Critical core mass for enriched envelopes: the role of H2O condensation

Context. Within the core accretion scenario of planetary formation, most simulations performed so far always assume the accreting envelope to have a solar composition. From the study of meteorite showers on Earth and numerical simulations, we know that planetesimals must undergo thermal ablation and disruption when crossing a protoplanetary envelope. Once the protoplanet has acquired an atmosphere, the primordial envelope gets enriched in volatiles and silicates from the planetesimals. This change of envelope composition during the formation can have a significant effect in the final atmospheric composition and on the formation timescale of giant planets. Aims. To investigate the physical implications of considering the envelope enrichment of protoplanets due to the disruption of icy planetesimals during their way to the core. Particular focus is placed on the effect on the critical core mass for envelopes where condensation of water can occur. Methods. Internal structure models are numerically solved with the implementation of updated opacities for all ranges of metallicities and the software CEA to compute the equation of state. CEA computes the chemical equilibrium for an arbitrary mixture of gases and allows the condensation of some species, including water. This means that the latent heat of phase transitions is consistently incorporated in the total energy budget. Results. The critical core mass is found to decrease significantly when an enriched envelope composition is considered in the internal structure equations. A particular strong reduction of the critical core mass is obtained for planets whose envelope metallicity is larger than Z=0.45 when the outer boundary conditions are suitable for condensation of water to occur in the top layers of the atmosphere. We show that this effect is qualitatively preserved when the atmosphere is out of chemical equilibrium.Comment: Accepted for publication in A&

Beam Induced Electron Cloud Resonances in Dipole Magnetic Fields

The buildup of low energy electrons in an accelerator, known as electron cloud, can be severely detrimental to machine performance. Under certain beam conditions, the beam can become resonant with the cloud dynamics, accelerating the buildup of electrons. This paper will examine two such effects: multipacting resonances, in which the cloud development time is resonant with the bunch spacing, and cyclotron resonances, in which the cyclotron period of electrons in a magnetic field is a multiple of bunch spacing. Both resonances have been studied directly in dipole fields using retarding field analyzers installed in the Cornell Electron Storage Ring (CESR). These measurements are supported by both analytical models and computer simulations

Skilled and Unskilled Wage Dynamics in Italy in the ‘90s: Changes in the individual characteristics, institutions, trade and technology.

In this paper we use individual micro data on workers combined with industry and regional data to study the wage dynamics of skilled and unskilled workers in Italy in the period 1991-1998. Being different to previous empirical studies, our data allow us to explore in a unique framework the role of many of the factors indicated in the literature as possible causes of the widening of the wage gap between skilled and unskilled workers: changes in the individual characteristics of workers, changes in the institutions of the labour market, increasing international integration and skill-biased technological progress. Our results show that international integration, both in terms of trade in goods and in terms of international labour mobility, plays a role in determining the wage dynamics of skilled (white collar) and of unskilled (blue collar) workers. In addition, in line with the research in labour economics, our findings show that the individual characteristics of workers, and the institutional variables matter more in explaining skilled and unskilled wage dynamics than differential wage one.Skilled and unskilled wages, individual characteristics, labour market institutions, international trade.

Capital heterogeneity and the decline of the labour share

We investigate the decline of the labour share in a world characterized by increasing heterogeneity of capital assets. Our results show that, over the 1970-2007 period, the decline of the labour share has been mainly driven by Information and Communication Technology (ICT) assets and is mitigated by increasing investments in R&Dbased knowledge assets. Extending to other forms of intangible capital from 1995 onwards, we find that intangible investments related to innovation increase the labour share while those related to the organisation of firms contribute to its decline, particularly for the low and intermediate skilled workers. Our results are robust to an array of econometric issues, namely heterogeneity, cross-sectional dependence, and endogeneit

Technology, intangible assets and the decline of the labor share

We investigate the decline of the labor share in a world characterized by rapid technological changes and increasing heterogeneity of capital assets. Our theoretical model allows for these assets to affect the labor share in different directions depending on the capital-labor substitution/complementary relationship and the workers' skill level. We test the predictions of our model using a large cross-country, cross-industry data set, considering different forms of tangible and intangible capital inputs. Our results show that, over the 1970-2007 period, the decline of the labor share has been mainly driven by technical change and Information and Communication Technology (ICT) assets, mitigated by increasing investments in R&D-based knowledge assets. Extending to other forms of intangible capital from 1995 onwards, we find that intangible investments related to innovation increase the labor share while those related to the organisation of firms contribute to its decline, particularly for the low and intermediate skilled workers. Our results are robust to an array of econometric issues, namely heterogeneity, cross-sectional dependence, and endogeneit

The Enhancement of Wild Bees (Hymenoptera: Apoidea) For Pollination Security

The acreage of pollinator-dependent crops continues to expand across the globe. Simultaneously, honey bee hives – an annually rented commodity that growers rely on – are more expensive every year and in some cases, scarce. In response, pollinator-dependent growers seek alternative pollinators. One approach is installing bee pasture on farms, a strategy that enables systems-based farmers to become in-situ farm-scale habitat managers. This thesis first presents a review of the literature on bee pasture plantings and provides a brief overview of some methods for assessing their impacts on the pollinator community. There are three major gaps in current bee pasture research. First, can bee pasture actually enhance bee populations? Second, what ratio of bee pasture to crop is required to significantly increase pollination services in a crop field? Last, research that assesses that attractiveness of easily established, phenologically diverse region- and crop-specific flowers that are unlikely to become weedy in crop fields is still rare. The second chapter of this thesis presents the results of a comprehensive two-year study of bee pasture plantings within the context of New England’s wild lowbush blueberry agroecosystem. Using a randomized complete block design I investigate the effects of nurse crops and mowing regimes on bee pasture establishment success in terms of floral density and species diversity. Three types of bee pasture (clovers, wildflowers, and naturally regenerating margins) were installed at four replicated sites in Maine. Bee pastures were compared in terms of both floral density and insect visitation. Bumble bees were collected at the four treatment sites, and the species’ group composition of their pollen loads were compared with those of bumble bees collected in three control sites. Similar patterns of visitation to bee pasture are apparent among years. Analysis of visitation in the second year alone suggests that naturally regenerating agricultural margins supported 3-4 times fewer wild bee pollinators than other treatments (2 = 5.808, P = 0.055). These differences are significant when wild bees are parsed into social and solitary groups. Social bees utilize clover plantings at a significantly greater rate than solitary bees (2 = 7.269, P = 0.026) and solitary bees utilize wildflower plantings over clover and naturally regenerating plots (2 = 7.423, P = 0.024). On average, across all blueberry fields adjacent to sown bee pasture, bumble bee pollen loads contained 37% bee pasture pollen. Our findings suggest that in lowbush blueberry fields, even relatively small sown flowering strips can provide over 1/3 of the dietary pollen for bumble bees, clover plantings are highly utilized by bumble bees, and wildflower plantings show great potential to provision resources for solitary bees

Superconducting Gap and Pseudogap in Bi-2212

We present results of Raman scattering experiments in differently doped Bi-2212 single crystals. Below Tc the spectra show pair-breaking features in the whole doping range. The low frequency power laws confirm the existence of a $d_{x^2-y^2}$-wave order parameter. In the normal state between Tc and T* = 200K we find evidence for a pseudogap in B2g symmetry. Upon doping its effect on the spectra decreases while its energy scale appears to be unchanged.Comment: 2 pages, 1 EPS figure; LT22 Proceedings to appear in Physica