Markov chain Monte Carlo methods are known for their effectiveness with a multitude of complex mathematical problems, including those in mixed spaces of continuous and discrete components. In this ...dissertation, we examine variations of complicated scheduling problems involving allocating spacecraft communication time on a fixed number of antenna resources located at several physical locations around the world. The antennas at these locations are used to communicate with various spacecraft sent to collect science data at many different destinations and orbits in the Solar System. Each scheduled tracking interval must satisfy several constraints enforcing various properties, and the amount of antenna resources is very scarce compared to how frequently these antennas have to be used for communicating with the spacecraft in competitive time intervals. In these scheduling problems, the scheduled tracking interval start and end times are continuous variables, while the index information for selecting antenna options are discrete variables. It is usually very hard to find a particular solver that can handle these mixed-integer models without spending lots of effort in fitting the constraints to the standard forms the solver can handle. We aim to find modern techniques that can be well adapted to solve our mixed-integer scheduling problems and perform very well. In particular, we want to focus on using the general probabilistic technique called simulated annealing, with constraints. The required Markov chain Monte Carlo sampler will be designed to use a random sampling method called the Gibbs sampling algorithm, which can be generalized to incorporate constraints. The complete system of problem modeling and its stochastic optimization will be demonstrated in some test problems.
A novel regio- and stereoselective Rh(CO)2Cl2-catalyzed allylic alkylation of unsymmetrical allylic carbonates was discovered. The regioselectivity of the reaction favors product ratios in which ...substitution occurs at the carbon bearing the leaving group. When an enantiomerically enriched carbonate (≥99% ee) was examined, the Rh(I)-catalyzed allylic alkylation proceeded stereoselectively to provide the alkylation product with retention of absolute stereochemistry (98% ee). To establish the scope of the Rh(CO)2Cl2-catalyzed allylic alkylation, a variety of carbon and heteroatom nucleophiles were examined and the results described. As an application of the Rh(I)-catalyzed allylic alkylation, a series of novel domino reactions have been developed that couple the unique regio- and stereoselective Rh(CO)2Cl2-catalyzed alkylation of allylic trifluoroacetates with an intramolecular Pauson−Khand annulation, a cycloisomerization, or a 5+2 cycloaddition. A unique aspect of the method described is the use of a single catalyst to effect sequential transformations in which the catalytic activity is moderated simply by controlling the reaction temperature. Implementation of such processes provides a rapid and efficient entry to a variety of bicyclic carbon skeletons from simple precursors.
A novel regio- and stereoselective Rh(CO)2Cl2-catalyzed allylic alkylation of unsymmetrical allylic carbonates was discovered. The regioselectivity of the reaction favors product ratios in which ...substitution occurs at the carbon bearing the leaving group. When an enantiomerically enriched carbonate (> or = 99% ee) was examined, the Rh(I)-catalyzed allylic alkylation proceeded stereoselectively to provide the alkylation product with retention of absolute stereochemistry (98% ee). To establish the scope of the Rh(CO)2Cl2-catalyzed allylic alkylation, a variety of carbon and heteroatom nucleophiles were examined and the results described. As an application of the Rh(I)-catalyzed allylic alkylation, a series of novel domino reactions have been developed that couple the unique regio- and stereoselective Rh(CO)2Cl2-catalyzed alkylation of allylic trifluoroacetates with an intramolecular Pauson-Khand annulation, a cycloisomerization, or a 5+2 cycloaddition. A unique aspect of the method described is the use of a single catalyst to effect sequential transformations in which the catalytic activity is moderated simply by controlling the reaction temperature. Implementation of such processes provides a rapid and efficient entry to a variety of bicyclic carbon skeletons from simple precursors.
Three novel domino reaction processes have been discovered and developed that employ the regioselective and stereoselective Rh(CO)2Cl2-catalyzed alkylations of allylic trifluoroacetates with ...α-substituted sodiomalonates followed by an intramolecular Pauson−Khand annulation, a 5 + 2 cycloaddition, or a cycloisomerization. A unique aspect of the methodology is that a single catalyst is used to effect sequential transformations simply by increasing the temperature for the second reaction.
An efficient and highly enantioselective total syntheses of MS-153 and manzacidin C are described. Synthetic efforts have led to the development of silicon Lewis acid promoted 3+2 cycloadditions of ...acylhydrazones with methallyl ethers along with the development of a new silane reagent. MS-153 was synthesized in three steps from the acetylaldehyde derived hydrazone in 70% overall yield and in ≥98% ee. A rapid and highly stereoselective synthesis of manzacidin C was achieved from an isopropyl glyoxylate derived N-acyl hydrazone in six steps, 94% ee, >15:1 dr, and 26% overall yield. An unexpected stereochemical switch was observed in the key silver triflate mediated cycloaddition leading to the hypothesis of a chiral hexacoordinate silicon transition state. This new avenue of reactivity led to the development of an enantioselective Friedel-Crafts cycloadditions of 2-pyridylbenzoylhydrazones. Absolute stereochemical proof of the substrates led to an adjustment in our stereochemical model of hexacoordinate silicon intermediates involving 2-pyridine as the Lewis basic binder.
Deciding which stocks to purchase and how to optimally allocate the total investment among them is a nontrivial task for every investor. In this article, we propose two adaptive techniques that would ...provide an optimal allocation maximizing the return over the investment period. The first approach is the adaptive power method (PM) which is a modification of the proper orthogonal decomposition method. The adaptive PM uses only the currently available information to compute the optimal allocations, yet its long-term solution approaches the dominant eigen solution, even though that solution would require having a priori knowledge of all stocks’ performance. The second approach is derived from the well-known Least Mean Square (LMS) method, where the optimal allocation can be computed by adaptively steering the overall return toward a desired value. The experimental results have indicated promising gains even when the general market trend is downward.
NASA's future scientific missions will place new demands on its deep space network (DSN). Depending on which missions fly and their particular design, NASA's communications ground assets (antennas) ...may require upgrade or enhancement. The purpose of the mission set analysis tool is to help forecast future demand by (1) cataloguing the characteristics of potential future DSN-user missions consistent with NASA's space communications mission model, (2) calculating the demands that these missions will place on the DSN, and (3) generating mission requirements for other DSN architectural analysis tools. This tool takes the information associated with the Space Communications Mission Model (SCMM) to the next level - using an Microsoft EXCEL reg -based database to catalog and process some 300 mission parameters. These parameters fall into one of five broad categories: mission identity and affiliation, operational schedule, communication system capabilities, data rates and ground tracking schedules. Because NASA's mission forecast changes frequently, analysis templates are used to select sets of missions from the database for analysis. Communication link budgets are calculated for particular dates during mission operation based on mission parameters and automated ephemeris algorithms. The result is expressed in terms of the receiving area on the ground required to close each particular communication link. Plots of this receiving area as a function of time and frequency band reveal future demand for different mission sets. The most demanding individual communication links are automatically identified. Radio-frequency (RF) uplinks (Earth to mission) and downlinks (mission to Earth) are treated separately. The Mission Set Analysis Tool also creates mission requirements used by other analysis tools to assess the cost, operability (link performance), and load capacity of proposed DSN architectures.
Brown fat is specialized for energy expenditure and has therefore been proposed to function as a defense against obesity. Despite recent advances in delineating the transcriptional regulation of ...brown adipocyte differentiation, cellular lineage specification and developmental cues specifying brown-fat cell fate remain poorly understood. In this study, we identify and isolate a subpopulation of adipogenic progenitors (Sca-1⁺/CD45⁻/Mac1⁻; referred to as Sca-1⁺ progenitor cells, ScaPCs) residing in murine brown fat, white fat, and skeletal muscle. ScaPCs derived from different tissues possess unique molecular expression signatures and adipogenic capacities. Importantly, although the ScaPCs from interscapular brown adipose tissue (BAT) are constitutively committed brown-fat progenitors, Sca-1⁺ cells from skeletal muscle and subcutaneous white fat are highly inducible to differentiate into brown-like adipocytes upon stimulation with bone morphogenetic protein 7 (BMP7). Consistent with these findings, human preadipocytes isolated from subcutaneous white fat also exhibit the greatest inducible capacity to become brown adipocytes compared with cells isolated from mesenteric or omental white fat. When muscle-resident ScaPCs are re-engrafted into skeletal muscle of syngeneic mice, BMP7-treated ScaPCs efficiently develop into adipose tissue with brown fat-specific characteristics. Importantly, ScaPCs from obesity-resistant mice exhibit markedly higher thermogenic capacity compared with cells isolated from obesity-prone mice. These data establish the molecular characteristics of tissue-resident adipose progenitors and demonstrate a dynamic interplay between these progenitors and inductive signals that act in concert to specify brown adipocyte development.
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