Search results for "Oscillation"

Methods for Transient Expression of Hetero-Oligomeric Ligand-Gated Ion Channels

2003

Recurrent daily rainfall patterns over South Africa and associated dynamics during the core of the austral summer

2010

This paper investigates the influence of some modes of climate variability on the spatio-temporal rainfall variability over South Africa during the core of the rainy season, December to February (DJF). All analyses are based directly on the rainfall field instead of atmospheric processes and dynamics. An original agglomerative hierarchical clustering approach is used to classify daily rainfall patterns recorded at 5352 stations from DJF 1971 to DJF 1999. Five clusters are retained for analysis. Amongst them, one cluster looks most like the rainfall and circulation mean picture. Another one, representing 37% of the days, describes strong negative rainfall anomalies over South Africa resultin…

Inter-Relationships Between Groundnut Yield in Senegal, Interannual Rainfall Variability and Sea-Surface Temperatures

1999

Groundnut production strongly contributes to Senegal’s economy. Interannual variations of groundnut yield for the country as a whole, and their relationship with rainfall amounts, are examined for the 31-yr period 1960–1990. It is shown that on that scale, and after removing decadal trends, almost half of the variance is explained by rainfall variability, especially that of the early part of the rainy season (July–August). Given the high spatial coherence of seasonal rainfall in the region, teleconnections with global- and regional-scale climate dynamics, including sea-surface temperatures, are assessed. Though some features are similar to the rest of the Sahel, others are more specific, su…

Comparison of rainfall structures between NCEP/NCAR reanalyses and observed data over tropical Africa

2000

A comparison is made between modelled (NCEP/NCAR reanalysis) and observed (CRC and CRU dataset) annual and monthly precipitation over tropical Africa during the period 1958–1997. The split moving-windows dissimilarity analysis (SMWDA) is used to locate abrupt changes in rainfall time series. In the NCEP reanalysis data, we identify a main abrupt shift, which occurs in 1967 and concerns more than 50% of grid points. In the observation, this shift is only found over parts of tropical North Africa. Three other NCEP abrupt shifts (1975, 1983 and 1987) in the reanalysis shown by the SMWDA, each concerning about 20% of tropical Africa, are not identified in the observation. One hypothesis concern…

WING FLUTTER SUPPRESSION ENHANCEMENT USING A WELL-SUITED ACTIVE CONTROL MODEL

2007

State-space theory is employed here to model a new active wing flutter suppression control. In this paper, the design of a flutter suppression control law, for the NASA Benchmark Active Control Technology wing, is proposed through a single input-single output controller and unsteady aerodynamics is modelled using the Theodorsen's theory. Wing dynamic model is obtained by combining the aeroelastic equations of motion with the actuator model presented. Open-loop dynamic behaviour is examined for a single feedback variable that combines pitch and plunge accelerations. Here, a new formulation of control law, based on classical control techniques and featuring two feedback closed-loops, is succ…

Contribution of mode coupling and phase-mixing of Alfv\'en waves to coronal heating

2017

This research has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 647214) and from the UK Science and Technology Facilities Council. This work used the DiRAC Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk. This equipment was funded by a BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/K00087X/1, DiRAC Operations grant ST/K003267/1 and Durham University. Context. Phase-mixing of Alfvén waves in the solar corona has been identified as one possible candid…

Experimental and Numerical Study on Linear Friction Welding of AA2011 Aluminum Alloy

2014

Linear Friction Welding (LFW) is a solid-state joining process used for non-axisymmetric components. LFW involves joining of materials through the relative motion of two components undergoing an axial force. In the process, the heat source is given by the frictional forces work decaying into heat and determining a local softening of the material and eventually the needed bonding conditions. In the paper, an experimental and numerical campaign is proposed for AA2011 aluminum alloys welding. Different case studies are considered with fixed oscillation frequency and varying pressure at the interface between the specimens. Constant oscillation amplitude and specimens geometry is used. The calcu…

Experimental characterization of a novel configuration of thermoelectric refrigerator with integrated finned heat pipes

2021

Abstract Thermoelectric refrigerating systems (TER) are environment-friendly technologies. They have several advantages such as low maintenance costs, are less cumbersome and long lifetime. However, these systems have low coefficient of performance and are limited in achieving low temperature levels. This study investigates a new configuration of TE refrigerator employing a novel arrangement of heat sinks with integrated flat and finned heat pipes. A mathematical model is firstly developed to predict transient temperatures and cooling limit time. An experimental characterization is then performed and it includes optimization of energy consumption, cooling time, temperature levels and TE ref…

Non-uniform Sediment Transport Estimation in Non-equilibrium Situations: Case Studies

2014

Abstract Quantitative estimate of sediment transport in alluvial channels is one of the most important task in river engineering. Even today, numerical models of sediment transport processes are confronted with some difficulties, often of conceptual nature. One of these difficulties is the simulation of non-uniform sediment transport in non-equilibrium situations, which requires the characterization of the ability of the alluvial system to immediately overcome the variations of the sediment boundary conditions. In this work a 1-D numerical model, which includes a new expression of the so-called “adaptation coefficient”, has been applied to test its capability to simulate the transient bed p…

An experimental analysis of self-Q-switching via stimulated Brillouin scattering in an ytterbium doped fiber laser

2013

An experimental study of self-Q-switching (SQS) in an ytterbium doped fiber laser (YDFL) arranged using a twin-core GTWave assembly is reported. The main mechanisms that initiate, amplify, and limit SQS pulses in amplitude are revealed to be stimulated Brillouin and Raman scattering (SBS/SRS) and Yb3+ amplified spontaneous emission. The parameters featuring SQS oscillation in terms of efficiency and stability of pulsing are found to be intra-cavity loss and feedback strength. An analysis of the YDFL SQS regime?s features?pulsing time series, optical and RF spectra, amplitude and timing jitter?is provided for the two experimental situations: (i) when SQS pulsing stochastically intermits with…