Tuning the wavelength of lasing emission in organic semiconducting laser by the orientation of liquid crystalline conjugated polymer

We report the optical pumping of one-dimensional distributed feedback (DFB) conjugated polymer devices using a uniaxially aligned liquid crystalline polymer, poly(9,9-dioctylfluorene). We can independently select the alignment direction (via a rubbed polyimide layer) and the DFB structure (via nanoimprinting). In comparison with unaligned film, we show that lasing threshold is substantially reduced when absorption is parallel to the aligned direction (similar to 20.0 mu J cm(-2) pulse(-1)). This is mainly due to the higher absorption coefficient estimated in the table by calculating the exciton densities at each threshold value. We also report the control of lasing wavelength through independent selection of alignment direction and DFB orientation, which is achieved through the control of the effective refractive index of waveguide (n(eff)).open171

Microstructure evolution and thermal durability with coating thickness in APS thermal barrier coatings

The effects of the coating thickness on the delamination or fracture behavior of thermal barrier coatings (TBCs) were investigated through the cyclic furnace thermal fatigue (CFTF) and thermal shock (TS) tests. The TBCs were prepared using a NiCrAlY bond coat and an yttria-stabilized zirconia top coat, which were formed using the air plasma spray (APS) process. The thicknesses of the top coat were 200 and 400 μm, and those of the bond coat were 100 and 200 μm. TBC samples with a thickness ratio of 2:1 in the top and bond coats were employed in the CFTF and TS tests. After CFTF for 1429 cycles, the interface microstructure of the relatively thick TBC was in a sound condition without any cracking or delamination; however, the relatively thin TBC was delaminated near the interface between the top and bond coats after 721 cycles. In the TS, the TBCs were fully delaminated (> 50%) after 140 and 194 cycles for thicknesses of 200 and 400 μm in the top coat, respectively. These observations allow us to control the thickness of TBC prepared using the APS process, and the thicker TBC is more efficient in improving thermal durability in the cyclic thermal exposure and thermal shock environments

Elevated intracellular cAMP exacerbates vulnerability to oxidative stress in optic nerve head astrocytes.

Glaucoma is characterized by a progressive loss of retinal ganglion cells and their axons, but the underlying biological basis for the accompanying neurodegeneration is not known. Accumulating evidence indicates that structural and functional abnormalities of astrocytes within the optic nerve head (ONH) have a role. However, whether the activation of cyclic adenosine 3',5'-monophosphate (cAMP) signaling pathway is associated with astrocyte dysfunction in the ONH remains unknown. We report here that the cAMP/protein kinase A (PKA) pathway is critical to ONH astrocyte dysfunction, leading to caspase-3 activation and cell death via the AKT/Bim/Bax signaling pathway. Furthermore, elevated intracellular cAMP exacerbates vulnerability to oxidative stress in ONH astrocytes, and this may contribute to axonal damage in glaucomatous neurodegeneration. Inhibition of intracellular cAMP/PKA signaling activation protects ONH astrocytes by increasing AKT phosphorylation against oxidative stress. These results strongly indicate that activation of cAMP/PKA pathway has an important role in astrocyte dysfunction, and suggest that modulating cAMP/PKA pathway has therapeutic potential for glaucomatous ONH degeneration

Understanding visual map formation through vortex dynamics of spin Hamiltonian models

The pattern formation in orientation and ocular dominance columns is one of the most investigated problems in the brain. From a known cortical structure, we build spin-like Hamiltonian models with long-range interactions of the Mexican hat type. These Hamiltonian models allow a coherent interpretation of the diverse phenomena in the visual map formation with the help of relaxation dynamics of spin systems. In particular, we explain various phenomena of self-organization in orientation and ocular dominance map formation including the pinwheel annihilation and its dependency on the columnar wave vector and boundary conditions.Comment: 4 pages, 15 figure

Zee Model Confronts SNO Data

We reexamine the solution of the minimal Zee model by comparing with the data of the SNO experiment, and conclude that the model is strongly disfavored but not yet excluded by the observations. Two extensions of the Zee model are briefly discussed both of which introduce additional freedom and can accommodate the data.Comment: 16 pages LaTeX including 7 figure

Localized Ca2+ uncaging reveals polarized distribution of Ca2+-sensitive Ca2+ release sites: mechanism of unidirectional Ca2+ waves

Ca2+-induced Ca2+ release (CICR) plays an important role in the generation of cytosolic Ca2+ signals in many cell types. However, it is inherently difficult to distinguish experimentally between the contributions of messenger-induced Ca2+ release and CICR. We have directly tested the CICR sensitivity of different regions of intact pancreatic acinar cells using local uncaging of caged Ca2+. In the apical region, local uncaging of Ca2+ was able to trigger a CICR wave, which propagated toward the base. CICR could not be triggered in the basal region, despite the known presence of ryanodine receptors. The triggering of CICR from the apical region was inhibited by a pharmacological block of ryanodine or inositol trisphosphate receptors, indicating that global signals require coordinated Ca2+ release. Subthreshold agonist stimulation increased the probability of triggering CICR by apical uncaging, and uncaging-induced CICR could activate long-lasting Ca2+ oscillations. However, with subthreshold stimulation, CICR could still not be initiated in the basal region. CICR is the major process responsible for global Ca2+ transients, and intracellular variations in sensitivity to CICR predetermine the activation pattern of Ca2+ waves

Comparison of the performance of photonic band-edge liquid crystal lasers using different dyes as the gain medium

The primary concern of this work is to study the emission characteristics of a series of chiral nematic liquid crystal lasers doped with different laser dyes (DCM, pyrromethene 580, and pyrromethene 597) at varying concentrations by weight (0.5-2 wt %) when optically pumped at 532 nm. Long-wavelength photonic band-edge laser emission is characterized in terms of threshold energy and slope efficiency. At every dye concentration investigated, the pyrromethene 597-doped lasers exhibit the highest slope efficiency (ranging from 15% to 32%) and the DCM-doped lasers the lowest (ranging from 5% to 13%). Similarly, the threshold was found to be, in general, higher for the DCM-doped laser samples in comparison to the pyrromethene-doped laser samples. These results are then compared with the spectral properties, quantum efficiencies and, where possible, fluorescence lifetimes of the dyes dispersed in a common nematic host. In accordance with the low thresholds and high slope efficiencies, the results show that the molar extinction coefficients and quantum efficiencies are considerably larger for the pyrromethene dyes in comparison to DCM, when dispersed in the liquid crystal host.open191

Impact of the gate geometry on adiabatic charge pumping in InAs double quantum dots

We compare the adiabatic quantized charge pumping performed in two types of InAs nanowire double quantum dots (DQDs), either with tunnel barriers defined by closely spaced narrow bottom gates, or by well-separated side gates. In the device with an array of bottom gates of 100 nm pitch and 10 mu m lengths, the pump current is quantized only up to frequencies of a few MHz due to the strong capacitive coupling between the bottom gates. In contrast, in devices with well-separated side gates with reduced mutual gate capacitances, we find well-defined pump currents up to 30 MHz. Our experiments demonstrate that high frequency quantized charge pumping requires careful optimization of the device geometry, including the typically neglected gate feed lines

Control of Interface Defects for Efficient and Stable Quasi-2D Perovskite Light-Emitting Diodes Using Nickel Oxide Hole Injection Layer.

Metal halide perovskites (MHPs) have emerged as promising materials for light-emitting diodes owing to their narrow emission spectrum and wide range of color tunability. However, the low exciton binding energy in MHPs leads to a competition between the trap-mediated nonradiative recombination and the bimolecular radiative recombination. Here, efficient and stable green emissive perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency of 14.6% are demonstrated through compositional, dimensional, and interfacial modulations of MHPs. The interfacial energetics and optoelectronic properties of the perovskite layer grown on a nickel oxide (NiO x ) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole injection interfaces are investigated. The better interface formed between the NiO x /perovskite layers in terms of lower density of traps/defects, as well as more balanced charge carriers in the perovskite layer leading to high recombination yield of carriers are the main reasons for significantly improved device efficiency, photostability of perovskite, and operational stability of PeLEDs