1,061 research outputs found
Extended Perturbation Theory for the Local Density Distribution Function
Perturbation theory makes it possible to calculate the probability
distribution function (PDF) of the large scale density field in the small
variance limit. For top hat smoothing and scale-free Gaussian initial
fluctuations, the result depends only on the linear variance, sigma_linear, and
its logarithmic derivative with respect to the filtering scale
-(n_linear+3)=dlog sigma_linear^2/dlog L (Bernardeau 1994). In this paper, we
measure the PDF and its low-order moments in scale-free simulations evolved
well into the nonlinear regime and compare the results with the above
predictions, assuming that the spectral index and the variance are adjustable
parameters, n_eff and sigma_eff=sigma, where sigma is the true, nonlinear
variance. With these additional degrees of freedom, results from perturbation
theory provide a good fit of the PDFs, even in the highly nonlinear regime. The
value of n_eff is of course equal to n_linear when sigma << 1, and it decreases
with increasing sigma. A nearly flat plateau is reached when sigma >> 1. In
this regime, the difference between n_eff and n_linear increases when n_linear
decreases. For initial power-spectra with n_linear=-2,-1,0,+1, we find n_eff ~
-9,-3,-1,-0.5 when sigma^2 ~ 100.Comment: 13 pages, 6 figures, Latex (MN format), submitted to MNRA
Collective migration and patterning during early development of zebrafish posterior lateral line
The morphogenesis of zebrafish posterior lateral line (PLL) is a good predictive model largely used in biology to study cell coordinated reorganization and collective migration regulating pathologies and human embryonic processes. PLL development involves the formation of a placode formed by epithelial cells with mesenchymal characteristics which migrates within the animal myoseptum while cyclically assembling and depositing rosette-like clusters (progenitors of neuromast structures). The overall process mainly relies on the activity of specific diffusive chemicals, which trigger collective directional migration and patterning. Cell proliferation and cascade of phenotypic transitions play a fundamental role as well. The investigation on the mechanisms regulating such a complex morphogenesis has become a research topic, in the last decades, also for the mathematical community. In this respect, we present a multiscale hybrid model integrating a discrete approach for the cellular level and a continuous description for the molecular scale. The resulting numerical simulations are then able to reproduce both the evolution of wild-type (i.e. normal) embryos and the pathological behaviour resulting form experimental manipulations involving laser ablation. A qualitative analysis of the dependence of these model outcomes from cell-cell mutual interactions, cell chemical sensitivity and internalization rates is included. The aim is first to validate the model, as well as the estimated parameter values, and then to predict what happens in situations not tested yet experimentally. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'
A comparison of estimators for the two-point correlation function
Nine of the most important estimators known for the two-point correlation
function are compared using a predetermined, rigorous criterion. The indicators
were extracted from over 500 subsamples of the Virgo Hubble Volume simulation
cluster catalog. The ``real'' correlation function was determined from the full
survey in a 3000Mpc/h periodic cube. The estimators were ranked by the
cumulative probability of returning a value within a certain tolerance of the
real correlation function. This criterion takes into account bias and variance,
and it is independent of the possibly non-Gaussian nature of the error
statistics. As a result for astrophysical applications a clear recommendation
has emerged: the Landy & Szalay (1993) estimator, in its original or grid
version Szapudi & Szalay (1998), are preferred in comparison to the other
indicators examined, with a performance almost indistinguishable from the
Hamilton (1993) estimator.Comment: aastex, 10 pages, 1 table, 1 figure, revised version, accepted in
ApJ
PERLINDUNGAN KONSUMEN TERHADAP MAKANAN JAJANAN YANG MENGANDUNG FORMALIN DAN BORAKS(SUATU PENELITIAN DI KOTA BANDA ACEH)
ABSTRAKNANDA MAULINA SAFIRA,PERLINDUNGAN KONSUMEN TERHADAP 2014MAKANAN JAJANAN YANG MENGANDUNG FORMALIN DAN BORAKS (Studi Penelitian di Kota Banda Aceh)Fakultas Hukum Universitas Syiah Kuala(iv, 63) pp., tabl., bibl., appdx.( RISMAWATI, S.H., M.Hum. )Dalam Pasal 4 huruf a Undang-Undang Perlindungan Konsumen dijelaskan bahwa konsumen memiliki hak atas keselamatan dalam mengkonsumsi barang. Dalam Pasal 67 Undang-Undang Nomor 18 Tahun 2012 tentang Pangan dijelaskan bahwa ketentuan keamanan pangan diselenggarakan untuk menjaga pangan tetap aman dikonsumsi, sehingga terhindar dari kemungkinan cemaran biologis atau kimia yang dapat membahayakan kesehatan manusia. Dalam Peraturan Menteri Kesehatan Nomor 33 Tahun 2012 tentang Bahan Tambahan Pangan disebutkan bahwa bahan yang dilarang digunakan sebagai bahan tambahan pangan diantaranya adalah formalin dan boraks. Pada kenyataannya, di Kota Banda Aceh terdapat masalah dalam mewujudkan perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks.Penulisan skripsi ini bertujuan untuk menjelaskan perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks, faktor penyebab tidak berjalannya perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks, dan upaya mengatasi hambatan perwujudan perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks.Data yang diperlukan dalam tulisan ini adalah data sekunder dan data primer. Data sekunder diperoleh melalui penelitian kepustakaan dilakukan dengan cara membaca peraturan perundang-undangan, buku-buku, surat kabar dan bahan-bahan lain yang berkaitan dengan penelitian ini, dan data primer diperoleh dengan cara mewancarai responden dan informan.Hasil penelitian menunjukkan bahwa perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks di Kota Banda Aceh, belum berjalan sebagaimana yang telah diatur dalam Undang-Undang Nomor 18 Tahun 2012 dan Peraturan Menteri Kesehatan Nomor 33 Tahun 2012. Faktor penyebab tidak berjalannya perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks yaitu kurangnya sosialisasi peraturan perundang-undangan, kurangnya pengawasan, kurangnya ketegasan dalam penerapan sanksi dan kurangnya laporan dari pihak masyarakat.Upaya mengatasi hambatan perwujudan perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks yaitu penyuluhan hukum, pengawasan, peringatan dan pembinaan.Disarankan kepada instansi pemerintahan seperti Dinas Kesehatan dan BBPOM untuk menambah jumlah petugas serta mengalokasikan dana dalam melakukan pemeriksaan dan pengujian makanan jajanan sehingga terselenggaranya perlindungan konsumen terhadap makanan jajanan yang mengandung formalin dan boraks.Banda Ace
Hyperextended Cosmological Perturbation Theory: Predicting Non-linear Clustering Amplitudes
We consider the long-standing problem of predicting the hierarchical
clustering amplitudes in the strongly non-linear regime of gravitational
evolution. N-body results for the non-linear evolution of the bispectrum (the
Fourier transform of the three-point density correlation function) suggest a
physically motivated ansatz that yields the strongly non-linear behavior of the
skewness, , starting from leading-order perturbation theory. When
generalized to higher-order () polyspectra or correlation functions, this
ansatz leads to a good description of non-linear amplitudes in the strongly
non-linear regime for both scale-free and cold dark matter models. Furthermore,
these results allow us to provide a general fitting formula for the non-linear
evolution of the bispectrum that interpolates between the weakly and strongly
non-linear regimes, analogous to previous expressions for the power spectrum.Comment: 20 pages, 6 figures. Final version accepted by ApJ. Includes new
paragraphs on factorizable hierarchical models and agreement of HEPT with the
excursion set model for white-noise Gaussian fluctuation
Production of high purity Mn from V targets with -beams at cyclotrons
Radioisotope Mn is of special interest for multimodal imaging. Using
state-of-art nuclear reaction codes, we study the alternative nuclear reaction
route V(,x)Mn in comparison with the standard
production routes based upon the use of chromium targets. The integral yields
of Mn and contaminants have been evaluated. The main outcome of this
investigation is that the production of the main contaminant isotope Mn
is expected to be lower than with Cr. The study also reveals a large
spread in the cross-section data set and points out the need of more precise
measurements of the reaction V(,x)Mn as well as the
need of a more accurate theoretical description.Comment: Keywords: Cyclotron radionuclide production, Mn, Mn,
Mn, multi-modal imaging,{\alpha}-induced reactions, nuclear reactions
modelin
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