10,030 research outputs found
N-body simulations with two-orders-of-magnitude higher performance using wavelets
Noise is a problem of major concern for N-body simulations of structure
formation in the early Universe, of galaxies and plasmas. Here for the first
time we use wavelets to remove noise from N-body simulations of disc galaxies,
and show that they become equivalent to simulations with two orders of
magnitude more particles. We expect a comparable improvement in performance for
cosmological and plasma simulations. Our wavelet code will be described in a
following paper, and will then be available on request.Comment: Mon. Not. R. Astron. Soc., in press. The interested reader is
strongly recommended to ignore the low-resolution Fig. 3 (and Fig. 4), and to
download the full-resolution paper (700 kb) from
http://www.oso.chalmers.se/~romeo/Paper_VI.ps.g
Non-universal relativistic kinematics
We present a systematic derivation of the constraints that the relativity
principle imposes between coefficients of a deformed (but rotational invariant)
momentum composition law, dispersion relation, and momentum transformation
laws, at first order in a power expansion of an ultraviolet energy scale. This
work generalizes previous results to the case of particle-dependent
relativistic kinematics, which can have interesting phenomenological
applications that we explore in the second part of the manuscript.Comment: 13 pages, no figure
Consumers Buying Behaviors’ Loans and Credits: A Situationer
This study aimed to describe the situation of the consumers buying behaviors loans\u27 and credits with the use of descriptive research design. The researchers found out that micro–financing business or lending institutions and private individuals are credit service providers of the respondents. The types of loan and credit they avail are investment loan or business loan which is worth more than Php 100,000 and consumer credit amounting to less than Php 20,000. Loans can provide their needs, they do not have stable source of income, their salary are not enough, they want to buy gadgets, apparels and vehicles are the main reasons why the respondents avail loans and credits. On the other hand, long process of approval, time to repayment of maturity date and high interest rate are problems encountered by the respondents in availing credit services. Complex–buying and habitual–buying are the consumer behaviors manifested by the respondents
A wavelet add-on code for new-generation N-body simulations and data de-noising (JOFILUREN)
Wavelets are a new and powerful mathematical tool, whose most celebrated
applications are data compression and de-noising. In Paper I (Romeo, Horellou &
Bergh 2003, astro-ph/0302343), we have shown that wavelets can be used for
removing noise efficiently from cosmological, galaxy and plasma N-body
simulations. The expected two-orders-of-magnitude higher performance means, in
terms of the well-known Moore's law, an advance of more than one decade in the
future. In this paper, we describe a wavelet add-on code designed for such an
application. Our code can be included in common grid-based N-body codes, is
written in Fortran, is portable and available on request from the first author.
The code can also be applied for removing noise from standard data, such as
signals and images.Comment: Mon. Not. R. Astron. Soc., in press. The interested reader is
strongly recommended to ignore the low-resolution Figs 10 and 11, and to
download the full-resolution paper (800 kb) from
http://www.oso.chalmers.se/~romeo/Paper_VII.ps.g
Low energy phases of bilayer Bi predicted by structure search in two dimensions
We employ an ab-initio structure search algorithm to explore the
configurational space of Bi in quasi two dimensions. A confinement potential
restricts the movement of atoms within a pre-defined thickness during structure
search calculations within the minima hopping method to find the stable and
metastable forms of bilayer Bi. In addition to recovering the two known
low-energy structures (puckered monoclinic and buckled hexagonal), our
calculations predict three new structures of bilayer Bi. We call these
structures the , , and phases of bilayer Bi, which are,
respectively, 63, 72, and 83 meV/atom higher in energy than that of the
monoclinic ground state, and thus potentially synthesizable using appropriate
substrates. We also compare the structural, electronic, and vibrational
properties of the different phases. The puckered monoclinic, buckled hexagonal,
and phases exhibit a semiconducting energy gap, whereas and
phases are metallic. We notice an unusual Mexican-hat type band
dispersion leading to a van Hove singularity in the buckled hexagonal bilayer
Bi. Notably, we find symmetry-protected topological Dirac points in the
electronic spectrum of the phase. The new structures suggest that
bilayer Bi provides a novel playground to study distortion-mediated
metal-insulator phase transitions
Remediation Technology Collaboration Development - A Compendium
During its multi-year period of performance, the Remediation Technology Collaboration Development (RTCD) task orders initial goals were to enhance the capability to specifically target reductions in the long-term liabilities associated with NASAs most challenging remediation sites. This was accomplished by identifying existing remediation processes and conditions, researching site-specific technologies (both past and present) while simultaneously looking for parallel situations where these technologies could be applied. In addition, the most promising of these solutions were developed from comprehensive research and bench studies into pilot studies or demonstration projects, which contributed significantly to the success of the RTCD program
The Structure of Isothermal, Self-gravitating Gas Spheres for Softened Gravity
A theory for the structure of isothermal, self-gravitating gas spheres in
pressure equilibrium in a softened gravitational field is developed. The one
parameter spline softening proposed by Hernquist & Katz (1989) is used. We show
that the addition of this extra scale parameter implies that the set of
equilibrium solutions constitute a one-parameter family, rather than the one
and only one isothermal sphere solution for Newtonian gravity. We demonstrate
the perhaps somewhat surprising result that for any finite choice of softening
length and temperature, it is possible to deposit an arbitrarily large mass of
gas in pressure equilibrium and with a non-singular density distribution inside
of r_0 for any r_0 > 0. The theoretical predictions of our models are compared
with the properties of the small, massive, quasi-isothermal gas clumps which
typically form in numerical Tree-SPH simulations of 'passive' galaxy formation
of Milky Way sized galaxies. We find reasonable agreement despite the neglect
of rotational support in the models. We comment on whether the hydrodynamical
resolution in our numerical simulation of galaxy formation is sufficient, and
finally we conclude that one should be cautious, when comparing results of
numerical simulations involving gravitational softening and hydrodynamical
smoothing, with reality.Comment: 22 pages Latex + 12 figure
Nucleotide sequence of the myxobacterial hemagglutinin gene contains four homologous domains.
The Formation of a Realistic Disk Galaxy in Lambda Dominated Cosmologies
We simulate the formation of a realistic disk galaxy within the hierarchical
scenario of structure formation and study its internal properties to the
present epoch. We compare results from a LambdaCDM simulation with a LambdaWDM
(2keV) simulation that forms significantly less small scale structure. We show
how high mass and force resolution in both the gas and dark matter components
play an important role in solving the angular momentum catastrophe claimed from
previous simulations of galaxy formation within the hierarchical framework. The
stellar material in the disk component has a final specific angular momentum
equal to 40% and 90% of that of the dark halo in the LambdaCDM and LambdaWDM
models respectively. The LambdaWDM galaxy has a drastically reduced satellite
population and a negligible stellar spheroidal component. Encounters with
satellites play only a minor role in disturbing the disk. Satellites possess a
variety of star formation histories linked to mergers and pericentric passages
along their orbit around the primary galaxy. In both cosmologies, the galactic
halo retains most of the baryons accreted and builds up a hot gas phase with a
substantial X-ray emission. Therefore, while we have been successful in
creating a realistic stellar disk in a massive galaxy within the LambdaCDM
scenario, energy injection emerges as necessary ingredient to reduce the baryon
fraction in galactic halos, independent of the cosmology adopted. (abridged)Comment: ApJ in press. Images and movies at
http://hpcc.astro.washington.edu/faculty/fabio/galform.html Significantly
expanded revised version. (9 pages vs the original 4
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