Mixed finite elements and Newton‐type linearizations for the solution of Richards' equation

We present the development of a two‐dimensional Mixed‐Hybrid Finite Element (MHFE) model for the solution of the non‐linear equation of variably saturated flow in groundwater on unstructured triangular meshes. By this approach the Darcy velocity is approximated using lowest‐order Raviart–Thomas (RT₀) elements and is ‘exactly’ mass conserving. Hybridization is used to overcome the ill‐conditioning of the mixed system. The scheme is globally first‐order in space. Nevertheless, numerical results employing non‐uniform meshes show second‐order accuracy of the pressure head and normal fluxes on specific grid points. The non‐linear systems of algebraic equations resulting from the MHFE discretization are solved using Picard or Newton iterations. Realistic sample tests show that the MHFE‐Newton approach achieves fast convergence in many situations, in particular, when a good initial guess is provided by either the Picard scheme or relaxation techniques. Copyright © 1999 John Wiley & Sons, Ltd.     

Approach for developing a large-signal model of a 150-GHz HEMT

In this study, the development of a large-signal model describing the electrical behavior of an InAIAs/InGaAs/InP-HEMT will be discussed. The transistors under question were fabricated at our laboratory. They revealed a transit frequency of 150 GHz, which is, to our knowledge, the best result obtained with a T-gate of 0.25-μm footprint. The aim of this project was to develop a model of this transistor for simulating nonlinear circuits with commercial simulator software like HP-MDS or SPICE. The procedure outlined results in an easily applicable model which produces very good fits to the measured S-parameters. © 1996 John Wiley & Sons, Inc.     

InP-InGaAs single HBT technology for photoreceiver OEIC's at 40Gb/s and beyond

We describe an advanced InP-InGaAs-based technology for the monolithic integration of pin-photodiodes and SHBT-transistors. Both devices are processed using the same epitaxial grown layer structure. Employing this technology, we have designed and fabricated two photoreceivers achieving transimpedance gains of 170 Ω/380 Ω and optical/electrical bandwidths of 50 GHz/34 GHz. To the best of our knowledge, this is the highest bandwidth of any heterojunction bipolar transistor (HBT)-based photoreceiver optoelectronic integrated circuit (OEIC) published to date. We even predict a bandwidth of 60 GHz for the same circuit topology by a simple reduction of the photodiode diameter and an adjustment of the feedback resistor value     

Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon

Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved organic carbon (DOC) concentration. Our data indicate that SUVA, determined at 254 nm, is strongly correlated with percent aromaticity as determined by 13C NMR for 13 organic matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estimating the dissolved aromatic carbon content in aquatic systems. Experiments involving the reactivity of DOC with chlorine and tetramethylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements are good predictors of general chemical characteristics of DOC, they do not provide information about reactivity of DOC derived from different types of source materials. Sample pH, nitrate, and iron were found to influence SUVA measurements.     

Acquisition and validation of complex object database schemata supporting multiple inheritance

We present an intelligent tool for the acquisition of object-oriented schemata supporting multiple inheritance, which preserves taxonomy coherence and performs taxonomic inferences. Its theoretical framework is based onterminological logics, which have been developed in the area of artificial intelligence. The framework includes a rigorous formalization of complex objects, which is able to express cyclic references on the schema and instance level; asubsumption algorithm, which computes all impliedspecialization relationships between types; and an algorithm to detectincoherent types, i.e., necessarily empty types. Using results from formal analyses of knowledge representation languages, we show that subsumption and incoherence detection are computationally intractable from a theoretical point of view. However, the problems appear to be feasible in almost all practical cases.     

An information integration framework for e-commerce

One of the main challenges for e-commerce infrastructure designers is to retrieve data from different sources and create a unified view that overcomes contradictions and redundancies. Virtual catalogs, such as the Momis project, can help synthesize data and present it in a unified manner to the customer.     

Protection from carcinogenic agents in work environments: considerations on Title VII of Legislative Decree 626/94

A variety of techniques are available for reconstruction of the wrist. The efficacy of wrist arthroplasty, however, is met with narrowed indications and does not enjoy the success that total joint replacement in other joints, such as the hip and knee, has enjoyed. With design improvements during the last decade, good short-term results from total wrist arthroplasty can be expected in the low-demand patient with rheumatoid arthritis. Wrist arthrodesis, either pancarpal or limited, is considered the primary surgical alternative in patients with most arthritic conditions of the wrist. The pancarpal arthrodesis is a predictable, durable alternative to a variety of post-traumatic, degenerative, or neoplastic conditions of the wrist; however, some authors report that complications may be prevalent. This procedure also may be modified and applied to the destroyed rheumatoid wrist. Overall, selection of fixation mode depends on bone quality. In an attempt to preserve motion, various limited arthrodeses of the carpus have been described. Although technically demanding, successful results may be expected, especially in conditions of carpal instability. With the current wide array of surgical alternatives, the surgeon must consider each case carefully and select the procedure that best applies to each particular situation. Furthermore, it is extremely important that the surgeon educate the patient on the limitations of each procedure.     

Control-flow versus data-flow-based scheduling: combining bothapproaches in an adaptive scheduling system

As high-level synthesis techniques gain acceptance among designers, it is important to be able to provide a robust system which can handle large designs in short execution times, producing high-quality results. Scheduling is one of the most complex tasks in high-level synthesis, and although many algorithms exist for solving the scheduling problem, it remains a main source of inefficiency by either not producing high-quality results, not taking into account realistic design requirements, or requiring unacceptable execution times. One of the main problems in scheduling is the dichotomy between control and data. Many algorithms to date have been able to provide scheduling solutions by looking only at either the data part or the control part of the design. This has been done in order to simplify the problem; however, it has resulted in many algorithms unable to handle efficiently large designs with complex control and data functionality. This paper presents algorithms for combining dataflow and control-flow techniques into a robust scheduling system. The main characteristics of this system are as follows: 1) it uses path-based techniques for efficient handling of control and mutual exclusiveness (for resource sharing), 2) it allows operation reordering and parallelism extraction within the context of path-based scheduling, 3) it contains a control partitioning algorithm for design space exploration as well as for reducing the number of control paths, and 4) it combines the above algorithms into an adaptive scheduling system which is capable of trading optimality for execution time on-the-fly. Results involving billions of paths are presented and analyzed