bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer, Fluid Flow, and Pressure Measurements Inside a Rotating Two-Pass Duct With Detached 90-Deg Ribs
Authors: Liou Tong-Miin , Chen Meng-Yu , Wang Yu-Ming
Published: August 2003

Transient thermochromic liquid crystal thermography, a laser-Doppler velocimeter, and pressure transducers have been used to measure the local heat transfer, velocity, and wall static-pressure distributions, respectively, in a rotating two-pass square duct with 90-deg ribs detached from the leading and trailing walls. The ribs were square in cross-section and their detached-distance/height ratio was 0.38. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number ranged from 0 to 0.2. Results are compared with attached rib cases in terms of regional averaged Nusselt number, transverse mean velocity component, pressure coefficient distributions and variation of friction factor with rotation number. The competition between convection effect of the wall jet and downwash effect of the rib-top separated shear layer on the heat transfer augmentation is addressed in detail. Discussion on local Nusselt number distribution, mean velocity components, and turbulent kinetic energy is included. Simple expressions are obtained to correlate friction factor with rotation number. Rib detachment is found to enhance heat transfer on the leading wall of the first outward pass and on the trailing wall of the second inward pass over as compared to the attached rib case. The trend is reversed on the other two walls. Nevertheless, detached ribs create more uniform heat transfer distributions on the leading and trailing walls than attached ribs.
Rate-Dependent Transition From Thermal Softening to Hardening in Elastomers
Authors: Chen Z. , Atwood J. L. , Mai Y.-W.
Published: August 2003

The thermal-mechanical properties of the materials currently used in packaging are being reexamined as the electronic packaging industry moves towards chip scale packages and wafer scale packages. The rate-dependent transition of elastic modulus and viscosity from thermal softening to thermal hardening with rising temperature, which does not involve any phase change, has been observed in certain elastomers. An explanation about this interesting phenomenon is given based on thermodynamic considerations. A theoretical analysis is performed to show the limitation of existing viscoelastic models in predicting the transition. It appears that macroscopic material properties should be reexamined based on the physics behind the interaction between ordinary elasticity and entropic elasticity.
Energy Considerations in Systems With Varying Stiffness
Authors: Barber J. R. , Grosh K. , Oh S.
Published: August 2003

If the stiffness of an elastic system changes with time, a conventional Newtonian statement of the equations of motion will generally lead to solutions that violate the fundamental mechanics principle that the work done by the external forces be equal to the increase in total energy of the system. Timoshenko’s discussion of the problem of a vehicle driven across an elastic bridge is generalized to show that energy conservation can be restored only if the local deformation of the components is taken into account in determining the direction of the contact force. This result has important consequences for the interaction of elastic systems in general, including, for example, the dynamic behavior of meshing gears.
The Mode III Crack Problem in Microstructured Solids Governed by Dipolar Gradient Elasticity: Static and Dynamic Analysis
Authors: Georgiadis H. G.
Published: August 2003

This study aims at determining the elastic stress and displacement fields around a crack in a microstructured body under a remotely applied loading of the antiplane shear (mode III) type. The material microstructure is modeled through the Mindlin-Green-Rivlin dipolar gradient theory (or strain-gradient theory of grade two). A simple but yet rigorous version of this generalized continuum theory is taken here by considering an isotropic linear expression of the elastic strain-energy density in antiplane shearing that involves only two material constants (the shear modulus and the so-called gradient coefficient). In particular, the strain-energy density function, besides its dependence upon the standard strain terms, depends also on strain gradients. This expression derives from form II of Mindlin’s theory, a form that is appropriate for a gradient formulation with no couple-stress effects (in this case the strain-energy density function does not contain any rotation gradients). Here, both the formulation of the problem and the solution method are exact and lead to results for the near-tip field showing significant departure from the predictions of the classical fracture mechanics. In view of these results, it seems that the conventional fracture mechanics is inadequate to analyze crack problems in microstructured materials. Indeed, the present results suggest that the stress distribution ahead of the tip exhibits a local maximum that is bounded. Therefore, this maximum value may serve as a measure of the critical stress level at which further advancement of the crack may occur. Also, in the vicinity of the crack tip, the crack-face displacement closes more smoothly as compared to the classical results. The latter can be explained physically since materials with microstructure behave in a more rigid way (having increased stiffness) as compared to materials without microstructure (i.e., materials governed by classical continuum mechanics). The new formulation of the crack problem required also new extended definitions for the J-integral and the energy release rate. It is shown that these quantities can be determined through the use of distribution (generalized function) theory. The boundary value problem was attacked by both the asymptotic Williams technique and the exact Wiener-Hopf technique. Both static and time-harmonic dynamic analyses are provided.
Stability Boundaries of a Conservative Gyroscopic System
Authors: Gladwell G. M. L. , Khonsari M. M. , Ram Y. M.
Published: August 2003

Depending on the speed of rotation, a gyroscopic system may lose or gain stability. The paper characterizes the critical angular velocities at which a conservative gyroscopic system may change from a stable to an unstable state, and vice versa, in terms of the eigenvalues of a high-order matrix pencil. A numerical method for evaluation of all possible candidates for such critical velocities is developed.
Aerodynamic-Rotordynamic Interaction in Axial Compression Systems—Part I: Modeling and Analysis of Fluid-Induced Forces
Authors: Al-Nahwi Ammar A. , Paduano James D. , Nayfeh Samir A.
Published: August 2003

This paper presents a first principles-based model of the fluid-induced forces acting on the rotor of an axial compressor. These forces are primarily associated with the presence of a nonuniform flow field around the rotor, such as that produced by a rotor tip clearance asymmetry. Simple, analytical expressions for the forces as functions of basic flow field quantities are obtained. These expressions allow an intuitive understanding of the nature of the forces and—when combined with a rudimentary model of an axial compressor flow field (the Moore-Greitzer model)—enable computation of the forces as a function of compressor geometry, torque and pressure-rise characteristics, and operating point. The forces predicted by the model are also compared to recently published measurements and more complex analytical models, and are found to be in reasonable agreement. The model elucidates that the fluid-induced forces comprise three main contributions: fluid turning in the rotor blades, pressure distribution around the rotor, and unsteady momentum storage within the rotor. The model also confirms recent efforts in that the orientation of fluid-induced forces is locked to the flow nonuniformity, not to tip clearance asymmetry as is traditionally assumed. The turning and pressure force contributions are shown to be of comparable magnitudes—and therefore of equal importance—for operating points between the design point and the peak of the compressor characteristic. Within this operating range, both “forward” and “backward” rotor whirl tendencies are shown to be possible. This work extends recent efforts by developing a more complete, yet compact, description of fluid-induced forces in that it accounts for all relevant force contributions, both tangential and radial, that may influence the dynamics of the rotor. Hence it constitutes an essential element of a consistent treatment of rotordynamic stability under the action of fluid-induced forces, which is the subject of Part II of this paper.
Dual-Species Transport Subject to Sorptive Exchange in Pipe Flow
Authors: Yip T. L. , Ng C. O.
Published: August 2003

The transport in pipe flow of a chemical species can be materially affected by the presence of solid suspension if the species is capable of partitioning into a solute phase and a solid phase sorbed onto the suspended particles. An asymptotic analysis is used in this work to deduce the effective transport equations for the two phases, with kinetic sorptive exchange taken into account. The effects of sorption on the advection and dispersion of a sorbing chemical are discussed and illustrated with a numerical example.
The Analysis of Constrained Impulsive Motion
Authors: Wang L.-S. , Chou W.-T.
Published: August 2003

Impulsive problems for mechanical systems subject to kinematic constraints are discussed in this paper. In addition to the applied impulses, there may exist suddenly changed constraints, or termed impulsive constraints. To describe the states of the system during the impulsive motion, three different phases, i.e., prior motion, virtual motion, and posterior motion, are defined which are subject to different sets of constraints, and thus have different degrees-of-freedom. A fundamental principle, i.e., the principle of velocity variation, for the constrained impulsive motion is enunciated as a foundation to derive the privileged impulse-momentum equations. It is shown that for a system with no applied impulse, a conservation law can be stated as the conservation of the virtual-privileged momenta. The proposed methodology provides a systematic scheme to deal with various types of impulsive constraints, which is illustrated in the paper by solving the constrained impulsive problems for the motion of a sleigh.
Predictions of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions Using an Intermittency Transport Equation
Authors: Suzen Y. B. , Huang P. G. , Hultgren Lennart S. , Ashpis David E.
Published: August 2003

A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, μt, with the intermittency factor, γ. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.
The Forced Oscillations of Submerged Bodies
Authors: Sanz-Andre´s Angel , Tevar Gonzalo , Rivas Francisco-Javier
Published: August 2003

The increasing use of very light structures in aerospace applications are given rise to the need of taking into account the effects of the surrounding media in the motion of a structure (as for instance, in modal testing of solar panels or antennae) as it is usually performed in the motion of bodies submerged in water in marine applications. New methods are in development aiming at to determine rigid-body properties (the center of mass position and inertia properties) from the results of oscillations tests (at low frequencies during modal testing, by exciting the rigid-body modes only) by using the equations of the rigid-body dynamics. As it is shown in this paper, the effect of the surrounding media significantly modifies the oscillation dynamics in the case of light structures and therefore this effect should be taken into account in the development of the above-mentioned methods. The aim of the paper is to show that, if a central point exists for the aerodynamic forces acting on the body, the motion equations for the small amplitude rotational and translational oscillations can be expressed in a form which is a generalization of the motion equations for a body in vacuum, thus allowing to obtain a physical idea of the motion and aerodynamic effects and also significantly simplifying the calculation of the solutions and the interpretation of the results. In the formulation developed here the translational oscillations and the rotational motion around the center of mass are decoupled, as is the case for the rigid-body motion in vacuum, whereas in the classical added mass formulation the six motion equations are coupled. Also in this paper the nonsteady motion of small amplitude of a rigid body submerged in an ideal, incompressible fluid is considered in order to define the conditions for the existence of the central point in the case of a three-dimensional body. The results here presented are also of interest in marine applications.
Effect of Reynolds Number and Surface Roughness on the Efficiency of Centrifugal Pumps
Authors: Gu¨lich J. F.
Published: August 2003

A procedure has been developed to predict the effects of roughness and Reynolds number on the change in efficiency from a model or baseline to a prototype pump (“efficiency scaling”). The analysis of individual losses takes into account different roughnesses of impeller, diffuser/volute, impeller side disks, and casing walls in the impeller side rooms. The method also allows to predict the effect of roughness and Reynolds number on the hydraulic efficiency. The calculations are based on physical models but the weighting of impeller versus diffuser/volute roughness and the fraction of scalable losses within impeller and diffuser/volute are determined empirically from the analysis of tests with industrial pumps. The fraction of scalable impeller/diffuser/volute losses is found to decrease with growing specific speed. Roughness effects in the diffuser/volute are stronger than in the impeller, but the dominance of the stator over the rotor decreases with increasing specific speed. The procedure includes all flow regimes from laminar to turbulent and from hydraulically smooth to fully rough. It is validated by tests with viscosities between 0.2 to 3000 cSt and Reynolds numbers between 1500 and 108. The hydraulic losses depend on the patterns of roughness, near-wall turbulence, and the actual velocity distribution in the hydraulic passages. These effects—which are as yet not amenable to analysis—limit the accuracy of any efficiency prediction procedure for decelerated flows.
The Discharge Coefficient of a Planar Submerged Slit-Jet
Authors: Ali S. K. , Foss J. F.
Published: August 2003

The discharge coefficient, CD, of a planar, submerged slit-jet has been determined experimentally over a relatively wide range of Reynolds number values: Re=100-6500, where the slit width (w) and the average streamwise velocity (〈U〉) at the exit plane are used to define the Reynolds number. The CD values exhibit a strong dependence on Re for Re<800. For Re>3000,CD achieves an apparent asymptotic value of 0.687 for the present nozzle design. This value is about 12% higher than the potential flow value. In contrast, the velocity distribution along the centerline was in excellent agreement with that of the potential flow solution. The experimental techniques that were used to evaluate the CDRe values, their numerical values, the corresponding uncertainties, and the possible influence of the geometrical design of the nozzle on the results are presented.
Entrainment Velocity in an Axisymmetric Turbulent Jet
Authors: Falcone Anthony M. , Cataldo Joseph C.
Published: August 2003

Mean radial and turbulent radial velocity profiles were measured in a circular jet at up to 40 jet diameters downstream of the jet exit using an LDA. The mean radial velocity in the ambient reservoir (the entrainment velocity) is found to be inversely proportional to the radial distance from the jet centerline. The coefficient of proportionality, c, increases in the zone of flow establishment and reaches a constant after the transition zone. It is suggested that the traditional definition of entrainment velocity, which maintains direct proportionality to the local jet velocity by the entrainment coefficient, should be augmented by this inverse function.
Numerical Study of Sheet Cavitation Breakoff Phenomenon on a Cascade Hydrofoil
Authors: Iga Yuka , Nohmi Motohiko , Goto Akira , Shin Byeong Rog , Ikohagi Toshiaki
Published: August 2003

Two-dimensional unsteady cavity flow through a cascade of hydrofoils is numerically calculated. Particular attention is focused on instability phenomena of a sheet cavity in the transient cavitation condition, and the mechanism of the breakoff phenomenon is examined. TVD-MacCormack’s scheme employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to analyze the cavity flows. The present method permits us to treat the entire cavitating/noncavitating unsteady flowfield. By analyzing the numerical results in detail, it becomes clear that there are at least two mechanisms in the breakoff phenomenon of the sheet cavity: one is that re-entrant jets play a dominant role in such a breakoff phenomenon, and the other is that pressure waves propagating inside the cavity bring about another type of breakoff phenomenon accompanying with cavity surface waves.
Benchmark Results for the Problem of Interaction Between a Crack and a Circular Inclusion
Authors: Wang, J. , Mogilevskaya, and S. G. , Crouch S. L.
Published: August 2003

This paper is a reply to the challenge by Helsing and Jonsson (2002, ASME J. Appl. Mech., 69, pp. 88–90) for other investigators to confirm or disprove their new numerical results for the stress intensity factors for a crack in the neighborhood of a circular inclusion. We examined the same problem as Helsing and Jonsson using two different approaches—a Galerkin boundary integral method (Wang et al., 2001, in Rock Mechanics in the National Interest, pp. 1453–1460) (Mogilevskaya and Crouch, 2001, Int. J. Numer. Meth. Eng., 52, pp. 1069–1106) and a complex variables boundary element method (Mogilevskaya, 1996, Comput. Mech., 18, pp. 127–138). Our results agree with Helsing and Jonsson’s in all cases considered.
Thermal Stresses in an Infinite Elastic Pipe Weakened by a Finite Cylindrical Crack
Authors: Itou S.
Published: August 2003

Axially symmetric thermal stresses in the vicinity of a finite cylindrical crack in an elastic pipe are calculated. The surfaces of the crack are assumed to be insulated. The outer surface of the pipe is heated so as to maintain a constant temperature Td, and the inner surface of the pipe is cooled so as to maintain a constant temperature Tb. Expressions developed by Sharma are used to solve the problem. Stress intensity factors are defined and calculated numerically for several configurations of the pipe.
Relationship Among Coefficient Matrices in Symmetric Galerkin Boundary Element Method for Two-Dimensional Scalar Problems
Authors: Yu G. Y.
Published: August 2003

Based on the assumption that solutions from different methods should be the same, the relationship among weakly singular, strongly singular and hypersingular matrices associated with symmetric Galerkin boundary element method (SGBEM) is derived in this paper. Hypersingularity is avoided through matrix manipulations so that only weakly and strongly singularities need to be solved. Compared with the advantages brought about by symmetry, the additional computation caused by matrix manipulations is not so important in many cases, especially for time-domain problems or when one wants to couple BEM with other symmetric schemes. Simplicity is the advantage of the current method over the traditional SGBEM. Both steady-state and time-domain potential problems have been studied, and two numerical examples are included to show the effectiveness and accuracy of the present formulation.
Auditory masking in three pinnipeds: Aerial critical ratios and direct critical bandwidth measurements
Authors: Southall Brandon L. , Schusterman Ronald J. , Kastak David
Published: August 2003

This study expands the limited understanding of pinniped aerial auditory masking and includes measurements at some of the relatively low frequencies predominant in many pinniped vocalizations. Behavioral techniques were used to obtain aerial critical ratios (CRs) within a hemianechoic chamber for a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Simultaneous, octave-band noise maskers centered at seven test frequencies (0.2–8.0 kHz) were used to determine aerial CRs. Narrower and variable bandwidth masking noise was also used in order to obtain direct critical bandwidths (CBWs). The aerial CRs are very similar in magnitude and in frequency-specific differences (increasing gradually with test frequency) to underwater CRs for these subjects, demonstrating that pinniped cochlear processes are similar both in air and water. While, like most mammals, these pinniped subjects apparently lack specialization for enhanced detection of specific frequencies over masking noise, they consistently detect signals across a wide range of frequencies at relatively low signal-to-noise ratios. Direct CBWs are 3.2 to 14.2 times wider than estimated based on aerial CRs. The combined masking data are significant in terms of assessing aerial anthropogenic noise impacts, effective aerial communicative ranges, and amphibious aspects of pinniped cochlear mechanics.
Influences of tongue biomechanics on speech movements during the production of velar stop consonants: A modeling study
Authors: Perrier Pascal , Payan Yohan , Zandipour Majid , Perkell Joseph
Published: August 2003

This study explores the following hypothesis: forward looping movements of the tongue that are observed in VCV sequences are due partly to the anatomical arrangement of the tongue muscles, how they are used to produce a velar closure, and how the tongue interacts with the palate during consonantal closure. The study uses an anatomically based two-dimensional biomechanical tongue model. Tissue elastic properties are accounted for in finite-element modeling, and movement is controlled by constant-rate control parameter shifts. Tongue raising and lowering movements are produced by the model mainly with the combined actions of the genioglossus, styloglossus, and hyoglossus. Simulations of V1CV2 movements were made, where C is a velar consonant and V is [a], [i], or [u]. Both vowels and consonants are specified in terms of targets, but for the consonant the target is virtual, and cannot be reached because it is beyond the surface of the palate. If V1 is the vowel [a] or [u], the resulting trajectory describes a movement that begins to loop forward before consonant closure and continues to slide along the palate during the closure. This pattern is very stable when moderate changes are made to the specification of the target consonant location and agrees with data published in the literature. If V1 is the vowel [i], looping patterns are also observed, but their orientation was quite sensitive to small changes in the location of the consonant target. These findings also agree with patterns of variability observed in measurements from human speakers, but they contradict data published by Houde [Ph.D. dissertation (1967)]. These observations support the idea that the biomechanical properties of the tongue could be the main factor responsible for the forward loops when V1 is a back vowel, regardless of whether V2 is a back vowel or a front vowel. In the [i] context it seems that additional factors have to be taken into consideration in order to explain the observations made on some speakers.
Properties of the zeroth-, first-, and higher-order approximations of attributes of elastic waves in weakly anisotropic media
Authors: Farra Véronique , Pšenčı́k Ivan
Published: August 2003

Use of the perturbation theory in the study of attributes of elastic waves propagating in weakly anisotropic media leads to approximate but transparent and simple formulas, which have many applications in forward and inverse wave modeling. We present and study such formulas. We show that all studied attributes depend on elements of a matrix linearly dependent on parameters of a medium. We study this dependence with the goal to understand which parameters of the medium, and in which combinations, affect individual wave attributes. Alternative auxiliar vector bases, in which the matrix can be specified, are proposed and studied. The vector bases offer alternative specifications of polarization vectors of qS waves. One of the important observations is that the higher-order (n⩾2) perturbation formulas for qS waves are obtained separately for qS1 and qS2 waves. We also study effects of the use of the perturbation theory on the accuracy of the determination of the acoustical axes in weakly anisotropic media. We show that longitudinal directions in the first-order approximation are identical with actual ones. In singular directions, however, the first-order formulas provide directions, which may deviate from the exact ones, or they may even indicate false singular directions. Again, the above-mentioned matrix depending linearly on the parameters of the medium plays a central role in this study.
Doppler sidebands in the cross-spectral density of narrow-band reverberation from a dynamic sea surface
Authors: Gragg Robert F.
Published: August 2003

Analytic methods are used to formulate the impact of a random dynamic sea surface on the space-frequency characteristics of bistatic reverberation. A narrow-band point source is positioned beneath the time-dependent surface of a range-independent ocean. The small-waveheight perturbative approximation is invoked, and attention is focused on the Doppler sideband contributions to the reverberation cross-spectral density for an arbitrarily placed receiver pair. The new expression that results is identified as an active scattering generalization of the van Cittert–Zernike theorem from classical partial coherence theory. This work is the first to explicitly predict the sideband structure in the cross-spectral density of the field scattered from a realistic moving sea surface. A numerical example is presented for a shallow source and shallow receivers in a homogeneous ocean.
Gas jets as ultrasonic waveguides
Authors: Choi D. W. , Hutchins D. A. , Billson D. R.
Published: August 2003

The study of the propagation of ultrasound within a gas jet is extended to obtain waveguide effects, where the jet collimates the ultrasonic beam from a transducer within the flow. Two methods have been investigated to achieve this—cooling the gas within the air jet, and using a different gas whose acoustic velocity is lower than air. Cooling an air jet to a temperature less than that of the surrounding air produced a noticeable waveguide effect. In addition, studies have been carried out using other selected gases, such as carbon dioxide (CO2) with a lower acoustic velocity than air, and helium (He) with a higher value. The former gas enhanced confinement of the ultrasonic beam, whereas the latter caused divergence. An ideal solution was found to be a CO2/air mixture, which produced a well-collimated sound field along the axis, while limiting the excess attenuation of pure CO2 gas jets. The effectiveness of the waveguide using mixed gas jets in producing images in air-coupled testing of solids is demonstrated.
Inverse ultrasonic determination of imperfect interfaces and bulk properties of a layer between two solids
Authors: Baltazar A. , Wang L. , Xie B. , Rokhlin S. I.
Published: August 2003

A method for determination of the complete set of physical, geometrical, and interfacial properties of an isotropic layer embedded between two known solids is discussed. These properties are: Lamé elastic moduli, density and thickness of the layer, and complex normal and transverse interfacial stiffnesses between the layer and the substrates. The properties are combined in the form of eight nondimensional parameters, which are determined from experimental reflection spectra at two incident angles: normal and oblique. The conditions for simultaneous determination of bulk layer properties and the interface normal and transverse springs with losses and the stability of the inversion method against data scatter are addressed. The inversion model is validated by experiment on normal and angular ultrasonic reflectivity from a layer between two semispaces in dry mechanical contact and from an environmentally degraded adhesive joint. The layer properties were measured independently, showing good agreement with the reconstructed results.
Ray dynamics in a long-range acoustic propagation experiment
Authors: Beron-Vera Francisco J. , Brown Michael G. , Colosi John A. , Tomsovic Steven , Virovlyansky Anatoly L. , Wolfson Michael A. , Zaslavsky George M.
Published: August 2003

A ray-based wave-field description is employed in the interpretation of broadband basin-scale acoustic propagation measurements obtained during the Acoustic Thermometry of Ocean Climate program’s 1994 Acoustic Engineering Test. Acoustic observables of interest are wavefront time spread, probability density function (PDF) of intensity, vertical extension of acoustic energy in the reception finale, and the transition region between temporally resolved and unresolved wavefronts. Ray-based numerical simulation results that include both mesoscale and internal-wave-induced sound-speed perturbations are shown to be consistent with measurements of all the aforementioned observables, even though the underlying ray trajectories are predominantly chaotic, that is, exponentially sensitive to initial and environmental conditions. Much of the analysis exploits results that relate to the subject of ray chaos; these results follow from the Hamiltonian structure of the ray equations. Further, it is shown that the collection of the many eigenrays that form one of the resolved arrivals is nonlocal, both spatially and as a function of launch angle, which places severe restrictions on theories that are based on a perturbation expansion about a background ray.
Acoustical losses in wet instrument bores (L)
Authors: Coltman John W.
Published: August 2003

The possibility that condensed water in wind instrument bores might contribute to acoustic losses through evaporation and condensation during the acoustic cycle was explored in a short experiment. A wet tube exhibited losses about 4% higher than when dry, the precision of the measurements being 0.6 percentage points, strongly suggesting that this mechanism is operative.
Fast Fourier transform and singular value decomposition formulations for patch nearfield acoustical holography
Authors: Williams Earl G. , Houston Brian H. , Herdic Peter C.
Published: August 2003

Nearfield acoustical holography (NAH) requires the measurement of the pressure field over a complete surface in order to recover the normal velocity on a nearby concentric surface, the latter generally coincident with a vibrator. Patch NAH provides a major simplification by eliminating the need for complete surface pressure scans—only a small area needs to be scanned to determine the normal velocity on the corresponding (small area) concentric patch on the vibrator. The theory of patch NAH is based on (1) an analytic continuation of the patch pressure which provides a spatially tapered aperture extension of the field and (2) a decomposition of the transfer function (pressure to velocity and/or pressure to pressure) between the two surfaces using the singular value decomposition (SVD) for general shapes and the fast Fourier transform (FFT) for planar surfaces. Inversion of the transfer function is stabilized using Tikhonov regularization and the Morozov discrepancy principle. Experimental results show that root mean square errors of the normal velocity reconstruction for a point-driven vibrator over 200–2700 Hz average less than 20% for two small, concentric patch surfaces 0.4 cm apart. Reconstruction of the active normal acoustic intensity was also successful, with less than 30% error over the frequency band.
Radiated fields of capacitive micromachined ultrasonic transducers in air
Authors: Hutchins David A. , McIntosh James S. , Neild Adrian , Billson Duncan R. , Noble Russell A.
Published: August 2003

This paper presents a study of the radiated ultrasonic fields of capacitive micromachined ultrasonic transducers (often referred to as cMUTs) in air. These fields were modeled theoretically and then compared to the experimental near-field amplitude variations and directivity patterns of square cMUTs. The good agreement between theory and experiment indicates that the devices can be approximated to plane piston radiators. The fields of multiple elements driven in phase on the same silicon substrate are presented, where again comparison is made to theory. The results indicate that individual elements are unaffected by radiation through the silicon substrate from adjacent devices. It will also be demonstrated that it is possible to use the knowledge of these fields to develop air-coupled ultrasonic surface imaging systems.
A Dearth of Dark Matter in Ordinary Elliptical Galaxies
Authors: Romanowsky Aaron J. , Douglas Nigel G. , Arnaboldi Magda , Kuijken Konrad , Merrifield Michael R. , Napolitano Nicola R. , Capaccioli Massimo , Freeman Kenneth C.
Published: September 2003

The kinematics of the outer parts of three intermediate-luminosity elliptical galaxies were studied with the Planetary Nebula Spectrograph. The galaxies' velocity-dispersion profiles were found to decline with the radius, and dynamical modeling of the data indicates the presence of little if any dark matter in these galaxies' halos. This unexpected result conflicts with findings in other galaxy types and poses a challenge to current galaxy formation theories.
Sequence-Dependent Pausing of Single Lambda Exonuclease Molecules
Authors: Perkins Thomas T. , Dalal Ravindra V. , Mitsis Paul G. , Block Steven M.
Published: September 2003

Lambda exonuclease processively degrades one strand of duplex DNA, moving 5′-to-3′ in an ATP-independent fashion. When examined at the single-molecule level, the speeds of digestion were nearly constant at 4 nanometers per second (12 nucleotides per second), interspersed with pauses of variable duration. Long pauses, occurring at stereotypical locations, were strand-specific and sequence-dependent. Pause duration and probability varied widely. The strongest pause, GGCGAT TCT, was identified by gel electrophoresis. Correlating single-molecule dwell positions with sequence independently identified the motif GGCGA. This sequence is found in the left lambda cohesive end, where exonuclease inhibition may contribute to the reduced recombination efficiency at that end.
LysM Domain Receptor Kinases Regulating Rhizobial Nod Factor-Induced Infection
Authors: Limpens Erik , Franken Carolien , Smit Patrick , Willemse Joost , Bisseling Ton , Geurts René
Published: September 2003

The rhizobial infection of legumes has the most stringent demand toward Nod factor structure of all host responses, and therefore a specific Nod factor entry receptor has been proposed. The
SYM2
gene identified in certain ecotypes of pea (
Pisum sativum
) is a good candidate for such an entry receptor. We exploited the close phylogenetic relationship of pea and the model legume
Medicago truncatula
to identify genes specifically involved in rhizobial infection. The
SYM2
orthologous region of
M. truncatula
contains 15 putative receptor-like genes, of which 7 are LysM domain–containing receptor-like kinases (LYKs). Using reverse genetics in
M. truncatula
, we show that two
LYK
genes are specifically involved in infection thread formation. This, as well as the properties of the LysM domains, strongly suggests that they are Nod factor entry receptors.
Characterization of Hybrid Toluate and Benzoate Dioxygenases
Authors: Ge Yong , Eltis Lindsay D.
Published: August 2003

Toluate dioxygenase of
Pseudomonas putida
mt-2 (TADO
mt2
) and benzoate dioxygenase of
Acinetobacter calcoaceticus
ADP1 (BADO
ADP1
) catalyze the 1,2-dihydroxylation of different ranges of benzoates. The catalytic component of these enzymes is an oxygenase consisting of two subunits. To investigate the structural determinants of substrate specificity in these ring-hydroxylating dioxygenases, hybrid oxygenases consisting of the α subunit of one enzyme and the β subunit of the other were prepared, and their respective specificities were compared to those of the parent enzymes. Reconstituted BADO
ADP1
utilized four of the seven tested benzoates in the following order of apparent specificity: benzoate > 3-methylbenzoate > 3-chlorobenzoate > 2-methylbenzoate. This is a significantly narrower apparent specificity than for TADO
mt2
(3-methylbenzoate > benzoate ∼ 3-chlorobenzoate > 4-methylbenzoate ∼ 4-chlorobenzoate ≫ 2-methylbenzoate ∼ 2-chlorobenzoate [Y. Ge, F. H. Vaillancourt, N. Y. Agar, and L. D. Eltis, J. Bacteriol. 184:4096-4103, 2002]). The apparent substrate specificity of the α
B
β
T
hybrid oxygenase for these benzoates corresponded to that of BADO
ADP1
, the parent from which the α subunit originated. In contrast, the apparent substrate specificity of the α
T
β
B
hybrid oxygenase differed slightly from that of TADO
mt2
(3-chlorobenzoate > 3-methylbenzoate > benzoate ∼ 4-methylbenzoate > 4-chlorobenzoate > 2-methylbenzoate > 2-chlorobenzoate). Moreover, the α
T
β
B
hybrid catalyzed the 1,6-dihydroxylation of 2-methylbenzoate, not the 1,2-dihydroxylation catalyzed by the TADO
mt2
parent. Finally, the turnover of this
ortho
-substituted benzoate was much better coupled to O
2
utilization in the hybrid than in the parent. Overall, these results support the notion that the α subunit harbors the principal determinants of specificity in ring-hydroxylating dioxygenases. However, they also demonstrate that the β subunit contributes significantly to the enzyme's function.
Overproduction of Inactive Variants of the Murein Synthase PBP1B Causes Lysis in
Escherichia coli
Authors: Meisel Ute , Höltje Joachim-Volker , Vollmer Waldemar
Published: August 2003

Penicillin-binding protein 1B (PBP1B) of
Escherichia coli
is a bifunctional murein synthase containing both a transpeptidase domain and a transglycosylase domain. The protein is present in three forms (α, β, and γ) which differ in the length of their N-terminal cytoplasmic region. Expression plasmids allowing the production of native PBP1B or of PBP1B variants with an inactive transpeptidase or transglycosylase domain or both were constructed. The inactive domains contained a single amino acid exchange in an essential active-site residue. Overproduction of the inactive PBP1B variants, but not of the active proteins, caused lysis of wild-type cells. The cells became tolerant to lysis by inactive PBP1B at a pH of 5.0, which is similar to the known tolerance for penicillin-induced lysis under acid pH conditions. Lysis was also reduced in mutant strains lacking several murein hydrolases. In particular, a strain devoid of activity of all known lytic transglycosylases was virtually tolerant, indicating that mainly the lytic transglycosylases are responsible for the observed lysis effect. A possible structural interaction between PBP1B and murein hydrolases in vivo by the formation of a multienzyme complex is discussed.
Jumping the Barrier to β-Lactam Resistance in
Staphylococcus aureus
Authors: Katayama Yuki , Zhang Hong-Zhong , Hong Dong , Chambers Henry F.
Published: August 2003

Although the staphylococcal methicillin resistance determinant,
mecA
, resides on a mobile genetic element, staphylococcus cassette chromosome
mec
(SCC
mec
), its distribution in nature is limited to as few as five clusters of related methicillin-resistant
Staphylococcus aureus
(MRSA) clones. To investigate the potential role of the host chromosome in clonal restriction of the methicillin resistance determinant, we constructed plasmid pYK20, carrying intact
mecA
, and introduced it into several methicillin-susceptible
Staphylococcus aureus
strains, five of which were naive hosts (i.e.,
mecA
not previously resident on the host chromosome) and five of which were experienced hosts (i.e., methicillin-susceptible variants of MRSA strains from which SCC
mec
was excised). We next assessed the effect of the recipient background on the methicillin resistance phenotype by population analysis, by assaying the
mecA
expression of PBP2a by Western blot analysis, and by screening for mutations affecting
mecA
. Each experienced host transformed with pYK20 had a resistance phenotype and expressed PBP2a similar to that of the parent with chromosomal SCC
mec
, but naive hosts transformed with pYK20 selected against its expression, indicative of a host barrier. Either inducible β-lactamase regulatory genes
blaR1
-
blaI
or homologous regulatory genes
mecR1
-
mecI
, which control
mecA
expression, acted as compensatory elements, permitting the maintenance and expression of plasmid-carried
mecA
.
DNA Topoisomerase III from the Hyperthermophilic Archaeon
Sulfolobus solfataricus
with Specific DNA Cleavage Activity
Authors: Dai Penggao , Wang Ying , Ye Risheng , Chen Liang , Huang Li
Published: August 2003

We report the production, purification, and characterization of a type IA DNA topoisomerase, previously designated topoisomerase I, from the hyperthermophilic archaeon
Sulfolobus solfataricus
. The protein was capable of relaxing negatively supercoiled DNA at 75°C in the presence of Mg
2+
. Mutation of the putative active site Tyr318 to Phe318 led to the inactivation of the protein. The
S. solfataricus
enzyme cleaved oligonucleotides in a sequence-specific fashion. The cleavage occurred only in the presence of a divalent cation, preferably Mg
2+
. The cofactor requirement of the enzyme was partially satisfied by Cu
2+
, Co
2+
, Mn
2+
, Ca
2+
, or Ni
2+
. It appears that the enzyme is active with a broader spectrum of metal cofactors in DNA cleavage than in DNA relaxation (Mg
2+
and Ca
2+
). The enzyme-catalyzed oligonucleotide cleavage required at least 7 bases upstream and 2 bases downstream of the cleavage site. Analysis of cleavage by the
S. solfataricus
enzyme on a set of oligonucleotides revealed a consensus cleavage sequence of the enzyme: 5′-G(A/T)CA(T)AG(T)G(A)X↓XX-3′. This sequence bears more resemblance to the preferred cleavage sites of topoisomerases III than to those of topoisomerases I. Based on these data and sequence analysis, we designate the enzyme
S. solfataricus
topoisomerase III.
Epoxyalkane:Coenzyme M Transferase in the Ethene and Vinyl Chloride Biodegradation Pathways of
Mycobacterium
Strain JS60
Authors: Coleman Nicholas V. , Spain Jim C.
Published: August 2003

Mycobacterium
strains that grow on ethene and vinyl chloride (VC) are widely distributed in the environment and are potentially useful for biocatalysis and bioremediation. The catabolic pathway of alkene assimilation in mycobacteria is not well characterized. It is clear that the initial step is a monooxygenase-mediated epoxidation that produces epoxyethane from ethene and chlorooxirane from VC, but the enzymes involved in subsequent transformation of the epoxides have not been identified. We investigated epoxyethane metabolism in
Mycobacterium
strain JS60 and discovered a coenzyme M (CoM)-dependent enzyme activity in extracts from VC- and ethene-grown cells. PCR amplifications using primers targeted at epoxyalkane:CoM transferase (EaCoMT) genes yielded part of the JS60 EaCoMT gene, which was used to clone an 8.4-kb genomic DNA fragment. The complete EaCoMT gene (
etnE
) was recovered, along with genes (
etnABCD
) encoding a four-component monooxygenase and two genes possibly involved in acyl-CoA ester metabolism. Reverse transcription-PCR indicated that the
etnE
and
etnA
genes were cotranscribed and inducible by ethene and VC. Heterologous expression of the
etnE
gene in
Mycobacterium smegmatis
mc
2
155 using the pMV261 vector gave a recombinant strain capable of transforming epoxyethane, epoxypropane, and chlorooxirane. A metabolite identified by mass spectrometry as 2-hydroxyethyl-CoM was produced from epoxyethane. The results indicate that the EaCoMT and monooxygenase enzymes encoded by a single operon (
etnEABCD
) catalyze the initial reactions in both the VC and ethene assimilation pathways. CoM-mediated reactions appear to be more widespread in bacteria than was previously believed.
A Dual Binding Site for Integration Host Factor and the Response Regulator CtrA inside the
Caulobacter crescentus
Replication Origin
Authors: Siam Rania , Brassinga Ann Karen C. , Marczynski Gregory T.
Published: August 2003

The response regulator CtrA controls chromosome replication by binding to five sites, a, b, c, d, and e, inside the
Caulobacter crescentus
replication origin (
Cori
). In this study, we demonstrate that integration host factor (IHF) binds
Cori
over the central CtrA binding site c. Surprisingly, IHF and CtrA share DNA recognition sequences. Rather than promoting cooperative binding, IHF binding hinders CtrA binding to site c and nearby site d. Unlike other CtrA binding sites, DNA mutations in the CtrA c/IHF site uniquely impair autonomous
Cori
plasmid replication. These mutations also alter transcription from distant promoters more than 100 bp away. When the CtrA c/IHF site was deleted from the chromosome, these cells grew slowly and became selectively intolerant to a CtrA phosphor-mimic allele (D51E). Since CtrA protein concentration decreases during the cell cycle as IHF protein concentration increases, we propose a model in which IHF displaces CtrA in order to bend
Cori
and promote efficient chromosome replication.
Autotransporters as Scaffolds for Novel Bacterial Adhesins: Surface Properties ofEscherichia coliCells Displaying Jun/Fos Dimerization Domains
Authors: Veiga Esteban , de Lorenzo Víctor , Fernández Luis Angel
Published: August 2003

Hybrid proteins containing the β-autotransporter domain of the immunoglobulin A (IgA) protease ofNeisseria gonorrhoea(IgAβ) and the partner leucine zippers of the eukaryotic transcriptional factors Fos and Jun were expressed inEscherichia coli.Such fusion proteins targeted the leucine zipper modules to the cell surface. Cells displaying the Junβ sequence flocculated shortly after induction of the hybrid protein.E. colicells expressing separately Fosβ and Junβ chimeras formed stable bacterial consortia. These associations were physically held by tight intercell ties caused by the protein-protein interactions of matching dimerization domains. The role of autotransporters in the emergence of new adhesins is discussed.