An Improved Kernel for the Flip Distance Problem on Simple Convex Polygons

The complexity of computing the flip distance between two triangulations of a simple convex polygon is unknown. Here we approach the problem from a parameterized complexity perspective and improve upon the 2k kernel of Lucas [10]. Specifically, we describe a kernel of size 43k and then show how it can be improved to (1+?)k for every constant ? > 0. By ensuring that the kernel consists of a single instance our result yields a kernel of the same magnitude (up to additive terms) for the almost equivalent rotation distance problem on rooted, ordered binary trees. The earlier work of Lucas left the kernel as a disjoint set of instances, potentially allowing very minor differences in the definition of the size of instances to accumulate, causing a constant-factor distortion in the kernel size when switching between flip distance and rotation distance formulations. Our approach avoids this sensitivity

An Improved Kernel for the Flip Distance Problem on Simple Convex Polygons

The complexity of computing the flip distance between two triangulations of a simple convex polygon is unknown. Here we approach the problem from a parameterized complexity perspective and improve upon the 2k kernel of Lucas [10]. Specifically, we describe a kernel of size 43k and then show how it can be improved to (1+?)k for every constant ? > 0. By ensuring that the kernel consists of a single instance our result yields a kernel of the same magnitude (up to additive terms) for the almost equivalent rotation distance problem on rooted, ordered binary trees. The earlier work of Lucas left the kernel as a disjoint set of instances, potentially allowing very minor differences in the definition of the size of instances to accumulate, causing a constant-factor distortion in the kernel size when switching between flip distance and rotation distance formulations. Our approach avoids this sensitivity

Numerical modeling of the electron beam welding and its experimental validation

Electron Beam Welding (EBW) is a highly efficient and precise welding method increasingly used within the manufacturing chain and of growing importance in different industrial environments such as the aeronautical and aerospace sectors. This is because, compared to other welding processes, EBW induces lower distortions and residual stresses due to the lower and more focused heat input along the welding line. This work describes the formulation adopted for the numerical simulation of the EBW process as well as the experimental work carried out to calibrate and validate it. The numerical simulation of EBW involves the interaction of thermal, mechanical and metallurgical phenomena. For this reason, in this work the numerical framework couples the heat transfer process to the stress analysis to maximize accuracy. An in-house multi-physics FE software is used to deal with the numerical simulation. The definition of an ad hoc moving heat source is proposed to simulate the EB power surface distribution and the corresponding absorption within the work-piece thickness. Both heat conduction and heat radiation models are considered to dissipate the heat through the boundaries of the component. The material behavior is characterized by an apropos thermo-elasto-viscoplastic constitutive model. Titanium-alloy Ti6A14V is the target material of this work. From the experimental side, the EB welding machine, the vacuum chamber characteristics and the corresponding operative setting are detailed. Finally, the available facilities to record the temperature evolution at different thermo-couple locations as well as to measure both distortions and residual stresses are described. Numerical results are compared with the experimental evidence.Peer ReviewedPostprint (author's final draft

Insights Into the Biogenesis and Emerging Functions of Lipid Droplets From Unbiased Molecular Profiling Approaches.

Lipid droplets (LDs) are spherical, single sheet phospholipid-bound organelles that store neutral lipids in all eukaryotes and some prokaryotes. Initially conceived as relatively inert depots for energy and lipid precursors, these highly dynamic structures play active roles in homeostatic functions beyond metabolism, such as proteostasis and protein turnover, innate immunity and defense. A major share of the knowledge behind this paradigm shift has been enabled by the use of systematic molecular profiling approaches, capable of revealing and describing these non-intuitive systems-level relationships. Here, we discuss these advances and some of the challenges they entail, and highlight standing questions in the field.MS-Á acknowledges support from the Tec4Bio consortium (of which MD is co-coordinator; ref. S2018/NMT4443, Actividades de I+D entre Grupos de Investigación en Tecnologías, Comunidad Autónoma de Madrid/FEDER, Spain) and a CNIC-IPP COFUND MSCA fellowship, and is currently a recipient of a Ramón y Cajal research contract from the Spanish Ministry of Science and Innovation (RYC2020-029690-I). MAdP is an elected EMBO member, and research at his lab is supported by grants from the Spanish Ministry of Science and Innovation (PID2020-118658RB-I00, SAF2017-83130-R), La Caixa Health Research Programme (HR20-00075, AtheroConvergence), La Marató TV3 (201936-30-31) and the Asociación Española Contra el Cáncer (PROYE20089DELP). AP is an ICREA research professor and was supported by the Ministerio de Ciencia e Investigacion (MICINN, RTI2018-098593-B-I00) and the CERCA Programme/Generalitat de Catalunya. The CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the Ministerio de Ciencia e Innovacion (MCIN) and the Pro CNIC Foundation), and is a Severo Ochoa Center of Excellence (grant CEX2020-001041-S funded by MICIN/ AEI/10.13039/501100011033).S

A PTAS for Triangle-Free 2-Matching

In the Triangle-Free (Simple) 2-Matching problem we are given an undirected graph $G=(V,E)$. Our goal is to compute a maximum-cardinality $M\subseteq E$ satisfying the following properties: (1) at most two edges of $M$ are incident on each node (i.e., $M$ is a 2-matching) and (2) $M$ does not induce any triangle. In his Ph.D. thesis from 1984, Harvitgsen presents a complex polynomial-time algorithm for this problem, with a very complex analysis. This result was never published in a journal nor reproved in a different way, to the best of our knowledge. In this paper we have a fresh look at this problem and present a simple PTAS for it based on local search. Our PTAS exploits the fact that, as long as the current solution is far enough from the optimum, there exists a short augmenting trail (similar to the maximum matching case).Comment: 27 pages, 18 figure

A 4/3 Approximation for 2-Vertex-Connectivity

The 2-Vertex-Connected Spanning Subgraph problem (2VCSS) is among the most basic NP-hard (Survivable) Network Design problems: we are given an (unweighted) undirected graph G. Our goal is to find a subgraph S of G with the minimum number of edges which is 2-vertex-connected, namely S remains connected after the deletion of an arbitrary node. 2VCSS is well-studied in terms of approximation algorithms, and the current best (polynomial-time) approximation factor is 10/7 by Heeger and Vygen [SIDMA\u2717] (improving on earlier results by Khuller and Vishkin [STOC\u2792] and Garg, Vempala and Singla [SODA\u2793]). Here we present an improved 4/3 approximation. Our main technical ingredient is an approximation preserving reduction to a conveniently structured subset of instances which are "almost" 3-vertex-connected. The latter reduction might be helpful in future work

Diseño de un sistema automático de organización de trabajadores de capacidades diversas en puestos de trabajo para un Centro Especial de Empleo (Espurna CEE, SLU)

[ES] El trabajo que se presenta consiste en el diseño de un sistema de organización para un centro especial de empleo. El documento constará de un análisis de la problemática del centro especial de empleo, un planteamiento de posibles soluciones, elección de una de ellas y desarrollo de esta. En el desarrollo se describirá el sistema de planificación y control que se ha diseñado para albergar los procesos y la herramienta de apoyo que permite automatizarlos. Posteriormente se describirá un plan de implantación y presupuesto. El problema principal que se intentará resolver es el de la distribución de los trabajadores del centro en los distintos enclaves en los que pueden ser enviados. Hay una gran cantidad de empleados para situar y el problema se vuelve complicado. Se resolverá aplicando un sistema de planificación para dividir el problema y definir las funciones de cada una de las partes y con la herramienta de apoyo se solucionará el reparto de los trabajadores. De esta manera el resultado será un plan de actuación, una herramienta para llevar a cabo esas instrucciones y un plan para poner en marcha todo el sistema.Bosch Calvo, M. (2019). Diseño de un sistema automático de organización de trabajadores de capacidades diversas en puestos de trabajo para un Centro Especial de Empleo (Espurna CEE, SLU). http://hdl.handle.net/10251/125742TFG

Control de calidad en la industria de la automoción

Peer Reviewe

Control de calidad en la industria de la automoción

Peer Reviewe

A mixed stabilized finite element formulation for strain localization analysis

This work exploits the concept of stabilization techniques to improve the behaviour of either mixed or pu/mixed u/εlinear/linear triangular elements when strain localization analysis is required. Different stabilization methods suitable for either Mode-I or Mode-II structural failure are proposed and compared to check the global stability of the corresponding discrete finite element formulation. Both elasto-J2-plastic and isotropic damage models have been used for the constitutive behaviour of the material. In both cases, exponential softening has been introduced in the post-peak regime. The results obtained do not suffer from spurious mesh-size or mesh-bias dependence, comparing very favorably with those obtained with standard approach.Postprint (published version