Microcontroller-based peak current mode control using digital slope compensation

Microcontroller-based peak current mode control of a buck converter is investigated. The new solution uses a discrete time controller with digital slope compensation. This is implemented using only a single-chip microcontroller to achieve desirable cycle-by-cycle peak current limiting. The digital controller is implemented as a two-pole, two-zero linear difference equation designed using a continuous time model of the buck converter and a discrete time transform. Subharmonic oscillations are removed with digital slope compensation using a discrete staircase ramp. A 16 W hardware implementation directly compares analog and digital control. Frequency response measurements are taken and it is shown that the crossover frequency and expected phase margin of the digital control system match that of its analog counterpart

Lateral Wall Protein Content Mediates Alterations in Cochlear Outer Hair Cell Mechanics Before and After Hearing Onset

Specialized outer hair cells (OHCs) housed within the mammalian cochlea exhibit active, nonlinear, mechanical responses to auditory stimulation termed electromotility. The extraordinary frequency resolution capacity of the cochlea requires an exquisitely equilibrated mechanical system of sensory and supporting cells. OHC electromotile length change, stiffness, and force generation are responsible for a 100-fold increase in hearing sensitivity by augmenting vibrational input to non-motile sensory inner hair cells. Characterization of OHC mechanics is crucial for understanding and ultimately preventing permanent functional deficits due to overstimulation or as a consequence of various cochlear pathologies. The OHCs\u27 major structural assembly is a highly-specialized lateral wall. The lateral wall consists of three structures; a plasma membrane highly-enriched with the motor-protein prestin, an actin-spectrin cortical lattice, and one or more layers of subsurface cisternae. Technical difficulties in independently manipulating each lateral wall constituent have constrained previous attempts to analyze the determinants of OHCs\u27 mechanical properties. Temporal separations in the accumulation of each lateral wall constituent during postnatal development permit associations between lateral wall structure and OHC mechanics. We compared developing and adult gerbil OHC axial stiffness using calibrated glass fibers. Alterations in each lateral wall component and OHC stiffness were correlated as a function of age. Reduced F-actin labeling was correlated with reduced OHC stiffness before hearing onset. Prestin incorporation into the PM was correlated with increased OHC stiffness at hearing onset. Our data indicate lateral wall F-actin and prestin are the primary determinants of OHC mechanical properties before and after hearing onset, respectively

Analytical calculation of resonant inductance for zero voltage switching in phase-shifted full-bridge converters

The phase shift full bridge (PSFB) converter allows high efficiency power conversion at high frequencies through zero voltage switching (ZVS); the parasitic drain-to-source capacitance of the MOSFET is discharged by a resonant inductance before the switch is gated resulting in near zero turn-on switching losses. Typically, an extra inductance is added to the leakage inductance of a transformer to form the resonant inductance necessary to charge and discharge the parasitic capacitances of the PSFB converter. However, many PSFB models do not consider the effects of the magnetizing inductance or dead-time in selecting the resonant inductance required to achieve ZVS. The choice of resonant inductance is crucial to the ZVS operation of the PSFB converter. Incorrectly sized resonant inductance will not achieve ZVS or will limit the load regulation ability of the converter. This paper presents a unique and accurate equation for calculating the resonant inductance required to achieve ZVS over a wide load range incorporating the effects of the magnetizing inductance and dead-time. The derived equations are validated against PSPICE simulations of a PSFB converter and extensive hardware experimentations

A clinical appraisal of the Greiner G300 clinical chemistry analyser.

Peer Reviewe

On gravity currents driven by constant fluxes of saline and particle-laden fluid in the presence of a uniform flow

Experiments are reported on the sustained release of saline and particle-laden fluid\ud into a long, but relatively narrow, flume, filled with fresh water. The dense fluid rapidly\ud spread across the flume and flowed away from the source: the motion was then essentially\ud two-dimensional. In the absence of a background flow in the flume, the motion\ud was symmetric, away from the source. However, in the presence of a background\ud flow the upstream speed of propagation was slowed and the downstream speed was\ud increased. Measurements of this motion are reported and, when the excess density was\ud due to the presence of suspended sediment, the distribution of the deposited particles\ud was also determined. Alongside this experimental programme, new theoretical models\ud of the motion were developed. These were based upon multi-layered depth-averaged\ud shallow-water equations, in which the interfacial drag and mixing processes were\ud explicitly modelled. While the early stages of the motion are independent of these\ud interfacial phenomena to leading order, they play an increasingly important dynamical\ud role as the the flow is slowed, or even arrested. In addition a new integral model is\ud proposed. This does not resolve the interior dynamics of the flow, but may be readily\ud integrated and obviates the need for more lengthy numerical calculations. It is shown\ud that the predictions from both the shallow-layer and integral models are in close\ud agreement with the experimental observations

An analysis of northern goshawk prey preferences by biogeoclimatic subzone across coastal British Columbia

This thesis investigates the dietary preferences of northern goshawk populations in second growth stands on Vancouver Island and the islands of the Johnstone Strait region on the BC Mainland Coast. Prey abundance was inferred through the analysis of pellets composed of regurgitated non-digested prey remains that were collected during the annual survey monitoring program carried out by Mosaic Forest Management and predecessor companies since 2012. The relative abundance of prey species was compared across three Coastal Western Hemlock subzones (CWHvm1, CWHmm1, CWHxm2) under the Biogeoclimatic Ecosystem Classification (BEC) system using the Chi-square test. No significant correlations were found between prey species abundance and BEC subzone (χ2 = 2.3, P = 0.32) in 2013 and (χ2 = 0.84, P = 0.66) in 2014. Trends within the dataset indicate coastal northern goshawks on Vancouver Island and the BC Mainland Coast show a general dietary propensity towards avian prey, which is consistent with findings from other studies. The variation in prey abundance and species diversity reported in this study is more likely a function of topography and forest structure, season and region than it is to BEC subzones. Findings from this study highlights how younger stands could be providing more suitable habitat than was traditionally thought

Requirement for the betaI and betaIV tubulin isotypes in mammalian cilia.

Nielsen et al., [2001: Curr Biol 11:529-533], based on studies in Drosophila, have proposed that beta tubulin in axonemal microtubules must contain a specific acidic seven amino acid sequence in its carboxyl terminus. In mammals, the two betaIV isotypes (betaIVa and betaIVb) contain that sequence. In order to test the application of this hypothesis to mammals, we have examined the expression of beta tubulin isotypes in four different ciliated tissues (trachea, ependyma, uterine tube, and testis) using isotype-specific antibodies and indirect immunofluorescence. We find that betaIV tubulin is present in all ciliated cell types examined, but so is betaI tubulin. Taken together with recent studies that show that betaI and betaIV tubulin are both present in the cilia of vestibular hair cells, olfactory neurons, and nasal respiratory epithelial cells, we propose that both betaI tubulin and betaIV tubulin may be required for axonemal structures in mammals