地磁感应电流（GIC）的作用与评估

地磁感应电流（GIC）可能对各种人工长距离导电体造成影响与危害.地磁扰动产生的感应电场的强度与地磁场强度、地下电阻率结构相关,在导电系统内生成的GIC的强度则同时与导电系统的内在结构有关.计算了加拿大Manitoba省三个典型地区在2000年7月15日的一个强烈磁暴期间产生的感应电场.通过对地磁活动性的统计分析,估计加拿大魁北克电网可能经受的最大GIC达每相78A（一年一次）和234A（每十年一次）.     

Vegetation and climate of the Lop Nur area, China, during the past 7 million years

Lop Nur in Xinjiang, Northwest China, is located in the lowest part of the Tarim Basin at an altitude of 780?m and experiences an extremely dry climate with an annual precipitation of only 17?mm and a high evaporation rate of 2,728?mm. The pollen and spores from the Late Miocene strata of a borehole in Lop Nur were analyzed with a view to interpreting the paleoenvironmental evolution of Lop Nur. Main types of pollen such as Chenopodiaceae, Nitraria, Ephedra and Artemisia reflect an arid climate. By collating the palynological data in this area as recorded in other literature and by applying the method of Coexistence Analysis, we have obtained the paleoclimatic parameters from Late Miocene to Holocene in Lop Nur. These suggest that temperatures increased from the Late Miocene (10.2°C) to the Pliocene (13.4°C), decreased from Pliocene to Pleistocene (4.7°C), and were more stable from Holocene (12.1°C) until now (11.5°C). The precipitation was stable (about 900?mm) from Late Miocene to Early Pleistocene, then decreased markedly (to about 300?mm) in Middle and Late Pleistocene, and reached its lowest value (17.4?mm) in the Holocene. The changes in paleoclimate at Lop Nur provide new evidence for understanding the uplift of the Qinghai-Tibetan Plateau.     

On the stereology of a spherical segment of one base,with applications to the petrography of “cleavage domes” in a metagreywacke

Mathematical Geosciences - Dome-shaped concentrations of mica adjacent to garnet porphyroblasts in a hornfelsed metagreywacke are seen in thin-section as “cleavage arcs.” This paper...     

Sensor position estimation and source ranging in a shallow water environment

Underwater acoustic transient signals are generated mechanically at known positions along a wharf. These signals are received by a wide aperture planar array of four underwater acoustic sensors, whose positions relative to the wharf are unknown. A method is described that enables the positions of the sensors to be estimated from accurate differential time-of-arrival measurements (with 0.1 /spl mu/s precision) as the signal wavefronts traverse the array. A comparison of the estimated positions with the nominal positions of the first three sensors, which form a 20-m-wide aperture horizontal line array, reveals a 2-cm displacement of the middle sensor from the line array axis. This slight bowing of the line array results in overranging (bias error of 3%) when the wavefront curvature method is used with the nominal collinear sensor positions to locate a static source of active sonar transmissions at a range of 59.2 m. The use of the spherical intersection method coupled with the estimated sensor positions of the line array provides an order of magnitude improvement in the range estimate (within 0.3% of the actual value). However, systematic ranging errors are observed when the sound propagation medium becomes nonstationary. Next, the differences in the arrival times of the direct path and boundary-reflected path signals at the middle sensor of the wide aperture line array are estimated using the differential phase residue of the analytic signal at the sensor output. These multipath delays are used to estimate the range and depth of the source. Although the average value of the multipath range estimates is within 0.5% of the actual value, the variance of the range estimates is 50 times larger when compared with the results of the spherical intersection and wavefront curvature methods. The multipath delay data are also processed to provide a reliable estimate of the temporal variation in the water depth enabling the tidal variation to be observed.     

The occurrence of ramsayite,titan-låvenite and a fluorine-rich eucolite in a nepheline-syenite inclusion from Tenerife,Canary Islands

A nepheline syenite inclusion found in an ignimbritic sequence from Tenerife has revealed a variety of minerals which indicate the strongly peralkaline nature of the rock. The major mineral, alkali feldspar, encloses earlier crystallized biotite, Mn-rich magnetite, sphene and perovskite. The late-crystallizing minerals in the interstices include clinopyroxene (aegirine-augite to titanian-aegirine), F-rich arfvedsonite, ramsayite, nepheline, pyrophanite, apatite, sodalite and rare F-rich eucolite and titan-låvenite. The data illustrate the important role of volatiles in the sub-volcanic equivalent of the phonolitic lavas.     

Determining the extent of weathering of spilled fuel in contaminated soil using the diastereomers of pristane and phytane

A method is described for determining the relative extent of weathering in moderately biodegraded, hydrocarbon-contaminated soils from Antarctica. Plotting the pristane diastereomer ratio (PrDR) vs. pristane/phytane (Pr/Ph) allows the relative extent of weathering (primarily evaporation in this case) to be determined. PrDR is used to account for biodegradation as it is independent of evaporation. The method is straightforward and as robust as conventional ratios.     

Central meridian passage dates of coronal holes,inferred from east-west solar scans at 692 and 1415 MHz,for the period January 1968–January 1974

The presence of solar coronal holes can be inferred from one-dimensional east-west scans at 692 and 1415 MHz. The scans indicate that coronal holes are stable structures with low-emissive characteristics and with lifetimes which can span several solar rotations, in agreement with observations using other techniques. This work focuses on the first half of 1973. The 1415 MHz data presented for this period show the radio analogues of two coronal holes, commonly referred to as CH1 and CH3. These holes were observed at soft X-ray and XUV wavelengths with the Skylab satellite and at EUV with the OSO-7 satellite. The analysis is then extended to cover the period from 1968 to 1974 with a central meridian passage date and a subjective classification being assigned to each coronal hole observation. This information is tabulated and provides a consistent set of coronal hole observations during the maximum and declining phases of solar cycle 20.     

Aeromagnetic surveying using a simulated unmanned aircraft system

Carleton University and Sander Geophysics are developing an unmanned aircraft system (UAS) for aeromagnetic surveying. As an early indication of the expected performance of the unmanned aircraft system, a simulated unmanned aircraft system (sUAS) was built. The simulated unmanned aircraft system is a T‐shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4.67 m apart, which is the same sensor geometry as planned for the unmanned aircraft system. The simulated unmanned aircraft system is flown suspended beneath a helicopter. An 8.5 km² area in the Central Metasedimentary Belt of the Grenville Province, near Plevna, Ontario, Canada, was surveyed with the simulated unmanned aircraft system suspended 50 m above ground. The survey site was chosen on the basis of its complex geological structure. The total magnetic intensity (TMI) data recorded were compared to that obtained during a conventional fixed‐wing survey and a ground survey. Transverse magneto‐gradiometric data were also recorded by the simulated unmanned aircraft system. The simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed‐wing data and were found to have a similar resolution to that of the ground survey data. The advantages of surveying with the simulated unmanned aircraft system were: (1) the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and (2) substantial saving of time and effort. In the survey site, the 4.67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground.