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关键词： Combinatorics   Convex and Discrete Geometry   Order   Lattices   Ordered Algebraic Structures   Computer Science   general   Group Theory and Generalizations  

摘要： Given a finite abelian group G, consider a uniformly random permutation of the set of all elements of G. Compute the difference of each pair of consecutive elements along the permutation. What is the number of occurrences of h is an element of G\{0} in this sequence of differences? How do these numbers of occurrences behave for several group elements simultaneously? Can we get similar results for non-abelian G? How do the answers change if differences are replaced by sums? In this paper, we answer these questions. Moreover, we formulate analogous results in a general combinatorial setting.

关键词： Feature extraction   Roads   Sensors   Safety   Urban areas   Law enforcement   Computer science   Crime inference   crime risk   heterogeneous open data   route recommendation   urban computing  

摘要： Crime has been a complex social problem worldwide, impacting numerous individuals in both property and psychology, and affecting public safety as well. To prevent and avoid crime is of great importance for urban authorities and citizens. Crime prediction using various urban sensing data provides a promising paradigm to cope with this challenging problem. However, previous studies on crime prediction mainly focus on coarse-grained prediction at the region level, which fail in fine-grained road-level crime inference due to data sparsity problems. This article proposes a road-level framework for fine-grained crime risk inference leveraging heterogeneous open data. We first extract a set of features from relevant external datasets and historical crime records, i.e., temporal, spatial, and recurrence crime features. We then establish a spatio-temporal crime pattern using spatio-temporal features, and further infer road-level crime risk incorporating with recurrence crime features. The framework not only considers a useful spatio-temporal pattern but also considers a unique crime near-repeat phenomenon, which helps address the data sparsity. We further present an application crime risk-aware route recommendation to demonstrate the effectiveness of our framework. This application cannot be solved well with coarse-grained (e.g., region-level) crime risk results since it is inconvenient for people to travel while avoiding large regions with potential crime risks. Experiments with the real-world datasets from New York City show that our framework accurately infers road-level crime risk and outperforms other baseline methods.

关键词： block-based visual programming   textual languages   dual-modality programming environments   hybrid   and CS0  

摘要： Block-based programming languages (BBLs) have been proposed as a way to prepare students for learning to program in more sophisticated, text-based languages, such as Java. Hybrid BBLs add the ability to view and edit the block commands in auto-generated, text-based code. We compared the use of a non-hybrid BBL (Scratch), a hybrid BBL (Pencil Code), and no BBL across three sections of an introductory CS course that taught Java programming, to determine whether either type of BBL offered cognitive or affective advantages for learning Java. Students in the BBL groups were surveyed about their perceptions of each BBL in terms of ease of use and helpfulness in learning Java, and all three groups were compared on their performance in Java programming. The results showed that, in this introductory CS course, neither type of BBL offered an advantage in preparing students for learning Java. These results held regardless of the students' level of Java knowledge prior to the course.

关键词： Productivity   Computer science   Mental health   Safety  

摘要： As enrollment in computer science (CS) programs increases and technical jobs become more available, the mental health of computer scientists and engineers requires wider discussion. Mental health constitutes of emotional, social, and psychological well-being, affecting how a person thinks, feels, and acts. Addressing issues surrounding mental health is critical in ensuring one's happiness, productivity, and, ultimately, safety.

关键词： Statistics   general   Statistical Theory and Methods   Statistics for Business   Management   Economics   Finance   Insurance   Statistics for Engineering   Physics   Computer Science   Chemistry and Earth Sciences   Statistics for Life Sciences   Medicine   Health Sciences   Statistics for Social Sciences   Humanities   Law  

摘要： An array of 22 dancers stride cheerfully in unison across the proscenium stage toward a jam-packed audience, often as richly diverse as the dancers themselves. Audience members take to their feet, singing, clapping, dancing in the aisle, an experience--that by choreographer's intention--recalls the celebratory abandon of a Black church revival. The magnetism of Ailey's Revelations has captivated audiences worldwide for over six decades. Through extensive domestic and international touring by the Alvin Ailey American Dance Theater, Revelations has appeared on six continents since its premiere. Revelations (1960) is the most performed and most viewed choreographic work of the twentieth century. During the Covid-19 pandemic in 2020 and 2021, a full-length recording of Revelations streamed on YouTube for over a year, providing hundreds of thousands of viewers free access to the piece from their computer screens.

关键词： Mobile handsets   Performance evaluation   Computer science   Portable document format   Delays   File systems   Data structures   Discard   F2FS   mobile device   TRIM   user experience  

摘要： TRIM is a recommended command to deliver data invalidation information of the file system to flash storage. It is issued on both system level and device level. Since it can reduce the number of data copies during device-level garbage collection (DGC), TRIM has been widely used to improve the endurance and performance of mobile devices. Contrary to the common belief, this work identifies that the default TRIM scheme has both merit and drawback to the performance of mobile devices, especially in flash-friendly file system (F2FS), which is a commonly used file system in mobile devices. On one hand, TRIM can reduce garbage collection migration to prolong the flash lifetime as well as improving I/O throughput;On the other hand, TRIM may induce I/O contentions. This article proposes a new TRIM scheme, iTRIM, to distribute the timing overheads to system idle time. To further reduce I/O contention and improve I/O performance, the design of iTRIM considers the TRIM size, and the logical addresses' pattern of victim invalidated data. Experimental results show that iTRIM can minimize I/O contentions while retaining the benefits of the default TRIM scheme for endurance and performance.

关键词： Graph theory   Linear codes   Decoding   Approximation algorithms   Standards   Labeling   Computer science   Error-correcting codes   list decoding   erasure decoding   expander codes  

摘要： We give a linear-time erasure list-decoding algorithm for expander codes. More precisely, let r > 0 be any integer. Given an inner code C-0 of length d, and a d-regular bipartite expander graph G with n vertices on each side, we give an algorithm to list-decode the code C = C(G, C-0) of length nd from approximately delta delta(r)nd erasures in time n center dot poly(d(2r) /delta), where delta and delta(r) are the relative distance and the r'th generalized relative distance of C-0, respectively. To the best of our knowledge, this is the first linear-time algorithm that can list-decode expander codes from erasures beyond their (designed) distance of approximately delta(2) nd. To obtain our results, we show that an approach similar to that of (Hemenway and Wootters, Information and Computation, 2018) can be used to obtain such an erasure-list-decoding algorithm with an exponentially worse dependence of the running time on r and delta;then we show how to improve the dependence of the running time on these parameters.

关键词： Educational robotics   Computer science education   Formal learning   Teacher professional development   Elementary education  

摘要： Educational Robotics (ER) has the potential to provide significant benefits to education, provided an increase in outreach by transitioning from the extra-curricular initiatives in which ER has thrived to formal education. As Computer Science (CS) Education is undergoing curricular reforms worldwide, the present study addresses the case of a Digital Education reform that included ER as a means to teach core CS concepts. Approximately 350 teachers from the first four grades of primary school participated in a mandatory two-year continuing professional development (CPD) program. The first year of the program was dedicated to CS and introduced teachers to CS Unplugged (CSU) and Robotics Unplugged (RU) activities. As such, we analyse the interplay between these activities and focus on teachers' voluntary adoption of the proposed content in classrooms. This is complemented by an analysis of their perception and recommendation of ER. The findings highlight three main points. Firstly, ER benefits from the integration in the CS CPD, as this provides the necessary traction to introduce ER into teacher practices (the teachers freely devoted 2275 h to ER activities in their classrooms, over two years). Secondly, the presence of ER activities in the CS-CPD allows a higher proportion of teachers to adopt the CS content, as there are teachers that favour one type of activity over the other. Finally, the globally positive perception of ER registered in this study is relevant for two reasons: teachers were not voluntarily participating in the CPD, and results did not differ between pioneers and novices.

关键词： Computer science   Complex networks  

摘要： From physics to engineering, biology and social science, natural and artificial systems are characterized by interconnected topologies whose features - e.g., heterogeneous connectivity, mesoscale organization, hierarchy - affect their robustness to external perturbations, such as targeted attacks to their units. Identifying the minimal set of units to attack to disintegrate a complex network, i.e. network dismantling, is a computationally challenging (NP-hard) problem which is usually attacked with heuristics. Here, we show that a machine trained to dismantle relatively small systems is able to identify higher-order topological patterns, allowing to disintegrate large-scale social, infrastructural and technological networks more efficiently than human-based heuristics. Remarkably, the machine assesses the probability that next attacks will disintegrate the system, providing a quantitative method to quantify systemic risk and detect early-warning signals of system's collapse. This demonstrates that machine-assisted analysis can be effectively used for policy and decision-making to better quantify the fragility of complex systems and their response to shocks. Network dismantling allows to find minimum set of units attacking which leads to system's break down. Grassia et al. propose a deep-learning framework for dismantling of large networks which can be used to quantify the vulnerability of networks and detect early-warning signals of their collapse.