Replication capability of micro injection moulding process for polymeric parts manufacturing

Micro injection moulding process represents a key technology for realizing micro components and micro devices used in several fields: IT components, biomedical and medical products, automotive industry, telecommunication area and aerospace. The development of new micro parts is highly dependent on manufacturing systems that can reliably and economically produce micro components in large quantities. In this work, the authors investigate the process parameters on the overall quality of a miniaturised dog-bone-shaped specimen in order to determine the process constraints. The factors affecting parts aspects and mass are studied by experimentation designed using DoE methodology and then discussed. Two polymer materials (polyoxymethylene and liquid crystal polymer), particularly suitable for injection moulding applications due to their flowability and stability, are tested and evaluated in relation to the process replication capability. It has been found that the holding pressure and holding time for POM and holding pressure and injection velocity for LCP have the highest influence on achieving high part mass. Differently, melt temperature has the highest influence on minimising the process variability for both tested polymers. A further investigation has been carried out on the relationship between the holding pressure and the part mass and dimensions demonstrating the existence of a linear correlation between specimens mass and dimensions.     

A finite element solution of coupled heat and mass transfer with chemical reaction

A finite element method is presented for solving the coupled non-linear parabolic differential equations describing transient transport of heat and mass in chemically reacting systems. The method appears to be a useful approximation for a wide variety of problems. Typical numerical results are reported for non isothermal catalytic solid—fluid reactions. Applications to other fields such as absorption accompanied by reaction and non-catalytic solid—fluid reaction models are also formulated.     

Windows and interpolation algorithms to improve electricalmeasurement accuracy

An FFT-based measurement technique, which can be easily used to determine accurately the frequency, amplitude, and phase of all the harmonic and interharmonic components of a distorted signal, is examined. Suitable windows and interpolation algorithms are examined in order to reduce undesirable effects due to spectral leakage caused by a sampling process that is not synchronized. Several results concerning the application of different windows on a set of simulated signals are compared to verify the capability of the proposed procedure. The influence of the noise is examined to study the filtering properties of the weighting functions     

Effect of thermal cycling through the martensitic transition on the internal friction and Young’s modulus of a Ni50.8Ti49.2 alloy

The internal friction (IF) and Young’s modulus (E) of a Ni_50.8Ti_49.2 is affected by thermal cycling. With increasing the number n of thermal cycles, the IF peak P_AM (P_MA) occurring at the austenite/martensite transition temperature decreases to disappear almost completely. Meanwhile the associated E(T) minimum at the beginning (n<250) deepens and then becomes progressively shallower and wider (3×10³≤n<18×10³). The strong sensitivity of P_AM (P_MA) to thermal cycling and to impurity (hydrogen) contents suggests that this peak is predominantly associated with stress-assisted collective motions of twin boundaries located inside the martensite platelets embedded within the austenite phase, rather than with the martensitic transition itself. However, as the high temperature tail of P_AM starts at temperatures appreciably higher than the martensite start-temperature M_s, a premartensitic contribution to damping is also present. The widening of the E(T) minimum indicates that, for n≥3×10³, the direct transformation is to some extent hindered by the dislocation network introduced by thermal cycling. A not thermally activated IF peak P_TWM, which is believed to be due to stress-assisted motions of (001) compound twin boundaries in the homogeneous martensite state, grows with increasing n.     

Martensitic transitions and mechanical spectroscopy of Ni50.8Ti49.2 alloy containing hydrogen

Hydrogen additions [n_H=H/(Ni+Ti)=0.003; 0.008; 0.013; 0.021; 0.029; 0.045 at.] to a Ni_50.8Ti_49.2 alloy produce several effects in the elastic and anelastic properties of the material. At temperatures between 100 and 150 K hydrogen atoms act as fixed pinning points for dislocations, as they cancel a newly observed dislocation relaxation. At low H contents (0<n_H≤0.008) the internal friction peak P_AM (P_RM) associated with austenite/martensite (A→M) or R-phase/martensite (R→M) transitions dramatically increases with increasing the H content, while the dip occurring in the Young's modulus (E) vs temperature curves becomes gradually wider and shallower. The enhancement of peak P_AM (P_RM) can be accounted for in terms of a mechanism involving the excitation of collective vibration modes (dyadons) of twin boundaries interacting with H or the stress-induced motion of parent/product interfaces. The widening of the dip in the Young's modulus is due to the introduction by H of a two-step transition (A→R→M). With increasing the H content n_H from 0.008 to 0.045 the height of peak P_AM (P_RM) decreases and a higher temperature peak (P_H) appears and progressively grows becoming the only internal friction feature for n_H=0.045. With increasing H content the thermal hysteresis in the E(T) curves occurring over the coexistence region of the A and M (R and M) phases decreases due to the inhibition caused by H of the martensitic transition. Peak P_H is most likely associated with stress-induced motion of H in solid solution within the R-phase or within a hydride.     

Conformational Ensembles Explored Dynamically from Disordered Peptides Targeting Chemokine Receptor CXCR4

This work reports on the design and the synthesis of two short linear peptides both containing a few amino acids with disorder propensity and an allylic ester group at the C-terminal end. Their structural properties were firstly analyzed by means of experimental techniques in solution such as CD and NMR methods that highlighted peptide flexibility. These results were further confirmed by MD simulations that demonstrated the ability of the peptides to assume conformational ensembles. They revealed a network of transient and dynamic H-bonds and interactions with water molecules. Binding assays with a well-known drug-target, i.e., the CXCR4 receptor, were also carried out in an attempt to verify their biological function and the possibility to use the assays to develop new specific targets for CXCR4. Moreover, our data indicate that these peptides represent useful tools for molecular recognition processes in which a flexible conformation is required in order to obtain an interaction with a specific target.     

Drawing Colored Graphs with Constrained Vertex Positions and Few Bends per Edge

Hamiltonicity, book embeddability, and point-set embeddability of planar graphs are strictly related concepts. We exploit the interplay between these notions to describe colored sets of points and to design polynomial-time algorithms to embed k-colored planar graphs on these sets such that the resulting drawings have O(k)\mathcal{O}(k) bends per edge.