The extension of Weyl-type relative perturbation bounds

Relative perturbation theory for eigenvalues of Hermitian positive definite matrices has been well-studied, and the major results were later derived analogously for Hermitian non-singular matrices. In this dissertation we extend several relative perturbation results to Hermitian matrices that are potentially singular, and also develop a general class of relative bounds for Hermitian matrices. As a result, corresponding relative bounds for singular values of rank-deficient $m\times n$ matrices are also obtained using related Jordan-Wielandt matrices. We also discuss a comparison between the main relative bound derived and the Weyl's absolute perturbation bound in terms of their sharpness and derivation in practice.Comment: 22 page

Network Characteristics of LEO Satellite Constellations: A Starlink-Based Measurement from End Users

Low Earth orbit Satellite Networks (LSNs) have been advocated as a key infrastructure for truly global coverage in the forthcoming 6G. This paper presents our initial measurement results and observations on the end-to-end network characteristics of Starlink, arguably the largest LSN constellation to date. Our findings confirm that LSNs are a promising solution towards ubiquitous Internet coverage over the Earth; yet, we also find that the users of Starlink experience much more dynamics in throughput and latency than terrestrial network users, and even frequent outages. Its user experiences are heavily affected by environmental factors such as terrain, solar storms, rain, clouds, and temperature, so is the power consumption. We further analyze Starlink's current bent-pipe relay strategy and its limits, particularly for cross-ocean routes. We have also explored its mobility and portability potentials, and extended our experiments from urban cities to wild remote areas that are facing distinct practical and cultural challenges.Comment: 12 pages, 20 figures, to be published in IEEE INFOCOM 202

Highly Crystalline and Semiconducting Imine-Based Two-Dimensional Polymers Enabled by Interfacial Synthesis

Single-layer and multi-layer 2D polyimine films have been achieved through interfacial synthesis methods. However, it remains a great challenge to achieve the maximum degree of crystallinity in the 2D polyimines, which largely limits the long-range transport properties. Here we employ a surfactant-monolayer-assisted interfacial synthesis (SMAIS) method for the successful preparation of porphyrin and triazine containing polyimine-based 2D polymer (PI-2DP) films with square and hexagonal lattices, respectively. The synthetic PI-2DP films are featured with polycrystalline multilayers with tunable thickness from 6 to 200 nm and large crystalline domains (100–150 nm in size). Intrigued by high crystallinity and the presence of electroactive porphyrin moieties, the optoelectronic properties of PI-2DP are investigated by time-resolved terahertz spectroscopy. Typically, the porphyrin-based PI-2DP 1 film exhibits a p-type semiconductor behavior with a band gap of 1.38 eV and hole mobility as high as 0.01 cm2 V−1 s−1, superior to the previously reported polyimine based materials. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Membrane Compression by Synaptic Vesicle Exocytosis Triggers Ultrafast Endocytosis

Compensatory endocytosis keeps the membrane surface area of secretory cells constant following exocytosis. At chemical synapses, clathrin-independent ultrafast endocytosis maintains such homeostasis. This endocytic pathway is temporally and spatially coupled to exocytosis; it initiates within 50 ms at the region immediately next to the active zone where vesicles fuse. However, the coupling mechanism is unknown. Here, we demonstrate that filamentous actin is organized as a ring, surrounding the active zone at mouse hippocampal synapses. Assuming the membrane area conservation is due to this actin ring, our theoretical model suggests that flattening of fused vesicles exerts lateral compression in the plasma membrane, resulting in rapid formation of endocytic pits at the border between the active zone and the surrounding actin-enriched region. Consistent with model predictions, our data show that ultrafast endocytosis requires sufficient compression by exocytosis of multiple vesicles and does not initiate when actin organization is disrupted, either pharmacologically or by ablation of the actin-binding protein Epsin1. Our work suggests that membrane mechanics underlie the rapid coupling of exocytosis to endocytosis at synapses

NeuroBench:A Framework for Benchmarking Neuromorphic Computing Algorithms and Systems

Neuromorphic computing shows promise for advancing computing efficiency and capabilities of AI applications using brain-inspired principles. However, the neuromorphic research field currently lacks standardized benchmarks, making it difficult to accurately measure technological advancements, compare performance with conventional methods, and identify promising future research directions. Prior neuromorphic computing benchmark efforts have not seen widespread adoption due to a lack of inclusive, actionable, and iterative benchmark design and guidelines. To address these shortcomings, we present NeuroBench: a benchmark framework for neuromorphic computing algorithms and systems. NeuroBench is a collaboratively-designed effort from an open community of nearly 100 co-authors across over 50 institutions in industry and academia, aiming to provide a representative structure for standardizing the evaluation of neuromorphic approaches. The NeuroBench framework introduces a common set of tools and systematic methodology for inclusive benchmark measurement, delivering an objective reference framework for quantifying neuromorphic approaches in both hardware-independent (algorithm track) and hardware-dependent (system track) settings. In this article, we present initial performance baselines across various model architectures on the algorithm track and outline the system track benchmark tasks and guidelines. NeuroBench is intended to continually expand its benchmarks and features to foster and track the progress made by the research community

Study on preparation of high performance CaO-MgO-Al2O3-SiO2 system glass-ceramic with industrial by-products

Blast furnace slag (BFS), iron ore tailings (IOT), and coal fly ash (CFA) are common industrial by-products with huge annual yield and low reuse rate (\u3c 30%). This research was intended to prepare high performance glass-ceramics from these three industrial by-products. What\u27s more, two energy saving methods were put forward. One was application of single-stage heat treatment, another was mixing cold solid raw material (IOT, CFA) with melted BFS discharged at 1500 in iron making process instead of mixing all the raw material in room temperature and then heating them to melt. Different binary basicity (MCaO /MSiO2 ) and content of Al2O3 had been studied to determine the best formula for high performance glass-ceramic in terms of mechanical properties. Sample 04 (MCaO /MSiO2 =0.4, Al2O3 wt. %=9%) and Sample 05Al-2 (MCaO /MSiO2 =0.5, Al2O3 wt. %=12%) were found with the highest bending strength, 94 MPa and 89 MPa respectively. In addition, with augite and diopside as primary crystalline phase, they also had a Vickers micro-hardness of 6.2 GPa and 6.3 GPa. When applied single-stage heat treatment, sample H4 obtained a bending strength of 77.89MPa and Vickers micro-hardness of 6.5 GPa, very close to H0. Meanwhile, when applied hot liquid-cold solid mixing method, M3 obtained a bending strength of 80.51 MPa, also very close to M0. Which indicates that these two energy saving method are all feasible to be applied to prepare high performance glass-ceramic

Study on preparation of high performance CaO-MgO-Al2O3-SiO2 system glass-ceramic with industrial by-products

Blast furnace slag (BFS), iron ore tailings (IOT), and coal fly ash (CFA) are common industrial by-products with huge annual yield and low reuse rate (\u3c 30%). This research was intended to prepare high performance glass-ceramics from these three industrial by-products. What\u27s more, two energy saving methods were put forward. One was application of single-stage heat treatment, another was mixing cold solid raw material (IOT, CFA) with melted BFS discharged at 1500 in iron making process instead of mixing all the raw material in room temperature and then heating them to melt. Different binary basicity (MCaO /MSiO2 ) and content of Al2O3 had been studied to determine the best formula for high performance glass-ceramic in terms of mechanical properties. Sample 04 (MCaO /MSiO2 =0.4, Al2O3 wt. %=9%) and Sample 05Al-2 (MCaO /MSiO2 =0.5, Al2O3 wt. %=12%) were found with the highest bending strength, 94 MPa and 89 MPa respectively. In addition, with augite and diopside as primary crystalline phase, they also had a Vickers micro-hardness of 6.2 GPa and 6.3 GPa. When applied single-stage heat treatment, sample H4 obtained a bending strength of 77.89MPa and Vickers micro-hardness of 6.5 GPa, very close to H0. Meanwhile, when applied hot liquid-cold solid mixing method, M3 obtained a bending strength of 80.51 MPa, also very close to M0. Which indicates that these two energy saving method are all feasible to be applied to prepare high performance glass-ceramic

An Engine Exhaust Utilization System by Combining CO₂ Brayton Cycle and Transcritical Organic Rankine Cycle

For engine exhaust gas heat recovery, the organic Rankine cycle (ORC) cannot be directly used due to the thermal stability and safety of organic fluids. Thus, a creative power system is given by integrating the supercritical CO2 Brayton cycle and transcritical ORC. This system can directly utilize the thermal energy of a high-temperature exhaust gas. The inefficiencies in the heat exchangers are highly reduced by using supercritical working fluid. The mathematical model of the system, covering both the thermodynamic and economic aspects, is built in detail. It is found that the highest irreversible loss takes place in the gas heater, taking 21.14% of the total exergy destruction. The ORC turbine and CO2 turbine have the priority for improvement, compared to the compressor and pump. The increase in CO2 turbine inlet pressure improves the system exergy efficiency and levelized cost of energy. Both the larger CO2 and ORC turbine inlet temperatures contribute to a decrease in levelized cost of energy and a rise in system exergy efficiency. There is a maximum value of system exergy efficiency and minimum value of levelized cost of energy by varying the ORC turbine inlet pressure. The determined exergy efficiency and levelized cost of energy in the proposed system are 54.63% and 36.95 USD/MWh after multi-objective optimization

An Engine Exhaust Utilization System by Combining CO2 Brayton Cycle and Transcritical Organic Rankine Cycle

For engine exhaust gas heat recovery, the organic Rankine cycle (ORC) cannot be directly used due to the thermal stability and safety of organic fluids. Thus, a creative power system is given by integrating the supercritical CO2 Brayton cycle and transcritical ORC. This system can directly utilize the thermal energy of a high-temperature exhaust gas. The inefficiencies in the heat exchangers are highly reduced by using supercritical working fluid. The mathematical model of the system, covering both the thermodynamic and economic aspects, is built in detail. It is found that the highest irreversible loss takes place in the gas heater, taking 21.14% of the total exergy destruction. The ORC turbine and CO2 turbine have the priority for improvement, compared to the compressor and pump. The increase in CO2 turbine inlet pressure improves the system exergy efficiency and levelized cost of energy. Both the larger CO2 and ORC turbine inlet temperatures contribute to a decrease in levelized cost of energy and a rise in system exergy efficiency. There is a maximum value of system exergy efficiency and minimum value of levelized cost of energy by varying the ORC turbine inlet pressure. The determined exergy efficiency and levelized cost of energy in the proposed system are 54.63% and 36.95 USD/MWh after multi-objective optimization

Research Progress in the Preparation of Aluminum Foam Composite Structures

Closed-cell aluminum foam has a porous structure and metal properties due to its unique composition. As a structural material, it has the advantages of being lightweight, having a large specific surface area, and having high specific strength and stiffness. As a functional material, it can be used for sound and noise reduction, heat insulation, electromagnetic shielding, damping, and energy absorption, but it also has poor mechanical properties and poor surface flatness, and can be easily corroded. Considering the abovementioned problems, researchers have gradually extended their research on foam materials. Under the research of many international scholars, studies have shifted from simple aluminum foam preparation to improving and optimizing aluminum foam composite structures (AFCSs). From the perspective of development prospects, AFCSs have better application prospects than single aluminum foam. In this paper, the research progress on the preparation technology of AFCSs in recent years was reviewed based on the performance enhancement mechanism of aluminum matrix composites and the structural characteristics of aluminum foam. The morphology and pore structures of closed-cell AFCSs under different preparation methods were summarized. However, due to the limitations of existing experimental conditions, this paper only considered the advantages and disadvantages of AFCS preparation methods. The improvement of AFCS preparation technology, the development of the potential properties of AFCSs, and the promotion of AFCS industrial applications were also considered