38,226 research outputs found
Absolute instabilities of travelling wave solutions in a Keller-Segel model
We investigate the spectral stability of travelling wave solutions in a
Keller-Segel model of bacterial chemotaxis with a logarithmic chemosensitivity
function and a constant, sublinear, and linear consumption rate. Linearising
around the travelling wave solutions, we locate the essential and absolute
spectrum of the associated linear operators and find that all travelling wave
solutions have essential spectrum in the right half plane. However, we show
that in the case of constant or sublinear consumption there exists a range of
parameters such that the absolute spectrum is contained in the open left half
plane and the essential spectrum can thus be weighted into the open left half
plane. For the constant and sublinear consumption rate models we also determine
critical parameter values for which the absolute spectrum crosses into the
right half plane, indicating the onset of an absolute instability of the
travelling wave solution. We observe that this crossing always occurs off of
the real axis
The climatology, propagation and excitation of ultra-fast Kelvin waves as observed by meteor radar, Aura MLS, TRMM and in the Kyushu-GCM
Wind measurements from a meteor radar on Ascension Island (8&deg; S, 14&deg; W) and simultaneous temperature measurements from the Aura MLS instrument are used to characterise ultra-fast Kelvin waves (UFKW) of zonal wavenumber 1 (E1) in the mesosphere and lower thermosphere (MLT) in the years 2005–2010. These observations are compared with some predictions of the Kyushu-general circulation model. Good agreement is found between observations of the UFKW in the winds and temperatures, and also with the properties of the waves in the Kyushu-GCM. UFKW are found at periods between 2.5–4.5 days with amplitudes of up to 40 m s<sup>−1</sup> in the zonal winds and 6 K in the temperatures. The average vertical wavelength is found to be 44 km. Amplitudes vary with latitude in a Gaussian manner with the maxima centred over the equator. Dissipation of the waves results in monthly-mean eastward accelerations of 0.2–0.9 m s<sup>−1</sup> day<sup>−1</sup> at heights around 95 km, with 5-day mean peak values of 4 m s<sup>−1</sup> day<sup>−1</sup>. Largest wave amplitudes and variances are observed over Indonesia and central Africa and may be a result of very strong moist convective heating over those regions. Rainfall data from TRMM are used as a proxy for latent-heat release in an investigation of the excitation of these waves. No strong correlation is found between the occurrence of large-amplitude mesospheric UFKW events and either the magnitude of the equatorial rainfall or the amplitudes of E1 signatures in the rainfall time series, indicating that either other sources or the propagation environment are more important in determining the amplitude of UFKW in the MLT. A strong semiannual variation in wave amplitudes is observed. Intraseasonal oscillations (ISOs) with periods 25–60 days are evident in the zonal background winds, zonal-mean temperature, UFKW amplitudes, UFKW accelerations and the rainfall rate. This suggests that UFKW play a role in carrying the signature of tropospheric ISOs to the MLT region
Review of Solar Neutrino Experiments
This paper reviews the constraints on the solar neutrino mixing parameters
with data collected by the Homestake, SAGE, GALLEX, Kamiokande,
SuperKamiokande, and SNO experiments. An emphasis will be given to the global
solar neutrino analyses in terms of matter-enhanced oscillation of two active
flavors. The results to-date, including both solar model dependent and
independent measurements, indicate that electron neutrinos are changing to
other active types on route to the Earth from the Sun. The total flux of solar
neutrinos is found to be in very good agreement with solar model calculations.
Future measurements will focus on greater accuracy for mixing parameters and on
better sensitivity to low neutrino energies.Comment: Prepared for the XXI International Symposium on Lepton and Photon
Interactions at High Energies, Fermilab, USA, 11-16 August 200
Semi-Empirical Bound on the Chlorinr-37 Solar Neutrino Experiment
The Kamiokande measurement of energetic Boron-8 neutrinos from the sun is
used to set a lower bound on the contribution of the same neutrinos to the
signal in the \Chlorine\ experiment. Implications for Beryllium-7 neutrinos are
discussed.Comment: Latex, 6 pages + 1 postscript figure (included). UTAPHY-HEP-
Compliance within a regulatory framework in implementing public road construction projects
© 2018 by the author(s). The construction industry faces a lack of compliance with policy that in Uganda public road construction projects affects the attainment of Government goals and disrupts infrastructure project delivery. For decades, public entities have been known for a lack of compliance that manifest in: poor performance, poor personnel management, poor resource utilization and unprofessionalism. In Uganda, this has resulted in several restructures aimed at improving service delivery. Despite this, compliance remains an issue. The purpose of this study is to establish factors affecting compliance within a public procurement regulatory framework in public road construction projects and foster economic development. A cross-sectional research design including a structured self-administered questionnaire survey and PLS-SEM data analysis by SmartPLS3 was conducted. The research reveals that three factors positively affect compliance with a regulatory framework that govern public road construction projects; sanctions on staff, inefficiency of the public procurement regulatory framework and contractors’ resistance to non-compliance. While a further three factors have little positive effect on compliance; familiarity, monitoring activities and professionalism. Hence, the research contributes to construction management by showing that sanctions, perceived inefficiency and contractors’ resistance significantly enhance compliance within a public procurement regulatory framework
Analysis of the EPSRC Principles of Robotics in regard to key research topics
© 2017 Informa UK Limited, trading as Taylor & Francis Group. In this paper, we review the five rules published in EPSRC Principles of Robotics with a specific focus on future robotics research topics. It is demonstrated through a pictorial representation of the five rules that these rules are questionably not sufficient, overlapping and not explicitly reflecting the true challenges of robotics ethics in relation to the future of robotics research
Do Solar Neutrino Experiments Imply New Physics?
None of the 1000 solar models in a full Monte Carlo simulation is consistent
with the results of the chlorine or the Kamiokande experiments. Even if the
solar models are forced artifically to have a \b8 neutrino flux in agreeement
with the Kamiokande experiment, none of the fudged models agrees with the
chlorine observations. The GALLEX and SAGE experiments, which currently have
large statistical uncertainties, differ from the predictions of the standard
solar model by and , respectively.Comment: 7 pages (figures not included), Institute for Advanced Study number
AST 92/51. For a hard copy with the figures, write: [email protected]
Truncated Cauchy Non-Negative Matrix Factorization
© 1979-2012 IEEE. Non-negative matrix factorization (NMF) minimizes the euclidean distance between the data matrix and its low rank approximation, and it fails when applied to corrupted data because the loss function is sensitive to outliers. In this paper, we propose a Truncated CauchyNMF loss that handle outliers by truncating large errors, and develop a Truncated CauchyNMF to robustly learn the subspace on noisy datasets contaminated by outliers. We theoretically analyze the robustness of Truncated CauchyNMF comparing with the competing models and theoretically prove that Truncated CauchyNMF has a generalization bound which converges at a rate of order where is the sample size. We evaluate Truncated CauchyNMF by image clustering on both simulated and real datasets. The experimental results on the datasets containing gross corruptions validate the effectiveness and robustness of Truncated CauchyNMF for learning robust subspaces
A new topological aspect of the arbitrary dimensional topological defects
We present a new generalized topological current in terms of the order
parameter field to describe the arbitrary dimensional topological
defects. By virtue of the -mapping method, we show that the topological
defects are generated from the zero points of the order parameter field , and the topological charges of these topological defects are topological
quantized in terms of the Hopf indices and Brouwer degrees of -mapping
under the condition that the Jacobian . When , it is shown that there exist the crucial case of branch process.
Based on the implicit function theorem and the Taylor expansion, we detail the
bifurcation of generalized topological current and find different directions of
the bifurcation. The arbitrary dimensional topological defects are found
splitting or merging at the degenerate point of field function but
the total charge of the topological defects is still unchanged.Comment: 24 pages, 10 figures, Revte
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