403 research outputs found
A High-Resolution Study of the HI Content of Local Group Dwarf Irregular Galaxy WLM
Dwarf irregular galaxies are unique laboratories for studying the interaction
between stars and the interstellar medium in low mass environments. We present
the highest spatial resolution observations to date of the neutral hydrogen
content of the Local Group dwarf irregular galaxy WLM. We find that WLM's
neutral hydrogen distribution is typical for a galaxy of its type and size and
derive an HI mass of 6.3e7 Msun for WLM. In addition, we derive an HI extent
for WLM of 30 arcmin, which is much less than the 45 arcmin extent found by
Huchtmeier, Seiradakis, and Materne (1981). We show that the broken ring of
high column density neutral hydrogen surrounding the center of WLM is likely
the result of star formation propagating out from the center of the galaxy. The
young stars and Ha emission in this galaxy are mostly correlated with the high
column density neutral hydrogen. The gap in the central ring is the result of
star formation in that region using up, blowing out, or ionizing all of the
neutral hydrogen. Like many late-type galaxies, WLM's velocity field is
asymmetric with the approaching (northern) side appearing to be warped and a
steeper velocity gradient for the approaching side than for the receding side
in the inner region of the galaxy. We derive a dynamical mass for WLM of 2.16e9
Msun.Comment: 38 pages, 15 figures, 5 tables, accepted by AJ, high resolution
version at http://www.astro.wisc.edu/~kepley/kepley_wlm.p
Information Transfer in Gonadotropin-releasing Hormone (GnRH) Signaling: extracellular signal-regulated kinase (ERK)-mediated feedback loops control hormone sensing
The computation model used in the study of GnRH signalling which was used to generate the data appearing in this paper is in ORE at http://hdl.handle.net/10871/27844Cell signaling pathways are noisy communication channels, and statistical measures derived from information theory can be used to quantify the information they transfer. Here we use single cell signaling measures to calculate mutual information as a measure of information transfer via gonadotropin-releasing hormone (GnRH) receptors (GnRHR) to extracellular signal-regulated kinase (ERK) or nuclear factor of activated T-cells (NFAT). This revealed mutual information values <1 bit, implying that individual GnRH-responsive cells cannot unambiguously differentiate even two equally probable input concentrations. Addressing possible mechanisms for mitigation of information loss, we focused on the ERK pathway and developed a stochastic activation model incorporating negative feedback and constitutive activity. Model simulations revealed interplay between fast (min) and slow (min-h) negative feedback loops with maximal information transfer at intermediate feedback levels. Consistent with this, experiments revealed that reducing negative feedback (by expressing catalytically inactive ERK2) and increasing negative feedback (by Egr1-driven expression of dual-specificity phosphatase 5 (DUSP5)) both reduced information transfer from GnRHR to ERK. It was also reduced by blocking protein synthesis (to prevent GnRH from increasing DUSP expression) but did not differ for different GnRHRs that do or do not undergo rapid homologous desensitization. Thus, the first statistical measures of information transfer via these receptors reveals that individual cells are unreliable sensors of GnRH concentration and that this reliability is maximal at intermediate levels of ERK-mediated negative feedback but is not influenced by receptor desensitization.This work was supported by a Biochemical and Biophysical Science Research Council award (BBSRC BB/J014699/1; to C. A. M. and K. T.-A.)
Protein Phosphorylation in Amyloplasts Regulates Starch Branching Enzyme Activity and Protein–Protein Interactions
The Factory and The Beehive II. Activity and Rotation in Praesepe and the Hyades
Open clusters are collections of stars with a single, well-determined age,
and can be used to investigate the connections between angular-momentum
evolution and magnetic activity over a star's lifetime. We present the results
of a comparative study of the relationship between stellar rotation and
activity in two benchmark open clusters: Praesepe and the Hyades. As they have
the same age and roughly solar metallicity, these clusters serve as an ideal
laboratory for testing the agreement between theoretical and empirical
rotation-activity relations at 600 Myr. We have compiled a sample of
720 spectra --- more than half of which are new observations --- for 516
high-confidence members of Praesepe; we have also obtained 139 new spectra for
130 high-confidence Hyads. We have collected rotation periods () for
135 Praesepe members and 87 Hyads. To compare emission, an indicator
of chromospheric activity, as a function of color, mass, and Rossby number
, we first calculate an expanded set of values, with which we can
obtain the to bolometric luminosity ratio, ,
even when spectra are not flux-calibrated and/or stars lack reliable distances.
Our values cover a broader range of stellar masses and colors (roughly
equivalent to spectral types from K0 to M9), and exhibit better agreement
between independent calculations, than existing values. We find no difference
between the two clusters in their equivalent width or
distributions, and therefore take the merged
and data to be representative of 600-Myr-old stars. Our analysis
shows that activity in these stars is saturated for
. Above that value activity declines as a
power-law with slope , before dropping off rapidly
at ...Comment: 17 pages, 15 figures, Accepted by Ap
Non-parametric kernel estimation for symmetric Hawkes processes. Application to high frequency financial data
We define a numerical method that provides a non-parametric estimation of the
kernel shape in symmetric multivariate Hawkes processes. This method relies on
second order statistical properties of Hawkes processes that relate the
covariance matrix of the process to the kernel matrix. The square root of the
correlation function is computed using a minimal phase recovering method. We
illustrate our method on some examples and provide an empirical study of the
estimation errors. Within this framework, we analyze high frequency financial
price data modeled as 1D or 2D Hawkes processes. We find slowly decaying
(power-law) kernel shapes suggesting a long memory nature of self-excitation
phenomena at the microstructure level of price dynamics.Comment: 6 figure
Profiling of spatial metabolite distributions in wheat leaves under normal and nitrate limiting conditions
The control and interaction between nitrogen and carbon assimilatory pathways is essential in both photosynthetic and non-photosynthetic tissue in order to support metabolic processes without compromising growth. Physiological differences between the basal and mature region of wheat (Triticum aestivum) primary leaves confirmed that there was a change from heterotrophic to autotrophic metabolism. Fourier Transform Infrared (FT-IR) spectroscopy confirmed the suitability and phenotypic reproducibility of the leaf growth conditions. Principal Component–Discriminant Function Analysis (PC–DFA) revealed distinct clustering between base, and tip sections of the developing wheat leaf, and from plants grown in the presence or absence of nitrate. Gas Chromatography-Time of Flight/Mass Spectrometry (GC-TOF/MS) combined with multivariate and univariate analyses, and Bayesian network (BN) analysis, distinguished different tissues and confirmed the physiological switch from high rates of respiration to photosynthesis along the leaf. The operation of nitrogen metabolism impacted on the levels and distribution of amino acids, organic acids and carbohydrates within the wheat leaf. In plants grown in the presence of nitrate there was reduced levels of a number of sugar metabolites in the leaf base and an increase in maltose levels, possibly reflecting an increase in starch turnover. The value of using this combined metabolomics analysis for further functional investigations in the future are discussed
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