bluuebunny/crossref_metadata_2025 huggingface dataset:
Stabilization of a Spatially Growing Wave by Feedback
Authors: Crowley Joseph M.
Published: December 2004

The kink mode of a planar highly conducting liquid jet traveling through a perpendicular electric field is unstable, in the sense that perturbations grow spatially. Control of this growing wave is shown by means of an electronic feedback system which measures the disturbance and applies a controlling force proportional to the measured disturbance. In a practical case, the feedback must be implemented by a finite number of stations in which the disturbance at some point within the station is sampled and a feedback force proportional to this disturbance is applied throughout the section. The response of a single station indicates that if the feedback gain exceeds a certain critical value, the sampled feedback system becomes temporally unstable. To study the spatial stability of a collection of these stations a new stability criterion has been formulated. This criterion indicates that while the sampled feedback may induce spatial instability at certain frequencies, it is possible to stabilize the system studied under certain operating conditions for all frequencies. Various experiments on a water jet confirm the existence of the feedback-induced temporal instability, and show that it is possible to stabilize a spatially unstable system by using sampled feedback.
Diffusion-Induced Interfacial Instability
Authors: Aranow R. H. , Witten L.
Published: December 2004

A theory has previously been developed of the effects of diffusion on interfacial instabilities at the liquid-liquid interface between two solvents when they are mutually immiscible and when a third species, the solute, is diffusing across the interface. The theory is extended to consider the effects of system inhomogeneities. These are expected to be large in the neighborhood of the interface, and the analysis shows their significance in changing the criterion for the onset of instability. An experiment is suggested which would test some consequences of the theory.
Effect of Grid Geometry on Turbulence Decay
Authors: Uberoi Mahinder S. , Wallis Stanley
Published: December 2004

Longitudinal and lateral turbulence intensities u2¯ and v2¯ are measured behind homogeneous grids of various geometries. For all grids used, the ratio u2¯/v2¯ is essentially constant during decay and lies between 1.2 and 1.35, depending on the grid geometry. The turbulence intensity u2¯∼t−n where n is constant during decay but depends on the grid geometry and varies from 1.22 to 1.48. This implies that the rate of decay depends on the initial energy spectrum and the energy-containing (large) eddies maintain a similarity during decay.
Experimental Study of Runaway Electrons in a Plasma Betatron
Authors: Ferrari L. A. , Rogers K. C.
Published: December 2004

Runaway electrons generated by induction acceleration in a plasma betatron with axially symmetric guide field Bz(r,z,t)=B0(r0/r)nf(z) sin 2πt/T; (n = 0.43, T = 16μsec, r0 = 4.8 cm) together with auxiliary azimuthal guide field Bθ(r) = const/r; (2 kG ≤ Bθ(r0) ≤ 5 kG) have been studied for a wide range of induction electric fields Eθ; (2.5 V/cm ≤ Eθ(r0) ≤ 26 V/cm). Experiments have been carried out in argon and krypton at ambient pressure of (0.5–2) × 10−3 Torr. Runaway currents of ≈ 1 A were observed as immersed in a background conduction current of 25–100 A. After a period of normal-betatron-acceleration-beam disruption occurs, and the energetic runaways strike the vacuum-chamber walls. The beam-disruption time tx has been measured as a function of Eθ and Bθ for several half-cycles of the betatron guide field. A space-charge theory is developed in order to explain the small runaway currents. Reasonably good agreement with the experimental results is obtained over a wide range of parameters. The reason for the beam disruption and subsequent x-ray emission is unexplained.
Development of Wind-Driven Waves in a Cylindrical Vessel
Authors: Auerbach J. , Richardson P. D.
Published: December 2004

Wind-driven waves in a cylindrical container have as final forms the first or second antisymmetric surface wave modes. The development of wave motion from rest compares qualitatively with Miles-Phillips theory and experiments in straight channels.
Mott-Smith Shock Thickness Calculations using the vxp Method
Authors: Rode Daniel L. , Tanenbaum B. Samuel
Published: December 2004

Shock thicknesses are calculated using the conservation equations and the vxp moment equation, with p an arbitrary integer. The results depend markedly on p and become unacceptable for p > 6, since they cannot match the boundary conditions.
Equations Modeling Spatially Variable Stochastic Processes
Authors: Mahony J. J. , Philip J. R.
Published: December 2004

A study of turbulent diffusion has led to a stochastic process stationary in time, but spatially variable, which is defined only by local specific rates of generation of zeroth, first and second moments. An analysis, based on appropriate integrations by parts, establishes the connection between the local specific rates of generation of various moments and the (spatially variable) coefficients of an associated trial partial differential equation. It is thus shown that the given process is correctly modeled by a spatially variable Fokker-Planck equation. The analysis is simply extended to yield the general result that a process defined by local specific rates of generation of zeroth to nth moments can be correctly modeled by an equation of first order in time and nth order in the space variables.
Power Series Expansion of the Electron Velocity Distribution Function
Authors: Morrone Terry
Published: December 2004

A power series expansion of the harmonic expansion coefficients of Margenau and Hartman is introduced. In principle all the harmonic coefficients may be computed using the expansion. The expansion parameter is the fraction of energy lost per collision or equivalently the electric field strength. By way of example the third and fifth harmonic electric current densities in a plasma are computed.
Two-Streaming Cyclotron Instability
Authors: Hall Laurence S. , Grewal Mahesh S.
Published: December 2004

A new electrostatic instability of counterstreaming ions occurring at cyclotron frequency is exhibited and discussed. It is conjectured that this instability may provide the mechanism for the enhanced trapping of the injected ion beam in DCX-II. Stability criteria are developed and in the limit of high anisotropy of the ions and not-too-cold electrons, the criterion becomes approximately 12M ivs2<κTe/4 (unstable), where Mi is the ion mass, ±vs are the counterstreaming velocities, and Te is the electron temperature.
Effect of Magnetic Curvature on the Drift-Cyclotron Instability
Authors: Krall N. A. , Fowler T. K.
Published: December 2004

The effect of magnetic curvature on drift-cyclotron instabilities is examined. These instabilities, driven by the density gradient, are expected to be the most important electrostatic instabilities in well-thermalized (Maxwellian) plasmas. It is found for the flute mode, K∥ = 0, that a moderate amount of good (cusp-like) magnetic curvature stabilizes the longest wavelengths most likely to cause anomalous diffusion and shifts the unstable frequencies below the cyclotron frequency. Curvature does not stabilize the convective modes, K∥ ≠ 0, but these modes can be stabilized by avoiding resonance. Results are applied, speculatively, to average minimum-B fields, for which an additional ``communication'' criterion is necessary for stability.
Influence of Static, Radial, Electric Fields on Trapped Particle Instabilities in Toroidal Systems
Authors: Galeev A. A. , Sagdeev R. Z. , Wong H. V.
Published: December 2004

The drift motion of trapped particles in toroidal systems leads to a new branch of gravitational instability. This is stabilized by radial electric fields. However, a new unstable mode then appears, which is similar to that due to ion impurity density gradients.
Adiabatic Time Development of Linear Theta-Pinch Plasma Profiles
Authors: Morse Richard L.
Published: December 2004

The formation of a θ-pinch plasma sheath is studied under the assumption that the sheath is initially relatively thin and must therefore contain a radial E field but that later it relaxes to a thickness of the order of the ion gyroradius because of line shorting. A family of the resulting self-consistent equilibria are computed for a Maxwellian plasma under the additional assumption that the radial adiabatic invariant, Ir = ∮ Pr dr, is conserved for all ions during the relaxation. These solutions predict that for particle line densities less than about 5 × 1016 cm−1, this relaxation will allow enough penetration of Bz to the center of the plasma to cause β to be significantly less than one. The resulting plasma angular momenta are obtained.
Steady-State Theory of a Low-Pressure Discharge Column in an Axial Magnetic Field
Authors: Self S. A.
Published: December 2004

A steady-state theory of a low-pressure discharge column in a magnetic field is derived in terms of the moments of the Boltzmann equation. For the electrons, the first-two moment equations are used with a scalar pressure. For the ions the first-three moment equations are used with an adiabatic assumption. Numerical solutions are given for the profiles of velocity, potential, density and ion stress tensor for both planar and cylindrical geometry for ranges of the parameters of practical interest. A discussion is given of the application of the theory to experimental situations.
Visco-Elastic Character of Fine-Grained Isotropic Turbulence
Authors: Crow S. C.
Published: December 2004

A visco-elastic theory for a limited class of turbulent shear flows is developed and applied to resolve a paradox arising from Lighthill's theory of aerodynamic sound—that the acoustic energy in an infinite field of turbulence is infinite.
Stability of Guiding-Center Plasmas in a Sheared Magnetic Field
Authors: Kadish Abraham
Published: December 2004

The stability of a plasma in a magnetic field with nonuniform orientation is investigated in the guiding center limit. Conditions sufficient for exponential stability are derived which are local analogs of those which have been obtained for uniform plasma equilibria. The existence of growth rates slower than exponential ones is considered.
Confirmation and Renumbering of the Discrete Heat Flux Transitions of Malkus
Authors: Willis G. E. , Deardorff J. W.
Published: December 2004

Discrete transitions in the heat flux through fluids confined between horizontal plates were first observed by Malkus. The transitions, and the remarkable linear segments in a linear plot of Nusselt number times Rayleigh number versus Rayleigh number, are confirmed experimentally up to a Rayleigh number of Ra = 2.8 × 106 in a convection chamber of different geometry and in fluids of different Prandtl numbers than those used by Malkus. Two transitions at Ra ≈ 8200 and 24 000 were always observed instead of the single transition suggested to occur at Ra ≈ 18 000. Numerical studies suggest that if the transitions are associated with instability of successive vertical modes, their explanation requires a fully nonlinear treatment.
Boundary Layers due to the Combined Effects of Rotation and Translation
Authors: Rott Nicholas , Lewellen William S.
Published: December 2004

Exact solutions of the Navier-Stokes equations are given for certain flows in which an infinite plane and the adjacent fluid have relative rotation and translation. Equations for the boundary-layer profiles are given in a general form that includes the possibility of time-dependent solutions. Numerical results are restricted to two cases of steady flow, in which either the fluid is translating and the plate is rotating, or the plate is in pure translation adjacent to a rotating fluid. Analytical solutions are discussed, including time-dependent cases, for vanishing and for small differences between the angular velocities of the plate and the fluid.
Kinetic Model Analysis of Light Scattering by Molecular Gases
Authors: Sugawara Akira , Yip Sidney
Published: December 2004

Density fluctuations in a polyatomic gas are studied with a kinetic description assuming constant relaxation times. Exact results for the initial-value problem are applied to laser scattering experiments. It is shown that the spectral distribution of scattered light can be predicted in terms of specific heats, transport coefficients, and measured values of the rotational relaxation number. Explicit considerations of CO2 spectra suggest that the technique of laser scattering is potentially useful for studying rotational relaxation phenomena. The kinetic calculations are supplemented by hydrodynamical analysis. It is found that internal relaxation plays a significant role even at small scattering angles.
Wave Propagaton in a Partly Ionized Gas. II
Authors: Tanenbaum B. Samuel , Meskan David A.
Published: December 2004

Simple dispersion relations for longitudinal waves are derived for plasmas satisfying the hydrodynamic equations subject to the conditions: 1010 < Nn0 < 1016 cm−3; 109 < Ne0 < 1014 cm−3; Te ≫ Ti,n; Ti,n < 104 °K < Te. In addition, the exact solutions to the dispersion equation are obtained (for arbitrary number densities and temperatures) in the low-frequency limit, and the damping factor for the low-frequency acoustic mode is calculated.
Expansion of a Cylindrical Piston into a Conducting Fluid
Authors: Snyder Martin Avery
Published: December 2004

The expansion of an infinitely long cylindrical piston into a compressible fluid permeated by a uniform magnetic field is considered. Conical solutions of the linearized Lundquist equations are obtained by an extension of Gardner's plane wave technique. A free-boundary solution is obtained which involves only subsonic flow. In general, subsonic, transonic, and supersonic flows are coupled to make up the solution. The linearized problem appears to be a faithful model of the nonlinear problem only for pistons whose cross section is nearly parallel to the undisturbed magnetic field. In other cases, the presence of a magnetic boundary layer is suggested.
Motion of Toroidal Magnetic Surfaces and Diffusion of a Plasma Ring
Authors: Bineau M.
Published: December 2004

The time derivative of the magnetic field can always be represented by a velocity field in a simply connected domain. However, in a toroidal domain the condition for such a representation with a single valued velocity is very stringent. The case considered here is that of initially nested magnetic surfaces in which a multivalued velocity is allowed provided that certain conditions are satisfied. These conditions imply that the component of the velocity normal to the magnetic surfaces is single valued. In this situation there is a convenient representation of the time derivative of the magnetic field. This representation can be applied to the description of resistive diffusion.
Plasma Production by a High-Power Q-Switched Laser
Authors: Sucov E. W. , Pack J. L. , Phelps A. V. , Engelhardt A. G.
Published: December 2004

Studies have been made of the confinement in a magnetic mirror of plasmas produced by focusing a Q-switched laser beam on aluminum disks, foils, and spheres. High speed photographs show that, in the absence of a confining magnetic field, the plasma generated from ball targets is roughly symmetrical whereas one component of the plasma generated from flat targets is asymmetric and moves toward the laser with a velocity of about 107 cm/sec. A second component which is more nearly symmetric expands with a velocity of approximately 2 × 106 cm/sec. The expansion velocities are not appreciably reduced in a 14–6-14 kG mirror field. However, the duration of the luminosity from a slower constituent of the plasma increases from 1 μsec to about 5 μsec and microwave interferometer measurements show an electron density of about 5 × 1011 cm−3 at times as late as 50 μsec. Electrostatic probes verify that the maximum expansion velocity corresponds to an ion kinetic energy of about 1.4 keV. Time integrated spectra of the plasma show lines from Al III. Microwave attenuation measurements lead to an apparent electron temperature of the order of 0.03 eV at times later than 1 μsec. Analysis of microwave data shows that radial density gradients probably exist in some plasmas.
Compression of a Rarefied Plasma by Converging Magnetic Mirrors
Authors: Bird G. A.
Published: December 2004

A solution is obtained for the temperature, density, total number, and energy of the particles trapped between magnetic mirrors which, at zero time, acquire a uniform velocity of convergence. It is assumed that collisions between particles may be neglected and that the collisions with the mirrors are adequately described by the guiding center theory. It is found that, for a given mirror strength and rate of convergence, there are mirror spacings at which the energy reaches a maximum and the temperature and density reach limiting values. Furthermore, there are optimum rates of convergence at which these maximum and limiting values are a maximum. During the early stages of compression at high rates of convergence, the temperature rises at a far greater rate than the square of the density.
Possible Definition of Entropy for Weak Turbulence in Plasmas
Authors: Nakayama Toshio
Published: December 2004

A possible definition of an H function which is appropriate to describe weak turbulence in plasmas is introduced in terms of a probability introduced in the functional space spanned by instantaneous solutions of the Vlasov equation. The main point in an introduction of this function is to use an approximate probability. The nature of the H function thus defined is similar to that introduced by Boltzmann in kinetic theory. The time rate of change of the H function is computed and it is shown that the rate of change is negative for a weakly turbulent plasma and is zero for a stable plasma.
Stability of Plane Couette-Poiseuille Flow
Authors: Hains F. D.
Published: December 2004

The stability of plane Couette-Poiseuille flow has been computed by a new numerical method. Results show that the unstable mode associated with Poiseuille flow is always stable for Couette flow.
Intermittency in the Very Small Scales of Turbulence
Authors: Kraichnan Robert H.
Published: December 2004

An elementary argument independent of Reynolds number implies strong intermittency in the very small scales of turbulence if all velocity derivatives exist in mean square. For very low Reynolds number, such intermittency is inferred from perturbation theory also.
On the Interpretation of Space-Time Correlation Measurements in Shear Flow
Authors: Sternberg Joseph
Published: December 2004

The problem of deducing the convective velocities for the turbulent fluctuations from cross correlation measurements using two hot wires is re-examined. It is shown that for large scale motions the path of the maximum space-time correlation will, in general, deviate from the local mean streamline because of the distorting effect of the mean shear on the turbulent vorticity field. Calculations are presented to show that this effect can account for the shapes of the curves of maximum correlation in a boundary layer as reported by Favre some years ago. These same considerations would indicate that the convective velocity of the large scale disturbances should be measured along the lines of maximum correlation rather than along the streamlines. The deduction of the general form of the eddies from the space-time correlation measurements is also examined. In the case of two hot wires set on a line orthogonal to the surface, the negative optimum delay for maximum correlation is shown to be consistent with the presence of eddies aligned in a downstream direction at a relatively small angle to the surface.
Some Properties of Turbulent Separated Flows
Authors: Kistler Alan L. , Tan Felix C.
Published: December 2004

An experimental study was made of the properties of the approximately two-dimensional flow in a rectangular cavity adjacent to a uniform stream in order to determine the principal mechanisms controlling the transport processes between the cavity and the stream. It was found that an important fraction of the transport depended on a three-dimensional effect not usually included when constructing analyzable models of this flow. This three-dimensional effect was a strong function of the cavity geometry. Several different types of flow could be identified.
Influence of Vibrations on the Flow Field behind a Cylinder
Authors: Wehrmann O. H.
Published: December 2004

The range of the forced oscillations behind a vibrating cylinder and the amplitude and phase distributions were measured for a Reynolds number range between 8–350. The distribution of the peak amplitude of the velocity fluctuations indicates three different flow modes depending on the Reynolds number.
Turbulent Swirling Jet
Authors: Craya A. , Darrigol M.
Published: December 2004

An extensive investigation has been made of eight jets with a degree of swirl varying from weak to very strong. The jets were either isothermal or heated. The measurements include both the mean and fluctuating kinematic and thermal fields. The theoretical analysis explains the observed axial velocity and turbulent shear stress profiles. The theoretical limiting case where affine profiles are possible is discussed.
Effect of Density Gradients on an Air Jet
Authors: Uberoi Mahinder S. , Garby Louis C.
Published: December 2004

Turbulent mixing of a cold axisymmetric jet with stagnant air at room temperature is studied experimentally. Cooling of the free jet reduces the width of the total head profile as compared with no cooling, and the width of the temperature profile decreases with increased cooling. The lowest initial temperature of the jet was 100°K.
Relationship between Different Correlation Coefficients in the Atmospheric Boundary Layer
Authors: Takeuchi K.
Published: December 2004

Analyzing some of the available atmospheric data, it is found that both the Eulerian and the quasi-Lagrangian correlation coefficients in the nondimensional representation can be determined only by the thermal stability under certain conditions, and the speculation could be made that the same is true with the Lagrangian one.
Spectrum of Isotropic Turbulence
Authors: Neumann J.
Published: December 2004

Two expressions are obtained for the turbulent viscosity associated with the transfer of mean-square vorticity across the spectrum. Both involve the three-dimensional energy-spectrum function E and on equating them, a differential equation for the spectrum is obtained. For small wavenumber magnitudes and at high Reynolds number, E = (27/3/3) ε2/3 k−5/3, where ε is the time rate of kinetic energy dissipation per unit mass, and k is the wavenumber magnitude. Thus the universal constant in Kolmogoroff's law for the inertial subrange is (27/3/3) = 1.679 ⋯. The solution of the differential equation for the high wavenumber magnitude end of the spectrum is yet to be found, but it is clear from the equation that a pure power function is not a solution, and thus Heisenberg's k−7 law is not supported.
Study of Turbulent Dispersion by Use of Lagrangian Diffusion Equation
Authors: Okubo Akira
Published: December 2004

Dispersion of diffusible, passive properties in an incompressible fluid is considered beginning with the Lagrangian diffusion equation, in which the displacements of fluid particles are governed by the Navier—Stokes equations in Lagrangian form. When a perturbation technique is applied to the system of equations, the zero- and first-order solutions provide an understanding of the interaction between the turbulence and molecular diffusion at all times. In general, the combined effect decreases the spreading of contaminant relative to the orgin, whereas the interaction accelerates the dispersion with respect to the centroid of a diffusing patch. The effect of the interaction between turbulence and molecular diffusion cannot be ignored unless the ratio of the molecular diffusivity to the kinematic viscosity is small compared with unity.
New Hypothesis for the Relationship between Eddy and Mean States
Authors: Lettau Heinz H.
Published: December 2004

A three-dimensional Eulerian vector of eddy displacements is formally defined which relates fluctuations locally to the mean states. In comparison with previous phenomenological theories, three-dimensionality of turbulent velocity is fully considered, even for one-dimensional mean motion. The existing tendency towards adaption of transferred fluid property along eddy trajectories is expressed by an equivalent Eulerian concept, in supplement of the tendency towards conservation as singled out in the classical Eulerian concepts of Prandtl and Taylor. Differences in transfer structure between free and wall turbulence are interpreted by the varying role played by a longitudinal versus a lateral length-scale of turbulence. Both lengths are rigorously defined by Eulerian variances and covariances of eddy displacement components. The latter can satisfy conditions of isotropy while eddy velocity components fail to do so.
Nonlinear Development of Disturbance in a Laminar Boundary Layer
Authors: Komoda H.
Published: December 2004

The nonlinear instability of the disturbances in a boundary layer having a periodic spanwise variation in the thickness was studied by using a multi-channel hot-wire technique and a synchronized sampling method. Measurement of the instantaneous flow field revealed the details of a new type of a nonlinear instability which in the case of a large thickness variation takes place differently from an ordinary two-dimensional boundary-layer case.
Implementation of group-covariant positive operator valued measures by orthogonal measurements
Authors: Decker Thomas , Janzing Dominik , Rötteler Martin
Published: December 2004

We consider group-covariant positive operator valued measures (POVMs) on a finite dimensional quantum system. Following Neumark’s theorem a POVM can be implemented by an orthogonal measurement on a larger system. Accordingly, our goal is to find a quantum circuit implementation of a given group-covariant POVM which uses the symmetry of the POVM. Based on representation theory of the symmetry group we develop a general approach for the implementation of group-covariant POVMs which consist of rank-one operators. The construction relies on a method to decompose matrices that intertwine two representations of a finite group. We give several examples for which the resulting quantum circuits are efficient. In particular, we obtain efficient quantum circuits for a class of POVMs generated by Weyl–Heisenberg groups. These circuits allow to implement an approximative simultaneous measurement of the position and crystal momentum of a particle moving on a cyclic chain.
S
-nitrosoprotein formation and localization in endothelial cells
Authors: Yang Yi , Loscalzo Joseph
Published: December 2004

Protein S-nitrosation represents a recently described form of post-translational modification that is rapid and reversible. However, the analysis of protein S-nitrosation
in situ
has been difficult because of the absence of specific probes and the instability of cellular protein
S
-nitrosothiols. We developed a rapid and specific method for detecting endothelial
S
-nitrosoproteins patterned after the biotin switch method that involves thiol alkylation followed by reductive generation of thiols from
S
-nitrosothiols, which are then labeled with either a biotin- or Texas red-derivative of methanethiosulfonate. When we used this methodology, we found that S-nitrosated proteins can form within endothelial cells from an exogenous
S
-nitrosothiol donor or from endogenous production of NO by endothelial NO synthase. When we used confocal microscopy, we found that these
S
-nitrosoproteins exist mainly in the mitochondria and peri-mitochondrial compartment, and that their half-life is ≈1 h. Cellular S-nitrosated protein abundance changed as expected, with changes in activity of NO synthase, and with impairment of mitochondrial function and scavenging of peroxynitrite. We used a proteomic approach involving two-dimensional gel electrophoresis and mass spectrometry, and found that a limited number of
S
-nitrosoproteins exist in endothelial cells (
S
-nitrosoproteome) and identified GAPDH, vimentin, β-galactosidase, peroxiredoxin 1, β-actin, and ubiquitin-conjugating enzyme E2 among them. The most abundant S-nitrosated protein in the resting endothelial cell is GAPDH, suggesting a regulatory function for NO in glycolysis. These data offer methods and insights into identifying the protein targets of S-nitrosation reactions and their potential role in cell function and phenotype.
The modular architecture of protein–protein binding interfaces
Authors: Reichmann D. , Rahat O. , Albeck S. , Meged R. , Dym O. , Schreiber G.
Published: December 2004

Protein–protein interactions are essential for life. Yet, our understanding of the general principles governing binding is not complete. In the present study, we show that the interface between proteins is built in a modular fashion; each module is comprised of a number of closely interacting residues, with few interactions between the modules. The boundaries between modules are defined by clustering the contact map of the interface. We show that mutations in one module do not affect residues located in a neighboring module. As a result, the structural and energetic consequences of the deletion of entire modules are surprisingly small. To the contrary, within their module, mutations cause complex energetic and structural consequences. Experimentally, this phenomenon is shown on the interaction between TEM1-βlactamase and β-lactamase inhibitor protein (BLIP) by using multiple-mutant analysis and x-ray crystallography. Replacing an entire module of five interface residues with Ala created a large cavity in the interface, with no effect on the detailed structure of the remaining interface. The modular architecture of binding sites, which resembles human engineering design, greatly simplifies the design of new protein interactions and provides a feasible view of how these interactions evolved.
Endometrial cancer is a receptor-mediated target for Mullerian Inhibiting Substance
Authors: Renaud Elizabeth J. , MacLaughlin David T. , Oliva Esther , Rueda Bo R. , Donahoe Patricia K.
Published: December 2004

Mullerian Inhibiting Substance (MIS), a 140-kDa homodimer glycoprotein member of the TGF-β superfamily of biological-response modifiers, causes regression of the Mullerian ducts in developing male embryos. MIS also can induce growth arrest and apoptosis in ovarian and cervical cancer cell lines. The embryonic progenitor of the ovarian and cervical epithelium is the coelomic epithelium, the same tissue that regresses under the direction of MIS in the male. The endometrium and uterus also arise from the coelomic epithelium and the Mullerian ducts. Here, we show that both normal human endometrium and endometrial cancers express the receptor for MIS and that MIS can inhibit the proliferation of a number of human endometrial cancer cell lines that express the MIS type II receptor. In the representative endometrial cancer cell line AN3CA, MIS affects the expression of key cell-cycle regulatory proteins. This work broadens the scope of tumors that MIS can potentially control and, by elucidating the MIS signaling pathway, identifies other potential avenues for intervention.
A Role of Arabidopsis Inositol Polyphosphate Kinase, AtIPK2α, in Pollen Germination and Root Growth
Authors: Xu Jun , Brearley Charles A. , Lin Wen-Hui , Wang Yuan , Ye Rui , Mueller-Roeber Bernd , Xu Zhi-Hong , Xue Hong-Wei
Published: December 2004

Inositol polyphosphates, such as inositol trisphosphate, are pivotal intracellular signaling molecules in eukaryotic cells. In higher plants the mechanism for the regulation of the type and the level of these signaling molecules is poorly understood. In this study we investigate the physiological function of an Arabidopsis (Arabidopsis thaliana) gene encoding inositol polyphosphate kinase (AtIPK2α), which phosphorylates inositol 1,4,5-trisphosphate successively at the D-6 and D-3 positions, and inositol 1,3,4,5-tetrakisphosphate at D-6, resulting in the generation of inositol 1,3,4,5,6-pentakisphosphate. Semiquantitative reverse transcription-PCR and promoter-β-glucuronidase reporter gene analyses showed that AtIPK2α is expressed in various tissues, including roots and root hairs, stem, leaf, pollen grains, pollen tubes, the flower stigma, and siliques. Transgenic Arabidopsis plants expressing the AtIPK2α antisense gene under its own promoter were generated. Analysis of several independent transformants exhibiting strong reduction in AtIPK2α transcript levels showed that both pollen germination and pollen tube growth were enhanced in the antisense lines compared to wild-type plants, especially in the presence of nonoptimal low Ca2+ concentrations in the culture medium. Furthermore, root growth and root hair development were also stimulated in the antisense lines, in the presence of elevated external Ca2+ concentration or upon the addition of EGTA. In addition, seed germination and early seedling growth was stimulated in the antisense lines. These observations suggest a general and important role of AtIPK2α, and hence inositol polyphosphate metabolism, in the regulation of plant growth most likely through the regulation of calcium signaling, consistent with the well-known function of inositol trisphosphate in the mobilization of intracellular calcium stores.
Complementation of sugary-1 Phenotype in Rice Endosperm with the Wheat Isoamylase1 Gene Supports a Direct Role for Isoamylase1 in Amylopectin Biosynthesis
Authors: Kubo Akiko , Rahman Sadequr , Utsumi Yoshinori , Li Zhongyi , Mukai Yasuhiko , Yamamoto Maki , Ugaki Masashi , Harada Kyuya , Satoh Hikaru , Konik-Rose Christine , Morell Matthew , Nakamura Yasunori
Published: December 2004

To examine the role of isoamylase1 (ISA1) in amylopectin biosynthesis in plants, a genomic DNA fragment from Aegilops tauschii was introduced into the ISA1-deficient rice (Oryza sativa) sugary-1 mutant line EM914, in which endosperm starch is completely replaced by phytoglycogen. A. tauschii is the D genome donor of wheat (Triticum aestivum), and the introduced fragment effectively included the gene for ISA1 for wheat (TaISA1) that was encoded on the D genome. In TaISA1-expressing rice endosperm, phytoglycogen synthesis was substantially replaced by starch synthesis, leaving only residual levels of phytoglycogen. The levels of residual phytoglycogen present were inversely proportional to the expression level of the TaISA1 protein, although the level of pullulanase that had been reduced in EM914 was restored to the same level as that in the wild type. Small but significant differences were found in the amylopectin chain-length distribution, gelatinization temperatures, and A-type x-ray diffraction patterns of the starches from lines expressing TaISA1 when compared with wild-type rice starch, although in the first two parameters, the effect was proportional to the expression level of TaISA. The impact of expression levels of ISA1 on starch structure and properties provides support for the view that ISA1 is directly involved in the synthesis of amylopectin.
The Sources of Carbon and Nitrogen Supplying Leaf Growth. Assessment of the Role of Stores with Compartmental Models
Authors: Lattanzi Fernando Alfredo , Schnyder Hans , Thornton Barry
Published: December 2004

Patterns of synthesis and breakdown of carbon (C) and nitrogen (N) stores are relatively well known. But the role of mobilized stores as substrates for growth remains less clear. In this article, a novel approach to estimate C and N import into leaf growth zones was coupled with steady-state labeling of photosynthesis (13CO2/12CO2) and N uptake (15NO3  −/14NO3  −) and compartmental modeling of tracer fluxes. The contributions of current C assimilation/N uptake and mobilization from stores to the substrate pool supplying leaf growth were then quantified in plants of a C3 (Lolium perenne) and C4 grass (Paspalum dilatatum Poir.) manipulated thus to have contrasting C assimilation and N uptake rates. In all cases, leaf growth relied largely on photoassimilates delivered either directly after fixation or short-term storage (turnover rate = 1.6–3.3 d−1). Long-term C stores (turnover rate < 0.09 d−1) were generally of limited relevance. Hence, no link was found between the role of stores and C acquisition rate. Short-term (turnover rate = 0.29–0.90 d−1) and long-term (turnover rate < 0.04 d−1) stores supplied most N used in leaf growth. Compared to dominant (well-lit) plants, subordinate (shaded) plants relied more on mobilization from long-term N stores to support leaf growth. These differences correlated well with the C-to-N ratio of growth substrates and were associated with responses in N uptake. Based on this, we argue that internal regulation of N uptake acts as a main determinant of the importance of mobilized long-term stores as a source of N for leaf growth.
Gene Expression Programs during Brassica oleracea Seed Maturation, Osmopriming, and Germination Are Indicators of Progression of the Germination Process and the Stress Tolerance Level
Authors: Soeda Yasutaka , Konings Maurice C.J.M. , Vorst Oscar , van Houwelingen Adele M.M.L. , Stoopen Geert M. , Maliepaard Chris A. , Kodde Jan , Bino Raoul J. , Groot Steven P.C. , van der Geest Apolonia H.M.
Published: December 2004

During seed maturation and germination, major changes in physiological status, gene expression, and metabolic events take place. Using chlorophyll sorting, osmopriming, and different drying regimes, Brassica oleracea seed lots of different maturity, stress tolerance, and germination behavior were created. Through careful physiological analysis of these seed lots combined with gene expression analysis using a dedicated cDNA microarray, gene expression could be correlated to physiological processes that occurred within the seeds. In addition, gene expression was studied during early stages of seed germination, prior to radicle emergence, since very little detailed information of gene expression during this process is available. During seed maturation expression of many known seed maturation genes, such as late-embryogenesis abundant or storage-compound genes, was high. Notably, a small but distinct subgroup of the maturation genes was found to correlate to seed stress tolerance in osmoprimed and dried seeds. Expression of these genes rapidly declined during priming and/or germination in water. The majority of the genes on the microarray were up-regulated during osmopriming and during germination on water, confirming the hypothesis that during osmopriming, germination-related processes are initiated. Finally, a large group of genes was up-regulated during germination on water, but not during osmopriming. These represent genes that are specific to germination in water. Germination-related gene expression was found to be partially reversible by physiological treatments such as slow drying of osmoprimed seeds. This correlated to the ability of seeds to withstand stress.
Manipulation of the Blue Light Photoreceptor Cryptochrome 2 in Tomato Affects Vegetative Development, Flowering Time, and Fruit Antioxidant Content
Authors: Giliberto Leonardo , Perrotta Gaetano , Pallara Patrizia , Weller James L. , Fraser Paul D. , Bramley Peter M. , Fiore Alessia , Tavazza Mario , Giuliano Giovanni
Published: December 2004

Cryptochromes are blue light photoreceptors found in plants, bacteria, and animals. In Arabidopsis, cryptochrome 2 (cry2) is involved primarily in the control of flowering time and in photomorphogenesis under low-fluence light. No data on the function of cry2 are available in plants, apart from Arabidopsis (Arabidopsis thaliana). Expression of the tomato (Solanum lycopersicum) CRY2 gene was altered through a combination of transgenic overexpression and virus-induced gene silencing. Tomato CRY2 overexpressors show phenotypes similar to but distinct from their Arabidopsis counterparts (hypocotyl and internode shortening under both low- and high-fluence blue light), but also several novel ones, including a high-pigment phenotype, resulting in overproduction of anthocyanins and chlorophyll in leaves and of flavonoids and lycopene in fruits. The accumulation of lycopene in fruits is accompanied by the decreased expression of lycopene β-cyclase genes. CRY2 overexpression causes an unexpected delay in flowering, observed under both short- and long-day conditions, and an increased outgrowth of axillary branches. Virus-induced gene silencing of CRY2 results in a reversion of leaf anthocyanin accumulation, of internode shortening, and of late flowering in CRY2-overexpressing plants, whereas in wild-type plants it causes a minor internode elongation.
Annotations and Functional Analyses of the RiceWRKYGene Superfamily Reveal Positive and Negative Regulators of Abscisic Acid Signaling in Aleurone Cells
Authors: Xie Zhen , Zhang Zhong-Lin , Zou Xiaolu , Huang Jie , Ruas Paul , Thompson Daniel , Shen Qingxi J.
Published: December 2004

The WRKY proteins are a superfamily of regulators that control diverse developmental and physiological processes. This family was believed to be plant specific until the recent identification of WRKY genes in nonphotosynthetic eukaryotes. We have undertaken a comprehensive computational analysis of the rice (Oryza sativa) genomic sequences and predicted the structures of 81 OsWRKY genes, 48 of which are supported by full-length cDNA sequences. Eleven OsWRKY proteins contain two conserved WRKY domains, while the rest have only one. Phylogenetic analyses of the WRKY domain sequences provide support for the hypothesis that gene duplication of single- and two-domain WRKY genes, and loss of the WRKY domain, occurred in the evolutionary history of this gene family in rice. The phylogeny deduced from the WRKY domain peptide sequences is further supported by the position and phase of the intron in the regions encoding the WRKY domains. Analyses for chromosomal distributions reveal that 26% of the predicted OsWRKY genes are located on chromosome 1. Among the dozen genes tested, OsWRKY24, -51, -71, and -72 are induced by abscisic acid (ABA) in aleurone cells. Using a transient expression system, we have demonstrated that OsWRKY24 and -45 repress ABA induction of the HVA22 promoter-β-glucuronidase construct, while OsWRKY72 and -77 synergistically interact with ABA to activate this reporter construct. This study provides a solid base for functional genomics studies of this important superfamily of regulatory genes in monocotyledonous plants and reveals a novel function for WRKY genes, i.e. mediating plant responses to ABA.
Deficiency of a Plastidial Adenylate Kinase in Arabidopsis Results in Elevated Photosynthetic Amino Acid Biosynthesis and Enhanced Growth
Authors: Carrari Fernando , Coll-Garcia Danahe , Schauer Nicolas , Lytovchenko Anna , Palacios-Rojas Natalia , Balbo Ilse , Rosso Mario , Fernie Alisdair R.
Published: December 2004

An Arabidopsis (Arabidopsis thaliana) L. Heynh mutant deficient in an isoform of adenylate kinase (ADK; At2g37250) was isolated by reverse genetics. It contains a T-DNA insertion 377 bp downstream of the start point of transcription. The mutant lacks At2g37250 transcripts and has a mild reduction in total cellular ADK activity. Green fluorescent protein-fusion based cellular localization experiments, carried out with the full-length At2g37250, suggested a plastidial localization for this isoform. In keeping with this observation, organelle isolation experiments revealed that the loss in ADK activity was confined to the inner plastid. This plastid stroma ADK gene was found to be expressed tissue constitutively but at much higher levels in illuminated leaves. Phenotypic and biochemical analyses of the mutant revealed that it exhibited higher amino acid biosynthetic activity in the light and was characterized by an enhanced root growth. When the mutant was subjected to either continuous light or continuous dark, growth phenotypes were also observed in the shoots. While the levels of adenylates were not much altered in the leaves, the pattern of change observed in the roots was consistent with the inhibition of an ATP-consuming reaction. Taken together, these data suggest a role for the plastid stromal ADK in the coordination of metabolism and growth, but imply that the exact importance of this isoform is tissue dependent.
The Relationship Between Passive and Active Vocabularies: Effects of LanguageLearning Context
Authors: Laufer Batia , Paribakht T. Sima
Published: December 2004

This study investigated the relationships among 3 types of vocabularyknowledge (passive, controlled active, and free active) within the same individuals, taking 4variables into consideration: passive vocabulary size, language learning context, second (L2) orforeign (FL), length of residence in L2 context and, among the Canadians, knowledge of French.Participants were adult learners of English in Israel (N = 79) and in Canada (N = 103) at different proficiency levels. We used The Levels Test for passivevocabulary size, a Controlled Active Vocabulary Test and The Lexical Frequency Profile (forlexical richness in free written expression). We found that the 3 dimensions of vocabularyknowledge developed at different rates. Active, particularly free active, vocabulary developedmore slowly and less predictably than did passive vocabulary. Furthermore, the relationshipsamong the 3 dimensions of vocabulary knowledge differed between the 2 learning contexts.Although passive vocabulary was always significantly larger than controlled active and freeactive, the passive‐active vocabulary gap was smaller in the FL than in the L2 context. Thebenefits of residence in an L2 context only began to appear after about 2 years, as passivevocabulary was activated and the gap reduced. In the Canadian context, knowledge of Frenchwas an asset at the earlier stages of ESL learning.
Grammars of Spoken English: New Outcomes of Corpus‐Oriented Research
Authors: Leech Geoffrey
Published: December 2004

Recently work on the grammar of spoken English has advanced through the use of large, general, and varied corpora of the language, including corpora of spoken discourse. Here I review the research that has been emerging from the availability of such corpora, much of it emphasizing the need for new ways ofconceptualizing spoken grammar, to replace the traditional reliance on grammatical models oriented to written language. Although such research tends to stress the need for a new descriptive apparatus for the language of speech, I present arguments for the view that spoken and written language utilize the same basic grammatical repertoire, however different their implementations of it may be.
Unified Imaging Approach for Measuring Aggregate Angularity and Texture
Authors: Masad Eyad , Button Joe W.
Published: December 2004

The effect of fine aggregate morphologic properties on asphalt mixtures' behavior is well recognized. However, the current procedures for measuring fine aggregate properties are at best indirect indicators of these properties. The indirect nature of the current measurements has led to inconsistency in predicting the extent to which the measured properties influence pavement performance. Two independent methods that integrate several aspects of image‐analysis techniques are presented for quantifying angularity and texture of fine aggregates. The first technique relies on the change of aggregate shape as it is subjected to a number of erosion‐dilatation morphologic operations. The second technique uses the change of an object perimeter with its shape. The analysis shows that the two methods are able to capture aggregate shape at two different scales. Angularity is captured using low‐resolution images, whereas surface texture is captured using high‐resolution images. The presented image‐analysis techniques have potential benefit in quantifying the effects of texture and angularity on asphalt pavement performance.