Showing papers by "University of Amsterdam published in 2004"

The Role of the Medial Frontal Cortex in Cognitive Control.

Abstract: Adaptive goal-directed behavior involves monitoring of ongoing actions and performance outcomes, and subsequent adjustments of behavior and learning. We evaluate new findings in cognitive neuroscience concerning cortical interactions that subserve the recruitment and implementation of such cognitive control. A review of primate and human studies, along with a meta-analysis of the human functional neuroimaging literature, suggest that the detection of unfavorable outcomes, response errors, response conflict, and decision uncertainty elicits largely overlapping clusters of activation foci in an extensive part of the posterior medial frontal cortex (pMFC). A direct link is delineated between activity in this area and subsequent adjustments in performance. Emerging evidence points to functional interactions between the pMFC and the lateral prefrontal cortex (LPFC), so that monitoring-related pMFC activity serves as a signal that engages regulatory processes in the LPFC to implement performance adjustments.

How important is methodology for the estimates of the determinants of happiness

Abstract: Psychologists and sociologists usually interpret happiness scores as cardinal and comparable across respondents, and thus run OLS regressions on happiness and changes in happiness. Economists usually assume only ordinality and have mainly used ordered latent response models, thereby not taking satisfactory account of fixed individual traits. We address this problem by developing a conditional estimator for the fixed-effect ordered logit model. We find that assuming ordinality or cardinality of happiness scores makes little difference, whilst allowing for fixed-effects does change results substantially. We call for more research into the determinants of the personality traits making up these fixed-effects.

Prevalence of age-related macular degeneration in the United States.

Abstract: Objective: To estimate the prevalence and distribution of age-related macular degeneration (AMD) in the United States by age, race/ethnicity, and gender.Methods: Summary prevalence estimates of drusen 125 pin or larger, neovascular AMD, and geographic atrophy were prepared separately for black and white persons in 5-year age intervals starting at 40 years. The estimated rates were based on a meta-analysis of recent population-based studies in the United States, Australia, and Europe. These rates were applied to 2000 US Census data and to projected US population figures for 2020 to estimate the number of the US population with drusen and AMD.Results: The overall prevalence of neovascular AMD and/or geographic atrophy in the US population 40 years and older is estimated to be 1.47% (95% confidence interval, 1.38%-1.55%), with 1.75 million citizens having AMD. The prevalence of AMD increased dramatically with age, with more than 15% of the white women older than 80 years having neovascular AMD and/or geographic atrophy. More than 7 million individuals had drusen measuring 125 pin or larger and were, therefore, at substantial risk of developing AMD. Owing to the rapidly aging population, the number of persons having AMD will increase by 50% to 2.95 million in 2020. Age-related macular degeneration was far more prevalent among white than among black persons.Conclusion: Age-related macular degeneration affects more than 1.75 million individuals in the United States. Owing to the rapid aging of the US population, this number will increase to almost 3 million by 2020.

How Important is Methodology for the estimates of the determinants of Happiness

Abstract: Psychologists and sociologists usually interpret happiness scores as cardinal and comparable across respondents, and thus run OLS regressions on happiness and changes in happiness. Economists usually assume only ordinality and have mainly used ordered latent response models, thereby not taking satisfactory account of fixed individual traits. We address this problem by developing a conditional estimator for the fixed-effect ordered logit model. We find that assuming ordinality or cardinality of happiness scores makes little difference, whilst allowing for fixed-effects does change results substantially. We call for more research into the determinants of the personality traits making up these fixed-effects.

Work group diversity and group performance: an integrative model and research agenda.

Abstract: Research on the relationship between work group diversity and performance has yielded inconsistent results. To address this problem, the authors propose the categorization-elaboration model (CEM), which reconceptualizes and integrates information/decision making and social categorization perspectives on work-group diversity and performance. The CEM incorporates mediator and moderator variables that typically have been ignored in diversity research and incorporates the view that information/decision making and social categorization processes interact such that intergroup biases flowing from social categorization disrupt the elaboration (in-depth processing) of task-relevant information and perspectives. In addition, the authors propose that attempts to link the positive and negative effects of diversity to specific types of diversity should be abandoned in favor of the assumption that all dimensions of diversity may have positive as well as negative effects. The ways in which these propositions may set the agenda for future research in diversity are discussed.

Improved adaptive Gaussian mixture model for background subtraction

Abstract: Background subtraction is a common computer vision task. We analyze the usual pixel-level approach. We develop an efficient adaptive algorithm using Gaussian mixture probability density. Recursive equations are used to constantly update the parameters and but also to simultaneously select the appropriate number of components for each pixel.

Infliximab Maintenance Therapy for Fistulizing Crohn's Disease

Abstract: BACKGROUND: Infliximab, a monoclonal antibody against tumor necrosis factor, is an effective maintenance therapy for patients with Crohn's disease without fistulas. It is not known whether infliximab is an effective maintenance therapy for patients with fistulas. METHODS: We performed a multicenter, double-blind, randomized, placebo-controlled trial to evaluate the efficacy of infliximab maintenance therapy in 306 adult patients with Crohn's disease and one or more draining abdominal or perianal fistulas of at least three months' duration. Patients received 5 mg of infliximab per kilogram of body weight intravenously on weeks 0, 2, and 6. A total of 195 patients who had a response at weeks 10 and 14 and 87 patients who had no response were then randomly assigned to receive placebo or 5 mg of infliximab per kilogram every eight weeks and to be followed to week 54. The primary analysis was the time to the loss of response among patients who had a response at week 14 and underwent randomization. RESULTS: The time to loss of response was significantly longer for patients who received infliximab maintenance therapy than for those who received placebo maintenance (more than 40 weeks vs. 14 weeks, P<0.001). At week 54, 19 percent of patients in the placebo maintenance group had a complete absence of draining fistulas, as compared with 36 percent of patients in the infliximab maintenance group (P=0.009). CONCLUSIONS: Patients with fistulizing Crohn's disease who have a response to induction therapy with infliximab have an increased likelihood of a sustained response over a 54-week period if infliximab treatment is continued every 8 weeks.

The Classification of Glomerulonephritis in Systemic Lupus Erythematosus Revisited

Abstract: The currently used classification reflects our understanding of the pathogenesis of the various forms of lupus nephritis, but clinicopathologic studies have revealed the need for improved categorization and terminology. Based on the 1982 classification published under the auspices of the World Health Organization (WHO) and subsequent clinicopathologic data, we propose that class I and II be used for purely mesangial involvement (I, mesangial immune deposits without mesangial hypercellularity; II, mesangial immune deposits with mesangial hypercellularity); class III for focal glomerulonephritis (involving or = 50% of total number of glomeruli) either with segmental (class IV-S) or global (class IV-G) involvement, and also with subdivisions for active and sclerotic lesions; class V for membranous lupus nephritis; and class VI for advanced sclerosing lesions]. Combinations of membranous and proliferative glomerulonephritis (i.e., class III and V or class IV and V) should be reported individually in the diagnostic line. The diagnosis should also include entries for any concomitant vascular or tubulointerstitial lesions. One of the main advantages of the current revised classification is that it provides a clear and unequivocal description of the various lesions and classes of lupus nephritis, allowing a better standardization and lending a basis for further clinicopathologic studies. We hope that this revision, which evolved under the auspices of the International Society of Nephrology and the Renal Pathology Society, will contribute to further advancement of the WHO classification.

genotype and genodive: two programs for the analysis of genetic diversity of asexual organisms

Abstract: Investigating diversity in asexual organisms using molecular markers involves the assignment of individuals to clonal lineages and the subsequent analysis of clonal diversity. Assignment is possible using a distance matrix in combination with a user-specified threshold, defined as the maximum distance between two individuals that are considered to belong to the same clonal lineage. Analysis of clonal diversity requires tests for differences in diversity and clonal composition between populations. We developed two programs, GENOTYPE and GENODIVE for such analyses of clonal diversity in asexually reproducing organisms. Additionally, genotype can be used for detecting genotyping errors in studies of sexual organisms.

Identification of a new human coronavirus

Abstract: Three human coronaviruses are known to exist: human coronavirus 229E (HCoV-229E), HCoV-OC43 and severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV). Here we report the identification of a fourth human coronavirus, HCoV-NL63, using a new method of virus discovery. The virus was isolated from a 7-month-old child suffering from bronchiolitis and conjunctivitis. The complete genome sequence indicates that this virus is not a recombinant, but rather a new group 1 coronavirus. The in vitro host cell range of HCoV-NL63 is notable because it replicates on tertiary monkey kidney cells and the monkey kidney LLC-MK2 cell line. The viral genome contains distinctive features, including a unique N-terminal fragment within the spike protein. Screening of clinical specimens from individuals suffering from respiratory illness identified seven additional HCoV-NL63-infected individuals, indicating that the virus was widely spread within the human population.

The concept of validity

Abstract: This article advances a simple conception of test validity: A test is valid for measuring an attribute if (a) the attribute exists and (b) variations in the attribute causally produce variation in the measurement outcomes. This conception is shown to diverge from current validity theory in several respects. In particular, the emphasis in the proposed conception is on ontology, reference, and causality, whereas current validity theory focuses on epistemology, meaning, and correlation. It is argued that the proposed conception is not only simpler but also theoretically superior to the position taken in the existing literature. Further, it has clear theoretical and practical implications for validation research. Most important, validation research must not be directed at the relation between the measured attribute and other attributes but at the processes that convey the effect of the measured attribute on the test scores.

Tonks–Girardeau gas of ultracold atoms in an optical lattice

Abstract: Strongly correlated quantum systems are among the most intriguing and fundamental systems in physics. One such example is the Tonks-Girardeau gas, proposed about 40 years ago, but until now lacking experimental realization; in such a gas, the repulsive interactions between bosonic particles confined to one dimension dominate the physics of the system. In order to minimize their mutual repulsion, the bosons are prevented from occupying the same position in space. This mimics the Pauli exclusion principle for fermions, causing the bosonic particles to exhibit fermionic properties. However, such bosons do not exhibit completely ideal fermionic (or bosonic) quantum behaviour; for example, this is reflected in their characteristic momentum distribution. Here we report the preparation of a Tonks-Girardeau gas of ultracold rubidium atoms held in a two-dimensional optical lattice formed by two orthogonal standing waves. The addition of a third, shallower lattice potential along the long axis of the quantum gases allows us to enter the Tonks-Girardeau regime by increasing the atoms' effective mass and thereby enhancing the role of interactions. We make a theoretical prediction of the momentum distribution based on an approach in which trapped bosons acquire fermionic properties, finding that it agrees closely with the measured distribution.

Clinical Features and Prognostic Factors in Adults with Bacterial Meningitis

Abstract: Background We conducted a nationwide study in the Netherlands to determine clinical features and prognostic factors in adults with community-acquired acute bacterial meningitis. Methods From October 1998 to April 2002, all Dutch patients with community-acquired acute bacterial meningitis, confirmed by cerebrospinal fluid cultures, were prospectively evaluated. All patients underwent a neurologic examination on admission and at discharge, and outcomes were classified as unfavorable (defined by a Glasgow Outcome Scale score of 1 to 4 points at discharge) or favorable (a score of 5). Predictors of an unfavorable outcome were identified through logistic-regression analysis. Results We evaluated 696 episodes of community-acquired acute bacterial meningitis. The most common pathogens were Streptococcus pneumoniae (51 percent of episodes) and Neisseria meningitidis (37 percent). The classic triad of fever, neck stiffness, and a change in mental status was present in only 44 percent of episodes; however, 95 percent had at least two of the four symptoms of headache, fever, neck stiffness, and altered mental status. On admission, 14 percent of patients were comatose and 33 percent had focal neurologic abnormalities. The overall mortality rate was 21 percent. The mortality rate was higher among patients with pneumococcal meningitis than among those with meningococcal meningitis (30 percent vs. 7 percent, P Conclusions In adults presenting with community-acquired acute bacterial meningitis, the sensitivity of the classic triad of fever, neck stiffness, and altered mental status is low, but almost all present with at least two of the four symptoms of headache, fever, neck stiffness, and altered mental status. The mortality associated with bacterial meningitis remains high, and the strongest risk factors for an unfavorable outcome are those that are indicative of systemic compromise, a low level of consciousness, and infection with S. pneumoniae.

Knowledge sharing in context: The influence of organizational commitment, communication climate and CMC use on knowledge sharing

Abstract: Determining which factors promote or impede the sharing of knowledge within groups and organizations constitutes an important area of research. This paper focuses on three such influences: “organizational commitment,” “organizational communication,” and the use of a specific instrument of communication – computer‐mediated communication (CMC). Two processes of knowledge sharing are distinguished: donating and collecting. A number of hypotheses are presented concerning the influence of commitment, climate and CMC on these processes. These hypotheses were tested in six case studies. The results suggest that commitment to the organization positively influences knowledge donating, and is in turn positively influenced by CMC use. Communication climate is found to be a key variable: a constructive communication climate was found to positively influence knowledge donating, knowledge collecting and affective commitment. Finally, a relationship was found that was not hypothesized: knowledge collecting influences knowledge donating in a positive sense – the more knowledge a person collects, the more he or she is willing to also donate knowledge to others. Based on these results, a number of theoretical and practical implications are discussed, and suggestions for further research are presented.

Towards a unified model for black hole X-ray binary jets

Abstract: We present a unified semiquantitative model for the disc–jet coupling in black hole X-ray binary systems. In the process we have compiled observational aspects from the existing literature, as well as performing new analyses. We argue that during the rising phase of a black hole transient outburst the steady jet known to be associated with the canonical ‘low/hard’ state persists while the X-ray spectrum initially softens. Subsequently, the jet becomes unstable and an optically thin radio outburst is always associated with the soft X-ray peak at the end of this phase of softening. This peak corresponds to a ‘soft very high state’ or ‘steep power-law’ state. Softer X-ray states are not associated with ‘core’ radio emission. We further demonstrate quantitatively that the transient jets associated with these optically thin events are considerably more relativistic than those in the ‘low/hard’ X-ray state. This in turn implies that, as the disc makes its collapse inwards, the jet Lorentz factor rapidly increases, resulting in an internal shock in the outflow, which is the cause of the observed optically thin radio emission. We provide simple estimates for the efficiency of such a shock in the collision of a fast jet with a previously generated outflow that is only mildly relativistic. In addition, we estimate the jet power for a number of such transient events as a function of X-ray luminosity, and find them to be comparable to an extrapolation of the functions estimated for the ‘low/hard’ state jets. The normalization may be larger, however, which may suggest a contribution from some other power source such as black hole spin, for the transient jets. Finally, we attempt to fit these results together into a coherent semiquantitative model for the disc–jet coupling in all black hole X-ray binary systems.

The similarity metric

Abstract: A new class of distances appropriate for measuring similarity relations between sequences, say one type of similarity per distance, is studied. We propose a new "normalized information distance," based on the noncomputable notion of Kolmogorov complexity, and show that it is in this class and it minorizes every computable distance in the class (that is, it is universal in that it discovers all computable similarities). We demonstrate that it is a metric and call it the similarity metric . This theory forms the foundation for a new practical tool. To evidence generality and robustness, we give two distinctive applications in widely divergent areas using standard compression programs like gzip and GenCompress. First, we compare whole mitochondrial genomes and infer their evolutionary history. This results in a first completely automatic computed whole mitochondrial phylogeny tree. Secondly, we fully automatically compute the language tree of 52 different languages.

An illustrated consensus on the classification of pancreatic intraepithelial neoplasia and intraductal papillary mucinous neoplasms

Abstract: Invasive pancreatic ductal adenocarcinoma is an almost uniformly fatal disease. Several distinct noninvasive precursor lesions can give rise to invasive adenocarcinoma of the pancreas, and the prevention, detection, and treatment of these noninvasive lesions offers the potential to cure early pancreatic cancers. Noninvasive precursors of invasive ductal adenocarcinoma of the pancreas include pancreatic intraepithelial neoplasias (PanINs), intraductal papillary mucinous neoplasms (IPMNs), and mucinous cystic neoplasms. Diagnostic criteria, including a distinct ovarian-type stroma, and a consistent nomenclature are well established for mucinous cystic neoplasms. By contrast, consistent nomenclatures and diagnostic criteria have been more difficult to establish for PanINs and IPMNs. Because both PanINs and IPMNs consist of intraductal neoplastic proliferations of columnar, mucin-containing cells with a variable degree of papilla formation, the distinction between these two classes of precursor lesions remains problematic. Thus, considerable ambiguities still exist in the classification of noninvasive neoplasms in the pancreatic ducts. A meeting of international experts on precursor lesions of pancreatic cancer was held at The Johns Hopkins Hospital from August 18 to 19, 2003. The purpose of this meeting was to define an international acceptable set of diagnostic criteria for PanINs and IPMNs and to address a number of ambiguities that exist in the previously reported classification systems for these neoplasms. We present a consensus classification of the precursor lesions in the pancreatic ducts, PanINs and IPMNs.

The value of human and social capital investments for the business performance of startups

Abstract: We investigate the manifold posed question: To what extent does investment in human and social capital, besides the effect of talent, enhance entrepreneurial performance? We distinguish between three different performance measures: survival, profits, and generated employment. On the basis of the empirical analysis of a rich Dutch longitudinal data set of firm founders, we conclude that specific investments indeed affect the three performance measures substantially and significantly. Specific attention is paid to the unobserved talent bias. Moreover, the effect of the emergence of so called "knowledge industries" is explored.

The routinization of innovation research : A constructively critical review of the state-of-the-science

Abstract: Summary In this review we argue that facilitators of innovation at the individual, group, and organizational levels have been reliably identified, and that validated process models of innovation have been developed. However, a content analysis of selected research published between 1997 and 2002 suggests a routinization of innovation research, with a heavy focus on replication–extension, cross-sectional designs, and a single level of analysis. We discuss five innovative pathways for future work: Study innovation as an independent variable, across cultures, within a multi-level framework, and use meta-analysis and triangulation. To illustrate we propose a ‘distress-related innovation’ model of the relations between negatively connotated variables and innovation at the individual, group, and organizational levels of analysis. Copyright # 2004 John Wiley & Sons, Ltd. Imaginative writers, the reader will have noticed, dropped out of this [Soviet] history when it moved from the 1920’s into the period of Stalinism. Of course industrious typewriters continued to manufacture novels, plays and poems, but they no longer revealed authors in search of the authentic self and true community, as the works of Olesha and Babel had, not to speak of the pre-revolutionary masters. From 1930 to 1953 Stalin’s engineers of human souls typed out their works to formula. Their product has its fascinations, like mass-market fiction and popular drama in the West, but hardly for understanding the psychologies of high culture. They help one understand mass psychology in its relation with the authorities.

Rectal Cancer: Local Staging and Assessment of Lymph Node Involvement with Endoluminal US, CT, and MR Imaging—A Meta-Analysis

Abstract: PURPOSE: To perform a meta-analysis to compare endoluminal ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging in rectal cancer staging. MATERIALS AND METHODS: Relevant articles published between 1985 and 2002 were included if more than 20 patients were studied, histopathologic findings were the reference standard, and data were presented for 2 × 2 tables; articles were excluded if data were reported elsewhere in more detail. Two reviewers independently extracted data on study characteristics and results. Bivariate random-effects approach was used to obtain summary estimates of sensitivity and specificity for invasion of muscularis propria, perirectal tissue, and adjacent organs and for lymph node involvement. Summary receiver operating characteristic (ROC) curves were fitted for perirectal tissue invasion and lymph node involvement. RESULTS: Ninety articles fulfilled all inclusion criteria. For muscularis propria invasion, US and MR imaging had similar sensitivities; speci...

A six-factor structure of personality-descriptive adjectives: solutions from psycholexical studies in seven languages.

Abstract: Standard psycholexical studies of personality structure have produced a similar 6-factor solution in 7 languages (Dutch, French, German, Hungarian, Italian, Korean, Polish). The authors report the content of these personality dimensions and interpret them as follows: (a) a variant of Extraversion, defined by sociability and liveliness (though not by bravery and toughness); (b) a variant of Agreeableness, defined by gentleness, patience, and agreeableness (but also including anger and ill temper at its negative pole); (c) Conscientiousness (emphasizing organization and discipline rather than moral conscience); (d) Emotionality (containing anxiety, vulnerability, sentimentality, lack of bravery, and lack of toughness, but not anger or ill temper); (e) Honesty-Humility; (f) Intellect/Imagination/Unconventionality. A potential reorganization of the Big Five factor structure is discussed.

Put your money where your mouth is! : Explaining collective action tendencies through group-based anger and group efficacy

Abstract: Insights from appraisal theories of emotion are used to integrate elements of theories on collective action. Three experiments with disadvantaged groups systematically manipulated procedural fairness (Study 1), emotional social support (Study 2), and instrumental social support (Study 3) to examine their effects on collective action tendencies through group-based anger and group efficacy. Results of structural equation modeling showed that procedural fairness and emotional social support affected the group-based anger pathway (reflecting emotion-focused coping), whereas instrumental social support affected the group efficacy pathway (reflecting problem-focused coping), constituting 2 distinct pathways to collective action tendencies. Analyses of the means suggest that collective action tendencies become stronger the more fellow group members "put their money where their mouth is." The authors discuss how their dual pathway model integrates and extends elements of current approaches to collective action.

Motivating Individuals and Groups at Work: A Social Identity Perspective on Leadership and Group Performance

Abstract: We argue that additional understanding of work motivation can be gained by incorporating current insights concerning self-categorization and social identity processes and by examining the way in which these processes influence the motivation and behavior of individuals and groups at work. This theoretical perspective that focuses on the conditions determining different self-definitions allows us to show how individual and group processes interact to determine work motivation. To illustrate the added value of this approach, we develop some specific propositions concerning motivational processes underpinning leadership and group performance.

Bidirectional Relation Between Inflammation and Coagulation

Abstract: Inflammation and coagulation play pivotal roles in the pathogenesis of vascular disease. Increasing evidence points to extensive cross-talk between these two systems, whereby inflammation leads not only to activation of coagulation, but coagulation also considerably affects inflammatory activity. Activation of coagulation and fibrin deposition as a consequence of inflammation is well known and can be viewed as an essential part of the host defense of the body against, for example, infectious agents or nonidentical cells, in an effort to contain the invading entity and the consequent inflammatory response to a limited area. An exaggerated or insufficiently controlled response may, however, lead to a situation in which coagulation and thrombosis contribute to disease, as illustrated by the fact that thrombus formation on a ruptured atherosclerotic plaque, containing abundant inflammatory cells, is the pathological basis of acute arterial thrombotic events such as myocardial infarction or unstable angina.1 Expression of procoagulant material by inflammatory cells in the unstable plaque (in particular tissue factor) may initiate activation of coagulation, and the thrombin generated will both activate platelets and result in the formation of a platelet-fibrin thrombus (Figure 1). Another example is the occurrence of systemic coagulation activation in combination with microvascular failure that results from the systemic inflammatory response to severe infection or sepsis and that contributes to multiple organ dysfunction.2 However, rather than this being a 1-way process with inflammation leading to coagulation, both systems closely interact, whereby coagulation can also substantially modulate inflammatory activity. Coagulation factors (such as thrombin) or anticoagulant proteins (such as activated protein C) may activate specific cell receptors on mononuclear cells or endothelial cells, which may affect, for example, cytokine production or inflammatory cell apoptosis. Figure 1. Schematic representation of activation of coagulation and inflammation on rupture of atherosclerotic plaque. Exposure of tissue factor-bearing inflammatory cells …