1,047 research outputs found
Harnessing open-source technology for low-cost automation in synthesis: flow chemical deprotection of silyl ethers using a homemade autosampling system.
An inexpensive homemade 3-axis autosampler was used to facilitate the automation of an acid catalysed flow chemical desilylation reaction. Harnessing open-source software technologies (Python, OpenCV), an automated computer-vision controlled liquid-liquid extraction step was used to provide effective inline purification. A Raspberry Pi single-board computer was employed to interface with the motors used in the autosampler and actuated fluidic valves
On The Age Estimation of LBDS 53W091
The recent spectral analysis of LBDS 53W091 by Spinrad and his collaborators
has suggested that this red galaxy at z=1.55 is at least 3.5 Gyr old. This
imposes an important constraint on cosmology, suggesting that this galaxy
formed at z > 6.5, assuming recent estimates of cosmological parameters. We
have performed chi^2 tests to the continuum of this galaxy using its UV
spectrum and photometric data (RJHK). We have used the updated Yi models that
are based on the Yale tracks. We find it extremely difficult to reproduce such
large age estimates, under the assumption of the most probable input
parameters. Using the same configuration as in Spinrad et al. (solar abundance
models), our analysis suggests an age of approximately 1.4 -- 1.8 Gyr. The
discrepancy between Spinrad et al.'s age estimate (based on the 1997 Jimenez
models) and ours originates from the large difference in the model integrated
spectrum: the Jimenez models are much bluer than the Yi models and the Bruzual
\& Charlot (BC) models. Preliminary tests favor the Yi and BC models. The
updated age estimate of LBDS 53W091 would suggest that this galaxy formed
approximately at z=2-3.Comment: LaTeX, 18 eps files Accepted for publication in ApJ (Feb 10, 2000,
vol 530), uses emulateapj.st
Spores of Clostridium engineered for clinical efficacy and safety cause regression and cure of tumors in vivo.
Spores of some species of the strictly anaerobic bacteria Clostridium naturally target and partially lyse the hypoxic cores of tumors, which tend to be refractory to conventional therapies. The anti-tumor effect can be augmented by engineering strains to convert a non-toxic prodrug into a cytotoxic drug specifically at the tumor site by expressing a prodrug-converting enzyme (PCE). Safe doses of the favored prodrug CB1954 lead to peak concentrations of 6.3 ÎŒM in patient sera, but at these concentration(s) known nitroreductase (NTR) PCEs for this prodrug show low activity. Furthermore, efficacious and safe Clostridium strains that stably express a PCE have not been reported. Here we identify a novel nitroreductase from Neisseria meningitidis, NmeNTR, which is able to activate CB1954 at clinically-achievable serum concentrations. An NmeNTR expression cassette, which does not contain an antibiotic resistance marker, was stably localized to the chromosome of Clostridium sporogenes using a new integration method, and the strain was disabled for safety and containment by making it a uracil auxotroph. The efficacy of Clostridium-Directed Enzyme Prodrug Therapy (CDEPT) using this system was demonstrated in a mouse xenograft model of human colon carcinoma. Substantial tumor suppression was achieved, and several animals were cured. These encouraging data suggest that the novel enzyme and strain engineering approach represent a promising platform for the clinical development of CDEPT
F stars, metallicity, and the ages of red galaxies at z > 1
We explore whether the rest-frame near-UV spectral region, observable in
high-redshift galaxies via optical spectroscopy, contains sufficient
information to allow the degeneracy between age and metallicity to be lifted.
We do this by testing the ability of evolutionary synthesis models to reclaim
the correct metallicity when fitted to the near-UV spectra of F stars of known
(sub-solar and super-solar) metallicity. F stars are of particular interest
because the rest-frame near-UV spectra of the oldest known elliptical galaxies
at z > 1 appear to be dominated by F stars near to the main-sequence turnoff.
We find that, in the case of the F stars, where the HST ultraviolet spectra
have high signal:noise, model-fitting with metallicity allowed to vary as a
free parameter is rather successful at deriving the correct metallicity. As a
result, the estimated turnoff ages of these stars yielded by the model fitting
are well constrained. Encouraged by this we have fitted these same variable-
metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio
galaxies 53W091 and 53W069 obtained with the Keck telescope. While the
age-metallicity degeneracy is not so easily lifted for these galaxies, we find
that even when metallicity is allowed as a free parameter, the best estimates
of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly
excluded. Furthermore, we find that a search of the entire parameter space of
metallicity and star formation history using MOPED (Heavens et al., 2000) leads
to the same conclusion. Our results therefore continue to argue strongly
against an Einstein-de Sitter universe, and favour a lambda-dominated universe
in which star formation in at least these particular elliptical galaxies was
completed somewhere in the redshift range z = 3 - 5.Comment: 10 pages, LaTeX, uses MNRAS style file, incorporates 14 postscript
figures, submitted to MNRAS. Changes include: inclusion of single stellar
atmosphere model fits; more rigorous calculation of confidence regions; some
re-structurin
Gaps between zeros of Dedekind zeta-functions of quadratic number fields. II
Let be a quadratic number field and be the associated
Dedekind zeta-function. We show that there are infinitely many normalized gaps
between consecutive zeros of on the critical line which are
greater than times the average spacing.Comment: 12 pages; to appear in the Quarterly Journal of Mathematic
Mass fluxes for O stars
The theory of moving reversing layers for hot stars is updated to include an
extensive line list, a radiative boundary condition from static model
atmospheres, line transfer by scattering, and continuation to supersonic
velocities. A Monte Carlo technique determines the theory's eigenvalue J, the
mass flux, and the derived J's are in good agreement with the wind models of
Pauldrach et al. (2001). The solutions' sensitivity to the photospheric
microturbulent velocity reveals that this parameter has a throttling effect on
J: turbulent line-broadening in the quasi-static layers reduces the radiation
force available to accelerate matter through the sonic point. If photospheric
turbulence approaches sonic velocities, this mechanism reduces mass loss rates
by factors > 3, which would partly account for the reduced rates found
observationally for clumpy winds.Comment: Accepted by A&A; 9 pages, 4 figure
Paraphrases and summaries: A means of clarification or a vehicle for articulating a preferred version of student accounts?
The use of group discussions as a means to facilitate learning from experiences is well documented in adventure education literature. Priest and Naismith (1993) assert that the use of the circular discussion method, where the leader poses questions to the participants, is the most common form of facilitation in adventure education. This paper draws on transcripts of facilitation sessions to argue that the widely advocated practice of leader summaries or paraphrases of student responses in these sessions functions as a potential mechanism to control and sponsor particular knowledge(s). Using transcripts from recorded facilitation sessions the analysis focuses on how the leader paraphrases the studentsâ responses and how these paraphrases or âformulationsâ function to modify or exclude particular aspects of the studentsâ responses. I assert that paraphrasing is not simply a neutral activity that merely functions to clarify a student response, it is a subtle means by which the leader of the session can, often inadvertently or unknowingly, alter the studentâs reply with the consequence of favouring particular knowledge(s). Revealing the subtle work that leader paraphrases perform is of importance for educators who claim to provide genuine opportunities for students to learn from their experience
The radial velocity curve of HD153919 (4U1700-37) revisited
We have re-analysed all available high-resolution ultraviolet IUE spectra of
the high-mass X-ray binary HD153919/4U1700-37. The radial velocity
semi-amplitude of 20.6 +/- 1.0 km/s and orbital eccentricity of 0.22 +/- 0.04
agree very well with the values obtained earlier from optical spectra. They
disagree with earlier conclusions for the same data reduced by Heap & Corcoran
(1992) and by Stickland & Lloyd (1993).Comment: 6 pages, latex, figure included, Astronomy & Astrophysics, in pres
Understanding Schools and Schooling. (Book Review)
A review of a book written by Clive Chitty (2002 with a useful focus on issues of equity and social justice, including prejudice, discrimination and bullying in secondary schools. Education policy makers need to explore the extent to which it is important to produce interested, motivated and socially balanced young adults. It is well researched and documented
Optical Structure and Proper-Motion Age of the Oxygen-rich Supernova Remnant 1E 0102-7219 in the Small Magellanic Cloud
We present new optical emission-line images of the young SNR 1E 0102-7219
(E0102) in the SMC obtained with the HST Advanced Camera for Surveys (ACS).
E0102 is a member of the oxygen-rich class of SNRs showing strong oxygen, neon
, and other metal-line emissions in its optical and X-ray spectra, and an
absence of H and He. The progenitor of E0102 may have been a Wolf-Rayet star
that underwent considerable mass loss prior to exploding as a Type Ib/c or
IIL/b SN. The ejecta in this SNR are fast-moving (V > 1000 km/s) and emit as
they are compressed and heated in the reverse shock. In 2003, we obtained
optical [O III], H-alpha, and continuum images with the ACS Wide Field Camera.
The [O III] image captures the full velocity range of the ejecta, and shows
considerable high-velocity emission projected in the middle of the SNR that was
Doppler-shifted out of the narrow F502N bandpass of a previous Wide Field and
Planetary Camera 2 image from 1995. Using these two epochs separated by ~8.5
years, we measure the transverse expansion of the ejecta around the outer rim
in this SNR for the first time at visible wavelengths. From proper-motion
measurements of 12 ejecta filaments, we estimate a mean expansion velocity for
the bright ejecta of ~2000 km/s and an inferred kinematic age for the SNR of
\~2050 +/- 600 years. The age we derive from HST data is about twice that
inferred by Hughes et al.(2000) from X-ray data, though our 1-sigma error bars
overlap. Our proper-motion age is consistent with an independent optical
kinematic age derived by Eriksen et al.(2003) using spatially resolved [O III]
radial-velocity data. We derive an expansion center that lies very close to
X-ray and radio hotspots, which could indicate the presence of a compact
remnant (neutron star or black hole).Comment: 28 pages, 8 figures. Accepted to the Astrophysical Journal, to appear
in 20 April 2006 issue. Full resolution figures are posted at:
http://stevenf.asu.edu/figure
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