Emerging Accessibility Patterns in Long Telomeric Overhangs

We present single molecule experimental and computational modeling studies investigating the accessibility and folding landscape of human telomeric overhangs of physiologically relevant lengths. The overhangs contain 4-28 repeats of GGGTTA (G-Tract) sequence and accommodate 1-7 tandem G-quadruplex (GQ) structures. Using FRET-PAINT, we probed the distribution of accessible sites via a short imager strand, which is complementary to a G-Tract and transiently binds to unfolded sites. We report accessibility patterns that periodically change with overhang length and provide insights about the underlying folding frustration. Overhangs that have 4n G-Tracts, (12, 16...), demonstrate maximum frustration, while those with 4n+2 G-Tracts, (14, 18...), have minimal frustration. We also developed a computational model that suggests positive folding cooperativity between neighboring GQs is required for persistence of such patterns. Our experimental and computational studies suggest lower folding stability at the junction between single and double stranded telomeric DNA, which has implications for Shelterin complex formation.

Wave Impact Loads on Vertical Seawalls: Effects of the Geometrical Properties of Recurve Retrofitting

This study investigates the variation of wave impact loads with the geometrical configurations of recurve retrofits mounted on the crest of a vertical seawall. Physical model tests were undertaken in a wave flume at the University of Warwick to investigate the effects of the geometrical properties of recurve on the pressure distribution, overall force, and overturning moment at the seawall, subject to both impulsive and non-impulsive waves. Additionally, the wave impact and quasi-static loads on the recurve portion of the retrofitted seawalls are investigated to understand the role of retrofitting on the structural integrity of the vertical seawall. Detailed analysis of laboratory measurements is conducted to understand the effects of overhang length and height of the recurve wall on the wave loading. It is found that the increase in both recurve height and overhang length lead to the increase of horizontal impact force at an average ratio of 1.15 and 1.1 times larger the reference case of a plain vertical wall for the tested configurations. The results also show that the geometrical shape changes in recurve retrofits, increasing the overturning moment enacted by the wave impact force. A relatively significant increase in wave loading (both impact and quasi-static loads) are observed for the higher recurve retrofits, while changes in the overturning moment are limited for the retrofits with longer overhang length. The data generated from the physical modelling measurements presented in this study will be particularly helpful for a range of relevant stakeholders, including coastal engineers, infrastructure designers, and the local authorities in coastal regions. The results of this study can also enable scientists to design and develop robust decision support tools to evaluate the performance of vertical seawalls with recurve retrofitting.

Fabrication defects and limitations of AlSi10Mg lattice structures manufactured by selective laser melting

Additive manufacturing has enabled the production of lattice structures with tailored mechanical properties. However, process limitations still exist, affecting the quality of the struts, practically limiting sizes and types of printable unit cells. Typically, long, thin, unsupported horizontal struts exhibit large deviations from ideal geometries, due to high surface roughness and internal porosity. AlSi10Mg specimens were designed and fabricated by laser powder bed fusion to investigate the role of strut orientation, size, and overhang length using different sets of process parameters. Visual inspection, three-dimensional scanning, and metallographic inspection of the cross-sections were performed. A quality control methodology based on dimensional and geometric tolerances has been defined in order to quantitatively characterize the quality of the struts. Optimized process parameters were selected and used to fabricate octet-truss specimens which were then characterized by compression testing.

Self-Support Topology Optimization With Horizontal Overhangs for Additive Manufacturing

Most of the existing self-support topology optimization methods restrict the overhang inclination angle to be larger than the self-support threshold value. However, for some additive manufacturing processes, such as fused deposition modeling, horizontal overhangs with zero inclination angle could be successfully printed while the overhang size plays a key role in determining the printability. Therefore, the self-support threshold condition should be re-developed to comprehensively consider the overhang size and inclination angle. At the same time, there raises the challenges of formulating the self-support constraints based on the new threshold condition. To address this difficulty, a novel method is proposed in this work to realize the design with horizontal overhangs. To be specific, the new method employs a skeleton-based structure decomposition approach to divide the structure into components based on the connectivity condition. Then, each component will be evaluated about its self-support status based on its overhang length and inclination angle. Finally, the self-support constraint will be activated only for those components that violate the threshold condition. An excellent feature of the method is that it can be adapted to address the only inclination angle self-support condition, or the comprehensive self-support condition that simultaneously considers the overhang length and inclination angle. Therefore, the new method serves for general applications to different additive manufacturing (AM) processes. Numerical examples will be studied to demonstrate the effectiveness of the proposed method.

Study on Effect of Tool Overhang on Machining Characteristics of Al 7075-T6 in Orthogonal Turning Process

In the present experimental study, the effect of turning tool overhang on the chip morphology and vibrations during orthogonal turning has been investigated. Orthogonal cutting (turning) setup was developed to ensure the cutting process happens in a 2-dimesional plane. Orthogonal cutting was realized by turning a circular tube with geometry of 33.88 mm external diameter and 3.5 mm wall thickness (7075-T6 Alloy). High speed steel (HSS) rod with a square cross-section (1⁄2 x 1⁄2 square inch) was used to fabricate the orthogonal turning tool with a geometry of 15 ̊ back rake angle and 9 ̊ clearance angle. The cutting experiments were conducted for different tool overhang lengths (2cm, 3cm, 4cm, 5cm & 6cm) by keeping constant cutting speed (25 m/min) and feed (0.15mm/rev). The vibrational characteristics were measured using accelerometer and Ni-DAQ card. The morphology and microstructure of the chips collected during cutting were studied under optical microscope using metallographic procedures. It was found that for increasing overhang length of cutting tool the chips serrations was found increasing. The frequency of cutting tool and amplitude of vibration was found increasing with increasing tool overhang length.

Prediction of the Frequency Response Function of a Tool Holder-Tool Assembly Based on Receptance Coupling Method

Regenerative chatter has a fatal influence on machine performance in high-speed milling process. Basically, machine condition without chattering can be selected from the stability lobes diagram, which is estimated from the tool point frequency response function (FRF). However, measurements of the tool point FRF would be a complicated and time-consuming task with less efficiency. Therefore prediction of the tool point FRF is of importance for further calculation of the machining stability. This study employed the receptance coupling analysis method to predict the FRF of a tool holder-tool module, which is normally composed of substructures, tool holder and cutter with different length. In this study, the angular components of FRFs of the substructures required for coupling operation were predicted by finite element analysis, apart from the translational components measured by vibration experiments. Using this method, the effects of the overhang length of the cutter on the dynamic characteristics have been proven and successfully verified by the experimental measurements. The proposed method can be an effective way to accurately predict the dynamic behavior of the spindle tool system with different tool holder-tool modules.