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In der Automobilindustrie ist die Anwendung von monolithischen Profilstrukturen etabliert. Jedoch bietet der Einsatz von Hybridprofilen, die aus einem faserverstarkten Polymer (FVK) und einer duktilen Metalllegierung bestehen, eine im Vergleich vorteilhafte Kombination aus mechanischen Eigenschaften und resultierendem Bauteilgewicht. Um eine effiziente Fertigung und damit den industriellen Einsatz von Metall-FVK-Hybridprofilen anzustreben, werden in diesem Kapitel zwei intrinsische Fertigungsprozesse vorgestellt. Dabei ermoglichen die Prozesse einerseits die Verarbeitung einer thermoplastischen und andererseits einer duroplastischen Kunststoffmatrix. Neben der Entwicklung und Validierung dieser Produktionsprozesse werden, mit dem Ziel einen bestmoglichen Korrosionsschutz bei einer zugleich hohen Haftfestigkeit zu realisieren, Konzepte zur Gestaltung der Grenzschicht der artverschiedenen Werkstoffe betrachtet. Des Weiteren werden Methoden zur Simulation und zur mechanischen Prufung der gefertigten Hybridprofile aufgezeigt. Zusatzlich soll dabei auch auf die Messung und die gezielte Modifikation von Eigenspannungen, die sich infolge der Verarbeitung der verschiedenen Materialien einstellen, eingegangen werden.

We studied the microstructural evolution of the low stacking fault energy $\alpha$-brass alloy CuZn15 during accumulative roll bonding (ARB). Most notably, the typical brass-type texture was clearly observed after four ARB passes (approx. 93.8 % total thickness reduction), before significant shear localization set in. This observation contradicts the widely accepted idea that shear band formation is a necessary prerequisite for the development of the brass type texture, indicating that the two phenomena, shear banding and development of the brass texture, are only correlated in ARB, and that their order of appearance can be switched depending on experimental parameters., Comment: 4 pages, 2 figures

Tube hydroforming is a well-established process in industry for producing complex shaped parts with closed cross section geometry and high geometrical accuracy. Hot-metal gas forming (HMGF) extends the conventional tube hydroforming process by a complex thermo-mechanical approach and thus potentially enables the complex processing of tubes from the relatively new class of quenching & partitioning-steels (Q&P steels). To prove the feasibility of an integrated Q&P treatment in the HMGF process, a simple demonstrator geometry is considered in the present study. The applied forming pressure is limited to 70 MPa, resulting in incomplete forming of the parts in the corner areas. The resulting, locally varying contact situation between workpiece and die allows the investigation of different cooling rates and their influence on local microstructural changes and on the corresponding mechanical properties. A numerical finite element simulation is used to estimate local cooling rates in three different areas of the tube (maximum cooling rates between 60 and 280 K/s), which are then correlated with hardness measurements and typical microstructural features. The hardness distribution is inhomogeneous over the cross section of the part (varies about 150 HV), with a minimum in the areas without die contact during quenching. Ferritic areas are observed in these regions due to the significantly lower cooling rates. Tensile tests show that the stress-strain behavior after the shortest partitioning time of 10 min is not only better from an energy efficiency point of view, but also provides both high strength (Rm =2050 MPa) and high ultimate strain (19.7 %), while longer partitioning times result in inferior properties. Thus, the present study shows that the Q&P treatment can be integrated into the HMGF process, but the local cooling rates must be taken into account as they strongly influence the final mechanical properties of the workpiece.

Severe plastic deformation techniques can produce ultrafine-grained aluminum alloys with high strength and ductility, but further processing often requires costly and/or time-consuming machining. In this study, we investigate the potential of an alternative processing route that operates below recrystallization temperature and that can produce fine-grained materials. Cast billets of the age hardening aluminum alloy AA6060 were solution annealed and then extruded at room temperature or at 170 °C (which corresponds to the aging temperature of the alloy, and allows for simultaneous forming and aging). The materials were then subjected to an aging treatment. Electron microscopy and mechanical testing were performed to characterize the resulting microstructural features and mechanical properties. Both extruded profiles exhibit similar, strongly graded microstructures with submicron-sized grains in the highly deformed surface layers, and a mixture of coarse and fine grains in the center regions. Despite different processing routes (i.e., cold vs. warm extrusion), both materials are characterized by similar mechanical properties in terms of maximum hardness, strength and ductility; these results are discussed in the light of the relevant microstructural deformation and precipitation mechanisms.

We present experimental results on the deposition of Nickel Titanium (NiTi) films on graphene substrates using a PVD magnetron sputter process. Characterization of the 2–4 micron thick NiTi films by electron microscopy, electron backscatter diffraction, and transmission electron microscopy shows that grain size and orientation of the thin NiTi films strongly depend on the type of combination of graphene and copper layers below. Our experimental findings are supported by density functional theory calculations: a theoretical estimation of the binding energies of different NiTi–graphene interfaces is in line with the experimentally determined microstructural features of the functional NiTi top layer.

Altres ajuts: SEV-2015-0563 Migration data remains scarce, particularly in the context of developing countries. We demonstrate how geo-referenced online search data can be used to measure migration intentions in origin countries and to predict bilateral migration flows. Our approach provides strong additional predictive power for international migration shows when compared to reference models from the migration and trade literature. We provide evidence, based on survey data, that our measures partly reflect genuine migration intentions and that they outperform any of the established predictors of migration flows in terms of predictive power, especially in the bilateral within dimension. Our findings contribute to the literature by (1) providing a novel way for the measurement of migration intentions, (2) allowing real-time predictions of current migration flows ahead of official statistics, and (3) improving the performance of conventional models of migration flows.

Diffusion bonding is a well-known technology for a wide range of advanced joining applications, due to the possibility of bonding different materials within a defined temperature-time-contact pressure regime in solid state. For this study, aluminium alloys AA 6060, AA 6082, AA 7020, AA 7075 and magnesium alloy AZ 31 B are used to produce dissimilar metal joints. Titanium and silver were investigated as interlayer materials. SEM and EDXS-analysis, micro-hardness measurements and tensile testing were carried out to examine the influence of the interlayers on the diffusion zone microstructures and to characterize the joint properties. The results showed that the highest joint strength of 48 N/mm2 was reached using an aluminium alloy of the 6000 series with a titanium interlayer. For both interlayer materials, intermetallic Al-Mg compounds were still formed, but the width and the level of hardness across the diffusion zone was significantly reduced compared to Al-Mg joints without interlayer.

Increasing labor migration and simultaneous aging of societies are two important demographic developments many poor countries face. Elderly people who are left behind may experience a decrease in welfare when their children migrate. This paper investigates the effect of migration on various dimensions of elderly health using unique data from Moldova, which has one of the highest emigration rates in the world. We find positive migration effects on body mass index (BMI), mobility and self-reported health. No effects are found on depression and cognitive capacity. We find evidence that these positive outcomes are linked to an income effect which leads to improvements in diet and identify a reallocation of time use from subsistence farming to leisure and sleep which may have further beneficial effects. These positive effects seem to compensate the elderly for decreasing social contact with their migrant family members.

This paper reviews existing theoretical and empirical evidence on the economic effects of immigration in developing countries. Specifically, it discusses how immigration may affect labour market, entrepreneurship, human capital, productivity, economic growth, the exchange rate, trade, prices, public finance and public goods in host countries. As the majority of the relevant literature has traditionally focused on the experience of high-income countries, the review highlights the unique context of developing countries and elaborates how outcomes may be similar or differ in low and middle-income countries. A general conclusion is that the economic effects of immigration to developing countries, a numerically important phenomenon, warrants additional theoretical and empirical research.

Employing a unique dataset that covers almost 6000 informal enterprises from six West African urban centers, this paper examines the backward and forward linkages of these enterprises to the formal sector. Authors first provide a descriptive analysis of the existing formal-informal linkages. It turns out that formal backward linkages are much more prevalent than formal forward linkages, and that linkages vary with the degree of informality, occurring less frequently if firms have no ties to the formal sector at all or low capital stocks. In the second step, authors employ a Probit approach to identify major factors associated with the observed backward linkages. The Probit analysis corroborates the importance of the degree of informality for the existence of linkages and shows various enterprise characteristics to be significant determinants as well. Finally, authors analyze whether backward linkages matter for enterprise performance using both Ordinary Least Squares (OLS) and four estimations. Authors find a positive and robust impact of backward linkages, whereas the degree of informality of the enterprises in our sample seems to affect firm performance only indirectly through their linkages to the formal sector.

Effizienter Leichtbau erfordert intelligente Werkstoffe, die vielseitige Funktionen erfullen. Ein Losungsansatz besteht darin, Kohlenstofffasergewebe galvanisch zu metallisieren, um funktionelle kohlenstofffaserverstarkte Kunststoffe (CFK) herzustellen. Es resultiert eine rissfreie, homogene Nickelschicht auf der Gewebeoberflache. Durch eine geeignete Wahl der Beschichtungsparameter wird daruber hinaus jede einzelne Faser des gesamten Gewebes gleichmasig metallisiert und eine Anwendung in funktionellen kohlenstofffaserverstarkten Kunststoffen fur Leichtbauwasserstoffspeicher ermoglicht. Schlusselworter: Metallisierte Kohlenstofffasern / funktionelle CFK / galvanische Abscheidung Efficient lightweight construction requires intelligent materials that meet versatile functions. One approach to produce functional carbon fiber-reinforced plastics (CFRPs) is the metallization of carbon fiber fabrics. This results in a crack-free, homogeneous nickel layer on the fabrics’surfaces. By selecting suitable layer parameters, every single fiber of the entire fabrics will be evenly metallized and allow the application of functional CFRPs as lightweight hydrogen storage.

Processing in the semi-solid state allows the benefits of the process of forming and casting to be combined. In addition to obtaining complicated shapes, unusual forms of structures with exceptional properties can also be formed. A special processing procedure in the semi-solid state for very small parts has been developed, which is called mini-thixoforming, is able to handle CPM15V steel powder. From the original ferrite matrix with primary chromium–vanadium carbides – a mixed structure was obtained by processing consisting of metastable austenite, rod-shaped chromium–vanadium carbides and the original chromium–vanadium carbides. Compared to the initial state (micro hardness approx. HV10 330), this structure achieved, as a result of the relatively high rate of cooling in the form, a hardness of approx. 730 HV10. Due to the fact that this is a metastable structure, experimental heating to temperatures 400, 500, 600, 700, 800 °C for 1 h was performed. With exposure at temperatures 400 and 500 °C there was a slight decrease in hardness of approx. 20 points, heat treatment at 600 °C achieved hardness of 960 HV10. This state corresponds to an equivalent value of compressive strength of approx. 2880 MPa, Further increase in temperature leads to a continuous decrease in hardness due to decomposition of the metastable matrix. Thermal exposure at 700 °C, resulted in hardness of 585 HV10. After exposure to 800 °C there was a significant decrease of hardness to 425 HV10.

We report on mini-thixoforming of a hard and wear-resistant crucible particle metallurgy tool steel. Significant microstructural modifications associated with the special semisolid forming process are characterized in detail by scanning electron microscopy and X-ray diffraction. The mechanical performance of the material is assessed both pre-thixoforming and post-thixoforming by nanoindentation of the constituent phases. The novel microstructural changes that result from mini-thixoforming, which are discussed in this article for the first time, are beneficial in further improving the hardness of the steel.

Employing a unique dataset that covers households from six West African capitals, this paper provides new evidence on the demand for informal sector products and services. We first investigate whether demand linkages exist between formal and informal products and distribution channels, and whether there is an overlapping customer base, which would imply that both formal sector wage earners and informal workers buy both formal and informal products using both formal and informal distribution channels. In a second step, we estimate demand elasticities based on Engel curves. We find a strongly overlapping customer base and strong demand-side linkages between the formal and informal sector, with the exception that informal goods are hardly bought through formal distribution channels. The estimated demand elasticities tend to show that rising incomes are associated with a lower propensity to consume informal sector goods and to use informal distribution channels. We therefore conclude that the informal sector in West Africa is likely to be constrained from the demand side.

This paper investigates the effects of oil financed public investment on poverty using a dynamic multisectoral general equilibrium model featuring inter-temporal productivity spillovers, which may exhibit a sector-specific and regional bias. In general, the results bear out the expectation that a surge of oil revenues leads to a real appreciation, distorting incentives which favor nontradable activities over export agriculture and manufacturing thereby increasing rural and national poverty. Whereas this result is familiar from other recent studies, the simulations show that beyond the short run, when conventional demand-side Dutch disease effects are present, the relationship between resource-rent flows and real exchange rates, output growth, and poverty is less straightforward than simple models of the "resource curse" suggest. Taking Ghana as a stylized agriculture-based economy with poverty most pronounced in a region with home biased agricultural production, a policy mix of smoothing the real exchange rate shock and an allocation of infrastructure spending in rural areas seems to be the most promising public investment strategy to enhance growth and reduce poverty.

Block copolymer (BCP) thin films have received enormous interest for possible applications in nanotechnology due to their self-assembled structure formation. However, synthesis of polymers with desired chemical and physical properties sometimes is not possible. During the past 6 years, our group developed a method to introduce certain functionality into self-assembled structures via the formation of supramolecular assemblies from BCPs and low molecular weight additives. Among several other materials, the most noteworthy is a system consisting of polystyrene-block-poly(4-vinylpyridine) and 2-(4′-hydroxybenzeneazo) benzoic acid which has been used as nanotemplate for the fabrication of materials with potentially exceptional electrical, optical, or magnetic properties. The present article summarizes the research done at our group on fundamental aspects of microphase separation in these supramolecular assemblies and also their further use as templates for nanofabrication.

The phase behavior of supramolecular assemblies (SMA) formed by polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with 2-(4′-hydroxybenzeneazo)benzoic acid (HABA) was investigated with respect to the molar ratio (X) between HABA and 4VP monomer unit in bulk as well as in thin films coated on a silicon substrate. In bulk, the SMA showed bcc packed spherical or hexagonally packed cylindrical microdomains composed of P4VP(HABA) blocks in PS matrix depending on the composition which varied with the HABA weight fraction. However, at a molar ratio of 2 where HABA was in excess, the cylindrical microdomains of P4VP(HABA) blocks were found to pack in a tetragonal lattice. The SMA in thin film also showed spherical or cylindrical morphology depending on the composition. Interestingly, the orientation of cylindrical microdomains of P4VP(HABA) depended on the selectivity of the solvent as well as on the degree of swelling. Hence, in a nonselective solvent like chloroform, the cylinders were found to lie parallel t...

Patterned media for future ultrahigh-density magnetic data storage can be prepared by electrodeposition into ordered arrays of nanostructured templates. Diblock copolymer templates have been proposed as a promising alternative to alumina templates. They possess smaller feature sizes than alumina and thereby allow for higher storage densities. Templates with pore diameters of ∼8 nm have been fabricated by dip-coating a conducting substrate into a solution of polystyrene- block -poly(4-vinylpyridine) (PS-b-P4VP) and 2-(4′-hydroxybenzeneazo) benzoic acid (HABA). A vapor annealing step was interposed for better ordering. The pores are opened by dissolving the HABA from the supramolecular assembly and afterwards filled by electrodeposition. Fe–Pt and Co–Pt alloys are the materials of choice for filling the pores due to their hard magnetic properties like high coercivity and anisotropy. Co-rich Co 80 Pt 20 was chosen for this study because it does not require post annealing as in the case of ordered L1 0 CoPt or FePt. Continuous films have been deposited in order to identify the optimum deposition conditions and the influence of deposition current density on chemical composition, growth morphology, and structural and magnetic properties has been studied systematically. The first results on templates electrochemically filled with Co–Pt are presented together with an analysis of their magnetic properties.

We develop a theoretical model of human skill formation and emigration. Additionally to existing brain drain models, we partly endogenize the heterogeneity of the individuals, by introducing aspirations. Emigration of an individual will result in a migration experience, which increases the migrant's aspirations. This will induce her to invest more in the education of her children back home. We find that this aspirations effect increases the average skill level in the society for a given migration rate. We show that the optimal migration rate that maximizes the post-migration skill-rate of the population is higher if we allow for the aspirations effect of migration. We use panel data from Indonesia to demonstrate that a migration experience has an aspirations increasing effect and calibrate our model accordingly. Our results suggest that there are potentially more countries than previously assumed which benefit from migration.

The effect of remittances on capital accumulation remains a contested topic. This paper uses a panel data set from rural Mexico to investigate the impact of remittances on agriculture and livestock investments. After controlling for the endogeneity of migration through an instrumental variable estimation our empirical results show that international migration has a significantly positive effect on the accumulated agricultural assets but not on livestock capital. This suggests that households use the capital obtained from international migration only to overcome liquidity constraints for subsistence production whereas migration itself seems to be the superior investment option compared to other productive activities such as livestock husbandry.

International migration not only enables individuals to earn higher wages but also exposes them to new environments. The norms and values experienced at the destination country could change the behavior of the migrant but also of family members left behind. In this paper we argue that a brain gain could take place due to a change in educational aspirations of caregivers in migrant households. Using unique survey data from Moldova, we find that international migration raises parental aspirations in households located at the lower end of the human capital distribution. The identification of these effects relies on GDP growth shocks in the destination countries and migration networks. We conclude that aspirations are a highly relevant determinant of intergenerational human capital transfer and that even temporary international migration can shift human capital formation to a higher steady state by inducing higher educational aspirations of caregivers

This paper provides evidence based guidance for practical survey work, namely choosing interviewers and their workload. Analyzing a survey of 3568 households obtained through computer assisted personal interviews (CAPI) we find that interviewers learn considerably while the survey progresses. Time requirements for field work increase concavely with sample size which allows larger samples to be realized with a given budget than would be expected in planning such projects with simplistic cost estimates. We find a decrease of interview duration of almost 50 percent which translates into a significant increase of the average hourly wage the interviewers receive. These learning effects cease after around 20 interviews. Based on our results we recommend targeting interviewer training by age and technology-affinity of interviewers for CAPI surveys

Employing a unique dataset that covers almost 6000 informal enterprises from six West African urban centers, this paper examines the backward and forward linkages of these enterprises to the formal sector. We first provide a descriptive analysis of the existing formal-informal linkages. It turns out that formal backward linkages are much more prevalent than formal forward linkages, and that linkages vary with the degree of informality, occurring less frequently if firms have no ties to the formal sector at all or low capital stocks. In the second step, we employ a Probit approach to identify major factors associated with the observed backward linkages. The Probit analysis corroborates the importance of the degree of informality for the existence of linkages and shows various enterprise characteristics to be significant determinants as well. Finally, we analyze whether backward linkages matter for enterprise performance using both OLS and IV estimations. We find a positive and robust impact of backward linkages, whereas the degree of informality of the enterprises in our sample seems to affect firm performance only indirectly through their linkages to the formal sector

We investigated the orientation changes of cylindrical P4VP microdomains in PS-b-P4VP thin films upon annealing in different solvent vapours using the time-resolved in situ grazing-incidence small-angle X-ray scattering (GISAXS) for the first time. Swelling of perpendicular cylinders (C ⊥) in a non-selective solvent vapours (chloroform) leads to the orientation change to in-plane cylinders (C//) and it occurs through a disordered state. On the other hand, swelling of perpendicular cylinders (C ⊥) in a selective solvent vapours (1,4-dioxane) leads the morphological change from cylindrical to BCC spherical morphology. Solvent evaporation results in shrinkage of the matrix in the vertical direction and subsequently merges the spheres into the perpendicularly aligned cylinders. The selectivity of the solvent to constituting blocks and the solvent evaporation rate may be mainly responsible for such orientation change of cylindrical P4VP microdomains in PS-b-P4VP thin films.

Highly dense arrays of ordered and aligned nanorods of polyaniline with 10 nm diameter on transparent ITO substrate have been successfully fabricated using supramolecular assemblies of block copolymer as scaffold material; the ordered arrays of polyaniline nanorods so fabricated were found to exhibit excellent electrochemical properties with an electrochemical capacitance value of 3407 F g(-1).

International migration not only enables individuals to earn higher wages but also exposes them to new environments. The norms and values experienced in destination countries can change the behavior of migrants and also of family members left behind. This paper suggests that brain gain can take place due to a change in the educational aspirations of caregivers in migrant households. Estimates for Moldova show that international migration raises parental aspirations in households located at the lower end of the human capital distribution. The identification of these effects relies on GDP growth shocks in the destination countries and migration networks. These results imply that aspirations are a highly relevant determinant of intergenerational human capital transfer and that even temporary international migration can shift human capital formation to a higher steady state by inducing higher educational aspirations among caregivers.JEL classification:D03, O12, I21, J61.