17,677 research outputs found
Preliminary results on two-dimensional interferometry of HL Tau
Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime
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Patterns of contribution to citizen science biodiversity projects increase understanding of volunteers’ recording behaviour
The often opportunistic nature of biological recording via citizen science leads to taxonomic, spatial and temporal biases which add uncertainty to biodiversity estimates. However, such biases may also give valuable insight into volunteers’ recording behaviour. Using Greater London as a case-study we examined the composition of three citizen science datasets – from Greenspace Information for Greater London CIC, iSpot and iRecord - with respect to recorder contribution and spatial and taxonomic biases, i.e. when, where and what volunteers record. We found most volunteers contributed few records and were active for just one day. Each dataset had its own taxonomic and spatial signature suggesting that volunteers’ personal recording preferences may attract them towards particular schemes. There were also patterns across datasets: species’ abundance and ease of identification were positively associated with number of records, as was plant height. We found clear hotspots of recording activity, the 10 most popular sites containing open water. We note that biases are accrued as part of the recording process (e.g. species’ detectability) as well as from volunteer preferences. An increased understanding of volunteer behaviour gained from analysing the composition of records could thus enhance the fit between volunteers’ interests and the needs of scientific projects
Noncommutative Field Theory and Lorentz Violation
The role of Lorentz symmetry in noncommutative field theory is considered.
Any realistic noncommutative theory is found to be physically equivalent to a
subset of a general Lorentz-violating standard-model extension involving
ordinary fields. Some theoretical consequences are discussed. Existing
experiments bound the scale of the noncommutativity parameter to (10 TeV)^{-2}.Comment: 4 page
The changing international network of sovereign debt and financial institutions
We develop a theoretical and empirical framework for the connections between global financial and sovereign CDS markets. The transmission of shocks is shown to affect the systemic default probability of the international network. The network is found to be "robust but fragile", meaning that a shock can result in the propagation of crises. Between 2003 and 2013, the probability of default in the network in the face of potentially poor investment outcomes and/or sovereign bond haircuts changes sub-stantially. The results suggest that it is the interconnectedness of the financial and sovereign debt markets that provides increased protection against financial fragility
Comparison of prediction methods and studies of relaxation in hypersonic turbulent nozzle-wall boundary layers
Turbulent boundary layer measurements on axisymmetric hypersonic nozzle wall
Electrometry Using Coherent Exchange Oscillations in a Singlet-Triplet-Qubit
Two level systems that can be reliably controlled and measured hold promise
in both metrology and as qubits for quantum information science (QIS). When
prepared in a superposition of two states and allowed to evolve freely, the
state of the system precesses with a frequency proportional to the splitting
between the states. In QIS,this precession forms the basis for universal
control of the qubit,and in metrology the frequency of the precession provides
a sensitive measurement of the splitting. However, on a timescale of the
coherence time, , the qubit loses its quantum information due to
interactions with its noisy environment, causing qubit oscillations to decay
and setting a limit on the fidelity of quantum control and the precision of
qubit-based measurements. Understanding how the qubit couples to its
environment and the dynamics of the noise in the environment are therefore key
to effective QIS experiments and metrology. Here we show measurements of the
level splitting and dephasing due to voltage noise of a GaAs singlet-triplet
qubit during exchange oscillations. Using free evolution and Hahn echo
experiments we probe the low frequency and high frequency environmental
fluctuations, respectively. The measured fluctuations at high frequencies are
small, allowing the qubit to be used as a charge sensor with a sensitivity of
, two orders of magnitude better than
the quantum limit for an RF single electron transistor (RF-SET). We find that
the dephasing is due to non-Markovian voltage fluctuations in both regimes and
exhibits an unexpected temperature dependence. Based on these measurements we
provide recommendations for improving in future experiments, allowing for
higher fidelity operations and improved charge sensitivity
Effect of Light Fermions on the Confinement Transition in QCD-like Theories
Dependence of the confinement transition parameters on the fermion content
provides information on the mechanism of confinement. Recent progress in
lattice gauge theories has allowed to study it for light flavor number and found this transition to shift toward significantly stronger
coupling. We propose an explanation for that: light fermions can occupy the
chromo-magnetic monopoles, via zero modes, making them "distinguishable" and
unsuitable for Bose-Einstein Condensation. Such dilution of unoccuplied
monopoles is compensated by stronger coupling that makes them lighter and more
numerous. We also suggest that flavor-carrying quark-monopole objects account
for the density beyond quark Fermi sphere seen in cold dense phase of
lattice QCD.Comment: 4 pages, 1 figure; few references added; close to the final published
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