3,394 research outputs found
Gas Anxiety and the Charging Choices of Plug-In Hybrid Electric Vehicle Drivers
Plug-in hybrid electric vehicles (PHEV) provide an opportunity to reduce petroleum consumption and greenhouse gas emissions without causing range anxiety. As a result, PHEV drivers are commonly assumed to be less dependent on the availability of charging infrastructure than battery electric vehicle (BEV) drivers. However there is also evidence that PHEVs plug in more often than BEVs because the owners have gas anxiety - a strong desire to avoid using gasoline. This work examines the existence of gas anxiety by analyzing the factors influencing charging decision of PHEV owners. A web-based stated preference survey was conducted and the data was analyzed using a latent class logit model. The result shows that there are two classes of decision making patterns among PHEV owners: those who value gasoline cost and recharging expenditure almost the same (class 1) and those who value gasoline cost more heavily than recharging cost (class 2). Among those in class 2, the amount of money spent on gasoline has much bigger influence on the utility of charging than the amount spent on electricity at the recharging station, which can be interpreted as a form of gas anxiety
Beyond Intuition, a Framework for Applying GPs to Real-World Data
Gaussian Processes (GPs) offer an attractive method for regression over
small, structured and correlated datasets. However, their deployment is
hindered by computational costs and limited guidelines on how to apply GPs
beyond simple low-dimensional datasets. We propose a framework to identify the
suitability of GPs to a given problem and how to set up a robust and
well-specified GP model. The guidelines formalise the decisions of experienced
GP practitioners, with an emphasis on kernel design and options for
computational scalability. The framework is then applied to a case study of
glacier elevation change yielding more accurate results at test time.Comment: Accepted at the 1st ICML Workshop on Structured Probabilistic
Inference and Generative Modelling (2023
UnLoc: A Unified Framework for Video Localization Tasks
While large-scale image-text pretrained models such as CLIP have been used
for multiple video-level tasks on trimmed videos, their use for temporal
localization in untrimmed videos is still a relatively unexplored task. We
design a new approach for this called UnLoc, which uses pretrained image and
text towers, and feeds tokens to a video-text fusion model. The output of the
fusion module are then used to construct a feature pyramid in which each level
connects to a head to predict a per-frame relevancy score and start/end time
displacements. Unlike previous works, our architecture enables Moment
Retrieval, Temporal Localization, and Action Segmentation with a single stage
model, without the need for action proposals, motion based pretrained features
or representation masking. Unlike specialized models, we achieve state of the
art results on all three different localization tasks with a unified approach.
Code will be available at: \url{https://github.com/google-research/scenic}.Comment: ICCV 202
The z=5 Quasar Luminosity Function from SDSS Stripe 82
We present a measurement of the Type I quasar luminosity function at z=5
using a large sample of spectroscopically confirmed quasars selected from
optical imaging data. We measure the bright end (M_1450<-26) with Sloan Digital
Sky Survey (SDSS) data covering ~6000 deg^2, then extend to lower luminosities
(M_1450<-24) with newly discovered, faint z~5 quasars selected from 235 deg^2
of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in
the Southern Galactic Cap). The faint sample includes 14 quasars with spectra
obtained as ancillary science targets in the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS), and 59 quasars observed at the MMT and Magellan
telescopes. We construct a well-defined sample of 4.7<z<5.1 quasars that is
highly complete, with 73 spectroscopic identifications out of 92 candidates.
Our color selection method is also highly efficient: of the 73 spectra
obtained, 71 are high redshift quasars. These observations reach below the
break in the luminosity function (M_1450* ~ -27). The bright end slope is steep
(beta <~ -4), with a constraint of beta < -3.1 at 95% confidence. The break
luminosity appears to evolve strongly at high redshift, providing an
explanation for the flattening of the bright end slope reported previously. We
find a factor of ~2 greater decrease in the number density of luminous quasars
(M_1450<-26) from z=5 to z=6 than from z=4 to z=5, suggesting a more rapid
decline in quasar activity at high redshift than found in previous surveys. Our
model for the quasar luminosity function predicts that quasars generate ~30% of
the ionizing photons required to keep the universe ionized at z=5.Comment: 29 pages, 22 figures, ApJ accepted (updated to published version
Candidate Type II Quasars at 2 < z < 4.3 in the Sloan Digital Sky Survey III
At low redshifts, dust-obscured quasars often have strong yet narrow
permitted lines in the rest-frame optical and ultraviolet, excited by the
central active nucleus, earning the designation Type II quasars. We present a
sample of 145 candidate Type II quasars at redshifts between 2 and 4.3,
encompassing the epoch at which quasar activity peaked in the universe. These
objects, selected from the quasar sample of the Baryon Oscillation
Spectroscopic Survey of the Sloan Digital Sky Survey III, are characterized by
weak continuum in the rest-frame ultraviolet (typical continuum magnitude of i
\approx 22) and strong lines of CIV and Ly \alpha, with Full Width at Half
Maximum less than 2000 kms-1. The continuum magnitudes correspond to an
absolute magnitude of -23 or brighter at redshift 3, too bright to be due
exclusively to the host galaxies of these objects. Roughly one third of the
objects are detected in the shorter-wavelength bands of the WISE survey; the
spectral energy distributions (SEDs) of these objects appear to be intermediate
between classic Type I and Type II quasars seen at lower redshift. Five objects
are detected at rest frame 6\mu m by Spitzer, implying bolometric luminosities
of several times 10^46 erg s-1. We have obtained polarization measurements for
two objects; they are roughly 3% polarized. We suggest that these objects are
luminous quasars, with modest dust extinction (A_V ~ 0.5 mag), whose
ultraviolet continuum also includes a substantial scattering contribution.
Alternatively, the line of sight to the central engines of these objects may be
partially obscured by optically thick material.Comment: 26 pages, 13 figures, 10 tables, 4 machine readable tables. Accepted
for publication in MNRA
A novel procedure for precise quantification of Schistosoma japonicum eggs in bovine feces
Schistosomiasis japonica is a zoonosis with a number of mammalian species acting as reservoir hosts, including water buffaloes which can contribute up to 75% to human transmission in the People's Republic of China. Determining prevalence and intensity of Schistosoma japonicum in mammalian hosts is important for calculating transmission rates and determining environmental contamination. A new procedure, the formalin-ethyl acetate sedimentation-digestion (FEA-SD) technique, for increased visualization of S. japonicum eggs in bovine feces, is described that is an effective technique for identifying and quantifying S. japonicum eggs in fecal samples from naturally infected Chinese water buffaloes and from carabao (water buffalo) in the Philippines. The procedure involves filtration, sedimentation, potassium hydroxide digestion and centrifugation steps prior to microscopy. Bulk debris, including the dense cellulosic material present in bovine feces, often obscures schistosome eggs with the result that prevalence and infection intensity based on direct visualization cannot be made accurately. This technique removes nearly 70% of debris from the fecal samples and renders the remaining debris translucent. It allows improved microscopic visualization of S. japonicum eggs and provides an accurate quantitative method for the estimation of infection in bovines and other ruminant reservoir hosts. We show that the FEA-SD technique could be of considerable value if applied as a surveillance tool for animal reservoirs of S. japonicum, particularly in areas with low to high infection intensity, or where, following control efforts, there is suspected elimination of schistosomiasis japonica.This work was partially supported by the following grants: The National High Technology Research and Development Program of China (grant
No. 2007AA02Z153), and National Science and Technology Major Program (grant Nos. 2009ZX10004-302, 2008ZX10004-011)
Probing the Circumgalactic Medium at High-Redshift Using Composite BOSS Spectra of Strong Lyman-alpha Forest Absorbers
We present composite spectra constructed from a sample of 242,150 Lyman-alpha
(Lya) forest absorbers at redshifts 2.4<z<3.1 identified in quasar spectra from
the Baryon Oscillation Spectroscopic Survey (BOSS) as part of Data Release 9 of
the Sloan Digital Sky Survey III. We select forest absorbers by their flux in
bins 138 km/s wide (approximately the size of the BOSS resolution element). We
split these absorbers into five samples spanning the range of flux -0.05 <
F<0.45. Tests on a smaller sample of high-resolution spectra show that our
three strongest absorption bins would probe circumgalactic regions (projected
separation < 300 proper kpc and |Delta v| < 300km/s) in about 60% of cases for
very high signal-to-noise ratio. Within this subset, weakening Lya absorption
is associated with decreasing purity of circumgalactic selection once BOSS
noise is included. Our weaker two Lya absorption samples are dominated by the
intergalactic medium.
We present composite spectra of these samples and a catalogue of measured
absorption features from HI and 13 metal ionization species, all of which we
make available to the community. We compare measurements of seven Lyman series
transitions in our composite spectra to single line models and obtain further
constraints from their associated excess Lyman limit opacity. This analysis
provides results consistent with column densities over the range 14.4 <~ Log
(N_HI) <~ 16.45. We compare our measurements of metal absorption to a variety
of simple single-line, single-phase models for a preliminary interpretation.
Our results imply clumping on scales down to ~30 pc and near-solar
metallicities in the circumgalactic samples, while high-ionization metal
absorption consistent with typical IGM densities and metallicities is visible
in all samples.Comment: 23 pages, 15 figures, 5 tables, link to downloadable data included.
Accepted by MNRAS 2014 March 20. New sections 3.4 and 6.1 limiting the
occurrence and impact of Lyman limit system
On Charged Lifshitz Black Holes
We obtain exact solutions of charged asymptotically Lifshitz black holes in
arbitrary (d+2) dimensions, generalizing the four dimensional solution
investigated in 0908.2611[hep-th]. We find that both the conventional
Hamiltonian approach and the recently proposed method for defining mass in
non-relativistic backgrounds do not work for this specific example. Thus the
mass of the black hole can only be determined by the first law of
thermodynamics. We also obtain perturbative solutions in five-dimensional
Gauss-Bonnet gravity. The ratio of shear viscosity over entropy density and the
DC conductivity are calculated in the presence of Gauss-Bonnet corrections.Comment: 24 pages, no figures, to appear in JHE
Thermal Correlators in Holographic Models with Lifshitz scaling
We study finite temperature effects in two distinct holographic models that
exhibit Lifshitz scaling, looking to identify model independent features in the
dual strong coupling physics. We consider the thermodynamics of black branes
and find different low-temperature behavior of the specific heat. Deformation
away from criticality leads to non-trivial temperature dependence of
correlation functions and we study how the characteristic length scale in the
two point function of scalar operators varies as a function of temperature and
deformation parameters.Comment: 28 pages, 8 figures; typos corrected, references added, published
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