Thermoelectric properties of organic charge transfer salts from first-principle investigations: Role of molecular packing and triiodide anions

The potency of charge transfer (CT) salts in thermoelectric (TE) applications based on (5-CNB-EDT-TTF)4I3 is systematically explored by first-principles calculations combined with Boltzmann transport theory and deformation potential theory, focusing...

Carrier mobility of one-dimensional vanadium selenide (V2Se9) monolayer and nanoribbon systems: DFT study

Vanadium selenide (V2Se9) is a true one-dimensional (1D) crystal composed of atomic nanochains bonded by van der Waals (vdW) interactions. Recent experiments revealed the mechanical exfoliation of newly synthesized V2Se9. In this study, we predicted the electronic and transport properties of V2Se9 through computational analyses. We calculated the intrinsic carrier mobility of V2Se9 monolayers (MLs) and nanoribbons (NRs) using density functional theory and deformation potential theory. We found that the electron mobility of the two-dimensional (2D) (010)-plane ML of V2Se9 is highly anisotropic, reaching μ_(2D,z)^e=1327 cm2 V−1 s−1 across the chain direction. The electron mobility of 1D NR systems in a (010)-plane ML of V2Se9 along the chain direction continuously increased as the thickness increased from 1-chain to 4-chain NR (width below 3 nm). Interestingly, the electron mobility of 1D 4-chain NR along the chain direction (μ_(1D,x)^e=775 cm2 V−1 s−1) was higher than that of a 2D (010)-plane ML (μ_(2D,x)^e=567 cm2 V−1 s−1). These results demonstrate the potential of vdW-1D crystal V2Se9 as a new nanomaterial for ultranarrow (sub-3-nm width) optoelectronic devices with high electron mobility.

Influence of Calcined Bauxite Aggregate on the Resistance of Cement Composites Subjected to Small Caliber Deformable Projectile Impact

This paper presents an experimental investigation on the influence of calcined bauxite aggregate (CBA) on the resistance of cement composites subjected to small caliber deformable projectile impact at a designed velocity of 400 m/s. The deformable projectile was made from copper with a purity of 99.5% and a diameter of 8.0 mm. Compared to mixtures with conventional coarse granite aggregate and/or siliceous fine aggregate, the incorporation of either fine or coarse CBA or their combination is beneficial in reducing the depth of penetration (DOP), equivalent crater diameter (CD), and crater volume (CV) caused by deformable projectile impact. CBA is found to be more effective in controlling the DOP and CV in comparison to the CD. Replacing of conventional aggregate with CBA leads to more severe damage to the projectiles (e.g., projectile length reduction, diameter increase, and mass loss). Relative effective hardness is an effective indicator to the deformation potential and penetration capacity of a deformable projectile to impact cement composites incorporating CBA.

Telematics of new vehicles for the purpose of pedestrian safety

Pedestrians are a vulnerable group of traffic users who most often suffer serious physical injuries in collisions with motor vehicles, which very often have a fatal outcome. The modern automotive industry is investing great efforts in the development of active and passive protection systems for all traffic participants, including pedestrians. Pedestrian protection is tried to be achieved by changing the shape of the front parts of the vehicle, by using plastic materials with higher deformation potential which, in collision with the body of the pedestrian, will spend most of the impact energy on its own deformation and thus maximally spare the delicate biological tissue of the pedestrian. Instead of protruding, rigid metal structures of insignificant elasticity and deformation potential, today’s cars are characterized by appropriate body design, use of high elasticity materials and deformation of contact surfaces, specially shaped and integrated bumpers, elastic and raised bonnet, headlights integrated into the contour of the vehicle front which are capable of absorbing part of the impact energy. Modern research shows a certain efficiency of these improvements on modern cars. Most of these studies are of the experimental type and are done in strictly controlled conditions on dolls, often commissioned and funded by wealthy automobile corporations, while there is less research in real field conditions. Recently, experiments have been made with testing the active bonnet, the airbag under the bonnet, and the google model of gluing the pedestrian body.

When band convergence is not beneficial for thermoelectrics

Band convergence is considered a clear benefit to thermoelectric performance because it increases the charge carrier concentration for a given Fermi level, which typically enhances charge conductivity while preserving the Seebeck coefficient. However, this advantage hinges on the assumption that interband scattering of carriers is weak or insignificant. With first-principles treatment of electron-phonon scattering in the CaMg2Sb2-CaZn2Sb2 Zintl system and full Heusler Sr2SbAu, we demonstrate that the benefit of band convergence can be intrinsically negated by interband scattering depending on the manner in which bands converge. In the Zintl alloy, band convergence does not improve weighted mobility or the density-of-states effective mass. We trace the underlying reason to the fact that the bands converge at a one k-point, which induces strong interband scattering of both the deformation-potential and the polar-optical kinds. The case contrasts with band convergence at distant k-points (as in the full Heusler), which better preserves the single-band scattering behavior thereby successfully leading to improved performance. Therefore, we suggest that band convergence as thermoelectric design principle is best suited to cases in which it occurs at distant k-points.

Negative pressure wound therapy updates for 2021

Negative pressure wound therapy (NPWT) has been used in clinical practice for 25 years. Worldwide, it has been used to treat more than 10 million wounds. The repertoire of NPWT procedures is still growing. This originally simple procedure entails a number of pitfalls and limits, and full utilisation of the micro-deformation potential of NPWT depends on many key details. We present the pathophysiology, effects and forms of NPWT use including our own experience, tips and a proposal for the use of NPWT during the COVID-19 pandemic.

Deformation Potentials: Towards a Systematic Way beyond the Atomic Fragment Approach in Orbital-Free Density Functional Theory

This work presents a method to move beyond the recently introduced atomic fragment approximation. Like the bare atomic fragment approach, the new method is an ab initio, parameter-free, orbital-free implementation of density functional theory based on the bifunctional formalism that treats the potential and the electron density as two separate variables, and provides access to the Kohn–Sham Pauli kinetic energy for an appropriately chosen Pauli potential. In the present ansatz, the molecular Pauli potential is approximated by the sum of the bare atomic fragment approach, and a so-called deformation potential that takes the interaction between the atoms into account. It is shown that this model can reproduce the bond-length contraction due to multiple bonding within the list of second-row homonuclear dimers. The present model only relies on the electron densities of the participating atoms, which themselves are represented by a simple monopole expansion. Thus, the bond-length contraction can be rationalized without referring to the angular quantum numbers of the participating atoms.