Structural Parameterizations with Modulator Oblivion

It is known that problems like Vertex Cover, Feedback Vertex Set and Odd Cycle Transversal are polynomial time solvable in the class of chordal graphs. We consider these problems in a graph that has at most k vertices whose deletion results in a chordal graph, when parameterized by k. While this investigation fits naturally into the recent trend of what are called "structural parameterizations", here we assume that the deletion set is not given. One method to solve them is to compute a k-sized or an approximate (f(k) sized, for a function f) chordal vertex deletion set and then use the structural properties of the graph to design an algorithm. This method leads to at least k^O(k)n^O(1) running time when we use the known parameterized or approximation algorithms for finding a k-sized chordal deletion set on an n vertex graph. In this work, we design 2^O(k)n^O(1) time algorithms for these problems. Our algorithms do not compute a chordal vertex deletion set (or even an approximate solution). Instead, we construct a tree decomposition of the given graph in time 2^O(k)n^O(1) where each bag is a union of four cliques and O(k) vertices. We then apply standard dynamic programming algorithms over this special tree decomposition. This special tree decomposition can be of independent interest. Our algorithms are, what are sometimes called permissive in the sense that given an integer k, they detect whether the graph has no chordal vertex deletion set of size at most k or output the special tree decomposition and solve the problem. We also show lower bounds for the problems we deal with under the Strong Exponential Time Hypothesis (SETH)

Desiccant cooling systems: a review

Desiccant cooling systems have been considered as an efficient method of controlling moisture content in supply air. They do not use any ozone-depleting coolants and consume less energy as compared with the vapour compression systems. This communication provides an extensive review of liquid desiccant systems (LDSs). All the components of an LDS such as dehumidifier, regenerator, packing material and liquid desiccant properties along with its energy storage capabilities have been discussed in detail. In addition, hybrid of LDSs with sensible cooling technologies has been studied. Various types of mathematical models to predict the outlet parameters of the desiccant system and current issues in liquid desiccants have been reviewed in detail. Moreover, solid and other advanced desiccants have also been discussed briefly. Finally, a summary of some successful case studies and economic evaluation of desiccant systems have been given

Tool wear during friction stir welding an experimental and numerical study during welding of CuCrZr alloy

by Pankaj SahlotPh.D

Estimation of tool wear during friction stir welding of CuCrZr alloy

by Pankaj Sahlot and Amit Aror

Tool wear during friction stir welding: state of the art and the challenges

by Pankaj Sahlot and Amit Aror

Numerical model for prediction of tool wear and worn-out pin profile during friction stir welding

Understanding tool wear during friction stir welding (FSW) is important for joining of high melting point metallic (HMPM) materials. Heat transfer and material flow based models developed in past have improved understanding of the FSW process. However, numerical models to predict tool wear and pin profile during FSW of HMPM materials are not available. Thus, the current research has focused on developing a heat transfer and material flow based model to predict tool wear and worn-out tool pin profile of H13 steel during FSW of Cu-0.8Cr-0.1Zr (CuCrZr) alloy. Temperature evolution and material flow are computed by solving conservation equations of mass, momentum and energy. The model thus developed is validated for thermal cycles and tool pin profile for various process parameters. Tool wear is predicted based on forces and stresses acting on the tool. Modified Archard's wear theory is applied to compute tool wear and worn-out tool pin profile. The wear model successfully predicts the worn-out tool pin profile and self-optimized phenomena for various process parameters. The model is also applied to understand the changes in worn-out pin profile during FSW process

Numerical model to estimate tool wear and worn-out pin shape during friction stir welding of CuCrZr alloy

by Pankaj Sahlot and Amit Aror