Complex dynamic behaviors of the complex Lorenz system

AbstractThis study compares the dynamic behaviors of the Lorenz system with complex variables to that of the standard Lorenz system involving real variables. Different methodologies, including the Lyapunov Exponents spectrum, the bifurcation diagram, the first return map to the Poincaré section and topological entropy, were used to investigate and compare the behaviors of these two systems. The results show that expressing the Lorenz system in terms of complex variables leads to more distinguished behaviors, which could not be achieved in the Lorenz system with real variables, such as quasi-periodic and hyper-chaotic behaviors

Tidal energy leasing and tidal phasing

In addition to technical and economic constraints, tidal energy leasing is generally governed by demand for sites which contain the highest tidal streams, and does not take into account the phase relationship (i.e. the time lag) between sites. Here, the outputs of a three-dimensional tidal model are analysed to demonstrate that there is minimal phase diversity among the high tidal stream regions of the NW European shelf seas. It is therefore possible, under the current leasing system, that the electricity produced by the first generation of tidal stream arrays will similarly be in phase. Extending the analysis to lower tidal stream regions, we demonstrate that these lower energy sites offer more potential for phase diversity, with a mean phase difference of 1.25 h, compared to the phase of high energy sites, and hence more scope for supplying firm power to the electricity grid. We therefore suggest that a state-led leasing strategy, favouring the development of sites which are complementary in phase, and not simply sites which experience the highest current speeds, would encourage a sustainable tidal energy industry

Realistic wave conditions and their influence on quantifying the tidal stream energy resource

AbstractWhen selecting suitable sites for tidal stream energy arrays a wide range of factors must be considered, from the magnitude of the tidal stream resource, to realistic oceanographic conditions. Previous computational and laboratory-scale investigations into the impact of waves upon tidal turbines (such as turbine blade loadings) and turbine arrays (such as array configuration) typically assume that waves propagate “inline” to the tidal current (waves following or waves opposing the tidal current with a 20° tolerance limit). We investigated the wave climate at typical tidal stream energy sites across the British Isles. The wave climate was simulated at 18 sites using a 7-year (2005–2011) SWAN wave model simulation of the northwest European shelf seas. The principal semi-diurnal lunar constituent (M2) was also estimated at these sites using the three-dimensional ROMS tidal model. A significant proportion of the wave climate (between 49% and 93% of the time), including extreme wave events (>10m wave heights), was found to be propagating in a direction which was “oblique” to the major axis of tidal flow (i.e. waves which propagate at an angle to the tidal current with a 20° tolerance limit) at all 18 selected sites. Furthermore, the average “inline” wave climate was 2.25m less in height and 2s less in wave period in comparison to the oblique wave climate. To understand the direct effect of waves upon the tidal stream resource, the dynamically wave-tide coupled COAWST modelling system was applied to an idealized headland case study, which represented the typical tide and wave conditions expected at first generation tidal stream energy sites. Waves were found to alter the simulated tidal velocity profile, which, because tidal stream power is proportional to velocity cubed, reduced the theoretical resource by 10% for every metre increase in wave height (R2 94% with 22 degrees of freedom) – depending upon wave period and direction. Our research indicates that wave angle should be considered when quantifying the impact of waves upon tidal turbines, such as computational fluid dynamic (CFD) studies, or laboratory-scale experiments of wake characteristics and turbine fatigue loading. Further, dynamically coupled tide-wave models may be necessary for a thorough resource assessment, since the complex wave-tide interaction affected the tidal resource; however, in situ observations of tidal velocity profiles during a range of wave events will be essential in validating such modelling approaches in the future

Resource assessment for future generations of tidal-stream energy arrays

AbstractTidal-stream energy devices currently require spring tide velocities (SV) in excess of 2.5 m/s and water depths in the range 25–50 m. The tidal-stream energy resource of the Irish Sea, a key strategic region for development, was analysed using a 3D hydrodynamic model assuming existing, and potential future technology. Three computational grid resolutions and two boundary forcing products were used within model configuration, each being extensively validated. A limited resource (annual mean of 4 TJ within a 90 km2 extent) was calculated assuming current turbine technology, with limited scope for long-term sustainability of the industry. Analysis revealed that the resource could increase seven fold if technology were developed to efficiently harvest tidal-streams 20% lower than currently required (SV > 2 m/s) and be deployed in any water depths greater than 25 m. Moreover, there is considerable misalignment between the flood and ebb current directions, which may reduce the practical resource. An average error within the assumption of rectilinear flow was calculated to be 20°, but this error reduced to ∼3° if lower velocity or deeper water sites were included. We found resource estimation is sensitive to hydrodynamic model resolution, and finer spatial resolution (<500 m) is required for regional-scale resource assessment when considering future tidal-stream energy strategies

Effect of waves on the tidal energy resource at a planned tidal stream array

Wave�current interaction (WCI) processes can potentially alter tidal currents, and consequently affect the tidal stream resource at wave exposed sites. In this research, a high resolution coupled wave-tide model of a proposed tidal stream array has been developed. We investigated the effect of WCI processes on the tidal resource of the site for typical dominant wave scenarios of the region. We have implemented a simplified method to include the effect of waves on bottom friction. The results show that as a consequence of the combined effects of the wave radiation stresses and enhanced bottom friction, the tidal energy resource can be reduced by up to 20% and 15%, for extreme and mean winter wave scenarios, respectively. Whilst this study assessed the impact for a site relatively exposed to waves, the magnitude of this effect is variable depending on the wave climate of a region, and is expected to be different, particularly, in sites which are more exposed to waves. Such effects can be investigated in detail in future studies using a similar procedure to that presented here. It was also shown that the wind generated currents due to wind shear stress can alter the distribution of this effect

Regional differences in cancer incidence trend in tehran, Iran: A contextual study on the effect of socioeconomic status at regional level

Background: Cancer is a major public health concern all over the world. The aim of the current study is to demonstrate changing trends of cancer incidence from 2006 to 2009 in Tehran (capital city of Iran) and evaluate the effect of living in different regions according to their median socioeconomic status (SES) on cancer cumulative incidence. Methods: The incident cases were obtainedfromthe population based cancer register of ministry of healthandmedicine in Iran; we examined the annual percent changes (APCs) and overall trends of total cancer incidence across regions in Tehran. The age and sex standardized incidence rates were computed by the direct method. Poisson regression and negative binominal regression model were used to assess the existence of trends across 4 consecutive years, as well as the effect of living in each region, literacy rate, and employment rate across regions on this trend. All the analyses were done by Stata 12.0 software. Results: The findings of this study showed downward and nonlinear trend during 4 years. The age-standardized incidence rate (ASR) was higher in men compared to women in this period. ASRs for overall 4 years were 114 and 101 per 10,0000 men and women, respectively. Average annual percent change based on ASR and regression model for each sex was the same and around -5 and -6, respectively. Incidence rate also differed between districts so that north and center districts had higher incidence than southern parts in both sexes. The lowest rate ratio attributed to district 17 and 18 located in south of Tehran and the highest rate ratio attributed to district 6 for each sex compared to the baseline district 16. Results reported the sharp increase of 59 and 37 in district 6 compared to district 16 in men and women, respectively. Better regional social status increased the risk of cancer among women. Also, the results showed a partially significant interaction with higher decrease in annual trend of cancer rate in socially more deprived regions. Conclusions: The results showeddownwardand nonlinear decreasing trend during 4 years, especially in regions with lower socioeconomic status. Incidence rate also differed between districts so that northern regions had higher incidence than southern regions. Spatio-temporal Analysis of these cancer rates with adjustment for more regional socio-economic characteristicsmaybetter explain the disparities in rate of cancer in different districts across time. © 2018, Cancer Research Center (CRC), Shahid Beheshti University of Medical Sciences

The effect of amino acids on the growth of microsporum canis and Trichophyton schoenleinii

Background: Amino acids have different effects on the growth of some dermatophytes. Some may encourage growth, while others inhibit it. The concentrations of some amino acids also are an important factor for their effect. To investigate the effects of amino acids on the growth of dermatophytes, the dermatophytes Trichophyton schoenleinii and Microsporum canis, obtained from Iran. Methods: In this study, two concentrations (1g/dL and 0.1g/dL) of 23 amino acids were added to the Sabouraud glucose agar media of these dermatophytes. The experiment was carried out three times. After two weeks, the means of the colonies were compared with the control, which had no amino acids added to the Sabouraud glucose media. Results: The results showed that L-cysteine hydrochloride, L-cysteine, L-aspartic acid, L-glutamic acid and DL-tryptophan and L-tyrosine had the most inhibitory effects on the studied dermatophytes, while arginine L-lysine and L-methionine had moderate effects and the rest of amino acids had less inhibitory, or even stimulatory, effects on the growth of the dermatophytes. M. canis and T. schoenleinii has a different sensitivity to amino acids. This data indicates that sulfur-containing amino acids and acetic amino acids have greater inhibitory effect against these two dermatophytes. This may be an indicator that such amino acids used in, for example, sweetener may have an important role in immunity to these dermatophytes. Thus, some amino acids may be used as a possible treatment for dermatophytosis. Conclusion: Among the amino acids L-cysteine hydrocholoride, glutamic acid, aspartic acid, and tryptophan are the most inhibitory effect s against of T. schoenleinii and M. canis. © 2008, Tehran University of Medical Sciences. All rights reserved