Light-emitting current of electrically driven single-photon sources

The time-dependent tunnelling current arising from the electron-hole recombination of exciton state is theoretically studied using the nonequilibrium Green's function technique and the Anderson model with two energy levels. The charge conservation and gauge invariance are satisfied in the tunnelling current. Apart from the classical capacitive charging and discharging behavior, interesting oscillations superimpose on the tunnelling current for the applied rectangular pulse voltage.Comment: 14 pages, 5 figure

Extreme morphologies of mantis shrimp larvae

Larvae of stomatopods (mantis shrimps) are generally categorized into four larval types: antizoea, pseudozoea (both representing early larval stages), alima and erichthus (the latter two representing later larval stages). These categories, however, do not reflect the existing morphological diversity of stomatopod larvae, which is largely unstudied. We describe here four previously unknown larval types with extreme morphologies. All specimens were found in the collections of the Zoological Museum, University of Copenhagen and were collected during the Danish Dana Expedition round the world 1928-30. These new larval types all represent erichthus-type larvae, especially differing in their shield morphologies. The shield morphology ranges from almost spherical to rather disc-like, with sometimes extremely elongated spines, but only a general systematic assignment of the larvae was possible. Further investigations of these larvae are crucial to understand their life habits and ecological impact, especially as stomatopod and other crustacean larvae might have a much more important position in the marine ecosystems than their corresponding adults

Untangling the Gordian knot — further resolving the super-species complex of 300-million-year-old xiphosurids by reconstructing their ontogeny

The group Xiphosurida (horseshoe “crabs”) is today only represented by four species. However, in the fossil record, several dozen species have been described, especially from the Carboniferous (about 300 million years ago). Several species have been interpreted as representatives of Euproops or Belinurus, but there is ongoing discussion which of these species are valid and how they can be differentiated. Recent studies suggested that differences in the timing of individual development could provide information for species distinction, exemplified by studies on Euproops danae (Mazon Creek, USA) and Euproops sp. (“Piesproops”; Piesberg, Germany). For this study, we reinvestigated all Carboniferous xiphosurids from the British Coal Measures stored in the collections of the Natural History Museum London. Size comparisons of the specimens revealed nine size groups; the smaller specimens were originally labelled as Belinurus, the larger ones as Euproops. The nine size groups exhibit five different morphotypes differing in structures surrounding the posterior shield (= thoracetron): spines of different lengths and, in larger specimens, a more or less developed flange. Two of these morphotypes show significantly longer spines than the remaining specimens and could be conspecific as E. anthrax. The remaining specimens are interpreted as growth series of another species, presumably of E. rotundatus. An ontogenetic flange formation is also known from E. danae and the “Piesproops”, but the timing differs between all three species. In E. rotundatus, the flange develops rather late, but then comparably abruptly, which makes this development more metamorphic in relation to development in the other species

YET ANOTHER UNUSUAL NEW TYPE OF LACEWING LARVA PRESERVED IN 100-MILLION-YEAR OLD AMBER FROM MYANMAR

Lacewing larvae are mostly predatory, highly mobile larval forms of Insecta. The modern fauna yields several morphotypes of lacewing larvae, each closely associated with a distinct evolutionary lineage within the group of lacewings, Neuroptera. Back in the Cretaceous, about 100 million years ago, many of these larval forms had already evolved. Additionally, many larval forms seem to have been present that are now extinct. We report here a new form, which appears to be extinct now. This new larva has a prominent forward projecting labrum like larval forms of Nevrorthidae and Psychopsidae. It furthermore has (again similar to the latter two) curved venom-injecting stylets formed by mandibles and maxillae. We used quantitative outline analysis to compare the new larva to those of Nevrorthidae and Psychopsidae. The results of this analysis demonstrate that the new larva differs in all aspects of head capsule shape from all known larvae of Nevrorthidae. Its head shape is more similar to that of many larvae of Psychopsidae, yet also here the new larva differs recognisably in one principal component. Also qualitative differences clearly differentiate the new larva from already known ones. Hence, the new larva represents a new, so far unknown morphotype of lacewing larva. This finding adds to the growing 'zoo' of unusual lacewing larvae back in the Cretaceous, indicating that form diversity and ecological diversity of lacewings were much higher 100 million years ago

Há estilos de artes marciais que representam sistemas naturais?

For didactics, systematically structured teaching contents are desirable, and natural systems would be most comprehensible. We tested whether serrada-escrima styles (SES), a type of Filipino martial arts, represent a natural system. Natural systems are considered to have an inner coherence. This means that based on some elements of the system the other elements can be predicted, based on knowledge of the characteristics of the elements of the system. SES is a good candidate to test this hypothesis, as it embraces only a relatively small set of techniques. It appears that SES indeed represents a natural, coherent system with 12 elements that can be grouped into three also coherent sets, each with four techniques. One basic pre-assumption is necessary to make SES a natural system; this pre-assumption is derived from knowledge of medieval European sword fighting, more precisely Messerfechten. We furthermore discuss indications for the historic background of SES.A efectos didácticos, son deseables los contenidos de enseñanza estructurados sistemáticamente, y los sistemas naturales serían los más comprensibles. Hemos puesto a prueba si la serrada escrima (SES), un tipo de arte marcial filipina, representan un sistema natural. Se considera que los sistemas naturales tienen una coherencia interna. Esto significa que partiendo de algunos elementos del sistema pueden llegar a predecirse otros, basándose en el conocimiento de las características de los elementos del sistema. La SES es una buena candidata para probar esta hipótesis, ya que solo abarca un conjunto relativamente pequeño de técnicas. Parece que la SES, de hecho, representa un sistema natural y coherente con doce elementos que pueden ser agrupados en tres conjuntos también coherentes, cada uno compuesto de cuatro técnicas. Para hacer de la SES un sistema natural es necesario asumir un supuesto a priori; este pre-supuesto se deriva del conocimiento del combate con espada medieval europeo, concretamente del Messerfechten. Este trabajo discute además algunos aspectos históricos de la SES.Aos efeitos didácticos, são desejáveis os conteúdos de ensino estruturados sistematicamente. Tendo isso como base, os sistemas naturais seriam mais compreensivos. Colocámos à prova a serrada escrima (SES), um tipo de arte marcial filipina, representando um sistema natural. Considera-se que os sistemas naturais têm uma coerência interna. Isto significa que, partindo de alguns elementos do sistema, se pode chegar a se prever outros, baseando-se no conhecimento das características dos elementos do sistema. A SES é uma boa candidata para se comprovar esta hipótese, na medida que ela abrange um conjunto relativamente pequeno de técnicas. Parece que a SES, de facto, representa um sistema natural e coerente com doze elementos que podem ser agrupados em três conjuntos também coerentes, cada um composto de quatro técnicas. Para se fazer da SES um sistema natural, é necessário assumir um pressuposto prévio. Este pressuposto prévio deriva do conhecimento do combate com espada medieval europeu, particularmente o Messerfechten. Este trabalho discute também alguns aspectos históricos da SES

100 Million-year-old straight-jawed lacewing larvae with enormously inflated trunks represent the oldest cases of extreme physogastry in insects

Physogastry is a phenomenon occurring in Euarthropoda and describes an extreme inflation of (parts of) the trunk. It is best known from ticks, termite queens, or honey-pot ants, but can also be found in several other representatives of Euarthropoda. Physogastry has so far rarely been seen in the fossil record. We describe here an example of physogastry in two lacewing larvae (Neuroptera) enclosed in a single piece of Kachin amber (ca. 100 Ma old). We measured head and trunk ratios of different physogastric and non-physogastric representatives of Euarthropoda. Plotting these ratios shows that the new larvae, which display quite extremely inflated trunks, are very similar to ticks or honey-pot ants, but also to certain lacewing larvae of the group Berothidae (beaded lacewings). Outline analysis of head capsule and mouthparts (stylets) further suggests a position within Berothidae. Physogastry is presumed to be linked with living in confined spaces such as wood galleries or soil. Indeed, at least some larvae of Berothidae are known to live inside termite nests for part of their larval life phase, a habit the new larvae may also have had. The new record represents the oldest case of extreme physogastry in insects known to date

Photon heat transport in low-dimensional nanostructures

At low temperatures when the phonon modes are effectively frozen, photon transport is the dominating mechanism of thermal relaxation in metallic systems. Starting from a microscopic many-body Hamiltonian, we develop a nonequilibrium Green's function method to study energy transport by photons in nanostructures. A formally exact expression for the energy current between a metallic island and a one-dimensional electromagnetic field is obtained. From this expression we derive the quantized thermal conductance as well as show how the results can be generalized to nonequilibrium situations. Generally, the frequency-dependent current noise of the island electrons determines the energy transfer rate.Comment: 4 pages, 3 Fig

Meservey-Tedrow-Fulde effect in a quantum dot embedded between metallic and superconducting electrodes

Magnetic field applied to the quantum dot coupled between one metallic and one superconducting electrode can produce a similar effect as has been experimentally observed by Meservey, Tedrow and Fulde [Phys. Rev. Lett. 25, 1270 (1970)] for the planar normal metal -- superconductor junctions. We investigate the tunneling current and show that indeed the square root singularities of differential conductance exhibit the Zeeman splitting near the gap edge features V = +/- Delta/e. Since magnetic field affects also the in-gap states of quantum dot it furthermore imposes a hyperfine structure on the anomalous (subgap) Andreev current which has a crucial importance for a signature of the Kondo resonance.Comment: 7 pages, 8 figure

Noise at a Fermi-edge singularity

We present noise measurements of self-assembled InAs quantum dots at high magnetic fields. In comparison to I-V characteristics at zero magnetic field we notice a strong current overshoot which is due to a Fermi-edge singularity. We observe an enhanced suppression in the shot noise power simultaneous to the current overshoot which is attributed to the electron-electron interaction in the Fermi-edge singularity