16,939 research outputs found
ASSET FIXITY IN U.S. AGRICULTURE: ROBUSTNESS TO FUNCTIONAL FORM
The sensitivity of asset fixity conclusions, input adjustment rates, and elasticities to choice of functional form is examined using a dynamic dual model of U.S. agriculture. A very general initial specification allows tests of instantaneous adjustment to be performed for every input. Test results are mixed across functional forms for all inputs except real estate, which is consistently found to be quasi-fixed. Important differences in estimated adjustment rates and elasticities are also found among the functional forms. The translog has higher likelihood support than either the generalized Leontief or normalized quadratic functional forms for this dynamic model specification and data set.Agricultural Finance, Research Methods/ Statistical Methods, Q11, C51,
Learning to Control in Metric Space with Optimal Regret
We study online reinforcement learning for finite-horizon deterministic
control systems with {\it arbitrary} state and action spaces. Suppose that the
transition dynamics and reward function is unknown, but the state and action
space is endowed with a metric that characterizes the proximity between
different states and actions. We provide a surprisingly simple upper-confidence
reinforcement learning algorithm that uses a function approximation oracle to
estimate optimistic Q functions from experiences. We show that the regret of
the algorithm after episodes is where is a
smoothness parameter, and is the doubling dimension of the state-action
space with respect to the given metric. We also establish a near-matching
regret lower bound. The proposed method can be adapted to work for more
structured transition systems, including the finite-state case and the case
where value functions are linear combinations of features, where the method
also achieve the optimal regret
Geometric phases for wave packets in a uniform magnetic field
A wave packet of a charged particle always make cyclic circular motion in a
uniform magnetic field, just like a classical particle. The nonadiabatic
geometric phase for an arbitrary wave packet can be expressed in terms of the
mean value of a number operator. For a large class of wave packets, the
geometric phase is proportional to the magnetic flux encircled by the orbit of
the wave packet. For more general wave packets, however, the geometric phase
contains an extra term.Comment: REVTeX4, 7 pages, no figur
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Effective video multicast over wireless internet
With the rapid growth of wireless networks and great success of Internet video, wireless video services are expected to be widely deployed in the near future. As different types of wireless networks are converging into all IP networks, i.e., the Internet, it is important to study video delivery over the wireless Internet. This paper proposes a novel end-system based adaptation protocol calledWireless Hybrid Adaptation Layered Multicast (WHALM) protocol for layered video multicast over wireless Internet. In WHALM the sender dynamically collects bandwidth distribution from the receivers and uses an optimal layer rate allocation mechanism to reduce the mismatches between the coarse-grained layer subscription levels and the heterogeneous and dynamic rate requirements from the receivers, thus maximizing the degree of satisfaction of all the receivers in a multicast session. Based on sampling theory and theory of probability, we reduce the required number of bandwidth feedbacks to a reasonable degree and use a scalable feedback mechanism to control the feedback process practically. WHALM is also tuned to perform well in wireless networks by integrating an end-to-end loss differentiation algorithm (LDA) to differentiate error losses from congestion losses at the receiver side. With a series of simulation experiments over NS platform, WHALM has been proved to be able to greatly improve the degree of satisfaction of all the receivers while avoiding congestion collapse on the wireless Internet
Electron-positron pair creation in a vacuum by an electromagnetic field in 3+1 and lower dimensions
We calculate the probability of electron-positron pair creation in vacuum in
3+1 dimensions by an external electromagnetic field composed of a constant
uniform electric field and a constant uniform magnetic field, both of arbitrary
magnitudes and directions. The same problem is also studied in 2+1 and 1+1
dimensions in appropriate external fields and similar results are obtained.Comment: REVTeX, 10 pages, no figure, a brief note and some more references
added in the proo
Scattering by a contact potential in three and lower dimensions
We consider the scattering of nonrelativistic particles in three dimensions
by a contact potential which is defined
as the limit of . It is
surprising that it gives a nonvanishing cross section when and
. When the contact potential is approached by a spherical square
well potential instead of the above spherical shell one, one obtains basically
the same result except that the parameter that gives a nonvanishing
cross section is different. Similar problems in two and one dimensions are
studied and results of the same nature are obtained.Comment: REVTeX, 9 pages, no figur
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