240 research outputs found
Plastic-damage smeared crack model to simulate the behaviour of structures made by cement based materials
This work proposes a constitutive model to simulate nonlinear behaviour of cement based materials subjected to
different loading paths. The model incorporates a multidirectional fixed smeared crack approach to simulate crack
initiation and propagation, whereas the inelastic behaviour of material between cracks is treated by a numerical strategy
that combines plasticity and damage theories. For capturing more realistically the shear stress transfer between the crack
surfaces, a softening diagram is assumed for modelling the crack shear stress versus crack shear strain. The plastic
damage model is based on the yield function, flow rule and evolution law for hardening variable, and includes an
explicit isotropic damage law to simulate the stiffness degradation and the softening behaviour of cement based
materials in compression. This model was implemented into the FEMIX computer program, and experimental tests at
material scale were simulated to appraise the predictive performance of this constitutive model. The applicability of the
model for simulating the behaviour of reinforced concrete shear wall panels submitted to biaxial loading conditions, and
RC beams failing in shear is investigated.The authors wish to acknowledge the FCT financial support provided by the Portuguese Foundation for Science and Technology in the scope of the SlabSys-HFRC research project, with reference PTDC/ECM/120394/2010
Behaviour of GFRP-steel reinforced I shape beams with steel fibers as shear reinforcement
This paper evaluates the possibility of developing prefabricated beams without stirrups by
using fiber reinforcement for increasing the concrete shear capacity, and a hybrid flexural
reinforcement system composed of glass fiber reinforced polymer (GFPR) and steel rebars.
A high compressive strength and high post-cracking tensile capacity steel fiber reinforced
self-compacting concrete (SFRSCC) was developed, aiming at supressing the need of steel
stirrups in this type of beams while providing sufficient ductility for structural applications.
The experimental results were analysed in terms of failure mode, deformational and cracking
behaviour, as well as load carrying capacity. A constitutive model, capable of simulating
three types of material nonlinearities simultaneously in an integration point (IP), was used
and its predictive performance was assessed by simulating the experimental tests. The
numerical approach was then used to assess the potentialities of this material system and
structural concept when applied to relatively large span beams.The authors wish to acknowledge the funding provided by project FOATIDE, reference POCI-01-
0145-FEDER-028112
Assessment of the sustainability of fibre-reinforced concrete by considering both environmental and mechanical properties
The environmental consequences of human activities, e.g., the depletion of non-renewable fuel resources, consumption of natural raw materials, and release of huge amounts of CO2 into the atmosphere, resulted in new challenges in materials engineering. Based on these challenges, building materials must fulfil not only mechanical performance criteria, but also produce the least environmental impact accompanied by their production. In the present study, the possibility of employing scrap tire recycled steel fibres (RSF) as a substitution to industrial steel fibres (ISF) for developing more sustainable fibre-reinforced concretes was explored by adopting a life-cycle approach, integrated both environmental and mechanical properties. Four different fibre-reinforced self-compacting concretesâFRSCCsâwere tailored by means of replacing the ISFs partially/totally (i.e., 0%, 50%, 67%, 100% by mass of) with the recycled ones. The effect of applying various dosages of RSFs on mechanical behavior of FRSCCânamely compressive, flexural, and splitting tensile responsesâwere evaluated experimentally. The environmental impacts associated with the production of each FRSCC were also assessed through life-cycle analysis. The potentiality of the RSFs to be used as concrete reinforcement with a comparable mechanical performance to that of ISF-reinforced concrete and lower environmental footprint was evaluated through a consolidated environmental and mechanical index (EM). In this study, using RSFs instead of industrial fibres for developing FRSCC has provided up to 37% higher EM index. The results confirmed the promising prospects for the application of RSFs in developing more eco-efficient and sustainable reinforced concrete.FOATIDE, reference POCI-01-0145-FEDER-028112, co-financed by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020), under Portugal 2020, and by the Fundação para a CiĂȘncia e a TecnologiaâFCT (National Agency for Science and Technology). The first author also acknowledges the Scientific Employment funding, No. CEECIND/01627/2017, provided by FCT. The financial support provided by FCT under the project UIDB/04033/2020 is kindly acknowledged by the last author
A microscopic theory of gauge mediation
We construct models of indirect gauge mediation where the dynamics
responsible for breaking supersymmetry simultaneously generates a weakly
coupled subsector of messengers. This provides a microscopic realization of
messenger gauge mediation where the messenger and hidden sector fields are
unified into a single sector. The UV theory is SQCD with massless and massive
quarks plus singlets, and at low energies it flows to a weakly coupled quiver
gauge theory. One node provides the primary source of supersymmetry breaking,
which is then transmitted to the node giving rise to the messenger fields.
These models break R-symmetry spontaneously, produce realistic gaugino and
sfermion masses, and give a heavy gravitino.Comment: 24 pages, 2 figures, accepted to JHEP for publicatio
Anomalous Dimensions and Non-Gaussianity
We analyze the signatures of inflationary models that are coupled to strongly
interacting field theories, a basic class of multifield models also motivated
by their role in providing dynamically small scales. Near the squeezed limit of
the bispectrum, we find a simple scaling behavior determined by operator
dimensions, which are constrained by the appropriate unitarity bounds.
Specifically, we analyze two simple and calculable classes of examples:
conformal field theories (CFTs), and large-N CFTs deformed by relevant
time-dependent double-trace operators. Together these two classes of examples
exhibit a wide range of scalings and shapes of the bispectrum, including nearly
equilateral, orthogonal and local non-Gaussianity in different regimes. Along
the way, we compare and contrast the shape and amplitude with previous results
on weakly coupled fields coupled to inflation. This signature provides a
precision test for strongly coupled sectors coupled to inflation via irrelevant
operators suppressed by a high mass scale up to 1000 times the inflationary
Hubble scale.Comment: 40 pages, 10 figure
A Hybrid Higgs
We construct composite Higgs models admitting a weakly coupled Seiberg dual
description. We focus on the possibility that only the up-type Higgs is an
elementary field, while the down-type Higgs arises as a composite hadron. The
model, based on a confining SQCD theory, breaks supersymmetry and electroweak
symmetry dynamically and calculably. This simultaneously solves the \mu/B_\mu
problem and explains the smallness of the bottom and tau masses compared to the
top mass. The proposal is then applied to a class of models where the same
confining dynamics is used to generate the Standard Model flavor hierarchy by
quark and lepton compositeness. This provides a unified framework for flavor,
supersymmetry breaking and electroweak physics. The weakly coupled dual is used
to explicitly compute the MSSM parameters in terms of a few microscopic
couplings, giving interesting relations between the electroweak and soft
parameters. The RG evolution down to the TeV scale is obtained and salient
phenomenological predictions of this class of "single-sector" models are
discussed.Comment: 56 pages, 7 figures, v2: discussion on FCNCs and references added,
v3: JHEP versio
Fano resonances in plasmonic core-shell particles and the Purcell effect
Despite a long history, light scattering by particles with size comparable
with the light wavelength still unveils surprising optical phenomena, and many
of them are related to the Fano effect. Originally described in the context of
atomic physics, the Fano resonance in light scattering arises from the
interference between a narrow subradiant mode and a spectrally broad radiation
line. Here, we present an overview of Fano resonances in coated spherical
scatterers within the framework of the Lorenz-Mie theory. We briefly introduce
the concept of conventional and unconventional Fano resonances in light
scattering. These resonances are associated with the interference between
electromagnetic modes excited in the particle with different or the same
multipole moment, respectively. In addition, we investigate the modification of
the spontaneous-emission rate of an optical emitter at the presence of a
plasmonic nanoshell. This modification of decay rate due to electromagnetic
environment is referred to as the Purcell effect. We analytically show that the
Purcell factor related to a dipole emitter oriented orthogonal or tangential to
the spherical surface can exhibit Fano or Lorentzian line shapes in the near
field, respectively.Comment: 28 pages, 10 figures; invited book chapter to appear in "Fano
Resonances in Optics and Microwaves: Physics and Application", Springer
Series in Optical Sciences (2018), edited by E. O. Kamenetskii, A. Sadreev,
and A. Miroshnichenk
The Cosmology of Composite Inelastic Dark Matter
Composite dark matter is a natural setting for implementing inelastic dark
matter - the O(100 keV) mass splitting arises from spin-spin interactions of
constituent fermions. In models where the constituents are charged under an
axial U(1) gauge symmetry that also couples to the Standard Model quarks, dark
matter scatters inelastically off Standard Model nuclei and can explain the
DAMA/LIBRA annual modulation signal. This article describes the early Universe
cosmology of a minimal implementation of a composite inelastic dark matter
model where the dark matter is a meson composed of a light and a heavy quark.
The synthesis of the constituent quarks into dark mesons and baryons results in
several qualitatively different configurations of the resulting dark matter
hadrons depending on the relative mass scales in the system.Comment: 31 pages, 4 figures; references added, typos correcte
BK virus encephalopathy and sclerosing vasculopathy in a patient with hypohidrotic ectodermal dysplasia and immunodeficiency
A Fat Higgs with a Magnetic Personality
We introduce a novel composite Higgs theory based on confining supersymmetric
QCD. Supersymmetric duality plays a key role in this construction, with a "fat"
Higgs boson emerging as a dual magnetic degree of freedom charged under the
dual magnetic gauge group. Due to spontaneous color-flavor locking in the
infrared, the electroweak gauge symmetry is aligned with the dual magnetic
gauge group, allowing large Yukawa couplings between elementary matter fields
and the composite Higgs. At the same time, this theory exhibits metastable
supersymmetry breaking, leading to low-scale gauge mediation via composite
messengers. The Higgs boson is heavier than in minimal supersymmetric theories,
due to non-decoupling D-terms and a large F-term quartic coupling. This theory
predicts quasi-stable TeV-scale pseudo-modulini, some of which are charged
under standard model color, possibly giving rise to long-lived R-hadrons at the
LHC.Comment: 33 pages, 6 figures, 6 table
- âŠ