9,714 research outputs found
The role of type 4 phosphodiesterases in generating microdomains of cAMP: Large scale stochastic simulations
Cyclic AMP (cAMP) and its main effector Protein Kinase A (PKA) are critical for several aspects of neuronal function including synaptic plasticity. Specificity of synaptic plasticity requires that cAMP activates PKA in a highly localized manner despite the speed with which cAMP diffuses. Two mechanisms have been proposed to produce localized elevations in cAMP, known as microdomains: impeded diffusion, and high phosphodiesterase (PDE) activity. This paper investigates the mechanism of localized cAMP signaling using a computational model of the biochemical network in the HEK293 cell, which is a subset of pathways involved in PKA-dependent synaptic plasticity. This biochemical network includes cAMP production, PKA activation, and cAMP degradation by PDE activity. The model is implemented in NeuroRD: novel, computationally efficient, stochastic reaction-diffusion software, and is constrained by intracellular cAMP dynamics that were determined experimentally by real-time imaging using an Epac-based FRET sensor (H30). The model reproduces the high concentration cAMP microdomain in the submembrane region, distinct from the lower concentration of cAMP in the cytosol. Simulations further demonstrate that generation of the cAMP microdomain requires a pool of PDE4D anchored in the cytosol and also requires PKA-mediated phosphorylation of PDE4D which increases its activity. The microdomain does not require impeded diffusion of cAMP, confirming that barriers are not required for microdomains. The simulations reported here further demonstrate the utility of the new stochastic reaction-diffusion algorithm for exploring signaling pathways in spatially complex structures such as neurons
Identifying galaxy candidates in WSRT HI imaging of ultra-compact high velocity clouds
Ultra-compact high velocity clouds (UCHVCs) were identified in the ALFALFA HI
survey as potential gas-bearing dark matter halos. Here we present higher
resolution neutral hydrogen (HI) observations of twelve UCHVCS with the
Westerbork Synthesis Radio Telescope (WSRT). The UCHVCs were selected based on
a combination of size, isolation, large recessional velocity and high column
density as the best candidate dark matter halos. The WSRT data were tapered to
image the UCHVCs at 210" (comparable to Arecibo) and 105" angular resolution.
In a comparison of the single-dish to interferometer data, we find that the
line flux recovered in the WSRT observations is comparable to that from the
single-dish ALFALFA data. In addition, any structure seen in the ALFALFA data
is reproduced in the WSRT maps at the same angular resolution. At 210'"
resolution all the sources are generally compact with a smooth HI morphology,
as expected from their identification as UCHVCs. At the higher angular
resolution, a majority of the sources break into small clumps contained in a
diffuse envelope. These UCHVCs also have no ordered velocity motion and are
most likely Galactic halo clouds. We identify two UCHVCs, AGC 198606 and AGC
249525, as excellent galaxy candidates based on maintaining a smooth HI
morphology at higher angular resolution and showing ordered velocity motion
consistent with rotation. A third source, AGC 249565, lies between these two
populations in properties and is a possible galaxy candidate. If interpreted as
gas-bearing dark matter halos, the three candidate galaxies have rotation
velocities of 8-15 km/s, HI masses of 0.6-50 x 10^5 Msun, HI radii of 0.3-2
kpc, and dynamical masses of 2-20 x 10^7 Msun for a range of plausible
distances. These are the UCHVCs with the highest column density values in the
ALFALFA HI data and we suggest this is the best way to identify further
candidates.Comment: Accepted for publication in A&A. 26 pages, 19 figures, 5 table
Localizing gravitational wave sources with optical telescopes and combining electromagnetic and gravitational wave data
Neutron star binaries, which are among the most promising sources for the
direct detection of gravitational waves (GW) by ground based detectors, are
also potential electromagnetic (EM) emitters. Gravitational waves will provide
a new window to observe these events and hopefully give us glimpses of new
astrophysics. In this paper, we discuss how EM information of these events can
considerably improve GW parameter estimation both in terms of accuracy and
computational power requirement. And then in return how GW sky localization can
help EM astronomers in follow-up studies of sources which did not yield any
prompt emission. We discuss how both EM source information and GW source
localization can be used in a framework of multi-messenger astronomy. We
illustrate how the large error regions in GW sky localizations can be handled
in conducting optical astronomy in the advance detector era. We show some
preliminary results in the context of an array of optical telescopes called
BlackGEM, dedicated for optical follow-up of GW triggers, that is being
constructed in La Silla, Chile and is expected to operate concurrent to the
advanced GW detectors.Comment: 8 pages, 8 figures, Proceeding for Sant Cugat Forum for Astrophysic
Mechanism of CDW-SDW Transition in One Dimension
The phase transition between charge- and spin-density-wave (CDW, SDW) phases
is studied in the one-dimensional extended Hubbard model at half-filling. We
discuss whether the transition can be described by the Gaussian and the
spin-gap transitions under charge-spin separation, or by a direct CDW-SDW
transition. We determine these phase boundaries by level crossings of
excitation spectra which are identified according to discrete symmetries of
wave functions. We conclude that the Gaussian and the spin-gap transitions take
place separately from weak- to intermediate-coupling region. This means that
the third phase exists between the CDW and the SDW states. Our results are also
consistent with those of the strong-coupling perturbative expansion and of the
direct evaluation of order parameters.Comment: 5 pages(REVTeX), 5 figures(EPS), 1 table, also available from
http://wwwsoc.nacsis.ac.jp/jps/jpsj/1999/p68a/p68a42/p68a42h/p68a42h.htm
Lessons from the Play Observatory: re-imagining learning through film-making and transludic practices in children’s pandemic play
This article focuses on children’s play during the pandemic and how some young people responded with hybrid, playful media-making. The Play Observatory was an ESRC-funded project led by UCL and the University of Sheffield, inviting children to make contributions to a national collection of stories, texts and artefacts linked with their play during lockdown. The cultural material generated by children is an important post-pandemic legacy that allows us to argue for informal film-making as a legitimate literacy practice. Insights gained from children’s creative film and animation work inspire new approaches to learning with media described as transludic, in which the characteristics of playful and improvised media production processes are given time and space to unfold
Phase Diagram of One-Dimensional Extended Hubbard Model at Half Filling
We reexamine the ground-state phase diagram of the one-dimensional
half-filled Hubbard model with on-site and nearest-neighbor repulsive
interactions. We calculate second-order corrections to coupling constants in
the g-ology to show that the bond-charge-density-wave (BCDW) phase exists for
weak couplings in between the charge density wave (CDW) and spin density wave
(SDW) phases. We find that the umklapp scattering of parallel-spin electrons
destabilizes the BCDW state and gives rise to a bicritical point where the
CDW-BCDW and SDW-BCDW continuous-transition lines merge into the CDW-SDW
first-order transition line.Comment: 4 pages, 3 figure
Clues on the evolution of the Carina dwarf spheroidal galaxy from the color distribution of its red giant stars
The thin red giant branch (RGB) of the Carina dwarf spheroidal galaxy appears
at first sight quite puzzling and seemingly in contrast with the presence of
several distinct bursts of star formation. In this Letter, we provide a
measurement of the color spread of red giant stars in Carina based on new BVI
wide-field observations, and model the width of the RGB by means of synthetic
color-magnitude diagrams. The measured color spread, Sigma{V-I}=0.021 +/-
0.005, is quite naturally accounted for by the star-formation history of the
galaxy. The thin RGB appears to be essentially related to the limited age range
of its dominant stellar populations, with no need for a metallicity dispersion
at a given age. This result is relatively robust with respect to changes in the
assumed age-metallicity relation, as long as the mean metallicity over the
galaxy lifetime matches the observed value ([Fe/H] = -1.91 +/- 0.12 after
correction for the age effects). This analysis of photometric data also sets
some constraints on the chemical evolution of Carina by indicating that the
chemical abundance of the interstellar medium in Carina remained low throughout
each episode of star formation even though these episodes occurred over many
Gyr.Comment: 4 pages, 3 figures, accepted for publication in the Astrophysical
Journal Letter
The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups
We present high-resolution Giant Metrewave Radio Telescope (GMRT) HI
observations and deep Canada-France-Hawaii Telescope (CFHT) optical imaging of
two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a
multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in
three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal
knots and one dIrr. Both tidal knots are located within a prominent HI tidal
tail, appear to have sufficient mass (M_gas~10^8 M_sol) to evolve into
long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC
3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and
four HI knots. Deep CFHT imaging confirms that the optical component of AGC
208457 is bluer -- with a 0.28 mag g-r colour -- and a few Gyr younger than its
purported parent galaxies. Combining the results for these groups with those
from the NGC 871/6/7 group reported earlier, we find that the HI properties,
estimated stellar ages and baryonic content of the gas-rich dwarfs clearly
distinguish tidal features from their classical counterparts. We optimistically
identify four potentially long-lived tidal objects associated to three separate
pairs of interacting galaxies, implying that TDGs are not readily produced
during interaction events as suggested by some recent simulations. The tidal
objects examined in this survey also appear to have a wider variety of
properties than TDGs of similar mass formed in current simulations of
interacting galaxies, which could be the result of pre- or post-formation
environmental influences.Comment: 18 pages, 14 figures, accepted for publication in MNRA
Efficiency of dairy rations containing various quantities of grain
The dairy cow is particularly well adapted for consuming and utilizing large quantities of roughages, though she responds well to grain feeding. The relative quantities of roughage and grain that should be fed are usually determined by the physiologic effects and economic efficiencies of such rations when fed to dairy cattle.
One would hardly expect high.producing cows to maintain a high yield when consuming roughage alone, because such a ration is so bulky that it prevents the intake of sufficient nutrients for maximum production. And yet, very good results have been obtained in certain areas by such a system of feeding. Then, too, the nutrients of roughage crops are usually produced at considerably less cost than those of grain crops (17) (3). Furthermore, rough. ages are more plentiful on most farms than grain crops, especially in recent years when there has been a marked increase in the production of hay and pasture crops at some sacrifice of grain production. Under these conditions the advisability of supplementing roughage rations with grain becomes a question of interest to dairy farmers
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