bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Dynamics of an Electrohydraulic Flapper Nozzle Valve
Authors: Liaw Chong-Jer , Brown F. T.
Published: March 2008

A nonlinear model of an electrohydraulic flapper-nozzle valve is developed, using an energy-based approach. Nonlinearities are found in the resistances, compliances, and the inertances; the latter produce state-dependent coupling terms. The model is applied to a valve designed for pulse-width modulation (PWM). Most model parameters are derived from a priori design parameters, but some were found from a series of experiments which also served to confirm the model. The valve and its model responded satisfactorily to PWM signals up to 500 Hz.
Reduced-Order Parameter Estimation for Continuous Systems From Sampled Data
Authors: Liaw C. M. , Ouyang M. , Pan C. T.
Published: March 2008

An indirect method for estimating the parameters of the reduced continuous-time model from the sampled input/output data is presented. In this method, a discrete-time ARMA model is first identified. Then, the order of the continuous-time model is minimized by the dispersion analysis and/or accumulated dispersion analysis with the criterion of minimum discrepancy in sense of energy contribution between the original system and the reduced model. Finally, the reduced continuous-time model is matched to the identified discrete ARMA model in frequency domain. The proposed approach is applied to the identification of a power system stabilizer. The results show that the estimated continuous-time models are rather close to those supplied by the vender.
Oscillations-Induced Transitions and Their Application in Control of Dynamical Systems
Authors: Bentsman J.
Published: March 2008

Studies of the use of oscillations for control purposes continue to reveal new practically important properties unique to the oscillatory open and closed loop control laws. The goal of this paper is to enlarge the available set of analytical tools for such studies by introducing a method of analysis of the qualitative changes in the behavior of dynamical systems caused by the zero mean parametric excitations. After summarizing and slightly refining a technique developed previously for the finite dimensional nonlinear systems, we consider an extension of this technique to a class of distributed parameter systems (DPS) governed by semilinear parabolic equations. The technique presented is illustrated by several examples.
Stability Robustness of Repetitive Control Systems With Zero Phase Compensation
Authors: Ma C. C. H.
Published: March 2008

It is shown that a special zero phase control (ZPC) system introduced by Tomizuka is L∞ stable against a large class of common nonlinearities. However, it still suffers from the generic nonrobustness problem associated with a linear repetitive control system when subjected to a saturation nonlinearity. For the special ZPC system, however, three solutions exist for the problem, two of which do not degrade the repetitive tracking performance.
H∞ Controllers With a PID Structure
Authors: Grimble M. J.
Published: March 2008

A review is given of the new H∞ Observations Weighted (HOW) optimal control law. The conditions under which the H∞ controller has a PID structure are identified and some implications for PID controller design are discussed. The simple form of this H∞ control law makes it easy to analyse and design. Examples are presented of the design procedure which involves the specification of the cost-function weighting transfer functions. The controller may be applied in applications where fast computational procedures are important.
A Comparison of Different Models for Beam Vibrations From the Standpoint of Control Design
Authors: Morris K. A. , Vidyasagar M.
Published: March 2008

In this paper we analyze different models for beam vibrations from the standpoint of designing finite-dimensional controllers to stabilize the beam vibrations. We show that a distributed system described by an undamped Euler-Bernoulli equation cannot be stabilized by any finite-dimensional controller, i.e., any controller which can be described an ordinary differential equation with constant coefficients. If viscous damping is included, a similar problem occurs in that all the poles can’t be moved to the left of a given vertical line. These negative results should be interpreted as a commentary on the limitations of these models, rather than on the control of real beams. We then show that if a Rayleigh damping model is used, a finite-dimensional controller may be designed to move the closed loop system poles essentially as far to the left in the complex plane as desired. This result will also hold for certain hysteresis damping models. This has implications for the settling time of the vibrations.
Integrated Communication and Control Systems: Part III—Nonidentical Sensor and Controller Sampling
Authors: Liou Luen-Woei , Ray A.
Published: March 2008

Networking in Integrated Communication and Control Systems (ICCS) introduces randomly varying delays which degrade the system dynamic performance and are a source of potential instability. In Part I [1] of this sequence of papers we developed a discrete-time, finite-dimensional model of the delayed control system for analysis and design of ICCS where the sensor and controller have identical sampling rates. In Part II [2] we proposed two alternative approaches for ICCS design, namely, identical and nonidentical sampling rates for sensor and controller. This Part III presents extended modeling of ICCS for nonidentical sensor and controller sampling rates. This model is also suitable for analyzing tracking problems, i.e., control systems with time-dependent reference inputs.
Performance Analysis of Integrated Communication and Control System Networks
Authors: Halevi Y. , Ray A.
Published: March 2008

This paper presents statistical analysis of delays in Integrated Communication and Control System (ICCS) networks [1–4] that are based on asynchronous time-division multiplexing. The models are obtained in closed form for analyzing control systems with randomly varying delays. The results of this research are applicable to ICCS design for complex dynamical processes like advanced aircraft and spacecraft, autonomous manufacturing plants, and chemical and processing plants.
Spatially Distributed Transducers: Part II—Augmented Transmission Line Models
Authors: Busch-Vishniac Ilene J.
Published: March 2008

Transducer models are typically comprised of a finite number of discrete lumped elements connected using circuit conventions. Such models are inappropriate for transducers which explicitly depend upon the continuous nature of one or more system element. These transducers must be modeled as spatially distributed devices. In this article we present a class of models which is useful for spatially distributed transducers in which the response at one location is coupled to that at other locations. The models use a transmission line to describe the mechanical coupling between locations on the transducer, but have been augmented to include interaction with the environment and sources everywhere along the line. If only one element is used at every location to represent the interaction of the transducer and the environment, and only one type of source is present, then there are only four general models which need to be considered. These models are analyzed for the general case of spatially varying sources and physical parameters. It is shown that it is possible to prescribe up to four response characteristics of the transducer if the physical parameters are permitted to vary with space. Examples of spatially distributed transducers are presented and applications discussed.
A New Strategy for Adaptive Motion Control of Robots
Authors: Gu Keqin , Tongue Benson H.
Published: March 2008

The Lyapunov function approach is used to derive a new algorithm for model based adaptive motion control as applied to robot manipulators. The technique does not require a knowledge of state accelerations and if the method is implemented through a Newton-Euler recursive formulation then the computational requirements are quite low. High feedback gains are not needed to ensure stability. The parameter ranges allowed for stability are explicitly expressed, making the design process fairly simple. The algorithm is conceptually simple and easily implemented in industrial robots.
On the Stability of Robot Compliant Motion Control: Theory and Experiments
Authors: Kazerooni H. , Waibel B. J. , Kim S.
Published: March 2008

The work presented here is a nonlinear approach for the stability analysis of robot manipulators in compliant maneuvers. Stability of the environment and the manipulator taken as a whole has been investigated, and a bound for stable manipulation has been derived. The stability analysis has been investigated using unstructured models for the dynamic behavior of the robot manipulator and the environment. This unified approach of modeling robot dynamics is expressed in terms of sensitivity functions as opposed to the rigid body dynamics derived by Lagrangian approach. It allows us to incorporate the dynamic behavior of all the elements of a robot manipulator (i.e., actuators, sensors and the structural compliance of the links) in addition to the rigid body dynamics. We show that for stability of the robot, there must be some initial compliancy either in the robot or in the environment. According to this stability condition, smaller sensitivity either in the robot or in the environment leads to a narrower stability range. In the limit, when both robot and environment have zero sensitivity, stability cannot be guaranteed. The general stability condition has been extended to the particular case where the environment is very rigid in comparison with the robot stiffness. This condition has been verified via simulation and experiment on the Minnesota direct drive robot.
A Robust Servo-Electronic Controller for Brake Force Distribution
Authors: Salman M. A.
Published: March 2008

In this paper a control system which achieves ideal brake force distribution between the front and the rear wheels of a vehicle during normal braking is studied. Ideal brake proportioning is achieved by dynamically controlling the rear-wheel speed to track the front-wheel speed. Electro-hydraulic brake actuators, which are installed at the rear brakes of the vehicle, are used to modulate the brake-line pressure. A simple linear model of the actuators was developed. This model is derived from experimental response data. Based on this model, a robust servomechanism controller, which achieves ideal brake proportioning by rear-wheel speed control, is designed, implemented, and tested. Test results indicate that the robust servo-mechanism controller achieves a very good wheel speed tracking performance.
Modeling of Oscillations in Partially Penetrated Weld Pools
Authors: Sorensen C. D. , Eagar T. W.
Published: March 2008

Several investigators have proposed controlling the size and shape of the weld pool based on the weld pool oscillations. This paper proposes two models that could be used to predict the weld pool geometry based on the natural frequency of the pool. The models, one a lumped parameter model and the other a distributed parameter model, included effects of liquid metal density and surface tension along with weld pool geometry. Weld pool oscillations were measured through signal processing of arc voltage and current for stationary gas-tungsten arc (GTA) welds. Welds were performed at different weld voltages and currents on different materials in order to vary width, depth, density, and surface tension. The models developed here were shown to have reasonable agreeement with experimentally measured weld pool resonant frequencies. Also, with geometric conditions similar to those commonly found in GTA weld pools, the different models tend to agree well with one another.
Optimal Control Theory Applied to Pressure-Controlled Axial Piston Pump Design
Authors: Lin S. J. , Akers A.
Published: March 2008

This work presents a study of the applicability of optimal control theory to the design of a pressure regulator by use of an axial piston pump with a two-stage electrohydraulic servovalve. The control valve has been modeled and an optimal control law has been formulated. The time response curves due to a step input in flow rate to the pump have been obtained for the open loop and the for the optimal control system. An examination of the results has shown that the performance, in terms of pressure peaks and frequency during recovery to the flow disturbance, is significantly improved over that obtained when a single-stage valve is used.
On Robust Parametric Dynamic Output Feedback
Authors: Zohdy M. A. , Abdul-Wahab A. A. , Loh N. K. , Liu Jun
Published: March 2008

This paper presents a new and unified treatment of feedback control for linear multivariable time-invariant systems, using reduced-order dynamic output feedback to recover state feedback properties. A set of free design parameters are effectively exploited in achieving desirable performance tradeoffs, through solving Lyapunov-like matrix equations.
Design of a Trajectory Insensitive Regulator With Prescribed Degree of Stability
Authors: Saif M.
Published: March 2008

The paper outlines an approach for designing a trajectory insensitive optimal linear quadratic regulator (LQR) with prescribed degree of stability for uncertain plants. The state trajectory insensitivity to structural uncertainties is achieved by designing a robust suboptimal controller of proportional state, and proportional derivative of state type. The prescribed degree of stability is obtained by appropriate modification of the quadratic cost functional. The proposed method is superior to some recent approaches as far as the computational complexity and robustness are concerned.
Trellis Representation and State Estimation for Dynamic Systems With a Kth Order Memory and Nonlinear Interference
Authors: Demirbas¸ Kerim
Published: March 2008

A fast state estimation scheme is presented for dynamic systems with a Kth order memory and nonlinear interference. This new scheme is based upon a trellis diagram representation of dynamic models and stack sequential algorithm of Information Theory.
New species and combinations of cleistothecial Ascomycetes
Authors: Malloch David , Cain R. F.
Published: March 2008

The following new species and combinations are proposed: Albertiniella polyporicola (Jaczevski) comb. nov., Emericella aurantiobrunnea (Atkins, Hindson and Russell) comb, nov., E. fruticulosa (Raper and Fennell) comb. nov., E. heterothallica (Kwon, Raper and Fennell) comb. nov., E. parvithecia (Raper and Fennell) comb. nov., E. striata (Rai, Tewari and Mukerji) comb. nov., E. unguis sp. nov., E. violacea (Fennell and Raper) comb. nov., Eupenicillium molle sp. nov., Eurotium carnoyi sp. nov., E. cristatum (Raper and Fennell) comb. nov., E. chevalieri var. intermedium (Thom and Raper) comb. nov., E. montevidense (Talice and MacKinnon) comb. nov., E. niveo-glaucum (Thom and Raper) comb. nov., E. pseudoglaucum (Blochwitz) comb. nov., E. umbrosum (Bainier and Sartory) comb. nov., Microthecium inordinatum sp. nov., Petriellidium angustum sp. nov., Phaeotrichum benjaminii sp. nov., P. cylindrosporum sp. nov., Preussia cylindrica sp. nov., Preussia indica var. oryzetorum (Montemartini) comb. nov., Roumegueriella rufula (Berk. and Br.) comb. nov., Thielavia albomyces (Cooney and Emerson) comb. nov., T. terrestris (Apinis) comb. nov., Tripterosporella Pakistani (Mirza) comb. nov., Zopfia biturbinata (Dur. and Mont.) comb. nov., Z. duplicispora (Janse) comb. nov.
Growth kinetics of Marquis wheat. I. Light dependence
Authors: Macdowall F. D. H.
Published: March 2008

As early growth is exponential it was measured as the pseudo-first-order rate coefficient, k1′. The growth coefficient is independent of the method of measurement, so different values derived from different measurements such as dry weight, fresh weight, chlorophyll content, and area reflected somewhat different aspects of growth in a given organ. At low light intensity k1′ was highest for lamina dry weight and lowest for root dry weight, and at high light intensity, highest and lowest k1′.were obtained for "stem" dry weight and lamina area, respectively. The differences in rate coefficients between organs were less than 10% of their values at high light intensity. The rectangular hyperbolic fit of the dependence of k1′ on light intensity was used to compute a maximum value (kmL) independent of light intensity. A kmL of 0.34 per day was obtained for plants of Marquis wheat grown at 25 °C with Hoagland's solution in Went's medium under controlled environment, and the highest value, 0.37, was achieved by dry weight of "stems." A complex form parameter was also computed, and it included a function of the efficiency of light use for growth, which was highest for leaf area and lowest for root dry weight. Measurements on complete morphological entities such as whole organs are best interpreted. Growth kinetics and its relationship to "growth analysis" were discussed in distinct favor of the former approach. The growth coefficient as the relative growth rate has been abused and that term should be dropped. The prospects of kinetic or primary analysis as the standard quantitative method are great, as initially envisaged by V. H. Blackman half a century ago.
A model for cultivar classification and identification with reference to oats (Avena). II. A probabilistic definition of cultivar groupings and their Bayesian identification
Authors: Baum B. R. , Lefkovitch L. P.
Published: March 2008

Using analysis of variance, four sequentially obtained characters were chosen from 21 to discriminate among 14 groupings (demes) proposed elsewhere. The 14 estimated sets of 36 multinomial probabilities obtained therefrom, together with the estimated probability of occurrence of each deme, were used to construct a Bayesian identification procedure. Computer simulation of identification suggested that 50 plants are sufficient for identification. The merits of Bayesian identification schemes for infraspecific categories are described.
Photosynthesis, translocation, and alginic acid synthesis in Laminaria digitata and Laminaria hyperborea
Authors: Hellebust Johan A. , Haug Arne
Published: March 2008

New and old tissues of L. digitata blades have very similar photosynthetic capacities on a fresh weight basis. Very little of the photoassimilate goes into alginic acid, or other macromolecular substances in old blade tissues. Less than 1% of the photoassimilated 14C in the old blade portion of a L. digitata blade was translocated to the new blade tissues in a 5-h experiment. In contrast, there is rapid transport of photoassimilate from bark cells to cells of the underlying tissues of L. digitata and L. hyperborea stipe sections. Isolated cortex and medulla tissues of L. digitata stipes have significant photosynthetic capacities, but are probably so strongly shaded by the darkly pigmented bark cells that little photosynthesis can normally occur in these tissues.A larger proportion of the photoassimilated carbon enters alginate in the cortex and medulla than in the bark of L. digitata and L. hyperborea stipes in short-term experiments. The time course for incorporation of photosynthate into alginate in continuous and pulse-labeling experiments indicates the presence of relatively large pools of alginate precursors. A large proportion of the total 14C incorporated into alginate in short-term experiments is found in the "M–M" (mannuronic acid) and "M–G" (alternating mannuronic and guluronic acid) block components.
In situ studies on alginic acid synthesis and other aspects of the metabolism of Laminaria digitata
Authors: Hellebust Johan A. , Haug Arne
Published: March 2008

Amino acids, particularly alanine and aspartate, become more strongly labeled than mannitol in short-term 14C-photoassimilation experiments. The amino acids are the most likely sources of carbon for alginic acid synthesis and respiration in the dark, in contrast to mannitol, which appears to be relatively unavailable. Temperature is very important in determining the rate of loss of recent photoassimilate in L. digitata. The rate of photosynthesis, on a fresh weight basis, is much higher for blades than for stipes.The time course for incorporation of photoassimilated carbon into alginate differs for the stipe and blade both in light and dark periods. Very little 14C enters alginate in blades in the dark, while alginate in stipes acquires considerable amounts of activity during dark periods. Alginate in both blade and stipe acquires 14C predominantly in mannuronic acid residues of their alginate during short-term photoassimilation periods, while guluronic acid residues become relatively more rapidly labeled during dark periods.
Sterols of healthy and rust-infected primary leaves of wheat and of non-germinated and germinated uredospores of wheat stem rust
Authors: Nowak R. , Kim W. K. , Rohringer R.
Published: March 2008

Sterols extracted from healthy and rust-infected primary leaves of wheat or from non-germinated and germinated uredospores of stem rust were analyzed by thin-layer, column, and gas–liquid chromatography.Wheat leaves of susceptible and resistant lines contained cholesterol, campesterol, stigmasterol, β-sitosterol, and an unknown sterol that accounted for 75% to 80% of total sterol content. A further sterol, stigmast-7-enol, occurred in all rust-infected leaves and in 1 of 11 samples of healthy leaves. Sterol levels were not related to susceptibility or resistance. The level of stigmast-7-enol in infected leaves appeared to be correlated with the amount of fungal mass in the host.Uredospores of stem rust contained trace amounts of an unknown sterol, cholesterol, and either ergost-7-enol or stigmasterol, and larger amounts of stigmast-7-enol. After germination, the level of cholesterol increased, especially in differentiating uredosporelings. The level of stigmast-7-enol tended to decrease after germination.Sterol fractions from wheat leaves (healthy and rust-infected) and from stem rust uredospores (non-germinated and germinated) were not phytotoxic. They did not inhibit rust development in susceptible leaves nor did they promote it in resistant leaves.
Medium and techniques for induction and growth of monocotyledonous and dicotyledonous plant cell cultures
Authors: Schenk Roy U. , Hildebrandt A. C.
Published: March 2008

The composition of a medium is described that proved useful to culture callus of a variety of monocotyledonous and dicotyledonous plants. Growth on the medium was often better than on some other excellent media. In addition to supporting rapid cell growth, a soft, friable type of colony growth was often obtained. This type of loose, friable cell growth facilitated work with single cells and the enzymatic removal of cell walls in related studies. A high level of auxin-type growth-regulating substances (AGRS) generally favored cell cultures of monocotyledonous plants, while low levels of cytokinin were essential for most dicotyledonous cell cultures. Some cultures of dicotyledonous plant cells adapted to a cytokinin-free medium containing a high level of 2,4-dichlorophenoxyacetic acid (2,4-D) or p-chlorophenoxyacetic acid (pCPA). The preferred AGRS were 2,4-D and pCPA. Citrate, succinate, and 2(N-morpholino) ethane sulfonic acid (MES) were effective medium buffers, but phosphate alone seemed adequate to buffer the medium at pH 5.8–5.9.
Simulation of the daily growth of an aspen population from the measured CO2-exchange rates of the components
Authors: Bate G. C. , Canvin D. T.
Published: March 2008

The daily total CO2-exchange of an aspen population (32 trees) was measured using a growth chamber gas analysis system which had been shown to measure accurately the actual carbon gain of the population. The CO2-exchange rates of the components (e.g. roots, stems, leaves) were measured in the light and dark and these rates were used to calculate the total CO2-exchange of the population using a computer model. The carbon gain during the photoperiod was underestimated by 25% in the simulation while the carbon loss during the nyctoperiod was overestimated 100% by the simulation.
Effects of chronic exposure to ozone on soluble sugar and ascorbic acid contents of pine seedlings
Authors: Barnes Robert L.
Published: March 2008

Small seedlings of five pine species (Pinus strobus, echinata, elliottii, serotina, and taeda) were exposed to low levels of ozone for periods from 5 to 22 weeks. Exposure to 5 parts per hundred million ozone resulted in significant increases in total soluble carbohydrates, reducing sugars, and ascorbic acid. In seedlings exposed to 15 pphm ozone, soluble sugars were higher than in the controls but ascorbic acid levels were not.
Reliability of electromyographic and force measures during prone isometric back extension in subjects with and without low back pain
Authors: Pitcher Mark J. , Behm David G. , MacKinnon Scott N.
Published: March 2008

Maximal voluntary isometric activations (MVIA) are frequently used as inputs for models attempting to predict muscle force and as normalization values in studies assessing muscle function. However, pain may adversely affect maximal muscle activation. The purpose of this study was to assess reliability of MVIA force and electromyographic (EMG) activity during prone isometric back extension in subjects with and without low back pain (LBP). A novel sub-maximal method using the percentages of the estimated mass of the head–arms–trunk (HAT) segment was also investigated. Repeated measures on 20 male volunteers divided into an LBP (n = 10) and a control group (n = 10) were made on 4 occasions. Force and EMG activity were recorded bilaterally from upper lumbar erector spinae (ULES), lower lumbar erector spinae (LLES), and biceps femoris (BF). Subjects exerted a maximal extension effort against a harness assembly that was attached to a force transducer. Submaximal exertions were also performed with an additional resistance of 100%, 110%, 120%, 130%, 140%, 150%, 160%, and 170% of HAT. Mean MVIA forces were significantly (p ≤ 0.05) lower in LBP vs. control. Intraclass correlation coefficients (ICC) for MVIA force, right and left ULES, and LLES EMG indicated high reliability in controls (R > 0.90), but were significantly less in LBP (R = 0.36–0.80). EMG of BF demonstrated excellent reliability across both groups (R > 0.90). The resistance at 100% HAT demonstrated the highest reliability for LBP patients, whereas higher percentages of HAT showed either similar or higher reliability for controls. Force output and back EMG activity are less reliable with LBP individuals and should be taken into consideration when testing.
Timing of creatine or protein supplementation and resistance training in the elderly
Authors: Candow Darren G. , Chilibeck Philip D.
Published: March 2008

Muscle loss with age has a negative effect on strength and functional independence. Age-related loss of muscle is the result of decreased muscle fiber number and size, which are functions of altered hormonal status, physical inactivity, and variations in nutritional intake. Resistance training has a positive effect on muscle mass and strength in the elderly. Studies of protein or creatine supplementation for increasing muscle mass and strength in older individuals are equivocal. The timing of nutritional supplementation may be more important than the absolute daily intake of supplements. Protein or creatine ingestion proximate to resistance-training sessions may be more beneficial for increasing muscle mass and strength than ingestion of protein or creatine at other times of the day, possibly because of increased blood flow and therefore increased transport of amino acids and creatine to skeletal muscle.
The potential benefits of creatine and conjugated linoleic acid as adjuncts to resistance training in older adults
Authors: Tarnopolsky Mark A. , Safdar Adeel
Published: March 2008

Human aging is associated with a significant reduction in muscle mass (sarcopenia) resulting in muscle weakness and functional limitations in the elderly. Sarcopenia has been associated with mitochondrial dysfunction and the accumulation of mtDNA deletions. Resistance training increases muscle strength and size and can increase mitochondrial capacity and decrease oxidative stress in older adults. Creatine monohydrate (CrM) and conjugated linoleic acid (CLA) have biological effects that could enhance some of the beneficial effects of resistance training in older adults (i.e., ↑ fat-free mass, ↓ total body fat). We have completed two resistance-training studies with CrM alone and CrM + CLA supplementation in older adults to evaluate the independent effects of exercise and dietary supplements, as well as  their interactive effects. Our studies, and several others, have found that CrM enhanced the resistance exercise mediated gains in fat-free mass and strength. More recently, we found that the addition of CLA also lead to a significant reduction of body fat after six months of resistance training in older adults. Older adults have fewer wild-type mtDNA copies and higher amounts of mtDNA deletions as compared with younger adults in mature skeletal muscle; however, these deletions are not seen in the satellite cell-derived myoblast cultures. These findings, and the fact that mtDNA deletions are lower and wild-type mtDNA copy number is higher after resistance training in older adults, suggests that activation of satellite cells secondary to resistance exercise-induced muscle damage can dilute or “shift” the proportion of mtDNA genotype towards that of a younger adult. Recent evidence suggests that CrM supplementation in combination with strength training can enhance satellite cell activation and total myonuclei number per muscle fiber in young men. Future studies are required to determine whether the mitochondrial adaptations to resistance exercise in older adults are further enhanced with CrM supplementation and whether this is due to increased recruitment of satellite cells. It will also be important to determine whether these changes are maintained over a longer time period.
Vascular biology of angiotensin and the impact of physical activity
Authors: Rush James W.E. , Aultman Crystal D.
Published: March 2008

The renin–angiotensin system (RAS) is important for regulating blood pressure and extracellular fluid. The concept of the RAS has recently evolved from a classical systemic endocrine system to an appreciation of local RASs functioning in a paracrine manner, including in the vascular wall. Angiotensin II (AII), the main effector of the RAS, is a potent vasoconstrictor formed by the action of angiotensin-converting enzyme (ACE). ACE is multifunctional and also destroys the endogenous vasodilator bradykinin. A recently discovered novel ACE2 enzyme is responsible for forming a vasodilatory compound, angiotensin 1–7, from AII. Thus, the actions of ACE and ACE2 are antagonistic. Tissue actions of AII are mediated by specific receptors, AT1 and AT2, with AT1 mediating the classical actions. AT1-stimulated vasoconstricton occurs via phospholipase-D-mediated second messenger generation directly, and indirectly via the coupling of AT1 to the prooxidant enzyme NADPH oxidase. Since the vascular NADPH oxidase is a major source of vascular reactive oxygen species generation and is responsible for the breakdown of the vasodilator nitric oxide (NO), there is another potential link between RAS and regulation of vasodilatory pathways. AT2 signaling is antagonistic to AT1 signaling, and results in bradykinin and NO formation. Chronic AII signaling induces vascular dysfunction, whereas pharmacological management of the RAS can not only control blood pressure, but also correct endothelial dysfunction in hypertensives. Exercise training can also improve endothelial function in hypertensives, raising the question of whether there is a potential role for RAS in mediating the vascular effects of exercise training. Recent studies have demonstrated reductions in the expression of NADPH oxidase components in the vascular wall in response to exercise training, thus tempering one of the main cellular effectors of AII, and this is associated with reduced vascular ROS production and enhanced NO bioavailability. Importantly, it has now been demonstrated in human arteries that exercise training also tempers vascular AT1 receptor expression and AII-induced vasoconstriction, while enhancing endothelium-dependent dilation. The signals responsible for these chronic adaptations are not clearly understood, and may include changes in RAS components prompted by acute exercise. ACE genotype may have an effect on physical activity levels and on the cardiovascular responses to exercise training, and the II genotype (compared with ID and DD) is associated with the largest endothelium-dependent dilations in athletes compared with those in sedentary individuals. Thus, the tissue location of the RAS, the complement of ACE/ACE2, the receptor expression of AT1/AT2, and the ACE genotype are all variables that could impact the vascular responses to exercise training, but the responses of most of these variables to regular exercise training and the mechanisms responsible have not been systematically studied.
A chronic increase in physical activity inhibits fed-state mTOR/S6K1 signaling and reduces IRS-1 serine phosphorylation in rat skeletal muscle
Authors: Glynn Erin L. , Lujan Heidi L. , Kramer Victoria J. , Drummond Micah J. , DiCarlo Stephen E. , Rasmussen Blake B.
Published: March 2008

A chronic increase in physical activity and (or) endurance training can improve insulin sensitivity in insulin-resistant skeletal muscle. Cellular mechanisms responsible for the development of insulin resistance are unclear, though one proposed mechanism is that nutrient overload chronically increases available energy, over-activating the mammalian target of rapamycin (mTOR) and ribosomal S6 kinase 1 (S6K1) signaling pathway leading to increased phosphorylation of serine residues on insulin receptor substrate-1 (IRS-1). The objective of this study was to determine if increased physical activity would inhibit mTOR/S6K1 signaling and reduce IRS-1 serine phosphorylation in rat skeletal muscle. Soleus muscle was collected from fed male Sprague–Dawley sedentary rats (Inactive) and rats with free access to running wheels for 9 weeks (Active). Immunoblotting methods were used to measure phosphorylation status of mTOR, S6K1, IRS-1, and PKB/Akt (protein kinase B/AKT), and total abundance of proteins associated with the mTOR pathway. Muscle citrate synthase activity and plasma insulin and glucose concentrations were measured. Phosphorylation of mTOR (Ser2448), S6K1 (Thr389), and IRS-1 (Ser636–639) was reduced in Active rats (p < 0.05). Total protein abundance of mTOR, S6K1, IRS-1, 4E-BP1, eEF2, PKB/Akt and AMPKα, and phosphorylation of PKB/Akt were unaffected (p > 0.05). Total SKAR protein, a downstream target of S6K1, and citrate synthase activity increased in Active rats (p < 0.05), though plasma insulin and glucose levels were unchanged (p > 0.05). Reduced mTOR/S6K1 signaling during chronic increases in physical activity may play an important regulatory role in the serine phosphorylation of IRS-1, which should be examined as a potential mechanism for attenuation of insulin resistance associated with increased IRS-1 serine phosphorylation.
Central venous thrombosis in patients receiving long-term parenteral nutrition
Authors: Duerksen Donald R.
Published: March 2008

Long-term parenteral nutrition (PN) is administered to patients who are unable to use their gastrointestinal tract to absorb sufficient nutrients and water to maintain their nutritional status. Patients receiving long-term parenteral nutrition are at risk of numerous complications including thrombosis of the central venous catheter used to provide nutrition. Central venous access is essential to the successful delivery of long-term PN. One of the strategies to lessen the frequency of this complication is anticoagulation therapy with warfarin. The effect of warfarin in preventing this complication may be modified by vitamin K intake. Individuals with gastrointestinal failure may receive vitamin K from a variety of sources. This review summarizes the role of warfarin in preventing central venous access thrombosis. It also summarizes potential sources of vitamin K intake in home parenteral nutrition patients, examines the evidence for recommendations regarding vitamin K intake, and considers the potential impact of increased vitamin K intake on home PN patients, particularly on the prevention of central venous thrombosis.
Antioxidant supplemention in the treatment of skeletal muscle insulin resistance: potential mechanisms and clinical relevance
Authors: Wright David , Sutherland Lindsey
Published: March 2008

The incidence of type 2 diabetes has increased dramatically over the past several decades and this trend is projected to continue into the foreseeable future. Skeletal muscle insulin resistance is thought to be a key development in the pathogenesis of type 2 diabetes. Given this fact, interventions that prevent or reverse impairments in skeletal muscle action can have profound effects on whole-body glucose homeostasis. Traditional approaches used in this regard include exercise, weight loss, and insulin-sensitizing drugs such as thiazolidinediones (TZDs). Although these interventions have proven effective in improving glucose homeostasis, there are adherence issues seen with lifestyle interventions and undesirable side effects have been reported with TZDs. With these points in mind, the development of alternative strategies to maintain or improve skeletal muscle insulin sensitivity is warranted. In this context, the purpose of the present review is to highlight the role of antioxidant compounds in the prevention and treatment of skeletal muscle insulin resistance. Specifically, we will briefly describe the mechanisms of insulin-stimulated skeletal muscle glucose uptake and the potential mediators of oxidative stress induced insulin resistance, highlight data suggesting that antioxidant compounds can have beneficial effects on skeletal muscle insulin action, and discuss potential mechanisms mediating this effect.
Alcohol consumption: the good, the bad, and the indifferent
Authors: Ferreira Maria Pontes , Willoughby Darryn
Published: March 2008

Dietary ethanol (alcohol) is the most widely consumed drug worldwide. High levels of mortality, morbidity, and social malaise are associated with abuse of alcohol, and increasing numbers of women and youth are abusing alcohol. However, strong epidemiological data demonstrate a U- or J-shaped relationship between volume of alcohol consumed and all-cause mortality or disease burden. Moderate alcohol consumption is associated with a lower risk of all-cause mortality and disease burden than are abstinence and immoderate drinking. A brief review of the absorption, distribution, metabolism, and excretion of ethanol is provided with a discussion of the impact of gender differences. Potential mechanisms by which ethanol, ethanol metabolites, and (or) phytochemicals, as associated with different types of ethanol-containing beverages, are discussed in regards to the beneficial and detrimental impacts they may have on physiological system functioning and mortality or disease burden. Per capita consumption of ethanol-containing beverages varies across geo-political regions worldwide. A more recent research focus is the impact of consumption patterns on consumption volumes as they relate to disease and mortality. Certain drinking patterns moderate overall volume of ethanol consumption. Thus, an emerging approach to the study of alcohol consumption in populations is to consider both the volume and pattern of consumption as they relate to mortality and disease burden. Alcohol consumption patterns among athletes are discussed; physiological implications of alcohol abuse in this population are outlined. Current guidelines for the consumption of alcohol are reviewed. Alcohol consumption guidelines reflect the current scientific understanding of both the benefits of moderate alcohol consumption and the detriments of immoderate alcohol consumption.
Root cold hardiness and native distribution of subalpine conifers
Authors: Coleman Mark D. , Hinckley Thomas M. , McNaughton Geoffrey , Smit Barbara A.
Published: March 2008

Root and needle cold hardiness were compared in seedlings of subalpine conifers to determine if differences existed among species originating from either cold continental climates or mild maritime climates. Abiesamabilis (Dougl.) Carr. and Tsugamertensiana (Bong.) Carr. are exclusively distributed in maritime environments, while Abieslasiocarpa (Hook.) Nutt. and Pinuscontorta Dougl. are more generally distributed in both continental and maritime environments. Because of the differing winter soil conditions of these two climatic types, special emphasis was placed on root cold hardiness. Cold hardiness for root samples, as measured by a decrease in the electrolyte leakage, was much greater for A. amabilis and A. lasiocarpa than for P. contorta and T. mertensiana (−11.4, −11.5, −7.5, and −7.5 °C, respectively). Thus, subalpine conifer species distribution was not found to be influenced by root cold hardiness. Root cold hardiness of field-grown seedlings paralleled changes in soil temperature through February. Under constant temperature conditions (3 °C) the maximum cold hardiness achieved in 6 weeks was not subsequently maintained in A. amabilis and A. lasiocarpa. Injury in unhardened roots was coincident with bulk freezing, whereas hardened roots were able to tolerate bulk freezing. Needles had more than three times the level of cold hardiness of roots when measured in December, All species except P. contorta reached needle cold hardiness levels below −40 °C.
Allozyme variation of old Ginkgobiloba memorial trees in western Japan
Authors: Tsumura Yoshihiko , Motoike Hiroshi , Ohba Kihachiro
Published: March 2008

Allozyme variation of 89 old memorial trees of Ginkgobiloba L. in western Japan were investigated. For 12 loci from 10 enzyme systems, the percentage of polymorphic loci (95% level), the number of alleles per locus, and the observed heterozygosity were 75.0%, 2.5, and 0.234, respectively. The variation of this species is relatively high in comparison with other gymnosperms. Genetic relationships between four regions (Kansai, Shikoku, North Kyushu, and South Kyushu) were investigated by using two multivariate procedures. Based on a principal component analysis, these four regional groups were not separated clearly, except for the Shikoku and South Kyushu groups, which were almost completely separated in opposite peripheral zones of a scatter diagram. The canonical discriminant analysis also almost completely separated the Shikoku and South Kyushu groups. These results indicate that most trees of the Shikoku and South Kyushu groups might be descendants of individuals from the Kansai and North Kyushu groups, respectively, excluding some exceptions.
Evaluating peat as a growing medium for jack pine seedlings. 2. Fertilizer-based indices
Authors: Timmer V. R. , Folk R. S.
Published: March 2008

Leaching tests with water and complete fertilizer solutions were conducted on 26 diverse peat sources to evaluate a new index for characterizing peat quality for containerized stock production. Growth and nutrition of jack pine seedlings were inconsistent on these peat types and related poorly with conventional indices of peat quality. A fertilizer-based extractant was expected to reflect specific substrate–fertilizer interactions more closely than conventional laboratory extractants. Chemical analyses of leachates exhibited large variations among growing media and generally poor retention capacity of applied fertilizer. Correlations of leachate chemistry with seedling growth response revealed that only one measure, the alkali-labile organic-N fraction, was strongly related (r = −0.85) to plant performance. The inverse relationship suggested possible inhibitory effects of alkali-labile organic N with seedling performance; levels were also negatively correlated with shoot N uptake (r = −0.88). Subsequent growth trials demonstrated that supplemental N fertilization based on initial alkali-labile organic-N status compensated for growth retardation of seedlings on poor-performing peat substrates. This measure has promise as an index of growing-medium suitability, but needs more extensive testing.
Elliptical-fire perimeter- and area-intensity distributions
Authors: Catchpole E. A. , Alexander M. E. , Gill A. M.
Published: March 2008

Equations are presented for determining the proportion of the total perimeter and area burned for a simple elliptically shaped fire for any specified range of Byram's fireline intensities. The same principles apply to any characteristic that is dependent on fireline intensity. Only three inputs are required: head-fire intensity; the elliptical shape factor; and the backfire spread rate. This last quantity is not required if it is assumed that the ignition point is at one focus of the ellipse. The spatial distributions produced have potential application to fire management.
Sample sizes for point, double sampling
Authors: Oderwald Richard G. , Jones Elizabeth
Published: March 2008

Formulas are derived for determining the total number of sample points and the number of volume points for a point, double sample with a ratio of means estimator to replace a point sample and achieve the same variance. A minimum ratio of the cost of measuring volume to the cost of measuring basal area at a point is determined for which the point, double sample will be less costly, in terms of time required to measure points, than the point sample.
Morphophysiological traits as markers for the early selection of conifer genetic families
Authors: Greenwood M.S. , Volkaert H.A.
Published: March 2008

The effectiveness of a number of morphophysiological traits as markers for the early selection (before 2 years) of conifer families is evaluated based on a number of retrospective studies involving primarily half-sib families. Traits discussed include height growth (with and without stress), shoot growth patterns, shoot–root ratio, nutrient and water use efficiency, gas exchange characteristics (including photosynthesis), injury indices, gibberellic acid levels, and metabolic efficiency. Taken singly, no one trait except height consistently predicts future field performance, but even height predictions, although reported for a number of species, are restricted to the performance of half-sib families. We propose that the prediction of future performance of full-sib or clonal families using height may be relatively more difficult, because genotype × environment interactions and maturational changes in growth behavior will decrease age–age correlations with increased genetic relatedness.
Using marker-aided selection to improve tree growth response to abiotic stress
Authors: Tauer C. G. , Hallgren S. W. , Martin B.
Published: March 2008

The ability to locate quantitative trait loci (QTL) on a restriction fragment length polymorphism (RFLP) genetic linkage map will provide tree breeders the means to overcome some currently intractable problems inherent to breeding long-lived tree species. These RFLP–QTL maps will allow early, indirect, marker-aided selection (MAS) in breeding programs. This paper explores the opportunities and limitations of MAS, an approach to developing an RFLP–QTL marker map, and use of the map in breeding loblolly pine (Pinustaeda L.) for improved growth response to abiotic stress; specifically, drought stress. Growth responses under moderate drought stress are important to long-term forest productivity, because on most sites loblolly pine is subjected to growth-limiting moisture stress during part of almost every growing season. MAS provides new precision and reliability in identifying and breeding trees that are able to continue growth under moderate stress, and perhaps provides a unique opportunity for improving tree productivity on moderately stressful sites. Traits potentially related to growth under stress are identified, and their suitability for placement and use on an RFLP–QTL linkage map is discussed.