Ab initio van der Waals interactions in simulations of water alter structure from mainly tetrahedral to high-density-like

The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations using van der Waals (vdW) density-functional theory, i.e. using the new exchange-correlation functionals optPBE-vdW and vdW-DF2. Inclusion of the more isotropic vdW interactions counteracts highly directional hydrogen-bonds, which are enhanced by standard functionals. This brings about a softening of the microscopic structure of water, as seen from the broadening of angular distribution functions and, in particular, from the much lower and broader first peak in the oxygen-oxygen pair-correlation function (PCF), indicating loss of structure in the outer solvation shells. In combination with softer non-local correlation terms, as in the new parameterization of vdW-DF, inclusion of vdW interactions is shown to shift the balance of resulting structures from open tetrahedral to more close-packed. The resulting O-O PCF shows some resemblance with experiment for high-density water (A. K. Soper and M. A. Ricci, Phys. Rev. Lett., 84:2881, 2000), but not directly with experiment for ambient water. However, an O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from experiment on low-density liquid water reproduces near-quantitatively the experimental O-O PCF for ambient water, indicating consistency with a two-liquid model with fluctuations between high- and low-density regions

Scientific drilling projects in ancient lakes: integrating geological and biological histories

Sedimentary sequences in ancient or long-lived lakes can reach several thousands of meters in thickness and often provide an unrivalled perspective of the lake's regional climatic, environmental, and biological history. Over the last few years, deep drilling projects in ancient lakes became increasingly multi- and interdisciplinary, as, among others, seismological, sedimentological, biogeochemical, climatic, environmental, paleontological, and evolutionary information can be obtained from sediment cores. However, these multi- and interdisciplinary projects pose several challenges. The scientists involved typically approach problems from different scientific perspectives and backgrounds, and setting up the program requires clear communication and the alignment of interests. One of the most challenging tasks, besides the actual drilling operation, is to link diverse datasets with varying resolution, data quality, and age uncertainties to answer interdisciplinary questions synthetically and coherently. These problems are especially relevant when secondary data, i.e., datasets obtained independently of the drilling operation, are incorporated in analyses. Nonetheless, the inclusion of secondary information, such as isotopic data from fossils found in outcrops or genetic data from extant species, may help to achieve synthetic answers. Recent technological and methodological advances in paleolimnology are likely to increase the possibilities of integrating secondary information, e.g., through molecular dating of molecular phylogenies. Some of the new approaches have started to revolutionize scientific drilling in ancient lakes, but at the same time, they also add a new layer of complexity to the generation and analysis of sediment core data. The enhanced opportunities presented by new scientific approaches to study the paleolimnological history of these lakes, therefore, come at the expense of higher logistic, communication, and analytical efforts. Here we review types of data that can be obtained in ancient lake drilling projects and the analytical approaches that can be applied to empirically and statistically link diverse datasets for creating an integrative perspective on geological and biological data. In doing so, we highlight strengths and potential weaknesses of new methods and analyses, and provide recommendations for future interdisciplinary deep drilling projects

A biomimetic approach to robot table tennis

Although human beings see and move slower than table tennis or baseball robots, they manage to outperform such robot systems. One important aspect of this better performance is the human movement generation. In this paper, we study trajectory generation for table tennis from a biomimetic point of view. Our focus lies on generating efficient stroke movements capable of mastering variations in the environmental conditions, such as changing ball speed, spin and position. We study table tennis from a human motor control point of view. To make headway towards this goal, we construct a trajectory generator for a single stroke using the discrete movement stages hypothesis and the virtual hitting point hypothesis to create a model that produces a human-like stroke movement. We verify the functionality of the trajectory generator for a single forehand stroke both in a simulation and using a real Barrett WAM

A Service of zbw Leibniz-Informationszentrum Wirtschaft Leibniz Information Centre for Economics The Phantom of the Opera: Cultural Amenities, Human Capital, and Regional Economic Growth NON-TECHNICAL SUMMARY

Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. www.econstor.eu We analyze the extent to which endogenous cultural amenities affect the spatial equilibrium share of high-human-capital employees. To overcome endogeneity, we draw on a quasinatural experiment in German history and exploit the exogenous spatial distribution of baroque opera houses built as a part of rulers' competition for prestigious cultural amenities. Robustness tests confirm our strategy and strengthen the finding that proximity to a baroque opera house significantly affects the spatial equilibrium share of high-human-capital employees. Then, a cross-region growth regression shows that these employees induce local knowledge spillovers and shift a location to a higher growth path. Terms of use: Documents in D I S C U S S I O N P A P E R S E R I E S NON-TECHNICAL SUMMARY Baroque rulers' pomposity and quest for prestige accidentally affect economic growth today. The theory that you can only spend what you have was not a popular one among the absolutistic rulers of this era and it was not uncommon for rulers to incur huge debts and engage in deficit spending in their quest for grandeur. One remnant of this time is the baroque opera houses that are still found throughout Germany. The regional distribution of baroque opera houses today suggests that it is not primarily the regions' historic economic prosperity that explains their existence. Based on this observation, the paper addresses the chicken and egg problem of whether economic success leads to a rich cultural life or vice versa. In light of studies that illustrate the concentration of both bohemians and human capital in prospering cities, one might assume that a concentration of cultural amenities attracts human capital. However, it could just as easily be the other way around, where a concentration of human capital in the form of highly skilled workers who have not only an appreciation for artistic output, but for the money to indulge in that taste, will attract bohemians. In our empirical analyses, we find that proximity to one of 29 baroque opera houses across Germany has a positive effect on the regional share of high-human-capital employees which then stimulates regional growth. Our advice to local policymakers is to be aware of the value of cultural amenities when competing for high-human-capital individuals. However, local policymakers should also carefully consider the possibility of unwanted side effects from redistributing resources to cultural amenities at the expense of other public spending or increased taxes because such a policy could result in relocation decisions by firms or individuals that do not value cultural amenities