The 22nd Workshop on Advances in Parallel and Distributed Computational Models (APDCM), which was held in conjunction with the International Parallel and Distributed Processing Symposium (IPDPS) on May 18 - May 22, 2020, aims to provide a timely forum for the exchange and dissemination of new ideas, techniques and research in the field of the parallel and distributed computational models. The APDCM workshop has a history of attracting participation from reputed researchers worldwide. The program committee has encouraged the authors of accepted papers to submit full-versions of their manuscripts to the International Journal of Networking and Computing (IJNC) after the workshop. After a thorough reviewing process, with extensive discussions, four articles on various topics have been selected for publication on the IJNC special issue on APDCM. On behalf of the APDCM workshop, we would like to express our appreciation for the large efforts of reviewers who reviewed papers submitted to the special issue. Likewise, we thank all the authors for submitting their excellent manuscripts to this special issue. We also express our sincere thanks to the editorial board of the International Journal of Networking and Computing, in particular, to the Editor-in-chief Professor Koji Nakano. This special issue would not have been possible without his support.

Automated tiered storage with fast memory and slow flash storage (ATSMF) is a hybrid storage system located between non-volatile memories (NVMs) and solid state drives (SSDs). ATSMF reduces the average response time for input-output (IO) accesses by migrating concentrated IO-access areas from an SSD to an NVM. However, the current ATSMF implementation cannot sufficiently reduce the average response time because of the bottleneck caused by the Linux brd driver, which is used for the NVM access The response time of the brd driver is more than ten times longer than memory-access speed. To sufficiently reduce the average response time, we developed a block-level driver for an NVM called a two-mode (2M) memory driver. This driver has a .map-access mode and direct-access mode to reduce the response time while maintaining compatibility with the Linux device-mapper framework. The direct-access mode has a drastically lower response time than the Linux brd driver because the ATSMF driver can directly execute the IO-access function of the 2M memory Experimental results indicate that ATSMF using the 2M memory driver reduced the IO access response time to less than that of ATSMF using the Linux brd driver in most cases.

The increasingly crowded wireless spectrum has led to the need of new paradigms in wireless communications and the cognitive radio techniques that can offer promising solutions to the spectrum scarcity. In cognitive radio networks licensed primary users and unlicensed secondary users are allowed to coexist in the same frequency spectrum. Beamforming and MIMO technology can be used to minimize the interference from the secondary users to the primary users while improving the quality of communications when each node is equipped with multiple antennas to form an antenna array. However, equipping multiple antennas at each radio node is not feasible in many applications. In this paper, we consider the radio network with single antenna at each node. We first propose a cooperative network architecture in the network layer. The architecture consists of cooperative clusters used for distributed beamforming, and a routing backbone of the clusters that can avoid the interference to the primary users in the relay route. Distributed algorithms are designed for self-formation of the cooperative clusters and routing backbone. Then we propose a computationally efficient secondary users selection scheme in the link layer for the communications between two cooperative clusters while minimizing the interference to the primary users. The simulation results show that the proposed protocols and algorithms are effective and efficient in terms of time and energy.

A transactional system consists of a concurrency control system and a recovery system. TicToc is one of the state of the art concurrency control protocols today, but it lacks recovery system. We studied the ways to integrate TicToc and recovery system. For efficiency, we adopted a parallel write ahead logging scheme for the recovery system. There are two methods to optimize the logging. First method is early lock release which executes lock release early on data objects. Second method is group commit which executes batched logs transfer to storage from memory. We integrated a transactional system consisted by TicToc and P-WAL logging system assuming non-volatile memory. We found that the two optimization methods incur performance degradation when storage access latency is equivalent to that of NVRAM.

In this study, we examine the relation between the spatio-temporal patterns generated by two-dimensional symmetrical elementary cellular automata and a singular function. In a previous paper, we proved that a specific cellular automaton admits a set (a limit on the series of spatio-temporal patterns contracted with time), and we calculated the fractal dimension of the boundary of this limit set. In this paper, we provide an overview of the previous results and a more precise analysis. Numerical simulations demonstrate that the essential fractal-like patterns created by two-dimensional cellular automata are also related to a singular function.

Order preserving encryption techniques are treated as some of the most efficient encryption schemes for securing numeric data in a database. Such schemes are popular because they resolve performance degradation issues, which are significant problems in database encryption. However, in some applications, the order itself is sensitive information, and should be hidden. Conventional order preserving encryption techniques published so far, did not consider this issue. Therefore, in this study, we consider three techniques that protect the order information and also show good performance. The three methods hide the data order such that comparison operators can be handled efficiently and performance degradation can be prevented. Our methods work on the top of an order preserving encryption scheme and enhance the security of data. Experimental results demonstrate the efficiency and effectiveness of the proposed three methods.

A cellular automaton (CA) is a well-studied non-linear computational model of complex systems in which an infinite one-dimensional array of finite state machines (cells) updates itself in a synchronous manner according to a uniform local rule. A sequence generation problem on the CA model has been studied for a long time and a lot of generation algorithms has been proposed for a variety of non-regular sequences such as {2^n | n = 1, 2, 3,...}, prime, and Fibonacci sequences etc. In this paper, we study a real-time sequence generator for {n^3 | n=1, 2, 3, ...}. In the previous studies, Kamikawa and Umeo(2018) showed that sequence {n^3 | n=1, 2, 3, ...} can be generated in real-time by an eight-state CA. We present a new six-state implementation of real-time sequence generator for {n^3 | n=1, 2, 3, ...} rather than reducing the internal state of the Kamikawa and Umeo's sequence generator and give a formal proof of the correctness of the generator. In addition, we show the number of state-changes and number of cells of sequence generators, and compare sequence generators.

The 20th Workshop on Advances in Parallel and Distributed Computational Models (APDCM), which was held in conjunction with the International Parallel and Distributed Processing Symposium (IPDPS) on May 21--May 25, 2018, in Vancouver, Canada, aims to provide a timely forum for the exchange and dissemination of new ideas, techniques and research in the field of the parallel and distributed computational models. The APDCM workshop has a history of attracting participation from reputed researchers worldwide. The program committee has encouraged the authors of accepted papers to submit full-versions of their manuscripts to the International Journal of Networking and Computing (IJNC) after the workshop. After a thorough reviewing process, with extensive discussions, five articles on various topics have been selected for publication on the IJNC special issue on APDCM. On behalf of the APDCM workshop, we would like to express our appreciation for the large efforts of reviewers who reviewed papers submitted to the special issue. Likewise, we thank all the authors for submitting their excellent manuscripts to this special issue. We also express our sincere thanks to the editorial board of the International Journal of Networking and Computing, in particular, to the Editor-in-chief Professor Koji Nakano. This special issue would not have been possible without his support.

In this paper, we propose a system for modeling fire dynamics with emphasis on realistic behavior as well as the extensive behavioral control system. We propose a wide range of parametric and procedural controls. Simulation of flame spread, and motion is governed using differential equations which takes into account wind forces, buoyancy forces, diffusion and velocity of the burning surface. We propose to enhance the realistic behavior by using stochastic simulation of flickering and buoyant diffusion. The proposed wind fields serve as added fire motion control by a user. Flame behavior covers moving sources, flickering, fire separation and fire merging.

The Fifth International Symposium on Networking and Computing (CANDAR 2017) was held in Aomori Japan, from November 19th to 22th, 2017. The organizers of the CANDAR 2017 invited authors to submit the extended version of the presented papers. As a result, 27 articles have been submitted to this special issue. This issue includes the extended version of 16 papers that have been accepted. This issue owes a great deal to a number of people who devoted their time and expertise to handle the submitted papers. In particular, I would like to thank the guest editors for the excellent review process: Professor Shuichi Ichikawa, Professor Katsunobu Imai, Professor Yasuaki Ito, Professor Yoshiaki Kakuda, Professor Eitaro Kohno, Professor Susumu Matsumae, Professor Toru Nakanishi, Professor Yasuyuki Nogami, Professor Fukuhito Ooshita, Professor Hiroyuki Sato, and Professor Shinya Takamaeda-Yamazaki. Words of gratitude are also due to the anonymous reviewers who carefully read the papers and provided detailed comments and suggestions to improve the quality of the submitted papers. This special issue would not have been without their efforts.