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Lewenstein, Maciej, J. Ignacio Cirac et Luis Santos. « Cooling of a small sample of Bose atoms with accidental degeneracy ». Journal of Physics B : Atomic, Molecular and Optical Physics 33, no 19 (15 septembre 2000) : 4107–29. http://dx.doi.org/10.1088/0953-4075/33/19/321.
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Tonn, Babette, Jacques Lacaze et Stephanie Duwe. « Degenerated Graphite Growth in Ductile Iron ». Materials Science Forum 925 (juin 2018) : 62–69. http://dx.doi.org/10.4028/www.scientific.net/msf.925.62.
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As part of a study devoted to the effect of trace elements on graphite degeneracy, near-eutectic ductile iron melts were prepared to which minute amounts of lead and of both lead and cerium were added. The melts were cast into an insulated Y4 mould, giving a solidification time of about 1 hour and a cooling time to room temperature of about 15 hours. In the thermal centre of the Pb containing sample graphite spheroids as well as intergranular lamellar graphite have been found. At the same location of the casting containing both Pb and Ce, exploded as well as chunky graphite could be observed, while the formation of intergranular lamellar graphite has been suppressed. Deep etching of the samples allowed reaching the following conclusions: i) intergranular graphite in the SG-Pb sample often, if not always, originates on graphite nodules and extends towards the last to freeze areas; ii) in one location of the SG-PbCe sample, chunky graphite strings were observed to originate on an exploded nodule, thus confirming the close relationship between these two forms of graphite. Because of the over-treatment in cerium of the SG-PbCe sample, other unusual degenerate graphite was observed which appears as coarse aggregates of "porous" graphite after deep etching.
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Perenon, L., S. Ilić, R. Maartens et A. de la Cruz-Dombriz. « Improvements in cosmological constraints from breaking growth degeneracy ». Astronomy & ; Astrophysics 642 (octobre 2020) : A116. http://dx.doi.org/10.1051/0004-6361/202038409.
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Context. The key probes of the growth of a large-scale structure are its rate f and amplitude σ8. Redshift space distortions in the galaxy power spectrum allow us to measure only the combination fσ8, which can be used to constrain the standard cosmological model or alternatives. By using measurements of the galaxy-galaxy lensing cross-correlation spectrum or of the galaxy bispectrum, it is possible to break the fσ8 degeneracy and obtain separate estimates of f and σ8 from the same galaxy sample. Currently there are very few such separate measurements, but even this allows for improved constraints on cosmological models. Aims. We explore how having a larger and more precise sample of such measurements in the future could constrain further cosmological models. Methods. We considered what can be achieved by a future nominal sample that delivers an ∼1% constraint on f and σ8 separately, compared to the case with a similar precision on the combination fσ8. Results. For the six cosmological parameters of ΛCDM, we find improvements of ∼5–50% on their constraints. For modified gravity models in the Horndeski class, the improvements on these standard parameters are ∼0–15%. However, the precision on the sum of neutrino masses improves by 65% and there is a significant increase in the precision on the background and perturbation Horndeski parameters.
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Sonnenfeld, Alessandro. « Statistical strong lensing ». Astronomy & ; Astrophysics 656 (décembre 2021) : A153. http://dx.doi.org/10.1051/0004-6361/202142062.
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Context. Time-delay lensing is a powerful tool for measuring the Hubble constant H0. However, in order to obtain an accurate estimate of H0 from a sample of time-delay lenses, very good knowledge of the mass structure of the lens galaxies is needed. Strong lensing data on their own are not sufficient to break the degeneracy between H0 and the lens model parameters on a single object basis. Aims. The goal of this study is to determine whether it is possible to break the H0-lens structure degeneracy with the statistical combination of a large sample of time-delay lenses, relying purely on strong lensing data with no stellar kinematics information. Methods. I simulated a set of 100 lenses with doubly imaged quasars and related time-delay measurements. I fitted these data with a Bayesian hierarchical method and a flexible model for the lens population, emulating the lens modelling step. Results. The sample of 100 lenses on its own provides a measurement of H0 with 3% precision, but with a −4% bias. However, the addition of prior information on the lens structural parameters from a large sample of lenses with no time delays, such as that considered in Paper I, allows for a 1% level inference. Moreover, the 100 lenses allow for a 0.03 dex calibration of galaxy stellar masses, regardless of the level of prior knowledge of the Hubble constant. Conclusions. Breaking the H0-lens model degeneracy with lensing data alone is possible, but 1% measurements of H0 require either many more than 100 time-delay lenses or knowledge of the structural parameter distribution of the lens population from a separate sample of lenses.
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Molenberghs, Geert, Michael G. Kenward, Marc Aerts, Geert Verbeke, Anastasios A. Tsiatis, Marie Davidian et Dimitris Rizopoulos. « On random sample size, ignorability, ancillarity, completeness, separability, and degeneracy : Sequential trials, random sample sizes, and missing data ». Statistical Methods in Medical Research 23, no 1 (18 avril 2012) : 11–41. http://dx.doi.org/10.1177/0962280212445801.
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Li, Tiancheng, Shudong Sun, Tariq Pervez Sattar et Juan Manuel Corchado. « Fight sample degeneracy and impoverishment in particle filters : A review of intelligent approaches ». Expert Systems with Applications 41, no 8 (juin 2014) : 3944–54. http://dx.doi.org/10.1016/j.eswa.2013.12.031.
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Ravel, Bruce. « Path degeneracy and EXAFS analysis of disordered materials ». Journal of Synchrotron Radiation 21, no 6 (1 octobre 2014) : 1269–74. http://dx.doi.org/10.1107/s1600577514014982.
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Analysis of EXAFS data measured on a material with a disordered local configuration environment around the absorbing atom can be challenging owing to the proliferation of photoelectron scattering paths that must be considered in the analysis. In the case where the absorbing atom exists in multiple inequivalent sites, the problem is compounded by having to consider each site separately. A method is proposed for automating the calculation of theory for inequivalent sites, then averaging the contributions from sufficiently similar scattering paths. With this approach, the complexity of implementing a successful fitting model on a highly disordered sample is reduced. As an example, an analysis of TiK-edge data on zirconolite, CaZrTi2O7, which has three inequivalent Ti sites, is presented.
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Andreon, S., G. Trinchieri et A. Moretti. « Low X-ray surface brightness clusters : implications on the scatter of the M–T and L–T relations ». Monthly Notices of the Royal Astronomical Society 511, no 4 (3 février 2022) : 4991–98. http://dx.doi.org/10.1093/mnras/stac307.
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ABSTRACT We aim at studying scaling relations of a small but well-defined sample of galaxy clusters that includes the recently discovered class of objects that are X-ray faint for their mass. These clusters have an average low X-ray surface brightness, a low gas fraction, and are underrepresented (by a factor of 10) in X-ray surveys or entirely absent in Sunyaev-Zeldovich (SZ) surveys. With the inclusion of these objects, we find that the temperature–mass relation has an unprecedentedly large scatter, 0.20 ± 0.03 dex at fixed mass, as wide as allowed by the temperature range, and the location of a cluster in this plane depends on its surface brightness. Clusters obey a relatively tight luminosity–temperature relation independently of their brightness. We interpret the wide difference in scatter around the two relations as due to the fact that X-ray luminosity and temperature are dominated by photons coming from small radii (in particular for T we used a 300 kpc aperture radius) and strongly affected by gas thermodynamics (e.g. shocks and cool cores), whereas mass is dominated by dark matter at large radii. We measure a slope of 2.0 ± 0.2 for the L500–T relation. Given the characteristics of our sample, this value is free from collinearity (degeneracy) between evolution and slope and from hypothesis on the undetected population, which both affect the analysis of X-ray-selected samples, and can therefore be profitably used both as reference and to break the aforementioned degeneracy of X-ray-selected samples.
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Repp, Andrew, et István Szapudi. « Galaxy bias and σ8 from counts in cells from the SDSS main sample ». Monthly Notices of the Royal Astronomical Society : Letters 498, no 1 (22 août 2020) : L125—L129. http://dx.doi.org/10.1093/mnrasl/slaa139.
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ABSTRACT The counts-in-cells (CIC) galaxy probability distribution depends on both the dark matter clustering amplitude σ8 and the galaxy bias b. We present a theory for the CIC distribution based on a previous prescription of the underlying dark matter distribution and a linear volume transformation to redshift space. We show that, unlike the power spectrum, the CIC distribution breaks the degeneracy between σ8 and b on scales large enough that both bias and redshift distortions are still linear; thus, we obtain a simultaneous fit for both parameters. We first validate the technique on the Millennium Simulation and then apply it to the Sloan Digital Sky Survey main galaxy sample. We find σ8 = 0.92 ± .08 and $b = 1.39^{+.11}_{-.09}$ consistent with previous complementary results from redshift distortions and from Planck.
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Kallend, John S., R. B. Schwarz et A. D. Rollett. « Resolution of Superimposed Diffraction Peaks in Texture Analysis of a YBa2Cu3O7 Polycrystal ». Textures and Microstructures 13, no 2-3 (1 janvier 1991) : 189–97. http://dx.doi.org/10.1155/tsm.13.189.
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Texture measurements in polycrystalline 123 oxide superconductors are complicated by the superposition of Bragg reflections in the pole figures due to the near degeneracy of the crystal structure. A method is described, based on an extension of the WIMV algorithm, for resolving these superpositions and determining the crystal orientation distribution (OD). The method is exemplified by OD analysis of a magnetically aligned, strongly textured powder sample of YBa2Cu3O7.
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Palmerio, J. T., et F. Daigne. « Constraining the intrinsic population of long gamma-ray bursts : Implications for spectral correlations, cosmic evolution, and their use as tracers of star formation ». Astronomy & ; Astrophysics 649 (mai 2021) : A166. http://dx.doi.org/10.1051/0004-6361/202039929.
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Aims. Long gamma-ray bursts (LGRBs) have been shown to be powerful probes of the Universe, in particular for studying the star formation rate up to very high redshift (z ∼ 9). Since LGRBs are produced by only a small fraction of massive stars, it is paramount to have a good understanding of their underlying intrinsic population in order to use them as cosmological probes without introducing any unwanted bias. The goal of this work is to constrain and characterise this intrinsic population. Methods. We developed a Monte Carlo model where each burst is described by its redshift and its properties at the peak of the light curve. We derived the best fit parameters by comparing our synthetic populations to carefully selected observational constraints based on the CGRO/BATSE, Fermi/GBM and Swift/BAT samples with appropriate flux thresholds. We explored different scenarios in terms of the cosmic evolution of the luminosity function and/or of the redshift distribution as well as including or not the presence of intrinsic spectral-energetics (Ep − L) correlations. Results. We find that the existence of an intrinsic Ep − L correlation is preferred but with a shallower slope than observed (αA ∼ 0.3) and a larger scatter (∼0.4 dex). We find a strong degeneracy between the cosmic evolution of the luminosity and of the LGRB rate, and show that a sample both larger and deeper than SHOALS by a factor of three is needed to lift this degeneracy. Conclusions. The observed Ep − L correlation cannot be explained only by selection effects although these do play a role in shaping the observed relation. The degeneracy between the cosmic evolution of the luminosity function and of the redshift distribution of LGRBs should be included in the uncertainties of star formation rate estimates; these amount to a factor of 10 at z = 6 and up to a factor of 50 at z = 9.
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Escamilla-Rivera, Celia, Geovanny Rave-Franco et Jackson Levi-Said. « f(T, B) Cosmography for High Redshifts ». Universe 7, no 11 (16 novembre 2021) : 441. http://dx.doi.org/10.3390/universe7110441.
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In light of the statistical performance of cosmological observations, in this work we present the cosmography in f(T,B) gravity. In this scenario we found a cosmological viable standard case that allows the reduction of the degeneracy between several f(T,B) models already proposed in the literature. Furthermore, we constrain this model using Pantheon SNeIa compilation, cosmic chronometers and a newly GRB calibrated data sample. We found that with an appropriate strategy for including the cosmographic parameter, we do produce a viable cosmology with our model within f(T,B) gravity.
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DIVAKARAN, P. P., et A. K. RAJAGOPAL. « QUANTUM THEORY OF LANDAU AND PEIERLS ELECTRONS FROM THE CENTRAL EXTENSIONS OF THEIR SYMMETRY GROUPS ». International Journal of Modern Physics B 09, no 03 (30 janvier 1995) : 261–94. http://dx.doi.org/10.1142/s0217979295000136.
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By Wigner’s theorem on symmetries, the total state space of a quantum system whose symmetries form the group G is the collection of all projective unitary representations of G; these are, in turn, realised as certain unitary representations of the set of all central extensions of G by U(1). Exploiting this relationship, we present in this paper a new approach to the quantum mechanics of an electron in a uniform magnetic field B, in the plane (the Landau electron) and on the 2-torus in the presence of a periodic potential V whose periodicity is that of an N×N lattice (the Peierls electron). For the Landau electron, G is the Euclidean group E(2) whose central extensions arise from the Heisenberg Lie group central extensions, determined by B, of the translation subgroup. The state space is a unitary representation of the direct product of two such groups corresponding to B and -B and the Hamiltonian is a unique element of the universal enveloping algebra of the centrally-extended E(2). The complete quantum theory of the Landau electron follows directly. For the Peierls electron, lattice translation-invariance is possible only if the flux per unit cell Φ takes rational values with denominator N. The state space is a unitary representation of the direct product of a finite Heisenberg group, which is a central extension of the translation group, and a Heisenberg Lie group, both characterised by Φ. The following new results are rigorous consequences. In the empty lattice limit V=0, the energy spectrum is the Landau spectrum with degeneracy equal to the total flux through the sample. As V moves away from zero, every Landau level splits into NΦ discrete sublevels, each of degeneracy N. More generally, for V≠0 of any strength and (periodic) form, and B such that Φ is nonintegral, every point in the spectrum has multiplicity N. The degeneracy is thus proportional to the linear size rather than the area of the sample. Throughout the paper, vector potentials and gauges are dispensed with and many misconceptions thereby removed.
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Lee, S., E. M. Huff, A. Choi, J. Elvin-Poole, C. Hirata, K. Honscheid, N. MacCrann et al. « Probing gravity with the DES-CMASS sample and BOSS spectroscopy ». Monthly Notices of the Royal Astronomical Society 509, no 4 (10 novembre 2021) : 4982–96. http://dx.doi.org/10.1093/mnras/stab3129.
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ABSTRACT The DES-CMASS sample (DMASS) is designed to optimally combine the weak lensing measurements from the Dark Energy Survey (DES) and redshift-space distortions (RSD) probed by the CMASS galaxy sample from the Baryonic Oscillation Spectroscopic Survey. In this paper, we demonstrate the feasibility of adopting DMASS as the equivalent of CMASS for a joint analysis of DES and BOSS in the framework of modified gravity. We utilize the angular clustering of the DMASS galaxies, cosmic shear of the DES metacalibration sources, and cross-correlation of the two as data vectors. By jointly fitting the combination of the data with the RSD measurements from the CMASS sample and Planck data, we obtain the constraints on modified gravity parameters $\mu _0=-0.37^{+0.47}_{-0.45}$ and $\Sigma _0=0.078^{+0.078}_{-0.082}$. Our constraints of modified gravity with DMASS are tighter than those with the DES Year 1 redMaGiC sample with the same external data sets by 29 per cent for μ0 and 21 per cent for Σ0, and comparable to the published results of the DES Year 1 modified gravity analysis despite this work using fewer external data sets. This improvement is mainly because the galaxy bias parameter is shared and more tightly constrained by both CMASS and DMASS, effectively breaking the degeneracy between the galaxy bias and other cosmological parameters. Such an approach to optimally combine photometric and spectroscopic surveys using a photometric sample equivalent to a spectroscopic sample can be applied to combining future surveys having a limited overlap such as DESI and LSST.
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Qin, Jianbo, Xian Zhong Zheng, Min Fang, Zhizheng Pan, Stijn Wuyts, Yong Shi, Yingjie Peng et al. « Systematic biases in determining dust attenuation curves through galaxy SED fitting ». Monthly Notices of the Royal Astronomical Society 511, no 1 (28 janvier 2022) : 765–83. http://dx.doi.org/10.1093/mnras/stac132.
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ABSTRACT While the slope of the dust attenuation curve (δ) is found to correlate with effective dust attenuation (AV) as obtained through spectral energy distribution (SED) fitting, it remains unknown how the fitting degeneracies shape this relation. We examine the degeneracy effects by fitting SEDs of a sample of local star-forming galaxies (SFGs) selected from the Galaxy And Mass Assembly survey, in conjunction with mock galaxy SEDs of known attenuation parameters. A well-designed declining starburst star formation history is adopted to generate model SED templates with intrinsic UV slope (β0) spanning over a reasonably wide range. The best-fitting β0 for our sample SFGs shows a wide coverage, dramatically differing from the limited range of β0 < −2.2 for a starburst of constant star formation. Our results show that strong degeneracies between β0, δ, and AV in the SED fitting induce systematic biases leading to a false AV–δ correlation. Our simulation tests reveal that this relationship can be well reproduced even when a flat AV–δ relation is taken to build the input model galaxy SEDs. The variations in best-fitting δ are dominated by the fitting errors. We show that assuming a starburst with constant star formation in SED fitting will result in a steeper attenuation curve, smaller degeneracy errors, and a stronger AV–δ relation. Our findings confirm that the AV–δ relation obtained through SED fitting is likely driven by the systematic biases induced by the fitting degeneracies between β0, δ, and AV.
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Enzi, Wolfgang, Simona Vegetti, Giulia Despali, Jen-Wei Hsueh et R. Benton Metcalf. « Systematic errors in strong gravitational lensing reconstructions, a numerical simulation perspective ». Monthly Notices of the Royal Astronomical Society 496, no 2 (16 mai 2020) : 1718–29. http://dx.doi.org/10.1093/mnras/staa1224.
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ABSTRACT We present the analysis of a sample of 24 SLACS-like galaxy–galaxy strong gravitational lens systems with a background source and deflectors from the Illustris-1 simulation. We study the degeneracy between the complex mass distribution of the lenses, substructures, the surface brightness distribution of the sources, and the time delays. Using a novel inference framework based on Approximate Bayesian Computation, we find that for all the considered lens systems, an elliptical and cored power-law mass density distribution provides a good fit to the data. However, the presence of cores in the simulated lenses affects most reconstructions in the form of a Source Position Transformation. The latter leads to a systematic underestimation of the source sizes by 50 per cent on average, and a fractional error in H0 of around $25_{-19}^{+37}$ per cent. The analysis of a control sample of 24 lens systems, for which we have perfect knowledge about the shape of the lensing potential, leads to a fractional error on H0 of $12_{-3}^{+6}$ per cent. We find no degeneracy between complexity in the lensing potential and the inferred amount of substructures. We recover an average total projected mass fraction in substructures of fsub < 1.7–2.0 × 10−3 at the 68 per cent confidence level in agreement with zero and the fact that all substructures had been removed from the simulation. Our work highlights the need for higher resolution simulations to quantify the lensing effect of more realistic galactic potentials better, and that additional observational constraint may be required to break existing degeneracies.
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Kaplan, Andee, Daniel J. Nordman et Stephen B. Vardeman. « On the S-instability and degeneracy of discrete deep learning models ». Information and Inference : A Journal of the IMA 9, no 3 (5 novembre 2019) : 627–55. http://dx.doi.org/10.1093/imaiai/iaz022.
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Abstract A probability model exhibits instability if small changes in a data outcome result in large and, often unanticipated, changes in probability. This instability is a property of the probability model, given by a distributional form and a given configuration of parameters. For correlated data structures found in several application areas, there is increasing interest in identifying such sensitivity in model probability structure. We consider the problem of quantifying instability for general probability models defined on sequences of observations, where each sequence of length $N$ has a finite number of possible values that can be taken at each point. A sequence of probability models, indexed by $N$, and an associated parameter sequence result to accommodate data of expanding dimension. Model instability is formally shown to occur when a certain log probability ratio under such models grows faster than $N$. In this case, a one component change in the data sequence can shift probability by orders of magnitude. Also, as instability becomes more extreme, the resulting probability models are shown to tend to degeneracy, placing all their probability on potentially small portions of the sample space. These results on instability apply to large classes of models commonly used in random graphs, network analysis and machine learning contexts.
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Li, Xiaolei, Ryan E. Keeley, Arman Shafieloo, Xiaogang Zheng, Shuo Cao, Marek Biesiada et Zong-Hong Zhu. « Hubble diagram at higher redshifts : model independent calibration of quasars ». Monthly Notices of the Royal Astronomical Society 507, no 1 (31 juillet 2021) : 919–26. http://dx.doi.org/10.1093/mnras/stab2154.
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ABSTRACT In this paper, we present a model-independent approach to calibrate the largest quasar sample. Calibrating quasar samples is essentially constraining the parameters of the linear relation between the log of the ultraviolet (UV) and X-ray luminosities. This calibration allows quasars to be used as standardized candles. There is a strong correlation between the parameters characterizing the quasar luminosity relation and the cosmological distances inferred from using quasars as standardized candles. We break this degeneracy by using Gaussian process regression to model-independently reconstruct the expansion history of the Universe from the latest type Ia supernova observations. Using the calibrated quasar data set, we further reconstruct the expansion history up to redshift of z ∼ 7.5. Finally, we test the consistency between the calibrated quasar sample and the standard Lambda cold dark matter ($\rm {\Lambda }CDM$) model based on the posterior probability distribution of the GP hyperparameters. Our results show that the quasar sample is in good agreement with the standard $\rm {\Lambda }CDM$ model in the redshift range of the supernova, despite the 2−3σ significant deviations taking place at higher redshifts. Fitting the standard $\rm {\Lambda }CDM$ model to the calibrated quasar sample, we obtain a high value of the matter density parameter $\Omega _m = 0.382^{+0.045}_{-0.042}$, which is marginally consistent with the constraints from other cosmological observations.
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Barron, Laurence D. « False Chirality, Absolute Enantioselection and CP Violation : Pierre Curie’s Legacy ». Magnetochemistry 6, no 1 (15 janvier 2020) : 5. http://dx.doi.org/10.3390/magnetochemistry6010005.
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The 1884 suggestion of Pierre Curie (1859–1906) that the type of dissymmetry shown by collinear electric and magnetic fields may induce an enantiomeric excess, in a chemical reaction that would otherwise produce a racemic mixture, is explored in the context of fundamental symmetry arguments. Curie’s arrangement exhibits false chirality (time-noninvariant enantiomorphism), and so it may not induce absolute enantioselection (ae) in a process that has reached thermodynamic equilibrium, since it does not lift the degeneracy of chiral enantiomers. However, it may do so in far-from-equilibrium processes via a breakdown in microscopic reversibility analogous to that observed in elementary particle processes under the influence of CP violation, the associated force possessing false chirality with respect to CP enantiomorphism. In contrast, an influence like circularly polarized light exhibiting true chirality (time-invariant enantiomorphism) lifts the degeneracy of enantiomers, and so may induce ae in all circumstances. Although to date, ae has not been observed under the influence of Curie’s arrangement of collinear electric and magnetic fields, it is argued that two different experiments have now demonstrated ae under a falsely chiral influence in systems far from equilibrium, namely in a spinning sample under a gravitational field, and in the separation of enantiomers at a ferromagnetic surface.
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MARASSI, L., J. V. CUNHA et J. A. S. LIMA. « CONSTRAINING THE NONEXTENSIVE MASS FUNCTION OF HALOS FROM BAO, CMB AND X-RAY DATA ». International Journal of Modern Physics D 19, no 08n10 (août 2010) : 1417–25. http://dx.doi.org/10.1142/s0218271810017901.
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Clusters of galaxies are the most impressive gravitationally-bound systems in the universe, and their abundance (the cluster mass function) is an important statistic to probe the matter density parameter (Ωm) and the amplitude of density fluctuations (σ8). The cluster mass function is usually described in terms of the Press–Schecther (PS) formalism where the primordial density fluctuations are assumed to be a Gaussian random field. In previous works we have proposed a non-Gaussian analytical extension of the PS approach with basis on the q-power law distribution (PL) of the nonextensive kinetic theory. In this paper, by applying the PL distribution to fit the observational mass function data from X-ray highest flux-limited sample (HIFLUGCS), we find a strong degeneracy among the cosmic parameters, σ8, Ωm and the q parameter from the PL distribution. A joint analysis involving recent observations from baryon acoustic oscillation (BAO) peak and Cosmic Microwave Background (CMB) shift parameter is carried out in order to break these degeneracy and better constrain the physically relevant parameters. The present results suggest that the next generation of cluster surveys will be able to probe the quantities of cosmological interest (σ8, Ωm) and the underlying cluster physics quantified by the q-parameter.
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Das, Payel, Ortwin Gerhard, Flavio de Lorenzi, Emily McNeil, Eugene Churazov et Lodovico Coccato. « The outer haloes of massive, elliptical galaxies ». Proceedings of the International Astronomical Union 5, H15 (novembre 2009) : 92. http://dx.doi.org/10.1017/s1743921310008446.
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The outer haloes of massive elliptical galaxies are dark-matter dominated regions where stellar orbits have longer dynamical timescales than the central regions and therefore better preserve their formation history. Dynamical models out to large radii suffer from a degeneracy between mass and orbital structure, as the outer kinematics are unable to resolve higher moments of the line-of-sight velocity distribution. We mitigate this degeneracy for a sample of quiescent, massive, nearby ellipticals by determining their mass distributions independently using a non-parametric method on X-ray observations of the surrounding hot interstellar medium. We then create dynamical models using photometric and kinematic constraints consisting of integral-eld, long-slit and planetary nebulae (PNe) data extending to ~50 kpc. The rst two galaxies of our sample, NGC 5846 and NGC 1399, were found to have very shallow pro jected light distributions with a power law index of ~1.5 and a dark matter content of 70–80% at 50 kpc. Spherical Jeans models of the data show that, in the outer haloes of both galaxies, the pro jected velocity dispersions are almost inde- pendent of the anisotropy and that the PNe prefer the lower end of the range of mass distributions consistent with the X-ray data. Using the N-body code NMAGIC, we cre- ated axisymmetric models of NGC 5846 using the individual PNe radial velocities in a likelihood method and found them to be more constraining than the binned velocity dispersions. Characterising the orbital structure in terms of spherically averaged proles of the velocity dispersions we nd σψ > σr > σθ.
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Du, Sichun, et Qing Deng. « Unscented Particle Filter Algorithm Based on Divide-and-Conquer Sampling for Target Tracking ». Sensors 21, no 6 (23 mars 2021) : 2236. http://dx.doi.org/10.3390/s21062236.
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Unscented particle filter (UPF) struggles to completely cover the target state space when handling the maneuvering target tracing problem, and the tracking performance can be affected by the low sample diversity and algorithm redundancy. In order to solve this problem, the method of divide-and-conquer sampling is applied to the UPF tracking algorithm. By decomposing the state space, the descending dimension processing of the target maneuver is realized. When dealing with the maneuvering target, particles are sampled separately in each subspace, which directly prevents particles from degeneracy. Experiments and a comparative analysis were carried out to comprehensively analyze the performance of the divide-and-conquer sampling unscented particle filter (DCS-UPF). The simulation result demonstrates that the proposed algorithm can improve the diversity of particles and obtain higher tracking accuracy in less time than the particle swarm algorithm and intelligent adaptive filtering algorithm. This algorithm can be used in complex maneuvering conditions.
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Sergeyev, Ivan V., Boris Itin, Rivkah Rogawski, Loren A. Day et Ann E. McDermott. « Efficient assignment and NMR analysis of an intact virus using sequential side-chain correlations and DNP sensitization ». Proceedings of the National Academy of Sciences 114, no 20 (1 mai 2017) : 5171–76. http://dx.doi.org/10.1073/pnas.1701484114.
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An experimental strategy has been developed to increase the efficiency of dynamic nuclear polarization (DNP) in solid-state NMR studies. The method makes assignments simpler, faster, and more reliable via sequential correlations of both side-chain and Cα resonances. The approach is particularly suited to complex biomolecules and systems with significant chemical-shift degeneracy. It was designed to overcome the spectral congestion and line broadening that occur due to sample freezing at the cryogenic temperatures required for DNP. Nonuniform sampling (NUS) is incorporated to achieve time-efficient collection of multidimensional data. Additionally, fast (25 kHz) magic-angle spinning (MAS) provides optimal sensitivity and resolution. Data collected in <1 wk produced a virtually complete de novo assignment of the coat protein of Pf1 virus. The peak positions and linewidths for samples near 100 K are perturbed relative to those near 273 K. These temperature-induced perturbations are strongly correlated with hydration surfaces.
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Maranville, Brian B., Brian J. Kirby, Alexander J. Grutter, Paul A. Kienzle, Charles F. Majkrzak, Yaohua Liu et Cindi L. Dennis. « Measurement and modeling of polarized specular neutron reflectivity in large magnetic fields ». Journal of Applied Crystallography 49, no 4 (9 juin 2016) : 1121–29. http://dx.doi.org/10.1107/s1600576716007135.
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The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin-up and spin-down neutrons. For polarized neutron reflectometry, this must be included in the reference potential energy of the Schrödinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin-flip scattering) and so this additional potential is constant throughout the scattering region. When there is non-collinear magnetization in the sample, however, there will be significant scattering from one spin state into the other, and the reference potentials will differ between the incoming and outgoing wavefunctions, changing the angle and intensities of the scattering. The theory of the scattering and recommended experimental practices for this type of measurement are presented, as well as an example measurement.
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Karpov, Petr, et Serguei Brazovskii. « Pattern Formation and Aggregation in Ensembles of Solitons in Quasi One-Dimensional Electronic Systems ». Symmetry 14, no 5 (10 mai 2022) : 972. http://dx.doi.org/10.3390/sym14050972.
Texte intégralRésumé :
Broken symmetries of quasi one-dimensional electronic systems give rise to microscopic solitons taking roles of carriers of the charge or spin. The double degeneracy gives rise to solitons as kinks of the scalar order parameter A; the continuous degeneracy for the complex order parameter Aexp(iθ) gives rise to phase vortices, amplitudes solitons, and their combinations. These degrees of freedom can be controlled or accessed independently via either the spin polarization or the charge doping. The long-range ordering in dimensions above one imposes super-long-range confinement forces upon the solitons, leading to a sequence of phase transitions in their ensembles. The higher-temperature T transition enforces the confinement of solitons into topologically bound complexes: pairs of kinks or the amplitude solitons dressed by exotic half-integer vortices. At a second lower T transition, the solitons aggregate into rods of bi-kinks or into walls of amplitude solitons terminated by rings of half-integer vortices. With lowering T, the walls multiply, passing sequentially across the sample. Here, we summarize results of a numerical modeling for different symmetries, for charged and neutral soliton, in two and three dimensions. The efficient Monte Carlo algorithm, preserving the number of solitons, was employed which substantially facilitates the calculations, allowing to extend them to the three-dimensional case and to include the long-range Coulomb interactions.
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GOLD, A., et O. ANTONIE. « MAGNETORESISTANCE OF A SILICON MOSFET ON THE (111) SURFACE IN A PARALLEL MAGNETIC FIELD ». International Journal of Modern Physics B 21, no 08n09 (10 avril 2007) : 1529–34. http://dx.doi.org/10.1142/s0217979207043142.
Texte intégralRésumé :
In comparison with silicon (100) we argue that the silicon (111) surface is a surface with higher mobility and stronger Coulomb interaction effects. For the resistance of the two-dimensional electron gas we discuss the effects of a magnetic field parallel to the surface: for zero temperature we present theoretical results for the magnetoresistance of an electron gas at the surface of silicon (111) with a six-fold valley degeneracy. Impurity scattering and interface roughness scattering are taken into account. A recent study of a hydrogen-passivated silicon (111) surface showed a mobility proportional to the electron density. We present, using a model for neutral impurities, predictions for the magnetoresistance of this sample in a parallel magnetic field.
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Sarron, F., N. Martinet, F. Durret et C. Adami. « Evolution of the cluster optical galaxy luminosity function in the CFHTLS : breaking the degeneracy between mass and redshift ». Astronomy & ; Astrophysics 613 (mai 2018) : A67. http://dx.doi.org/10.1051/0004-6361/201731981.
Texte intégralRésumé :
Obtaining large samples of galaxy clusters is important for cosmology: cluster counts as a function of redshift and mass can constrain the parameters of our Universe. They are also useful in order to understand the formation and evolution of clusters. We develop an improved version of the Adami & MAzure Cluster FInder (AMACFI), now the Adami, MAzure & Sarron Cluster FInder (AMASCFI), and apply it to the 154 deg2 of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) to obtain a large catalogue of 1371 cluster candidates with mass M200 > 1014 M⊙ and redshift z ≤ 0.7. We derive the selection function of the algorithm from the Millennium simulation, and cluster masses from a richness–mass scaling relation built from matching our candidates with X-ray detections. We study the evolution of these clusters with mass and redshift by computing the i′-band galaxy luminosity functions (GLFs) for the early-type (ETGs) and late-type galaxies (LTGs). This sample is 90% pure and 70% complete, and therefore our results are representative of a large fraction of the cluster population in these redshift and mass ranges. We find an increase in both the ETG and LTG faint populations with decreasing redshift (with Schechter slopes αETG = −0.65 ± 0.03 and αLTG = −0.95 ± 0.04 at z = 0.6, and αETG = −0.79 ± 0.02 and αLTG = −1.26 ± 0.03 at z = 0.2) and also a decrease in the LTG (but not the ETG) bright end. Our large sample allows us to break the degeneracy between mass and redshift, finding that the redshift evolution is more pronounced in high-mass clusters, but that there is no significant dependence of the faint end on mass for a given redshift. These results show that the cluster red sequence is mainly formed at redshift z > 0.7, and that faint ETGs continue to enrich the red sequence through quenching of brighter LTGs at z ≤ 0.7. The efficiency of this quenching is higher in large-mass clusters, while the accretion rate of faint LTGs is lower as the more massive clusters have already emptied most of their environment at higher redshifts.
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Ghisletta, Paolo, Delphine Fagot, Thierry Lecerf et Anik de Ribaupierre. « Amplitude of Fluctuations and Temporal Dependency in Intraindividual Variability ». GeroPsych 26, no 3 (janvier 2013) : 141–51. http://dx.doi.org/10.1024/1662-9647/a000091.
Texte intégralRésumé :
In a sample of 165 older individuals assessed twice at a 2-year interval on tasks of fluid and crystallized intelligence, and intensively (120 trials) on a simple reaction time task, we applied an autoregressive model to estimate both (1) amplitude and (2) time dependency in intraindividual variability (IIV). Results indicate that both IIV features are stronger predictors than the overall mean of intelligence scores 2 years later. Individuals that produced more (1) variable but also (2) erratic latencies of responses at baseline had lower intelligence scores 2 years later. We speculate that weaker time dependency in latency of response in simple reaction time tasks in older adults may be symptomatic of reduced brain integrity or more advanced degeneracy in functional brain circuitry.
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Scannapieco, Evan, et Crystal L. Martin. « Constraining the Intergalactic Medium Enrichment History with QSO Pairs ». Proceedings of the International Astronomical Union 5, S265 (août 2009) : 163–66. http://dx.doi.org/10.1017/s1743921310000463.
Texte intégralRésumé :
AbstractIntergalactic metals are ubiquitous, but their sources remain unknown. A key constraint on these sources is the spatial distributions of metals. Yet, the clustering of metals is difficult to interpret along single lines-of-sight, because distance and velocity information are mixed in redshift space. To overcome this situation we are carrying out detailed comparisons between the line-of-sight and transverse distributions of metal line absorption systems observed in a large sample of QSO pairs and simulations including a wide range of IGM-enrichment scenarios. The degeneracy between distance and velocity is broken by the transverse information available in pairs of sightlines, and thus these comparisons are providing unique new constraints on when and where metals were ejected from galaxies.
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Naqib, Ankur, Silvana Poggi et Stefan J. Green. « Deconstructing the Polymerase Chain Reaction II : an improved workflow and effects on artifact formation and primer degeneracy ». PeerJ 7 (14 juin 2019) : e7121. http://dx.doi.org/10.7717/peerj.7121.
Texte intégralRésumé :
Polymerase chain reaction (PCR) amplification of complex microbial genomic DNA templates with degenerate primers can lead to distortion of the underlying community structure due to inefficient primer-template interactions leading to bias. We previously described a method of deconstructed PCR (“PEX PCR”) to separate linear copying and exponential amplification stages of PCR to reduce PCR bias. In this manuscript, we describe an improved deconstructed PCR (“DePCR”) protocol separating linear and exponential stages of PCR and allowing higher throughput of sample processing. We demonstrate that the new protocol shares the same benefits of the original and show that the protocol dramatically and significantly decreases the formation of chimeric sequences during PCR. By employing PCR with annealing temperature gradients, we further show that there is a strong negative correlation between annealing temperature and the evenness of primer utilization in a complex pool of degenerate primers. Shifting primer utilization patterns mirrored shifts in observed microbial community structure in a complex microbial DNA template. We further employed the DePCR method to amplify the same microbial DNA template independently with each primer variant from a degenerate primer pool. The non-degenerate primers generated a broad range of observed microbial communities, but some were highly similar to communities observed with degenerate primer pools. The same experiment conducted with standard PCR led to consistently divergent observed microbial community structure. The DePCR method is simple to perform, is limited to PCR mixes and cleanup steps, and is recommended for reactions in which degenerate primer pools are used or when mismatches between primers and template are possible.
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Ryu, Yoon-Hyun, Youn Kil Jung, Hongjing Yang, Andrew Gould, Michael D. Albrow, Sun-Ju Chung, Cheongho Han et al. « Mass Production of 2021 KMTNet Microlensing Planets. I ». Astronomical Journal 164, no 5 (10 octobre 2022) : 180. http://dx.doi.org/10.3847/1538-3881/ac8d6c.
Texte intégralRésumé :
Abstract We inaugurate a program of “mass production” of microlensing planets discovered in 2021 KMTNet data, with the aim of laying the basis for future statistical studies. While we ultimately plan to quickly publish all 2021 planets meeting some minimal criteria, the current sample of four was chosen simply on the basis of having low initial estimates of the planet–host mass ratio, q. It is therefore notable that two members of this sample suffer from a degeneracy in the normalized source radius ρ that arises from different morphologies of closely spaced caustics. All four planets (KMT-2021-BLG-1391, KMT-2021-BLG-1253, KMT-2021-BLG-1372, KMT-2021-BLG-0748) have well-characterized mass ratios, q, and therefore are suitable for mass-ratio frequency studies. Both of the ρ degeneracies can be resolved by future adaptive optics (AO) observations on 30 m class telescopes. We provide general guidance for such AO observations for all events in anticipation of the prospect that they will revolutionize the field of microlensing planets.
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LI, ZHI-YUAN, RONG-JUAN LIU, LIN GAN, JIN-XIN FU et JIN LIAN. « NONRECIPROCAL ELECTROMAGNETIC DEVICES IN GYROMAGNETIC PHOTONIC CRYSTALS ». International Journal of Modern Physics B 28, no 02 (15 décembre 2013) : 1441010. http://dx.doi.org/10.1142/s0217979214410100.
Texte intégralRésumé :
Gyromagnetic photonic crystal (GPC) offers a promising way to realize robust transport of electromagnetic waves against backscattering from various disorders, perturbations and obstacles due to existence of unique topological electromagnetic states. The dc magnetic field exerting upon the GPC brings about the time-reversal symmetry breaking, splits the band degeneracy and opens band gaps where the topological chiral edge states (CESs) arise. The band gap can originate either from long-range Bragg-scattering effect or from short-range localized magnetic surface plasmon resonance (MSP). These topological edge states can be explored to construct backscattering-immune one-way waveguide and other nonreciprocal electromagnetic devices. In this paper we review our recent theoretical and experimental studies of the unique electromagnetic properties of nonreciprocal devices built in GPCs. We will discuss various basic issues like experimental instrumental setup, sample preparations, numerical simulation methods, tunable properties against magnetic field, band degeneracy breaking and band gap opening and creation of topological CESs. We will investigate the unidirectional transport properties of one-way waveguide under the influence of waveguide geometries, interface morphologies, intruding obstacles, impedance mismatch, lattice disorders, and material dissipation loss. We will discuss the unique coupling properties between one-wave waveguide and resonant cavities and their application as novel one-way bandstop filter and one-way channel-drop filter. We will also compare the CESs created in the Bragg-scattering band gap and the MSP band gap under the influence of lattice disorders. These results can be helpful for designing and exploring novel nonreciprocal electromagnetic devices for optical integration and information processing.
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Iwanowicz, Deborah D., Judy Y. Wu-Smart, Tugce Olgun, Autumn H. Smart, Clint R. V. Otto, Dawn Lopez, Jay D. Evans et Robert Cornman. « An updated genetic marker for detection of Lake Sinai Virus and metagenetic applications ». PeerJ 8 (17 juillet 2020) : e9424. http://dx.doi.org/10.7717/peerj.9424.
Texte intégralRésumé :
Background Lake Sinai Viruses (LSV) are common RNA viruses of honey bees (Apis mellifera) that frequently reach high abundance but are not linked to overt disease. LSVs are genetically heterogeneous and collectively widespread, but despite frequent detection in surveys, the ecological and geographic factors structuring their distribution in A. mellifera are not understood. Even less is known about their distribution in other species. Better understanding of LSV prevalence and ecology have been hampered by high sequence diversity within the LSV clade. Methods Here we report a new polymerase chain reaction (PCR) assay that is compatible with currently known lineages with minimal primer degeneracy, producing an expected 365 bp amplicon suitable for end-point PCR and metagenetic sequencing. Using the Illumina MiSeq platform, we performed pilot metagenetic assessments of three sample sets, each representing a distinct variable that might structure LSV diversity (geography, tissue, and species). Results The first sample set in our pilot assessment compared cDNA pools from managed A. mellifera hives in California (n = 8) and Maryland (n = 6) that had previously been evaluated for LSV2, confirming that the primers co-amplify divergent lineages in real-world samples. The second sample set included cDNA pools derived from different tissues (thorax vs. abdomen, n = 24 paired samples), collected from managed A. mellifera hives in North Dakota. End-point detection of LSV frequently differed between the two tissue types; LSV metagenetic composition was similar in one pair of sequenced samples but divergent in a second pair. Overall, LSV1 and intermediate lineages were common in these samples whereas variants clustering with LSV2 were rare. The third sample set included cDNA from individual pollinator specimens collected from diverse landscapes in the vicinity of Lincoln, Nebraska. We detected LSV in the bee Halictus ligatus (four of 63 specimens tested, 6.3%) at a similar rate as A. mellifera (nine of 115 specimens, 7.8%), but only one H. ligatus sequencing library yielded sufficient data for compositional analysis. Sequenced samples often contained multiple divergent LSV lineages, including individual specimens. While these studies were exploratory rather than statistically powerful tests of hypotheses, they illustrate the utility of high-throughput sequencing for understanding LSV transmission within and among species.
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Taggart, K., et D. A. Perley. « Core-collapse, superluminous, and gamma-ray burst supernova host galaxy populations at low redshift : the importance of dwarf and starbursting galaxies ». Monthly Notices of the Royal Astronomical Society 503, no 3 (2 mars 2021) : 3931–52. http://dx.doi.org/10.1093/mnras/stab174.
Texte intégralRésumé :
ABSTRACT We present a comprehensive study of an unbiased sample of 150 nearby (median redshift, z = 0.014) core-collapse supernova (CCSN) host galaxies drawn from the All-Sky Automated Survey for Supernovae (ASAS-SN) for direct comparison to the nearest long-duration gamma-ray burst (LGRB) and superluminous supernova (SLSN) hosts. We use public imaging surveys to gather multiwavelength photometry for all CCSN host galaxies and fit their spectral energy distributions (SEDs) to derive stellar masses and integrated star formation rates (SFRs). CCSNe populate galaxies across a wide range of stellar masses, from blue and compact dwarf galaxies to large spiral galaxies. We find 33$^{+4}_{-4}$ per cent of CCSNe are in dwarf galaxies (M* < 109 M⊙) and 2$^{+2}_{-1}$ per cent are in dwarf starburst galaxies [specific star formation rate (sSFR) > 10−8 yr−1]. We reanalyse low-redshift SLSN and LGRB hosts from the literature (out to z < 0.3) in a homogeneous way and compare against the CCSN host sample. The relative SLSN to CCSN supernova rate is increased in low-mass galaxies and at high sSFRs. These parameters are strongly covariant and we cannot break the degeneracy between them with our current sample, although there is some evidence that both factors may play a role. Larger unbiased samples of CCSNe from projects such as ZTF and LSST will be needed to determine whether host-galaxy mass (a proxy for metallicity) or sSFR (a proxy for star formation intensity and potential IMF variation) is more fundamental in driving the preference for SLSNe and LGRBs in unusual galaxy environments.
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BOUMRAR, H., O. RAFIL, M. TAMINE et R. TIGRINE. « DYNAMICAL PROPERTIES OF THE INTERFACE BETWEEN TWO THIN FILMS ». Surface Review and Letters 12, no 01 (février 2005) : 85–96. http://dx.doi.org/10.1142/s0218625x05006810.
Texte intégralRésumé :
The effect on the vibrational properties of nanostructures at the interface between two thin films is presented. The model used consists of the coupling of two semi-infinite plans A and B having three and two atomic layers, respectively. Theoretical calculations of localized phonon modes and vibrational field were carried out using the matching procedure. Close to the interface, the transversal translational symmetry is broken down inducing Raleigh-like branches. The polarization degeneracy of the ordered surface Raleigh mode in the longitudinal direction is lifted. The presence of acoustic and optical-like phonons is discussed in terms of the elastic constant forces. The density of states and the spectral densities are presented for sample atomic sites. A hyperfine resonance structure is obtained. It allows the analysis of the dynamical evolution from thin film A to thin film B.
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Hanif, Ayub, et Robert Elliott Smith. « State Space Modeling & ; Bayesian Inference with Computational Intelligence ». New Mathematics and Natural Computation 11, no 01 (mars 2015) : 71–101. http://dx.doi.org/10.1142/s1793005715500040.
Texte intégralRésumé :
Recursive Bayesian estimation using sequential Monte Carlos methods is a powerful numerical technique to understand latent dynamics of nonlinear non-Gaussian dynamical systems. It enables us to reason under uncertainty and addresses shortcomings underlying deterministic systems and control theories which do not provide sufficient means of performing analysis and design. In addition, parametric techniques such as the Kalman filter and its extensions, though they are computationally efficient, do not reliably compute states and cannot be used to learn stochastic problems. We review recursive Bayesian estimation using sequential Monte Carlo methods highlighting open problems. Primary of these is the weight degeneracy and sample impoverishment problem. We proceed to detail synergistic computational intelligence sequential Monte Carlo methods which address this. We find that imbuing sequential Monte Carlos with computational intelligence has many advantages when applied to many application and problem domains.
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de Oliveira, Paulo Murilo Castro. « Broad Histogram Simulation : Microcanonical Ising Dynamics ». International Journal of Modern Physics C 09, no 03 (mai 1998) : 497–503. http://dx.doi.org/10.1142/s012918319800039x.
Texte intégralRésumé :
We revisit here a new Monte Carlo approach, namely the Broad Histogram Method. It is based on two quantities, the numbers N up and N dn of potential modifications which could be performed starting from the system's current state, increasing or decreasing its energy E, respectively. Thus, the energy degeneracy g(E) can be directly determined from the microcanonical averages <N up (E)> and <N dn (E)> of these two quantities. This method was first tested by sampling states from a random walk along the energy axis, for which the control of possible correlations between successive averaging states is not an easy task. Neverthless, the resulting microcanonical averages could not depend upon the particular dynamics used to sample the Markovian chain of averaging states. Here, we test the same method within an alternative dynamics for which the quoted control becomes trivial.
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Hafner, Christian M., Sebastien Laurent et Francesco Violante. « WEAK DIFFUSION LIMITS OF DYNAMIC CONDITIONAL CORRELATION MODELS ». Econometric Theory 33, no 3 (13 juin 2016) : 691–716. http://dx.doi.org/10.1017/s0266466616000128.
Texte intégralRésumé :
The properties of dynamic conditional correlation (DCC) models, introduced more than a decade ago, are still not entirely known. This paper fills one of the gaps by deriving weak diffusion limits of a modified version of the classical DCC model. The limiting system of stochastic differential equations is characterized by a diffusion matrix of reduced rank. The degeneracy is due to perfect collinearity between the innovations of the volatility and correlation dynamics. For the special case of constant conditional correlations, a nondegenerate diffusion limit can be obtained. Alternative sets of conditions are considered for the rate of convergence of the parameters, obtaining time-varying but deterministic variances and/or correlations. A Monte Carlo experiment confirms that the often used quasi-approximate maximum likelihood (QAML) method to estimate the diffusion parameters is inconsistent for any fixed frequency, but that it may provide reasonable approximations for sufficiently large frequencies and sample sizes.
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Yao, Wenlong, Yuan Liu, Honghai Sun, Guichen Zhang, Jundong Zhang, Mingshun Zhou, Ming Sun et Dezhi Jiang. « Optimal Control Strategy for Marine Ssp Podded Propulsion Motor Based on Strong Tracking-Epf ». Polish Maritime Research 22, s1 (1 septembre 2015) : 4–9. http://dx.doi.org/10.1515/pomr-2015-0024.
Texte intégralRésumé :
Abstract Aiming at the non-linearity of state equation and observation equation of SSP (Siemen Schottel Propulsor) propulsion motor, an improved particle filter algorithm based on strong tracking extent Kalman filter (ST-EKF) was presented, and it was imported into the marine SSP propulsion motor control system. The strong tracking filter was used to update particles in the new algorithm and produce importance densities. As a result, the problems of particle degeneracy and sample impoverishment were ameliorated, the propulsion motor states and the rotor resistance were estimated simultaneously using strong track filter (STF), and the tracking ability of marine SSP propulsion motor control system was improved. Simulation result shown that the improved EPF algorithm was not only improving the prediction accuracy of the motor states and the rotor resistance, but also it can satisfy the requirement of navigation in harbor. It had the better accuracy than EPF algorithm.
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Elbrecht, Vasco, Thomas W. A. Braukmann, Natalia V. Ivanova, Sean W. J. Prosser, Mehrdad Hajibabaei, Michael Wright, Evgeny V. Zakharov, Paul D. N. Hebert et Dirk Steinke. « Validation of COI metabarcoding primers for terrestrial arthropods ». PeerJ 7 (7 octobre 2019) : e7745. http://dx.doi.org/10.7717/peerj.7745.
Texte intégralRésumé :
Metabarcoding can rapidly determine the species composition of bulk samples and thus aids biodiversity and ecosystem assessment. However, it is essential to use primer sets that minimize amplification bias among taxa to maximize species recovery. Despite this fact, the performance of primer sets employed for metabarcoding terrestrial arthropods has not been sufficiently evaluated. This study tests the performance of 36 primer sets on a mock community containing 374 insect species. Amplification success was assessed with gradient PCRs and the 21 most promising primer sets selected for metabarcoding. These 21 primer sets were also tested by metabarcoding a Malaise trap sample. We identified eight primer sets, mainly those including inosine and/or high degeneracy, that recovered more than 95% of the species in the mock community. Results from the Malaise trap sample were congruent with the mock community, but primer sets generating short amplicons produced potential false positives. Taxon recovery from both mock community and Malaise trap sample metabarcoding were used to select four primer sets for additional evaluation at different annealing temperatures (40–60 °C) using the mock community. The effect of temperature varied by primer pair but overall it only had a minor effect on taxon recovery. This study reveals the weak performance of some primer sets employed in past studies. It also demonstrates that certain primer sets can recover most taxa in a diverse species assemblage. Thus, based our experimental set up, there is no need to employ several primer sets targeting the same gene region. We identify several suitable primer sets for arthropod metabarcoding, and specifically recommend BF3 + BR2, as it is not affected by primer slippage and provides maximal taxonomic resolution. The fwhF2 + fwhR2n primer set amplifies a shorter fragment and is therefore ideal when targeting degraded DNA (e.g., from gut contents).
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Casey, Caitlin M. « Seeking Completeness for high-z ULIRGs : from SCUBA to Herschel ». Proceedings of the International Astronomical Union 6, S277 (décembre 2010) : 142–45. http://dx.doi.org/10.1017/s1743921311022642.
Texte intégralRésumé :
AbstractSelection effects in the submillimeter/far-infrared inhibit detailed analysis of extreme starbursts in the early Universe. Submillimeter Galaxy (SMG) detection and characterization biases against warm temperature SEDs Tdust ~50 K, against the highest redshift ULIRGs z > 3, and has so far been limited to a small sample of ~100 sources that have reliably identified optical or radio counterparts and spectroscopic redshifts. Recent observations by Herschel ⋅ ⋅ ⋅ ⋅ and ⋅ ⋅ ⋅⋅ ⋅ in the ~70–500 μm wavelength range provide a more complete census of high-z ULIRG activity than previous SMG surveys. However, source confusion and lack of spectroscopic identification of reliable counterparts limit the analysis of extreme ULIRGs to the most basic calculations, frought with a priori assumptions (e.g. Tdust/(1+z) degeneracy, far-IR/radio relation, confusion boosting factors, etc). Herein I address the biases on conclusions of SMG work and I demonstrate the need for thorough, spectroscopic follow-up of high-z ULIRGs in order to infer their physical conditions.
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Minhas, Shahryar, Peter D. Hoff et Michael D. Ward. « Inferential Approaches for Network Analysis : AMEN for Latent Factor Models ». Political Analysis 27, no 2 (20 novembre 2018) : 208–22. http://dx.doi.org/10.1017/pan.2018.50.
Texte intégralRésumé :
We introduce a Bayesian approach to conduct inferential analyses on dyadic data while accounting for interdependencies between observations through a set of additive and multiplicative effects (AME). The AME model is built on a generalized linear modeling framework and is thus flexible enough to be applied to a variety of contexts. We contrast the AME model to two prominent approaches in the literature: the latent space model (LSM) and the exponential random graph model (ERGM). Relative to these approaches, we show that the AME approach is (a) to be easy to implement; (b) interpretable in a general linear model framework; (c) computationally straightforward; (d) not prone to degeneracy; (e) captures first-, second-, and third-order network dependencies; and (f) notably outperforms ERGMs and LSMs on a variety of metrics and in an out-of-sample context. In summary, AME offers a straightforward way to undertake nuanced, principled inferential network analysis for a wide range of social science questions.
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Tress, M., I. Ferreras, P. G. Pérez-González, A. Bressan, G. Barro, H. Domínguez-Sánchez et C. Eliche-Moral. « A deeper look at the dust attenuation law of star-forming galaxies at high redshift ». Monthly Notices of the Royal Astronomical Society 488, no 2 (8 juillet 2019) : 2301–11. http://dx.doi.org/10.1093/mnras/stz1851.
Texte intégralRésumé :
ABSTRACT A diverse range of dust attenuation laws is found in star-forming galaxies. In particular, Tress et al. (2018) studied the SHARDS survey to constrain the NUV bump strength (B) and the total-to-selective ratio (RV) of 1753 star-forming galaxies in the GOODS-N field at 1.5 < z < 3. We revisit here this sample to assess the implications and possible causes of the correlation found between RV and B. The UVJ bicolour plot and main sequence of star formation are scrutinized to look for clues into the observed trend. The standard boundary between quiescent and star-forming galaxies is preserved when taking into account the wide range of attenuation parameters. However, an additional degeneracy – regarding the effective attenuation law – is added to the standard loci of star-forming galaxies in the UVJ diagram. A simple phenomenological model with an age-dependent extinction (at fixed dust composition) is compatible with the observed trend between RV and B, whereby the opacity decreases with the age of the populations, resulting in a weaker NUV bump when the overall attenuation is shallower (greyer). In addition, we compare the constraints obtained by the SHARDS sample with dust models from the literature, supporting a scenario where geometry could potentially drive the correlation between RV and B.
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Howard, Ward S., et Meredith A. MacGregor. « No Such Thing as a Simple Flare : Substructure and Quasi-periodic Pulsations Observed in a Statistical Sample of 20 s Cadence TESS Flares ». Astrophysical Journal 926, no 2 (1 février 2022) : 204. http://dx.doi.org/10.3847/1538-4357/ac426e.
Texte intégralRésumé :
Abstract A 20 s cadence Transiting Exoplanet Survey Satellite monitoring campaign of 226 low-mass flare stars during Cycle 3 recorded 3792 stellar flares of ≥1032 erg. We explore the time-resolved emission and substructure in 440 of the largest flares observed at high signal-to-noise, 97% of which released energies of ≥1033 erg. We discover degeneracy present at 2 minute cadence between sharply peaked and weakly peaked flares is common, although 20 s cadence breaks these degeneracies. We better resolve the rise phases and find 46% of large flares exhibit substructure during the rise phase. We observe 49 candidate quasi-periodic pulsations (QPP) and confirm 17 at ≥3σ. Most of our QPPs have periods less than 10 minutes, suggesting short-period optical QPPs are common. We find QPPs in both the rise and decay phases of flares, including a rise-phase QPP in a large flare from Proxima Cen. We confirm that the Davenport et al. template provides a good fit to most classical flares observed at high cadence, although 9% favor Gaussian peaks instead. We characterize the properties of complex flares, finding 17% of complex flares exhibit “peak-bump” morphologies composed of a large, highly impulsive peak followed by a second, more gradual Gaussian peak. We also estimate the UVC surface fluences of temperate planets at flare peak and find one-third of 1034 erg flares reach the D90 dose of Deinococcus radiodurans in just 20 s in the absence of an atmosphere.
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Lombardo, Linda, Patrick François, Piercarlo Bonifacio, Elisabetta Caffau, Aroa del Mar Matas Pinto, Corinne Charbonnel, Georges Meynet, Lorenzo Monaco, Gabriele Cescutti et Alessio Mucciarelli. « Young giants of intermediate mass ». Astronomy & ; Astrophysics 656 (décembre 2021) : A155. http://dx.doi.org/10.1051/0004-6361/202141408.
Texte intégralRésumé :
Context. In the search of a sample of metal-poor bright giants using Strömgren photometry, we serendipitously found a sample of 26 young (ages younger than 1 Gyr) metal-rich giants, some of which have high rotational velocities. Aims. We determined the chemical composition and rotational velocities of these stars in order to compare them with predictions from stellar evolution models. These stars where of spectral type A to B when on the main sequence, and we therefore wished to compare their abundance pattern to that of main-sequence A and B stars. Methods. Stellar masses were derived by comparison of the position of the stars in the colour-magnitude diagram with theoretical evolutionary tracks. These masses, together with Gaia photometry and parallaxes, were used to derive the stellar parameters. We used spectrum synthesis and model atmospheres to determine chemical abundances for 16 elements (C, N, O, Mg, Al, Ca, Fe, Sr, Y, Ba, La, Ce, Pr, Nd, Sm, and Eu) and rotational velocities. Results. The age-metallicity degeneracy can affect photometric metallicity calibrations. We identify 15 stars as likely binary stars. All stars are in prograde motion around the Galactic centre and belong to the thin-disc population. All but one of the sample stars present low [C/Fe] and high [N/Fe] ratios together with constant [(C+N+O)/Fe], suggesting that they have undergone CNO processing and first dredge-up. The observed rotational velocities are in line with theoretical predictions of the evolution of rotating stars.
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Byun, Joyce, Felipe Oliveira Franco, Cullan Howlett, Camille Bonvin et Danail Obreschkow. « Constraining the growth rate of structure with phase correlations ». Monthly Notices of the Royal Astronomical Society 497, no 2 (13 juillet 2020) : 1765–90. http://dx.doi.org/10.1093/mnras/staa2020.
Texte intégralRésumé :
ABSTRACT We show that correlations between the phases of the galaxy density field in redshift space provide additional information about the growth rate of large-scale structure that is complementary to the power-spectrum multipoles. In particular, we consider the multipoles of the line correlation function (LCF), which correlates phases between three collinear points, and use the Fisher forecasting method to show that the LCF multipoles can break the degeneracy between the measurement of the growth rate of structure f and the amplitude of perturbations σ8 that is present in the power-spectrum multipoles at large scales. This leads to an improvement in the measurement of f and σ8 by up to 220 per cent for $k_{\rm max} = 0.15 \, h\, \mathrm{Mpc}^{-1}$ and up to 50 per cent for $k_{\rm max} = 0.30 \, h\, \mathrm{Mpc}^{-1}$ at redshift z = 0.25, with respect to power-spectrum measurements alone for the upcoming generation of galaxy surveys like DESI and Euclid. The average improvements in the constraints on f and σ8 for $k_{\rm max} = 0.15 \, h\, \mathrm{Mpc}^{-1}$ are ∼90 per cent for the DESI BGS sample with mean redshift $\overline{z}=0.25$, ∼40 per cent for the DESI ELG sample with $\overline{z}=1.25$, and ∼40 per cent for the Euclid Hα galaxies with $\overline{z}=1.3$. For $k_{\rm max} = 0.30 \, h\, \mathrm{Mpc}^{-1}$, the average improvements are ∼40 per cent for the DESI BGS sample and ∼20 per cent for both the DESI ELG and Euclid Hα galaxies.
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Yang, Ming, Alceste Z. Bonanos, Bi-Wei Jiang, Jian Gao, Panagiotis Gavras, Grigoris Maravelias, Shu Wang et al. « Evolved massive stars at low metallicity ». Astronomy & ; Astrophysics 639 (juillet 2020) : A116. http://dx.doi.org/10.1051/0004-6361/201937168.
Texte intégralRésumé :
We present the most comprehensive red supergiant (RSG) sample for the Small Magellanic Cloud (SMC) to date, including 1239 RSG candidates. The initial sample was derived based on a source catalog for the SMC with conservative ranking. Additional spectroscopic RSGs were retrieved from the literature, and RSG candidates were selected based on the inspection of Gaia and 2MASS color-magnitude diagrams (CMDs). We estimate that there are in total ∼1800 or more RSGs in the SMC. We purify the sample by studying the infrared CMDs and the variability of the objects, though there is still an ambiguity between asymptotic giant branch stars (AGBs) and RSGs at the red end of our sample. One heavily obscured target was identified based on multiple near-IR and mid-IR (MIR) CMDs. The investigation of color-color diagrams shows that there are fewer RSGs candidates (∼4%) showing PAH emission features compared to the Milky Way and LMC (∼15%). The MIR variability of RSG sample increases with luminosity. We separate the RSG sample into two subsamples (risky and safe), and identify one M5e AGB star in the risky subsample based on simultaneous inspection of variabilities, luminosities, and colors. The degeneracy of mass loss rate (MLR), variability, and luminosity of the RSG sample is discussed, indicating that most of the targets with high variability are also the bright ones with high MLR. Some targets show excessive dust emission, which may be related to previous episodic mass loss events. We also roughly estimate the total gas and dust budget produced by entire RSG population as ∼1.9−1.1+2.4 × 10−6 M⊙ yr−1 in the most conservative case, according to the derived MLR from IRAC1–IRAC4 color. Based on the MIST models, we derive a linear relation between Teff and observed J − KS color with reddening correction for the RSG sample. By using a constant bolometric correction and this relation, the Geneva evolutionary model is compared with our RSG sample, showing a good agreement and a lower initial mass limit of ∼7 M⊙ for the RSG population. Finally, we compare the RSG sample in the SMC and the LMC. Despite the incompleteness of LMC sample in the faint end, the result indicates that the LMC sample always shows redder color (except for the IRAC1–IRAC2 and WISE1–WISE2 colors due to CO absorption) and higher variability than the SMC sample, which is likely due to a positive relation between MLR, variability and the metallicity.
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Kumar, Suresh, Rafael C. Nunes et Priya Yadav. « Updating non-standard neutrinos properties with Planck-CMB data and full-shape analysis of BOSS and eBOSS galaxies ». Journal of Cosmology and Astroparticle Physics 2022, no 09 (1 septembre 2022) : 060. http://dx.doi.org/10.1088/1475-7516/2022/09/060.
Texte intégralRésumé :
Abstract Using the latest observational data from Planck-CMB and its combination with the pre-reconstructed full-shape (FS) galaxy power spectrum measurements from the BOSS DR12 sample and eBOSS LRG DR16 sample, we report the observational constraints on the cosmic neutrino properties given by the extended ΛCDM scenario: ΛCDM + N eff + ∑ mν + c 2 eff + c 2 vis + ξν , and its particular case ΛCDM + c 2 eff + c 2 vis + ξν , where N eff, ∑ mν , c 2 eff, c 2 vis, ξν are the effective number of species, the total neutrino mass, the sound speed in the neutrinos rest frame, the viscosity parameter and the degeneracy parameter quantifying a cosmological leptonic asymmetry, respectively. We observe that the combination of FS power spectrum measurements with the CMB data significantly improves the parametric space of the models compared to the CMB data alone case. We find no evidence for neutrinos properties other than the ones predicted by the standard cosmological theory. Our most robust observational constraints are given by CMB + BOSS analysis. For the generalized extended ΛCDM scenario, we find c 2 eff = 0.3304+0.0064 -0.0075, c 2 vis = 0.301+0.037 -0.033, ξν < 0.05, N eff = 2.90 ± 0.15 at 68% CL, with ∑ mν < 0.116 eV at 95% CL. These are the strongest limits ever reported for these extended ΛCDM scenarios.
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Divya, G. Naga, et S. Koteswara Rao. « Application of Sigma Point Particle Filter Method for Passive State Estimation in Underwater ». Defence Science Journal 71, no 4 (1 juillet 2021) : 507–14. http://dx.doi.org/10.14429/dsj.71.16284.
Texte intégralRésumé :
Bearings-only tracking (BOT) plays a vital role in underwater surveillance. In BOT, measurement is tangentially related to state of the system. This measurement is also corrupted with noise due to turbulent underwater environment. Hence state estimation process using BOT becomes nonlinear. This necessitates the use of nonlinear filtering algorithms in place of traditional linear filters like Kalman filter. In general, these nonlinear filters utilize the assumption of measurements being corrupted with Gaussian noise for state estimation. The measurements cannot be always corrupted with Gaussian noise because of the highly unstable sea environment. These problems indicate the necessity for development of nonlinear non-Gaussian filters like particle filter (PF) for underwater tracking. However, PF suffers from severe problems like sample degeneracy and impoverishment and also it is tedious to select an appropriate technique for resampling. To overcome these difficulties in PF implementation, the strategy of combining PF with another filter like unscented Kalman filter is proposed for target’s state estimation. The detailed analysis of the same is presented in comparison with other particle filter combinations using the simulation results obtained in Matlab.
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Banerjee, Soumya, et S. Jonathan Chapman. « Influence of correlated antigen presentation on T-cell negative selection in the thymus ». Journal of The Royal Society Interface 15, no 148 (novembre 2018) : 20180311. http://dx.doi.org/10.1098/rsif.2018.0311.
Texte intégralRésumé :
The thymus is the primary organ for the generation of naive T cells, a key component of the immune system. Tolerance of T cells to self is achieved primarily in the thymic medulla, where immature T cells (thymocytes) sample self-peptides presented by medullary thymic epithelial cells (mTECs). A sufficiently strong interaction activates the thymocytes leading to negative selection. A key question of current interest is whether there is any structure in the manner in which mTECs present peptides: can any mTEC present any peptide at any time, or are there particular patterns of correlated peptide presentation? We investigate this question using a mathematical model of negative selection. We find that correlated patterns of peptide presentation may be advantageous in negatively selecting low-degeneracy thymocytes (that is, those thymocytes which respond to relatively few peptides). We also quantify the probability that an auto-reactive thymocyte exits the thymus before it encounters a cognate antigen. The results suggest that heterogeneity of gene co-expression in mTECs has an effect on the probability of escape of autoreactive thymocytes.