Surface Hot Spot Research Articles

Basal Mantle Flow Over LLSVPs Explains Differences in Pacific and Indo‐Atlantic Hotspot Motions

AbstractSurface hotspot motions are approximately a factor of two faster in the Pacific than the Indo‐Atlantic, and the Indo‐Atlantic large low shear velocity province (LLSVP) appears to be significantly taller than the Pacific LLSVP. Hypothesizing that surface hotspot motions are correlated with the motion of plume sources on the upper surface of chemically distinct, intrinsically dense LLSVPs, we use 3D spherical mantle convection models to compute the velocity of plume sources and compare with observed surface hotspot motions. No contrast in the mean speed of Pacific and Indo‐Atlantic hotspots is predicted if the LLSVPs are treated as purely thermal anomalies and plume sources move laterally across the core‐mantle boundary. However, when LLSVP topography is included in the model, the predicted hotspot speeds are, on average, faster in the Pacific than the Indo‐Atlantic, even when modest topography is assigned to both LLSVPs (e.g., 100–300 km). The difference in mean hotspot speed increases to a factor of two for larger and laterally variable LLSVP topography estimated from seismic tomographic model S40RTS (up to 1,100–1,500 km for the Indo‐Atlantic region vs. 700–1,400 km for the Pacific region) and our results also broadly reproduce the convergence of Pacific hotspots toward the center of the Pacific LLSVP. These largescale features of global hotspot motions are only reproduced when ambient mantle material flows over large, relatively stable topographical features, suggesting that LLSVPs are chemically distinct and intrinsically dense relative to ambient mantle material.

Mid-mantle seismic scatterers beneath the Samoan hotspot

We analyze teleseismic array data of deep and intermediate-depth earthquakes in the Fiji-Tonga-Kermadec region recorded at seismic networks at the west coast of US and Alaska with the aim of mapping seismic scatterers in the lower mantle and in the upper mantle transition zone beneath the Samoan hotspot. Short period and broadband waveform data are array-processed in order to detect coherent but anomalous phases in the P coda up to nearly 120 s after direct P waves and locate where they arrive from. Updating the data set reported in our previous study (Kaneshima and Helffrich, 2010; Kaneshima, 2018; Kaneshima, 2019), we examine nine scatterers near the hotspot, seven in the lower mantle and two in the transition zone, with the main focus on three lower mantle scatterers nearest to the hotspot at 1000 to 1200 km depths. We observe S-to-P waves generated from the three lower mantle scatterers for earthquakes with a wide range of hypocenters from 17°S to 24°S, while hardly any signs of corresponding P-to-P scattering waves are observed. The pulse shapes of the S-to-P waves from the three scatterers are simple and their pulse widths do not significantly differ from those of direct P waves when the signal quality is high enough. The geometry of the scatterers suggested by these observations is a steeply dipping sheet-like structure with the thickness less than several kilometers. The material consisting of the sheet needs to have a Vs value at least several percent lower than the surrounding mantle, as required by the amplitudes of S-to-P scattering waves relative to P, which is typically several percent. The low Vs anomaly of basaltic rocks relative to pyrolite under the shallow lower mantle conditions may be consistent with the observations (Wang et al., 2020). Seismic tomography models suggest that the nine scatterers tend to be located around the edge of a plume that ascends from the Pacific LLSVP to the Samoan hotspot. Numerical simulations of ascending plumes from a thermo-chemical pile at the bottom of the mantle show that the plumes tend to rise preferentially in the vicinity of the edge of the pile. Other simulations also show that blobs of recycled former oceanic crust subducting to the bottom of mantle are entrained into a plume and stretched vertically to a significant degree, consistently with the images suggested by geochemical studies of OIB. The scattering observations therefore may elucidate the structure of entrained basaltic blobs on their way of returning back to the surface hotspot.

Proton acceleration from thin foils by extremely short PW laser pulse

In the context of current efforts to compress PW-level laser pulses to an order of 10 fs, the 3D optimization particle-in-cell (PIC) simulations of proton acceleration have been performed to maximize the proton energy cutoffs using CH2 foils as an example. This was complemented by a simple theoretical model to which PIC simulation results were qualitatively compared. Such a model accounted for a fast increase in a backside surface hot spot, transition of plasma expansion from isothermal regime to the adiabatic one, and effect of target semitransparency that is important for the considered extremely short pulses. It was found that the twofold increase in a shortened laser pulse focal spot size is fraught with a loss in the maximum energy of accelerated protons even when the pulse energy is the same. The PIC simulation optimization study revealed the optimal target thicknesses and the corresponding maximum energies of accelerated protons for shortened PW pulses, and also showed that advantage from their use to increase the proton energy occurs only if the focusability at the target is not worsened.

Main protease inhibitors and drug surface hotspots for the treatment of COVID-19: A drug repurposing and molecular docking approach

Here, drug repurposing and molecular docking were employed to screen approved MPP inhibitors and their derivatives to suggest a specific therapeutic agent for the treatment of COVID-19. The approved MPP inhibitors against HIV and HCV were prioritized, while RNA dependent RNA Polymerase (RdRp) inhibitor remdesivir including Favipiravir, alpha-ketoamide were studied as control groups. The target drug surface hotspot was also investigated through the molecular docking technique. Molecular dynamics was performed to determine the binding stability of docked complexes. Absorption, distribution, metabolism, and excretion analysis was conducted to understand the pharmacokinetics and drug-likeness of the screened MPP inhibitors. The results of the study revealed that Paritaprevir (−10.9 kcal/mol) and its analog (CID 131982844) (−16.3 kcal/mol) showed better binding affinity than the approved MPP inhibitors compared in this study, including remdesivir, Favipiravir, and alpha-ketoamide. A comparative study among the screened putative MPP inhibitors revealed that the amino acids T25, T26, H41, M49, L141, N142, G143, C145, H164, M165, E166, D187, R188, and Q189 are at potentially critical positions for being surface hotspots in the MPP of SARS-CoV-2. The top 5 predicted drugs (Paritaprevir, Glecaprevir, Nelfinavir, and Lopinavir) and the topmost analog showed conformational stability in the active site of the SARS-CoV-2 MP protein. The study also suggested that Paritaprevir and its analog (CID 131982844) might be effective against SARS-CoV-2. The current findings are limited to in silico analysis and lack in vivo efficacy testing; thus, we strongly recommend a quick assessment of Paritaprevir and its analog (CID 131982844) in a clinical trial.

Prediction of potential inhibitors for RNA-dependent RNA polymerase of SARS-CoV-2 using comprehensive drug repurposing and molecular docking approach

The pandemic prevalence of COVID-19 has become a very serious global health issue. Scientists all over the world have been seriously attempting in the discovery of a drug to combat SARS-CoV-2. It has been found that RNA-dependent RNA polymerase (RdRp) plays a crucial role in SARS-CoV-2 replication, and thus could be a potential drug target. Here, comprehensive computational approaches including drug repurposing and molecular docking were employed to predict an effective drug candidate targeting RdRp of SARS-CoV-2. This study revealed that Rifabutin, Rifapentine, Fidaxomicin, 7-methyl-guanosine-5′-triphosphate-5′-guanosine and Ivermectin have a potential inhibitory interaction with RdRp of SARS-CoV-2 and could be effective drugs for COVID-19. In addition, virtual screening of the compounds from ZINC database also allowed the prediction of two compounds (ZINC09128258 and ZINC09883305) with pharmacophore features that interact effectively with RdRp of SARS-CoV-2, indicating their potentiality as effective inhibitors of the enzyme. Furthermore, ADME analysis along with analysis of toxicity was also undertaken to check the pharmacokinetics and drug-likeness properties of the two compounds. Comparative structural analysis of protein-inhibitor complexes revealed that the amino acids Y32, K47, Y122, Y129, H133, N138, D140, T141, S709 and N781 are crucial for drug surface hotspot in the RdRp of SARS-CoV-2.

Stereoscopic detection of hot spots in superfluid 4He (He II) for accelerator-cavity diagnosis

Superconducting radio-frequency (SRF) cavities cooled by superfluid 4He (He II) are building blocks of many modern particle accelerators due to their high quality factor. However, Joule heating from sub-millimeter surface defects on cavities can lead to cavity quenching, which limits the maximum acceleration gradient of the accelerators. Developing a non-contacting detection technology to accurately locate these surface hot spots is the key to improve the performance of SRF cavities and hence the accelerators. In a recent proof-of-concept experiment (Phys. Rev. Applied, 11, 044003 (2019)), we demonstrated that a molecular tagging velocimetry (MTV) technique based on the tracking of a He2* molecular tracer line created nearby a surface hot spot in He II can be utilized to locate the hot spot. In order to make this technique practically useful, here we describe our further development of a stereoscopic MTV setup for tracking the tracer line’s motion in three-dimensional (3D) space. We simulate a quench spot by applying a transient voltage pulse to a small heater mounted on a substrate plate. Images of the drifted tracer line, taken with two cameras from orthogonal directions, are used to reconstruct the line profile in 3D space. A new algorithm for analyzing the 3D line profile is developed, which incorporates the finite size effect of the heater. We show that the center location of the heater can be reproduced on the substrate surface with an uncertainty of only a few hundred microns, thereby proving the practicability of this method.

East African topography and volcanism explained by a single, migrating plume

Anomalous topographic swells and Cenozoic volcanism in east Africa have been associated with mantle plumes. Several models involving one or more fixed plumes beneath the northeastward migrating African plate have been suggested to explain the space-time distribution of magmatism in east Africa. We devise paleogeographically constrained global models of mantle convection and, based on the evolution of flow in the deepest lower mantle, show that the Afar plume migrated southward throughout its lifetime. The models suggest that the mobile Afar plume provides a dynamically consistent explanation for the spatial extent of the southward propagation of the east African rift system (EARS), which is difficult to explain by the northeastward migration of Africa over one or more fixed plumes alone, over the last ≈45 Myr. We further show that the age-progression of volcanism associated with the southward propagation of EARS is consistent with the apparent surface hotspot motion that results from southward motion of the modelled Afar plume beneath the northeastward migrating African plate. The models suggest that the Afar plume became weaker as it migrated southwards, consistent with trends observed in the geochemical record.

A systematic study of soft X-ray pulse profiles of magnetars in quiescence

Abstract Magnetars are neutron stars with extremely high surface magnetic fields. They show diverse X-ray pulse profiles in the quiescent state. We perform a systematic Fourier analysis of their soft X-ray pulse profiles. We find that most magnetars have a single-peaked profile and hence have low amplitudes of the second Fourier harmonics (A2). On the other hand, the pulsed fraction (PF) spreads over a wide range. We compared the results with theoretical profiles assuming various surface hotspot asymmetries, viewing geometries, and beaming functions. We found that a single value of the intensity ratio r between two antipodal hotspots is unable to reproduce the observed distribution of A2 and PF for all magnetars. The inferred r is probably anticorrelated with the thermal luminosity, implying that high-luminosity magnetars tend to have two symmetric hotspots. Our results are consistent with theoretical predictions, for which the existence of an evolving toroidal magnetic field breaks the symmetry of the surface temperature.

Estimation the tumor temperature in magnetic nanoparticle hyperthermia by infrared thermography: Phantom and numerical studies

The treatment of cancer by hyperthermia requires prediction, monitoring and control of the temperature within the tumor. Infrared thermography (IRT) was presented in this paper as a noninvasive temperature monitoring method used in magnetic nanoparticle hyperthermia (MNH). We tried to use this surface temperature measurement method to get information about the intratumoral temperature. Experimental in vitro MNH studies were performed on gel tumor-tissue phantoms which were constructed to simulate the real tumor and overlying healthy tissue. Magnetic nanoparticles were dispersed uniformly in the tumor part of phantom. During the process of in vitro MNH, an alternating magnetic field (AMF) was applied for heating, an IR thermal camera monitored the surface temperature and a fiber optical sensor measured the tumor temperature. A numerical finite element models of thermal analyses was built to simulate the MNH phantom experiments. Both experimental and numerical results indicate that the temperature difference between the surface hot spot and the tumor inner will reach a fixed value while the heating is going on. This value is correlated to factors such as heat generation of hyperthermia, size and depth of the tumor. A regression functions is established to describe the relationship, which is helpful for fast tumor inner temperature estimation by infrared thermography.

Anomalous mantle transition zone beneath the Yellowstone hotspot track

The origin of the Yellowstone and Snake River Plain volcanism has been strongly debated. The mantle plume model successfully explains the age-progressive volcanic track, but a deep plume structure has been absent in seismic imaging. Here I apply diffractional tomography to receiver functions recorded at USArray stations to map high-resolution topography of mantle transition-zone discontinuities. The images reveal a trail of anomalies that closely follow the surface hotspot track and correlate well with a seismic wave-speed gap in the subducting Farallon slab. This observation contradicts the plume model, which requires anomalies in the mid mantle to be confined in a narrow region directly beneath the present-day Yellowstone caldera. I propose an alternative interpretation of the Yellowstone volcanism. About 16 million years ago, a section of young slab that had broken off from a subducted spreading centre in the mantle first penetrated the 660 km discontinuity beneath Oregon and Idaho, and pulled down older stagnant slab. Slab tearing occurred along pre-existing fracture zones and propagated northeastward. This reversed-polarity subduction generated passive upwellings from the lower mantle, which ascended through a water-rich mantle transition zone to produce melting and age-progressive volcanism. The mantle transition zone in the western United States is perturbed along a path that mirrors the line of the Yellowstone hotspot track at the surface, according to analysis of tomographic data.

SN 1986J VLBI. IV. The Nature of the Central Component

Abstract We report on Very Large Array measurements between 1 and 45 GHz of the evolving radio spectral energy distribution (SED) of SN 1986J, made in conjunction with very long baseline interferometry (VLBI) imaging. The SED of SN 1986J is unique among supernovae, and shows an inversion point and a high-frequency turnover. Both are due to the central component seen in the VLBI images, and both are progressing downward in frequency with time. The optically thin spectral index of the central component is almost the same as that of the shell. We fit a simple model to the evolving SED consisting of an optically thin shell and a partly absorbed central component. The evolution of the SED is consistent with that of a homologously expanding system. Both components are fading, but the shell is fading more rapidly. We conclude that the central component is physically inside the expanding shell, and not a surface hotspot central only in projection. Our observations are consistent with the central component being due to interaction of the shock with the dense and highly structured circumstellar medium that resulted from a period of common-envelope evolution of the progenitor. However, a young pulsar-wind nebula or emission from an accreting black hole can also not be ruled out at this point.

Abstract AP03: OVARIAN CANCER AND PULP AND PAPER MANUFACTURING IN THE US: A GEOSPATIAL ANALYSIS

Abstract The goals of this research were to: 1) utilize geographic and geostatistical methods available in geographic information systems (GIS) software to gain an in-depth understanding of the spatial distribution of ovarian cancer incidence rates, at national, state and county levels; and2) based on patterns identified from the first goal, conduct a preliminary assessment of the hypothesized association between ovarian cancer occurrence and pulp and paper manufacturing. We used the following approaches: 1) exploratory spatial data analysis of 2008-2012 ovarian cancer incidence at the county level – choropleth mapping, trend surface analysis, spatial autocorrelation and hot spot analysis;2) exploratory spatial data analysis of pulp and paper production sites, using EPA's Toxic Release Inventory data from 1988-2012;3) geographically weighted regression analysis to examine the relationship between ovarian cancer incidence and toxic emissions to air and surface water; and4) preliminary fate and transport modeling of a case study area (Wisconsin) to examine river effluent and atmospheric dispersion of chemical by-products. Results indicate that there is a strong north-to-south trend (i.e. higher rates in the north) in ovarian cancer incidence at both state and county levels. This coincides with historically higher numbers of pulp and paper mills in northern states. Exceptions to this overall trend are statistically significant multi-county clusters of high rates in Georgia and Alabama, both of which have high levels of pulp and paper production. The hypothesis is weakly supported by geographically weighted regression, when migration patterns are taken into account. In conclusion, this research indicates that there is some support, at an ecological level, for the hypothesized association between ovarian cancer incidence rates and pulp and paper production. Citation Format: Carol L. Hanchette, PhD. OVARIAN CANCER AND PULP AND PAPER MANUFACTURING IN THE US: A GEOSPATIAL ANALYSIS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr AP03.

Fermi surface topology and hot spot distribution in the Kondo lattice systemCeB6

We present high-resolution angle-resolved photoemission spectroscopy studies of trivalent CeB6 and divalent BaB6 rare-earth hexaborides. We find that the Fermi surface electronic structure of CeB6 consists of large oval-shape pockets around the X points of the Brillouin zone, while the states around the zone centre 'Gamma' point are strongly renormalized. Our first-principles calculations agree with data around the X points, but not at the 'Gamma' points, indicating areas of strong renormalization located around 'Gamma'. The Ce quasi-particle states participate in formation of hotspots at the Fermi surface, while the incoherent f states hybridize and lead to the emergence of dispersive features absent in non-f counterpart BaB6. These experimental and theoretical results provide a new understanding of rare-earth hexaboride materials.

Freeform illumination lens design using composite ray mapping

We develop a new ray mapping approach to address the surface error and hot spot issues in designing a freeform total internal reflection (TIR) lens for nonrotational uniform illumination. Our proposed ray mapping approach partitions the source intensity distribution in the peripheral regions using the traditional spherical coordinate system to design the freeform TIR surfaces and in the central regions using the modified spherical coordinate system to design the freeform refractive surface. This new design method will reduce the surface error in the current ray mapping methods, therefore improving the illumination uniformity significantly. In addition, the freeform lens designed with this approach is much more robust than the lenses designed using other ray mapping methods.

Experimental and Modeling Analysis of the Thermal Behavior of an Autothermal C3H8Catalytic Partial Oxidation Reformer

In this work, a spatially resolved sampling technique is applied to characterize the performance of a C3H8 CPO reformer and to compare it with that of a CH4 reformer. The case of Rh-coated honeycomb catalysts is examined. The axial profiles show that higher temperatures are reached in C3H8 CPO, especially at the reactor inlet. Surface hot-spot temperatures around 950 °C lead the catalyst to rapid loss of activity. A detailed model analysis is also applied to better understand the reasons for the observed differences of the thermal behavior. On one hand, the heat release via oxidation reactions is controlled by O2 mass transfer rate and thus proportional to O2 inlet concentration, which is ∼20% higher in the C3H8/air mixture at equal C/O ratio. On the other hand, while CH4 steam reforming is partly chemically controlled, C3H8 steam reforming is mainly limited by gas–solid diffusion. Thus, a less efficient balance between exo- and endothermic reactions occurs in the case of C3H8 CPO, and this results in muc...

Structure–Function Analysis of the Short Splicing Variant Carboxypeptidase Encoded by Drosophila melanogaster silver

Drosophila melanogaster silver gene is the ortholog of the coding gene of mammalian carboxypeptidase D (CPD). The silver gene gives rise to eight different splicing variants of differing length that can contain up to three homologous repeats. Among the protein variants encoded, the short form 1B alias DmCPD1Bs (D. melanogaster CPD variant 1B short) is necessary and sufficient for viability of the fruit fly. It has one single repeat, it is active against standard peptide substrates, and it is localized to the secretory pathway. In this work, the enzyme was found as a monomer in solution and as a homodimer in the crystal structure, which features a protomer with an N-terminal 311-residue catalytic domain of α/β-hydrolase fold and a C-terminal 84-residue all-β transthyretin-like domain. Overall, DmCPD1Bs conforms to the structure of N/E-type funnelins/M14B metallopeptidases, but it has two unique structural elements potentially involved in regulation of its activity: (i) two contiguous surface cysteines that may become palmitoylated and target the enzyme to membranes, thus providing control through localization, and (ii) a surface hot spot targetable by peptidases that would provide a regulatory mechanism through proteolytic inactivation. Given that the fruit fly possesses orthologs of only two out of the five proteolytically competent N/E-type funnelins found in higher vertebrates, DmCPD1Bs may represent a functional analog of at least one of the missing mammalian CPs.

Insights into the recruitment of the NMD machinery from the crystal structure of a core EJC-UPF3b complex.

In mammals, Up-frameshift proteins (UPFs) form a surveillance complex that interacts with the exon junction complex (EJC) to elicit nonsense-mediated mRNA decay (NMD). UPF3b is the component of the surveillance complex that bridges the interaction with the EJC. Here, we report the 3.4 A resolution crystal structure of a minimal UPF3b-EJC assembly, consisting of the interacting domains of five proteins (UPF3b, MAGO, Y14, eIF4AIII, and Barentsz) together with RNA and adenylyl-imidodiphosphate. Human UPF3b binds with the C-terminal domain stretched over a composite surface formed by eIF4AIII, MAGO, and Y14. Residues that affect NMD when mutated are found at the core interacting surfaces, whereas differences between UPF3b and UPF3a map at peripheral interacting residues. Comparison with the binding mode of the protein PYM underscores how a common molecular surface of MAGO and Y14 recognizes different proteins acting at different times in the same pathway. The binding mode to eIF4AIII identifies a surface hot spot that is used by different DEAD-box proteins to recruit their regulators.

Soft X-ray polarization in thermal magnetar emission

Emission spectra from magnetars in the soft X-ray band likely contain a thermal component emerging directly from the neutron star surface. However, the lack of observed absorption-like features in quiescent spectra makes it difficult to directly constrain physical properties of the atmosphere. We argue that future X-ray polarization measurements represent a promising technique for directly constraining the magnetar magnetic field strength and geometry. We construct models of the observed polarization signal from a finite surface hotspot, using the latest NS atmosphere models for magnetic fields B = 4 x 10^13--5 x 10^14 G. Our calculations are strongly dependent on the NS magnetic field strength and geometry, and are more weakly dependent on the NS equation of state and atmosphere composition. We discuss how the complementary dependencies of phase-resolved spectroscopy and polarimetry might resolve degeneracies that currently hamper the determination of magnetar physical parameters using thermal models.

Geographic correlation between hot spots and deep mantle lateral shear-wave velocity gradients

Hot spot volcanism may originate from the deep mantle in regions exhibiting the Earth’s most pronounced lateral S-wave velocity gradients. These strong gradient regions display an improved geographic correlation over S-wave velocities to surface hot spot locations. For the lowest velocities or strongest gradients occupying 10% of the surface area of the core–mantle boundary (CMB), hot spots are nearly twice as likely to overlie the anomalous gradients. If plumes arise in an isochemical lower mantle, plume initiation should occur in the hottest (thus lowest velocity) regions, or in the regions of strongest temperature gradients. However, if plume initiation occurs in the lowest velocity regions of the CMB lateral deflection of plumes or plume roots are required. The average lateral deflections of hot spot root locations from the vertical of the presumed current hot spot location ranges from ∼300 to 900 km at the CMB for the 10–30% of the CMB covered by the most anomalous low S-wave velocities. The deep mantle may, however, contain strong temperature gradients or be compositionally heterogeneous, with plume initiation in regions of strong lateral S-wave velocity gradients as well as low S-wave velocity regions. If mantle plumes arise from strong gradient regions, only half of the lateral deflection from plume root to hot spot surface location is required for the 10–30% of the CMB covered by the most anomalous strong lateral S-wave velocities. We find that strong gradient regions typically surround the large lower velocity regions in the base of the mantle, which may indicate a possible chemical, in addition to thermal, component to these regions.

Paleolatitudes of the Kerguelen hotspot: new paleomagnetic results and dynamic modeling

The Kerguelen Plateau, a Large Igneous Province in the southern Indian Ocean, was formed as a product of the Kerguelen hotspot in several eruptive phases during the last 120 Myr. We obtained new paleolatitudes for the central and northern Kerguelen Plateau from paleomagnetic investigations on basalts, which were drilled during ODP Leg 183 to the Kerguelen Plateau–Broken Ridge. The paleolatitudes coincide with paleolatitudes from previous investigations at the Kerguelen Plateau and Ninetyeast Ridge (the track of the Kerguelen hotspot) and indicate a difference between paleolatitudes and present position at 49°S of the Kerguelen hotspot. We show that true polar wander, the global motion between the mantle and the rotation axis, cannot explain this difference in latitudes. We present numerical model results of plume conduit motion in a large-scale mantle flow and the resulting surface hotspot motion. A large number of models all predict southward motion between 3° and 10° for the Kerguelen hotspot during the last 100 Myr, which is consistent with our paleomagnetic results.