bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified PIO Design for Robust Unknown Input Estimation
Authors: Krajcin Idriz , So¨ffker Dirk
Published: June 2008

In this contribution, an extension for the Proportional-integral-Observer (PIO) is presented. The observer can estimate unknown forces with impact character or e.g. friction forces acting on a system. Therefore, the observer does not use any information about the contact. The classical PIO is in the case of relevant measurement noise not able to achieve satisfactory performance. The new formulated observer design permits to estimate unknown input forces acting on a system while measurement noise is present. The main focus of the paper is a new extension of the PIO for general applications and an experimental improvement of the performance, given for the first time with this paper. The introduced extension is especially to improve the observer robustness to measurement noise. This is an issue of high practical importance due to the fact that the PIO-scheme works with high gains, getting sensitive to measurement noise. With the introduced extension, the sensitivity problem is attenuated. The estimation of impact forces acting on a fixed elastic beam is used as a principle example. The introduced method works generally and can be applied to different tasks for elastic structures.
Stability Analysis of the Rocking Block: Numerical Investigations on Analytical Stability Boundaries
Authors: Ageno Alessio , Sinopoli Anna
Published: June 2008

The present paper illustrates some recently developed techniques to evaluate stability features, such as characteristic multipliers and Lyapunov’s exponents, for a problem with strong discontinuities. The problem analyzed concerns the plane dynamics of a rigid block simply supported on a harmonically moving rigid ground. In previous papers [1–3] many aspects have been investigated and the following results have been carried out: 1. the general procedure to approach numerically the problem has been outlined; 2. a rigorous method has been established to calculate characteristic multipliers and Lyapunov’s exponents at the instants of discontinuities; 3. the stability boundaries of symmetric sub-harmonic responses have been drafted by means of closed-form analytical methods based on various hypotheses of linearization. In this paper the new capacities allowed by the techniques and methods pointed out at the previous points 1., 2. and 3. are exploited with the aims: • to investigate numerically in the occurrence of dissipative impacts the features of dynamic responses across the upper boundary of a stability range (i.e. that of the (1,3) sub-harmonic response) included in a larger one (i.e. that of the (1,1) response); • to analyze the responses attainable with a value of the restitution coefficient equal to 1 to describe the impulsive phases (namely for non-dissipative impacts); in previous works, these responses have been classified as quasi-periodic or chaotic [4]. By means of the new techniques proposed and implemented, it has been possible to classify and analyze more deeply such presumed quasi-periodic or chaotic responses and at the same time to clarify the role played by the initial conditions.
Modeling and Numerical Investigation of Non-Linear Dynamics of a Mono-Cylinder Combustion Engine
Authors: Awrejcewicz Jan , Kudra Grzegorz
Published: June 2008

A mono-cylinder combustion engine is modeled as the triple physical pendulum with barriers. The proposed model exhibits well known six stages of sliding of a piston along a cylinder per engine cycle and it can be useful while investigating impacts between the piston and the cylinder.
Modeling and Identification of Polyurethane Foam in Uniaxial Compression: Combined Elastic and Viscoelastic Response
Authors: Ippili Rajani K. , Widdle Richard D. , Davies Patricia , Bajaj Anil K.
Published: June 2008

Polyurethane foam used in automotive seating applications is a highly nonlinear and viscoelastic material. These properties are manifested even in its quasi-static response. In this paper, two different approaches to model and identify these material properties are presented. In both the approaches the viscoelastic property is assumed linear and modeled by a convolution of the input with a relaxation kernel that is a sum of exponentials (hereditary integral approach). The elastic force contribution is however assumed nonlinear and modeled by a polynomial in one approach, and by a model derived from Ogden strain energy function in the other. Uniaxial compression data from experiments is used to identify the parameters of the models. The robustness of the identification procedures and the issues associated with them are also discussed.
Low-Cost Control of Impact Hammer Performance
Authors: Jerrelind Jenny , Dankowicz Harry
Published: June 2008

This paper considers the dependence of the performance of a Braille printer impact hammer on system parameters, specifically the lag time between subsequent current pulses and the location of a back stop constraining the oscillations of the hammer core. Here, the goal is to improve the printer speed while maintaining readability of the Braille type and preventing tears in the paper. Based on observations of the limit sets for the hammer-core dynamics, a low-cost feedback control algorithm is proposed for affecting the stability of otherwise unstable periodic oscillations with more desirable operating characteristics.
The Application of Adaptive Canceling in Chaos Identification
Authors: Liu Shuyong , Zhu Shijian , Liu Zhenming , Qian Weiian
Published: June 2008

The time domain response of a system is inevitably contaminated by noise arising from the environment as well as the measuring system itself. So an effective method is needed to reduce the noise components. The characteristic of the chaotic signal and noise in the frequency domain is analyzed. An adaptive canceling system based on the LMS algorithm is applied to process the contaminated signal. The simulation result shows that the adaptive technique can meet the goal.
A Proper Orthogonal Decomposition Analysis to Identify the Dominant Modes of the Steady State Acoustic Pressure Field in a Cavity
Authors: Georgiou Ioannis T. , Papadopoulos Christos I.
Published: June 2008

The technique of Proper Orthogonal Decomposition (POD) has been used to develop an identification tool to analyze steady state dynamics in acoustics. The information on the dynamics needed for the POD technique is obtained by solving numerically with the method of finite elements the wave equation inside a cavity. The POD technique identifies optimum spatial patterns it terms of Proper Orthogonal Modes. The steady state sound pressure field in a cavity excited by a single harmonic source responds with a very small number of POD modes. Under certain forcing conditions, the POD modes are identical to the Fourier acoustic modes. The POD technique of Proper Orthogonal Decomposition (POD) proves to be a very effective identification tool.
Nonlinear Averaging of Multi-Sensor Data
Authors: Suranthiran Sugathevan , Jayasuriya Suhada
Published: June 2008

Considered in this paper is a framework for combining multiple sensor data to obtain a single inference. The task of fusing multi-sensor data is very challenging when no information about the sensor or estimation models is available. Kalman Filtering and other model-based techniques cannot be used to obtain a reliable inference. Linear Averaging of data is probably the simplest technique available, however, there is no guarantee that the fused measurement is, in fact, the best estimation. The problem will be worsened if one or more sensor measurements are faulty. In this paper, we analyze this problem and propose an effective multi-sensor fusion methodology. It is shown that a reliable solution can be obtained by nonlinearly averaging the multiple measurements. The proposed technique is well suited to identify outliers in the sensor measurements as well as to detect faulty sensor measurements. The developed algorithm is versatile in the sense that prior knowledge or information about sensors can be easily incorporated to improve the accuracy further. Illustrative examples and simulation data are presented to validate the proposed scheme.
Dynamics and Touchdown in Electrostatic MEMS
Authors: Flores Gilberto , Mercado Gema A. , Pelesko John A.
Published: June 2008

Perhaps the most widely known nonlinear phenomena in nano- and microelectromechanical systems is the “pull-in” or “jump-to-contact” instability. In this instability, when applied voltages are increased beyond a certain critical voltage there is no longer a steady-state configuration of the device where mechanical members remain separate. This instability affects the design of many devices. It may present a limitation on the stable range of operation, as with a micropump, or may be utilized to create contact, as with a microvalve. Here, a mathematical model of an idealized electrostatically actuated MEMS or NEMS device is constructed for the purpose of studying the dynamics and touchdown behavior of systems operated in the pull-in regime. The model is analyzed in the viscosity dominated limit. This gives rise to a non-linear parabolic equation of reaction-diffusion type. The model is studied using a combination of analytical and numerical techniques.
Nonlinear Vibrations in Contact Atomic Force Microscopy
Authors: Turner Joseph A.
Published: June 2008

The nonlinear vibration response of an atomic force microscope cantilever in contact with a vibrating sample is investigated. The tip-sample contact is modeled using Hertzian contact mechanics. The method of multiple scales is used to analyze this problem in which it is assumed that the beam remains in contact with the moving surface at all times. The primary result from this analysis is the amplitude-frequency relation for the various flexural modes. The amplitude-frequency curves exhibit softening behavior as expected. The amount of softening is shown to depend on the linear contact stiffness as well as the specific mode. The modal sensitivity to nonlinearity is the result of the nonlinearity being restricted to a single position. The mode shape greatly affects the degree to which the nonlinearity influences the frequency response. The Hertzian restriction is then loosened slightly such that variations in nonlinear contact stiffness are examined. These results depend on the linear contact stiffness and mode number as well. The nonlinear vibration response is expected to provide new insight on the nonlinear tip mechanics present in these systems.
A Reduced-Order Model for Electrically Actuated Clamped Circular Plates
Authors: Vogl Gregory W. , Nayfeh Ali H.
Published: June 2008

We present an analytical reduced-order model (macromodel) for an electrostatically actuated clamped circular plate. After establishing the equations governing the plate, we discretize the system by using a Galerkin approach. Accordingly, the distributed-parameter equations are reduced to a finite system of ordinary-differential equations in time. We solve the equations for the equilibrium states due to a general electric potential and determine the natural frequencies of the axisymmetric modes for the stable deflected position. Finally, we validate the model by using data from experiments performed on silicon-based microelectromechanical systems (MEMS). The reduced-order model accounts for residual stress, allows for general design variables, and is also robust up to the pull-in instability. Consequently, our macromodel is general and computationally strong enough to be an effective design tool.
Design and Control of Active Magnetic Bearing System With Lorentz Force Type Axial Actuator
Authors: Kim Ha-Yong , Lee Chong-Won
Published: June 2008

As the size of 5-axis active magnetic bearing (AMB) gets smaller, the space limitation for installation of axial magnetic bearing unit becomes stringent. In this paper, a new type of compact, high-performance 5-axis AMB with solid cores and rotor is proposed, which consists of four permanent magnets, four U-shaped cores and 16 control coils. The proposed homopolar AMB system is levitated by the Lorentz type axial as well as Maxwell type radial forces. Based on the magnetic flux distribution analysis, the control algorithm is designed to account for the coupled effect between the radial and axial control fluxes. Experiments are also carried out with a prototype AMB system to validate the new design concept.
High-Performance Micro-Electrohydrodynamic Pump Actuator
Authors: Ali Kazim M. , Kashani Reza , Hallinan Kevin
Published: June 2008

The research aims at building a highly effective, miniaturized electrohydrodynamic pumped actuator. The actuator would provide greater performance in terms of higher force, higher displacement and equivalent bandwidth to the so-called smart materials (piezoelectric and magnetostrictive) actuators of comparable size. The EHD actuators find applications in active structure-borne noise abatement, active vibration control, precision pointing. The on-going research aims at parametrically understanding the actuator with respect to its geometry, contained dielectric fluid medium and electric fields. A multitude of prototypes will be designed, fabricated and tested to provide experimental benchmarking of the model predictions. At the same time, this experimental bench marking will provide practical expertise in both fabricating the concept and incorporating it into smart structures.
Viscoelastic Rotational Vibration Absorber for Remote Sensing Applications
Authors: Webster Adam L. , Semke William H.
Published: June 2008

The ability to eliminate, or effectively control, vibration in remote sensing applications is critical. Any perturbations of an imaging system are greatly magnified over the hundreds of kilometers from the orbiting space platform to the Earth’s surface. Space platforms, such as the International Space Station, are not as predictable or stable as many other spacecraft. Therefore, an effective vibration isolation and/or absorber system is needed that operates over a wide range of excitation frequencies. A passive system is also preferred to reduce the resources required, as well as provide a reliable and self-contained system. To accomplish these goals, a vibration amplitude limiting system has been developed that uses both vibration isolation and absorber components. Viscoelastic structural elements that act as both a spring and a damper in a single element are implemented in the design. This configuration also demonstrates a favorable frequency dependent response and produces a system with improved dynamic behavior compared to conventional spring and damper designs. This rotation limiting vibration system has been designed and analyzed for use in digital remote sensing imaging. The transmissibility and the ground jitter associated with the system are determined. A summary of these results will be presented along with a comparison to a more conventional vibration isolation/absorber system.
Control Modeling of Flexible Wall Cavity Vibroacoustic Systems
Authors: Kashani Reza
Published: June 2008

Vibroacoustic modeling of an enclosure with flexible walls is discussed. The block-diagram modeling method is based on formulating the modal parameters of the cavity with rigid walls and the structure with no fluid interaction, i.e. in-vacuo. Having the uncoupled modal models, the rigid wall cavity and in-vacuo structural modal are coupled, “in modal domain”, in a feedback manner. In addition to being computationally efficient, this modeling technique offers a very convenient platform, especially in block diagram based modeling softwares such as Simulink, for synthesis and analysis of active sound control in vibroacoustic systems. It allows for easy access to acoustic (pressure) or structural (acceleration/strain) variables for feedback or feedforward control purposes using structural (force/moment) or acoustic (volume velocity) actuation.
Energy Regenerative and Active Control Suspension
Authors: Okada Yohji , Kim Sang-Soo , Ozawa Keisuke
Published: June 2008

This paper introduces a variable resistance type energy regenerative suspension using PWM step-up chopper. The energy regenerative suspension has nonlinear characteristics with dead zone for low speed motion. Hence the energy is not regenerated nor has it damping force. In order to overcome this problem, a step-up chopper is introduced between the actuator and the charging circuit. This chopper is controlled by velocity-dependent PWM signal to improve the damping characteristics and the efficiency of the regenerative suspension. The suspension system changes its height according to the carrier load. Hence linear AC motor is used to the isolation actuator. A simple experiment was performed and the results showed better performance than the standard regenerative suspension. The system is planned to be modified incorporating active control. The fundamental idea and the configuration are introduced.
Effect of a Pothole on the Dynamics of an MDOF Vehicle
Authors: Pesterev Alexander V. , Bergman Lawrence A. , Tan Chin An , Yang Bingen
Published: June 2008

A technique is developed to assess the dynamic contact forces arising from passage of road surface irregularities by a vehicle modeled as a general MDOF system. The equations governing vibration of a vehicle moving along an uneven profile are, first, transformed to the state-space form and, then, to a system of uncoupled first-order complex differential equations. For a local roadway irregularity described functionally, all equations are solved analytically. The solutions obtained are combined to give dependencies of the harmonic components of the contact forces on the vehicle speed and irregularity dimensions. The technique developed is applied to the calculation of the coefficients of the harmonic components of the contact forces arising after the passage of a “cosine” pothole. One interesting phenomenon reported in the DIVINE project [1], regarding the replacement of a steel suspension by an air suspension resulting in an increase in the maximum response of short-span bridges, is explained by applying the technique suggested. The discussion is amply illustrated by examples of the application of the technique to the calculation of the tire forces due to a pothole for two simple vehicle models.
A New Perturbation Method for Oscillatory Systems
Authors: Mickens Ronald E.
Published: June 2008

We present preliminary results on a new perturbation technique that combines the fundamental elements of the methods of equivalent linearization and first-order averaging. The importance of this procedure is derived from the fact that it can be applied to ODE’s having oscillatory solutions, but for which no harmonic oscillator limiting equation exists. The procedure is illustrated by showing how it can be used to calculate analytical approximations to two nonlinear ODE’s. Comparison with the corresponding accurate numerical solutions is also given. The work presented here was supported in part by research grants from DOE and the MBRS-SCORE Program at Clark Atlanta University.
Degenerate Cases in Using the Direct Method
Authors: Sipahi Rifat , Olgac Nejat
Published: June 2008

A practical stability analysis, the Direct Method, for linear time invariant, time delayed systems (LTI-TDS) is revisited in this work considering the degenerate system dynamics. The principal strengths and enabling novelties of the method are reviewed along with its structured steps involved for assessing the stability. Uncommon in the literature, the Direct Method can handle large dimensional systems (e.g. larger than 2) very comfortably, it returns an explicit formula for the exact stability posture of the system for a given time delay, as such it reveals the possible detached stability pockets throughout the time delay axis. Both retarded and neutral classes of LTI-TDS are considered in this work. The main contribution here is to demonstrate the ability of the Direct Method in tackling degenerate cases. Along with the analytical arguments, example case studies are provided for a group of degeneracies. It is shown that the new method is capable of resolving them without any difficulty.
Modeling and Free Vibration of Flex Circuits in Hard Disk Drives
Authors: Wickert Jonathan
Published: June 2008

A flex circuit connects the stationary electronic components in a hard disk drive to the rotating arm that carries the read/write heads and positions them above data tracks on the disk. Flex circuits are conventionally formed as a laminate of polyimide substrate, adhesive, and copper conductors. Deformation of a flex circuit is discussed in the context of the following stages: the initial unstressed shape, configurations in which stresses set and relax in response to elevated temperature, equilibrium, and small amplitude vibration. The model involves displacements of the flex circuit in the directions tangent and normal to the local equilibrium shape, and those motions couple with the arm’s dynamics. Nonlinearity associated with finite curvature, partial elastic springback, and the arm’s geometry and inertia properties are incorporated within the vibration model to predict system-level natural frequencies, mode shapes, and coupling factors between the circuit and the arm. Laboratory measurements using noncontact laser interferometry validate the model with respect to the circuit’s shape, stiffness, restoring moment, and natural frequencies. The primary degrees of freedom for optimizing flex circuit design are the thicknesses of the individual layers within the circuit, free length, and the locations and slopes of the circuit’s attachment points to the arm and electronics block. The model’s predictions and trends developed from a case study in free length are discussed with a view toward reducing coupling between the circuit and arm in certain vibration modes.
Nonlinear Dynamics of Single-Cylinder Flexible Reciprocating Engines
Authors: Goudas I. , Stavrakis I. , Natsiavas S.
Published: June 2008

In the present study, dynamic response of single-cylinder reciprocating engines is investigated. The models examined take into account the flexibility of the engine mechanism associated with either its connecting rod or its supporting bearings. In addition, both the driving and the resisting moments are expressed as functions of the crankshaft motion. This leads to dynamic models with equations of motion appearing in a strongly nonlinear form. These equations are then solved numerically, by employing methodologies of both the time and the frequency domain. In particular, these methodologies include determination of transient response by direct integration or direct determination of complete branches of steady state response. The first set of numerical results refers to engine mechanisms with a flexible connecting rod. After dealing briefly with the special case of constant crank angular velocity, which can be investigated more easily and provides valuable insight into some aspects of the system dynamics, the emphasis is shifted to the general case of non-ideal forcing. Next, numerical results are presented for engine models with flexible bearings. Initially, mechanisms with rigid members supported by bearings involving linear anisotropic or isotropic properties are considered. Finally, similar results are also presented for hydrodynamic bearings, whose behavior is governed by the classical finite-length impedance theory. In all cases, the attention is focused on investigating the influence of the system parameters on its dynamics.
Computation of Normal Forms for High Dimensional Nonlinear Systems and Application to Nonplanar Motions of a Cantilever Beam
Authors: Zhang Wei , Wang Feng-Xia , Zu Jean W.
Published: June 2008

A new and efficient computation of normal forms is developed in this paper for high dimensional nonlinear systems, and the computational method is applied to nonplanar motion of a cantilever beam. The method is based on the adjoint operator method and has the advantage of directly calculating coefficients of normal forms. Moreover, the new method is easy to apply to engineering applications, and the final partial differential equations of various resonant cases appear in a canonical form whose solutions can be conveniently obtained using polynomial equations. With the aid of the Maple software, a symbolic program for computing the normal forms of high dimensional nonlinear systems is developed. Based on the symbolic program, the normal forms and their coefficients of the averaged equations for nonplanar motions of a cantilever beam are calculated for two resonant cases.
Domains of Attraction for an Autoparametric Mass-Pendulum System: A Lyapunov Exponent Map Approach
Authors: El-Rifai Khalid , Haller George , Bajaj Anil K.
Published: June 2008

Many recent studies have been performed on resonantly excited mass-pendulum systems with autoparametric (internal) resonance capturing interesting local steady state phenomena. The objective of this work is to explore the transient behavior in such systems. The domains of attraction of the time-periodic system provide some help in understanding the transient dynamics, and these are sought using a recently developed algorithm that solves for the finite-time Lyapunov exponent over a grid of initial conditions. Though the use of finite-time Lyapunov exponents in nonlinear dynamical analyses is not novel, its application to multi-degree-offreedom forced nonlinear systems has not been reported in the literature. In addition to identifying regions of different final states, the technique used captures different levels of attraction within a domain. This sheds some light on the role played by other modes present in a multi-degree-of-freedom system in shaping the overall system response.
Effect of Feedback Control on the Bifurcation Stability of a Nonlinear Servohydraulic System: An Experimental Investigation
Authors: Shukla Amit , Thompson David F. , Kowta Srinivas
Published: June 2008

Servo-hydraulic systems are commonly used for motion and force control. In this work, an experimental investigation is performed to study the effect of feedback control on the bifurcation stability of a nonlinear servo-hydraulic system. A low-order model of the experimental test stand is developed, validated and analyzed. It is shown that the use of appropriate feedback control structure can improve the bifurcation stability of a nonlinear servo-hydraulic system. Parametric space investigation is conducted to study the bifurcation stability behavior of the system and stability boundaries are developed to demonstrate the effect of linear feedback on the nonlinear systems.
Rotordynamics Analysis: Experimental and Numerical Investigations
Authors: Sinou Jean-Jacques , Demailly David , Villa Cristiano , Thouverez Fabrice , Massenzio Michel , Laurant Franck
Published: June 2008

This paper presents a research devoted to the study of vibration problems in turbofan application. Several numerical and experimental tools have been developed. An experimental test rig that simulates the vibrational behavior of a turbofan engine is presented. Moreover, a finite element model is used in order to predict the non-linear dynamic behavior of rotating machines and to predict the first critical speed of engineering machine. A comparison between the experimental tests and the numerical model is conducted in order to evaluate the critical speed of the rotating structure and to update the finite element model.
Stick-Slip Chaos in a Non-Ideal Self-Excited System
Authors: Pontes B. R. , Balthazar J. M. , Oliveira V. A.
Published: June 2008

In engineering practical systems the excitation source is generally dependent on the system dynamic structure. In this paper we analyze a self-excited oscillating system due to dry friction which interacts with an energy source of limited power supply (non ideal problem). The mechanical system consists of an oscillating system sliding on a moving belt driven by a limited power supply. In the oscillating system considered here, dry friction acts as an excitation mechanism for stick-slip oscillations. The stick-slip chaotic oscillations are investigated because the knowledge of their dynamic characteristics is an important step in system design and control. Many engineering systems present stick-slip chaotic oscillations such as machine tools, oil well drillstrings, car brakes and others.
Modeling Lubricated Revolute Clearance Joints in Multibody Mechanical Systems
Authors: Flores P. , Lankarani H. M. , Ambro´sio J. , Claro J. C. P.
Published: June 2008

This work is concerned with the modeling of lubricated revolute clearance joints in multibody mechanical systems. The existence of the clearance at revolute joints is inevitable in all mechanical systems, and most of them are designed to operate with a lubricant fluid. It is known that the use of lubricant at revolute joints is demonstrated to be an effective way to ensuring better performance of the mechanical systems. The long journal-bearing theory for dynamic loads is used to evaluate the resulting hydrodynamic forces of the pressure distribution in the lubricated revolute joints. These hydrodynamic forces are included into the governing equations of motion of the system. A numerical example is presented in order to demonstrate the efficiency and accuracy of the methodology and procedures adopted. The results are close to those obtained with ideal joints even when simulated in a high-speed mechanism.
High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years
Authors: Steffensen Jørgen Peder , Andersen Katrine K. , Bigler Matthias , Clausen Henrik B. , Dahl-Jensen Dorthe , Fischer Hubertus , Goto-Azuma Kumiko , Hansson Margareta , Johnsen Sigfús J. , Jouzel Jean , Masson-Delmotte Valérie , Popp Trevor , Rasmussen Sune O. , Röthlisberger Regine , Ruth Urs , Stauffer Bernhard , Siggaard-Andersen Marie-Louise , Sveinbjörnsdóttir Árný E. , Svensson Anders , White James W. C.
Published: June 2008

The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.
Structure and development of shoots in Cytisus scoparius
Authors: Zhou Tian Su , Hara Noboru
Published: June 2008

The vegetative winter bud of Cytisus scoparius Link contains about nine leaf primordia. It grows into a main axis during the current growing season. At the end of the growing season, a shoot system consisting of a main axis and many lateral branches is formed. The lateral branch originates as a primordium when winter buds expand in spring, from the axil between the sixth and eighth leaves (numbered from the base of the bud), following which the succeeding primordia of branches appear sequentially. These lateral primordia continue to extend synchronously with the extension of the main axis during the growing season. By the end of the growing season, the lateral branches have reached various lengths and are arranged in a somewhat characteristic manner on the main axis; the relatively long branches are often located on the portions with ternately compound leaves and are associated with the vigorous elongation of the main axis. The relationship between the growth of the lateral branches and the main axis is discussed. Key words: axillary meristem, Cytisus, proleptic shoot, sylleptic shoot.
Somatic embryo maturation, germination, and soil establishment of plants of black and white spruce (Picea mariana and Picea glauca)
Authors: Attree S. M. , Tautorus T. E. , Dunstan D. I. , Fowke L. C.
Published: June 2008

Somatic embryo maturation, germination, and soil establishment frequencies were compared for two conifer species, white and black spruce (Picea glauca and Picea mariana). The comparison of the two species regenerated and established in soil under the same conditions showed black spruce to be the most responsive. Shorter exposure times to 32 μM abscisic acid were not as effective as maturation on a medium containing 16 μM abscisic acid for 28 days. This gave similar maturation frequencies for the two species (6–8%), and germination frequencies of 64% for white spruce and over 73% for black spruce. Over 1800 black and white spruce plantlets were recovered, and more than 400 were transferred from in vitro to nonsterile conditions. Sixty percent (160) of the black spruce plantlets survived transfer and continued to grow vigorously. By comparison only 18% (29) of the white spruce plantlets survived, and half of these rapidly produced dormant buds and underwent no further shoot growth. White spruce plants that did not produce dormant buds grew vigorously. These results indicate that there are large differences in the ability of these closely related species to respond to plantlet establishment following regeneration from somatic embryos, and that black spruce is highly responsive to micropropagation by this method. Key words: Picea glauca, Picea mariana, somatic embryogenesis, maturation, germination, soil establishment.
Gremmeniella abietina and G. laricina in Europe: characterization and identification of isolates and laboratory strains by soluble protein electrophoresis
Authors: Petrini O. , Toti L. , Petrini L. E. , Heiniger U.
Published: June 2008

Forty-four isolates of Gremmeniella abietina from different European regions and laboratory strains of G. abietina and Ascocalyx abietis, which originated from regenerated protoplasts, were characterized morphologically and by protein electrophoresis. On the basis of the electrophoretic profiles of all isolates tested, the North American race of G. abietina is not present in Europe. Isolates from Pinus cembra and two Finnish isolates differed slightly from the tester strain for the European race; their electromorphs were very similar to that of the European race on other hosts but differences were noticed that would support the maintenance of the variety cembrae. Gremmeniella abietina var. balsamea, common on Abies balsamea and Picea spp. in Quebec, Canada, seems to be absent from the European counterparts Abies alba and Picea abies. The isolates from P. abies belong unequivocally to the European race of G. abietina. European isolates of G. laricina were morphologically and electrophoretically indistinguishable from the North American ones. The P. cembra and Larix decidua endophytes showed the same electrophoretic profile as the isolates from diseased pines identified as Brunchorstia pinea var. cembrae. No changes in the electrophoretic patterns of laboratory strains derived from regenerated protoplasts, compared with those of the original isolates, were observed. Two isolates from Abies do not belong to any known species of Brunchorstia; on the basis of morphological, electrophoretic, and immunological evidence they belong to a taxon taxonomically close to G. abietina. Key words: Gremmeniella abietina, protein electrophoresis, Pinus cembra, Picea abies, European isolates.
Response of wheat growth and CO2 assimilation to altering root-zone temperature
Authors: Al-Hamdani S. H. , Todd G. W. , Francko D. A.
Published: June 2008

Wheat plants (Triticum aestivum L. var. Chisholm) grown at an air temperature of 23 °C and a root-zone temperature of 3 °C exhibited a significant reduction in shoot and root dry weight and leaf area compared with plants grown at a root-zone temperature of 23 °C. This reduction was correlated with a significantly lower CO2 assimilation rate that was associated with lower leaf conductance, lower internal CO2 concentration, and more negative water potential. Low CO2 assimilation rate was also associated with high starch and total soluble sugar levels in the shoot, less translocation of photosynthate, and possibly less sink demand. Leaf chlorophyll concentration was not affected by altering the root-zone temperature, whereas water use efficiency of plants grown at a root-zone temperature of 3 °C was as much as 1.5 times higher as those grown at 23 °C. Key words: carbohydrate, chlorophyll, photosynthate partitioning, leaf conductance, water potential, water use efficiency.
Enhanced hyphal body production by Entomophaga aulicae protoplasts in the presence of a neutral and a positively charged surface under mass fermentation conditions
Authors: Nolan Richard A.
Published: June 2008

The effects of two disks, one with a net neutral charge (Mylar) and one with a positive charge (polypropylene), on hyphal body production from protoplasts of the fungus Entomophaga aulicae under mass fermentation conditions were determined. The results were compared with those obtained with a vessel lacking a disk (control). The presence of either disk greatly enhanced hyphal body production, especially by day 4 of incubation. A maximum level of 94.1% hyphal body production was achieved using the disks as compared to a maximum level of 42% under control conditions. With the exception of aspartic acid, which was produced under control conditions and not utilized when the disks were present, the amino acids were removed from the medium earlier and (or) more completely in the presence of the disks. Glucose utilization and oxygen consumption were greater in the presence of the disks. The utilization of fermentation vessel configurations employing neutral or positively charged disks (surfaces) offers a method for greatly enhancing hyphal body production for biocontrol of the larval stages of forest defoliators. Key words: Entomophaga aulicae, hyphal body production, biological control, mass fermentation, neutral and positively charged surfaces.
The relationship of the soil seed bank and understory vegetation in old-growth northern hardwood–hemlock treefall gaps
Authors: Mladenoff David J.
Published: June 2008

In mature northern hardwood forests, small treefall gaps constitute an important mode of compositional and structural change within the long return time of larger catastrophic disturbances. The soil seed bank and patterns in vegetation layers are described in this disturbance regime context. In these small treefall gaps, herbaceous and woody vegetation species present are similar to those of forest understory plots, differing primarily in abundance. Seed bank communities are compositionally more similar among gaps than forest understory plots, but vegetation similarity is equal among forest plots and among gaps. Seed bank-vegetation similarity is greater among forest plots than in gaps. Seed bank strategies differ among the plant species characteristic of the differing forest layers. Dominant canopy tree species (Acer saccharum, Tsuga canadensis, Betula alleghaniensis) are not an important component of the seed bank. Bird-dispersed shrub and herbaceous species and ant-dispersed herbs are important in the seed bank, especially in gaps. In particular, based on gap seed bank response, it appears that understory shrub abundance and pattern within the forest change with the time since large-scale disturbance, in accordance with species adaptations to the size and increase in number of small treefalls in the mature forest. These species patterns may relate to the patchy nature of resource availability that develops, especially that of nitrogen, which is controlled by the canopy species–gap mosaic. Key words: treefall gaps, soil seed bank, disturbance, northern hardwoods, old growth, succession, shrubs.
Development of endodermal Casparian bands and xylem in lateral roots of broad bean
Authors: Peterson Carol A. , Lefcourt Barbara E. M.
Published: June 2008

A clearing and fluorochrome staining procedure for broad bean (Vicia faba L. cv. Windsor) roots with laterals was devised which allowed observation of their tracheary elements and Casparian bands in situ. The Casparian band of the main root overlying the primordium disappeared early in its development and the margins of the remaining band were displaced outward during subsequent growth of the lateral. The Casparian band matured centripetally in parenchyma across the base of the lateral as far as the endodermis of the lateral and then acropetally into the lateral itself. Casparian bands of the laterals were always connected to those of the main roots. In actively growing roots, the primordium may have emerged as far as 2.7 mm from the main root and still contain no differentiating xylem or Casparian band. Longer laterals contained differentiating xylem 3 mm from the tip and maturing Casparian bands 5 mm from the tip. In nongrowing roots, some primordia not yet emerged from the main root had mature xylem tracheary elements 0.4 mm from the tip and mature Casparian bands 0.25 mm from the tip. Key words: Casparian band, primary xylem, lateral roots, endodermis.
A quantitative scale for assessing chickpea reaction to Ascochyta rabiei
Authors: Riahi H. , Harrabi M. M. , Halila M. H. , Strange R. N.
Published: June 2008

Hybrid generations obtained from crosses between several chickpea cultivars were used to develop a quantitative scale to assess the reaction of chickpea (Cicer arietinum) to Ascochyta rabiei under controlled conditions. The number of lesions, their average and total lengths, and the linear infection index were used to establish a quantitative scale. The distribution frequency of the number of lesions, average and total lengths of lesions, and the linear infection index showed that the latter best described the reaction of chickpea seedlings to A. rabiei. This index provided a satisfactory separation between resistant and susceptible plants. The linear infection index was based on a quantitative measurement of the disease expression on plants, whereas the 1–9 scale developed at the International Crops Research Institute for the Semi-Arid Tropics uses mostly visual disease assessment. The linear infection index was used to establish a new scale of eight classes in which plants rated from class 0 to class 3 were considered resistant, and those rated from class 4 to class 7 were considered susceptible. Key words: Cicer arietinum, Ascochyta rabiei.
Numerical modeling of sand drain performance — a case study of the Salter Street Bridge construction
Authors: Van Helden Michael J. , Blatz James A. , Ferreira Nelson J. , Skaftfeld Ken
Published: June 2008

Several bridge crossings proposed for the Red River Floodway expansion project were recently constructed using vertical sand drains to accelerate excess pore-water pressure dissipation and settlement caused by embankment fill loading. With limited local data regarding the performance of sand drains, the calibrated model presented here addresses the need to optimize the design of sand drain configurations, maximize cost savings, and minimize construction delays for future structures. This study presents a coupled finite element embankment consolidation model calibrated against measured pore-water pressure and settlement data from the Salter Street Bridge embankment fill construction, which used vertical sand drains to dissipate excess pore-water pressures. A hydraulic conductivity modification procedure was used to simulate the axisymmetric flow conditions with a plane-strain model neglecting well resistance but incorporating the effects of a smear zone. A sensitivity analysis was performed using the calibrated model by varying the smear zone radius and hydraulic conductivity and the undisturbed soil hydraulic conductivity. The sensitivity analysis predicted that the observed behaviour was predominantly sensitive to the hydraulic conductivity of the smear zone and the surrounding soil.
Parameter estimation for modelling clogging of granular medium permeated with leachate
Authors: VanGulck Jamie F. , Rowe R. Kerry
Published: June 2008

A numerical model called BioClog is used to backcalculate biological activity rate constants using measured values of water quality and clog chemical characteristics from well-controlled laboratory column experiments that contained a granular-sized material permeated with synthetic and real leachates. BioClog is a multispecies, reactive chemical transport model capable of predicting clogging of a porous media caused by the accumulation of biofilms, chemical precipitates, and entrained particles. Monod kinetic constants for acetate- and butyrate-degrading bacteria were obtained through inverse modelling of granular-sized material permeated with synthetic leachate. The model predicted the changes in concentrations of volatile fatty acids and dissolved calcium and it predicted the changes in clog composition from a juvenile clog containing biofilm to a mature clog containing biofilm with mineral matter. The kinetic constants were then applied to predict spatial and temporal water quality and clog composition for a granular-sized material permeated with real leachate. The kinetic constants deduced through inverse modelling of the synthetic leachate column experiments provided reasonable predictions of the behaviour of the columns permeated with real leachate.
The segregation potential of a freezing soil
Authors: Konrad Jean-Marie , Morgenstern Norbert R.
Published: June 2008

In previous work it has been shown that when a soil sample freezes in a one-dimensional manner under different cold-side step temperatures but the same warm-side temperature, at the formation of the final ice lens the water intake flux is proportional to the temperature gradient across the frozen fringe. The constant of proportionality has been called the segregation potential and this linear relation constitutes the coupling between heat and mass flow in a general theory of frost heave. This paper shows experimentally that the segregation potential is also a function of the average suction in the frozen fringe which is readily expressed in terms of the suction at the frost front. As a result it is also shown that measured water intake flux during freezing is dependent on the freezing path used to initiate the final ice lens. A thermodynamic explanation of the dependence of segregation potential on suction in the frozen fringe is also offered.
The performance of marine anchors with planar flukes in sand
Authors: LeLievre B. , Tabatabaee J.
Published: June 2008

The problem of determining the holding capacity of flat plates and marine anchors in cohesionless soils is briefly reviewed and the reasons for the difference in the performance of marine anchors and that of simple flat plates are identified. The role which each anchor component plays during the embedment process is discussed.An analytical procedure to estimate the holding capacity of anchors with planar flukes, such as the Danforth anchor, as a function of soil properties and the depth of penetration into the soil is presented and checked against data from laboratory and published field tests.Factors such as anchor stability and characteristics of the pulling cable which can affect both anchor orientation and the maximum depth to which a particular anchor can penetrate the soil have not been included in the analysis. Consequently, it is not yet possible to predict the ultimate holding capacity that a particular anchor may achieve if pulled through an adequate distance.