When does charisma matter for top-level leaders? Effect of attributional ambiguity

One stream of leadership theory suggests leaders are evaluated via inferential observer processes that compare the fit of the target to a prototype of an ideal (charismatic) leader. Attributional theories of leadership suggest that evaluations depend on knowledge of past organizational performance, which is attributed to the leader's skills. We develop a novel theory showing how inferential and attributional processes simultaneously explain top-level leader evaluation and ultimately leader retention and selection. We argue that observers will mostly rely on attributional mechanisms when performance signals clearly indicate good or poor performance outcomes. However, under conditions of attributional ambiguity (i.e., when performance signals are unclear), observers will mostly rely on inferential processes. In Study 1 we tested our theory in an unconventional context-the U.S. presidential election-and found that the two processes, due to the leader's charisma and country economic performance, interact in predicting whether a leader is selected. Using a business context and an experimental design, in Study 2 we show that CEO charisma and firm performance interact in predicting leader retention, confirming the results we found in Study 1. Our results suggest that this phenomenon is quite general and can apply to various performance domains

Causality and endogeneity: Problems and solutions

Most leadership and management researchers ignore one key design and estimation problem rendering parameter estimates uninterpretable: Endogeneity. We discuss the problem of endogeneity in depth and explain conditions that engender it using examples grounded in the leadership literature. We show how consistent causal estimates can be derived from the randomized experiment, where endogeneity is eliminated by experimental design. We then review the reasons why estimates may become biased (i.e., inconsistent) in non-experimental designs and present a number of useful remedies for examining causal relations with non-experimental data. We write in intuitive terms using nontechnical language to make this chapter accessible to a large audience

The Dark Galaxy Hypothesis

Gravitational interactions allowed astronomers to conclude that dark matter rings all luminous galaxies in gigantic halos, but this only accounts for a fraction of the total mass of dark matter believed to exist. Where is the rest? We hypothesize that some of it resides in dark galaxies, pure dark matter halos that either never possessed or have totally lost their baryonic matter. This paper explores methodological challenges that arise due to the nature of observation in astrophysics, and examines how the blend of observation, simulation, and theory we call the Observing the Invisible approach might make detecting such dark objects possible

Charisma: An ill-defined and ill-measured gift

We take historical stock of charisma, tracing its origins and how it has been conceptualized in the sociological and organizational sciences literatures. Although charisma has been intensely studied, the concept is still not well understood and much of the research undertaken cannot inform policy. We show that the major obstacles to advancing our understanding of charisma have included issues with its definition, its confusion with transformational leadership, the use of questionnaire measures, and that it has not been studied using correctly-specified causal models. To help spawn a new genre of research in charisma, we use signaling theory to provide a general definition of charisma, and make suggestions about how charisma should be conceptualized, operationalized, and modeled. We also describe trends and patterns in articles we reviewed, using co-citation as well as bibliometric analyses, and discuss the practical implications of our findings

Mechanical properties of self-setting composites: influence of the carboxymethylcellulose content and hydration state

The impact of the carboxymethylcellulose (CMC) content on the mechanical properties of calcium phosphate–calcium carbonate–CMC composite cements for bone substitution was investigated. The relevance of the compressive test conditions (wet or dried composite cements) is discussed and models are proposed to better understand the mechanisms involved in the mechanical properties of the composite materials. Based on a modellisation using the Voigt model for dried composite cements, we show that a minimum of CMC content of around 10–20 % is needed to enhance the mechanical properties of the dried composite materials (up to 86 MPa for the composite including 50 wt% CMC) through the formation of a mineral–organic entangled network. The compressive strength of the wet samples is low (\3 MPa) but the gain observed in the dried composites is encouraging and might be extrapolated to wet conditions if we were to use a less hydrophilic polysaccharid

Development of an injectable composite for bone regeneration

With the development of minimally invasive surgical techniques, there is a growing interest in the research and development of injectable biomaterials especially for orthopedic applications. In a view to enhance the overall surgery benefits for the patient, the BIOSINJECT project aims at preparing a new generation of mineral-organic composites for bone regeneration exhibiting bioactivity, therapeutic activity and easiness of use to broaden the application domains of the actual bone mineral cements and propose an alternative strategy with regard to their poor resorbability, injectability difficulties and risk of infection. First, a physical-chemical study demonstrated the feasibility of self-setting injectable composites associating calcium carbonate-calcium phosphate cement and polysaccharides (tailor-made or commercial polymer) in the presence or not of an antibacterial agent within the composite formulation. Then, bone cell response and antimicrobial activity of the composite have been evaluated in vitro. Finally, in order to evaluate resorption rate and bone tissue response an animal study has been performed and the histological analysis is still in progress. These multidisciplinary and complementary studies led to promising results in a view of the industrial development of such composite for dental and orthopaedic applications

Optimization of spray-dried hyaluronic acid microspheres to formulate drug-loaded bone substitute materials

Wepresent here our first results concerning the evaluation of hyaluronic acid (HA) as a candidate to formulate an organic–mineral cement with sustained release properties. Incorporating drug-loaded microspheres in mineral bone cements is an alternative strategy to improve their ability as drug delivery materials. To synthesize microspheres according to a reproducible process and control at the same time their morphology and their encapsulation efficiency is one of the main challenges of the conception of such drug-loaded bone substitute. In this context, we investigated the potentialities of two HA, differing by theirmolecular weight, to form microspheres by a spray-drying technique. Erythrosin B (EB) was encapsulated as a model drug and spray-drying process conditionswere optimized. To performthis, the rheological behavior and viscosity of HA solutions have been related to their spray-drying ability, and then to the resulting microparticles morphological properties and size distribution. Reproducible microspheres, answering to the requirements in terms of size and encapsulation efficiency, have been obtained from both HA. However the HA exhibiting the lowest molecular weight, HA600, led to smaller microparticles, with a higher polydispersity index. Their swelling ability, related to their stability upon rehydration, also appeared reduced. In this context, HA850, with the highest molecular weight, was selected and the possibility to modulate drug release by HA850 microspheres incorporation into a mineral cement was explored. EB release kinetics from HA microspheres, HA microspheres loaded cement and reference cement were followed at 37 °C, in Tris buffer at pH 7.4, using European Pharmacopoeia flow-through cells. Results showed that HA microspheres incorporation into a mineral cement permitted to modify the cement drug release profile and led to a sustained release