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  • 1
    Monograph available for loan
    Monograph available for loan
    Nations at war : A scientific study of international conflict (1998)
    Cambridge : Cambridge University Press
    Details Availability
    Call number: PIK D 025-99-0446
    Type of Medium: Monograph available for loan
    Pages: 242 p.
    Edition: 1. ed.
    ISBN: 0521629063
    Series Statement: Cambridge Studies in International Relations 58
    Location: A 18 - must be ordered
    Branch Library: PIK Library
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  • 2
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    A new EPMA method for fast trace element analysis in simple matrices (2016)
    Mineralogical Society of America
    Details
    Publication Date: 2016-08-03
    Description: It is well known that trace element sensitivity in electron probe microanalysis (EPMA) is limited by intrinsic random variation in the X-ray continuum background and weak signals at low concentrations. The continuum portion of the background is produced by deceleration of the electron beam by the Coulombic field of the specimen atoms. In addition to the continuum, the background also includes interferences from secondary emission lines, "holes" in the continuum from secondary Bragg diffraction, non-linear curvature of the wavelength-dispersive spectrometer (WDS) continuum and other background artifacts. Typically, the background must be characterized with sufficient precision (along with the peak intensity of the emission line of interest, to obtain the net intensity for subsequent quantification), to attain reasonable accuracy for quantification of the elements of interest. Traditionally we characterize these background intensities by measuring on either side of the emission line and interpolate the intensity underneath the peak to obtain the net intensity. Instead, by applying the mean atomic number (MAN) background calibration curve method proposed in this paper for the background intensity correction, such background measurement artifacts are avoided through identification of outliers within a set of standards. We divide the analytical uncertainty of the MAN background calibration between precision errors and accuracy errors. The precision errors of the MAN background calibration are smaller than direct background measurement, if the mean atomic number of the sample matrix is precisely known. For a simple matrix and a suitable blank standard, a high-precision blank correction can offset the accuracy component of the MAN uncertainty. Use of the blank-corrected-MAN background calibration can further improve our measurement precision for trace elements compared to traditional off-peak measurements because the background determination is not limited by continuum X-ray counting statistics. For trace element mapping of a simple matrix, the background variance due to major element heterogeneity is exceedingly small and high-precision two-dimensional background correction is possible.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 3
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    Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm-time substorms (2016)
    Wiley
    Details
    Publication Date: 2016-05-12
    Description: We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on June 23, 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived Earthward (downward) intense field-aligned current sheets with thicknesses of a few 10s of km, which is well below the ion-scale, on flux tubes moving equatorward/Earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multi-scale processes in PSBL as a consequence of magnetotail reconnection.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Increasing the sensitivity of controlled-source electromagnetics with synthetic aperture (2012)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2012-03-01
    Description: Controlled-source electromagnetics (CSEM) has been used as a derisking tool in the hydrocarbon exploration industry. We apply the concept of synthetic aperture to the low-frequency electromagnetic field in CSEM. Synthetic aperture sources have been used in radar imaging for many years. Using the synthetic aperture concept, big synthetic sources can be constructed by adding the response to small sources (building blocks) in different ways, and consequently, big sources with different radiation patterns can be created. We show that the detectability of hydrocarbons is significantly enhanced by applying synthetic aperture to CSEM data. More challenging targets such as deep reservoirs (4 km below sea floor) can be detected. The synthetic aperture technique also increases the sensitivity of the field to subsurface targets in the towing streamer acquisition. We also show that a pseudovertical source (orthogonally distributed dipole pairs) can be constructed synthetically, and that the detection capability of this pseudovertical source is increased by applying field steering. The synthetic aperture concept opens a new line of research in CSEM, with the freedom to design suitable synthetic aperture sources for a given purpose.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists (SEG)
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  • 5
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    Artificial neural network forward modelling and inversion of electrokinetic logging data (2011)
    Wiley
    Details
    Publication Date: 2011-03-02
    Description: ABSTRACT An artificial neural network method is proposed as a computationally economic alternative to numerical simulation by the Biot theory for predicting borehole seismoelectric measurements given a set of formation properties. Borehole seismoelectric measurements are simulated using a finite element forward model, which solves the Biot equations together with an equation for the streaming potential. The results show that the neural network method successfully predicts the streaming potentials at each detector, even when the input pressures are contaminated with 10% Gaussian noise. A fast inversion methodology is subsequently developed in order to predict subsurface material properties such as porosity and permeability from streaming potential measurements. The predicted permeability and porosity results indicate that the method predictions are more accurate for the permeability predictions, with the inverted permeabilities being in excellent agreement with the actual permeabilities. This approach was finally verified by using data from a field experiment. The predicted permeability results seem to predict the basic trends in permeabilities from a packer test. As expected from synthetic results, the predicted porosity is less accurate. Investigations are also carried out to predict the zeta potential. The predicted zeta potentials are in agreement with values obtained through experimental self potential measurements.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
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  • 6
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    Proton and Electron Injection Path at Geosynchronous Altitude (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Using tens to hundreds of keV proton and electron flux measurements and simultaneous magnetic field measurements from three Geostationary Operational Environmental Satellites [GOES‐13 (75°W), GOES‐14 (105°W), and GOES‐15 (135°W)], we investigate proton and electron injections and their relationship to the substorm current wedge at geosynchronous altitude. Proton and electron injection processes occur only in the initial formation of the substorm current wedge, the width of which is less than 2 hr in local time in the premidnight region, for moderate substorms. Proton injections are closely related to the formation of a substorm current wedge at geosynchronous altitude, and thus the onset of a substorm, even before local dipolarization in the magnetic field. Proton injections take place only under the western upward field‐aligned currents of the current wedge. Electron injections in the energy range of 〈100 keV are tightly coupled with local dipolarization in the magnetic field, and these take place mostly in the central region of the current wedge, extending in the region under the western upward field‐aligned currents.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Testing a two-loop pattern of the substorm current wedge (SCW2L) (2014)
    Wiley
    Details
    Publication Date: 2014-01-19
    Description: [1]  Recent testing of a quantitative model describing the classical (region-1-sense, referred to as the R1 current loop) substorm current wedge (SCW) revealed systematic discrepancies between the observed and predicted amplitudes, which suggested us to include additional region-2-sense currents (R2-loop) earthward of the dipolarized region (SCW2L model). In this paper we discuss alternative circuit geometries of the 3d substorm current system and interpret simultaneous observations of the magnetic field dipolarizations by NOAA Geostationary Operational Environmental Satellite (GOES) and by NASA Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, to quantitatively investigate the SCW2L model parameters. During two cases of a dipole-like magnetotail configuration, the dipolarization/injection front fortuitously stopped at r  ∼ 9 Re for the entire duration of ∼ 30 min-long SCW-related dipolarization within a unique, radially-distributed multi-spacecraft constellation, which allowed us to determine the locations and total currents of both SCW2L loops. In addition, we conducted a survey of the dipolarization amplitudes in events, simultaneously observed at 6.6 Re (GOES) and 11 Re (THEMIS) under a wide range of magnetotail conditions. We infer that the ratio I 2 / I 1 varies in the range 0.2 to 0.6 (median value 0.4) and that the equatorial part of the R2 current loop stays at the distance r  〉 6.6 Re in the case of a dipole-like field geometry ( BZ 0  〉 75 nT at 6.6 Re prior to the onset), but it is located at r  〈 6.6 Re in the case of a stretched magnetic field configuration (with BZ 0  〈 60 nT). Since the ground midlatitude perturbations are sensitive to the combined effect of the R1- and R2-sense current loops with the total current roughly equal to I 1  −  I 2 , the ratio I 2 / I 1 becomes an important issue when attempting to monitor the current disruption intensity from ground observations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Event study combining magnetospheric and ionospheric perspectives of the substorm current wedge modeling (2014)
    Wiley
    Details
    Publication Date: 2014-11-18
    Description: Unprecedented spacecraft and instrumental coverage and the isolated nature and distinct step-like development of a substorm on 17 March 2010 has allowed validation of the two-loop substorm current wedge model (SCW2L). We find a close spatio-temporal relationship of the SCW with many other essential signatures of substorm activity in the magnetotail and demonstrate its azimuthally localized structure and step-wise expansion in the magnetotail. We confirm that ground SCW diagnostics makes it possible to reconstruct and organize the azimuthal spatio-temporal substorm development pattern with accuracy better than 1 h MLT in the case of medium-scale substorm. The AMPERE-based study of global field-aligned current distribution indicates that: (a) the SCW-related FAC system consists of simultaneously activated R1- and R2-type currents; (b) their net currents have a R1-sense; and (c) locations of net current peaks are consistent with the SCW edge locations inferred from midlatitude variations. Thanks to good azimuthal coverage of four GOES and three THEMIS spacecraft, we evaluated the intensities of the SCW R1- and R2-like current loops (using the SCW2L model) obtained from combined magnetospheric and ground midlatitude magnetic observations and found the net currents consistent (within a factor of 2) with the AMPERE-based estimate. We also ran an adaptive magnetospheric model and show that SCW2L model outperforms it in predicting the magnetic configuration changes during substorm dipolarizations.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Creation and utility of a large fit-for-purpose earth model in a giant mature field: Kern River field, California (2014)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2014-06-27
    Description: Reservoir management studies of California’s Kern River field rely on a full-field 155-million cell three-dimensional (3D) earth model. This full-field model provides input for reserves estimation as well as the identification, targeting, and ranking of remaining opportunities. The earth model is regarded as "fit for purpose" in that characteristics of the model are aligned with specific needs for reservoir management. Normalized resistivity logs from more than 12,000 wells are used to establish lithology and reservoir architecture. Temperature, steam, gas, and oil saturation logs from over 650 boreholes provide regular periodic surveillance for identifying changes in fluids and temperature. Changes in fluid contacts and saturations are integrated with reservoir architecture three times each year. These model updates are important to the development teams for staying current on changes in their project area. The integration of these data provides the basis for linked reserves and resource estimation and the identification and development of remaining opportunities. Kern River reserves and resources are estimated from the model for over 130 internal reporting entities. For asset reservoir management purposes, reserves are updated for over 160,000 entities (based on patterns, zones, and reserves) across the 12-sq-mi (31-sq-km) field. The updated reserves supply input to reserves distribution maps and spreadsheets used for evaluating workover and new development opportunities. Some of these opportunities represent heat mining of untapped hot oil zones whereas other opportunities are cold and require the introduction of steam to mobilize the oil. Using multiple reservoir property characteristics as filter criteria for identifying remaining opportunities is an important tool used at Kern River. Reservoir volumes containing hot moveable oil below steam zones in non-producing areas can be quickly and efficiently identified and prioritized with this method. This has helped lead to the success of our current field-wide horizontal infill drilling program that identifies geobodies based on these filtering criteria.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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  • 10
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    Large amplitude GPS TEC variations associated with Pc5-6 magnetic field variations observed on the ground and at geosynchronous orbit (2015)
    Wiley
    Details
    Publication Date: 2015-08-08
    Description: Large amplitude variations in GPS total electron content (TEC) at Pc5-6 (〈6.67 mHz) frequencies have been observed, using a high data rate Global Positioning System (GPS) receiver of the Canadian High Arctic Ionospheric Network (CHAIN). TEC variations with peak-to-peak amplitudes of 2-7 TEC units (TECU) were observed over a 2.5 hour period in the post-noon sector on 09 September 2011, during a period of high auroral activity within a moderate geomagnetic storm. TEC observations were from the Sanikiluaq, Nunavut (56.54°N, 280.77°E) GPS receiver located in the auroral region. Over this same time period, compressional Pc5-6 magnetic field variations were observed by the geosynchronous GOES 13 magnetometer and the ground-based Sanikiluaq magnetometer. GOES 13 has a northern magnetic footprint in close proximity to Sanikiluaq. Cross correlation analysis indicates that magnetic field and TEC variations were possibly linked. No natural hazards or nuclear explosions capable of exciting TEC perturbations were reported on this day. Using a triangulation technique involving TEC measurements of multiple GPS satellites, the propagation velocity of TEC variations in the ionosphere was also calculated. This calculation revealed two distinct events: lower frequency (~0.9 mHz) TEC variations that propagated westward, consistent with the westward propagation of compressional Pc5 waves observed by GOES 13 and 15 satellites, and higher frequency (~3.3 mHz) TEC variations that propagated southward. This is the first report of variations in ionospheric TEC linked to satellite observations of Pc5-6 ULF waves.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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