Polarization properties in the transition from below to above lasing threshold in broad-area vertical-cavity surface-emitting lasers

For highly divergent emission of broad-area vertical-cavity surface-emitting lasers (VCSELs) a rotation of the polarization direction by up to 90 degrees occurs when the pump rate approaches the lasing threshold. Well below threshold the polarization is parallel to the direction of the transverse wave vector and is determined by the transmissive properties of the Bragg reflectors that form the cavity mirrors. In contrast, near-threshold and above-threshold emission is more affected by the reflective properties of the reflectors and is predominantly perpendicular to the direction of transverse wave vectors. Two qualitatively different types of polarization transition are demonstrated: an abrupt transition, where the light polarization vanishes at the point of the transition, and a smooth one, where it is significantly nonzero during the transition

Transverse mode dynamics in vertical cavity surface emitting lasers excited by fast electrical pulses

Includes bibliographical references (page 592).We report measurements of the transient multimode dynamics of vertical cavity surface emittin glasers excited by short (100-200 ps rise times, 1 ns duration) electrical pulses. Fast changes on the spatial distribution of the output power and strong mode competition are observed. Numerical simulations show that the observed dynamics are due to the partial overlap of the different transverse modes through spatial hole burning

Study of a novel type of the optical modes in VCSELs

We study novel side-emitting modes in VCSEL microcavities. These modes correspond to π-shaped propagation along the mesa diameter, reflection from angled mesa walls and bottom Bragg reflector. We believe this study of π-modes is important for optimization of VCSEL design for improvement of efficiency

Hydrophilic antioxidant compounds in orange juice from different fruit cultivars: Composition and antioxidant activity evaluated by chemical and cellular based (Saccharomyces cerevisiae) assays

Antioxidant capacity was evaluated by a cellular model (Saccharomyces cerevisiae) and chemical methods (FRAP, TEAC and total phenols by Folin-Ciocalteu assay) in the hydrophilic fraction (phenolic compounds and ascorbic acid) of orange juices (OJs) from six varieties (Midknight, Delta Seedless, Rohde Red, Seedless, Early and clone Sambiasi), harvested in two seasons. The contents of phenolic compounds and ascorbic acid analyzed, respectively, by UPLC and HPLC were 370.04 76.97 mg/L and 52.05 6.69 mg/100 mL. Variety and season significantly influenced (p < 0.05) composition and antioxidant capacity. TEAC and FRAP values correlated well with individual hydrophilic compounds (R2 > 0.991) but no correlation with cellular assay was observed. An increase in survival rates between 23% and 38% was obtained, excepting for two varieties that showed no activity (Rohde Red and Seedless). Narirutin, naringin-d, ferulic acid-d2, didymin, neoeriocitrin and sinapic acid hexose and caffeic acid-d1 were the phenolic compounds which contributed to survival rates (R2 = 0.979, p < 0.01

Zyxin Links Fat Signaling to the Hippo Pathway

Using genetic and molecular analyses, the authors identify Zyx as a positive regulator of Hippo signaling and characterize its role within the pathway

The (n, gamma) campaigns at EXILL

At the PF1B cold neutron beam line at the Institut Laue Langevin, the EXILL array consisting of EXOGAM, GASP and ILL-Clover detectors was used to perform (n, gamma) measurements at very high coincidence rates. About ten different reactions were measured in autumn 2012 using a highly collimated cold neutron beam. In spring 2013, the EXOGAM array was combined with 16 LaBr3(Ce) scintillators in the EXILL&FATIMA campaign for the measurement of lifetimes using the generalised centroid difference method. We report on the properties of the set-ups and present first results from both campaigns

Bak Conformational Changes Induced by Ligand Binding: Insight into BH3 Domain Binding and Bak Homo-Oligomerization

Recently we reported that the BH3-only proteins Bim and Noxa bind tightly but transiently to the BH3-binding groove of Bak to initiate Bak homo-oligomerization. However, it is unclear how such tight binding can induce Bak homo-oligomerization. Here we report the ligand-induced Bak conformational changes observed in 3D models of Noxa·Bak and Bim·Bak refined by molecular dynamics simulations. In particular, upon binding to the BH3-binding groove, Bim and Noxa induce a large conformational change of the loop between helices 1 and 2 and in turn partially expose a remote groove between helices 1 and 6 in Bak. These observations, coupled with the reported experimental data, suggest formation of a pore-forming Bak octamer, in which the BH3-binding groove is at the interface on one side of each monomer and the groove between helices 1 and 6 is at the interface on the opposite side, initiated by ligand binding to the BH3-binding groove

Mechanisms and mechanics of cell competition in epithelia

When fast-growing cells are confronted with slow-growing cells in a mosaic tissue, the slow-growing cells are often progressively eliminated by apoptosis through a process known as cell competition. The underlying signalling pathways remain unknown, but recent findings have shown that cell crowding within an epithelium leads to the eviction of cells from the epithelial sheet. This suggests that mechanical forces could contribute to cell elimination during cell competition