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## IS THE DENSITY DISTRIBUTION OF CLUSTERS NON-GAUSSIAN ?

Kolatt, Tsafrir
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
The one-point probability distribution function (pdf) is computed for the $25\hmpc$-smoothed density field of rich clusters of galaxies in the Abell/\aco\ catalogs. The observed pdf is compared to the pdf s drawn similarly from mock catalogs of clusters in cosmological simulations of Gaussian and several non-Gaussian initial conditions. Several statistics allow significant rejection of the non-Gaussian models tested here, and fail to reject the Gaussian model. A comparison with the predictions of second-order perturbation theory and a log-normal model for cdm Gaussian initial conditions yield a linear biasing factor $b_c/b_o \simeq 4$ and $b_c/b_o\simeq 3.7$ for $R\geq 0$ clusters.; Comment: To appear in the proceedings of the XXXth MORIOND meeting: "Clustering in the Universe". 8 pages, compressed uuencoded file

## Stochastic $\phi^4-$Theory in the Strong Coupling Limit

Abedpour, N.; Niry, M. D.; Bahraminasab, A.; Masoudi, A. A.; Davoudi, J.; Sahimi, Muhammad; Tabar, M. Reza Rahimi
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
The stochastic $\phi^4$-theory in $d-$dimensions dynamically develops domain wall structures within which the order parameter is not continuous. We develop a statistical theory for the $\phi^4$-theory driven with a random forcing which is white in time and Gaussian-correlated in space. A master equation is derived for the probability density function (PDF) of the order parameter, when the forcing correlation length is much smaller than the system size, but much larger than the typical width of the domain walls. Moreover, exact expressions for the one-point PDF and all the moments $<\phi^n>$ are given. We then investigate the intermittency issue in the strong coupling limit, and derive the tail of the PDF of the increments $\phi(x_2) - \phi(x_1)$. The scaling laws for the structure functions of the increments are obtained through numerical simulations. It is shown that the moments of field increments defined by, $C_b=< |\phi(x_2)-\phi(x_1)|^b>$, behave as $|x_1-x_2|^{\xi_b}$, where $\xi_b=b$ for $b\leq 1$, and $\xi_b=1$ for $b\geq1$; Comment: 22 pages, 6 figures. to appear in Nuclear. Phys. B

## Fisher information as a performance metric for locally optimum processing

Duan, Fabing; Chapeau-Blondeau, Francois; Abbott, Derek
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
For a known weak signal in additive white noise, the asymptotic performance of a locally optimum processor (LOP) is shown to be given by the Fisher information (FI) of a standardized even probability density function (PDF) of noise in three cases: (i) the maximum signal-to-noise ratio (SNR) gain for a periodic signal; (ii) the optimal asymptotic relative efficiency (ARE) for signal detection; (iii) the best cross-correlation gain (CG) for signal transmission. The minimal FI is unity, corresponding to a Gaussian PDF, whereas the FI is certainly larger than unity for any non-Gaussian PDFs. In the sense of a realizable LOP, it is found that the dichotomous noise PDF possesses an infinite FI for known weak signals perfectly processed by the corresponding LOP. The significance of FI lies in that it provides a upper bound for the performance of locally optimum processing.; Comment: 8 pages, 1 figure

## Excitons in a Photosynthetic Light-Harvesting System: A Combined Molecular Dynamics/Quantum Chemistry and Polaron Model Study

Damjanovic, Ana; Kosztin, Ioan; Schulten, Klaus
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
The dynamics of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with a novel approach which combines molecular dynamics (MD) simulations with quantum chemistry (QC) calculations. The MD simulations of an LH-II complex, solvated and embedded in a lipid bilayer at physiological conditions (with total system size of 87,055 atoms) revealed a pathway of a water molecule into the B800 binding site, as well as increased dimerization within the B850 BChl ring, as compared to the dimerization found for the crystal structure. The fluctuations of pigment (B850 BChl) excitation energies, as a function of time, were determined via ab initio QC calculations based on the geometries that emerged from the MD simulations. From the results of these calculations we constructed a time-dependent Hamiltonian of the B850 exciton system from which we determined the linear absorption spectrum. Finally, a polaron model is introduced to describe quantum mechanically both the excitonic and vibrational (phonon) degrees of freedom. The exciton-phonon coupling that enters into the polaron model, and the corresponding phonon spectral function are derived from the MD/QC simulations. It is demonstrated that, in the framework of the polaron model...

## Inverse Bayesian Estimation of Gravitational Mass Density in Galaxies from Missing Kinematic Data

Chakrabarty, Dalia; Saha, Prasenjit
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
In this paper we focus on a type of inverse problem in which the data is expressed as an unknown function of the sought and unknown model function (or its discretised representation as a model parameter vector). In particular, we deal with situations in which training data is not available. Then we cannot model the unknown functional relationship between data and the unknown model function (or parameter vector) with a Gaussian Process of appropriate dimensionality. A Bayesian method based on state space modelling is advanced instead. Within this framework, the likelihood is expressed in terms of the probability density function ($pdf$) of the state space variable and the sought model parameter vector is embedded within the domain of this $pdf$. As the measurable vector lives only inside an identified sub-volume of the system state space, the $pdf$ of the state space variable is projected onto the space of the measurables, and it is in terms of the projected state space density that the likelihood is written; the final form of the likelihood is achieved after convolution with the distribution of measurement errors. Application motivated vague priors are invoked and the posterior probability density of the model parameter vectors, given the data is computed. Inference is performed by taking posterior samples with adaptive MCMC. The method is illustrated on synthetic as well as real galactic data.

## Impact of QED radiative corrections on Parton Distribution Functions

Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
The level of precision achieved by the experimental measurements at the LHC requires the inclusion of higher order electroweak effects to the processes of $pp$ scattering. In particular the photon-induced process $\gamma\gamma \to \ell^+\ell^-$ make a significant contribution ($\sim 10 \%$) to the dilepton invariant mass distribution. To evaluate the cross-section of this process one need to know the parton distribution function (PDF) of the photon in the proton $\gamma (x,\mu^2)$. The aim of the current study is to investigate the impact of QED corrections on PDFs and describe the implementation of QED-modified evolution equations into beta release of new version of {\tt QCDNUM} program. The {\tt APPLGRID} interface to {\tt SANC} Monte Carlo generator for fast evaluation of photon-induced cross-section is also outlined. The results were cross-checked with {\tt partonevolution} program, {\tt MRST2004QED} PDF set and {\tt APFEL} program. The described developments are planned to include into {\tt HERAFitter} package and can be used to determine the photon PDF using new data from the LHC experiments.

## Dynamics of gravitational clustering III. The quasi-linear regime for some non-Gaussian initial conditions

Valageas, P.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
144.84746%
Using a non-perturbative method developed in a previous work (paper II), we derive the probability distribution $P(\delta_R)$ of the density contrast within spherical cells in the quasi-linear regime for some non-Gaussian initial conditions. We describe three such models. The first one is a straightforward generalization of the Gaussian scenario. It can be seen as a phenomenological description of a density field where the tails of the linear density contrast distribution would be of the form $P_L(\delta_L) \sim e^{-|\delta_L|^{-\alpha}}$, where $\alpha$ is no longer restricted to 2 (as in the Gaussian case). We derive exact results for $P(\delta_R)$ in the quasi-linear limit. The second model is a physically motivated isocurvature CDM scenario. Our approach needs to be adapted to this specific case and in order to get convenient analytical results we introduce a simple approximation (which is not related to the gravitational dynamics but to the initial conditions). Then, we find a good agreement with the available results from numerical simulations for the pdf of the linear density contrast for $\delta_{L,R} \ga 0$. We can expect a similar accuracy for the non-linear pdf $P(\delta_R)$. Finally, the third model corresponds to the small deviations from Gaussianity which arise in standard slow-roll inflation. We obtain exact results for the pdf of the density field in the quasi-linear limit...

## Dynamics of gravitational clustering IV. The probability distribution of rare events

Valageas, P.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
144.84746%

## Charge-Stripe Ordering From Local Octahedral Tilts: Underdoped and Superconducting La2-xSrxCuO4 (0 < x < 0.30)

Bozin, E. S.; Billinge, S. J. L.; Kwei, G. H.; Takagi, H.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
144.84746%
The local structure of La2-xSrxCuO4, for 0 < x < 0.30, has been investigated using the atomic pair distribution function (PDF) analysis of neutron powder diffraction data. The local octahedral tilts are studied to look for evidence of [110] symmetry (i.e., LTT-symmetry) tilts locally, even though the average tilts have [010] symmetry (i.e., LTO-symmetry) in these compounds. We argue that this observation would suggest the presence of local charge-stripe order. We show that the tilts are locally LTO in the undoped phase, in agreement with the average crystal structure. At non-zero doping the PDF data are consistent with the presence of local tilt disorder in the form of a mixture of LTO and LTT local tilt directions and a distribution of local tilt magnitudes. We present topological tilt models which qualitatively explain the origin of tilt disorder in the presence of charge stripes and show that the PDF data are well explained by such a mixture of locally small and large amplitude tilts.; Comment: 11 two-column pages, 11 figures

## High Resolution Studies of Radio Sources in the Hubble Deep and Flanking Fields

Muxlow, T. W. B.; Richards, A. M. S.; Garrington, S. T.; Wilkinson, P. N.; Anderson, B.; Richards, E. A.; Axon, D. J.; Fomalont, E. B.; Kellermann, K. I.; Partridge, R. B.; Windhorst, R. A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
144.84746%
Eighteen days of MERLIN data and 42 hours of A-array VLA data at 1.4 GHz have been combined to image a 10-arcmin field centred on the Hubble Deep and Flanking Fields (HDF and HFF). A complete sample of 92 radio sources with 1.4-GHz flux densities above 40 microJy has been imaged using MERLIN+VLA. The images are amongst the most sensitive yet made at 1.4 GHz, with rms noise levels of 3.3 microJy/beam in the 0.2-arcsec images. Virtually all the sources are resolved, with angular sizes in the range 0.2 to 3 arcsec. No additional sources were detected down to 23 microJy in the central 3 arcmin, indicating that sources fainter than 40 microJy are heavily resolved with MERLIN and must have typical angular sizes greater than 0.5 arcsec. Compact radio sources were used to align the optical data to the ICRF, to <50 mas in the HDF. We find a statistical association of very faint (2 microJy and above) radio sources with optically bright HDF galaxies down to about 23 mag. Of the 92 radio sources above 40 microJy, about 85 percent are identified with galaxies brighter than about I = 25 mag; the remaining 15 percent are associated with optically faint systems. We identify several very red, optically faint systems including the the strongest sub-mm source in the HDF...

## Probability density derivation and analysis of SINR in massive MIMO systems with MF beamformer

Feng, Shu; Chen, Gu; Mao, Wang; Berber, Stevan; Xiaohu, You