Threshold Region Research Articles

Measurement of the branching fraction of the decay J/ψ→pp¯η

A high-precision measurement of the branching fraction of the decay J/ψ→pp¯η is performed using (10 087±44)×106 J/ψ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of the two decays J/ψ→pp¯η(η→γγ) and J/ψ→pp¯η(η→π+π−π0) are measured individually to be B(J/ψ→pp¯η(η→γγ))=(1.480±0.001±0.024)×10−3 and B(J/ψ→pp¯η(η→π+π−π0))=(1.557±0.003±0.038)×10−3, where the first uncertainties are statistical and the second systematic. Both results are compatible within their uncorrelated systematic uncertainties. The combined result is B(J/ψ→pp¯η)=(1.495±0.001±0.023)×10−3, where the first uncertainty is the combined statistical uncertainty and the second one the combined systematic uncertainty of both analyses, incorporating correlations between them. In addition, the pp¯ threshold region is investigated for a potential threshold enhancement, and no evidence for one is observed. Published by the American Physical Society 2024

Finite-Time Stability Analysis and Stabilization of Switched Affine Systems via an Event-Triggered Strategy.

This article investigates the finite-time control problem of the switched affine systems via an event-triggered strategy. It is well known that the existence of affine terms brings great difficulties in analysis of the finite-time property of such systems. Furthermore, the design of the globally feasible event-triggered mechanism (ETM) under a finite-time control framework is challenging. Thus, a two-step hybrid control scheme is proposed in this article. The first step focuses on the event-triggered finite-time control for practical stability, while the second step aims to achieve finite-time stabilization. Particularly, in step one, by constructing the intersection between the affine term's threshold and feasible state region of the established ETM, it is verified that the Zeno behavior can be excluded. Thereafter, an affine state-dependent switching law and sufficient conditions are provided for achieving practical stability. Meanwhile, an estimation for the practical settling time to enter the bounded set is provided. In step two, the criteria for finite-time stabilization of the considered systems are further presented, and an overall settling-time upper bound is derived. Finally, a numerical example is illustrated to demonstrate the effectiveness of our proposed method.

Photoproduction of ηc,b near threshold

We analyze the photoproduction of ηc,b off a proton in the threshold region, in terms of C-odd gluonic correlations in the off-forward proton matrix element. Near threshold, the skewness is large, leading to a production amplitude that is dominated by four C-odd twist-3 gluon GPDs. We use the QCD instanton vacuum to estimate these C-odd contributions in the proton. The results are used to estimate the differential cross sections for coherent photoproduction of ηc,b in the threshold region, at current electron facilities. Published by the American Physical Society 2024

Assessment of internal defects in flush ground butt welds in marine structures

In this paper, acceptance criteria of internal planar defects for the highest design S-N curve for surface ground butt welds in fatigue design standards has been assessed based on fatigue tests of tethers containing internal defects. The results from crack growth analysis from defects placed close to the surface are compared with test data from constant amplitude testing of tethers with circumferential welds that includes flaws or small planar defects close to the surface. Floating structures and support structures are subjected to variable loads and the calculated response leads to a long-term stress range distribution with many small stress ranges. This means that if the cracks are small, the resulting stress intensity may be less than the threshold stress intensity factor and the crack does not grow for this stress cycle, or it grows at a reduced crack growth rate in the near threshold region. A methodology to account for this is presented based on a two-parameter Weibull long-term stress range distribution that is representative for load response of floating structures and for support structures for wind turbines. It is shown that the threshold value and the reduced crack growth rate in the near threshold region for small internal defect heights can be used to lift the fatigue test data from constant amplitude testing to be in better correspondence with a higher S-N curve when considering an actual long-term loading.

Missing-Mass Measurement of the 12C(K-, K+) Reaction at 1.8 GeV/c with the Superconducting Kaon Spectrometer

Abstract We performed a measurement of the inclusive missing-mass spectrum of the $^{12}$C$(K^-, K^+)$ reaction at an incident beam momentum of 1.8 GeV/c. This measurement was carried out by using the Superconducting Kaon Spectrometer (SKS) and the K1.8 beamline spectrometer at the Hadron Experimental Facility in J-PARC. From the missing-mass of the $^{12}$C$(K^-, K^+)$ reaction, the binding energy of a $\Xi ^-$ hyperon in a core $^{11}$B nucleus, $B_{\Xi ^-}$, can be calculated. Our experimental setup yielded a good energy resolution of 8.2 MeV (full width at half maximum), which allowed us to observe significant enhancements in the proximity of the $^{12}_{\Xi }$Be production threshold region. In order to extract information from the missing-mass spectrum, we employed several fitting parameters assumptions. A good agreement with the spectrum shape was obtained by adding two Gaussian functions, with the constant experimental resolution for the $\Xi$-hypernuclear states, to the background distribution. The peak positions were obtained to be $B_{\Xi ^-} = 8.9 \pm 1.4$ (stat.) $^{+3.8}_{-3.1}$ (syst.) MeV and $B_{\Xi ^-} = -2.4 \pm 1.3$ (stat.) $^{+2.8}_{-1.2}$ (syst.) MeV. Another model assumption, one Breit–Wigner function with $B_{\Xi ^-} = -2.7 \pm 2.2$ (stat.) $^{+0.5}_{-0.7}$ (syst.) MeV and $\Gamma = 4.1 \pm 2.1$ (stat.) $^{+1.2}_{-0.7}$ (syst.) MeV, also yielded a similar $\chi ^2$ value.

A Detection Algorithm for Metal-Bearing Roller Microcracks with Global Contrast and Threshold Region Growth

A Detection Algorithm for Metal-Bearing Roller Microcracks with Global Contrast and Threshold Region Growth

Photoionization of hydrogen halides using the R-matrix method

Abstract In this study, we use the UK Molecular R-matrix (UKRMol) codes in the close-coupling approximation to examine the photoionization of hydrogen halides (hydrogen fluoride, hydrogen chloride, and hydrogen bromide). This article reports the total and partial photoionization cross sections for the X2Π, A2Σ+, and B2Σ+ ionic states of these halides. The calculated cross sections are compared with the available literature, which does not accurately represent the effective cross sections near the threshold region, which is dominated by the Rydberg series autoionization resonances converging to the A2Σ+ ionic state. There seems to have been minimal effort to investigate the Rydberg-bound states of these halides. Meanwhile, the R-matrix approaches have traditionally excelled at characterizing such studies. This indicates the effectiveness of this method for molecular photoionization as well as for understanding the resonant contribution to the photoionization cross sections. The detailed cross sections calculated comprise the complex autoionizing resonance structures capable of significantly contributing to the computations of total photoionization rates, which are necessary to maintain a steady state of ionization in astrophysical plasmas. Comparisons with the experimental measurements and the theoretical data generally show reasonable agreement across the reported energy range.

Quantum Dynamics Studies of the Li + Na2 (V = 0, j = 0) → Na + NaLi Reaction on a New Neural Network Potential Energy Surface.

The ultracold reaction offers a unique opportunity to elucidate the intricate microscopic mechanism of chemical reactions, and the Na2Li system serves as a pivotal reaction system in the investigation of ultracold reactions. In this work, a high-precision potential energy surface (PES) of the Na2Li system is constructed based on high-level ab initio energy points and the neural network (NN) method, and a proper asymptotic functional form is adopted for the long-range interaction, which is suitable for the study of cold or ultracold collisions. Based on the new NN PES, the dynamics of the Li + Na2 (v = 0, j = 0) → Na + NaLi reaction are studied in the collision energy range of 10-7 to 80 cm-1. In the high collision energy range of 8 to 80 cm-1, the dynamics of the reaction is studied using the time-dependent wave packet method and the statistical quantum mechanical (SQM) method. Comparing the results of the two methods, it is found that the SQM method provides a rough description of the product ro-vibrational state distribution but overestimates the integral cross-section values. With the decrease of collision energy, the reaction differential cross section gradually changes from forward-backward symmetric scattering to predominant forward scattering. In the low collision energy range from 10-7 to 8 cm-1, the SQM method is used to study the reaction dynamics, and the rate constant in the Wigner threshold region is estimated to be 2.87 × 10-10 cm3/s.

Photoionization cross sections measurements of the excited states of lutetium and ytterbium in the near threshold region.

In this work, the threshold photoionization cross sections from the excited states of lutetium and ytterbium atoms were investigated by the laser pump-probe scheme under the condition of saturated resonant excitation. We obtained the resonance enhanced multiphoton ionization spectra of the lutetium and ytterbium atoms of the lanthanide metals in the range of 307.50-312.50nm and 265.00-269.00nm, respectively; the photoionization cross sections of the 5d6s(1D)6p(2D05/2) and 5d6s(3D)6p(2P01/2) states of lutetium and the 4f13(2F0)5d6s2(J = 1) states of ytterbium above threshold regions (0.4-1.6eV) were measured, and measured values ranged from 2.3 ± 0.2 to 17.7 ± 1.5 Mb.

Reanalysis of the top-quark pair production via the e+e− annihilation near the threshold region up to N3LO QCD corrections

In this paper, we present an improved analysis of the top-quark pair production via the process e+e−→γ⁎→tt¯ near the threshold region up to next-to-next-to-next-to-leading order (N3LO) QCD corrections. Near the threshold region, the top-quark velocity v tends to zero, leading to Coulomb singularity. To achieve a reasonable prediction in the threshold region, we reconstruct the analytical expression for the Coulomb-terms up to N3LO accuracy by using the PSLQ algorithm, whose numerical values agree well with the previous N3LO-level calculations. It is found that the N3LO series still has sizable renormalization scale dependence, and to improve the precision of the series, we apply the Principle of Maximum Conformality to eliminate such scale dependence. After that, the Coulomb part is resummed into a Sommerfeld-Gamow-Sakharov factor, which finally leads to a much more reasonable behavior near the threshold region.

Dissociative properties of C4F6 obtained using computational chemistry

The electronic properties of C4F6 were investigated by using computational chemistry to clarify the dissociative channels in the process plasma. The results show the mainly ionized ion is C3F3 + (CF2=C=CF+; propargyl ion) which is observed in the mass spectrum with the electron energy of 70 eV, and the intermediate molecular structure to produce C3F3 + ion is methyl allene ion (CF2=C=CF–CF3 +). The molecular ion C4F6 + is also mainly produced in the ionization threshold region. For the excited states, the calculated results suggest that CF2CFCF + CF2 dissociation takes place in the energy region higher than 7.0 eV and C2F3 + C2F3 dissociation takes place in the energy region higher than 8.0 eV. In the electron attachment process, the vertical electron attachment energy was calculated as 1.1 eV and the nonadiabatic negative ion energy was −0.2 eV lower than the energy of neutral C4F6.

Investigating the Impact of Technology Scaling on Stability Performance of Sub-threshold Static Random Access Memory Bitcell Topologies

Static random-access memory (SRAM) is increasingly being used in VLSI circuits as a result of the development of portable devices. As the demand for low-power devices increases, sub-threshold operation of SRAMs has become a popular method to reduce power consumption but at the cost of reduced stability. The work aims to propose design parameters for SRAM bit cell topologies- 6T and 10T with proper device sizing and to investigate the impact of technology scaling on its stability performance in the sub threshold region. Moreover, analysis demonstrates the impact of variations of device sizing in terms of Cell ratio and Pull up ratio on stability margins of designed SRAM topologies. Simulations are carried out in the HSPICE environment using 16 nm and 22 nm CMOS process nodes. We find that the stability margins of 10T SRAM cell outperform the 6T SRAM cell; however stability margin decreases with decreasing technology nodes. The Read Static Noise Margin (RSNM) and Write Static Noise Margin (WSNM) of 10T SRAM cell is improved by 48.38% and 308.64% respectively in 22nm and 53.04% and 243.93% respectively in 16nm process technology as compare to 6T SRAM cell.

High-cycle and low-cycle fatigue life prediction under random multiaxial loadings without cycle counting

A novel fatigue life prediction method under random multiaxial loadings is proposed in this paper. One unique benefit of the proposed method is that it is based on the time-derivative fatigue crack growth formulation and does not need cycle counting under arbitrary loadings. First, a brief review of subcycle fatigue crack growth (FCG) analysis and the equivalent initial flaw size (EIFS) concept for life prediction is introduced. Next, the existing subcycle fatigue crack growth model is extended to near-threshold conditions. An intrinsic fatigue threshold of the material is introduced, and a hypothesis is proposed that the crack only grows when the local stress intensity factor is beyond the intrinsic threshold. Following this, the analogy of stress intensity factor and strain intensity factor is used to extend the fatigue life prediction model to strain-based fatigue analysis. Correction for large plastic deformation is included to handle low-cycle fatigue life prediction. The novelties of this model are that it considers the FCG at the threshold and near-threshold region and it is able to predict both HCF and LCF conditions using FCG-based life prediction. Following this, extensive in-house and literature data for AL-7075-T6 under uniaxial and multiaxial, constant, and random loadings are used for model validation. Discussions for the effect of model parameters are provided based on parametric analysis. Conclusions and future work are mentioned. Code and data are released in public cloud service for interested readers.

The defect feature extraction of ultrasonic phased array detection based on adaptive region growth.

An ultrasonic phased array defect extraction method based on adaptive region growth is proposed, aiming at problems such as difficulty in defect identification and extraction caused by noise interference and complex structure of the detected object during ultrasonic phased array detection. First, bilateral filtering and grayscale processing techniques are employed for the purpose of noise reduction and initial data processing. Following this, the maximum sound pressure within the designated focusing region serves as the seed point. An adaptive region iteration method is subsequently employed to execute automatic threshold capture and region growth. In addition, mathematical morphology is applied to extract the processed defect features. In the final stage, two sets of B-scan images depicting hole defects of varying sizes are utilized for experimental validation of the proposed algorithm's effectiveness and applicability. The defect features extracted through this algorithm are then compared and analyzed alongside the histogram threshold method, Otsu method, K-means clustering algorithm, and a modified iterative method. The results reveal that the margin of error between the measured results and the actual defect sizes is less than 13%, representing a significant enhancement in the precision of defect feature extraction. Consequently, this method establishes a dependable foundation of data for subsequent tasks, such as defect localization and quantitative and qualitative analysis.

Non-Linear Relationship between Bond Prices and Electricity Prices in India: An Analysis using Threshold Regression Approach

This research article scrutinises the connotation among bond prices and electricity prices (EP) across different threshold regions in India using threshold regression analysis. We resolve to investigate whether or not there exists a non-linear association between bond prices and EP and if this relationship differs across different threshold regions. The data covers a period of five years from 2018 to 2022, and the analysis includes three different threshold regions based on different threshold bond prices. The results show that there exists significant non-linear association between bond prices and EP, and this relationship differs across the three threshold regions. We surmise presence of an optimality between bond prices (interest rates) and EP, beyond which the EP increase. We conclude that as interest rates increase, the cost of financing for electricity companies also increases, which may lead to higher EP. However, there may be a certain threshold beyond which the cost of financing becomes too high, leading to a decrease in investment and ultimately a decrease in electricity supply, which in turn could lead to higher EP.

Positron scattering from structurally related biomolecules.

We report the integral elastic, momentum transfer, and inelastic (positronium formation and ionisation) cross sections for positron scattering from structurally related molecules. The molecules chosen for the current investigation are formamide, formylphosphine, formic acid, N-methylformamide, acetone, acetic acid, and formaldehyde. The cross sections were calculated using the optical potential approach and the complex scattering potential-ionisation contribution method for impact energies between 1 and 5 keV. A sizable repository of data is now available for positron scattering from various atoms and molecules; however, data on the impact of positrons on current targets is still scarce and fragmented. While most cross sections are the first of their kind, we analyze our total cross sections (TCSs) with the previous literature available, which has become attractive to researchers trying to model the tracks of charged particles in matter. TCSs have recently seen a resurgence in popularity thanks to their utility in specifying the mean-free path between the collisions of such simulations. We find good qualitative convergence between experimental and theoretical results below and above the positronium formation threshold. However, around the threshold region, a significant discrepancy is encountered, which can be accounted for due to the experiment's lack of forward angle scattering effect discrimination. This level of agreement evolves to become quantitative at intermediate and higher energies.

Mass transfer of microbubble in liquid under multifrequency acoustic excitation - A theoretical study

Microbubble’s mass transfer under external acoustic excitation holds immense potential across various technological fields. However, the current state of acoustic technology faces limitations due to inadequate control over bubble size in liquids under external excitation. Here, we conducted numerical investigations of the mass transfer behavior of microbubbles in liquids under multifrequency acoustic excitations with different frequencies (in the MHz range), pressure amplitudes (in the range of several atmospheric pressures), and amplitude ratios. We identified various pressure threshold regions for the growth of gas bubbles (radii range from a few microns to tens of microns) and observed common intersections between single and multifrequency excitations that enable effective control of the growth intervals and final size of bubbles by adjusting the ratio of pressure amplitude and frequency value. Allocating power to the lower frequency component of multifrequency acoustic excitation is recommended to facilitate mass transfer or diffusion, as small-frequency acoustic excitation has a more significant effect than the higher frequency in the growth region. Our study provides a better understanding of the dynamics of bubbles under complex excitations and has practical implications for developing methods to control and promote bubble-related processes.

A combined experimental and numerical analysis framework for the design of aluminum windows

Windows form an essential part of modern architecture owing to their crucial role in the energy efficiency of the building, functionality, durability, and aesthetic appeal. Despite their relevance, window designs are mainly carried out in an ad-hoc fashion. At the same time, more sophisticated approaches rely on trial-and-error experiments involving expensive custom die-casting and wind load experiments. This study proposes a robust numerical framework for economically designing new Aluminum window profiles. Specifically, we use a finite element model to determine the maximum threshold wind load and regions of failure for an Aluminum sliding window. The model is validated against experimental results. Further, a comparative study between windows made of regular 6063-Al alloy and Duranium™ (patented new aluminum alloy) is also performed to evaluate the role of material properties in the structural response of window sections. Interestingly, despite having comparable elastic modulus, we noted that the windows made of Duranium™ survive higher loads and exhibit significantly lower plasticity. Altogether, the present work demonstrates that the numerical model can accurately predict the failure patterns, loads, and deflections for the window frames and, hence, can easily be developed into an automated analysis framework for the optimal design of window frames. This could potentially improve the overall safety, comfort, energy efficiency, and sustainability of buildings at both the construction and usage stages.

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The Excitation of the 3D and 4D States of Atomic Hydrogen by Electron Impact

The excitation cross-sections of the 3D and 4D states of atomic hydrogen at low incident energies (from 0.90 to 5.00 Ry) were calculated using the variational polarized orbital method, which is also called the hybrid theory. Up to 12 partial waves (L = 2 to 13) were used to obtain converged cross-sections at high energies. The importance of the long-range forces near the threshold region and the behavior of the cross-sections in that region are indicated. The S, P, and D cross-sections are needed if the total excitation cross-sections are measured in addition to the elastic cross-sections. These cross-sections are also useful if the cascade from the D to the P to the S states is considered in the diagnostics of solar and astrophysical observations.