401 research outputs found
Draft of a zoning ordinance for the city of Waltham, Massachusetts
Thesis (M.C.P.) Massachusetts Institute of Technology. Dept. of Architecture and City Planning, 1947.by John T. Blackwell.M.C.P
Process for the production of 2-alkyl or 2-cycloalkyl-4-methyl-6-hydroxypyrimidines
Production of 2-alkyl or 2-cycloalkyl-4-methyl-6-hydroxy pyrimidines by sequentially reacting without isolation of any intermediates in an organic solvent (1) diketene and ammonia to produce .beta.-aminocrotonamide and (2) .beta.-aminocrotonamide, after water removal therefrom, a lower alkanoic or cycloalkanoic acid ester and an alkali metal alkoxide
Core magnetic islands and plasma confinement in the H-1NF heliac
Plasma confinement in the vicinity of vacuum magnetic islands near the magnetic axis in the H-1NF heliac [S. M. Hamberger et al., Fusion Technol.17, 123 (1990)] has been experimentally studied in a low temperature argon plasma. Experimental results indicate that, under favorable conditions, these low order (m=2)islands near the core of the plasma serve as âpocketsâ of higher electron density. This results in significant profile modifications including enhancement of the core radial electric field to a large positive value, possibly through an electron-root ambipolar condition. The characteristics of islands are found to be dependent on the plasma collisionality and island width.This research was supported in part by the Australian
Research Council Grant No. DP0344361 and the U.S.
Department of Energy under Contract No. DE-AC05-
00OR22725 with UT-Battelle, LLC
Three view electronically scanned interferometer for plasma electron density measurements on the H-1 heliac
We report the development of a three view electronically scanned millimeter-wave interferometer for plasma electron density profile measurement on the H-1 heliac. The system utilizes an electronically tunable backward-wave oscillator whose output is incident on a fixed blazed diffraction grating such that sweeping the source frequency effects a spatial scan of the plasma cross section. Two diagonal views essentially span most of the plasma cross section, while the horizontal arm views the lower half of the plasma. The diffracted beams traverse the plasma in <1ms with a spatial resolution âŒ20mm. A study of the density projection dependence on magnetic configuration shows that the presence of low-order rational surfaces in the plasma gives rise to sharp density gradients in the vicinity of the surface
A Process for the Production of 2-Alkyl or 2-Cycloalkyl-4-methyl-6-hydroxypyrimidines
Production of 2-alkyl- or cycloalkyl-4-methyl-6- hydroxypyrimidines by first neutralizing an alkyl imidate ester hydrochloride with a base in the presence of a water-immiscible solvent for the alkyl imidate ester to be freed thereby; condensing the alkyl imidate ester with diketene to form an oxazinone intermediate, which is then reacted in organic solution with gaseous ammonia and recovering the desired substituted 6-hydroxypyrimidine
The Chemical Composition of Carbon-Rich, Very Metal-Poor Stars: A New Class of Mildly Carbon-Rich Objects Without Excess of Neutron-Capture Elements
We report on an analysis of the chemical composition of five carbon-rich,
very metal-poor stars based on high-resolution spectra. One star, CS22948-027,
exhibits very large overabundances of carbon, nitrogen, and the neutron-capture
elements, as found in the previous study of Hill et al.. This result may be
interpreted as a consequence of mass transfer from a binary companion that
previously evolved through the asymptotic giant branch stage. By way of
contrast, the other four stars we investigate exhibit no overabundances of
barium ([Ba/Fe]<0), while three of them have mildly enhanced carbon and/or
nitrogen ([C+N]+1). We have been unable to determine accurate carbon and
nitrogen abundances for the remaining star (CS30312-100). These stars are
rather similar to the carbon-rich, neutron-capture-element-poor star
CS22957-027 discussed previously by Norris et al., though the carbon
overabundance in this object is significantly larger ([C/Fe]=+2.2). Our results
imply that these carbon-rich objects with ``normal'' neutron-capture element
abundances are not rare among very metal-deficient stars. One possible process
to explain this phenomenon is as a result of helium shell flashes near the base
of the AGB in very low-metallicity, low-mass (M~< 1M_sun) stars, as recently
proposed by Fujimoto et al..
The moderate carbon enhancements reported herein ([C/Fe]+1) are similar to
those reported in the famous r-process-enhanced star CS22892-052. We discuss
the possibility that the same process might be responsible for this similarity,
as well as the implication that a completely independent phenomenon was
responsible for the large r-process enhancement in CS22892-052.Comment: 53 pages, 8 figures, to appear in Ap
Chemical Composition of the Planet-Harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star of the
transiting extrasolar planet TrES-1. Based on high-resolution Keck/HIRES and
HET/HRS spectra, we have determined abundances relative to the Sun for 16
elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba).
The resulting average abundance of is in good
agreement with initial estimates of solar metallicity based on iron. We compare
the elemental abundances of TrES-1 with those of the sample of stars with
planets, searching for possible chemical abundance anomalies. TrES-1 appears
not to be chemically peculiar in any measurable way. We investigate possible
signs of selective accretion of refractory elements in TrES-1 and other stars
with planets, and find no statistically significant trends of metallicity
[/H] with condensation temperature . We use published abundances and
kinematic information for the sample of planet-hosting stars (including TrES-1)
and several statistical indicators to provide an updated classification in
terms of their likelihood to belong to either the thin disk or the thick disk
of the Milky Way Galaxy. TrES-1 is found to be a very likely member of the thin
disk population. By comparing -element abundances of planet hosts and a
large control sample of field stars, we also find that metal-rich
([Fe/H]) stars with planets appear to be systematically
underabundant in [/Fe] by dex with respect to comparison
field stars. The reason for this signature is unclear, but systematic
differences in the analysis procedures adopted by different groups cannot be
ruled out.Comment: 52 pages, 15 figures, 5 tables, accepted for publication in the
Astronomical Journa
Spatial variation in the fine-structure constant -- new results from VLT/UVES
(abridged) We present a new analysis of a large sample of quasar
absorption-line spectra obtained using UVES (the Ultraviolet and Visual Echelle
Spectrograph) on the VLT (Very Large Telescope) in Chile. In the VLT sample
(154 absorbers), we find evidence that alpha increases with increasing
cosmological distance from Earth. However, as previously shown, the Keck sample
(141 absorbers) provided evidence for a smaller alpha in the distant absorption
clouds. Upon combining the samples an apparent variation of alpha across the
sky emerges which is well represented by an angular dipole model pointing in
the direction RA=(17.3 +/- 1.0) hr, dec. = (-61 +/- 10) deg, with amplitude
(0.97 +0.22/-0.20) x 10^(-5). The dipole model is required at the 4.1 sigma
statistical significance level over a simple monopole model where alpha is the
same across the sky (but possibly different to the current laboratory value).
The data sets reveal a number of remarkable consistencies: various data cuts
are consistent and there is consistency in the overlap region of the Keck and
VLT samples. Assuming a dipole-only (i.e. no-monopole) model whose amplitude
grows proportionally with `lookback-time distance' (r=ct, where t is the
lookback time), the amplitude is (1.1 +/- 0.2) x 10^(-6) GLyr^(-1) and the
model is significant at the 4.2 sigma confidence level over the null model
[Delta alpha]/alpha = 0). We apply robustness checks and demonstrate that the
dipole effect does not originate from a small subset of the absorbers or
spectra. We present an analysis of systematic effects, and are unable to
identify any single systematic effect which can emulate the observed variation
in alpha.Comment: 47 pages, 35 figures. Accepted for publication by Monthly Notices of
the Royal Astronomical Society. Please see
http://astronomy.swin.edu.au/~mmurphy/pub.html for an ASCII version of table
A1 and the full set of Voigt profile fits for appendix
Prediction of Spontaneous Preterm Birth Among Nulliparous Women With a Short Cervix
To evaluate whether demographic and sonographic factors associated with spontaneous preterm birth (sPTB) among nulliparous women with a cervical length (CL) < 30 mm could be combined into an accurate prediction model for sPTB
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