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Performance of bolted steel-beam to CFST-column joints using stiffened angles in column-removal scenario
This paper presents three experimental investigations on the performance of steel-beam to CFST-column joints using stiffened angle, long bolts and fin plate under a middle column removal scenario. Three specimens were designed and tested. The failure modes and catenary action are investigated in detail. The test results show that increasing the angle plate thickness at the joint could not only improve its performance significantly, but also trigger an early formation of catenary action. Increasing the length of short-limb had influence on the deformation ability of the proposed joint, rather than the load capacity. The buckling of stiffeners could prevent the brittle failure of the joints. With the contribution of catenary action, the joint shows much higher rotation capacities than that required in DoD design guidance. The initial stiffness of the joint was calculated using an analytical model with consideration of bolt pretension. Good agreement to the test results is achieved. A numerical analysis is also carried out, whose results show that adding additional row of bolts would improve the redundancy of the joint under column loss. An equivalent dynamic response evaluation of the joints was also performed. The results show that dynamic amplification coefficient should be worked out considering catenary action under large deformation
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The Influence of Water on Dielectric Behavior of Silica-filled Epoxy Nano-composites and Percolation Phenomenon
The dielectric properties of epoxy resin were studied as a function of hydration by dielectric spectroscopy. The dielectric spectroscopy measurements show different conduction and quasi-DC behaviors at very low frequencies (<10-2 Hz) with activation energies dependent on the hydration. These observations lead to the development of a model in which a “water shell” is formed around the nano-particles. The multiple shell model, originally proposed by Lewis and developed by Tanaka, has been further developed to explain low frequency dielectric spectroscopy results in which percolation of charge carriers through overlapping water shells was shown to occur. At 100% relative humidity, water is believed to surround the nanoparticles to a depth of approximately 10 monolayers as the first layer. A second layer of water is proposed that is dispersed by sufficiently concentrated to be conductive. If all the water had existed in a single layer surrounding a nanoparticle, this layer would have been approximately 5 nm thick at 100% RH. Filler particles that have surfaces that are functionalized to be hydrophobic considerably reduce the amount of water absorbed in nanocomposites under the same conditions of humidity. PEA results show that the wetted epoxy specimens have a higher threshold field of space charge accumulation than such dry specimens since water enhances charge decay
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Influence of absorbed water on the dielectric properties and glass-transition temperature of silica-filled epoxy nanocomposites
Work on dielectric spectroscopy of epoxy resin filled with nano-SiO2 at different relative humidities and temperatures is reported. Above the glass-transition temperature (Tg), dc-like imperfect charge transport (QDC or LFD) dominates the low frequency dielectric spectrum. Another mid-frequency relaxation process was found in the non-dried composites. Water also induces glass-transition temperature decreases, which can be measured both by dielectric spectroscopy and DSC. Both theory and experiment demonstrated that a higher water content could exist in nanocomposites than unfilled epoxy suggesting a bigger free volume when nanostructured. In our system, the hydrophilic surface of silica is likely to cause water to surround and lead to delamination of the epoxy from SiO2. This is a potential mechanical and dielectric weakness in the nanocomposites, which may lead to an ageing phenomenon. Hydrophobic surface group may reduce the water adsorption in nanocomposites
Spherical to deformed shape transition in the nucleon-pair shell model
A study of the shape transition from spherical to axially deformed nuclei in
the even Ce isotopes using the nucleon-pair approximation of the shell model is
reported. As long as the structure of the dominant collective pairs is
determined using a microscopic framework appropriate to deformed nuclei, the
model is able to produce a shape transition. However, the resulting transition
is too rapid, with nuclei that should be transitional being fairly well
deformed, perhaps reflecting the need to maintain several pairs with each
angular momentum.Comment: 7 pages, 5 figure
Phenomenology from a U(1) gauged hidden sector
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the matter content are uncharged
under the SM gauge groups. We consider a simple case where the hidden sector is
gauged under a U(1) with one Higgs singlet. The only couplings between SM and
the hidden sector are through mixings between the neutral gauge bosons of the
two respective sectors, and between the Higgs bosons. We find signals testable
at the LHC that can reveal the existence and shed light on the nature of such a
hidden sector.Comment: 5 pages, 2 figures. Talk given at the Lake Louise Winter Institute
2007, Feb. 19-24, Alberta, Canad
Local Spin Susceptibility of the S=1/2 Kagome Lattice in ZnCu3(OD)6Cl2
We report single-crystal 2-D NMR investigation of the nearly ideal spin S=1/2
kagome lattice ZnCu3(OD)6Cl2. We successfully identify 2-D NMR signals
originating from the nearest-neighbors of Cu2+ defects occupying Zn sites. From
the 2-D Knight shift measurements, we demonstrate that weakly interacting Cu2+
spins at these defects cause the large Curie-Weiss enhancement toward T=0
commonly observed in the bulk susceptibility data. We estimate the intrinsic
spin susceptibility of the kagome planes by subtracting defect contributions,
and explore several scenarios.Comment: 4 figures; published in PR-B Rapid Communication
A Very Narrow Shadow Extra Z-boson at Colliders
We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the ``shadow Higgs'' are uncharged
under the SM gauge groups. We consider a simple U(1) model with one Higgs
singlet. One mechanism which sheds light on the shadow sector is the mixing
between the neutral gauge boson of the SM and the additional U(1) gauge group.
The mixing happens through the usual mass-mixing and also kinetic-mixing, and
is the only way the ``shadow '' couples to the SM. We study in detail
modifications to the electroweak precision tests (EWPTs) that the presence of
such a shadow sector would bring, which in turn provide constraints on the
kinetic-mixing parameter, , left free in our model. The shadow
production rate at the LHC and ILC depends on . We find that
observable event rate at both facilities is possible for a reasonable range of
allowed by EWPTs.Comment: 10 pages, 7 figures. Note and refs. adde
Testing Realistic Quark Mass Matrices in the Custodial Randall-Sundrum Model with Flavor Changing Top Decays
We study quark mass matrices in the Randall-Sundrum (RS) model with bulk
symmetry . The Yukawa couplings are
assumed to be within an order of magnitude of each other, and perturbative. We
find that quark mass matrices of the symmetrical form proposed by Koide
\textit{et. al.} [Y. Koide, H. Nishiura, K. Matsuda, T. Kikuchi and T.
Fukuyama, Phys. Rev. D {\bf 66}, 093006 (2002)] can be accommodated in the RS
framework with the assumption of hierarchyless Yukawa couplings, but not the
hermitian Fritzsch-type mass matrices. General asymmetrical mass matrices are
also found which fit well simultaneously with the quark masses and the
Cabibbo-Kobayashi-Maskawa matrix. Both left-handed (LH) and right-handed (RH)
quark rotation matrices are obtained that allow analysis of flavour changing
decay of both LH and RH top quarks. At a warped down scale of 1.65 TeV, the
total branching ratio of t \ra Z + jets can be as high as for symmetrical mass matrices and for
asymmetrical ones. This level of signal is within reach of the LHC.Comment: 30 pages, 6 figures. Reference added, typos corrected, discussions in
Sec. IV B expanded. Version conforms to the published versio
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