Showing papers by "University of Mannheim published in 2003"

Model-driven development: a metamodeling foundation

Abstract: Metamodeling is an essential foundation for MDD, but there's little consensus on the precise form it should take and role it should play. The authors analyze the underlying motivation for MDD and then derive a concrete set of requirements that a supporting infrastructure should satisfy. They discuss why the traditional "language definition" interpretation of metamodeling isn't a sufficient foundation and explain how it can be extended to unlock MDD's full potential.

A routing strategy for vehicular ad hoc networks in city environments

Abstract: Routing of data in a vehicular ad hoc network is a challenging task due to the high dynamics of such a network. Recently, it was shown for the case of highway traffic that position-based routing approaches can very well deal with the high mobility of network nodes. However, baseline position-based routing has difficulties to handle two-dimensional scenarios with obstacles (buildings) and voids as it is the case for city scenarios. In this paper we analyze a position-based routing approach that makes use of the navigational systems of vehicles. By means of simulation we compare this approach with non-position-based ad hoc routing strategies (dynamic source routing and ad-hoc on-demand distance vector routing). The simulation makes use of highly realistic vehicle movement patterns derived from Daimler-Chrysler's Videlio traffic simulator. While DSR's performance is limited due to problems with scalability and handling mobility, both AODV and the position-based approach show good performances with the position-based approach outperforming AODV.

Overconfidence and trading volume

Abstract: Theoretical models predict that overconfident investors will trade more than rational investors. We directly test this hypothesis by correlating individual overconfidence scores with several measures of trading volume of individual investors (number of trades, turnover). Approximately 3000 online broker investors were asked to answer an internet questionnaire which was designed to measure various facets of overconfidence (miscalibration, the better than average effect, illusion of control, unrealistic optimism). The measures of trading volume were calculated by the trades of 215 individual investors who answered the questionnaire. We find that investors who think that they are above average in terms of investment skills or past performance trade more. Measures of miscalibration are, contrary to theory, unrelated to measures of trading volume. This result is striking as theoretical models that incorporate overconfident investors mainly motivate this assumption by the calibration literature and model overconfidence as underestimation of the variance of signals. The results hold even when we control for several other determinants of trading volume in a cross-sectional regression analysis. In connection with other recent findings, we conclude that the usual way of motivating and modelling overconfidence which is mainly based on the calibration literature has to be treated with caution. We argue that our findings present a psychological foundation for the differences of opinion'' explanation of high levels of trading volume. In addition, our way of empirically evaluating behavioral finance models - the correlation of economic and psychological variables and the combination of psychometric measures of judgment biases (such as overconfidence scores) and field data - seems to be a promising way to better understand which psychological phenomena drive economic behavior.

Contention-based forwarding for mobile ad-hoc networks

Abstract: Existing position-based unicast routing algorithms which forward packets in the geographic direction of the destination require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. In this paper, we propose a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding scheme (CBF) the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy position-based routing approach by means of simulation with ns-2. Our results show that CBF significantly reduces the load on the wireless channel required to achieve a specific delivery rate compared to the load a beacon-based greedy forwarding strategy generates.

Costs, Commitment and Compliance: The Impact of EU Democratic Conditionality on Latvia, Slovakia and Turkey

Abstract: ‘Democratic conditionality’ is the core strategy of the EU to induce candidate states to comply with its human rights and democracy standards. How does it work and when is it effective? This article reports findings of a comparative study of ‘hard cases’: Slovakia under Meciar; Turkey; and Latvia. We argue that EU democratic conditionality is a strategy of ‘reinforcement by reward’ which works through intergovernmental material bargaining. Its efficacy depends on the candidate governments’ domestic political costs of compliance. By contrast, social influence and transnational mobilization have proved ineffective.

Bridging Uncertainty in Management Consulting: The Mechanisms of Trust and Networked Reputation

Abstract: This article analyzes the market of management consulting and identifies institutional and transactional uncertainty as its principal features. Based on these uncertainties, we argue that competition in this market takes place on entirely different grounds than in other business sectors. We suggest that the main drivers of competitiveness are neither price nor measurable quality, but rather experience-based trust and a mechanism we label ‘networked reputation.’ An embeddedness perspective is employed to develop the concept of networked reputation as an intermediate mechanism that complements the duality of system versus personal trust and accounts for firm growth. We reinterpret secondary data on the German consulting market, illustrate the significance of these mechanisms, and demonstrate how management consulting is situated in structures of social relations.

Stereotype Threat in the Classroom: Dejection Mediates the Disrupting Threat Effect on Women’s Math Performance

Abstract: Research on stereotype threat, which is defined as the risk of confirming a negative stereotypic expectation about one's group, has demonstrated that the applicability of negative stereotypes disrupts the performance of stigmatized social groups. While it has been shown that a reduction of stereotype threat leads to improved performance by members of stigmatized groups, there is a lack of clear-cut findings about the mediating processes. The aim of the present study is to provide a better understanding of the mechanisms that stereotype threat causes in women working on mathematical problems. In addition, the study set out to test stereotype threat theory in a natural environment: high school classrooms. The experiment involved the manipulation of the gender fairness of a math test. The results indicate that the stereotype threat effect exists in this everyday setting. Moreover, it appears that dejection emotions mediate the effect of threat manipulation.

Intraorganizational Determinants of Key Account Management Effectiveness

Abstract: While there is a significant amount of research on determinants of selling effectiveness for individual salespeople, there is a surprising lack of study offactors that affect selling effectiveness in team-selling situations The authors focus on the context of key account management (KAM) and develop a conceptual model offactors that affect KAM effectiveness They test hypotheses with data from 385 firms using structural equation modeling and find that firms should seek to build esprit de corps among those involved in KAM, should proactively initiate activities with key accounts and do these activities more intensively, should ensure that key account managers have access to key resources within the marketing and sales organization, and should involve top managers of the firm

The EU, NATO and the Integration of Europe: Rules and Rhetoric

Abstract: Why did Western European states agree to the enlargement of the EU and NATO? Frank Schimmelfennig analyzes the history of the enlargement process and develops a theoretical approach of 'rhetorical action' to explain why it occurred. While rationalist theory explains the willingness of East European states to join the NATO and EU, it does not explain why member states decided to admit them. Using original data, Schimmelfennig shows that expansion to the East can be understood in terms of liberal democratic community building. Drawing on the works of Jon Elster and Erving Goffman, he demonstrates that the decision to expand was the result of rhetorical action. Candidates and their supporters used arguments based on collective identity, norms and values of the Western community to shame opponents into acquiescing to enlargement. This landmark book makes an enormous contribution to theory in international relations and to the study of European politics.

Measuring social capital: Orthodoxies and continuing controversies

Abstract: Studying social capital is widely spread and the concept entered almost each and every field of the social sciences in the last decade. An overview of the available research strategies and empirical approaches of social capital is presented here. Surprisingly, the conceptual heterogenuity is much less reflected in operational and empirical heterogenuity than expected. The field is characterized by several orthodoxies, mainly related to the dominant position of polling methods and the use of straightforward survey questions. Available alternative approaches are limited to the use of official statistics as inverse indicators and to some experiments. The major pitfalls in empirical research on social capital are discussed. Urgently needed are multi-method and multi-level strategies in order to strengthen the role of empirical evidence in the debates on social capital, civil society, and citizenship.

Information Acquisition and Decision Making in Committees: A Survey

Abstract: This is a survey on the recent game theoretic literature on committee decision making. We consider theoretical work on the role of (i) strategic voting, (ii) costly information acquisition, (iii) conflicting interests, and (iv) communication in committees. Moreover, we review recent experimental evidence on these issues. Our analysis focuses on the optimal size, composition, and decision rules of committees. We discuss implications for the design of monetary policy committees.

Sodium channel gene (SCN5A) mutations in 44 index patients with Brugada syndrome: different incidences in familial and sporadic disease.

Abstract: The Brugada syndrome (BS) is a distinct form of idiopathic ventricular fibrillation and may cause sudden cardiac death in healthy young individuals. In the surface ECG, BS can be recognized by an atypical right bundle branch block and ST-segment elevation in the right precordial leads. Mutations in the cardiac sodium channel gene SCN5A are only known to cause BS. In a multi-center effort, we have collected clinical data on 44 unrelated index patients and family members and performed a complete genetic analysis of SCN5A. In 37% the disease was familial, whereas in the majority it was sporadic (63%). Five novel SCN5A mutations (2602delC, resulting in: E867X; 2581_2582del TT: F861fs951X; 2673G>A: E1225K; 4435_4437delAAG: K1479del; and 5425C>A: S1812X) were found and were randomly located in SCN5A. Mutation frequencies (SCN5A+) differed significantly between familial (38%) and sporadic disease (0%) (p=0.001). Disease penetrance was complete in the SCN5A+ adult patients, but incomplete in SCN5A+ children (17%). Genetic testing of SCN5A is especially useful in familial disease to identify individuals at cardiac risk. In sporadic cases, however, a genetic basis and the value of mutation screening has to be further determined. These results are in line with a possibly genetic and clinical heterogeneity of BS.

A closer look beneath the surface : Various facets of the think-manager-think-male stereotype

Abstract: Previous research has indicated that successful managers are perceived as possessing characteristics that belong to a global masculine stereotype. This study was designed to compare the gender-stereotypical perception of leadership by investigating global and leadership-specific gender stereotypes and contrasting self-perception and the perceptionby others. Descriptive and prescriptive norms were analyzed and abilities studied in a leadership context. The sample consists of 215 management students, and the results indicate an impact of gender stereotypes on the perception of leadership by women and men. Ratings of the importance of leadership characteristics yielded a less gender-stereotypic view, especially by female participants. In their self-evaluations women and men did not differ in the degree in which they possess person- and task-oriented skills. They also did not differ in their ratings of the importance of possessing these skills themselves. Finally, women reported that they possess task-oriented abilities more seldom than such abilities were attributed to leaders-in-general.

Position-based multicast routing for mobile Ad-hoc networks

Abstract: In this paper we present Position-Based Multicast (PBM), a multicast routing algorithm for mobile ad-hoc networks which does neither require the maintenance of a distribution structure (e.g., a tree or a mesh) nor resorts to flooding of data packets. Instead a forwarding node uses information about the positions of the destinations and its own neighbors to determine the next hops that the packet should be forwarded to and is thus very well suited for highly dynamic networks. PBM is a generalization of existing position-based unicast routing protocols such as face-2 or GPSR. The key contributions of PBM are rules for the splitting of multicast packets and a repair strategy for situations where there exists no direct neighbor that makes progress toward one or more destinations. The characteristics of PBM are evaluated in detail by means of simulation.

Algebraic Attacks on Combiners with Memory

Abstract: Recently, algebraic attacks were proposed to attack several cryptosystems, e.g. AES, LILI-128 and Toyocrypt. This paper extends the use of algebraic attacks to combiners with memory. A (k,l)-combiner consists of k parallel linear feedback shift registers (LFSRs), and the nonlinear filtering is done via a finite automaton with k input bits and l memory bits. It is shown that for (k,l)-combiners, nontrivial canceling relations of degree at most ⌈k(l+1)/2⌉ exist. This makes algebraic attacks possible. Also, a general method is presented to check for such relations with an even lower degree. This allows to show the invulnerability of certain (k,l)-combiners against this kind of algebraic attacks. On the other hand, this can also be used as a tool to find improved algebraic attacks.

The Role of Soft Factors in Implementing a Service-Oriented Strategy in Industrial Marketing Companies

Abstract: It has been recognized that in today's highly competitive industrial markets, one of the few ways left to gain differentiation from competitors is by offering value-added services. To do so, however, requires a service-oriented strategy and the active implementation of this strategy which includes significant internal changes in management philosophy and approach. Unfortunately, no study has examined the implementation aspects of a service-oriented strategy. In this context, our research focuses on two important “soft factors,” corporate culture and human resource management, that are necessary for a successful implementation of a service-oriented strategy in industrial marketing companies. We analyze the mediating role of these two soft factors in the causal chain leading from a service-oriented strategy to organizational performance. We find that the soft factors play an important mediating role in the link between a service-oriented strategy and organizational performance.

Firm Turnover in Imperfectly Competitive Markets

Abstract: This paper is motivated by the empirical regularity that industries differ greatly in the level of firm turnover, and that entry and exit rates are positively correlated across industries. Our objective is to investigate the effect of sunk costs and, in particular, market size on entry and exit rates, and hence on the age distribution of firms. We analyze a stochastic dynamic model of a monopolistically competitive industry. Each firm's efficiency is assumed to follow a Markov process. We show existence and uniqueness of a stationary equilibrium with simultaneous entry and exit: efficient firms survive while inefficient ones leave the market and are replaced by new entrants. We perform comparative dynamics with respect to the level of sunk costs: entry costs are negatively and fixed production costs positively related to entry and exit rates. A central empirical prediction of the model is that the level of firm turnover is increasing in market size. The intuition is as follows. In larger markets, price-cost margins are smaller since the number of active firms is larger. This implies that the marginal surviving firm has to be more efficient than in smaller markets. Hence, in larger markets, the expected life span of firms is shorter, and the age distribution of firms is first-order stochastically dominated by that in smaller markets. In an extension of the model with time-varying market size, we explore the comovements between market size and entry and exit rates. It is shown that both entry and exit rates tend to rise over time in growing markets. In the empirical part, the prediction on market size and firm turnover is tested on industries where firms compete in well-defined geographical markets of different sizes. Using data on hair salons in Sweden, we show that an increase in market size or fixed costs shifts the age distribution of firms towards younger firms, as predicted by the model.

Optimal Monetary Policy Under Commitment with a Zero Bound on Nominal Interest Rates

Abstract: We compute the optimal non-linear interest rate policy under commitment for a forward-looking stochastic model with monopolistic competition and sticky prices when nominal interest rates are bounded below by zero. When the lower bound binds, the optimal policy is to reduce the real rate by generating inflation expectations. This is achieved by committing to increase future interest rates by less than what purely forward-looking policy would suggest. As a result, there is a 'commitment bias', i.e., average output and inflation turn out to be higher than their target values. Calibrating the model to the US economy, we find that the quantitative importance of the average effects on output and inflation are negligible. Moreover, the empirical magnitude of US mark-up shocks is too small to entail zero nominal interest rates. Real rate shocks, however, plausibly lead to a binding lower bound under optimal policy, albeit relatively infrequently. Interestingly, the presence of binding real rate shocks alters the optimal policy response to (non-binding) mark-up shocks.

Optimal Monetary Policy with Imperfect Common Knowledge

Abstract: This paper determines optimal nominal demand policy in a flexible price economy in which firms pay limited attention to aggregate variables. Firms' inattentiveness gives rise to idiosyncratic information errors and imperfect common knowledge about the shocks hitting the economy. This is shown to have strong implications for optimal nominal demand policy. In particular, if firms' prices are strategic complements and economic shocks display little persistence, monetary policy has strong real effects, making it optimal to stabilize the output gap. Weak complementarities and sufficient shock persistence, however, cause price level stabilization to become increasingly optimal. With persistent shocks, optimal monetary policy shifts from output gap stabilization in initial periods following the shock to price level stabilization in later periods, potentially rationalizing the medium-term approach to price stability adopted by some central banks.

Price Competition and Product Differentiation when Consumers Care for the Environment

Abstract: Increasing environmental awareness may affect the pleasure of consuming a good for which an environmental friendly substitute is available. When deciding to buy differentiated products, a compromise is sometimes made between preferred characteristics of the good and its environmental properties. In this paper we investigate the market implication of product differentiation when customers are concerned about environmental aspects of the good. We use the spatial duopoly model to determine how environmental concern affects prices, product characteristics and market shares of the competing firms. Our analysis is based on a two-stage game where at the first stage each firm chooses the characteristic of its product. At the second stage each firm chooses its price. The unique equilibrium prices and market shares are affected by consumer awareness of the environment and by the higher costs for producing those goods. As for the Nash equilibria in the characteristics we find three equilibria depending on the parameter constellation. In order to find out whether the market functions in an optimal way we determined the choice of environmental characteristics by a welfare maximizing authority. The result of this analysis is that characteristics differ under private decision making and social one. It can be shown, however, that it is possible to choose environmental policy instruments in order to stimulate private firms to produce the social optimal qualities.

Helix: Fast Encryption and Authentication in a Single Cryptographic Primitive

Abstract: Helix is a high-speed stream cipher with a built-in MAC functionality. On a Pentium II CPU it is about twice as fast as Rijndael or Twofish, and comparable in speed to RC4. The overhead per encrypted/authenticated message is low, making it suitable for small messages. It is efficient in both hardware and software, and with some pre-computation can effectively switch keys on a per-message basis without additional overhead.

Mood and the reliance on the ease of retrieval heuristic.

Abstract: Four studies investigate the relationship between individuals' mood and their reliance on the ease retrieval heuristic. Happy participants were consistently more likely to rely on the ease of retrieval heuristic, whereas sad participants were more likely to rely on the activated content. Additional analyses indicate that this pattern is not due to a differential recall (Experiment 2) and that happy participants ceased to rely on the ease of retrieval when the diagnosticity of this information was called into question (Experiment 3). Experiment 4 shows that reliance on the ease of retrieval heuristic resulted in faster judgments than reliance on content, with the former but not the latter being a function of the amount of activated information.

Towards recognition-based variational segmentation using shape priors and dynamic labeling

Abstract: We propose a novel variational approach based on a level set formulation of the Mumford-Shah functional and shape priors. We extend the functional by a labeling function which indicates image regions in which the shape prior is enforced. By minimizing the proposed functional with respect to both the level set function and the labeling function, the algorithm selects image regions where it is favorable to enforce the shape prior. By this, the approach permits to segment multiple independent objects in an image, and to discriminate familiar objects from unfamiliar ones by means of the labeling function. Numerical results demonstrate the performance of our approach.

An update on the diagnosis and treatment of sinusitis and nasal polyposis

Abstract: IntroductionTerminologySinusitis (more properly known as rhinosinusitis due tothe regular involvement of the nasal cavity) is a conditionwith a high and clearly increasing prevalence. According1to figures from IMS Health,acute sinusitis was diagnosed6.3 million times and chronic sinusitis 2.6 million times ina country like Germany over the course of one year (July2000–June 2001),resulting in 8.5 million and 3.4 millionprescriptions,respectively. The number of diagnoses of‘‘nasal polyposis’’ was approximately 221 000 (accordingto IMS Health 2001). Even though no reliable epidemi-ological studies of the incidence of sinusitis exist,thesefigures do indicate that sinusitis represents a considerablesocioeconomic problem. Alongside allergic and viralconditions of the upper airways,sinusitis thereforeconstitutes one of the most common respiratory tractconditions in humans.Similar data are reported from the USA: in 1997,sinusitis was prevalent in approximately 15% of thepopulation. In the last decade,the frequency of diagnosisin the USA rose by around 18%. The economicsignificance of sinusitis is huge: for 1992,the total cost,including costs resulting from loss of work,was estima-ted at over 6 billion dollars for the USA. In the periodfrom 1985 to 1992,the number of antibiotic prescrip-tions for sinusitis rose from 7.2 million to 13 million(1,2).Sinusitis is an inflammatory process involving themucous membranes of one or more sinuses. Generallyspeaking,the mucous lining of the nose is also involved.Even in the presence of a viral cold,a CT scan will revealthe involvement of the paranasal sinuses in 87% of cases,which is why we speak of rhinosinusitis (3). Bacterialrhinosinusitis (acute sinusitis) is generally preceded by avirus-induced inflammation of the sinuses; approximately5–10% of childhood upper airway infections develop intoacute sinusitis (4). The swelling and ‘‘immunologicalweakness’’ of the mucous membrane and the blockageof the ostia by the viral infection are today believed tocause bacterial infection of the intrinsically sterile para-nasal sinuses by local microorganisms. This gives rise toacute sinusitis,with severe inflammatory infiltration ofC.Bachert

Redundant representations in evolutionary computation

Abstract: This paper discusses how the use of redundant representations influences the performance of genetic and evolutionary algorithms. Representations are redundant if the number of genotypes exceeds the number of phenotypes. A distinction is made between synonymously and non-synonymously redundant representations. Representations are synonymously redundant if the genotypes that represent the same phenotype are very similar to each other. Non-synonymously redundant representations do not allow genetic operators to work properly and result in a lower performance of evolutionary search. When using synonymously redundant representations, the performance of selectorecombinative genetic algorithms (GAs) depends on the modification of the initial supply. We have developed theoretical models for synonymously redundant representations that show the necessary population size to solve a problem and the number of generations goes with O(2kr/r), where kr is the order of redundancy and r is the number of genotypic building blocks (BB) that represent the optimal phenotypic BB. As a result, uniformly redundant representations do not change the behavior of GAs. Only by increasing r, which means overrepresenting the optimal solution, does GA performance increase. Therefore, non-uniformly redundant representations can only be used advantageously if a-priori information exists regarding the optimal solution. The validity of the proposed theoretical concepts is illustrated for the binary trivial voting mapping and the real-valued link-biased encoding. Our empirical investigations show that the developed population sizing and time to convergence models allow an accurate prediction of the empirical results.