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  • Author: Radu Constantinescu x
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Silviu Alexandru Constantinescu and Ionuț Radu Răcănel

Abstract

This paper presents a new type of seismic isolator that uses the principle of electromagnetic attraction and repulsion, to control the friction force between two electromagnets during earthquakes. The two electromagnets are used in conjunction with a secondary high friction dissipating and damping mechanism composed from a 10mm thick neoprene ring layer and two steel surfaces coated with Si3N4 that are used to dissipate the kinetic energy in the bridge deck at some maximum ground accelerations. The isolator utilizes tri-axial accelerometers embedded in the abutments, high current rechargeable batteries and an automated controlling unit. The presented isolator was developed specifically for a concrete bridge deck with a span of 36 meters and simple supported on two abutments, using time history electromagnetic and structural analyses. The paper presents the advantages of using this active seismic isolation system, compared to classical passive devices and the important results obtained in terms of decreasing internal forces on the substructure elements cross sections together with the reduction of relative displacements between the two electromagnets.

Open access

Cătălina Anca Cucoș, Radu Constantinescu, Ateș Barut, Iuliana Ionașcu and Constantin Vlăgioiu

Abstract

Chiari-like malformation represents a congenital anomaly that affects the bony cranial base and the hindbrain, leading to fluid filled cavities formation in the spinal cord, condition named Syringomyelia. This paper aims to assess the variety of the clinical signs and to evaluate the magnetic resonance imaging findings in thirty- seven Cavalier King Charles Spaniel dogs. The study was performed over a four-year period, from 2013 to 2017, all cases underwent neurological examination, full diagnostic work-up, including magnetic resonance imaging scans of the brain, cervical and upper thoracic spinal cord. Thirty-seven dogs were included in this study, 23 females and 14 males, with a mean age of 3.6±2.1years. The commonest clinical findings encountered were neuropathic pain and vocalization, seen in all 37 cases, followed by scratching, facial rubbing, paw licking, air licking, tail chasing, seizures and unilateral facial paralysis. Different grades of cerebellar herniation and cervical syrinxes were noted in all cases, other magnetic resonance imaging findings encountered were medullary kinking, presyrinx and ventriculomegaly. In establishing the diagnosis of the Chiari-like malformation and Syringomyelia, the breed, clinical history and the symptomatology are very important, but only magnetic resonance imaging technique can provide quantitative assessment of the nervous system lesions.

Open access

Dan Mihai Constantinescu, Radu Catalin Picu, Marin Sandu, Dragos Alexandru Apostol, Adriana Sandu and Florin Baciu

Abstract

Specific manufacturing technologies were applied for the fabrication of epoxy-based nanocomposites with silica nanoparticles. For dispersing the fillers in the epoxy resin special equipment such as a shear mixer and a high energy sonicator with temperature control were used. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%.. The obtained nanocomposites were subjected to monotonic uniaxial and creep loading at room temperature. The static mechanical properties were not significantly improved regardless the filler percentage and type of epoxy resin. Under creep loading, by increasing the stress level, the nanocomposite with 0.1 wt% silica creeps less than all other materials. Also the creep rate is reduced by adding silica nanofillers.