julilili42/papers huggingface dataset:
On the optimality of kernels for high-dimensional clustering
2022-02-26

This paper studies the optimality of kernel methods in high-dimensional data clustering. Recent works have studied the large sample performance of kernel clustering in the high-dimensional regime, where Euclidean distance becomes less informative. However, it is unknown whether popular methods, such as kernel k-means, are optimal in this regime. We consider the problem of high-dimensional Gaussian clustering and show that, with the exponential kernel function, the sufficient conditions for partial recovery of clusters using the NP-hard kernel k-means objective matches the known information-theoretic limit up to a factor of for large . It also exactly matches the known upper bounds for the non-kernel setting. We also show that a semi-definite relaxation of the kernel k-means procedure matches up to constant factors, the spectral threshold, below which no polynomial-time algorithm is known to succeed. This is the first work that provides such optimality guarantees for the kernel k-means as well as its convex relaxation. Our proofs demonstrate the utility of the less known polynomial concentration results for random variables with exponentially decaying tails in a higher-order analysis of kernel methods.
Book Embeddings of Nonplanar Graphs with Small Faces in Few Pages
2022-02-26

An embedding of a graph in a book, called book embedding, consists of a linear ordering of its vertices along the spine of the book and an assignment of its edges to the pages of the book, so that no two edges on the same page cross. The book thickness of a graph is the minimum number of pages over all its book embeddings. For planar graphs, a fundamental result is due to Yannakakis, who proposed an algorithm to compute embeddings of planar graphs in books with four pages. Our main contribution is a technique that generalizes this result to a much wider family of nonplanar graphs, which is characterized by a biconnected skeleton of crossing-free edges whose faces have bounded degree. Notably, this family includes all 1-planar, all optimal 2-planar, and all k-map (with bounded k) graphs as subgraphs. We prove that this family of graphs has bounded book thickness, and as a corollary, we obtain the first constant upper bound for the book thickness of optimal 2-planar and k-map graphs.
Applying Transparency in Artificial Intelligence based Personalization Systems
2022-02-26

Artificial Intelligence based systems increasingly use personalization to provide users with relevant content, products, and solutions. Personalization is intended to support users and address their respective needs and preferences. However, users are becoming increasingly vulnerable to online manipulation due to algorithmic advancements and lack of transparency. Such manipulation decreases users' levels of trust, autonomy, and satisfaction concerning the systems with which they interact. Increasing transparency is an important goal for personalization based systems. Unfortunately, system designers lack guidance in assessing and implementing transparency in their developed systems. In this work we combine insights from technology ethics and computer science to generate a list of transparency best practices for machine generated personalization. Based on these best practices, we develop a checklist to be used by designers wishing to evaluate and increase the transparency of their algorithmic systems. Adopting a designer perspective, we apply the checklist to prominent online services and discuss its advantages and shortcomings. We encourage researchers to adopt the checklist in various environments and to work towards a consensus-based tool for measuring transparency in the personalization community.
Stability of radical-functionalized gold surfaces by self-assembly and on-surface chemistry
2022-02-26

We have investigated the radical functionalization of gold surfaces with a derivative of the perchlorotriphenylmethyl (PTM) radical, using two methods: by chemisorption from the radical solution and by on surface chemical derivatization from a precursor. We have investigated the obtained self-assembled monolayers by photon-energy dependent X-ray photoelectron spectroscopy. Our results show that the molecules were successfully anchored on the surfaces. The monolayers are characterized by air and beam stability unprecedented for films of organic radicals. Over very long beam exposure we observed a dynamic nature of the radical-Au complex. The results clearly indicate that (mono)layers of PTM; radical derivatives have the necessary stability to stand device applications.
From orders to prices: A stochastic description of the limit order book to forecast intraday returns
2022-02-26

We propose a microscopic model to describe the dynamics of the fundamental events in the limit order book (LOB): order arrivals and cancellations. It is based on an operator algebra for individual orders and describes their effect on the LOB. The model inputs are arrival and cancellation rate distributions that emerge from individual behavior of traders, and we show how prices and liquidity arise from the LOB dynamics. In a simulation study we illustrate how the model works and highlight its sensitivity with respect to assumptions regarding the collective behavior of market participants. Empirically, we test the model on a LOB snapshot of XETRA, estimate several linearized model specifications, and conduct in- and out-of-sample forecasts.The in-sample results based on contemporaneous information suggest that our model describes returns very well, resulting in an adjusted of roughly 80%. In the more realistic setting where only past information enters the model, we observe an adjusted around 15%. The direction of the next return can be predicted (out-of-sample) with an accuracy above 75% for time horizons below 10 minutes. On average, we obtain an RMSPE that is 10 times lower than values documented in the literature.
Cerium cyclotrisilazides†
2022-02-26

The 6-membered 3,5-bis(dimethylsilyl)-2,2,4,4,6,6-hexamethyl-1,3,5,2,4,6-triazatrisilinan-1-ido ligand (dhts) was accessed in the potassium dimer [K(dhts)(thf)]2 (1thf), when treating KH with excess HN(SiHMe2)2 in the presence of THF. 1thf engaged in salt metathesis with CeCl3(thf)1.05 in THF, giving Ce(dhts)3(thf) (2thf). An attempted metathesis reaction in toluene failed, leading only to the recovery of 1thf. Attempts at generating potassium-ate complex {KCe(dhts)4} from salt metathesis between CeCl3(thf)1.05 and four equivalents of 1thf in THF, followed by crystallisation from toluene, resulted in the formation of both 2thf and [K(dhts)(toluene)]2 (1tol). Oxidation of 2thf with trityl chloride led to the isolation of the metastable tetravalent heteroleptic cerium complex Ce(dhts)3Cl (3), characterised by both 1H NMR spectroscopy and X-ray crystallography. Compound 3 is a new addition to a prominent class of cerium(IV) silylamides, and an understudied class of triazatrisilinanides.
Flexibly Fair Representation Learning by Disentanglement
2022-02-27

We consider the problem of learning representations that achieve group and subgroup fairness with respect to multiple sensitive attributes. Taking inspiration from the disentangled representation learning literature, we propose an algorithm for learning compact representations of datasets that are useful for reconstruction and prediction, but are also \\emph{flexibly fair}, meaning they can be easily modified at test time to achieve subgroup demographic parity with respect to multiple sensitive attributes and their conjunctions. We show empirically that the resulting encoder---which does not require the sensitive attributes for inference---enables the adaptation of a single representation to a variety of fair classification tasks with new target labels and subgroup definitions.
Using a Passive Back Exoskeleton During a Simulated Sorting Task: Influence on Muscle Activity, Posture, and Heart Rate
2022-02-27

Objective To evaluate using a back exoskeleton in a simulated sorting task in a static forward bent trunk posture on muscle activity, posture, and heart rate (HR). Background Potentials of exoskeletons for reducing musculoskeletal demands in work tasks need to be clarified. Methods Thirty-six healthy males performed the sorting task in 40°-forward bent static trunk posture for 90 seconds, in three trunk orientations, with and without exoskeleton. Muscle activity of the erector spinae (ES), biceps femoris (BF), trapezius descendens (TD), rectus abdominis (RA), vastus laterals (VL), and gastrocnemius medialis was recorded using surface electromyography normalized to a submaximal or maximal reference electrical activity (%RVE (reference voluntary electrical activity)/%MVE). Spine and lower limb postures were assessed by gravimetric position sensors, and HR by electrocardiography. Results Using the exoskeleton resulted in decreased BF muscle activity [−8.12%RVE], and minor changes in ES [−1.29%MVE], RA [−0.28%RVE], VL [−0.49%RVE], and TD [+1.13%RVE] muscle activity. Hip and knee flexion increased [+8.1°; +6.7°]. Heart rate decreased by 2.1 bpm. Trunk orientation had an influence on BF muscle activity. Conclusion Using the back exoskeleton in a short sorting task with static trunk posture mainly reduced hip extensor muscle activity and changed lower limb but not spine posture. Implications of using a back exoskeleton for workers’ musculoskeletal health need further clarification. Application The detected changes by using the Laevo® illustrate the need for further investigation prior to practical recommendations of using exoskeletons in the field. Investigating various work scenarios in different kind of workers and long-term applications would be important elements.
Expression of Channelrhodopsin‐2 in Rod Bipolar Cells Restores ON and OFF Responses at High Spatial Resolution in Blind Mouse Retina
2022-02-27

Abstract Rod bipolar cells (rBCs) represent a promising target for vision restoration as they relay information to the major image processing pathways in the retina. However, the diversity of the retinal output and the resolution obtained by optogenetic actuation of rBCs is unclear. Herein, the photostimulation of rBCs expressing channelrhodopsin‐2 is studied in a transgenic, photoreceptor‐degeneration mouse (rd10) while simultaneously recording the retinal output using a high‐density microelectrode array. After analyzing several hundred retinal output neurons, both optogenetic ON and OFF type responses are identified at similar ratio at stimulation thresholds well below photodamage intensity. The temporal latency of both response types is in the same range ( 50 ms) as reported for healthy mouse retinal ganglion cells. The spatial resolution ranges between 0.1 and 0.2 cycles deg ‐1 , which is close to that found in healthy mice. Photostimulation over an extended area (29 deg) but not localized stimuli induces strong bursting activity, which may originate from large‐scale activation of a coupled network of retinal cells. The distinct ON and OFF optogenetically induced activity patterns in retinal ganglion cells and the high temporal and spatial resolution demonstrate that near‐physiological vision restoration may be achieved under optimal conditions in late stage retinal degeneration.
The experiential basis of compatibility effects in reading-by-rotating paradigms
2022-02-27

Abstract The current study originates from inconsistent findings within the framework of embodied language processing, specifically in the reading-by-rotating literature: whereas some studies report a match advantage (e.g., Zwaan and Taylor (J Exp Psychol 135:1, 2006)), i.e., shorter reading times when the direction of a linguistically conveyed manual rotation matched rather than mismatched the direction of an actually to be performed manual rotation Claus (Acta Psychol 156:104–113, 2015) found a mismatch advantage. The current study addresses two explanations that were previously discussed as potentially responsible for this inconsistency: on the one hand, differences in the knob devices employed; on the other hand, differences in the perspectives adopted by the readers depending on the number of characters involved in the narratives. Concurrently, the study exploits individual differences in motoric experience to explore the experiential basis of action-sentence compatibility effects. The results are inconclusive with respect to the two explanations. However, in their overall picture, they contribute suggestive considerations for the ongoing debate on action-simulation effects by pointing to the potential role of interindividual variation in motoric experience.
Realistic collisional water transport during terrestrial planet formation: Self-consistent modeling by an N-body--SPH hybrid code
2022-02-27

According to current evidence the water inventory of Earth (and perhaps similar exoplanets) was transported inwards via (giant) collisions during the chaotic final phase of planet formation. In dynamical simulations water delivery is still studied almost exclusively by assuming oversimplified perfect merging (PM), even though it is particularly prone to collisional transfer and loss. To close this gap we have developed a framework to model collisional water transport by direct combination of long-term N-body computations with dedicated 3D SPH simulations for each collision. Post-collision water inventories are self-consistently traced further, in accretionary or erosive as well as hit-and-run encounters. The latter are frequent outcomes among protoplanets, where besides collisional losses, water transfer between the encountering bodies has to be considered. This hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of ~200 bodies throughout the whole late-stage accretion phase (several 100 Myrs). As a first application we choose a Solar System-like architecture, with already formed giant planets on either circular or eccentric orbits and a debris disk spanning from 0.5 - 4 au. Realistic collision treatment leads to considerably different results than PM, with lower mass planets and water inventories reduced by a factor of two or more. Due to a combination of collisional losses and considerably lengthened accretion, final water contents especially with giant planets on circular orbits are strongly reduced to more Earth-like values. Water delivery to potentially habitable planets is dominated by few decisive collisions, mostly with embryo-sized or larger bodies. The high frequency of hit-and-run, with generally low water (and mass) transfer efficiencies, are a crucial part of this process, and of system-wide evolution in general.
Absorbing Boundary Condition as Limiting Case of Imaginary Potentials
2022-02-27

Imaginary potentials such as (with a constant, a subset of 3-space, and its characteristic function) have been used in quantum mechanics as models of a detector. They represent the effect of a "soft" detector that takes a while to notice a particle in the detector volume . In order to model a "hard" detector (i.e., one that registers a particle as soon as it enters ), one may think of taking the limit of increasing detector strength . However, as pointed out by Allcock, in this limit the particle never enters ; its wave function gets reflected at the boundary of in the same way as by a Dirichlet boundary condition on . This phenomenon, a cousin of the "quantum Zeno effect," might suggest that a hard detector is mathematically impossible. Nevertheless, a mathematical description of a hard detector has recently been put forward in the form of the "absorbing boundary rule" involving an absorbing boundary condition on the detecting surface . We show here that in a suitable (non-obvious) limit, the imaginary potential yields a non-trivial distribution of detection time and place in agreement with the absorbing boundary rule. That is, a hard detector can be obtained as a limit, but it is a different limit than Allcock considered.
P4-MACsec: Dynamic Topology Monitoring and Data Layer Protection with MACsec in P4-SDN
2022-02-27

We propose P4-MACsec to protect network links between P4 switches through automated deployment of MACsec, a widespread IEEE standard for securing Layer 2 infrastructures. It is supported by switches and routers from major manufacturers and has only little performance limitations compared to VPN technologies such as IPsec. P4-MACsec introduces a data plane implementation of MACsec including AES-GCM encryption and decryption directly on P4 switches. P4-MACsec features a two-tier control plane structure where local controllers running on the P4 switches interact with a central controller. We propose a novel secure link discovery mechanism that leverages protected LLDP frames and the two-tier control plane structure for secure and efficient management of a global link map. Automated deployment of MACsec creates secure channel, generates keying material, and configures the P4 switches for each detected link between two P4 switches. It detects link changes and performs rekeying to provide a secure, configuration-free operation of MACsec. In this paper, we review the technological background of P4-MACsec and explain its architecture. To demonstrate the feasibility of P4-MACsec, we implement it on the BMv2 P4 software switch and validate the prototype through experiments. We evaluate its performance through experiments that focus on TCP throughput and round-trip time. We publish the prototype and experiment setups on Github.
Approximating CNNs with Bag-of-local-Features models works surprisingly well on ImageNet
2022-02-27

Deep Neural Networks (DNNs) excel on many complex perceptual tasks but it has proven notoriously difficult to understand how they reach their decisions. We here introduce a high-performance DNN architecture on ImageNet whose decisions are considerably easier to explain. Our model, a simple variant of the ResNet-50 architecture called BagNet, classifies an image based on the occurrences of small local image features without taking into account their spatial ordering. This strategy is closely related to the bag-of-feature (BoF) models popular before the onset of deep learning and reaches a surprisingly high accuracy on ImageNet (87.6% top-5 for 33 x 33 px features and Alexnet performance for 17 x 17 px features). The constraint on local features makes it straight-forward to analyse how exactly each part of the image influences the classification. Furthermore, the BagNets behave similar to state-of-the art deep neural networks such as VGG-16, ResNet-152 or DenseNet-169 in terms of feature sensitivity, error distribution and interactions between image parts. This suggests that the improvements of DNNs over previous bag-of-feature classifiers in the last few years is mostly achieved by better fine-tuning rather than by qualitatively different decision strategies.
Confidence-Calibrated Adversarial Training: Generalizing to Unseen Attacks
2022-02-27

Adversarial training yields robust models against a specific threat model, e.g., adversarial examples. Typically robustness does not generalize to previously unseen threat models, e.g., other norms, or larger perturbations. Our confidence-calibrated adversarial training (CCAT) tackles this problem by biasing the model towards low confidence predictions on adversarial examples. By allowing to reject examples with low confidence, robustness generalizes beyond the threat model employed during training. CCAT, trained only on adversarial examples, increases robustness against larger , , and attacks, adversarial frames, distal adversarial examples and corrupted examples and yields better clean accuracy compared to adversarial training. For thorough evaluation we developed novel white- and black-box attacks directly attacking CCAT by maximizing confidence. For each threat model, we use attacks with up to restarts and iterations and report worst-case robust test error, extended to our confidence-thresholded setting, across all attacks.
Evaluating Weakly Supervised Object Localization Methods Right
2022-02-27

Weakly-supervised object localization (WSOL) has gained popularity over the last years for its promise to train localization models with only image-level labels. Since the seminal WSOL work of class activation mapping (CAM), the field has focused on how to expand the attention regions to cover objects more broadly and localize them better. However, these strategies rely on full localization supervision to validate hyperparameters and for model selection, which is in principle prohibited under the WSOL setup. In this paper, we argue that WSOL task is ill-posed with only image-level labels, and propose a new evaluation protocol where full supervision is limited to only a small held-out set not overlapping with the test set. We observe that, under our protocol, the five most recent WSOL methods have not made a major improvement over the CAM baseline. Moreover, we report that existing WSOL methods have not reached the few-shot learning baseline, where the full-supervision at validation time is used for model training instead. Based on our findings, we discuss some future directions for WSOL.
Towards neural networks that provably know when they don't know
2022-02-27

It has recently been shown that ReLU networks produce arbitrarily over-confident predictions far away from the training data. Thus, ReLU networks do not know when they don't know. However, this is a highly important property in safety critical applications. In the context of out-of-distribution detection (OOD) there have been a number of proposals to mitigate this problem but none of them are able to make any mathematical guarantees. In this paper we propose a new approach to OOD which overcomes both problems. Our approach can be used with ReLU networks and provides provably low confidence predictions far away from the training data as well as the first certificates for low confidence predictions in a neighborhood of an out-distribution point. In the experiments we show that state-of-the-art methods fail in this worst-case setting whereas our model can guarantee its performance while retaining state-of-the-art OOD performance.
On the structure of RCD spaces with upper curvature bounds
2022-02-27

We develop a structure theory for RCD spaces with curvature bounded above in Alexandrov sense. In particular, we show that any such space is a topological manifold with boundary whose interior is equal to the set of regular points. Further the set of regular points is a smooth manifold and is geodesically convex. Around regular points there are DC coordinates and the distance is induced by a continuous BV Riemannian metric.
Compositional uncertainty in deep Gaussian processes
2022-02-27

Gaussian processes (GPs) are nonparametric priors over functions. Fitting a GP implies computing a posterior distribution of functions consistent with the observed data. Similarly, deep Gaussian processes (DGPs) should allow us to compute a posterior distribution of compositions of multiple functions giving rise to the observations. However, exact Bayesian inference is intractable for DGPs, motivating the use of various approximations. We show that the application of simplifying mean-field assumptions across the hierarchy leads to the layers of a DGP collapsing to near-deterministic transformations. We argue that such an inference scheme is suboptimal, not taking advantage of the potential of the model to discover the compositional structure in the data. To address this issue, we examine alternative variational inference schemes allowing for dependencies across different layers and discuss their advantages and limitations.