Efficient Exact Algorithms on Planar Graphs: Exploiting Sphere Cut Decompositions

We present a general framework for designing fast subexponential exact and parameterized algorithms on planar graphs. Our approach is based on geometric properties of planar branch decompositions obtained by Seymour and Thomas, combined with refined techniques of dynamic programming on planar graphs based on properties of non-crossing partitions. To exemplify our approach we show how to obtain an  $O(2^{6.903\sqrt{n}})We present a general framework for designing fast subexponential exact and parameterized algorithms on planar graphs. Our approach is based on geometric properties of planar branch decompositions obtained by Seymour and Thomas, combined with refined techniques of dynamic programming on planar graphs based on properties of non-crossing partitions. To exemplify our approach we show how to obtain an  O(2^6.903?n)O(2^{6.903\sqrt{n}}) time algorithm solving weighted Hamiltonian Cycle on an n-vertex planar graph. Similar technique solves Planar Graph Travelling Salesman Problem with n cities in time O(2^9.8594?n)O(2^{9.8594\sqrt{n}}) . Our approach can be used to design parameterized algorithms as well. For example, we give an algorithm that for a given k decides if a planar graph on n vertices has a cycle of length at least k in time O(2^13.6?kn+n³)O(2^{13.6\sqrt{k}}n+n^{3}) .     

Technology and properties of a vector hall sensor

Symmetrical four-sided 12-μm-high pyramids with 30°-tilted sides were revealed by the etching of semi-insulating (1 0 0) GaAs substrates in 1H₃PO₄:×H₂O₂:8H₂O at 25 °C via sacrificial 0 0 1-oriented Ti/GaAs/AlAs (100/2000/100 nm) etching mask patterns. The pyramids, MOCVD overgrown with InGaP/AlGaAs/GaAs heterostructure pyramids, were used as the base for magnetic field vector sensors. Each sensor consisted of three Hall probes defined on the sides of a pyramid. The device processing was realized via AZ5214-E layers deposited conformally over the pyramids by draping from water surface. While the planar reference 5×5-μm²-sized Hall probes exhibited a sensitivity of 930 VA⁻¹T⁻¹ at 298 K, the sensitivity of those on the 30°-tilted facets was impossible to determine because they had a resistance of 100 kΩ at 298 K. Further work is necessary to optimize the InGaP/AlGaAs/GaAs heterostructure growth and dopant incorporation on the 30°-tilted pyramidal facets.     

More About Subcolorings

A subcoloring is a vertex coloring of a graph in which every color class induces a disjoint union of cliques. We derive a number of results on the combinatorics, the algorithmics, and the complexity of subcolorings. On the negative side, we prove that 2-subcoloring is NP-hard for comparability graphs, and that 3-subcoloring is NP-hard for AT-free graphs and for complements of planar graphs. On the positive side, we derive polynomial time algorithms for 2-subcoloring of complements of planar graphs, and for r-subcoloring of interval and of permutation graphs. Moreover, we prove asymptotically best possible upper bounds on the subchromatic number of interval graphs, chordal graphs, and permutation graphs in terms of the number of vertices. Received June 11, 2002; revised September 13, 2002 Published online: November 25, 2002 RID="*" ID="*" The work of HJB and FVF is sponsored by NWO-grant 047.008.006. FVF acknowledges support by EC contract IST-1999-14186, Project ALCOM-FT (Algorithms and Complexity – Future Technologies). Part of this work was done while FVF was visiting the University of Twente, and while he was a visiting postdoc at DIMATIA-ITI (supported by GAČR 201/99/0242 and by the Ministry of Education of the Czech Republic as project LN00A056). JN acknowledges support of ITI – the Project LN00A056 of the Czech Ministery of Education. GJW acknowledges support by the START program Y43-MAT of the Austrian Ministry of Science.     

Progress towards robotic exploration of extreme terrain

A high degree of mobility, reliability, and efficiency are needed for autonomous exploration of extreme terrain. These requirements have guided the development of the Ambler, a six-legged robot designed for planetary exploration. To address issues of efficiency and mobility, the Ambler is configured with a stacked arrangement of orthogonal legs and exhibits a unique circulating gait, where trailing legs recover directly from rear to front. The Ambler is designed to stably traverse a 30 degree slope while crossing meter sized features. The same three principles have provided many constraints on the design of a software system that autonomously navigates the Ambler through natural terrain using 3-D perception and a combined deliberative/reactive architecture. The software system has required research advances in real-time control, perception of rugged terrain, motion planning, task-level control, and system integration. This paper presents many of the factors that influenced the design of the Ambler and its software system. In particular, important assumptions regarding the mechanism, perception, planning, and control are presented and evaluated in light of experimental and theoretical research of this project.     

Investigating newcomer expectations and job-related outcomes.

The initial experiences of newcomers as they enter an organization can provide important information that substantially influences the subsequent relationship between the individual and the organization. For example, the application of realistic job previews (RJPs) often results in desirable organizational outcomes (e.g., increased satisfaction and reduced turnover). RJPs are typically job specific and job-content laden and serve to reduce the expectations of organizational newcomers. The present study indicates that an expectation lowering procedure (ELP), which is not job specific and is relatively content free, may yield similar benefits (i.e., reduce expectations). Both the organizational implications of this research and suggestions for using ELPs in conjunction with RJPs in the newcomer socialization process are offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of transformational and change leadership on employees' commitment to a change: A multilevel study.

The effects of transformational leadership on the outcomes of specific change initiatives are not well understood. Conversely, organizational change studies have examined leader behaviors during specific change implementations yet have failed to link these to broader leadership theories. In this study, the authors investigate the relationship between transformational and change leadership and followers' commitment to a particular change initiative as a function of the personal impact of the changes. Transformational leadership was found to be more strongly related to followers' change commitment than change-specific leadership practices, especially when the change had significant personal impact. For leaders who were not viewed as transformational, good change-management practices were found to be associated with higher levels of change commitment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pulse electro-thermal de-icer (PETD)

De-icing is a process in which interfacial ice attached to a structure is either broken or melted and then the ice is removed by some sort of external force (e.g. gravity or wind-drag). Conventional thermal de-icing is effective but requires too much energy. Mechanical de-icing requires less energy but is less effective, often leaving significant amounts of ice behind, and may also damage structures and accelerate wear. We have invented, developed, and tested a pulse electro-thermal de-icer (PETD) that reduces the energy needed for de-icing by up to a factor of one hundred. PETD achieves this by melting only a thin layer of interfacial ice, leaving the temperature of the environment unchanged.In conventional de-icers, the heater is thermally connected to the ice, the structure, and the outside environment. This makes heat losses through conduction and convection inevitable to the point where the losses exceed by orders of magnitude the amount of “useful” heat needed to melt the interfacial ice. PETD cuts these losses by using a short heating pulse - approximately 1 ms to 5s long - to heat a minimal layer of interfacial ice. This short heating time limits the heat penetration depth into both the ice and the structure. A PETD pulse heats the ice-structure interface just above the melting point causing the ice to slide off on the resulting thin water film.PETD was successfully tested for a variety of applications including the de-icing of airplanes, car windshields, bridge over-structures, glass roofs, commercial and residential icemakers, and windmill rotors. The tests demonstrated almost instant action along with up to 99% savings of the electricity required by conventional thermal de-icers.This paper presents the PETD method, its theory, results of computer simulations, and extensive data from laboratory tests as well as several large-scale implementations of PETD on an airplane, a bridge, a building roof (> 10,000 m²), a car windshield, and a commercial ice maker.