Parametric Investigation of Viscous Dissipation Effects on Optimized Air Cooling Microchanneled Heat Sinks

The effects of viscous dissipation of working fluid on the optimum heat sink parameters are investigated for the case of air cooling with a micro-/narrow-channeled compact heat sink. For this purpose, an optimization method is introduced first on the basis of dimensionless groups while employing several assumptions. This method yields minimum pumping work or pressure drop with a set of optimized geometric/hydrodynamic parameters when outer dimension of a heat sink and imposed thermal load are specified. Especially for the case of laminar flow, the procedure presents an explicit existence of cooling limit by the viscous heat generation, giving an analytical expression of the maximum removable heat Q max . The relationships between thermal load and each parameter are calculated for both laminar and turbulent regimes under the conditions of compact heat sink dimension (20 mm 2 20 mm 2 2 mm) and circular cross-sectional shape of channels. The results show that the cooling capability under such conditions is largely limited by the salient manifestation of viscous dissipation, when compared with our previous investigation on water cooling presented in [1]. From the discussion, it was concluded that when a micro-/narrow-channeled heat sink is to be designed with air, the effect of viscous dissipation should be taken into account in order to avoid falling on wrong optimum solutions.     

A novel SON2‐based similarity index and its application for the rationalization of river water quality monitoring network

In this paper, a novel self‐organizing network (SON) based similarity index and its application for the optimization of sampling locations in an existing river water quality monitoring network (WQMN) is presented. A rationalization of the River Danube WQMN on its stretch through Serbia was performed using the proposed SON²‐based similarity index. A high‐dimensional dataset was used, which is composed of 18 water quality parameters that were collected during the period 2002–2010 at 17 monitoring locations. The SON‐based seasonal classification that divides 12 months into the cold, moderate, and warm seasons was employed, whereas its second application on each seasonal class yielded subclasses that were used to compare the monitoring locations. The obtained SON²‐based similarity index can be utilized for analysing seasonal variations, as well as overall similarities among neighbouring sites. Based on the calculated similarities of locations and characteristics of the River Danube basin a rationalized WQMN, which uses 30% less monitoring sites, has been proposed.     

STRATIGRAPHY AND PETROLEUM GEOLOGY OF THE CROATIAN PART OF THE ADRIATIC BASIN

Coastal parts of Croatia are dominated by the SW‐verging Dinaric foldbelt, to the west and SW of which is the Adriatic Basin (the stable foreland). In both areas, the stratigraphic column is dominated by a thick carbonate succession ranging from Carboniferous to Miocene. Four megasequences have been identified: (i) a pre‐platform succession ranging in age from Late Carboniferous (Middle Pennsylvanian: Moscovian) to Early Jurassic (Early Toarcian; Bru?ane and Ba?ke Ostarije Formations); (ii) an Early Jurassic to Late Cretaceous platform megasequence (Mali Alan Formation); (iii) a Paleogene to Neogene post‐platform megasequence (Ra?a Formation); and (iv) a Neogene to Quaternary (Pliocene to Holocene) megasequence (Istra and Ivana Formations). A number of organic‐rich intervals with source rock potential have been identified on‐ and offshore Croatia: Middle and Upper Carboniferous, Upper Permian, Lower and Middle Triassic, Lower and Upper Jurassic, Lower and Upper Cretaceous, Eocene, and Pliocene – Pleistocene. Traps and potential plays have been identified from seismic data in the Dinaric belt and adjacent foreland. Evaporites of Permian, Triassic and Neogene (Messinian) ages form potential regional seals, and carbonates with secondary porosity form potential reservoirs. Oil and gas shows in wells in the Croatian part of the Adriatic Basin have been recorded but no oil accumulations of commercial value have yet been discovered. In the northern Adriatic offshore Croatia, Pliocene hemi‐pelagic marlstones and shales include source rocks which produce commercial volumes of biogenic gas. The gas is reservoired in unconsolidated sands of the Pleistocene Ivana Formation.     

Negative bias temperature instability in n-channel power VDMOSFETs

Negative gate bias is used in some applications for faster switching off the n-channel MOS devices. It is shown in this study that NBT stress-related instability in commercial n-channel power VDMOSFETs could be actually more serious than in corresponding p-channel devices. NBT stress is found to create equal V_T shifts in both device types, whereas the subsequent positive bias annealing results in more serious overall V_T instability in n-channel devices. The changes in the densities of stress-induced interface traps in two device types are equal as well, but significant amounts of NBT stress-induced border traps are only found in n-channel devices. All the results are discussed in terms of hydrogen reaction and diffusion model.     

Adaptive nonuniform polar quantization application to high quality speech compression

The logarithmic companding technique has shown to be extremely useful in speech quantization with rate of 8 bits/sample. However, for lower bit rates it is not the ideal solution for high quality speech coding. Because of that, in this paper we establish source coding scheme which enables better spectrum efficiency for input that has a large dynamic range. Since our wish is also to improve signal quality in comparison with quality defined with standards G.711 and G.712, we opt for adaptive technique application to the speech coding. Our research shows that proper design of forward gain-adaptive polar quantization can enable compression of about 1 bit/sample as well as significantly better quality than in case of using coder designed according to standard G.711. Furthermore, performances can be sustained over the whole speech dynamic range. Also, if the requisite speech quality is not supposed to be lower than G.712 standard quality, the achieved compression can be almost 1.5 bits/sample. Besides, we propose knew simple encoding rule which can additionally reduce bit rate for 0.1 bit/sample.     

Computer-controlled mechanical simulation of the artificially ventilated human respiratory system

A mechanical lung simulator can be used to simulate specific lung pathologies, to test lung-function equipment, and in instruction. A new approach to mechanical simulation of lung behavior is introduced that uses a computer-controlled active mechatronic system. The main advantage of this approach is that the static and dynamic properties of the simulator can easily be adjusted via the control software. A nonlinear single-compartment mathematical model of the artificially ventilated respiratory system has been derived and incorporated into the simulator control system. This model can capture both the static and dynamic compliance of the respiratory system as well as nonlinear flow-resistance properties. Parameters in this model can be estimated by using data from artificially ventilated patients. It is shown that the simulation model fits patient data well. This mathematical model of the respiratory system was then matched to a model of the available physical equipment (the simulator, actuators, and the interface electronics) in order to obtain the desired lung behavior. A significant time delay in the piston motion control loop has been identified, which can potentially cause oscillations or even instability for high compliance values. Therefore, a feedback controller based on the Smith-predictor scheme was developed to control the piston motion. The control system, implemented on a personal computer, also includes a user-friendly interface to allow easy parameter setting.     

A novel structure of the fully differential CMOS amplifier with symmetric active load

In this article, we propose a novel general structure of a linear symmetric fully differential voltage amplifier with a symmetric output. It is applicable to all sets of complementary component pairs such as BJT, JFET and MOSFET. We demonstrate the superiority of the proposed circuit in comparison with the state-of-the-art solutions. The characteristics are illustrated in both frequency and time domains, and a comparison is given between the proposed amplifier and the traditional differential amplifier with a current mirror as an active load for the same set of complementary components in CMOS equally sized W/L = 150/3 technology. The static voltage transfer characteristic of the proposed amplifier has an extremely small linearity error. The deviation from the linear characteristics is less than 0.018 mV for the amplitude of the output differential voltage of 1 Vpp. The common-mode gain by symmetric output is negligible because the proposed structure is fully symmetric. The simulation results demonstrate the efficiency of the proposed amplifier.     

Phase-synchroniser based on gm-C all-pass filter chain with sliding mode control

Phase-synchronisers have many applications in VLSI circuit designs. They are used in CMOS RF circuits including phase (de)modulators, phase recovery circuits, multiphase synthesis, etc. In this article, a phase-synchroniser based on g_m-C all-pass filter chain with sliding mode control is presented. The filter chain provides good controllable delay characteristics over the full range of phase and frequency regulation, without deterioration of input signal amplitude and waveform, while the sliding mode control enables us to achieve fast and predetermined finite locking time. IHP 0.25 µm SiGe BiCMOS technology has been used in design and verification processes. The circuit operates in the frequency range from 33 MHz up to 150 MHz. Simulation results indicate that it is possible to achieve very fast synchronisation time period, which is approximately four time intervals of the input signal during normal operation, and 20 time intervals during power-on.     

Reducing sensing error in cognitive PANs through reduction of the channel set and split sensing

Cognitive radio technology necessitates accurate and timely sensing of the primary users’ activity on the chosen set of channels. If sensing error is unacceptably high, we can reduce the number of working channels so as to improve the channels-vs.-sensing nodes ratio, and undertake differential or split sensing in which subsets of sensing nodes target idle and active channels, respectively. The paper presents a probabilistic analysis of the sensing process, including the split sensing policy, and investigates the range of values in which such, incomplete sensing is capable of maintaining an accurate view of the status of the working channel set.     

Numerical model of gaseous fuel jet injection into a fluidized furnace

The paper presents a fluid-porous medium model, developed for stationary 2D predictions of fluidized bed. Dense phase is considered a fixed porous medium, while gas–particle interactions and bubbling phase are modeled regarding balance of friction forces between gas and particles. Like referent measurements, predictions of lateral jet injection into the bed suggest the jet penetration length is strongly affected by fluid velocity at the nozzle outlet, while influences of the nozzle vertical position and inclination angle are not significant. Also, the fluid velocity and the nozzle vertical position exert pronounced effects on mixing rate of components (fuel and oxidizer).