Identification of force from response data of a nonlinear system

Force identification is a type of system identification procedure which determines applied force from system responses; it has engineering applications where direct measurements of forces are not feasible. To identify the force, one can consider that the system model and its parameters are known, and then use the measured response of the system to determine the unknown forces. In contrast, postulating the system model and its parameter values is a difficult task, especially when considering a nonlinear system where the model poses many unknowns or inherent mathematical problems. In this research, a more direct way to identify the unknown force without knowing the model of the system is proposed. The approach, called the sum of weighted acceleration technique (SWAT), is a method that can predict input forces with measured linear and nonlinear structural responses. SWAT employs measured accelerations multiplied by effective or optimal weights to estimate the input force. Results using this method show that the force calculated using SWAT accurately predicts the force which excites a nonlinear structure response. The technique could be applied to both constrained and unconstrained structures.     

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO₃), nitrate radicals (NO₃) and dinitrogen pentoxide (N₂O₅) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO₃ a rate constant of k<7×10^-19 cm³ molecule^-1 s^-1 was derived for the reaction of HONO with HNO₃. From the observed decay of HONO in the presence of mixtures of N₂O₅ and NO₂ we have also derived upper limits for the rate constants of the reactions of HONO with NO₃ and N₂O₅ of 2×10^-15 and 7×10^-19 cm³ molecule^-1 s^-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.     

The strontium and oxygen isotopic record of hydrothermal alteration of syenites from the Abu Khruq complex,Egypt

Hydrothermal convection initiated by emplacement of the gabbro-syenite complex of Abu Khruq into the Egyptian basement 89 Ma ago systematically altered the trace element and isotopic compositions of the syenites. The scale of Sr transport in migrating solutions was far larger than the scale of Sr isotopic equilibration within rocks. As a result, Sr exchange was heterogeneous in the syenites, an effect which can be observed on three different scales. Within grains of a single mineral species, heterogeneities are related to grain boundaries and microfractures through which fluids migrated. Among minerals within rock samples, heterogeneities are related to differences in susceptibility to Sr alteration. Among samples within a single unit, heterogeneous alteration is apparently related to differences in permeability close to fracture zones.During the early stages of alteration radiogenic Sr derived from the country rocks was added to the syenites, causing small net changes in concentration (5 ppm ave.). Some Rb-Sr mineral isochrons from single rock samples yield the emplacement age because isotopic equilibration of this added Sr sometimes occurred within rock specimens. However, regressions of the whole-rock Rb-Sr data yield apparent ages that are about 10 Ma too old. Later stage alteration involved larger changes in whole-rock Sr concentration (45 ppm ave.) but had little further effect on the isotopic relationships because the Sr was derived from cogenetic gabbros rather than the country rocks.Alterations of Rb, Sr, and Sr isotopic compositions are not well correlated with changes in ¹⁸O/¹⁶O ratio because mineralogy played an important role in decoupling trace element and oxygen isotopic alteration. In general, the absence of such correlations for whole-rock data is not diagnostic of rocks with unaltered trace element and isotopic compositions. Mineral-scale Sr isotopic heterogeneities associated with grain boundaries and microfractures may be the most unambiguous evidence of trace element mobility.Deceased on 9/81     

Evidence suggesting anaerobic oxidation of the bisulfide ion in Chesapeake Bay

Upper Chesapeake Bay bottom waters are stratified in the summer. In the water column below the pycnocline, anoxic and sulfidic conditions exist. Hydrogen sulfide concentrations approach 60 μM or greater and elemental sulfur is also present. Water samples brought on board ship, exposed to light, and not treated with formaldehyde show rapid sulfide decomposition which is significantly faster than sulfide oxidation by molecular oxygen. The data presented show evidence for anaerobic, sulfide oxidation. The kinetics of the decomposition are consistent with possible biological mediation. Hydrogen, peroxide produced by microorganisms may be the chemical oxidant responsible for the oxidation. Alternately, solid metal oxides such as colloidal manganese oxide phases may be reponsible.     

Structural characterization of labradorite-bytownite plagioclase from volcanic,plutonic and metamorphic environments

The transmission electron microscope and the electron microprobe are used to characterize calcic plagioclase (An₆₅ to An₈₅) from a variety of geological environments. The cooling histories of samples from volcanic, plutonic and metamorphic environments are estimated and the transformation and exsolution sequence is inferred from observations in the transmission electron microscope. Several distinctive textural modifications occur depending both on bulk composition and cooling history. (1) Exsolution occurs in increasingly calcic bulk compositions upon slower cooling, and the coexisting phases are An₆₆ intermediate plagioclase and An_85–90 P¯1, c=14 Å plagioclase in the sample from the metamorphic environment, (2) the morphology of b antiphase boundaries (APBs) in An₇₅ to An₈₅ plagioclase changes from smoothly curving (rapid cooling and calcic compositions) to zig-zag (slower cooling or sodic compositions). (3) The concentration of defects in the intermediate plagioclase superstructure changes from a high density in rapidly cooled plagioclase to a lower density in slowly cooled plagioclase. In all plagioclases except for the rapidly cooled, volcanic specimens there is evidence in images and diffraction patterns for short-range ordered domains with P¯1 symmetry. The observations allow the microstructure of a single zoned plagioclase to be used as an indication of the geologic environment under which it cooled.     

The migration of geese as an indicator of climate change in the southern Hudson Bay region between 1715 and 1851

Observations and records maintained by the Hudson's Bay Company at York Factory and Churchill Factory on Hudson Bay between 1714 and 1825, serve as the source of information for a study of changes in the date of arrival of geese as a phonological indicator of climatic change. Changes in the migration pattern of geese are reflected in the changing date of arrival at the same location over a long period of time. Variations in this date are determined to be a function of southerly or tailwinds in the northward spring migration.     

Hydrothermal origin of mafic layers in alpine-type peridotites: Evidence from the seiad ultramafic complex,California, USA

Cretaceous alkaline intrusive rocks present in the Bitterfontein area comprise a suite having compositions ranging from olivine melilitite to syenite. These rocks which include some of lamprophyric affinity form part of the widespread dominantly alkaline suite of intrusives occurring in a broad zone parallel to the south western African coastal regions. This paper presents the petrology of the Bitterfontein alkaline rocks together with mineral and rock analyses. The chemistry of the rocks shows the suite to define a SiO₂ enrichment trend linking the compositions of olivine melilitite to oversaturated basic rocks. This trend is compared with trends defined by essentially tholeiitic volcanics and kimberlite-olivine melilitite compositions and a genetic relationship with the latter is apparent. Polybaric crystallisation of a larnite normative liquid in a crustal environment coupled with fractionation especially of phlogopite is important in the generation of members of the Bitterfontein suite. Phlogopite fractionation represents a deviation by the Bitterfontein suite from the evolutionary trend predicted by experimental work for low pressure anhydrous compositions in the Fo-La-Ne-SiO₂ system.     

Reaction of zoning of garnet

Compositional zoning of garnet in metamorphic or igneous rocks preserves evidence of the equilibration history of the sample and can be interpreted in terms of a growth-fractionation, diffusion-exchange, or diffusion-reaction model. Diffusion zoning is usually assumed to result from exchange reactions between garnet and other phases as the partitioning coefficient varies in response to changing environmental conditions, primarily temperature. However, in many natural environments where garnet grew originally in divariant equilibrium with other phases, changing conditions can promote continuous or “divariant” reactions and consequent compositional shifts of phases that can be much greater in some systems showing these reactions than those related to the small changes of partitioning. Diffusional zoning related to overstepping of these continuous reactions must be related to incongruent reaction and necessitates formulation of a kinetic diffusion-reaction model involving moving phase boundaries as well as solid-state diffusion. Three samples containing zoned garnets from the metamorphic aureole around the Ronda ultramafic intrusion in southern Spain are used to illustrate two possible models of diffusion-reaction processes. The examples are particularly informative because the reactions are demonstrably irreversible and evidence of the reaction system is preserved. Partitioning data indicates that compositions of product phases are not in equilibrium with the original garnet and do not vary with extent of reaction; therefore, exchange reactions with garnet were not possible and garnet changed composition only by incongruent reaction. After a small amount of reaction, Mg/Fe of the rim composition approaches a value apparently in equilibrium with product phases, but the garnets are zoned inward to the original garnet composition preserved in the interior. Grossularite content is approximately constant and spessartite content variable but small, thus, the rim composition of pyrope or almandine is assumed to be fixed by the external reaction process and is taken as a boundary condition in the following models. The zoning profile of pyrope or almandine component between the fixed rim and core compositions (assumed to extend to ∞) is described in semiinfinite, half-space models appropriate for large garnets with narrow rims. The first model corresponds to a reaction system in which all garnet compositions are metastable (case 1) and zoning depends on the independent variables of the diffusion constant, velocity of the interface between garnet and matrix, and time. The second model, corresponding to systems in which the initial garnet composition is metastable but an equilibrium composition is stable (case 2), depends on the independent variables diffusion constant, time, and a function of reaction compositions. In case 1 the consumption velocity is assumed constant and a steady state zoning profile is reached at large time, whereas, in case 2, the velocity decreases with the concentration gradient and steady state is not possible. The models were tested using a reaction time estimated from cooling models of the aureole, mass of garnet consumed, determined petrographically, and phase compositions. The two cases are somewhat independent in that different parameters are independent variables. The estimate of the diffusion constant of 10^?18±2 cm²/sec (assumed to be a mutual or binary coefficient for almandine and pyrope) is considered reasonable for the temperature range of reaction (probably 600–900° C), and the two models are consistent considering the probable error and possible real temperature differences. It is obvious that details of the metamorphic reaction system must be known to successfully apply diffusion models. Kinetic models, involving consumption or growth of the phase as well as diffusion are probably necessary when dealing with natural rocks. Several possible and interesting complications, such as cross coupling between components, can be investigated if more data were available. Experimental determination of diffusion constants allow natural reaction rates to be estimated by this method. Diffusion zoning is an important consideration that could increase the efficiency of experimentation with chemically recalcitrant phases.