Parameterized Local Search for Vertex Cover: When Only the Search Radius Is Crucial

A k-swap W for a vertex cover S of a graph G is a vertex set of size at most k such that S\u27 = (S ? W) ? (W ? S), the symmetric difference of S and W, is a vertex cover of G. If |S\u27| < |S|, then W is improving. In LS-Vertex Cover, one is given a vertex cover S of a graph G and wants to know if there is an improving k-swap for S in G. In applications of LS-Vertex Cover, k is a very small parameter that can be set by a user to determine the trade-off between running time and solution quality. Consequently, k can be considered to be a constant. Motivated by this and the fact that LS-Vertex Cover is W[1]-hard with respect to k, we aim for algorithms with running time ?^f(k) ? n^?(1) where ? is a structural graph parameter upper-bounded by n. We say that such a running time grows mildly with respect to ? and strongly with respect to k. We obtain algorithms with such a running time for ? being the h-index of G, the treewidth of G, or the modular-width of G. In addition, we consider a novel parameter, the maximum degree over all quotient graphs in a modular decomposition of G. Moreover, we adapt these algorithms to the more general problem where each vertex is assigned a weight and where we want to find a d-improving k-swap, that is, a k-swap which decreases the weight of the vertex cover by at least d

The Interplay of Structure and Dynamics in the Raman Spectrum of Liquid Water over the Full Frequency and Temperature Range

While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems

String Factorizations Under Various Collision Constraints

In the NP-hard Equality-Free String Factorization problem, we are given a string S and ask whether S can be partitioned into k factors that are pairwise distinct. We describe a randomized algorithm for Equality-Free String Factorization with running time 2^k? k^{?(1)}+?(n) improving over previous algorithms with running time k^{?(k)}+?(n) [Schmid, TCS 2016; Mincu and Popa, Proc. SOFSEM 2020]. Our algorithm works for the generalization of Equality-Free String Factorization where equality can be replaced by an arbitrary polynomial-time computable equivalence relation on strings. We also consider two factorization problems to which this algorithm does not apply, namely Prefix-Free String Factorization where we ask for a factorization of size k such that no factor is a prefix of another factor and Substring-Free String Factorization where we ask for a factorization of size k such that no factor is a substring of another factor. We show that these two problems are NP-hard as well. Then, we show that Prefix-Free String Factorization with the prefix-free relation is fixed-parameter tractable with respect to k by providing a polynomial problem kernel. Finally, we show a generic ILP formulation for R-Free String Factorization where R is an arbitrary relation on strings. This formulation improves over a previous one for Equality-Free String Factorization in terms of the number of variables

A Graph-Theoretic Formulation of Exploratory Blockmodeling

We present a new simple graph-theoretic formulation of the exploratory blockmodeling problem on undirected and unweighted one-mode networks. Our formulation takes as input the network G and the maximum number t of blocks for the solution model. The task is to find a minimum-size set of edge insertions and deletions that transform the input graph G into a graph G\u27 with at most t neighborhood classes. Herein, a neighborhood class is a maximal set of vertices with the same neighborhood. The neighborhood classes of G\u27 directly give the blocks and block interactions of the computed blockmodel. We analyze the classic and parameterized complexity of the exploratory blockmodeling problem, provide a branch-and-bound algorithm, an ILP formulation and several heuristics. Finally, we compare our exact algorithms to previous ILP-based approaches and show that the new algorithms are faster for t ? 4

Experience of Robotic Exoskeleton Use at Four Spinal Cord Injury Model Systems Centers

Background and Purpose: Refinement of robotic exoskeletons for overground walking is progressing rapidly. We describe clinicians\u27 experiences, evaluations, and training strategies using robotic exoskeletons in spinal cord injury rehabilitation and wellness settings and describe clinicians\u27 perceptions of exoskeleton benefits and risks and developments that would enhance utility. Methods: We convened focus groups at 4 spinal cord injury model system centers. A court reporter took verbatim notes and provided a transcript. Research staff used a thematic coding approach to summarize discussions. Results: Thirty clinicians participated in focus groups. They reported using exoskeletons primarily in outpatient and wellness settings; 1 center used exoskeletons during inpatient rehabilitation. A typical episode of outpatient exoskeleton therapy comprises 20 to 30 sessions and at least 2 staff members are involved in each session. Treatment focuses on standing, stepping, and gait training; therapists measure progress with standardized assessments. Beyond improved gait, participants attributed physiological, psychological, and social benefits to exoskeleton use. Potential risks included falls, skin irritation, and disappointed expectations. Participants identified enhancements that would be of value including greater durability and adjustability, lighter weight, 1-hand controls, ability to navigate stairs and uneven surfaces, and ability to balance without upper extremity support. Discussion and Conclusions: Each spinal cord injury model system center had shared and distinct practices in terms of how it integrates robotic exoskeletons into physical therapy services. There is currently little evidence to guide integration of exoskeletons into rehabilitation therapy services and a pressing need to generate evidence to guide practice and to inform patients\u27 expectations as more devices enter the market. Background and Purpose: Refinement of robotic exoskeletons for overground walking is progressing rapidly. We describe clinicians\u27 experiences, evaluations, and training strategies using robotic exoskeletons in spinal cord injury rehabilitation and wellness settings and describe clinicians\u27 perceptions of exoskeleton benefits and risks and developments that would enhance utility. Methods: We convened focus groups at 4 spinal cord injury model system centers. A court reporter took verbatim notes and provided a transcript. Research staff used a thematic coding approach to summarize discussions. Results: Thirty clinicians participated in focus groups. They reported using exoskeletons primarily in outpatient and wellness settings; 1 center used exoskeletons during inpatient rehabilitation. A typical episode of outpatient exoskeleton therapy comprises 20 to 30 sessions and at least 2 staff members are involved in each session. Treatment focuses on standing, stepping, and gait training; therapists measure progress with standardized assessments. Beyond improved gait, participants attributed physiological, psychological, and social benefits to exoskeleton use. Potential risks included falls, skin irritation, and disappointed expectations. Participants identified enhancements that would be of value including greater durability and adjustability, lighter weight, 1-hand controls, ability to navigate stairs and uneven surfaces, and ability to balance without upper extremity support. Discussion and Conclusions: Each spinal cord injury model system center had shared and distinct practices in terms of how it integrates robotic exoskeletons into physical therapy services. There is currently little evidence to guide integration of exoskeletons into rehabilitation therapy services and a pressing need to generate evidence to guide practice and to inform patients\u27 expectations as more devices enter the market

Reliability of autoregressive error models as post-processors for probabilistic streamflow forecasts

In this study, the reliability of different versions of autoregressive error models as post-processors for probabilistic streamflow forecasts is evaluated. Rank histograms and reliability indices are used as performance measures. An algorithm for the construction of confidence intervals to indicate ranges of reliable forecasts within the rank histograms is presented. To analyse differences in performance of the post-processors, scatter plots of the standardized residuals of the error models are generated to assess the homoscedacity of the residuals with respect to streamflow. A problem of distorted impressions may appear when such plots are generated with a regular x-scale. The problem is analysed with both synthetic and real data, and a rank scaled x-axis is proposed to remedy the problem. The results of the study reveal large differences in the reliability of the post-processors. Versions with empirical distribution functions are clearly superior to those with standard normal distribution, but for validations with independent data their rank histograms still lie outside of the confidence bands for reliable forecasts

Mauer-Frei : generating transformation at the Berlin-Brandenburg border

Whether architectural or urban in scale, the basic building element of the wall is invariably a product of its sociopolitical context. While often deceptively simple in form, walls embody complex political maneuvering and perpetuate tremendous divisive power. A striking instance of this at a large scale was the descent of the Iron Curtain across Europe, which, through the aggressive imposition of walls, literally and metaphorically concretized the ideological contention between democracy and communism in the twentieth century. Taking Berlin as a vivid case through which to investigate the legacy of this polarizing divider, this thesis offers a timely reflection on the potential and relevance of subverting the inherent divisiveness of walls. Titled MauerFrei (or, “Wall-Free”), this thesis project advances an antithetical elaboration on the restrictive and imposing influence of the Berlin Wall and positively engages those traversing the zone demarcated by the former DreilindenDrewitz (East) and Checkpoint Bravo (West) border crossings.Master of Architecture (M.Arch

Experimentelle Analyse von horizontalen und leicht geneigten Zwei-Phasen-Thermosiphons für die solarthermische Fassadenintegration

Die vorliegende Dissertation dient der experimentellen Analyse von horizontalen und leicht geneigten Zwei-Phasen-Thermosiphons für die solarthermische Fassadenintegration. Zwei-Phasen-Thermosiphons, die den Verdampfungs-/Kondensationskreislauf über die Schwerkraft aufrechterhalten, sind in der Lage, auch unter horizontaler Ausrichtung hohe Wärmeleistungen zu erzielen. Die gegenwärtig bestehende Datenlage zu thermischem Widerstand und Leistungsgrenzen von horizontalen und leicht geneigten Zwei-Phasen-Thermosiphons zeichnet jedoch, insbesondere für die Abhängigkeit von Füllgrad und Neigungswinkel, kein einheitliches Bild. Zudem wird ein häufig instationäres Verhalten beim Betrieb um die Horizontale beschrieben. Es ist nicht auszuschließen, dass das instationäre Verhalten von Zwei-Phasen-Thermosiphons im Horizontalen, gepaart mit unterschiedlichen Definitionen und Methoden zur Bestimmung der Leistungsgrenze, seinen Anteil an der unklaren Datenlage hat. Eine allein auf Literaturdaten beruhende Auslegung von Zwei-Phasen-Thermosiphons für die winkelflexible, auch horizontale Fassadenintegration ist folglich nicht möglich. Im ersten Teil der vorliegenden Arbeit werden verschiedene Definitionen und Messmethoden zur Bestimmung der Leistungsgrenze hinsichtlich ihrer Eignung zur Beschreibung von solaren horizontalen und leicht geneigten Zwei-Phasen-Thermosiphons untersucht. Die Arbeit stellt dabei einen umfassenden Überblick über Definitionen der Leistungsgrenze und den möglichen Einfluss auf die gemessene Leistungsgrenze solarer horizontaler und leicht geneigter Wärmerohre zur Verfügung. Es wird erkannt, dass keine der in der Literatur vorhandenen Definitionen der Leistungsgrenze alleinstehend für die Beschreibung des komplexen instationären Betriebsverhaltens von Zwei-Phasen-Thermosiphons um die Horizontale geeignet ist. Stattdessen wird die Analyse und Bewertung des Grenzbetriebsverhaltens von horizontalen und leicht geneigten Zwei-Phasen-Thermosiphons anhand von sogenannten „Temperaturphänomen-Karten“ vorgeschlagen. Damit wird in der Arbeit eine Methodik entwickelt, mit der das komplexe Betriebsverhalten von horizontalen und leicht geneigten Zwei-Phasen-Thermosiphons abgebildet werden kann und die – in Verbindung mit einer breiten experimentellen Analyse – die Basis für eine fundierte Auslegung von Zwei-Phasen-Thermosiphons um die Horizontale liefern könnte. Im zweiten Teil der Arbeit wird ein für die Anwendung in einem Test-Fassadenkollektor des Projekts „ArKol“ vorgesehener solarer Zwei-Phasen-Thermosiphon hinsichtlich seines Betriebsverhaltens – auch unter Anwendung der neu entwickelten Methodik der Temperaturphänomen-Karten – analysiert. Es zeigt sich, dass der thermische Widerstand des Test-Thermosiphons für einen Füllgrad von 30 % bei einer Neigung von 0° und +0,5° bei geringen Temperaturen vom erhöhten Widerstand zwischen Verdampfer und adiabater Zone dominiert wird. Für einen Füllgrad von 45 % wird der thermische Widerstand dagegen bei geringen bis mäßigen Temperaturen für alle gemessenen Winkel zwischen 0° und +10° vom Widerstand zwischen der adiabaten Zone und dem Kühlwasser bestimmt. Für 30 % Füllgrad wird in den betreffenden Betriebspunkten eine Austrocknung des Verdampfers, für 45 % Füllgrad eine Teilflutung des Kondensators vermutet. Die zur Analyse des Grenzbetriebsverhaltens herangezogenen Temperaturphänomen-Karten offenbaren, dass für einen Betrieb bei horizontaler Ausrichtung deutlich mehr Betriebspunkte vorliegen, denen ein stationäres oder nur leicht instationäres Verhalten zugeordnet werden kann, als bei geneigter Ausrichtung. Gleichzeitig treten in horizontaler Ausrichtung jedoch häufiger Phänomene hoher Instationarität auf, die den Wärmerohrbetrieb massiv gefährden. Ob eine geringere Leistungsgrenze für horizontale oder leicht geneigte Zwei-Phasen-Thermosiphons erkannt wird, hängt damit von der Definition des Leistungsgrenzphänomens ab. Auf Basis der durchgeführten Untersuchungen kann ein horizontaler Betrieb des Test-Thermosiphons im Test-Fassadenkollektor nicht ohne das Auftreten von den Wärmerohrbetrieb gefährdenden Temperaturphänomenen garantiert werden. Die Machbarkeit einer leicht geneigten Installation ist aufgrund der unter diesen Winkeln über einen breiten Betriebsbereich auftretenden mäßigen Instationaritäten in Dauer- und Geräuschtests zu prüfen