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Representações hierárquicas de vocábulos de línguas indígenas brasileiras: modelos baseados em mistura de Gaussianas; Hierarchical representations of words of brazilian indigenous languages: models based on Gaussian mixture

Sepúlveda Torres, Lianet
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/12/2010 Português
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Apesar da ampla diversidade de línguas indígenas no Brasil, poucas pesquisas estudam estas línguas e suas relações. Inúmeros esforços têm sido dedicados a procurar similaridades entre as palavras das línguas indígenas e classificá-las em famílias de línguas. Seguindo a classificação mais aceita das línguas indígenas do Brasil, esta pesquisa propõe comparar palavras de 10 línguas indígenas brasileiras. Para isso, considera-se que estas palavras são sinais de fala e estima-se a função de distribuição de probabilidade (PDF) de cada palavra, usando um modelo de mistura de gaussianas (GMM). A PDF foi considerada um modelo para representar as palavras. Os modelos foram comparados utilizando medidas de distância para construir estruturas hierárquicas que evidenciaram possíveis relações entre as palavras. Seguindo esta linha, a hipótese levantada nesta pesquisa é que as PDFs baseadas em GMM conseguem caracterizar as palavras das línguas indígenas, permitindo o emprego de medidas de distância entre elas para estabelecer relações entre as palavras, de forma que tais relações confirmem algumas das classificações. Os parâmetros do GMM foram calculados utilizando o algoritmo Maximização da Expectância (em inglês...

Late Pleistocene-Holocene environmental change in Serra do Espinhaço Meridional (Minas Gerais State, Brazil) reconstructed using a multi-proxy characterization of peat cores from mountain tropical mires; Reconstrução paleoambiental da Serra do Espinhaço Meridional (Minas Gerais, Brasil) durante o Pleistoceno tardio e Holoceno usando uma caracterização multi-proxy de testemunhos de turfeiras tropicais de montanha

Terra, Ingrid Horak
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/02/2014 Português
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The peatlands are ecosystems extremely sensitive to changes in hydrology, and are considered as faithful "natural archives of ecological memory". In the Serra do Espinhaço Meridional, Minas Gerais State, Brazil, mountain peatlands has been studied by soil scientists, but until now multi-proxy studies are almost absent. The location of these peatlands is ideal because they are in an area influenced by the activity of the South America Monsoon Systems (SAMS), which controls the amount and distribution of annual rainfall. The aim of this work was to reconstruct the environmental changes occurred throughout the late Pleistocene and Holocene, both at the local and regional scale by using a multi-proxy approach (stratigraphy, physical properties, 14C and OSL datings, pollen and geochemistry). However, determining of the processes involved in the genesis and evolution of peatlands soils was also necessary step. The physico-chemical properties and elemental composition of five peat cores (PdF-I, PdF-II, SJC, PI and SV) from four selected mires (Pau de Fruta, São João da Chapada, Pinheiros and Sempre Viva) seem to have responded to four main processes: relative accumulation of organic and mineral matter, linked to the evolution of the catchment soils (local erosion); deposition of dust from distant/regional sources; preservation of plant remains; and long and short-term peat decomposition. The combination of proxies of PdF-I core defined six main phases of change during the Holocene: (I) 10-7.4 cal kyr BP...

Reatividade de ligantes na química dos cianoferratos; The chemical reactivity of ligands cianoferratos

Iha, Neyde Yukie Murakami
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/09/1981 Português
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As reações entre o íon pentacianoferrato(II) e os isômeros de acetilpiridina (py(CO)CH3) foram estudadas com o intuito de estabelecer o mecanismo da reação de ataque nucleofílico ao grupo nitrosilo coordenado. Estas reações de adição foram acompanhadas pela técnica stopped flow ll a 25,OºC, em condições de pseudo primeira ordem, em meio alcalino com força iônica 0,10 M ajustada com LiC104 . Durante o processo, constatou-se que a formação dos produtos é precedida pelo aparecimento de intermediário azul com pequenos tempos de vida. A formação deste intermediário envolve o ataque da acetilpiridina na forma de carbânion, ao grupo nitrosilo coordenado, em competição com a adição do íon hidroxila. A lei da velocidade para o mecanismo proposto nesta etapa, tem a expressão abaixo para a constante de velocidade observada kobsl= KkL [py(CO)CH3] [OH-] + kOH [OH-] + k-L Os valores de KkL e k-L são respectivamente 1,91 ± 0,05 X 102M-2s-1 e 0,90± 0,02 X 10-1 s-1

Peptide Deformylase as an Antibacterial Drug Target: Target Validation and Resistance Development

Apfel, Christian M.; Locher, Hans; Evers, Stefan; Takács, Béla; Hubschwerlen, Christian; Pirson, Wolfgang; Page, Malcolm G. P.; Keck, Wolfgang
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /04/2001 Português
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New inhibitors of peptide deformylase (PDF) which are very potent against the isolated enzyme and show a certain degree of antibacterial activity have recently been synthesized by our group. Several lines of experimental evidence indicate that these inhibitors indeed interfere with the target enzyme in the bacterial cell. (i) The inhibition of Escherichia coli growth could be counteracted by overexpression of PDF from different organisms, including E. coli, Streptococcus pneumoniae, and Haemophilus influenzae. Conversely, reduced expression of PDF in S. pneumoniae resulted in an increased susceptibility to the inhibitors. (ii) Proteome analysis on two-dimensional gels revealed a shift for many proteins towards lower pI in the presence of PDF inhibitors, as would be expected if the proteins still carry their N-formyl-Met terminus. (iii) PDF inhibitors show no antimicrobial activity against E. coli under conditions that make growth independent of formylation and deformylation. The antibacterial activity in E. coli was characterized as bacteriostatic. Furthermore, the development of resistance in E. coli was observed to occur with high frequency (10−7). Resistant mutants show a reduced growth rate, and DNA sequence analysis revealed mutations in their formyl transferase gene. Taking all these aspects into account...

Increased Killing of Staphylococci and Streptococci by Daptomycin Compared with Cefazolin and Vancomycin in an In Vitro Peritoneal Dialysate Model

Hermsen, Elizabeth D.; Hovde, Laurie B.; Hotchkiss, John R.; Rotschafer, John C.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /12/2003 Português
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Peritoneal dialysate fluid (PDF) is a bacteriostatic medium that compromises the antibacterial activity of cell wall-active agents. By use of an in vitro static model, methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible S. aureus (MSSA), methicillin-susceptible Staphylococcus epidermidis (MSSE), and Streptococcus sanguis were exposed to daptomycin at concentrations of 10, 30, and 100 mg/liter, cefazolin at 125 mg/liter, and vancomycin at 25 mg/liter in cation-adjusted Mueller-Hinton Broth or Todd Hewitt Broth (for S. sanguis) and PDF at pHs of 5.5 and 7.4. The pH had no effect on antibacterial activity. Neither cefazolin nor vancomycin produced a bactericidal or a bacteriostatic effect versus MRSA, MSSA, MSSE, or S. sanguis in PDF, while all concentrations of daptomycin were bactericidal against all organisms in PDF. Daptomycin did not exhibit concentration-dependent activity in PDF. Daptomycin appears to be a promising agent for use in peritoneal dialysis-associated peritonitis, producing bacterial kill to a greater extent and at a higher rate than cefazolin or vancomycin in PDF.

Zinc Is the Metal Cofactor of Borrelia burgdorferi Peptide Deformylase†

Nguyen, Kiet T.; Wu, Jen-Chieh; Boylan, Julie A.; Gherardini, Frank C.; Pei, Dehua
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Peptide deformylase (PDF, E.C. 3.5.1.88) catalyzes the removal of N-terminal formyl groups from nascent ribosome-synthesized polypeptides. PDF contains a catalytically essential divalent metal ion, which is tetrahedrally coordinated by three protein ligands (His, His, and Cys) and a water molecule. Previous studies revealed that the metal cofactor is a Fe2+ ion in Escherichia coli and many other bacterial PDFs. In this work, we found that PDFs from two iron-deficient bacteria, Borrelia burgdorferi and Lactobacillus plantarum, are stable and highly active under aerobic conditions. The native B. burgdorferi PDF (BbPDF) was purified 1200-fold and metal analysis revealed that it contains ~1.1 Zn2+ ion/polypeptide but no iron. Our studies suggest that PDF utilizes different metal ions in different organisms. These data have important implications in designing PDF inhibitors and should help address some of the unresolved issues regarding PDF structure and catalytic function.

THE PROPORTION OF MUTANTS IN BACTERIAL CULTURES

Northrop, John H.; Kunitz, M.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/09/1957 Português
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The proportion of mutants in a growing culture of organisms will depend upon (a) the rate at which the wild cells produce them (with or without growth), (b) the back mutation rate, and (c) the growth rates of the wild and mutant cells. If the mutation rate without growth and the back mutation rate are neglected, the growth of a mutant is expressed by See PDF for Equation and the ratio of the mutant to wild by See PDF for Equation in which λ = mutation frequency rate constant, "mutation rate," A = growth rate constant of wild cells W, B = growth rate constant of mutant cells M. If the term [B – (1 – 2λ)A] is positive, the proportion of mutants increases continuously. If it is negative, the proportion of mutants reaches a constant value See PDF for Equation If mutation is assumed to occur without growth at the rate C, then the corresponding equations are (11), (12), and (14). See PDF for Equation If (B + C – A) is negative and t = ∞, See PDF for Equation If C << A, See PDF for Equation

Pigment Dispersing Factor-Dependent and -Independent Circadian Locomotor Behavioral Rhythms

Sheeba, Vasu; Sharma, Vijay K.; Gu, Huaiyu; Chou, Yu-Ting; O’Dowd, Diane K.; Holmes, Todd C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 02/01/2008 Português
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Circadian pacemaker circuits consist of ensembles of neurons, each expressing molecular oscillations, but how circuit-wide coordination of multiple oscillators regulates rhythmic physiological and behavioral outputs remains an open question. To investigate the relationship between the pattern of oscillator phase throughout the circadian pacemaker circuit and locomotor activity rhythms in Drosophila, we perturbed the electrical activity and pigment dispersing factor (PDF) levels of the lateral ventral neurons (LNv) and assayed their combinatorial effect on molecular oscillations in different parts of the circuit and on locomotor activity behavior. Altered electrical activity of PDF-expressing LNv causes initial behavioral arrhythmicity followed by gradual long-term emergence of two concurrent short- and long-period circadian behavioral activity bouts in ~60% of flies. Initial desynchrony of circuit-wide molecular oscillations is followed by the emergence of a novel pattern of period (PER) synchrony whereby two subgroups of dorsal neurons (DN1 and DN2) exhibit PER oscillation peaks coinciding with two activity bouts, whereas other neuronal subgroups exhibit a single PER peak coinciding with one of the two activity bouts. The emergence of this novel pattern of circuit-wide oscillator synchrony is not accompanied by concurrent change in the electrical activity of the LNv. In PDF-null flies...

Fragile X Mental Retardation Protein is Required for Programmed Cell Death and Clearance of Developmentally-Transient Peptidergic Neurons

Gatto, Cheryl L.; Broadie, Kendal
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Fragile X syndrome (FXS), caused by loss of fragile X mental retardation 1 (FMR1) gene function, is the most common heritable cause of intellectual disability and autism spectrum disorders. The FMR1 product (FMRP) is an RNA-binding protein best established to function in activity-dependent modulation of synaptic connections. In the Drosophila FXS disease model, loss of functionally-conserved dFMRP causes synaptic overgrowth and overelaboration in pigment dispersing factor (PDF) peptidergic neurons in the adult brain. Here, we identify a very different component of PDF neuron misregulation in dfmr1 mutants: the aberrant retention of normally developmentally-transient PDF tritocerebral (PDF-TRI) neurons. In wild-type animals, PDF-TRI neurons in the central brain undergo programmed cell death and complete, processive clearance within days of eclosion. In the absence of dFMRP, a defective apoptotic program leads to constitutive maintenance of these peptidergic neurons. We tested whether this apoptotic defect is circuit-specific by examining crustacean cardioactive peptide (CCAP) and bursicon circuits, which are similarly developmentally-transient and normally eliminated immediately post-eclosion. In dfmr1 null mutants, CCAP/bursicon neurons also exhibit significantly delayed clearance dynamics...

Pigment Dispersing Factor Regulates Ecdysone Biosynthesis via Bombyx Neuropeptide G Protein Coupled Receptor-B2 in the Prothoracic Glands of Bombyx mori

Iga, Masatoshi; Nakaoka, Takayoshi; Suzuki, Yutaka; Kataoka, Hiroshi
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 29/07/2014 Português
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Ecdysone is the key hormone regulating insect growth and development. Ecdysone synthesis occurs in the prothoracic glands (PGs) and is regulated by several neuropeptides. Four prothoracicotropic and three prothoracicostatic factors have been identified to date, suggesting that ecdysone biosynthesis is intricately regulated. Here, we demonstrate that the neuropeptide pigment dispersing factor (PDF) stimulates ecdysone biosynthesis and that this novel signaling pathway partially overlaps with the prothoracicotropic hormone (PTTH) signaling pathway. We performed transcriptome analysis and focused on receptors predominantly expressed in the PGs. From this screen, we identified a candidate orphan G protein coupled receptor (GPCR), Bombyx neuropeptide GPCR-B2 (BNGR-B2). BNGR-B2 was predominantly expressed in ecdysteroidogenic tissues, and the expression pattern in the PGs corresponded to the ecdysteroid titer in the hemolymph. Furthermore, we identified PDF as a ligand for BNGR-B2. PDF stimulated ecdysone biosynthesis in the PGs, but the stimulation was only observed in the PGs during a specific larval stage. PDF did not affect the transcript level of known ecdysone biosynthetic enzymes, and inhibiting transcription did not suppress ecdysone biosynthesis...

Representation of water table dynamics in a land surface scheme : observations, models, and analyses

Yeh, Pat Jen-Feng, 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 212 leaves; 15911365 bytes; 15911172 bytes; application/pdf; application/pdf
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A recent regional-scale water balance analysis has indicated that the groundwater storage and groundwater runoff are significant terms in the monthly and annual water balance for areas with a shallow water table. However, most of the current land surface parameterization schemes lack any representation of regional groundwater aquifers. Such a simplified representation of subsurface hydrological processes would result in significant errors in the predicted land-surface states and fluxes especially for the shallow water table areas in humid regions. This study attempts to address this deficiency. To incorporate the water table dynamics into a land surface scheme LSX, a lumped aquifer model is developed to represent the regional unconfined aquifer as a nonlinear reservoir, in which the aquifer simultaneously receives the recharge from the overlying soils, and discharges runoff into streams. The dependence of groundwater runoff on the water table depth (WTD), i.e., groundwater rating-curve, is parameterized empirically based on the observations in Illinois. The unconfined aquifer model is linked to the soil model in a land surface scheme LSX through the groundwater recharge flux (i.e., soil drainage flux). The total thickness of the unsaturated zone varies in response to the water table fluctuations...

Probability Density Function of Underwater Bomb Trajectory Deviation due to Stochastic Ocean Surface Slope

Chu, Peter C.; Fan, Chenwu; Watson, Kennard P.
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
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Journal of Dynamic Systems, Measurement and Control, American Society of Mechanical Engineers, in press; Ocean wave propagation causes random change of ocean surface slope and in turn affects the underwater bomb trajectory deviation (r) through water column. This trajectory deviation is crucial for the clearance of obstacles such as sea mines or maritime improvised explosive device (IED) in coastal oceans using bombs. A nonlinear six degrees of freedom (6-DOF) model has been recently developed and verified at the Naval Postgraduate School with various surface impact speeds and surface slopes as model inputs. The surface slope (s) randomly changes between 0 and π/2 with a probability density function (PDF) p(s), or called the s-PDF. After s is discretized into I intervals by s1, s2, ?, si , ? sI+1, the 6-DOF model is integrated with a given surface impact speed (v0) and each slope si to get bomb trajectory deviation ?ir at depth (h) as a model output. The calculated series of {?ir } is re-arranged into monotonically increasing order (rj}. The bomb trajectory deviation r within (rj, rj+1) may correspond to one interval or several intervals of s. The probability of r falling into (rj, rj+1) can be obtained from the probability of s...

Cosmology with Standard Sirens: the Importance of the Shape of the Lensing Magnification Distribution

Shang, Cien; Haiman, Zoltan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/04/2010 Português
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The gravitational waves (GWs) emitted by inspiraling binary black holes, expected to be detected by the Laser Interferometer Space Antenna (LISA), could be used to determine the luminosity distance to these sources with the unprecedented precision of <~ 1%. We study cosmological parameter constraints from such standard sirens, in the presence of gravitational lensing by large-scale structure. Lensing introduces magnification with a probability distribution function (PDF) whose shape is highly skewed and depends on cosmological parameters. We use Monte-Carlo simulations to generate mock samples of standard sirens, including a small intrinsic scatter, as well as the additional, larger scatter from lensing, in their inferred distances. We derive constraints on cosmological parameters, by simultaneously fitting the mean and the distribution of the residuals on the distance vs redshift (d_L - z) Hubble diagram. We find that for standard sirens at redshift z ~ 1, the sensitivity to a single cosmological parameter, such as the matter density Omega_m, or the dark energy equation of state w, is ~ 50%-80% tighter when the skewed lensing PDF is used, compared to the sensitivity derived from a Gaussian PDF with the same variance. When these two parameters are constrained simultaneously...

Gravitational Evolution of the Large-Scale Probability Density Distribution: The Edgeworth & Gamma Expansions

Gaztanaga, E.; Fosalba, P.; Elizalde, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/06/1999 Português
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The gravitational evolution of the cosmic one-point probability distribution function (PDF) has been estimated using an analytic approximation that combines gravitational perturbation theory with the Edgeworth expansion around a Gaussian PDF. Despite the remarkable success of the Edgeworth expansion in modeling the weakly non-linear growth of fluctuations around the peak of the cosmic PDF, it fails to reproduce the expected behaviour in the tails of the distribution. Besides, this expansion is ill-defined as it predicts negative densities and negative probabilities for the cosmic fields. This is a natural consequence of using an expansion around the Gaussian distribution, which is not rigorously well-defined when describing a positive variate, such as the density field. Here we present an alternative to the Edgeworth series based on an expansion around the Gamma PDF. The Gamma expansion is designed to converge when the PDF exhibits exponential tails. The proposed expansion is better suited for describing a real PDF as it always yields positive densities and the PDF is effectively positive-definite. We compare the performance of the Edgeworth and the Gamma expansions for a wide dynamical range making use of cosmological N-body simulations and assess their range of validity. In general...

Improving parton distribution uncertainties in a W mass measurement at the LHC

Sullivan, Zack; Quackenbush, Seth
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We reexamine the dominant contribution of parton distribution function (PDF) uncertainties to the W mass measurement, and determine their contribution is +-39(30) MeV when running the Large Hadron Collider at 7(13) TeV. We find that spurious correlations in older PDF sets led to over-optimistic assumptions regarding normalization to Z observables. In order to understand the origin of the large uncertainties we break down the contribution of the PDF errors into effects at the hard matrix element level, in showering, and in sensitivity to finite detector resolutions. Using CT10, CT10W, and charm enhanced PDF sets in comparison to older PDF sets, we develop a robust analysis that examines correlations between transverse mass reconstructions of W and Z decays (scaled by cos $\theta_W$) to leptons. We find that central leptons (|$\eta_l$| < 1.3) from W and Z bosons carry the most weight in reducing the PDF uncertainty, and estimate a PDF error of +10/-12 MeV is achievable in a W mass measurement at the LHC. Further reductions of the W mass uncertainty will require improved fits to the parton distribution functions.; Comment: 6 pages, Presentation at the DPF 2015 Meeting of the American Physical Society Division of Particles and Fields...

Extreme deviations and applications

Frisch, U.; Sornette, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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Stretched exponential probability density functions (pdf), having the form of the exponential of minus a fractional power of the argument, are commonly found in turbulence and other areas. They can arise because of an underlying random multiplicative process. For this, a theory of extreme deviations is developed, devoted to the far tail of the pdf of the sum $X$ of a finite number $n$ of independent random variables with a common pdf $e^{-f(x)}$. The function $f(x)$ is chosen (i) such that the pdf is normalized and (ii) with a strong convexity condition that $f''(x)>0$ and that $x^2f''(x)\to +\infty$ for $|x|\to\infty$. Additional technical conditions ensure the control of the variations of $f''(x)$. The tail behavior of the sum comes then mostly from individual variables in the sum all close to $X/n$ and the tail of the pdf is $\sim e^{-nf(X/n)}$. This theory is then applied to products of independent random variables, such that their logarithms are in the above class, yielding usually stretched exponential tails. An application to fragmentation is developed and compared to data from fault gouges. The pdf by mass is obtained as a weighted superposition of stretched exponentials, reflecting the coexistence of different fragmentation generations. For sizes near and above the peak size...

The Probability Distribution for Non-Gaussianity Estimators

Smith, Tristan L.; Kamionkowski, Marc; Wandelt, Benjamin D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/04/2011 Português
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One of the principle efforts in cosmic microwave background (CMB) research is measurement of the parameter fnl that quantifies the departure from Gaussianity in a large class of non-minimal inflationary (and other) models. Estimators for fnl are composed of a sum of products of the temperatures in three different pixels in the CMB map. Since the number ~Npix^2 of terms in this sum exceeds the number Npix of measurements, these ~Npix^2 terms cannot be statistically independent. Therefore, the central-limit theorem does not necessarily apply, and the probability distribution function (PDF) for the fnl estimator does not necessarily approach a Gaussian distribution for N_pix >> 1. Although the variance of the estimators is known, the significance of a measurement of fnl depends on knowledge of the full shape of its PDF. Here we use Monte Carlo realizations of CMB maps to determine the PDF for two minimum-variance estimators: the standard estimator, constructed under the null hypothesis (fnl=0), and an improved estimator with a smaller variance for |fnl| > 0. While the PDF for the null-hypothesis estimator is very nearly Gaussian when the true value of fnl is zero, the PDF becomes significantly non-Gaussian when |fnl| > 0. In this case we find that the PDF for the null-hypothesis estimator fnl_hat is skewed...

Exploring the beta distribution in variable-density turbulent mixing

Bakosi, J.; Ristorcelli, J. R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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In assumed probability density function (pdf) methods of turbulent combustion, the shape of the scalar pdf is assumed a priori and the pdf is parametrized by its moments for which model equations are solved. In non-premixed flows the beta distribution has been a convenient choice to represent the mixture fraction in binary mixtures or a progress variable in combustion. Here the beta-pdf approach is extended to variable-density mixing: mixing between materials that have very large density differences and thus the scalar fields are active. As a consequence, new mixing phenomena arise due to 1) cubic non-linearities in the Navier-Stokes equation, 2) additional non-linearities in the molecular diffusion terms and 3) the appearance of the specific volume as a dynamical variable. The assumed beta-pdf approach is extended to transported pdf methods by giving the associated stochastic differential equation (SDE). The beta distribution is shown to be a realizable, consistent and sufficiently general representation of the marginal pdf of the fluid density, an active scalar, in non-premixed variable-density turbulent mixing. The moment equations derived from mass conservation are compared to the moment equations derived from the governing SDE. This yields a series of relations between the non-stationary coefficients of the SDE and the mixing physics. Our treatment of this problem is general: the mixing is mathematically represented by the divergence of the velocity field which can only be specified once the problem is defined. In this paper we seek to describe a theoretical framework to subsequent applications. We report and document several rigorous mathematical results...

Non-Gaussian Tails of Cosmological Density Distribution Function from Dark Halo Approach

Taruya, Atsushi; Hamana, Takashi; Kayo, Issha
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/10/2002 Português
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We present a simple model based on the dark halo approach which provides a useful way to understand key points determining the shape of the non-Gaussian tails of the dark matter one-point probability distribution function(PDF). In particular, using the scale-free models with power-law profile of dark halos, we derive a simple analytic expression for the one-point PDF. It is found that the shape of the PDF changes at the characteristic value of $\delta_*$ which is defined by the smoothed density of a halo with the characteristic mass $M_*$ at the epoch. In cold dark matter models with top-hat smoothing filters, the characteristic smoothed density at present time typically takes the value $\delta_*\gg 1$ for a small smoothing scale $\rth\sim 1$Mpc$/h$ and conversely $\delta_*\ll 1$ for a large smoothing scale $\rth > 10$Mpc$/h$. On the range $\delta/\delta_*<1$, the shape of the PDF is almost solely determined by the outer slope of halos and scales as a power-law. The resultant non-Gaussian tails of PDF then resemble the log-normal PDFs in that range and show a good agreement with N-body simulations, which can be ascribed to the universality of the outer slope of the halo profile. In contrast, tails of one-point PDF in the range $\delta/\delta_*>1$ basically follow the steep exponential tails of the halo mass function...

Probability distribution for non-Gaussianity estimators

Smith, Tristan L.; Kamionkowski, Marc; Wandelt, Benjamin D.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 23/09/2011 Português
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One of the principle efforts in cosmic microwave background (CMB) research is measurement of the parameter fnl that quantifies the departure from Gaussianity in a large class of nonminimal inflationary (and other) models. Estimators for f_(nl) are composed of a sum of products of the temperatures in three different pixels in the CMB map. Since the number ~N_(pix)^2 of terms in this sum exceeds the number N_(pix) of measurements, these ~N_(pix)^2 terms cannot be statistically independent. Therefore, the central-limit theorem does not necessarily apply, and the probability distribution function (PDF) for the f_(nl) estimator does not necessarily approach a Gaussian distribution for N_(pix)≫1. Although the variance of the estimators is known, the significance of a measurement of fnl depends on knowledge of the full shape of its PDF. Here we use Monte Carlo realizations of CMB maps to determine the PDF for two minimum-variance estimators: the standard estimator, constructed under the null hypothesis (f_(nl)=0), and an improved estimator with a smaller variance for f_(nl) ≠ 0. While the PDF for the null-hypothesis estimator is very nearly Gaussian when the true value of f_(nl) is zero, the PDF becomes significantly non-Gaussian when f_(nl) ≠ 0. In this case we find that the PDF for the null-hypothesis estimator f_(nl) is skewed...