SE Structures Research Articles

Chemostratigraphy and mineralogical characterization of Piacenzian sapropels cluster A (2.75–2.57 Ma) in the Gelasian GSSP type-section of Monte San Nicola (Sicily, Italy): Paleoenvironmental and paleogeographic implications

Mineralogical, geochemical and stable isotope (δ18O, δ13C) data from Marine Isotope Stages (MIS) G4 to 103 are here presented. The studied interval includes the sapropelic cluster A (A2-A5) from the Gelasian GSSP type-section, outcropping at Monte San Nicola (Sicily, Italy). The studied section exhibits a good response of the δ18O measured on the bulk carbonate to the Earth's astronomical parameters. The sapropelic red/brown layers (A2- A5) are alternated to grey marls and this cyclicity is clearly evident by the difference in colour, organic matter content, redox-sensitive elements and runoff indicators, tied to the precession/insolation cycles. Further, the obliquity signal is well evident in paleoproductivity indicators and mineralogical composition, driven by glacial-interglacial cycles. The obtained dataset has allowed the reconstruction of the paleoenvironmental conditions during marls/sapropels deposition, which appears to be influenced by the precessional forcing that induced strong changes in the marine water circulation. This scenario is also integrated by an original paleogeographic model including the presence of a high topographic structure in SE Sicily that limited water exchanges between the Ionian and Central Mediterranean Seas during sea level drawdowns, caused by glacial phases, triggered by obliquity minima.

Genesis of Rare Metal Granites in the Nubian Shield: Tectonic Control and Magmatic and Metasomatic Processes

The Igla Ahmr region in the Central Eastern Desert (CED) of Egypt comprises mainly syenogranites and alkali feldspar granites, with a few tonalite xenoliths. The mineral potential maps were presented in order to convert the concentrations of total rare earth elements (REEs) and associated elements such as Zr, Nb, Ga, Y, Sc, Ta, Mo, U, and Th into mappable exploration criteria based on the line density, five alteration indices, random forest (RF) machine learning, and the weighted sum model (WSM). According to petrography and geochemical analysis, random forest (RF) gives the best result and represents new locations for rare metal mineralization compared with the WSM. The studied tonalites resemble I-type granites and were crystallized from mantle-derived magmas that were contaminated by crustal materials via assimilation, while the alkali feldspar granites and syenogranites are peraluminous A-type granites. The tonalites are the old phase and are considered a transitional stage from I-type to A-type, whereas the A-type granites have evolved from the I-type ones. Their calculated zircon saturation temperature TZr ranges from 717 °C to 820 °C at pressure < 4 kbar and depth < 14 km in relatively oxidized conditions. The A-type granites have high SiO2 (71.46–77.22 wt.%), high total alkali (up to 9 wt.%), Zr (up to 482 ppm), FeOt/(FeOt + MgO) ratios > 0.86, A/CNK ratios > 1, Al2O3 + CaO < 15 wt.%, and high ΣREEs (230 ppm), but low CaO and MgO and negative Eu anomalies (Eu/Eu* = 0.24–0.43). These chemical features resemble those of post-collisional rare metal A-type granites in the Arabian-Nubian Shield (ANS). The parent magma of these A-type granites was possibly derived from the partial melting of the I-type tonalitic protolith during lithospheric delamination, followed by severe fractional crystallization in the upper crust in the post-collisional setting. Their rare metal-bearing minerals, including zircon, apatite, titanite, and rutile, are of magmatic origin, while allanite, xenotime, parisite, and betafite are hydrothermal in origin. The rare metal mineralization in the Igla Ahmr granites is possibly attributed to: (1) essential components of both parental peraluminous melts and magmatic-emanated fluids that have caused metasomatism, leading to rare metal enrichment in the Igla Ahmr granites during the interaction between rocks and fluids, and (2) structural control of rare metals by the major NW–SE structures (Najd trend) and conjugate N–S and NE–SW faults, which all are channels for hydrothermal fluids that in turn have led to hydrothermal alteration. This explains why rare metal mineralization in granites is affected by hydrothermal alteration, including silicification, phyllic alteration, sericitization, kaolinitization, and chloritization.

Exploring electronic features in monolayer and bilayer MX2 (M = Hf, Zr; X = S, Se) structures under shear strain

This study employed first-principles calculations to investigate the dynamic stability of monolayer, bilayer, and heterostructure systems of four MX2 (M = Hf, Zr and X = S, Se) TMDCs, as well as the influence of shear strain on their electronic properties. The computed binding energies and phonon dispersions demonstrate the excellent dynamic stability of bilayer systems, while the small effective masses of electrons and holes in monolayer systems suggest high carrier mobility. Under shear strain, the bandgap size and type of monolayer MX2 system and their vdW heterostructures are effectively modulated, transitioning to metallic behavior under certain strain conditions. Both types of heterostructures exhibit type-II band alignment, serving as direct bandgap semiconductors, facilitating effective electron-hole separation between different layers and thereby reducing recombination. This study elucidates the tunability of the electronic properties of monolayers, bilayers, and heterostructures of MX2 systems under shear strain, which is important for expanding material functionalities and optimizing device performance.

Preservice Teachers’ Assessment Literacy Within Models-Based Practice

Purpose: Using the assessment literacy framework, the purpose of this study was to explore preservice teachers understanding and enactment of the message system during an early field experience. Method: Six PTs employed SE seasons totaling 540 min. Seven qualitative data methods were utilized. Data analysis included deductive and inductive analysis using a thematic approach. Trustworthiness included data triangulation, peer debriefing, negative case analysis, and the maintenance of an audit trail. Results: Three main themes derived from the data included: instructional decisions were driven by the SE model and informal assessment; formal assessment was driven by the structure of SE; and high assessment value but low assessment literacy. Discussion/Conclusion: The SE model drove PTs to use formal assessment, but primarily in an evaluative manner. The PTs lacked assessment literacy, felt pressure to follow the model, did not use assessment to inform teaching, and had concerns for future assessment use.

Structure of Amorphous Selenium: Small Ring, Big Controversy.

Selenium (Se) discovered in 1817 belongs to the family of chalcogens. Surprisingly, despite the long history of over two centuries and the chemical simplicity of Se, the structure of amorphous Se (a-Se) remains controversial to date regarding the dominance of chains versus rings. Here, we find that vapor-deposited a-Se is composed of disordered rings rather than chains in melt-quenched a-Se. We further reveal that the main origin of this controversy is the facile transition of rings to chains arising from the inherent instability of rings. This transition can be inadvertently triggered by certain characterization techniques themselves containing above-bandgap illumination (above 2.1 eV) or heating (above 50 °C). We finally build a roadmap for obtaining accurate Raman spectra by using above-bandgap excitation lasers with low photon flux (below 1017 phs m-2 s-1) and below-bandgap excitation lasers measured at low temperatures (below -40 °C) to minimize the photoexcitation- and heat-induced ring-to-chain transitions.

On the Construction of Confidence Regions for Uncertain Planar Displacements.

This paper studies the statistical concept of confidence region for a set of uncertain planar displacements with a certain level of confidence or probabilities. Three different representations of planar displacements are compared in this context and it is shown that the most commonly used representation based on the coordinates of the moving frame is the least effective. The other two methods, namely the exponential coordinates and planar quaternions, are equally effective in capturing the group structure of SE(2). However, the former relies on the exponential map to parameterize an element of SE(2), while the latter uses a quadratic map, which is often more advantageous computationally. This paper focus on the use of planar quaternions to develop a method for computing the confidence region for a given set of uncertain planar displacements. Principal component analysis (PCA) is another tool used in our study to capture the dominant direction of movements. To demonstrate the effectiveness of our approach, we compare it to an existing method called rotational and translational confidence limit (RTCL). Our examples show that the planar quaternion formulation leads to a swept volume that is more compact and more effective than the RTCL method, especially in cases when off-axis rotation is present.

Structure, bonding and electronic characteristics of amorphous Se.

Ovonic threshold switching (OTS) selectors can effectively improve the storage density and suppress the leakage current of advanced phase-change memory devices. As a prototypical OTS material, amorphous GeSe is widely investigated. But the attention paid to amorphous Se (i.e., the functional constituent in amorphous GeSe) has been very limited up to now. Here we have explored the structure, bonding and electronic characteristics of amorphous Se using ab initio molecular dynamics simulations. The results reveal that the Se atoms in amorphous Se tend to form 2-coordinated configurations, and they connect with each other to form long chains. The fraction of the vibrational density of state located in the high frequency range is relatively large, and the formation energy of the Se-Se bond is as large as 4.44 eV, hinting that the Se-Se bonds in chains possess high stability. In addition, the mid-gap state related to the OTS behavior is also found in amorphous Se despite the small proportion. Our findings enrich the knowledge of amorphous Se, which aids the applications of Se-based OTS selectors.

Self-assembled microflower-like NiCo2X4 (X = O, S, Se) as electrodes for asymmetric supercapacitors

The substitution of chalcogen elements has a notable influence on the microstructure and electrochemical properties of transition metal oxides. However, the underlying mechanism necessitates clarification. In this investigation, self-assembled microflower-like NiCo2X4 (X = O, S, Se) structures were successfully synthesized, and their microstructures and electrochemical performance were systematically examined using both theoretical and experimental approaches. Theoretical analysis demonstrated that the replacement of chalcogen elements significantly enhances the energy band structure of the material, thus effectively improving its electrochemical performance. Experimental results revealed that, in comparison to NiCo2O4 and NiCo2S4, NiCo2Se4 displayed remarkable electrochemical performance, with a specific capacitance of 1899 F g–1 at a current density of 1 A g–1 and a promising rate capability (with a capacitance retention increase of up to 71.9% when the current density was elevated from 1 A g–1 to 10 A g–1). Additionally, the asymmetric device (NiCo2Se4//AC), composed of NiCo2Se4 as the positive electrode and activated carbon (AC) as the negative electrode, exhibited an energy density of 42.44 Wh kg–1 at a power density of 1600 W kg–1. As a result, this study offers novel insights into the fabrication of transition metal compounds for energy storage applications.

Seismotectonic role of transversal structures in the Plio-Quaternary evolution of the external Marche Apennines (Italy)

We defined the seismotectonic setting of the external Marche Apennines (central Italy) by integrating geomorphological, structural and seismological data. The area is characterized by strong historical earthquakes, but the geometries and kinematics of the seismogenic sources have not previously been well defined. Plio-Quaternary Apennine compressional NW–SE structures are segmented by NE–SW-oriented transversal faults, the origin and role of which are still debated. We characterized the geometry, kinematics and activity of the four main transversal faults to better define their seismogenic potential. These high-angle, deeply rooted transversal fault systems have been mapped and separate the external Apennine sector into blocks and sub-blocks with different structural and evolutionary features. The integrated dataset showed that some inherited fault segments have recently been reactivated, displacing Quaternary deposits. The spatial distribution of seismicity indicates that some clusters of hypocentres are located within the basement. Stress field analysis using available focal mechanism solutions confirms the prevalence of left-lateral kinematics on roughly SW–NE-oriented structures. The transversal structures thus contribute to the longitudinal segmentation of the Apennine structures and, more generally, are involved in the northern part of the Adria plate kinematics towards the north and NNW. The assessment of seismic hazards and planning to mitigate risks in populated areas close to the Adriatic coast should consider these potentially active faults evidenced by instrumental seismicity and important historical earthquakes.

Facile Synthesis of Microsphere-like Co0.85Se Structures on Nickel Foam for a Highly Efficient Hydrogen Evolution Reaction.

Microsphere-shaped cobalt selenide (Co0.85Se) structures were efficiently synthesized via a two-step hydrothermal process. Initially, cobalt hydroxide fluoride (Co(OH)F) microcrystals were prepared using a hydrothermal method. Subsequently, Co0.85Se microsphere-like structures were obtained through selenization. Compared to Co(OH)F, the microsphere-like Co0.85Se structure exhibited outstanding catalytic activity for the hydrogen evolution reaction (HER) in a 1.0 M KOH solution. Electrocatalytic experiments demonstrated an exceptional HER performance by the Co0.85Se microspheres, characterized by a low overpotential of 148 mV and a Tafel slope of 55.7 mV dec-1. Furthermore, the Co0.85Se electrocatalyst displayed remarkable long-term stability, maintaining its activity for over 24 h. This remarkable performance is attributed to the excellent electrical conductivity of selenides and the highly electroactive sites present in the Co0.85Se structure compared to Co(OH)F, emphasizing its promise for advanced electrocatalytic applications.

New insight into flavivirus maturation from structure/function studies of the yellow fever virus envelope protein complex.

All enveloped viruses enter cells by fusing their envelope with a target cell membrane while avoiding premature fusion with membranes of the producer cell-the latter being particularly important for viruses that bud at internal membranes. Flaviviruses bud in the endoplasmic reticulum, are transported through the TGN to reach the external milieu, and enter other cells via receptor-mediated endocytosis. The trigger for membrane fusion is the acidic environment of early endosomes, which has a similar pH to the TGN of the producer cell. The viral particles therefore become activated to react to mildly acidic pH only after their release into the neutral pH extracellular environment. Our study shows that for yellow fever virus (YFV), the mechanism of activation involves actively knocking out the fusion brake (protein pr) through a localized conformational change of the envelope protein upon exposure to the neutral pH external environment. Our study has important implications for understanding the molecular mechanism of flavivirus fusion activation in general and points to an alternative way of interfering with this process as an antiviral treatment.

Antibacterial Effect of Shrimp By-Products Hydrolysate on Specific Spoilage Organisms of Squid.

In order to further develop and utilize shrimp processing by-products, in this study, a novel antibacterial hydrolysate of shrimp by-products by pepsin hydrolysis (SPH) was prepared. The antibacterial effect of SPH on specific spoilage organisms of squid after end storage at room temperature (SE-SSOs) was investigated. SPH showed an antibacterial effect on the growth of SE-SSOs, with (23.4 ± 0.2) mm of inhibition zone diameter. The cell permeability of SE-SSOs was enhanced after SPH treatment for 12 h. Some bacteria were twisted and shrunk, while pits and pores formed and intracellular contents leaked under scanning electron microscopy observation. The flora diversity of SE-SSOs treated with SPH was determined by a 16S rDNA sequencing technique. Results showed that SE-SSOs were mainly composed of the phyla of Firmicutes and Proteobacteria, among which Paraclostridium (47.29%) and Enterobacter (38.35%) were dominant genera. SPH treatment resulted in a significant reduction in the relative abundance of the genus Paraclostridium and increased the abundance of Enterococcus. Linear discriminant analysis (LDA) of LEfSe conveyed that SPH treatment had a significant impact on altering the bacterial structure of SE-SSOs. The 16S PICRUSt of Cluster of Orthologous Group (COG) annotation revealed that SPH treatment for 12 h could significantly increase the function of transcription level [K], while SPH treatment for 24 h could downregulate post-translational modifications, protein turnover, and chaperone metabolism functions [O]. In conclusion, SPH has a proper antibacterial effect on SE-SSOs and can change the flora structure of SE-SSOs. These findings will provide a technical basis for the development of inhibitors of squid SSOs.

A first principles study on electronic structure, magnetic and optical characteristics of Se doped CoNiFe2O4 spinel ferrites

Employing first principles calculations within the Density Functional Theory, the influence of Se dopants on electronic structure, magnetic and optical characteristics of CoNiFe2O4 (CNFO) spinel ferrites (SFs) is elucidated. The role of Se dopants replacing the O atoms in the supercell is revealed by means of spin-asymmetric density of states, magnetic moment, and optical spectra. The findings suggest that electronic structure, magnetism and optical properties are determined by both Se content and atomic arrangment due to doping sites. It is shown that the energy band gap declines with increasing Se concentration and that, based on site occupation, a half metallic characteristic can be achieved. An appreciable spin polarization and relevant data on optical characteristics demonstrate that Se doped CNFO SFs are promising candidates for prospective spin dependent applications and visible light photocatalysis.

Solid-state molecular structures of Se(IV) and Te(IV) dihalides X2Se(CH3)(C6F5) and the gas-phase structure of Se(CH3)(C6F5)

Abstract In a systematic study the Se(IV) and Te(IV) dihalides F2E(CH3)(C6F5), Cl2E(CH3)(C6F5) and Br2E(CH3)(C6F5) (E = Se, Te) have been synthesized and their crystal and molecular structures been investigated by X-ray diffraction and computational methods. The solid-state structures of all compounds show significant correlations between the lengths of the E–C1 bond and the intermolecular E···X (X = F, Cl and Br) contacts, indicating the presence of σ-hole interactions. For comparison, the crystal and gas phase (electron diffraction) structures of Se(CH3)(C6F5) are presented as well. They show very similar structural parameters in both phases. The structures of the single molecules X2E(CH3)(C6F5) have been analyzed by quantum-chemical methods in terms of their surface potentials. They show significant similarities of their molecular electrostatic-potential topologies (V s,max). The magnitude of V s,max correlates with the aggregation pattern.

Bandgap reduction at wrinkles on the cleavage surfaces of GeSe single crystals

Germanium selenide (GeSe), a van der Waals semiconductor, is heavily investigated due to its suitable bandgap of ∼ 1.2 eV for various applications. Herein, we investigate the atomic and electronic structures of GeSe single crystals using scanning tunneling microscopy/spectroscopy (STM/S). STM topography shows a rectangular lattice at GeSe surfaces, which are attributed to Se atom. We find that the highly localized state of an STM tungsten tip can allow for detection of the hidden Ge atoms, showing the zigzag structures of Se and Ge atoms in topography. It is also found that the cleavage surface of GeSe contains various wrinkles formed during mechanical exfoliations. Interestingly, STS spectra indicate that the bandgap is reduced to ∼ 1.0 eV at a wrinkle due to local strain. The uniaxial strain at the wrinkle is indeed estimated to be ∼ 7.4%, explaining such bandgap reductions. Our results provide important information for understanding the properties of GeSe.

Geometric Impedance Control on SE(3) for Robotic Manipulators

After its introduction, impedance control has been utilized as a primary control scheme for robotic manipulation tasks that involve interaction with unknown environments. While impedance control has been extensively studied, the geometric structure of SE(3) for the robotic manipulator itself and its use in formulating a robotic task has not been adequately addressed. In this paper, we propose a differential geometric approach to impedance control. Given a left-invariant error metric in SE(3), the corresponding error vectors in position and velocity are first derived. We then propose the impedance control schemes that adequately account for the geometric structure of the manipulator in SE(3) based on a left-invariant potential function. The closed-loop stabilities for the proposed control schemes are verified using Lyapunov function-based analysis. The proposed control design clearly outperformed a conventional impedance control approach when tracking challenging trajectory profiles.

Retention mechanism of calcium ferrite and compositions of ash on selenium during chemical looping gasification

Selenium pollution by coal utilization is of increasing concern. Calcium-iron (Ca–Fe) oxygen carriers (OCs) and alkali metal ions have strong inhibitory effects on selenium, which can reduce the emissions of selenium vapor. The retention mechanisms of selenium by Fe2O3, CaFe2O4, Ca2Fe2O5 and bottom ash are investigated during chemical looping gasification (CLG). Iron-based OC can oxidize H2Se(g) to SeO2(g); furthermore, lattice oxygen is released by Fe2O3, contributing to the formation of an Fe–O–Se structure to retain selenium and form selenite. Because calcium ferrite is poorly oxidizing, it cannot oxidize H2Se(g), but the CaO produced when OCs are reduced can react with H2Se(g) to form CaSe(s), and this process can be promoted by H2S(g). The best retention rates reached 32.301% when Ca2Fe2O5 was used. In the cyclic experiment, the selenium retention of the bottom ash gradually increases. Alkali metal ions in bottom ash are the main factor in retaining selenium. Ca2+ and Mg2+ do not easily vaporize due to their high melting points; therefore, their selenium retention is significantly better than that of K+ and Na+. This research provided a new idea for the removal of selenium by using OCs and bottom ash particles during CLG.

Insights into the impact of defect states and temperature on the performance of kesterite-based thin-film solar cells

In this study, we explore the influence of defect states density and operating temperatures on the performance of kesterite-based (CZT(S,Se)) solar cells such as CZTS, CZTSe, and CZTSSe. SCAPS codes were used as a constructive technique in modeling all structures. The CZT(S,Se) structures were modified by incorporating a p-Mo(S,Se)2 interfacial layer between the back contact and the absorber. Interestingly, only a 100 nm thick layer of p-Mo(S,Se)2 can establish a quasi-ohmic configuration at a CZT(S,Se)/Mo heterojunction, which was demonstrated by an increase in the slope of the J-V characteristics. In the active layer region, a series of systematic simulations were conducted depicting the response of CZTSSe/MoSSe structures to defect density states ranging from 1013 cm-3 to 1017 cm-3. The recombination behavior of CZTSSe/MoSSe solar cells is significantly superior to those made of CZTS/MoS2 or CZTSe/MoSe2, with a minimum increase in recombination current of 2.03 mA/cm2. The increased recombination rates are attributed to a shorter minority carrier lifetime at the buffer-absorber interface due to a reduced diffusion length between electrons and holes. Additionally, the photovoltaic parameters of the CZT(S,Se) structures were examined over a wide temperature range, from 275 K to 475 K, including open-circuit voltage (Voc), short circuit current (Jsc), fill factor (FF), and power conversion efficiency (PCE). A CZTS/MoS2-based structure exhibited the most stable performance at elevated temperatures up to 395 K with minimum degradation in PCE of approximately 2% compared to other solar cells. As a result, the voltage variation to temperature coefficients obtained for the CZTS and CZTSe solar cells were − 0.75 mV/K and − 1.2 mV/K, respectively. These findings support the use of CZTS/MoS2 structures in the development of photovoltaic modules that are capable of operating at high temperatures.

Preparation, Physicochemical and Hypoglycemic Properties of Natural Selenium-Enriched Coarse Tea Glycoproteins.

Various functional components in tea have been well developed, but less research has been explored on glycoproteins in tea. In this paper, three types of glycoprotein fractions, namely tea selenium-binding glycoprotein1-1 (TSBGP1-1), TSBGP2-1, and TSBGP3-1, respectively, were extracted and purified from selenium-enriched coarse green tea. Chemical analysis revealed that three fractions were glycoproteins, but their selenium content, molecular weight, and monosaccharide composition were significantly different. Fourier transforms infrared (FT-IR) analysis indicated that three fractions contained characteristic absorption peaks of glycoproteins but differed in secondary structural composition. Thermogravimetric (TG) analysis showed that the thermal stability of the three fractions was dramatically distinct. The in vitro hypoglycemic activity showed that TSBGPs significantly activated the insulin receptor substrate 2 (IRS2)/protein kinase B (Akt) pathway in LO2 cells, then enhanced glucose metabolism and inhibited gluconeogenesis, and finally ameliorated insulin resistance (IR) and glucose metabolism disorders. Furthermore, Pearson correlation analysis reveals that the hypoglycemic activity was significantly correlated with Se, protein, monosaccharide composition (especially glucose), molecular weight, and secondary structure. Our results show that Se-enriched tea glycoprotein is a desirable candidate for developing anti-diabetic food, and TSBGP-2 and TSBGP-3 had a better regulation effect. Our results can provide a research reference for the extraction, physicochemical property, and function of selenium-enriched plant glycoproteins.

Electronic band structure and chemical bonding in trigonal Se and Te

Herein, the electronic band structure and charge density distribution are theoretically studied in trigonal Se and Te to clarify the uncertainty stemming from the different views on the types of chemical bonding in their crystals and to reconsider the role of valence s- and p-electrons in bonding. The lack of overlapping of the lower and upper bands of valence p-electrons in trigonal Se and the large band separation of valence s- and p-electrons present an opportunity to estimate the contributions of valence s- and p-electrons to the charge densities of two types of bond critical points (BCPs) in trigonal Se. Valence s-electrons and lower p-electrons significantly contribute to the charge density of BCPs of the first type, covalently connecting the nearest neighboring atoms within helical chains. In contrast, the lower and upper valence p-electrons are mainly responsible for the BCPs of the second type linking the neighboring chains in the Se and Te trigonal crystal structures. The nonlocal long-range van der Waals (vdW) correlation functional vdW-DF2, which is important for determining lattice constants, has a minimal effect on BCP parameters, which define the chemical bonding types. The exchange potential of Becke and Johnson modified by Tran and Blaha and the short-range electron–electron correlations considered in the local density approximation correctly reproduce not only the energy bandgap values but also various peculiarities in the electronic band structure of trigonal Se and Te, such as band crossings (Weyl nodes) of the valence p-electrons recently found in trigonal Te via angle-resolved photoemission spectroscopy experiments.