20,945 research outputs found
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
Building the red sequence through gas-rich major mergers
Understanding the details of how the red sequence is built is a key question
in galaxy evolution. What are the relative roles of gas-rich vs. dry mergers,
major vs. minor mergers or galaxy mergers vs. gas accretion? In Wild et al.
2009 we compare hydrodynamic simulations with observations to show how gas-rich
major mergers result in galaxies with strong post-starburst spectral features,
a population of galaxies easily identified in the real Universe using optical
spectra. Using spectra from the VVDS deep survey with z~0.7, and a principal
component analysis technique to provide indices with high enough SNR, we find
that 40% of the mass flux onto the red-sequence could enter through a strong
post-starburst phase, and thus through gas-rich major mergers. The deeper
samples provided by next generation galaxy redshift surveys will allow us to
observe the primary physical processes responsible for the shut-down in
starformation and build-up of the red sequence.Comment: 4 pages, 7 figures, proceedings of IAU symposium 262 "Stellar
populations, planning for the next decade
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
Atomic Processes in Planetary Nebulae and H II Regions
Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.Comment: 9 pages, 1 figur
Optimal Topological Test for Degeneracies of Real Hamiltonians
We consider adiabatic transport of eigenstates of real Hamiltonians around
loops in parameter space. It is demonstrated that loops that map to nontrivial
loops in the space of eigenbases must encircle degeneracies. Examples from
Jahn-Teller theory are presented to illustrate the test. We show furthermore
that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let
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
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 on a single compute node. This allows
us to perform no-core shell model (NCSM) calculations for 6Li in model spaces
up to 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
Simultaneous readout of two charge qubits
We consider a system of two solid state charge qubits, coupled to a single
read-out device, consisting of a single-electron transistor (SET). The
conductance of each tunnel junction is influenced by its neighboring qubit, and
thus the current through the transistor is determined by the qubits' state. The
full counting statistics of the electrons passing the transistor is calculated,
and we discuss qubit dephasing, as well as the quantum efficiency of the
readout. The current measurement is then compared to readout using real-time
detection of the SET island's charge state. For the latter method we show that
the quantum efficiency is always unity. Comparing the two methods a simple
geometrical interpretation of the quantum efficiency of the current measurement
appears. Finally, we note that full quantum efficiency in some cases can be
achieved measuring the average charge of the SET island, in addition to the
average current.Comment: 11 pages with 5 figure
Experimental f-value and isotopic structure for the Ni I line blended with [OI] at 6300A
We have measured the oscillator strength of the Ni I line at 6300.34 \AA,
which is known to be blended with the forbidden [O I] 6300 line, used
for determination of the oxygen abundance in cool stars. We give also
wavelengths of the two isotopic line components of Ni and Ni
derived from the asymmetric laboratory line profile. These two line components
of Ni I have to be considered when calculating a line profile of the 6300 \AA\
feature observed in stellar and solar spectra. We also discuss the labelling of
the energy levels involved in the Ni I line, as level mixing makes the
theoretical predictions uncertain.Comment: Accepted for publication in ApJLetter
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