Cosmological models in energy-momentum-squared gravity

We study the cosmological effects of adding terms of higher-order in the usual energy-momentum tensor to the matter lagrangian of general relativity. This is in contrast to most studies of higher-order gravity which focus on generalising the Einstein-Hilbert curvature contribution to the lagrangian. The resulting cosmological theories give rise to field equations of similar form to several particular theories with different fundamental bases, including bulk viscous cosmology, loop quantum gravity, K-essence, and brane-world cosmologies. We find a range of exact solutions for isotropic universes, discuss their behaviours with reference to the early and late-time evolution, accelerated expansion, and the occurrence or avoidance of singularities. We briefly discuss extensions to anisotropic cosmologies and delineate the situations where the higher-order matter terms will dominate over anisotropies on approach to cosmological singularities

Screening Λ in a new modified gravity model

Abstract We study a new model of Energy-Momentum Squared Gravity (EMSG), called Energy-Momentum Log Gravity (EMLG), constructed by the addition of the term $$f(T_{\mu \nu }T^{\mu \nu })=\alpha \ln (\lambda \,T_{\mu \nu }T^{\mu \nu })$$f(TμνTμν)=αln(λTμνTμν), envisaged as a correction, to the Einstein–Hilbert action with cosmological constant $$\Lambda$$Λ. The choice of this modification is made as a specific way of including new terms in the right-hand side of the Einstein field equations, resulting in constant effective inertial mass density and, importantly, leading to an explicit exact solution of the matter energy density in terms of redshift. We look for viable cosmologies, in particular, an extension of the standard $$\Lambda$$ΛCDM model. EMLG provides an effective dynamical dark energy passing below zero at large redshifts, accommodating a mechanism for screening $$\Lambda$$Λ in this region, in line with suggestions for alleviating some of the tensions that arise between observational data sets within the standard $$\Lambda$$ΛCDM model. We present a detailed theoretical investigation of the model and then constrain the free parameter $$\alpha '$$α′, a normalisation of $$\alpha$$α, using the latest observational data. The data does not rule out the $$\Lambda$$ΛCDM limit of our model ($$\alpha '= 0$$α′=0), but prefers slightly negative values of the EMLG model parameter ($$\alpha '= -0.032\pm 0.043$$α′=-0.032±0.043), which leads to the screening of $$\Lambda$$Λ. We also discuss how EMLG relaxes the persistent tension that appears in the measurements of $$H_0$$H0 within the standard $$\Lambda$$ΛCDM model.</jats:p

Synthesis, structural and magnetic characterization of lead-metaniobate/cobalt-ferrite nanocomposite films deposited by pulsed laser ablation

Detailed structural, microstructural and magnetic measurements were performed on (PbNb2O6)(1-x) -(CoFe2O4) (x) nanocomposite thin films deposited by laser ablation on Si(001)\Pt substrates, with different cobalt ferrite concentrations. The tuning of the lead concentration, due to the lead volatility, was found to be particularly important in order to obtain the orthorhombic (ferroelectric) lead niobate phase. The lattice parameter of CoFe2O4 was below the bulk value, indicating the presence of compressive strains on this phase. A magnetic anisotropy was observed, which favored the orientation of the magnetization in the direction perpendicular to the plane of the films, for cobalt ferrite concentrations 40-50 %. The shape, stress and magnetocrystalline anisotropy fields on the composites were calculated and compared. It was found that the perpendicular magnetic anisotropy was induced by the presence of strain on the ferrite phase in the films.- This work has been supported by Fundacao para a Ciencia e Tecnologia (FCT) and FEDER, through the projects POCI/CTM/60181/2004 and PTDC/CTM/099415/2008. J. Barbosa and I. T. Gomes gratefully acknowledge Ph.D. grants from Fundacao para a Ciencia e Tecnologia (SFRH/BD/41913/2007 and SFRH/BD/36348/2007, respectively).info:eu-repo/semantics/publishedVersio

Chat Application Using Homomorphic Encryption

Chat applications nowadays have evolved into one of the most significant and widely used applications on smart devices. They are capable of sending and receiving messages, documents, and images with zero cost to any part of the world. All the messages should be protected. All the chat applications today are used to send messages quickly and securely. The actuality of the situation is that the messages sent are not as secure as they claim to be. So, to bridge this gap, in this paper Homomorphic Encryption is used to secure the messages further while also not reducing the speed of the transaction. This paper aims to implement a Chat application using Homomorphic Encryption which adds a layer of security over end-to-end encryption

Effect of wearing a helmet on the occurrence of head injuries in motorcycle riders in Benin: a case-control study

BACKGROUND: In Benin, motorcycles are the main means of transport for road users and are involved in more than half of crashes. This study aims to determine the effect of wearing a helmet on reducing head injuries in road crashes in Benin. METHODS: This case-control study took place in 2020 and focused on road trauma victims. The sample, consisting of 242 cases (trauma victims with head injuries) for 484 controls (without head injuries), was drawn from a database of traffic crash victims recruited from five hospitals across the country from July 2019 to January 2020. Four groups of independent variables were studied: socio-demographic and economic variables, history, behavioural variables including helmet use and road-related and environmental variables. To assess the shape of the association between the independent variables and the dependent variable, a descending step-by-step binary logistic regression model was performed using an explanatory approach. RESULTS: Fewer of the subjects with a head injury were wearing a helmet at the time of the crash 69.8% (95% CI = 63.6-75.6) compared to those without a head injury 90.3% (95% CI = 87.3-92.8). Adjusting for the other variables, subjects not wearing helmets were at greater risk of head injuries (OR = 3.8, 95% CI (2.5-5.7)); the head injury rating was 1.9 (95% CI = 1.2-3.3) times higher in subjects who were fatigued during the crash than among those who were not and 2.0 (95% CI = 1.2-3.3) times higher in subjects with no medical history. CONCLUSION: Failure to wear a helmet exposes motorcyclists to the risk of head injuries during crashes. It is important to increase awareness and better target such initiatives at the subjects most at risk