148 research outputs found
Mapping Luminous Blue Compact Galaxies with VIRUS-P: morphology, line ratios and kinematics
[abridged] We carry out an integral field spectroscopy (IFS) study of a
sample of luminous BCGs, with the aim to probe the morphology, kinematics, dust
extinction and excitation mechanisms of their warm interstellar medium (ISM).
IFS data for five luminous BCGs were obtained using VIRUS-P, the prototype
instrument for the Visible Integral Field Replicable Unit Spectrograph,
attached to the 2.7m Harlan J. Smith Telescope at the McDonald Observatory.
VIRUS-P consists of a square array of 247 optical fibers, which covers a
109"x109" field of view, with a spatial sampling of 4.2" and a 0.3 filling
factor. We observed in the 3550-5850 Angstrom spectral range, with a resolution
of 5 A FWHM. From these data we built two-dimensional maps of the continuum and
the most prominent emission-lines ([OII]3727, Hgamma, Hbeta and [OIII]5007),
and investigate the morphology of diagnostic emission-line ratios and the
extinction patterns in the ISM as well as stellar and gas kinematics.
Additionally, from integrated spectra we infer total line fluxes and
luminosity-weighted extinction coefficients and gas-phase metallicities. All
galaxies exhibit an overall regular morphology in the stellar continuum, while
their warm ISM morphology is more complex: in II Zw 33 and Mrk 314, the
star-forming regions are aligned along a chain-structure; Haro 1, NGC 4670 and
III Zw 102 display several salient features, such as extended gaseous filaments
and bubbles. A significant intrinsic absorption by dust is present in all
galaxies, the most extreme case being III Zw 102. Our data reveal a manifold of
kinematical patterns, from overall regular gas and stellar rotation to complex
velocity fields produced by structurally and kinematically distinct components.Comment: Accepted for publication in A&A. 16 pages, 10 figure
Multi-seeded multi-mode formation of embedded clusters in the RMC: Structured star formation toward the south-east boundary
The Rosette Molecular Complex contains embedded clusters with diverse
properties and origins. We have previously explored the shell mode of formation
in the north (Regions A & B) and the massive concentrations in the ridge
(Region C). Here, we explore star formation towards the south of the complex,
Region D, based on data from the spatially complete 2 Micron All Sky Survey. We
find that stars are forming prolifically throughout this region in a highly
structured mode with both clusters and loose aggregates detected. The most
prominent cluster (Region D1) lies in the north-center. This cluster is over 20
pc to the south of the Monoceros ridge, the interface of the emerging young OB
cluster NGC 2244 with its ambient molecular clouds. In addition, there are
several branches stemming from AFGL 961 in Region C and extending to the
south-east boundary of the cloud. We invoke a tree model to interpret this
pattern, corresponding to probable tracks of abrupt turbulent excitation and
subsequent decay. Alternatively, we discuss gravoturbulent collapse scenarios
based on numerical simulations. Relative stellar ages and gas flow directions
will differentiate between these mechanisms.Comment: 9 figures, the 4th of a series of paper
Mid-IR emission of galaxies in the Virgo cluster and in the Coma supercluster.IV. The nature of the dust heating sources
We study the relationship between the mid-IR (5-18 m) emission of
late-type galaxies and various other star formation tracers in order to
investigate the nature of the dust heating sources in this spectral domain. The
analysis is carried out using a sample of 123 normal, late-type, nearby
galaxies with available data at several frequencies. The mid-IR luminosity
(normalized to the H-band luminosity) correlates better with the far-IR
luminosity than with more direct tracers of the young stellar population such
as the H and the UV luminosity. The comparison of resolved images
reveals a remarkable similarity in the H and mid-IR morphologies, with
prominent HII regions at both frequencies. The mid-IR images, however, show in
addition a diffuse emission not associated with HII regions nor with the
diffuse H emission. This evidence indicates that the stellar population
responsible for the heating of dust emitting in the mid-IR is similar to that
heating big grains emitting in the far-IR, including relatively evolved stars
responsible for the non-ionizing radiation. The scatter in the mid-IR vs.
H, UV and far-IR luminosity relation is mostly due to metallicity
effects, with metal-poor objects having a lower mid-IR emission per unit star
formation rate than metal-rich galaxies. Our analysis indicates that the mid-IR
luminosity is not an optimal star formation tracer in normal, late-type
galaxies.Comment: accepted for publication on A&
An Aromatic Inventory of the Local Volume
Using infrared photometry from the Spitzer Space Telescope, we perform the
first inventory of aromatic feature emission (AFE, but also commonly referred
to as PAH emission) for a statistically complete sample of star-forming
galaxies in the local volume. The photometric methodology involved is
calibrated and demonstrated to recover the aromatic fraction of the IRAC 8
micron flux with a standard deviation of 6% for a training set of 40 SINGS
galaxies (ranging from stellar to dust dominated) with both suitable
mid-infrared Spitzer IRS spectra and equivalent photometry. A potential factor
of two improvement could be realized with suitable 5.5 and 10 micron
photometry, such as what may be provided in the future by JWST. The resulting
technique is then applied to mid-infrared photometry for the 258 galaxies from
the Local Volume Legacy (LVL) survey, a large sample dominated in number by
low-luminosity dwarf galaxies for which obtaining comparable mid-infrared
spectroscopy is not feasible. We find the total LVL luminosity due to five
strong aromatic features in the 8 micron complex to be 2.47E10 solar
luminosities with a mean volume density of 8.8E6 solar luminosities per cubic
Megaparsec. Twenty-four of the LVL galaxies, corresponding to a luminosity cut
at M = -18.22 in the B band, account for 90% of the aromatic luminosity. Using
oxygen abundances compiled from the literature for 129 of the 258 LVL galaxies,
we find a correlation between metallicity and the aromatic to total infrared
emission ratio but not the aromatic to total 8 micron dust emission ratio. A
possible explanation is that metallicity plays a role in the abundance of
aromatic molecules relative to the total dust content, but other factors such
as star formation and/or the local radiation field affect the excitation of
those molecules.Comment: ApJ in press; 29 pages, 14 figures, 3 tables; emulateapj forma
β-Elemene Piperazine Derivatives Induce Apoptosis in Human Leukemia Cells through Downregulation of c-FLIP and Generation of ROS
β-Elemene is an active component of the herb medicine Curcuma Wenyujin with reported antitumor activity. To improve its antitumor ability, five novel piperazine derivatives of β-elemene, 13-(3-methyl-1-piperazinyl)-β-elemene (DX1), 13-(cis-3,5-dimethyl-1-piperazinyl)-β-elemene (DX2), 13-(4-ethyl-1-piperazinyl)-β-elemene (DX3), 13-(4-isopropyl-1-piperazinyl)-β-elemene (DX4) and 13-piperazinyl-β-elemene (DX5), were synthesized. The antiproliferative and apoptotic effects of these derivatives were determined in human leukemia HL-60, NB4, K562 and HP100-1 cells. DX1, DX2 and DX5, which contain a secondary amino moiety, were more active in inhibiting cell growth and in inducing apoptosis than DX3 and DX4. The apoptosis induction ability of DX1 was associated with the generation of hydrogen peroxide (H2O2), a decrease of mitochondrial membrane potential (MMP), and the activation of caspase-8. Pretreatment with the antioxidants N-acetylcysteine and catalase completely blocked DX1-induced H2O2 production, but only partially its activation of caspase-8 and induction of apoptosis. HL-60 cells were more sensitive than its H2O2-resistant subclone HP100-1 cells to DX1-induced apoptosis. The activation of caspase-8 by these compounds was correlated with the decrease in the levels of cellular FLICE-inhibitory protein (c-FLIP). The proteasome inhibitor MG-132 augmented the decrease in c-FLIP levels and apoptosis induced by these derivatives. FADD- and caspase-8-deficient Jurkat subclones have a decreased response to DX1-induced apoptosis. Our data indicate that these novel β-elemene piperazine derivatives induce apoptosis through the decrease in c-FLIP levels and the production of H2O2 which leads to activation of both death receptor- and mitochondrial-mediated apoptotic pathways
Vital function of PRELI and essential requirement of its LEA motif
Proteins containing the late embryogenesis abundant (LEA) motif comprise a conserved family, postulated to act as cell protectors. However, their function and mechanisms of action remain unclear. Here we show that PRELI, a mammalian LEA-containing homolog of yeast Ups1p, can associate with dynamin-like GTPase Optic Atrophy-1 (OPA1) and contribute to the maintenance of mitochondrial morphology. Accordingly, PRELI can uphold mitochondrial membrane potential (ΔΨm) and enhance respiratory chain (RC) function, shown by its capacity to induce complex-I/NADH dehydrogenase and ATP synthase expression, increase oxygen consumption and reduce reactive oxygen species (ROS) production. PRELI can also inhibit cell death induced by STS, TNF-α or UV irradiation. Moreover, in vitro and in vivo dominant-negative overexpression of mutant PRELI/LEA− (lacking the LEA motif) and transient in vitro PRELI-specific knockdown can render lymphocytes vulnerable to apoptosis, cause mouse embryo lethality and revert the resistance of lymphoma cells to induced death. Collectively, these data support the long-presumed notion of LEA protein-dependent mechanisms of cytoprotection and suggest that PRELI interacts with OPA1 to maintain mitochondria structures intact, sustain balanced ion−/proton+ gradients, promote oxidative phosphorylation reactions, regulate pro- and antiapoptotic protein traffic and enable cell responses to induced death. These findings may help to understand how bioenergetics is mechanistically connected with cell survival cues
ISM Properties in Low-Metallicity Environments III. The Dust Spectral Energy Distributions of II Zw 40, He 2-10 and NGC 1140
We present new 450 and 850 micron SCUBA data and 1.3 mm MAMBO data of the
dwarf galaxies II Zw 40, He 2-10 and NGC 1140. Additional ISOCAM, IRAS as well
as ground based data are used to construct the observed mid-infrared to
millimeter spectral energy distribution of these galaxies. These spectral
energy distributions are modeled in a self-consistent way, as was achieved with
NGC 1569 (Galliano et al., 2003), synthesizing both the global stellar
radiation field and the dust emission, with further constraints provided by the
photoionisation of the gas. Our study shows that low-metallicity galaxies have
very different dust properties compared to the Galaxy.
Our main results are: (i) a paucity of PAHs which are likely destroyed by the
hard penetrating radiation field, (ii) a very small (3-4 nm) average size of
grains, consistent with the fragmentation and erosion of dust particles by the
numerous shocks, (iii) a significant millimetre excess in the dust spectral
energy distribution which can be explained by the presence of ubiquitous very
cold dust (T=5-9 K) accounting for 40 to 80 % of the total dust mass, probably
distributed in small clumps. We derive a range of gas-to-dust mass ratios
between 300 and 2000, larger than the Galactic values and dust-to-metals ratios
of 1/30 to 1/2. The modeled dust size distributions are used to synthesize an
extinction curve for each galaxy. The UV slopes of the extinction curves
resemble that observed in some regions in the Large Magellanic Cloud. The 2175
angstrom bumps of the modeled extinction curves are weaker than that of the
Galaxy, except in the case of II Zw 40, where we are unable to accurately
constrain the 2175 angstrom bump carrier.Comment: A&A, 19 pages, 31 figure
Quantum transport and utilization of free energy in protein -helices
The essential biological processes that sustain life are catalyzed by protein
nano-engines, which maintain living systems in far-from-equilibrium ordered
states. To investigate energetic processes in proteins, we have analyzed the
system of generalized Davydov equations that govern the quantum dynamics of
multiple amide I exciton quanta propagating along the hydrogen-bonded peptide
groups in -helices. Computational simulations have confirmed the
generation of moving Davydov solitons by applied pulses of amide I energy for
protein -helices of varying length. The stability and mobility of these
solitons depended on the uniformity of dipole-dipole coupling between amide I
oscillators, and the isotropy of the exciton-phonon interaction. Davydov
solitons were also able to quantum tunnel through massive barriers, or to
quantum interfere at collision sites. The results presented here support a
nontrivial role of quantum effects in biological systems that lies beyond the
mechanistic support of covalent bonds as binding agents of macromolecular
structures. Quantum tunneling and interference of Davydov solitons provide
catalytically active macromolecular protein complexes with a physical mechanism
allowing highly efficient transport, delivery, and utilization of free energy,
besides the evolutionary mandate of biological order that supports the
existence of such genuine quantum phenomena, and may indeed demarcate the
quantum boundaries of life.Comment: 40 pages, 20 figure
Robust estimation of bacterial cell count from optical density
Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data
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