22,382 research outputs found
How to support growth with less energy
There is considerable potential to support growth with less use of primary energy and lower carbon emissions. This can be achieved through technical solutions (existing and new), as well as behavioural change. The goal of securing growth with lower carbon emissions is just one of several strategic goals that need to be satisfied. Of the others, the need to develop alternatives to an energy system heavily dependent on oil and natural gas and to maintain security of energy supply are likely to be the most important.
The strategic goals are to achieve major reductions in the energy intensity of transport, buildings in use, and to achieve corresponding reductions in energy intensity of the major building materials. Key challenges associated with these strategic goals include:
• the development of technologies to produce carbon-free cement, carbon-free steel, carbon-free glass
• enabling infrastructural developments that provide a framework for a wide range of low-carbon technologies and increase energy diversity and security of supply
• identification of key energy-efficiency tipping points and the construction of technology policy
• development of methane-fired modular fuel cells
• improved capabilities to model whole energy systems, i.e. adequately modelling both demand and supply, social/economic as well as technical, and assessing the impact outside of the UK system boundary
• better low-carbon planning and improved co-ordination of planning, building control and other policy tools
• better monitoring and feedback on the real performance of energy efficient technologies.
The implication of the Energy White Paper goal of reducing CO2 emissions by 60% by 2050 is a six-fold reduction in the carbon intensity of the UK economy. In the longer run, it is clear that we will move towards a carbon-free economy. Within this transition, developments in supply, distribution and end-use technologies will be multiplicative, while action to constrain demand growth is crucial to the rate of the overall transition
Population inversion of driven two-level systems in a structureless bath
We derive a master equation for a driven double-dot damped by an unstructured
phonon bath, and calculate the spectral density. We find that bath mediated
photon absorption is important at relatively strong driving, and may even
dominate the dynamics, inducing population inversion of the double dot system.
This phenomenon is consistent with recent experimental observations.Comment: 4 Pages, Added Reference [30] to Dykman, 1979, available at
http://www.pa.msu.edu/people/dykman/pub/Sov.J.LowTemp.Phys_5.pd
Personal propulsion unit Patent
Lightweight propulsion unit for movement of personnel and equipment across lunar surfac
Improving Performance of Iterative Methods by Lossy Checkponting
Iterative methods are commonly used approaches to solve large, sparse linear
systems, which are fundamental operations for many modern scientific
simulations. When the large-scale iterative methods are running with a large
number of ranks in parallel, they have to checkpoint the dynamic variables
periodically in case of unavoidable fail-stop errors, requiring fast I/O
systems and large storage space. To this end, significantly reducing the
checkpointing overhead is critical to improving the overall performance of
iterative methods. Our contribution is fourfold. (1) We propose a novel lossy
checkpointing scheme that can significantly improve the checkpointing
performance of iterative methods by leveraging lossy compressors. (2) We
formulate a lossy checkpointing performance model and derive theoretically an
upper bound for the extra number of iterations caused by the distortion of data
in lossy checkpoints, in order to guarantee the performance improvement under
the lossy checkpointing scheme. (3) We analyze the impact of lossy
checkpointing (i.e., extra number of iterations caused by lossy checkpointing
files) for multiple types of iterative methods. (4)We evaluate the lossy
checkpointing scheme with optimal checkpointing intervals on a high-performance
computing environment with 2,048 cores, using a well-known scientific
computation package PETSc and a state-of-the-art checkpoint/restart toolkit.
Experiments show that our optimized lossy checkpointing scheme can
significantly reduce the fault tolerance overhead for iterative methods by
23%~70% compared with traditional checkpointing and 20%~58% compared with
lossless-compressed checkpointing, in the presence of system failures.Comment: 14 pages, 10 figures, HPDC'1
Observation of spinor dynamics in optically trapped 87Rb Bose-Einstein Condensates
We measure spin mixing of F=1 and F=2 spinor condensates of 87Rb atoms
confined in an optical trap. We determine the spin mixing time to be typically
less than 600 ms and observe spin population oscillations. The equilibrium spin
configuration in the F=1 manifold is measured for different magnetic fields and
found to show ferromagnetic behavior for low field gradients. An F=2 condensate
is created by microwave excitation from F=1 manifold, and this spin-2
condensate is observed to decay exponentially with time constant 250 ms.
Despite the short lifetime in the F=2 manifold, spin mixing of the condensate
is observed within 50 ms.Comment: 4 pages, 6 figure
- …