Solitonic supersymmetry restoration

Q-balls are a possible feature of any model with a conserved, global U(1) symmetry and no massless, charged scalars. It is shown that for a broad class of models of metastable supersymmetry breaking they are extremely influential on the vacuum lifetime and make seemingly viable vacua catastrophically short lived. A net charge asymmetry is not required as there is often a significant range of parameter space where statistical fluctuations alone are sufficient. This effect is examined for two supersymmetry breaking scenarios. It is found that models of minimal gauge mediation (which necessarily have a messenger number U(1)) undergo a rapid, supersymmetry restoring phase transition unless the messenger mass is greater than 10^8 GeV. Similarly the ISS model, in the context of direct mediation, quickly decays unless the perturbative superpotential coupling is greater than the Standard Model gauge couplings.Comment: 17 pages, 3 figures, minor comments added, accepted for publication in JHE

Performance of nitrogen gas as a coolant in machining of titanium

Machining of titanium and its alloys is still the subject of research and researchers' interest despite some improvement in its machinability from several machining methods. This research presents performance of nitrogen gas in machining titanium. Machining of titanium is carried out on conventional turning center with triangular insert and holder according to ISO designation. Compressed nitrogen gas contained a cylindrical tank is supplied to the cutting zone via specially-designed valve that controls pressure and volume of nitrogen. The gas outlet pipe of diameter 2 mm is directed to just-above the tool rake face. During machining, the gas is supplied with high pressure so that the cutting zone receives an effective cooling as well as the chip will easily break. The effectiveness of this new cooling strategy is demonstrated by tool condition after machining, and also by comparing with performance of conventional coolant. The result is found to be excellent in terms of relative amount of tool wear. The cutting insert has surprisingly been almost intact when using nitrogen gas as coolant whereas tool wear at failure state has occurred with conventional coolant for the same machining parameters

Genetic algorithm and simulated annealing to estimate optimal process parameters of the abrasive waterjet machining

In this study, two computational approaches, Genetic Algorithm and Simulated Annealing, are applied to search for a set of optimal process parameters value that leads to the minimum value of machining performance. The objectives of the applied techniques are: (1) to estimate the minimum value of the machining performance compared to the machining performance value of the experimental data and regression modeling, (2) to estimate the optimal process parameters values that has to be within the range of the minimum and maximum coded values for process parameters of experimental design that are used for experimental trial and (3) to evaluate the number of iteration generated by the computational approaches that lead to the minimum value of machining performance. Set of the machining process parameters and machining performance considered in this work deal with the real experimental data of the non-conventional machining operation, abrasive waterjet. The results of this study showed that both of the computational approaches managed to estimate the optimal process parameters, leading to the minimum value of machining performance when compared to the result of real experimental data

Characterization and biological properties of nanostructured clinoenstatite scaffolds for bone tissue engineering applications

With the enhancement of bone-tissue regeneration technologies, there is an increment request for perfect bio-ceramic scaffolds with multifunctional properties, including high mechanical strength as well as biological and controlled drug-release potential. In the present work, extremely porous clinoenstatite (CLEN; MgSiO3) scaffolds with different micropore sizes and great interconnectivity were fabricated for the first time via the space holder method and subsequent sintering. The NaCl particle size escalation as spacer results in an increase of the pore size and interconnectivity and reduction of the compressive strength. According to the results, nanostructured CLEN scaffolds contain pore sizes in the range of ~450–650 µm and porosity more than ~77–81%, which offered greater compressive strength (0.9 MPa) in comparison with the other CLEN scaffolds. Favorable burst release was noticed throughout the first 8 h, and right after the early burst, the dose was progressively reduced until 35 h, and subsequently, a sustained release was noticed. In vitro examinations verified the antimicrobial performance of the metronidazole (MTZ)-embedded CLEN scaffolds towards the Fusobacterium nucleatum (Fn) and Aggregatibacter actinomycetemcomitans (Aa) bacteria. In this context, the antibacterial performance is enhanced with escalating MTZ loading into scaffolds, which is directly linked with the increase of MTZ concentration. The results exhibited that both CLEN and MTZ-embedded CLEN scaffolds presented apatite formation capability in SBF. The biological test showed that the MG63 cell adhesion and proliferation on the CLEN scaffold were comparable with their counterpart loaded with low MTZ concentration. Also, the scaffold's ALP activity with low MTZ concentration was considerably greater than that of the scaffold with high MTZ concentration. The results presented here demonstrate that the fabricated CLEN scaffold with 1–3 wt% MTZ concentration has a great potential to be utilized as a bone repair material for tissue engineering applications