Particle size dependent response of aerosol counters

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.     

Pseudodynamic tests on rubber base isolators with numerical substructuring of the superstructure and strain‐rate effect compensation

A pseudodynamic testing procedure has been applied by which the seismic response of a base‐isolated building is obtained by using as specimen the isolators, while the superstructure is numerically simulated. The procedure also takes advantage of the continuous pseudodynamic testing capabilities of the ELSA laboratory, which increase the accuracy of the results and reduce the strain‐rate effect of the rubber bearings. A simple proportional correction of the measured forces compensates the remaining strain‐rate effect due to the unrealistic speed of the test. The correction factor is obtained by means of a characterizing test on the specific rubber isolators. The developed method has been successfully applied to the prediction of the seismic response of a base‐isolated four‐storey building submitted to several specified accelerograms. The results for those earthquakes as well as the effects of some changes of the parameters of the system are discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Towards a direct collapse–load method of design for concrete frames subjected to severe ground motions

Most current methods of design for concrete structures under earthquake loads rely on highly idealized ‘equivalent’ static representations of the seismic loads and linear‐elastic methods of structural analysis. With the continuing development of non‐linear methods of dynamic analysis for the overload behaviour and collapse of complete concrete structures, a more direct and more accurate design procedure becomes possible which considers conditions at system collapse. This paper describes an evaluation procedure that uses non‐linear dynamic collapse–load analysis together with global safety coefficients. A back‐calibration procedure for evaluating the global safety coefficients is also described. The aim of this paper is to open up discussion of alternative methods of design with improved accuracy which are necessary to move towards a direct collapse–load method of design. Copyright © 2002 John Wiley & Sons, Ltd.     

Seismic Hazard for Selected Sites in Greece: A Bayesian Estimate of Seismic Peak Ground Acceleration

A procedure for estimating maximum values of seismic peak ground accelerationat the examined site and quantiles of its probabilistic distribution in a future timeinterval of a given length is considered. The input information for the method areseismic catalog and regression relation between peak seismic acceleration at a givenpoint and magnitude and distance from the site to epicenter (seismic attenuation law).The method is based on Bayesian approach, which simply accounts for influenceof uncertainties of seismic acceleration values. The main assumptions for the method are Poissonian character of seismic events flow and distribution law of Gutenberg-Richter's type. The method is applied to seismic hazard estimation in six selected sitesin Greece.     

A double-head photon-counting photometer for fast timing observations

The structure of the electronics of the two-head, high-speed photometer operating on the 152-cm G.D. Cassini telescope of Bologna University has been fully redesigned for high-time-resolution observations of fast variable sources, in particular, of the optical counterparts of X-ray binary systems. The fast photometer now permits sampling times from 0.1 ms to 100 s. The handling of the system clock and I/O configuration have been modified to provide rigorous synchronization of the sampling time with an external high-stability clock and the continuous acquisition of an uninterrupted data stream. The continuous data-acquisition process, which is driven by an external clock, is limited only by the capacity of the hard disk and is supported by a double-buffer SRAM memory designed to overcome any discontinuity in the asynchronous communication with the computer. Real-time monitoring of the data enables continuous evaluation of the weather conditions, and the directly displayed light curve can be used to determine the optimal management of the observations.     

Simultaneous use of geochemical and geophysical methods to characterise abandoned landfills

. Groundwater sampling and geophysical methods determined a serious contamination problem associated with refilled exploitation sites at the Cal Dimoni area, Llobregat delta, Barcelona, Spain. To characterise this process, hydrogeochemical analyses were performed and showed the following modifications to groundwater chemical composition: increasing pH values, changing redox conditions, significant increases in total organic carbon (TOC) and certain trace elements, and high groundwater conductivity values. Major ion content accumulations were found under the refilled area. In contrast, elements involved in the oxidation–reduction processes, such as iron, manganese and nitrates, clearly diminished. Electromagnetic prospecting methods were also performed and delineated the contamination plume extent. These methods also showed separate sources of contamination, one clearly related to the groundwater–refilled zone leachate interaction, another as a consequence of the manure–accumulation surface site. Geochemical and geophysical methods have shown similar results for locating groundwater contamination sources, and for determining leachate generation mechanisms and flow paths.     

Isotope Evidences of the Paleozoic Stage of Epigenetic Transformation of Vendian Sediments of the Russian Platform

The Rb–Sr characteristics of whole-rock samples of Upper Vendian clayey rocks recovered by Gavrilov-Yam boreholes are studied. The Rb–Sr age versus sampling depth relationship has been revealed. Three sample assemblages are identified. The errorchron relationship of samples in the first interval (1760–2400 m) fits the age of 390 ± 40 Ma corresponding to the initial Hercynian history characterized by the transformation of platformal sediments. The other two assemblages (2410–2525 and 2528–2560 m) make up isochrons with slopes corresponding to 590 ± 50 and 690 ± 10 Ma, respectively. Their geochronological meaning is unclear.     

A Platinum Group Element and Re-Os Isotope Investigation of Siderophile Element Recycling in Subduction Zones: Comparison of Grenada, Lesser Antilles Arc, and the Izu-Bonin Arc

The picritic (MgO >13·5%) lavas of Grenada providea unique opportunity to evaluate the platinum group elements(PGE) and Os isotope compositions of primitive subduction-generatedmelts. Compared with other arc lavas they have undergone verylimited crustal contamination (     

Equilibrium and Disequilibrium Trace Element Partitioning in Hydrous Eclogites (Trescolmen, Central Alps)

Despite the widespread presence of hydrous phases in subduction-related systems, experimental D^Min/Fluid trace element valuesfor many hydrous phases are lacking. To fill this gap, we presenta set of D^{Min/Clinopyroxene} values (where Min indicates amphibole,zoisite, phengite, paragonite or apatite) derived from equilibriumparageneses of eclogites from Trescolmen (Central Alps, Switzerland).These data can be combined with experimental data for D^{Clinopyroxene/Fluid},to estimate D^Min/Fluid values for the hydrous phases, thus circumventingexperimental problems with the direct determination of suchvalues. We analysed Li, Be, B, Sr, Y, Zr, Nb, Ba, Ce, Nd, Sm,Pb, Th and U in coexisting phases by laser ablation microprobeinductively coupled plasma mass spectrometry. Many of the valuesare extremely low; for example, Nb, Ba, Ce, Th and U are inthe lower ppb range in clinopyroxene. Attainment of equilibriumwas evaluated by textural, and major and trace element characteristics.Non-equilibrated assemblages are common in most eclogite localities,including Trescolmen, and using such samples would lead to thederivation of erroneous values for equilibrium partitioning.However, four of the 10 studied eclogites from Trescolmen havinghomogeneous clinopyroxene compositions and preferred orientationof high-pressure phases yielded consistent D^{Min/Clinopyroxene}values in all four samples (where Min indicates amphibole, phengite,paragonite, apatite), and hence were studied in detail. Thelow abundances in some phases result from strong preferentialincorporation of trace elements into other minor phases. Fromthe investigated hydrous phases (amphibole, zoisite, clinozoisite,phengite, paragonite, apatite and talc), zoisite was found tobe the most important carrier of Sr, light rare earth elements,Pb, Th and U, whereas phengite hosts Ba and is, along with clinopyroxeneand paragonite, an important phase for B. However, because oftheir low modal abundance in eclogite-facies rocks, phengiteand paragonite do not control the B whole-rock budget. We inferthat estimated D^{Min/Clinopyroxene} values from equilibrium assemblagescan be used as a good approximation for partition coefficientsunder the given PT conditions (