366 research outputs found
Ammonia in the hot core W51-IRS2: 12 new maser lines and a maser component with a velocity drift
With the 100-m telescope at Effelsberg, 19 ammonia (NH3) maser lines have
been detected toward the prominent massive star forming region W51-IRS2. Eleven
of these inversion lines, the (J,K) = (6,2), (5,3), (7,4), (8,5), (7,6), (7,7),
(9,7), (10,7), (9,9), (10,9), and (12,12) transitions, are classified as masers
for the first time in outer space. All detected masers are related to highly
excited inversion doublets. The (5,4) maser originates from an inversion
doublet 340 K above the ground state, while the (12,12) transition, at 1450 K,
is the most highly excited NH3 maser line so far known. Strong variability is
seen not only in ortho- but also in para-NH3 transitions. Bright narrow
emission features are observed, for the first time, in (mostly) ortho-ammonia
transitions, at V ~ 45 km/s, well separated from the quasi-thermal emission
near 60 km/s. These features were absent 25 years ago and show a velocity drift
of about +0.2 km/s/yr. The component is likely related to the SiO maser source
in W51-IRS2 and a possible scenario explaining the velocity drift is outlined.
The 57 km/s component of the (9,6) maser line is found to be strongly linearly
polarized. Maser emission in the (J,K) to (J+1,K) inversion doublets is
strictly forbidden by selection rules for electric dipole transitions in the
ground vibrational state. However, such pairs (and even triplets with (J+2,K))
are common toward W51-IRS2. Similarities in line widths and velocities indicate
that such groups of maser lines arise from the same regions, which can be
explained by pumping through vibrational excitation. The large number of NH3
maser lines in W51-IRS2 is most likely related to the exceptionally high
kinetic temperature and NH3 column density of this young massive star forming
region.Comment: Accepted for publication in Astronomy & Astrophysics, 11 pages, 12
postscript figures, 1 tabl
Vibrational Stability of NLC Linac and Final Focus Components
Vertical vibration of linac components (accelerating structures, girders and
quadrupoles) in the NLC has been studied experimentally and analytically.
Effects such as structural resonances and vibration caused by cooling water
both in accelerating structures and quadrupoles have been considered.
Experimental data has been compared with analytical predictions and simulations
using ANSYS. A design, incorporating the proper decoupling of structure
vibrations from the linac quadrupoles, is being pursued.Comment: 3 pages, 8 figures presented at the LINAC 2002 conference, Gyeongju
Kore
Effect of Cooling Water on Stability of NLC Linac Components
Vertical vibration of linac components (accelerating structures, girders and
quadrupoles) in the NLC has been studied experimentally and analytically.
Effects such as structural resonances and vibration caused by cooling water
both in accelerating structures and quadrupoles have been considered.
Experimental data has been compared with analytical predictions and simulations
using ANSYS. A design, incorporating the proper decoupling of structure
vibrations from the linac quadrupoles, is being pursued.Comment: 6 Pages 13 Figures Presented at The Nanobeam 2002 Workshop (Lausanne
Switzerland
Pyran-Squaraine as Photosensitizers for Dye-Sensitized Solar Cells: DFT/TDDFT Study of the Electronic Structures and Absorption Properties
In an effort to provide, assess, and evaluate a theoretical approach which enables designing efficient donor-acceptor dye systems, the electronic structure and optical properties of pyran-squaraine as donor-acceptor dyes used in dye-sensitized solar cells were investigated. Ground state properties have been computed at the B3LYP/6-31+G** level of theory. The long-range corrected density functionals CAM-B3LYP, PBEPBE, PBE1PBE (PBE0), and TPSSH with 6-311++G** were employed to examine absorption properties of the studied dyes. In an extensive comparison between experimental results and ab initio benchmark calculations, the TPSSH functional with 6-311++G** basis set was found to be the most appropriate in describing the electronic properties for the studied pyran and squaraine dyes. Natural transition orbitals (NTO), frontier molecular orbitals (FMO), LUMO, HOMO, and energy gaps, of these dyes, have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of pyran and squaraine dyes was investigated to understand the recombination process and charge-transfer process involving these dyes. Additionally, we performed natural bond orbital (NBO) analysis to investigate the role of charge delocalization and hyperconjugative interactions in the stability of the molecule
3-(Adamantan-1-yl)-1-[(4-benzylpiperazin-1-yl)methyl]-4-phenyl-1H-1,2,4-triazole-5(4H)-thione
The title molecule, C30H37N5S, displays a chair-shaped piperazine ring, as well as an approximately planar triazole ring [maximum deviation = 0.002 (2) Å] whose phenyl substituent is nearly perpendicular to the mean plane of the five-membered ring [dihedral angle = 80.4 (1)°]. The substituents on the piperazine ring occupy equatorial sites. Weak intermolecular C—H⋯S hydrogen bonding is present in the crystal structure
On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
Using the IRAM 30-m telescope, CN and CO isotopologues have been measured
toward the central regions of the nearby starburst galaxy NGC253 and the
prototypical ultraluminous infrared galaxy Mrk231. In NGC253, the 12C/13C ratio
is 40+-10. Assuming that the ratio also holds for the CO emitting gas, this
yields 16O/18O = 145+-36 and 16O/17O = 1290+-365 and a 32S/34S ratio close to
that measured for the local interstellar medium (20-25). No indication for
vibrationally excited CN is found. Peak line intensity ratios between NGC253
and Mrk231 are ~100 for 12C16O and 12C18O J=1-0, while the ratio for 13C16O
J=1-0 is ~250. This and similar 13CO and C18O line intensities in the J=1-0 and
2-1 transitions of Mrk231 suggest 12C/13C ~ 100 and 16O/18O ~ 100, in agreement
with values obtained for the less evolved ultraluminous merger Arp220. Also
accounting for other extragalactic data, 12C/13C ratios appear to vary over a
full order of magnitude, from >100 in ultraluminous high redshift galaxies to
~100 in more local such galaxies to ~40 in weaker starbursts not undergoing a
large scale merger to 25 in the Central Molecular Zone of the Milky Way. With
12C being predominantly synthesized in massive stars, while 13C is mostly
ejected by longer lived lower mass stars at later times, this is qualitatively
consistent with our results of decreasing carbon isotope ratios with time and
rising metallicity. It is emphasized, however, that both infall of poorly
processed material, initiating a nuclear starburst, as well as the ejecta from
newly formed massive stars (in particular in case of a top-heavy stellar
initial mass function) can raise the carbon isotope ratio for a limited amount
of time.Comment: Accepted by Astronomy & Astrophysics, 6 figures, 4 table
Increasing efficiency of perovskite solar cells using low concentrating photovoltaic systems
This is the final version. Available from Royal Society of Chemistry via the DOI in this record. Perovskite solar cell (PSC) technology is the flag bearer for the future of photovoltaics allowing unlimited possibilities for its application. This technology is currently limited by issues related to its scale-up, stability and the composition of the materials used in its preparation. Using small sized solar cells with higher efficiency under solar concentration is gaining traction as a methodology for scaling up this technology and broadening its applications. However, this has only been reported in devices with size <1 mm2 neglecting the series resistance of the device. Here, we report the performance of a 9 mm2 PSC at varying solar concentration levels and correlate it with the series resistance of the solar cell. The n–i–p structured device using a triple cation perovskite absorber with a mesoporous titanium oxide/SnO2 layer as the electron transporting layer and Spiro-OMeTAD as the hole transporting material achieved a peak efficiency of 21.6% under 1.78 Suns as compared to the 21% obtained under 1 Sun (1000W m−2) and AM1.5G. We further boosted the power output up to 15.88 mW under 10.7 Suns compared to the 1.88 mW obtained under 1 Sun; however this results in an actual efficiency drop of the PSC owing to the device series resistance. Further, we investigated the impact of the increasing solar cell temperature at higher concentration levels and identified the influence of series resistance on the performance of the PSC. Our work identifies the potential of concentrating photovoltaics and highlights the challenges and makes recommendations for future development.EPSRCEuropean Union's Horizon 202
3-(Adamantan-1-yl)-4-phenyl-1-[(4-phenylpiperazin-1-yl)methyl]-1H-1,2,4-triazole-5(4H)-thione
The title molecule, C29H35N5S, displays a chair-shaped piperazine ring, as well as an approximately planar triazole ring (r.m.s. deviation = 0.001 Å) whose phenyl substituent is nearly perpendicular to the mean plane of the five-membered ring [dihedral angle = 88.9 (1)°]. The substituents on the piperazine ring occupy equatorial sites. In the crystal, the adamantyl cage is disordered over two sets of sites with a major component of 67.8 (5)%. Weak intermolecular C—H⋯S hydrogen bonding is present in the crystal
The Status of Digital Dental Technology Implementation in the Saudi Dental Schools' Curriculum: A National Cross-Sectional Survey for Healthcare Digitization.
Objective: The primary objective of this cross-sectional national study was to investigate the status of digital dental technology (DDT) adoption in Saudi Arabian undergraduate dental education. A secondary objective was to explore the impact of dental schools' funding sources to incorporate digital technologies. Methods: A self-administered questionnaire was distributed to the chairpersons of prosthetic sciences departments of the 27 dental schools in Saudi Arabia. If any department chairman failed to respond to the survey, a designated full-time faculty member was contacted to fill out the form. The participants were asked about the school's sector, DDT implementation in the curriculum, implemented level, their perceptions of the facilitators and challenges for incorporating DDT. Results: Of the 27 dental schools (18 public and 8 private), 26 responded to the questionnaire (response rate: 96.3%). The geographic distribution of the respondent schools was as follows: 12 schools in the central region, 6 in the western region, and 8 in other regions. Seventeen schools secure and preserve patients' records using electronic software, whereas nine schools use paper charts. Seventeen schools (64,4%) implemented DDT in their curricula. The schools that did not incorporate DDT into their undergraduate curricula were due to not being included in the curriculum (78%), lack of expertise (66%), untrained faculty and staff (44%), and cost (33%). Conclusions: This national study showed that digital components still need to be integrated into Saudi Arabian dental schools' curricula and patient care treatment. Additionally, there was no association between funding sources and the DDT implementation into the current curricula. Consequently, Saudi dental schools must emphasize the implementation and utilization of DDT to align with Saudi Vision 2030 for healthcare digitization and to graduate competent dentists in digital dental care
Ethyl 4-{[3-(adamantan-1-yl)-4-phenyl-5-sulfanylidene-4,5-dihydro-1H-1,2,4-triazol-1-yl]methyl}piperazine-1-carboxylate
The title molecule, C26H35N5O2S, displays a chair-shaped piperazine ring, as well as a planar triazole ring whose phenyl substituent is perpendicular to the mean plane of the five-membered ring [dihedral angle = 90.00 (13)°]. The methylene substituent on the piperazine ring occupies an equatorial site. Weak intermolecular C—H⋯O hydrogen bonding is present in the crystal structure. The crystal studied was a non-merohedral twin, with a 33.9 (3)% minor component
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