On the evolution of online tourism communities - Network battle or longtail niches?

Even though the emergence or respectively the construction of online communities is of great interest for scientists and community engineers, only few empirical data has been presented on community growth. This article starts with a reflection on possible growth curves of virtual communities. It contrasts a network externality perspective that produces clear winners and losers in a market with a long tail perspective that also allows small niche products to be successful. These considerations are empirically tested with a sample of 74 travel communities whose numbers of registered members were recorded at two measure points. The results show that online travel communities develop into an archetypical long tail. A very small number of communities with exceedingly high numbers of members are accompanied by a vast amount of communities with only few members. An analysis of the long tail, however, reveals that the community tail is not dead but is populated by a large number of especially regional communities that show considerable growth rates

The Dynamic Effects of Information on Political Corruption: Theory and Evidence from Puerto Rico

Does the disclosure of information about corrupt activities induce a sustained reduction in corruption? We use publicly released routine audits of municipal governments in Puerto Rico to answer this question. We first develop a political agency model where voters re-elect incumbents based on their performance while in office. We show that, because voters cannot directly observe incumbents’ actions, an incumbent whose reputation improved in the previous term is likely to engage in more rent-seeking activities in a future term. Guided by this model, we use longitudinal data on audit results to examine the long-term consequences of providing information to voters on levels of political corruption. We find that municipal corruption levels in subsequent audits are on average the same in municipalities audited preceding the previous election and those not audited then. In spite of this, mayors in municipalities audited preceding the previous election have higher re-election rates, suggesting that audits enable voters to select more competent politicians. We conclude that short-term information dissemination policies do not necessarily align politicians’ long-term actions with voter preferences as politicians exploit their reputational gains by extracting more rents from office.corruption; information; political agency; dynamic incentives

Axon Trapping: Constructing the Visual System One Layer at a Time

The molecular mechanisms that instruct the formation of synaptic layers are only incompletely understood. In this issue of Neuron, Timofeev et al. (2012) describe an instructive role for the guidance molecule Netrin and its receptor Frazzled in mediating layer-specific targeting of one photoreceptor cell type in the Drosophila visual system

Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram

Based on the extended Greenwich-NOAA/USAF catalogue of sunspot groups it is demonstrated that the parameters describing the latitudinal width of the sunspot generating zone (SGZ) are closely related to the current level of solar activity, and the growth of the activity leads to the expansion of SGZ. The ratio of the sunspot number to the width of SGZ shows saturation at a certain level of the sunspot number, and above this level the increase of the activity takes place mostly due to the expansion of SGZ. It is shown that the mean latitudes of sunspots can be reconstructed from the amplitudes of solar activity. Using the obtained relations and the group sunspot numbers by Hoyt and Schatten (1998), the latitude distribution of sunspot groups ("the Maunder butterfly diagram") for the 18th and the first half of the 19th centuries is reconstructed and compared with historical sunspot observations.Comment: 16 pages, 11 figures; accepted by Solar Physics; the final publication will be available at www.springerlink.co

A functional genomic screen in Saccharomyces cerevisiae reveals divergent mechanisms of resistance to different alkylphosphocholine chemotherapeutic agents

The alkylphosphocholine (APC) class of antineoplastic and antiprotozoal drugs, such as edelfosine and miltefosine, are structural mimics of lyso-phosphatidylcholine (lyso-PC), and are inhibitory to the yeast Saccharomyces cerevisiae at low micromolar concentrations. Cytotoxic effects related to inhibition of phospholipid synthesis, induction of an unfolded protein response, inhibition of oxidative phosphorylation, and disruption of lipid rafts have been attributed to members of this drug class, however, the molecular mechanisms of action of these drugs remain incompletely understood. Cytostatic and cytotoxic effects of the APCs exhibit variability with regard to chemical structure, leading to differences in effectiveness against different organisms or cell types. We now report the comprehensive identification of S. cerevisiae titratableessential gene and haploid nonessential gene deletion mutants that are resistant to the APC drug miltefosine (hexadecyl-O-phosphocholine). Fifty-eight strains out of~5600 tested displayed robust and reproducible resistance to miltefosine. This gene set was heavily enriched in functions associated with vesicular transport steps, especially those involving endocytosis and retrograde transport of endosome derived vesicles to the Golgi or vacuole, suggesting a role for these trafficking pathways in transport of miltefosine to potential sites of action in the endoplasmic reticulum and mitochondrion. In addition, we identified mutants with defects in phosphatidylinositol-4-phosphate synthesis (TetO::STT4) and hydrolysis (sac1Δ), an oxysterol binding protein homolog (osh2Δ), a number of ER-resident proteins, and multiple components of the eisosome. These findings suggest that ER-plasma membrane contact sites and retrograde vesicle transport are involved in the interorganelle transport of lyso-PtdCho and related lyso-phospholipid-like analogs to their intracellular sites of cytotoxic activity

HIV/AIDS prevalence among South African health workers

Introduction. Studies on HIV prevalence among health workers usually focus on occupational exposure to HIV. Little is known about HIV prevalence in this group. However, it is expected that HIV prevalence among health workers will reflect prevalence in their society. Objective. To determine HIV prevalence among South African health workers. Method. A stratified cluster sample was drawn of 5% of health facilities in South Africa (N = 222) representative of the public and private health sectors in South Africa. The sample was designed to obtain a nationwide representative sample of medical professionals and non-professional health workers. A subsample comprising health workers in four provinces was tested for HIV status. The Orasure HIV-1 device in combination with the Vironostika HIV UNI-Form II plus O enzyme-linked immunosorbent assay (ELISA) kits were used to collect oral fluid specimens for HIV testing. Results. Based on a sample of 721 health workers and a response rate of 82.5% (or 595 respondents), the study found that an estimated 15.7% (95% confidence interval (CI): 12.2 - 19.9%) of health workers employed in the public and private health facilities located in four South African provinces, were living with HIV/AIDS in 2002. Among younger health workers, the risk is much higher. This group (aged 18 - 35 years) had an estimated HIV prevalence of 20% (95% CI: 14.1 - 27.6%). Non-professionals had an HIV prevalence of 20.3%, while professionals had a prevalence of 13.7%. Conclusion. HIV prevalence among health workers in South Africa is high; this calls for the introduction of antiretroviral programmes targeting them. In addition, there is a need for the development of new policy regarding placement of infected health workers in tuberculosis (TB) wards, coupled with vigorous human resource planning to replace the health workers likely to die from AIDS. Infection control procedures also need to be reviewed. S Afr Med J 2004; 94: 846-850

Fibroblasts in liver cancer: functions and therapeutic translation

Accumulation of fibroblasts in the premalignant or malignant liver is a characteristic feature of liver cancer, but has not been therapeutically leveraged despite evidence for pathophysiologically relevant roles in tumour growth. Hepatocellular carcinoma is a largely non-desmoplastic tumour, in which fibroblasts accumulate predominantly in the pre-neoplastic fibrotic liver and regulate the risk for hepatocellular carcinoma development through a balance of tumour-suppressive and tumour-promoting mediators. By contrast, cholangiocarcinoma is desmoplastic, with cancer-associated fibroblasts contributing to tumour growth. Accordingly, restoring the balance from tumour-promoting to tumour-suppressive fibroblasts and mediators might represent a strategy for hepatocellular carcinoma prevention, whereas in cholangiocarcinoma, fibroblasts and their mediators could be leveraged for tumour treatment. Importantly, fibroblast mediators regulating hepatocellular carcinoma development might exert opposite effects on cholangiocarcinoma growth. This Review translates the improved understanding of tumour-specific, location-specific, and stage-specific roles of fibroblasts and their mediators in liver cancer into novel and rational therapeutic concepts.Copyright © 2023 Elsevier Ltd. All rights reserved

pShuffle: A Plasmid for in vitro Evolution

Multi-gene shuffling is a powerful method used to combine and optimize attributes of various proteins. Here we report on the design and construction of the plasmid “pShuffle” which is suited for a variety of in vitro DNA-recombination techniques. The multiple cloning site (MCS) of pShuffle was designed to allow for the cloning of genes as well as their expression under control of either a lac- or a T7-promoter. As a specific feature, this MCS allows for the fusion of special linker sequences to both ends of cloned genes. After subsequent DNA-recombination steps, these linkers facilitate reamplification of generated gene variants, and thus may be used to construct clone libraries for activity screenings. The suitability of pShuffle for multi-gene shuffling applications was further shown with a set of styrene monooxygenase genes originating from proteo- and actinobacteria