Preferential localization of a vesicular monoamine transporter to dense core vesicles in PC12 cells.

Neurons and endocrine cells have two types of secretory vesicle that undergo regulated exocytosis. Large dense core vesicles (LDCVs) store neural peptides whereas small clear synaptic vesicles store classical neurotransmitters such as acetylcholine, gamma-aminobutyric acid (GABA), glycine, and glutamate. However, monoamines differ from other classical transmitters and have been reported to appear in both LDCVs and smaller vesicles. To localize the transporter that packages monoamines into secretory vesicles, we have raised antibodies to a COOH-terminal sequence from the vesicular amine transporter expressed in the adrenal gland (VMAT1). Like synaptic vesicle proteins, the transporter occurs in endosomes of transfected CHO cells, accounting for the observed vesicular transport activity. In rat pheochromocytoma PC12 cells, the transporter occurs principally in LDCVs by both immunofluorescence and density gradient centrifugation. Synaptic-like microvesicles in PC12 cells contain relatively little VMAT1. The results appear to account for the storage of monoamines by LDCVs in the adrenal medulla and indicate that VMAT1 provides a novel membrane protein marker unique to LDCVs

Physical conditions in the transition regions around the Ring Nebula and NGC 7027

Deep long-slit spectra have been obtained in order to map the electron temperature and density in the warm transition regions around the Ring Nebula using the optical [C I] and [N I] forbidden lines. For the first time the [C I] λ8727 line is detected and mapped in this nebula. The temperature-sensitive [C I] nebular to auroral line ratio (λ9824 + λ9850)/λ8727 yields a mean electron temperature of 8250 K, while variations of up to 2000 K can be seen for emission from the different parts of the nebula. The electron density derived from the density-sensitive [N I] doublet ratio, λ5198/λ5200, is similar to that deduced for the fully ionized regions using the [Cl III] λ5517/λ5537 doublet ratio. As compared with lines from ionized regions, the [C I] and [N I] lines show dramatic and complex variations, both in their surface brightness distributions and in their radial velocities along the nebular minor axis, in a manner largely consistent with the bipolar model proposed by Bryce, Balick & Meaburn for the Ring Nebula. The bulk material movement revealed by the large outflow velocities in the transition regions (up to ±35 km s-1), relative to the ionized regions, is likely to generate strong shocks, and thus provides a natural excitation mechanism for the strong near-infrared H2 emission lines observed in the Ring Nebula. We have also observed NGC 7027. The new observations confirm the earlier results of Danziger & Goad, who found a very small (λ9824 + λ9850)/λ8727 ratio for NGC 7027 and correctly attributed it as due to collisional de-excitation of the upper levels of the [C I] nebular lines under the very high-density conditions found in NGC 7027

Highly Stable Luminous "snakes" from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires

CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material's instability toward polar solvents, heat, or UV irradiation greatly limits its further applications. Herein, an efficient in situ growing strategy has been developed to give highly stable perovskite NC composites (abbreviated CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 μm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (∼8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X = Cl, Br, or I), and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability toward water, heat, and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources

Mid-infrared broadband modulation instability and 50 dB Raman assisted parametric gain in silicon photonic wires

Abstract: We demonstrate broadband modulation instability, > 40 dB parametric amplification with on-chip gain bandwidth > 580 nm, and narrowband Raman-assisted peak on-chip gain exceeding 50 dB, using mid-infrared dispersion-engineered silicon nanophotonic wires

Chemical abundances of planetary nebulae from optical recombination lines - II. The neon abundance of NGC 7009

We present high-quality observations of Ne II optical recombination lines (ORLs) for the bright Saturn Nebula NGC 7009. The measured line fluxes are used to determine Ne2+/H+ abundance ratios. The results derived from individual multiplets of the 3s–3p and 3p–3d configurations agree reasonably well, although values derived from the 3d–4f transitions, for which only preliminary effective recombination coefficients are available, tend to be higher by a factor of 2 than those derived from the 3–3 transitions – a pattern also seen in other nebulae analysed by us previously. The ORL Ne2+/H+ abundance ratios of NGC 7009 are found to be higher by a factor of 4 than those derived from the optical collisionally excited lines [Ne III] λλ3868, 3967 and from the infrared fine-structure lines [Ne III] 15.5 and 36 μm, similar to the patterns found for C, N and O, analysed previously by Liu et al. The result is in line with the general conclusion that while the ratios of heavy-element abundances, derived from ORLs on the one hand and from CELs on the other hand, vary from target to target and cover a wide range from unity to more than an order of magnitude, the discrepancy factor for the individual elements, C, N, O and Ne, is found to be approximately the same magnitude for a given nebula, a result which may have a fundamental implication for understanding the underlying physical cause(s) of the large discrepancies between heavy-element abundances derived from these two types of emission line. The result also indicates that while the absolute abundances of heavy elements relative to hydrogen remain uncertain, the abundance ratios of heavy elements, such as C/O, N/O and Ne/O, are probably secure, provided that the same type of emission line, i.e. ORLs or CELs, is used to determine the abundances of both heavy elements involved in the ratio. For NGC 7009, the total neon abundances derived from the CELs and ORLs, on a logarithmic scale where H=12.0, are 8.24±0.08 and 8.84±0.25, respectively. The latter is about a factor of 5.5 higher than the solar neon abundance

One-by-one trap activation in silicon nanowire transistors

Flicker or 1/f noise in metal-oxide-semiconductor field-effect transistors (MOSFETs) has been identified as the main source of noise at low frequency. It often originates from an ensemble of a huge number of charges trapping and detrapping. However, a deviation from the well-known model of 1/f noise is observed for nanoscale MOSFETs and a new model is required. Here, we report the observation of one-by-one trap activation controlled by the gate voltage in a nanowire MOSFET and we propose a new low-frequency-noise theory for nanoscale FETs. We demonstrate that the Coulomb repulsion between electronically charged trap sites avoids the activation of several traps simultaneously. This effect induces a noise reduction by more than one order of magnitude. It decreases when increasing the electron density in the channel due to the electrical screening of traps. These findings are technologically useful for any FETs with a short and narrow channel.Comment: One file with paper and supplementary informatio

Electron tunneling through alkanedithiol molecules

We report on first principles calculations of the tunneling current across n-alkanedithiol molecules (n = 4,6,8,10,12) sandwiched between two Au {111} electrodes. The conductance drops exponentially with increased chain length with decay parameter βn= 0.9. The results are compared with scanning tunneling microscopy measurements on decanedithiol and with other n-alkanedithiol (n = 6,8,10) results in the literature. The theoretical results are found to be an order of magnitude larger than experimental values but follow the same trend. However, two additional, more realistic, geometries are modeled by changing the bond type and by combining the first-principles results with a Wentzel-Kramer-Brillouin (WKB) expression for tunneling across the air gap that is invariably present during scanning tunneling microscopy (STM) measurements. These results are more compatible with the experimental data