Peer influence in network markets: a theoretical and empirical analysis

Network externalities spur the growth of networks and the adoption of network goods in two ways. First, they make it more attractive to join a network the larger its installed base. Second, they create incentives for network members to actively recruit new members. Despite indications that the latter "peer effect" can be more important for network growth than the installed-base effect, it has so far been largely ignored in the literature. We address this gap using game-theoretical models. When all early adopters can band together to exert peer influence-an assumption that fits, e.g., the case of firms supporting a technical standard-we find that the peer effect induces additional growth of the network by a factor. When, in contrast, individuals exert peer influence in small groups of size n, the increase in network size is by an additive constant-which, for small networks, can amount to a large relative increase. The difference between small, local, personal networks and large, global, anonymous networks arises endogenously from our analysis. Fundamentally, the first type of networks is "tie-reinforcing," the other, "tie-creating". We use survey data from users of the Internet services, Skype and eBay, to illustrate the main logic of our theoretical results. As predicted by the model, we find that the peer effect matters strongly for the network of Skype users-which effectively consists of numerous small sub-networks-but not for that of eBay users. Since many network goods give rise to small, local networks

Antenatal steroids in preterm labour for the prevention of neonatal deaths due to complications of preterm birth

Background In high-income countries, administration of antenatal steroids is standard care for women with anticipated preterm labour. However, although >1 million deaths due to preterm birth occur annually, antenatal steroids are not routine practice in low-income countries where most of these deaths occur

A Review of NEST Models, and Their Application to Improvement of Particle Identification in Liquid Xenon Experiments

Liquid xenon is a leader in rare-event physics searches. Accurate modeling of charge and light production is key for simulating signals and backgrounds in this medium. The signal- and background-production models in the Noble Element Simulation Technique (NEST) are presented. NEST is a simulation toolkit based on experimental data, fit using simple, empirical formulae for the average charge and light yields and their variations. NEST also simulates the final scintillation pulses and exhibits the correct energy resolution as a function of the particle type, the energy, and the electric fields. After vetting of NEST against raw data, with several specific examples pulled from XENON, ZEPLIN, LUX/LZ, and PandaX, we interpolate and extrapolate its models to draw new conclusions on the properties of future detectors (e.g., XLZD's), in terms of the best possible discrimination of electron(ic) recoil backgrounds from a potential nuclear recoil signal, especially WIMP dark matter. We discover that the oft-quoted value of 99.5% discrimination is overly conservative, demonstrating that another order of magnitude improvement (99.95% discrimination) can be achieved with a high photon detection efficiency (g1 ~ 15-20%) at reasonably achievable drift fields of 200-350 V/cm.Comment: 24 Pages, 6 Tables, 15 Figures, and 15 Equation

Preventing the diversion of Turkish opium

Turkey was once one of the world’s largest sources of illicit opium; the majority diverted from sparsely regulated licit production. Since 1972, however, it has contributed almost no opium to the global black market. As such, Turkey is one of a small number of states to have eradicated, or severally reduced, the national supply of illicit opium. This article reconsiders post-1974 Turkish controls from a situational crime prevention perspective. It is suggested that Turkish success was founded upon reducing opportunities for diversion from regulated production by hardening targets, increasing formal and informal surveillance, assisting compliance through fair procurement practices and increasing the risk of non-compliance

Heterogeneous natural selection on oxidative phosphorylation genes among fishes with extreme high and low aerobic performance

Background: Oxidative phosphorylation (OXPHOS) is the primary source of ATP in eukaryotes and serves as a mechanistic link between variation in genotypes and energetic phenotypes. While several physiological and anatomical factors may lead to increased aerobic capacity, variation in OXPHOS proteins may influence OXPHOS efficiency and facilitate adaptation in organisms with varied energy demands. Although there is evidence that natural selection acts on OXPHOS genes, the focus has been on detection of directional (positive) selection on specific phylogenetic branches where traits that increase energetic demands appear to have evolved. We examined patterns of selection in a broader evolutionary context, i.e., on multiple lineages of fishes with extreme high and low aerobic performance. Results: We found that patterns of natural selection on mitochondrial OXPHOS genes are complex among fishes with different swimming performance. Positive selection is not consistently associated with high performance taxa and appears to be strongest on lineages containing low performance taxa. In contrast, within high performance lineages, purifying (negative) selection appears to predominate. Conclusions: We provide evidence that selection on OXPHOS varies in both form and intensity within and among lineages through evolutionary time. These results provide evidence for fluctuating selection on OXPHOS associated with divergence in aerobic performance. However, in contrast to previous studies, positive selection was strongest on low performance taxa suggesting that adaptation of OXPHOS involves many factors beyond enhancing ATP production in high performance taxa. The broader pattern indicates a complex interplay between organismal adaptations, ATP demand, and OXPHOS function.This work was supported by NSF award DEB-0732988 (to REB).Ye

Reflections on the 'History and Historians' of the black woman's role in the community of slaves: enslaved women and intimate partner sexual violence

Taking as points of inspiration Peter Parish’s 1989 book, Slavery: History and Historians, and Angela Davis’s seminal 1971 article, “Reflections on the black woman’s role in the community of slaves,” this probes both historiographically and methodologically some of the challenges faced by historians writing about the lives of enslaved women through a case study of intimate partner violence among enslaved people in the antebellum South. Because rape and sexual assault have been defined in the past as non-consensual sexual acts supported by surviving legal evidence (generally testimony from court trials), it is hard for historians to research rape and sexual violence under slavery (especially marital rape) as there was no legal standing for the rape of enslaved women or the rape of any woman within marriage. This article suggests enslaved women recognized that black men could both be perpetrators of sexual violence and simultaneously be victims of the system of slavery. It also argues women stoically tolerated being forced into intimate relationships, sometimes even staying with “husbands” imposed upon them after emancipation

The sarcoplasmic reticulum plays a major role in isometric contraction in atrial muscle of yellowfin tuna

We used an isometric muscle preparation to test the hypothesis that yellowfin tuna Thunnus albacares utilize the intracellular Ca2+ storage sites of the sarcoplasmic reticulum (SR) during routine contractions. Ryanodine (a blocker of SR Ca2+ release) reduced the force of contraction by approximately 50 % and the rates of contraction and relaxation by 60 % in yellowfin tuna atrium. High levels of adrenaline were unable to ameliorate the effects of ryanodine. We conclude that the SR is active in contributing Ca2+ to Summary force development at physiological contraction frequencies. Further, we suggest that, by using intracellular Ca 2+ cycling, the yellowfin tuna is able to increase the maximum contraction frequency of its cardiac muscle beyond that of most other fishes