Polarized laser light scattering applied to surface morphology characterization of epitaxial III–V semiconductor layers

11 pages.-- PACS: 68.35.Bs; 81.05.Ea; 81.15.Hi; 78.35.+c; 78.66.FdIn this paper, we analyze typical morphologies of epitaxial III–V semiconductor layers by using a polarized laser light scattering technique. Crosshatched topographies, which are developed during heteroepitaxial growth, are studied. A sample with an intentionally high density of oval defects is also explored to establish how the laser light scattering pattern is affected by the presence of these defects, which are unavoidable in the epitaxial layers grown by molecular beam epitaxy. The former topographies produce a scattered light pattern that is highly anisotropic, with the intensity concentrated along two preferential directions; the latter defects give rise to a fairly isotropic pattern. Employing a perturbation-theoretical model, whose applicability and consistency are explicitly demonstrated by our results, the surface power spectral density is retrieved from the angle-resolved light scattering experimental data. For the samples exhibiting crosshatched topography, the scattering measurements provide information that allows us to model the roughness of the surface in terms of two quasi-one-dimensional, anisotropic components, and one two-dimensional, isotropic, long-range background. The root mean square heights and the typical lateral distances between ridges are obtained in quantitative agreement with the values extracted from the atomic force microscopy measurements. For the sample presenting oval defects, we consider their contribution to the surface power spectral density by means of a simple model of randomly distributed particles on a surface, and we compare the resulting power spectral density with typical behavior found in the literature for good-morphology GaAs layers. With the help of the ex situ information thus obtained, we also discuss the implementation of the light scattering technique for in situ monitoring during epitaxial growth.The authors wish to acknowledge the Spanish CICYT for financial support under Project No. TIC96-1020-C02. M.U.G. thanks the Consejería de Educación y Cultura de la Comunidad de Madrid for financial support. J.A.S.-G. acknowledges financial support from the Spanish DGESIC Grant No. PB97-1221.Spanish CICYTConsejería de Educación y Cultura de la Comunidad de MadridPeer reviewe

Does students that receive additional support needs with higher risk for learning disabilities in writing?

Actualmente la escritura es considerada como un proceso cognitivo complejo en el que intervienen diversos factores que conducen a un correcto uso de la escritura en la edad adulta. Este proceso está formado por distintos subprocesos. Entre ellos cabe destacar la transcripción. La capacidad de transcripción adquiere un papel importante en la adquisición de la escritura, siendo de especial importancia en el inicio de la escolaridad. Si los niños son lentos e inexactos en el proceso de la transcripción conlleva a que su capacidad y calidad compositiva global en la producción de textos se vea gravemente perjudicada. La transcripción tiene un efecto significativo sobre la escritura global y el rendimiento académico de los niños en edad escolar, tanto es así que es considerada como un potente predictor para identificar a niños en riesgo de desarrollar déficits más graves en la escritura. Un hallazgo que refuerza la importancia de identificar las dificultades de escritura tan pronto como sea posible. A esto, hay que añadir que actualmente la enseñanza de la escritura en los primeros años de escolaridad se centra casi única y exclusivamente en los aspectos más formales del texto como la caligrafía o la legibilidad, excluyendo la instrucción en la fluidez. La presente investigación analiza las diferencias entre niños que reciben apoyo educativo por presentar retraso en la adquisición de las competencias del currículo escolar con niños que no lo reciben, considerando la fluidez y la exactitud en la escritura. Para ello se seleccionó una muestra de 181 alumnos que reciben apoyo educativo y 181 alumnos que no lo reciben, pertenecientes a los tres primeros cursos de Educación Primaria y cuyas edades oscilan entre 6 y 9 años. Los resultados obtenidos muestran que los niños que reciben apoyo educativo, aún recibiendo este apoyo, presentan mayores carencias en la fluidez y exactitud en la escritura, carencias que sin una apropiada instrucción podrían desembocar en futuras dificultades de aprendizaje en escritura.Nowadays, writing is considered as a complex cognitive process in which several factors are involved that lead to a right writing use in adult age. This process is set up by different sub-processes, between which we can highlight transcription. The transcription skill takes a relevant place in writing acquisition, being of a special importance in the school beginning. If children are imprecise and slow in the transcription process it can lead to a serious setback in to their composition ability and quality. Transcription has a significant effect into the global writing and the academic efficiency in school age even that is considered as a powerful predictor to identify children that are more likely to show severe deficit in the acquisition of writing skills. A discovery that strengthen the importance of identifying writing difficulties as soon as possible. It should be added that nowadays writing teaching at the beginning is focused almost, solely and exclusively, in the most formal text aspects, just like handwriting or legibility, excluding fluency instruction. The current study analyzes the differences in writing fluency and accuracy between children that receive educational support because of their backwardness in the education program and normally achieving children. For this purpose, we selected a sample of 181 normally achieving children and 181 children receiving educational support, belonging to Primary Education and whose ages are in 6 – 9 years old range. Obtained results show that children that receive educational support present a lack of writing fluency and accuracy, problems that without an appropriate instruction could lead in future writing difficulties.peerReviewe

Global effects of US uncertainty: real and financial shocks on real and financial markets

We estimate the effects of financial, macroeconomic and policy uncertainty from the United States on the dynamics of credit growth, stock prices, economic activity, bond yields and inflation in five of the main receptors of US foreign direct investment from 1950 to 2019: The United Kingdom, The Netherlands, Ireland, Canada and Switzerland. Our multicounty approach allows us to clearly identify the effects of the different sources of uncertainty by imposing natural contemporaneous exogenity restrictions which cannot be used in a single-country perspective, frequently undertaken by the literature. It also considers international common cycle factors that have been previously identified and which are key to adequately measure the dynamics of the effects of uncertainty shocks on financial and real markets, on a global basis (...

Asymmetric Sovereign Risk: Implications for Climate Change Preparation

Sovereign risk exhibits significantly asymmetric reactions to its determinants across the conditional distribution of credit spreads. This aspect, previously overlooked in the literature, carries relevant policy implications. Countries with elevated risk levels are disproportionately affected by climate change vulnerability compared to their lower-risk counterparts, especially in the short term. Factors such as inflation, natural resource rents, and the debt-to-GDP ratio exert different effects between low and high-risk spreads as well. Real growth and terms of trade have a stable but modest impact across the spread distribution. Notably, investing in climate change preparedness proves effective in mitigating vulnerability to climate change, in terms of sovereign risk, particularly for countries with low spreads and long-term debt (advanced economies), where readiness and vulnerability tend to counterbalance each other. However, for countries with high spreads and short-term debt, additional measures are essential as climate change readiness alone is insufficient to offset vulnerability effects in this case. Results also demonstrate that the actual occurrence of natural disasters is less influential than vulnerability to climate change in determining spreads

Interdependent Capital Structure Choices and the Macroeconomy

This study shows that capital structure choices of US corporations are interdependent across time. We follow a two-step estimation approach. First, using a large cross-section of firms we estimate year-by-year average capital structure choices, i.e., the average firm’s percentage of new funding that is secured through debt, its term composition, and the percentage of new equity represented by retained earnings. Second, these time series are included in a Factor Augmented Vector Autoregressive model in which three factors representing real economic activity, expected future funding conditions, and prices, are included. We test for the interdependence between optimal capital structure decisions and for the influence exerted by macroeconomic conditions on these decisions. Results show there is a hierarchical order in which firms make capital structure decisions. They first decide on the share of debt out of total new funding they will hire. Conditional on this they decide on the term of their debt and on their earnings retention policy. Of outmost importance, macroeconomic factors are key for making capital structure decisions

Does economic complexity reduce the probability of a fiscal crisis?

Higher economic complexity of a country reduces the probability of suffering a fiscal crisis between 46% and 57%. Along with institutional factors, complexity is shown to be sufficient to describe the risk of facing episodes of fiscal distress. On the contrary, the role of variables frequently emphasized by the literature and policy markets, such as the debt-output ratio, real growth, inflation, terms of trade or fiscal balance, is very modest or insignificant. Development strategies that aim for greater economic complexity also promise to reduce countries’ fiscal vulnerabilit

Risk Spillovers between Global Corporations and Latin American Sovereigns: Global Factors Matter

We study volatility spillovers between the corporate sector’s and Latin American countries’ CDS. Daily data from October 14 2006 to August 23 2021 are employed. Spillovers are computed both for the raw data and for filtered series which factor out the effect of global common factors on the various CDS series. Results indicate that most spillovers occur within groups, i.e., within countries and within global corporations. However, considerable spillovers are also registered from LAC sovereigns to corporations and vice versa. Interesting differences are encountered between filtered and unfiltered data. Specifically, spillovers from countries to corporations are overestimated (in about 4.3 percentage points) and spillovers from corporations to sovereigns are underestimated (in about 5.8 percentage points) when unfiltered data is used. This result calls for a revision of results obtained from studies that do not consider the role of global common factors on system spillovers. Like in most related studies, spillovers show considerable time-variation, being larger during times of financial or economic distress. When looking at total system spillovers over time, those corresponding to unfiltered series are always larger than those corresponding to filtered series. The difference between the two time-series is largest in times of distress, indicating that global factors play a major role in times of crises. Similar conclusions are derived from network analysis

Sovereign Risk and Economic Complexity: Machine Learning Insights on Causality and Prediction

We investigate how a country’s economic complexity influences its sovereign yield spread with respect to the US. We analyze various maturities across 28 countries, consisting of 16 emerging and 12 advanced economies. Notably, a one-unit increase in the economic complexity index is associated to a reduction of about 87 basis points in the 10-year yield spread (p<0.01). However, this effect is largely non-significant for maturities under 3 years and, when significant (p<0.1), the reduction is around 54 bps. This suggests that economic complexity affects not only the level of the sovereign yield spreads but also the curve slope. Our first set of models utilizes Advanced causal machine learning tools, allowing us to control for a large set of potential confounders. This is crucial given our relatively small dataset of countries and roughly 15 years of data, as well as the low frequency of annual variables. In the second part of our analysis, we shift our focus to economic complexity’s predictive power. Our findings reveal that econòmic complexity is a robust predictor of sovereign spreads at 5-year and 10-year maturities, ranking among the top three predictors, alongside inflation and institutional factors like the rule of law. We also discuss the potential mechanisms through which economic complexity reduces sovereign risk and emphasize its role as a long-run determinant of productivity, output and income stability, and the likelihood of fiscal crises

Can patients without early, prominent visual deficits still be diagnosed of posterior cortical atrophy?

BACKGROUND: Early and progressive disabling visual impairment is a core feature for the diagnosis of posterior cortical atrophy (PCA). However, some individuals that fulfil criteria over time might initially present with an onset of prominent posterior dysfunction other than visuoperceptual. METHODS: The clinical profile of five patients with a predominantly 'non-visual' posterior presentation (PCA2) was investigated and compared with sixteen individuals with visually predominant PCA (PCA1) and eighteen with typical amnestic Alzheimer disease (tAD). RESULTS: PCA2 patients showed significantly better performance than PCA1 in one visuospatial task and were free of Balint's syndrome and visual agnosia. Compared to tAD, PCA2 showed trends towards significantly lower performance in visuoperceptual tasks, more severe apraxia and more symptoms of Gerstmann's syndrome. CONCLUSIONS: Our sample of PCA2 patients did not present with clinically prominent visual symptoms but did show visual dysfunction on formal neuropsychological assessment (less pronounced than in PCA1 but more than in tAD) in addition to other posterior deficits. Broadening the definition of PCA to encompass individuals presenting with prominent 'non-visual' posterior dysfunction should be potentially considered in clinical and research contexts

US uncertainty shocks, credit, production, and prices: The case of fourteen Latin American countries

The extant literature has examined the impact of United States’ uncertainty shocks on developed and large emerging market economies. However, this research has not accounted for global cycles in production, credit, and prices, which can influence the estimates of the effects of US uncertainty on the rest of the world. The effects of uncertainty in highly indebted emerging open economies, which depend heavily on US financial and real conditions, have not been studied. We analyze the effects of uncertainty shocks on 14 Latin American countries (LACs) of various sizes and various levels of dependence on US financial and real flows. Latin America is a highly indebted and heterogeneous region that is sensitive to US economic and financial conditions, particularly uncertainty, in its various dimensions: real, financial, and policy related (including monetary policy). Our results show that the effects of real and financial uncertainty are more significant and long lasting than the effects of economic and monetary policy uncertainty, as measured by the use of uncertainty-related key words. All forms of uncertainty have a larger and more persistent impact on the gross domestic product of countries than the impact on credit and prices. In general, uncertainty in the US depresses economic activity in Latin America, although there is significant heterogeneity in the effects, which warrants detailed analysis of individual countries when considering policy implementation and portfolio diversificatio