197 research outputs found
Improved Damping Control of Grid-forming Inverter Using DC Dynamics
The DC side of the grid-forming inverter is usually simplified as an ideal source when considering the AC dynamics. However, the DC dynamics actually contain useful information of the AC side. This paper proposes an improved damping control for the grid-forming inverter using the DC dynamics. The error of the DC voltage is introduced into the active power loop through a proportional controller. As a result, an extra freedom in addition to the virtual inertia can be adjusted. A small-signal analysis is carried out in detail to study the impact of the DC dynamics. Compared with other damping methods, the proposed method can simultaneously improve the performance of not only the AC side but also the DC side without increasing the order of the system The simulation results verify the effectiveness of the proposed method.</p
On the analysis of the dc dynamics of multi-terminal VSC-HVDC systems using small signal modeling
In this paper, an analysis of the dc dynamics of multiterminal VSC-HVDC systems using the small signal modeling method is presented. Usually, the VSC controllers are designed under the consideration that they operate independently of each other. However, the possible interactions among them and the dc grid should be studied, especially in multi-terminal topologies. In this paper, three VSC-HVDC systems are modeled and, after linearization, the eigenvalues of the system are calculated for different loading conditions. The results from this analysis are compared to those obtained from more detailed models using PSCAD. It is shown that the operating point, the gains of the direct-voltage controller and the cable dynamics have an impact on the system performance
Altered Glycosylation Contributes to Placental Dysfunction Upon Early Disruption of the NK Cell-DC Dynamics
Immune cells [e. g., dendritic cells (DC) and natural killer (NK) cells] are critical players during the pre-placentation stage for successful mammalian pregnancy. Proper placental and fetal development relies on balanced DC-NK cell interactions regulating immune cell homing, maternal vascular expansion, and trophoblast functions. Previously, we showed thatin vivodisruption of the uterine NK cell-DC balance interferes with the decidualization process, with subsequent impact on placental and fetal development leading to fetal growth restriction. Glycans are essential determinants of reproductive health and the glycocode expressed in a particular compartment (e.g., placenta) is highly dependent on the cell type and its developmental and pathological state. Here, we aimed to investigate the maternal and placental glycovariation during the pre- and post-placentation period associated with disruption of the NK cell-DC dynamics during early pregnancy. We observed that depletion of NK cells was associated with significant increases of O- and N-linked glycosylation and sialylation in the decidual vascular zone during the pre-placental period, followed by downregulation of core 1 and poly-LacNAc extended O-glycans and increased expression of branched N-glycans affecting mainly the placental giant cells and spongiotrophoblasts of the junctional zone. On the other hand, expansion of DC induced a milder increase of Tn antigen (truncated form of mucin-type O-glycans) and branched N-glycan expression in the vascular zone, with only modest changes in the glycosylation pattern during the post-placentation period. In both groups, this spatiotemporal variation in the glycosylation pattern of the implantation site was accompanied by corresponding changes in galectin-1 expression. Our results show that pre- and post- placentation implantation sites have a differential glycopattern upon disruption of the NK cell-DC dynamics, suggesting that immune imbalance early in gestation impacts placentation and fetal development by directly influencing the placental glycocode
Cytoskeletal turnover and Myosin contractility drive cell autonomous oscillations in a model of Drosophila Dorsal Closure
Oscillatory behaviour in force-generating systems is a pervasive phenomenon
in cell biology. In this work, we investigate how oscillations in the
actomyosin cytoskeleton drive cell shape changes during the process of Dorsal
Closure, a morphogenetic event in Drosophila embryo development whereby
epidermal continuity is generated through the pulsatile apical area reduction
of cells constituting the amnioserosa (AS) tissue. We present a theoretical
model of AS cell dynamics by which the oscillatory behaviour arises due to a
coupling between active Myosin-driven forces, actin turnover and cell
deformation. Oscillations in our model are cell-autonomous and are modulated by
neighbour coupling, and our model accurately reproduces the oscillatory
dynamics of AS cells and their amplitude and frequency evolution. A key
prediction arising from our model is that the rate of actin turnover and Myosin
contractile force must increase during DC in order to reproduce the decrease in
amplitude and period of cell area oscillations observed in vivo. This
prediction opens up new ways to think about the molecular underpinnings of AS
cell oscillations and their link to net tissue contraction and suggests the
form of future experimental measurements.Comment: 17 pages, 6 figures; added references, modified and corrected Figs. 1
and 3, corrected typos, expanded discussio
Hysteretic dynamics of domain walls at finite temperatures
Theory of domain wall motion in a random medium is extended to the case when
the driving field is below the zero-temperature depinning threshold and the
creep of the domain wall is induced by thermal fluctuations. Subject to an ac
drive, the domain wall starts to move when the driving force exceeds an
effective threshold which is temperature and frequency-dependent. Similarly to
the case of zero-temperature, the hysteresis loop displays three dynamical
phase transitions at increasing ac field amplitude . The phase diagram in
the 3-d space of temperature, driving force amplitude and frequency is
investigated.Comment: 4 pages, 2 figure
Diffusion-controlled annihilation with initially separated reactants: The death of an particle island in the particle sea
We consider the diffusion-controlled annihilation dynamics with
equal species diffusivities in the system where an island of particles is
surrounded by the uniform sea of particles . We show that once the initial
number of particles in the island is large enough, then at any system's
dimensionality the death of the majority of particles occurs in the {\it
universal scaling regime} within which of the particles die at
the island expansion stage and the remaining at the stage of its
subsequent contraction. In the quasistatic approximation the scaling of the
reaction zone has been obtained for the cases of mean-field ()
and fluctuation () dynamics of the front.Comment: 4 RevTex pages, 1 PNG figure and 1 EPS figur
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