178,155 research outputs found
Applications of concurrent access patterns in web usage mining
This paper builds on the original data mining and modelling research which has proposed the discovery of novel structural relation patterns, applying the approach in web usage mining. The focus of attention here is on concurrent access patterns (CAP), where an overarching framework illuminates the methodology for web access patterns post-processing. Data pre-processing, pattern discovery and patterns analysis all proceed in association with access patterns mining, CAP mining and CAP modelling. Pruning and selection of access pat-terns takes place as necessary, allowing further CAP mining and modelling to be pursued in the search for the most interesting concurrent access patterns. It is shown that higher level CAPs can be modelled in a way which brings greater structure to bear on the process of knowledge discovery. Experiments with real-world datasets highlight the applicability of the approach in web navigation
Galaxy Ecosystems: gas contents, inflows and outflows
We use a set of observational data for galaxy cold gas mass fraction and gas
phase metallicity to constrain the content, inflow and outflow of gas in
central galaxies hosted by halos with masses between to
. The gas contents in high redshift galaxies are obtained by
combining the empirical star formation histories of Lu et al. (2014) and star
formation models that relate star formation rate with the cold gas mass in
galaxies. We find that the total baryon mass in low-mass galaxies is always
much less than the universal baryon mass fraction since , regardless of
star formation model adopted. The data for the evolution of the gas phase
metallicity require net metal outflow at , and the metal loading
factor is constrained to be about , or about of the metal yield.
Based on the assumption that galactic outflow is more enriched in metal than
both the interstellar medium and the material ejected at earlier epochs, we are
able to put stringent constraints on the upper limits for both the net
accretion rate and the net mass outflow rate. The upper limits strongly suggest
that the evolution of the gas phase metallicity and gas mass fraction for
low-mass galaxies at is not compatible with strong outflow. We
speculate that the low star formation efficiency of low-mass galaxies is owing
to some preventative processes that prevent gas from accreting into galaxies in
the first place.Comment: 15 pages, 10 figures, submitted to MNRA
(1 + p)-Dimensional Open D(p - 2) Brane Theories
The dynamics of a Dp brane can be described either by an open string ending
on this brane or by an open D(p - 2) brane ending on the same Dp brane. The
ends of the open string couple to a Dp brane worldvolume gauge field while the
boundary of the open D(p - 2) brane couples to a (p - 2)-form worldvolume
potential whose field strength is Poincare dual to that of the gauge field on
the Dp-brane worldvolume. With this in mind, we find that the Poincare dual of
the fixed rank-2 magnetic field used in defining a (1 + p)-dimensional
noncommutative Yang-Mills (NCYM) gives precisely a near-critical electric field
for the open D(p - 2) brane. We therefore find (1 + p)-dimensional open D(p -
2) brane theories along the same line as for obtaining noncommutative open
string theories (NCOS), OM theory and open Dp brane theories (ODp) from NS5
brane. Similarly, the Poincare dual of the near-critical electric field used in
defining a (1 + p)-dimensional NCOS gives a fixed magnetic-like field. This
field along with the same bulk field scalings defines a (1 + p)-dimensional
noncommutative field theory. In the same spirit, we can have various (1 +
5)-dimensional noncommutative field theories resulting from the existence of
ODp if the description of open D(4 - p) brane ending on the NS5 brane is
insisted.Comment: 35 pages, references added and discussion on decoupled field theories
refine
On the relationship of gravitational constants in KK reduction
In this short note, we try to clarify a seemly trivial but often confusing
question in relating a higher-dimensional physical gravitational constant to
its lower-dimensional correspondence in Kaluza-Klein reduction. In particular,
we re-derive the low-energy M-theory gravitational constant in terms of type
IIA string coupling and constant through the metric relation
between the two theories.Comment: Final version published in JHE
Phenomenological Analysis of and Elastic Scattering Data in the Impact Parameter Space
We use an almost model-independent analytical parameterization for and
elastic scattering data to analyze the eikonal, profile, and
inelastic overlap functions in the impact parameter space. Error propagation in
the fit parameters allows estimations of uncertainty regions, improving the
geometrical description of the hadron-hadron interaction. Several predictions
are shown and, in particular, the prediction for inelastic overlap
function at TeV shows the saturation of the Froissart-Martin
bound at LHC energies.Comment: 15 pages, 16 figure
Some aspects of interaction amplitudes of D branes carrying worldvolume fluxes
We report a systematic study of the stringy interaction between two sets of
Dp branes placed parallel at a separation in the presence of two worldvolume
fluxes for each set. We focus in this paper on that the two fluxes on one set
have the same structure as those on the other set but they in general differ in
values, which can be both electric or both magnetic or one electric and one
magnetic. We compute the respective stringy interaction amplitude and find that
the presence of electric fluxes gives rise to the open string pair production
while that of magnetic ones to the open string tachyon mode. The interplay of
these two leads to the open string pair production enhancement in certain cases
when one flux is electric and the other is magnetic. In particular, we find
that this enhancement occurs even when the electric flux and the magnetic one
share one common field strength index which is impossible in the one-flux case
studied previously by the present author and his collaborator in [17]. This
type of enhancement may have realistic physical applications, say, as a means
to explore the existence of extra dimensions.Comment: 49 pages, improved discussion on the matrix element evaluations in
section 2, a few footnotes added, typos correcte
Elastic Properties of Carbon Nanotubes and Nanoropes
Elastic properties of carbon nanotubes and nanoropes are investigated using
an empirical force-constant model. For single and multi-wall nanotubes the
elastic moduli are shown to be insensitive to details of the structure such as
the helicity, the tube radius and the number of layers. The tensile Young's
modulus and the torsion shear modulus calculated are comparable to that of the
diamond, while the the bulk modulus is smaller. Nanoropes composed of
single-wall nanotubes possess the ideal elastic properties of high tensile
elastic modulus, flexible, and light weight.Comment: 10 page
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