3D printing of shape memory Alloys for complex architectures of smart structures

Shape Memory Alloys (SMA) are materials used to design smart structures with intrinsic functional properties and improved efficiency. This is a key aspect of aerospace industry and makes SMA good candidates in this field. One of the most widespread SMA is the equiatomic NiTi alloy which, however, has the strong limitation of poor machinability, so only simple shapes can be obtained. Additive Manufacturing processes allow to overcome this limit and to design complex shapes. Compared to other metallic materials, the optimization of the process for NiTi alloy is complicated because, beside mechanical properties and presence of defects, considerable attention needs to be dedicated to the material functionality. The high temperatures involved in the additive process significantly affect the material properties due to possible evaporation of Ni and formation of precipitates that enable a shift of the phase transformation temperatures. This paper is focused on the optimization of the process parameters of the NiTi alloy printed through the Laser Powder Bed Fusion (L-PBF) to ensure optimal pseudo-elastic behaviour, which is essential for the design of structural dampers. This was accomplished starting from simple structures and then designing a damper that couples the pseudoelasticity of NiTi with load support capacity. The L-PBF is a powder-bed technique that selectively melts layers of micrometric metal powder. A pseudoelastic NiTi powder with 50.8 at. % of Ni content was selected and characterized through scanning electron microscope (SEM) and observations connected to an Energy Dispersive X-ray Spectroscopy (EDX) probe. After that, some cubic samples were manufactured, with the dimension of 3 × 3 × 15 mm3. A set of different laser powers and scanning speeds were used to find the set of process parameters that optimize the functional properties of the printed parts. Near fully dense specimens with density higher than 99.5 % were selected for further investigations. Differential scanning calorimetry (DSC) and mechanical tests were performed on as-built and heat-treated samples. Quasi-static mechanical tests were accomplished in compression mode, at different strains, up to 8 %. It was observed that the residual strain for cyclic loading at 4 % is lower than 1 %, so good recovery of the deformation was shown. Moreover, numerical analyses that mimic the pseudoelastic behaviour in compression tests were implemented. Finally, the best set of parameters was selected on the basis of the material's ability to recover deformations and its loss factor

A trimodal resonator for three mutually perpendicular magnetic fields

We describe a trimodal resonator for the simultaneous delivery of three perpendicular magnetic fields. The resonator consists of a shielded loop single-mode radio frequency (rf) resonator placed inside of a bimodal waveguide microwave resonator. The microwave modes are nondegenerate, tunable over a range of 100 MHz, and have typical Q factors of 150 and 200. The rf mode is tunable over a range of 125 MHz, and has a typical Q of 45. Control of the relative phase between the three fields is demonstrated. The resonator will be used to drive three magnetic dipole transitions coherently between Zeeman states in the ground state of 87Rb.87Rb. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71204/2/RSINAK-70-3-1780-1.pd

Diagnosi differenziale dei tumori parotidei: quali caratteristiche di risonanza magnetica considerare?

La finalità del nostro lavoro è di valutare le caratteristiche di risonanza magnetica (RM) tipiche dei tumori parotidei maligni e benigni. Questo studio retrospettivo si basa sulla valutazione di esami RM pre-chirurgici di 94 pazienti con tumori parotidei. I risultati istologici erano disponibili in tutti i casi; abbiamo analizzato 69 lesioni erano benigne (73%) e 25 maligne (27%): 44 adenomi pleomorfi, 18 tumori di Warthin, 7 tumori benigni di diverso istotipo, 6 carcinomi squamocellulari, 3 carcinomi ex-adenomi pleomorfi, 2 carcinomi mucoepidermoidi, 1 tumore adenoidocistico, 13 tumori maligni di diverso istotipo. Sono state valutate le seguenti caratteristiche RM: morfologia, sede, dimensioni, margini, intensità di segnale nelle sequenze T2-pesate e T1-pesate, impregnazione dopo mezzo di contrasto (mdc), intensità di segnale della porzione cistica, presenza o assenza di una capsula, diffusione perineurale, pattern di crescita extraghiandolare e linfoadenopatie laterocervicali. È stata effettuata un’analisi statistica per identificare le caratteristiche RM più indicative di malignità e per definire l’aspetto tipico degli istotipi più comuni. I parametri significativamente predittivi di malignità sono risultati i margini mal-definiti (p < 0,001), le linfoadenopatie (p < 0,001) ed il pattern di crescita infiltrativo (p < 0,001). Le caratteristiche tipiche dell’adenoma pleomorfo sono risultate l’iperintensità di segnale nelle immagini T2-pesate (p = 0,02), l’intensa impregnazione dopo mdc (p < 0,001) ed i margini lobulati (p = 0,04). Le caratteristiche tipiche del tumore di Warthin sono risultate le componenti iperintense nelle immagini T1-pesate (p < 0,001), la localizzazione nel processo parotideo inferiore (p < 0,001) e l’impregnazione post-contrastografica lieve/incompleta (p = 0,01). L’intensità di segnale nelle immagini T1-pesate e T2- pesate e l’impregnazione post-contrastografica si sono rivelate utili nella diagnosi differenziale tra adenoma pleomorfo e tumore di Warthin

Linear frictional forces cause orbits to neither circularize nor precess

For the undamped Kepler potential the lack of precession has historically been understood in terms of the Runge-Lenz symmetry. For the damped Kepler problem this result may be understood in terms of the generalization of Poisson structure to damped systems suggested recently by Tarasov[1]. In this generalized algebraic structure the orbit-averaged Runge-Lenz vector remains a constant in the linearly damped Kepler problem to leading order in the damping coeComment: 16 pages. 1 figure, Rewrite for resubmissio

Biogenesis of the inner membrane complex is dependent on vesicular transport by the alveolate specific GTPase Rab11B

Apicomplexan parasites belong to a recently recognised group of protozoa referred to as Alveolata. These protists contain membranous sacs (alveoli) beneath the plasma membrane, termed the Inner Membrane Complex (IMC) in the case of Apicomplexa. During parasite replication the IMC is formed de novo within the mother cell in a process described as internal budding. We hypothesized that an alveolate specific factor is involved in the specific transport of vesicles from the Golgi to the IMC and identified the small GTPase Rab11B as an alveolate specific Rab-GTPase that localises to the growing end of the IMC during replication of Toxoplasma gondii. Conditional interference with Rab11B function leads to a profound defect in IMC biogenesis, indicating that Rab11B is required for the transport of Golgi derived vesicles to the nascent IMC of the daughter cell. Curiously, a block in IMC biogenesis did not affect formation of sub-pellicular microtubules, indicating that IMC biogenesis and formation of sub-pellicular microtubules is not mechanistically linked. We propose a model where Rab11B specifically transports vesicles derived from the Golgi to the immature IMC of the growing daughter parasites

Intramedullary melanotic schwannoma

We present a case of an intramedullary melanotic schwannoma (IMS) of the thoracic spinal cord. To our knowledge, this is the seventh reported case of an IMS of the central nervous system. Schwannomas are benign nerve sheath tumors of neural crest origin composed entirely of well differentiated Schwann cells that typically occur in peripheral nerves. Both the intramedullary location and the melanotic component of the reported lesion make it exceedingly rare. We will present our case, theories as to the origin of these tumors, clues in radiographic identification, and current clinical follow-up recommendations

Modelling tumour volume variations in head and neck cancer: contribution of magnetic resonance imaging for patients undergoing induction chemotherapy

La valutazione del volume del tumore primitivo ha mostrato un valore predittivo per la stima dei risultati della sopravvivenza. Usando i dati volumetrici acquisiti con la Risonanza Magnetica (RM) nei pazienti sottoposti a chemioterapia di induzione (CI), tali risultati sono stati stimati nei pazienti con tumore del testa e collo, prima del trattamento radiante. Le immagini RM acquisite prima e dopo CI in 36 pazienti con tumore avanzato della testa e del collo sono state analizzate per valutarne il volume del tumore primitivo. I due volumi sono stati correlati utilizzando la regressione lineare locale tra i volume valutati nelle immagini della prima e quelli della seconda RM. Sono stati definiti i modelli di rischio proporzionale di COX per la valutazione del controllo locoregionale, la sopravvivenza libera da malattia e la sopravvivenza globale. La regressione lineare locale ha mostrato un buon valore predittivo per tutti i risultati di sopravvivenza nei modelli di rischio proporzionale di COX. I modelli predittivi per il controllo locoregionale di malattia e la sopravvivenza libera da malattia a 24 mesi ha mostrato una ottima discriminazione e capacità di previsione. La valutazione delle variazioni dei volumi dei tumori primitivi della testa e del collo dopo CI fornisce un esempio di modello che può essere facilmente utilizzato per altri approcci terapeutici. Una valutazione completa delle variabili nelle covariate è un prerequisito necessario per la creazione di modelli clinicamente attendibili