440 research outputs found
Clues to the nature of high-redshift OVI absorption systems from their (lack of) small-scale structure
We present results of the first survey of high-redshift ( ~ 2.3) OVI
absorption systems along parallel lines of sight toward two lensed QSOs. After
a careful and well-defined search, we find ten intervening OVI systems. Within
the errors, all OVI systems appear at the same redshift and have similar line
strengths in front of both QSO images, whereas in most cases CIV or SiIV show
more differences across the lines of sight, either in radial velocity or line
strength. We conclude that (1) the coherence length of OVI must be much larger
than ~ 1 kpc, and (2) an important fraction of the CIV absorbers may not reside
in the same volume as OVI. Since Doppler parameters are consistent with
photoionization, we propose a model in which CIV occurs in two different
photoionized phases, one large, with characteristic sizes of a few hundred kpc
and bearing OVI, and another one a factor of ten smaller and containing CIII.
This model is able to explain the various transverse differences observed in
column density and kinematics. We apply the model successfully to 2 kinds of
absorbers, with low and high metallicity. In the low-metallicity regime, [C/H]
\~ -2, we find that [C/O] ~ -0.7 is required to explain the observations, which
hints at late (z < 6) rather than early metal enrichment. In the
high-metallicity regime, the observed dissociation between OVI and CIV gas
might be produced by galactic outflows. Altogether, the relative abundances,
inhomogeneous CIV and featureless OVI are consistent with gas that has been
processed recently before the absorption occurred (thus close to star-forming
regions). Finally, we discuss briefly three associated systems (z_abs ~ z_em)
that also show OVI. (abridged)Comment: Accepted by A&A, 22 page
Differentiation of mammary tumors and reduction in metastasis upon Malat1 lncRNA loss
Genome-wide analyses have identified thousands of long noncoding RNAs (lncRNAs). Malat1 (metastasis-associated lung adenocarcinoma transcript 1) is among the most abundant lncRNAs whose expression is altered in numerous cancers. Here we report that genetic loss or systemic knockdown of Malat1 using antisense oligonucleotides (ASOs) in the MMTV (mouse mammary tumor virus)-PyMT mouse mammary carcinoma model results in slower tumor growth accompanied by significant differentiation into cystic tumors and a reduction in metastasis. Furthermore, Malat1 loss results in a reduction of branching morphogenesis in MMTV-PyMT- and Her2/neu-amplified tumor organoids, increased cell adhesion, and loss of migration. At the molecular level, Malat1 knockdown results in alterations in gene expression and changes in splicing patterns of genes involved in differentiation and protumorigenic signaling pathways. Together, these data demonstrate for the first time a functional role of Malat1 in regulating critical processes in mammary cancer pathogenesis. Thus, Malat1 represents an exciting therapeutic target, and Malat1 ASOs represent a potential therapy for inhibiting breast cancer progression
Hot Halos around High Redshift Protogalaxies: Observations of O VI and N V Absorption in Damped Lyman Alpha systems
(ABRIDGED) We present a study of the highly ionized gas (plasma) associated
with damped Lyman-alpha (DLA) systems at z=2.1-3.1. We search for O VI
absorption and corresponding Si IV, C IV, and N V in a Very Large
Telescope/Ultraviolet-Visible Echelle Spectrograph (VLT/UVES) sample of 35 DLA
systems with data covering O VI at S/N>10. We report twelve DLAs (nine
intervening and three at <5000 km/s from the QSO redshift) with detections of O
VI absorption. There are no clear O VI non-detections, so the incidence of O VI
in DLAs is between 34% (12/35) and 100%. Analysis of the line widths together
with photoionization modelling suggests that two phases of DLA plasma exist: a
hot, collisionally ionized phase (seen in broad O VI components), and a warm,
photoionized phase (seen just in narrow C IV and Si IV components). We find
tentative evidence (98% confidence) for correlations between the DLA
metallicity (measured in the neutral gas) and high-ion column density, and
between the DLA metallicity and high-ion line width, as would be expected if
supernova-driven galactic outflows rather than accretion produced the high
ions. Using conservative ionization corrections, we find lower limits to the
total hydrogen column densities in the hot (O VI-bearing) and warm (C
IV-bearing) phases in the range log N(Hot H II) >19.5 to >21.1, and log N(Warm
H II) >19.4 to >20.9. On average, the hot and warm phases thus contain >40% and
>20% of the baryonic mass of the neutral phase in DLAs, respectively. If the
temperature in the O VI phase is ~10^6 K and so f(O VI)=O VI/O<<0.2 the plasma
can make a significant contribution to the metal budget at high redshift.Comment: 18 pages, 7 figures (3 in color), accepted to A&
Scholarship Series: KSU Faculty Showcase
Kennesaw State University School of Music presents Faculty Showcase, a KSU School of Music Scholarship Series concert.https://digitalcommons.kennesaw.edu/musicprograms/1534/thumbnail.jp
9th Annual Kennesaw State University School of Music Collage Concert
KSU School of Music presents the 9th Annual Kennesaw State University School of Music Collage Concert.https://digitalcommons.kennesaw.edu/musicprograms/1203/thumbnail.jp
A simple model for the evolution of disc galaxies: The Milky Way
A simple model for the evolution of disc galaxies is presented. We adopt
three numbers from observations of the Milky Way disc, the local surface mass
density, the stellar scale length (of the assumedly exponential disc) and the
amplitude of the (assumedly flat) rotation curve, and physically, the (local)
dynamical Kennicutt star formation prescription, standard chemical evolution
equations assuming and a model for spectral evolution of stellar populations.
We can determine the detailed evolution of the model with only the addition of
standard cosmological scalings with time of the dimensional parameters. A
surprising wealth of detailed specifications follows from this prescription
including the gaseous infall rate as a function of radius and time, the
distribution of stellar ages and metallicities with time and radius, surface
brightness profiles at different wavelengths, colours etc. At the solar
neighbourhood stars start to form ago at an increasing rate
peaking 4 billion years ago and then slowly declining in good agreement with
observations. The mean age of long lived stars at the solar neighbourhood is
about . The local surface density of the stars and gas are 35 and , respectively. The metallicity distribution of the stars at
the solar radius is narrow with a peak at .Both a
Salpeter IMF and a Chabrier IMF are consistent with observations. Comparisons
with the current and local fossil evidence provides support for the model which
can then be used to assess other local disc galaxies, the evolution of disc
galaxies in deep optical surveys and also for theoretical investigations such
as simulations of merging disc galaxies (abbreviated).Comment: acceppted for publication in MNRA
In vivo Imaging and Drug Storage by Quantum-Dot-Conjugated Carbon Nanotubes
A specially designed carbon nanotube (CNT) is developed for use in the early detection and treatment of cancer. The key functionalities for biomedical diagnosis and drug delivery are incorporated into the CNTs. In vivo imaging of live mice is achieved by intravenously injecting quantum dot (QD)-conjugated CNT for the first time. With near infrared emission around 752 nm, the CNT with surface-conjugated QD (CNT-QD) exhibit a strong luminescence for non-invasive optical in vivo imaging. CNT surface modification is achieved by a plasma polymerization approach that deposited ultra-thin acrylic acid or poly(lactic- co -glycolic acid) (PLGA) films (∼3 nm) onto the nanotubes. The anticancer agent paclitaxel is loaded at 112.5 ± 5.8 µg mg −1 to PLGA-coated CNT. Cytotoxicity of this novel drug delivery system is evaluated in vitro using PC-3MM2 human prostate carcinoma cells and quantified by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The in vivo distribution determined by inductively coupled plasma mass spectrometry (ICP-MS) indicates CNT-QD uptake in various organs of live animals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60988/1/2489_ftp.pd
Spectral shape of the UV ionizing background and OVI absorbers at z ~ 1.5 towards HS0747+4259
We report on high resolution spectra of the bright QSO HS0747+4259 (zem =
1.90, V = 15.8) observed to search for intermediate redshift OVI absorption
systems. The spectra were obtained by means of the Space Telescope Imaging
Spectrograph (STIS) at the Hubble Space Telescope (HST) and the High Resolution
Echelle Spectrometer (HIRES) at the W. M. Keck telescope. We identify 16 OVI
systems in the range 1.07 <= z <= 1.87. Among them, six systems with zabs =
1.46-1.8 exhibit a sufficient number of lines of different ionic transitions to
estimate the shape of the ionizing radiation field in the range 1 Ryd < E < 10
Ryd. All recovered UV ionizing spectra are characterized by the enhanced
intensity at E > 3 Ryd compared to the model spectrum of Haardt and Madau
(1996). This is in line with the observational evidence of a deficiency of
strong Ly-alpha absorbers with N(HI) > 10^{15} cm^{-2}, at z < 2. The UV
background shows significant local variations: the spectral shape estimated at
z = 1.59 differs from that obtained at z = 1.81 and 1.73. A possible cause of
these variations is the presence of a QSO/AGN at z ~= 1.54-1.59 close to the
line of sight. No features favoring the input of stellar radiation to the
ionizing background are detected, limiting the escape fraction of the galactic
UV photons to f_esc < 0.05.Comment: 14 pages, 7 figures, 5 tables; accepted for publication in A&
Cationic Amino Acid Uptake Constitutes a Metabolic Regulation Mechanism and Occurs in the Flagellar Pocket of Trypanosoma cruzi
Trypanosomatids' amino acid permeases are key proteins in parasite metabolism since they participate in the adaptation of parasites to different environments. Here, we report that TcAAP3, a member of a Trypanosoma cruzi multigene family of permeases, is a bona fide arginine transporter. Most higher eukaryotic cells incorporate cationic amino acids through a single transporter. In contrast, T. cruzi can recognize and transport cationic amino acids by mono-specific permeases since a 100-fold molar excess of lysine could not affect the arginine transport in parasites that over-express the arginine permease (TcAAP3 epimastigotes). In order to test if the permease activity regulates downstream processes of the arginine metabolism, the expression of the single T. cruzi enzyme that uses arginine as substrate, arginine kinase, was evaluated in TcAAP3 epimastigotes. In this parasite model, intracellular arginine concentration increases 4-folds and ATP level remains constant until cultures reach the stationary phase of growth, with decreases of about 6-folds in respect to the controls. Interestingly, Western Blot analysis demonstrated that arginine kinase is significantly down-regulated during the stationary phase of growth in TcAAP3 epimastigotes. This decrease could represent a compensatory mechanism for the increase in ATP consumption as a consequence of the displacement of the reaction equilibrium of arginine kinase, when the intracellular arginine concentration augments and the glucose from the medium is exhausted. Using immunofluorescence techniques we also determined that TcAAP3 and the specific lysine transporter TcAAP7 co-localize in a specialized region of the plasma membrane named flagellar pocket, staining a single locus close to the flagellar pocket collar. Taken together these data suggest that arginine transport is closely related to arginine metabolism and cell energy balance. The clinical relevance of studying trypanosomatids' permeases relies on the possibility of using these molecules as a route of entry of therapeutic drugs
A General Definition and Nomenclature for Alternative Splicing Events
Understanding the molecular mechanisms responsible for the regulation of the transcriptome present in eukaryotic cells is one of the most challenging tasks in the postgenomic era. In this regard, alternative splicing (AS) is a key phenomenon contributing to the production of different mature transcripts from the same primary RNA sequence. As a plethora of different transcript forms is available in databases, a first step to uncover the biology that drives AS is to identify the different types of reflected splicing variation. In this work, we present a general definition of the AS event along with a notation system that involves the relative positions of the splice sites. This nomenclature univocally and dynamically assigns a specific “AS code” to every possible pattern of splicing variation. On the basis of this definition and the corresponding codes, we have developed a computational tool (AStalavista) that automatically characterizes the complete landscape of AS events in a given transcript annotation of a genome, thus providing a platform to investigate the transcriptome diversity across genes, chromosomes, and species. Our analysis reveals that a substantial part—in human more than a quarter—of the observed splicing variations are ignored in common classification pipelines. We have used AStalavista to investigate and to compare the AS landscape of different reference annotation sets in human and in other metazoan species and found that proportions of AS events change substantially depending on the annotation protocol, species-specific attributes, and coding constraints acting on the transcripts. The AStalavista system therefore provides a general framework to conduct specific studies investigating the occurrence, impact, and regulation of AS
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