Dielectric and EM properties of carbon filled epoxy resin

Questa tesi riguarda le proprietà dielettriche e di assorbimento alle microonde della resina epossidica caricata di nanocariche. Tre differenti nanocariche a base di carbonio sono state usate in questa tesi: Carbon black (CB) nanofibre di carbonio (CNF) e nanotubi di carbonio (CNT). Inoltre,sono stati provati vari processi di dispersione delle nanocariche nella resina, per analizzare gli effetti della distribuzione delle nanocariche sulle proprietà dielettriche dei composti che ne risultavano. È stata misurata la permettività usando un sistema VNA nella banda-X (8,2-12,4 GHz) usando il metodo della guida d’onda. La morfologia dei campioni è stata studiata con un sistema FEG-SEM. usando il modello del circuito equivalente è stata tentata una connessione tra la morfologia dei campioni e la permettività. Infine si è giunti alla conclusione se questi materiali sono adatti ad essere usati come materiali che assorbenti le microonde elettromagnetiche. Nei campioni di CB, realizzati usando cariche con differenti aree di superficiali specifiche la distribuzione delle cariche nella resina é differente, quando si usano cariche di alta area di superficiale producendo piccoli corti clusters ramificati, e nell’altro caso aggregati lunghi spessi e serpeggianti. In entrambi i casi i clusters sono vicini a una forma cilindrica e possono essere visti come condensatori a cilindri paralleli, immersi nella resina. Di conseguenza, i campioni di alta area di superficie presentano valori più bassi di permettività reale (misura la capacita del sistema), dovute alla minore lunghezza dei clusters (armature dei condensatori), ma una maggiore permettività immaginaria (legata agli effetti della conduttività e della dispersione) perché come è stato fatto notare precedentemente i clusters sono disposti in maniera molto ravvicinata permettendo l’attivazione di modelli di conduzione hopping and tunnelling. i campioni CB hanno dimostrato buoni risultati come assorbitori di EM raggiungendo un picco di 38dB usando un campione spesso 4mm. Nei campioni caricati con cariche con alto aspect ratio (CNF e CNT) il parametro principale è la loro dispersione nella resina,nelle prove con campioni caricati con CNF, nonostante l’uso di metodologie differenti,è stata raggiunta una dispersione non soddisfacente,con la microstruttura risultante composta di aggregati. Le misurazioni EM hanno messo in luce che maggiore il numero e più piccola la dimensione degli aggregati,maggiori sono ε’ e ε” per la stessa ragione trovata nel caso dei campioni caricati con CB. Nel caso dei campioni CNT, invece una dispersione veramente buona stata raggiunta con l’aiuto di un surfactante ed un sonicatore più potente. I risultati dimostrano di nuovo che la permettività è legata alla microstruttura, con la stessa tendenza stabilita con altri tipi di nanocariche, tuttavia,in questo caso è stata rinvenuto un nuovo caso che mette in luce che c’è un ottimo livello di dispersione sopra quale i CNT non interagiscono tra di loro risultando in un ε’ molto alto e in un ε” molto basso visto che la dispersione attraverso l’effetto Joule è limitata. Le prestazioni di assorbimento di CNF e CNT dimostra che sia una percentuale troppo elevata sia la troppa dispersione porta ad un materiale soprattutto riflettente, con basse prestazioni di assorbimento. Un buon compromesso, perciò ,deve essere trovato per ogni sistema come compromesso tra la composizione del materiale, la microstruttura e lo spessore. Parte del lavoro sperimentale e stata condotta presso l’università di Monash (Clayton, Victoria Australia) sotto la supervisione del Prof. George Simon.This thesis deals with the dielectric and absorbing properties at microwaves (x-band) of epoxy resin filled nanocomposites. Three different carbonaceous nanofillers were used in the experimental: carbon black (CB), carbon nanofibers (CNF) and carbon nanotubes (CNT). Moreover, various dispersion processes of nanofiller in the resin were tried, in order to analyze the effect of filler distribution on the dielectric properties of the resulting composites. Permittivity was measured using a vector network analyzer in x-band (8,2-12,4 GHz) using the waveguide method. Samples morphology was studied by FEG-SEM. Using the equivalent circuit analogy, a link between samples morphology and permittivity was attempted. The suitability of these materials as electromagnetic microwaves absorbers was finally assessed. In carbon black samples, realized using fillers with different specific surface areas, the filler distribution within the resin is very different, producing small short branched clusters when using high surface areas filler, and long thick and meandering aggregates in the other case. In both samples the clusters are close to cylindrical shape and may be seen as parallel cylinders capacitors in the resin. As a consequence, high surface area samples present lower values of real permittivity (that takes into account capacity of the system), due to the smaller length of capacitor plates, but higher imaginary permittivity (linked to conductivity and dissipations effects) because, as noted above, the clusters are closely spaced, permitting the activation of hopping and tunnelling conduction modes. CB samples showed good performances as EM absorbers, reaching a peak of -38 dB using a sample 4 mm thick. In samples loaded with high aspect ratio (CNF and CNT) the key parameter is their dispersion in the resin. In CNF experimentation, despite the use of different methodologies, an unsatisfying dispersion was achieved, with the resulting microstructure made of aggregates. The EM measurements highlighted that the higher the number and the smaller the dimension of the aggregates, the higher are ε’ and ε”,for the same reason found in the case of CB. With CNT, instead, very good dispersions were achieved, by means of the aid of surfactants and of a more powerful sonicator. The results demonstrate again that permittivity is linked to microstructure, with the same trend established with the other type of nanofillers. Nevertheless, in this case, a new evidence was found highlighting that there is an optimum level of dispersion, above which the CNT do not interact each other, resulting in very high ε’ and very low ε”, since dissipation through Joule effect is limited. The absorbing performance of CNF and CNT demonstrate that too much filler, or too much dispersion of it (i.e. Low ε”), bring to a mostly reflective medium, with low absorbing performance. An optimum formulation needs, therefore, to be found for every system as a compromise among material composition, microstructure and thickness. Part of the experimental work (most of chapter 6 ) was carried out during the author secondment to Monash University (Clayton, Victoria Australia) under the supervision of Prof. George Simon

Big data problems we face today can be traced to the social ordering practices of the 19th century.

In the 19th century, changes in knowledge were facilitated not only by large quantities of new information pouring in from around the world but by shifts in the production, processing and analysis of that information. Hamish Robertson and Joanne Travaglia trace the connections between the 19th century data revolution and the present day one, outlining the implications this may have for the politics of big data in contemporary society. Two centuries after the first big data revolution, many of the problems and their solutions persist down to the present era

The necropolitics of COVID-19: will the COVID-19 pandemic reshape national healthcare systems?

The COVID-19 pandemic has made necropolitics – the politics of life and death – unavoidable . Drawing on the work of Achille Mbembe, Hamish Robertson and Joanne Travaglia argue that, as in previous crises, COVID-19 reveals many of the hidden assumptions underpinning national healthcare systems. As the current crisis continues to bring these assumptions into the mainstream and disrupts business as usual, they suggest that COVID-19 points towards opportunities to reshape the relationship of society to its most vulnerable members

Ferromagnetism of the Hubbard Model at Strong Coupling in the Hartree-Fock Approximation

As a contribution to the study of Hartree-Fock theory we prove rigorously that the Hartree-Fock approximation to the ground state of the d-dimensional Hubbard model leads to saturated ferromagnetism when the particle density (more precisely, the chemical potential mu) is small and the coupling constant U is large, but finite. This ferromagnetism contradicts the known fact that there is no magnetization at low density, for any U, and thus shows that HF theory is wrong in this case. As in the usual Hartree-Fock theory we restrict attention to Slater determinants that are eigenvectors of the z-component of the total spin, {S}_z = sum_x n_{x,\uparrow} - n_{x,\downarrow}, and we find that the choice 2{S}_z = N = particle number gives the lowest energy at fixed 0 < mu < 4d.Comment: v2: Published version. 30 pages latex. Changes in title, abstract, introductio

Workplace bullying in the Australian health context: a systematic review

© 2017, © Emerald Publishing Limited. Purpose: During the past decade, there has been increased attention into bullying behaviours in workplaces. Research to date has varied in design, the definition of what constitutes bullying behaviour, as well as the methods used to collect data and measure bullying incidence and prevalence. Nonetheless, studies demonstrate that bullying is a significant issue, which warrants an increased research focus to develop greater understanding of the concept, its effects and implications in, and for, the workplace. The purpose of this paper is to focus on capturing a range of international and Australian literature regarding workplace bullying behaviours in a health context from a management perspective. As a result, this paper identified the gaps in the literature when expanded specifically to an Australian health context. Design/methodology/approach: The purpose of this review is to summarise the existing literature, both internationally and in Australia which examines workplace bullying behaviours in a health context from a management perspective. This describes the review of the literature on workplace bullying in a health context undertaken from January to April 2014. The “Preferred Reporting Systematic Reviews and Meta-Analyses” method was used to structure the review, which covered a wide range of literature from databases including MEDLINE, Embase, CINAHL and InformIT, as well as reports, and grey literature. Findings: The review included 62 studies that met the inclusion criteria and reported either: factors contributing to workplace bullying, at least one significant example of workplace bullying behaviour or the impact of workplace bullying behaviours in a health context. Originality/value: There is limited data on workplace bullying behaviours in an Australian health context. The literature supports there is value in future research to develop consistent definitions, policies, procedures and frameworks, which could help to prevent or address workplace bullying behaviours based on work being undertaken internationally

Without a critical approach to big data it risks becoming an increasingly sophisticated paradigm for coercion

We are in the midst of a data revolution, one reliant on the capture, analysis, and visual representation of enlarged quantitative data, in increasingly digital formats. Hamish Robertson and Joanne Travaglia argue that big data quantification is now not only a mechanism for extracting information but has become an idea with social and political power in its own right. The lack of critique of quantitative methods and their application contributes to the existing and potentially coercive power of digital information systems and their attendant methods, and enhances the potential for “collateral damage” associated with such applications

One- and Multi-dimensional CWENOZ Reconstructions for Implementing Boundary Conditions Without Ghost Cells

We address the issue of point value reconstructions from cell averages in the context of third-order finite volume schemes, focusing in particular on the cells close to the boundaries of the domain. In fact, most techniques in the literature rely on the creation of ghost cells outside the boundary and on some form of extrapolation from the inside that, taking into account the boundary conditions, fills the ghost cells with appropriate values, so that a standard reconstruction can be applied also in the boundary cells. In Naumann et al. (Appl. Math. Comput. 325: 252-270. https://doi.org110.1016/j.amc.2017.12.041, 2018), motivated by the difficulty of choosing appropriate boundary conditions at the internal nodes of a network, a different technique was explored that avoids the use of ghost cells, but instead employs for the boundary cells a different stencil, biased towards the interior of the domain. In this paper, extending that approach, which does not make use of ghost cells, we propose a more accurate reconstruction for the one-dimensional case and a two-dimensional one for Cartesian grids. In several numerical tests, we compare the novel reconstruction with the standard approach using ghost cells

Developing allied health leaders to enhance person-centred healthcare

© 2018, Emerald Publishing Limited. Purpose: The purpose of this paper is to present findings from a mixed methods study investigating leadership development of allied health practitioners within a large public healthcare organization in Australia. Design/methodology/approach: The South Eastern Sydney Local Health District Allied Health Leadership Development Program was undertaken with an allied health cohort (n=16) between May 2014 and March 2015 and comprised all-day workshops, action learning sets and individual coaching. Using experiential learning, the program tested whether practice development methods and action learning approaches developed the leadership skills of participants compared with a control group (n=17). Descriptive statistics were collected to evaluate participant and program outcomes. Leadership, workplace culture and engagement measures were analyzed as part of the study. Findings: The Allied Health Leadership Development Program received high ratings by participants. They reported enhanced skills in leading self and others through mechanisms such as critical reflection and facilitation, and greater confidence managing change and with engaging staff, colleagues and patients in decision making, affecting the quality and safety of healthcare. Statistically significant differences were found with transformational leadership elements, leadership outcomes, and measures of workplace culture and engagement after program completion for intervention group participants, compared with the control group. Research limitations/implications: Results provide new empirical evidence about the effectiveness of using practice development for allied health leadership development. Practical implications: This low-cost leadership program can be replicated by other organizations. Originality/value: Outcomes from an Allied Health Leadership Development Program have not been previously reported in the literature