Stability investigation for InP DHBT mm‐wave power amplifier

In this article, we discuss stability issues for mm‐wave monolithic integrated power amplifiers using InP double heterojunction bipolar transistor (DHBT) technology targeting E‐band applications at 71–76 GHz and 81–86 GHz. Different stability detection methods based on the classical two‐port K‐Δ_s pair, linear three‐port graphical analysis, system identifications, circuit modal analysis, and normalized determinant function are all reviewed. The corresponding techniques are employed to predict the occurrence of instability at 15 GHz observed during measurements on a fabricated monolithic microwave integrated circuit power amplifier. Experimental results from a redesigned power amplifier with improved stability are presented to confirm that the previously detected oscillation loop is removed using odd‐mode stabilization resistors with the correct choice of values and locations. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 662–674, 2013.     

EGO: A personalized multimedia management and retrieval tool

The problems of content‐based image retrieval (CBIR) systems can be attributed to the semantic gap between the low‐level data representation and the high‐level concepts the user associates with images, on the one hand, and the time‐varying and often vague nature of the underlying information need, on the other. These problems can be addressed by improving the interaction between the user and the system. In this article, we sketch the development of CBIR interfaces and introduce our view on how to solve some of the problems these interfaces present. To address the semantic gap and long‐term multifaceted information needs, we propose a “retrieval in context” system, EGO. EGO is a tool for the management of image collections, supporting the user through personalization and adaptation. We will describe how it learns from the user's personal organization, allowing it to recommend relevant images to the user. The recommendation algorithm is described, which is based on relevance feedback techniques. Additionally, we provide results of a performance analysis of the recommendation system and of a preliminary user study. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 725–745, 2006.     

Introducing fuzziness in object models and database interfaces through aspects

Imperfection in information can be considered a crosscutting concern that manifests itself in diverse kinds of imprecision, uncertainty, or inconsistency in the data models of a software system. The extension of existing programming and querying interfaces for the different aspects of information imperfection requires a proper modularization of the different concerns of numerical imprecision handling, so that the extensions do not interfere with existing programming practices and do not obscure the original design. Aspect‐oriented design (AOD) enables such a form of nonintrusive extensions to be added to existing software libraries, clearly separating fuzziness or other imperfections in data as a differentiated concern that can be considered from the early phases of development. In this article, a general framework for aspect‐based extension of data models and fuzzy databases is described, and some design and implementation issues of such AOD‐based extensions on OJB database libraries are described as a case study. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 1199–1216, 2006.     

Design of active inductors in SiGe/SiGe:C processes for RF applications

Applicability of silicon‐based heterojunction bipolar processes is investigated for designing active inductors with high quality factors (Q). Results for grounded type one‐port active inductor incorporating frequency‐dependent as well as frequency‐independent negative resistances are examined. Later, the negative resistance aspect is extended from one‐port to two‐port active inductor circuit to ensure its use as a series element. The enhanced Q‐values of all the inductive circuits are observed in accordance with the theory. Moderately high‐Q values (～100) with considerable inductances (～0.2–1 nH) are obtained in the RF frequency ranges (～5–9 GHz). © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Recurrent neural network technique for behavioral modeling of power amplifier with memory effects

A new technique for behavioral modeling of power amplifier (PA) with short‐ and long‐term memory effects is presented here using recurrent neural networks (RNNs). RNN can be trained directly with only the input–output data without having to know the internal details of the circuit. The trained models can reflect the behavior of nonlinear circuits. In our proposed technique, we extract slow‐changing signals from the inputs and outputs of the PA and use these signals as extra inputs of RNN model to effectively represent long‐term memory effects. The methodology using the proposed RNN for modeling short‐term and long‐term memory effects is discussed. Examples of behavioral modeling of PAs with short‐ and long‐term memory using both the existing dynamic neural networks and the proposed RNNs techniques are shown. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:289–298, 2015.     

Closed‐form approach to design distributed matching networks for high‐frequency amplifiers

Based on the use of distributed lossless elements, a closed‐form synthesis for double‐frequency‐matching networks is introduced with an emphasis on the design of high‐frequency amplifiers. Three different circuit conditions are considered and design relationships are provided and discussed. Finally, the proposed approach, which uses the circle method, is successfully employed to design a Ka‐band (26–32 GHz) linear amplifier with gain equal to 8 dB and return loss greater than 10 dB for the considered band. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

A model of an information retrieval system with unbalanced fuzzy linguistic information

Most information retrieval systems based on linguistic approaches use symmetrically and uniformly distributed linguistic term sets to express the weights of queries and the relevance degrees of documents. However, to improve the system–user interaction, it seems more adequate to express these linguistic weights and degrees by means of unbalanced linguistic scales, that is, linguistic term sets with different discrimination levels on both sides of the middle linguistic term. In this contribution we present an information retrieval system that accepts weighted queries whose weights are expressed using unbalanced linguistic term sets. Then, the system provides the retrieved documents classified in linguistic relevance classes assessed on unbalanced linguistic term sets. To do so, we propose a methodology to manage unbalanced linguistic information and we use the linguistic 2‐tuple model as the representation base of the unbalanced linguistic information. Additionally, the linguistic 2‐tuple model allows us to increase the number of relevance classes in the output and also to improve the performance of the information retrieval system. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 1197–1214, 2007.     

Study on battlespace ontology construction approach

In Network Centric Warfare, the sensor network's capability is much stronger than ever; the force can get a mass of information about battlespace in real or near‐real time. How to utilize the information about battlespace effectively and transform the information superiority into knowledge superiority is a key problem for NCW research. To solve this problem, first we need to establish a suitable knowledge infrastructure. In this article, battlespace ontology is considered as the knowledge infrastructure of NCW, and we propose a battlespace ontology construction approach based on OWL, which consists of two parts: formal ontology construction approach to construct subdomain ontologies of battlespace and formal ontology integration approach to integrate subdomain ontologies of battlespace. Then a concrete application of the approach to an air combat battlespace is given. © 2005 Wiley Periodicals, Inc. Int J Int Syst 20: 1219–1231, 2005.     

Nonlinear circuit stability under large‐signal pumping: Three‐port μ stability factor versus conversion matrix system identification—application to a millimeter‐wave band MMIC up‐converter

This article presents and discusses a method to determine stability in nonlinear three‐port circuits based on a generalized three‐port μ stability factor applied to linearized S parameters under large‐signal pumping. A comparison with an extension of the conversion matrix–based, system pole–zero identification used to analyze circuit stability is also presented. The relationship between the two techniques has been verified by means of an ideal two‐port nonlinear circuit, and then, it has been applied in the design of a three‐port millimeter‐wave Monolithic Microwave Integrated Circuit (MMIC) up‐converter. The circuit has been fabricated in a commercial GaAs process. On‐wafer measurements showed an average conversion loss about 3.5 dB in a RF bandwidth between 40.4 and 41.5 GHz with local oscillator (LO) frequency fixed at 42.5 GHz. A RF/LO isolation better than 25 dB was measured in the whole band, also showing outstanding intermodulation performance. With the proposed approach, the appearance of spurious oscillations was prevented. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

An arithmetic approach for the computing with words paradigm

Computing with words applications are mostly built using rule‐based systems, which have some important deficits: First, it is not easy to deal with high dimension problems because the size of the rule base increases exponentially; second, it is not possible to concatenate two or more systems without losing information; and third, there are no ways to compute inputs from outputs. In this article we show an alternative kind of system that remedies those deficits in many applications. It is based on fuzzy arithmetic rather than fuzzy logic. We also show application examples. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 121–142, 2006.     

Scene similarity measure for video content segmentation in the framework of a rough indexing paradigm

This article presents a scene similarity measure for video content segmentation. In the context of the rough indexing paradigm, we extract only partial information from MPEG compressed streams to measure the similarity of video frames through time. The similarity measure of I‐Frames is defined based on motion compensation of DC images and local contrast computation. The method allows a real‐time segmentation of the video content. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 765–783, 2006.     

Trust ontologies for e‐service environments

In this article, we introduce trust ontologies. An ontology represents a set of concepts that are commonly shared and agreed to by all parties in a particular domain. Here, we introduce generic and specific trust ontologies. These ontologies include the following: an agent trust ontology and trustworthiness; agents include sellers, service providers, Web sites, brokers, shops, suppliers, buyers, or reviewers. A services trust ontology and trustworthiness assists in measuring the quality of service that agents provide in the service‐oriented environment such as sales, orders, track and trace, warehousing, logistics, education, governance, advertising, entertainment, trading, online databases, virtual community services, security, information services, opinions, and e‐reviews. A goods or products trust ontology and trustworthiness is useful for measuring the quality of products such as commercial products, information products, entertainment products, or second‐hand products. We present a trust ontology that is suitable for all types of agents that exist in the service‐oriented environment. As agent trust is measured through the quality of goods and services, we introduce two additional distinct concepts of service trust ontology and product trust ontology. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 519–545, 2007.     

Mining for video production invariants to measure style similarity

This article focuses on video document comparison using audiovisual production invariants (API). API are characterized by invariant segments obtained on a set of low‐level features. We propose an algorithm to detect production invariants throughout a collection of audiovisual documents. The algorithm runs on low‐level features, considered as time series, and extracts invariant segments using a one‐dimensional morphological envelop comparison. Then, based on the extracted results, we define a style similarity measure between two video documents. A derivative pseudo distance is also proposed. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 747–763, 2006.     

On the consistency of rule bases based on lattice‐valued first‐order logic LF(X)

The consistency of a rule base is an essential issue for rule‐based intelligent information processing. Due to the uncertainty inevitably included in the rule base, it is necessary to verify the consistency of the rule base while investigating, designing, and applying a rule‐based intelligent system. In the framework of the lattice‐valued first‐order logic system LF(X), which attempts to handle fuzziness and incomparability, this article focuses on how to verify and increase the consistency degree of the rule base in the intelligent information processing system. First, the representations of eight kinds of rule bases in LF(X) as the generalized clause set forms based on these rule bases' nonredundant generalized Skolem standard forms are presented. Then an α‐automated reasoning algorithm in LF(X), also used as an automated simplification algorithm, is proposed. Furthermore, the α‐consistency and the α‐simplification theories of the rule base in LF(X) are formulated, and especially the coherence between these two theories is proved. Therefore, the verification of the α‐consistency of the rule base, often an infinity problem that is difficult to solve, can be transformed into a finite and achievable α‐simplification problem. Finally, an α‐simplification stepwise search algorithm for verifying the consistency of the rule base as well as a kind of filtering algorithm for increasing the consistency level of the rule base are proposed. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 399–424, 2006.