Scalar-Tensor Dark Energy Models

We present here some recent results concerning scalar-tensor Dark Energy models. These models are very interesting in many respects: they allow for a consistent phantom phase, the growth of matter perturbations is modified. Using a systematic expansion of the theory at low redshifts, we relate the possibility to have phantom like DE to solar system constraints.Comment: Submitted to the Proceedings of the Marcel Grossmann Conference MG11, July 2006, Berlin; 3 page

The control of the administrative judge on the reconciliation between individual freedoms and health security

Sporovi povezani s pandemijom COVID-19 doveli su do velike „aktivnosti“ upravnih sudova, a posebno francuskog Državnog savjeta. Osim toga, većina pokrenutih sporova zahtijevala je hitno rješavanje koje ima za cilj obustavu akta kada postoji ozbiljna sumnja u njegovu zakonitost. Rješenja usvojena u sporovima vođenim povodom pandemije Covid-19 istaknuli su učinkovitost „hitnog postupka“ u fazi popuštanja ograničenja.Disputes related to the COVID-19 pandemic have led to a great deal of “activity” by the administrative courts, and especially by the French Council of State. In addition, most of the disputes raised required an urgent resolution aimed at suspending the act when there is serious doubt about its legality. The solutions adopted in disputes related to the Covid-19 pandemic highlighted the effectiveness of the “emergency procedure” in the phase of easing restrictions

Experimental and computational validation of models of fluorescent and luminescent reporter genes in bacteria

<p>Abstract</p> <p>Background</p> <p>Fluorescent and luminescent reporter genes have become popular tools for the real-time monitoring of gene expression in living cells. However, mathematical models are necessary for extracting biologically meaningful quantities from the primary data.</p> <p>Results</p> <p>We present a rigorous method for deriving relative protein synthesis rates (mRNA concentrations) and protein concentrations by means of kinetic models of gene expression. We experimentally and computationally validate this approach in the case of the protein Fis, a global regulator of transcription in <it>Escherichia coli</it>. We show that the mRNA and protein concentration profiles predicted from the models agree quite well with direct measurements obtained by Northern and Western blots, respectively. Moreover, we present computational procedures for taking into account systematic biases like the folding time of the fluorescent reporter protein and differences in the half-lives of reporter and host gene products. The results show that large differences in protein half-lives, more than mRNA half-lives, may be critical for the interpretation of reporter gene data in the analysis of the dynamics of regulatory systems.</p> <p>Conclusions</p> <p>The paper contributes to the development of sound methods for the interpretation of reporter gene data, notably in the context of the reconstruction and validation of models of regulatory networks. The results have wide applicability for the analysis of gene expression in bacteria and may be extended to higher organisms.</p

Optimizing drip irrigation for eggplant crops in semi-arid zones using evolving thresholds

AbstractField experiments were combined with a numerical model to optimize drip irrigation management based on soil matric potential (SMP) measurements. An experimental crop of eggplant was grown in Burkina Faso from December 2014 to March 2015 and plant response to water stress was investigated by applying four different irrigation treatments. Treatments consisted in using two different irrigation depths (low or high), combined with a water provision of 150%, 100% or 66% (150/100/66) of the maximum crop evapotranspiration (T150low, T66low, T100high, T66high). Soil matric potential measurements at 5, 10 and 15cm depth were taken using a wireless sensor network and were compared with measurements of plant and root biomass and crop yields. Field data were used to calibrate a numerical model to simulate triggered drip irrigation. Different simulations were built using the software HYDRUS 2D/3D to analyze the impact of the irrigation depth and frequency, the irrigation threshold and the soil texture on plant transpiration and water losses. Numerical results highlighted the great impact of the root distribution on the soil water dynamics and the importance of the sensor location to define thresholds. A fixed optimal sensor depth of 10 cm was found to manage irrigation from the vegetative state to the end of fruit development. Thresholds were defined to minimize water losses while allowing a sufficient soil water availability for optimal crop production. A threshold at 10cm depth of −15kPa is recommended for the early growth stage and −40kPa during the fruit formation and maturation phase. Simulations showed that those thresholds resulted in optimal transpiration regardless of the soil texture so that this management system can constitute the basis of an irrigation schedule for eggplant crops and possibly other vegetable crops in semi-arid regions

On the equation of state of Dark Energy

The formalism in order to obtain the Dark Energy equation of state is extended to non-flat universes and we consider the inequalities that must be satisfied by Phantom Dark Energy in this case. We show that due to a non-vanishing spatial curvature satisfying the observational bounds, the uncertainty on the determination of the Dark Energy equation of state parameter $w$, when it is taken constant, can be significant and that it is minimal for some redshift $z_{cr}\sim 3$. We consider the potential of future measurements of the gravitational waves emitted by binaries at high redshifts $z>z_{cr}$ to reduce this uncertainty. Results obtained here should also be relevant for a weakly varying equation of state with $w\approx -1$.Comment: 11 pages, 4 figures;typo corrected, final version to appear in Phys. Lett.

On compatibility of string effective action with an accelerating universe

In this paper, we fully investigate the cosmological effects of the moduli dependent one-loop corrections to the gravitational couplings of the string effective action to explain the cosmic acceleration problem in early (and/or late) universe. These corrections comprise a Gauss-Bonnet (GB) invariant multiplied by universal non-trivial functions of the common modulus $\sigma$ and the dilaton $\phi$. The model exhibits several features of cosmological interest, including the transition between deceleration and acceleration phases. By considering some phenomenologically motivated ansatzs for one of the scalars and/or the scale factor (of the universe), we also construct a number of interesting inflationary potentials. In all examples under consideration, we find that the model leads only to a standard inflation ($w \geq -1$) when the numerical coefficient $\delta$ associated with modulus-GB coupling is positive, while the model can lead also to a non-standard inflation ($w<-1$), if $\delta$ is negative. In the absence of (or trivial) coupling between the GB term and the scalars, there is no crossing between the $w -1$ phases, while this is possible with non-trivial GB couplings, even for constant dilaton phase of the standard picture. Within our model, after a sufficient amount of e-folds of expansion, the rolling of both fields $\phi$ and $\sigma$ can be small. In turn, any possible violation of equivalence principle or deviations from the standard general relativity may be small enough to easily satisfy all astrophysical and cosmological constraints.Comment: 30 pages, 8 figures; v2 significant changes in notations, appendix and refs added; v3 significant revisions, refs added; v4 appendix extended, new refs, published versio

Isolation and identification of cobalt- and caesium-resistant bacteria from a nuclear fuel storage pond

One of the issues facing the nuclear power industry is how to store spent nuclear fuel which is contaminated with radionuclides produced during nuclear fission, including caesium ((134)Cs(+), (135)Cs(+) and (137)Cs(+)) and cobalt ((60)Co(2+)). In this study, we have isolated Co(2+)- and Cs(+)-resistant bacteria from water collected from a nuclear fuel storage pond. The most resistant Cs(+) and Co(2+) isolates grew in the presence of 500 mM CsCl and 3 mM CoCl2. Strain Cs67-2 is resistant to fourfold more Cs(+) than Cupriavidus metallidurans str. CH34 making it the most Cs(+)-resistant strain identified to date. The Cs(+)-resistant isolates were closely related to bacteria in the Serratia and Yersinia genera, while the Co(2+)-resistant isolates were closely related to the Curvibacter and Tardiphaga genera. These new isolates could be used for bioremediation

Scalar-Tensor Models of Normal and Phantom Dark Energy

We consider the viability of dark energy (DE) models in the framework of the scalar-tensor theory of gravity, including the possibility to have a phantom DE at small redshifts $z$ as admitted by supernova luminosity-distance data. For small $z$, the generic solution for these models is constructed in the form of a power series in $z$ without any approximation. Necessary constraints for DE to be phantom today and to cross the phantom divide line $p=-\rho$ at small $z$ are presented. Considering the Solar System constraints, we find for the post-Newtonian parameters that $\gamma_{PN}<1$ and $\gamma_{PN,0}\approx 1$ for the model to be viable, and $\beta_{PN,0}>1$ (but very close to 1) if the model has a significantly phantom DE today. However, prospects to establish the phantom behaviour of DE are much better with cosmological data than with Solar System experiments. Earlier obtained results for a $\Lambda$-dominated universe with the vanishing scalar field potential are extended to a more general DE equation of state confirming that the cosmological evolution of these models rule them out. Models of currently fantom DE which are viable for small $z$ can be easily constructed with a constant potential; however, they generically become singular at some higher $z$. With a growing potential, viable models exist up to an arbitrary high redshift.Comment: 30 pages, 4 figures; Matches the published version containing an expanded discussion of various point

Crossing the Phantom Divide: Theoretical Implications and Observational Status

If the dark energy equation of state parameter w(z) crosses the phantom divide line w=-1 (or equivalently if the expression d(H^2(z))/dz - 3\Omega_m H_0^2 (1+z)^2 changes sign) at recent redshifts, then there are two possible cosmological implications: Either the dark energy consists of multiple components with at least one non-canonical phantom component or general relativity needs to be extended to a more general theory on cosmological scales. The former possibility requires the existence of a phantom component which has been shown to suffer from serious theoretical problems and instabilities. Therefore, the later possibility is the simplest realistic theoretical framework in which such a crossing can be realized. After providing a pedagogical description of various dark energy observational probes, we use a set of such probes (including the Gold SnIa sample, the first year SNLS dataset, the 3-year WMAP CMB shift parameter, the SDSS baryon acoustic oscillations peak (BAO), the X-ray gas mass fraction in clusters and the linear growth rate of perturbations at z=0.15 as obtained from the 2dF galaxy redshift survey) to investigate the priors required for cosmological observations to favor crossing of the phantom divide. We find that a low \Omega_m prior (0.2<\Omega_m <0.25) leads, for most observational probes (except of the SNLS data), to an increased probability (mild trend) for phantom divide crossing. An interesting degeneracy of the ISW effect in the CMB perturbation spectrum is also pointed out.Comment: Accepted in JCAP (to appear). Comments added, typos corrected. 19 pages (revtex), 8 figures. The numerical analysis files (Mathematica + Fortran) with instructions are available at http://leandros.physics.uoi.gr/pdl-cross/pdl-cross.htm . The ppt file of a relevant talk may be downloaded from http://leandros.physics.uoi.gr/pdl-cross/pdl2006.pp