On the stability of Cosmic String Y-junctions

We study the evolution of non-periodic cosmic string loops containing Y-junctions, such as may form during the evolution of a network of (p,q) cosmic superstrings. We set up and solve the Nambu-Goto equations of motion for a loop with junctions, focusing attention on a specific static and planar initial loop configuration. After a given time, the junctions collide and the Nambu-Goto description breaks down. We also study the same loop configuration in a U(1)xU(1) field theory model that allows composite vortices with corresponding Y-junctions. We show that the field theory and Nambu-Goto evolution are remarkably similar until the collision time. However, in the field theory evolution a new phenomenon occurs: the composite vortices can unzip, producing in the process new Y-junctions, whose separation may grow significantly, destabilizing the configuration. In particular, an initial loop with two Y-junctions may evolve to a configuration with six Y-junctions (all distant from each other). Setting up this new configuration as an initial condition for Nambu Goto strings, we solve for its evolution and establish conditions under which it is stable to the decay mode seen in the field theory case. Remarkably, the condition closely matches that seen in the field theory simulations, and is expressed in terms of simple parameters of the Nambu-Goto system. This implies that there is an easy way to understand the instability in terms of which region of parameter space leads to stable or unstable unzippings.Comment: 16 pages, 11 figures, typos correcte

Food systems for sustainable development: Proposals for a profound four-part transformation

Evidence shows the importance of food systems for sustainable development: they are at the nexus that links food security, nutrition, and human health, the viability of ecosystems, climate change, and social justice. However, agricultural policies tend to focus on food supply, and sometimes, on mechanisms to address negative externalities. We propose an alternative. Our starting point is that agriculture and food systems' policies should be aligned to the 2030 Agenda for Sustainable Development. This calls for deep changes in comparison with the paradigms that prevailed when steering the agricultural change in the XXth century. We identify the comprehensive food systems transformation that is needed. It has four parts: first, food systems should enable all people to benefit from nutritious and healthy food. Second, they should reflect sustainable agricultural production and food value chains. Third, they should mitigate climate change and build resilience. Fourth, they should encourage a renaissance of rural territories. The implementation of the transformation relies on (i) suitable metrics to aid decision-making, (ii) synergy of policies through convergence of local and global priorities, and (iii) enhancement of development approaches that focus on territories. We build on the work of the “Milano Group,” an informal group of experts convened by the UN Secretary General in Milan in 2015. Backed by a literature review, what emerges is a strategic narrative linking climate, agriculture and food, and calling for a deep transformation of food systems at scale. This is critical for achieving the Sustainable Development Goals and the Paris Agreement. The narrative highlights the needed consistency between global actions for sustainable development and numerous local-level innovations. It emphasizes the challenge of designing differentiated paths for food systems transformation responding to local and national expectations. Scientific and operational challenges are associated with the alignment and arbitration of local action within the context of global priorities

User-centered development of a Virtual Research Environment to support collaborative research events

This paper discusses the user-centred development process within the Collaborative Research Events on the Web (CREW) project, funded under the JISC Virtual Research Environments (VRE) programme. After presenting the project, its aims and the functionality of the CREW VRE, we focus on the user engagement approach, grounded in the method of co-realisation. We describe the different research settings and requirements of our three embedded user groups and the respective activities conducted so far. Finally we elaborate on the main challenges of our user engagement approach and end with the project’s next steps

Valorización de Ferreycorp S.A.A.

El objetivo del presente informe es hallar el valor intrínseco de la acción de Ferreycorp S.A.A., una empresa peruana dedicada a la comercialización de bienes de capital y servicios especializados que remonta su origen desde el año 1922 y que cotiza en la bolsa de valores de Lima. El grupo económico se ha consolidado como el líder en el Perú, a raíz de un manejo financiero responsable, un portafolio de marcas reconocidas a nivel mundial y un servicio post venta oportuno y eficiente. Para la estimación, utilizamos el método de flujo de caja descontado, así como la valorización por múltiplos. Para tal efecto hemos ahondado en el comportamiento de la inversión privada peruana como principal input para la estimación de los ingresos de la compañía, considerando que la línea de negocio de Caterpillar Perú explica el 74% de los ingresos del grupo económico. Hemos tomado tres escenarios base, uno pesimista, moderado y optimista, considerando la coyuntura política nacional en la que se ha realizado la presente investigación

A Case Study of Low-Mass Star Formation

This article synthesizes observational data from an extensive program aimed toward a comprehensive understanding of star formation in a low-mass star-forming molecular cloud. New observations and published data spanning from the centimeter wave band to the near infrared reveal the high and low density molecular gas, dust, and pre-main sequence stars in L1551.Comment: 24 pages, 21 figures, ApJS accepte

Dirac Born Infeld (DBI) Cosmic Strings

Motivated by brane physics, we consider the non-linear Dirac-Born-Infeld (DBI) extension of the Abelian-Higgs model and study the corresponding cosmic string configurations. The model is defined by a potential term, assumed to be of the mexican hat form, and a DBI action for the kinetic terms. We show that it is a continuous deformation of the Abelian-Higgs model, with a single deformation parameter depending on a dimensionless combination of the scalar coupling constant, the vacuum expectation value of the scalar field at infinity, and the brane tension. By means of numerical calculations, we investigate the profiles of the corresponding DBI-cosmic strings and prove that they have a core which is narrower than that of Abelian-Higgs strings. We also show that the corresponding action is smaller than in the standard case suggesting that their formation could be favoured in brane models. Moreover we show that the DBI-cosmic string solutions are non-pathological everywhere in parameter space. Finally, in the limit in which the DBI model reduces to the Bogomolnyi-Prasad-Sommerfield (BPS) Abelian-Higgs model, we find that DBI cosmic strings are no longer BPS: rather they have positive binding energy. We thus argue that, when they meet, two DBI strings will not bind with the corresponding formation of a junction, and hence that a network of DBI strings is likely to behave as a network of standard cosmic strings.Comment: 25 pages, 12 figure

CARMA Millimeter-Wave Aperture Synthesis Imaging of the HD 32297 Debris Disk

We present the first detection and mapping of the HD 32297 debris disk at 1.3 mm with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). With a sub-arcsecond beam, this detection represents the highest angular resolution (sub)mm debris disk observation made to date. Our model fits to the spectral energy distribution from the CARMA flux and new Spitzer MIPS photometry support the earlier suggestion that at least two, possibly three, distinct grain populations are traced by the current data. The observed millimeter map shows an asymmetry between the northeast and southwest disk lobes, suggesting large grains may be trapped in resonance with an unseen exoplanet. Alternatively, the observed morphology could result from the recent breakup of a massive planetesimal. A similar-scale asymmetry is also observed in scattered light but not in the mid-infrared. This contrast between asymmetry at short and long wavelengths and symmetry at intermediate wavelengths is in qualitative agreement with predictions of resonant debris disk models. With resolved observations in several bands spanning over three decades in wavelength, HD 32297 provides a unique testbed for theories of grain and planetary dynamics, and could potentially provide strong multi-wavelength evidence for an exoplanetary system.Comment: 4 pages, 4 figures; Accepted to ApJL: 25 Aug 200