Study of the generator/motor operation of induction machines in a high frequency link space power system

Static power conversion systems have traditionally utilized dc current or voltage source links for converting power from one ac or dc form to another since it readily achieves the temporary energy storage required to decouple the input from the output. Such links, however, result in bulky dc capacitors and/or inductors and lead to relatively high losses in the converters due to stresses on the semiconductor switches. The feasibility of utilizing a high frequency sinusoidal voltage link to accomplish the energy storage and decoupling function is examined. In particular, a type of resonant six pulse bridge interface converter is proposed which utilizes zero voltage switching principles to minimize switching losses and uses an easy to implement technique for pulse density modulation to control the amplitude, frequency, and the waveshape of the synthesized low frequency voltage or current. Adaptation of the proposed topology for power conversion to single-phase ac and dc voltage or current outputs is shown to be straight forward. The feasibility of the proposed power circuit and control technique for both active and passive loads are verified by means of simulation and experiment

Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film

We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential transmission experiments were done using 80 fs laser pulses centered at 395 nm and 790 nm on gold clusters encased inside cyclodextrin cavities. We show that two photon absorption coefficient is enhanced by an order of magnitude as compared to that when the clusters are on pristine glass plate. The enhancement for the nonlinear optical refraction coefficient is ~3 times. The photo-induced excited state absorption using pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also show an enhancement by an order of magnitude. These results attributed to the excited state energy transfer in the coupled gold cluster-ITO system are different from the enhancement seen so far in charge donor-acceptor complexes and nanoparticle-conjugate polymer composites.Comment: To appear in Optics Express (2013); http://dx.doi.org/10.1364/OE.21.00848

Yield and Yield Component Development in Dual-Purpose Barley

Barley (Hordeum vulgare L.) is a widely adapted small-grain annual cereal and is a key feed and fodder in India (Kharub et al., 2013). Barley can provide nutrition to the animals through its green fodder at vegetative stage and grains after harvest from the regenerated plants. The vegetative portion of the crop is valuable as a source of pasture, cut green forage, and straw. Their relative importance is determined at different ontogenetic stages of plant. An area of barley breeding receiving increasing attention is the development of dual-purpose (green forage and grain) varieties for plains as well as hills. Up to certain yield level grain yield and vegetative yield are correlated, difficulty may arrive when attempts will be made to combine maximum grain yield with maximum forage yield. Objectives of this study was to compare yield and yield development component in barley cut 55-60 days after sowing (DAS) and harvested after regeneration at maturity

Estimation of Columbia River Virgin Flow: 1879 to 1928

The Columbia River has historically been a major source of economic activity for the Pacific Northwest, and is one of the more heavily modified rivers in the United States today. Understanding human and climate-induced changes in its hydrologic properties is, therefore, a topic of considerable interest. Long streamflow records are essential to determining how runoff has changed over time. Daily streamflow records of the Columbia River at The Dalles dates back to June 1978. However, the observed daily flow does not alone provide enough information to understand or separate anthropogenic and climate effects. It is necessary also to have an estimate of virgin flow of the river to provide a historical perspective of water resources development, separate anthropogenic and climate effects, and compare present water use scenarios with those of the past decades. The United State Geological Survey (USGS) has calculated a monthly averaged adjusted river flow at The Dalles for 1879-1999 that accounts for the effects of flow regulation. The Bonneville Power Administration (BPA) has estimated the monthly averaged virgin (or naturalized) flow at The Dalles, i.e., the flow in the absence of both flow regulation and irrigation depletion for 1929-89. We have estimated the monthly virgin flow of the Columbia River at The Dalles from records of irrigated area for the missing years, i.e., for the period 1879-1928. In addition, a filtered version of the daily observed flows were combined with monthly virgin flow corrections to obtain estimates of daily virgin flows with realistic higher moments and spectral properties. Examination of the virgin flow record shows that climate change since late 19th century has caused a decrease of \u3e7% in its annual average flow volume. The decrease in flow due to irrigation diversion during the same period is also ~7%. Broadly speaking, there are three periods of Columbia River flow management. Before 1900, mainstem dams were absent and flow diversions relatively small. Numerous dams were constructed between 1900 and 1970, and irrigation depletion increased 500%. Since about 1970, river flows have been managed on a system-wide basin, effecting significant interannual transfers of flows for the first time

Nonlinear control of magnetic bearings

In this paper we present a variety of nonlinear controllers for the magnetic bearing that ensure both stability and robustness. We utilize techniques of discontinuous control to design novel control laws for the magnetic bearing. We present in particular sliding mode controllers, time optimal controllers, winding algorithm based controllers, nested switching controllers, fractional controllers, and synchronous switching controllers for the magnetic bearing. We show existence of solutions to systems governed by discontinuous control laws, and prove stability and robustness of the chosen control laws in a rigorous setting. We design sliding mode observers for the magnetic bearing and prove the convergence of the state estimates to their true values. We present simulation results of the performance of the magnetic bearing subject to the aforementioned control laws, and conclude with comments on design

Modelling and control of a rotor supported by magnetic bearings

In this paper we develop a dynamical model of a rotor and the active magnetic bearings used to support the rotor. We use this model to develop a stable state feedback control of the magnetic bearing system. We present the development of a rigid body model of the rotor, utilizing both Rotation Matrices (Euler Angles) and Euler Parameters (Quaternions). In the latter half of the paper we develop a stable state feedback control of the actively controlled magnetic bearing to control the rotor position under inbalances. The control law developed takes into account the variation of the model with rotational speed. We show stability over the whole operating range of speeds for the magnetic bearing system. Simulation results are presented to demonstrate the closed loop system performance. We develop the model of the magnetic bearing, and present two schemes for the excitation of the poles of the actively controlled magnetic bearing. We also present a scheme for averaging multiple sensor measurements and splitting the actuation forces amongst redundant actuators

Wind Pressure Distribution on Trough Canopy Roofs

Wind tunnel experiments are carried out to obtain the wind pressure distribution on trough canopy roof. The model made of Perspex sheet at a scale of 1:100 is tested in open circuit wind tunnel under boundary layer flow. Effects of wind incidence angle are studied y changing wind angle. Values of wind pressure coefficients are calculated from the values of wind pressures measured at numerous pressure points on upper and lower surfaces of the trough roof and are reported in the form of cross sectional variation of pressure coefficient and pressure contours. It is observed that the wind pressure distribution on the trough canopy roof is highly influenced by incident wind direction

Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study

We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal to orthorhombic structural transition as well as magnetic transition at Tsm ~ 160K. The mode frequencies of two first-order Raman modes B1g and Eg, both involving displacement of Fe atoms, show sharp increase below Tsm. Concomitantly, the linewidths of all the first-order Raman modes show anomalous broadening below Tsm, attributed to strong spin-phonon coupling. The high frequency modes observed between 400-1200 cm-1 are attributed to the electronic Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which increases as temperature decreases below Tsm. A broad Raman band observed at ~ 3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d antiferromagnet.Comment: Accepted for Publication in JPC

Anomalous Raman scattering from phonons and electrons of superconducting FeSe0.82_{0.82}

We report interesting anomalies in the temperature dependent Raman spectra of FeSe$_{0.82}$ measured from 3K to 300K in the spectral range from 60 to 1800 cm$^{-1}$ and determine their origin using complementary first-principles density functional calculations. A phonon mode near 100 cm$^{-1}$ exhibits a sharp increase by $\sim$ 5% in frequency below a temperature T$_s$ ($\sim$ 100 K) attributed to strong spin-phonon coupling and onset of short-range antiferromagnetic order. In addition, two high frequency modes are observed at 1350 cm$^{-1}$ and 1600 cm$^{-1}$, attributed to electronic Raman scattering from ($x^2-y^2$)to $xz$ / $yz$ $d$-orbitals of Fe.Comment: 19 pages, 4 figures, 1 tabl

Dynamic Response of Heterogeneity and Reinforcement on the Propagation of Torsional Surface Waves

This paper aims to investigate the effect of reinforcement and heterogeneity on the propagation of torsional surface waves. Geometry of the problem is consists of heterogeneous fibre-reinforced layer lying over a heterogeneous isotropic half-space. Heterogeneity in the layer is caused due to exponential variation of elastic parameters whereas quadratic variation in elastic parameters is considered for half-space. Dispersion relation for torsional surface waves has been obtained and matched with classical Love wave equation by taking an isotropic homogeneous layer lying over an isotropic homogeneous half-space. Some existing results have been deduced as particular case of the present study. Velocity profile of surface waves is compared for both, reinforced and reinforced free cases. Numerical examples have been discussed by taking steel fibre-reinforced material. Graphical representation has been made to exhibit the findings