Capacity Bounded Grammars and Petri Nets

A capacity bounded grammar is a grammar whose derivations are restricted by assigning a bound to the number of every nonterminal symbol in the sentential forms. In the paper the generative power and closure properties of capacity bounded grammars and their Petri net controlled counterparts are investigated

Accepting Hybrid Networks of Evolutionary Processors with Special Topologies and Small Communication

Starting from the fact that complete Accepting Hybrid Networks of Evolutionary Processors allow much communication between the nodes and are far from network structures used in practice, we propose in this paper three network topologies that restrict the communication: star networks, ring networks, and grid networks. We show that ring-AHNEPs can simulate 2-tag systems, thus we deduce the existence of a universal ring-AHNEP. For star networks or grid networks, we show a more general result; that is, each recursively enumerable language can be accepted efficiently by a star- or grid-AHNEP. We also present bounds for the size of these star and grid networks. As a consequence we get that each recursively enumerable can be accepted by networks with at most 13 communication channels and by networks where each node communicates with at most three other nodes.Comment: In Proceedings DCFS 2010, arXiv:1008.127

Strominduziertes magnetisches Schalten von einkristallinen Eisenschichten

In this thesis I describe the development of a new process to nanostructure a layered magnetic system. The diameter of the pillar-like structures is smaller than 200 nm. The structures are designed to allow measurements of the electrical resistance in a temperature range from ambient temperature down to 4 K. Thus, it is possible to measure the giant magneto resistance with current perpendicular to the plane of the layers (CPP-GMR) for the first time at the Forschungszentrum Jülich. Furthermore I present the first measurements of current induced magnetic switching and magnetic excitations by spin-transfer of single-crystalline iron layers. I discuss two epitaxial systems that are prepared using molecular beam epitaxy. The first one is Fe(10) / Cr(1.2) / Fe(2) [in nm] which gives a GMR= 0.1% at ambient temperature and 0.6% at 4 K. By increasing a DC current the magnetic system is excited for both polarities of the current. This feature could be explained by the interlayer exchange coupling which leads to a simultaneous excitation of both iron layers. Therefore, hysteretic switching could not be observed. The second system is Fe(14) / Cr(0.9) / Fe(10) / Ag(6) / Fe(2). The value of the CPP-GMR is around 2.6% at room temperature and 5.6% at 4 K. A DC current gives hysteretic current induced magnetic switching at small external magnetic fields at both polarities of the current. This observation is explained by theoretical different signs of the spin scattering asymmetry of the Fe / Cr and Fe / Ag interfaces. At high fields of $\thicksim$ 1T only one peak in the differential resistance is observed which is a clear evidence of magnetic excitations by spintransfer. The observed switching indicates a very complex remagnetization process of the nanostructured system. Therefore, it is not possible to discuss the data more quantitatively. Micromagnetic simulations identify the problems of the structuring process and possible improvements are suggested

Grammars with valuations — a discrete model for self-organization of biopolymers

AbstractWe define a new type of formal grammars where the derivation process is regulated by a certain function which evaluates the words. These grammars can be regarded as a model for the molecular replication process with selective character. We locate the associated family of languages in the Chomsky hierarchy, prove some closure properties, and solve some decision problems which are of interest in formal language theory and in biophysics

Intensity of Brillouin light scattering from spin waves in magnetic multilayers with noncollinear spin configurations: Theory and experiment

The scattering of photons from spin waves (Brillouin light scattering -- BLS) is a well-established technique for the study of layered magnetic systems. The information about the magnetic state and properties of the sample is contained in the frequency position, width, and intensity of the BLS peaks. Previously [Phys. Rev. B 67, 184404 (2003)], we have shown that spin wave frequencies can be conveniently calculated within the ultrathin film approach, treating the intralayer exchange as an effective bilinear interlayer coupling between thin virtual sheets of the ferromagnetic layers. Here we give the consequent extension of this approach to the calculation of the Brillouin light scattering (BLS) peak intensities. Given the very close relation of the BLS cross-section to the magneto-optic Kerr effect (MOKE), the depth-resolved longitudinal and polar MOKE coefficients calculated numerically via the usual magneto-optic formalism can be employed in combination with the spin wave precessional amplitudes to calculate full BLS spectra for a given magnetic system. This approach allows an easy calculation of BLS intensities even for noncollinear spin configurations including the exchange modes. The formalism is applied to a Fe/Cr/Fe/Ag/Fe trilayer system with one antiferromagnetically coupling spacer (Cr). Good agreement with the experimental spectra is found for a wide variety of spin configurations.Comment: 19 pages, 5 figure

Effect of uniform load on the shear strength of slender beams without shear reinforcement

textPrevious studies have shown that a uniform distribution of load may increase the shear strength of a slender member by as much as 40 percent (Leonhardt and Walther 1964). The increase of shear strength is potentially due to clamping stresses induced from the uniform load, although a mathematical equation to quantify the effect of clamping stress in slender uniformly loaded members has yet to be derived (Acevedo et al. 2009). Only a small percentage of all shear tests on slender specimens without shear reinforcement were completed with uniform load. Additionally, the majority of uniform load data consists of specimens with small specimen depths (d) and large longitudinal reinforcement ratios (ρ). Six shear tests on specimens without shear reinforcement were completed at the University of Texas at Austin. Three of the six specimens were subjected to concentrated load, and the remaining three companion specimens were loaded uniformly. These specimens are among the deepest slender members without shear reinforcement that have ever been tested under a uniform load distribution. Importantly, the ratio of maximum shear to maximum moment was maintained between concentrated and uniform load tests which ensures directly comparable tests results. The experimental results were shown to be influenced by load distribution. Uniformly loaded specimens had an average increase in first diagonal cracking shear capacity of 17 percent with a range of increase between 10 and 23 percent when compared with specimens subjected to concentrated loads.Civil, Architectural, and Environmental Engineerin