College admissions with stable score-limits

A common feature of the Hungarian, Irish, Spanish and Turkish higher education admission systems is that the students apply for programmes and they are ranked according to their scores. Students who apply for a programme with the same score are in a tie. Ties are broken by lottery in Ireland, by objective factors in Turkey (such as date of birth) and other precisely defined rules in Spain. In Hungary, however, an equal treatment policy is used, students applying for a programme with the same score are all accepted or rejected together. In such a situation there is only one question to decide, whether or not to admit the last group of applicants with the same score who are at the boundary of the quota. Both concepts can be described in terms of stable score-limits. The strict rejection of the last group with whom a quota would be violated corresponds to the concept of H-stable (i.e. higher-stable) score-limits that is currently used in Hungary. We call the other solutions based on the less strict admission policy as L-stable (i.e. lower-stable) score-limits. We show that the natural extensions of the Gale-Shapley algorithms produce stable score-limits, moreover, the applicant-oriented versions result in the lowest score-limits (thus optimal for students) and the college-oriented versions result in the highest score-limits with regard to each concept. When comparing the applicant-optimal H-stable and L-stable score-limits we prove that the former limits are always higher for every college. Furthermore, these two solutions provide upper and lower bounds for any solution arising from a tie-breaking strategy. Finally we show that both the H-stable and the L-stable applicant-proposing scorelimit algorithms are manipulable

Editorial: special issue on matching under preferences

This special issue of Algorithms is devoted to the study of matching problems involving ordinal preferences from the standpoint of algorithms and complexit

Grain boundaries in graphene grown by chemical vapor deposition

The scientific literature on grain boundaries (GBs) in graphene was reviewed. The review focuses mainly on the experimental findings on graphene grown by chemical vapor deposition (CVD) under a very wide range of experimental conditions (temperature, pressure hydrogen/hydrocarbon ratio, gas flow velocity and substrates). Differences were found in the GBs depending on the origin of graphene: in micro-mechanically cleaved graphene (produced using graphite originating from high-temperature, high-pressure synthesis), rows of non-hexagonal rings separating two perfect graphene crystallites are found more frequently, while in graphene produced by CVD—despite the very wide range of growth conditions used in different laboratories—GBs with more pronounced disorder are more frequent. In connection with the observed disorder, the stability of two-dimensional amorphous carbon is discussed and the growth conditions that may impact on the structure of the GBs are reviewed. The most frequently used methods for the atomic scale characterization of the GB structures, their possibilities and limitations and the alterations of the GBs in CVD graphene during the investigation (e.g. under e-beam irradiation) are discussed. The effects of GB disorder on electric and thermal transport are reviewed and the relatively scarce data available on the chemical properties of the GBs are summarized. GBs are complex enough nanoobjects so that it may be unlikely that two experimentally produced GBs of several microns in length could be completely identical in all of their atomic scale details. Despite this, certain generalized conclusions may be formulated, which may be helpful for experimentalists in interpreting the results and in planning new experiments, leading to a more systematic picture of GBs in CVD graphene

Matching with Couples: a Multidisciplinary Survey

This survey deals with two-sided matching markets where one set of agents (workers/residents) has to be matched with another set of agents (firms/hospitals). We first give a short overview of a selection of classical results. Then, we review recent contributions to a complex and representative case of matching with complementarities, namely matching markets with couples. We discuss contributions from computer scientists, economists, and game theorists

Statistical analysis of data describing the relationship between driver, truck and characteristics of the road

Road vehicles equipped with appropriate measurement equipment, computing facilities, data storage and data communication capabilities can be considered valuable data sources for the description and quantitative characterisation of road traffic. The data obtained from these vehicles provide valuable direct and indirect information pertaining to traffic states and various aspects of traffic safety in respect of the analysed road network. In this study, trucks’ abrupt braking events, detected by the trucks’ on-board safety protection units, were analysed. The road locations of the detected abrupt braking events can be characterised by a number of features ranging from the specific traffic regulations (e.g., speed limits) in force to the socio-cultural environment of the location. The abrupt braking data evidence was used for identification and description of non-trivial interactions of drivers, trucks and roads. Some of the more interesting results and conclusions of the experiments are reported herein

Matching couples with Scarf's algorithm

Scarf's algorithm [18] provides fractional core elements for NTU-games. Bir¢ and Fleiner [3] showed that Scarf's algorithm can be extended for capacitated NTU-games. In this setting agents can be involved in more than one coalition at a time, cooperations may be performed with different intensities up to some limits, and the contribution of the agents can also differ in a coalition. The fractional stable solutions for the above model, produced by the extended Scarf algorithm, are called stable allocations. In this paper we apply this solution concept for the Hospitals Residents problem with Couples (HRC). This is one of the most important general stable matching problems due to its relevant applications, also well-known to be NP-hard. We show that if a stable allocation yielded by the Scarf algorithm turns outto be integral then it provides a stable matching for an instance of HRC, so this method can be used as a heuristic. In an experimental study, we compare this method with other heuristics constructed for HRC that are applied in practice in the American and Scottish resident allocation programs, respectively. Our main finding is that the Scarf algorithm outperforms all the other known heuristics when the proportion of couples is high

Remembering and Forgetting: Lizkor VeLishkoach for String Quartet, after Schubert

Lizkor VeLishkoach (to Remember and to Forget) is a piece that is to be played together with Franz Schubert’s Quartet in G Major D887. Lizkor VeLishkoach (hebrew for “to remember and to forget”) forms its meaning from the roots of the words of its title. The root of “lizkor” is “zekher”, which means both “memory” and “imprint.” Embedded within the verb “lishkoakh” is the word “koakh” meaning “power.” In this paper, I explore aspects of time, memory and place within my quartet, aspects that have become “imprinted” within a personal subjective and larger collective memory. Investigating my own reaction to Schubert’s quartet, I examine how its form and material is re-collected within my own composition. Retracing the re-membering of Schubert’s quartet, I also speculate about my own re-membering and forgetting within the context of this chosen form.Lizkor VeLishkoach est une pièce qui est conçue pour être au même programme que le Quatuor en sol majeur D887 de Franz Schubert. Lizkor VeLishkoach (qui signifie « Se souvenir et oublier » en hébreu) trouve tout son sens dans la racine des mots qui forment son titre. La racine de « lizkor » est « zekher », qui singnifie à la fois « mémoire » et « impression ». Le verbe « lishkoakh » contient le mot « koakh », qui singifie « pouvoir ». Dans cet article, l’auteur explore des aspects du temps, de la mémoire et du lieu auquels se rattache son quatuor, des aspects qui sont « imprimés » dans sa propre mémoire subjective, mais aussi dans une plus vaste mémoire collective. Analysant sa propre perception du quatuor de Schubert, il vérifie à quel point sa forme et son matériau sont réappropriés dans son oeuvre à lui. Retraçant les rappels au quatuor de Schubert, il spécule sur ses propres souvenirs et oublis dans le contexte de la forme choisie

Black hole horizons can hide positive heat capacity

Regarding the volume as independent thermodynamic variable we point out that black hole horizons can hide positive heat capacity and specific heat. Such horizons are mechanically marginal, but thermally stable. In the absence of a canonical volume definition, we consider various suggestions scaling differently with the horizon radius. Assuming Euler-homogeneity of the entropy, besides the Hawking temperature, a pressure and a corresponding work term render the equation of state at the horizon thermally stable for any meaningful volume concept that scales larger than the horizon area. When considering also a Stefan--Boltzmann radiation like equation of state at the horizon, only one possible solution emerges: the Christodoulou--Rovelli volume, scaling as $V\sim R^5$, with an entropy $S = \frac{8}{3}S_{BH}$.Comment: 5 pages, no figures, to be published in Phys. Lett.