Anaerobic 4-hydroxyproline utilization: Discovery of a new glycyl radical enzyme in the human gut microbiome uncovers a widespread microbial metabolic activity.

The discovery of enzymes responsible for previously unappreciated microbial metabolic pathways furthers our understanding of host-microbe and microbe-microbe interactions. We recently identified and characterized a new gut microbial glycyl radical enzyme (GRE) responsible for anaerobic metabolism of trans-4-hydroxy-l-proline (Hyp). Hyp dehydratase (HypD) catalyzes the removal of water from Hyp to generate Δ1-pyrroline-5-carboxylate (P5C). This enzyme is encoded in the genomes of a diverse set of gut anaerobes and is prevalent and abundant in healthy human stool metagenomes. Here, we discuss the roles HypD may play in different microbial metabolic pathways as well as the potential implications of this activity for colonization resistance and pathogenesis within the human gut. Finally, we present evidence of anaerobic Hyp metabolism in sediments through enrichment culturing of Hyp-degrading bacteria, highlighting the wide distribution of this pathway in anoxic environments beyond the human gut

Hispanismo y becquerianismo en José Martí.

Sin resume

Diffraction in time of a confined particle and its Bohmian paths

Diffraction in time of a particle confined in a box which its walls are removed suddenly at $t=0$ is studied. The solution of the time-dependent Schr\"{o}dinger equation is discussed analytically and numerically for various initial wavefunctions. In each case Bohmian trajectories of the particles are computed and also the mean arrival time at a given location is studied as a function of the initial state.Comment: 8 pages, 6 figure

An accelerated closed universe

We study a model in which a closed universe with dust and quintessence matter components may look like an accelerated flat Friedmann-Robertson-Walker (FRW) universe at low redshifts. Several quantities relevant to the model are expressed in terms of observed density parameters, $\Omega_M$ and $\Omega_{\Lambda}$, and of the associated density parameter $\Omega_Q$ related to the quintessence scalar field $Q$.Comment: 11 pages. For a festschrift honoring Alberto Garcia. To appear in Gen. Rel. Gra

Disclosing hidden information in the quantum Zeno effect: Pulsed measurement of the quantum time of arrival

Repeated measurements of a quantum particle to check its presence in a region of space was proposed long ago [G. R. Allcock, Ann. Phys. {\bf 53}, 286 (1969)] as a natural way to determine the distribution of times of arrival at the orthogonal subspace, but the method was discarded because of the quantum Zeno effect: in the limit of very frequent measurements the wave function is reflected and remains in the original subspace. We show that by normalizing the small bits of arriving (removed) norm, an ideal time distribution emerges in correspondence with a classical local-kinetic-energy distribution.Comment: 5 pages, 4 figures, minor change

The Euler-Betti Algorithm to identify foliations in Hilbert Scheme

Foliations in the complex projective plane are uniquely determined by their singular locus, which is in correspondence with a zero-dimensional ideal. However, this correspondence is not surjective. We give conditions to determine whether an ideal arises as the singular locus of a foliation or not. Furthermore, we give an effective method to construct the foliation in the positive case

Dynamics of a Tonks-Girardeau gas released from a hard-wall trap

We study the expansion dynamics of a Tonks-Girardeau gas released from a hard wall trap. Using the Fermi-Bose map, the density profile is found analytically and shown to differ from that one of a classical gas in the microcanonical ensemble even at macroscopic level, for any observation time larger than a critical time. The relevant time scale arises as a consequence of fermionization.Comment: 4 pages, 6 figure

Open inflationary universes in a brane world cosmology

In this paper, we study a type of one-field model for open inflationary universe models in the context of the brane world models. In the scenario of a one-bubble universe model, we determine and characterize the existence of the Coleman-De Lucia instanton, together with the period of inflation after tunneling has occurred. Our results are compared to those found in the Einstein theory of Relativistic Models.Comment: 8 pages, 4 Figures, accepted in Physical Review