Nonparametric instrumental regression with non-convex constraints

This paper considers the nonparametric regression model with an additive error that is dependent on the explanatory variables. As is common in empirical studies in epidemiology and economics, it also supposes that valid instrumental variables are observed. A classical example in microeconomics considers the consumer demand function as a function of the price of goods and the income, both variables often considered as endogenous. In this framework, the economic theory also imposes shape restrictions on the demand function, like integrability conditions. Motivated by this illustration in microeconomics, we study an estimator of a nonparametric constrained regression function using instrumental variables by means of Tikhonov regularization. We derive rates of convergence for the regularized model both in a deterministic and stochastic setting under the assumption that the true regression function satisfies a projected source condition including, because of the non-convexity of the imposed constraints, an additional smallness condition

Network Analysis Identifies SOD2 mRNA as a Potential Biomarker for Parkinson's Disease

Increasing evidence indicates that Parkinson's disease (PD) and type 2 diabetes (T2DM) share dysregulated molecular networks. We identified 84 genes shared between PD and T2DM from curated disease-gene databases. Nitric oxide biosynthesis, lipid and carbohydrate metabolism, insulin secretion and inflammation were identified as common dysregulated pathways. A network prioritization approach was implemented to rank genes according to their distance to seed genes and their involvement in common biological pathways. Quantitative polymerase chain reaction assays revealed that a highly ranked gene, superoxide dismutase 2 (SOD2), is upregulated in PD patients compared to healthy controls in 192 whole blood samples from two independent clinical trials, the Harvard Biomarker Study (HBS) and the Diagnostic and Prognostic Biomarkers in Parkinson's disease (PROBE). The results from this study reinforce the idea that shared molecular networks between PD and T2DM provides an additional source of biologically meaningful biomarkers. Evaluation of this biomarker in de novo PD patients and in a larger prospective longitudinal study is warranted

Electronic Portfolios in the Classroom: Factors Impacting Teachers’ Integration of New Technologies and New Pedagogies

This article presents the findings of a study on the use of an electronic portfolio (EP) in 16 elementary classrooms across Canada. Using a mixed-methods approach, data were collected to understand how teachers used EPs in their classrooms, to what extent they integrated the EP into their practice, and the factors influencing their use. Using expectancy theory, findings indicate that low implementers experienced significant technical obstacles and/or were reluctant to change their established practices, whereas high implementers reported feeling supported by their administration, experiencing growth in their teaching practice, and using more pedagogical practices that support self-regulated learning as a result of the scaffolding provided by the software

Untersuchungen zur Bedeutung modaler und amodaler Perzepte in der visuellen Wahrnehmung

Eine erstaunliche Leistung des Wahrnehmungssystems besteht darin, trotz fragmentierter und unvollständiger sensorischer Informationen im proximalen Reiz, beispielsweise aufgrund von Verdeckung, stabile und vollständige Perzepte hervorzubringen. Die Wahrnehmung von Verdeckung kann hierbei sog. amodale Ergänzungen und Vervollständigungen von Objekten hervorrufen und die Interpretation einer Szene dadurch erheblich beeinflussen. Im Gegensatz zu amodalen Vervollständigungen verdeckter Objekte und Objektbereiche werden perzeptuelle Vervollständigungen unverdeckter Objekte und Objektbereiche als modal bezeichnet. Die Arbeit beginnt mit einer theoretischen Analyse der Dichotomie von modaler und amodaler Vervollständigung, die sich auf phänomenologische Beobachtungen und vorliegende empirische Befunde stützt. Dabei wird gezeigt, dass diese traditionelle Dichotomie nicht nur unvollständig, sondern auch inkonsistent ist. Das Kriterium der phänomenalen Präsenz, durch die sich modale und amodale Perzepte qualitativ voneinander unterscheiden sollen, erscheint aus theoretischer Sicht willkürlich und aus phänomenologischer Sicht ungerechtfertigt und daher insgesamt fragwürdig. Die dichotome Unterscheidung zwischen modalen und amodalen Perzepten ist außerdem häufig mit der impliziten Annahme verknüpft, modale Perzepte repräsentierten geometrisch-optische Sichtbarkeit und amodale Perzepte geometrisch-optische Unsichtbarkeit aufgrund von Verdeckung. Diese Annahme einer direkten Kopplung von phänomenaler Sichtbarkeit/Verdeckung an geometrisch-optische Sichtbarkeit/Verdeckung erweist sich jedoch unter empirischen Gesichtspunkten als fragwürdig, da einerseits auch bei phänomenaler Verdeckung modale Attribute wahrgenommen und sogar in ihrer Ausprägung beeinflusst werden können, andererseits wiederum auch unverdeckte Figuren einen amodalen Charakter besitzen können. Anknüpfend an diese theoretischen Überlegungen wird die Unangemessenheit der klassischen Dichotomie von modaler und amodaler Wahrnehmung und insbesondere die damit verbundene direkte Kopplung von phänomenaler an geometrisch-optische Sichtbarkeit/Verdeckung in mehreren empirischen Untersuchungen aufgezeigt. Der experimentelle Fokus liegt hierbei exemplarisch auf dem Nachweis des Einflusses von perzeptueller Verdeckung auf zwei explizit modale Aspekte der Wahrnehmung, nämlich auf die wahrgenommene Glattheit von Scheinbewegung und auf die phänomenale Sichtbarkeit von Objektoberflächen bei Verdeckung. In fünf Experimenten zum sog. Glättungseffekt wird nachgewiesen, dass die wahrgenommene Glattheit von ansonsten ruckartiger Scheinbewegung verbessert werden kann, wenn die räumlichen und ggf. auch zeitlichen Lücken in diskreten Bewegungsreizen durch geeigente Verdeckungshinweise maskiert werden. Der Effekt lässt sich erklären, wenn man annimmt, dass die ansonsten unerklärbaren Lücken im Reiz, die die Bewegungswahrnehmung beeinträchtigen, ganz oder teilweise kompensiert werden können, wenn diese vom visuellen System ursächlich auf Verdeckung zurückgeführt und somit plausibel "erklärt" werden können. Diese Erklärung greift konstruktivistische Theorievorstellungen auf, wonach Wahrnehmung intelligentem Problemlösen ähnelt (Rock, 1983, 1997) und auf abduktiven Inferenzprozessen basiert (Mausfeld, 2011a). In zwei weiteren Experimenten wird das sog. Sichtbarkeitsparadoxon nachgewiesen und seine Ausprägung quantifiziert. Das Paradoxon besteht darin, dass Teile der verdeckten Bereiche eines partiell verdeckten Objekts trotz deutlich erkennbarer Verdeckung gleichzeitig phänomenal sichtbar erscheinen. Dieser vermeintliche Widerspruch lässt sich auflösen, wenn man die klassische Annahme einer direkten Kopplung von phänomenaler Sichtbarkeit an geometrisch-optische Sichtbarkeit aufgibt und statt dessen die phänomenale Sichtbarkeit eines perzeptuellen Attributs (wie Form, Kontur, Oberflächenfarbe) als Repräsentation der Schlüssigkeit und Klarheit der sensorischen Hinweise für eine spezifische perzeptuelle Deutung hinsichtlich dieses Attributs auffasst, also als eine Art Maß für die Verlässlichkeit der Deutung. Aus dieser Perspektive lassen sich auch andere vermeintlich paradoxe Beobachtungen wie beispielsweise der amodale Charakter der verdeckten Bewegung beim Tunneleffekt (Burke, 1952) oder die partiell modale Ergänzung bei der Verdeckungstäuschung (Kanizsa, 1979; Palmer et al., 2007) in konsistenter Weise erklären. Die beschriebene Perspektive ist zwar zum jetzigen Zeitpunkt empirisch nur schwach gestützt, bietet aber eine vielversprechende Grundlage für weitere empirische Forschungen zur Bedeutung modaler und amodaler Perzepte. Zusammenfassend stellen die Ergebnisse dieser Arbeit die traditionelle Vorstellung über modale und amodale Perzepte, die eng an geometrisch-optische Sichtbarkeit/Verdeckung geknüpft ist, in Frage. Die vorgeschlagene alternative Perspektive, die die Bedeutung dieser Konzepte für die abduktiven Inferenzprozesse in der Wahrnehmung hervorhebt, steht mit den experimentellen Befunden dieser Arbeit in Einklang. Eine gründlichere Prüfung, inwieweit bestehende Hypothesen und Erklärungen für Vervollständigungsphänomene mit den neugewonnenen Erkenntnissen verträglich sind, erscheint deshalb lohnenswert.One of the most intriguing characteristics of the perceptual system is that it is able to produce stable, continuous, and complete percepts even if the sensory information available in the proximal stimulus is fragmented or incomplete, for instance due to occlusion. The perception of occlusion can provoke so-called amodal completion of objects, which may influence the interpretation of a scene substantially. In contradistinction to amodal completions, perceptual completions of non-occluded objects and object regions are termed modal. This dissertation begins with a theoretical analysis of the dichotomy of modal and amodal completion that draws on phenomenological observations and existing empirical findings. It is shown that the traditional dichotomy is both incomplete and inconsistent. In addition, it is argued that the claim that phenomenal presence can be used as a criterion to distinguish between modal and amodal percepts is theoretically ad-hoc and inconsistent with phenomenology and therefore highly questionable. A further issue is that the dichotomous distinction between modal and amodal percepts is often linked with the implicit assumption that modal percepts represent geometric-optical visibility, whereas amodal percepts represent geometric-optical invisibility due to occlusion. There are, however, two empirical findings that speak against this assumption of a direct coupling of phenomenal visibility/occlusion and geometric-optical visibility/occlusion: First, modal aspects of the percept are not only available in the case of direct visibility but may also be present under phenomenal occlusion. Moreover, the modal characteristics of a percept may even be influenced by occlusion cues. Second, amodal characteristics of a percept do not only occur in the case of occlusion. Instead, the perceptual presence of non-occluded figures may, under appropriate conditions, also have an amodal character, even though the figures are phenomenally clearly visible. Based on these theoretical considerations, several experiments were conducted with the aim to provide direct empirical evidence for the claim that the classical dichotomy of modal and amodal perception is inadequate, including the aforementioned "coupling assumption" of phenomenal and geometric-optical visibility/occlusion, which is often associated with the classical dichotomy. These experiments investigate the effect of perceptual occlusion on two explicitly modal aspects of perception, namely on the perceived smoothness of apparent motion and on the phenomenal visibility of object surfaces under occlusion. In a series of five experiments on the so-called smoothing effect it is shown that the perceived smoothness of apparent motion can be considerably improved when the spatial gaps (and temporal gaps, if applicable) in discrete motion stimuli are masked with appropriate occlusion cues. The effect can be explained if one assumes that the—otherwise inexplicable—gaps in the stimulus, which typically impair the perception of motion, are (partly) compensated whenever the visual system can "explain" the gaps in a plausible manner by attributing them to an external occluder rather than to the moving object itself. This explanation ties in with theoretical ideas of constructivists claiming that perception is a process similar to intelligent problem solving (Rock, 1983, 1997) and that it is based on abductive inferences (Mausfeld, 2011a). In two further experiments the existence of the so-called visibility paradox is rigorously demonstrated and the strength of the paradoxical effect is quantified. The paradox consists of the observation that portions of a partially occluded object are, at the same time, perceived as occluded and as phenomenally visible. This seeming contradiction may be resolved if one gives up the classical assumption of a direct coupling of phenomenal visibility and geometric-optical visibility. Instead, one might conceive of the phenomenal visibility of a particular attribute (such as shape, contour, surface color) as a representation of the conclusiveness of the sensory evidence underlying perceptual inferences regarding this attribute, i. e., as reflecting the reliability of the perceptual construction. From this perspective a number of other seemingly paradoxical observations can also be explained in a consistent manner, e. g., the amodal character of hidden movement reported in Burke’s (1952) study on the tunnel effect and the partial modal completion observed in the occlusion illusion (Kanizsa, 1979; Palmer et al., 2007). Admittedly, this perspective has currently only weak empirical support, but it seems to provide a promising basis for future empirical research on the meaning of modal and amodal percepts. In summary, the results of this dissertation challenge the traditional conception of modal and amodal percepts, which is closely tied to geometric-optical visibility/occlusion. The proposed alternative view that emphasizes the role of these concepts in abductive inferences seems to be in line with the results of the experiments reported in this work. Therefore it seems worthwhile to scrutinize in a more comprehensive way to what extent existing hypotheses and explanations of completion phenomena are compatible with the findings presented here

Association of low level viremia with inflammation and mortality in HIV-infected adults.

BackgroundWhether HIV viremia, particularly at low levels is associated with inflammation, increased coagulation, and all-cause mortality is unclear.MethodsThe associations of HIV RNA level with C-reactive protein (CRP), fibrinogen, interleukin (IL)-6 and mortality were evaluated in 1116 HIV-infected participants from the Study of Fat Redistribution and Metabolic Change in HIV infection. HIV RNA level was categorized as undetectable (i.e., "target not detected"), 1-19, 20-399, 400-9999, and ≥ 10,000 copies/ml. Covariates included demographics, lifestyle, adipose tissue, and HIV-related factors.ResultsHIV RNA level had little association with CRP. Categories of HIV RNA below 10,000 copies/ml had similar levels of IL-6 compared with an undetectable HIV RNA level, while HIV RNA ≥ 10,000 copies/ml was associated with 89% higher IL-6 (p<0.001). This association was attenuated by ~50% after adjustment for CD4+ cell count. Higher HIV RNA was associated with higher fibrinogen. Compared to an undetectable HIV RNA level, fibrinogen was 0.6%, 1.9%, 4.5%, 4.6%, and 9.4% higher across HIV RNA categories, respectively, and statistically significant at the highest level (p = 0.0002 for HIV RNA ≥ 10,000 copies/ml). Higher HIV RNA was associated with mortality during follow-up in unadjusted analysis, but showed little association after adjustment for CD4+ cell count and inflammation.ConclusionHIV RNA ≥ 10,000 copies/ml was associated with higher IL-6 and fibrinogen, but lower levels of viremia appeared similar, and there was little association with CRP. The relationship of HIV RNA with IL-6 was strongly affected by CD4 cell depletion. After adjustment for CD4+ cell count and inflammation, viremia did not appear to be substantially associated with mortality risk over 5 years

Discretization of variational regularization in Banach spaces

Consider a nonlinear ill-posed operator equation $F(u)=y$ where $F$ is defined on a Banach space $X$. In general, for solving this equation numerically, a finite dimensional approximation of $X$ and an approximation of $F$ are required. Moreover, in general the given data \yd of $y$ are noisy. In this paper we analyze finite dimensional variational regularization, which takes into account operator approximations and noisy data: We show (semi-)convergence of the regularized solution of the finite dimensional problems and establish convergence rates in terms of Bregman distances under appropriate sourcewise representation of a solution of the equation. The more involved case of regularization in nonseparable Banach spaces is discussed in detail. In particular we consider the space of finite total variation functions, the space of functions of finite bounded deformation, and the $L^\infty$--space

Modification of the carbide microstructure by N- and S-functionalization of the support in MoxC/CNT catalysts

A series of catalysts based on molybdenum carbide nanoparticles supported on carbon were prepared by carburization of an oxidic Mo precursor impregnated on differently treated multi-walled carbon nanotubes (CNTs) and reference carbons, respectively. The effects of surface defects and decoration of the support with heteroatoms (O, N, and S), as analyzed by IR and Raman spectroscopy as well as by TPD, were investigated. The catalysts were characterized by XRD, N2 physisorption, and electron microscopy. The catalytic performance in steam reforming of methanol was used as a probe to indicate changes in the catalyst surface during catalytic action. The surface chemistry of the carbon supports influences the process of carburization and the nature of resulting supported MoxC (nano) particles. This includes crystal phase composition (α- and β-MoxC) and crystallite as well as particle diameter. However, if the surface decoration of the support is limited to oxygen groups, these differences are not reflected in the catalytic action, which is almost identical for oxygen functionalized carriers. A significant modification of the catalytic performance can only be achieved by surface modification of a CNT support with S- or N-containing functionalities, which causes changes in the lattice constant of the resulting carbide compared to reference systems. These changes are sensitivily reflected in activity and CO2/CH4 product ratio in steam reforming of methanol

Computing Topology Preservation of RBF Transformations for Landmark-Based Image Registration

In image registration, a proper transformation should be topology preserving. Especially for landmark-based image registration, if the displacement of one landmark is larger enough than those of neighbourhood landmarks, topology violation will be occurred. This paper aim to analyse the topology preservation of some Radial Basis Functions (RBFs) which are used to model deformations in image registration. Mat\'{e}rn functions are quite common in the statistic literature (see, e.g. \cite{Matern86,Stein99}). In this paper, we use them to solve the landmark-based image registration problem. We present the topology preservation properties of RBFs in one landmark and four landmarks model respectively. Numerical results of three kinds of Mat\'{e}rn transformations are compared with results of Gaussian, Wendland's, and Wu's functions

Sparse Regularization with lql^q Penalty Term

We consider the stable approximation of sparse solutions to non-linear operator equations by means of Tikhonov regularization with a subquadratic penalty term. Imposing certain assumptions, which for a linear operator are equivalent to the standard range condition, we derive the usual convergence rate $O(\sqrt{\delta})$ of the regularized solutions in dependence of the noise level $\delta$. Particular emphasis lies on the case, where the true solution is known to have a sparse representation in a given basis. In this case, if the differential of the operator satisfies a certain injectivity condition, we can show that the actual convergence rate improves up to $O(\delta)$.Comment: 15 page