434,617 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
Dynamics and constraints of state-led global city formation in emerging economies: The case of Shanghai
This article seeks to contribute to a better understanding of the role of the state in influencing the formation of global cities in emerging economies, and highlights the complexity of this role due to challenging external environment, divergent interests of the state actors, and the socio-economic and institutional constraints that these actors are under. At an empirical level, it examines the progress of Shanghai in its state-led development as an emerging global city and the respective roles of the nationalcentral and local states in this process
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
Precision measurement of cosmic magnification from 21 cm emitting galaxies
We show how precision lensing measurements can be obtained through the
lensing magnification effect in high redshift 21cm emission from galaxies.
Normally, cosmic magnification measurements have been seriously complicated by
galaxy clustering. With precise redshifts obtained from 21cm emission line
wavelength, one can correlate galaxies at different source planes, or exclude
close pairs to eliminate such contaminations.
We provide forecasts for future surveys, specifically the SKA and CLAR. SKA
can achieve percent precision on the dark matter power spectrum and the galaxy
dark matter cross correlation power spectrum, while CLAR can measure an
accurate cross correlation power spectrum. The neutral hydrogen fraction was
most likely significantly higher at high redshifts, which improves the number
of observed galaxies significantly, such that also CLAR can measure the dark
matter lensing power spectrum. SKA can also allow precise measurement of
lensing bispectrum.Comment: 11 pages, 8 figures. Accepted to MNRAS. We deleted two figures and
shortened the paper to meet MNRAS's requirement. All main results remain
unchange
Multiband Emission from Pulsar Wind Nebulae: A Possible Injection Spectrum
A recent research shows that particles with a spectrum of a relativistic
Maxwellian plus a high-energy tail can be accelerated by relativistic
collisionless shocks. We investigate the possibility of the high-energy
particles with this new spectrum injected in pulsar wind nebulae (PWNe) from
the terminate shock based on the study of multiwavelength emission from PWNe.}
{The dynamics of a supernova remnant (SNR) and multiband nonthermal emission
from the PWN inside the remnant are investigated using a dynamical model with
electrons/positrons injected with the new spectrum. In this model, the
dynamical and radiative evolution of a pulsar wind nebula in a non-radiative
supernova remnant can be self-consistently described.} {This model is applied
to the three composite SNRs, G0.9+0.1, MSH 15-52, G338.3-0.0, and the multiband
observed emission from the three PWNe can be well reproduced.} {Our studies on
the three remnant provide evidence for the new spectrum of the particles, which
are accelerated by the terminate shock, injected into a PWN.Comment: 9 pages, 9 figures, accepted by A&
Understanding the performance of the electric power industry in China
© 2012 The Earth Institute at Columbia University and the Massachusetts
Institute of Technology.Despite three decades of reform, China's electricity sector is still organized by a “new reformed plan” where capacity investment has been liberalized but prices and production remain controlled. This paper examines the impact of the current plan prices on end-users with reference to the OECD and how the plan price of electricity supply is formed. We argue that the plan price is set in an attempt to balance the interests of the public and the power industry. We find that China's industries do not pay a cheaper price for electricity than the West, and the plan price is formed through bargain between the firm and the state, which allows the firm to have a soft price constraint on its costs
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