1,662 research outputs found
Improving Simulation Efficiency of MCMC for Inverse Modeling of Hydrologic Systems with a Kalman-Inspired Proposal Distribution
Bayesian analysis is widely used in science and engineering for real-time
forecasting, decision making, and to help unravel the processes that explain
the observed data. These data are some deterministic and/or stochastic
transformations of the underlying parameters. A key task is then to summarize
the posterior distribution of these parameters. When models become too
difficult to analyze analytically, Monte Carlo methods can be used to
approximate the target distribution. Of these, Markov chain Monte Carlo (MCMC)
methods are particularly powerful. Such methods generate a random walk through
the parameter space and, under strict conditions of reversibility and
ergodicity, will successively visit solutions with frequency proportional to
the underlying target density. This requires a proposal distribution that
generates candidate solutions starting from an arbitrary initial state. The
speed of the sampled chains converging to the target distribution deteriorates
rapidly, however, with increasing parameter dimensionality. In this paper, we
introduce a new proposal distribution that enhances significantly the
efficiency of MCMC simulation for highly parameterized models. This proposal
distribution exploits the cross-covariance of model parameters, measurements
and model outputs, and generates candidate states much alike the analysis step
in the Kalman filter. We embed the Kalman-inspired proposal distribution in the
DREAM algorithm during burn-in, and present several numerical experiments with
complex, high-dimensional or multi-modal target distributions. Results
demonstrate that this new proposal distribution can greatly improve simulation
efficiency of MCMC. Specifically, we observe a speed-up on the order of 10-30
times for groundwater models with more than one-hundred parameters
3β-HydroxyÂfriedelan-17β-carboxylic acid
The title compound, C30H50O3, which was isolated from a marine endophytic fungus, is a new friedelan derivative. The molÂecule contains five six-membered rings, which exhibit boat (ring A), distorted boat (ring B) and chair (rings C–E) conformations. The crystal structure is stabilized by interÂmolecular O—H⋯O hydrogen bonds, which link neighbouring molÂecules into 12-membered rings
The investigations of the -wave states combining quark model and lattice QCD in the coupled channel framework
Combining the quark model, the quark-pair-creation mechanism and
interaction, we have investigated the near-threshold -wave states in
the framework of the Hamiltonian effective field theory. With the heavy quark
flavor symmetry, all the parameters are determined in the sector by
fitting the lattice data. The masses of the bottom-strange partners of the
and are predicted to be
MeV and MeV, respectively, which are well consistent with the
lattice QCD simulation. The two P-wave states are the mixtures of the
bare core and component. Moreover, we find a crossing
point between the energy levels with and without the interaction Hamiltonian in
the finite volume spectrum in the case, which corresponds to a CDD
(Castillejo-Dalitz-Dyson) zero in the -matrix of the scattering. This
CDD zero will help deepen the insights of the near-threshold states and can be
examined by the future lattice calculation.Comment: 20 pages, 4 figure
Optimal estimation and control for lossy network: stability, convergence, and performance
In this paper, we study the problems of optimal estimation and control, i.e., the linear quadratic Gaussian (LQG) control, for systems with packet losses but without acknowledgment. Such acknowledgment is a signal sent by the actuator to inform the estimator of the incidence of control packet losses. For such system, which is usually called as a user datagram protocol (UDP)-like system, the optimal estimation is nonlinear and its calculation is time-consuming, making its corresponding optimal LQG problem complicated. We first propose two conditions: 1) the sensor has some computation abilities; and 2) the control command, exerted to the plant, is known to the sensor. For a UDP-like system satisfying these two conditions, we derive the optimal estimation. By constructing the finite and infinite product probability measure spaces for the estimation error covariances (EEC), we give the stability condition for the expected EEC, and show the existence of a measurable function to which the EEC converges in distribution, and propose some practical methods to evaluate the estimation performance. Finally, the LQG controllers are derived, and the conditions for the mean square stability of the closed-loop system are established
Experimental Decoy Quantum Key Distribution Up To 130KM Fiber
Decoy State Quantum Key Distribution (QKD), being capable of beating PNS
attack and uncon- ditionally secure, have become an attractive one recently.
But, in many QKD systems, disturbances of transmission channel make quantum bit
error rate (QBER) increase which limits both security distance and key bit rate
of real-life decoy state QKD systems. We demonstrate the two-intensity decoy
QKD with one-way Faraday-Michelson phase modulation system, which is free of
channel dis- turbance and keeps interference fringe visibility (99%) long
period, near 130KM single mode optical fiber in telecom (1550 nm) wavelength.
This is longest distance fiber decoy state QKD system based on two intensity
protocol.Comment: 4 pages, 2figure
- …