A Finite Element Computational Method for Gas Hydrate. Part I: Theory

A finite element scheme is presented to model the dissociation of gas hydrates in porous media by hot water injection. We show a complete derivation of the finite element formulation, including the associated mass and energy conservation equations capable of performing transient analysis of both conductive and convective heat transfer for gas and liquid flow in porous media. The scheme also includes the latent heat effect to accommodate the change of phase due to melting of hydrate. In the companion paper, Part II, this method is successfully applied to hydrate reservoirs.     

GaAs pHEMT-based technology for microwave applications in a volume MMIC production environment on 150-mm wafers

The establishment of a 150-mm (6-in) gallium arsenide (GaAs) facility is described together with the development of very high yielding and cost-effective semiconductor device technologies and a manufacturing capacity of over 40000 wafers/annum. The background to the demand for very high volumes of RF products for this market is discussed, together with the prospects for future growth. The paper describes recent process development by the utilization of a data-driven yield management system to support the delivery of high-quality RF products to customers. Finally, "end of line" DC and RF testing of finished 150-mm GaAs pHEMT foundry wafers is described, enabling scalar measurements of power, noise, and intermodulation products as well as vector measurements of S-parameters and noise parameters at frequencies of up to 40 GHz.     

Blind equalization - case of an unknown symbol period

We address the problem of estimating blindly a linearly modulated sequence of unknown rate transmitted over an unknown frequency selective channel. We achieve the goal by extending the concept of deconvolution to a cyclo-stationary context and present a generic class of functionals, the minimization of which achieves the equalization. This defines estimates of the symbol rate: by construction, they are insensitive to a lack of excess bandwidth, bestowing a clear advantage on them over the estimates of the literature.     

Phases Resulting from the Reduction of Manganese Metaniobate by Niobium and Tantalum

The sequence of reactions in the reduction of manganese metaniobate with Nb, NbO, and Ta is studied. The reduction of MnNb₂O₆ by Nb or NbO differs in some respects from that by Ta. No Mn(Nb_{2 – x} Ta _x )O_4.33 or Mn(Nb_{2 – x} Ta _x )O_3.67 solid solutions were detected in the reduction products. Tantalum converts directly into manganese metatantalate, without oxidation according to the scheme Ta–TaO–TaO₂–Ta₂O₅. A reaction scheme is suggested for the reduction of MnNb₂O₆ by niobium and tantalum. The unit-cell parameters of the orthorhombic phase MnNb₂O_4.33 resulting from the reduction of MnNb₂O₆ with Nb or Ta are determined.     

A single-chip tuner for DVB-T

A new architecture is presented for a single-chip tuner for digital terrestrial television, based on existing double conversion and direct conversion topologies. The new design forms part of a mixed-signal Digital Video Broadcasting-Terrestrial (DVB-T) receiver system, employing digital signal processing at baseband to ensure minimal performance requirements for the analog circuitry. To evaluate the potential performance of this new tuner/receiver system, high-level system simulations have been performed, followed by the construction of a prototype DVB-T receiver using a custom-designed analog ASIC which integrates all analog tuner blocks (including channel filtering) on one chip. Measured results from this chip, implemented in a 20-GHz bipolar technology, show an overall third-order input referred intercept point of 116 dB/spl mu/V, a noise figure of 14 dB and an automatic gain control range of 71.4 dB, drawing 250 mA at a 5-V supply.     

Complex amplitude estimation in the known steering matrix and generalized waveform case

We consider a special growth-curve (SGC) model with a known steering matrix and generalized waveform in the presence of unknown interference and noise. Several estimators of the complex amplitude based on this model are derived, including the methods of approximate maximum likelihood (AML), minimum variance distortionless response (MVDR), and amplitude and phase estimation (APES). We analyze the statistical properties of these estimators and show that in the presence of temporally white but spatially correlated noise and interference, AML is asymptotically statistically efficient for a large snapshot number while MVDR and APES are asymptotically equivalent but not statistically efficient. Via several numerical examples, we also show that when the noise and interference are both spatially and temporally correlated, the APES estimator can achieve better estimation accuracy and exhibit greater robustness than the other methods.     

Adsorption of H2S or SO2 on an activated carbon cloth modified by ammonia treatment

The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H₂S and SO₂ in humid air at 25 °C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 °C or with ammonia/steam at 800 °C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H₂S and SO₂ and the subsequent catalyst/support regeneration process.     

Orthogonal space-time block codes: maximum likelihood detection for unknown channels and unstructured interferences

Space-time coding (STC) schemes for communication systems employing multiple transmit and receive antennas have been attracting increased attention. The so-called orthogonal space-time block codes (OSTBCs) have been of particular interest due to their good performance and low decoding complexity. In this paper, we take a systematic maximum-likelihood (ML) approach to the decoding of OSTBC for unknown propagation channels and unknown noise and interference conditions. We derive a low-complexity ML decoding algorithm based on cyclic minimization and assisted by a minimum amount of training data. Furthermore, we discuss the design of optimal training sequences and optimal information transfer to an outer decoder. Numerical examples demonstrate the performance of our algorithm.     

QMTool: an XML-based management platform for QoS-aware IP networks

Technological and human factors have contributed to the increasing complexity of the network management problem. Heterogeneity and globalization of network resources have, on one hand, increased user expectations for flexible and easy-to-use environments and, on the other, propounded entirely novel ways to face the management problem. Several research efforts recognize the need for integrated solutions to manage both network resources and services in open and global environments. Undoubtedly, these solutions should permit the coexistence of different management models and should interoperate with legacy systems. The presented management system, QoS management tool (QMTool), aspires to address the heterogeneity, complexity, and dynamic behavior of QoS-enabled IP networks by taking advantage of the optimum fit of a number of novel technologies. A layered framework architecture, including element, network management, and visualization service, is provided, and a high level of information abstraction in network configuration and monitoring is introduced mainly based on the capabilities of the Extensible Markup Language (XML). Moreover, the functional components for providing (re-)configuration, fault management monitoring, and network visualization facilities are also presented, followed by notes of implementation issues.     

Optical properties of Nd-doped Ca3(VO4)2 single crystal fiber

Optical absorption and photoluminescence of Ca₃(VO₄)₂ single crystal grown by a floating-zone technique and containing Nd³⁺ ions were investigated. High absorption coefficients and broadening of most absorption bands are present at 300 K, while substructures in some of the same bands can be evidenced at 12 K. Most features of measured spectra are characteristic of random occupation of more than a single Ca²⁺ site by the Nd³⁺ ion and of distortions provoked by different charge compensation mechanisms involving oxygen vacancies promotion in the crystal lattice. Nd³⁺ optical properties were studied by using the Judd-Ofelt theory to calculate the spectral parameters relevant for laser applications.