Phytographia canariensis / par P. Barker-Webb et Sabin Berthelot.

Berthelot, Sabin; Montagne, Camille; Webb, Philip Barker

doi:10.5962/bhl.title.41386

Cited by 13 publications

(15 citation statements)

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“…According to Ref. [16], n * should point towards right ascension 17.3 ± 0.6 hours and declination −61 ± 9 deg. (b) On a constant time hypersurface, the wall cross our Hubble horizon so that the fine structure constant takes 2 values: α+ in our neighborhood and α− on the other side of the wall.…”

Section: Fig 1: (A)mentioning

confidence: 95%

“…This could give rise to a dipolar modulation of the constants if the observer (us) is not located at the center of the universe. Such a cosmological dipole should also reflect itself on other cosmological observations such as the cosmic microwave background (CMB) anisotropies, which does not seem to match with the required dipole in α [16,17]. Note also that such large scale deviations from homogeneity are constrained observationally [22].…”

Section: Pacs Numbersmentioning

confidence: 95%

“…However, there have been a series of recent puzzling observational results. First, the combined positive Keck/Hires and negative VLT results for a change in α could be interpreted as a dipole in the spatial distribution of α [16][17][18]. Then, it has also been claimed that the ratio m p /m e has a small spatial variation in the Milky Way [19].…”

Section: Pacs Numbersmentioning

confidence: 99%

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Wall of fundamental constants

2011

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We consider the signatures of a domain wall produced in the spontaneous symmetry breaking involving a dilaton-like scalar field coupled to electromagnetism. Domains on either side of the wall exhibit slight differences in their respective values of the fine-structure constant, α. If such a wall is present within our Hubble volume, absorption spectra at large redshifts may or may not provide a variation in α relative to the terrestrial value, depending on our relative position with respect to the wall. This wall could resolve the "contradiction" between claims of a variation of α based on Keck/Hires data and of the constancy of α based on VLT data. We derive the properties of the wall and the parameters of the underlying microscopic model required to reproduce the possible spatial variation of α. We discuss the constraints on the existence of the low-energy domain wall and describe its observational implications concerning the variation of the fundamental constants. PACS numbers:There are very few observations which can be directly and unambiguously related to new physics. The study of relative wavelength shifts in quasar absorption spectra at high redshift is indeed one of them as systematic achromatic shifts in these spectra can be attributed to changes in fundamental constants, and in particular in the finestructure constant, α. This would most certainly call for physics beyond the standard model. Study of the variation of constants on cosmological scales is also the best way to test the equivalence principle on cosmological and astrophysical scales [1]. It opens a window on deviations from general relativity on scales where it is necessary to introduce dark energy and dark matter and on which we have very little constraint on the validity of general relativity [2].Claims of a variation in α from observations of quasar absorption spectra using the many multiplet method [3] had sparked an enormous amount of theoretical activity in attempts to explain a temporal variation in the fine structure constant [4][5][6][7][8]. If confirmed, the Keck/Hires data which yielded a statistically significant trend indicating ∆α/α = (−0.54±0.12)×10 −5 over a redshift range 0.5 < ∼ z < ∼ 3.0 (the minus sign indicates a smaller value of α in the past) could indeed point to new physics. However, subsequent studies based on VLT data using the same method have shown ∆α to be consistent with zero [9,10]. These results remain somewhat controversial [11].If the low energy constants of physics depend on some dynamical scalar field, φ, they become dynamical and may well be space-time dependent. On cosmological scales, it is usually thought that the time variation dominates over spatial fluctuations, as suggested by most models. The reasoning here is straightforward. For a scalar field coupled to electromagnetism, the Lagrangian contains a term BF (φ) 4 F µν F µν , F µν being the Faraday tensor and B F an arbitrary function of φ. This will necessarily induce a coupling to matter which is generated radiatively if not present at the tree lev...

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Section: Fig 1: (A)mentioning

confidence: 95%

Section: Pacs Numbersmentioning

confidence: 95%

Section: Pacs Numbersmentioning

confidence: 99%

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Wall of fundamental constants

2011

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“…"By creating the necessary structures and processes around IT investments, management can ensure that only those IT projects that are aligned with strategic business objectives are approved, funded, and prioritized" highlighted Symons in [21]. Webb et al [22] underlined performance and risk management as essential part of IT governance. Moreover, their study has proven that companies with good IT governance model generate higher results than competitors.…”

Section: It Governance Frameworkmentioning

confidence: 99%

Representing IT Performance Management as Metamodel

Pajic¹,

Pantelić²,

Stanojević³

2014

INT J COMPUT COMMUN

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Many empirical studies have shown that the business value from investment in IT projects can be greater than the one being currently achieved. Thus it calls for specific focus on IT governance in order to reach fusion between business and IT goals. Good IT performance management should enable the business and IT executives to understand how IT is contributing to the achievement of business goals. The paper addresses the issue of representing IT governance best practice frameworks as ontological metamodels. Special attention is dedicated to VAL IT framework, which represents a comprehensive framework to maximize business value from IT investments. The paper points out the necessity of analyzing, comparing and integrating IT governance frameworks in order to complement different knowledge and generate ontological metamodel of IT performance management. Scope of our work is in the static aspect of the framework and as the metalanguage Extended Entity/Relationship model is used.

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“…The practical InP/InGaAs APD based on the separate absorption, grading, charge and multiplication (SAGCM) structure [1,2] is of particular importance with demonstrated performance such as high internal gain, improved reliability, low multiplication noise, high quantum efficiency, maximum unity-gain bandwidth, and high gain-bandwidth product [3][4][5][6], especially when the SAGCM structure unit is coupled with a resonant cavity [3,4] or integrated as waveguide APDs [5,6].…”

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confidence: 99%

Dynamic drift‐diffusion simulation of InP/InGaAs SAGCM APD

Xiao

2007

Phys. Status Solidi (c)

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In this work, based on the advanced drift and diffusion model with commercial software, the Crosslight APSYS, InP/InGaAs separate absorption, grading, charge and multiplication APDs for high bit-rate operation have been modeled. Basic physical quantities such as band diagram, optical absorption and generation are calculated. Performance characteristics such as dark-and photo-current, photoresponsivity, multiplication gain, breakdown voltage, excess noise, frequency response and bandwidth etc., are simulated. The modeling results are selectively presented, analyzed, and some results are compared with experiments. Device design optimization issues are further discussed with respect to the applicable features of the Crosslight APSYS within the framework of the drift-diffusion theory.1 Introduction As one of the front-end photodetectors for high sensitive optical receivers, InP/InGaAs avalanche photodiodes (APDs) play an important role for modern long haul and high bit-rate optical fiber communication systems. The practical InP/InGaAs APD based on the separate absorption, grading, charge and multiplication (SAGCM) structure [1, 2] is of particular importance with demonstrated performance such as high internal gain, improved reliability, low multiplication noise, high quantum efficiency, maximum unity-gain bandwidth, and high gain-bandwidth product [3][4][5][6], especially when the SAGCM structure unit is coupled with a resonant cavity [3,4] or integrated as waveguide APDs [5,6].Whereas technological development on APD fabrication has been advanced during the past years, better modeling methods and software, especially compact packages with full breadth, are increasingly demanded because of their advantages in saving the R&D time and cost and capability in optimizing device design. In this work, based on Crosslight's APSYS [7], dynamic drift-diffusion simulations have been performed on InP/InGaAs SAGCM APDs.

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Phytographia canariensis / par P. Barker-Webb et Sabin Berthelot.

Cited by 13 publications

References 0 publications

Wall of fundamental constants

Wall of fundamental constants

Representing IT Performance Management as Metamodel

Dynamic drift‐diffusion simulation of InP/InGaAs SAGCM APD

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