Transition Range Research Articles

Intermittent Precipitation-Dependent Interactions, Encompassing Allee Effect, May Yield Vegetation Patterns in a Transitional Parameter Range.

We construct a spatial model that incorporates Allee-type and competition interactions for vegetation as an evolving random field of biomass density. The cumulative effect of close-range precipitation-dependent interactions is controlled by a parameter defining precipitation frequency. We identify a narrow parameter range in which the behavior of the system changes from survival of vegetation to extinction, via a transitional aggregation pattern. The aggregation pattern is tied to the initial configuration and appears to arise differently from Turing's diffusion and differential flow patterns of other models. There is close agreement of our critical transition parameter range with that of the corresponding evolving random mean-field model.

Effect of Mn concentration on the polar optical phonons frequencies in Cd1− xMnxTe thin films

Cd1−xMnxTe (CMT) is a wide bandgap semiconductor that stands out among the ternary compounds in several industrial applications, such as optoelectronic and solar cell devices. Therefore, it is worth understanding the mechanisms of light interaction with CMT produced by growth techniques. In this work, we investigate the room temperature Raman scattering by longitudinal optical phonon modes CdTe-like (LO1) and MnTe-like (LO2) in CMT thin films grown on Si(111) by molecular-beam epitaxy. The well-known linear dependence of LO1 and LO2 frequencies on x is observed in Raman spectra when the excitation photon energy is above the bandgap energy. As expected, for the excitation energy of the incident laser line near the fundamental gap of CMT, the resonance becomes evident in the Raman results. However, for a specific resonance condition due to tuning of the bandgap energy dependence on Mn concentration, the frequencies of the LO1 and LO2 phonon modes remain constant as the average manganese concentration increases to values x≳ 0.30. From micro-photoluminescence spectroscopy investigations, we concluded that for Mn concentration above 0.3, a broad range of optical transitions provides the required conditions for a resonant Raman scattering selected by the incident photon energy. It introduces a resonant selectivity of regions where the incident excitation energy coincides with a bandgap energy associated with a specific value of x, even for samples with nominally different compositions. The results show the sensitivity of resonant Raman to express diagnostics of ternary compound growth.

Hygromechanical Behavior of Polyamide 6.6: Experiments and Modeling.

This paper investigates water absorption in polyamide 6.6 and the resulting hygroscopic swelling and changes in mechanical properties. First, sorption and swelling experiments on specimens from injection molded plates are presented. The observed swelling behavior is dependent on the melt flow direction of the injection molding process. Additionally, thermal analysis and mechanical tensile tests were performed for different conditioning states. The water sorption is accompanied by a decrease in the glass transition temperature and a significant reduction in stiffness and strength. Next, a sequentially coupled modeling approach is presented. A nonlinear diffusion model is followed by mechanical simulations accounting for swelling and concentration-dependent properties. For the mechanical properties, the notion of a "gap" temperature caused by the shift of the glass transition range due to water-induced plasticization is employed. This model enables the computation of local moisture concentration fields and the resultant swelling and changes in stress-strain behavior.

Synergistic redox of dual-shaped silver nanostructures for highly selective sensing of hydrogen peroxide

A novel growth-based plasmonic sensor for hydrogen peroxide (H2O2) determination was developed from dual-shaped silver nanostructures consisting of starch-stabilized yellow silver nanospheres (AgNSs) and citrate-capped red silver nanoprisms (AgNPrs). AgNPrs were enlarged through a unique mechanism of AgNSs dissolution to silver ions which are subsequently reduced to silver metal by H2O2. Citrate-capping maintains the lateral anisotropic growth by protecting the AgNPrs from oxidation while exposing the sensitive edges to Ostwald ripening. This highly unique process addresses the selectivity issues encountered with decomposition-based AgNSs/NPrs sensors. Absorbance values from the AgNSs decomposition and AgNPrs growth facilitated a more sensitive spectrophotometric assay through ratiometric analysis. Increasing the concentration of the AgNSs/NPrs sensor to 80:40 ppm also improved sensitivity of naked eye detection of H2O2 by generating a wide range of color transitions. Furthermore, selectivity, accuracy and precision evaluation suggest that the dual-shaped silver nanostructure sensor is a potential alternative to H2O2 determination by allowing a simple, rapid, highly selective, and sensitive measurement.

Biomechanical evaluation of different semi-rigid junctional fixation techniques using finite element analysis

BackgroundProximal junctional failure is a common complication attributed to the rigidity of long pedicle screw fixation constructs used for surgical correction of adult spinal deformity. Semi-rigid junctional fixation achieves a gradual transition in range of motion at the ends of spinal instrumentation, which could lead to reduced junctional stresses, and ultimately reduce the incidence of proximal junctional failure. This study investigates the biomechanical effect of different semi-rigid junctional fixation techniques in a T8-L3 finite element spine segment model. MethodsFirst, degeneration of the intervertebral disc was successfully implemented by altering the height. Second, transverse process hooks, one- and two-level clamped tapes, and one- and two-level knotted tapes instrumented proximally to three-level pedicle screw fixation were validated against ex vivo range of motion data of a previous study. Finally, the posterior ligament complex forces and nucleus pulposus stresses were quantified. FindingsSimulated range of motions demonstrated the fidelity of the general model and modelling of semi-rigid junctional fixation techniques. All semi-rigid junctional fixation techniques reduced the posterior ligament complex forces at the junctional zone compared to pedicle screw fixation. Transverse process hooks and knotted tapes reduced nucleus pulposus stresses, whereas clamped tapes increased nucleus pulposus stresses at the junctional zone. InterpretationThe relationship between the range of motion transition and the reductions in posterior ligament complex and nucleus pulposus stresses was complex and dependent on the fixation techniques. Clinical trials are required to compare the effectiveness of semi-rigid junctional fixation techniques in terms of reducing proximal junctional failure incidence rates.

Ultrasensitive and highly selective detection of nickel ion by two novel optical sensors.

Novel optical sensors for nickel determination by incorporation of 5-(2`-bromo-phenylazo)-6-hydroxypyrimidine-2,4-dione (I), 5-(2`,4`-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (II), dibutylphthalate (DBP) and sodium tetra-phenylborate (Na-TPB) to the plasticized polyvinyl chloride matrices were prepared. The introduction of DBP in the membrane substantially increased the ability of both ionophores I and II to function as chromo ionophores. The advantages of the reported sensors include great stability, reproducibility, and relatively long lifespan, as well as excellent selectivity for Ni2+ ion detection across a wide range of alkali, alkaline earth, transition, and heavy metal ions.Under optimized membrane compositions and experimental parameters, the response of both sensors was linear throughout a concentration range of 3.5 × 10-8 to 8.1 × 10-5 and 2.0 × 10-8 to 5.1 × 10-5M for I and II, respectively. Sensor detection and quantification limits based on the definition that the concentration of the sample leads to a signal equal to the blank signal plus three and ten times its standard deviation were determined to be 1.15 × 10-8 and 3.45 × 10-8M when utilizing I, whereas they were 0.61 × 10-8 and 1.95 × 10-8M when utilizing II, respectively. The reaction time of optodes is defined as the period required achieving 95% of based sensors and found to be 8.0 and 5.0min using I and II, respectively. Ni2+ ion concentrations in water, food, and environmental samples were effectively determined using the proposed optical sensors. Representative diagram for preparation of the sensing Ni2+ sensor.

Influence of the Valid Test Temperature Range on Master Curve Analyses of Large Fracture Toughness Data Sets

Abstract ASTM E1921, Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range, standardizes the Master Curve procedure for determining the reference temperature, T0, of ferritic steels in the ductile-to-brittle transition range. In order for toughness test results to be included in the analyses, the corresponding test temperatures, T, must currently lie within the valid range defined as T0 – 50°C ≤ T ≤ T0 + 50°C. This study investigated the possibility of extending the valid test temperature range in a future revision of ASTM E1921 by assessing the consequences on the values of homogeneous (T0) and inhomogeneous (T0IN, Tm) reference temperatures calculated on 10 large “historical” data sets, already examined by the author in previous papers. The effect of expanding the valid temperature range on the macroscopical nature (homogeneous or inhomogeneous) of each data set was also considered by using the screening criterion presently proposed by ASTM E1921-22a. The results obtained appear to warrant a possible revision of the standard in this direction.

Characteristics of Separation-Bubble Formation on Finite Circular Cylinder in Critical Transition Range

Experiments were conducted for three finite circular cylinder models for which the aspect ratios were two, three and four, respectively, in the critical transition range. Oil-film flow visualization was performed at Reynolds numbers at the initiation of the critical transition range, which unveiled the three-dimensionality and nonstationarity of multiple separation lines on each of the model surfaces due to intermittent formation of a separation bubble. Moreover, based on the time-averaged pressure coefficients obtained at three heights on each of the models, it was seen that the symmetry of flow varied with Reynolds number. A modified peak–valley method was proposed to identify the intermittent events of separation-bubble formation. By this method, pronounced variations in the real-time signals due to intermittent formation of the separation bubble were identified, which were referred as to the characteristic events. Interesting findings included that the average normalized timescales of the characteristic events fell within 0.1 and 0.6, whereas the average normalized timescales obtained from the real-time traces of the lift coefficient were mostly around 0.08. The difference between these is discussed in this paper.

Pinched hysteresis loop and internal bias field in Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics

A-site high entropy Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics were designed and prepared by a standard solid state sintering process. First-order ferroelectric transition occurs around 240 °C on heating, while around 136 °C on cooling. Pinched and asymmetric P–E hysteresis loops were observed within and below the thermal hysteresis temperature range of the ferroelectric transition. Pinched P–E hysteresis loops were attributed to the coupling between the ferroelectric transition and the commensurate/incommensurate modulation transition. The reason for the asymmetry of the hysteresis loop was the presence of an internal bias electric field. Different measuring procedures were designed to clarify the evolution of hysteresis loop asymmetry. The existence of oxygen vacancy and Eu3+/Eu2+ was identified by x-ray photoemission spectroscopy. The electric field cycling with elevated temperatures caused defect dipoles incline to align along the direction of spontaneous polarization leading to the internal bias electric field. Due to the A-site high entropy effect, dielectric strength of Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 ceramics is up to 300 kV/cm, which is increased by more than 50% than that with the single element in the A1-site.

Linear-in-temperature resistivity for optimally superconducting (Nd,Sr)NiO2.

The occurrence of superconductivity in proximity to various strongly correlated phases of matter has drawn extensive focus on their normal state properties, to develop an understanding of the state from which superconductivity emerges1-4. The recent finding of superconductivity in layered nickelates raises similar interests5-8. However, transport measurements of doped infinite-layer nickelate thin films have been hampered by materials limitations of these metastable compounds: in particular, a high density of extended defects9-11. Here, by moving to a substrate (LaAlO3)0.3(Sr2TaAlO6)0.7 that better stabilizes the growth and reduction conditions, we can synthesize the doping series of Nd1-xSrxNiO2 essentially free from extended defects. In their absence, the normal state resistivity shows a low-temperature upturn in the underdoped regime, linear behaviour near optimal doping and quadratic temperature dependence for overdoping. This is phenomenologically similar to the copper oxides2,12 despite key distinctions-namely, the absence of an insulating parent compound5,6,9,10, multiband electronic structure13,14 and a Mott-Hubbard orbital alignment rather than the charge-transfer insulator of the copper oxides15,16. We further observe an enhancement of superconductivity, both in terms of transition temperature and range of doping. These results indicate a convergence in the electronic properties of both superconducting families as the scale of disorder in the nickelates is reduced.

Temperature Dependence of Cleavage Fracture Toughness for an Ultrahigh Strength Martensitic Steel

Abstract This work conducts an exploratory evaluation of the brittle fracture behavior for an ultrahigh strength martensitic steel using conventional three-point bend SE(B) and precracked Charpy V-notch (PCVN) specimens. A primary purpose of this study is to verify the effectiveness of the Master Curve methodology in providing a reliable estimate of the reference temperature (T0) derived from fracture toughness data sets measured in the ductile-to-brittle transition (DBT) region of an ultrahigh strength, low alloy martensitic steel. Fracture toughness testing conducted on three-point bend SE(B) specimens and PCVN configurations at different test temperatures in the DBT region provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc, and its corresponding KJc-values for the tested material. Although this class of ultrahigh strength steel having a martensitic microstructure is currently beyond the reach of ASTM E1921, Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range, the analyses described here show that the predicted normalized curves of median fracture toughness versus temperature are in good agreement with the experimental measurements.

Loading Rate of Fracture Toughness Tests in Transition Regime

Abstract ASTM E1921-21, Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range, contains a limitation on the stress intensity factor loading rate (K˙) for the quasistatic loading. The specimens should be loaded at a rate such that K˙ during the initial elastic portion is between 0.1 and 2 MPa√m/s. However, based on recent improvements in the test technique, it should be possible to narrow the loading rate range in order to reduce variability and have more comparable results between laboratories. For all users to be able to achieve the reduced range, clear guidelines are needed, which are not yet available. The Belgian Nuclear Research Centre (SCK CEN) has extensive experience in fracture toughness testing and has constructed a large database on which statistical studies were performed. This paper illustrates, using the SCK CEN database, that Wallin’s theoretical displacement formulas can only be used in the case in which the compliance of the testing setup is taken into account. An improved equation is proposed, guidelines for implementing the equation are drawn up, and these are verified using the database. It is clear that the methodology is sufficiently robust to provide an average loading rate within the suggested range of 0.5 and 2 MPa√m/s. This methodology could thus be integrated into the testing standard ASTM E1921-21.

Benchmark to Evaluate Revised Censoring Procedures for ASTM E1921

Abstract ASTM E1921, Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range, contains a censoring criterion, KJΔa, that limits the amount of ductile tearing prior to cleavage in specimen data used to calculate the reference temperature, T0. A frequent complaint from users is that the requirements for both determining and implementing KJΔa are unclear and difficult to apply. These provisions require that KJΔa be determined using either the maximum valid KJc data from another result within the data set (i.e., one with an acceptance amount ductile tearing prior to cleavage) or a K-value based on the material’s JIc value (i.e., KJIc). Both options are potentially problematic as the JIc value is often unknown and assigning other test data as the censoring value can cause situations where this value is higher than the measured KJc value for that specimen. A benchmark analysis evaluated two alternative options for ductile-tearing censoring requirements proposed to rectify these inadequacies. The first option uses an absolute ductile-tearing-limit criterion and is simpler to apply. The second option employs a ductile tearing limit that varies with the KJc result but is designed to minimize the conservative bias associated with excessive ductile tearing. Data sets for low upper-shelf materials with sufficient data to calculate valid T0 values, yet with a significant percentage of data with measurable ductile tearing prior to cleavage were selected for evaluation. The benchmark results illustrated that although there is no obviously better censoring option, the option that uses an absolute ductile-tearing-limit is simpler to implement, whereas the T0 results are generally consistent with those calculated for the option with the variable ductile-tearing-limit.

Cooperative melting in double-stranded peptide chains through local mechanical interactions

The separation of double-stranded peptide chains can occur in two ways: cooperatively or non-cooperatively. These two regimes can be driven either by chemical or thermal effects, or through non-local mechanical interactions. Here, we show explicitly that local mechanical interactions in biological systems may regulate the stability, the reversibility, and the cooperative/non-cooperative character of the debonding transition. We show that this transition is characterized by a single parameter depending on an internal length scale. Our theory describes a wide range of melting transitions found in biological systems such as protein secondary structures, microtubules and tau proteins, and DNA molecules. In these cases, the theory gives the critical force as a function of the chain length and its elastic properties. Our theoretical results provide quantitative predictions for known experimental effects that appear in different biological and biomedical fields.

Fracture Load Prediction of Non-Linear Structural Steels through Calibration of the ASED Criterion

In this work, the application of the Average Strain Energy Density (ASED) criterion for the estimation of failure loads in materials with nonlinear behavior containing U-shaped notches is presented. The ASED criterion was originally defined to predict failure in the presence of notches in materials with linear-elastic behavior. However, most structural materials (e.g., ferritic-pearlitic steels) can develop non-linear behavior (e.g., elastoplastic). In this sense, this work proposes to extend the use of the ASED criterion to materials that exhibit plasticity by a thorough calibration of their characteristic parameters, and the subsequent extrapolation of the liner-elastic formulation of the ASED criterion to non-linear situations. To validate this methodology, a wide range of structural steels (S275JR, S355J2, S460M, and S690Q) were used operating in the ductile-to-brittle transition range, with six different notch radii (0 mm, 0.15 mm, 0.25 mm, 0.50 mm, 1.0 mm, and 2.0 mm). The results obtained demonstrate that the proposed calibration of the ASED criterion allows for accurate predictions of failure loads. Therefore, it is shown that, for the notch radii analyzed in this work and for testing temperatures within the material ductile-to-brittle transition range, it is possible to extrapolate the ASED criterion to obtain estimates of failure loads in materials with U-shaped notches that exhibit ductile behavior.

Markov chain analysis indicates that positive and negative emotions have abnormal temporal interactions during daily life in schizophrenia

Abnormalities in positive and negative emotional experience have been identified in laboratory-based studies in schizophrenia (SZ) and associated with poorer clinical outcomes. However, emotions are not static in daily life–they are dynamic processes that unfold across time and are characterized by temporal interactions. Whether these temporal interactions are abnormal in SZ and associated with clinical outcomes is unclear (i.e., whether the experience of positive/negative emotions at time t increases or decreases the intensity of positive/negative emotions at time t+1). In the current study, participants with SZ (n = 48) and healthy controls (CN; n = 52) completed 6 days of ecological momentary assessment (EMA) surveys that sampled state emotional experience and symptoms. The EMA emotional experience data was submitted to Markov chain analysis to evaluate transitions among combined positive and negative affective states from time t to t+1. Results indicated that: (1) In SZ, the emotion system is more likely to stay in moderate or high negative affect states, regardless of positive affect level; (2) SZ transition to co-activated emotional states more than CN, and once emotional co-activation occurs, the range of emotional states SZ transition to is more variable than CN; (3) Maladaptive transitions among emotional states were significantly correlated with greater positive symptoms and poorer functional outcome in SZ. Collectively, these findings clarify how emotional co-activation occurs in SZ and its effects on the emotion system across time, as well as how negative emotions dampen the ability to sustain positive emotions across time. Treatment implications are discussed.

A power-law exponential model for variograms with quick transition and known range: Construction and application to geostatistical time series

The variogram is an important element in geostatistical studies that has been used as a tool to investigate the variability and continuity of the study phenomenon. The classical Matheron estimator for calculating the experimental variogram is used in this paper. A new variogram model is proposed, the power-law exponential model and a comparative study of three-time series datasets with the characteristic of being periodic is performed: rainfalls, particulate matter PM10, and Ozone series. Three other models were considered for comparison: spherical, exponential, and quadratic–exponential. The numerical fit and analysis are carried out using the least-squares method provided by the R statistics software, and testing the solutions by the coefficient of determination R2 and the RMSE measure. Our results provided a good adaptation of the proposed model to the different datasets, satisfying the equality of variances, and also showing a robust fit when adding noise. Moreover, our model presented several advantages over the others, regarding the mentioned characteristics. This suggests that the power-law exponential model is a variant that adds new attributes to the set of existing variogram models.

Elastic Snap-Through Instabilities Are Governed by Geometric Symmetries.

Many elastic structures exhibit rapid shape transitions between two possible equilibrium states: umbrellas become inverted in strong wind and hopper popper toys jump when turned inside out. This snap through is a general motif for the storage and rapid release of elastic energy, and it is exploited by many biological and engineered systems from the Venus flytrap to mechanical metamaterials. Shape transitions are known to be related to the type of bifurcation the system undergoes, however, to date, there is no general understanding of the mechanisms that select these bifurcations. Here we analyze numerically and analytically two systems proposed in recent literature in which an elastic strip, initially in a buckled state, is driven through shape transitions by either rotating or translating its boundaries. We show that the two systems are mathematically equivalent, and identify three cases that illustrate the entire range of transitions described by previous authors. Importantly, using reduction order methods, we establish the nature of the underlying bifurcations and explain how these bifurcations can be predicted from geometric symmetries and symmetry-breaking mechanisms, thus providing universal design rules for elastic shape transitions.

Molecular dynamics simulation of the transformation of Fe-Co alloy by machine learning force field based on atomic cluster expansion

The force field describing the calculated interaction between atoms or molecules is the key to the accuracy of many molecular dynamics (MD) simulation results. Compared with traditional or semi-empirical force fields, machine learning force fields have the advantages of faster speed and higher precision. We have employed the method of atomic cluster expansion (ACE) combined with first-principles density functional theory (DFT) calculations for machine learning, and successfully obtained the force field of the binary Fe-Co alloy. Molecular dynamics simulations of Fe-Co alloy carried out using this ACE force field predicted the correct phase transition range of Fe-Co alloy.

The influence of refractive index disturbance of ring-core fiber with central air hole on modes separating

In this paper, the influences of the ring thickness, the maximum refractive index of the ring and curve steepness on the mode separation are analyzed. The model is established with considering the actual fiber fabrication, especially the transition range between two adjacent layers are studied. Then we manufacture the ring-core fiber with central air hole. This study has reference significance for the structure design of vortex optical fibers.