Monotonic Change Research Articles

Features of the defect structure of a lithium-gradient nonlinear optical single crystal LiNbO3 and their manifestation in the Raman spectra

LiNbO3 crystal with a lithium composition gradient of Li/Nb = 0.8 wt%/cm (Li0.97..1.01Nb1.03..0.99O3) were obtained. A monotonic change in the edge of the UV absorption edge is observed when scanning the surface of the gradient crystal along the growth direction. Raman spectra from different areas of studied crystal were analyzed in a wide frequency range, which includes the region of fundamental vibrations of the crystal lattice (100–900 cm−1) and the region of overtone processes (900–3000 cm−1). A compositionally homogeneous, congruent LiNbO3 crystal was used as a comparison sample. It was found that in the spectra obtained from different parts of the gradient crystal, there is a significant scatter in the frequency values of the lines corresponding to the fundamental vibrations of the crystal lattice, but at the same time, the number of lines corresponding to the fundamental vibrations of the lattice for the gradient and compositionally homogeneous LiNbO3 crystals is the same. Moreover, in the spectrum of a gradient crystal in the region of overtone processes of fundamental vibrations, significantly more lines (35 lines) are observed than in the spectrum of compositionally homogeneous crystals (15 lines). The data obtained show that the state of the defect structure of compositionally homogeneous crystals and gradient LiNbO3 crystal is significantly different. The discovered differences between the defective structure of a gradient crystal and the defective structure of a compositionally homogeneous crystal may be the reason for compensation (damping) of distortions during nonlinear optical conversion of laser radiation by a gradient crystal due to the uneven temperature distribution along the length of the crystal. In compositionally homogeneous crystals, such temperature distortions significantly limit the efficiency of nonlinear optical conversion.

Analysis of Thermal Isotropy of Parallelepiped Shape of Bronze Samples for Mechanical Engineering Applications

Objective: The need to find out whether the specimens are ‘thermally thin’ or not is the basis for applying the law of conservation of energy or the Fourier differential equation of heat conduction in finding the time dependence of the specimen temperature. The aim of this study is to find out the thermal field distribution in a parallelepiped shaped bronze specimen and to verify the Bio number. Methods: A number of external variables make it difficult to maintain a monotonic change in sample temperature during the ‘heating’ stage. These factors led to the use of the cooling method to study tiny samples with low inertia of the thermal process. We used the cooling method to experimentally verify the isotropy of the thermal field in the sample and to study the kinetics of cooling relative to the sample axes over a wide range of temperatures. Results: It was found out that in natural air cooling the main mechanisms are conductive, convective and radiative heat transfer. The contribution of thermal radiation to the cooling process is noticeable at high temperatures. It was found that the typical cooling time increases with sequential radiative, conductive and convective heat transfer. By extending the temperature study area to, for the first time, we were able to observe each component of the heat transfer process independently. The values of the typical cooling time on all axes correspond to the experimental error bounds. It was found that the temperature value of the sample is independent of the coordinates and depends only on time. In this case, the law of conservation of energy can be used to explain the dependence of body temperature on cooling time. Conclusion: It is shown that the sample under study is ‘thermally thin’, i.e. the thermal field is constant in all directions. In this situation, the thermal balance equation should be applied rather than the Fourier differential equation of heat conduction, since the temperature gradient inside the body is practically zero. The results obtained are of great importance for the study of cooling processes of metallic products in thermal power engineering, heat engineering and thermophysics.

A greater negative impact of future climate change on vegetation in Central Asia: Evidence from trajectory/pattern analysis

In the context of global warming, vegetation changes exhibit various patterns, yet previous studies have focused primarily on monotonic changes, often overlooking the complexity and diversity of multiple change processes. Therefore, it is crucial to further explore vegetation dynamics and diverse change trajectories in this region under future climate scenarios to obtain a more comprehensive understanding of local ecosystem evolution. In this study, we established an integrated machine learning prediction framework and a vegetation change trajectory recognition framework to predict the dynamics of vegetation in Central Asia under future climate change scenarios and identify its change trajectories, thus revealing the potential impacts of future climate change on vegetation in the region. The findings suggest that various future climate scenarios will negatively affect most vegetation in Central Asia, with vegetation change intensity increasing with increasing emission trajectories. Analyses of different time scales and trend variations consistently revealed more pronounced downward trends. Vegetation change trajectory analysis revealed that most vegetation has undergone nonlinear and dramatic changes, with negative changes outnumbering positive changes and curve changes outnumbering abrupt changes. Under the highest emission scenario (SSP5-8.5), the abrupt vegetation changes and curve changes are 1.7 times and 1.3 times greater, respectively, than those under the SSP1-2.6 scenario. When transitioning from lower emission pathways (SSP1-2.6, SSP2-4.5) to higher emission pathways (SSP3-7.0, SSP5-8.5), the vegetation change trajectories shift from neutral and negative curve changes to abrupt negative changes. Across climate scenarios, the key climate factors influencing vegetation changes are mostly evapotranspiration and soil moisture, with temperature and relative humidity exerting relatively minor effects. Our study reveals the negative response of vegetation in Central Asia to climate change from the perspective of vegetation dynamics and change trajectories, providing a scientific basis for the development of effective ecological protection and climate adaptation strategies.

In-Situ structural and Adsorbate Induced Surface Evolutions Monitored By Electrochemical Stress Measurements

We report on in-situ electrochemical stress measurements of well-defined surfaces during electrochemical reactions in aqueous media. Electrochemical stress measurements during hydrogen evolution reaction (HER) on Pt surfaces shows distinct pH-dependent features which we assign to anion adsorption/desorption and hydrogen adsorption/desorption. Our surface stress analysis shows higher hydrogen induced stresses at alkaline environments than stresses observed at acidic pHs. This observation is consistent with the monotonic change in apparent hydrogen binding energy with pH, most likely due to the changes in water interactions with surface. However, H-induced surface stress shows a dramatic increase around neutral pH. We will present our analysis of how interfacial water may explain this effect. Additionally, we will show how in-situ underpotential deposition of Cu on Pt and Ni on Au changes Had induced effects on these surfaces.We will also discuss the structural and compositional evolution of Sr2Fe2O6-δ thin films during oxygen evolution reaction (OER). Interestingly, in-situ electrochemical stress measurements show a tensile stress response during OER which is different from Au model surfaces. We will present our analysis of how potential controlled formation of iron (oxy)hydorxides may explain in-situ stress response and structural evolution of perovskite type structures during OER.In summary, our analysis shows how adsorbate-induced effects can be used to explain surface reactions, and particularly explain and provide insight into interfacial structural changes and water interactions at different pHs.

Study of spin-phonon interaction in multiferroic La0.9Bi0.1CrO3 by Raman spectroscopy

Spin-phonon interaction is an interesting phenomenon that may find applications in spintronics, quantum information processing, etc. In multiferroic materials, spin-phonon interaction, if exists, may provide additional degrees of freedom that could lead to the development of novel technologies. Thus, investigating and understanding this interaction in a multiferroic material is of both fundamental and applied interests. Perovskite La1-xBixCrO3 is a mutiferroic material which turns from antiferromagnetic/antiferroelectric to ferromagnetic/ferroelectric with 10 % substitution of Bi3+ for La3+. Raman spectrum feature changes dramatically with 10 % substitution of Bi3+ for La3+ also, indicating a spin-phonon interaction. Furthermore, in La0.9Bi0.1CrO3, the ∼700 cm−1 mode is split into two Raman sub-modes. The intensity of the lower frequency (680 cm−1) sub-mode starts increasing sharply around the Néel temperature TN = 269 K upon cooling. Below TN, the monotonic change in intensity reflects the magnetic exchange modulation, resulted from the interacting with the chromium atoms oscillation at the original Cr4+ position in LaCrO3, related to the competing ferromagnetic and antiferromagnetic interactions, with the former prevailing at low temperatures. The interplay of magnetic exchange modulation interactions and chromium atoms oscillation (decreasing of the lower frequency sub-mode of the Bi3+ doping related John-Teller-like 700 cm−1 mode) coincides with the corresponding magnetic phase transition (TN), demonstrating a spin-phonon coupling in La0.9Bi0.1CrO3 which may find applications in magnonic devices.

Long-term continuous changes of vegetation cover in desert oasis of a hyper-arid endorheic basin with LandTrendr algorithm

Ecological water diversion projects (EWDP) is one of the most important initiatives for oases restoration in arid endorheic basins. Fine monitoring of the long-term and continuous changes in vegetation cover before and after the EWDP is important to evaluate the effects of EWDP on ecosystem restoration. In this study, a trajectory-based change detection approach was applied with the Landsat-based detection of trends in disturbance and recovery (LandTrendr) algorithm on Google Earth Engine to map vegetation cover change trajectories in Ejina Oasis in the lower Heihe River Basin of China during 1990–2020. In addition to monotonic changes (i.e., continuous greening and continuous browning), LandTrendr also can flexibly capture the breaks of greening or browning events, including the greening with negative break, browning with positive break, browning to greening, and greening to browning. These changes mainly happened in shrub land and the area with land use transition. Approximately 82 % of the oasis ecosystem has been restored by the implementation of EWDP since 2000. However, in the past decade, the EWDP also caused some negative effects on vegetation cover in some areas. Both the categories of browning with positive break and greening to browning became widespread after 2010, with the cumulative proportions accounting for 79.4 % and 70.1 % of each category. The mean magnitude and slope of change in NDVI in these two categories after 2010 were −0.03 and −0.008 yr−1, −0.12 and −0.035 yr−1, respectively. This research demonstrated that the proposed approach was effective and useful for continuously monitoring the timing and extent of vegetation recovery processes in the hyper-arid endorheic basin. The EWDP plays an important role in vegetation restoration, but we also need to continuously monitor negative impacts which are crucial for environmental assessment and policy making in the arid endorheic basin.

Effects of interlayer spacing and applied pressure on the lanthanide transport in MoS2-based two-dimensional channels

ABSTRACT Rare-earth elements (REEs) are critical to modern industry but difficult to separate due to their subtle and monotonic changes in physicochemical properties. MoS2-based two-dimensional (2D) materials offer novel opportunities for enhancing REE separation, exhibiting a distinct volcano-shaped transport performance distribution that peaks at Sm3+. However, the specific contributions of thermodynamic and kinetic factors to ion transport within 2D confinement remain unclear. In this study, we conducted a series of non-equilibrium all-atom molecular dynamics (MD) simulations to explore the effects of interlayer spacing and external pressure on the transport of lanthanide ions in Å-scale acetate functionalized 2D MoS2 (MoS2-COOH) channels. We examined ion entry and permeation rates, water flux, dehydration, and binding modes. The simulation results reveal that the transport trends of lanthanide ions are jointly driven by the dehydration degree and the relative-binding strengths of ions to water and to the acetate within the 2D channels. Notably, the dehydration pattern of lanthanide ions during permeation is closely linked to kinetic factors. Overall, this study provides a detailed atomistic understanding of the mechanisms underlying lanthanide ion transport under confinement. These findings point to the significant potential for tuning confinement and chemical functionalization within Å-scale channels for more efficient REE separation.

A hybrid approach for estimating monotonic change points in the parameters of simple linear profiles in multistage processes

In this paper, a hybrid method is proposed for estimating monotonic change points in multistage processes where, at each stage, the quality of the process is represented by simple linear profile models. In the case of monotonic changes, the change type is not known a priori, and the only assumption is that the changes are non-decreasing or non-increasing in nature. In the proposed method, a support vector machine (SVM) algorithm is first developed to identify the parameters experiencing a change in each process stage. Then, the second SVM algorithm is applied to identify the type of change occurring in the related parameters. Finally, considering the identified parameters and change types, the maximum likelihood estimator (MLE) is proposed to estimate the change points of the process under different scenarios, including single and multiple change points, upward and downward step changes, increasing and decreasing linear trends, shift in both parameters of the profiles, shift in different stages of the process, and weak and strong autocorrelation coefficients. The performance of the proposed method is evaluated through extensive simulation experiments. The results indicate that the proposed method recognizes the patterns and estimates the monotonic change points accurately.

Spatial structure and potential processes linking fish and benthic communities in a protected reef ecosystem in SE Brazil

Top-down and bottom-up processes can mediate the structuring of biological communities. Several studies have provided separate support for those processes in pelagic and benthic compartments of reef systems but studies focusing on whole-reef processes are less common. Here, we sampled 3 ‘reef compartments’ in the Alcatrazes Archipelago in Southeastern Brazil: benthic cover of colonial organisms, solitary organisms, and reef fish (i.e. pelagic) to identify the groups responsible for spatial community structure among reefs. A dynamic mosaic structure best defines the assemblages of each compartment, with substantial changes observed among sites over 2 consecutive years and at 2 depth strata, separated by a sharp thermocline. Changes in benthic cover of colonial organisms are largely due to the extent of the blooming of Sargassum canopies, algal turfs, and the zoanthid Palythoa caribaeorum. Solitary organisms show a consistent monotonic change in the abundance of sea urchins, ascidians, and snails. Fish assemblage structure differed among reefs; however, we observed that large invertivore fish tended to concentrate in warmer water above the thermocline and small fish of different feeding habits were found in deeper and colder water in all reefs. We observed a potential strong link between the reefscape and solitary organisms, with a negative relationship between the abundance of urchins and the cover of Sargassum spp. suggesting top-down control. A second link is indicated by a positive relationship between low-lying cover composed of articulated turf and P. caribaeorum and larger invertivorous fish, suggesting bottom-up control through the provision of favorable foraging grounds.

Generation and propagation mechanism of cracks in welded joints of thin-walled capsules during hot isostatic pressing

The quality of the capsule has an important effect on the quality of hot isostatic pressing (HIP) products. The reliability of the capsule is a key factor in determining the success or failure of HIP. The capsule is mainly formed through a sheet welding process. In order to ensure the reliability of the weld in HIP, stainless steel with better high-temperature and high-pressure performance than Q235 steel needs to be used. In this case, the fusion line becomes a dissimilar-material interface, which is more prone to fusion-line failure. This paper focuses on examining and studying the formation mechanism of fusion line cracks in welded joints during HIP. The results show that, first, the increase of the HIP temperature weakens the strength near the fusion line significantly. Second, the higher the HIP temperature, the more severe the grain coarsening, and the grain size along the radial direction of the capsule exhibits a monotonic change. Third, since the HIP process changes the micro-zone grain orientation of mild steel, the distribution characteristics of ferrite and pearlite change as well. when the temperature and pressure are higher, the texture still exhibits a strong and complex distribution.

Identifying and Interpreting Hydrological Model Structural Nonstationarity Using the Bayesian Model Averaging Method

Understanding hydrological nonstationarity under climate change is important for runoff prediction and it enables more robust decisions. Regarding the multiple structural hypotheses, this study aims to identify and interpret hydrological structural nonstationarity using the Bayesian Model Averaging (BMA) method by (i) constructing a nonstationary model through the Bayesian weighted averaging of two lumped conceptual rainfall–runoff (RR) models (the Xinanjiang and GR4J model) with time-varying weights; and (ii) detecting the temporal variation in the optimized Bayesian weights under climate change conditions. By combining the BMA method with period partition and time sliding windows, the efficacy of adopting time-varying model structures is investigated over three basins located in the U.S. and Australia. The results show that (i) the nonstationary ensemble-averaged model with time-varying weights surpasses both individual models and the ensemble-averaged model with time-invariant weights, improving NSE[Q] from 0.04 to 0.15; (ii) the optimized weights of Xinanjiang model increase and that of GR4J declines with larger precipitation, and vice versa; (iii) the change in the optimized weights is proportional to that of precipitation under monotonic climate change, as otherwise the mechanism changes significantly. Overall, it is recommended to adopt nonstationary structures in hydrological modeling.

Achieving high ductility at medium temperature in a nonequiatomic CoCrNi alloy

The tensile strength and ductility of face-centered cubic (FCC) multi-principal element alloys (MPEAs) typically decline monotonically with increasing temperature. In this work, we conducted tensile tests at different temperatures and characterized deformation microstructures for a nonequiatomic CoCrNi alloy with low stacking fault energy (SFE). Exceptional ductility is obtained at medium temperature, breaking the general sense of monotonic change with temperature. The effect of deformation mechanisms of dislocations, stacking faults and phase transformation on the ductility was discussed. This work reveals the unique temperature effect on the mechanical properties of metals with very low SFE.

Dynamic thermal response characteristics of a metal foam enhanced horizontal loop thermosyphon

A metal foam horizontal loop thermosyphon (MF-HLTS) for a solar receiver was proposed and investigated under the variable conditions. Meanwhile, a dynamic response model for predicting the thermal response characteristics of MF-HLTS was established using Nusselt theory and lumped parameter method. Results of the dynamic model show good agreement with the experimental data, with a maximum deviation of 3.5 % for temperature response. Under sudden power conditions, the temperature variation curve of MF-HLTS shows a progressive monotonic change with two stages: both rising and decreasing rates of temperature show linear and rapidly changes at first stage, and them begins to decrease and gradually tends to 0 at second stage. The time required to reach steady-state increases with the increase of power step. For start-stop of power and cooling, the recovery time gradually increases with increasing stop time, but start-stop ratio firstly decreases rapidly and then tends to be flat. Dynamic response of MF-HLTS is relatively fast with a temperature time lag of 2 s to 4 s, which can meet the requirements of dynamic regulation of system temperature under actual conditions.

Layer-stacked polyaniline/silver nanowire composite film for multicolor electrochromic smart windows with dual-band optical modulation

Dual-band electrochromic smart windows (DESWs) have attracted widely concern for their potential in significantly reducing building energy consumption by selectively controlling near-infrared (NIR) and visible light (VIS) transmittance. However, its monotonous color changes limit its large-scale application. In this study, we designed a DESW based on the layer-stacked polyaniline (PANI)/silver Nanowires (Ag NWs) composite films. When PANI films is stacked layer by layer with Ag NWs, it not only performs dual band regulation, but also exhibits impressive electrochromic performance with rich color conversions (light yellow, yellow-green and blue-black). The four-layer PANI/Ag NWs composite film outperformed the pure single-layer PANI film because of the faster electron transfer, its coloring time and bleaching time at 525 nm were shortened to 6.7 s and 18.0 s, respectively, and the coloring efficiency was increased to 45.5 cm2 C-1. After 2500 cycles, the PANI/Ag NWs films tend to have better cycle stability. Therefore, the incorporation of Ag NWs enhances the electrochromic performance of PANI films, providing valuable insights for advancing single-component organic electrochromic materials.

Phase Engineering on MoS2 to Realize Dielectric Gene Engineering for Enhancing Microwave Absorbing Performance

AbstractPolarization relaxation loss caused by defects and interfaces has become a fascinating electromagnetic wave (EMW) loss mechanism. However, the logical relationship between impedance matching and various loss mechanisms requires further elucidation to facilitate more comprehensive and in‐depth research. Herein, phase engineering on molybdenum disulfide (MoS2) is proposed as the main controller of permittivity, offering a straightforward and highly effective method for regulating permittivity. Through the main control of phase engineering, a small gradient, monotonic change of the permittivity across a substantial area is achieved, leading to the gradual transition of the material system from strong loss but impedance mismatching to weak loss but EMW transparent phase. Thanks to the fundamental regulation of impedance characteristic and attenuation capacity by the dielectric gene engineering controlled by the phase engineering, combined with the ingenious coordination of sulfur vacancy‐induced polarization and interfacial polarization, t‐60 harvests an effective absorption band of 6.8 GHz and a minimum reflection loss of −59.8 dB. This study effectively expands the dielectric gene pool and improves the research logic for various loss mechanisms, offering valuable insights for the development of advanced EMW absorbing materials.

Performance evaluation of a magnetic NDE technique to assess residual fatigue life of the retired hydraulic cylinders

Metal magnetic memory (MMM) method is a novel and potential nondestructive evaluation (NDE) technique to assess residual fatigue life of the ferromagnetic structure, such as hydraulic cylinder. In this paper, an evaluation framework was proposed. Firstly, the MMM signals under different fatigue cycles were recorded in the tensile-tensile experiment. A representative signal characteristic Hpp was defined as an evaluation index. The monotonic change trend and abrupt change point was investigated. Statistical results show that Hpp can be used to predict residual fatigue life. Except for a few specimens, almost all specimens produced an abrupt change at the normalized fatigue life coefficient k = 0.91. This can be used to distinguish different stages of fatigue life. The sensitivity, specificity, and diagnostic performance were analyzed using Receiver Operating Characteristic (ROC) curves. The statistical results show that when the coefficient k = 0.91, the diagnostic performance is relatively best with an area under the curve (AUC) is about 0.85, and Jorden's index is about 0.75.

Phase transitions of choline dihydrogen phosphate: A vibrational spectroscopy and periodic DFT study.

Choline dihydrogen phosphate, [Chol][H2PO4], is a proton-conducting ionic plastic crystal exhibiting a complicated sequence of phase transitions. Here, we address the argument in the literature around the thermal properties of [Chol][H2PO4] using Raman and infrared microspectroscopy. The known structure of the low-temperature crystal, which contains the anti-conformer of [Chol]+ and hydrogen-bonded dimers of anions, was used to do periodic density functional theory calculations of the vibrational frequencies. Raman spectra indicate that the solid-solid transition at 20 °C is linked to a conformational change to the gauche [Chol] conformer with a concurrent local rearrangement of the anions. The distinct bands of lattice modes in the low-frequency range of the Raman spectra vanish at the 20 °C transition. Given the ease with which metastable crystals can be produced, Raman mappings demonstrate that a sample of [Chol][H2PO4] at ambient temperature can contain a combination of anti- and gauche conformers. Heating to 120 °C causes continuous changes in the local environment of anions rather than melting as suggested by a recent calorimetric investigation of [Chol][H2PO4]. The monotonic change in vibrational spectra is consistent with earlier observations of a very small entropy of fusion and no abrupt jump in the temperature dependence of ionic conductivity along the phase transitions of [Chol][H2PO4].

Spectroscopic studies of TeO2-based glasses doped with Sm3+ and its use as an optical temperature sensor

This study reports the synthesis and characterization of glasses in the (100-x)65TeO2-15Li2O-20ZnO + xSm2O3 system doped with Sm2O3, denoted as Sm3+: TLZ glasses, with varying doping concentrations from 0.1, 0.15, 0.2, 0.35, 0.5, and 1 mol%. The structural and optical properties, as well as the temperature dependence of luminescence, were investigated. Excitation at 405nm resulted in strong orange-red luminescence at 566, 600, and 646 nm. The local environment surrounding Sm3+ ions was explored using the intensity ratio of electric and magnetic dipole transitions. The non-radiative energy transfer between neighboring Sm3+ ions was evaluated using the Inokuti-Hirayama model, allowing for the determination of the critical transfer distance. The temperature dependence of luminescence, displayed by Commission Internationale de L’Eclairage (CIE) chromaticity coordinates, exhibited a monotonic change from (0.611, 0.387) at 295 K to (0.605, 0.393) at 479 K. The Sm3+:TLZ glasses doped with 0.15 mol% showed the highest relative thermal sensitivity of 0.10%K-1 at 479 K, suggesting their potential as luminescent thermometers.

Data-driven detection of age-related arbitrary monotonic changes in single-cell gene expression distributions.

Identification of genes whose expression increases or decreases with age is central to understanding the mechanisms behind aging. Recent scRNA-seq studies have shown that changes in single-cell expression profiles with aging are complex and diverse. In this study, we introduce a novel workflow to detect changes in the distribution of arbitrary monotonic age-related changes in single-cell expression profiles. Since single-cell gene expression profiles can be analyzed as probability distributions, our approach uses information theory to quantify the differences between distributions and employs distance matrices for association analysis. We tested this technique on simulated data and confirmed that potential parameter changes could be detected in a set of probability distributions. Application of the technique to a public scRNA-seq dataset demonstrated its potential utility as a straightforward screening method for identifying aging-related cellular features.

1/f Noise During Thermal Treatment of Amorphous Films

Flicker noise is a sensitive tool for probing the dynamics of two‐level systems. Herein, this technique is employed to study the dependence of conductance noise on disorder for two versions of amorphous indium oxide films. The disorder in these substances may be tuned by thermal treatment that is manifested by enhanced conductivity. Structural studies reveal that this is mainly due to densification of the material. A similar reduction of volume has been achieved in glasses when subjected to high pressures. Both protocols, pressure and heat treatment, initiate nonequilibrium state that slowly relaxes. This relaxation is reflected in the sample conductivity and its optical transmission as a monotonic change. The magnitude of 1/f noise during these events turns out to fluctuate appreciably following changes in the sample conductance caused by thermal treatment. This may overshadow the tendency of the noise level to increase with disorder. Possible reasons for the fluctuations of noise levels in highly disordered systems are discussed.