bluuebunny/crossref_metadata_2025 huggingface dataset:
A Theoretical Investigation of the Behavior of Droplets in Axial Acoustic Fields
Authors: Sujith R. I. , Waldherr G. A. , Jagoda J. I. , Zinn B. T.
Published: February 2008

This paper describes a theoretical investigation of the behavior of small droplets in an acoustic field. It was motivated by the increasing interest in the use of pulsations to improve the performance of energy intensive, industrial processes which are controlled by rates of mass momentum and heat transfer. The acoustic field is expected to enhance heat and mass transfer to and from the droplets, probably because of the relative motion between the droplets and the gas phase. Relative motion is traditionally quantified by an entrainment factor which is defined as the ratio between the amplitude of the droplet and the gas phase oscillations, and a phase delay. In an alternate approach, these two quantities are combined into a single quantity called the “degree of opposition” (DOP), which is defined as the ratio of the amplitude of the relative velocity between the droplet and the gas phase to the amplitude of the acoustic velocity. The equation for the droplet motion is solved using two methods; by numerical integration and by using a spectral method. Despite the nonlinear nature of the problem, the results were found not to be sensitive to initial conditions. The DOP was predicted to increase with increasing droplet diameter and frequency. In other words, larger diameters and higher acoustic frequencies reduce the ability of the droplets to follow the gas phase oscillations. The DOP also decreases with increasing acoustic velocity. It was shown that the amplitude of the higher harmonics are very small and that the droplet mean terminal velocity decreases with increasing acoustic velocity. Theoretical predictions were compared with experimental data and good agreement was observed.
Modeling the Lateral Vibration of Hydraulic Turbine-Generator Rotors
Authors: Bettig B. P. , Han R. P. S.
Published: February 2008

An extensive hydro-generator rotordynamic model is presented along with a technique for determining imbalances and shaft misalignments using the model and mechanical run vibration measurements. The hydro-generator model combines a finite element rotor model with a finite difference guide bearing model, generator magnetic forces and turbine hydraulic forces to calculate natural frequencies, stability and steady-state response. The complete model allows a great number of inputs including imbalances, rotation speed, guide bearing misalignments, coupling misalignments, bearing clearances, bearing temperatures, generator stator and rotor center misalignments, generator average air gap, generator power output and turbine blade tip clearance, all of which are described in this paper. Finally, the numerical results are compared with vibration data from the mechanical run and load test of an actual hydro generator unit.
Experimental Investigations on Noise Attenuation of a Twin Cylinder Stationary Diesel Engine with Different Types of Mufflers
Authors: Venkanna B. K. , Wadawadagi Swati B.
Published: February 2008

Together with atmospheric and water pollution, noise pollution is threatening human society with vehicles constituting the major source of noise. The available literature on control measures (1, 2, 3) indicates purely reactive mufflers in general are of more use for fixed speed machinery and dissipative attenuators have the ability to filler out acoustic energies over a wide range of frequencies. This paper presents cm attempt made to use a combination of these major types of mufflers fitted in the exhaust line of a four stroke, twin cylinder stationary diesel engine to attenuate exhaust noise to an acceptable level. A sound attenuation of 19 dBA has been obtained for combined reactive and dissipative (Model—M2, loosely packed with glass wool) attenuator through entire the load range without affecting the engine performance and a sound attenuation of 21 dBA has been obtained for reactive (with baffle plate. Model—M3) muffler through the entire load range with a nominal increase in BSFC at higher loads.
Prediction of Machine Deterioration Using Vibration Based Fault Trends and Recurrent Neural Networks
Authors: Tse P. W. , Atherton D. P.
Published: February 2008

High market competition for sales requires companies to reduce the cost of production if they are to maintain their market shares. Since the cost of maintenance contributes a substantial portion of the production cost, companies must budget maintenance effectively. Machine deterioration prognosis can decrease the cost of maintenance by minimizing the loss of production due to machine breakdown and avoiding the overstocking of spare parts. A new prognostic method is described in this paper which has been developed to forecast the rate of machine deterioration using recurrent neural networks. From tests applying the method to the prediction of nonlinear sunspot activities and vibration based fault trends of several industrial machines, the results have shown that the method is promising. It not only evaluates the seriousness of damage caused by faults, but also forecasts the remaining life span of defective components.
An In-situ Identification Method for Joint Parameters in Mechanical Structures
Authors: Hong S. W. , Shamine D. M. , Shin Y. C.
Published: February 2008

This paper presents an improved scheme based on the frequency response functions (FRFs) for in-situ identification of joint parameters of mechanical structures. Despite that measurement of FRFs at joint locations is essential for identifying the joint parameters of a structural dynamic system, it is often impossible to measure FRFs at joint locations. To this end, the present paper suggests an indirect estimation technique for unmeasured FRFs which are required for identification but not available. Theoretical investigation is made to delineate the effects of measurement noise and modeling error on indirect estimation and identification. Two index functions are introduced, which can indicate the quality of estimation or identification along the frequency. The index functions are proven to be useful not only as a weighting function in the identification procedure but also for evaluating the frequency region appropriate for identification. A series of simulations as well as experiments are performed for validation of the method.
Adaptive Vibration Control by a Variable-Damping Dynamic Absorber Using ER Fluid
Authors: Hidaka Shoshi , Ahn Young Kong , Morishita Shin
Published: February 2008

This paper describes a variable-damping dynamic absorber applying Electrorheological (ER) fluid to the damping element of a conventional-type dynamic absorber. A prototype of variable-damping dynamic absorber was constructed and its performance was verified with a three-story structural model. The special ability of the present dynamic absorber is to reduce the vibration amplitude at several frequencies by a single dynamic absorber. ER fluid is functional fluid whose yield shear stress can be changed by the applied electric field strength. Because of its peculiar property, ER fluid has been applied to various mechanical components such as shock absorbers and engine mounts for vehicles, clutches, valves, etc. One of the practical ways in applying ER fluid to mechanical components may be to expand the performance of conventional mechanical components by combining ER fluid effectively with them. In this sense, this paper shows a successful application of ER fluid to a conventional-type dynamic absorber. An adaptive neural network control system composed of a forward model network for system identification and a controller network was introduced to control the variable-damping element of the dynamic absorber. The numerical simulations show good agreements with the experimental results.
Vibration Control of Rotationally Periodic Structures Using Passive Piezoelectric Shunt Networks and Active Compensation
Authors: Tang J. , Wang K. W.
Published: February 2008

This paper proposes a multi-mode vibration suppression scheme for rotationally periodic structures. Identical active-passive hybrid piezoelectric networks are applied on each of the substructures, where active charge and current feedback is used together with passive piezoelectric shunts to optimize the network performance. By exploiting the rotational periodicity, a new algorithm is synthesized to analytically determine the control parameters. It is shown that this hybrid approach can suppress all the spatial harmonics, which cannot be achieved by purely passive piezoelectric shunts. It is also observed that such a configuration requires much less control effort (voltage and power) when compared to a purely active approach.
Optimal Estimation of Dynamic Loads for Multiple-Input System
Authors: Rao Zhushi , Shi Qinzhong , Hagiwara Ichiro
Published: February 2008

An optimal method is developed to estimate the dynamic loads for systems subjected to multiple inputs. The method focuses on minimizing the ensemble mean square error of the estimation. First, the inverse system analysis technique is employed to establish the error estimation equation. Then, by applying the noncausal Wiener filtering theory, the optimal estimator of dynamic loads is derived out. Numerical simulation work demonstrates that the method is of a good ability in suppressing the influence of measurement noises on estimation accuracy. Meanwhile, the simulating calculation of load estimation by a conventional method is also performed and the comparison of both results shows that the method proposed in this paper is rather effective and practicable for dynamic load estimation.
Damping Behavior Of Cantilevered Structronic Systems with Boundary Control
Authors: Tzou H. S. , Johnson D. D. , Liu K. J.
Published: February 2008

Distributed control of cantilever distributed systems using fully distributed piezoelectric layers has been investigated for years. The equivalent control actuation is introduced at the free end of the cantilever distributed systems, and the control action is equivalent to a counteracting control moment determined by the geometry, material properties, sensor signal, and control laws. In the negative proportional velocity feedback, the control effect is proportional to the feedback voltage and the controlled damping ratio usually exhibits linear behavior, if the feedback voltage is low. In this study, nonlinear damping behavior and an (equivalent) boundary changes of cantilever beams and plates with full-range feedback voltages are studied. Analytical solutions are compared with finite element simulations and experimental data. Studies suggest that the controlled damping ratio increases at low control gains and it decreases at high control gains induced by the boundary control moment. Furthermore, due to the highly constrained boundary control moment at high gains, the original fixed-free boundary condition can be approximated by an equivalent fixed/sliding-roller boundary condition.
Determining the Loss Factor by the Power Input Method (PIM), Part 1: Numerical Investigation
Authors: Carfagni M. , Pierini M.
Published: February 2008

Damping must be accurately determined in the design and/or optimization of vehicle and aircraft trim. Yet, owing to the complexity of the dynamic interaction among the components in trimmed panel systems, until now it has been difficult to obtain reliable damping estimates. In this work, the power input method (PIM), which compares dissipated energy to the structure’s strain energy, was evaluated as a damping evaluation tool. Numerical simulations were used to analyze the lumped mass system (with custom software) and the plates (with commercial finite element software) and consequently to evaluate the assumptions required to apply the PIM. It was thus possible to find a way of minimizing the effect of the assumptions on the results, whose importance would be fundamental in the successive phase involving the experimental application of the method.
Determining the Loss Factor by the Power Input Method (PIM), Part 2: Experimental Investigation with Impact Hammer Excitation
Authors: Carfagni M. , Pierini M.
Published: February 2008

Damping must be accurately determined in the design and/or optimization of vehicle and aircraft trim. Yet, owing to the complexity of the dynamic interaction among the components in trimmed panel systems, until now it has been difficult to obtain reliable damping estimates. The power input method (PIM) was numerically investigated in Part 1 of this work. The results regarding how to reduce the effects of the assumptions required to apply the method were put into practice through the experimental activity with impact hammer excitation described in this work. The experimental testing was conducted on flat and bent steel plates of various sizes trimmed with damping material. A method, called the “numerical updating technique” (NUT), was developed to reduce the number of measuring points and the effects of the discretization on the kinetic energy estimation. Comparison of the numerical and experimental results has validated the reliability and suitability of the proposed method.
Experimental Robust Control of Structural Acoustic Radiation
Authors: Cox D. E. , Gibbs G. P. , Clark R. L. , Vipperman J. S.
Published: February 2008

This work addresses the design and application of robust controllers for structural acoustic control. Both simulation and experimental results are presented. H∞ and μ-synthesis design methods were used to design feedback controllers which minimize power radiated from a panel while avoiding instability due to unmodeled dynamics. Specifically, high-order structural modes which couple strongly to the actuator-sensor path were poorly modeled. This model error was analytically bounded with an uncertainty model which allowed controllers to be designed without artificial limits on control effort. It is found that robust control methods provide the control designer with physically meaningful parameters with which to tune control designs and can be very useful in determining limits of performance. However, experimental results also showed poor robustness properties for control designs with ad-hoc uncertainty models. The importance of quantifying and bounding model errors is discussed.
Piezoelectric Array Sensing for Real-Time, Broad-Band Sound Radiation Measurement
Authors: Preumont A. , Franc¸ois A. , Dubru S.
Published: February 2008

This paper proposes a noise radiation sensor consisting of an array of independent piezoelectric patches connected to an adaptive linear combiner. The coefficients of the linear combiner are adapted in such a way that the mean-square error between the reconstructed volume displacement (or velocity) and either numerical or experimental data is minimized. A numerical study is conducted, to analyze the influence of the size of the piezoelectric array on the reconstructed volume velocity.
Analytical Implementation of Wave-Absorbing Control for Flexible Beams Using Synchronization Condition
Authors: Utsumi M.
Published: February 2008

For wave-absorbing control, the ideal controller transfer function H(s), which connects the sensor output to the control force, contains the imaginary unit i = −1 explicitly. Therefore, H(s) cannot be implemented directly by convolution integration of the sensor output with the inverse Laplace transform of H(s). In this paper, this problem is solved by imposing the synchronization condition on the bases of H(s). The condition requires that the instantaneous frequencies of the control force and the incident wave be the same. In other words, the instantaneous frequency of the control force varies with time in synchronization with the frequency components of the wave that are arriving at the wave-absorbing point with different group velocities. Therefore, the condition is referred to as the synchronization condition in this paper. The solution method is applicable to various combinations of sensor and actuator. Experimental verification is presented for a simulated case. The parameters of the digital algorithm for the experiment are determined analytically by using a complex error function and a generating function expansion of the Bessel function.
A Study of Control Strategies for the Reduction of Structural Vibration Transmission
Authors: Gardonio P. , Elliott S. J.
Published: February 2008

A theoretical study of the active control of structural vibration transmission in a multiple isolator system comprising a piece of equipment mounted on a base structure via active mounts is presented. Two types of problem have been studied with a common framework: first, the active isolation of vibration transmission from the equipment to the base structure and, second, the active isolation of vibration transmission from the base structure to the equipment. Four different control strategies using the measured axial velocity or/and axial force underneath or at the top of the mounts have been investigated and compared with the effectiveness of the reference control approaches of minimizing the total power transmitted from the equipment to the flexible base structure or minimizing the total kinetic energy of the suspended rigid equipment when driven by the base structure. For the first type of isolation problem the best control is achieved when a cost function which minimizes the weighted mm of the square values of the axial velocities and axial forces is implemented. For the second isolation problem the best control performance is given by the minimization of an estimate of the kinetic energy of the suspended equipment related to the translational degrees of freedom.
Characterization of Nonlinear Vibrating Systems Using Internal Feedback and Frequency Response Modulation
Authors: Adams D. E. , Allemang R. J.
Published: February 2008

The authors have developed a general frequency response function formulation in a previous article that relates the frequency responses of linear and nonlinear systems. This formulation is based on a spatial perspective of the nonlinearity as an internal feedback force. The present article gives a general interpretation of both the feedback perspective and the previously derived modulation frequency response relationships. A new method of characterizing nonlinear structural dynamic systems that is based on the frequency response relationships is then introduced.
Torsional Wave Propagation in a Circular Cylinder with a Periodically Corrugated Outer Surface
Authors: Kim J. O.
Published: February 2008

The paper describes a theoretical study on the speed of torsional elastic waves propagating in a circular cylinder whose outer radius varies periodically as a harmonic function of the axial coordinate. An approximate solution for the phase speed was obtained by using the perturbation technique for sinusoidal modulation of a small amplitude. This shows that the wave speed in the cylinder with a corrugated outer surface is less than that in a smooth cylinder by the square of the amplitude of the surface perturbation. This theoretical prediction reasonably agrees with an experimental observation reported earlier. It is also shown that the wave speed reduction due to the surface corrugation becomes larger for a thinner cylinder and for a bigger density of corrugation.
Cyclin E low molecular weight isoforms occur commonly in early-onset gastric cancer and independently predict survival
Authors: Milne A N A , Carvalho R , Jansen M , Kranenbarg E K , van de Velde C J H , Morsink F M , Musler A R , Weterman M A J , Offerhaus G J A
Published: February 2008

Background:

Post-translational cleavage of full-length cyclin E from the N-terminus can produce low molecular weight (LMW) isoforms of cyclin E containing the C-terminus only.

Aim:

To assess their presence in early-onset gastric cancer (EOGC), stump cancers and conventional gastric cancers and ascertain how they influence survival in EOGC.

Methods:

The expression of full-length and LMW isoforms of cyclin E in 330 gastric cancers, including early-onset gastric cancer (EOGC), stump cancer and conventional gastric cancer (>45 years old) was compared using antibodies targeted to the N- and C-terminals.

Results:

LMW isoforms were found in 35% of EOGCs, compared to 8% of conventional gastric cancers and 4% of stump cancers; their presence was visualised in cell lines using western blot analysis. In addition, C-terminal staining was a positive predictor of survival in EOGC. In contrast, no correlation with survival was found with the N-terminal antibody which detects only full-length cyclin E.

Conclusion:

EOGCs have a unique molecular phenotype and LMW isoforms of cyclin E may independently influence survival in EOGC.
The clinical significance of antinucleolar antibodies
Authors: Khan S , Alvi A , Holding S , Kemp M L , Raine D , Doré P C , Sewell W A C
Published: February 2008

Background:

The importance of antinucleolar antibodies seen by indirect immunofluorescence on HEp-2 cells, although associated with systemic sclerosis (SSc), in unselected patients is unknown.

Aims:

To determine the true clinical significance of antinucleolar antibodies in an unselected patient population.

Methods:

Antinucleolar antibody (ANoA) positive samples were identified in the immunology laboratory during routine autoimmune screening tests; case notes were reviewed using a standard proforma.

Results:

104 patients with ANoA were identified and ANoA+samples were subclassified into homogeneous, clumpy and speckled antinucleolar types. SSc was evident in only two (1.8%) patients. Other connective tissue diseases were identified in 33 patients (32%); 22 patients (21%) had evidence of various malignancies. Both disordered liver function and anaemia were seen in 22 patients and were the commonest laboratory abnormalities.

Conclusions:

Neither the presence nor subtype of ANoA is specific for systemic sclerosis. Laboratory comments appended to results should reflect this fact.
Ontogenetic study of the fusion of floral organs in the normal and "solanifolia" mutant of tomato (Lycopersicon esculentum)
Authors: Sekhar K. N. Chandra , Sawhney V. K.
Published: February 2008

A comparative study on the ontogeny of the fusion of floral organs of the normal (cv. Pearson) and a single-gene mutant, "solanifolia" (sf/sf), of tomato (Lycopersicon esculentum Mill.) was conducted. In the normal, floral organs were laterally fused, although the degree and the region of fusion varied in each organ type. In the mutant, the various organs either did not fuse or, if they did, were individually recognizable. The sepals and petals of mutant flowers, unlike those of the normal, did not form a calyx cup and a corolla tube, respectively, and this was related to the limited lateral growth of mutant primordia and the absence of growth in the interprimordial region. Also, petal primordia of the mutant were narrower in width at inception. The stamens of normal flowers were fused by interweaving rows of lateral and adaxial hairs on the anthers. The mutant stamens produced lateral and adaxial hairs, yet they were free. The nonfusion of mutant stamens was related to the smaller primordium widths, greater distance between the primordia, and the larger apex diameter at the time of stamen initiation. The gynoecium of normal flowers consisted of a single ovary, style, and stigma formed by the fusion of carpel primordia. In the mutant, the gynoecium consisted of several carpels, laterally adhered to each other, and each had a recognizable style and stigma. The lack of fusion of mutant carpels was attributed to the larger apex diameter of the mutant during carpel initiation.
Chara buckellii, a euryhaline charophyte from an unusual saline environment. II. Membrane potential and membrane conductance at steady state
Authors: Hoffmann Rosanne , Bisson Mary A.
Published: February 2008

Electrophysiological experiments were performed on internodal cells of Chara buckellii cultured in saline and freshwater media to see whether the membrane potential (Evo) and membrane conductance (Gm) are dominated by passive K+ conductance (K state), passive H+ conductance (H state), or active proton pumping (P state). Unlike other euryhaline charophytes, C. buckellii cells cultured under saline conditions were not dominated by any one state, showing little dependence on external K+ concentration and pH (pH°). Chara buckellii cells cultured in freshwater share some membrane properties with other freshwater charophytes. Freshwater cells appeared to be in the P state between pH° 5 and 7 as expected but never attained the H state usually observed at high pH° (> 10). Freshwater cells also showed a temporary, threefold increase in Gm at pH° 5, which could not be explained by an increase in passive Cl− or K+ conductance. Evidence consistent with an electrogenic Cl−/2H+ symport in freshwater-grown C. buckellii at pH° 5 and 7 is also presented.
Charomyces, a new genus of Hyphomycetes with thallic–arthric conidia
Authors: Seifert Keith A.
Published: February 2008

Charomyces amphimelas is described as the type species of a new anamorph genus of Hyphomycetes. The species produces verticillate conidiogenous hyphae that become chains of cylindrical brown ameroconidia with black polar bands. Conidium ontogeny is apparently thallic–arthric, and conidia secede rhexolytically.
Major polypeptides associated with differentiation in psychrophilic fungi
Authors: Newsted W. J. , Huner N. P. A.
Published: February 2008

Major polypeptides were observed upon one-dimensional sodium dodecyl sulfate gel electrophoresis of sclerotial extracts of the following psychrophiles: Myriosclerotinia borealis, Coprinus psychromorbidus, Typhula idahoensis, and Typhula incarnata. In general, the number, molecular mass, and relative proportion of these major sclerotial polypeptides varied considerably from species to species. Furthermore, in the case of M. borealis, the major sclerotial polypeptide did not appear to be an artifact of culturing conditions since a major polypeptide of similar molecular mass was also present in sclerotia of M. borealis collected from the field. Generally, the major sclerotial polypeptides were visible in the sclerotial initials but were not apparent in the vegetative hyphae. Thus, these major sclerotial polypeptides appear to be expressed as a function of sclerotial development. Electrophoresis of protein extracts of T. idahoensis and T. incarnata initially solubilized either in sodium dodecyl sulfate or urea sample buffer indicated that the type of denaturant initially used had a profound influence on the relative proportions of the major polypeptides and the overall polypeptide profile. Isoelectric focusing of sclerotial extracts indicated that the isoelectric points of the major sclerotial polypeptides of M. borealis ranged from 6.2 to 6.7, whereas the values of the major sclerotial polypeptides of the other three species were basic and ranged from 7.0 to 7.7.
Effects of canopy light gap and early emergence on the growth and reproduction of Geranium maculatum
Authors: Dahlem Theresa Schutte , Boerner Ralph E. J.
Published: February 2008

Biomass and reproduction of Geranium maculatum L. were measured in an artificial canopy light gap and under a closed canopy. The effects of emergence date were also compared. Increased light in the canopy gap resulted in increased biomass, rhizome mass, and percent of plants flowering in the second growing season after gap formation. The importance of proximate carbon in reducing fruit abortion was determined experimentally. The rate of fruit abortion increased and the number of days required for leaf expansion decreased when the plants were shaded by neutral screens. The reproductive effort of G. maculatum is thus primarily controlled by the previous year's carbon gain, while the proportion of flowers that matured to seeds was a function of proximate carbon gain. Shoots of G. maculatum emerged over a period of approximately 6 weeks in early spring, with canopy closure occurring midway through this interval. Early emergence of plants under the intact canopy permitted exploitation of the increased light levels in the period prior to canopy closure. This led to slightly increased aboveground growth and rhizome storage and a significant increase in the time spent in leaf expansion, though no differences in reproductive output existed between early and later emerging plants. Early emergence was less advantageous for gap plants. The role of gap-phase growth in G. maculatum is in increased genetic recombination and dispersal during this short period when the balance of sexual versus asexual reproduction is altered.
Stomatal responses of Populus to leaf water potential
Authors: Schulte P. J. , Hinckley T. M. , Stettler R. F.
Published: February 2008

The leaf conductance responses of clones of Populus trichocarpa, P. deltoides, and hybrids to changing leaf water potential were examined. Unlike the other species, P. trichocarpa not acclimated to water stress showed an inability to control water loss at low leaf water potential. It is suggested that stomata of P. trichocarpa plants grown under well-watered conditions remain open in spite of a loss of turgor in the leaf. Preconditioning through water stress of developing leaves, however, leads to greater stomatal control in foliage following rewatering. Leaf conductance of stressed and rewatered P. deltoides and hybrids remained near zero, while the leaf conductance of P. trichocarpa was partially reduced.
Effets des rayons γ 60Co sur des tigelles de Gerbera jamesonii irradiées in vitro
Authors: Dubuc-Lebreux M. -A. , Vieth J.
Published: February 2008

The aim of this work was to determine the direct inhibitory effects of 60Co γ-rays on plantlets and to control them in a future program of experimental mutagenesis. Gerbera jamesonii plantlets were irradiated in vitro using two sources of 60Co γ-rays. The following variables were tested: dose rate, total dose, irradiation of the growth medium, time interval between the exposure to γ-rays and the subdivision and transfer to fresh medium, and dose fractionation. These variables were evaluated using regeneration rate of new shoots, callus production, and plantlet growth rate (fresh weight). The optimal dose ranged around 50 Gy at a low dose rate (8.4 Gy∙h−1) and 30 Gy at high dose rate (600 Gy∙h−1). These conditions assured minimal development of callus and 50% of the normal multiplication rate. The γ-irradiation may be done during a 1-week interval before or after transfer on fresh medium, without causing any additional effects. Interrupted doses (3 × 10 Gy at 48-h intervals) caused less important inhibitory effects than a single dose (30 Gy), but the intensity of the reaction varied according to clone and the measured parameter. The clone "Duplex" reacted favourably; this type of treatment ensured better callus and plantlet growth and a higher rate of regeneration. In the case of "Mardi Gras," which is less sensitive to fractionated doses, only the weight of the plantlets was significantly less reduced.
Modifications structurales des faisceaux vasculaires primaires de la tige de Cordyline indivisa (Agavaceae). 1. Analyse du patron de conversion
Authors: Laliberté Sylvie , Vieth Joachim
Published: February 2008

In Cordyline indivisa Kunth, the primary bundles change from the collateral type (distal part) to the amphivasal type (proximal part). This conversion is related to the pattern of the longitudinal course of the bundles. Ontogenically, this reflects the two stages in the construction of a vascular bundle: the formation of the lower segment, characterized by its indefinite distal end and its subsequent junction with a leaf primordium. That part of the lower segment, which is amphivasal when fully differentiated, is axial in nature; its differentiation proceeds independently of the junction with the primordium. The collateral and intermediate stages are characteristic of the junction strand and that part of the lower segment having a reoriented differentiation. Since their presence depends on the junction with the primordium and is under the influence of the latter, we relate them to the leaf trace. According to our view of vascularization, each "developmental unit" consists of an axial segment which extends in a leaf trace; new axial bundles may be emitted from one part or the other. Consequently, our definition of the leaf trace is opposed to the classical one which states that the leaf traces diverge at intervals from continuous axial bundles.
Leakage of sodium ions from plasma membrane modification, associated with permeability change, in host cells treated with a host-specific toxin from a Japanese pear pathotype of Alternaria alternata
Authors: Park Pyoyun , Ohno Tohgo , Nishimura Syoyo , Kohmoto Keisuke , Otani Hiroshi
Published: February 2008

Ultrastructural sites for leakage of sodium ions in susceptible leaves of Japanese pear treated with AK-toxin I were examined by a precipitation method for sodium ions and analytical electron microscopy. The earliest effect of the toxin (50 μg/mL) appeared on the plasmodesmatal regions of the susceptible vascular bundle sheath and phloem cells within 5 min of the exposure where two cellular events were found at about the same time: plasma membrane modification and the precipitation of sodium antimonates. The precipitates were first found at the cell walls near plasmodesmata in susceptible cells, prior to the occurrence of the modification. Afterwards, susceptible plasma membrane became invaginated at both ends of plasmodesmata and the invaginations grew larger with the time of exposure. As the modification developed, the precipitates spread from the cell walls near plasmodesmata to the neighbouring or remote areas. These events were observed only in the toxin-treated susceptible cells. This work indicated that plasmodesmata of susceptible cells were the initial sites of toxin attack and sodium ions were leached as a result of the modification of plasma membrane near plasmodesmata. The results showed that the modification apparently was associated with a permeability change in the toxin-treated susceptible cells, and the active sites of toxin might be located on the plasma membrane of plasmodesmata.
Étude comparée de la structure foliaire et de l'ultrastructure des stomates chez deux cultivars de Pelargonium × hortorum, l'un chlorophyllien et l'autre mutant à feuilles blanches, vertes ou panachées
Authors: Couot-Gastelier J. , Louguet P.
Published: February 2008

L'étude en microscopie électronique des feuilles de Pelargonium × hortorum mutant a montré que les feuilles blanches ont un mésophylle composé de cellules ne comportant que des polyphénols et des plastes à structure rudimentaire, dépourvus d'amidon et de grana. Les feuilles vertes des plantes mutantes possèdent des chloroplastes de structure particulière à plasto-globules nombreux et volumineux rappelant les chromoplastes. Les cellules de garde possèdent la même ultrastructure dans toutes les feuilles des plantes mutantes, qu'elles soient vertes ou blanches. Leurs plastes sont dépourvus de grana et de chlorophylle et contiennent une grande quantité d'amidon. Ces modifications ultrastructurales sont liées à une ouverture maximale des stomates en atmosphère privée de CO2 et sont semblables à celles qui ont été décrites pour d'autres plantes non mutantes. Chez les plantes mutantes exposées à la lumière en présence de CO2, les stomates des feuilles blanches ne s'ouvrent pas, tandis que s'ouvrent ceux qui sont situés au-dessus d'un mésophylle chlorophyllien, bien que toujours dépourvus de chlorophylle. Ce résultat montre l'importance de la chlorophylle et de la photosynthèse au niveau du mésophylle pour le fonctionnement stomatique à la lumière.
Galtiera bostonensis, gen. et sp. nov., a protostelic calamopityacean from the New Albany shale of Kentucky
Authors: Beck Charles B. , Stein Jr. William E.
Published: February 2008

Two parts of a single, anatomically preserved stem fragment form the basis of a new Lower Mississippian taxon that is characterized here in detail. Stelar morphology, leaf trace departure, secondary xylem, outer sparganum cortex, and Kalymma-like leaf bases provide evidence of taxonomic relationship with the Calamopityaceae. The primary vascular column is deeply three ribbed with protoxylem strands restricted to the periphery of the xylem. Trace departure is associated with a dextral shift in the position of primary xylem ribs such that the tip of each rib describes a helical course through the axis. The result is a Fibonacci phyllotactic fraction of at least 2/5. On the basis of our observations, we hypothesize that the protoxylem strands may comprise five sympodia and, further, that although protostelic in gross morphology, the primary vascular system of Galtiera might actually be more similar to typical eusteles of the Calamopityaceae than protosteles of any other major group. Sclerotic clusters and strands in the cortex are of interest because they are unusually numerous and are usually associated with the phloem either of the main stem vascular column or of leaf traces. The evidence is consistent with the hypothesis that this morphology reflects a pathological response by the plant to viral or other infectious agents.
Peroxidase, polyphenoloxidase, and phenols in relation to resistance against Pseudomonas syringae pv. tomato in tomato plants
Authors: Bashan Y. , Okon Y. , Henis Y.
Published: February 2008

Peroxidase, polyphenoloxidase, and phenols were evaluated for their involvement in the resistance mechanism of tomato plants against Pseudomonas syringae pv. tomato (Okabe) Young, Dye & Wilkie. Healthy and infected leaf extracts of susceptible and resistant tomato cultivars were examined for their phenol content and activity of peroxidase and polyphenoloxidase. Peroxidase activity increased to a similar extent in infected mature and young leaves and in resistant and susceptible tomato cultivars. A positive correlation was found between the number of bacteria in the tissue and peroxidase activity in susceptible plants. Four different peroxidase isozymes were found in extracts from diseased plants, compared with only one in healthy plants. These facts indicated that peroxidase increases are not directly involved in the resistance mechanism of tomato plants. Significant positive correlations were found among resistance, polyphenoloxidase activity, and phenol accumulation in 20 different infected tomato cultivars, ranging from highly susceptible to highly resistant. Polyphenoloxidase activity and phenol accumulation were higher in inoculated, resistant cultivars than in inoculated susceptible ones. Inoculated resistant mature leaves showed both a higher polyphenoloxidase activity and a higher phenol content than younger susceptible leaves. A direct correlation was found between disease index, polyphenoloxidase activity, and phenol content in the tissue. Eight different polyphenoloxidase isozymes were found in susceptible diseased plants. Phenols extracted from inoculated resistant tomato plants inhibited pathogen growth. Our data suggest that the oxidative phenol system of tomato plants contributes to resistance to P. syringae pv. tomato.
Understanding the long-term effect of CO2 enrichment on a pasture: the importance of disturbance
Authors: Taylor Kevin , Potvin Catherine
Published: February 2008

This study is part of a research program examining the effects of elevated atmospheric carbon dioxide on a pasture. It was designed to examine (i) the interaction between disturbance and the atmospheric CO2 concentration at the community level, and (ii) the response of a major weed Chenopodium album to CO2 enrichment in a natural field situation. Although both the total number of species and Simpson's index increased upon disturbance, these traits did not respond to CO2 fertilization. Counter to our expectation, we found no significant interaction between disturbance and CO2. The composition of the community that established in the open, disturbed spaces was a function of seed availability and as such independent of the atmospheric CO2 concentration. Using height of the background vegetation to assess the impact of elevated CO2, we found some evidence for density dependence in the undisturbed quadrats but not in the disturbed ones. For C. album, the disturbance regimes outweigh the CO2 increase in importance. Neighboring plants have a strong influence on C. album growth, this even though the C. album photosynthetic mechanisms are potentially responsive to elevated CO2. The present study highlights the complex feed-back interactions occurring when a community is exposed to elevated CO2 concentration. Key words: elevated carbon dioxide, disturbance, Chenopodium album, open-top chambers.
Response to stem bending in forest shrubs: stem or shoot reorientation and shoot release
Authors: Wilson Brayton F.
Published: February 2008

Shrubs in the forest understory may be bent by their own weight or by overstory debris. To maintain height growth they must respond to bending by vertical growth of new shoots, reorientation of older axes, or by releasing preventitious buds to form epicormic shoots. I tested for these responses in Ilex verticillata L., Cornus amomum Mill., Gaylussacia baccata (Wang.) K. Koch, Viburnum cassinoides L., Hamamelis virginiana L., and Kalmia latifolia L. For each species, I removed potentially supporting vegetation adjacent to 20 stems, left 10 stems untreated to test for bending by self weight, and bent the remaining 10 stems to 45° to simulate effects of fallen debris. Stem angles and curvatures were measured from before leaf out until just before leaf fall to detect either sagging from self weight or upward bending from tension wood action. Control stems initially leaned out of vertical and five of six species sagged further into a cantilever form. Several control stems failed and bent to the ground. Stems of H. virginiana, I. verticillata, and C. amomum formed tension wood, but only the first two species bent upward. Viburnum cassinoides, G. baccata, and K. latifolia formed no tension wood and sagged further down after being bent. Epicormic shoots formed with varying frequencies in all species except K. latifolia. Epicormic shoots were the major response in C. amomum, V. cassinoides, and G. baccata. New terminal shoots on bent stems recovered toward vertical in I. verticillata and K. latifolia. Negative gravitropic response of shoots was the only recovery mechanism for K. latifolia. Key words: forest shrubs, tension wood, epicormic shoots, bending, stem architecture.
Biological activities of seaweed extracts from British Columbia, Canada, and Korea. I. Antiviral activity
Authors: Kim J. H. , Huang A. M. , Bannister K. , Choi T. J. , Towers G. H. N. , DeWreede R. E. , Hudson J. B. , Jin H. , Hong Y. K.
Published: February 2008

We report the results of the first screening of 89 seaweeds collected from British Columbia, Canada, and Korea for antiviral activity. Various concentrations of methanol extracts of dried algae were tested against 100 plaque-forming units of herpes simplex virus type 1 and Sindbis virus in Vero cell monolayers. Eleven extracts inhibited both viruses, and 22 extracts were active against only one of the viruses. Thus, in total 37% of the species were active, and only two of these extracts also showed cytotoxicity at the concentrations tested. The antiviral activities were proportionately more frequent in the Korean extracts (56% compared with 27% of Canadian extracts), but in general the more potent extracts were of Canadian origin. Analipus japonicus was the most potent anti-herpes species, and the Korean species of Codium fragile was the most potent against both viruses. This high yield of antiviral extracts illustrates the potential of seaweeds as a resource for bioactive compounds. Key words: seaweeds, algal extracts, antiviral activities.
Changes in actin filament arrays in protocorm cells of the orchid species, Spiranthes sinensis, induced by the symbiotic fungus Ceratobasidium cornigerum
Authors: Uetake Yukari , Peterson R. Larry
Published: February 2008

Seeds of the terrestrial orchid, Spiranthes sinensis, were germinated in vitro in association with the symbiotic fungus, Ceratobasidium cornigerum. Resulting colonized protocorms were prepared for light microscopy, transmission electron microscopy, and fluorescence labelling of actin filaments for examination with laser scanning confocal microscopy. Fungal hyphae invaded the suspensor end of embryos, formed typical hyphal coils (pelotons) within parenchyma cells, and then underwent lysis resulting in degraded hyphal masses. Hyphae and hyphal masses were enveloped by host-derived membrane. Changes in actin filament arrays accompanied fungal colonization. Uncolonized cells had a network of actin filaments and actin bundles (cables) located in the cortical region of the cell cytoplasm; some of these were associated with the nucleus and amyloplasts. Although actin filament arrays were still present in protocorm cell cytoplasm during fungal entry and peloton formation, most of the cortical network disappeared and instead actin filaments radiated from the periphery of developing pelotons towards the cell wall. Degraded hyphal masses also had actin filament arrays associated with them, again radiating toward the cell periphery; a network of cortical actin filaments reappeared in the protocorm cell cytoplasm at this stage. Actin filaments did not appear to have a close physical association with fungal hyphae except in the epidermal hairs that developed from protocorms; this differs from our previous observations on microtubules in this system. Key words: actin, actin filaments, orchids, mycorrhizas, laser scanning confocal microscopy.
Gas exchange and water relations responses to drought of fast- and slow-growing black spruce families
Authors: Tan Weixing , Blake Terence J.
Published: February 2008

To determine how different mechanisms of drought tolerance contribute to growth rate under drought, this study compared four full-sib black spruce (Picea mariana (Mill.) B.S.P.) families which differed in growth rate when soil water became limiting, stomatal conductance, photosynthesis, and water relations responses to drought. Repeated drought cycles were imposed by withholding soil water in a nursery and physiological responses were measured near the end of the first and third cycle. The most vigorous family under drought had greater osmotic adjustment and maintained higher rates of net photosynthesis during the first cycle of drought and resumed higher rates of photosynthesis sooner upon stress relief, compared with two slow-growing families. Pressure–volume analysis of drought-stressed shoot tissues indicated that the fast-growing family exhibited a larger degree of elastic enhancement (i.e., decrease in bulk modulus of elasticity), which would explain its higher turgor pressure, compared with the two less vigorous families. However, family differences in gas exchange and water relations largely diminished when seedlings were exposed to repeated cycles of drought. Therefore, fast-growing black spruce families under drought may gain selective growth advantage by a better ability to tolerate, rather than postpone, momentary dehydration. Short-term screening trials could be used to detect drought tolerant genotypes in black spruce. Key words: drought, family variation, photosynthesis, Picea mariana, stomatal conductance, water relations.