Potential Hysteresis Research Articles

Wind Tunnel Tests of a Two-Element Wingsail with Focus on Near-Stall Aerodynamics

_ Modern wind propulsion systems on ocean-going cargo vessels require automated trimming. Rigid wingsail designs often incorporate more than one degree of freedom enabling to trim for optimal performance in all sailing conditions. A profound understanding of the aerodynamic behavior is the basis for any trimming strategy. The region around stall is of particular importance as this is where the largest lift but also potential hysteresis effects are expected. In the present research, a two-element wingsail (main wing and flap) was tested in wind tunnel experiments investigating the two available degrees of freedom: the orientation of the main wing to the inflow and the deflection of the flap. Aerodynamic loads were measured in dynamic actuation sequences over both degrees of freedom capturing stall and reattachment. The consistent data reveals two stall stages. In the region between the first and the second stall, when changing the direction of rotation, the flow is found to be reversible. The hysteresis loop is in this case smaller and reattachment occurs at larger angles compared to when both stall stages occur. This smaller hysteresis loop could be exploited in trimming. The second stall stage, however, is identified as detrimental both in the forces and the amount of required actuation to allow the flow to reattach. A considerate flap trim, i.e. the adjustment of the wingsail curvature, is suggested to avoid the second stall. Keywords Wind propulsion; Wind tunnel tests; Stall hysteresis; Two-element wing; Rigid wingsail; Trimming; Automation

Mathematical model for characterization of temperature-responsive polymers: A study on the rheological behavior of gelatin and poly(N-isopropylacrylamide)

This study introduces a mathematical model for detailed characterization of temperature-responsive polymers, focusing on critical temperature, viscosity, storage modulus, their rate of change in the transition region, flow behavior, and potential hysteresis. Applied to gelatin (GEL) and poly(N-isopropylacrylamide) (pNIPAm), the model analyzes their rheological responses across various temperatures. It was observed that gel's critical temperature is slightly above its polymer's lower critical solution temperature, and vice versa for upper critical solution temperature polymers. The critical temperature for GEL was 28 °C, as opposed to 37 °C for pNIPAm. While concentration changes affected these values, the contribution of tetramethylethylenediamine (typically used in combination with various initiators to start the polymerization reaction) was found to be insignificant. GEL exhibited significant hysteresis, unlike pNIPAm's rapid transition. Their storage modulus and viscosity showed a linear correlation with concentration, with deviations at high pNIPAm concentrations suggesting the influence of polymer interactions and crosslinking. These findings offer valuable insights for applications requiring temperature sensitivity.

Pair Distribution Function Analysis of Local Structural Rearrangement in Spinel Vanadium Oxide Cathodes

Being a divalent cation with the lowest mass, Mg2+ has garnered quite attention in recent times due to the high volumetric capacity of it’s batteries. Theoretical studies reveal that the combination of a Mg anode and a spinel oxide cathode would be able to surpass the current limits found in widely used Li-ion batteries Therefore, to design materials with high diffusion and reversible insertion capacity, a conclusive demonstration of the intercalation mechanism of Mg2+ into metal oxides, is required.Among the numerous options for cathodes, vanadium oxides show evidence of the largest capability toward reversible intercalation of Mg ions. In particular, spinel-type MgV2O4 shows a capacity of 200 mAh/g, corresponding to the cycling of ~0.7 mol Mg2+ per mol of oxide, and layered α-V2O5 reaches 300 mAhg-1, intercalating 1 mol Mg2+ per mol of oxide. The extent and reversibility of these reactions were confirmed by elemental, redox and structural characterization in recent work [1,2]. This high capacity is only observed at 110°C and it is accompanied by a large hysteresis in potential during the electrochemical cycling. The push to overcome these bottlenecks demands a more comprehensive definition of the underlying mechanisms of reaction than is currently available.Previous X-ray Diffraction (XRD) measurements conducted on the oxide indicated a loss of reflection intensity due to a loss in their crystallinity which makes structural characterization using typical diffraction techniques difficult. Through this work, we mainly make use of pair distribution function techniques to study the changes in the local structures of these oxides in both their pristine and charged state, and the effect of annealing for longer hours with the goal of further pushing the efficiency of multivalent battery materials.Reference: Hu, L., Jokisaari, J.R., Kwon, B.J., Yin, L., Kim, S., Park, H., Lapidus, S.H., Klie, R.F., Key, B., Zapol, P. and Ingram, B.J., 2020. High capacity for Mg2+ deintercalation in spinel vanadium oxide nanocrystals. ACS Energy Letters, 5(8), pp.2721-2727. Yoo, H.D., Jokisaari, J.R., Yu, Y.S., Kwon, B.J., Hu, L., Kim, S., Han, S.D., Lopez, M., Lapidus, S.H., Nolis, G.M. and Ingram, B.J., 2019. Intercalation of magnesium into a layered vanadium oxide with high capacity. ACS Energy Letters, 4(7), pp.1528-1534.

Na(Co,Ti)O2 Cathodes for Na-Ion Batteries: A Proper Choice

Increased attention to sodium-containing materials during the last several years is caused by the rapid development of sodium-ion batteries (NIBs), considered as a potential successor for lithium-ion batteries (LIBs) [1]. Especially layered sodium oxides have gained large interest due to their potential applicability as electrode materials (both, as cathodes and anodes). Similar to LiCoO2 in LIBs, NaCoO2 shows an immense potential as a cathode in NIBs. A partial replacement of Co by Ti in a Na(Co,Ti)O2 cathode can stabilize the crystal structure during (de)sodiation and reduce the number of phase transformations. Although the phase diagram of the Na-Co-Ti-O system has not been studied yet, existence of single-phase and multi-phase regions in dependence on the Na-content and temperature is reported in the literature [2]. Typically, layered Na,Co,Ti-oxides adopt three very close structure types P2, O3 and P3, which differ in the oxygen surrounding for Na-cations (octahedral or prismatic) and in the number of the formula units in the crystal unit cell (2 or 3). For application in Na-batteries, however, a trial-and-error approach is mostly needed to evaluate a composition with outstanding electrochemical performance.The redox activity of Co and Ti cations is usually characterized by two well-separated cell potentials. The Co-oxidation (Co2+ → Co3+ and Co3+→ Co4+) occurs mostly at potentials between 3 and 4 V vs. Na+/Na, qualifying the material as cathode while Ti4+/Ti3+ redox process takes place below 1.5 V, as common for anode materials. Based on our experimental studies of layered Na,Co,Ti-oxides with different compositions as NaCo0.5Ti0.5O2 (O3) [3], Na0.65Co0.5Ti0.5O2 (P3) [3], Na0.67Co0.33Ti0.67O2 (P2- and O3-structures) [4] and Na0.8Co0.8Ti0.2O2 (P2) [5] as well as on literature report [6], we can conclude that the most stable cycling behavior can be realized, if the composition in the initial (discharged) state contains mainly Co3+ and not Co2+. The reason for this is a first-order spin-state transition of high-spin HS-Co2+ to low-spin LS-Co3+ and back upon (de)sodiation, which is accompanied by a phase transformation, leading to a huge potential hysteresis of about 2 V. This hysteresis only slightly depends on the temperature between 0 °C and 40 °C. Among the compositions mentioned above, Na0.8Co0.8Ti0.2O2 with the P2-structure is the best candidate for application as a cathode in Na-batteries. However, a deep discharge of the material below 1.6 V to reach the Na1.0Co0.8Ti0.2O2 composition is detrimental as well, since some amount of Co2+ appears, negatively influencing the cycling behavior.

DBD plasma‐assisted coating of metal alkoxides on sulfur powder for Li–S batteries

AbstractSulfur particles coated by activation of metal alkoxide precursors, aluminum–sulfur (Alu–S) and vanadium–sulfur (Van–S), were produced by dielectric barrier discharge (DBD) plasma technology under low temperature and ambient pressure conditions. We report a safe, solvent‐free, low‐cost, and low‐energy consumption coating process that is compatible for sustainable technology up‐scaling. NMR, XPS, SEM, and XRD characterization methods were used to determine the chemical characteristics and the superior behavior of Li–S cells using metal oxide‐based coated sulfur materials. The chemical composition of the coatings is a mixture of the different elements present in the metal alkoxide precursor. The presence of alumina Al2O3 within the coating was confirmed. Multi‐C rate and long‐term galvanostatic cycling at rate C/10 showed that the rate capability losses and capacity fade could be highly mitigated for the Li–S cells containing the coated sulfur materials in comparison to the references uncoated (raw) sulfur. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) confirm the lower charge‐transfer resistance and potential hysteresis in the electrodes containing the coated sulfur particles. Our results show that the electrochemical performance of the Li–S cells based on the different coating materials can be ranked as Alu‐S > Van‐S > Raw sulfur.

Overcoming hysteresis in ligand binding potential of mean force calculations.

Accurate estimation of ligand binding free energy and elucidation of the corresponded binding pathway are key challenges in computational drug design. Umbrella sampling (US) molecular dynamic simulations are widely used to tackle these challenges; however, they frequently suffer from massive hysteresis between the ligand binding and unbinding pathways, limiting the applicability of US for ligand-protein interaction studies. The convergence of US is affected by the complexity of the system, the selection of reaction coordinate(s), simulation time, and by the selection of additional restraints.

Chemical and electrochemical synergistic weaving stable interface enabling longevous zinc plating/stripping process

Dendrites growth and hydrogen evolution reaction of Zn anode greatly hinder the practical application of aqueous zinc ion batteries. Interface engineering strategies have attracted immense interest in addressing these challenges. Herein, a chemical and electrochemical method is proposed to synergistically weave a stable interface by introducing AgNO3 additive in conventional aqueous ZnSO4 electrolyte. The formed compact Ag layer acts as zincophilic sites, which is beneficial for zinc ion nucleation and growth. Consequently, the cell cycled in 2 M ZnSO4 with 3 mM AgNO3 electrolyte exhibits much more stable electrochemical properties than its counterpart. To be specific, the Zn || Zn half cell using the electrolyte with 3 mM AgNO3 shows reversible Zn plating/stripping behavior over 1350 h at 5.0 mA cm−2 with an ultra-low potential hysteresis. Moreover, Zn || V2O5 full cell using the electrolyte with 3 mM AgNO3 exhibits glorious rate capability and more stable cycling performance, attributing to the inhibited zinc dendrites growth by the weaved interfacial layer. This work sheds new light on improving the electrochemical performance of rechargeable batteries.

Voltage hysteresis loop as a fingerprint of slow kinetics Co2+-to-Co3+ transition in layered NaxCox/2Ti1−x/2O2 cathodes for sodium batteries

The P2- and O3-Na0.67Co0.33Ti0.67O2 cathodes undergo a very slow transformation during charge and discharge in sodium batteries due to a valence and spin-state transition of cobalt cations. As a result, a big potential hysteresis of 2.5–3 V arises.

Engineering of the Crystalline Lattice of Hard Carbon Anodes Toward Practical Potassium‐Ion Batteries

AbstractHard carbons have attracted increased interest as an alternative of graphite for the anodes of potassium‐ion batteries (PIBs). However, the practical applications of hard carbon anodes are hampered by their low capacities, high potential platforms, and large potential hysteresis. Hard carbons coupled with graphitic nanodomains can achieve stable potassium‐ion storage behaviors with low potential platforms and low potential hysteresis. Herein, the crystalline lattice in hard carbon anodes is tuned by incorporating graphene oxide in renewable lignin precursors. The modified hard carbon (i.e., QLGC) anodes show graphitized nanodomains in the carbon matrix with an expanded interlayer spacing (0.42 nm) in the amorphous regions, which results in a stable potassium‐ion (de)intercalation behavior. Thus, the QLGC anodes exhibit a high capacity of 164 mAh g−1 with low potential hysteresis in the low potential platform region. Moreover, the QLGC anode delivered a highly stabilized capacity of 283 mAh g−1 at 50 mA g−1, a high‐rate capability, and stable cycling performance. Furthermore, the charge storage mechanisms of QLGC anode are elucidated by electro‐kinetic analysis and ex/in situ physicochemical characterizations. This study opens a new avenue for designing hard carbon anodes with engineered crystalline lattices toward practical PIBs.

Critical Analysis of MXene Production with In‐Situ HF Forming Agents for Sustainable Manufacturing

AbstractMXenes are an emerging class of materials considered for many applications, such as sensors, catalysis, energy storage devices. The main obstacle towards their massive implementation is the synthesis requiring the direct use of HF as etching agent. The development of alternative synthetic routes exploiting in‐situ forming HF agents is the main strategies to overcome this limitation. In this study four different etching methods based on the use of NH4HF2, NaF−HCl, HBF4, and NaBF4−HCl are compared to produce Ti3C2Tx from Ti3AlC2 towards the application of MXenes in sodium ion batteries. Three of such etching methods have already been reported while one is here presented for the first time. The structural analysis of the obtained products is based on X‐ray diffraction (XRD), scanning electron microscopy‐energy dispersive X‐ray spectroscopy (SEM‐EDX), and X‐ray photoelectron spectroscopy (XPS) analysis. All the materials have been tested in half‐cell configuration vs. Na; the charge/discharge profiles and the C‐rate tests are discussed and related to specific structural features. Overall, the results reveal that the MXene obtained using the HBF4 etching agent under mild conditions is comparable both in structure and functional properties to the benchmark material, i. e., the MXene produced using HF at 5 % concentration. Indeed, the MXene synthetized with the HBF4 presents the lowest mean voltage and potential hysteresis and shows the highest first cycle efficiency (69.7 %), overcoming the performance of the MXene produced with 5 % HF (67 %). This study proves the possibility to produce MXene with a more sustainable route.

Entropy Profiling for the Diagnosis of NCA/Gr-SiOx Li-Ion Battery Health

Graphite-silicon (Gr-Si) blends have become common in commercial Li-ion battery negative electrodes, offering increased capacity over pure graphite. Lithiation/delithiation of the silicon particles results in volume changes, which may be associated with increased hysteresis of the open circuit potential (OCP). The OCP is a function of both concentration and temperature. Entropy change measurement—which probes the response of the OCP to temperature—offers a unique battery diagnostics tool. While entropy change measurements have previously been applied to study degradation, the implications of Si additives on the entropy profiles of commercial cells have not been explored. Here, we use entropy profiling to track ageing markers in the same way as differential voltage analysis. In addition to lithiation/delithiation hysteresis in the OCP of Gr-Si blends, cells with Gr-Si anodes also exhibit differences in entropy profile depending on cycling direction, reflecting degradation-related morphological changes. For cycled cells, entropy change decreased during discharge, likely corresponding to graphite particles breaking and cracking. However, entropy change during charge increased with cycling, likely due to the volume change of silicon. Over a broad voltage range, these combined effects led to the observed rise in entropy hysteresis with age. Conversely, for calendar aged cells entropy hysteresis remained stable.

An Artificial Interphase Engineering Simultaneously Suppressing Hydrogen Evolution Reaction and Controlling Zinc Dendrite Growth to Achieve Stable Zinc Metal Anodes

AbstractZinc metal anode, the most promising candidate material for rechargeable aqueous zinc‐ion batteries, has attracted considerable attention due to its abundant resources and low cost. However, hydrogen evolution reaction and uncontrollable zinc dendrite growth on zinc metal anode are the essential issues that strictly limit their practical application. Here, a modified Zn with a titanium nitride (TiN) protective layer (TiN@Zn) using a simple solvent casting approach is developed, which can simultaneously suppress the hydrogen evolution reaction and control the zinc dendrite growth when acting like a protective layer on the Zn anode. In situ differential electrochemical mass spectrometry approach shows that the TiN coating layer can effectively suppress the hydrogen evolution. Additionally, the TiN can offer large Zn nucleation sites, narrowing the Zn nucleation energy barrier, leading to a uniform Zn deposition. Thus, in symmetric cells, the TiN@Zn electrode presents a stable Zn plating/striping (600 h at 1 mA cm−2) and lower potential hysteresis (38 mV), resulting in an improved electrochemical performance for TiN@Zn||MnO2 full cell.

Double gas treatment: A successful approach for stabilizing the Li and Mn-rich NCM cathode materials’ electrochemical behavior

Herein, a systematic surface modification approach via double gas (SO2 and NH3) treatment at elevated temperatures is described, aimed to achieve a stable electrochemical performance of Li and Mn-rich NCM cathode materials of a typical composition 0.33Li2MnO3·0.67LiNi0.4Co0.2Mn0.4O2 (HE-NCM). Partial surface reduction of Mn4+ and the formation of a modified interface comprising Li-ions conductive nano-sized Li2SO4/Li2SO3 phases are established. Li-coin cells’ prolonged cycling performance demonstrated significantly improved capacity retention (∼2.2 times higher than untreated cathode materials) for the double-gas-treated cathodes after 400 cycles at a 1.0 C rate. Stable discharge potential and lower voltage hysteresis during cycling were also achieved through the double gas treatment. Comparative electrochemical studies in full-pouch cells [vs. Graphite anodes] also demonstrated considerably stabilized electrochemical behavior for the double-gas-treated HE-NCM cathode materials. Lower gasses (O2, CO2, and H2) evolution in the first charge-discharge cycle and improved thermal stability are indeed crucial achievements of this treatment. Electrodes’ post-cycling investigation revealed morphological integrity of the gas-treated cathode materials and lower transition metals (TMs) dissolution from the active cathodes. The positive effects of the double gas treatment are clearly related to the modified surfaces and lessening undesirable side reactions at the electrode-electrolyte solution interface.

Addressing the High-Voltage Structural and Electrochemical Instability of Ni-Containing Layered Transition Metal (TM) Oxide Cathodes by "Blocking" the "TM-Migration" Pathway in the Lattice.

"Layered"/"cation-ordered"/O3-type Li-TM-oxides (TM: transition metal) suffer from structural instability due to "TM migration" from the TM layer to the Li layer upon Li removal (viz., "cation disordering"). This phenomenon gets exacerbated upon excessive Li removal, with Ni ions being particularly prone to migration. When used as cathode material in Li-ion batteries, the "TM migration" and associated structural changes cause rapid impedance buildup and capacity fade, thus limiting the cell voltages to ≤4.3 V for stable operation and lowering the usable Li-storage capacity (concomitantly, energy density). Looking closely at the "TM migration" pathway, one realizes that the tetrahedral site (t-site) of the Li layer forms an intermediate site. Accordingly, the present work explores a new idea concerning suppression of "Ni migration" by "blocking" the intermediate crystallographic site (viz., the t-site) with a dopant, which is the most stable at that site. In this regard, density functional theory (DFT)-based simulations indicate that the concerned t-site is energetically the most preferred and stable site for d10 Zn2+. Detailed analysis of crystallographic data (including bond valence sum) obtained with the as-prepared Zn-doped Li-NMC supports the same. Furthermore, the simulations also predict that Zn doping is likely to suppress "Ni migration" upon Li removal. Supporting these predictions, galvanostatic delithiation/lithiation studies with Zn-doped and undoped Li-NMCs demonstrate significantly improved cyclic stability, near-complete suppression of "cation mixing", and negligible buildup of impedance (as well as potential hysteresis) for the former, even upon being subjected to long-term cycling using a high upper cut-off potential of 4.7 V (vs Li/Li+). Accordingly, such subtle tuning of the composition and structure, in the light of electronic configuration of the dopant and specific crystallographic site occupancy, is likely to pave the way toward the development of Ni-containing stable high voltage O3-type Li-TM-oxide cathodes for the next-generation Li-ion batteries.

Hysteresis effect in organic thin film transistors based on naphthalene tetracarboxylic diimide derivatives

Controlling the hysteresis effect in organic field-effect transistors (OFETs) is imperative to attain reliable devices that can be applied to complicated circuits for practical applications. In this Letter, we compare two naphthalene tetracarboxylic diimide (NDI) derivatives, namely, N,N′-bis(4-trifluoromethoxybenzyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-BOCF3) and N,N′-bis(hexyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-C6), which are comprised of different side chains and exhibit significant variations in the hysteresis of electronic transfer potential caused by the electronic traps. Among them, NDI-BOCF3 manifests negligible hysteresis in OFETs, while the counterparts based on NDI-C6 show notable hysteresis. This work presents insight into the hysteresis phenomenon of NDIs in OFETs, which depends on various critical factors, including interfacial trap density, molecular structure, thin film growth mode, and surface energy. Particularly, NDI-C6 demonstrates two orders of magnitude higher interfacial trap density than that of NDI-BOCF3. Moreover, NDI-BOCF3 thin film displays small surface energy and higher surface coverage on the substrate, but the results are diametrically opposite in the case of NDI-C6. Considering these observations, we propose that the introduction of OCF3 group in NDI not only endues a well-matched surface energy that promotes uniform distribution of the thin film on n-Octyltrichlorosilane-modified SiO2 substrate but also provides a water-spelling feature which leads to fewer H2O/O2 absorption in the resulting thin films. Our findings offer a fundamental guideline to rationally design n-type organic semiconductors for the development of efficient OFETs with negligible hysteresis.

Core–shell structured monodisperse carbon-rich SiO1.31C1.46H0.81 ceramic spheres as anodes for high-capacity lithium-ion batteries

SiOC ceramic material is a promising anode material for lithium-ion batteries. However, due to its intrinsically low electronic conductivity, it often suffers from a much lower specific capacity than the theoretical value, poor rate capability and serious potential hysteresis. In this paper, we report a core–shell structured monodisperse carbon-rich SiO1.31C1.46H0.81 submicron ceramic sphere with a free carbon content of 13.7 wt%, which is synthesized by directly annealing polysiloxane spheres derived from vinyltrimethoxysilane without adding external carbon resources. The SiO1.31C1.46H0.81 sphere has a unique microstructure, the core of which is organically assembled by large amounts of SiO1.31C1.46H0.81 primary particles of less than 20 nm and coated by a shell of 20–50 nm. As anodes for lithium-ion batteries, it presents much higher reversible capacity, initial Coulomb efficiency (ICE) and rate performance than the SiOC-based ceramic materials reported in the literature to date. At 100 mA g−1, its first reversible capacity and ICE reach ∼1107 mAh g−1 and 78.2%, respectively. At 1600 mA g−1, its stable discharge capacity is still as high as 610 mAh g−1. The excellent electrochemical performance is attributed to the moderate composition, spherical morphology and unique microstructure of the synthesized material.

High storage capacity and small volume change of potassium-intercalation into novel vanadium oxychalcogenide monolayers V2S2O, V2Se2O and V2Te2O: An ab initio DFT investigation

A new category of two-dimensional electrode materials, i.e., V2Ch2O (Ch = S, Se and Te) monolayers was explored for K-ion batteries (PIBs) based on principle of chemical exfoliation, density functional theory and ab initio molecular dynamics simulations. The V2Ch2O monolayers show low cleavage energies and excellent thermal, dynamical and mechanical stabilities. Adsorption energies of a potassium atom on the V2Ch2O monolayers are exothermic, which are of benefit to prevent forming dendrites. The existence of electrode potentials substantially decreases the diffusion barriers of potassium atoms on the three V2Ch2O monolayers. The V2Ch2O monolayers are able to maintain their metallic characteristics and single surface phase during the whole K-intercalation process, avoiding the decrease in electronic conductivity and the appearance of potential hysteresis. The theoretical specific capacities of the V2S2O, V2Se2O and V2Te2O monolayers are predicted to be 883.6, 583.1 and 431.0 mAh g−1, respectively, and the corresponding average open-circuit voltages are 0.449, 0.390 and 0.293 V, respectively. The maximum percentage changes in lattice parameters are 4.21%, 6.07% and 7.26% for the V2S2O, V2Se2O and V2Te2O monolayers, respectively. All the calculated properties indicate that the V2Ch2O monolayers are promising electrode materials for PIBs with high capacities and long cycle lives.

Enhance cycle life of Na3.32Fe2.34(P2O7)2 cathode by pillar cations

As a safe and sustainable cathode material for reversible Na-ion storage, the electrochemical performance of Na3.32Fe2.34(P2O7)2 with high operational safety can be enhanced via ion-doping engineering strategy. However, the rationale behind has remained unclear. In this study, we partially replace the Na+ and Fe2+ cations with K+ and Mg2+, respectively, where the K+ and Mg2+ dopants serve as pillars to support the crystallographic framework and thus reduce potential hysteresis. It is found that, compared to K doping at the Na site, Mg doping at the Fe site contributes to a more stable crystal structure and renders higher rate capability and cycling stability due to the inhibition of Fe migration and the reduction of structural disorder. The cation pillar strategy reported herein may shed light on enhancing cycling performance of other cathode materials for stable storage of not only Na ions but also other metals.

Influence of heated forming tools on corrosion behavior of high strength aluminum alloys

AbstractIn this study forming tools temperated at 24 °C and 350 °C were used to systematically investigate the influence of different cooling rates on the mechanical and corrosion properties of a high strength aluminum alloy AA7075 within a novel thermo‐mechanical process that combines forming and quenching simultaneously. The samples formed within heated tools reveal higher ductility and lower material strength compared to the parts processed in cold tools. In addition, the corrosion behavior changed between samples formed with 24 °C forming tools and 350 °C forming tools, respectively. Through cyclic polarization in chloride containing aqueous media a change in the hysteresis and shift of open circuit potential was observed. Metallographic investigation revealed that there was also a very different corrosion morphology for the samples formed within the heated tools. No change in average grain size could be detected but changes of the microstructure in subgrain scale that occur during the forming within the heated tools are responsible for this effect. In further research, the effect of various cooling rates on mechanical and corrosion behavior and the microstructure will be investigated by variation of the forming tool temperature.

Epidemic spreading under infection-reduced-recovery

The pandemic transition is a hallmark of current epidemiological models, predicting a continuous shift from a healthy to a pandemic state, whose critical point is driven by the parameters of the disease, e.g., its infection, recovery or mortality rates. These parameters, characterizing the disease cycle, are tuned by the biological characteristics of the pathogen, capturing its natural time-scales, often considered independent of the state of the spread itself. If, however, the disease gains a population-wide impact, its prevalence may exceed the health-care system capacity, resulting in sub-optimal treatment, and hence a potential feedback mechanism, in which the disease cycle is no longer decoupled from the state of the spread. Such dependence was demonstrated during the spread of COVID-19, for instance, where hard-hit places showed elevated mortality rates, likely due to an over-stressed health-care system. We therefore introduce an infection-reduced recovery mechanism, linking an individual’s rate of recovery to the prevalence of the disease. The outcome, we show, may have dramatic consequences on the observed patterns of spread. For instance, under rather broad conditions, the pandemic transition becomes discontinuous, exhibiting an abrupt shift from a healthy to a pandemic state. In some cases the disease reaches population-wide coverage even below the classically predicted critical transition point. We also observe a potential multi-stability and hysteresis, capturing an irreversible pandemic transition, in which overcoming the disease requires us to quench infection rates significantly below the critical threshold. These findings not only provide hints on the current difficulties to contain COVID-19, but more broadly, they set the bar for sustaining a stably functioning treatment capacity in the face of population-wide demand.