Effect of the velocit profile of incoming flow on the performance of a horizontal axis tidal stream turbine

Compared to solar and wind power generating technologies, tidal stream technology is relatively new and there are many problems that hinder the deployment of tidal stream turbines. One such problem is the effect of the tidal stream velocity profile resulting in varying velocity magnitude and its effect on turbine performance. A study incorporating experimental data and computational fluid dynamics (CFD) simulation is carried out in order to start to understand such effects. A CFD model based on an existing turbine was created and validated by comparing its results against experimental results of a previous study. A velocity profile was measured in a water flume experiment, which was then applied to the CFD model as a new upstream boundary condition. The results show that, due to the variation in flow velocity, the torque generated by each blade will fluctuate as it travels through a complete rotation. Despite this, the trend of torque distribution on individual blade has very little change throughout the rotation. Similar effect also takes place on thrust loading of the blades, meaning that blade deflection will change as the turbine rotates, inevitably affecting the fluid dynamics of the turbine

Adaptations of locusts and grasshoppers to the low and variable rainfall of Australia

In Australia, where approximately 80% of the land area is arid or semiarid, rainfall is the major factor limiting acridid populations. Rainfall is not only limiting in terms of quantity but also in being highly variable, both temporally and spatially. In this paper, the main adaptations seen in Australian Acrididae to overcome limiting rainfall are discussed with special reference to economically important species. In the arid to semiarid subtropics (lat 23–33°S) rainfall is slightly summer-dominant but extended dry periods can occur in any season. Chortoicetes terminifera, the main pest species, avoids dry periods through embryonic diapause or survives dry periods as quiescent eggs or adults. Migration is critical for survival as it allows locusts to locate areas of localized rainfall. Outbreaks are frequent and develop when enough rain falls to allow continuous breeding over three to four generations. In temperate areas of subcoastal southern Australia, summers are dry and most rain falls in winter or early spring. Austroicetes cruciata, a univoltine pest species, avoids the dry summers by having an embryonic diapause between summer and early winter. In the tropical north (lat 13–23°S), rainfall is strongly summer-dominant and Austracris guttulosa, another univoltine species, survives the dry winter as immature adults in reproductive diapause. Adults mature after feeding on the green vegetation present following early rains of the wet season. But the early rains are often localized and adults migrate until they encounter these localized areas of rain. Adults then mature and lay, but the survival of their offspring eggs and very young nymphs is assured only if there is further rain within 6 weeks. Outbreaks develop only when there are several years of regular rains both in outbreak areas and adjacent areas of the arid zone. Locusta migratoria does not have a stage that can survive extended dry periods. Consequently, it is mainly restricted to subcoastal areas of moderate rainfall. In the main outbreak areas of subtropical Queensland, populations often decline during the commonly dry winters but outbreaks develop when good rain falls in all seasons

The Value of Transcranial Doppler in Predicting Cerebral Ischaemia During Carotid Endarterectomy

AbstractObjectives: transcranial Doppler (TCD) measurement of middle cerebral artery velocity (MCAV) is an indirect method of assessing cerebral blood flow and therefore predicting patients at risk of stroke during carotid endarterectomy (CEA), and may be used to determine the need for shunting. This study evaluates the accuracy of three accepted TCD criteria in predicting the need for a shunt. Design: prospective study. Methods: one hundred and twenty consecutive CEA were performed under loco/regional anaesthesia. Patients monitored by TCD and Awake neurological examination were included. Shunts were inserted if there was neurological deterioration. Awake patient monitoring was compared with the three TCD criteria. Results: inadequate TCD recordings were obtained in 16 operations (13%). In the remainder (104 cases), 12 developed symptoms of cerebral ischaemia and required a shunt (12%). Comparisons with the three accepted criteria were as follows: (1) m MCAV <30 cm/s had a sensitivity, specificity, PPV and NPV of 92%, 49%, 19%, and 98%, respectively; (2) clamp/pre-clamp ratio <0.6 had a sensitivity, specificity, PPV and NPV of 92%, 75%, 33% and 99%, respectively; (3) greater than 50% reduction in m MCAV had a sensitivity, specificity, PPV and NPV valves of 83%, 77%, 32% and 97%, respectively. Conclusions: TCD flow velocities are not a reliable method for detecting cerebral ischaemia and therefore determining the need for a shunt in CEA

Estimation of erosion model erodibility parameters from media properties

The aim of this research was to enable erodibility values for hillslope-scale erosion prediction models to be determined from easily measured media properties. Simulated rainfall and overland flow experiments were carried out on 34 soils and overburdens from 15 Queensland open-cut coal mines at The University of Queensland Erosion Processes Laboratory. Properties of the 34 media determined included aggregate stability, Atterberg limits, bulk density, cation exchange capacity, dispersion ratios, electrical conductivity, exchangeable sodium percentage, organic carbon content, pH, texture, and water content at field capacity and wilting point. Correlation and stepwise multiple regression procedures were used to determine those media properties that could best be used to predict rill and interill erodibility. Correlations between media properties and sediment delivery at each of 5, 10, 15, 20, and 30% slope revealed that different media properties were correlated with erosion rates at different slopes. A media property could show a strong correlation with erodibility at 30% slope, and a low correlation at 5% slope. Splitting the data set into soils only, and overburdens only, showed that properties that were positively correlated with erosion rates for one group could be negatively correlated for the other group. Therefore, in this study, erodibility could not be explicitly linked to one set of media properties for all medium types and erosive conditions. It was concluded that a single regression equation could not be used to predict erodibility under all conditions. Instead, 4 equations were developed to predict rill and interill erodibility, for soils and overburdens separately. The need for separate regression equations was attributed to the presence of different erosive sub-processes for specific combinations of medium type and slope gradient

Structure of protease-cleaved escherichia coliα-2-macroglobulin reveals a putative mechanism of conformational activation for protease entrapment

Bacterial -2-macroglobulins have been suggested to function in defence as broad-spectrum inhibitors of host proteases that breach the outer membrane. Here, the X-ray structure of protease-cleaved Escherichia coli -2-macroglobulin is described, which reveals a putative mechanism of activation and conformational change essential for protease inhibition. In this competitive mechanism, protease cleavage of the bait-region domain results in the untethering of an intrinsically disordered region of this domain which disrupts native interdomain interactions that maintain E. coli -2-macroglobulin in the inactivated form. The resulting global conformational change results in entrapment of the protease and activation of the thioester bond that covalently links to the attacking protease. Owing to the similarity in structure and domain architecture of Escherichia coli -2-macroglobulin and human -2-macro­globulin, this protease-activation mechanism is likely to operate across the diverse members of this group

Rapid conformational analysis of semi-flexible liquid crystals.

We present an approach for rapid conformational analysis of semi-flexible liquid crystals. We use a simple graphical user interface (GUI) tool that leverages rules-based methods for efficient generation of bend-angle distributions, offering a significant improvement over traditional single-conformer analysis. Our methods demonstrated proficiency in approximating molecular shapes comparable to those obtained from molecular dynamics (MD) simulations, albeit with notable deviations in the under sampling of hairpin conformations and oversampling of extended configurations. Re-evaluation of existing data revealed an apparent weak correlation between NTB transition temperatures and bend angles, underscoring the complexity of molecular shapes beyond mere geometry. Furthermore, we integrated this conformational analysis into a pipeline of algorithmic molecular design, utilising a fragment-based genetic algorithm to generate novel cyanobiphenyl-containing materials. This integration opens new avenues for the exploration of liquid crystalline materials, particularly in systems where systematic conformer searches are impractical, such as large oligomeric systems. Our findings highlight the potential and growing importance of computational approaches in accelerating the design and synthesis of next-generation liquid crystalline materials

Use of laboratory-scale rill and interill erodibility measurements for the prediction of hillslope-scale erosion on rehabilitated coal mine soils and overburdens

Prediction of hillslope-scale soil erosion traditionally involves extensive data collection from field plots under natural rainfall, or from field rainfall simulation programs. Recognising the high costs and inconvenience associated with field-based studies, a method was developed and tested for predicting hillslope-scale soil erosion from laboratory-scale measurements of erodibility. A laboratory tilting flume and rainfall simulator were used to determine rill and interill erodibility coefficients for 32 soils and overburdens from Queensland open-cut coal mines. Predicted sediment delivery rates based on laboratory determinations of erodibility were tested against field measurements of erosion from 12-m-long plots under simulated rainfall at 100 mm/h on slopes ranging from 5% to 30%. Regression analysis demonstrated a strong relationship between predicted and measured sediment delivery rates, giving an r2 value of up to 0.74, depending on the particular modeling approach used. These results demonstrate that soil losses due to the combined processes of rill and interill erosion at the hillslope scale can successfully be predicted from laboratory-scale measurements of erodibility, provided a suitable methodology and modelling approach is adopted. The success of this approach will greatly reduce the cost and effort required for prediction of hillslope scale soil erosion

Derivation of the formyl-group oxygen of chlorophyll b from molecular oxygen in greening leaves of a higher plant (Zea mays)

Using mass spectroscopy, we demonstrate as much as 93% enrichment of the 7-formyl group oxygen of chlorophyll b when dark-grown, etiolated maize leaves are greened under white light in the presence of 18O2. This suggests that a mono-oxygenase is involved in the oxidation of its methyl group precursor. The concomitant enrichment of about 75% of the 131-oxygen confirms the well-documented finding that this oxo group, in both chlorophyll a and b, also arises from O2. High 18O enrichment into the 7-formyl oxygen relative to the substrate 18O2 was achieved by optimization of the greening conditions in combination with a reductive extraction procedure. It indicates not only a single pathway for Chl b formyl group formation, but also unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen

Modelling and Prediction of Global Magnetic Disturbance in Near-Earth Space: a Case Study for Kp Index using NARX Models

Severe geomagnetic disturbances can be hazardous for mod-ern technological systems. The reliable forecast of parameters related to thestate of the magnetosphere can facilitate the mitigation of adverse effects ofspace weather. This study is devoted to the modeling and forecasting of theevolution of the Kp index related to global geomagnetic disturbances. Through-out this work the Nonlinear AutoRegressive with eXogenous inputs (NARX)methodology is applied. Two approaches are presented: i) a recursive slid-ing window approach, and ii) a direct approach. These two approaches arestudied separately and are then compared to evaluate their performances.It is shown that the direct approach outperforms the recursive approach, butboth tend to produce predictions slightly biased from the true values for lowand high disturbances

Prediction of Kp Index Using NARMAX Models with A Robust Model Structure Selection Method

The severity of global magnetic disturbances in Near-Earth space can crucially affect human life. These geomagnetic disturbances are often indicated by a Kp index, which is derived from magnetic field data from ground stations, and is known to be correlated with solar wind observations. Forecasting of Kp index is important for understanding the dynamic relationship between the magnetosphere and solar wind. This study presents 3 hours ahead prediction for Kp index using the NARMAX model identified by a novel robust model structure detection method. The identified models are evaluated using 4 years of Kp data. Overall, the models with robust structure can produce very good Kp forecast results and provide transparent and compact representations of the relationship between Kp index and solar wind variables. The robustness and conciseness of the models can highly benefit the space weather forecast tasks