Non-uniform Power Distribution Research Articles

A New Definition of Fairness for Non-Orthogonal Multiple Access

Fairness in non-orthogonal multiple access (NOMA) may be defined in different ways, taking into account the physical layer alone or also including the process of radio resource management. The latter has been frequently used in the recent literature, implying a significant advantage of this technique compared with conventional orthogonal multiple access (OMA). In this letter, we look at the fairness issue from another angle and introduce a fundamental definition of fairness, which measures the difference between the rates that can be achieved by the users and the fair rates suggested by the power distribution among them. With this definition, the fairness issue is inexistent in OMA and it appears as a NOMA-specific problem due to interference between users and the detection process. The new fairness index we advocate incorporates the power distribution of different users. Thus, in a cell with a non-uniform power distribution, fairness implies that a user with a higher power should get a higher rate, and hence, the index should measure the rate of each user by accounting for the fraction of total power allocated to it. Our index achieves its maximum value of 1 only when all users get their fair rates, and it goes to zero when one user gets all resources in the case of uniform power distribution. We provide an asymptotic analysis of fairness at high and low signal-to-noise ratio (SNR) values and give a comprehensive illustration in the two-user case.

Experimental tests and post-test analysis of non-uniformly heated 19-pins fuel bundle cooled by Heavy Liquid Metal

An experimental campaign was performed on a non-uniformly heated 19-pins wire-spaced fuel pin bundle simulator, cooled by Heavy Liquid Metal and installed in the NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The experimental tests concerned mass flow rate transition of the primary coolant from forced to natural circulation, with fuel pin bundle simulator characterized by non-uniform power distribution. The main objective of the experimental campaign was to perform integral system and local thermal-hydraulic analysis, investigate different flow regimes and the transition from forced to natural circulation flow and, more specifically, analyze the behavior of the 19-pins wire-spaced Fuel Pin Simulator (FPS) during such transient. Indeed, the performed test were characterized by non-uniform heating of the bundle (i.e. just some pins switched on), so the effects of this non-uniformity on the local temperatures and on the overall system behavior was evaluated. A deep investigation on the local temperature distribution was performed thanks to the accurate instrumentation provided in the bundle (67 thermocouples). The obtained experimental data provided useful information for the characterization of the bundle and the computation of the heat transfer coefficient.A post-test validation is made by a detailed CFD model of the test section. Three monitored section at different levels are compared both for wall and bulk temperatures. This post-test comparison with this experimental configuration is unique and represents a further step towards the validation of the CFD models and methods in fuel bundle geometries cooled by HLM.

Investigation of cross flow mixing on rod bundle safety margins using sub-channel analysis framework

An investigation on effect of cross flow mixing on rod bundle thermal hydraulic safety margins is carried out using a sub-channel analysis framework. In the present study, general purpose automated sub-channel analysis framework is developed to carry out the thermal hydraulic analysis of nuclear reactor core. The framework involves the preprocessor to generate the sub-channel layout of the fuel assemblies of different sizes and shapes such as square and triangular pitched pin bundle. The analyses are carried out for different simulated rod bundles of square pitched array of typical nuclear fuel assembly. The parameters considered in this study are the size of the bundle, p/d ratio, intensity of turbulent mixing, mass flux, uniform and non-uniform axial power distribution. The coolant local conditions are significantly affected due to the inter channel mixing between sub-channels. The sub-channel layouts for fuel bundles of different sizes varying from 2 × 2 to 10 × 10 and 17 × 17 for same p/d and w/d ratios of 1.05 to 1.3 are generated. The analyses are carried out by varying the intensity of turbulent mixing parameter (c) from 0 (no mixing) to 0.1 (high mixing) using the developed framework. It is found that hot channel temperature decreased by 26% in smaller bundle due to strong interaction between wall and corner channel. In case of large sized assembly above 5 × 5, hot channel temperature is less affected. The estimation of coolant temperature, fuel pin surface temperature and local quality are also carried out without considering the inter-channel mixing. The results are compared with a change in the local conditions for different degree of mixing among the fuel bundle sub-channels. The developed Framework is used for performing the sensitivity-studies during the design and analysis phase of nuclear reactor core for estimation of thermal hydraulic safety margins in an efficient way with minimum human intervention.

Symmetry of Arc Furnace Operation

The electrical asymmetry in the operation of arc furnace with an asymmetric triangular configuration of the electrodes is noted. Experimental data from the DSP-100 furnace permit analysis of how the electrical parameters affect the arc characteristics. Nonuniform power distribution over the phases of the electrofurnace decreases the component of the useful power consumed in heating the metal and slag. The power consumption by the furnace may potentially be reduced by 7.4% and the electrode consumption by 9%. The results confirm the need for research on phase-by-phase regulation of the power of ac arc furnaces.

All-Normal Dispersion Chalcogenide PCF for Ultraflat Mid-Infrared Supercontinuum Generation

We numerically study the dispersion-engineered chalcogenide photonic crystal fiber (PCF), which allows us to generate ultraflat broadband supercontinuum (SC) spectra in all-normal dispersion regime. A 1-cm-long chalcogenide hexagonal PCF made using Ge11.5As24Se64.5 glass pumped at $1.55~\mu \text{m}$ produced an SC bandwidth 700 nm at a peak power of 1 kW. By shifting pump at $2~\mu \text{m}$ , SC spectra can be extended with a bandwidth of 1900 nm at the same peak power level. In both cases, nonuniform spectral power distribution observes over the entire output bandwidth owing to the lower dispersion slop on the long wavelength side of the dispersion curve. To spanning SC further in the mid-infrared as well as to reduce the spectral asymmetry, we optimize another design for pumping at 3.1 $\mu \text{m}$ in such a way that the pump source can be employed vicinity to the peak of the dispersion curve. Employing the largest pump peak power up to 5 kW, SC can be extended up to 6 $\mu \text{m}$ (1.5 octaves), and the power distribution among the spectral components over the entire SC bandwidth can be improved significantly by this design. To enhance the spectral flatness, we optimize a second PCF geometry by reducing its pitch length, and it is possible to obtain ultraflat coherent SC spanning from 2 to 5.5 $\mu \text{m}$ (>1 octave) by this structure maintaining nearly symmetric power distribution between both side of its spectral components.

Laser particle counter validation for aeolian sand transport measurements using a highspeed camera

Abstract Measuring aeolian sand transport rates in the field has been a long-standing challenge. In this paper, we present the results of a laboratory experiment to test the ability of a laser particle counter sensor (Wenglor) to accurately count sand grains of various grain size classes and stainless steel beads. We compared the count data collected by the Wenglor with images from a Highspeed camera which revealed the actual number of grains passing the laser beam. A Silicon photodiode was used to record the laser intensity reduction induced by the sand grain passage through the laser beam to derive the minimal necessary reduction for the Wenglor to count grains. For the two possible settings of the Wenglor, i.e., Minimal Teach-in or Normal Teach-in, a minimum of 18% and 78% blocking of the laser beam was required for recording a count. This implies that the minimum grain size that can be observed by the Wenglor is 210 ± 3 μ m and 495 ± 10 μ m for the two settings respectively, which is considerably coarser than previously assumed. Due to the non-uniform power distribution of the laser sensor intensity, at the detection limit of 210 μm, only grains passing through the centre of the beam will be counted.

Performance Evaluation of Space Shift Keying in Free-Space Optical Communication

In this paper, we study the performance of a space shift keying (SSK) scheme in a free-space optical (FSO) communication system under indoor and outdoor conditions. For the outdoor N t χ 1 FSO-SSK system, where N t is the number of transmitters (Txs), a novel closed-form mathematical expression for the probability density function (pdf) of the difference between two weighted gamma-gamma random variables is derived. Using this pdf, a new analytical expression is obtained for the tight upper bound of the average bit error rate (ABER) of this system. We also study the analytical bit error rate (BER) of an indoor N t χ 1 FSO-SSK system experiencing a deterministic channel. For this system, optimized values of transmit power weights are obtained by minimizing the analytical BER; it is observed that the optimized nonuniform power distribution is better than the uniform power distribution. However, for the outdoor FSO-SSK system, the best error performance can be achieved by employing uniform transmit power. An asymptotic BER analysis of uniformly weighted general outdoor FSO-SSK with an arbitrary number of Tx and receiver (Rx) apertures is also performed. Furthermore, the analytical coding gain and diversity order of the considered system are found based on the derived analytical BER expression. An interesting result observed from the coding gain analysis is that the performance of the outdoor FSO-SSK system remains unaltered from a moderate to a strong atmospheric turbulence regime, which makes the considered system nearly independent of turbulence. In addition, it is found by simulation and analysis that the considered system performs more poorly under the weak turbulence regime as compared to the other (strong and moderate) turbulence regimes. Our analysis also shows that the diversity order of the outdoor FSO-SSK system is N r /2, where N r is the number of Rx apertures, irrespective of the number of optical sources and turbulence conditions. In addition, it is observed that the performance of the FSO-SSK system degrades with an increasing number of optical sources under both indoor and outdoor conditions. Therefore, a trade-off between spectral efficiency and ABER is observed.

Flow regimes and convective heat transfer of refrigerant flow boiling in ultra-small clearance microgaps

Understanding two-phase convective heat transfer under extreme conditions of high heat and mass fluxes and confined geometry is of fundamental interest and practical significance. In particular, next generation electronics are becoming thermally limited in performance, as integration levels increase due to the emergence of ‘hotspots’ featuring up to ten-fold increase in local heat fluxes, resulting from non-uniform power distribution. An ultra-small clearance, 10μm microgap, was investigated to gain insight into physics of high mass flux refrigerant R134a flow boiling, and to assess its utility as a practical solution for hotspot thermal management. Two configurations – a bare microgap, and inline micro-pin fin populated microgap – were tested in terms of their ability to dissipate heat fluxes approaching 1.5kW/cm2. Extreme flow conditions were investigated, including mass fluxes up to 3000kg/m2s at inlet pressures up to 1.5MPa and exit vapor qualities approaching unity. Dominant flow regimes were identified and correlated to two phase heat transfer coefficients which were obtained using model-based data reduction for both device configurations. The results obtained were compared to predictions using correlations from literature, with the maximum heat transfer coefficient reaching 1.5MW/m2K in the vapor plume regime in the case of the finned microgap.

Optimization of the printed circuit boards placement at thermal design of the units with natural air cooling

It is considered an influence of printed circuit boards placement on temperature distribution in electronic equipment units with natural air cooling. Modeling of the temperature distribution in the unit and research of mass-dimension characteristics were carried out by means of CADs and engineering analysis. There are developed simplified geometric and thermal models of the unit. Here we analyze specificities of heat exchange in the units of radio electronic equipment with natural air cooling. It is developed an algorithm for optimization of printed circuit boards placement in radio electronic equipment with natural air cooling taking into account non-uniform power distribution between printed circuit boards. Proposed algorithm can be used as one of the stage of optimization of size, carrying or mass-dimension factors of the unit in case where unit powers are distributed non-uniformly.

Design of a Microstrip Series Power Divider for Sequentially Rotated Nonuniform Antenna Array

This paper deals with the design of a microstrip series power divider for circularly polarized sequential rotational antenna array. The theoretical description of the design is firstly proposed, comprising the cases of nonuniform weighted antenna arrays. A more flexible open octagon shape instead of the classical open ring is suggested, highlighting benefits in the case of nonuniform power distribution. A design example of an ultra-high frequency (UHF) band 4×4 sequentially rotated Tschebischeff antenna array finally demonstrates the effectiveness of the proposed implementation.

1-D dynamic stability analysis of mixed-spectrum supercritical water reactor core

The supercritical water reactor (SCWR) is one of the most prominent Generation IV reactors due to its high efficiencies. However, the stability issues, which are mainly caused by the great changes of thermodynamic properties and transport properties of supercritical water near the pseudo-critical temperature, are a challenge to the system safety and must be studied carefully. This paper is focused on 1-D dynamic stability analysis of mixed-spectrum SCWR (SCWR-M) reactor core. To this end, a frequency-domain model has been developed for linear stability analysis, and marginal stability boundaries under both the fixed inlet flow boundary conditions and the fixed external pressures boundary conditions are generated, which indicate that the system normal operational condition is in stable regions. Parametric sensitivity studies in frequency domain have been carried out. Increasing the wall thermal conductivity and mass flows can increase system stability. The system is more stable if the thermal zone has a lower power fraction. System with the designed non-uniform axial power distribution is also more stable than with the uniform distribution. A time-domain model has also been developed for nonlinear analysis, and the system marginal stability boundaries calculated by this method is consistent with those by frequency domain method. The existence of transitional stable region has been observed. A more reasonable definition for system logarithmic decay ratio has been achieved. The SCWR-M core has a subcritical bifurcation characteristic under fixed external pressures boundary conditions, thus its dynamic behaviors are not only related to systematic parameters, but also to the amplitudes of perturbations.

New models of droplet deposition and entrainment for prediction of liquid film flow in vertical annuli

Droplet deposition and entrainment significantly affect dryout occurrences in annular two-phase flow. Currently, most of the correlations for droplet deposition and entrainment are derived from flows in tubes. However, the main challenge in thermal-hydraulic analyses of BWRs is the prediction of dryout occurrence in the rod bundle geometry of fuel assemblies. In the work reported here, the applicability of several tube-based droplet deposition and entrainment correlations to the annular geometry (effectively a “one-rod” bundle) is checked. It is found that the prediction values from all those correlations deviate from the experimental measurements. Therefore, a set of simple and easy-to-implement models for deposition and entrainment rates in annuli is developed based on the tube-based Hewitt-Govan correlations (Hewitt and Govan, 1990), with considering the liquid film flow characteristics in annuli and the geometry effect of the annulus. The present models are verified by comparison with experimental data for developing liquid films in adiabatic annuli. By using these models to predict dryout in heated annuli, we find that these new relationships have good capability in predicting dryout occurrence in annuli with uniform as well as non-uniform axial power distribution.

Modular Single-Active Bridge DC-DC Converters: Efficiency Optimization over a Wide Load Range

Multiple single-active bridge (SAB) DC-DC converters are connected in the input-parallel and outputparallel (IPOP) configuration to achieve higher power output in many applications. Module shutdown, known as phase shedding, is used to improve light-load efficiency in the IPOP modular converter. The SAB is known for its simplicity and robustness, but it is only moderately efficient; therefore, larger snubber capacitance is used to lower switching and conduction losses in the SAB and improve efficiency. However, larger snubber capacitance increases minimum power and reduces load range in the SAB, resulting in the unattainability of certain load-range segments in the IPOP converter because capacitance increases when phase shedding is used. Hence, snubber capacitances across the modules are optimized to improve average efficiency while maintaining the existing load range. As a result, snubber capacitances differ across SAB modules. With nonidentical modules, nonuniform module power distribution is used in the IPOP converter for higher light-load efficiency with selective phase shedding. This increases the average IPOP converter efficiency from 92.5% to 94.1% across the load range of 260 W to 13.6 kW. Peak efficiency is also increased from 93% to 95.5%. In this article, we present a method to optimize the modular SAB IPOP system for high efficiency over a wide load range.

Cavity-Backed Angled-Dipole Antennas for Millimeter-Wave Wireless Applications

A cavity-backed angled-dipole antenna is proposed for millimeter-wave wireless applications. The angled-dipole radiator is built on both sides of an RT/Duroid 5880 substrate (εr=2.2) and fed by a parallel-plate transmission line. The cavity-backed reflector is utilized to improve the radiation characteristics of the angled dipole, such as gain, back-radiation, symmetric pattern, and similar 3 dB beamwidth in theE- andH-planes. The design, with a cavity aperture of0.5λ28-GHz×0.5λ28-GHz, results in aS11<-10 dB bandwidth of 26.7–30.6 GHz, a gain of 6.6–8.0 dB, and a similar 3 dB beamwidth of approximately 70° for both theE- andH-planes. Eight-element linear arrays with the proposed antenna having a center-to-center spacing of 5.6 mm(0.52λ28-GHz)are characterized, fabricated, and measured. By applying nonuniform power distribution across excitations, the array achieves a scan angle up to 40° and a sidelobe level below −15 dB.

Research Regarding Improvement of Torsional Stiffness for Planetary Speed Reducers Used in the Actuation of Industrial Robots

Planetary speed reducers are used in the actuation of the revolute kinematic joints thanks to their specific advantages. However, in order to achieve a good positioning accuracy for the kinematic chains, these must have reduced backlash and high torsional stiffness. Therefore the deformations of the elements composing the mechanical structure under the action of gearing forces should be as low as possible, thus leading to backlash reduction. This also becomes important since the presence of backlash in the structure of the planetary speed reducer affects the stability of the overall kinematic chain. In this paper, a novel computation method for bearing deflections is proposed, starting from the kinematic diagram of the planetary speed reducer. Having known the kinematic diagram, it becomes possible to compute the gearing forces, keeping in mind the non-uniform power distribution on the planetary gears. The bearing reactions were computed in two cases: when the planetary gears are free to spin on the planetary carrier and when the planetary gears are fixed on the planet carrier, being supported at the extremities. Based on the computed values for bearing reactions, the corresponding deflections are determined. Once the values of the bearing reactions and deflections had been determined, the load-deflection and stiffness-deflection diagrams were elaborated for ball and roller bearings, allowing the determination of the bearing type that ensures low deflections and high stiffness. Based on the results, some recommendations are made, allowing the reduction of bearing deflections, and increasing the torsional stiffness.

Flow Boiling in an In-Line Set of Short Narrow Gap Channels

Heat transfer coefficients in a set of three symmetrically heated narrow gap channels arranged in line are reported at power densities of 1 kW/cm3 and wall heat flux of 3–40 W/cm2. This configuration emulates an electronics system wherein power dissipation can vary across an array of processors, memory chips, or other components. Three pairs of parallel ceramic resistance heaters in a nearly adiabatic housing form the flow passage, and length-to-gap ratios for each pair of heaters are 34 at a gap of 0.36 mm. Novec™ 7200 and 7300 are used as the heat transfer fluids. Nonuniform longitudinal power distributions are designed with the center heater pair at 1.5X and 2X the level of the first and third heater pairs. At all levels of inlet subcooling, single-phase heat transfer dominates over the first two heater pairs, while the third pair exhibits significant increases because of the presence of flow boiling. Reynolds numbers range from 250 to 1200, Weber numbers from 2 to 14, and boiling numbers from O(10−4) to O(10−3). Exit quality can reach 30% in some cases. Overall heat transfer coefficients of 40 kW/m2K are obtained. Pressure drops for both Novec™ heat transfer fluids are approximately equal at a given mass flux, and a high ratio of heat transfer to pumping power (coefficient of performance (COP)) is obtained. With a mass flux of 250 kg/m2s, heater temperatures can exceed 95 °C, which is the acceptable limit of steady operation for contemporary high performance electronics. Thus, an optimal operating point involving power density, power distribution, mass flux, and inlet subcooling is suggested by the data set for this benchmark multiheater configuration.

Simulation of a beam rotation system for a spallation source

With a nominal beam power of nearly 1 MW on target, the Swiss Spallation Neutron Source (SINQ), ranks among the world's most powerful spallation neutron sources. The proton beam transport to the SINQ target is carried out exclusively by means of linear magnetic elements. In the transport line to SINQ the beam is scattered in two meson production targets and as a consequence, at the SINQ target entrance the beam shape can be described by Gaussian distributions in transverse $x$ and $y$ directions with tails cut short by collimators. This leads to a highly nonuniform power distribution inside the SINQ target, giving rise to thermal and mechanical stresses. In view of a future proton beam intensity upgrade, the possibility of homogenizing the beam distribution by means of a fast beam rotation system is currently under investigation. Important aspects which need to be studied are the impact of a rotating proton beam on the resulting neutron spectra, spatial flux distributions and additional---previously not present---proton losses causing unwanted activation of accelerator components. Hence a new source description method was developed for the radiation transport code MCNPX. This new feature makes direct use of the results from the proton beam optics code TURTLE. Its advantage to existing MCNPX source options is that all phase space information and correlations of each primary beam particle computed with TURTLE are preserved and transferred to MCNPX. Simulations of the different beam distributions together with their consequences in terms of neutron production are presented in this publication. Additionally, a detailed description of the coupling method between TURTLE and MCNPX is provided.

Modified uniform-fission-site algorithm in Monte Carlo simulation of reactor criticality problem

Because of a very non-uniform power distribution in core region, a very non-uniform distribution of relative uncertainties exists for tallies in Monte Carlo criticality calculations of pin-by-pin reactor model. To make a large part of cells obtain small enough relative uncertainties with reasonable time costs, increasing the total sample scale is not a good choice. By realizing a modified uniform-fission-site algorithm on the basis of source iteration algorithm of parallel Monte Carlo transport code JMCT, we obtain higher efficiencies for tallies in the calculations of pin-by-pin model of the Dayawang reactor plant. This work supplies a useful tool for matching the goal of simulating the benchmark pin-by-pin reactor models with a pre-described standard(the so called Kord-Smith challenge).

Performance Comparison of RFID Tag at UHF Band and Millimeter-Wave Band

The ultra high frequency (UHF) band spectrum will likely be congested in near future since the next generation wireless as well as Radio Frequency Identification (RFID) system users will witness the use of UHF band technology with increased demand of bandwidth, bit rate, frequency spectrum and power consumption. The alternate solution is the use of millimeter-wave band technology. It is possible to improve data throughput, range resolution and multi-user capability in mm-wave band RFID system. ‘Higher power reception efficiency and lower side lobe level (SLL) of radiation pattern’ is required for RFID system that will increase the tag range and transmission bit rate. At the same time lower SLL will minimize the interference level. Beam pointing error is another problem of UHF band antenna which reduces the tag range and bit rate. These problems can be minimized by using large number of antenna elements. But with UHF band signal it is practically difficult to construct large array antenna; since the array size becomes tremendously larger with the increase of antenna elements. ‘Higher power reception efficiency and lower SLL’ can practically be obtained by using non-uniform power distribution of large number of antenna elements in millimeter wave band. A new and technically better method of beam forming by implementing the concept of staircase power distribution (SPD) of antenna elements at 60 GHz has been investigated and presented in the paper. The SPD method is compared with Gaussian edge tapering method. It was found that the maximum SLL (MSLL) is the lowest in case of SPD. The beam efficiency of SPD is also equivalent to that of Gaussian edge tapering method. It is easier to fabricate a larger number of antenna elements within smaller area with SPD at 60 GHz system; since the antenna size is smaller and the number of different power distribution in SPD case is less and stepwise uniform. Uniform and less number of different power distribution of SPD also minimizes other technical errors.

Optimization of Thermoelectric Coolers for Hotspot Cooling in Three-Dimensional Stacked Chips

Three-dimensional (3D) chip stacking architecture is expected to reduce form factor, improve performance, and decrease power consumption in future microelectronics. High power density and nonuniform power distribution in stacked dies are expected to bring significant thermal challenges for 3D packages due to localized hot spots. Embedded thermoelectric coolers (TECs) have potential to provide reliable and localized cooling at these hot spots. In this work, peak package temperature or active cooling per power consumption of TECs are optimized, considering applied current and thickness of TECs as parameters, for a 3D electronic package with two stacked dies. Each die has two hot spots and one TEC is paired with each hot spot. Three different optimization methods are considered in order to ensure a robust solution. The optimization suggests that both the peak temperature in package and energy efficiency of the cooling system can be significantly improved through the optimization of TECs. TECs are also compared against a configuration where they are replaced by copper blocks or thermal vias. A total of 4.7 °C of additional localized cooling is observed using TECs which is beyond what is achievable with copper vias in place of the TECs. The study also suggests that it is better to use TECs to cool only the hottest portions of the package to avoid introducing additional thermal resistance and Joule heating in the package.