Disruption of Molecular Clouds by Expansion of Dusty H II Regions

Dynamical expansion of H II regions around star clusters plays a key role in dispersing the surrounding dense gas and therefore in limiting the efficiency of star formation in molecular clouds. We use a semi-analytic method and numerical simulations to explore expansion of spherical dusty H II regions and surrounding neutral shells and the resulting cloud disruption. Our model for shell expansion adopts the static solutions of Draine (2011) for dusty H II regions and considers the contact outward forces on the shell due to radiation and thermal pressures as well as the inward gravity from the central star and the shell itself. We show that the internal structure we adopt and the shell evolution from the semi-analytic approach are in good agreement with the results of numerical simulations. Strong radiation pressure in the interior controls the shell expansion indirectly by enhancing the density and pressure at the ionization front. We calculate the minimum star formation efficiency $\epsilon_{min}$ required for cloud disruption as a function of the cloud's total mass and mean surface density. Within the adopted spherical geometry, we find that typical giant molecular clouds in normal disk galaxies have $\epsilon_{min} \lesssim 10$%, with comparable gas and radiation pressure effects on shell expansion. Massive cluster-forming clumps require a significantly higher efficiency of $\epsilon_{min} \gtrsim 50$% for disruption, produced mainly by radiation-driven expansion. The disruption time is typically of the order of a free-fall timescale, suggesting that the cloud disruption occurs rapidly once a sufficiently luminous H II region is formed. We also discuss limitations of the spherical idealization.Comment: 23 pages, 14 figures; Accepted for publication in Ap

Modeling UV Radiation Feedback from Massive Stars: I. Implementation of Adaptive Ray Tracing Method and Tests

We present an implementation of an adaptive ray tracing (ART) module in the Athena hydrodynamics code that accurately and efficiently handles the radiative transfer involving multiple point sources on a three-dimensional Cartesian grid. We adopt a recently proposed parallel algorithm that uses non-blocking, asynchronous MPI communications to accelerate transport of rays across the computational domain. We validate our implementation through several standard test problems including the propagation of radiation in vacuum and the expansions of various types of HII regions. Additionally, scaling tests show that the cost of a full ray trace per source remains comparable to that of the hydrodynamics update on up to $\sim 10^3$ processors. To demonstrate application of our ART implementation, we perform a simulation of star cluster formation in a marginally bound, turbulent cloud, finding that its star formation efficiency is $12\%$ when both radiation pressure forces and photoionization by UV radiation are treated. We directly compare the radiation forces computed from the ART scheme with that from the M1 closure relation. Although the ART and M1 schemes yield similar results on large scales, the latter is unable to resolve the radiation field accurately near individual point sources.Comment: 20 pages, 14 figures; accepted for publication in Ap

Physiological Functions of Mitochondrial Reactive Oxygen Species

Mitochondria are the major energy producers within a cell in the form of adenosine triphosphate by oxidative phosphorylation. Normal mitochondrial metabolism inevitably generates reactive oxygen species (ROS), which have been considered to solely cause cellular damage. Increase of oxidative stress has been linked to various pathologies. Thus, mitochondrial ROS (mROS) were basically proposed as byproducts of oxidative metabolism, which undergo normalized by antioxidant enzymes. However, the mROS have extensively been esteemed to function as signalling molecules to regulate a wide variety of physiology. These phenomena are indeed dependent on mitochondrial redox status, which is dynamically altered under different physiological and pathological conditions. The oxidative stress is incurred by which the redox status is inclined to exceeded oxidation or reduction. Here, we attempt to integrate the recent advances in our understanding of the physiological functions of mROS

Effects of beta-Casomorphins on Metabolism of Dairy Cows

1. The studies presented in this thesis investigated some metabolic actions of beta-casomorphins in dairy cows. Three beta-casomorphins (beta-casomorphin-4-amide, -5 and -7) were used. Investigations of the actions of the beta-casomorphins in dairy cows require gram quantities of each peptide. This was achieved by synthesising the peptides using solid phase peptide synthesis combined with FMOC chemistry. 2. The first experiment examined possible stimulatory actions of the peptides on amino acid uptake by the mammary gland using explants of lactating rat mammary glands as a model in vitro system. There was no evidence of their actions on amino acid uptake by the mammary gland as judged by the lack of their effects on the uptakes of four amino acids (glutamate, histidine, leucine and lysine). Because of the inability to demonstrate effects of the peptides at the mammary gland level, it was decided to focus on their effects at the level of the gut. 3. As a first step, the extent of ruminal degradation of the beta-casomorphins was determined in incubations in rumen liquor in vitro. All three peptides were degraded rapidly with half-lives of only 15 to 20 minutes. In a subsequent experiment, an attempt was made to chemically protect the peptides from the ruminal degradation using N-terminal acetylation. The half-lives of the N-acetyl beta-casomorphins were markedly increased to 6 1/2, 7 1/2 and 4 hours for beta-casomorphin-4-amide, -5 and -7 respectively. However, it was recognised that, whilst the method would be a simple and effective method for the protection of the peptides, further developments of the method would be necessary to ensure their release in active form at their sites of their action in vivo. 4. In experiments on the actions of the beta-casomorphins in vivo, the peptides were infused direct into the abomasum. The first experiment compared hormonal responses to the abomasal infusion of sodium caseinate, a potential source of beta-casomorphins, and an acid hydrolysate of casein, which was not a potential source of beta-casomorphins. There were clear suggestions of differences in responses of some hormones, notably insulin and GIP. In the second experiment, effects of abomasal infiisions of mixtures of the ?- casomorphins themselves at three different dose levels on changes in concentrations of the hormones were investigated in lactating dairy cows. There was no clear effect of the beta-casomorphin infusions on insulin concentrations except for some tendency towards inhibition at some time points. However, the incremental response of glucagon to the beta-casomorphin infusions was linearly increased (P < 0.05) leading to statistically significant decreases in the insulin / glucagon ratio at 4 hours by all beta-casomorphin infusions compared with control. 5. In the final section of the thesis, attention was focused on the possible inhibitory effects of the beta-casomorphins on insulin secretion. Three experiments were carried out. Experiment 1 was designed to detect the inhibitory action of the beta-casomorphins on the insulin level prestimulated by an abomasal infusion of glucose. The insulin concentration rise was significantly inhibited by the beta-casomorphins (P < 0.05). The inhibitory action of beta-casomorphin was shown to be compatible with the action of SS- 28 as judged from the effects of SS-28 on the insulin secretion when administered intravenously in the same experiment. However, the inhibitory action was not evident in the next experiment in which lactating animals were used, probably because of differences in the sensitivity of insulin secretion in lactating versus non-lactating animals. The final experiment confirmed the insulinopenic effect of the ?- casomorphins by demonstrating their inhibitory action on the insulin concentrations prestimulated by an intravenous infusion of glucose. 6. Taken together, the results of the experiments described show effects of beta-casomorphin infusions on circulating levels of hormones in the ruminant. The most pronounced effect was the modulation of the insulin response to abomasal or intravenous administration of glucose

Modeling UV Radiation Feedback from Massive Stars: II. Dispersal of Star-Forming Giant Molecular Clouds by Photoionization and Radiation Pressure

UV radiation feedback from young massive stars plays a key role in the evolution of giant molecular clouds (GMCs) by photoevaporating and ejecting the surrounding gas. We conduct a suite of radiation hydrodynamic simulations of star cluster formation in marginally-bound, turbulent GMCs, focusing on the effects of photoionization and radiation pressure on regulating the net star formation efficiency (SFE) and cloud lifetime. We find that the net SFE depends primarily on the initial gas surface density, $\Sigma_0$, such that the SFE increases from 4% to 51% as $\Sigma_0$ increases from $13\,M_{\odot}\,{\rm pc}^{-2}$ to $1300\,M_{\odot}\,{\rm pc}^{-2}$. Cloud destruction occurs within $2$-$10\,{\rm Myr}$ after the onset of radiation feedback, or within $0.6$-$4.1$ freefall times (increasing with $\Sigma_0$). Photoevaporation dominates the mass loss in massive, low surface-density clouds, but because most photons are absorbed in an ionization-bounded Str\"{o}mgren volume the photoevaporated gas fraction is proportional to the square root of the SFE. The measured momentum injection due to thermal and radiation pressure forces is proportional to $\Sigma_0^{-0.74}$, and the ejection of neutrals substantially contributes to the disruption of low-mass and/or high-surface density clouds. We present semi-analytic models for cloud dispersal mediated by photoevaporation and by dynamical mass ejection, and show that the predicted net SFE and mass loss efficiencies are consistent with the results of our numerical simulations.Comment: Accepted to ApJ. 26 pages, 18 figures, 2 tables. For a simulation movie, see http://www.youtube.com/watch?v=_YC-ueHvEW

Applicaton of USB Serial Communication to Radon Measuring System

The USB serial communication such as USB-Serial-for PC and USB-Serial-for-Android is studied in order to monitor the measure radon data using a PC screen or a smart phone screen. Through some experimental studies, we believe that the USB serial communication module is useful for checking the data transmitted to a PC from a microcontroller