3D printing of optical materials: an investigation of the microscopic properties

3D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally doped with active molecular compounds and nanoparticles, is still limited by the poor uniformity of the printed structures. Both bulk inhomogeneities and surface roughness of the printed structures can negatively affect the propagation of light in 3D printed optical components. Here we investigate photopolymerization-based printing processes by laser confocal microscopy. The experimental method we developed allows the printing process to be investigated in-situ, with microscale spatial resolution, and in real-time. The modelling of the photo-polymerization kinetics allows the different polymerization regimes to be investigated and the influence of process variables to be rationalized. In addition, the origin of the factors limiting light propagation in printed materials are rationalized, with the aim of envisaging effective experimental strategies to improve optical properties of printed materials.Comment: 8 pages, 3 figure

The amazing graphene: an educational bridge connecting different Physics concepts

The purpose of this work is to present a learning workshop covering various physics concepts aimed at strengthening physics/engineering student understanding about the remarkable properties of two dimensional materials, graphene in particular. At the basis of this learning experience is the idea of blending and interconnecting separate pieces of knowledge already acquired by undergraduates in different courses and to help them visualize and link the concepts lying beyond separate chunks of information or equations. Graphene represents an appropriate unifying framework to achieve this task in view of its monatomic structure and various exotic processes peculiar to this and some other two dimensional crystals. We first discuss essential elements of group theory and their application to the symmetry properties of graphene with the aim of presenting to physics/electronic engineering undergraduates that in a system characterized by symmetry properties such as a crystal, the acquisition of the solutions of the Schr\uf6dinger equation is simpler and easier to visualize than when these properties are ignored. We have then selected and discussed some remarkable properties of graphene: the linear electron energy-momentum dispersion relation in proximity of some edge points of the Brillouin zone; the consequential massless Dirac behaviour of the electrons; their tunnelling behaviour and the related Klein paradox; the chiral behaviour of electrons and holes; the fractional quantum Hall effect in massless particles; and the quantum behaviour of correlated quasiparticles observable at macroscopic level. These arguments are presented in a context covering related pieces of knowledge about classical, quantum and relativistic mechanics. Finally, we mention current applications and possible future ones with the aim of providing students with an expertise that could be useful for further work experiences and scientific investigations regarding new materials, having farreaching implications in various fields such as basic physics, materials science and engineering applications

New insights into electron spin dynamics in the presence of correlated noise

The changes of the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which keeps into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examinating the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, for electric field amplitude lower than the Gunn field, the dephasing length shortens with the increasing of the noise intensity. Moreover, a nonmonotonic behavior of spin depolarization length with the noise correlation time is found, characterized by a maximum variation for values of noise correlation time comparable with the dephasing time. Instead, in high field conditions, we find that, critically depending on the noise correlation time, external fluctuations can positively affect the relaxation length. The influence of the inclusion of the electron-electron scattering mechanism is also shown and discussed.Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track Communications", 11 pages, 9 figure

Surface-enhanced Raman spectroscopy in 3D electrospun nanofiber mats coated with gold nanorods

Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments.Comment: 29 pages, 9 figures, 1 Tabl

Control of photon transport properties in nanocomposite nanowires

Active nanowires and nanofibers can be realized by the electric-field induced stretching of polymer solutions with sufficient molecular entanglements. The resulting nanomaterials are attracting an increasing attention in view of their application in a wide variety of fields, including optoelectronics, photonics, energy harvesting, nanoelectronics, and microelectromechanical systems. Realizing nanocomposite nanofibers is especially interesting in this respect. In particular, methods suitable for embedding inorganic nanocrystals in electrified jets and then in active fiber systems allow for controlling light-scattering and refractive index properties in the realized fibrous materials. We here report on the design, realization, and morphological and spectroscopic characterization of new species of active, composite nanowires and nanofibers for nanophotonics. We focus on the properties of light-confinement and photon transport along the nanowire longitudinal axis, and on how these depend on nanoparticle incorporation. Optical losses mechanisms and their influence on device design and performances are also presented and discussed.Comment: 7 pages, 3 figures, 29 references. Invited contribution. Copyright (2016) Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibite

INCIDENCE AND PREVENTION OF DEEP VEIN THROMBOSIS IN RESTRAINED PSYCHIATRIC PATIENTS

Background: Although physical restraint is still used in psychiatric inpatient settings, it sometimes causes serious side effects, including deep vein thrombosis (DVT) and resulting pulmonary embolism. The aim of this study was to review the literature investigating the incidence of the DVT in restrained psychiatric patients, to identify the risk factors of this condition and the effectiveness of routine prophylaxis. Subjects and methods: Studies investigating associations between deep vein thrombosis and restrained psychiatric patients were searched in the Pubmed database. More than 700 articles were sorted independently by two of the authors using predefined criteria. Only research articles, reviews and meta-analyses were selected for this review. Results: 5 articles published between 2010 and 2016 were selected. Although antipsychotics and restrain are known to be thrombogenenic, in all retrospective studies, with anticoagulant prophylaxis for those restrained for more than 12 or 24 h, incidence of DVT in restrained psychiatric patients was almost not existent. Controversially, in a comparative study by Ishida, although deep sedation and physical comorbidities were associated with the occurrence of DVT, not using of anticoagulants was not associated with any increased incidence of DVT. DVT may be overlooked because psychiatric patients are often unaware of leg symptoms because of their psychiatric disease and induced sedation. Furthermore most DVT, in particular distal DVT are asymptomatic. When screened and assessed with more appropriate methods such as plasma D Dimer and ultrasound scanning the incidence of DVT reaches 11.6%. Conclusion: The incidence of DVT in restrained psychiatric patients was not low in spite of prophylaxis. These findings emphasize the importance of regular screening of and thorough assessments of DVT, especially in restrained psychiatric patients

INCIDENCE AND PREVENTION OF DEEP VEIN THROMBOSIS IN RESTRAINED PSYCHIATRIC PATIENTS

Background: Although physical restraint is still used in psychiatric inpatient settings, it sometimes causes serious side effects, including deep vein thrombosis (DVT) and resulting pulmonary embolism. The aim of this study was to review the literature investigating the incidence of the DVT in restrained psychiatric patients, to identify the risk factors of this condition and the effectiveness of routine prophylaxis. Subjects and methods: Studies investigating associations between deep vein thrombosis and restrained psychiatric patients were searched in the Pubmed database. More than 700 articles were sorted independently by two of the authors using predefined criteria. Only research articles, reviews and meta-analyses were selected for this review. Results: 5 articles published between 2010 and 2016 were selected. Although antipsychotics and restrain are known to be thrombogenenic, in all retrospective studies, with anticoagulant prophylaxis for those restrained for more than 12 or 24 h, incidence of DVT in restrained psychiatric patients was almost not existent. Controversially, in a comparative study by Ishida, although deep sedation and physical comorbidities were associated with the occurrence of DVT, not using of anticoagulants was not associated with any increased incidence of DVT. DVT may be overlooked because psychiatric patients are often unaware of leg symptoms because of their psychiatric disease and induced sedation. Furthermore most DVT, in particular distal DVT are asymptomatic. When screened and assessed with more appropriate methods such as plasma D Dimer and ultrasound scanning the incidence of DVT reaches 11.6%. Conclusion: The incidence of DVT in restrained psychiatric patients was not low in spite of prophylaxis. These findings emphasize the importance of regular screening of and thorough assessments of DVT, especially in restrained psychiatric patients

Noise influence on electron dynamics in semiconductors driven by a periodic electric field

Studies about the constructive aspects of noise and fluctuations in different non-linear systems have shown that the addition of external noise to systems with an intrinsic noise may result in a less noisy response. Recently, the possibility to reduce the diffusion noise in semiconductor bulk materials by adding a random fluctuating contribution to the driving static electric field has been tested. The present work extends the previous theories by considering the noise-induced effects on the electron transport dynamics in low-doped n-type GaAs samples driven by a high-frequency periodic electric field (cyclostationary conditions). By means of Monte Carlo simulations, we calculate the changes in the spectral density of the electron velocity fluctuations caused by the addition of an external correlated noise source. The results reported in this paper confirm that, under specific conditions, the presence of a fluctuating component added to an oscillating electric field can reduce the total noise power. Furthermore, we find a nonlinear behaviour of the spectral density with the noise intensity. Our study reveals that, critically depending on the external noise correlation time, the dynamical response of electrons driven by a periodic electric field receives a benefit by the constructive interplay between the fluctuating field and the intrinsic noise of the system.Comment: 9 pages, 4 figures, to appear in J. Stat. Mechanics: Theory and Experim., 200

Electrically controlled white laser emission through liquid crystal/polymer multiphases

White lasers are becoming increasingly relevant in various fields since they exhibit unprecedented properties in terms of beam brightness and intensity modulation. Here we introduce a white laser based on a polymer matrix encompassing liquid crystals and multiple organic chromophores in a multifunctional phase-separation system. The separation of the hydrophilic matrix and the hydrophobic liquid crystals leads to the formation of a complex optically active layer, featuring lasing emission tuneable from blue to red. White laser emission is found with an optical excitation threshold of approximately 12 mJ/cm2. Importantly, an external electric field can be used to control the device emission intensity. White lasers with low-voltage (≤10 V) controllable emission might pave the way for a new generation of broadband light sources for analytical, computational, and communication applications

Nonlinear relaxation phenomena in metastable condensed matter systems

Nonlinear relaxation phenomena in three different systems of condensed matter are investigated. (i) First, the phase dynamics in Josephson junctions is analyzed. Specifically, a superconductor-graphene-superconductor (SGS) system exhibits quantum metastable states, and the average escape time from these metastable states in the presence of Gaussian and correlated fluctuations is calculated, accounting for variations in the the noise source intensity and the bias frequency. Moreover, the transient dynamics of a long-overlap Josephson junction (JJ) subject to thermal fluctuations and non-Gaussian noise sources is investigated. Noise induced phenomena are observed, such as the noise enhanced stability and the stochastic resonant activation. (ii) Second, the electron spin relaxation process in a n-type GaAs bulk driven by a fluctuating electric field is investigated. In particular, by using a Monte Carlo approach, we study the influence of a random telegraph noise on the spin polarized transport. Our findings show the possibility to raise the spin relaxation length by increasing the amplitude of the external fluctuations. Moreover, we find that, crucially, depending on the value of the external field strength, the electron spin depolarization length versus the noise correlation time increases up to a plateau. (iii) Finally, the stabilization of quantum metastable states by dissipation is presented. Normally, quantum fluctuations enhance the escape from metastable states in the presence of dissipation. We show that dissipation can enhance the stability of a quantum metastable system, consisting of a particle moving in a strongly asymmetric double well potential, interacting with a thermal bath. We find that the escape time from the metastable region has a nonmonotonic behavior versus the system- bath coupling and the temperature, producing a stabilizing effect