Revisiting Vinti theory : generalized equinoctial elements and applications to spacecraft relative motion

Early phases of complex astrodynamics applications often require broad searches of large solution spaces. For these studies, mission complexity generally motivates the use of the coarsest dynamical models with analytical solutions because of the implied lightening of the computational load. In this context, two-body dynamics are typically employed in practice, but higher-fidelity models with analytical solutions exist, an attractive prospect for modern applications that may require or benefit from greater accuracy. Vinti theory, which prescribes one of the many alternative described models known as intermediaries, is revisited because it leads to a direct generalization of two-body dynamics, naturally incorporating the dominant effect of oblateness and optionally the top/bottom-heavy characteristic of a celestial body without recourse to perturbation methods. Prior to the innovations introduced in this dissertation, Vinti theory and associated solutions possessed many singularities in popular orbital regimes. The theory has received limited use. The goals of this dissertation are to assess Vinti theory's effectiveness in a modern application and remove its long-standing disincentives. These objectives inform the two main contributions, respectively: 1) Vinti theory is applied to the relative motion problem through the development of a state transition matrix (STM), enabled by improvements to the existing theory; 2) a new nonsingular element set is introduced. The relative motion application leverages Vinti's approximate analytical solution with J₃. An analytical relative motion model is derived and subsequently reformulated so that Vinti's solution is piecewise differentiable, developed alongside boosts in accuracy and removal of singularities in polar and nearly circular or equatorial orbits. Some of these singularities reside in the solution, others in the partials. Solving the problem in oblate spheroidal elements leads to large linear regions of validity. The new STM is compared with side-by-side simulations of a benchmark STM obtained from perturbation methods and is shown to offer improved accuracy over a broad design space. To defray the costs of software development, robust code is provided online. The second major thrust area is the introduction of a nonsingular element set that is at once novel and familiar. Vinti theory suffers from other well-known singularities, strictly artifacts of classical elements that are detrimental to many applications. To mitigate these singularities, the standard (spherical) equinoctial elements are chosen to inform in a natural way their generalization to a new nonsingular element set: the oblate spheroidal equinoctial orbital elements. The new elements are derived without J₃ and concise algorithms presented for common coordinate transformations. The transformations are valid away from the nearly rectilinear orbital regime and are exact except near the poles. When near the poles, the transformations match the accuracy of the approximate analytical solution. As a result, the singularity on the poles is completely eliminated for the first time. Analytical state propagation of the new elements in time for bounded orbits completes their formal introduction. Benefits of the new elements are identified. The dissertation is organized as follows. To convey Vinti theory's broader context, extensive background on intermediaries and related topics is provided in Chapter 1. General enhancements that grew out of the main efforts, including the removal of some singularities, are consolidated in Chapter 2 along with mathematical preliminaries. Relative motion is explored as the selected application in Chapter 3 and the major deficiencies of Vinti theory are removed in Chapter 4 with the introduction of the new element set. Analytical orbit propagation in the new set is developed in Chapter 5.Aerospace Engineerin

Contributory Role of Pre-task Planning in Improving Iranian EFL Learners’ Writing of Argumentative Essays: The Case of Accuracy and Complexity

Generally, Task-Based Language Teaching (TBLT) is an approach which places a high premium on the utilization of tasks as fundamental units of planning language instruction in L2 writing classroom. Accordingly, the present study sought to investigate the extent to which pre-task planning can influence the accuracy and complexity of the sentence structures in the argumentative essays written by male and female Iranian EFL learners with an intermediate proficiency level. As such, a Quick Oxford Proficiency Test (Q.O.P.T) was administered to a population of intermediate students learning English in a language institute in Isfahan. Based on their scores, two intermediate samples, 25 each, were randomly selected and labeled as control and experimental groups. While learners in the control group received writing instruction by a product based approach, the learners in the treatment sample were taught by a task based approach focusing on pre-task planning. At the end of the treatment, a full term, the analysis of the data obtained from the essays written by the participants revealed that pre-task planning improved the accuracy and complexity of the structures in the essays written by both male and female learners in the treatment group compared with those in the control group. Additionally, the results indicated that there was a meaningful interaction between pre-task planning and gender

A review on preventive measures and treatment of white spot lesions in patients with fixed orthodontic appliances

Objective: One complication of fixed orthodontic treatment in patients with poor oral hygiene is development of demineralized enamel lesions compromising esthetics. This study aimed to review preventive measures and treatment of white spot lesions (WSLs) in patients with fixed orthodontic appliances.Review of Literature: In this review study, PubMed and Google Scholar databases were searched for articles published during 1964-2013 using the keywords “white spot lesions”, “demineralization”, “mastic gum”, “casein phosphopeptide amorphous calcium phosphate or CPP-ACP”, “chitosan” and “orthodontics”; 96 articles were evaluated.Conclusion: White spot lesions can be prevented by conventional plaque control and adjunct measures such as the use of fluoride-containing compounds, chlorhexidine (CHX), xylitol gums, chitosan compounds and laser. Low-concentration fluoride, CPP-ACP compounds and laser help remineralize these lesions. If not treated, bleaching, microabrasion and tooth restoration are the final solutions

A Generic Assessment of Persian Translations of English Fairy Tales and Fairy Tales Written in Persian: From a Cultural Perspective

It is a commonly held belief that fairy tales as a major literary genre play a pivotal role in children's literature. Accordingly, the present study sought to investigate how the generic skeleton of fairy tales influences the quality of their translations into Persian for the children between 6 and 12 years old. To achieve this purpose, from among the English fairy tales translated into Persian, 15 works were selected based on a purposive sampling method. The contrastive analysis of the targeted texts written in both English and Persian revealed insightful facts about the interconnection between translators’ consideration of SL text generic sensitivities and the quality of translation. The findings revealed that there were no significant differences between English fairy tales and their corresponding Persian translations, in general. However, the results reflected particular cultural variations existing between SL and TL texts- that is, English fairy tales and fairy tales written in Persian. Notably, the results of the study may have important implications for both translation students and translation trainers

Figurative Language in the Immigration Debate: Comparing Early 20th Century and Current U.S. Debate with the Contemporary European Debate

This study analyzes newspaper coverage of immigration reform in mainstream newspapers prior to, and following the debate in June 2007. The newspaper text is analyzed using metaphor interpretation supported by content analysis. The quantitative result categorizes the identified metaphors in three distinct metaphor categories about: immigrants and immigration, immigration policy and enforcement, and metaphors about the debate and immigration issue itself. The relative distribution of metaphors among categories is provided. Using an open coding process, emergent metaphor categories are identified. The qualitative findings describe metaphors and schemas that were potentially activated by particular metaphorical phrases in this context. Lastly, this research compares the similarities and differences of the immigration debate of the early 20th century with the contemporary U.S. and European debate

Impact of Highlighting Techniques on the Retention of Unfamiliar Words in L2 Classrooms

Since L2 learners cannot learn the mass of words potentially available to them, it would be more useful to teach them specific strategies for dealing with unfamiliar words. One possible solution these days is to provide learners with useful guidance by which they can tackle the problem efficiently. However, the question is how much noticing in the input may result in acquisition and retrieval of information concerning unfamiliar words. Accordingly, the present essay sought to investigate the extent to different types of highlighting techniques can improve the retention of unfamiliar words by L2 learners. To this end, from the population of first graders studying at a boys and a girls high school a sample of 240 pre-intermediate students  (120 girls and 120 boys) were randomly selected based on their scores on an OPT test. The intended words for the experiment were selected through a pre-test containing vocabulary items which were unknown to the participants.  Using   these words, a reading text with three passages each containing 30 words unknown to the participants was given to the targeted participants. The new, unfamiliar words were highlighted for the experimental groups (by color for the first group, underlined for the second group and written in italics for the third group). Apparently, no highlighting techniques were used for the control groups. The Persian translations of the new words were also provided given at the end of the passage. To measure the acquisition of unfamiliar target words three types of tests; namely, recall, recognition, and comprehension tests were administered twice - one immediately after reading passages and the other two weeks later. The findings revealed that the retention of the words was significantly higher in experimental groups than that of the control groups. More specifically, the retention of the words was not only significantly higher in underlining group compared to other types of highlighting techniques but it also  was meaningfully higher in both immediate and delayed tests for  the experimental groups compared to those in the  control groups. Notably, the participants performed better in recognition  than the recall test and  the results did not show any interaction between retention of unfamiliar words and gender.

Comparison of Antimicrobial Effects of Stevia Rebaudiana Extract and Xylitol on Dental Biofilm: An In Vitro Study

Objectives This study aimed to assess the antibacterial effects of xylitol and Stevia rebaudiana (S. rebaudiana) ethanolic extract on oral biofilm. Methods A total of 96 acrylic discs were divided into two main groups for inoculation with Streptococcus mutans (S. mutans) and Streptococcus sobrinus (S. sobrinus). Each group consisted of 6 subgroups including a positive control subgroup and 5 subgroups of discs immersed in 1% or 3% xylitol solutions, 2 or 4 mg/mL S. rebaudiana, or a combination of 3% xylitol and 4 mg/mL S. rebaudiana. After incubation, the discs were rinsed and transferred to fluid universal medium. The solutions were cultured on specific culture media and incubated. The colony-forming units (CFUs) were counted for each disc. The structure of biofilm in each group was evaluated under a scanning electron microscope (SEM). Results ANOVA revealed significant differences between the subgroups in both S. mutans and S. sobrinus groups (P=0.03 and P=0.01, respectively). In S. mutans group, the logarithmic mean of colony count in the positive control subgroup was 6.75 while this value was significantly lower in 2 mg/mL (5.81) and 4mg/mL (5.92) S. rebaudiana subgroups using the post hoc Dunnett's test (P=0.01 and P=0.04, respectively). The three other subgroups did not show significant differences. In S. sobrinus group, all five experimental subgroups demonstrated significantly lower colony count than the positive control group (P<0.05).  Conclusion S. rebaudiana extract appears to be more potent than xylitol against dental biofilm

Decolonizing the “Universal” Human Rights Regime: Questioning American Exceptionalism and Orientalism

This article aims to decolonize the discourse of the Universal Declaration of Human Rights through the lens of Critical Muslim Studies, arguing that such systems of “international norms” are Eurocentric in character and hegemonic in practice. I argue that the promotion of a Western system of human rights as universal works through the two pillars of Orientalism and Eurocentrism, focusing particularly on the discourse of American exceptionalism as a distinct American form of Eurocentrism. Such a critique is a necessary first step for creating the grounds for alternative human rights orders, such as the notion of Islamic human rights. To be successful, any alternative Islamic system for alleviating human oppression and suffering should first dismantle the hegemonic grip of Orientalism and Eurocentrism on human rights