Bandpass calibration of a wideband spectrometer using coherent pulse injection

We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2–13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment.     

Determination of arsenic(III) for the investigation of the microbial oxidation of arsenic(III) to arsenic(V)

Recent evaluations of acute and chronical toxicity of arsenic resulted in a reduction of the standard value for total arsenic from 40 μg/L to 10 μg/L in drinking water which will be valid in Germany after a transition period as from January 1996. Arsenic is well known as substance of deep groundwaters, mainly of geogenic origin and normally found as As(III) or As(V). As(V) is well removable by flocculation and filtration after adding iron salts. As(III), however, has to be oxidized first to As(V). Therefore, it is important for treatment techniques to be able to distinguish between As(III) and As(V). A modified determination of As(III) using flow injection analysis was installed and optimized in order to investigate whether As(III) may be oxidized to As(V) by bacteria in natural waters. The results showed that at 4°C, no As(III)-oxidation was observed within 14 days. At room temperature, however, in the bacteria-containing samples, an As(III)-oxidation was found starting after 3 to 7 days. After 14 days, no As(III) was left over. In contrast, in the sterile samples, no As(III)-oxidation could be observed within 14 days. These results demonstrated that microbial processes influence the oxidation of As(III) to As(V) in natural waters.     

Earth Dam-foundation interaction during earthquakes

Several significant parameters that could affect interaction in a dam-foundation system are discussed. These parameters are: (1) Fundamental periods of the dam and the foundation layer. (2) Lateral extent of the dam. (3) The material properties of the dam and the foundation layer. Five cases are analysed to illustrate the influence of these parameters on interaction. An interaction ratio, R₁, relating the response of the dam-foundation system at the base of the dam to the free field response is introduced and interaction effects are expressed in terms of this ratio; the smaller this ratio, the less are the interaction effects. For very small values of R₁, it is shown that the dam-foundation system could be decoupled The results of the studies presented in the paper suggest that the interaction effects cannot be uniquely related to either the ratio of the period of the dam to the period of the foundation layer, or to the material properties of the dam and foundation layer. However, for the limited number of cases investigated, the interaction effects were found to be uniquely related to the ratio D/B, where D is the depth of the foundation layer and B is the width of the dam section. For values of D/B less than unity, strong interaction effects were obtained and the dam-foundation system could only be analysed as a coupled system. For values of D/B greater than unity, the interaction appeared negligible and the dam and its foundation layer could be decoupled. It should be noted, however, that for very small values of D/B the interaction effects would decrease becaase as D approaches zero, there would be no interaction The use of the interaction ratio, R₁, and the parameter D/B should aid in assessing the need for analysing the response of the dam-foundation as a coupled or as a decoupled system.     

Remote sensing analysis of desert vegetation and its landscape changes: The case in middle reaches of Tarim River Basin,Xinjiang, China

Based on remote sensing information sources including B/W aerial photos of 1983, pseudo-color aerial photos of 1992 and JERS-1/OPS VNIR image of 1996, vegetation types of Yingbazha, in the middle reaches of the Tarim River Basin in Xinjiang, China are mapped using ARC/INFO and related software. The changes in vegetation areas and distribution conditions are analyzed. As a result of natural and human influences, vegetation changes have temporal and spatial characteristics. According to the principles of landscape ecology and geographical information science, the landscape changes are indicated. Moreover, the remote sensing and GIS techniques are integrated to study vegetation and its landscape.     

Factors driving riverbed scouring and sedimentation in the Bayangaole to Toudaoguai reaches of the Upper Yellow River

The Inner Mongolia reaches of the Yellow River face problems of severe sedimentation caused by a variety of complex factors. The sedimentation process in those reaches has been characterized using the sediment balance method, and the key factors affecting the process have been analyzed using the correlation analysis method. The results show that during the period 1952–2012 the Bayangaole (Bayan Gol) to Toudaoguai reaches in Inner Mongolia have undergone successive processes of accumulative sedimentation, then relative balance, and then accumulative sedimentation once again. The total annual sedimentation is 12.0341×10⁸ m³, of which accumulations from July to October account for 95.1% and the reaches from Sanhuhekou to Toudaoguai account for 98.5%. The main factor affecting scouring and sedimentation of the Bayangaole to Sanhuhekou reaches is the combined water and sediment condition. The critical conditions for equilibrium are an incoming sediment coefficient < 0.007 kg·s·m^–6 and a flow discharge > 700 m³·s^–1. The main factor affecting scouring and sedimentation of the Sanhuhekou to Toudaoguai reaches is the incoming sediment from the tributaries on the south bank and the combined water and sediment condition of the main stream. The critical conditions of the main stream for maintaining equilibrium status are a flow discharge of the main stream exceeding 800 m³·s^–1 and a comprehensive incoming sediment coefficient < 0.005 kg·s·m^–6. The incoming sediment from the tributaries has little impact on the main stream when the annual sediment load is less than 0.1×10⁸ t. The incoming sediment coefficient of the main stream and the incoming sediment from the tributaries both play vital roles in the riverbed evolution of the Inner Mongolia reaches, but the latter contributes the most.     

Identification and delineation of saline soils using aerial photographs in Yamuna Alluvial plain,Haryana

Salinity is creating great problems in the Yamuna Alluvial Plain. State Government is taking steps for reclaiming these lands to increase agricultural production. Impeded drainage, excess canal irrigation, topography parent material, shallow depth and bad quality of ground water are the main factors which are responsible for the genesis of saline soils in the alluvial plains of Haryana. On the arial photographs tonal differences on account of salt concentration in the soil are clearly seen. These differences are aslo associated with physiography and soil conditions which can be easily delineated. The information thus; collected can be used for reclamation of saline soils.     

Lake-Sediment Records of Recent Environmental Change on Svalbard: Results of Diatom Analysis

Surface sediments from 23 lakes on Svalbard were analysed for diatoms. About 182 taxa were found but samples generally have a low richness, with the majority of sites dominated by benthic genera such as Fragilaria, Navicula, and Achnanthes. Centric Cyclotella species occur at only three sites. Modern relationships between diatom abundance and water chemistry and other environmental variables were explored numerically and a preliminary transfer function for pH was developed. Lakes fell into three groups on the basis of their diatom assemblages: (1) high pH, high cation, high conductivity sites characterised by Amphora libyca, (2) shallow sites with relatively high nutrient values characterised by Fragilaria species, and (3) more acid and dilute sites with high amounts of snow cover in the catchments characterised by small Achnanthes species and Navicula digitulus. Five sediment cores representing the recent past were also analysed for diatoms. Three shallow sites were dominated by Fragilaria species throughout the period represented by the cores and no shifts in inferred pH were found. At two deeper sites (Arresjøen, Birgervatnet) major assemblage shifts are found which are unrelated to independent evidence for atmospheric contamination. Early (ca. 1200 AD) changes found at both sites are possibly related to the onset of the ‘Little Ice Age’. Later changes are neither synchronous nor similar in nature and might be best explained as individual responses to the recovery from the ‘Little Ice Age’ and subsequent climatic warming.     

Natural background levels and threshold values for groundwater in fluvial Pleistocene and Tertiary marine aquifers in Flanders,Belgium

Aquifers from the same typology can have strongly different groundwater chemistry. Deducing the groundwater quality of less well-characterized aquifers from well-documented aquifers belonging to the same typology should be done with great reserve, and can only be considered as a preliminary approach. In the EU’s 6th FP BRIDGE project “Background cRiteria for the IDentification of Groundwater thrEsholds”, a methodology for the derivation of threshold values (TV) for groundwater bodies is proposed. This methodology is tested on four aquifers in Flanders of the sand and gravel typology. The methodology works well for all but the Ledo-Paniselian aquifer, where the subdivision into a fresh and saline part is disproved, as a gradual natural transition from fresh to saline conditions in the aquifer is observed. The 90 percentile is proposed as natural background level (NBL) for the unconfined Pleistocene deposits, ascribing the outliers to possible influence of pollution. For the Tertiary aquifers, high values for different parameters have a natural origin and the 97.7 percentile is preferred as NBL. The methodology leads to high TVs for parameters presenting low NBL, when compared to the standard used as a reference. This would allow for substantial anthropogenic inputs of these parameters.