3,510 research outputs found
Influence of different fibers on the change of pore pressure of self-consolidating concrete exposed to fire
The focus of this paper is given to investigate the effect of different fibers on the pore pressure of fiber reinforced self-consolidating concrete under fire. The investigation on the pore pressure-time and temperature relationships at different depths of fiber reinforced self-consolidating concrete beams was carried out. The results indicated that micro PP fiber is more effective in mitigating the pore pressure than
macro PP fiber and steel fiber. The composed use of steel fiber, micro PP fiber and macro PP fiber showed
clear positive hybrid effect on the pore pressure reduction near the beam bottom subjected to fire.
Compared to the effect of macro PP fiber with high dosages, the effect of micro PP fiber with low fiber
contents on the pore pressure reduction is much stronger. The significant factor for reduction of pore pressure depends mainly on the number of PP fibers and not only on the fiber content. An empirical formula was proposed to predict the relative maximum pore pressure of fiber reinforced self-consolidating concrete exposed to fire by considering the moisture content, compressive strength and various fibers.
The suggested model corresponds well with the experimental results of other research and tends to prove that the micro PP fiber can be the vital component for reduction in pore pressure, temperature as well spalling of concrete.National Natural Science Foundation of China (Grant: 51121005), DUT and Fundaçãopara a Ciência e
a Tecnologia (SFRH/BPD/22680/2005), the FEDER Funds through “Programa Operacional Factores
de Competitividade - COMPETE" and by Portuguese Funds through FCT-within the Projects
PEst-CMAT/UI0013/2011 and PTDC/MAT/112273/2009
Classical Duals, Legendre Transforms and the Vainshtein Mechanism
We show how to generalize the classical duals found by Gabadadze {\it et al}
to a very large class of self-interacting theories. This enables one to adopt a
perturbative description beyond the scale at which classical perturbation
theory breaks down in the original theory. This is particularly relevant if we
want to test modified gravity scenarios that exhibit Vainshtein screening on
solar system scales. We recognise the duals as being related to the Legendre
transform of the original Lagrangian, and present a practical method for
finding the dual in general; our methods can also be applied to
self-interacting theories with a hierarchy of strong coupling scales, and with
multiple fields. We find the classical dual of the full quintic galileon theory
as an example.Comment: 16 page
The dark flow induced small scale kinetic Sunyaev Zel'dovich effect
Recently Kashlinsky et al. 2008, 2010 reported a discovery of a
km/ bulk flow of the universe out to , through the dark flow
induced CMB dipole in directions of clusters. We point out that, if this dark
flow exists, it will also induce observable CMB temperature fluctuations at
multipole , through modulation of the inhomogeneous electron
distribution on the uniform dark flow. The induced small scale kinetic Sunyaev
Zel'dovich (SZ) effect will reach \sim 1\muk^2 at multipole 10^3\la \ell\la
10^4, only a factor of smaller than the conventional kinetic SZ
effect. Furthermore, it will be correlated with the large scale structure (LSS)
and its correlation with 2MASS galaxy distribution reaches K at
, under a directional dependent optimal weighting scheme. We
estimate that, WMAP plus 2MASS should already be able to detect this dark flow
induced small scale kinetic SZ effect with confidence. Deeper
galaxy surveys such as SDSS can further improve the measurement. Planck plus
existing galaxy surveys can reach \ga 14\sigma detection. Existing CMB-LSS
cross correlation measurements shall be reanalyzed to test the existence of the
dark flow and, if it exists, shall be used to eliminate possible bias on the
integrated Sachs-Wolfe effect measurement through the CMB-LSS cross
correlation.Comment: Minor revisions. 5 pages, 3 figures. MNRAS letters in pres
Relations Between Closed String Amplitudes at Higher-order Tree Level and Open String Amplitudes
KLT relations almost factorize closed string amplitudes on by two open
string tree amplitudes which correspond to the left- and the right- moving
sectors. In this paper, we investigate string amplitudes on and .
We find that KLT factorization relations do not hold in these two cases. The
relations between closed and open string amplitudes have new forms. On
and , the left- and the right- moving sectors are connected into a single
sector. Then an amplitude with closed strings on or can be given
by one open string tree amplitude except for a phase factor. The relations
depends on the topologies of the world-sheets.Under T-duality, the relations on
and give the amplitudes between closed strings scattering from
D-brane and O-plane respectively by open string partial amplitudes.In the low
energy limits of these two cases, the factorization relations for graviton
amplitudes do not hold. The amplitudes for gravitons must be given by the new
relations instead.Comment: 19 page
Classical Stability of the Galileon
We consider the classical equations of motion for a single Galileon field
with generic parameters in the presence of non-relativistic sources. We
introduce the concept of absolute stability of a theory: if one can show that a
field at a single point---like infinity for instance---in spacetime is stable,
then stability of the field over the rest of spacetime is guaranteed for any
positive energy source configuration. The Dvali-Gabadadze-Porrati (DGP) model
is stable in this manner, and previous studies of spherically symmetric
solutions suggest that certain classes of the single field Galileon (of which
the DGP model is a subclass) may have this property as well. We find, however,
that when general solutions are considered this is not the case. In fact, when
considering generic solutions there are no choices of free parameters in the
Galileon theory that will lead to absolute stability except the DGP choice. Our
analysis indicates that the DGP model is an exceptional choice among the large
class of possible single field Galileon theories. This implies that if general
solutions (non-spherically symmetric) exist they may be unstable. Given
astrophysical motivation for the Galileon, further investigation into these
unstable solutions may prove fruitful.Comment: 23 pages, 3 figure
Recommended from our members
Human Immunodeficiency Virus (HIV)-Infected CCR6+ Rectal CD4+ T Cells and HIV Persistence On Antiretroviral Therapy.
BackgroundIdentifying where human immunodeficiency virus (HIV) persists in people living with HIV and receiving antiretroviral therapy is critical to develop cure strategies. We assessed the relationship of HIV persistence to expression of chemokine receptors and their chemokines in blood (n = 48) and in rectal (n = 20) and lymph node (LN; n = 8) tissue collected from people living with HIV who were receiving suppressive antiretroviral therapy.MethodsCell-associated integrated HIV DNA, unspliced HIV RNA, and chemokine messenger RNA were quantified by quantitative polymerase chain reaction. Chemokine receptor expression on CD4+ T cells was determined using flow cytometry.ResultsIntegrated HIV DNA levels in CD4+ T cells, CCR6+CXCR3+ memory CD4+ T-cell frequency, and CCL20 expression (ligand for CCR6) were highest in rectal tissue, where HIV-infected CCR6+ T cells accounted for nearly all infected cells (median, 89.7%). Conversely in LN tissue, CCR6+ T cells were infrequent, and there was a statistically significant association of cell-associated HIV DNA and RNA with CCL19, CCL21, and CXCL13 chemokines.ConclusionsHIV-infected CCR6+ CD4+ T cells accounted for the majority of infected cells in rectal tissue. The different relationships between HIV persistence and T-cell subsets and chemokines in rectal and LN tissue suggest that different tissue-specific strategies may be required to eliminate HIV persistence and that assessment of biomarkers for HIV persistence may not be generalizable between blood and other tissues
Cluster number counts dependence on dark energy inhomogeneities and coupling to dark matter
Cluster number counts can be used to test dark energy models. We investigate
dark energy candidates which are coupled to dark matter. We analyze the cluster
number counts dependence on the amount of dark matter coupled to dark energy.
Further more, we study how dark energy inhomogeneities affect cluster
abundances. It is shown that increasing the coupling reduces significantly the
cluster number counts, and that dark energy inhomogeneities increases cluster
abundances. Wiggles in cluster number counts are shown to be a specific
signature of coupled dark energy models. Future observations will possibly
detect such oscillations and discriminate among the different dark energy
models.Comment: 9 pages, 8 figures. Further extensions on section on discriminating
models with future surveys. Accepted for publication in Mon. Not. Roy. Astro.
So
Strengthening the Reporting of Genetic Risk Prediction Studies: The GRIPS Statement
Cecile Janssens and colleagues present the GRIPS Statement, a checklist to help strengthen the reporting of genetic risk prediction studies
Schwarzschild black hole surrounded by quintessence: Null geodesics
We have studied the null geodesics of the Schwarzschild black hole surrounded
by quintessence matter. Quintessence matter is a candidate for dark energy.
Here, we have done a detailed analysis of the geodesics and exact solutions are
presented in terms of Jacobi-elliptic integrals for all possible energy and
angular momentum of the photons. The circular orbits of the photons are studied
in detail. As an application of the null geodesics, the angle of deflection of
the photons are computed.Comment: 25 pages, 20 figures. typos corrected and some of the notation
change
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