64,687 research outputs found
Intertemporal Risk Management Decisions of Farmers under Preference, Market, and Policy Dynamics
This paper adapts a generalized expected utility (GEU) maximization model (Epstein and Zin, 1989 and 1991) to examine the intertemporal risk management of wheat producers in the Pacific Northwest. Optimization results based on simulated data indicate the feasibility of the GEU optimization as a modeling framework. It further extends the GEU model by incorporating a welfare measure, the certainty equivalent, to investigate the impacts of U.S. government programs and market institutions on farmers' risk management decisions and welfare. A comparison between the GEU and other expected utility models further implies GEU has the advantage of specifying farmers' intertemporal preferences separately and completely. Impact analysis results imply that farmers' optimal hedging is sensitive to changes in the preferences and the effects of these preference changes are intertwined. Target price and loan rate levels, offered by certain government payment programs, can lead to the substitution of government programs for hedging. The evaluation of current risk management tools shows both crop insurance and government payments can improve farmers' welfare significantly. Government payment programs have a greater effect on farmers' welfare than crop insurance and crop insurance outperforms hedging.generalized expected utility, risk management, multi-period production, dynamic optimization, intertemporal preference, market institution, government payments, Risk and Uncertainty, Q14, D9, C61,
Dynamical Behavior of a stochastic SIRS epidemic model
In this paper we study the Kernack - MacKendrick model under telegraph noise.
The telegraph noise switches at random between two SIRS models. We give out
conditions for the persistence of the disease and the stability of a disease
free equilibrium. We show that the asymptotic behavior highly depends on the
value of a threshold which is calculated from the intensities of
switching between environmental states, the total size of the population as
well as the parameters of both SIRS systems. According to the value of
, the system can globally tend towards an endemic case or a disease
free case. The aim of this work is also to describe completely the omega-limit
set of all positive solutions to the model. Moreover, the attraction of the
omega-limit set and the stationary distribution of solutions will be pointed
out.Comment: 16 page
On the Approximability and Hardness of the Minimum Connected Dominating Set with Routing Cost Constraint
In the problem of minimum connected dominating set with routing cost
constraint, we are given a graph , and the goal is to find the
smallest connected dominating set of such that, for any two
non-adjacent vertices and in , the number of internal nodes on the
shortest path between and in the subgraph of induced by is at most times that in . For general graphs, the only
known previous approximability result is an -approximation algorithm
() for by Ding et al. For any constant , we
give an -approximation
algorithm. When , we give an -approximation
algorithm. Finally, we prove that, when , unless , for any constant , the problem admits no
polynomial-time -approximation algorithm, improving
upon the bound by Du et al. (albeit under a stronger hardness
assumption)
Robustness of Network of Networks with Interdependent and Interconnected links
Robustness of network of networks (NON) has been studied only for dependency
coupling (J.X. Gao et. al., Nature Physics, 2012) and only for connectivity
coupling (E.A. Leicht and R.M. D Souza, arxiv:0907.0894). The case of network
of n networks with both interdependent and interconnected links is more
complicated, and also more closely to real-life coupled network systems. Here
we develop a framework to study analytically and numerically the robustness of
this system. For the case of starlike network of n ER networks, we find that
the system undergoes from second order to first order phase transition as
coupling strength q increases. We find that increasing intra-connectivity links
or inter-connectivity links can increase the robustness of the system, while
the interdependency links decrease its robustness. Especially when q=1, we find
exact analytical solutions of the giant component and the first order
transition point. Understanding the robustness of network of networks with
interdependent and interconnected links is helpful to design resilient
infrastructures
Comment on ``Evidence for Anisotropic State of Two-Dimensional Electrons in High Landau Levels''
In a recent letter M. Lilly et al [PRL 82, 394 (1999)] have shown that a
highly anisotropic state can arise in certain two dimensional electron systems.
In the large square samples studied, resistances measured in the two
perpendicular directions are found to have a ratio that may be 60 or larger at
low temperature and at certain magnetic fields. In Hall bar measurements, the
anisotropy ratio is found to be much smaller (roughly 5). In this comment we
resolve this discrepancy by noting that the anisotropy of the underlying sheet
resistivities is correctly represented by Hall bar resistance measurements but
shows up exponentially enhanced in resistance measurements on square samples
due to simple geometric effects. We note, however, that the origin of this
underlying resistivity anisotropy remains unknown, and is not addressed here.Comment: 1 page, minor calculational error repaire
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