The influence of preform on the modes of vibrating beams

A theoretical analysis is presented of a vibratory system in which it is possible to eliminate an unwanted mode of vibration by using that mode as an initial deformation of the system. The analysis shows that this is possible in straight beams with end restraints in axial deformation. The mathematical problem leads to an eigenvalue problem of a type not normally encountered. In the paper examples are given for the changes in eigenfrequency and mode shape produced by the initial preformed shape of the beam for cases where the preform is proportional to a mode of the straight beam and when the preform is unrelated to any mode. The analysis shows that, while elimination of a mode in the strict sense is not achieved, the results can be interpreted for practical purposes in this way.     

Response of fixed offshore structures in random sea

An integrated model is developed for the short-term and long-term dynamic response of an offshore structure subjected to random wave excitation. A discrete linear, elastic model of the upper structure is coupled with an iterative linear quasi-three-dimensional finite element model for the pile-soil medium, and the system is subjected to stochastic storms described by mean rate of arrival, joint probability distribution of storm duration and average intensity, and a random process that describes the variations of a statistical wave height measure during each storm. Sarpkaya's 1977 experimental information is used to specify values for C_M and C_D, in Morison's equation, consistent with the flow and response characteristics. Soil (clay) degradation, due to cyclic excitation, is followed during the passage of a storm. The indicator of soil degradation is taken to be the value of the horizontal foundation stiffness and the stiffness degradation is modelled by a homogeneous Markov process.     

Solubility equilibrium constant of α-hopeite

The saturation curve for synthetic α-hopeite, Zn₃(PO₄)₂·4H₂O in dilute phosphoric acid solutions has been determined at 25°C as a function of pH. Interpretation of the data in terms of a model which assumes the formation of the ion-pairs ZnHPO₄⁰ and ZnH₂PO₄⁺ in these solutions resulted in the solubility product constant for α-hopeite of 10^?35.3±0.1. The data show that the formation of hopeite may influence both the availability of zinc in soils and the zinc levels in natural water systems.     

The age of SNC meteorites and the antiquity of the Martian surface

We report new Sm-Nd, Lu-Hf, and Pb-Pb mineral and whole-rock isotope data for the basaltic shergottite Zagami, as well as Pb-Pb whole-rock isotope data for the basaltic shergottite Los Angeles, the lherzolitic shergottite Dar-al-Gani 476 (DaG 476), and the clinopyroxenite Nakhla. In agreement with previous findings, our new Sm-Nd and Lu-Hf mineral ages on the Martian meteorite Zagami are young (155 and 185 Ma, respectively). The ²⁰⁷Pb/²⁰⁶Pb-²⁰⁴Pb/²⁰⁶Pb compositions of the insoluble fractions of shergottites (Zagami, Los Angeles, and literature data for Shergotty and EETA79001) form an excellent alignment indicative of a 4.0 Ga crystallization age. The range of Pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial Pb and argues against mixing relationships. The age of 4.048 ± 0.017 Ga (MSWD = 1.5) provided by the Pb isotope compositions of the Zagami whole-rock and residues is therefore taken to date the crystallization of this rock, which, so far, was believed to be only ∼ 180 Ma old. Based on this result, we argue that the lithosphere of Mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the Martian surface. This interpretation is consistent with photographic interpretations of erosional features on Mars. It also relieves the constraint imposed by the presence of anomalies of ¹⁴²Nd and ¹⁸²W (both products of extinct radioactive nuclides) that the Martian mantle should have preserved primordial isotopic heterogeneities, thus allowing for the planet interior to be actively convecting.     

Preliminary landfill siting and related analysis using simple modeling techniques

The evaluation of existing and new landfills requires considerable consideration of environmental factors for the protection of groundwater resources. The initial evaluation of sites can be time-consuming and expensive depending on the assessment approach selected. General planning methods, such as the DRASTIC procedure, coupled with the use of analytical or numerical groundwater models can provide useful site selection tools by improving the quality and quantity of analysis. This paper presents an overview of some promising methods for landfill site evaluation and suggests alternative data sources where few data are present. Examples of some of the methods are given.     

AUTOMATED GEOGRAPHY

Analytical methods and computer technology for spatial analysis have advanced rapidly. Geographers can now consider a general form of automated geography which integrates all of the new techniques into an analytical whole. Computer cartography, computer graphics, digital remote sensing, geographic information systems, spatial statistics, and quantitative spatial modeling can be combined eclectically with traditional manual techniques to address geographic problems that are too large and complex for manual treatment alone. Small systems are widely available to facilitate small, less complex problems. Automation can assist in all forms of geography—scientific and humanistic, nomothetic and idiographic, basic and applied—but its adoption is likely to be highest among applied scientists. The immediate challenge is to prepare for a major shift toward computer instruction and automated geography in the late 1980s. Long term effects will include improved contributions by geographers to national and international policy analyses, a greater emphasis on team-work and sharing, stronger ties with other disciplines, and a generally more viable discipline.     

THE NEEDLES (CALIFORNIA) IRON METEORITE

The Needles fine octahedrite, which weighs 45.3 kg, was found in 1962 in the Turtle Mountains, about 50 km SSW of Needles, California. It contains 10.3% Ni, 77 ppm Ga, 93 ppm Ge and 4.8 ppm Ir, and is a member of chemical group II D. It is rather similar to the Wallapai, Arizona, meteorite, and may possibly be a transported mass from this multiple fall. The compositional evidence slightly favors the interpretation that Needles is a distinct fall.     

Acoustic density measurements of consolidating cohesive sediment beds by means of a non-intrusive “Micro-Chirp” acoustic system

A non-intrusive “Micro-Chirp” acoustic system and a signal-processing protocol have been developed to estimate the bulk density of consolidating cohesive sediment beds. Using high-frequency (300–700 kHz) Chirp acoustic waves, laboratory measurements were conducted with clay–water mixtures. Because acoustic echo strength is proportional to variations in acoustic impedance, and the speed of sound in the clay bed hardly changed during consolidation, the bulk density could be successfully estimated without disturbing the sediment bed. Based on acoustic signal analysis, this study demonstrates that the reflection coefficient and bulk density at the water–sediment interface increase with consolidation time, and that a single speed of sound value can be used for practical bulk density estimation in muddy environments.     

The Meteoritical Bulletin,no. 108

Meteoritical Bulletin 108 contains 2141 meteorites including 12 falls (Aguas Zarcas, Benenitra, Jalangi, Komaki, Ksar El Goraane, Mhabes el Hamra, Natun Balijan, Oued Sfayat, Shidian, Taqtaq‐e Rasoul, Tocache, Viñales), with 1640 ordinary chondrites, 149 carbonaceous chondrites, 134 HED achondrites, 45 lunar meteorites, 38 ureilites, 27 iron meteorites, 23 Martian meteorites, 22 primitive achondrites, 19 Rumuruti chondrites, 15 mesosiderites, 10 enstatite chondrites, 7 ungrouped achondrites, 4 pallasites, 4 ungrouped chondrites, and 4 angrites. Nine hundred and nine meteorites are from Africa, 747 from Antarctica, 279 from South America, 148 from Asia, 29 from North America, 18 from Oceania, 6 from Europe (including 2 from Russia), and 5 from unknown locations.