Delineating groundwater-surface water exchange flux using temperature-time series analysis methods

Groundwater-surface water interactions can play a crucial role in river-, riparian and wetland management. Their delineation and quantification at various spatial and temporal scales has become an important aspect in the study of contaminant transport and attenuation processes at the groundwater-surface water interface. One of the main parameters of interest is the groundwater-surface water exchange flux, which provides indications regarding stream-aquifer connectivity, the local flow regime as well as hydrogeological properties of the streambed. One of the methods to assess vertical exchange flux is through the analysis of temperature time-series. In this paper we delineate vertical exchange flux from temperature-time series collected at a Belgian River by comparing established numerical and analytical techniques with a novel approach. Results indicate a spatial variability of vertical fluxes over two orders of magnitude at the site

Multirate cascaded discrete-time low-pass ΔΣ modulator for GSM/Bluetooth/UMTS

This paper shows that multirate processing in a cascaded discrete-time ΔΣ modulator allows to reduce the power consumption by up to 35%. Multirate processing is possible in a discrete-time ΔΣ modulator by its adaptibility with the sampling frequency. The power reduction can be achieved by relaxing the sampling speed of the first stage and increasing it appropriately in the second stage. Furthermore, a cascaded ΔΣ modulator enables the power efficient implementation of multiple communication standards.@The advantages of multirate cascaded ΔΣ modulators are demonstrated by comparing the performance of single-rate and multirate implementations using behavioral-level and circuit-level simulations. This analysis has been further validated with the design of a multirate cascaded triple-mode discrete-time ΔΣ modulator. A 2-1 multirate low-pass cascade, with a sampling frequency of 80 MHz in the first stage and 320 MHz in the second stage, meets the requirements for UMTS. The first stage alone is suitable for digitizing Bluetooth and GSM with a sampling frequency of 90 and 50 MHz respectively. This multimode ΔΣ modulator is implemented in a 1.2 V 90 nm CMOS technology with a core area of 0.076 mm2. Measurement results show a dynamic range of 66/77/85 dB for UMTS/ Bluetooth/GSM with a power consumption of 6.8/3.7/3.4 mW. This results in an energy per conversion step of 1.2/0.74/2.86 pJ