9,476 research outputs found
How mobile are dye adsorbates and acetonitrile molecules on the surface of TiO2 nanoparticles? A quasi-elastic neutron scattering study
Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2 nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2 on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results
Meiotic DSB patterning: A multifaceted process
Meiosis is a specialized two-step cell division responsible for genome haploidization and the generation of genetic diversity during gametogenesis. An integral and distinctive feature of the meiotic program is the evolutionarily conserved initiation of homologous recombination (HR) by the developmentally programmed induction of DNA double-strand breaks (DSBs). The inherently dangerous but essential act of DSB formation is subject to multiple forms of stringent and self-corrective regulation that collectively ensure fruitful and appropriate levels of genetic exchange without risk to cellular survival. Within this article we focus upon an emerging element of this control—spatial regulation—detailing recent advances made in understanding how DSBs are evenly distributed across the genome, and present a unified view of the underlying patterning mechanisms employed
On the Neutral Gas Content and Environment of NGC 3109 and the Antlia Dwarf Galaxy
As part of a continuing survey of nearby galaxies, we have mapped the neutral
gas content of the low surface brightness, Magellanic-type galaxy NGC 3109 ---
and its environment, including the Antlia dwarf galaxy --- at unprecedented
velocity resolution and brightness sensitivity. The HI mass of NGC 3109 is
measured to be (3.8 +/- 0.5) x 10^8 Msun. A substantial warp in the disk of NGC
3109 is detected in the HI emission image in the form of an extended low
surface brightness feature. We report a positive detection in HI of the nearby
Antlia dwarf galaxy, and measure its total neutral gas mass to be (6.8 +/- 1.4)
x 10^5 Msun. We show the warp in NGC 3109 to lie at exactly the same radial
velocity as the gas in the Antlia dwarf galaxy and speculate that Antlia
disturbed the disk of NGC 3109 during a mild encounter ~1 Gyr in the past. HI
data for a further eight galaxies detected in the background are presented.Comment: Accepted for publication in A
Geometrically induced modification of surface plasmons in the optical and telecom regimes
We demonstrate that the introduction of a subwavelength periodic modulation
into a metallic structure strongly modifies the guiding characteristics of the
surface plasmon modes supported by the system. Moreover, it is also shown how a
new type of a tightly confined surface plasmon polariton mode can be created by
just milling a periodic corrugation into a metallic ridge placed on top of a
metal surface
N-body simulations of galaxies and groups of galaxies with the Marseille GRAPE systems
I review the Marseille GRAPE systems and the N-body simulations done with
them. I first describe briefly the available hardware and software, their
possibilities and their limitations. I then describe work done on interacting
galaxies and groups of galaxies. This includes simulations of the formation of
ring galaxies, simulations of bar destruction by massive compact satellites, of
merging in compact groups and of the formation of brightest members in clusters
of galaxies.Comment: 13 pages, 5 figures, to be published in "Non-linear Dynamics and
Chaos in Astrophysics", eds. J.R. Buchler, S. Gottesman, J. Hunter and H.
Kandrup, Annals of the New York Academy of Science
VPLanet: The Virtual Planet Simulator
We describe a software package called VPLanet that simulates fundamental
aspects of planetary system evolution over Gyr timescales, with a focus on
investigating habitable worlds. In this initial release, eleven physics modules
are included that model internal, atmospheric, rotational, orbital, stellar,
and galactic processes. Many of these modules can be coupled simultaneously to
simulate the evolution of terrestrial planets, gaseous planets, and stars. The
code is validated by reproducing a selection of observations and past results.
VPLanet is written in C and designed so that the user can choose the physics
modules to apply to an individual object at runtime without recompiling, i.e.,
a single executable can simulate the diverse phenomena that are relevant to a
wide range of planetary and stellar systems. This feature is enabled by
matrices and vectors of function pointers that are dynamically allocated and
populated based on user input. The speed and modularity of VPLanet enables
large parameter sweeps and the versatility to add/remove physical phenomena to
assess their importance. VPLanet is publicly available from a repository that
contains extensive documentation, numerous examples, Python scripts for
plotting and data management, and infrastructure for community input and future
development.Comment: 75 pages, 34 figures, 10 tables, accepted to the Proceedings of the
Astronomical Society of the Pacific. Source code, documentation, and examples
available at https://github.com/VirtualPlanetaryLaboratory/vplane
Photometric study of the IC 65 group of galaxies
We carry out a photometric study of a poor group of late-type galaxies around
IC 65, with the aim: (a) to search for new dwarf members and to measure their
photometric characteristics; (b) to search for possible effects of mutual
interactions on the morphology and star-formation characteristics of luminous
and faint group members; (c) to evaluate the evolutionary status of this
particular group. We make use of our BRI CCD observations, DPOSS blue and red
frames, and the 2MASS JHK frames. In addition, we use the HI imaging data, the
far-infrared and radio data from the literature. Search for dwarf galaxies is
made using the SExtractor software. Detailed surface photometry is performed
with the MIDAS package. Four LSB galaxies were classified as probable dwarf
members of the group and the BRI physical and model parameters were derived for
the first time for all true and probable group members. Newly found dIrr
galaxies around the IC 65 contain a number of H II regions, which show a range
of ages and propagating star-formation. Mildly disturbed gaseous and/or stellar
morphology is found in several group members. Various structural, dynamical,
and star-forming characteristics let us conclude that the IC 65 group is a
typical poor assembly of late-type galaxies at an early stage of its dynamical
evolution with some evidence of intragroup (tidal) interactions.Comment: 21 pages, 16 figures, submitted to A&
The imprint of dissipation on the shapes of merger remnant LOSVDs
The properties of elliptical galaxies are broadly consistent with simulated
remnants of gas-rich mergers between spirals, motivating more detailed studies
of the imprint of this formation mechanism on the remnant distribution
function. Gas has a strong impact on the non-Gaussian shapes of the
line-of-sight velocity distributions (LOSVDs) of the merger remnant, owing to
the embedded disk that forms out of the gas that retains its angular momentum
during the merger, and the strong central mass concentration from the gas that
falls to the center. The deviations from Gaussianity are parametrized by the
Gauss-Hermite moments h_3 and h_4, which are related to the skewness and
kurtosis of the LOSVDs. We quantify the dependence of the (h_3,h_4)-v/sigma
relations on the initial gas fraction of the progenitor disks in 1:1 mergers,
using Gadget-2 simulations including star formation, radiative cooling, and
feedback from supernovae and AGN. For gas fractions f_gas < ~15% the overall
correlation between h_3 and v/sigma is weak, consisting of a flat negatively
correlated component arising from edge-on viewing angles plus a steep
positively correlated part from face-on projections. The spread in v/sigma
values decreases toward high positive h_4, and there is a trend toward lower
h_4 as the gas fraction increases from 0 to 15%. For f_gas > ~20% the (h_3,4)-
v/sigma distributions look quite different - there is a tight negative h_3-
v/sigma correlation, and a wide spread in v/sigma values at all h_4, in better
agreement with observations. Re-mergers of the high-f_gas remnants (dry
mergers) produce slowly rotating systems with nearly Gaussian LOSVDs. We
explain all of these trends in terms of the underlying orbit structure of the
remnants, as molded by their dissipative formation histories.Comment: ApJ accepted - added some references and background on previous
studies. 9 pages, 4 figure
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