14,253 research outputs found
A Simple Linear Ranking Algorithm Using Query Dependent Intercept Variables
The LETOR website contains three information retrieval datasets used as a
benchmark for testing machine learning ideas for ranking. Algorithms
participating in the challenge are required to assign score values to search
results for a collection of queries, and are measured using standard IR ranking
measures (NDCG, precision, MAP) that depend only the relative score-induced
order of the results. Similarly to many of the ideas proposed in the
participating algorithms, we train a linear classifier. In contrast with other
participating algorithms, we define an additional free variable (intercept, or
benchmark) for each query. This allows expressing the fact that results for
different queries are incomparable for the purpose of determining relevance.
The cost of this idea is the addition of relatively few nuisance parameters.
Our approach is simple, and we used a standard logistic regression library to
test it. The results beat the reported participating algorithms. Hence, it
seems promising to combine our approach with other more complex ideas.Comment: 5 page
Revealing common artifacts due to ferromagnetic inclusions in highly-oriented pyrolytic graphite
We report on an extensive investigation to figure out the origin of
room-temperature ferromagnetism that is commonly observed by SQUID magnetometry
in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray
microanalysis revealed the presence of micron-size magnetic clusters
(predominantly Fe) that are rare and would be difficult to detect without
careful search in a scanning electron microscope in the backscattering mode.
The clusters pin to crystal boundaries and their quantities match the amplitude
of typical ferromagnetic signals. No ferromagnetic response is detected in
samples where we could not find such magnetic inclusions. Our experiments show
that the frequently reported ferromagnetism in pristine HOPG is most likely to
originate from contamination with Fe-rich inclusions introduced presumably
during crystal growth.Comment: 8 pages, 7 figure
Three-Dimensional Modeling of Transport Phenomena and their Effect on the Formation of Ripples in Gas Metal Arc Welding
Distinct, periodic arc-shaped ripples are observed on the surface of the weld bead in almost any welded components which have a significant effect on weld quality. This article presents the complex transport phenomena and their effect on the formation of ripples in three-dimensional moving gas metal arc welding. The transient distributions of the melt flow velocity and temperature in the weld pool, weld pool shape and dynamics, and solidified weld bead are calculated. It is found that the surface ripples are formed by the interplay between the up-and-down weld pool dynamics, caused mainly by the periodic droplet impingements, and the rate of weld pool solidification. The effects of various welding parameters, including the welding current, droplet size, droplet frequency, droplet impinging velocity, and travel speed on the pitch (distance between two ripples) and height of the ripple are investigated. This study provides fundamental understanding to the underlying physics that cause the formation of ripples with different pitches and heights
Two semi-Lagrangian fast methods for Hamilton-Jacobi-Bellman equations
In this paper we apply the Fast Iterative Method (FIM) for solving general
Hamilton-Jacobi-Bellman (HJB) equations and we compare the results with an
accelerated version of the Fast Sweeping Method (FSM). We find that FIM can be
indeed used to solve HJB equations with no relevant modifications with respect
to the original algorithm proposed for the eikonal equation, and that it
overcomes FSM in many cases. Observing the evolution of the active list of
nodes for FIM, we recover another numerical validation of the arguments
recently discussed in [Cacace et al., SISC 36 (2014), A570-A587] about the
impossibility of creating local single-pass methods for HJB equations
Progress towards quantum simulating the classical O(2) model
We connect explicitly the classical model in 1+1 dimensions, a model
sharing important features with lattice gauge theory, to physical models
potentially implementable on optical lattices and evolving at physical time.
Using the tensor renormalization group formulation, we take the time continuum
limit and check that finite dimensional projections used in recent proposals
for quantum simulators provide controllable approximations of the original
model. We propose two-species Bose-Hubbard models corresponding to these finite
dimensional projections at strong coupling and discuss their possible
implementations on optical lattices using a Rb and K Bose-Bose
mixture.Comment: 7 pages, 6 figures, uses revtex, new material and one author added,
as to appear in Phys. Rev.
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