56,331 research outputs found
Prediction of vertical bearing capacity of waveform micropile
This study proposes a predictive equation for bearing capacity considering the behaviour characteristics of a waveform micropile that can enhance the bearing capacity of a conventional micropile. The bearing capacity of the waveform micropile was analysed by a three-dimensional numerical model with soil and pile conditions obtained from the field and centrifuge tests. The load-transfer mechanism of the waveform micropile was revealed by the numerical analyses, and a new predictive equation for the bearing capacity was proposed. The bearing capacities of the waveform micropile calculated by the new equation were comparable with those measured from the field and centrifuge tests. This validated a prediction potential of the new equation for bearing capacity of waveform micropiles
Flavor changing t -> c l_1^- l_2^+ decay in the general two Higgs doublet model
We study the flavor changing t-> c l_1^- l_2^+ decay in the framework of the
general two Higgs doublet model, the so called model III. We predict the
branching ratio for l_1=\tau, l_2=\mu at the order of magnitude of BR \sim
10^{-8}.Comment: 12 Pages, 5 Figure
Astrometric Method to Break the Photometric Degeneracy between Binary-source and Planetary Microlensing Perturbations
An extra-solar planet can be detected by microlensing because the planet can
perturb the smooth lensing light curve created by the primary lens. However, it
was shown by Gaudi that a subset of binary-source events can produce light
curves that closely resemble those produced by a significant fraction of
planet/star lens systems, causing serious contamination of a sample of
suspected planetary systems detected via microlensing. In this paper, we show
that if a lensing event is observed astrometrically, one can unambiguously
break the photometric degeneracy between binary-source and planetary lensing
perturbations. This is possible because while the planet-induced perturbation
in the trajectory of the lensed source image centroid shifts points away from
the opening of the unperturbed elliptical trajectory, while the perturbation
induced by the binary source companion points always towards the opening.
Therefore, astrometric microlensing observations by using future high-precision
interferometers will be important for solid confirmation of microlensing planet
detections.Comment: total 5 pages, including 1 figure and no table, ApJ, submitted,
better quality pdf file is avalilable at
http://astroph.chungbuk.ac.kr/~cheongho/publication.htm
Population synthesis of accreting white dwarfs: II. X-ray and UV emission
Accreting white dwarfs (WDs) with non-degenerate companions are expected to
emit in soft X-rays and the UV, if accreted H-rich material burns stably. They
are an important component of the unresolved emission of elliptical galaxies,
and their combined ionizing luminosity may significantly influence the optical
line emission from warm ISM. In an earlier paper we modeled populations of
accreting WDs, first generating WD with main-sequence, Hertzsprung gap and red
giant companions with the population synthesis code \textsc{BSE}, and then
following their evolution with a grid of evolutionary tracks computed with
\textsc{MESA}. Now we use these results to estimate the soft X-ray
(0.3-0.7keV), H- and He II-ionizing luminosities of nuclear burning WDs and the
number of super-soft X-ray sources for galaxies with different star formation
histories. For the starburst case, these quantities peak at Gyr and
decline by orders of magnitude by the age of 10 Gyr. For stellar
ages of ~10 Gyr, predictions of our model are consistent with soft X-ray
luminosities observed by Chandra in nearby elliptical galaxies and He II
4686 line ratio measured in stacked SDSS spectra of retired
galaxies, the latter characterising the strength and hardness of the UV
radiation field. However, the soft X-ray luminosity and
He~II~4686 ratio are significantly overpredicted for stellar
ages of Gyr. We discuss various possibilities to resolve this
discrepancy and tentatively conclude that it may be resolved by a modification
of the typically used criteria of dynamically unstable mass loss for giant
stars.Comment: 13 pages, 12 figures, MNRAS accepte
Anisotropy, Itineracy, and Magnetic Frustration in High-Tc Iron Pnictides
Using first-principle density functional theory calculations combined with
insight from a tight-binding representation, dynamical mean field theory, and
linear response theory, we have extensively investigated the electronic
structures and magnetic interactions of nine ferropnictides representing three
different structural classes. The calculated magnetic interactions are found to
be short-range, and the nearest () and next-nearest () exchange
constants follow the universal trend of J_{1a}/2J_{2}\sim 1, despite their
itinerant origin and extreme sensitivity to the z-position of As. These results
bear on the discussion of itineracy versus magnetic frustration as the key
factor in stabilizing the superconducting ground state. The calculated spin
wave dispersions show strong magnetic anisotropy in the Fe plane, in contrast
to cuprates.Comment: Fig.4 updated: Phys. Rev. Lett (in press
Next generation population synthesis of accreting white dwarfs: I. Hybrid calculations using BSE + MESA
Accreting, nuclear-burning white dwarfs have been deemed to be candidate
progenitors of type Ia supernovae, and to account for supersoft X-ray sources,
novae, etc. depending on their accretion rates. We have carried out a binary
population synthesis study of their populations using two algorithms. In the
first, we use the binary population synthesis code \textsf{BSE} as a baseline
for the "rapid" approach commonly used in such studies. In the second, we
employ a "hybrid" approach, in which we use \textsf{BSE} to generate a
population of white dwarfs (WD) with non-degenerate companions on the verge of
filling their Roche lobes. We then follow their mass transfer phase using the
detailed stellar evolution code \textsf{MESA}. We investigate the evolution of
the number of rapidly accreting white dwarfs (RAWDs) and stably nuclear-burning
white dwarfs (SNBWDs), and estimate the type Ia supernovae (SNe Ia) rate
produced by "single-degenerate" systems (SD). We find significant differences
between the two algorithms in the predicted numbers of SNBWDs at early times,
and also in the delay time distribution (DTD) of SD SNe Ia. Such differences in
the treatment of mass transfer may partially account for differences in the SNe
Ia rate and DTD found by different groups. Adopting 100\% efficiency for helium
burning, the rate of SNe Ia produced by the SD-channel in a Milky-way-like
galaxy in our calculations is , more than an
order of magnitude below the observationally inferred value. In agreement with
previous studies, our calculated SD DTD is inconsistent with observations.Comment: 13 pages,11 figures, accepted by MNRA
Asymptotics of Spinfoam Amplitude on Simplicial Manifold: Lorentzian Theory
The present paper studies the large-j asymptotics of the Lorentzian EPRL
spinfoam amplitude on a 4d simplicial complex with an arbitrary number of
simplices. The asymptotics of the spinfoam amplitude is determined by the
critical configurations. Here we show that, given a critical configuration in
general, there exists a partition of the simplicial complex into three type of
regions R_{Nondeg}, R_{Deg-A}, R_{Deg-B}, where the three regions are
simplicial sub-complexes with boundaries. The critical configuration implies
different types of geometries in different types of regions, i.e. (1) the
critical configuration restricted into R_{Nondeg} is degenerate of type-A in our definition of degeneracy, but implies
a nondegenerate discrete Euclidean geometry on R_{Deg-A}, (3) the critical
configuration restricted into R_{Deg-B} is degenerate of type-B, and implies a
vector geometry on R_{Deg-B}. With the critical configuration, we further make
a subdivision of the regions R_{Nondeg} and R_{Deg-A} into sub-complexes (with
boundary) according to their Lorentzian/Euclidean oriented 4-simplex volume
V_4(v), such that sgn(V_4(v)) is a constant sign on each sub-complex. Then in
the each sub-complex, the spinfoam amplitude at the critical configuration
gives the Regge action in Lorentzian or Euclidean signature respectively on
R_{Nondeg} or R_{Deg-A}. The Regge action reproduced here contains a sign
factor sgn(V_4(v)) of the oriented 4-simplex volume. Therefore the Regge action
reproduced here can be viewed a discretized Palatini action with on-shell
connection. Finally the asymptotic formula of the spinfoam amplitude is given
by a sum of the amplitudes evaluated at all possible critical configurations,
which are the products of the amplitudes associated to different type of
geometries.Comment: 54 pages, 2 figures, reference adde
Phenomenology of a lepton triplet
The most general phenomenological model involving a lepton triplet with
hypercharge is constructed. A distinctive feature of this model is the
prediction of a doubly charged lepton, and a new heavy Dirac neutrino. We study
the phenomenology of these exotic leptons in both low-energy experiments and at
the LHC. The model predicts FCNC processes such as rare muon decays, which are
studied in detail in order to constrain the model parameters. All the decay
channels of the exotic leptons are described for a wide range of parameters. It
is found that, if the mixing parameters between the exotic and light leptons
are not too small (), then they can be observable to a
statistical significance at the 7 TeV LHC with 10-50 fb luminosity for a
400 GeV mass, and 14 TeV with 100-300 fb luminosity for a 800 GeV mass.Comment: 28 pages, 17 figures. Version to appear in PR
Anomalous t-c-g coupling: The connection between single top production and top decay
Continuing earlier work, we examine the constraint on an anomalous t-c-g
coupling from top quark decay. We find that from current CDF measurements of
the branching ratio , the minimum scale at which new physics
can strongly modify the t-c-g coupling is \Ltcg about 950 GeV. At the
upgraded Tevatron, single top production can constrain \Ltcg 4.5 TeV.
The connection between t-c production and the decay is
examined, showing how constraints on one lead to a constraint on the other.Comment: 5 pages. Requires epsf.sty to process .eps formatted figure
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