37 research outputs found
Identification and characterization of PlAlix, the Alix homologue from the Mediterranean sea urchin Paracentrotus lividus.
The sea urchin provides a relatively simple and tractable system for analyzing the early stages of embryo development. Here, we use the sea urchin species, Paracentrotus lividus, to investigate the role of Alix in key stages of embryogenesis, namely the egg fertilization and the first cleavage division. Alix is a multifunctional protein involved in different cellular processes including endocytic membrane trafficking, filamentous (F)-actin remodeling, and cytokinesis. Alix homologues have been identified in different metazoans; in these organisms, Alix is involved in oogenesis and in determination/differentiation events during embryo development. Herein, we describe the identification of the sea urchin homologue of Alix, PlAlix. The deduced amino acid sequence shows that Alix is highly conserved in sea urchins. Accordingly, we detect the PlAlix protein cross-reacting with monoclonal Alix antibodies in extracts from P. lividus, at different developmental stages. Focusing on the role of PlAlix during early embryogenesis we found that PlAlix is a maternal protein that is expressed at increasingly higher levels from fertilization to the 2-cell stage embryo. In sea urchin eggs, PlAlix localizes throughout the cytoplasm with a punctuated pattern and, soon after fertilization, accumulates in larger puncta in the cytosol, and in microvilli-like protrusions. Together our data show that PlAlix is structurally conserved from sea urchin to mammals and may open new lines of inquiry into the role of Alix during the early stages of embryo development
Improving the vibration suppression capabilities of a magneto-rheological damper using hybrid active and semi-active control
This paper presents a new hybrid active & semi-active control method
for vibration suppression in flexible structures. The method uses a combination of a
semi-active device and an active control actuator situated elsewhere in the structure
to suppress vibrations. The key novelty is to use the hybrid controller to enable
the magneto-rheological damper to achieve a performance as close to a fully active
device as possible. This is achieved by ensuring that the active actuator can assist
the magneto-rheological damper in the regions where energy is required. In addition,
the hybrid active & semi-active controller is designed to minimize the switching of the
semi-active controller. The control framework used is the immersion and invariance
control technique in combination with sliding mode control. A two degree-of-freedom
system with lightly damped resonances is used as an example system. Both numerical
and experimental results are generated for this system, and then compared as part
of a validation study. The experimental system uses hardware-in-the-loop to simulate
the effect of both the degrees-of-freedom. The results show that the concept is viable
both numerically and experimentally, and improved vibration suppression results can
be obtained for the magneto-rheological damper that approach the performance of an
active device