Conformal gravitational theories in the Barthel-Kropina type Finslerian geometry, and their cosmological implications

We consider dark energy models obtained from the general conformal transformation of the Kropina metric, representing an $(\alpha, \beta)$ type Finslerian geometry, constructed as the ratio of the square of a Riemannian metric $\alpha$, and of the one-form $\beta$. Conformal symmetries do appear in many fields of physics, and they may play a fundamental role in the understanding of the Universe. We investigate the possibility of obtaining conformal theories of gravity in the osculating Barthel-Kropina geometric framework, where gravitation is described by an extended Finslerian type model, with the metric tensor depending on both the base space coordinates, and on a vector field. We show that it is possible to formulate a family of conformal Barthel-Kropina theories in an osculating geometry with second-order field equations, depending on the properties of the conformal factor, whose presence leads to the appearance of an effective scalar field, of geometric origin, in the gravitational field equations. The cosmological implications of the theory are investigated in detail, by assuming a specific relation between the component of the one-form of the Kropina metric, and the conformal factor. The cosmological evolution is thus determined by the initial conditions of the scalar field, and a free parameter of the model. We analyze in detail three cosmological models, corresponding to different values of the theory parameters. Our results show that the conformal Barthel-Kropina model could give an acceptable description of the observational data, and may represent a theoretically attractive alternative to the standard $\Lambda$CDM cosmology.Comment: 19 pages, 6 figures, accepted for publication in EPJ

Stiffness prediction for bolted moment-connections in cold-formed steel trusses

The purpose of this research was to study the behavior of cold-formed steel cantilever truss structures. A cantilever truss structure and bolt-moment connection were tested and verified by the 3D-finite element model. The verification results showed a good correlation between an experimental test and finite element analysis. An analytical method for elastic rotational stiffness of bolt-moment connection was proposed. The equation proposed in the analytical method was used to approximate the elastic rotational stiffness of the bolt group connection, and was also applied to the Richard-Abbott model for generating the nonlinear moment-rotation curve which modeled the semi-rigid connection stiffness. The 2D-finite element analysis was applied to study the behavior of the truss connection, caused by semi-rigid connection stiffness which caused a change of force to the truss elements. The results showed that the force in the structural members increased by between 13.62%-74.32% of the axial forces, and the bending moment decreased by between 33.05%-100%. These results strongly suggest that the semi-rigid connection between cold-formed steel cantilever truss structures should be considered in structural analysis to achieve optimum design, acknowledging this as the real behavior of the structure

Dark energy and accelerating cosmological evolution from osculating Barthel-Kropina geometry

Finsler geometry is an important extension of Riemann geometry, in which to each point of the spacetime manifold an arbitrary internal variable is associated. Interesting Finsler geometries, with many physical applications, are the Randers and Kropina type geometries, respectively. A subclass of Finsler geometries is represented by the osculating Finsler spaces, in which the internal variable is a function of the base manifold coordinates only. In an osculating Finsler geometry one introduces the Barthel connection, which has the remarkable property that it is the Levi-Civita connection of a Riemannian metric. In the present work we consider the gravitational and cosmological implications of a Barthel-Kropina type geometry. We assume that in this geometry the Ricci type curvatures are related to the matter energy-momentum tensor by the standard Einstein equations. The generalized Friedmann equations in the Barthel-Kropina geometry are obtained by considering that the background Riemannian metric is of Friedmann-Lemaitre-Robertson-Walker type. The matter energy balance equation is also derived. The cosmological properties of the model are investigated in detail, and it is shown that the model admits a de Sitter type solution, and that an effective dark energy component can also be generated. Several cosmological solutions are also obtained by numerically integrating the generalized Friedmann equations. A comparison of two specific classes of models with the observational data and with the standard $\Lambda$CDM model is also performed, and it turns out that the Barthel-Kropina type models give a satisfactory description of the observations.Comment: 25 pages, 7 figures, accepted for publication in EPJ

Prediction of In-plane Stiffness for the Cold-formed Steel Frame of the Wall Panel Structure

The purpose of this research was to study the lateral deformation behavior of cold-formed steel wall panel structures using experimental tests, finite element analysis and analytical methods to study the lateral stiffness of these structures. The wall panel structures were tested by full-scale experiments the experimental results of which were verified by a 3D-finite element model. The verification results showed a good correlation between the experimental tests and a finite element model. The single-column spring model was proposed for an elastic lateral stiffness analysis of the cold-formed steel wall panel structures that were formed by combinations of a guide cantilever beam and springs connection. The spring constants were defined by using the stiffness of the stub-chord connection and the bending stiffness of the chord. The experiments tests and finite element analysis were used to verify this single-column spring model. The comparison results showed good agreement between the analytical prediction, finite element analysis and experimental data in the case of the primary type of cold-formed wall structure. The proposed procedure was an efficient method for elastic lateral deformation analysis of cold-formed wall panel structures which can be used for such configurations

Study of the NaOH concentration and aluminium compound on the ettringite formation in fluidized bed combustion (FBC) fly ash geopolymer

AbstractFluidized bed combustion (FBC) fly ash contains high amount of calcium sulfate (CaSO4) due to feeding of lime into the combustion process to capture the SOx gases. The CaSO4 can be formed and react with alumina in the FBC fly ash under base condition resulted in calcium sulfoaluminate (ettringite). Therefore, effect of sodium hydroxide (NaOH) concentration on ettringite formation in FBC fly ash geopolymer was studied. In addition, the properties of geopolymer was improved by the addition of aluminium compound. The geopolymer was prepared from FBC fly ash mixed with aluminum hydroxide (Al(OH)3),sodium silicate and sodium hydroxide solution which Al(OH)3 could convert the calcium compound in FBC fly ash to calcium aluminate hydrate and aluminosilicate. It exhibited the strength gain of geopolymer. It was found that there is no sign of ettringite formation when 15 M NaOH was used. Use of Al(OH)3 not exceed 2.5% by weight of FBC fly ash in geopolymer preparation gave the compressive strength of 35 MPa at 90 days, while that of Al(OH)3 at 5% by weight resulted in sodium aluminateformation and strength reduction

Randers metrics on two-spheres of revolution with simple cut locus

In the present paper, we study the Randers metric on two-spheres of revolution in order to obtain new families of Finsler of Randers type metrics with simple cut locus. We determine the geodesics behavior, conjugate and cut loci of some families of Finsler metrics of Randers type whose navigation data is not a Killing field and without sectional or flag curvature restrictions. Several examples of Randers metrics whose cut locus is simple are shown

Strength behavior of fly ash geopolymer with microwave pre-radiation curing

AbstractThis research studied on the effect of microwave energy on the compressive strength of geopolymer and comparedwith that of geopolymer curing with the conventional heat system. Geopolymer was produced by the reaction between a pozzolan and the highly concentrated alkali and sodium silicate solutions, and then cured at the temperature of 65oC. Pre–radiation of microwave energy was applied before heat curing. Microwave energy helped the geopolymerization reaction resulting in the increase in leaching of silica and alumina on the fly ash surfaces and development of compressive strength. System with 90 watt microwave pre – radiation for 5 min plus 6 h heat curing gave a compressive strength of 34 MPa, which was higher than that of system with 65oC heat curing for 24 h (31 MPa). Therefore, the microwave energy could reduce the curing time and save energy obtaining the higher strength of geopolymer

Effect of metakaolin replaced granulated blast furnace slag on fresh and early strength properties of geopolymer mortar

We report the effect of metakaolin (MK) substituted granulated blast furnace slag (GBFS) on the early strength of geopolymer mortars (GPMs) for potential repair applications. Such GPMs were prepared by activating MK (0-15%) replaced GBFS. Solution concentrations ratio of SiO2:Na2O were varied in the range of 1.08-1.26 to achieve appropriate geopolymerization. Various proportion of Na2O:dry binder (7, 8, 9, 11 and 13%) were used. The mass ratios of sodium silicate to sodium hydroxide (NS:NH) and the binder to fine aggregate (B:A) were fixed to 3.0 and 0.90, respectively. The mechanical properties of the synthesized GPMs were determined at ambient temperature after 24h of casting and curing. It is demonstrated that 5% of MK replaced GBFS with 1.16 of SiO2:Na2O and 0.40 of S:B achieved an early compressive strength as much as 47.84MPa at 24h. The bond strength results exhibited the prospect of such GPMs as suitable alternative repair material

Study of the binary system fly ash/sugarcane bagasse ash (FA/SCBA) in SiO2/K2O alkali-activated binders

Due environmental problems related to Portland cement consumption, many studies have been performed to diminish its use. One solution is the development of alkali-activated binders, which can decrease CO2 emissions and energy consumption by 70% when compared to Portland cement production. In addition, an alkali-activated binder presents mechanical properties similar to Portland cement mixtures, which turns into an interesting material in civil construction. Aluminosilicate-based materials are important raw materials to produce the alkali-activated binders. Therefore, two residues are presented as an aluminosilicate source in this study: fly ash (FA) and sugarcane bagasse ash (SCBA). Both residues were obtained from a combustion process to generate energy, the former from coal and the latter from the bagasse of the sugarcane industry. In addition, the alkaline activating solution is an important factor to achieve improved mechanical properties. In this context, this study investigated the influence of four different SiO2/K2O molar ratios (0, 0.36, 0.75 and 1.22) in the activating solution with a constant water content, and three FA/SCBA binder proportions (75/25, 50/50 and 25/75). Microstructural characterization was carried out by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, mercury intrusion porosimetry, pH and electrical conductivity measurements to study the evolution of the reaction process. The compressive strength of mortars was assessed in order to determine the optimum SiO2/K2O molar ratio and FA/SCBA ratio. The tests showed that a SiO2/K2O molar ratio of 0.75 and FA/SCBA proportion of 75/25 provided the best mechanical properties.The authors would like to thank the Ministerio de Educacion, Cultura y Deporte of Spain (Cooperacion Interuniversitaria program with Brazil, Project PHB-2011-0016-PC), CAPES Brazil (Project CAPES/DGU No. 266/12) and CNPq (process no 401724/2013-1).Castaldelli, V.; Moraes, J.; Akasaki, JL.; Pinheiro Melges, JL.; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Soriano Martínez, L.... (2016). Study of the binary system fly ash/sugarcane bagasse ash (FA/SCBA) in SiO2/K2O alkali-activated binders. Fuel. 174:307-316. https://doi.org/10.1016/j.fuel.2016.02.020S30731617