Vertical motions that accompany the passage of the lithosphere over a mantle hotspot can shed light on the nature of the hotspot and its effect on the lithosphere. However, quantifying the temporal ...vertical and spatial extent, is challenging due to the paucity of evidence in the geological record. Here, we utilize dense seismic and well data covering the intersection of the Great Meteor Hotspot (GMH) track with the U.S. Atlantic continental margin to constrain the surface expression of the hotspot passage under the lithosphere. The continuous sedimentary record of the eastern North American margin during its passage over the hotspot allows determination of the timing, magnitude, width and rate of denudation. We find that a ∼300 km wide region was denuded by up to 850 m between ∼97 and 86 Ma, ∼10 m.y. after the passage of the GMH. Stratigraphic relationships suggest a decaying rock uplift rate with time and no subsequent sagging. The broad, long‐lasting, and delayed uplift was modeled as a surface manifestation of either sub‐lithospheric mantle depletion, permanently eroded base of the continental lithosphere, or intrusions of depleted magma. We consider sub‐lithospheric depletion to be the most likely cause, based on seismic imaging results.
Key Points
A continental lithosphere surface response to its passage over a hotspot is quantified via stratigraphic analysis of a passive margin
Ten m.y. after its passage over the Great Meteor Hotspot, the Georges Bank Basin was denuded by up to 850 m across a 300 km wide zone
Asthenosphere depletion, lithospheric thinning or intrusion of depleted material triggered uplift and the consequent denudation
Herein, a reliable surface-enhanced Raman scattering (SERS)-active substrate has been prepared by synthesizing gold nanoparticles (AuNPs)-decorated MoS2 nanocomposite. The AuNPs grew in situ on the ...surface of MoS2 nanosheet to form efficient SERS hot spots by a spontaneous redox reaction with tetrachloroauric acid (HAuCl4) without any reducing agent. The morphologies of MoS2 and AuNPs-decorated MoS2 nanosheet were characterized by TEM, HRTEM, and AFM. The formation of hot spots greatly depended on the ratio of MoS2 and HAuCl4. When the concentration of HAuCl4 was 2.4 mM, the as-prepared AuNPs@MoS2-3 nanocomposite exhibited a high-quality SERS activity toward probe molecule due to the generated hot spots. The spot-to-spot SERS signals showed that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1362, 1511, and 1652 cm–1) of Rhodamine 6G were about 20%, which displayed good uniformity and reproducibility. The AuNPs@MoS2-based substrate was reliable, sensitive, and reproducible, which showed great potential to be an excellent SERS substrate for biological and chemical detection.
•Field test of cleaning robot’s moving shadow on operating PV string.•Much larger power drop for landscape modules than portrait.•Larger power drop for full-cell modules than half-cut.•No cell ...hotspots created.•Bypass diode heated when module stopped, but not while moving.
PV cleaning robots cast a shadow on the PV modules which they are cleaning, if used in daylight. The shadow affects the electrical characteristics (current and voltage) of the module string, and could potentially also create hot spots in modules' cells or bypass diodes. The severity of these effects depends on the layout of cells and bypass diodes and the module’s orientation, among other factors. In this study we tested a commercial cleaning robot on strings of two kinds of PV modules with different cell formats, connected to a grid-tied inverter. It was found that the string power was greatly reduced when modules were in landscape orientation, but barely affected in portrait orientation. The robot shadow caused slightly greater power reduction for full-cell than half-cut modules. While the robot was in motion, no heating of cells or bypass diodes was observed, although diode heating did occur if the robot stopped on a module. For the worst case of full-cell landscape modules, a simplified estimate of the energy loss due to one robot pass was roughly equivalent to 0.16% of the string’s daily energy production. The results suggest that if PV cleaning robots are used in daylight, the power loss from their shadow could be almost eliminated by installing modules in portrait orientation.
The most prominent hotspot in the South Atlantic is Tristan da Cunha, which is widely considered to be underlain by a mantle plume. But the existence, location and size of this mantle plume have not ...been established due to the lack of regional geophysical observations. A passive seismic experiment using ocean bottom seismometers aims to investigate the lithosphere and upper mantle structure beneath the hotspot. Using the Ps receiver function method we calculate a thickness of 5 to 8km for the oceanic crust at 17 ocean-bottom stations deployed around the islands. Within the errors of the method the thickness of the oceanic crust is very close to the global mean. The Tristan hotspot seems to have contributed little additional magmatic material or heat to the melting zone at the mid-oceanic ridge, which could be detected as thickened oceanic crust. Magmatic activity on the archipelago and surrounding seamounts seems to have only affected the crustal thickness locally. Furthermore, we imaged the mantle transition zone discontinuities by analysing receiver functions at the permanent seismological station TRIS and surrounding OBS stations. Our observations provide evidence for a thickened (cold) mantle transition zone west and northwest of the islands, which excludes the presence of a deep-reaching mantle plume. We have some indications of a thinned, hot mantle transition zone south of Tristan da Cunha inferred from sparse and noisy observations, which might indicate the location of a Tristan mantle plume at mid-mantle depths. Sp receiver functions image the base of lithosphere at about 60 to 75km beneath the islands, which argues for a compositionally controlled seismological lithosphere-asthenosphere boundary beneath the study area.
•Receiver functions reveal no significant crustal thickening in the surrounding of the Tristan da Cunha hot spot.•The mantle transition zone to the NW of Tristan da Cunha is thickened and cool.•The mantle transition zone is potentially thinned to the south/southwest of Tristan da Cunha.•A thickness of 60 to 75km argues for a compositional control on the seismological lithosphere beneath Tristan da Cunha.
The Northern Appalachian Anomaly (NAA) is an intense, laterally localized (400 km diameter) low‐velocity anomaly centered in the asthenosphere beneath southern New England. Its maximum shear velocity ...contrast, at 200 km depth, is about 10%, and its compressional‐to‐shear velocity perturbation ratio is about unity, values compatible with it being a modern thermal anomaly. Although centered close to the track of the Great Meteor hot spot, it is not elongated parallel to it and does not crosscut the cratonic margin. In contrast to previous explanations, we argue that the NAA's spatial association with the hot spot track is coincidental and that it is caused by small‐scale upwelling associated with an eddy in the asthenospheric flow field at the continental margin. That the NAA is just one of several low‐velocity features along the eastern margin of North America suggests that this process may be globally ubiquitous.
Key Points
The Northern Appalachian Anomaly is an intense low‐velocity anomaly in the asthenosphere just east of the cratonic margin
Its seismic attributes are consistent with a modern thermal origin related to small‐scale upwelling at the continental margin
Its spatial association with the Great Meteor hot spot track is coincidental
Hot spotting is a problem in photovoltaic (PV) systems that reduces panel power performance and accelerates cell degradation. In present day systems, bypass diodes are used to mitigate hot spotting, ...but it does not prevent hot spotting or the damage it causes. This paper presents an active hot-spot detection method to detect hot spotting within a series of PV cells, using ac parameter characterization. A PV cell is comprised of series and parallel resistances and parallel capacitance, which are affected by voltage bias, illumination, and temperature. Experimental results have shown that when a PV string is under a maximum power point tracking control, hot spotting in a single cell results in a capacitance increase and dc impedance increase. The capacitance change is detectable by measuring the ac impedance magnitude in the 10-70 kHz frequency range. An impedance value change due to hot spotting can be detected by monitoring one high-frequency measurement in the capacitive region and one low-frequency measurement in the dc impedance region. Alternatively, the dc impedance can also be calculated using dc operating point measurements. The proposed hot-spot detection method can be integrated into a dc-dc power converter that operates at the panel or subpanel level.
Outgassing of sulfur (as SO2) is one of the principal hazards posed by volcanic eruptions. However, S emission potentials of most volcanoes globally are poorly constrained due to a short ...observational record and an incomplete understanding of the magmatic processes that influence pre‐eruptive S concentrations. Here, we use a compilation of published and new data from melt inclusions (MIs)—which can preserve magmatic S concentrations prior to eruptive degassing—from the Iceland hotspot to evaluate the effects of mantle melting and crustal magmatic processes on the S budgets of Icelandic melts. We use MI data to estimate S emission potentials (ΔSmax, in ppm S) for 73 eruptions from 22 of Iceland's presently active ∼33 volcanic systems. We show that the S systematics of Icelandic melts are strongly regulated by the sulfide solubility limit. Sulfide‐saturated conditions during lower‐degree mantle melting, prevalent at off‐rift zones, likely explains observed decoupling between S and Cl. During magmatic differentiation, a local maximum in modeled sulfide solubility occurs in evolved basalts (4–6 wt.% MgO), coinciding with highest MI S concentrations. Highest ΔSmax values (2,100–2,600 ppm) are found in the Hekla 1913 CE, Eldgjá 939 CE, and Surtsey 1963–1967 CE eruptions in the South Iceland Volcanic Zone. Our results extend the record of volcanic sulfur emissions back in time and can be used to assess volcanic gas hazards at Icelandic volcanoes where no direct measurements are available. Broadly, the results underline the governing role of sulfide saturation during melting and magma differentiation in controlling the eruptible S contents of Icelandic magmas.
Key Points
Maximum eruptible S contents (ppm S) are estimated for 73 Icelandic eruptions based on melt inclusion data
Pre‐eruptive S contents are mostly controlled by sulfide saturation during both melting and crustal magmatic differentiation
Icelandic basalts often erupt at compositions close to a compositional maximum in sulfide solubility, leading to relatively high S emissions
The Yellowstone supervolcano is one of the largest active continental silicic volcanic fields in the world. An understanding of its properties is key to enhancing our knowledge of volcanic mechanisms ...and corresponding risk. Using a joint local and teleseismic earthquake P-wave seismic inversion, we revealed a basaltic lower-crustal magma body that provides a magmatic link between the Yellowstone mantle plume and the previously imaged upper-crustal magma reservoir. This lower-crustal magma body has a volume of 46,000 cubic kilometers, ∼4.5 times that of the upper-crustal magma reservoir, and contains a melt fraction of ∼2%. These estimates are critical to understanding the evolution of bimodal basaltic-rhyolitic volcanism, explaining the magnitude of CO2 discharge, and constraining dynamic models of the magmatic system for volcanic hazard assessment.
The efficient and low-energy dehydrogenation process of methylcyclohexane catalyzed by Pt/Al2O3 is a crucial step in hydrogen storage using the organic chemical hydride method, aiming to avoid ...catalyst deactivation at high temperatures. This study utilized SiC as a catalyst support to facilitate the dehydrogenation of methylcyclohexane (MCH) using Pt/Al2O3 catalysts. Additionally, a multi-field coupled numerical model was developed to elucidate the observed temperature increase phenomenon during the process. Experimental results demonstrate that the efficiency of the microwave reactor surpasses that of traditional thermal reactors, with the catalyst exhibiting characteristics of resistance to coking and high activity under microwave irradiation. Finally, based on the above results, we discuss the impact of "hot spots" during microwave heating on heterogeneous gas-phase catalytic reactions, and by dynamically adjusting the sample position in the microwave field, the adverse effects of fixed "hot spots" accumulation on the catalytic process are mitigated.
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•Feasibility of microwave enhancement of methylcyclohexane dehydrogenation.•Microwave heating can significantly reduce the carbon deposition rate of catalyst.•Dynamic heating avoids hot spot accumulation and further improves catalyst activity.
A novel algorithm which combined the merits of the clustering strategy and the compressive sensing-based (CS-based) scheme was proposed in this paper. The lemmas for the relationship between any two ...adjacent layers, the optimal size of clusters, the optimal distribution of the cluster head (CH), and the corresponding proofs were presented first. In addition, to alleviate the "hot spot problem" and reduce the energy consumption resulted from the rotation of the role of CHs, a third role of backup CH (BCH) as well as the corresponding mechanism to rotate the roles between the CH and BCH were proposed. Subsequently, the energy-efficient compressive sensing-based clustering routing (EECSR) protocol was presented in detail. Finally, extensive simulation experiments were conducted to evaluate its energy performance. Comparisons with the existing clustering algorithms and the CS-based algorithm verified the effect of EECSR on improving energy efficiency and extending the lifespan of wireless sensor networks.
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