Singular topologies in the Boulatov model

Through the question of singular topologies in the Boulatov model, we illustrate and summarize some of the recent advances in Group Field Theory.Comment: 4 pages; proceedings of Loops'11 (May 2011, Madrid); v2: minor modifications matching published versio

Editorial for the special issue “progress in group field theory and related quantum gravity formalisms”

This editorial introduces the Special Issue “Progress in Group Field Theory and Related Quantum Gravity Formalisms” which includes a number of research and review articles covering results in the group field theory (GFT) formalism for quantum gravity and in various neighbouring areas of quantum gravity research. We give a brief overview of the basic ideas of the GFT formalism, list some of its connections to other fields, and then summarise all contributions to the Special Issue

Renormalization of an SU(2) Tensorial Group Field Theory in Three Dimensions

We address in this paper the issue of renormalizability for SU(2) Tensorial Group Field Theories (TGFT) with geometric Boulatov-type conditions in three dimensions. We prove that tensorial interactions up to degree 6 are just renormalizable without any anomaly. Our new models define the renormalizable TGFT version of the Boulatov model and provide therefore a new approach to quantum gravity in three dimensions. Among the many new technical results established in this paper are a general classification of just renormalizable models with gauge invariance condition, and in particular concerning properties of melonic graphs, the second order expansion of melonic two point subgraphs needed for wave-function renormalization

Investigating Complex Geometrical Features in LPBF-Produced Parts: A Material-Based Comparison Between Different Titanium Alloys

The Ti–6Al–4V (Ti64) alloy is a well-established material to be processed via laser powder bed fusion (LPBF). Recently, other α + β titanium alloys are receiving attention, such as Ti–6Al–2Sn–4Zr–6Mo (Ti6246). Their typical industrial fields of application (aerospace, automotive), often require critical design choices, such as low wall thicknesses and hollow channels. Thus, a comparative analysis between these two competitor alloys in terms of processability was conducted in this work. To do so, specific sample designs were developed. The specimens were analyzed in terms of geometrical compliance with the initial design, porosity, and microstructure. A correlation between the width of the specimens and their porosity, micro- structure and hardness was found. Overall, both the alloys proved to be well processable, even for very low wall thickness (300 μm) and channel diameter (1 mm) values. Nevertheless, the Ti6246 alloy seemed to behave better in specific scenarios. For instance, some Ti64 specimens provided delamination. The hollow channels proved to be challenging for both materi- als, mainly due to the high amount of residual powder particles adhered to the upper part of the holes. This works aims at giving a materials perspective on process-related issues, considering the LPBF-induced defectology and microstructural variations in these Ti alloys

Electrochemical study of the diffusion of cupric ion in aqueous and aqueous-glycerol solutions containing sulphuric acid

The diffusion coefficient of cupric ion in sulphuric acid solutions containing glycerol from 0 to 10 M has been determined with the aid of the rotating disk electrode. The viscosity of the solutions has also been measured. Experiments covered a temperature range from 18 to 40°C. The experimental results are in agreement with the predictions of the Einstein-Stokes theory for diffusivity and viscosity. The ratio Dη/T is (2·23 ± 0·31) × 10−10 cm2 poise/s°K and it is reasonably constant within the whole range of viscosity and temperature investigated.Le coefficient de diffusion de l'ion cuivre(II) dans des solutions d'acide sulfurique contenant du glycérol d'une concentration de 0 à 10 M a été déterminé au moyen d'une electrode à disque tournante. La viscosité des solutions a également été mesurée. Les expériences furent effectuées à une témperature entre 18 et 40°C. Les résultats se rapprochent d'une façon satisfaisante des prédictions de la théorie d'Einstein-Stokes pour la diffusivité et la viscosité. Le rapport Dη/T est (2,23 ± 0,37) × 10−10 cm2poise/sec°K et reste assez constant dans tout le champ de la viscosité et de la témperature étudiés.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Electrochemical study of the diffusion of cupric ion in aqueous and aqueous-glycerol solutions containing sulphuric acid

The diffusion coefficient of cupric ion in sulphuric acid solutions containing glycerol from 0 to 10 M has been determined with the aid of the rotating disk electrode. The viscosity of the solutions has also been measured. Experiments covered a temperature range from 18 to 40°C. The experimental results are in agreement with the predictions of the Einstein-Stokes theory for diffusivity and viscosity. The ratio Dη/T is (2·23 ± 0·31) × 10−10 cm2 poise/s°K and it is reasonably constant within the whole range of viscosity and temperature investigated.Le coefficient de diffusion de l'ion cuivre(II) dans des solutions d'acide sulfurique contenant du glycérol d'une concentration de 0 à 10 M a été déterminé au moyen d'une electrode à disque tournante. La viscosité des solutions a également été mesurée. Les expériences furent effectuées à une témperature entre 18 et 40°C. Les résultats se rapprochent d'une façon satisfaisante des prédictions de la théorie d'Einstein-Stokes pour la diffusivité et la viscosité. Le rapport Dη/T est (2,23 ± 0,37) × 10−10 cm2poise/sec°K et reste assez constant dans tout le champ de la viscosité et de la témperature étudiés.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Control of multifunctional prosthetic hands by processing the electromyographic signal

The human hand is a complex system, with a large number of degrees of freedom (DoFs), sensors embedded in its structure, actuators and tendons, and a complex hierarchical control. Despite this complexity, the efforts required to the user to carry out the different movements is quite small (albeit after an appropriate and lengthy training). On the contrary, prosthetic hands are just a pale replication of the natural hand, with significantly reduced grasping capabilities and no sensory information delivered back to the user. Several attempts have been carried out to develop multifunctional prosthetic devices controlled by electromyographic (EMG) signals (myoelectric hands), harness (kinematic hands), dimensional changes in residual muscles, and so forth, but none of these methods permits the "natural" control of more than two DoFs. This article presents a review of the traditional methods used to control artificial hands by means of EMG signal, in both the clinical and research contexts, and introduces what could be the future developments in the control strategy of these devices

Upper Limb Spasticity Reduction Following Active Training: A Robot-Mediated Study In Patients With Chronic Hemiparesis

sion of the arm. A 3-month follow-up was performed. Results: Statistically significant improvements were found in both groups after treatment. Some differences were found in elbow motor improvement between the 2 groups. Conclusion: Comparison between groups confirms that active movement training does not result in increased hypertonia, but results in spasticity reduction in antagonist muscles by activating the reciprocal inhibition mechanism. Furthermore, robot-mediated therapy contributes to a decrease in motor impairment of the upper limbs in subjects with chronic hemiparesis, resulting in a reduction in shoulder pain

Assessing Mn as an antioxidant agent in bioactive glasses by quantification of catalase and superoxide dismutase enzymatic mimetic activities

The antioxidant activity of Mn as additive in a 45S5 type glass system with and without P2O5 was studied by mimicking the activity of catalase (CMA) and superoxide dismutase (SOD) enzymes. Glasses were melted either under oxidizing or reducing atmosphere (N2/H2) to compare the processing influence on the Mn oxidation state. Thermal (DTA) and optical (UV–Vis) characterizations of the glass powders were carried out to obtain further insight into the structural role of Mn. A correlation of in vitro apatite formation between Tris buffer solution and Simulated Body Fluid (SBF) was performed to optimise Mn substitution, where a decrease in apatite formation was observed by increasing Mn content. Despite this, glasses with up to 1.0 mol% MnO did not show any delay in apatite formation and maintained their CMA and SOD activity. The antioxidant effect of Mn can be attributed to the interconversion Mn2+ ↔ Mn3+ occurring on the glass surface through a heterogeneous catalysis. P2O5 plays an important role in the antioxidant effect of the glass, possibly by charge balancing Mn ions and forming more stable units compared to those formed with Ca and Na. The amount of Mn2+ is predominant in the glass network with respect to Mn3+ in all synthetized glasses. Moreover, glass melting in a reducing atmosphere further avoided Mn oxidation

An innovative approach on directed energy deposition optimization: A study of the process environment's influence on the quality of Ti-6Al-4V Samples

Blown powder additive manufacturing technologies are not restricted to the use of a process chamber. This feature allows to build larger components with respect to conventional powder bed processes. This peculiarity is mostly promising for manufacturing large components or repairing/rebuilding parts of large systems. The main downside of using an open environment, even if a protective shielding gas system is adopted, is the lack of control of process atmosphere. This is particularly critical for titanium alloys which are very sensitive to oxygen/nitrogen pick-up; they have a detrimental effect on ductility, by causing embrittlement and possibly leading to the formation of cracks. It is then important to address how environmental factors, such as process atmosphere and platform temperature, impact not only on the processability but also on the final component properties, both from a compositional and mechanical point of view. The correlations between these environmental factors and microstructure, interstitials content, grain size, and hardness were investigated. Moreover, the Hall-Petch equation was then adopted to additive manufacturing microstructures, characterized by a columnar grain morphology, and used to further investigate the relationship intercurring between grains and hardness and how different microstructures might influence this correlation