We report here results from a Chandra ACIS observation of the stellar populations in and around the Messier 17 HII region. The field reveals 886 sources with observed X-ray luminosities (uncorrected for absorption) between ∼ 29.3 < log L x < 32.8 ergs s −1 , 771 of which have stellar counterparts in infrared images. In addition to comprehensive tables of X-ray source properties, several results are presented:1. The X-ray Luminosity Function is calibrated to that of the Orion Nebula Cluster population to infer a total population of roughly 8000-10,000 stars in M17, one-third lying in the central NGC 6618 cluster.2. About 40% of the ACIS sources are heavily obscured with A V > 10 mag. Some are concentrated around well-studied star-forming regions-IRS 5/UC1, the Kleinmann-Wright Object, and M17-North-but most are distributed across the field. As previously shown, star formation appears to be widely distributed in the molecular clouds. X-ray emission is detected from 64 of the hundreds of Class I protostar candidates that can be identified by near-and mid-infrared colors. These constitute the most likely protostar candidates known in M17.3. The spatial distribution of X-ray stars is complex: in addition to the central NGC 6618 cluster and well-known embedded groups, we find a new embedded cluster (designated M17-X), a 2 pc-long arc of young stars along the southwest edge of the M17 HII region, and 0.1 pc substructure within various populations. These structures may indicate that the populations are dynamically young.4. All (14/14) of the known O stars but only about half (19/34) of the known B0-B3 stars in the M17 field are detected. These stars exhibit the long-reported correlation between X-ray and bolometric luminosities of L x ∼ 10 −7 L bol . While many O and early B stars show the soft X-ray emission expected from microshocks in their winds or moderately hard emission that could be caused by magnetically channeled wind shocks, six of these stars exhibit very hard thermal plasma components (kT > 4 keV) that may be due to colliding wind binaries. More than 100 candidate new OB stars are found, including 28 X-ray detected intermediateand high-mass protostar candidates with infrared excesses.5. Only a small fraction (perhaps 10%) of X-ray selected high-and intermediate-mass stars exhibit K-band emitting protoplanetary disks, providing further evidence that inner disks evolve very rapidly around more massive stars.Subject headings: open clusters and associations: individual (M17) -X-rays: individual (M17) -stars: early-type -stars: pre-main-sequence -X-Rays: starsIn the high-energy regime, lower-mass young stars in nearby star-forming regions were studied extensively with X-ray missions during the 1980-90s (Feigelson & Montmerle 1999), but studies of the more distant MSFRs were hampered by the limited spatial resolution of these telescopes. The launch of the Chandra X-ray Observatory (Weisskopf et al. 2002) in 1999 makes X-ray studies of MSFRs much more feasible, due to the sub-arcsecond spatial resolution of its mir...

Aims. Massive stars form in clusters, and they are often found in different evolutionary stages located close to each other. To understand evolutionary and environmental effects during the formation of high-mass stars, we observed three regions of massive star formation at different evolutionary stages, and all are found that in the same natal molecular cloud. Methods. The three regions, S255IR, S255N, and S255S, were observed at 1.3 mm with the submillimeter array (SMA), and followup short spacing information was obtained with the IRAM 30 m telescope. Near infrared (NIR) H + K-band spectra and continuum observations were taken for S255IR with VLT-SINFONI to study the different stellar populations in this region.Results. This combination of millimeter (mm) and near infrared data allow us to characterize different stellar populations within the young forming cluster in detail. While we find multiple mm continuum sources toward all regions, their outflow, disk, and chemical properties vary considerably. The most evolved source S255IR exhibits a collimated bipolar outflow visible in CO and H 2 emission, and the outflows from the youngest region S255S are still small and fairly confined in the regions of the mm continuum peaks. Also the chemistry toward S255IR is the most evolved, exhibiting strong emission from complex molecules, while much fewer molecular lines are detected in S255N, and in S255S we detect only CO isotopologues and SO lines. Also, rotational structures are found toward S255N and S255IR. Furthermore, a comparison of the NIR SINFONI and mm data from S255IR clearly reveal two different (proto) stellar populations with an estimated age difference of approximately 1 Myr. Conclusions. A multiwavelength spectroscopy and mapping study reveals different evolutionary phases of the star formation regions. We propose the triggered outside-in collapse star formation scenario for the bigger picture and the fragmentation scenario for S255IR.

The dynamics of the CdSe nanorod synthesis reaction have been studied, giving attention to the kinetics of magic-sized clusters (MSCs) that form as intermediates in the overall reaction. The MSCs have a distinct absorption peak, and the kinetics of this peak give insight into the overall reaction mechanism. In these studies, the reaction mixture consists primarily of Cd(phosphonate)(2) and trioctyl phosphine selenium in a solution of trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO). We find that the rate at which precursors react to form CdSe monomers and the rates at which monomers react to form nanoparticles can be varied by changing the chemistry of the reaction mixture. Decreasing the TOP concentration decreases the extent to which selenium is bound, both in the precursors and on the particles' surfaces, and thereby increases both the precursor to monomer and monomer to particle reaction rates. Decreasing the phosphonate concentration decreases the extent to which phosphonate binds cadmium in the precursors and on the surface of the nanoparticles, also increasing the rates of both reactions. This is also accomplished by the addition of inorganic acids which protonate the phosphonates. The presence of inorganic acids (impurities) is the primary reason that the overall synthesis reaction is faster in solutions made with technical grade rather than purified TOPO. The TOP and phosphonic acid concentrations are coupled because excess phosphonic acids react with TOP, forming TOPO and less strongly binding species, specifically phosphinic acids, phosphine oxides, and phosphines.

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Transient absorption spectroscopy has been used to study the rates of electron transfer (ET) from CdSe and CdSe/ZnS core/shell nanorods to adsorbed methyl viologen, MV 2þ . The nanorods are excited with 387 nm light, producing electrons 7700 cm -1 above the conduction band edge. Kinetics are measured in particles without adsorbed MV 2þ , giving electron cooling and electron-hole recombination times. The kinetics obtained with and without adsorbed MV 2þ are compared to infer the ET rates. The results indicate that electron cooling occurs on the 0.7-1.8 ps time scale, with the fastest cooling occurring from the highest energy states. Hot electron transfer from the highest energy levels competes with electron cooling, occurring on the 0.5 ps time scale. Bare particle (relaxed) electron transfer occurs on the time scale of less than or about 4 ps. This is faster than biexciton Auger recombination which occurs on the 50 ps time scale. The energy dependence of the ET times can be semiquantitatively understood in terms of penetration of the conduction band wave function past the particle surface and overlap with the adsorbed MV 2þ . In CdSe/ZnS particles, ET to adsorbed MV 2þ is slower than electron cooling, and hot electron transfer does not occur. For a 1.0 nm thick ZnS shell, the ET from the bottom of the conduction band occurs on a range of time scales, with the fastest component of about 45 ps.

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The rapid development of many emerging technologies (e.g., electric vehicles and smart grids) requires advanced energy storage and conversion systems that have higher energy and power density, longer operational life, and better safety. A low‐cost, green, and sustainable process for fabrication of all‐solid‐state asymmetric supercapacitors (ASC) composed of a hierarchically porous carbonized wood (CW) anode, a cellulose paper separator, and a Co(OH)2@CW cathode is reported here. The hierarchically porous wood‐derived electrode exhibits a high areal capacitance of 3.723 F cm−2 (with an areal loading Co(OH)2 of 5.7 mg cm−2) at a current density 1.0 mA cm−2, and 1.568 F cm−2 at a current density of 30 mA cm−2. Moreover, the all‐solid‐state ASC exhibits outstanding energy density of 0.69 mWh cm−2 (10.87 Wh kg−1) at power density of 1.126 W cm−2 (17.75 W kg−1) while maintaining a capacitance retention of 85% after 10 000 continuous charge–discharge cycles. The high energy/power‐densities are attributed to the unique architecture of the electrodes derived from natural wood, which allow full exposure of active electrode materials, efficient current collection, and fast ion transport. Further, the materials are renewable, environmentally friendly, and biodegradable.

Over the past decade, wood‐derived materials have attracted enormous interest for both fundamental research and practical applications in various functional devices. In addition to being renewable, environmentally benign, naturally abundant, and biodegradable, wood‐derived materials have several unique advantages, including hierarchically porous structures, excellent mechanical flexibility and integrity, and tunable multifunctionality, making them ideally suited for efficient energy storage and conversion. In this article, the latest advances in the development of wood‐derived materials are discussed for electrochemical energy storage systems and devices (e.g., supercapacitors and rechargeable batteries), highlighting their micro/nanostructures, strategies for tailoring the structures and morphologies, as well as their impact on electrochemical performance (energy and power density and long‐term durability). Furthermore, the scientific and technical challenges, together with new directions of future research in this exciting field, are also outlined for electrochemical energy storage applications.