arXiv subjects

Feng Pan

Publications and source records attributed to Feng Pan.

At least 127 records · Page 7Linked to original sources

arXiv2015

Maximizing electrical power supply using FACTS devices

Modern society critically depends on the services electric power provides. Power systems rely on a network of power lines and transformers to deliver power from sources of power (generators) to the consumers (loads). However, when power lines fail (for example, through lightning or natural disasters) or when the system is heavily used, the network is often unable to fulfill all of the demand for power. While systems are vulnerable to these failures, increasingly, sophisticated control devices are being deployed to improve the efficiency of power systems. Such devices can also be used to improve the resiliency of power systems to failures. In this paper, we focus on using FACTS devices in this context. A FACTS device allows power grid operators to adjust the impedance parameters of power lines, thereby redistributing flow in the network and potentially increasing the amount of power that is supplied. Here we develop new approaches for determining the optimal parameter settings for FACTS devices in order to supply the maximal amount of power when networks are stressed, e.g. power line failures and heavy utilization.

eess.SY↗

arXiv2015

Shape phase transition in the odd Sm nuclei: effective order parameter and odd-even effect

Some binding-energy-related quantities serving as effective order parameters have been used to analyze the shape phase transition in the odd Sm nuclei. It is found that the signals of phase transition in the odd Sm nuclei are greatly enhanced in contrast to the even Sm nuclei. A further analysis shows that the transitional behaviors related to pairing in the Sm nuclei can be well described by the mean field plus pairing interaction model, with a monotonic decrease in the pairing strength $G$.

nucl-th↗

arXiv2015

Triaxial dynamics in the quadrupole-deformed rotor

The triaxial dynamics of the quadrupole-deformed rotor model of both the rigid and the irrotational type have been investigated in detail. The results indicate that level patterns and E2 transitional characters of the two types of the model can be matched with each other to the leading order of the deformation parameter $β$. Especially, it is found that the dynamical structure of the irrotational type with most triaxial deformation ($γ=30^\circ$) is equivalent to that of the rigid type with oblate deformation ($γ=60^\circ$), and the associated spectrum can be classified into the standard rotational bands obeying the rotational $L(L+1)$-law or regrouped into a new ground- and $γ$-band with odd-even staggering in the new $γ$-band commonly recognized as a signature of the triaxiality. The differences between the two types of the model in this case are emphasized especially on the E2 transitional characters.

nucl-th↗

arXiv2015

Electrical control of exchange spring in antiferromagnetic metals

Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. In spite of the electrical modulation of insulated AFMs through coupling between their intrinsic ferroelectricity and antiferromagnetism, direct electrical control of AFM metals remains challenging due to the screening effect by the surface charge, and the manipulation is confined to a limited depth of atomic dimensions, which is insufficient to form a stable AFM exchange spring. In the present letter we primarily report a reversible electrical control of exchange spring in AFM metals, using an ionic liquid to exert a substantial electric-field effect. The exchange spring could transfer the force to the ferromagnet/antiferromagnet interface, enabling a deeper modulation depth in AFM metals. The manipulation of AFM moments by gate voltage is demonstrated in [Co/Pt]/IrMn model system and a single IrMn layer with the IrMn thickness up to 5 nm. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.

cond-mat.mtrl-sci↗

arXiv2015

Silicene Nanomesh

Similar to graphene, zero band gap limits the application of silicene in nanoelectronics despite of its high carrier mobility. By using first-principles calculations, we reveal that a band gap is opened in silicene nanomesh (SNM) when the width W of the wall between the neighboring holes is even. The size of the band gap increases with the reduced W and has a simple relation with the ratio of the removed Si atom and the total Si atom numbers of silicene. Quantum transport simulation reveals that the sub-10 nm single-gated SNM field effect transistors show excellent performance at zero temperature but such a performance is greatly degraded at room temperature.

cond-mat.mtrl-sci↗

arXiv2014

The emergent dynamical symmetry at the triple point of nuclear deformations

Based on the boson realization of the Euclidean algebras, it is shown that the five-dimensional Euclidean dynamical symmetry may emerge at the triple point of the shape phase diagram of the interacting boson model, which thus offers a symmetry-based understanding of this isolated point. It is further shown that the low-lying dynamics in $^{108}$Pd, $^{134}$Ba, $^{64}$Zn, and $^{114}$Cd may be dominated by the Euclidean dynamical symmetry.

nucl-th↗

arXiv2014

Electrical manipulation of orbital occupancy and magnetic anisotropy in manganites

Electrical manipulation of lattice, charge, and spin has been realized respectively by the piezoelectric effect, field-effect transistor, and electric field control of ferromagnetism, bringing about dramatic promotions both in fundamental research and industrial production. However, it is generally accepted that the orbital of materials are impossible to be altered once they have been made. Here we use electric-field to dynamically tune the electronic phase transition in (La,Sr)MnO3 films with different Mn^4+/(Mn^3+ + Mn^4+) ratios. The orbital occupancy and corresponding magnetic anisotropy of these thin films are manipulated by gate voltage in a reversible and quantitative manner. Positive gate voltage increases the proportion of occupancy of the orbital and magnetic anisotropy that were initially favored by strain (irrespective of tensile and compressive), while negative gate voltage reduces the concomitant preferential orbital occupancy and magnetic anisotropy. Besides its fundamental significance in orbital physics, our findings might advance the process towards practical oxide-electronics based on orbital.

cond-mat.mtrl-sci↗

arXiv2014

Euclidean Dynamical Symmetry in Nuclear Shape Phase Transitions

The Euclidean dynamical symmetry hidden in the critical region of nuclear shape phase transitions is revealed by a novel algebraic F(5) description. With a nonlinear projection, it is shown that the dynamics in the critical region of the spherical--axial deformed and the spherical--$γ$ soft shape phase transitions can indeed be manifested by this description, which thus provides a unified symmetry--based interpretation of the critical phenomena in the region.

nucl-th↗

arXiv2014

Uncertainty quantification for CO2 sequestration and enhanced oil recovery

This study develops a statistical method to perform uncertainty quantification for understanding CO2 storage potential within an enhanced oil recovery (EOR) environment at the Farnsworth Unit of the Anadarko Basin in northern Texas. A set of geostatistical-based Monte Carlo simulations of CO2-oil-water flow and reactive transport in the Morrow formation are conducted for global sensitivity and statistical analysis of the major uncertainty metrics: net CO2 injection, cumulative oil production, cumulative gas (CH4) production, and net water injection. A global sensitivity and response surface analysis indicates that reservoir permeability, porosity, and thickness are the major intrinsic reservoir parameters that control net CO2 injection/storage and oil/gas recovery rates. The well spacing and the initial water saturation also have large impact on the oil/gas recovery rates. Further, this study has revealed key insights into the potential behavior and the operational parameters of CO2 sequestration at CO2-EOR sites, including the impact of reservoir characterization uncertainty; understanding this uncertainty is critical in terms of economic decision making and the cost-effectiveness of CO2 storage through EOR.

physics.geo-ph↗

arXiv2014

Optimal compression in natural gas networks: a geometric programming approach

Natural gas transmission pipelines are complex systems whose flow characteristics are governed by challenging non-linear physical behavior. These pipelines extend over hundreds and even thousands of miles. Gas is typically injected into the system at a constant rate, and a series of compressors are distributed along the pipeline to boost the gas pressure to maintain system pressure and throughput. These compressors consume a portion of the gas, and one goal of the operator is to control the compressor operation to minimize this consumption while satisfying pressure constraints at the gas load points. The optimization of these operations is computationally challenging. Many pipelines simply rely on the intuition and prior experience of operators to make these decisions. Here, we present a new geometric programming approach for optimizing compressor operation in natural gas pipelines. Using models of real natural gas pipelines, we show that the geometric programming algorithm consistently outperforms approaches that mimic existing state of practice.

eess.SY↗

arXiv2014

The physical limit of logical compare operation

In this paper two connected Szilard single molecule engines (with different temperature) model of Maxwell's demon are used to demonstrate and analysis the logical compare operation. The logical and physical complexity of compare operations are both showed to be kTln2. Then this limit was used to prove the time complexity lower bound of sorting problem. It confirmed the proposed way to measure the complexity of a problem, provided another evidence of the equivalence between information theoretical and thermodynamic entropies.

physics.data-an↗

arXiv2014

Exact solutions of an extended Bose-Hubbard model with E2 symmetry

An extended Bose-Hubbard (BH) model with number-dependent multi-site and infinite-range hopping is proposed, which, similar to the original BH model, describes a phase transition between the delocalized super-fluid (SF) phase and localized Mott insulator (MI) phase. It is shown that this extended model with local Euclidean E2 symmetry is exactly solvable when on-site local potential or disorder is included, while the model without local potential or disorder is quasi-exactly solvable, which means only a part of the excited states including the ground state being exactly solvable. As applications of the exact solution for the ground state, phase diagram of the model in 1D without local potential and on-site disorder for filling factor rho = 1 with M = 6 sites and that with M = 10 are obtained. The probabilities to detect n particles on a single site, Pn, for n = 0, 1, 2 as functions of the control parameter U/t in these two cases are also calculated. It is shown that the critical point in Pn and in the entanglement measure is away from that of the SF-MI transition determined in the phase analysis. It is also shown that the the model-independent entanglement measure is related with Pn, which, therefore, may be practically useful because Pn is measurable experimentally.

cond-mat.str-el↗

arXiv2013

Interdiction Problems on Planar Graphs

Interdiction problems are leader-follower games in which the leader is allowed to delete a certain number of edges from the graph in order to maximally impede the follower, who is trying to solve an optimization problem on the impeded graph. We introduce approximation algorithms and strong NP-completeness results for interdiction problems on planar graphs. We give a multiplicative $(1 + ε)$-approximation for the maximum matching interdiction problem on weighted planar graphs. The algorithm runs in pseudo-polynomial time for each fixed $ε> 0$. We also show that weighted maximum matching interdiction, budget-constrained flow improvement, directed shortest path interdiction, and minimum perfect matching interdiction are strongly NP-complete on planar graphs. To our knowledge, our budget-constrained flow improvement result is the first planar NP-completeness proof that uses a one-vertex crossing gadget.

cs.DS↗

arXiv2013

Problem Complexity Research from Energy Perspective

Computational complexity is a particularly important objective. The idea of Landauer principle was extended through mapping three classic problems (sorting,ordered searching and max of N unordered numbers) into Maxwell demon thought experiment in this paper. The problems'complexity is defined on the entropy basis and the minimum energy required to solve them are rigorous deduced from the perspective of energy (entropy) and the second law of thermodynamics. Then the theoretical energy consumed by real program and basic operators of classical computer are both analyzed, the time complexity lower bounds of three problems'all possible algorithms are derived in this way. The lower bound is also deduced for the two n*n matrix multiplication problem. In the end, the reason why reversible computation is impossible and the possibility of super-linear energy consumption capacity which may be the power behind quantum computation are discussed, a conjecture is proposed which may prove NP!=P. The study will bring fresh and profound understanding of computation complexity.

cs.CC↗

arXiv2013

Construction of Basis Vectors For Symmetric Irreducible Representations of O(5) supset O(3)

A recursive method for construction of symmetric irreducible representations of O(2l+1) in the O(2l + 1) supset O(3) basis for identical boson systems is proposed. The formalism is realized based on the group chain U(2l + 1) supset U(2l- 1) x U(2), of which the symmetric irreducible representations are simply reducible. The basis vectors of the O(2l+1) supset O(2l-1) x U(1) can easily be constructed from those of U(2l + 1) supset U(2l-1) x U(2) supset O(2l-1) x U(1) with no boson pairs, from which one can construct symmetric irreducible representations of O(2l+1) in the O(2l-1) x U(1) basis when all symmetric irreducible representations of O(2l-1) are known. As a starting point, basis vectors of symmetric irreducible representations of O(5) are constructed in the O1(3) x U(1) basis. Matrix representations of O(5) supset O1(3) x U(1), together with the elementary Wigner coefficients, are presented. After the angular momentum projection, a three-term relation in determining the expansion coefficients of the O(5) supset O(3) basis vectors in terms of those of the O1(3) x U(1) is derived. The eigenvectors of the projection matrix with zero eigenvalues constructed according to the three-term relation completely determine the basis vectors of O(5) supset O(3). Formulae for evaluating the elementary Wigner coefficients of O(5) supset O(3) are derived explicitly. Analytical expressions of some elementary Wigner coefficients of O(5) supset O(3) for the coupling (tau, 0) x (1,0) with resultant angular momentum quantum number L = 2 tau+ 2 - k for k = 0, 2, 3,...,6 with a multiplicity 2 case for k = 6 are presented.

math-ph↗

arXiv2013

The Heine-Stieltjes correspondence and a new angular momentum projection for many-particle systems

A new angular momentum projection for systems of particles with arbitrary spins is formulated based on the Heine-Stieltjes correspondence, which can be regarded as the solutions of the mean-field plus pairing model in the strong pairing interaction G ->Infinity limit. Properties of the Stieltjes zeros of the extended Heine-Stieltjes polynomials, of which the roots determine the projected states, and the related Van Vleck zeros are discussed. The electrostatic interpretation of these zeros is presented. As examples, applications to n nonidentical particles of spin-1/2 and to identical bosons or fermions are made to elucidate the procedure and properties of the Stieltjes zeros and the related Van Vleck zeros. It is shown that the new angular momentum projection for n identical bosons or fermions can be simplified with the branching multiplicity formula of U(N) supset O(3) and the special choices of the parameters used in the projection. Especially, it is shown that the solutions for identical bosons can always be expressed in terms of zeros of Jacobi polynomials. However, unlike non-identical particle systems, the n-coupled states of identical particles are non-orthogonal with respect to the multiplicity label after the projection.

nucl-th↗

arXiv2012

Quasi-exactly solvable cases of the N-dimensional symmetric quartic anharmonic oscillator

The O(N) invariant quartic anharmonic oscillator is shown to be exactly solvable if the interaction parameter satisfies special conditions. The problem is directly related to that of a quantum double well anharmonic oscillator in an external field. A finite dimensional matrix equation for the problem is constructed explicitly, along with analytical expressions for some excited states in the system. The corresponding Niven equations for determining the polynomial solutions for the problem are given.

quant-ph↗

arXiv2011

The extended Heine-Stieltjes polynomials associated with a special LMG model

New polynomials associated with a special Lipkin-Meshkov-Glick (LMG) model corresponding to the standard two-site Bose-Hubbard model are derived based on the Stieltjes correspondence. It is shown that there is a one-to-one correspondence between zeros of this new polynomial and solutions of the Bethe ansatz equations for the LMG model.A one-dimensional classical electrostatic analogue corresponding to the special LMG model is established according to Stieltjes early work. It shows that any possible configuration of equilibrium positions of the charges in the electrostatic problem corresponds uniquely to one set of roots of the Bethe ansatz equations for the LMG model, and the number of possible configurations of equilibrium positions of the charges equals exactly to the number of energy levels in the LMG model. Some relations of sums of powers and inverse powers of zeros of the new polynomials related to the eigenenergies of the LMG model are derived.

quant-ph↗