895 research outputs found
Low order harmonic cancellation in a grid connected multiple inverter system via current control parameter randomization
In grid connected multiple inverter systems, it is normal to synchronize the output current of each inverter to the common network voltage. Any current controller deficiencies, which result in low order harmonics, are also synchronized to the common network voltage. As a result the harmonics produced by individual converters show a high degree of correlation and tend to be additive. Each controller can be tuned to achieve a different harmonic profile so that harmonic cancellation can take place in the overall system, thus reducing the net current total harmonic distortion level. However, inter-inverter communication is required. This paper presents experimental results demonstrating an alternative approach, which is to arrange for the tuning within each inverter to be adjusted automatically with a random component. This results in a harmonic output spectrum that varies with time, but is uncorrelated with the harmonic spectrum of any other inverter in the system. The net harmonics from all the inverters undergo a degree of cancellation and the overall system yields a net improvement in power quality
How to derive expected values of structural equation model parameters when treating discrete data as continuous
Comprehensive Solution to the Cosmological Constant, Zero-Point Energy, and Quantum Gravity Problems
We present a solution to the cosmological constant, the zero-point energy,
and the quantum gravity problems within a single comprehensive framework. We
show that in quantum theories of gravity in which the zero-point energy density
of the gravitational field is well-defined, the cosmological constant and
zero-point energy problems solve each other by mutual cancellation between the
cosmological constant and the matter and gravitational field zero-point energy
densities. Because of this cancellation, regulation of the matter field
zero-point energy density is not needed, and thus does not cause any trace
anomaly to arise. We exhibit our results in two theories of gravity that are
well-defined quantum-mechanically. Both of these theories are locally conformal
invariant, quantum Einstein gravity in two dimensions and Weyl-tensor-based
quantum conformal gravity in four dimensions (a fourth-order derivative quantum
theory of the type that Bender and Mannheim have recently shown to be
ghost-free and unitary). Central to our approach is the requirement that any
and all departures of the geometry from Minkowski are to be brought about by
quantum mechanics alone. Consequently, there have to be no fundamental
classical fields, and all mass scales have to be generated by dynamical
condensates. In such a situation the trace of the matter field energy-momentum
tensor is zero, a constraint that obliges its cosmological constant and
zero-point contributions to cancel each other identically, no matter how large
they might be. Quantization of the gravitational field is caused by its
coupling to quantized matter fields, with the gravitational field not needing
any independent quantization of its own. With there being no a priori classical
curvature, one does not have to make it compatible with quantization.Comment: Final version, to appear in General Relativity and Gravitation (the
final publication is available at http://www.springerlink.com). 58 pages,
revtex4, some additions to text and some added reference
Efficiency and power enhancement of combined cycle power plants by inlet air conditioning techniques
Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.The combined gas/steam turbine cycle power plants offer an
efficient and environment friendly system for electric power
generation. However the power output from a gas turbine
decreases significantly with increase in ambient temperature.
This is a serious condition especially in hot climatic
environments. Best method to tackle this situation is to
condition the inlet air to the gas turbine using innovative
techniques for augmenting power and efficiency improvement.
This paper illustrates the influence of various inlet air
conditioning techniques. A computational model of the
Combined Cycle Gas Turbine (CCGT) plant was developed
and applied to a typical 350 MW Combined Cycle Power Plant
(CCPP), operational in Kerala, India. The model is based on
thermodynamics, heat transfer and psychrometric principles.
With the help of this model, a parametric analysis of combined
cycle gas turbine plant for various temperatures and humidity
with swirl flash technology was carried out and results plotted.
Evaporative cooling and refrigerated inlet cooling techniques
were compared with the swirl flash technology to establish that
the swirl flash is superior to other methods in efficiency and
power enhancement.vk201
Exact Path-Integral Representations for the -Matrix in Nonrelativistic Potential Scattering
Several path integral representations for the -matrix in nonrelativistic
potential scattering are given which produce the complete Born series when
expanded to all orders and the eikonal approximation if the quantum
fluctuations are suppressed. They are obtained with the help of "phantom"
degrees of freedom which take away explicit phases that diverge for asymptotic
times. Energy conservation is enforced by imposing a Faddeev-Popov-like
constraint in the velocity path integral. An attempt is made to evaluate
stochastically the real-time path integral for potential scattering and
generalizations to relativistic scattering are discussed.Comment: 6 pages, 2 figures. Contribution to the workshop "Relativistic
Description of Two- and Three-Body Systems in Nuclear Physics", ETC*, October
19-23, 2009. v2: typo corrected, matches published version + additional
reference
Higher order contributions to the effective action of N=2 super Yang-Mills
We apply heat kernel techniques in N=1 superspace to compute the one-loop
effective action to order for chiral superfields coupled to a non-Abelian
super Yang-Mills background. The results, when combined with those of
hep-th/0210146, yield the one-loop effective action to order for any N=2
super Yang-Mills theory coupled to matter hypermultiplets.Comment: 23 pages, references adde
Acoustic and Seismic Fields of Hydraulic Jumps at Varying Froude Numbers
Mechanisms that produce seismic and acoustic wavefields near rivers are poorly understood because of a lack of observations relating temporally dependent river conditions to the near-river seismoacoustic fields. This controlled study at the Harry W. Morrison Dam (HWMD) on the Boise River, Idaho, explores how temporal variation in fluvial systems affects surrounding acoustic and seismic fields. Adjusting the configuration of the HWMD changed the river bathymetry and therefore the form of the standing wave below the dam. The HWMD was adjusted to generate four distinct wave regimes that were parameterized through their dimensionless Froude numbers (Fr) and observations of the ambient seismic and acoustic wavefields at the study site. To generate detectable and coherent signals, a standing wave must exceed a threshold Fr value of 1.7, where a nonbreaking undular jump turns into a breaking weak hydraulic jump. Hydrodynamic processes may partially control the spectral content of the seismic and acoustic energies. Furthermore, spectra related to reproducible wave conditions can be used to calibrate and verify fluvial seismic and acoustic models
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