Autonomous optimal deorbit guidance

The objective of this dissertation is to solve an optimal deorbit guidance problem given initial orbit and vehicle parameters as inputs. Currently, the problem is computationally intensive to solve and approximate methods such as impulsive maneuvers are utilized. The problem is formulated as a fuel-optimal control problem that allows for a variety of terminal conditions at entry interface (EI). Using optimal control methods, the engine on time, engine off time as well as the direction of the thrust vector are solved for a variety of circular and elliptic initial orbits. Single and multiple burn maneuvers for both circular and elliptic orbits are explored. The J2 gravitational term is added as part of the solution process. The numerical solution is obtained using an analytical multiple shooting method. The results show promising potential of the proposed method and are comparable to NASA\u27s Shuttle results

Robust Controller for Constrained Relative Motion Maneuvering with Disturbance Rejection

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106488/1/AIAA2013-4721.pd

Price Volatility and Structural Breaks In U.S. Dairy Markets

This paper examines whether price volatility has increased for the all-milk price and milk margin over the past 25 years. It focuses on the impact of export and attempts to establish the existence of structural changes in the market. Various models are applied to analyze the stated question and results discussed. This paper finds that there was a distinct structural break in the milk price and possibly in the milk margin. Trade has limited correlation to volatility in the milk margin and milk price

Safe Positively Invariant Sets for Spacecraft Obstacle Avoidance

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140643/1/1.g000115.pd

From Business Model to Business Modelling: Modularity and Manipulation

The concept of modularity has gained considerable traction in technology studies as a way to conceive, describe and innovate complex systems, such as product design or organizational structures. In the recent literature, technological modularity has often been intertwined with business model innovation, and scholarship has started investigating how modularity in technology affects changes in business models, both at the cognitive and activity system levels. Yet we still lack a theoretical definition of what modularity is in the business model domain. Business model innovation also encompasses different possibilities of modeling businesses, which are not clearly understood nor classified. We ask when, how and if modularity theory can be extended to business models in order to enable effective and efficient modeling. We distinguish theoretically between modularity for technology and for business models, and investigate the key processes of modularization and manipulation. We introduce the basic operations of business modeling via modular operators adapted from the technological modularity domain, using iconic examples to develop an analogical reasoning between modularity in technology and in business models. Finally, we discuss opportunities for using modularity theory to foster the understanding of business models and modeling, and develop a challenging research agenda for future investigations

Using the Perceptual Experience Laboratory (PEL) to simulate tourism environments for hedonic wellbeing

Measuring the relationship between stress, mood and tourism in natural settings is problematic in terms of the ability to undertake detailed, systematic and accurate monitoring. This paper presents the results of a preliminary investigation into the use of an immersive simulated tourism environment to measure tourisms’ potential to alleviate physiological and psychological stress and enhance mood. The objectives of the study were to record and analyse participants’ heart-rate data before, during and after three experiences (workplace setting, TV-watching setting and simulated tourism setting) and to undertake completion of mood questionnaires before and after each of these three experiences, allowing comparative pre- and post-mood analysis. Qualitative data was also gathered from the participants about these three experiences, in particular the simulated tourism environment. The preliminary results demonstrate that PEL effectively creates a simulated tourism environment which can be used for measuring stress and mood as signifiers of hedonic wellbeing

Grid-texture mechanisms in human vision:contrast detection of regular sparse micro-patterns requires specialist templates

Previous work has shown that human vision performs spatial integration of luminance contrast energy, where signals are squared and summed (with internal noise) over area at detection threshold. We tested that model here in an experiment using arrays of micro-pattern textures that varied in overall stimulus area and sparseness of their target elements, where the contrast of each element was normalised for sensitivity across the visual field. We found a power-law improvement in performance with stimulus area, and a decrease in sensitivity with sparseness. While the contrast integrator model performed well when target elements constituted 50–100% of the target area (replicating previous results), observers outperformed the model when texture elements were sparser than this. This result required the inclusion of further templates in our model, selective for grids of various regular texture densities. By assuming a MAX operation across these noisy mechanisms the model also accounted for the increase in the slope of the psychometric function that occurred as texture density decreased. Thus, for the first time, mechanisms that are selective for texture density have been revealed at contrast detection threshold. We suggest that these mechanisms have a role to play in the perception of visual textures

What is the Definition of Cure in Non-small Cell Lung Cancer?

The concept of cure from cancer is important to patients, but can be difficult to communicate in terms that are meaningful. This is because there are a number of definitions of cure that are applied by clinicians, patients and the public, and by policymakers that have a different meaning and significance. In this article, we provide a narrative review of the evidence concerning cure in lung cancer and show how the different definitions may apply in different settings. A better understanding of the various concepts of cure will improve communication with patients on this important topic. This article is based on previously conducted studies and does not contain any new studies with human participants or animals performed by any of the authors

New insight into the relation between star formation activity and dust content in galaxies

(Abridged) We assemble a sample of 3258 low-redshift galaxies from the SDSS DR6 with complementary photometric observations by GALEX, 2MASS and IRAS at far-ultraviolet and infrared wavelengths. We use a recent, simple but physically motivated model to interpret the observed spectral energy distributions of the galaxies in this sample in terms of statistical constraints on physical parameters describing the star formation history and dust content. The focus on a subsample of 1658 galaxies with highest S/N observations enables us to investigate most clearly several strong correlations between various derived physical properties of galaxies. We find that the typical dust mass of a star-forming correlates remarkably well with the star formation rate (SFR). We also find that the dust-to-stellar mass ratio, the ratio of dust mass to star formation rate and the fraction of dust luminosity contributed by the diffuse interstellar medium all correlate strongly with specific SFR. A comparison with recent models of chemical and dust evolution of galaxies suggests that these correlations could arise, at least in part, from an evolutionary sequence. As galaxies form stars, their ISM becomes enriched in dust, while the drop in gas supply makes the specific SFR decrease. Interestingly, as a result, a young, actively star-forming galaxy with low dust-to-gas ratio may still be highly dusty because it contains large amounts of interstellar gas. This may be important for the interpretation of the infrared emission from young, gas-rich star-forming galaxies at high redshift. Our study provides a useful local reference for future statistical studies of the star formation and dust properties of galaxies at high redshifts.Comment: 15 pages, 10 figures, accepted for publication in MNRAS. Full-resolution figures available from http://users.physics.uoc.gr/~dacunha/paper_dacunha.pd