Hall Thruster Direct-Drive Assessment and Demonstration

This thesis involves the theoretical and experimental study of the Hall thruster Direct-Drive configuration: a innovative way to deliver power to the electric thrusters and candidate for future propulsion system of spacecraft. The direct connection between the solar array and the thruster anode, made possible by the current development of technology, allows a drastic simplification of the power processing unit of the propulsion system. This has an immediate impact on the propulsion system and its thermal control system which can be consequently lightened. Then, additional mass benefits can be exploited in other parts of the spacecraft such as the electric power system. The work is mainly divided in two parts. The first one assesses in terms of mass reduction the impact that the Direct-Drive configuration entails in the spacecraft systems. Different kind of space missions with different level of Hall thruster power are considered. The second part of thesis concerns an experimental demonstration of a Direct-Drive system supplying the HT-100, the low power electric thruster developed at Alta. The test required the procurement of the solar panel and the design of an electrical filter. By means of simulations with Pspice, a LC filter was developed and then arranged between the solar modules and thruster in order to dampen the current oscillations. This test successfully proved the correct ignition and operations of the thruster, representing in this way the first attempt in Europe of a Direct-Drive demonstration

Organizational Communication (COM 317) City as Classroom Project Report

Organizational Communication focuses on the study and implementation of effective communication within various types of organizations, including corporations, nonprofits, and institutions. It examines how communication acts as the foundation of all organizations by considering major schools of thought about organizations and communication networks, functions, and practices. It also explore significant issues in organizational settings including leadership, conflict, power, ethics, culture, and technology. Students in this class are required to interview a (non-family member) professional in a field they may be interested in pursuing to see how various aspects of organizational communication are used in the workplace. As a result of the City and Region initiative, students were encouraged to interview people in the city (by providing names of communication alumni who offered to be interviewed, and offering subway tokens), and questions were added specific to how being located here influences what the organization does and how they communicate

Lo Sviluppo agricolo nel quadro dello sviluppo economico globale: riflessioni in margine agli "Incontri di studio sui problemi dell'agricoltura sarda"

L’articolo descrive il problema dello sviluppo agricolo trattato negli “Incontri di studio sui problemi dell’agricoltura sarda”; i relatori si sono preoccupati, fino dall'inizio, di affrontare il suo ruolo in relazione alle sue possibilità e ai suoi limiti. Verificata positivamente, l'importanza di tale ruolo, si è passati a esaminare, nel contesto della evoluzione dell'economia sarda, se gli obiettivi posti, nei confronti dell'agricoltura, dalla programmazione nazionale e regionale, e, più tardivamente, da quella europea, siano stati adeguati a tale ruolo e fra loro compatibili. Partendo da tali problemi di fondo si è poi cercato di mettere in evidenza le attuali principali carenze dell'agricoltura sarda e i tipi di intervento e di strumentazioni che sarebbero auspicabili per superarle, il tutto in un quadro criticamente valutato delle norme regionali, nazionali e comunitarie vigenti o imminenti

The impact of carbon based materials on hippocampal cells: from neurons to networks.

Tissue engineering and regenerative medicine require the constant development of synthetic materials to manufacture scaffolds thatbetter integrate into the target tissues (O\u2019Brien, 2011; Ku et al, 2013; Harrison et al, 2014). In this framework, newly synthesized nanomaterials made of pure carbon, in particular Carbon Nanotubes (Ijima, 1991) and Graphene (Novoselov et al, 2004) applications to biology received particular attention due to their outstanding physicochemical properties (Hirsch, 2010). Our team has performed pioneer works during the last decade, about the interactions of neural cells with carbon nanotubes (Lovat et al, 2005; Mazzatenta et al, 2007; Cellot et al, 2009; Cellot et al, 2011; Fabbro et al, 2012; Bosi et al, 2015), and with graphene (Fabbro et al, 2015; Rauti et al, 2016) or, more in general, with synthetic substrates (Cellot et al, 2016). The major aim of my work has been to use traditional and novel physiology tools to investigate further these \u201cneuro-hybrid systems\u201d, and to understand how far Carbon Nanotubes and Graphene can be pushed in neuroscience applications. With this aim, in the first part of my PhD I further elucidated the behavior of newly formed synapses in primary dissociated neurons when interfaced to bi-dimensional substrates of Multi-walled Carbon Nanotubes. I then addressed the homeostasis of invitro neural networks interfaced to pure graphene and I characterized for the first time the changes induced by this material in neurons. As last step, I set up a more complex biological in-vitro model, consisting of lesioned organotypic Entorhinal-Hippocampal cultures (Perederiy and Westbrook, 2013) and we described the regenerative features of Carbon Nanotubes in this lesion model. During my PhD I was also involved in two side projects: in the first one, in collaboration with Sebastian Reinhartz and Matthew Diamond (SISSA), we refine the possible approaches of the optogenetic technique, by manipulating neuronal responses with different light waveforms (Reinhartz et al, MS in preparation, in the appendix). In the second one, in collaboration with the group of Manus Biggs, from the National University of Galway, Ireland, we tested the biocompatibility and addressed the neural behavior of primary neural cells interfaced with Indium Tin Oxide (ITO) substrates with different roughness, thickness and conducting profiles (Vallejo-Giraldo et al, 2017)

Characterization and Thermal Activation of Adducts of Group 4 Tetrahalides with 1,2-Dialkoxyalkanes

Coordination compounds of general formula MX4[κ2-O(R)CH2CH(R′)OR′′], 2a–i, have been prepared in high yield upon addition of a variety of 1,2-dialkoxyalkanes, ROCH2CH(R′)OR′′, to MX4 (M = Ti, X = F, 1a, I, 1b; M = Zr, X = Br, 1c, I, 1d). The new complexes have been characterized by elemental analysis and NMR spectroscopy. The thermal stability of 2 has been studied. Fragmentation of the TiI4 adducts takes place in chloroform solution at 90 °C: after hydrolysis of the reaction mixtures, MeI and CH2ICH2I have been detected from TiI4[dme] [dme = MeO(CH2)2OMe], MeI and Me2O from TiI4[MeOCH2CH(Me)OMe], and MeI, CH2ICH2I, Me2O, CH2ClI from TiI4[MeO(CH2)2OCH2Cl]. The diether MeO(CH2)2OCH2Cl is thermally activated also when coordinated to ZrX4 (X = Br, I): after hydrolysis, MeBr, CH2BrCH2Br, O(CH2CH2Cl)2 and Me2O (X = Br) and MeI, CH2ClI and CH2ICH2I (X = I) have been found, respectively

Microtubule dynamics depart from wormlike chain model

Thermal shape fluctuations of grafted microtubules were studied using high resolution particle tracking of attached fluorescent beads. First mode relaxation times were extracted from the mean square displacement in the transverse coordinate. For microtubules shorter than 10 um, the relaxation times were found to follow an L^2 dependence instead of L^4 as expected from the standard wormlike chain model. This length dependence is shown to result from a complex length dependence of the bending stiffness which can be understood as a result of the molecular architecture of microtubules. For microtubules shorter than 5 um, high drag coefficients indicate contributions from internal friction to the fluctuation dynamics.Comment: 4 pages, 4 figures. Updated content, added reference, corrected typo

Slow excitatory synaptic currents generated by AMPA receptors

Decades of literature indicate that the AMPA‐type glutamate receptor is among the fastest acting of all neurotransmitter receptors. These receptors are located at excitatory synapses, and conventional wisdom says that they activate in hundreds of microseconds, deactivate in milliseconds due to their low affinity for glutamate and also desensitize profoundly. These properties circumscribe AMPA receptor activation in both space and time. However, accumulating evidence shows that AMPA receptors can also activate with slow, indefatigable responses. They do so through interactions with auxiliary subunits that are able promote a switch to a high open probability, high‐conductance ‘superactive’ mode. In this review, we show that any assumption that this phenomenon is limited to heterologous expression is false and rather that slow AMPA currents have been widely and repeatedly observed throughout the nervous system. Hallmarks of the superactive mode are a lack of desensitization, resistance to competitive antagonists and a current decay that outlives free glutamate by hundreds of milliseconds. Because the switch to the superactive mode is triggered by activation, AMPA receptors can generate accumulating ‘pedestal’ currents in response to repetitive stimulation, constituting a postsynaptic mechanism for short‐term potentiation in the range 5–100 Hz. Further, slow AMPA currents span ‘cognitive’ time intervals in the 100 ms range (theta rhythms), of particular interest for hippocampal function, where slow AMPA currents are widely expressed in a synapse‐specific manner. Here, we outline the implications that slow AMPA receptors have for excitatory synaptic transmission and computation in the nervous system. imagePeer Reviewe

The chemistry of Niobium and Tantalum halides, MX5, with haloacetic acids and their related anhydrides: anhydride C–H bond activation promoted by MF5

Niobium and tantalum pentahalides, MX5 (1), react with acetic acid and halo-substituted acetic acids, in 1:1 ratio, to give the dinuclear complexes [MX4(μ-OOCMe)]2 [M = Nb, X = Cl, 2a; M = Ta, X = Cl, 2b; Br, 2c] and [MCl4(μ-OOCR)]2 [M = Nb, R = CH2Cl, 4a; CHCl2, 4c; CCl3, 4e; CF3, 4g; CHBr2, 4i; CH2I, 4j; M = Ta, R = CH2Cl, 4b; CHCl2, 4d; CCl3, 4f; CF3, 4h]. The solid state structures of 2b and 4e have been ascertained by X-ray diffraction studies. The reactions of 1 with acetic anhydride and halo-substituted acetic anhydrides result in C–O bond activation and afford 2 and 4, respectively, with concomitant formation of acetyl halides. Moreover, the complexes MCl5[OC(Cl)Me] [M = Nb, 3a; M = Ta, 3b] have been detected in significant amounts within the mixtures of the reactions of MCl5 with acetic anhydride. TaI5 is unreactive, at room temperature, towards both MeCOOH and (MeCO)2O. MF5 react with RCOOH (R = Me, CH2Cl) in 1:1 molar ratio, to afford the ionic compounds [MF4(RCOOH)2][MF6], 5a–d, in high yields. The additions of (RCO)2O (R = Me, CH2Cl) to MF5 give 5, suggesting that anhydride C–H and C–O bonds activation is operative during the course of these reactions