Initial Mode Research Articles

CPAP Versus NIPPV Postextubation in Preterm Neonates: A Comparative-Effectiveness Study.

Nasal intermittent positive pressure ventilation (NIPPV) has been shown to be superior to nasal continuous positive airway pressure (CPAP) postextubation in preterm neonates. However, studies have not permitted high CPAP pressures or rescue with other modes. We hypothesized that if CPAP pressures >8 cmH2O and rescue with other modes were permitted, CPAP would be noninferior to NIPPV. We conducted a pragmatic, comparative-effectiveness, noninferiority study utilizing network-based real-world data from 22 Canadian NICUs. Centers self-selected CPAP or NIPPV as their standard postextubation mode for preterm neonates <29 weeks' gestation. The primary outcome was failure of the initial mode ≤72 hours. Secondary outcomes included failure ≤7 days, and reintubation ≤72 hours and ≤7 days. Groups were compared using a noninferiority adjusted risk-difference (aRD) margin of 0.05, and margin of no difference. A total of 843 infants extubated to CPAP and 974 extubated to NIPPV were included. CPAP was not noninferior (and inferior) to NIPPV for failure of the initial mode ≤72 hours (33.0% vs 26.3%; aRD 0.07 [0.03 to 0.12], Pnoninferiority(NI) = .86), and ≤7 days (40.7% vs 35.8%; aRD 0.09 [0.05 to 0.13], PNI = 0.97). However, CPAP was noninferior (and equivalent) to NIPPV for reintubation ≤72 hours (13.2% vs 16.1%; aRD 0.01 [-0.05 to 0.02], PNI < .01), and noninferior (and superior) for reintubation ≤7 days (16.4% vs 22.8%; aRD -0.04 [-0.07 to -0.001], PNI < .01). CPAP was not noninferior to NIPPV for failure ≤72 hours postextubation; however, it was noninferior to NIPPV for reintubation ≤72 hours and ≤7 days. This suggests CPAP may be a reasonable initial postextubation mode if alternate rescue strategies are available.

Fast breakdown process and characteristics diagnosis of nanosecond pin–pin discharge

In this paper, the characteristics of a nanosecond spark discharge with a pin–pin electrode configuration have been systematically studied. Both a streak camera with high temporal resolution and an intensified charge-coupled device (ICCD) camera are employed together to investigate the breakdown and evolution process of the discharge. The formation of initial breakdown and mode transition from streamer to spark in the electrode gap are clearly observed on the time scale of several nanoseconds with a temporal resolution of 100 ps. In addition, the time-resolved spectra technology is also used to analyze the generation and quenching mechanisms of reactive species, the electron density, and the electron temperature. The results show that there is a 1.25 ns initial discharge breakdown and that a bright cathode spot exists before the transformation from streamer to spark channel. After a faster cathode filament and a slower anode filament propagate and merge at the electrode gap, the spark discharge phase begins. The generation processes of different reactive species depend on the discharge phase to a great extent. The N2* is first generated during the streamer phase while the O*, N*, and N+ are mainly generated under the spark phase, in which the electron temperature calculated by Boltzmann plots is 2.74 eV, and the electron density determined from the Stark broadening of O lines is on the order of 1016 cm−3.

Numerical study on dynamic cracking characteristic and mechanism of quasi-brittle materials under impulsive loading

This study focuses on investigating the dynamic cracking behaviors of quasi-brittle materials under impulsive loading using the extended non-ordinary state-based peridynamic (NOSB-PD) model. This extended model incorporates two stress-based failure criteria: Mohr-Coulomb and maximum tensile stress criteria, to represent shear and tensile fractures of quasi-brittle materials, respectively. By analyzing the evolution characteristics of the maximum principal stress obtained from the NOSB-PD model, the fracture mechanisms of quasi-brittle materials subjected to impulsive loading are explored. The research reveals that tensile failure predominantly governs the initiation and propagation processes of quasi-brittle materials under impulsive loading. The stress concentration effect, transfer effect, and dissipation effect observed in the maximum principal stress fields provide insights into the cracking mechanism during the failure processes of such materials. To validate the findings, the crack initiation modes and crack propagation paths obtained from the NOSB-PD model are compared with those obtained from the existing experimental and numerical approaches. The results demonstrate that the extended NOSB-PD model is effective in addressing fracture problems associated with quasi-brittle materials under impulsive loading conditions.

Characteristics, treatment patterns and burden of illness in US patients with asthma newly initiating multiple-inhaler triple therapy

IntroductionFor patients with asthma who remain symptomatic on medium-dose inhaled corticosteroid/long-acting β2-agonist, add-on long-acting muscarinic antagonist is a treatment option, which can be administered as multiple-inhaler triple therapy (MITT). A...

Hydrogen peroxide sensitivity connects the activity of COX5A and NPR3 to the regulation of YAP1 expression.

Reactive oxygen species (ROS) are among the most severe types of cellular stressors with the ability to damage essential cellular biomolecules. Excess levels of ROS are correlated with multiple pathophysiological conditions including neurodegeneration, diabetes, atherosclerosis, and cancer. Failure to regulate the severely imbalanced levels of ROS can ultimately lead to cell death, highlighting the importance of investigating the molecular mechanisms involved in the detoxification procedures that counteract the effects of these compounds in living organisms. One of the most abundant forms of ROS is H2 O2 , mainly produced by the electron transport chain in the mitochondria. Numerous genes have been identified as essential to the process of cellular detoxification. Yeast YAP1, which is homologous to mammalian AP-1 type transcriptional factors, has a key role in oxidative detoxification by upregulating the expression of antioxidant genes in yeast. The current study reveals novel functions for COX5A and NPR3 in H2 O2 -induced stress by demonstrating that their deletions result in a sensitive phenotype. Our follow-up investigations indicate that COX5A and NPR3 regulate the expression of YAP1 through an alternative mode of translation initiation. These novel gene functions expand our understanding of the regulation of gene expression and defense mechanism of yeast against oxidative stress.

A quasi‐31‐vibrator method for the characterization of piezoelectric full matrix parameters using a single sample

AbstractThe full matrix parameters of a piezoelectric material are crucial for designing and evaluating piezoelectric devices. However, due to their inverse problematic nature, commonly used single‐sample characterization methods heavily depend on the accuracy of initial values and mode matching. In this paper, we propose a quasi‐31‐vibrator method to directly evaluate these parameters by designing the sample geometry and establishing the relationship equation between the parameters. This approach completely bypasses the need for characteristic spectrum simulation and mode identification processes. Subsequently, we tested the full matrix parameters of PZT‐5H ceramics and compared the simulated impedance spectra with the measured ones. The presence of well‐fitting spectra validates the feasibility of the method. This method will contribute to characterize the parameters of new piezoelectric materials and advance the intelligent implementation of measuring full matrix parameters.

The Effect of Microstructure on the Very High Cycle Fatigue Behavior of Ti-6Al-4V Alloy

Crack initiation plays a major role in very high cycle fatigue (VHCF) life, and the initiation of cracks is related to slip behavior. There is a need for improvement in the understanding of the influence of Ti-6Al-4V microstructures on VHCF performance and crack initiation modes. In this study, through an investigation of Ti-6Al-4V VHCF in equiaxed and bimodal microstructures, two different crack initiation modes were identified. The change in crack initiation mode is related to the variation in microtexture, for which a corresponding model is proposed. The VHCF performance of the bimodal microstructure is significantly improved compared to that of the equiaxed microstructure.

Nonlinear in-plane buckling of small-curved and large-curved FG porous microbeams via strain gradient-based isogeometric collocation formulations

In the current investigation, for the first time, the changes in the limit loads and equilibrium branches associated with the nonlinear in-plane stability characteristics of curved microbeams are explored in the presence of different microstructural gradient tensors. In this regard, multiple microsize-dependent equilibria are analyzed relevant to thermomechanical loaded small-curved, medium-curved, and large-curved microbeams made of functionally graded porous (FGP) metal reinforced with nanofillers possessing clamped end supports. To this purpose, based upon the strain gradient elasticity within the framework of the third-order shear flexible curved beam model, the isogeometric collocation formulations incorporating Greville abscissae are constructed resulting in higher-continuity characters as well as remarkable accuracy for higher-order approximations. It is deduced that for the small-curved FGP reinforced microbeam, no limit load can be found due to the absence of the buckling phenomenon, but after rising the temperature by an enough amount, the initial instability mode appears. However, for the medium-curved FGP reinforced microbeam, the limit instability mode of buckling occurs which results in the normalized upper limit load equal to 0.7161 based on the classical theory and 0.7606 based on the strain gradient elasticity (6.21% enhancement). Also, it results in the normalized lower limit load equal to 0.3060 based on the classical theory and 0.3521 based on the strain gradient elasticity (15.07% enhancement). On the other hand, for the large-curved FGP reinforced microbeam, the bifurcation mode of buckling occurs which results in the normalized upper limit load equal to 1.0494 based on the classical theory and 1.1358 based on the strain gradient elasticity (8.23% enhancement). Also, it results in the normalized lower limit load equal to 0.2225 based on the classical theory and 0.2513 based on the strain gradient elasticity (12.94% enhancement).

Geometry Effects on Joint Strength and Failure Modes of Hybrid Aluminum-Composite Countersunk bolted Joints

This paper presents the effects of geometry parameters (width/hole diameter, and edge distance/hole diameter ratios) on the damage initiation and growth in the CFRP (Carbon Fiber Reinforced Polymer) composite-aluminum countersunk bolted joints. Strain gauge measurements conducted with an Instron testing machine along with a detailed 3D finite element model incorporating geometric, material, and friction-based contact nonlinearities were used to investigate the geometry parameters on the Progressive Damage Analysis (PDA) of the orthotropic material model. The PDA material model integrates the lamina nonlinear shear deformation, Hashin-type failure criteria, and strain-based continuum degradation rules, using the UMAT user subroutine in the MSC Software Corporation Patran-Nastran commercial software. The results showed that the geometry effects on damage initiation and failure modes are quite accurately predicted by the PDA material model, which proved to be computationally efficient, and therefore can predict failure propagation and damage mechanisms. Plate geometry is an important parameter in the design process of an adequate bolted joint while its effects on damage initiation and failure modes were quite accurately predicted by the analysis. The latter proved to be computationally efficient, and could successfully predict failure propagation and damage mechanism in hybrid metal-composite countersunk bolted joints.

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Research on the anisotropic mechanism of plastic behavior during tensile process of textured pure titanium

The presence of texture has an important influence on the deformation behavior of titanium. In this study, the anisotropy of the macro-mesoscopic deformation behavior of the material and its evolution with strain were systematically studied by uniaxial tensile test and electron backscatter diffraction (EBSD) technique. Based on the above results, the calculation formula of Schmid factor (SF) for each variant of the slip system expressed by the crystal orientation angle was derived, and the influence of initial texture and texture redirection on the activability of each deformation mode was explored. The impact of the ratios between the critical resolved shear stress (CRSS) of the three deformation modes on the predictions of the dominant deformation mode of yield was systematically assessed, using the CRSS as the standard. The initial yield mode of RD tensile is prismatic <a>slip, while TD tensile may be a combination of multiple slip modes. One of the primary reasons of the evolution of the basal split texture components is the activation of dislocation slip, while the twinning mainly plays a role in coordinating the deformation. According the Taylor axis analysis, the prismatic <a> slip is the primary deformation mode during RD and TD tensile, followed by pyramidal <a> slip, while the basal <a> slip is difficult to be activated or the activability decreases with the increase of strain.

Coordination of cohesin and DNA replication observed with purified proteins.

Two newly duplicated copies of genomic DNA are held together by the ring-shaped cohesin complex to ensure faithful inheritance of the genome during cell division1-3. Cohesin mediates sister chromatid cohesion by topologically entrapping two sister DNAs during DNA replication4,5, but how cohesion is established at the replication fork is poorly understood. Here, we studied the interplay between cohesin and replication by reconstituting a functional replisome using purified proteins. Once DNA is encircled before replication, the cohesin ring accommodates replication in its entirety, from initiation to termination, leading to topological capture of newly synthesized DNA. This suggests that topological cohesin loading is a critical molecular prerequisite to cope with replication. Paradoxically, topological loading per se is highly rate limiting and hardly occurs under the replication-competent physiological salt concentration. This inconsistency is resolved by the replisome-associated cohesion establishment factors Chl1 helicase and Ctf4 (refs. 6,7), which promote cohesin loading specifically during continuing replication. Accordingly, we found that bubble DNA, which mimics the state of DNA unwinding, induces topological cohesin loading and this is further promoted by Chl1. Thus, we propose that cohesin converts the initial electrostatic DNA-binding mode to a topological embrace when it encounters unwound DNA structures driven by enzymatic activities including replication. Together, our results show how cohesin initially responds to replication, and provide a molecular model for the establishment of sister chromatid cohesion.

Effect of high humidity on the initial mechanical properties and failure modes of thin spray-on liners (TSLs)

Thin Spray-on Liners (TSLs) are a novel rock support technology used in underground projects, which often encounter harsh environments such as high humidity. The mechanical properties of TSLs are affected by the high humidity environment. This study aims to summarize the support mechanisms of TSLs and evaluate the effects of humidity on their performance. Two cement-based TSLs were prepared. They used vinyl acetate-ethylene copolymer emulsion (VAE emulsion) and polyacrylate emulsion as modifying materials, respectively. Specimens were subjected to four different humidity environments for 7 days. The mechanical properties of the specimens were evaluated through compressive, flexural and pull-out tests. The impermeability test was utilized to test the sealing of TSLs. Microscopic observation was conducted using a Lecia microscope. The study also analyzed the interfacial failure modes observed in the pull-out test. The results indicated that increasing humidity hindered the film formation reaction of TSLs, preventing the formation of a continuous three-dimensional spatial polymer mesh structure. Instead, cohesive large particles were formed, negatively impacting the mechanical properties. Additionally, increasing humidity led to the formation of large pores and crack lines within TSLs, further decreasing their mechanical and sealing properties. The increase in humidity also weakened the dry shrinkage effect of TSLs, resulting in increased bond strength. Therefore, analyzing the initial mechanical properties of TSLs under high humidity conditions is crucial for guiding their application in underground projects.

Survey Protocols, Response Rates, and Representation of Underserved Patients

Surveys often underrepresent certain patients, such as underserved patients. Methods that improve their response rates (RRs) would help patient surveys better represent their experiences and assess equity and equity-targeted quality improvement efforts. To estimate the effect of adding an initial web mode to existing Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) survey protocols and extending the fielding period on RR and representativeness of underserved patient groups. This randomized clinical trial included 36 001 patients discharged from 46 US hospitals from May through December 2021. Data analysis was performed from May 2022 to September 2023. Patients were randomized to 1 of 6 survey protocols: 3 standard HCAHPS protocols (mail only, phone only, mail-phone) plus 3 web-enhanced protocols (web-mail, web-phone, web-mail-phone). RR and number of respondents per 100 survey attempts (yield) were calculated and compared for each of the 6 survey protocols, overall, and by patient age, service line, sex, and race and ethnicity. A total of 34 335 patients (median age range, 55-59 years; 59.3% female individuals and 40.7% male individuals) were eligible and included in the study. Of the respondents, 6.9% were Asian American or Native Hawaiian or Other Pacific Islander, 0.7% were American Indian or Alaska Native, 11.5% were Black, 17.4% were Hispanic, 61.0% were White, and 2.6% were multiracial. Of the 6 protocols, RRs were highest in web-mail-phone (36.5%), intermediate for the 3 two-mode survey protocols (mail-phone, web-mail, web-phone, 30.3%-31.1%), and lowest for the 2 single-mode protocols (mail only, phone only, 22.1%-24.3%). Web-mail-phone resulted in the highest yield for 3 racial and ethnic groups (Black, Hispanic, and White patients) and second highest for another (multiracial patients). Otherwise, the highest or second highest yield was almost always a 2-mode protocol. Mail only was the lowest-yield protocol for Black, Hispanic, and multiracial patients and phone-only was the lowest-yield protocol for White patients; these 2 protocols tied for lowest-yield for Asian American or Native Hawaiian or Other Pacific Islander patients. Gains from multimode approaches were often 2 to 3 times as large for Asian American or Native Hawaiian or Other Pacific Islander, Black, Hispanic, and multiracial patients as for White patients. Web-mail-phone had the highest RR for 6 of 8 age groups and 4 of 5 combinations of service line and sex. In this randomized clinical trial, web-first multimode survey protocols significantly improved the RR and representativeness of patient surveys. The best-performing protocol based on RR and representativeness was web-mail-phone. Web-phone performed well for young and diverse patient populations, and web-mail for older and less diverse patient populations. The US Centers for Medicare & Medicaid Services will allow hospitals to use the web-mail, web-phone, and web-mail-phone protocols for HCAHPS administration beginning in 2025.

Damage and failure characteristics of single fractured cyan sandstone subjected to freeze–thaw cycles under uniaxial compression

In order to explore the freeze–thaw (FT) damage characteristics of fractured rock masses, FT cycle tests and uniaxial compression tests were conducted on intact and pre-cracked cyan sandstone samples, respectively. The degradation laws of physical and mechanical properties of samples under FT cycle conditions were analyzed, and the FT damage mechanism and failure mechanism were explored accordingly. The results indicate that as the number of FT cycles (N) increases, the saturation weight change rate and porosity of the sample continue to increase, while the P-wave velocity continues to decrease. The closure stress, initiation stress, damage stress, and peak stress decrease linearly with increasing FT cycles, and increase linearly with increasing crack inclination angle (β). Moreover, as FT cycles increase, the geological strength index GSI decreases linearly, while the damage factor (D) increases linearly. A Hoek Brown strength degradation model for fractured rocks subjected to FT damage under uniaxial compression was obtained, and its high reliability was verified using test results. The FT damage of cyan sandstone is mainly dominated by the frost heave force inside the rock, and the degree of FT damage of fractured samples is much higher than that of intact ones. The concentration of frost heave force at the crack tip leading to cracking is the key to exacerbating the FT damage in fractured rock masses. However, the crack initiation mechanism is still controlled by β. Whenβ = 90°, it exhibits tensile initiation mode, and whenβ = 45°, it mainly exhibits shear initiation mode. Moreover, the fracture of the single crack sample conforms to the compression-shear fracture criterion. Taking the sample with pre-crack inclination angle of 45° as an example, the variation of KI and KII, and the relationship between them are discussed accordingly. The results of this paper are beneficial to clarify the influence of FT cycles on the mechanical properties of cyan sandstone, and can provide reference for the study of related issues.

Adsorption of hydrocarbon pollutants from wastewater using Cu‐ and Zn‐loaded activated carbon derived from waste tires

AbstractPetroleum refinery effluents contain hazardous aromatic and polyaromatic hydrocarbons that causes environmental degradation, that is, water, land, and air pollution; therefore, it should be properly treated before its discharge into environment. Adsorption serves an efficient route to treatment of refinery wastewater; but the high production cost and selectivity of the modern adsorbent used limits their industrial scale application. On the other hand, activated carbon due to desirable adsorption characteristics and low cost seems to hold the promise if properly modified to improve its efficiency. In this study, Cu and Zn impregnated on activated carbon (AC) derived from waste tires was used for adsorption of hydrocarbon pollutants from wastewater. AC was prepared from scrap tires through thermal pyrolysis, followed by chemical activation with KOH. Cu and Zn were loaded on AC through wet impregnation method. Initial batch mode adsorption experiments were carried out using aniline and phenol as model hydrocarbons, which indicated that maximum adsorption of aniline and phenol over Zn/AC and Cu/AC occurs in 10 min contact time, temperature 30°C, pH 6, 100 ppm initial concentration, and adsorbent dose of 0.1 g/10 mL. The removal of hydrocarbon pollutants from real refinery wastewater was also investigated under optimized conditions. Results show that the COD of the refinery wastewater decreased from 963 to 73 mg/L in case of Cu/AC (92% removal) and 78 mg/L in case of Zn/AC (91% removal), respectively. The adsorbent showed many folds reusability, and in first cycle, the removal efficiency of phenol and aniline was observed to be above 95%, whereas in second, third and fourth cycles, the removal percentage was 85%, 80%, and 70%, respectively.

VIV of two rigidly coupled side-by-side cylinders at subcritical [formula omitted

Cross-flow vortex-induced vibration (VIV) of two rigidly coupled circular cylinders in side-by-side arrangement at a Reynolds number of 1000 is numerically investigated using direct numerical simulation. A low mass ratio of 1.27 is considered and the nondimensional centre-to-centre spacing ratio is fixed at 2.0. The reduced velocity ranges from 2 to 13. Three response branches are identified and these responses result in different wake and hydrodynamic characteristics. The cases with large amplitudes feature the co-shedding and lower pressure in the gap, while those with small amplitudes are characterised by two parallel vortex streets. Characterisation and quantification of the flow fields of two rigidly coupled side-by-side cylinders undergoing VIV, which have seldom been reported in the existing research, are elaborated on in this study via the statistical analysis in terms of the turbulent wake visualisation, Reynolds stresses, turbulence kinetic energy (TKE) and proper orthogonal decomposition (POD) analysis. It is found that the cases with large amplitudes show a more unstable wake with sharp increases in the Reynolds stresses and TKE in the near wake. Moreover, the large amplitudes are seen to weaken the asymmetry of the wake and the initial POD modes are more energetic. A reformulated version of the novel force decomposition technique is used to realise the measurement of the time-dependent contributions from each mode to the pressure drag. The large amplitude cases are associated with the drag mode and the lift mode, whereas three modes are observed as the amplitude decreases.

Effect of core structure on the quasi-static bending behaviors and failure mechanisms of aluminum foam sandwiches at elevated temperatures

In this study, a novel three-step method involving liquid casting, hot-rolling, and foaming was employed to fabricate three types of metallurgical bonded aluminum foam sandwich (AFS): AFS with a uniform foam core (UAFS), AFS with a density-graded foam core (GAFS), and AFS with an interlayer plate (IAFS). The bending behaviors of different AFS structures in four cases were investigated using the digital image correlation (DIC) technique to examine the effect of foam core structure, loading direction, and loading temperature. The results showed that the initial peak load (Fp), plateau load (Fpl) and load oscillation decreased with increasing loading temperature. IAFS demonstrated the low sensitivity to loading temperature, an important reason was the addition of interlayer plate. The deformation mode involved interface separation and foam core detachment occurring in the interface vicinity beneath the indenter at the lower temperatures (≤300 °C) shifted towards well-bonded interface and foam core densification at the higher temperatures (400 °C and 500 °C). Different core structures and loading directions gave rise to four distinct modes of crack initiation and propagation. In addition, as the loading temperature increased, the strain localization effect was diminished, accompanied by hindering in crack formation. The fracture mode of core shear transitioned from brittle to ductile with increasing loading temperature.

A comparative study on the linear scaling relations for the diffusion of S-vacancies on MoS2 and WS2.

This work uses density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations to compare the diffusion of S-vacancies on defective MoS2 and WS2, two structures that are often discussed as catalysts. Similar to what has been discussed for MoS2, the vacancy diffusion barriers on WS2 also follow Brønsted-Evans-Polanyi (BEP) type linear scaling relations. The vacancy diffusion kinetics is discussed at the example of a large vacancy cluster consisting of 37 unoccupied sites in direct vicinity and how its structure changes with time. Using barriers estimated via linear scaling relations as input for the kMC simulations yields results that qualitatively agree with results calculated self-consistently at DFT level. As the diffusion barriers for WS2 are significantly higher than those for MoS2, the vacancy diffusion on WS2 is poorly described by the linear scaling relations derived from MoS2 and vice versa. This work further shows that one needs DFT level barriers of about 40% of all S-vacancy diffusion processes on a material to derive sufficiently reliable linear scaling relations. This means that computational costs for future studies may be reduced by only explicitly computing one fraction of the diffusion barriers while estimating the remaining ones via linear scaling. However, in this case, one would lack information about the partition function of the transition states, which are needed for calculating the rate constants. Thus, we have also proposed a scheme to estimate the contribution of the partition functions based only on the initial state's vibrational modes.

Initial and Transient Growth of Symmetric Instability

Abstract The mechanism of initial and transient perturbations of symmetric instability (SI) in a hydrostatic flow with lateral shear is analyzed by applying the generalized stability analysis. It is well known that the SI’s most rapidly growing motion is along isopycnals, and the growth rates consist of growing, neutral, and decaying modes. The eigenvectors of these three modes are not orthogonal to each other, hence the initial and transient perturbations bear little resemblance to the normal mode. Our findings indicate that the emergence of normal modes occurs within a time span of 1–3 inertial periods, which we refer to as the transient state. The overall growth of perturbation energy is divided into three components: geostrophic shear production (GSP), lateral shear production (LSP), and meridional buoyancy flux (MB). During the transient state, the perturbation energy is partly driven by MB, contrary to the normal mode which has zero MB. The relative energy contribution is evaluated through the ratio to GSP. While the MB-to-GSP ratio of the initial mode is higher than that of the normal mode, the LSP-to-GSP ratio remains constant. In the absence of the fastest-growing normal mode, MB can serve as the predominant initial energy source. The precise transition in the energy regime is contingent upon the geostrophic Richardson number and Rossby number. Significance Statement Fronts can be unstable to instabilities, which generate disturbance growth and lead to the mixing of water masses. We wanted to understand the initial and transient development of disturbance growth leading to the well-known exponentially growing state. While the exponentially growing disturbance is dominant in the long run, the disturbance growth may not have enough time to achieve the exponentially growing state. We find that the initial disturbance growth bears little resemblance to the exponentially growing state. Capturing the complete spectrum of front evolution remains challenging, and observations have thus far been limited to short-term records. The insights learned from this study can aid in better characterizing the disturbance growth captured in these short-term records.