In cases of controlling parallel robots, however, the iterative computation due to the complexity of the dynamic models can result in difficulties in controller implementations and system stability analysis. To avoid this problem, simplified dynamic models can be obtained through approximation, nevertheless, performance accuracy will suffer due to simplification. This paper suggests applying the effective Design For Control (DFC) approach to handle this problem. The underlying idea of the DFC approach is that, no matter how complex a system is, as long as its mechanical structure can be judiciously designed such that it results in a simple dynamic model, a simple control algorithm may be good enough for a satisfactory control performance. Through out the discussion in the paper, the integrated design and control of a two DOF parallel robot is studied as an illustration example. Experimental validation has demonstrated the effectiveness of the DFC approach.
Flow and Mass Transfer for an Unsteady Stagnation-Point Flow Over a Moving Wall Considering Blowing Effects
Authors: Fang Tiegang
Published: February 2014

In this paper, the flow and mass transfer of a two-dimensional unsteady stagnation-point flow over a moving wall, considering the coupled blowing effect from mass transfer, is studied. Similarity equations are derived and solved in a closed form. The flow solution is an exact solution to the two-dimensional unsteady Navier–Stokes equations. An analytical solution of the boundary layer mass transfer equation is obtained together with the momentum solution. The examples demonstrate the significant impacts of the blowing effects on the flow and mass transfer characteristics. A higher blowing parameter results in a lower wall stress and thicker boundary layers with less mass transfer flux at the wall. The higher wall moving parameters produce higher mass transfer flux and blowing velocity. The Schmidt parameters generate a local maximum for the mass transfer flux and blowing velocity under given wall moving and blowing parameters.
Thrust Force Characterization of Oscillating Cantilevers Operating Near Resonance
Authors: Eastman Andrew , Kimber Mark L.
Published: February 2014

Harmonic oscillations from cantileverlike structures have found use in applications ranging from thermal management to atomic force microscopy and propulsion, due to their simplicity in design and ease of implementation. In addition, making use of resonance conditions, a very energy efficient solution is achievable. This paper focuses on the application of providing thrust through cantilever oscillations at or near the first mode of resonance. This method of actuation provides a balance between full biomimicry and ease of fabrication. Previous studies have shown promise in predicting the propulsion performance based on the operating parameters, however, they have only considered a single cantilever geometry. Here, additional cantilever sizes and materials are included, yielding a much larger design space to characterize the thrust trends. The thrust data is experimentally captured and is assembled into two sets of predictive correlations. The first is based on Reynolds and Strouhal numbers, while the second only employs the Keulegan–Carpenter number. Both correlations are proven to predict the experimental data and can be shown to yield nearly identical proportional relationships after accounting for the cantilever frequency response. The findings presented in this research will aid in further understanding and assessing the capabilities of thrust generation for oscillating cantilevers, but also provides a foundation for other applications such as convection heat transfer and fluid transport.
Bi-Linear Fatigue and Fracture Approach for Safety Analysis of an Offshore Structure
Authors: Khan Rizwan A. , Ahmad Suhail
Published: February 2014

The design of welded structures for the fatigue limit state is normally carried out by means of either linear or bilinear S-N curves, which have been found adequate to predict crack initiation only. To properly assess the effects of the design, fabrication, inspection, and repair strategy for structure degradation due to crack growth, fracture mechanics (FM) models need to be applied. In this paper, alternative S-N and FM formulations of fatigue are investigated. The probabilistic fracture mechanics approach predicts the fatigue life of welded steel structures in the presence of cracks under random spectrum loading. It is based on a recently proposed bi-linear relationship to model fatigue crack growth. Uncertainty modeling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bilinear crack growth relationship. Results pertaining to the fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo simulation technique and the emphasis is placed on a comparison between the linear and bilinear crack growth models. Variations in the system configuration, service life, and coefficients of crack growth laws have been studied on the parametric basis
Comparative Study of the Shock Resistance of Rubber Protective Coatings Subjected to Underwater Explosion
Authors: Xiao Feng , Chen Yong , Hua Hongxing
Published: February 2014

Finite element simulations of rubber protective coatings with different structures under two dynamic loading cases were performed. They were monolithic coating and honeycomb structures with three different cell topologies (hexachiral honeycomb, reentrant honeycomb, and circular honeycomb). The two loading cases were a dynamic compression load and water blast shock wave. The dynamic mechanical responses of those coatings under these two loading cases were compared. Finite element simulations have been undertaken using the ABAQUS/Explicit software package to provide insights into the coating's working mechanism and the relation between compression behavior and water blast shock resistance. The rubber materials were modeled as hyperelastic materials. The reaction force was selected as the major comparative criterion. It is concluded that when under dynamic compressive load, the cell topology played an important role at high speed, and when under underwater explosion, the honeycomb coatings can improve the shock resistance significantly at the initial stage. For honeycomb coatings with a given relative density, although structural absorbed energy has a significant contribution in the shock resistance, soft coating can significantly reduce the total incident impulse at the initial fluid-structure interaction stage. Further, a smaller fraction of incident impulse is imparted to the honeycomb coating with lower compressive strength.
A Study of Three-Dimensional Acoustic Scattering by Arbitrary Distribution Multibodies Using Extended Immersed Boundary Method
Authors: Jiang Yongsong , Wang Xiaoyu , Jing Xiaodong , Sun Xiaofeng
Published: February 2014

A three-dimensional computational model for acoustic scattering with complex geometries is presented, which employs the immersed boundary technique to deal with the effect of both hard and soft wall boundary conditions on the acoustic fields. In this numerical model, the acoustic field is solved on uniform Cartesian grids, together with simple triangle meshes to partition the immersed body surface. A direct force at the Lagrangian points is calculated from an influence matrix system, and then spreads to the neighboring Cartesian grid points to make the acoustic field satisfy the required boundary condition. This method applies a uniform stencil on the whole domain except at the computational boundary, which has the benefit of low dispersion and dissipation errors of the used scheme. The method has been used to simulate two benchmark problems to validate its effectiveness and good agreements with the analytical solutions are achieved. No matter how complex the geometries are, single body or multibodies, complex geometries do not pose any difficulty in this model. Furthermore, a simple implementation of time-domain impedance boundary condition is reported and demonstrates the versatility of the computational model.
Bryan's Factor for Truncated Spherical and Conical Shells
Authors: Narasimhan K. Y.
Published: February 2014

Closed-form expressions are derived for the Bryan's factor of truncated spherical and conical shells through a Galerkin procedure. Results lead to the value obtained by G. H. Bryan for the case of the ring, thereby demonstrating accuracy of the method. It is shown that the Bryan's factor depends only on the shape of the structure and the modes of vibration. The material properties are required to determine the resonating frequency and the Q-factor.
Elasto-Dynamic Behavior of a Two-Dimensional Square Lattice With Entrained Fluid II: Microstructural and Homogenized Models
Authors: Dorodnitsyn Vladimir , Spadoni Alessandro
Published: February 2014

This paper presents a detailed study of the pressure waves and effective mechanical properties of a closed-cell cellular solid with entrained fluid. Plane-harmonic-waves are analyzed in a periodic square with a finite-element model of a representative-volume element, which explicitly considers fluid-structure interactions, structural deformations, and the fluid dynamics of entrained fluid. The wall, cavity, and coupled-system resonance frequencies are identified as key parameters that describe the propagation characteristics. A tube-piston model based on computed microstructural deformations allows us to determine the effective stiffness tensor of an equivalent continuum at the macroscale. The analysis of dispersion surfaces indicates a single isotropic pressure mode for frequencies below resonance of the lattice walls, unlike Biot's theory which predicts two pressure modes. Shear modes are instead strongly anisotropic for all values of relative density ρ* describing both cellular ρ*<0.3 and porous solids ρ*≥0.3. The dependence of the pressure wave phase velocity on the relative density is analyzed for varying properties of the entrained fluid. Depending on the relative density and mass coupling of the solid and fluid phases, the microstructural deformations can be of three types: bending, through-the-thickness, and the combination of the two. For heavy and stiff entrained fluid, the bending regime is confined to extremely small values of relative density, whereas for light fluid such as a gas, deformations are of the bending-type for ρ*<0.1. Through-the-thickness deformations appear only for the heavy entrained fluid for large values of ρ*.
Syngas and Hydrogen Production by Cyclic Redox of ZrO2-Supported CeO2 in a Volumetric Receiver-Reactor
Authors: Tak Jang Jong , June Yoon Ki , Young Han Gui
Published: February 2014

In order to utilize sustainable solar energy, cyclic operations of syngas production by methane reforming (reduction) and subsequent hydrogen production by water splitting (oxidation) were performed by using simulated solar-light irradiation to ZrO2-supported CeO2 particles which were coated on a SiC ceramic foam disk. This redox process is a promising chemical pathway for storage and transportation of solar heat by converting solar energy to chemical energy. By properly adjusting the methane reforming time, carbon deposition due to the undesirable methane decomposition could be avoided. The produced syngas had the H2/CO ratio of 2.0, which is suitable for the Fischer–Tropsch synthesis or methanol synthesis, and the produced pure hydrogen can be used for fuel cells. When the cyclic reactions were repeated several times at two temperatures (800 °C, 900 °C), the conversion of CeO2 and the H2 yield were reasonable and were maintained nearly constant from the second cycle, exhibiting good stability of the redox process.
Analysis of a Hybrid PV/T Concept Based on Wavelength Selective Mirror Films
Authors: Ulavi Tejas U. , Davidson Jane H. , Hebrink Tim
Published: February 2014

The technical performance of a nontracking hybrid PV/T concept that uses a wavelength selective film is modeled. The wavelength selective film is coupled with a compound parabolic concentrator (CPC) to reflect and concentrate the infrared portion of the solar spectrum onto a tubular absorber while transmitting the visible portion of the spectrum to an underlying thin-film photovoltaic module. The optical performance of the CPC/selective film is obtained through Monte Carlo ray tracing (MCRT). The CPC geometry is optimized for maximum total energy generation for a roof-top application. Applied to a roof-top in Phoenix, AZ, the hybrid PV/T provides 20% more energy compared with a system of the same area with independent side-by-side solar thermal and PV modules, but the increase is achieved at the expense of a decrease in the electrical efficiency from 8.8% to 5.8%.
Energy Analysis of Solar Home Lighting System With Microcontroller-Based Charge Controller
Authors: Werulkar Ashutosh S. , Kulkarni P. S.
Published: February 2014

In this paper, a solar powered home lighting system in the Electrical Engineering Department of Visvesvaraya National Institute of Technology (VNIT), Nagpur is analyzed for energy using a personal computer simulation program with integrated circuit emphasis (circuit simulation software, PSpice 9.1). The home lighting system consists of a solar panel of 37 Wp, a 45 Ah battery, a solar charge controller, dc loads of two 9 W compact fluorescent lamps (CFLs), and a dc fan of 14 W. Through the solar panel, the battery is charged during day time. In the night, when solar power is not available, the battery provides power as a backup to the dc load consisting of two CFLs and a dc fan. The aim of the paper is to analyze the solar home lighting system for energy gain/loss with a microcontroller-based charge controller. From the analysis, it is concluded that the solar home lighting system is not designed for continuous energy gain as per manufacturer's specifications. The design needs to be modified to have energy gain in the system for Nagpur, India. A designed microcontroller-based charge controller is also analyzed. The advantages of a microcontroller 89C2051-based charge controller are its simple design, low cost, logic change facility with change of programming of microcontroller, presence of liquid crystal display (LCD) with battery charge status, and display of different messages. Ride software is used as an assembler for generating the required hex file of program and it is used for burning in the microcontroller IC with the help of Vegarobokit (a microcontroller programmer developer) to make a microcontroller programmer.
Robust Stabilization of a Class of Nonaffine Quadratic Polynomial Systems: Application in Magnetic Ball Levitation System
Authors: Binazadeh T. , Shafiei M. H. , Rahgoshay M. A.
Published: February 2014

In this paper, a new approach is suggested for asymptotic stabilization of a class of nonaffine quadratic polynomial systems in the presence of uncertainties. The designed controller is based on the sliding mode (SM) technique. This technique is basically introduced for nonlinear affine systems and in facing with nonaffine systems; attempts have been made to transform the system into an affine form. Lake of robustness is the main problem of the transformation approach. In this paper, a simple but effective idea is suggested to stabilize a system in its nonaffine structure and, therefore, a nonrobust transformation is not needed. In the proposed method, according to upper and lower bounds of uncertainties, two quadratic polynomials are constructed and with respect to the position of the roots of these polynomials, a new SM controller is proposed. This idea is also used for robust stabilization of a practical nonaffine quadratic polynomial system (magnetic ball levitation system). Computer simulations show the efficiency of the proposed control law.
Time-Dependent Corrosion Growth Modeling Using Multiple In-Line Inspection Data
Authors: Zhang Shenwei , Zhou Wenxing , Al-Amin Mohammad , Kariyawasam Shahani , Wang Hong
Published: February 2014

This paper describes a nonhomogeneous gamma process-based model to characterize the growth of the depth of corrosion defect on oil and gas pipelines. All the parameters in the growth model are assumed to be uncertain; the probabilistic characteristics of these parameters are evaluated using the hierarchical Bayesian methodology by incorporating the defect information reported by the multiple in-line inspections (ILIs) as well as the prior knowledge about these parameters. The bias and random measurement error associated with the ILI tools as well as the correlation between the measurement errors associated with different ILI tools are taken into account in the analysis. The application of the model is illustrated using an example involving real ILI data on a pipeline that is currently in service. The results suggest that the model in general can predict the growth of corrosion defects reasonably well. The proposed model can be used to facilitate the development and application of reliability-based pipeline corrosion management.
Inextensible Beam and Plate Theory: Computational Analysis and Comparison With Experiment
Authors: Tang Deman , Zhao Minghui , Dowell Earl H.
Published: February 2014

A new inextensible theory of beam and plate deformation has been developed. For validation of this inextensible beam and plate theory, computational codes for the static and dynamic nonlinear beam and plate modal equations have been developed. The computations and experiments for static loading and deformation of a beam show that the inextensible theory produces results in excellent agreement with experiment. Also, a comparison of the inextensible theory for a plate with a static experiment is encouraging. Finally, a numerical study of dynamic deflection for an inextensible beam and plate has also been made. The results show a hysteresis dynamic response that depends on whether the excitation frequency is increasing or decreasing for the stiffness nonlinearity only or for the inertia nonlinearity only. The inertia nonlinear force has a significant effect on the dynamic response in the resonant frequency range.
Numerical Study of Multistage Transcritical Organic Rankine Cycle Axial Turbines
Authors: Sciacovelli L. , Cinnella P.
Published: February 2014

Transonic flows through axial, multistage, transcritical organic rankine cycle (ORC) turbines are investigated by using a numerical solver including advanced multiparameter equations of state and a high-order discretization scheme. The working fluids in use are the refrigerants R134a and R245fa, classified as dense gases due to their complex molecules and relatively high molecular weight. Both inviscid and viscous numerical simulations are carried out to quantify the impact of dense gas effects and viscous effects on turbine performance. Both supercritical and subcritical inlet conditions are studied for the considered working fluids. In the former case, flow across the turbine is transcritical, since turbine output pressure is subcritical. Numerical results show that, due to dense gas effects characterizing the flow at supercritical inlet conditions, supercritical ORC turbines enable, for a given pressure ratio, a higher isentropic efficiency than subcritical turbines using the same working fluid. Moreover, for the selected operating conditions, R134a provides a better performance than R245fa.
Unsteady Analysis on the Effects of Tip Clearance Height on Hot Streak Migration Across Rotor Blade Tip Clearance
Authors: Liu Zhaofang , Liu Zhao , Feng Zhenping
Published: February 2014

This paper presents an investigation on the hot streak migration across rotor blade tip clearance in a high pressure gas turbine with different tip clearance heights. The blade geometry is taken from the first stage of GE-E3 turbine engine. Three tip clearances, 1.0%, 1.5%, and 2.5% of the blade span with a flat tip were investigated, respectively, and the uniform and nonuniform inlet temperature profiles were taken as the inlet boundary conditions. A new method for heat transfer coefficient calculation recommended by Maffulli and He has been adopted. By solving the unsteady compressible Reynolds-averaged Navier–Stokes equations, the time dependent solutions were obtained. The results indicate that the large tip clearance intensifies the leakage flow, increases the hot streak migration rate, and aggravates the heat transfer environment on the blade tip. However, the reverse secondary flow dominated by the relative motion of casing is insensitive to the change of tip clearance height. Attributed to the high-speed rotation of rotor blade and the low pressure difference between both sides of blade, a reverse leakage flow zone emerges over blade tip near trailing edge. Because it is possible for heat transfer coefficient distributions to be greatly different from heat flux distributions, it becomes of great concern to combine both of them in consideration of hot streak migration. To eliminate the effects of blade profile variation due to twist along the blade span on the aerothermal performance in tip clearance, the tested rotor (straight) blade and the original rotor (twisted) blade of GE-E3 first stage with the same tip profile are compared in this paper.
Simple Mechanistically Consistent Formulation for Volume-of-Fluid Based Computations of Condensing Flows
Authors: Rattner Alexander S. , Garimella Srinivas
Published: February 2014

Numerous investigations have been conducted to extend adiabatic liquid–gas volume-of-fluid (VOF) flow solvers to include condensation phenomena by adding an energy equation and phase-change source terms. Some proposed phase-change models employ empirical rate parameters, or adapt heat-transfer correlations, and thus must be tuned for specific applications. Generally applicable models have also been developed that rigorously resolve the phase-change process, but require interface reconstruction, significantly increasing computational cost, and software complexity. In the present work, a simplified first-principles-based condensation model is developed, which forces interface-containing mesh cells to the equilibrium state. The operation on cells instead of complex interface surfaces enables the use of fast graph algorithms without reconstruction. The model is validated for horizontal film condensation, and converges to exact solutions with increasing mesh resolution. Agreement with established results is demonstrated for smooth and wavy falling-film condensation.
Arginine-glycine-glutamine and serine-isoleucine-lysine-valine-alanine-valine modified poly(l-lactide) films: Bioactive molecules used for surface grafting to guide cellular contractile phenotype
Authors: Boccafoschi Francesca , Fusaro Luca , Botta Margherita , Ramella Martina , Chevallier Pascale , Mantovani Diego , Cannas Mario
Published: February 2014

Tissue engineering is defined as “an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function.” The biological substitutes can be developed with the help of natural or synthetic materials. Polymeric materials are primarily used, because of the high variability in mechanical, physical, and chemical properties. Biodegradable polymers are object of the majority of studies, because of the ability to be degraded by the host organism, avoiding late stent thrombosis unlike permanent grafts. Poly-l-lactide acid (PLLA) is one of the most used polymers in research. In order to improve the material's bioactivity, in this work, PLLA surface was modified by grafted arginine-glycine-glutamine (RGD), a fibronectin derived adhesion motif, and serine-isoleucine-lysine-valine-alanine-valine (SIKVAV), a laminin derived motif, and rat cardiac (H9C2) and mouse (C2C12) myoblasts proliferation and differentiation on modified PLLA were evaluated. In order to verify the surface modification, x-ray photoelectron spectroscopy analysis was performed. After seeding, cells’ viability was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay while proliferating cell nuclear antigen expression was used to investigate cell proliferation. Myf5, Myogenin and Myosin heavy chain were used to analyze cell differentiation. Moreover, RGD peptide slightly inhibited rat myoblast (H9C2) proliferation, whereas less strong effect was observed on C2C12. However, both cell lines showed to enhance the contractile phenotype in the presence of SIKVAV peptides. These results suggest that bioactive molecules grafting could be useful on polymeric scaffolds for guiding cell phenotype expression, and, to ultimately maintain adequate biological characteristics suitable for the tissue functional regeneration.
Optimum growth window for InAs/GaInSb superlattice materials tailored for very long wavelength infrared detection
Authors: Haugan Heather J. , Brown Gail J. , Mahalingam Krishnamurthy , Grazulis Larry , Noe Gary T. , Ogden Nathan E. , Kono Junichiro
Published: February 2014

The authors report growth studies to develop an InAs/GaInSb superlattice (SL) material for very long wavelength infrared detection. They select a SL structure of 47.0 Å InAs/21.5 Å Ga0.75In0.25Sb that is designed for the greatest possible detectivity, and tune growth conditions to achieve the best quality ternary material. Since the material quality of grown layers is particularly sensitive to extrinsic defects such as nonradiative recombination centers generated during the growth process, the authors investigate the effect of the growth temperature (Tg) on the spectral photoresponse (PR) and carrier recombination lifetime using photoconductivity and time-resolved differential reflectivity measurements. Results indicate that a molecular beam epitaxy growth process the authors developed produces a consistent energy gap around 50 meV, determined from the PR spectra, but the intensity of the spectra is sensitive to Tg. For SLs grown at Tg between 390 and 470 °C, the PR signal intensity gradually increases as Tg increases from 400 to 440 °C, reaching a maximum at 440 °C. Outside this growth window, the SL quality deteriorates very rapidly. However, the carrier recombination lifetime measured at 300 K was not sensitive to Tg. Although the SL sample grown at 430 °C produced the longest lifetime of 84 ns, the average 300 K lifetime value remained around 74 ns.
Effects of Contralateral Movement on the Soleus H-Reflex During In-Phase and Antiphase Movements of the Ankles
Authors: Hiraoka Koichi , Chujyo Yuta , Hatano Sakiko , Fukuhara Kohei , Yamanaka Yuki
Published: February 2014

We investigated the effects of contralateral movement on the soleus H-reflex during bilateral movement of the ankles. The soleus H-reflex was evoked during unilateral or in-phase or antiphase bilateral ankle movement in healthy humans. The soleus H-reflex amplitude during antiphase movement was not significantly different from that during in-phase movement. The H-reflex amplitude during inphase movement was not significantly different from that during unilateral movement of the tested ankle. The H-reflex amplitude in the maximal plantar flexion phase of the tested ankle during antiphase movement was significantly smaller than that in the corresponding phase during unilateral movement. The amount of the decrease was 21%. The effect of contralateral movement is prominent during antiphase movement of the ankles.
A Matter of Timing
Authors: Hines Pamela
Published: February 2014

A regulatory circuit controlling plant flowering genes leads the way to reconstruction of a time-delay control system.
Battle of the Sexes
Authors: Ray L. Bryan
Published: February 2014

Merely perceiving the opposite sex can shorten an animal’s life span.
Pharmacokinetics of Isoniazid in Low-Birth-Weight and Premature Infants
Authors: Bekker A. , Schaaf H. S. , Seifart H. I. , Draper H. R. , Werely C. J. , Cotton M. F. , Hesseling A. C.
Published: February 2014

Isoniazid (INH) is recommended for use as posttuberculosis exposure preventive therapy in children. However, no pharmacokinetic data are available for INH treatment in low-birth-weight (LBW) infants, who undergo substantial developmental and physiological changes. Our objectives in this study were to determine the pharmacokinetic parameters of INH at a dose of 10 mg/kg of body weight/day and to define its pharmacokinetics relative to the arylamine
N
-acetyltransferase-2 (
NAT2
) genotype. An intensive prospective pharmacokinetic sampling study was conducted at Tygerberg Children's Hospital, South Africa, in which we measured INH blood plasma concentrations at 2, 3, 4 and 5 h postdose. Twenty LBW infants (14 male, 16 exposed to HIV) were studied. The median birth weight was 1,575 g (interquartile range, 1,190 to 2,035 g) and the median gestational age was 35 weeks (interquartile range, 34 to 38 weeks). The
NAT2
acetylation statuses of the infants were homozygous slow (SS) (5 infants), heterozygous intermediate (FS) (11 infants), and homozygous fast (FF) (4 infants). Using a noncompartmental analysis approach, the median maximum drug concentration in blood serum (
C
max
) was 5.63 μg/ml, the time after drug administration to reach
C
max
T
max
) was 2 h, the area under the concentration-time curve from 2 to 5 h (AUC
2–5
) was 13.56 μg · h/ml, the half-life (
t
1/2
) was 4.69 h, and the elimination constant rate (
k
el
) was 0.15 h
−1
. The alanine aminotransferase levels were normal, apart from 2 isolated values at two and three times above the normal levels. Only the three-times-elevated value was repeated at 6 months and normalized. All LBW infants achieved target INH blood plasma concentrations comparable to the adult values. Reduced elimination was observed in smaller and younger infants and in slow acetylators, cautioning against higher doses. The safety data, although limited, were reassuring. More data, however, are required for newborn infants.
Interspecific Quorum Sensing Mediates the Resuscitation of Viable but Nonculturable Vibrios
Authors: Ayrapetyan Mesrop , Williams Tiffany C. , Oliver James D.
Published: February 2014

Entry and exit from dormancy are essential survival mechanisms utilized by microorganisms to cope with harsh environments. Many bacteria, including the opportunistic human pathogen
Vibrio vulnificus
, enter a form of dormancy known as the viable but nonculturable (VBNC) state. VBNC cells can resuscitate when suitable conditions arise, yet the molecular mechanisms facilitating resuscitation in most bacteria are not well understood. We discovered that bacterial cell-free supernatants (CFS) can awaken preexisting dormant vibrio populations within oysters and seawater, while CFS from a quorum sensing mutant was unable to produce the same resuscitative effect. Furthermore, the quorum sensing autoinducer AI-2 could induce resuscitation of VBNC
V. vulnificus in vitro
, and VBNC cells of a mutant unable to produce AI-2 were unable to resuscitate unless the cultures were supplemented with exogenous AI-2. The quorum sensing inhibitor cinnamaldehyde delayed the resuscitation of wild-type VBNC cells, confirming the importance of quorum sensing in resuscitation. By monitoring AI-2 production by VBNC cultures over time, we found quorum sensing signaling to be critical for the natural resuscitation process. This study provides new insights into the molecular mechanisms stimulating VBNC cell exit from dormancy, which has significant implications for microbial ecology and public health.
Viruses in a 14th-Century Coprolite
Authors: Appelt Sandra , Fancello Laura , Le Bailly Matthieu , Raoult Didier , Drancourt Michel , Desnues Christelle
Published: February 2014

Coprolites are fossilized fecal material that can reveal information about ancient intestinal and environmental microbiota. Viral metagenomics has allowed systematic characterization of viral diversity in environmental and human-associated specimens, but little is known about the viral diversity in fossil remains. Here, we analyzed the viral community of a 14th-century coprolite from a closed barrel in a Middle Ages site in Belgium using electron microscopy and metagenomics. Viruses that infect eukaryotes, bacteria, and archaea were detected, and we confirmed the presence of some of them by
ad hoc
suicide PCR. The coprolite DNA viral metagenome was dominated by sequences showing homologies to phages commonly found in modern stools and soil. Although their phylogenetic compositions differed, the metabolic functions of the viral communities have remained conserved across centuries. Antibiotic resistance was one of the reconstructed metabolic functions detected.
Growth of Myxococcus xanthus in Continuous-Flow-Cell Bioreactors as a Method for Studying Development
Authors: Smaldone Gregory T. , Jin Yujie , Whitfield Damion L. , Mu Andrew Y. , Wong Edward C. , Wuertz Stefan , Singer Mitchell
Published: February 2014

Nutrient sensors and developmental timers are two classes of genes vital to the establishment of early development in the social soil bacterium
Myxococcus xanthus
. The products of these genes trigger and regulate the earliest events that drive the colony from a vegetative state to aggregates, which ultimately leads to the formation of fruiting bodies and the cellular differentiation of the individual cells. In order to more accurately identify the genes and pathways involved in the initiation of this multicellular developmental program in
M. xanthus
, we adapted a method of growing vegetative populations within a constant controllable environment by using flow cell bioreactors, or flow cells. By establishing an
M. xanthus
community within a flow cell, we are able to test developmental responses to changes in the environment with fewer concerns for effects due to nutrient depletion or bacterial waste production. This approach allows for greater sensitivity in investigating communal environmental responses, such as nutrient sensing. To demonstrate the versatility of our growth environment, we carried out time-lapse confocal laser scanning microscopy to visualize
M. xanthus
biofilm growth and fruiting body development, as well as fluorescence staining of exopolysaccharides deposited by biofilms. We also employed the flow cells in a nutrient titration to determine the minimum concentration required to sustain vegetative growth. Our data show that by using a flow cell,
M. xanthus
can be held in a vegetative growth state at low nutrient concentrations for long periods, and then, by slightly decreasing the nutrient concentration, cells can be allowed to initiate the developmental program.
Conventional and Real-Time PCRs for Detection of Erwinia piriflorinigrans Allow Its Distinction from the Fire Blight Pathogen, Erwinia amylovora
Authors: Barbé Silvia , Bertolini Edson , Roselló Montserrat , Llop Pablo , López María M.
Published: February 2014

Erwinia piriflorinigrans
is a new pathogenic species of the bacterial genus
Erwinia
that has been described recently in Spain. Accurate detection and identification of
E. piriflorinigrans
are challenging because its symptoms on pear blossoms are similar to those caused by
Erwinia amylovora
, the causal agent of fire blight. Moreover, these two species share phenotypic and molecular characteristics. Two specific and sensitive conventional and real-time PCR protocols were developed to identify and detect
E. piriflorinigrans
and to differentiate it from
E. amylovora
and other species of this genus. These protocols were based on sequences from plasmid pEPIR37, which is present in all strains of
E. piriflorinigrans
analyzed. After the stability of the plasmid was demonstrated, the specificities of the protocols were confirmed by the amplification of all
E. piriflorinigrans
strains tested, whereas 304 closely related pathogenic and nonpathogenic
Erwinia
strains and microbiota from pear trees were not amplified. In sensitivity assays, 10
3
cells/ml extract were detected in spiked plant material by conventional or real-time PCR, and 10
2
cells/ml were detected in DNA extracted from spiked plant material by real-time PCR. The protocols developed here succeeded in detecting
E. piriflorinigrans
in 102 out of 564 symptomatic and asymptomatic naturally infected pear samples (flowers, cortex stem tissue, leaves, shoots, and fruitlets), in necrotic
Pyracantha
sp. blossoms, and in necrotic pear and apple tissues infected with both
E. amylovora
and
E. piriflorinigrans
. Therefore, these new tools can be used in epidemiological studies that will enhance our understanding of the life cycle of
E. piriflorinigrans
in different hosts and plant tissues and its interaction with
E. amylovora
.
Farm Management, Environment, and Weather Factors Jointly Affect the Probability of Spinach Contamination by Generic Escherichia coli at the Preharvest Stage
Authors: Park Sangshin , Navratil Sarah , Gregory Ashley , Bauer Arin , Srinath Indumathi , Szonyi Barbara , Nightingale Kendra , Anciso Juan , Jun Mikyoung , Han Daikwon , Lawhon Sara , Ivanek Renata
Published: February 2014

The National Resources Information (NRI) databases provide underutilized information on the local farm conditions that may predict microbial contamination of leafy greens at preharvest. Our objective was to identify NRI weather and landscape factors affecting spinach contamination with generic
Escherichia coli
individually and jointly with farm management and environmental factors. For each of the 955 georeferenced spinach samples (including 63 positive samples) collected between 2010 and 2012 on 12 farms in Colorado and Texas, we extracted variables describing the local weather (ambient temperature, precipitation, and wind speed) and landscape (soil characteristics and proximity to roads and water bodies) from NRI databases. Variables describing farm management and environment were obtained from a survey of the enrolled farms. The variables were evaluated using a mixed-effect logistic regression model with random effects for farm and date. The model identified precipitation as a single NRI predictor of spinach contamination with generic
E. coli
, indicating that the contamination probability increases with an increasing mean amount of rain (mm) in the past 29 days (odds ratio [OR] = 3.5). The model also identified the farm's hygiene practices as a protective factor (OR = 0.06) and manure application (OR = 52.2) and state (OR = 108.1) as risk factors. In cross-validation, the model showed a solid predictive performance, with an area under the receiver operating characteristic (ROC) curve of 81%. Overall, the findings highlighted the utility of NRI precipitation data in predicting contamination and demonstrated that farm management, environment, and weather factors should be considered jointly in development of good agricultural practices and measures to reduce produce contamination.