81,839 research outputs found
Building stock dynamics and its impacts on materials and energy demand in China
China hosts a large amount of building stocks, which is nearly 50 billion square meters. Moreover, annual new construction is growing fast, representing half of the world's total. The trend is expected to continue through the year 2050. Impressive demand for new residential and commercial construction, relative shorter average building lifetime, and higher material intensities have driven massive domestic production of energy intensive building materials such as cement and steel. This paper developed a bottom-up building stock turnover model to project the growths, retrofits and retirements of China's residential and commercial building floor space from 2010 to 2050. It also applied typical material intensities and energy intensities to estimate building materials demand and energy consumed to produce these building materials. By conducting scenario analyses of building lifetime, it identified significant potentials of building materials and energy demand conservation. This study underscored the importance of addressing building material efficiency, improving building lifetime and quality, and promoting compact urban development to reduce energy and environment consequences in China
Frequency pulling and mixing of relaxation oscillations in superconducting nanowires
Many superconducting technologies such as rapid single flux quantum computing
(RSFQ) and superconducting quantum interference devices (SQUIDs) rely on the
modulation of nonlinear dynamics in Josephson junctions for functionality. More
recently, however, superconducting devices have been developed based on the
switching and thermal heating of nanowires for use in fields such as single
photon detection and digital logic. In this paper, we use resistive shunting to
control the nonlinear heating of a superconducting nanowire and compare the
resulting dynamics to those observed in Josephson junctions. We show that
interaction of the hotspot growth with the external shunt produces high
frequency relaxation oscillations with similar behavior as observed in
Josephson junctions due to their rapid time constants and ability to be
modulated by a weak periodic signal. In particular, we use a microwave drive to
pull and mix the oscillation frequency, resulting in phase locked features that
resemble the AC Josephson effect. New nanowire devices based on these
conclusions have promising applications in fields such as parametric
amplification and frequency multiplexing
Signatures of Emerging Subsurface Structures in Acoustic Power Maps
We show that under certain conditions, subsurface structures in the solar
interior can alter the average acoustic power observed at the photosphere above
them. By using numerical simulations of wave propagation, we show that this
effect is large enough for it to be potentially used for detecting emerging
active regions before they appear on the surface. In our simulations,
simplified subsurface structures are modeled as regions with enhanced or
reduced acoustic wave speed. We investigate the dependence of the acoustic
power above a subsurface region on the sign, depth, and strength of the wave
speed perturbation. Observations from the Solar and Heliospheric
Observatory/Michelson Doppler Imager (SOHO/MDI) prior and during the emergence
of NOAA active region 10488 are used to test the use of acoustic power as a
potential precursor of magnetic flux emergence.Comment: 7 pages, 5 figures, accepted for publication in Solar Physics on 21
March 201
Hardening mechanism of commercially pure Mg processed by high pressure torsion at room temperature
Coarse-grained Mg in the as-cast condition and fine-grained Mg in the extruded condition were processed by high pressure torsion (HPT) at room temperature for up to 16 turns. Microstructure observation and texture analysis indicate that to fulfil the Von Mises criterion, the non-basal slip is activated in the as-cast Mg and tension twinning is activated in the as-extruded Mg. Although the deformation mechanism is different in the as-cast Mg and the as-extruded Mg during HPT, their hardening evolutions are similar, i.e. after 1/8 turn of HPT, microhardness of the as-cast Mg and the extruded Mg both show a significant increase and further HPT processing does not significantly further increase the microhardness. Texture strengthening can explain the rapid hardening. Hardness anisotropy and texture data results suggest that texture strengthening plays an important role for both types of samples. Texture strengthening weakens with decreasing grain size
Spatially resolved femtosecond pump-probe study of topological insulator Bi2Se3
Carrier and phonon dynamics in Bi2Se3 crystals are studied by a spatially
resolved ultrafast pump-probe technique. Pronounced oscillations in
differential reflection are observed with two distinct frequencies, and are
attributed to coherent optical and acoustic phonons, respectively. The rising
time of the signal indicates that the thermalization and energy relaxation of
hot carriers are both sub-ps in this material. We found that the thermalization
and relaxation time decreases with the carrier density. The expansion of the
differential reflection profile allows us to estimate an ambipolar carrier
diffusion coefficient on the order of 500 square centimeters per second. A
long-term slow expansion of the profile shows a thermal diffusion coefficient
of 1.2 square centimeters per second.Comment: 8 pages, 6 figure
Building Smart Space Applications with PErvasive Computing in Embedded Systems (PECES) Middleware
The increasing number of devices that are invisibly embedded into our surrounding environment as well as the proliferation of wireless communication and sensing technologies are the basis for visions like ambient intelligence, ubiquitous and pervasive computing. PErvasive Computing in Embedded Systems (PECES) project develops the technological basis to enable the global cooperation of embedded devices residing in different smart spaces in a context-dependent, secure and trustworthy manner. This paper presents PECES middleware that consists of flexible context ontology, a middleware that is capable of dynamically forming execution environments that are secure and trustworthy. This paper also presents set of tools to facilitate application development using the PECES middleware
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