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Non-linear magnetotropic susceptibility in FePS3
No full textMagnetotropic susceptibility is the thermodynamic coefficient that maps the curvature of free energy with respect to an applied magnetic field orientation, providing a means to quantify the magnetic anisotropy of a crystal. In this context, non-linear magnetic torque behavior has been reported in FePS3, motivating the investigation of similar non-linear characteristics in its magnetotropic susceptibility. In this work, we derive the non-linear magnetotropic susceptibility expressions for FePS3 in both ac*-and bc*-planes using complementary approaches: by taking the first derivative of torque and through the formal calculation of the magnetotropic susceptibility. Higher-order terms in the magnetization are included, and the final equations are obtained by applying symmetry constraints imposed by the C2h point group of the material. We analyze the behavior of the resulting non-linear expressions and identify the contributions of each parameter. Our theoretical results show good agreement with preliminary, unpublished experimental data, offering meaningful guidance for ongoing and future experimental work
Exploring the probing power of γ Dor's inertial dip for core magnetism: The case of a toroidal field
No full textContext. γ Dor stars are ideal targets for studies of the innermost dynamical properties of stars, due to their rich asteroseismic spectrum of gravity modes. Integrating internal magnetism to the picture appears as the next milestone of detailed asteroseismic studies, for its prime importance on stellar evolution. The inertial dip in prograde dipole modes period-spacing pattern of γ Dors stands out as a unique window on the convective core structure and dynamics. Recent studies have highlighted the dependence of the dip structure on core density stratification, the contrast of the near-core Brunt-Väisälä frequency and rotation rate, as well as the core-to-near-core differential rotation. In addition, the effect of envelope magnetism has been derived on low-frequency magneto-gravito-inertial waves.
Aims. We revisited the inertial dip formation including core and envelope magnetism, and explored the probing power of this feature on dynamo-generated core fields.
Methods. We considered as a first step a toroidal magnetic field with a bi-layer (core and envelope) Alfvén frequency. This configuration allowed us to revisit the coupling problem using our knowledge on both core magneto-inertial modes and envelope magneto-gravito-inertial modes. Using this configuration, we were able to stay in an analytical framework to exhibit the magnetic effects on the inertial dip shape and location. This configuration allowed a laboratory to be set up that moves us towards the comprehension of magnetic effects on the dip structure.
Results. We show a shift of the inertial dip towards lower spin parameter values and a thinner dip with increasing core magnetic field’s strength, quite similar to the signature of differential rotation. The magnetic effects become sizeable when the ratio of the magnetic to the Coriolis effects is high enough. We explored the potential degeneracy of the magnetic effects with differential rotation. We studied the detectability of core magnetism, considering both observational constraints on the periods of the modes and potential gravito-inertial mode suppression
No Time for Surface Charge: How Bulk Conductivity Hides Charge Patterns from Kelvin Probe Force Microscopy in Contact-Electrified Surfaces
No full textIncludes all data and Python code needed to reproduce figures for the publication: No Time for Surface Charge: How Bulk Conductivity Hides Charge Patterns from Kelvin Probe Force Microscopy in Contact-Electrified Surfaces
Transiting planetary debris near the Roche limit of a white dwarf on a 4.97 hr orbit—and its vanishing
No full textWe present the discovery of deep, irregular, periodic transits toward the white dwarf ZTF J1944+4557 using follow-up time-series photometry and spectroscopy from Palomar, Keck, McDonald, Perkins, and Lowell observatories. We find a predominant period of 4.9704 hr, consistent with an orbit near the Roche limit of the white dwarf, with individual dips over 30% deep and lasting between 15 and 40 minutes. Similar to the first known white dwarf with transiting debris, WD 1145+017, the transit events are well-defined with prominent out-of-transit phases where the white dwarf appears unobscured. Spectroscopy concurrent with transit photometry reveals that the average Ca K equivalent width remains constant in and out of transit. The broadening observed in several absorption features cannot be reproduced by synthetic photospheric models, suggesting the presence of circumstellar gas. Simultaneous g + r- and g + i-band light curves from the CHIMERA instrument reveal no color dependence to the transit depths, requiring transiting dust grains to have sizes s ≳ 0.2 μm. The transit morphologies appear to be constantly changing at a rate faster than the orbital period. Overall transit activity varies in the system, with transit features completely disappearing during the seven months between our 2023 and 2024 observing seasons and then reappearing in 2025 March, still repeating at 4.9704 hr. Our observations of the complete cessation and resumption of transit activity provide a novel laboratory for constraining the evolution of disrupted debris and processes like disk exhaustion and replenishment timescales at white dwarfs
Scalable multitemperature free energy sampling of classical Ising spin states
No full textGenerative models have advanced significantly in sampling material systems with continuous variables, such as atomistic structures. However, their application to discrete variables, like atom types or spin states, remains underexplored. In this work, we introduce a discrete flow matching model, tailored for systems with discrete phase-space coordinates (e.g., the Ising model or a multicomponent system on a lattice). This approach enables a single model to sample free energy surfaces over a wide temperature range with minimal training overhead, and the model generation is scalable to larger lattice sizes than those in the training set. We demonstrate our approach on the 2D Ising model, showing efficient and reliable free energy sampling. These results highlight the potential of flow matching for low-cost, scalable free energy sampling in discrete systems and suggest promising extensions to alchemical degrees of freedom in crystalline materials. The codebase developed for this work is openly available at https://github.com/tuoping/alchemicalFES
Mitigating the rock-salt phase transformation in disordered LNMO through synergetic solid-state AlF3/LiF modifications
No full textHigh-voltage disordered spinel LiNi0.5Mn1.5O4 is a promising cathode material for high power density in lithium-ion batteries. However, it suffers from poor cycle life associated with the rock-salt phase transformation. This study presents a straightforward synthesis approach to enhance the electrochemical performance of LiNi0.5Mn1.5O4 through a synergistic solid-state modification with LiF and AlF3. This dual modification promotes rapid Li⁺ diffusion, enables near-complete delithiation/lithiation, approaching the theoretical capacity of disordered LiNi0.5Mn1.5O4, and, more importantly, effectively mitigates the formation of the rock-salt phase, thereby enhancing structural stability, as confirmed by operando X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (SXRD). As a result, the optimized LiNi0.5Mn1.5O4 (10 mg AlF3 + 30 mg LiF) delivers high reversible capacities of 142.1, 139.1, 129.2, 121.6, 110.3, 93.5, and 76.1 mAh∙g−1 at 0.2C, 0.5C, 1.0C, 2.0C, 3.0C, 4.0C, and 5.0C, respectively. Full cells using graphite as the anode and a high-loading cathode exhibit excellent cycling performance. They retain 80% of their capacity after 200 cycles at 0.5C within a voltage window of 3.5–4.9 V with cathode loading of 11 mg∙cm−2. The findings of this study will significantly advance high-power LiNi0.5Mn1.5O4 materials, offering improved battery life and thereby enhancing their potential for practical applications
Class numbers and integer points on some Pellian surfaces
No full textWe provide an estimate for the number of nontrivial integer points on the Pellian surface t^2 - du^2 = 1 in a bounded region. We give a lower bound on the size of fundamental solutions for almost all d in a certain class, based on a recent conjecture of Browning and Wilsch about integer points on log K3 surfaces. We also obtain an upper bound on the average of class number in this class, assuming the same conjecture.Nous donnons une estimation du nombre de points entiers non triviaux sur la surface pellienne
t^2 - du^2 = 1 dans une région bornée. Nous établissons une borne inférieure pour la taille des solutions fondamentales pour presque tout d appartenant à une certaine classe, en nous fondant sur une conjecture récente de Browning et Wilsch concernant les points entiers sur les surfaces log K3. Nous obtenons également une borne supérieure pour la moyenne du nombre de classes dans cette classe, sous la même hypothèse conjecturale
ISTA Thesis
No full textThis thesis deals with eigenvalue and eigenvector universality results for random matrix ensembles equipped with non-trivial spatial structure. We consider both mean-field models with a general variance profile (Wigner-type matrices) and correlation structure (correlated matrices) among the entries, as well as non-mean-field random band matrices with bandwidth W >> N^(1/2).
To extract the universal properties of random matrix spectra and eigenvectors, we obtain concentration estimates for their resolvent, the local laws, which generalize the celebrated Wigner semicircle law for a broad class of random matrices to much finer spectral scales. The local laws hold for both a single resolvent as well as for products of multiple resolvents, known as resolvent chains, and express the remarkable approximately-deterministic behavior of these objects down to the microscopic scale.
Our primary tool for establishing the local laws is the dynamical Zigzag strategy, which we develop in the setting of spatially-inhomogeneous random matrices. Our proof method systematically addresses the challenges arising from non-trivial spatial structures and is robust to all types of singularities in the spectrum, as we demonstrate in the correlated setting. Furthermore, we incorporate the analysis of the deterministic resolvent chain approximations into the dynamical framework of the Zigzag strategy, synthesizing a unified toolkit for establishing multi-resolvent local laws.
Using these methods, we prove complete eigenvector delocalization, the Eigenstate Thermalization Hypothesis, and Wigner-Dyson universality in the bulk for random band matrices down to the optimal bandwidth W >> N^(1/2). For mean-field ensembles, we establish universality of local eigenvalue statistics at the cups for random matrices with correlated entries, and the Eigenstate Thermalization Hypothesis for Wigner-type matrices in the bulk of the spectrum.
Finally, this thesis also contains other applications of the multi-resolvent local laws to spatially-inhomogeneous random matrices, obtained prior to the development of the Zigzag strategy. In particular, we provide a complete analysis of mesoscopic linear-eigenvalue statistics of Wigner-type matrices in all spectral regimes, including the novel cusps, and rigorously establish the prethermalization phenomenon for deformed Wigner matrices.
The main body of this thesis consists of seven research papers (listed on page xi), each presented in a separate chapter with its own introduction and all relevant context, suitable to be read independently. We ask the reader’s indulgence for the repetitions in the historical overviews and other minor redundancies that remain among the chapters as a result. The overall Introduction, preceding the chapters, provides a condensed, informal summary of the main ideas and concepts at the core of these works
Projecting the morbidity burden of mental and behavioral disorders associated with increasing humid heat in Shanghai
No full textResidents of low-latitude megacities face growing vulnerability to humid-heat stress under urbanization and global warming, yet limited research has assessed the morbidity burden of mental and behavioral disorders (MBDs) linked to humid-heat exposures in these cities. Here we quantify the hospital admissions of MBDs in Shanghai, a megacity of over 25 million inhabitants, attributable to humid heat, and project future burdens under various greenhouse gas (GHG)-emission and population scenarios. Humid heat drives a higher morbidity burden than high temperature alone, especially in humid-heat nights. Without population change, the humid-heat-related morbidity burden of MBDs would increase by 68.2% (95% empirical confidence interval 56.7%–81.6%) under the highest-GHG-emission scenario by the 2090s, while 8,465 (95% empirical confidence interval 6,928–10,053) cases would be avoided by reducing emissions to the lowest pathway. With projected population decline, the attributable hospital admissions will decrease toward century’s end. These findings highlight the benefit of GHG mitigation in reducing the growing MBD risks posed by extreme humid heat
‘Mini analysis’ misrepresents changes in synaptic properties due to incomplete event detection
No full textPatch-clamp recording of miniature postsynaptic currents (mPSCs, or ‘minis’) is used extensively to investigate the functional properties of synapses. With this approach, spontaneous synaptic transmission events are recorded in an attempt to determine quantal synaptic parameters or the effect of synaptic manipulations. However, at the majority of brain synapses these events are small, with many undetectable due to recording noise. The effects of incomplete detection were well appreciated in the early years of synaptic physiology analysis, but appear to be increasingly forgotten. Here we sought to characterise the consequences of incomplete detection on the interpretability of mini analysis, using simulated mPSC data to give full control over event parameters. We demonstrate that commonly reported measures such as mean event amplitude and frequency, are misrepresented by the loss of undetected events. Probabilistic loss of small events results in detected event amplitude distributions that appear biologically complete, yet do not reflect the underlying synaptic properties. With both simulated and experimental datasets, we demonstrate that specific changes in event amplitude are primarily detected as changes in frequency, compromising classical biological interpretations. To facilitate more robust data analysis and interpretation, we detail a means for experimental estimation of the event detection limit and provide practical recommendations for data analysis. Together, our study highlights how mini analysis is prone to falsely reporting synaptic changes, raising awareness of these considerations, and provides a framework for more robust data analysis and interpretation