Structure of the twin-arginine signal-binding protein DmsD from Escherichia coli

The translocation of folded proteins via the twin-arginine translocation (Tat) pathway is regulated to prevent the futile export of inactive substrate. DmsD is part of a class of cytoplasmic chaperones that play a role in preventing certain redox proteins from premature transport. DmsD from Escherichia coli has been crystallized in space group P4_12_12, with unit-cell parameters a = b = 97.45, c = 210.04 Å, in the presence of a small peptide. The structure has been solved by molecular replacement to a resolution of 2.4 Å and refined to an R factor of 19.4%. There are four molecules in the asymmetric unit that may mimic a higher order structure in vivo. There appears to be density for the peptide in a predicted binding pocket, which lends support to its role as the signal-recognition surface for this class of proteins

Geometry of Locomotion

Many animals and robots move through the world by coupling cyclical changes in shape called gaits to an interaction with the environment. Because mobility is an important aspect of such robots, a key metric when evaluating design and performance of mobile robots is the efficiency of their optimal gaits. The major contribution of this thesis is a set of geometric principles for understanding the geometry of optimal gaits for drag-dominated kinematic systems. We demonstrate these principles on a variety of system geometries (including Purcell's swimmer) and for optimization criteria that include maximizing displacement and efficiency of motion for both translation and turning motions. We also demonstrate how these principles can be used to simultaneously optimize a system's gait kinematics and physical design. We present an analysis of how the shape of these optimal gaits are altered by the presence of passive elements like springs. We use frequency domain analysis to relate the motion of the passive joint to the motion of the actuated joint. We couple this analysis with elements of the geometric framework introduced in our first contribution, to identify speed-maximizing and efficiency-maximizing gaits for drag-dominated swimmers with a passive elastic joint

optical measurement of surface topographies with transparent coatings

Abstract Manufacturers nowadays have access to state-of-the-art areal surface topography measurement instruments that allow investigation of surface topography at unprecedented levels of detail and over a wide range of scales. However, high value-added products have demanding requirements, pushing measurement technologies to their limits. Therefore, a deeper insight and more comprehensive understanding of performance and behaviour of current areal surface topography measurement solutions is often needed. In this work, we investigate and compare the results when measuring the same surface with different, state-of-the-art areal surface topography measurement solutions involving the principal optical technologies, notably focus variation microscopy, coherence scanning interferometry, imaging confocal microscopy and point autofocus instrument, operated using different set-ups. The test case is a highly engineered surface obtained through a sequence of mechanical and chemical surface modification processes. The surface has complex topographic formations at micrometre and sub-micrometre scales, and is characterised by the presence of a thin transparent layer, notoriously challenging for optical measurement. The topographies reconstructed from measurement are compared both in terms of visual appearance and texture parameters

Geometric analysis of gaits and optimal control for three-link kinematic swimmers

Many robotic systems locomote using gaits - periodic changes of internal shape, whose mechanical interaction with the robot's environment generate characteristic net displacements. Prominent examples with two shape variables are the low Reynolds number 3-link "Purcell swimmer" with inputs of 2 joint angles and the "ideal fluid" swimmer. Gait analysis of these systems allows for intelligent decisions to be made about the swimmer's locomotive properties, increasing the potential for robotic autonomy. In this work, we present comparative analysis of gait optimization using two different methods. The first method is variational approach of "Pontryagin's maximum principle" (PMP) from optimal control theory. We apply PMP for several variants of 3-link swimmers, with and without incorporation of bounds on joint angles. The second method is differential-geometric analysis of the gaits based on curvature (total Lie bracket) of the local connection for 3-link swimmers. Using optimized body-motion coordinates, contour plots of the curvature in shape space give visualization that enables identifying distance-optimal gaits as zero level sets. Combining and comparing results of the two methods enables better understanding of changes in existence, shape and topology of distance-optimal gait trajectories, depending on the swimmers' parameters.Comment: accepted to Automatica, 202

A novel hybrid topology for power quality improvement using multilevel inverter for the reduction of vibration and noise in brushless DC motor for industrial applications

The proposed research involves the design and implementation of a novel hybrid Topology for Power Quality Improvement using Multilevel Inverter to reduce vibration and noise in BLDC motor for industrial applications. The utility of power electronics device plays a vital role for various applications in recent days. Similarly, the power consumption is also important for all processing units. The power electronic devices contain a lot of converters for processing the energy. During such cases, the harmonics are produced in different ways. Hence, a system analysis is necessary to find the problem at conventional methods. Hence the problem is identified on the distribution static compensator (DSTATCOM) component module whose harmonics are high, and it is important module for the circuit, hence preventive action to be taken to reduce the harmonics. To limit or reduce the harmonics, it is required to modify the triggering mechanism and control unit of Multi level inverter. Hence, the proposed hybrid method is implemented with the developed H-bridge and diode clamped topology with a brushless dc motor. In addition, the vibrations and the noise level are also reduced due to the reduced total harmonic distortion. The proposed module is simulated on MATLAB Simulink, and an experimental analysis is carried out to verify functionality tools with various operating conditions, the proposed method proves more efficient than the switches and complex networks present in traditional methods

Multi-scale data fusion for surface metrology

The major trends in manufacturing are miniaturization, convergence of the traditional research fields and creation of interdisciplinary research areas. These trends have resulted in the development of multi-scale models and multi-scale surfaces to optimize the performance. Multi-scale surfaces that exhibit specific properties at different scales for a specific purpose require multi-scale measurement and characterization. Researchers and instrument developers have developed instruments that are able to perform measurements at multiple scales but lack the much required multi- scale characterization capability. The primary focus of this research was to explore possible multi-scale data fusion strategies and options for surface metrology domain and to develop enabling software tools in order to obtain effective multi-scale surface characterization, maximizing fidelity while minimizing measurement cost and time. This research effort explored the fusion strategies for surface metrology domain and narrowed the focus on Discrete Wavelet Frame (DWF) based multi-scale decomposition. An optimized multi-scale data fusion strategy ‘FWR method’ was developed and was successfully demonstrated on both high aspect ratio surfaces and non-planar surfaces. It was demonstrated that the datum features can be effectively characterized at a lower resolution using one system (Vision CMM) and the actual features of interest could be characterized at a higher resolution using another system (Coherence Scanning Interferometer) with higher capability while minimizing the measurement time