Control Synthesis for an Underactuated Cable Suspended System Using Dynamic Decoupling

This article studies the dynamics and control of a novel underactuated system, wherein a plate suspended by cables and with a freely moving mass on top, whose other ends are attached to three quadrotors, is sought to be horizontally stabilized at a certain height, with the ball positioned at the center of mass of the plate. The freely moving mass introduces a 2-degree of underactuation into the system. The design proceeds through a decoupling of the quadrotors and the plate dynamics. Through a partial feedback linearization approach, the attitude of the plate and the translational height of the plate is initially controlled, while maintaining a bounded velocity along the $y$ and $x$ directions. These inputs are then synthesized through the quadrotors with a backstepping and timescale separation argument based on Tikhonov's theorem

‘Food Was My Medicine, My Medicine to Recovery And Healing’ - A Phenomenological Study of Posttraumatic Growth through Positive Nutrition

The purpose of this study is to provide an in-depth account of the subjective experiences of adults who felt that positive nutrition played an essential role in their growth following their highly stressful life event(s), with a distinctive focus on exploring the embodied experience of posttraumatic growth within this group. Qualitative semi-structured interviews were conducted amongst seven female participants and analyzed using Interpretative Phenomenological Analysis. Three superordinate themes and nine subordinate themes emerged: (i) discovering the nutritional sanctuary through an embodied healing from foods, enjoying positive emotions and spiritual nourishment (ii) experiencing metamorphosis in the body through physical transformation, embodiment and discovering the ‘new body’, and finally (iii) through an eudaimonic journey manifesting in the form of deepened relationships, heightened personal growth and an acceptance of self. This study is the first of its kind to use positive nutrition to explore growth after trauma. The findings concluded that growth was seen to be processed through the body and posttraumatic growth attained via the embodied route of positive nutrition. Some elements of posttraumatic growth outcomes were found to be more prominent in participants who experienced a body related trauma, in comparison to those who underwent a non-body related trauma and vice versa

Glassy Dielectric Response in Tb_2NiMnO_6 Double Perovskite with Similarities to a Griffiths Phase

Frequency-dependent and temperature-dependent dielectric measurements are performed on double perovskite Tb$_2$NiMnO$_6$. The real ($\epsilon_1$) and imaginary ($\epsilon_2$) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from bulk, grain boundaries and the sample-electrode interfaces respectively. The temperature and frequency variation of $\epsilon_1$ and $\epsilon_2$ are successfully simulated by a $RC$ circuit model. The complex plane of impedance, $Z'$-$Z"$, is simulated using a series network with a resistor $R$ and a constant phase element. Through the analysis of frequency-dependent dielectric constant using modified-Debye model, different relaxation regimes are identified. Temperature dependence of dc conductivity also presents a clear change in slope at, $T^*$. Interestingly, $T^*$ compares with the temperature at which an anomaly occurs in the phonon modes and the Griffiths temperature for this compound. The components $R$ and $C$ corresponding to the bulk and the parameter $\alpha$ from modified-Debye fit tend support to this hypothesis. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is marked.Comment: Accepted in Europhysics Letter

File Fragmentation over an Unreliable Channel

It has been recently discovered that heavy-tailed file completion time can result from protocol interaction even when file sizes are light-tailed. A key to this phenomenon is the RESTART feature where if a file transfer is interrupted before it is completed, the transfer needs to restart from the beginning. In this paper, we show that independent or bounded fragmentation guarantees light-tailed file completion time as long as the file size is light-tailed, i.e., in this case, heavy-tailed file completion time can only originate from heavy-tailed file sizes. If the file size is heavy-tailed, then the file completion time is necessarily heavy-tailed. For this case, we show that when the file size distribution is regularly varying, then under independent or bounded fragmentation, the completion time tail distribution function is asymptotically upper bounded by that of the original file size stretched by a constant factor. We then prove that if the failure distribution has non-decreasing failure rate, the expected completion time is minimized by dividing the file into equal sized fragments; this optimal fragment size is unique but depends on the file size. We also present a simple blind fragmentation policy where the fragment sizes are constant and independent of the file size and prove that it is asymptotically optimal. Finally, we bound the error in expected completion time due to error in modeling of the failure process

Microfluidic systems for in situ formation of nylon 6,6 membranes.

A microfluidics based, localised formation of nylon 6,6 membranes has been undertaken. The study demonstrates the feasibility of maintaining stable aqueous/organic interfaces for xylene within simple linear flow channels. Glass fabricated structures were used with adipoyl chloride and hexamethylenediamine in the organic and aqueous phases, respectively, in order to achieve nylon 6,6 interfacial polymerisation. Localised membrane formation was investigated in flow channels of different geometries over a wide range of flow rates (500–4000 μl/min), with Reynolds numbers ranging from 8.4 to 67.2. The results demonstrate that interfacial polymerisation occurs consistently over a wide range of flow rates and of flow entry angles for dual aqueous/organic solvent input. However, creation of uniform planar film structures required careful optimisation, and these were best achieved at 2000 μl/min with a flow entry angle of 45°. The resulting membranes had thicknesses in the range between 100 and 300 μm. Computational modelling of the aqueous/organic flow was performed in order to characterise flow stability and wall shear-stress patterns. The flow arrangement establishes a principle for the fabrication of micromembrane structures designed for low sample volume separation, where the forming reaction is a facile and rapid interfacial process