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关键词： Object oriented programming  

摘要： Early programming methodologies proved inadequate for the reliable implementation of the large programs enabled by rapidly growing computer memories, resulting in prohibitively long times for software development. Attempts to solve this problem by limiting control structure primitives within programming languages or by imposing external design methodologies to enforce ill-defined notions of modularity proved unsuccessful. Barbara Liskov's definition of abstract data types in 1973 and her embodiment of this notion in the programming language CLU provided a major step toward solving this problem. The key idea was to define the fundamental building blocks of programs as a set of abstractions, each of which resulted from the combination of a data type with all the operations that needed to be performed on the data type. Data abstraction is now fundamental to all modern programming languages. A second key innovation of Liskov's was what she called "behavioral subtyping" for object-oriented programming, now known as the Liskov Substitution Principle (LSP). The LSP formally defines when objects of subclasses can be safely substituted for the parent class, a crucial requirement of bug-free programming within this programming paradigm. In addition, Liskov has made several key contributions to distributed computer systems, including the first use of atomic actions for successful concurrency and providing a practical solution to the problem of Byzantine faults.

关键词： K-12 computer science education   computer science curriculum   curriculum design   culturally responsive pedagogy  

摘要： Objectives. The goal of this paper is to introduce and describe a new introductory computer science course. Research results from the implementation of this curriculum will be presented to demonstrate the nature of teachers' experiences with the curriculum. Participants. Participants are teachers implementing the new curriculum at two schools in the metro Atlanta area. Study Method. This paper is partly descriptive, presenting the theory underlying the newly developed curriculum as well as its various features. An organizing framework, the Teacher Accessibility, Equity, and Content (TEC) rubric from Weintrop et al. (2019) [1], is used to structure the curriculum description. Teacher perceptions were gathered via both structured interviews and short online enactment surveys. These perceptions are summarized and presented thematically, corresponding to the features of the curriculum. Findings. A newly developed introductory computer science (CS) curriculum, Student-Centered Computing (SCC), utilizes project-based learning (PBL) and culturally authentic practices (CAPs) to help promote a sense of belonging and intent to persist within computer science among all students. Teachers successfully implemented the curriculum and generally found it to be beneficial for their students, though they struggled with some of the pedagogical demands of project-based learning as well as some of the most advanced technical content associated with the music coding and app development platforms. Conclusions. This paper provides a detailed overview of a year-long introductory computer science curriculum focused on the creation of culturally relevant digital artifacts. The curriculum represents a strong effort to make CS content relevant and appealing to the full range of students by relating it to their lives and experiences. Teacher surveys and interviews revealed that both teachers and students had positive views of the course. However, teaching using inclusive PBL pedagogy and cultura

关键词： artificial intelligence   chatbots   computer science   embodiment   moral theology   natural language processing   pragmatism   sociotechnical systems   systems theory   theological anthropology  

摘要： As artificial intelligence (AI) becomes progressively more engaged with society, its shift from technical tool to participating in society raises questions about AI personhood. Drawing upon developmental psychology and systems theory, a mediating structure for AI proto-personhood is defined analogous to an early stage of human development. The proposed AI bridges technical, psychological, and theological perspectives on near-future AI and is structured by its hardware, software, computational, and sociotechnical systems through which it experiences its world as embodied (even for putatively disembodied AI). Further social and moral construction can occur building upon a simple "self" for AI synthesized from symbolic and statistical approaches to AI.

关键词： Authentication   Aggregates   Vehicular ad hoc networks   Privacy   Fault tolerant systems   Fault tolerance   Computer science   Vehicular ad hoc networks (VANETs)   infrastructure-less vehicular networks   authenticated key management   aggregate authentication   fault-tolerance  

摘要： In recent years, growing research interest from both industry and academia has been aroused to the vehicular networks, which is regarded as the fundamental component of the modern intelligent transportation system (ITS). Lots of remarkable research outputs with respect to secure vehicular data interactions and user privacy preservation has been witnessed. However, the existing schemes all focus on the common vehicular communication scenarios where facilities are deployed, whereas the secure data exchange in the abnormal infrastructure-less vehicular environment has not been properly investigated. To deal with unpredictable abnormal situations caused by artificial or natural disasters such as earthquakes and floods, a distinctive vehicle-assisted aggregate authentication mechanism for infrastructure-less vehicular networks is presented in this paper. With assistance from the neighboring vehicles, the homomorphic signature involving all requesting vehicles is generated and forwarded to the remaining functional RSUs. Meanwhile, vehicular group communication among the validated entities is enabled. Additionally, the fault-tolerant verification method is adopted such that the ineffective entities can be easily distinguished and removed without interfering with other requesting vehicles. The security proofs and discussions regarding vital security properties are presented, while the performance analysis follows. Compared with the state-of-the-art, advantages in terms of security and performance properties can be proved.

关键词： Three-dimensional displays   Time factors   Memory management   Flash memories   Computer science   Waste handling   3-D NAND flash   garbage collection   page waste   parity restriction  

摘要： Garbage collection or GC running in the controller of 3-D NAND flash-based solid-state disks-SSDs-plays a critical role in the performance of storage systems. SSD manufacturers have developed various GC solutions based on internal data movement or IDM to mitigate the impacts of GC on request latency. Due to the circuit characteristics of flash memory, the existing IDM-based GC strategies are restricted by page parity during data movement: odd pages must be migrated to odd pages, and even pages to even pages. When migrating two consecutive pages with the same parity, the free page between the two migrated pages will be wasted after the migration is complete. This ever-increasing page waste problem inevitably deteriorates the storage space utilization of flash memory, thereby degrading the overall performance of 3-D NAND flash-based SSDs. To address this issue, we propose a parity-check GC scheme called PcGC to revamp SSD performance by alleviating page waste during GC. We build a parity-check unit in PcGC to facilitate checking the parity of migrated valid pages and destination pages. According to the parity results offered by the parity-check unit, PcGC dynamically adjusts the migration order of valid pages during the course of GC. In doing so, PcGC fundamentally averts page waste caused by the page parity restriction, thereby enhancing 3-D NAND flash performance. We quantitatively evaluate the performance of PcGC in terms of wasted pages, storage utilization, GC counts, write amplification, and average response time. We compare PcGC against the two state-of-the-art schemes-Amphibian and Tiny-tail flash (TTflash). The experimental results derived from the nine real-world workload traces unfold that compared with Amphibian and TTflash: 1) PcGC curtails the number of wasted pages by up to 91.4% with an average of 53.75%;2) cuts back the number of GC counts by up to 52.2% with an average of 11.9%;and 3) slashes average write response time by up to 77.8% with an average

关键词： Computer science curricula   computational thinking   secondary school education  

摘要： In recent years, the push for secondary school students to "learn to code" has increased significantly. Currently, about half of secondary schools in the United States have computer science education available to students in some form. Unfortunately, many of these schools choose a curriculum bogged down in the nuances of programming language syntax, leaving students bored, confused, unable to apply their learning to useful problems outside the classroom, and therefore disheartened about further pursuing a more conceptual computer science education in college. As a current undergraduate who has helped teach secondary school computer science, I witnessed firsthand the problems with current approaches. I, therefore, propose a shift in the focus of computing education research away from teaching "coding" effectively to elucidating a more abstract but nevertheless more pragmatic characterization of computer science as an academic field, rather than programming as a trade.

关键词： Philosophy of computer science   Foundations of computing   Implementation   Software correctness   Miscomputation   Unconventional computing  

摘要： This paper introduces the Global Philosophy symposium on Giuseppe Primiero's book On the Foundations of Computing (2020). The collection gathers commentaries and responses of the author with the aim of engaging with some open questions in the philosophy of computer science. Firstly, this paper introduces the central themes addressed in Primiero's book;secondly, it highlights some of the main critiques from commentators in order to, finally, pinpoint some conceptual challenges indicating future directions for the philosophy of computer science.

关键词： crappie   incubation temperature   ovarian cell isolation   primary cell culture   TrypLE (TM) express  

摘要： Investigations were conducted to develop a general protocol for the isolation and in vitro culture of ovary-derived cells from black crappie, Pomoxis nigromaculatus, and white crappie, P. annularis. Five digestive enzymes: 500 U/mL collagenase type I, 500 U/mL collagenase type IV, 0.05% trypsin-EDTA, 0.25% trypsin-EDTA, and 1X TrypLE (TM) Express were evaluated for live cell isolation. The isolated cells were cultured in 10 or 20% fetal bovine serum (FBS) in L-15 growth media. In addition, four incubation temperatures (15 degrees C, 20 degrees C, 25 degrees C, and 30 degrees C) were also evaluated. The number of live cells obtained from the 0.25% trypsin and TrypLE (TM) Express treatments was significantly higher than other treatments. No difference in cell growth was observed between the two FBS treatments. Cells isolated using TrypLE (TM) Express and 0.25% trypsin reached 80% to 90% confluency in 12.5 cm(2) cell culture flasks within 5 days of inoculation at 20 and 25 degrees C. At 15 degrees C, 10 days were required to reach 80%-90% confluency. Morphologically, cells incubated at 15 degrees C, 20 degrees C, and 25 degrees C appeared healthier than cells incubated at 30 degrees C, where irregular cell shape and substrate detachment were observed. We concluded TrypLE (TM) Express and 0.25% trypsin were optimal for cell dissociation and isolation of crappie ovarian cells. An incubation temperature of 20 degrees C-25 degrees C was favorable for cell culture in L-15 media supplemented with either 10% or 20% FBS.