12,382 research outputs found
Rheological aging and rejuvenation in solid friction contacts
We study the low-velocity (0.1--100 m.s) frictional properties of
interfaces between a rough glassy polymers and smooth silanized glass, a
configuration which gives direct access to the rheology of the adhesive joints
in which shear localizes. We show that these joints exhibit the full
phenomenology expected for confined quasi 2D soft glasses: they strengthen
logarithmically when aging at rest, and weaken (rejuvenate) when sliding.
Rejuvenation is found to saturate at large velocities. Moreover, aging at rest
is shown to be strongly accelerated when waiting under finite stress below the
static threshold
Clustering files of chemical structures using the Szekely-Rizzo generalization of Ward's method
Ward's method is extensively used for clustering chemical structures represented by 2D fingerprints. This paper compares Ward clusterings of 14 datasets (containing between 278 and 4332 molecules) with those obtained using the Szekely–Rizzo clustering method, a generalization of Ward's method. The clusters resulting from these two methods were evaluated by the extent to which the various classifications were able to group active molecules together, using a novel criterion of clustering effectiveness. Analysis of a total of 1400 classifications (Ward and Székely–Rizzo clustering methods, 14 different datasets, 5 different fingerprints and 10 different distance coefficients) demonstrated the general superiority of the Székely–Rizzo method. The distance coefficient first described by Soergel performed extremely well in these experiments, and this was also the case when it was used in simulated virtual screening experiments
Dust properties in the cold and hot gas phases of the ATLAS3D early-type galaxies as revealed by AKARI
The properties of the dust in the cold and hot gas phases of early-type
galaxies (ETGs) are key to understand ETG evolution. We thus conducted a
systematic study of the dust in a large sample of local ETGs, focusing on
relations between the dust and the molecular, atomic, and X-ray gas of the
galaxies, as well as their environment. We estimated the dust temperatures and
masses of the 260 ETGs from the ATLAS3D survey, using fits to their spectral
energy distributions primarily constructed from AKARI measurements. We also
used literature measurements of the cold (CO and HI) and X-ray gas phases. Our
ETGs show no correlation between their dust and stellar masses, suggesting
inefficient dust production by stars and/or dust destruction in X-ray gas. The
global dust-to-gas mass ratios of ETGs are generally lower than those of
late-type galaxies, likely due to dust-poor HI envelopes in ETGs. They are also
higher in Virgo Cluster ETGs than in group and field ETGs, but the same ratios
measured in the central parts of the galaxies only are independent of galaxy
environment. Slow-rotating ETGs have systematically lower dust masses than
fast-rotating ETGs. The dust masses and X-ray luminosities are correlated in
fast-rotating ETGs, whose star formation rates are also correlated with the
X-ray luminosities. The correlation between dust and X-rays in fast-rotating
ETGs appears to be caused by residual star formation, while slow-rotating ETGs
are likely well evolved, and thus exhausting their dust. These results appear
consistent with the postulated evolution of ETGs, whereby fast-rotating ETGs
form by mergers of late-type galaxies and associated bulge growth, while
slow-rotating ETGs form by (dry) mergers of fast-rotating ETGs. Central cold
dense gas appears to be resilient against ram pressure stripping, suggesting
that Virgo Cluster ETGs may not suffer strong related star formation
suppression.Comment: 18 pages, 7 figures, accepted for publication in A&
Non-Amontons behavior of friction in single contacts
We report on the frictional properties of a single contact between a glassy
polymer lens and a flat silica substrate covered either by a disordered or by a
self-assembled alkylsilane monolayer. We find that, in contrast to common
belief, the Amontons proportionality between frictional and normal stresses
does not hold. Besides, we observe that the velocity dependence of the sliding
stress is strongly sensitive to the structure of the silane layer. Analysis of
the frictional rheology observed on both disordered and self-assembled
monolayers suggests that dissipation is controlled by the plasticity of a
glass-like interfacial layer in the former case, and by pinning of polymer
chains on the substrate in the latter one.Comment: submitted to Eur. Phys. J.
Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85-xAgx (0 <= x <= 0.20) glasses
Temperature modulated Alternating Differential Scanning Calorimetric (ADSC)
studies show that Se rich Ge0.15Se0.85-xAgx (0 <= x <= 0.20) glasses are
microscopically phase separated, containing Ag2Se phases embedded in a
Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase
percolates in the Ge-Se matrix, with a well-defined percolation threshold at x
= 0.10. A signature of this percolation transition is shown up in the thermal
behavior, as the appearance of two exothermic crystallization peaks. Density,
molar volume and micro-hardness measurements, undertaken in the present study,
also strongly support this view of percolation transition. The super-ionic
conduction observed earlier in these glasses at higher silver proportions, is
likely to be connected with the silver phase percolation.Comment: 4 pages, 7 figure
Developing Intensity-Duration-Frequency (IDF) Curves From Satellite-Based Precipitation: Methodology and Evaluation
Given the continuous advancement in the retrieval of precipitation from satellites, it is important to develop methods that incorporate satellite-based precipitation data sets in the design and planning of infrastructure. This is because in many regions around the world, in situ rainfall observations are sparse and have insufficient record length. A handful of studies examined the use of satellite-based precipitation to develop intensity-duration-frequency (IDF) curves; however, they have mostly focused on small spatial domains and relied on combining satellite-based with ground-based precipitation data sets. In this study, we explore this issue by providing a methodological framework with the potential to be applied in ungauged regions. This framework is based on accounting for the characteristics of satellite-based precipitation products, namely, adjustment of bias and transformation of areal to point rainfall. The latter method is based on previous studies on the reverse transformation (point to areal) commonly used to obtain catchment-scale IDF curves. The paper proceeds by applying this framework to develop IDF curves over the contiguous United States (CONUS); the data set used is Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks – Climate Data Record (PERSIANN-CDR). IDFs are then evaluated against National Oceanic and Atmospheric Administration (NOAA) Atlas 14 to provide a quantitative estimate of their accuracy. Results show that median errors are in the range of (17–22%), (6–12%), and (3–8%) for one-day, two-day and three-day IDFs, respectively, and return periods in the range (2–100) years. Furthermore, a considerable percentage of satellite-based IDFs lie within the confidence interval of NOAA Atlas 14
WTO accession, the changing competitiveness of foreign-financed firms and regional development in Guangdong of southern China
This paper investigates the changing competitiveness of foreign-financed manufacturing firms and its implications for regional development in Guangdong province of southern China in the run-up to World Trade Organization (WTO) accession. It is argued that transnational corporations (TNCs) and some competitive, large-scale, locally-funded firms in Guangdong will triumph after WTO accession. The crowding-out process of small and medium sized enterprises (SMEs) in Guangdong will be accelerated in the near future, as they are competing directly with TNCs, and as their competitive advantages are diminishing, due to bureaucratic red tape and the rigorous enforcement of new government policies. Due to close business linkages with local privately-funded firms, the competitiveness and vitality of foreign-financed enterprises will have profound long term effects on the economic development of Guangdong, before and after WTO accession
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