Splitting Values Research Articles

Valley splitting of monolayer Hf3C2O2 by the spin-orbit coupling effect: first principles calculations using the HSE06 methods.

Electrons have not only charge and spin degrees of freedom, but also additional valley degrees of freedom. The search for valleytronic materials with large valley splits is important for the development of valleytronics. In this work, we applied first principles computations to calculate 1 L Hf3C2O2 at the level of HSE06. When the spin-orbit coupling (SOC) effect is considered, 1 L Hf3C2O2 is an indirect bandgap semiconductor with a bandgap of 0.952 eV. Meanwhile, valley splitting occurs between the conduction bands Γ and K, with a valley splitting value as high as 98.228 meV. Bader charge analysis was used to determine that Hf-O and Hf-C are ionic bonds. The computed elastic constants and phonon spectra proved that 1 L Hf3C2O2 is mechanically and dynamically stable. In addition, the Berry curvature of 1 L Hf3C2O2 is non-zero. In the work the effect of the electronic properties of 1 L Hf3C2O2 was also calculated with respect to the biaxial strain. The results show that the biaxial strain can well regulate the band gap and valley splitting. Finally, we calculated the effects of hole and electron doping on the band gap and valley splitting of 1 L Hf3C2O2. The results show that the band gap and valley splitting are linearly related to the doping concentration. Our study shows that 1 L Hf3C2O2 is a promising two-dimensional valleytronics material.

The Large Magellanic Cloud: expanding the low-mass parameter space of dark matter direct detection

We investigate how the Large Magellanic Cloud (LMC) impacts the predicted signals in near-future direct detection experiments for non-standard dark matter (DM) interactions, using the Auriga cosmological simulations. We extract the local DM distribution of a simulated Milky Way-like halo that has an LMC analogue and study the expected signals in DarkSide-20k, SBC, DARWIN/XLZD, SuperCDMS, NEWS-G, and DarkSPHERE considering DM-nucleon effective interactions, as well as inelastic DM scattering. We find that the LMC causes substantial shifts in direct detection exclusion limits towards smaller cross sections and DM masses for all non-relativistic effective field theory (NREFT) operators, with the impact being highly pronounced for velocity-dependent operators at low DM masses. For inelastic DM, where the DM particle up-scatters to a heavier state, the LMC shifts the direct detection exclusion limits towards larger DM mass splitting and smaller cross sections. Thus, we show that the LMC significantly expands the parameter space that can be probed by direct detection experiments towards smaller DM-nucleon cross sections for all NREFT operators and larger values of mass splitting for inelastic DM.

Pyrochlore-like Local Structure in Globally Disordered Y2Zr2O7: Evidence and Reasoning by Combined Theoretical and Experimental Study.

Even though technological relevance for nuclear and oxide fuel cell application has persuaded a large number of investigations on the Y2Zr2O7 system, its local structure still remains ambiguous and debatable. While diffraction-based investigations claim a lack of local ordering, the MAS NMR and Raman spectroscopic investigations speculate the presence of local ordering. Besides, a correlation between the local and global structures of Y2Zr2O7 is also missing to date. Present work attempts to get deeper insights into the local structure of Y2Zr2O7 and correlate the local structure with global disordering. Complementary investigation using multiple strategies (XRD, RAMAN, electron microscopy, DFT calculations) revealed the presence of pyrochlore-like features in globally disordered Y2Zr2O7. Globally distributed "local probe ions" (Sn4+ by MAS NMR and Eu3+ by photoluminescence (PL)) were utilized for establishing the correlation between local and global structures. The 119Sn MAS NMR spectra possess the shoulder peak bearing chemical shift values, which are improbable under complete cationic randomization. The emission and decay profiles of the Eu3+ ion recommend positioning of few probe ions at the centrosymmetric site, which was further reinforced by crystal field splitting and lifetime values. Thus, both NMR and PL results reaffirm the existence of a pyrochlore-like atomic arrangement in predominantly defective fluorite Y2Zr2O7 phase. These discernible pyrochlore-like features have been envisaged to be emanating from unevenness in bond strength and ionicity/covalency of Y-O and Zr-O bonds. Cationic and anionic randomization energetically endorses global disordering, but the bonding disparity induces short-range ordering. It is believed that the presented findings will guide future research in regulating the physicochemical properties of Y2Zr2O7 for the target applications.

Mechanical Properties of Concrete Blended with Rice Husk Ash, Oyster Shell Powder, and Ferrous Powder

Due to emerging global environmental awareness, the increasing demand on synthesizing green materials for structural purposes became prevalent. This study utilized agricultural, aquacultural, and industrial waste as partial replacement for fine aggregates in concrete. One standard and six concrete samples with various proportions (20% and 40%) of rice husk ash (RHA), oyster shell powder (OSP), and ferrous powder (FeP) were constructed and tested for their mechanical properties (i.e., compressive and split tensile strength). The samples containing 20% and 40% FeP attained the highest compressive (22.71 MPa) and split tensile strength (1.379 MPa), respectively, which are closest to the control, M25 grade concrete (C-M25), (23.87 MPa), and (1.44 MPa), respectively. Concrete fracture analysis indicated that the cylinders were well constructed as implied by the fracture types. The C-FeP is the best concrete mixture attaining superior compressive and split tensile strength values.

A Supervised Ml Algorithm for Detecting and Predicting Fraud Credit Card Transactions

A Credit card fraud presents an escalating threat in today's digital economy, leading to significant financial losses for consumers, businesses, and financial institutions. Traditional detection methods are increasingly inadequate due to the rise in online transactions and the evolving complexity of fraudulent activities. This research aims to create a reliable supervised machine learning model designed to detect and predict fraudulent credit card transactions in real-time. Our approach leverages advanced algorithms and extensive datasets to enhance transaction security, thereby mitigating financial risks. Current systems, like FICO's Fraud Detection System (FDS), utilize a range of supervised learning techniques, including Decision Trees, Random Forests, and Neural Networks. However, they face limitations, including data quality issues, high false positive rates, and the need for continuous retraining to adapt to evolving fraud patterns. To address these challenges, we propose an innovative anomaly detection method based on the Isolation Forest algorithm. Unlike traditional methods that rely on distance and density measures, Isolation Forests isolate anomalies by randomly selecting features and split values, making it more efficient in identifying fraudulent transactions, especially in imbalanced datasets. The proposed system boasts low linear time complexity and minimal memory requirements, enabling the construction of high-performing models even with large datasets. The research demonstrates that the Isolation Forest approach significantly outperforms traditional models in detecting credit card fraud, offering a promising solution for enhancing security in the financial ecosystem.

How symmetry helps to improve the estimation of the hyperfine splitting of torsional levels due to tunneling. The case of the HSSSH molecule

In this study, we analyze a series of molecules belonging to the C2V(M) molecular symmetry group which are characterized by several conformers. The use of molecular symmetry at each stage of calculating the energy of stationary torsional states is demonstrated. In particular, the importance is shown of preliminary symmetrization of physical characteristics of the molecules obtained by quantum chemical calculations. For the first time, symmetry-adapted basis functions for the diagonal kinetic coefficients are presented, which for the analyzed molecules do not satisfy all symmetry operations of the C2V(M) group. Using the HSSSH molecule as an example, it is shown how the full or partial accounting for molecular symmetry influences the calculated values of ultra-small tunneling splittings of the ground torsional states of the trans- and cis-conformers. It has also been established that the Hamiltonian matrix is characterized by symmetry which, when taken into account, makes it possible to halve the time of calculation of its elements.

High resolution laser diode spectroscopy of the hot bands of C2HD in the first overtone region of C-H stretching

The frequencies of C2HD hot bands ro-vibrational lines of the first overtone of C-H stretching were measured using tunable diode lasers. To expand the measuring range to the region of the large rotational numbers, a heated gas cell was used. Measurements were made in the range R1–R36 and P2–P14 for the transition (2,0,0,1,0) ← (0,0,0,1,0), and in the range R1–R18 for the transition (2,0,0,0,1) ← (0,0,0,0,1). The rotational parameters of the upper and lower states for the band (2,0,0,1,0) ← (0,0,0,1,0) were determined. The doublet structure of ro-vibrational lines was studied. For the transition (2,0,0,1,0) ← (0,0,0,1,0), a sharp increase in the splitting value was detected at J > 25.

Family of Quasi-Isotropic MnII and Mn2II Complexes Exhibiting Slow Relaxation of the Magnetization.

Slow relaxation of magnetization has been studied for a family of mononuclear MnII complexes and one ferromagnetic dinuclear system, all of them presenting very weak anisotropy. Complexes with formula [{NiL1Mn(H2O)2(MeOH)}{NiL1}2](ClO4)2 (1), [Mn{NiL1}2](ClO4)2 (2), [Mn{NiL2}2](ClO4)2 (RR-L22-, 3RR, SS-L22-, 3SS), [Mn{NiL3}2](ClO4)2 (RR-L32-, 4RR, SS-L32-, 4SS) and (μ1,1-N3)2[Ni2Mn2(L1)2(N3)2] (5) are derived from compartmental Schiff bases, in which the NiII environment is square planar and thus diamagnetic. All of the systems have been structurally and magnetically characterized. Zero field splitting (D) values for the MnII cations have been obtained from EPR spectroscopy and NEVPT2 calculations. The slow relaxation of the magnetization for 1-5 has been studied by means of ac magnetometry and rationalized on the basis of their low, but not zero, anisotropy, providing the first example of a polynuclear MnII complex, with S = 5 ground state, exhibiting slow relaxation.

Quantitative assessment of kidney split function and mean transit time in healthy patients using dynamic 18F-FDG PET/MRI studies with denoising and deconvolution methods making use of Legendre polynomials

PurposeOur objective was to assess a deconvolution and denoising technique based on Legendre polynomials compared to matrix deconvolution on dynamic 18F-FDG renography of healthy patients.MethodThe study was carried out and compared to the data of 24 healthy patients from a published study who underwent examinations with 99mTc-MAG3 planar scintigraphy and 18F-FDG PET/MRI. Due to corruption issues in some data used in the published article, post-publication measurements were provided. We have been warned that post-publication data were treated differently. The smoothing method switched from Bezier to Savitzky–Golay and the deconvolution from matrix-based (with Tikhonov Regularization) to Richardson–Lucy. A comparison of the split function and mean transit times of the published and post-publication data against our method based on Legendre polynomials was performed.ResultsFor split function, we only observed a good agreement between the processing methods for the 99mTc-MAG3 and the post-published data. No correlation was found between the split functions obtained on the 99mTc-MAG3 and the 18F-FDG, contrary to the published study. However, all calculated split function values for 18F-FDG and 99mTc-MAG3 were within the established normal range. For the mean transit time, the correlation was moderate with published data and very good with the post-publication measurements for both 99mTc-MAG3 and 18F-FDG. Bias of the Bland–Altman analysis of the mean transit times for 99mTc-MAG3 versus 18F-FDG was 1.1 min (SD 1.7 min) for the published data, − 0.11 min (SD 1.9 min) for the post-publication results and .05 min (SD 1.9 min) for our method.ConclusionsThe processing methods used in the original publication and in the post-publication work were quite complex and required adaptation of the fitting parameters for each individual and each type of examination. Our method did not require any specific adjustment; the same unmodified and fully automated algorithm was successfully applied to all data.

Protoporphyrin IX iron(II) revisited. An overview of the Mössbauer spectroscopic parameters of low-spin porphyrin iron(II) complexes

Mössbauer parameters of low-spin six-coordinate [Fe(II)(Por)L2] complexes (where Por is a synthetic porphyrin; L is a nitrogenous aliphatic, an aromatic base or a heterocyclic ligand, a P-bonding ligand, CO or CN) and low-spin [Fe(Por)LX] complexes (where L and X are different ligands) are reported. A known point charge calculation approach was extended to investigate how the axial ligands and the four porphyrinato-N atoms generate the observed quadrupole splittings (ΔEQ) for the complexes. Partial quadrupole splitting (p.q.s.) and partial chemical shifts (p.c.s.) values were derived for all the axial ligands, and porphyrins reported in the literature. The values for each porphyrin are different emphasising the importance/uniqueness of the [Fe(PPIX)] moiety, (which is ubiquitous in nature). This new analysis enabled the construction of figures relating p.c.s and p.q.s values. The relationships presented in the figures indicates that strong field ligands such as CO can, and do change the sign of the electric field gradient in the [Fe(II)(Por)L2] complexes. The limiting p.q.s. value a ligand can have and still form a six-coordinate low-spin [Fe(II)(Por)L2] complex is established. It is shown that the control the porphyrin ligands exert on the low-spin Fe(II) atom limits its bonding to a defined range of axial ligands; outside this range the spin state of the iron is unstable and five-coordinate high-spin complexes are favoured. Amongst many conclusions, it was found that oxygen cannot form a stable low-spin [Fe(II)(Por)L(O2)] complex and that oxy-haemoglobin is best described as an [Fe(III)(Por)L(O2−)] complex, the iron is ferric bound to the superoxide molecule.Graphical abstract

Kajian Laboratorium Kuat Tarik Belah Beton Egg Tray Dengan Penambahan Superplasticizer

Using egg tray waste as a fine aggregate substitute can be an alternative for making environmentally friendly concrete. The weaknesses of concrete with egg trays can corrected by adding a superplasticizer to both the compressive strength and split tensile strength of the concrete. This study used an egg tray waste as a fine aggregate substitution of 3% with variations in superplasticizer content. The test specimens were by a concrete cylinder with a diameter of 15 cm and a height of 30 cm, which varied the superplasticizer content by 0%, 0.5%, 1%, 1.5%, 2%, and 5% compared to normal concrete conditions. The test results show that concrete given a 3% egg tray waste as a substitute for fine aggregate has a lower split tensile strength value than normal concrete. Adding superplasticizer material can increase the value of split tensile strength up to 1% superplasticizer content. As the superplasticizer content increases, the value of the split tensile strength will again decrease.

Asteroseismic signatures of core magnetism and rotation in hundreds of low-luminosity red giants

ABSTRACT Red giant stars host solar-like oscillations which have mixed character, being sensitive to conditions both in the outer convection zone and deep within the interior. The properties of these modes are sensitive to both core rotation and magnetic fields. While asteroseismic studies of the former have been done on a large scale, studies of the latter are currently limited to tens of stars. We aim to produce the first large catalogue of both magnetic and rotational perturbations. We jointly constrain these parameters by devising an automated method for fitting the power spectra directly. We successfully apply the method to 302 low-luminosity red giants. We find a clear bimodality in core rotation rate. The primary peak is at $\delta \nu _{\mathrm{rot}}$ = 0.32 $\mu$Hz, and the secondary at $\delta \nu _{\mathrm{rot}}$ = 0.47 $\mu$Hz. Combining our results with literature values, we find that the percentage of stars rotating much more rapidly than the population average increases with evolutionary state. We measure magnetic splittings of 2$\sigma$ significance in 23 stars. While the most extreme magnetic splitting values appear in stars with masses $\gt $1.1 M$_{\odot }$, implying they formerly hosted a convective core, a small but statistically significant magnetic splitting is measured at lower masses. Asymmetry between the frequencies of a rotationally split multiplet has previously been used to diagnose the presence of a magnetic perturbation. We find that of the stars with a significant detection of magnetic perturbation, 43 per cent do not show strong asymmetry. We find no strong evidence of correlation between the rotation and magnetic parameters.

Spin-orbit coupling in monolayer graphene doped by Cd and Te atoms

Using the density functional theory, the electronic band structure of pure and doped by cadmium and tellurium atoms monolayer graphene has been studied. It is shown that doping by cadmium and tellurium leads to the appearance of an energy gap, as well as an enhancement of spin-orbit interaction in graphene. The maximum value of spin-orbit splitting in doped graphene obtained from energy spectra is 0.23 eV. The value of spin-orbit splitting for different doped atoms varies in the range of 0.08–0.23 eV. It should also be noted that the enhancement of spin-orbit interaction in graphene depends on the concentration of atoms doped into the lattice. At low concentrations, the energy states splitting caused by spin-orbit interaction is not observed.

Pemanfaatan Abu Cangkang Kopi Sebagai Substitusi Semen Untuk Bahan Beton Ringan Menggunakan Bahan Tambah Sikament NN

The chemical reaction of cement and water produces compounds that are alkaline and react with various acids so that they can reduce the quality of concrete. To minimize this effect, pozzolanic materials need to be added. Organic pozzolan materials such as coffee shell ash waste can be used as material for making lightweight foam concrete which can be applied to non-structural buildings such as lightweight bricks. This research was conducted to see the effect of coffee shell ash substitution for cement on the properties of fresh concrete and the mechanical properties of lightweight foam concrete and to find the most optimal substitution composition for coffee shell ash for cement as well as lightweight foam concrete with FAS 0.5. Substitution of coffee shell ash for cement weight was carried out with variations of 0% BBN, 5% BBAAK1, 10% BBAAK2, and 15% BBAAK3 using 1% superplasticizer additive. The test object used is a cylinder with dimensions of 15 cm x 30 cm. The number of test objects used was 24 pieces. Tests for compressive strength and split tensile strength were carried out at the age of 28 days. The results of compressive strength tests carried out at 28 days for the lightweight foam concrete variations BBN, BBAAK 1, BBAAK 2 and BBAAK 3 were respectively 15.29 MPa, 12.21 MPa, 18.29 MPa and 19.52 MPa. The greater showing variation in the percentage of coffee shell ash substitution used, the greater the resulting compressive strength and split tensile strength values. This is because Sikament NN also plays a role in increasing the compressive strength of concrete

A perspective on boron-based multiple resonance narrowband emitters and devices

Boron-based multiple resonance thermally activated delayed fluorescent (MR-TADF) emitters have shown great promises for applications in high-definition displays. This class of heteroatom-doped nanographene materials typically show very narrow-band emission, small singlet–triplet split (ΔEST) values, high Photoluminescence quantum yield, quality chemical and thermal stabilities. Undoubtedly, boron-based MR-TADF emitters hold a leading position in satisfying the wide-color gamut standard of BT. 2020 (The International Telecommunication Union announced a new color gamut standard of broadcast service television for ultra-high-definition TV in 2012). Thus, the development of novel boron-based MR-TADF emitters attracted a great deal of attention from both academia and industry. Here, a comprehensive overview of the latest advances in boron-based MR-TADF emitters is presented, therein, rational strategies for molecular designs, as well as the consequent optical behavior and efficiency and lifetime improvement in organic light-emitting diodes (OLED) devices are discussed. Finally, the challenges as well as some future research directions to unlock the full potential of this fascinating class of materials are provided.

НЕЧЕТКИЙ МЕТОД ПОВЫШЕНИЯ КОНТРАСТНОСТИ КАРТОГРАФИЧЕСКИХ ИЗОБРАЖЕНИЙ НИЗКОГО КАЧЕСТВА

In this study, we have developed a new image enhancement method that uses fuzzy logic. This method allows us to split pixel values into different levels of importance, which helps to compensate for the loss of local brightness in dark and bright areas of an image. The goal is to increase the overall brightness of the image while preserving details. The process involves three stages. Firstly, the satellite image is transformed into a membership space using the c-means clustering algorithm. This creates a model that can be used to convert each pixel value into a level of importance. Secondly, a corresponding model is created for each level of importance based on the membership data. Finally, the image is transformed back into a standard brightness space by combining the grayscale values for each level. Our results show that this method improves the visual quality and accuracy of measurements when compared to traditional methods.

Spin Polarization Enhances the Catalytic Activity of Monolayer MoSe2 for Oxygen Reduction Reaction.

The key factors in achieving high energy efficiency for proton exchange membrane fuel cells are reducing overpotential and increasing the oxygen reduction rate. Based on first-principles calculations, we induce H atom adsorption on 4 × 4 × 1 monolayer MoSe2 to induce spin polarization, thereby improving the catalytic performance. In the calculation of supercells, the band unfolding method is used to address the band folding effect in doped systems. Furthermore, it is evident from analyzing the unique energy band configuration of MoSe2 that a higher valley splitting value has better catalytic effects on the oxygen reduction reaction. We believe that the symmetries of the distinct adsorption site result in different overpotentials. In addition, when an even number of hydrogen atoms is adsorbed, the monolayer MoSe2 has no spin polarization. The spin can affect the electron transfer process and alter the hybrid energy with the reaction products, thereby regulating its catalytic performance.

Large valley splitting induced by spin-orbit coupling effects in monolayer Hf3N2O2

Valleytronics is an emerging field of electronics that aims to utilize valley degrees of freedom in materials for information processing and storage. Nowadays, the valley splitting of 2D materials is not particularly large, therefore, the search for large valley splitting materials is very important for the development of valleytronics. This work theoretically predicts that MXene Hf3N2O2 is a 2D material with large valley splitting. It is an indirect bandgap semiconductor with a bandgap of 0.32 eV at the PBE level and increases to 0.55 eV at the HSE06 level. Since Hf3N2O2 breaks the symmetry of spatial inversion, when we consider spin–orbit coupling (SOC), there is a valley splitting at K/K′ of the valence band with a valley splitting value of 98.76 meV. The valley splitting value slightly decreases to 88.96 meV at the HSE06 level. In addition, The phonon spectrum and elastic constants indicate that it is both dynamically and mechanically stable. According to the maximum localization of the Wannier function, it is obtained that the Berry curvature is not zero at K/K′. When a biaxial strain is applied, Hf3N2O2 transitions from metal to semiconductor. With increasing biaxial strain, the valley splitting value increased from 70.13 meV to 109.11 meV. Our research shows that Hf3N2O2 is a promising material for valleytronics.

Unveiling the impact of Fe-doping concentration on the local structure and morphological evolution of Cr2O3 nanoparticles

A series of Cr2−xFexO3 (0.0 ≤ x ≤ 0.3) nanoparticles were successfully synthesized using a sol-gel-based method. Analysis through XRD and SAED of both pure and Fe-doped Cr2O3 nanoparticles revealed a rhombohedral structure belonging to the R3‾cD3d6 space group, without the formation of secondary phases or Fe clusters. Fe ions were well integrated, as indicated by fluctuations in lattice parameters, and lattice strain. The crystallite size decreased from 38.42 to 27.54 nm with increasing doping concentration. HRTEM images depicted evenly distributed nanoparticles. At lower dopant concentrations (x = 0.1), smaller and more heterogeneous nanorod-like structures emerged, with average sizes and lengths of 36.56 and 39 nm, respectively. Increasing the doping content to x = 0.2 resulted in a morphological shift towards semi-spherical and ellipsoidal shapes, with average dimensions of 22.84 and 31 nm, respectively. At higher doping levels (x = 0.3), nanoparticles grew to 66.5 nm in size and exhibited a spherical morphology. Raman and Fourier transform infrared spectra showed red-shifting of absorption bands with increasing Fe content, attributed to variations in bond length and Cr/Fe–O–Cr/Fe structural perturbation. XPS and Mössbauer spectroscopy analyses confirmed the oxidation states of Fe3+ and ionized oxygen vacancies in the crystal lattice of Cr2O3 nanoparticles. Higher values of quadrupolar splitting Δ indicated greater structural disorder induced by Fe3+ in octahedral positions and in an oxygen-deficient environment. Atomistic simulations confirmed that Fe3+ dopants can induce the presence of vacancy-complexes, forming a stable double-defect configuration with vacant Cr sites along the c-axis, proximal to oxygen vacancies with a single positive charge. These findings offer both experimental and theoretical insights into the dynamics of structural defects in trivalent transition metal doping of Cr2O3 nanoparticles, which holds significant implications for spintronics research.

Giant asymmetric proximity-induced spin–orbit coupling in twisted graphene/SnTe heterostructure

We analyze the spin–orbit coupling effects in a 3∘-degree twisted bilayer heterostructure made of graphene and an in-plane ferroelectric SnTe, with the goal of transferring the spin–orbit coupling from SnTe to graphene, via the proximity effect. Our results indicate that the point-symmetry breaking due to the incompatible mutual symmetry of the twisted monolayers and a strong hybridization has a massive impact on the spin splitting in graphene close to the Dirac point, with the spin splitting values greater than 20 meV. The band structure and spin expectation values of graphene close to the Dirac point can be described using a symmetry-free model, triggering different types of interaction with respect to the threefold symmetric graphene/transition-metal dichalcogenide heterostructure. We show that the strong hybridization of the Dirac cone’s right movers with the SnTe band gives rise to a large asymmetric spin splitting in the momentum space. Furthermore, we discover that the ferroelectricity-induced Rashba spin–orbit coupling in graphene is the dominant contribution to the overall Rashba field, with the effective in-plane electric field that is almost aligned with the (in-plane) ferroelectricity direction of the SnTe monolayer. We also predict an anisotropy of the in-plane spin relaxation rates. Our results demonstrate that the group-IV monochalcogenides MX (M = Sn, Ge; X = S, Se, Te) are a viable alternative to transition-metal dichalcogenides for inducing strong spin–orbit coupling in graphene.