Control Technique for Series Input-Parallel Output Converter Topologies

A series input-parallel output DC-DC converter topology inherently provides output current sharing among the phases, provided the input voltages are forced to share. With conventional output voltage feedback controls, input voltage sharing is unstable. Recent literature work proposes complicated feedback loops to provide stable voltage sharing, at the expense of dynamic performance. In the current work, a simple controller based on the sensorless current mode approach (SCM) stabilizes voltage sharing without compromising system performance. The SCM controllers reject source disturbances, and allow the output voltage to be tightly regulated by additional feedback control. With SCM control in place, a #super-matched# current sharing control emerges. Sharing occurs through transients, evolving naturally according to the power circuit parameters. The control approach has considerable promise for high-performance voltage regulator modules, and for other applications requiring high conversion ratios. Experimental results confirm the control operation. A sample four-phase converter has demonstrated good disturbance rejection, static sharing, and dynamic sharing

A Stabilizing, High-Performance Controller for Input Series-Output Parallel Converters

A form of sensorless current mode (SCM) control stabilizes sharing in multiphase input-series-output-parallel (ISOP) dc-dc converter topologies. Previously, ISOP converters have been proposed to reduce the voltage and current ratings of switching devices. Since the inputs are all connected in series, each phase need only be rated for a fraction of the total input voltage. Voltage and current sharing are key - if there is any phase-to-phase imbalance, the system benefits are substantially reduced. In the present work, a simple SCM controller is shown to guarantee stable sharing. Each phase acts independently on the same output reference and desired input voltage. The algorithm and the physics of the circuit lead to balanced input voltages and output currents, even during transients. The ISOP topology is a special case of an interleaved multiphase system. A reduced-order small-signal model is presented. The model is composed of two factors, a single-phase equivalent and a multidelay comb filter. The model fits a measured transfer function well and can be used in feedback design. Experimental results for a five-phase converter demonstrate fast response to a load step, line disturbance rejection, accurate static and dynamic sharing, and high efficiency

Evaluation of “Dream Herb,” Calea zacatechichi

A recent surge in the use of dietary supplements, including herbal remedies, necessitates investigations into their safety profiles. “Dream herb,” Calea zacatechichi, has long been used in traditional folk medicine for a variety of purposes and is currently being marketed in the US for medicinal purposes, including diabetes treatment. Despite the inherent vulnerability of the renal system to xenobiotic toxicity, there is a lack of safety studies on the nephrotoxic potential of this herb. Additionally, the high frequency of diabetes-associated kidney disease makes safety screening of C. zacatechichi for safety especially important. We exposed human proximal tubule HK-2 cells to increasing doses of this herb alongside known toxicant and protectant control compounds to examine potential toxicity effects of C. zacatechichi relative to control compounds. We evaluated both cellular and mitochondrial functional changes related to toxicity of this dietary supplement and found that even at low doses evidence of cellular toxicity was significant. Moreover, these findings correlated with significantly elevated levels of nephrotoxicity biomarkers, lending further support for the need to further scrutinize the safety of this herbal dietary supplement

Design and assembly of covalently functionalised polyoxofluorovanadate molecular hybrids

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species showing a wide range of structural features and properties. We report the facile preparation and functionalization of a mixed-valent polyoxofluorovanadates where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12VIV2O16(μ-O)10(μ3-O)10(μ3-F)2(L)2]6-, where L: py = pyridine (1); pyr = pyrazine (2); im = imidazole (3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1 - 3 were characterized by single-crystal X-ray diffractometry and electrospray ionization mass spectrometry. Electron paramagnetic resonance spectroscopy revealed the two well-separated VIV ions in each cluster are fully uncoupled with J = 0 giving a degenerate singlet-triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that detail the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties with an organic handle with which they can be integrated into spintronic circuitry for molecular devices

Directed self-assembly, symmetry breaking, and electronic modulation of metal oxide clusters by pyramidal heteroanions

Mixed valence/metal polyoxometalate (POM) clusters are one of the most interesting host species showing the ability to incorporate a wide range of heteroatoms of various charges and geometries. We report herein, the incorporation of different pyramidal EO32- heteroanions (E = PH, S, Se, Te) which are responsible not only for directing the templated assembly of a family of mixed-metal POMs but also for the symmetry-breaking of the traditional Dawson architecture and modulation of the electronic characteristics of the cluster's shell. The isolated family of POMs consists of four members: (Me2NH2)5Na2[Mo11V7O52(HPO3)]·MeOH·5H2O (1), (NH4)7[Mo11V7O52(SO3)]·12H2O (2), K7[Mo11V7O52(SeO3)]·31H2O (3), (Me2NH2)6Na[Mo11V7O52(TeO3)]·15H2O (4), and were characterized by X-ray structural analysis, electrospray ionization mass spectrometry (ESI-MS), thermogravimetric analysis (TGA), UV-vis, IR, elemental and flame atomic absorption spectroscopy (FAAS) analysis, and inductively coupled plasma optical emission spectroscopy (ICP-OES). Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) spectroscopic studies in concert with density functional theoretical (DFT) calculations elucidate the effect of the heteroatom on the electronic properties of the cluster

Current Analytical Techniques for Food Lipids

Thee analysis of food lipids presents significant challenges due to the wide variety of sample matrices, large range of total fat contents, and complex compositions of fatty acids. This is chapter reviews conventional analytical techniques for the quantification of total fat and fatty acids in foods and food ingredients, including the gravimetric determination of total fat, the calculation of fat and fatty acids using gas chromatography (GC), and the analysis of proximates content (i.e., fat, protein, carbohydrate, moisture, and ash) by Fourier transform infrared (FTIR) spectroscopy. Current official methods of analysis are evaluated and the use of certified reference materials and spike-recovery experiments for verifying method performance is discussed. Recent advances in automated and semi-automated sample preparation systems and rapid and portable spectroscopic devices are highlighted for their potential to significantly improve the speed by which accurate determinations of total fat and fatty acids may be achieved