Metamodulation of a spinal locomotor network by nitric oxide

Flexibility in the output of spinal networks can be accomplished by the actions of neuromodulators; however, little is known about how the process of neuromodulation itself may be modulated. Here we investigate the potential "meta"-modulatory hierarchy between nitric oxide (NO) and noradrenaline (NA) in Xenopus laevis tadpoles. NO and NA have similar effects on fictive swimming; both potentiate glycinergic inhibition to slow swimming frequency and GABAergic inhibition to reduce episode durations. In addition, both modulators have direct effects on the membrane properties of motor neurons. Here we report that antagonism of noradrenergic pathways with phentolamine dramatically influences the effect of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) on swimming frequency, but not its effect on episode durations. In contrast, scavenging extracellular NO with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(PTIO) does not influence any of the effects of NA on fictive swimming. These data place NO above NA in the metamodulatory hierarchy, strongly suggesting that NO works via a noradrenergic pathway to control glycine release but directly promotes GABA release. We confirmed this possibility using intracellular recordings from motor neurons. In support of a natural role for NO in the Xenopus locomotor network, PTIO not only antagonized all of the effects of SNAP on swimming but also, when applied on its own, modulated both swimming frequency and episode durations in addition to the underlying glycinergic and GABAergic pathways. Collectively, our results illustrate that NO and NA have parallel effects on motor neuron membrane properties and GABAergic inhibition, but that NO serially metamodulates glycinergic inhibition via NA.Publisher PDFPeer reviewe

The spectroscopic indistinguishability of red giant branch and red clump stars

Stellar spectroscopy provides useful information on the physical properties of stars such as effective temperature, metallicity and surface gravity (log g). However, those photospheric characteristics are often hampered by systematic uncertainties. The joint spectro-seismo project (APOKASC) of field red giants has revealed a puzzling offset between the log g determined spectroscopically and those determined using asteroseismology, which is largely dependent on the stellar evolutionary status. Therefore, in this letter, we aim to shed light on the spectroscopic source of the offset using the APOKASC sample. We analyse the log g discrepancy as a function of stellar mass and evolutionary status and discuss the impact of He and carbon isotopic ratio. We first show that for stars at the bottom of the red giant branch, the discrepancy between spectroscopic and asteroseismic log g depends on stellar mass. This indicates that the discrepancy is related to CN cycling. We demonstrate that the C isotopic ratio ($\rm ^{12}C/^{13}C$) has the largest impact on the stellar spectrum. We find that this log g discrepancy shows a similar trend in mass as the $\rm ^{12}C/^{13}C$ ratios expected by stellar evolution theory. Although we do not detect a direct signature of $\rm ^{13}C$, the data suggests that the discrepancy is tightly correlated to the production of $\rm ^{13}C$. Moreover, by running a data-driven algorithm (the Cannon) on a synthetic grid trained on the APOGEE data, we quantitatively evaluate the impact of various $\rm ^{12}C/^{13}C$ ratios. While we have demonstrated that $\rm ^{13}C$ impacts all parameters, the size of the impact is smaller than the observed offset in log g. If further tests confirm that $\rm ^{13}C$ is not the main element responsible of the log g problem, the number of spectroscopic effects remaining to be investigated is now relatively limited. [Abridged]Comment: 4 Pages, 6 Figures. Accepted for publication in A&

Kaluza-Klein Towers in the Early Universe: Phase Transitions, Relic Abundances, and Applications to Axion Cosmology

We study the early-universe cosmology of a Kaluza-Klein (KK) tower of scalar fields in the presence of a mass-generating phase transition, focusing on the time-development of the total tower energy density (or relic abundance) as well as its distribution across the different KK modes. We find that both of these features are extremely sensitive to the details of the phase transition and can behave in a variety of ways significant for late-time cosmology. In particular, we find that the interplay between the temporal properties of the phase transition and the mixing it generates are responsible for both enhancements and suppressions in the late-time abundances, sometimes by many orders of magnitude. We map out the complete model parameter space and determine where traditional analytical approximations are valid and where they fail. In the latter cases we also provide new analytical approximations which successfully model our results. Finally, we apply this machinery to the example of an axion-like field in the bulk, mapping these phenomena over an enlarged axion parameter space that extends beyond those accessible to standard treatments. An important by-product of our analysis is the development of an alternate "UV-based" effective truncation of KK theories which has a number of interesting theoretical properties that distinguish it from the more traditional "IR-based" truncation typically used in the extra-dimension literature.Comment: 30 pages, LaTeX, 18 figures. Replaced to match published versio

Distinguishing Dynamical Dark Matter at the LHC

Dynamical dark matter (DDM) is a new framework for dark-matter physics in which the dark sector comprises an ensemble of individual component fields which collectively conspire to act in ways that transcend those normally associated with dark matter. Because of its non-trivial structure, this DDM ensemble --- unlike most traditional dark-matter candidates --- cannot be characterized in terms of a single mass, decay width, or set of scattering cross-sections, but must instead be described by parameters which describe the collective behavior of its constituents. Likewise, the components of such an ensemble need not be stable so long as lifetimes are balanced against cosmological abundances across the ensemble as a whole. In this paper, we investigate the prospects for identifying a DDM ensemble at the LHC and for distinguishing such a dark-matter candidate from the candidates characteristic of traditional dark-matter models. In particular, we focus on DDM scenarios in which the component fields of the ensemble are produced at colliders alongside some number of Standard-Model particles via the decays of additional heavy fields. The invariant-mass distributions of these Standard-Model particles turn out to possess several unique features that cannot be replicated in most traditional dark-matter models. We demonstrate that in many situations it is possible to differentiate between a DDM ensemble and a traditional dark-matter candidate on the basis of such distributions. Moreover, many of our results also apply more generally to a variety of other extensions of the Standard Model which involve multiple stable or metastable neutral particles.Comment: 17 pages, LaTeX, 10 figure

A Tale of Two Timescales: Mixing, Mass Generation, and Phase Transitions in the Early Universe

Light scalar fields such as axions and string moduli can play an important role in early-universe cosmology. However, many factors can significantly impact their late-time cosmological abundances. For example, in cases where the potentials for these fields are generated dynamically --- such as during cosmological mass-generating phase transitions --- the duration of the time interval required for these potentials to fully develop can have significant repercussions. Likewise, in scenarios with multiple scalars, mixing amongst the fields can also give rise to an effective timescale that modifies the resulting late-time abundances. Previous studies have focused on the effects of either the first or the second timescale in isolation. In this paper, by contrast, we examine the new features that arise from the interplay between these two timescales when both mixing and time-dependent phase transitions are introduced together. First, we find that the effects of these timescales can conspire to alter not only the total late-time abundance of the system --- often by many orders of magnitude --- but also its distribution across the different fields. Second, we find that these effects can produce large parametric resonances which render the energy densities of the fields highly sensitive to the degree of mixing as well as the duration of the time interval over which the phase transition unfolds. Finally, we find that these effects can even give rise to a "re-overdamping" phenomenon which causes the total energy density of the system to behave in novel ways that differ from those exhibited by pure dark matter or vacuum energy. All of these features therefore give rise to new possibilities for early-universe phenomenology and cosmological evolution. They also highlight the importance of taking into account the time dependence associated with phase transitions in cosmological settings.Comment: Comments: 35 pages, LaTeX, 31 figures, 1 tabl

ACTUARIAL EFFECTS OF UNIT STRUCTURE IN THE U.S. ACTUAL PRODUCTION HISTORY CROP INSURANCE PROGRAM

This paper examines the effects of optional subdivision on APHP losses for wheat, corn, and soybeans. Thirty-seven state/crop programs are analyzed and the implications of the results are discussed in relation to newly developed crop and revenue insurance programs. The results illustrate the importance of incorporating actuarial experience into the premium rate structure and contract provisions of an insurance program.Actual Production History Program (APHP), crop insurance programs, Risk and Uncertainty,