2,450 research outputs found
Problems in the classic frequency shift islanding detection methods applied to energy storage converters and a coping strategy
This paper first derives a usable formula based on the parallel R, L, C load and the conclusions from frequency shift islanding detection methods in current literature: the angle by which the total output current of the distributed resources (DR) units leads the point of common coupling (PCC) voltage must be conducted to have the same shifting direction as the load admittance angle during the variation of the frequency. On the basis of the formula and multi-DR operation, the scenarios in which the classic frequency shift methods are applied to energy storage converters are analyzed. The results indicate that the setting of the angle by which the energy storage converter current leads the PCC voltage may need to be modified when running state changes. It results in the problems that the classic methods are not applicable for non-UPF (unity power factor) control and have to distinguish between generation mode and consumption mode for UPF control. On account of the problems, a coping strategy, i.e. an improved method, is proposed. The analyses indicate that the improved method is applicable in every state. The last simulations and experiments confirm the preceding conclusions
An irregular current injection islanding detection method based on an improved impedance measurement scheme
One class of islanding detection methods, known as impedance measurement-based methods and voltage change monitoring-based methods, are implemented through injecting irregular currents into the network, for which reason they are defined in this paper as irregular current injection methods. This paper indicates that such methods may be affected by distributed generation (DG) unit cut-in events. Although the network impedance change can still be used as a judgment basis for islanding detection, the general impedance measurement scheme cannot separate island events from DG unit cut-in events in multi-DG operation. In view of this, this paper proposes a new islanding detection method based on an improved impedance measurement scheme, i.e., dynamic impedance measurement, which will not be affected by DG unit cut-in events and can further assist some other equipment in islanding detection. The simulations and experiments verify the stated advantages of the new islanding detection method
Computational study of the dissociation reactions of secondary ozonide
This contribution presents a comprehensive computational study on the reactions of secondary ozonide (SOZ) with ammonia and water molecules. The mechanisms were studied in both a vacuum and the aqueous medium. All the molecular geometries were optimized using the B3LYP functional in conjunction with several basis sets. M06-2X, APFD, and ωB97XD functionals with the full basis set were also used. In addition, single-point energy calculations were performed with the G4MP2 and G3MP2 methods. Five different mechanistic pathways were studied for the reaction of SOZ with ammonia and water molecules. The most plausible mechanism for the reaction of SOZ with ammonia yields HC(O)OH, NH3, and HCHO as products, with ammonia herein acting as a mediator. This pathway is exothermic and exergonic, with an overall barrier height of only 157 kJ mol−1 using the G3MP2 method. All the reaction pathways between SOZ and water molecules are endothermic and endergonic reactions. The most likely reaction pathway for the reaction of SOZ with water involves a water dimer, in which the second water molecule acts as a mediator, with an overall barrier height of only 135 kJ mol−1 using the G3MP2 method. Solvent effects were found to incur a significant reduction in activation energies. When the second H2O molecule acts as a mediator in the reaction of SOZ with water, the barrier height of the rate-determining step state decreases significantly
Configuration Of Grafted Polystyrene Chains In The Melt: Temperature And Concentration Dependence
The concentration profiles of carboxy-terminated polystyrene chains in the melt grafted onto oxide-covered silicon substrates were measured using secondary-ion mass spectroscopy. The grafting density increased with temperature and an enthalpy of +7.4 kcal/mole was deduced for the grafting reaction, SiOH + R(COOH) ⇄ R(COOSi) + H2O. Relatively high grafting densities (σ∼6.6·mg/m2) were achieved with minimal chain distortion or displacement of long chains by shorter ones. Significant stretching of the grafted chains occurred for σ > 10 mg/m2. An equilibrium constant for the grafting reaction incorporating entropy is discussed.69577677
Compatibility Issues With Irregular Current Injection Islanding Detection Methods in Multi-DG Units Equipped With Grid-Connected Transformers
Compatibility issues with irregular current injection islanding detection methods are actually the problem that some irregular currents at the same frequency injected into the same line may cancel each other out and then the islanding detection may be impaired, which have been discussed under direct couple conditions (i.e., conditions without grid-connected transformers) in the literature. This article analyzes the issues under the opposite conditions where distributed generation (DG) units are equipped with grid-connected transformers, and is aimed at finding a solution. The analysis derives the setting formulas of key parameters for both three-phase and single-phase DG units, and shows that considering fault tolerance and practicability, only specific frequencies can be used for irregular currents. The usable frequencies are different under different cases. These conclusions are different from those based on direct couple conditions. By summarizing the conclusions based on conditions with grid-connected transformers achieved in this article and those based on direct couple conditions in the literature, a complete solution to compatibility issues is obtained. The conclusions in this article have been verified by the experiments and simulations at the end of this article
Remarks on self-interaction correction to black hole radiation
In the work [P. Kraus and F. Wilczek, \textit{Self-interaction correction to
black hole radiation, Nucl. Phys.} B433 (1995) 403], it has been pointed out
that the self-gravitation interaction would modify the black hole radiation so
that it is no longer thermal, where it is, however, corrected in an approximate
way and therefore is not established its relationship with the underlying
unitary theory in quantum theory. In this paper, we revisit the
self-gravitation interaction to Hawking radiation of the general spherically
symmetric black hole, and find that the precisely derived spectrum is not only
deviated from the purely thermal spectrum, but most importantly, is related to
the change of the Bekenstein-Hawking entropy and consistent with an underlying
unitary theory.Comment: 14 page
Interference between the halves of a double-well trap containing a Bose-Einstein condensate
Interference between the halves of a double-well trap containing a
Bose-Einstein condensate is studied. It is found that when the atoms in the two
wells are initially in the coherent state, the intensity exhibits collapses and
revivals, but it does not for the initial Fock states. Whether the initial
states are in the coherent states or in a Fock states, the fidelity time has
nothing to do with collision. We point out that interference and its fidelity
can be adjusted experimentally by properly preparing the number and initial
states of the system.Comment: 10 pages, 3 figures, accepted by Phy. rev.
Influence of microwave fields on the electron transport through a quantum dot in the presence of a direct tunneling between leads
We consider the time-dependent electron transport through a quantum dot
coupled to two leads in the presence of the additional over-dot (bridge)
tunneling channel. By using the evolution operator method together with the
wide-band limit approximation we derived the analytical formulaes for the
quantum dot charge and current flowing in the system. The influence of the
external microwave field on the time-average quantum dot charge, the current
and the derivatives of the average current with respect to the gate and
source-drain voltages has been investigated for a wide range of parameters.Comment: 28 Pages, 11 Postscript figure
Influence of the starting composition on the structural and superconducting properties of MgB2 phase
We report the preparation of MgB (0x0.5) compounds
with the nominal compositions. Single phase MgB was obtained for x=0
sample. For 0x0.5, MgB coexists with "MgB" and the amount
of MgB increases with x. With the increase of x, the lattice parameter
of "MgB" increases and the lattice parameter
decreases, correspondingly T of MgB decreases. The results
were discussed in terms of the presence of Mg vacancies or B interstitials in
the MgB structure. This work is helpful to the understanding of the
MgB films with different T, as well as the Mg site doping effect
for MgB.Comment: 11 pages, 4 figure
Demonstration of Feed-Forward Control for Linear Optics Quantum Computation
One of the main requirements in linear optics quantum computing is the
ability to perform single-qubit operations that are controlled by classical
information fed forward from the output of single photon detectors. These
operations correspond to pre-determined combinations of phase corrections and
bit-flips that are applied to the post-selected output modes of
non-deterministic quantum logic devices. Corrections of this kind are required
in order to obtain the correct logical output for certain detection events, and
their use can increase the overall success probability of the devices. In this
paper, we report on the experimental demonstration of the use of this type of
feed-forward system to increase the probability of success of a simple
non-deterministic quantum logic operation from approximately 1/4 to 1/2. This
logic operation involves the use of one target qubit and one ancilla qubit
which, in this experiment, are derived from a parametric down-conversion photon
pair. Classical information describing the detection of the ancilla photon is
fed-forward in real-time and used to alter the quantum state of the output
photon. A fiber optic delay line is used to store the output photon until a
polarization-dependent phase shift can be applied using a high speed Pockels
cell
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