Evaluation of Interoperability Criteria and Mechanisms for Seamless Inter-Working Between UMTS-HSDPA and WLAN Networks Enhanced with MIMO Techniques

This article proposes criteria and mechanisms that achieve seamless inter-working between the multi-radio access technologies that will compose the fourth-generation (4G) wireless mobile environment. We address the problem of incorporating system interoperability in order to provide the user with seamless mobility across different radio access technologies; namely we focus on inter-working UMTS-High Speed Downlink Packet Access (HSDPA) and WLAN networks, as these two networks are believed to be major components of the 4G wireless network. Interoperability results in providing the user with a rich range of services across a wide range of propagation environment and mobility conditions, using a single terminal. Specifically, the article aims at defining the criteria and mechanisms for interoperability between the two networks. Our approach considers the use of Cost functions to monitor the essential parameters at the system level in order to trigger an interoperability procedure. Initial user assignment and inter-system handover are considered the incidents that initiate the interoperability algorithm execution. The overall objective of this work is to assess the performance of our developed interoperability platform and to optimize system performance by guarantying a minimum QoS requirement and maximizing network capacity.     

Residential hot water use patterns in Greece

This paper presents the results from the monitoring of hot water consumption in four apartment buildings that are located in Solar Village 3, in Greece. The buildings were monitored centrally for hot water consumption using a Data Acquisition System (DAS). The hot water is prepared in one building by an air-to-water heat pump and in the other three buildings by central solar plants. The main objective of the paper is the development of average residential hot water use patterns based on data from actual measurements conducted over the period September 1990 to August 1991. Average hourly, daily, and yearly profiles, which refer to central DHW systems, are presented and discussed. The average hot water consumption “per person” is also concluded. In addition, the effect of “family size” in hot water use is examined. It was found that the majority of the families consume between 25 and 35 liters per person per day, and the mean annual energy consumption is 0.83 kWh per person per day.     

A general approach to the derivation of peak area flow dependence in FIA and HPLC amperometric detection

The dependence of the peak area, Q, on the analyte volumetric flow rate, U, in flow injection analysis (FIA) and high performance liquid chromatography (HPLC) with amperometric detection, was studied for typical electroactive species and in a wide flow rate range. Based on the hydrodynamics of thin channel flow cells (as established by steady state experiments) and simple dispersion theory considerations, a linear relationship between log Q and log U with a −2/3 slope has been derived in a general manner (irrespective to the type of dispersion) for amperometric detectors operated in the limiting current potential region. In the case of mixed mass transfer and kinetic control the variation of Q with U is more complicated but the peak area is still smoothly decreasing with the flow rate. These predictions were found to be in reasonable agreement with experiment for a few indicative systems both in FIA and HPLC experiments. On the contrary, the non-steady state current corresponding to the peak maximum of FIA and HPLC exhibited local maxima and the former could not be described by any of the equations proposed for the dispersion in FIA experiments. The practical implications of the form of integrated signal, Q, dependence on flow rate for FIA and HPLC amperometric detection are also discussed.     

Three-Dimensional Numerical Modeling of Initial Mixing of Thermal Discharges at Real-Life Configurations

A three-dimensional Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) model is developed for simulating initial mixing in the near field of thermal discharges at real-life geometrical configurations. The domain decomposition method with multilevel embedded overset grids is employed to handle the complexity of real-life diffusers as well as to efficiently account for the large disparity in length scales arising from the relative size of the ambient river reach and the typical diffuser diameter. An algebraic mixing length model with a Richardson-number correction for buoyancy effects is used for the turbulence closure. The governing equations are solved with a second-order-accurate, finite-volume, artificial compressibility method. The model is validated by applying it to simulate thermally stratified shear flows and negatively buoyant wall jet flows and the computed results are shown to be in good overall agreement with the experimental measurements. To demonstrate the potential of the numerical model as a powerful engineering simulation tool we apply it to simulate turbulent initial mixing of thermal discharges loaded from both single-port and multiport diffusers in a prismatic channel and a natural river. Comparisons of the CFD model results with those obtained by applying two widely used empirical mixing zone models show that the results are very similar in terms of both the rate of dilution and overall shape of the plumes. The CFD model further resolves the complex three-dimensional features of such flows, including the complex interplay of the ambient flow and thermal discharges as well as the interaction between each of discharges loaded from multiple ports, which are obviously not accessible by the simpler empirical models.     

Phase Interpolator with Improved Linearity

An analog phase interpolator with improved step linearity is presented in this paper. The linearity is improved by setting the time constant of the output nodes in suitable value and by employing a fine trimming technique. The performance and the improved linearity have been verified with post-layout simulations using a well-established CMOS 65 nm technology and transistors with standard threshold voltages. The clock frequency is at 2.5 GHz and the core voltage supply at 1.2 V. Its low phase noise makes the circuit suitable for high-speed systems where low jitter performance is required.     

Numerical simulation of methane fuelled cogenerative SOFCs for the production of synthesis gas and electrical energy

Numerical simulation has been used to show the feasibility of the autothermal cogeneration of synthesis gas and electricity in a solid oxide fuel cell (SOFC) by the electrochemical partial oxidation of CH₄. Owing to the large positive entropy change of the CH₄ partial oxidation reaction and its low heating value, severe cooling effect is being induced in the SOFC due to heat absorbance by the reaction products. For this reason the autothermal operation of the SOFC reactor cannot be secured. As it is shown this can be overcome by combining the dynamic operation of the SOFC under forced periodic reversal of the flow and the bleeding of a small amount of CH₄(<2.5%) in the oxidant stream (cathode). In this respect the catalytic combustion of CH₄, on the perovskite cathodic electrode, provides the necessary energy demand so that in combination with flow reversal operation the SOFC is maintained ignited even at inlet temperature as low as 300 K. It is shown that the overall thermodynamic efficiency of the process can by far exceed unity (η^′>2), thus revealing the unique property of the SOFCs to produce high-quality energy and useful chemicals.     

Numerical Modeling of Helical Static Mixers for Water Treatment

To improve the understanding of how static mixers work and how to better utilize them in environmental engineering (or, specifically, drinking water treatment), a numerical model for simulating turbulent flows in helical static mixers is developed. The model solves the three-dimensional, Reynolds-averaged Navier-Stokes equations, closed with the k-ω turbulence model, using a second-order-accurate finite-volume numerical method. Numerical simulations are carried out for a two-element helical static mixer, and the computed results are analyzed to elucidate the complex, three-dimensional features of the flow. The results show that the flow field within the mixer is characterized by the presence of pockets of reversed flow and the growth and interaction of strong longitudinal vortices. As an example of the kind of practical insights that can be gained from such detailed three-dimensional computations, the simulated flow field is used to investigate two quantities that are often used to characterize mixing within a static mixer and to discuss the merits of these quantities for coagulant mixing in drinking water treatment.     

Effects of near-tip inhomogeneities on scattering of ultrasonic waves by cracks

The efficacy of ultrasonic methods to detect and characterize a crack depends on topographical features of the crack faces, the presence of inhomogeneities in the crack's environment, and the mechanical properties in the near-crack region. In this paper, the effects on the scattered ultrasonic field of various features of fatigue and stress corrosion cracks such as partial crack closure, the presence of microcracks and microvoids, and near-tip zones of different mechanical properties have been investigated. A representation integral for the scattered field has been used to formulate the ultrasonic scattering problem. Numerical results have been obtained for some canonical configurations. For the configurations examined in this paper, crack closure has the most significant effect on far-field scattering.     

A motion control framework for autonomous water sampling and swing-free transportation of a multirotor UAV with a cable-suspended mechanism

In this work, we present an end-to-end solution for autonomous water sampling by utilizing an unmanned aerial vehicle (UAV) with a cable-suspended mechanism. Towards this direction, a sampling mechanism is initially designed in such a manner that the water sampling success ratio is maximized. However, the disturbances, acting on the submerged mechanism due to the water flow during the sampling procedure, impede the stabilization of the vehicle above the desired sampling position. Consequently, to achieve the precise hovering of the UAV, the vehicle's sensor suite is further augmented with a load cell, a depth sensor, an ultrasonic sensor, and a camera. The respective measurements are appropriately fused by employing an extended Kalman filter (EKF). Hence, an estimate of the disturbances is available in real-time and is incorporated into a Model Predictive Control scheme which compensates for the aforementioned disturbances and stabilizes the vehicle above the sampling location. Finally, a complete water sampling mission entails the safe and swing-free transportation of the mechanism towards the sampling location and, then, to a position where the collected samples are postprocessed by human operators. Consequently, a model predictive controller is employed which ensures the navigation of the vehicle to the desired waypoints while minimizing the swinging motion of the mechanism. The state of the mechanism is obtained by fusing measurements provided by the load cell and the camera with an EKF. The performance of the proposed framework, which aims to address all the aspects of a water sampling mission, is demonstrated through real experiments with an octorotor.