66,897 research outputs found
The demagnetization factor for randomly packed spheroidal particles
We investigate if the demagnetization factor for a randomly packed powder of
magnetic spheroidal particles depend on the shape of the spheroidal particles
and what the internal variation in magnetization is within such a powder. A
spheroid is an ellipsoid of revolution, i.e. an ellipsoid with two semi-major
axis being equal. The demagnetization factor is calculated as function of
particle aspect ratio using two independent numerical models for several
different packings, and assuming a relative permeability of 2. The calculated
demagnetization factor is shown to depend on particle aspect ratio, not because
of direct magnetic interaction but because the particle packing depend on the
aspect ratio of the particles. The relative standard deviation of the
magnetization across the powder was 3\%-8\%, increasing as the particle shape
deviates from spherical, while the relative standard deviation within each
particle was relatively constant around 5\%.Comment: 7 pages, 9 figure
Is the meson a dynamically generated resonance? -- a lesson learned from the O(N) model and beyond
O(N) linear model is solvable in the large limit and hence
provides a useful theoretical laboratory to test various unitarization
approximations. We find that the large limit and the
limit do not commute. In order to get the correct large spectrum one has
to firstly take the large limit. We argue that the meson may
not be described as generated dynamically. On the contrary, it is most
appropriately described at the same level as the pions, i.e, both appear
explicitly in the effective lagrangian. Actually it is very likely the
meson responsible for the spontaneous chiral symmetry breaking in a lagrangian
with linearly realized chiral symmetry.Comment: 15 pages, 3 figurs; references added; discussions slightly modified;
revised version accepted by IJMP
Scalars in the hadron world: the Higgs sector of the strong interaction
Scalar mesons are a key expression of the strong physics regime of QCD and
the role condensates, particularly , play in breaking chiral
symmetry.
What new insights have been provided by recent experiments on and
decays to light hadrons is discussed. We need to establish whether all
the claimed scalars , , , etc., really exist and
with what parameters before we can meaningfully speculate further about which
is transiently , , multi-meson molecule or largely
glue.Comment: 10 pages, 4 figures. Invited talk at the International Conference on
QCD and Hadronic Physics, Beijing, June 2005. A shortened version will appear
in the Proceeding
Search for a circum-planetary material and orbital period variations of short-period Kepler exoplanet candidates
A unique short-period Mercury-size Kepler exoplanet candidate KIC012557548b
has been discovered recently by Rappaport et al. (2012). This object is a
transiting disintegrating exoplanet with a circum-planetary material -
comet-like tail. Close-in exoplanets, like KIC012557548b, are subjected to the
greatest planet-star interactions. This interaction may have various forms. In
certain cases it may cause formation of the comet-like tail. Strong interaction
with the host star, and/or presence of an additional planet may lead to
variations in the orbital period of the planet. Our main aim is to search for
comet-like tails similar to KIC012557548b and for long-term orbital period
variations. We are curious about frequency of comet-like tail formation among
short-period Kepler exoplanet candidates. We concentrate on a sample of 20
close-in candidates with a period similar to KIC012557548b from the Kepler
mission.Comment: 19 pages, 75 figures, AN accepte
Numerical Analysis of Shear-off Failure of Keyed Epoxied Joints in Precast Concrete Segmental Bridges
Precast concrete segmental box girder bridges (PCSBs) are becoming increasingly popular in modern bridge construction. The joints in PCSBs are of critical importance, which largely affects the overall structural behavior of PCSBs. The current practice is to use unreinforced small epoxied keys distributed across the flanges and webs of a box girder cross section forming a joint. In this paper, finite-element analysis was conducted to simulate the shear behavior of unreinforced epoxied joints, which are single keyed and three keyed to represent multikeyed epoxied joints. The concrete damaged plasticity model along with the pseudodamping scheme was incorporated to analyze the key assembly for microcracks in the concrete material and to stabilize the solution, respectively. In numerical analyses, two values of concrete tensile strength were adapted: one using a Eurocode formula and one using the general assumption of tensile strength of concrete as 10%fcm. The epoxy was modeled as linear elastic material because the tensile and shear strength of the epoxy were much higher than those of the concrete. The numerical model was calibrated by full-scale experimental results from literature.Moreover, it was found that the numerical results of the joints, such as ultimate shear load and crack initiation and propagation, agreed well with experimental results. Therefore, the numerical model associated with relevant parameters developed in this study was validated. The numerical model was then used for a parametric study on factors affecting shear behavior of keyed epoxied joints, which are concrete tensile strength, elastic modulus of epoxy, and confining pressure. It has been found that the tensile strength of concrete has a significant effect on the shear capacity of the joint
and the displacement at the ultimate load. A linear relationship between the confining pressure and the shear strength of single-keyed epoxied joints was observed. Moreover, the variation in the elastic modulus of epoxy does not affect the ultimate shear strength of the epoxied joints when it is greater than 25% of the elastic modulus of concrete. Finally, an empirical formula published elsewhere for assessing the shear strength of single-keyed epoxied joints was modified, based on the findings of this research, to be an explicit function
of the tensile strength of concrete
An analytical law for size effects on thermal conductivity of nanostructures
The thermal conductivity of a nanostructure is sensitive to its dimensions. A
simple analytical scaling law that predicts how conductivity changes with the
dimensions of the structure, however, has not been developed. The lack of such
a law is a hurdle in "phonon engineering" of many important applications. Here,
we report an analytical scaling law for thermal conductivity of nanostructures
as a function of their dimensions. We have verified the law using very large
molecular dynamics simulations
Analyticity and the counting rule of matrix poles
By studying scattering amplitudes in the large limit, we
clarify the dependence of the matrix pole position. It is
demonstrated that analyticity and the counting rule exclude the existence
of matrix poles with . Especially the properties
of and with respect to the expansion are discussed.
We point out that in general tetra-quark resonances do not exist.Comment: This paper replaces hep-ph/0412175. The latter is withdraw
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