Influence of superconductivity on magnetic exchange interactions

Using the formulation due to Fedro and Robinson of magnetic exchange in the presence of superconductivity, the mean field magnetic interaction energy has been calculated for rare earth (RE) ions in the RERh₄B₄ lattice. It is shown that increasing the strength of the superconducting interaction relative to the magnetic interaction results in a decrease of ferromagnetic coupling, and in some cases may drive ferromagnetic systems into antiferromagnetism.     

Processing of iron-titanium powder mixtures by transient liquid phase sintering

Transient liquid phase sintering was examined for Fe-Ti powder mixtures. The experimental plan included the effects of several processing variables, such as green density, particle size, composition, heating rate, sintering temperature, and sintering time. During heating, pores form at the Ti particle sites. At the first eutectic temperature (1085 °C), liquid spreading is inhibited by a surrounding intermetallic envelope, leading to swelling. At the second eutectic temperature (1289 °C), the liquid penetrates along the iron grain boundaries and provides densification. The amount of densification depends on the amount of liquid formed at the second eutectic temperature and its duration as determined by the titanium content and heating rate. Formerly Research Assistant at Rensselaer Polytechnic Institute.     

Ionic Liquid‐Directed Nanoporous TiNb2O7 Anodes with Superior Performance for Fast‐Rechargeable Lithium‐Ion Batteries

Nanoporous TiNb₂O₇ (NPTNO) material is synthesized by a sol–gel method with an ionic liquid (IL) as the nanoporous structure directing template. NPTNO exhibits a high reversible capacity of 210 mAh g^–1 even at the charging rate of 50 C and an excellent cyclability of half‐cell capacity retention of 74% for 1000 cycles at 5 C and LiNi_0.5Mn_1.5O₄‐coupled full‐cell capacity retentions of 81% and 87% for 1000 cycles at 1 C and 2 C, respectively. The studies of the 1000 cycled NPTNO electrode illustrate that the IL‐directed mesoporous structure can enhance the cyclability of NPTNO cells due to the alleviation of repetitive mechanical stress and volume fluctuation induced by the repetitive Li⁺ insertion‐extraction processes. The measured Li⁺ diffusion coefficients from the galvanostatic intermittent titration technique suggest that the IL‐templating strategy indeed ensures the fast rechargeability of NPTNO cells based on the fast Li⁺ diffusion kinetics. Benefitting from the nanoporous structure, NPTNO with unhindered Li⁺ diffusion pathways achieves a superior rate capability in the titanium‐based oxide materials and the best full‐cell cyclability in the TNO materials. Therefore, the templating potential of IL is demonstrated, and the superb electrochemical performance establishes the IL‐directed NPTNO as a promising anode candidate for fast‐rechargeable LIBs.     

Automated synthesis of analog electrical circuits by means ofgenetic programming

Analog circuit synthesis entails the creation of both the topology and the sizing (numerical values) of all of the circuit's components. This paper presents a single uniform approach using genetic programming for the automatic synthesis of both the topology and sizing of a suite of eight different prototypical analog circuits, including a low-pass filter, a crossover filter, a source identification circuit, an amplifier, a computational circuit, a time-optimal controller circuit, a temperature-sensing circuit, and a voltage reference circuit. The problem-specific information required for each of the eight problems is minimal and consists of the number of inputs and outputs of the desired circuit, the types of available components, and a fitness measure that restates the high-level statement of the circuit's desired behavior as a measurable mathematical quantity. The eight genetically evolved circuits constitute an instance of an evolutionary computation technique producing results on a task that is usually thought of as requiring human intelligence     

A ferromagnetic resonance study of as-quenched and annealed amorphous Fe78Cr2B12Si8

Ferromagnetic resonance (FMR) studies of as-quenched and annealed amorphous Fe₇₈Cr₂B₁₂Si₈ are presented. For short annealing times (30 min) and low annealing temperatures (473 K) the resonant field,H ₁, and the FMR line width, H, are essentially constant. This can be explained in terms of a combination of effects due to magnetic anisotropy and the in homogeneous demagnetization due to stress relief in the sample. For larger annealing times or higher annealing temperatures,H ₁ and H increase due to the percipitation of crystallites in the amorphous structure. X-ray diffraction, selected area electron diffraction patterns and transmission electron micrographs are consistent with this interpretation.     

Structure and stability of rapidly quenched Al86Cr14−x Fe x alloys

The structural and thermal properties of melt spun Al₈₆Cr_14–x Fe _x , alloys have been investigated using X-ray diffraction, transmission electron microscopy, electron diffraction and differential thermal analysis. Electron diffraction patterns indicate that all alloys contain quasicrystalline nodules with icosahedral symmetry in a matrix of f cc aluminium. Microscopically the alloys fall into two categories; those with x 6 and those withx > 6. The first class alloys shows large (>1m) icosahedral crystallites with well defined dendritic crystallite growth and sharp quasicrystalline X-ray diffraction peaks. The latter alloys show quasicrystalline crystallites which are predominantly much smaller as well as considerably broadened X-ray diffraction peaks. Thermal analysis measurements indicate that the activation energy for crystallization in these alloys is about 1.5 eV.     

The effects of melt history,crystallization pressure,and crystallization temperature on the crystallization and resultant structure of bulk isotactic polypropylene

A study of the effects of constant-pressure isothermal crystallization on polymer structure was conducted in bulk isotactic polypropylene. The investigation was designed to determine the influence of pressure, temperature, and melt history variables on the structure of this bulk polymer. Results demonstrate that the effects of pressure and crystallization temperature can be quite adequately combined into one processing parameter, undercooling (defined as the melting temperature minus the crystallization temperature), by use of the Clausius-Clapeyron equation. This parameter is demonstrated to be important in determining the kinetics of crystallization and the resultant structure. The moderate to high undercoolings involved in this study are representative of commercial injection-molding processes, and a number of conclusions regarding commercial processing are made based on these laboratory investigations.