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In a poorly understood yet recurring phenomenon, communities occupying diverse settings within a region may undertake large-scale migrations that cannot be easily attributed to single variables such as climate change. As a result, the study of these movements has increasingly focused on the distinct histories of localities to address how they may have articulated as large-scale abandonments. We adopt this micro-history perspective on the fourteenth to fifteenth century depopulation of a large portion of the North American Midwest and Southeast, popularly referred to as the Vacant Quarter. Our research on the Middle Cumberland drainage within the Vacant Quarter suggests that a significant exodus began slowly ca. 1300 CE; then, it accelerated extremely rapidly in the first half of the fifteenth century CE. This genesis of this trajectory seems to be related to a pattern of severe droughts, but it was brought to a close by social and demographic challenges such as endemic conflict and adverse health conditions. [ABSTRACT FROM AUTHOR]

GaN has been demonstrated as an important wide-bandgap semiconductor in many applications, especially in optoelectronic and high-power electronics. Two-dimensional (2D) GaN, with increased bandgap compared to the bulk counterpart, not only amplifies existing functionalities but also opens up fresh possibilities for compact electronics. Although several methods have recently been developed to synthesize 2D GaN, their practical application is hampered by either harsh growth conditions (e.g., high temperature and ultrahigh vacuum) or unsatisfactory performance due to grain boundaries. Here, we report the realization of few-nanometer-thick GaN crystals via in situ atomic substitution of layered GaS flakes at a relatively low temperature (590°C). GaN with tunable thickness from 50 nm down to 0.9 nm (~2 atomic layers) is achieved by applying the atomic substitution reaction to GaS with different numbers of layers. The obtained ultrathin GaN flakes retain the morphology inherited from the GaS flakes and show high crystallinity by transmission electron microscopy (TEM) characterization, while the thickness of GaN decreases to about 72% of the corresponding GaS flakes from the atomic force microscopy characterization. A time-dependent mechanism study reveals both horizontal and vertical conversion paths, with Ga2S3 as intermediate. Photoluminescence (PL) spectroscopy measurements show that the band edge PL of 2D ultrathin GaN is blue-shifted as compared with bulk GaN, suggesting that the bandgap increases with the decrease in thickness. This study provides a promising method for obtaining ultrathin, high-crystallinity GaN with tunable thicknesses, utilizing a minimal thermal budget. This breakthrough lays a solid foundation for future investigations into fundamental physics and potential device applications. [ABSTRACT FROM AUTHOR]

In this work, ambient pressure x-ray photoelectron spectroscopy (APXPS) is used to study the initial stages of water adsorption on vanadium oxide surfaces. V 2p, O 1s, C 1s, and valence band XPS spectra were collected as a function of relative humidity in a series of isotherm and isobar experiments. Experiments were carried out on two VO2 thin films on TiO2 (100) substrates, prepared with different surface cleaning procedures. Hydroxyl and molecular water surface species were identified, with up to 0.5 ML hydroxide present at the minimum relative humidity, and a consistent molecular water adsorption onset occurring around 0.01% relative humidity. The work function was found to increase with increasing relative humidity, suggesting that surface water and hydroxyl species are oriented with the hydrogen atoms directed away from the surface. Changes in the valence band were also observed as a function of relative humidity. The results were similar to those observed in APXPS experiments on other transition metal oxide surfaces, suggesting that H2O–OH and H2O–H2O surface complex formation plays an important role in the oxide wetting process and water dissociation. Compared to polycrystalline vanadium metal, these vanadium oxide films generate less hydroxide and appear to be more favorable for molecular water adsorption. [ABSTRACT FROM AUTHOR]

Efficient energy-level alignment is crucial for achieving high performance in organic electronic devices. Because the electronic structure of an organic semiconductor is significantly influenced by its molecular orientation, comprehensively understanding the molecular orientation and electronic structure of the organic layer is essential. In this study, we investigated the interface between a 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) hole injection layer and a zinc-phthalocyanine (ZnPc) p-type organic semiconductor. To determine the energy-level alignment and molecular orientation, we conducted in situ ultraviolet and X-ray photoelectron spectroscopies, as well as angle-resolved X-ray absorption spectroscopy. We found that the HAT-CN molecules were oriented relatively face-on (40°) in the thin (5 nm) layer, whereas they were oriented relatively edge-on (62°) in the thick (100 nm) layer. By contrast, ZnPc orientation was not significantly altered by the underlying HAT-CN orientation. The highest occupied molecular orbital (HOMO) level of ZnPc was closer to the Fermi level on the 100 nm thick HAT-CN layer than on the 5 nm thick HAT-CN layer because of the higher work function. Consequently, a considerably low energy gap between the lowest unoccupied molecular orbital level of HAT-CN and the HOMO level of ZnPc was formed in the 100 nm thick HAT-CN case. This may improve the hole injection ability of the anode system, which can be utilized in various electronic devices. [ABSTRACT FROM AUTHOR]

We grew highly textured phase pure VO2 thin films on c-plane Al2O3 substrates with different oxygen partial pressure. X-ray absorption and photoemission spectroscopy confirm the identical valence state of vanadium ions despite the different oxygen pressure during the deposition. As the O2 flow rate increases, the [010] lattice parameter for monoclinic VO2 was reduced and coincidently distinctive changes in the metal-semiconductor transition (MST) and transport behaviors were observed despite the identical valence state of vanadium in these samples. We discuss the effect of the oxygen partial pressure on the monoclinic structure and electronic structure of VO2, and consequently the MST. [ABSTRACT FROM AUTHOR]

Reports on the measurement of the elementally resolved electronic structure on a thin film silicon oxynitride gate dielectric used in commercial device fabrication using soft x-ray emission and absorption spectroscopies. Measurement of the valence and conduction band partial density of states in the interfacial region of both the nitrogen and oxygen states.

The article offers information on the Mississippian Four-Crested-Bird (FCB) marine shell gorgets from Tennessee and Alabama. Topics discussed include design of the gorgets, distinctions between the FCB gorgets and other Mississippian gorgets, and questions that remain to be examined further about FCB gorgets.

The article focuses on the finding of the three shell gorgets masterpieces between the 1930s and 1950s in a cave near the confluence of the Caney Fork and Cumberland Rivers in Smith County, Tennessee. The article also mentions about the collection of antique guns as well as antique statues collection of Lillard D. Yeaman.

The article discusses explorer John Wesley Powell and his workmen uncovered the Nashville Scalloped Triskele gorgets from a mound on the Bowling and Bosley Farm site in Nashville, Tennessee on September 1877. It mentions that George Lankford examined the distribution of Native American folklore relating to the asterism called the Pleiades.

The article reviews the exhibition "Ancestors: Ancient Native American Stone Sculpture of Tennessee held at the Tennessee State Museum in Nashville, Tennessee from 2015 to 2016.

In organic photovoltaics (OPVs), determining the energy-level alignment of a donor and an acceptor is particularly important since the interfacial energy gap between the highest occupied molecular orbital (HOMO) level of a donor and the lowest unoccupied molecular orbital (LUMO) level of an acceptor (EDHOMO–EALUMO) gives the theoretical maximum value of the open-circuit voltage (VOC). To increase the EDHOMO–EALUMO, non-fullerene acceptors, which have a lower electron affinity (EA) than C60, are receiving increasing attention. In this study, we investigated the energy-level alignment at the interface of a boron chloride subphthalocyanine (SubPc) donor and a halogenated SubPc (Cl6SubPc) acceptor using soft X-ray spectroscopy techniques. The estimated EDHOMO–EALUMO of Cl6SubPc/SubPc was 1.95 eV, which was significantly higher than that of 1.51 eV found at the interface of C60/SubPc. This increased EDHOMO–EALUMO was the origin of the enhanced VOC in OPVs. Additionally, we studied the molecular orientation of Cl6SubPc using angle-dependent X-ray absorption spectroscopy. The highly disordered Cl6SubPc molecules result in low carrier mobility, which contributes to the lower short-circuit current density of the Cl6SubPc acceptor OPVs than the C60 acceptor OPVs. [ABSTRACT FROM AUTHOR]

To date, scale-up fabrication of transition metal dichalcogenide (TMD-) based 2D/2D or 2D/3D heterostructures with specific functionalities is still a great challenge. This study, for the first time, reports on the controllable synthesis of large-area and continuous 2D/3D semiconductor/metal heterostructures consisting of monolayer MoS2 and bulk MoO2 with unique electrical and optical properties via one-step, vapor-transport-assisted rapid thermal processing. The temperature-dependent electrical transport measurements reveal that the 2D/3D MoS2-MoO2 heterostructure grown on SiO2/Si substrates exhibits metallic phase, while this heterostructure becomes a low-resistance semiconductor when it is grown on fused silica, which is attributed to the different degrees of sulfurization on different substrates, as being confirmed by surface potential analyses. Photoluminescence measurements taken on the MoS2-MoO2 heterostructures reveal the simultaneous presence of both negative trions and neutral excitons, while only neutral excitons are observed in the monolayer MoS2. The trion-binding energy is determined to be ≈27 meV, and the trion signal persists up to 330 K, indicating significant stability at room temperature. This work not only provides a new platform for understanding the intriguing physics in TMD-based heterostructures but also enables the design of more complicated devices with potential applications in nanoelectronics and nanophotonics. [ABSTRACT FROM AUTHOR]

Doped BiVO4 is a promising photoelectrochemical water splitting anode, whose activity is hampered by poor charge transport. Here we use a set of X-ray spectroscopic methods to probe the origin and nature of localized electron states in W:BiVO4. Furthermore, using the polarized nature of the X-rays, we probe variations in the electronic structure along the crystal axes. In this manner, we reveal aspects of the electronic structure related to electron localization and observations consistent with conductivity anisotropy between the ab-plane and c-axis. We verify that tungsten substitutes as W6+ for V5+ in BiVO4. This is shown to result in the presence of inter-band gap states related to electrons at V4+ sites of e symmetry. The energetic position of the states in the band gap suggest that they are highly localized and may act as recombination centres. Polarization dependent X-ray absorption spectra reveal anisotropy in the electronic structure between the ab-plane and c-axis. Results show the superior hybridization between V 3d and O 2p states, higher V wavefunction overlap and broader conduction bands in the ab-plane than in the c-axis. These insights into the electronic structure are discussed in the context of existing experimental and theoretical reports regarding charge transport in BiVO4. [ABSTRACT FROM AUTHOR]

The mixed-phase nature of P25 TiO2 (85 % anatase/15 % rutile) plays a key role in the high H2 production rates shown by Au/P25 TiO2 photocatalysts in alcohol/water systems. However, a full understanding of the synergistic charge transfer mechanisms between the TiO2 polymorphs that drive the high rates is yet to be realised. Here, we deconstruct P25 TiO2 into its component phases, functionalise the phases with Au nanoparticles and explore charge transfer in Au/TiO2 systems using EPR spectroscopy. EPR spectroscopy and photocatalytic data provide direct evidence that electrons excited across the rutile band gap move to anatase lattice traps through interfacial surface sites, which decreases electron-hole pair recombination and increases charge carrier availability for photoreactions. In particular, three-phase interfacial sites between Au, anatase and rutile appear to be H2 evolution 'hot spots'. The results isolate the origin of high photocatalytic H2 production rates seen in Au/P25 TiO2 systems. [ABSTRACT FROM AUTHOR]

The Electrical Systems Division at the NASA Kennedy Space Center has developed and deployed an agent-based tool to monitor the space shuttle's ground processing telemetry stream. The application, the NASA Engineering Shuttle Telemetry Agent (NESTA), increases situational awareness for system and hardware engineers during ground processing of the shuttle's subsystems. The agent provides autonomous monitoring of the telemetry stream and automatically alerts system engineers when predefined criteria have been met. Efficiency and safety are improved through increased automation. Sandia National Labs' Java Expert System Shell is employed as the rule engine. The shell's predicate logic lends itself well to capturing the heuristics and specifying the engineering rules of this spaceport domain. The declarative paradigm of the rule-based agent yields a highly modular and scalable design spanning multiple subsystems of the shuttle. Several hundred monitoring rules have been written thus far with corresponding notifications sent to shuttle engineers. This article discusses the rule-based telemetry agent used for space shuttle ground processing and explains the problem domain, development of the agent software, benefits of AI technology, and deployment and sustaining engineering of the product. [ABSTRACT FROM AUTHOR]

The articles reports on the NESTA software tool which was developed to enhance insight into space shuttle ground processing and improve situational awareness at the NASA Kennedy Space Center. NESTA assists the Launch Processing System (LPS) by continuously monitoring the data going through the real-time telemetry system. LPS-processed measurements are distributed on a local area network as the Shuttle Data Stream, offering real-time data telemetry from shuttle ground-processing and launch operations. NESTA performs the function of a software agent for the NASA engineer.

Ironsand is an abundant and inexpensive magnetic mineral resource. However, the magnetic properties of unprocessed ironsand are often inadequate for any practical applications. In this work, the applicability of ironsand for use as a component in a soft magnetic composite for large-scale inductive power transfer applications was investigated. After magnetic separation, the chemical, structural and magnetic properties of ironsand sourced from different locations were compared. Differences observed in the DC magnetic properties were consistent with changes in the chemical compositions obtained from X-ray Absorption Near-Edge Spectroscopy (XANES), which suggests varying the titanohematite to titanomagnetite content. Increased content in titanomagnetite and magnetic permeability correlated well with the total Fe content in the materials. The best-performing ironsand with the highest permeability and lowest core losses was used alongside Mn,Zn-Ferrite particles (ranging from ∼100 μ m to 2 mm) to fabricate toroid cores with varying magnetic material loading. It was shown that ironsand can be used to replace up to 15 wt.% of the magnetic materials with minimal impact on the composite magnetic performance, thus reducing the cost. Ironsand was also used as a supporting material in a single-rail wireless power transfer system, effectively increasing the power transfer, demonstrating potential applications to reduce flux leakage. [ABSTRACT FROM AUTHOR]

The article offers information on the use of mussel shells by potters from the Cumberland River in Middle Tennessee in the history. It discusses the discovery of effigy bowls created using mussel shells in the region along with mussel shell spoons which were depicted by iconographers as Crested Bird due to the design.

Stoichiometric CaVO3 (CVO) thin films of various thicknesses were grown on single crystal SrTiO3 (STO) (001) substrates using a pulsed electron-beam deposition technique. The CVO films were capped with a 2.5 nm STO layer. We observed a temperature driven metal-insulator transition (MIT) in CVO films with thicknesses below 4 nm that was not observed in either thick CVO films or STO films. The emergence of this MIT can be attributed to the reduction in effective bandwidth due to a crossover from a three-dimensional metal to a two-dimensional insulator. The insulating phase was only induced with a drive current below 0.1 μA. X-ray absorption measurements indicated different electronic structures for thick and very thin films of CVO. Compared with the thick film (∼60 nm), thin films of CVO (2-4 nm) were more two-dimensional with the V charge state closer to V4+. [ABSTRACT FROM AUTHOR]