3,154 research outputs found
Deriving item features relevance from collaborative domain knowledge
An Item based recommender system works by computing a similarity between
items, which can exploit past user interactions (collaborative filtering) or
item features (content based filtering). Collaborative algorithms have been
proven to achieve better recommendation quality then content based algorithms
in a variety of scenarios, being more effective in modeling user behaviour.
However, they can not be applied when items have no interactions at all, i.e.
cold start items. Content based algorithms, which are applicable to cold start
items, often require a lot of feature engineering in order to generate useful
recommendations. This issue is specifically relevant as the content descriptors
become large and heterogeneous. The focus of this paper is on how to use a
collaborative models domain-specific knowledge to build a wrapper feature
weighting method which embeds collaborative knowledge in a content based
algorithm. We present a comparative study for different state of the art
algorithms and present a more general model. This machine learning approach to
feature weighting shows promising results and high flexibility
First principles characterization of reversible martensitic transformations
Reversible martensitic transformations (MTs) are the origin of many
fascinating phenomena, including the famous shape memory effect. In this work,
we present a fully ab initio procedure to characterize MTs in alloys and to
assess their reversibility. Specifically, we employ ab initio molecular
dynamics data to parametrize a Landau expansion for the free energy of the MT.
This analytical expansion makes it possible to determine the stability of the
high- and low-temperature phases, to obtain the Ehrenfest order of the MT, and
to quantify its free energy barrier and latent heat. We apply our model to the
high-temperature shape memory alloy Ti-Ta, for which we observe remarkably
small values for the metastability region (the interval of temperatures in
which the high-and low-temperature phases are metastable) and for the barrier:
these small values are necessary conditions for the reversibility of MTs and
distinguish shape memory alloys from other materials
Photoinduced inverse spin Hall effect in Pt/Ge(001) at room temperature
We performed photoinduced inverse spin Hall effect (ISHE) measurements on a
Pt/Ge(001) junction at room temperature. The spin-oriented electrons,
photogenerated at the direct gap of Ge using circularly polarized light,
provide a net spin current which yields an electromotive field E_ISHE in the Pt
layer. Such a signal is clearly detected at room temperature despite the strong
{\Gamma} to L scattering which electrons undergo in the Ge conduction band. The
ISHE signal dependence on the exciting photon energy is in good agreement with
the electron spin polarization expected for optical orientation at the direct
gap of Ge
Satellite Altimetry and Current-Meter Velocities in the Malvinas Current at 41°S: Comparisons and Modes of Variations
Three year long current-meter arrays were deployed in the Malvinas Current at 418S below a satellite altimeter track at about 10 years intervals. Surface geostrophic velocities (SGV) derived from satel- lite altimetric data are compared with the in situ velocities at the upper current meter (􏰁300 m). Multisatel- lite gridded SGV compare better with in situ observations than along-track SGV. In spite of the proximity of the moorings to the complex Brazil-Malvinas Confluence (BMC) region, satellite SGV are significantly corre- lated with the 20 day low-passed in situ velocities (0.85 for along-isobaths velocities, 0.8 for cross-isobaths velocities). The recent in situ measurement period (2014?2015) stands out in the altimetry record with a long-lasting (4 months) high level of eddy kinetic energy at the mooring site and a southernmost location of the Subantarctic Front (SAF). The first two modes of variations of sea level anomaly (SLA) over the BMC remarkably match the first two modes of the low-passed in situ velocities. The first mode is associated with a latitudinal migration of the SAF, and the second with a longitudinal displacement of the Brazil Current overshoot. The two modes dominate the 24 year long record of SLA in the BMC, with energy peaks at the annual and semiannual periods for the first mode and at 3?5 months for the second mode. The SLA over the Southwest Atlantic was regressed onto the two confluence modes of SLA variations and showed remarkable standing wave train like structures in the Argentine Basin.Fil: Ferrari, Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Artana, Camila Indira. Universite de Paris VI; FranciaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Provost, Christine. Universite de Paris VI; Franci
- …