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Abstract: In this work, we study the effect of additional InAlAs or GaAs barriers to enhance the confinement of carriers into quantum dots (QDs) in metamorphic QD nanostructures for long-wavelength light-emission. Such barriers are used in order to compensate for the reduction in band discontinuities that occurs when using InGaAs confining layers (CL) to red-shift the emission towards the spectral windows of optoelectronic interest; as a side effect, such a reduction causes a decrease of carrier confinement and then an inefficient emission at room temperature. By photoluminescence characterization of metamorphic QD structures grown by molecular beam epitaxy, we study the effect of barriers with different compositions, thicknesses and positions relative to QDs on the QD emission and the activation energy for confined carriers'' thermal escape; our experimental data clearly show that the insertion of additional barriers results in larger emission efficiencies at room temperature and in blue-shifts of emission wavelengths. To counterbalance the blue-shift resulting from the use of these additional barriers, we introduce a red-shift by using the QD strain engineering approach, based on the reduction of QD strain, deriving from the decrease of the QD-CL mismatch; the combined use of QD strain engineering and enhanced barriers to confine carriers into QDs allows us to obtain room temperature emission up to 1.46 μm. These findings indicate that QD strain engineering with the use of additional barriers is a viable approach to achieve efficient room temperature emission from QD structures in the long wavelength spectral windows for telecom application. [Copyright &y& Elsevier]

Ocular allergy ( OA) includes a group of common and less frequent hypersensitivity disorders frequently misdiagnosed and not properly managed. The diagnosis of OA is usually based on clinical history and signs and symptoms, with the support of in vivo and in vitro tests when identification of the specific allergen is required. To date, no specific test is available for the diagnosis of the whole spectrum of the different forms of OA. The lack of recommendations on diagnosis of OA is considered a medical need not only for allergists but also for ophthalmologists. This position paper aims to provide a comprehensive overview of the currently available tools for diagnosing OA to promote a common nomenclature and procedures to be used by different specialists. Questionnaires, sign and symptom grading scales, tests, and potential biomarkers for OA are reviewed. We also identified several unmet needs in the diagnostic tools to generate interest, increase understanding, and inspire further investigations. Tools, recommendations, and algorithms for the diagnosis of OA are proposed for use by both allergists and ophthalmologists. Several unmet needs in the diagnostic tools should be further improved by specific clinical research in OA. [ABSTRACT FROM AUTHOR]

Conjunctival allergen provocation test ( CAPT) reproduces the events occurring by instilling an allergen on the ocular surface. This paper is the compilation of a task force focussed on practical aspects of this technique based on the analysis of 131 papers. Main mechanisms involved are reviewed. Indications are diagnosing the allergen(s)-triggering symptoms in IgE-mediated ocular allergy in seasonal, acute or perennial forms of allergic conjunctivitis, especially when the relevance of the allergen is not obvious or in polysensitized patients. Contraindications are limited to ongoing systemic severe pathology, asthma and eye diseases. CAPT should be delayed if receiving systemic steroids or antihistamines. Local treatment should be interrupted according to the half-life of each drug. Prerequisites are as follows: obtaining informed consent; evidencing of an allergen by skin prick tests and/or serum-specific IgE dosages; being able to deal with an unlikely event such as acute asthma exacerbation, urticaria or anaphylaxis, or an exacerbation of allergic conjunctivitis. Allergen extracts should be diluted locally prior to administration. Positive criteria are based on itching or quoted according to a composite score. An alternative scoring is based on itching. CAPT remains underused in daily practice, although it is a safe and simple procedure which can provide valuable clinical information. [ABSTRACT FROM AUTHOR]

Abstract: This study deals with the preliminary development of a powder-free process called calcined resin microsphere pelletization (CRMP) used for the fabrication of metallic oxide pellets. This dustless process could be used for the fabrication of mixed U1−y Am y O2±x pellets dedicated to the transmutation of Am in fast neutron reactors. In this study, porous CeO2 microspheres, used as a surrogate of AmO2, were obtained after mineralization of cerium loaded ion exchange resin beads. These millimetric oxide microspheres were die-pressed into pellets which were then sintered under air to form ceramic pellets. Their densities approached 95% of theoretical density of CeO2 and a homogeneous microstructure was obtained by using optimized microspheres. The influence of calcination parameters on the characteristics of microspheres and on the properties of sintered pellets is discussed. [Copyright &y& Elsevier]

Abstract: We have investigated a 25.75-year old leaching experiment to improve our understanding of the mechanisms controlling glass dissolution in geological disposal conditions. A SON68 glass block was leached in slowly renewed synthetic groundwater (at 90°C, 100bar) in contact with some pieces of granite and Ni–Cr–Mo alloy as environmental storage materials. One hundred and sixty-three samplings were carried out over the entire duration of the experiment and were used to calculate the mean thickness of the altered glass (28 (±9) μm) and the glass dissolution rate. After few months, the rate remained very constant at 6×10−3 gm−2 d−1 which is about 20times higher than the residual rate measured in a batch reactor at the same temperature. At the end of the experiment, mainly SEM analyses were performed on the entire glass block. Surprisingly, the glass alteration layer has neither a homogeneous thickness, nor a homogeneous morphology. The location of the sampling valve (at half height of the glass block) seems to divide the glass block into two parts. In the upper half (above the sampling valve), the general morphology of the alteration layer consists in a relatively simple and uniform gel and some secondary phases which are rare-earth phosphates. The mean measured thickness of this alteration layer is 6.7 (±0.3) μm. However, in the lower half of the glass block, the gel is globally larger and frequently contains rounded shapes which are rare-earth phosphates. This section is edged by secondary phases bearing Mg, Na, Zn and Ni. The mean measured thickness is 81.3 (±1.1) μm in the lower half. In this experiment, the flow rate which leads to the hydrodynamic transport of the soluble species must be a key factor for the local glass alteration process. We have also shown that this unexpected behavior is likely due to heterogeneities of the chemistry of the solution. This conclusion is supported by the behavior of Mg. This element, supplied by the inlet solution, precipitates with Si and forms clay minerals and therefore weakens the passivating properties of the gel. Mg-rich clay minerals are only observed in the lower half of the glass block. Further investigations are necessary to better understand the coupling between the hydrodynamics and chemistry in this experiment. However, based on this study, we can conclude that glass in disposal should be very sensitive to the water renewal near the glass surface. [Copyright &y& Elsevier]

Abstract: The light-emission energy E of self-assembled semiconductor quantum dots (QDs) is determined by the complex interplay of parameters such as compositions of QDs and confining layers (CLs), strain of QDs (imposed by the QD mismatch to CLs) and sizes and shapes of QDs. In order to have RT emission in the 1.55 μm photonic window from InAs QDs, the QD–CL lattice mismatch should be in the 4–5% range, values much lower than that of pseudomorphic InAs on GaAs (7%). We show that by: i) growing InAs QDs on virtual substrates consisting of metamorphic InGaAs buffers on GaAs and ii) using the thickness-dependent partial relaxation of buffers (acting also as lower CLs, LCLs) and suitable InGaAs compositions, the QD–CL mismatch can be tuned in the 5–7% range. Our experimental results on MBE-grown metamorphic InAs/In x Ga1−x As QD structures show that for x and LCL thicknesses d in the 0.09–0.35 and 20 nm–1000 nm ranges, respectively, the band-gap of the QD material and the band-discontinuities that confine carriers are such that the RT emission wavelengths range from 1.3 μm up to values that may exceed 1.55 μm. By using x and d as two degrees-of-freedom, not only that E can be selected but also the barrier energy for confined carriers'' thermal escape can be maximised, in order to achieve efficient emission at RT. [Copyright &y& Elsevier]

We designed and prepared by molecular beam epitaxy strain-engineered InAs/InGaAs/GaAs quantum dot (QD) nanostructures where we separately controlled: (i) the mismatch f between QDs and confining layers (CLs), and, then, the QD strain, by changing the thickness of a partially relaxed InGaAs lower CL and (ii) the CL composition x. The appropriate values of f and x to tune the emission energies at wavelengths in the 1.3–1.55 μm range were calculated by means of a simple model. Comparing model calculations and activation energies of photoluminescence quenching, we also concluded that quenching is due to both intrinsic and extrinsic processes; we show that the structures can be designed so as to maximize the activation energy of the intrinsic process, while keeping the emission energy at the intended value in the 1.3–1.55 μm range. [ABSTRACT FROM AUTHOR]

We prepared by molecular-beam epitaxy and studied structures of InAs quantum dots embedded in In[sub x]Ga[sub 1-x]As confining layers. The structures were designed so that the strain of quantum dots could be controlled independently of In composition of confining layers. In such a way, we single out the effect of strain in quantum dots on the energy of photoluminescence emission. We show that strain can be effectively used to tune the emission energy of quantum dots, and that room-temperature emission at 1.3 μm can be obtained. Our results suggest that by quantum-dot strain engineering, it will be possible to extend emission wavelength beyond 1.55 μm. [ABSTRACT FROM AUTHOR]

We present a study on low-temperature photoluminescence (PL) of Si-doped Ga1-xAlxAs (n ∼ 1×1017 cm-3, 0.2≤x≤ 0.5) grown by molecular beam epitaxy (MBE) either in the presence and in the absence of a hydrogen backpressure and/or post-growth hydrogenated by exposure to a hydrogen plasma; we show that GaAlAs grown with hydrogen has a PL efficiency higher than that of material grown without hydrogen by a factor of up to 20; even more interestingly, the relative enhancement of transitions related to excitons and to shallow donors and acceptors is so large that the two kinds of PL spectra are qualitatively different. On the contrary, independently on whether material grown without hydrogen is post-growth hydrogenated, the spectral features of PL spectra are dominated by transitions involving relatively deep donors and/or acceptors. Our results suggest that the two treatments with hydrogen act on deep levels of different origin. [ABSTRACT FROM AUTHOR]