Distributed hierarchical automata with applications to genetics in procaryotes.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Includes bibliographical references.Ph.D

Viability in hybrid systems

AbstractHybrid systems are interacting systems of digital automata and continuous plants subject to disturbances. The digital automata are used to force the state trajectory of the continuous plant to obey a performance specification. For the basic concepts and notation for hybrid systems, see Kohn and Nerode (1993), and other papers in the same volume. Here we introduce tools for analyzing enforcing viability of all possible plant state trajectories of a hybrid system by suitable choices of finite state control automata. Thus, the performance specification considered here is that the state of the plant remain in a prescribed viability set of states at all times (Aubin, 1991). The tools introduced are local viability graphs and viability graphs for hybrid systems. We construct control automata which guarantee viability as the fixpoints of certain operators on graphs. When control and state spaces are compact, the viability set is closed, and a non-empty closed subset of a viability graph is given with a sturdiness property, one can extract finite state automata guaranteeing viable trajectories. This paper is a sequel to Kohn and Nerode (1993), especially Appendix II

The Ursinus Weekly, November 16, 1964

11 students elected to Who\u27s who in American colleges • Museum director Turner speaks on American art • Lord and Lady, class officers named at Senior Ball, Friday: Extensive decorations create Camelot atmosphere • Curtain Club stages Fall play this weekend: Free student performance Friday • Temple scientists to visit campus, discuss careers • Summer harvest movie shown to PSEA members • Karen Wagner chosen Jr. Miss Montgomery Co. • German Club discusses life in Europe • Local NAACP members to speak to student tutors • PAC sponsors work camp talk • Editorial: Our policing system • Life up the hill at Fircroft social club • Letters to the editor • Questions and answers about Giefan • UC history: Cheerleaders • How to be an All-American; A case study • Hockey undefeated 3rd year in a row: Gettysburg succumbs 4-1 in final game; Victory extends unbeaten streak record • Friday 13 unlucky soccermen fall 1-0 to Muhlenberg foe • Football beaten 47-22 by Lebanon Valley: Injury-racked squad no match for foe; Degenhardt scores all U.C. points • Greek gleaningshttps://digitalcommons.ursinus.edu/weekly/1234/thumbnail.jp

Half-metallic ferrimagnet formed by substituting Fe for Mn in semiconductor MnTe

A ternary ferrimagnetic half-metal, constructed through substituting 25% Fe for Mn in zincblende semiconductor MnTe, is predicted in terms of accurate first-principles calculations. It has a large half-metallic (HM) gap of 0.54eV and its ferrimagnetic order is very stable against other magnetic fluctuations. The HM ferrimagnetism is formed because the complete moment compensation in the antiferromagnetic MnTe is replaced by an uncomplete one in the Fe-substituted MnTe. This should make a novel approach to new HM materials. The half-metal could be fabricated because Fe has good affinity with Mn, and useful for spintronics.Comment: 5 pages with figures include

Influence of oxygen addition on the structural and elastic properties of TiC thin films

We have studied the structural, electronic and mechanical properties of TiCxOy, using first principles calculations based on the density functional theory and pseudopotential method, within the generalized gradient approximation for the exchange–correlation functional. These calculations provide the lattice parameter, density of states, cohesive energy, elastic constants and moduli as a function of carbon and oxygen content. The calculated values of lattice parameters and elastic moduli are generally in good agreement with experiments and compare well with other theoretical results

Saturation of electrical resistivity in metals at large temperatures

We present a microscopic model for systems showing resistivity saturation. An essentially exact quantum Monte-Carlo calculation demonstrates that the model describes saturation. We give a simple explanation for saturation, using charge conservation and considering the limit where thermally excited phonons have destroyed the periodicity. Crucial model features are phonons coupling to the hopping matrix elements and a unit cell with several atoms. We demonstrate the difference to a model of alkali-doped C60 with coupling to the level positions, for which there is no saturation.Comment: 4 page, RevTeX, 3 eps figures, additional material available at http://www.mpi-stuttgart.mpg.de/andersen/fullerene

Natural age dispersion arising from the analysis of broken crystals, part II. Practical application to apatite (U-Th)/He thermochronometry

We describe a new numerical inversion approach to deriving thermal history information from a range of naturally dispersed single grain apatite (U-Th)/He ages. The approach explicitly exploits the information about the shape of the 4He diffusion profile within individual grains that is inherent in the pattern of dispersion that arises from the common and routine practice of analysing broken crystals. Additional dispersion arising from differences in grain size and in U and Th concentration of grains, and the resultant changes to helium diffusivity caused by differential accumulation and annealing of radiation damage, is explicitly included. In this approach we calculate the ingrowth and loss, due to both thermal diffusion and the effects of α-ejection, of helium over time using a finite cylinder geometry. Broken grains are treated explicitly as fragments of an initially larger crystal. The initial grain lengths, L0, can be treated as unknown parameters to be estimated, although this is computationally demanding. A practical solution to the problem of solving for the unknown initial grain lengths is to simply apply a constant and sufficiently long L0 value to each fragment. We found that a good value for L0 was given by the maximum fragment length plus two times the maximum radius of a given set of fragments. Currently whole crystals and fragments with one termination are taken into account. A set of numerical experiments using synthetic fragment ages generated for increasingly complex thermal histories, and including realistic amounts of random noise (5-15%), are presented and show that useful thermal history information can be extracted from datasets showing very large dispersion. These include experiments where dispersion arises only from fragmentation of a single grain (length 400μm and radius 75μm, c. 6-50% dispersion), including the effects of grain size variation (for spherical equivalent grain radii between 74-122 μm, c. 10-70% dispersion) and the combined effects of fragmentation, grain size and radiation damage (for eU between 5-150 ppm, c.10-107% dispersion). Additionally we show that if the spherical equivalent radius of a broken grain is used as a measure of the effective diffusion domain for thermal history inversions then this will likely lead to erroneous thermal histories being obtained in many cases. The viability of the new technique is demonstrated for a real data set of 25 single grain (U-Th)/He apatite ages obtained for a gabbro sample from the BK-1 (Bierkraal) borehole drilled through the Bushveld Complex in South Africa. The inversion produces a well constrained thermal history consistent with both the (U-Th)/He data and available fission track analysis data. The advantage of the new approach is that it can explicitly accommodate all the details of conventional schemes, such as the effects of temporally variable diffusivity, zonation of U and Th and arbitrary grain size variations, and it works equally effectively for whole or broken crystals, and for the most common situation where a mixture of both are analysed. For the routine application of the apatite (U-Th)/He thermochronometry technique with samples where whole apatite grains are rare our experiments indicate that 15-20 single grain analyses are typically required to characterise the age dispersion pattern of a sample. The experiments also suggest that picking very short crystal fragments as well as long fragments, or even deliberately breaking long crystals to maximise the age dispersion in some cases, would ensure the best constraints on the thermal history models. The inversion strategy described in this paper is likely also directly applicable to other thermochronometers, such as the apatite, rutile and titanite U-Pb systems, where the diffusion domain is approximated by the physical grain size

Time-dependent screening of a positive charge distribution in metals: Excitons on an ultra-short time scale

Experiments determining the lifetime of excited electrons in crystalline copper reveal states which cannot be interpreted as Bloch states [S. Ogawa {\it et al.}, Phys. Rev. B {\bf 55}, 10869 (1997)]. In this article we propose a model which explains these states as transient excitonic states in metals. The physical background of transient excitons is the finite time a system needs to react to an external perturbation, in other words, the time which is needed to build up a polarization cloud. This process can be probed with modern ultra-short laser pulses. We calculate the time-dependent density-response function within the jellium model and for real Cu. From this knowledge it is possible within linear response theory to calculate the time needed to screen a positive charge distribution and -- on top of this -- to determine excitonic binding energies. Our results lead to the interpretation of the experimentally detected states as transient excitonic states.Comment: 24 pages, 9 figures, to appear in Phys. Rev. B, Nov. 15, 2000, issue 2

Recent Progress in the Computational Many-Body Theory of Metal Surfaces

In this article we describe recent progress in the computational many-body theory of metal surfaces, and focus on current techniques beyond the local-density approximation of density-functional theory. We overview various applications to ground and excited states. We discuss the exchange-correlation hole, the surface energy, and the work function of jellium surfaces, as obtained within the random-phase approximation, a time-dependent density-functional approach, and quantum Monte Carlo methods. We also present a survey of recent quasiparticle calculations of unoccupied states at both jellium and real surfaces.Comment: 17 pages, 1 figure, to appear in Comput. Phys. Commu