2,695 research outputs found
Entanglement and its Role in Shor's Algorithm
Entanglement has been termed a critical resource for quantum information
processing and is thought to be the reason that certain quantum algorithms,
such as Shor's factoring algorithm, can achieve exponentially better
performance than their classical counterparts. The nature of this resource is
still not fully understood: here we use numerical simulation to investigate how
entanglement between register qubits varies as Shor's algorithm is run on a
quantum computer. The shifting patterns in the entanglement are found to relate
to the choice of basis for the quantum Fourier transform.Comment: 15 pages, 4 eps figures, v1-3 were for conference proceedings (not
included in the end); v4 is improved following referee comments, expanded
explanations and added reference
Atmospheric, climatic and environmental research
Work performed on the three tasks during the report period is summarized. The climate and atmospheric modeling studies included work on climate model development and applications, paleoclimate studies, climate change applications, and SAGE II. Climate applications of Earth and planetary observations included studies on cloud climatology and planetary studies. Studies on the chemistry of the Earth and the environment are briefly described. Publications based on the above research are listed; two of these papers are included in the appendices
An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres
The nature of aerosols in hot exoplanet atmospheres is one of the primary
vexing questions facing the exoplanet field. The complex chemistry, multiple
formation pathways, and lack of easily identifiable spectral features
associated with aerosols make it especially challenging to constrain their key
properties. We propose a transmission spectroscopy technique to identify the
primary aerosol formation mechanism for the most highly irradiated hot Jupiters
(HIHJs). The technique is based on the expectation that the two key types of
aerosols -- photochemically generated hazes and equilibrium condensate clouds
-- are expected to form and persist in different regions of a highly irradiated
planet's atmosphere. Haze can only be produced on the permanent daysides of
tidally-locked hot Jupiters, and will be carried downwind by atmospheric
dynamics to the evening terminator (seen as the trailing limb during transit).
Clouds can only form in cooler regions on the night side and morning terminator
of HIHJs (seen as the leading limb during transit). Because opposite limbs are
expected to be impacted by different types of aerosols, ingress and egress
spectra, which primarily probe opposing sides of the planet, will reveal the
dominant aerosol formation mechanism. We show that the benchmark HIHJ,
WASP-121b, has a transmission spectrum consistent with partial aerosol coverage
and that ingress-egress spectroscopy would constrain the location and formation
mechanism of those aerosols. In general, using this diagnostic we find that
observations with JWST and potentially with HST should be able to distinguish
between clouds and haze for currently known HIHJs.Comment: 10 pages, 4 figures, accepted to ApJ Letter
Resonance bifurcations of robust heteroclinic networks
Robust heteroclinic cycles are known to change stability in resonance
bifurcations, which occur when an algebraic condition on the eigenvalues of the
system is satisfied and which typically result in the creation or destruction
of a long-period periodic orbit. Resonance bifurcations for heteroclinic
networks are more complicated because different subcycles in the network can
undergo resonance at different parameter values, but have, until now, not been
systematically studied. In this article we present the first investigation of
resonance bifurcations in heteroclinic networks. Specifically, we study two
heteroclinic networks in and consider the dynamics that occurs as
various subcycles in each network change stability. The two cases are
distinguished by whether or not one of the equilibria in the network has real
or complex contracting eigenvalues. We construct two-dimensional Poincare
return maps and use these to investigate the dynamics of trajectories near the
network. At least one equilibrium solution in each network has a
two-dimensional unstable manifold, and we use the technique developed in [18]
to keep track of all trajectories within these manifolds. In the case with real
eigenvalues, we show that the asymptotically stable network loses stability
first when one of two distinguished cycles in the network goes through
resonance and two or six periodic orbits appear. In the complex case, we show
that an infinite number of stable and unstable periodic orbits are created at
resonance, and these may coexist with a chaotic attractor. There is a further
resonance, for which the eigenvalue combination is a property of the entire
network, after which the periodic orbits which originated from the individual
resonances may interact. We illustrate some of our results with a numerical
example.Comment: 46 pages, 20 figures. Supplementary material (two animated gifs) can
be found on
http://www.maths.leeds.ac.uk/~alastair/papers/KPR_res_net_abs.htm
Structure of fish assemblages on coastal rocky shores of the Azores
Bol. Mus. Mun. Funchal, Sup. N.Âş 6: 127-138, 2001The structure of fish assemblages was investigated from the surface down to 25 m depth on Azorean rocky shores. A total of 57 fish species was recorded by visual censuses, most species (66%) occurring in the whole depth range studied. Fish abundance was dominated by 11 species, mainly sparids, labrids, carangids and pomacentrids, which constituted over 88% of the total number of individuals recorded. The trophic structure of the fish assemblages studied in the Azores was characterized by the dominance of benthic mesocarnivores and high proportions of herbivores and pelagic macrocarnivores.A estrutura das comunidades ictiolĂłgicas dos fundos rochosos dos Açores foi estudada desde a superfĂcie atĂ© aos 25 m de profundidade. Um total de 57 espĂ©cies de peixes foi identificado com recurso a censos visuais. A maioria das espĂ©cies (66%) ocorreu em toda a gama de profundidades estudada. A fauna ictiolĂłgica era dominada, em termos de abundância, por 11 espĂ©cies, principalmente pertencentes Ă s famĂlias Sparidae, Labridae, Carangidae e Pomacentridae, os quais constituĂram mais de 88% do nĂşmero total de indivĂduos observados. A estrutura trĂłfica das comunidades ictiolĂłgicas estudadas nos Açores apresentouse dominada por meso-carnĂvoros bentĂłnicos e proporções elevadas de herbĂvoros e macro-carnĂvoros pelágico
The effect of symmetry breaking on the dynamics near a structurally stable heteroclinic cycle between equilibria and a periodic orbit
The effect of small forced symmetry breaking on the dynamics near a structurally stable heteroclinic
cycle connecting two equilibria and a periodic orbit is investigated. This type of system is known
to exhibit complicated, possibly chaotic dynamics including irregular switching of sign of various
phase space variables, but details of the mechanisms underlying the complicated dynamics have
not previously been investigated. We identify global bifurcations that induce the onset of chaotic
dynamics and switching near a heteroclinic cycle of this type, and by construction and analysis
of approximate return maps, locate the global bifurcations in parameter space. We find there is a
threshold in the size of certain symmetry-breaking terms below which there can be no persistent
switching. Our results are illustrated by a numerical example
Preliminary results on production and calcification of coral reefs communities of Tikehau atoll
The carbon and oxygen metabolism of some coral reef communities of Tikehau atoll were studied in November 1989. Calcification, photosynthèse and respiration were measured during incubation experiments in transparent plastic bags. Over 24 hours period, we observed a net calcification rate for the three studied communities. However, only #Halimeda$ community presented an excess production. (Résumé d'auteur
Basic Parameter Estimation of Binary Neutron Star Systems by the Advanced LIGO/Virgo Network
Within the next five years, it is expected that the Advanced LIGO/Virgo
network will have reached a sensitivity sufficient to enable the routine
detection of gravitational waves. Beyond the initial detection, the scientific
promise of these instruments relies on the effectiveness of our physical
parameter estimation capabilities. The majority of this effort has been towards
the detection and characterization of gravitational waves from compact binary
coalescence, e.g. the coalescence of binary neutron stars. While several
previous studies have investigated the accuracy of parameter estimation with
advanced detectors, the majority have relied on approximation techniques such
as the Fisher Matrix. Here we report the statistical uncertainties that will be
achievable for optimal detection candidates (SNR = 20) using the full parameter
estimation machinery developed by the LIGO/Virgo Collaboration via Markov-Chain
Monte Carlo methods. We find the recovery of the individual masses to be
fractionally within 9% (15%) at the 68% (95%) credible intervals for equal-mass
systems, and within 1.9% (3.7%) for unequal-mass systems. We also find that the
Advanced LIGO/Virgo network will constrain the locations of binary neutron star
mergers to a median uncertainty of 5.1 deg^2 (13.5 deg^2) on the sky. This
region is improved to 2.3 deg^2 (6 deg^2) with the addition of the proposed
LIGO India detector to the network. We also report the average uncertainties on
the luminosity distances and orbital inclinations of ideal detection candidates
that can be achieved by different network configurations.Comment: Second version: 15 pages, 9 figures, accepted in Ap
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