301 research outputs found
Diet diversification through local foods: experiences from traditional vegetable promotion work in Kenya
DEVELOPMENT OF A SNUBBER TYPE MAGNETORHEOLOGICAL FLUID ELASTOMERIC LAG DAMPER FOR HELICOPTER STABILITY AUGMENTATION
Most advanced helicopter rotors are typically fitted with lag dampers, such as elastomeric or hybrid fluid-elastomeric (FE) lag dampers, which have lower parts counts, are lighter in weight, easier to maintain, and more reliable than conventional hydraulic dampers. However, the damping and stiffness properties of elastomeric and fluid elastomeric lag dampers are non-linear functions of lag/rev frequency, dynamic lag amplitude, and operating temperature. It has been shown that elastomeric damping and stiffness levels diminish markedly as amplitude of damper motion increases. Further, passive dampers tend to present severe damping losses as damper operating temperature increases either due to in-service self-heating or hot atmospheric conditions. Magnetorheological (MR) dampers have also been considered for application to helicopter rotor lag dampers to mitigate amplitude and frequency dependent damping behaviors. MR dampers present a controllable damping with little or no stiffness. Conventional MR dampers are similar in configuration to linear stroke hydraulic type dampers, which are heavier, occupy a larger space envelope, and are unidirectional. Hydraulic type dampers require dynamic seal to prevent leakage, and consequently, frequent inspections and maintenance are necessary to ensure the reliability of these dampers. Thus, to evaluate the potential of combining the simplicity and reliability of FE and smart MR technologies in augmenting helicopter lag mode stability, an adaptive magnetorheological fluid-elastomeric (MRFE) lag damper is developed in this thesis as a retrofit to an actual fluid-elastomeric (FE) lag damper. Consistent with the loading condition of a helicopter rotor system, single frequency (lag/rev) and dual frequency (lag/rev at 1/rev) sinusoidal loading were applied to the MRFE damper at varying temperature conditions. The complex modulus method was employed to linearly characterize and compare the performance of the MRFE damper with the baseline FE damper performance. Based on experimental measurements, it is shown in the research that at all test temperatures, a significant damping control range, extending beyond the baseline FE damper, can be provided by the MRFE damper with the application of varying magnetic fields. This controllable damping range can be programmed to potentially provide the required damping augmentation as a function of different flight conditions. The added benefits of employing smart MR fluids in MRFE lag dampers are to produce adequate damping at critical flight conditions while concurrently reducing periodic hub loads at other flight conditions and to compensate damping losses associated with temperature.
The other main objective of the present research is to develop and formulate a comprehensive analytical model that can accurately describe the non-linear hysteretic behavior that is demonstrated by the MRFE lag damper. Thus, a hydromechanical model, which can delineate the physical flow motion of the system and accurately describe the non-linear hysteretic behavior of the MRFE damper is proposed. The hydromechanical model explored in this study is a design-based model which describes the damper system with a series of lumped hydraulic, mechanical and magnetorheological components. The model employs physical parameters such as inertia, damping, yield force and compliances that are dependent on damper geometry and material properties of components and which can potentially be approximated a priori. Further, temperature variation will mainly cause material properties to change. Once model parameters have been established, the model is shown to simulate accurately the measured hysteretic force-displacement history under single and dual frequency excitations, and varying temperatures
A gain-loss framework based on ensemble flow forecasts to switch the urban drainage-wastewater system management towards energy optimization during dry periods
Precipitation is the cause of major perturbation to the flow in urban
drainage and wastewater systems. Flow forecasts, generated by coupling
rainfall predictions with a hydrologic runoff model, can potentially be used
to optimize the operation of integrated urban drainage–wastewater systems
(IUDWSs) during both wet and dry weather periods. Numerical weather prediction
(NWP) models have significantly improved in recent years, having increased their
spatial and temporal resolution. Finer resolution NWP are suitable for urban-catchment-scale applications, providing longer lead time than radar
extrapolation. However, forecasts are inevitably uncertain, and fine
resolution is especially challenging for NWP. This uncertainty is commonly
addressed in meteorology with ensemble prediction systems (EPSs). Handling
uncertainty is challenging for decision makers and hence tools are necessary
to provide insight on ensemble forecast usage and to support the rationality
of decisions (i.e. forecasts are uncertain and therefore errors will be made;
decision makers need tools to justify their choices, demonstrating that these
choices are beneficial in the long run).
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This study presents an economic framework to support the decision-making
process by providing information on when acting on the forecast is
beneficial and how to handle the EPS. The relative economic value (REV)
approach associates economic values with the potential outcomes and determines
the preferential use of the EPS forecast. The envelope curve of the REV diagram
combines the results from each probability forecast to provide the highest
relative economic value for a given gain–loss ratio. This approach is
traditionally used at larger scales to assess mitigation measures for
adverse events (i.e. the actions are taken when events are forecast). The
specificity of this study is to optimize the energy consumption in IUDWS
during low-flow periods by exploiting the electrical smart grid market (i.e.
the actions are taken when no events are forecast). Furthermore, the results
demonstrate the benefit of NWP neighbourhood post-processing methods to
enhance the forecast skill and increase the range of beneficial uses
Experimental ionization of atomic hydrogen with few-cycle pulses
We present the first experimental data on strong-field ionization of atomic
hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10%
level between the data and an {\it ab initio} simulation over a wide range of
laser intensities and electron energies
Measurement of laser intensities approaching 10 15 W/cm 2 with an accuracy of 1%
Accurate knowledge of the intensity of focused ultrashort laser pulses is crucial to the correct interpretation of experimental results in strong-field physics. We have developed a technique to measure laser intensities approaching 1015W/cm2 with an accu
Hypoxia Reduces Arylsulfatase B Activity and Silencing Arylsulfatase B Replicates and Mediates the Effects of Hypoxia
This report presents evidence of 1) a role for arylsulfatase B (ARSB; N-acetylgalactosamine-4-sulfatase) in mediating intracellular oxygen signaling; 2) replication between the effects of ARSB silencing and hypoxia on sulfated glycosaminoglycan content, cellular redox status, and expression of hypoxia-associated genes; and 3) a mechanism whereby changes in chondroitin-4-sulfation that follow either hypoxia or ARSB silencing can induce transcriptional changes through galectin-3. ARSB removes 4-sulfate groups from the non-reducing end of chondroitin-4-sulfate and dermatan sulfate and is required for their degradation. For activity, ARSB requires modification of a critical cysteine residue by the formylglycine generating enzyme and by molecular oxygen. When primary human bronchial and human colonic epithelial cells were exposed to 10% O2×1 h, ARSB activity declined by ∼41% and ∼30% from baseline, as nuclear hypoxia inducible factor (HIF)-1α increased by ∼53% and ∼37%. When ARSB was silenced, nuclear HIF-1α increased by ∼81% and ∼61% from baseline, and mRNA expression increased to 3.73 (±0.34) times baseline. Inversely, ARSB overexpression reduced nuclear HIF-1α by ∼37% and ∼54% from baseline in the epithelial cells. Hypoxia, like ARSB silencing, significantly increased the total cellular sulfated glycosaminoglycans and chondroitin-4-sulfate (C4S) content. Both hypoxia and ARSB silencing had similar effects on the cellular redox status and on mRNA expression of hypoxia-associated genes. Transcriptional effects of both ARSB silencing and hypoxia may be mediated by reduction in galectin-3 binding to more highly sulfated C4S, since the galectin-3 that co-immunoprecipitated with C4S declined and the nuclear galectin-3 increased following ARSB knockdown and hypoxia
Human PAPS Synthase Isoforms Are Dynamically Regulated Enzymes with Access to Nucleus and Cytoplasm
In higher eukaryotes, PAPS synthases are the only enzymes producing the essential sulphate-donor 3′-phospho-adenosine-5′-phosphosulphate (PAPS). Recently, PAPS synthases have been associated with several genetic diseases and retroviral infection. To improve our understanding of their pathobiological functions, we analysed the intracellular localisation of the two human PAPS synthases, PAPSS1 and PAPSS2. For both enzymes, we observed pronounced heterogeneity in their subcellular localisation. PAPSS1 was predominantly nuclear, whereas PAPSS2 localised mainly within the cytoplasm. Treatment with the nuclear export inhibitor leptomycin B had little effect on their localisation. However, a mutagenesis screen revealed an Arg-Arg motif at the kinase interface exhibiting export activity. Notably, both isoforms contain a conserved N-terminal basic Lys-Lys-Xaa-Lys motif indispensable for their nuclear localisation. This nuclear localisation signal was more efficient in PAPSS1 than in PAPSS2. The activities of the identified localisation signals were confirmed by microinjection studies. Collectively, we describe unusual localisation signals of both PAPS synthase isoforms, mobile enzymes capable of executing their function in the cytoplasm as well as in the nucleus
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