Strongly enhanced shot noise in chains of quantum dots

We study charge transport through a chain of quantum dots. The dots are fully coherent among each other and weakly coupled to metallic electrodes via the dots at the interface, thus modelling a molecular wire. If the non-local Coulomb interactions dominate over the inter-dot hopping we find strongly enhanced shot noise above the sequential tunneling threshold. The current is not enhanced in the region of enhanced noise, thus rendering the noise super-Poissonian. In contrast to earlier work this is achieved even in a fully symmetric system. The origin of this novel behavior lies in a competition of "slow" and "fast" transport channels that are formed due to the differing non-local wave functions and total spin of the states participating in transport. This strong enhancement may allow direct experimental detection of shot noise in a chain of lateral quantum dots.Comment: 4 pages, 2 figures, submitted to PR

Practices of place-making through locative media artworks

Peer-reviewedIn recent years, the vast increase in information flows has made it possible to instantly connect location-dependent information with physical spaces. These technologies have provided new forms of the representation of space as much as new forms of perception through tools and techniques used in land surveying, remote sensing, etc. From a critical point of view, pervasive computing, location-based applications, or, in other words, "locative media" provide an interesting framework to understand how these technologies relate to our understanding of space and place. Concretely, we want to examine how the uses of locative media in social-oriented artworks interact with people's sense of place. This article therefore discusses contemporary theories on space related to media and technology with a specific focus on the conceptualization of the notion of place. It also relates these theories to the study of different locative media artworks: Canal Accessible (2006), Bio Mapping (2004), Disappearing Places (2007), and Coffee Deposits (2010). We contend that locative media artworks act upon distinctive ways to understand the mediation of technology in current placemaking practices.En los últimos años, el aumento de los flujos de información ha hecho posible conectar instantáneamente la información dependiente de ubicación con los espacios físicos. Estas tecnologías han facilitado tanto nuevas formas de representación del espacio como nuevas formas de percepción a través de herramientas y técnicas usadas en topografía, teledetección, etc. Desde un punto de vista crítico, la computación ubicua, las aplicaciones de localización, o en otras palabras, los "medios locativos" proporcionan un marco interesante para entender cómo estas tecnologías se relacionan con nuestra comprensión del espacio y el lugar. Concretamente, queremos examinar cómo los usos de los medios locativos en la vida social orientados a obras de arte interactuan con el sentimiento de lugar. En este artículo se analizan tanto las teorías contemporáneas sobre el espacio en relación con los medios de comunicación y la tecnología con un enfoque específico en la conceptualización de la noción de lugar. Estas teorías se refieren también al estudio de diferentes obras de arte de medios locativos: Canal Accesible (2006), Bio Mapping (2004), Lugares Disappearing (2007), y los restos de café (2010). Sostenemos que las obras de arte de medios locativos actuan de maneras distintas para entender la mediación de la tecnología en las prácticas de Placemaking actuales.En els últims anys, l'augment dels fluxos d'informació ha fet possible connectar instantàniament la informació dependent d'ubicació amb els espais físics. Aquestes tecnologies han facilitat tant noves formes de representació de l'espai com noves formes de percepció a través d'eines i tècniques utilitzades en topografia, teledetecció, etc. Des d'un punt de vista crític, la computació ubiqua, les aplicacions de localització o, en altres paraules, els "mitjans locatius" proporcionen un marc interessant per entendre com aquestes tecnologies es relacionen amb la nostra comprensió de l'espai i el lloc. Concretament, volem examinar com els usos dels mitjans locatius en la vida social orientats a obres d'art interactuen amb el sentiment de lloc. En aquest article s'analitzen tant les teories contemporànies sobre l'espai en relació amb els mitjans de comunicació i la tecnologia amb un enfocament específic en la conceptualització de la noció de lloc. Aquestes teories es refereixen també a l'estudi de diferents obres d'art de mitjans locatius: Canal Accessible (2006), Bio Mapping (2004), Llocs Disappearing (2007), i les restes de cafè (2010). Sostenim que les obres d'art de mitjans locatius actuen de maneres diferents per entendre la mediació de la tecnologia en les pràctiques de Placemaking actuals

Ten steps toward a better personality science - How quality may be rewarded more in research evaluation

This target article is part of a theme bundle including open peer commentaries (https://doi.org/10.5964/ps.9227) and a rejoinder by the authors (https://doi.org/10.5964/ps.7961). We point out ten steps that we think will go a long way in improving personality science. The first five steps focus on fostering consensus regarding (1) research goals, (2) terminology, (3) measurement practices, (4) data handling, and (5) the current state of theory and evidence. The other five steps focus on improving the credibility of empirical research, through (6) formal modelling, (7) mandatory pre-registration for confirmatory claims, (8) replication as a routine practice, (9) planning for informative studies (e.g., in terms of statistical power), and (10) making data, analysis scripts, and materials openly available. The current, quantity-based incentive structure in academia clearly stands in the way of implementing many of these practices, resulting in a research literature with sometimes questionable utility and/or integrity. As a solution, we propose a more quality-based reward scheme that explicitly weights published research by its Good Science merits. Scientists need to be increasingly rewarded for doing good work, not just lots of work

Super-poissonian noise, negative differential conductance, and relaxation effects in transport through molecules, quantum dots and nanotubes

We consider charge transport through a nanoscopic object, e.g. single molecules, short nanotubes, or quantum dots, that is weakly coupled to metallic electrodes. We account for several levels of the molecule/quantum dot with level-dependent coupling strengths, and allow for relaxation of the excited states. The current-voltage characteristics as well as the current noise are calculated within first-order perturbation expansion in the coupling strengths. For the case of asymmetric coupling to the leads we predict negative-differential-conductance accompanied with super-poissonian noise. Both effects are destroyed by fast relaxation processes. The non-monotonic behavior of the shot noise as a function of bias and relaxation rate reflects the details of the electronic structure and level-dependent coupling strengths.Comment: 8 pages, 7 figures, submitted to Phys. Rev. B, added reference

Flux measurements of biogenic VOCs during ECHO 2003

International audienceWithin the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany using the eddy covariance (EC) technique. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. As a consequence, a considerable fraction of the measurements did not qualify for flux calculations by EC and had to be discarded. The validated results show light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average emissions (normalised to 30°C and 1000 µmoles m?2 s?1 PAR) of 1.5 and 0.39 µg m?2 s?1, respectively. Emissions of methanol reached on average 0.087 µg m?2 s?1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. The observed fluxes are consistent with upscalings from leaf-level emission measurements of representative tree species in this forest and, in the case of MVK and MACR, can plausibly be explained by chemical production through oxidation of isoprene within the canopy. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement

Signals of slab breakoff- and tearing in the stratigraphic architecture of a foreland basin

A significant change in the architecture of peripheral pro-foreland basins observed in all natural examples is the flysch to molasse transition (i.e., shift from underfilled- to overfilled conditions). Forcing mechanisms for pro-foreland basin architecture include changes in sediment supply from the adjacent growing orogen and flexural subsidence in the basin. As these forcing mechanisms themselves are driven by orogenic processes in the adjacent mountain range, the flysch to molasse transition can be regarded as the sedimentary fingerprint of hinterland tectonics. Slab breakoff of the foreland plate leading to isostatic rebound of both the pro-foreland basin and adjacent orogen (leading to increased sediment supply) has been suggested to be a driver of the flysch to molasse transition. However, this cause-and-effect relationship between slab breakoff and the flysch to molasse transition is based on qualitative assessments. This raises the question whether other external forcings may have masked the contribution of slab breakoff to the flysch to molasse transition. In this study we investigate the stratigraphic signal of slab breakoff in a pro-foreland basin. To quantitatively assess the relationship between slab breakoff and the flysch to molasse transition, we coupled 2D geodynamic models (GMs) of slab breakoff using LaMEM with 2D forward stratigraphic modelling (FSM) using the GPM software (SLB). To better understand the influence of slab breakoff on pro-foreland basin architecture, we tested slab breakoff scenarios in our GMs for varying 1) slab bending angles and 2) slab necking durations (depending on slab rheology). To test whether the stratigraphic signal of slab breakoff may be masked by other external forcings, we introduced eustatic sea level changes (50 m amplitude with a 1 My period). From our FSMs we generated sediment thickness maps used to reconstruct sediment supply rates, grain size distribution- and facies maps and synthetic seismic data to compare with observed seismic data. Our preliminary results indicate that vertical uplift due to isostatic rebound in the pro-foreland basin (1.5 – 7 cm/yr, where fast necking of steep slabs yields higher values) decreases the accommodation space, leading to a stratigraphically upward shallowing. Furthermore, isostatic rebound of the adjacent mountain range (2-5 cm/yr, same relationship with slab dynamics as pro-foreland basin) results in up to 2.5x increased rates of sediment supply with very little lag time, adding to the stratigraphically upward shallowing. The eustatic sea level changes do not mask the stratigraphic signal of slab breakoff. Lastly, the facies of the flysch to molasse transition in our synthetic seismics looks similar to that observed on seismics of the Austrian Molasse which occurred coeval with slab breakoff under the Eastern Alps

Shot noise in tunneling transport through molecules and quantum dots

We consider electrical transport through single molecules coupled to metal electrodes via tunneling barriers. Approximating the molecule by the Anderson impurity model as the simplest model which includes Coulomb charging effects, we extend the ``orthodox'' theory to expand current and shot noise systematically order by order in the tunnel couplings. In particular, we show that a combined measurement of current and shot noise reveals detailed information of the system even in the weak-coupling limit, such as the ratio of the tunnel-coupling strengths of the molecule to the left and right electrode, and the presence of the Coulomb charging energy. Our analysis holds for single-level quantum dots as well.Comment: 8 page

An airborne regional carbon balance for central amazonia

We obtained regional estimates of surface CO2 exchange rates using atmospheric boundary layer budgeting techniques above tropical forest near Manaus, Brazil. Comparisons were made with simultaneous measurements from two eddy covariance towers below. Although there was good agreement for daytime measurements, large differences emerged for integrating periods dominated by the night-time fluxes. These results suggest that a systematic underestimation of night time respiratory effluxes may be responsible for the high Amazonian carbon sink suggested by several previous eddy covariance studies. Large CO2 fluxes from riverine sources or high respiratory losses from recently disturbed forests do not need to be invoked in order to balance the carbon budget of the Amazon. Our results do not, however, discount some contribution of these processes to the overall Amazon carbon budget