Controllable plasma energy bands in a 1D crystal of fractional Josephson vortices

We consider a 1D chain of fractional vortices in a long Josephson junction with alternating $\pm\kappa$ phase discontinuities. Since each vortex has its own eigenfrequency, the inter-vortex coupling results in eigenmode splitting and in the formation of an oscillatory energy band for plasma waves. The band structure can be controlled at the design time by choosing the distance between vortices or \emph{during experiment} by varying the topological charge of vortices or the bias current. Thus one can construct an artificial vortex crystal with controllable energy bands for plasmons.Comment: 4 pages, 2 Fig

Oscillatory eigenmodes and stability of one and two arbitrary fractional vortices in long Josephson 0-kappa-junctions

We investigate theoretically the eigenmodes and the stability of one and two arbitrary fractional vortices pinned at one and two $\kappa$-phase discontinuities in a long Josephson junction. In the particular case of a single $\kappa$-discontinuity, a vortex is spontaneously created and pinned at the boundary between the 0 and $\kappa$-regions. In this work we show that only two of four possible vortices are stable. A single vortex has an oscillatory eigenmode with a frequency within the plasma gap. We calculate this eigenfrequency as a function of the fractional flux carried by a vortex. For the case of two vortices, pinned at two $\kappa$-discontinuities situated at some distance $a$ from each other, splitting of the eigenfrequencies occur. We calculate this splitting numerically as a function of $a$ for different possible ground states. We also discuss the presence of a critical distance below which two antiferromagnetically ordered vortices form a strongly coupled ``vortex molecule'' that behaves as a single object and has only one eigenmode.Comment: submitted to Phys. Rev. B (

Ashkin-Teller universality in a quantum double model of Ising anyons

We study a quantum double model whose degrees of freedom are Ising anyons. The terms of the Hamiltonian of this system give rise to a competition between single and double topologies. By studying the energy spectra of the Hamiltonian at different values of the coupling constants, we find extended gapless regions which include a large number of critical points described by conformal field theories with central charge c=1. These theories are part of the Z_2 orbifold of the bosonic theory compactified on a circle. We observe that the Hilbert space of our anyonic model can be associated with extended Dynkin diagrams of affine Lie algebras which yields exact solutions at some critical points. In certain special regimes, our model corresponds to the Hamiltonian limit of the Ashkin-Teller model, and hence integrability over a wide range of coupling parameters is established.Comment: 11 pages, minor revision

Wall roughness induces asymptotic ultimate turbulence

Turbulence is omnipresent in Nature and technology, governing the transport of heat, mass, and momentum on multiple scales. For real-world applications of wall-bounded turbulence, the underlying surfaces are virtually always rough; yet characterizing and understanding the effects of wall roughness for turbulence remains a challenge, especially for rotating and thermally driven turbulence. By combining extensive experiments and numerical simulations, here, taking as example the paradigmatic Taylor-Couette system (the closed flow between two independently rotating coaxial cylinders), we show how wall roughness greatly enhances the overall transport properties and the corresponding scaling exponents. If only one of the walls is rough, we reveal that the bulk velocity is slaved to the rough side, due to the much stronger coupling to that wall by the detaching flow structures. If both walls are rough, the viscosity dependence is thoroughly eliminated in the boundary layers and we thus achieve asymptotic ultimate turbulence, i.e. the upper limit of transport, whose existence had been predicted by Robert Kraichnan in 1962 (Phys. Fluids {\bf 5}, 1374 (1962)) and in which the scalings laws can be extrapolated to arbitrarily large Reynolds numbers

At the gymnasium through your football buddy's aunt. Accessibility of classical education in the Netherlands

How accessible is the field of Latin and ancient Ancient Greek languages in the Dutch education system? In recent years this discussion has resurfaced in the light of societal developments which focus on equality of opportunities. Moreover, our field faces the challenge to explain in both international and national discussions what makes its study so relevant in the current times, both in secondary and tertiary education. This article provides a short overview of the current situation of Latin and ancient Ancient Greek education within the Dutch secondary education system before looking in more detail at its impact on Dutch students. It ends with directions for improving the accessibility of the field of Classics education. In order to illustrate the functioning and consequences of the current situation, in June 2021 a large-scale survey among 1,700 Dutch students of the gymnasium (secondary education with Latin and ancient Greek) provides us with interesting experiences, biases and thoughts about the accessibility of classical education. If we believe that knowledge of the ancient languages and literatures is a valuable resource for the younger generations of our modern society and in addition we see that our field, as any field, would profit from a more diverse group of researchers and teachers, the direction for future improvements is clear; but concrete steps in that direction should be taken at various levels. With this article, I hope to contribute to such improvements to the educational system and contemporaneously to our field.<br/

The effect of microcredit on women's control over household spending in developing countries: a systematic review

Background: Over the past three decades, microfinance activities have spread across the globe, reaching tens of millions of poor households with tailored financial services. Microfinance can best be described as a field of intervention rather than a particular instrument. Initially, microfinance usually meant microcredit for working capital and very small investments, but increasingly it has been broadened to include savings/deposits, a limited range of micro-insurance and payment services (including micro-leasing) as well as a somewhat broader range of credit products for more substantial investments. In this study we focused on microcredit activities, constituting the bulk of microfinance activities across the globe. Microcredit activities have affected the lives of clients and others in multiple ways. The most frequently reported types of effects of credit at individual, enterprise and household level are the following: income, expenditure smoothing, and poverty alleviation effects; business growth and employment effects; schooling effects; and effects in terms of women's empowerment. Despite the diversity in microcredit schemes, many share two characteristics: they target poor women and often rely on some type of group-based lending. Women's empowerment in relation to microcredit has been studied extensively within the context of this type of microcredit scheme. Most of these studies have been carried out in the context of microcredit group schemes in South Asia. It has been argued that access to microcredit can foster changes in individual attitudes of women (e.g. increased self-reliance), power relations within the household (e.g. control over resources) and social status. An important dimension of empowerment concerns women's control over household spending. The main assumption is that by providing credit to poor women, their direct control over expenditures within the household increases, with subsequent implications for the status of women and the well-being of women and other household members. Women's control over household spending is a frequently recurring aspect analyzed within the context of microcredit interventions, which allows us to study whether microcredit targeted at women affects women's control over household spending decisions and the circumstances in which this occurs. Despite the central and recurrent role across studies of this aspect of women's empowerment in relation to microcredit activities, there has been no previous review on this topic. The growing importance of microcredit has resulted in a vast number of research and evaluation studies, including impact studies. Consequently, the microfinance literature harbors a substantial number of synthesis studies which discuss a set of microcredit interventions and aim to generate overall conclusions on their effects. However, most of these studies face limitations in terms of depth of empirical assessment and the extent to which the identified effects can be attributed to microcredit. Moreover, methodological principles regarding comprehensive searches and principles of selection, coding, extraction and aggregation are often lacking in review studies. Partial exceptions are three recent systematic reviews which all differ in scope from the present one (Stewart et al., 2010; Duvendack et al. 2011; Stewart et al., 2012). The reviews respectively focus on microfinance (credit and savings) in Sub-Sahara Africa, microcredit worldwide, and microfinance worldwide (credit, saving and leasing). Overall, these reviews suggest that the effects of microcredit on women's empowerment are at best mixed. In part this can be explained by the heterogeneity in microcredit interventions, contexts and target groups. However, the existing reviews did not use statistical meta-analysis to synthesise evidence of effects, nor context-mechanism-outcome synthesis to understand the variation in effects. Objectives: The main objective of this study was to provide a systematic review of the evidence on the effects of microcredit on women's control over household spending in developing countries. More specifically, we aimed to answer two related research questions: 1) what does the impact evaluative evidence say about the causal relationship between microcredit and specific dimensions of women's empowerment (women'ss control over household spending); and 2) what are the mechanisms which mediate this relationship. We prioritise depth of analysis over breadth, thus the scope of this review is narrower than previous systematic reviews on microfinance (Stewart et al., 2010; Duvendack et al. 2011; Stewart et al., 2012). We focused on specific aspects of women's empowerment which allowed us to combine statistical meta-analysis and realist (context-mechanism-outcome) synthesis. Criteria for considering studies for this review: We included studies that analyzed the effects of microcredit schemes targeting poor women in low and middle income countries, as defined by the World Bank. Studies that did not include analysis on microcredit and the effect on one or more dimensions (specified in main body of the report) of women's control over household expenditures were excluded. Studies which gave evidence of addressing the attribution problem either through randomised design, quasi-experimental matching, or regression analysis, were included. In practice, women's control over household spending (as a key dimension of empowerment) is influenced by many different factors. By focusing on those studies which explicitly addressed the challenge of separating the effect of microcredit from other influencing factors, we developed what we consider to be the most credible evidence base for drawing conclusions about the effects of microcredit on women's control over household expenditures in different contexts. SEARCH STRATEGY We conducted a comprehensive search covering all relevant academic databases, internet search engines and web sites with published and unpublished research, and also carried out extensive manual searches of books and additional journals not included in electronic data bases (searches were concluded on December 31, 2011). We used back-referencing from recent studies as well as citation-tracking to identify additional relevant studies. Finally, authors of studies which we were unable to retrieve were contacted. In addition, we contacted experts on microcredit and women's empowerment for additional references which we might have missed. Search strategies in databases and journals were adapted for each source. Where possible we used the existing keyword indices of particular databases. In addition, we applied our own list of combinations of keywords covering all relevant terms relating to the independent variable (i.e. credit and its variations) and the dependent variable (i.e. dimensions of women's control over household spending, empowerment). Data collection and analysis: From the different searches we identified an initial number of 310 papers that were selected for full text examination. Eventually, 29 papers were retained for further analysis, corresponding to 25 unique studies. These 25 independent findings were included in the synthesis. However, based on a systematic risk of bias assessment we found that more than half of the included studies had high threats to internal validity. Moreover, only about half of the studies show a clear and coherent link between a theoretical framework on microcredit and women's control over household spending and empirical data analysis. It should be noted that reviewing and synthesizing quantitative results from studies is only one side of the coin. The other side is to understand what makes them work, or what prevents them from working. Consequently, we conducted a qualitative synthesis of the included studies, which focused on identifying the mechanisms which underlie the causal relationship between microcredit and women's control over household spending. RESULTS The results of the meta-analysis indicated that the effect sizes from experimental studies examining effects of microcredit on women's control over household spending are not statistically significantly different from zero. The effects from quasi-experimental studies are statistically insignificant overall, and at best of small magnitude for those studies assessed of being of high risk of bias. We conclude that there is no consistent evidence for an effect of microcredit on women's control over household spending. In the qualitative analysis, using Coleman's (1986, 1990) typology of mechanisms, we identified five different situational mechanisms and eight different action-formation mechanisms. Due to the combination of substantial heterogeneity in contexts (e.g. existing gender relations) and interventions (e.g. microcredit versus microcredit and additional services), and the lack of information in the studies on this heterogeneity, it was not possible to go beyond the identification of mechanisms, in terms of generating empirically tested articulated theories of change which are representative beyond a specific study context. Authors' conclusions: In line with three recent other reviews on microfinance (Stewart et al., 2010; Duvendack et al., 2011; Stewart et al. 2012) we found that the microcredit evidence base is extensive, yet most studies are weak methodologically. From those studies deemed comparable and of minimum acceptable quality, we concluded that overall there is no evidence for an effect of microcredit on women's control over household spending. Women's control over household resources constitutes an important intermediary dimension in processes of women's empowerment. Given the overall lack of evidence for an effect of microcredit on women's control over household resources it is therefore very unlikely that, overall, microcredit has a meaningful and substantial impact on empowerment processes in a broader sense. While impacts on empowerment may appear to have occurred in particular studies, the high risk of bias of studies providing positive assessments suggests that such findings are of limited validity. Our conclusions on the effects of microcredit on empowerment are also in line with previous systematic reviews by Duvendack et al. (2011) and Stewart (et al. 2010) who report to a limited extent on empowerment effects. Consequently, there appears to be a gap between the often optimistic societal belief in the capacity of microcredit to ameliorate the position of women in decision-making processes within the household on the one hand, and the empirical evidence base on the other hand. However, our review markedly differs from previous reviews in two regards. First, we specifically focused on microcredit and women's empowerment captured through women's control over household expenditures. Second, as a result of this narrower focus, we were able to conduct statistical meta-analysis and extract behavioral mechanisms which can help to explain why and how microcredit can make a difference. The advantage of our approach was that the identified mechanisms all stem from studies which show evidence of addressing the attribution problem. Consequently, we can be quite confident of the insights that they provided on the effects of microcredit on women's control over household spending for particular populations of microcredit female clients and their families. Those studies that showed evidence of addressing the attribution problem were relatively weak on underlying theory. Moreover, they often lacked essential information such as the nature of the intervention and how it related to empowerment (e.g. how solidarity groups affect empowerment processes) or the slowly evolving gender relations in different contexts (e.g. the evolution of societal norms and the relationship with power relations in the household). A next logical step would be to undertake a systematic review of qualitative studies which often provide rich and context-specific information on microcredit and women's decision-making power in the household. Such a review should ideally build on the mechanisms identified in the present review and would bring us closer to uncovering credible theories of microcredit and the circumstances in which it may change women's decision-making power

Cardiac Shear Wave Elastography Using a Clinical Ultrasound System

The propagation velocity of shear waves relates to tissue stiffness. We prove that a regular clinical cardiac ultrasound system can determine shear wave velocity with a conventional unmodified tissue Doppler imaging (TDI) application. The investigation was performed on five tissue phantoms with different stiffness using a research platform capable of inducing and tracking shear waves and a clinical cardiac system (Philips iE33, achieving frame rates of 400-700 Hz in TDI by tuning the normal system settings). We also tested the technique in vivo on a normal individual and on typical pathologies modifying the consistency of the left ventricular wall. The research platform scanner was used as reference. Shear wave velocities measured with TDI on the clinical cardiac system were very close to those measured by the research platform scanner. The mean difference between the clinical and research systems was 0.18 ± 0.22 m/s, and the limits of agreement, from -0.27 to +0.63 m/s. In vivo, the velocity of the wave induced by aortic valve closure in the interventricular septum increased in patients with expected increased wall stiffness

Determination of Matter Surface Distribution of Neutron-rich Nuclei

We demonstrate that the matter density distribution in the surface region is determined well by the use of the relatively low-intensity beams that become available at the upcoming radioactive beam facilities. Following the method used in the analyses of electron scattering, we examine how well the density distribution is determined in a model-independent way by generating pseudo data and by carefully applying statistical and systematic error analyses. We also study how the determination becomes deteriorated in the central region of the density, as the quality of data decreases. Determination of the density distributions of neutron-rich nuclei is performed by fixing parameters in the basis functions to the neighboring stable nuclei. The procedure allows that the knowledge of the density distributions of stable nuclei assists to strengthen the determination of their unstable isotopes.Comment: 41 pages, latex, 27 figure