Gap Function Research Articles

Accuracy of approximate methods for the calculation of fluorescence-type linear spectra with a complex system-bath coupling.

Much can be learned about molecular aggregates by modeling their fluorescence-type spectra. In this study, we systematically describe the accuracy of various methods for simulating fluorescence-type linear spectra in a dimer system with a complex system-environment interaction, which serves as a model for various molecular aggregates, including most photosynthetic light-harvesting complexes (LHCs). We consider the approximate full cumulant expansion (FCE), complex time-dependent Redfield (ctR), time-independent Redfield, and modified Redfield methods and calculate their accuracy as a function of the site energy gap and coupling, excitonic energy gap, and dipole factor (i.e., type of spectrum). We find that the FCE method is the most accurate method for couplings smaller than 300cm-1 at 300K, but this method fails for very strong couplings or low temperatures due to inaccurate modeling of the equilibrium initial state. The ctR method performs well for the calculation of fluorescence and linear anisotropy spectra but poorer for circularly polarized fluorescence spectra or for all spectra when the coupling is strong (∼100cm-1). The Redfield and modified Redfield methods generally perform much more poorly than the ctR and FCE methods-especially for small excitonic energy gaps and strong couplings. We show that accurate modeling of the Stokes shift is crucial and present a version of the ctR method that treats both the Stokes shift and initial state correctly for the parameter ranges in plant LHCs. Apart from the application to LHCs, our results will be useful for the spectral characterization and design of organic molecular aggregates.

The BCS-Bogoliubov gap equation with external magnetic field and the first-order phase transition

Abstract We deal with a type I superconductor in a constant external magnetic field. We obtain the BCS-Bogoliubov gap equation with external magnetic field and apply the implicit function theorem to it. We show that there is a unique magnetic field (the critical magnetic field) given by a smooth function of the temperature and that there is also a unique nonnegative solution (the gap function) given by a smooth function of both the temperature and the external magnetic field. Using the grand potential, we show that the transition from the normal state to the superconducting state in a type I superconductor is of the first order. Moreover we obtain the explicit expression for the entropy gap.

Adsorption and Sensing Performance of Transition Metal Decorated Graphene Quantum Dots for AsH3, NH3, PH3, and H2S.

We have conducted a systematic study employing density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) to explore the gas sensing capabilities of nitrogen-doped single vacancy graphene quantum dots (SV/3N) decorated with transition metals (TM = Mn, Co, Cu). We have studied the interactions between TM@SV/3N and four different target gases (AsH3, NH3, PH3, and H2S) through the computation of adsorption energies, charge transfer, noncovalent interaction, density of states, band gap, and work function for 12 distinct adsorption systems. Our comprehensive analysis included an in-depth assessment of sensors' stability, sensitivity, selectivity, and reusability for practical applications. Our findings indicate that the Co@SV/3N surface strongly interacts with PH3, with the highest adsorption energy (-1.15 eV). It shows remarkable sensitivity and selectivity toward PH3, making it a promising candidate for PH3 gas sensing applications. Similarly, Mn@SV/3N exhibits high sensitivity and selectivity toward NH3, positioning it as a suitable candidate for NH3 gas sensing applications. We believe this study will provide valuable theoretical guidance for developing TM@SV/3N-based gas sensors.

Steric Engineering of Exciton Fine Structure in 2D Perovskites

AbstractA comprehensive study of excitonic properties of 2D layered perovskites is provided, with an emphasis on understanding and controlling the exciton fine structure. First, an overview of the optical properties is presented, discussing the challenges in determining the bandgap and exciton binding energies. Through magneto‐optical spectroscopic measurements (up to B = 140 T), scaling laws are established for exciton binding energy as a function of the band gap and the diamagnetic coefficient. Using an in‐plane magnetic field, the exciton fine structure for various 2D perovskites is examined to measure the energy splitting between the excitonic levels. The exciton fine structure and exchange interaction are correlated with structural parameters, employing an effective mass model, to highlight the role of steric effect on the exchange interaction. These findings reveal that lattice distortions, introduced by organic spacers, significantly influence the exchange interaction, driving a tunable energy spacing between dark and bright excitons. This unique feature of 2D perovskites, not present in other semiconductors, offers a novel tuning mechanism for exciton control, making these materials highly promising for efficient light emitters and advanced quantum technologies.

Superconductivity in a background of topological spin texture

Motivated by a recent experiment on high-temperature superconductors (Wang Z. C. et al., Nature, 615, (2023) 405), we perform a theoretical study to distinguish the nature of the topological spin texture in the superconducting phase of an underdoped cuprate. We propose a phenomenological tight-binding model of electrons with spin-singlet pairing hopping in the background of topological spin texture on the square lattice to capture the coupling of electrons and the topological spin texture. Two types of topological spin texture relevant to the experiment are considered, i.e., Bloch skyrmion and sinusoidal vortex, and the Bogoliubov-de Gennes mean-field theory is employed to calculate the gap functions and local density of states. We discover an emergent d xy -wave component in the imaginary part of the gap function for skyrmion, but this is not present for vortex. For skyrmion, each coherent peak in the local density of states splits into two spatially uniform peaks, while for vortex, it splits into two spatially modulated peaks. Our study reveals the qualitatively different consequences of two types of topological spin texture, and can be possibly detected in the further STM experiment.

Frozen autocatalytic fronts in a radial flow

Autocatalytic reaction-diffusion fronts are localized reaction zones propagating at a constant speed with a constant width. We show both theoretically and experimentally that, if the reactant Y of the autocatalytic reaction is injected radially at a constant flow rate in a sea of the autocatalytic species X, a stationary front can be maintained at a fixed position that scales linearly with the flow rate. When this reaction front is about to reach a stationary state, a second outward traveling front emerges to adapt the outer concentration of the autocatalytic species to the stoichiometry ratio between X and Y. Simple analytical solutions to the reaction-diffusion-advection equations governing the dynamics are computed for both fronts. The analytical predictions for the stationary front position and moving front dynamics as a function of injection flow rate, reactant concentration, and gap of the quasi-two-dimensional reactor agree well with experimental results obtained with the autocatalytic chlorite-tetrathionate reaction. Published by the American Physical Society 2024

Macro-financial linkage, endogenous risk premium and monetary policy: evidence from a semi-structural model estimated for Morocco

PurposeThis paper seeks to investigate the amplitude of macro-financial linkage for an emerging country like Morocco.Design/methodology/approachFor this purpose, it presents a semi-structural new-Keynesian model. In the blocks of the former, a risk premium is charged on the lending rate in addition to the policy rate. To identify the macro-financial linkage, the risk premium is considered endogenous. It is represented as a function of the borrower’s probability of default, which is, in turn, a function of the GDP gap. To identify this two-wave relationship, we estimate an ARDL model between 2009Q1 and 2020Q1. Therefore, we integrate the estimation results into the new-Keynesian semi-structural model.FindingsThe results reveal a significant impact of the financial condition on the path of the business cycle. In fact, demand shocks and nonperforming loan shocks (NPLs) are exacerbated by the presence of macro-financial linkage. Under this condition, the amplitude and persistence of the shocks are amplified and extended.Originality/valueThis paper extends the literature on the interconnection between the real and financial economies by considering the endogeneity of the credit risk premium and modeling its dynamics.

Probing p-wave superconductivity in UTe2 via point-contact junctions

Uranium ditelluride (UTe2) is the strongest contender to date for a p-wave superconductor in bulk form. Here we perform a spectroscopic study of the ambient pressure superconducting phase of UTe2, measuring conductance through point-contact junctions formed by metallic contacts on different crystalline facets down to 250 mK and up to 18 T. Fitting a range of qualitatively varying spectra with a Blonder-Tinkham-Klapwijk (BTK) model for p-wave pairing, we can extract gap amplitude and interface barrier strength for each junction. We find good agreement with the data for a dominant py-wave gap function with amplitude 0.26 ± 0.06 meV. Our work provides spectroscopic evidence for a gap structure consistent with the proposed spin-triplet pairing in the superconducting state of UTe2.

A semi-definite optimization method for maximizing the shared band gap of topological photonic crystals

Topological photonic crystals (PCs) can support robust edge modes to transport electromagnetic energy in an efficient manner. Such edge modes are the eigenmodes of the PDE operator for a joint optical structure formed by connecting together two photonic crystals with distinct topological invariants, and the corresponding eigenfrequencies are located in the shared band gap of two individual photonic crystals. This work is concerned with maximizing the shared band gap of two photonic crystals with different topological features in order to increase the bandwidth of the edge modes. We develop a semi-definite optimization framework for the underlying optimal design problem, which enables efficient update of dielectric functions at each time step while respecting symmetry constraints and, when necessary, the constraints on topological invariants. At each iteration, we perform sensitivity analysis of the band gap function and the topological invariant constraint function to linearize the optimization problem and solve a convex semi-definite programming (SDP) problem efficiently. Numerical examples show that the proposed algorithm is superior in generating optimized optical structures with robust edge modes.

Association between albumin-corrected anion gap and kidney function in individuals with hypertension – NHANES 2009–2016 cycle

Objectives Long-term uncontrolled hypertension increases the risk of kidney decompensation. This study aimed to explore the connection between albumin-corrected anion gap (ACAG) and kidney function in hypertensive patients. Methods This study utilized data from 1988 participants diagnosed with hypertension sourced from the NHANES database. Binary logistic regression analysis and subgroup analysis were utilized to investigate the relationship between ACAG and kidney function. The study employed restricted cubic spline (RCS) to assess the non-linear associations between ACAG and eGFR, as well as ACAG and ACR. Furthermore, mediation and moderation effect analyses were carried out, with blood pressure serving as the mediator and moderator, ACAG as the independent variable, and eGFR and ACR as the dependent variables. Finally, the study developed ACAG-based models for predicting kidney function decline. Results Higher ACAG is identified as an independent risk factor for eGFR < 60 mL/minute/1.73 m2 and ACR ≥ 30 mg/g. Results from RCS indicate a non-linear relationship between ACAG and eGFR, as well as between ACAG and ACR. The mediation effect analysis revealed that DBP mediated the relationship between ACAG and eGFR. Analysis on moderation effect demonstrated that SBP played a significant role in moderating the interaction between ACAG and ACR. Moreover, the models based on ACAG showed strong performance. Conclusions The levels of ACAG are found to be independently associated with both eGFR and ACR. Additionally, ACAG shows promise as a new and dependable biomarker for predicting the decline in kidney function in hypertensive patients.

AlN Nanotube Decorated with Small Tin Oxide Clusters as a Novel CH4 Sensing Material.

The success of carbon nanotubes has triggered a great deal of research interest in other one-dimensional nanomaterials with the aim of designing innovative nanostructures with attractive and distinctive attributes for applications in sensing gas molecules and toxic substances. In the present study, first-principles density functional theory calculations were exploited to assess the capability of the small tin oxide cluster (SnxOy)-decorated (6,0)aluminum nitride (AlN) nanotube for detecting methane(CH4) in terms of energetic, structural, and electronic properties. We found that SnxOy clusters were chemisorbed on the surface of the AlN nanotube due to the considerable adsorption energy and the notable charge transfer from the former to the latter. Further calculations demonstrate that the energy band gap and work function of the AlN nanotube were reduced in the presence of additives. Benefiting from the higher affinity of SnxOy toward the CH4 molecule, the Sn3O3-decorated AlN nanotube exhibited the greatest CH4 adsorption energy. The electrical conductivity increased as the energy band gap and effective mass decreased dramatically. Additionally, the type of Sn3O3-decorated AlN nanotube changed from a p-type semiconductor to an n-type one after adsorbing the CH4 molecule. Therefore, the Sn3O3-decorated AlN nanotube endows great promise as a thermopower-based, resistance-based, and Seebeck-effect-based CH4 sensing material.

The gender factor in monetary policy: An event-study design

This article assesses whether central bankers’ monetary policy preferences differ by gender. Based on a monetary policy rule in which the inflation rate is a function of the output gap, we estimated differences in this rule between central banks with female presidents and those with male presidents. Using an original database of 159 countries observed from 1980 to 2018, we adopted an event-study design, which, compared with the related literature, offers a novel approach to evaluate gender differences in inflation changes in the years following a new presidential appointment. A difference-in-differences strategy with propensity score matching showed that men central bank presidents are strongly conservative (hawks) in their monetary policy, at least in the first years after taking office. On the contrary, women central bank presidents are progressive (doves). This implies that women let the inflation rate fluctuate more—in relation to the output gap—than do men.

Structural, morphological and optical properties of the La2W2O9/Fe2O3 composite for UV-shielding applications

Currently, research has been conducted on the individual oxides La2W2O9 and Fe2O3 but not on its composite form. Using a solid-state reaction technique, a La2W2O9/Fe2O3 composite was created. A particular calcination cycle was followed by mixing the raw precursors. Scanning electron microscopy (SEM) was used to investigate the morphological microstructure, and X-ray diffraction (XRD) was used to examine the structural characteristics. The thermal and gravimetric properties were examined via differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The optical characteristics were investigated via UV–visible spectroscopy, which investigated included the transmittance, absorbance, absorption coefficient, band gap (Eg), penetration depth (β), Urbach energy (EU), refractive index, optical conductivity, and dielectric function. These findings indicate that the optical properties improved after the addition of Fe2O3 compared with those of pure La2W2O9. The La2W2O9/Fe2O3 composite holds promise as a prospective material for use in the fields of sunscreen products, UV shielding or solar filtration.

Understanding the effect of physical aging on slip dynamics in soft-glassy materials using pure elongation flow

Slip over a solid surface is a very common occurrence in industrial scale transport and the processing of complex fluids. The knowledge of slip also plays a huge role in the correct estimation of rheological properties. In this work, we have studied the slip dynamics in a model soft-glassy material that exhibits physical aging, wherein the structure evolves gradually toward a more solid-like character via rearrangement of constituents. More precisely, we have investigated the impact of physical aging on slip associated with pure elongation flow of the material. We have allowed the sample to age over different waiting times, followed by the sample being deformed slowly in elongation mode by pulling the top plate to achieve a pure elongation flow. Normal force as a function of gap has been recorded during such pure elongation. These normal force–gap curves demonstrated a remarkable gap-waiting time superposition, manifesting the strong signature of self-similarity in the pure elongation flow of the soft-glassy system. We have adopted a slip layer model, which predicted these normal force–gap flow curves remarkably well. Such prediction also rendered slip layer thickness as a function of waiting time, using which we have explained the intriguing self-similar nature of normal force–gap dependence. Finally, we have established a relationship between the slip layer thickness and the age-dependent bulk rheological properties. We have provided a possible physical reasoning to explain this link between the physical aging-driven state of material and the slip dynamics.

DFT study of adsorption and potential detection of carbonyl fluoride on B-doped aluminum nitride nanosheets

Carbonyl fluoride (COF2) is a decomposition product that can be used to find failures in gas-insulated switchgear equipment. In this study, we applied Density Functional Theory (DFT) calculations to examine the suitability of pristine and boron-doped aluminum nitride nanosheets (AlNNS) for COF2 adsorption and sensing applications. Our investigation suggested a dissociative COF2 adsorption on pristine AlNNS, resulting in important adsorption energy (–2.19 eV), the releasing of a fluorine atom from the molecule and formation of new C–N, O–Al and F–Al bonds. Two preferential chemisorption geometries were achieved on the B-doped N-vacancy monolayer (B-vN-AlNNS), with adsorption energies of –1.04 and –3.44 eV. In the first geometry, only an O–B bond was formed, whereas in the another one similar interactions as in COF2/AlNNS took place. Furthermore, we analyzed the evolution of electronic properties in order to evaluate the performance of these nanosheets for COF2 detection purposes. Our results showed significant modifications in both energy gap and work function only after COF2 adsorption on B-vN-AlNNS. Finally, charge transfer analysis revealed electron exchange from the studied surfaces to the gas molecule. These findings suggest that B-doped AlNNS exhibits good performance for COF2 detection, and could encourage further experimental research to develop efficient sensing materials.

Epitaxial growth of single unit-cell superconducting β-Bi2Pd

Bismuth-based binary alloy β-Bi2Pd has recently been suggested as a connate topological superconductor with immense promise for Majorana zero modes. However, the epitaxial thin films down to the ultimate level of single unit-cell have been challenging. Here, we employed the state-of-the-art molecular beam epitaxy to prepare single unit-cell superconducting β-Bi2Pd films with lateral dimensions of hundreds of nanometers. Utilizing in situ scanning tunneling microscopy/spectroscopy, we uncover evidence of anisotropic superconductivity whose spectra are well fit by anisotropic s-wave gap functions and demonstrate that the epitaxial growth of β-Bi2Pd films relies substantially on the substrate temperature, flux ratio, growth rate, and coverage. The high-quality epitaxial films provide a promising platform to investigate the topological superconductivity at the two-dimensional limit.

A theoretical investigation into the impact of temperature and band gap variation of La2NiMnO6 oxide double perovskite nanostructures on the performance of La2NiMnO6/MASnI3 based hybrid solar cells

The study aimed at simulating a model of bilayer La2NiMnO6/MASnI3 hybrid perovskite solar cell having a potential benefit of better stability at higher operating temperature with higher band gap of LNMO. This numerical analysis of La2NiMnO6/MASnI3 based hybrid solar cell performance parameters has been carried out as a function of temperature and optical band gap (Eg) of La2NiMnO6 (LNMO). The analysis reveals that the fill factor of solar cells operated at room temperature has not been affected too much on varying Eg of LNMO and decreases non-linearly with increasing operating temperature. The open circuit voltage of solar cells operated at room temperature increases with increasing Eg of LNMO and drops linearly with increasing operating temperature. The short-circuit current density (JSC) increases non-linearly at different rates with increasing the operating temperature. The value of dη/dT increases up to a critical temperature (Tc) and then decreases in the solar cells comprised with higher Eg of LNMO (Eg ∼ 1.50 eV–1.60 eV). The Tc value was shifted towards higher operating temperature in the higher Eg of LNMO (Eg ≥ 1.50 eV), enabling more stable solar cell at higher operating temperature.

Generalization gap estimation for damage classification tasks when finite element simulated data is used for training: A numerical study and experimental validation on a steel truss

Labeled simulated structural responses by Finite Element (FE) methods may be used to construct training sets for monitoring the health state of structures. Such an approach appears to be an attractive way to avoid experimental costs. However, the main obstacle is the simulation error contained in such numerical responses. The error can contaminate the training data and lead to wrong conclusions when the learned features try to generalize on subsequent online experimental data. It is therefore very important to have an estimation of how good the available simulated data is for a given problem. The present work gives a novel methodology where classifiers trained by FE vibration response data are subjected to inputs of various perturbations, emulating in such way the generalization gap (classification errors) due to simulation errors. The response of the classifiers is gathered afterwards in a dataset which is used to construct a function that estimates the generalization gap based on the perturbed intact state response. Results are presented that show the behavior of the proposed gap estimation function for different binary damage classification scenarios. A numerical truss structure is used to test the concept. Convolutional Neural Networks (CNN) are applied for all data-driven related tasks, such as learning of health state features in vibration responses or evaluation of the gap function. The results show a promising methodology that can be used to estimate the reliability of numerically trained classifiers. In the final part of this study, the framework is tested on an experimental truss structure. The presented methodology contributes to the quantitative study of uncertainty when extrapolating from the numerical to the experimental domain in the presence of modeling errors.

Phase jumps in coupled magnonic waveguides

In this work we present an experimental study of the phase characteristics of magnetostatic quasi-surface waves (MQSW) in a tangentially magnetized yttrium iron garnet (YIG) thin film bilayer. The phase of MQSWs was measured as a function of air gap (g) between two magnonic waveguides. It is shown that the energy exchange between two YIG layers is accompanied by relatively sharp π-radian phase jumps of MQSWs, at specific values of g. The effect was studied at large wavelengths of the MQSWs, and at a propagation distance of 1 cm. The theory predicts that the slope of the phase shift (∂φ/∂g) at submicrometric values of g can be of the order of a few degrees per nm.

DFT assessment of the alizarin dye pollutant adsorption by a customized graphene adsorbent

The alizarin (ALZ) dye pollutant adsorption by a customized zinc-atom decorated graphene (ZGR) adsorbent was assessed by density functional theory (DFT) computations. The interactions between ALZ and ZGR were explored to approach an adsorption process, in which different configurations of ALZ@ZGR complexes; A1, A2, and A3, were found. A dominant O…Zn interaction was found for all complexes in addition to the complementary C…C interaction between two substances. Accordingly, different strengths of adsorptions were determined to be meaningful for the removal purpose of ALZ by the ZGR adsorbent. The electronic molecular orbital features were also extracted to approach a sensing function of r ALZ@ZGR complexes formations, in which the variations of such features were mainly monitored by the changes of energy gap and work function. As a consequence, a platform for sensing and removal of the ALZ dye pollutant was proposed in the water and octanol solvents.