1,945 research outputs found
Melting of peridotites through to granites: a simple thermodynamic model in the system KNCFMASHTOCr
A new set of thermodynamic models is presented for calculating phase relations in bulk compositions extending from peridotite to granite, from 0.001 to 70 kbar and from 650â°C to peridotite liquidus temperatures, in the system K2OâNa2OâCaOâFeOâMgOâAl2O3âSiO2âH2OâTiO2âFe2O3âCr2O3 (KNCFMASHTOCr). The models may be used to calculate phase equilibria in partial melting of a large range of mantle and crustal compositions. They provide a good fit to experimental phase relation topologies and melt compositions across the compositional range of the model. Compared with the preliminary model of Jennings & Holland (2015) for peridotiteâbasalt melting relations, the inclusion of K2O and TiO2 allows for better modelling of small melt fractions in peridotite melting, and in reproducing rutile-bearing eclogite melting at high pressures. An improved orderâdisorder model for spinel is now incorporated. Above 10 kbar pressure, wet partial melting relations may be significantly affected by the dissolution of silicates in aqueous fluid, so the set of models includes an aqueous low-density silicate-bearing fluid in addition to a high-density H2O-bearing silicate melt. Oxygen fugacity may be readily calculated for the whole range of bulk compositions investigated, and the effect of water content on melt fO2 is assessed
A low-wear onload tap changer diverter switch for frequent voltage control on distribution networks
This paper presents a fast mechanical diverter switch design suitable for new âarclessâ hybrid onload tap-changing systems. In such systems, arcing at contact separation and contact closure is almost completely eliminated by the inclusion of alternate current paths incorporating semiconductor devices. This allows the use of compact, air-insulated mechanical contacts that do not need to withstand significant arc erosion or provide arc quenching. As a result, the moving mass and the drive system for the switch may be dramatically reduced in size, leading to low inertia of the moving parts and resulting in very rapid operation times. An integrated, high-torque, low-mass permanent-magnet actuator is presented that provides detent (unpowered) contact force coupled with a cantilever spring contact system sized for an 11-kV 2-MVA onload tap changer. The design delivers operation times of under 20 ms and is capable of sustaining more than operations. The complete design is experimentally verified under representative electrical conditions, and contact wear levels comparable to pure mechanical (zero current) operation are demonstrated
An Analysis of the Environments of FU Orionis Objects with Herschel
We present Herschel-HIFI, SPIRE, and PACS 50-670 {\mu}m imaging and
spectroscopy of six FU Orionis-type objects and candidates (FU Orionis, V1735
Cyg, V1515 Cyg, V1057 Cyg, V1331 Cyg, and HBC 722), ranging in outburst date
from 1936-2010, from the "FOOSH" (FU Orionis Objects Surveyed with Herschel)
program, as well as ancillary results from Spitzer-IRS and the Caltech
Submillimeter Observatory. In their system properties (Lbol, Tbol, line
emission), we find that FUors are in a variety of evolutionary states.
Additionally, some FUors have features of both Class I and II sources: warm
continuum consistent with Class II sources, but rotational line emission
typical of Class I, far higher than Class II sources of similar
mass/luminosity. Combining several classification techniques, we find an
evolutionary sequence consistent with previous mid-IR indicators. We detect [O
I] in every source at luminosities consistent with Class 0/I protostars, much
greater than in Class II disks. We detect transitions of 13CO (J_up of 5 to 8)
around two sources (V1735 Cyg and HBC 722) but attribute them to nearby
protostars. Of the remaining sources, three (FU Ori, V1515 Cyg, and V1331 Cyg)
exhibit only low-lying CO, but one (V1057 Cyg) shows CO up to J = 23 - 22 and
evidence for H2O and OH emission, at strengths typical of protostars rather
than T Tauri stars. Rotational temperatures for "cool" CO components range from
20-81 K, for ~ 10^50 total CO molecules. We detect [C I] and [N II] primarily
as diffuse emission.Comment: 31 pages, 15 figures; accepted to Ap
CO in Protostars (COPS): -SPIRE Spectroscopy of Embedded Protostars
We present full spectral scans from 200-670m of 26 Class 0+I
protostellar sources, obtained with -SPIRE, as part of the
"COPS-SPIRE" Open Time program, complementary to the DIGIT and WISH Key
programs. Based on our nearly continuous, line-free spectra from 200-670
m, the calculated bolometric luminosities () increase by 50%
on average, and the bolometric temperatures () decrease by 10% on
average, in comparison with the measurements without Herschel. Fifteen
protostars have the same Class using and /. We identify rotational transitions of CO lines from J=4-3 to J=13-12,
along with emission lines of CO, HCO, HO, and [CI]. The ratios
of CO to CO indicate that CO emission remains optically
thick for < 13. We fit up to four components of temperature from
the rotational diagram with flexible break points to separate the components.
The distribution of rotational temperatures shows a primary population around
100 K with a secondary population at 350 K. We quantify the correlations
of each line pair found in our dataset, and find the strength of correlation of
CO lines decreases as the difference between -level between two CO lines
increases. The multiple origins of CO emission previously revealed by
velocity-resolved profiles are consistent with this smooth distribution if each
physical component contributes to a wide range of CO lines with significant
overlap in the CO ladder. We investigate the spatial extent of CO emission and
find that the morphology is more centrally peaked and less bipolar at high-
lines. We find the CO emission observed with SPIRE related to outflows, which
consists two components, the entrained gas and shocked gas, as revealed by our
rotational diagram analysis as well as the studies with velocity-resolved CO
emission.Comment: 50 pages, 18 figures, accepted to ApJS. Revised for Table 6 and
Figure
Immigration into the mainstream: Conflicting ideological streams, strategic reasoning and party competition
The Extended Overlap Alternate Arm Converter:A Voltage Source Converter with DC Fault Ride-Through Capability and a Compact Design
The Alternate Arm Converter (AAC) was one of the first modular converter topologies to feature DC-side fault ride-through capability with only a small penalty in power efficiency. However, the simple alternation of its arm conduction periods (with an additional short overlap period) resulted in (i) substantial 6-pulse ripples in the DC current waveform, (ii) large DC-side filter requirements, and (iii) limited operating area close to an energy sweet-spot. This paper presents a new mode of operation called Extended Overlap (EO) based on the extension of the overlap period to 60 ⊠which facilitates a fundamental redefinition of the working principles of the AAC. The EO-AAC has its DC current path decoupled from the AC current paths, a fact allowing (i) smooth DC current waveforms, (ii) elimination of DC filters, and (iii) restriction lifting on the feasible operating point. Analysis of this new mode and EO- AAC design criteria are presented and subsequently verified with tests on an experimental prototype. Finally, a comparison with other modular converters demonstrates that the EO-AAC is at least as power efficient as a hybrid MMC (i.e. a DC fault ride-through capable MMC) while offering a smaller converter footprint because of a reduced requirement for energy storage in the submodules and a reduced inductor volume
The Pan-STARRS Moving Object Processing System
We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern
software package that produces automatic asteroid discoveries and
identifications from catalogs of transient detections from next-generation
astronomical survey telescopes. MOPS achieves > 99.5% efficiency in producing
orbits from a synthetic but realistic population of asteroids whose
measurements were simulated for a Pan-STARRS4-class telescope. Additionally,
using a non-physical grid population, we demonstrate that MOPS can detect
populations of currently unknown objects such as interstellar asteroids.
MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope
despite differences in expected false detection rates, fill-factor loss and
relatively sparse observing cadence compared to a hypothetical Pan-STARRS4
telescope and survey. MOPS remains >99.5% efficient at detecting objects on a
single night but drops to 80% efficiency at producing orbits for objects
detected on multiple nights. This loss is primarily due to configurable MOPS
processing limits that are not yet tuned for the Pan-STARRS1 mission.
The core MOPS software package is the product of more than 15 person-years of
software development and incorporates countless additional years of effort in
third-party software to perform lower-level functions such as spatial searching
or orbit determination. We describe the high-level design of MOPS and essential
subcomponents, the suitability of MOPS for other survey programs, and suggest a
road map for future MOPS development.Comment: 57 Pages, 26 Figures, 13 Table
L-5-methyltetrahydrofolate supplementation increases blood folate concentrations to a greater extent than folic acid supplementation in Malaysian women
Background: Folic acid fortification of grains is mandated in many countries to prevent neural tube defects. Concerns regarding excessive intakes of folic acid have been raised. A synthetic analog of the circulating form of folate, l-5-methyltetrahydrofolate (l-5-MTHF), may be a potential alternative. Objective: The objective of this study was to determine the effects of folic acid or l-5-MTHF supplementation on blood folate concentrations, methyl nutrient metabolites, and DNA methylation in women living in Malaysia, where there is no mandatory fortification policy. Methods: In a 12-wk, randomized, placebo-controlled intervention trial, healthy Malaysian women (n = 142, aged 20â45 y) were randomly assigned to receive 1 of the following supplements daily: 1 mg (2.27 ÎŒmol) folic acid, 1.13 mg (2.27 ÎŒmol) l-5-MTHF, or a placebo. The primary outcomes were plasma and RBC folate and vitamin B-12 concentrations. Secondary outcomes included plasma total homocysteine, total cysteine, methionine, betaine, and choline concentrations and monocyte long interspersed nuclear element-1 (LINE-1) methylation. Results: The folic acid and l-5-MTHF groups had higher (P < 0.001) RBC folate (mean ± SD: 1498 ± 580 and 1951 ± 496 nmol/L, respectively) and plasma folate [median (25th, 75th percentiles): 40.1 nmol/L (24.9, 52.7 nmol/L) and 52.0 nmol/L (42.7, 73.1 nmol/L), respectively] concentrations compared with RBC folate (958 ± 345 nmol/L) and plasma folate [12.6 nmol/L (8.80, 17.0 nmol/L)] concentrations in the placebo group at 12 wk. The l-5-MTHF group had higher RBC folate (1951 ± 496 nmol/L; P = 0.003) and plasma folate [52.0 nmol/L (42.7, 73.1 nmol/L); P = 0.023] at 12 wk than did the folic acid group [RBC folate, 1498 ± 580 nmol/L; plasma folate, 40.1 nmol/L (24.9, 52.7 nmol/L)]. The folic acid and l-5-MTHF groups had 17% and 15%, respectively, lower (P < 0.001) plasma total homocysteine concentrations than did the placebo group at 12 wk; there were no differences between the folic acid and l-5-MTHF groups. No differences in plasma vitamin B-12, total cysteine, methionine, betaine, and choline and monocyte LINE-1 methylation were observed. Conclusion: These findings suggest differential effects of l-5-MTHF compared with folic acid supplementation on blood folate concentrations but no differences on plasma total homocysteine lowering in Malaysian women. This trial was registered at clinicaltrials.gov as NCT01584050
Phase effects on the masking of speech by harmonic complexes: Variations with level
Speech reception thresholds were obtained in normally hearing listeners for sentence targets masked by harmonic complexes constructed with different phase relationships. Maskers had either a constant fundamental frequency (F0), or had F0 changing over time, following a pitch contour extracted from natural speech. The median F0 of the target speech was very similar to that of the maskers. In experiment 1 differences in the masking produced by Schroeder positive and Schroeder negative phase complexes were small (around 1.5âdB) for moderate levels [60 dB sound pressure level (SPL)], but increased to around 6âdB for maskers at 80âdB SPL. Phase effects were typically around 1.5âdB larger for maskers that had naturally varying F0 contours than for maskers with constant F0. Experiment 2 showed that shaping the long-term spectrum of the maskers to match the target speech had no effect. Experiment 3 included additional phase relationships at moderate levels and found no effect of phase. Therefore, the phase relationship within harmonic complexes appears to have only minor effects on masking effectiveness, at least at moderate levels, and when targets and maskers are in the same F0 range
Integrating coaching and positive psychology: Concepts and practice
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