104 research outputs found
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
Synthesis, Characterisation and 3D Printing of an Isosorbide Based, Light Curable, Degradable Polymer for Potential Application in Maxillofacial Reconstruction
Although emergence of bone tissue engineering techniques has revolutionised the field of maxillofacial reconstruction, the successful translation of such products, especially concerning larger sized defects, still remains a significant challenge. Light curable methacrylate based polymers have ideal properties for bone repair. These materials are also suitable for 3D printing which can be applicable for restoration of both function and aesthetics. The main objective of this research was to synthesise a mechanically stable and biologically functional polymer for reconstruction of complex craniofacial defects. The experimental work initially involved synthesis of (((3R,3aR,6S,6aR)-hexahydrofuro[3,2-b]furan-3,6-diyl)bis(oxy))bis(ethane-2,1-diyl) bis((4-methyl-3-oxopent-4-en-1-yl)carbamate), CSMA-1, and ((((((((((((3R,3aR,6S,6aR)-hexahydrofuro[3,2-b]furan-3,6-diyl)bis(oxy))bis(ethane-2,1 diyl))bis(oxy))bis(carbonyl))bis(azanediyl))bis(methylene))bis(3,3,5-trimethylcyclohexane-5,1-diyl))bis(azanediyl))bis(carbonyl))bis(oxy))bis(ethane-2,1-diyl) bis(2-methylacrylate), CSMA-2; Nuclear Magnetic Resonance (NMR) analysis confirmed formation of the monomers and composite samples were fabricated respectively by exposing 11 mm diameter discs to blue light. Modulus of the tensile elasticity was tested using a biaxial flexural test and the values were found to be between 1 and 3 GPa in CMA-1, CSMA-2 and their composites. In vitro cell culture, using human Bone Marrow Derived Mesenchymal Stem Cells (BMSCs), confirmed non-toxicity of the samples and finally 3D printing allowed direct extrusion and setting of the bio ink into a mesh-like construct
Effect of the “Orem Self Care Model”-based Educational-Supportive Intervention on the Anxiety of Primigravidae
Aims: The health of mother and fetus might be affected by anxiety during pregnancy. Training interventions can prevent the anxiety disorders. The aim of the study was to investigate the effectiveness of the supportive-educational intervention based on Orem self-care model on the anxiety of primigravidae.
Materials & Methods: In the single-blind clinical trial study, sixty 28- to 34-week pregnant women in their first pregnancy, referred to the health centers of Mashhad, were studied in 2015. The subjects, selected via purposeful cluster sampling method, were randomly divided into two 30-person groups including experimental and control groups. Data was collected by demographic and pregnancy questionnaires and Spielberger anxiety scale. Four 60-minute supportive-educational program sessions were conducted based on Orem self-care model in experimental group. The manifest anxiety was measured in both groups at the beginning of the conduction of the intervention and one week after the end of the intervention. Data was analyzed by SPSS 18 software using Chi-square, Mann-Whitney, independent T, and paired T tests.
Findings: Before the intervention, the mean scores of manifest anxiety in the groups were not significantly different (p=0.793). Nevertheless, after the intervention, the scores were significantly different (p=0.0001). In addition, the mean scores of manifest anxiety were significantly different before and after the intervention in experimental group (p=0.006). However, the difference was not significant in control group (p=0.086).
Conclusion: Supportive-educational intervention based on Orem self-care model reduces anxiety in 3-month primigravidae
Poly-ε-Caprolactone/Fibrin-Alginate Scaffold: A New Pro-Angiogenic Composite Biomaterial for the Treatment of Bone Defects
We hypothesized that a composite of 3D porous melt-electrowritten poly-É›-caprolactone (PCL) coated throughout with a porous and slowly biodegradable fibrin/alginate (FA) matrix would accelerate bone repair due to its angiogenic potential. Scanning electron microscopy showed that the open pore structure of the FA matrix was maintained in the PCL/FA composites. Fourier transform infrared spectroscopy and differential scanning calorimetry showed complete coverage of the PCL fibres by FA, and the PCL/FA crystallinity was decreased compared with PCL. In vitro cell work with osteoprogenitor cells showed that they preferentially bound to the FA component and proliferated on all scaffolds over 28 days. A chorioallantoic membrane assay showed more blood vessel infiltration into FA and PCL/FA compared with PCL, and a significantly higher number of bifurcation points for PCL/FA compared with both FA and PCL. Implantation into a rat cranial defect model followed by microcomputed tomography, histology, and immunohistochemistry after 4- and 12-weeks post operation showed fast early bone formation at week 4, with significantly higher bone formation for FA and PCL/FA compared with PCL. However, this phenomenon was not extrapolated to week 12. Therefore, for long-term bone regeneration, tuning of FA degradation to ensure syncing with new bone formation is likely necessary
Numerical study of the thermoelectric power factor in ultra-thin Si nanowires
Low dimensional structures have demonstrated improved thermoelectric (TE)
performance because of a drastic reduction in their thermal conductivity,
{\kappa}l. This has been observed for a variety of materials, even for
traditionally poor thermoelectrics such as silicon. Other than the reduction in
{\kappa}l, further improvements in the TE figure of merit ZT could potentially
originate from the thermoelectric power factor. In this work, we couple the
ballistic (Landauer) and diffusive linearized Boltzmann electron transport
theory to the atomistic sp3d5s*-spin-orbit-coupled tight-binding (TB)
electronic structure model. We calculate the room temperature electrical
conductivity, Seebeck coefficient, and power factor of narrow 1D Si nanowires
(NWs). We describe the numerical formulation of coupling TB to those transport
formalisms, the approximations involved, and explain the differences in the
conclusions obtained from each model. We investigate the effects of cross
section size, transport orientation and confinement orientation, and the
influence of the different scattering mechanisms. We show that such methodology
can provide robust results for structures including thousands of atoms in the
simulation domain and extending to length scales beyond 10nm, and point towards
insightful design directions using the length scale and geometry as a design
degree of freedom. We find that the effect of low dimensionality on the
thermoelectric power factor of Si NWs can be observed at diameters below ~7nm,
and that quantum confinement and different transport orientations offer the
possibility for power factor optimization.Comment: 42 pages, 14 figures; Journal of Computational Electronics, 201
Neutrino-electron scattering in noncommutative space
Neutral particles can couple with the gauge field in the adjoint
representation at the tree level if the space-time coordinates are
noncommutative (NC). Considering neutrino-photon coupling in the NC QED
framework, we obtain the differential cross section of neutrino-electron
scattering. Similar to the magnetic moment effect, one of the NC terms is
proportional to , where is the electron recoil energy.
Therefore, this scattering provides a chance to achieve a stringent bound on
the NC scale in low energy by improving the sensitivity to the smaller electron
recoil energy.Comment: 12 pages, 2 figure
Nanomechanical probing of the layer/substrate interface of an exfoliated InSe sheet on sapphire
Van der Waals (vdW) layered crystals and heterostructures have attracted substantial interest for potential applications in a wide range of emerging technologies. An important, but often overlooked, consideration in the development of implementable devices is phonon transport through the structure interfaces. Here we report on the interface properties of exfoliated InSe on a sapphire substrate. We use a picosecond acoustic technique to probe the phonon resonances in the InSe vdW layered crystal. Analysis of the nanomechanics indicates that the InSe is mechanically decoupled from the substrate and thus presents an elastically imperfect interface. A high degree of phonon isolation at the interface points toward applications in thermoelectric devices, or the inclusion of an acoustic transition layer in device design. These findings demonstrate basic properties of layered structures and so illustrate the usefulness of nanomechanical probing in nanolayer/nanolayer or nanolayer/substrate interface tuning in vdW heterostructures
Thermoelectric power factor under strain-induced band-alignment in the half-Heuslers NbCoSn and TiCoSb
Band convergence is an effective strategy to improve the thermoelectric
performance of complex bandstructure thermoelectric materials. Half-Heuslers
are good candidates for band convergence studies because they have multiple
bands near the valence bad edge that can be converged through various band
engineering approaches providing power factor improvement opportunities.
Theoretical calculations to identify the outcome of band convergence employ
various approximations for the carrier scattering relaxation times (the most
common being the constant relaxation time approximation) due to the high
computational complexity involved in extracting them accurately. Here, we
compare the outcome of strain-induced band convergence under two such
scattering scenarios: i) the most commonly used constant relaxation time
approximation and ii) energy dependent inter- and intra-valley scattering
considerations for the half-Heuslers NbCoSn and TiCoSb. We show that the
outcome of band convergence on the power factor depends on the carrier
scattering assumptions, as well as the temperature. For both materials
examined, band convergence improves the power factor. For NbCoSn, however, band
convergence becomes more beneficial as temperature increases, under both
scattering relaxation time assumptions. In the case of TiCoSb, on the other
hand, constant relaxation time considerations also indicate that the relative
power factor improvement increases with temperature, but under the energy
dependent scattering time considerations, the relative improvement weakens with
temperature. This indicates that the scattering details need to be accurately
considered in band convergence studies to predict more accurate trends.Comment: 21 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1905.0795
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