The boundary integral calculations of the forward problem for D.C. sounding and MMR methods for a 3-D body near a vertical contact

Summary The paper presents comprehensive theory based on the boundary integral method for calculations of the electric potential, electric field and corresponding magnetic field due to a pair of D.C. source electrodes near a vertical resistivity contact in the halfspace, indlucing a 3-D disturbing body in the vicinity of the contact. Special attention is paid to the case when the disturbing body touches the vertical contact. Results of numerical calculations are presented in the form of sounding curves and a set of isoline graphs for potential, components of the electric and magnetic field (total and anomalous) on the surface of the Earth. It is shown that the presence of the disturbing body at the contact is most pronounced in the electrical characteristics. Anomalies in the magnetic field are small in comparison to the field due to the electric current in the electrode cable and primary currents flowing from the electrodes.     

Reverse flow in turbidity currents: the role of internal solitons

Pickering & Hiscott, (1985) have demonstrated amply the presence of reverse-flow units within the thick-bedded calcareous wacke (TCW) beds of the turbiditic Cloridorme Formation (Middle Ordovician, Gaspé Peninsula, Quebec, Canada). These reverse-flow units are underlain and overlain by units which reveal flow in the primary (obverse) direction. In this paper, a model is proposed for this reverse flow, based on the probable nature of the primary turbidity flow. It appears that the initial flow was highly elongated (thickness h? length L), with h～ 500 m, velocity U～ 2 m s^-1 and sediment concentration C～ 1·25%_o. The rate of momentum loss of the flow is estimated by means of a useful parameter which we call the ‘drag distance’, symbol d_D, defined by where h and L are the thickness and length of the flow, respectively; _cC_d is a combined drag coefficient representing friction on the bottom and at the upper interface; and _fC_d is a form-drag coefficient related to the shape and size of the head. d_D is the distance travelled by a current of constant h and L, flowing over a horizontal bottom and obeying a quadratic friction law, for an e-fold reduction in velocity. Simple considerations, confirmed by our own experiments (described in this paper), show that such an elongated turbidity current cannot be reflected as a whole from an adverse slope: when the nose of the current reaches the slope, it forms a hump, which surges backwards and sooner or later breaks up into a series of internal solitons. The latter, probably numbering 4–7, will cause reverse flow at a given point as they pass by, provided that the residual velocity in the tail is not too great. Flow in the original (obverse) direction will be re-established after the passage of the solitons. Quiescent periods in front of, between and behind the solitons, when soliton-associated currents cancelled out the residual obverse flow, would allow the deposition of thin mud-drapes. Additional flow reversals observed in a few of the TCW beds cannot be explained readily by the re-passage of solitons, since wave breaking at the ends of the basin would cause massive energy loss; internal seiches are the preferred explanation for these later reversals.     

Mathematical modeling of membrane polarization occurring in rocks due to applied electrical field

Membrane polarization occurs in sediments with different surface area of capillaries (pores) and is regarded as a slow type of polarization. This phenomenon is the foundation of the well known methods of induced polarization (IP): time domain and frequency domain induced polarization. The characteristic parameters of induced polarization which are required for studying physical properties of rocks are measured in the laboratory. Data measured in the laboratory confirmed the distinctions of IP processes at time-on and time-off. Additionally linear dependence of voltage and applied current is not always observed. This paper presents the first step of studying: theoretical consideration for time-on and mathematical modeling of membrane polarization, ion concentrations of electrolyte in the pores of different models of pores space, and arising voltage. The problem of concentration of ions along the pores can be solved using the diffusion equation with specified initial and boundary conditions. Reduced boundary conditions for time-on show that transient concentrations at the boundaries are linear with time. It allows obtaining the analytical solution for this equation. Mathematical modeling has been performed for different combinations of pores. It is shown that if electrical current flows from the pores with greater transfer numbers to the pores with smaller transfer numbers, an excess of ions will be observed at this boundary. If the difference of transfer numbers is negative, there is a decrease in the concentration of ions at the vicinity of the boundary. This decrease will continue until the concentration at this boundary reaches zero. In this case the galvanic chain will be interrupted and electrical current flowing through the sample does not penetrate to this cell. The duration of the process of ions distribution in the pore and time of blockage t ₀ is proportional to the radii of contacted pores and inversely proportional to the transfer number difference and square of the current flowing through this cell. It was shown by both laboratory measurement and field processes that induced polarization relates to low porous rocks with small transfer number differences.     

Using tornado climatology to help plan a Doppler radar network

Using the tornado climatology and population statistics for Canada, a method of ranking population centres is proposed. Using as a basis a list of cities and census divisions ranked by population-weighted tornado incidence (a measure of risk), a first estimate is made of where to site 22 Doppler radars. It is estimated that this network will provide protection to about 82% of Canada's population.     

Rock salt mass in the Paleoproterozoic sequence of the Onega trough in Karelia (from the Onega parametric well data)

A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb—Pb method.     

Developing a modern pollen–climate calibration data set for Norway

Bjune, A. E., Birks, H. J. B., Peglar, S. M. & Odland, A. 2010: Developing a modern pollen–climate calibration data set for Norway. Boreas, Vol. 39, pp. 674–688. 10.1111/j.1502‐3885.2010.00158.x. ISSN 0300‐9483. Modern pollen–climate data sets consisting of modern pollen assemblages and modern climate data (mean July temperature and mean annual precipitation) have been developed for Norway based on 191 lakes and 321 lakes. The original 191‐lake data set was designed to optimize the distribution of the lakes sampled along the mean July temperature gradient, thereby fulfilling one of the most critical assumptions of weighted‐averaging regression and calibration and its relative, weighted‐averaging partial least‐squares regression. A further 130 surface samples of comparable taphonomy, taxonomic detail and analyst became available as a result of other projects. These 130 samples, all from new lakes, were added to the 191‐lake data set to create the 321‐lake data set. The collection and construction of these data sets are outlined. Numerical analyses involving generalized linear modelling, constrained ordination techniques, weighted‐averaging partial least‐squares regression, and two different cross‐validation procedures are used to asses the effects of increasing the size of the calibration data set from 191 to 321 lakes. The two data sets are used to reconstruct mean July temperature and mean annual precipitation for a Holocene site in northwest Norway and a Lateglacial site in west‐central Norway. Overall, little is to be gained by increasing the modern data set beyond about 200 lakes in terms of modern model performance statistics, but the down‐core reconstructions show less between‐sample variability and are thus potentially more plausible and realistic when based on the 321‐lake data set.     

Metal accumulation in mussels of the Kuril Islands, north-west Pacific Ocean

Concentrations of cadmium, copper, iron, lead, manganese, nickel and zinc were investigated in two species of mussel from the Kuril Islands in the north-western Pacific Ocean: the short-lived mussel Mytilus trossulus and the much larger and longer-lived Crenomytilus grayanus. The concentrations of most elements were low, and these reported levels are believed to reflect background values for pristine locations. However, both iron and zinc concentrations were elevated in some samples taken from areas of hydrothermal vent activity, and these are believed to reflect the enrichment of the two metals in solution at such sites. Furthermore, the concentrations of cadmium were unusually elevated in both species of mussel, especially in the longer-lived C. grayanus. The high accumulation of cadmium in mussels from the Kuril Islands is believed to reflect regional upwelling, but it is also postulated that filtration rates of the mussels are high due to low levels of suspended matter, and this leads to a high assimilation efficiency for cadmium. The distribution of cadmium amongst the tissues of C. grayanus is also reported, and the need for further ecotoxicological studies in the area is proposed.     

Design Screening Tools for Passive Funnel and Gate Systems

The funnel and gate remediation concept (Star and Cherry 1993) represents a promising, yet relatively under-developed, technology for the passive control and in situ remediation of contaminated ground water. Effective design and implementation of such a system may, however, prove difficult under conditions of large or unpredictable variations in contaminant migration or ground water flow.
Numerical modeling of two-dimensional ground water flow has been used to predict the hydraulic performance of passive, straight, or winged funnel and gate configurations over a range of hydrogeologic and ambient ground water flow conditions. The results of these analyses were used to construct generic correlation diagrams relating upstream capture zone or gale through put to the barrier, gale, and aquifer characteristics. These diagrams serve as useful screening tools to (1) quantitatively estimate the capture zone of pre-determined funnel and gale configurations, or (2) develop preliminary funnel and gale designs that will yield a desired capture zone, independent of aquifer characteristics.