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In this article, we study the existence of periodic solutions to a class of distributed delay differential equations. We transform the search for periodic solutions with the special symmetry of a delay differential equation to the problem of finding periodic solutions of an associated Hamiltonian system. Using the critical point theory and the pseudo-index theory, we obtain some sufficient conditions for the multiplicity of periodic solutions. This is the first time that critical point theory has been used to study the existence of periodic solutions to distributed delay differential equations.

In this article, we use the Nehari manifold method to study a class of fourth-order even difference systems. First, we show that there exist multiple periodic solutions to the non-autonomous system. Second, we obtain sufficient conditions to guarantee the existence of solutions with prescribed minimal periods to the autonomous system. Our results generalize the results in reference.

Background: Double expression lymphoma (DEL) is a subtype of primary central nervous system lymphoma (PCNSL) that often has a poor prognosis. Currently, there are limited noninvasive ways to detect protein expression. Purpose: To detect DEL in PCNSL using multiparametric MRI‐based machine learning. Study Type: Retrospective. Population: Forty PCNSL patients were enrolled in the study among whom 17 were DEL (9 males and 8 females, 61.29 ± 14.14 years) and 23 were non‐DEL (14 males and 9 females, 55.57 ± 14.16 years) with 59 lesions (28 DEL and 31 non‐DEL). Field Strength/Sequence: ADC map derived from DWI (b = 0/1000 s/mm2), fast spin echo T2WI, T2FLAIR, and contrast‐enhanced T1 weighted imaging (T1CE) were collected at 3.0 T. Assessment: Two raters manually segmented lesions by ITK‐SNAP on ADC, T2WI, T2FLAIR and T1CE. A total of 2234 radiomics features from the tumor segmentation area were extracted. The t‐test was conducted to filter the features, and elastic net regression algorithm combined with recursive feature elimination was used to calculate the essential features. Finally, 12 groups with combinations of different sequences were fitted to 6 classifiers, and the optimal models were selected. Statistical tests: Continuous variables were assessed by the t‐test, while categorical variables were assessed by the non‐parametric test. Interclass correlation coefficient tested variables' consistency. Sensitivity, specificity, accuracy F1‐score, and area under the curve (AUC) were used to evaluate model performance. Results: DEL status could be identified to varying degrees with 72 models based on radiomics, and model performance could be improved by combining different sequences and classifiers. Both SVMlinear and logistic regression (LR) combined with four sequence group had similar largest AUCmean (0.92 ± 0.09 vs. 0.92 ± 0.05), and SVMlinear was considered as the optimal model in this study since the F1‐score of SVMlinear (0.88) was higher than that of LR (0.83). Data Conclusion: Multiparametric MRI‐based machine learning is promising in DEL detection. Evidence Level: 4 Technical Efficacy Stage: 2 [ABSTRACT FROM AUTHOR]

In the present paper, we consider the existence of solutions with a prescribed l 2 -norm for the following discrete Schrödinger equations, { − Δ 2 u k − 1 − f (u k) = λ u k k ∈ Z , ∑ k ∈ Z | u k | 2 = α 2 , where Δ 2 u k − 1 = u k + 1 + u k − 1 − 2 u k , f ∈ C (R) , α is a fixed constant, and λ ∈ R arises as a Lagrange multiplier. To get the solutions, we investigate the corresponding minimizing problem with the l 2 -norm constraint: E α = inf { 1 2 ∑ | Δ u k − 1 | 2 − ∑ F (u k) : ∑ | u k | 2 = α 2 }. An elaborative analysis on a minimizing sequence with respect to E α is obtained. We prove that there is a constant α 0 ≥ 0 such that there exists a global minimizer if α > α 0 , and there exists no global minimizer if α < α 0 . It seems that it is the first time to consider the solution with a prescribed l 2 -norm of the discrete Schrödinger equations. [ABSTRACT FROM AUTHOR]

In this paper, we study the multiplicity of periodic solutions for a class of fourth-order difference equations. We estimate a lower bound on the number of periodic solutions when the nonlinearity is asymptotic both at the origin and at infinity. Our results generalize the reference' results. [ABSTRACT FROM AUTHOR]

In this article, the soft-switching technique is an important way to achieve high frequency and high conversion efficiency for transformerless grid-connected inverters (TLIs) with distributed photovoltaic generation. Meanwhile, new technical standards require TLIs to have a wider power factor operation range to support grid voltage, which means that there are positive power regions and negative power regions in a grid period. In order to fulfill soft-switching for high-frequency working switches during all power regions, a pair of zero-voltage-transition (ZVT) resonant cells with different capacitor connections are first derived in this article, and two equivalent two-quadrant resonance networks are originated by using the pair of ZVT resonant cells alternatively. Furthermore, defined connection points of the obtained two-quadrant resonance networks in TLIs are explored, and a guideline to invent new ZVT-TLIs is summarized. As a result, two families of ZVT-TLIs with full power factor range (ZVT-TLIs-FPF) are obtained. In order further to verify the correctness of the proposed guideline, the obtained ZVT-HERIC-FPF is taken as an example to analyze its operation principle. Finally, experimental results from a 1 kW prototype at 100 kHz are provided to verify the effectiveness of the proposed structuring method. [ABSTRACT FROM AUTHOR]

The grid inverters play an important role in renewable energy systems, transferring the dc power to the ac grid. Galvanic isolation is usually needed between the dc source and the grid due to safety reasons and grounding leakage current mitigation. In this article, a soft-switching isolated grid inverter is proposed based on the current-fed matrix-type configuration. The topology of this converter is composed of a current-fed H-bridge on the side of dc source and a direct matrix converter on the grid side, which are linked by a high-frequency transformer. The current-fed H-bridge on the primary-side can smooth the dc-source current and control the dc-source current directly. The avoidance of dc-link energy-storage element in the single-stage matrix converter can prolong the system's life. A space-vector-modulation-based soft-switching scheme is proposed for the matrix converter on the grid side and a model-based commutation method is adopted in the current-fed H-bridge on the dc side. With the proposed modulation methods, the soft switching can be realized for all devices in the converter. Finally, a laboratory prototype of the proposed converter has been built to verify the effectiveness of the proposed method experimentally. [ABSTRACT FROM AUTHOR]

For current-controlled grid-connected inverters with LCL filter, the essence of grid voltage full feedback is to improve the output impedance of grid-connected inverters to infinity, which can eliminate the influences of grid voltage distortion and the non-negligible grid impedance. However, existing full feedforward strategies are complex and control delay cannot be compensated precisely, which leads to the instability of system when the full feedforward of the voltage at the point of common coupling under the weak grid is adopted. This article first proposes a simplified full feedforward strategy based on grid-side inductor volt-age differential feedback active damping (GIVD-AD). Second, repetitive prediction (RP) is used to compensate for the control delay. Then, a virtual impedance branch is added and an adaptive algorithm for modifying virtual impedance based on the difference between predicted grid voltages by Newton interpolation prediction (NIP) and RP is proposed. With the proposed method, grid-connected inverters can work stably when grid impedance changes suddenly and exhibit strong rejection ability against grid-voltage harmonics. Finally, simulative and experimental results from a 3-kW single-phase grid-connected inverter are provided to prove the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Soft-switching technique contributes to higher conversion efficiency and switching frequency for transformerless grid-connected inverters (TLIs), which is beneficial to improve power density and reduce cost. However, existing soft-switching TLIs can only operate with unity power factor; as a consequence, they could not supply reactive power required by newly technical standards. In order to solve this issue, a novel zero-voltage-transition (ZVT) scheme has been proposed in this article, and two resonant tanks with a compact structure are applied in H6-type topology. The derived ZVT inverter enables high-frequency switches of both positive and negative power regions to be turned on and off under zero-voltage conditions, as well as all auxiliary switches can be turned on with zero-current switching. Meanwhile, unipolar differential-mode voltage and constant common-mode voltage characteristics are also maintained. Finally, comprehensive experiment results from a 100-kHz/1-kW prototype are provided to verify the correctness of the proposed inverter. [ABSTRACT FROM AUTHOR]

In this paper, we study the existence of periodic solutions of the following differential delay equations z ′ ′ (t) = ∑ k = 1 M − 1 (− 1) k f (z (t − k)) , z ′ ′ (t) = ∑ k = 1 M − 1 (− 1) k f (z (t − k)) , where f ∈ C (R N , R N) f ∈ C (R N , R N) , M , N ∈ N M , N ∈ N and M M is odd. By making use of S 1 S 1 -geometrical index theory, we obtain an estimation about the number of periodic solutions in term of the difference between eigenvalues of asymptotically linear matrices at the origin and at infinity. [ABSTRACT FROM AUTHOR]

This letter proposes a fast current control scheme for ac drives by minimizing the latency from current sampling to the updation of a pulsewidth-modulation (PWM) command. By reconstructing the architecture of a linear controller, the minimal necessary steps to obtain the output voltage are deduced as the primary calculation, and the other computation work of the current loop is done in the postcalculation after updating the PWM command. With the proposed method, the computational delay is reduced with negligible loss in the available modulation index, and a higher stability margin or system bandwidth is realized. Also, the developed controller structure exhibits inherited antiwindup characteristics. The technique has been validated by experimental investigations on a permanent magnet synchronous motor. [ABSTRACT FROM AUTHOR]

Global bifurcation and spatio-temporal patterns of periodic solutions (with prescribed period) to second order reversible equivariant autonomous systems with commensurate delays are studied using the Brouwer/Leray–Schauder O (2) × Γ × ℤ 2 -equivariant degree theory. Here, O (2) is related to the reversal symmetry combined with the autonomous form of the system, Γ reflects extra spacial symmetries of the system, and ℤ 2 is related to the oddness of the right-hand side. Abstract results are supported by a concrete example with Γ = D 6 — the dihedral group of order 12. [ABSTRACT FROM AUTHOR]

This article proposes an improved space vector modulation (SVM) for the current-source rectifier (CSR). Due to the overlap time during commutations of power switches, the pulsewidth-modulation (PWM) currents of CSR may suffer from a number of low-order (mainly fifth and seventh) harmonics, which seriously degrade the harmonic performance of currents and voltages on the grid side. Especially, the overlap-time effect becomes an important issue when the increased switching frequency is applied to CSR. To mitigate these low-order harmonics of the PWM converter currents resulted from the overlap-time effect, the relationship between the overlap time and the low-order harmonics in PWM currents and grid currents are analyzed at first. Then, the design process of the LC filter and the proposed SVM with optimal overlap-time distribution is presented in details. Finally, experimental results are conducted on a low power laboratory prototype to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Brushless modular spoke type permanent magnet (MSTPM) machine has exhibited prior electromagnetic (EM) performance over conventional surface-mounted PM machines for in-wheel traction system in electric vehicles (EVs). However, analysis of thermal behavior of MSTPM machines is rather insufficient, even accurate thermal analysis is of significant importance due to poor heat dissipation condition inside the wheel hub. Conventionally, the losses produced in electrical machines by EM prediction is equivalent to the heat source in normal thermal analysis, and only the resultant thermal behavior is investigated. However, the reaction of temperature rising on the EM performance is neglected. In this article, a bi-directional coupled electromagnetic-thermal analysis method is proposed and carried out by a combination of lumped parameter thermal network (LPTN) model and finite element method (FEM), where both steady-state temperature distribution and transient-state temperature rise are investigated for MSTPM machines. By finite number of iterations between magnetic and thermal fields, the electromagnetic performance and thermal behavior can be predicted more accurately due to the coupling effect considered. The coupled model-predicted results are verified by 3D-FEM and experimental measurement, which shows that the proposed method has advantages in both computational efficiency and accuracy as well as can be applied to other electrical machines. [ABSTRACT FROM AUTHOR]

Transformerless grid-connected inverters (TLI) feature high efficiency, low cost, low volume, and weight due to using neither line-frequency transformers nor high-frequency transformers. Therefore, TLIs have been extensively investigated in the academic community and popularly installed in distributed photovoltaic grid-connected systems during the past decade. This article analyzes and summarizes the state of the art of TLI techniques, three rules of maintaining constant common-mode voltage (CMV) of TLIs at switching frequency have been concluded from a generic CMV analysis model at the beginning. Second, suppression methods of leakage current (LC) and dc current injection (DCCI), so-called two key challenges for first-generation TLIs, have been classified and discussed in detail, respectively. Finally, future trends and some challenges of TLIs based on wide bandgap devices named second-generation TLIs have been presented in this article. [ABSTRACT FROM AUTHOR]

Thermal drift-caused current measurement offset error usually results in unfavorable torque ripples of fundamental frequency, and hence a compensation method for current offset error is proposed in this article, which is initially derived based on the nonsalient-pole machines and then extended to the salient-pole machines. By filtering the difference between the predicted currents from a simple nominal model and the measured currents, the offset error is directly estimated and then compensated with minimal effects on the current dynamics. It is proved that the estimation is accurate if the filter has unity gain at the frequency of the offset error. Therefore, the proposed method is free of the current regulator type and shows strong robustness against machine parameter deviations. It can also stably work even when the output voltage is saturated. Two kinds of filters are designed in the stationary reference frame, and the low-pass filter with low bandwidth is recommended for its easy implementation. Finally, the effectiveness of the proposed method is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

A stage-structured predator-prey model with prey refuge is considered. Using the geometric stability switch criteria, we establish stability of the positive equilibrium. Stability and direction of periodic solutions arising from Hopf bifurcations are obtained by using the normal form theory and center manifold argument. Numerical simulations confirm the above theoretical results. [ABSTRACT FROM AUTHOR]

Soft-switching techniques of transformerless photovoltaic grid-connected inverters (TLIs) can significantly reduce switching losses, as well as soften switching processes. Conventional dc–ac soft-switching configurations proposed by Dr. Deepakraj M. Divan are invalid in TLIs because of the leakage current problem. In order to develop soft-switching techniques in TLIs, this paper proposes a new soft-switching configuration and a procedure to guide the invention of soft-switching TLIs. First, this paper proposes two basic resonance tanks related to dc bus polarities, and then, uses these basic tanks to elevate four popular full-bridge-type TLIs according to the proposed guideline. As a result, four soft-switching TLIs are gained. Second, this paper picks obtained soft-switching highly efficient and reliable inverter concept (HERIC) as example to analyze its soft-switching operation principle and performance. As a consequence, all active switches of the gained soft-switching HERIC circuit are switched under both of zero-current turn-on and turn-off conditions; the reverse recovery problem of freewheeling diodes is alleviated owing to the zero-current turn-off of diodes; meanwhile, the common-mode voltage at the switching frequency scale is still constant. Finally, some experimental results from a 3-kW universal prototype at 50-kHz switching frequency are provided to verify the effectiveness of the main contributions of this paper. [ABSTRACT FROM AUTHOR]

Ligupurpuroside A is one of the major glycoside in Ku-Din-Cha, a type of Chinese functional tea. In order to better understand its digestion and metabolism in humans, the interaction between Ligupurpuroside A and pepsin has been investigated by fluorescence spectra, UV–vis absorption spectra and synchronous fluorescence spectra along with molecular docking method. The fluorescence experiments indicate that Ligupurpuroside A can effectively quench the intrinsic fluorescence of pepsin through a combined quenching way at the low concentration of Ligupurpuroside A, and a static quenching procedure at the high concentration. The binding constant, binding sites of Ligupurpuroside A with pepsin have been calculated. The thermodynamic analysis suggests that non-covalent reactions, including electrostatic force, hydrophobic interaction and hydrogen bond are the main forces stabilizing the complex. According to the Förster’s non-radiation energy transfer theory, the binding distance between pepsin and Ligupurpuroside A was calculated to be 3.15 nm, which implies that energy transfer occurs between pepsin and Ligupurpuroside A. Conformation change of pepsin was observed from UV–vis absorption spectra and synchronous fluorescence spectra under experimental conditions. In addition, all these experimental results have been validated by the protein-ligand docking studies which show that Ligupurpuroside A is located in the cleft between the domains of pepsin. [ABSTRACT FROM AUTHOR]

[Display omitted] • GmoDetector could detect more than 251 commercialized GMOs and their hybrid crosses. • GmoDetector covered 64 commonly used transgenic elements and their possible combinations, which can identify both authorized and unauthorized GMOs. • GmoDetector can identify and remove the contamination of donor (micro)organisms of transgenic elements. • The sensitivity of GmoDetector has achieved the threshold of GMO labeling required by worldwide. The rapid increase of genetically modified organisms (GMOs) entering the food and feed markets, and the contamination of donor (micro)organisms of transgenic elements make it more challenging for the existing GMO detection. In this study, we developed a high-throughput and contamination-removal GMO detection approach named as GmoDetector. GmoDetector targeted 64 common transgenic elements and 76 GMO-specific events collected from 251 singular GM events, and combined with next generation sequencing (NGS) and target enrichment technology to detect various GMOs. As a result, GmoDetector was able to exclude the donor (micro)organism contamination, and detect the authorized and unauthorized GMOs (UGMOs) in any forms of food or feed, such as processed or unprocessed. The sensitivity of GmoDetector is as low as 0.1% (GMO content), which has met the GMO labeling threshold for all countries. Therefore, GmoDetector is a robust tool for accurate and efficient detection of the authorized and UGMOs. [ABSTRACT FROM AUTHOR]

Carryover contamination during amplicon sequencing workflow (AMP-Seq) put the accuracy of the high-throughput detection for pathogens at risk. The purpose of this study is to develop a carryover contaminations-controlled AMP-Seq (ccAMP-Seq) workflow to enable accurate qualitative and quantitative detection for pathogens. By using the AMP-Seq workflow to detect SARS-CoV-2, Aerosols, reagents and pipettes were identified as potential sources of contaminations and ccAMP-Seq was then developed. ccAMP-Seq used filter tips and physically isolation of experimental steps to avoid cross contamination, synthetic DNA spike-ins to compete with contaminations and quantify SARS-CoV-2, dUTP/uracil DNA glycosylase system to digest the carryover contaminations, and a new data analysis procedure to remove the sequencing reads from contaminations. Compared to AMP-Seq, the contamination level of ccAMP-Seq was at least 22-folds lower and the detection limit was also about an order of magnitude lower-as low as one copy/reaction. By testing the dilution series of SARS-CoV-2 nucleic acid standard, ccAMP-Seq showed 100% sensitivity and specificity. The high sensitivity of ccAMP-Seq was further confirmed by the detection of SARS-CoV-2 from 62 clinical samples. The consistency between qPCR and ccAMP-Seq was 100% for all the 53 qPCR-positive clinical samples. Seven qPCR-negative clinical samples were found to be positive by ccAMP-Seq, which was confirmed by extra qPCR tests on subsequent samples from the same patients. This study presents a carryover contamination-controlled, accurate qualitative and quantitative amplicon sequencing workflow that addresses the critical problem of pathogen detection for infectious diseases. IMPORTANCE Accuracy, a key indicator of pathogen detection technology, is compromised by carryover contamination in the amplicon sequencing workflow. Taking the detection of SARS-CoV-2 as case, this study presents a new carryover contamination-controlled amplicon sequencing workflow. The new workflow significantly reduces the degree of contamination in the workflow, thereby significantly improving the accuracy and sensitivity of the SARS-CoV-2 detection and empowering the ability of quantitative detection. More importantly, the use of the new workflow is simple and economical. Therefore, the results of this study can be easily applied to other microorganism, which has great significance for improving the detection level of microorganism., Competing Interests: The authors declare no conflict of interest.

Background: Tumor recurrence and pseudoprogression (PsP) have similar imaging manifestations in conventional magnetic resonance imaging (MRI), although the subsequent treatments are completely different. This study aimed to evaluate the value of perfusion-weighted imaging (PWI) in differentiating PsP from glioma recurrence., Methods: A comprehensive literature search was performed to evaluate clinical studies focused on differentiating recurrent glioma from PsP using PWI, including dynamic susceptibility contrast MRI (DSC-MRI), dynamic contrast enhanced MRI (DCE-MRI), and arterial spin labeling (ASL). Study selection and data extraction were independently completed by two reviewers. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was applied to evaluate the quality of the included studies. The software Stata 16.0 and Meta-Disc 1.4 were used for the meta-analysis. Meta-regression and subgroup analyses were applied to identify the sources of heterogeneity in the studies. This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) prior to initiation (CRD42022304404)., Results: A total of 40 studies were included, including 27 English studies and 13 Chinese studies. There were 1,341 patients with glioma recurrence and 876 patients with PsP. The pooled sensitivity and specificity of DSC-MRI for differentiating glioma recurrence from PsP were 0.82 [95% confidence interval (CI): 0.78 to 0.86] and 0.87 (95% CI: 0.80 to 0.92), respectively. The pooled sensitivity and specificity of DCE-MRI were 0.83 (95% CI: 0.76 to 0.89) and 0.83 (95% CI: 0.78 to 0.87), respectively. The pooled sensitivity and specificity of ASL were 0.80 (95% CI: 0.73 to 0.86) and 0.86 (95% CI: 0.76 to 0.92), respectively., Discussion: The DSC-MRI, DCE-MRI, and ASL perfusion techniques displayed high accuracy in distinguishing glioma recurrence from PsP, and DSC-MRI had a higher diagnostic performance than the other two techniques. However, due to the diversity of the parameters and threshold differences, further investigation and standardization are needed., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-22-32/coif). Yulin Wang reports that this study was supported by China Postdoctoral Science Foundation (No. 2020T130779). The other authors have no conflicts of interest to declare., (2022 Quantitative Imaging in Medicine and Surgery. All rights reserved.)