Trade and Variety in a Model of Endogenous Product Differentiation

This paper sets up a model of endogenous product differentiation to analyze the variety effects of international trade. In our model multi-product firms decide not only about the number of varieties they supply but also about the degree of horizontal differentiation between these varieties. Firms can raise the degree of differentiation by investing variety-specific fixed costs. In this setting, we analyze how trade integration, i.e. an increase in market size, influences the number of firms in the market, the number of product varieties supplied by each firm, and the degree of differentiation.Product differentiation, multi-product firms, international trade.

Absolute absorption and fluorescence measurements over a dynamic range of 106^6 with cavity-enhanced laser-induced fluorescence

We describe a novel experimental setup that combines the advantages of both laser-induced fluorescence and cavity ring-down techniques. The simultaneous and correlated measurement of the ring-down and fluorescence signals yields absolute absorption coefficients for the fluorescence measurement. The combined measurement is conducted with the same sample in a single, pulsed laser beam. The fluorescence measurement extends the dynamic range of a stand-alone cavity ring-down setup from typically three to at least six orders of magnitude. The presence of the cavity improves the quality of the signal, in particular the signal-to-noise ratio. The methodology, dubbed cavity-enhanced laser-induced fluorescence (CELIF), is developed and rigorously tested against the spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell. We outline how the method can be utilised to determine absolute quantities: absorption cross sections, sample densities and fluorescence quantum yields.Comment: 12 pages, 6 figures, submitted to J. Chem. Phy

Switching Propulsion Mechanisms of Tubular Catalytic Micromotors

Different propulsion mechanisms have been suggested for describing the motion of a variety of chemical micromotors, which have attracted great attention in the last decades due to their high efficiency and thrust force, enabling several applications in the fields of environmental remediation and biomedicine. Bubble-recoil based motion, in particular, has been modeled by three different phenomena: capillary forces, bubble growth, and bubble expulsion. However, these models have been suggested independently based on a single influencing factor (i.e., viscosity), limiting the understanding of the overall micromotor performance. Therefore, the combined effect of medium viscosity, surface tension, and fuel concentration is analyzed on the micromotor swimming ability, and the dominant propulsion mechanisms that describe its motion more accurately are identified. Using statistically relevant experimental data, a holistic theoretical model is proposed for bubble-propelled tubular catalytic micromotors that includes all three above-mentioned phenomena and provides deeper insights into their propulsion physics toward optimized geometries and experimental conditions

Spatial distribution of core monomers in acrylamide-based core-shell microgels with linear swelling behaviour

The peculiar linear temperature-dependent swelling of core-shell microgels has been conjectured to be linked to the core-shell architecture combining materials of different transition temperatures. Here the structure of pNIPMAM-core and pNNPAM-shell microgels in water is studied as a function of temperature using small-angle neutron scattering with selective deuteration. Photon correlation spectroscopy is used to scrutinize the swelling behaviour of the colloidal particles and reveals linear swelling. Moreover, these experiments are also employed to check the influence of deuteration on swelling. Using a form free multi-shell reverse Monte Carlo approach, the small-angle scattering data are converted into radial monomer density profiles. The comparison of 'core-only' particles consisting of identical cores to fully hydrogenated core-shell microgels, and finally to H core/D shell architectures unambiguously shows that core and shell monomers display gradient profiles with strong interpenetration, leading to cores embedded in shells which are bigger than their isolated 'core only' precursor particles. This surprising result is further generalized to different core cross linker contents, for temperature ranges encompassing both transitions. Our analysis demonstrates that the internal structure of pNIPMAM-core and pNNPAM-shell microgels is heterogeneous and strongly interpenetrated, presumably allowing only progressive core swelling at temperatures intermediate to both transition temperatures, thus promoting linear swelling behaviour

Collaborative and Robot-Based Plug & Produce for Rapid Reconfiguration of Modular Production Systems

Wojtynek M, Oestreich H, Beyer O, Wrede S. Collaborative and Robot-Based Plug & Produce for Rapid Reconfiguration of Modular Production Systems. In: Proceedings of the 2017 IEEE/SICE International Symposium on System Integration. Piscataway, NJ: IEEE; 2017.The manufacturing of individualized products down to batch size 1 poses ongoing challenges for the design and integration of future production systems. Today’s production lines with a high degree of automation achieve high efficiency, but usually come with high costs for adaptation to product variants. In order to combine full automation with high flexibility, we propose a concept for the dynamic composition of automation components in a modular production system that facilitates the rapid adaptation of collaborative and robot-supported manufacturing processes. To achieve this, we integrate self-descriptive automation components at runtime into the control architecture of the production system using a Plug-and-Produce approach. While the location and orientation of automation components in the modular production system are derived from physical human-robot interaction, the adaptation and verification of the robot behavior is made possible through a simulation-based planning subsystem. Once this dynamic reconfiguration process by the machine setter is finished, the adapted production process is executed in a fully automated way with high efficiency. A case study carried out in an industrial collaboration project on flexible assembly demonstrates the benefits of the presented approach

Smart Homopolymer Microgels: Influence of the Monomer Structure on the Particle Properties

Wedel B, Hertle Y, Wrede O, Bookhold J, Hellweg T. Smart Homopolymer Microgels: Influence of the Monomer Structure on the Particle Properties. Polymers. 2016;8(4): 162.In this work, we compare the properties of smart homopolymer microgels based on N-n-propylacrylamide (NNPAM), N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) synthesized under identical conditions. The particles are studied with respect to size, morphology, and swelling behavior using scanning electron and scanning force microscopy. In addition, light scattering techniques and fluorescent probes are employed to follow the swelling/de-swelling of the particles. Significant differences are found and discussed. Poly(N-n-propylacrylamide) (PNNPAM) microgels stand out due to their very sharp volume phase transition, whereas Poly(N-isopropylmethacrylamide) (PNIPMAM) particles are found to exhibit a more homogeneous network structure compared to the other two systems

Absolute fluorescence and absorption measurements over a dynamic range of 106 with cavity-enhanced laser-induced fluorescence

We present a novel spectroscopic technique that exhibits high sensitivity and a large dynamic range for the measurement of absolute absorption coefficients. We perform a simultaneous and correlated laser-induced fluorescence and cavity ring-down measurement of the same sample in a single pulsed laser beam. The combined measurement offers a large dynamic range and a lower limit of detection than either technique on its own. The methodology, dubbed cavity-enhanced laser-induced fluorescence, is developed and rigorously tested against the electronic spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell. We outline how the method can be used to determine absolute quantities, such as sample densities, absorption cross sections, and fluorescence quantum yields, particularly in spatially confined samples

Volume phase transition kinetics of smart N-n-propylacrylamide microgels studied by time-resolved pressure jump small angle neutron scattering

Wrede O, Reimann Y, Lülsdorf S, et al. Volume phase transition kinetics of smart N-n-propylacrylamide microgels studied by time-resolved pressure jump small angle neutron scattering. Scientific Reports. 2018;8(1): 13781.The use of smart colloidal microgels for advanced applications critically depends on their response kinetics. We use pressure jump small angle neutron scattering with supreme time resolution to study the rapid volume phase transition kinetics of such microgels. Utilizing the pressure induced microphase separation inside the microgels we were able to resolve their collapse and swelling kinetics. While the collapse occurs on a time scale of 10 ms, the particle swelling turned out to be much faster. Photon correlation spectroscopy and static small angle neutron scattering unambiguously show, that the much slower collapse can be associated with the complex particle architecture exhibiting a loosely-crosslinked outer region and a denser inner core region. These insights into the kinetics of stimuli-responsive materials are of high relevance for their applications as nano-actuators, sensors or drug carriers. Moreover, the used refined pressure jump small angle neutron scattering technique is of broad interest for soft matter studies

Dialects, Cultural Identity, and Economic Exchange

We study the effect of cultural ties on economic exchange using a novel measure for cultural identity: dialect similarity across regions of the same country. We evaluate linguistic micro-data from a unique language survey conducted between 1879 and 1888 in about 45,000 German schools. The recorded geography of dialects comprehensively portrays local cultural ties that have been evolving for centuries, and provides an ideal opportunity to measure cul-tural barriers to economic exchange. In a gravity analysis, we then show that cross-regional migration flows in the period 2000–2006 are positively affected by historical dialect similari-ty. Using different empirical strategies, we show that this finding indicates highly time-persistent cultural borders that impede economic exchange even at a fine geographical scale