Quantum limit of photothermal cooling

We study the problem of cooling a mechanical oscillator using the photothermal (bolometric) force. Contrary to previous attempts to model this system, we take into account the noise effects due to the granular nature of photon absorption. This allows us to tackle the cooling problem down to the noise dominated regime and to find reasonable estimates for the lowest achievable phonon occupation in the cantilever

RDNA: Arquitetura Definida por Resíduos para Redes de Data Centers

"Recentemente, temos observado o crescente uso das tecnologias de informação e da comunicação. Instituições e usuários simplesmente necessitam de alta qualidade na conectividade de seus dados, com expectativa de acesso instantâneo a qualquer hora e em qualquer lugar. Um elemento essencial para garantir qualidade na conectividade da nuvem é a arquitetura da rede de comunicação no Data Center (DCNs - Data Center Networks). Isso ocorre porque uma parte significativa do tráfego da Internet é baseada na comunicação de dados e no processamento que acontece dentro da infraestrutura do Data Center (DC). No entanto, os protocolos de roteamento, a forma de encaminhamento e gerenciamento que são executados atualmente, se revelam insuficientes para atender as demandas atuais por conectividade na nuvem. Isto ocorre principalmente pela dependência da operação de busca nas tabelas de encaminhamento, levando à um incremento de latência fim a fim, ademais, mecanismos de recuperação tradicionais utilizam estados adicionais nas tabelas, aumentando a complexidade nas rotinas de gerenciamento, além de reduzir drasticamente a escalabilidade de proteção nas rotas. Outra dificuldade é a comunicação multicast dentro do DC, as soluções existentes são complexas de implementar e não suportam a configuração dos grupos nas taxas atuais requeridas. Neste contexto, essa tese explora o sistema numérico de resíduos centrado no Teorema Chinês do Resto (TCR) como fundamento, aplicado no projeto de um novo sistema de roteamento para DCN. Mais especificamente, introduzimos a arquitetura RDNA que avança o estado da arte a partir de uma simplificação do modelo de encaminhamento para o núcleo, baseado em uma operação de resíduo (resto da divisão). Nesse sentido, a rota é definida como resíduo entre um identificador de rota e identificadores locais (números primos) atribuídos aos switches de núcleo. Os switches de borda, recebem entradas configurando os fluxos de acordo com a política de rede definida pelo controlador. Cada fluxo é mapeado na borda, através de um identificador de rota principal e um emergencial. Essas operações de resíduos permitem encaminhar os pacotes pela respectiva porta de saída. Em situações de falha, o identificador de rota emergencial viabiliza rápida recuperação enviando os pacotes por uma porta de saída alternativa. A RDNA é escalável assumindo uma topologia 2-tier Clos Network amplamente utilizada em DCNs. Com o objetivo de confrontar a RDNA com outros trabalhos da literatura, analisamos a escalabilidade em termos de número de bits necessário para comunicação unicast e multicast. Na análise, variou-se o número de nós na rede, o grau dos nós e o número de hosts físicos para cada topologia. Na comunicação unicast, a RDNA reduziu em 4.5 vezes o tamanho do cabeçalho, comparada à proposta COXCast. Na comunicação multicast, um modelo de programação linear foi concebido para minimizar uma função polinomial. A RDNA reduziu em até 50% o tamanho do cabeçalho comparando com a mesma quantidade de membros por grupo. Como prova de conceito, dois protótipos foram implementados, um no ambiente emulado Mininet e outro na plataforma NetFPGA SUME. Os resultados mostraram que a RDNA alcança latência determinística no encaminhamento dos pacotes, 600 nanosegundos no tempo de comutação por elemento de núcleo, recuperação de falha ultra-rápida na ordem de microssegundos e sem variação de latência (jitter) no núcleo da rede.

Fermionized photons in an array of driven dissipative nonlinear cavities

We theoretically investigate the optical response of a one-dimensional array of strongly nonlinear optical microcavities. When the optical nonlinearity is much larger than both losses and inter-cavity tunnel coupling, the non-equilibrium steady state of the system is reminiscent of a strongly correlated Tonks-Girardeau gas of impenetrable bosons. Signatures of strong correlations are identified in the absorption spectrum of the system, as well as in the intensity correlations of the emitted light. Possible experimental implementations in state-of-the-art solid-state devices are discussed

Optical properties of atomic Mott insulators: from slow light to dynamical Casimir effects

We theoretically study the optical properties of a gas of ultracold, coherently dressed three-level atoms in a Mott insulator phase of an optical lattice. The vacuum state, the band dispersion and the absorption spectrum of the polariton field can be controlled in real time by varying the amplitude and the frequency of the dressing beam. In the weak dressing regime, the system shows unique ultra-slow light propagation properties without absorption. In the presence of a fast time modulation of the dressing amplitude, we predict a significant emission of photon pairs by parametric amplification of the polaritonic zero-point fluctuations. Quantitative considerations on the experimental observability of such a dynamical Casimir effect are presented for the most promising atomic species and level schemes

Il Progetto EnCoRe : una iniziativa sovranazionale per promuovere il concetto di sostenibilità del calcestruzzo e dei materiali cementizi

Environmental issues are getting more and more relevant in several fields of human activities and the building industry is fully concerned by these concerns. Recycled concrete aggregates (RCA) can be produced by existing concrete members resulting by either industrial processes (i.e., precast structures) or demolitions of existing structures as a whole. Moreover, waste resulting from industrial processes other than the building industry (i.e., production of steel, management of glass, powders resulting from other depuration processes) could be efficiently disposed as concrete aggregates or employed as reinforcement for Fiber-Reinforced Concretes (FRC). The use of natural fibres can also result into an environmentally-friendly and cost-effective solution, especially in developing countries, because of the local availability of raw materials. In order to promote the use of concretes with recycled and/or natural constituents as construction materials, the compatibility between the non conventional constituents and the concrete matrix have to be deeply investigated and correlated to the resulting mechanical and durability properties of the composite. This is the main goal of the EnCoRe Project (www.encore-fp7.unisa.it), a EU-funded initiative, whose activities and main findings will be summarized in this paper

The encore project: sustainable solutions for cementitious materials

Since concrete is the most widely utilized construction material, several solutions are currently being developed and investigated for enhancing the sustainability of cementitious materials. One of these solutions is based on producing Recycled Concrete Aggregates (RCA) from existing concrete members resulting by either industrial processes or demolitions of existing structures as a whole. Moreover, waste resulting from industrial processes other than the building construction (i.e., tire recycling, production of steel, powders resulting from other depuration processes) are also being considered as possible low-impact constituents for producing structural concrete and Fiber-Reinforced Cementitious Composites (FRCC). Furthermore, the use of natural fibers is another option for producing environmentally-friendly and cost-effective materials, depending on the local availability of raw materials. To promote the use of concretes partially composed of recycled constituents, their influence on the mechanical and durability performance of these concretes have to be deeply investigated and correlated. This was the main goal of the EnCoRe Project (www.encore-fp7.unisa.it), a EU-funded initiative, whose activities and main findings are summarized in this paper.The authors wish to acknowledge the support to the networking activities provided by "EnCoRe" project (www.encore-fp7.unisa.it) (FP7-PEOPLE-2011-IRSES, n. 295283) funded by the European Union as part of the 7th Framework Programme for Research and Innovation

In situ transmission electron microscopy study of electron beam-induced transformations in colloidal cesium lead halide perovskite nanocrystals

An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr3) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb2+ ions to Pb0. Subsequently Pb0 atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. The diffusion is facilitated by both high temperature and electron beam irradiation. The early stage Pb nanoparticles are epitaxially bound to the parent CsPbBr3 lattice, and evolve into nonepitaxially bound Pb crystals upon further irradiation, leading to local amorphization and consequent dismantling of the CsPbBr3 lattice. The comparison among CsPbBr3 nanocrystals with various shapes and sizes evidences that the damage is particularly pronounced at the corners and edges of the surface, due to a lower diffusion barrier for Pb0 on the surface than inside the crystal and the presence of a larger fraction of under-coordinated atoms

Observation of the Dynamical Casimir Effect in a Superconducting Circuit

One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. While initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences, for instance producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed if it might instead be possible to more directly observe the virtual particles that compose the quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. This effect was later named the dynamical Casimir effect (DCE). Using a superconducting circuit, we have observed the DCE for the first time. The circuit consists of a coplanar transmission line with an electrical length that can be changed at a few percent of the speed of light. The length is changed by modulating the inductance of a superconducting quantum interference device (SQUID) at high frequencies (~11 GHz). In addition to observing the creation of real photons, we observe two-mode squeezing of the emitted radiation, which is a signature of the quantum character of the generation process.Comment: 12 pages, 3 figure