Tens Of Millimeters Research Articles

Nonsteady lamination of the flow of biphase helium in horizontal channels

A distinguishing design feature of modern physical installations [i] cooled at the level of 4.2 K is the presence of horizontal channels for the reverse flow of biphase helium relative to the large diameter (up to some tens of millimeters) characterized by considerable local hydraulic resistance at the inlet which ensures the condition of constant flow rate of helium at the inlet to the channels with different cryostating regimes, and also characterized by constant pressure of the cryogenic agent at the outlet from these channels. The mass velocity of the cryogenic agent in such channels is not high, amounting to 10-30 kg/(m2"sec): this corresponds to laminated (stratified) flow of helium in channels [2, 3]. Besides that, a characteristic feature of systems for the cryostating of physical installations is a dynamic thermal regime of operation. Heat liberations are uniformly distributed over the length of the cryostating channels, their magnitude is much smaller than the critical density of the heat flow, and the length of the thermal pulse attains some tens of seconds. At the same time the permissible magnitude of change of the temperature of helium does not exceed several tenths of a centigrade, i.e., even with an imperceptible change of pressure in the reverseflow channels of biphase helium, the conditions of cryostabilization of the flow carrying elements may be infringed. The literature does not contain any data on investigations of the dynamic characteristics of horizontal channels with laminated flow of biphase helium.

Global Positioning System Network analysis with phase ambiguity resolution applied to crustal deformation studies in California

A 5‐year campaign is in progress in central and southern California to monitor tectonic motions using observations of the Global Positioning System (GPS) satellites. Evidence from geological and space‐geodetic data indicates that significant horizontal deformations of order 10 mm/yr are occurring west of the San Andreas fault along the California margin. We demonstrate, using data from initial epoch measurements in January 1987, that the goal of measuring horizontal deformations with an accuracy of 5 mm/yr over the duration of the campaign should be readily achievable. The GPS network was designed to span a wide range of baseline lengths within California and across North America to aid in phase ambiguity resolution, an important factor in achieving highest‐accuracy baseline determinations. We present an efficient algorithm for multisession network analysis of GPS data with simultaneous orbit determination and ambiguity resolution. Using this algorithm with the California data, we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved. We demonstrate several millimeters +1 part in 108 short‐term repeatability over five single‐session (daily) analyses for horizontal baseline components and length and several tens of millimeters for the vertical. Comparison with the independently determined very long baseline interferometry baseline between Mojave and Owens Valley suggests that the accuracy is at the same level as the repeatability. We show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single‐session analyses. With the single‐session analyses we were able to resolve all phase ambiguities on baselines within California. With the multisession analyses we were able to resolve the phase ambiguities for most of the network, over regional and continental scales.

Atomic Emission Characteristics of Laser-Induced Plasmas in an Argon Atmosphere at Reduced Pressure

The emission characteristics of laser-induced plasma, with the use of a Q-switched ruby laser of 1.5 J, were studied in argon atmosphere at reduced pressure. The time- and spatially resolved emission profiles were measured. In argon atmosphere at reduced pressure, the emission period of plasma is elongated to over a hundred microseconds, and the emissive region expands to more than a few tens of millimeters above the sample surface. The emission intensities of atomic lines increase severalfold in an argon atmosphere, in comparison with those obtained in air at the same pressure. Moderate confinement of plasmas and a resultant increase of emission intensities are achieved at 50 Torr. These results are explained by the chemical inertness and the thermal characteristics of the argon atmosphere and the decrease in absorption of the laser pulse by the plasma plume. The re-excitation of emissive species by collisions with metastable argon atoms seems to be less important.

Dynamics of fault creep

Observations along the surface traces of active faults in California and elsewhere indicate that tectonic displacement can occur as seismic slip or as aseismic fault creep. Fault creep occurs as secular displacement and as displacement episodes, called “creep events,” which last a few hours to days and include from a millimeter or less to a few tens of millimeters of displacement. Instrumental measurements of displacement versus time during creep events show that many events have a characteristic, simple form, including a steep beginning, followed by a gradual decay in the rate of displacement. Some creep events display small amounts of precursory slip, and many seem to be composed of several discrete “simple” events. Propagation of creep events along the San Andreas, Calaveras, and Imperial faults in California has been inferred from the nearly simultaneous observation of creep events at nearby creepmeters and from kinematic modeling of continuous measurements of strain during creep events. Fault creep can be viewed as arising from the interplay of three factors: stress applied to the fault from external sources; stress caused by the geometry and distribution of displacement on the fault, arising from the elastic response of the surrounding medium to the displacements within the anelastic fault zone itself; and the constitutive relations characterizing the resistance to slip on the fault. Analytic solutions are presented for a simple, rectangular dislocation, quasi‐static model of nonpropagating fault creep assuming viscous and quasi‐plastic (power law creep) fault zone rheology and for a multi‐element (composed of several rectangular or striplike dislocation surfaces), quasi‐static model assuming a viscous rheology. Viscous rheology implies solutions composed of exponentials that decay with time. The simple, one‐element, quasi‐plastic model is in agreement with the form of creep events observed at Melendy Ranch, California. A matrix formulation is presented to calculate dislocation stresses on a fault zone in a half‐space or plate. The formulation involves the division of the dislocation surface into strips or rectangles and the use of published solutions to calculate the stress resulting from displacement on each individual element. Results from the matrix method agree with analytic results for equilibrium displacements on “stress‐free” cracks. The matrix formulation is then used as the basis for a numerical method to simulate one‐ and two‐dimensional propagating creep assuming a quasi‐plastic rheology on the fault zone. Results from this method agree reasonably well with observations of afterslip from the 1966 Parkfield, 1975 Oroville, and 1979 Imperial Valley, California, earthquakes and of a propagating creep event observed along the southern Calaveras fault, central California, during July 1977. This method of analysis, and the assumption that creep at each point on the fault zone follows a power law rheology after the applied stress reaches a spatially varying yield stress, can explain the secular and episodic nature of fault creep; afterslip; the simple shape of some individual events and the multiple, composite shape of others; and the propagation of creep events. On the southern Calaveras fault, observations of propagating creep indicate a yield stress near zero at the surface and throughout much of the fault zone. However, they also indicate the presence of a zone at a depth of about 0.5 km, and about 5 km long, with a yield stress of about 15 bars (1.5 MPa). The methods of solution presented here should be applicable to many problems in the dynamics of faulting.

X-Ray Scattering above 100KeV

Conventional x-ray scattering studies have been limited to photon energies (wavelengths) in the 5 to 20 KeV (approx. 2A to 0..5A) regime. With these energies absorption lengths limit the volume of illumination to the first tens of microns of samples. If it were possible to use x-rays of very high energies, true bulk (tens of millimeters) samples could be studied. The availability, intensity and resolution possible with high energies will be discussed and their role in the expanding field of x-ray scattering presented. Preliminary studies at the Cornell High Energy Synchrotron Source (CHESS) will form the basis of these discussions.

Ultrasonic probing of the fracture process zone in rock using surface waves : Swanson, P L; Spetzler, H In: rock mechanics in productivity and protection (paper to the 25th symposium on rock mechanics, Evanston, Illinois, 25–27 June 1984) P67–76. Publ New York: AIME, 1984

A microcrack process zone is frequently suggested to accompany macrofractures in rock and play an important role in the resistance to fracture propagation. Attenuation of surface waves propagating through mode I fractures in wedge-loaded double-cantilever beam specimens of Westerly granite has been recorded in an attempt to characterize the structure of the fracture process zone. The ultrasonic measurements do not support the generally accepted model of a macroscopic fracture that incrementally propagates with the accompaniment of a cloud of microcracks. Instead, fractures in Westerly granite appear to form as gradually separating surfaces within a zone having a width of a few millimeters and a length of several tens of millimeters. A fracture process zone of this size would necessitate the use of meter-sized specimens in order for linear elastic fracture mechanics to be applicable.

Spatial variability in selected geotechnical property measurements from three sedimentary provinces in the Venezuela Basin

Relatively undisturbed surficial sediment samples from three sedimentary provinces (pelagic, turbidite dominated and hemipelagic) in the Venezuela Basin were examined for spatial variability in water content and undrained shear strength. A miniature vane shear apparatus boring method which minimized sample disturbance was used to determine variability of sediment shear strength directly within individual box-core samples. The variability of water content and sediment shear strength was also determined from subsamples (61 mm ID cores) collected from replicate box cores at each province. Sediments at the turbidite site yielded a higher average lateral coefficient of variation in water content and sediment shear strength (both methods of measurement) than sediments from the pelagic and hemipelagic sites. Vertical coefficients of variation were consistently higher than lateral coefficients of variations for all measured parameters. Between box-core variability in sediment shear strength was less than within box-core variability reflecting differences in measuring techniques and sample disturbance rather than actual differences. Biological activity, primarily compaction by burrowing polychaetes, maintains steep gradients of decreasing water content and increasing shear strength in the upper 100–200 mm of sediments at all three sites. The biologically controlled gradients and the occasional deposition of turbidites results in much higher vertical compared to lateral variability of some sediment geotechnical properties on scales of tens of millimeters (within box cores) and kilometers (between box cores collected at the same site).

Speckle interferometry and other inspection techniques

This paper discusses some of the general methods by which laser light has been used in engineering measurement. Some objectives set for optical measurement in this field are high repeatability, good resolution and employment of non‐contacting equipment, in the sense of both light source and detector being some tens of millimetres away from the object avoiding obstruction to other processes.

Geodetic evidence for subsidence due to groundwater withdrawal in many parts of the United States of America

Analysis of repeated levelings conducted by the National Geodetic Survey indicates many locations of relative subsidence in the U.S.A. Specific criteria are used to identify those subsidence features which most likely result from sediment compaction due to lowering of water levels in underground aquifer systems. Previously reported areas of such subsidence that seem to be confirmed by this study include: south-central Arizona; Savannah, Georgia; Pecos and Houston-Galveston, Texas; Denver, Colorado; San Joaquin Valley, Santa Clara Valley, Saugus Basin, Los Angeles Basin and Bunker Hill-San Timoteo, California; Milford, Utah; Raft River Valley, Idaho; Baton Rouge and New Orleans, Louisiana; and Las Vegas, Nevada. In addition, our analysis indicates that such subsidence is more widespread than previously reported occurring in a number of locations within the Atlantic and Gulf of Mexico coastal plains and along the Mississippi Valley as well as in many other unconsolidated sedimentary basins from which groundwater has been extracted and for which repeated leveling measurements are available. More than 30 new locations of subsidence possibly due to water withdrawal have been identified. The best documented of these include: Ventura, Ontario and San Pedro-Santa Monica, California; Monroe and Alexandria, Louisiana, and Jackson, Mississippi. Subsidence in newly identified locations ranges from several tens of millimeters to a few hundred millimeters over distances of ∼ 10–60 km and times of 2–48 yr. Subsidence may also have occurred in other groundwater basins where water levels have been drawn down, and remained undetected because of a lack of repeated levelings. It is important to be aware of and to continue to monitor such effects because of increasing rates of utilization of groundwater resources and the potential for significant engineering problems due to surface movements. In addition, identifying cases of subsidence due to water withdrawal is essential in order to use effectively releveling observations for investigating tectonic deformation. Along these lines, our analysis suggests that some of the releveling observations used to define a region of tectonic uplift in southern California more likely reflect subsidence due to water-level declines within sedimentary basins around the periphery of the presumed zone of uplift.

Visual indication of locally varying photoconductivity

The paper deals with the visual indication of a locally varying carrier density or photoconductivity, which is optically generated within a semiconductor substrate and extends over a distance of some millimetres up to some tens of millimetres. The induced profile is conventionally displayed on a CRT using a special substrate-edge excited microstrip device that works as the sensing element. The technique can be adapted to CW or pulse excitation, and allows an immediate study of absorption and diffusion effects under varying excitation conditions.

Convective thinning of the lithosphere: A mechanism for rifting and mid-plate volcanism on Earth, Venus, and Mars

Thinning of the Earth's lithosphere by heat advected to its base is a possible mechanism for continental rifting and continental and oceanic mid-plate volcanism. It might also account for continental rifting-like processes and volcanism on Venus and Mars. The Earth's continental lithosphere can be thinned to the crust in a few tens of million years by heat advected at a rate of 5–10 times the normal basal heat flux. This much heat is easily carried to the lithosphere by mantle plumes. The continent is not required to rest over the mantle hot spot but may move at tens of millimeters per year. Because of the constant level of crustal radioactive heat production, the ratio of the final to the initial surface heat flow increases much less than the ratio of the final to initial basal heat flow. For large increases in asthenospheric heat flow, the lithosphere is almost thinned to the crust before any significant change in surface heat flow occurs. Uplift due to thermal expansion upon thinning is a few kilometers. The oceanic lithosphere can be thinned to the crust in less than 10 million years if the heat advection is at a rate around five or more times the basal heat flow into 100 Ma old lithosphere. Uplift upon thinning can compensate the subsidence of spreading and cooling lithosphere. The swells will rise to a common depth of about 4 km below sea-level if the uppermost mantle beneath the mid-oceanic ridge is partially melted to a slightly larger degree than the uppermost mantle beneath the swells. Uplift upon thinning on Mars is up to 10 km or more, thus explaining the height of volcanic regions like Tharsis. On Venus, uplift upon thinning would range from 0.5 to 4 km, in agreement with observed topographic variations.

Massive Siliciclastic Deposits Juxtaposed Against Massive Carbonate Bodies: Paradox of Eastern Gulf of Mexico: ABSTRACT

The eastern Gulf of Mexico is the location of a major and dramatic transition from siliciclastic to carbonate deposits and deposition. The massive lutites that make the Mississippi Cone are juxtaposed against the equally massive carbonates intercalated with evaporites that make the western portion of the Florida Platform. The region now occupied by the continental margin of the eastern Gulf has been cut off from clastic sedimentation since Late Jurassic or Early Cretaceous time, and over 5,000 m (16,404 ft) of predominantly carbonate sediments have built up. Surficial sediments of the carbonate portion of the transition zone are called the West Florida Lime Mud Facies. A foraminifera-coccolith ooze is still being deposited in water depths as shallow as 200 m (656 ft); this facies covers over 40,000 km2 (15,444 mi2) and in many respects resembles a deep-sea ooze. However, in some places shelf carbonate debris, including whole valves of mid-shelf oysters, have cascaded over the shelf-slope break and are incorporated into the slope ooze. Composition, rates of accumulation, and relatively shallow deposition suggest that this sedimentary body may be an analog of some of the chalk deposits of northwestern Europe. It has long been considered axiomatic that planktonic foraminifera and coccolith oozes are deep-sea deposits that accumulate at rates of a few tens of millimeters per thousand years. However, radiocarbon dates show that the eastern Gulf margin ooze has accumulated rapidly. Prior to the last rise in sea level, deposition rates were as high as 65 cm/1,000 years (25 in./1,000 years); and ever since sea level began to rise sedimentation rates have still been as high as 20 cm/1,000 years (8 in./1,000 years). Such a rapid buildup of the carbonate sediments has led to widespread mass wasting and all forms, from creep to massive multiple slide deposits containing thousands of cubic kilometers of material, are represented in our set of high resolution seismic profiles. The actual contact between carbonates and siliciclastics occurs in a variety of styles. Carbonate rubble is found in a terrigenous lutite matrix at the base of the West Florida Escarpment. Farther west on the Mississippi Cone the brown and yellow-brown siliceous lutites contain carbonate turbidites with provenance the West Florida slope. Another type of contact is shown in some piston cores with carbonate ooze in normal and alternating depositional End_Page 453------------------------------ contact with Mississippi siliceous lutite. The position and timing of alternating carbonate and fine terrigenous deposition, as well as the loci of carbonate buildups on the slope, must be affected and perhaps even controlled by the positioning of the Loop Current, a major precursor to the Gulf Stream which, depending upon factors as yet not totally understood, irregularly advances into or retreats from the eastern Gulf. When the loop is up and sweeps from north to south along the West Florida slope, it blocks or deflects Mississippi sedimentation. When the loop is restricted to the area of the Florida Straits, fines derived from the Mississippi River can be deposited at the base of the escarpment and even on the slope. End_of_Article - Last_Page 454------------

Studies of the Dales Gorge Member of the Brockman Iron Formation, Western Australia

A drill core consisting of unaltered banded iron-formation from Paraburdoo, Western Australia, representing the entire Dales Gorge Member of the Brockman Iron Formation, has been analyzed in short units of about 300 mm or in groups of units of up to 1 m. These analyses have been combined to give average compositions for each of the 33 macrobands of the member. The average compositions for the 17 oxide facies BIF macrobands and the 16 intercalated chert-carbonate and silicate facies S macrobands are, respectively, 43.15 and45.78 percent SiO 2 , 0.09 and 2.04 percent Al 2 O 3 , 46.37 and 27.77 percent Fe 2 O 3 (total iron), 2.69 and 5.21 percent MgO, 1.65 and 2.85 percent CaO, 0.04 and 0.02 percent Na 2 O, 0.01 and 0.09 percent TiO 2 , 0.21 and 0.16 percent P 2 O 5 , 0.05 and 0.02 percent MnO, and 0.03 and 0.32 percent S. The analyses are similar to those reported by Trendall and Pepper (1977) for a part of the Dales Gorge Member at Wittenoom, 130 km away. These data, together with documented evidence of lateral continuity of both major and minor banding across the Hamersley Iron Province, support an assumption that the primary deposits were chemically similar throughout the area. Mineralogical variations between sites indicate low but variable metamorphism in the area, and magnetite-hematite ratios and textural relations suggest increasing grade from Paraburdoo to Wittenoom to Tom Price.A short length of drill core from Tom Price, representing two complete macrobands and parts of two others, was also analyzed, and the results were found to vary significantly from the Paraburdoo and Wittenoom data. These differences are attributed to metasomatism of the rocks at Tom Price.Primary precipitation of iron in BIF macrobands was caused by oxidation and was dominated by gels containing iron(III) hydroxyoxides and silica in varying proportions, depending both on seasonal conditions and on supply. These variations were responsible for the wide range in composition and in thickness of banding, from tens of micrometers (submicrobanding), to millimeters (microbanding), to tens of millimeters (mesobanding). Preservation of micro- and submicrobanding within specific mesobands is due to very early consolidation and accentuation of primary depositional layering during diagenesis. In other mesobands, crystallization was evidently delayed and, under deeper burial conditions, tended to destroy primary lamination. In S macrobands, iron was precipitated as siderite and silicates. Mineralogical and chemical data show that the apparently sharp lithological boundaries between BIF and S macrobands are in fact gradational. Such contacts are attributed to a more or less continuous precipitation of silica and iron, interrupted periodically and changed in character by increase in pH and/or f (sub CO 2 ) . These changes were initiated by additions of volcanic ash. S macrobands are characterized by increases in the overall content of CO 2 , Ca, Mg, Mn, Al, Ti, K, and Zr.Podding, and other localized distortion, of mesobands is attributed mainly to lateral flow of silica during compression. It appears to have been inhibited in mesobands where early crystallization of components, particularly iron oxides, enhanced the mechanical stability of the dehydrating gel.The logistics of supplying sufficient iron to the Brockman Iron Formation, together with the absence of terrigeneous material in the deposits, suggests open access of the depositional area to a large and constantly replenished reservoir of dissolved iron. A shelf model is preferred.

Estimation of Calcium Sulfate Solution Rate and Effective Aquifer Surface Area in a Ground‐Water System Near Carlsbad, New Mexico

ABSTRACTThe geochemistry of a very permeable ground‐water system containing calcium sulfate was studied to determine the present rate of dissolution. An estimate was made of the chemical composition of water recharging the system and the difference between that estimate and the composition of the ground water in the system was used to determine the minimum amount of calcium sulfate being dissolved under existing hydrologic conditions. This result was used, with published data on rates of calcium‐sulfate dissolution, to determine the effective surface area involved in solution processes. Results indicate that flow in this system is through large solution openings, which are growing larger at a rate of a few tens of millimeters per year.

Effect of Normal Pressure on Glacier Sliding (Abstract only)

Mercury is used to force a block of ice, measuring 0.20 ⨯ 0.45 m in area and 0.20 m in height, over an irregular bed. Normal and shear stresses on the bed can be varied up to 15 and 3 ⨯ 105 Pa respectively, so the apparatus permits a full-scale simulation of sliding of a 150 m thick glacier over irregularities a few tens of millimeters in height.Preliminary results of an experiment in which ice slid over a bed consisting of two streamlined bumps, roughly 15 mm in height, suggest that sliding velocity is independent of normal pressure in the absence of cavitation. This is consistent with existing theoretical models of glacier sliding (Weertman 1964, Kamb 1970, Lliboutry 1979), but is not consistent with the experimental results of Budd and others (1979). Further studies are needed to determine the reasons for this disagreement.

Le désert de l'Afar (Ethiopie)

Summary. The Afar Desert is the most arid part of the Dankalia (country of the Danakil people). Situated at a very low latitude (11 to 15 degrees North) and isolated from the sea by the Danakil mountains, this desert is particularly torrid, and exceptionally receives winter rains that do not exceed a few tens of millimeters per year. But this aridity is locally compensated by the surface or underground waters coming from the Ethiopian Plateau. They supply some lakes that were much more extensive at the Quaternary. In the Afar there is a particular instability of the earth-crust, the volcanic edifices and the fault-scarps are very numerous. We observe many different topographic manifestations of faulting, from the fresh scarps to fault-slopes bordered by large pediments. Among the volcanic reliefs, some hyaloclastite cones, formed under water, put difficult questions about the reconstitutions of Quaternary lakes.

Lunar gravity estimate: Independent confirmation

Reduction of 2½ days of Lunar Orbiter 4 radio tracking data has provided an independent estimate of the low-degree spherical harmonic coefficients in the lunar potential model. The estimate is in good agreement with previous results and confirms that the moon is essentially homogeneous. These Doppler data, never incorporated in other gravity estimates, were obtained at relatively high spacecraft altitudes (2700–6000 km). This high-altitude data allowed the model to fit to the noise level of 1 mm/sec, unlike previous results, where systematic residuals of tens of millimeters per second occurred, owing to local gravity anomalies detectable at low spacecraft altitudes (≈100 km).

On recent vertical movements of the earth's crust in seismically active areas of Middle Asia

Recent crustal movements in Middle Asia, measured by repeated levelling, are subdivided, according to their magnitudes, into general background (or regional) and local movements, in particular, those above faults. The velocities of the movements above active faults were measured as being in the range of a few millimetres per year to a few tens of millimetres per year, which is greater by one order than those of regional movements. The velocity gradient of the above-fault movements is one or two orders higher than that outside of the differential movement zones and varies from 10 −6 to 10 −5 year −1. Young movements (thousands to several thousands of years B.P.) determined by geomorphological and geological methods are quite similar to recent ones as to the value and distribution pattern of the velocity and velocity gradient. Just prior to earthquakes, the recent movements are one or two orders greater than secular back-ground ones as to the velocity and two or three orders as to velocity gradient, attaining tens to hundreds of millimetres per year and 10 −6–10 −4 year −1, respectively. This regularity agrees with the results obtained in Japan and Alaska and is of importance for solving the problem of earthquake prediction.