An experimental comparison of a genetic algorithm and a hill-climber for term selection

Purpose – The term selection problem for selecting query terms in information filtering and routing has been investigated using hill-climbers of various kinds, largely through the Okapi experiments in the TREC series of conferences. Although these are simple deterministic approaches which examine the effect of changing the weight of one term at a time, they have been shown to improve the retrieval effectiveness of filtering queries in these TREC experiments. Hill-climbers are, however, likely to get trapped in local optima, and the use of more sophisticated local search techniques for this problem that attempt to break out of these optima are worth investigating. To this end, we apply a genetic algorithm (GA) to the same problem. Design/Methodology/Approach – We use a standard TREC test collection from the TREC-8 filtering track, recording mean average precision and recall measures to allow comparison between the hillclimber and GA algorithms. We also vary elements of the GA, such as probability of a word being included, probability of mutation and population size in order to measure the effect of these variables. Different strategies such as Elitist and Non-Elitist methods are used, as well as Roulette Wheel and Rank selection GA algorithms. Findings – The results of tests suggest that both techniques are, on average, better than the baseline, but the implemented GA does not match the overall performance of a hill-climber. The Rank selection algorithm does better on average than the Roulette Wheel algorithm. There is no evidence in this study that varying word inclusion probability, mutation probability or Elitist method make much difference to the overall results. Small population sizes do not appear to be as effective as larger population sizes. Research limitations/implications – The evidence provided here would suggest that being stuck in a local optima for the term selection optimization problem does not appear to be detrimental to the overall success of the hill-climber. The evidence from term rank order would appear to provide extra useful evidence which hill-climbers can use efficiently and effectively to narrow the search space. Originality/Value – The paper represents the first attempt to compare hill-climbers with GAs on a problem of this type

Personal circulation in the Dutch second chamber 1888-1993: towards institutionalization and professionalization and then?

Der vorliegenden Beitrag beschreibt die Institutionalisierung des niederländischen Parlaments (Zweite Kammer) hinsichtlich der Professionalisierung der Abgeordneten während des letzten Jahrhunderts anhand folgender Kategorien von Daten: die vorparlamentarischen Erfahrungen und Karrieren der Mitglieder, Alter und die Dauer der Amtsinhabe. Generell läßt sich folgende Entwicklung feststellen: bis Anfang des Zweiten Weltkriegs kann von einer 'Fossilisierung' des Parlaments im Sinne einer Honoratiorenpartei mit fast 'lebenslangen' Amtszeiten gesprochen werden. Diese Entwicklung ist seitdem stark rückläufig. Immer wichtiger werden die vor- und außerparlamentarischen Erfahrungen als Rekrutierungskriterium für die Abgeordneten. Dabei spielt die Parteikarriere die zunehmend entscheidende Rolle wie in allen westlichen modernen Demokratien. (pmb)'This article describes developments regarding institutionalization of the Dutch Second Chamber and professionalization of its members during a century, using two categories of data: on pre-parliamentarian political experience of the members on the one hand, on turnover, tenure and age at the other hand. Not all of the here investigated aspects lead to the same conclusion concerning the process of institutionalization. Institutionalization seems to be confirmed by the fact that the renewal rate points, in the postwar decades at least, more or less to some 'fossilization'. Tenure of parliamentary mandate, however, in the whole rather tends to decrease over time at least until the seventies. In these last decades the renewal rate no longer was as strongly connected to the mean age as before. Pre-parliamentary political experience has been an important recruiting factor during the entire period. While local political experience slightly decreases, party-experience among new members of parliament even increased since the thirties. MP's with previous political experience have been re-elected more frequently. Recent complaints about 'petrification' of parliament are less firmly grounded than supposed.' (author's abstract

Political-administrative elites in the Netherlands: profiles and perceptions

Der vorliegende Beitrag vergleicht die Karrieren der folgenden vier niederländischen politisch-administrativen Eliten: Mitglieder des Kabinetts, der Zweiten Kammer, hohe Beamte der Verwaltung und der Justiz seit dem Ende des Zweiten Weltkriegs. Aspekte ihres sozialen Hintergrunds, der politischen und professionellen Merkmale und die Wahrnehmung ihrer Rollen werden auf die Kompatibilität mit den generellen Rollenerwartungen an Elitepositionen verglichen. An Hand der verfügbaren Daten arbeitet die Autorin folgende Charakteristika heraus: eine ausgeprägt maskuline Kultur der Umgangsformen, eine weitgehende Selbstrekrutierung der Eliten und weitgehend ähnliche Muster im den Berufskarrieren. Die Öffnung der relative gegeneinander abgeschlossenen Eliten füreinander und die fortschreitende Professionalisierung der Ämter und Positionen hat den Trend zur Angleichung der Karrieremuster in den letzten Jahren noch verstärkt. (ICE)'The purpose of this article is a comparison of four Dutch political-administrative elites, i.e. Members of Cabinets and of the Second Chamber, high level civil servants members of the Judiciary since the last half century. The article investigates some aspects of their social background, political and professional background and some role perceptions, in order to see whether cohesive behaviour is to be expected, taking common background characteristics as indicators. Some commonly shared features have been traced: a hitherto mainly masculine culture, (not exclusively) high social origins, similar occupational patterns in bureaucracy, at the bar and in universities. Proportionally less higher bureaucrats had received an academic education. Judges counted relatively more catholics than the other elites did. Notwithstanding these and other dissimilarities cohesive behaviour patterns can be discerned more clearly between the two political elites and the bureaucrats than compared to the fourth depicted elite, the judiciary. However, recently introduced new rules of external recruitment of magistrates tend to a growing professional and political congruence between all four elites. A solid basis for cohesive and cooperational behaviour seems at hand.' (author's abstract

Scattering hypervolume for ultracold bosons from weak to strong interactions

The elastic scattering properties of three bosons at low energy enter the many-body description of ultracold Bose gases via the three-body scattering hypervolume $D$. We study this quantity for identical bosons that interact via a pairwise finite-range potential. Our calculations cover the regime from strongly repulsive potentials towards attractive potentials supporting multiple two-body bound states and are consistent with the few existing predictions for $D$. We present the first numerical confirmation of the universal predictions for $D$ in the strongly interacting regime, where Efimov physics dominates, for a local nonzero-range potential. Our findings highlight how $D$ is influenced by three-body quasibound states with strong $d$-wave or $g$-wave characteristics in the weakly interacting regime.Comment: 13 pages, 8 figure

The multichannel nature of three-body recombination for ultracold 39^{39}K

We develop a full multichannel spin model in momentum space to investigate three-body recombination of identical alkali-metal atoms colliding in a magnetic field. The model combines the exact three-atom spin structure and realistic pairwise atom-atom interactions. By neglecting the interaction between two particles when the spectating particle is not in its initial spin state we arrive at an approximate model. With this approximate model we achieve excellent agreement with the recent precise measurement of the ground Efimov resonance position in potassium-39 close to 33.58 G [Chapurin $et$ $al$., Phys. Rev. Lett. 123, 233402 (2019)]. We analyze the limitations of our approximation by comparing to the numerical results for the full system and find that it breaks down for Feshbach resonances at larger magnetic fields in the same spin channel. There the relevant three-body closed channel thresholds are much closer to the open channel threshold, which enhances the corresponding multichannel couplings. Therefore the neglected components of the interaction should be included for those Feshbach resonances

Enhancing teaching and learning at UCL: the Access to Core Course Materials Project and the Key Skills Web Development Project

Reports on two projects at University College London (UCL) involving collaboration between information specialists and academic departments to support the university’s Learning and Teaching strategy. The Access Project is developing an electronic course materials system, and the Key Skills Web Development project is delivering customised skills resource material online

Still dreaming: service users' employment, education & training goals

Background: Enabling service users to find and keep real jobs is a significant strand of UK mental health policy. An evidence-based approach to employment support is well documented, but is not widely implemented in the UK. Aim: To inform the development of vocational services in South Essex by ascertaining service users' employment, education and training goals. Method: Face-to-face interviews with a randomly selected sample of service users on enhanced CPA carried out by a team of service user researchers using an adapted version of a questionnaire developed for a previous similar survey. A postal survey of a further randomly selected sample of service users on enhanced CPA using a brief version of the questionnaire was also carried out. Results: Interviews were carried out with 82 service users. A further 159 returned a postal questionnaire. 42.7% had no regular day time activity. Only 15% were in paid work. 60.6% were definitely interested in finding work. Seventy-seven percent of respondents to the interviews who were interested in work were not currently receiving support to achieve this. The main help wanted was support in work, help with mental health problems and benefits advice. The main barriers identified were employers' attitudes and threat to benefits. Service user researchers reported benefits from undertaking the work. Conclusions: High numbers of mental health service users are interested in pursuing employment, education or training goals but currently lack the support they need to do so. Implementation of an evidence-based approach to employment support has the potential to enable service users to achieve their goals. Service users are well able to undertake research with considerable benefits for themselves and other stakeholders

Probability and consequences of a rapid boron dilution sequence in a PWR

The reactor restart scenario is one of several beyond-design-basis events in a pressurized water reactor (PWR) which can lead to rapid boron dilution in the core. This in turn can lead to a power excursion and the potential for fuel damage. A probabilistic analysis had been done for this event for a European PWR. The estimated core damage frequency was found to be high partially because of a high frequency for a LOOP and assumptions regarding operator actions. As a result, a program of analysis and experiment was initiated and corrective actions were taken. A system was installed so that the suction of the charging pumps would switch to the highly borated refueling water storage tank (RWST) when there was a trip of the RCPs. This was felt to reduce the estimated core damage frequency to an acceptable level. In the US, this original study prompted the Nuclear Regulatory Commission to issue an information notice to follow work being done in this area and to initiate studies such as the work at BNL reported herein. In order to see if the core damage frequency might be as high in US plants, a probabilistic assessment of this scenario was done for three plants. Two important conservative assumptions in this analysis were that (1) the mixing of the injectant was insignificant and (2) fuel damage occurs when the slug passes through the core. In order to study the first assumption, analysis was carried out for two of the plants using a mixing model. The second assumption was studied by calculating the neutronic response of the core to a slug of deborated water for one of the plants. All three types of analyses are summarized below. More information is available in the original report