Voyager Neptune radio science data were collected using three antennas on Earth on August 25, 1989. A parabolic antenna at Canberra, Australia, of 70 meter diameter received 2.3GHz and 8.4GHz carriers. The 64 meter parabolic antennas at Parkes. Australia and Usuda, Japan, received only the 8.4GHz and only the 2.3GHz carriers, respectively. It is necessary to reduce the frequency variation in the received signal carrier to extract accurate information on physically interesting objects such as Neptune's atmosphere, ionosphere, or the rings. After the frequency stabilization process, the frequency drift was reduced from 180Hz down to a maximum of 5Hz, making it possible to reduce the data bandwidth and, consequently, the data volume, by a factor of 30. The uncertainty of the signal frequency estimates were also reduced from 5 down to 510-3Hz/sec above the atmosphere, from 5 down to 0.5Hz/sec in the atmosphere, and from 50 down to 3Hz/sec at the beginning and the end of the atmospheric occultation. Much of the remaining uncertainty is due to scintillations in Neptune's atmosphere and cannot be reduced further. The estimates are thus meaningfully accurate and suitable for scientific analysis and coherent arraying of data from different antennas. Two results based on these estimates are shown: a preliminary temperature-pressure (T-p) profile of Neptune's atmosphere down to a pressure level of 2 bar computed using the Usuda 2.3GHz data, and a multipath phenomenon in the atmosphere seen in Canberra 8.4GHz data. Our T-p profile shows good agreement with the results presented by Lindal et al. within 1K below 100mbar pressure level, even though our result is based on an independent data set and processing. A comparison of the multipath phenomena at Neptune with that at Uranus implies that it was created by a cloud layer with a smaller scale height than the atmosphere above and below it. The processing methods described were developed in part with the interest to coherently array Canberra, Parkes and Usuda data. In this sense, while this paper does not extend any science results, the observations and results are derived independently from other published results, and in the case of Usuda, are completely new.

Hydrogen termination of HF-treated Si surfaces and the oxidation kinetics have been studied by x-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FT-IR) Attenuated Total Reflection (ATR). The oxidation of hydrogen-terminated Si in air or in pure water proceeds parallel to the surface presumably from step edges, resulting in the layer-by-layer oxidation. The oxide gryowth rate on an Si(100) surface is faster than (110) and (111) when the wafer is stored in pure water. This is interpreted in terms of the steric hindrance against molecular oxygen penetration throughth the (110) and (111) surfaces where the atom void size is equal to or smaller than O2 molecule. The oxide growth rate in pure water for heavily doped n-type Si is significantly high compared to that of heavily doped p-type Si. This is explained by the conduction electron tunneling from Si to absorbed O2 molecule to form the O2- state. O2- ions easily decompose and induce the surface electric field, enhancing the oxidation rate. It is found that the oxidation of heavily doped n-type Si in pure water is effectively suppressed by adding a small amount (1003600 ppm) of HCl.

The main objective of this paper is to propose a new top-down subcube allocation scheme which has complete subcube recognition capability with quick response time. The proposed subcube allocation scheme, called Heuristic Subcube Allocation (HSA) strategy, is based on a heuristic and undirected graph, called Subcube (SC)-graph, whose vertices represent the free subcubes, and edge represents inter-relationships between free subcubes. It helps to reduce the response time and internal/external fragmentation. When a new subcube is released, the higher dimension subcube is generated by the cycle detection in the SC-graph, and the heuristic is used to reduce the allocation time and to maintain the dimension of the free subcube as high as possible. It is theoretically shown that the HSA strategy is not only statically optimal but also it has a complete subcube recognition capability in a dynamic environment. Extensive simulation results show that the HSA strategy improves the performance and significantly reduces the response time compared to the previously proposed schemes.

Lexical-Functional Grammars (LFG's) were introduced to define the syntax of natural languages. In LFG's, each node of a derivation tree has some attributes. An LFG G consists of a context-free grammar (cfg) G0 called the underlying cfg of G and a description Pfs of constraints between the values of the attributes. Pfs can specify (1) constraints between the value of an attribute of a node and those of its children, and (2) constraints between the value of an attribute of a node called a controller and that of a node called its controllee. RLFG's were introduced as a subclass of LFG's. In RLFG's, only constraints between the value of an attribute of a node and those of its children can be specified. It is shown in this paper that the class of languages generated by RLFG's is equal to the class of recursively enumerable languages. Some restrictions on LFG's were proposed for the purpose of efficient parsing. Among them are (1) the condition called a valid derivation, and (2) the condition that the underlying cfg is cycle-free. For an RLFG G, if the production rules of the underlying cfg of G are of the form AaB or Aa for nonterminal symbols A, B and a terminal symbol a, then G is called an R-RLFG. Every R-RLFG satisfies the above restriction (1) and (2). It is also shown in this paper that the class of languages generated by R-RLFG's contains an NP-hard language, which means that parsing in deterministic polynomial time of LFG's is impossible in general (unless PNP) even if the above restrictions (1) and (2) are satisfied.

The motion of particles in low-pressure chemical vapor deposition (LPCVD) (0.4 Torr) equipment has been investigated by a numerical simulation. The effects of wafer orientation, electrostatic forces, and thermophoresis were evaluated. Horizontal surface-down processing and vertical processing can reduce particulate contamination remarkably compared with horizontal surface-up processing. Static electricity control is essential. Weakly charged wafers (several V to several 10 V) can significantly increase submicron particle deposition. In the absence of electrical forces, thermophoresis prevents deposition of particles in the size range 0.03 µmDp0.6 µm, when the temperature difference between the wafer surface and the gas inlet temperature exceeds 100. Deposition of particles smaller than 0.03 µm still occurs by diffusion.

There has been much interest in building corporate private communication networks. This aim requires a method that optimizes the economical aspect of network configurations. The authors propose a network design method supported by knowledge-base. This method is used to design a cost-effective corporate communication network, using leased lines. The knowledge-base description depends on the production rule. The network configuration is improved by introducing expert knowledge, after designing the network by a conventional algorithm. Design results show the advantages of the proposed method.

The effects of changing system parameters on job scheduling policies are studied for load balancing of multi-class jobs in a distributed computer system that consists of heterogeneous host computers connected by a single-channel communications network. A job scheduling policy decides which host should process the arriving jobs. We consider two job scheduling policies. The one is the overall optimal policy whereby jobs are scheduled so as to minimize the overall mean job response time. Tantawi and Towsley obtained the algorithm that gives the solution of the policy in the single class job environment and Kim and Kameda extended it to the multiple job class environment. The other is the individually optimal policy whereby jobs are scheduled so that every job may feel that its own expected response time is minimized. We can consider three important system parameters in a distributed computer system: the communication time of the network, the processing capacity of each node, and the job arrival rate of each node. We examine the effects of these three parameters on the two load balancing policies by numerical experiment.

In this paper, we present an automatic implementation method by which executable communication programs in C can be generated from protocol specifications in LOTOS. The implementation method consists of two parts: 1) An implementation strategy and 2) a set of translation rules. The first part consists of the basic ideas on how to realize the primary mechanisms in LOTOS specifications. The second part formulates the implementation method by way of the translation rules based on the implementation strategy. The characteristics of our method can be summarized as follows: We formulate our implementation method by way of translation rules. These rules are defined topdown in the form of syntax-directed translation function. The mechanism for controlling concurrency and communication among the user processes corresponding to the processes in LOTOS specification is easily realized by using UNIX operating system functions. The translation rules have been implemented on the AS 3000 (SUN3) workstation. An application of this implementation method is demonstrated by a simplified token-ring-protocol.

Parallel multiple context-free grammars (pmcfg's) and multiple context-free grammars (mcfg's) were introduced as extensions of context-free grammars to describe the syntax of natural languages. Pmcfg's and mcfg's deal with tuples of strings, and it has been shown that the universal recognition problem for mcfg's is EXP-POLY time-complete where the universal recognition problem is the problem to decide whether G generates w for a given grammar G and string w. In this paper, the universal recognition problems for the class of pmcfg's and for the subclass of pmcfg's with the information-lossless condition are shown to be EXP-POLY time-complete and PSPACE-complete, respectively. It is also shown that the problems for pmcfg's and for mcfg's with a bounded dimension are both -complete and those for pmcfg's and for mcfg's with a bounded degree are both -complete. As a corollary, the problem for modified head grammars introduced by Vijay-Shanker, et al. to define the syntax of natural languages is shown to be in deterministic polynomial time.

In the approximate learning model introduced by Valiant, it has been shown by Blumer et al. that an Occam algorithm is immediately a PAC-learning algorithm. An Occam algorithm is a polynomial time algorithm that produces, for any sequence of examples, a simple hypothesis consistent with the examples. So an Occam algorithm is thought of as a procedure that compresses information in the examples. Weakening the compressing ability of Occam algorithms, a notion of weak Occam algorithms is introduced and the relationship between weak Occam algorithms and PAC-learning algorithms is investigated. It is shown that although a weak Occam algorithm is immediately a (probably) consistent PAC-learning algorithm, the converse does not hold. On the other hand, we show how to construct a weak Occam algorithm from a PAC-learning algorithm under some natural conditions. This result implies the equivalence between the existence of a weak Occam algorithm and that of a PAC-learning algorithm. Since the weak Occam algorithms constructed from PAC-learning algorithms are deterministic, our result improves a result of Board and Pitt's that the existence of a PAC-learning algorithm is equivalent to that of a randomized Occam algorithm.

This paper describes a method of evaluating operations effort for fiber optic subscriber loops, such as the Central Terminal/Remote Terminal (CT/RT) system, which can economically provide a variety of telecommunication services. Four system configurations with different operation procedures are evaluated by simulation. By evaluating the operating costs associated with service provisioning, it is shown that automatic distributing frames are cost effective in subscriber loops with CT/RT systems. Moreover, the most economical operation strategies for installing and extending subscriber boards are discussed in terms of facility and operations cost.

The Asynchronous Transfer Mode (ATM) is expected to be the basic transmission technology for B-ISDN. Before this happens, however, it will be necessary to predict the impact of fully-deployed ATM-based networks quantitatively. This paper compares the cost-efficiency of an ATM-based network with that of an STM-based network and clarifies the applicable areas of ATM network configurations, in terms of required facilities and considering the effect of statistical multiplexing. It shows cost-effective network configurations based on different service classes and a network configuration suited to ATM. It also discusses the effect of a Synchronous Digital Hierarchy architecture for Virtual Path dimensioning.

It is crucial to make Si wafer surfaces ultraclean in order to realize such advanced processes as the low-temperature process and the high-selectivity in the ULSI production. The ultra clean wafer surface must be perfectly free from particles, organic materials, metallic impurities, native oxide, surface microroughness, and adsorbed molecule impurities. Since the metallic contamination on the wafer surface, which is one of the major contaminants to be overcome in order to come up with the ultra clean wafer surface, has the fatal effect on the device characteristics, the metallic impurities in the wafer surface must be suppressed at least below 1010 atoms/cm2. Meanwhile the current dry processes such as reactive ion etching or ion implantation, suffer the metallic contamination of 10121013 atoms/cm2. The wet process becomes increasingly important to remove the metallic impurities introduced in the dry process. Employing a new evaluation method, the metallic impurity segregations at the inrerface between the Si and liquid employed in the wet cleaning process of the Si surface such as ultrapure water and various clemicals were studied. This article clearly indicate that it is important to suppress the metallic impurities, such as Cu, which can exchange electrons with Si to be segregated, at least below the 10 ppt level in ultrapure water and liquid chemical such as HF, H2O2, which are employed in the final step of the wet cleaning. When the ultrapure water rinsing is performed in the ambience containing oxygen, the native oxide grows accompanying an inclusion of metals featuring lower electron negativity than Si. It is revealed that, in order to provent the metallic impurity precipitation, it is require not only to remove metallic impurities from ultrapure water but also to keep the cleaning ambience without oxygen, such as the nitrogen ambience, so as to suppress the native oxide formation.

The two most important parameters in reactive ion etching process, ion bombardment energy and flux, were extracted through a simple RF waveform measurement at the excitation electrode in a conventional cathode-coupled plasma RIE system. By using the extracted plasma parameters, damage and contamination in Si substrates induced by reactive ion etching in a SiCl4 plasma were investigated. A very convenient map representation of ion energy and ion flux was introduced in understanding the etching process occurring in the RIE system.

Plasmaless etching using ClF3 gas has been investigated on nitride films with different composition. For the sputter deposited and thermally grown silicon nitride films containing no hydrogen, the etch rate increases and the activation energy decreases with increase of the composition ratio of silicon to nitrogen between 0.75 and 1.3. This fact indicates that the etching is likely to proceed through the reaction between Si and ClF3. The native oxide on the silicon-nitride films can also be removed with ClF3 gas. Ultra-violet light irradiation from a low pressure mercury lamp remarkably accelerates the removal of the native oxide and the etch rate of the thermally grown silicon-nitride films. For the plasma deposited films, the etch rate is strongly accelerate with increasing hydrogen content in the films, but the activation energy hardly depends on the bounded hydrogen in the films, consistent with the results for Si etching.

Synchrotron radiation (SR) irradiation of amorphous SiO2 (a-SiO2) induces continuous removal of the SiO2 film without the use of etching gas. The dependence of the photostimulated evaporation rate on substrate temperature and SR intensity was measured and the reaction mechanism is discussed in detail separately for surface and bulk. Using the high material selectivity of the Sr-stimulated evaporation, a sefl-aligned process to fabricate a 0.6 µm line-and-space pattern is presented. Si surface cleaning is demonstrated as an example of application of this reaction to thin native oxide film grown by wet pretreatment. Si(100)-21 and Si(111)-77 structures were observed by reflection high energy electron diffraction (RHEED) at temperatures as low as 650. The difference between a-SiO2 and native oxide on the evaporation rate is higlighted. Epitaxial Si growth using disilane (Si2H6) gas occurs selectively in the SR-irradiated region on a Si(100) surface. Using SR irradiation in an ultrahigh vacuum, followed by residual oxide reduction by disilane, is proposed as an effective cleaning method.

As part of Hitachi's development of clean semiconductor processing equipment, the Fluids Modeling Group of the Mechanical Engineering Research Laboratory is developing a computer model, CONTAMINATE, for simulating contamination of wafers in chemical vapor deposition (CVD) systems. CONTAMINATE is based on a 2D implementation of the SIMPLER algorithm for simulating convection/diffusion transport processes. The new model includes modules for simulating fluid flow, heat transfer, chemical reactions, and gas-phase formation and deposition of clusters and particles. CONTAMINATE outputs property fields and estimates of various film quality indices. Using CONTAMINATE we simulated a SiH4: O2: N2 gas mixture at 300 K flowing over a wafer heated to 700 K. System pressures were varied from 1-100 torr and SiH4 pressures from 0.1 to 10 torr. Deposition characteristics are in qualitative agreement with actual systems and are summarized as follows: (1) No particles larger than 0.1µm deposited for any of the conditions tested. (2) Film damage occurred above 10 torr, but no damage occurred below 10 torr. (3) Increasing SiH4 pressure at constant system pressure eliminated particle deposition because particles grew large enought that thermophoresis blocked particle diffusion. (4) Conformal deposition of featured surfaces was achieved only at 1 torr. (5) Film thickness variation over the diameter of the wafer was 15% at 100 torr, 3% at 10 torr, and 1% at 1 torr.

A pattern is a finite string of constant symbols and variable symbols. The language of a pattern is the set of all strings obtained by substituting any nonnull constant string for each variable symbol in the pattern. The class of pattern languages was introduced by Angluin in 1979 as a concrete class which is inferable from positive data. In this paper, we consider the decision problem whether for given two patterns there is a containment relation between their languages, which was posed by Angluin and its decidability remains open. We give some sufficient conditions to make this problem decidable. We also introduce the notions of generalizations and minimal generalizations common to a set of patterns. We characterize the above open problem using the minimal generalization.

This paper proposes design schemes which obtain an efficient spare-channel assignment against single and double link failures for a self-healing network. Spare-channel design problems can be formulated as a linear-programming (LP) problem when variables are assumed to be continuous. For the problem, the proposed algorithm effectively solves a sub-set of whole constraints by making use of a maximum-flow algorithm in an iterative manner. It is shown that the maximum number of iteration times is limited by the number of links in the network. Moreover, the relation between the design function and the self-healing function is discussed. It is also shown that the cooperation of the two functions can realize more effective control in large scale networks.

This paper deals with the problem of translating Japanese adnominal particles into English according to the idea of Example-Based Machine Translation (EBMT) proposed by Nagao. Japanese adnominal particles are important because: (1) they are frequent function words; (2) to translate them into English is difficult because their translations are diversified; (3) EBMT's effectiveness for adnominal particles suggests that EBMT is effective for other function words, e. g., prepositions of European languages. In EBMT, (1) a database which consists of examples (pairs of a source language expression and its target language translation) is prepared as knowledge for translation; (2) an example whose source expression is similar to the input phrase or sentence is retrieved from the example database; (3) by replacements of corresponding words in the target expression of the retrieved example, the translation is obtained. The similarity in EBMT is computed by the summation of the distance between words multiplied by the weight of each word. The authors' method differs from preceding research in two important points: (1) the authors utilize a general thesaurus to compute the distance between words; (2) the authors propose a weight which changes for every input. The feasibility of our approach has been proven through experiments concerning success rate.