Heat transfer between nanoparticles: Thermal conductance for near-field interactions

We analyze the heat transfer between two nanoparticles separated by a distance lying in the near-field domain in which energy interchange is due to the Coulomb interactions. The thermal conductance is computed by assuming that the particles have charge distributions characterized by fluctuating multipole moments in equilibrium with heat baths at two different temperatures. This quantity follows from the fluctuation-dissipation theorem for the fluctuations of the multipolar moments. We compare the behavior of the conductance as a function of the distance between the particles with the result obtained by means of molecular dynamics simulations. The formalism proposed enables us to provide a comprehensive explanation of the marked growth of the conductance when decreasing the distance between the nanoparticles.

Metastable liquid-liquid phase transition in a single-component system with only one crystal phase and no density anomaly

We investigate the phase behavior of a single-component system in three dimensions with spherically-symmetric, pairwise-additive, soft-core interactions with an attractive well at a long distance, a repulsive soft-core shoulder at an intermediate distance, and a hard-core repulsion at a short distance, similar to potentials used to describe liquid systems such as colloids, protein solutions, or liquid metals. We showed [Nature (London) 409, 692 (2001)] that, even with no evidence of the density anomaly, the phase diagram has two first-order fluid-fluid phase transitions, one ending in a gas¿low-density-liquid (LDL) critical point, and the other in a gas¿high-density-liquid (HDL) critical point, with a LDL-HDL phase transition at low temperatures. Here we use integral equation calculations to explore the three-parameter space of the soft-core potential and perform molecular dynamics simulations in the interesting region of parameters. For the equilibrium phase diagram, we analyze the structure of the crystal phase and find that, within the considered range of densities, the structure is independent of the density. Then, we analyze in detail the fluid metastable phases and, by explicit thermodynamic calculation in the supercooled phase, we show the absence of the density anomaly. We suggest that this absence is related to the presence of only one stable crystal structure.

A Thermokinetic approach to radiative heat transfer at the nanoscale

Radiative heat exchange at the nanoscale presents a challenge for several areas due to its scope and nature. Here, we provide a thermokinetic description of microscale radiative energy transfer including phonon-photon coupling manifested through a non-Debye relaxation behavior. We show that a lognormal-like distribution of modes of relaxation accounts for this non-Debye relaxation behavior leading to the thermal conductance. We also discuss the validity of the fluctuation-dissipation theorem. The general expression for the thermal conductance we obtain fits existing experimental results with remarkable accuracy. Accordingly, our approach offers an overall explanation of radiative energy transfer through micrometric gaps regardless of geometrical configurations and distances.

Poly(butylene terephthalate-co-5-tert-butyl isophthalate) Copolyesters: Synthesis, Characterization and Properties

A series of poly(butylene terephthalate) copolyesters containing 5-tert-butyl isophthalate units up to 50%-mole, as well as the homopolyester entirely made of these units, were prepared by polycondensation from the melt. The microstructure of the copolymers was determined by NMR to be at random for the whole range of compositions. The effect exerted by the 5-tert-butyl isophthalate units on thermal, tensile and gas transport properties was evaluated. Both Tm and crystallinity as well as the mechanical moduli were found to decrease steadily with copolymerization whereas Tg increased and the polyesters became more brittle. Permeability and solubility sligthly increased also with the content in substituted units whereas the diffusion coefficient remained practically constant. For the homopolyester poly(5-tert-butyl isophthalate), all these properties were found to deviate significantly from the general trend displayed by copolyesters suggesting that a different chain mode of packing in the amorphous phase is likely adopted in this case.

Characterization of Mechanically Alloyed Nanocrystalline Fe(Al): Crystallite Size and Dislocation Density

A nanostructured disordered Fe(Al) solid solution was obtained from elemental powders of Fe and Al using a high-energy ball mill. The transformations occurring in the material during milling were studied with the use of X-ray diffraction. In addition lattice microstrain, average crystallite size, dislocation density, and the lattice parameter were determined. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Thermal behaviour of the milled powders was examined by differential scanning calorimetry (DSC). The results, as well as dissimilarity between calorimetric curves of the powders after 2 and 20 h of milling, indicated the formation of a nanostructured Fe(Al) solid solution

Simulació del comportament d'uns individus en un entorn i desenvolupament d'un videojoc educatiu de programació

Aquest projecte tracta la implementació d’una aplicació capaç de simular el comportament d’uns individus que segueixen el seu propi algorisme en un entorn que planteja certes dificultat per a la supervivència: hi ha obstacles i fonts que proveeixen energia que els individus necessiten per existir. S’han desenvolupat les eines necessàries perquè l’usuari pugui visualitzar, recollir dades i interactuar amb l’entorn d’una forma còmoda i intuïtiva. Sobre aquesta base, s’ha implementat un videojoc que planteja reptes a l’usuari que es poden resoldre a través de l’edició dels algorismes d’un o més individus, és a dir, a través de la programació. D’aquesta manera s’introdueix a l’usuari en els principis de l’algorismia d’una forma lúdica i molt visual.

Heat transfer between nanoparticles: Thermal conductance for near-field interactions

We analyze the heat transfer between two nanoparticles separated by a distance lying in the near-field domain in which energy interchange is due to the Coulomb interactions. The thermal conductance is computed by assuming that the particles have charge distributions characterized by fluctuating multipole moments in equilibrium with heat baths at two different temperatures. This quantity follows from the fluctuation-dissipation theorem for the fluctuations of the multipolar moments. We compare the behavior of the conductance as a function of the distance between the particles with the result obtained by means of molecular dynamics simulations. The formalism proposed enables us to provide a comprehensive explanation of the marked growth of the conductance when decreasing the distance between the nanoparticles.

Guia per a l'adaptació a l'espai europeu d'educació superior: 9. Fer docència a la UdG

La docència és una de les principals funcions de la universitat. Se situa just al costat de la recerca, amb la qual forma un conjunt simbiòtic que cal entendre com a tal en el desenvolupament de l’una i de l’altra. A la Universitat de Girona s’entén que l’exercici de la docència és responsabilitat del professorat, que, amb la seva expertesa i la seva professionalitat, busca en tot moment la millor manera d’aconseguir bons aprenentatges per als estudiants. Tot i això, la UdG, especialment arran de la creació de l’espai europeu d’educació superior, s’ha dotat d’un conjunt de definicions, procediments i eines de suport per al personal docent que, a més de facilitar la docència, els proporciona un segell propi, sempre amb el respecte a la iniciativa docent del professorat. Aquest quadern és la presentació d’aquestes definicions, procediments i eines, alhora que vol ser una breu guia de la UdG per al professorat que hi entra a treballar de bell nou

The politics of memory in Harold Pinter's Ashes to Ashes

The present work proposes an investigation of the treatment given to memory in Pinter’s latest play, Ashes to Ashes, and of its function in the development of Pinter’s work. In order to do that, different aspects of the construction of meaning in the theatre are analysed, so that the specificity of its reception is determined. A survey of techniques used to present information, time and space in the theatre is made. The analytical drama, the history drama, and the theatre of the absurd are defined. After that, the evolution of the author’s work is analysed to determine what characterises Pinter’s work, while at the same time determining how his treatment of themes like menace, memory, and political oppression of the individual has evolved. Finally, a detailed survey of the apparently disconnected elements that are mentioned in Ashes to Ashes is made. The intertextual analysis allied to a study of the analytical form as used in this play enables the discovery of several layers of meaning. Through the connection established between the Holocaust and man’s fall followed by expulsion from Eden, Pinter examines the use of memory as a way of dealing with personal and collective responsibility and guilt. It is through the recovery of memory (also through writing) that the present can establish a critical and responsible relation with the past.

Documentação museológica: uma reflexão sobre o tratamento descritivo do objeto no Museu Paulista

Pós-graduação em Ciência da Informação - FFC

Efeito do oxigênio intersticial nas propriedades mecânicas e biocompatibilidade da Liga Ti-5Ni

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Comparação dos efeitos de compressão isostática e compressão uniaxial na obtenção da liga NiTi por metalurgia do pó

Several alloys present the shape memory effect and among them, the equiatomic NiTi alloy, nitinol, is the most important one. It is usually used in several engineering applications and also in biomedical devices, in the fabrication of orthodontic wire, stents and Judet staples. Although a considerable amount of these biomedical devices is utilized in Brazil and a fraction of it is already made here, all nitinol used is bought abroad. Thus, it is important to develop the necessary know-how to fabricate NiTi wire and sheet. It would mean less importation with job creation and wealth generation for the country. In this work nitinol was obtained powder metallurgy from elemental powders of Ti and Ni using uniaxial compression and uniaxial compression followed by isostatic compression. The final densities achieved were determined by the Archimedes method. The precipitation of intermetallic secondary phases was studied and the samples were characterized by metallographic analysis, optical microscopy and X-ray diffraction. Results indicated that 50 hours sintering route showed a low amount of intermetallics, and no trace of unreacted powder. XRD and metallography at room temperature indicated B19’ as the predominant phase, which corresponds to martensite. Although density results showed little dispersion, the most dense sample was compacted under uniaxial compression and presented 4.8 g/cm3, corresponding to 20.84% porosity. Density variation was considered normal to the measurement process and independent of the compaction mode

Estudo de tempos e temperaturas de sinterização na obtenção da liga NiTi por metalurgia do pó

The nickel-titanium alloys are very attractive and so it is widely used in industry, engineering applications in general and also in biomedical and dental applications. Besides showing the shape of memory effect, biocompatibility and superelastic, the alloy commercially known as Nitinol, has excellent mechanical properties. Most devices used in Brazil have been produced nationally, but using imported material is also necessary, which shows the need of produce the alloy nationally. In this study we have investigated the influence of sintering temperatures and times to obtain nickel-titanium alloys by powder metallurgy alloys and the characterization of the precipitated intermetallic phases by using the post-mix of elemental nickel and titanium in proportion of 49.5% Ti - 50.5% Ni. The samples were sintered at 930ºC for periods of 30, 40 and 50 hours and were characterized by optical microscopy using metallography and x-ray diffraction. The results of the study show that the 50 hours sintering time was the most suitable time for obtaining the alloy, observing a low volume of precipitated intermetallic phases and absence of Ni and Ti residuals

Fios ortodônticos superelásticos e sua aplicabilidade na clínica ortodôntica: revisão da literatura

During clinical routine, the orthodontist uses several materials, which include metallic alloys in the form of metallic wires. However, it is necessary that the professional has some knowledge of the properties of those wires. Different types of wires are commercially available: stainless steel wires, chrome-cobalt wires, nickel-titanium wires and beta-titanium wires. Among the nickel-titanium wires, there are three subdivisions: a conventional alloy and two superelastic alloys. The superelasticity, associated to the effect of form memory, is a property used in orthodontics to initiate the dental movement in the first phase of the orthodontic treatment. This property is considered to be biologically compatible with the effective dental movement. These wires are available at the market in different transformation temperatures, and they offer the best adaptation in the groove of the bracket, simplicity and a faster treatment. However, they present little formability, and they don’t accept solder. They are also more onerous than other wires. Moreover, the low rigidity of these wires doesn’t allow them to be used for the retraction of the anterior teeth or closing of spaces. Therefore, the coherent use of superelastic orthodontic wires is recommended, accompanied by a detailed diagnosis and planning, so the result will be an efficient orthodontic correction, accomplished in a shorter period of time.