The Economics of 'Acting White'

This paper formalizes a sociological phenomenon entitled 'acting white'. The key idea is that individuals face a tension between signaling their type to the outside labor market and signaling their type to a peer group: signals that induce high wages can be signals that induce peer rejection. We prove three basic results: (1) there exists no equilibria in which all types of individuals adopt distinct educational investment levels; (2) when individuals are not too patient, all equilibria satisfying a standard refinement involve a binary partition of the type space in which all types accepted by the group pool on a common low education level and all types rejected by the group separate at distinctly higher levels of education with correspondingly higher wages; and (3) when individuals are very patient, there is an increase in the variation of education levels within the group and an increase in the variance of types deemed acceptable by the group. The more those involved discount the future, the more salient peer pressure becomes and the more homogenous groups become.

Experimental tests of the endowment effect

The discrepancy between WTA and WTP is supposed to be a manifestation of the endowment effect (KKT). The discrepancy between the average WTA-WTP disappears in the sense of statistical significance (Shogren et. at.) in settings with repeated interactions. In this paper we reexamine the KKT experimental procedures for identifying an endowment effect for consumer goods. No evidence of income or role effects is found. We show that even though the discrepancy between WTA-WTP diminishes undertrading can still persist in markets

Impacts of natural factors and farming practices on greenhouse gas emissions in the North China Plain : A meta-analysis

This work received support from the National Science and Technology Support Program (No. 2012BAD14B01), the National 948 Project (No. 2011-G30), and the Non-profit Research Foundation for Agriculture (201103039). Thanks are expressed to the anonymous reviewers for their helpful comments and suggestions that greatly improved the manuscript. The authors declare that they have no competing interests.Peer reviewedPublisher PD

Region-specific dendritic simplification induced by Aβ, mediated by tau via dysregulation of microtubule dynamics: a mechanistic distinct event from other neurodegenerative processes.

BackgroundDendritic simplification, a key feature of the neurodegenerative triad of Alzheimer's disease (AD) in addition to spine changes and neuron loss, occurs in a region-specific manner. However, it is unknown how changes in dendritic complexity are mediated and how they relate to spine changes and neuron loss.ResultsTo investigate the mechanisms of dendritic simplification in an authentic CNS environment we employed an ex vivo model, based on targeted expression of enhanced green fluorescent protein (EGFP)-tagged constructs in organotypic hippocampal slices of mice. Algorithm-based 3D reconstruction of whole neuron morphology in different hippocampal regions was performed on slices from APPSDL-transgenic and control animals. We demonstrate that induction of dendritic simplification requires the combined action of amyloid beta (Aβ) and human tau. Simplification is restricted to principal neurons of the CA1 region, recapitulating the region specificity in AD patients, and occurs at sites of Schaffer collateral input. We report that γ-secretase inhibition and treatment with the NMDA-receptor antagonist, CPP, counteract dendritic simplification. The microtubule-stabilizing drug epothilone D (EpoD) induces simplification in control cultures per se. Similar morphological changes were induced by a phosphoblocking tau construct, which also increases microtubule stability. In fact, low nanomolar concentrations of naturally secreted Aβ decreased phosphorylation at S262 in a cellular model, a site which is known to directly modulate tau-microtubule interactions.ConclusionsThe data provide evidence that dendritic simplification is mechanistically distinct from other neurodegenerative events and involves microtubule stabilization by dendritic tau, which becomes dephosphorylated at certain sites. They imply that treatments leading to an overall decrease of tau phosphorylation might have a negative impact on neuronal connectivity

Engaging Community and Developing Leadership Through Adventure and Experiential Learning

During this project seventh grade students and I collaborated to accomplish the goal of building a relationship between the seventh and fifth grades so the younger students could feel safe and welcome at our school. I used a teaching approach based on the elements of adventure and the experiential cycle of learning to help seventh grade students develop leadership skills. Team building activities and a community adventure brought the seventh and fifth graders together. The leadership role of the seventh graders during these events served as the catalyst for building a positive caring relationship between the two grades

Harmonic mapping of spheres

This thesis is addressed to the following fundamental problem: given a homotopy class of maps between compact Riemannian manifolds N and M, is there a harmonic representative of that class? Eells and Sampson have given a general existence theorem for the case that M has no positive sectional curvatures [ESJ. Otherwise, very little is known. Certainly no counter-example has ever been established. The most important contributions of this dissertation are two: firstly, we have a direct construction technique for producing some essential harmonic maps between Euclidean spheres. Topologically, this consists simply of joining two harmonic polynomial mappings (e.g., the Hopf fibrations). Analytically, however, this method has a novel physical motivation: we study the equation of motion of an exotic pendulum driven by a gravity which chances sign. If this system has an exceptional trajectory of the right sort, it defines a harmonic map of spheres. One consequence or our theorem is that πn(Sn) is represented by harmonic maps for n= 1,...,7. Finally, the rudiments of an equivariant theory of harmonic maps having been set out earlier, we find that our examples can also be put in this framework. The second significant result which arose from this study is a strong candidate for a counterexample: suppose Sn is stretched to a length b in one direction to make an ellipsoid En(b). Then if n > 3 and b is large enough, there is no harmonic stretching (of degree one) of Sn onto En(b). However, if b=1 the identity is such a harmonic map, so it certainly appears that the existence of a harmonic representative in a homotopy class can depend upon the metric. We also examine here a large collection of examples of harmonic maps of spheres which are defined by harmonic polynomials and orthogonal multiplications. The last chapter takes up the study of the Morse theory of a harmonic map: amongst several pleasing results, we have an example of a simple map whose index and degeneracy can be made arbitrarily large by equally simple changes in the metrics

Cytochrome P450 CYP1B1 interacts with 8-<i>methoxypsoralen</i> (8-MOP) and influences psoralen-Ultraviolet A (PUVA) sensitivity

Background: There are unpredictable inter-individual differences in sensitivity to psoralen-UVA (PUVA) photochemotherapy, used to treat skin diseases including psoriasis. Psoralens are metabolised by cytochrome P450 enzymes (P450), and we hypothesised that variability in cutaneous P450 expression may influence PUVA sensitivity. We previously showed that P450 CYP1B1 was abundantly expressed in human skin and regulated by PUVA, and described marked inter-individual differences in cutaneous CYP1B1 expression.Objectives: We investigated whether CYP1B1 made a significant contribution to 8-methoxypsoralen (8-MOP) metabolism, and whether individuality in CYP1B1 activity influenced PUVA sensitivity.Methods: We used E. coli membranes co-expressing various P450s and cytochrome P450 reductase (CPR) to study 8-MOP metabolism and cytotoxicity assays in CYP1B1-expressing mammalian cells to assess PUVA sensitivity.Results: We showed that P450s CYP1A1, CYP1A2, CYP1B1, CYP2A6 and CYP2E1 influence 8-MOP metabolism. As CYP1B1 is the most abundant P450 in human skin, we further demonstrated that: (i) CYP1B1 interacts with 8-MOP (ii) metabolism of the CYP1B1 substrates 7-ethoxyresorufin and 17-b-estradiol showed concentration-dependent inhibition by 8-MOP and (iii) inhibition of 7-ethoxyresorufin metabolism by 8-MOP was influenced by CYP1B1 genotype. The influence of CYP1B1 on PUVA cytotoxicity was further investigated in a Chinese hamster ovary cell line, stably expressing CYP1B1 and CPR, which was more sensitive to PUVA than control cells, suggesting that CYP1B1 metabolises 8-MOP to a more phototoxicmetabolite(s).Conclusion: Our data therefore suggest that CYP1B1 significantly contributes to cutaneous 8-MOP metabolism, and that individuality in CYP1B1 expression may influence PUVA sensitivity