Approximating Spectral Impact of Structural Perturbations in Large Networks

Determining the effect of structural perturbations on the eigenvalue spectra of networks is an important problem because the spectra characterize not only their topological structures, but also their dynamical behavior, such as synchronization and cascading processes on networks. Here we develop a theory for estimating the change of the largest eigenvalue of the adjacency matrix or the extreme eigenvalues of the graph Laplacian when small but arbitrary set of links are added or removed from the network. We demonstrate the effectiveness of our approximation schemes using both real and artificial networks, showing in particular that we can accurately obtain the spectral ranking of small subgraphs. We also propose a local iterative scheme which computes the relative ranking of a subgraph using only the connectivity information of its neighbors within a few links. Our results may not only contribute to our theoretical understanding of dynamical processes on networks, but also lead to practical applications in ranking subgraphs of real complex networks.Comment: 9 pages, 3 figures, 2 table

High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers

In recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated

High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers

In recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated

Optical Quality Resorbable Calcium-Phosphate Glasses for Biophotonic Applications

Recently developed calcium-phosphate glass formulations are proposed in this chapter as a new class of materials for biomedical optics and photonics. The glasses have been designed and carefully prepared in our laboratory to be dissolvable in biological fluids while being optically transparent, mechanically reliable both in dry and humid environments, and suitable for both preform extrusion and fiber drawing. Optical fibers have been drawn from these glasses using our custom-made induction heated drawing tower and showed attenuation loss values from one to two orders of magnitude lower than the counterpart polymeric-based bioresorbable devices reported in literature. In addition, the optical fibers have been implanted in living rats for several weeks and no clinical signs of any adverse effect have been found. Results on the inscription and characterization of different types of fiber Bragg grating-based optical filters will be also shown, together with the demonstration of the suitability of the above-mentioned bioresorbable optical fibers for time-domain diffuse optical spectroscopy

TeO2-ZnO-La2O3 glass composition for mid infrared wavelengths generation and transmission in optical fibers

Numerous applications in the Mid InfraRed (Mid IR) wavelength region still require basic optical components such as sources and optical fibers as transmission medium. Thanks to its mid IR transparency and nonlinearity, tellurite glass allows for developing both these types of components. However, practical applications require materials able to handle high optical intensity through enhanced material damage threshold. We report on the synthesis of a tellurite glass in the TeO2-ZnO-La2O3 (TZL) system which presents enhanced thermo mechanical properties with respect to typical tellurite glass compositions. We measured for the TZL composition a glass transition of 626 K, hence 70 K higher than the glass transition temperature of “standard” TZN compositions. The coefficient of thermal expansion was measured to be 138.10-6/K as compared to typical value of 180.10-6/K for TZN glass. We manufactured two types of fibers to assess the prospect for achieving high average power SC sources and Mid IR transmission in TZL glass fibers. First, a high Numerical Aperture (NA) aperture fiber was developed through standard rod in tube technique, where the cladding glass tube was manufactured by extrusion. The 50 μm core fiber presents an optical attenuation value of 0.26 dB/m at 1.55 μm. As an intermediate step towards the fabrication of an antiresonant hollow core fiber for high power transmission, we manufactured a preform and drew it into a cane. A TZL glass tube, 120 mm long and 9 mm/12 mm of inner/outer diameters (ID/OD) was manufactured via rotational casting technique. This latter tube was drawn into a tube of 2 mm in diameter which was cut into sections 130 mm long. Seven of those were stacked in another tellurite glass tube 6.5 mm/12 mm of ID/OD diameters, respectively. This preform was then drawn into a microstructured cane 1.6 mm in diameter which features tubular structures periodically arranged and of uniform thickness

Assessment of a desiccant cooling system in a traditional and innovative nanofluid HVAC system

The topic of energy saving is a constant in everyday life, and it is widespread all over the world. Space heating using solar panels is the most used renewable source of energy, but the application of solar energy for cooling the fluids used for refrigeration is growing very fast. Among the techniques used for refrigeration, this work focused on Desiccant Cooling. In particular, with the use of dynamic simulation software, it was possible to study the heat supplied and the energy consumption of a Heating Ventilation Air Conditioning (HVAC) system of a university building and to compare consumption with those of a Desiccant Cooling system applied to the same building. Four different cases were simulated: two related to the HVAC system, one of which operates with water and glycol and the other one with nanofluid, and the other ones to the Desiccant Cooling system with both types of fluids mentioned above. Keeping the same energy demand of the building in all the simulations, it was found that in summer the Desiccant Cooling system had higher performance than the traditional HVAC system and that the use of the nanofluid in both types of conditioning systems further increased the performance of 21%. Simulations were carried out using TRNSYS software

A multistationary loop model of ALS unveils critical molecular interactions involving mitochondria and glucose metabolism

Amyotrophic lateral sclerosis (ALS) is a poor-prognosis disease with puzzling pathogenesis and inconclusive treatments. We develop a mathematical model of ALS based on a system of interactive feedback loops, focusing on the mutant SOD1G93A mouse. Misfolded mutant SOD1 aggregates in motor neuron (MN) mitochondria and triggers a first loop characterized by oxidative phosphorylation impairment, AMP kinase over-activation, 6-phosphofructo-2-kinase (PFK3) rise, glucose metabolism shift from pentose phosphate pathway (PPP) to glycolysis, cell redox unbalance, and further worsening of mitochondrial dysfunction. Oxidative stress then triggers a second loop, involving the excitotoxic glutamatergic cascade, with cytosolic Ca2+ overload, increase of PFK3 expression, and further metabolic shift from PPP to glycolysis. Finally, cytosolic Ca2+ rise is also detrimental to mitochondria and oxidative phosphorylation, thus closing a third loop. These three loops are overlapped and positive (including an even number of inhibitory steps), hence they form a candidate multistationary (bistable) system. To describe the system dynamics, we model the interactions among the functional agents with differential equations. The system turns out to admit two stable equilibria: the healthy state, with high oxidative phosphorylation and preferential PPP, and the pathological state, with AMP kinase activation, PFK3 over expression, oxidative stress, excitotoxicity and MN degeneration. We demonstrate that the loop system is monotone: all functional agents consistently act toward the healthy or pathological condition, depending on low or high mutant SOD1 input. We also highlight that molecular interactions involving PFK3 are crucial, as their deletion disrupts the system\u2019s bistability leading to a single healthy equilibrium point. Hence, our mathematical model unveils that promising ALS management strategies should be targeted to mechanisms that keep low PFK3 expression and activity within MNs

Phosphate glass fibrous scaffolds: tailoring of the properties and improvement of the bioactivity through the incorporation of mesoporous glasses

Introduction. Synthetic bone scaffolds are proposed as an alternative to the use of bone grafting technique for bone regeneration. Porous scaffold obtained from glass fibres randomly arranged into a mould shows an interconnected porosity generated by the free space between fibres and they do not need of any further material or processing step before sintering. In this work, a resorbable phosphate glass was selected for the fibre drawing and bioactive mesoporous glasses with different morphology and size were incorporated into the fibrous scaffold to combine the resorption property of the fibres with the bioactivity of the mesoporous powders. Materials and methods. Fibres of a TiO2-containing phosphate glass (TiPS2.5) were fabricated following the preform drawing approach as described elsewhere [1]. A dense silica-based bioactive glass (CEL2) [2] was produced by melt quenching as reference sample. Spherical micro-sized mesoporous glass based on SiO2-CaO system (SD_MBG) was produced by an aerosol-assisted spray-drying technique [3]. Cu-containing (85SiO2-13CaO-2CuO, % mol, referred as Cu_BGn2%) mesoporous glass nanoparticles were synthetized by an ultra-sound assisted sol-gel method to impart antibacterial properties. To fabricate the fibrous scaffolds, the selected powder and phosphate glass fibres, cut at precise length, were placed in a beaker containing 2 ml of ethanol. After ethanol evaporation, the powder/fibre mixture was randomly placed inside a zirconia cylindrical mould [4]. After the thermal treatment, the scaffolds were analyzed through micro-CT in order to investigate their inner structure. Furthermore, their ability to form hydroxyapatite was studied by soaking them in a simulated body fluid (SBF). The scaffold morphology before and after immersion in SBF was studied by FESEM. Results and discussion. FESEM micrographs show that CEL2 are not well incorporated into the fibre surface. On the contrary, SD-MBG (Figure 1.a, Figure 1.b and Figure 1.d) and Cu_BGn2% particles homogeneously cover the whole surface. Micro-CT analysis did not reveal the presence of powder agglomerates for all the observed scaffolds and showed a homogeneous porosity of 58 vol.% for CEL2/fibre scaffold, 53 vol.% for SD_MBG/scaffold (Figure 1.c) and 33% for Cu_BGn2%/scaffold. In CEL2/fibre scaffolds, glass particles were removed during soaking in SBF, leaving some pits on the fibre surface: FESEM analysis revealed few particles still anchored to the scaffold surface after 7 days. On the contrary, after 7 days in SBF, SD-MBG and Cu_BGn2% particles were clearly visible on the surface of the scaffolds and after 1 day of soaking in SBF, they appeared (Figure 2) fully covered with a HA layer, showing the typical "cauliflower-like" morphology. Conclusion. The incorporation of mesoporous bioactive glass powder in the phosphate glass fibrous scaffold resulted to be a very interesting strategy to impart multifunctional properties to the scaffold. These promising results encourage further investigation in order to fully exploit the ability of mesoporous particles to act as a system for smart release of therapeutic ions and drugs

Multifunctional bioresorbable phosphate glass optical fibers for theranostics

We report on the design and development of microstructured phosphate glass optical fibers for minimally invasive diagnosis and therapy. We discuss preliminary results of fiber drawing and characterization