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With the increasing integration of inverter-based resources into the power grid, there has been a notable reduction in system inertia, potentially compromising frequency stability. To assess the suitability of existing area inertia estimation techniques for real-world power systems, this paper presents a rigorous comparative analysis of system identification, measurement reconstruction, and electromechanical oscillation-based area inertia estimation methodologies, specifically applied to the large-scale and multi-area WECC 240-bus power system. Comprehensive results show that the system identification-based approach exhibits superior robustness and accuracy relative to its counterparts.

Due to the rising privacy concerns on sensitive client data and trained models like Transformers, secure multi-party computation (MPC) techniques are employed to enable secure inference despite attendant overhead. Existing works attempt to reduce the overhead using more MPC-friendly non-linear function approximations. However, the integration of quantization widely used in plaintext inference into the MPC domain remains unclear. To bridge this gap, we propose the framework named Ditto to enable more efficient quantization-aware secure Transformer inference. Concretely, we first incorporate an MPC-friendly quantization into Transformer inference and employ a quantization-aware distillation procedure to maintain the model utility. Then, we propose novel MPC primitives to support the type conversions that are essential in quantization and implement the quantization-aware MPC execution of secure quantized inference. This approach significantly decreases both computation and communication overhead, leading to improvements in overall efficiency. We conduct extensive experiments on Bert and GPT2 models to evaluate the performance of Ditto. The results demonstrate that Ditto is about $3.14\sim 4.40\times$ faster than MPCFormer (ICLR 2023) and $1.44\sim 2.35\times$ faster than the state-of-the-art work PUMA with negligible utility degradation., Comment: to be published in ICML 2024

In this paper, we investigate the well-posedness and ill-posedness issues for the incompressible stationary Hall-magnetohydrodynamic (Hall-MHD) system in $\mathbb{R}^3.$ We first show the existence and uniqueness of solutions provided with the forces in $\dot B^{3/p-3}_{p,r}(\mathbb{R}^3)$ for $1\leq p <3$ and $r=1$. Moreover, this result can be extended to any $1\leq r\leq \infty$ whenever $p=2,$ without any additional assumption on the physical parameters. On the other hand, we establish some ill-posedness results for Hall-MHD system by using the discontinuity of the solution mapping of the three-dimensional stationary Navier-Stokes equations in \emph{critical} function spaces $\dot{B}^{3/p-1}_{p,r}(\mathbb{R}^3)$ ($p\geq 3$)., Comment: 22 pages

The deposition and intercalation of metal atoms can induce superconductivity in monolayer and bilayer graphenes. For example, it has been experimentally proved that Li-deposited graphene is a superconductor with critical temperature $T_{c}$ of 5.9 K, Ca-intercalated bilayer graphene C$_{6}$CaC$_{6}$ and K-intercalated epitaxial bilayer graphene C$_{8}$KC$_{8}$ are superconductors with $T_{c}$ of 2-4 K and 3.6 K, respectively. However, the $T_{c}$ of them are relatively low. To obtain higher $T_{c}$ in graphene-based superconductors, here we predict a new Ca-intercalated bilayer graphene C$_{2}$CaC$_{2}$, which shows higher Ca concentration than the C$_{6}$CaC$_{6}$. It is proved to be thermodynamically and dynamically stable. The electronic structure, electron-phonon coupling (EPC) and superconductivity of C$_{2}$CaC$_{2}$ are investigated based on first-principles calculations. The EPC of C$_{2}$CaC$_{2}$ mainly comes from the coupling between the electrons of C-$p_{z}$ orbital and the high- and low-frequency vibration modes of C atoms. The calculated EPC constant $\lambda$ of C$_{2}$CaC$_{2}$ is 0.75, and the superconducting $T_{c}$ is 18.9 K, which is much higher than other metal-intercalated bilayer graphenes. By further applying -4\% biaxial compressive strain to C$_{2}$CaC$_{2}$, the $T_{c}$ can be boosted to 26.6 K. Thus, the predicted C$_{2}$CaC$_{2}$ provides a new platform for realizing superconductivity with the highest $T_{c}$ in bilayer graphenes., Comment: 29 pages,11 figures

We investigate the global-in-time existence and uniqueness of weak solutions for a family of equations introduced by Moffatt to model magnetic relaxation. These equations are topology-preserving and admit all stationary solutions to the classical incompressible Euler equations as steady states. In the work of Beekie, Friedlander and Vicol, global regularity results have been established for initial magnetic field B0 $\in$ Hs(Td)(s > d/2+1) when the regularization parameter $\gamma$ in the equations satisfies $\gamma$ > $\gamma$c := d/2+1. Global regularity for $\gamma$ $\in$ [0, $\gamma$c] is left as an open problem, as well as the existence of weak solutions with rough initial data for any $\gamma$ $\ge$ 0. In this paper, we show that for any solenoidal magnetic field B0 $\in$ L2(Td) there exists a unique global weak solution when $\gamma$ > $\gamma$c. Moreover, the solution can propagate higher-order Sobolev regularity. These results hold true for the borderline case $\gamma$ = $\gamma$c only if B0 $\in$ L2+(Td). Finally, we discuss Moffatt's magnetic relaxation procedure.To prove the existence and uniqueness of weak solutions, we establish a key compactness result for an active vector equation and provide some estimates for fractional Laplacian after the Lagrangian change of variables, which may have independent interest.

We present Neural Signal Operated Intelligent Robots (NOIR), a general-purpose, intelligent brain-robot interface system that enables humans to command robots to perform everyday activities through brain signals. Through this interface, humans communicate their intended objects of interest and actions to the robots using electroencephalography (EEG). Our novel system demonstrates success in an expansive array of 20 challenging, everyday household activities, including cooking, cleaning, personal care, and entertainment. The effectiveness of the system is improved by its synergistic integration of robot learning algorithms, allowing for NOIR to adapt to individual users and predict their intentions. Our work enhances the way humans interact with robots, replacing traditional channels of interaction with direct, neural communication. Project website: https://noir-corl.github.io/.

In the well-known book of Lions [{\em Mathematical topics in fluid mechanics. Incompressible models}, 1996], global existence results of finite energy weak solutions of the inhomogeneous incompressible Navier-Stokes equations (INS) were proved without assuming positive lower bounds on the initial density, hence allowing for vacuum. Uniqueness, regularity and persistence of boundary re\-gularity of density patches were listed as open problems. A breakthrough on Lions' problems was recently made by Danchin and Mucha [The incompressible Navier-Stokes equations in vacuum, {\em Comm. Pure Appl. Math.}, 72 (2019), 1351--1385] in the case where the fluid domain is either bounded or the torus. However, the case of unbounded domains was left open because of the lack of Poincar\'{e}-type inequalities. In this paper, we obtain regularity and uniqueness of Lions' weak solutions for (INS) with \emph{only bounded and nonnegative initial density} and additional regularity only assumed for the initial velocity, in the whole-space case $\mathbb R^d$, $d=2$ or $3$. In particular, our result allows us to study the evolution of a vacuum bubble embedded in an incompressible fluid, as well as a patch of a homogeneous fluid embedded in the vacuum, which provides an answer to Lions' question in the whole-space case., Comment: 45 pages, 1 figure

With ChatGPT as a representative, tons of companies have began to provide services based on large Transformers models. However, using such a service inevitably leak users' prompts to the model provider. Previous studies have studied secure inference for Transformer models using secure multiparty computation (MPC), where model parameters and clients' prompts are kept secret. Despite this, these frameworks are still limited in terms of model performance, efficiency, and deployment. To address these limitations, we propose framework PUMA to enable fast and secure Transformer model inference. Our framework designs high quality approximations for expensive functions such as GeLU and softmax, and significantly reduce the cost of secure inference while preserving the model performance. Additionally, we design secure Embedding and LayerNorm procedures that faithfully implement the desired functionality without undermining the Transformer architecture. PUMA is about $2\times$ faster than the state-of-the-art framework MPCFORMER(ICLR 2023) and has similar accuracy as plaintext models without fine-tuning (which the previous works failed to achieve). PUMA can even evaluate LLaMA-7B in around 5 minutes to generate 1 token. To our best knowledge, this is the first time that a model with such a parameter size is able to be evaluated under MPC. PUMA has been open-sourced in the Github repository of SecretFlow-SPU.

The last decade has witnessed the emergence of hydrovoltaic technology, which can harvest electricity from different forms of water movement, such as raindrops, waves, flows, moisture, and natural evaporation. In particular, the evaporation-induced hydrovoltaic effect received great attention since its discovery in 2017 due to its negative heat emission property. Nevertheless, the influence of electrode reactions in evaporation-induced power generation is not negligible due to the chemical reaction between active metal electrodes and water, which leads to " exceptional " power generation. Herein, we designed a series of experiments based on air-laid paper devices with electrodes of different activities as the top and bottom electrodes. To verify the contribution of electrodes, we compared the output performance of different electrode combinations when the device is partially-wetted and fully-wetted. The device hydrophilicity, salt concentration, and acidity or basicity of solutions are also comprehensively investigated. It is demonstrated that the chemical reaction of active metals (Zn, Cu, Ag, etc.) with different aqueous solutions can generate considerable electrical energy and significantly distort the device performance, especially for Zn electrodes with an output voltage from ~1.26 to ~1.52 V and current from ~1.24 to ~75.69 {\mu}A. To promote the long-term development of hydrovoltaic technology, we recommend use of inert electrodes in hydrovoltaic studies, such as Au and Pt, especially in water and moisture environment.

In heavy quark limit, the lowest-lying charmed baryons with two light quarks can form an SU(3) triplet and sextet. The $\Xi_c$ in the SU(3) triplet and $\Xi_c'$ in the sextet have the same $J^{PC}$ quantum number and can mix due to the finite charm quark mass and the fact the strange quark is heavier than the up/down quark. We explore the $\Xi_c$-$\Xi_c'$ mixing by calculating the two-point correlation functions of the $\Xi_c$ and $\Xi_c'$ baryons from lattice QCD. Based on the lattice data, we adopt two independent methods to determine the mixing angle between $\Xi_c$ and $\Xi_c'$. After making the chiral and continuum extrapolation, it is found that the mixing angle $\theta$ is $1.2^{\circ}\pm0.1^{\circ}$, which seems insufficient to account for the large SU(3) symmetry breaking effects found in weak decays of charmed baryons.

Inspired by an open question by Chemin and Zhang about the regularity of the 3D Navier-Stokes equations with one initially small component, we investigate symmetry breaking and symmetry preservation. Our results fall in three classes. First we prove strong symmetry breaking. Specifically, we demonstrate third component norm inflation (3rdNI) and Isotropic Norm Inflation (INI) starting from zero third component. Second we prove symmetry breaking for initially zero third component, even in the presence of a favorable initial pressure gradient. Third we study certain symmetry preserving solutions with a shear flow structure. Specifically, we give applications to the inviscid limit and exhibit explicit solutions that inviscidly damp to the Kolmogorov flow., Comment: Theorem added regarding isotropic norm inflation. Updated the introduction and acknowledgements. 33 pages, 2 figures

This letter discusses the 18-20 Hz oscillation event at 05:30 am on November 21, 2021, in Kaua`i's power system following the trip of an oil power plant. As far as the authors are aware, this is the first report of a transmission system-wide subsynchronous oscillation driven by inverter-based resources (though the system in question is relatively small). In this letter, we leverage two data-based methods-the dissipating energy flow method and the sub/super-synchronous power flow method-to locate the sources of the oscillation. Also, we build an electromagnetic transient model of the Kaua`i power system and replay the 18-20 Hz oscillation. Finally, we propose two mitigation methods and validate their effectiveness via numerical simulation.

Secure multi-party computation (MPC) enables computation directly on encrypted data and protects both data and model privacy in deep learning inference. However, existing neural network architectures, including Vision Transformers (ViTs), are not designed or optimized for MPC and incur significant latency overhead. We observe Softmax accounts for the major latency bottleneck due to a high communication complexity, but can be selectively replaced or linearized without compromising the model accuracy. Hence, in this paper, we propose an MPC-friendly ViT, dubbed MPCViT, to enable accurate yet efficient ViT inference in MPC. Based on a systematic latency and accuracy evaluation of the Softmax attention and other attention variants, we propose a heterogeneous attention optimization space. We also develop a simple yet effective MPC-aware neural architecture search algorithm for fast Pareto optimization. To further boost the inference efficiency, we propose MPCViT+, to jointly optimize the Softmax attention and other network components, including GeLU, matrix multiplication, etc. With extensive experiments, we demonstrate that MPCViT achieves 1.9%, 1.3% and 3.6% higher accuracy with 6.2x, 2.9x and 1.9x latency reduction compared with baseline ViT, MPCFormer and THE-X on the Tiny-ImageNet dataset, respectively. MPCViT+ further achieves a better Pareto front compared with MPCViT. The code and models for evaluation are available at https://github.com/PKU-SEC-Lab/mpcvit., Comment: Accepted by ICCV 2023 conference

In this paper we investigate two types of relaxation processes quantitatively in the context of small data global-in-time solutions for compressible one-velocity multi-fluid models. First, we justify the pressure-relaxation limit from a one-velocity Baer-Nunziato system to a Kapila model as the pressure-relaxation parameter tends to zero, in a uniform manner with respect to the time-relaxation parameter associated to the friction forces modeled in the equation of the velocity. This uniformity allows us to further consider the time-relaxation limit for the Kapila model. More precisely, we show that the diffusely time-rescaled solution of the Kapila system converges to the solution of a two-phase porous media type system as the time-relaxation parameter tends to zero. For both relaxation limits, we exhibit explicit convergence rates. Our proof of existence results are based on an elaborate low-frequency and high-frequency analysis via the Littlewood-Paley decomposition and it includes three main ingredients: a refined spectral analysis for the linearized problem to determine the threshold of frequencies explicitly in terms of the time-relaxation parameter, the introduction of an effective flux in the low-frequency region to overcome the loss of parameters due to the overdamping phenomenon, and the renormalized energy estimates in the high-frequency region to cancel higher-order nonlinear terms. To show the convergence rates, we discover several auxiliary unknowns that reveal better structures. In conclusion, our approach may be applied to a class of non-symmetric partially dissipative hyperbolic system with rough coefficients which do not have any time-integrability, in the context of overdamping phenomenon. It extends the latest results of Danchin and the first author [15, 16].

Understanding of the complex mechanical behavior of metal-organic frameworks (MOF) beyond their elastic limit will allow the design of real-world applications in chemical engineering, optoelectronics, energy conversion apparatus, and sensing devices. Through in situ compression of micropillars, the uniaxial stress-strain curves of a copper paddlewheel MOF (HKUST-1) were determined along two unique crystallographic directions, namely the (100) and (111) facets. We show strongly anisotropic elastic response where the ratio of the Young's moduli are E(111) ~ 3.6 x E(100), followed by extensive plastic flows. Likewise, the yield strengths are considerably different, in which Y(111) ~ 2 x Y(100) because of the underlying framework anisotropy. We measure the fracture toughness using micropillar splitting. While in situ tests revealed differential cracking behavior, the resultant toughness values of the two facets are comparable, yielding Kc ~ 0.5 MPa m^1/2. This work provides new insights of porous framework ductility at the micron scale and failure by bonds breakage., Comment: 20 pages, 4 figures, Supplementary Information

Luminescent metal-organic frameworks (LMOFs) are promising materials for organic light-emitting diode (OLED) alternatives to silicate-based LEDs due to their tuneable structure and programmability. Yet, the 3D nature of LMOFs creates challenges for stability, optical transparency, and device integration. Metal-organic nanosheets (MONs) potentially overcome these limitations by combining the benefits of MOFs with an atomically thin morphology of large planar dimensions. Here, we report the bottom-up synthesis of atomically thin ZIF-7-III MONs via facile low-energy salt-templating. Employing guest@MOF design, the fluorophores Rhodamine B and Fluorescein were intercalated into ZIF-7 nanosheets (Z7-NS) to form light emissive systems exhibiting intense and highly photostable fluorescence. Aggregation and F\"orster resonance energy transfer, enabled by the MON framework, were revealed as the mechanisms behind fluorescence. By varying guest concentration, these mechanisms provided predictable quantified control over emission chromaticity of a dual-guest Z7-NS material and the definition of an 'emission chromaticity fingerprint' - a unique subset of the visible spectrum which a material can emit by fluorescence., Comment: 27 Pages, 7 Figures, Supplementary Information

Monolithic metal-organic frameworks (MOFs) represent a promising solution for the industrial implementation of this emerging class of multifunctional materials, due to their structural stability. When compared to MOF powders, monoliths exhibit other intriguing properties like hierarchical porosity, that significantly improves volumetric adsorption capacity. The mechanical characterization of MOF monoliths plays a pivotal role in their industrial expansion, but so far, several key aspects remain unclear. In particular, the fracture behavior of MOF monoliths has not been explored. In this work, we studied the initiation and propagation of cracks in four prototypical MOF monoliths, namely ZIF-8, HKUST-1, MIL-68 and MOF-808. We observed that shear faults inside the contact area represent the main failure mechanism of MOF monoliths and are the source of radial cracks. MIL-68 and MOF-808 showed a remarkably high resistance to cracking, which can be ascribed to their consolidated nanostructure., Comment: 15 pages, 5 figures, Supporting Information

Organic photoswitchable molecules have struggled in solid state form to fulfill their remarkable potential, in terms of photoswitching performance and long-term stability when compared to their inorganic counterparts. We report the concept of non-electron deficient host's surface with optimal porosity and hydrophobicity, as a priori strategy to design photoefficient organic solid-state photochromic materials with outstanding mechanical robustness. When exposed to a light stimulus including natural sunlight, the photoswitchable nanocomposite changes color promptly and reversibly, in a matter of seconds along with excellent photo-fatigue resistance, which are on a par with inorganic photochromes. Exemplars of commercially viable prototypes that are optically clear, comprising smart windows, complex photochromic sculptures, and self-erasing rewritable devices, were engineered by direct blending with resilient polymers; particularly, the use of high-stiffness polymer (> 2 GPa) is no longer an insurmountable challenge. Finally, photochromic films with anticounterfeiting features could be manufactured through precision inkjet printing of nanocrystals., Comment: 12 pages, 5 figures, Supplementary Information

With more inverter-based resources (IBRs), our power systems have lower frequency nadirs following N-1 contingencies, and undesired under-frequency load shedding (UFLS) can occur. To address this challenge, IBRs can be programmed to provide at least three types of fast frequency response (FFR), e.g., step response, proportional response (P/f droop response), and derivative response (synthetic inertia). However, these heterogeneous FFR challenge the study of power system frequency dynamics. Thus, this paper develops an analytical frequency nadir prediction method that allows for the consideration of all three potential forms of FFR provided by IBRs. The proposed method provides fast and accurate frequency nadir estimation after N-1 generation tripping contingencies. Our method is grounded on the closed-form solution for the frequency nadir, which is solved from the second-order system frequency response model considering the governor dynamics and three types of FFR. The simulation results in the IEEE 39-bus system with different types of FFR demonstrate that the proposed method provides an accurate and fast prediction of the frequency nadir under various disturbances.

Ultra-sensitive and highly selective iodine gas sensors play a crucial role during the nuclear radiation leak for a timely detection and mitigation of pollution, ensuring the safety of a vast number of operators and subsequent integrity of the facility. Herein, we rationally designed a metal-organic framework (MOF) that exhibits an outstanding performance with an almost billion-fold enhancement in the electrical response due to its optimized hydrophobicity, which allows the easy migration of iodine molecules though the channels and the presence of suitable interaction sites, temporarily anchoring the target molecule for ultra-trace sensing. The prototype sensor tested in demanding environments demonstrates its high selectivity, ultra-trace parts per billion (ppb)-level sensitivity, good reversibility, and a very fast response time even at high frequencies compared to existing adsorbents, including commercially available materials. Further, the iodine sensing at the atomic level was studied in detail by measuring the electrical response of a single crystal and, the optimal thickness of the MOF layer was identified for an industrially-viable prototype sensor by using inkjet printing. In a wider perspective, we propose a general strategy towards electrically efficient sensing materials with hybrid functionalities for engineering high-sensitivity iodine sensors for a safe and sustainable future., Comment: 14 Pages, 5 Figures, 1 Supporting Information (32 pages)