8,241 research outputs found
A Revisit to Quadratic Programming with One Inequality Quadratic Constraint via Matrix Pencil
The quadratic programming over one inequality quadratic constraint (QP1QC) is
a very special case of quadratically constrained quadratic programming (QCQP)
and attracted much attention since early 1990's. It is now understood that,
under the primal Slater condition, (QP1QC) has a tight SDP relaxation (PSDP).
The optimal solution to (QP1QC), if exists, can be obtained by a matrix rank
one decomposition of the optimal matrix X? to (PSDP). In this paper, we pay a
revisit to (QP1QC) by analyzing the associated matrix pencil of two symmetric
real matrices A and B, the former matrix of which defines the quadratic term of
the objective function whereas the latter for the constraint. We focus on the
\undesired" (QP1QC) problems which are often ignored in typical literature:
either there exists no Slater point, or (QP1QC) is unbounded below, or (QP1QC)
is bounded below but unattainable. Our analysis is conducted with the help of
the matrix pencil, not only for checking whether the undesired cases do happen,
but also for an alternative way to compute the optimal solution in comparison
with the usual SDP/rank-one-decomposition procedure.Comment: 22 pages, 0 figure
Deflationary Expansion : an Overshooting Perspective to the Recent Business Cycle in China
Deflationary expansion has puzzled economists both in and outside China. We study this business cycles phenomenon within a model of discrete time dynamics. We find that deflationary expansion could be possible if driven by an overshooting in investing and if the state of the economy maintains high rate of growth. This expression is consistent with the recent variables. The high steady state of growth could be explained by the current institutional environment of China.Deflationary Expansion, China, Existence and Stability Conditions of Equilibrium, Business Fluctuations, monetary policy, Central Banking, Supply of Money and Credit
Ds+ -- Ds- Asymmetry in Photoproduction
Considering of the possible difference in strange and antistrange quark
distributions inside nucleon, we investigate the Ds+ -- Ds- asymmetry in
photoproduction in the framework of heavy-quark recombination mechanism. We
adopt two distribution models of strange sea, those are the light-cone
meson-baryon fluctuation model and the effective chiral quark model. Our
results show that the asymmetry induced by the strange quark distributions is
distinct, which is measurable in experiments. And, there are evident
differences between the predictions of our calculation and previous estimation.
Therefore, the experimental measurements on the Ds+ -- Ds- asymmetry may impose
a unique restriction on the strange-antistrange distribution asymmetry models.Comment: 11 page, 5 figure
Possible Deuteron-like Molecular States Composed of Heavy Baryons
We perform a systematic study of the possible loosely bound states composed
of two charmed baryons or a charmed baryon and an anti-charmed baryon within
the framework of the one boson exchange (OBE) model. We consider not only the
exchange but also the , , , and
exchanges. The mixing effects for the spin-triplets are also taken into
account. With the derived effective potentials, we calculate the binding
energies and root-mean-square (RMS) radii for the systems
, ,
,
and
. Our numerical results indicate that: (1)
the H-dibaryon-like state does not exist; (2) there may
exist four loosely bound deuteron-like states and
with small binding energies and large RMS radii.Comment: 17 pages, 32 figure
Prompt heavy quarkonium production in association with a massive (anti)bottom quark at the LHC
In this work, we investigate the associated production of prompt heavy
quarkonium with a massive (anti)bottom quark to leading order in the NRQCD
factorization formalism at the LHC. We present numerical results for the
processes involving and . From our work,
we find that the production rates of these processes are quite large, and these
processes have the potential to be detected at the LHC. When is smaller
than about 10 GeV, the state give the main
contribution to the distribution of prompt with a (anti)bottom
quark production. For the process of , the
contribution of the CSM is larger than that in the COM at low region. We
also investigate the processes of and , in these processes, the distribution are dominated
by the CO Fock state contribution at the large region. These processes
provide an interesting signature that could be studied at the LHC, and the
measurement of these processes is useful to test the CSM and COM.Comment: 14 pages, 11 figures, accepted by Phys.Rev.
B_{s1}(5830) and B_{s2}^*(5840)
In this paper we investigate the strong decays of the two newly observed
bottom-strange mesons and in the framework of
the quark pair creation model. The two-body strong decay widths of
and are
calculated by considering to be a mixture between and
states, and to be a state. The double pion
decay of and is supposed to occur via the
intermediate state and . Although the double pion decay
widths of and are smaller than the two-body
strong decay widths of and , one suggests future
experiments to search the double pion decays of and
due to their sizable decay widths.Comment: 9 pages, 8 figures and 6 tables. More references and discussions
added, typos corrected, some descriptions changed. Publication version in PR
Virtual inertia for suppressing voltage oscillations and stability mechanisms in DC microgrids
Renewable energy sources (RES) are gradually penetrating power systems through power electronic converters (PECs), which greatly change the structure and operation characteristics of traditional power systems. The maturation of PECs has also laid a technical foundation for the development of DC microgrids (DC-MGs). The advantages of DC-MGs over AC systems make them an important access target for RES. Due to the multi-timescale characteristics and fast response of power electronics, the dynamic coupling of PEC control systems and the transient interaction between the PEC and the passive network are inevitable, which threatens the stable operation of DC-MGs. Therefore, this dissertation focuses on the study of stabilization control methods, the low-frequency oscillation (LFO) mechanism analysis of DC-MGs and the state-of-charge (SoC) imbalance problem of multi-parallel energy storage systems (ESS).
Firstly, a virtual inertia and damping control (VIDC) strategy is proposed to enable bidirectional DC converters (BiCs) to damp voltage oscillations by using the energy stored in ESS to emulate inertia without modifications to system hardware. Both the inertia part and the damping part are modeled in the VIDC controller by analogy with DC machines. Simulation results verify that the proposed VIDC can improve the dynamic characteristics and stability in islanded DC-MG. Then, inertia droop control (IDC) strategies are proposed for BiC of ESS based on the comparison between conventional droop control and VIDC. A feedback analytical method is presented to comprehend stability mechanisms from multi-viewpoints and observe the interaction between variables intuitively. A hardware in the loop (HIL) experiment verifies that IDC can simplify the control structure of VIDC in the promise of ensuring similar control performances. Subsequently, a multi-timescale impedance model is established to clarify the control principle of VIDC and the LFO mechanisms of VIDC-controlled DC-MG. Control loops of different timescales are visualized as independent loop virtual impedances (LVIs) to form an impedance circuit. The instability factors are revealed and a dynamic stability enhancement method is proposed to compensate for the negative damping caused by VIDC and CPL. Experimental results have validated the LFO mechanism analysis and stability enhancement method. Finally, an inertia-emulation-based cooperative control strategy for multi-parallel ESS is proposed to address the SoC imbalance and voltage deviation problem in steady-state operation and the voltage stability problem. The contradiction between SoC balancing speed and maintaining system stability is solved by a redefined SoC-based droop resistance function. HIL experiments prove that the proposed control performs better dynamics and static characteristics without modifying the hardware and can balance the SoC in both charge and discharge modes
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