494 research outputs found
Characterization of the Small RNA Transcriptome of the Marine Coccolithophorid, Emiliania huxleyi
Small RNAs (smRNAs) control a variety of cellular processes by silencing target genes at the transcriptional or post-transcription level. While extensively studied in plants, relatively little is known about smRNAs and their targets in marine phytoplankton, such as Emiliania huxleyi (E. huxleyi). Deep sequencing was performed of smRNAs extracted at different time points as E. huxleyi cells transition from logarithmic to stationary phase growth in batch culture. Computational analyses predicted 18 E. huxleyi specific miRNAs. The 18 miRNA candidates and their precursors vary in length (18-24 nt and 71-252 nt, respectively), genome copy number (3-1,459), and the number of genes targeted (2-107). Stem-loop real time reverse transcriptase (RT) PCR was used to validate miRNA expression which varied by nearly three orders of magnitude when growth slows and cells enter stationary phase. Stem-loop RT PCR was also used to examine the expression profiles of miRNA in calcifying and non-calcifying cultures, and a small subset was found to be differentially expressed when nutrients become limiting and calcification is enhanced. In addition to miRNAs, endogenous small RNAs such as ra-siRNAs, ta-siRNAs, nat-siRNAs, and piwiRNAs were predicted along with the machinery for the biogenesis and processing of si-RNAs. This study is the first genome-wide investigation smRNAs pathways in E. huxleyi. Results provide new insights into the importance of smRNAs in regulating aspects of physiological growth and adaptation in marine phytoplankton and further challenge the notion that smRNAs evolved with multicellularity, expanding our perspective of these ancient regulatory pathways
V-Shape Liquid Crystal-Based Retromodulator Air to Ground Optical Communications
This paper describes the use of a 2D liquid crystal retro-modulator as a free space, wireless, optical link. The retro-modulator is made up of a retro-reflecting cornercube onto which 2 cascaded V-shape smectics liquid crystal modulators are mounted. The communication link differs with respect to more conventional optical links in not using amplitude (nor frequency) modulation, but instead state-of-polarisation (SOP) modulation known as Polarisation Shift Keying (PolSK). PolSK has the advantage over amplitude modulation, that it is less sensitive to changes in the visibility of the atmosphere, and increases inherently the bandwidth of the link. The implementation of PolSK both in liquid crystal based and in retro-modulated communication are novelties
A Multiple System of Radio Sources at the Core of the L723 Multipolar Outflow
We present high angular resolution Very Large Array multi-epoch continuum
observations at 3.6 cm and 7 mm towards the core of the L723 multipolar outflow
revealing a multiple system of four radio sources suspected to be YSOs in a
region of only ~4 arcsecs (1200 AU) in extent. The 3.6 cm observations show
that the previously detected source VLA 2 contains a close (separation ~0.29
arcsecs or ~90 AU) radio binary, with components (A and B) along a position
angle of ~150 degrees. The northern component (VLA 2A) of this binary system is
also detected in the 7 mm observations, with a positive spectral index between
3.6 cm and 7 mm. In addition, the source VLA 2A is associated with extended
emission along a position angle of ~115 degrees, that we interpret as
outflowing shock-ionized gas that is exciting a system of HH objects with the
same position angle. A third, weak 3.6 cm source, VLA 2C, that is detected also
at 7 mm, is located ~0.7 arcsecs northeast of VLA 2A, and is possibly
associated with the water maser emission in the region. The 7 mm observations
reveal the presence of an additional source, VLA 2D, located ~3.5 arcsecs
southeast of VLA 2A, and with a 1.35 mm counterpart. All these radio continuum
sources have a positive spectral index, compatible with them being YSOs. We
also propose that the high velocity CO emission observed in the region could be
the superposition of multiple outflows (at least three independent bipolar
outflows) excited by the YSOs located at the core, instead of the previous
interpretations in terms of only one or two outflows.Comment: Accepted for publication in The Astrophysical Journal (2007 December
6
Clash of Titans: The Impact of Cluster Mergers in the Galaxy Cluster Red Sequence
Merging of galaxy clusters are some of the most energetic events in the
Universe, and they provide a unique environment to study galaxy evolution. We
use a sample of 84 merging and relaxed SPT galaxy clusters candidates, observed
with the Dark Energy Camera in the redshift range, to build
colour-magnitude diagrams to characterize the impact of cluster mergers on the
galaxy population. We divided the sample between relaxed and disturbed, and in
two redshifts bin at . When comparing the high-z to low-z clusters we
find the high-z sample is richer in blue galaxies, independently of the cluster
dynamical state. In the high-z bin we find that disturbed clusters exhibit a
larger scatter in the Red Sequence, with wider distribution and an excess of
bluer galaxies compared to relaxed clusters, while in the low-z bin we find a
complete agreement between the relaxed and disturbed clusters. Our results
support the scenario in which massive cluster halos at galaxies are
quenched as satellites of another structure, i.e. outside the cluster, while at
the quenching is dominated by in-situ processes.Comment: 9 pages, 5 figures, paper accepted in MNRA
Cellular lethal damage of 64Cu incorporated in mammalian genome evaluated with Monte Carlo methods
PurposeTargeted Radionuclide Therapy (TRT) with Auger Emitters (AE) is a technique that allows targeting specific sites on tumor cells using radionuclides. The toxicity of AE is critically dependent on its proximity to the DNA. The aim of this study is to quantify the DNA damage and radiotherapeutic potential of the promising AE radionuclide copper-64 (64Cu) incorporated into the DNA of mammalian cells using Monte Carlo track-structure simulations.MethodsA mammalian cell nucleus model with a diameter of 9.3 μm available in TOPAS-nBio was used. The cellular nucleus consisted of double-helix DNA geometrical model of 2.3 nm diameter surrounded by a hydration shell with a thickness of 0.16 nm, organized in 46 chromosomes giving a total of 6.08 giga base-pairs (DNA density of 14.4 Mbp/μm3). The cellular nucleus was irradiated with monoenergetic electrons and radiation emissions from several radionuclides including 111In, 125I, 123I, and 99mTc in addition to 64Cu. For monoenergetic electrons, isotropic point sources randomly distributed within the nucleus were modeled. The radionuclides were incorporated in randomly chosen DNA base pairs at two positions near to the central axis of the double-helix DNA model at (1) 0.25 nm off the central axis and (2) at the periphery of the DNA (1.15 nm off the central axis). For all the radionuclides except for 99mTc, the complete physical decay process was explicitly simulated. For 99mTc only total electron spectrum from published data was used. The DNA Double Strand Breaks (DSB) yield per decay from direct and indirect actions were quantified. Results obtained for monoenergetic electrons and radionuclides 111In, 125I, 123I, and 99mTc were compared with measured and calculated data from the literature for verification purposes. The DSB yields per decay incorporated in DNA for 64Cu are first reported in this work. The therapeutic effect of 64Cu (activity that led 37% cell survival after two cell divisions) was determined in terms of the number of atoms incorporated into the nucleus that would lead to the same DSBs that 100 decays of 125I. Simulations were run until a 2% statistical uncertainty (1 standard deviation) was achieved.ResultsThe behavior of DSBs as a function of the energy for monoenergetic electrons was consistent with published data, the DSBs increased with the energy until it reached a maximum value near 500 eV followed by a continuous decrement. For 64Cu, when incorporated in the genome at evaluated positions (1) and (2), the DSB were 0.171 ± 0.003 and 0.190 ± 0.003 DSB/decay, respectively. The number of initial atoms incorporated into the genome (per cell) for 64Cu that would cause a therapeutic effect was estimated as 3,107 ± 28, that corresponds to an initial activity of 47.1 ± 0.4 × 10−3 Bq.ConclusionOur results showed that TRT with 64Cu has comparable therapeutic effects in cells as that of TRT with radionuclides currently used in clinical practice
The Star Formation History of the Disk of the Starburst galaxy M82
Spectroscopic, photometric and dynamical data of the inner 3 kpc part of the
starburst galaxy M82 are analyzed in order to investigate the star formation
history of the stellar disk. The long-slit spectra along the major axis are
dominated by Balmer absorption lines in the region outside the nuclear
starburst all the way up to ~3.5 scalelengths (mu_B=22 mag/arcsec**2). Single
Stellar Population (SSP) spectra of age 0.4-1.0 Gyr match well the observed
spectra in the 1-3 kpc zone, with a mean age of the stellar population
marginally higher in the outer parts. The mass in these populations, along with
that in the gas component, make up for the inferred dynamical mass in the same
annular zone for a Kroupa initial mass function, with a low mass cut-off
m_l=0.4 Msun. The observed ratio of the abundances of alpha elements with
respect to Fe, is also consistent with the idea that almost all the stars in
M82 disk formed in a burst of short duration (0.3 Gyr) around 0.8 Gyr ago. We
find that the optical/near infrared colors and their gradients in the disk are
determined by the reddening with visual extinction exceeding 1 mag even in the
outer parts of the disk, where there is apparently no current star formation.
The disk-wide starburst activity was most likely triggered by the interaction
of M82 with its massive neighbor M81 around 1~Gyr ago. The properties of the
disk of M82 very much resemble the properties of the disks of luminous compact
blue galaxies seen at 0.2-1.0 redshift.Comment: 7 pages, Accepted for publication in Ap
Theoretical study of incoherent phi photoproduction on a deuteron target
We study the photoproduction of phi mesons in deuteron, paying attention to
the modification of the cross section from bound protons to the free ones with
the aim of comparing with recent results at LEPS. For this purpose we take into
account Fermi motion in single scattering and rescattering of the phi to
account for phi absorption on a second nucleon as well as the rescattering of
the proton. We find that the contribution of the double scattering is much
smaller than the typical cross section of gamma p to phi p in free space, which
implies a very small screening of the phi production in deuteron. The
contribution from the proton rescattering, on the other hand, is found to be
not negligible compared to the cross section of gamma p to phi p in free space,
and leads to a moderate reduction of the phi photoproduction cross section on a
deuteron at forward angles if LEPS set up is taken into account. The Fermi
motion allows contribution of the single scattering in regions forbidden by
phase space in the free case. In particular, we find that for momentum
transferred squared close to the maximum value, the Fermi motion changes
drastically the shape of d sigma / dt, to the point that the ratio of this
cross section to the free one becomes very sensitive to the precise value of t
chosen, or the size of the bin used in an experimental analysis. Hence, this
particular region of t does not seem the most indicated to find effects of a
possible phi absorption in the deuteron. This reaction is studied theoretically
as a function of t and the effect of the experimental angular cuts at LEPS is
also discussed, providing guidelines for future experimental analyses of the
reaction.Comment: 17 pages, 16 figure
- …