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On the occasion of the centennial of his mentor Alvin Hansen, Paul Samuelson published in 1988 a modified version of his seminal 1939 multiplier-accelerator model to address aspects of Hansen's secular stagnation hypothesis. The "Keynes-Hansen-Samuelson" model (or KHS, as he called it) was built to analyse the effects of population growth on the economy's trajectory. Several changes were then made. Instead of difference equations and a tight accelerator, as in his 1939 model, Samuelson deployed differential equations and a flexible accelerator to produce a nonlinear limit cycle. Despite Samuelson's strong claims for the analytical contributions of his 1988 paper, it has – in contrast with the 1939 model – received only scant attention by macroeconomists and historians of economics alike. Samuelson's 1988 paper was his last published macroeconomic model, based on his long-established tradition of non-optimising macro-dynamics. Our paper provides a close reading of that article and some analytical results that shed new light on the formal aspects of Samuelson's 1988 model. We also discuss how it historically links up with business cycle models advanced by John Hicks, Nicholas Kaldor, Roy Harrod and Richard Goodwin and examine how far Samuelson's use of the term secular stagnation differs from Larry Summers's recent reconstruction of it. [ABSTRACT FROM AUTHOR]

The commonly used household plumbing pipes are made of polyvinyl chloride (PVC) pipes. However, there are concerns regarding their role as source of microplastics (MPs) in the water supply system. This study aimed to investigate the leachability of MPs from PVC pipes under stagnant conditions. Laboratory experiments were conducted in PVC pipes to simulate MP leaching at varying pH, chlorine doses, and stagnation times. Water samples from the experiments were tested for different water quality parameters, including MPs using standard procedures. The total organic carbon concentration in the water samples increased with stagnation period indicating that organic substances including MPs were leaching from the pipes. The concentration of leached particles as well as the MPs count increased with stagnation period. A strong correlation was found between the MPs count and the mass concentration of leached particles retained on the filter papers leading to the conclusion that most of the leached particles were MPs. Attenuated total reflectance-Fourier-transform infrared spectroscopy analysis showed peaks associated with C-Cl and C-H bonds that are typical for PVC suggesting that particles retained in the filter are likely PVC microplastics. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis identified particles that have elemental compositions like that of PVC further strengthening the conclusion that MPs were leaching from the PVC pipe. [ABSTRACT FROM AUTHOR]

This paper studies two formal models of long run growth with a medium-run distributive cycle, both of which feature causal links from the rise in inequality to a deterioration of long run macroeconomic performance. Both versions feature an endogenous income-capital ratio: one through the Keynesian notion of effective demand, the other building on induced bias in technical change. A key focus of the analysis is on the assumptions necessary in both frameworks to generate policy implications consistent with the observed decline of the labor share, the income-capital ratio, and labor productivity growth during the neoliberal era. Importantly, both theories: (a) provide space for mutually reinforcing pro-labor and pro-growth policies in the long run, although they differ in the mechanisms at play in these processes; (b) imply a potential tradeoff between pro-labor policies and growth on one hand, and long-run employment on the other; (c) are consistent with the evidence on the distributive cycle at business cycle frequency. [ABSTRACT FROM AUTHOR]

In early 2000s, long-distance wind dispersal of mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) resulted in massive outbreaks in the northern Rocky Mountains, Alberta, Canada, outside of the beetle's natural range. We analyzed data from permanent plots measured for up to 15 years after MPB outbreaks in fire-origin, mature lodgepole pine (Pinus contorta var. latifolia Engelm.)-dominated stands scattered over an area of ∼ 75,000 km2. We evaluated stand level stocking, regeneration, and ingrowth of three species groups (pine, shade-tolerant conifers, and broadleaves) in stands where > 50 % of pine basal area was killed. Using multiple linear regression analysis, we examined the relationship between stand and climatic covariates and basal area growth, density of regeneration, and ingrowth into the sapling size class at 9–15 years post-outbreak. Results showed that total live basal area for all species combined in trees with height ≥ 1.3 m occupies on average < 50 % of the pre-MPB levels and is unchanged between both post-MPB measurements at 19.5 m2 ha−1. Ongoing pine mortality led to negative net growth, which exceeded the positive net growth in other conifers and resulted in zero net change for the whole stand. Post-MPB ingrowth and regeneration rates were close to zero for pine but increased slightly in other conifers and broadleaf species. Regression analysis revealed a negative relation between post-MPB growth and quadratic mean diameter of the reconstructed pre-MPB total basal area, while initial basal area and composition post-MPB varied among species. Our findings support the hypothesis that, post-MPB, mature pine dominated stands stagnate due to ongoing pine mortality, the maturity of remnant overstory, and a lack of adequate understory and regeneration that can accumulate sufficient growth at short-to mid-term post-outbreak. Our conclusions contrast other research, suggesting that outbreaks leave degraded residual stands with declining pine overstory and that transition to vigorous productive mixed stands is impossible in the absence of stand-replacing disturbance or silvicultural investment. • Total live basal area remained unchanged post-attack at less than 50 % of pre-attack. • For all species together total net growth after MPB is zero to slightly negative. • Growth reflects the stagnation of these mature stands in terms of timber production. • Pine regeneration lacking and that of other species highly variable after attack. • Weak relation between post-MPB growth and stand structure and composition variables. [ABSTRACT FROM AUTHOR]

The development of aquaculture is a story of international success, but not in the EU. The present study investigates why the development of aquaculture is stalling or sometimes even follows a downward trend in some countries, using Germany as a case study. The EU framework for aquaculture policies has established a "twin logic" as a long-term strategy: Protection of the environment and economic growth. The present sociological approach uses qualitative data from group discussions with aquaculture stakeholders from industries, politics, regulation, environmental protection agencies, and NGOs. The stakeholders indicated that a small, fragmented sector without economic and political power on the one hand, and an overregulated, complex governance on the other hand are the main barriers to economic growth. Applying Parsons' Action Frame of Reference, the article argues that the German stakeholders are not able to adopt the EU twin logic as a clear solution for overcoming the stagnation of aquaculture in Germany in practice. For the stakeholders, the twin logic results in confusing framework conditions in terms of societal expectations, values, norms, regulations, and their national implementation. The uncertainty is rooted in diametrically societal values and leads to conflicts at the individual level of stakeholders' decision-making for investments. In consequence, the societal environment for aquaculture investment measures is uncertain. This exploration results in an empirical-grounded hypothesis, that aquaculture is a dysfunctional system of action. • Stakeholders discuss barriers for the development of aquaculture in Germany. • Germany as a case study for EU aquaculture. • Sociological explanation of why aquaculture development stagnates in Germany. • Empirical hypothesis of a dysfunctional action frame for aquaculture stakeholders. • Lessons learned on how to improve the action frame towards a path of aquaculture development. [ABSTRACT FROM AUTHOR]

• Eyewash stations are important safety equipment characterized by long water age. • Significant increases in microbial contamination were detected in eyewash stations. • Eyewash stations may serve as potential sources of pathogen exposure. • Proper eyewash flushing was effective in reducing microbial contamination. Emergency eyewash stations are important safety equipment characterized by long water age. Significant increases in microbial contamination were detected in eyewash stations with water ages longer than 1 day. Enterobacter and Mycobacterium were identified in high abundance in eyewash stations with prolonged water age, suggesting eyewash stations as potential sources of pathogen exposure. Proper eyewash flushing was shown to be an effective practice to mitigate risks of exposure to microbial contaminants from eyewash use. [ABSTRACT FROM AUTHOR]

• Conceptualization of stagnant water based on ethnography of downstream neighbourhoods of Semarang. • Rethinking the concept of the hydrosocial cycle through an appreciation of stagnation is proposed. • Brings Povinelli's concept of quasi-events in dialogue with scholarship on the hydrosocial. • Stagnation is product of urbanization, marginalization, and uncoordinated infrastructural repairs. • Initiates a needed reflection on margins of the hydrosocial. This article investigates stagnation as a product of hydrosocial relations in light of ethnographic research conducted in the port city of Semarang, Indonesia. In Semarang's coastal north, river water spills daily into neighbourhoods during high tide, and often stagnates in houses and streets. While recent studies have shown that water governance is a form of social control, reproducing (infra)structures of subjugation and social inequality, little attention has been paid to the margins of water infrastructure, especially in cities. By focusing on stagnation, this article examines hydrosocial arrangements in the margins of postcolonial drainage infrastructure. When the peripheral and densely populated neighbourhoods in Semarang's north are flooded during high tide, residents resort to private or semi-public pumps to get rid of stagnant water. Residents deplore insufficient state attention to their area, reflected in collapsing or seeping riverbanks. A relatively reliable flood prevention is the timely and regular raising of house floors and streets. The municipality responds to dramatic rates of land subsidence (10–15 cm/year) by raising roads and riverbanks. Yet, many dwellings along the Banger River have been destroyed by intruding sea water and left behind in ruins, suggesting a permanent failure of the city's drainage system. Residents bear the brunt of supplementary infrastructural labour, their efforts of infrastructural repair and maintenance sustaining a bare minimum of safety. The article mobilizes Elizabeth Povinelli's concept of quasi-events to understand the hydrosocial relations that shape peoples' precarious relation with drainage infrastructure as unequal yet generalized. Quasi-events, that is, efforts to hold water at bay, suck energy and resources from marginalized residents. As such, the article argues that the margin of the hydrosocial is integral to the political configuration of land and water. [ABSTRACT FROM AUTHOR]

This paper presents a macroeconomic agent based model with endogenous innovation-driven growth and knowledge accumulation which aims to analyze the underlying causes of the recent increase in market concentration, by focusing on the interplay of technical change and market power, and the resulting macroeconomic consequences in terms of higher inequality and lower growth. The source of concentration lies in the fact that heterogeneous firms do not have equal access to capital-embodied innovations, as we assume that this depends on the "knowledge gap", i.e., the difference between the degree of capital good's technical advancement and the firm's accumulated technological knowledge. The analysis shows that, in the absence of consistent knowledge spillovers and as long as capital goods remain considerably different from each other, technical progress generates systematic differences in productivity across firms, leading to a reallocation of market shares towards more productive firms. Consequently, as the newly-emerging large firms seek to translate the enhanced market power into higher mark-ups, the resulting shift in the income distribution from wages to profits eventually undermines aggregate demand and growth. Yet, simulation experiments reveal that the evolution of market concentration over time as well as its macroeconomic effects crucially depend on the presence (or lack thereof) of legal entry barriers, which, by influencing the process of diffusion of technological innovations, reinforce (or attenuate) the large firms' ability to consolidate their dominant position and thus exploit their market power. [ABSTRACT FROM AUTHOR]

How do inequality and growth evolve in the long run and why? We address this question by analyzing the interplay between household debt, growth and inequality within a monetary, stock-flow consistent framework. We first consider a Goodwin–Keen model where household consumption, rather than investment by firms, is the key behavioural driver for the dynamics of the economy. Whenever consumption exceeds current income, households can borrow from the banking sector. The resulting three dimensional dynamical system for wage share, employment rate, and household debt exhibits the characteristic asymptotic equilibria of the original Keen model, namely the analogue of Solow's balanced-growth path, where all state variables converge to an interior point, in addition to deflationary equilibria with explosive debt and collapsing employment. We then extend this set-up by separating the household sector into workers and investors, obtaining a four-dimensional system with analogous types of asymptotic behaviour. Our main result is that long-run increasing inequality between these two classes of households occurs if and only if the system approaches one of the equilibria with unbounded debt ratios. More specifically, we find that one essential channel of increased inequality is the wealth transfer from workers to investors due to interest paid on debt from the former to the latter. Finally, when properly rewritten, the celebrated inequality r > g turns out to be a necessary condition for the asymptotic stability of long-run debt-deflation. Our findings shed new light on the relationships between fairness and efficiency, and have implications for public economic policy. [ABSTRACT FROM AUTHOR]

The flow field of cyclone separators was simulated with different vortex finder diameters and inlet dimensions using the Reynolds Stress Model to determine the mechanism of stagnation of axial velocity. Two flow patterns of axial velocity in cyclone were observed with changing vortex finder diameter and inlet dimension. As vortex finder diameter and inlet dimension increased, stagnation worsened. If the pressure gradient at the centerline of cyclone separator is positive, stagnation of axial velocity appears in the separation space of cyclone. The variation of the dimensionless critical vortex finder diameter of stagnation with inlet dimension was attributed to the proportion distribution of energy loss in cyclone. Finally, response surface methodology and Muschelknautz method of modeling (MM) were applied and yielded parameters with significant effects on stagnation. The variance analysis confirmed a larger quantitative contribution from inlet dimension on stagnation compared to that of vortex finder diameter, which will be useful for the structural optimization of cyclone. Unlabelled Image • Give the effect of D er and K a on stagnation in detail for the first time. • Acquire the condition for stagnation just appearing in the separation space. • The mechanism of axial velocity stagnation is revealed. • Provide quantitative contribution from D er and K a on stagnation by RSM. • Reveal the variation of D cer with K a. [ABSTRACT FROM AUTHOR]

• Common measures to control the spread of COVID-19 include building closures. • Prolonged building closures result in extreme stagnation in building water systems. • Extreme water stagnation is linked to significantly increased presence of Legionella. • Re-opening of buildings should mitigate elevated exposure risks to Legionella. Prolonged building closures are prevalent during the COVID-19 pandemic, resulting in extreme stagnation in building water systems. High-throughput sequencing analysis revealed significantly increased presence of Legionella due to extreme water stagnation, highlighting elevated exposure risks to Legionella from building water systems during re-opening of previously closed buildings. [ABSTRACT FROM AUTHOR]

• Comprehensive market survey on commercially-available absorber coatings. • Modelling of the efficiency parameters with a validated steady-state collector model. • Simulation of the thermal system performance of different collector absorbers. • Analysis of the impact of the optical properties on the stagnation behavior. We present a comparative simulative study to evaluate the efficiency and stagnation behavior of commercially available absorber coatings for solar thermal flat-plate collectors. A market survey has revealed different absorber coatings, which exhibit solar absorptances of α > 90% and thermal emittances ε of 5–90%. All these coatings can be classified as wet-chemically electroplated coatings on the basis of black chrome, highly selective sputtered PVD coatings, solar paints and novel thermochromic coatings. We calculated the annual solar collector energy output by means of collector simulations with the tool ScenoCalc and compared the collector efficiency of several absorber coatings. We have carried out TRNSYS simulations both with systems for solar domestic hot water preparation and solar-assisted space heating. In a solar domestic hot water system with a daily tapping volume of 100 L we report an increase in the auxiliary energy demand of up to 6% with black chrome, 7% with thermochromic and 21% with solar paint coatings compared to sputtered PVD coatings. In a solar combisystem the increase in the auxiliary energy demand does not exceed 1.4% for thermochromic and black chrome coatings and 6.1% for solar paints. The stagnation period can be reduced from 178 h per year (PVD coatings) to 118 h, 62 h and 11 h for black chrome, thermochromic and solar paint coatings, respectively. The maximum absorber temperatures decrease from 175 °C (PVD coatings) to 165 °C for black chrome, 145 °C for thermochromic and 135 °C for solar paint coatings. [ABSTRACT FROM AUTHOR]

Abstract A multi-stream Flamelet Progress Variable (FPV) model, specifically developed for coal combustion, is proposed. The model accounts for the different fuel streams associated with the volatile and char burnout products. The applicability of the new FPV model is investigated in a laminar stagnation pulverized coal flame. The flame considered is a premixed mixture of CH 4 , O 2 and N 2 , carrying pulverized coal particles, stabilized in an impinging wall. Spontaneous emissions of OH*, CH* and C 2 * are measured to identify the flame. The 1D numerical simulations of the experimental conditions are able to reproduce the main features of the flame. The applicability of the multi-stream FPV model to coal combustion is further evaluated with the a posteriori analysis of the FPV results, comparing the results with a reference model, where the species are fully transported and the chemistry directly evaluated. Then, with the budget analysis, the influence of the control variables used to build the look-up table is assessed by examining the conditional contributions to the overall transport terms of scalar quantities (e.g. species, temperature). The results of both analyses show that the proposed multi-stream FPV model can accurately predict the main features of coal combustion, with only minor issues related to the manifold used to build the look-up table. [ABSTRACT FROM AUTHOR]

Abstract Air quality is closely related to the synoptic circulation and local wind field affecting a certain area as they have distinct influence on the path and speed of pollutants. The Yangtze River Delta is located on the eastern coast, and the air returning from coastal areas has a detrimental effect on air quality in the area. This study proposes to analyze if certain circulation types and the occurrence of recirculation are predominantly related to the occurrence of bad air quality in the Yangtze River Delta. Using sea level pressure data from 2006 to 2016, we used T-mode objective classification to classify circulation in the Yangtze River Delta into nine categories. At the same time, using the Allwine and Whiteman (AW) method, we categorized local winds in the region as ventilation, stagnation, and recirculation types, and we found that the local wind tends to be under recirculation conditions when the region was controlled by circulation types 3 (CT3, southeast low pressure), CT4 (northeast low pressure), CT7 (northwest high pressure), and CT8 (north high pressure, south low pressure, with a large pressure gradient). By comparing concentrations of pollutants and different local wind types, we found that recirculation tended to promote high pollution situations. Use of the HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model to simulate the diffusion of pollutants by recirculation in Shanghai in March 2016 confirmed this conclusion. The outputs of HYSPLIT model can show the track of air mass intuitively, and then reflect the effect of recirculation. Graphical abstract Unlabelled Image Highlights • Stagnation and recirculation in the Yangtze River Delta often co-occurred. • Stagnation and recirculation's occurrence was much greater than that of ventilation. • Average PM 2.5 was higher under stagnation and recirculation. • Recirculation had a slightly greater impact on Shanghai and Hangzhou than on Wuxi. • The 2016 pollution episode was ruled by recirculation and by the presence of CT6. [ABSTRACT FROM AUTHOR]

We analyse an algorithm for the calculation of travelling water waves in flows with constant and variable vorticity. The algorithm is based on numerical continuation techniques, which are suitably adapted to the water wave problem. Numerical examples illustrate the performance of the algorithm for flows of constant vorticity, where the results are compared with the literature. We observe agreement with already existing results, but we also have some new qualitative and quantitative results considering the characteristics of the water waves both for constant and variable vorticity. [ABSTRACT FROM AUTHOR]

This paper analyzes the thermal performance of a typical building-integrated solar wall (we’ll call it solar wall later in this paper) which integrates flat plate solar thermal collector with building wall. The thermal performance of the solar wall during stagnation, temperature of the absorber plate and heat flow on the inner wall, is studied by space state method in summer and winter respectively. If the collector of solar wall stops running, the maximum absorber plate temperature during summer daytime can reach 92.2 °C, and the total heat flow on the inner wall in one day is 1063 kJ/m² which is about 5 times of the normal operation condition. In winter, the temperature and heat flow of solar wall is higher too, which is beneficial to reduce the space heating load and the room can obtain heat from the outside in some time. [ABSTRACT FROM AUTHOR]

For the first time, a series of concurrent-flow rod flammability tests were conducted in microgravity aboard the International Space Station. A small flow duct was used to create 0 to 55 cm/s flows past three sizes of clear and black PMMA rods. The ambient oxygen concentration in the Microgravity Science Glovebox was varied from 13.6% to 22.2%. Oxygen, carbon dioxide, and carbon monoxide gas sensors provide initial and final readings for each test and indicate that the flames are globally stoichiometric at higher oxygen concentrations, but become more globally fuel rich as the minimum oxygen concentration is approached due to excess pyrolyzate leakage out of the open tail of the hemispherical flames. Quenching extinction occurs at very low forced flows, where the flame shrinks to a hemispherical blue flame and oscillates with increasing amplitude just before going out. Blowoff extinction is initiated by the formation of a hole in the flame sheet in the stagnation region of the flame. A critical Damkohler number formulation is applied across the flammability boundary, and the critical flame temperatures are derived. These critical flame temperatures are then used in a Nusselt number correlation to estimate the convective heat flux to the stagnation region of the rod. A model of surface energy balance is formulated that uses the critical flame temperature and convective heat flux to derive the mass burning rate along the boundary. The rod regression rates calculated from this model compare favorably with the experimental measurements. The surface energy balance reveals that along the blowoff branch, heat losses are negligible whereas in the quenching region, surface radiative loss dominates. At the bottom of the flammability map, the transition from blowoff to quenching occurs when the convective flows become the same order of magnitude as diffusive flows, shifting the critical Damkohler number from residence time limitations to diffusive time limitations. [ABSTRACT FROM AUTHOR]

The Jacobi–Davidson method is one of the most popular approaches for iteratively computing a few eigenvalues and their associated eigenvectors of a large matrix. The key of this method is to expand the search subspace via solving the Jacobi–Davidson correction equation, whose coefficient matrix is singular. It is believed by scholars that the Jacobi–Davidson correction equation is consistent and has a unique solution. In this paper, however, we point out that the correction equation either has a unique solution or has no solution, and we derive a computable necessary and sufficient condition for cheaply judging the existence and uniqueness of the solution. Furthermore, we consider the problem of stagnation and verify that if the Jacobi–Davidson method stagnates, then the corresponding Ritz value is a defective eigenvalue of the projection matrix. Finally, we provide a computable criterion for expanding the search subspace successfully. The properties of some alternative Jacobi–Davidson correction equations are also discussed. [ABSTRACT FROM AUTHOR]

Path planning problem for large number of robots is a quite challenging problem in mobile robotics since their control and coordination becomes unreliable and sometimes unfeasible. Particle Swarm Optimization (PSO) has been demonstrated to be a useful technique in the field of robotic research. This paper discusses an optimal path planning algorithm based on a Dynamic Distributed Particle Swarm Optimization Algorithm (D 2 PSO). The purpose of this approach is to find collision free optimal paths using two local optima detectors. This would add diversity to the population and hence avoid stagnation problem. The results show that the D 2 PSO has a better ability to get away from local optimums than the distributed PSO (dPSO). Simulations prove that this methodology is effective for every robot in multi-robot framework to discover its own proper path from the start to the destination position with minimum distance and no collision with obstacles. [ABSTRACT FROM AUTHOR]

The Yakima Air Wintertime Nitrate Study (YAWNS) was conducted in January 2013 to investigate the drivers of elevated levels of fine particulate matter (PM 2.5 ) frequently present in the region during winter stagnation periods. An extended stagnation period occurred during the study. For the first four days of the event, skies were clear and the strong diel variation in air pollution patterns were consistent with the expected effects of strong low-level nighttime temperature inversions with moderate mixing during daylight hours. Later in the event a low-level cloud layer formed that persisted over the Yakima Valley for the next seven days while regional conditions remained stagnant. Coincident with the onset of cloud, the levels of all measured primary pollutants, including CO 2 , CO, NO x , particle number concentration, and black carbon, dropped dramatically and remained low with negligible diel variation for as long as the cloud layer was present. The observed patterns for these air pollutants are consistent with decreased stability and enhanced mixing associated with the cloud-topped boundary layer. Interestingly, levels of secondary pollutants, most notably particulate ammonium nitrate, did not exhibit the same decline. This difference may be due to shifts in the chemical production of secondary pollutants during cloudy conditions, or may merely reflect a further influence of mixing. The results imply that the best strategies for managing wintertime air quality during episodes of persistent cloud are likely different from those needed during clear-sky stagnation events. [ABSTRACT FROM AUTHOR]

Differential evolution (DE) algorithm suffers from high computational time due to slow nature of evaluation. Micro-DE (MDE) algorithms utilize a very small population size, which can converge faster to a reasonable solution. Such algorithms are vulnerable to premature convergence and high risk of stagnation. This paper proposes a MDE algorithm with vectorized random mutation factor (MDEVM), which utilizes the small size population benefit while empowers the exploration ability of mutation factor through randomizing it in the decision variable level. The idea is supported by analyzing mutation factor using Monte-Carlo based simulations. To facilitate the usage of MDE algorithms with very-small population sizes, a new mutation scheme for population sizes less than four is also proposed. Furthermore, comprehensive comparative simulations and analysis on performance of the MDE algorithms over various mutation schemes, population sizes, problem types (i.e. uni-modal, multi-modal, and composite), problem dimensionalities, and mutation factor ranges are conducted by considering population diversity analysis for stagnation and pre-mature convergence. The MDEVM is implemented using a population-based parallel model and studies are conducted on 28 benchmark functions provided for the IEEE CEC-2013 competition. Experimental results demonstrate high performance in convergence speed of the proposed MDEVM algorithm. [ABSTRACT FROM AUTHOR]

Highly efficient solar thermal systems generally undergo stagnation conditions with temperature inside the solar collectors as high as 190-200 °C, as soon as the domestic hot water demand is poor or when the system is off while the collectors are still submitted to a strong solar radiation (> 950 W/m 2 ). These stagnation conditions are known to be one of the major problem of thermal solar systems and often lead to vaporization and glycol degradation, loss of performances, and the need for regular maintenance with associated costs for the end user. Thanks to a novel smart selective coating, characterized by a strong increase of its infrared emissivity (thermochromic effect) at a critical temperature, stagnation temperatures can be reduced to 150 °C for solar radiation and ambient temperature of 1000 W/m 2 and 35 °C, respectively. As the novel smart selective coating presents a high solar absorption coefficient (>94%) and a low emissivity (∼6%) at low temperature, and because the thermochromic effect starts at a temperature around 70 °C, the high performance of the new thermochromic thermal solar systems is guaranteed for domestic hot water heating. The properties of this new generation of selective coatings, based on a mixture of vanadium and aluminum oxides (VO 2 /V n O 2n±1 /Al 2 O 3 /SiO 2 ), are presented and discussed with regard to composition, structure and optical properties analysis. FTIR spectroscopy and infrared camera pictures clearly show the strong increase of emissivity for temperature higher than 70 °C. Aging performances (high temperature, humidity, thermal cycling) are also presented in order to guarantee a minimum life time of 25 years for the new generation of thermochromic solar collectors. Finally, stagnation temperatures recorded under the same natural sun radiation on scale one (2.3m 2 ) standard and thermochromic collectors are compared. [ABSTRACT FROM AUTHOR]

The stagnation temperatures experienced by glazed photovoltaic-thermal (PV-T) collectors pose a threat to their performance and longevity, in part due to the limited temperature stability of ethylene vinyl acetate (EVA) encapsulants. In order to identify suitable solutions for application in residential solar domestic hot water (SDHW) PV-T systems, a comparative analysis of known overheating prevention and stagnation handling measures was conducted and dynamic simulations were used to support the analysis. While no measure was found to comply with all desirable goals including reliability, implementation and operation costs, integral venting mechanisms were identified as the most promising among the control systems reviewed. Moreover, active collector heat dumping and automatic collector shading led to minimal electrical efficiency increases and decreases, respectively, while purging tank water when the collector overheats was found to be ineffective due to delays in the start of circulation. [ABSTRACT FROM AUTHOR]

The IEA SHC Task 45 Large Scale Solar Heating and Cooling Systems, carried out between January 2011 and December 2014, had the main objective to assist in the development of a strong and sustainable market of large solar heating systems by focusing on high performance and reliability of systems. Within this project, subtask A had the more specific objectives of investigating ways to evaluate the influence that different operating conditions can have on the collector performance, assure proper and safe installation of large solar collector fields, and guarantee their performance and yearly energy output. The results of the different investigations are presented, with a particular focus on how different parameters such as tilt, flow rate and fluid type, can affect the collector efficiency. Other presented results include methods to guarantee and check the thermal performance of a solar collector field and guidelines to design collector fields in such a way that the flow distribution is improved and the risks related to stagnation are minimized. [ABSTRACT FROM AUTHOR]

Coastal zones are under increasing development and experience air pollution episodes regularly. These episodes are often related to peaks in local emissions from industry or transportation, but can also be associated with regional transport from neighbour urban areas influenced by land-sea breeze recirculation. This study intends to analyze the relation between circulation weather patterns, air mass recirculation and pollution levels in three coastal airsheds of Portugal (Lisbon, Porto and Sines) based on the application of an objective quantitative measure of potential recirculation. Although ventilation events have a dominant presence throughout the studied 9-yrs period on all the three airsheds, recirculation and stagnation conditions occur frequently. The association between NO 2 , SO 2 and O 3 levels and recirculation potential is evident during summer months. Under high average recirculation potential and high variability, NO 2 and SO 2 levels are higher for the three airsheds, whilst for O 3 each airshed responds differently. This indicates a high heterogeneity among the three airsheds in (1) the type of emission – traffic or industry – prevailing for each contaminant, and (2) the response to the various circulation weather patterns and recirculation situations. Irrespectively of that, the proposed methodology, based on iterative K-means clustering, allows to identify which prevailing patterns are associated with high recirculation potential, having the advantage of being applicable to any geographical location. [ABSTRACT FROM AUTHOR]

Differential evolution (DE) is a simple, yet efficient, population-based global evolutionary algorithm. DE may suffer from stagnation. This study presents a DE framework with guiding archive (GAR-DE) to help DE escape from the situation of stagnation. The proposed framework constructs a guiding archive and executes stagnation detection at each iteration. Guiding archive is composed of a certain number of relatively high-quality solutions. These solutions are collected in terms of fitness as well as diversity. If a stagnated individual is detected, the proposed framework selects a solution from guiding archive to replace the base vector in mutation operator. In this way, more promising solutions are provided to guide the evolution and effectively help DE escape from the situation of stagnation. The proposed framework is applied to six original DE algorithms, as well as two advanced DE variants. Experimental results on 28 benchmark functions and 8 real-world application problems show that the proposed framework can enhance the performance of most DE algorithms studied. [ABSTRACT FROM AUTHOR]

Air quality is significantly influenced by the synoptic, regional and local meteorological conditions. This study aims at elucidating the relation between synoptic flow patterns and low visibility events of haze and fog over the North China Plain (NCP), and the contribution of synoptic flow patterns and boundary layer structure to the severe haze events over the NCP in January 2013. Nine synoptic flow types are statistically identified over the Northern China for autumn and winter of 2004–2014. The flow types with high pressure to the northeast of the NCP (NEH, type 8), weak low pressure band (L-, type 5), high pressure to the southeast (SHE, type 4), and high pressure to the north (NH, type 6) are associated with high occurrence frequencies of low visibility events (48.3%, 42.0%, 37.2%, and 36.7%). The meteorological conditions of these flow patterns reveal synergistic contribution of weak wind and high relative humidity (RH) to low visibility. Quantitative measures for dispersion conditions (recirculation, ventilation, and stagnation) suggest undesirable ventilation and frequent stagnation of the flow types 9 (EH, high pressure to the east), 4, 5, and 8. In January 2013 three regional haze episodes are identified from the distribution of visibility over the NCP, i.e., 10–16 January (EP 1), 22–24 January (EP 2), and 28 January–1 February (EP 3), which were largely associated with the flow types 5, 8, 4, and 9. Coverage of the hazy area exhibited northward expansion in the EP 2 and EP 3 when the RH increased. The abnormally high RH could be attributed to the flow type 6 (NH), which has the highest frequency of precipitation (13.7%) and RH among the nine flow types, and occurred more frequently in that month than in January 2004–2014. The simulation results indicate the evolution of the planetary boundary layer and southerly advection, which was responsible for the high RH and persistent temperature inversion that contributed to the long-lasting haze events. [ABSTRACT FROM AUTHOR]

Methodologically this research is based on the approach of many social scientists who argue that there is a bidirectional link: one runs from economic growth (EG) to human development (HD), as the resources from national income are allocated to activities contributing to HD; the other runs from HD to EG, when human capital helps increase national income. The background of this study is based also on the previous empirical researches of the authors, where they found statistically significant tendency of a middle strong negative correlation (r=-0.615, p=0.000) between the achieved competitiveness level of a country and its growth capacity – so-called “developed” countries have lower growth capacity. This tendency made the authors think of the HD trends. What if countries with higher indicators of HD also have lower growth capacity in the development of their people? And how are GC and HD trends interconnected? So, the purpose of this study is to take a fresh look at HD in global comparative researches, taking into consideration the abovementioned previous findings in global competitiveness trends. Correlation analysis of HDI 2006 and average annual change of HDI 2006-2012 showed that similarly with GCI growth trends countries with higher HD level also have lower growth capacity in this indicator (r=-0.573, p=0.000). The authors also found out that global growth trends of GCI and HDI are interconnected with statistically significant positive correlation (r=+0.364, p=0.000). The authors conclude that globally more developed countries are currently losing not only their GC, but also HD capacity, and both these trends are statistically significant. [ABSTRACT FROM AUTHOR]

Highlights: [•] Differential Evolution algorithms applied to ANN training suffer from stagnation. [•] The lack of difference vectors of small magnitude is noted during ANN training by Differential Evolution methods. [•] In case of benchmark problems the lack of difference vectors of small magnitude is only occasionally observed. [•] DEGL algorithm outperforms other Differential Evolution variants for ANN training. [•] Best algorithms found for benchmark problems do not perform well for ANN training. [ABSTRACT FROM AUTHOR]

Why has the American economy performed so poorly in the past decade, especially in comparison with the two prior decades? This paper makes the theoretical and empirical case that a series of economic policy decisions provides the most satisfactory explanation and that policy reform will restore good economic performance. The paper also considers alternative explanations including the idea of a new secular stagnation unrelated to policy and the view that the deep financial crisis inevitably delayed recovery from the recession. [ABSTRACT FROM AUTHOR]

Abstract: This report illustrates the experimental data associated with solar overheating. The experimental data has validated an analytical model which allows for the study of the influences a primary circuit's design has on the overheating of the solar tank. Secondly, the report includes a study of the stagnation in a solar facility. The evolution of the temperature in the hydraulic circuit by means of its measurement at 30 different points, together with the data of the pressure and flow, allow for the real behavior of the solar installation in stagnation conditions to be investigated. Finally, the study shows the measurements obtained on a solar thermal installation located in Alicante (southern Spain). Every installation has been monitored for several months and the main temperatures and pressures around the solar circuit have been noted. The measurements and their processing have allowed for the detection of overheating and stagnation problems in real operating conditions. [Copyright &y& Elsevier]

Abstract: This paper presents a new flat plate collector technology based on heat pipes. The use of heat pipes can lead to several advantages over direct flow collectors: A simple hydraulic interconnection, an inherently limited stagnation temperature and substitution of copper. This flat plate collector prototype with aluminum heat pipes features all three aspects in one collector. The paper outlines the theoretical modeling approaches and presents the construction of the collector as well as detailed results of measurements of the collector performance. By use of specially designed heat pipes the heat transfer is limited at higher temperatures, which leads to a maximum stagnation temperature of 140°C at the manifold of the collector, thus preventing damages to the solar circuit fluid and solar components. Therefore, cost savings regarding the collector by substituting copper with aluminum and cost savings regarding the solar system due to lowered stagnation temperatures can be achieved. [Copyright &y& Elsevier]

• A target vector replacement strategy (TVRS) is proposed. • Various differential evolution algorithms can be improved by TVRS. • The TVRS can be easily applied to the existing differential evolution algorithms. Individuals find it difficult to avoid stagnation in the iterative process of the differential evolution (DE) algorithm, and the stagnant individuals have restricted improvement in the population, which will have a negative effect on its performance. This research put forward a target vector replacement strategy (TVRS) for reducing the impact of stagnant individuals on the DE algorithm's performance. For stagnant target vectors, while executing mutation operation and crossover operation, TVRS selects non-stagnant individuals in the population to replace the stagnant target vectors with a specific probability. Because improving stagnant individuals are difficult, TVRS provides more opportunities for improvement to those who are not stagnant, while the opportunities for stagnant individuals to be improved are decreased. For assessing the efficiency of TVRS, TVRS was implemented to six DE algorithms and compared to their original algorithms. Judging from the performance outcomes of TVRS in the CEC 2014 benchmark test set, TVRS can greatly increase the DE algorithm's performance. This study will show the evolutionary opportunity that is obtained by an individual should be related to the individual state. Adjusting the individual evolutionary opportunity based on the individual state is helpful for improving the stagnation problem of the differential evolution algorithm. This study will provide a new way for improving the stagnation problem of the differential evolution algorithm and other evolutionary algorithms. [ABSTRACT FROM AUTHOR]

Objectives: Previous studies have identified different, but highly correlated variables explaining the effects of mindfulness training. Many of them are limited by tautological explanation. Under the framework of the mind--body connection, mindfulness training cultivates body awareness and promotes self-management of illness. Stagnation, a concept from Chinese medicine, may help explain the mechanism of change in mindfulness training. Methods: Individuals with depressive and anxiety symptoms (n = 82) were randomized to either a Compassion-Mindfulness Therapy (C-MT) program or a waitlist control condition. The effect of stagnation as a mediator was investigated for dependent variables including depression, anxiety, and other physical and mental health variables. Major outcome measures: Depression, anxiety, stagnation, physical distress, daily functioning, positive affect, negative affect. Results: Compared with the participants in the control group, those who completed CMT demonstrated significant decreases in depression, F(1, 78) = 15.67, p < .001, anxiety, F(1, 78) = 7.72, p < .001, stagnation, F(1, 78) = 4.96, p < .001, and other body-mind-spirit well-being measures. After entering the change in stagnation as the mediator, the effect of treatment reduced: depression (.35-.22), anxiety (.33-.05), and same patterns in other three secondary measures. The Sobel test was administered and significant reductions between group and depression (z = 2.18, p = .029), anxiety (z = 2.21, p = .027), and three secondary other measures (p < .05) were indicated. Conclusion: The study provides initial support for the role of stagnation in mediating changes in mindfulness training. It adds evidence to body-mind nondualism and offers new possibilities in studying treatment process and change mechanism. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this cross-sectional study was to assess whether stagnation dimensions and depression were associated with perceived disability in chronic migraineurs. Methods: Participants were 69 consecutive adult outpatients admitted to the Regional Referral Headache Centre of the Sant'Andrea Hospital in Rome, Italy. Patients were administered the Center for Epidemiologic Studies Depression Scale, the Stagnation Scale, and the Italian Perceived Disability Scale. They also compiled a headache diary to compute headache frequency. Results: Patients with higher perceived disability (compared to patients with lower perceived disability) reported higher depression and higher symptoms of stagnation. The effect of Overattachment, a dimension of the Stagnation Scale, on perceived disability was only in part mediated by the severity of depressive symptoms. Conclusion: Our results confirm that many patients with chronic migraine report symptoms of stagnation, and that investigating the presence of the stagnation syndrome may be useful for understanding the psychology of chronic migraineurs. [ABSTRACT FROM AUTHOR]

Abstract: The collision of two aluminium plasmas was investigated by combining both time and space resolved spectroscopy and Langmuir probe measurements. Plasma plumes were produced by a Continuum™ Surelite Nd:YAG Laser System with pulse duration of FWHM of 6ns and wavelength of 1064nm, at a laser irradiance of 1011 W/cm2 on slab Al targets. By analyzing the emission spectra, the temporally and spatially resolved electron density and electron temperature at the stagnation layer were extracted, with a time resolution of 10ns. Data analysis confirms that the electron density of the stagnation layer evolves over a longer timescale than in the single plume case. On the other hand, the temperature trends show that the electron temperature decreases much more rapidly at the stagnation layer than in the case for the single expanding plasma. In addition, a Langmuir probe was used to investigate the properties of the collisional front evolution. The overall experimental results show that colliding laser produced plasmas could be useful in the design of experiments devoted to fusion reaction rate measurements in a low energy domain by including the effect of the electron screening (ES). [Copyright &y& Elsevier]

Abstract: The transient cooling of hot stainless steel surface of 0.25mm thickness is done with round water jet impingement. Initially, the surface was heated up to the temperature of 800°C before the water was injected through straight tube type nozzle of 2.5mm diameter and 250mm length. During impingement cooling, the surface temperature was measured up to 12mm radial distance away from the stagnation point. The jet exit to surface spacing, z/d, and jet Reynolds number, Re, varied in the range of 4–16 and 5000–24,000 respectively. The surface rewetting and transient heat flux of the test-surface was studied for these operating parameters. During impingement cooling process the initial rewetting occurred at stagnation region with the lowest wetting delay period. In fact, the rewetting temperature, rewetting velocity and the maximum heat flux reduced for extreme spatial location. However, the wetting delay increased significantly for the locations away from the stagnation point. The surface rewetting and transient heat flux were increased with the rise in jet Reynolds number, resulting in the enhancement in rewetting temperature, rewetting velocity and reduced wetting delay. The maximum heat flux was obtained for 4–6mm radial location. The effect of jet exit to surface spacing on the rewetting parameters is found to be marginal. A correlation has been developed which predicted the maximum heat flux within an error band of ±10%. [Copyright &y& Elsevier]

Abstract: During the roughly 190,000 years between the emergence of anatomically modern humans and the transition to agriculture, sustained economic progress was rare. Although there were important innovations in the Upper Paleolithic, evidence from paleodemography indicates that population densities were driven more by climatic conditions than by technological innovations in food acquisition. We develop a model in which technological knowledge is subject to mutation and selection across generations. In a static environment, long run stagnation is the norm. However, climate shocks can induce experimentation with latent resources. This generates punctuated equilibria with greater technical capabilities and higher population densities at successive plateaus. The model is consistent with archaeological data on climate, population, diet, and technology from the Upper Paleolithic through the early Neolithic. [Copyright &y& Elsevier]

Abstract: We applied a multiple linear regression (MLR) model to study the correlations of total PM2.5 and its components with meteorological variables using an 11-year (1998–2008) observational record over the contiguous US. The data were deseasonalized and detrended to focus on synoptic-scale correlations. We find that daily variation in meteorology as described by the MLR can explain up to 50% of PM2.5 variability with temperature, relative humidity (RH), precipitation, and circulation all being important predictors. Temperature is positively correlated with sulfate, organic carbon (OC) and elemental carbon (EC) almost everywhere. The correlation of nitrate with temperature is negative in the Southeast but positive in California and the Great Plains. RH is positively correlated with sulfate and nitrate, but negatively with OC and EC. Precipitation is strongly negatively correlated with all PM2.5 components. We find that PM2.5 concentrations are on average 2.6 μg m−3 higher on stagnant vs. non-stagnant days. Our observed correlations provide a test for chemical transport models used to simulate the sensitivity of PM2.5 to climate change. They point to the importance of adequately representing the temperature dependence of agricultural, biogenic and wildfire emissions in these models. [ABSTRACT FROM AUTHOR]

Abstract: Drinking water quality is routinely monitored in the distribution network but not inside households at the point of consumption. Fluctuating temperatures, residence times (stagnation), pipe materials and decreasing pipe diameters can promote bacterial growth in buildings. To test the influence of stagnation in households on the bacterial cell concentrations and composition, water was sampled from 10 separate households after overnight stagnation and after flushing the taps. Cell concentrations, measured by flow cytometry, increased (2–3-fold) in all water samples after stagnation. This increase was also observed in adenosine tri-phosphate (ATP) concentrations (2–18-fold) and heterotrophic plate counts (4–580-fold). An observed increase in cell biovolume and ATP-per-cell concentrations furthermore suggests that the increase in cell concentrations was due to microbial growth. After 5 min flushing of the taps, cell concentrations and water temperature decreased to the level generally found in the drinking water network. Denaturing gradient gel electrophoresis also showed a change in the microbial composition after stagnation. This study showed that water stagnation in household pipes results in considerable microbial changes. While hygienic risk was not directly assessed, it emphasizes the need for the development of good material validation methods, recommendations and spot tests for in-house water installations. However, a simple mitigation strategy would be a short flushing of taps prior to use. [ABSTRACT FROM AUTHOR]