Fast and accurate evaluation of Wigner 3j, 6j, and 9j symbols using prime factorisation and multi-word integer arithmetic

We present an efficient implementation for the evaluation of Wigner 3j, 6j, and 9j symbols. These represent numerical transformation coefficients that are used in the quantum theory of angular momentum. They can be expressed as sums and square roots of ratios of integers. The integers can be very large due to factorials. We avoid numerical precision loss due to cancellation through the use of multi-word integer arithmetic for exact accumulation of all sums. A fixed relative accuracy is maintained as the limited number of floating-point operations in the final step only incur rounding errors in the least significant bits. Time spent to evaluate large multi-word integers is in turn reduced by using explicit prime factorisation of the ingoing factorials, thereby improving execution speed. Comparison with existing routines shows the efficiency of our approach and we therefore provide a computer code based on this work.Comment: 7 pages, 2 figures. Accepted for publication in SIAM Journal on Scientific Computing (SISC

Constrained simulations of the Antennae Galaxies: Comparison with Herschel-PACS observations

We present a set of hydro-dynamical numerical simulations of the Antennae galaxies in order to understand the origin of the central overlap starburst. Our dynamical model provides a good match to the observed nuclear and overlap star formation, especially when using a range of rather inefficient stellar feedback efficiencies (0.01 < q_EoS < 0.1). In this case a simple conversion of local star formation to molecular hydrogen surface density motivated by observations accounts well for the observed distribution of CO. Using radiative transfer post-processing we model synthetic far-infrared spectral energy distributions (SEDs) and two-dimensional emission maps for direct comparison with Herschel-PACS observations. For a gas-to-dust ratio of 62:1 and the best matching range of stellar feedback efficiencies the synthetic far-infrared SEDs of the central star forming region peak at values of ~65 - 81 Jy at 99 - 116 um, similar to a three-component modified black body fit to infrared observations. Also the spatial distribution of the far-infrared emission at 70 um, 100 um, and 160 um compares well with the observations: >50% (> 35%) of the emission in each band is concentrated in the overlap region while only < 30% (< 15%) is distributed to the combined emission from the two galactic nuclei in the simulations (observations). As a proof of principle we show that parameter variations in the feedback model result in unambiguous changes both in the global and in the spatially resolved observable far-infrared properties of Antennae galaxy models. Our results strengthen the importance of direct, spatially resolved comparative studies of matched galaxy merger simulations as a valuable tool to constrain the fundamental star formation and feedback physics.Comment: 17 pages, 8 figures, 4 tables, submitted to MNRAS, including revisions after first referee report, comments welcom

Large-scale exact diagonalizations reveal low-momentum scales of nuclei

Ab initio methods aim to solve the nuclear many-body problem with controlled approximations. Virtually exact numerical solutions for realistic interactions can only be obtained for certain special cases such as few-nucleon systems. Here we extend the reach of exact diagonalization methods to handle model spaces with dimension exceeding $10^{10}$ on a single compute node. This allows us to perform no-core shell model (NCSM) calculations for 6Li in model spaces up to $N_\mathrm{max} = 22$ and to reveal the 4He+d halo structure of this nucleus. Still, the use of a finite harmonic-oscillator basis implies truncations in both infrared (IR) and ultraviolet (UV) length scales. These truncations impose finite-size corrections on observables computed in this basis. We perform IR extrapolations of energies and radii computed in the NCSM and with the coupled-cluster method at several fixed UV cutoffs. It is shown that this strategy enables information gain also from data that is not fully UV converged. IR extrapolations improve the accuracy of relevant bound-state observables for a range of UV cutoffs, thus making them profitable tools. We relate the momentum scale that governs the exponential IR convergence to the threshold energy for the first open decay channel. Using large-scale NCSM calculations we numerically verify this small-momentum scale of finite nuclei.Comment: Minor revisions.Accepted for publication in Physical Review

Study of pollution in the El Jadida-Safi Atlantic coastal zone (Morocco) by using PIXE and SSNTD methods

In this work PIXE experiments were performed for measuring heavy and light elements (ranging from aluminium to lead) concentrations inside various polluted and unpolluted soils as well as liquid samples collected from different phosphate factory sewers in the El Jadida-Safi Atlantic coastal region (Morocco). In addition, uranium (238U) and thorium (232Th) contents were evaluated in the same samples studied by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). The influence of the phosphate industry wastes on the concentrations of both radioactive and non-radioactive elements of the samples studied was investigated

DPTC -- an FPGA-based trace compression

Recording of flash-ADC traces is challenging from both the transmission bandwidth and storage cost perspectives. This paper presents a configuration-free lossless compression algorithm which addresses both limitations, by compressing the data on-the-fly in the controlling field-programmable gate array (FPGA). Thus the difference predicted trace compression (DPTC) can easily be used directly in front-end electronics. The method first computes the differences between consecutive samples in the traces, thereby concentrating the most probable values around zero. The values are then stored as groups of four, with only the necessary least-significant bits in a variable-length code, packed in a stream of 32-bit words. To evaluate the efficiency, the storage cost of compressed traces is modeled as a baseline cost including the ADC noise, and a cost for pulses that depends on their amplitude and width. The free parameters and the validity of the model are determined by comparing it with the results of compressing a large set of artificial traces with varying characteristics. The compression method was also applied to actual data from different types of detectors, thereby demonstrating its general applicability. The compression efficiency is found to be comparable to popular general-purpose compression methods, while available for FPGA implementation using limited resources. A typical storage cost is around 4 to 5 bits per sample. Code for the FPGA implementation in VHDL and for the CPU decompression routine in C of DPTC are available as open source software, both operating at multi-100 Msamples/s speeds.Comment: 9 pages, 7 figure

Identification of Emission Lines in the Low-Ionization Strontium Filament Near Eta Carinae

We have obtained deep spectra from 1640 to 10100A with the Space Telescope Imaging Spectrograph (STIS) of the Strontium Filament, a largely neutral emission nebulosity lying close to the very luminous star Eta Carinae and showing an uncommon spectrum. Over 600 emission lines, both permitted and forbidden, have been identified. The majority originates from neutral or singly-ionized iron group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the only neutron capture element detected. The presence of Sr II, numerous strong Ti II and V II lines and the dominance of Fe I over Fe II are notable discoveries. While emission lines of hydrogen, helium, and nitrogen are associable with other spatial structures at other velocities within the Homunculus, no emission lines from these elements correspond to the spatial structure or velocity of the Sr Filament. Moreover, no identified Sr Filament emission line requires an ionization or excitation energy above approximately 8 eV. Ionized gas extends spatially along the aperture, oriented along the polar axis of the Homunculus, and in velocity around the Strontium Filament. We suggest that the Strontium Filament is shielded from ultraviolet radiation at energies above 8 eV, but is intensely irradiated by the central star at wavelengths longward of 1500A.Comment: 28 pages, 5 figures, 4 tables. Accepted by A&A. High resolution pictures can be found at http://www.astro.lu.se/~henrikh/srpaper/srpaper.pd

KPZ equation in one dimension and line ensembles

For suitably discretized versions of the Kardar-Parisi-Zhang equation in one space dimension exact scaling functions are available, amongst them the stationary two-point function. We explain one central piece from the technology through which such results are obtained, namely the method of line ensembles with purely entropic repulsion.Comment: Proceedings STATPHYS22, Bangalore, 200

Structure and kinematics of the molecular spiral arms in M51

Mapping of the CO(1-0) emission from the spiral galaxy was made with the Onsala 20 m antenna. The observations show that the emission is considerably enhanced in spiral arms which appear to originate as intense ridges of emission about 1 kpc from the nucleus. One of the main objectives for the 1986 observations was to study the variations of the tangential velocity component of molecular gas across a spiral arm. The radial velocity was found to have a velocity shift similar to that predicted by the density wave theory. The present (1986) observations of the inner southern spiral arm of M51 show that the tangential velocity component also behaves in a way which conforms with the density wave model. The molecular arms were compared with the H alpha ionized gas arms of Tully (1974) and it was found that the ionized gas appears to have its maximum intensity slightly outside the molecular arm