Moderate temperature rechargeable sodium batteries

Cells utilizing the organic electrolyte, NaI in triglyme, operated at approx. 130 C with Na(+) - intercalating cathodes. However, their rate and stability were inadequate. NaAlCl4 was found to be a highly useful electrolyte for cell operation at 165-190 C. Na(+) intercalating chalcogenides reacted with NaAlCl4 during cycling to form stable phases. Thus, VS2 became essentially VS2Cl, with reversible capacity of approx 2.8 e(-)/V, and a mid-discharge voltage of approx 2.5V and 100 deep discharge cycles were readily achieved. A positive electrode consisting of VCl3 and S plus NaAlCl4 was subjected to deep-discharge cycles 300 times and it demonstrated identity with the in-situ-formed BSxCly cathode. NiS2 and NiS which are not Na(+)-intercalating structures formed highly reversible electrodes in NaAlCl4. The indicated discharge mechanism implies a theoretical capacity 4e(-)/Ni for NiS2 and 2e(-)/Ni for NiS. The mid-discharge potentials are, respectively, 2.4V and 2.1V. A Na/NiS2 cell cycling at a C/5 rate has exceeded 500 deep discharge cycles with 2.5e(-)/Ni average utilization. A 4 A-hr nominal capacity prototype Na/NiS2 cell was tested at 190 C. It was voluntarily terminated after 80 cycles. Further development, particularly of cathode structure and hardware should produce a battery capable of at least 50-W-hr/lb and more than 1000 cycles

Comparative analysis of efficiency of the neural multi-class recognition of objects technical condition for diagnostic features of different orders

Роботу присвячено дослідженню ефективності класифікатора на основі імовірнісної нейронної мережі для багатокласової діагностики складних просторових об‘єктів з багатоосердковими пошкодженнями. Для розпізнавання технічного стану використовуються багатовимірні вектори діагностичних ознак, які, в загальному випадку, можуть мати значення різних порядків. У результаті навчання та тестування нейромережевого класифікатора визначено інтервал значень параметру впливу мережі для безпомилкового багатокласового розпізнавання технічного стану об‘єкта.The work is devoted to research efficiency classifier based on probabilistic neural network to multi-class diagnosis of complex spatial objects at the presence of multi-site damages. Multidimensional vectors of diagnostic features are used for recognition of technical condition, features are values of different order. The classifier is trained and tested, the values range of network influence parameter is obtained for correct multi-class recognition

The effects of superconductor-stabilizer interfacial resistance on quench of a pancake coil made out of coated conductor

We present the results of numerical analysis of normal zone propagation in a stack of $YBa_2Cu_3O_{7-x}$ coated conductors which imitates a pancake coil. Our main purpose is to determine whether the quench protection quality of such coils can be substantially improved by increased contact resistance between the superconducting film and the stabilizer. We show that with increased contact resistance the speed of normal zone propagation increases, the detection of a normal zone inside the coil becomes possible earlier, when the peak temperature inside the normal zone is lower, and stability margins shrink. Thus, increasing contact resistance may become a viable option for improving the prospects of coated conductors for high $T_c$ magnets applications.Comment: 9 pages, 4 figure

Self-Assembled Nanoparticle Drumhead Resonators

The self-assembly of nanoscale structures from functional nanoparticles has provided a powerful path to developing devices with emergent properties from the bottomup. Here we demonstrate that freestanding sheets selfassembled from various nanoparticles form versatile nanomechanical resonators in the megahertz frequency range. Using spatially resolved laser-interferometry to measure thermal vibrational spectra and image vibration modes, we show that their dynamic behavior is in excellent agreement with linear elastic response for prestressed drumheads of negligible bending stiffness. Fabricated in a simple one-step drying-mediated process, these resonators are highly robust and their inorganic−organic hybrid nature offers an extremely low mass, low stiffness, and the potential to couple the intrinsic functionality of the nanoparticle building blocks to nanomechanical motion