Thermal Behaviour of Microgels Composed of Interpenetrating Polymer Networks of Poly(N-isopropylacrylamide) and Poly(Acrylic Acid): A Calorimetric Study

Stimuli-responsive microgels have recently attracted great attention in fundamental research as their soft particles can be deformed and compressed at high packing fractions resulting in singular phase behaviours. Moreover, they are also well suited for a wide variety of applications such as drug delivery, tissue engineering, organ-on-chip devices, microlenses fabrication and cultural heritage. Here, thermoresponsive and pH-sensitive cross-linked microgels, composed of interpenetrating polymer networks of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAAc), are synthesized by a precipitation polymerization method in water and investigated through differential scanning calorimetry in a temperature range across the volume phase transition temperature of PNIPAM microgels. The phase behaviour is studied as a function of heating/cooling rate, concentration, pH and PAAc content. At low concentrations and PAAc contents, the network interpenetration does not affect the transition temperature typical of PNIPAM microgel in agreement with previous studies; on the contrary, we show that it induces a marked decrease at higher concentrations. DSC analysis also reveals an increase of the overall calorimetric enthalpy with increasing concentration and a decrease with increasing PAAc content. These findings are discussed and explained as related to emerging aggregation processes that can be finely controlled by properly changing concentration, PAAc content an pH. A deep analysis of the thermodynamic parameters allows to draw a temperature– concentration state diagram in the investigated concentration range.

On the behavior of nonlinear hydrodynamic coefficients of a submerged cylinder beneath the water surface

This study aims at numerically exploring the behavior of flow fields and nonlinear hydrodynamic coefficients of a horizontal cylinder beneath the free surface flow considering the effects of nonlinear surface waves and various cylinder shapes. The computational model is based on two-dimensional incompressible Navier-Stokes solvers along with the treatment of the free surface flow using the volume of fluid method. The effect of the turbulent flow is also considered by using the shear stress transport turbulence model. The simulation result of a benchmark case study of the submerged cylinder is first validated with available experiment data, where a mesh convergence analysis is also performed. Afterward, the flow fields and hydrodynamic force coefficients around the cylinder surface are analyzed, and the influences of various cylinder shapes and Reynolds numbers on the hydrodynamic coefficients are investigated. A state diagram representing the hydrodynamic behavior including stable and unstable stages is finally proposed; this is an important criterion for the practice design of submerged civil structures under the free surface flow.

Dependence between structure of cast Al-Ni-La alloys and their chemical composition

The peculiarities of cast Al-Ni-La alloys structure formation depending on the content and ratio of the main components are analyzed in the work. It is shown, that so far the studied system has been considered mainly for the creation of amorphous materials. At the same time, Al-Ni and Al-La systems have phase diagrams that allow us to consider double and triple alloys of these systems to create promising creep-resistant alloys for casting. At the same time, the peculiarities of their structure formation in this context were not determined. Samples with different contents of nickel and lanthanum were prepared for research and analyzed how each of the elements, their number and ratio affect the formation of their structural-phase state. It is shown, that low nickel content of about 2 wt. % and lanthanum up to 5 wt. % eutectic is formed like thin almost monolithic intermetallic plates. As the number of components increases and, accordingly, the number of eutectics increases, the dispersion of its components increases. The analysis of the alloy structure dependence due to studied system on their chemical composition showed that, most likely, during the formation of the eutectic, Al11La3 particles, which may have the form of nanosized fibers, are formed first of all. It should be noted that at the eutectic content of lanthanum in the alloys no primary-formed Al11La3 particles were found. This may indicate that nickel shifts the eutectic concentration of lanthanum toward higher values. At the same time, at the hypoeutectic concentration of lanthanum and the hypereutectic concentration of nickel, some Al11La3 formations were outside the regions of the main eutectic with nickel aluminide. Such questions necessitate further studies of the aluminum angle of the triple state diagram of the Al-Ni-La system. Keywords: Al-Ni-La system, creep-resistant cast aluminum alloys, structure, eutectic.

Spontaneous trail formation in populations of auto-chemotactic walkers

We study the formation of trails in populations of self-propelled agents that make oriented deposits of pheromones and also sense such deposits to which they then respond with gradual changes of their direction of motion. Based on extensive off-lattice computer simulations aiming at the scale of insects, e.g., ants, we identify a number of emerging stationary patterns and obtain qualitatively the non-equilibrium state diagram of the model, spanned by the strength of the agent–pheromone interaction and the number density of the population. In particular, we demonstrate the spontaneous formation of persistent, macroscopic trails, and highlight some behaviour that is consistent with a dynamic phase transition. This includes a characterisation of the mass of system-spanning trails as a potential order parameter. We also propose a dynamic model for a few macroscopic observables, including the sub-population size of trail-following agents, which captures the early phase of trail formation.

Pedestrian dynamics at the running of the bulls evidence an inaccessible region in the fundamental diagram

We characterize the dynamics of runners in the famous “Running of the Bulls” Festival by computing the individual and global velocities and densities, as well as the crowd pressure. In contrast with all previously studied pedestrian systems, we unveil a unique regime in which speed increases with density that can be understood in terms of a time-dependent desired velocity of the runners. Also, we discover the existence of an inaccessible region in the speed–density state diagram that is explained by falls of runners. With all these ingredients, we propose a generalization of the pedestrian fundamental diagram for a scenario in which people with different desired speeds coexist.

Structure and electrical resistance of the passivating ZnSe layer on Ge

In this article, we have considered the p-i-n Ge photodetector with ZnSe passivating layer. Passivation layer needs to be protected photodetector from dust, rain drops and other external influences. However, this passivation layer can cause errors in photodetector image. When creating a passivating ZnSe layer on Ge, which is used in p-i-n Ge photodetectors, we found two additional phases GeSe and GeSe2 that do not contradict with their state diagram. The above phases can have an essential effect on performances of the passivating layer. Therefore, to study the electrical resistance of this layer, we prepared model samples of layers containing the GeSe and GeSe2 with the thickness 0.5…1.8 µm and area 1 cm2. To measure the electrical resistance of these layers, we used elastic contacts. The performed measurements have shown that Se layers on Ge have an intermediate resistance between that of ZnSe on Ge and pure Ge, and, therefore, the effect of additional phases practically does not worsen the passivating properties of the ZnSe layer on Ge.

PHASE DIAGRAM OF THE PB-MNSE SYSTEM

Methods of physical and chemical analysis (DTA, MSA, RFA, as well as the definition of microhardness and density) studied the phase equilibrium in the system Pb-MnSe and built its state diagram. It is established that the Pb-MnSe system is a quasi-binary cross-section of the triple system Mn-Pb-Se and is of the eutectic type. The components Pb and MnSe form between the degenerate eutectic composition, which corresponds to 3 mol. % MnSe and melts at 310 ° C. It was found that solid solutions on the basis of MnSe in the system at room temperature reach 3.5 mol. % Pb, and solid solutions on the basis of Pb is practically not installed.

Application of Lean Manufacturing Concepts to Evolving a Policy for Engineering Education

This work analyzes the current situation of engineering education in India, especially technical universities characterized by low-quality infrastructure, inflexible curricula, and poor teaching resources including faculty, usually resulting in low student learning and very low graduate placement rates, and identifies the root causes of these problems, summarizes the methodologies adapted by previous researchers in the lean area, and applies the lean manufacturing philosophy to engineering education. This paper applies a value stream map to analyze the current state of engineering education. This technique identifies eight wastes and is given in form of a current state diagram. A future state diagram is presented that recommends solutions to eliminate these wastes. These recommendations make learning processes responsive to needs and provide long-lasting value to students. Overall, it is beneficial in developing a policy for engineering education.