223,864 research outputs found
Restricted Value Iteration: Theory and Algorithms
Value iteration is a popular algorithm for finding near optimal policies for
POMDPs. It is inefficient due to the need to account for the entire belief
space, which necessitates the solution of large numbers of linear programs. In
this paper, we study value iteration restricted to belief subsets. We show
that, together with properly chosen belief subsets, restricted value iteration
yields near-optimal policies and we give a condition for determining whether a
given belief subset would bring about savings in space and time. We also apply
restricted value iteration to two interesting classes of POMDPs, namely
informative POMDPs and near-discernible POMDPs
The structure and magnetism of graphone
Graphone is a half-hydrogenated graphene. The structure of graphone is
illustrated as trigonal adsorption of hydrogen atoms on graphene at first.
However, we found the trigonal adsorption is unstable. We present an
illustration in detail to explain how a trigonal adsorption geometry evolves
into a rectangular adsorption geometry. We check the change of magnetism during
the evolution of geometry by evaluating the spin polarization of the
intermediate geometries. We prove and clarify that the rectangular adsorption
of hydrogen atoms on graphene is the most stable geometry of graphone and
graphone is actually antiferromagnetic.Comment: 11 pages, 4 figure
A Model Approximation Scheme for Planning in Partially Observable Stochastic Domains
Partially observable Markov decision processes (POMDPs) are a natural model
for planning problems where effects of actions are nondeterministic and the
state of the world is not completely observable. It is difficult to solve
POMDPs exactly. This paper proposes a new approximation scheme. The basic idea
is to transform a POMDP into another one where additional information is
provided by an oracle. The oracle informs the planning agent that the current
state of the world is in a certain region. The transformed POMDP is
consequently said to be region observable. It is easier to solve than the
original POMDP. We propose to solve the transformed POMDP and use its optimal
policy to construct an approximate policy for the original POMDP. By
controlling the amount of additional information that the oracle provides, it
is possible to find a proper tradeoff between computational time and
approximation quality. In terms of algorithmic contributions, we study in
details how to exploit region observability in solving the transformed POMDP.
To facilitate the study, we also propose a new exact algorithm for general
POMDPs. The algorithm is conceptually simple and yet is significantly more
efficient than all previous exact algorithms.Comment: See http://www.jair.org/ for any accompanying file
A Primary Study of Heavy Baryons Lambda_Q, Xi_Q, Sigma_Q and Omega_Q
We perform a preliminary study of the 1/2+ and 3/2+ ground-state baryons
containing a heavy quark in the framework of the chiral SU(3) quark model. By
using the calculus of variations, masses of Lambda_Q, Sigma_Q, Xi_Q, Omega_Q,
Sigma_Q^*, Xi_Q^* and Omega_Q^*, where Q means c or b quark, are calculated.
With taking reasonable model parameters, the numerical results of established
heavy baryons are generally in agreement with the available experimental data,
except that those of Xi_Q are somewhat heavier. For Omega_b with undetermined
experimental mass and nobserved Xi_b^*, Omega_b^*, reasonable theoretical
predictions are obtained. Interactions inside baryons are also discussed.Comment: 5 page
Observation of Terahertz Radiation via the Two-Color Laser Scheme with Uncommon Frequency Ratios
In the widely-studied two-color laser scheme for terahertz (THz) radiation
from a gas, the frequency ratio of the two lasers is usually fixed at
1:2. We investigate THz generation with uncommon frequency
ratios. Our experiments show, for the first time, efficient THz generation with
new ratios of 1:4 and 2:3. We observe that the THz
polarization can be adjusted by rotating the longer-wavelength laser
polarization and the polarization adjustment becomes inefficient by rotating
the other laser polarization; the THz energy shows similar scaling laws with
different frequency ratios. These observations are inconsistent with multi-wave
mixing theory, but support the gas-ionization model. This study pushes the
development of the two-color scheme and provides a new dimension to explore the
long-standing problem of the THz generation mechanism.Comment: 6 pages, 3 figure
Measurement of surface potential decay of corona-charged polymer films using the pulsed electroacoustic method
In this paper, the pulsed electroacoustic (PEA) technique that allows the determination of space charge in a dielectric material has been used to monitor the electrical potential decay of corona-charged polyethylene films of different thicknesses. To prevent possible disturbance on the surface charge during the PEA measurements, two thin polyethylene films were placed on both sides of the corona-charged sample. Charge profiles measured at different times were used to calculate the potential across the sample. The obtained potential decay was compared with the potential measured using the conventional method. A good agreement has been obtained. More importantly, the charge profile obtained using the PEA technique indicates that bipolar charge injection has taken place
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