20,762 research outputs found
Sea-level change and storm surges in the context of climate change
This paper reviews the latest research in New Zealand surrounding the issues of sea-level rise and extreme sea levels in the context of global warming and variability in the Pacific-wide El Ninoâ Southern Oscillation (ENSO). Past records of climate, sea level (excluding tides) and sea and air temperatures have shown that they are continuously fluctuating over various long-term timescales of years, decades and centuries. This has made it very difficult to determine whether the anthropogenic
effects such as increased levels of âgreenhouseâ gases are having an accelerating effect on global sea levels or an increased incidence of extreme storms. Over the past century, global sea level has risen by 10â25 cm, and is in line with the rise in relative sea level at New Zealandâs main ports of +1.7 mm yr â1. What has become very clear is the need to better understand interannual (year-to-year) and decadal variability in sea-level, as these larger signals of the order of 5â15 cm in annual-mean sea level have a significant âflow-onâ effect on the long-term trend in sea level. The paper describes sea level variability in northern New Zealandâboth long- and short-termâinvolved in assessing the regional trends in sea level. The paper also discusses the relative contributions of tides, barometric pressure and wind set-up in causing extreme sea levels during storm surges. Some recent research also looked at a related questionâIs there any sign of increased storminess, and hence storm surge, in northern New Zealand due to climate change? The paper concludes that, while no one can be completely sure how sea-level and the degree of storminess will respond in the near future, what is clear is that interannual and decadal variability in sea level is
inextricably linked with Pacific-wide ENSO response and longer inter-decadal shifts in the Pacific climate regime, such as the latest shift in 1976
Single-spin magnetometry with multi-pulse sensing sequences
We experimentally demonstrate single-spin magnetometry with multi-pulse
sensing sequences. The use of multi-pulse sequences can greatly increase the
sensing time per measurement shot, resulting in enhanced ac magnetic field
sensitivity. We theoretically derive and experimentally verify the optimal
number of sensing cycles, for which the effects of decoherence and increased
sensing time are balanced. We perform these experiments for oscillating
magnetic fields with fixed phase as well as for fields with random phase.
Finally, by varying the phase and frequency of the ac magnetic field, we
measure the full frequency-filtering characteristics of different multi-pulse
schemes and discuss their use in magnetometry applications.Comment: 4 pages, 4 figures. Final versio
Volcanic Generation of Tsunamis: Two New Zealand Palaeo-Events
Rapid emplacement of a mass via pyroclastic flows, or edifice failure, generates volcanic tsunamis. Physical modelling demonstrates that the efficiency of tsuna-mi generation is influenced by the angle the mass enters the ocean. Efficiency de-creases with increasing slope angle from 20° to 60°, before increasing to a maxi-mum at 90°, which corresponds to a mass falling directly into the ocean without interacting with the slope (impact tsunami). Further, in the case of surging pyro-clastic flows or regressive failures, successive closely spaced events may generate larger tsunami waves than a single event of comparable volume.
It is difficult to assess if physical model results are meaningful for real world tsu-nami events due to limited observational data. This paper compares numerical models developed from physical simulations with palaeotsunami deposits from two New Zealand palaeo-events â pyroclastic flows from Mt Tarawera and edi-fice failure at Whakaari (White Island) â which constrains numerical simulations of the source mechanisms. The Mt Tarawera event involved multiple pyroclastic flows entering a lake during the AD 1314±12 Kaharoa Eruption. The interaction of multiple closely spaced pyroclastic flows is necessary to generate the 6-7 m maximum wave height inferred from near source tsunami deposits. Tsunami de-posits in the Bay of Plenty, dated to 2962±52 BP, are consistent with edifice fail-ure at Whakaari. In this case a single event with a volume of 0.23 km3 is suffi-cient to account for the tsunami deposits. Hence, if the failure was regressive, the successive stages were sufficiently close together to be indistinguishable from a large single event
Nanopositioning of a diamond nanocrystal containing a single NV defect center
Precise control over the position of a single quantum object is important for
many experiments in quantum science and nanotechnology. We report on a
technique for high-accuracy positioning of individual diamond nanocrystals. The
positioning is done with a home-built nanomanipulator under real-time scanning
electron imaging, yielding an accuracy of a few nanometers. This technique is
applied to pick up, move and position a single NV defect center contained in a
diamond nanocrystal. We verify that the unique optical and spin properties of
the NV center are conserved by the positioning process.Comment: 3 pages, 3 figures; high-resolution version available at
http://www.ns.tudelft.nl/q
Entanglement genesis by ancilla-based parity measurement in 2D circuit QED
We present an indirect two-qubit parity meter in planar circuit quantum
electrodynamics, realized by discrete interaction with an ancilla and a
subsequent projective ancilla measurement with a dedicated, dispersively
coupled resonator. Quantum process tomography and successful entanglement by
measurement demonstrate that the meter is intrinsically quantum non-demolition.
Separate interaction and measurement steps allow commencing subsequent data
qubit operations in parallel with ancilla measurement, offering time savings
over continuous schemes.Comment: 5 pages, 4 figures; supplemental material with 5 figure
Reversing quantum trajectories with analog feedback
We demonstrate the active suppression of transmon qubit dephasing induced by
dispersive measurement, using parametric amplification and analog feedback. By
real-time processing of the homodyne record, the feedback controller reverts
the stochastic quantum phase kick imparted by the measurement on the qubit. The
feedback operation matches a model of quantum trajectories with measurement
efficiency , consistent with the result obtained by
postselection. We overcome the bandwidth limitations of the amplification chain
by numerically optimizing the signal processing in the feedback loop and
provide a theoretical model explaining the optimization result.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures
Theory of pinning in a Superconducting Thin Film Pierced by a Ferromagnetic Columnar Defect
This is an analytical study of pinning and spontaneous vortex phase is a
system consisting of a superconducting thin film pierced by a long
ferromagnetic columnar defect of finite radius . The magnetic fields,
screening currents, energy and pinning forces for this system are calculated.
The interaction between the magnetic field of vortices and the magnetization
outside the plane of the film and its close proximity enhances vortex pinning
significantly. Spontaneous vortex phase appears when the magnetization of the
columnar defect is increased above a critical value. Transitions between phases
characterized by different number of flux quanta are also studied. These
results are generalized to the case when the superconductor is pierced by an
array of columnar defects.Comment: 6 pages, 4 figures, Accepted for publication in Phys. Rev.
Bootstrap tomography of high-precision pulses for quantum control
Long-time dynamical decoupling and quantum control of qubits require
high-precision control pulses. Full characterization (quantum tomography) of
imperfect pulses presents a bootstrap problem: tomography requires initial
states of a qubit which can not be prepared without imperfect pulses. We
present a protocol for pulse error analysis, specifically tailored for a wide
range of the single solid-state electron spins. Using a single electron spin of
a nitrogen-vacancy (NV) center in diamond, we experimentally verify the
correctness of the protocol, and demonstrate its usefulness for quantum control
tasks
Strategic manoeuvres and impression management: communication approaches in the case of a crisis event
This historical study examines the actions of the Australian former asbestos company, James Hardie, when faced with a potentially ruinous corporate scandal between 2001 and 2007. The company became vilified as public awareness grew of the damage to public health its use of asbestos had caused. In response, it set- up a knowingly underfunded compensation fund supported by a strategy of misinformation and denial. Its actions are analysed using Oliverâs typology of strategic responses and theories of crisis management and crisis communications, providing insights into the companyâs motivations for adopting strategies that took it to the brink of financial collaps
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