26,218 research outputs found
Challenges of Primary Frequency Control and Benefits of Primary Frequency Response Support from Electric Vehicles
As the integration of wind generation displaces conventional plants, system inertia provided by rotating mass declines, causing concerns over system frequency stability. This paper implements an advanced stochastic scheduling model with inertia-dependent fast frequency response requirements to investigate the challenges on the primary frequency control in the future Great Britain electricity system. The results suggest that the required volume and the associated cost of primary frequency response increase significantly along with the increased capacity of wind plants. Alternative measures (e.g. electric vehicles) have been proposed to alleviate these concerns. Therefore, this paper also analyses the benefits of primary frequency response support from electric vehicles in reducing system operation cost, wind curtailment and carbon emissions
Compact and High Performance Dual-band Bandpass Filter Using Resonator-embedded Scheme for WLANs
A compact microstrip dual-band bandpass filter (DBBPF) with high selectivity and good suppression for wireless local area networks (WLANs) is proposed utilizing a novel embedded scheme resonator. Two passbands are produced by a pair of embedded half-wavelength meandered stepped-impedance resonator (MSIR) and a quadwavelength short stub loaded stepped-impedance resonator (SIR) separately. The resonator is fed by folded Tshaped capacitive source-load coupling microstrip feed line, and four transmission zeros are obtained at both sides of the bands to improve selectivity and suppression. Simultaneously, the size of the filter is extermely compact because embedding half-wavelength MSIR only changes the interior configuration of quad-wavelength SIR. To validate the design method, the designed filter is fabricated and measured. Both simulated and measured results indicate that good transmission property has been achieved
A Unifying Quantum Speed Limit For Time-Independent Hamiltonian Evolution
Quantum speed limit (QSL) is the study of fundamental limits on the evolution
time of quantum systems. For instance, under the action of a time-independent
Hamiltonian, the evolution time between an initial and a final quantum state
obeys various mutually complementary lower bounds. They include the
Mandelstam-Tamm bound, the Margolus-Levitin bound, the Luo-Zhang bound and the
Lee-Chau bound. Here we show that the Mandelstam-Tamm bound can be obtained by
optimizing the Lee-Chau bound over a certain parameter. More importantly, we
report a QSL that includes all the above bounds as special cases before
optimizing over the physically meaningless reference energy level of a quantum
system. This unifying bound depends on a certain parameter . For any fixed
, we find all pairs of time-independent Hamiltonian and initial pure quantum
state that saturate this unifying bound. More importantly, these pairs allow us
to compute this bound accurately and efficiently using an oracle that returns
certain th moments related to the absolute value of energy of the quantum
state. Moreover, this oracle can be simulated by a computationally efficient
and accurate algorithm for finite-dimensional quantum systems as well as for
certain infinite-dimensional quantum states with bounded and continuous energy
spectra. We further compare the performance of this bound for the case of a
fixed as well as the case of optimizing over with existing QSLs. We
find that if the dimension of the underlying Hilbert space is ,
our unifying bound optimized over can be computed accurately in a few
minutes using Mathematica code with just-in-time compilation in a typical
desktop. Besides, this optimized unifying QSL is at least as good as all the
existing ones combined and can occasionally be a few percent to a few times
better.Comment: 20 pages, 3 figure
Microwave-induced nonequilibrium temperature in a suspended carbon nanotube
Antenna-coupled suspended single carbon nanotubes exposed to 108 GHz
microwave radiation are shown to be selectively heated with respect to their
metal contacts. This leads to an increase in the conductance as well as to the
development of a power-dependent DC voltage. The increased conductance stems
from the temperature dependence of tunneling into a one-dimensional electron
system. The DC voltage is interpreted as a thermovoltage, due to the increased
temperature of the electron liquid compared to the equilibrium temperature in
the leads
Quantum asymmetric cryptography with symmetric keys
Based on quantum encryption, we present a new idea for quantum public-key
cryptography (QPKC) and construct a whole theoretical framework of a QPKC
system. We show that the quantum-mechanical nature renders it feasible and
reasonable to use symmetric keys in such a scheme, which is quite different
from that in conventional public-key cryptography. The security of our scheme
is analyzed and some features are discussed. Furthermore, the state-estimation
attack to a prior QPKC scheme is demonstrated.Comment: 8 pages, 1 figure, Revtex
Intrinsic Percolative Superconductivity in KxFe2-ySe2 Single Crystals
Magnetic field penetration and magnetization hysteresis loops (MHLs) have
been measured in KxFe2-ySe2 single crystals. The magnetic field penetration
shows a two-step feature with a very small full-magnetic-penetration field
(Hp1= 300 Oe at 2 K), and accordingly the MHL exhibits an abnormal vanishing of
the central peak near zero field below 13 K. The width of the MHL in KxFe2-ySe2
at the same temperature is in general much smaller than that measured in the
relatives Ba0.6K0.4Fe2As2 and Ba(Fe0.92Co0.08)2As2, and the MHLs in the latter
two samples show the normal central peak near zero field. All these anomalies
found in KxFe2-ySe2 can be understood in the picture that the sample is
percolative with weakly coupled superconducting islands.Comment: 5 page, 4 figure
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