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We study morphological changes on the Si surface induced by the C60 ion beam under various irradiation conditions. The fluence and incident energy of the C60 ion beam was 1 × 1016–1 × 1019 ions/m2 and 50 keV–9 MeV, respectively. The beam's incident angle to the surface normal was 0° or 60°. As a result of the changes in these variables, three types of nanostructures were observed: concave and convex, stringlike, and ripple structures. Structure shapes or sizes varied with changes in the parameters. Almost all cases showed concave and convex structures at an incident angle of 0°. At a 60° incident angle, stringlike or ripple structures were formed. Stringlike structures were formed at higher incident energy, while ripple structures were formed at lower incident energy. We found that both stringlike and ripple structures can form from sputtering and thermal effects. The formation of string structure requires a thicker amorphous layer and the proper balance of sputtering and annealing. [ABSTRACT FROM AUTHOR]

Quantification of the development of solution dolines provides important information for understanding the long-term evolution of karst landscapes. This study reports the initial results of an investigation of the long-term denudation rates along the side slopes of a solution doline based on analyses of cosmogenic [sup.36]Cl in calcite. The denudation rates increase in proportion with increasing size of the topographic contributing area, thereby supporting the hypothesis that the rate of surface lowering in carbonate terrains is controlled by water convergence in the epikarst. A simple model based on the empirical correlation between denudation rate and contributing area is successful in explaining the form of several solution dolines located close to the analyzed doline. The model reveals that these solution dolines, which have varying diameters, developed over similar time scales of the order of [l0.sup.5] yr. doi: 10.1130/G31302.1

This study investigates the potential of 36Cl in tracing young groundwater with residence times of up to ∼50 years. Groundwater samples were obtained from 16 irrigation wells in paddy fields located within an upland-lowland system in the Yoro River basin, Central Japan. The 36Cl/Cl ratios were in the range of 17 to 362 x 10-15. Among the samples with higher Cl- concentrations (>10 mg/L), two samples showed high nitrate concentrations as well (>30 mg/L). Except for these samples, the distribution of 36Cl in groundwater was essentially consistent with previous tritium concentration data measured in 1982 and 1994, considering the time that has elapsed since these earlier measurements were performed. 36Cl/Cl values were less than 30 x 10-15 in lowland areas, with higher values in and around upland areas. The results indicate longer residence times in the regional groundwater flow system (>50 years) than those estimated in previous studies, especially in the area west of the Yoro River. The results demonstrate the ability of 36Cl to trace young groundwater flow, particularly because high values of bomb-derived 36Cl/Cl are easily discriminated from pre-bomb water with low 36Cl/Cl values. Because of its very long half-life (3.01 x 105 years), 36Cl remains even after tritium is no longer available. [ABSTRACT FROM AUTHOR]

Abstract: Essential parameters for the applications of 36Cl as a tracer in groundwater studies include the initial 36Cl/Cl ratio, at the time of recharge, and/or the natural background deposition flux of 36Cl in the recharge area. To facilitate the hydrological use of 36Cl in central Japan, this study aimed to obtain a precise estimate of the long-term average local 36Cl flux and to characterize its seasonal variability. The 36Cl in precipitation was continuously monitored in Tsukuba, central Japan over a period of >5 years. The 36Cl flux showed a clear seasonal variation with an annual peak during the spring, which was attributed to the seasonal variability of tropopause height. The long-term average 36Cl flux (32±2atomsm−2 s−1), estimated from the measured data, was consistent with the prediction from the 36Cl latitudinal fallout model scaled using the global mean production rate of 20atomsm−2 s−1. The initial 36Cl/Cl ratio was estimated to be (41±6)×10−15, which is similar to that of pre-bomb groundwater in the Tsukuba Upland. An observation period covering an 11-year solar cycle would yield more accurate estimates of the values, given the increased 36Cl flux during the solar minimum. [Copyright &y& Elsevier]

Quantification of the development of solution dolines provides important information for understanding the long-term evolution of karst landscapes. This study reports the initial results of an investigation of the long-term denudation rates along the side slopes of a solution doline based on analyses of cosmogenic 36Cl in calcite. The denudation rates increase in proportion with increasing size of the topographic contributing area, thereby supporting the hypothesis that the rate of surface lowering in carbonate terrains is controlled by water convergence in the epikarst. A simple model based on the empirical correlation between denudation rate and contributing area is successful in explaining the form of several solution dolines located close to the analyzed doline. The model reveals that these solution dolines, which have varying diameters, developed over similar time scales of the order of 105 yr. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the contribution of ions to gas nucleation, we have performed experiments on the formation of water droplets in H2O/N2 and H2O/Ar gas mixtures by irradiation with a 20MeV proton beam and by positive corona discharge. The size of the formed nanoparticles was measured using a differential mobility analyzer equipped with a Faraday cup electrometer. Using the proton beam, droplets around 10nm in diameter were observed for both positively and negatively charged particles, but none were found when the corona discharge was used. This implies the importance of the presence of both positive and negative ions for the formation of nanosize droplets, which attract each other by Coulomb interactions, enhancing the collision frequency and leading to the formation of the 10nm droplets. [Copyright &y& Elsevier]

Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO 2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.