Algebraic Boundaries of Convex Semi-algebraic Sets

We study the algebraic boundary of a convex semi-algebraic set via duality in convex and algebraic geometry. We generalize the correspondence of facets of a polytope to the vertices of the dual polytope to general semi-algebraic convex bodies. In the general setup, exceptional families of extreme points might exist and we characterize them semi-algebraically. We also give an algorithm to compute a complete list of exceptional families, given the algebraic boundary of the dual convex set.Comment: 13 pages, 2 figures; Comments welcom

The pay-as-you-go pension system as fertility insurance and an enforcement device

A PAYGO system may serve as insurance against not having children and as an enforcement device for ungrateful children who are unwilling to pay their parents a pension. In fact, the latter was Bismarck’s historic motive for introducing this system. It is true that the PAYGO system reduces the investment in human capital, but if it is run on a sufficiently small scale, it may nevertheless bring about a welfare improvement. If, on the other hand, the scale of the system is so large that parents bequeath some of their pensions to their children, it is overdrawn and creates unnecessarily strong disincentives for human capital investment

Measuring international capital mobility: A critical assessment of the use of saving and investment correlations

Economists have been interested in the degree of international capital mobility for a variety of reasons. E.g., the extent to which public deficits crowd out domestic investments depends on the ease with which domestic firms may access the international capital market. The welfare reduction due to a temporary negative shock to an economy (earthquake) is much less pronounced if it can borrow resources from abroad in order to tide itself over the initial period of reconstruction.

Fisherian and Ricardian trade

This paper discusses the difference between Fisherian and Ricardian trade in terms of a simple two-period model of a small open economy. Fisherian or intertemporal trade occurs when goods are traded today against the promise to deliver goods in the future. The resulting net resource transfer is equal to an international flow of capital. Ricardian trade occurs when there are no international capital flows and the trade account is balanced. The model suggests that once international trade is primarily of Fisherian nature, the direction and volume of trade are best explained by variables that take intertemporal aspects into consideration such as the interest rate and the expected prices of goods.International capital mobility,saving,investment,current account adjustment

Multibody dynamics for biologically inspired smart space structure

Structures in space are often just serving a single purpose. By developing a structure which is able to change it properties and adapt to changing environmental conditions, the costs of space missions can be decreased significantly. The design and simulation of such a structure is presented in this paper. The developed structure consists of an array of interconnected cells which are each able to alter their volume due to internal pressure change. By coordinated cell actuation in a specific pattern, the global structure can be deformed to obtain a desired shape. A multibody code was developed which constantly solves the equation of motion with inputs from internal actuation and external perturbation forces. During the inflation and actuation of the structure, the entities of the mass matrix and the stiffness matrix are changed due to changing properties of the cells within the array based on their state and displacement. This paper outlines the principles behind the developed code and gives examples in two dimensional and three dimensional space

Weyl-Heisenberg Spaces for Robust Orthogonal Frequency Division Multiplexing

Design of Weyl-Heisenberg sets of waveforms for robust orthogonal frequency division multiplex- ing (OFDM) has been the subject of a considerable volume of work. In this paper, a complete parameterization of orthogonal Weyl-Heisenberg sets and their corresponding biorthogonal sets is given. Several examples of Weyl-Heisenberg sets designed using this parameterization are pre- sented, which in simulations show a high potential for enabling OFDM robust to frequency offset, timing mismatch, and narrow-band interference

Inflatable structures for Mars Base 10

A permanent manned settlement on the Martian surface requires the use of advanced technology concepts in order to become technically and financially feasible. The former developed Mars Base 10 concept incorporates novel ideas, increasing the feasibility of a continous human base on Mars. The most advanced feature of the MB10 design is the concept of increasing the habitable space of the Mars base once landed with an inflatable torus like structure. This paper gives an overview on the MB10 design and has its primary focus on the deployment of the inflatable structure. The deployment simulations show the final inflated shape of the MB10 concept on Mars from an un-inflated initial shape on Earth. The deployment strategy, simulations and rigidization techniques are discussed to provide a conceptual solution for large inflatable components of the MB10 habitat. Further applications of secondary inflatable smart structures are presented as well. These secondary structures are self deploying at the Martian ambient pressure which results in low storage volume and mass. These structures are well-suited to carry on for astronauts on EVAs for example