On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4

Potassium aluminium tetrahydride KAlH4 of high phase purity (space group Pnma (62)) was synthesized via a mechanochemical route. The thus obtained material was studied by 27Al and 39K MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T=295 K were derived (27Al: delta_iso=(107.6+-0.2) ppm, C_Q = (1.29+-0.02) MHz and eta = 0.64+-0.02; 39K: delta_iso=(6.1+-0.2) ppm, C_Q = (0.562+-0.005) MHz and eta = 0.74+-0.02). The straightforward NMR spectroscopic approach applied here should also work for other complex aluminium hydrides and for many other materials containing half-integer nuclei experiencing small to medium-sized quadrupole couplings.Comment: 27 pages, 5 figures, final version as published in PCCP, with reviewer reports attached to the ES

Convergence or divergence? Immigrant wage assimilation patterns in Germany

Using a rich German panel data set, I estimate wage assimilation patterns for immigrants in Germany. This study contributes to the literature by performing separate estimations by skill groups and controlling for a wide range of socio-economic background variables. It aims to answer the question whether Germany can be considered an attractive host country from an immigrant's perspective. Comparisons with similar natives reveal that immigrants' experience earnings profiles are flatter on average, although clear differences show up among skill groups. The effect of time spent in the host country is significantly positive for all skill groups and thus partly offsetting the diverging trend in the experience earnings profiles. Still, wage differences between natives and immigrants remain. They are particularly noticeable for highly skilled immigrants, the group needed most in Germany's skill intensive labor market. Separate estimations for immigrant subgroups confirm the general validity of the results. --international migration,wage differentials,assimilation,longitudinal data

On the use of Solomon echoes in 27Al NMR studies of complex aluminium hydrides

The quadrupole coupling constant $C_Q$ and the asymmetry parameter $\eta$ have been determined for two complex aluminium hydrides from $^{27}$Al NMR spectra recorded for stationary samples by using the Solomon echo sequence. The thus obtained data for KAlH4 ($C_Q=(1.30\pm0.02)$ MHz, $\eta=(0.64\pm0.02)$) and NaAlH4 ($C_Q=(3.11\pm0.02)$ MHz, $\eta<0.01$) agree very well with data previously determined from MAS NMR spectra. The accuracy with which these parameters can be determined from static spectra turned out to be at least as good as via the MAS approach. The experimentally determined parameters ($\delta_{iso}$, $C_Q$ and $\eta$) are compared with those obtained from DFT-GIPAW (density functional theory - gauge-including projected augmented wave) calculations. Except for the quadrupole coupling constant for KAlH4, which is overestimated in the GIPAW calculations by about 30%, the agreement is excellent. Advantages of the application of the Solomon echo sequence for the measurement of less stable materials or for in-situ studies are discussed.Comment: 26 pages, 7 figure

Aufsätze zur Arbeitsmarkt- und Migrationsökonomie

This thesis provides important empirical evidence on the German labor market which faces tremendous challenges by ongoing demographic changes. With an expected decrease in its labor force and an aging society, Germany has to find ways to maintain its economic stability and the functioning of its welfare state. Two possible solutions are discussed: immigration – especially of highly skilled immigrants – and investments in human capital that allow individuals to find better paying and more stable jobs. Section 2 addresses the question to what extent immigrants are able to overcome initial wage disadvantages vis-à-vis comparable natives. Adding to the extant literature on this topic, the analysis particularly takes into account differences between skill groups and how these differences may be responsible for different wage assimilation patterns. The results show that highly skilled immigrants are not able to catch up with their native peers in terms of wages, while the initial wage gap between low/medium skilled immigrants and natives narrows over time. This can be in part explained by theoretical considerations such as Merton’s (1968) theory of cumulative advantages or may simply be the result of employers’ discrimination against immigrants, e.g., by hindering the promotion of immigrants into better paying jobs (“glass ceilings”). Section 3 also refers to Merton’s (1968) theory of cumulative advantages and looks at one of the sources of initial disparities between immigrants and natives, i.e., the occurrence of youth unemployment. As Burgess (2003) points out, youth unemployment has long-lasting negative consequences particularly for lower skilled individuals. The analysis in Section 3 thus considers only graduates from lower and intermediate secondary schools, i.e., Hauptschule and Realschule. By using proportional hazard models I show that controlling for individual, parental, and regional background can only explain part of the difference in the risk of becoming unemployed between immigrants and natives. However, second generation immigrants of Turkish origin, an especially vulnerable group also in other countries, stand out as the group with the highest unemployment risk, ceteris paribus. While immigration offers one possible solution to address Germany’s demographic challenges, increasing the overall skills of its population may be another means to help alleviate the economic pressure caused by the shortage of skilled labor. Germany’s vocational training system is often praised for its effectiveness in providing young adults with the necessary human capital to smoothly enter the labor market (e.g., Heckman, 1994). In addition, Germany’s “dual system” (duales System) is seen as being largely responsible for the low youth unemployment rates in Germany compared to other Western countries. This thesis investigates the extent to which human capital investments, e.g. in form of apprenticeship or vocational training, are beneficial with respect to labor market outcomes early in individuals’ careers. Using a sample of 25 years old East and West German youths who graduated from lower or intermediate secondary school, i.e., Hauptschule or Realschule, Section 4 examines the returns to apprenticeship and vocational training (AVT) regarding three early labor market outcomes: non-employment, fulltime employment, and wages. As predicted by Becker’s (1964) human capital theory, AVT is beneficial with respect to all three outcomes. AVT graduates have c.p. significantly lower risks of non-employment, significantly higher propensities of having a fulltime permanent job, and they earn significantly higher wages than their peers without a vocational degree. Interestingly, we find no significant differences in the returns between apprenticeship degrees and degrees from other forms of vocational training at an early stage in young persons’ careers. Despite differences in general economic conditions, returns to AVT do not differ between East and West Germany. They also show no significant decline over time even in light of an ongoing educational expansion that leads to an increase in the share of graduates from higher secondary schools.Die vorliegende Dissertation beschreibt empirisch verschiedene Aspekte des deutschen Arbeitsmarktes, der sich aufgrund des demografischen Wandels einer Vielzahl von Herausforderungen gegenübersieht. Um dem prognostizierten Rückgang der Arbeitsbevölkerung und einer alternden Gesellschaft entgegenzusteuern muss Deutschland Wege finden, um seine wirtschaftliche Stabilität und seinen Wohlfahrtsstaat zu erhalten. Zwei Möglichkeiten werden in dieser Dissertation angesprochen: Zuwanderung – besonders von hochqualifizierten Migranten – und Humankapitalinvestitionen, die es den Menschen erlauben besserbezahlte und stabilere Arbeitsplätze zu finden. Abschnitt 2 adressiert die Frage in welchem Umfang Zuwanderer in der Lage sind, anfängliche Lohnunterschied im Vergleich zu Einheimischen überwinden. Aufbauend auf bestehender Literatur in diesem Feld konzentriert sich die vorliegende Arbeit insbesondere auf die Unterschiede in den Assimilationsmustern verschiedener Bildungsgruppen. Die Ergebnisse zeigen, dass hochqualifizierte Zuwanderer nicht in der Lage sind, den Lohnunterschied gegenüber vergleichbaren Einheimischen aufzuholen, während die anfänglichen Lohnunterschiede zwischen gering- und mittelqualifizierten Einheimischen und Zuwanderern sich im Zeitverlauf verkleinern. Dies kann zum Teil durch theoretische Überlegungen wie Mertons (1968) Theorie der kumulativen Vorteile erklärt werden oder kann schlicht das Resultat arbeitgeberseitiger (Lohn-) Diskriminierung sein, z.B. durch schlechtere Aufstiegsmöglichkeiten für Zuwanderer in besser bezahlte Jobs („gläserne Decken“). Abschnitt 3 bezieht sich ebenfalls auf Mertons (1968) Theorie kumulativer Vorteile und betrachtet eine der Quellen anfänglicher Ungleichheit zwischen Einheimischen und Zuwanderern, nämlich das Auftreten von Jugendarbeitslosigkeit. Wie Burgess (2003) beschreibt führt Jugendarbeitslosigkeit zu langfristig negativen Konsequenzen, besonders für Geringqualifizierte. Die Untersuchungen in Abschnitt 3 betrachten deshalb insbesondere Schulabgänger aus Haupt- und Realschule. Unter Verwendung proportionaler Hazardraten-Modelle zeige ich, dass durch die Kontrolle für individuelle, elternbezogene und regionale Hintergrundvariablen nur ein Teil des Unterschieds im Arbeitslosigkeitsrisiko zwischen Einheimischen und Zuwanderern erklärt werden kann. Türkische Zuwanderer, insbesondere der zweiten Generation, stechen mit ceteris paribus besonders hohen Arbeitslosigkeitsrisiken weiterhin deutlich hervor. Während Zuwanderung eine Möglichkeit ist, die demografie-induzierten Probleme des deutschen Arbeitsmarktes anzugehen, besteht eine weitere Möglichkeit darin, das allgemeine Bildungsniveau der Bevölkerung anzuheben um dem drohenden Fachkräftemangel entgegenzuwirken. Das deutsche Ausbildungssystem wird oftmals dafür gelobt, junge Menschen durch die Vermittlung arbeitsmarktrelevanter Fähigkeiten effektiv auf den Eintritt ins Erwerbsleben vorzubereiten (vergl. Heckman, 1994). Das deutsche „Duale System“ wird auch hauptsächlich für die im Vergleich zu anderen Industrieländern sehr niedrige Jugendarbeitslosigkeit in Deutschland verantwortlich gemacht. Diese Dissertation untersucht, in welchem Umfang Humankapitalinvestitionen – beispielsweise in Lehre oder berufliche Bildung – vorteilhaft im Hinblick auf verschiedene Arbeitsmarktergebnisse sind. Unter Verwendung einer Stichprobe 25jähriger ost- und westdeutscher Jugendlicher mit Haupt- oder Ralschulabschluss untersucht Abschnitt 4 die Rendite beruflicher Bildung im Hinblick auf drei Arbeitsmarktergebnisse: Nicht-Beschäftigung, Vollzeit-Beschäftigung und Löhne. Wie von Beckers (1964) Humankapitaltheorie vorhergesagt hat berufliche Bildung in allen Fällen einen positiven Einfluss auf die betrachteten Merkmale. Diejenigen mit einem beruflichen Bildungsabschluss haben ceteris paribus ein signifikant niedrigeres Risiko, nichterwerbstätig zu sein, eine signifikant höhere Wahrscheinlichkeit, einen festen Vollzeit-Job zu haben, und verdienen signifikant höhere Löhne wie diejenigen ohne Berufsbildungsabschluss. Interessanterweise lassen sich keine signifikanten Renditeunterschiede zwischen Lehre und anderen Formen der beruflichen Bildung feststellen. Trotz unterschiedlicher wirtschaftlicher Rahmenbedingungen unterscheiden sich die Renditen der beruflichen Bildung zwischen Ost- und Westdeutschland nicht. Auch im Hinblick auf die Bildungsexpansion der vergangenen Jahre lässt sich kein Zeittrend in den Renditen feststellen

Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties

Transition-metal phosphates show a wide range of chemical compositions, variations of the valence states, and crystal structures. They are commercially used as solid-state catalysts, cathode materials in rechargeable batteries, or potential candidates for proton-exchange membranes in fuel cells. Here, we report on the successful ab initio structure determination of two novel titanium pyrophosphates, Ti(III)p and Ti(IV)p, from powder X-ray diffraction (PXRD) data. The low-symmetry space groups P2$_1$/c for Ti(III)p and P$\overline{1}$ for Ti(IV)p required the combination of spectroscopic and diffraction techniques for structure determination. In Ti(III)p, trivalent titanium ions occupy the center of TiO$_6$ polyhedra, coordinated by five pyrophosphate groups, one of them as a bidentate ligand. This secondary coordination causes the formation of one-dimensional six-membered ring channels with a diameter d$_{max}$ of 3.93(2) Å, which is stabilized by NH$_{4}$$^{+}$ ions. Annealing Ti(III)p in inert atmospheres results in the formation of a new compound, denoted as Ti(IV)p. The structure of this compound shows a similar three-dimensional framework consisting of [PO$_4$]3– tetrahedra and Ti$^{IV+}$O$_6$ octahedra and an empty one-dimensional channel with a diameter d$_{max}$ of 5.07(1) Å. The in situ PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH$_{4}$$^{+}$ ions in a first step and subsequent structure relaxation. The specific proton conductivity and activation energy of the proton migration of Ti(III)p, governed by the Grotthus mechanism, belong to the highest and lowest, respectively, ever reported for this class of materials, which reveals its potential application in electrochemical devices like fuel cells and water electrolyzers in the intermediate temperature range

The invasive coral Oculina patagonica has not been recently introduced to the Mediterranean from the western Atlantic

BACKGROUND: Effective policies, management, and scientific research programs depend on the correct identification of invasive species as being either native or introduced. However, many species continue to be misidentified. Oculina patagonica, first recorded in the Mediterranean Sea in 1966, is believed to have been introduced in anthropogenic times and expanding in a west to east direction. However, its present identification and status as a recently introduced species remain to be explored. In this study, we used multi-locus genetic data to test whether O. patagonica in the Mediterranean has been recently introduced from the western North Atlantic. RESULTS: We found no genetic or historical demographic evidence to support a recent introduction of O. patagonica from the western North Atlantic or an expansion across the Mediterranean. Instead, Mediterranean and Atlantic populations are genetically distinct and appear to have begun diverging about 5 Mya. We also found evidence of a fossil record of Oculina spp. existing in the eastern North Atlantic millions of years before the present. CONCLUSIONS: Our results suggest that Mediterranean populations of O. patagonica have long been isolated from the western Atlantic, either in undetectable numbers or overlooked and undersampled sites and habitats, and have only recently been expanding to invasive levels as a result of environmental changes. Accurate identification of species’ invasive statuses will enable more effective research programs aimed at better understanding the mechanisms promoting the invasive nature of species, which can then lead to the implementation of efficient management plans. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12862-015-0356-7) contains supplementary material, which is available to authorized users