464 research outputs found
Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at IsfallsglaciÀren
Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small-scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor-relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close-range aerial photography of the foreland of IsfallsglaciĂ€ren, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2âcm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss-side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee-side flute. This is consistent with the lee-side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study
Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at IsfallsglaciÀren
Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small-scale fragile geomorphological
features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor-relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close-range aerial photography of the foreland of IsfallsglaciÀren, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2cm horizontal resolution were created from this photography
using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss-side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore,
the size of this boulder was found to strongly correlate with the width and relief of the lee-side flute. This is consistent with the lee-side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study
Landau-Ginzburg Description of Boundary Critical Phenomena in Two Dimensions
The Virasoro minimal models with boundary are described in the
Landau-Ginzburg theory by introducing a boundary potential, function of the
boundary field value. The ground state field configurations become non-trivial
and are found to obey the soliton equations. The conformal invariant boundary
conditions are characterized by the reparametrization-invariant data of the
boundary potential, that are the number and degeneracies of the stationary
points. The boundary renormalization group flows are obtained by varying the
boundary potential while keeping the bulk critical: they satisfy new selection
rules and correspond to real deformations of the Arnold simple singularities of
A_k type. The description of conformal boundary conditions in terms of boundary
potential and associated ground state solitons is extended to the N=2
supersymmetric case, finding agreement with the analysis of A-type boundaries
by Hori, Iqbal and Vafa.Comment: 42 pages, 13 figure
Resonances in radiative hyperon decays
The importance of resonances for the radiative hyperon decays is examined in
the framework of chiral perturbation theory. Low lying baryon resonances are
included into the effective theory and tree contributions to these decays are
calculated. We find significant contributions to both the parity-conserving and
parity-violating decay amplitudes and a large negative value for the asymmetry
parameter in polarized Sigma^+ -> p gamma is found, in agreement with the
experimental result alpha(p Sigma^+) = -0.76 +/- 0.08.Comment: 14 pages, 2 figure
Azimuthal correlation in DIS
We introduce the azimuthal correlation for the deep inelastic scattering
process. We present the QCD prediction to the level of next-to-leading log
resummation, matching to the fixed order prediction. We also estimate the
leading non-perturbative power correction. The observable is compared with the
energy-energy correlation in e+e- annihilation, on which it is modelled. The
effects of the resummation and of the leading power correction are both quite
large. It would therefore be particularly instructive to study this observable
experimentally.Comment: 33 pages, 4 figures, JHEP class included. One figure and some
clarifications adde
Geochemical analysis of bulk marine sediment by Inductively Coupled PlasmaâAtomic Emission Spectroscopy on board the JOIDES Resolution
Geochemical analyses on board the JOIDES Resolution have been enhanced with the addition of a Jobin-Yvon Ultrace inductively coupled plasma-atomic emission spectrometer (ICP-AES) as an upgrade from the previous X-ray fluorescence facility. During Leg 199, we sought to both challenge and utilize the capabilities of the ICP-AES in order to provide an extensive bulk-sediment geochemical database during the cruise. These near real-time analyses were then used to help characterize the recovered sedimentary sequences, calculate mass accumulation rates of the different sedimentary components, and assist with cruise and postcruise sampling requests. The general procedures, sample preparation techniques, and basic protocol for ICP-AES analyses on board ship are outlined by Murray et al. (2000) in Ocean Drilling Program Tech Note, 29. We expand on those concepts and offer suggestions for ICP-AES methodology, calibration by standard reference materials, data reduction procedures, and challenges that are specific to the analysis of bulk-sediment samples. During Leg 199, we employed an extensive bulk-sediment analytical program of ~600 samples of varying lithologies, thereby providing several opportunities for refinement of techniques. We also discuss some difficulties and challenges that were faced and suggest how to alleviate such occurrences for sedimentary chemical analyses during future legs
Multimode interferometry for entangling atoms in quantum networks
© 2019 IOP Publishing Ltd. We bring together a cavity-enhanced light-matter interface with a multimode interferometer (MMI) integrated onto a photonic chip and demonstrate the potential of such hybrid systems to tailor distributed entanglement in a quantum network. The MMI is operated with pairs of narrowband photons produced a priori deterministically from a single 87Rb atom strongly coupled to a high-finesse optical cavity. Non-classical coincidences between photon detection events show no loss of coherence when interfering pairs of these photons through the MMI in comparison to the two-photon visibility directly measured using Hong-Ou-Mandel interference on a beam splitter. This demonstrates the ability of integrated multimode circuits to mediate the entanglement of remote stationary nodes in a quantum network interlinked by photonic qubits
Wave decay on convex co-compact hyperbolic manifolds
For convex co-compact hyperbolic quotients X=\Gamma\backslash\hh^{n+1}, we
analyze the long-time asymptotic of the solution of the wave equation
with smooth compactly supported initial data . We show that, if
the Hausdorff dimension of the limit set is less than , then
u(t) = C_\delta(f) e^{(\delta-\ndemi)t} / \Gamma(\delta-n/2+1) +
e^{(\delta-\ndemi)t} R(t) where and
||R(t)||=\mc{O}(t^{-\infty}). We explain, in terms of conformal theory of the
conformal infinity of , the special cases \delta\in n/2-\nn where the
leading asymptotic term vanishes. In a second part, we show for all \eps>0
the existence of an infinite number of resonances (and thus zeros of Selberg
zeta function) in the strip \{-n\delta-\eps<\Re(\la)<\delta\}. As a byproduct
we obtain a lower bound on the remainder for generic initial data .Comment: 18 page
Chaos and the Quantum Phase Transition in the Dicke Model
We investigate the quantum chaotic properties of the Dicke Hamiltonian; a
quantum-optical model which describes a single-mode bosonic field interacting
with an ensemble of two-level atoms. This model exhibits a zero-temperature
quantum phase transition in the N \go \infty limit, which we describe exactly
in an effective Hamiltonian approach. We then numerically investigate the
system at finite and, by analysing the level statistics, we demonstrate
that the system undergoes a transition from quasi-integrability to quantum
chaotic, and that this transition is caused by the precursors of the quantum
phase-transition. Our considerations of the wavefunction indicate that this is
connected with a delocalisation of the system and the emergence of macroscopic
coherence. We also derive a semi-classical Dicke model, which exhibits
analogues of all the important features of the quantum model, such as the phase
transition and the concurrent onset of chaos.Comment: 51 pages, 15 figures, late
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