Showing papers by "University of Paderborn published in 2010"

Mapping the institutional capital of high-tech firms: A fuzzy-set analysis of capitalist variety and export performance

Abstract: We examine how institutional configurations, not single institutions, provide companies with institutional capital. Building on the varieties-of-capitalism approach, it is argued that competitive advantage in high-tech industries with radical innovation may be supported by combinations of certain institutional conditions: lax employment protection, weak collective bargaining coverage, extensive university training, little occupational training, and a large stock market. Furthermore, multinational enterprises engage in “institutional arbitrage”: they allocate their activities so as to benefit from available institutional capital. These hypotheses are tested on country-level data for 19 OECD economies in the period 1990 to 2003. A fuzzy-set qualitative comparative analysis yields several interesting findings. A high share of university graduates and a large stock market are complementary institutions leading to strong export performance in high-tech. Employment protection is neither conducive nor harmful to export performance in high-tech. A high volume of cross-border mergers and acquisitions, as a form of institutional arbitrage leading to knowledge flows, acts as a functional equivalent to institutions that support knowledge production in the home economy. Implications of these findings for theory, policy, and the analysis of firm-level behavior are developed.

Porous Graphene as an Atmospheric Nanofilter

Abstract: The fabrication of nanoscale membranes exhibiting high selectivity is an emerging field of research. The possibility to use bottom-up approaches to fabricate a filter with porous graphene and analyze its functionality with first principle calculations is investigated. Here, the porous network is produced by self-assembly of the hexaiodo-substituted macrocycle cyclohexa-m-phenylene (CHP). The resulting porous network exhibits an extremely high selectivity in favor of H(2) and He among other atmospheric gases, such as Ne, O(2), N(2), CO, CO(2), NH(3), and Ar. The presented membrane is superior to traditional filters using polymers or silica and could have great potential for further technological applications such as gas sensors or fuel cells.

Modeling the Impact of Corporate Reputation on Customer Satisfaction and Loyalty Using Partial Least Squares

Abstract: Reputation is one of the most important intangible assets of a firm. For the most part, recent articles have investigated its impact on firm profitability whereas its effects on individual customers have been neglected. Using data from consumers of an international consumer goods producer, this paper (1) focuses on measuring and discussing the relationships between corporate reputation, consumer satisfaction, and consumer loyalty and (2) examines possible moderating and mediating effects among the constructs. We find that reputation is an antecedent of satisfaction and loyalty that has hitherto been neglected by management. Furthermore, we find that more than half of the effect of reputation onto loyalty is mediated by satisfaction. This means that reputation can only partially be considered a substitute for a consumer’s own experiences with a firm. In order to achieve consumer loyalty, organizations need to create both, a good reputation and high satisfaction.

StreamKM++: a clustering algorithm for data streams

Abstract: We develop a new k-means clustering algorithm for data streams, which we call StreamKM++. Our algorithm computes a small weighted sample of the data stream and solves the problem on the sample using the k-means++ algorithm [1]. To compute the small sample, we propose two new techniques. First, we use a non-uniform sampling approach similar to the k-means++ seeding procedure to obtain small coresets from the data stream. This construction is rather easy to implement and, unlike other coreset constructions, its running time has only a low dependency on the dimensionality of the data. Second, we propose a new data structure which we call a coreset tree. The use of these coreset trees significantly speeds up the time necessary for the non-uniform sampling during our coreset construction. We compare our algorithm experimentally with two well-known streaming implementations (BIRCH [16] and StreamLS [4, 9]). In terms of quality (sum of squared errors), our algorithm is comparable with StreamLS and significantly better than BIRCH (up to a factor of 2). In terms of running time, our algorithm is slower than BIRCH. Comparing the running time with StreamLS, it turns out that our algorithm scales much better with increasing number of centers. We conclude that, if the first priority is the quality of the clustering, then our algorithm provides a good alternative to BIRCH and StreamLS, in particular, if the number of cluster centers is large. We also give a theoretical justification of our approach by proving that our sample set is a small coreset in low dimensional spaces.

Entrepreneurship and Structural Economic Transformation

Abstract: This paper provides an endogenous growth model to illuminate the role of entrepreneurial start-up firms in structural economic transformation. We follow the Lewis-model distinction between a traditional and modern sector and underpin this distinction with micro-foundations. We specify mature and start-up entrepreneurs and make a distinction between survivalist self-employment activities in the traditional sector and opportunity-driven entrepreneurship in the modern. The model shows how opportunity-driven entrepreneurship can drive structural transformation in both the modern and traditional sectors through innovation and the provision of intermediate inputs and services (which permits greater specialization in manufacturing) and by increasing employment and productivity.

A Subthreshold to Above-Threshold Level Shifter Comprising a Wilson Current Mirror

Abstract: In this brief, we propose a novel level shifter circuit that is capable of converting subthreshold to above-threshold signal levels. In contrast to other existing implementations, it does not require a static current flow and can therefore offer considerable static power savings. The circuit has been optimized and simulated in a 90-nm process technology. It operates correctly across process corners for supply voltages from 100 mV to 1 V on the low-voltage side. At the target design voltage of 200 mV, the level shifter has a propagation delay of 18.4 ns and a static power dissipation of 6.6 nW. For a 1-MHz input signal, the total energy per transition is 93.9 fJ. Simulation results are compared to an existing subthreshold to above-threshold level shifter implementation from the paper of Chen et al.

Efficient implementation of the GW approximation within the all-electron FLAPW method

Abstract: We present an implementation of the $GW$ approximation for the electronic self-energy within the full-potential linearized augmented-plane-wave (FLAPW) method. The algorithm uses an all-electron mixed product basis for the representation of response matrices and related quantities. This basis is derived from the FLAPW basis and is exact for wave-function products. The correlation part of the self-energy is calculated on the imaginary-frequency axis with a subsequent analytic continuation to the real axis. As an alternative we can perform the frequency convolution of the Green function $G$ and the dynamically screened Coulomb interaction $W$ explicitly by a contour integration. The singularity of the bare and screened interaction potentials gives rise to a numerically important self-energy contribution, which we treat analytically to achieve good convergence with respect to the $\mathbf{k}$-point sampling. As numerical realizations of the $GW$ approximation typically suffer from the high computational expense required for the evaluation of the nonlocal and frequency-dependent self-energy, we demonstrate how the algorithm can be made very efficient by exploiting spatial and time-reversal symmetry as well as by applying an optimization of the mixed product basis that retains only the numerically important contributions of the electron-electron interaction. This optimization step reduces the basis size without compromising the accuracy and accelerates the code considerably. Furthermore, we demonstrate that one can employ an extrapolar approximation for high-lying states to reduce the number of empty states that must be taken into account explicitly in the construction of the polarization function and the self-energy. We show convergence tests, CPU timings, and results for prototype semiconductors and insulators as well as ferromagnetic nickel.

Positive Frequency Shifts Observed Upon Adsorbing Micron-Sized Solid Objects to a Quartz Crystal Microbalance from the Liquid Phase

Abstract: By specifically binding derivatized colloidal particles and physisorbing nonderivatized particles to the surface of a quartz crystal microbalance (QCM), we have observed positive shifts of frequency, Δf, in contrast to the negative frequency shifts typically found in adsorption experiments. Evidently, the Sauerbrey relation does not apply to this situation. A comparison of frequencies shifts and bandwidths on different overtones reveals a coupled resonance: at low overtones, Δf is negative, whereas it is positive at high overtones, with maximal resonance bandwidth observed at the crossover point. As predicted by the Dybwad model,(1) the spheres bound to the surface form resonating systems on their own. A composite resonator is formed, consisting of a large crystal with resonance frequency ω and the adsorbed spheres with resonance frequency ωS. In the case in which the resonance frequency of the small spheres (firmly attached to crystal), ωS, is higher than the resonance frequency of the crystal, ω, Δf of ...

A Time-Space Network Approach for the Integrated Vehicle-and Crew-Scheduling Problem with Multiple Depots

Abstract: This paper discusses the integrated vehicle-and crew-scheduling problem in public transit with multiple depots. It is well known that the integration of both planning steps discloses additional flexibility that can lead to gains in efficiency, compared to sequential planning. We present a new modeling approach that is based on a time-space network representation of the underlying vehicle-scheduling problem. The integrated problem is solved with column generation in combination with Lagrangian relaxation. The column generation subproblem is modeled as a resource-constrained shortest-path problem based on a novel time-space network formulation. Feasible solutions are generated by a heuristic branch-and-price method that involves fixing service trips to depots. Numerical results show that our approach outperforms other methods from the literature for well-known test problems.

Clustering for metric and nonmetric distance measures

Abstract: We study a generalization of the k-median problem with respect to an arbitrary dissimilarity measure D Given a finite set P of size n, our goal is to find a set C of size k such that the sum of errors D(P,C) = ∑p i P minc i C {D(p,c)} is minimized The main result in this article can be stated as follows: There exists a (1+ϵ)-approximation algorithm for the k-median problem with respect to D, if the 1-median problem can be approximated within a factor of (1+ϵ) by taking a random sample of constant size and solving the 1-median problem on the sample exactly This algorithm requires time n2O(mklog(mk/ϵ)), where m is a constant that depends only on ϵ and D Using this characterization, we obtain the first linear time (1+ϵ)-approximation algorithms for the k-median problem in an arbitrary metric space with bounded doubling dimension, for the Kullback-Leibler divergence (relative entropy), for the Itakura-Saito divergence, for Mahalanobis distances, and for some special cases of Bregman divergences Moreover, we obtain previously known results for the Euclidean k-median problem and the Euclidean k-means problem in a simplified manner Our results are based on a new analysis of an algorithm of Kumar et al [2004]

Lithium niobate X -cut, Y -cut, and Z -cut surfaces from ab initio theory

Abstract: Density-functional theory calculations of the ${\text{LiNbO}}_{3}$ $(2\overline{1}\overline{1}0)$, $(1\overline{1}00)$, and (0001) surfaces, commonly referred to as $X$, $Y$, and $Z$ cuts, are presented. In case of the $Z$ cut, we find a pronounced dependence of the surface structure and stoichiometry on the direction of the ferroelectric polarization. In contrast, the influence of the chemical potentials of the surface constituents is limited. Rather electrostatics governs the surface stability. Different from the $Z$ cut, the stoichiometry of the $X$ cut and $Y$ cut is clearly dependent on the preparation conditions. The surface charge observed for the nominal nonpolar $Y$ cut is traced back to the formation of a strong surface dipole.

Pricing randomized allocations

Abstract: Randomized mechanisms, which map a set of bids to a probability distribution over outcomes rather than a single outcome, are an important but ill-understood area of computational mechanism design. We investigate the role of randomized outcomes (henceforth, "lotteries") in the context of a fundamental and archetypical multi-parameter mechanism design problem: selling heterogeneous items to unit-demand bidders. To what extent can a seller improve her revenue by pricing lotteries rather than items, and does this modification of the problem affect its computational tractability? Our results show that the answers to these questions hinge on whether consumers can purchase only one lottery (the buy-one model) or purchase any set of lotteries and receive an independent sample from each (the buy-many model). In the buy-one model, there is a polynomial-time algorithm to compute the revenue-maximizing envy-free prices (thus overcoming the inapproximability of the corresponding item pricing problem) and the revenue of the optimal lottery system can exceed the revenue of the optimal item pricing by an unbounded factor as long as the number of item types is at least 4. In the buy-many model with n item types, the profit achieved by lottery pricing can exceed item pricing by a factor of Θ(log n) but not more, and optimal lottery pricing cannot be approximated within a factor of O(ne) for some e > 0, unless NP ⊆ ∩δ>0 BPTIME(2O(nδ)). Our lower bounds rely on a mixture of geometric and algebraic techniques, whereas the upper bounds use a novel rounding scheme to transform a mechanism with randomized outcomes into one with deterministic outcomes while losing only a bounded amount of revenue.

Fluctuating emg signals: Investigating long-term effects of pattern matching algorithms

Abstract: In this paper, we investigate the behavior of state-of-the-art pattern matching algorithms when applied to electromyographic data recorded during 21 days. To this end, we compare the five classification techniques k-nearest-neighbor, linear discriminant analysis, decision trees, artificial neural networks and support vector machines. We provide all classifiers with features extracted from electromyographic signals taken from forearm muscle contractions, and try to recognize ten different hand movements. The major result of our investigation is that the classification accuracy of initially trained pattern matching algorithms might degrade on subsequent data indicating variations in the electromyographic signals over time.

Blind speech separation employing directional statistics in an Expectation Maximization framework

Abstract: In this paper we propose to employ directional statistics in a complex vector space to approach the problem of blind speech separation in the presence of spatially correlated noise. We interpret the values of the short time Fourier transform of the microphone signals to be draws from a mixture of complexWatson distributions, a probabilistic model which naturally accounts for spatial aliasing. The parameters of the density are related to the a priori source probabilities, the power of the sources and the transfer function ratios from sources to sensors. Estimation formulas are derived for these parameters by employing the Expectation Maximization (EM) algorithm. The E-step corresponds to the estimation of the source presence probabilities for each time-frequency bin, while the M-step leads to a maximum signal-to-noise ratio (MaxSNR) beamformer in the presence of uncertainty about the source activity. Experimental results are reported for an implementation in a generalized sidelobe canceller (GSC) like spatial beamforming configuration for 3 speech sources with significant coherent noise in reverberant environments, demonstrating the usefulness of the novel modeling framework.

Grain boundary characterization and energetics of superalloys

Abstract: In many engineering alloys, there exists a wide distribution of grain sizes; we investigate the role of grain boundaries as a strengthening mechanism in such a material. The coincidental site lattice (CSL) model is a powerful mathematical tool to characterize grain boundaries (GBs) and identify ‘special’ boundaries, which display beneficial mechanical behavior. We define the CSL and describe a detailed procedure to obtain this information from the grain orientation mapping via electron back scattering diffraction (EBSD). From this information, we show the evolution of the CSL for a nickel-based superalloy, Udimet 720 (U720), throughout various stages of processing (billet and forging) and experiments (tension, compression, and fatigue). A deeper level of understanding the GB's role in the mechanical behavior of the material is investigated through atomic simulations using molecular dynamics (MD) as the GB energy is determined for the most prevalent GBs within this material. The spatial map of the orientation and grain sizes measured from EBSD is linked to the GB energies calculated from MD. Based upon the large number of boundaries analyzed (29,035), there is a strong inverse correlation between GB energy and grain size for every specimen examined during the various processing and testing conditions.

Theoretical and experimental studies on N-(6-methylpyridin-2-yl-carbamothioyl)biphenyl-4-carboxamide

Abstract: A novel thiourea derivative, N -(6-methylpyridin-2-yl-carbamothioyl)biphenyl-4-carbox amide, is synthesized and characterized by elemental analysis, FT-IR, NMR and single crystal X-ray diffraction study. There are two independent molecules A and B in the asymmetric unit. The short bond lengths of the C-N bonds in the central thiourea fragment indicate partial double bond character in this fragment of the title compound. These results can be explained by the existence of resonance in this part of the molecule. Each A and B molecule is stabilized with an intramolecular N-H•••O hydrogen bond which results in the formation of a pseudo six membered ring. In addition, the independent molecules are linked into a chain along the c axis by weak N-H•••S intermolecular hydrogen bonds. The conformational behavior and structural stability of the optimized geometry of the title compound were also investigated by utilizing ab- initio calculations with 6-31G* basis set at HF, BLYP, and B3LYP levels. The calculated parameters are in good agreement with the corresponding X-ray diffraction values.

Non-intrusive virtualization management using libvirt

Abstract: The success of server virtualization has let to the deployment of a huge number of virtual machines in today's data centers, making a manual virtualization management very labor-intensive. The development of appropriate management solutions is hindered by the various management interfaces of different hypervisors. Therefore, a uniform management can be simplified by a layer abstracting from these dedicated hypervisor interfaces. The libvirt management library provides such an interface to different hypervisors. Unfortunately, remote hypervisor management using libvirt has not been possible without altering the managed servers. To overcome this limitation, we have integrated remote hypervisor management facilities into the libvirt driver infrastructure for VMware ESX and Microsoft Hyper-V. This paper presents the resulting architecture as well as experiences gained during the implementation process.

Football to tackle overweight in children.

Abstract: The present study aimed at analyzing the efficacy of a 6-month football training program compared with a standard exercise program on health and fitness parameters in overweight children. The study design was a 6-month, two-arm, parallel-group randomized trial. Twenty-two overweight children were randomly assigned to two groups (age=10.8+/-1.2 years, height=1.56+/-0.08 m, weight= 65.1+/-11.4 kg). One group conducted a football training program, and the other group an established standard sports program. Both interventions took place three times per week from mid-May to mid-November. Before, after 3 months and after the training period, comprehensive testing was conducted: anthropometric characteristics, cycling ergometry, psychometric monitoring as well as several motor ability tests. Maximal performance capacity increased and submaximal heart rate during cycling ergometry decreased significantly. Several motor skills as well as self-esteem also improved considerably. Body composition and other psychometric variables remained nearly unchanged. No relevant differences were observed between both exercise programs. It can be concluded that a 6-month football training is as efficacious in improving the physical capacity, health-related fitness parameters and self-esteem of overweight children as a standard exercise program. These results provide further evidence that playing football has significant health effects.

Computing Nash Equilibria for Scheduling on Restricted Parallel Links

Abstract: We consider the problem of routing n users on m parallel links under the restriction that each user may only be routed on a link from a certain set of allowed links for the user. So, this problem is equivalent to the correspondingly restricted scheduling problem of assigning n jobs to m parallel machines. In a Nash equilibrium, no user may improve its own Individual Cost (latency) by unilaterally switching to another link from its set of allowed links. For identical links, we present, as our main result, a polynomial time algorithm to compute from any given assignment a Nash equilibrium with non-increased makespan. The algorithm gradually transforms the assignment by pushing the unsplittable user traffics through a flow network, which is constructed from the users and the links. The algorithm uses ideas from blocking flows. Furthermore, we use techniques simular to those in the generic PreflowPush algorithm to approximate in polynomial time a schedule with optimum makespan. This results to an improved approximation factor of $2-\frac{1}{w_{1}}$for identical links, where w 1 is the largest user traffic, and to an approximation factor of 2 for related links.

Fatigue crack growth—Microstructure relationships in a high-manganese austenitic TWIP steel

Abstract: The crack growth behavior of a high-manganese austenitic steel, which exhibits the twinning-induced plasticity (TWIP) effect, was investigated under positive stress ratios. An experimental study making use of miniature compact tension (CT) specimens and thorough microstructural analyses including transmission electron microscopy and fracture analyses demonstrated that the microstructural evolution in the plastic zone of the fatigued TWIP CT specimens is substantially different as compared to the monotonic plastic deformation case. Specifically, the twin density in the plastic zone of the CT specimens is very low, leading to the conclusion that the deformation mechanisms depend drastically on the loading conditions. The absence of twinning under cyclic loading in the plastic zone of the CT specimens indicates that even large accumulated plastic strains are not sufficient to cause substantial twinning in the TWIP steel. This lack of hardening preserves the ductile character of the TWIP steel in the plastic zone ahead of the crack tip and provides for a crack growth rate in the Paris regime lower than reported for other high strength steels.

Do we know the band gap of lithium niobate

Abstract: Given the vast range of lithium niobate (LiNbO3) applications, the knowledge about its electronic and optical properties is surprisingly limited. The direct band gap of 3.7 eV for the ferroelectric phase – frequently cited in the literature – is concluded from optical experiments [1]. Recent theoretical investigations [2] show that the electronic band-structure and optical properties are very sensitive to quasiparticle and electron-hole attraction effects, which were included using the GW approximation for the electron self-energy and the Bethe-Salpeter equation respectively, both based on a model screening function. The calculated fundamental gap was found to be at least 1 eV larger than the experimental value. To resolve this discrepancy we performed first-principles GW calculations for lithium niobate using the full-potential linearized augmented plane-wave (FLAPW) method [3]. Thereby we use the parameter-free random phase approximation for a realistic description of the nonlocal and energydependent screening. This leads to a band gap of about 4.7 (4.2) eV for ferro(para)-electric lithium niobate (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optimal energy management for a hybrid energy storage system for electric vehicles based on Stochastic Dynamic Programming

Abstract: For electric and hybrid electric cars, commonly nickel-metal hydride and lithium-ion batteries are used as energy storage. The size of the battery depends not only on the driving range, but also on the power demands for accelerating and braking and life-time considerations. This becomes even more apparent with short driving ranges, e.g. in commuter traffic. By hybridization of the storage, adding double layer capacitors, the battery can be relieved from the stress of peak power and even downsized to the energy demands instead of power demands. The dimensioning of the storage is performed by a parametric study via Deterministic Dynamic Programming. To determine an energy management to control the power flows to the storage online during operation which considers the stochastic influences of traffic and the driver, Stochastic Dynamic Programming is investigated and compared to the optimal strategy found during the dimensioning.

Comparing relational model transformation technologies: implementing Query/View/Transformation with Triple Graph Grammars

Abstract: The Model Driven Architecture (MDA) is an approach to develop software based on different models. There are separate models for the business logic and for platform specific details. Moreover, code can be generated automatically from these models. This makes transforma- tions a core technology for MDA and for model-based software engineering approaches in general. Query/View/Transformation (QVT) is the transformation technology recently proposed for this purpose by the OMG. Triple Graph Grammars (TGGs) are another transformation technology proposed in the mid-nineties, used for example in the FUJABA CASE tool. In contrast to many other transformation technologies, both QVT and TGGs declaratively define the relation between two models. With this definition, a transformation engine can execute a transformation in either direction and, based on the same definition, can also propagate changes from one model to the other. In this paper, we compare the concepts of the declarative languages of QVT and TGGs. It turns out that TGGs and declarative QVT have many concepts in common. In fact, QVT-Core can be mapped to TGGs. We show that QVT-Core can be implemented by transforming QVT-Core mappings to TGG rules, which can then be executed by a TGG transformation engine that performs the actual QVT transformation. Furthermore, we discuss an approach for mapping QVT-Relations to TGGs. Based on the semantics of TGGs, we clarify semantic gaps that we identified in the declarative languages of QVT and, furthermore, we show how TGGs can benefit from the concepts of QVT.