Spin crossover in liquid (Mg,Fe)O at extreme conditions

We use first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O, whereby the magnetic moments of Fe ions vanish gradually over a range of hundreds of GPa. Because electronic entropy strongly favors the nonmagnetic low-spin state of Fe, the crossover has a negative effective Clapeyron slope, in stark contrast to the crystalline counterpart of this transition-metal oxide. Diffusivity of liquid (Mg,Fe)O is similar to that of MgO, displaying a weak dependence on element and spin state. Fe-O and Mg-O coordination increases from approximately 4 to 7 as pressure goes from 0 to 200 GPa. We find partitioning of Fe to induce a density inversion between the crystal and melt, implying separation of a basal magma ocean from a surficial one in the early Earth. The spin crossover induces an anomaly into the density contrast, and the oppositely signed Clapeyron slopes for the crossover in the liquid and crystalline phases imply that the solid-liquid transition induces a spin transition in (Mg,Fe)O

Managerial Incentives and Capital Management

In Holmstrom (1982) an example is given, which shows that a manager’s concern for the value of his human capital will lead to a natural incongruity in risk-preferences between himself and the owners, even when no effort considerations are involved. In this paper we present a formal model of this channel of incongruity based on learning about managerial talent. We also explore the nature of an optimal incentive contract in the case where the manager may withhold but not misrepresent information about investment returns. The optimal contract is an option on the manager’s human capital value with a possible bonus for investing. The optimal investment rule accepts fewer investments than under the cost of capital — a commonly observed real world feature. Another phenomena the model helps explain is the extensive use of capital budgeting and rationing schemes in place of linear or non-linear price decentralization, which are shown to be less efficient modes of allocation

Exclusive Neutral Pion Electroproduction in the Deeply Virtual Regime

We present measurements of the ep→epπ0 cross section extracted at two values of four-momentum transfer Q2=1.9 GeV2 and Q2=2.3 GeV2 at Jefferson Lab Hall A. The kinematic range allows one to study the evolution of the extracted cross section as a function of Q2 and W. Results are confronted with Regge-inspired calculations and GPD predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering is also discussed

E00-110 experiment at Jefferson Lab Hall A: Deeply virtual Compton scattering off the proton at 6 GeV

We present final results on the photon electroproduction ((e) over right arrowp - \u3e ep gamma) cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region from Jefferson Lab experiment E00-110. Results from an analysis of a subset of these data were published before, but the analysis has been improved, which is described here at length, together with details on the experimental setup. Furthermore, additional data have been analyzed, resulting in photon electroproduction cross sections at new kinematic settings for a total of 588 experimental bins. Results of the Q(2) and x(B) dependencies of both the helicity-dependent and the helicity-independent cross sections are discussed. The Q(2) dependence illustrates the dominance of the twist-2 handbag amplitude in the kinematics of the experiment, as previously noted. Thanks to the excellent accuracy of this high-luminosity experiment, it becomes clear that the unpolarized cross section shows a significant deviation from the Bethe-Heitler process in our kinematics, compatible with a large contribution from the leading twist-

Exclusive neutral pion electroproduction in the deeply virtual regime

We present measurements of the ep -\u3e ep pi(0) cross section extracted at two values of four-momentum transfer Q(2) = 1.9 GeV(2) and Q(2) = 2.3 GeV(2) at Jefferson Lab Hall A. The kinematic range allows one to study the evolution of the extracted cross section as a function of Q(2) and W. Results are confronted with Regge-inspired calculations and GPD predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering is also discussed

Corporate Hierarchies and the Size of Nations: Theory and Evidence

Corporate organization varies within a country and across countries with country size. The paper starts by establishing some facts about corporate organization based on unique data of 660 Austrian and German corporations. The larger country (Germany) has larger firms with flatter more decentral corporate hierarchies compared to the smaller country (Austria). Firms in the larger country change their organization less fast than firms in the smaller country. Over time firms have been introducing less hierarchical organizations by delegating power to lower levels of the corporation. We develop a theory which explains these facts and which links these features to the trade environment that countries and firms face. We introduce firms with internal hierarchies in a Krugman (1980) model of trade. We show that international trade and the toughness of competition in international markets induce a power struggle in firms which eventually leads to decentralized corporate hierarchies. We offer econometric evidence which is consistent with the models predictions

ECCC TEST PROGRAMME AND DATA ASSESSMENT ON GTD111 CREEP RUPTURE, STRAIN AND DUCTILITY

GTD111, a creep resistant Ni-based superalloy developed by GE, is widely used in land-based gas turbine first stage blades. However, there is little published information on its creep properties and microstructure. The European Creep Collaborative Committee (ECCC) Working Group 3C consequently selected GTD111 as a model material for testing and complementary data assessment. The aim of this paper is to present the results from the ECCC test program and data assessment, and to compare equiaxed (EA) and directionally solidified (DS) material performance. Testing and metallographic laboratories from six European nations collaborated to produce strain monitored creep rupture data on four EA and DS materials out to beyond 10,000 hours within a wide range of temperatures, 850-950°C, and stresses, 293-99 MPa. Available (generally short term) results from other sources were also included in the compiled, small but viable, 51-test data set. Assessment was carried out by three different assessors using different tools and adopting different prediction models. Conventional ECCC post-assessment techniques and novel “back-fitting” methods were used to identify a preferred model. It was shown that assessing all the EA and DS data together can lead to non-conservative predictions for EA materials, but separating the two classes creates small data subsets which cannot be modelled effectively. As a pragmatic compromise, the DS data and those EA data which also showed good ductility were included in a final "ductile GTD111" assessment. The resulting creep rupture material models and rupture strength predictions are presented up to 3 times the longest test duration. It was then shown that the performance of lower ductility EA materials can also be predicted effectively with the "ductile" model by truncating the rupture time at the measured fracture strain. For this exercise, a creep strain model based on rupture and time to strain data was fitted. In parallel, microstructural examination was performed to characterize the damage modes involved in the low ductility failures. It was thereby shown that the creep rupture strength shortfall of an EA material compared to its DS equivalent is not a constant factor, but is primarily governed by the reduced creep ductility. Hence, the shortfall varies between different EA casts, and tends to become greater in the longer term.JRC.F.4-Innovative Technologies for Nuclear Reactor Safet