Thermal conductivity and photoluminescence of light-emitting silicon nitride films

Silicon-rich and rare-earth-doped nitride materials are promising candidates for silicon-compatible photonic sources. This work investigates the thermal conductivity and photoluminescence (PL) of light emitting samples fabricated with a range of excess silicon concentrations and annealing temperatures using time-domain picosecond thermoreflectance and time-resolved photoluminescence. A direct correlation between the thermal conductivity and photoluminescence dynamics is demonstrated, as well as a significant reduction of thermal conductivity upon incorporation of erbium ions. These findings highlight the role of annealing and stoichiometry control in the optimization of light emitting microstructures suitable for the demonstration of efficient Si-compatible light sources based on the silicon nitride platform. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3682508

Gratings with an aperiodic basis: single-mode emission in multi-wavelength lasers

We propose a new class of gratings having multiple spatial frequencies. Their design relies on the use of small aperiodic grating sequences as unit cells whose repetition forms a superlattice. The superlattice provides well-defined Fourier components, while the choice of the unit cell structure enables the selection, modulation or suppression of certain Fourier components. Using these gratings to provide distributed feedback in mid-infrared quantum cascade lasers, we demonstrate simultaneous lasing on multiple well-defined and isolated longitudinal modes, each one having a sidemode suppression ratio of about 20 dB.United States. Air Force Office of Scientific Research (MURI 67N-1069926)Harvard University (Nanoscale Systems and Engineering Center)United States. Air Force (‘Deterministic Aperiodic Structures for Onchip Nanophotonic and Nanoplasmonic Device Applications’ under award no. FA9550-10-1- 0019)National Science Foundation (U.S.) (NSF CAREER Award ECCS-0846651)Georgia Institute of Technology (Steve W. Chaddick Endowed Chair of OptoElectronics

Long term behavior of two component back-fill grout mix used in full face mechanized tunneling

In mechanized tunneling the annular gap between the segmental lining and the surrounding soil caused by tunnel driving, must be backfilled almost instantaneously with an adequate grouting mortar when tunnelling in soils and particularly in urban area at low overburden. The main goal of this research is to investigate the grouting performance of two-component grout mix also when long curing time is considered

Essential amino acid supplementation in patients with severe COPD: a step towards home rehabilitation

Background. Pulmonary Rehabilitation ("Rehabilitation") can improve both lung function and quality of life in patients suffering from chronic obstructive pulmonary disease (COPD) even if only a very small proportion of patients have access to Rehabilitation. Supplementation of Essential Amino Acids (EAAs) might allow COPD patients to achieve some typical Rehabilitation outcomes such as a better physical performance and an improved health status. Methods. 88 COPD out-patients (GOLD class 3-4) with a body mass index (BMI) <23 Kg/m2 were randomised to receive EAAs (n=44) or placebo (n=44) for twelve weeks. Primary outcome measures were changes in both physical activities in daily life (measured by Sense Wear Armband in terms of mean steps walked in one week) and in quality of life (measured by the St George's Respiratory Questionnaire, SGRQ). Results. After 12 weeks, the physical performance was significantly increased vs baseline only in patients who received EAAs (1140.33 ± 524.69 and 638.68 ± 662.1 steps/day, respectively; p=0.02), being also the comparison vs the placebo group highly significant (p=0.003). Similarly, the SGRQ score improved significantly only in EAA patients (69.35 ± 9.51 vs baseline 72.04 ± 8.62; p<0.01), and changes were significantly different from those measured in the placebo group (p<0.001). Furthermore, when compared to those who received placebo, EAAs patients significantly increased their fat-free mass (p=0.04), muscle strength (p<0.01), saturation of oxygen (p=0.05), serum albumin (p<0.001), and also ameliorated their original cognitive dysfunction (p=0.02). Conclusions. Oral supplementation with EAAs contribute to improve the daily-life performance in domiciliary severe COPD patients who can not enter any Rehabilitation programme, together with their quality of life; nutritional and cognitive status, and muscle strength

Effect of erdosteine on the rate and duration of COPD exacerbations: the RESTORE study

Oxidative stress contributes to chronic obstructive pulmonary disease (COPD) exacerbations and antioxidants can decrease exacerbation rates, although we lack data about the effect of such drugs on exacerbation duration. The RESTORE (Reducing Exacerbations and Symptoms by Treatment with ORal Erdosteine in COPD) study was a prospective randomised, double-blind, placebo-controlled study, enrolling patients aged 40–80 years with Global Initiative for Chronic Obstructive Lung Disease stage II/III. Patients received erdosteine 300 mg twice daily or placebo added to usual COPD therapy for 12 months. The primary outcome was the number of acute exacerbations during the study. In the pre-specified intention-to-treat population of 445 patients (74% male; mean age 64.8 years, forced expiratory volume in 1 s 51.8% predicted) erdosteine reduced the exacerbation rate by 19.4% (0.91 versus. 1.13 exacerbations·patient−1·year−1 for erdosteine and placebo, respectively; p=0.01), due to an effect on mild events; the reduction in the rate of mild exacerbations was 57.1% (0.23 versus 0.54 exacerbations·patient−1·year−1 for erdosteine and placebo, respectively; p=0.002). No significant difference was observed in the rate of moderate and severe exacerbations (0.68 versus 0.59 exacerbations·patient−1·year−1 for erdosteine and placebo, respectively; p=0.054) despite a trend in favour of the comparison group. Erdosteine decreased the exacerbation duration irrespective of event severity by 24.6% (9.55 versus 12.63 days for erdosteine and placebo, respectively; p=0.023). Erdosteine significantly improved subject and physician subjective severity scores (p=0.022 and p=0.048, respectively), and reduced the use of reliever medication (p<0.001), but did not affect the St George's Respiratory Questionnaire score or the time to first exacerbation. In patients with COPD, erdosteine can reduce both the rate and duration of exacerbations. The percentage of patients with adverse events was similar in both the placebo and erdosteine treatment groups

Electrospun amplified fiber optics

A lot of research is focused on all-optical signal processing, aiming to obtain effective alternatives to existing data transmission platforms. Amplification of light in fiber optics, such as in Erbium-doped fiber amplifiers, is especially important for an efficient signal transmission. However, the complex fabrication methods, involving high-temperature processes performed in highly pure environment, slow down the fabrication and make amplified components expensive with respect to an ideal, high-throughput and room temperature production. Here, we report on near infrared polymer fiber amplifiers, working over a band of about 20 nm. The fibers are cheap, spun with a process entirely carried out at room temperature, and show amplified spontaneous emission with good gain coefficients as well as low optical losses (a few cm^-1). The amplification process is favoured by the high fiber quality and low self-absorption. The found performance metrics promise to be suitable for short-distance operation, and the large variety of commercially-available doping dyes might allow for effective multi-wavelength operation by electrospun amplified fiber optics.Comment: 27 pages, 8 figure

Novel hybrid organic/inorganic 2D quasiperiodic PC: from diffraction pattern to vertical light extraction

Recently, important efforts have been dedicated to the realization of a fascinating class of new photonic materials or metamaterials, known as photonic quasicrystals (PQCs), in which the lack of the translational symmetry is compensated by rotational symmetries not achievable by the conventional periodic crystals. As ever, more advanced functionality is demanded and one strategy is the introduction of non-linear and/or active functionality in photonic materials. In this view, core/shell nanorods (NRs) are a promising active material for light-emitting applications. In this article a two-dimensional (2D) hybrid a 2D octagonal PQC which consists of air rods in an organic/inorganic nanocomposite is proposed and experimentally demonstrated. The nanocomposite was prepared by incorporating CdSe/CdS core/shell NRs into a polymer matrix. The PQC was realized by electron beam lithography (EBL) technique. Scanning electron microscopy, far field diffraction and spectra measurements are used to characterize the experimental structure. The vertical extraction of the light, by the coupling of the modes guided by the PQC slab to the free radiation via Bragg scattering, consists of a narrow red emissions band at 690 nm with a full width at half-maximum (FWHM) of 21.5 nm. The original characteristics of hybrid materials based on polymers and colloidal NRs, able to combine the unique optical properties of the inorganic moiety with the processability of the host matrix, are extremely appealing in view of their technological impact on the development of new high performing optical devices such as organic light-emitting diodes, ultra-low threshold lasers, and non-linear devices