394 research outputs found
Modeling the organization of the WUSCHEL expression domain in the shoot apical meristem
Motivation: The above-ground tissues of higher plants are generated from a small region of cells situated at the plant apex called the shoot apical meristem. An important genetic control circuit modulating the size of the Arabidopsis thaliana meristem is a feed-back network between the CLAVATA3 and WUSCHEL genes. Although the expression patterns for these genes do not overlap, WUSCHEL activity is both necessary and sufficient (when expressed ectopically) for the induction of CLAVATA3 expression. However, upregulation of CLAVATA3 in conjunction with the receptor kinase CLAVATA1 results in the downregulation of WUSCHEL. Despite much work, experimental data for this network are incomplete and additional hypotheses are needed to explain the spatial locations and dynamics of these expression domains. Predictive mathematical models describing the system should provide a useful tool for investigating and discriminating among possible hypotheses, by determining which hypotheses best explain observed gene expression dynamics. Results: We are developing a method using in vivo live confocal microscopy to capture quantitative gene expression data and create templates for computational models. We present two models accounting for the organization of the WUSCHEL expression domain. Our preferred model uses a reaction-diffusion mechanism in which an activator induces WUSCHEL expression. This model is able to organize the WUSCHEL expression domain. In addition, the model predicts the dynamical reorganization seen in experiments where cells, including the WUSCHEL domain, are ablated, and it also predicts the spatial expansion of the WUSCHEL domain resulting from removal of the CLAVATA3 signal
3D Spectroscopic Observations of Star-Forming Dwarf Galaxies
We give an introduction into the observational technique of integral field or
3D spectroscopy. We discuss advantages and drawbacks of this type of
observations and highlight a few science projects enabled by this method. In
the second part we describe our 3D spectroscopic survey of Blue Compact Dwarf
Galaxies. We show preliminary results from data taken with the VIMOS integral
field unit and give an outlook on how automated spectral analysis and
forthcoming instruments can provide a new view on star formation and associated
processes in dwarf galaxies.Comment: To appear in the proceedings of the JENAM 2010 Symposium "Dwarf
Galaxies: Keys to Galaxy Formation and Evolution" (Lisbon, 9-10 September
2010), P. Papaderos, S. Recchi, G. Hensler (eds.), Springer Verlag (2011), in
pres
COLA II - Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies
We present optical spectroscopic observations of 93 galaxies taken from the
infra-red selected COLA (Compact Objects in Low Power AGN) sample. The sample
spans the range of far-IR luminosities from normal galaxies to LIRGs. Of the
galaxies observed, 78 (84%) exhibit emission lines. Using a theoretically-based
optical emission-line scheme we classify 15% of the emission-line galaxies as
Seyferts, 77% as starbursts, and the rest are either borderline AGN/starburst
or show ambiguous characteristics. We find little evidence for an increase in
the fraction of AGN in the sample as a function of far-IR luminosity but our
sample covers only a small range in infrared luminosity and thus a weak trend
may be masked. As a whole the Seyfert galaxies exhibit a small, but
significant, radio excess on the radio-FIR correlation compared to the galaxies
classified as starbursts. Compact (<0.05'') radio cores are detected in 55% of
the Seyfert galaxies, and these galaxies exhibit a significantly larger radio
excess than the Seyfert galaxies in which cores were not detected. Our results
indicate that there may be two distinct populations of Seyferts,
``radio-excess'' Seyferts, which exhibit extended radio structures and compact
radio cores, and ``radio-quiet'' Seyferts, in which the majority of the radio
emission can be attributed to star-formation in the host galaxy. No significant
difference is seen between the IR and optical spectroscopic properties of
Seyferts with and without radio cores. (Abridged)Comment: 24 pages, 4 figures, 6 tables. Accepted for publication in ApJ,
February 200
Hubble Space Telescope Photometry of the Dwarf Spheroidal Galaxy ESO 410-G005
We present HST WFPC2 imaging of the nearby low-surface-brightness dwarf
spheroidal galaxy ESO 410-G005, which has been resolved into stars for the
first time. The resulting color-magnitude diagram for about 2500 stars shows a
red giant branch branch with a tip at I=(22.4+-0.15), which yields a distance
of D=(1.9+-0.2) Mpc. ESO 410-G005 is found to be metal-poor with a mean
metallicity of (-1.8+-0.4) dex estimated from its red giant branch. Upper
asymptotic giant branch stars appear to be present near the center of the
galaxy, indicative of a substantial, centrally concentrated intermediate-age
population, unless these objects are artifacts of crowding. Previous studies
did not detect ESO 410-G005 in H alpha or in HI. ESO 410-G005 is a probable
member of the Sculptor group. Its linear separation from the nearest spiral,
NGC 55, is 230 kpc on the sky. The deprojected separation ranges from 340 to
615 kpc depending on the assumed distance of NGC 55. ESO 410 G005 appears to be
a relatively isolated dSph within the Sculptor group. Its absolute magnitude,
Mv = (-12.1+-0.2) mag, its central surface brightness, mu_V = (22.7+-0.1)
mag/arcsec^2, and its mean metallicity, [Fe/H] = (-1.8+-0.4) dex, follow the
trend observed for dwarf galaxies in the Local Group. (abridged)Comment: Accepted for publication in the Astrophysical Journal, Vol. 542 (Oct
20). 23 pages in AASTEX style, 9 figures, partially in gif format to save
spac
Merging of globular clusters within inner galactic regions. I. Do they survive the tidal interaction?
The main topic of this paper is the investigation of the modes of interaction
of globular clusters (GCs) moving in the inner part of a galaxy. This is
tackled by means of high-resolution N-body simulations, whose first results are
presented in this article. Our simulations dealt with primordial very massive
(order of 10^7 solar masses) GCs that were able to decay, because of dynamical
friction, into the inner regions of triaxial galaxies on a time much shorter
than their internal relaxation time. To check the disruptive role of both tidal
forces and GC-GC collisions, we maximised the tidal interaction considering GCs
on quasi-radial orbits.
The available CPU resources allowed us to follow 8 oscillations of the GCs
along their orbits and the main findings are: i) clusters with an initial high
enough King concentration parameter (c>=1.2), preserve up to 50% of their
initial mass; ii) the inner density distribution of the survived clusters keep
a King model profile; iii) GC-GC collisions have a negligible effect with
respect to that caused by the passage through the galactic center; iv) the
orbital energy dissipation due to the tidal interaction is of the same order of
that caused by dynamical friction; v) complex sub-structures like "ripples" and
"clumps" formed, as observed around real clusters.
These findings support the validity of the hypothesis of merging of GCs in
the galactic central region, with modes that deserve further careful
investigations.Comment: LaTeX 2e, AASTeX v5.x, 23 pages with 14 figures. Accepted for
publication on the Astrophysical Journal. Final version with major change
Binary Galaxies in the Local Supercluster and Its Neighborhood
We report a catalog of 509 pairs identified among 10403 nearby galaxies with
line-of-sight velocities V_LG < 3500 km/s.We selected binary systems in
accordance with two criteria (bounding and temporal), which require the
physical pair of galaxies to have negative total energy and its components to
be located inside the zero-velocity surface. We assume that individual galaxy
masses are proportional to their total K-band luminosities, M = L_K x 6M/L. The
catalog gives the magnitudes and morphological types of galaxies and also the
projected (orbital) masses and pair isolation indices. The component
line-of-sight velocity differences and projected distances of the binary
systems considered have power-law distributions with the median values of 35
km/s and 123 kpc, respectively. The median mass-to-K-band luminosity ratio is
equal to 11 M/L, and its uncertainty is mostly due to the errors of measured
velocities. Our sample of binary systems has a typical density contrast of d
ro/ro_c ~ 500 and a median crossing time of about 3.5 Gyr. We point out the
substantial fraction of binary systems consisting of late-type dwarf galaxies,
where the luminosities of both components are lower than that of the Small
Magellanic Cloud. The median projected distance for 41 such pairs is only 30
kpc, and the median difference of their line-of-sight velocities is equal to 14
km/s which is smaller than the typical error for radial-velocity (30 km/s).
This specific population of gas-rich dwarf binary galaxies such as I Zw 18 may
be at the stage immediately before merging of its components. Such objects,
which are usually lost in flux-limited (and not distance-limited) samples
deserve a thorough study in the HI radio line with high spatial and velocity
resolution.Comment: published in Astrophysical Bulletin, 2008, Vol. 63, No. 4, pp.
299-34
Two-Dimensional Electronic Spectroscopy of Chlorophyll a: Solvent Dependent Spectral Evolution
The interaction of the monomeric chlorophyll Q-band electronic transition with solvents of differing physical-chemical properties is investigated through two-dimensional electronic spectroscopy (2DES). Chlorophyll constitutes the key chromophore molecule in light harvesting complexes. It is well-known that the surrounding protein in the light harvesting complex fine-tunes chlorophyll electronic transitions to optimize energy transfer. Therefore, an understanding of the influence of the environment on the monomeric chlorophyll electronic transitions is important. The Q-band 2DES is inhomogeneous at early times, particularly in hydrogen bonding polar solvents, but also in nonpolar solvents like cyclohexane. Interestingly this inhomogeneity persists for long times, even up to the nanosecond time scale in some solvents. The reshaping of the 2DES occurs over multiple time scales and was assigned mainly to spectral diffusion. At early times the reshaping is Gaussian-like, hinting at a strong solvent reorganization effect. The temporal evolution of the 2DES response was analyzed in terms of a Brownian oscillator model. The spectral densities underpinning the Brownian oscillator fitting were recovered for the different solvents. The absorption spectra and Stokes shift were also properly described by this model. The extent and nature of inhomogeneous broadening was a strong function of solvent, being larger in H-bonding and viscous media and smaller in nonpolar solvents. The fastest spectral reshaping components were assigned to solvent dynamics, modified by interactions with the solute
Alignment between PIN1 Polarity and Microtubule Orientation in the Shoot Apical Meristem Reveals a Tight Coupling between Morphogenesis and Auxin Transport
Morphogenesis during multicellular development is regulated by intercellular signaling molecules as well as by the mechanical properties of individual cells. In particular, normal patterns of organogenesis in plants require coordination between growth direction and growth magnitude. How this is achieved remains unclear. Here we show that in Arabidopsis thaliana, auxin patterning and cellular growth are linked through a correlated pattern of auxin efflux carrier localization and cortical microtubule orientation. Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature. Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis
Efeito da agitação, local de coleta e tempo de resfriamento na qualidade do leite de vacas Jersey - Effect of agitation, gathering place and cooling time on milk quality of Jersey cows.
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Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study
The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at 80 cm–1, which is assigned to a bending of the protein amide chain
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