Analyzing distortion in ASDMs with loop delay

Recently nearly exact expressions for the distortion in a commonly used family of Pulse Width Modulators (PWMs) known as Asynchronous Sigma Delta Modulators (ASDMs) were presented. Such an ASDM consists of a feedback loop with a schmitt-trigger (or a comparator), and a continuous time loop filter. However these previous results are not yet practically applicable because the effect of unavoidable loop delay (e.g. in the schmitt trigger) was not taken into account. Therefore we now present a more general theory that is also valid when there is a nonzero loop delay. A comparison of the resulting equations with computer simulations demonstrated a very good matching, confirming the validness of the theory. This way, a designer can now easily understand the relationship between the loop filter dynamics and the linearity of an ASDM

Design of a low-voltage op-amp-less ASDM to linearise VCO-ADC

A very simple asynchronous sigma delta modulator design for linearisation of VCO ADC's is presented. The circuit only consists of a passive feedback filter and a Schmitt Trigger. By proper sizing, the non-linearity error can be reduced to well below 0.12% for input signals that go almost rail-to-rail. The design has been manufactured in the low power version of TSMC 65 nm technology and was measured at a 1 V power supply

Expression of renal distal tubule transporters TRPM6 and NCC in a rat model of cyclosporine nephrotoxicity and effect of EGF treatment

Renal magnesium (Mg(2+)) and sodium (Na(+)) loss are well-known side effects of cyclosporine (CsA) treatment in humans, but the underlying mechanisms still remain unclear. Recently, it was shown that epidermal growth factor (EGF) stimulates Mg(2+) reabsorption in the distal convoluted tubule (DCT) via TRPM6 (Thebault S, Alexander RT, Tiel Groenestege WM, Hoenderop JG, Bindels RJ. J Am Soc Nephrol 20: 78-85, 2009). In the DCT, the final adjustment of renal sodium excretion is regulated by the thiazide-sensitive Na(+)-Cl(-) cotransporter (NCC), which is activated by the renin-angiotensin-aldosterone system (RAAS). The aim of this study was to gain more insight into the molecular mechanisms of CsA-induced hypomagnesemia and hyponatremia. Therefore, the renal expression of TRPM6, TRPM7, EGF, EGF receptor, claudin-16, claudin-19, and the NCC, and the effect of the RAAS on NCC expression, were analyzed in vivo in a rat model of CsA nephrotoxicity. Also, the effect of EGF administration on these parameters was studied. CsA significantly decreased the renal expression of TRPM6, TRPM7, NCC, and EGF, but not that of claudin-16 and claudin-19. Serum aldosterone was significantly lower in CsA-treated rats. In control rats treated with EGF, an increased renal expression of TRPM6 together with a decreased fractional excretion of Mg(2+) (FE Mg(2+)) was demonstrated. EGF did not show this beneficial effect on TRPM6 and FE Mg(2+) in CsA-treated rats. These data suggest that CsA treatment affects Mg(2+) homeostasis via the downregulation of TRPM6 in the DCT. Furthermore, CsA downregulates the NCC in the DCT, associated with an inactivation of the RAAS, resulting in renal sodium loss

Analyzing the effect of clock jitter on self-oscillating sigma delta modulators

This paper presents simple but accurate expressions for the noise components caused by clock jitter, in the output signal of self-oscillating sigma delta modulators (SOSDM). Contrary to conventional continuous time sigma delta modulators (CTSDM), the SOSDM's loop contains a strong oscillation, whose attribution to the system's jitter caused noise has not previously been explored. In this paper, the SOSDM system is modeled, and the effect of the self oscillation, the input signal and the quantization noise on the jitter caused noise in the output signal, is calculated. Results are confirmed by system level simulations

Eddy Kovarianz Gastransfermessungen. Regionale Quellen und Limitierungen

Eddy covariance is a technique to measure air-sea gas exchange directly. A direct flux measurement has the advantage that, without parameterizations or major simplifications of processes. Section 3 focuses on the efflux of these aerosol predecessors together with aerosol numbers in the atmosphere. The oceanic emissions are tracked using the FLEXPART forward trajectory model, which provides the locations and the times for the satellite remote sensing. The averaged satellite aerosol numbers along the 12 h downwind trajectory were correlated with the magnitude of the oceanic sources, which was found to be a significant positive correlation. The results point to a local influence of air-sea fluxes on the aerosol number, which could give rise to local feedbacks. My investigation in Section 4 uses gas transfer velocities derived from DMS and CO2 eddy covariance measurements to describe gas transfer limitations which is caused by a wind-wave interaction. This process is parameterized using the transformed Reynolds number Retr. Below a threshold of |Retr| <6.7·105, flow separation develops at the wave’s lee side and causes a decoupling between the flow above the wave and the ocean surface. The gas exchange is then highly likely to be suppressed. In Section 5, the impact of gas transfer limitation on gas transfer parameterizations and global climatologies of DMS and CO2 is calculated. The data sets of two highly cited gas transfer parameterizations are investigated with respect to gas transfer limitation. Based on these algorithms the Nightingale 2000 parameterization is found to be heavily gas transfer limited and its gas transfer velocity will increase on average by 22% if the correction is applied. The Wanninkhoff 2014 parameterization increases by 9.85% after correction. The correction is applied to the global air-sea flux climatologies of DMS and CO2 for the year 2014.Die Eddy-Kovarianz-Methode ist eine Technik zur direkten Messung des Gasaustauschs zwischen Atmosphäre und Ozean. DMS, Isopren und Gischt sind in der marinen Atmosphäre Ausgangsstoffe für Schwefelaerosole, sekundäre organischen Aerosole und primäre organische/anorganische Aerosole. In Kapitel 3 wird der Einfluss dieser Aerosolquellen auf Aerosolkonzentrationen in der Atmosphäre untersucht. Die Emissionen werden mit Hilfe des FLEXPART-Transportmodells in Windrichtung verfolgt. Die gemittelten Aerosolkonzentrationen entlang der Trajektorie wurden dann mit der Größe der Quelle korreliert. Die Ergebnisse deuten auf einen lokalen Einfluss des Gasaustauschs auf die Aerosolkonzentration hin. Der Gasaustausch zwischen Atmosphäre und Ozean kann durch die Gasaustauschgeschwindigkeit k beschrieben und modelliert werden. Diese Geschwindigkeit k ist normalerweise von der Windgeschwindigkeit anhängig und bezogen auf diese monoton ansteigend. Messungen haben gezeigt, dass die Relation zwischen k und Windgeschwindigkeit bei mittlerer bis hoher Windgeschwindigkeit jedoch abnehmen kann. In Kapitel 4 werden Gasaustauschgeschwindigkeiten verwendet um einen Prozess zu beschreiben, der eine Begrenzung des Gastransfers bewirkt. Dieser Prozess ist eine Wind-Wellen-Interaktion und wird mit Hilfe der transformierten Reynoldszahl Retr beschrieben. In Kapitel 5 wird die Auswirkungen der Limitierung des Gasaustausches auf den Gasaustausch von globalen DMS und CO2 Klimatologien berechnet. Zwei häufig verwendete Parametrisierungen des Gasaustauschs werden auf das Auftreten von Limitierung in Ihren Datensätzen untersucht. Basierend auf diesen Berechnungen sind die Nightingale 2000 und die Wanninkhoff 2014 Parametrisierungen einer sehr starken Limitierung ausgesetzt. Der Korrekturalgorithmus für das Jahr 2014 wird dann auf die globalen Klimatologien von DMS und CO2 angewendet

Eddy covariance air-sea gas flux measurements: Regional sources and gas transfer limitation

Eddy covariance is a technique to measure air-sea gas exchange directly. A direct flux measurement has the advantage that, without parameterizations or major simplifications of processes. Section 3 focuses on the efflux of these aerosol predecessors together with aerosol numbers in the atmosphere. The oceanic emissions are tracked using the FLEXPART forward trajectory model, which provides the locations and the times for the satellite remote sensing. The averaged satellite aerosol numbers along the 12 h downwind trajectory were correlated with the magnitude of the oceanic sources, which was found to be a significant positive correlation. The results point to a local influence of air-sea fluxes on the aerosol number, which could give rise to local feedbacks. My investigation in Section 4 uses gas transfer velocities derived from DMS and CO2 eddy covariance measurements to describe gas transfer limitations which is caused by a wind-wave interaction. This process is parameterized using the transformed Reynolds number Retr. Below a threshold of |Retr| <6.7·105, flow separation develops at the wave’s lee side and causes a decoupling between the flow above the wave and the ocean surface. The gas exchange is then highly likely to be suppressed. In Section 5, the impact of gas transfer limitation on gas transfer parameterizations and global climatologies of DMS and CO2 is calculated. The data sets of two highly cited gas transfer parameterizations are investigated with respect to gas transfer limitation. Based on these algorithms the Nightingale 2000 parameterization is found to be heavily gas transfer limited and its gas transfer velocity will increase on average by 22% if the correction is applied. The Wanninkhoff 2014 parameterization increases by 9.85% after correction. The correction is applied to the global air-sea flux climatologies of DMS and CO2 for the year 2014

Asynchronous Representation and Processing of Analog Sparse Signals Using a Time-Scale Framework

In this dissertation we investigate the problem of asynchronous representation and processing of analog sparse signals using a time-scale framework. Recently, in the design of signal representations the focus has been on the use of application-driven constraints for optimality purposes. Appearing in many fields such as neuroscience, implantable biomedical diagnostic devices, and sensor network applications, sparse or burst--like signals are of great interest. A common challenge in the representation of such signals is that they exhibit non--stationary behavior with frequency--varying spectra. By ignoring that the maximum frequency of their spectra is changing with time, uniformly sampling sparse signals collects samples in quiescent segments and results in high power dissipation. Also, continuous monitoring of signals challenges data acquisition, storage, and processing; especially if remote monitoring is desired, as this would require that a large number of samples be generated, stored and transmitted. Power consumption and the type of processing imposed by the size of the devices in the aforementioned applications has motivated the use of asynchronous approaches in our research. First, we work on establishing a new paradigm for the representation of analog sparse signals using a time-frequency representation. Second, we develop a scale-based signal decomposition framework which uses filter-bank structures for the representation-analysis-compression scheme of the sparse information. Using an asynchronous signal decomposition scheme leads to reduced computational requirements and lower power consumption; thus it is promising for hardware implementation. In addition, the proposed algorithm does not require prior knowledge of the bandwidth of the signal and the effect of noise can still be alleviated. Finally, we consider the synthesis step, where the target signal is reconstructed from compressed data. We implement a perfect reconstruction filter bank based on Slepian wavelets to use in the reconstruction of sparse signals from non--uniform samples. In this work, experiments on primary biomedical signal applications, such as electrocardiogram (EEG), swallowing signals and heart sound recordings have achieved significant improvements over traditional methods in the sensing and processing of sparse data. The results are also promising in applications including compression and denoising

Course Manual Winter School on Structure and Functions of Marine Ecosystem: Fisheries

Marine ecosystems comprises of diverse organisms and their ambient abiotic components in varied relationships leading to an ecosystem functioning. These relationships provides the services that are essential for marine organisms to sustain in the nature. The studies examining the structure and functioning of these relationships remains unclear and hence understanding and modelling of the ecological functioning is imperative in the context of the threats different ecosystem components are facing. The relationship between marine population and their environment is complex and is subjected to fluctuations which affects the bottom level of an ecosystem pyramid to higher trophic levels. Understanding the energy flow within the marine ecosystems with the help of primary to secondary producers and secondary consumers are potentially important when assessing such states and changes in these environments. Many of the physiological changes are known to affect the key functional group, ie. the species or group of organisms, which play an important role in the health of the ecosystem. In marine environment, phytoplankton are the main functional forms which serves as the base of marine food web. Any change in the phytoplankton community structure may lead to alteration in the composition, size and structure of the entire ecosystem. Hence, it is critical to understand how these effects may scale up to population, communities, and entire marine ecosystem. Such changes are difficult to predict, particularly when more than one trophic level is affected. The identification and quantification of indicators of changes in ecosystem functioning and the knowledge base generated will provide a suitable way of bridging issues related to a specific ecosystem. New and meaningful indicators, derived from our current understanding of marine ecosystem functioning, can be used for assessing the impact of these changes and can be used as an aid in promoting responsible fisheries in marine ecosystems. Phytoplantkon is an indicator determining the colour of open Ocean. In recent years, new technologies have emerged which involves multidisciplinary activities including biogeochemistry and its dynamics affecting higher trophic levels including fishery. The winter school proposed will provide the insights into background required for such an approach involving teaching the theory, practical, analysis and interpretation techniques in understanding the structure and functioning of marine ecosystems from ground truth measurements as well as from satellite remote sensing data. This is organized with the full funding support from Indian council of Agricultural Research (ICAR) New Delhi and the 25 participants who are attending this programme has been selected after scrutiny of their applications based on their bio-data. The participants are from different States across Indian subcontinent covering north, east, west and south. They are serving as academicians such as Professors/ scientists and in similar posts. The training will be a feather in their career and will enable them to do their academic programmes in a better manner. Selected participants will be scrutinized initially to understand their knowledge level and classes will be oriented based on this. In addition, all of them will be provided with an e-manual based on the classes. All selected participants are provided with their travel and accommodation grants. The faculty include the scientists who developed this technology, those who are practicing it and few user groups who do their research in related areas. The programme is coordinated by the Fishery Resources Assessment Division of CMFRI. This programme will generate a team of elite academicians who can contribute to sustainable management of marine ecosystem and they will further contribute to capacity building in the sector by training many more interested researchers in the years to come