272 research outputs found
Building a CCD Spectrograph for Educational or Amateur Astronomy
We discuss the design of an inexpensive, high-throughput CCD spectrograph for
a small telescope. By using optical fibers to carry the light from the
telescope focus to a table-top spectrograph, one can minimize the weight
carried by the telescope and simplify the spectrograph design. We recently
employed this approach in the construction of IntroSpec, an instrument built
for the 16-inch Knowles Telescope on the Harvard College campus.Comment: 17 pages including 7 figures, PASP, accepted (higher resolution
figures at http://cfa-www.harvard.edu/~sheila/introspec.ps.gz
Targeting Inflammatory Pathways by Triterpenoids for Prevention and Treatment of Cancer
Traditional medicine and diet has served mankind through the ages for prevention and treatment of most chronic diseases. Mounting evidence suggests that chronic inflammation mediates most chronic diseases, including cancer. More than other transcription factors, nuclear factor-kappaB (NF-κB) and STAT3 have emerged as major regulators of inflammation, cellular transformation, and tumor cell survival, proliferation, invasion, angiogenesis, and metastasis. Thus, agents that can inhibit NF-κB and STAT3 activation pathways have the potential to both prevent and treat cancer. In this review, we examine the potential of one group of compounds called triterpenes, derived from traditional medicine and diet for their ability to suppress inflammatory pathways linked to tumorigenesis. These triterpenes include avicins, betulinic acid, boswellic acid, celastrol, diosgenin, madecassic acid, maslinic acid, momordin, saikosaponins, platycodon, pristimerin, ursolic acid, and withanolide. This review thus supports the famous adage of Hippocrates, “Let food be thy medicine and medicine be thy food”
Physical Sources of Scatter in the Tully-Fisher Relation
We analyze residuals from the Tully-Fisher relation for the emission-line
galaxies in the Nearby Field Galaxy Survey, a broadly representative survey
designed to fairly sample the variety of galaxy morphologies and environments
in the local universe. For spirals brighter than M_R^i=-18, we find strong
correlations between Tully-Fisher residuals and both B-R color and EW(Halpha).
The extremes of the correlations are populated by Sa galaxies, which show
consistently red colors, and spirals with morphological peculiarities, which
are often blue. If we apply an EW(Halpha)-dependent or B-R color-dependent
correction term to the Tully-Fisher relation, the scatter in the relation no
longer increases from R to B to U but instead drops to a nearly constant level
close to the scatter we expect from measurement errors. We argue that these
results probably reflect correlated offsets in luminosity and color as a
function of star formation history. Broadening the sample in morphology and
luminosity, we find that most non-spirals brighter than M_R^i=-18 follow the
same correlations as do spirals, albeit with greater scatter. However, the
color and EW(Halpha) correlations do not apply to galaxies fainter than
M_R^i=-18 or to emission-line S0 galaxies with anomalous gas kinematics. For
the dwarf galaxy population, the parameters controlling Tully-Fisher residuals
are instead related to the degree of recent disturbance: overluminous dwarfs
have higher rotation curve asymmetries, brighter U-band effective surface
brightnesses, and shorter gas consumption timescales than their underluminous
counterparts. As a result, sample selection strongly affects the measured
faint-end slope of the Tully-Fisher relation. Passively evolving, rotationally
supported galaxies display a break toward steeper slope at low luminosities.Comment: 58 pages including 21 figures, AJ, accepte
Forming Young Bulges within Existing Disks: Statistical Evidence for External Drivers
Contrary to traditional models of galaxy formation, recent observations
suggest that some bulges form within preexisting disk galaxies. Such late-epoch
bulge formation within disks seems to be linked to disk gas inflow and central
star formation, caused by either internal secular processes or galaxy mergers
and interactions. We identify a population of galaxies likely to be
experiencing active bulge growth within disks, using the criterion that the
color within the half-light radius is bluer than the outer disk color. Such
blue-centered galaxies make up >10% of star-forming disk galaxies within the
Nearby Field Galaxy Survey, a broad survey designed to represent the natural
diversity of the low-z galaxy population over a wide range of luminosities and
environments. Blue-centered galaxies correlate at 99% confidence with
morphological peculiarities suggestive of minor mergers and interactions. From
this and other evidence, we argue that external drivers rather than internal
secular processes probably account for the majority of blue-centered galaxies.
We go on to discuss quantitative plausibility arguments indicating that
blue-centered evolutionary phases may represent an important mode of bulge
growth for most disk galaxies, leading to significant changes in bulge-to-disk
ratio without destroying disks. If this view is correct, bulge growth within
disks may be a natural consequence of the repeated galaxy mergers and
interactions inherent in hierarchical galaxy formation.Comment: 18 pages including 12 figures, AJ, accepte
Cyclodextrin-complexed curcumin exhibits anti-inflammatory and antiproliferative activities superior to those of curcumin through higher cellular uptake (vol 80, vol 1021, 2010)
Retraction notice to “Cyclodextrin-complexed curcumin exhibits anti-inflammatory and antiproliferative activities superior to those of curcumin through higher cellular uptake” [Biochem. Pharmacol. 80 (2010) 1021–1032].Non peer reviewe
Microstructure and wear behaviour of high alloyed hot-work tool steels 1.2343 and 1.2367 under thermo-mechanical loading
Tools and their maintenance costs in hot forging processes account for a considerable proportion of the total components' costs. Forging tools undergo extreme heating and subsequent cooling during the forging process and between the forging cycles, respectively. This cyclic heating and cooling of the tool surfaces leads to local changes in the tool microstructure which result in hardening or softening of the material in different regions of the tool and consequently influence the tool strength. Temperature in the tool areas experiencing high thermo-mechanical loadings can exceed the austenitic temperature. Hence, a strong cooling, for example by spraying or lubrication, can lead to formation of a martensitic layer in the boundary zone of the tool. Due to its higher hardness, martensitic layer has greater resistance to wear as compared to the basic or tempered materials. In the scope of this paper, the austenitisation behaviours of two high alloyed hot-work tool steels, 1.2343 and 1.2367, have been characterized by means of dilatometer tests to obtain time-temperature-austenitisation (TTA) diagrams for specimen under thermo-mechanical loads. Moreover, continuous-cooling-transformation (CCT) diagrams were recorded. Metallographic investigations were carried out to gather a detailed understanding of the microstructure behaviour and its resulting hardness. With the results of this works, it is aimed to gather a detailed and accurate insight into the arising hardening and softening effects. This would eventually lead to an optimisation of the numerical modelling for tool wear prediction
A forming disk at z~0.6: Collapse of a gaseous disk or major merger remnant?
[Abridged] We present and analyze observations of J033241.88-274853.9 at
z=0.6679, using multi-wavelength photometry and imaging with FLAMES/GIRAFFE 3D
spectroscopy. J033241.88-274853.9 is found to be a blue, young (~320Myr)
stellar disk embedded in a very gas-rich (fgas=73-82% with
log(Mstellar/Mo)=9.45) and turbulent phase that is found to be rotating on
large spatial scales. We identified two unusual properties of
J033241.88-274853.9. (1) The spatial distributions of the ionized gaseous and
young stars show a strong decoupling; while almost no stars can be detected in
the southern part down to the very deep detection limit of ACS/UDF images,
significant emission from the [OII] ionized gas is detected. (2) We detect an
excess of velocity dispersion in the southern part of J033241.88-274853.9 in
comparison to expectations from a rotating disk model. We considered two disk
formation scenarios, depending on the gaseous phase geometry. In the first one,
we examined whether J033241.88-274853.9 could be a young rotating disk that has
been recently collapsed from a pre-existing, very gas-rich rotating disk. This
scenario requires two (unknown) additional assumptions to explain the
decoupling between the distribution of stars and gas and the excess of velocity
dispersion in the same region. In a second scenario, we examine whether
J033241.88-274853.9 could be a merger remnant of two gas-rich disks. In this
case, the asymmetry observed between the gas and star distributions, as well as
the excess of velocity dispersion, find a common explanation. Shocks produced
during the merger in this region can be ionized easily and heat the gas while
preventing star formation. This makes this scenario more satisfactory than the
collapse of a pre-existing, gas-rich rotating disk.Comment: Accepted for publication in A&A. 8 pages & 5 figure
The Bimodal Galaxy Stellar Mass Function in the COSMOS Survey to z~1: A Steep Faint End and a New Galaxy Dichotomy
We present a new analysis of stellar mass functions (MF) in the COSMOS field
to fainter limits than has been previously probed to z~1. Neither the total nor
the passive or star-forming MF can be well fit with a single Schechter function
once one probes below 3e9 Msun. We observe a dip or plateau at masses ~1e10
Msun, and an upturn towards a steep faint-end slope of -1.7 at lower mass at
any z<1. This bimodal nature of the MF is not solely a result of the blue/red
dichotomy. The blue MF is by itself bimodal at z~1. This suggests a new
dichotomy in galaxy formation that predates the appearance of the red sequence.
We propose two interpretations for this bimodality. If the gas fraction
increases towards lower mass, galaxies with M_baryon~1e10 Msun would shift to
lower stellar masses, creating the observed dip. This would indicate a change
in star formation efficiency, perhaps linked to supernovae feedback becoming
much more efficient. Therefore, we investigate whether the dip is present in
the baryonic (stars+gas) MF. Alternatively, the dip could be created by an
enhancement of the galaxy assembly rate at ~1e11 Msun, a phenomenon that
naturally arises if the baryon fraction peaks at M_halo ~1e12 Msun. In this
scenario, galaxies occupying the bump around M* would be identified with
central galaxies and the second fainter component having a steep faint-end
slope with satellites. While the dip is apparent in the total MF at any z, it
appears to shift from the blue to red population, likely as a result of
transforming high-mass blue galaxies into red ones. At the same time, we detect
a drastic upturn in the number of low-mass red galaxies. Their increase with
time reflects a decrease in the number of blue systems and so we tentatively
associate them with satellite dwarf galaxies that have undergone quenching.Comment: 16 pages, 10 figures, accepted for publication in Ap
HI Observations of the Ca II absorbing galaxies Mrk 1456 and SDSS J211701.26-002633.7
In an effort to study Damped Lyman Alpha galaxies at low redshift, we have
been using the Sloan Digital Sky Survey to identify galaxies projected onto QSO
sightlines and to characterize their optical properties. For low redshift
galaxies, the HI 21cm emission line can be used as an alternate tool for
identifying possible DLA galaxies, since HI emitting galaxies typically exhibit
HI columns that are larger than the classical DLA limit. Here we report on
follow-up HI 21 cm emission line observations of two DLA candidates that are
both low-redshift spiral galaxies, Mrk 1456 and SDSS J211701.26-002633.7. The
observations were made using the Green Bank and Arecibo Telescopes,
respectively. Analysis of their HI properties reveal the galaxies to be about
one and two M_HI* galaxies, respectively, and to have average HI mass,
gas-richness, and gas mass fraction for their morphological types. We consider
Mrk 1456 and SDSS J211701.26-002633.7 to be candidate DLA systems based upon
the strength of the CaII absorption lines they cause in their QSO's spectra,
and impact parameters to the QSO that are smaller than the stellar disk.
Compared to the small numbers of other HI-detected DLA and candidate DLA
galaxies, Mrk 1456 and SDSS J211701.26-002633.7 have high HI masses. When
compared with the expected properties of low-z DLAs from an HI-detected sample
of galaxies, Mrk 1456 and SDSS J211701.26-002633.7 fall within the ranges for
impact parameter and B-band absolute magnitude; and the HI mass distribution
for the HI-detected DLAs agrees with that of the expected HI mass distribution
for low-z DLAs. Our observations support galaxy-evolution models in which high
mass galaxies make up an increasing contribution to the DLA cross-section at
lower redshifts. [abridged]Comment: 12 pages, 5 figures, 5 tables; to be published in The Astronomical
Journa
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