Effects of inhomogeneities on apparent cosmological observables: “fake” evolving dark energy

Using the exact Lemaitre?CBondi?CTolman solution with a non-vanishing cosmological constant ??, we investigate how the presence of a local spherically symmetric inhomogeneity can affect apparent cosmological observables, such as the deceleration parameter or the effective equation of state of dark energy (DE), derived from the luminosity distance under the assumption that the real space-time is exactly homogeneous and isotropic. The presence of a local underdensity is found to produce apparent phantom behavior of DE, while a locally overdense region leads to apparent quintessence behavior. We consider relatively small large scale inhomogeneities which today are not linear and could be seeded by primordial curvature perturbations compatible with CMB bounds. Our study shows how observations in an inhomogeneous ??CDM universe with initial conditions compatible with the inflationary beginning, if interpreted under the wrong assumption of homogeneity, can lead to the wrong conclusion about the presence of ??fake?? evolving dark energy instead of ??.     

Spazi proiettivamente piani (1)

Sunto L'A. espone nella prima parte, coordinandoli, i principali risultati delle ricerche finora condotte sugli spazi proiettivamente piani, apportandovi qualche complemento (relativo ad esempio alle ipersuperficie diE _n affine per le quali la connessione affineintrinseca è proiettivamente piana). Nella seconda parte, dà una costruzione geometrica, basata sulla teoria delle connessioni proiettive, di tutte le connessioni affini simmetriche proiettivamente piane, e coglie l'occasione per introdurre e studiare certe connessioni proiettive,metriche enon affini, determinate da un campo di quadriche associate ai punti dello spazio supposto; connessioni cui può subordinarsi una metrica riemannianaqualunque, come alla geometria proiettiva ordinaria, in relazione a una quadrica data come assoluto, si subordina la geometria metrica riemannianaa curvatura costante. Questo lavoro riproduce, con alcuni complementi e modificazioni, una comunicazione (con lo stesso titolo) fatta alla XX Riunione della Soc. Italiana per il Progresso delle Scienze (Milano, 18-9-1931). Negli Atti della Società verrà pubblicato soltanto un brevissimo sommario. Ved. anche ? Bollettino Un. Matem. Italiana ?, X, 1931, pp. 254–255.     

Nucleobases modified azo‐polysiloxanes,materials with potential application in biomolecules nanomanipulation

Here we show the possibility to obtain azopolysiloxanes modified with nucleobases (adenine and thymine) with potential application in immobilization and nanomanipulation of biomolecules. We propose a photofluidization mechanism based on the concept of the conformational instability, which can explain the presence of the fluid state below the glass transition. The azopolymers were characterized by ¹H NMR, GPC, DSC, DTG, UV spectroscopy, AFM analysis, and molecular simulations. Depending on the type of nucleobase used, the surface of the azopolysiloxane film can be structured in different ways under UV irradiation. Photoisomerization studies in solid state were carried out to demonstrate the influence of the operational conditions (presence or absence of natural visible light) on the polymeric film UV response. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4240–4248, 2007     

Conditions for low-redshift positive apparent acceleration in smooth inhomogeneous models

It is known that a smooth LTB model cannot have a positive apparent central acceleration. Using a local Taylor expansion method we study the low-redshift conditions to obtain an apparent negative deceleration parameter $q^{app}(z)$ derived from the luminosity distance $D_L(z)$ for a central observer in a LTB space, confirming that central smoothness implies a positive central deceleration. Since observational data is only available at redshift greater than zero we find the critical values of the parameters defining a centrally smooth LTB model which give a positive apparent acceleration at $z>0$ , providing a graphical representation of the conditions in the $q_0^{app},q_1^{app}$ plane, which are respectively the zero and first order terms of the central Taylor expansion of $q^{app}(z)$ . We finally derive a coordinate independent expression for the apparent deceleration parameter based on the expansion of the relevant functions in red-shift rather than in the radial coordinate. We calculate $q^{app}(z)$ with two different methods to solve the null geodesic equations, one based on a local central expansion of the solution in terms of cosmic time and the other one using the exact analytical solution in terms of generalized conformal time.     

Statistical aspects of fuzzy monotone set-valued stochastic processes. Application to birth-and-growth processes

The paper considers a particular family of fuzzy monotone set-valued stochastic processes. The proposed setting allows us to investigate suitable α-level sets of such processes, modeling birth-and-growth processes. A decomposition theorem is established to characterize the nucleation and the growth. As a consequence, different consistent set-valued estimators are studied for growth process. Moreover, the nucleation process is studied via the hitting function, and a consistent estimator of the nucleation hitting function is derived.     

A Native Ternary Complex Trapped in a Crystal Reveals the Catalytic Mechanism of a Retaining Glycosyltransferase

Glycosyltransferases (GTs) comprise a prominent family of enzymes that play critical roles in a variety of cellular processes, including cell signaling, cell development, and host–pathogen interactions. Glycosyl transfer can proceed with either inversion or retention of the anomeric configuration with respect to the reaction substrates and products. The elucidation of the catalytic mechanism of retaining GTs remains a major challenge. A native ternary complex of a GT in a productive mode for catalysis is reported, that of the retaining glucosyl‐3‐phosphoglycerate synthase GpgS from M. tuberculosis in the presence of the sugar donor UDP‐Glc, the acceptor substrate phosphoglycerate, and the divalent cation cofactor. Through a combination of structural, chemical, enzymatic, molecular dynamics, and quantum‐mechanics/molecular‐mechanics (QM/MM) calculations, the catalytic mechanism was unraveled, thereby providing a strong experimental support for a front–side substrate‐assisted S_Ni‐type reaction.     

The influence of tie strength on evolutionary games on networks: An empirical investigation

Extending previous work on unweighted networks, we present here a systematic numerical investigation of standard evolutionary games on weighted networks. In the absence of any reliable model for generating weighted social networks, we attribute weights to links in a few ways supported by empirical data ranging from totally uncorrelated to weighted bipartite networks. The results of the extensive simulation work on standard complex network models show that, except in a case that does not seem to be common in social networks, taking the tie strength into account does not change in a radical manner the long-run steady-state behavior of the studied games. Besides model networks, we also included a real-life case drawn from a coauthorship network. In this case also, taking the weights into account only changes the results slightly with respect to the raw unweighted graph, although to draw more reliable conclusions on real social networks many more cases should be studied as these weighted networks become available.