bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Loss from a Theta Pinch
Authors: Green T. S. , Fisher D. L. , Gabriel A. H. , Morgan F. J. , Newton A. A.
Published: December 2004

Electron temperatures measured in a megajoule theta pinch are found to be limited to ∼300 eV over the pressure range 10–50 mTorr and to vary during the discharge time in a nonadiabatic manner. The plasma diamagnetism shows a rapid decay at the time of maximum Poynting flux and since there is no particle loss at this time there must be an energy loss of the order of the energy input rate. Variation of the concentration of oxygen, which is the major impurity, by addition of known amounts or by reduction of the intrinsic 1.5% an order of magnitude with a new pre-ionization technique, indicates an energy loss rate of 2 × 1013 erg cm−3 sec−1 at zero oxygen concentration. It is not possible to account for this loss by radiation in the continuum spectrum. A simple model of axial thermal conduction is developed in which the energy is transported to cold regions beyond the ends of the theta-pinch coil. The model predicts a limiting temperature due to the steep temperature dependence of the conductivity coefficient K = αT5/2. Other predictions of the model concerning the variation of diamagnetism are found to be valid. Finally the results of other theta-pinch experiments are examined and some are found to fit the model.
Hot-Electron Plasma Confinement in Magnetic Fields with Compensating Curvature
Authors: Hartman Charles W.
Published: December 2004

Loss of plasma across B is observed when the average field curvature is destabilizing in the hydromagnetic sense. Under stable curvature conditions loss across B is suppressed and enhanced end-loss bursts appear.
Statistical Frameworks for Weak Plasma Turbulence
Authors: Davidson R. C.
Published: December 2004

A hierarchy is constructed describing the time evolution of correlations due to collective interactions in a weakly turbulent, spatially uniform ensemble of Vlasov plasmas. It is shown that this ``Vlasov hierarchy'' is identical to the Bogoliubov—Born—Green—Kirkwood—Yvon (BBGKY) hierarchy for irreducible correlations in a spatially homogeneous plasma, provided the effects of single particle encounters are deleted from the BBGKY framework. In addition, the random phase approximation used in conventional treatments of weak plasma turbulence is shown to be automatically embodied by such a formalism. Upon ordering the system of equations in the weak turbulence parameter, 〈E2〉/nmvav2, the questions of closure and time validity are examined.
Anomalous Diffusion in a Weakly Turbulent Plasma
Authors: Macmahon Alan B. , Drummond William E.
Published: December 2004

A given spectrum of plasma oscillations, representing a state of weak turbulence, is considered in a uniform Vlasov plasma in a strong magnetic field. The parallel velocity and transverse spatial diffusion coefficients for thermal particles are found by studying the motion of a test particle. Diffusion results from the zero-frequency component of the electric field seen by the test particle. Two nonlinear processes contribute to this component: modification of the field seen by the test particle by high-frequency modulation of its velocity, and excitation of low-frequency ``virtual waves'' by nonresonant mode coupling. The latter effect dominates ion diffusion, increasing it by the factor (mi/me)2; for electrons, the two effects almost cancel, decreasing the diffusion by the factor (kλD)4. Thus the low-frequency virtual waves must not be neglected in estimating anomalous diffusion or heating associated with a given high-frequency spectrum.
Correlation Measurement in a Turbulent Flow using High-Speed Computing Methods
Authors: Frenkiel François N. , Klebanoff Philip S.
Published: December 2004

Third-order time-correlations downstream of a grid were measured with a hot-wire anemometer using high-speed computing methods. The nonlinear response of the hot-wire to the fluctuations of velocities is taken into account as well as the effect of transverse velocities. It is found that the correlations Rt2,1(h)=u′2(t)u′(t+h)¯/(u′2)¯3/2 and Rt1,2(h)=u′(t)u′2(t+h)¯/(u′2)¯3/2 are substantially different from previous results and demonstrate that the assumption of isotropy is not adequate for these correlations downstream of a grid. The nonlinear response does not significantly affect the difference ½(Rt2,1 − Rt1,2). Since previous conclusions concerning the nature of third-order correlations were based on the measurements of such differences they masked the effects of nonlinearity on the individual correlations. Correlations of fifth-order are also presented and their relations to the third-order correlation are discussed. Although the nonlinear corrections are quite important for odd-order correlations they are negligible for correlations of even-order.
Measurement of Shock-Wave Structure in Helium-Argon Mixtures
Authors: Center R. E.
Published: December 2004

Shock-wave density profiles have been measured for each component in helium-argon mixtures over the argon mole fraction range from 0.011 to 0.87. The shock waves were produced by a shock holder in the flow field near the exit of a Mach 2 nozzle. The species densities were derived from spectrally resolved measurements of the radiation from gas atoms excited by an electron beam. The measured species density ratios across the shock waves agreed within 7% with each other and with theory. Diffusive separation of the mixture was observed within the shock wave and the helium was compressed upstream of the argon in all cases. No initial acceleration of the argon was observed for small argon mole fractions contrary to the continuum calculations of Sherman. Diffusion effects resulted in considerable broadening of the shock wave, and for argon mole fractions of 0.1 to 0.2 the maximum-slope thickness of the mixture was almost three times the corresponding value for a pure gas.
Radiative Transfer Effects on the Flow Field and Heat Transfer behind a Reflected Shock Wave in Air
Authors: Anderson John D.
Published: December 2004

The effects of radiative transfer on the high-temperature heat-conducting flow field and end-wall heat transfer behind a reflected shock wave is investigated for air in local thermodynamic and chemical equilibrium. A numerical solution is obtained using a finite-difference method, and calculations are carried out for transparent, gray, and non-gray gas models of the radiative transport at conditions corresponding to an incident shock wave moving at a velocity of 8.85 km/sec into air at 1 mm Hg. The results obtained show that end-wall radiative heat transfer is markedly reduced due to both radiative cooling and self-absorption, but conductive heat transfer and reflected shock wave velocity are only slightly affected. The results also show that if self-absorption is to be realistically accounted for, a non-gray model must be employed. In addition, the results indicate a limited analogy between end wall and blunt body stagnation point radiative heat transfers.
Theoretical Considerations on Precursor Waves in Electromagnetically Driven Shock Tubes
Authors: Lubin M. J.
Published: December 2004

A possible mechanism to explain the wavelike behavior of precursors in electromagnetically driven shock tubes is considered. By considering the electromagnetically driven shock tube as an electromagnetic transmission line, the main features of this wave are deduced and compared with available experimental data. Good agreement is obtained with available wave velocity, and wavefront thickness measurements.
Thermal Instability in a Spherical Region Heated from Below
Authors: Sherman Michael , Catton Ivan
Published: December 2004

The classical Rayleigh thermal stability problem of an infinite horizontal fluid layer heated from below is extended to the case of a fluid, confined within a rigid sphere whose wall is nonuniformly heated. The temperature distribution on the wall is specified so that a constant temperature gradient is established in the direction of the body force acting on the fluid (``heated from below''). Two different variational principles are presented, each equivalent to the eigenvalue problem for the critical Rayleigh number (the stability criterion). These principles form the basis for two approximate methods of determining upper bounds to the critical Rayleigh number. The critical Rayleigh number obtained is 16 132 (based on a unit diameter) which is almost ten times greater than that of the horizontal-layer configuration (based on a unit height). The results are compared with a previously published analysis and are found to be 10% lower.
Transport Coefficients of Ionized Gases
Authors: Mason E. A. , Munn R. J. , Smith Francis J.
Published: December 2004

The repulsive and attractive screened Coulomb potentials may be used to represent interactions among charged particles in a gas. The classical Chapman-Enskog collision integrals are calculated for these potentials over a wide range of reduced temperatures, equivalent to a wide range of electron densities and temperatures. At high temperatures the repulsive and attractive collision integrals are equal and agree with the earlier calculations of Kihara and Liboff. At lower temperatures the attractive collision integrals grow larger than the repulsive collision integrals as the temperature falls, and both grow apart from the previous results. It is shown that quantum effects are large in high-density plasmas at all temperatures and in low-density plasmas at very high temperatures.
Model Dependence of the Slip Coefficient
Authors: Loyalka S. K. , Ferziger Joel H.
Published: December 2004

The slip flow or Kramers problem for rarefied gas flow is studied by the use of a number of models. The models employed include the Bhatnagar-Gross-Krook model, Maxwell molecules, the Gross-Jackson model, Cercignani's variable-collision-frequency model, and a new model which allows variable collision frequency, the correct Chapman-Enskog solution and the correct Prandtl number. The Kramers problem is solved by means of an approximation scheme based on the method of elementary solutions for the constant-collision-frequency models and by a variational method for the variable-collision-frequency model. Numerical results show that the slip coefficient is only slightly model-dependent.
Self-Excitation of Acoustic Oscillations by Gaseous Adsorption
Authors: Porter J. W.
Published: December 2004

An analysis is made of the stability of a one-component gas in a one-dimensional system closed by boundaries capable of gaseous adsorption. It is shown that coupling between small disturbances and adsorption rate processes creates an infinite number of unstable modes with discrete frequencies ranging from zero to infinity—the instability increasing with frequency, to a limiting value that depends only on the surface accommodation coefficient. In addition, a finite number of positively damped modes are generated. In the limit as the interface becomes nonadsorbing, the unstable modes become neutrally stable with natural frequencies identical to those of an organ pipe closed at both ends, and the positively damped modes disappear. Speculation based on these results leads to the possibility of adsorption instability as a mechanism for the transition from laminar to turbulent flow in a channel whose walls are capable of gaseous adsorption.
Magnetohydrodynamic Boundary Layers with Variable Properties
Authors: Gribben R. J.
Published: December 2004

Boundary layers in fluids, whose diffusivities of vorticity ν, heat κ, and magnetic field η satisfy ν<<κ<<η have thicknesses differing in order of magnitude. Uniformly valid solutions are obtained by matching series for each layer at the two interfaces.
Cyclotron Harmonic Resonances in the Frequency Conversion Output Power of a Plasma
Authors: Tetenbaum S. J.
Published: December 2004

Electron cyclotron harmonic resonances have been found in the second harmonic and sum frequency powers emerging from an electrodeless helium discharge. The resonances are due to cyclotron harmonic interactions with the incident waves followed by frequency conversion.
Time-Dependent Numerical Study of Taylor Vortex Flow
Authors: Meyer Kenneth A.
Published: December 2004

Finite difference techniques applied to the time-dependent Navier-Stokes equations are used to study the development of Taylor vortices in the flow between circular cylinders. A series of preferred stable steady states defined by the variation of axial cell wavelength with Reynolds number is obtained for a radius ratio of inner to outer cylinder of 1.2. The numerically obtained critical Reynolds number for the onset of Taylor vortices at this radius ratio agrees within 3% to that obtained from linear theory. Streamline plots are included to show the effect of nonlinearity on the cell patterns. The relationship between initial conditions and the resulting steady flow pattern is discussed for the case of a radius ratio of 1.2 and a Reynolds number of 1500.
Relaxation Constants of a Uniform Hard-Sphere Gas
Authors: Kuščer I. , Williams M. M. R.
Published: December 2004

A uniform hard-sphere gas with a small departure from a Maxwellian velocity distribution is considered, and the approach towards equilibrium investigated. Methods adapted from the theory of neutron thermalization are used to show that an infinite sequence of discrete relaxation constants λn exists, corresponding to exponentially decaying modes. The sequence begins with the degenerate eigenvalue λ0 = 0, and converges towards the lower bound of the continuous spectrum set by the minimum value of the scattering rate, Vmin = V(0).
Equations for Gas Mixtures
Authors: Goldman Edward , Sirovich Lawrence
Published: December 2004

Starting with the exact Boltzmann equations for gas mixtures with arbitrary intermolecular potentials, a macroscopic theory of mixtures is obtained. For a binary gas with masses mα, mβ total number density n, viscosity μ, and diffusion coefficient Dαβ, it is shown that the classical Chapman-Enskog theory of mixtures holds when C = 2μ/[(mα + mβ)nDαβ] (which is related to the Schmidt number) is near unity. This criterion delimits the region of validity of the Chapman-Enskog equations. For situations outside the Chapman-Enskog range a new system of equations, referred to as the two-temperature theory, is shown to be valid. The latter includes a new diffusion effect which involves temperature differences. The temperature difference in the Chapman-Enskog regime which becomes higher order is also explicitly obtained. For problems widely removed from equilibrium a two-fluid theory is advanced. The last has the Chapman-Enskog and two-temperature theories as limiting forms in near equilibrium situations. A heat flow problem illustrating the new equations is discussed.
Review of Some Experimental Results on Boundary-Layer Transition
Authors: Tani Itiro
Published: December 2004

A review is presented of some experimental results on transition from laminar to turbulent flow in a boundary layer of an incompressible fluid on a flat plate with no pressure gradient. In the absence of large disturbing influences, transition involves the sequence of processes occurring in the following order: The amplification of weak disturbances; the nonlinear development of disturbances; the development of high-shear layer and high-frequency disturbances; and the development of turbulent randomness. The interpretation of these processes is reviewed and brought up to date.
Nonlinear Instability of Plane Couette Flow
Authors: Kuwabara S.
Published: December 2004

On the basis of the Meksyn-Stuart method, nonlinear instability of the plane Couette flow is investigated. The perturbed stream function and the mean flow field are determined by the Galerkin method. A neutral surface is obtained in a three-dimensional space of the Reynolds number, wave-number, and amplitude. The critical Reynolds number based on the width and the relative velocity is estimated to be about 190 000.
Study of Turbulence Close to a Solid Wall
Authors: Hanratty Thomas J.
Published: December 2004

Electrochemical techniques have been used to determine (1) the local average and fluctuating mass transfer rates in a large mass transfer surface: (2) local average and fluctuating velocity gradient at the wall; and (3) the limiting value of the eddy diffusion coefficient at the wall. These results reflect properties of the fluctuating flow field at locations much closer to the wall that can be examined with the hot-wire anemometer.
Importance of the Atmospheric Boundary Layer over the Oceans in Synoptic Scale Meteorology
Authors: Pierson Willard J.
Published: December 2004

The problems of turbulence in geophysics are usually thought of as encompassing a microscale, a mesoscale and a synoptic scale, and often it is not clear how they can be interrelated and how to obtain useful information at the synoptic scale. The rate of growth of a spectral component in a building wind-generated sea has been related to derivatives of the mean wind profile. The properties of the wind profile over water may best be determined at the microscale but the waves over the ocean are a synoptic scale phenomenon. These facts would be academic were it not for the additional fact that polar orbiting spacecraft may soon make it possible to measure the waves over the ocean on a global scale twice a day and that if the conditions defining the mesoscale were better understood a very high quality surface synoptic weather map for wind fields and pressure patterns could be produced. Progress in this area is described.
Joint Density Functions of Turbulent Variables in the Atmospheric Boundary Layer
Authors: Holland J. Z.
Published: December 2004

Empirical joint probability density functions of filtered, unlagged velocity components and temperature and of certain physically meaningful sums have been examined using Round Hill Field Station data series. The patterns contain information not contained in the variance and covariance spectra or other simple moments usually analyzed. In particular an apparent downward transport of high-frequency eddy kinetic energy in stable conditions is illustrated and shown to be related to the dominant effect of low-frequency total velocity fluctuations.
Thermal Turbulence in Forced Convection
Authors: Elder J. W.
Published: December 2004

The role of the Peclét number in forced convection in a fluid layer randomly heated from below is studied experimentally and numerically. The main features of thermal turbulence, especially the intermittency arising from irregular growth of buoyant plumes, are well reproduced numerically.
Turbulent Transfer Processes for Quasi-Homogeneous Flows within the Atmospheric Surface Layer
Authors: Cramer H. E.
Published: December 2004

Comprehensive time-series measurements of the fluctuations in air temperature and the orthogonal components of wind velocity, made simultaneously for periods of 1h at heights of 40 and 16 m, are analyzed to test the validity of the Monin-Obukhov similarity theory and to establish characteristic features of energy exchange processes for air flows over a nonhomogeneous surface. The results show that many of the similarity theory predictions concerning the statistics of turbulence are valid and indicate that the disparity in previous measurements is in part due to the short length of the observation period. Also, direct measurements of the vertical fluxes of momentum and sensible heat reveal a significant height dependence that varies with thermal stratification and length of the observation period.
Similarity of Thermally Stratified Shear Flows in the Laboratory and Atmosphere
Authors: Chuang H. , Cermak J. E.
Published: December 2004

Mean wind velocity and temperature profiles were measured in a wind-tunnel boundary layer (approximately 1m thick) made thermally stable or unstable by flow over a horizontal flat plate (29 m long, and 2 m wide) which was either cooled or heated along the downstream 13 m. Laboratory and field mean velocity profiles were found to be similar as were the mean temperature profiles when compared on the basis of a log-plus-linear relationship. For thermally unstable flows, the dimensionless wind shear is approximated by the form (1+z/L)n with n = 32. The transition from forced- to free-convection flow for unstable stratification was gradual and occurred in a Richardson number range predicted by Gurvich and Priestley. Both laboratory and field data for ζ < 0 are best represented by a function of the form Ri = −(1−S2/3/αS).
Use of Radioactive Tracers in Studying Mass Transfer in the Atmospheric Boundary Layer
Authors: Barry P. J. , Munn R. E.
Published: December 2004

Certain natural surfaces such as snow act as almost perfect sinks for some radioactive gases. Experiments in which tracers of differing molecular diffusivities are released simultaneously, therefore, permit inferences to be drawn about the importance of the lowest few millimeters of the atmosphere in regulating vertical fluxes. The results of some tracer field experiments at Chalk River, Canada, are described, and the implications are discussed.
Statistical Properties of the Sea
Authors: Benney D. J. , Newell A. C.
Published: December 2004

The long-time behavior of weakly interacting random waves on the ocean surface is shown to be a solvable theoretical problem. Asymptotic closures are obtained for both the free and forced cases.
Wind Amplification of Water Waves
Authors: Bryant P. J.
Published: December 2004

The interaction between wind and water waves is investigated in terms of the correlations between the air and water motions. A representation of the water surface as a sum of nearly sinusoidal wave trains is used to describe the form of the correlations. Attention is drawn, in particular, to the wave amplification resulting from the nonlinear part of the forced response of the turbulent air flow to the water wave motion.
Recent Mathematical Treatments of Laminar Flow and Transition Problems
Authors: Görtler H. , Velte W.
Published: December 2004

Recent progress made in nonlinear stability theory of viscous, incompressible flows is discussed. First, progress made by means of the energy method is considered. In some cases the stability bounds obtained with the energy method coincide or nearly coincide with the critical values given by the linear stability theory. Further, a survey of recent mathematical investigations on the branching of steady solutions at the critical Reynolds (or Rayleigh) numbers is given. Finally, numerical methods solving the steady Navier—Stokes equations by finite differences are briefly mentioned.
Mechanics of the Air—Sea Interface
Authors: Stewart R. W.
Published: December 2004

Within the last decade there has been a great increase in the sophistication of ideas on wave generation, but the more complex observational data required to check these theoretical ideas are still lacking. Such data as do exist seem to support, at least qualitatively, the Phillips idea of the nature of the initial wave generation mechanism, but indications are that the Miles mechanism of wave generation at later stages is inadequate to explain the observed increase of wave energy. New ideas involving the effect of the turbulence in the air, and of different flow configurations from that proposed by Miles, are being proposed. The available observations are still inadequate to test these ideas. Of particular importance to the theory are measurements in the air below the level of the wave creasts.
Weakly nonlinear statistics of high random waves
Authors: Fedele Francesco , Arena Felice
Published: December 2004

It is well known that in a Gaussian sea state for an infinitely narrow spectrum the crest height and the trough depth follow the same Rayleigh distribution, because of linearity of the first order Stokes expansion solution. For spectra of finite bandwidth, Boccotti obtained, as a corollary of his first formulation of the theory of quasideterminism (which is exact to the first order in a Stokes expansion), that the crest height and the trough depth still follow asymptotically the Rayleigh law for high waves in Gaussian sea states. In this paper we extend the theory of quasideterminism of Boccotti to the second-order, deriving new wave crest and wave trough distributions that take into account nonlinear effects and are valid for finite bandwidth of the spectrum in deep water. Nonlinear Monte Carlo simulations validate our theoretical predictions and comparisons with experimental data and the recent model of Forristall are finally presented.
A speed limit for conformational change of an allosteric membrane protein
Authors: Chakrapani Sudha , Auerbach Anthony
Published: December 2004

Neuromuscular acetylcholine receptors are synaptic ion channels that open and close with rate constants of ≈48,000 s
-1
and ≈1,700 s
-1
, respectively (in adult mouse, at 24°C, -100 mV membrane potential). Perturbations of many different sites in the protein can change these rate constants, with those in the extracellular domain mainly affecting channel-opening and many of those in the membrane and intracellular domains mainly affecting channel-closing. We used single-channel recordings to measure the total open time per activation (τ
b
) elicited by a low concentration of the natural transmitter, acetylcholine. τ
b
increased in constructs with mutations that increased the gating equilibrium constant by either increasing the opening or decreasing the closing rate constant. However, τ
b
did not approach the same asymptote in fast-opening and slow-closing constructs. The maximum value for the slow closers was about twice that for the fast openers. One interpretation of this difference is that there is an upper limit to the channel-opening rate constant, which we estimate to be ≈0.86 μs
-1
. One possibility is that this limit is the rate of conformational change in the absence of an overall activation barrier and thus reflects the kinetic prefactor for the acetylcholine receptor opening isomerization.
The descent of the antibody-based immune system by gradual evolution
Authors: Klein Jan , Nikolaidis Nikolas
Published: December 2004

The antibody-based immune system (AIS) is one of many means by which organisms protect themselves against pathogens and parasites. The AIS is present in jawed vertebrates (gnathostomes) but absent in all other taxa, including jawless vertebrates (agnathans). We argue that the AIS has been assembled from elements that have primarily evolved to serve other functions and incorporated existing molecular cascades, resulting in the appearance of new organs and new types of cells. Some molecules serving other functions have been appropriated by the AIS, whereas others have been modified to serve new functions, either after the duplication of their encoding genes or through the acquisition of an additional function without gene duplication. A few molecules may have been created
de novo
. The deployment and integration of the ready-made elements gives the impression of a sudden origin of the AIS. In reality, however, the AIS is an example of an organ system that has evolved gradually through a series of small steps over an extended period.
The cAMP binding domain: An ancient signaling module
Authors: Berman Helen M. , Ten Eyck Lynn F. , Goodsell David S. , Haste Nina M. , Kornev Alexandr , Taylor Susan S.
Published: December 2004

cAMP-binding domains from several different proteins were analyzed to determine the properties and interactions of this recognition motif. Systematic computational analyses, including structure-based sequence comparison, surface matching, affinity grid analysis, and analyses of the ligand protein interactions were carried out. These analyses show distinctive roles of the sugar phosphate and the adenine in the cAMP-binding module. We propose that the cAMP-binding regulatory proteins function by providing an allosteric system in which the presence or absence of cAMP produces a substantial structural change through the loss of hydrophobic interactions with the adenine ring and consequent repositioning of the C helix. The modified positioning of the helix in turn is recognized by a protein-binding event, completing the allostery.
Insect-Induced Conifer Defense. White Pine Weevil and Methyl Jasmonate Induce Traumatic Resinosis, de Novo Formed Volatile Emissions, and Accumulation of Terpenoid Synthase and Putative Octadecanoid Pathway Transcripts in Sitka Spruce
Authors: Miller Barbara , Madilao Lufiani L. , Ralph Steven , Bohlmann Jörg
Published: December 2004

Stem-boring insects and methyl jasmonate (MeJA) are thought to induce similar complex chemical and anatomical defenses in conifers. To compare insect- and MeJA-induced terpenoid responses, we analyzed traumatic oleoresin mixtures, emissions of terpenoid volatiles, and expression of terpenoid synthase (TPS) genes in Sitka spruce (Picea sitchensis) following attack by white pine weevils (Pissodes strobi) or application of MeJA. Both insects and MeJA caused traumatic resin accumulation in stems, with more accumulation induced by the weevils. Weevil-induced terpenoid emission profiles were also more complex than emissions induced by MeJA. Weevil feeding caused a rapid release of a blend of monoterpene olefins, presumably by passive evaporation of resin compounds from stem feeding sites. These compounds were not found in MeJA-induced emissions. Both weevils and MeJA caused delayed, diurnal emissions of (−)-linalool, indicating induced de novo biosynthesis of this compound. TPS transcripts strongly increased in stems upon insect attack or MeJA treatment. Time courses and intensity of induced TPS transcripts were different for monoterpene synthases, sesquiterpene synthases, and diterpene synthases. Increased levels of weevil- and MeJA-induced TPS transcripts accompanied major changes in terpenoid accumulation in stems. Induced TPS expression profiles in needles were less complex than those in stems and matched induced de novo emissions of (−)-linalool. Overall, weevils and MeJA induced similar, but not identical, terpenoid defense responses in Sitka spruce. Findings of insect- and MeJA-induced accumulation of allene oxide synthase-like and allene oxide cyclase-like transcripts are discussed in the context of traumatic resinosis and induced volatile emissions in this gymnosperm system.
Subcellular Localization of Arabidopsis 3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase
Authors: Leivar Pablo , González Víctor M. , Castel Susanna , Trelease Richard N. , López-Iglesias Carmen , Arró Montserrat , Boronat Albert , Campos Narciso , Ferrer Albert , Fernàndez-Busquets Xavier
Published: December 2004

Plants produce diverse isoprenoids, which are synthesized in plastids, mitochondria, endoplasmic reticulum (ER), and the nonorganellar cytoplasm. 3-Hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) catalyzes the synthesis of mevalonate, a rate-limiting step in the cytoplasmic pathway. Several branches of the pathway lead to the synthesis of structurally and functionally varied, yet essential, isoprenoids. Several HMGR isoforms have been identified in all plants examined. Studies based on gene expression and on fractionation of enzyme activity suggested that subcellular compartmentalization of HMGR is an important intracellular channeling mechanism for the production of the specific classes of isoprenoids. Plant HMGR has been shown previously to insert in vitro into the membrane of microsomal vesicles, but the final in vivo subcellular localization(s) remains controversial. To address the latter in Arabidopsis (Arabidopsis thaliana) cells, we conducted a multipronged microscopy and cell fractionation approach that included imaging of chimeric HMGR green fluorescent protein localizations in transiently transformed cell leaves, immunofluorescence confocal microscopy in wild-type and stably transformed seedlings, immunogold electron microscopy examinations of endogenous HMGR in seedling cotyledons, and sucrose density gradient analyses of HMGR-containing organelles. Taken together, the results reveal that endogenous Arabidopsis HMGR is localized at steady state within ER as expected, but surprisingly also predominantly within spherical, vesicular structures that range from 0.2- to 0.6-μm diameter, located in the cytoplasm and within the central vacuole in differentiated cotyledon cells. The N-terminal region, including the transmembrane domain of HMGR, was found to be necessary and sufficient for directing HMGR to ER and the spherical structures. It is believed, although not directly demonstrated, that these vesicle-like structures are derived from segments of HMGR-ER. Nevertheless, they represent a previously undescribed subcellular compartment likely capable of synthesizing mevalonate, which provides new evidence for multiorganelle compartmentalization of the isoprenoid biosynthetic pathways in plants.
More Than a Leak Sealant. The Mechanical Properties of Callose in Pollen Tubes
Authors: Parre Elodie , Geitmann Anja
Published: December 2004

While callose is a well-known permeability barrier and leak sealant in plant cells, it is largely unknown whether this cell wall polymer can also serve as a load-bearing structure. Since callose occurs in exceptionally large amounts in pollen, we assessed its role for resisting tension and compression stress in this cell. The effect of callose digestion in Solanum chacoense and Lilium orientalis pollen grains demonstrated that, depending on the species, this cell wall polymer represents a major stress-bearing structure at the aperture area of germinating grains. In the pollen tube, it is involved in cell wall resistance to circumferential tension stress, and despite its absence at the growing apex, callose is indirectly involved in the establishment of tension stress resistance in this area. To investigate whether or not callose is able to provide mechanical resistance against compression stress, we subjected pollen tubes to local deformation by microindentation. The data revealed that lowering the amount of callose resulted in reduced cellular stiffness and increased viscoelasticity, thus indicating clearly that callose is able to resist compression stress. Whether this function is relevant for pollen tube mechanics, however, is unclear, as stiffened growth medium caused a decrease in callose deposition. Together, our data provide clear evidence for the capacity of cell wall callose to resist tension and compression stress, thus demonstrating that this amorphous cell wall substance can have a mechanical role in growing plant cells.
Integration of Flowering Signals in Winter-Annual Arabidopsis
Authors: Michaels Scott D. , Himelblau Edward , Kim Sang Yeol , Schomburg Fritz M. , Amasino Richard M.
Published: December 2004

Photoperiod is the primary environmental factor affecting flowering time in rapid-cycling accessions of Arabidopsis (Arabidopsis thaliana). Winter-annual Arabidopsis, in contrast, have both a photoperiod and a vernalization requirement for rapid flowering. In winter annuals, high levels of the floral inhibitor FLC (FLOWERING LOCUS C) suppress flowering prior to vernalization. FLC acts to delay flowering, in part, by suppressing expression of the floral promoter SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1). Vernalization leads to a permanent epigenetic suppression of FLC. To investigate how winter-annual accessions integrate signals from the photoperiod and vernalization pathways, we have examined activation-tagged alleles of FT and the FT homolog, TSF (TWIN SISTER OF FT), in a winter-annual background. Activation of FT or TSF strongly suppresses the FLC-mediated late-flowering phenotype of winter annuals; however, FT and TSF overexpression does not affect FLC mRNA levels. Rather, FT and TSF bypass the block to flowering created by FLC by activating SOC1 expression. We have also found that FLC acts as a dosage-dependent inhibitor of FT expression. Thus, the integration of flowering signals from the photoperiod and vernalization pathways occurs, at least in part, through the regulation of FT, TSF, and SOC1.
The ATE Genes Are Responsible for Repression of Transdifferentiation into Xylem Cells in Arabidopsis
Authors: Sawa Shinichrio , Demura Taku , Horiguchi Gorou , Kubo Minoru , Fukuda Hiroo
Published: December 2004

We isolated three recessive mutants of Arabidopsis (Arabidopsis thaliana) showing ectopic expression of the xylem-specific marker, pAtxyn3::YFP. Genetic analysis indicated that the phenotypes were caused by mutations in three different genes, designated Abnormal Tracheary Element formation-related gene expression (ate1–3). The ate1 mutants showed a normal DR5::GUS gene expression pattern, and the ate1 mutation did not affect the abnormal vascular pattern formation in the van3 and pin1 mutants, indicating that the ate1 mutation does not affect the vascular pattern organization governed by auxin. The ate mutants showed ectopic lignin deposition, patterned secondary wall thickenings, and cell death, which are characteristic of mature tracheary elements (TEs) in cells ectopically expressing the pAtxyn3::YFP gene. Ectopic TE formation was rapidly induced in parenchymal tissue of the ate mutants in a TE-inducible system with excised hypocotyl. Furthermore, reverse transcription-polymerase chain reaction experiments showed that the expression of TE formation-related genes is up-regulated in the ate mutants. The ate1 mutation also caused ectopic expression of another xylem-specific marker gene, pAt3g62160::YFP. Overall, our results suggest that the ATE genes are responsible for the in situ repression of transdifferentiation into TEs in Arabidopsis and could be participants in the transdifferentiation-masking system.
Identification of a Novel Enzyme Required for Starch Metabolism in Arabidopsis Leaves. The Phosphoglucan, Water Dikinase
Authors: Kötting Oliver , Pusch Kerstin , Tiessen Axel , Geigenberger Peter , Steup Martin , Ritte Gerhard
Published: December 2004

The phosphorylation of amylopectin by the glucan, water dikinase (GWD; EC 2.7.9.4) is an essential step within starch metabolism. This is indicated by the starch excess phenotype of GWD-deficient plants, such as the sex1-3 mutant of Arabidopsis (Arabidopsis thaliana). To identify starch-related enzymes that rely on glucan-bound phosphate, we studied the binding of proteins extracted from Arabidopsis wild-type leaves to either phosphorylated or nonphosphorylated starch granules. Granules prepared from the sex1-3 mutant were prephosphorylated in vitro using recombinant potato (Solanum tuberosum) GWD. As a control, the unmodified, phosphate free granules were used. An as-yet uncharacterized protein was identified that preferentially binds to the phosphorylated starch. The C-terminal part of this protein exhibits similarity to that of GWD. The novel protein phosphorylates starch granules, but only following prephosphorylation with GWD. The enzyme transfers the β-P of ATP to the phosphoglucan, whereas the γ-P is released as orthophosphate. Therefore, the novel protein is designated as phosphoglucan, water dikinase (PWD). Unlike GWD that phosphorylates preferentially the C6 position of the glucose units, PWD phosphorylates predominantly (or exclusively) the C3 position. Western-blot analysis of protoplast and chloroplast fractions from Arabidopsis leaves reveals a plastidic location of PWD. Binding of PWD to starch granules strongly increases during net starch breakdown. Transgenic Arabidopsis plants in which the expression of PWD was reduced by either RNAi or a T-DNA insertion exhibit a starch excess phenotype. Thus, in Arabidopsis leaves starch turnover requires a close collaboration of PWD and GWD.
EFL Business Writing Behaviors in Differing Feedback Environments
Authors: Warden Clyde A.
Published: December 2004

To understand students' reaction to feedback, path analysis was used to generate models of student writing activity. Three groups received differing combinations of feedback and redrafting opportunity over four assignments. A total of 563 first drafts from 141 students were analyzed, resulting in 5,630 data points for modeling. Results suggest that Taiwan business English writingstudents may implement proofreading and self‐directed redrafting behaviors aimed towards improving their writing when objective sentence‐level error feedback is supplied with no opportunity for further correction. The addition of redrafting opportunity resulted in generally unproductive writing strategies but also lower objective error rates. Students receiving general teacher‐based feedback exhibited redrafting behaviors and a tendency to copy directly from reference material.
Focus on Form Through Interaction Enhancement: Integrating Formal Instruction Into a Communicative Task in EFL Classrooms
Authors: Muranoi Hitoshi
Published: December 2004

This study examines the impact of interaction enhancement (IE) on the learning of English articles. IE is a treatment that guides learners to focus on form by providing interactional modifications and leads learners to produce modified output within a problem‐solving task (strategic interaction). Two different IE treatments were employed: IE plus formal debriefing (IEF), and IE plus meaning‐focused debriefing (IEM). Outcomes of these treatments were compared with the effects of non‐enhanced interaction in a quasi‐experimental study involving 91 Japanese EFL learners. Progress was measured with a pretest and two post‐tests, yielding these major findings: (1) IE had positive effects on the learning of English articles; (2) the IEF treatment had a greater impact than the IEM treatment.
An Adaptive Conjugate Gradient Neural Network–Wavelet Model for Traffic Incident Detection
Authors: Adeli H. , Samant A.
Published: December 2004

Artificial neural networks are known to be effective in solving problems involving pattern recognition and classification. The traffic incident‐detection problem can be viewed as recognizing incident patterns from incident‐free patterns. A neural network classifier has to be trained first using incident and incident‐free traffic data. The dimensionality of the training input data is high, and the embedded incident characteristics are not easily detectable. In this article we present a computational model for automatic traffic incident detection using discrete wavelet transform, linear discriminant analysis, and neural networks. Wavelet transform and linear discriminant analysis are used for feature extraction, denoising, and effective preprocessing of data before an adaptive neural network model is used to make the traffic incident detection. Simulated as well as actual traffic data are used to test the model. For incidents with a duration of more than 5 minutes, the incident‐detection model yields a detection rate of nearly 100 percent and a false‐alarm rate of about 1 percent for two‐ or three‐lane freeways.
Significance of Modeling Error in Structural Parameter Estimation
Authors: Sanayei Masoud , Arya Behnam , Santini Erin M. , Wadia‐Fascetti Sara
Published: December 2004

Structural health monitoring systems rely on algorithms to detect potential changes in structural parameters that may be indicative of damage. Parameter‐estimation algorithms seek to identify changes in structural parameters by adjusting parameters of an a priori finite‐element model of a structure to reconcile its response with a set of measured test data. Modeling error, represented as uncertainty in the parameters of a finite‐element model of the structure, curtail capability of parameter estimation to capture the physical behavior of the structure. The performance of four error functions, two stiffness‐based and two flexibility‐based, is compared in the presence of modeling error in terms of the propagation rate of the modeling error and the quality of the final parameter estimates. Three different types of parameters are used in the parameter estimation procedure: (1) unknown parameters that are to be estimated, (2) known parameters assumed to be accurate, and (3) uncertain parameters that manifest the modeling error and are assumed known and not to be estimated. The significance of modeling error is investigated with respect to excitation and measurement type and locations, the type of error function, location of the uncertain parameter, and the selection of unknown parameters to be estimated. It is illustrated in two examples that the stiffness‐based error functions perform significantly better than the corresponding flexibility‐based error functions in the presence of modeling error. Additionally, the topology of the structure, excitation and measurement type and locations, and location of the uncertain parameters with respect to the unknown parameters can have a significant impact on the quality of the parameter estimates. Insight into the significance of modeling error and its potential impact on the resulting parameter estimates is presented through analytical and numerical examples using static and modal data.
Documentation of Changes in Modal Properties of a Concrete Box‐Girder Bridge Due to Environmental and Internal Conditions
Authors: Bolton R. , Stubbs N. , Park S. , Choi S. , Sikorsky C.
Published: December 2004

The results of two modal tests preformed on a concrete box girder bridge are presented. The two modal tests were performed on the bridge sequentially with a 9‐month time interval between tests. This sequence of tests form the initial phase of a modal‐based level IV nondestructive damage‐evaluation process implemented to establish the rate of structural deterioration and remaining service life of the tested structure. A level IV process detects, locates, and sizes damage and determines the impact of the damage on the performance of the structure. A novel feature of the field testing is the execution of an incremental and minimally intrusive (to existing traffic flow) modal test procedure. The instrumentation, experimental test plan, and resulting modal analyses are discussed. In addition, the changes in the two modal data sets are discussed.
Field Verification of the Damage Index Method in a Concrete Box‐Girder Bridge via Visual Inspection
Authors: Park Sooyong , Stubbs Norris , Bolton Robert , Choi Sanghyun , Sikorsky Charles
Published: December 2004

The structural condition of a concrete box‐girder bridge is monitored twice by detecting and localizing potential damage in the bridge superstructure. Experimental field data were collected on the bridge in December 1997 and 9 months later in September 1998. Modal parameters for the structure are extracted from the measured frequency‐response functions, and the resulting resonant frequencies and modeshapes are fed into a proven systems identification procedure. Modal parameters from the identified baseline structure and the modal parameters determined in the field are used as input to a field‐tested nondestructive damage‐evaluation method (the damage index method) to localize damage in the bridge superstructure. To provide some evidence of the veracity of the predictions of the possible damage locations, a visual inspection was performed on the bridge in May 1999, and surface cracks on the deck were recorded. A comparison of the predicted damage locations on the superstructure with the surface cracks documented via visual inspection is provided. The results indicate that a strong correlation exists between the predicted damage locations and the observed surface crack pattern.
GIS‐Based Analysis of Railway’s Origin/Destination Path‐Selecting Behavior
Authors: Yang Zhongzhen , Hayashi Yoshitsugu
Published: December 2004

This study aims to analyze a railway’s OD path‐selecting behavior with microsimulation analysis in big cities. In big cities, railway networks often consist of lines belonging to several different companies, making railway OD path‐selecting behavior very complex. Usually, the second or third nearest stations are used instead of the nearest station. This study takes buildings rather than zones as origins or destinations for simulating railway path‐selecting behavior. First, in the GIS database, we consider whether the destinations are within walking distance of their origins. Then we modify the map‐based railway network with GIS to make it represent the real urban railway network more clearly. Then, from all the available stations for each building, and all the paths between the origin and destination stations, the one involving the shortest distance is the one used.