Flexible multivariate GARCH modeling with an application to international stock markets

The goal of this paper is to estimate time-varying covariance matrices. Since the covariance matrix of financial returns is known to change through time and is an essential ingredient in risk measurement, portfolio selection, and tests of asset pricing models, this is a very important problem in practice. Our model of choice is the Diagonal-Vech version of the Multivariate GARCH(1,1) model. The problem is that the estimation of the general Diagonal-Vech model model is numerically infeasible in dimensions higher than 5. The common approach is to estimate more restrictive models which are tractable but may not conform to the data. Our contribution is to propose an alternative estimation method that is numerically feasible, produces positive semi-definite conditional covariance matrices, and does not impose unrealistic a priori restrictions. We provide an empirical application in the context of international stock markets, comparing the new estimator to a number of existing ones.Diagonal-Vech model multivariate GARCH, unrestricted estimation

Comparing the fertility of Ghanaian migrants in Europe with nonmigrants in Ghana

The fertility behaviour of migrants is often studied by examining migrants and native nonmigrants in the country of destination. To understand the mechanisms for migrant fertility, it is important to know what distinguishes them from the population they originate from. The Ghanaian sample of the "Migrations between Africa and Europe" project allows us to contrast the fertility of those who never emigrated from Ghana and Ghanaian migrants who are residing in the UK or the Netherlands. First, we estimate discrete‐time hazard models of first birth to evaluate whether first birth timing is influenced by migration. Second, we apply Poisson regression techniques to examine differentials in completed fertility. We find that Ghanaian migrants postpone first childbirth compared with nonmigrants. Differences are largest at ages 20 to 24 for women and 20 to 29 for men. Ghana experiences a typical brain drain, which means that especially the highly skilled emigrate. In our sample, this is particularly true for women. Education seems to be an important determinant of the postponement of first childbirth in Ghana, although we cannot clearly attribute migrants' later first births to their higher level of education. However, our findings on completed fertility reveal that migrants have fewer children than nonmigrants and this difference diminishes considerably if we take into account their level of education. Apparently, migrants do not fully catch up after postponing first childbirth and end up with a lower number of children by the age of 40

Resilience by diversity: Large intraspecific variation in climate change responses of an Arctic diatom

Primary productivity in the Arctic Ocean is vastly driven by single-celled phytoplankton. Within a comparably short growing season, they provide most of the carbon and energy for higher trophic levels and simultaneously influence biogeochemical cycles and the global climate. With the Arctic Ocean being one of the few regions that are expected to increase their productivity with future global change, it is especially important to understand how phytoplankton there is going to adapt. The potential for this adaptation to future climate change is often extrapolated from studies using single strains of a representative species that were cultured in laboratories for years. Since several decades, however, it is known that phytoplankton species and even local populations can exhibit large intraspecific diversity. During a field campaign on Svalbard, we isolated different strains of the Arctic diatom Thalassiosira hyalina from community incubations, which resembled present and future climate conditions. We then exposed these freshly isolated monocultures again to a matrix of CO and temperature. The results revealed that even within a single species, response patterns can differ greatly, comparable to variations seen between diatom species. Moreover, while only minor reactions of the communities were observed, the strain responses corresponded strongly with the previous selection environment. A strain isolated from future-like treatments, for instance, had its growth optimum at a higher temperature and pCO than another strain isolated from more present-like conditions. This suggests that intraspecific variability and the selection between coexisting ecotypes may be an underestimated source of species’ plasticity under changing environmental conditions and could ‘buffer’ functional species shifts. Adaptation of phytoplankton assemblages may therefore occur also by selection within rather than only between species, and species-wide inferences from single strain experiments should be handled with great care

Pelagic and ice-associated microalgae under elevated light and pCO2: Contrasting physiological strategies in two Arctic diatoms

Sea ice retreat, changing stratification and ocean acidification are fundamentally changing the light availability and physico-chemical conditions for primary producers in the Arctic ocean. However, detailed studies on ecophysiological strategies and performance of key species in the pelagic and ice-associated habitat remain scarce. We therefore investigated the acclimated responses of the diatoms Thalassiosira hyalina and Melosira arctica towards elevated irradiance and CO2 partial pressures. Next to growth, elemental composition and biomass production, we assessed detailed photophysiological responses through fluorometry and gas-flux measurements, including respiration and carbon acquisition. In the pelagic T. hyalina, growth rates remained high in all treatments and biomass production increased strongly with light. Even under low irradiances cells maintained a high-light acclimated state, allowing them to opportunistically utilize high irradiances by means of a highly plastic photosynthetic machinery and carbon uptake. The ice-associated M. arctica proved to be less plastic and more specialized on low-light. Its acclimation to high irradiances was characterized by minimizing photon harvest and photosynthetic efficiency, which led to lowered growth. Comparably low growth rates and strong silification advocate a strategy of persistence rather than of fast proliferation, which is also in line with the observed formation of resting stages under low-light conditions. In both species, responses to elevated pCO2 were comparably minor. Although both diatom species persisted under the applied conditions, their competitive abilities and strategies differ strongly. With the anticipated extension of Arctic pelagic habitats, flexible high-light specialists like T. hyalina seem to face a brighter future

Resilience and adaptive mechanisms of Arctic phytoplankton under heatwaves: Acclimation, microevolution and community resilience

Trait adjustments of phytoplankton communities to changing environmental conditions can take place through responses on several fundamental ecological levels. These include physiological acclimation of single genotypes, evolution through sorting among genotypes of the same species, and selection within the entire multi-species community. Which of these different levels responds to environmental change can have large ecological and biogeochemical implications, but especially in protists, these levels are extremely difficult to disentangle. Arctic phytoplankton at base of the foodweb in one of the most rapidly warming regions on the planet, are faced with especially large changes, but often show high resilience. Among these changes are more frequent and intense heatwaves, which expose organisms to vast temperature fluctuations. In dedicated experimental setups of different ecological complexity, we investigated how phytoplankton responds and adjusts to heatwaves, and on which of the mentioned levels shifts can be observed. We resolved not only physiological features and productivity, but also composition on the species as well as the intraspecific level, using a novel molecular approach to efficiently examine the composition of protist populations in diverse contexts. This setup provides a comprehensive approach to investigate how phytoplankton communities respond to stable and fluctuating temperature scenarios, physiologically and ecologically

The hidden flows within species: Phytoplankton population dynamics in Arctic assemblages

Progressing climate change and concurrent alterations of environmental conditions pose challenges of adaptation on organisms and ecosystems, especially in rapidly changing places like the Arctic. While more diverse systems are usually considered to be more resilient, biodiversity does not only describe the number of species, but can also consist of diverse individuals within a species. Especially in protists, with large census sizes and fast proliferation, intraspecific lineage sorting can be an important mechanism of plasticity and trait adjustment. For phytoplankton communities at the base of the foodweb, physiological acclimation and species shifts are frequently described, but intraspecific composition and diversity are methodologically still difficult to resolve, especially in diverse natural contexts and at temporal resolution. Therefore, our knowledge on the functioning and importance of intraspecific selection dynamics in phytoplankton is still limited. In recent years, we have developed and applied a new, high throughput methodology for phytoplankton population composition, which can make temporal and spatial population dynamics visible that were before extremely difficult to resolve. Next to experiments with natural phytoplankton communities and artificial populations under controlled settings, a time-series of Arctic spring blooms has been investigated towards the year-to year composition of species but also of intraspecific populations of a dominant diatom. Datasets emerging now thanks to such novel technologies can offer new, more comprehensive perspectives on our understanding of the mechanisms and results of microevolution and local adaptation, and can reveal formerly hidden patterns of species’ strategies of persistence and development

Improving the Census Legal and Policy Reforms for a More Accurate, Equitable, and Legitimate Count

The census is a cornerstone of American democracy. The results of this constitutionally required, once-a-decade count of every person living in the United States dictate how seats in the House of Representatives are divided among the states, how state and local governments draw electoral districts, and how more than $1.5 trillion annually in federal funds is distributed for essential services such as health care, food assistance, and education. At its best, the census offers an authentic picture of who we are as a diverse and growing nation.The 2020 census struggled. It faced a barrage of obstacles, from executive interference to chronic underfunding to the Covid-19 pandemic. In the face of these challenges, it ultimately failed to reach 18.8 million people — more than 5 percent of the country's population. What's more, the census once again disproportionately undercounted people of color, with the Latino undercount rate more than tripling from the prior decade. And multiple states were undercounted by significant margins. These inaccuracies compromise the census's ability to fairly distribute political power and federal funding both across states and across communities, undercutting the democratic promise of our political system. Meanwhile, overall census response rates remain stuck in a rut, costs are rising, and the bureau's reliance on labor-intensive door-to-door outreach is showing its limits. The census is too critical to continue in this precarious state.This paper sets forth a blueprint for reforming the law and policy of the decennial population count. Our goal is to make future censuses more accurate, equitable, and legitimate. An accurate census correctly captures the number and demographic characteristics of all people residing in the country. An equitable census is designed, funded, and run to count all groups precisely and to distribute political power and economic support commensurate with each community's fair share. A legitimate census — one that is scientifically rigorous and democratically accountable and boasts universal participation — warrants and inspires widespread trust. Legitimacy and accuracy require equity; an equitable census is free from the long-running tendency to undercount Black, Latino, and Native American communities in comparison with white ones, inspiring confidence in its fundamental fairness

Ligand-binding and -scavenging of the chemerin receptor GPR1

Tight regulation of cytokines is essential for the initiation and resolution of inflammation. Chemerin, a mediator of innate immunity, mainly acts on chemokine-like receptor 1 (CMKLR1) to induce the migration of macrophages and dendritic cells. The role of the second chemerin receptor, G protein-coupled receptor 1 (GPR1), is still unclear. Here we demonstrate that GPR1 shows ligand-induced arrestin3 recruitment and internalization. The chemerin C-terminus triggers this activation by folding into a loop structure, binding to aromatic residues in the extracellular loops of GPR1. While this overall binding mode is shared between GPR1 and CMKLR1, differences in their respective extracellular loop 2 allowed for the design of the first GPR1-selective peptide. However, our results suggest that ligand-induced arrestin recruitment is not the only mode of action of GPR1. This receptor also displays constitutive internalization, which allows GPR1 to internalize inactive peptides efficiently by an activation-independent pathway. Our results demonstrate that GPR1 takes a dual role in regulating chemerin activity: as a signaling receptor for arrestin-based signaling on one hand, and as a scavenging receptor with broader ligand specificity on the other. Graphic abstractDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Universität Leipzig (1039)Peer Reviewe

Resilience by diversity: Large intraspecific differences in climate change responses of an Arctic diatom

The potential for adaptation of phytoplankton to future climate is often extrapolated based on single strain responses of a representative species, ignoring variability within and between species. The aim of this study was to approximate the range of strain-specific reaction patterns within an Arctic diatom population, which selection can act upon. In a laboratory experiment, we first incubated natural communities from an Arctic fjord under present and future conditions. In a second step, single strains of the diatom Thalassiosira hyalina were isolated from these selection environments and exposed to a matrix of temperature (38C and 68C) and pCO 2 levels (180 latm, 370 latm, 1000 latm, 1400 latm) to establish reaction norms for growth, production rates, and elemental quotas. The results revealed interactive effects of temperature and pCO 2 as well as wide tolerance ranges. Between strains, however, sensitivities and optima differed greatly. These strain-specific responses corresponded well with their respective selection environments of the previous com- munity incubation. We therefore hypothesize that intraspecific variability and the selection between coexist- ing strains may pose an underestimated source of species’ plasticity. Thus, adaptation of phytoplankton assemblages may also occur by selection within rather than only between species, and species-wide inferences from single strain experiments should be treated with caution

Diffusion-weighted MRI reflects proliferative activity in primary CNS lymphoma

Purpose: To investigate if apparent diffusion coefficient (ADC) values within primary central nervous system lymphoma correlate with cellularity and proliferative activity in corresponding histological samples. Materials and Methods: Echo-planar diffusion-weighted magnetic resonance images obtained from 21 patients with primary central nervous system lymphoma were reviewed retrospectively. Regions of interest were drawn on ADC maps corresponding to the contrast enhancing parts of the tumors. Biopsies from all 21 patients were histologically analyzed. Nuclei count, total nuclei area and average nuclei area were measured. The proliferation index was estimated as Ki-67 positive nuclei divided by total number of nuclei. Correlations of ADC values and histopathologic parameters were determined statistically. Results: Ki-67 staining revealed a statistically significant correlation with ADCmin (r = -0.454, p = 0.038), ADCmean (r = -0.546, p = 0.010) and ADCmax (r = -0.515, p = 0.017). Furthermore, ADCmean correlated in a statistically significant manner with total nucleic area (r = -0.500, p = 0.021). Conclusion: Low ADCmin, ADCmean and ADCmax values reflect a high proliferative activity of primary cental nervous system lymphoma. Low ADCmean values—in concordance with several previously published studies—indicate an increased cellularity within the tumor