Time Horizon and Cooperation in Continuous Time

When subjects interact in continuous time, their ability to cooperate may dramatically increase. In an experiment, we study the impact of different time horizons on cooperation in (quasi) continuous time prisoner's dilemmas. We find that cooperation levels are similar or higher when the horizon is deterministic rather than stochastic. Moreover, a deterministic duration generates different aggregate patterns and individual strategies than a stochastic one. For instance, under a deterministic horizon subjects show high initial cooperation and a strong end-of-period reversal to defection. Moreover, they do not learn to apply backward induction but to postpone defection closer to the end.

Larva of Atractocerus Brasiliensis (Lepeletier & Audinet-Serville, 1825) (Lymexylidae, Atractocerinae)

The larva of Atractocerus brasiliensis (Lepeletier & Audinet-Serville, 1825), collected for the first time in Pinus oocarpa Schiede ex Schltdl. (Pinaceae) is described and illustrated. Until now, for Lymexylidae, only the larva of Melittomma sp. (Melittomminae) was known from the neotropical region (Brazil). Biological notes, a comparison with the description of A. brevicornis, the type-species of the genus (recorded from Africa and Madagascar), and history of the known lymexylid larvae are also included.A larva de Atractocerus brasiliensis (Lepeletier & Audinet-Serville, 1825), coletada pela primeira vez em Pinus oocarpa Schiede ex Schltdl. (Pinaceae) é descrita e ilustrada. Até o momento, em Lymexylidae, apenas a larva de Melittomma sp. (Melittomminae) era conhecida do Brasil. Notas biológicas, uma comparação com a descrição de A. brevicornis, a espécie-tipo do gênero (da África e Madagascar) e o histórico das larvas de limexilídeo conhecidas também estão incluídos

Full 3D numerical analysis of a twin screw compressor by employing open-source software

The push for having more reliable and efficient positive displacement machines (both compressors and expanders) for vapor compression and power generation (e.g., ORCs) applications has moved researchers to an always more spread employment of computational fluid dynamics (CFD). In particular, twin screw compressors, because of their high efficiency compared to other compressor types, have received interest over the last years. The numerical analysis of such machines is challenging: the deforming working chambers are very difficult to be correctly replicated. The relative motion of the rotors and the variation of the gaps during machine operation are few of the major difficulties in implementing reliable CFD models. A custom mesh generation algorithm is therefore often required for sumulating the machine operation. In this work, SCORG-V5.2.2 was used to generate the meshes of the deforming domain around rotating parts of the machines. The open-source software OpenFOAM-v1606+ is then employed to compute the flow field associated with the operation of the twin screw. The coupling of the two tools has been carried out in this work, applying the methodology to a twin screw machine

Bulk Cr tips for scanning tunneling microscopy and spin-polarized scanning tunneling microscopy

A simple, reliable method for preparation of bulk Cr tips for Scanning Tunneling Microscopy (STM) is proposed and its potentialities in performing high-quality and high-resolution STM and Spin Polarized-STM (SP-STM) are investigated. Cr tips show atomic resolution on ordered surfaces. Contrary to what happens with conventional W tips, rest atoms of the Si(111)-7x7 reconstruction can be routinely observed, probably due to a different electronic structure of the tip apex. SP-STM measurements of the Cr(001) surface showing magnetic contrast are reported. Our results reveal that the peculiar properties of these tips can be suited in a number of STM experimental situations

Fabrication and Characterization of Molybdenum Tips for Scanning Tunneling Microscopy and Spectroscopy

We present a method for the preparation of bulk molybdenum tips for scanning Tunneling Microscopy and Spectroscopy (STM - STS) and we assess their potential in performing high resolution imaging and local spectroscop by measurements on different single crystal surfaces in UHV, namely Au(111), Si(111)-7x7 and titanium oxide 2D ordered nanostructures supported on Au(111). The fabrication method is versatile and can be extended to other metals, e.g. cobalt

Vibrational - Electrical Properties Relationship in Donor Doped TiO2 by Raman Spectroscopy

Transparent conducting TiO2, obtained by Nb or Ta doping of the anatase structure, is gaining increasing attention for the development of transparent electrodes. Usually, regardless the deposition technique, a crystallization process in reducing atmosphere is necessary to achieve large mobility; in addition, electrical and optical properties are also strongly sensitive to the oxygen deposition pressure. These facts reveal that the defect chemistry of donor doped TiO2 is not trivial and involves a strict interplay among extrinsic dopant atoms, oxygen vacancies and ‘electron killer’ defects such as Ti vacancies and O interstitials. We here present a Raman characterization of donor-doped TiO2 films synthesized under several deposition and post-annealing conditions, employing different doping levels and dopant elements (i.e. Ta and Nb). Correlations between structure, crystallinity, shift and width of Raman peaks and electrical properties are shown and discussed. In particular, a clear relationship between the shift of the Eg(1) anatase Raman mode and the charge carrier density is found, while the B1g(1) mode connected to Ti-Ti vibrations is significantly affected by the extrinsic doping level. In this complex framework Raman spectroscopy can provide an invaluable contribution towards understanding the material structure and its influence on the functional properties

Pulsed Laser Deposition of two-dimensional ZnO nanocrystals on Au(111): Growth, surface structure and electronic properties

Two-dimensional (2D) ZnO structures have been deposited on the Au(111) surface by means of the pulsed laser deposition (PLD) technique. In situ scanning tunneling microscopy (STM) and spectroscopy (STS) measurements have been performed to characterize morphological, structural and electronic properties of 2D ZnO at the nanoscale. Starting from a sub-monolayer coverage, we investigated the growth of ZnO, identifying different atomic layers (up to the 5th). At low coverage, we observed single- and bi-layer nanocrystals, characterized by a surface moire pattern that is associated to a graphene-like ZnO structure. By increasing the coverage, we revealed a morphological change starting from the 4th layer, which was attributed to a transition toward a bulk-like structure. Investigation of the electronic properties revealed the semiconducting character of 2D ZnO. We observed a dependence of the density of states (DOS) and, in particular, of the conduction band (CB) on the ZnO thickness, with a decreasing of the CB onset energy for increasing thickness. The CB DOS of 2D ZnO shows a step-like behaviour which may be interpreted as due to a 2D quantum confinement effect in ZnO atomic layer

Low-frequency modes in the Raman spectrum of sp-sp2 nanostructured carbon

A novel form of amorphous carbon with sp-sp2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp2 phase.Comment: 15 pages, 5 figures, 1 tabl

User defined nodal displacement of numerical mesh for analysis of screw machines in FLUENT

Growing demands to reduce energy consumption are driving researchers towards in-depth analysis of positive displacement machines. Twin screw compressors are amongst the most common types of positive displacement machines. These machines have inherently complex geometry due to intricate rotor profiles used. As the details of the internal flows are difficult to obtain experimentally, Computational Fluid Dynamics (CFD) offers a good alternative for evaluation of internal flow patterns. However, implementation of CFD is challenging due complex deforming geometries. In this paper, a customised grid generator SCORGTM developed by authors is used to generate numerical meshes for commercially available solver ANSYS FLUENT. FLUENT is an unstructured solver which offers flexibility of using both segregated and coupled solution algorithms. Segregated algorithms are generally faster which results in shorter product development time. Interface with FLUENT is implemented by performing User Defined Nodal Displacements (UDND) of grids generated by SCORG in a parallel framework. For this purpose, SCORG and UDND are coupled and extended to work with FLUENT's parallel architecture. The developed code is compiled within the solver. The oil free air screw compressor with 'N' profile rotors and 3/5 lobe combination is modelled for 8000 RPM and 6000 RPM. Finally, the predicted performance values with FLUENT are compared to previously calculated CFX predictions and experimental results. FLUENT requires shorter solution time to obtain same accuracy of CFX