The octopus effect: when and who platform companies acquire

After their launch, Amazon, Apple, Airbnb, and Google, giant platforms of the digital economy, all followed a similar pattern. They quickly bought competing platform companies in their same market niche before growing tentacles through acquisitions in other sectors. Margherita Pagani, Milan Miric, and Omar El Sawy call this phenomenon “octopus effect” and wonder what the next evolutionary stage of platforms will be

Resonance in Large Benzenoid Hydrocarbons

Pi-sextet resonance between Kekulé valence structures of benzenoid hydrocarbons are depicted by benzenoid resonance graphs. We outline the construction of the resonance graphs for families of benzenoid compounds. For the compounds considered the resonance graphs are built from fused ra-dimensional cubes. We report the leading eigenvalue of the resonance graphs (A) and two different bounds to the leading eigenvalue. Correlation between X and RE is examined

Modules in the photoreceptor RGS9-1•Gβ5L GTPase-accelerating protein complex control effector coupling, GTPase acceleration, protein folding, and stability

RGS (regulators of G protein signaling proteins regulate G protein signaling by accelerating GTP hydrolysis, but little is known about regulation of GTPase-accelerating protein (GAP) activities or roles of domains and subunits outside the catalytic cores. RGS9-1 is the GAP required for rapid recovery of light responses in vertebrate photoreceptors and the only mammalian RGS protein with a defined physiological function. It belongs to an RGS subfamily whose members have multiple domains, including G gamma -like domains that bind G(beta5) proteins. Members of this subfamily play important roles in neuronal signaling, Within the GAP complex organized around the RGS domain of RGS9-1, we have identified a functional role for the G gamma -like-G(beta 5L) complex in regulation of GAP activity by an effector subunit, cGMP phosphodiesterase gamma and in protein folding and stability of RGS9-1, The C-terminal domain of RGS9-1 also plays a major role in conferring effector stimulation. The sequence of the RGS domain determines whether the sign of the effector effect will be positive or negative. These roles were observed in, vitro using full-length proteins or fragments for RGS9-1, RGS7, G(beta 5S), and G(beta 5s), The dependence of RGS9-1 on Gp, co-expression for folding, stability, and function has been confirmed in vivo using transgenic Xenopus laevis, These results reveal how multiple domains and regulatory polypeptides work together to fine tune G(t alpha) inactivation

Regulation of development by Rx genes

The paired-like homeobox-containing gene Rx has a critical role in the eye development of several vertebrate species including Xenopus, mouse, chicken, medaka, zebrafish and human. Rx is initially expressed in the anterior neural region of developing embryos, and later in the retina and ventral hypothalamus. Abnormal regulation or function of Rx results in severe abnormalities of eye formation. Overexpression of Rx in Xenopus and zebrafish embryos leads to overproliteration of retinal cells. A targeted elimination of Rx in mice results in a lack of eye formation. Mutations in Rx genes are the cause of the mouse mutation eyeless (ey1), the medaka temperature sensitive mutation eyeless (el) and the zebrafish mutation chokh. In humans, mutations in Rx lead to anophthalmia. All of these studies indicate that Rx genes are key factors in vertebrate eye formation. Because these results cannot be easily reconciled with the most popular dogmas of the field, we offer our interpretation of eye development and evolution

Effect of protonation state and N-acetylation of chitosan on its interaction with xanthan gum: a molecular dynamics simulation study

Hydrophilic matrices composed of chitosan (CS) and xanthan gum (XG) complexes are of pharmaceutical interest in relation to drug delivery due to their ability to control the release of active ingredients. Molecular dynamics simulations (MDs) have been performed in order to obtain information pertaining to the effect of the state of protonation and degree of N-acetylation (DA) on the molecular conformation of chitosan and its ability to interact with xanthan gum in aqueous solutions. The conformational flexibility of CS was found to be highly dependent on its state of protonation. Upon complexation with XG, a substantial restriction in free rotation around the glycosidic bond was noticed in protonated CS dimers regardless of their DA, whereas deprotonated molecules preserved their free mobility. Calculated values for the free energy of binding between CS and XG revealed the dominant contribution of electrostatic forces on the formation of complexes and that the most stable complexes were formed when CS was at least half-protonated and the DA was ≤50%. The results obtained provide an insight into the main factors governing the interaction between CS and XG, such that they can be manipulated accordingly to produce complexes with the desired controlled-release effect

Temperature dependence of the electrochemical behavior of the 690 Ni-base alloy between 25 and 325 °C

International audienceThe electrochemical behavior and the chemical composition of passive films formed on the Alloy 690 at room temperature in borate buffer solution (pH = 9.0) was studied with different techniques for two surface finishings. XPS and quantum yield measurements showed the presence of Ni and Cr oxides and hydroxides for passive films formed on both the as received and the mechanically polished one, whereas the presence of mixed spinel type Ni (1-x) Fe x Cr 2 O 4 was only observed on the as received material. Additionally, Electrochemical Impedance Spectroscopy (EIS) highlighted a higher corrosion resistance for the as received alloy in comparison with the mechanically polished alloy, which was linked to the chemical composition of the oxide film. Electrochemical measurements were performed before, during, and after oxidation of the Alloy 690 of Steam Generator (SG) tube of Pressurized Water Reactor (PWR) at high temperature and high pressure in the simulated primary circuit of PWR. At high temperature, the interface becomes electrochemically active yielding the precipitation of the corrosion products which form a few tens of nm thick diffusion barrier for the released metal cations. This overlayer is built on the top of a few nm thick, Cr rich inner layer at the alloy/oxide interface which was found to behave similarly to that initially formed at ambient temperature. It is concluded that high temperature oxidation in the static condition of an autoclave at 325°C does not promote a better passivation state than the one already existing initially