Showing papers by "Johannes Kepler University of Linz published in 2006"

Finite Mixture and Markov Switching Models

Abstract: WINNER OF THE 2007 DEGROOT PRIZE! The prominence of finite mixture modelling is greater than ever. Many important statistical topics like clustering data, outlier treatment, or dealing with unobserved heterogeneity involve finite mixture models in some way or other. The area of potential applications goes beyond simple data analysis and extends to regression analysis and to non-linear time series analysis using Markov switching models. For more than the hundred years since Karl Pearson showed in 1894 how to estimate the five parameters of a mixture of two normal distributions using the method of moments, statistical inference for finite mixture models has been a challenge to everybody who deals with them. In the past ten years, very powerful computational tools emerged for dealing with these models which combine a Bayesian approach with recent Monte simulation techniques based on Markov chains. This book reviews these techniques and covers the most recent advances in the field, among them bridge sampling techniques and reversible jump Markov chain Monte Carlo methods. It is the first time that the Bayesian perspective of finite mixture modelling is systematically presented in book form. It is argued that the Bayesian approach provides much insight in this context and is easily implemented in practice. Although the main focus is on Bayesian inference, the author reviews several frequentist techniques, especially selecting the number of components of a finite mixture model, and discusses some of their shortcomings compared to the Bayesian approach. The aim of this book is to impart the finite mixture and Markov switching approach to statistical modelling to a wide-ranging community. This includes not only statisticians, but also biologists, economists, engineers, financial agents, market researcher, medical researchers or any other frequent user of statistical models. This book should help newcomers to the field to understand how finite mixture and Markov switching models are formulated, what structures they imply on the data, what they could be used for, and how they are estimated. Researchers familiar with the subject also will profit from reading this book. The presentation is rather informal without abandoning mathematical correctness. Previous notions of Bayesian inference and Monte Carlo simulation are useful but not needed.

Morphology of polymer/fullerene bulk heterojunction solar cells

Abstract: Within the different organic photovoltaic devices the conjugated polymer/fullerene bulk heterojunction approach is one of the foci of today's research interest. These devices are highly dependent on the solid state nanoscale morphology of the two components (donor/acceptor) in the photoactive layer. The need for finely phase separated polymer–fullerene blends is expressed by the limited exciton diffusion length present in organic semiconductors. Typical distances that these photo-excitations can travel within a pristine material are around 10–20 nm. In an efficient bulk heterojunction the scale of phase separation is therefore closely related to the respective exciton diffusion lengths of the two materials involved. Once the excitons reach the donor/acceptor interface, the photoinduced charge transfer results in the charge separation. After the charges have been separated they require percolated pathways to the respective charge extracting electrodes in order to supply an external direct current. Thus also an effective charge transport relies on the development of a suitable nanomorphology i.e. bicontinuous interpenetrating phase structures within these blend films. The present feature article combines and summarizes the experimental findings on this nanomorphology–efficiency relationship.

Detection and localization of single molecular recognition events using atomic force microscopy

Abstract: Because of its piconewton force sensitivity and nanometer positional accuracy, the atomic force microscope (AFM) has emerged as a powerful tool for exploring the forces and the dynamics of the interaction between individual ligands and receptors, either on isolated molecules or on cellular surfaces. These studies require attaching specific biomolecules or cells on AFM tips and on solid supports and measuring the unbinding forces between the modified surfaces using AFM force spectroscopy. In this review, we describe the current methodology for molecular recognition studies using the AFM, with an emphasis on strategies available for preparing AFM tips and samples, and on procedures for detecting and localizing single molecular recognition events.

Self-cooling of a micromirror by radiation pressure

Abstract: Cooling of mechanical resonators is currently a popular topic in many fields of physics including ultra-high precision measurements1, detection of gravitational waves, and the study of the transition between classical and quantum behaviour of a mechanical system. Here we report the observation of self-cooling of a micromirror by radiation pressure inside a high-finesse optical cavity. In essence, changes in intensity in a detuned cavity, as caused by the thermal vibration of the mirror, provide the mechanism for entropy flow from the mirror's oscillatory motion to the low-entropy cavity field. The crucial coupling between radiation and mechanical motion was made possible by producing free-standing micromirrors of low mass (m ≈ 400 ng), high reflectance (more than 99.6%) and high mechanical quality (Q ≈ 10,000). We observe cooling of the mechanical oscillator by a factor of more than 30; that is, from room temperature to below 10 K. In addition to purely photothermal effects we identify radiation pressure as a relevant mechanism responsible for the cooling. In contrast with earlier experiments, our technique does not need any active feedback. We expect that improvements of our method will permit cooling ratios beyond 1,000 and will thus possibly enable cooling all the way down to the quantum mechanical ground state of the micromirror.

Prognostic value of indoleamine 2,3-dioxygenase expression in colorectal cancer: effect on tumor-infiltrating T cells.

Abstract: PURPOSE: The pathologic interactions between tumor and host immune cells within the tumor microenvironment create an immunosuppressive network that promotes tumor growth and protects the tumor from immune attack. In this study, we examined the contribution of the immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO) on this phenomenon. EXPERIMENTAL DESIGN: Expression of IDO was analyzed in colorectal cancer cell lines by reverse transcription-PCR and functional enzyme activity was assessed by high-pressure liquid chromatography. Semiquantitative immunohistochemistry was used to evaluate IDO expression in the tissue samples of 143 patients with colorectal carcinoma, and was then correlated with the number of tumor-infiltrating T cells and clinical variables. RESULTS: In vitro IDO expression and functional enzyme activity in colorectal cancer cells was found to be strictly dependent on IFN-gamma stimulation. Immunohistochemical scores revealed IDO-high expression in 56 of 143 (39.2%) tumor specimens, whereas 87 of 143 (60.8%) cases showed low IDO expression levels. IDO-high expression was associated with a significant reduction of CD3+ infiltrating T cells (46.02 +/- 7.25) as compared with tissue samples expressing low IDO (19.42 +/- 2.50; P = 0.0003). Furthermore, IDO-high immunoreactivity significantly correlated with the frequency of liver metastases (P = 0.003). Kaplan-Meier analysis showed the crossing of survival curves at 45 months. By multivariate Cox9s analysis, IDO-high expression emerged as an independent prognostic variable ( 45 months, P = 0.04). CONCLUSION: IDO-high expression by colorectal tumor cells enables certain cancer subsets to initially avoid immune attack and defeat the invasion of T cells via local tryptophan depletion and the production of proapoptotic tryptophan catabolites. Thus, IDO significantly contributes to disease progression and overall survival in patients with colorectal cancer.

Who Trusts? Personality, Trust and Knowledge Sharing:

Abstract: The strategic importance of knowledge sharing and its relationships with organizational and managerial (i.e. environmental) factors have been well documented. The effects of some context-specific individual factors—including interpersonal trust—on knowledge sharing have also been investigated. The effects of enduring and pervasive individual factors (i.e, personality) on knowledge sharing have not been adequately described empirically. This article links personality, specifically agreeableness, a broad personality domain and propensity to trust, a narrow personality facet, to knowledge sharing via interpersonal trust, thereby clarifying substantial person-related effects within these important workplace phenomena.

Analysis of Thin Beams and Cables Using the Absolute Nodal Co-ordinate Formulation

Abstract: The purpose of this paper is to present formulations for beam elements based on the absolute nodal co-ordinate formulation that can be effectively and efficiently used in the case of thin structural applications. The numerically stiff behaviour resulting from shear terms in existing absolute nodal co-ordinate formulation beam elements that employ the continuum mechanics approach to formulate the elastic forces and the resulting locking phenomenon make these elements less attractive for slender stiff structures. In this investigation, additional shape functions are introduced for an existing spatial absolute nodal co-ordinate formulation beam element in order to obtain higher accuracy when the continuum mechanics approach is used to formulate the elastic forces. For thin structures where bending stiffness can be important in some applications, a lower order cable element is introduced and the performance of this cable element is evaluated by comparing it with existing formulations using several examples. Cables that experience low tension or catenary systems where bending stiffness has an effect on the wave propagation are examples in which the low order cable element can be used. The cable element, which does not have torsional stiffness, can be effectively used in many problems such as in the formulation of the sliding joints in applications such as the spatial pantograph/catenary systems. The numerical study presented in this paper shows that the use of existing implicit time integration methods enables the simulation of multibody systems with a moderate number of thin and stiff finite elements in reasonable CPU time.

Individual determinants of brand affect: the role of the personality traits of extraversion and openness to experience

Abstract: Purpose – The purpose of this paper is to explore the relationship among two personality traits (extraversion and openness), hedonic value, brand affect and loyalty. It argues that individual differences account for differences in the values sought by the consumer and in the formation of brand affect and loyalty.Design/methodology/approach – Two samples are drawn (running shoes and mobile phone users) and the effect of personality traits on the other constructs have been tested using the Partial Least Squares approach (PLS) to structural equation modeling.Findings – It was found that extraversion and openness are positively related to hedonic product value and that the personality traits directly (openness) and indirectly (extraversion, via hedonic value) influence brand affect which in turn drives attitudinal and purchase loyalty.Research limitations/implications – The paper introduces personality as determinants of perceived value and brand affect. Future studies should aim at including the other person...

Au-free epitaxial growth of InAs nanowires.

Abstract: III-V nanowires have been fabricated by metal-organic vapor-phase epitaxy without using Au or other metal particles as a catalyst. Instead, prior to growth, a thin SiOx layer is deposited on the substrates. Wires form on various III-V substrates as well as on Si. They are nontapered in thickness and exhibit a hexagonal cross-section. From high-resolution X-ray diffraction, the epitaxial relation between wires and substrates is demonstrated and their crystal structure is determined.

Progress in plastic electronics devices

Abstract: ▪ Abstract Organic field-effect transistors (OFETs) based on solution-processible polymeric as well as small molecular semiconductors have shown impressive improvements in their performance during recent years. These devices have been developed to realize low-cost, large-area electronic products. This review gives an overview of the materials’ aspect, charge-transport, and device physics of OFETs, focusing mainly on the organic semiconductor and organic dielectric materials and their mutual interface. Recent developments in the understanding of the relationship between microstructure and charge transport, the influence of processing techniques, and gate dielectric are reviewed. Comparative data of charge-carrier mobility of most organic semiconductors have been compiled. Ambipolar charge transport in OFETs and its applications to integrated circuits as well as ambipolar light-emitting transistors are also reviewed. Many interesting questions regarding how the molecular and electronic structures at the int...

The Relationship between Interpersonal Trust, Employee Satisfaction, and Employee Loyalty

Abstract: Employee satisfaction is considered to be one of the most important drivers of quality, customer satisfaction and productivity. In this study we investigate an important driver of employee satisfaction. We argue that interpersonal trust (trust in management and trust in peers) strongly influences employee satisfaction and, as a consequence, employee loyalty. To test the relationships between these constructs we measured trust in management and trust in peers, satisfaction and loyalty of employees of an Austrian company in the energy sector (N = 131). The results of the statistical analysis using structural equation modeling with Partial Least Squares (PLS) confirm a strong link between trust, employee satisfaction and employee loyalty.

Shadow Economies and Corruption All Over the World: What Do We Really Know?*

Abstract: Estimations of the size and development of the shadow economy for 145 countries, including developing, transition and highly developed OECD economies over the period 1999 to 2003 are presented. The average size of the shadow economy (as a percent of “official” GDP) in 2002/03 in 96 developing countries is 38.7%, in 25 transition countries 40.1%, in 21 OECD countries 16.3% and in 3 Communist countries 22.3%. An increased burden of taxation and social security contributions, combined with a labor market regulation are the driving forces of the shadow economy. Furthermore, the results show that the shadow economy reduces corruption in high income countries, but increases corruption in low income countries. Finally, the various estimation methods are discussed and critically evaluated.

Colloidal HgTe nanocrystals with widely tunable narrow band gap energies : From telecommunications to molecular vibrations

Abstract: A convenient, aqueous-based synthesis of stable HgTe nanocrystals with widely size-tunable room temperature emission between wavelengths of 1.2 to 3.7 μm is demonstrated. By the choice of the thiols, applied as stabilizers, we optimized the growth dynamics, the luminescence quantum yields (up to 40%), and a ligand-exchange procedure, required to transfer the nanocrystals from water to nonpolar organic solvents. The latter is greatly improved and facilitated by the use of mercaptoethylamine as initial stabilizer. The possibility to tune the HgTe nanocrystal sizes from 3 to 12 nm and to control their surface functionalities (hydrophobic and hydrophilic) makes them very promising for the development of infrared optical devices, emitting in the wavelength region between the telecommunications and the molecular vibrations.

Dimensions of price satisfaction: a study in the retail banking industry

Abstract: Purpose – The purpose of this paper is to explore the dimensionality of price satisfaction. It argues that price satisfaction is composed of several dimensions (price transparency, price‐quality ratio, relative price, price confidence, price reliability, and price fairness) and that companies should consider these dimensions when monitoring customer satisfaction.Design/methodology/approach – Based on a theoretical discussion of the price dimensions, a questionnaire is developed that measures customer satisfaction with individual price dimensions. Using regression analysis the impact of price satisfaction dimensions on overall price satisfaction is measured, using a sample of 160 students.Findings – The results show that price satisfaction can be conceptualized as a multidimensional construct and that five dimensions influence overall price satisfaction. The application of the questionnaire allows for measuring price satisfaction in firms.Research limitations/implications – The paper introduces price satis...

Molecular recognition imaging and force spectroscopy of single biomolecules.

Abstract: In recent years, considerable attention has focused on biological applications of the atomic force microscope (AFM), in particular on high-resolution imaging of individual biological molecules and on the measurement of molecular forces under near-physiological conditions. The detection of intermolecular forces in the piconewton range has paved the way to investigate details on structural parameters of the binding pockets and the energy landscapes of many biomolecular interactions. The capability of AFM to resolve nanometer-sized details, together with its force detection sensitivity, led to the development of molecular recognition imaging. By a combination of topographical imaging with force measurements, receptor sites are localized with nanometer accuracy. Topography and recognition of target molecules are thereby simultaneously mapped. Thus the AFM can identify specific components in a complex biological sample and retain its high resolution in imaging.

Augmented reality navigation systems

Abstract: The augmented reality (AR) research community has been developing a manifold of ideas and concepts to improve the depiction of virtual objects in a real scene. In contrast, current AR applications require the use of unwieldy equipment which discourages their use. In order to essentially ease the perception of digital information and to naturally interact with the pervasive computing landscape, the required AR equipment has to be seamlessly integrated into the user’s natural environment. Considering this basic principle, this paper proposes the car as an AR apparatus and presents an innovative visualization paradigm for navigation systems that is anticipated to enhance user interaction.

Phase-Field Relaxation of Topology Optimization with Local Stress Constraints

Abstract: We introduce a new relaxation scheme for structural topology optimization problems with local stress constraints based on a phase-field method In the basic formulation we have a PDE-constrained optimization problem, where the finite element and design analysis are solved simultaneously The starting point of the relaxation is a reformulation of the material problem involving linear and 0-1 constraints only The 0-1 constraints are then relaxed and approximated by a Cahn-Hilliard-type penalty in the objective functional, which yields convergence of minimizers to 0-1 designs as the penalty parameter decreases to zero A major advantage of this kind of relaxation opposed to standard approaches is a uniform constraint qualification that is satisfied for any positive value of the penalization parameter The relaxation scheme yields a large-scale optimization problem with a high number of linear inequality constraints We discretize the problem by finite elements and solve the arising finite-dimensional programming problems by a primal-dual interior point method Numerical experiments for problems with local stress constraints based on different criteria indicate the success and robustness of the new approach

Photoinduced charge and energy transfer involving fullerene derivatives.

Abstract: In this feature article, a brief overview over the photoinduced energy and charge transfer mechanisms involving fullerenes will be presented. The photoinduced charge separation between organic donor and acceptor molecules is the basic photophysical mechanism for natural photosynthesis and nearly all organic solar cell concepts. We will give a short introduction to the mechanisms of excited state charge transfer and resonant energy transfer and present examples of relevant applications in organic optoelectronics and photodynamic tumor therapy.

Self-organized minimum-energy structures for dielectric elastomer actuators

Abstract: When a stretched elastomer is laminated to a flat plastic frame, a complex shape is formed, which is termed a minimum-energy structure. It is shown how self-organized structures can be applied in the development of actuators with complex, out-of-plane actuationmodes. This unusual concept is then demonstrated in the case of dielectric elastomer actuators. Among advantages of this approach are the simplicity in manufacturing, the potential complexity and sophistication of the manufactured structures, and the general benefits of the concept when applied to other electro-mechanically active materials.

Piezo-, pyro- and ferroelectrets: soft transducer materials for electromechanical energy conversion

Abstract: Cellular space charge polymer electrets significantly enlarge the basis of pyro- and piezoelectric as well as ferroic materials. Since the first review of the field has been published in this journal (R. Gerhard-Multhaupt, Less can be more: Holes in polymers lead to a new paradigm of piezoelectric materials for electret transducers, IEEE Trans. Dielectr. Electr. Insul. Vol.9, pp.850-859, 2002), progress has been achieved in the understanding, preparation and characterization of cellular space charge electrets. Advanced applications arise in stacked microphones, artificial sonar systems, and in the combination of piezo- and ferroelectrets with flexible electronics. In the present survey an update of the developments since 2002 is provided

C-terminal modulator controls Ca2+-dependent gating of Cav1.4 L-type Ca2+ channels

Abstract: Tonic neurotransmitter release at sensory cell ribbon synapses is mediated by calcium (Ca2+) influx through L-type voltage-gated Ca2+ channels. This tonic release requires the channels to inactivate slower than in other tissues. Ca(v)1.4 L-type voltage-gated Ca2+ channels (LTCCs) are found at high densities in photoreceptor terminals, and alpha1 subunit mutations cause human congenital stationary night blindness type-2 (CSNB2). Ca(v)1.4 voltage-dependent inactivation is slow and Ca2+-dependent inactivation (CDI) is absent. We show that removal of the last 55 or 122 (C122) C-terminal amino acid residues of the human alpha1 subunit restores calmodulin-dependent CDI and shifts voltage of half-maximal activation to more negative potentials. The C terminus must therefore form part of a mechanism that prevents calmodulin-dependent CDI of Ca(v)1.4 and controls voltage-dependent activation. Fluorescence resonance energy transfer experiments in living cells revealed binding of C122 to C-terminal motifs mediating CDI in other Ca2+ channels. The absence of this modulatory mechanism in the CSNB2 truncation mutant K1591X underlines its importance for normal retinal function in humans.

Lifting metamodels to ontologies: a step to the semantic integration of modeling languages

Abstract: The use of different modeling languages in software development makes their integration a must. Most existing integration approaches are metamodel-based with these metamodels representing both an abstract syntax of the corresponding modeling language and also a data structure for storing models. This implementation specific focus, however, does not make explicit certain language concepts, which can complicate integration tasks. Hence, we propose a process which semi-automatically lifts metamodels into ontologies by making implicit concepts in the metamodel explicit in the ontology. Thus, a shift of focus from the implementation of a certain modeling language towards the explicit reification of the concepts covered by this language is made. This allows matching on a solely conceptual level, which helps to achieve better results in terms of mappings that can in turn be a basis for deriving implementation specific transformation code.

Glass surfaces grafted with high-density poly(ethylene glycol) as substrates for DNA oligonucleotide microarrays.

Abstract: Surfaces carrying a dense layer of poly(ethylene glycol) (PEG) were prepared, characterized, and tested as substrates for DNA oligonucleotide microarrays. PEG bis(amine) with a molecular weight of 2000 was grafted onto silanized glass slides bearing aldehyde groups. After grafting, the terminal amino groups of the PEG layer were derivatized with the heterobifunctional cross-linker succinimidyl 4-[p-maleimidophenyl]butyrate to permit the immobilization of thiol-modified DNA oligonucleotides. The stepwise chemical modification was validated with X-ray photoelectron spectroscopy. Goniometry indicated that the PEG grafting procedure reduced surface inhomogeneities present after the silanization step, while atomic force microscopy and ellipsometry confirmed that the PEG layer was dense and monomolecular. Hybridization assays using DNA oligonucleotides and fluorescence imaging showed that PEG grafting improved the yield in hybridization 4-fold compared to non-PEGylated maleimide-derivatized surfaces. In additio...