1925 research outputs found
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Enhancing cryptographic systems with ternary-based methodologies and physical unclonable functions
No full textHistorically, the practical use of ternary algebra has had limited success amongst the various fields of computer science. Likewise, in the past two decades alone, the advent of physical unclonable functions (PUFs) has created a new avenue for security in numerous applications. To this day, however, the thorn in the side of the real world deployment in PUF technology has consistently been the limitation of noise. Thus, the majority of PUF research is still primarily focused on mitigating the issue of errors when extracting fingerprints and cryptographic keys from many types of PUFs by using client-focused techniques, such as fuzzy extraction and helper functions. This research describes an alternative methodology: by utilizing the long since disregarded ternary state, it broadens the avenue of PUF cryptography in a new direction.
Public Key Exchange that is Addressable (PKA) is a recent scheme that proposes a solution to the vulnerability of current generation public key infrastructures. In particular, currently employed PKIs are vulnerable to future quantum computers due to their reliance on the discrete logarithm problem. PKA sidesteps the issue by utilizing cryptographic hash functions and a "crypto table" to secure the generate the same symmetric key between two entities. However, the scheme only exists in concept, and no implementation has yet to be proposed. Here, the first known implementation of PKA is proposed. This is referred to as Ternary Addressable Public Key Infrastructure (TAPKI).
In TAPKI, the original PKA's proposed crypto table is imrpvoed by introducing a third state of uncertainty: a ternary state. Traditionally, crytpographic functions are only designed with binary computing in mind. By adding a third state, an attacker cannot easily reverse engineer the structure of the crypto table. Furthermore, ternary naturally lends itself to the concept of cells that may contain errors.
As PUFs have an inherent level of physical randomness, TAPKI can be further strengthened by replacing the crypto table with a PUF-based device altogether. While there exists previous cryptosystems that take advantage of PUFs, all of them must manage errors in some way. Usually, this is in the form of an error correction code or helper function that must be sent amongst peers. However, this places more responsibility and vulnerability on behalf of the client in context of server-client relationships. These clients, particularly those designed around IoT devices, do not have much in the way of compute power and resources to implement such error correction. For illustrative purposes, this concept is referred to as ?challenge-based cryptography."
An alternative error correction approach is proposed, where instead the key issuer searches through different possible message digests based on previous knowledge of a user's PUF. This is innovated upon by describing an algorithm that is capable of searching through possible key errors in an efficiently parallel manner. In direct contrast with "challenge-based cryptography," this approach will be referred to as "response-based cryptography (RBC)." Experimentally, it will be shown that this solution is able to search through 5 bit errors in a 256-bit cryptographic key under 1.65 seconds using 512 ranks with 91.77% parallel efficiency. This algorithm can be further optimized by the splitting up the key into even n-bit chunks and padding each chunk with mutually-known secret information.
Lastly, the overarching design is completed with post-quantum cryptographic digital signature algorithms, such as CRYSTALS-Dilithium. Rather than having the DSA generate the public-private key via a cryptographically secure pseudo-random number generator, it is replaced by the deterministic, but still secure, output of TAPKI. This cryptosystem combines the use of ternary, hash functions, PUFs, RBC, and PQC to form a cohesive public key infrastructure that is reliable, sufficiently random, and post-quantum safe for server-client architecture. Finally, it will be shown its real world practicality by implementing it around the use of SRAM-based PUFs, both with server-to-client and peer-to-peer communication
Into the canopy: advancing forest resource characterizations with lidar
Get PDFForests around the world are facing radical shifts in distributions and disturbances resulting from climate change that are exacerbated by anthropogenically caused novel uncharacteristic forest conditions. This is especially true in the western US where shifts in structure and composition have resulted in denser (i.e., more trees), fire-intolerant and tree-dominated ecosystems with reductions in function and ecosystem services. To address this, ecological restoration has been proposed across millions of hectares with the goal of shifting forest structure and composition closer to its historical range of variability (HRV). However, forest restoration necessarily alters existing, degraded forest conditions – conditions wildlife have adapted to occupy - and while increased function and health is known, impacts to habitat and resulting animal behavior is still being studied. This knowledge gap has created a need to quantify present forest conditions at a higher fidelity and at landscape scales to develop a deeper understanding of restoration practices and wildlife habitat interactions. In this dissertation, I investigated recent developments in methodologies using light detection and ranging (lidar) and machine learning to create workflows to better assess forest conditions. I used three separate studies conducted in the Southwest to validate methods for quantifying forest structure and composition and to provide insights into spatially-explicit conditions around Mexican Spotted Owl (Strix occidentalis lucida; MSO) nesting habitat. To quantify forest structure, I compared three different approaches (i.e., area-based, tree-based, voxel-based) for estimating forest attributes (i.e., basal area, volume, biomass) across 1,680 field plots in Arizona and New Mexico using random forests and ridge regression. Boruta feature selection was performed on variable subsets, including a mixture of all lidar-derived predictors (my application of Boruta using the “Kitchen Sink”, or KS-Boruta). A corrected paired t-test was utilized to compare six validated models (area-Boruta, tree-Boruta, voxel-Boruta, KS-Boruta, KS-all, ridge-all) for each forest attribute. Based on significant reductions in the symmetrical median absolute percent error, basal area and biomass were best modeled with KS-Boruta, while volume was best modeled with KS-all or the “kitchen sink” using voxel, tree and area-based approaches. Analysis of variable importance showed voxel-based predictors are critical for the prediction of the three forest attributes. This study highlights the importance of multi-resolution voxel-based variables for modeling forest attributes in an area-based context.
To assess forest composition, I used deep learning techniques to create a classification model for seven species from lidar imagery within the Mogollon Rim Ranger District of the Coconino National Forest. I compared individual tree segmentation images of unmanned aerial vehicle laser scanning (UAV-LS) and airborne laser scanning (ALS) data colored by different eigenvalues in a multi-view 2D convolutional Neural Network. The final models for each acquisition type were curvature-colored ALS imagery (88% accuracy) and verticality-colored UAV-LS imagery (88% accuracy). This highlights the capability of species classification across landscapes using ALS data alone.
Finally, I use lidar to assess forest conditions over varying spatial extents around MSO nesting habitat. I explored changes over varying spatial extents in 137 lidar-derived forest attributes including the voxel metrics found important in my first manuscript chapter. I focused primarily on canopy strata, gap sizes, snags, the mean frequency ratio voxel-based variable, and the coefficient of variation for the mean percentage of points greater than two meters above the ground. The goal of the study was to determine which forest attributes were most strongly associated with MSO nesting habitat by assessing 10-meter annuli around owl nests and manager-delineated owl habitat areas such as cores and protected area centers (PACs). Additionally, I wanted to determine if there were differences between manager-delineated PACs and circular buffered areas of 243 hectares (i.e., recommended minimum PAC size; P880) in the immediate vicinity of the nest tree. I explored niche overlap between each owl habitat area and between each annulus and the P880 region. Kruskal-Wallis and post-hoc Dunn’s tests were performed across regions to determine significant differences. Many of the forest attributes had differing niche overlaps between core and PAC. However, PAC and P880 comparisons did not have as many differing attributes. Kruskal-Wallis results also confirmed that some variables differed between core and PAC regions, but not PACs and P880s. Tall trees (18-34 meters) and the mean frequent ratio were important indicators of MSO nesting habitat structure across all analyses. This study indicated that owl habitat is a more nuanced structure and that increased forest cover canopy cover (where the cover of tall trees is commonly found) is an inadequate description. Recently occupied Mexican Spotted Owl habitat might best be characterized as areas with higher canopy cover, but also with tall trees and open sub-canopies.
This dissertation provides building blocks on a larger body of literature pushing forest management and monitoring into a new technological age where comprehension of fine-grain attributes over landscape-scale extents is no longer out of reach
Looking out for the little guys: measuring M-dwarf multiplicity with high-resolution imaging
No full textThe M dwarfs have become primary targets for the detection and characterization of habitable, Earth-sized exoplanets due to their small sizes, their low temperatures, and their abundance in the Solar neighborhood. However, unknown stellar multiplicity can inhibit planet detection and lead to obstacles in planet characterization, and stellar companions can hinder planet formation and/or the long-term stability of any inner planets that they host. Fortunately, speckle interferometry has become a leading technique to search for unknown stellar companions, and to investigate the region around candidate exoplanet hosts. We therefore used speckle interferometry to explore the multiplicity of both planet-hosting and non-planet-hosting M dwarfs. These multiplicity measurements revealed a dearth of close-in stellar companions to M-dwarf TESS Objects of Interest, a new stellar companion to an F1V star, and 26 new companions to nearby field M dwarfs. Additionally, we present a next-generation speckle camera that is optimized for investigating low-mass pairs. These studies have generated two main conclusions: (1) the stellar companions that planet-hosting M dwarfs host differ from those that non-planet-hosting M dwarfs host, and (2) recent advances in speckle interferometry have made speckle cameras substantially more sensitive than in the past, allowing us to probe novel M-dwarf discovery space
Soil microbial responses to climate change in the arctic Tundra
No full textIncreases in Arctic temperatures have thawed permafrost and accelerated tundra soil microbial activity, releasing greenhouse gases that amplify climate warming. Warming has also accelerated shrub encroachment across the tundra, altering litter quality and causing further changes to soil microbial processes. Understanding how individual microbial taxa will respond to warming and resultant ecosystem changes can provide insights into the underlying mechanisms that will determine net soil carbon flux to the atmosphere. We quantified the growth response of individual bacterial and fungal taxa to the long-term effects of warming using a 29-year field experiment in moist acidic tussock tundra. To uncouple the direct effects of warming on microbial growth rates from effects mediated by other ecosystem responses to warming, we conducted a parallel short-term warming experiment (3 months). Intact soil was assayed in the field for 30 days using 18O-labeled water, and taxon-specific rates of 18O incorporation into DNA were estimated as a proxy for growth. We evaluated the responses of taxonomic and functional groups and explored possible interactions among taxa via microbial growth network analysis. The phylogenetic conservation of bacterial and fungal growth rates was also investigated. Short-term warming was found to increase the average growth rates of the bacterial community, and an cohort of bacteria emerged that did not have measurable growth in other treatments. However, fungal growth rates did not change, and the diversity of fungal growers decreased. Thus, increases in bacterial growth and emergent growing bacteria in short-term warming could be interpreted as a warming-induced shift from a fungi-dominated community to a community of predominately disturbance-associated bacteria. The long-term warming increased the growth of both kingdoms, especially bacteria for which the average relative growth rate was approximately 2.5-fold higher than the control. Further, the stimulated growing community was similar to the control suggesting resilience in the long-term. Network analysis corroborated these findings as short-term warming largely altered network structure and reduced network stability while long-term warming supported much of the network structure that occurred in the control and increased network stability. Growth network analysis also revealed that negative correlations involving fungi contributed to network stability. Many microbial functional groups responded strongly to long-term warming that have consequential effect on tundra ecosystem processes, namely bacterial methanotrophs (Methylacidiphilales) and shrub-associated nitrogen fixers (Rhizobiales and Frankiales) and ectomycorrhizal fungi and wood saprotrophs. The investigation of the phylogenetic organization of bacterial growth detected coherence in relative growth rates within broad taxonomic levels with orders tending to have similar growth rates in all treatments. However, we found less consistent evidence for phylogenetic organization of fungal growth rates. Phylogenetic and functional coherence of microbial growth rates could facilitate predictions of the effects of climate change on microbial growth and explicit incorporation of soil microorganisms into taxonomically informed soil models
Sub-quadratic area-under-the-curve optimization
No full textThe Receiver Operating Characteristic (ROC) curve is a plot of the false positive rate(FPR) versus the true positive rate (TPR) that is often used for evaluating the
performance of binary classification models. Maximizing the Area Under the Curve (AUC)
has been shown to be beneficial when the difference between the number of positive and
negative labels is drastic. Because the AUC is is a piece-wise constant function, learning
algorithms instead optimize convex relaxations that sum over all of the pairs of labeled
positive and negative examples. The na ̈ıve approach to summing over all of these pairs of
examples takes quadratic time which quickly becomes unfeasible for large batch sizes. In
this document, the necessary background to understand the problem, a summary of related
approaches to solving this problem, and proposals for computing the square and
squared-hinge loss in either liner or log-linear time are presented. Finally, a empirical study
that shows the improved time complexity of these algorithms, shows there are situations
where it is advantageous to make use of larger batch sizes, and that it is possible to achieve
improved model performance using these proposed methods
Scale effects of forest fragmentation on neotropical and temperate bat species
No full textHuman-driven disturbances like habitat degradation, fragmentation, and loss are some of the main threats to biodiversity worldwide. The fragmentation of forest habitats can create favorable conditions for edge-dwelling and open forest species which means that the effects of disturbances can be varied, ranging from positive to negative across different taxa and environments. Bats (Order Chiroptera) are the second most diverse order of mammals and play equally diverse and important roles in the function of ecosystems, from tropical to temperate regions globally. Bats, like all wildlife species, select their environment at multiple spatial and temporal scales that correspond with morphological and behavioral traits. However, landscape-species relationships are not well understood, especially in hotspots of bat diversity such as the tropics and subtropics. I conducted three studies focused on exploring, describing, and summarizing bat species interactions with landscape conditions (structure: composition and configuration) across all continents but with emphasis in the Neotropics and forest-associated species. First, I conducted a literature review focusing on bat research studies conducted at landscape scales globally. I identified knowledge gaps, taxonomical and geographical biases, and summarized trends in research subjects, methodological approaches, and findings. I found that bat diversity hotspots were understudied and knowledge for responses to landscape for some bat families was completely lacking. Bat responses were highly species-specific and varied greatly, even among taxonomically closely-related species. However, intra-specific conditions (e.g., demographic, behavioral) also altered responses to landscape features both spatially and temporally. Next, I used a country-wide bat capture dataset and land cover and land use data layers to conduct a landscape analysis across the entirety of Nicaragua, a country in the Neotropics with high bat diversity. I quantified and compared landscape metrics that offered insight on the spectrum of tolerance to forest fragmentation among six bat species in the leaf-nosed family (Phyllostomidae). The results of this analysis quantified not only a difference in the tolerance to landscape fragmentation between habitat generalist (subfamily Stenodermatinae) and forest-specialist (subfamily Phyllostominae) species, but among the species within each group. This corresponded to empirical knowledge on these two major groups and provided further support about the associations of these species with their environment. Lastly, I used radio-telemetry and DNA metabarcoding to describe movement and diet of a forest habitat specialist and carnivorous bat (Vampyrum spectrum). I used natural history data to identify habitat and prey selection for this rare bat species listed as Near Threatened by the International Union for Conservation of Nature about which little is known. My observations in movement and roosting supported long-standing assumptions on the relationship of this rare species with mature forests. Activity patterns and diet of V. spectrum indicated an opportunistic foraging strategy, preying predominately on birds, other bat species, and terrestrial rodents. The information in these three chapters will help orient and prioritize areas of research. Additionally, our understanding about species responses to changes in the landscape structure will inform management and conservation policies that maximize the use of resources to retain important landscape conditions for bat diversity
Border Communities: Race, Gender, and Community Formation in Arizona's Verde Valley Copper Towns, 1875-1941
No full textThis thesis examines community formation among diverse groups of women in Jerome, Clarkdale, and Clemenceau, Arizona, from the late-nineteenth to early-twentieth centuries. During the late-nineteenth century, environmental and landscape limitations, anxieties about settling in an alien place and society, and crude, masculine social settings compelled women to remain within the sanctity of their homes. Consequently, community development was largely delayed. In the first decades of the twentieth century, a sense of belonging emerged, but it was contained within ethnic-specific locales. Ethnic enclaves in neighborhoods and organizations emerged from external pressures and internal preferences. Like individuals created neighborly networks and organizations for companionship and out of necessity. Throughout the 1920s and 1930s, the inter-ethnic image of community expanded in tandem with increased cross-cultural communications. Americanization programs, the Great Depression and New Deal, mass culture, and a rebellion against gendered standards and roles all factored into a more pluralistic community that included different generations, classes, races, and nationalities. Of course, persistent discriminatory policies and practices ensured that true integration into mainstream American society was reserved for select European ethnicities. Nevertheless, there was greater social harmony in the 1920s and 1930s than in previous decades. Women were at the center of each phase of community development
Family supportive supervisor and partner’s support as a moderator of the demands-stress relationship
No full textThe number of dual income families has increased over the years, with mothers continuing to report being responsible for all the home duties and responsibilities despite
working the same number of hours per week as their partner. Previous literature has
demonstrated that social support can have a positive impact on the health and psychological
well-being of individuals. The purpose of the current study was to examine the role of supervisor
and partner support on the demands-distress relationship in the biggest minority in the workforce
– Hispanics. This study also aimed to examine how similarities (or differences) with the source
of support would moderate the perception of support received. Data were collected through
Amazon Mechanical Turk (MTurk) and by contacting different Hispanic organizations. A nonrandom
sample of Hispanic mothers, who had a partner, a supervisor, at least one child 12 years
or younger, and who were working full time were recruited (N = 205). Results indicated that
there was no relationship between the home demands and psychological distress experienced by
Hispanic working mothers. Additionally, no moderating effects were found for supervisor or
partner support on the demands-distress relationship. These and other results, strengths,
weaknesses, as well as future directions for this field of research are discussed
First-generation college students and climate change: an underreserached and vital relationship
No full textFirst-generation college students are rarely researched in their climate change attitudes. Because first-generation students are more likely to come from low socioeconomic backgrounds, they go through their own unique set of challenges when it comes to college and climate change. Inclusivity is a main pillar in climate justice, and more research on minorities and their relationship with climate change is vital envisioning with sustainable solutions. There is little research done on the difference between the way first-generation and continuing-generation view climate change and solutions, even though first-generation students make up a sizable portion of college students. This research was conducted in order to compare the differences, if any, on attitudes on climate change between first-generation students and continuing-generation students attending Northern Arizona University (NAU). To conduct this research a survey was developed for primarily freshman NAU students in order to delve further into attitudes on climate change to draw comparisons between the two groups of students. Also, two focus groups were held, with one containing only freshman first-generation students and the other with only freshman continuing-generation students for comparison. I analyzed literature discussing climate change attitudes, first-generation challenges, empowerment, and higher education institutions to get a full picture of first-generation attitudes.
Based on my research, I was able to conclude that there were multiple differences between first-generation students’ attitudes towards climate change than continuing-generation students. Five key differences between the two groups were observed from the focus groups and survey data. This research is limited by small sample sizes for both the survey and focus groups and I recommend that future research be done with a larger, more diverse population. Five recommendations were made to NAU utilizing the data presented and extensive literature review
Interpreting the Maya ideoscape through monumental reuse and spoliation
No full textThis pilot project research examines the Maya reuse of monuments and spoliated objects and its implications for understanding the role played by multi-directional power and ideological negotiation between non-elite and elite members in ancient Maya society. To demonstrate how reuse and alteration can inform on social roles and identity, this thesis employs mixed methods analysis. The use of pedestrian survey, GIS spatial analysis, and quantitative analysis provided clues to the disintegration of structural power and increased agency among non-elites. The results of the study led to the discovery of new and relocated spolia and demonstrated an ideological shift in how spolia were used through time from the Early Classic period to the Postclassic period. These findings also indicate that the greatest frequency of spolia were+ observed during the Late and Terminal Classic periods. Through the analysis of regional, inter-regional, and local patterns, the study was able to detect events related to the perpetuation of Maya elite ideology during the Late Classic period, as well as the role of non-elites in defining their own sacred landscapes through time. The pilot project will provide a foundation to the emerging study of Maya spoliation. Lastly, the study of spoliation supports the investigation of multi-vocal and multi-ideological understandings of how monuments were reused to promote, reinterpret, and redefine ideologies