Typical Beds Research Articles

Effects of solvent‐particle interaction kinetics on microstructure formation during three‐dimensional printing

AbstractLactone‐based absorbable polyesters, such as polylactide‐co‐glycolides, are commonly used for the construction of biomedical devices. Many such devices can be constructed by a novel manufacturing technology known as three dimensional printingTM (3DPTM), which fabricates complex structures by ink‐jet liquid binder onto loose powder in a laminated fashion. The predominant 3DP binding mechanism for lactone based absorbable polyester powder is dissolution‐reprecipitation. The objective of this study is to compare the relative time scales for particle dissolution and solvent evaporation during 3DP processing. An experimental setup was devised to determine the time scale for particle dissolution. This time scale was found to be particle size independent for small particles, but size dependent for larger particles. The time scale for chloroform evaporation from typical 3DP powder beds was determined to be on the same order as the particle dissolution time scale. Dissolution‐evaporation (DE) plots were constructed to illustrate the relationship between evaporation time scale, dissolution time scale, particle size, printing conditions, and external mass transfer conditions. The DE plot provides a good estimate of the necessary printing conditions under which the evaporation time is sufficient for particle dissolution for a given particle dimension. Microstructural analysis of the printed structures demonstrated the importance of the relative time scales of particle dissolution and solvent evaporation. Practical implications of these findings in 3DP are described.

Anatomy of an Anomaly: The Devonian Catastrophic Alamo Impact Breccia of Southern Nevada

The Alamo Breccia is a carbonate rock breccia of Late Devonian age in southern Nevada. It is an anomalous sedimentary unit because it has the properties of a massive debris-flow and turbidity-current deposit that would be expected to occur in deep water, but is intercalated over much of its area with typical shallow-water carbonate-platform beds. The Breccia was created by the catastrophic detachment and flow, over a nearly horizontal surface, of previously deposited platform carbonates. It crops out in 14 or more mountain ranges that cover an area of ∼10,000 km2, conservatively averages ∼50 m in thickness, and contains a volume of 500+ km3. Along the base it contains trains of individual detached blocks as much as 500 m long and 90 m high. Clasts generally grade upward to gravel-, sand-, or mud-sized particles at the top. The Breccia was generated by forces unleashed during the impact of an extraterrestrial object with Earth. The impact produced shocked quartz grains, unique ejecta spherules, and an iridium anomaly–which are present within the Breccia but absent from confining beds. Internally the Breccia is segmented vertically into as many as five sequentially thinner graded units created by successive tsunamis. In one range, peculiar deformed dolostone, shocked quartz sandstone, and sedimentary dikes and sills occur under the Breccia and deep-water limestones rest over it, indicating a near-crater location. Surrounding detached megablocks and tsunamites suggest an annular crater trough. The Breccia formed within the span of a few hours or days, and falls entirely within a single early Frasnian conodont zone, at ∼367 Ma. The welldocumented middle Late Devonian (Frasnian/Famennian) extinctions are ∼3 Ma later. An impact scenario explains the known features of the Alamo Breccia: impact occurred on the Late Devonian outer platform or slope; seismic shock delaminated the upper ∼50 to 100 m of the platform, loosening carbonate-platform bedrock and creating trains of large blocks that may rest in an annular trough; successive tsunamis reworked the loosened material, which was augmented by unknown proportions of ejecta containing shocked quartz from the crater, carbonate spherules from the vapor cloud, and iridium from the projectile. Mass flows west of the platform likely represent tsunami backwash, shock-induced failure along the platform margin, and slumps from offshore topographic highs.

Facies and environment of the Leckkogel beds (Carnian;Alps)

The Carnian Leckkogel beds represent a carbonate sequence, which was deposited in front of an actively spreading carbonate platform. The typical Leckkogel beds are characterized by highly diverse sponge buildups. Sphinctozoan sponges predominate together with rare bryozoans and hydrozoans as well as red algae and thin crusts of cyanophyceans. Foraminifera are very rare and dasycladaceans are missing altogether. Oncoidal limestones containing predominantly inozoans are coeval with the Leckkogel beds. They represent a short-lived colonization of the sea-floor within a basinal environment. In addition to this autochthonous development, allochthonous intercalations of debris-flow sediments occur. The basinal facies consists of shales and argillaceous schists. Towards the edge of the platform the Leckkogel beds interfinger laterally with the Tisovec limestone, which exhibits two main facies types, a reef facies and a lagoonal facies.

Sialic acid-depleted red cells following acute myocardial infarction

A reduction of red cell SA in patients following acute myocardial infarction is reported and the effects of SA-depleted red cells on cardiac index and alveolar capillary blood flow in the dog are described. The mean red cell SA in 26 patients following acute myocardial infarction was 0.021 ± 0.001 compared with a mean of 0.031 ± 0.002 μmol./0.1 ml. RBC in 12 normal subjects (p < 0.01). In five dogs injected with neuraminidase, an enzyme which removes SA from the red cell membrane, a 43% decrease in mean cardiac index from 2.3 ± 0.22 to 1.3 ± 0.16 (p < 0.01) occurred. In films of the pulmonary microcirculation the mean widths of typical alveolar capillary beds decreased 42.6% ± 5% (p < 0.01). In three other dogs, autotransfusion with SA-depleted stored blood resulted in a 25% decrease in mean cardiac index from 2.0 ± 0.21 to 1.5 ± 0.21 (p < 0.2), and a 21.7% ± 0.9% (p < 0.01) decrease in mean widths of typical alveolar capillary beds. We conclude that a reduction of red cell SA follows acute myocardial infarction and that SA-depleted red cells decrease cardiac index and alveolar capillary blood flow in the dog.

MORE ON THE LATEROLOG* DEVICE**

AbstractBasic Laterolog devices employ a measure‐current focusing technique to provide well logs of formation resistivity that feature sharp vertical definition combined with a depth of investigation much improved over those of normals of comparable spacings.To develop the concept of measure‐current focusing, a disk‐electrode arrangement analogous to a guard‐ring capacitor is considered first, leading finally to consideration of a real sonde in a cylindrical borehole. In the latter, auxiliary currents are adjusted to maintain substantially at zero the vertical potential gradients above and below the central measure‐current electrode; this has the effect of focusing the measure‐current beam.However, prediction of sonde responses on the basis of current patterns can in some cases be misleading. Indeed, for a given Laterolog array, one may use a (reciprocalmode) current pattern radically different from the one defined by the basic (direct‐mode) measure‐current focusing scheme and still obtain the same resistivity measurement. This feature is illustrated for Laterolog 3 by use of transfer impedances, and demonstrated for certain more general cases using the reciprocity theorem.Comparisons of Laterolog responses across typical thin beds, both non‐invaded and invaded, with those of normal devices of a comparable range of spacings illustrate the improved vertical resolution obtained with Laterolog devices. The examples also show the different magnitudes of the auxiliary currents (thenceforth designated “bucking”‐ or “focusing” currents) used in the direct and reciprocal modes and illustrate how these currents must continuously vary in order to maintain the focused condition as the sonde moves through the bed.Finally, briefly considering possible applications of Laterolog‐type arrays in surface prospecting, it is shown that a one‐dimensional array laid out on the surface does not provide the same degree of measure‐current focusing as is obtained in a borehole. Some improvement is obtained with a combination of two crossed linear arrays. Much more is obtained using a circular array.

Dish Structure, a Primary Sedimentary Structure in Coarse Turbidites: ABSTRACT

Some clean but poorly sorted sandstone beds in California contain vertical progressions of thin lens-shaped structures, here termed dish structures. Individuals are 4-50 centimeters long, 1 to a few centimeters thick, oval in plan, and are oriented parallel with bedding. Each dish has a fine-grained, slightly clayey lower surface that is concave-up, and from which clay content decreases and sand size increases upward to a coarse, clay-free top. The size of the structures decreases and the concavity of their bottoms increases higher in the bed. The margins of each dish are truncated by adjacent and overlying dishes, except where they occur along individual horizons with their joined margins forming upward-pointing peaks. Steeply oriented elutriation columns lacking clay an finer sand commonly accompany dish structure. They disrupt or turn up dish surfaces through which they pass, and terminate beneath overlying dishes. Typical sandstone beds containing dish structure are about 1 meter thick and progress upward from a base of coarse, structureless sand (interval a of Bouma, 1962) through flat lamination, dish structure, and overlying flat lamination (b), to a top of very fine-grained sand containing convolute lamination (c). Dish structure also occurs as a central interval within an otherwise nearly structureless, very thick bed. Antidunes may produce simple dish structure by alternate scour, and by breaking and deposition in the troughs during aggrading suspension flow in a turbidity current that has declined from dispersion flow (after Bagnold). Middleton (1965) reports structures similar to some dish structures in size and shape resulting from antidune flow. Some characteristics, possibly including clay distribution, may result from sporadic water expulsion, related sediment flowage, and general de-watering of the bed. Dish structure between structureless intervals would require dispersion flow to progress to antidune flow, then revert to dispersion flow. End_of_Article - Last_Page 485------------

Oil Migration: ABSTRACT

Physical analysis of oil migration through a water-saturated, hydrophilic, porous sediment suggests the following mechanisms of migration: (1) continuous-phase flow, (2) colloidal dispersion in water, and (3) molecular solubility in water. The first mechanism, continuous-phase flow, is a major factor in controlling the movement of oil through porous reservoir rocks, the migration of oil into traps, or leakage of oil out of traps. Relatively high saturation of hydrocarbons (15-25 per cent of pore volume) must exist to create the continuity of the oil phase necessary for migration by this mechanism. The relatively low residual hydrocarbon saturations observed in many shales considered as probable source beds suggest that migration by this mechanism has not occurred therein. The second mechanism, colloidal dispersion in water, appears to be a major factor in controlling the primary migration of oil out of many typical source beds. These migrating colloids may vary from the partially reduced organic complexes found colloidally dispersed in sea water and sea-bottom muds to oil solubilized by naturally occurring soap micelles or other solubilizing agents. If this mechanism has occurred in a shale, the organic content of the shale source bed may be low, and the residual hydrocarbon content in per cent of pore volume may be almost nil. Two primary requirements for the operation of this second migration mechanism are the following. 1. The source-bed mineral surfaces must be hydrophilic. Experimental evidence indicates that the predominantly sodium-based mineral surfaces found in a normal marine sediment are generally hydrophilic and, therefore, could be source beds; whereas the predominantly calcium-magnesium-based mineral surfaces of many non-marine sediments may commonly be oleophilic and, consequently, probably are non-source beds. 2. The organic colloid, soap micelle, or other solubilizing agent must be stable and mobile within the source bed and must become unstable, immobile, or dissociated somewhere End_Page 1770------------------------------ within the reservoir bed. The flocculation or dissociation of these colloids appears to be greatly affected by the Donnan-equilibrium-controlled anion-exclusion and cation-absorption properties of high-electrical-charge-density materials such as shales. When the migration is terminated by either dissociation or flocculation, the resulting finely dispersed unstable organic particles or oil droplets will start to aggregate. Consequently, buoyancy will cause them to rise (or fall) through the water phase to the top (or bottom) few inches of the porous reservoir. If the oil or oil-forming material accumulates in the top few inches of the reservoir bed in sufficient concentration to subsequently produce extensive oil-phase continuity, then additional migration by the continuous-phase flow mechanism can occur. The third mechanism, molecular solubility in water, may be a significant factor in selectively transporting certain hydrocarbon fractions and thereby modifying the oil characteristics. If only the first mechanism were operative, source beds should be detectable by their high residual hydrocarbon content. If the second mechanism were commonly operative, such source beds could not be identified simply by measuring the residual oil saturation; and if source beds of this type are throughout most marine sedimentary sections, the limited occurrence of major oil production must be related to conditions required for continuous entrapment and preservation of oil since the time of origin. The entrapment of oil is primarily controlled by the first mechanism--continuous-phase flow. Therefore, a critical evaluation of this mechanism under both hydrodynamic and hydrostatic conditions throughout the geologic history of an area is recommended for finding both broad oil provinces and specific oil fields. End_of_Article - Last_Page 1771------------

Lower Cretaceous ammonites in marine intercalations in the "Nubian Sandstone" of the Eastern Desert of Egypt

In 1910, the late Dr. W. F. Hume, Director of the Geological Survey of Egypt, reported Cretaceous fossils from limestones intercalating the “ Nubian Sandstones ” at the head of Wadi Qena, about 205 kilometres (128 miles) north of the town of that name in the Nile Valley. He divided the strata into three typical sandstone beds, namely (1) an upper Nubian at the base of the Campanian, (2) a middle Nubian above the Turonian ammonite bed, and (3) a lower Nubian below the Cenomanian strata and closely related to them (Hume 1911). During the season 1950–51, while a topographical survey expedition was mapping an area lower down the same Wadi Qena, one of us (G. W. M.) noted a considerable extension of the fossiliferous limestones intercalating the Nubian Sandstones and brought in a good collection of specimens from them to the Geological Survey of Egypt. The area covered by this note lies between latitudes 27° 00' and 27° 30' and longitudes 32° 35' and 32° 52'. The Nubian Sandstone in this area outcrops as a narrow stretch running roughly N.-S. and is overlaid on the west by Middle and Upper Cretaceous limestones etc., and rests in the east on granites etc. forming the Red Sea hills. Fossils were collected from eight separate localities, four of which were near the base of the Nubian Sandstone where it rests on the granite while the rest were from higher horizons. The four localities near the base yielded :— Diplopodia cf. variolaris

VII.—Note on a Section in Probable Bagshot Beds on Shooters Hill, Kent

In 1905 trenches for electric mains were carried up the northeastern slope of Shooters Hill, along Shrewsbury Lane to “The Bull”, and thence down the western hill-slope along the Dover Road. From about 350 O.D. in Plum Lane to 424 O.D. at “The Bull” the trench ran for nearly two-thirds of a mile along the junction of the London Clay with the overlying group of sands, pebbles, and clayey gravels which form the ‘gravel cap’ of Shooters Hill. Neither the exact age of these superficial deposits nor their mode of formation—whether marine or fluviatile beds—is as yet known, but the general coarseness of the sands, the presence of pebbles of Lower Greensand chert, and the very stiff clayey matrix of the gravel distinguish them from typical Bagshot Beds, and moreover throughout the greater part of the section a sharp and irregular junction could be traced between them and the brown London Clay. At a few points, however, the top of the London Clay was seen to pass into pale-brown and yellowish sandy clays, sometimes of significant thickness. Thus in the Dover Road, about 100 yards above Christ Church, below the thick red clayey gravel of the ‘cap’, lay about 3 feet of yellow loam, the lower part of which became a pale-brown clay passing quite gradually into normal blue or brown London Clay with septarian nodules. In the same series of excavations (1905) a trench at the junction of Shrewsbury Lane with the Dover Road showed the Shooters Hill gravel resting irregularly on a bed of fine clean yellowish sand quite unlike anything previously noted in the numerous pits and trenches opened upon the Hill, but as unfortunately the trench was only a few feet deep the relation of this fine sand to the London Clay could not then be made out.