Showing papers on "Slab published in 1985"

The slab geometry laser - Part II: Thermal effects in a finite slab

Abstract: This paper presents two methods for calculating the thermally induced stress, focusing, and depolarization in a pumped zigzag-slab solid-state laser. A computer program capable of detailed calculations of thermal effects in the general case is described. An approximate analysis of slab thermal effects in many cases allows calculation of these effects without use of the computer model directly. The analysis predicts that slabs of square cross section can be designed to have low depolarization and thermal focusing compared to Nd:YAG laser rods.

A simple model of whole-mantle convection

Abstract: Isotopic evidence of the chemical variability of basalts implies the existence of distinct, long-lived chemical reservoirs in the mantle. This has commonly been interpreted as evidence that mantle convection is layered, since known models of whole-mantle convection have too much shearing to allow preservation of these reservoirs. However, the geochemical evidence requires at least three reservoirs and models of layered convection have dynamical difficulties, casting serious doubt on the viability of these models. This difficulty has been resolved in the present paper by the development of a simple model of whole-mantle convection which allows the preservation of chemically distinct reservoirs. In this model, heating of the mantle from below produces axisymmetric plumes which carry heat upward through the mantle without causing overturning. Hence the lower mantle is much less sheared than in the usual two-dimensional model. Mantle convection is driven by the penetration of cold lithospheric slabs from above. It is argued that the pattern of convection is governed primarily by the dependence of viscosity on temperature and this dependence drives the mantle toward an isoviscous state. These ideas are quantified in a simple one-dimensional model of mantle convection in which the slab mass flux as a function of radius is governed by the requirement that the temperature profile remains isoviscous. The resulting convection cycles material through the upper mantle more rapidly than through the lower mantle. This provides a mechanism for an initially homogeneous mantle to become chemically stratified with a depleted upper mantle and primitive lower mantle.

The Oaxaca, Mexico, earthquake of 1931: lithospheric normal faulting in the subducted Cocos plate

Abstract: A study of the great earthquake in Oaxaca, Mexico, on 15 January 1931 shows that it was a normal fault earthquake striking east-west. The lack of evidence of surface faulting near the source region1 and the focal depth of ∼40 km inferred from body-wave modelling suggest that the earthquake occurred within the subducted slab. The large size of the earthquake (Ms = 8.0) strongly suggests that the rupture broke through the entire lithosphere of the subducted Cocos plate. Other large, normal fault earthquakes in the Japanese2, Aleutian3, Peruvian4 and Sumba5 arcs show lithospheric faulting seawards of the trench or very close to it. The 1931 event, however, occurred farther down-dip in the slab (∼150 km landward of the trench), below the bottom of what appears to be the seismogenic plate interface. We speculate here that large, although infrequent, normal fault earthquakes such as the 1931 Oaxaca earthquake may have a role in decoupling at depth the subducted slab from the upper part of the slab and perhaps from the overriding Mexican continental plate. The epicentral location of the 1858 Michoacan earthquake6 (Ms≍7.5) suggests that it may represent another example of lithospheric normal faulting in the Middle American arc. Such earthquakes, for which the periods of recurrence are unknown, constitute an extremely high seismic risk to population centres of Mexico.

Bridge Analysis Simplified

Abstract: Contents: Principles of Load Distribution; Calculation of Characterizing Parameters; Bridge Responses; Methods for Longitudinal Moments in Shallow Superstructures; Methods for Longitudinal Shears in Shallow Superstructures; Methods for Transverse Moments in Shallow Superstructures; Methods for Transverse Shear; Analysis of Multispan and Variable Section Bridges; Analysis for Edge Stiffening and Vehicle Edge Distance; Analysis of Cellular and Voided Slab Bridges; Analysis of Multibeam and Multispine Bridges; Analysis of Floor Systems of Truss and Similar Bridges and Methods for Analyzing Deck Slab Overhangs.

Construction Load Analysis for Concrete Structures

Abstract: A common practice in multistory reinforced concrete building construction is to shore a freshly placed concrete floor on several previously cast floors. The construction loads on the supporting floors may exceed the slab design loads during maturity, especially when the design live load is small compared with the dead load. A few studies have been conducted to analytically model the construction loading process. However, these early models are based on a number of simplifying assumptions. The objective of this paper is to develop a three‐dimensional computer model which can be used to evaluate the effect of variations of the foundation rigidity, column axial stiffness, slab aspect ratio, and shore stiffness distribution on the values of the shore loads and slab moments.

Analysis of rib dielectric waveguides

Abstract: An analysis of rib dielectric waveguides based on a mode matching technique is presented. When the constituent slab guides support only one guided mode, it is shown that the cutoff condition for the higher order modes is the same as the result of the effective dielectric constant method. However, when the rib region is thick enough to support two guided slab modes, the cutoff conditions are significantly different. For this case universal design curves are produced and plotted. The results are also compared with another theory that exists to analyze such structures.

Uplift Wave Forces Due to Compression of Enclosed Air Layer and Their Similitude Law

Abstract: Uplift forces on the ceiling slab of a wave dissipating caisson are a typical example of the impact wave force due to compression of an entrapped air layer. A theoretical model is introduced in ord...

Structure of the Benioff Zone beneath the Shumagin Islands, Alaska: Relocation of local earthquakes using three-dimensional ray tracing

Abstract: Seismic rays are traced through a prescribed three-dimensional inhomogeneity that simulates the subducted slab below the Shumagin Islands region to calculate local station delays for a given hypocenter and a slab model. Hypocenters determined by the Shumagin seismic network are then relocated using the station delays, a flat-layered velocity structure and a standard earthquake location computer program. Station delays are calculated for 12 hypocenters with respect to six different slab models to identify the slab model that is most consistent with the available arrival time and waveform data. A set of path corrections that is calculated for each grid point-station pair on a preliminary grid of 36 points in the depth range from 60 to 300 km is used to recalculate the hypocenters for all of the 1982 earthquakes with depths greater than 50 km. Application of this method to data from 1982 for the digitally recording Shumagin seismic network shows the following results: (1) a previously observed apparent increase in dip of the subducted slab at depths of ≈ 100 km disappears, (2) the subducted slab can be modeled as a dipping structure that dips at a constant angle of 45° toward north-northwest at depths between 80 and 250–300 km and has a 7% higher velocity than the surrounding mantle, (3) hypocenters determined from Shumagin network data are located only 10–20 km south of high-quality hypocenters determined from teleseismic data alone, (4) qualitative comparison of digitally recorded seismograms with calculated ray paths shows enrichment of high-frequency coda, possible converted phases, and low amplitudes of first P arrivals for rays that travel mostly along the slab. Conversely, for rays that travel almost vertically through the upper plate the seismograms show a high amplitude of first P arrivals that are followed by an insignificant coda and low-amplitude S waves.

Integrally-anchored fiber-reinforced concrete overlays and surfacings and method of making same

Abstract: A procedure for providing an overlay on a concrete slab or similar subsurface including the steps of placing a plurality of anchor holes into the concrete slab to be repaired and/or providing an anchor channel at its periphery, providing a bed of fibers on the exposed surface of said concrete slab and extending into and filling said anchor holes and/or channel, infiltrating a flowable cement slurry throughout the fibers and into the anchor holes and/or anchor channel, and curing the slurry to form an overlay which has integral fiber-reinforced anchor portions extending into the slab.

Model calculations of regional network locations for earthquakes in subduction zones

Abstract: Algorithms for locating earthquakes recorded by local networks commonly assume a flat-layered velocity structure, even in island arc regions where the presence of a dipping lithospheric slab introduces large lateral velocity variations. Moreover, because seismic stations occur along the narrow island arc, the resulting linear network geometry degrades earthquake location. To model this situation, we trace rays in a spherical earth from hypothetical earthquakes through appropriate velocity models to networks of various geometries. To isolate the effect of the slab, most of the velocity models consist simply of a planar-dipping constant velocity region embedded in a sphere with a constant lower seismic velocity. We then use the calculated P and S travel times to relocate the hypothetical earthquakes with a flat-layered velocity structure. We perform calculations of this kind in a variety of models, varying the dip of the slab, the velocity contrast between the slab and the mantle, the station geometry, and the distance between the earthquakes and the slab-mantle boundary. We also perform calculations in more realistic models with geometry closely resembling two seismic networks in Alaska. These model calculations emphasize the great care that seismologists should exercise when interpreting local network locations in island arc regions. In the present study, all the relocations incorporate P and S arrivals at all stations, and include no random or “picking” errors. Nevertheless, the relocated hypocenters differ from the “actual” model hypocenters by up to 100 km or more and produce significant distortions in the Wadati-Benioff zone. The most prominent spurious feature is a clear increase in the apparent dip of the Wadati-Benioff zone beneath a certain depth. Furthermore, the relocation reduces the width or apparent thickness of the Wadati-Benioff zone, e.g., they produce an apparent thickness of 5 km or smaller for a zone of earthquakes with an “actual” thickness of 20 km. However, if different combinations of stations report different events, it is possible to determine an apparent thickness which exceeds the “actual” thickness. For local networks near subduction zones, it is useful to estimate the mislocation and rms residual expected for each event recorded and located. This can be accomplished by performing model calculations in a simple model with a constant velocity, dipping slab embedded in a half-space. For such a simple model, there exists only one ray path from each earthquake within the slab to each station, and the travel time for this path can be calculated as a part of the routine network location process. A relocation using the routine network location algorithm and these calculated travel times provides an indication of the expected mislocation and rms residual for the actual recorded event.

Satellite magnetic anomalies over subduction zones: The Aleutian Arc anomaly

Abstract: Positive magnetic anomalies seen in MAGSAT average scalar anomaly data overlying some subduction zones can be explained in terms of the magnetization contrast between the cold subducted oceanic slab and the surrounding hotter, nonmagnetic mantle. Three-dimensional modeling studies show that peak anomaly amplitude and location depend on slab length and dip. A model for the Aleutian Arc anomaly matches the general trend of the observed MAGSAT anomaly if a slab thickness of 7 km and a relatively high (induced plus viscous) magnetization contrast of 4 A/m are used. A second source body along the present day continental margin is required to match the observed anomaly in detail, and may be modeled as a relic slab from subduction prior to 60 m.y. ago.

Velocity structure in the Izu-Bonin seismic zone and the depth of the olivine-spinel phase transition in the slab

Abstract: In this study a method is presented for determining the in situ elastic wave velocities of slabs simultaneously with the relative relocations of earthquakes. The method is an extended arrival time difference (ATD) scheme that incorporates a realistic model. Several assumptions are made about the characteristics of ray paths in and around the slab in order to take advantage of the realism of the model without completely sacrificing the simplicity inherent in the ATD technique. The errors introduced by these approximate rays are estimated by comparing them with more exact rays calculated with a three-dimensional ray-tracing routine. In general, the comparisons suggest that these errors are usually much less than 0.1 s. The inverse method is tested on the same set of hypothetical data. The results of these tests show that the parameters that influence the arrival time differences the most are the amplitude of the slowness anomaly within the slab and the azimuths and takeoff angles for rays leaving the master event. The arrival time differences are relatively insensitive to the other parameters describing the slab (strike, dip, half width, and the position of the master event), which implies that the scheme is fairly insensitive to the particular choice of analytic function to describe the slowness variation within the slab. Convergence of the inverse routine is rapid in the tests; usually less than five iterations are required before a stable solution is reached. It appears that coupling between solutions for slab parameters and ray directions is insignificant. Unlike the standard ATD approach, solutions for hypocenters and velocities are not directly coupled in this scheme, although well-located events are required to insure that the hypocenters are not unduly biased by variations in structure. Once the velocity structure of the slab is determined, that information can be used routinely by this scheme to relocate less well-recorded events. This method was applied to arrival time data from earthquakes located between 200 and 600 km depth in the Izu-Bonin subduction zone. Structure in the 200–300 km depth range could not be resolved, and results in the 500–600 km depth range proved to be too sensitive to noise. Data from events between 27°N and 31°N show that P wave velocities within the slab from 400 to 500 km depth are 4–6% higher than those of the ambient mantle. Between 300 and 400 km depth the slab structure varies regionally. North of about 32.5°N the P wave velocity within the slab is 3–4% higher than ambient from 180 to 375 km depth. In contrast, the velocities south of 32.5°N increase from 6–7% higher than ambient in the 375–410 km depth range to 8–10% higher in the 325–375 km depth range and appear to be 9% higher than ambient in the 270–325 km depth range. The determination of the high velocities in this region between 325 and 375 km depth proved to be independent of the selection of data and of the choice of starting model. Above 325 km depth, however, the velocity determinations are somewhat dependent on the choice of starting model. As a result of this dependence, no upper bound on the depth of the high velocities could be resolved. A plausible explanation for the exceptionally high P wave velocities within the slab south of 32.5°N is that the olivine-spinel phase change boundary is elevated in this part of the slab, while north of 32.5°N it is not significantly elevated. It is not known if the phase change is elevated south of 31°N, but the velocities between 400 and 500 km depth in this region imply that it is not depressed. The high-velocity zone south of 32.5°N lies in an area that marks the beginning of a seismic gap, increasing in breadth to the south, between deep and shallow seismicity. The dip of the slab also becomes gradually steeper to the south of this region. In contrast, the lower velocities north of 32.5°N occur in a region where the seismicity is fairly continuous and is aligned along a shallow dipping plane. If the seismic gap south of 32.5°N represents a region of high velocity, then the increasingly vertical dip of the slab in the south could be due to a substantial gravitational force provided by the excess mass extending above the ambient olivine-spinel phase boundary. The decreasing width of the gap to the north suggests that the evolution of the Izu-Bonin seismic zone has been governed by a propagating instability from the south.

Propagation of high‐frequency seismic waves inside the subducted lithosphere from intermediate‐depth earthquakes recorded in the Vanuatu Arc

Abstract: Three seismic phases associated with the slab of subducted lithosphere are identified on seismograms of intermediate-depth earthquakes (depths >70 km) recorded in the distance range up to 350 km by the Vanuatu (formerly New Hebrides) seismograph network. They are interpreted as (1) a P wave refracting into the inner portion of the slab, (2) a P wave traveling mainly through the outer(upper) portion of the slab, and (3) a P to S converted wave in which the conversion occurs across the upper surface of the slab. The existence of the two P arrivals from intermediate-depth earthquakes suggests that these earthquakes are not located in the strong and cold inner core of the slab but within an outer zone where the velocity is lower than that within the inner portion of the slab. The low-frequency character of the shear wave converted from the P wave across the outer “boundary” of the slab indicates that either the boundary is a transition layer with a finite thickness or the material above the slab has high attenuation for high-frequency shear waves. Large spatial variations in the transmission of high-frequency shear waves also indicate that there is a localized zone of anomalous shear wave attenuation in the mantle wedge lying just above the subducted slab and beneath the active volcanos.

Void detection for jointed concrete pavements

Abstract: Procedures for the detection of voids or loss of support under jointed concrete pavements by using nondestructive deflection testing measurements are presented. A rapid field-applicable procedure is presented to quickly determine the presence of voids by analysis of the load and deflection response at slab corners. A more detailed method is presented in which deflection measurements from center slab and corner locations are used to locate and determine the approximate size of any existing voids. The procedures were developed by using computer modeling of loadings with the ILLISLAB finite-element computer program. The procedures were field verified on several test projects. Basic guidelines for testing, locating joints or cracks requiring subsealing, and estimating grout quantities for jointed concrete pavements are presented.

Numerical modeling of magnetic-field-sensitive semiconductor devices

Abstract: Semiconductor devices in the presence of a magnetic field have been modeled numerically. The two-dimensional distributions of the electric potential, the electron concentration, and the hole concentration in a silicon slab exposed to a magnetic field have been computed. We have generalized the well-known Scharfetter-Gummel scheme to the case of two dimensions and nonzero magnetic field and employed a finite-difference technique. Our results are in support of earlier results in case of Hall plates. In intrinsic or closely intrinsic silicon, our results show both magnetoconcentration and space-charge effects. As a realistic example of a magnetic-field sensor, we have modeled a p+-i-n+silicon diode with split contacts.

Face pumped rectangular slab laser apparatus having an improved optical resonator cavity

Abstract: A face pumped slab laser in which the slab (10) is of a rectangular configuration, favoring use of an optical resonator cavity, (12, 13) capable of producing a rectangular beam of good quality within the cavity. The novel optical resonator cavity, which produces this rectangular beam, is stable on one axis corresponding to the smaller beam dimension and unstable on an axis orthogonal to the first axis corresponding to the larger beam dimension. The result is both high efficiency, excellent power and a good quality output beam, (26) is produced.

One-directional gradient-index slab lens.

Abstract: A gradient-index slab lens (2.5–3.4 mm thick) with parabolic-index profiles along the direction of thickness has been fabricated by a molecular stuffing process, and its refractive-index profiles have been evaluated.

Tubes of microporous thermal insulation material

Abstract: Tubes of microporous thermal insulation material are manufactured by compacting microporous material to a slab having a density of about 150-400 Kg/m 3 and a thickness of about 1-5 mm, applying to one surface of the slab a membrane, for example of self-adhesive aluminum foil, wrapping the slab around a mandrel so that the ends of the slab abut substantially against each other, and securing the ends of the slab relative to each other, for example by means of a protruding flap of aluminum foil.

Method and device for reducing width of slab

Abstract: PURPOSE:To reduce a crop part at the rear end of a slab and to manufacture a steel sheet in high yield by forming the rear end of the slab to be reduced in width into a shape consisting of a straight part and a slant part before reducing the width of rear end by pressing its both side faces in the sheet width direction of rear end. CONSTITUTION:In reducing the width of a slab throughout its whole length, by transporting the slab, a blank material to be hot rolled, in its longitudinal direction, and pressing both side faces in the width direction of slab by a press tool 3, having a pressing face consisting of a face 3A parallel to the side face and a slant face 3B slanted with respect to the face 3A, by periodically vibrating the tool 3 in the sheet width direction of slab; the side faces of said rear end are previously pressed by another pressing face of tool 3 consisting of a slant face 3D slanted to the slab outlet side and a face 3C parallel to the side face of slab, before reducing the width of the rear end of slab. In this way, an ordinary width reduction is provided to the slab after forming its rear end into the shape consisting of a straight part and a slant part, to reduce the quantity of a crop part and a dog bone generating at the slab rear-end thereby improving the yield in steel sheet manufacturing.

The fundamental constants of orthotropic affine slab/plate equations

Abstract: The global constants associated with orthotropic slab/plate equations are discussed, and the rotational behavior of the modulus/compliance components associated with orthotropic slabs/plates are addressed. It is concluded that one cluster constant is less than or equal to unity for all physically possible materials. Rotationally anomalous behavior is found in two materials, and a simple inequality which can be used to identify regular or anomalous behavior is presented and discussed in detail.

Post-tensioned floor with in-floor distribution system

Abstract: This disclosure relates to a floor construction comprising a concrete slab which is supported adjacent its edges of the slab. A plurality of cellular raceways are embedded in the slab, and at least one intermittently bottomless trench runs across the raceways. The trench is located along a line where the bending moment on the slab is substantially zero. The construction further comprises a plurality of post-tensioned tendons which extend across the slab, underneath the trench and between the raceways.