5,786 research outputs found
A Theoretical Analysis of Two-Stage Recommendation for Cold-Start Collaborative Filtering
In this paper, we present a theoretical framework for tackling the cold-start
collaborative filtering problem, where unknown targets (items or users) keep
coming to the system, and there is a limited number of resources (users or
items) that can be allocated and related to them. The solution requires a
trade-off between exploitation and exploration as with the limited
recommendation opportunities, we need to, on one hand, allocate the most
relevant resources right away, but, on the other hand, it is also necessary to
allocate resources that are useful for learning the target's properties in
order to recommend more relevant ones in the future. In this paper, we study a
simple two-stage recommendation combining a sequential and a batch solution
together. We first model the problem with the partially observable Markov
decision process (POMDP) and provide an exact solution. Then, through an
in-depth analysis over the POMDP value iteration solution, we identify that an
exact solution can be abstracted as selecting resources that are not only
highly relevant to the target according to the initial-stage information, but
also highly correlated, either positively or negatively, with other potential
resources for the next stage. With this finding, we propose an approximate
solution to ease the intractability of the exact solution. Our initial results
on synthetic data and the Movie Lens 100K dataset confirm the performance gains
of our theoretical development and analysis
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Analysis of a transient load measuring system
An analysis of the performance of a load measuring system is presented. The load system was designed to measure the weight of a pressure vessel containing high pressure and temperature water. The uncertainty and frequency response of the system are quantified for both steady state and dynamic conditions as is the repeatability of the test rig. Computation of the mass flow exiting the system during explosive decompression of the system is also presented
The Digital Sky Project: Prototyping Virtual Observatory Technologies
Astronomy is entering a new era as multiple, large area, digital sky surveys
are in production. The resulting datasets are truly remarkable in their own
right; however, a revolutionary step arises in the aggregation of complimentary
multi-wavelength surveys (i.e., the cross-identification of a billion sources).
The federation of these large datasets is already underway, and is producing a
major paradigm shift as Astronomy has suddenly become an immensely data-rich
field. This new paradigm will enable quantitatively and qualitatively new
science, from statistical studies of our Galaxy and the large-scale structure
in the universe, to discoveries of rare, unusual, or even completely new types
of astronomical objects and phenomena. Federating and then exploring these
large datasets, however, is an extremely challenging task. The Digital Sky
project was initiated with this task in mind and is working to develop the
techniques and technologies necessary to solve the problems inherent in
federating these large databases, as well as the mining of the resultant
aggregate data.Comment: 8 pages, 3 Figures, uses newpasp.sty (included). To be published in
the proceedings of the conference "Virtual Observatories of the Future,"
editors R.J. Brunner, S.G. Djorgovski, and Alex S. Szala
Design of the Spitzer Space Telescope Heritage Archive
It is predicted that Spitzer Space Telescope’s cryogen will run out in April 2009, and the final reprocessing for the cryogenic mission is scheduled to end in April 2011, at which time the Spitzer archive will be transferred to the NASA/IPAC Infrared Science Archive (IRSA) for long-term curation. The Spitzer Science Center (SSC) and IRSA are collaborating to design and deploy the Spitzer Heritage Archive (SHA), which will supersede the current Spitzer archive. It will initially contain the raw and final reprocessed cryogenic science products, and will eventually incorporate the final products from the Warm mission. The SHA will be accompanied by tools deemed necessary to extract the full science content of the archive and by comprehensive documentation
Rotational period of WD1953-011 - a magnetic white dwarf with a star spot
WD1953-011 is an isolated, cool (7920 +/- 200K, Bergeron, Legget & Ruiz,
2001) magnetic white dwarf (MWD) with a low average field strength (~70kG,
Maxted et al. 2000) and a higher than average mass (~0.74 M_sun, Bergeron et
al. 2001). Spectroscopic observations taken by Maxted et al. (2000) showed
variations of equivalent width in the Balmer lines, unusual in a low field
white dwarf. Here we present V band photometry of WD1953-011 taken at 7 epochs
over a total of 22 months. All of the datasets show a sinusoidal variation of
approximately 2% peak-to-peak amplitude. We propose that these variations are
due to a star spot on the MWD, analogous to a sunspot, which is affecting the
temperature at the surface, and therefore its photometric magnitude. The
variations have a best-fit period over the entire 22 months of 1.4418 days,
which we interpret as the rotational period of the WD.Comment: (1) University of Southampton, (2) University of Warwick, (3)
University of Nijmegen, (4) Keele University, (5) University of Leicester. 6
pages, 5 figs, accepted MNRA
Developmental Changes in Pedunculopontine Nucleus (PPN) Neurons
The developmental decrease in rapid-eye-movement (REM) sleep in man occurs between birth and after puberty. We hypothesize that if this decrease in REM sleep does not occur, lifelong increases in REM sleep drive may ensue. Such disorders are characterized by hypervigilance and sensory-gating deficits, such as are present in postpubertal onset disorders like schizophrenia, panic attacks (a form of anxiety disorder), and depression. The decrease in REM sleep in the rat occurs between 10 and 30 days of age. We studied changes in size and physiological properties of pedunculopontine nucleus (PPN) cells involved in the control of arousal, i.e., waking and REM sleep. During the largest decrease in REM sleep (12–21 days), cholinergic PPN neurons doubled in cell area, the hypertrophy peaking at 15–16 days, then decreasing in area by 20–21 days. Noncholinergic PPN cells did not change in area during this period. We confirmed the presence of two populations of PPN neurons based on action potential (AP) duration, with the proportion of short-AP-duration cells increasing and long AP duration decreasing between 12 and 21 days. Most cholinergic and noncholinergic cells had short AP durations. Afterhyperpolarization (AHP) duration became segregated into long and short AHP duration after 15 days. Cells with short AP duration also had short AHP duration. The proportion of PPN cells with Ih current increased gradually, peaking at 15 days, then decreased by 21 days. These changes in morphological and physiological properties are discussed in relation to the developmental decrease in REM sleep
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