New Relations for Gauge-Theory Amplitudes

We present an identity satisfied by the kinematic factors of diagrams describing the tree amplitudes of massless gauge theories. This identity is a kinematic analog of the Jacobi identity for color factors. Using this we find new relations between color-ordered partial amplitudes. We discuss applications to multi-loop calculations via the unitarity method. In particular, we illustrate the relations between different contributions to a two-loop four-point QCD amplitude. We also use this identity to reorganize gravity tree amplitudes diagram by diagram, offering new insight into the structure of the KLT relations between gauge and gravity tree amplitudes. This can be used to obtain novel relations similar to the KLT ones. We expect this to be helpful in higher-loop studies of the ultraviolet properties of gravity theories.Comment: 40 pages, 7 figures, RevTex, v2 minor correction

Observing the onset of outflow collimation in a massive protostar

The current paradigm of star formation through accretion disks, and magnetohydrodynamically driven gas ejections, predicts the development of collimated outflows, rather than expansion without any preferential direction. We present radio continuum observations of the massive protostar W75N(B)-VLA 2, showing that it is a thermal, collimated ionized wind and that it has evolved in 18 years from a compact source into an elongated one. This is consistent with the evolution of the associated expanding water-vapor maser shell, which changed from a nearly circular morphology, tracing an almost isotropic outflow, to an elliptical one outlining collimated motions. We model this behavior in terms of an episodic, short-lived, originally isotropic, ionized wind whose morphology evolves as it moves within a toroidal density stratification.Comment: See also Supplementary Materials (SupMat_carrasco-gonzalez_etal_astroph.pdf) within the source file

Closing oil palm yield gaps among Indonesian smallholders through industry schemes, pruning, weeding and improved seeds

Oil palm production has led to large losses of valuable habitats for tropical biodiversity. Sparing of land for nature could in theory be attained if oil palm yields increased. The efficiency of oil palm smallholders is below its potential capacity, but the factors determining efficiency are poorly understood. We employed a two-stage data envelopment analysis approach to assess the influence of agronomic, supply chain and management factors on oil palm production efficiency in 190 smallholders in six villages in Indonesia. The results show that, on average, yield increases of 65% were possible and that fertilizer and herbicide use was excessive and inefficient. Adopting industry-supported scheme management practices, use of high-quality seeds and higher pruning and weeding rates were found to improve efficiency. Smallholder oil palm production intensification in Indonesia has the capacity to increase production by 26%, an equivalent of 1.75 million hectares of land

Localized waves in silicates. What do we know from experiments?

Since the latest review about solitary localized waves in muscovite, called quodons, (F.M. Russell in Quodons in Mica. Springer, Cham, pp. 475–559, 2015a [1], F.M. Russell in Quodons in Mica. Springer, Cham, pp. 3–33, 2015b [2]) there have been many developments, specially from the point of view of experiments, published in several journals. The breakthrough hypothesis that was advanced in that review that dark tracks were produced by positive electrical charge moving in a localized wave, either transported by swift particles or by nonlinear localized waves, has been confirmed by experiments in muscovite and other silicates. In this paper we review the experimental results, some already published and some new, specially the phenomenon of charge transport without an electric field, called hyperconductivity. We also consider alternative explanations as phase transitions for other tracks. We also attempt to describe numerical simulations that have confirmed the order of magnitude of quodons energy and calculations underway to determine more properties of electron and hole transport by quodons.Ministerio de Ciencia e Innovación MICINN PID2019-109175GB-C22Junta de Andalucía PAIDI 2019/FQM-280Universidad de Sevilla VIPPITUS 2020Universiad de Sevilla VIPPITUS 201

Generic multiloop methods and application to N=4 super-Yang-Mills

We review some recent additions to the tool-chest of techniques for finding compact integrand representations of multiloop gauge-theory amplitudes - including non-planar contributions - applicable for N=4 super-Yang-Mills in four and higher dimensions, as well as for theories with less supersymmetry. We discuss a general organization of amplitudes in terms of purely cubic graphs, review the method of maximal cuts, as well as some special D-dimensional recursive cuts, and conclude by describing the efficient organization of amplitudes resulting from the conjectured duality between color and kinematic structures on constituent graphs.Comment: 42 pages, 18 figures, invited review for a special issue of Journal of Physics A devoted to "Scattering Amplitudes in Gauge Theories", v2 minor corrections, v3 added reference

Low X-Ray Luminosity Galaxy Clusters: Main goals, sample selection, photometric and spectroscopic observations

We present the study of nineteen low X-ray luminosity galaxy clusters (L$_X \sim$ 0.5--45 $\times$ $10^{43}$ erg s$^{-1}$), selected from the ROSAT Position Sensitive Proportional Counters (PSPC) Pointed Observations (Vikhlinin et al. 1998) and the revised version of Mullis et al. (2003) in the redshift range of 0.16 to 0.7. This is the introductory paper of a series presenting the sample selection, photometric and spectroscopic observations and data reduction. Photometric data in different passbands were taken for eight galaxy clusters at Las Campanas Observatory; three clusters at Cerro Tololo Interamerican Observatory; and eight clusters at the Gemini Observatory. Spectroscopic data were collected for only four galaxy clusters using Gemini telescopes. With the photometry, the galaxies were defined based on the star-galaxy separation taking into account photometric parameters. For each galaxy cluster, the catalogues contain the PSF and aperture magnitudes of galaxies within the 90\% completeness limit. They are used together with structural parameters to study the galaxy morphology and to estimate photometric redshifts. With the spectroscopy, the derived galaxy velocity dispersion of our clusters ranged from 507 km~s$^{-1}$ for [VMF98]022 to 775 km~s$^{-1}$ for [VMF98]097 with signs of substructure. Cluster membership has been extensively discussed taking into account spectroscopic and photometric redshift estimates. In this sense, members are the galaxies within a projected radius of 0.75 Mpc from the X-ray mission peak and with cluster centric velocities smaller than the cluster velocity dispersion or 6000 km~s$^{-1}$, respectively. These results will be used in forthcoming papers to study, among the main topics, the red cluster sequence, blue cloud and green populations; the galaxy luminosity function and cluster dynamics.Comment: 13 pages, 6 tables, 9 figures. Uses emulateapj. Accepted for publication in The Astronomical Journal. Some formatting errors fixe

Rare event simulation for dynamic fault trees

Fault trees (FT) are a popular industrial method for reliability engineering, for which Monte Carlo simulation is an important technique to estimate common dependability metrics, such as the system reliability and availability. A severe drawback of Monte Carlo simulation is that the number of simulations required to obtain accurate estimations grows extremely large in the presence of rare events, i.e., events whose probability of occurrence is very low, which typically holds for failures in highly reliable systems. This paper presents a novel method for rare event simulation of dynamic fault trees with complex repairs that requires only a modest number of simulations, while retaining statistically justified confidence intervals. Our method exploits the importance sampling technique for rare event simulation, together with a compositional state space generation method for dynamic fault trees. We demonstrate our approach using two parameterized sets of case studies, showing that our method can handle fault trees that could not be evaluated with either existing analytical techniques, nor with standard simulation techniques

Towards the construction of health workforce metrics for Latin America and the Caribbean

<p>Abstract</p> <p>Introduction</p> <p>One of the components of the Health Observatory for Latin American and the Caribbean (HO-LAC) is the design and implementation of metrics for human resources for health. Under the HO-LAC initiative, researchers from nine countries in the region formed the Collaborative Community on Human Resources for Health in Latin America and the Caribbean to identify common metrics applicable to the field of human resources for health (HRH).</p> <p>Case description</p> <p>The case description comprises three stages: a) the origins of an initiative in which a non-governmental organization brings together researchers involved in HRH policy in LAC, b) a literature search to identify initiatives to develop methods and metrics to assess the HRH field in the region, and c) subsequent discussions held by the group of researchers regarding the possibilities of identifying an appropriate set of metrics and indicators to assess HRH throughout the region.</p> <p>Discussion and evaluation</p> <p>A total of 101 documents produced between 1985 and 2008 in the LAC region were identified. Thirty-three of the papers included a variety of measurements comprising counts, percentages, proportions, indicators, averages and metrics, but only 13 were able to fully describe the methods used to identify these metrics and indicators. Of the 33 articles with measurements, 47% addressed labor market issues, 25% were about working conditions, 23% were on HRH training and 5% addressed regulations. Based on these results, through iterative discussions, metrics were defined into three broad categories (training, labor market and working conditions) and available sources of information for their estimation were proposed. While only three of the countries have data on working conditions, all countries have sufficient data to measure at least one aspect of HRH training and the HRH labor market.</p> <p>Conclusions</p> <p>Information gleaned from HRH metrics makes it possible to carry out comparisons on a determined experience in space and time, in a given country and/or region. The results should then constitute evidence for policy formulation and HRH planning and programs, with improved health system performance ultimately contributing to improved population health. The results of this study are expected to guide decision making by incentivizing the construction of metrics that provide information about HRH problems in LAC countries.</p