Synergistically Enhancing Thermoelectric Performance of n-Type PbTe with Indium Doping and Sulfur Alloying

To achieve high-performance n-type PbTe-based thermoelectric materials, this work provides a synergetic strategy to improve electrical transport property with indium (In) element doping and reduces thermal conductivity with sulfur (S) element alloying. In n-type PbTe, In doping can tune the carrier density in the whole working temperature range, causing the carrier density to increase from 2.18 × 10¹⁹ cm⁻³ at 300 K to 4.84 × 10¹⁹ cm⁻³ at 823 K in Pb_0.98In_0.005Sb_0.015Te. The optimized carrier density can further modulate electrical conductivity and Seebeck coefficient, finally contributing to a substantial increase of power factor, and a maximum power factor increase from 19.7 µW cm⁻¹ K⁻² in Pb_0.985Sb_0.015Te to 28.2 µW cm⁻¹ K⁻² in Pb_0.9775In_0.0075Sb_0.015Te. Based on the optimally In-doped PbTe, S alloying is introduced to suppress phonon propagation by forming a complete solid solution, which could effectively reduce lattice thermal conductivity and simultaneously benefit carrier mobility to maintain high power factor. With S alloying, the minimum lattice thermal conductivity decreases from 0.76 Wm⁻¹ K⁻¹ in Pb_0.985Sb_0.015Te to 0.42 Wm⁻¹ K⁻¹ in Pb_0.98In_0.005Sb_0.015Te_0.88S_0.12. Combining the advantages of both In doping and S alloying, the peak ZT value and averaged ZT (ZT_ave) (300–873 K) are boosted from 1.0 and 0.60 in Pb_0.985Sb_0.015Te to 1.4 and 0.87 in Pb_0.98In_0.005Sb_0.015Te_0.94S_0.06.     

具反应梯度项的多重非线性抛物方程解的渐近行为

对一类具非线性内吸收、反应梯度项及边界流的半线性抛物方程,研究了更加困难的临界情形下的爆破解的渐近行为,填补了先前工作遗留的缺口.为此,引入了改进的伸缩变换方法.     

Critical Fujita exponents for degenerate parabolic equations coupled via nonlinear boundary flux

We establish the critical Fujita exponents for degenerate parabolic equations coupled via nonlinear boundary flux and then determine the blow-up rates and the blow-up sets for the nonglobal solutions.     

Molecular dynamics in low vibrational states investigated by fs time-resolved coherent anti-Stokes Raman spectroscopy technique

The molecular dynamics process is investigated in this paper using a broadband fs time-resolved coherent anti-Stokes Raman spectroscopy (CARS) technique. By varying the timing of laser pulses, low vibrational states are started and studied on both the electronically excited B(³Π_0u⁺) state and ground X(¹Σ_0g⁺) state of iodine in the gas phase at room temperature. According to change the pump wavelength or Stokes pulse as well as the wavelength of the detection window for the CARS signal, dynamics on different potential-energy surfaces can be accessed and detected by the CARS spectroscopy. Results show that the period of the oscillation is decreased for the excited B(³Π_0u⁺) state as the wavelength of the pump pulses is increased, while it is increased for the ground X(¹Σ_0g⁺) state with the increase of the Stokes wavelength.     

Improved conversion efficiency in dye-sensitized solar cells based on electrospun Al-doped ZnO nanofiber electrodes prepared by seed layer treatment

The application of electrospun nanofibers in electronic devices is limited due to their poor adhesion to conductive substrates. To improve this, a seed layer (SD) is introduced on the FTO substrate before the deposition of the electrospun composite nanofibers. This facilitates the release of interfacial tensile stress during calcination and enhances the interfacial adhesion of the AZO nanofiber films with the FTO substrate. Dye-sensitized solar cells (DSSC) based on these AZO nanofiber photoelectrodes have been fabricated and investigated. An energy conversion efficiency (η) of 0.54-0.55% has been obtained under irradiation of AM 1.5 simulated sunlight (100 mW/cm²), indicating a massive improvement of η in the AZO nanofiber film DSSCs after SD-treatment of the FTO substrate as compared to those with no treatment. The SD-treatment has been demonstrated to be a simple and facile method to solve the problem of poor adhesion between electrospun nanofibers and the conductive substrate.     

Boundedness of solutions to a quasilinear parabolic–elliptic Keller–Segel system with logistic source

We study a quasilinear parabolic–elliptic Keller–Segel system involving a source term of logistic type u_t = ? ? (?(u) ? u) ? χ ? ? (u ? v) + g(u), ? Δv = ? v + u in Ω × (0,T), subject to nonnegative initial data and the homogeneous Neumann boundary condition in a bounded domain with smooth boundary, n ≥ 1, χ > 0, ? ≥ c₁s^p for s ≥ s₀ > 1, and g(s) ≤ as ? μs² for s > 0 with a,g(0) ≥ 0, μ > 0. There are three nonlinear mechanisms included in the chemotaxis model: the nonlinear diffusion, aggregation and logistic absorption. The interaction among the triple nonlinearities shows that together with the nonlinear diffusion, the logistic absorption will dominate the aggregation such that the unique classical solution of the system has to be global in time and bounded, regardless of the initial data, whenever , or, equivalently, , which enlarge the parameter range , or , required by globally bounded solutions of the quasilinear K‐S system without the logistic source. Copyright © 2013 John Wiley & Sons, Ltd.