Low-density Body Research Articles

Motion of low-density gaseous bodies in the atmosphere

The problem of motion of low-density deformable bodies in an atmosphere is interesting in reference to the hypothesis that the Tungussk catastrophe of 1908 resulted from atmospheric deceleration of a body of large size and low density (less than 0.01 g/cm3) [1]. Article [2] investigated the region of earth destruction caused by the shock wave formed ahead of a meteorite body. The motion of the meteorite is modeled here by explosion of a linear charge of variable cross section. Article [3] examined deceleration in an exponential atmosphere of a body whose shape and size are given functions of time. It was shown that under certain conditions the shock wave separates from the body and detaches. However, the body shape is not known beforehand, in fact, and a law for its variation can be obtained only by simultaneous consideration of flow in the shock layer, the wake, and the gas cloud. With an initial cloud velocity on the order of 40 km/sec this is a difficult problem. The present author knows of no attempt to solve the problem formulated in this way. The present paper addresses the problem of motion of a gas cloud in an exponential atmosphere with large initial velocity. The cloud gas and the atmospheric gas are assumed to be perfect and ideal. The problem is solved numerically by the direct finite-difference method of Godunov [4], using a moving mesh and isolated discontinuities. The objective of the work is to elucidate the basic aerodynamic effects arising when a low-density body enters the atmosphere.

Subsurface distribution of granitic rocks, south-central Maine

Two- and three-dimensional modeling of gravity data from the area north of Penobscot Bay in south-central Maine reveals that major granitic intrusive masses there are tabular in shape. Batholiths are less than 7 km thick on the average and have nearly vertical contacts. Smaller granitic bodies average less than 3 km thick. Structural and contact metamorphic features of granite and surrounding rocks suggest that felsic masses of batholithic proportions were emplaced at a late stage in the tectonic history of the area. Model configurations combined with structural evidence indicate that the batholiths were probably intruded along faults. Several previously unmapped felsic masses have been located and defined, mainly within the Passagassawakeag Gneiss. The largest of these is the Stricklen Ridge Granite, an igneous mass up to 3 km thick and 11 km long. The near-surface dip of the Passagassawakeag Gneiss contact northeast of the Mount Waldo batholith is calculated to be 45°N to 55°N on the basis of gravity evidence. A sill-like tongue of high-density rocks related to the Bays-of-Maine complex has been postulated to extend under the Ellsworth Schist north from Mount Desert Island and approach the Lucerne batholith near its southeastern contact. The Lucerne Granite is bounded on the north by a low-density body, proposed to represent a distinctly earlier felsic intrusion, now covered by a thin veneer of Lucerne Granite.

The geological significance of a negative gravity anomaly in the South Wales Coalfield

AbstractThree gravity traverses across the eastern half of the South Wales Coalfield indicate a local, elongate, negative Bouguer anomaly of a few milligals amplitude bordering the southern rim. The anomaly has a maximum amplitude of 4 mgal near Maesteg and attenuates eastward, dying out in the vicinity of the East Crop. Two possible geological causes of the anomaly are examined, namely a local thick sequence of normal Upper Carboniferous strata and a discrete, low‐density body of Carboniferous age with no apparent surface expression. The former, uncontroversial explanation requires rock densities at variance with measured values. In the case of the hypothetical low density body which can explain the anomaly, a variety of possible ages and configurations are discussed.

Ancient continental mantle beneath oceanic ridges

The petrology, bulk chemistry, and Sr-isotopic chemistry of ultramafic rocks from the equatorial mid-Atlantic ridge indicate that: (1) the ultramafics are derived from the upper mantle; (2) they are not genetically related to oceanic gabbros and basalts; (3) they are residual and were depleted of lithophile elements at some early stage in the history of the earth; (4) they are similar to alpine-type peridotites from the continents. These results suggest that a zone of alpine-type residual peridotitic material exists in the upper mantle beneath the mid-Atlantic ridge. This zone is tentatively identified with the anomalous, low-density mantle body observed beneath the ridge in seismic and gravity profiles. The alpine-type residual peridotitic upper mantle beneath the ridge was originally part of a layer of ‘continental’ mantle located below a pre-Atlantic rift super-continent (Pangea); it constituted the material left over from the differentiation of the sialic body from the primitive mantle. Upon rifting of the sialic body, the upper mantle ‘continental’ layer is carried along by convection currents except for a central block caught in a stagnant zone at the divergence of the two rising limbs; such block is left behind and is presently beneath the mid-Atlantic ridge; fragments of it become exposed by upward intrusion. The stagnant ‘continental’ mantle should be present below the Atlantic and Indian ridges, which originated by rifting of continental blocks, but not below the East Pacific rise, because the latter probably initiated in a ‘protooceanic’ area. This hypothesis may help explain contrasting features of the two types of ridges; for instance, why a larger heat-flow anomaly is associated with the East Pacific rise than with the mid-Atlantic and Indian ridges.

Are Meteors a Tool for Studying the Asteroids? Or Vice Versa?

The bulk of the comments I made at the colloquium are to be found in two recent papers (McCrosky and Ceplecha, 1970; McCrosky et al., 1971). The following summary is offered in place of a full text.Most interpretations of all meteor data rely on knowledge of the relationship (luminous efficiency) between mass and luminosity. Discussions of recent experiments made to determine the luminous efficiency are found in papers by Ayers et al. (1970) and Becker and Friichtenicht (1971). Faint meteor phenomena can be understood if the meteoroids are weak, low-density (pm ≈ 0.25 g/cm3) “fluff balls” such as can be expected on the basis of Whipple's comet model (Jacchia, 1955; Jacchia et al., 1967). Alternative explanations, not requiring low densities, have been offered. Jones and Kaiser (1966) propose thermal shock of strong, high-density material as a fragmentation mechanism. Allen and Baldwin (1967) and Baldwin and Allen (1968) have reanalyzed Jacchia's data in terms of phenomena observed in the laboratory in simulated reentry experiments. Here, a high-density meteoroid froths and thereafter behaves as a low-density body. They also revise the luminosity law to account for blackbody radiation of refractory material. McCrosky and Ceplecha (1970) show that neither of these alternative explanations can apply to large bodies and, using photographic observations of bright fireballs, they defend Jacchia's original proposal for all meteors.

The Specific Gravity of Japanese Quail (Coturnix Coturnix Japonica)

Some methods of indirect calorimetry are based on a knowledge of the net volume of the metabolism unit (MacLagan and Sheahan, 1950). To accurately determine this volume it is necessary to know the average density of the subjects placed in the chamber. It is well known that the respiratory system of birds includes air sacs (Sturkie, 1965). It appears possible, in theory, that birds may be less dense than mammals due to the volume of the respiratory system or due to other low density body components such as pneumatic bones.The following study was undertaken to determine the specific gravity of Japanese quail. PROCEDUREMature Japanese quail which were between 19 and 20 weeks of age were used for this experiment. Following anesthetization with sodium phenobarbital, they were dispatched by occluding the trachea with a large hemostat. Occlusion was effected at the midpoint of inspiration or expiration. A small screw …

On meteoroids and penetration

Estimates of the meteoroid penetration of vehicles in space are improved from the author's 1957 values. The meteoritic data are improved by the measurement of luminous efficiency in the artificial meteor experiment of Trailblazer 1 analyzed by McCrosky and Soberman, and by independent determinations from three asteroidal meteors by Cook, Jaechia, and McCrosky. A review of the photographic meteor data leads to an adopted meteoroid density of 0.44 g cm−3 and a mass of 1.0 gram for a zero-magnitude visual meteor of velocity 30 km sec−1. Hawkins and Upton's influx rate of visual meteors is utilized after correction for the zero-magnitude mass. A mean velocity of 22 km sec−1 is adopted. The formula by Herrmann and Jones from their summary of hypervelocity impact experiments provides the penetration of a low-density body against a semi-infinite target. The ratio of perforation thicloiess for a thin target to the penetration in a semi-infinite target is adopted as 1.5. The calculated perforation rate on a 0.1-cm-thick plate of aluminum in the earth's neighborhood is reduced by a factor of more than 3000 from the 1957 estimate. The change logarithmically is divided about equally between the changes in meteoroid data and in the impact formula. The present calculations are still subject to considerable uncertainty and can be greatly improved by further research in both the areas of radar-meteors and hypervelocity experiments at velocities exceeding 20 km sec−1. Possibly an unobserved, large flux rate in the mass range 103 to 107 gram may exist.

Variations in Floating Ability with Age in the Male

Abstract One thousand and forty males between the ages of 9 and 24 years were subjected to the following four tests of notation. 1. A tuck float (knees bent to chest, arms encircling knees, forehead on knees) with lungs fully inflated.2. A tuck float during normal respiration.3. A tuck float during maximum exhalation under water.4. A horizontal float on the back. The results showed a significant decrease in the percentage of floaters from the age of 13 years onwards compared with the other age groups tested, a pronounced peak in both horizontal and tuck floating ability between the ages of 10 and 13 years, and an almost complete incapacity for horizontal floating from the age of 15 years onwards. Inferences drawn from these results were that an increase in fat tissue occurred between the ages of 10 and 13 years; that marked variations in the acquisition and distribution of high and low density body tissues occurred between childhood and maturity; that decisions regarding the teaching of swimming at particular age levels could be based on the physiological variations apparent from the above results.