Development of a renewable hybrid power plant with extended utilization of pumped storage unit equipment

The scheme of a renewable hybrid power plant with the extended use of the installed equipment of the pumped storage unit for the conversion of the photovoltaic and wind generators direct current to the alternating one is proposed. The scheme is based on existing components with widely used proven technology. To output the power of solar and wind generators to the grid and for DC to AC conversion, a synchronous generator of the pumped storage unit is used in addition to grid inverters. An induction motor, powered through a variable frequency drive from a common DC bus, is used together with a hydraulic turbine to rotate the generator. In addition, batteries and capacitors banks are connected to the DC bus. The possibility of using various types of electric machines to drive a synchronous generator is analyzed and the preference of an induction motor is shown. The response of an induction motor to rotational speed fluctuations is modeled and its capability to participate in the network frequency regulation is shown. With the example of a typical daily load and generation profile, it is shown that the proposed solution for DC to AC conversion has an efficiency close to that of the grid inverter. The proposed scheme of the hybrid power plant can increase the reliability of renewable energy sources and the stability of the network frequency. This is achieved due to increasing the inertia of the rotating masses in the power system, the power factor control capabilities of the synchronous generator and the proper response of induction motor to rapid fluctuations of the rotation speed. The creation of such hybrid power plants opens the way for a further increase in the share of renewable energy sources in the power system.Запропоновано схему гібридної відновлюваної електричної станції з розширеним використанням встановленого обладнання гідроакумулюючого блока для перетворення постійного струму фотоелектричних та вітрових генераторів в змінний. Схема базується на наявних компонентах з широко використовуваною відпрацьованою технологією. Для видачі потужності та перетворення постійного струму сонячних та вітрових генераторів в змінний окрім мережевих інверторів використовується синхронний генератор гідроакумулюючого блоку. Для обертання генератора крім гідротурбіни також використовується асинхронний двигун, підключений через частотно-регульований привод до загальної шини постійного струму станції. Крім того, до шини постійного струму підключені електрохімічні акумулятори і батареї конденсаторів. Проаналізовано можливість використання різних типів електричних машин для приводу синхронного генератора і показано перевагу асинхронного двигуна. Змодельовано реакцію асинхронного двигуна на коливання швидкості обертання і показано його здатність брати участь в регулюванні частоти мережі. На прикладі типового добового графіка навантаження і генерації показано, що запропоноване рішення по перетворенню постійного струму в змінний має ККД, близький до ККД мережевого інвертора. Запропонована схема гібридної станції дозволяє підвищити надійність роботи відновлюваних джерел енергії і стабільність частоти мережі. Це досягається завдяки збільшенню інерції обертових мас в енергосистемі, можливості управління коефіцієнтом потужності синхронного генератора і властивій асинхронному двигуну реакції на коливання швидкості обертання. Створення таких гібридних станцій відкриває шлях до подальшого збільшення частки відновлюваних джерел в енергосистемі

Aging in Dense Colloids as Diffusion in the Logarithm of Time

The far-from-equilibrium dynamics of glassy systems share important phenomenological traits. A transition is generally observed from a time-homogeneous dynamical regime to an aging regime where physical changes occur intermittently and, on average, at a decreasing rate. It has been suggested that a global change of the independent time variable to its logarithm may render the aging dynamics homogeneous: for colloids, this entails diffusion but on a logarithmic time scale. Our novel analysis of experimental colloid data confirms that the mean square displacement grows linearly in time at low densities and shows that it grows linearly in the logarithm of time at high densities. Correspondingly, pairs of particles initially in close contact survive as pairs with a probability which decays exponentially in either time or its logarithm. The form of the Probability Density Function of the displacements shows that long-ranged spatial correlations are very long-lived in dense colloids. A phenomenological stochastic model is then introduced which relies on the growth and collapse of strongly correlated clusters ("dynamic heterogeneity"), and which reproduces the full spectrum of observed colloidal behaviors depending on the form assumed for the probability that a cluster collapses during a Monte Carlo update. In the limit where large clusters dominate, the collapse rate is ~1/t, implying a homogeneous, log-Poissonian process that qualitatively reproduces the experimental results for dense colloids. Finally an analytical toy-model is discussed to elucidate the strong dependence of the simulation results on the integrability (or lack thereof) of the cluster collapse probability function.Comment: 6 pages, extensively revised, final version; for related work, see http://www.physics.emory.edu/faculty/boettcher/ or http://www.fysik.sdu.dk/staff/staff-vip/pas-personal.htm

Time Resolved Correlation measurements of temporally heterogeneous dynamics

Time Resolved Correlation (TRC) is a recently introduced light scattering technique that allows to detect and quantify dynamic heterogeneities. The technique is based on the analysis of the temporal evolution of the speckle pattern generated by the light scattered by a sample, which is quantified by $c\_I(t,\tau)$, the degree of correlation between speckle images recorded at time $t$ and $t+\tau$. Heterogeneous dynamics results in significant fluctuations of $c\_I(t,\tau)$ with time $t$. We describe how to optimize TRC measurements and how to detect and avoid possible artifacts. The statistical properties of the fluctuations of $c\_I$ are analyzed by studying their variance, probability distribution function, and time autocorrelation function. We show that these quantities are affected by a noise contribution due to the finite number $N$ of detected speckles. We propose and demonstrate a method to correct for the noise contribution, based on a $N\to \infty$ extrapolation scheme. Examples from both homogeneous and heterogeneous dynamics are provided. Connections with recent numerical and analytical works on heterogeneous glassy dynamics are briefly discussed.Comment: 19 pages, 15 figures. Submitted to PR

The power of PISA – limitations and possibilities for educational research

On 6th December 2016, the Programme for International Student Assessment (PISA) releases its report on the achievements of 15-year-olds from 72 countries and economies around the world. This triennial international survey aims to evaluate education systems across 72 contexts by testing skills in Mathematics, Science and Reading Literacy. This is the sixth cycle of PISA and the OECD suggests countries and economies now have the capability to compare the results over time to ‘assess the impact of education policy decisions’ . Compared to other education studies, the media coverage of PISA must be described as massive (Meyer and Benavot, 2013, Baird et al., 2016) and, as with previous years, it is expected that PISA will attract considerable discussion among policy makers, educators and researchers (Wiseman, 2014). It is therefore timely to present a thematic issue of Assessment in Education, where we publish four articles that have analysed previous datasets from the PISA studies each commenting upon the challenges, limitations and potential future assessment research on the PISA data. The articles touch upon issues regarding sampling, language, item difficulty and demands, as well as the secondary analyses of students’ reported experiences of formative assessment in the classroom. One important message from the authors in this thematic Special Issue is the need for a more complex discussion around the use and misuse of PISA data, and the importance of pointing to the limitations of how the results are presented to policy makers and the public. In an area where the media produces narratives on schools and education systems based upon rankings in PISA, researchers in the field of large-scale assessment studies have a particularly important role in stepping up and advising on how to interpret and understand these studies, while warning against potential misuse. </p

Laboratory Tests of Low Density Astrophysical Equations of State

Clustering in low density nuclear matter has been investigated using the NIMROD multi-detector at Texas A&M University. Thermal coalescence modes were employed to extract densities, $\rho$, and temperatures, $T$, for evolving systems formed in collisions of 47 $A$ MeV $^{40}$Ar + $^{112}$Sn,$^{124}$Sn and $^{64}$Zn + $^{112}$Sn, $^{124}$Sn. The yields of $d$, $t$, $^{3}$He, and $^{4}$He have been determined at $\rho$ = 0.002 to 0.032 nucleons/fm$^{3}$ and $T$= 5 to 10 MeV. The experimentally derived equilibrium constants for $\alpha$ particle production are compared with those predicted by a number of astrophysical equations of state. The data provide important new constraints on the model calculations.Comment: 5 pages, 3 figure

The role of temporary accommodation buildings for post-disaster housing reconstruction

The number of houses damaged or destroyed after disasters is frequently large, and re-housing of homeless people is one of the most important tasks of reconstruction programmes. Reconstruction works often last long and during that time, it is essential to provide victims with the minimum conditions to live with dignity, privacy, and protection. This research intends to demonstrate the crucial role of temporary accommodation buildings to provide spaces where people can live and gradually resume their life until they have a permanent house. The study also aims to identify the main problems of temporary accommodation strategies and to discuss some principles and guidelines in order to reach better design solutions. It is found that temporary accommodation is an issue that goes beyond the simple provision of buildings, since the whole space for temporary settlement is important. Likewise, temporary accommodation is a process that should start before a disaster occurs, as a preventive pre-planning. In spite of being temporary constructions, these housing buildings are one of the most important elements to provide in emergency scenarios, contributing for better recovery and reconstruction actions.The first author gratefully acknowledges the financial support of Fundacao para a Ciencia e a Tecnologia, FCT, through grant SFRH/BD/73853/2010

Experimental Determination of In-Medium Cluster Binding Energies and Mott Points in Nuclear Matter

In medium binding energies and Mott points for $d$, $t$, $^3$He and $\alpha$ clusters in low density nuclear matter have been determined at specific combinations of temperature and density in low density nuclear matter produced in collisions of 47$A$ MeV $^{40}$Ar and $^{64}$Zn projectiles with $^{112}$Sn and $^{124}$Sn target nuclei. The experimentally derived values of the in medium modified binding energies are in good agreement with recent theoretical predictions based upon the implementation of Pauli blocking effects in a quantum statistical approach.Comment: 5 pages, 3 figure

On the use of MODIS EVI to assess gross primary productivity of North American ecosystems

[1] Carbon flux models based on light use efficiency (LUE), such as the MOD17 algorithm, have proved difficult to parameterize because of uncertainties in the LUE term, which is usually estimated from meteorological variables available only at large spatial scales. In search of simpler models based entirely on remote‐sensing data, we examined direct relationships between the enhanced vegetation index (EVI) and gross primary productivity (GPP) measured at nine eddy covariance flux tower sites across North America. When data from the winter period of inactive photosynthesis were excluded, the overall relationship between EVI and tower GPP was better than that between MOD17 GPP and tower GPP. However, the EVI/GPP relationships vary between sites. Correlations between EVI and GPP were generally greater for deciduous than for evergreen sites. However, this correlation declined substantially only for sites with the smallest seasonal variation in EVI, suggesting that this relationship can be used for all but the most evergreen sites. Within sites dominated by either evergreen or deciduous species, seasonal variation in EVI was best explained by the severity of summer drought. Our results demonstrate that EVI alone can provide estimates of GPP that are as good as, if not better than, current versions of the MOD17 algorithm for many sites during the active period of photosynthesis. Preliminary data suggest that inclusion of other remote‐sensing products in addition to EVI, such as the MODIS land surface temperature (LST), may result in more robust models of carbon balance based entirely on remote‐sensing data

The Physics of the Colloidal Glass Transition

As one increases the concentration of a colloidal suspension, the system exhibits a dramatic increase in viscosity. Structurally, the system resembles a liquid, yet motions within the suspension are slow enough that it can be considered essentially frozen. This kinetic arrest is the colloidal glass transition. For several decades, colloids have served as a valuable model system for understanding the glass transition in molecular systems. The spatial and temporal scales involved allow these systems to be studied by a wide variety of experimental techniques. The focus of this review is the current state of understanding of the colloidal glass transition. A brief introduction is given to important experimental techniques used to study the glass transition in colloids. We describe features of colloidal systems near and in glassy states, including tremendous increases in viscosity and relaxation times, dynamical heterogeneity, and ageing, among others. We also compare and contrast the glass transition in colloids to that in molecular liquids. Other glassy systems are briefly discussed, as well as recently developed synthesis techniques that will keep these systems rich with interesting physics for years to come.Comment: 56 pages, 18 figures, Revie