Two-dimensional state sum models and spin structures

The state sum models in two dimensions introduced by Fukuma, Hosono and Kawai are generalised by allowing algebraic data from a non-symmetric Frobenius algebra. Without any further data, this leads to a state sum model on the sphere. When the data is augmented with a crossing map, the partition function is defined for any oriented surface with a spin structure. An algebraic condition that is necessary for the state sum model to be sensitive to spin structure is determined. Some examples of state sum models that distinguish topologically-inequivalent spin structures are calculated.Comment: 43 pages. Mathematica script in ancillary file. v2: nomenclature of models and their properties changed, some proofs simplified, more detailed explanations. v3: extended introduction, presentational improvements; final versio

SOCIAL IDENTITY AND MANIPULATIVE INTERHOUSEHOLD TRANSFERS AMONG EAST AFRICAN PASTORALISTS

We model interhousehold transfers between nomadic livestock herders as the state-dependent consequence of individuals' strategic interdependence resulting from the existence of multiple, opposing externalities. A public good security externality among individuals sharing a social (e.g., ethnic) identity in a potentially hostile environment creates incentives to band together. Self-interested interhousehold wealth transfers from wealthier herders to poorer ones may emerge endogenously within a limited wealth space as a means to motivate accompanying migration by the recipient. The distributional reach and size of the transfer are limited, however, by a resource appropriation externality related to the use of common property grazing lands. When this effect dominates, it can induce distributionally regressive transfers from ex ante poor households who want to relieve grazing pressures caused by larger herds. As compared to the extant literature on transfers, our model appears more consistent with the limited available empirical evidence on heterogeneous and changing transfers patterns among east African pastoralists.Agribusiness, D, O, Q18,

Perceptions of Risk within Pastoralist Households in Northern Kenya and Southern Ethiopia

Perceptions of risk may vary within households as well as across households and communities. In this paper, we take advantage of panel survey data collected quarterly over a period of 2 ½ years to see how perceptions of risk vary across individuals over time. The surveyed households are in pastoralist communities in Northern Kenya and Southern Ethiopia and the survey period coincides with a severe drought in this region and the beginning of the recovery. We identify the structural heterogeneity of the perceptions of risk of these individuals. Because of the nature of panel data, we can also test how the perceptions of risk are affected by shocks in previous periods. In particular, we ask how an individual's risk perceptions change when shocks happen to him or herself, to other members of his or her, family, or to members of his or her community. This allows us to ask how expectations adapt based on the things that are happening to others and allows us to look at issues of social networks and learning.Risk and Uncertainty,

Asymptotics of Relativistic Spin Networks

The stationary phase technique is used to calculate asymptotic formulae for SO(4) Relativistic Spin Networks. For the tetrahedral spin network this gives the square of the Ponzano-Regge asymptotic formula for the SU(2) 6j symbol. For the 4-simplex (10j-symbol) the asymptotic formula is compared with numerical calculations of the Spin Network evaluation. Finally we discuss the asymptotics of the SO(3,1) 10j-symbol.Comment: 31 pages, latex. v3: minor clarification

BAYESIAN HERDERS: ASYMMETRIC UPDATING OF RAINFALL BELIEFS IN RESPONSE TO EXTERNAL FORECASTS

Temporal climate risk weighs heavily on many of the world's poor. Recent advances in model-based climate forecasting have expanded the range, timeliness and accuracy of forecasts available to decision-makers whose welfare depends on stochastic climate outcomes. There has consequently been considerable recent investment in improved climate forecasting for the developing world. Yet, in cultures that have long used indigenous climate forecasting methods, forecasts generated and disseminated by outsiders using unfamiliar methods may not readily gain the acceptance necessary to induce behavioral change. The value of model-based climate forecasts depends critically on the premise that forecast recipients actually use external forecast information to update their rainfall expectations. We test this premise using unique survey data from pastoralists and agropastoralists in southern Ethiopia and northern Kenya, specifying and estimating a model of herders updating seasonal rainfall beliefs. We find that those who receive and believe model-based seasonal climate forecasts indeed update their priors in the direction of the forecast received, assimilating optimistic forecasts more readily than pessimistic forecasts.Agribusiness, O1, D1, Q12,

Finite element approximation of the transport of reactive solutes in porous media .2. Error estimates for equilibrium adsorption processes

Published versio

An algebraic interpretation of the Wheeler-DeWitt equation

We make a direct connection between the construction of three dimensional topological state sums from tensor categories and three dimensional quantum gravity by noting that the discrete version of the Wheeler-DeWitt equation is exactly the pentagon for the associator of the tensor category, the Biedenharn-Elliott identity. A crucial role is played by an asymptotic formula relating 6j-symbols to rotation matrices given by Edmonds.Comment: 10 pages, amstex, uses epsf.tex. New version has improved presentatio

Social Identity and Manipulative Interhousehold Transfers Among East African Pastoralists

We model interhousehold transfers between nomadic livestock herders as the state-dependent consequence of individuals\u27 strategic interdependence resulting from the existence of multiple, opposing externalities. A public good security externality among individuals sharing a social (e.g., ethnic) identity in a potentially hostile environment creates incentives to band together. Self-interested interhousehold wealth transfers from wealthier herders to poorer ones may emerge endogenously within a limited wealth space as a means to motivate accompanying migration by the recipient. The distributional reach and size of the transfer are limited, however, by a resource appropriation externality related to the use of common property grazing lands. When this effect dominates, it can induce distributionally regressive transfers from ex ante poor households who want to relieve grazing pressures caused by larger herds. As compared to the extant literature on transfers, our model appears more consistent with the limited available empirical evidence on heterogeneous and changing transfers\u27 patterns among east African pastoralists

Understanding Declining Mobility and Interhousehold Transfers Among East African Pasoralists

We model interhousehold transfers between nomadic livestock herders as the state-dependent consequence of individuals\u27 strategic interdependence resulting from the existence of multiple, opposing externalities. A public good security externality among individuals sharing a social (e.g., ethnic) identity in a potentially hostile environment creates incentives to band together. Self-interested interhousehold wealth transfers from wealthier herders to poorer ones may emerge endogenously within a limited wealth space as a means to motivate accompanying migration by the recipient. The distributional reach and size of the transfer are limited, however, by a resource appropriation externality related to the use of common property grazing lands. When this effect dominates, it can induce transfers from households who want to relieve grazing pressures caused by others\u27 herds. Our model augments the extant literature on transfers, and is perhaps more consistent with the limited available empirical evidence on heterogeneous and changing transfers\u27 patterns among east African pastoralists. The core principles of our model possibly apply more broadly, for example to long-distance migrants or even among foot soldiers in street gangs

Understanding Declining Mobility and Interhousehold Transfers among East African Pastoralists

We model interhousehold transfers between nomadic livestock herders as the state-dependent consequence of individuals\u27 strategic interdependence resulting from the existence of multiple, opposing externalities. A public good security externality among individuals sharing a social (e.g., ethnic) identity in a potentially hostile environment creates incentives to band together. Self-interested interhousehold wealth transfers from wealthier herders to poorer ones may emerge endogenously within a limited wealth space as a means to motivate accompanying migration by the recipient. The distributional reach and size of the transfer are limited, however, by a resource appropriation externality related to the use of common property grazing lands. When this effect dominates, it can induce transfers from households who want to relieve grazing pressures caused by others\u27 herds. Our model augments the extant literature on transfers, and is perhaps more consistent with the limited available empirical evidence on heterogeneous and changing transfers - patterns among east African pastoralists. The core principles of our model possibly apply more broadly, for example to long-distance migrants or even among foot soldiers in street gangs