Avian Communities of the Northern Mackenzie Mountains, Northwest Territories, Canada

Basic knowledge of the abundance and distribution of birds and their habitats and the relationships between them is limited for many parts of Arctic Canada, including montane regions. This information is important for conservation purposes as bird populations and habitats shift and as interest in development of northern areas increases. We characterized bird communities in the Mackenzie Mountains of the Northwest Territories by conducting point counts (n = 376) in June 2009 and 2010 and using community analysis metrics (multiple response permutation procedures, indicator species analysis, non-metric multidimensional scaling) to statistically and graphically describe bird data in six habitat types: coniferous forest, deciduous forest, shrub (short and tall), alpine tundra, and open water wetlands. Distinct habitats had significantly different bird communities, as shown by using multiple response permutation procedures (p < 0.005). Of 51 species, 32 had significant (p < 0.05) indicator values for one habitat type (n = 15) or groups of habitats (n = 17) in an indicator species analysis. The tall shrub habitat type had the most indicator species (six species) followed by alpine tundra (five species), then the combined conifer, deciduous, and wetland habitat group (four species) and the deciduous forest habitat types (three species). Species richness was highest in the tall shrub (n = 37), alpine (n = 30), and conifer and short shrub (n = 29) habitats. We also observed eight bird species not previously known to occur in the area, or which were outside published ranges. Our results highlight the variability in bird community composition between the major habitat types in the Mackenzie Mountains, serve as a baseline for future bird studies in the region, and underscore the need for more research in the area with impending anthropogenic changes.Pour de nombreuses parties de l’Arctique canadien, y compris les régions montagnardes, les connaissances de base portant sur l’abondance et la répartition des oiseaux et de leurs habitats, de même que sur leurs relations entre eux, sont restreintes. Ces renseignements revêtent de l’importance en matière de conservation, au moment où les habitats et les populations d’oiseaux changent et où l’on s’intéresse de plus en plus au développement des régions du nord. Nous avons caractérisé les communautés d’oiseaux des monts Mackenzie, dans les Territoires du Nord-Ouest, en effectuant des dénombrements ponctuels (n = 376) en juin 2009 et 2010 et en recourant à diverses mesures d’analyse des communautés (test de permutations multiples, analyse des espèces indicatrices, analyse multidimensionnelle non métrique) afin de décrire à l’aide de statistiques et de graphiques les données relatives aux oiseaux de six types d’habitats : forêts de conifères, forêts de feuillus, arbustaies (petits arbustes et grands arbustes), toundra alpine et terres humides avec étendues d’eaux libres. D’après les tests de permutations multiples (p < 0,005), les communautés d’oiseaux diffèrent considérablement en présence d’habitats distincts. L’analyse des espèces indicatrices a également permis de démontrer que parmi les 51 espèces, 32 avaient des valeurs indicatrices importantes (< 0,05) pour un type d’habitat (n = 15) ou des groupes d’habitats (n = 17). L’habitat des grands arbustes comptait le plus grand nombre d’espèces indicatrices (six espèces), suivi de la toundra alpine (cinq espèces), puis du groupe composé de la forêt de conifères, de la forêt de feuillus et des terres humides (quatre espèces), et de la forêt de feuillus (trois espèces). La richesse des espèces était plus grande dans les habitats des grands arbustes (n = 37), de la toundra alpine (n = 30) et des conifères et petits arbustes (n = 29). Nous avons également observé huit espèces d’oiseaux qui n’avaient jamais été répertoriées dans la région ou qui se trouvaient en dehors de leur parcours naturel. Nos résultats mettent en évidence la variabilité de la composition des communautés d’oiseaux dans les principaux types d’habitats des monts Mackenzie. Ils serviront également de référence aux autres études d’oiseaux qui seront effectuées dans la région, et font ressortir la nécessité de faire d’autres recherches dans la région à la lumière des changements anthropiques imminents

High speed single photon detection in the near-infrared

InGaAs avalanche photodiodes (APDs) are convenient for single photon detection in the near-infrared (NIR) including the fibre communication bands (1.31/1.55 $\mu$m). However, to suppress afterpulse noise due to trapped avalanche charge, they must be gated with MHz repetition frequencies, thereby severely limiting the count rate in NIR applications. Here we show gating frequencies for InGaAs-APDs well beyond 1 GHz. Using a self-differencing technique to sense much weaker avalanches, we reduce drastically afterpulse noise. At 1.25 GHz, we obtain a detection efficiency of 10.8% with an afterpulse probability of 6.16%. In addition, the detector features low jitter (55 ps) and a count rate of 100 MHz

The role of ion exchange in the passivation of In Zn P nanocrystals with ZnS

We have investigated the chemical state of In(Zn)P/ZnS core/shell nanocrystals (NCs) for color conversion applications using hard X-ray absorption spectroscopy (XAS) and photoluminescence excitation (PLE). Analyses of the edge energies as well as the X-ray absorption fine structure (XAFS) reveal that the Zn(2+) ions from ZnS remain in the shell while the S(2−) ions penetrate into the core at an early stage of the ZnS deposition. It is further demonstrated that for short growth times, the ZnS shell coverage on the core was incomplete, whereas the coverage improved gradually as the shell deposition time increased. Together with evidence from PLE spectra, where there is a strong indication of the presence of P vacancies, this suggests that the core-shell interface in the In(Zn)P/ZnS NCs are subject to substantial atomic exchanges and detailed models for the shell structure beyond simple layer coverage are needed. This substantial atomic exchange is very likely to be the reason for the improved photoluminescence behavior of the core-shell particles compare to In(Zn)P-only NCs as S can passivate the NCs surfaces

Spin-orbit coupling in interacting quasi-one-dimensional electron systems

We present a new model for the study of spin-orbit coupling in interacting quasi-one-dimensional systems and solve it exactly to find the spectral properties of such systems. We show that the combination of spin-orbit coupling and electron-electron interactions results in: the replacement of separate spin and charge excitations with two new kinds of bosonic mixed-spin-charge excitation, and a characteristic modification of the spectral function and single-particle density of states. Our results show how manipulation of the spin-orbit coupling, with external electric fields, can be used for the experimental determination of microscopic interaction parameters in quantum wires.Comment: 5 pages including 4 figures; RevTeX; to appear in Phys.Rev.Let

Metal-Insulator oscillations in a Two-dimensional Electron-Hole system

The electrical transport properties of a bipolar InAs/GaSb system have been studied in magnetic field. The resistivity oscillates between insulating and metallic behaviour while the quantum Hall effect shows a digital character oscillating from 0 to 1 conducatance quantum e^2/h. The insulating behaviour is attributed to the formation of a total energy gap in the system. A novel looped edge state picture is proposed associated with the appearance of a voltage between Hall probes which is symmetric on magnetic field reversal.Comment: 4 pages, 5 Postscript figures: revised versio

Measuring measurement

Measurement connects the world of quantum phenomena to the world of classical events. It plays both a passive role, observing quantum systems, and an active one, preparing quantum states and controlling them. Surprisingly - in the light of the central status of measurement in quantum mechanics - there is no general recipe for designing a detector that measures a given observable. Compounding this, the characterization of existing detectors is typically based on partial calibrations or elaborate models. Thus, experimental specification (i.e. tomography) of a detector is of fundamental and practical importance. Here, we present the realization of quantum detector tomography: we identify the optimal positive-operator-valued measure describing the detector, with no ancillary assumptions. This result completes the triad, state, process, and detector tomography, required to fully specify an experiment. We characterize an avalanche photodiode and a photon number resolving detector capable of detecting up to eight photons. This creates a new set of tools for accurately detecting and preparing non-classical light.Comment: 6 pages, 4 figures,see video abstract at http://www.quantiki.org/video_abstracts/0807244

Introduction to the Physics of Quantum Dots

Quantum dots contain only a few well-defined energy levels for electron and/or holes as a result of the confinement of charge in all three spatial dimensions. Here, we describe both the application of photoluminescence spectroscopy and transport measurements to the characterisation of quantum dots and the novel phenomena that they exhibit. These include the Coulomb blockade, single electron tunnelling and single photon detection. The impact of quantum dots on future electronics and directions for future research, such as in quantum computing and cryptography, are addressed