27,188 research outputs found
Consumer Demand for Healthy Diet: New Evidence from Healthy Eating Index
Replaced with revised version of paper 07/20/10.Food Consumption/Nutrition/Food Safety, Health Economics and Policy,
Inefficient Star Formation In Extremely Metal Poor Galaxies
The first galaxies contain stars born out of gas with little or no metals.
The lack of metals is expected to inhibit efficient gas cooling and star
formation but this effect has yet to be observed in galaxies with oxygen
abundance relative to hydrogen below a tenth of that of the Sun. Extremely
metal poor nearby galaxies may be our best local laboratories for studying in
detail the conditions that prevailed in low metallicity galaxies at early
epochs. Carbon Monoxide (CO) emission is unreliable as tracers of gas at low
metallicities, and while dust has been used to trace gas in low-metallicity
galaxies, low-spatial resolution in the far-infrared has typically led to large
uncertainties. Here we report spatially-resolved infrared observations of two
galaxies with oxygen abundances below 10 per cent solar, and show that stars
form very inefficiently in seven star-forming clumps of these galaxies. The
star formation efficiencies are more than ten times lower than found in normal,
metal rich galaxies today, suggesting that star formation may have been very
inefficient in the early Universe.Comment: Author's version (10 pages, 4 figures). Published in Natur
The Weak Carbon Monoxide Emission In An Extremely Metal Poor Galaxy, Sextans A
Carbon monoxide (CO) is one of the primary coolants of gas and an easily
accessible tracer of molecular gas in spiral galaxies but it is unclear if CO
plays a similar role in metal poor dwarfs. We carried out a deep observation
with IRAM 30 m to search for CO emission by targeting the brightest far-IR peak
in a nearby extremely metal poor galaxy, Sextans A, with 7% Solar metallicity.
A weak CO J=1-0 emission is seen, which is already faint enough to place a
strong constraint on the conversion factor (a_CO) from the CO luminosity to the
molecular gas mass that is derived from the spatially resolved dust mass map.
The a_CO is at least seven hundred times the Milky Way value. This indicates
that CO emission is exceedingly weak in extremely metal poor galaxies,
challenging its role as a coolant in these galaxies.Comment: 4 pages, 1 table, 4 figures. ApJL in pres
Pair-breaking scattering interference as a mechanism for superconducting gap modulation
We propose the "pair-breaking scattering interference" as a general source of
coherence peak modulations in superconductors. Assuming this mechanism, we
present a simple physical picture for the coherence peak modulations in
overdoped cuprate BiSrCaCuO (Bi-2223),
ferromagnetic iron pnictide EuRbFeAs (Eu-1144), and kagome metals
VSb ( K, Rb, and Cs). Specifically, we explain the wavevectors,
the particle-hole symmetry, and the dependence on the internal or external
Zeeman-field of the coherence peak modulations. This work is intended as a
cautious reminder to the scientific community when asserting the existence of a
pair density wave phenomenon in the absence of tunneling conductance
modulations in the normal state.Comment: 5+6 pages, 3+2 figure
On the use of an explicit chemical mechanism to dissect peroxy acetyl nitrate formation.
Peroxy acetyl nitrate (PAN) is a key component of photochemical smog and plays an important role in atmospheric chemistry. Though it has been known that PAN is produced via reactions of nitrogen oxides (NOx) with some volatile organic compounds (VOCs), it is difficult to quantify the contributions of individual precursor species. Here we use an explicit photochemical model--Master Chemical Mechanism (MCM) model--to dissect PAN formation and identify principal precursors, by analyzing measurements made in Beijing in summer 2008. PAN production was sensitive to both NOx and VOCs. Isoprene was the predominant VOC precursor at suburb with biogenic impact, whilst anthropogenic hydrocarbons dominated at downtown. PAN production was attributable to a relatively small class of compounds including NOx, xylenes, trimethylbenzenes, trans/cis-2-butenes, toluene, and propene. MCM can advance understanding of PAN photochemistry to a species level, and provide more relevant recommendations for mitigating photochemical pollution in large cities
Regression Analysis of Beijing Hotels Customer Satisfaction Based upon Data from TripAdvisor
Big data is being used by many organizations to make decisions about the efficiency and effectiveness of their operation. One of the data sets that are used most frequently is TripAdvisor. This article explores the advantages and disadvantages of using such a data set. The case study chosen was the hotel services in Beijing, China. A new approach is being proposed in which baseline information is used on a regional basis to establish the uniqueness of a region. Many times the data does not give the proper perspective because it incorporates the larger perspective and does not provide for regional differences. The other dimension developed in the article is a statistical approach that tries to define a better understanding instead of using a descriptive method. Keywords: Big data, TripAdvisor, Beijing, Statistical analysi
Variance-Preserving-Based Interpolation Diffusion Models for Speech Enhancement
The goal of this study is to implement diffusion models for speech
enhancement (SE). The first step is to emphasize the theoretical foundation of
variance-preserving (VP)-based interpolation diffusion under continuous
conditions. Subsequently, we present a more concise framework that encapsulates
both the VP- and variance-exploding (VE)-based interpolation diffusion methods.
We demonstrate that these two methods are special cases of the proposed
framework. Additionally, we provide a practical example of VP-based
interpolation diffusion for the SE task. To improve performance and ease model
training, we analyze the common difficulties encountered in diffusion models
and suggest amenable hyper-parameters. Finally, we evaluate our model against
several methods using a public benchmark to showcase the effectiveness of our
approac
Genomic and biologic comparisons of cyprinid herpesvirus 3 strains
Cyprinid herpesvirus 3 (CyHV-3) is the archetypal fish alloherpesvirus and the etiologic agent of a lethal disease in common and koi carp. To date, the genome sequences of only four CyHV-3 isolates have been published, but no comparisons of the biologic properties of these strains have been reported. We have sequenced the genomes of a further seven strains from various geographical sources, and have compared their growth in vitro and virulence in vivo. The major findings were: (i) the existence of the two genetic lineages previously described as European and Asian was confirmed, but inconsistencies between the geographic origin and genotype of some strains were revealed; (ii) potential inter-lineage recombination was detected in one strain, which also suggested the existence of a third, as yet unidentified lineage; (iii) analysis of genetic disruptions led to the identification of non-essential genes and their potential role in virulence; (iv) comparison of the in vitro and in vivo properties of strains belonging to the two lineages revealed that inter-lineage polymorphisms do not contribute to the differences in viral fitness observed; and (v) a negative correlation was observed among strains between viral growth in vitro and virulence in vivo. This study illustrates the importance of coupling genomic and biologic comparisons of viral strains in order to enhance understanding of viral evolution and pathogenesis
Rethinking solar photovoltaic parameter estimation: global optimality analysis and a simple efficient differential evolution method
Accurate, fast, and reliable parameter estimation is crucial for modeling,
control, and optimization of solar photovoltaic (PV) systems. In this paper, we
focus on the two most widely used benchmark datasets and try to answer (i)
whether the global minimum in terms of root mean square error (RMSE) has
already been reached; and (ii) whether a significantly simpler metaheuristic,
in contrast to currently sophisticated ones, is capable of identifying PV
parameters with comparable performance, e.g., attaining the same RMSE. We
address the former using an interval analysis based branch and bound algorithm
and certify the global minimum rigorously for the single diode model (SDM) as
well as locating a fairly tight upper bound for the double diode model (DDM) on
both datasets. These obtained values will serve as useful references for
metaheuristic methods, since none of them can guarantee or recognize the global
minimum even if they have literally discovered it. However, this algorithm is
excessively slow and unsuitable for time-sensitive applications (despite the
great insights on RMSE that it yields). Regarding the second question,
extensive examination and comparison reveal that, perhaps surprisingly, a
classic and remarkably simple differential evolution (DE) algorithm can
consistently achieve the certified global minimum for the SDM and obtain the
best known result for the DDM on both datasets. Thanks to its extreme
simplicity, the DE algorithm takes only a fraction of the running time required
by other contemporary metaheuristics and is thus preferable in real-time
scenarios. This unusual (and certainly notable) finding also indicates that the
employment of increasingly complicated metaheuristics might possibly be
somewhat overkill for regular PV parameter estimation. Finally, we discuss the
implications of these results and suggest promising directions for future
development.Comment: v2, see source code at https://github.com/ShuhuaGao/rePVes
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