Use of Pitzer's equations to determine the media effect on the formation of lead chloro complexes

The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl₂ and CaCl₂ solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl⁺, PbCl₂⁰ and PbCl₃^? have been determined for the various media. Values of $\text{K}{}_1\text{= 30.0 ± 0.6}$, $\text{K}{}_2\text{= 106.7 ± 2.1}$ and $\text{K}{}_3\text{= 73.0 ± 1.5}$ were obtained for the cumulative formation constants. [$\text{Pb}{}^{\mathrm{2+}}\text{+ nCl}{}^{\mathrm{?}}\text{→ PbCl}{}_{\mathrm{n}}{}^{\mathrm{2?n}}\text{)}$]. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb²⁺ in an artificial seawater solution.     

Deriving rules from activity diary data: A learning algorithm and results of computer experiments

 Activity-based models consider travel as a derived demand from the activities households need to conduct in space and time. Over the last 15 years, computational or rule-based models of activity scheduling have gained increasing interest in time-geography and transportation research. This paper argues that a lack of techniques for deriving rules from empirical data hinders the further development of rule-based systems in this area. To overcome this problem, this paper develops and tests an algorithm for inductively deriving rules from activity-diary data. The decision table formalism is used to exhaustively represent the theoretically possible decision rules that individuals may use in sequencing a given set of activities. Actual activity patterns of individuals are supplied to the system as examples. In an incremental learning process, the system progressively improves on the selection of rules used for reproducing the examples. Computer experiments based on simulated data are performed to fine-tune rule selection and rule value update functions. The results suggest that the system is effective and fairly robust for parameter settings. It is concluded, therefore, that the proposed approach opens up possibilities to derive empirically tested rule-based models of activity scheduling. Follow-up research will be concerned with testing the system on empirical data. Received: 31 January 2001 / Accepted: 13 September 2001     

Spatial Response to Major Volcanic Events in or about AD 536, 934 and 1258: Frost Rings and Other Dendrochronological Evidence from Mongolia and Northern Siberia: Comment on R. B. Stothers, ‘Volcanic Dry Fogs, Climate Cooling, and Plague Pandemics in Europe and the Middle East’ (Climatic Change, 42, 1999)

Hypothesized large-scale climatic extremes require verification from distantregions in order toconfirm the magnitude and timing of such events. Three of the most massivehypothesized volcanic events of the past two millennia, occurring in or aboutAD 536, 934 and1258, had profound climatic and demographic repercussions over much of Europe,the MiddleEast, and other areas, according to historical accounts recently described inStothers (1998, 1999,2000) as well as other research. Here we report on frost ring and otherdendrochronologicalevidence derived from a 1738-year tree-ring chronology from Mongolia andmillennial-scaletree-ring data from northern Siberia which demonstrate that these three eventsmay have alsoimpacted conditions in these distant regions.     

Direct measurements of volume transports through Fram Strait

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.     

Lunar structure and dynamics - results from the apollo passive seismic experiment

Analysis of seismic signals from man-made impacts, moonquakes, and meteoroid impacts has established the presence of a lunar crust, approximately 60 km thick in the region of the Apollo seismic network; an underlying zone of nearly constant seismic velocity extending to a depth of about 1000 km, referred to as the mantle; and a lunar core, beginning at a depth of about 1000 km, in which shear waves are highly attenuated suggesting the presence of appreciable melting. Seismic velocitites in the crust reach 7 km s^–1 beneath the lower-velocity surface zone. This velocity corresponds to that expected for the gabbroic anorthosites found to predominate in the highlands, suggesting that rock of this composition is the major constituent of the lunar crust. The upper mantle velocity of about 8 km s^–1 for compressional waves corresponds to those of terrestrial olivines, pyroxenites and peridotites. The deep zone of melting may simply represent the depth at which solidus temperatures are exceeded in the lower mantle. If a silicate interior is assumed, as seems most plausible, minimum temperatures of between 1450°C and 1600°C at a depth of 1000 km are implied. The generation of deep moonquakes, which appear to be concentrated in a zone between 600 km and 1000 km deep, may now be explained as a consequence of the presence of fluids which facilitate dislocation. The preliminary estimate of meteoroid flux, based upon the statistics of seismic signals recorded from lunar impacts, is between one and three orders of magnitude lower than previous estimates from Earth-based measurements.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April, 1973.