Entropy as a Gene‐Like Performance Indicator Promoting Thermoelectric Materials

High‐throughput explorations of novel thermoelectric materials based on the Materials Genome Initiative paradigm only focus on digging into the structure‐property space using nonglobal indicators to design materials with tunable electrical and thermal transport properties. As the genomic units, following the biogene tradition, such indicators include localized crystal structural blocks in real space or band degeneracy at certain points in reciprocal space. However, this nonglobal approach does not consider how real materials differentiate from others. Here, this study successfully develops a strategy of using entropy as the global gene‐like performance indicator that shows how multicomponent thermoelectric materials with high entropy can be designed via a high‐throughput screening method. Optimizing entropy works as an effective guide to greatly improve the thermoelectric performance through either a significantly depressed lattice thermal conductivity down to its theoretical minimum value and/or via enhancing the crystal structure symmetry to yield large Seebeck coefficients. The entropy engineering using multicomponent crystal structures or other possible techniques provides a new avenue for an improvement of the thermoelectric performance beyond the current methods and approaches.     

The peak in the thermal conductivity of Cu-O superconductors: Electronic or phononic origin?

The thermal conductivity of hole-doped Cu-O plane high-T _c perovskites exhibits a dramatic increase belowT _c which results in a pronounced peak nearT _c /2. The origin of this peak was initially thought to arise from an enhancement in the mean-free path of phonons as the charge carriers undergo condensation. Indeed, excellent fits to the data can be obtained with physically reasonable parameters using the conventional theory of lattice conduction in superconductors. In contrast, a recently observed sharp decrease in the quasiparticle scattering rate of YBCO single crystals belowT _c has motivated proposals for an electronic origin of the thermal conductivity peak. We shall critically examine experimental evidence and highlight relative advantages and shortcomings of the two contrasting interpretations. Furthermore, we shall draw attention to recently available data on the relaxation time of out-of-equilibrium carriers in Cu-O superconductors obtained using pump-probe femtosecond laser studies and what new light they shed on the controversy.     

Cold and cryotherapy. A review of the literature on general principles and practical applications

Cryotherapy increases the threshold of pain and induces physiological changes. It influences hemodynamics (reduction of skin- and muscle temperature through vasoconstriction), metabolism (reduction of ischemia due to hypoxia), and neural control (reduction of nerve conduction velocity and muscle tone). Cryotherapy is indicated mainly in locomotor system related pain. Such pain can be induced by degenerative changes, postoperatively, and during mobilisation of contracted joints. Cryotherapy may be used as short term therapy (less than 15 min) as well as long term therapy (more than 20 min). For maximal efficacy the intensity of application as well as the application medium must be considered. Due to biorhythm, cold application seems to be more effective in the afternoon.     

The Poly‐Rho Test as a Screening Tool for Explosive Performance

A screening test was developed at Los Alamos National Laboratory [1] that can be used to decide if a newly synthesized/formulated explosive might warrant further development. The test consists of firing a rate‐stick composed of 12.7 mm diameter by 12.7 mm high pellets of different densities ordered from lowest to highest, initiated by a detonator at the low‐density end of the stick. This poly‐rho test yields detonation velocities over a range of densities using only the small amount of the explosive typically generated by the synthetic organic chemist at an early stage of the scale‐up process. The amount of material required is far less than that required for the typical rate‐stick series. This paper presents results on poly‐rho tests that were conducted on three explosives commonly used at Los Alamos National Laboratory, namely PBX 9501, PBX 9502 and PETN. The results are compared with empirical detonation‐theory predictions and existing explosive experimental data, with good agreement in all cases.     

Rapid fabrication and thermoelectric performance of SnTe via non-equilibrium laser 3D printing

Thermoelectric technologies based on Seebeck and Peltier effects,as energy techniques able to directly convert heat into electricity and vice versa, hold promise for addressing the global energy and environmental problems. The development of efficient and low-cost thermoelectric modules is the key to their large-scale commercial applications. In this paper, using a non-equilibrium laser3 D printing technique, we focus an attention on the fabrication of mid-temperature p-type SnTe thermoelectric materials. The influence of laser power, scanning speed and layer thickness on the macro-defects, chemical and phase composition, micro structure and thermoelectric performance was systematically investigated. First and foremost,the processing parameter window for printing a highquality layer is determined. This is followed by the finite element method used to simulate and verify the influence of the laser-induced molten pool temperature distribution on the final composition and microstructure. Finally, the high-performance SnTe layer with 10 mm × 10 mm in area is produced within seconds with room temperature Seebeck coefficient close to that of SnTe manufactured by the traditional methods. Consequently,this work lays a solid foundation for the future fabrication of thermoelectric modules using laser non-equilibrium printing techniques.     

Nanoforest Nb2O5 photoanodes for dye-sensitized solar cells by pulsed laser deposition

Vertically aligned bundles of Nb(2)O(5) nanocrystals were fabricated by pulsed laser deposition (PLD) and tested as a photoanode material in dye-sensitized solar cells (DSSC). They were characterized using scanning and transmission electron microscopies, optical absorption spectroscopy (UV-vis), and incident-photon-to-current efficiency (IPCE) experiments. The background gas composition and the thickness of the films were varied to determine the influence of those parameters in the photoanode behavior. An optimal background pressure of oxygen during deposition was found to produce a photoanode structure that both achieves high dye loading and enhanced photoelectrochemical performance. For optimal structures, IPCE values up to 40% and APCE values around 90% were obtained with the N(3) dye and I(3)(-)/I(-) couple in acetonitrile with open circuit voltage of 0.71 V and 2.41% power conversion efficiency.     

Analysis and design of circular ridged waveguide components

A fast and efficient radial mode-matching technique (RMMT) is applied to the analysis and design of components in circular ridge waveguide technology. Five different structures are investigated with respect to their performance as filters and polarizers. For fast computation, pie-shaped metal ridges and septa are assumed to better fit the cylindrical coordinate system. In practice, the pie-shaped structures are approximated by rectangular cross-section metal inserts. The validity of this approximation is investigated by comparing with measurements and finite-element analysis. It is found that for thin etchable inserts, the measured filter response is in excellent agreement with the theoretical prediction and that for polarizers, the axial ratio response is not particularly sensitive to the ridge shape. Differences between computed and measured results occur only at return loss and isolation levels beyond 25 dB. A central processing unit time comparison with HFSS (4.0) results in a 10-min versus 3-h advantage in favor of the RMMT