Conversion Point Research Articles

The invasive Egeria densa macrophyte and its potential as a new renewable energy source: A study of degradation kinetics and thermodynamic parameters

The increase in global demand, along with environmental concerns, has led to the need for new sources that can supply the energy needed for socioeconomic development while reducing pollutant emissions. Aquatic biomasses, especially those of invasive aquatic macrophytes, can be potential energy sources, and this study evaluated the thermal degradation of the invasive Egeria densa macrophytes (EDM) in an inert environment at four heating rates to evaluate its potential as a low-cost biomass and bioenergy source. Pyrolysis experiments were performed using a thermogravimetric analyzer. The thermal profile of invasive EDM has three main events (multiple stages). Stages (i) and (ii) occur at a temperature range of 125–395 °C and represent the decomposition of carbohydrates such as hemicellulose and cellulose. Stage (iii) occurs between 395 and 500 °C and mainly relates to the decomposition of lignin. Thermal data have been used to analyze kinetic parameters through isoconversional methods, and the activation energy (Ea) value of EDM showed variation at different conversion points. The highest Ea values were observed for conversion rates of 0.3–0.6 due to the increased energy required to break down the lignocellulosic chains during decomposition. The small difference between the enthalpy change and Ea values for the different isoconversional methods can be due to a small potential energy barrier, which reflects the feasibility that the reaction can occur under the expected conditions. Gibbs free energy (137–145 kJ mol−1) and high heating value (13.40 MJ/kg) revealed a significant bioenergy potential for EDM biomass.

NIfTI-MRS: A standard data format for magnetic resonance spectroscopy.

Multiple data formats in the MRS community currently hinder data sharing and integration. NIfTI-MRS is proposed as a standard spectroscopy data format, implemented as an extension to the Neuroimaging informatics technology initiative (NIfTI) format. This standardized format can facilitate data sharing and algorithm development as well as ease integration of MRS analysis alongside other imaging modalities. A file format using the NIfTI header extension framework incorporates essential spectroscopic metadata and additional encoding dimensions. A detailed description of the specification is provided. An open-source command-line conversion program is implemented to convert single-voxel and spectroscopic imaging data to NIfTI-MRS. Visualization of data in NIfTI-MRS is provided by development of a dedicated plugin for FSLeyes, the FMRIB Software Library (FSL) image viewer. Online documentation and 10 example datasets in the proposed format are provided. Code examples of NIfTI-MRS readers are implemented in common programming languages. Conversion software, spec2nii, currently converts 14 formats where data is stored in image-space to NIfTI-MRS, including Digital Imaging and Communications in Medicine (DICOM) and vendor proprietary formats. NIfTI-MRS aims to solve issues arising from multiple data formats being used in the MRS community. Through a single conversion point, processing and analysis of MRS data are simplified, thereby lowering the barrier to use of MRS. Furthermore, it can serve as the basis for open data sharing, collaboration, and interoperability of analysis programs. Greater standardization and harmonization become possible. By aligning with the dominant format in neuroimaging, NIfTI-MRS enables the use of mature tools present in the imaging community, demonstrated in this work by using a dedicated imaging tool, FSLeyes, for visualization.

Early Dynamics of Hepatitis B Virus (HBV)-DNA and Surface Antigen (HBsAg) in Ramp-Up Phase of Viremia: Implications for Performance Evaluation of Blood Screening Assays.

The Common Specifications/EU 2017/746 regulation for market approval of class D in vitro diagnostic devices (IVDs) intended for detection of blood borne viruses requires testing of the International Standard and 10–30 seroconversion panels to demonstrate ‘state of the art’ assay performance. We examined whether these requirements for performance evaluation are reasonable for HBV-DNA and HBsAg assays. For this purpose, we quantified HBsAg and HBV-DNA (genotype A) in the ramp-up phase of five seroconversion panels and demonstrated a remarkably parallel increase in the Log concentration of both analytes over time. Testing of seroconversion panels by three nucleic acid amplification technology (NAT) methods in multiple replicates and probit analysis with sufficient critical samples from all five panels taken together showed detection limits in copies/mL that were comparable to those on a HBV-DNA genotype A standard dilution panel. This indicates that the viral doubling time in the ramp-up phase is equal above and below the quantification limit of the viral load assay. The geometric mean HBsAg (PRISM) cutoff crossing point was 20 days later than the 50% NAT (Ultrio Plus) conversion point equivalent to 1500 (range: 1100–2200) and 4.8 (CI: 3.7–6.4) HBV-DNA copies/mL, respectively. Analytical sensitivity data of different NAT assay versions obtained over a decade demonstrated that the detection limit on the International Standard is not representative of all genotyped reference samples. From our detailed mathematical analysis, we conclude that HBV-DNA and HBsAg standard dilution series are functionally equivalent to seroconversion panels. A general requirement of a 95% detection limit ≤100 HBV-DNA copies/mL for different viral genotypes would be a better-defined regulation for EU market approval of NAT blood screening assays than the testing of multiple seroconversion panels to claim ‘state of the art’ performance.

Test of P-wave receiver functions for a seismic velocity and gravity model across the Baikal Rift Zone

SUMMARY The seismic receiver function (RF) technique is widely used as an economic method to image earth's deep interior in a large number of seismic experiments. P-wave receiver functions (RFs) constrain crustal thickness and average Vp/Vs in the crust by analysis of the Ps phase and multiples (reflected/converted waves) from the Moho. Regional studies often show significant differences between the Moho depth constrained by RF and by reflection/refraction methods. We compare the results from RF and controlled source seismology for the Baikal Rift Zone by calculating 1480 synthetic RFs for a seismic refraction/reflection velocity model and processing them with two common RF techniques [H–κ and Common Conversion Point (CCP) stacking]. We compare the resulting synthetic RF structure with the velocity model, a density model (derived from gravity and the velocity model), and with observed RFs. Our results demonstrate that the use of different frequency filters, the presence of complex phases from sediments and gradual changes in the properties of crustal layers can lead to erroneous interpretation of RFs and incorrect geological interpretations. We suggest that the interpretation of RFs should be combined with other geophysical methods, in particular in complex tectonic regions and that the long-wavelength Bouguer gravity anomaly signal may provide effective calibration for the determination of the correct Moho depth from RF results. We propose and validate a new automated, efficient method for this calibration.

Evidence of secular variation in Archean crust formation in the Eastern Indian Shield

Understanding the dominant crustal accretion model in any Archean craton is the key to understanding the dominant geodynamic process responsible for early crust formation during the Hadean (> 4.0 Ga) and Archaean (4.0–2.5 Ga). The continental crust has been proposed to have formed through either horizontal/vertical accretion related to subduction or mantle plume tectonic processes. Here, the Moho depths and average crustal Vp/Vs ratios are modelled at 16 broadband stations in the Eastern Indian Shield (EIS) through HK stacking of radial P-receiver functions (PRFs). These modelled parameters are used to test both plume and subduction models, which might have played a key role in the crustal accretion of the EIS throughout the Archean. We observe a correlation between crustal age and composition within the ellipsoidal Paleoarchean cratonic domain in the Singhbhum-Odisha-Craton (SOC), which reveals an increase in age from the younger granitoid core of the SOC (with thinning of felsic crust) to the surrounding older greenstone belts (with thickening of felsic crust). A thinner mafic crust resulting from multiple magmatic events characterizes the neighbouring Meso-Proterozoic Chotanagpur Granitic Gneissic terrain (CGGT). The Common Conversion Point (CCP) image of radial PRFs reveals northward subduction of the Paleoarchean SOC below the Meso-Proterozoic CGGT.

Fabrication of UiO-66-NH2/Ce(HCOO)3 heterojunction with enhanced photocatalytic reduction of CO2 to CH4

The development of efficient and highly selective photocatalysts is a key point for the photocatalytic conversion of CO2. In this paper, a composite catalyst UiO-66-NH2/Ce(HCOO)3 (simplified to UNH/Ce(HCOO)3) was fabricated by one pot method with CeCO3OH as the precursor. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) characterizations results confirmed that UNH was dispersed on the surface of Ce(HCOO)3 and strongly interacted with it via Ce-N bond. The yield of CH4 on the optimal UNH/Ce(HCOO)3 catalyst reached 3 times of that on pristine UNH, up to 128.81 μmol g−1, with the CH4 selectivity of 71.9 %, and the Relectron reached 286.46 μmol g−1 h−1. The UV–vis diffuse reflection spectra and photoelectrochemical tests results confirmed that the improved photocatalytic CO2 reduction performance and high CH4 selectivity could be attributed to the formation of the type-Ⅱheterojunction of UNH/Ce(HCOO)3 with abundant Ce3+, which expanded the visible light absorption range, accelerated the separation and transfer rates of photogenerated charges, and thus efficiently promoted the multi-electron reduction reaction of CO2 to CH4. In addition, the reaction temperature affected profoundly the cycle performance of the catalyst. The results presented here illustrated the possibility for improving the stability of UNH/Ce(HCOO)3-1.80 by decreasing reaction temperature.

Ten simple rules to host an inclusive conference

Conferences are spaces to meet and network within and across academic and technical fields, learn about new advances, and share our work. They can help define career paths and create long-lasting collaborations and opportunities. However, these opportunities are not equal for all. This article introduces 10 simple rules to host an inclusive conference based on the authors’ recent experience organizing the 2021 edition of the useR! statistical computing conference, which attracted a broad range of participants from academia, industry, government, and the nonprofit sector. Coming from different backgrounds, career stages, and even continents, we embraced the challenge of organizing a high-quality virtual conference in the context of the Coronavirus Disease 2019 (COVID-19) pandemic and making it a kind, inclusive, and accessible experience for as many people as possible. The rules result from our lessons learned before, during, and after the organization of the conference. They have been written mainly for potential organizers and selection committees of conferences and contain multiple practical tips to help a variety of events become more accessible and inclusive. We see this as a starting point for conversations and efforts towards building more inclusive conferences across the world. * Translated versions of the English abstract and the list of rules are available in 10 languages in S1 Text: Arabic, French, German, Italian, Japanese, Korean, Portuguese, Spanish, Tamil, and Thai.

Evolution of the Western Ghats: Constraints from receiver function imaging and harmonic decomposition

The Western Ghats (WG), with an average elevation of ~1.2 km, is one of the greatest escarpments that spans ~1500 km parallel to the west coast of India. It is a mosaic of disparate geological formations having distinct structural and physical characteristics. In this study, the lithospheric structure in terms of crustal thickness, sub-Moho layer and deformation along and across the WG are investigated using receiver functions (RFs) at 30 broadband seismological stations. Techniques like slant stacking, common conversion point imaging and harmonic decomposition are applied to the RFs. Results reveal a large crustal thickness of ~45 km in the central part of the WG, which decreases to ~39 km in the southern and ~ 37 km in the northern parts, in conformity with the geology. The variation in crustal thickness beneath the WG could be due to the effect of hotspot impingement and subsequent rifting mechanism. Further, the RFs reveal a strong sub-Moho low velocity layer (LVL) along the WG. This observation gains support from a previous inference of a low-density zone in the uppermost mantle beneath the west coast of India. Harmonic decomposition of the RFs reveals that this LVL is anisotropic, while the Moho is dipping/ anisotropic in nature. The trend of the symmetry axis of anisotropy (of the LVL) varies from 58.2∘ to 134.4∘, almost perpendicular to the west coast of India. We postulate that the origin of this LVL can be linked to different rifting episodes along the west coast of India, since LVLs are manifestations of thermal/chemical anomalies. These results support the rifting model proposed for the evolution of WG.

Chatbots to Support Young Adults’ Mental Health: An Exploratory Study of Acceptability

Despite the prevalence of mental health conditions, stigma, lack of awareness, and limited resources impede access to care, creating a need to improve mental health support. The recent surge in scientific and commercial interest in conversational agents and their potential to improve diagnosis and treatment seems a potentially fruitful area in this respect, particularly for young adults who widely use such systems in other contexts. Yet, there is little research that considers the acceptability of conversational agents in mental health. This study, therefore, presents three research activities that explore whether conversational agents and, in particular, chatbots can be an acceptable solution in mental healthcare for young adults. First, a survey of young adults (in a university setting) provides an understanding of the landscape of mental health in this age group and of their views around mental health technology, including chatbots. Second, a literature review synthesises current evidence relating to the acceptability of mental health conversational agents and points to future research priorities. Third, interviews with counsellors who work with young adults, supported by a chatbot prototype and user-centred design techniques, reveal the perceived benefits and potential roles of mental health chatbots from the perspective of mental health professionals, while suggesting preconditions for the acceptability of the technology. Taken together, these research activities: provide evidence that chatbots are an acceptable solution to offering mental health support for young adults; identify specific challenges relating to both the technology and environment; and argue for the application of user-centred approaches during development of mental health chatbots and more systematic and rigorous evaluations of the resulting solutions.

Imprints of subducted Palaeo-Tethys oceanic lithosphere on upper-mantle discontinuities and the formation of the Emeishan large igneous province

SUMMARYGenerally, the upwelling of a mantle plume is suggested to have led to the formation of the Emeishan large igneous province (ELIP). However, this idea has been challenged by recent geological and seismological studies. In this investigation, three profiles of velocity perturbations crossing the ELIP are drawn following previous tomographic studies, and common conversion point (CCP) stacking of receiver functions in the ELIP is carried out. A slab-like high-velocity structure is revealed, which may be associated with the lithosphere of the Palaeo-Tethys Ocean (LPTO) subducting toward the northeast. CCP stacking of receiver functions shows that the LPTO generated imprints on the 410- and 660-km discontinuities. A comprehensive analysis suggests that the LPTO may have induced large-scale mantle upwelling, which contributed to the formation of the ELIP.

Rationale for and design of a multicenter, placebo-controlled, phase 3 study to assess efficacy and safety of intranasal etripamil for the conversion of paroxysmal supraventricular tachycardia

Presently, acute pharmacological termination of paroxysmal supraventricular tachycardia (PSVT) unresponsive to patient-initiated vagal maneuvers requires in-hospital intervention. Etripamil, a fast-acting, nondihydropyridine, L-type calcium channel blocker, is formulated as an intranasal spray to rapidly terminate atrioventricular (AV) nodal-dependent PSVT in a medically unsupervised setting. The NODE-301 study did not meet its prespecified primary end point of PSVT conversion over 5 hours following a single dose of etripamil 70 mg. However, analysis at earlier time points demonstrated etripamil treatment effect during the first 30 minutes, consistent with its expected rapid onset and short duration of action. This led to the design of the RAPID study, which includes a new dosing regimen (up to 2 etripamil 70 mg doses separated by 10 minutes) to increase the exposure and pharmacodynamic effect of etripamil. The primary objective of RAPID (NCT03464019) is to determine if etripamil self-administered by patients is superior to placebo in terminating PSVT in an at-home setting. The secondary objective is to evaluate the safety of etripamil when self-administered by patients without medical supervision. Additional efficacy end points include the proportion of patients requiring additional medical intervention in an emergency department to terminate PSVT and patient-reported outcomes. After successfully completing a test dose to assess the safety of 2 70 mg doses of etripamil during sinus rhythm, approximately 500 patients will be randomized 1:1 to etripamil or placebo to accrue 180 positively adjudicated AV nodal-dependent PSVT events for treatment with the study drug. Etripamil may offer a new alternative to the current in-hospital treatment modality, providing for safe and effective at-home termination of PSVT.

Effect of Freeze–Thaw cycles on the pavement performance of SBS modified and composite crumb rubber modified asphalt mixtures

The effect of freeze–thaw cycles on the pavement performance of SBS modified asphalt mixture (SBSMA) and SBS/crumb rubber composite modified asphalt mixture (CCRMA) was studied using a triaxial repeated creep test, semicircular bending fatigue test based on digital image correlation (DIC), and thermal stress restrained specimen test. The mechanical model of the residual strain (RS) of the asphalt mixtures is established, and the residual viscous flow strain (εRvf,N) and residual viscoelastic strain (εRve,N) are separated. Based on the horizontal strain (Exx) of DIC, a new mesofatigue damage variable (D) is proposed. According to the characteristic curve of D, the antifatigue damage parameter (AFDP) is established and the correlation between AFDP and fatigue life (Nf) is analyzed. Simultaneously, a calculation model of the relaxation temperature stress (σRts(T)) of the asphalt mixture at different cooling rates (v) is established based on the finite element method. Results showed that the growth rates of RS, εRvf,N, and D of both asphalt mixtures accelerate, AFDP decreases, and freeze–break temperature (TD) rises with increasing freeze–thaw cycles. However, the growth rates of RS, εRvf,N, and D of CCRMA are always slower than SBSMA, the AFDP is larger than SBSMA, TD is lower than SBSMA, εRve,N is a fixed value under specific conditions, and a good correlation exists between the AFDP and Nf. The pavement performance of the asphalt mixtures worsens after the freeze–thaw cycles, and the influence of a salt freeze–thaw cycles is greater than that of a water freeze–thaw cycles. Moreover, CCRMA has better high-temperature deformation resistance, fatigue damage resistance, and low-temperature cracking resistance than SBSMA. The conversion point temperature (TZ) increases with the acceleration of v, and the σRts(T) calculation model can accurately reflect the σRts(T) of the asphalt mixture at different v.

A simplified approach to modelling temperature rises in battery cells and modules

An analytical model to predict the maximum temperature rise in a battery cell or module given a certain cooling regime was developed. The novel analytical model combines a micromechanical model, to compute the effective thermal conductivity of the cells, with a solution of the heat equation. The boundary conditions, geometric parameters and material properties were varied in representative ranges. The temperature fields across the battery were predicted with a very good agreement between the analytical model and the numerical simulations, for a wide variety of configurations under steady-state conditions. The analytical solution can be used as a fast and reliable tool to estimate the heat transfer between the cells and their thermal management system. The results from the analytical model were compared to those estimated by an Artificial Neural Network and found to be equal or better in performance than a data-driven approach. An experimental validation of the analytically predicted temperatures of interest showed a very good agreement. The experimental results reveal the requirement for good thermal management solutions from an efficient energy conversion point of view.

Combination of protein engineering and metabolic engineering to enhance (+)‐nootkatone production in Saccharomyces cerevisiae

AbstractThe introduction of heterologous pathways into microorganisms for high‐level synthesis of valuable compounds would be extremely meaningful. However, the endogenous heterologous pathway conversion point frequently serves as a bottleneck that limits product synthesis. (+)‐Nootkatone is an important functional sesquiterpenoid with a unique grapefruit flavor, which is frequently used as a fragrance. The low catalytic efficiency of the valencene synthase CnVS, the first heterologous enzyme in the biosynthesis of (+)‐nootkatone, is the major challenge that restricts the production of (+)‐nootkatone in Saccharomyces cerevisiae. In this study, we modified CnVS on the basis of the catalytic environment and mechanism of the enzyme. The residue M560 involving in alkyl transfer during substrate cyclization was found to affect activity. By tuning the residue, mutant M560L exhibited a 60% increase in the unit cell yield of (+)‐valencene, which is the precursor of (+)‐nootkatone. Furthermore, multistep strategies of metabolic engineering were employed that transferred the metabolic flux to the target product synthesis pathway and displayed the superimposed effect of metabolic and protein engineering on (+)‐nootkatone yield. Finally, multicopy integration of tHMG1 and ERG20ERG20‐GSG‐CnVSM560L boosted the production of (+)‐nootkatone to 85.43 mg/L in flask and 804.96 mg/L (5.29 mg/[L h]) in bioreactor. In conclusion, this study presents a paradigm for constructing microbial cell factories using a combination of protein and metabolic engineering in S. cerevisiae.

Crustal and Uppermost Mantle Heterogeneities Across the Ailaoshan Red River Shear Zone, SE Tibet: Implications for Cenozoic Magmatic Activity

AbstractThe Ailaoshan Red River shear zone (ARSZ) was formed in the Mesozoic as a suture zone between the Indochina block and the Yangtze craton. Since the Cenozoic, block extrusion due to the Indo‐Asian collision has reactivated the fault zone and caused large‐scale shearing. Affected by the Cenozoic orogeny, a large volume of magmatic and metamorphic rocks developed in the ARSZ, forming many orogenic gold deposits. However, the source and the geodynamic process of these magmatic activities are still unclear. To gain a basic understanding of the subsurface magmatic activity, we deployed a dense array of 24 broadband seismic stations across the Daping and Chang'an gold deposits at the southern end of the ARSZ. Receiver function analysis, common conversion point stacking, and a joint inversion of receiver functions and surface wave dispersions are performed to image the detailed structure of the crust and uppermost mantle. Low‐velocity zones in the mid‐lower crust and thinned lithosphere (∼70 km) are imaged under the ARSZ. The observed subsurface structures are verified by 3D numerical modeling with the SEM‐FK method. We speculate that the mantle upwelling caused by lithospheric delamination has provided the main source of the mantle component in the magmatic rocks since ∼35 Ma; afterward, high temperatures produced partial melting in the lower crust, which was emplaced along active shear zones.

Crustal structure along the Wanzai–Yongchun profile in the Cathaysia Block, Southeast China, constrained by a joint active- and passive-source seismic experiment

SUMMARY Since the Mesozoic, the South China Block (SCB) has experienced multiple episodes of tectonic magmatism accompanied by metallogenesis. To explore the seismic velocity structure of the crust and its connection with mineralization, we constructed a wide-angle reflection and refraction (WARR) profile by deploying 435 short-period seismometers across the Cathaysia Block in Southeast China. Receiver functions and the H–κ stacking method were applied using a reference 2-D velocity model obtained from the analysis of WARR data. Integration of active- and passive-source seismic data enabled us to obtain an image of the crust and the average Vp/Vs ratio value of the SCB and produce several results: (1) The crustal thickness varies west-to-east from 28 km below the Qinhang metallogenic belt to 32 km below the Wuyishan metallogenic belt, and the average value of the Vp/Vs ratio for the crust is 1.71. Both the thickness of the crust and the average Vp/Vs ratio are lower than the average global values for the continental crust. (2) The relatively low Vp/Vs ratio and thin crust along the profile could be generated by thinning of the lower crust in the SCB as a result of the backarc extension related to westward subduction of the Paleo-Pacific plate below East Asia. (3) The Moho depth estimated from H–κ stacking with the help of the background P-wave velocity model modified by the WARR model fits better than using a global seismic velocity model with its common conversion point image, which supports a potential seismic data analysis technique provided with a joint deployment of both active- and passive-source seismic observation system with a shorter period.

A Meeting Point for STS Interventions and Conversations

A Meeting Point for STS Interventions and Conversations

Creating a symbol of hope for 2021

The idea behind our project was to encourage nursing and midwifery teams to create artistic symbols of hope amid the challenges posed by the global Covid-19 pandemic. Our experiences working with teams using arts-informed approaches have shown us that they offer a space for deeper reflection and a change from more traditional reflection models. The outcome of such projects are unique visual representations of what a subject or event means to the team, and of their emotions and experiences. These are displayed in individual wards and units for all staff, patients, relatives and other visitors to see, often becoming a focal point for conversation. In November 2020, our practice development unit invited teams from across the local health district to create a symbol of hope for 2021. This was inspired by reading an article in AI Practitioner, the international journal of appreciative inquiry, entitled ‘Hope and appreciative inquiry during a pandemic’ (Houston, 2020). The author describes hope as something that is ‘an inescapable part of being a human. Both aspiration, belief in our future and reflection, how we view our past’ (p 49). The importance of finding reasons to ‘live, share, cry, sing, laugh, love, be fearful’ (p 51) is also expressed, with the contention that embracing these as our strengths is where hope lies. One aspect of the work of the practice development unit is inspiring nurses and midwives to capture the essence of experiences that occur in everyday practice using creative approaches. Arts-informed approaches provide a way for individuals and teams to express their experiences, thoughts and feelings visually and creatively (McCormack and Titchen, 2006; Horsfall and Titchen, 2009). Creative approaches such as painting, photo elicitation, creative writing, music and dancing can be used to engage our senses, helping us to access, pay attention to and express feelings and experiences, that might initially be difficult to put into words (Horsfall and Titchen, 2009; Sullivan, 2012; Weber, 2012). This is referred to as embodied knowledge, in which the body is the source of knowing rather than the mind (Weber, 2012).

Seismic Evidence for Stepwise Lithospheric Delamination Beneath the Tibetan Plateau

AbstractSeveral models were proposed to account for the tectonic evolution of Tibetan Plateau, among which delamination of the Tibetan lithosphere is suggested to be a leading process. However, direct evidence for the removed Tibetan lithosphere in the deep mantle remains highly lacking. Here we image the mantle transition zone (MTZ) structure beneath western Tibet and Himalaya by common conversion point stacking of 25254 receiver functions (RFs) with unprecedented clarity. One striking feature is the significant depression (15–20 km) of 660‐km discontinuity beneath Himalaya, which indicates the presence of the detached Lhasa lithospheric mantle (∼26 Ma) at the bottom of the MTZ. Our results also show ∼15 km uplift of 410‐km discontinuity (d410) and small d410 amplitude beneath western Tibet, which we ascribe to the more recently delaminated Qiangtang lithosphere (∼15 Ma). Furthermore, the small dependence of d410 amplitude on frequency indicates that the MTZ is anhydrous in the study area.

Characteristics and Removal of Continuous Topographic Scattering in Dense Array Receiver Function Imaging

With dense nodal seismic arrays growing rapidly, receiver function (RF) imaging has revealed unprecedented small-scale features. However, whether these fine signals represent real intra-crustal structures needs to be verified. In this study, we take the RF profiles recorded by a dense array in Ruoergai basin in northeastern Tibet as an example and demonstrate that continuous dipping phases in receiver functions (RFs) could be generated from the interference between the incoming P-wave and dramatic topographic variations. Full-waveform modeling illustrates that when an incident P-wave encounters a topographic peak, it can induce scattered P- and Rayleigh waves that propagate in backward and forward directions, consistent with the observations. The scattered Rayleigh waves exhibit a cosine radiation pattern in R-components, which explains the azimuthal-dependent observation of dipping phases in RF profiles. We then propose a two-step separation method to suppress the continuous topographic scattered phases in RF imaging, which involves a time-domain adaptive matched filtering and a curvelet-based separation. The resulting common conversion point (CCP) images show that the method can effectively suppress the continuous scattered phases induced by topography. CCP images exhibit flat intra-crustal layers, suggesting a decoupled deformation style in the upper and lower crust in NE Tibet. The upper crustal layer may represent the basement of the décollement layer, and the intermittent lower crustal interfaces are likely to indicate the partial melt within the crustal channel flow. The separation method is applicable for dense nodal array RF imaging to reveal reliable, detailed intra-crustal structures in tectonically active regions that developed dramatic topography.