A novel boundary element method using surface conductive absorbers for full-wave analysis of 3-D nanophotonics

Fast surface integral equation (SIE) solvers seem to be ideal approaches for simulating 3-D nanophotonic devices, as these devices generate fields both in an interior channel and in the infinite exterior domain. However, many devices of interest, such as optical couplers, have channels that can not be terminated without generating reflections. Generating absorbers for these channels is a new problem for SIE methods, as the methods were initially developed for problems with finite surfaces. In this paper we show that the obvious approach for eliminating reflections, making the channel mildly conductive outside the domain of interest, is inaccurate. We describe a new method, in which the absorber has a gradually increasing surface conductivity; such an absorber can be easily incorporated in fast integral equation solvers. Numerical experiments from a surface-conductivity modified FFT-accelerated PMCHW-based solver are correlated with analytic results, demonstrating that this new method is orders of magnitude more effective than a volume absorber, and that the smoothness of the surface conductivity function determines the performance of the absorber. In particular, we show that the magnitude of the transition reflection is proportional to 1/L^(2d+2), where L is the absorber length and d is the order of the differentiability of the surface conductivity function.Comment: 10 page

Changes in the characteristics of ‘wet’ and ‘dry’ Red Sea Trough over the Eastern Mediterranean in CMIP5 climate projections

The Eastern Mediterranean resides on the border between the temperate and semi-arid and arid climate zones, and is thus influenced by both mid-latitude and sub-tropical weather systems. Precipitation and extreme weather in this region are mainly associated with either Cyprus Lows or the “wet” Red Sea Troughs. Current regional climate projections indicate that the region may become warmer and drier in future decades. Here, we analyze the influence of enhanced greenhouse gas forcing on the climatological properties of the ‘wet’ and ‘dry’ Red Sea Trough (WRST & DRST, respectively). With this aim, a regional synoptic classification and a downscaling algorithm based on past analogs are applied to eighteen rain stations over the main ground water basins in Israel. The algorithms are applied to the NCEP/NCAR reanalysis data for 1986–2005 and to eight CMIP5 model simulations for the historical (1986–2005) and end of the century (2081–2100) climate conditions according to the RCP8.5 scenario. For the historical period, the CMIP5 models are largely able to represent the characteristics of the Red Sea Trough. Based on the multi-model mean, significant changes are found for WRST and DRST for the late XXI Century. First, an increase in the meridional pressure gradient is found for both the WRST and the DRST, implying stronger horizontal winds. Furthermore, a significant decrease in the occurrence of the WRST (− 20%) and a significant increase in the frequency of the DRST (+ 19%) are identified. Accordingly, the persistence of the WRST decreases (− 9%), while for DRST increases (+ 9%). The decline in the frequency of WRST occurs primarily in the transition seasons, while the increase for DRST is found throughout the wet season. In total, the daily rainfall associated with the WRST system is projected to significantly decline (− 37%) by the end of the XXI century. These results document the projected changes in a dominant synoptic system in this area, which can facilitate a better estimation of the arising challenges, e.g., related to shortage of water resources and associated political unrest, reduced agricultural potential, and increased air pollution and forest fires. Such a pathway can ultimately foster novel mitigation strategies for water resources management and regional climate change adaptation

Cuidar, Controlar, Curar: Ensaios Históricos Sobre Saúde E Doença Na América Latina E Caribe

Traz um conjunto variado de ensaios representativos das atuais - e diversas - tendências historiográficas a respeito dos discursos e das práticas sociais que, em diferentes cenários latino-americanos e caribenhos, organizaram-se em torno de questões relativas à saúde e à doença. A intenção é pôr em evidência aspectos relevantes da experiência histórica dos países quanto a ações individuais e coletivas relacionadas à manutenção e à restauração da saúde, bem como ao cuidado, ao controle e à cura das doenças. A preferência pelo local e pelo específico não visa à mitificação das práticas culturais, pois, nas abordagens aqui desenvolvidas, os eventos históricos alcançam significado num quadro de referência mais amplo. Assim, os temas da saúde e da doença se entrelaçam com outras realidades coetâneas: penetração e avanço de formas capitalistas, mudanças do perfil demográfico e acelerada urbanização, formação material e simbólica dos estados nacionais, dinâmicas socioprofissionais, dentre outros. Os artigos selecionados apresentam o que há de melhor nas análises históricas sobre saúde e doença em nossas regiões, e certamente são, desde já, leitura obrigatória para profissionais, professores e estudantes das áreas de saúde coletiva, história, medicina, ciências sociais e humanidades

Small union with large set of centers

Let $T\subset{\mathbb R}^n$ be a fixed set. By a scaled copy of $T$ around $x\in{\mathbb R}^n$ we mean a set of the form $x+rT$ for some $r>0$. In this survey paper we study results about the following type of problems: How small can a set be if it contains a scaled copy of $T$ around every point of a set of given size? We will consider the cases when $T$ is circle or sphere centered at the origin, Cantor set in ${\mathbb R}$, the boundary of a square centered at the origin, or more generally the $k$-skeleton ($0\le k<n$) of an $n$-dimensional cube centered at the origin or the $k$-skeleton of a more general polytope of ${\mathbb R}^n$. We also study the case when we allow not only scaled copies but also scaled and rotated copies and also the case when we allow only rotated copies

A new view of heat wave dynamics and predictability over the eastern Mediterranean

Skillful forecasts of extreme weather events have a major socioeconomic relevance. Here, we compare two complementary approaches to diagnose the predictability of extreme weather: recent developments in dynamical systems theory and numerical ensemble weather forecasts. The former allows us to define atmospheric configurations in terms of their persistence and local dimension, which provides information on how the atmosphere evolves to and from a given state of interest. These metrics may be used as proxies for the intrinsic predictability of the atmosphere, which only depends on the atmosphere\u27s properties. Ensemble weather forecasts provide information on the practical predictability of the atmosphere, which partly depends on the performance of the numerical model used. We focus on heat waves affecting the eastern Mediterranean. These are identified using the climatic stress index (CSI), which was explicitly developed for the summer weather conditions in this region and differentiates between heat waves (upper decile) and cool days (lower decile). Significant differences are found between the two groups from both the dynamical systems and the numerical weather prediction perspectives. Specifically, heat waves show relatively stable flow characteristics (high intrinsic predictability) but comparatively low practical predictability (large model spread and error). For 500 hPa geopotential height fields, the intrinsic predictability of heat waves is lowest at the event\u27s onset and decay. We relate these results to the physical processes governing eastern Mediterranean summer heat waves: adiabatic descent of the air parcels over the region and the geographical origin of the air parcels over land prior to the onset of a heat wave. A detailed analysis of the mid-August 2010 record-breaking heat wave provides further insights into the range of different regional atmospheric configurations conducive to heat waves. We conclude that the dynamical systems approach can be a useful complement to conventional numerical forecasts for understanding the dynamics and predictability of eastern Mediterranean heat waves

Dynamics and predictability of cold spells over the Eastern Mediterranean

The accurate prediction of extreme weather events is an important and challenging task, and has typically relied on numerical simulations of the atmosphere. Here, we combine insights from numerical forecasts with recent developments in dynamical systems theory, which describe atmospheric states in terms of their persistence (θ$^{-1}$) and local dimension (d), and inform on how the atmosphere evolves to and from a given state of interest. These metrics are intuitively linked to the intrinsic predictability of the atmosphere: a highly persistent, low-dimensional state will be more predictable than a low-persistence, high-dimensional one. We argue that θ$^{-1}$ and d, derived from reanalysis sea level pressure (SLP) and geopotential height (Z500) fields, can provide complementary predictive information for mid-latitude extreme weather events. Specifically, signatures of regional extreme weather events might be reflected in the dynamical systems metrics, even when the actual extreme is not well-simulated in numerical forecasting systems. We focus on cold spells in the Eastern Mediterranean, and particularly those associated with snow cover in Jerusalem. These rare events are systematically associated with Cyprus Lows, which are the dominant rain-bearing weather system in the region. In our analysis, we compare the ‘cold spell Cyprus Lows’ to other ‘regular’ Cyprus Low days. Significant differences are found between cold spells and ‘regular’ Cyprus Lows from a dynamical systems perspective. When considering SLP, the intrinsic predictability of cold spells is lowest hours before the onset of snow. We find that the cyclone’s location, depth and magnitude of air-sea fluxes play an important role in determining its intrinsic predictability. The dynamical systems metrics computed on Z500 display a different temporal evolution to their SLP counterparts, highlighting the different characteristics of the atmospheric flow at the different levels. We conclude that the dynamical systems approach, although sometimes challenging to interpret, can complement conventional numerical forecasts and forecast skill measures, such as model spread and absolute error. This methodology outlines an important avenue for future research, which can potentially be fruitfully applied to other regions and other types of weather extremes

Understanding summer wind systems over the eastern Mediterranean in a high‐resolution climate simulation

Regional and local wind systems are often complex, particularly near coastal areas with a highly variable orography. Thus, the realistic representation of regional wind systems in weather and climate models is of strong relevance. Here, we evaluate the ability of a 13-year convection-permitting climate simulation in reproducing the interaction of several regional summer wind systems over the complex orography in the eastern Mediterranean region. The COSMO-CLM simulations are driven by hourly ERA-5 reanalysis and have a spatial resolution of 2.8 and 7.0 km. The simulated near-surface wind fields are compared with unique very high-resolution wind observations collected within the “Dead Sea Research Venue” project (DESERVE) and data from the Israel Meteorological Service synop network. The high-resolution COSMO-CLM simulations largely reproduce the main characteristics of the regional wind systems (Mediterranean and Dead Sea breeze, slope winds in the Judean Mountains and winds along the Jordan Rift valley), whereas ERA-5 is only able to represent the Mediterranean Sea breeze. The high-resolution simulations substantially improve the representation of regional winds, particularly over complex orography. Indeed, the 2.8 km simulation outperforms the 7.0 km run, on 88% of the days. Two mid-July 2015 case studies show that only the 2.8 simulation can realistically simulate the penetration of the Mediterranean Sea Breeze into the Jordan Rift valley and complex interactions with other wind systems like the Dead Sea breeze. Our results may have profound implications for regional weather and climate prediction since very high-resolution information seems to be necessary to reproduce the main summertime climatic features in this region. We envisage that such simulations may also be required at other regions with complex orography

Extreme weather and societal impacts in the eastern Mediterranean

Gaining a holistic understanding of extreme weather, from its physical drivers to its impacts on society and ecosystems, is key to supporting future risk reduction and preparedness measures. Here, we provide an overview of the state of the art, knowledge gaps and key open questions in the study of extreme weather events over the vulnerable eastern Mediterranean. This region is situated in a transition zone between subtropical and mid-latitude climates. The large-scale atmospheric circulation and its interaction with regional synoptic systems (i.e., Cyprus Lows, Red Sea Troughs, Persian Troughs, “Sharav” Lows) and high-pressure systems mainly govern extreme weather. Complex orographic features further play an important role in the generation of extreme weather. Most extreme weather events, including heavy precipitation, cold spells, floods and windstorms, are associated with Cyprus Lows or active Red Sea Troughs, whereas heat waves are related with either Persian Troughs and sub-tropical high-pressure systems in summer or the Sharav Low during springtime. In future decades, heat waves and droughts are projected to significantly increase in both frequency and intensity. Changes in heavy precipitation may vary in sign and magnitude depending on the scale, severity and region of interest. There are still relatively large uncertainties concerning the physical understanding and the projected changes of cold spells, windstorms and compound extremes, as these types of events received comparatively little attention in the literature. We further identify knowledge gaps that relate to the societal impacts of extreme weather. These gaps mainly relate to the effects extreme weather may have on mortality, morbidity and infrastructure in the eastern Mediterranean. Research is currently limited in this context, and we recommend strengthening the database of analyzed case studies. We trust that this can only be suitably accomplished by inter-disciplinary and international regional collaboration (in spite of political unrest)