Numerical analysis of the beneficial effect of the double symmetric patch repair compared to single one in aircraft structures

This paper concerns a numerical study by the finite element method of the cracked structure repaired by single and double bonded composite patches. The stress intensity factor is used as fracture criteria. The obtained results showed the advantage of the double patch compared to single on the reduction of the stress intensity factor at the crack tip. The effects of the properties of the plate and the patch and the adhesive on the beneficial effect of the double patch are highlighted. The adhesive properties must be optimised in order to increase the advantage of the double patch and to avoid the adhesive failure. The patch properties have a significant effect on the beneficial effects of the double symmetric patch.     

Indirect approaches for estimating the efficiency of the cold metal transfer welding process

In this work, two indirect approaches are compared to estimate the efficiency of the cold metal transfer welding process with two different current waveforms. The first approach is based on an analytical heat transfer model coupled with thermocouple measurements. The second method includes numerical heat transfer simulation of aluminium filler on the galvanised steel sheet. Then a diffusional-growth model allows evaluating the thickness of the Fe–Al intermetallic layer that was compared it to that of the experimental one. Results show that both methods give very similar process efficiencies. The process efficiency reaches a high value (0.92) with current waveforms using high-intensity pulses of short duration, whereas it decreases to 0.78 with current waveforms using low-intensity pulses of long duration.     

Nitroxide-mediated radical polymerization of styrene: Experimental evidence of chain transfer to monomer

Chain transfer to monomer during nitroxide-mediated radical polymerization of styrene has been investigated for 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1) mediated polymerizations at 125 and 110 °C, respectively. A novel technique employing a fluorescence-labelled polystyrene-TEMPO macroinitiator enabled separate detection of the total chain distribution and the distribution of chains containing the original macroinitiator, thus directly confirming the presence of chains not containing macroinitiator. Chain transfer to monomer results in a low molecular weight tail, which can be very much pronounced, in particular in the number distributions. Quantitative analysis of the total number of chains in both the TEMPO and the SG1 systems, correcting for the contribution of thermal initiation of styrene, yielded chain transfer to monomer constants in agreement with the literature.     

A first-principles study of the structural,elastic, electronic,vibrational, and optical properties of BaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The structural, elastic, electronic, vibrational, and optical properties of BaSe_1?xTe_x alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA?+?mBJ schemes of the generalized gradient approximation. Ternary BaSe_1?xTe_x compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA?+?mBJ approach yield accurate results. Ternary BaSe_1?xTe_x alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe_1?xTe_x alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ?₁(0) and the static refractive index n₀ are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe_1?xTe_x should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.     

Magnetic,Optoelectronic, and Thermodynamic Properties of Sr<Subscript>2</Subscript>Cr<Emphasis Type="Italic">X</Emphasis>O<Subscript>6</Subscript> (<Emphasis Type="Italic">X</Emphasis> = La and Y): Half-Metallic and Ferromagnetic Behavior

The effects of spin polarization on the structure, magnetic, and optoelectronic properties of Cr-based series of double perovskites Sr₂CrXO₆ (X = La and Y) have been studied by using the full-potential linearized augmented plane-wave method (FP-LAPW), based on the density functional theory (DFT) as implemented in the Wien2k code, within the generalized gradient approximation (GGA), GGA + U, and GGA plus Trans-Blaha-modified Becke–Johnson (TB-mBJ) as the exchange correlation. Our results show a similar half-metallic ferromagnetic ground state for both materials. From the electronic properties, it is found that Sr₂CrYO₆ has a direct band gap at (Γ-Γ) direction and Sr₂CrLaO₆ has an indirect band gap at (Γ-W) direction. Furthermore, we have computed the optic and thermodynamic properties which are investigated for the first time. Consequently, the magnetic, optoelectronic, and thermodynamic properties show these compounds are promising for high technological applications, namely spintronic materials.     

Nano-confinement of biomolecules: Hydrophilic confinement promotes structural order and enhances mobility of water molecules

Molecular dynamics simulations have been used to investigate the confinement packing characteristics of small hydrophilic (N-acetyl-glycine-methylamide, Nagma) and hydrophobic (N-acetyl-leucine-methylamide, Nalma) biomolecules in large diameter single-wall carbon nanotubes (SWCNTs). We find that hydrophilic biomolecules easily fill the nanotube and self organize into a geometrical configuration which reminds the water structural organization under SWCNT confinement. The packing of hydrophilic biomolecules inside the cylinder confines all water molecules in its core, which enhances their mobility. Conversely, hydrophobic biomolecules accommodate into the nanotubes with a trend for homogeneous filling, which generate unstable small pockets of water and drive toward a state of dehydration. These results shed light on key parameters important for the encapsulation of biomolecules with direct relevance for long-term storage and prevention of degradation.

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Priority-aware optical shared protection: An offline evaluation study

The availability of an optical connection is considered to be a critical service differentiator in WDM optical networks. In this regard, the design of a protection scheme that improves the availability of high priority optical connections and makes efficient use of optical resources is a major challenge faced by optical network operators. In a previous study, we proposed the so-called priority-aware shared protection survivability scheme as a potential solution to this design issue.In this paper, we complement our previous study. More specifically, we develop an offline study whose main purpose is to assess the efficiency of the priority-aware shared protection scheme. Through this study, we show that the priority-aware shared protection strategy as opposed to existing protection strategies is able to achieve the best tradeoff between optical resource usage and optical connections’ availability satisfaction.     

Heuristics for a two-stage assembly flowshop with bicriteria of maximum lateness and makespan

We consider a two-stage assembly flowshop scheduling problem with the objective of minimizing a weighted sum of makespan and maximum lateness. The problem is known to be NP-hard, and therefore, we propose heuristics to solve the problem. The proposed heuristics are Tabu search (Tabu), particle swarm optimization (PSO), and self-adaptive differential evolution (SDE). An extensive computational experiment is conducted to compare performances of the proposed heuristics. The computational experiment reveals that both PSO and SDE are much superior to Tabu. Moreover, it is statistically shown that PSO performs better than SDE. The computation times of both PSO and SDE are close to each other and they are less than 40 and 45 s, respectively, for the largest size problem considered.     

The Biaxial Strain Dependence of Magnetic Order in Spin Frustrated Mn3NiN Thin Films

Multicomponent magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetization for energy efficient memory, data storage, and cooling applications. Strong spin‐lattice coupling extends this functionality further by allowing electric‐field‐control of magnetization via strain coupling with a piezoelectric. Here this work explores the magnetic phase diagram of piezomagnetic Mn₃NiN thin films, with a frustrated noncollinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain, the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρ_xy, at low temperature, that transforms at a well‐defined Néel transition temperature (T_N) into a soft ferrimagnetic‐like (FIM) state at high temperatures. In stark contrast, under tensile strain, the low temperature canted AFM phase transitions to a state where ρ_xy is an order of magnitude smaller and therefore consistent with a low magnetization phase. Neutron scattering confirms that the high temperature FIM‐like phase of compressively strained films is magnetically ordered and the transition at T_N is first‐order. The results open the field toward future exploration of electric‐field‐driven piezospintronic and thin film caloric cooling applications in both Mn₃NiN itself and the broader Mn₃AN family.     

Study of metamaterial surface wave antenna based on split ring resonator

Microsystem Technologies - In this paper, a new metamaterial-inspired high frequency surface wave antenna is designed. An artificial magnetic conductor surface is introduced into the near field...