775 research outputs found
Maximum power point tracking control of hydrokinetic turbine and low-speed high-thrust permanent magnet generator design
River-based hydrokinetic turbine power generation systems have been studied to introduce an effective energy flow control method. Hydrokinetic turbine systems share a lot of similarities with wind turbine systems in terms of physical principles of operation, electrical hardware, and variable speed capability for optimal energy extraction. A multipole permanent magnet synchronous generator is used to generate electric power because of its ability to reach high power density and high thrust at low speed. A 3-phase diode rectifier is used to convert AC power from the generator into DC power and a boost converter is used to implement energy flow control. On the load side, an electronic voltage load is used for test purposes to simulate a constant DC bus voltage load, such as a battery. A dynamic model of the entire system is developed and used to analyze the interaction between the mechanical structure of water turbine and electrical load of the system, based on which a maximum power point tracking control algorithm is developed and implemented in the boost converter. Simulation and experimental results are presented to validate the proposed MPPT control strategy for hydrokinetic turbine system. Similar to the wind turbine system, hydrokinetic turbine system usually requires a gear box to couple the turbine and the generator because the operating speed range for the hydrokinetic turbine is much lower than the operating speed range for most PMSGs. However, the gear box coupling adds additional transmission power losses. Therefore a high-thrust low-speed permanent magnet synchronous generator is designed to couple with the water turbine without a gear box --Abstract, page iii
Dynamical quantum phase transitions in non-Hermitian lattices
In closed quantum systems, a dynamical phase transition is identified by
nonanalytic behaviors of the return probability as a function of time. In this
work, we study the nonunitary dynamics following quenches across exceptional
points in a non-Hermitian lattice realized by optical resonators. Dynamical
quantum phase transitions with topological signatures are found when an
isolated exceptional point is crossed during the quench. A topological winding
number defined by a real, noncyclic geometric phase is introduced, whose value
features quantized jumps at critical times of these phase transitions and
remains constant elsewhere, mimicking the plateau transitions in quantum Hall
effects. This work provides a simple framework to study dynamical and
topological responses in non-Hermitian systems.Comment: 7 pages, 5 figure
High-energy proton beam obtained by single high-power LG laser acceleration
We used 3D particle-in-cell (PIC) simulations to investigate the eff ect of a single high-energy Laguerre-Gaussian laser pulse
interacting with an underdense plasma on the acceleration process of a proton beam. The single-beam LG laser drive solves the problem of
the need for external proton injection and the synchronization of two laser pulses. The circularly polarized LG laser fi rst takes protons out
of the high-density plasma target and pre-accelerates them through the radiation pressure acceleration mechanism (RPA). Then, when the
LG laser pulse enters the low-density plasma, a special cavity structure with electron columns will be formed due to the special transverse
intensity distribution of the LG laser. The self-injected proton in the special cavity will be accelerated while being confi ned to the center and
steadily accelerated by the tail fi eld of the cavity at very long distances.3D PIC simulation results show when using power density when
the LG laser is captured, the self-injected protons are accelerated to very high energies(the maximum energy of a proton is )and lower
divergence
Aspects of Floquet Bands and Topological Phase Transitions in a Continuously Driven Superlattice
Recently the creation of novel topological states of matter by a periodic
driving field has attracted great attention. To motivate further experimental
and theoretical studies, we investigate interesting aspects of Floquet bands
and topological phase transitions in a continuously driven Harper model. In
such a continuously driven system with an odd number of Floquet bands, the
bands are found to have nonzero Chern numbers in general and topological phase
transitions take place as we tune various system parameters, such as the
amplitude or the period of the driving field. The nontrivial Floquet band
topology results in a quantized transport of Wannier states in the lattice
space. For certain parameter choices, very flat yet topologically nontrivial
Floquet bands may also emerge, a feature that is potentially useful for the
simulation of physics of strongly correlated systems. Some cases with an even
number of Floquet bands may also have intriguing Dirac cones in the spectrum.
Under open boundary conditions, anomalous counter-propagating chiral edge modes
and degenerate zero modes are also found as the system parameters are tuned.
These results should be of experimental interest because a continuously driven
system is easier to realize than a periodically kicked system.Comment: 29 pages, 9 figures. Comments are welcom
BLISS: biding site level identification of shared signal-modules in DNA regulatory sequences
BACKGROUND: Regulatory modules are segments of the DNA that control particular aspects of gene expression. Their identification is therefore of great importance to the field of molecular genetics. Each module is composed of a distinct set of binding sites for specific transcription factors. Since experimental identification of regulatory modules is an arduous process, accurate computational techniques that supplement this process can be very beneficial. Functional modules are under selective pressure to be evolutionarily conserved. Most current approaches therefore attempt to detect conserved regulatory modules through similarity comparisons at the DNA sequence level. However, some regulatory modules, despite the conservation of their responsible binding sites, are embedded in sequences that have little overall similarity. RESULTS: In this study, we present a novel approach that detects conserved regulatory modules via comparisons at the binding site level. The technique compares the binding site profiles of orthologs and identifies those segments that have similar (not necessarily identical) profiles. The similarity measure is based on the inner product of transformed profiles, which takes into consideration the p values of binding sites as well as the potential shift of binding site positions. We tested this approach on simulated sequence pairs as well as real world examples. In both cases our technique was able to identify regulatory modules which could not to be identified using sequence-similarity based approaches such as rVista 2.0 and Blast. CONCLUSION: The results of our experiments demonstrate that, for sequences with little overall similarity at the DNA sequence level, it is still possible to identify conserved regulatory modules based solely on binding site profiles
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