1,077 research outputs found
Understanding the defect chemistry of alkali metal strontium silicate solid solutions: Insights from experiment and theory
Recent reports of remarkably high oxide ion conduction in a new family of strontium silicates have been
challenged. It has recently been demonstrated that, in the nominally potassium substituted strontium
germanium silicate material, the dominant charge carrier was not the oxygen ion, and furthermore that
the material was not single phase (R. D. Bayliss et. al., Energy Environ. Sci., 2014, DOI: 10.1039/
c4ee00734d). In this work we re-investigate the sodium-doped strontium silicate material that was
reported to exhibit the highest oxide ion conductivity in the solid solution, nominally Sr0.55Na0.45SiO2.775.
The results show lower levels of total conductivity than previously reported and sub-micron elemental
mapping demonstrates, in a similar manner to that reported for the Sr0.8K0.2Si0.5Ge0.5O2.9 composition,
an inhomogeneous chemical distribution correlating with a multiphase material. It is also shown that the
conductivity is not related to protonic mobility. A density functional theory computational approach
provides a theoretical justification for these new results, related to the high energetic costs associated
with oxygen vacancy formation
Who is the best player ever? A complex network analysis of the history of professional tennis
We consider all matches played by professional tennis players between 1968
and 2010, and, on the basis of this data set, construct a directed and weighted
network of contacts. The resulting graph shows complex features, typical of
many real networked systems studied in literature. We develop a diffusion
algorithm and apply it to the tennis contact network in order to rank
professional players. Jimmy Connors is identified as the best player of the
history of tennis according to our ranking procedure. We perform a complete
analysis by determining the best players on specific playing surfaces as well
as the best ones in each of the years covered by the data set. The results of
our technique are compared to those of two other well established methods. In
general, we observe that our ranking method performs better: it has a higher
predictive power and does not require the arbitrary introduction of external
criteria for the correct assessment of the quality of players. The present work
provides a novel evidence of the utility of tools and methods of network theory
in real applications.Comment: 10 pages, 4 figures, 4 table
Recommended from our members
Dominant role of greenhouse-gas forcing in the recovery of Sahel rainfall
Sahelian summer rainfall, controlled by the West African
monsoon, exhibited large-amplitude multidecadal variability
during the twentieth century. Particularly important was the
severe drought of the 1970s and 1980s, which had widespread
impacts1–6. Research into the causes of this drought has
identified anthropogenic aerosol forcing3,4,7 and changes in
sea surface temperatures (SSTs; refs 1,2,6,8–11) as the most
important drivers. Since the 1980s, there has been some
recovery of Sahel rainfall amounts2–6,11–14, although not to
the pre-drought levels of the 1940s and 1950s. Here we
report on experiments with the atmospheric component of a
state-of-the-art global climate model to identify the causes
of this recovery. Our results suggest that the direct influence
of higher levels of greenhouse gases in the atmosphere
was the main cause, with an additional role for changes
in anthropogenic aerosol precursor emissions. We find that
recent changes in SSTs, although substantial, did not have a
significant impact on the recovery. The simulated response
to anthropogenic greenhouse-gas and aerosol forcing is
consistent with a multivariate fingerprint of the observed
recovery, raising confidence in our findings. Although robust
predictions are not yet possible, our results suggest that the
recent recovery in Sahel rainfall amounts is most likely to be
sustained or amplified in the near term
Adaptation of a Smoking Cessation and Prevention Website for Urban American Indian/Alaska Native Youth
Tobacco use among American Indian youth is a disproportionately significant problem. We adapted and modified an existing web-based and youth-focused tobacco control program to make it appropriate for young urban American Indian/Alaska Natives (AI/ANs). The results of the focus group indicate that AI/AN youth were very receptive to the use of a web-based Zine-style intervention tool. They wanted the look and feel of the website to be more oriented toward their cultural images. Future research should examine if successful programs for reducing non-ceremonial tobacco use among urban AI/AN youth can keep young irregular smokers from becoming adult smokers
Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter
Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients
The Relationship Between Alcohol Symptoms and Consumption Among Older Drinkers
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66310/1/j.1530-0277.1996.tb01104.x.pd
Hand gesture-based interactive puppetry system to assist storytelling for children
© 2016 The Author(s)Digital techniques have been used to assist narrative and storytelling, especially in many pedagogical practices. With the rapid development of HCI techniques, saturated with digital media in their daily lives, young children, demands more interactive learning methods and meaningful immersive learning experiences. In this paper, we propose a novel hand gesture-based puppetry storytelling system which provides a more intuitive and natural human computer interaction method for young children to develop narrative ability in virtual story world. Depth motion sensing and hand gestures control technology is utilized in the implementation of user-friendly interaction. Young players could intuitively use hand gestures to manipulate virtual puppet to perform story and interact with different items in virtual environment to assist narration. Based on the result of the evaluation, this novel digital storytelling system shows positive pedagogical functions on children’s narrating ability as well as the competencies of cognitive and motor coordination. The usability of the system is preliminary examined in our test, and the results which showed that young children can benefit from playing with Puppet Narrator
Non-thermal emission processes in massive binaries
In this paper, I present a general discussion of several astrophysical
processes likely to play a role in the production of non-thermal emission in
massive stars, with emphasis on massive binaries. Even though the discussion
will start in the radio domain where the non-thermal emission was first
detected, the census of physical processes involved in the non-thermal emission
from massive stars shows that many spectral domains are concerned, from the
radio to the very high energies.
First, the theoretical aspects of the non-thermal emission from early-type
stars will be addressed. The main topics that will be discussed are
respectively the physics of individual stellar winds and their interaction in
binary systems, the acceleration of relativistic electrons, the magnetic field
of massive stars, and finally the non-thermal emission processes relevant to
the case of massive stars. Second, this general qualitative discussion will be
followed by a more quantitative one, devoted to the most probable scenario
where non-thermal radio emitters are massive binaries. I will show how several
stellar, wind and orbital parameters can be combined in order to make some
semi-quantitative predictions on the high-energy counterpart to the non-thermal
emission detected in the radio domain.
These theoretical considerations will be followed by a census of results
obtained so far, and related to this topic... (see paper for full abstract)Comment: 47 pages, 5 postscript figures, accepted for publication in Astronomy
and Astrophysics Review. Astronomy and Astrophysics Review, in pres
Mechanically assisted electrochemical degradation of alumina-TiC composites
Alumina-TiC composite material is a tough ceramic composite with excellent hardness, wear resistance and oxidation resistance in dry and high-temperature conditions. In aqueous conditions, however, it is likely to be electrochemically active facilitating charge transfer processes due to the conductive nature of TiC. For application as an orthopedic biomaterial, it is crucial to assess the electrochemical behavior of this composite, especially under a combined mechanical and electrochemical environment. In this study, we examined the mechanically assisted electrochemical performance of alumina-TiC composite in an aqueous environment. The spontaneous electrochemical response to brushing abrasion was measured. Changes in the magnitude of electrochemical current with abrasion test conditions and possible causal relationship to the alteration in surface morphology were examined. Results showed that the alumina matrix underwent abrasive wear with evidence of microploughing and grain boundary damage. Chemical analysis revealed TiO2 formation in the abraded region, indicating oxidation of the conductive TiC domain. Furthermore, wear debris from alumina abrasion appeared to affect reaction kinetics at the composite-electrolyte interface. From this work, we established that the composite undergoes abrasion assisted electrochemical degradation even in gentle abrasive conditions and the severity of degradation is related to temperature and conditions of test environment
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