From rice to cocoa through a political economy of dishonesty, Sulawesi, Indonesia

Sulawesi has been the theatre of a spectacular cocoa boom, which started from scratch in the late 1970s, with production exceeding the 200,000-tonne threshold in the mid-1990s. Sulawesi also used to be a rice granary for Indonesia. Although it still exports rice to other provinces, Sulawesi turned its dynamism towards cocoa. They mostly are Bugis farmers. Then Balinese and Javanese transmigrants started to follow. From that historical development in Sulawesi, the objective is to analyze at the microeconomic level, how Indonesia switched back from rice self-sufficiency to structural dependency on imports since 1994. Bugis used their experience and capital built on rice to start cocoa pioneer lives that proved to be highly successful. They also benefited of involuntary helpful policies such as fertilizer subsidies that were conceived for rice self-sufficiency, not for cocoa. Within official projects, Balinese and Javanese transmigrants were often obliged not to plant tree crops, or at least not beyond the 0.25ha backyard. How did these policies involuntarily trigger new impetus to cocoa and eventually hamper the development of paddy cultivation in the 1990s? The Sulawesi cocoa story may be a showcase for understanding why the gap between the national demand and supply of rice increased since the mid-1990s

The Uniform Integrability of Martingales. On a Question by Alexander Cherny

Let $X$ be a progressively measurable, almost surely right-continuous stochastic process such that $X_\tau \in L^1$ and $E[X_\tau] = E[X_0]$ for each finite stopping time $\tau$. In 2006, Cherny showed that $X$ is then a uniformly integrable martingale provided that $X$ is additionally nonnegative. Cherny then posed the question whether this implication also holds even if $X$ is not necessarily nonnegative. We provide an example that illustrates that this implication is wrong, in general. If, however, an additional integrability assumption is made on the limit inferior of $|X|$ then the implication holds. Finally, we argue that this integrability assumption holds if the stopping times are allowed to be randomized in a suitable sense.Comment: Revised version. Accepted for publication in Stochastic Processes and their Application

Discrete stochastic approximations of the Mumford-Shah functional

We propose a $\Gamma$-convergent discrete approximation of the Mumford-Shah functional. The discrete functionals act on functions defined on stationary stochastic lattices and take into account general finite differences through a non-convex potential. In this setting the geometry of the lattice strongly influences the anisotropy of the limit functional. Thus we can use statistically isotropic lattices and stochastic homogenization techniques to approximate the vectorial Mumford-Shah functional in any dimension.Comment: 47 pages, reorganized versio

Real-time on-board obstacle avoidance for UAVs based on embedded stereo vision

In order to improve usability and safety, modern unmanned aerial vehicles (UAVs) are equipped with sensors to monitor the environment, such as laser-scanners and cameras. One important aspect in this monitoring process is to detect obstacles in the flight path in order to avoid collisions. Since a large number of consumer UAVs suffer from tight weight and power constraints, our work focuses on obstacle avoidance based on a lightweight stereo camera setup. We use disparity maps, which are computed from the camera images, to locate obstacles and to automatically steer the UAV around them. For disparity map computation we optimize the well-known semi-global matching (SGM) approach for the deployment on an embedded FPGA. The disparity maps are then converted into simpler representations, the so called U-/V-Maps, which are used for obstacle detection. Obstacle avoidance is based on a reactive approach which finds the shortest path around the obstacles as soon as they have a critical distance to the UAV. One of the fundamental goals of our work was the reduction of development costs by closing the gap between application development and hardware optimization. Hence, we aimed at using high-level synthesis (HLS) for porting our algorithms, which are written in C/C++, to the embedded FPGA. We evaluated our implementation of the disparity estimation on the KITTI Stereo 2015 benchmark. The integrity of the overall realtime reactive obstacle avoidance algorithm has been evaluated by using Hardware-in-the-Loop testing in conjunction with two flight simulators.Comment: Accepted in the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Scienc

A one-dimensional diffusion hits points fast

A one-dimensional, continuous, regular, and strong Markov process $X$ with state space $E$ hits any point $z \in E$ fast with positive probability. To wit, if $\tau_z = \inf \{t \geq 0:X_{t} = z\}$, then $P_\xi({ \tau}_z0$ for all $\xi \in E$ and $\varepsilon>0$

Convergence in Models with Bounded Expected Relative Hazard Rates

We provide a general framework to study stochastic sequences related to individual learning in economics, learning automata in computer sciences, social learning in marketing, and other applications. More precisely, we study the asymptotic properties of a class of stochastic sequences that take values in $[0,1]$ and satisfy a property called "bounded expected relative hazard rates." Sequences that satisfy this property and feature "small step-size" or "shrinking step-size" converge to 1 with high probability or almost surely, respectively. These convergence results yield conditions for the learning models in B\"orgers, Morales, and Sarin (2004), Erev and Roth (1998), and Schlag (1998) to choose expected payoff maximizing actions with probability one in the long run.Comment: After revision. Accepted for publication by Journal of Economic Theor