Showing papers on "Deformation (meteorology) published in 1999"

Surgical staples with deformation zones of non-uniform cross section

Abstract: An improved staple for use in internal surgery is disclosed. This improved staple has a deformation zone in each leg that varies in cross section along the length of the deformation zone. These cross sections are shaped so as to control staple leg deformation during staple installation into tissue in order to more effectively produce hemostasis and unite tissues and minimize tissue damage.

Developing stable fine–grain microstructures by large strain deformation

Abstract: Methods of deforming metals to large strains are reviewed and the process of equal channel angular extrusion is analysed in detail. The development of microstructure during large strain deformation is discussed, and it is concluded that the main criterion for the formation of a sub–micron grain structure is the generation of a sufficiently large fraction (> 0.7) of high–angle grain boundary during the deformation process. For aluminium alloys, it is found that a low–temperature anneal is required to convert the deformed microstructure into an equi–axed grain structure. The material, microstructural and processing factors that influence the formation of such fine–grain microstructures are discussed, and the stability of these microstructures at elevated temperatures is considered.

Developing stable fine-grain microstructures by large strain deformation - Discussion

Abstract: Methods of deforming metals to large strains are reviewed and the process of equal channel angular extrusion is analysed in detail. The development of microstructure during large strain deformation is discussed, and it is concluded that the main criterion for the formation of a sub–micron grain structure is the generation of a sufficiently large fraction (> 0.7) of high–angle grain boundary during the deformation process. For aluminium alloys, it is found that a low–temperature anneal is required to convert the deformed microstructure into an equi–axed grain structure. The material, microstructural and processing factors that influence the formation of such fine–grain microstructures are discussed, and the stability of these microstructures at elevated temperatures is considered.

Present-Day Deformation Across the Basin and Range Province, Western United States

Abstract: The distribution of deformation within the Basin and Range province was determined from 1992, 1996, and 1998 surveys of a dense, 800-kilometer-aperture, Global Positioning System network. Internal deformation generally follows the pattern of Holocene fault distribution and is concentrated near the western extremity of the province, with lesser amounts focused near the eastern boundary. Little net deformation occurs across the central 500 kilometers of the network in western Utah and eastern Nevada. Concentration of deformation adjacent to the rigid Sierra Nevada block indicates that external plate-driving forces play an important role in driving deformation, modulating the extensional stress field generated by internal buoyancy forces that are due to lateral density gradients and topography near the province boundaries.

A Process Model for Latex Film Formation: Limiting Regimes for Individual Driving Forces

Abstract: The deformation of particles, to produce a structure without voids, has been an issue of contention in the film formation community for many years. Four different mechanisms have been proposed. Three involve homogeneous deformation throughout the film, although all are built on the deformation of two isolated particles, described in the viscous limit by Frenkel and in the elastic limit by Hertz and Johnson, Kendall, and Roberts. We derive a linear viscoelastic generalization of Frenkel's model that predicts the deformation of two spheres compressed by a force, F, and surface tension, γ. The resulting equation is then embedded in field equations governing the collapse of macroscopic films. Assuming a uniaxial compression allows derivation of limits for the proposed modes of homogeneous deformation. These limits are shown as surfaces in parameter space. Since temperature alters most profoundly the rheological response of viscoelastic polymers, the controlling deformation mechanism is defined as a function o...

Simultaneous three-dimensional dynamic deformation measurements with pulsed digital holography

Abstract: The three deformation components x, y, z of a vibrating object are measured simultaneously by use of digital holography with a double-pulse ruby laser source. The object is illuminated from three different directions, each optically path matched with three reference beams such that three independent digital holograms are formed and added incoherently in one single CCD image. The optical phase difference between the two recordings taken for each hologram is quantitatively evaluated by the Fourier-transform method so that a set of three phase maps is obtained, representing the deformation along three sensitivity vectors. The total object deformation is obtained as a vector resultant from the data of the three phase maps. To give the full three-dimensional (3-D) description, the shape of the object is measured by the two-wavelength contouring method. Experiments are performed with a cylinder as the test object, transiently and harmonically excited. The 3-D deformation and shape measurement results are presented graphically.

Flexible Multibody Simulation and Choice of Shape Functions

Abstract: The approach most widely used for the modelling of flexible bodies in multibody systems has been called the floating frame of reference formulation. In this methodology the flexible body motion is subdivided into a reference motion and deformation. The displacement field due to deformation is approximated by the Ritz method as a product of known shape functions and unknown coordinates depending on time only. The shape functions may be obtained using finite-element-models of flexible bodies in multibody systems, resulting in a detailed system representation and a high number of system equations. The number of system equations of such a nodal approach can be reduced considerably using a modal representation of deformation. This modal approach, however, leads to the fundamental problem of selecting the shape functions. The floating frame of reference formulation is reviewed here using a generic flexible body model, from which the various body models used in multibody simulations may be derived by formulation of specific constraint equations. Special attention is given in this investigation to the following subjects: • The separation of flexible body motion into a reference motion and deformation requires the definition of a body reference frame, which in turn affects the choice of shape functions. Some alternatives will be outlined together with their advantages and disadvantages. • Assuming the body deformation to be small, the system equations can be linearized. This may require considering geometric stiffening terms. The problem of how to compute these terms has been solved in literature on the instability of structures under critical loads. For finite element models the geometric stiffening terms are obtained from the tangential stiffness matrix. • The generality of the flexible body model allows the definition of an object oriented data base to describe the system bodies. Such a data base includes a general interface between multibody- and finite-element-codes. • By combining eigenfunctions and static deformation modes to represent body deformation one obtains a set of so-called quasi-comparison functions. When selected properly these functions can be shown to improve the representation of stresses significantly.

Ellipsoidal deformation of vertical quantum dots

Abstract: Addition energy spectra at 0 T of circular and ellipsoidally deformed few-electron vertical quantum dots are measured and compared to results of model calculations within spin-density-functional theory. Because of the rotational symmetry of the lateral harmonic confining potential, circular dots show a pronounced shell structure. With the lifting of the single-particle level degeneracies, even a small deformation is found to radically alter the shell structure leading to significant modifications in the addition energy spectra. Breaking the circular symmetry with deformation also induces changes in the total spin. This ``piezomagnetic'' behavior of quantum dots is discussed, and the addition energies for a set of realistic deformation parameters are provided. For the case of the four-electron ground state at 0 T, a spin-triplet to spin-singlet transition is predicted, i.e., Hund's first rule no longer applies. Application of a magnetic field parallel to the current confirms that this is the case, and also suggests that the anisotropy of an elliptical dot, in practice, may be higher than that suggested by the geometry of the device mesa in which the dot is located.

Thermocapillary migration of bubbles and drops at moderate to large Marangoni number and moderate Reynolds number in reduced gravity

Abstract: Results from experiments on the thermocapillary migration of air bubbles and Fluorinert drops in a Dow–Corning silicone oil aboard a NASA Space Shuttle mission are presented and discussed. The experiments cover a wider range of Marangoni and Reynolds numbers than that attained in a prior flight experiment. The data are consistent with earlier results, and are compared with theoretical predictions. Large air bubbles were found to deform slightly in shape to oblate spheroids while the deformation of even the largest drops was within the uncertainty of the size measurements.

Characterising the pre-failure deformation properties of geomaterials, Theme Lecture for the Plenary Session No. 1

Abstract: Recent developments in the characterization of geomaterial prefailure deformation properties are reviewed, focusing on the data required to predict ground deformations and structural displacement at working loads. Descriptions are given of the deformation characteristics developed at very small to intermediate strains, of a variety of geomaterials, in testing using modern laboratory and field techniques. The relationships between static and dynamic experiments, between laboratory and field techniques, and between testing and field full scale behavior are discussed. Important features that are highlighted include: kinematic yielding, effects of recent stress-time history, anisotropy, structuration and destructuration, non-linearity by strain and pressure and effects of cyclic loading. Careful distinctions are made between elastic, plastic and viscous properties.

The interplay of faulting and folding during the evolution of the Zagros deformation belt

Abstract: Abstract In this short paper satellite images, aerial photographs and seismic sections are used to show that pure buckle folds, pure forced folds and folds intermediate between the two have all formed, and are still forming, in association with the compression tectonics currently occurring in the Zagros deformation belt which is situated along the northeastern margin of the Arabian plate. The type of folding and its distribution can be linked directly to the distribution of ancient basement faults and to the rheological profile of the cover sequence.

Models of ground deformation from vertical volcanic conduits with application to eruptions of Mount St. Helens and Mount Etna

Abstract: We present simple analytical models of ground deformation from inflation of vertical volcanic conduits or pipes. We compare three cases corresponding to (1) a pressurized pipe with closed end at the top that resists the internal pressure, (2) a pressurized pipe with top open for which the internal deformation is mainly dislocation of the cylindrical walls, and (3) a pipe-shaped region that dilates. For the closed pipe we use Eshelby's inclusion theory to model deformation from a thin, pressurized, elongated, prolate ellipsoid in a full-space, which we express in terms of double forces. To satisfy surface boundary conditions, we superimpose image solutions by using double forces derived from Mindlin's half-space solution for the point force. For the open pipe we apply the Volterra integral to dislocation across a cylindrical surface and generalize it to the half-space using Mindlin's point force solution. These two solutions show marked differences from the line of dilatation solution. Ratios of maximum horizontal deformation to maximum vertical deformation for the pipe models are significantly greater than values for the center or line of dilatation models. This, and the more gradual fall off of the deformation with distance may be used as diagnostics for discriminating between pipe-like sources and dilatational sources on volcanoes, where both components of the deformation field are available. As examples, we compare the closed pipe model with deformation associated with dome building on Mount St. Helens volcano, and tilt predicted by the open pipe model with tilt measured during a period of explosive eruptive activity on Mount Etna, Sicily, in 1995. Comparison between model values and the measurements suggests that the effective elastic moduli of the volcanic cones are very low.

Ductile deformation and mass loss in the Franciscan Subduction Complex: implications for exhumation processes in accretionary wedges

Abstract: Abstract Deformation measurements from 64 sandstone samples collected in three study areas from the Eastern Belt of the Franciscan Complex are used to evaluate how the high-pressure metamorphic interior of the Franciscan wedge was exhumed. Pressure estimates indicate 25–30 km of exhumation in this part of the Franciscan Complex. Much of the Eastern Belt has a semi-penetrative cleavage that formed by solution mass transfer (SMT) while the rocks were moving through the wedge. Individual samples have absolute principal stretches of SX = 1.00–1.52, SY = 0.60–1.21, and SZ = 0.33–0.81. Strain magnitudes and directions are quite variable at the local scale. The deformation at the regional scale is estimated by calculating tensor averages for groups of measurements. The three study areas, which are spaced over a distance of c. 500 km along the Franciscan margin, give remarkably similar averages, which indicates that the deformation of the Eastern Belt is consistent at the regional scale. The tensor average for all data indicates a nearly vertical Z direction with SX = 0.96, SY = 0.92, and SZ = 0.70. SX and SY are near one because at the local scale, the X and Y directions vary considerably in orientation, which means that their stretch contributions are averaged out at the regional scale. This unusual strain type, consisting of both plane strain and uniaxial shortening, results from the fact that shortening in Z was balanced by a pervasive mass-loss volume strain, averaging about 38%. The geometry of directed fibre overgrowths was used to measure internal rotations. These data indicate that in sandstones, SMT deformation was nearly coaxial (mean kinematic vorticity number is 0.05 at the regional scale and generally <0.4 for individual samples). A simple one-dimensional steady-state model indicates that ductile thinning accounted for only c. 10% of the overall exhumation. Ductile shortening across the Franciscan wedge was very slow, at rates <8 × 10−17 s−1 (<0.3% Ma−1). Assuming that this strain was active in an across-strike zone <200 km wide, we estimate that horizontal ductile flow would have accounted for <0.25% of the total convergence across the Franciscan margin. We conclude that the SMT mechanism operated slowly as a background deformation process, and that the dislocation glide mechanism was completely inactive down to depths of 25–30 km. Thus, the stability of the Franciscan wedge was probably better defined by the Coulomb wedge criterion than by a viscous wedge criterion. No definitive normal faults have been found in or adjacent to the Eastern Belt. Therefore, we infer that wedge taper was mainly controlled by deep accretion and erosion of an emergent forearc high.

The deformation theorem for flat chains

Abstract: We prove that the deformation procedure of Federer and Fleming gives good approximations to arbritrary flat chains, not just those of finite mass and boundary mass. This implies, for arbitrary coefficient groups, that flat chains of finite mass and finite size are rectifiable, and also, for finite coefficient groups, that flat chains supported in sets of finite Hausdorff measure (or even finite integral geometric measure) have finite mass. The deformation theorem of Federer and Fleming [FF] is a fundamental tool in geometric measure theory. The theorem gives a way of approximating (in the so-called flat norm) a very general k-dimensional surface (flat chain) A in R by a polyhedral surface P consisting of k-cubes from a cubical lattice in R . Unfortunately, the theorem requires the original surface to have finite mass and finite boundary mass. In this paper, we remove these finiteness restrictions. That is, we show (in §1.1, 1.2, and 1.3) that the Federer-Fleming deformation procedure gives good approximations to an arbitrary flat chain A. Also, the approximating polyhedral surface depends only on the way in which typical translates of A intersect the (N − k) skeleton of the dual lattice. This lets us answer several open questions about flat chains: (1) For an arbitrary coefficient group, a nonzero flat k-chain cannot be supported in a set of k-dimensional measure 0. (2) For an arbitrary coefficient group, a flat chain of finite mass and finite size must be rectifiable. In particular, for any discrete group, finite mass implies rectifiability. (3) Let G be a normed group with sup{|g| : g ∈ G} = λ < ∞. Then for any flat chain with coefficients in G, M(A) ≤ λH(sptA). (Special cases of (1) and (2) are mentioned as open questions in [FL], and the special case G = Zp of (3) is mentioned as an open question in [F1]. Federer and Fleming [FF] proved (1) for real flat chains (and therefore also for integral flat chains). Almgren [A] introduced the notion of size and proved (2) for real flat chains; Federer [F2] then gave a much shorter proof.) 1991 Mathematics Subject Classification. Primary 49Q15; secondary 49Q20. The author was partially funded by NSF grants DMS-95-04456 and DMS-98-03493.

Long-period seafloor seismology and deformation under ocean waves

Abstract: The deformation of the seafloor under loading by long-period ocean waves raises vertical component noise levels at the deep seafloor by 20 to 30 dB above noise levels at good continental sites in the band from 0.001 to 0.04 Hz. This noise substantially limits the detection threshold and signal-to-noise ratio for long-period phases of earthquakes observed by seafloor seismometers. Borehole installation significantly improves the signal-to-noise ratio only if the sensor is installed at more than 1 km below the seafloor because the deformation signal decays slowly with depth. However, the vertical-component deformation signal can be predicted and suppressed using seafloor measurements of pressure fluctuations observed by differential pressure gauges. The pressure observations of ocean waves are combined with measurements of the transfer function between vertical acceleration and pressure to predict the vertical component deformation signal. Subtracting the predicted deformation signal from pressure observations can reduce vertical component noise levels near 0.01 Hz by more than 25 dB, significantly improving signal-to-noise ratios for long-period phases. There is also a horizontal-component deformation signal but it is smaller than the vertical-component signal and only significant in shallow water (

Flexible impact-resistant materials

Abstract: Flexible impact or blast-resistant composite material comprising:a strike-face (1) comprising impact-resistant, adjacent tiles (2) having complementary mating edges, and a flexible material (4) having at least one layer, the material having a high resistance to local deformation and by itself being of non-ballistic properties, wherein the tiles of the strike-face are integral with the flexible material.