Synthesis and cure characterization of high temperature polymers for aerospace applications

The E-beam curable BMI resin systems and phenylethynyl terminated AFR-PEPA-4 oligomer together with an imide model compound N-phenyl-[4-(phenylethynyl) phthalimide] were synthesized and characterized. E-beam exposure cannot propagate the polymerization of BMI system until the temperature goes up to 100oC. However, a small amount of oligomers may be generated from solid-state cure reaction under low E-beam intensity radiation. Higher intensity E-beam at 40 kGy per pass can give above 75% reaction conversion of BMI with thermal cure mechanism involved. NVP is a good reactive diluent for BMI resin. The cure extents of BMI/NVP increase with the increase of the dosage and applied dosage per pass. The reaction rate is much higher at the beginning of the E-beam cure and slows down after 2 dose passes due to diffusion control. Free radical initiator dicumyl peroxide can accelerate the reaction rate at the beginning of E-beam cure reaction but doesnÂt affect final cure conversion very much. According to the results from FT-IR, 200 kGy total dosage E- beam exposure at 10 kGy per pass can give 70% reaction conversion of BMI/NVP with the temperature rise no more than 50oC. The product has a Tg of 180oC. The predicted ultimate Tg of cured AFR-PEPA-4 polyimide is found to be 437.2oC by simulation of DSC Tg as a function of cure. The activation energy of thermal cure reaction of AFR-PEPA-4 oligomer is 142.6 ± 10.0 kJ/mol with the kinetic order of 1 when the reaction conversion is less than 80%. The kinetics analysis of the thermal cure of N-phenyl-[4-(phenylethynyl) phthalimide] was determined by FT-IR spectroscopy by following the absorbance of the phenylethynyl triple bond and conjugated bonds. The thermal crosslinking of N-phenyl-[4-(phenylethynyl) phthalimide] through phenylethynyl addition reaction has a reaction order of 0.95 and an activation energy of 173.5 ± 8.2 kJ/mol. The conjugated bond addition reactions have a lower reaction order of 0.94 and lower activation energy (102.7 ± 15.9 kJ/mol). The cure reaction of N-phenyl-[4-(phenylethynyl) phthalimide] can be described as a fast first-order reaction stage followed by a slow second stage that is kinetically controlled by diffusion

SheetCopilot: Bringing Software Productivity to the Next Level through Large Language Models

Computer end users have spent billions of hours completing daily tasks like tabular data processing and project timeline scheduling. Most of these tasks are repetitive and error-prone, yet most end users lack the skill to automate these burdensome works. With the advent of large language models (LLMs), directing software with natural language user requests become a reachable goal. In this work, we propose a SheetCopilot agent that takes natural language task and control spreadsheet to fulfill the requirements. We propose a set of atomic actions as an abstraction of spreadsheet software functionalities. We further design a state machine-based task planning framework for LLMs to robustly interact with spreadsheets. We curate a representative dataset containing 221 spreadsheet control tasks and establish a fully automated evaluation pipeline for rigorously benchmarking the ability of LLMs in software control tasks. Our SheetCopilot correctly completes 44.3\% of tasks for a single generation, outperforming the strong code generation baseline by a wide margin. Our project page:https://sheetcopilot.github.io/.Comment: Accepted to NeurIPS 202

Endogenous TGF-β activation by reactive oxygen species is key to Foxp3 induction in TCR-stimulated and HIV-1-infected human CD4+CD25- T cells

<p>Abstract</p> <p>Background</p> <p>CD4⁺CD25⁺T regulatory cells (Tregs) play an important role in regulating immune responses, and in influencing human immune diseases such as HIV infection. It has been shown that human CD4⁺CD25⁺Tregs can be induced in vitro by TCR stimulation of CD4⁺CD25^-T cells. However, the mechanism remains elusive, and intriguingly, similar treatment of murine CD4⁺CD25^-cells did not induce CD4⁺CD25⁺Foxp3⁺Tregs unless exogenous TGF-β was added during stimulation. Thus, we investigated the possible role of TGF-β in the induction of human Tregs by TCR engagement. We also explored the effects of TGF-β on HIV-1 infection mediated induction of human Tregs since recent evidence has suggested that HIV-1 infection may also impact the generation of Tregs in infected patients.</p> <p>Results</p> <p>We show here that endogenous TGF-β is key to TCR induction of Foxp3 in human CD4⁺CD25^-T cells. These events involve, first, the production of TGF-β by TCR and CD28 stimulation and the activation of latent TGF-β by reactive oxygen species generated from the activated T cells. Biologically active TGF-β then engages in the induction of Foxp3. Neutralization of active TGF-β with anti-TGF-β antibody or elimination of ROS with MnTBAP abrogated Foxp3 expression. HIV-1 infection enhanced Foxp3 expression in activated CD4⁺CD25^-T cells; which was also abrogated by blockade of endogenous TGF-β.</p> <p>Conclusion</p> <p>Several conclusions can be drawn from this work: (1) TCR and CD28-induced Foxp3 expression is a late event following TCR stimulation; (2) TGF-β serves as a link in Foxp3 induction in human CD4⁺CD25^-T cells following TCR stimulation, which induces not only latent, but also active TGF-β; (3) the activation of TGF-β requires reactive oxygen species; (4) HIV infection results in an increase in Foxp3 expression in TCR-activated CD25^-T cells, which is also associated with TGF-β. Taken together, our findings reinforce a definitive role of TGF-β not only in the generation of Tregs with respect to normal immune responses, but also is critical in immune diseases such as HIV-1 infection.</p

Mining and Predicting Smart Device User Behavior

Three types of user behavior are mined in this paper: application usage, smart device usage and periodicity of user behavior. When mining application usage, the application installation, most frequently used applications and application correlation are analyzed. The application usage is long-tailed. When mining the device usage, the mean, variance and autocorrelation are calculated both for duration and interval. Both the duration and interval are long-tailed but only duration satisfies power-law distribution. Meanwhile, the autocorrelation of both duration and interval is weak, which makes predicting user behavior based on adjacent behavior not so reasonable in related works. Then DFT (Discrete Fourier Transform) is utilized to analyze the periodicity of user behavior and results show that the most obvious periodicity is 24 hours, which is in agreement with related works. Based on the results above, an improved user behavior predicting model is proposed based on Chebyshev inequality. Experiment results show that the performance is good in accurate rate and recall rate

Visual Confusion Label Tree For Image Classification

Convolution neural network models are widely used in image classification tasks. However, the running time of such models is so long that it is not the conforming to the strict real-time requirement of mobile devices. In order to optimize models and meet the requirement mentioned above, we propose a method that replaces the fully-connected layers of convolution neural network models with a tree classifier. Specifically, we construct a Visual Confusion Label Tree based on the output of the convolution neural network models, and use a multi-kernel SVM plus classifier with hierarchical constraints to train the tree classifier. Focusing on those confusion subsets instead of the entire set of categories makes the tree classifier more discriminative and the replacement of the fully-connected layers reduces the original running time. Experiments show that our tree classifier obtains a significant improvement over the state-of-the-art tree classifier by 4.3% and 2.4% in terms of top-1 accuracy on CIFAR-100 and ImageNet datasets respectively. Additionally, our method achieves 124x and 115x speedup ratio compared with fully-connected layers on AlexNet and VGG16 without accuracy decline.Comment: 9 pages, 5 figures, conferenc

Light-Induced Microwave Noise in Superconducting Microwave-Optical Transducers

Microwave-to-optical transducers are integral to the future of superconducting quantum computing, as they would enable scaling and long-distance communication of superconducting quantum processors through optical fiber links. However, optically-induced microwave noise poses a significant challenge in achieving quantum transduction between microwave and optical frequencies. In this work, we study light-induced microwave noise in an integrated electro-optical transducer harnessing Pockels effect of thin film lithium niobate. We reveal three sources of added noise with distinctive time constants ranging from sub-100 nanoseconds to milliseconds. Our results gain insights into the mechanisms and corresponding mitigation strategies for light-induced microwave noise in superconducting microwave-optical transducers, and pave the way towards realizing the ultimate goal of quantum transduction

Influence of air supply velocity on temperature field in the self heating process of coal

The air supply velocity is an important factor affecting the spontaneous combustion of coal. The appropriate air velocity can not only provide the oxygen required for the oxidation reaction, but maintains the good heat storage environment. Therefore, it is necessary to study the influence of the actual air velocity in the pore space on the self-heating process of coal particles. This paper focuses on studying the real space piled up by spherical particles. CFD simulation software is used to establish the numerical model from pore scale. Good fitness of the simulation results with the existing results verifies the feasibility of the calculation method. Later, the calculation conditions are changed to calculate and analyze the velocity field and the temperature field for self-heating of some particles (the surface of the particles is at a certain temperature) and expound the effect of different air supply velocities on gathering and dissipating the heat