Random walks with imperfect trapping in the decoupled-ring approximation

We investigate random walks on a lattice with imperfect traps. In one dimension, we perturbatively compute the survival probability by reducing the problem to a particle diffusing on a closed ring containing just one single trap. Numerical simulations reveal this solution, which is exact in the limit of perfect traps, to be remarkably robust with respect to a significant lowering of the trapping probability. We demonstrate that for randomly distributed traps, the long-time asymptotics of our result recovers the known stretched exponential decay. We also study an anisotropic three-dimensional version of our model, where for sufficiently large transverse diffusion the system is described by the mean-field kinetics. We discuss possible applications of some of our findings to the decay of excitons in semiconducting organic polymer materials, and emphasize the crucial influence of the spatial trap distribution on the kinetics.Comment: 10 page

Corporate impression formation in online communities: a qualitative study

Purpose: This study aims to evaluate elements of corporate communication in online communities (OCs) and their influence on corporate impression formation. Interactive online platforms such as OCs are growing. Companies are discovering their importance and increasingly include OCs in their communication activities. The present study identifies the underlying components relevant to successful corporate communication in OCs, and further explore if and how online community members (OCMs) expect companies to communicate with them, explaining how corporate impressions are formed. Design/methodology/approach: A qualitative research method was chosen, consisting of two stages. In stage one, seventeen expert interviews with academics and practitioners were conducted, and in stage two, twelve OCMs were interviewed to clarify the concepts and gain new insights. Findings: The study gains new knowledge relating to corporate communication in OCs and image formation. Specifically, the authors identify and confirm important key constructs in corporate impression formation in OCs, namely, relevance of messages, communication style, social context cues, affiliation, perceived similarity, source credibility and interpersonal communication. Furthermore, a conceptual model is proposed on the relationship between communication elements relevant in online communities and their influence on corporate impression. Theoretical and practical implications: The study helps to refine existing concepts of corporate impression formation in OCs. It is suggested that understanding how corporate impression is formed in OCs helps companies to participate in virtual networks, improving their corporate impression

Localization of computer-mediated communication and corporate impression on online communities

Purpose The purpose of this paper is to investigate the importance of localizing online communities (OCs) and examines how OC members form impressions of organizations that use OCs in their communication activities. A conceptual framework and measurement scale are developed that consist of complex latent constructs. Design/methodology/approach A sequential multi-method approach is adopted with both qualitative and quantitative investigations. Using Structural equation modeling, the research refines and validates the measurement scales of impression formation in OCs. Findings Findings reveal that comprehensive messages have a direct effect on the impressions that an OC member forms. In particular, social context cues are an important predictor of online community corporate impression (OCCIP). Source credibility, affiliation, characteristics and interpersonal communication are all critical to OCCIP, which in turn, influence members’ attitudes toward the company and the intention to use it again. Surprisingly, relevance, timeliness, accuracy and perceived similarity did not have any significant effect on the corporate impression. Originality/value Three contributions are offered: First, the study provides reliable scales for measuring OCCIP. Second, support is given to the conceptual model that links OCCIP to a set of consequences, namely, attitudes toward the company, intention to use the company, and word-of-mouth. Finally, the study is conducted across two different and unique types of OC contexts, stipulating further insights into the localization of OCs

Corporate impression formation in online communities: a qualitative study

Purpose: This study aims to evaluate elements of corporate communication in online communities (OCs) and their influence on corporate impression formation. Interactive online platforms such as OCs are growing. Companies are discovering their importance and increasingly include OCs in their communication activities. The present study identifies the underlying components relevant to successful corporate communication in OCs, and further explore if and how online community members (OCMs) expect companies to communicate with them, explaining how corporate impressions are formed. Design/methodology/approach: A qualitative research method was chosen, consisting of two stages. In stage one, seventeen expert interviews with academics and practitioners were conducted, and in stage two, twelve OCMs were interviewed to clarify the concepts and gain new insights. Findings: The study gains new knowledge relating to corporate communication in OCs and image formation. Specifically, the authors identify and confirm important key constructs in corporate impression formation in OCs, namely, relevance of messages, communication style, social context cues, affiliation, perceived similarity, source credibility and interpersonal communication. Furthermore, a conceptual model is proposed on the relationship between communication elements relevant in online communities and their influence on corporate impression. Theoretical and practical implications: The study helps to refine existing concepts of corporate impression formation in OCs. It is suggested that understanding how corporate impression is formed in OCs helps companies to participate in virtual networks, improving their corporate impression

Geostatistical radar-raingauge combination with nonparametric correlograms: methodological considerations and application in Switzerland

Modelling spatial covariance is an essential part of all geostatistical methods. Traditionally, parametric semivariogram models are fit from available data. More recently, it has been suggested to use nonparametric correlograms obtained from spatially complete data fields. Here, both estimation techniques are compared. Nonparametric correlograms are shown to have a substantial negative bias. Nonetheless, when combined with the sample variance of the spatial field under consideration, they yield an estimate of the semivariogram that is unbiased for small lag distances. This justifies the use of this estimation technique in geostatistical applications. Various formulations of geostatistical combination (Kriging) methods are used here for the construction of hourly precipitation grids for Switzerland based on data from a sparse realtime network of raingauges and from a spatially complete radar composite. Two variants of Ordinary Kriging (OK) are used to interpolate the sparse gauge observations. In both OK variants, the radar data are only used to determine the semivariogram model. One variant relies on a traditional parametric semivariogram estimate, whereas the other variant uses the nonparametric correlogram. The variants are tested for three cases and the impact of the semivariogram model on the Kriging prediction is illustrated. For the three test cases, the method using nonparametric correlograms performs equally well or better than the traditional method, and at the same time offers great practical advantages. Furthermore, two variants of Kriging with external drift (KED) are tested, both of which use the radar data to estimate nonparametric correlograms, and as the external drift variable. The first KED variant has been used previously for geostatistical radar-raingauge merging in Catalonia (Spain). The second variant is newly proposed here and is an extension of the first. Both variants are evaluated for the three test cases as well as an extended evaluation period. It is found that both methods yield merged fields of better quality than the original radar field or fields obtained by OK of gauge data. The newly suggested KED formulation is shown to be beneficial, in particular in mountainous regions where the quality of the Swiss radar composite is comparatively low. An analysis of the Kriging variances shows that none of the methods tested here provides a satisfactory uncertainty estimate. A suitable variable transformation is expected to improve this

Horizontal gene transfer contributed to the evolution of extracellular surface structures

The single-cell layered ectoderm of the fresh water polyp Hydra fulfills the function of an epidermis by protecting the animals from the surrounding medium. Its outer surface is covered by a fibrous structure termed the cuticle layer, with similarity to the extracellular surface coats of mammalian epithelia. In this paper we have identified molecular components of the cuticle. We show that its outermost layer contains glycoproteins and glycosaminoglycans and we have identified chondroitin and chondroitin-6-sulfate chains. In a search for proteins that could be involved in organising this structure we found PPOD proteins and several members of a protein family containing only SWT (sweet tooth) domains. Structural analyses indicate that PPODs consist of two tandem β-trefoil domains with similarity to carbohydrate-binding sites found in lectins. Experimental evidence confirmed that PPODs can bind sulfated glycans and are secreted into the cuticle layer from granules localized under the apical surface of the ectodermal epithelial cells. PPODs are taxon-specific proteins which appear to have entered the Hydra genome by horizontal gene transfer from bacteria. Their acquisition at the time Hydra evolved from a marine ancestor may have been critical for the transition to the freshwater environment

Dynamics of charge-displacement channeling in intense laser-plasma interactions

The dynamics of transient electric fields generated by the interaction of high intensity laser pulses with underdense plasmas has been studied experimentally with the proton projection imaging technique. The formation of a charged channel, the propagation of its front edge and the late electric field evolution have been characterised with high temporal and spatial resolution. Particle-in-cell simulations and an electrostatic, ponderomotive model reproduce the experimental features and trace them back to the ponderomotive expulsion of electrons and the subsequent ion acceleration.Comment: 5 figures, accepted for publication in New Journal of Physic