Uniform Modulation Research Articles

Uniform Distribution Pulsewidth Modulation Strategy for Three-Phase Converters to Reduce Conducted EMI and Switching Loss

It is necessary to suppress the emission level of conducted electromagnetic interference (EMI) for the power electronics converters, and the variable switching frequency pulsewidth modulation (VSFPWM) is an alternative approach to reduce conducted EMI without adding bulky passive components. However, the experimental results indicate that many obvious EMI spikes in spectrum remain so that the conducted EMI reduction for VSFPWM is limited. In order to eliminate the EMI spikes in spectrum, this article first investigates the cause of the EMI spikes for VSFPWM, and the analysis results show that the nonuniform distribution of switching frequency is the primary reason. Then, a novel PWM strategy called uniform distribution PWM (UDPWM) is proposed to eliminate the EMI spikes and to further reduce conducted EMI. The design of a UDPWM is based on the uniform distribution of switching frequency and the principle of less switching loss. Moreover, the analytical formula of switching frequency is also deduced in detail, which adopts fixed variation range of switching frequency whatever the modulation index is. Finally, the experiments are carried out to validate the effectiveness of the UDPWM in reducing conducted EMI and switching loss. The UDPWM can approximately reduce conducted EMI by 20 dB compared with the conventional constant switching frequency PWM, and all obvious spikes in the spectrum are eliminated compared with VSFPWM.

Blind Carrier Frequency Offset Estimation in Coherent Optical Communication Systems With Probabilistically Shaped M-QAM

We find that the conventional 4th power and circular harmonic expansion (CHE) algorithms, which are originally devised for blind frequency offset estimation (FOE) in the uniform M-quadrature amplitude modulation (MQAM) systems, cannot work properly for probabilistically shaped (PS)-MQAM under moderate or strong shaping. To solve this issue, two novel blind FOE algorithms, namely the radius directed (RD)-4th power algorithm and the generalized circular harmonic expansion (GCHE) algorithm, are proposed. The former one adopts QPSK-selection based on a radius threshold optimized for a specific constellation entropy; while the later one conducts maximum likelihood (ML) estimation with a theoretically derived nonlinear radius transfer function in the GCHE. Several issues related to the practical implementation, including the optimization of the radius threshold in the RD-4th power algorithm, the impact of SNR-mismatch in the GCHE algorithm, and the computational complexities of the proposed algorithms, are analyzed. The Monte-Carlo simulation results show that: (1) the RD-4th power algorithm works properly in most of the cases except for very weak shaping, whereas the GCHE algorithm offers robust performance regardless of the shaping strength and outperforms the RD-4th power algorithm in all cases; (2) the performance gap between the two algorithms, which have the same computational complexity, enlarges for a larger constellation entropy. These observations indicate that the GCHE algorithm is a promising blind FOE algorithm, in terms of high estimation accuracy and robust performance, for applications that leverage the rate adaptability of the PS-MQAM, such as flexible optical networks.

Spectral Analysis of UPWM Signals for Filterless Digital Class D Power Amplifiers

Filterless digital class D power amplifiers usually utilize three-level uniform sampling pulse width modulation (UPWM) technique to convert the digital input signal into a UPWM signal which is used to drive the power stage. Therefore, the spectral estimation expressions for different three-level UPWM signals obtained by modulating the digital signal can be an evaluation tool for signal distortion and electromagnetic interference when filterless digital class D power amplifiers are designed. Based on the time-domain characteristics of three-level UPWM signals, the spectral estimation expressions for six types of three-level UPWM signals are proposed in this paper by using the discrete Fourier transform technique and the frequency response of the zero-order holder. According to these expressions, the relationships among the total harmonic distortion, the pulse repetition frequency and the pulse width resolution of the UPWM signal are studied. A UPWM generator test system based on field-programmable gate array is designed and implemented to measure the spectra of different UPWM signals. The measured results are compared with the calculated results obtained by the proposed expressions to verify the correctness of the proposed expressions.

Time-energy filtering of single electrons in ballistic waveguides

Characterizing distinct electron wave packets is a basic task for solid-state electron quantum optics with applications in quantum metrology and sensing. A important circuit element for this task is a non-stationary potential barrier that enables backscattering of chiral particles depending on their energy and time of arrival. Here we solve the quantum mechanical problem of single-particle scattering by a ballistic constriction in an fully depleted quantum Hall system under spatially uniform but time-dependent electrostatic potential modulation. The result describes electrons distributed in time-energy space according to a modified Wigner quasiprobability distribution and scattered with an energy-dependent transmission probability that characterizes constriction in the absence of modulation. Modification of the incoming Wigner distribution due to external time-dependent potential simplifies in case of linear time-dependence and admits semiclassical interpretation. Our results support a recently proposed and implemented method for measuring time and energy distribution of solitary electrons as a quantum tomography technique, and offer new paths for experimental exploration of on-demand sources of coherent electrons.

Joint Vehicular and Static Users Multiplexing Transmission With Hierarchical Modulation for Throughput Maximization in Vehicular Networks

With the rapid development of intelligent transportation system (ITS), increasing the throughput of all kinds of users in the mobile communication network is a pressing problem. We consider there are two types of users, i.e. vehicular users (VUs) and static users (SUs), in a vehicular communication network. Since the channel characteristics of VUs and SUs are different, designing a multi-user multiplexing transmission strategy to provide an efficient and reliable transmission for two types of users is quite challenging. We propose a dynamic cross-layer transmission strategy with joint admission control, user association and resource allocation to increase the total throughput of VUs and SUs while satisfying the different quality of service (QoS) requirements. First, we formulate a throughput utility maximization problem subject to the QoS and maximum transmit power constraints. Second, with the help of Lyapunov optimization theory, the problem can be decomposed into three subproblems including traffic admission control, user association and resource allocation. Third, a novel robust resource allocation scheme with discrete-rate hierarchical modulation (HM) is designed for the reliable multiplexing transmission of two types of users. In addition, an optimal algorithm and a low complexity suboptimal algorithm are presented to solve the user association subproblem. For two types of users, comparing with uniform modulation schemes, the proposed transmission strategy with HM scheme can improve the throughput by more than 15%.

Quantitative evaluation of image quality of megavoltage computed tomography for guiding helical tomotherapy

To quantitatively analyze image quality of two sets of phantom (CatPhan504 and Cheese) Megavoltage computed tomography (MVCT) images acquired by Helical Tomotherapy with three scanning modes (Fine, Normal and Coarse), and to explore and validate a semi-automatic quality assurance procedure for MVCT images of Helical Tomotherapy. On Helical Tomotherapy, CatPan504 and Cheese phantoms were scanned with three pitch levels (Fine, Normal, Coarse: 4 mm, 8 mm, 12 mm/circle) respectively. Pylinac, Matlab and Eclipse were used to calculate and compare spatial resolution, noise level and low contrast resolution of images obtained under three scanning modes respectively. The spatial resolution can be evaluated by the blurring of line-pair CT value in the images of CatPhan504's CTP528 module. The noise level can be evaluated by the integral non-uniformity in the images of Cheese's uniformity module. the low contrast resolution can be evaluated by contrast-to-noise ratio of both phantoms' plug-in module, or visibility of the region of interest (Supra-Slice) in the images of CatPhan504's CTP515 module. Analyses on CatPhan504's line pair module(CTP528 module) showed that the first three line pairs(the gap size are 0.500 cm, 0.250 cm and 0.167 cm respectively) could be clearly observed but blurring began to occur from the fourth line pair(the gap size is 0.125 cm) under Coarse mode. Meanwhile, the first four line pairs were all observable under the Normal and Fine modes. Integral non-integrity index(the value negatively correlated with the noise level) were 0.155 7, 0.136 8 and 0.122 9 for Coarse, Normal and Fine modes respectively. None of the Supra-Slice in CatPhan504's CTP515 module could be observed under three imaging modes. Low contrast contrast-to-noise ratio of Cheese phantom was similar under three modes and the insert visibility exhibited nearly linear growth with the increasing difference between CT average value of the insert material and background. Superiority and inferiority of three image modes in terms of the three image quality index was not consistent. Evaluation results above could provide reference for more rational decision on scanning modes selection of helical tomotherapy, which was based on image visualization demands in clinical practice. The proposed method could also provide guidance for similar image quality assessment and periodic quality assurance.

Superchannel Multicasting Module Placement Algorithm Applied to Elastic Optical Networks

The spectral fragmentation problem in elastic optical networks decreases the spectral usage provided by this technology. One way to tackle this problem is by the use of the optical inverse multiplexing technique based on superchannel multicasting (SM). This technique allows to fill the fragments presented in the network with requests, by either modifying the original central frequency of the request or by dividing the original request superchannel into discontiguous sets of slots, in part of the route. These two forms of SM usage are investigated in this paper, in order to evaluate the advantage of applying descontiguity. An algorithm for an efficient superchannel multicasting module distribution among the network nodes with this capability is the main subject of this article. The effectiveness of the heuristics is assessed by comparing its call request blocking probability with that provided by the uniform SM module distribution. We analyze three distinct topologies under multiple network loads and amount of SM modules. In all cases, our proposed module distribution provides reductions of 25% to 48% in the call request blocking probability when compared to the uniform SM module distribution.

Strongly ∩ –Reversible Extending Acts over Monoids

In this work, we present and investigate the class of acts that are strongly extending relative to -reversible subacts in the category of S-acts with zero element. Many characterizations and properties of -reversible extending acts are described. Many results which are known for strongly uniform extending modules and strongly uniform continuous modules are generalized to S-acts with zero element.

Implications of Distributed Link Polarization-Dependent Loss on Bitwise Achievable Information Rates for Probabilistically Shaped and Uniform DP 64-QAM

The statistical behaviors of bitwise achievable information rates (BW AIRs) and effective signal-to-noise ratios (SNRs) due to polarization-dependent loss (PDL) are experimentally characterized for probabilistically shaped and uniform dual-polarization 64-ary quadrature amplitude modulation with a bit rate of 250 Gb/s. A single-span recirculating loop is used to emulate distributed link PDL. Histograms for the BW AIR and effective SNR following offline signal processing resemble shifted, mirror-image Maxwell probability density functions for both constellations and two different per-loop PDL values. For a transmission distance of 1200 km and a per-loop PDL of 1.3 dB, the outage probabilities for the shaped and uniform constellations are estimated to be $1.1\times 10^{-3}$ and $4.4\times 10^{-1}$ , respectively. Moreover, for an outage probability $\leq$ $4.0\times 10^{-3}$ , the increase in transmission distance due to shaping is reduced by 50% compared to that for PDL free transmission.

Uniform Thermo-Optic Tunability of Dielectric Metalenses

The advent of low-loss dielectric metasurfaces offers a paradigm of miniaturization for free-space optical elements like lenses and deflectors, but these are limited to static functionality. This study illustrates the possibility to tune the focal length of a metalens through spatially uniform modulation of refractive index. Using traditional thermo-optic effects, the authors demonstrate large refractive index changes ($\mathrm{\ensuremath{\Delta}}\phantom{\rule{0}{0ex}}n$ = 0.15) in InSb Mie resonators. They furthermore show how to form a metasurface from a single material, enabling easier wafer-scale production.

The effect of transcutaneous spinal direct current stimulation on corticospinal excitability in chronic incomplete spinal cord injury.

OBJECTIVES:This study investigated the feasibility of modulating bilateral corticospinal excitability with different polarities of transcutaneous spinal direct current stimulation (tsDCS) in chronic, incomplete spinal cord injury (SCI).METHODS:Six subjects with chronic incomplete SCI (>12 months post injury) participated in this crossover study. Intervention consisted of 3 sessions, separated by at least 1 week, in which each subject received the conditions cathodal, anodal, and sham tsDCS. Stimulation was delivered at 2.5 mA for 20 minutes with the active electrode positioned over the spinous processes of T10-T11 and the reference electrode over left deltoid. To measure the effects of tsDCS on corticospinal excitability, motor evoked potentials (MEPs) from transcranial magnetic stimulation were measured bilaterally from soleus before and after tsDCS.RESULTS:Five subjects completed all 3 sessions. One subject withdrew after 2 sessions due to complications unrelated to the study. MEPs were measurable in 5 subjects. No significant differences in change of MEP amplitudes were found between the 3 conditions. However, there were trends that indicated laterality of response, particularly with cathodal tsDCS increasing corticospinal excitability contralateral to the reference electrode and decreasing corticospinal excitability ipsilateral to the reference electrode.CONCLUSION:Corticospinal excitability may be modulated with laterality by tsDCS in individuals with chronic, incomplete SCI. Further research is needed to 1) determine whether different placement of the reference electrode can lead to uniform modulation bilaterally, and 2) reveal whether these alterations in corticospinal excitability can lead to improved movement function in individuals with chronic, incomplete SCI.

Family of isolated bidirectional resonant converters with duty‐cycle control and automatic power flow transition

This study proposes a family of duty-cycle controlled bidirectional resonant converters and its uniform modulation schemes. This family of converters is composed of a current-fed stage, a transformer with LC resonant tank and a voltage-fed stage. Therefore, high-voltage gain and low-current ripple can be achieved. With the proposed uniform modulation schemes, automatic forward and backward mode transition is realised. Furthermore, the voltage gain is only determined by the duty cycle, independent of load and power flow direction, thus simple control can be adopted and voltage can be regulated in a wide range. Zero-voltage switching of all switches can be achieved over a wide load range. The operation principle and analysis of one of the converters are presented as an example. Design considerations are provided. Experimental results are shown to verify the theoretical analysis.

Reconstructing the Neanderthal brain using computational anatomy

The present study attempted to reconstruct 3D brain shape of Neanderthals and early Homo sapiens based on computational neuroanatomy. We found that early Homo sapiens had relatively larger cerebellar hemispheres but a smaller occipital region in the cerebrum than Neanderthals long before the time that Neanderthals disappeared. Further, using behavioural and structural imaging data of living humans, the abilities such as cognitive flexibility, attention, the language processing, episodic and working memory capacity were positively correlated with size-adjusted cerebellar volume. As the cerebellar hemispheres are structured as a large array of uniform neural modules, a larger cerebellum may possess a larger capacity for cognitive information processing. Such a neuroanatomical difference in the cerebellum may have caused important differences in cognitive and social abilities between the two species and might have contributed to the replacement of Neanderthals by early Homo sapiens.

Multistage electronic nematic transitions in cuprate superconductors: A functional-renormalization-group analysis

Recently, complex phase transitions accompanied by the rotational symmetry breaking have been discovered experimentally in cuprate superconductors. To find the realized order parameters, we study various charge susceptibilities in an unbiased way, by applying the functional-renormalization-group method to the realistic $d$-$p$ Hubbard model. Without assuming the wavevector of the order parameter, we reveal that the most dominant instability is the uniform ($q = 0$) charge modulation on the $p_x$ and $p_y$ orbitals, which possesses the d-symmetry. This uniform nematic order triggers another nematic p-orbital density wave along the axial (Cu-Cu) direction at $Q_a = (\pi/2,0)$. It is predicted that uniform nematic order is driven by the spin fluctuations in the pseudogap region, and another nematic density-wave order at $q = Q_a$ is triggered by the uniform order. The predicted multistage nematic transitions are caused by the Aslamazov-Larkin-type fluctuation-exchange processes.

On line rates, information rates, and spectral efficiencies in probabilistically shaped QAM systems

We carefully revisit the definitions of line rates, information rates, and spectral efficiencies in probabilistically shaped optical transmission systems. Generally accepted definitions for uniform quadrature amplitude modulation (QAM) systems are extended to more generally apply to systems with probabilistically shaped QAM, as well as to systems using pilot symbols of different QAM order than the information symbols. Based on the proper definitions, we correct erroneous claims in a recently reported work.

Robust adaptive multi-service transmission with hierarchical modulation for OFDM systems in high mobility scenarios

Wireless communications play a key role in intelligent transportation systems for bearing multiple application services with different quality of service (QoS) requirements. Hierarchical modulation (HM) is an effective technique to increase the spectral efficiency (SE) of differentiated services multiplexing transmissions. In high mobility scenario, due to the impact of the feedback delay and channel estimation error, only the imperfect channel state information is available at the transmitter. Thus, the performance of the existing HM schemes degrades severely. In this paper, we propose a robust adaptive HM scheme to increase the overall SE in the mobile orthogonal frequency division multiplexing system. The bit error rate of the HM symbol is derived for the reliable QoS-aware multi-service transmission, and the strategies of bit assignment and modulation parameters selection for different services are designed. Finally, comparing with the traditional uniform modulation scheme, the proposed robust adaptive HM scheme increases the overall SE of multiplexing transmissions by $$15\%$$ at $$300\,\hbox { km}/\hbox {h}$$ .

Минимизация репутационного ущерба при аварии на газотранспортной системе с использованием умных контрактов и технологий интеграции SAP (на примере ПАО «Газпром»).

In this paper an integrated approach to a problem related to minimization of gas supplier’s reputation losses connected with accidents on a gas pipeline and disruption of gas delivery to a consumer with the help of smart contracts is stated. Nowadays analysts and methodologists of pipeline companies perform assessment of expected and actual material expenses at an accident on GTS objects. Account and analytics of reputation losses either isn’t conducted in all, or is implemented in the frame of separate business processes which aren’t integrated into processes of enterprise budget’s management and planning. Such situation is disconcertingly. In the era of globalization the cost of a company and its business reputation depends significantly on the attitude towards it in society. In Europe and USA the major oil and gas companies invest huge money in increasing of their positive image in the eyes of population. Any significant accident which has happened in unforeseen time and unsuccessful place can completely destroy reputation of any company. Modern corporate IT-decisions allow unite a number of data flows in the uniform analytical module now. Information collected in such modules in Gazprom PJSC helps to solve optimizing problems both within planning of material inputs, and within accounting of reputation expenses. In this work a theoretical model for assessment of reputation losses at an accident on a linear part of a gas transmission system (GTS) of Gazprom PJSC is given. Modern theoretical models for definition of function of supplier’s reputation losses have been used. The review of possible application for SAP decisions and Blockchain technology in current business processes of Gazprom JSC in the frame of the problem solution is given. For a clear understanding how to integrate this decision into existing business processes the graphic description of the decision work scheme is given. The principles of this approach can be applied not only in working processes of Gazprom PJSC, but also adapted according to other pipeline companies’ needs. Possible fast introduction of cryptoruble in Russia can offer new prospects for mass introduction of this tool in the context of smart contracts.

Dependence of optical phase modulation on anchoring strength of dielectric shield wall surfaces in small liquid crystal pixels

We demonstrated that the uniform phase modulation in a pixel can be realized by optimizing the anchoring strength on the walls and the wall width in the dielectric shield wall structure, which is the needed pixel structure for realizing a 1-µm-pitch optical phase modulator. The anchoring force degrades the uniformity of the phase modulation in ON-state pixels, but it also keeps liquid crystals from rotating against the leakage of an electric field. We clarified that the optimal wall width and anchoring strength are 250 nm and less than 10−4 J/m2, respectively.

Broadband nonlinear optical response of monolayer MoSe2 under ultrafast excitation

Due to their strong light-matter interaction, monolayer transition metal dichalcogenides (TMDs) have proven to be promising candidates for nonlinear optics and optoelectronics. Here, we characterize the nonlinear absorption of chemical vapour deposition (CVD)-grown monolayer MoSe2 in the 720–810 nm wavelength range. Surprisingly, despite the presence of strong exciton resonances, monolayer MoSe2 exhibits a uniform modulation depth of ∼80 ± 3% and a saturation intensity of ∼2.5 ± 0.4 MW/cm2. In addition, pump-probe spectroscopy is performed to confirm the saturable absorption and reveal the photocarrier relaxation dynamics over hundreds of picoseconds. Our results unravel the unique broadband nonlinear absorptive behavior of monolayer MoSe2 under ultrafast excitation and highlight the potential of using monolayer TMDs as broadband ultrafast optical switches with customizable saturable absorption characteristics.

Frequency‐dependent principal component analysis of multicomponent earthquake ground motions

SummaryStochastic ground motion simulation techniques are becoming increasingly popular because of enhanced computation power enabling direct simulation of complex response quantities. Priestley process assumption is the most general approach for stochastic modeling of earthquake ground motion. However, a framework for multicomponent ground motion simulation using the general Priestley process assumption is not available. Multicomponent motions are useful especially when the correlation structure between them significantly influences the response. The present study proposes a framework for frequency‐dependent principal component analysis (PCA), which facilitates Priestley process–based simulation of multicomponent ground motions. The study focuses only on the frequency‐dependent PCA part, and the results show high dependency of the principal components/directions on the frequency bands of the signals. The present work also advocates that the frequency‐dependent PCA should be preferred to the conventional PCA as the former can address the issues related to the frequency‐independent uniform modulation associated with the latter.