Robust Adaptive Terrain-Relative Navigation

Dektor, Shandor ProQuest Dissertations & Theses Stanford Universit 2015 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Terrain-Relative Navigation (TRN) is an emerging technique for localization in natural environments. TRN augments a dead-reckoned solution with position fixes based on correlations with pre-stored maps. TRN is a particularly valuable tool for enabling missions for robots in regions without GPS, a category that includes the underwater environment as well as missions on other bodies in the solar system. The algorithms underlying TRN, however, have known issues with overconfidence in uninformative (e.g. flat) terrain. Overconfident estimates, also known as false peaks, are a significant problem as they can result in dangerous trajectories and mission failure. Making TRN robust to uninformative terrain is the focus of the work presented in this thesis.The interplay between map error, terrain correlation, and TRN filter overconfidence is the first focus of this thesis. TRN correlation techniques are shown to include, either implicitly or explicitly, a probabilistic model of terrain correlation, and that the most common method of TRN weighting implicitly models the terrain as uncorrelated. The degree of auto-correlation present in the terrain is related to the amount of variation in the terrain: greater variation in terrain height corresponds to lower correlation in the terrain and vice-versa. The uncorrelated terrain assumption is then demonstrated to be a source of false peaks. In informative terrain, where the variation in the terrain is large with respect to error in the map, the standard calculation produces reasonable results: peaks at the correct location. In uninformative terrain, when the variation in the terrain is small with respect to map error, standard correlation breaks down and is shown to produce overconfidence in the filter.Techniques are then developed for mitigating false peaks in uninformative terrain. The first technique developed in this thesis focuses on explicitly accounting for terrain correlation by using correlated Gaussian terrain models; while these methods have success in simulation, the computational cost of explicitly modeling terrain correlation makes them impractical for field applications. An alternate approach, exponentially down-weighting the standard weighting to account for the impact of the uncorrelated terrain assumption, is then proposed as a computationally tractable means of accounting for unmodeled terrain correlation.The exponential down-weighting technique is termed the adaptive TRN filter. It follows on work from the statistics community designed to improve the robustness of probabilities computed using incorrect models, and achieves this robustness by matching a bound on the likelihood of false peaks. The "robust adjusted likelihood'' approach is adapted to the TRN likelihood function and used to develop the relation between terrain correlation and the necessary degree of down-weighting. The adaptive technique is further developed for field work using real-time TRN filters.The adaptive TRN filter is validated using two platforms: an Autonomous Underwater Vehicle (AUV) and an ATRV-Jr ground rover. The AUV TRN filter is developed for an AUV correlating with range measurements of the terrain. The ground rover filter is developed for operations on the Moon or Mars, where direct measurements of altitude are unavailable, and the TRN filter must therefore correlate on gradient. As most maps are elevation based and must be differentiated to produce a gradient map, the map noise is increased and makes accounting for map error critical in this case.The effectiveness of the adaptive TRN filter is demonstrated using field data from MBARI AUV runs over flat terrain in Monterey Bay, and on ATRV-Jr field data taken at the Stanford campus. Both cases demonstrate meter-level performance when operating in informative terrain, and effective mitigation of false convergence over uninformative terrain when compared to filter performance using the unadjusted weighting.

Negotiating Equality at Home: A Historical Study of Informal Intimate Relationships in 20th Century Colombia

Castrellon Perez, Mariana ProQuest Dissertations & Theses Stanford Universit 2022 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This dissertation’s main goal is to unearth the history of the legal changes that granted property rights protections to concubine women living in out-of-wedlock families in 20th century Colombia. Departing from 1886, when the country became a centralized nation, this dissertation traces concubine women’s legal battles for their property rights up until 1990 when three congresswomen successfully enacted Law 54 of 1990, through which a de facto community property regime was created for informal intimate partners. With Law 54’s legal framework, concubine women’s position in the home was radically altered by the right to legally own half of the property simply by virtue of cohabitation.Through the study of court cases, oral history interviews, newspapers, and legislative initiatives, I discover the agents of change, detail their strategies, and elucidate their losses and victories. I found that the absence of family law regulations deepened structural conditions of gender inequality in out-of-wedlock families, as control over property and economic means in informal relationships fell decidedly on men’s side. Facing a total absence of Family Law protections, concubine women turned to the civil and labor courts to fight for their property. Therefore, the study of concubine women’s fights reveals how these women attempted to alter the gendered order inside the family, rejecting the role of dependent and unpaid laborer.This dissertation sits at the intersection of legal history, family law, and feminist studies, and contributes to these distinct scholarly fields. First, I shed light on the urgency of studying the relationship between property and gender in informal intimate relationships as a separate study of the role of property within marriage. I find that there are significant differences between married and unmarried women and their access to property rights, especially for concubine women who were poor, uneducated, and lived in rural areas.Second, I propose to add a level of complexity to the feminist critique of marriage. What I find with this research is that marriage is a double-edge sword as both an engine of women’s oppression and a guarantor of certain property rights for women who enter it. Third, I propose a revision of the role of the Colombian feminist movement and its involvement with changes to Family Law. Recent scholarship has shown the important role that the feminist movement played in supporting and advocating changes to Family Law during the 20th century. With this dissertation I show how the feminist movement was absent from the fight to enact Law 54 of 1990; the congresswomen who achieved this momentous legal change were alone in their effort.

Investing In Socialist Poland: A Transnational History of Finance In the Cold War, 1944-1991

Dovern, Lukas ProQuest Dissertations & Theses Stanford Universit 2019 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This dissertation explores socialist Poland's ties to international financial institutions during the Cold War era. Revealing the extent to which individuals and institutions cooperated across the Iron Curtain, it challenges the idea of a bipolar world order as an all-encompassing description of international relations in the second half of the twentieth century. Studying socialist Poland solely within the framework of Soviet politics and the bipolarity of the Cold War omits a crucial part of its international history; the country's development followed worldwide patterns of globalization, not just the rhythm of superpower politics. This dissertation argues that the end of communist rule in Eastern Europe cannot be understood without considering the region's integration into global financial markets.While the topic of international finance falls into the realm of the economic, this dissertation’s approach is decidedly historical. It relies on material from archives in the United States, Germany, Poland, and Russia to offer an empirically grounded behind-thescenes look at the workings of global finance and its effects on international politics. The narrative focusses on negotiations of loans and the designs of international financial institutions, giving ample space to the little-known economists, technocrats, and bankers who crafted international financial agreements of great consequence. It makes visible the power structures embedded in these agreements and the specific relationships between debtors and creditors that they produced. Rather than a highly stylized depiction of past economic life relying on theoretic models, it offers a description of how Poland’s socialist system operated in practice, how it changed over time, how it interacted with the larger world, and how it differed from socialism in other places. In the realm of international monetary relations, for example, Polish officials often disagreed with their Soviet counterparts. This dissertation, then, highlights differences within the socialist world, showing that the Soviet sphere of influence was by no means a single monolithic bloc.

Evaluating Diagnostics Under Dependency

Michael, Haben ProQuest Dissertations & Theses Stanford Universit 2017 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This thesis contains two independent parts. Only the first part relates to the title of the thesis.• The first part considers generalizations of the Receiver Operating Characteristic (ROC) curve and derived statistics to accommodate cohort data. In this setting, data is collected on a number of patients at a sequence of time points. This part of the thesis is based on an article co-written with Lu Tian and Musie Ghebremichael.Though estimation and inference procedures for the receiver operator characteristic (”ROC”) curve are well studied in the cross-sectional setting, there is less research when both biomarker measurements and disease statuses are observed longitudinally. In a motivating example, we are interested in characterizing the value of longitudinally measured CD4 counts for predicting the presence or absence of a transient spike in HIV viral load, also time-dependent. The most common existing method neither appropriately characterizes the diagnostic value of observed CD4 counts nor efficiently uses status history in predicting current spike status. We propose parametric and nonparametric procedures to estimate the ROC in the longitudinal setting. Extensive simulations have been conducted to examine the small sample operational characteristics of the proposed methods.• The second part proposes a method of performing inference on meta-analyses based on very few primary studies. This part of the thesis is based on an article co-written with Lu Tian. This part describes an exact, unconditional, non-randomized procedure for producing confidence intervals for the grand mean in a random effects meta-analysis. The procedure targets meta-analyses based on too few primary studies, ≤ 7, say, to allow for the conventional asymptotic estimators, e.g., DerSimonian and Laird (1986), or non-parametric resampling-based procedures, e.g., Liu and others (2017). Meta-analyses with such few studies are common, with one recent sample of 22453 heath-related metaanalsyes finding a median of 3 primary studies per meta-analysis (Davey and others, 2011). There is therefore a need for reliable and efficient procedures to address this setting.

Same Same (But Different): Accidental Feminism and Unintended Parity in India's Professional Firms

Ballakrishnen, Swethaa S ProQuest Dissertations & Theses Stanford Universit 2015 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This dissertation explores one set of recent changes in the structure of global gender inequality by studying the case of Indian professional women who have been at the forefront of unprecedented career success. While India as a country has been rife with less than optimal gender updates, women in a little known enclave of recently established corporate law firms seem to have leveraged a sweet spot within this grander mosaic of inequality. For women attorneys in these elite firms, gender doesn't relay traditional workplace disadvantages: they are promoted at the same rate as men, paid the same salaries and become partners at roughly the same rate. This is not just at odds with the broader literature on women in the workforce but also empirically peculiar for the Indian context.To unpack the various mechanisms and structural conditions that result in this positive – but unusual – empirical context, my project employs an embedded, multi-case study drawing on fieldwork between 2011-2014 and the analysis of over 135 in-depth interviews with elite law, banking and consulting professionals in Mumbai, India. In the recent decades following international market liberalization in 1991, Indian professional service firms have had to contend with new kinds of work, environments and management. One key change brought about by this exposure to foreign markets and investment has been the exposure to new kinds of global actors and audiences and the growing commitment to global norms of meritocracy. Leveraging the value of this comparative contrast, I highlight the ways in which the same exposure has had very different kinds of gender outcomes in different kinds of firms and unpack the structural mechanisms that engender this variance in internal stratification.Gender equality and parity are often thought of as the hard-earned rewards of long and agentic social movements. Here, I unpack a scenario in which a set of firms backed into a position of producing parity. Specifically, over the course of this dissertation, I unpack four specific structural conditions that play off each other to create this surprising result – Frames, Firms, Facings and Families. I argue from the perspective of each of these factors that the creation of egalitarian outcomes is not intentional, but, instead, accidental and at the cost of other existing inequalities.In the first empirical chapter "Frames" (Ch. 3), I focus on the framework of an ideal worker (Acker: 1990) and the advantage of new institutions to challenge and reorganize these expectations. I argue that as new firms doing new work, elite law firms are advantaged in being able to escape strong background frameworks (Ridgeway: 2012). But as firms recruiting from a new neo-liberal workforce that is committed to meritocracy, women in these firms are doubly advantaged to sidestep steep gendered assumptions. I show how meritocracy (and education as a new arbiter of such "merit") has, without especial intention, offered a new window of gender blind opportunity to a select set of professional women.In the second empirical chapter "Firms" (Ch. 4), I set up how as domestic firms struggling to be legitimate in a global market for legal services, Indian law firms are structurally positioned in ways that advantages their female professionals. By assuming global firms to be deeply committed to meritocracy but at the same time not being tied to them in any substantive way, elite law firms mimic imagined and idealized scripts to be more "global". In doing so, their commitment to inclusion and meritocracy is used both as a tool to differentiate themselves in a market ripe with traditional assumptions about gender; as well as a way of signaling like-mindedness with their global peers. Unlike other neoliberal professional service firms are products of domestic emergence and management, I show how this domestic emergence then sets up a kind of speculative isomorphism that advantages women within these elite legal firms.In the third empirical chapter "Facings" (Ch. 5), I argue that although supportive peer interactions are necessary to create an environment of parity, women in elite law firms are also especially backed by an important external audience that do not activity discriminate on the basis of gender – their clients. As firms that retained recurring international clients, these firms exposed their lawyers to a selection of sophisticated clients who were both unlikely to prime disadvantageous gendered expectations in interactions. What was more, the nature of the work valorizes positively otherwise "feminine" qualities like attention to detail and soft negotiation skills. Together, this set up of being domestically managed but international-client facing, makes women in elite law firms leverage advantages that women in other kinds of firms (that were internationally managed but domestic-client facing) don't enjoy. In the final empirical chapter "Families" (Ch. 6), I trace the role of families and temporality in determining this unlikely gender outcome in these elite law firms. I show that, as one would expect, the origin families that most professionals come from is deeply homogenous (middle class, high caste, urban) but that similar class and caste advantages did not transfer gender-blind outcomes in other professional careers. I show how the temporality of the elite law firm careers were specifically crucial to enabling parity for law firm women in India. In doing so, I highlight two more structural features that engender this accidental parity – a ready, caste dependent labor force that supplies housework support and childcare and a penultimate generation of close female family members who are not in the workforce and available to provide free and ready household support.Together, the convergence of these four structural conditions have come together to produce gender parity in ways that other, more targeted endeavors have failed to produce. The overarching finding in this dissertation is that gender egalitarian outcomes can be created and supported without intention and that these forms of unintended parity are often buttressed by other inequalities and mechanisms of stratification. In my final chapter (Ch. 7), I consider the futures of these accidental mechanisms to sustain the parity outcomes they have managed to create in these small enclaves – what do the futures of these institutions look like? I explore whether this is a short-term advantage for one particular cohort of women who are at the receiving end of structural, accidental advantages – or if these patterns in early institutional emergence can be capitalized on to build sustainable and egalitarian organizations.The unlikely case of the elite Indian law firm shows us how gender egalitarian change is not just accidental or unintended, but also that it can flow out of a conjuncture of seemingly minor and inconsequential institutional characteristics. Paying attention to this butterfly effect that transcends the sum of its narrow-gauge parts is at the root of this dissertation.

The Malarial Landscapes of Roman Central Italy: An Archaeological Study of Disease Exposure

Pickel, David Gerald ProQuest Dissertations & Theses Stanford Universit 2021 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This dissertation presents a study of malaria's ancient epidemiology in Roman central Italy. While current evidence indicates that malaria was present in Italy during the Roman period, little work has been done regarding malaria's impact on and interaction with Romans and Roman society overall.This is largely due to the presumed inability of this evidence to specify where and to what degree the disease was present in antiquity. In this dissertation I address this evidentiary constraint by reconceptualizing the focus of research, considering both the context of the disease and the disease as context. To do this, I combine spatial epidemiological theories and methods with close analysis of paleo-environmental data, ancient texts, and material remains to learn how the environment, human practices, and artifacts bounded malaria's distribution, affected its prevalence, and ultimately exposed people in the past to this disease. In this way, I build a model of ancient malaria transmission risk, with major emphasis placed on the unfolding entanglement between malaria and Roman villa estates between 200 BCE and 500 CE.In Chapter One, all current evidence for malaria in the ancient Roman world is categorized according to the ability of each to support a malaria identification. Chapter Two outlines this dissertation's theoretical framework and method, central to which is the idea that landscapes of disease and disease exposures therein are the emergent outcome of the interdependent activity between the social world of humans and the material world of living and non-living things. In Chapter Three, GIS software is used to create suitability maps of relative malaria transmission risk in Roman central Italy. These maps reflect temperature's effect on the development and activity of mosquitoes and malaria parasites. In Chapter Four, the risk maps created in the previous chapter are juxtaposed with a geodatabase of 501 central Italian villa estates datable between 200 BCE and 500 CE. This juxtaposition discloses a tension that has not been satisfactorily considered in studies of Roman central Italy: growth and activity despite malaria's concurrent presence and naturally high risk of transmission. This tension is reconciled in the final two chapters. Chapter Five explores the potential for villa estate agricultural practices to effectively control malaria transmission. Chapter Six explores how the artifacts of those practices impacted their effectiveness in terms of malaria control, as well as the ways in which these artifacts themselves promoted malaria exposure as they fell into disrepair and dilapidated.This dissertation reveals that the Romans, although unaware of malaria's etiology, very likely incidentally reduced the risk of its transmission by embracing intensive farming practices, attentive local reclamation, and the employment of artifacts that curtailed substantive contact between susceptible human hosts and infected mosquito vectors. At the same time, this dissertation indicates that malaria's entrenchment within Italy, lasting until its elimination in the middle 20th century, was in part a consequence of the breakdown of those very same artifacts and practices that, for a time, curtailed its transmission.

Oddball Realizations of "Geometry = Entanglement"

Sorce, Jonathan Robert ProQuest Dissertations & Theses Stanford Universit 2022 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

The four chapters of this thesis consist of three published papers to which I contributed. as well as a draft of a theorem & proof that I will be contributing to a forthcoming paper. The four subjects presented here all have, as their ur-ancestor, Mark Van Raamsdonk's observation that in holographic theories of quantum gravity, entanglement in the boundary state seems to be a prerequisite for connected geometry in the bulk state [1]. The common goal of the four chapters of this thesis is to sniff out concrete, specific, and weird realizations of this principle.The first chapter is adapted from [2]. co-authored with Ning Bao. Geoff Penington. and Aron Wall. The starting point of that paper was the observation that the large- N-extensivity of holographic Renyi entropies implies, via a saddle point calculation, that bipartite entanglement in classical holographic states is highly compressible, with the rate of compression for a given state controlled by geometric objects in that state's bulk dual. This was used to show that there exist accurate tensor-network representations of genuine holographic states that reflect coarse features of those states' bulk geometries. We also gave a prescription for how more detailed geometric features could be captured by tensor network constructions if one accepts the entanglement of purification conjecture [3, 4] and some natural generalizations.The main idea behind the compressibility proof came from Geoff Penington, based on conversations with our advisor Patrick Hayden. The idea that one could apply the entanglement of purification conjecture to construct detailed tensor network representations of holographic states came from Ning Bao and Aron Wall. The observation that a tensor network representing intersecting extremal surfaces cannot have isometric nodes (see section 7.3 of that paper) came from Aron Wall. This was the first project I undertook as a grad student, and my role was primarily to simplify/improve calculations and exposition. I also contributed significantly to the details of the prescription for iterating the entanglement of purification conjecture to produce tensor networks with local geometric structure. Most of the actual text of the paper was written by me, as were all of the figures.The second chapter is adapted from [5], co-authored with Alex May and Geoff Penington. The purpose of the paper is to prove the connected wedge theorem, which shows that a certain simple causal structure in a semiclassical asymptotically AdS3 bulk - a "2+2 scattering region" must be supported by extensive-in-N mutual information between corresponding regions in its boundary state. This theorem was conjectured by Alex May in his previous paper [6] using quantum information reasoning. Our paper improved the quantum information reasoning and provided a proof for classical spacetimes using the HRRT formula [7], the maximin prescription [8], and the focusing theorem. A proof for semiclassical spacetimes would follow immediately from the quantum extremal surface formula [9], quantum maximin [10], and the quantum focusing conjecture [11].The improved quantum information argument presented in that paper is largely due to Alex May, with input from Geoff Penington. The idea that the connected wedge theorem could be proved by some combination of the maximin prescription and the focusing theorem came from Geoff Penington. The actual machinery of the proof- the precise application of the focusing theorem and the construction of the "null membrane" came primarily from me.

Macro-Adaptive Algorithms

Wong, Hoi ProQuest Dissertations & Theses Stanford Universit 2015 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Traditionally, new adaptive algorithms were developed `microscopically' by changing the internal structure of LMS, Recursive Least Squares (RLS) and their variants, such as update equations and optimization criteria. This research attempts to reignite the interest in improving adaptive algorithms by considering a different question: by treating any known adaptive algorithm as a black-box learning agent, what can we do to leverage these little learner(s) to form a more intelligent adaptive algorithm? A framework is developed in this thesis to guide the design process, in which algorithms created from the framework are only allowed to manipulate these little black-boxes without hacking into their inner workings. Since it is a block-level (macroscopic) design strategy, the framework is called `Macro-Adaptive Framework' (MAF) and algorithms developed from the framework are called `Macro-Adaptive Algorithms' (MAA), hence the name of the thesis. In this thesis, macro-adaptive framework (MAF) will be defined. Algorithms satisfying the framework, including new ones developed by the author, will be discussed, analyzed, and compared with other existing algorithms, followed by simulation results in adaptive system identification. Since MAF opened the flood-gate for aggressive optimization (squeezing more information out of limited number of samples) that was not previously available, one possible side effect is over-adaptation, which is rarely studied in adaptive filtering literature. In addition to solutions developed in the thesis, the author did some original research on the phenomenon and the results are presented in the thesis as well.

Foreign at Home: Turkish-German Migrants and the Boundaries of Europe, 1961-1990

Kahn, Michelle Lynn ProQuest Dissertations & Theses Stanford Universit 2018 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

This dissertation examines the transnational history of Turkish guest worker families in Germany, emphasizing how their physical mobility across national borders, as well as state-driven efforts to facilitate or impede their mobility, reshaped ideas about German, Turkish, and European identities in a globalizing postwar world. It begins in 1961, when the West German government first began recruiting Turkish guest workers, and ends in 1990, a year marked by several developments: German reunification, the liberalization of German citizenship law, and renewed discussions about Turkey's compatibility with a post-Cold War conception of European belonging. At the core of the dissertation is an examination of the gradual process by which guest worker families came to feel foreign in both Germany and Turkey, the two countries they considered home. It traces the historical development of the term "Almanci, " a derogatory Turkish term that still today connotes the impression that the migrants living in Germany (Almanya) have undergone a process of Germanization and have become not only physically but also culturally estranged from the Turkish national community. The origins of this term extend as far back as the formal recruitment years (1961-1973), when guest workers were first separated from their families and rumors about adultery and infidelity spread. Simultaneously, as guest workers returned to their home cities and villages with cars and other luxurious western consumer goods, the stereotype developed that the migrants had transformed into a nouveau-riche class of superfluous spenders out of touch with the economic needs of their homeland. This history is deeply entwined with the rising xenophobia in 1980s West Germany. The dissertation's centerpiece is an investigation of the motivations and consequences of West German government's 1983 Law for the Promotion of Voluntary Return (Ruckkehrforderungsgesetz), which paid unemployed former guest workers a "remigration premium" (Ruckkehrpramie) of 10,500 Deutschmarks to pack their bags, take their spouses and children, and return to their home country within a brief timespan of just ten months. The dissertation traces how this controversial effort to "kick out the Turks" provoked the ire of the Turkish government, which used humanitarian rhetoric to obscure the underlying motivation for its opposition to the law: for largely economic reasons, the Turkish government did not desire an influx of return migrants. The migrants were thus left unwanted by the governments of both countries they considered home. Finally, the dissertation examines the consequences of the 1983 law, which brought about the largest remigration wave in the countries' postwar history, with 15% of West Germany's Turkish population (approximately 250,000 men, women, and children) returning to Turkey in 1984 alone. The final chapter emphasizes the struggles of the archetypical second-generation "return children" (Ruckkehrkinder) who accompanied their parents to Turkey following the 1983 remigration law and became symbols of the possibilities and limitations of national belonging in both countries. Turning the concept of "integration" on its head, the dissertation argues that, amid the longstanding discourses about Germanization and cultural estrangement, many "Almanci" found that reintegration in their own homeland was often just as difficult as integration in Germany.

Multiple Facets in the Assessment of English Learners: Challenges and Possibilities

Biernacki, Paulina Julia ProQuest Dissertations & Theses Stanford Universit 2022 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

Tests are woven into the fabric of the most fundamental educational processes. Yet testing programs, models and practices do not systematically account for the unique and varied needs of students categorized as English Learners (ELs) and who can be defined as students who are developing English as a second language (Linquanti et al., 2016). Although these students enter school halls with a rich array of linguistic, cultural and academic strengths, the EL label misleads teachers to approach these students with a deficit framing (Valdes, 2004). An obvious contributing factor is that these students tend to underperform on tests of academic achievement -- which stems, in part, from the lack of design considerations for ELs' needs (Duran, 2008). Another contributing factor is that there is still much room for improvement in the uses of ELs' assessment data by educational practitioners.This dissertation addresses multiple facets of applied issues in assessment that relate to fairness and validity, for which educators and assessment experts urgently require guidance. Specifically, it examines educational assessment issues and their impacts on K-12 students who have been categorized as ELs. In this dissertation, I address gaps in the literature at the intersection of language, learning, and assessment. I weave together interdisciplinary concepts and methods that span across sociolinguistics, sociology, psychology, and the learning sciences.This dissertation consists of three related studies with distinct motivations and origins. While the first chapter relates to linguistic and cultural issues in assessment, the other two chapters address disparities in opportunities to access rigorous academic content. These issues are interrelated, given that disparities in students' opportunities to learn are strongly impacted by inappropriate test design, development, and use. The first study is a conceptual framework originally commissioned by the Smarter Balanced Assessment Consortium, which sought conceptual guidance in developing culturally sustaining assessment systems. Thus, the target audience for this first chapter is assessment developers. The second and third studies, on the other hand, were developed as part of a five-year research-practice partnership. These two studies would not have been possible without funding from the Stanford's Graduate School of Education, and without facilitation from the California Education Partners. Collectively, these two studies examine the consequences of test misuse. The primary audience for these two papers comprises educators and researchers.In the first study, I report on a critical synthesis of the literature that explores the complexities of considering cultural relevance and provision of choice in assessments. I synthesize this information into key considerations for flexible assessment designs that allow students to more fully utilize their personal, cultural, and linguistic skills in demonstrating what they know and can do on assessments. In this paper, I ask: What considerations about ways of knowing and choice should be integrated into test design and development? I also ask, What actionable steps can assessment experts take to design assessments that promote flexibility and personalization? Although the literature to date on culturally sustaining pedagogy and students' ways of knowing is growing, the extensions to individual assessments and to comprehensive and coherent assessment systems are more recent developments.