Skewed Factor Models Using Selection Mechanisms

Traditional factor models explicitly or implicitly assume that the factors follow a multivariate normal distribution; that is, only moments up to order two are involved. However, it may happen in real data problems that the first two moments cannot explain the factors. Based on this motivation, here we devise three new skewed factor models, the skew-normal, the skew-t, and the generalized skew-normal factor models depending on a selection mechanism on the factors. The ECME algorithms are adopted to estimate related parameters for statistical inference. Monte Carlo simulations validate our new models and we demonstrate the need for skewed factor models using the classic open/closed book exam scores dataset

MFCS\u2798 Satellite Workshop on Cellular Automata

For the 1998 conference on Mathematical Foundations of Computer Science (MFCS\u2798) four papers on Cellular Automata were accepted as regular MFCS\u2798 contributions. Furthermore an MFCS\u2798 satellite workshop on Cellular Automata was organized with ten additional talks. The embedding of the workshop into the conference with its participants coming from a broad spectrum of fields of work lead to interesting discussions and a fruitful exchange of ideas. The contributions which had been accepted for MFCS\u2798 itself may be found in the conference proceedings, edited by L. Brim, J. Gruska and J. Zlatuska, Springer LNCS 1450. All other (invited and regular) papers of the workshop are contained in this technical report. (One paper, for which no postscript file of the full paper is available, is only included in the printed version of the report). Contents: F. Blanchard, E. Formenti, P. Kurka: Cellular automata in the Cantor, Besicovitch and Weyl Spaces K. Kobayashi: On Time Optimal Solutions of the Two-Dimensional Firing Squad Synchronization Problem L. Margara: Topological Mixing and Denseness of Periodic Orbits for Linear Cellular Automata over Z_m B. Martin: A Geometrical Hierarchy of Graph via Cellular Automata K. Morita, K. Imai: Number-Conserving Reversible Cellular Automata and Their Computation-Universality C. Nichitiu, E. Remila: Simulations of graph automata K. Svozil: Is the world a machine? H. Umeo: Cellular Algorithms with 1-bit Inter-Cell Communications F. Reischle, Th. Worsch: Simulations between alternating CA, alternating TM and circuit families K. Sutner: Computation Theory of Cellular Automat

Atomisers for the Aerial Application of Pesticides in Tsetse (Glossina sp) and Armyworm (Spodoptera exempta) Control

Aerial application of insecticides is likely to remain an important component in realistically-costed vector and migratory pest control operations for the foreseeable future. The objective of this work was to identify or design improved atomisers for use in two such operations, tsetse (Glossina sp. ) and African armyworm (Spodoptera exempta) control, the former requiring an insecticide aerosol ýx'ith a VMD of 20 to 30ýim at rates upto 0.5 litres/minute and the latter a fine spray with a VMD of 80 to 120ýtm at rates around 16 litres/minute. In both cases rotary atomisation was confirmed as the most appropriate technique. Assessments were made of seven commerciall%, available atomisers and two existinc, prototypes, on the basis of existing reports and new data generated under simulated flight conditions in a wind tunnel. Droplet sizing was carried out using an optical array probe set to give a resolution of 54m over a range of 3.6 -3) 12.54m. None of the atomisers tested met the specification for tsetse-spraying, the limiting factors being rotation speed and inability to distribute low volumes of liquid across their full atomising surface. The Micronair AU4000 and AU5000 and the Micron X-I were found to be suitable for armyworm control, the Micron X-1 having the additional ability to produce spray with VMDs down to 40ýim. A review of rotary atomiser literature provided design guidelines for the design of an atomiser capable of meeting tsetse specifications. The principle effect of liquid flow 4D within the atomiser was found to be on the uniformity of fluid distribution. Premature ligament formation and formation of cross-flow vortices were identified as factors which could adversely influence fluid distribution under some conditions. Ligzan ment seperation from disks can be aided byI slender teeth, providing that these have a spaciniz similar to the natural spacing of ligaments predicted by Taylor instability theoInry . The effect of rotation speed and atomiser diameter on droIp let diameter is determined by the degree of stretching of the ligament due to its acceleration relative to the atomiser, implying that a finer spray would be achieved using a smaller rotating diameter disc than a larger diameter disc with the same peripheral speed. A series of experimental studies was carried out usinrgD higZDh speed photogZ_r_a phy in conjunction with the droplet sizinaprobe. Disturbancesh a,,i,n, g the forrn predicted for C cross-flow vortices were observed in liquid on a plain spinning disc. A sin(-)'Ieligament generator was constructed. With increasing rotation speed this rt\'taled a series of increasingly unstable ligament disintegration modes in which interaction with the surroundin4g15 air became a controlling-- factor. Complete shattering of the ligament occured at a Weber number of between 4 and 5, similar to reported values for liquid jets in a cross flo%v of cyas. Droplet sizing indicated that the specified performance for tsetse operations could be obtained from 50mm diameter atomisers with a total of around _'30000is suing points at a rotation speed of 26000 RPNI. This Zý sucy(yestecdN l,i ndcr rather than disc-based atomisers. A slit was found to be impractical as a means of distributing liquid unifom-ily at high rotation speeds but distribution was sucýe: ssfully achieved using a porous flow resistor. Prototype wind- and electi-ically-driven atornisers were constructed using rotating porous cylinders fed internally by spray bars designed with the help of finite element methods. Ligament formation was found to occur from a film of liquid on the outer surface of the cylinder, the variation in spacing with feedrate and rotation speed suggesting Taylor instability to be the controlling factor. The prototype atomisers achieved a performance suitable for tsetse control operations. This was not enhanced by the provision of discrete issuing points

Neural avalanches at the edge-of-chaos?

Does the brain operate at criticality, to optimize neural computation? Literature uses different fingerprints of criticality in neural networks, leaving the relationship between them mostly unclear. Here, we compare two specific signatures of criticality, and ask whether they refer to observables at the same critical point, or to two differing phase transitions. Using a recurrent spiking neural network, we demonstrate that avalanche criticality does not necessarily lie at edge-of-chaos

Conformational Change and Topological Stability of Proteins

The conformation and topology of a protein changes when stabilizing forces are absent, but the mechanisms by which these changes occur remains elusive. This dissertation aims to broaden the understandings. On the conformational level, the M20 loop conformers of E. coli dihydrofolate reductase are interrogated to identify factors responsible for their stability as well as to determine how one conformer might change into another. Molecular dynamics is used to simulate the open, closed and occluded conformers (observed in X-ray crystal structures) under a series of different single ligand conditions. Analysis shows that all open conformers move to a similar new conformation. Free energy methods examine the stability of the new loop conformer relative to the others. External perturbation molecular dynamics simulations and normal mode analysis methods examine possible M20 loop pathways occurring either when one loop conformer is forced to change into another or when a ligand is pulled out of its binding site. On the topological level, conserved residue-residue interaction networks found among three different protein superfamilies (the all α-helix death domains, the α/β-plaits and the all β-sheet immunoglobulins), each of different secondary structure but sharing the Greek-Key topology, are assessed for any inherent stability they might contain relative to randomly selected interaction networks. This assessment is achieved by simulating one protein from each family at different temperatures, ranging from 300 to 600 K, and observing that adding thermal energy to the system causes the random interaction networks to fall apart more easily than the conserved networks. When considered together, the conformational and topological projects, although very different from each other, both demonstrate the same idea - that regardless of scale, instability causes change and vice versa. This dissertation is divided into five chapters: Introduction, Theoretical Background, M20 Loop Conformers of Dihydrofolate Reductase, Conserved Contact Networks of Greek-Key Proteins and Summary