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 concretes–FRSCCs–were 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 FRSCC–namely compressive, flexural, and splitting tensile responses–were 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 Ciência e a Tecnologia—FCT (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

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