15064 research outputs found
Sort by
Nonlinear diffusion and decay of a blob of turbulence spreading into a quiescent fluid
No full textTurbulence, left unforced, evolves under its own dynamics, invading surrounding quiescent fluid as it decays. A ubiquitous and familiar phenomenon, this fundamental aspect of turbulence has resisted the marriage of principled theory and experiment with no universal law yet capturing its evolution. Conventional flow chamber experiments have been hampered by boundary effects or strong mean flows that obscure the intrinsic dynamics of relaxation to quiescence. To circumvent these limitations, we create a spatially localized blob of turbulence using eight converging vortex generators focused at the center of a water tank, and observe its decay and expansion over decades in time using particle image velocimetry with logarithmic time sampling. The blob initially expands and decays until it reaches the walls of the tank and eventually transitions to a second regime of approximately spatially uniform decay. We interpret the turbulent dynamics as an interplay of nonlinear diffusion with associated steep fronts separating the turbulent and quiescent regions, and nonlinear decay, as described by the Kolmogorov–Barenblatt equation. We find direct evidence for this model within the expansion phase and decay phases of our turbulent blob and use it to account for the detailed behavior we observe. Our work provides a detailed spatially resolved narrative for the behavior of turbulence once the forcing is removed, and demonstrates unexpectedly that the turbulent cascade leaves an indelible footprint far into the decay process.</p
Preservational Controls on Patterns of Mammalian Turnover
No full textOne of the long-standing concerns of paleobiologists is in identifying major faunal turnovers in the fossil record, that is, when many taxa either disappear permanently or appear for the first time, and then disentangling the biological and environmental conditions that caused them. Increments of time that are especially dense in ‘range end-points’ are generally thought to arise as a response to exceptional climatic or environmental stress that intensified the loss of incumbent taxa and/or the arrival and success of new taxa. However, prior to evaluating such possibilities, one should be confident that the stratigraphic pattern of taxonomic first and last appearances does not simply arise from hiatuses, or gaps in sediment accumulation, which can concentrate range endpoints along a single horizon. This challenge is especially pronounced for vertebrate fossil records in terrestrial settings. Fossil remains are typically scarce in terrestrial sediments, and a single locality can represent fossils collected from a wide area and stratigraphic thickness, as opposed to the finer sampling of invertebrate and micropaleontological fossils in marine successions. Yet, unlike marine settings, terrestrial sedimentary records are also subject to long phases of sediment starvation or bypass and subaerial weathering in between relatively short phases of active sediment deposition, making the formal identification of hiatuses and their paleobiological implications especially challenging. Here, I develop a framework for estimating the relative magnitude of hiatuses and test for the extent to which major hiatuses coincide with the positioning and nature of mammalian faunal turnovers in the Eocene Washakie Formation of Wyoming. After remapping all known fossil localities across the basin, and adding some new ones of my own, I evaluated the rocks for physical evidence of phases of non-deposition. I find that, while the formation contains signatures of high-magnitude, seasonally-variable flooding regimes that result in rapid deposition, nearly all range endpoints of mammalian genera are still associated with major hiatuses. In addition, some of the faunal turnovers that previously appeared to have occurred suddenly actually proceeded in a more stepwise and gradual fashion. The significance of these findings extends beyond the Washakie record and creates a model for re-evaluating fossil records in other intermontane basins in the western United States. Lastly, my final chapter addresses the potential spatial incompleteness of fossil records by using point occurrence data to estimate the occupancy of extant mammal species in five 1-degree x 1-degree quadrants in the United States. Within these quadrants, I estimate the zones of potential sediment accumulation by identifying areas with both a low slope and a high area of contributing surface flow, which is requisite for sediment delivery to a low-slope sink. I find that, among the five test areas, 82-96% of species have occurrences that overlap with a sediment sink, indicating that the lenticularity of potential deposition in terrestrial systems is unlikely to be a first-order limit on fossil preservation. Thus, other taphonomic controls notwithstanding, a local fossil record of terrestrial mammals, even in inland settings, is likely to capture the presence of most species living in a region
THE FEAR OF THE FUTURE: AN ANALYSIS OF THE ESSENCE OF ANXIETY IN THE THOUGHT OF PAUL TILLICH AND SIGMUND FREUD
No full textNo abstrac
Clinical characteristics of natural recovery in trichotillomania and skin picking disorder
No full textBackground: Approximately 25% of people with trichotillomania recover without receiving formal treatment. Rates of natural recovery in skin picking disorder are unknown. More importantly, variables that predict natural recovery in trichotillomania and skin picking disorder have been understudied. This study aims to examine these variables in a sample of individuals with trichotillomania and/or skin picking disorder. Methods: 21 adults (76.2% trichotillomania only, 14.3% skin picking disorder only, 9.5% both; 85.7% female; mean age=32.19, SD = 10.21) who reported naturally recovering (i.e., not meeting full DSM-5 diagnostic criteria in the previous 12 months) from trichotillomania or skin picking disorder completed a virtual interview and self-report forms. The mean number of years since criteria was unmet was 5.95 (SD = 6.27). 41 participants with current trichotillomania or skin picking disorder were matched to naturally recovered participants on sex, diagnosis, and age (mean age=31.02, SD = 7.95; 2 matches for each participant except for one participant who has 1 match). They were compared on demographics, clinical characteristics, and treatment history. Results: When asked about their pulling or picking at its worst, there were no significant differences in self-reported days per week or time per day spent pulling or picking, or functional interference from pulling or picking. Participants with current trichotillomania or skin picking disorder reported greater distress from their pulling or picking, but this did not remain significant after controlling for current comorbidities. Naturally recovered participants were significantly less likely to have a current comorbid psychiatric disorder, specifically depression and ADHD. However, they were significantly more likely to have a lifetime substance use disorder and current alcohol use disorder. In total, 77.8% of participants either still pulled or picked occasionally and/or replaced it with another behavior. Conclusion: Although it may seem intuitive that those who naturally recover can do so because their disorder is less severe, these results indicate that severity was not associated with natural recovery. Given the persistence of subclinical symptoms after natural recovery, the effectiveness of natural recovery over recovery via treatment is questionable. A major limitation of this study is its small sample size and limited power. Future research should use larger sample sizes and further explore potential differences in comorbidities.</p
The Drivers of Microevolutionary Divergence in Avian Systems
No full textThe divergence of conspecific populations is a central process in evolutionary ecology, with relevance to speciation, range boundaries, and local adaptation. Advances in our understanding of avian ecology and understanding at the species level have led to substantial insights into the constraints and drivers of macroevolutionary diversification in birds, but comparative trait-based study of diversification within species remains rare. In this dissertation I use population genomics and phylogenetic comparative methods alongside measurements of phenotypic and niche variation to examine population divergence in three avian systems. In Chapter 2, I examine the species-level drivers of gene flow in 44 passerine species along the elevational gradient of the Ecuadorian Andes. I found that detectable genomic divergence with elevation was widespread, and was stronger in taxa that lived at high elevations and had lower dispersal capabilities. I also found evidence of morphological differentiation that was largely decoupled from genomic differentiation. These results highlight the potential for multidimensional environmental gradients to drive microevolutionary diversity. In Chapter 3, I explore comparative patterns of population structuring across fragmented habitat at the southern edge of the Chocó biodiversity hotspot. I found that the 15 forest-dependent species I studied all showed some evidence of population structure across regions of unsuitable habitat. I found that population differentiation was stronger in large understory insectivores, primarily antbirds (Thamnophilidae). I found strong evidence for isolation-by-distance, but little evidence for isolation-by-resistance: associations between population differentiation and traits were generally weak. In Chapter 4, I conduct a case study of population differentiation in a putative recent range expansion in the barred owl (Strix varia) across the continental United States from an ancestral range in the eastern half of the continent. I found strong population differentiation between individuals on the west coast and in the rest of the range, suggesting a considerably older origin for western populations than previously thought. This result was borne out by demographic history analyses. Taken in concert, my thesis chapters showcase the power of comparative population genomics, highlighting the potential for environmental heterogeneity to drive population differentiation. This work simultaneously showcases the ways in which a complex evolutionary history can create idiosyncratic outcomes, reinforcing the need for taxonomic breadth and diversity in trait-space for comparative studies
Involving End Users in Co-Designing Mobile Health Interventions for Hypertension Self-Management: Formative Study
No full textBackground: Mobile health (mHealth) interventions are prevalent, yet people from marginalized communities are less likely to use digital health technologies to support self-management behaviors. Community engagement can inform health care design to enhance a hypertension self-management mHealth intervention. Objective: We applied human-centered design (HCD) to determine appropriate iterations of an existing hypertension intervention. Methods: Through an equity-focused, community-centered approach, we strove to optimize an mHealth app. We used validated theories and frameworks as well as an HCD methodology organized into three fundamental design skills: (1) methods to directly observe user experiences, (2) methods to analyze barriers to ideal intervention use, and (3) methods to design future iterations. Results: In October 2023, we conducted a series of HCD activities with a community advisory board (n=8) to refine an mHealth intervention for hypertension. Participants tested app prototypes with blood pressure monitors and suggested content modifications to enhance intervention fidelity. Among 6 participants, usability testing scored 67.5 (benchmark 68, “above average”), with all users finding the tool easy to use. Feedback identified critical needs, barriers, and work-arounds for future mHealth iterations. Conclusions: This study was a novel use case example of HCD as a patient-centered methodology to improve a hypertension management tool.</p
The Load Paths in the Jaws of Extant Mammals and Fossil Mammaliaforms and Their Significance for Mammal Ear and Jaw Evolution
No full textThe early evolution of mammals involved major transformations of their jaw and middle ear, with profound changes in feeding and hearing functions. The novel dentary and squamosal jaw joint in mammals evolved from a double joint of fossil mammaliaforms, formed by the dentary-squamosal articulation and ear bones fully attached to the dentary. Thus, the mandibular middle ear is structurally a part of the musculoskeletal system that resists forces of chewing. How could mammaliaforms maintain a delicate mandibular ear on the robust dentary while resisting high stresses during feeding? Here I developed a new biomechanical analysis, load path analysis, to shed light on how the mandibular middle ear was retained and could be functional for hearing in stem mammals. The mechanics of mandibular middle ear function was approached via four different aims: the development of a load path analysis for mandibles, the search for morphological markers of load paths in mammal jaws, using load paths to identify load bearing structures in the mammaliaform Morganucodon, and vibroacoustic analysis of the mandibular middle ear in the more stemward cynodont Thrinaxodon. The results of these aims demonstrate that load paths are found in the medial ridge of the dentary in mammaliaforms, a conserved osteological feature that insulated the mandibular middle ear from feeding stresses. All the while, the tympanum on the mandibular middle ear was a functional sound receiver. Thus, the medial ridge facilitated the transition of the postdentary bones from a jaw joint into a purely sensory organ system
Direct Synthesis of III-V Nanocrystals in Molten Inorganic Salt
No full textColloidal quantum dots (CQDs) are semiconductor nanocrystals with sizes typically ranging from 2 to 20 nm. Due to quantum confinement, their bandgap can be tuned by controlling particle size, so that materials with the same chemical composition (e.g., CdSe) exhibit size-dependent optical properties. For example, smaller CQDs emit in the blue or cyan region, whereas larger CQDs emit deep red light. Using colloidal synthesis techniques such as hot-injection and heat-up methods in high-boiling-point organic solvents (e.g., 1-octadecene, oleylamine), relatively monodisperse CQDs can be obtained. Further size-selective precipitation can yield nearly monodisperse CQDs. These methodologies have been generalized to most II–VI and IV–VI semiconductors, halide perovskites, and InP and InAs nanocrystals. With appropriate surface treatment and epitaxial shell growth, highly emissive CQDs can be synthesized, achieving photoluminescence quantum yields (PLQYs) as high as 100%. Despite the extensive development of II–VI and In–V nanomaterials, gallium pnictide nanomaterials have lagged behind. Gallium pnictides, such as GaAs and GaP, are among the most widely used semiconductors for electronic, optoelectronic, and photonic applications. However, solution-phase syntheses of gallium pnictide nanomaterials remain much less developed than those of many other colloidal semiconductors, including indium pnictides, II–VI and IV–VI compounds, and lead halide perovskites. In Chapter II, I demonstrate that the Wells dehalosilylation reaction can be carried out in molten inorganic salt solvents to synthesize colloidal GaAs, GaP, and GaP₁-ₓAsₓ nanocrystals. I show that discrete colloidal nanocrystals can be nucleated and grown in a molten salt medium with control over both size and composition. Additionally, I find that reaction temperatures above 400 °C are crucial for annealing structural defects in GaAs nanocrystals. We also highlight the utility of the as-synthesized GaP nanocrystals by demonstrating that GaP can be solution-processed into high-refractive-index coatings and patterned by direct optical lithography with micron-scale resolution. Finally, we show that dehalosilylation reactions in molten salts can be generalized to synthesize indium pnictide (Pn = As, P) and ternary (In₁–ₓGaₓAs and In₁–ₓGaₓP) quantum dots. Beyond isotropic nanomaterials, I also carried out extensive research on anisotropic nanomaterial synthesis in molten salts. Based on the Solution–Liquid–Solid (SLS) growth mechanism, I introduced gold nanoseeds into the molten salt reaction system and successfully produced GaAs nanowires. The as-synthesized GaAs nanowires exhibit band-edge photoluminescence. We further generalized this strategy to synthesize GaP and GaPₓAs₁-ₓ nanowires. These one-dimensional nanowire syntheses are discussed in detail in Chapter III. Redox chemistry in molten salts has proven effective for GaAs nanocrystal synthesis, but for indium-based systems, it is challenging to use In₂Br₄ to reduce pnictide halides. In Chapter IV, I demonstrate that AlBr3 can be used to activate InBr. The resulting InBr–AlBr3 adduct can reduce pnictide halides to form indium pnictides. Moreover, transmission electron microscopy (TEM) analysis reveals that the as-synthesized InP structures adopt a two-dimensional morphology. In summary, molten salts provide a versatile platform for semiconductor nanocrystal synthesis. By adapting strategies originally developed in organic solvents, one-dimensional nanostructures can be realized in molten salt media. Furthermore, employing Lewis acid adducts enhances the reducing power of indium halides (e.g., InI/InBr in InAlBr4), enabling the synthesis of indium pnictides with controlled morphology. Notably, the InP produced from InAlBr₄ exhibits a distinct 2D morphology, highlighting the potential of molten salt chemistry for accessing new classes of semiconductor nanostructures
Qayt Sharīfī’s Turkic Class Notes and Tamurbāy’s First Arabic Scribbles: Language and Education at the Mamluk Barracks in Light of Ayasofya MS 1448
No full textThe manuscript Ayasofya 1448 is not the umpteenth graduation copy of a mamluk trainee that ended up as a khazāʾinī manuscript in the library of Sultan Qāytbāy, but something far more exciting: a manuscript copied by one such mamluk trainee, Qayt Sharīfī, and then presumably passed on to another trainee, Tamurbāy. Given its provenance and contents, Ayasofya 1448 sheds some unique light on the mamluks’ non-military curriculum inside the barracks: kitābah and legal-religious training, Turkic and Arabic. Included in the composite manuscript and undoubtedly written in Qayt’s advanced yet still unprofessional hand are (1) the rather common Turkic interlinear translation of al-Samarqandī’s Al-Muqaddimah fī al-Ṣalāh, (2) a unique bilingual commentary on that same Muqaddimah—one that allows us to finally identify an already known Turkic interlinear Quran translation as undeniably Mamluk—and (3) a unique Turkic story on the provenance of the Arabic yā mujīr supplication. Rather than leaving the Burhānīyah barracks following Qayt’s manumission, his notebook was then used by Tamurbāy—assumedly a younger trainee stationed at the same barracks—to put down his very first clumsy scribbles. Thus making sense of what must have been an emblematic rather than exceptional manuscript, this article presents an exercise that is imaginative yet informed by a wide array of Mamluk-Arabic and Mamluk-Turkic parallel sources. A full edition and translation of its two unique Turkic texts is appended
Sacred Tokugawa Authority: Hegemonic Deification in the Domains of the Tokugawa Princes
No full textIn the forested mountains ninety miles north of Tokyo, elaborate processions venerating the deified founder of the Tokugawa government have been held at the sprawling shrine complex of Tōshōgū for over four centuries. My project situates the Tōshōgū shrines and their attendant faith as the central ideological undertaking of the early Tokugawa administration and explores how this initially exclusive politico-religious program was gradually co-opted by non-elites over the course of the early modern period. Drawing on illustrated narrative scrolls, domain histories, gazetteers, and hagiographies, this study examines the contradictions inherent in Tokugawa modes of power production and the spaces they created that enabled a proto-public sphere to emerge within the realm of festival. This dissertation argues that the rapid spread of a network of Tōshōgū shrines and their festivals was driven by a desire to reproduce the elite culture of the mainline Tokugawa. The three Gosanke branch houses were among the first to establish satellite shrines and annual festivals, doing so to craft microcosms of authority that mirrored mainline precedent. Yet the very act of reproducing mainline elite culture in geographical and ideological peripheries generated unintended slippages. Over the 250 years following the first shogun’s death and deification, these branch-family festivals shifted from elite affairs to public spectacles in which townspeople played increasingly active roles. By the end of the Tokugawa period, the name Tōshōgū—by this time synonymous with the Tokugawa clan itself—appeared in commoner parodies, signaling a surprising co-option of symbols once closely guarded by the ruling house.</p