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Intelligent Transportation Systems (ITS) have become a focus for many countries. To achieve ITS, Inter Vehicle Communication (IVC) is required for the exchange and distribution of data such as congestion or emergency information. If this communication can be done without fixed infrastructure, the systems can be deployed quickly and on a larger scale. Ad hoc networking technologies are one such technology to achieve IVC. However, if generic ad hoc network solutions are applied directly to IVC, performance can degrade quickly as the system scales particularly for broadcast type messages. In this paper we propose two new broadcast protocols that reduce bandwidth required for broadcast communication by taking advantage of a vehicle's highly directional movement and Global Positioning Information. To show the performance of our new protocols, we compare our approach with generic ad hoc broadcasting techniques. Our results show that it is possible to achieve several hundred percent improvement of bandwidth utilization with very slight sacrifice of reachability.

The intelligent transportation systems (ITS) use advanced communications and control technologies to improve current transportation systems. To achieve many ITS applications, the ability to exchange messages between vehicles is necessary. This is generally required as inter vehicle communication (IVC). IVC can be considered as a special case of ad hoc networks, where nodes only move along predefined road paths. We propose new broadcast protocols that make use of global positioning system (GPS) information to enhance the performance of broadcast service in IVC. The ability to efficiently broadcast messages is necessary for any communications in IVC (e.g, updating routing tables, etc). We propose two algorithms that effectively reduce the number of re-broadcast messages without affecting the number of hosts (vehicles) that receive the broadcast. The simulation results show up to several hundred percentage of bandwidth utilization improvement can be achieved by our proposed broadcast protocols.

In order to realize the intelligent transport system (ITS) without any road facilities, inter-vehicle communications (IVC) is considered as preferable. IVC makes it possible to exchange real-time information among vehicles. This paper focuses on the packet-based IVC, and presents the vehicular information broadcasting relay (VIBROR) protocol to realize an effective multi-hop transmission scheme for broadcasting information without any complex negotiation among the vehicles.

We consider the optimal mirror allocation problems for the purpose of load balance in network servers. We focus on constructing high-reliability networks, and propose the optimal mirror allocation model such that the system reliability is maximized subject to costs and delays, in view of the trading-off relationship between the reliability and cost. This optimization model is capable of dealing with various kinds of network topology. We formulate this optimization problem as a 0-1 integer programming in this model, and we can find the place where each mirror server should be and the concrete assignment of files to mirror servers. Our objective is to find the optimal mirror allocation by solving this model, and to show the general characteristics about the load balance and the improvement of the system reliability by the distributed mirror allocation, quantitatively.

The adequate interpretation of scanning tunneling microscopy (STM) images of the clean Si(001) surface is presented. We have performed both STM observations and {\it ab initio} simulations of STM images for buckled dimers on the clean Si(001) surface. By comparing experimental results with theoretical ones, it is revealed that STM images depend on the sample bias and the tip-sample separation. This enables us to elucidate the relationship between the corrugation in STM images and the atomic structure of buckled dimers. Moreover, to elucidate these changes, we analyze details of the spatial distributions of the $\pi$, $\pi^{\ast}$ surface states and $\sigma$, $\sigma^{\ast}$ Si-Si bond states in the local density of states which contribute to STM images., Comment: 8 pages, 7 figures

The D2194G mutation is responsible for increased levels of FV1 in carriers of the factor V R2 haplotype

An interpretation of the scanning tunneling microscopy (STM) image of a Cl-adsorbed Si(001) surface is reported based on first-principles calculations of its electronic structure. From the analysis of the spatial distribution of the local density of states, we show that the STM image of this surface calculated under the Tersoff–Hamann approximation is in disagreement with the observed STM image. Some remarks associated with the discrepancy are given to further studies.

A novel packet switch architecture is proposed based on a channel grouped virtual circuit (CG-VC) scheme for high-speed communication networks. The case is considered in which there are several parallel channels between two switching nodes. The CG-VC scheme allows a packet to select an available channel in such a way as to avoid congested channels using a simple, hardware-based, self-routing mechanism. As a result, the architecture provides efficient channel use and low switching delay. The performance of the proposed switch is evaluated by simulation. The results show the proposed switch significantly improves channel utilization and switching delay compared with conventional single-channel allocation transmission policies. >

This paper presents an analysis of the frame ALOHA scheme in the multiple-access broadcasting channel with the capture effect, which has not been taken into consideration in past analysis. First, the transmission-success rate, together with its expectation and variance, are determined, which indicate the basic performance of the group with various capture rates. The case is discussed where the capture rate is physically limited. Then two optimization problems are considered to maximize the number of terminals with access success. The first approach considers only a particular group, and a necessary condition is derived for the optimization of that group. Second, the performance of the whole system is improved, and the optimum solution is derived for the group assignment from the viewpoint of the capture rate. Finally, a discussion is made based on the numerical example, and it is shown that a higher throughput than in the past is realized in the multiple-access broadcasting transmission with capture effect. Furthermore, it is shown that a higher performance is realized if all terminals are optimized utilizing the capture effect.

Investigation on water balance, water temperature, dissolved oxygen and other chemical analyses were made for Lake Saino-ko, Nikko, from May 1980 to April 1983.The results are as follows :(1) As estimated by electric prospecting of geology around the lake, the lake was dammed by coarse gravel from the river. Because of this permeable material in the downstream section, the water level of the lake shows a wide seasonal variation. The level falls by about 11m in winter compared with early summer, then the water surface area and the water volume decrease to 1/2 and 1/6, respectively, in winter.(2) The rate of leakage from the lake is estimated from water balance in winter when noticeable inflows are not observed. A high rate of leakage is obtained at a high water level and vice versa.(3) In summer, water balance calculated including the effect of water level has a close relationship to the effective precipitation. The equilibrium water level in summer is estimated to be 13.3m.(4) Water circulation is effective in shallow layers as deduced from dissolved oxygen and water temperature. This may be influenced by the position of leakage. A phenomenal circulation was observed during and after floods.

A new configuration for packet radio networks, called local/global (LG) network configuration, is proposed, aiming at total throughput improvement. By using two kinds of channels (local channel and global channel) and geographically partitioning the total area, the spatial reuse of channel capacity is realized. The performance of this LG configuration is analyzed for a fixed radio network by introducing the delay ratio γ between local and global channels. s-ALOHA protocol is used under heavy overload. By the performance analysis and numerical results, it is concluded that the improvement of the total throughput is attained for a typical network configuration without greatly increasing the mean delay. Also, various schemes for determining the allocation ratio of channel capacity to the local and global channels are presented and studied to apply this LG configuration effectively.

A multichannel CSMA/CD scheme has been proposed which aims at utilizing the merits of CSMA/CD, a typical access control scheme in bus-type LAN, while overcoming the demerits. For this multichannel CSMA/CD scheme, the following three schemes have been proposed: node distribution, region distribution, and load distribution schemes. First, this paper compares and discusses the proposed schemes, especially the load and region distribution schemes. The effective range for each scheme is determined. Then a hybrid load distribution/region distribution scheme is proposed which aims at improving the performance and enlarging the range of applications by dynamically switching between the load distribution and the region distribution schemes, according to the load level of the network. Discussions and qualitative performance evaluations are presented for the protocol, realizability and reliability of the scheme. It is shown that the load distribution/region distribution scheme in the multichannel CSMA/CD scheme exhibits a very satisfactory performance over the entire range of the load, with excellent reliability and expandability.

The CSMA/CD method, one of the communication schemes for bus-type LANs, has problems with respect to transmission capability and its function. This paper presents an access control method named multichannel CSMA/CD for local area networks. In this method, CSMA/CD combined with a new load distribution mechanism and channel selection function is extended to multichannel organization. This method aims at LANs having high performance and multiple functions. As a result of performance evaluation, multichannel CSMA/CD is shown to be superior to the original CSMA/CD with respect to (1) total transmission capacity, (2) throughput-delay characteristic performance, (3) channel stability and (4) adaptability to various kinds of user demands in networks.

The objectives of this study are: (1) to show numerically the performance advantages of the resolvable-contention-ring (ReC-ring) in comparison with typical ring control methods like IEEE 802.5 token-ring, ANSI FDDI I token-ring, slotted-ring and contention-ring, and (2) to consider the possibility of using the priority mechanism of the ReC-ring for multimedia high-speed communications networks. The authors present a simple priority control mechanism based on the time-token scheme for multimedia communications of ReC-rings. The performance of the prioritized and nonprioritized ReC-rings is compared by computer simulation, and the priority mechanism presented is proved to have sufficient validity for multimedia communications networks. >