On-demand learning for a wireless campus

The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment.     

On the macroscopic optimization of multicell wireless systems with multiuser detection and multiple antennas - uplink analysis

In this paper, we consider a system with K single-antenna client users, n/sub B/ base stations (each base station has n/sub R/ antennas), as well as a centralized controller. A client user could be associated with a single base station at any time. All the base stations operate at the same frequency and have optimal multiuser detection per base station which cancels intracell interference only. We consider a general problem of uplink macroscopic resource management where the centralized controller dynamically determines an appropriate association mapping of the K users with respect to the n/sub B/ base stations over a macroscopic time scale. We propose a novel analytical framework for the above macroscopic scheduling problems. A simple rule is to associate a user with the strongest base station (camp-on-the-strongest-cell), and this has been widely employed in conventional cellular systems. However, based on the optimization framework, we found that this conventional approach is in fact not optimal when multiuser detection is employed at the base station. We show that the optimal macroscopic scheduling algorithm is of exponential complexity, and we propose a simple greedy algorithm as a feasible solution.     

Gastrointestinal autonomic nerve tumour presenting as small bowel volvulus: a rare disease with a rare presentation

A 78-year-old Chinese woman presented with recurrent postprandial abdominal pain. Computerised tomography revealed a small bowel tumour causing volvulus of a segment of the small bowel. Laparotomy confirmed an extraluminal ileal tumour with partial volvulus of the involved small bowel segment. Small bowel resection was done. Histological and ultrastructural studies confirmed a gastrointestinal autonomic nerve tumour. We review the medical literature on this rare tumour.     

The prediction of solute transport in surcharged manholes using CFD.

Solute transport processes occur within a wide range of water engineering structures, and urban drainage engineers increasingly rely on modelling tools to represent the transport of dissolved materials. The models take as input representative travel time and dispersion characteristics for key system components, and these generally have to be identified via field or laboratory measurements. Computational Fluid Dynamics (CFD) has the potential to reveal the underlying hydraulic processes that control solute transport, and to provide a generic means of identifying relevant parameter values. This paper reports on a study that has been undertaken to evaluate the feasibility of utilising a CFD-based approach to modelling solute transport. Discrete phase modelling has been adopted, as this is computationally efficient and robust when compared with the time-dependent solution of the advection-dispersion equation. Simulation results are compared with published laboratory data characterising the dispersion effects of surcharged manholes, focusing specifically on an 800 mm diameter laboratory manhole for a flowrate of 0.002 m(3)/s and a range of surcharge depths. Preliminary indications are that the CFD results adequately replicate the measured downstream temporal concentration profiles, and that a threshold surcharge depth, corresponding to a change in hydraulic regime within the manhole, can also be identified.     

Transformations for nonideal uniform circular arrays operating in correlated signal environments

The Davies transformation is a method to transform the steering vector of a uniform circular array (UCA) to one with Vandermonde form. As such, it allows techniques such as spatial smoothing for direction-of-arrival (DOA) estimation in a correlated signal environment, developed originally for uniform linear arrays, to be applied to UCAs. However, the Davies transformation can be highly sensitive to perturbations of the underlying array model. This paper presents a method for deriving a more robust transformation using optimization techniques. The effectiveness of the method is illustrated through a number of DOA estimation examples.     

Performance analysis of adaptive interleaving for OFDM systems

We proposed a novel interleaving technique for orthogonal frequency division multiplexing (OFDM), namely adaptive interleaving, which can break the bursty channel errors more effectively than traditional block interleaving. The technique rearranges the symbols according to instantaneous channel state information of the OFDM subcarriers so as to reduce or minimize the bit error rate (BER) of each OFDM frame. It is well suited to OFDM systems because the channel state information (CSI) values of the whole frame could be estimated at once when transmitted symbols are framed in the frequency dimension. Extensive simulations show that the proposed scheme can greatly improve the performance of the coded modulation systems utilizing block interleaving. Furthermore, we show that the adaptive interleaving out performs any other static interleaving schemes, even in the fast fading channel (with independent fading between symbols). We derived a semi-analytical bound for the BER of the adaptive interleaving scheme under correlated Rayleigh fading channels. Furthermore, we discussed the transmitter-receiver (interleaving pattern) synchronization problem     

Semiautomatic implementation of protocols using an Estelle-Ccompiler

The basic ideas underlying an Estelle-C compiler, which accepts an Estelle protocol specification and produces a protocol implementation in C, are presented. The implementation of the ISO (International Organization for Standardization) class-2 transparent protocol, using the semiautomatic approach, is discussed. A manual implementation of the protocol is performed and compared to the semiautomatic implementation. The semiautomatic approach to protocol implementation offers several advantages over the conventional manual one, including correctness and modularity in protocol implementation code, conformance to the specification, and reduction in implementation time. Finally, ongoing development of a new Estelle-C compiler is presented     

Pressurized fluidized-bed hydro retort ing of raw and beneficiated Eastern oil shales

Bench-scale tests were conducted with raw and beneficiated shales in an advanced multi-purpose research reactor. Raw Alabama shale and raw and beneficiated Indiana shales were retorted at 515 °C using hydrogen pressures of 4 and 7 MPa. Shale feed rates were 15 to 34 kg h⁻¹. High oil yields and carbon conversions were achieved in all tests. Oil yield from Alabama shale hydroretorted at 7 MPa was 200% of Fischer assay. Raw and beneficiated Indiana shales hydroretorted at 7 MPa produced oil yields of 170 and 195% of Fischer assay respectively. Total carbon conversions were >70% for all tests conducted at 7 MPa.