Frontally polymerizable shape memory polymer for 3D printing of free-standing structures

Four-dimensional (4D) printing is used to describe three-dimensional (3D)-printed objects with properties that change over time. Shape memory polymers (SMPs) are representative materials for 4D printing technologies. The ability to print geometrically complex, free-standing forms with SMPs is crucial for successful 4D printing. In this study, an SMP capable of frontal polymerization featuring exothermic self-propagation was synthesized by adding cyclooctene to a poly(dicyclopentadiene) network, resulting in switching segments. The rheological properties of this SMP were controlled by adjusting incubation time. A nozzle system was designed such that the SMP could be printed with simultaneous polymerization to yield a free-standing structure. The printing speed was set to 3 cm/min according to the frontal polymerization speed. A free-standing, hexagonal spiral was successfully printed and printed spiral structure showed excellent shape memory performance with a fixity ratio of about 98% and a recovery ratio of 100%, thereby demonstrating the 3D printability and shape memory performance of frontally polymerizable SMPs.

Real-Time Shape Estimation for Concentric Tube Continuum Robots with a Single Force/Torque Sensor

Shape-sensing in real-time is a key requirement for the development of advanced algorithms for concentric tube continuum robots when safe interaction with the environment is important e.g., for path planning, advanced control, and human-machine interaction. We propose a real-time shape-estimation algorithm for concentric tube continuum robots based on the force-torque information measured at the tubes’ basis. It extends a shape estimation algorithm for elastic rods based on discrete Kirchhoff rod theory. For simplicity and efficiency of calculation, we combine it with a model under piece-wise constant curvature assumption, in which we model a concentric tube continuum robot as a combination of segments of planar constant curvatures lying on different equilibrium planes. We evaluate our approach for a single and two combined additively manufactured tubes and achieve an estimation frequency of 333 Hz for two combined tubes with a mean deviation along the backbone of the tubes of 1.91–5.22 mm.

Digital Humanism: Epistemological, Ontological and Praxiological Foundations

It is said that the distinction between the human and the artificial gets more and more blurred. Some are in favour of that development, some in fear of it. Some say humanism is outdated, some say digitalisation is necessarily undesirable. The paper analyses those positions from the perspectives of epistemology, ontology and praxeology and give a fresh answer to the seemingly irreconcilable points of view. A new conception of Digital Humanism can conserve what are true values in humanism and, at the same time, shape digitalisation such that those values are cultivated.

Micro and Nano Plastics Distribution in Fish as Model Organisms: Histopathology, Blood Response and Bioaccumulation in Different Organs

Micro- and nano-plastic (MP/NP) pollution represents a threat not only to marine organisms and ecosystems, but also a danger for humans. The effects of these small particles resulting from the fragmentation of waste of various types have been well documented in mammals, although the consequences of acute and chronic exposure are not fully known yet. In this review, we summarize the recent results related to effects of MPs/NPs in different species of fish, both saltwater and freshwater, including zebrafish, used as model organisms for the evaluation of human health risk posed by MNPs. The expectation is that discoveries made in the model will provide insight regarding the risks of plastic particle toxicity to human health, with a focus on the effect of long-term exposure at different levels of biological complexity in various tissues and organs, including the brain. The current scientific evidence shows that plastic particle toxicity depends not only on factors such as particle size, concentration, exposure time, shape, and polymer type, but also on co-factors, which make the issue extremely complex. We describe and discuss the possible entry pathways of these particles into the fish body, as well as their uptake mechanisms and bioaccumulation in different organs and the role of blood response (hematochemical and hematological parameters) as biomarkers of micro- and nano-plastic water pollution.

All Cops are Trusted? How Context and Time Shape Immigrants' Trust in the Police in Europe

The relationships between police and minorities have received increasing interest in many Western societies in recent years. We examine first-generation immigrants’ trust in the police in Europe from a comparative and longitudinal perspective. On the contextual level, we test the impact of police size on trust and, on the individual level, we analyze the role of assimilation processes and discrimination experiences. We draw upon data of roughly 21,500 immigrants observed in 24 countries over 13 years contained in the European Social Survey. Results show that immigrants in countries with more police trust the police less, which is partly, but not fully, explained by cross-national differences in crime, rule of law, and GDP. However, there is no longitudinal effect of police size within countries, mostly because the national police size hardly changes over time. On the individual level, we show that initially high levels of trust in the police among immigrants tend to erode with length of stay in a country. We argue that two simultaneous processes drive this pattern: A fading reference effect (downward assimilation) and an increasing discrimination effect. We discuss implications for future research and policy development based on this reasoning.

Modified Lorentz transformations and quantum mechanics

We live in the 4-D Euclidean space. The 4th dimension is assigned as the absolute time (ct) axis and energy axis (cPt = E0) based on 4-dimensional Euclidean space. This 4th dimension can be indirectly felt through the observable relative time (ctl) and observable total energy (cPtl = E). The space-time distance is d(x1x2x3x4) = ctl. The modified Lorentz transformations are introduced by the time-matching of the absolute times in the 4-D Euclidean space. The size of x’ (or Dx’) of the moving object is expanded to the size of x = gx’ (or Dx = gDx’). These modified Lorentz transformations are approximated to the Lorentz transformations as t à tl when v/c << 1 and to the Galilean transformations as v/c is close to zero. The relative time (tl) and energy (E) are defined as the 4-dimensional distance and 4-dimensional volume, respectively. The geometrical space-time shape has the (x1,x2,x3,ct) coordinate system with the metric signature of (+ + + +) but not the (x1,x2,x3,ctl) coordinate system with the metric signature of (+ - - -). Therefore, d(x1x2x3x4)2 = (ctl)2 = (ct)2 +x2 = x12 + x22 + x32 + x42 and V(x1x2x3x4) = E = mc2 = D(ct)Dx1Dx2Dx3 from (x1,x2,x3,x4) of the geometrical space-time shape. The warped shape can be described as the wave function of the quantum mechanics. The instant force action, twin paradox and possible space travel are explained by the absolute time and wave function collapse of the modified Lorentz transformations and quantum mechanics.

ELECTROMAGNETIC PROCESSES IN A FLAT RECTANGULAR SYSTEM WITH AN INDUCTOR BETWEEN THIN BIFILAR COILS

The aim of the research is the analysis and evaluation of the electromagnetic processes characteristics in the proposed flat rectangular system consisting of a thin solenoid-inductor located between the branches of the bifilar, thin-walled multi-turn coils. The analysis of electromagnetic processes and the obtained estimates of the excited currents are carried out. It is shown that with a minimum gap between the windings of the solenoid-inductor and the bifilar, the time functions of the exciting current and the current induced in the bifilar windings are the same, and the amplitude of the latter is maximum and equal to half the current amplitude in the inductor. It was found that the proposed system has a practical invariance of the time shape and amplitude of the induced current in a wide range of variable geometric parameters. The minimal effect of the fields of induced currents on the processes in the solenoid-inductor and the minimum losses when removing the induced signal from the bifilar windings are noted. Physically, the first is due to the asymmetry of the excited magnetic field relative to the plane of the solenoid-inductor, the second is due to a significant decrease in spurious inter-turn capacitance due to the thinness of the bifilar windings. The obtained results allow us to give practical recommendations when choosing design solutions for elements of new circuits of equipment for magnetic pulse metal processing. References 14, figures 2.