13,941 research outputs found
The Octonions
The octonions are the largest of the four normed division algebras. While
somewhat neglected due to their nonassociativity, they stand at the crossroads
of many interesting fields of mathematics. Here we describe them and their
relation to Clifford algebras and spinors, Bott periodicity, projective and
Lorentzian geometry, Jordan algebras, and the exceptional Lie groups. We also
touch upon their applications in quantum logic, special relativity and
supersymmetry.Comment: 56 pages LaTeX, 11 Postscript Figures, some small correction
An Analysis of Consuming Behavior Model for Adopting Knowledge Intensive Technological Product: The Case of MDA
The objective of this research is to analyze the correlation between consumers’ adoption of MDA and some of its influential variables, namely innovativeness, procurement types, involvement, the degree of Internet used and the basic characteristics of consumers. This paper provides a new model to explain the influent effects between consumers’ adoption of MDA and its influential factors mentioned above. The conclusions of this study are: (1) the curves of consumers’ basic characteristics versus adoption of MDA are convex-type. (2) The consumers’ age, name-list size, innovation adoption, goal-oriented and Internet usage frequency attributes have direct and positive effects on PDA adoption. (3) The innovativeness of consumers may be used to explain the reason of Consumers’ procurement style. (4) The innovativeness of consumers may be used to exploit and design the product differentiation strategy. (5) The basic characteristics of consumers may be used to exploit and design the promotion and market segmentation strategies
Evaluation of primary water stress corrosion cracking growth rates by using the extended finite element method
AbstractBackgroundMitigation of primary water stress corrosion cracking (PWSCC) is a significant issue in the nuclear industry. Advanced nickel-based alloys with lower susceptibility have been adopted, although they do not seem to be entirely immune from PWSCC during normal operation. With regard to structural integrity assessments of the relevant components, an accurate evaluation of crack growth rate (CGR) is important.MethodsFor the present study, the extended finite element method was adopted from among diverse meshless methods because of its advantages in arbitrary crack analysis. A user-subroutine based on the strain rate damage model was developed and incorporated into the crack growth evaluation.ResultsThe proposed method was verified by using the well-known Alloy 600 material with a reference CGR curve. The analyzed CGR curve of the alternative Alloy 690 material was then newly estimated by applying the proven method over a practical range of stress intensity factors.ConclusionReliable CGR curves were obtained without complex environmental facilities or a high degree of experimental effort. The proposed method may be used to assess the PWSCC resistance of nuclear components subjected to high residual stresses such as those resulting from dissimilar metal welding parts
The Extended Virgo Cluster Catalog
We present a new catalog of galaxies in the wider region of the Virgo
cluster, based on the Sloan Digital Sky Survey (SDSS) Data Release 7. The
Extended Virgo Cluster Catalog (EVCC) covers an area of 725 deg^2 or 60.1
Mpc^2. It is 5.2 times larger than the footprint of the classical Virgo Cluster
Catalog (VCC) and reaches out to 3.5 times the virial radius of the Virgo
cluster. We selected 1324 spectroscopically targeted galaxies with radial
velocities less than 3000 kms^-1. In addition, 265 galaxies that have been
missed in the SDSS spectroscopic survey but have available redshifts in the
NASA Extragalactic Database are also included. Our selection process secured a
total of 1589 galaxies of which 676 galaxies are not included in the VCC. The
certain and possible cluster members are defined by means of redshift
comparison with a cluster infall model. We employed two independent and
complementary galaxy classification schemes: the traditional morphological
classification based on the visual inspection of optical images and a
characterization of galaxies from their spectroscopic features. SDSS u, g, r,
i, and z passband photometry of all EVCC galaxies was performed using Source
Extractor. We compare the EVCC galaxies with the VCC in terms of morphology,
spatial distribution, and luminosity function. The EVCC defines a comprehensive
galaxy sample covering a wider range in galaxy density that is significantly
different from the inner region of the Virgo cluster. It will be the foundation
for forthcoming galaxy evolution studies in the extended Virgo cluster region,
complementing ongoing and planned Virgo cluster surveys at various wavelengths.Comment: 69 pages, 29 figures, 4 tables, accepted for publication in the ApJ
The properties of early-type galaxies in the Ursa Major cluster
Using SDSS-DR7 and NASA/IPAC Extragalactic Database spectroscopic data, we
identify 166 galaxies as members of the Ursa Major cluster with Mr < -13.5 mag.
We morphological classify all galaxies by means of carefully inspecting g-, r-,
i-band colour and monochromatic images. We show that the Ursa Major cluster is
dominated by late-type galaxies, but also contains a significant number of
early- type galaxies, particularly in the dwarf regime. We present further
evidence for the existence of several subgroups in the cluster, consistent with
previous findings. The early-type fraction is found to correlate with the mass
of the subgroup. We also investigate environmental effects by comparing the
properties of the Ursa Major early-type dwarf galaxies to those of the Virgo
cluster. In contrast to the Virgo, the red sequence of the Ursa Major cluster
is only sparsely populated in the optical and ultraviolet colour-magnitude
relations. It also shows a statistically significant gap between -18 < Mr < -17
mag, i.e. the Ursa Major cluster lacks early-type dwarf galaxies at the bright
end of their luminosity function. We discover that the majority of early-type
dwarf galaxies in the Ursa Major cluster have blue cores with hints of recent
or ongoing star formation. We suggest that gravitational tidal interactions can
trigger central blue star forming regions in early-type dwarfs. After that,
star formation would only fade completely when the galaxies experience ram
pressure stripping or harassment, both of which are nearly absent in the Ursa
Major cluster.Comment: 19 pages, 18 figures, 2 tables, Accepted for publication in MNRA
HI properties and star formation history of a fly-by pair of blue compact dwarf galaxies
A fly-by interaction has been suggested to be one of the major explanations
for enhanced star formation in blue compact dwarf (BCD) galaxies, yet no direct
evidence for this scenario has been found to date. In the HI Parkes all-sky
survey (HIPASS), ESO 435-IG 020 and ESO 435- G 016, a BCD pair were found in a
common, extended gas envelope of atomic hydrogen, providing an ideal case to
test the hypothesis that the starburst in BCDs can be indeed triggered by a
fly-by interaction. Using high-resolution data from the Australia Telescope
Compact Array (ATCA), we investigated HI properties and the spectral energy
distribution (SED) of the BCD pair to study their interaction and star
formation histories. The high-resolution HI data of both BCDs reveal a number
of peculiarities, which are suggestive of tidal perturbation. Meanwhile, 40% of
the HIPASS flux is not accounted for in the ATCA observations with no HI gas
bridge found between the two BCDs. Intriguingly, in the residual of the HIPASS
and the ATCA data, 10% of the missing flux appears to be located between the
two BCDs. While the SED-based age of the most dominant young stellar population
is old enough to have originated from the interaction with any neighbors
(including the other of the two BCDs), the most recent star formation activity
traced by strong H emission in ESO 435-IG 020 and the shear motion of
gas in ESO 435- G 016, suggest a more recent or current tidal interaction.
Based on these and the residual emission between the HIPASS and the ATCA data,
we propose an interaction between the two BCDs as the origin of their recently
enhanced star formation activity. The shear motion on the gas disk, potentially
with re-accretion of the stripped gas, could be responsible for the active star
formation in this BCD pair.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in A&
Large-scale filamentary structures around the Virgo cluster revisited
We revisit the filamentary structures of galaxies around the Virgo cluster,
exploiting a larger dataset based on the HyperLeda database than previous
studies. In particular, this includes a large number of low-luminosity
galaxies, resulting in better sampled individual structures. We confirm seven
known structures in the distance range 4~~Mpc~ SGY~ 16~
Mpc, now identified as filaments, where SGY is the axis of the supergalactic
coordinate system roughly along the line of sight. The Hubble diagram of the
filament galaxies suggests they are infalling toward the main-body of the Virgo
cluster. We propose that the collinear distribution of giant elliptical
galaxies along the fundamental axis of the Virgo cluster is smoothly connected
to two of these filaments (Leo~II~A and B). Behind the Virgo cluster
(16~~Mpc~ SGY~ 27~~Mpc), we also identify a new filament
elongated toward the NGC 5353/4 group ("NGC 5353/4 filament") and confirm a
sheet that includes galaxies from the W and M clouds of the Virgo cluster ("W-M
sheet"). In the Hubble diagram, the NGC 5353/4 filament galaxies show infall
toward the NGC 5353/4 group, whereas the W-M sheet galaxies do not show hints
of gravitational influence from the Virgo cluster. The filamentary structures
identified can now be used to better understand the generic role of filaments
in the build-up of galaxy clusters at z~~0.Comment: 8 pages, 4 figures, accepted for publication in Ap
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