Snap Parameters Research Articles

Constraints on energy conditions in f(R,Lm) gravity

In this paper, we consider the extension of the Hilbert–Einstein action to analyze several interesting features of the theory. More specifically, the Lagrangian [Formula: see text] is replaced by [Formula: see text] in action, where [Formula: see text] is the Ricci scalar, and [Formula: see text] is the matter Lagrangian. We derive the motion equations for a test particle in the Friedmann–Lemaître–Robertson–Walker (FLRW) flat and homogeneous spacetime. We also derive the energy conditions in this framework. Then, we use the cosmographic parameter such as Hubble, deceleration, jerk and snap parameters to constraint the model parameters. As a result, we observe that with the constraint range of model parameters, our model shows the current accelerated expansion of the universe.

State finder and Om diagnostics in modified and generalised Chaplygin gas from recent data

A modified and generalised Chaplygin gas (MCG, [Formula: see text] and GCG, [Formula: see text]) has been separately chosen here as a constituent of the universe. Concept of state finder and Om diagnostics are introduced to track the dark energy in the models. Here, observed Hubble data (OHD) and binned Pantheon data of supernovae are used to determine the best-fit equation-of-state (EoS) parameters of these models and these are compared with the [Formula: see text]CDM model. The best-fit value and expected values of cosmological jerk parameter [Formula: see text], snap parameter [Formula: see text] are determined, which are close to each other. A plot of [Formula: see text] with red-shift, with themselves, as well as with deceleration parameter [Formula: see text], shows the evolution of the universe and its possible future. Variations of [Formula: see text] and EoS parameter [Formula: see text] with red-shift show acceleration–deceleration phase transition in the recent past. Lastly, the state finder pair [Formula: see text] and Om diagnostic have been utilized to discriminate the models.

Formula omitted] gravity bouncing universe with cosmological parameters

In recent few years, the Gauss-Bonnet f(G,T) theory of gravity has fascinated considerable researchers owing to its coupling of trace of the stress-energy tensor T with the Gauss-Bonnet term G. In this context, we focuss ourselves to study bouncing universe with in f(G,T) gravity background. Some important preliminaries are presented along with the discussion of cosmological parameters to develop a minimal background about f(G,T) theory of gravity. The exact bouncing solutions with physical analysis are provided with the choice of two equation of state parameters. It is shown that the results do agree with the present values of deceleration, jerk and snap parameters. Moreover, it is concluded that the model parameters are quite important for the validity of conservation equation (as the matter coupled theories do not obey the usual conservation law).

Energy condition in unimodular f(R,\xa0T) gravity

We study an interesting alternative of modified gravity theory, namely, the unimodular f(R, T) gravity in which R is the Ricci scalar and T is the trace of the stress–energy tensor. We study the viability of the model by using the energy conditions. We discuss the strong, weak, null and dominant energy conditions in terms of deceleration, jerk and snap parameters. We investigate energy conditions for reconstructed unimodular f(R, T) models and give some constraints on the parametric space of the model. We observe that by setting appropriately free parameters, energy conditions can be satisfied. Furthermore, we study the stability of the solutions in perturbations framework. In this case, we investigate stability conditions for de Sitter and power law solutions and we examine viability of cosmological evolution of these perturbations. The results show that for some values of the input parameters, for which energy conditions are satisfied, de Sitter and power-law solutions may be stable.

Statefinder and Om diagnostics in emergent universe model

The emergent universe scenario is obtained in a flat universe with the equation of state (EoS) ( $$p=B\rho -A\rho ^{\frac{1}{2}}$$ ) (where A and B are constants) as per Mukherjee et al. Here observed Hubble data (OHD) and binned Pantheon data of supernovae are used to determine the best-fit EoS parameters of the emergent universe models. Evolution of deceleration parameter q and EoS $$(\omega =\frac{p}{\rho })$$ has been studied through their plots with redshift. The statefinder diagnostics consisting of jerk parameter j, snap parameter s and Om diagnostics are introduced to make a comparative study of the emergent universe models. The parameters j, s have been plotted with redshift, with themselves, with q, to examine the evolution of the universe and its possible future in these models. Present values of q, $$\omega $$ , j, s along with their cosmological averages have been determined for the emergent universe models $$(B=-\frac{1}{3},0,\frac{1}{3},1)$$ . Akaike information criterion (AIC) and Bayesian information criterion (BIC) are the two model selection tools used here, according to it $$B=\frac{1}{3}$$ is the better model, then the $$B=0$$ model. Squared adiabatic sound speed $$c_{s}^{2}$$ is required to be positive in order that structure formation is a reality. Models with $$B=1,\frac{1}{3}$$ show clear signs and $$B=0$$ model shows hints of structure formation in the past. However, $$B=1$$ model is not compatible with the observational data. The $$B=-\frac{1}{3}$$ model does not show any signs of structure formation $$(c_{s}^{2}<0)$$ , so is plagued with instability. Best-fit values of the two suitable emergent universe model with (i) $$B=0$$ are $$H_{0}=69.29$$ , $$A_{s}=0.61$$ , $$q(0)=-0.42$$ , $$\omega (0)=-0.61$$ , $$j(0)=0.47$$ , $$s(0)=0.20$$ and (ii) $$B=\frac{1}{3}$$ are $$H_{0}=70.21$$ , $$A_{s}=0.77$$ , $$q(0)=-0.54$$ , $$\omega (0)=-0.69$$ , $$j(0)=0.75$$ , $$s(0)=0.08$$

Normal neurophysiologic parameters of the sural nerve among adult healthy Sudanese population

Background: Nerve conduction studies (NCSs) are of central importance for the assessment of peripheral nervous system disorders. They help in the diagnosis, extent distribution of neural lesion as well as the prognosis of a disease process. The aim of this study is to establish normative NCS reference data of the sural nerve in Sudanese population for our EMG electrodiagnostic center; and to survey the effects of age, gender, height, weight and temperature on conduction Parameters. Methods: The study was conducted in Elmagzoub Neuroscience Electrodiagnostic Centre; supported by the Faculty of Medicine, National Ribat University, Khartoum, Sudan. NCSs were performed in 210 sural nerves of 105 adult healthy Sudanese subjects using standardized techniques. Results: The Right sural nerve SNAP parameters in the whole subjects were set as (mean ±standard deviation) for onset latency. peak latency, amplitude and conduction velocity. The values were 2.73±0.42 ms, 3.32±0.46 ms, 8.39±3.49 uV and 52.05±8.47 m/s, respectively. The Left sural nerve SNAP parameters in the whole study group were 2.71±0.50 ms, 3.29 ±0.52 ms, 8.54±4.56 uV and 52.66 ±8.95, respectively. Conclusion: The sural sensory nerve conduction parameters compared favorably with the existing literature. Age showed a positive correlation with latencies, and negative correlation with amplitude and velocity. Gender has conspicuous effect on all sural nerve conduction parameters. Height showed an effect on latency and conduction velocity whereas BMI revealed a negative correlation with amplitude and conduction velocity of sural nerve.

Evolution of FLRW universe in Brans-Dicke gravity theory

This study aims to examine the dynamics of flat Friedmann-Lemaitre-Robertson-Walker (FLRW) model of universe with time varying cosmological constant $\Lambda (t)$ in Brans-Dicke theory of gravity. The authors find a solution of the field equations using simple parametrization of scale factor $a(t)$ i.e. $a(t)=\exp \{(\alpha t+\beta )^{p}\}$ , and power law relation between $a(t)$ and Brans-Dicke scalar field $\phi $ . The derived cosmological model shows transition from early cosmic deceleration to present cosmic acceleration. Such feature of cosmic expansion is in agreement with recent empirical observations. The behaviour of cosmographic parameters such as Hubble parameter, deceleration parameter, jerk, snap and lerk parameters is examined graphically. It is observed that model behaves like $\Lambda CDM$ model in late cosmic evolution. We also use statefinder and Om diagnostic tools to differentiate various dark energy models from $\Lambda CDM$ model. Moreover, model parameter $p$ and present value of deceleration parameter $q_{0}$ is also estimated using Hubble data set and Pantheon Type 1a supernova data set.

The cosmological behavior and the statefinder diagnosis for the New Tsallis agegraphic dark energy

In this work, we have considered the recently proposed new Tsallis agegraphic dark energy (NTADE) model [Mod. Phys. Lett. A 34, 1950086 (2019)] within the framework of a flat Friedmann–Robertson–Walker (FRW) Universe by taking various values of the parameter [Formula: see text]. The NTADE model shows the current phase transition of the Universe from decelerated to accelerated phase. The NTADE equation of state (EoS) parameter shows a rich behavior as it can be quintessence-like or phantom-like depending on the value of [Formula: see text]. For discriminating the NTADE model from [Formula: see text]CDM, we have plotted the statefinder parameters [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] pair. The NTADE model shows distinct evolutionary trajectories of their evolution in ([Formula: see text]) and ([Formula: see text]) plane. An analysis using the snap parameter and the [Formula: see text] pair dynamical analysis have also been performed.

Constraining f(T, B) teleparallel gravity from energy conditions

f(T, B) teleparallel gravity is a recently proposed straightforward generalization of the popular f(T) teleparallel gravity by the incorporation of a boundary term B=2e∂i(eTi)=▽iTi where T denote the torsion scalar (Bahamonde et al., 2015). In this work, I investigate the viability of some well motivated f(T, B) teleparallel gravity models of the forms f=αBn+βTm,f=αBnTm and f=αlog(B)+βT where α, β, n and m are free parameters from the inequalities imposed the weak energy condition. I use the recent estimates of Hubble, deceleration, jerk and snap parameters in finding corners in parameter spaces for the cosmological models for which the energy density remain positive and the weak energy condition (i.e, ρ+p≥0, where p and ρ represent respectively the cosmological pressure and energy density) attains a minute positive value, as this implies the EoS parameter ω=p/ρ≃−1 and therefore consistent with an accelerating universe.

Energy bounds in f(R, ϕ) gravity with anisotropic backgrounds

This research work discusses the energy bounds in f(R, ϕ) with anisotropic background. For this purpose, a BT-I cosmological model in f(R, ϕ) is considered. After calculating field equations, we find the exact solutions by considering field equations of the f(R, ϕ) gravity model. To investigate the cosmic expansion, we explore the model f(R, ϕ) for f(R,ϕ)=R(1+α2R2ϕ2) and f(R,ϕ)=ϕ(R+αR2). We formulate the inequalities in energy constraints and use the Hubble, deceleration, jerk and snap parameters to evaluate the feasibility of the models given above. Graphical analysis shows that the NEC, WEC and DEC are satisfied with the appropriate anisotropy values and model parameters for the given above two f(R, ϕ) gravity models. In fact, for both of considered models, SEC is violated and models are found favorable for cosmic expansion.

P39-S Multimodal evoked potentials in patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)

Background The central nervous system in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is involved in about 5% of patients. The aim of the study was the assessment of the prevalence of central sensory impairment, and its reliance on peripheral nerve damage in patients with CIDP. Materials and methods The study group consisted of 24 patients with mean age of 60.7, who fulfilled the diagnostic criteria of typical form of CIDP at the time of multimodal (visual - VEP, brainstem auditory - BAEP, somatosensory SEP) evoked potentials (EPs) study. Each patient underwent a neurological examination, as well as a CT/MRI scan of the head. The evoked potentials was conducted according to the International Federation of Clinical Neurophysiology (IFCN) guidelines. Results Mean latency of most components of EP were considerably prolonged in patients compared to the control group. Negative correlations of SNAP amplitudes and sensory conduction velocities in peripheral nerves were obtained for I-V and III-V inter-latencies BAEP, for N20, P16, P22 SEP and the central conduction time TT for all sensory fibers of the left upper limb nerves. Conclusions Correlations of SNAP and EP parameters indicate subclinical damage to the central sensory pathways. The CIDP pathomechanism is still unclear and needs further research.

O-34 Hereditary or inflammatory childhood neuropathy – Electrophysiological abnormalities helpful in the differentiation

Background The differentiation between hereditary neuropathy and chronic inflammatory demyelinating polyneuropathy (CIDP) in children is especially significant because of completely different treatment possibilities and prognosis in these conditions. The aim of the study was to compare electrophysiological abnormalities in a group of children and young adults with demyelinating neuropathy of chronic or subacute onset. Material and methods Retrospective analysis of clinical and nerve conduction study (NCS) data included 3 children and 4 young adults with Charcot-Marie-Tooth Neuropathy X type 1 (CMTX1), 24 children with Charcot-Marie-Tooth Neuropathy type 1a (CMT1a), 8 with hereditary neuropathy with pressure palsy (HNPP) and 18 children with CIDP. Results In our study 6/7 CMTX1 had both axonal and demyelinating changes in NCS study. The AAN and EFNS electrophysiological CIDP criteria were fulfilled in 2/7 CMTX1, 23/24 CMT1a, 4/8 HNPP and 17/18 CIDP patients. Additionally 3 patients with CMTX1 are classified with EFNS criteria as “probable/possible CIDP”. A distal compound muscle action potential (dCMAP) was >9 ms in all CMT1a and 14/18 CIDP patients but none with CMTX1 nor HNPP. Abnormal median/normal sural SNAP (AMNS) or while abnormal sural/normal median SNAP (ASNM) parameter and a difference between conduction velocities (CV) of two corresponding nerves > 10 m/s were not observed in any CMT1a patient. Conclusion Our study has showed that presented above electrophysiological parameters are useful in differentiation between these neuropathies.

A study of modified holographic Ricci dark energy in the framework of f(T) modified gravity and its statefinder hierarchy

Inspired by the work of Bamba et al. (Phys. Rev. D, 85, 104036 (2012)) the present paper reports a study on the reconstruction of modified holographic Ricci dark energy (MHRDE) in the framework of modified gravity taken as f(T) gravity. A correspondence between modified Chaplygin gas and MHRDE has also been considered and thereinafter the f(T) gravity has been reconstructed via reconstruction of the Hubble parameter. The reconstructed equation of state (EoS) parameter obtained this way has been found to be able to cross the phantom boundary. In the next phase of the work, a viable model of f(T) gravity has been considered and MHRDE has been discussed in this modified gravity frame. The EoS parameter due to the torsion contribution obtained this way has been found to behave like quintessence. The transition of the universe from the dark matter dominated to dark energy (DE) dominated phase is apparent from this model. Also, the model is exhibiting DE domination of the current universe. Finally, the statefinder hierarchy has been discussed through the statefinder and snap parameters. The model has been found to be able to attain the ΛCDM fixed point in the statefinder trajectory.

Cosmography of the Dynamical Cosmological «Constant»

The paper considers a cosmographical approach to analyze cosmological models. Cosmography is a method to describe the kinematics of the cosmological expansion based only on the cosmological principle. We consider a method of treating free parameters of a cosmological model in terms of the directly observable cosmographic values related to the time-derivatives of the Hubble parameter (deceleration, jerk, snap). The method is applied to analyze two cosmological models involving the time-dependence of the cosmological constant in the form Λ(t)→Λ(H) when this approach is especially efficient. Both models interpret the dark energy in the form of the cosmological constant as energy of physical vacuum, which is currently the most supported treatment. The first one means being proportional to the Hubble parameter, and the second one involves a constant and a quadratic term. As a result, the free parameters of both models are expressed in terms of the currently observed values of the Hubble parameter, deceleration, and jerk. The obtained expressions for model parameters are exact, as the method does not involve any additional assumptions. Furthermore, it leads to deal with algebraic equations instead of differential ones. After this procedure, solutions of the evolution equations are obtained in the form of the time-dependence of the Hubble parameter. The obtained model parameters are substituted to the solutions, which are analyzed for a typical range of cosmographic scalars taken from recent observations. Finally, the proposed approach is used to eliminate free parameters from both models and to obtain constraints for the directly observable cosmographic values that can be tested to correspond to present observations data. For the considered cases, such constraints are received respectively for the jerk and the snap parameters with respect to the deceleration. The constraint for the linear model is compared with current observational value ranges for the deceleration and the jerk parameters.

Energy bounds in f(R,G) gravity with anisotropic background

This paper investigates the energy bounds in modified Gauss–Bonnet gravity with anisotropic background. Locally rotationally symmetric Bianchi type [Formula: see text] cosmological model in [Formula: see text] gravity is considered to meet this aim. Primarily, a general [Formula: see text] model is used to develop the field equations. In this aspect, we investigate the viability of modified gravitational theory by studying the energy conditions. We take in account four [Formula: see text] gravity models commonly discussed in the literature. We formulate the inequalities obtained by energy conditions and investigate the viability of the above-mentioned models using the Hubble, deceleration, jerk and snap parameters. Graphical analysis shows that for first two [Formula: see text] gravity models, null energy condition (NEC), weak energy condition (WEC) and strong energy condition (SEC) are satisfied under suitable values of anisotropy and model parameters involved. Moreover, SEC is violated for the third and fourth models which predicts the cosmic expansion.

Model-independent reconstruction of f(T) teleparallel cosmology

We propose a model-independent formalism to numerically solve the modified Friedmann equations in the framework of $f(T)$ teleparallel cosmology. Our strategy is to expand the Hubble parameter around the redshift $z=0$ up to a given order and to adopt cosmographic bounds as initial settings to determine the corresponding $f(z)\equiv f(T(H(z)))$ function. In this perspective, we distinguish two cases: the first expansion is up to the jerk parameter, the second expansion is up to the snap parameter. We show that inside the observed redshift domain $z\leq1$, only the net strength of $f(z)$ is modified passing from jerk to snap, whereas its functional behavior and shape turn out to be identical. As first step, we set the cosmographic parameters by means of the most recent observations. Afterwards, we calibrate our numerical solutions with the concordance $\Lambda$CDM model. In both cases, there is a good agreement with the cosmological standard model around $z\leq 1$, with severe discrepancies outer of this limit. We demonstrate that the effective dark energy term evolves following the test-function: $f(z)=\mathcal A+\mathcal Bz^2e^{\mathcal Cz}$. Bounds over the set $\left\{\mathcal A, \mathcal B, \mathcal C\right\}$ are also fixed by statistical considerations, comparing discrepancies between $f(z)$ with data. The approach opens the possibility to get a wide class of test-functions able to frame the dynamics of $f(T)$ without postulating any model \emph{a priori}. We thus re-obtain the $f(T)$ function through a back-scattering procedure once $f(z)$ is known. We figure out the properties of our $f(T)$ function at the level of background cosmology, to check the goodness of our numerical results. Finally, a comparison with previous cosmographic approaches is carried out giving results compatible with theoretical expectations.

Energy conditions in $$f(\mathcal {G},T)$$ f ( G , T ) gravity

The aim of this paper is to introduce a new modified gravity theory named as $f(\mathcal{G},T)$ gravity ($\mathcal{G}$ and $T$ are the Gauss-Bonnet invariant and trace of the energy-momentum tensor, respectively) and investigate energy conditions for two reconstructed models in the context of FRW universe. We formulate general field equations, divergence of energy-momentum tensor, equation of motion for test particles as well as corresponding energy conditions. The massive test particles follow non-geodesic lines of geometry due to the presence of extra force. We express energy conditions in terms of cosmological parameters like deceleration, jerk and snap parameters. The reconstruction technique is applied to this theory using de Sitter and power-law cosmological solutions. We analyze energy bounds and obtain feasible constraints on free parameters.

Energy constraints and F ( T , T G ) $F(T,T_{G})$ cosmology

The present paper is elaborated to discuss the energy condition bounds in a modified teleparallel gravity namely $F(T,T_{G})$, involving torsion invariant $T$ and contribution from a term $T_G$, the teleparallel equivalent of the Gauss-Bonnet term. For this purpose, we consider flat FRW universe with matter contents as perfect fluid. We formulate the SEC, NEC, WEC and DEC in terms of some cosmic parameters including Hubble, deceleration, jerk and snap parameters. By taking two interesting models for $F(T,T_{G})$ and some recent limits of these cosmic parameters, we explore the constraints on the free parameters present in both assumed models. We also discuss these constraints graphically in terms of cosmic time by taking power law cosmology into account.

Modified Chaplygin gas cosmology with observational constraints

The spatially homogeneous and totally anisotropic Bianchi type-II space-time models with modified Chaplygin gas having the equation of state p=Aρ−Bρα, 0 ≤ A ≤ 1, 0 ≤ α ≤ 1, where A, α and B are positive constants, have been investigated. It has been shown that the equation of state for such modified model is valid from the radiation era to the ΛCDM. The statefinder, which is the cosmological diagnostic pair {r, s} has been adopted to characterize different phases of the universe. The physical and geometrical properties of the corresponding cosmological models have been discussed. The observational constraints, essentially dependent on the hubble parameter H0 and deceleration parameter q0 have been investigated using 28 data points of H(z), SNe Ia and H(z)+ SNe Ia [57]. It has been seen that the average scale factor a(t) can be expanded in terms of an infinite convergent series around the current value of the average scale factor a0 using Taylor’s theorem, in which the current value of the deceleration parameter q0, the dimensionless jerk parameter j0, the snap parameter s0* and the lerk parameter ℓ0 appeared.

Role of conharmonic flatness in Friedmann cosmology

In this paper, investigation of conharmonically flat FRW space-time is considered in presence of perfect fluid as a matter source. To get the deterministic model, we have employed the condition between vacuum density Λ and the Hubble parameter H as Λ=3βH2, where β is a constant (Astrophys. Space Sci. 314:83, 2008). Physical features of the model are discussed in detail. An estimate of the statefinder and snap parameters is also carried out for the model. The observed values of these parameters agree ΛCDM model. We see that the model is in agreement with recent observations.