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Titanium Substitution to Advance the Prospect of NaMnO Cathodes for Practical Application in Sodium-Ion Batteries
No full textO3-type layered oxides stand out among various Na-ion battery cathodes due to their unparalleled theoretical specific capacities. As a representative of low-cost, Mn-based cathode materials, -NaMnO (NMO) has attracted great attention. However, its practical application is hindered by poor reversibility. Compared to other O3 or O′3-type layered oxides, such as NaNiO2, NMO undergoes multiple phase transitions, with the final O1 phase negatively affecting cycling performance. In this study, precipitated MnO was employed, to our knowledge for the first time, as a precursor in the synthesis of NMO, and the cathode material was systematically optimized through incremental improvement via titanium substitution. NaMnTiO was found to exhibit enhanced stability, with the capacity retention increasing from 42 to 70% after 50 cycles at C/10, along with superior rate capability over NMO. This is due in part to titanium’s role in facilitating primary particle (grain) growth and suppressing O1 phase formation, thereby preserving structural integrity and mitigating degradation caused by volume variations and irreversible oxygen redox during battery operation. This work not only provides valuable insights into the development of next-generation NMO cathodes but also advances their potential for practical applications
Non-singular solutions to the Boltzmann equation with a fluid Ansatz
No full textCosmological phase transitionscan give rise to intriguing phenomena, such as baryogenesis or a stochastic gravitational wave background, due to nucleation and percolation of vacuum bubbles in the primordial plasma. A key parameter for predicting these relics is the bubble wall velocity, whose computation relies onsolving the Boltzmann equations of the various speciesalong the bubble profile. Recently it has been shown that an unphysical singularity emerges if one assumes these local quantities to be described as small fluctuations on a constant equilibrium background.In this work we solve this issue by including the spatial dependence of thebackground into the fluid Ansatz. This leads to a modification of the Boltzmann equation, and all terms that would give rise to a singularity now vanish.We recalculate the different contributions to the counter-pressure of the plasma on the expanding wall, and discuss their relative importance. The Standard Model with a low cutoff is chosen as benchmark model and the results are shown for different values of the cutoff scale Λ. In this setup, deflagration solutions are found for almost all the values of Λ considered, while detonations are found only for some restricted corner of the parameter space
Two-state reaction path search using a quantum Monte Carlo-inspired approach
No full textWe present an algorithm for finding chemical reaction pathways using a Monte Carlo transition state search (MCTSS) scheme. Our strategy is a bidirectional two-state approach that simultaneously drives two Monte Carlo trajectories from reactants to products, and vice versa, until the trajectories meet. The trajectories are driven in a Metropolis-like procedure with transition probabilities based on the real-space diffusion Monte Carlo algorithm. A computationally inexpensive structure preselection procedure is used to guide the two trajectories toward each other. We performed a proof-of-principle demonstration of the MCTSS algorithm for the model two-dimensional double-well potential and for the halogen anion S2-substitution in halogenated methane. The MCTSS approach presented here is expected to be particularly useful when employing electronic structure methods that do not provide analytic gradients
Searches for the decays using an inclusive tagging method at the Belle II experiment
No full textThe rare decays B → Kν ¯ν represent a class of flavor-changing neutral current processes that are highlysuppressed in the Standard Model and thus serve as sensitive probes for new physics. These decays aretheoretically clean, with uncertainties primarily stemming from hadronic form factors, and their branchingfractions are predicted with high precision. However, their experimental study poses significant challengesdue to the presence of two undetectable neutrinos in the final state, necessitating sophisticated reconstruc-tion techniques and robust background suppression.This thesis investigates the decays B+ → K+ν ¯ν and B0 → K∗0ν ¯ν using data corresponding to 365 fb−1collected at the Υ(4S) resonance within the Belle II experiment. The analyses employ the inclusive taggingmethod, in which the companion B meson is reconstructed inclusively to infer the kinematics of the signal-side decay. This approach provides substantial gains in signal efficiency compared to exclusive tagging, albeitat the cost of increased background complexity.The branching fraction of B+ → K+ν ¯ν is extracted from a maximum likelihood fit, yielding [2.7±0.5(stat)±0.5(syst)] × 10−5, which corresponds to a significance of 2.9 standard deviations from the Standard Modelexpectation. This measurement establishes the experimental viability of the inclusive tagging techniqueand has already prompted refinements of theoretical predictions, motivating renewed investigations intopotential new physics effects.Building upon this framework, the analysis of B0 → K∗0ν ¯ν is currently in the pre-unblinding stage. Thischannel poses additional challenges due to the more complex form-factor structure of the K∗0 meson andthe higher track multiplicity of its final states. Nevertheless, the analysis follows a similar strategy to theB+ → K+ν ¯ν case, with dedicated improvements in background modeling and event selection tailored tothe K∗0 topology. While no results are presented at this stage, the B0 → K∗0ν ¯ν study is expected to providecomplementary sensitivity to new physics through its unique helicity structure and kinematic features.In addition, this thesis includes a complementary study on a background filter in the central drift chamber,aimed at improving Belle II tracking performance under high-background conditions. While independent ofthe B → K(∗)ν ¯ν analyses, this work constitutes an independent contribution to optimization of the detectorperformance
Insights into the mechanism of electrode degradation and performance enhancing strategies for iron-ion batteries using X-ray absorption spectroscopy
No full textRechargeable iron-ion (Fe-ion) batteries are gaining attention due to their unique characteristics, including earth abundance, cost-effectiveness, eco-friendly nature, and high electrochemical performance. However, capacity degradation during cycling hinders their effective use. To investigate the material's degradation in rechargeable Fe-ion batteries, two different coin cells are fabricated utilizing mild steel (MS) and ZnO-coated mild steel (ZnO@MS) as anodes. In both cases, VO is used as the cathode, along with a non-aqueous electrolyte. Cyclic voltammetry and galvanostatic charge–discharge analyses are conducted at different cycling stages, viz. 20, 40, 60, and 80 cycles, for determining the electrochemical performance of these anode-based coin cell batteries. The coin cells are dismantled after cycling, and the post-cycled electrodes are subjected to ex situ scanning electron microscopy, X-ray diffraction, and X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements to probe the structural and chemical degradation mechanisms of the electrode materials. The results from the XANES and EXAFS measurements provide critical insights into the evolution of the electronic structure and local atomic environment, revealing degradation trends correlated with the cycling performance. The comparison between the MS and ZnO@MS anodes highlights the protective role of ZnO coating in mitigating degradation. In both cases, the VO cathode exhibits significant transformation after cycling, possibly due to changes in the oxidation states due to the insertion of Fe ions in the cathode. Thus, these findings offer a deeper understanding of the stability of materials in Fe-ion batteries and anode modification possibilities, which are crucial for developing durable, cost-effective energy storage systems
Dark vector boson bremsstrahlung: New form factors for a broader class of models
No full textWe explore the sensitivity of collider experiments to a broad class of GeV-scale dark vector models of new physics via production in proton and neutron bremsstrahlung and initial state radiation. This is achieved using a new physically motivated model for timelike vector form factors with generic charges for both protons and neutrons, which is fit to a variety of timelike and spacelike data with quantified uncertainties. The production model for both proton and neutron bremsstrahlung is applied to recast and extend the reach of existing FASER data to GeV-mass dark photons, U(1)B, U(1)B-L, and protophobic vectors, as well as forecasts for millicharged particles at FORMOSA
An unconventional pathway to correlate the octahedral tilt coupling and spin-orbit reconstruction at oxide interfaces
No full textThe direct experimental probing and detailed imaging of octahedral tilt, along with the control of magnetic ground state and spin-orbit occupancies in an artificially engineered heterointerface through the strain manipulation via interface engineering, is the long-standing challenging issue addressed here. We introduce an innovative methodology to measure the projected O-O-O angles (O-O-Oproj) between the neighboring in-plane BO6 octahedra of perovskite oxide (ABO3), demonstrating a precise quantification of strain-manipulated octahedral tilt in atomically engineered LaCoO3 (LCO)/La0.7Sr0.3MnO3 (LSMO) bilayer interfaces. The pronounced octahedral tilt on SrTiO3 (STO) substrate (tensile strain) compared to LaAlO3 (LAO) substrate (compressive strain) correlates to the magnetism especially within the framework of bond angle geometry and spin-charge-orbital reconstructions, contrasting with individual single-phase films. Interfacial orbital reconstruction, Co/Mn antiferromagnetic coupling and their strain manipulation are quantified through X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD) measurements, further confirmed by both molecular orbital theory and Goodenough-Kanamori-Anderson rules. First principles calculations unveil a higher (lower) magnetic moment of individual magnetic atoms with tensile (compressive) strain, including unusual interfacial antiferromagnetism arising d-orbital occupations, and bond angle geometry. This endeavor paves a potential method to manipulate the octahedral tilt to tailor emergent phenomena at heterointerfaces via atomically precise strain-interface engineering
Structural Porosity and Low Mineral Density in Enamel Rods Drive Molar Incisor Hypomineralisation
No full textEnamel – the hardest material in the human body – protects against wear during mastication and resists chemical degradation. In the condition termed molar incisor hypomineralisation (MIH), impaired enamel quality leads to rapid tooth decay, hypersensitivity, and frequent need for early tooth extraction. MIH is highly prevalent in children, affecting ≈14.2% of the global population, yet the mechanisms underlying the accelerated decay and structural breakdown of the enamel crown remain unclear. In this study, comprehensive multiscale material characterization is applied to focal MIH-affected regions and adjacent non-MIH enamel. MIH lesions display reduced mineral content, increased organic content, and micron-scale widening of prism sheaths accompanied by elevated carbon levels. Interrod regions exhibit altered mineral organization compared with enamel rods, resulting in distinct local material properties. These spatially heterogeneous changes appear to facilitate acid penetration and diminish several extrinsic toughening mechanisms that normally enhance enamel resilience. The findings highlight that MIH involves coordinated compositional and microstructural alterations across multiple length scales, underscoring the need for scale-dependent assessment to guide the development of effective preventive and therapeutic strategies
The complex stacking disorder of Fe- and Ru-based 1,1′-(3,6-pyrazabolyl)metallocenes
No full text1,10-(3,6-Pyrazabolyl)ferrocene [Fc(BHpz)2] and the corresponding ruthenocene [Rc(BHpz)2] crystallize as order–disorder (OD) structures with layers of Pma(m) symmetry. Since the m[100] reflection and the a[010] glide reflection planes of adjacent layers do not overlap, given one layer, the adjacent layer can be placed in four distinct, but geometrically equivalent, positions. There are accordingly four polytypes of a maximum degree of order (MDO). One analyzed Fc(BHpz)2 crystal was composed of a mixture of the MDO1 polytype in four distinct orientations and the MDO3 polytype. A second crystal was essentially a single crystal of one out of two orientation of MDO3. In two analyzed crystals of Rc(BHpz)2, the MDO1 polytype (P-1) was the major polytype and was observed in four or two orientation states, respectively. Pronounced diffuse scattering is attributed to a complex disorder, which cannot be explained by simple growth models. One Rc(BHpz)2 crystal features additional peaks in the diffraction pattern attributed to fragments of MDO3
Measurement of the Higgs boson total decay width using the H WW e decay channel in proton-proton collisions at = 13 TeV
No full textThe Higgs boson (H) decay width is determined from the ratio of off- and on-shell production of H WW e using proton-proton collision data corresponding to an integrated luminosity of 138 fb collected at = 13 TeV by the CMS experiment at the LHC. The off-shell signal strength is measured as = 1.2. The Higgs boson total decay width is = 3.9 MeV, in agreement with the standard model prediction. The uncertainty in this result represents a factor of three improvement over the previous CMS result in this decay channel