Influence of heterogeneous and anisotropic tissue conductivity on electric field distribution in deep brain stimulation The aim was to quantify the influence of heterogeneous isotropic and heterogeneous anisotropic tissue on the spatial distribution of the electric field during deep brain stimulation (DBS). Three finite element tissue models were created of one patient treated with DBS. Tissue conductivity was modelled as (I) homogeneous isotropic, (II) heterogeneous isotropic based on MRI, and (III) heterogeneous anisotropic based on diffusion tensor MRI. Modelled DBS electrodes were positioned in the subthalamic area, the pallidum, and the internal capsule in each tissue model. Electric fields generated during DBS were simulated for each model and target-combination and visualized with isolevels at 0.20 (inner), and 0.05 V mm -1 (outer). Statistical and vector analysis was used for evaluation of the distribution of the electric field. Heterogeneous isotropic tissue altered the spatial distribution of the electric field by up to 4% at inner, and up to 10% at outer isolevel. Heterogeneous anisotropic tissue influenced the distribution of the electric field by up to 18 and 15% at each isolevel, respectively. The influence of heterogeneous and anisotropic tissue on the electric field may be clinically relevant in anatomic regions that are functionally subdivided and surrounded by multiple fibres of passage. Deep brain stimulation (DBS) is a widely used therapy for selected patients with severe Parkinson's disease (PD), essential tremor, and primary dystonia. The overall clinical outcome of DBS depends on several biological variables such as severity of disease, duration of disease since the onset of symptoms, type of symptoms, and drug sensibility [1] [2] [3] . DBS acts as a local delivery treatment and so is dependent on the volume of tissue influenced by the stimulation [4] . Thus, knowledge of the anatomical distribution of electric field generated during DBS is crucial for maximizing the therapeutic effects of this therapy. Several technical aids for pre-, intra-, and post-surgery are currently being developed and enhanced [5] . An example is patient-specific computer simulations of the electric field generated during DBS [6, 7] . Å ström et al. [6, 8] , have previously used pre-and postoperative MRI acquired during the planning and the postoperative follow-up of the surgical DBS procedure for creating patient-specific models and simulations of DBS. Brain tissue is classified in the MRI and material properties from the literature are allotted to each classified MRI-voxel. However, models based on regular MRI neglect the directional dependency, the anisotropy, of the electrical conductivity of brain tissue. The impedance of myelinated fibre bundles in the internal capsule of a cat has been measured to be approximately nine times greater perpendicular to the axonal fibres than M. Å ström (&) Á K. Wårdell Department of Biomedical Engineering, Linköping University, 581 85 Linköping, Sweden e-mail: matas@imt.liu.se along these fibres [9] . Sotiropoulos and Steinmetz [10] incorporated non patient-specific heterogeneous and anisotropic tissue for simulations of DBS in the subthalamic nucleus (STN). It has been suggested by Tuch and co-workers [11] [12] [13] that diffusion tensor magnetic resonance imaging (DTI) can be used to calculate anisotropic electrical conductivity tensors in patient-specific anatomy. The basis for a general relationship between diffusion of water and electrical conductivity in biological tissue is the mutual geometrical restrictions for both ionic and water mobility [12] . Because of the effective electrical shielding of the neuronal membranes, both the electric conductivity and water diffusion are primarily mediated in the extracellular pathways. This predicts a linear scaling relationship between water diffusion and electrical conductivity. Walackier et al. [14] have previously created DBS models based on patient DTI, and Butson et al. [7, 15] created a finite element tissue model based on a DTI atlas that has been fitted to patient-specific anatomy. This approach has recently been used to study the influence of different model complexity on neural activation [16] . In this study patientspecific stereotactic MRI, and DTI acquired during the surgical DBS procedure was used to create patient-specific models of the brain. The overall aim was to quantify the influence of heterogeneous isotropic and heterogeneous anisotropic tissue on the spatial distribution of the electric field during DBS by means of patient-specific models and simulations. Heterogeneous isotropic tissue altered the spatial distribution of the electric field by up to 4% at the 0.20 V mm -1 isolevel, and up to 10% at the 0.05 V mm -1 isolevel in certain directions. Heterogeneous anisotropic tissue had a larger impact on the distribution of the electric field with an influence of up to 18 and 15% at the 0.20 and 0.05 V mm -1 isolevel, respectively. The influence of heterogeneous and anisotropic tissue on the electric field may have a clinical relevance, especially in anatomic regions that are functionally subdivided and surrounded by multiple fibres of passage such as the subthalamic area. At this point patient-specific models based on either MRI or DTI data are suitable for presenting a rough estimation of the spatial distribution of the electric field in the anatomy. In this study the influence of heterogeneous and anisotropic tissue on the spatial distribution of the electric field during DBS was quantified and compared by means of patientspecific computer models and simulations in realistic DBS targets. The inner and outer isolevel (0.20 and 0.05 V mm -1 ) were altered (reduced or extended) in various directions compared to baseline model. In Model II, the alteration of the inner and outer isolevel diameter in various directions was up to 4 and 10%, respectively. In Model III the corresponding values were up to 18 and 15%, respectively.. Electric field isolevels were visualized and not the response of neural tissue as calculated by the activating function [23] commonly used by others [7, 16, 24] . This was an intentional choice in order to present the results in a general manner without restricting the interpretation of the results to specific axon orientations and diameters, along with additional assumptions regarding the electrode encapsulation tissue [25] and the voltage drop at the electrode-tissue interface [26] . Angles in degrees were calculated between corresponding vectors of Model II and III, and baseline model (Model I). Large angles correspond to large differences in the shape of the electric field compared to baseline model The effect on the electric field was specific to each anatomic region and also to each hemisphere. A combination of MRI and DTI data together with simulated electric field provided a detailed visual feed-back of anatomy, microstructure, and electric field during DBS. In Model III, the distribution of the electric field was finely tuned with respect to the tissue microstructure as presented by the superquadric glyphs (Fig. 5) . Thus, the orientation and shape of the superquadric glyphs may provide an indication of the spatial distribution of the electric field, even without simulations of the electric field.. The electric field was measured at two different isolevels, inner and outer, in order to evaluate the influence of heterogeneous and anisotropic tissue on the electric field at different distances away from the electrode. The inner and outer isolevels were located approximately 2.7 and 6.1 mm away from the surface of the active electrode contact.. Although the exact volume of neural tissue influenced during DBS is not known, the radial distance to the outer isolevel is considered to be outside the region where the major effect is taking place during stimulation at -3 V [27, 28] . The distance to the inner isolevel, however, may be regarded as within or at the border of the region of influence during standard DBS settings [29] . Thus, although the influence of heterogeneous and anisotropic tissue on the electric field was generally in the sub-millimetre level there were cases where the electric field diameter was altered by up to 1.2 mm at the inner isolevel (Table 4) . Such alterations may possibly have an impact on the clinical outcome during DBS because of modulation of the activity of neurons within the targeted nucleus as well as neighbouring myelinated fibres. This could be the case when targeting the subthalamus area, where STN is subdivided into different functional parts and surrounded and crossed by several fibre paths such as the ansa lenticularis and the superior thalamic radiations. In comparison it is well known that changing the active contact of Medtronic's model 3389 DBS TM Lead to a more superior or inferior contact, and thereby moving the current source by 2 mm, may result in a different clinical outcome.. The analysis of the effect of heterogeneous isotropic and heterogeneous anisotropic tissue on the spatial distribution of the electric field during DBS was limited by several reasons. Only nine diameters were measured of each electric field isolevel which does not provide a full representation of its spatial distribution. Patient-specific models based on DTI [30, 31] or MRI [8] have already been used in clinical investigations. However, the realism of models based on DTI or MRI are limited by several, but different factors. The major limitations of models based on MRI are the isotropic representation of the tissue-medium and the variations in the measured electrical conductivity of brain tissue found in the literature. The conductivity of grey and white matter tissue is dependent on frequency and measurements are substantially different in the literature. Tissue conductivity from standard references such as Geddes and Baker [32] or Schwan and Kay [33] are measured in tissue samples at frequencies way beyond standard DBS frequencies. Other factors that may influence measurements In model III, which was based on DTI, the electric field was further extended in the direction of the main axis of the superquadric glyphs and compressed perpendicular to the main axis performed in vivo is the tissue temperature, bleeding, leakage of CSF, decreased blood-flow due to anaesthetic agents, or increased pressure caused by the probe [34] . In addition, Hemm et al. [35] showed significant individual variations between patients during impedance measurements in the pallidum. In 1996, Gabriel et al. [36] extracted dielectric properties of tissues from the literature of the past five decades. These values together with new measurements [37] were used to described dielectric tissue properties for any frequency in the range of 10 Hz-100 GHz [38] . The data was made available online by Andreuccetti et al. [17] [39] . A major limitation of models based on DTI is the lowimage resolution in relation to the targeted anatomic regions. In addition, the performance of DTI is still limited in regions of crossing fibres because of multiple intra-voxel orientations [40] . As previously mentioned, a strong linear relationship between tissue electric conductivity and DTI was indicated by Tuch et al. [11] . However, this relationship has not been thoroughly evaluated, and in particular it has not been evaluated for different frequencies.. In addition to the tissue electrical conductivity there are other factors that may influence the outcome of DBS simulations. Butson et al. [25] evaluated the effects of various electrical tissue properties and electrode-tissue interface during DBS. Wei and Grill [41] , used finite element models to study the effects of varying electrode characteristics on the current density and field distributions in an idealized electrolytic medium. Yousif et al. [26] simulated the electric field during DBS for investigation of the voltage drop at the electrode-tissue interface at the acute, transitional, and chronic post-implantation stages of DBS. Johnson and McIntyre [42] used general finite element models together with a more detailed neuron model to examined how various stimulation paradigms affected the neural output of the pallidum, and the resulting stimulation-induced network-effects within the basal ganglia. The influence of electrode and tissue capacitance on the volume of tissue activated has previously been studied where inclusion of a capacitance of 3.3 lF had a minor effect on the stimulation waveform [24, 43] . During model-based investigations of DBS all of these factors may influence the results.. DTI is performed in some institutions in order to analyse white matter fascicles when planning trajectories during primary anatomical targeting during DBS [44] . However, a complicating factor of using DTI for patient-specific investigations is that it is not acquired on routine during DBS surgery in many clinics and therefore not available for multi-patient studies. In this study only one patient was included. Simulations were carried out bilaterally in three different anatomic regions for three different tissue models with a total of 162 measurements. Owing to the small size of the study care should be exercised in drawing general conclusion from these results. The spatial distribution of the electric field was mainly affected by the tissue within a few millimetres away from the electrode. Thus, a slight adjustment of the electrode locations would affect the results. In addition, stimulation with other electrode configurations such as bipolar or tripolar would generate a spatial distribution of the electric field different from that of monopolar stimulation. In addition, if more patients were studied the results would be affected by inter-subject anatomic variability.. In view of the anisotropic information provided by the DTI it may be suggested that DBS models based on DTI are more realistic than models based on anatomical MRI. However, this may not always be evident when the larger voxel volume of the DTI is taken into consideration. In this study, the voxel volume of DTI was approximately 17 times larger than for MRI (9.72 vs. 0.56 mm 3 ). For instance, previous studies by our group have shown that small cerebrospinal fluid (CSF) filled cystic cavities that may be visible in the MRI but not in the DTI can have substantial impact on the electric field because of the approximately 20 times larger conductivity of CSF than grey matter [45] . Thus, under such conditions tissue models based on DTI may not always be more realistic than tissue models based on MRI. Owing to the known and unknown limitations patient-specific computer models based on either structural MRI or DTI may be appropriate as long as the result is considered on a rough level. Patient-specific MRI and DTI data were visualized on axial and coronal slices together with contours of the inner and outer isolevels in the SubT, GPi, and IC (Fig. 4) . We found that the spatial distribution of the electric field was altered by the heterogeneous isotropic (Model II) and heterogeneous anisotropic (Model III) tissue compared to baseline model (Model I). In general, vector analysis showed that the shape of the electric field isolevel was altered to a smaller extent in Model II than in Model III (Table 2 ). In Fig. 4 Simulated electric field isolevels at 0.20 and 0.05 V mm -1 presented on axial (left column) and coronal (right column) MRI slices. Simulations were performed within the dorso-lateral-STNsubthalamic-area (SubT), pallidum (GPi), and the foremost part of anterior limb of the internal capsule (IC) for tissue Model I (white), Model II (red), and Model III (yellow). DTI was displayed with colourcoded superquadric glyphs from blue, isotropic, to red highly anisotropic. The superquadric glyphs were intersected at their centre by the MRI slice showing the structural anatomy. The level of the axial and coronal MRI and superquadric glyphs was chosen as a compromise between closest to the active electrode contacts of the left and right electrodes (colour figure online) tissue Model II the mean angles for all anatomic regions were 0.8, and 1.8°at the inner and outer isolevels, respectively. In Model III the corresponding angles were 3.1 and 3.0°. The influence of heterogeneous and anisotropic tissue on the electric field varied in different anatomic regions. Vector analysis showed largest angles in GPi for both Model II and III, at both isolevels.. In agreement with the vector analysis, the descriptive statistics showed lower standard deviations of the measured diameters in Model II than in Model III (Table 3 ). In tissue Model II the mean standard deviation for all anatomic regions were 0.12, and 0.41 mm at the inner and outer isolevels, respectively. In Model III the corresponding values were 0.39 and 0.75 mm.. The diameters of Model II and III were directly compared with the corresponding diameters of baseline model by calculating the mean, minimum, and maximum of the diameters differences (Table 4 ). In general, Model II showed smaller diameters differences than Model III. The minimum and maximum differences of Model II were (-0.2, 0.3) and (-1.3, 1.1) mm at the inner and outer isolevels, respectively. Expressed as a percentage of the mean diameter of baseline model for each isolevel (6.7 and 13.4 mm, respectively) this corresponded to (-3, 4%) and (-10, 8%). In Model III the corresponding values were (-0.5, 1.2), and (-1.8, 2.0) mm. Expressed as a percentage this corresponded to (-7, 18%), and (-13, 15%).. In Model III, anisotropic tissue had a marked directional influence on the electric field. Largest diameter difference compared to baseline model was 1.2 and 2.0 mm at the inner and outer isolevels, and was found in the right GPi parallel to the internal capsule, direction xz. The alterations of the electric field were related to the tissue micro-structure as presented by the superquadric glyphs. Because of linear anisotropy in this region, the electric field was further extended in the direction of the main axis of the conductivity tensor, and compressed perpendicular to the main axis (Fig. 5) .

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Modeling Wikipedia admin elections using multidimensional behavioral social networks Abstract Wikipedia admins are editors entrusted with special privileges and duties, responsible for the community management of Wikipedia. They are elected using a special procedure defined by the Wikipedia community, called Request for Adminship (RfA). Because of the growing amount of management work (quality control, coordination, maintenance) on the Wikipedia, the importance of admins is growing. At the same time, there exists evidence that the admin community is growing more slowly than expected. We present an analysis of the RfA procedure in the Polish-language Wikipedia, since the procedure's introduction in 2005. With the goal of discovering good candidates for new admins that could be accepted by the community, we model the admin elections using multidimensional behavioral social networks derived from the Wikipedia edit history. We find that we can classify the votes in the RfA procedures using this model with an accuracy level that should be sufficient to recommend candidates. We also propose and verify interpretations of the dimensions of the social network. We find that one of the dimensions, based on discussion on Wikipedia talk pages, can be validly interpreted as acquaintance among editors, and discuss the relevance of this dimension to the admin elections. Wikipedia is one of the most popular websites on the Internet. It is a collaborative effort to organize and present human knowledge, similarly to traditional encyclopedias. Its most distinctive feature is the fact that anyone may edit the content. Thanks to the Wiki technology, anyone may become the editor. This fact causes the sustained growth of Wikipedia (Spinellis and Louridas 2008) , but also possible scalability problems in the future.. Nowadays in the Web 2.0 era, there are a lot of sites where user contributed content plays a major role. Many other public Wiki sites may face similar problems as Wikipedia. Due to Wikipedia's openess and lack of centralized supervision, authors need to overcome problems, that are not found in editing of traditional encyclopedias.. The most notable example is vandalism, which is mostly the deliberate deletion of content or putting false or irrelevant information. The effect of vandalizing Wikipedia may have serious consequences for real people, especially when a biographical article becomes vandalized. While the global impact of this kind of damage is rather low, it is rising (Priedhorsky et al. 2007) . Even though the anti-vandalism bots created to automatically prevent the damage do a good job, there is always the need of human reviewers.. Another problem connected with lack of central supervision arises when editors have different points of view which may result in an edit war, when two or more contributors or groups try to enforce their version of the article. This violates one of the key Wikipedia rules, which mandates the contributors to keep a neutral point of view. Viégas et al. (2004) noted that edit wars are a threat not only for controversial articles.. The mentioned problems are caused mostly by human factors and at least some of their instances cannot be resolved without another human intervention. This is the role of administrators to constantly monitor Wikipedia and make sure that rules established by the community are obeyed. In this article, we have studied the Request for Adminship votes on the Polish-language Wikipedia. We have noticed the decreasing amount of successful admin elections and have formulated two hypotheses that could explain this phenomenon. Hypothesis A stated that new admins are elected on the basis of acquaintance of the voter and candidate. If this would be a valid explanation, we could conclude that the community of admins is becoming increasingly closed, which would be detrimental to the sustainable development of the Wikipedia.. Hypothesis B stated that new admins are elected on the basis of similarity of experience in editing various topics of the voter and candidate. Since voters are other active admins whose experience increases with time, their thresholds of accepting a candidate are likely to increase (as has been observed from the simple statistics of RfA votings).. It should be possible to improve the likelihood of electing new, good admins by changing the criteria of nomination for the RfA procedure. Currently, these criteria are based just on the number of edits and are much lower than the real thresholds of candidate acceptance. Our research suggests that there could be two criteria: one based on the number of edits, the other based on edit diversity (measured by the number of topical categories in which a candidate has edited). It would also be possible to use automatic classification based on the MBSN to recommend candidates with a high likelihood of acceptance (based on past votes). The recommendation could be made in an impartial manner (not depending on the identity of the voter) by using only variables based on the Topics dimension of the MBSN.. In order to validate the two hypotheses, we have used the Multidimensional Behavioral Social Network created from edit history of the Polish-language Wikipedia. The MBSN network can be used as a general model of the Wikipedia knowledge community and is versatile enough to model various social phenomena, such as teamwork (Turek et al. 2010 . This article shows that the MBSN can also model admin elections. A data mining model for classifying RfA votes for and against a candidate has been based mostly on variables derived from the MBSN. The model has an accuracy which of about 84 %, which should be sufficient to recommend good candidates for elections.. A variable which expresses the number of common topics in which both the voter and the candidate have edited has been found to be highly important in decision trees for classifying votes. This observation validates the hypothesis B: similarity of experience in editing various topics among the voter and the candidate significantly increases the likelihood of a vote for that candidate. On the other hand, the same does not hold for a variable derived from the Discussion dimension of the MBSN (based on close edits on Wikipedia talk pages) by selecting the strongest relations. We have used a survey of Wikipedia editors that supports the interpretation of such strong relations in the Discussion dimension as real acquaintance among editors. Because of this fact, we claim that hypothesis A does not hold: acquaintance of the voter and candidate does not play a significant role in the RfA votings. This is fortunate and shows that the admin elections are open to new candidates outside the acquaintances of current admins. The increase in acceptance criteria is not a sign of a closing community of admins.. The sustainable development of the Wikipedia is of importance to all Internet users worldwide. Our study of the Polish-language Wikipedia shows that it is possible to understand and model the process of electing new admins, who play a critical role in maintaining and increasing the quality of the Wikipedia. It should also be able to support that process by recommending new candidates based on edit history. We hope that these contributions can play a small role in supporting Wikipedia development. To calculate edge strength in the Discussion network we looked at the articles' and users' talk pages. The measure is proportional to the amount of text added by one author next (that is in response) to the text written by the other author. Activity on talk pages has been used in the literature to evaluate the amount of collaboration between editors. We hypothesize that the Discussion network may be interpreted as the social relation of acquaintance.. The strength of a discussion edge between authors A 1 and A 2 is given by: Discussion(A 1 -[ A 2 ) = count(w) where word w is written by A 1 after the text by A 2 but no further than discussion_distance words away. discussion_distance is a parameter with a typical value of 20.. A typical case for the discussion on talk pages is that at least 20 words are written by each participant. However, increasing the discussion_distance parameter would result in ignoring shorter exchanges. The effect is that typically, after each exchange between authors A 1 and A 2 , the value of the strength of the edge in the discussion network between them increases stepwise by 210 = P i=1 20 i. Wikipedia has been a subject of several studies in the past few years. Most notable example of research topic is assessing content quality (Priedhorsky et al. 2007; Adler et al. 2008; Vuong et al. 2008; Zhang et al. 2010) . The trustworthiness of Wikipedia is one of the key concerns related to its usefulness and generally, success.. The problem of recommending and evaluating candidates for administrators has not been extensively studied, but this topic is slowly growing in popularity. The most similar work that we have found is (Burke and Kraut 2008) . The authors present an idea of recommending and evaluating candidates for administrators based on behavioral data and comments, not the page text. They counted each candidate's edits in various namespaces (article, article talk, Wikipedia, Wikipedia talk, Wiki projects etc.) to calculate total contribution as well as contribution diversity. They also measured user interaction, mainly activity on talk pages, but also participation on arbitration or meditation committee pages and a few others. There are also several other statistics, but the ones mentioned seemed to be the most relevant to the candidate's success. Especially successful were candidates with strong edit diversity, mere edits in Wikipedia articles did not add much more chance of success. In user interactions, article talk page edits were the best predictor of success, with other authors talk page edits being rather poor. Authors also confirmed Kittur et al.'s (2007) results that the percentage of indirect work (coordination, discussion, etc.) grows over time, the share of articles in all Wikipedia edits is decreasing.. The problem of evaluating voters and candidates has been also studied in the social context in (Leskovec et al. 2010) . The authors found out that the probability of one person's vote to be positive is correlated with the basic relative figures such as: who-voter or candidate has more edits, who has more barnstars (awards given by other Wikipedia users), the extent of collaboration of the two, etc. Authors strongly noted that the vote value (positive or negative) is not just a function of candidate, but both voter and candidate. They also studied the relationship between past votes (which are public) and next votes given by other voters. The ''response function'' (function estimating vote value based on voter and previously cast votes) varied from one user to another. This suggests that each voter has a certain policy of looking or not looking at previous votes.. Multidimensional social networks have been studied in the work of Kazienko et al. (2011) , Kennedy (2009) and Rodriguez and Shinavier (2009) .

O B O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Methodologies for the analysis and classification of PET neuroimages Abstract Neuroimaging analysis aims to support clinicians in the diagnosis of neurological diseases by using radiological images. Positron emission tomography (PET) is a nuclear medicine imaging technique used to produce threedimensional images of the human brain for neurological studies. Due to the large number of generated images, there is a lot of effort in defining computer based tools to analyze and classify brain images. Such analyses are used to identify cerebral regions of interest (ROI) related to specific neurodegenerative diseases. Statistical tools, such as SPM (for Statistical Parametric Mapping) and its MarsBar plugin, are largely used by physicians for ROIs identification and for image analysis. Nevertheless, large datasets analysis (e.g. studying pathologies for many patients and for large sets of PET images) requires repetitive SPM procedures for each patient's image, mainly due to the lack of (i) automatic procedures for analysing set of patients, and (ii) validation of using SPM versus patient magnetic resonance as reference brain templates. Finally, SPM analysis requires human intervention, and there is no automatic system guiding physicians for pathologies identification. As a contribution for the latter issue, we defined an automatic classification tool using topological relations among ROIs to support physicians while studying a new patient. Starting from a set of known pathologies associated to medical annotated PET images (i.e. associated to neurological pathologies), we used SPM and MarsBaR tools to define a reference PET images dataset; ROIs extracted from input PET images have been compared with known dataset and classified, suggesting physicians with (a subset of) pathologies associated to those PET images. Experiments showed that the classifier performs well. Moreover, in order to improve the repeatability of experiments with large datasets, we use an SPM plugin called AutoSPET, which allows to perform SPM analysis on a large PET images dataset, using different SPM plugins within a unified user interface, and allowing to simply run statistical analyses. AutoSPET is available on our server and also as an SPM plugin on the SPM website. Finally we report experiments to validate the use of the standard T1 SPM template versus the magnetic resonance ones. We developed an algorithm for disease classification based on region of interests extracted from PET images. The experiments show interesting results for a semi automatic process to support physicians in images analysis and diseases identification. Moreover, we performed statistical analysis on PET images relative to different diseases, and we tested the reliability of T1 SPM template, as reference space for PET image analysis, with respect to magnetic resonances (MR). Finally, by using AutoSPET it is possible to perform and repeat experiments several times avoiding manual invocation of SPM and Matlab interfaces. Methodologies for the analysis and classification of PET neuroimages 207

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A memetic algorithm for graph coloring Given an undirected graph G = (V, E) with a set V of vertices and a set E of edges, the graph coloring problem consists of partitioning all vertices into k independent sets and the number of used colors k is minimized. This paper presents a memetic algorithm (denoted by MACOL) for solving the problem of graph coloring. The proposed MACOL algorithm integrates several distinguished features such as an adaptive multi-parent crossover (AMPaX) operator and a distance-and-quality based replacement criterion for pool updating. The proposed algorithm is evaluated on the DIMACS challenge benchmarks and computational results show that the proposed MACOL algorithm achieves highly competitive results, compared with 11 state-of-the-art algorithms. The influence of some ingredients of MACOL on its performance is also analyzed. Given an undirected graph G = (V, E) with a set V of vertices and a set E of edges, a legal k-coloring of G corresponds to a partition of V into k independent sets where an independent set is a subset of non-adjacent vertices of G. Graph coloring aims at finding the smallest k for a given graph G (its chromatic number χ(G)) such that G has a legal k-coloring.. Besides its theoretical significance as a canonical NP-Hard problem [19] , graph coloring arises naturally in a variety of real-world applications, such as register allocation [7] , timetabling [4] , frequency assignment [37] , crew scheduling [17] , printed circuit testing [18] , satellite range scheduling [38] as well as manufacturing [20] . Due to its NP-Hardness, heuristics and metaheuristics are Email addresses: zhipeng.lui@gmail.com, lu@info.univ-angers.fr (Zhipeng Lü), hao@info.univ-angers.fr (Jin-Kao Hao).. preferred to handle large and hard coloring problems. We briefly review below some of the most representative algorithms.. The first heuristic approaches to solving the graph coloring problem were based on greedy construction, which color the vertices of the graph one by one guided by a predefined greedy function. These algorithms are very fast by nature but their quality is generally unsatisfactory. The best known algorithms in this class are the largest saturation degree heuristic (DSATUR) [3] and the recursive largest first heuristic (RLF) [28] . In recent decades, these greedy constructive heuristics are often used to generate initial solutions for advanced metaheuristic algorithms.. On the other hand, local search based metaheuristic algorithms have been widely used to tackle the graph coloring problem in recent decades. One representative example is the so-called Tabucol algorithm which is the first application of Tabu Search to graph coloring [23] . Tabucol has been latter improved by several researchers and used as subcomponent of more elaborate coloring algorithms (see for examples [8, 11, 14] ). Other local search metaheuristic methods include Simulated Annealing [5, 25] , Iterated Local Search [6] , Reactive Partial Tabu Search [2] , GRASP [27] , Variable Neighborhood Search [1] , Variable Space Search [24] and Clustering-Guided Tabu Search [35] . Interested readers are referred to [15] for a comprehensive survey of the local search approaches for graph coloring presented in recent years.. In parallel, researchers have also proposed other different approaches for solving the graph coloring problem, especially for tackling some large random graphs. One of the most recent and very promising approaches is based upon hybridization that embeds a local search algorithm into the framework of an evolutionary algorithm in order to achieve a better tradeoff between intensification and diversification (see for examples [9, 14, 16, 29, 34] ).. Another approach for dealing with large graphs is to first extract several large independent sets and then solve the residual graph. This approach is particularly useful for very large graphs (see for example [12] ) and can be employed as a pre-processing step for other search algorithms. This paper presents MACOL, a hybrid metaheuristic algorithm integrating a tabu search procedure with an evolutionary algorithm for solving the graph coloring problem. In this algorithm, we highlight the importance of the diversity of individuals and the balance between intensification and diversification. To achieve this goal, we devise an adaptive multi-parent crossover operator, which is an extension of the greedy partition crossover (GPX) presented in [14] . Furthermore, we highlight the diversity of the population by defining a new replacement criterion for the population updating. This replacement criterion takes into account both the quality and the diversity among individuals.. Experiments are presented on the set of DIMACS challenge benchmark graphs, showing the proposed algorithm achieves very competitive results matching many and improving some previous best solutions. Furthermore, we carefully analyze the influence of some critical components of the proposed hybrid algorithm, showing the essential factors of the proposed algorithm and shedding light on the possible ways to further improve its performance.. The rest of this paper is organized as follows. Section 2 describes the general framework and each main component of the proposed MACOL algorithm. In Section 3 computational results are presented and compared with 11 stateof-the-art algorithms in the literature. Section 4 investigates several essential parts of the proposed memetic algorithm, followed by some conclusions. In this paper, we have presented MACOL, a memetic algorithm for the graph coloring problem. The proposed algorithm integrates a number of original features. First, we have proposed an Adaptive Multi-Parent crossover operator. Second, based on the definition of the distance between two k-colorings, we introduced the distance between a k-coloring and a population. Third, we proposed a new goodness score function considering both solution quality and diversity of individuals. These strategies provide the algorithm with a good tradeoff between intensification and diversification.. We have shown that this hybrid heuristic obtains highly competitive results on a large number of DIMACS challenge benchmark graphs. Compared with a number of reference algorithms, our MACOL algorithm is quite effective and has a robust behavior on all the considered instances.. Additionally, we investigated several essential parts of our proposed algorithm. We first carried out experiments to demonstrate that the multi-parent crossover is more powerful than the traditional 2-parent crossover in this context. Moreover, we showed that the proposed distance-and-quality based goodness score function for pool updating is quite useful.. The success of the MACOL algorithm on graph coloring problem reminds us that it is essential to introduce meaningful diversification mechanisms and highlight the tradeoff between intensification and diversification in designing heuristic search algorithms. Following this spirit, we hope to design even more robust and effective heuristic algorithms for solving graph coloring problem and other optimization problems. Table 4 Computational results of MACOL algorithm on the easy DIMACS benchmarks

O B I O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O


An evaluation of keyword, string similarity and very shallow syntactic matching for a university admissions processing infobot Abstract. "Infobots" are small-scale natural language question answering systems drawing inspiration from ELIZA-type systems. Their key distinguishing feature is the extraction of meaning from users' queries without the use of syntactic or semantic representations. Three approaches to identifying the users' intended meanings were investigated: keywordbased systems, Jaro-based string similarity algorithms and matching based on very shallow syntactic analysis. These were measured against a corpus of queries contributed by users of a WWW-hosted infobot for responding to questions about applications to MSc courses. The most effective system was Jaro with stemmed input (78.57%). It also was able to process ungrammatical input and offer scalability. University student recruitment administration is an application where there is potential for a large volume of enquiries of a fairly routine and predictable nature from a world-wide pool of applicants. The costs of call centres (both in terms of running the centres and recruiting and retaining a knowledgeable workforce) make such ventures unattractive. On the other hand, it should be possible to implement a technological solution beyond adding over-large FAQs to web pages. The amount and breadth of information required to answer the applicants' questions would require a large number of long FAQs with quite possibly a complex net of interrelations.. Student recruitment, particularly at graduate level, is international in outlook: in UK postgraduate computing degrees, it is not unusual for international students to outnumber UK students by two to one. Communicating with international applicants brings with it all the problems of understanding versions of English that can vary from the excellent to the less than adequate. Most applicants have a strong commitment to accessing the information that they need to be able to make a choice of what and where to study. Varying language capabilities notwithstanding, many applicants are very articulate (and so able to frame precise requests for information) and discriminating in making their choices based on that information. Although universities work hard at providing prospectus information that ranges from detail of the structure of courses to the accommodation packages and sports facilities available, many applicants still find themselves wanting to ask highly targeted questions about, for instance, module choice deadlines and visa requirements. Given the wide range of time zones that applicants come from and that 24 hour access to staff is not a possibility, the work reported here emanated from projects to implement a web-based infobot application for answering applicants' enquiries.. The aim was to provide a service where users could ask questions in English about making applications. (The system was not intended to be able to answer highly specific questions such as the reason for rejection of a particular application.) In doing this, the system would have to be able to process input in the syntactic form of questions over the relatively narrow semantic domain of applications for graduate study asked in versions of English that are not always those of a native speaker.. A number of organizations (for instance in the UK, the Alliance & Leicester bank and the O 2 mobile phone company) have made chatbots available on their websites. Chatbots have a long history and the first implementation, ELIZA [30] , is particularly famous. Recent bots owe much to the ALICE software which consists of a matching engine and an XML-based language for writing rules to transform input [1] .. We argue that the use of traditional chatbots for informational systems is inappropriate. Writing of the first extensive script he prepared for ELIZA which parodied "the responses of a nondirective psychotherapist", Weizenbaum [30, p. 188 ] stated "I chose this script because it enabled me to temporarily sidestep the problem of giving the program a database of real-world knowledge." ELIZA was a conversational agent: whatever happened and wherever the dialogue went, the aim was to keep the conversation going. Being a nondirective psychotherapist, information content was low, the main tactic being to use keywords from the user's input to fill slots in the system's output. In the following, ELIZA [30, p. 2] has used boyfriend and depressed to fill pre-prepared templates:. Well, my boyfriend made me come here. ELIZA: Your boyfriend made you come here. User:. He says I'm depressed much of the time. ELIZA: I am sorry to hear you are depressed. To avoid the conversation becoming too repetitive, ELIZA used two ways of introducing variety into its responses. For each keyword there could be a number of possible responses; each was used in turn to introduce some variation. Also previous topics were stored on a stack (thus keeping a record of the conversation) so that, should it be impossible to match a keyword with a template, a previous keyword could be revisited. This had the significant effect of making it seem as if there was some larger dialogue management taking place.. The ELIZA/ALICE model is essentially conversational: the chatbot attempts to maintain a dialogue exchange above all else. The communication of information is very much a secondary objective; hence Weizenbaum's choice of a nondirective psychotherapist.. Both the Alliance & Leicester and O 2 chatbots try to communicate information about products while trying to maintain a dialogue. In particular, they use an avatar figure to represent the computer partner in the chatbot dialogue. Although it might seem attractive from a marketing point of view to present the user with a "chatbot friend" in the hope they will bond with it, many users must be sufficiently ICT-literate and the chatbots so limited that the illusion of a conversational friend is shattered. However, behind such systems, the information content is equivalent to an over-large FAQ. This paper focuses on providing a natural language interface to a set of FAQ-like topics where the number of topics is too large for a conventional WWW-based FAQ and too small for a full database natural language interface system. While a small FAQ list ranging over a very limited topic area is usually an ideal way of presenting information, a larger FAQ list ranging over a broader topic area or areas is less effective. For the information seeker, the organization of the question list may seem unfamiliar or unintuitive and the length of the list makes is difficult to locate the perhaps small piece of information. It may seem that the FAQ writer has not predicted the user's question or the information being sought is given as the part answer to several questions. For the work presented here, the user may not find their question expressed in a form they recognize, perhaps because of differing levels of competence in the language of the FAQ [25, p. 97] .. More specifically, the aims of the natural language interface investigated here can be stated as:. 1. robustness -capable of processing well-formed English or ill-formed either because the user's command of English is poor or because of ellipsis; 2. low cost -such a system should use relatively simple techniques to extract meaning from input and to return outputs, thus reducing the cost of implementation and maintenance; 3. low-skilled maintenance -it is essential that adding to and modifying the knowledge base of the application should be as simple as possible, allowing changes to be made by IT literate rather than computer science trained colleagues.. As explained above, the context of this investigation was a system for responding to natural language enquiries about applications to MSc courses. Such a system would consist of a WWW interface to a bank of 50-100 topics (i.e. too many for a manageable unhierarchically structured FAQ). Two main ways of accessing the bank of topics were chosen:. -keywords -keywords were manually assigned to each topic, together with a weight in the range 1. . . 5 (where 1 was relatively insignificant and 5 extremely significant);. -sentences -one or more stereotypical interrogative sentences were assigned to each topic. No weights were assigned to these sentences. (These are referred to in the remainder of the paper as "stereotypical queries".). In both cases, it would be relatively easy for non-computer scientists to annotate the topic banks. This system is termed an "infobot" to distinguish its informational and non-conversational functionality from that of chatbots. Experiments were designed to assess the effectiveness of a number of methods of matching queries with either sets of keywords or stereotypical queries. The latter were also used as the source for syntactically selected sets of keywords. ELIZA [28] was one of three well-recognized natural language processing systems developed at much the same time. Raphael's SIR system [19] and Bobrow's STUDENT [4] answered mathematical questions. That they were both based on very formal domains of knowledge contributed to their success. As Weizenbaum himself noted "from the purely technical programming point of view, the psychiatric interview [which ELIZA modelled] has the advantage that it eliminates the need for storing explicit information about the real world." [29, p. 474] , [14, pp. 28-41; 110-111] .. ELIZA has a long-enduring popularity. Implementations are still widely available 13 and its reputation has outlasted STUDENT and SIR. Much of ELIZA's reputation is attributable to its domain: a psychiatric therapist was novel and still is very accessible (and even attention catching) to the less-than-expert AI practitioner. This alone does not account for its reputation and longevity: it was an early example of robust processing in that it could deal with ungrammatical input and conversations where topics were abandoned and returned to later, or the changing themes of the conversation were unrelated. Most of all, ELIZA offered an early prospect of a system that could pass the popularized notion of the Turing Test. Weizenbaum himself (incidentally rather than intentionally, it seems) raised this prospect in reporting that, although his secretary knew that in using it she was "talking to a machine", she asked "'Would you mind leaving the room, please?' I [i.e. Weizenbaum] believe the anecdote testifies to the success with which the program maintains the illusion of understanding." [29, p. 478 ].. Weizenbaum attempted to show the potential for question-answering systems using a refinement of the ELIZA system 14 , i.e. by developing it into what this paper terms an infobot. He chose to demonstrate his ideas by providing another system to answer maths problems, which necessitated the addition of an expression evaluator. Changes were made to the store of templates. It was divided into what Weizenbaum likened to a routine (i.e. controlling set of templates which he termed a "script") and subroutines (i.e. groups of closely related templates on very narrow topics). The reason for this hierarchical organization seems to be both practical (in that it allowed larger dialogues to be handled in small memories) and theoretical (reflecting a concern with being able to distinguish between alternative word senses). This development did not have the impact of the first ELIZA, failing to develop the ELIZA techniques in any important way, and remains a curiosity.. Shapiro and Kwasny's 1975 development of an ELIZA infobot [24] proved more influential. In part, their success can be attributed to the development of real-time time-sharing interactive computing. Newly developing operating systems and databases were applications which allowed greater user interaction but also required quite detailed knowledge of command languages. A common theme amongst the approaches being developed to help systems was how the user could find what they needed without first knowing the appropriate technical vocabulary or command language. Shapiro and Kwasny demonstrated a straightforward development of ELIZA to provide help for the DECsystem-10.. Their evaluation was slight by modern standards but their work was highly regarded for providing access to naïve or casual users 15 [9] , [18] , [20] . 1991 saw the beginning of the Loebner Prize contests in which competing chatbots attempt to persuade a jury of their ability to pass the Turing Test. To succeed, it is necessary for a chatbot to chat, irrespective of topic or quality of responses. In this respect, the Loebner Prize has not directly contributed to the development of infobots. The attachment of a virtual character, an avatar, to a chatbot has become fairly common [2] . There has been a return to the chatbot as therapist with avatars being added to systems for education (e.g. [21] ) and psychiatric therapy and counselling [26] . Some organizations, such as Ikea, Alliance & Leicester bank and the O 2 mobile phone company (see p. 1704 above) have used chatbots and avatar interfaces as product advisors. The development of such systems has been encouraged in part by the availability of the ALICE system with the AIML (Artificial Intelligence Markup Language) [1] . This provides a more formal way of specifying ELIZA-like templates together with a slightly more sophisticated matching algorithm which allows for some non-determinism. One addition beyond that of the original ELIZA is the "predicate" feature which allows the "botmaster" to write rules that contain is/or facts, for instance: "Samuel Clemens is Mark Twain". This provides a method, albeit unsophisticated, to store factual information.. In common with any developer of a natural language-interfaced information retrieval system, infobot developers have the twin problems of ensuring the coverage of their information resource is correct and complete and their interface covers the range of inputs users wish to employ. The capability for the user to add novel ways of expressing queries was introduced in Weizenbaum's second ELIZA [29, p. 479] where there is an impressive learning of German queries. This kind of learning was included in CSIEC, where it stored all inputs and used them in its responses [11] . The difficulty for infobots is that extending the language coverage alone might not be sufficient: it may also be necessary to extend or improve the information content. CSIEC allowed the user to add new information (i.e. by adding new facts which would be matched to existing templates and so were analysable, such as "Australia is in the Pacific"). Learning additional information by the kinds of infobot discussed in this paper would be problematic because the information to be added would usually be beyond simple facts (e.g. "Australia is in the Pacific") and the quality of newly learned information would have to be assured by the system operators.. Some infobots have been part of larger systems that include, amongst other components, a database. Sammut's system [22] provided an infobot for a museum collection. The pattern matching of natural language inputs to rules (written in production rule form) did not extend the capabilities of ELIZA (or even ALICE) and it is not clear that the incorporation of a database made any differ- 15 Cuff [8, p. 168 ] offered a more rigorous analysis of what was meant by "casual user", perhaps from a less favourable standpoint when he stated: ". . . the author's [sic] discussion is a piece of special pleading for a natural language understanding program which will explain unfamiliar parts of a computer system.". ence to the processing of natural language inputs. Similar comments apply to a system that provides information about student loans [15] . Regretfully, there is often a lack of rigorous evaluation in this work, the notable exception being Carroll and McKendree's evaluation of three types of interface (including ELIZA) to expert systems [6] . Some researchers have, like the work reported here, tried to find alternative ways of matching inputs with FAQ-type information sources. Banchs and Li developed IRIS, a system they described as "a chat-oriented dialogue system." [3] Rather than using templates, they used a vector space model, searching over previous dialogues. Information retrieval systems for FAQs that made no claim to chatting (i.e. are less infobot and more conventional information retrieval system) have used similar, statistically-based matching techniques [12] , [5] . Both of these systems identify questions within FAQs and use these to match with the users' queries. This is similar to the use of "stereotypical queries" in the current work.. Shallowness in language analysis is, it seems, a vague term. The work described here is "very shallow" in that, where is uses syntactic processing, it does so only to isolate keywords of particular grammatical classes. Wang, Ming and Chua use slightly less shallow parsing in that they (more conventionally) isolate phrase groups (e.g. VP) to find similar questions which have been asked of services such as Yahoo. They are able to claim that their technique offers robustness when presented with ungrammatical inputs [27] . At the opposite extreme, Sneiders' interpretation of shallow is, if anything, as shallow as the weighted keyword matching presented here. "Shallow language understanding" is implemented in what he terms "prioritized keyword matching" where he divides keywords into four groups: required, optional, forbidden and stop-list (i.e. high-frequency function words). There is no syntactic analysis. Perhaps to solve problems of conflicting word senses, Sneiders uses multiple lexicons, as many as one per FAQ text [25] .. The work surveyed shows the tension between chatting -the need to keep the conversation going whatever the topic of ungrammaticality of the input -and the desire to provide users with information. Infobots (as opposed to chatbots) are very much rarer in the literature. While they can respond robustly to all inputs, the accuracy of their responses is disappointing. Work on developing template matching, such as reported here, has been rare. Those systems that have provided information retrieval for the kind of FAQ system used in this work have tended to use statistical techniques with limited robustness.

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O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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Quality of Service Control for WLAN-based Converged Personal Network Service Abstract: This paper proposes a framework for quality of service (QoS) control in WLAN-based converged personal network service (CPNS). First, we show that the CPNS devices in WLANs occupy the shared wireless channel in an unfair manner; and thus, QoS is degraded. The reasons of such problem are analyzed from two viewpoints of (i) channel access mechanism according to carrier sensing multiple access protocol of WLAN and (ii) TCP congestion control mechanism in response to packet loss. To improve QoS and assure fair channel sharing, we propose an integrated QoS control framework consisting of admission control and rate control. Based on the available capacity, the admission control determines whether or not a specific QoS service can be admitted. The rate control is implemented using congestion window control or token bucket algorithm. The proposed mechanism differentiates QoS service from best-effort (BE) service such that the QoS service is preferentially served to satisfy its QoS requirements and the BE service is served to share the remaining resource in a fair manner. The extensive simulation results confirm that the proposed scheme assures QoS and fair channel sharing for WLAN-based CPNS. In this paper, we proposed a generalized framework to assure QoS and fairness for WLANbased CPNS. We identified the problem of QoS degradation and unfair channel sharing that occurs in the existing WLAN-based CPNS, and analyzed its cause from the viewpoints of unfair channel access of MAC and asymmetric congestion control of TCP. By employing admission control and rate control, the proposed mechanism provides absolute guarantee for QoS service in terms of data rate, at the same time, it provides weighted fairness for BE service without decreasing the efficiency of channel sharing. Moreover, the assurance of QoS and fairness is effective, regardless of service direction, packet size, transmission rate, and transport-layer protocol. Through analysis and simulation, it was confirmed that the proposed mechanism effectively achieve QoS assurance for QoS service and fair channel access for BE service. Adjustment of the required data for admission control. The proposed admission control makes the decision on the admission of QoS service by comparing the required data rate and the available capacity, as shown in (10) . However, the total capacity, C, is not constant but depends on several factors such as packet size, transportlayer protocol, number of contending nodes, and channel quality. For example, the capacity of WLAN decreases as the packet size decreases, because the MAC/PHY overhead required to transmit a frame becomes relatively large as the packet size decreases. Recall that the analytical capacity in Section 3.3 is derived under the condition that the stations send/receive l-byte TCP packets. Also note that the maximum size of Ethernet frame is 1500 bytes and the size of VoIP packet is typically a few hundreds bytes, and that the data service is usually served with TCP while some real-time service may be served with UDP. We need to cope with the variation of capacity due to difference in the packet size, transport-layer protocol, and channel quality. For this purpose, we propose an approach of adjusting the required data rate of QoS service, instead of adjusting the total capacity.. Consider that a QoS service is requested with the required data rate of R QoS,i and the average TCP packet size of l byte, which is different from the standard packet size of l o used in the capacity estimation. Also, consider that the transmission rate for the service is r Mb/s 5 . In order to deal with the capacity variation due to different packet size, the required data rate for the QoS service with the packet size of l is adjusted to the equivalent data rate, R ′ QoS,i ;. From (19) , R ′ QoS,i increases as the packet size decreases to compensate for the decrease of capacity. Similarly, R ′ QoS,i decreases if the channel quality for the service is relatively good because the time required to send a packet with the higher transmission rate is smaller than that with the lower transmission rate, i.e., a station in good channel quality consumes less resource to serve a 724 E.-C. Park, I.-H. Kim, G.-M. Jeong, B. Moon packet. Note that the adjusted rate requirement, R ′ QoS,i is used not only in the admission control (10), but also in the TCP window control (4).. In the same way, the required data rate for a QoS service with UDP can be adjusted. In contrast to TCP, UDP does not require transport-layer ACK transmission from the receiver, resulting in less overhead and higher capacity. The capacity with UDP traffic, denoted as C udp (r, l) can be estimated by replacing (17) with (20);. Then, the equivalent required data rate for a UDP QoS service, R ′ QoS,i , becomes. Extension to support weighted fairness for BE services. The proposed scheme can be easily extended to support weighted fairness for BE services. Consider that a BE service has the corresponding service weight w BE (≥ 1), whose value is integer and determined by a service operator of CPNS depending on the relative service priority. Also, we consider the service weight is delivered to the PN GW in the S-REQ message. Then, the PN GW calculates the maximum congestion window (CGW max ) for TCP BE service and the token generation rate (R token ) for UDP BE service as. These values of CGW max and R token are delivered to PNEs in the S-RSP message. Receiving the S-RSP message, each PNE sets the congestion window size and token generation rate for its BE service that has the service weight of w BE,k , each of which is denoted as CGW ′ max,k and R ′ token,k , respectively, as;. Note that CGW ′ max,k = CGW max and R ′ token,k = R token for a normal BE service with w BE,k = 1. From (22) and (23), we observe that BE services share the buffer and capacity in a weighted manner and this extension for weighted service does not degrade QoS service since. (24)

O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O B O B O O B O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O


The Effects of Leader-Member Exchange on Member Performance in Virtual World Teams Abstract This paper examines how the leader-member relationship influences member performance. Building on LMX theory, our study proposed that higher-quality leader-member relationships would have a direct impact on the degree to which members were allocated and developed resources. Higher resource levels would enable members to perform better than their peers. Evidence from a longitudinal study of 61 members of a VWT generally suggests the leader-member relationship does impact members' allocation and development of resources. Furthermore, this study's findings suggest that it is the quantity and the type of resources that impacts performance, not the leader-member relationship.. This research makes important contributions about understanding LMX theory and how to influence member performance. From a theoretical standpoint, this study explored more precise causal mechanisms by which leader-member relationships impact performance. Consistent with LMX theory, the findings suggest that the leader-member relationship is important, and that it has a positive influence on nearly all the resource variables. However, further examination helps tease out what the influential resources on member performance are. In particular, self-confidence, self-determination, group assignments, obligation to and identification with the team influenced member performance. Also, contrary to expectations, trust was not influenced by leadership, nor did trust directly influence performance. The unique nature of collaboration in metaverses, where one's avatar may be directly observed and later evaluated via collected logs, provides one explanation for this finding.. Practically, this study furthers our understanding about how large virtually distributed teams may be managed. As technology enables increasingly larger team sizes, leaders must think past the traditionally emphasized transactional-based approaches in which they concentrate on controlling, monitoring, and evaluating each individual team member. Rather, our study suggests that all relationships, individually and collectively, matter for team performance, not just the relationship with the leader. Leaders should pay careful attention to build self-reliance in their members, avoid micromanagement, provide the requisite resources, and focus on strategies that enable members to transform self-interest into collective interest.. As more work becomes distributed, future generations of workers experienced with collaborating in VWTs will enter the workforce, and larger technology-enabled teams and collectives will emerge. Thus, understanding new ways lead, assign, and motivate people in virtual environments will continue to be a critical issue for the successful accomplishment of work. In all, we collected 61 usable responses from the VWT members, an 89.7 percent response rate. On average, subjects were 33.62 years old, had 9.1 years of MMOG experience, had been members of the VWT for 2.5 years, and spent 27.69 a week in Everquest. The sample was 77 percent male. Also, 91.8 percent had some college or higher education experience, and 86.9 percent were employed. Over the eight-week study timeframe, objective raid data was available from 124 usable snapshots out of a total possible 157 database entries (78.9 percent). The VWT spent an average of 21.45 hours per week during this timeframe on raiding activities. Because an average of 51 guild members attended each raid, this sampling frame captures approximately 6,000 avatar-hours of work.. To ensure that there was agreement between the leader's and the member's assessment of their relationships, we first established that the leader-member perspectives were strongly correlated (r=0.62). Also, the results of an exploratory factor analysis revealed that the LMX items from both perspectives exhibited factor loadings exceeding 0.7 on the same factor. Therefore, we felt confident in combining the LMX measures to better assess the overall dyadic leader-member relationship.. We tested the hypotheses = using SmartPLS 2.0 by Ringle, Wende, and Will (2005) . Partial least squares (PLS) is a commonly accepted method of structural equation modeling (SEM) analysis in information systems (IS) studies, and is robust to conditions that include small sample sizes, nonnormal data, and multicollinearity (Chin, 1998b) . In addition, PLS offers advantages over firstgeneration regression techniques, such as the ability to assess measurement and structural models simultaneously (Gefen, Straub, & Boudreau, 2000) . Because this study uses multi-item scales, and because the model to be tested is a path model with a small sample size, these conditions are ideally suited to SEM analysis using PLS. In order to test our hypotheses, the unit of analysis for this study is the individual guild member in a MMOG, where a guild is an example of a large VWT. Our population of interest includes guilds where the primary purpose is to raid. A raid is a large-scale, real-time collaboration by members of a VWT towards a common goal, and raiding-oriented guilds share many similarities with teams in real-world organizations in terms of makeup, shared sense of purpose, and the interdependent nature of how work is performed (Castronova, 2005; Ducheneaut et al., 2007; Williams et al., 2006) .. We chose a 68-member guild in the MMOG EverQuest as the VWT for this study. Data collection occurred in 3 stages and spanned an eight-week time frame. In stage 1, we collected data that assessed the quality of the leader-member relationship, member demographics, and control variables via surveys. During stage 2, which spanned five-and-a-half weeks, the principal investigator actively participated in guild raids in order to gather objective data assessing each team member's resource allocation. We collected these data by using the built-in guild organization tool in the EverQuest client and exporting it to a text-based log. In stage 3, following this five-and-a-half week time period of active raiding, we sent guild members follow-up web-based surveys to assess resources (mediating variables) and team member performance (the dependent variable).

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Robust location transportation problems under uncertain demands In robust optimization, the multi-stage context (or dynamic decision-making) assumes that the information is revealed in stages. So, part of the decisions must be taken before knowing the real values of the uncertain parameters, and another part, called recourse decisions, is taken when the information is known. In this paper, we are interested in a robust version of the location transportation problem with an uncertain demand using a 2-stage formulation. The obtained robust formulation is a convex (not linear) program, and we apply a cutting plane algorithm to exactly solve the problem. At each iteration, we have to solve an NPhard recourse problem in an exact way, which is time-consuming. Here, we go further in the analysis of the recourse problem of the location transportation problem. In particular, we propose a mixed integer program formulation to solve the quadratic recourse problem and we define a tight bound for this reformulation. We present an extensive computation analysis of the 2-stage robust location transportation problem. The proposed tight bound allows us to solve large size instances. Robust optimization is a recent methodology for handling problems affected by uncertain data, and where no probability distribution is available on the ambiguous parameters.. The goal of the robust optimization framework is to obtain a ''robust'' solution, which protects the decision maker against adverse realizations of the uncertainty. A specific definition of robustness depends on the modeling of the uncertainty, the location of the uncertainty within the problem (in the objective function and/or in the constraints), and the decision-making context (in particular, the way information is revealed over time). Within the problem under consideration in this paper, the uncertainty concerns the constraints, or in other words the feasibility of a solution.. According to the decision-making context, the robust approaches can be divided into two categories. The first category is suited to the single-stage context, where the decision-maker has to select a solution before knowing the real value of each uncertain parameter. When uncertainty affects the feasibility of a solution (because constraint coefficients are uncertain), robust optimization seeks to obtain a solution that will be feasible for any realization taken by the unknown coefficients (Soyster [15] ); however, complete protection from adverse realizations often comes at the expense of a severe deterioration in the objective. This extreme approach can be justified in some engineering applications of robustness, such as robust control theory, but is less advisable in operations research, where adverse events such as low customer demand do not produce the high-profile repercussions that engineering failures -such as a doomed satellite launch or a destroyed unmanned robot -can have. To make the robust methodology appealing to business practitioners, robust optimization thus focuses on obtaining a solution that will be feasible for any realization taken by the unknown coefficients within a smaller, ''realistic'' set, called the uncertainty set. The specific choice of the set plays an important role in ensuring computational tractability of the robust problem and limiting deterioration of the objective at optimality, and must be thought through The aim of this paper is to solve a robust version of the location transportation problem. The 2-stage robust approach, presented here, offers more flexibility to the decision maker than the single-stage approach. Indeed, there are some recourse variables to be decided once the uncertainty has been revealed. Furthermore, the uncertain set is less conservative than the classical worst case approach since it considers a limited number of demands deviating from their nominal values. Previously, the 2-stage formulation has been considered by [1, 16] . Nevertheless, the limit size of solved instances was performed for at most 50 uncertain parameters. Here, we present the first (to our knowledge) extensive computation

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