Detecting Differential Item and Step Functioning with Rating Scale and Partial Credit Trees

Several statistical procedures have been suggested for detecting differential item functioning (DIF) and differential step functioning (DSF) in polytomous items. However, standard procedures are designed for the comparison of pre-specified reference and focal groups, such as males and females. Here, we propose a framework for the detection of DIF and DSF in polytomous items under the rating scale and partial credit model, that employs a model-based recursive partitioning algorithm. In contrast to existing procedures, with this approach no pre-specification of reference and focal groups is necessary, because they are detected in a data-driven way. The resulting groups are characterized by (combinations of) covariates and thus directly interpretable. The statistical background and construction of the new procedures are introduced along with an instructive example. Four simulation studies illustrate and compare their statistical properties to the well-established likelihood ratio test (LRT). While both the LRT and the new procedures respect a given significance level, the new procedures are in most cases equally (simple DIF groups) or more powerful (complex DIF groups) and can also detect DSF. The sensitivity to model misspecification is investigated. An application example with empirical data illustrates the practical use. A software implementation of the new procedures is freely available in the R system for statistical computing

Molecular Topology and Molecular Properties I. »Sequence« Labels of Cata-Condensed Benzenoid Hydrocarbons Containing up to Five Rings

An algorithm ds described for the systematic numbering o,f benz,enoid hydrocarbons. The sum of decimal contributions of all vertices (carbon atoms) in th.e molecular graph is called the hydrocarbon label, L. These labels, which are based on pua:ely structural elements order a set o{ isomeric benzenoid hydrocarbons according to their properties including resonance and total pi-energies, ionization potent~als, heats of atomization, energies of lowest vacant and lo·west filled molecular orbitals and polarographic haLf-wave reduction potentials. Such hydrocarbon labels might easily be computed without resort to a computer

Processing of sky compass signals at different stages of the polarization-vision pathway in the brain of the desert locust (Schistocerca gregaria)

Obwohl Insekten ein relativ kleines Gehirn aufweisen, zeigen sie außergewöhnliche Leistungen in räumlicher Orientierung und Navigation. Während langer Wanderflüge oder der Rückkehr zu einem Nestplatz können sie die ideale Route bestimmen und verfolgen, die sie auf kürzestem und schnellstem Weg zu ihrem Ziel führt. Hierbei können vor allem Kompasssignale des Himmels eine erhebliche Rolle spielen. Neben der Sonne, dem hellsten Punkt am Himmel, liefern weitere Himmelssignale wie der Farbgradient oder das Polarisationsmuster des Himmels Möglichkeiten zur Orientierung. Beide Himmelserscheinungen entstehen als Resultat der Streuung von Sonnenlicht an atmosphärischen Partikeln und bilden präzise Referenzen am Himmel. Verhaltensversuche haben gezeigt, dass Wüstenheuschrecken der Gattung Schistocerca gregaria während ihren langen Wanderungen über Nordafrika und Ostasien linear polarisiertes Licht des Himmels zur Navigation nutzen können. Hierfür verfügen sie über eine spezialisierte Augenregion zur Detektion von polarisiertem Licht, die sich dorsal am Komplexauge morphologisch vom restlichen Auge hervorhebt und als dorsale Randregion bezeichnet wird. Angesichts ihres relativ großen Gehirnes und der damit einhergehenden guten physiologischen Zugänglichkeit hat sich die Wüstenheuschrecke Schistocerca gregaria als hervorragendes Modellobjekt erwiesen, um die neuronalen Prinzipien der Verarbeitung von polarisiertem Licht im Insektengehirn zu erforschen. Die Prozessierung von Polarisationssignalen findet in sukzessiv angeordneten Gehirnarealen der Heuschrecke statt, die die sogenannte Polarisationssehbahn bilden. Die Axone der Fotorezeptoren in der dorsalen Randregion ziehen aus dem Auge in zwei distinkte, ebenfalls dorsal lokalisierte Randregionen der optischen Neuropile Lamina und Medulla. Über Transmedulla-Neurone – auch als „Line Tangential“-Neurone bezeichnet – ist die dorsale Randregion der Medulla mit einem Bereich im Zentralhirn verbunden, der als anteriorer optischer Tuberkel bezeichnet wird. Die Polarisationsinformation wird dann zu den nächsten Stationen der Polarisationssehbahn, der medianen Olive und dem lateralen Dreieck geleitet. Hier transferieren Neurone die Polarisationssignale auf Eingangsneurone des Zentralkomplexes. Der Zentralkomplex ist das zentrale Prozessierungsareal für polarisiertes Licht und erfüllt möglicherweise eine Rolle als interner Kompass im Heuschreckengehirn, in dem die räumliche Orientierung des Tieres relativ zum solaren Meridian kodiert wird. Ausgangsneurone des Zentralkomplexes könnten die Polarisationssignale auf absteigende Neurone übertragen, deren Axone wiederum zu den Kontrollzentren in den Thorakalganglien projizieren. Um die Kombination der Polarisationsinformation mit weiteren visuellen Reizen zu untersuchen, und um einen tieferen Einblick in Vorgänge der Zeitkompensation und Modulation des Polarisationsnetzwerks zu gewinnen, wurden in dieser Arbeit elektrophysiologische und anatomische Untersuchungen polarisationssensitiver Neurone durchgeführt

An Easy Combinatorial Algorithm for the Construction of Sextet Polynomials of Cata-Condensed Benzenoid Hydrocarbons

Two types oif i>mning techniques for cer.tain trees are described and utilized into an easy combinatorial a1gorithm for the f:?YStematic construction o.f sextet polynomials of catacon.densed benzenoid hydrocarbons of large sizes. The a1gori.thm oiffers an ailte!l\u27na.tive to ex~sting methods !or the enumeration of Kekule structures which is not restricted to non-branched systems

On the use of vertically averaged models to simulate CO2 migration in a layered saline aquifer

Geologic and flow characteristics such as permeability and porosity, capillary pressure, geologic structure, and thickness all influence and affect CO2 plume distribution to varying degrees. These parameters do not necessarily act independently. Depending on the variations in these parameters one may dominate the shape and size of the plume. In this master thesis, we consider the long-term fate and migration of a large CO2 plume that takes place in a heterogeneous (two-layer) sloping saline aquifer. We consider a vertical equilibrium (VE) mathematical model to study the effect of two different permeability layers on the shape, speed and migrated distance of the CO2 plume. The layer-permeability-ratio is k2/k1, where k2 and k1 are the permeabilities in the upper and lower layer of the aquifer, respectively. We also study the effect the thickness ratio of the lower permeability(h=H/2, h=H/4, h=H/8), where H is the thickness of the aquifer. We attain these goals by comparing the simulation results of Eclipse and VE simulators, where both simulate the movement of CO2 plume in homogeneous and layered aquifers. A VE model has been built considering one-dimensional flow in the x-direction, due to the big difference in scale length between vertical and horizontal directions. We model a 2D vertical section in Eclipse simulator, taking the vertically averaged of this section ends up with a 1D results that can compared with the VE solution. Our results shows that the variations in the vertical permeability layers may have a dramatic effects on the CO2 plume shape. Relatively lower permeability layer reduces the velocity of CO2 through it, and an increase of CO2 saturation occurs below this layer. At early time, the build up in saturation increases, and the lateral growth of the CO2 immediately below this layer increases. At later time, the saturation decreases and the vertical flow of the CO2 in this layer increases. The k2/k1 ratio and thickness of the lower permeability layer determines the plume shape and distance migrated. In some of our simulations, the results show two connected/disconnected plumes.Master i Anvendt og beregningsorientert matematikkMAMN-MABMAB39

Reactions of organoboranes with carbanions bearing three potential leaving groups: unusual processes, products and mechanisms

Known reagents that transfer three alkyl groups of a trialkylborane intramolecularly to a single carbon atom lack features to influence stereochemistry. We have investigated four reagents of type LiCCl2X, where X might be amenable to variation. All behaved differently. With X=OR (R=cyclohexyl, menthyl), the reagent decomposed, leading to only low yields of triple migration products. With X=S(O)Ph, a single migration occurred, followed by isomerisation to boron enolate-like species that hydrolysed to α-chloroalkyl phenyl sulfoxides or reacted with aldehydes to aldol-like products. With X=SO2Ph, the major product was the corresponding α,α-dichloroalkyl phenyl sulfone, apparently formed through a redox reaction. With X=S(O)(NMe)Ph, products of three intramolecular alkyl migrations were obtained with unhindered trialkylboranes. Attempts have been made to gain understanding of the sulfoxide process by investigating proportions of aldol-like products, using X-ray crystallography and ab initio calculations

Hybrid Takagi‐Sugeno Fuzzy FED PID Control of Nonlinear Systems

The new method of proportional‐integral‐derivative (PID) controller is proposed in this paper for a hybrid fuzzy PID controller for nonlinear system. The important feature of the proposed approach is that it combines the fuzzy gain scheduling method and a fuzzy fed PID controller to solve the nonlinear control problem. The resultant fuzzy rule base of the proposed controller contains one part. This single part of the rules uses the Takagi–Sugeno method for solving the nonlinear problem. The simulation results of a nonlinear system show that the performance of a fed PID Hybrid Takagi‐Sugeno fuzzy controller is better than that of the conventional fuzzy PID controller or Hybrid Mamdani fuzzy FED PID controller

Two axes sun tracker using fuzzy controller via PIC16F877A

This paper presents sun tracking generating power system designed and implemented in real time. A tracking mechanism composed of photovoltaic module, stepper motor, sensors, input/output interface and expert FLC implemented on PIC, that to track the sun and keep the solar cells always face the sun in most of the day time. The proposed sun tracking controller is tested using Matlab/Simulink program, the results show that the controller have a good respons