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Essays in Dynamic Factor Models with Smooth Structural Changes
No full textThis dissertation develops novel econometric approaches to improve macroeconomic and financial forecasting in the presence of structural instability. Motivated by the observation that traditional factor-augmented regression models often assume time-invariant relationships, which are inadequate during periods of gradual economic change, this research advances dynamic forecasting methods that incorporate smooth structural shifts in high-dimensional environments. The first essay introduces a time-varying extension of the three-pass regression filter (3PRF) by incorporating locally adaptive rolling window estimation. This approach addresses the instability of forecast coefficients by allowing them to evolve smoothly over time. A data-driven method for selecting the optimal window size is developed, balancing forecast bias and variance. The resulting model demonstrates superior out-of-sample forecasting performance compared to static and full-sample alternatives in both simulated and empirical settings. The second essay proposes a time-varying factor-augmented regression model that allows for smoothly changing factor loadings and forecast coefficients. Using boundary-corrected kernel principal component analysis, latent factors are estimated in a localized manner, enabling the model to adapt to evolving economic regimes. Theoretical results establish the consistency and asymptotic normality of the proposed estimators. Empirical applications to U.S. macroeconomic data highlight the advantages of accommodating smooth parameter changes in both the factor structure and the predictive relationship. Together, these essays contribute to the growing literature on forecasting with high-dimensional data under structural change. By integrating time-varying estimation techniques into dynamic factor models, this dissertation provides robust tools for real-time forecasting in nonstationary environments and offers practical guidance for empirical economists and policymakers
[Palladium-decabismuth(4+)]-tetrakis(tetrachloridoaluminate) Cluster Compound, [Pd@Bi10][AlCl4]4: Synthesis, Crystal Structure, and Electronic Structure
No full textBlack, needle-like single crystals of [Pd@Bi10][AlCl4]4 were synthesized in a one-pot reaction between PdCl2, Bi, and BiCl3 at 180 °C in the Lewis acidic ionic liquid (LAIL) medium [BMIm]Cl∙4.2AlCl4 (BMIm = 1-n-butyl-3-methylimidazolium). Single-crystal X-ray diffraction revealed that the compound crystallizes in the triclinic space group P (Formula presented.) with the unit cell parameters a = 11.0233(5) Å, b = 26.1892(14) Å, c = 26.2687(14) Å, α = 90.842(2)°, β = 92.1940(10)°, γ = 91.164(2)°, closely matching its platinum-containing analog. The structure features pentagonal antiprismatic [Pd@Bi10]4+ cluster cations charge-balanced by tetrahedral [AlCl4]− anions. Bonding and charge analysis reveal unoptimized Pd–Bi and strong Bi–Bi covalent interactions consistent with electronegativity trends and the previously reported host–guest model. Electronic structure calculations performed with the TB-LMTO-ASA program show that [Pd@Bi10][AlCl4]4 exhibits semiconducting behavior, suggesting a bandgap opening of 0.71 eV
Complex Structural Disorder in Thermoelectric Zintl Phases Eu21M4As18 (M = Mn, Zn)
No full textTernary Zintl arsenides Eu21Mn4As18, Eu21Zn4As18, and quaternary solid solution Eu21Mn4As15.4Sb2.6 have been synthesized and structurally characterized using single-crystal X-ray diffraction. Eu21Mn4As18 and Eu21Mn4As15.4Sb2.6 are reported here for the first time, whereas new structural insights are presented for the previously known Eu21Zn4As18. All title compounds crystallize in the Sr21Mn4Sb18 structure type (space group C2/m) and exhibit pronounced positional disorder affecting both cationic and anionic sites. This includes disorder on Eu atoms and As2 dimers, as well as split M (M = Mn, Zn) sites within the anionic [M8As22]48− clusters. Despite the disorder, the Zintl concept remains applicable to the novel Eu21Mn4As18 phase, and the charge-balanced composition can be expressed as 2 × Eu21Mn4As18 = [Eu2+]42{[Mn8As22]48-}{[As2]4-}3[As3-]8. Electronic structure calculations performed on the disorder-free model of Eu21Zn4As18 predict a bandgap of ≈1.1 eV
Revealing the Water Structure at Neutral and Charged Graphene/Water Interfaces through Quantum Simulations of Sum Frequency Generation Spectra
No full textThe structure and dynamics of water at charged graphene interfaces fundamentally influence molecular responses to electric fields with implications for applications in energy storage, catalysis, and surface chemistry. Leveraging the realism of the MB-pol data-driven many-body potential and advanced path-integral quantum dynamics, we analyze the vibrational sum frequency generation (vSFG) spectrum of graphene/water interfaces under varying surface charges. Our quantum simulations reveal a distinctive dangling OH peak in the vSFG spectrum at neutral graphene, consistent with recent experimental findings yet markedly different from those of earlier studies. As the graphene surface becomes positively charged, interfacial water molecules reorient, decreasing the intensity of the dangling OH peak as the OH groups turn away from the graphene. In contrast, water molecules orient their OH bonds toward negatively charged graphene, leading to a prominent dangling OH peak in the corresponding vSFG spectrum. This charge-induced reorganization generates a diverse range of hydrogen-bonding topologies at the interface driven by variations in the underlying electrostatic interactions. Importantly, these structural changes extend into deeper water layers, creating an unequal distribution of molecules with OH bonds pointing toward and away from the graphene sheet. This imbalance amplifies bulk spectral features, underscoring the complexity of many-body interactions that shape the molecular structure of water at charged graphene interfaces
Effects of Nitro-Substitution on the Spectroscopic and Self-Assembly Properties of BODIPY Dyes
Get PDFA series of boron dipyrromethene (BODIPY) dyes were nitrated in high yields using nitronium tetrafluoroborate at positions 2, 3, and 2,6 of the BODIPY core. This method allows for the regioselective nitration of the pyrrolic positions under milder conditions than previously reported methods. The photophysical properties and electronic transitions of these BODIPYs were investigated by using UV-vis spectroscopy, fluorescence spectroscopy, and density-functional theory (DFT) calculations. The introduction of one nitro group dramatically increases the dipole moment of the molecule, induces marked blue shifts in the absorption and emission bands, decreases the molar absorptivity, and increases the Stokes shifts of the BODIPYs. When a second nitro group is symmetrically introduced, the calculated dipole moments of the BODIPYs decrease in both the ground and excited states. Our studies show that the spectroscopic and self-assembly properties of nitro-substituted BODIPYs are highly dependent on solvent polarity and polarizability. In a polar organic solvent, nitro-substitution tends to quench the characteristic fluorescence of BODIPYs, while in a nonpolar solvent, significantly higher absolute fluorescence quantum yields are observed. On the other hand, aggregates are formed in aqueous solution, as observed by atomic force microscopy (AFM). Our results suggest a potential application of nitro-BODIPYs as polarity sensors
Multiple fluid interactions recorded in tourmaline from the Dorothy China Clay Pit, St. Austell, Cornwall, U.K.
No full textElaborately zoned blue-grey tourmaline from the Dorothy China Clay Pit, St. Austell, Cornwall, U.K. reveals a history of hydrothermal activity in an open system. At least five distinct generations of tourmaline are identified within a single crystal. They are characterised by complex replacement textures displaying dissolution and reprecipitation features and compositional variations identified through optical microscopy, BSE imaging and EPMA. The Li-rich, alkali-poor rossmanite core of the grain is considered the generation 1 tourmaline. Generation 2 tourmaline is comprised of Na-richer species, especially elbaite. Generation 3, partially replacing the core, is composed of Fe-richer tourmaline species, mostly schorl and foitite. Generation 4, primarily Fe-rich dravite, forms an Mg-enriched rim around generations 1-3. Generation 5 fluor-schorl replaces all previous tourmaline generations and parts of the quartz matrix. Each generation corresponds to a chemically distinct fluid event suggested by dissolution textures and compositionally differing overgrowths. Infiltration of B-bearing, neutral to acidic fluids facilitated the growth of tourmaline. These fluids contained varying amounts of major elements reflected in the changing tourmaline composition. Dissolution likely occurred because of an increase in fluid pH or a change in major cation compositions. Generation 1 tourmaline crystallized in equilibrium with a Li-rich, Na-poor granitic host rock. From generations 1 to 3, fluids generally increased in Na and Fe while decreasing in Al and Li. Fluids increased in F at generation 3, followed by the influx of more oxidizing, Mg-enriched fluids at generation 4. The final generation 5 represents a return to Fe-And F-richer compositions. The episodic changes in fluid composition preserved by each generation of tourmaline records fluid infiltration. These differing compositions may reflect, in part, progression of kaolinisation of the host granites or changes in the magmatic hydrothermal fluids. The St. Austell kaolinite deposits formed from hydrothermal alteration of the preexisting granite through multiple stages of reactive fluid infiltration as recorded in tourmaline
Compound-Specific Isotope Records of Dust Provenance and Hydroclimate in the North Pacific and Marginal Seas of East Asia: Integrating n-Alkane δ13C and δD with Standardized Analytical Frameworks
Get PDFThis dissertation presents advancements in compound-specific isotope analysis (CSIA) through methodological innovation and paleoclimate reconstruction in Central and East Asia. Utilizing plant wax n-alkanes from International Ocean Discovery Program (IODP) and Ocean Drilling Program (ODP) sediment cores, this research reconstructs atmospheric circulation shifts responding to tectonic evolution and climate transitions since the Late Miocene.
Chapter 1 investigates hydrogen isotope compositions (δDwax) from IODP U1430 (Sea of Japan), ODP 886, and ODP 1208 (North Pacific) to trace dust provenance and hydroclimate changes since ~13 Ma. Results reveal persistently segmented source-to-sink systems: the Sea of Japan dominated by westerly input from northern Tibetan Plateau, Gobi Desert, and Eastern China, while the North Pacific integrates broader Asian interior material. Three phases emerge: Late Miocene deuterium depletion (13–6.2 Ma), Mio-Pliocene transition with increased δDwax (6.2–3.8 Ma), and Plio-Pleistocene decline corresponding to Northern Hemisphere glaciation.
Chapter 2 combines carbon isotope analysis (δ13Cwax) with published Sr-Nd provenance tracers to identify atmospheric organic matter sources. The δ13Cwax values show consistent shifts toward more negative values, demonstrating increasing C3-dominated arid interior contributions from the Gobi Desert, Hexi Corridor, Taklimakan Desert, and Qaidam Basin. Arid interior C3 signatures dominated despite localized C4 expansion in humid lowlands, reflecting atmospheric circulation reorganization during global cooling.
Chapter 3 introduces Chroma, a MATLAB package streamlining gas chromatograph flame ionization detector analysis for hydrocarbon indices (CPI, ACL, Paq). The tool enables automated peak identification and integration, reducing subjectivity and enhancing reproducibility, demonstrated through Qaidam Basin n-alkane data.
Chapter 4 presents SINC (Standardized Isotope Normalization for CSIA), a MATLAB toolkit for GC-IRMS data processing with improved drift correction, scale normalization, and uncertainty propagation. SINC enhances data comparability and interpretability for robust paleoenvironmental reconstructions.
These geochemical records provide new insights into vegetation dynamics, hydrological variability, and sediment provenance. The computational advances create a scalable platform for future CSIA work, improving inter-laboratory consistency and enabling sophisticated paleoclimate proxy applications through enhanced resolution and reliability of compound-specific isotope records
A Decentralized Primal-Dual Method With Quasi-Newton Tracking
No full textThis paper considers the decentralized optimization problem of minimizing a finite sum of strongly convex and twice continuously differentiable functions over a fixed-connected undirected network. A fully decentralized primal-dual method (DPDM) and its generalization (GDPDM), which allows for multiple primal steps per iteration, are proposed. In our methods, both primal and dual updates use second-order information obtained by quasi-Newton techniques which only involve matrix-vector multiplication. Specifically, the primal update applies a Jacobi relaxation step using the BFGS approximation for both computation and communication efficiency. The dual update employs a new second-order correction step. We show that the decentralized local primal updating direction on each node asymptotically approaches the centralized quasi-Newton direction. Under proper choice of parameters, GDPDM including DPDM has global linear convergence for solving strongly convex decentralized optimization problems. Our numerical results show both GDPDM and DPDM are very efficient compared with other state-of-the-art methods for solving decentralized optimization
Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806-20 Magnetar Giant Flare
No full textThe origin of heavy elements synthesized through the rapid neutron capture process (r-process) has been an enduring mystery for over half a century. J. Cehula et al. recently showed that magnetar giant flares, among the brightest transients ever observed, can shock heat and eject neutron star crustal material at high velocity, achieving the requisite conditions for an r-process. A. Patel et al. confirmed an r-process in these ejecta using detailed nucleosynthesis calculations. Radioactive decay of the freshly synthesized nuclei releases a forest of gamma-ray lines, Doppler broadened by the high ejecta velocities v ≳ 0.1c into a quasi-continuous spectrum peaking around 1 MeV. Here, we show that the predicted emission properties (light curve, fluence, and spectrum) match a previously unexplained hard gamma-ray signal seen in the aftermath of the famous 2004 December giant flare from the magnetar SGR 1806-20. This MeV emission component, rising to peak around 10 minutes after the initial spike before decaying away over the next few hours, is direct observational evidence for the synthesis of ∼10−6 M☉ of r-process elements. The discovery of magnetar giant flares as confirmed r-process sites, contributing at least ∼1%-10% of the total Galactic abundances, has implications for the Galactic chemical evolution, especially at the earliest epochs probed by low-metallicity stars. It also implicates magnetars as potentially dominant sources of heavy cosmic rays. Characterization of the r-process emission from giant flares by resolving decay line features offers a compelling science case for NASA’s forthcoming COSI nuclear spectrometer, as well as next-generation MeV telescope missions
Beyond the Madrasah: Digital Pedagogies and Nigerian Yoruba Muslim Women\u27s Engagement with Islamic Knowledge
No full textThis paper explores how digital pedagogies are reshaping the landscape of Islamic education among Nigerian Muslim women, with a primary focus on Yoruba communities in Southern Nigeria. Historically, Islamic learning in Nigeria has been rooted in traditional institutions, notably the madrasa, characterized by face-to-face instruction and rigid gender norms. However, the proliferation of digital technologies - particularly online madrasas, WhatsApp study groups, Zoom-based Qur’anic classes, and Islamic mobile applications - has significantly altered women’s access to religious knowledge. Utilizing ethnographic evidence and qualitative interviews, this interdisciplinary study examines how digital platforms enhance accessibility, overcome sociocultural barriers, and enable Nigerian Yoruba Muslim women to engage with a global Islamic discourse. The analysis underscores the benefits of digital transformation, including increased autonomy in learning, flexibility, and expanded religious authority, while critically addressing challenges such as digital literacy gaps, infrastructural disparities, and concerns about content authenticity. By applying perspectives from digital pedagogy, Islamic educational traditions, and gender studies, this research highlights how technological innovations facilitate a dynamic, responsive form of Islamic scholarship that meets contemporary educational needs. Finally, the study outlines avenues for future research, emphasizing the need for deeper investigations into equitable access and sustained integration of digital and traditional Islamic learning frameworks