Initial Mode Research Articles

Effect of long-wavelength perturbations in nonlinear evolution of the ablative Rayleigh–Taylor mixing

We investigate herein how long-wavelength perturbations affect the nonlinear evolution of the multimode ablative Rayleigh–Taylor instability (ARTI). A single-mode ARTI with an initial small amplitude is first investigated to validate the reliability of the proposed simulation code. The results show that both linear growth rates and asymptotic bubble velocities obtained from simulations are in reasonable agreement with theoretical results. Initial perturbations with different long-wavelength perturbations are compared to investigate the contribution of the long-wavelength perturbations to the nonlinear evolution of the ARTI mixing. Beyond the nonlinear saturation limit [S. W. Haan, Phys. Rev. A 39, 5812 (1989)], the long-wavelength perturbation promotes the ARTI mixing and facilitates the development of the large-scale structure on the ablation surface. In the self-similar analysis, the simulation results indicate that the self-similar growth parameters decrease with increasing initial longest-wavelength modes.

Effect of hydrogen on very high cycle fatigue properties of 17-4 PH martensite stainless steel

Very high cycle fatigue properties of 17-4 PH stainless steel aged for 1 h and 4 h after hydrogen charging were studied. Results show that hydrogen reduces fatigue strength and changes crack initiation mode to mainly inducing by inclusions. The existence of intergranular facets on fracture surface indicates that hydrogen accelerates crack initiation and early crack growth. Hydrogen-granular bright facet (GBF) mechanism may be interpreted as lath martensite fracture and dislocation cells formation, where hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanisms occur. The degradation of hydrogen on fatigue properties is suppressed by hydrogen trapping effect of ε-copper precipitates.

Investigation of the composition, structure and magnetic properties of the Nd2Fe14B ceramics dependence on the initial powder characteristics and spark plasma sintering modes

High phase and structural sensitivity of magnetic properties strongly impacts the fabrication quality of the permanent magnets, therefore revealing effects of synthesis conditions on physico-chemical characteristics of magnetic materials is of paramount importance for optimization of magnet production especially in case when non-conventional techniques are involved. Here we report for the influence of pulse current frequency on structure, composition, and magnetic properties of an industrially-important Nd2Fe14B magnetic ceramics on the initial powder characteristics and the modes of its spark plasma sintering (SPS) in a vacuum environment. The influence of initial powder mechanical grinding as well as the number of generated electric current pulses (in the range from 3.3 to 326.7 ms) in SPS conditions on the structure (defects and pores formation, grain size), phase and element composition (formation of secondary nonmagnetic phases and oxides, impurities) of Nd2Fe14B alloy was studied by SEM, TEM, EDS and XRD methods. The regularity of changes in the magnetization saturation value (σ) and coercive force (Нс) depending on the morphology, structure and composition of the initial Nd2Fe14B powder and the alloy obtained by mechanical milling and subsequent sintering at different modes of pulse current has been established.

Centrifugal Model Study of Seepage and Seismic Behavior in a Homogeneous Reservoir Dam with Parapet

This study examines the effectiveness of parapets in preventing overtopping failures of small-scale homogeneous reservoir dams under seismic loads. In this study, a parapet covered the entire width of the dam crest and was designed to ensure its weight is transmitted to the dam crest. The test included four modes: initial mode, first seepage, seismic, and second seepage. The results show that without parapets the crack length and width expand significantly in the dam crest during the seismic mode, and the effect was large in the second seepage mode. The crack depth increased by 11.3–24 times during the seismic mode and expanded up to 73.3% of the dam height in the longitudinal direction along the axis of the crack formed in the dam crest during the second seepage mode. These findings suggest that the earthquake weakened the dam body, making it vulnerable to penetration. In contrast, the parapet structure effectively suppressed most of the tensile cracks by increasing the constraint force. Additionally, no crack expansion or tearing occurred during the second seepage mode post-earthquake, indicating improved seismic performance and suppression of seepage deformation.

Anisotropic assembly and reorganization of noble metals on black phosphorus van der Waals template

Black phosphorus (BP), an emerging layered semiconducting crystal, exhibits intriguing properties associated with its puckered in-plane structure. In particular, BP can serve as a template with remarkable van der Waals epitaxial effect owing to its strong anisotropic template effect. Herein, we investigated the assembly behavior of Au and Ag physically deposited on a BP template via transmission electron microscopy techniques. The results show that the orientation, assembly morphology, and crystallinity of metals can be tuned by controlling the BP substrate temperature during deposition. Electron diffraction analysis confirmed that elevated substrate temperature aids the selective formation of [110] oriented Ag and Au films by suppressing the [111] orientation. Moreover, the morphological shape and crystallinity of metals in the initial assembly mode showed temperature-dependent anisotropic effect. This study aids in understanding mechanisms of oriented metal epitaxy on anisotropic two-dimensional crystals, leading to the formation of high-quality metal-semiconductor van der Waals heterojunctions.

Numerical investigation on fracture characteristic and failure mechanism of rock-like materials with intermittent flaws under compressive-shear loading

An extended non-ordinary state-based peridynamic (NOSB-PD) theory is utilized to investigate the fracture characteristics of rock-like materials containing intermittent flaws under compressive-shear loading. The stress-based failure criteria, i.e., the maximum tensile stress criterion and the Mohr-Coulomb criterion, are integrated into the NOSB-PD theory to respectively determine the tensile failure and shear failure of flawed rock-like materials. The distribution characteristics of maximum principal stress and shear stress acquired by the NOSB-PD theory are employed to analyze the fracture failure mechanism of flawed rock-like materials under compressive-shear loading. The effects of inclination angle of the central flaw on the initiation and coalescence modes of flawed rock-like specimens are investigated. The numerical results of flawed rock-like materials are in good agreement with the experimental results. The extended NOSB-PD has the ability to simulate the fracture processes under compressive-shear loading.

Integrated acoustic-optic-mechanics (AOM) multi-physics field characterization methods for a crack: Tension vs. shear

Rock macrofracturing often involves the tension-shear coexistence mechanism on the microscopic scale. This paper addresses the occurrence of tension and shear mechanisms in rock macrofracturing process based on the self-developed integrated acoustic-optic-mechanics (AOM) multi-physics field monitoring technique. With this advanced technique, three-point bending (3-p-b) tests with conventional loading and unconventional loading, as a control of the conditions that produce the different mechanisms, are first carried out on sandstone to establish AOM criteria for crack nature classifications. By using the AF-RA-based Kernel density median criterion and the optical angular bisector criterion, a coupled analysis of acoustical-optical data for the distinction of tension- vs shear-induced cracks in two different flaw configurations under uniaxial compression has been available. Results show that the crack initiation mode in tension-type rock bridge tests is dominated by the tension mechanism, while the ultimate failure pattern is shear-dominated. Comparably, failure of shear-type rock bridge is faithfully dominated by the shear mechanism. The paper, therefore, makes two contributions—a better understanding of rock fracturing process and providing a method of establishing the simple and intuitive criteria to justify the crack natures.

Intratracheal budesonide mixed with surfactant to increase survival free of bronchopulmonary dysplasia in extremely preterm infants: study protocol for the international, multicenter, randomized PLUSS trial

BackgroundBronchopulmonary dysplasia (BPD), an inflammatory-mediated chronic lung disease, is common in extremely preterm infants born before 28 weeks’ gestation and is associated with an increased risk of adverse neurodevelopmental and respiratory outcomes in childhood. Effective and safe prophylactic therapies for BPD are urgently required. Systemic corticosteroids reduce rates of BPD in the short-term but are associated with poorer neurodevelopmental outcomes if given to ventilated infants in the first week after birth. Intratracheal administration of corticosteroid admixed with exogenous surfactant could overcome these concerns by minimizing systemic sequelae. Several small, randomized trials have found intratracheal budesonide in a surfactant vehicle to be a promising therapy to increase survival free of BPD.MethodsAn international, multicenter, double-blinded, randomized trial of intratracheal budesonide (a corticosteroid) mixed with surfactant for extremely preterm infants to increase survival free of BPD at 36 weeks’ postmenstrual age (PMA; primary outcome). Extremely preterm infants aged < 48 h after birth are eligible if: (1) they are mechanically ventilated, or (2) they are receiving non-invasive respiratory support and there is a clinical decision to treat with surfactant. The intervention is budesonide (0.25 mg/kg) mixed with poractant alfa (200 mg/kg first intervention, 100 mg/kg if second intervention), administered intratracheally via an endotracheal tube or thin catheter. The comparator is poractant alfa alone (at the same doses). Secondary outcomes include the components of the primary outcome (death, BPD prior to or at 36 weeks’ PMA), potential systemic side effects of corticosteroids, cost-effectiveness, early childhood health until 2 years of age, and neurodevelopmental outcomes at 2 years of age (corrected for prematurity).DiscussionCombining budesonide with surfactant for intratracheal administration is a simple intervention that may reduce BPD in extremely preterm infants and translate into health benefits in later childhood. The PLUSS trial is powered for the primary outcome and will address gaps in the evidence due to its pragmatic and inclusive design, targeting all extremely preterm infants regardless of their initial mode of respiratory support. Should intratracheal budesonide mixed with surfactant increase survival free of BPD, without severe adverse effects, this readily available intervention could be introduced immediately into clinical practice.Trial registrationAustralian New Zealand Clinical Trials Registry (https://www.anzctr.org.au), ACTRN12617000322336. First registered on 28th February 2017.

Engaging Public Health Alumni in the Tracking of Career Trends: Results From a Large-Scale Experiment on Survey Fielding Mode.

We sought to understand the relative impact of fielding mode on response rate among public health alumni. As part of the 2021 Career Trends Survey of alumni from the University of Minnesota School of Public Health, we designed a fielding mode experiment to ascertain whether a paper survey, a postcard with a custom survey link ("postcard push-to-web"), a mobile telephone call or text (mobile), or an email invitation would garner the highest response rates. Invitations were randomly assigned from available contact information. Of 8531 alumni invited, 1671 alumni (19.6%) completed the survey. Among the initial fielding modes, the paper survey had the highest response rate (28%), followed by mobile (19%), email (10%), and postcard push-to-web (10%). More robust recent engagement with alumni relations, paper survey invitation or mode switch, and recent graduation were all significantly associated with a higher likelihood of response. Paper and mobile invitations had the highest response rates to our survey among public health alumni. Findings from this fielding mode experiment are relevant to schools and programs of public health seeking to capture similar information among their alumni, especially given current trends in investment in the public health workforce.

A Hemilabile NHC-Gold Complex and its Application to the Redox Neutral 1,2-Oxyarylation of Feedstock Alkenes.

We describe a AuI complex of a hemi-labile (C^N) N-heterocyclic carbene ligand that is able to mediate oxidative addition of aryl iodides. Detailed computational and experimental investigations have been undertaken to verify and rationalize the oxidative addition process. Application of this initiation mode has resulted in the first examples of "exogenous oxidant-free" AuI /AuIII catalyzed 1,2-oxyarylations of ethylene and propylene. These demanding yet powerful processes establish these commodity chemicals as nucleophilic-electrophilic building blocks in catalytic reaction design.

A Hemilabile NHC‐Gold Complex and its Application to the Redox Neutral 1,2‐Oxyarylation of Feedstock Alkenes

AbstractWe describe a AuI complex of a hemi‐labile (C^N) N‐heterocyclic carbene ligand that is able to mediate oxidative addition of aryl iodides. Detailed computational and experimental investigations have been undertaken to verify and rationalize the oxidative addition process. Application of this initiation mode has resulted in the first examples of “exogenous oxidant‐free” AuI/AuIII catalyzed 1,2‐oxyarylations of ethylene and propylene. These demanding yet powerful processes establish these commodity chemicals as nucleophilic‐electrophilic building blocks in catalytic reaction design.

Exergy-economic assessment of a hybrid power, cooling and heating generation system based on SOFC

In this research, a combined cycle using a solid oxide fuel cell system, a single-stage H2O–NH3 absorption chiller and a residential hot water HX, is developed for the electricity production, hot water and cooling all at the same time, and it is studied from an exergy, energy, and exergoeconomic standpoint. Performance of system under the design condition is analyzed and the mathematical model is simulated. After analyzing the results in the initial input mode, changing the fuel cell current density effect and fuel utilization factor on the system efficiency is evaluated. The result indicates that total energy is 4.418 kW, the total exergy efficiency is 37.8%. And the overall irreversibility is 1.650 kW. On the other hand, the air HX, fuel cell and water HX are designed as elements that must be given more attention than others from the exergoeconomic perspective, because they have nearly the most amount of price compared to other parts.

Demonstration of a photonic router via quantum walks

Motivated by the need for quantum computers to communicate between multiple, well separated qubits, we introduce the task of routing the quantum state from one input mode to a superposition of several output modes coherently. We report an experimental demonstration of a deterministic photonic routing protocol applied to an entangled state. We show in a quantum walk architecture, quantum networks perfectly route entangled states from an initial input mode to an arbitrary output mode coherently and deterministically. Our results demonstrate the key principle of a perfect router, opening a route toward data routing and transferring for quantum computing systems. The routing algorithm in our work can be applied to a wide range of physical systems, which provides a way for effective design of efficient routing protocols on practical quantum networks.

Modeling simulation on amplifying magnetic fields in supernova remnants with an intense laser

Local magnetic field enhancement in supernova remnants (SNRs) is a natural laboratory for studying the amplification effect of turbulent magnetic fields. In recent years, high-power laser devices have gradually matured as a tool for astronomical research that perfects observations and theoretical models. In this study, a model of the amplification effect of the turbulent magnetic field in SNRs by an intense laser is simulated using the radiation magnetohydrodynamic simulation program. We investigate and compare the evolutionary processes of unstable turbulence under different initial disturbance modes, directions, and intensities of external magnetic fields and obtain the magnetic energy spectrum and magnetic field magnification. The results demonstrate that the fluid motion associated with Rayleigh–Taylor instability will stretch the environmental magnetic field significantly, with an intensity amplified by two orders of magnitude. The environmental magnetic field perpendicular to the laser injection direction is decisive during magnetic field amplification which is necessary to clarify the physical mechanism of magnetic field amplification in SNRs. Furthermore, it will deepen the understanding of the interstellar magnetic field’s evolution. The results also establish a reference for laser-driven magnetized plasma experiments in a robust magnetic environment.

Associations with youth psychotic-like experiences over time: Evidence for trans-symptom and specific cognitive and neural risk factors.

The current study examined whether impairments in cognitive and neural factors at baseline (ages 9-10) predict initial levels or changes in psychotic-like experiences (PLEs) and whether such impairments generalize to other psychopathology symptoms (i.e., internalizing and externalizing symptoms). Using unique longitudinal Adolescent Brain Cognitive Development Study data, the study examined three time points from ages 9 to 13. Univariate latent growth models examined associations between baseline cognitive and neural metrics with symptom measures using discovery (n = 5,926) and replication (n = 5,952) data sets. For symptom measures (i.e., PLEs, internalizing, externalizing), we examined mean initial levels (i.e., intercepts) and changes over time (i.e., slopes). Predictors included neuropsychological test performance, global structural MRI, and several a priori within-network resting-state functional connectivity metrics. Results showed a pattern whereby baseline cognitive and brain metric impairments showed the strongest associations with PLEs over time. Lower cognitive, volume, surface area, and cingulo-opercular within-network connectivity metrics showed associations with increased PLEs and higher initial levels of externalizing and internalizing symptoms. Several metrics were uniquely associated with PLEs, including lower cortical thickness with higher initial PLEs and lower default mode network connectivity with increased PLEs slopes. Neural and cognitive impairments in middle childhood were broadly associated with increased PLEs over time, and showed stronger associations with PLEs compared with other psychopathology symptoms. The current study also identified markers potentially uniquely associated with PLEs (e.g., cortical thickness). Impairments in broad cognitive metrics, brain volume and surface area, and a network associated with information integration may represent risk factors for general psychopathology. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Microstructural effects on fatigue crack initiation mechanisms in a near-alpha titanium alloy

The role of different microstructural constituents on crack initiation in two-phase titanium alloys is still an area of great controversy. The present study investigates the effects of primary α volume fraction and concomitant macrozones on two different fatigue crack initiation modes concurrently observed in a near-α titanium alloy. Statistically representative regions were monitored in quasi-in-situ studies by interrupting fatigue testing to detect slip trace formation leading to crack initiation. In addition, high-resolution 2D strain maps were generated to quantify in-plane shear strains of slip traces related to microstructural features. The detailed analysis demonstrates that at 90% of the proof stress basal 〈a〉 slip plays a crucial role in crack initiation, regardless of whether cracking is transgranular or intergranular. In addition, a distinct shift from transgranular to intergranular crack initiation was observed with increasing αp fraction driven by the increased number of αp/αp grain boundaries. The high-resolution 2D strain mapping suggest that these intergranular cracks initiated from a burst of basal 〈a〉 slip starting from (0001) twist grain boundaries but penetrating one side of the grain pair in case of a partial (0001) twist grain boundary. From these observations, a new criterion for intergranular cracking is proposed based on a geometrical grain boundary parameter and the preference of neighbouring αp grain pair well aligned for basal 〈a〉 slip. It was found that while (0001) twist grain boundaries increase with increasing αp fraction, macrozones do not further enhance their frequency. However, macrozones of hard orientated grains did enhance transgranular crack formation by potentially higher local stress and increasing slip length over clustered αp grains with low misorientation reducing the requirement for out-of-plane shear.

Effect of Third-Particle Material and Contact Mode on Tribology Contact Characteristics at Interface

A moving pair with two-body contact is the ideal situation assumed in previous analyses. However, all moving pairs are in a three-body contact state at the start of operation or immediately after the start of operation, such as bearings, ball-screws, gears and engines. This work studies the influence of wear particles (SUJ2), environmental particles (SiO2 and Al2O3) and nano-additives (CuO) on the tribological contact characteristics under different particle concentrations, particle sizes, surface roughnesses and contact modes. The three-body microcontact analysis revealed that the differences in the real contact area, particle contact area and separation of the four-particle materials in the three-body s–s and p–s contact modes are rather small. Under the three-body hybrid contact mode, the difference is relatively large and the sequence of the real contact area value obtained due to the elastic modulus for the four-particle material at this interface is Al2O3 &gt; SUJ2 &gt; CuO &gt; SiO2. The order of the other two contact characteristics is reversed. The difference increases as the particle size or particle concentration increases. The order of the critical load required to transform three kinds of contact modes is SiO2 &gt; CuO &gt; SUJ2 &gt; Al2O3. On the nearly initial three-body hybrid contact mode, the plastic contact area ratio at the interface first increases to a critical value and then decreases as the load increases because the original plastic contact spot area and contact spot number increases with the increase in load. At the same time, the elasto-plastic contact area ratio decreases to a low value and then increases. The elastic contact area ratio at the interface decreases as the load increases. Among the four third-particle materials, the experimental results and theoretical predictions show that the environmental particles, Al2O3, cause the maximum friction and wear observed at the interface.

Influence of combination of coaxial cylindrical explosives on fragmentation and shock waves of a shelled composite charge

AbstractThis paper investigates fragmentation and shock waves generated by a novel coaxial cylindrical composite charge composed of an inner explosive, an intermediate inert material and an outer explosive widely used in tunable ammunition. Charges containing two types of explosive combinations were designed, and explosion experiments were conducted in two initiation modes: detonating only an inner explosive and detonating inner and outer explosives simultaneously. Results suggest the composite charge with higher inner‐detonation velocity and lower outer‐detonation velocity achieves more differentiated power output under different initiations. The differences in the average fragment mass and peak overpressure are as high as 34.5 % and 39.9 %, respectively, which are larger than 4.4 % and 8.4 % under the contrary explosive combination. On the basis of this observation, corresponding 2‐D and 3‐D models were simulated using AUTODYN code to investigate the evolution of the detonation waveform and detonation energy release. The numerically simulated initial shell expansion and later shock wave propagation of the composite charge agreed well with the experimental data. The errors in expansion radius and shock wave parameters (peak overpressure and specific impulse) are less than 6.6 % and 16.9 %, respectively, between the simulations and experiments. It was found that the particle velocity profile in the charge with lower outer‐detonation velocity lagged behind that of the charge with higher inner‐detonation velocity under inner initiation, while a wave front collision zone close to the outer charge appeared in the non‐detonation layer under simultaneous initiation.

A fresh look at thermal cycling absorption process for hydrogen isotopes separation by dynamic simulation: Initial feeding process and total reflux mode

Thermal Cycling Absorption Process (TCAP) is an important method to separate hydrogen isotopes for the production and engineering application of tritium. There are so many influencing factors that it is difficult to fully understand the influence mechanisms only through experiments. A new simulation model of TCAP was developed. Using the simulation model, the influencing trend and optimized value of parameters of initial feeding process and total reflux mode in TCAP are obtained as follows. (1) The temperatures of initial feeding and the cold cycle are not the lower the better as commonly assumed but exists an optimal value of 30 °C in initial feeding and -20 °C in the cold cycle. (2) The heating rate and cooling rate also exist optimal values of 45 °C/min and 55 °C/min (3) Lower feeding rate is conducive to a better separation effect of hydrogen isotopes. (4) Increasing the reflux ratio benefits the enrichment of heavy hydrogen isotope at the product side but not the light hydrogen isotope at the tail side. (5) It needs more cycles to achieve the same isotope abundance in D/T separation than H/D separation and the separation degree of hydrogen isotopes exists a maximum value after multiple cycles. The findings can provide references for the process optimization and the device design of TCAP, and also can shed new light on the understanding of the basic physical and chemical process of TCAP.

Probing the initial state of inflation: analytical structure of cosmological correlators

We study the analytic structure of in-in correlation functions in a deSitter background. The aim of this study is to probe the initial conditions for inflation through the features of correlation functions of the field fluctuations, and understand precisely how an in-in correlator responds to particles in the initial state. We emphasize that the choice of vacuua and the corresponding particle interpretation for these fluctuations is flexible, and we clarify the role of this choice at the level of calculations and their diagrammatic interpretation. We consider several possibilities aside from the standard Bunch Davies (BD) vacuum prescription for the initial state, and trace the change in pole structure as one begins adding excitations; starting from just a single particle, to highly excited states and special cases such as a coherent state. We also go beyond the pole structure of the bispectrum, and calculate the 4 point classical and quantum correlators.We illustrate — with the example of coherent states — the subtleties in concluding a Bunch Davies initial state from the absence of physical poles in the bispectrum, which is interesting in light of some recent literature.Initial states with a finite number of excitations are plagued with disconnected diagrams isolated in phase space, and we highlight their implications on the observation of these signals, and how the situation changes as one begins to excite more and more particles. We also comment about the implications of various initial conditions on the squeezed limit of the bispectrum.These new pole structures are a direct consequence of mixing of positive and negative frequency modes which is a characteristic of curved spacetimes; in particular, we see in detail how particles in an initial state replicate mode mixing structures. This study aims to clarify the missing details that link quantum and classical initial conditions, and sharpen our understanding of in-in correlators in inflation.