In this work, we propose MUSTACHE, a new page cache replacement algorithm whose logic is learned from observed memory access requests rather than fixed like existing policies. We formulate the page request prediction problem as a categorical time series forecasting task. Then, our method queries the learned page request forecaster to obtain the next $k$ predicted page memory references to better approximate the optimal B\'el\'ady's replacement algorithm. We implement several forecasting techniques using advanced deep learning architectures and integrate the best-performing one into an existing open-source cache simulator. Experiments run on benchmark datasets show that MUSTACHE outperforms the best page replacement heuristic (i.e., exact LRU), improving the cache hit ratio by 1.9% and reducing the number of reads/writes required to handle cache misses by 18.4% and 10.3%.

事实证明，图形神经网络（GNN）在图形结构数据的几个预测建模任务中已被证明。在这些任务中，链接预测是许多现实世界应用（例如推荐系统）的基本问题之一。但是，GNN不能免疫对抗攻击，即精心制作的恶意例子，旨在欺骗预测模型。在这项工作中，我们专注于对基于GNN的链接预测模型进行特定的白盒攻击，其中恶意节点的目的是出现在给定目标受害者的推荐节点列表中。为了实现这一目标，攻击者节点还可以指望它直接控制的其他现有同伴的合作，即在网络中注入许多``vicious''节点的能力。具体而言，所有这些恶意节点都可以添加新的边缘或删除现有的节点，从而扰乱原始图。因此，我们提出了野蛮人，一种新颖的框架和一种安装这种链接预测攻击的方法。野蛮人将对手的目标制定为一项优化任务，从而达到了攻击的有效性与所需的恶意资源的稀疏之间的平衡。在现实世界和合成数据集上进行的广泛实验表明，通过野蛮人实施的对抗性攻击确实达到了很高的攻击成功率，但使用少量恶性节点。最后，尽管这些攻击需要完全了解目标模型，但我们表明它们可以成功地转移到其他黑框方法以进行链接预测。

最近，图形神经网络（GNN）已被广泛用于开发成功的推荐系统。尽管功能强大，但基于GNN的建议系统很难附上明显的解释，说明为什么特定项目最终在给定用户的建议列表中。确实，解释基于GNN的建议是独特的，而现有的GNN解释方法是不合适的，原因有两个。首先，传统的GNN解释方法是为节点，边缘或图形分类任务而不是排名而设计的，如推荐系统中。其次，标准的机器学习解释通常旨在支持熟练的决策者。相反，建议是为任何最终用户设计的，因此应以用户理解的方式提供其解释。在这项工作中，我们提出了润滑脂，这是一种新的方法，用于解释任何基于黑盒GNN的建议系统提供的建议。具体而言，Grease首先在目标用户项目对及其$ L $ -HOP社区上训练替代模型。然后，它通过找到最佳的邻接矩阵扰动来捕获足够和必要的条件，分别推荐一个项目，从而生成事实和反事实解释。在现实世界数据集上进行的实验结果表明，油脂可以为流行的基于GNN的推荐模型产生简洁有效的解释。

反事实示例（CFS）是将事后解释附加到机器学习（ML）模型的最流行方法之一。但是，现有的CF生成方法要么利用特定模型的内部或取决于每个样本的邻域，因此很难对复杂模型进行推广，并且对于大型数据集而言效率低下。这项工作旨在克服这些局限性并引入放松身心，这是一种模型不足的算法，旨在生成最佳的反事实解释。具体而言，我们制定了将CFS作为顺序决策任务的问题，然后通过深入加固学习（DRL）使用离散连续的混合动作空间找到最佳CFS。在几个表格数据集上进行的广泛实验表明，放松胜过现有的CF生成基线，因为它会产生更稀疏的反事实，更可扩展到复杂的目标模型以解释，并且可以概括地分类和回归任务。最后，为了证明我们方法在现实世界中的用例中的有用性，我们利用了Rase产生的CFS来建议一个国家应采取的行动，以减少COVID-19引起的死亡风险。有趣的是，我们的方法推荐的行动与许多国家实际实施的策略相对应，以对抗COVID-19-19的大流行。

Diffusion models have achieved justifiable popularity by attaining state-of-the-art performance in generating realistic objects from seemingly arbitrarily complex data distributions, including when conditioning generation on labels. Unfortunately, however, their iterative nature renders them very computationally inefficient during the sampling process. For the multi-class conditional generation problem, we propose a novel, structurally unique framework of diffusion models which are hierarchically branched according to the inherent relationships between classes. In this work, we demonstrate that branched diffusion models offer major improvements in efficiently generating samples from multiple classes. We also showcase several other advantages of branched diffusion models, including ease of extension to novel classes in a continual-learning setting, and a unique interpretability that offers insight into these generative models. Branched diffusion models represent an alternative paradigm to their traditional linear counterparts, and can have large impacts in how we use diffusion models for efficient generation, online learning, and scientific discovery.

The polynomial kernels are widely used in machine learning and they are one of the default choices to develop kernel-based classification and regression models. However, they are rarely used and considered in numerical analysis due to their lack of strict positive definiteness. In particular they do not enjoy the usual property of unisolvency for arbitrary point sets, which is one of the key properties used to build kernel-based interpolation methods. This paper is devoted to establish some initial results for the study of these kernels, and their related interpolation algorithms, in the context of approximation theory. We will first prove necessary and sufficient conditions on point sets which guarantee the existence and uniqueness of an interpolant. We will then study the Reproducing Kernel Hilbert Spaces (or native spaces) of these kernels and their norms, and provide inclusion relations between spaces corresponding to different kernel parameters. With these spaces at hand, it will be further possible to derive generic error estimates which apply to sufficiently smooth functions, thus escaping the native space. Finally, we will show how to employ an efficient stable algorithm to these kernels to obtain accurate interpolants, and we will test them in some numerical experiment. After this analysis several computational and theoretical aspects remain open, and we will outline possible further research directions in a concluding section. This work builds some bridges between kernel and polynomial interpolation, two topics to which the authors, to different extents, have been introduced under the supervision or through the work of Stefano De Marchi. For this reason, they wish to dedicate this work to him in the occasion of his 60th birthday.

This paper presents the development of a system able to estimate the 2D relative position of nodes in a wireless network, based on distance measurements between the nodes. The system uses ultra wide band ranging technology and the Bluetooth Low Energy protocol to acquire data. Furthermore, a nonlinear least squares problem is formulated and solved numerically for estimating the relative positions of the nodes. The localization performance of the system is validated by experimental tests, demonstrating the capability of measuring the relative position of a network comprised of 4 nodes with an accuracy of the order of 3 cm and an update rate of 10 Hz. This shows the feasibility of applying the proposed system for multi-robot cooperative localization and formation control scenarios.

Steerable convolutional neural networks (CNNs) provide a general framework for building neural networks equivariant to translations and other transformations belonging to an origin-preserving group $G$, such as reflections and rotations. They rely on standard convolutions with $G$-steerable kernels obtained by analytically solving the group-specific equivariance constraint imposed onto the kernel space. As the solution is tailored to a particular group $G$, the implementation of a kernel basis does not generalize to other symmetry transformations, which complicates the development of group equivariant models. We propose using implicit neural representation via multi-layer perceptrons (MLPs) to parameterize $G$-steerable kernels. The resulting framework offers a simple and flexible way to implement Steerable CNNs and generalizes to any group $G$ for which a $G$-equivariant MLP can be built. We apply our method to point cloud (ModelNet-40) and molecular data (QM9) and demonstrate a significant improvement in performance compared to standard Steerable CNNs.

The development and adoption of artificial intelligence (AI) technologies in space applications is growing quickly as the consensus increases on the potential benefits introduced. As more and more aerospace engineers are becoming aware of new trends in AI, traditional approaches are revisited to consider the applications of emerging AI technologies. Already at the time of writing, the scope of AI-related activities across academia, the aerospace industry and space agencies is so wide that an in-depth review would not fit in these pages. In this chapter we focus instead on two main emerging trends we believe capture the most relevant and exciting activities in the field: differentiable intelligence and on-board machine learning. Differentiable intelligence, in a nutshell, refers to works making extensive use of automatic differentiation frameworks to learn the parameters of machine learning or related models. Onboard machine learning considers the problem of moving inference, as well as learning, onboard. Within these fields, we discuss a few selected projects originating from the European Space Agency's (ESA) Advanced Concepts Team (ACT), giving priority to advanced topics going beyond the transposition of established AI techniques and practices to the space domain.

The term ``neuromorphic'' refers to systems that are closely resembling the architecture and/or the dynamics of biological neural networks. Typical examples are novel computer chips designed to mimic the architecture of a biological brain, or sensors that get inspiration from, e.g., the visual or olfactory systems in insects and mammals to acquire information about the environment. This approach is not without ambition as it promises to enable engineered devices able to reproduce the level of performance observed in biological organisms -- the main immediate advantage being the efficient use of scarce resources, which translates into low power requirements. The emphasis on low power and energy efficiency of neuromorphic devices is a perfect match for space applications. Spacecraft -- especially miniaturized ones -- have strict energy constraints as they need to operate in an environment which is scarce with resources and extremely hostile. In this work we present an overview of early attempts made to study a neuromorphic approach in a space context at the European Space Agency's (ESA) Advanced Concepts Team (ACT).