1,052 research outputs found
KBGAN: Adversarial Learning for Knowledge Graph Embeddings
We introduce KBGAN, an adversarial learning framework to improve the
performances of a wide range of existing knowledge graph embedding models.
Because knowledge graphs typically only contain positive facts, sampling useful
negative training examples is a non-trivial task. Replacing the head or tail
entity of a fact with a uniformly randomly selected entity is a conventional
method for generating negative facts, but the majority of the generated
negative facts can be easily discriminated from positive facts, and will
contribute little towards the training. Inspired by generative adversarial
networks (GANs), we use one knowledge graph embedding model as a negative
sample generator to assist the training of our desired model, which acts as the
discriminator in GANs. This framework is independent of the concrete form of
generator and discriminator, and therefore can utilize a wide variety of
knowledge graph embedding models as its building blocks. In experiments, we
adversarially train two translation-based models, TransE and TransD, each with
assistance from one of the two probability-based models, DistMult and ComplEx.
We evaluate the performances of KBGAN on the link prediction task, using three
knowledge base completion datasets: FB15k-237, WN18 and WN18RR. Experimental
results show that adversarial training substantially improves the performances
of target embedding models under various settings.Comment: To appear at NAACL HLT 201
Dynamics of the sub-Ohmic spin-boson model: a time-dependent variational study
The Dirac-Frenkel time-dependent variation is employed to probe the dynamics
of the zero temperature sub-Ohmic spin-boson model with strong friction
utilizing the Davydov D1 ansatz. It is shown that initial conditions of the
phonon bath have considerable influence on the dynamics. Counterintuitively,
even in the very strong coupling regime, quantum coherence features still
manage to survive under the polarized bath initial condition, while such
features are absent under the factorized bath initial condition. In addition, a
coherent-incoherent transition is found at a critical coupling strength alpha ~
0.1 for s=0.25 under the factorized bath initial condition. We quantify how
faithfully our ansatz follows the Schr\"{o}dinger equation, finding that the
time-dependent variational approach is robust for strong dissipation and deep
sub-Ohmic baths (s<<1).Comment: 8 pages, 6 figure
Simple Modelling of Undrained Shear Response of Granular Materials
A vast amount of past experimental investigations reported that the internal peak angle of sand was jointly governed by the density and effective stress level. Several relationships were proposed between these elements. The dependence of dilatancy characteristics on the internal state of a granular material was examined and revealed. A simple constitutive model framework was established on a basis of several well-proven and experienced relationships for granular materials to simulate their undrained shear behaviour. A basic hardening law connecting the varying tendency of the stress ratio with shear strain was employed. This model is capable of predicting the undrained monotonic stress-strain relationship of granular materials at different densities and various confining pressures. A series of parametric studies are conducted to investigate the susceptibility of the simulation results to the selected parameters. The simulation results also confirm the influential influences of dilatancy and deformability on the shear characteristics of granular materials at the critical state
Sub-Ohmic spin-boson model with off-diagonal coupling: Ground state properties
We have carried out analytical and numerical studies of the spin-boson model
in the sub-ohmic regime with the influence of both the diagonal and
off-diagonal coupling accounted for via the Davydov D1 variational ansatz.
While a second-order phase transition is known to be exhibited by this model in
the presence of diagonal coupling only, we demonstrate the emergence of a
discontinuous first order phase transition upon incorporation of the
off-diagonal coupling. A plot of the ground state energy versus magnetization
highlights the discontinuous nature of the transition between the isotropic
(zero magnetization) state and nematic (finite magnetization) phases. We have
also calculated the entanglement entropy and a discontinuity found at a
critical coupling strength further supports the discontinuous crossover in the
spin-boson model in the presence of off-diagonal coupling. It is further
revealed via a canonical transformation approach that for the special case of
identical exponents for the spectral densities of the diagonal and the
off-diagonal coupling, there exists a continuous crossover from a single
localized phase to doubly degenerate localized phase with differing
magnetizations.Comment: 11 pages, 7 figure
Entanglement dynamics of a two-qubit system coupled individually to Ohmic baths
Developed originally for the Holstein polaron, the Davydov D1 ansatz is an
efficient, yet extremely accurate trial state for time-dependent variation of
the spin-boson model [J. Chem. Phys. 138, 084111 (2013)]. In this work, the
Dirac-Frenkel time-dependent variational procedure utilizing the Davydov D1
ansatz is implemented to study entanglement dynamics of two qubits under the
influence of two independent baths. The Ohmic spectral density is used without
the Born-Markov approximation or the rotating-wave approximation. In the strong
coupling regime finite-time disentanglement is always found to exist, while at
the intermediate coupling regime, the entanglement dynamics calculated by
Davydov D1 ansatz displays oscillatory behavior in addition to entanglement
disappearance and revival.Comment: 8 pages, 3 figure
Modeling and Simulation of Working Characteristics of Lithium Titanate Batteries for Emergency Power Transmission
This paper presents a battery model applied to dynamic simulation software. The simulation model uses only the battery State-Of-Charge (SOC) as a state variable in order to avoid the algebraic loop problem. It is shown that this model, composed of a controlled voltage source in series with a resistance, can accurately describe the lithium titanate battery discharge process. The model’s parameters can be easily extracted from the manufacturer’s discharge curve. In this paper, it is actually applied to the self-starting system after the emergency stop of the EMU, the simulation model of the system is established by MATLAB/Simulink, and the ground test platform is used to simulate the actual working condition of EMU to complete the experimental verification. The results of both simulation and experiment proved that the scheme of battery self-shifting driven system is feasible and correct
Asymptotic Properties of Some Freud Polynomials
We study the asymptotic properties of monic orthogonal polynomials (OPs) with
respect to some Freud weights when the degree of the polynomial tends to
infinity, including the asymptotics of the recurrence coefficients, the
nontrivial leading coefficients of the monic OPs, the associated Hankel
determinants and the squares of -norm of the monic OPs. These results are
derived from the combination of the ladder operator approach, Dyson's Coulomb
fluid approach and some recent results in the literature
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