Uniform Modulation Research Articles

Comparison of Probabilistically Shaped 64QAM With Lower Cardinality Uniform Constellations in Long-Haul Optical Systems

In this paper, we compare the performance of probabilistically shaped 64QAM with uniform 16QAM and 32QAM modulation formats at the same net data rate in long-haul coherent optical communications systems. Experimental results at 16 GBaud are shown, with offline postprocessing of the data performed using either an ideal or a realistic carrier phase estimation (CPE) scheme. We show that the choice of the CPE algorithm at the receiver is crucial, since, as predicted by current models, most of the additional nonlinear noise introduced by the shaping is nonlinear phase noise (NLPN). Thanks to the use of probabilistic shaping (PS), maximum reach gains ranging from 15.5% and 34% are obtained over pure silica-core fiber, where the NLPN can be efficiently compensated for by standard CPE algorithms, while over nonzero dispersion-shifted fiber, the gain of PS is drastically reduced, due to residual short-correlated NLPN.

Commutative rings whose proper ideals are direct sums of uniform modules

ABSTRACTAn interesting result, obtaining by some theorems of Asano, Köthe and Warfield, states that: “for a commutative ring R, every module is a direct sum of uniform modules if and only if R is an Artinian principal ideal ring.” Moreover, it is observed that: “every ideal of a commutative ring R is a direct sum of uniform modules if and only if R is a finite direct product of uniform rings.” These results raise a natural question: “What is the structure of commutative rings whose all proper ideals are direct sums of uniform modules?” The goal of this paper is to answer this question. We prove that for a commutative ring R, every proper ideal is a direct sum of uniform modules, if and only if, R is a finite direct product of uniform rings or R is a local ring with the unique maximal ideal ℳ of the form ℳ = U⊕S, where U is a uniform module and S is a semisimple module. Furthermore, we determine the structure of commutative rings R for which every proper ideal is a direct sum of cyclic uniform modules (resp., cocyclic modules). Examples which delineate the structures are provided.

Uniform field loop-gap resonator and rectangular TEU02 for aqueous sample EPR at 94 GHz

In this work we present the design and implementation of two uniform-field resonators: a seven-loop–six-gap loop-gap resonator (LGR) and a rectangular TEU02 cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94GHz. The LGR geometry employs low-loss Rexolite end-sections to improve the field homogeneity over a 3mm sample region-of-interest from near-cosine distribution to 90% uniform. The LGR was designed to accommodate large degassable Polytetrafluorethylen (PTFE) tubes (0.81mm O.D.; 0.25mm I.D.) for aqueous samples. Additionally, field modulation slots are designed for uniform 100kHz field modulation incident at the sample. Experiments using a point sample of lithium phthalocyanine (LiPC) were performed to measure both the uniformity of the microwave magnetic field and 100kHz field modulation, and confirm simulations. The rectangular TEU02 cavity resonator employs over-sized end-sections with sample shielding to provide an 87% uniform field for a 0.1×2×6mm3 sample geometry. An evanescent slotted window was designed for light access to irradiate 90% of the sample volume. A novel dual-slot iris was used to minimize microwave magnetic field perturbations and maintain cross-sectional uniformity. Practical EPR experiments using the application of light irradiated rose bengal (4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein) were performed in the TEU02 cavity. The implementation of these geometries providing a practical designs for uniform field resonators that continue resonator advancements towards quantitative EPR spectroscopy.

Quality Assurance of Solid Oxide Fuel Cell (SOFC) and Electrolyser (SOEC) Stacks

Many research facilities and industrial companies worldwide are engaged in the development and the improvement of solid oxide fuel cells/stacks (SOFC) and also of solid oxide electrolysis cells/stacks (SOEC). However, the different stacks cannot be easily compared due to non-standardized test programs. Therefore the EU-funded project “SOCTESQA” which started in May 2014 has the aim to develop uniform and industry wide test modules and programs for SOC cells/stacks. New application fields which are based on the operation of the SOC cell/stack assembly in the fuel cell (SOFC), in the electrolysis (SOEC) and in the combined SOFC/SOEC mode are addressed. This covers the wide range of power generation systems, e.g. stationary SOFC µ-CHP, mobile SOFC auxiliary power unit (APU) and SOFC/SOEC power-to-gas systems. In order to optimize the test programs, which consist of different test modules, several testing campaigns have been performed. The project partners apply the developed test procedures on identical SOC stacks. In this project 5-cell short-stacks with anode supported cells (ASC) were used, which were provided by an established stack supplier. Altogether 10 pre-normative test modules were developed: Start-up, current-voltage curve, electrochemical impedance spectroscopy, reactant utilization, reactant gas composition, temperature sensitivity, operation at constant current, operation at varying current, thermal cycling and shut-down. The presentation compares the results of the test modules of the different project partners. Important aspects are the evaluation of the results in terms of repeatability of the different testing campaigns and the reproducibility of the results among the partners. Electrochemical properties, e.g. open circuit voltage (OCV), area specific resistance (ASR), power density, fuel utilization (FU) and impedance values of both stack and repeat units (RU) are presented. Moreover, the results are discussed in context to the test input parameters. Another important issue is the reproducibility of the different test methods, e.g. jV-characteristics and EIS-spectra. Finally, important aspects for the determination of reproducible degradation rates of SOC stacks will be presented and discussed.

Efficiency of Metasurface Antennas

Different types of efficiencies are introduced for metasurface (MTS) antennas based on single point-source excitation: 1) the feed efficiency $\varepsilon _{\mathrm{ feed}} $ is the power delivered by the feed to surface wave (SW) over the input power; 2) the tapering efficiency $\varepsilon _{\mathrm{ tap}} $ quantifies the deviation with respect to a uniform illumination; 3) the conversion efficiency $\varepsilon _{\mathrm{ conv}} $ defines the capability of the MTS to transform the SW power into leaky-wave power; and 4) the ohmic efficiency $\varepsilon _{\Omega } $ accounts for the antenna losses. The product of all of these factors provides the overall efficiency of the antenna. New, quite general analytical formulas are suggested to estimate any individual efficiency. In particular, it is seen that $\varepsilon _{\mathrm{ feed}} $ can reach also 90% by using planar or quasi-planar circularly symmetric sources. It is also proven that the product $\varepsilon _{\mathrm{ conv}} \varepsilon _{\mathrm{ tap}} $ cannot be larger than 58% for a uniform modulation; however, by using a nonuniform modulation, it can be increased to reach $\varepsilon _{\mathrm{ conv}} \varepsilon _{\mathrm{ tap}} \approx a / \lambda /(a / \lambda +2)$ , where $a/\lambda $ is the antenna radius in free-space wavelengths. A new closed-form formula for estimating the losses is given. In accordance with the prescription given here, one can reach 75% of global efficiency, including losses, until a radius of 20 wavelengths with commercially available substrates.

A Harmonic Suppression Scheme for Full Speed Range of a Two-Level Inverter Fed Induction Motor Drive Using Switched Capacitive Filter

This paper proposes a novel harmonic suppression scheme for two-level inverter fed three-terminal induction motor drives using switched capacitive filter. Capacitor fed H-bridges used as filters are cascaded to conventional two-level inverter to eliminate fifth-and seventh-order harmonics for the full modulation range including a six-step operation. For the first time, two-level dodecagonal voltage space vector is implemented with single dc supply for three-terminal induction motor drive. Enabling the switched capacitive filtering at low-voltage domain and shifting the high frequency switching to the switched capacitive filter is shown. A uniform pulse width modulation technique is shown which charges and maintains the capacitor voltages while eliminating the fifth-and seventh-order harmonics for the full speed range.

Uniform almost relative injective modules

The concept of a module M being almost N-injective where N is some module, was introduced by Baba (1989). For a given module M, the class of modules N, for which M is almost N-injective, is not closed under direct sums. Baba gave a necessary and sufficient condition under which a uniform finite length module U is almost V-injective, where V is a finite direct sum of uniform, finite length modules, in terms of extending properties of simple submodules of V. Let U be a uniform module and V be a finite direct sum of indecomposable modules. Recently, Singh (2016), has determined some conditions under which U is almost V injective, which generalize Baba's result. In the present paper some more results in this direction are proved. A module M is said to be completely almost self-injective, if for any two subfactors A, B of M, A is almost B-injective. A necessary and sufficient condition for a module M to be completely almost self-injective is given. Using this, it is proved that a Von Neumann ring R is completely almost right self-injective if and only if Rsoc(RR) is semi-simple and every minimal right ideal of R is injective.

A Quantitative and Computer-Aided Thermography-Based Diagnostics for PV Devices—Part II: Platform and Results

This paper, Part II, deals with the software platform that implements the workflow described in Part I, i.e., a thermography-based diagnostics able to provide a detailed, clear, and unambiguous information on the health state of photovoltaic (PV) modules. The methodology, in fact, allows a numerical and qualitative evaluation of each cell of the PV module. In particular, this paper deeply describes the main features of the software platform and introduces the graphical user interface that makes the framework efficiently and effectively adoptable since it leads to the automatic generation of a report. In order to show the manifold features, three cases of study, which have been derived from a real monitoring survey, are discussed, highlighting the critical situations revealed neither with a direct observation of the infrared image nor with its manual processing: The first case in regard to a defected PV module and the second one an almost completely uniform module, while the third one deals with a dishomogeneous module.

Mechanism of Four de Novo Designed Antimicrobial Peptides

As pathogenic bacteria become resistant to traditional antibiotics, alternate approaches such as designing and testing new potent selective antimicrobial peptides (AMP) are increasingly attractive. However, whereas much is known regarding the relationship between the AMP sequence and potency, less research has focused on developing links between AMP properties, such as design and structure, with mechanisms. Here we use four natural AMPs of varying known secondary structures and mechanisms of lipid bilayer disruption as controls to determine the mechanisms of four rationally designed AMPs with similar secondary structures and rearranged amino acid sequences. Using a Quartz Crystal Microbalance with Dissipation, we were able to differentiate between molecular models of AMP actions such as barrel-stave pore formation, toroidal pore formation, and peptide insertion mechanisms by quantifying differential frequencies throughout an oscillating supported lipid bilayer. Barrel-stave pores were identified by uniform frequency modulation, whereas toroidal pores possessed characteristic changes in oscillation frequency throughout the bilayer. The resulting modes of action demonstrate that rearrangement of an amino acid sequence of the AMP resulted in identical overall mechanisms, and that a given secondary structure did not necessarily predict mechanism. Also, increased mass addition to Gram-positive mimetic membranes from AMP disruption corresponded with lower minimum inhibitory concentrations against the Gram-positive Staphylococcus aureus.

Air staging strategies in biomass combustion-gaseous and particulate emission reduction potentials

Gaseous and particulate emissions have been investigated with different air staging strategies over a wide range of secondary air flow rates. Laboratory scale wood pellet combustor, supplied by an underfeed fuel bed input, is used. The air staging strategies have been employed to study burning rate, temperature in primary and post combustion zones, and NO, CO and PM emissions, taking into account the air to fuel stoichiometric ratio. 50% CO reduction and 9 times less particle mass concentration than non-staged combustion are achieved by deploying a uniform secondary air module in a higher position from the bed. The minimum NO (37% reduction than non-staged) measured in the non-uniform air distribution module at the higher flow rate with lower distance from the fuel bed. The results demonstrate a trade-off between NO and CO, PM emissions but also significant potential for reducing particulate and gaseous emissions by deploying air staging in the pellet combustor.

Axially uniform magnetic field-modulation excitation for electron paramagnetic resonance in rectangular and cylindrical cavities by slot cutting

In continuous-wave (CW) Electron Paramagnetic Resonance (EPR) a low-frequency time-harmonic magnetic field, called field modulation, is applied parallel to the static magnetic field and incident on the sample. Varying amplitude of the field modulation incident on the sample has consequences on spectral line-shape and line-height over the axis of the sample. Here we present a method of coupling magnetic field into the cavity using slots perpendicular to the sample axis where the slot depths are designed in such a way to produce an axially uniform magnetic field along the sample. Previous literature typically assumes a uniform cross-section and axial excitation due to the wavelength of the field modulation being much larger than the cavity. Through numerical analysis and insights obtained from the eigenfunction expansion of dyadic Green’s functions, it is shown that evanescent standing-wave modes with complex cross-sections are formed within the cavity. From this analysis, a W-band (94GHz) cylindrical cavity is designed where modulation slots are optimized to present a uniform 100kHz field modulation over the length of the sample.

An experimental study into the effect of air staging distribution and position on emissions in a laboratory scale biomass combustor

Air staging strategy is a proven technology to provide efficient biomass combustion with less gaseous and particulate emissions. In this study, two different secondary air distribution modules are employed at two different axial positions from the bed surface in a 15 kW fixed-bed laboratory scale combustion system includes grate and underfeed bed stocker. The effects of air staging on temperature, burning rate, gaseous and particulate emissions have been assessed over a selected primary air flow rate and a range of secondary air flow rates. Secondary air inlet module with uniform distribution of air results in 50% CO reduction by shifting the combustion to a more fuel lean environment and high temperature in the post-combustion zone. Remarkable decrease in particulate matters smaller than 1 μm is achievable through adjusting a uniform secondary air module in an appropriate distance from the bed. The non-uniform secondary air configuration increases the gaseous and particulate emissions than the uniform configuration. These results emphasise the need for further studies to better understand the effect of air staging on particulate and gaseous emissions.

Local filtration based scatter correction for cone-beam CT using primary modulation.

Excessive scatter contamination fundamentally limits the image quality of cone-beam CT (CBCT), hindering its quantitative use in clinical applications. The author has previously proposed an effective scatter correction method for CBCT using primary modulation. A Fourier transform-based algorithm (FTPM) was implemented to estimate scatter from modulated projections, with a few limitations including the assumption of uniform modulation frequency and magnitude that becomes less accurate in the presence of beam-hardening and other nonideal effects. This paper aims to overcome the above drawbacks by developing a new algorithm for the primary modulation method with improved accuracy and reliability. Incident x-ray intensities for each detector pixel with and without the interception of the modulator blocker are estimated from a modulated flat-field image. A new signal relationship is then developed to obtain a first scatter estimate from a modulated projection using a spatially varying modulation distribution. The method empirically adjusts the effective modulation magnitude for each projection ray to account for the beam-hardening effects. Estimated scatter signals with high expected errors are discarded in the generation of the final scatter distribution. The author proposes a technique of local filtration to accelerate major portions of the signal processing, and the new algorithm is referred to as local filtration based primary modulation (LFPM). The study on the Catphan® 600 phantom shows that LFPM effectively removes scatter-induced cupping artifacts on CBCT images and reduces the CT image error from 222 to 15 HU. In addition, the image contrast on eight contrast rods of the phantom is enhanced by a factor of 2 on average. On an anthropomorphic head phantom, LFPM reduces the CT image error from 153 to 18 HU and eliminates the streak artifacts observed on the result of FTPM with substantially improved image uniformity. On the Rando® phantom, LFPM reduces the CT image error from 278 to 4 HU around the object center. As compared with the previously developed FTPM algorithm, LFPM enhances the imaging performance by using a more flexible data processing framework that does not require projection data downsampling or uniform modulation frequency and magnitude. It also becomes possible to discard suspicious scatter estimate values prior to the generation of a final scatter distribution and to model the beam-hardening effects on modulation for improved scatter estimation accuracy. The presented research further exploits the potential of the primary modulation method on scatter correction and facilitates its clinical adoption in CBCT imaging.

Time reversal of a wave packet with temporal modulation of gauge potential

We show that time reversal can be achieved with a spatially uniform temporal modulation of the gauge potential. The method can be applied to the quantum wave function of electrons where there are natural gauge potentials, and to classical waves such as the acoustic and optical waves where effective gauge potentials have been demonstrated recently. This time-reversal process can provide a compensation of higher-order dispersion effects. Moreover, our approach can be used to time reverse the propagation of a wave packet in three dimensions, as well as a topologically protected one-way edge state where the underlying Hamiltonian does not have time-reversal symmetry. Our work shows that modulation of gauge potentials provides a versatile approach for dynamically controlling wave propagation.

Modules with ascending chain condition on annihilators and Goldie modules

ABSTRACTUsing the concepts of prime module, semiprime module and the concept of ascending chain condition (ACC) on annihilators for an R-module M, we prove that if M is semiprime and projective in σ[M], such that M satisfies ACC on annihilators, then M has finitely many minimal prime submodules. Moreover, if each submodule N⊆M contains a uniform submodule, we prove that there is a bijective correspondence between a complete set of representatives of isomorphism classes of indecomposable non-M-singular injective modules in σ[M] and the set of minimal primes in M. If M is a Goldie module, then , where each Ei is a uniform M-injective module. As an application, new characterizations of left Goldie rings are obtained.

Low-Complexity Demapping Algorithm for Two-Dimensional Non-Uniform Constellations

Non-uniform constellations (NUCs) have been recently introduced in digital broadcasting systems to close the remaining gap to the unconstrained Shannon theoretical limit. Compared to uniform quadrature amplitude modulation (QAM) constellations, NUCs provide a signal-to-noise ratio (SNR) gain (i.e., a reduction in the required SNR), especially for high-order constellations. One-dimensional NUCs (1D-NUC) have a squared shape with non-uniform distance between the constellation symbols. Since the I and Q components remain as two independent signals, a 1D-demapper as for uniform QAM constellations is feasible. Two-dimensional NUCs (2D-NUC) provide a better performance than 1D-NUCs, since they are designed by relaxing the square shape constraint, with arbitrary shape along the complex plane. However, the main drawback of 2D-NUCs is the higher complexity at the receiver, since a 2D-demapper is needed. In this paper, we propose a demapping algorithm that reduces from 69% to 93% the number of required distances when using 2D-NUCs. The algorithm discards or replicates those constellation symbols that provide scarce information, with a performance degradation lower to 0.1 dB compared to the optimal maximum likelihood demapper.

Convex Channel Power Optimization in Nonlinear WDM Systems Using Gaussian Noise Model

Optimization of channel powers to maximize minimum margin or total capacity in WDM systems is studied. Using a Gaussian noise nonlinearity model, the signal-to-noise ratio (SNR) in each channel is expressed as a convex function of the channel powers. Using the SNR expression, convex optimization problems with objectives of maximizing the minimum channel margin or maximizing the fiber capacity minus a coding cap are formulated. Performance gains from software-based power optimization are observed in mesh networks and in point-to-point links having heterogeneous SNR requirements. By contrast, in systems with uniform amplifier noise and modulation formats, the optimized power allocation provides very little improvement over a traditional flat power allocation. In the 14-node NSFNET network, a margin gain of 1.5 dB on average is achieved through power optimization, as compared to a flat power allocation. Margin gains averaging 1.4 dB are found for subsets of this network with three to 13 nodes.

Practical considerations for noise power spectra estimation for clinical CT scanners.

Local noise power spectra (NPS) have been commonly calculated to represent the noise properties of CT imaging systems, but their properties are significantly affected by the utilized calculation schemes. In this study, the effects of varied calculation parameters on the local NPS were analyzed, and practical suggestions were provided regarding the estimation of local NPS for clinical CT scanners. The uniformity module of a Catphan phantom was scanned with a Philips Brilliance 64 slice CT simulator with varied scanning protocols. Images were reconstructed using FBP and iDose4 iterative reconstruction with noise reduction levels 1, 3, and 6. Local NPS were calculated and compared for varied region of interest (ROI) locations and sizes, image background removal methods, and window functions. Additionally, with a predetermined NPS as a ground truth, local NPS calculation accuracy was compared for computer simulated ROIs, varying the aforementioned parameters in addition to ROI number. An analysis of the effects of these varied calculation parameters on the magnitude and shape of the NPS was conducted. The local NPS varied depending on calculation parameters, particularly at low spatial frequencies below ∼0.15 mm−1. For the simulation study, NPS calculation error decreased exponentially as ROI number increased. For the Catphan study the NPS magnitude varied as a function of ROI location, which was better observed when using smaller ROI sizes. The image subtraction method for background removal was the most effective at reducing low‐frequency background noise, and produced similar results no matter which ROI size or window function was used. The PCA background removal method with a Hann window function produced the closest match to image subtraction, with an average percent difference of 17.5%. Image noise should be analyzed locally by calculating the NPS for small ROI sizes. A minimum ROI size is recommended based on the chosen radial bin size and image pixel dimensions. As the ROI size decreases, the NPS becomes more dependent on the choice of background removal method and window function. The image subtraction method is most accurate, but other methods can achieve similar accuracy if certain window functions are applied. All dependencies should be analyzed and taken into account when considering the interpretation of the NPS for task‐based image quality assessment.PACS number(s): 87.57.C‐, 87.57.Q‐

Almost relative injective modules

The concept of a module $M$ being almost $N$-injective, where $N$ is some module, was introduced by Baba (1989). For a given module $M$, the class of modules $N$, for which $M$ is almost $N$-injective, is not closed under direct sums. Baba gave a necessary and sufficient condition under which a uniform, finite length module $U$ is almost $V$-injective, where $V$ is a finite direct sum of uniform, finite length modules, in terms of extending properties of simple submodules of $V$. Let $M$ be a uniform module and $V$ be a finite direct sum of indecomposable modules. Some conditions under which $M$ is almost $V$-injective are determined, thereby Baba's result is generalized. A module $M$ that is almost $M$-injective is called an almost self-injective module. Commutative indecomposable rings and von Neumann regular rings that are almost self-injective are studied. It is proved that any minimal right ideal of a von Neumann regular, almost right self-injective ring, is injective. This result is used to give an example of a von Neumann regular ring that is not almost right self-injective.

Thermal management of Li-ion battery with liquid metal

Thermal management especially cooling of electric vehicles (EVs) battery pack is of great significance for guaranteeing the performance of the cells as well as safety and high-efficiency working of the EVs. Liquid cooling is a powerful way to keep the battery temperature in a proper range. However, the efficiency of conventional liquid cooling is still limited due to the inherently low thermal conductivity of the coolant which is usually water or aqueous ethanol. In this paper, a new kind of coolant, liquid metal, is proposed to be used for the thermal management of the battery pack. Mathematical analysis and numerical simulations are conducted to evaluate the cooling capability, pump power consumption and module temperature uniformity of the liquid metal cooling system, in comparison with that of water cooling. The results show that under the same flow conditions, a lower and more uniform module temperature can be obtained and less pump power consumption are needed in the liquid metal cooling system. In addition, liquid metal has an excellent cooling capability coping with stressful conditions, such as high power draw, defects in cells, and high ambient temperature. This makes it a promising coolant for the thermal management of high driving force EVs and quick charge batteries.