多尺度突变现象的扫描式t检验方法及其相干性分析

阐明了将检测两子样本平均值之差的学生氏t检验推广到对多尺度突变现象进行扫描式检测的计算方法;对于t检验要求序列独立的限制,引用了初步的订正方法;还给出了检测两个序列间多尺度突变相干性的计算公式.扫描式t检验不仅具有相当于子波变换检测多尺度突变现象的功能,而且解决了子波变换检测突变时缺少临界值的问题.由于t统计量包含有二阶矩均方差,它不能像子波变换那样作为分解工具,但检测的尺度参数也就不必局限于2的整数幂,因而可以进行扫描式检测.应用于尼罗河年最高与最低水位历史序列(AD622—1470),能较客观和精确地检测出两序列在某些尺度上的相干性(同步或反位相)变化;并由此重新划分了该流域几十年至百余年时间尺度的相对干湿期.结果与目前查阅到的埃及灾荒历史记载相吻合.     

Competitive effects of fish in structurally simple habitats: perch,invertebrates, and goldeneye in small boreal lakes

We determined the associations between Eurasian perch Perca fluviatilis, invertebrates, and common goldeneye Bucephala clangula in boreal lakes. Our aim was to test the hypothesis that perch play a controlling role in small, oligotrophic, acidic, and poorly vegetated boreal lakes, affecting both invertebrate numbers and community structure. In addition, we predicted that perch impact lake usage by goldeneye. In the observational part of our study, we first explored the association between perch, invertebrates and goldeneye (pairs and broods per shore km) in 18 boreal, poorly vegetated lakes. Perch densities were associated negatively with invertebrate abundance and lake usage by goldeneye broods. In the experimental part in three fish-free lakes, we found that upon successful perch introductions, the number and biomass of invertebrates, the proportion of large dytiscids, and lake usage by goldeneye broods significantly decreased. We conclude that perch apparently plays a key role as a predator of invertebrates in boreal lakes with few aquatic macrophytes. It is evident that perch can strongly affect their prey populations and communities, and this predation may have an indirect effect on species, e.g. goldeneye, that consume the same prey.     

Colliding plasma experiments to study astrophysical-jet relevant physics

We present the results of experiments in which jets are created through the collision of two laser-produced plasmas. These experiments use a simple ‘v-foil’ target design: two thin foils are placed at an angle of 140° to each other, and irradiated with a high-energy laser. The plasmas from the rear face of these foils collide and drive plasma jets moving with a velocity of ～300 km?s^?1. By choosing the foil thickness and material to suit the laser conditions available, it has proven possible to create plasma jets for which the relevant scaling parameters show significant overlap with those of outflows associated with young stellar objects (YSOs). Preliminary results are also shown from experiments to study the effect of an ambient gas on jet propagation. Nominally identical experiments are conducted either in vacuum or in an ambient medium of 5 mbar of nitrogen gas. The gas is seen to increase the jet collimation, and to introduce shock structures at the head of the outflow.     

Optical variability of the blazar S4 0954+658 in 2008–2012

The results of multi-color photometric and polarization observations of the blazar S4 0954+658 carried out mainly in the Astronomical Institute of St. Petersburg State University and the Central Astronomical Observatory of the Russian Academy of Sciences in 2008–2012 are analyzed. Individual variable components that are responsible for the activity are distinguished; the power-law spectrum and high degree of polarization confirm that the emission is synchrotron radiation. Modeling the observed dependences between the parameters of the polarization and intensity is used to derive parameters of both the constant and the variable components of the radiation. The observed color variability (“the brighter, the bluer”) can be explained by the superposition of a red constant component and a bluer variable component with a constant relative spectral energy distribution.     

Effect of bed load supply on sediment transport in mountain streams

Mountain streams with their tributary torrents build the upper part of the fluvial network. They are important regarding the transfer of sediment from headwaters to lower basins. Channels are typically steep with wide grain size distributions, ranging from fine sand up to large boulders, and a stabilized bed surface. Mountain streams often are supply-limited with respect to mobile bed load, which needs to be addressed when bed load transport equations are applied to such streams. To better understand supply limitation, laboratory experiments highlighting the effect of bed load supply on incipient motion and bed load transport rate are discussed. Experimental tests were done in which fine bed load was supplied to a previously armored channel bed, with flow conditions ranging from one-third to twice the critical dis-charge for the bed surface. At flows not exceeding the critical discharge, the time series of the bed load transport rate at the downstream model boundary featured consistent patterns which are attributed to distinct phases: (i) a temporal lag, (ii) an equilibrium state, and (iii) a post-supply phase. Bed load transport occurred even at flows distinctly below that for incipient motion of the bed surface. But, with the mass of total bed load outflow approaching the supply amount, the mass did not exclusively consist of supplied grains. The coarser the supplied bed load, the more sediment was mobilized from the bed surface. At higher flows, processes differed. Total bed load outflow exceeded the supply amount and the break-up of the armor layer caused a refining of the bed surface.     

Analysis of the influence of parameter and scale uncertainties on a local multi-criteria land use evaluation model

Land use evaluation involves careful consideration of several environmental factors and their relative importance quantified by factor weights. Local multi-criteria evaluation provides a mechanism for computing factor (criteria) weights within local neighborhoods that capture spatial heterogeneity and contribute to more accurate evaluation results. The accuracy of results, however, is tempered by the potential uncertainty of criteria weights. The paper presents a spatially explicit approach to uncertainty and sensitivity analysis of local criteria weights and modeling scale on the variability of model output. The efficacy of the approach is presented on the example of Environmental Benefit Index (EBI) model used by the U.S. Department of Agriculture Conservation Reserve Program (CRP) to select environmentally sensitive agricultural areas for conservation. The uncertainty analysis resulted in identifying robust areas for CRP selection characterized by high suitability and low uncertainty. The sensitivity analysis focused on the next-best group of candidates characterized by high suitability and high uncertainty. The results show that there is a relationship between spatial heterogeneity, data representation scale, and the level of uncertainty in the results of EBI model. The sensitivity of model output can be attributed to both the uncertainty of criteria weights and the modeling scale. A potential practical value of this approach is the improved analytical support for land suitability evaluation requiring a consideration of sub-optimal land units (high suitability/high uncertainty). Also, this approach can guide modelling effort by allowing the analyst to visualize spatial distribution and patterns of model output uncertainty and focus data collection on influential model input factors.     

Selection of the data time interval for the prediction of maximum ozone concentrations

This paper highlights the problem of step-length selection for the one-step-ahead prediction of ozone called the data time interval. This is done using a case study-based comparison of two approaches for predicting the maximum daily values of tropospheric ozone. The first approach is the 1-day-ahead prediction and the second is the prediction of the maximum values based on a multi-step-ahead iteration of 1-h predictions. Gaussian process modelling is utilised for this comparison. In particular, evolving Gaussian-process models are used that update on-line with the incoming measurement data. These sorts of models have been successfully used in the past for the prediction of ozone pollution. This paper contributes an assessment of the way that the maximum ozone values are predicted. A comparison of the daily maximum ozone values forecasted by a model based on 1-day-ahead predictions with those obtained by iterated 1-h-ahead predictions of the ozone with predictions at predetermined hours of the day is given. The forecast results are in favour of the on-line model based on hourly predictions when approaching closer to the real maximum values of ozone, and in favour of the daily predictions when they are made on a daily basis.     

Climate change scenarios of heat waves in Central Europe and their uncertainties

The study examines climate change scenarios of Central European heat waves with a focus on related uncertainties in a large ensemble of regional climate model (RCM) simulations from the EURO-CORDEX and ENSEMBLES projects. Historical runs (1970–1999) driven by global climate models (GCMs) are evaluated against the E-OBS gridded data set in the first step. Although the RCMs are found to reproduce the frequency of heat waves quite well, those RCMs with the coarser grid (25 and 50 km) considerably overestimate the frequency of severe heat waves. This deficiency is improved in higher-resolution (12.5 km) EURO-CORDEX RCMs. In the near future (2020–2049), heat waves are projected to be nearly twice as frequent in comparison to the modelled historical period, and the increase is even larger for severe heat waves. Uncertainty originates mainly from the selection of RCMs and GCMs because the increase is similar for all concentration scenarios. For the late twenty-first century (2070–2099), a substantial increase in heat wave frequencies is projected, the magnitude of which depends mainly upon concentration scenario. Three to four heat waves per summer are projected in this period (compared to less than one in the recent climate), and severe heat waves are likely to become a regular phenomenon. This increment is primarily driven by a positive shift of temperature distribution, but changes in its scale and enhanced temporal autocorrelation of temperature also contribute to the projected increase in heat wave frequencies.     

青藏工程走廊热融湖湖底热状态

热融湖塘对寒区环境可产生较大影响, 其侧向热侵蚀会诱发冻土工程病害.选取青藏工程走廊热融湖塘分布密集的楚玛尔河、五道梁、北麓河3个亚区, 于2009—2010年通过HOBO水位传感器对4个固定湖塘的连续监测和大量湖塘的随机观测, 探讨了不同季节、不同水深湖底的热状态.在结冰期的1月中旬, 楚玛尔河90%以上的湖塘湖底温度都在0 ℃以下, 主要与湖塘较浅和湖水高矿化度有关.五道梁和北麓河湖底温度相对较高, 只有约20%的湖底温度低于0 ℃, 这些湖水深小于最大冻结冰层厚度; 最高温度高于4 ℃, 主要与湖较深有关.但3个亚区湖底温度均随着水深增加而增加.在6~9月融冰期, 湖底温度普遍增加, 最高达到18 ℃以上, 浅湖增温快于深湖, 湖底温度随着水深增加而递减.湖底温度年际变化近似为正弦曲线, 在1~2月, 湖底温度最低, 之后逐渐升高, 到7~8月, 湖底温度达到最高.