The application of interactive graphics to large time-dependent hydrodynamics problems

A written companion of a movie entitled "Interactive Graphics at Los Alamos Scientific Laboratory" was presented. While the movie presents the actual graphics terminal and the functions performed on it, the paper attempts to put in perspective the complexity of the application code and the complexity of the interaction that is possible

The rich cluster of galaxies ABCG~85. IV. Emission line galaxies, luminosity function and dynamical properties

This paper is the fourth of a series dealing with the cluster of galaxies ABCG 85. Using our two extensive photometric and spectroscopic catalogues (with 4232 and 551 galaxies respectively), we discuss here three topics derived from optical data. First, we present the properties of emission line versus non-emission line galaxies, showing that their spatial distributions somewhat differ; emission line galaxies tend to be more concentrated in the south region where groups appear to be falling onto the main cluster, in agreement with the hypothesis (presented in our previous paper) that this infall may create a shock which can heat the X-ray emitting gas and also enhance star formation in galaxies. Then, we analyze the luminosity function in the R band, which shows the presence of a dip similar to that observed in other clusters at comparable absolute magnitudes; this result is interpreted as due to comparable distributions of spirals, ellipticals and dwarfs in these various clusters. Finally, we present the dynamical analysis of the cluster using parametric and non-parametric methods and compare the dynamical mass profiles obtained from the X-ray and optical data.Comment: accepted for publication in A&

Semiclassical geons as solitonic black hole remnants

We find that the end state of black hole evaporation could be represented by non-singular and without event horizon stable solitonic remnants with masses of the order the Planck scale and up to 16 units of charge. Though these objects are locally indistinguishable from spherically symmetric, massive electric (or magnetic) charges, they turn out to be sourceless geons containing a wormhole generated by the electromagnetic field. Our results are obtained by interpreting semiclassical corrections to Einstein's theory in the first-order (Palatini) formalism, which yields second-order equations and avoids the instabilities of the usual (metric) formulation of quadratic gravity. We also discuss the potential relevance of these solutions for primordial black holes and the dark matter problem.Comment: 9 pages, 1 figur

Crystal clear lessons on the microstructure of space-time and modified gravity

We argue that a microscopic structure for space-time such as that expected in a quantum foam scenario, in which microscopic wormholes and other topological structures should play a relevant role, might lead to an effective metric-affine geometry at larger scales. This idea is supported by the role that microscopic defects play in crystalline structures. With an explicit model we show that wormhole formation is possible in a metric-affine scenario, where the wormhole and the matter fields play a role analogous to that of defects in crystals. We also point out that in metric-affine geometries Einstein's equations with an effective cosmological constant appear as an attractor in the vacuum limit for a vast family of theories of gravity. This illustrates how lessons from solid state physics can be useful in unveiling the properties of the microcosmos and defining new avenues for modified theories of gravity.Comment: 7 pages; some minor corrections adde

f(R,T) gravity

We consider f(R,T) modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R and of the trace of the stress-energy tensor T. We obtain the gravitational field equations in the metric formalism, as well as the equations of motion for test particles, which follow from the covariant divergence of the stress-energy tensor. Generally, the gravitational field equations depend on the nature of the matter source. The field equations of several particular models, corresponding to some explicit forms of the function f(R,T), are also presented. An important case, which is analyzed in detail, is represented by scalar field models. We write down the action and briefly consider the cosmological implications of the $f(R,T^{\phi})$ models, where $T^{\phi}$ is the trace of the stress-energy tensor of a self-interacting scalar field. The equations of motion of the test particles are also obtained from a variational principle. The motion of massive test particles is non-geodesic, and takes place in the presence of an extra force orthogonal to the four-velocity. The Newtonian limit of the equation of motion is further analyzed. Finally, we provide a constraint on the magnitude of the extra-acceleration by analyzing the perihelion precession of the planet Mercury in the framework of the present model.Comment: 14 pages. V2: minor corrections, to appear in PR

Correlation between Local Structure Distortions and Martensitic Transformation in Ni-Mn-In alloys

The local structural distortions arising as a consequence of increasing Mn content in Ni_2Mn_1+xIn_1-x (x=0, 0.3, 0.4, 0.5 and 0.6) and its effect on martensitic transformation have been studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni and Mn K-edges in the above compositions, the changes associated with respect to the local structure of these absorbing atoms are compared. It is seen that in the alloys exhibiting martensitic transformation ($x \ge 0.4$) there is a significant difference between the Ni-In and Ni-Mn bond lengths even in the austenitic phase indicating atomic volume to be the main factor in inducing martensitic transformation in Ni-Mn-In Heusler alloys.Comment: 8 pages, 2 figure

Effects of ionizing radiation on normal and tumor-associated lymphatic vessels

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007."June 2007."Includes bibliographical references (p. 37-43).Lymphatic vessels play a crucial role in both the pathophysiology of tumors and in the spread cancer cells to lymph nodes. The effects of radiation on these vessels, however, are largely unknown. Here, we seek to describe the effects of ionizing radiation on normal and tumor-associated lymphatic vessels in vitro and in vivo. Clonogenic assays were employed to study the radiation dose response of lymphatic endothelial cells. Putative lymphatic endothelial cell mitogens and antiproliferative agents, including vascular endothelial growth factor-A (VEGF-A), VEGF-C and AZD2171, a tyrosine kinase inhibitor of the VEGF receptors, were tested as radiation sensitizers and protectors. Our results indicate that VEGF-A and VEGF-C are radiosensitizers while AZD2171 did not modulate the radioresponse. In vivo, normal lymphatics were studied with the experimental group receiving a single fraction of 8 Gy and the control group receiving no radiation. We observed no difference in the average lymphatic vessel diameter between these two groups over the course of 6 months. VEGF-C overexpressing tumor-associated lymphatic vessels were studied in vivo with four treatment groups: control animals (no irradiation), 8 Gy two weeks prior to implantation, 8 Gy at the time of implantation and 16 Gy given in two fractions before implantation (two weeks prior to and at the time of implantation). The average lymphatic vessel diameter and frequency of lymph node metastasis in these four groups indicates that the ability of radiation to prevent VEGF-C driven lymph node metastases is time-dependent; radiation must be delivered in close proximity to VEGF-C overexpressing tumor cell implantation to impact nodal metastases. This suggests that VEGF-C may be a functional lymphatic vessel radiosensitizer in vivo.(cont.) However, reductions in lymphatic hyperplasia, as measured by lymphatic vessel diameter, did not explain the observed differential effects of radiation timing on lymph node metastasis rate.by Jennifer D. Lobo.S.B

An anti-Schwarzshild solution: wormholes and scalar-tensor solutions

We investigate a static solution with an hyperbolic nature, characterised by a pseudo-spherical foliation of space. This space-time metric can be perceived as an anti-Schwarzschild solution, and exhibits repulsive features. It belongs to the class of static vacuum solutions termed "a degenerate static solution of class A". In the present work we review its fundamental features, discuss the existence of generalised wormholes, and derive its extension to scalar-tensor gravity theories in general.Comment: 3 pages, contribution to the proceedings of the Spanish Relativity Meeting-ERE200

On the Transferability of Knowledge among Vehicle Routing Problems by using Cellular Evolutionary Multitasking

Multitasking optimization is a recently introduced paradigm, focused on the simultaneous solving of multiple optimization problem instances (tasks). The goal of multitasking environments is to dynamically exploit existing complementarities and synergies among tasks, helping each other through the transfer of genetic material. More concretely, Evolutionary Multitasking (EM) regards to the resolution of multitasking scenarios using concepts inherited from Evolutionary Computation. EM approaches such as the well-known Multifactorial Evolutionary Algorithm (MFEA) are lately gaining a notable research momentum when facing with multiple optimization problems. This work is focused on the application of the recently proposed Multifactorial Cellular Genetic Algorithm (MFCGA) to the well-known Capacitated Vehicle Routing Problem (CVRP). In overall, 11 different multitasking setups have been built using 12 datasets. The contribution of this research is twofold. On the one hand, it is the first application of the MFCGA to the Vehicle Routing Problem family of problems. On the other hand, equally interesting is the second contribution, which is focused on the quantitative analysis of the positive genetic transferability among the problem instances. To do that, we provide an empirical demonstration of the synergies arisen between the different optimization tasks.Comment: 8 pages, 1 figure, paper accepted for presentation in the 23rd IEEE International Conference on Intelligent Transportation Systems 2020 (IEEE ITSC 2020