Superposition Of Mechanisms Research Articles

Turning of high strength, austenitic stainless steels

High interstitial austenitic stainless CrMn steels are characterised by significantly increased work hardening ability and strength compared with conventional CrNi austenites, yet maintaining very high ductility and toughness. The machining of high interstitial CrMnCN steels is challenging in terms of process stability and economic efficiency. In this context, unfavourable chip forms, high thermomechanical loads and the superposition of different wear mechanisms in particular lead to challenges in turning operations. In the following article, different lubricant strategies are analysed for machining of CrMnN and CrMnCN austenitic stainless steels regarding chip form, mechanical tool loads and wear. Furthermore, the workpiece properties are considered with regard to surface roughness and microstructural changes.

Implication of initial grain size on DRX mechanism and grain refinement in super-304H SS in a wide range of strain rates during large-strain hot deformation

In this work, we studied the effect of initial grain size on the hot compression characteristics of super-304H austenitic stainless steel in a range of strain rates (0.001–1 s−1) at a fixed temperature of 1223 K. Analysis of the flow curves reveals that the flow stress is inversely proportional to the average sub-grain diameter in both coarse and fine-grained specimens at higher strain (≥0.5) levels. Further, the fine-grained specimen following deformation at a low strain rate (0.001 s−1) reveals the occurrence of both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) mechanisms. In this condition, the CDRX is characterized by a progressive increase of boundary misorientation, while the DDRX is characterized by bulging and strain-induced boundary migration. In contrast, the CDRX characterized by the formation of microbands is majorly responsible for the grain refinement in the fine-grained specimen at higher strain rates (∼1 s−1) and in the coarse-grained specimen at all strain rates (0.001–1 s−1). The superposition of different DRX mechanisms leads to significant variations in grain refinement kinetics with strain rates and initial grain sizes. The findings of this investigation provide a foundation for the accurate control of the microstructures in the studied alloy with different initial grain sizes during the hot working at various strain rates.

Quantum Legacies: Dispatches from an Uncertain World

Quantum Legacies: Dispatches from an Uncertain World

High-temperature electromechanical loss in piezoelectric langasite and catangasite crystals

Temperature-dependent acoustic loss Q−1 is studied in partially disordered langasite (LGS, La3Ga5SiO14) and ordered catangasite (CTGS, Ca3TaGa3Si2O14) crystals and compared with previously reported CTGS and langatate (LGT, La3Ga5.5Ta0.5O14) data. Two independent techniques, a contactless tone-burst excitation technique and contacting resonant piezoelectric spectroscopy, are used in this study. Contributions to the measured Q−1(T) are determined through fitting to physics-based functions, and the extracted fit parameters, including the activation energies of the processes, are discussed. It is shown that losses in LGS and CTGS are caused by a superposition of several mechanisms, including intrinsic phonon–phonon loss, point-defect relaxations, and conductivity-related relaxations.

Investigation of frequency dependent mechanical properties of porous materials using dynamic mechanical analyzer and frequency-temperature superposition theory

In acoustic design of engineering applications - such as in the acoustic analysis of passenger vehicles - poroelastic materials are of great importance. One of the most influencing properties in determining their noise-reduction potential is the storage modulus. The purpose of this study is to examine the frequency dependence of storage modulus of selected porous acoustic materials at least up to 1000 Hz. This is executed by using the combined use of dynamic mechanical analyzer and frequency-temperature superposition theory. All other methods for measuring the storage modulus fall short in determining frequency-dependence above 100 Hz: quasi-static mechanical analyzer is mostly used for determining an averaged constant value deduced from low-frequency measurements, while the usage of an electromagnetic shaker capable for high-frequency excitation may include effects of fluid motion inside the pores, thus significantly modifying the results. Frequency-temperature superposition enables to determine the storage modulus values in a wide frequency range, based on low-frequency measurements, where fluid-structure interaction is negligible. It was found that the modulus varied significantly up to and beyond 1000 Hz, and thus, acoustical characterization of these materials can be significantly improved using the proposed method. The work concludes with recommendations to improve the accuracy of the results.

Spin diffusion length associated with out-of-plane conductivity of Pt in spin pumping experiments

We present a broadband ferromagnetic resonance study of the Gilbert damping enhancement ($\Delta \alpha$) due to spin pumping in NiFe/Pt bilayers. The bilayers, which have negligible interfacial spin memory loss, are studied as a function of the Pt layer thickness ($t_{\text{Pt}}$) and temperature (100-293 K). Within the framework of diffusive spin pumping theory, we demonstrate that Dyakonov-Perel (DP) or Elliot-Yaffet (EY) spin relaxation mechanisms acting alone are incompatible with our observations. In contrast, if we consider that the relation between spin relaxation characteristic time ($\tau_{\text{s}}$) and momentum relaxation characteristic time ($\tau_{\text{p}}$) is determined by a superposition of DP and EY mechanisms, the qualitative and quantitative agreement with experimental results is excellent. Remarkably, we found that $\tau_{\text{p}}$ must be determined by the out-of-plane electrical resistivity ($\rho$) of the Pt film and hence its spin diffusion length ($\lambda_{\text{Pt}}$) is independent of $t_{\text{Pt}}$. Our work settles the controversy regarding the $t_{\text{Pt}}$ dependence of $\lambda_{\text{Pt}}$ by demonstrating its fundamental connection with $\rho$ considered along the same direction of spin current flow. \end{abstract}

(Invited) Hybrid Van Der Waals Heterostructures: From Fundamentals to Applications

2D materials are held together by weak interplanar van der Waals (vdW) interactions. The incorporation of molecules in such materials holds an immense potential to understand and modify the fundamental physical properties of the pristine materials while creatin new artificial materials. Whilst nature offers a finite number of 2D materials, an almost unlimited variety of molecules can be designed and synthesized with predictable functionalities. The possibilities offered by systems in which continuous molecular layers are interfaced with inorganic 2D materials to form hybrid organic/inorganic van der Waals heterostructures (H-vdWH) are emphasized. Similar to their inorganic counterpart, the hybrid structures have been exploited to suggest novel device architectures. Moreover, specific molecular groups can be employed to modify intrinsic properties and confer new capabilities to 2D materials. In particular, I will highlight how molecular self-assembly at the surface of 2D materials can be mastered to achieve precise control over position and density of (molecular) functional groups, paving the way for a new class of hybrid functional materials.In particular, within such vdW heterostructures, currently assembled by mechanical superposition of different layers, periodic potentials naturally occur at the interface between the 2D materials. These potentials significantly modify the electronic structure of the individual 2D components within the stack and their alignment, thus offering the possibility to build up hybrid and novel materials with unique properties.Also, I will show how the presence of ordered supramolecular assemblies bearing different functional groups can modify the pristine Shubnikov-De Haas oscillations occurring in graphene.Finally, an example will be given of how a carefully designed H-vdWH could be used for sensing of different biomarkers.

Quantitative prediction of multiperiod fracture distributions in the Cambrian-Ordovician buried hill within the Futai Oilfield, Jiyang Depression, East China

In the Futai carbonate oilfield of the Jiyang Depression, Bohai Bay Basin, oil enrichment is significantly related to fracture development during the oil production process. In this research, by methods of core observation and image logging interpretation, the tectonic fractures’ characteristics were distinguished. Numerically, through the elastoplastic mechanics method of finite element (FE) simulation, the three-dimensional (3-D) paleotectonic stress field (two key fracture-generating periods) and the current stress field in the Futai buried hill were quantitatively simulated. The equations between fracture parameters and tectonic stresses were deduced to predict the fracture distribution and development in various periods. Simultaneously, through the mechanical superposition algorithm, the fracture parameters under the present conditions were simulated by modifying the current stress field from preexisting fractures. The results indicated that: (1) The Yanshanian maximum principal stress ranged from −85 MPa to −435 MPa in the NWN-SES (344°) (343°–164°) direction. (2) The Himalayan minimum principal stress ranged from 5 to 30 MPa in the NWN–SES direction. (3) The fracture formation during the Yanshanian and Himalayan orogeny was primarily influenced by the regional stress field in the Jiyang Depression or the secondary stress field derived from the Tanlu fault zone, followed by the lithology. The current fracture porosity was primarily controlled by fold, followed by the large faults oriented by N–S direction and then by the secondary faults oriented by E-W direction. With successful calculations, the developed 3-D FE geomechanical modeling and fracture parameter calculation method holds great promise for characterizing fractures in other carbonate reservoirs.

Quantum Clocks with Double Audit and Relations with Gravity

In this paper, a non-repeating quantum algorithm is introduced that depends on detectable Byzantine’s quantum solution that attains Clk synchronization in the arbitrary faultier processes’ presence through utilizing a double quantum system only. Precisely, it has been shown that general relativistic mass–energy equivalences intimate gravitational relation among Clks, however, energy’s quantum mechanical superposition resulted in a non-fixed metric background. Depending only on assumptions that gravitational principles held in such conditions, it has been shown that the Clks essentially gets involve over time dilation effect that ultimately results in a double Clk coherence loss. Therefore, the measured time through a double Clk is not defined precisely. Although, the time’s general relativistic notion is recuperated in the Clks conventional limits.

Investigating the Hall-Petch Constants for As-Cast and Aged AZ61/CNTs Metal Matrix Composites and Their Role on Superposition Law Exponent

AZ61/carbon nanotubes (CNTs) (0, 0.1, 0.5, and 1 wt.%) composites were successfully fabricated by using the stir-casting method. Hall–Petch relationship and superposition of different strengthening mechanisms were analyzed for aged and as-cast AZ61/CNTs composites. Aged composites showed higher frictional stress (108.81 MPa) than that of as-cast (31.56 Mpa) composites when the grain size was fitted directly against the experimentally measured yield strength. In contrast, considering the superposition of all contributing strengthening mechanisms, the Hall–Petch constants contributed by only grain-size strengthening were found (σ0 = 100.06 Mpa and Kf = 0.3048 Mpa m1/2) for as-cast and (σ0 = 87.154 Mpa and Kf = 0.3407 Mpa m1/2) for aged composites when superposition law exponent is unity. The dislocation density for the as-cast composites was maximum (8.3239 × 1013 m−2) in the case of the AZ61/0.5 wt.%CNT composite, and for aged composites, it increased with the increase in CNTs concentration and reached the maximum value (1.0518 × 1014 m−2) in the case of the AZ61/1 wt.%CNT composite.

Degradation study on tin- and bismuth-based gas-diffusion electrodes during electrochemical CO2 reduction in highly alkaline media

This work investigated the degradation of tin – based gas-diffusion electrodes (GDE) and also a promising Bi2O3 GDE in electrochemical CO2 reduction in highly alkaline media which has not been studied before. The contributions of the electrode wetting (or flooding, if excessively) and catalyst leaching on the degradation were analyzed. Therefore, electrochemical impedance spectroscopy was used to monitor the wetted surface area of the GDE in combination with post-mortem analysis of the penetration depth by visualizing the electrolyte’s cation in the GDE cross-section. Furthermore, to reveal a possible degradation of the electrocatalyst, its distribution was mapped in the GDEs cross-section after operation while the catholyte was additionally analyzed via ICP-MS. The results clearly demonstrate that the SnO2 catalyst dissolves in the reaction zone inside the GDE and might be partially redeposited near the GDEs surface. Since the redeposition process occurs only partially a steady loss of catalyst was observed impeding a clear distinction of the two degradation phenomena. Nevertheless, the deterioration of the electrode performance measured as faraday efficiency (FE) of the parasitic hydrogen evolution reaction (HER) qualitatively correlates with the differential double layer capacitance (Cdl). A significant difference of the rate of increase for the hydrogen FE and Cdl can be ascribed to the superposition of both above-mentioned degradation mechanisms. The demonstrated instability of SnO2 contrasts with the behavior of Bi2O3 GDE which is stabilized during CO2 conversion by redeposition of the diluted dissolved species as metallic Bi which is active for the CO2 reduction reaction.

The precipitation behaviours and strengthening mechanism of a Cu-0.4 wt% Sc alloy

The phase transformation sequence of the precipitation in Cu-Sc alloy is found as: supersaturated solid solution→Sc-rich atomic clusters→coherent metastable phase→Cu 4 Sc phase. The tetragonal structured lamellar Cu 4 Sc precipitates with orientation relationships of 0 2 ¯ 2 α / / 211 and 011 α / / [ 11 3 ¯ ] are homogenously distributed in the matrix. A combined process of cryogenic rolling and aging is designed for optimization of the mechanical and electric properties. An excellent integration of yield strength (695.8 MPa) and electrical conductivity (62.84% IACS) is achieved by cryogenic rolling and subsequent aging at 400 °C for 4 h. This high effective strengthening effect of Cu-0.4 wt% Sc alloy is probably due to the superposition of coherent strengthening and Orowan strengthening. • A new type binary copper alloy with scandium addition is designed. • The process of cryogenic rolling and aging is designed for properties optimization. • Lamellar Cu 4 Sc precipitates of tetragonal structure are found in the matrix. • Precipitation strengthening effect attributes to the mechanism superposition. The precipitation behaviours during the aging process and the corresponding strengthening mechanism of a Cu-0.4 wt% Sc alloy were systematically investigated in this study. The phase transformation sequence of the precipitation in the aging process of the Cu-0.4 wt% Sc alloy was found to be: supersaturated solid solution→ Sc-enriched atomic clusters→ metastable phase→Cu 4 Sc phase. The tetragonal structured lamellar Cu 4 Sc precipitates, with a habit plane parallel to the {111} plane of the Cu matrix and orientation relationships of 0 2 ¯ 2 α / / 211 Cu4Sc and 011 α / / [ 11 3 ¯ ] Cu4Sc , are found homogeneously distributed in the matrix. A combined process of cryogenic rolling (CR) and aging was designed for optimization of the mechanical and electrical properties. Excellent integration of yield strength (696 MPa) and electrical conductivity (62.8 % IACS) of this alloy was achieved by cryogenic rolling and subsequent aging process at 400 °C for 4 h. The significant precipitation strengthening effect of this alloy is attributed to the Cu 4 Sc precipitates with an extremely small size of only 1.5–3 nm. The leading strengthening mechanism is considered as the superposition of both coherent strengthening and Orowan strengthening effects.

Quantum network probing with indefinite routing

Quantum network probing is experimental estimation of network parameters by passing probes through the network. In probing with indefinite routing (IR), the probe traces a quantum mechanical superposition of different paths through the network. We consider a quantum network modeled by three identical qudit depolarizing channels, each channel with state preservation probability $$\theta $$ and dimension d. Using quantum Fisher (QF) information as our measure of merit, we comprehensively assess the advantage associated with maximal IR for estimating the network depolarization rate $$1-\theta $$ . A three-channel network admits three distinctive types of IR, cyclical, directional, and full. Definite routing is the case where the probe is confined to a single path through the network. We find that compared to this baseline case all three IR types yield a gain in QF information, the gain being greatest with full IR. Comparing the information gains with cyclical and directional IR shows that, for $$\theta $$ above a dimensional threshold, directional IR offers greater advantage, while below this threshold cyclical IR is more advantageous. Our results show further that the joint effect of cyclical IR and directional IR can be synergistic or antagonistic, depending on $$\theta $$ and d. With our analytical approach, the network output states are quasi-classical, greatly simplifying the derivation of the QF information involved. This approach can be extended to larger networks with different IR schemes.

Inversion in a four-terminal superconducting device on the quartet line. II. Quantum dot and Floquet theory

In this paper, we consider a quantum dot connected to four superconducting terminals biased at opposite voltages on the quartet line. The grounded superconductor contains a loop threaded by the magnetic flux $\Phi$. We provide Keldysh microscopic calculations and physical pictures for the voltage-$V$ dependence of the quartet current. Superconductivity is expected to be stronger at $\Phi/\Phi_0=0$ than at $\Phi/\Phi_0=1/2$. However, inversion $I_{q,c}(V,0)<I_{q,c}(V,1/2)$ is obtained in the critical current $I_{q,c}(V,\Phi/\Phi_0)$ on the quartet line in the voltage-$V$ ranges which match avoided crossings in the Floquet spectrum at $(V,\Phi/\Phi_0=0)$ but not at $(V,1/2)$. A reduction in $I_{q,c}$ appears in the vicinity of those avoided crossings, where Landau-Zener tunneling produces dynamical quantum mechanical superpositions of the Andreev bound states. In addition, $\pi$-$0$ and $0$-$\pi$ cross-overs emerge in the current-phase relations as $V$ is further increased. The voltage-induced $\pi$-shift is interpreted as originating from the nonequilibrium Floquet populations produced by voltage biasing. The numerical calculations reveal that the inversion is robust against strong Landau-Zener tunneling and many levels in the quantum dot. Our theory provides a simple ``Floquet level and population'' mechanism for inversion tuned by the bias voltage $V$, which paves the way towards more realistic models for the recent Harvard group experiment where the inversion is observed.

Ta181 nuclear quadrupole resonance study of the noncentrosymmetric superconductor PbTaSe2

We report on a pure $^{181}$Ta-nuclear quadrupole resonance (NQR) measurement of PbTaSe$_2$ at zero magnetic field, which has the advantage of directly probing the intrinsic superconducting phase and electronic states of the TaSe$_2$ layer. We observed the $^{181}$Ta-NQR spectrum of the intrinsic structure with space group $P6$-$m2$, which agrees well with density functional theory (DFT) calculations. The nuclear spin relaxation rate ($1/T_1$) shows an exponential decrease well below $T_{\rm_c}$, indicating that the superconducting state is fully gapped in the framework of Bardeen-Cooper-Schrieffer (BCS) theory. The gap size obtained by $^{181}$Ta-NQR was smaller than the value in previous reports, which may imply that the Fermi surfaces composed of Ta-5$d$ orbitals, where the average pairing interactions are expected to be weaker than in BCS model, are primarily probed. The temperature dependence of $1/T_1$ below $T_{\rm_c}$ can be reproduced well by the superposition of quadrupole and magnetic relaxation mechanisms, together with the distribution of superconducting gap size inherent to multiple Fermi surfaces theoretically proposed in PbTaSe$_2$.

Transient heat exchanges under fast Reactivity-Initiated Accident

Heat exchanges during fast transient are very complex phenomena. Many studies have been led in this field, trying to quantify the heat exchanges between a heating wall, under fast increasing power, and a coolant. This kind of situation is encountered for instance during RIA (Reactivity-Initiated Accidents) in nuclear reactors, whose characteristics times of wall heat flux excursion can be as low as orders of 1 ms. The CABRI reactor, an experimental pulse reactor funded by the french Institute for Radiological protection and Nuclear Safety (IRSN) and operated by CEA at the Cadarache nuclear center (France), was build in order to study and thus to better understand RIA effects on nuclear fuels. Heat exchanges characterization is definitely one of major points to tackle in the understanding and modeling of such transients, involving single and two phase flows.This paper broaches the question of single phase heat exchanges coefficients during fast transient power excursions in the CABRI reactor.The single phase pure convection is the overlap of two main mechanisms: the advection (wall axial supply in upstream cold water) and the turbulent mixing inside the boundary layer. This latter phenomenon is due to vortices in boundary layers inducing radial mixing through the velocity boundary layer. In most cases involving turbulent flows, the turbulent mixing phenomenon is preponderant. To these mechanisms is added a pure conduction heat exchange mechanism through the thermal boundary layer. Convection and conduction overlap defining a conducto-convective heat transfer coefficient, improperly only called “convection” coefficient. This paper suggests a way to model this coefficient during a CABRI-RIA transient by a non-linear superposition of transient pure conduction and convection mechanisms. Two distinct transient phases are considered; the first one presenting a wall heat flux of exponential shape followed by the second one during which the wall heat flux remains constant. The potency of this analytical model, which is implementable into computational system tools, is demonstrated.

Orbital angular momentum superposition states in transmission electron microscopy and bichromatic multiphoton ionization

The coherent control of electron beams and ultrafast electron wave packet dynamics have attracted significant attention in electron microscopy as well as in atomic physics. In order to unify the conceptual pictures developed in both fields, we demonstrate the generation and manipulation of tailored electron orbital angular momentum (OAM) superposition states either by employing customized holographic diffraction masks in a transmission electron microscope or by atomic multiphoton ionization utilizing pulse-shaper generated carrier-envelope phase stable bichromatic ultrashort laser pulses. Both techniques follow similar physical mechanisms based on Fourier synthesis of quantum mechanical superposition states allowing the preparation of a broad set of electron states with uncommon symmetries. We describe both approaches in a unified picture based on an advanced spatial and spectral double slit and point out important analogies. In addition, we analyze the topological charge and discuss the control mechanisms of the free-electron OAM superposition states. Their generation and manipulation by phase tailoring in transmission electron microscopy and atomic multiphoton ionization is illustrated on a 7-fold rotationally symmetric electron density distribution.

Sand deformation mechanisms mobilised with active retaining wall movement

A series of centrifuge tests was conducted to explore the deformation mechanisms mobilised in loose and dense sand for a complete set of active rigid retaining wall movement modes: rotation about the base and top and translation. The sand deformation was measured by particle image velocimetry and data relating to displacements and strains are reported. A simplified deformation mechanism is proposed for sand behind a rigid wall rotating about the top and this is validated with the centrifuge test results. The paper reveals that the sand deformation caused by wall translation can be well characterised by the superposition of mechanisms with equal but opposite wall rotation about the top and base. Integration of these displacement mechanisms together with a constitutive law into an equilibrium solution for wall bending would allow designers to predict deformations during construction as well as ultimate collapse.

Differences in the heterogeneous nature of hydriding/dehydriding kinetics of MgH2 - TiH2 nanocomposites

Fine powder dispersions of MgH2 - TiH2 composites were obtained through different manufacturing routes using reactive mechanical grinding. The as prepared powder dispersions were subjected to hydrogen sorption kinetics and the results clearly revealed a heterogeneous kinetic nature already reported in nanocrystalline MgH2. The differences observed in the heterogeneous kinetic of isothermal kinetics reveal a strong dependence on grain boundaries microstructure of the prepared hydrides. The basic findings described here suggest the need for studies to understand how the superposition of complex mechanisms are involved in kinetics regarding the microstructure.

QSARs in prooxidant mammalian cell cytotoxicity of nitroaromatic compounds: the roles of compound lipophilicity and cytochrome P-450- and DT-diaphorase-catalyzed reactions

Frequently, the aerobic mammalian cell cytotoxicity of nitroaromatic compounds (ArNO2) increases with their single-electron reduction potential (E17), thus reflecting the relationship between their enzymatic single-electron reduction rate and E17. This shows that the main factor of ArNO2 cytotoxicity is redox cycling and oxidative stress. In this work, we found that the reactivity of a series of nitrobenzenes, nitrofurans and nitrothiophenes towards single-electron transferring NADPH:cytochrome P-450 reductase and adrenodoxin reductase/adrenodoxin increases with their E17. However, their cytotoxicity in mouse hepatoma MH22a and human colon carcinoma HCT-116 cells exhibited a poorly expressed dependence on E17. The correlations were significantly improved after the introduction of compound octanol/water distribution coefficient at pH 7.0 (log D) as a second variable. This shows that the lipophilicity of ArNO2 enhances their cytotoxicity. The inhibitors of cytochromes P-450, α-naphthoflavone, isoniazid and miconazole, and an inhibitor of DT-diaphorase, dicoumarol, in most cases decreased the cytotoxicity of several randomly chosen compounds. This shows that the observed cytotoxicity vs E17 relationships in fact reflect the superposition of several cytotoxicity mechanisms.