2,522 research outputs found
Control of MTDC Transmission Systems under Local Information
High-voltage direct current (HVDC) is a commonly used technology for
long-distance electric power transmission, mainly due to its low resistive
losses. In this paper a distributed controller for multi-terminal high-voltage
direct current (MTDC) transmission systems is considered. Sufficient conditions
for when the proposed controller renders the closed-loop system asymptotically
stable are provided. Provided that the closed loop system is asymptotically
stable, it is shown that in steady-state a weighted average of the deviations
from the nominal voltages is zero. Furthermore, a quadratic cost of the current
injections is minimized asymptotically
Photon generation in an electromagnetic cavity with a time-dependent boundary
We report the observation of photon generation in a microwave cavity with a
time-dependent boundary condition. Our system is a microfabricated quarter-wave
coplanar waveguide cavity. The electrical length of the cavity is varied using
the tunable inductance of a superconducting quantum interference device. It is
measured in the quantum regime, where the temperature is significantly less
than the resonance frequency (~ 5 GHz). When the length is modulated at
approximately twice the static resonance frequency, spontaneous oscillations of
the cavity field are observed. Time-resolved measurements of the dynamical
state of the cavity show multiple stable states. The behavior is well described
by theory. Connections to the dynamical Casimir effect are discussed.Comment: 5 pages, 3 Figure
Photon creation from vacuum and interactions engineering in nonstationary circuit QED
We study theoretically the nonstationary circuit QED system in which the
artificial atom transition frequency, or the atom-cavity coupling, have a small
periodic time modulation, prescribed externally. The system formed by the atom
coupled to a single cavity mode is described by the Rabi Hamiltonian. We show
that, in the dispersive regime, when the modulation periodicity is tuned to the
`resonances', the system dynamics presents the dynamical Casimir effect,
resonant Jaynes-Cummings or resonant Anti-Jaynes-Cummings behaviors, and it can
be described by the corresponding effective Hamiltonians. In the resonant
atom-cavity regime and under the resonant modulation, the dynamics is similar
to the one occurring for a stationary two-level atom in a vibrating cavity, and
an entangled state with two photons can be created from vacuum. Moreover, we
consider the situation in which the atom-cavity coupling, the atomic frequency,
or both have a small nonperiodic time modulation, and show that photons can be
created from vacuum in the dispersive regime. Therefore, an analog of the
dynamical Casimir effect can be simulated in circuit QED, and several photons,
as well as entangled states, can be generated from vacuum due to the
anti-rotating term in the Rabi Hamiltonian.Comment: 14 pages, 6 figures. Talk presented at the International Workshop "60
Years of Casimir Effect", 23 - 27 June, 2008, Brasili
Fast tuning of superconducting microwave cavities
Photons are fundamental excitations of the electromagnetic field and can be
captured in cavities. For a given cavity with a certain size, the fundamental
mode has a fixed frequency {\it f} which gives the photons a specific "color".
The cavity also has a typical lifetime , which results in a finite
linewidth {\it f}. If the size of the cavity is changed fast compared
to , and so that the frequency change {\it f} {\it
f}, then it is possible to change the "color" of the captured photons. Here we
demonstrate superconducting microwave cavities, with tunable effective lengths.
The tuning is obtained by varying a Josephson inductance at one end of the
cavity. We show data on four different samples and demonstrate tuning by
several hundred linewidths in a time . Working in the few
photon limit, we show that photons stored in the cavity at one frequency will
leak out from the cavity with the new frequency after the detuning. The
characteristics of the measured devices make them suitable for different
applications such as dynamic coupling of qubits and parametric amplification.Comment: 2nd International Workshop on Solid-State Quantum Computing, June
2008, Taipei, Taiwa
Proteomic Analysis of the Differential Protein Expression Reveals Nuclear GAPDH in Activated T Lymphocytes
Despite the important role of T cell activation in the adaptive immunity, very little is known about the functions of proteins that are differentially expressed in the activated T cells. In this study, we have employed proteomic approach to study the differentially expressed proteins in activated T cells. A total of 25 proteins was characterized that displayed a decreased expression, while a total of 20 proteins was characterized that displayed an increased expression in the activated T cells. Among them, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was identified unexpectedly as one of the up-regulated proteins. Western blot analysis of proteins separated by 2-dimensional gel electrophoresis had identified several modified GAPDHs which were detectable only in the activated T cells, but not in resting T cells. These modified GAPDHs had higher molecular mass and more basic PI, and were present in the nucleus of activated T cells. Promoter occupancy studies by chromatin immunoprecipitation assay revealed that nuclear GAPDH could be detected in the promoter of genes that were up-regulated during T cell activation, but not in the promoter of genes that were not unaffected or down-regulated. Our results suggest that nuclear GAPDH may function as transcriptional regulator in activated T cells
Possible impact of the “yellow card” antimicrobial scheme on meat inspection lesions in Danish finisher pigs
In 2010, the “yellow card scheme” adopted by the Danish Veterinary and Food Administration imposed restrictions on pig farmers who used more antimicrobials than twice the average. We studied the impact on antimicrobial consumption and vaccine use based on data from the monitoring programme Vetstat covering the time period January 2010 and July 2011. The decrease in antimicrobial consumption was pronounced for all age groups treated for either gastro-intestinal or respiratory disease. Data from meat inspection of finisher pigs from before and after introduction of the scheme were compared (N=1.7 million finisher pigs)
Direct numerical simulations of a high-pressure turbine vane
In this paper, we establish a benchmark data set of a generic high-pressure (HP) turbine vane generated by direct numerical simulation (DNS) to resolve fully the flow. The test conditions for this case are a Reynolds number of 0.57 × 106 and an exit Mach number of 0.9, which is representative of a modern transonic HP turbine vane. In this study, we first compare the simulation results with previously published experimental data. We then investigate how turbulence affects the surface flow physics and heat transfer. An analysis of the development of loss through the vane passage is also performed. The results indicate that freestream turbulence tends to induce streaks within the near-wall flow, which augment the surface heat transfer. Turbulent breakdown is observed over the late suction surface, and this occurs via the growth of two-dimensional Kelvin–Helmholtz spanwise roll-ups, which then develop into lambda vortices creating large local peaks in the surface heat transfer. Turbulent dissipation is found to significantly increase losses within the trailing-edge region of the vane.Partnership
for Advanced Computing in Europe (PRACE) and the UK
Turbulence Consortium funded by the EPSRC under Grant No.
EP/L000261/
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