Riboflavin photodegradation and photosensitizing effects are highly dependent on oxygen and ascorbate concentrations

Riboflavin (RF) is a normal component of the eye lens which triggers a strong photosensitizing activity when exposed to light. Upon irradiation with short wavelength radiations below 400 nm, RF-photosensitized damage may occur. However, vitamin C is present at high concentrations in the normal lens and plays an important role in inhibiting these photosensitization processes. An in vitro simple model was used with the objective of understanding better the relationships between vitamin C and oxygen concentrations on the mechanisms of RF-mediated photodegradation of tryptophan (Trp), a target particularly sensitive to photo-oxidation. Under nitrogen, the RF decomposition reached its maximal value, and vitamin C and Trp photo-oxidation was negligible. When increasing oxygen pressure, RF photodegradation dropped and vitamin C photo-oxidation strongly increased and was maximal at 100% O2. RF-induced photodegradation of Trp first increased with oxygen concentration, up to 40 microM O2, and then decreased. RF and Trp degradation were significantly protected by vitamin C so that no more than 20% of the substrates concentration were oxidized in the presence of vitamin C higher than 0.8 mM. From our results we conclude that in the specific conditions of the normal lens, the high vitamin C concentration (2 mM) is compatible with the UVA radiation hazard, despite the presence of RF. However, if lenticular vitamin C decreases below 0.8 mM, photodegradation of RF may occur and Trp may therefore be photo-oxidized by a Type-I mechanism.     

Implication of ultraviolet light in the etiology of uveal melanoma: A review

Uveal melanoma is the most frequent intraocular cancer and the second most common form of melanoma. It metastasizes in half of the patients and the prognostic is poor. Although ultraviolet (UV) radiation is a proven risk factor for skin melanoma, the role of UV light in the etiology of uveal melanoma is still contradictory. We have compared epidemiological and genetic evidences of the potential role of UV radiation in uveal melanoma with data on cutaneous melanoma. Even though frequently mutated genes in skin melanoma (e.g. BRAF) differ from those found in uveal melanoma (i.e. GNAQ, GNA11), their mutation pattern bears strong similarities. Furthermore, we provide new results showing that RAC1, a gene recently found harboring UV‐hallmark mutation in skin melanoma, is also mutated in uveal melanoma. This article aims to review the work done in the last decades to understand the etiology of uveal melanoma and discuss new avenues, which shed some light on the potential role of UV exposure in uveal melanoma.     

Numerical Simulation of Darcy and Forchheimer Force Distribution in a HBC Fuse

We present the breaking of a short-circuit current in a HBC fuse simulation based on an isentropic non-stationary model in a porous medium for a one dimensional geometry. The fluid flow is affected by the nature of the gas and by the morphology of the silica sand. To model the gas–silica sand interaction, we introduce two classical laws: the Darcy's law due to the viscous interaction and the Forchheimer's law due to the inertial force. Numerical simulations with realistic physical parameters have been performed using a finite volume scheme with a fractional step technique. We show the evolution of Darcy and Forchheimer forces during time and according to the position in the fuse. We place in prominent position the fact that either force is predominant in the fuse according to the time and the position which justifies a numerical treatment to cover all the situations.     

Impact of chromatic dispersion and group delay ripple on self-phase modulation based optical regenerators

We demonstrate that chromatic dispersion and group delay ripple limit the performance of all-optical regeneration based on self-phase modulation. The level of degradation depends in detail on the type of phase distortions introduced. The regenerator performance is measured using the optical signal to noise ratio (OSNR) margin provided to the system for a given bit error ratio. The addition of chromatic dispersion and group delay ripple induces a significant reduction in this OSNR margin.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.