The solder material should have a melting point near the melting point of the aluminium to be joined, which means it is necessary to apply very precise temperature control to achieve good aluminium ...brazing. ...recently there have been only two main ways of brazing aluminium parts: - preheating in an oven with good heating temperature control, and; - heating by an open gas flame. The flux, which is added at the beginning of the process dissolves the oxide on the surfaces and thereby allows the solder to bond to a clean metal surface. Since the melting point of the solder and the material to be brazed are normally close it is necessary to reduce the induction heating power source as soon as the liquid state of the solder is reached.
Controlling the exact Cartesian stiffness values of a robot end-effector (EE) is troublesome because of difficulties associated with estimating the stiffness and controllability of a full Cartesian ...stiffness matrix. However, most practical applications require only quantitative (high/low) stiffness values in the EE motion direction (or perpendicular direction). Full control of the stiffness matrix requiring too many control inputs which is hardly possible in practical applications. To ensure the efficiency of execution for a range of redundant robots, we present an algorithm for shaping a robot’s Cartesian stiffness ellipsoid, a more intuitive and visual stiffness representation, using a nonlinear sequential least square programming optimization. The algorithm is designed to optimize the joint stiffness values and the trajectory of the robot’s joints, using null-space exploration, for a given task. Using eigenvalue decomposition of the stiffness matrix, the algorithm minimizes the orientation difference between the major axis of the current and the desired stiffness ellipsoid and specify a scaling factor between the major and the minor axis. The presented approach allows the user to better understand and control of a robot, regardless of the user’s knowledge of the achievable stiffness range and the interdependencies of the Cartesian stiffness matrix elements.
Amyloid fibrils are highly ordered self-assembled (poly)peptide aggregates with cross-β structural pattern. Ovalbumin was used as a model for exploring the potential of infrared spectroscopy in ...detecting structural transitions and quantitative monitoring of amyloid fibrillation.
Low pH (pH 2) and high temperature (90 °C) over the course of 24 h were conditions applied for amyloid formation. Fibrillation of ovalbumin was monitored by ThT and ANS fluorescence, and SDS PAGE. A significant increase in ThT fluorescence with a plateau reached after 4 h of incubation, without the lag phase, was detected. Structural transitions leading to amyloid fibrillation were analysed using all three Amide regions in ATR-FTIR spectra. Significant changes were detected in Amide I and Amide III region (decrease of α-helix and increase of β-sheet peaks). To establish a fast, precise and simple method for quantitative monitoring of amyloid fibrillation, the Amide I/Amide II ratios of aggregation specific β-sheets (1625 and 1695 cm−1, respectively) with 1540 cm−1 as internal standard were used, resulting in good correlation (R2 = 0.93 and 0.95) with the data observed by monitoring ThT fluorescence. On the other hand, assessing aggregation specific β-sheet contents by self-deconvolution showed lower correlation with ThT fluorescence (R2 = 0.75 and 0.64).
Here we examined structural transitions during ovalbumin fibrillation in a qualitative and quantitative manner by exploiting the full potential of Amide regions simultaneously. Secondary structure distribution was monitored using second derivative spectra in Amide I region. A novel, simple mathematical calculation for quantitative monitoring of fibrils formation was presented employing that the increase in low and high frequency aggregation specific β-sheet in Amide I region compared to the internal standard in Amide II region is suitable for fibril formation monitoring.
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•Mature ovalbumin amyloid fibrils are obtained after only 24 h at pH 2, 90 °C.•In addition to Amide I, Amide III region offers qualitative fibrillation evidence.•Second derivative spectrum is more sensitive in detecting structural transitions.•Amide I/Amide II ratio is a facile method for quantitative fibrillation monitoring.
Tremoctopods are epipelagic argonautoid octopods characterized by their expanded dorsal webs and strong sexual size dimorphism, with dwarfed males. The scarcity of taxonomic features attributed to ...this genus presents a challenge, and there is growing evidence of species misidentification in Tremoctopus genus on a molecular level. In this study, we investigated four female specimens of blanket octopus Tremoctopus violaceus caught by purse seine fishing in the Central Eastern Adriatic Sea in 2019. Individuals had smooth, firm and muscular bodies, dark bluish purple on the dorsal and iridescent silvery on the ventral side, with dorsal mantle lengths of 113, 82, 80 and 78 mm. The constructed phylogenetic trees based on the 16S ribosomal RNA and cytochrome c oxidase subunit I sequences of investigated Adriatic specimens and publicly available sequences showed strong support for the T. violaceus clade, consisting of individuals collected from the Adriatic Sea, Mediterranean Sea and Atlantic Ocean, with the exclusion of Indo-Pacific clade most probably corresponding to T. gracilis. To fully understand the life-history traits of Tremoctopus species, future research should focus on DNA-based methods for correct species identification combined with morphological characters, geographic distribution and ecological information.
This paper presents a universal approach to shaping the mechanical properties of the interaction between a collaborative robot and its environment through an end-effector Cartesian compliance ...shaping. More specifically, the focus is on the class of kinematically redundant robots, for which a novel redundancy reconfiguration scheme for online optimization of the Cartesian compliance of the end-effector is presented. The null-space reconfiguration aims to enable the more efficient and versatile use of collaborative robots, including robots with passive compliant joints. The proposed approach is model-based and gradient-based to enable real-time computation and reconfiguration of the robot for Cartesian compliance while ensuring accurate position tracking. The optimization algorithm combines two coordinate frames: the global (world) coordinate frame commonly used for end-effector trajectory tracking; and the coordinate frame fixed to the end-effector in which optimization is computed. Another attractive feature of the approach is the bound on the magnitude of the interaction force in contact tasks. The results are validated on a torque-controlled 7-DOF KUKA LWR robot emulating joint compliance in a quasi-static experiment (the robot exerts a force on an external object) and a peg-in-hole experiment emulating an assembly task.
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