Exact Conditions Research Articles

Converging Roles of the Metal Transporter SMF11 and the Ferric Reductase FRE1 in Iron Homeostasis of Candida albicans.

Pathogenic fungi must appropriately sense the host availability of essential metals such as Fe. In Candida albicans and other yeasts, sensing of Fe involves mitochondrial Fe-S clusters. Yeast mutants for Fe-S cluster assembly sense Fe limitation even when Fe is abundant and hyperaccumulate Fe. We observe this same disrupted Fe sensing with C. albicans mutants of SMF11, a NRAMP transporter of divalent metals. Mutants of smf11 hyperaccumulate both Mn and Fe and the elevated Mn is secondary to Fe overload. As with Fe-S biogenesis mutants, smf11∆/∆ mutants show upregulation of ferric reductases that are normally repressed under high Fe, and Fe import is activated. However, unlike Fe-S biogenesis mutants, smf11∆/∆ mutants show no defects in mitochondrial Fe-S enzymes. Intriguingly, this exact condition of disrupted Fe sensing without inhibiting Fe-S clusters occurs with C. albicans fre1∆/∆ mutants encoding a ferric reductase. Mutants of fre1 and smf11 display similar perturbations in the cell wall, in filamentation and in the ROS burst of morphogenesis, a Fe-dependent process. As with FRE1, SMF11 is important for virulence in a mouse model for disseminated candidiasis. We propose a model in which FRE1 and SMF11 operate outside the mitochondrial Fe-S pathway to donate ferrous Fe for Fe sensing.

The fronting of back vowels after *j in Slavonic

Abstract In the field of Slavonic historical phonology, it has long been known that many of the Proto-Indo-European back vowels become front after *j in Late Common Slavonic (henceforth LCS). We call this sound change Vowel Fronting. Vowel Fronting plays an important role in the rise of one of the major characteristics of the Slavonic languages, namely, the distinction between hard and soft declensions. However, not all the back vowels become front after *j in LCS, and the exact conditions for the vowel fronting have not been found yet. Here we show that the fronting is a regular sound change. The presence or absence of the etymological syllable-final consonants, which are lost in LCS, plays a decisive role in Vowel Fronting. By assuming that Vowel Fronting occurred before syllable-final consonants are lost, we define Vowel Fronting as a sound law that occurs in the following four environments without any exception: (1) in final closed syllables, (2) in light syllables, (3) between two *j’s, and (4) when the nucleus is *y [ɨ].

Comovement of Labor Supply and Human Capital Investment in Policy Analysis

Quantitative studies of human capital report the comovement of labor and human capital investment in response to policy changes, which is usually understood based on the intuition that human capital is utilized only while working: both inputs are complements in the formation of effective labor. Given the lack of (i) theoretical analysis of exact conditions and (ii) the preference-side intuition that both inputs involve disutility leading to a similar comovement, we fill the gap. The general condition for the comovement specifies the minimum extent of disutility smoothing between labor and human capital investment, and the prior intuition relaxes this condition, raising comovement possibilities. The conclusion has wide applicabilities in policy analysis.

Gately values of cooperative games

AbstractWe investigate Gately’s solution concept for cooperative games with transferable utilities. Gately’s conception introduced a bargaining solution that minimises the maximal quantified “propensity to disrupt” the negotiation process of the players over the allocation of the generated collective payoffs. We show that Gately’s solution concept is well-defined for a broad class of games and that it can be interpreted as a compromise solution. We also consider a generalisation based on a parameter-based quantification of the propensity to disrupt. We provide an axiomatic characterisation of the original Gately value as well as these generalised Gately values. Furthermore, we investigate the relationship of these Gately values with the Core and the Nucleolus and show that Gately’s solution is in the Core for all regular 3-player games, but is fundamentally different from the Nucleolus. We identify exact conditions under which these Gately values are Core imputations for arbitrary regular cooperative games. Finally, we investigate the relationship of the Gately value with the Shapley value.

Fractional Brownian motion in confining potentials: non-equilibrium distribution tails and optimal fluctuations

Abstract At long times, a fractional Brownian particle in a confining external potential reaches a non-equilibrium (non-Boltzmann)
steady state. Here we consider scale-invariant power-law potentials $V(x)\sim |x|^m$, where $m>0$, and employ the optimal fluctuation method (OFM) to determine the large-$|x|$ tails of the steady-state probability distribution $\mathcal{P}(x)$ of the particle position. The calculations involve finding the optimal (that is, the most likely) path of the particle, which determines these tails, via a minimization of the exact action functional for this system, which has recently become available. Exploiting dynamical scale invariance of the model in conjunction with the OFM ansatz, we establish the large-$|x|$ tails of $\ln \mathcal{P}(x)$ up to a dimensionless factor $\alpha(H,m)$, where $0<H<1$ is the Hurst exponent. We determine $\alpha(H,m)$ analytically (i) in the limits of $H\to 0$ and $H\to 1$, and (ii) for $m=2$ and arbitrary $H$, corresponding to the fractional Ornstein-Uhlenbeck (fOU) process. Our results for the fOU process are in agreement with the previously known exact $\mathcal{P}(x)$ and autocovariance. The form of the tails of $\mathcal{P}(x)$ yields exact conditions, in terms of $H$ and $m$, for the particle confinement in the potential.
For $H\neq 1/2$, the tails encode the non-equilibrium character of the steady state distribution, and we observe violation of time reversibility of the system except for $m=2$. To compute the optimal paths and the factor $\alpha(H,m)$ for arbitrary permissible $H$ and $m$, one needs to solve an (in general nonlinear) integro-differential equation. To this end we develop a specialized numerical iteration algorithm which
accounts analytically for an intrinsic cusp singularity of the optimal paths for $H<1/2$.


Microcrystalline and nanocrystalline structure of diamond films grown by MPCVD with nitrogen additions: Study of transitional synthesis conditions

This research explores the complex influence of nitrogen concentration and substrate temperature on the resultant properties of polycrystalline diamond (PCD) films grown by microwave plasma chemical vapor deposition (CVD). In particular, we investigated the growth parameters to find the exact conditions for changing the morphology of the resulting film from microcrystalline (MCD) to nanocrystalline (NCD). A series of 2 µm-thick polycrystalline diamond films was grown on Si substrates in methane-hydrogen–nitrogen gas mixtures with varied: (i) nitrogen concentration (0–2 %) and (ii) substrate temperature (700–1050 °C). Comprehensive characterization techniques, including scanning electron microscopy (SEM), micro-Raman spectroscopy, and X-ray diffraction, were employed to assess the morphological, structural, and spectroscopic properties of the films. The study reveals that even minor additions of nitrogen significantly modulate secondary nucleation, impacting both film morphology and phase composition. Furthermore, substrate temperature emerges as another critical parameter, influencing the growth kinetics and crystallite size. The comparison of the characteristics of grown PCD films allowed us to find conditions for the formation of NCD films with minimal surface roughness and maximal growth rate: nitrogen concentration [N2] ≈ 0.2–0.5 % and temperature T ≈ 850–900 °C. These findings can be used to optimize the CVD synthesis parameters of PCD films for applications as protective or friction-reducing layers, as well as for superhard cutting tools and optical devices.

Resonant effects of long-period ship-induced waves near shallow coasts

This work analyzes the propagation properties of long-period ship-induced waves of vessels in confined waterways that are surrounded by wide and shallow water bodies using numerical simulations. Previous measurements indicated that, in the presence of shallow water surroundings, the drawdown being part of the long-period wave system can travel in the form of depression waves over several ship lengths distance [Parnell et al., “Ship-induced solitary Riemann waves of depression in Venice Lagoon,” Phys. Lett. A 379, 555–559 (2015); Scarpa et al., “The effects of ship wakes in the Venice Lagoon and implications for the sustainability of shipping in coastal waters,” Sci. Rep. 9, 19014 (2019)]. The exact conditions leading to these unexpectedly large propagation distances could to date not be clarified [Parnell et al., “Depression Waves Generated by Large Ships in the Venice Lagoon,” J. Coastal Res. 75, 907–911 (2016)]. In this work, evidence from numerical simulations is presented, indicating that the far-field propagation properties are governed by the wave speed of the shallow water surroundings. In case the ship speed is larger than the surrounding wave speed (supercritical conditions), a free wave is continuously generated traveling over the shallow water with only minimal height decay. In the simulations, depression waves can travel over a distance of three ship-lengths with a height reduction below 10% in the supercritical regime, as compared to 80% height reduction in the sub-critical regime. In a one-dimensional environment, this agreement of free and forced wave speed is known as Proudman resonance.

Boundary conditions in flutter simulations of subsonic, transonic and supersonic blade cascades

Simulations of blade flutter are highly sensitive to undesired wave reflections at inlet and outlet boundaries. A careful treatment of boundary conditions is required to prevent the generation of perturbations. This study is motivated by the need to perform flutter analysis of low-pressure steam turbine blades, for which supersonic inflow conditions may occur in the near-tip region. The exact steady non-reflecting boundary condition (NRBC), the spectral NRBC and a simple isentropic boundary condition are implemented in a time-marching flow solver and applied to turbomachinery flutter simulations covering a wide range of operating conditions. For the first time, the spectral NRBC is applied to a blade flutter simulation with a supersonic inlet and its performance is analysed and compared with other boundary condition formulations. It is shown that an effective non-reflective treatment in the design of the boundary condition is essential for an accurate aeroelastic prediction at all operating conditions, including the subsonic flow regime. The limitation of the exact steady NRBC to spatial modes causes it to perform poorly in some unsteady flow simulations, whereas the spectral NRBC achieves a satisfactory suppression of undesired wave reflections in all investigated cases.

Rayleigh Waves in a Thermoelastic Half-Space Coated by a Maxwell–Cattaneo Thermoelastic Layer

This paper investigates the propagation of in-plane surface waves in a coated thermoelastic half-space. First, it investigates a special case where the surface layer is described by the Maxwell–Cattaneo thermoelastic approach, while the half-space is filled by a thermoelastic material described by the classical Fourier law for the heat flux. The contact between the layer and the half-space is assumed to be welded, i.e., the displacements and the temperature, as well as the stresses and the heat flux are continuous through the interface of the layer and the half-space. The boundary and continuity conditions of the problem are formulated and then the exact dispersion relation of the surface waves is established. An illustrative numerical simulation is presented for the case of an aluminum thermoelastic layer coating a thermoelastic copper half-space, highlighting important aspects regarding the propagation of Rayleigh waves in such structures. The exact effective boundary conditions at the interface are also established replacing the entire effect of the layer on the half-space. The general case of the problem is also investigated when both the surface layer and the half-space are described by the Maxwell–Cattaneo thermoelasticity theory. This study helps to further understand the propagation characteristics of elastic waves in layered structures with thermal effects described by the Maxwell–Cattaneo approach.

Exploring the interaction between aminobutyric acid and epigenetics in modulating ash dieback response in european ash (Fraxinus excelsior)

AbstractEuropean ash populations face a significant threat from the invasive fungus Hymenoscyphus fraxineus, leading to ash dieback disease. The absence of resistant individuals and restrictions on biotechnological solutions hinder the ability to combat this widespread illness in the near term. Priming strategies offer an alternative approach to boost stress tolerance not only in this scenario but also in other endangered tree species by triggering plant defense mechanisms. The non-proteinogenic amino acid β-aminobutyric acid (BABA) has demonstrated potential in enhancing resistance to diverse stressors in plants. Despite limited research on forest tree species, the current study evaluated BABA’s effectiveness in mitigating ash dieback disease severity and explored potential correlations between priming treatments and epigenetic modifications. The results indicated that BABA enhanced stress tolerance in ash seedlings following inoculation with Hymenoscyphus fraxineus. BABA effectively decreased the development of necrosis associated with ash dieback disease in seedlings five months post-inoculation. Additionally, treatments involving BABA were linked to observed epigenetic alterations. Elevated levels of the non-canonical deoxynucleosides 5-(hydroxymethyl)-2'-deoxycytidine (5-hmdC) and 5-(hydroxymethyl)-2'-deoxyuridine (5-hmdU) were confirmed subsequent to the treatments. This study highlights the potential of BABA and other priming strategies in enhancing disease tolerance in forest tree species like European ash. Short-term improved stress tolerance and epigenetic changes were confirmed. Yet, the exact priming conditions for inducing long-term effects in plants, including long-living forest trees, remain unknown, posing a challenge for applying priming strategies to manage ash dieback and protect many other endangered tree species.

Dramatic Impact of Materials Combinations on the Chemical Organization of Core-Shell Nanocrystals: Boosting the Tm3+ Emission above 1600 nm.

This article represents the first foray into investigating the consequences of various material combinations on the short-wave infrared (SWIR, 1000-2000 nm) performance of Tm-based core-shell nanocrystals (NCs) above 1600 nm. In total, six different material combinations involving two different types of SWIR-emitting core NCs (α-NaTmF4 and LiTmF4) combined with three different protecting shell materials (α-NaYF4, CaF2, and LiYF4) have been synthesized. All corresponding homo- and heterostructured NCs have been meticulously characterized by powder X-ray diffraction and electron microscopy techniques. The latter revealed that out of the six investigated combinations, only one led to the formation of a true core-shell structure with well-segregated core and shell domains. The direct correlation between the downshifting performance and the spatial localization of Tm3+ ions within the final homo- and heterostructured NCs is established. Interestingly, to achieve the best SWIR performance, the formation of an abrupt interface is not a prerequisite, while the existence of a pure (even thin) protective shell is vital. Remarkably, although all homo- and heterostructured NCs have been synthesized under the exact same experimental conditions, Tm3+ SWIR emission is either fully quenched or highly efficient depending on the type of material combination. The most efficient combination (LiTmF4/LiYF4) achieved a high photoluminescence quantum yield of 39% for SWIR emission above 1600 nm (excitation power density in the range 0.5-3 W/cm2) despite significant intermixing. From now on, highly efficient SWIR-emitting probes with an emission above 1600 nm are within reach to unlock the full potential of in vivo SWIR imaging.

Frozen condition of quantum coherence

Quantum coherence as an important physical resource plays the key role in implementing various quantum tasks, whereas quantum coherence is generally nonincreasing under incoherent operations. In this paper, we analyse under which dynamical conditions the l 1-norm or the relative entropy of coherence can remain unchanged under strictly incoherent operations (freezing coherence). We provide a detailed analysis of their structure together with exact geometric conditions of freezing coherence. It reveals a remarkable feature: any strictly incoherent operation freezing coherence can be decomposed as a convex combination of unitary operations. This partially answers an open question named unitary decomposition of doubly-stochastic quantum operations [M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information, (Cambridge University Press, Cambridge, 2000)]. Based on this analysis, we also give a complete classification of coherent states from operational coherence theory. This builds the counterpart of entanglement classification under LOCC.

Comparative study of adaptive trajectory tracking controller for four-wheel mobile robot with prescribed-prediction performance

The nonlinear external disturbances and unmodeled dynamics characteristics have crucial impacts on trajectory tracking control accuracy of a four-wheel mobile robot (FWMR) under complicated working conditions. In this work, an adaptive trajectory tracking controller is designed for the FWMR to achieve the prescribed-prediction performance. On the basis of establishing the FWMR’s dynamics equations, an enhanced prescribed performance function (EPPF) is constructed to restrain the tracking errors of the FWMR within a certain range without requiring the exact initial conditions, thus guaranteeing the transient performance of the control system. Then, an optimal-predictive control (OPC) approach is presented to fulfill the asymptotic stability of the tracking errors of the FWMR. Specifically, the radial basis function neural network (RBFNN) incorporating a minimum parameter learning approach that are implanted into the expected controller is designed to attenuate the nonlinear external disturbances and the unmodeled dynamics of the FWMR. Lastly, comparative simulation investigations are carried out to illustrate the superiority of the proposed EPPF-OPC controller, and moreover, the comparative experiments are further performed to validate the practical effectiveness of the EPPF-OPC controller based on a self-established robot operating system (ROS) test platform of the FWMR.

Small amendment arguments: how they work and what they do and do not show

AbstractThe small improvement argument has been said to establish that the standard weak preference or value relation can be incomplete. We first show that the argument is one of three possible ‘small amendment arguments’, each of which would yield the same conclusion. Generalizing the analysis thus, we subsequently present a strong and a weak version of small amendment arguments and derive the exact rationality conditions under which they reveal incompleteness. The results show that the arguments (in any of their variants) need not reveal a problem for the possibility of rational choice. In fact, it can be argued that they only reveal such a problem if the underlying relation is complete rather than incomplete.

Exact quantization conditions and full transseries structures for PT symmetric anharmonic oscillators

We study exact Wentzel–Kramers–Brillouin analysis (EWKB) for a PT symmetric quantum mechanics (QM) defined by the potential VPT(x)=ω2x2+gx2K(ix)ϵ with ω∈R≥0, g∈R>0 and K,ϵ∈N to clarify its perturbative/nonperturbative structure. In our analysis, we mainly consider the massless cases, i.e., ω=0, and derive the exact quantization conditions (QCs) for arbitrary (K,ϵ) including all perturbative/nonperturbative corrections. From the exact QCs, we clarify full transseries structure of the energy spectra with respect to the inverse energy level expansion, and then formulate the Gutzwiller trace formula, the spectral summation form, and the Euclidean path integral. For the massive cases, i.e., ω>0, we show the fact that, by requiring the existence of the solution of the exact QCs, the path of analytic continuation in EWKB is uniquely determined for a given N=2K+ϵ, and in consequence the exact QCs, the energy spectra, and the three formulas are all perturbative. Similarities to Hermitian QMs and resurgence are also discussed as additional remarks. Published by the American Physical Society 2024

Quantification of O2 Crossover and Concurrent Faradaic Efficiency Loss of H2 Production Via PEM Water Electrolysis

PEM water electrolyzers (PEMWEs) are considered to be a key technology for the decarbonization of major sectors by being able to store fluctuating renewable energy as chemical energy in the form of hydrogen gas. While the scarcity of the necessary iridium catalyst on the anode limits widespread application minding the high loadings still needed today,1 there are additional efficiency losses that are still to be fully understood.By employing a proton exchange membrane, PEMWEs are able to produce hydrogen at elevated pressure on the cathode while keeping the balance of plant costs low as the anode can still be operated with liquid water at close to ambient pressure. Hydrogen crossover to the anode compartment through the membrane is significantly increased at elevated cathode pressures, which is majorly considered a safety issue. As the anode catalyst does not serve as a good hydrogen oxidation reaction catalyst, explosive mixtures of hydrogen and oxygen can form at the anode (and its exhaust) depending on the membrane type and thickness, current density, temperature, hydrogen partial pressure at the cathode, cathode catalyst layer structure etc.2-4 Aside of safety concerns – which can be bypassed by the use of recombination interlayers in the membrane5 – gas crossover also reduces the Faradaic efficiency of the system as parts of the hydrogen produced cannot be used further because it does not reach the cathode exhaust.A so far not majorly considered additional Faradaic efficiency loss stems from oxygen crossover from the anode to the cathode. As the platinum based cathode catalyst is very active for the oxygen reduction reaction, basically all of the oxygen crossing over to the cathode compartment recombines with the hydrogen present, forming liquid water.6 The permeability of oxygen through common PEM materials is significantly lower than that of hydrogen.7 But due to the osmotic drag from the anode to the cathode as well as possibly high bubble pressures of oxygen at the anode catalyst layer / membrane interface,8 oxygen crossover deserves closer attention.In this study we show quantification of the oxygen crossover in operating PEMWE single cells by a full balance of the gases detected at both the anode and cathode exhaust using an online mass spectrometer. A direct correlation of Faradaic efficiency of the oxygen and hydrogen produced matches the expected chemical recombination on the cathode, which serves as a direct measure of the oxygen crossover to the cathode compartment during PEMWE operation. Depending on the exact operating conditions the Faradaic efficiency loss caused by oxygen crossover can easily be in the percentage range, stressing the importance of having a closer look at the oxygen crossover characteristics of PEMWE cells in order to improve the Faradaic efficiency of the system. Taie, Z.; Peng, X.; Kulkarni, D.; Zenyuk, I. V.; Weber, A. Z.; Hagen, C.; Danilovic, N., Pathway to Complete Energy Sector Decarbonization with Available Iridium Resources using Ultralow Loaded Water Electrolyzers. ACS Appl Mater Interfaces 2020, 12, 52701-52712.Bernt, M.; Schröter, J.; Möckl, M.; Gasteiger, H. A., Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 2020, 167.Ito, H.; Miyazaki, N.; Ishida, M.; Nakano, A., Cross-permeation and consumption of hydrogen during proton exchange membrane electrolysis. Int. J. Hydrogen Energy 2016, 41, 20439-20446.Trinke, P.; Keeley, G. P.; Carmo, M.; Bensmann, B.; Hanke-Rauschenbach, R., Elucidating the Effect of Mass Transport Resistances on Hydrogen Crossover and Cell Performance in PEM Water Electrolyzers by Varying the Cathode Ionomer Content. J. Electrochem. Soc. 2019, 166, F465-F471.Zhang, Z.; Han, Z.; Testino, A.; Gubler, L., Platinum and Cerium-Zirconium Oxide Co-Doped Membrane for Mitigated H2 Crossover and Ionomer Degradation in PEWE. J. Electrochem. Soc. 2022, 169.Schalenbach, M.; Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., Pressurized PEM water electrolysis: Efficiency and gas crossover. Int. J. Hydrogen Energy 2013, 38, 14921-14933.Schalenbach, M.; Hoefner, T.; Paciok, P.; Carmo, M.; Lueke, W.; Stolten, D., Gas Permeation through Nafion. Part 1: Measurements. The Journal of Physical Chemistry C 2015, 119, 25145-25155.Weber, C. C.; Wrubel, J. A.; Gubler, L.; Bender, G.; De Angelis, S.; Buchi, F. N., How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis. ACS Appl Mater Interfaces 2023, 15, 34750-34763.

Revealing the Path-Dependence of Catalyst Degradation in Polymer Electrolyte Fuel Cells

Electro-catalyst plays a central role in many clean energy technology applications including water electrolysis for green hydrogen generation, emission free fuel cells for transportation, electrochemical CO2 reduction and combine heat and power generation. Electro-catalysts degrade via multiple mechanisms, depending on the exact operating conditions in its life cycles. In this presentation, we demonstrate the dependance of the electro-catalyst degradation in polymer electrolyte fuel cell (PEFC) on the specific “paths” that the fuel cell takes to age. Specifically, differently ordered aging protocols with the same total number of accelerated stress tests (ASTs) cycles (i.e., 31,000 total cycles including 30,000 cycles of square-wave load/unload ASTs and 1000 cycles of triangular-wave carbon corrosion ASTs) were used to degrade membrane electrode assemblies (MEAs). At the end-of-life, performances were distinct, indicating that depending on the specific aging route taken, the fuel cell catalyst layer degrades differently after same number of total AST cycles. The load/unload aging protocol led to more severe losses of performance when preceding after the carbon corrosion aging ASTs

A hybrid FEM-IBM-level set algorithm for water entry of deformable body

Water entry of deformable bodies has been investigated extensively despite the major challenges in precise simulations of the whole physical process. Inspired by the basic idea of immersed boundary method (IBM), a hybrid FEM-IBM-level set algorithm is proposed where structural compliance is considered. The flow is described by Navier-Stokes equations with an added body force while the drastically moving object of arbitrary geometry is represented by several Lagrangian points on solid boundary. The direct forcing IBM is enhanced and coupled with finite element method (FEM) to facilitate simulation of severe fluid-structure interactions. Consequently, the added body force is calculated implicitly based on the exact velocity boundary condition with divergence-free condition ensured simultaneously. The improved conservative level set technique is adopted for accurate depiction of instantaneously distorted water surface, and the strongly coupled system is resolved iteratively through a partitioned scheme. Examples including sedimentation of a disk, water entry of deformable wedge and cylindrical shell are performed for validation. Specifically, hydroelastic impact of a three-dimensional conical shell is investigated, and the influence factors of entry dynamics are discussed. The results demonstrate the reliability and great potential of present algorithm for practical applications in ocean engineering, naval architecture and military engineering, etc.

Does the capacitor analogy model in fracture mechanics of elastic dielectrics constitute an appropriate approximation?

The analytical solution of an elliptic dielectric cavity in an infinite dielectric plate is taken as basis to investigate a Griffith crack problem which is obtained by letting the semi-minor axis tend towards zero. In the course of this, an erroneous conformal mapping, commonly employed in literature and correctly reproducing the electric field only in a part of the physical space, is rectified. Interpreting the elliptic interface as faces of a mechanically opened crack which is exposed to an oblique remote electric field, surface charges and electrostatic tractions are calculated. In contrast to the established capacitor analogy model, approximately yielding electric charge densities and Coulombic tractions from displacements and electric potentials in the undeformed crack configuration, the work at hand provides exact solutions accounting for different implications of the crack curvature and for the inclination of the electric field. Crack weight functions are finally used to calculate stress and electric displacement intensity factors. As turns out, the surface charges of the capacitor analogy represent an excellent substitute for the exact electric boundary conditions within a relevant range of parameters, whereas inaccurate Coulombic tractions in the vicinity of crack tips may lead to a significantly overestimated mode I stress intensity factor.

Isotope effects and Alfvén eigenmode stability in JET H, D, T, DT, and He plasmas

While much about Alfvén eigenmode (AE) stability has been explored in previous and current tokamaks, open questions remain for future burning plasma experiments, especially regarding exact stability threshold conditions and related isotope effects; the latter, of course, requiring good knowledge of the plasma ion composition. In the JET tokamak, eight in-vessel antennas actively excite stable AEs, from which their frequencies, toroidal mode numbers, and net damping rates are assessed. The effective ion mass can also be inferred using measurements of the plasma density and magnetic geometry. Thousands of AE stability measurements have been collected by the Alfvén Eigenmode Active Diagnostic in hundreds of JET plasmas during the recent Hydrogen, Deuterium, Tritium, DT, and Helium-4 campaigns. In this novel AE stability database, spanning all four main ion species, damping is observed to decrease with increasing Hydrogenic mass, but increase for Helium, a trend consistent with radiative damping as the dominant damping mechanism. These data are important for confident predictions of AE stability in both non-nuclear (H/He) and nuclear (D/T) operations in future devices. In particular, if radiative damping plays a significant role in overall stability, some AEs could be more easily destabilized in D/T plasmas than their H/He reference pulses, even before considering fast ion and alpha particle drive. Active MHD spectroscopy is also employed on select HD, HT, and DT plasmas to infer the effective ion mass, thereby closing the loop on isotope analysis and demonstrating a complementary method to typical diagnosis of the isotope ratio.