VictorJuiz/thesis huggingface dataset:
Locality sensitive hashing for real time and distributed computation [electronic resource]
Keywords: Computational and Mathematical Engineering.

Similarity Search (SS) involves retrieving objects from a data set similar to a query object. In most applications, objects are represented by feature vectors in a high dimensional space. In this setting, Locality sensitive hashing(LSH) has emerged as the method of choice to implement large-scale SS. LSH uses random projections to insert data into a number of hash tables. SS queries are answered by performing a lookup operation in these hash tables. Although LSH is widely used in data mining and machine learning applications, it requires a large number of hash tables in order to guarantee accurate search results. This makes it difficult to implement LSH in high speed real time applications (due to slow query processing) and distributed systems (due to network load), since each query lookup in a hash bucket requires a network call. In this thesis we describe new techniques to implement SS via LSH in these settings. For Real Time SS, we describe a variant of LSH, Ternary Locality Sensitive Hashing (TLSH), for implementing SS on TCAMs (Ternary Content Addressable Memories), a ternary associative memory popular in networking equipments like routers and switches. Our approach critically exploits the wild-card matching capability of TCAMs. Our TLSH-based TCAM implementation has near-linear space complexity and answers SS queries in a single lookup, thus offering an exponential improvement over existing LSH solutions, which have a run time that grows as a fractional power of the data set size and sub quadratic space complexity. This enables efficient implementation of SS in real-time, at the cost of using a hardware primitive, the TCAM. Our solution works around known LSH lower bounds, as well as the (more generic) cell probe model lower bounds for near neighbor and nearest neighbor problems. The simulations and experiments we perform indicate that our proposed architecture can handle millions of SS queries per second. Distributed SS: We design a new implementation of LSH, called Layered LSH, for distributed (Key, Value) based frameworks. Layered LSH offers an exponential improvement over the in the network cost per query incurred by simple distributed implementations of LSH. In contrast with simple implementations whose network cost increases with increase in desired quality of SS, we prove that network costs associated with Layered LSH are independent of the search quality. Our experiments using the MapReduce framework indicate that this improvement in network efficiency leads to large improvements in run-time, in scenarios where SS needs to be implemented with high accuracy on data sets containing tens of millions of data points. We also prove that despite being network efficient (achieved by co-locating points near points on the same machine), Layered LSH sends points that are a constant distance apart to different machines with high likelihood. This shows that Layered LSH hits the right tradeoff between network efficiency and load balance across machines.
Low-delay robust video multicast [electronic resource]
Keywords: Electrical Engineering

Video multicast offers a scalable solution for large-scale television distribution. For commercial-grade video multicast services such as Internet Protocol Television (IPTV), it is often challenging to meet a set of conflicting design goals, including high video quality, low request response time and good system scalability. This dissertation addresses these issues by developing a decentralized peer-assistance architecture and integrating it with streaming-specific source and channel coding techniques to deliver multicast video in a timely, reliable and scalable way. Video quality is negatively affected by network packet loss. An existing framework to simultaneously address packet loss and request response delay is to combine multicast with a unicast service that provides both packet loss repair and fast stream startup functionalities. Typically, servers that provide the unicast service could become the system bottleneck. To mitigate this problem, we propose an alternative distributed solution to partially shift the burden of the unicast servers to receivers of the multicast. Using a Peer-Assisted Repair (PAR) protocol, we demonstrate that packet repairs can be delivered reliably on time using a combination of server-peer coordination and redundant repairs. PAR can be naturally extended to a Peer-Assisted Startup (PAS) protocol to facilitate fast stream startup, where a missing portion of the multicast stream is treated as a long erasure burst to be repaired. In these applications, we show that video transcoding can be seamlessly integrated to provide improved robustness to packet loss, reduced stream startup latency and improved system scalability. Erasure correcting coding plays an essential role in the peer-assistance architecture. To understand how to mitigate its delay into the stream startup process, we explore the design of erasure correcting codes that takes into account a decoding delay constraint. Modeling the peer-assisted unicast service as communication over a set of parallel links, we propose a practical construction of parallel-link block erasure correcting code, where each source packet is decoded at the sink on-the-fly with a strict decoding deadline. The proposed code handles two types of common errors in the upper layers of packet-switched networks -- bursty packet loss and link outages. We further show that the proposed code construction is delay-optimal among all codes that achieve the Singleton bound. The proposed decentralized architecture requires in-network video transcoding at the multicast peer receivers, where it is often desirable to use a scheme with low complexity, such as open-loop requantization-based transcoding. A known drawback of this scheme is the requantization distortion drift problem. We develop an analytical model to capture the distortion drift effect and show that this drawback can be largely mitigated through parameter optimization. We demonstrate its effectiveness in the transcoded-to-primary stream switching problem in fast stream startup.
Low-voltage, low-power, high-resolution, broadband oversampling analog-to-digital conversion [electronic resource]
Keywords: Electrical Engineering

Oversampling A/D converters exchange resolution in time for that in amplitude by oversampling the input signal and employing sigma-delta modulators that suppress quantization error within the signal bandwidth. As a result, a high-precision A/D converter output can be generated by using back-end digital decimation filtering. However, the use of oversampling converters is typically limited to low bandwidth applications, such as digital audio systems. Recently, sigma-delta modulators operating at relatively low oversampling ratios have been shown to be effective at achieving high-performance A/D conversion for signal bandwidths of several megahertz. However, the limited signal swings and voltage headroom that accompany the aggressive scaling of CMOS technology result in high power dissipation of the analog circuits in conventional modulator architectures. Although sigma-delta modulators based on input feedforward architectures enable reduced analog power dissipation, they require a high-speed quantizer and feedback DAC with attendant high power dissipation. The objective of this research is to investigate means of power minimization for both analog and digital circuits in sigma-delta modulators operating from low supply voltages over several mega-hertz of signal bandwidth while maintaining high precision. To relax the timing constraints on the quantizer and feedback DAC, a half-sample delayed-input feedback architecture is employed in the implementation of a second-order sigma-delta modulator. Power dissipation in the analog amplifiers of the feedforward architecture is reduced by using a single amplifier to implement the two integrators. This amplifier sharing also reduces the area occupied by the integrators. The power scaling of amplifiers in discrete-time multi-order amplifier-based analog integrators is exploited by dynamically biasing the shared amplifier. A low-power, high-speed charge pump circuit for dynamic biasing minimizes the power overhead. Finally, a multi-bit quantizer, which effectively reduces the output amplitude and power dissipation of the integrators, employs interpolated preamplifiers to conserve power and area in the preamplifiers. A 2-2 cascaded sigma-delta modulator, operating from a 1.0-V supply, has been designed using a half-sample delayed-input feedforward architecture for each stage, dynamically-biased amplifier sharing for realization of the integrators, and interpolated multi-bit quantization. An experimental prototype of the proposed modulator has been integrated in a 0.18-[micrometer] CMOS technology. At a 40-MHz sampling rate, the prototype achieves 92 dB of dynamic range, a 91-dB peak SNR and an 84-dB peak SNDR for a signal bandwidth of 1.25 MHz, while consuming only 24.3 mW of total power from a 1.0-V supply.
Lyric cities [electronic resource] : poet, performance, and community
Keywords: Classics

My dissertation analyzes how poets in archaic Greece interacted with their own local communities and how they positioned themselves within the community through their poetry. Archaic Greece (ca. 800-480 BC) was a time of great political and social change as interactions between the various autonomous Greek city-states intensified. Recent research has emphasized the role that poets had in negotiating local identities within this growing network of Greek states. Instead of studying how poets communicate with and praise other communities, this study will analyze how poets interact with and position themselves within their own community. As I argue in this study, a poet adapts a fundamentally different persona at home rather than abroad.
Lyric physicality [electronic resource] : bodies and objects in archaic Greek lyric poetry
Keywords: Classics

This dissertation investigates the way that archaic Greek lyric performance represents and displays itself a physical practice. Focusing specifically on descriptions of the bodies of performers and the objects used in performance, it argues that lyric poets do not simply reflect the physical and material conditions of their occasion, but in fact thematize physicality. The dissertation describes the various ways in which the physicality of performance is foregrounded and concludes that Greek lyric poets employ this strategy of physical self-display in order to constitute the parameters and significance of their poetic practice.
The magnetic solar photosphere and corona [electronic resource] : observation, modeling, and prediction
Keywords: Physics

The Sun's magnetic field drives the dynamic behavior of its atmosphere and modulates the space weather conditions that we experience at the Earth. This dissertation focuses on the recent advances in understanding magnetic field measurements, static-state modeling of the corona, and their applications in space weather forecasting. We revisit the full-Sun line-of-sight magnetic field data archive from the Michelson Doppler Imager (MDI). Using the Wang-Sheeley-Arge (WSA) model coupled with the potential field source surface (PFSS) model, we retrospectively optimize the space weather forecasting scheme for the MDI data. We evaluate the long-term performance of the model: the solar wind speed prediction near the Earth yields a 16% error over solar cycle 23, and the interplanetary magnetic field polarity is correctly predicted 81% of time. The prediction accuracy is strongly correlated with the activity cycle phase. We design a new interpolation scheme to estimate the unobserved magnetic field in the polar region which improves the solar wind speed prediction. Making use of the PFSS model and the MDI data, we characterize the global-scale coronal and heliospheric magnetic field structure and its evolution during cycle 23. The modeled features agree reasonably well with remote-sensing and in-situ observations. The recent cycle displayed an extended minimum activity period, whose peculiar heliospheric consequences can be partly explained by a reduction of the polar magnetic field strength. The PFSS model may need to adopt a smaller source surface radius to better fit some observations. We use a series of vector magnetograms from the Heliospheric and Magnetic Imager (HMI) to study the magnetic field and energy evolution of NOAA active region (AR) 11158. With the aid of a non-linear force-free field (NLFFF) extrapolation, we find substantial electric current and magnetic free energy increase during early flux emergence. The computed free energy is enough to power the ensuing X-class flare. We find a step-wise energy decrease during the flare, but the value is likely underestimated. The new observations confirm the rapid and irreversible change of the photospheric field during a major flare. The horizontal field was enhanced, with the field becoming more inclined and more parallel to the polarity inversion line. Such change is consistent with the conjectured coronal field "implosion". Observation and modeling of this AR also illustrates the important role of magnetic topology. A small bipole emerged in the sunspot complex, subsequently created a quadrupolar flux system, and induced a series of eruptions with highly inclined trajectory. Field extrapolation suggests complicated magnetic connectivity with a coronal null point, which is supported by coronal observations. Owing to the asymmetrical photospheric flux distribution, the confining magnetic pressure decreases much faster horizontally than upward, and thus likely guided the non-radial eruption during its initial stage.
Making silence together [electronic resource] : collaboration in the silent gatherings of Quakers
Keywords: Education.

The central phenomenon of interest in this text is silence, specifically group silence in social interaction. I offer insights gained from a mixed-method, multi-year ethnographic investigation among the Religious Society of Friends, commonly known as Quakers. For more than three and a half centuries, Quakers have practiced group silence. It forms the very core of their collective approach to religious life and a mystical experience they call 'unity.' Part of what makes Quakers' long, deliberate silences compelling and worthy of study is how strikingly they contrast to situations of silence outside the Quaker Meetinghouse. In Anglo-American culture, group silence is often experienced as uncomfortable, sometimes painfully so: the 'awkward silence, ' scrupulously avoided in conversation among people who have just met, or that hangs in the classroom air after a teacher's question, or that falls inexplicably and contagiously over a room full (now suddenly empty) of conversation. Silence has developed a reputation for being an uncomfortable void, empty of words and thus empty of sense. Compounding this reputation, scholars have been relatively quiet on the subject of silence compared to the attention given linguistic phenomena. The Quaker community I describe, Pacific Friends Meeting (PFM), is a contemporary instance of a centuries-old religious movement, organized around weekly leaderless gatherings as occasions for shared spiritual experience. The gathering is called 'Meeting for Worship.' The most distinctive aspect of a Quaker worship gathering is that it is conducted almost entirely in silence, punctuated by brief, occasional speech acts by participants moved to share an insight that has just occurred to them during worship. Contemporary Quakers are not well-represented in the social science literature. This dissertation contributes one of the few ethnographic studies of contemporary Quaker worship practice, conducted over four years, and is the first to introduce video recordings of Quaker worship into the scholarly record. I developed custom software to analyze these videos and my analysis shows that Quakers demonstrate synchrony in their embodied practice of silence: the tiny body movements and sounds that Quakers make (coughs, fidgets, sniffles, scratches) become coordinated in the silence into waves of synchronous activity. The empirical evidence suggests that Quakers tune into one other's bodily presence in the silence. The experiential evidence, drawn from Quakers' own accounts, confirms this and indicates that the co-presence of others provides social support to participants in their religious practice. My mixed-method approach lends support for the dissertation's central thesis that Quaker group silence is: embodied (multi-sensory), collaborative (multi-body), a means for mystical experience.
Management Practices and Productivity: the Case of Saudi Arabia
Keywords:  Department of Economics
Management Practices
Productivity
Saudi Arabia
Stanford Department of Economics
Thesis

In my Economics honor’s thesis, I examine management practices in Saudi Arabia and see if and how they correlate with firm productivity. Recent evidence points to strong correlation between “good” management practices - defined as practices that emphasize goal targeting, performance monitoring, and human resource management - and firm performance. That is to say, firms that employ good management practices are more likely to be more productive than their industry counter-parts, performing better in terms of sales, output, and survival. However the evidence is centered around and limited to the industrial sector in developed countries. So, I extend the research to Saudi Arabia, a Middle Eastern developing country. Replicating the survey study outlined in Bloom and Van Reenen (2007), I observe 26 Saudi firms and look at how their management scores correlate with their labor productivity. While I do find a positive correlation between the variables, the results are not statistically significant. Nonetheless, the evidence points to consistency between my results and those in the current literature, thus making an
argument for the existence of universally “good” management practices.
The mandate of heaven (Tianming) and the Zuo commentary [electronic resource]
Keywords: East Asian Languages and Cultures.

The ideology of the Mandate of Heaven, or tianming ,is central to the conceptual framework of the Zuozhuan [Zuo Commentary] and lends coherence to its narratives. The Zuozhuan posits that the Zhou royal house still holds the Mandate of Heaven, despite its decline. At the same time, while Zhou Mandate ideology also explains the rise of other lineages with the potential for obtaining the Mandate and becoming the new royal dynasty, the Zuozhuan suppresses this possibility by suggesting that the greatest achievement other lineages can attain is zhuhou status--that of a regional lord still acknowledging the suzerainty of the Zhou king. The study is divided into three sections. The first section sets the baseline by unpacking Western Zhou period (1045-771 BCE) articulations of the Mandate. It analyzes Shangshu texts, Shijing poems, and bronze inscriptions for this purpose. The second section argues that the Zuozhuan demonstrates the legitimacy of the Zhou royal house in its narratives. The authority of the Zhou has been codified and translated into various practices, customs and institutions that help entrench the Zhou. Even the position of the hegemon, usually regarded as a Spring and Autumn period (770-481 BCE) invention, is subsumed under the rubric of traditional service that the zhuhou provide to the Zhou. The third section examines the Zuozhuan's depiction of several lineages and the limitations the text places on their rise. This is accomplished through an array of tools: predictions and divination, delineation of the origins of various lineages, and descriptions of the behaviors of lineage heads in each generation. The Zuozhuan's position is further supported by the purely historical serendipity of the fall of a few key zhuhou lineages, like the ducal houses of Jin and Qi, at the end of the Spring and Autumn period. Therefore, no other lineage can threaten the Zhou royal position, though the most powerful ones attempt to do so.
Maximizing the information content of dual energy x-ray and CT imaging [electronic resource]
Keywords: Electrical Engineering

Computed tomography (CT) has become an essential tool in modern medicine since its introduction in the early 1970s. It generates cross-sectional images of the body's x-ray attenuation by measuring the transmission of x-rays in many directions. Because CT uses ionizing radiation, a governing principle is to use the least amount of radiation dose that still provides diagnostic-quality images. One approach to ensure that dose is appropriately used is to explore the information content of CT scans. This work examines efficient methods for encoding, storing, and extracting information from CT scans, especially as they pertain to spectral x-ray imaging. CT systems that can take advantage of the different attenuation properties of x-rays at different energies can provide additional diagnostic information, known as dual energy imaging. A new technique called Synthetic CT is introduced that enables images from CT protocols other than what was acquired to be retrospectively synthesized. With this tool, the information contained within a dual energy scan can be used to demonstrate the effect of protocol selection on image quality and dose distribution. In addition to experimentally validating the developed synthetic CT theory, further efforts have led to image-based synthetic CT, incorporation of electronic noise models for ultra low dose simulation, and a simple graphical user interface that demonstrates the flexibility of synthetic CT. We also explore an important spectral imaging technology -- photon counting detectors with energy discrimination capabilities. In principle, these detectors capture all the spectral information of transmitted x-rays by counting the number of photons at each energy. Optimal configurations of ideal photon counting detectors are first investigated, leading to the elegant discovery that two energy-dependent weighted counts can form a sufficient statistic for dual energy imaging. In practice, photon counting detectors have count rate limitations and imperfect spectral responses. The performance of realistic photon counting detectors is modeled and compared to conventional dual kV techniques. We find that both optimized photon counting and dual kV systems can significantly increase the dose efficiency of dual energy imaging.