884 research outputs found
Intertrochanteric fracture below Birmingham Hip Resurfacing: Successful non-operative management in two cases
Concept study for a high-efficiency nanowire-based thermoelectric
Materials capable of highly efficient, direct thermal-to-electric energy
conversion would have substantial economic potential. Theory predicts that
thermoelectric efficiencies approaching the Carnot limit can be achieved at low
temperatures in one-dimensional conductors that contain an energy filter such
as a double-barrier resonant tunneling structure. The recent advances in growth
techniques suggest that such devices can now be realized in heterostructured,
semiconductor nanowires. Here we propose specific structural parameters for
InAs/InP nanowires that may allow the experimental observation of near-Carnot
efficient thermoelectric energy conversion in a single nanowire at low
temperature
Predictive control co-design for enhancing flexibility in residential housing with battery degradation
Buildings are responsible for about a quarter of global energy-related CO2 emissions. Consequently, the decarbonisation of the housing stock is essential in achieving net-zero carbon emissions. Global decarbonisation targets can be achieved through increased efficiency in using energy generated by intermittent resources. The paper presents a co-design framework for simultaneous optimal design and operation of residential buildings using Model Predictive Control (MPC). The framework is capable of explicitly taking into account operational constraints and pushing the system to its efficiency and performance limits in an integrated fashion. The optimality criterion minimises system cost considering time-varying electricity prices and battery degradation. A case study illustrates the potential of co-design in enhancing flexibility and self-sufficiency of a system operating under different conditions. Specifically, numerical results from a low-fidelity model show substantial carbon emission reduction and bill savings compared to an a-priori sizing approach
Antiproteases as Therapeutics to Target Inflammation in Chronic Obstructive Pulmonary Disease
Efficiency in nanostructured thermionic and thermoelectric devices
Advances in solid-state device design now allow the spectrum of transmitted
electrons in thermionic and thermoelectric devices to be engineered in ways
that were not previously possible. Here we show that the shape of the electron
energy spectrum in these devices has a significant impact on their performance.
We distinguish between traditional thermionic devices where electron momentum
is filtered in the direction of transport only and a second type, in which the
electron filtering occurs according to total electron momentum. Such 'total
momentum filtered' kr thermionic devices could potentially be implemented in,
for example, quantum dot superlattices. It is shown that whilst total momentum
filtered thermionic devices may achieve efficiency equal to the Carnot value,
traditional thermionic devices are limited to efficiency below this. Our second
main result is that the electronic efficiency of a device is not only improved
by reducing the width of the transmission filter as has previously been shown,
but also strongly depends on whether the transmission probability rises sharply
from zero to full transmission. The benefit of increasing efficiency through a
sharply rising transmission probability is that it can be achieved without
sacrificing device power, in contrast to the use of a narrow transmission
filter which can greatly reduce power. We show that devices which have a
sharply-rising transmission probability significantly outperform those which do
not and it is shown such transmission probabilities may be achieved with
practical single and multibarrier devices. Finally, we comment on the
implications of the effect the shape of the electron energy spectrum on the
efficiency of thermoelectric devices.Comment: 11 pages, 15 figure
Analysis of surface waves generated on subwavelength-structured silver films
Using transmission electron microscopy (TEM) to analyse the physical-chemical
surface properties of subwavlength structured silver films and
finite-difference time-domain (FDTD) numerical simulations of the optical
response of these structures to plane-wave excitation, we report on the origin
and nature of the persistent surface waves generated by a single slit-groove
motif and recently measured by far-field optical interferometry. The surface
analysis shows that the silver films are free of detectable oxide or sulfide
contaminants, and the numerical simulations show very good agreement with the
results previously reported.Comment: 9 Figure
Atenção pré-hospitalar móvel às urgências: análise de implantação no estado do Rio de Janeiro, Brasil
Off-limb (spicule) DEM distribution from SoHO/SUMER observations
In the present work we derive a Differential Emission Measure (DEM) dis-
tribution from a region dominated by spicules. We use spectral data from the
Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
on-board the Solar Heliospheric Observatory (SoHO) covering the entire SUMER
wavelength range taken off-limb in the Northern polar coronal hole to construct
this DEM distribution using the CHIANTI atomic database. This distribution is
then used to study the thermal properties of the emission contributing to the
171 {\AA} channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar
Dynamics Observatory (SDO). From our off-limb DEM we found that the radiance in
the AIA 171 {\AA} channel is dominated by emission from the Fe ix 171.07 {\AA}
line and has sparingly little contribution from other lines. The product of the
Fe ix 171.07 {\AA} line contribution function with the off-limb DEM was found
to have a maximum at logTmax (K) = 5.8 indicating that during spicule
observations the emission in this line comes from plasma at transition region
temperatures rather than coronal. For comparison, the same product with a quiet
Sun and prominence DEM were found to have a maximum at logT max (K) = 5.9 and
logTmax (K) = 5.7, respectively. We point out that the interpretation of data
obtained from the AIA 171 {\AA} filter should be done with foreknowledge of the
thermal nature of the observed phenomenon. For example, with an off-limb DEM we
find that only 3.6% of the plasma is above a million degrees, whereas using a
quiet Sun DEM, this contribution rises to 15%.Comment: 12 pages, 6 figures accepted by Solar Physic
Conical refraction with low-coherence light sources
We report on conical refraction (CR) with low-coherence light sources, such as light-emitting diodes and decoherentized HeNe laser radiation, and demonstrate different CR patterns. In our experiments, a variation of the pinhole sizes from 25 to 100 µm and the distances to pinhole from 50 to 5 cm reduced spatial coherence of radiation that resulted in the disappearance of the dark Poggendorff’s ring in the Lloyd’s plane. This is attributed to the interference nature of the Lloyd’s distribution and found to be in excellent agreement with the paraxial dual-cone model of conical refraction
Charge injection instability in perfect insulators
We show that in a macroscopic perfect insulator, charge injection at a
field-enhancing defect is associated with an instability of the insulating
state or with bistability of the insulating and the charged state. The effect
of a nonlinear carrier mobility is emphasized. The formation of the charged
state is governed by two different processes with clearly separated time
scales. First, due to a fast growth of a charge-injection mode, a localized
charge cloud forms near the injecting defect (or contact). Charge injection
stops when the field enhancement is screened below criticality. Secondly, the
charge slowly redistributes in the bulk. The linear instability mechanism and
the final charged steady state are discussed for a simple model and for
cylindrical and spherical geometries. The theory explains an experimentally
observed increase of the critical electric field with decreasing size of the
injecting contact. Numerical results are presented for dc and ac biased
insulators.Comment: Revtex, 7pages, 4 ps figure
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