MMC Model Research Articles

Improved AAVM and Small-Signal Model of Hybrid MMC Considering Dynamic Differences Between Full-Bridge and Half-Bridge Submodules

Improved AAVM and Small-Signal Model of Hybrid MMC Considering Dynamic Differences Between Full-Bridge and Half-Bridge Submodules

An uncoupled ductile fracture model considering void shape change and necking coalescence

In order to accurately describe the fracture behaviour of ductile metals in a wide range of stress states, based on the mechanism of void nucleation, growth, and coalescence during plastic deformation, an uncoupled isotropic ductile fracture model was established, which considered the combination of void shape change and void coalescence through internal necking. Firstly, the effect of the volume and shape changes on the fracture behaviour of the material was summarized and discussed, and the mechanism of interpore dimple shrinkage and consolidation during the void coalescence was studied. Secondly, the parameters of the proposed model are studied in detail to verify the flexibility of the new model. Then, the proposed ductile fracture model was used to construct the 3D fracture locus of AA 2024-T351, AISI 1045, Q460, Mg-Al-Zn-RE, and Ti-6Al-4V materials, and the predicted fracture strain values under corresponding stress states were compared with the experimental results of previous scholars. The effectiveness of the proposed new model is verified. Finally, to demonstrate the superiority of the proposed new model, the predicted results were compared with those of the widely used DF2016, MMC, and Hu models. The prediction results show that the new model has the highest precision compared to the other three. The void shape change and the void coalescence through internal necking play an essential role in the ductile metal fracture process, which should be fully considered.

Allogenic umbilical cord-derived mesenchymal stromal cells improve motor function in prenatal surgical repair of myelomeningocele: An ovine model study.

To investigate the effects of an adjuvant allogenic umbilical cord mesenchymal stromal cell (UC-MSC) patch applied during fetal surgery on motor and sphincter function in the ovine MMC model. MMC defects were surgically created at 75 days of gestation and repaired 14 days later. Ovine MMC model: fetal lambs. We compared lambs that received a UC-MSC patch with a control group of lambs that received an acellular patch. Clinical neurological assessment was performed at 2 and 24 hours of life and included determination of the Sheep Locomotor Rating scale (SLR), which has been validated in the ovine MMC model. Electrophysical examinations, spine scans and histological analyses were also performed. Of the 13 operated lambs, nine were born alive: five had of these had received a UC-MSC patch and four an acellular patch. At 24 hours of life, lambs in the UC-MSC group had a significantly higher score (14 versus 5, P = 0.04). Amyotrophy was significantly more common in the control group (75% versus 0%, P = 0.02). All the lambs in the control group and none of those in the UC-MSC group were incontinent. No significant differences were observed between the UC-MSC and control groups in terms of the presence of spontaneous EMG activity, nerve conduction or spinal evoked potentials. In the microscopic examination, lambs in the UC-MSC group had less fibrosis between the spinal cord and the dermis (mean thickness, 453 versus 3921 μm, P = 0.03) and around the spinal cord (mean thickness, 47 versus 158 μm, P < 0.001). Examination of the spinal cord in the area of the MMC defect showed a higher large neuron density in the UC-MSC group (14.5 versus 5.6 neurons/mm2, P < 0.001). No tumours were observed. Fetal repair of MMC using UC-MSC patches improves motor and sphincter function as well as spinal preservation and reduction of fibrosis.

Global Asymptotic Stability of Submodule Capacitor Voltage Self-converging Modular Multilevel Converters Based on Characteristic Root Method

This study presents global asymptotic stability verification of submodule capacitor voltage self-converging modular multilevel converters (SC-MMCs) according to the characteristic root method, which constructs a submodule switching state matrix for voltage balancing control. The mathematical model of MMC is established in form of the state-space equation. It is proved that SC-MMCs have the characteristic of global asymptotic stability at a certain time from the perspective of switching state matrix characteristic roots, according to the theories of Lyapunov stability and continuous-time piecewise linear system stability. Then, the submodule capacitor voltage self-convergence over a period of time is deduced based on the capacitor voltage deviation vector. Under the constraints of linearly independent switching state matrix row vectors, submodule capacitor voltage self-convergence without real-time voltage calculation and feedback can be achieved. The global asymptotic stability of SC-MMCs and the efficacy of submodule capacitor voltage self-convergence based on switching state matrix are testified by simulations.

Study on Parameters of Modified Mohr–Coulomb Model for Water-rich Soft Soil in Tianjin, China

Foundation pit excavation through the soft layer has great technical challenges and potential safety risks, especially in soft soil area. In this study, we use a 3D numerical model of Foundation pit to simulate the excavation process. Based on the simulation, the sensitivity analysis of the three stiffness parameters ({mathrm{E}}_{mathrm{ur}}^{mathrm{ref}},{mathrm{E}}_{50}^{mathrm{ref}} and {mathrm{E}}_{mathrm{oed}}^{mathrm{ref}}) of the Modified Mohr–Coulomb model was carried out by using the Latin hypercube-one factor at a time method. During the simulation, the three stiffness parameters are changed with the perturbation amplitude of (± 20%) and (± 40%). In addition, the sensitivity of three stiffness parameters was calculated by taking the horizontal displacement of diaphragm wall as the observation index. Furthermore, by comparing the results of simulation with the measured data, the stiffness ratio relationship suitable for foundation pit simulation in Tianjin water-rich soft soil area are obtained. Our findings present that {mathrm{E}}_{mathrm{ur}}^{mathrm{ref}} is the parameter that has the largest influence on the uncertainty in the MMC model, while {mathrm{E}}_{mathrm{oed}}^{mathrm{ref}} is the least sensitive to horizontal displacement of diaphragm wall. The proportion rates of {mathrm{E}}_{mathrm{oed}}^{mathrm{ref}}/{mathrm{E}}_{50}^{mathrm{ref}} and {mathrm{E}}_{mathrm{ur}}^{mathrm{ref}}{/mathrm{E}}_{50}^{mathrm{ref}} provide a promising reference for simulating the foundation pit excavation in Tianjin water-rich soft soil area.

Identification of Neurocan and Phosphacan as Early Biomarkers for Open Neural Tube Defects

Open neural tube defects (NTDs) such as myelomeningocele (MMC) are debilitating and the most common congenital defects of the central nervous system. Despite their apparent clinical importance, the existing early prenatal diagnostic options for these defects remain limited. Using a well-accepted retinoic-acid-induced model of MMC established in fetal rats, we discovered that neurocan and phosphacan, the secreted chondroitin sulfate proteoglycans of the developing nervous system, are released into the amniotic fluid (AF) of fetal rats displaying spinal cord defects. In contrast to normal controls, elevated AF levels of neurocan and phosphacan were detected in MMC fetuses early in gestation and continued to increase during MMC progression, reaching the highest level in near-term fetuses. The molecular forms of neurocan and phosphacan identified in the AF of MMC fetuses and those found in MMC spinal cords were qualitatively similar. In summary, this is the first report demonstrating the presence of neurocan and phosphacan in the AF of MMC fetuses. The identification of elevated levels of neurocan and phosphacan in the AF of MMC fetuses provides two prospective biomarkers with the potential for early prenatal diagnosis of open NTDs.

Dynamic interaction analysis among different control loops and stability enhancement strategy for MMC-HVDC systems

This paper presents the dynamic interaction analysis method among different control loops of MMC-HVDC (Modular Multilevel Converter High Voltage Direct Current) systems, and proposes an improved control strategy with feedback regulation loop and low-pass filter loop for stability enhancement. The small-signal cascade model of MMC with dc voltage control loop, ac current control loop and differential-mode ripple capacitor voltages loop is firstly established, which clearly shows the analytical interactions of inner capacitor voltage response and system input power’s dynamics with simplified closed/open-loop transfer functions. Then the small-signal dynamic analysis of MMC is conducted based on the derived closed/open-loop transfer functions, which reveals the interactions between the system stability and key control loops, as well as the main parameters of the MMC-HVDC system by both the Nyquist criteria and the pole-zero theory. Next, the feedback regulation loop and low-pass filter loop are proposed and introduced in the MMC control system to maximize stability enhancement performance during disturbances, and system dynamic response under the proposed control with different parameters are also explored through theoretical analysis. Finally, several cases on a benchmark two-terminal MMC-HVDC simulation model are carried out in PSCAD/EMTDC to verify the proposed control strategy.

Equivalent Impedance Modeling and Stability Analysis of MMC-HVDC with Wind Farm

The risk of resonances may exist in the power electronic transmission systems composed of wind farm (WF) and the high-voltage direct-current system consisting of modular multilevel converter (MMC-HVDC). And the oscillation frequency will show coupling characteristics. The frequency dynamic interaction effect causes the WF interconnected with MMC-HVDC system exhibit multiple-input multiple-output (MIMO) characteristics. The stability determination of the system will become very difficult. Therefore, using frequency dynamic interaction effect as one of the constraints, this paper uses the harmonic state space (HHS) method to establish the two-dimensional impedance model of the wind farm side MMC(WFMMC) and the grid-side converter (GSC) of the wind farm, and further an accurate dimensionality reduction method is proposed. Finally, the results of the simulation system built based on MATLAB/Simulink verify the accuracy of the established impedance model and show that using the established model for stability analysis can obtain more accurate analysis results.

Intrauterine neuromuscular and stromal dysplasia of the bladder in retinoic acid-induced myelomeningocele fetal rats

ObjectivesTo observe the changes in the bladder of fetal rats with myelomeningocele (MMC) induced by all-trans retinoic acid (atRA) during the embryonic development stages. MethodsThe fetal rat model of MMC was induced by intragastric administration of atRA to pregnant rats on embryonic day 10 (E10). Fetal rats were harvested at E16, E18, E20, and E21 for observation and further testing. Those with MMC were classified as the MMC group, while those without MMC as the RA group. The areas of MMC skin defect, the crown-rump length (CRL), and body weight in different groups were compared. The histopathological changes in the bladder were compared. The expression levels of alpha-smooth muscle actin (αSMA), smooth muscle myosin heavy chain (SMMHC), connexin 43 (Cx43), desmin, β3 tubulin, and vesicular acetylcholine transporter (VAChT) in the bladder were investigated by immunohistochemical staining and Western blotting. Pregnant rats given intragastric administration with olive oil (OIL group) at E10 were set as the blank control group. ResultsA total of 415 fetal rats of different gestational ages were harvested with an MMC incidence of 56.05 % (139/248). The incidence rate increased with embryonic days (p < 0.001). Compared with the other two control groups, the CRL and bodyweight of MMC fetal rats were significantly delayed at E21 (p < 0.001). The expression levels of αSMA, SMMHC, Cx43, desmin, β3 tubulin and VAChT in the bladder of MMC fetal rats were significantly decreased at E21 (p < 0.05). ConclusionsIn atRA-induced MMC fetal rats, there is neural, muscular, and stromal dysplasia in the bladder at an early gestational age. Further investigations on neurogenic bladder secondary to MMC are applicable using this animal model.

Analysis of the Unsymmetrical Operation of the DC/DC MMC Considering the DC-Link Impedance

This paper analyzes the unsymmetrical operation of the dc/dc MMC caused by parametric uncertainty. The unsymmetrical operation is referred to as the condition in which parameters involved in ac power generation are not equal in the phase-legs of the converter. Because existing models in the literature cannot exhibit the unsymmetrical operation of the dc/dc MMC, new detailed and simplified steady-state models are developed in this paper. In the developed models, the connection between the operation of different phase-legs shows itself when the dc-link impedance is considered. Using the developed models, the parameters that can force the converter to operate in unsymmetrical conditions are identified, and the maximum variation that the converter can tolerate is found. It is shown that even a small parameter variation leads to the leakage of the ac circulating current into the dc-link, which is not acceptable. By conducting various case studies, the impacts of the dc-link length, the transmitted power, and the conversion ratio on the unsymmetrical operation of the dc/dc MMC are characterized. The results showed that the converter would be more sensitive to the parameter variation as these parameters increase. Comparative analysis and simulation results confirm the validity and effectiveness of the presented models and analysis method.

Intra-amniotic Injection of Poly(lactic-co-glycolic Acid) Microparticles Loaded with Growth Factor: Effect on Tissue Coverage and Cellular Apoptosis in the Rat Model of Myelomeningocele.

Myelomeningocele (MMC) is a devastating congenital neurologic disorder that can lead to lifelong morbidity and has limited treatment options. This study investigates the use of poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) loaded with fibroblast growth factor (FGF) as a platform for in utero treatment of MMC. Intra-amniotic injections of PLGA MPs were performed on gestational day 17 (E17) in all-trans retinoic acid-induced MMC rat dams. MPs loaded with fluorescent dye (DiO) were evaluated 3 hours after injection to determine incidence of binding to the MMC defect. Fetuses were then treated with PBS or PLGA particles loaded with DiO, bovine serum albumin, or FGF and evaluated at term (E21). Fetuses with MMC defects were evaluated for gross and histologic evidence of soft tissue coverage. The effect of PLGA-FGF treatment on spinal cord cell death was evaluated using an in situ cell death kit. PLGA-DiO MPs had a binding incidence of 86% and 94% 3 hours after injection at E17 for doses of 0.1 mg and 1.2 mg, respectively. Incidence of soft tissue coverage at term was 19% (4 of 21), 22% (2 of 9), and 83% (5 of 6) for PLGA-DiO, PLGA-BSA, and PLGA-FGF, respectively. At E21, the percentage of spinal cord cells positive for in situ cell death was significantly higher in MMC controls compared with wild-type controls or MMC pups treated with PLGA-FGF. PLGA MPs are an innovative minimally invasive platform for induction of soft tissue coverage in the rat model of MMC and may reduce cellular apoptosis.

Pattern of distant metastases and predictive nomograms in colorectal mucinous adenocarcinoma: a SEER analysis.

We evaluated the metastatic patterns and explored the prognostic value of distant metastasis pattern in patients with metastatic colorectal mucinous adenocarcinoma (MC) using the Surveillance, Epidemiology, and End Results (SEER) database. Between 2010 and 2015, newly diagnosed colorectal MC patients were selected using the SEER database. Patient prognosis was compared based on the clinicopathological parameters, treatment method, and the site and number of metastatic organs. Cox analyses were used to identify factors associated with overall survival (OS). A nomogram was built to predict the patient's survival. Harrell's concordance index (c-index) and calibration curves were used to analyze the discriminative ability of the prognostic factors. Of 3,088 patients diagnosed with colorectal MC, the liver was the only metastatic organ in 78.4% (997/1,271) of all liver metastasis cases, the lung was the only metastatic organ in 41.0% (164/400) of all lung metastasis cases, bone was the only metastatic organ in 26.6% (29/109) of all bone metastasis cases, and the brain was the only metastatic organ in 23.5% (4/17) of all brain metastasis cases. Compared with the untreated cases, those treated with chemotherapy, surgery, and radiotherapy had better OS (P<0.001). There were marked OS differences (P<0.001) between patients with and without liver and bone metastases. Patients with bone metastasis had the best survival, while those with brain metastasis had the worst survival (P<0.001). Patients with one metastatic site had better prognosis compared to those with two or three (P<0.001). Patients with liver metastasis had the best survival, while those with bone and brain metastasis had the worst survival (P<0.001). Multivariate analysis showed that age <65 years, non-black race, grade I, N0 stage, chemotherapy, radiation, surgery, liver metastasis, and bone metastasis were independent prognostic factors. A nomogram was constructed to predict survival probability. The c-index value was up to 0.745. The calibration plot showed that the nomogram was clinically useful. Metastatic MC (mMC) patients had a characteristic distant metastasis pattern. This study constructed a new and sufficiently accurate prognostic model of mMC based on population-based data. These findings can be utilized to predict prognosis and guide mMC patient management.

Fetal and Perinatal Expression Profiles of Proinflammatory Cytokines in the Neuroplacodes of Rats with Myelomeningoceles: A Contribution to the Understanding of Secondary Spinal Cord Injury in Open Spinal Dysraphism.

The cellular and molecular mechanisms that presumably underlie the progressive functional decline of the myelomeningocele (MMC) placode are not well understood. We previously identified key players in post-traumatic spinal cord injury cascades in human MMC tissues obtained during postnatal repair. In this study, we conducted experiments to further investigate these mediators in the prenatal time course under standardized conditions in a retinoic acid-induced MMC rat model. A retinoic acid MMC model was established using time-dated Sprague-Dawley rats, which were gavage-fed with all-trans retinoic acid (RA; 60 mg/kg) dissolved in olive oil at E10. Control animals received olive oil only. Fetuses from both groups were obtained at E16, E18, and E22. The spinal cords (SCs) of both groups were formalin-fixed or snap-frozen. Tissues were screened by real-time reverse transcription polymerase chain reaction for the expression of cytokines and chemokines known to play a role in the lesion cascades of the central nervous system after trauma. MMC placodes exhibited inflammatory cells and glial activation in the later gestational stages. At the messenger RNA (mRNA) level, interleukin-1 beta, tumor necrosis factor alpha, and tumor necrosis factor receptor type 1 exhibited significant induction at E22. interleukin-1 beta receptor type 1 mRNA was induced significantly at E16 and E22. Double labeling experiments confirmed the co-staining of these cytokines and their receptors with ionized calcium-binding adapter molecule 1 (i.e., inflammatory cells), vimentin, and nestin in different anatomical SC areas and neuronal nuclear protein in ventral horn neurons. C-X-C motif chemokine 12 mRNA was elevated in control and MMC animals at E16 compared with E18 and E22. C-X3-C motif ligand 1 mRNA was lower in MMC tissues than in control tissues on E16. The presented findings contribute to the concept that pathophysiological mechanisms, such as cytokine induction in the neuroplacode, in addition to the "first hit," promote secondary spinal cord injury with functional loss in the late fetal time course. Further, these mediators should be taken into consideration in the development of new therapeutic approaches for open spinal dysraphism.

Preliminary Results of a Reverse Thermal Gel Patch for Fetal Ovine Myelomeningocele Repair

BackgroundPrenatal surgical closure of Myelomeningocele (MMC) is considered part of the current age armamentarium. Clinical data has demonstrated the need for innovative patches to maximize the benefits and decrease the risks of this approach. Our team has developed a minimally invasive reverse thermal gel (RTG) patch with cellular scaffolding properties. Here, we demonstrate the initial gross and microscopic histological effects of this RTG patch in the fetal ovine model of MMC. Materials and MethodsA fetal ovine MMC defect was created at 68-75 days gestation, RTG patch application or untreated at 100-103 days, and harvest at 135-140 days. The RTG was applied to the defect and secured in place with an overlay sealant. Defect areas underwent gross and microscopic analysis for inflammation and skin development. Brains were analyzed for hindbrain herniation and hydrocephalus. ResultsThe untreated fetus (n = 1) demonstrated an open defect lacking tissue coverage, evidence of spinal cord injury, increased caspase-3, Iba1 and GFAP in spinal cord tissues, and hindbrain herniation and ventricular dilation. RTG treated fetuses (n = 3) demonstrated defect healing with well-organized dermal and epidermal layers throughout the entire healed tissue area overlaying the defect with minimal inflammation, reduced caspase-3, Iba1 and GFAP in spinal cord tissues, and no hindbrain herniation or ventricular dilation. ConclusionAn RTG patch applied to MMC defects in fetal sheep promoted skin coverage over the defect, was associated with minimal inflammation of the spinal cord tissues and prevented brain abnormalities. The present findings provide exciting results for future comprehensive radiological, functional, and mechanistic evaluation of the RTG.

Computer Simulation Research of MMC Control in DC Power Network Using RTDS

With the development of DC power network, MMC has become an important AC/DC converter. MMC adopts the basic double closed-loop control composed of inner loop current control and outer loop power control. The modulation strategy adopts the nearest level approximation modulation and the capacitor voltage sequence method to ensure the capacitor voltage equalization of the sub-modules. The circulation suppression strategy can suppress the internal circulation of MMC. Finally, the simulation model of MMC was built based on RTDS, and the double closed-loop control strategy and circulation suppression strategy of MMC were verified.

Diffusion weighted imaging as a biomarker of retinoic acid induced myelomeningocele

Neural tube defects are a common congenital anomaly involving incomplete closure of the spinal cord. Myelomeningocele (MMC) is a severe form in which there is complete exposure of neural tissue with a lack of skin, soft tissue, or bony covering to protect the spinal cord. The all-trans retinoic acid (ATRA) induced rat model of (MMC) is a reproducible, cost-effective means of studying this disease; however, there are limited modalities to objectively quantify disease severity, or potential benefits from experimental therapies. We sought to determine the feasibility of detecting differences between MMC and wild type (WT) rat fetuses using diffusion magnetic resonance imaging techniques (MRI). Rat dams were gavage-fed ATRA to produce MMC defects in fetuses, which were surgically delivered prior to term. Average diffusion coefficient (ADC) and fractional anisotropy (FA) maps were obtained for each fetus. Brain volumes and two anatomically defined brain length measurements (D1 and D2) were significantly decreased in MMC compared to WT. Mean ADC signal was significantly increased in MMC compared to WT, but no difference was found for FA signal. In summary, ADC and brain measurements were significantly different between WT and MMC rat fetuses. ADC could be a useful complementary imaging biomarker to current histopathologic analysis of MMC models, and potentially expedite therapeutic research for this disease.

Efficacy of clinical-grade human placental mesenchymal stromal cells in fetal ovine myelomeningocele repair

BackgroundWhile fetal repair of myelomeningocele (MMC) revolutionized management, many children are still unable to walk independently. Preclinical studies demonstrated that research-grade placental mesenchymal stromal cells (PMSCs) prevent paralysis in fetal ovine MMC, however this had not been replicated with clinical-grade cells that could be used in an upcoming human clinical trial. We tested clinical-grade PMSCs seeded on an extracellular matrix (PMSC-ECM) in the gold standard fetal ovine model of MMC. MethodsThirty-five ovine fetuses underwent MMC defect creation at a median of 76 days gestational age, and defect repair at 101 days gestational age with application of clinical-grade PMSC-ECM (3 × 105 cells/cm2, n = 12 fetuses), research-grade PMSC-ECM (3 × 105 cells/cm2, three cell lines with n = 6 (Group 1), n = 6 (Group 2), and n = 3 (Group 3) fetuses, respectively) or ECM without PMSCs (n = 8 fetuses). Three normal lambs underwent no surgical interventions. The primary outcome was motor function measured by the Sheep Locomotor Rating scale (SLR, range 0: complete paralysis to 15: normal ambulation) at 24 h of life. Correlation of lumbar spine large neuron density with SLR was evaluated. ResultsClinical-grade PMSC-ECM lambs had significantly better motor function than ECM-only lambs (SLR 14.5 vs. 6.5, p = 0.04) and were similar to normal lambs (14.5 vs. 15, p = 0.2) and research-grade PMSC-ECM lambs (Group 1: 14.5 vs. 15, p = 0.63; Group 2: 14.5 vs. 14.5, p = 0.86; Group 3: 14.5 vs. 15, p = 0.50). Lumbar spine large neuron density was strongly correlated with motor function (r = 0.753, p<0.001). ConclusionsClinical-grade placental mesenchymal stromal cells seeded on an extracellular matrix rescued ambulation in a fetal ovine myelomeningocele model. Lumbar spine large neuron density correlated with motor function, suggesting a neuroprotective effect of the PMSC-ECM in prevention of paralysis. A first-in-human clinical trial of PMSCs in human fetal myelomeningocele repair is underway.

Engineering alginate microparticles for optimized accumulation in fetal rat myelomeningocele

IntroductionIntraamniotic microparticle injection is a novel technique for the treatment of myelomeningocele (MMC) in which microparticles are delivered in-utero in a minimally invasive fashion to bind to and protect the exposed spinal cord. This technique could offer earlier intervention and greater access to prenatal treatment of MMC. Here we demonstrate progress on the engineering of the microparticles to promote binding to the MMC defect. We hypothesized that when the particle's surface charge was decreased and delivery concentration increased, particles would bind to the MMC defect more frequently and more specifically. MethodsAlginate microparticles underwent surface modification to alter the particle charge. Dye-loaded alginate, alginate- dextran sulfate, and alginate- chitosan were injected on e17 into the amnion of a rat model of MMC and the incidence of successful binding and specificity of particle binding to the MMC defect were calculated. Specificity of binding was described using a defect-to-skin brightness ratio based on specimen imaging. Comparisons were made with chi-square, p< 0.05 marked significance. ResultsThere was no difference in the incidence of successful binding at e17 with 0.6 mg/fetal kg between the three tested alginate particles. However, alginate- dextran sulfate bound most specifically to the defect (p< 0.05). Alginate-dextran sulfate also demonstrated more frequent binding at higher doses than lower doses (79% at 1.2 mg/kg vs 38% at 0.6 mg/kg and 24% at 0.8 mg/kg, p< 0.01 for both). Specificity was not sacrificed at higher dose injections: defect-to-skin brightness ratio of 5.4 at 1.2 mg/kg vs 1.8 at 0.6 mg/kg (p< 0.05) ConclusionWe demonstrate that the intraamniotic injection of alginate-dextran sulfate microparticles at high concentration bind more frequently and more specifically to MMC defects than the previously tested unmodified alginate microparticles.

Analysis and Suppression Control of High Frequency Resonance for MMC-HVDC System

The high-frequency resonances (HFRs) around 700 Hz and 1.8 kHz have occurred in Yu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">′</sup> E project. Mechanism studies indicate that HFRs are caused by the interactions between the negative damping inductance characteristics of the MMC and the capacitive characteristics of the AC system. In this paper, two optimized methods regarding the current control loop are presented to suppress the HFRs. The first one is to use a round(x) function inserted into voltage feed-forward loop instead of low pass filter (LPF). The proposed method has less negative impact on transient characteristics of an MMC. The second one is to employ a second-order damping controller, including the parameters design, to reshape the MMC impedance around the multiple risky regions. The core of HFRs suppression is that the real part of the MMC impedance near the multiple intersection frequencies should be positive according to impedance stability theory. Combined with the proposed control methods and core of HFRs suppression, the simplified model of MMC is adopted to design the parameters using the analytical expressions. Moreover, the general steps of parameters design are presented. Finally, the optimized methods to suppress HFRs are verified by time-domain simulations.

Surviving Lambs with Myelomeningocele Repaired in utero with Placental Mesenchymal Stromal Cells for 6 Months: A Pilot Study

Background: Fetal repair of myelomeningocele (MMC) with placental mesenchymal stromal cells (PMSCs) rescues ambulation in the ovine model up to 48 h postnatally. Outcomes past 48 h are unknown as MMC lambs have not been survived past this timepoint. Objective: We aimed to survive lambs for 6 months following the fetal repair of MMC with PMSCs. Methods: Fetal MMC lambs were repaired with PMSCs. Lambs received either no additional treatment or postnatal bracing and physical therapy (B/PT). Motor function was assessed with the sheep locomotor rating (SLR). Lambs with an SLR of 15 at birth were survived for 6 months or until a decline in SLR less than 15, whichever came first. All lambs underwent a perimortem MRI. Results: The lambs with no postnatal treatment (n = 2) had SLR declines to 7 and 13 at 29 and 65 days, respectively, and were euthanized. These lambs had a spinal angulation of 57° and 47°, respectively. The B/PT lamb (n = 1) survived for 6 months with a sustained SLR of 15 and a lumbar angulation of 42°. Conclusion: Postnatal physical therapy and bracing counteracted the inherent morbidity of the absent paraspinal muscles in the ovine MMC model allowing for survival and maintenance of rescued motor function of the prenatally treated lamb up to 6 months.