1,635 research outputs found
Creating Full Individual-level Location Timelines from Sparse Social Media Data
In many domain applications, a continuous timeline of human locations is
critical; for example for understanding possible locations where a disease may
spread, or the flow of traffic. While data sources such as GPS trackers or Call
Data Records are temporally-rich, they are expensive, often not publicly
available or garnered only in select locations, restricting their wide use.
Conversely, geo-located social media data are publicly and freely available,
but present challenges especially for full timeline inference due to their
sparse nature. We propose a stochastic framework, Intermediate Location
Computing (ILC) which uses prior knowledge about human mobility patterns to
predict every missing location from an individual's social media timeline. We
compare ILC with a state-of-the-art RNN baseline as well as methods that are
optimized for next-location prediction only. For three major cities, ILC
predicts the top 1 location for all missing locations in a timeline, at 1 and
2-hour resolution, with up to 77.2% accuracy (up to 6% better accuracy than all
compared methods). Specifically, ILC also outperforms the RNN in settings of
low data; both cases of very small number of users (under 50), as well as
settings with more users, but with sparser timelines. In general, the RNN model
needs a higher number of users to achieve the same performance as ILC. Overall,
this work illustrates the tradeoff between prior knowledge of heuristics and
more data, for an important societal problem of filling in entire timelines
using freely available, but sparse social media data.Comment: 10 pages, 8 figures, 2 table
Photoluminescent characteristics of Ni-catalyzed GaN nanowires
The authors report on time-integrated and time-resolved photoluminescence (PL) of GaN nanowires grown by the Ni-catalyst-assisted vapor-liquid-solid method. From PL spectra of Ni-catalyzed GaN nanowires at 10 K, several PL peaks were observed at 3.472, 3.437, and 3.266 eV, respectively. PL peaks at 3.472 and 3.266 eV are attributed to neutral-donor-bound excitons and donor-acceptor pair, respectively. Furthermore, according to the results from temperature-dependent and time-resolved PL measurements, the origin of the PL peak at 3.437 eV is also discussed. (c) 2006 American Institute of Physics.X1147sciescopu
Susceptibility of South Korea to Extremes Affecting the Global Food System
Food security in South Korea is tightly linked to the global food system. The country's production of major grains declined from 5.8 million metric tons (mmt) in 1998 to 4.8 mmt in 2014, which caused the country's grain self suciency to decline from 31.4% to 24%. This decline is a consequence of several factors including reductions in domestic agricultural land, governmental policies supporting industry over agriculture, and a push towards trade liberalization. South Korea's self suciency is now one of the lowest among Organisation for Economic Co-operation and Development (OECD) countries, leaving it vulnerable to disruptions in the global food system
Real-time Measurement of Stress and Damage Evolution During Initial Lithiation of Crystalline Silicon
Crystalline to amorphous phase transformation during initial lithiation in
(100) silicon-wafers is studied in an electrochemical cell with lithium metal
as the counter and reference electrode. It is demonstrated that severe stress
jumps across the phase boundary lead to fracture and damage, which is an
essential consideration in designing silicon based anodes for lithium ion
batteries. During initial lithiation, a moving phase boundary advances into the
wafer starting from the surface facing the lithium electrode, transforming
crystalline silicon into amorphous LixSi. The resulting biaxial compressive
stress in the amorphous layer is measured in situ and it was observed to be ca.
0.5 GPa. HRTEM images reveal that the crystalline-amorphous phase boundary is
very sharp, with a thickness of ~ 1 nm. Upon delithiation, the stress rapidly
reverses, becomes tensile and the amorphous layer begins to deform plastically
at around 0.5 GPa. With continued delithiation, the yield stress increases in
magnitude, culminating in sudden fracture of the amorphous layer into
micro-fragments and the cracks extend into the underlying crystalline silicon.Comment: 12 pages, 5 figure
Lensed CMB power spectra from all-sky correlation functions
Weak lensing of the CMB changes the unlensed temperature anisotropy and
polarization power spectra. Accounting for the lensing effect will be crucial
to obtain accurate parameter constraints from sensitive CMB observations.
Methods for computing the lensed power spectra using a low-order perturbative
expansion are not good enough for percent-level accuracy. Non-perturbative
flat-sky methods are more accurate, but curvature effects change the spectra at
the 0.3-1% level. We describe a new, accurate and fast, full-sky
correlation-function method for computing the lensing effect on CMB power
spectra to better than 0.1% at l<2500 (within the approximation that the
lensing potential is linear and Gaussian). We also discuss the effect of
non-linear evolution of the gravitational potential on the lensed power
spectra. Our fast numerical code is publicly available.Comment: 16 pages, 4 figures. Changes to match PRD version including new
section on non-linear corrections. CAMB code available at http://camb.info
RXCJ1111.6+4050 galaxy cluster: the observational evidence of a transitional fossil group
We present a detailed kinematical and dynamical study of the galaxy cluster
RXCJ1111.6+4050 (RXCJ1111), at z = 0.0756 using 104 new spectroscopic redshifts
of galaxies observed at the TNG 3.5m telescope and SDSS DR16 public archive.
Our analysis is performed in a multiwavelength context in order to study and
compare mainly optical and X-ray properties using XMM-Newton data. We find that
RXCJ1111 is a galaxy cluster showing a velocity distribution with clear
deviations from Gaussianity, that we are able to explain by the presence of a
substructure within the cluster. The two cluster components show velocity
dispersions of km/s and km/s, which yield dynamical
masses of M= M and M for the main system and substructure, respectively.
RXCJ1111 presents an elongation in the North-South direction and a gradient of
250-350 km/s/Mpc in the velocity field, suggest that the merger axis between
the main system and substructure is slightly tilted with respect to the
line-of-sight. The substructure is characterized by a magnitude gap , so it fits the "fossil-like" definition of a galaxy group.
Mass estimates derived from X-ray and optical are in good agreement when two
galaxy components are considered separately. We propose a 3D merging model and
find that the fossil group is in an early phase of collision with the RXCJ1111
main cluster and almost aligned with the line-of-sight. This merging model
would explain the slight increase found in the T with respect to what we
would expect for relaxed clusters. Due to the presence of several brightest
galaxies, after this collision, the substructure would presumably lose its
fossil condition. Therefore, RXCJ1111 represents the observational evidence
that the fossil stage of a system can be temporary and transitional.Comment: 16 pages, 11 figures, 3 tables and 1 appendi
Development of ultra-light pixelated ladders for an ILC vertex detector
The development of ultra-light pixelated ladders is motivated by the
requirements of the ILD vertex detector at ILC. This paper summarizes three
projects related to system integration. The PLUME project tackles the issue of
assembling double-sided ladders. The SERWIETE project deals with a more
innovative concept and consists in making single-sided unsupported ladders
embedded in an extra thin plastic enveloppe. AIDA, the last project, aims at
building a framework reproducing the experimental running conditions where sets
of ladders could be tested
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