Showing papers by "Leibniz University of Hanover published in 1997"

The impact of customer satisfaction and relationship quality on customer retention: A critical reassessment and model development

Abstract: Customer satisfaction with a company’s products or services is often seen as the key to a company’s success and long-term competitiveness. In the context of relationship marketing, customer satisfaction is often viewed as a central determinant of customer retention. However, the few empirical investigations in this area indicate that a direct relationship between these constructs is weak or even nonexistent. The overall purpose of this article is to develop a conceptual foundation for investigating the customer retention process, with the use of the concepts of customer satisfaction and relationship quality. The article involves a critical examination of the satisfaction ‐ retention relationship, and the development of a more comprehensive view of the customer’s quality perception. ©1997 John Wiley & Sons, Inc.

Ablation of metals by ultrashort laser pulses

Abstract: Ablation of metal targets by Ti:sapphire laser radiation is studied. The ablation depth per pulse is measured for laser pulse durations between 150 fs and 30 ps and fluences ranging from the ablation threshold ∼0.1 J/cm2 up to 10 J/cm2. Two different ablation regimes are observed for the first time. In both cases the ablation depth per pulse depends logarithmically on the laser fluence. A simple theoretical model for a qualitative description of the experimental results is presented.

Cross sections for the production of residual nuclides by low- and medium-energy protons from the target elements c, n, o, mg, al, si, ca, ti, v, mn, fe, co, ni, cu, sr, y, zr, nb, ba and au

Abstract: Cross sections for residual nuclide production by p-induced reactions were measured from thresholds up to 2.6 GeV using accelerators at CERN/Geneve, IPN/Orsay, KFA/Julich, LANL/Los Alamos, LNS/Saclay, PSI/Villigen, TSL/Uppsala, LUC/Louvain La Neuve. The target elements C, N, O, Mg, Al, Si, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Ba and Au were investigated. Residual nuclides were measured by X- and γ-spectrometry and by Accelerator Mass Spectrometry (AMS). The measured cross sections were corrected for interfering secondary particles in experiments with primary proton energies above 200 MeV. Our consistent database covers presently ca 550 nuclear reactions and contains nearly 15000 individual cross sections of which about 10000 are reported here for the first time. They provide a basis for model calculations of the production of cosmogenic nuclides in extraterrestrial matter by solar and galactic cosmic ray protons. They are of importance for many other applications in which medium energy nuclear reactions have to be considered ranging from astrophysics over space and environmental sciences to accelerator technology and accelerator-based nuclear waste transmutation and energy amplification. The experimental data are compared with theoretical ones based on calculations using an INC/E model in form of the HETC/KFA2 code and on the hybrid model of preequilibrium reactions in form of the AREL code.

A Modern Model of Consumption for a Sustainable Society

Abstract: The importance of consumption in modern societies is constantly growing. To guide consumer oriented policy, a model of consumption is needed which reflects consumers increased significance. The model of consumption prevailing in the theory of market economies as well as in consumer policy was traditionally based upon the notion of consumers sovereignty. This model served both as a description and as the ethical foundation of the market economy. In the first part of this paper, the authors show the need for a new model of consumption by making clear the descriptive and normative shortcomings of consumer sovereignty. In view of the reality of modern societies, it is neither possible nor ethically justifiable to make purchase decisions according to the individual maximization of utility only. The second part presents the idea, the ethical foundation, and the contents of the new model of "sustainable consumption." This model is proposed to serve as a guideline for both responsible consumers and consumer policymakers and for all institutions concerned with the creation of a sustainable development.

Dynamics of oscillators with impact and friction

Abstract: In the present paper two types of nonsmooth oscillators are investigated: an impact oscillator and a self-sustained friction oscillator. Both are nonsmooth one degree of freedom oscillators with harmonic external excitation. Here the different types of motion, bifurcation diagrams and Poincare maps are determined from experiments. These results will be compared with numerical results on the basis of the identified impact and friction models. The nonsmooth third-order systems show rich bifurcational behaviour which is analysed by numerical simulations but also using mapping approaches. Two different formalisms for the calculation of the Lyapunov exponents are applied. The latter one requires special considerations in the given case of nonsmooth systems. Furthermore, the embedding dimension is gained applying the method of false nearest neighbours. In the case of coexisting solutions further analysis is done by means of bifurcation and stability analysis and the cell-mapping approach.

Induction of callose formation is a sensitive marker for genotypic aluminium sensitivity in maize

Abstract: The screening of 37 Zea mays L. cultivars in nutrient solution using root elongation (24 h) as a parameter showed large genotypic differences in Al resistance among the genetic material evaluated. Callose concentrations in root tips were closely and positively related to Al-induced inhibition of root elongation. Therefore, Al-induced callose formation in root tips appears to be an excellent indicator of Al injury and can be used as a selection criteria for Al sensitivity. In contrast, aluminium concentrations in root tips were not related to Al-induced inhibition of root elongation, nor to Al-induced callose formation. Callose formation was also induced by short-term A1 treatment in root tip protoplasts, and the response of protoplasts clearly reflected the cultivar-specific response to Al of intact roots. This indicates that in maize, Al sensitivity is expressed on the protoplast level.

One- or two-plate fixation of mandibular angle fractures?

Abstract: Standard treatment of mandibular angle fractures with miniplates, according to the recommendations of Champy et al. (1976), consists of fixation with one plate at the superior border of the mandible ventral to the external oblique line. In certain constellations, a second miniplate at the lower mandibular margin may provide additional stability. In contrast, extremely high complication rates following two-plate fixation of mandibular angle fractures were reported by Ellis and Walker (1994). In a prospective randomized study, 31 consecutive patients were treated with 2.0 mm (mini) plates (Synthes Co., Switzerland). One group was treated with one plate, the other one with two plates. In none of the patients was intermaxillary immobilization used. Follow-up was performed 6 months postoperatively, consisting of clinical and radiographic examination. No significant differences (P = 0.74 for infection, and P = 1.0 for occlusal and postoperative sensory disturbance) in postoperative short- or long-term complications were found between the two groups. The results are compared with our experimental investigations presented at the annual congress of the Germany Society of Oral and Maxillofacial Surgery, 1995. Two-plate fixation may not offer advantages over single-plate fixation in general. However, individual fracture constellations may benefit from variation in plate(s) localization. Factors contributing to complications in mandibular angle fractures are discussed.

Biological aspects of root canal filling materials – histocompatibility, cytotoxicity, and mutagenicity

Abstract: In order to minimize the incidence of local and/or systemic side effects, the biocompatibility of all endodontic materials should be investigated by various in vitro and in vivo tests prior to clinical application. The battery of in vitro tests includes determinations of mutagenicity, cytotoxicity, and antibacterial effects. Several reports have shown that paraformaldehyde-containing ZnO-eugenol cements in particular, such as Endomethasone and N2, are antibacterial. On the other hand, it has been found that endodontic materials with strong antimicrobial activity are frequently mutagenic, i.e., primarily those which release formaldehyde. Cell culture tests clearly show significantly different cytocompatibility of the various types of endodontic sealers: in general, formaldehyde-containing ZnO-eugenol cements are classified as highly/extremely cytotoxic, whereas most Ca(OH)2-based sealers are rated as possessing good or excellent cytocompatibility. These results were confirmed by numerous histological studies in vivo. Sealers with inferior biocompatibility, such as formaldehyde-releasing materials, should no longer be applied in practice because safer alternatives are available.

Impairment of calcineurin function in Neurospora crassa reveals its essential role in hyphal growth, morphology and maintenance of the apical Ca2+ gradient

Abstract: The function of Neurospora crassa calcineurin was investigated in N. crassa strains transformed with a construct that provides for the inducible expression of antisense RNA for the catalytic subunit of calcineurin (cna-1). Induction of antisense RNA expression was associated with reduced levels of cna-1 mRNA and of immunodetectable CNA1 protein and decreased calcineurin enzyme activity, indicating that a conditional reduction of the target function had been achieved in antisense transformants with multiple construct integrations. Induction conditions caused growth arrest which indicated that the cna-1 gene is essential for growth of N. crassa. Growth arrest was preceded by an increase in hyphal branching, changes in hyphal morphology and concomitant loss of the distinctive tip-high Ca2+ gradient typical for growing wild-type hyphae. This demonstrates a novel and specific role for calcineurin in the precise regulation of apical growth, a common form of cellular proliferation. In vitro inhibition of N. crassa calcineurin by the complex of cyclosporin A (CsA) and cyclophilin20, and increased sensitivity of the induced transformants to the calcineurin-specific drugs CsA and FK506 imply that the drugs act in N. crassa, as in T-cells and Saccharomyces cerevisiae, by inactivating calcineurin. The finding that exposure of growing wild-type mycelium to these drugs leads to a phenotype very similar to that of the cna-1 antisense mutants is consistent with this idea.

N-methoxy-n-methylamides (weinreb amides) in modern organic synthesis

Abstract: N-Methoxy-N-methylamides (Weinreb amides) have facililated access to functionalized aldehydes and ketones in organic synthesis, including the total synthesis of complex natural products.

Characterizations of the disjunctive stable semantics by partial evaluation

Abstract: There are three most prominent semantics defined for certain subclasses of disjunctive logic programs: GCWA (for positive programs), PERFECT (for stratified programs), and STABLE (defined for the whole class of all disjunctive programs). While there are various competitors based on 3-valued models, notably WFS and its disjunctive counterparts, there are no other semantics consisting of two-valued models. We argue that the reason for this is the Partial Evaluation property (also called Unfolding or Partial Deduction) well known from logic programming. In fact, we prove characterizations of these semantics and show that if a semantics SEM satisfies Partial Evaluation and Elimination of Tautologies, then (1) SEM is based on two-valued minimal models for positive programs, and (2) if SEM satisfies in addition Elimination of Contradictions, it is based on stable models. We also show that if we require Isomorphy and Relevance, then STABLE is completely determined on the class of all stratified disjunctive logic programs.

The complex Ginzburg - Landau equation on large and unbounded domains: sharper bounds and attractors

Abstract: Using weighted -norms we derive new bounds on the long-time behaviour of the solutions improving on the known results of the polynomial growth with respect to the instability parameter. These estimates are valid for quite arbitrary, possibly unbounded domains. We establish precise estimates on the maximal influence of the boundaries on the dynamics in the interior. For instance, the attractor for the domain with periodic boundary conditions is upper semicontinuous to .

Instability and Stability of Rolls in the Swift–Hohenberg Equation

Abstract: We develop a method for the stability analysis of bifurcating spatially periodic patterns under general nonperiodic perturbations. In particular, it enables us to detect sideband instabilities. We treat in all detail the stability question of roll solutions in the two–dimensional Swift–Hohenberg equation and derive a condition on the amplitude and the wave number of the rolls which is necessary and sufficent for stability. Moreover, we characterize the set of those wave vectors which give rise to unstable perturbations. Dedicated to Professor K. Kirchgassner on the occasion of his sixty-fifth birthday

The influence of tool coatings in machining of magnesium

Abstract: Magnesium is the lightest metal used in construction and therefore offers the greatest potential for weight reduction. The automotive industry in particular has an upcoming interest in the use of magnesium alloys. To observe the interactions between workpiece material and tool material and coating, respectively, turning experiments were carried out machining the alloy AZ91 HP. When machining magnesium dry, flank build-up due to adhesion between cutting tool and workpiece can occur at cutting speeds of vc = 900 m/min and more for uncoated and TiN-coated cemented carbide tools. Tools with either polycrystalline diamond (PCD) insert or coating can be used to reduce friction and adhesion in the tool-workpiece contact resulting in low machining forces as well as a superior surface quality even at high cutting speeds of vc = 2400 m/min. PCD coatings can also be applied to complex tool geometries. As tool wear can hardly be observed when machining magnesium alloys, a magnesium-based metal matrix composite (MMC) is machined to combine the adhesive effects of magnesium with the abrasive load caused by a reinforcement component. Excessive tool wear can be observed for TiN-coated carbides even at low cutting speeds of fvc = 100 m/min. PCD coatings show better results but cannot compete with tools having a PCD insert if a low film thickness is chosen.

Physical urticaria: classification and diagnostic guidelines. An EAACI position paper.

Abstract: Kontou-Fili K, Borici-Mazi R, Kapp A, Matjevic LJ, Mitchel FB Physical urticaria: classification and diagnostic guidelines An EAACI position paper

Phase transitions in elastoplastic materials: Continuum thermomechanical theory and examples of control—part I

Abstract: A general thermomechamcal theory of phase transitions (PT) in elastoplastic materials is presented. The PT criterion and extremum principle for the determination of all unknown parameters are derived. We obtain the result that the dissipative threshold in the PT criterion is proportional to yield stress. Two boundary-value problems are solved analytically: PT in a thin layer (horizontally and optimally inclined) in a rigid-plastic half-space under the action of applied pressure and shear stresses and PT under compression and shear of materials in Bridgman anvils. The solutions illustrate the fundamental difference in PT conditions for the homogeneously distributed pressure and shear stresses in the first problem and strongly nonhomogeneous pressure distribution in the second problem. In particular, in the first problem additional shearing significantly improves the condition of appearance of soft materials and does not affect the appearance of strong materials. In the second problem, rotation of an anvil works much more effectively for the synthesis of strong phases than weak ones. A number of experimental results are explained, and some of the interpretations are completely unexpected. It is found that an improvement in PT condition due to a rotation of an anvil is attributed not to the plastic strain, but to the possibility of an additional displacement, compensating a volume decrease because of PT. It is connected with a reduction of frictional shear stress in a radial direction.

Diamond-like carbon-gate pH-ISFET

Abstract: A novel chemical-resistant ion-selective field-effect transistor (ISFET) array is introduced, using amorphous diamond-like carbon (DLC) films for passivation and as pH-sensitive layer. A DLC coating technology is developed, useful for depositing and patterning final thin films on active and passive surfaces of ISFET devices. The DLC films are produced by a low-temperature dual rf methane–helium gas mixture plasma. DLC thin films show complete chemical inert behaviour in aggressive aqueous electrolytes. The high film hardness in addition to the chemically inert behaviour makes DLC films more suitable as passivation layers for sensor devices than other materials (i.e. Si 3 N 4 , SiO 2 , etc.). It is shown from the results of electrochemical and electronic characterization of ISFET devices with DLC thin films that DLC is suitable for sensor applications. A comparative characterization of DLC-coated ISFET with a Ta 2 O 5 -coated ISFET on a single chip sensor is shown in this work. The pH response of the DLC ISFET shows lower drift than that of the Ta 2 O 5 -coated ISFET. No redox cross-sensitivity was found for DLC-coated ISFET. The shift of the sensor response is only slightly dependant on temperature.

RNase H-independent antisense activity of oligonucleotide N3′→P5′ phosphoramidates

Abstract: Oligonucleotide N3'-->P5'phosphoramidates are a new and promising class of antisense agents. Here we report biological properties of phosphoramidate oligonucleotides targeted against the human T cell leukemia virus type-I Tax protein, the major transcriptional transactivator of this human retrovirus. Isosequential phosphorothioate oligodeoxynucleotides and uniformly modified and chimeric phosphoramidate oligodeoxynucleotides containing six central phosphodiester linkages are all quite stable in cell nuclei. The uniformly modified anti-tax phosphoramidate oligodeoxynucleotide does not activate nuclear RNase H, as was shown by RNase protection assay. In contrast, the chimeric phosphoramidate-phosphodiester oligodeoxynucleotide is an efficient activator of RNase H. The presence of one or two mismatched nucleotides in the phosphodiester portion of oligonucleotides affected this activation only negligibly. When introduced into tax-transformed fibroblasts ex vivo, only the uniformly modified anti-tax phosphoramidate oligodeoxynucleotide caused a sequence-dependent reduction in the Tax protein level. Neither the chimeric phosphoramidate nor the phosphorothioate oligodeoxynucleotides significantly reduced tax expression under similar experimental conditions.

Light-microscopical investigation of the distribution of extracellular matrix molecules and calcifications in human dental pulps of various ages.

Abstract: The distribution of extracellular matrix molecules, especially collagen types I, III, V, and VI, in the extracellular matrix of the connective tissue of human dental pulp of various ages was studied by polarization and indirect immunofluorescence microscopy by using a conventional fluorescence microscope and a confocal laser scanning microscope. Polarization and immunofluorescence microscopy of paraffin sections showed thick fibers of collagen type I, which represented the main component of the connective tissue matrix of the dental pulp. By indirect immunofluorescence, thin fibers and small bundles of collagen type III were determined to be one of the main fibrillar elements present in the dental pulp matrix. Collagen type IV was detected by a clear intense staining of the basement membrane of blood vessels at all ages examined. Collagens type V and VI formed a dense meshwork of thin microfibrils throughout the stroma of the connective tissue of the dental pulp. These fibers were localized around blood vessels and appeared to be enriched in the subodontoblastic layer. Investigations by means of confocal laser scanning microscopy revealed fibers of collagen type VI spiralling between fully differentiated odontoblasts toward the predentin layer. With advancing age, the connective tissue matrix appeared to be condensed and aggregates of thick fiber bundles could be observed. Furthermore, the participation of various collagen types in the composition of pulp stones was shown. These calcifications and diffuse calcifications increased in frequency with advancing age in a statistically significant manner.