用高应变法确定预制桩承载力的拟合参数

采用高应变法确定预制桩承载力时,通过拟合得到的承载力具有多解性。因此提出了拟合参数的选取不一定要限定在规定的范围内,同时还 要根据预制桩设计参数、施工工艺或土体工程性质来选取拟合参数,解读高应变曲线,这样才能得到符合实际情况的预制桩承载力。     

Terrestrial ages of meteorites from the Nullarbor region,Australia, based on 14C and 14C–10Be measurements

Abstract– We have investigated the terrestrial ages, or residence times, of 78 meteorites (representing 73 discrete falls) recovered in Western Australia, and one from South Australia, using both ¹⁴C measurements and also ¹⁴C/¹⁰Be. The samples studied included two ureilites, one CK and one EL chondrite. We have included ¹⁰Be measurements from 30 meteorites, including some meteorites for which the ¹⁴C terrestrial age was previously determined. We find that the ¹⁴C/¹⁰Be terrestrial ages are more precise than ¹⁴C alone, as we can correct for shielding effects. In general, the two different age determinations age by ¹⁴C–¹⁰Be are precise to 0.5–1 ka and ¹⁴C alone within 1–2 ka. However, measurement of the ¹⁴C age alone gives good agreement with the ¹⁴C–¹⁰Be for most samples. The study of the terrestrial ages of meteorites gives us useful information concerning the storage and weathering of meteorites and the study of fall times and terrestrial age. We have compared the terrestrial ages to weathering, degree of oxidation (estimated from Mössbauer studies) and Δ¹⁷O. In this study, we found that weathering is not well correlated with terrestrial age for Nullarbor meteorites. However, there is a good correlation between degree of oxidation and Δ¹⁷O. The implications for the study of terrestrial ages and weathering from other desert environments will be discussed.     

The 30–60-day oscillation in the East Asian summer monsoon and its time-dependent association with the ENSO

Based on 30–60-day oscillation in the East Asian summer monsoon (EASM), the relationship between its northward propagation and ENSO (El Niño and Southern Oscillation) was investigated. To explicitly describe the 30–60-day monsoonal evolution, an empirical orthogonal function (EOF) analysis was carried out on the temporal-latitude section of the longitudinal average for 115°E–120°E. The principal 30–60-day EASM mode captures a northward propagation of well-organized intraseasonal oscillation (NISO). Using the associated time series of the first mode, we found a significant lagged correlation between interannual variability of the NISO and ENSO. Its lagged correlations with NINO indices have a quasi-biennial (QB) characteristic through the preceding summer and the concurrent summer. Their relationship was found by the regression analysis relating the low-level circulation to the ocean temperature. The western North Pacific anticyclone and the anticyclone-induced easterly vertical wind shear anomalies induce the dynamical linkage between the NISO and QB-type ENSO. It is shown that the NISO is more closely tied with QB-type ENSO in its phase than in its amplitude, and may be connected to the anomalous easterly wind and the eastward evolution of an oceanic Kelvin wave, which is associated with abrupt ENSO transition. The predictability on ENSO and NISO is examined through the canonical correlation analysis.     

Excess 210Po in the coastal atmosphere

Many researchers have reported the widespread occurrence of excess ²¹⁰ Po in the global atmosphere and suggested probable sources such as resuspension of top soils, stratospheric aerosols, sea spray of the surface micro‐layer, volcanic emission, and bio‐volatile ²¹⁰Po species from the productive ocean. We have observed excess ²¹⁰Po on aerosols in the coastal atmosphere of the Chesapeake and Delaware Bays. On‐board measurements in the Chesapeake Bay atmosphere show that the increase of this excess ²¹⁰Po is dependent upon wind speed. Simultaneously measured activity ratios of ⁷Be/²¹⁰Pb and ²¹⁰Pb/²²²Rn argue against either higher altitude air or continental soils as the source of this excess. We hypothesize that the excess ²¹⁰Po originates mainly from surface waters either by the sea‐spray of the surface microlayer, or more likely, by gas exchange. We conclude gas exchange as the mechanism since the polonium excess increases linearly with wind speed over a threshold of 3 m s⁻¹(mean) similar to other gases (i.e., CO₂, SF₆ , and DMS). In addition, higher ²¹⁰Po excess with lower ²²²Rn is observed in on‐shore marine air at Lewes, DE. This suggests sea‐air exchange of volatile Po along with other bio‐volatile species (i.e., DMS, DMSe, and MMHg) in the coastal productive ocean during high wind speeds.     

Late Pleistocene remains of giant deer (Megaloceros giganteus Blumenbach) in Scandinavia: chronology and environment

This article presents new data on the Late Pleistocene giant deer, Megaloceros giganteus (Blumenbach), describing its distribution in time and space, geographical and sexual variation and general biology. Twenty‐three south Scandinavian fossils found in situ in lacustrine sediments or redeposited in glaciofluvial material form the basis of this investigation. Fourteen C dates show that the giant deer inhabited southern Scandinavia in the ice‐free late Middle Weichselian from c. 40000 to 28000 BP (the Sandnes Interstadial) and again in the Late Weichselian from c. 12000 to 10700 BP (Older Dryas, Allerød and early Younger Dryas Chronozones), corresponding to a calibrated range from c. 14300 to 12400 cal. yr BP. Osteometric analyses show that the Scandinavian giant deer belonged to the upper size range of the lateglacial Irish population and that a marked sexual dimorphism existed, the males being 10–11% larger than the females. Investigations furthermore point at an antler cycle similar to that among extant northern cervids, and subsequently at a rutting season in autumn. The skeletal remains also prove the occurrence of twin delivery and the possibility of reaching an ontogenetic age of at least 23 years. During both occurrences the Scandinavian giant deer population was part of the northernmost distribution of the species in Europe and the palaeogeographical settings and palaeoenvironmental conditions of the two periods show striking similarities. Clearly, the giant deer were able to colonize and survive in a landscape dominated by grasses and sedges with scattered shrubs and dwarf shrubs. They came as close as 200–250 km to the ice front and their distribution included coastal areas along a cold sea with drifting icebergs. They were present in the area at least from March until November. However, the pure arctic conditions created during the early phase of the Younger Dryas event led to a new local extinction around 10700 ¹⁴C yr BP. This was the beginning of a total Eurasian extinction which, at least in Europe, was completed before the Pleistocene/Holocene transition.     

Variability and Risk Analysis of Hong Kong Air Quality Based on Monsoon and El Nino Conditions

This study presents an exploratory analysis aimed at improving understanding of the variability of Hong Kong air quality associated with different climate conditions. Significantly negative correlations were found when Nino 3 led particulate matter ≤10 μm PM₁₀) and NO₂ by 2--3 months over the Hong Kong territory, while the other pollutants (e.g., O₃, SO₂) showed modest correlations. A significant decreasing trend in visibility was observed during the autumn and winter, which has potential implications for the air-quality degradation and the endangerment of human health in Hong Kong. In an El Nino summer, the visibility was relatively better, while visibility in other seasons was diminished. On the other hand, in La Nina events, significant changes occurred in visibility in winter and autumn. Air pollution indices were less sensitive to the South China Summer Monsoon (SCSM), but a relatively high correlation existed between the East Asian Winter Monsoon (EAWM) and air pollutants. Rainfall was lower during most of the strong EAWM years compared to the weak years. This result suggests that the pollutants that accumulate in Hong Kong are not easy to wash out, so concentrations remain at a higher level. Finally, based on the conditional Air Pollution Index (API) risk assessment, site-specific vulnerabilities were analyzed to facilitate the development of the air-quality warning systems in Hong Kong.