Strong HF Research Articles

Realizing in-situ preparation of ZnAl layered double hydroxide film on titanium alloy through one-step hydrothermal reaction

A hydrothermal process was proposed for in-situ preparation of ZnAl layered double hydroxides with nitrate (ZnAl-NO3-LDHs) on a Ti6Al4V titanium alloy. To destroy the dense and stable TiO2 film on the titanium alloy, mild NH4F instead of strong HF was used as a F− ion source in the growth solution of the hydrothermal reaction, and ammonia water instead of urea was used to adjust the pH value, both of which helped to realize in situ growth of ZnAl-LDHs films on titanium alloys. The structure and morphology of the LDHs films were characterized using X-ray diffraction and scanning electron microscopy. The corrosion resistance and stability of the LDHs films were evaluated using potentiodynamic polarization curves and immersion tests. The results show that a uniform ZnAl-NO3-LDHs film was formed in situ on the titanium alloy with the help of NH4F and NH3·H2O. The formation mechanism of ZnAl-NO3-LDHs on the TC4 titanium alloy was determined. The ZnAl-NO3-LDHs film improved the corrosion resistance of the titanium alloys and has the potential to improve anti-fouling properties by loading anti-fouling substances; however, the laminates of the LDHs fell off after long-term immersion in marine environments.

Dissolved neodymium and hafnium isotopes and rare earth elements in the Congo River Plume: Tracing and quantifying continental inputs into the southeast Atlantic

The Congo River is the second largest river by discharge in the world and a major source of element inputs into the South Atlantic Ocean. Yet, the element fluxes and transport mechanisms across and beyond its estuary and their impacts on the marine distribution and cycling of many major and trace elements are not well understood. We present the first combined dissolved neodymium (Nd) and hafnium (Hf) isotope and rare earth element (REE) concentration distributions following the Congo River plume along its flow path off the West African coast and along a connected offshore latitudinal section at 3°S. The Congo River freshwater itself is characterized by extraordinarily high Nd and Hf concentrations of up to 4000 pmol/kg and 54 pmol/kg, and by Nd (εNd) and Hf (εHf) isotope compositions that range between −15.6 and −16.4 and between 0.35 and −1.4, respectively. Our near- and offshore data indicate that at salinities above 23 conservative mixing of Congo-derived Nd and Hf concentrations and isotopic signatures with ambient surface seawater occurs for at least 1000 km to the northwest of the river mouth. This demonstrates a large spatial extent of the influence of the Congo plume on trace metal distributions in the eastern south Atlantic surface waters. A comparison between dissolved Nd and Hf fluxes from the Congo River and the shelf zone estimated based on radium isotope compositions indicate that release from Congo-derived particulate phases likely balances strong estuarine REE and Hf removal in the low salinity zone. The combined riverine and shelf zone flux for Nd is almost twice as high as that estimated for the Amazon River, despite that the Amazon discharge is about five times higher than that of the Congo River. Even the offshore Nd flux estimated for the 3 °S transect based on radium isotope compositions still corresponds to ∼40% of the Congo-shelf-zone flux and reaches 150 ± 50 Mg/year for Nd. Moreover, intermediate waters below the plume are strongly affected by exchange with particulate inputs from the Congo River given that Nd isotope signatures are inconsistent with values expected from large-scale water mass mixing and instead support unradiogenic Nd release either from sinking or deposited Congo-derived detrital material. Deep and bottom water isotopic signatures are also slightly affected by interaction with particles and benthic Nd release.

Petrogenesis and Mo prospecting significance of Sadaigoumen granites on the northern margin of the North China Craton

The Sadaigoumen porphyry Mo deposit lies on the northern margin of the North China Craton. Molybdenum mineralization occurs mainly as veins and veinlets, or is disseminated within alkali feldspar granite and granite porphyry, which yield weighted-mean 206Pb/238U ages (±2σ) of 243.7 ± 1.6 to 242.2 ± 2.0 Ma and 240.0 ± 1.7 Ma, respectively. ReOs dating of molybdenite from Stage 3 mineralization yields an isochron age of 238.0 ± 1.9 Ma. The Sadaigoumen ore-related granites have petrological, mineralogical, and geochemical characteristics of I-type granite. Ore-related granites exhibit low (87Sr/86Sr)i ratios of 0.710256–0.711463, negative εNd(t) values of −16.4 to −15.4 with corresponding TDM2 (Nd) ages of 2061–1870 Ma, and negative εHf(t) values of −21.2 to −11.2 with corresponding TDM2 (Hf) ages of 2614–1983 Ma, indicating that the primary magma was derived by partial melting of ancient lower crust. In chondrite- and primitive-mantle-normalized trace element diagrams, the Sadaigoumen ore-related granites are characterized by moderate enrichment of light rare earth elements (REE) relative to heavy REE, moderate to strong negative Nb, Ta, Zr, Hf, and Ti anomalies, and increasing Rb/Sr ratios with decreasing Sr content, all attributed to fractional crystallization. Fractionation of amphibole, muscovite, and possibly minor biotite and garnet (and/or zircon) produced the variations in most elements. Together with the regional geology, the data imply that the Sadaigoumen ore-related granites and corresponding mineralization formed in a syn-collision to post-collision transitional setting during the Early–Middle Triassic. These fractionated Triassic alkaline granites or syenogranites potentially contain new porphyry Mo deposits.

Atomic level termination for passivation and functionalisation of silicon surfaces.

Chemical treatments play an essential role in the formation of high quality interfaces between materials, including in semiconductor devices, and in the functionalisation of surfaces. We have investigated the effects of hydrogen and fluorine termination of (100)-orientation silicon surfaces over a range of length scales. At the centimetre scale, lifetime measurements show clean silicon surfaces can be temporarily passivated by a short treatment in both HF(2%) : HCl(2%) and HF(50%) solutions. The lifetime, and hence surface passivation, becomes better with immersion time in the former, and worse with immersion time in the latter. At the nanometre scale, X-ray photoelectron spectroscopy and atomic force microscopy show treatment with strong HF solutions results in a roughened fluorine-terminated surface. Subsequent superacid-derived surface passivation on different chemically treated surfaces shows considerably better passivation on surfaces treated with HF(2%) : HCl(2%) compared to HF. Lifetime data are modelled to understand the termination in terms of chemical and field effect passivation at the centimetre scale. Surfaces passivated with Al2O3 grown by atomic layer deposition behave similarly when either HF(2%) : HCl(2%) or HF(50%) are used as a pre-treatment, possibly because of the thin silicon dioxide interlayer which subsequently forms. Our study highlights that chemical pre-treatments can be extremely important in the creation of high quality functionalised surfaces.

Magenetic field induced proton transfer of 18-crown-6-ether/fluoroboric acid/water system: Crystal structure and Hirshfeld surfaces

A new complex of the title system ([2(H3O+)·18-crown-6]·2[BF4−]), which was induced by external magnetic field, has been prepared and characterized. When compared with other two members of the same system, the proton transfer induced by magnetic field from HBF4 to H2O has leads to the co-plane of six oxygen atoms in the crown and stronger HF and OF intermolecular interactions, which can be attributed to the closer contacts between 18-crown-6, oxonium ion H3O+ and counterion BF4−. In addition, a compression effect of crystals stacking has been observed. These results are of importance for the evaluation the effect of magnetic field on the host–guest systems.

Catalyst Nuclearity Effects on Stereo- and Regioinduction in Pyridylamidohafnium-Catalyzed Propylene and 1-Octene Polymerizations

In comparison to monometallic controls, bimetallic olefin polymerization catalysts often exhibit superior performance in terms of higher polyolefin Mw, higher comonomer incorporation, and higher polar comonomer tolerance. However, using cooperating catalyst centers to modulate stereoselectivity in α-olefin polymerizations is relatively unexplored. In this contribution, the monometallic Hf(IV) complex, L1-HfMe2 (catalyst A, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline), and homo-bimetallic Hf(IV) complexes, L2-Hf2Me5 (catalyst B) and L2-Hf2Me4 (catalyst C) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), are activated with Ph3C+B(C6F5)4– and investigated in propylene and 1-octene homopolymerizations. In propylene polymerizations, the conformationally flexible catalyst B-derived bimetallic dicationic catalyst produces higher Mw polypropylene (up to 7.8×), higher total stereo- and regiodefect densities (up to 3.5×), and lower Tm (by as much as ∼14 °C) versus the monometallic catalyst A-derived control. In 1-octene polymerizations, the conformationally flexible catalyst B-derived bimetallic dicationic catalyst induces greatly reduced isotacticity (23% reduction in [mmmm]) versus the catalyst A-derived monometallic control ([mmmm] > 99%). Interestingly, conformationally flexible catalyst B-derived cationic bimetallic Hf catalysts are also known to undergo rapid intramolecular/intermetal methyl exchange and to exhibit strong Hf···Hf cooperative enchainment effects in ethylene homo- and copolymerizations. Steric effects and intramolecular intermetal chain transfer likely both contribute to the increased isotactic polyolefin stereo- and regiodefect content.

Carbonate–silicate melt immiscibility, REE mineralising fluids, and the evolution of the Lofdal Intrusive Suite, Namibia

The Lofdal Intrusive Suite, Namibia, consists of calcio-carbonatite and silica-undersaturated alkaline intrusive rocks ranging in composition from phono-tephrite to phonolite (and nepheline syenite). The most primitive of these rocks is the phono-tephrite, which, on the basis of its Y/Ho and Nb/Ta ratios, is interpreted to have formed by partial melting of the mantle. Roughly linear trends in major and trace element contents from phono-tephrite to phonolite and nepheline syenite indicate that the latter two rock types evolved from the phono-tephrite by fractional crystallisation. The nepheline syenite, however, has a lower rare earth element (REE) content than the phonolite. The carbonatite has a primitive mantle-normalised REE profile roughly parallel to that of the silica-undersaturated alkaline igneous rocks, although the absolute REE concentrations are higher. Like the phono-tephrite, it also has a mantle Y/Ho ratio. However, the Nb/Ta and Zr/Hf ratios are significantly higher. Moreover, the carbonatite displays strong negative Ta, Zr and Hf anomalies on spidergrams, whereas the silicate rocks display positive anomalies for these elements. Significantly, this behaviour is predicted by the corresponding carbonatite-silicate melt partition coefficients, as is the behaviour of the REE. Based on these observations, we interpret the carbonatite to represent an immiscible liquid that exsolved from the phono-tephrite or possibly the phonolite melt. The result was a calcio-carbonatite that is enriched in the heavy REE (HREE) relative to most other carbonatites. Fluids released from the corresponding magma are interpreted to have been the source of the REE mineralisation that is currently the target of exploration.

Oxygen and hydroxyl adsorption on MS2 (M = Mo, W, Hf) monolayers: a first‐principles molecular dynamics study

In this paper, we study the oxygen and hydroxyl adsorption on both pristine and S deficient MS2 (M = Mo, W, Hf) monolayers, using first‐principles molecular dynamics calculations. Our simulations reveal that single‐layer HfS2 suffers severely from oxidation, which results in the formation of strong Hf–O bonds, likely degrading the transport properties of the material. Oxygen adsorption on S deficient monolayers acts as a passivation mechanism, both ”structurally” by saturating the dangling bonds of neighboring metal atoms and ”electronically” by removing the S vacancy induced gap states. Hydroxyl adsorption on pristine monolayers generates spin‐polarized gap states, and for HfS2 in particular, causes the Fermi level pinning close to the conduction band edge.

Ionospheric Sounding Using Real‐Time Amateur Radio Reporting Networks

AbstractAmateur radio reporting networks, such as the Reverse Beacon Network (RBN), PSKReporter, and the Weak Signal Propagation Network, are powerful tools for remote sensing the ionosphere. These voluntarily constructed and operated networks provide real‐time and archival data that could be used for space weather operations, forecasting, and research. The potential exists for the study of both global and localized effects. The capability of one such network to detect space weather disturbances is demonstrated by examining the impacts on RBN‐observed HF propagation paths of an X2.9 class solar flare detected by the GOES 15 satellite. Prior to the solar flare, the RBN observed strong HF propagation conditions between multiple continents, primarily Europe, North America, and South America. Immediately following the GOES 15 detection of the solar flare, the number of reported global RBN propagation paths dropped to less than 35% that of prior observations. After the flare, the RBN showed the gradual recovery of HF propagation conditions.

Sporadic E ionization layers observed with radar imaging and ionospheric modification

AbstractSporadic E ionization layers have been observed in the daytime subauroral ionospheric E layer by a 30 MHz radar in Alaska. The radar detects coherent backscatter from meter‐scale field‐aligned plasma density irregularities. The irregularities were generated by ionospheric modification—by the emission of strong HF electromagnetic waves directly beneath the layers—making the layers visible to the radar. Aperture‐synthesis methods are used to generate imagery of the layers from the radar data. The layers are patchy, with patches organized along fronts spaced by tens of kilometers and propagating slowly toward the southwest. Similar, naturally occurring layers are commonly observed at middle latitudes at night in the absence of ionospheric modification. That the patchy layers can be found at high magnetic latitudes during the day argues that they are most likely produced through the interaction of the ionospheric layer with neutral atmospheric waves and instabilities. Attenuation of the radar echoes when the HF emission frequency exceeded the third harmonic of the electron gyrofrequency was observed and is discussed.

Occurrence modes and cleaning potential of sulfur and some trace elements in a high-sulfur coal from Pu’an coalfield, SW Guizhou, China

In this research, a float-sink test was applied to a Late Permian high-sulfur coal collected from Pu’an coalfield, Southwest in Guizhou, China. To investigate the occurrence modes and the mobility of various trace elements, as well as the cleaning potential of some harmful elements in density separation, coal quality parameters and concentrations of 46 elements of 7 density fractionated samples were determined and statistically analyzed. Results show that larger size and higher density fractions have higher total sulfur content and ash yield than the smaller and lower ones. In fact, most (74.39 %) of the total sulfur occurs in the inorganic matter. Affinity and correlation analysis show that Mo and Ni have apparently strong organic affinity, whereas Rh, Cs, Sr, Co, Nb, Zr, V, Ga, Sc, Be, Ge, Hf, Th, U, Ag, As, In, Cu, Cd, Ta, Li, TI, and Ba are mostly in the heavy fractions. Rare earth element (REE) patterns for the seven density fractions present good uniformity and show that they are of right-inclined pattern type characterized by Light REE (LREE, La ~ Eu) enrichment relative to Heavy REE (HREE, Gd ~ Lu) and pronounced negative δ Eu anomalies. This suggests that REE was mainly derived from basalt-weathered materials. LRREE/HREE ratio variations reveal that LREE has stronger affinity with the organic matter relative to the HREE, while high LRREE/HREE in heavy fractions may be related to pyrite. Supposing the maximum sulfur content of the cleaned coal is 1.00 %, the theoretical removal ratios of Co, TI, and Ba are as high as 90.94, 93.73, and 92.29 %, respectively, while those of As, Ni and Mo are only 56.33, 48.85, and 45.05 %, respectively. As these figures change with different maximum sulfur contents required for the cleaned coal, not only the decrease of sulfur and ash in coal washing, but also the mobility of some harmful trace elements should be taken into consideration.

Tectonomagmatic evolution of the Early Ordovician suprasubduction-zone ophiolites of the Trondheim Region, Mid-Norwegian Caledonides

Abstract The Trondheim Region ophiolites in the Mid-Norwegian Caledonides represent variably tectonized ophiolite fragments. We present high-precision thermal-ionization mass spectrometry and secondary-ion mass spectrometry (SIMS) U–Pb zircon dates, whole-rock geochemical and Sm–Nd data and Lu–Hf zircon analyses that permit the timing and nature of various stages in the evolution of the ophiolite to be elucidated. Plagiogranite intrusions dated at 487 and 480 Ma have relatively juvenile Nd and Hf isotopic compositions (ε Nd( t ) =6.3, ε Hf( t ) =8.2–12.4). Geochemical data indicate a subduction-zone influence, suggesting formation in an oceanic back-arc setting. At 481 Ma, a granitoid body with a relatively strong unradiogenic Nd and Hf isotopic composition (ε Nd( t ) =−2.6 to −4.0, ε Hf( t ) =3.8–6.4) and subduction-zone geochemical signature intruded the ophiolite. We interpret this stage to reflect the formation or migration of an oceanic arc above a subduction zone influenced by continentally derived sediments. At c. 475–465 Ma, a greenstone-dominated conglomerate and volcaniclastic sequence was deposited on the eroded ophiolite, indicating obduction between about 480 and 475 Ma. At c. 468–467 Ma, the deformed ophiolite and its sedimentary cover was intruded by trondhjemite dykes and shoshonitic volcanic rocks with intermediate Nd and Hf isotopic compositions (ε Nd( t ) =3.0–3.9, ε Hf( t ) =4.4–10.2). We interpret this magmatism to reflect subduction-polarity reversal and establishment of a magmatic arc at the continental margin shortly after obduction. Supplementary material: Whole-rock geochemistry, Sm–Nd isotopic data, SHRIMP U–Pb zircon, TIMS U–Pb zircon and Lu–Hf isotopic data are available at http://www.geolsoc.org.uk/SUP18689 .

Broadband analysis of chaotic pulse trains generated by negative cloud-to-ground lightning discharge

[1] This paper presents direct broadband measurements of the electromagnetic radiation produced by so-called chaotic pulse trains (CPTs) in the frequency range from 0.1 to 40 MHz. We identify CPTs as a kind of pulse train with irregular pulse characteristics and erratic amplitudes, which are associated with the leader stage of subsequent strokes in negative cloud-to-ground lightning. The average duration of a CPT is 472 μs. In integrated E waveform, individual CPT pulse width varies in the range of 0.5–8 μs, and the most probable value is 1–2 μs. We find that 48% of subsequent strokes were preceded by a chaotic component. CPTs often produce strong HF radiation. From broadband waveforms, one can clearly see the intense radiation activity above the background noise level during the chaotic period. The average power spectral density (PSD) is used to measure the HF radiation intensity. The PSD distribution of CPTs shows substantially higher radiation power than that of “nonchaotic” subsequent leaders over the entire observation band. Two-site VHF interferometer data are recorded to investigate the fine structure of CPTs. The results of radiation source mapping indicate that CPTs during subsequent leaders occur with a channel propagation speed of 2 × 107 m/s. The data presented here suggest that it is proper to interpret CPTs as pulse activity associated with the dart phase of a subsequent leader.

Focusing of HF radio-waves by ionospheric ducts

This paper presents the first direct observations of HF focusing induced by natural and artificial ionospheric ducts along with a simple theoretical model. The experiments were conducted by injecting HF radio-waves using the Ionospheric Research Instrument of the High Frequency Active Auroral Research Program located in Gakona, Alaska and detecting them with instruments on the overflying French micro-satellite DEMETER. The latter observed a multiple frequency band structure, which is characteristic of a strong HF signal exceeding the detector's saturation level. Analysis of the O + density measured by DEMETER along its orbit shows that the strong radio signal coincides with the presence of a “negative” duct in the ionosphere. “Negative” refers to the presence of a plasma density depletion with the peak depletion located near the center of the duct. Such ducts induce changes in the index of refraction leading to the focusing of HF waves in a manner equivalent to a “thick” plasma lens. Examination of the data along with a simple plasma lens model indicates the presence of focal node(s) in the vicinity of the overflying satellite. Two examples, one corresponding to focusing by a natural duct and one by an artificial one are presented.

Separation Method in the Problem of a Beam-Plasma Interaction in a Cylindrical Warm Plasma Waveguide

The stabilization effect of a strong HF electric field on beam-plasma instability in a cylindrical warm plasma waveguide is discussed. A mathematical technique “separation method” applied to the two-fluid plasma model to separate the equations, which describe the system, into two parts, temporal and space parts. Plasma electrons are considered to have a thermal velocity. It is shown that a HF electric field has no essential influence on dispersion characteristics of unstable surface waves excited in a warm plasma waveguide by a low-density electron beam. The region of instability only slightly narrowing and the growth rate decreases by a small parameter and this result has been reduced compared to cold plasma. Also, it is found that the plasma electrons have not affected the solution of the space part of the problem.

Structural Changes of La2O3-doped Hf-based High-k Dielectrics during Aqueous HF Treatment

The wet removal of La2O3-doped Hf-based dielectrics is examined for future high-k metal-insulator-semiconductor field-effect-transistor (MIS-FET) processing. XPS observations reveal that aqueous HF treatment removes Hf and Si components from La2O3-doped HfSiON, and LaFx residue remains on the processed wafer surface. It is shown that the sequential treatment of strong acid and HF is effective to reduce unfavorable LaFx adhesion. It is pointed out that HF-treatment fluorinates La in HfO2 film with no-film-dissolution and reactive-ion-etching (RIE) must be selected to remove La2O3-doped HfO2 film. To clarify the effect of removal processing on actual MIS-FET structure, SEM and high resolution STEM observations are carried out. The observations suggest that both the side etching of HfSiON dielectrics during HF-treatment and the substrate recess during HfO2 film removal with RIE are serious issues for the manufacturing of La2O3-doped high-k MIS-FETs.

Nature and evolution of the lithospheric mantle beneath the passive margin of East Oman: Evidence from mantle xenoliths sampled by Cenozoic alkaline lavas

Cenozoic alkaline lavas from the Al Ashkharah area, facing the Indian ocean along the North-East Oman coastline, contain numerous small (< 2 cm) mantle xenoliths. They provide a unique opportunity to investigate the nature and evolution of the upper mantle beneath the Oman passive margin, bordering the Owen Basin. All studied xenoliths are porphyroclastic to equigranular spinel lherzolites and harzburgites. They are all devoid of amphibole and phlogopite. The composition of their clinopyroxenes, orthopyroxenes, olivines and spinels indicate that these samples are derived from a typical sub continental lithospheric upper mantle and are quite distinct from the peridotites cropping out in the nearby Oman ophiolite. The clinopyroxene major element composition record an evolution from fertile lherzolites (Mg#: 89 and Al 2O 3: 7.5 wt.%) to refractory harzburgites (Mg#: 93.5 and Al 2O 3: 2.5 wt.%). The clinopyroxene of most samples are characterised by REE patterns evolving continuously from spoon-shaped to LREE-enriched with almost flat HREE spectra (La N /Yb N : 2.5–30; La N /Sm N : 3.2–24; Sm N /Yb N : 0.25–4.6; Ho N /Lu N : 0.88–1.15) and strong negative Ba, Nb, Zr, Hf and Ti anomalies. We propose that these geochemical fingerprints can be accounted for by two processes; (1) a — relatively old (pre-Cenozoic rifting) — decompression melting event characterised by ~ 1 to a maximum of 13% partial melting and unrelated to the recent (Eocene) tectonic evolution of the Oman margin, followed by (2) metasomatic transformation possibly related to the circulation of alkaline mafic silicate melt displaying geochemical similarities with the host basanites during the Cenozoic rifting event that led to the opening of the Owen basin.

Relativistic warm plasma waveguide under the effects of plasma electrons and HF electrical field on Buneman instability

Abstract The stabilization effect of a strong HF (pump) electrical field and plasma electrons on a two-stream (Buneman) instability in a plane relativistic warm plasma waveguide is investigated; using the separation method to solve the two-fluid plasma model we separate the problem into two parts. The “temporal” (dynamical) part enables us to determine the frequencies and growth rates of unstable waves; this part within the redefinition of natural frequencies coincides with the system describing HF suppression of Buneman instability in uniform unbounded plasma. Natural frequencies of oscillations and spatial distribution of the amplitude of the self-consistent electrical field are determined from the solution of a boundary-value problem (“space part”) taking into account specific spatial distribution of plasma density. Plasma electrons are considered to have a relativistic thermal velocity. It is shown that the growth rate of instability in relativistic warm plasma is reduced compared to non-relativistic (cold or warm) plasma and relativistic cold plasma. In addition, it is found that the plasma electrons have no effect on the solution of the space part of the problem.

Effects of segregating elements on the adhesive strength and structure of the α-Al 2O 3/β-NiAl interface

We investigate with first-principles density functional theory (DFT) the adhesion of the Al 2O 3(0 0 0 1)/NiAl(1 1 0) interface as a model for the thermally grown oxide/bond coat alloy interface in thermal barrier coatings. We find that the clean interface has an ideal work of adhesion of 0.66 J m −2. We predict that S impurities reduce interfacial adhesion significantly, due to a reduction in cross-interface bonds. The presence of Pt alters the interface adhesion only slightly, while Hf dopants dramatically increase adhesion via formation of strong Hf–O bonds, as expected from Hf’s open-shell character. We discuss the implications of these predictions, which are consistent with experimental observations of the effects of S, Pt, and Hf on the lifetime of thermal barrier coatings.

An interhemispheric model of artificial ionospheric ducts

A duct in Earth's ionosphere is characterized by density gradients perpendicular to the magnetic field, which enhance refractive indices and act as waveguides to whistler‐range waves. Interhemispheric ducts along magnetic field lines have implications for the transmission of ELF radio waves across the globe. Strong HF ionospheric heating has been shown to create a depletion of electrons at the heated region and could lead to a pressure perturbation that propagates along the entire magnetic field line, potentially forming an artificial duct. Here we present results from an ionospheric numerical model used to study the effects of localized HF heating on an interhemispheric magnetic flux tube. The existing Sami2 is Another Model of the Ionosphere (SAMI2) ionospheric model has been modified to include a flexible source of strong HF heating that can be varied to mimic the fluctuations in HF heating efficiencies and ionospheric conditions. Our parametric study includes varying the heating source intensity and location along the magnetic field line, revealing both linear and nonlinear relationships connecting these source parameters to maximum pressure, temperature, and density perturbations; propagation velocity of density perturbations; and characteristic heating and cooling times of the irradiated region. After a transient state, the duct structure achieves a quasi‐steady state, showing electron depletion at the heated region and density enhancements in the regions just below and above the heated region. The density perturbations propagate deep inside the plasmasphere to the conjugate F2 peak, with density enhancements along the traveling pulse boundary. The possibility of generating interhemispheric ducts is discussed.