62 research outputs found
Radiocarbon dating of a raised beach at 10 m in the South Shetland Islands
Recently dated organic remains from the South Shetland Islands extend the absolute chronology for this area after deglaciation
The evolution of pebble size and shape in space and time
We propose a mathematical model which suggests that the two main geological
observations about shingle beaches, i.e. the emergence of predominant pebble
size ratios and strong segregation by size are interrelated. Our model is a
based on a system of ODEs called the box equations, describing the evolution of
pebble ratios. We derive these ODEs as a heuristic approximation of Bloore's
PDE describing collisional abrasion. While representing a radical
simplification of the latter, our system admits the inclusion of additional
terms related to frictional abrasion. We show that nontrivial attractors
(corresponding to predominant pebble size ratios) only exist in the presence of
friction. By interpreting our equations as a Markov process, we illustrate by
direct simulation that these attractors may only stabilized by the ongoing
segregation process.Comment: 22 pages, 8 figure
Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide
Access to the electron spin is at the heart of many protocols for integrated
and distributed quantum-information processing [1-4]. For instance, interfacing
the spin-state of an electron and a photon can be utilized to perform quantum
gates between photons [2,5] or to entangle remote spin states [6-9].
Ultimately, a quantum network of entangled spins constitutes a new paradigm in
quantum optics [1]. Towards this goal, an integrated spin-photon interface
would be a major leap forward. Here we demonstrate an efficient and optically
programmable interface between the spin of an electron in a quantum dot and
photons in a nanophotonic waveguide. The spin can be deterministically prepared
with a fidelity of 96\%. Subsequently the system is used to implement a
"single-spin photonic switch", where the spin state of the electron directs the
flow of photons through the waveguide. The spin-photon interface may enable
on-chip photon-photon gates [2], single-photon transistors [10], and efficient
photonic cluster state generation [11]
Morphological cells in the Ragusa littoral (Sicily, Italy)
Geomorphologic information, topographic maps
(dated 1967), aerial photographs (dated 1999 and 2008), and
spatial analysis procedures were used to investigate a 90 km
long coastal sector in South Sicily (Italy). Information was
obtained on coastal erosion/accretion areas, general sediment
circulation pattern and littoral cell distribution. Human-made
structures and natural headlands constituted important artificial
limits dividing littoral in morphological cells. Ports and
harbours were observed at Scoglitti, Punta Secca, Marina di
Ragusa, Donnalucata and Pozzallo. Most of them worked as
“transit” limits which interrupted predominant, eastward directed
sedimentary transport, this way generating accretion in
updrift (west) side of mentioned structures and erosion in
downdrift (east) side. During the 1967–2008 period, about
62,000 m2 and 42,000 m2 of beach surface were respectively
formed updrift of Scoglitti and Donnalucata ports. The construction
of Pozzallo port gave rise to the formation of a
“convergent” limit which favoured large accretion
(94,000 m2) east of port structure. Most important natural
structures were observed at Punta Zafaglione, P. Braccetto
and Cava d’Aliga. The knowledge of littoral cell distribution
acquires a great importance for appropriate management of
coastal erosion processes which may be mitigated installing
by-passing systems in ports and harbours and carrying out
nourishment works in eroding areas, often located downdrift
of ports and harbours (when these structures work as transit
limits) and in central part of littoral cells (when these structures
work as convergent limits)
Multi-wave coherent control of a solid-state single emitter
The authors acknowledge support by the European Research Council Starting Grant 'PICSEN' contract no. 306387.Coherent control of individual two-level systems (TLSs) is at the basis of any implementation of quantum information. An impressive level of control is now achieved using nuclear, vacancies and charge spins. Manipulation of bright exciton transitions in semiconductor quantum dots (QDs) is less advanced, principally due to the sub-nanosecond dephasing. Conversely, owing to their robust coupling to light, one can apply tools of nonlinear spectroscopy to achieve all-optical command. Here, we report on the coherent manipulation of an exciton via multi-wave mixing. Specifically, we employ three resonant pulses driving a single InAs QD. The first two induce a four-wave mixing (FWM) transient, which is projected onto a six-wave mixing (SWM) depending on the delay and area of the third pulse, in agreement with analytical predictions. Such a switch enables to demonstrate the generation of SWM on a single emitter and to engineer the spectro-temporal shape of the coherent response originating from a TLS. These results pave the way toward multi-pulse manipulations of solid state qubits via implementing the NMR-like control schemes in the optical domain.PostprintPeer reviewe
Simple model for linear and nonlinear mixing at unstable fluid interfaces with variable acceleration
Managing lakeshore erosion: impacts of bank protection on Loch Lomond, Scotland
The shoreline of Loch Lomond is currently undergoing erosion not only because of passive natural changes but also because of active changes produced by the interaction of shoreline protection structures and natural processes. In order to assess the influence of protection structures on different types of loch shore, the shores were classified and their total extent, including the extent of artificial shore, was quantified. The effect of structures is often felt on adjacent shores as well as on those that the structure is designed to protect. In order to assess the extent of impact of structures, sediment cells were identified along the loch shore within which the effects of a structure may produce compensatory effects but beyond which they will not. A management strategy is presented that is aimed at minimising the detrimental effects of any future intervention in the shore system
A Markov model for beach changes on the holderness coast of England
Markov models offer an objective and quantitative method of assessing beach changes. For a stretch of the Holderness coast a beach classification scheme was devised and a probabilistic first order matrix model based on surveyed profile data was produced. This could describe and predict transitions between beach types and between different time periods. Different profile types dominated different coastal locations and seasonal variations were seen. In order to improve the accuracy of prediction throughout the year a second, ‘winter’, model was added to the original ‘summer’ one. Although the models had been prepared independently of wave conditions, a comparison of the wave record and beach transitions revealed that waves under 0·3–0·5 m high produced fairly static beaches; when waves were between 0·5 and 1·0 m the beach was more dynamic and variable, while waves over 1·0 m led to the depletion of the upper beach. This was broadly in accordance with published theory. Markov models have the advantage that they can be adjusted periodically if conditions change, and are thus useful for prediction on coasts for which no wave records exist
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