17,192 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
Molecular Gas and Star Formation in the SAURON Early-type Galaxies
We present the results of a survey of CO emission in 43 of the 48
representative E/S0 galaxies observed in the optical with the SAURON
integral-field spectrograph. The CO detection rate is 12/43 or 28%. This is
lower than previous studies of early-types but can probably be attributed to
different sample selection criteria. As expected, earlier type, more luminous
and massive galaxies have a relatively lower molecular gas content. We find
that CO-rich galaxies tend to have higher H\beta but lower Fe5015 and Mgb
absorption indices than CO-poor galaxies. Those trends appear primarily driven
by the age of the stars, an hypothesis supported by the fact that the galaxies
with the strongest evidence of star formation are also the most CO-rich. In
fact, the early-type galaxies from the current sample appear to extend the
well-known correlations between FIR luminosity, dust mass and molecular mass of
other galaxy types. The star formation interpretation is also consistent with
the SAURON galaxies' radio continuum and FIR flux ratios, and their inferred
star formation efficiencies are similar to those in spiral galaxies. It thus
appears that we have identified the material fueling (residual) star formation
in early-type galaxies, and have demonstrated that it is actively being
transformed. Nevertheless, the lack of strong correlations between the CO
content and most stellar parameters is compatible with the idea that, in a
significant number of sample galaxies, the molecular gas has been accreted from
the outside and has properties rather independent from the old, pre-existing
stellar component.Comment: 14 pages, 9 figures, accepted in MNRA
The contribution of Chinese exports to climate change
Within 5 years, China's CO2 emissions have nearly doubled, and China may already be the world's largest emitter of CO2. Evidence suggests that exports could be a main cause for the rise in Chinese CO2 emissions; however, no systematic study has analyzed this issue, especially over time. We find that in 2005, around one-third of Chinese emissions (1700 Mt CO2) were due to production of exports, and this proportion has risen from 12% (230 Mt) in 1987 and only 21% (760 Mt) as recently as 2002. It is likely that consumption in the developed world is driving this trend. A majority of these emissions have largely escaped the scrutiny of arguments over “carbon leakage” due to the current, narrow definition of leakage. Climate policies which would make the developed world responsible for China's export emissions have both benefits and costs, and must be carefully designed to achieve political consensus and equity. Whoever is responsible for these emissions, China's rapidly expanding infrastructure and inefficient coal-powered electricity system need urgent attention
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.
The drivers of Chinese CO2 emissions from 1980 to 2030
China's energy consumption doubled within the first 25 years of economic reforms initiated at the end of the 1970s, and doubled again in the past 5 years. It has resulted of a threefold CO2 emissions increase since early of 1980s. China's heavy reliance on coal will make it the largest emitter of CO2 in the world. By combining structural decomposition and input–output analysis we seek to assess the driving forces of China's CO2 emissions from 1980 to 2030. In our reference scenario, production-related CO2 emissions will increase another three times by 2030. Household consumption, capital investment and growth in exports will largely drive the increase in CO2 emissions. Efficiency gains will be partially offset the projected increases in consumption, but our scenarios show that this will not be sufficient if China's consumption patterns converge to current US levels. Relying on efficiency improvements alone will not stabilize China's future emissions. Our scenarios show that even extremely optimistic assumptions of widespread installation of carbon dioxide capture and storage will only slow the increase in CO2 emissions
Size matters: the value of small populations for wintering waterbirds
Protecting systematically selected areas of land is a major step towards biodiversity conservation worldwide. Indeed, the identification and designation of protected areas more often than not forms a core component of both national and international conservation policies. In this paper we provide an overview of those Special Protection Areas and Ramsar Sites that have been classified in Great Britain as of 1998/99 for a selection of wintering waterbird species, using bird count data from the Wetland Bird Survey.
The performance of this network of sites is remarkable, particularly in comparison with published analyses of networks elsewhere in the world. Nevertheless, the current site-based approach, whilst having the great benefit of simplicity, is deliberately biased towards aggregating species at the expense of the more dispersed distribution species. To ensure that the network continues successfully to protect nationally and internationally important waterbird populations, efforts now need to concentrate on the derivation of species-specific representation targets and, in particular, the ways in which these can be incorporated into the site selection process. Although these analyses concern the performance of protected areas for waterbirds in Great Britain, the results have wide-ranging importance for conservation planning in general and the design of protected area networks
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