Late Quaternary vegetation and climate in the Escalante River Basin on the central Colorado Plateau

Five alcoves (rock shelters) in the Forty-Mile Canyon—Willow Gulch area of the Escalante River Basin in southeastern Utah yielded rich deposits of late Quaternary macrobotanical remains. The deposits were sampled and the contents identified in order to construct a chronology of vegetational change. Fourteen radiocarbon dates indicate that the fossils were deposited between 12,690 and 7510 yr B.P. (years before present). Ninety-one plant taxa were identified, 62 to species. Six species were common to all alcoves: Gambel oak ( Quercus gambelii ), box-elder ( Acer negundo ), prickly pear ( Opuntia subgenus Platyopuntia), skunkbush ( Rhus aromatica var. trilobata ), serviceberry ( Amelanchier utahensis ), and Indian ricegrass ( Oryzopsis hymenoides ). Late Pleistocene samples (>11,000 yr B.P.) contain extralocal, elevationally depressed species such as Douglas fir ( Pseudotsuga menziesii ), spruce ( Picea sp.), and mountain mahogany ( Cercocarpus ledifolius ), and mesophytic species such as rose ( Rosa woodsii ) and water birch ( Betula occidentalis ). Early Holocene samples (11,000-8000 yr B.P.) contain no elevationally depressed conifers, and the remaining mesophytic species decrease in relative abundance. Reticulated hackberry ( Celtis reticulata ) becomes common. The terminal Early Holocene sample (8000-7000 yr B.P.) contains abundant Gambel oak and prickly pear, but little else. Paleoclimatic interpretations for the Late Pleistocene correspond well to those of most other workers on the Colorado Plateau. Climates that were wetter and at least seasonally cooler than they are today are inferred from the macrobotanical assemblage. However, the increased moisture is attributed to higher stream base levels and increased groundwater rather than directly to increased precipitation. Early Holocene climates are interpreted as warmer and drier than those of the Late Pleistocene but still wetter than the present climate. Groundwater levels appear to be decreasing due to stream entrenchment. Terminal Early Holocene climates were much warmer and at least seasonally drier. By the end of the period, groundwater levels had decreased so much that the alcoves were unable to sustain plant communities; stream base level was probably near the present level.     

International Evidence on GFC‐Robust Forecasts for Risk Management under the Basel Accord

A risk management strategy designed to be robust to the global financial crisis (GFC), in the sense of selecting a value‐at‐risk (VaR) forecast that combines the forecasts of different VaR models, was proposed by McAleer and coworkers in 2010. The robust forecast is based on the median of the point VaR forecasts of a set of conditional volatility models. Such a risk management strategy is robust to the GFC in the sense that, while maintaining the same risk management strategy before, during and after a financial crisis, it will lead to comparatively low daily capital charges and violation penalties for the entire period. This paper presents evidence to support the claim that the median point forecast of VaR is generally GFC robust. We investigate the performance of a variety of single and combined VaR forecasts in terms of daily capital requirements and violation penalties under the Basel II Accord, as well as other criteria. In the empirical analysis we choose several major indexes, namely French CAC, German DAX, US Dow Jones, UK FTSE100, Hong Kong Hang Seng, Spanish Ibex 35, Japanese Nikkei, Swiss SMI and US S&P 500. The GARCH, EGARCH, GJR and RiskMetrics models as well as several other strategies, are used in the comparison. Backtesting is performed on each of these indexes using the Basel II Accord regulations for 2008–10 to examine the performance of the median strategy in terms of the number of violations and daily capital charges, among other criteria. The median is shown to be a profitable and safe strategy for risk management, both in calm and turbulent periods, as it provides a reasonable number of violations and daily capital charges. The median also performs well when both total losses and the asymmetric linear tick loss function are considered Copyright © 2012 John Wiley & Sons, Ltd.     

矩形平面直流磁控溅射装置工作区域磁场分析

通过分析磁场对磁控溅射过程的影响,总结出了矩形平面直流磁控溅射装置工作区域磁场的设计原则,并给出了两种磁体结构.采用有限元方法对一套装置的磁场进行了计算,磁场计算结果与测量值吻合较好.基于上述分析计算,研究了磁场分布对靶材刻蚀形貌的影响,并进一步提出了具体的磁场改进措施.采用分流条垫补方法可以改进磁场分布,如果磁场水平分量呈马鞍形分布,靶材的利用率可以提高,采用磁极斜面结构对磁场分布的改进意义不大.另外,错开磁体间安装接缝和对永磁体精确充磁能够有效提高工作区域磁场分布的均匀性.     

Philosophical Differences: The Case of Architects' Reluctance to Use Strategic Planning Software

A briefing workshop was run in an effort to involve its participants in choosing a strategic direction, and eventual form, for a proposed facility. The workshop was an action research, participative process that sought to improve final design by preconsultation with some relevant stakeholders. This paper will specifically focus on our attempt to use strategic planning software at an early stage of such a workshop. It discusses and illustrates the difficulties of importing a new technique into an established, professional setting where activities and roles may be expressed, or assumed, on the basis of previous experience. More exactly, although we hoped to use our software to analyze and explore participants' design styles, and so predict their likely choice of design option, the architects present undermined such analyzes by playing a role rather than telling the software what they really thought about the various strategic choices. Hence it was, in some ways, a waste of time using our software. We speculate below whether such undermining might be symptomatic of deep philosophical differences between the workshop organizers, planners, and architects. We also examine whether such differences bode ill for the future of architecture.     

Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch

The stability of the Antarctic ice shelves in a warming climate has long been discussed, and the recent collapse of a significant part, over 12,500 km2 in area, of the Larsen ice shelf off the Antarctic Peninsula has led to a refocus toward the implications of ice shelf decay for the stability of Antarctica's grounded ice. Some smaller Antarctic ice shelves have undergone periodic growth and decay over the past 11,000 yr (refs 7-11), but these ice shelves are at the climatic limit of ice shelf viability and are therefore expected to respond rapidly to natural climate variability at century to millennial scales. Here we use records of diatoms, detrital material and geochemical parameters from six marine sediment cores in the vicinity of the Larsen ice shelf to demonstrate that the recent collapse of the Larsen B ice shelf is unprecedented during the Holocene. We infer from our oxygen isotope measurements in planktonic foraminifera that the Larsen B ice shelf has been thinning throughout the Holocene, and we suggest that the recent prolonged period of warming in the Antarctic Peninsula region, in combination with the long-term thinning, has led to collapse of the ice shelf.