Shaping an optical dome: The size and shape of the insect compound eye

The insect compound eye is the most abundant eye architecture on earth. It comes in a wide variety of shapes and sizes, which are exquisitely adapted to specific ecosystems. Here, we explore the organisational principles and pathways, from molecular to tissular, that underpin the building of this organ and highlight why it is an excellent model system to investigate the relationship between genes and tissue form. The compound eye offers wide fields of view, high sensitivity in motion detection and infinite depth of field. It is made of an array of visual units called ommatidia, which are precisely tiled in 3D to shape the retinal tissue as a dome-like structure. The eye starts off as a 2D epithelium, and it acquires its 3D organisation as ommatidia get into shape. Each ommatidium is made of a complement of retinal cells, including light-detecting photoreceptors and lens-secreting cells. The lens cells generate the typical hexagonal facet lens that lies atop the photoreceptors so that the eye surface consists of a quasi-crystalline array of these hexagonal facet-lenses. This array is curved to various degree, depending on the size and shape of the eye, and on the region of the retina. This curvature sets the resolution and visual field of the eye and is determined by i) the number and size of the facet lens – large ommatidial lenses can be used to generate flat, higher resolution areas, while smaller facets allow for stronger curvature of the eye, and ii) precise control of the inter facet-lens angle, which determines the optical axis of the each ommatidium. In this review we discuss how combinatorial variation in eye primordium shape, ommatidial number, facet lens size and inter facet-lens angle underpins the wide variety of insect eye shapes, and we explore what is known about the mechanisms that might control these parameters

The retinal determination gene dachshund restricts cell proliferation by limiting the activity of the Homothorax-Yorkie complex

The Drosophila transcriptional co-activator protein Yorkie and its vertebrate orthologs YAP and TAZ are potent oncogenes, whose activity is normally kept in check by the upstream Hippo kinase module. Upon its translocation into the nucleus, Yorkie forms complexes with several tissue-specific DNA-binding partners, which help to define the tissue-specific target genes of Yorkie. In the progenitor cells of the eye imaginal disc, the DNA-binding transcription factor Homothorax is required for Yorkie-promoted proliferation and survival through regulation of the bantam microRNA (miRNA). The transit from proliferating progenitors to cell cycle quiescent precursors is associated with the progressive loss of Homothorax and gain of Dachshund, a nuclear protein related to the Sno/Ski family of co-repressors. We have identified Dachshund as an inhibitor of Homothorax-Yorkie-mediated cell proliferation. Loss of dachshund induces Yorkie-dependent tissue overgrowth. Conversely, overexpressing dachshund inhibits tissue growth, prevents Yorkie or Homothorax-mediated cell proliferation of disc epithelia and restricts the transcriptional activity of the Yorkie-Homothorax complex on the bantam enhancer in Drosophila cells. In addition, Dachshund collaborates with the Decapentaplegic receptor Thickveins to repress Homothorax and Cyclin B expression in quiescent precursors. The antagonistic roles of Homothorax and Dachshund in Yorkie activity, together with their mutual repression, ensure that progenitor and precursor cells are under distinct proliferation regimes. Based on the crucial role of the human dachshund homolog DACH1 in tumorigenesis, our work suggests that DACH1 might prevent cellular transformation by limiting the oncogenic activity of YAP and/or TAZ.Spanish Ministry of Economy and Competitiveness (MINECO), EU Feder Funds: (BFU2012-34324), Consolider 'From Genes to Shape' (MICINN), FCT fellowships: (SFRH/BPD/46983/2008, IF/01031/2012)

The mass of X-Ray Nova Scorpii 1994 (=GRO J1655--40)]

We have obtained high and intermediate resolution optical spectra of the black-hole candidate Nova Sco 1994 in May/June 1998, when the source was in complete (X-ray) quiescence. We measure the radial velocity curve of the secondary star and obtain a semi-amplitude of K_2=215.5+/-2.4 km/s, which is 6 per cent lower than the only previously determined value. This new value for K_2 thus reduces the binary mass function to f(M) = 2.73+/-0.09 Mo. Using only the high resolution spectra we constrain the rotational broadening of the secondary star, vsini, to lie in the range 82.9-94.9 km/s (95 per cent confidence) and thus constrain the binary mass ratio to lie in the range 0.337--0.436 (95 per cent confidence). We can also combine our results with published limits for the binary inclination to constrain the mass of the compact object and secondary star to the ranges 5.5 -- 7.9 and 1.7 -- 3.3 Mo respectively (95 per cent confidence). Finally, we report on the detection of the Lithium resonance line at 6707.8 A, with an equivalent width of 55+/-8 mA.Comment: 5 pages, 5 figures, accepted by MNRA

The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton

We present XMM observations of the black hole X-ray nova V404 Cygni in quiescence. Its quiescent spectrum can be best fitted by a simple power-law with slope 2. The spectra are consistent with that expected for the advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in luminosity compared to the previous observation of Chandra. We see variability of a factor of 4 during the observation. We find no evidence for the presence of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and 110 eV respectively. The limit on the fluorescent emission is improved by a factor of 15 over the previous estimate, and the restriction on H-like/He-like emission is lower than predicted from models by a factor of roughly 2.Comment: 6 pages, 7 figures, ApJ accepte

Staff experiences of formulating within a team setting

This study evaluates psychology-led formulation sessions within an assessment and treatment service. Five staff members completed interviews exploring their experiences of formulation and their perception of its usefulness to clients. Results suggested that they perceived formulation to be beneficial on a number of levels for themselves and their practice but were uncertain about the tangible benefits for clients

Events leading up to the June 2015 outburst of V404 Cyg

On 2015 June 15 the burst alert telescope (BAT) on board {\em Swift} detected an X-ray outburst from the black hole transient V404 Cyg. We monitored V404 Cyg for the last 10 years with the 2-m Faulkes Telescope North in three optical bands (V, R, and i$^{'}$). We found that, one week prior to this outburst, the optical flux was 0.1--0.3 mag brighter than the quiescent orbital modulation, implying an optical precursor to the X-ray outburst. There is also a hint of a gradual optical decay (years) followed by a rise lasting two months prior to the outburst. We fortuitously obtained an optical spectrum of V404 Cyg 13 hours before the BAT trigger. This too was brighter ($\sim1\rm\,mag$) than quiescence, and showed spectral lines typical of an accretion disk, with characteristic absorption features of the donor being much weaker. No He II emission was detected, which would have been expected had the X-ray flux been substantially brightening. This, combined with the presence of intense H$\alpha$ emission, about 7 times the quiescent level, suggests that the disk entered the hot, outburst state before the X-ray outburst began. We propose that the outburst is produced by a viscous-thermal instability triggered close to the inner edge of a truncated disk. An X-ray delay of a week is consistent with the time needed to refill the inner region and hence move the inner edge of the disk inwards, allowing matter to reach the central BH, finally turning on the X-ray emission.Comment: Accepted by ApJ Letter, 7 pages, 5 figure

Local Anchor Based Location Management Schemes for Small Cells in HetNets

(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.[EN] Existing location management (LM) methods for macrocells in LTE-Advanced have tracking area list (TAL) granularity. Therefore, a user equipment (UE) triggers a location update (LU) whenever it leaves its current TAL, and it is searched through paging (PG) with TAL accuracy. However, these procedures are not well-suited for small cells (SCs). The reasons are twofold. First, dense deployments of SCs imply that paging has a low probability to be successful in the first attempt, increasing the signaling overhead in the core network (CN). Second, smaller coverage areas lead to a higher mobility among cells, increasing the signaling overhead in the CN due to LUs. In this work, two LM schemes with fine granularity are proposed. These schemes update UE's location to a local anchor (LA) in a SC or tracking area (TA) basis, respectively. By increasing the accuracy of UE's location, a significant reduction of signaling overhead in the CN due to PG is achieved. Moreover, LUs to the LA are performed through direct X2-interface links to avoid signaling overhead in the CN. A versatile mobility model is developed and closed-form expressions for UEs' mobility metrics are found to validate the proposed schemes through variations of critical parameters such as TA/TAL configuration, UE's mobility patterns and cell residence times.This work has been supported by European Commission under the FP7 S2EuNet project and the Spanish Government through project TIN2013-47272-C2-1-RPacheco-Paramo, DF.; Akyildiz, IF.; Casares Giner, V. (2016). Local Anchor Based Location Management Schemes for Small Cells in HetNets. IEEE Transactions on Mobile Computing. 15(4):883-894. https://doi.org/10.1109/TMC.2015.2431717S88389415

Intercellular communication and the organization of simple multicellular animals

Animal cells are amazing examples of decentralized systems: By interchanging information about their position and internal state, cells coordinate their behavior and organize themselves in time and space. Examples of this behavior are the development of an embryo or of an organoid. In this work we have asked which are the “rules of intercellular relationship” that allow the organization of an abstract cell collective into structures similar to simple metazoans, without being specific about the (molecular, cellular or physical) nature of the processes involved. To do so, we have used a computational modeling approach following a modified version of the “Swarmalator” concept introduced by O'Keeffe, Hong and Strogatz (2017): a collection of interacting particles (“swarmalators”), each of which defined by a position in space and an internal state (a phase). The key feature is that swarmalators are coupled, so that their position and internal state are both affected by the position and state of all other swarmalators. This model can be easily analogized to biological systems, with “cells” being the swarmalators, and their phase the cell's internal state or “cell type”. With this model we explore the conditions (represented by the coupling parameters) that would allow the organization of a multicellular “bioswarmer” and its dynamics along a sort of life cycle. Originally developed in 2D, we implement the model in 3D as well. We describe how changing the strength of intercellular communication can alter the structure and differentiation state of the bioswarmer, how internal polarization can arise and trigger collective directed migration, or how partly erasing the cellular memory of cell state is critical to allow bioswarmers to transit through different states. In addition, we show that the size of a multicellular ensemble might control the differentiation of its constituent cells without changing its rules of relationship.Ministerio de Economía y Competitividad PGC2018-474 093704-B-I00, MDM-2016-068

El hombre de campo y el hombre de ciudad

Me lleva a presentar esta comunicación a la Academia, el estado actual de incomprensión entre la población campesina, hoy indefensa, y la urbana que orienta la opinión del país. La buena voluntad entre ambas colectividades es obvia, más las separa cierta antinomia circunstante que proviene, casi diría, del contraste entre sus respectivos modos de vida. Hasta hace pocas décadas, cuando no se menospreciaban las principales fuentes de riqueza de la nación, la influencia del estanciero y de instituciones nétamente agrarias contribuía eficazmente en nuestra legislación rural y ello permitía condicionar las reglamentaciones al medio en que debieron ser aplicadas. Para dar claridad a mi exposición comenzaré describiendo las características más salientes de ambos tipos de vida, la campesina y la urbana, para poder luego de una rápida visión histórica señalar la importancia de la sociología rural como disciplina necesaria para encauzar los actos de gobierno en su obra de fomento agrario.Academia Nacional de Agronomía y Veterinari