Observational Constraints on the Generalized Chaplygin Gas

In this paper we study a quintessence cosmological model in which the dark energy component is considered to be the Generalized Chaplygin Gas and the curvature of the three-geometry is taken into account. Two parameters characterize this sort of fluid, the $\nu$ and the $\alpha$ parameters. We use different astronomical data for restricting these parameters. It is shown that the constraint $\nu \lesssim \alpha$ agrees enough well with the astronomical observations.Comment: Accepted by IJMPD; 18 pages; 10 Figure

Dark energy FRW cosmology - dynamical system reconstruction

We develop a simple method of dark energy reconstruction using a geometrical form of the luminosity-distance relation. In this method the FRW dynamical system with dark energy is reconstructed instead of the equation of state parameter. We give several examples which illustrate the usefulness of our method in fitting the redshift transition from the decelerating to accelerating phase as the value of the Hubble function at the transition.Comment: Talk presented at Spanish Relativity Meeting 2007, Puerto de la Cruz, Tenerife, Spain, 10-14 September 200

Cosmic acceleration from modified gravity with Palatini formalism

We study new FRW type cosmological models of modified gravity treated on the background of Palatini approach. These models are generalization of Einstein gravity by the presence of a scalar field non-minimally coupled to the curvature. The models employ Starobinsky's term in the Lagrangian and dust matter. Therefore, as a by-product, an exhausted cosmological analysis of general relativity amended by quadratic term is presented. We investigate dynamics of our models, confront them with the currently available astrophysical data as well as against LCDM model. We have used the dynamical system methods in order to investigate dynamics of the models. It reveals the presence of a final sudden singularity. Fitting free parameters we have demonstrated by statistical analysis that this class of models is in a very good agreement with the data (including CMB measurements) as well as with the standard LCDM model predictions. One has to use statefinder diagnostic in order to discriminate among them. Therefore Bayesian methods of model selection have been employed in order to indicate preferred model. Only in the light of CMB data the concordance model remains invincible.Comment: 32 pages, jcappub style, 28 figures, final improved version, to be published in JCA

Dusty Universe viewed by AKARI far infrared detector

We present the results of the analysis of multiwavelength Spectral Energy Distributions (SEDs) of far-infrared galaxies detected in the AKARI Deep Field-South (ADF--S) Survey. The analysis uses a carefully selected sample of 186 sources detected at the 90 $\mu$m AKARI band, identified as galaxies with cross-identification in public catalogues. For sources without known spectroscopic redshifts, we estimate photometric redshifts after a test of two independent methods: one based on using mainly the optical -- mid infrared range, and one based on the whole range of ultraviolet -- far infrared data. We observe a vast improvement in the estimation of photometric redshifts when far infrared data are included, compared with an approach based mainly on the optical -- mid infrared range. We discuss the physical properties of our far-infrared-selected sample. We conclude that this sample consists mostly of rich in dust and young stars nearby galaxies, and, furthermore, that almost 25% of these sources are (Ultra)Luminous Infrared Galaxies. Average SEDs normalized at 90 $\mu$m for normal galaxies (138 sources), LIRGs (30 sources), and ULIRGs (18 galaxies) a the significant shift in the peak wavelength of the dust emission, and an increasing ratio between their bolometric and dust luminosities which varies from 0.39 to 0.73.Comment: 8 pages, 7 figures, published in Earth, Planets and Spac

Fatigue cracking of aluminium alloy AlZn6Mg0.8Zr subjected to thermomechanical treatment

The paper presents the results of experimental test of the fatigue of aluminium alloy type AlZn6Mg0,8Zr exposed to various low temperature thermomechanical treatment. Basquin’s characteristics of fatigue have been determined in mechanical test on smooth specimens at a simple state of loading in conditions of alternating bending. The tests were carried out on a fatigue test stand constructed by the authors – MZGS 100. The development of fatigue cracking has been described based on metallographic and fractographic investigations of the fractured samples making use of a scanning electron microscope (SEM). The results of qualitative microfractography of the tested samples in the low-cycle temporal range of fatigue strength revealed fractures of the transcrystalline quasi-cleavage type. It has also been found that local effects of intercrystalline brittle cracking of this type do occur

Biophysical Measurements of Cells, Microtubules, and DNA with an Atomic Force Microscope

Atomic force microscopes (AFMs) are ubiquitous in research laboratories and have recently been priced for use in teaching laboratories. Here we review several AFM platforms (Dimension 3000 by Digital Instruments, EasyScan2 by Nanosurf, ezAFM by Nanomagnetics, and TKAFM by Thorlabs) and describe various biophysical experiments that could be done in the teaching laboratory using these instruments. In particular, we focus on experiments that image biological materials and quantify biophysical parameters: 1) imaging cells to determine membrane tension, 2) imaging microtubules to determine their persistence length, 3) imaging the random walk of DNA molecules to determine their contour length, and 4) imaging stretched DNA molecules to measure the tensional force.Comment: 29 page preprint, 7 figures, 1 tabl

Observational hints on the Big Bounce

In this paper we study possible observational consequences of the bouncing cosmology. We consider a model where a phase of inflation is preceded by a cosmic bounce. While we consider in this paper only that the bounce is due to loop quantum gravity, most of the results presented here can be applied for different bouncing cosmologies. We concentrate on the scenario where the scalar field, as the result of contraction of the universe, is driven from the bottom of the potential well. The field is amplified, and finally the phase of the standard slow-roll inflation is realized. Such an evolution modifies the standard inflationary spectrum of perturbations by the additional oscillations and damping on the large scales. We extract the parameters of the model from the observations of the cosmic microwave background radiation. In particular, the value of inflaton mass is equal to $m=(2.6 \pm 0.6) \cdot 10^{13}$ GeV. In our considerations we base on the seven years of observations made by the WMAP satellite. We propose the new observational consistency check for the phase of slow-roll inflation. We investigate the conditions which have to be fulfilled to make the observations of the Big Bounce effects possible. We translate them to the requirements on the parameters of the model and then put the observational constraints on the model. Based on assumption usually made in loop quantum cosmology, the Barbero-Immirzi parameter was shown to be constrained by $\gamma<1100$ from the cosmological observations. We have compared the Big Bounce model with the standard Big Bang scenario and showed that the present observational data is not informative enough to distinguish these models.Comment: 25 pages, 8 figures, JHEP3.cl

Lorentz Invariance Violation induced time delays in GRBs in different cosmological models

Lorentz Invariance Violation (LIV) manifesting itself by energy dependent modification of standard relativistic dispersion relation has recently attracted a considerable attention. Ellis et al. previously investigated the energy dependent time offsets in different energy bands on a sample of gamma ray bursts and, assuming standard cosmological model, they found a weak indication for redshift dependence of time delays suggestive of LIV. Going beyond the $\Lambda$CDM cosmology we extend this analysis considering also four alternative models of dark energy (quintessence with constant and variable equation of state, Chaplygin gas and brane-world cosmology). It turns out that the effect noticed by Ellis et al. is also present in those models and is the strongest for quintessence with variable equation of state.Comment: 14 pages, 1 figur

Density growth in Kantowski-Sachs cosmologies with cosmological constant

In this work the growth of density perturbations in Kantowski-Sachs cosmologies with a positive cosmological constant is studied, using the 1+3 and 1+1+2 covariant formalisms. For each wave number we obtain a closed system for scalars formed from quantities that are zero on the background and hence are gauge-invariant. The solutions to this system are then analyzed both analytically and numerically. In particular the effects of anisotropy and the behaviour close to a bounce in the cosmic scale factor are considered. We find that typically the density gradient in the bouncing directions experiences a local maximum at or slightly after the bounce.Comment: 33 pages, 17 picture