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This paper presents a new approach to controlling and optimizing a single-stage boost-integrated full-bridge dc–dc converter for a stand-alone photovoltaic-battery-powered dc motor system by combining pulse-frequency modulation (PFM), pulsewidth modulation (PWM), and phase angle shift (PAS). Unlike most of the existing multiport dc–dc converters, which aim at regulating the output voltage (first- or second-quadrant operation), the dc motor load requires both voltage and current reversals (four-quadrant operation). The converter is able to perform three tasks simultaneously: maximum power point tracking (MPPT), battery charging/discharging, and driving the dc motor at variable speeds including bidirectional and stall motions. To achieve these control objectives, the boost inductor and the motor inductance operate in different modes such that PFM and PWM can be used to achieve MPPT and a wide motor voltage range, respectively. By properly adjusting the PAS of the duty cycles, the capacitor and battery rms current value can be reduced, while the operation of the converter remains unchanged, hence improving the conversion efficiency. Experimental results of a 26-W laboratory prototype converter confirmed the proposed design and operation and the efficiency improvement by 2–6%. [ABSTRACT FROM AUTHOR]

The design, fabrication, and characterization of a multiple-stage Si microfabricated preconcentrator-focuser (µPCF) for a micro gas chromatography (µGC) system that can provide real-time quantification and identification of complex organic vapor mixtures are presented. The µPCF consists of a Si microheater loaded with Carbopack B, Carbopack X, and Carboxen 1000 carbon adsorbent granules, and a Si micromachined cover plate. Deep reactive ion etching is utilized to produce mechanically robust fluidic interconnection adapters hermetically sealed to fused silica capillary tubing for connection to the other components in the µGC. This three-stage device is designed to capture compounds spanning up to 4 orders of magnitude in volatility. The dead volume, thermal mass, heating efficiency, and pressure drop of the three-stage µPCF are improved significantly over its single-stage µPCF predecessor. We demonstrate the successful capture, desorption, and high-resolution chromatographic separation of a mixture of 30 common organic vapors using our three-stage µPCF in a conventional GC system. The peak width at half height is <2.05 s for all compounds after elution from the GC column. [ABSTRACT FROM AUTHOR]

The design, fabrication, and testing of a preconcentrator-focuser (PCF), consisting of a thick micromachined Si heater packed with a small quantity of a granular adsorbent material are described. The PCF is developed to capture and concentrate vapors for subsequent focused thermal desorption and analysis in a micro gas chromatograph. The microheater contains an array of high-aspect-ratio, etched-Si heating elements, 520 µm (h) × 50 µm (w) × 3000 µm (1), bounded by an annulus of Si and thermally isolated from the remaining substrate by an air gap. This structure is sandwiched between Pyrex glass plates with inlet/outlet ports that accept capillary tubes for sample flow and is sealed by anodic bonding (bottom) and rapidly annealed glass/metal/Si solder bonding (top). The large microheater surface area allows for high adsorption capacity and efficient, uniform thermal desorption of vapors captured on the adsorbent within the structure. The adsorbent consists of roughly spherical granules, ∼200-µm in diameter, of a high-surface-area, graphitized carbon. Key design considerations, fabrication technologies, and results of performance tests are presented with an emphasis on the thermal desorption characteristics of several representative volatile organic compounds as a function of volumetric flow rates and heating rates. Preconcentration factors as high as 5600 and desorbed peak widths as narrow as 0.8 s are achieved from 0.25-L samples of benzene at modest heating rates. The effects of operating variables on sensitivity, chromatographic resolution, and detection limits are assessed. Testing of this PCF with a micromachined separation column and integrated sensor array is discussed briefly. [ABSTRACT FROM AUTHOR]

(${\text{Li}}_{1-x} {\text{Fe}}_{x}$)OHFeSe single crystals have been synthesized with a hydrothermal ion-exchange growth method. The physical properties are characterized by electrical and magnetic measurements. (${\text{Li}}_{1-x} {\text{Fe}}_{x}$)OHFeSe undergoes a resistive superconducting (SC) transition in zero field at Tc(onset) = 41.4 K. The broadening effect of the magnetic (resistive) SC transition width is anisotropic and is larger for magnetic fields parallel to the c-axis than for fields parallel to the ab-plane. The layered crystal structure plays an important role in the anisotropic broadening. The tuning effects of magnetic field on the anisotropies are observed, which shed light on the SC mechanism and the emerging device applications. [ABSTRACT FROM AUTHOR]