307 research outputs found
Catchment travel time distributions and water flow in soils
No full textMany details about the flow of water in soils in a hillslope are unknowable given current technologies. One way of learning about the bulk effects of water velocity distributions on hillslopes is through the use of tracers. However, this paper will demonstrate that the interpretation of tracer information needs to become more sophisticated. The paper reviews, and complements with mathematical arguments and specific examples, theory and practice of the distribution(s) of the times water particles injected through rainfall spend traveling through a catchment up to a control section (i.e., “catchment” travel times). The relevance of the work is perceived to lie in the importance of the characterization of travel time distributions as fundamental descriptors of catchment water storage, flow pathway heterogeneity, sources of water in a catchment, and the chemistry of water flows through the control section. The paper aims to correct some common misconceptions used in analyses of travel time distributions. In particular, it stresses the conceptual and practical differences between the travel time distribution conditional on a given injection time (needed for rainfall‐runoff transformations) and that conditional on a given sampling time at the outlet (as provided by isotopic dating techniques or tracer measurements), jointly with the differences of both with the residence time distributions of water particles in storage within the catchment at any time. These differences are defined precisely here, either through the results of different models or theoretically by using an extension of a classic theorem of dynamic controls. Specifically, we address different model results to highlight the features of travel times seen from different assumptions, in this case, exact solutions to a lumped model and numerical solutions of the 3‐D flow and transport equations in variably saturated, physically heterogeneous catchment domains. Our results stress the individual characters of the relevant distributions and their general nonstationarity yielding their legitimate interchange only in very particular conditions rarely achieved in the field. We also briefly discuss the impact of oversimple assumptions commonly used in analyses of tracer data
EMG of Electrically Stimulated Muscles
No full textThis chapter addresses stimulation techniques, the issue of the stimulation electrode positioning, motor unit (MU) activation order, and spinal involvement in electrically elicited contractions. Two stimulation techniques are commonly used: bipolar, and monopolar stimulation. The differences between these two methods concern the geometry and relative position of the stimulation electrodes. Surface electromyography (sEMG) signals can be detected during selective electrical stimulation of a nerve branch or of a motor point of a muscle. The resultant sEMG signal is a compound motor action potential (CMAP), also termed as M-wave. Since the M-wave represents the sum of the potentials of the concurrently activated MUs, its change is generally assumed to reflect changes either in the number or in the sarcolemmal properties of activated MUs. Neuromuscular electrical stimulation (NMES) combined with sEMG isolates the contributions of peripheral fatigue because it gives the experimenter control of MU firing frequency and recruitment
Sensitivity of Regulated Streamflow Regimes to Interannual Climate Variability
No full textThe simultaneous growth in climate‐driven alterations of the hydrologic cycle and global freshwater demand threatens the security of anthropogenic and ecologic uses of streamflows. However, the impact of damming on the response of river regimes to long‐term climate variability has not been fully disclosed yet. Here, this issue is assessed by investigating temporal patterns in the occurrence probability of different flow ranges upstream and downstream of a selection of dams in the Central‐Eastern United States. We found that long‐term fluctuations of low flows are propagated unaltered from unregulated to regulated regimes. In the majority of cases, the same applies to the entire spectrum of streamflows, although discharge interannual variability is significantly amplified by large multipurpose structures. Water supply dams instead smooth long‐term streamflow fluctuations, though at the cost of systematically filtering out medium‐to‐high discharges. Accordingly, in Central‐Eastern United States, dams are unable to mitigate the sensitivity of flow regimes to long‐term hydroclimatic fluctuations and, thus, do not support the security of anthropogenic and ecologic uses of regulated streamflows
Climatic signatures in regulated flow regimes across the Central and Eastern United States
No full textStudy region: 42 catchments distributed throughout Central and Eastern U.S. Study focus: Enhanced hydroclimatic variability threatens human water uses, and there is an urgent need to quantify projected alterations of flow regimes. This issue has been largely addressed in unregulated rivers through the development of similarity frameworks relating climate properties with the hydrologic response of catchments. However, the impact of damming on climate signatures of river flow regimes is largely unexplored. To fill this gap, this study investigates unregulated streamflows of a selection of sites using a climate-based similarity framework. Then, the corresponding regulated regimes are analyzed to understand how the obtained regime classification is affected by regulation. New hydrological insights for the region: Our results reveal that flood control dams retain but dampen climate signatures of flow regimes, reducing the regional heterogeneity of downstream hydrographs. Conversely, in the study area, urban water supply structures promote climate-independence of river regimes and tend to break the link between climate and river flows, thereby promoting the spatial diversification of the hydrologic response. The observed impact of each specific water use is explained based on quantitative indexes that relates to the regulation capacity of reservoirs and their degree of exploitation. Overall, climatic signatures are still detectable in most regulated streamflows, though climatic control on river regimes is largely concealed by the profound hydrological alterations induced by dams
Rheological properties of silica and kaolin dispersions in mineral paraffinic oil: effect of water films adsorbed on the solid particles
No full textDecomposition-sintering dilatometer method to study the effect of limestone impurities on lime microstructure
No full textMetodo dilatometrico di decomposizione-sinterizzazione per lo studio degli effetti delle impurezze presenti nelle rocce carbonatiche sulla microstruttura della calcite prodotta
No full textDetection and Conditioning of Surface EMG Signals
No full textThis chapter presents the detection and conditioning of surface electromyographic (EMG) signals. More advanced techniques are now widely used in research laboratories and are being adopted in clinical settings. Such techniques are based on multichannel detection by means of one dimensional (1-D) or two dimensional (2-D) electrode arrays. The chapter describes the electrode-skin interface and the front-end amplifier stage. The impedance between two electrodes is the sum of two electrode-skin impedances plus the interposed tissue impedance. Conventional electrodes, either wet or dry, behave like transducers converting ionic current (in tissue and gel) into flow of electrons in the metal. These electrical sensors require a careful skin preparation to reduce the impedance and noise associated to this interface. The biomedical sector offers small-sized, high-cost application-specific integrated circuits (ASIC) devices for biopotential measurements. Applications are expected to range from physiopathological investigations, to rehabilitation games, biofeedback applications, and sport training
Production and characterisation of pellets from rice straw and rice husk
No full textResidues from rice harvest (i.e. straw and husk) were pelletised and the main properties of the products were evaluated. Pellets were produced in a commercial pelletiser with a maximum capacity of 200 kg/h from the local company Nova Pellet (Novara, Italy). The feedstock was collected from a nearby farm and left to air dry. No ligand was necessary as moisture of biomass was in the range 10–14%. The samples were characterized in terms of their physical, chemical and physico-chemical properties. In addition, their mechanical performance was assessed by means of axial and diametral compression tests and durability tests. All the analysed properties were compared with the established quality standards for non woody pellets. In general, rice straw pellets presented better properties with all their parameters falling into the quality standards. On the contrary, rice husk pellets fell out of the standards in several tests such as recommended size or durability. For this reason, rice straw pellets were found suitable for their use as fuels whereas the use of rice husk pellets was recommended for other applications as for example adsorbent agents
Variability in the Shape of the Active Length–Streamflow Relationship in Temporary Streams: Insights From an Empirical Analysis
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