Palatini approach to 1/R gravity and its implications to the late Universe

By applying the Palatini approach to the 1/R-gravity model it is possible to explain the present accelerated expansion of the Universe. Investigation of the late Universe limiting case shows that: (i) due to the curvature effects the energy-momentum tensor of the matter field is not covariantly conserved; (ii) however, it is possible to reinterpret the curvature corrections as sources of the gravitational field, by defining a modified energy-momentum tensor; (iii) with the adoption of this modified energy-momentum tensor the Einstein's field equations are recovered with two main modifications: the first one is the weakening of the gravitational effects of matter whereas the second is the emergence of an effective varying "cosmological constant"; (iv) there is a transition in the evolution of the cosmic scale factor from a power-law scaling $a\propto t^{11/18}$ to an asymptotically exponential scaling $a\propto \exp(t)$; (v) the energy density of the matter field scales as $\rho_m\propto (1/a)^{36/11}$; (vi) the present age of the Universe and the decelerated-accelerated transition redshift are smaller than the corresponding ones in the $\Lambda$CDM model.Comment: 5 pages and 2 figures. Accepted in PR

Rhinosporidium seeberi proven as a fungus for the first time after a century since its discovery

The 18S rRNA gene sequencing of a pure microorganism isolated in pure culture from human rhinosporidiosis cases coded UMH.48 and preserved at 4oC, and, the fungal extracts of biopsy from new cases of nasal rhinosporidiosis were done. Both the sequences were compared for the presence any identical regions by BLAST tool. Astonishingly both the sequences showed 100% identity with each other. The sequences were further compared with the sequences present in NCBI database, followed by sequences of specific organisms like Mesomycetozoa sp and Synchytrium sp. Based on the morphological features, life cycle and BLAST analysis the organism UMH.48 was categorized as a Fungus. The sequences of UMH.48 and sequences from the fungus extracts from new tissue biopsies were deposited in Genbank with accession numbers JN807465 and JN807466 respectively. This paper reports the identity of 18S rRNA sequences between the pure, preserved, isolate with those obtained from biopsies of nasal rhinosporidiosis obtained from totally new cases. Our isolate has been tentatively identified as a lower aquatic fungus with 100% alignment with Colletotrichum truncatum and Glomerulla sps and lesser score similarity with Synchytrium minutum. Yet the absence of a perfect sexual phase or any asexual fungal spores, very rare  microscopic morphology, life cycle and remarkable resemblance with members of lower aquatic fungi led us to surmise (also through personal communication with NCBI, Taxonomy expert) that the isolate is a Fungus (unknown) and not an Ascomycete

Friction and wear reduction by graphene nano platelets for hybrid nano Aluminium matrix composite under dry sliding conditions

Friction losses and wear losses are the main failure reasons in the internal combustion (IC) engine components i.e., cylinder liner and piston. So, it demands lightweight self-lubricating low friction and wear-resistant materials to increase the efficiency and reduce the emission issue of the IC engine. In this concern, tribological tests are performed on self-lubricating aluminium composites samples reinforced with 6 wt.% of γ-Al2O3 and Graphene Nano Platelets (GNP) with varying concentration (0.5 wt.% - 5 wt.%), using ball-on-disc tribo-configuration under dry sliding conditions. The scope of this study is to investigate the anti-friction and anti-wear properties of GNP as reinforcement in the hybrid nanocomposite. The hybrid nanocomposite samples are fabricated using Spark Plasma Sintering (SPS) fabrication route. From the results, it is reported that friction and wear reduction percentage is 37.43 % and 51.64 %, respectively for the hybrid nanocomposite with 5 wt. % GNP. It is attributed to the inclusion of GNP, which reduces the Coefficient of Friction (COF) and improves wear resistance of the composite significantly

A mathematical analysis of the evolution of perturbations in a modified Chaplygin gas model

One approach in modern cosmology consists in supposing that dark matter and dark energy are different manifestations of a single `quartessential' fluid. Following such idea, this work presents a study of the evolution of perturbations of density in a flat cosmological model with a modified Chaplygin gas acting as a single component. Our goal is to obtain properties of the model which can be used to distinguish it from another cosmological models which have the same solutions for the general evolution of the scale factor of the universe, without the construction of the power spectrum. Our analytical results, which alone can be used to uniquely characterize the specific model studied in our work, show that the evolution of the density contrast can be seen, at least in one particular case, as composed by a spheroidal wave function. We also present a numerical analysis which clearly indicates as one interesting feature of the model the appearence of peaks in the evolution of the density constrast.Comment: 21 pages, accepted for publication in General Relativity and Gravitatio

Constraining the dark energy with galaxy clusters X-ray data

The equation of state characterizing the dark energy component is constrained by combining Chandra observations of the X-ray luminosity of galaxy clusters with independent measurements of the baryonic matter density and the latest measurements of the Hubble parameter as given by the HST key project. By assuming a spatially flat scenario driven by a "quintessence" component with an equation of state $p_x = \omega \rho_x$ we place the following limits on the cosmological parameters $\omega$ and $\Omega_{\rm{m}}$: (i) $-1 \leq \omega \leq -0.55$ and $\Omega_{\rm m} = 0.32^{+0.027}_{-0.014}$ (1$\sigma$) if the equation of state of the dark energy is restricted to the interval $-1 \leq \omega < 0$ (\emph{usual} quintessence) and (ii) $\omega = -1.29^{+0.686}_{-0.792}$ and $\Omega_{\rm{m}} = 0.31^{+0.037}_{-0.034}$ ($1\sigma$) if $\omega$ violates the null energy condition and assume values $< -1$ (\emph{extended} quintessence or ``phantom'' energy). These results are in good agreement with independent studies based on supernovae observations, large-scale structure and the anisotropies of the cosmic background radiation.Comment: 6 pages, 4 figures, LaTe

Observational Constraints on Chaplygin Quartessence: Background Results

We derive the constraints set by several experiments on the quartessence Chaplygin model (QCM). In this scenario, a single fluid component drives the Universe from a nonrelativistic matter-dominated phase to an accelerated expansion phase behaving, first, like dark matter and in a more recent epoch like dark energy. We consider current data from SNIa experiments, statistics of gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in galaxy clusters. We investigate the constraints from this data set on flat Chaplygin quartessence cosmologies. The observables considered here are dependent essentially on the background geometry, and not on the specific form of the QCM fluctuations. We obtain the confidence region on the two parameters of the model from a combined analysis of all the above tests. We find that the best-fit occurs close to the $\Lambda$CDM limit ($\alpha=0$). The standard Chaplygin quartessence ($\alpha=1$) is also allowed by the data, but only at the $\sim2\sigma$ level.Comment: Replaced to match the published version, references update

Deviation From \Lambda CDM With Cosmic Strings Networks

In this work, we consider a network of cosmic strings to explain possible deviation from \Lambda CDM behaviour. We use different observational data to constrain the model and show that a small but non zero contribution from the string network is allowed by the observational data which can result in a reasonable departure from \Lambda CDM evolution. But by calculating the Bayesian Evidence, we show that the present data still strongly favour the concordance \Lambda CDM model irrespective of the choice of the prior.Comment: 15 Pages, Latex Style, 4 eps figures, Revised Version, Accepted for publication in European Physical Journal

Wormholes and Ringholes in a Dark-Energy Universe

The effects that the present accelerating expansion of the universe has on the size and shape of Lorentzian wormholes and ringholes are considered. It is shown that, quite similarly to how it occurs for inflating wormholes, relative to the initial embedding-space coordinate system, whereas the shape of the considered holes is always preserved with time, their size is driven by the expansion to increase by a factor which is proportional to the scale factor of the universe. In the case that dark energy is phantom energy, which is not excluded by present constraints on the dark-energy equation of state, that size increase with time becomes quite more remarkable, and a rather speculative scenario is here presented where the big rip can be circumvented by future advanced civilizations by utilizing sufficiently grown up wormholes and ringholes as time machines that shortcut the big-rip singularity.Comment: 11 pages, RevTex, to appear in Phys. Rev.

Characterization of Alcaligenes faecalis GPA-1 producing thermostable extracellular α-amylase

The bacterium coded GPA-1(isolated by Dr V Thankamani in 1990) was characterized by standard methods including microscopy, special stains, biochemical tests and growth on various types of media for systematic identification up to genus level. With 16S rRNA gene sequencing, the isolate was identified as Alcaligenes faecalis and deposited in NCBI with GenBank Accession number HQ 848384. The isolate was screened for the production of enzymes like amylase, protease and carboxy methyl  cellulase (CMC). This isolate showed a clear zone of lysis on starch agar, yellow zone on CMC agar when stained with Congo red and a clear zone of casein hydrolysis in skim milk agar indicating amylase, cellulose and proteolytic activity respectively. Preliminary characterization of extra  cellular amylase was done. The strain was found to be alkalophilic as it grew well in pH 9.0 and 10.0. The optimum temperature and salinity were found to be 37oC and 3% respectively. Growth curve experiments of the organism in nutrient broth containing 1% starch at varying physical and nutritional parameters were done up to 72 hrs, and the samples were also  tested for pH changes, biomass, total protein, reducing sugars and  α-amylase activity. Soluble starch (1%) in standard nutrient broth and pH 8.0, 37oC, shaking at100 rpm and 40-44 hours incubation were found to be the optimum conditions for maximal enzyme production

Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at root s=13 TeV

Peer reviewe