Computer image generation: Reconfigurability as a strategy in high fidelity space applications

The demand for realistic, high fidelity, computer image generation systems to support space simulation is well established. However, as the number and diversity of space applications increase, the complexity and cost of computer image generation systems also increase. One strategy used to harmonize cost with varied requirements is establishment of a reconfigurable image generation system that can be adapted rapidly and easily to meet new and changing requirements. The reconfigurability strategy through the life cycle of system conception, specification, design, implementation, operation, and support for high fidelity computer image generation systems are discussed. The discussion is limited to those issues directly associated with reconfigurability and adaptability of a specialized scene generation system in a multi-faceted space applications environment. Examples and insights gained through the recent development and installation of the Improved Multi-function Scene Generation System at Johnson Space Center, Systems Engineering Simulator are reviewed and compared with current simulator industry practices. The results are clear; the strategy of reconfigurability applied to space simulation requirements provides a viable path to supporting diverse applications with an adaptable computer image generation system

Traversing non-convex regions

This paper considers a method for dealing with non-convex objective functions in optimization problems. It uses the Hessian matrix and combines features of trust-region techniques and continuous steepest descent trajectory-following in order to construct an algorithm which performs curvilinear searches away from the starting point of each iteration. A prototype implementation yields promising resultsPeer reviewe

First-Order Stable Model Semantics with Intensional Functions

In classical logic, nonBoolean fluents, such as the location of an object, can be naturally described by functions. However, this is not the case in answer set programs, where the values of functions are pre-defined, and nonmonotonicity of the semantics is related to minimizing the extents of predicates but has nothing to do with functions. We extend the first-order stable model semantics by Ferraris, Lee, and Lifschitz to allow intensional functions -- functions that are specified by a logic program just like predicates are specified. We show that many known properties of the stable model semantics are naturally extended to this formalism and compare it with other related approaches to incorporating intensional functions. Furthermore, we use this extension as a basis for defining Answer Set Programming Modulo Theories (ASPMT), analogous to the way that Satisfiability Modulo Theories (SMT) is defined, allowing for SMT-like effective first-order reasoning in the context of ASP. Using SMT solving techniques involving functions, ASPMT can be applied to domains containing real numbers and alleviates the grounding problem. We show that other approaches to integrating ASP and CSP/SMT can be related to special cases of ASPMT in which functions are limited to non-intensional ones.Comment: 69 page

1 Online appendix for the paper On the Stable Model Semantics for Intensional Functions published in Theory and Practice of Logic Programming

We say that a formula F is in Clark normal form (relative to a list c of intensional constants) if it is a conjunction of sentences of the form ∀x(G → p(x)) (A1) and ∀xy(G → f(x)=y) one for each intensional predicate p and each intensional function f, where x is a list of distinct object variables, y is an object variable, and G is an arbitrary formula that has no free variables other than those in x and y. The completion of a formula F in Clark normal form (relative to c) is obtained from F by replacing each conjunctive term (A1) with and each conjunctive term (A2) with ∀x(p(x) ↔ G) ∀xy(f(x)=y ↔ G). An occurrence of a symbol or a subformula in a formula F is called strictly positive in F if that occurrence is not in the antecedent of any implication in F. The dependency graph of F (relative to c) is the directed graph that • has all members of c as its vertices, and • has an edge from c to d if, for some strictly positive occurrence of G → H in F, — c has a strictly positive occurrence in H, and — d has a strictly positive occurrence in G. We say that F is tight (on c) if the dependency graph of F (relative to c) is acyclic. The following theorem relates the Cabalar semantics to completion, which follows immediatel

Imide and isatin derivatives as β-lactam mimics of β-lactam antibiotics

Activated γ-lactams, which are derivatives of succinimide, phthalimide and isatin with suitable elements of molecular recognition, have been synthesised as mimics of the ß-lactam antibiotics and their chemical and biological reactivity determined

Soluble amyloid precursor protein: a novel proliferation factor of adult progenitor cells of ectodermal and mesodermal origin

Introduction: Soluble amyloid precursor protein a (sAPPa) is a proteolyte of APP cleavage by a-secretase. The significance of the cleavage and the physiological role of sAPPa are unknown. A crystal structure of a region of the amino terminal of sAPPa reveals a domain that is similar to cysteine-rich growth factors. While a previous study implicates sAPPa in the regulation of neural progenitor cell proliferation in the subventricular zone of adult mice, the ubiquitous expression of APP suggests that its role as a growth factor might be broader. Methods: sAPPa and a-secretase activities were determined in neural progenitor cells (NPCs), mesenchymal stem cells (MSC) and human decidua parietalis placenta stem cells (hdPSC). Inhibition of a-secretase was achieved by treatment with the matrixmetalloproteinase inhibitor GM6001, and proliferation was determined using clonogenic and immunocytochemical analysis of cell-lineage markers. Recovery of proliferation was achieved by supplementing GM6001-treated cells with recombinant soluble APPa. Expression of APP and its cellular localization in the subventricular zone was determined by Western blot and immunohistochemical analyses of APP wild type and knockout tissue. Alterations in pERK and pAKT expression as a function of soluble APPa production and activity in NPCs were determined by Western blot analysis. Results: Here we show that sAPPa is a proliferation factor of adult NPCs, MSCs and hdpPSC. Inhibition of asecretase activity reduces proliferation of these stem cell populations in a dose-dependent manner. Stem cell proliferation can be recovered by the addition of sAPPa in a dose-dependent manner, but not of media depleted of sAPPa. Importantly, sAPPa operates independently of the prominent proliferation factors epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), but in association with ERK signaling and MAP-kinase signaling pathways. Levels of sAPPa and putative a-secretase, ADAM10, are particularly high in the subventricular zone of adult mice, suggesting a role for sAPPa in regulation of NPCs in this microenvironment. Conclusions: These results determine a physiological function for sAPPa and identify a new proliferation factor of progenitor cells of ectodermal and mesodermal origin. Further, our studies elucidate a potential pathway for sAPPa signaling through MAP kinase activation

Trauma care in Sub-Saharan Africa: challenges and opportunities in Botswana and Tanzania for implementing Afrocentric systems.

Doctoral Degree. University of KwaZulu-Natal, Durban.Summary available in PDF

Development of top-down mass spectrometry methods for the characterization of nucleic acids

This dissertation is focused on the development of top-down mass spectrometry methods for characterization of proteins and nucleic acids, including investigations into tandem mass spectrometry (MS/MS) activation methods, implementation of an on-line desalting workflow, and application of custom-built fragment ion identification software. Each section of this dissertation employs software developed for the identification of fragment ions produced by MS/MS activation based on their observed isotopic distributions in the m/z domain. The fragment ions generated by MS/MS of protein ions depends heavily on the activation method used and the primary structure of the molecule. Fragmentation induced by ultraviolet photodissociation (UVPD) often exhibits little dependence on the primary structure of the protein compared to collision activated dissociation (CAD), however, dissociation induced by lasers of different wavelengths exhibit nuanced differences in their fragmentation propensities. A comparative study of UVPD employing a 193 nm excimer laser and a 213 nm solid-state laser was undertaken, revealing that 213 nm UVPD exhibited a higher degree of preferential cleavage N-terminal to proline residues in various model proteins. Top-down mass spectrometry was also developed for analysis of nucleic acids, with a focus on examination of covalent modifications introduced either synthetically or in a biological context. Methods for top-down mass spectrometry analysis of nucleic acids tend to be less advanced than those for proteins. To progress this area, a nanoflow on-line desalting strategy was developed alongside optimization of MS/MS parameters, and development of an automated fragment ion identification approach. Utilizing a high-performance liquid chromatography approach incorporating basic mobile phases, nucleic acids up to 100 nt (30 kDa) were effectively desalted in a high-throughput manner with low sample usage, enabling MS/MS experiments. MS/MS using UVPD and CAD was applied to a purified yeast phenylalanine tRNA, where thorough characterization of multiple isoforms was achieved after fragment identification with a custom software approach named NucleoSAFARI. This technique was extended to a highly heterogeneous tRNA extract, where a gas-phase fractionation approach was employed to isolate small (2 m/z) regions across the m/z domain and identify charge-reduced precursor ions produced by UVPD. Subsequent identification of fragment ions in CAD spectra of the same 2 m/z region was informed by the precursors identified by UVPD, resulting in identification and analysis of several tRNAs heretofore never examined by top-down mass spectrometry.Chemistr