A Universal Session Type for Untyped Asynchronous Communication

In the simply-typed lambda-calculus we can recover the full range of expressiveness of the untyped lambda-calculus solely by adding a single recursive type U = U -> U. In contrast, in the session-typed pi-calculus, recursion alone is insufficient to recover the untyped pi-calculus, primarily due to linearity: each channel just has two unique endpoints. In this paper, we show that shared channels with a corresponding sharing semantics (based on the language SILL_S developed in prior work) are enough to embed the untyped asynchronous pi-calculus via a universal shared session type U_S. We show that our encoding of the asynchronous pi-calculus satisfies operational correspondence and preserves observable actions (i.e., processes are weakly bisimilar to their encoding). Moreover, we clarify the expressiveness of SILL_S by developing an operationally correct encoding of SILL_S in the asynchronous pi-calculus

Template and Temperature Controlled Polymorph Formation in Squaraine Thin Films

Controlling the polymorph formation in organic semiconductor thin films by the choice of substrate and deposition temperature is a key factor for targeted device performance. Small molecular semiconductors such as the quadrupolar donor-acceptor-donor (D-A-D) type squaraine compounds allow both solution and vapor phase deposition methods. A prototypical anilino squaraine with branched butyl chains as terminal functionalization (SQIB) has been considered for photovoltaic applications due to its broad absorption within the visible to deep-red spectral range. Its opto-electronic properties depend on the formation of the two known polymorphs adopting a monoclinic and orthorhombic crystal phase. Both phases emerge with a strongly preferred out-of-plane and rather random in-plane orientation in spincasted thin films depending on subsequent thermal annealing. Upon vapor deposition on dielectric and conductive substrates, such as silicon dioxide, potassium chloride, graphene and gold, the polymorph expression depends on the choice of growth substrate. In all cases the same pronounced out-of-plane orientation is adopted, but with a surface templated in-plane alignment in case of crystalline substrates. Combining X-ray diffraction, atomic force microscopy, ellipsometry and polarized spectro-microscopy we identify the processing dependent evolution of the crystal phases, correlating morphology and molecular orientations within the textured SQIB films.Comment: 10 pages, 7 figure

Shell Nutzfahrzeug-Studie Diesel oder Alternative Antriebe - Womit fahren Lkw und Bus morgen

Die Shell Nutzfahrzeug-Studie 2016 ist die Nachfolgestudie der ersten Shell Lkw-Studie 2010 (Shell 2010). Sie wurde inhaltlich auf Nutzfahrzeuge erweitert und behandelt nun auch die Kraftomnibusse. Shell knüpft damit im Nutzfahrzeugbereich an die seit 1958 veröffentlichten Shell Pkw-Szenarien an, die inzwischen in der 26. Auflage erschienen sind (Shell 2014). Die Shell Nutzfahrzeuge-Studie 2016 wurde erneut in Zusammenarbeit mit dem Institut für Verkehrsforschung im Deutschen Zentrum für Luft- und Raumfahrt erstellt. Ziel der Shell Nutzfahrzeug-Studie 2016 ist es, die Zukunft des Straßengüterverkehrs sowie des öffentlichen Straßenpersonenverkehrs mit Bussen bis in das Jahr 2040 zu erforschen. Hierzu wurden zum einen aktuelle Trends in der Transportlogistik für Güter und Personen und der Nutzfahrzeugstatistik untersucht sowie Potenzialabschätzungen relevanter Technologien vorgenommen. Zum anderen erfolgte mit Hilfe von Güterverkehrsmodellierung und Szenariotechnik sowie der Verknüpfung wichtiger verkehrs-, energie- und umweltpolitischer Parameter des Lkw- und Busverkehrs eine umfassende Betrachtung der Entwicklung in Deutschland. Die wichtigsten Ergebnisse der Shell Nutzfahrzeug-Studie lassen sich wie folgt zusammenfassen: 1) Die Logistikwirtschaft ist ein wichtiger, wachsender Wirtschaftszweig; Deutschland ist ein weltweit führender Logistikstandort. Die Güterverkehrsleistung in Deutschland ist in den vergangenen 25 Jahren um 60 % gewachsen und wird bis 2040 nochmals um 50 % zulegen. Die Straße ist und bleibt der Hauptverkehrsträger für den Gütertransport. 2) In Deutschland sind heute (2016) knapp drei Mio. Lkw und knapp 80.000 Busse zugelassen. Die Bestandsentwicklung wird von leichten Nutzfahrzeugen bestimmt. Die Schadstoffklassen (Euro-Normen) variieren deutlich nach Fahrzeugsegmenten. Dieselfahrzeuge besitzen einen Flottenanteil von insgesamt 95 %. 3) Der Dieselantrieb als Standard für Nutzfahrzeuge besitzt weitere Effizienzpotenziale. Für Fernverkehrs-Lkw könnten Gasantriebe auf Basis verflüssigten Erdgases (LNG) eine Alternative darstellen. Potenziale für Elektromobilität weisen leichte Nutzfahrzeuge und Fahrzeuge mit urbanen Fahrprofilen auf. 4) Bis 2040 wird der Nutzfahrzeugbestand in Deutschland auf 3,5 Mio. Fahrzeuge zulegen; die Lkw-Fahrleistungen steigen um 39 %. Aufgrund von Effizienzfortschritten sinkt der Energiebedarf aller Nutzfahrzeuge von heute bis 2040 um bis zu 13 %. Die gesamten CO2-Emissionen gehen um bis zu 20 % zurück. Die 1990er CO2-Emissionswerte werden in 2040 noch deutlich überschritten

Spotlight on Charge-Transfer Excitons in Crystalline Textured n-Alkyl Anilino Squaraine Thin Films

Prototypical n-alkyl terminated anilino squaraines for photovoltaic applications show characteristic double-hump absorption features peaking in the green and deep-red spectral range. These signatures result from coupling of an intramolecular Frenkel exciton and an intermolecular charge transfer exciton. Crystalline, textured thin films suitable for polarized spectro-microscopy have been obtained for compounds with n-hexyl (nHSQ) and n-octyl (nOSQ) terminal alkyl chains. The here released triclinic crystal structure of nOSQ is similar to the known nHSQ crystal structure. Consequently, crystallites from both compounds show equal pronounced linear dichroism with two distinct polarization directions. The difference in polarization angle between the two absorbance maxima cannot be derived by spatial considerations from the crystal structure alone but requires theoretical modeling. Using an essential state model, the observed polarization behavior was discovered to depend on the relative contributions of the intramolecular Frenkel exciton and the intermolecular charge transfer exciton to the total transition dipole moment. For both nHSQ and nOSQ, the contribution of the charge transfer exciton to the total transition dipole moment was found to be small compared to the intramolecular Frenkel exciton. Therefore, the net transition dipole moment is largely determined by the intramolecular component resulting in a relatively small mutual difference between the polarization angles. Ultimately, the molecular alignment within the micro-textured crystallites can be deduced and, with that, the excited state transitions can be spotted.Comment: 12 pages, 8 figure

In situ–Directed Growth of Organic Nanofibers and Nanoflakes: Electrical and Morphological Properties

Organic nanostructures made from organic molecules such as para-hexaphenylene (p-6P) could form nanoscale components in future electronic and optoelectronic devices. However, the integration of such fragile nanostructures with the necessary interface circuitry such as metal electrodes for electrical connection continues to be a significant hindrance toward their large-scale implementation. Here, we demonstrate in situ–directed growth of such organic nanostructures between pre-fabricated contacts, which are source–drain gold electrodes on a transistor platform (bottom-gate) on silicon dioxide patterned by a combination of optical lithography and electron beam lithography. The dimensions of the gold electrodes strongly influence the morphology of the resulting structures leading to notably different electrical properties. The ability to control such nanofiber or nanoflake growth opens the possibility for large-scale optoelectronic device fabrication

The Influence of the Degree of Heterogeneity on the Elastic Properties of Random Sphere Packings

The macroscopic mechanical properties of colloidal particle gels strongly depend on the local arrangement of the powder particles. Experiments have shown that more heterogeneous microstructures exhibit up to one order of magnitude higher elastic properties than their more homogeneous counterparts at equal volume fraction. In this paper, packings of spherical particles are used as model structures to computationally investigate the elastic properties of coagulated particle gels as a function of their degree of heterogeneity. The discrete element model comprises a linear elastic contact law, particle bonding and damping. The simulation parameters were calibrated using a homogeneous and a heterogeneous microstructure originating from earlier Brownian dynamics simulations. A systematic study of the elastic properties as a function of the degree of heterogeneity was performed using two sets of microstructures obtained from Brownian dynamics simulation and from the void expansion method. Both sets cover a broad and to a large extent overlapping range of degrees of heterogeneity. The simulations have shown that the elastic properties as a function of the degree of heterogeneity are independent of the structure generation algorithm and that the relation between the shear modulus and the degree of heterogeneity can be well described by a power law. This suggests the presence of a critical degree of heterogeneity and, therefore, a phase transition between a phase with finite and one with zero elastic properties.Comment: 8 pages, 6 figures; Granular Matter (published online: 11. February 2012