3,634 research outputs found
Mining Web Dynamics for Search
Billions of web users collectively contribute to a dynamic web that preserves how information sources and descriptions change over time. This dynamic process sheds light on the quality of web content, and even indicates the temporal properties of information needs expressed via queries. However, existing commercial search engines typically utilize one crawl of web content (the latest) without considering the complementary information concealed in web dynamics. As a result, the generated rankings may be biased due to the efficiency of knowledge on page or hyperlink evolution, and the time-sensitive facet within search quality, e.g., freshness, has to be neglected. While previous research efforts have been focused on exploring the temporal dimension in retrieval process, few of them showed consistent improvements on large-scale real-world archival web corpus with a broad time span.We investigate how to utilize the changes of web pages and hyperlinks to improve search quality, in terms of freshness and relevance of search results. Three applications that I have focused on are: (1) document representation, in which the anchortext (short descriptive text associated with hyperlinks) importance is estimated by considering its historical status; (2) web authority estimation, in which web freshness is quantified and utilized for controlling the authority propagation; and (3) learning to rank, in which freshness and relevance are optimized simultaneously in an adaptive way depending on query type. The contributions of this thesis are: (1) incorporate web dynamics information into critical components within search infrastructure in a principled way; and (2) empirically verify the proposed methods by conducting experiments based on (or depending on) a large-scale real-world archival web corpus, and demonstrated their superiority over existing state-of-the-art
Vaccine Types
There are several different types of vaccines. Each type is designed to teach your immune system how to fight off certain kinds of germs and the serious diseases they cause. There are four main types of vaccines: live attenuated vaccines; inactivated vaccines; subunit, recombinant, polysaccharide, and conjugate vaccines; and toxoid vaccines
Stochastic Nonlinear Control via Finite-dimensional Spectral Dynamic Embedding
Optimal control is notoriously difficult for stochastic nonlinear systems.
Ren et al. introduced Spectral Dynamics Embedding for developing reinforcement
learning methods for controlling an unknown system. It uses an
infinite-dimensional feature to linearly represent the state-value function and
exploits finite-dimensional truncation approximation for practical
implementation. However, the finite-dimensional approximation properties in
control have not been investigated even when the model is known. In this paper,
we provide a tractable stochastic nonlinear control algorithm that exploits the
nonlinear dynamics upon the finite-dimensional feature approximation, Spectral
Dynamics Embedding Control (SDEC), with an in-depth theoretical analysis to
characterize the approximation error induced by the finite-dimension truncation
and statistical error induced by finite-sample approximation in both policy
evaluation and policy optimization. We also empirically test the algorithm and
compare the performance with Koopman-based methods and iLQR methods on the
pendulum swingup problem
Bulk viscosity of Mixed nucleon-hyperon-quark Matter in Neutron stars
We calculate the coefficient of bulk viscosity by considering the
non-leptonic weak interactions in the cores of hybrid stars with both hyperons
and quarks. We first determine the dependence of the production rate of
neutrons on the reaction rate of quarks in the non-leptonic processes, that is
. The
conversion rate, in our scenario is a complicated function of baryon
number density. We also consider medium effect of quark matter on bulk
viscosity. Using these results, we estimate the limiting rotation of the hybrid
stars, which may suppress the r-mode instability more effectively. Hybrid stars
should be the candidates for the extremely rapid rotators .Comment: This paper contains 17 pages,8 figures and 1 table and is accepted by
Monthly Notices of the Royal Astronomical Societ
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