Dynamics for a 2-vertex Quantum Gravity Model

We use the recently introduced U(N) framework for loop quantum gravity to study the dynamics of spin network states on the simplest class of graphs: two vertices linked with an arbitrary number N of edges. Such graphs represent two regions, in and out, separated by a boundary surface. We study the algebraic structure of the Hilbert space of spin networks from the U(N) perspective. In particular, we describe the algebra of operators acting on that space and discuss their relation to the standard holonomy operator of loop quantum gravity. Furthermore, we show that it is possible to make the restriction to the isotropic/homogeneous sector of the model by imposing the invariance under a global U(N) symmetry. We then propose a U(N) invariant Hamiltonian operator and study the induced dynamics. Finally, we explore the analogies between this model and loop quantum cosmology and sketch some possible generalizations of it.Comment: 28 pages, v2: typos correcte

Pleuritis en la Valencia romana

X Congreso Nacional de Paleopatología. Univesidad Autónoma de Madrid, septiembre de 200

Thermal Excitation of Broadband and Long-range Surface Waves on SiO 2 Submicron Films

We detect thermally excited surfaces waves on a submicron SiO 2 layer, including Zenneck and guided modes in addition to Surface Phonon Polaritons. The measurements show the existence of these hybrid thermal-electromagnetic waves from near-(2.7 $\mu$m) to far-(11.2 $\mu$m) infrared. Their propagation distances reach values on the order of the millimeter, several orders of magnitude larger than on semi-infinite systems. These two features, spectral broadness and long range propagation, make these waves good candidates for near-field applications both in optics and thermics due to their dual nature.Comment: Applied Physics Letters, American Institute of Physics, 201

New Histone Incorporation Marks Sites of UV Repair in Human Cells

SummaryChromatin organization is compromised during the repair of DNA damage. It remains unknown how and to what extent epigenetic information is preserved in vivo. A central question is whether chromatin reorganization involves recycling of parental histones or new histone incorporation. Here, we devise an approach to follow new histone deposition upon UV irradiation in human cells. We show that new H3.1 histones get incorporated in vivo at repair sites. Remarkably we find that H3.1, which is deposited during S phase, is also incorporated outside of S phase. Histone deposition is dependent on nucleotide excision repair (NER), indicating that it occurs at a postrepair stage. The histone chaperone chromatin assembly factor 1 (CAF-1) is directly involved in the histone deposition process in vivo. We conclude that chromatin restoration after damage cannot rely simply on histone recycling. New histone incorporation at repair sites both challenges epigenetic stability and possibly contributes to damage memory

TFAP2C regulates transcription in human naive pluripotency by opening enhancers.

Naive and primed pluripotent human embryonic stem cells bear transcriptional similarity to pre- and post-implantation epiblast and thus constitute a developmental model for understanding the pluripotent stages in human embryo development. To identify new transcription factors that differentially regulate the unique pluripotent stages, we mapped open chromatin using ATAC-seq and found enrichment of the activator protein-2 (AP2) transcription factor binding motif at naive-specific open chromatin. We determined that the AP2 family member TFAP2C is upregulated during primed to naive reversion and becomes widespread at naive-specific enhancers. TFAP2C functions to maintain pluripotency and repress neuroectodermal differentiation during the transition from primed to naive by facilitating the opening of enhancers proximal to pluripotency factors. Additionally, we identify a previously undiscovered naive-specific POU5F1 (OCT4) enhancer enriched for TFAP2C binding. Taken together, TFAP2C establishes and maintains naive human pluripotency and regulates OCT4 expression by mechanisms that are distinct from mouse

Revisiting the Simplicity Constraints and Coherent Intertwiners

In the context of loop quantum gravity and spinfoam models, the simplicity constraints are essential in that they allow to write general relativity as a constrained topological BF theory. In this work, we apply the recently developed U(N) framework for SU(2) intertwiners to the issue of imposing the simplicity constraints to spin network states. More particularly, we focus on solving them on individual intertwiners in the 4d Euclidean theory. We review the standard way of solving the simplicity constraints using coherent intertwiners and we explain how these fit within the U(N) framework. Then we show how these constraints can be written as a closed u(N) algebra and we propose a set of U(N) coherent states that solves all the simplicity constraints weakly for an arbitrary Immirzi parameter.Comment: 28 page