80264 research outputs found
Sort by
Evolutionary History, Extinction, and Environmental Variability Shape the Tropical and Subtropical Diversity Disparity of Terrestrial Mammals
No full textEMBARGO NOTE: This item is embargoed until 2026-08-01Tropical and subtropical moist forests are home to over half of all extant vertebrate species worldwide, yet they face increasing anthropogenic pressures that are degrading multiple facets of their diversity. High tropical species diversity has been hypothesized to have resulted from an evolutionary history of high species diversification in stable environments relative to temperate regions. However, recent studies have found that varying degrees of environmental variability and historical extinction of large-bodied vertebrates likely lead to the uneven distribution of species richness and body sizes among tropical regions (i.e., tropical diversity disparity) on different continents. However, little is known about how evolutionary history, historical extinction, and environmental variability have shaped the geographic differences among tropical regions in other facets of their diversity. This limited knowledge not only hinders our ability to unravel fundamental questions about drivers of biodiversity distributions but also to assess biodiversity changes that have implications for conservation given ongoing anthropogenetic pressure and environmental change.
Hence, to address this research gap, I tested the relative effects of evolutionary and macroecological drivers on 1) community structure, 2) predator-prey interactions, and 3) functional diversity of vertebrate assemblages in tropical and subtropical moist forests globally. I focused on mammals because this well-studied vertebrate class has species-level functional trait data, a well-resolved phylogeny, and community composition data available from both in-situ observations and the reconstructed ranges of extinct species.
First, using in-situ observations from 15 protected tropical forests worldwide, I found that the coupled phylogenetic and functional community structure of ground-dwelling mammals has been shaped by slow niche evolution, and phylogenetic clustering tendencies were predicted by colonization time. Second, I found geographic differences in the dietary breadth of carnivoran predators among 380 large mammal communities in the Neotropical, Afrotropical, and Indomalayan realms, for which speciation rates and present temperature seasonality supported dietary niche generalization while historical extinction led to dietary niche specialization. Thirdly, I found geographic differences in the vulnerability to functional diversity loss of tropical and subtropical moist forest mammals from historical and predicted future extinctions. Functional vulnerability to loss increased in mammal assemblages with slower niche evolution but decreased under greater present environmental variability. By integrating evolutionary and macroecological approaches, this dissertation has unraveled the essential roles of evolutionary history, extinction, and present environmental variability in shaping multiple facets of the diversity of extant forest mammals in the global tropics and subtropics
Wireless Magnetoelectric Communication for Bioelectronics
No full textImplantable bioelectronics hold great potential to improve the diagnosis and treatment of myriad chronic health conditions. Wireless bioelectronic implants that continuously monitor the patient’s physiological state and transmit these data in real-time without tethers would improve diagnosis and facilitate adaptive therapeutic interventions. However, existing wireless communication modalities, such as Bluetooth, radio frequency, and ultrasound, have performance trade-offs regarding implant size, misalignment tolerance, power consumption, and operational distance.
In this dissertation, I present the first wireless backscatter magnetoelectric communication system that features a miniaturized size, ultra-low power consumption, and deep operational distance with high misalignment tolerance. The system leverages two fundamental characteristics of the magnetoelectric transducers. Firstly, magnetoelectric materials generate a backscattered magnetic field when excited by an external field; we exploit these fields as a carrier signal. The magnetoelectric implant consumes negligible power for carrier generation since the external field that induces this signal is generated outside the body. Secondly, the characteristics of the backscattered field can be modulated by an external electric load; thus, we can use load modulation for digital data encoding.
This design enables continuous, real-time data transmission from a mm-sized magnetoelectric.
bioimplant to a custom-designed external transceiver. Our benchtop testing shows that the system can support an operational range within 55 mm while maintaining a bit error rate (BER) of less than 1E-6. Furthermore, the system is robust to translational misalignment; the system performance is maintained with a misalignment of more than 10 mm.
To validate the system reliability in real-life applications and facilitate the clinical
translation of this technology, we tested the system operation in a porcine model. We have shown two demonstrations of in-vivo studies: wireless monitoring of stimulation electrode impedance for cortical brain implants and real-time remote monitoring of electrical intracardiac signals for cardiac implants. The proposed technology could
enable the design of next-generation bioelectronics that feature real-time physiology monitoring for more precise diagnosis, as well as closed-loop systems for personalized therapies
Technology and health inequities in diabetes care: How do we widen access to underserved populations and utilize technology to improve outcomes for all?
Get PDFAbstract Digital health technologies are being utilized increasingly in the modern management of diabetes. These include tools such as continuous glucose monitoring systems, connected blood glucose monitoring devices, hybrid closed-loop systems, smart insulin pens, telehealth, and smartphone applications (apps). Although many of these technologies have a solid evidence base, from the perspective of a person living with diabetes, there remain multiple barriers preventing their optimal use, creating a digital divide. In this article, we describe many of the origins of these barriers and offer recommendations on widening access to digital health technologies for underserved populations living with diabetes to improve their health outcomes
PDRs4All - IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
No full textContext. Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 µm. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. These high-quality data allow for an unprecedentedly detailed view of AIBs.Aims. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR (i.e. the three H2 dissociation fronts), the atomic PDR, and the H II region. Methods. We used JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extracted five template spectra to represent the morphology and environment of the Orion Bar PDR. We investigated and characterised the AIBs in these template spectra. We describe the variations among them here. Results. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. The Orion Bar spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 µm with well-defined profiles. In addition, the spectra display a wealth of weaker features and sub-components. The widths of many AIBs show clear and systematic variations, being narrowest in the atomic PDR template, but showing a clear broadening in the H II region template while the broadest bands are found in the three dissociation front templates. In addition, the relative strengths of AIB (sub-)components vary among the template spectra as well. All AIB profiles are characteristic of class A sources as designated by Peeters (2022, A&A, 390, 1089), except for the 11.2 µm AIB profile deep in the molecular zone, which belongs to class B11.2. Furthermore, the observations show that the sub-components that contribute to the 5.75, 7.7, and 11.2 µm AIBs become much weaker in the PDR surface layers. We attribute this to the presence of small, more labile carriers in the deeper PDR layers that are photolysed away in the harsh radiation field near the surface. The 3.3/11.2 AIB intensity ratio decreases by about 40% between the dissociation fronts and the H II region, indicating a shift in the polycyclic aromatic hydrocarbon (PAH) size distribution to larger PAHs in the PDR surface layers, also likely due to the effects of photochemistry. The observed broadening of the bands in the molecular PDR is consistent with an enhanced importance of smaller PAHs since smaller PAHs attain a higher internal excitation energy at a fixed photon energy. Conclusions. Spectral-imaging observations of the Orion Bar using JWST yield key insights into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 µm AIB emission from class B11.2 in the molecular PDR to class A11.2 in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a “weeding out” of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called ‘grandPAHs’
Advancing Precision and Controllable Molecular Tools for Genetic Engineering and Disease Treatment
No full textEMBARGO NOTE: This item is embargoed until 2026-05-01The emergence of programmable gene editing tools has transformed life sciences by empowering researchers to execute precise and targeted genomic alterations in living cells. The advent of the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (CRISPR-Cas) technology has greatly accelerated genome editing research and applications. However, CRISPR-Cas faces limitations due to the low efficiency of homology-directed repair after Cas nuclease- induced double-stranded DNA breaks (DSBs), which can result in unintended genomic alterations and raise safety concerns. Base editors (BEs), leveraging a catalytically impaired nuclease and a single-stranded DNA deaminase enzyme, offer a promising alternative by facilitating targeted point mutations without requiring DSBs or donor DNA templates. However, the challenge of off-target effects and the lack of temporal control over BE activity when delivered via viral vectors remain significant hurdles.
My thesis describes two projects that I lead: (1) A split and inducible adenine base editor for precise in vivo base editing, and (2) Precision A3G base editors and prime editors for cystic fibrosis modeling and correction. These projects explore the underlying principles of BEs, detailing engineering strategies for achieving small-molecule-controlled base editing in vivo and outline efforts to enhance the specificity of adenine and cytosine base editors. Additionally, these projects involve viral and non-viral delivery methods for BEs, emphasizing their applications in human disease modeling, treatment, and prevention. Lastly, my projects contain applications of prime editing technology, a more versatile gene-editing tool than BE, highlighting its promise for biological research and therapeutic applications
Evolution of Electron-Scale Reconnection Near the Subsolar Point
No full textMagnetic reconnection allows adjacent magnetized plasmas to interact and convert magnetic energy into kinetic energy, energizing the constituent particles of the plasmas. The Magnetospheric Multiscale (MMS) mission, launched by NASA, was designed to study reconnection. The four identical MMS spacecraft in Earth orbit take high-resolution measurements while passing through regions of space plasma where reconnection is occurring. The small-scale, electron-driven physics inside of the central electron diffusion region (EDR) of a reconnection site were not accessible to previous missions before MMS due to limitations of temporal instrument resolution. We present a collection of 32 encounters during which the spacecraft passed through or very near an asymmetric EDR at Earth’s dayside magnetopause. Despite many events occurring near the subsolar magnetopause region, significant differences in upstream plasma conditions still exist, and produce considerable contrasts in the electron velocity space and associated plasma waves. Several distinct types of waves are observed near the EDR, but the biggest fluctuations are seen inside of the thin electron current layer nearest the X-line, which displaces the layer by distances on the order of the layer’s thickness, and produces very localized electric field oscillations of large amplitude (~100 mV/m). Electron-scale turbulence is greatest on the low-density side of asymmetric reconnection, near the electron flow stagnation region along the magnetospheric (low mass density side) separatrix. Generally, we find good agreement with 2D and 2.5D computational models of asymmetric reconnection, although 3D simulations may be required to reproduce the small-scale turbulence seen by MMS. We focus on several EDR events where an in-plane magnetic null (or X-line) reforms in a location separate from a previous null. Flux ropes of varying scale-sizes result. Significant variations in the rate at which magnetic field lines are reconnected on electron timescales can be remotely inferred when MMS is on newly-opened field lines downstream of the X-line, and/or near the EDR. Electron-scale reconnection rate variations, including X-line dissolution and reformation, roughly average out over longer timescales to support a steadier ion-scale reconnection rate. A better understanding of electron-scale reconnection will help with progress towards stable magnetic confinement fusion
Tibetan Life Writings of Adzom Drukpa (1842-1924): Meeting the Lady of the Skies
No full textEMBARGO NOTE: This item is embargoed until 2025-12-01This dissertation analyzes the life writings of Adzom Drukpa (1842-1924) including a Tibetan language autobiography by Adzom Drukpa and a biography of Adzom Drukpa written by his son Gyurme Dorje (1895-1959). Comparison of these texts demonstrates they paint distinct yet resonant portraits of Adzom Drukpa, one emphasizing his human limitations and the other portraying him as a Buddhist deity. While many scholars argue such hagiographical and idealizing conventions in Tibetan life writing obscure its historical qualities, this dissertation examines instead how Adzom Drukpa's life writings creatively balance the human and divine, even while providing specific details about circumstances in eastern Tibet during the tumultuous nineteenth and twentieth centuries. The texts feature accounts of political violence and Buddhist institution building. This dissertation's analysis centers the life writings' depictions of Adzom Drukpa meeting a mysterious lady who appears in the sky. She gives Adzom Drukpa instructions that reverberate throughout his life, including advising Adzom Drukpa not to be a celibate monk but rather to find a woman consort. This dissertation contextualizes Adzom Drukpa's life writings through analyses based in gender, sexuality, and women's studies. Considering the lives and writings of women who were Adzom Drukpa's associates such as Sakya Jetsunma (1836-1896) and Sera Khandro (1892-1940) permits deeper engagement with how Adzom Drukpa's own life writings depict particular women's lives and how these narratives depict gender and sexuality in the context of Buddhist practice. The dissertation also considers Adzom Drukpa's conversation with the lady of the skies using analyses based in religious studies, considering how the narratives depict other paranormal encounters with non-human beings, including animals, ghosts, and a range of deities and demons. Many scholars argue the prevalence of such extraordinary accounts in Tibetan life writing renders the narratives unrealistic. However I examine how these texts depict such events as grounded both in everyday life and in Buddhist philosophy and practice. Like the texts' dual depictions of Adzom Drukpa's character as human and divine, Adzom Drukpa's conversations with the lady of the skies show how these life writings take a creative, considerate, and critical approach to humanity, divinity, and revelation
Unconventional nanophotonic thermal emitters for imaging and energy applications
No full textAll objects above absolute zero temperature emit thermal radiation. Seamless control over this thermal
radiation can unlock solutions to fundamental and technological challenges in imaging, energy harvesting, and utilization. Existing thermal emitter designs are limited by various trade-offs involving spectral selectivity, brightness, and directionality of thermal radiation. In this thesis, I demonstrate unconventional ways to achieve spectral and spatial control over thermal radiation by engineering complex permittivity of the emitter surface. First, using the principles of non-Hermitian physics, a hybrid plasmonic-photonic coupled resonator metasurface is designed and experimentally verified to exhibit strong spectral selectivity at elevated temperatures. I demonstrate that the designed selective thermal emitter on a refractory metal platform surpasses the spectral efficiency limit set by existing thermal emitter designs used in thermophotovoltaics--a solid-state scheme to convert heat into electricity. A transparent, asymmetrically emitting thermal metasurface is realized based on similar concepts. The designed metasurface enhanced the image contrast while performing thermal imaging in high-temperature environments. Further, the k-space of metasurface is explored, revealing additional tunable parameters for engineering thermal radiation. Finally, a way to achieve broadband IR emission/absorption is proposed and demonstrated using aligned carbon nanotube films with anisotropic permittivity tensor
Modal Interactions and Jointed Structures
No full textEMBARGO NOTE: This item is embargoed until 2025-08-01Understanding the nonlinear vibration behavior of structures is critical to ensuring reliability and improving efficiency. Jointed connections, integral to assembled structures, introduce contact and friction resulting in nonlinear vibration behavior. Specifically, properties of linear modal analysis including constant modal frequencies and damping and the decoupling of modes break down in the case of nonlinear vibration. Of interest here, modal interactions occur when multiple nonlinear modes respond simultaneously modifying the total response characteristics, potentially increasing vibration amplitudes and causing structural failures. An understanding of modal interactions is predicated on capturing the nonlinear effects of friction in joints, so this thesis investigates physics-based friction modeling to numerically simulate responses of benchmark jointed structures. To address computational costs, a new method is developed to analyze modal interactions utilizing the developed friction model. In the case of a single mode, frictional contact results in a decrease in modal frequency and an increase in modal damping as the vibration amplitude increases. This behavior is well captured by the proposed friction modeling approach. Beyond the single mode case, the state of the art for modeling modal interactions is thoroughly reviewed, and open challenges are discussed. To better understand modal interactions, a numerical method termed variable phase resonance nonlinear modes (VPRNM) is proposed for tracking superharmonic resonances, a specific type of modal interaction. Superharmonic resonances occur at steady-state when a mode responds in resonance at an integer multiple of the forcing frequency (e.g., with amplitude on the order of the response at the forcing frequency). When a superharmonic resonance occurs simultaneously with a primary resonance, the response is further complicated and termed an internal resonance. Utilizing VPRNM, a reduced order modeling approach (VPRNM ROM) is proposed to reconstruct frequency response curves with significantly reduced computational cost compared to existing approaches. This thesis compares the proposed modeling approaches to new experimental results for the Half Brake-Reuss Beam, a benchmark jointed structure. Overall, this thesis provides significant insights into the phenomena of modal interactions for jointed connections and approaches for computationally efficiently modeling such interactions
Unraveling the spatial imprint of hominin and carnivore accumulations in Early Pleistocene African sites
Get PDFReconstructions of palimpsest formation and dynamics in Early Pleistocene African archaeological deposits have undergone significant advances thanks to taphonomic research. However, the spatial imprint of different agents implicated in most of these accumulations still needs to be addressed. We hypothesize that different site formation dynamics may yield diverse spatial distributions of archaeological remains, reflecting the intervention of different agents (i.e., hominins, felids, hyaenids) in palimpsests. This study aims to investigate the spatial patterns of archaeological remains in a selected sample of Early Pleistocene accumulations with the goal of understanding and characterizing their spatial dynamics. Building on previous taphonomic interpretations of twelve paradigmatic archaeological deposits from Olduvai Bed I (FLK Zinj 22 A, PTK 22 A, DS 22B, FLK N 1–2 to 5, FLK NN 3, DK 1–3) and Koobi Fora (FxJj50, FxJj20 East and FxJj20 Main), we explore the spatial patterns of remains statistically and use hierarchical clustering on principal components analysis (HCPC) to group the highest-density spots at these sites based on a number of spatial variables. The results of this approach show that despite sharing a similar inhomogeneous pattern, anthropogenic sites and assemblages where carnivores played the main role display fundamentally different spatial features. Both types of spatial distributions also show statistical differences from modern hunter-gatherer campsites. Additional taphonomic particularities and differing formation processes of the analyzed accumulations also appear reflected in the classifications. This promising approach reveals crucial distinctions in spatial imprints related to site formation and agents’ behavior, prompting further exploration of advanced spatial statistical techniques for characterizing archaeological intra-site patterns