Introducing TIGRESS-NCR: I. Co-Regulation of the Multiphase Interstellar Medium and Star Formation Rates

Massive, young stars are the main source of energy that maintains multiphase structure and turbulence in the interstellar medium (ISM), and without this "feedback" the star formation rate (SFR) would be much higher than is observed. Rapid energy loss in the ISM and efficient energy recovery by stellar feedback lead to co-regulation of SFRs and the ISM state. Realistic approaches to this problem should solve the dynamical evolution of the ISM, including star formation, and the input of feedback energy self-consistently and accurately. Here, we present the TIGRESS-NCR numerical framework, in which UV radiation, supernovae, cooling and heating processes, and gravitational collapse are modeled explicitly. We use an adaptive ray tracing method for UV radiation transfer from star clusters represented by sink particles, accounting for attenuation by dust and gas. We solve photon-driven chemical equations to determine the abundances of H (time-dependent) and C/O-bearing species (steady-state), which then set cooling and heating rates self-consistently. Applying these methods, we present high-resolution magnetohydrodynamics simulations of differentially rotating local galactic disks representing typical conditions of nearby star-forming galaxies. We analyze ISM properties and phase distributions and show good agreement with existing multiwavelength galactic observations. We measure midplane pressure components (turbulent, thermal, and magnetic) and the weight, demonstrating that vertical dynamical equilibrium holds. We quantify the ratios of pressure components to the SFR surface density, which we call the feedback yields. The TIGRESS-NCR framework will allow for a wide range of parameter exploration, including low metallicity system.Comment: ApJ submitted. 28 pages, 13 figures excluding Appendi

Photochemistry and Heating/Cooling of the Multiphase Interstellar Medium with UV Radiative Transfer for Magnetohydrodynamic Simulations

We present an efficient heating/cooling method coupled with chemistry and ultraviolet (UV) radiative transfer, which can be applied to numerical simulations of the interstellar medium (ISM). We follow the time-dependent evolution of hydrogen species (H$_2$, H, H$^+$), assume carbon/oxygen species (C, C$^+$, CO, O, and O$^+$) are in formation-destruction balance given the non-steady hydrogen abundances, and include essential heating/cooling processes needed to capture thermodynamics of all ISM phases. UV radiation from discrete point sources and the diffuse background is followed through adaptive ray tracing and a six-ray approximation, respectively, allowing for H$_2$ self-shielding; cosmic ray (CR) heating and ionization are also included. To validate our methods and demonstrate their application for a range of density, metallicity, and radiation field, we conduct a series of tests, including the equilibrium curves of thermal pressure vs. density, the chemical and thermal structure in photo-dissociation regions, H I-to-H$_2$ transitions, and the expansion of H II regions and radiative supernova remnants. Careful treatment of photochemistry and CR ionization is essential for many aspects of ISM physics, including identifying the thermal pressure at which cold and warm neutral phases co-exist. We caution that many current heating and cooling treatments used in galaxy formation simulations do not reproduce the correct thermal pressure and ionization fraction in the neutral ISM. Our new model is implemented in the MHD code Athena and incorporated in the TIGRESS simulation framework, for use in studying the star-forming ISM in a wide range of environments.Comment: 57 pages, 22 figures; accepted for publication in ApJ

The environmental dependence of the X_CO conversion factor

CO is the most widely used observational tracer of molecular gas. The observable CO luminosity is translated to H_2 mass via a conversion factor, X_CO, which is a source of uncertainty and bias. Despite variations in X_CO, the empirically-determined solar neighborhood value is often applied across different galactic environments. To improve understanding of X_CO, we employ 3D magnetohydrodynamics simulations of the interstellar medium (ISM) in galactic disks with a large range of gas surface densities, allowing for varying metallicity, far-ultraviolet (FUV) radiation, and cosmic ray ionization rate (CRIR). With the TIGRESS simulation framework we model the three-phase ISM with self-consistent star formation and feedback, and post-process outputs with chemistry and radiation transfer to generate synthetic CO(1--0) and (2--1) maps. Our models reproduce the observed CO excitation temperatures, line-widths, and line ratios in nearby disk galaxies. X_CO decreases with increasing metallicity, with a power-law slope of -0.8 for the (1--0) line and -0.5 for the (2--1) line. X_CO also decreases at higher CRIR, and is insensitive to the FUV radiation. As density increases, X_CO first decreases due to increasing excitation temperature, and then increases when the emission is fully saturated. We provide fits between X_CO and observable quantities such as the line ratio, peak antenna temperature, and line brightness, which probe local gas conditions. These fits, which allow for varying beam size, may be used in observations to calibrate out systematic biases. We also provide estimates of the CO-dark H_2 fraction at different gas surface densities, observational sensitivities, and beam sizes.Comment: Accepted by Ap

Diffuse Ionized Gas in Simulations of Multiphase, Star-Forming Galactic Disks

It has been hypothesized that photons from young, massive star clusters are responsible for maintaining the ionization of diffuse warm ionized gas seen in both the Milky Way and other disk galaxies. For a theoretical investigation of the warm ionized medium (WIM), it is crucial to solve radiation transfer equations where the ISM and clusters are modeled self-consistently. To this end, we employ a Solar neighborhood model of TIGRESS, a magnetohydrodynamic simulation of the multiphase, star-forming ISM, and post-process the simulation with an adaptive ray tracing method to transfer UV radiation from star clusters. We find that the WIM volume filling factor is highly variable, and sensitive to the rate of ionizing photon production and ISM structure. The mean WIM volume filling factor rises to ~0.15 at |z|~1 kpc. Approximately half of ionizing photons are absorbed by gas and half by dust; the cumulative ionizing photon escape fraction is 1.1%. Our time-averaged synthetic H$\alpha$ line profile matches WHAM observations on the redshifted (outflowing) side, but has insufficient intensity on the blueshifted side. Our simulation matches the Dickey-Lockman neutral density profile well, but only a small fraction of snapshots have high-altitude WIM density consistent with Reynolds Layer estimates. We compute a clumping correction factor C = /sqrt~0.2 that is remarkably constant with distance from the midplane and time; this can be used to improve estimates of ionized gas mass and mean electron density from observed H$\alpha$ surface brightness profiles in edge-on galaxies.Comment: Accepted to ApJ; 31 pages, 17 figure

The full repertoire of Drosophila gustatory receptors for detecting an aversive compound.

The ability to detect toxic compounds in foods is essential for animal survival. However, the minimal subunit composition of gustatory receptors required for sensing aversive chemicals in Drosophila is unknown. Here we report that three gustatory receptors, GR8a, GR66a and GR98b function together in the detection of L-canavanine, a plant-derived insecticide. Ectopic co-expression of Gr8a and Gr98b in Gr66a-expressing, bitter-sensing gustatory receptor neurons (GRNs) confers responsiveness to L-canavanine. Furthermore, misexpression of all three Grs enables salt- or sweet-sensing GRNs to respond to L-canavanine. Introduction of these Grs in sweet-sensing GRNs switches L-canavanine from an aversive to an attractive compound. Co-expression of GR8a, GR66a and GR98b in Drosophila S2 cells induces an L-canavanine-activated nonselective cation conductance. We conclude that three GRs collaborate to produce a functional L-canavanine receptor. Thus, our results clarify the full set of GRs underlying the detection of a toxic tastant that drives avoidance behaviour in an insect

Information quality assessment in Korean manufacturing organization

Information quality is a complex problem. Issues relating to information quality are strongly embedded in the context of the operations of information systems. Information quality issues, therefore, have qualitative as well as quantitative underpinnings, which affect on the various dimensions of information quality. In order to improve information quality, it is essential to assess its various dimensions. This assessment provides the gaps that work as the building blocks for improving quality of information. However, assessing information quality dimensions is extremely intricate because each dimension depends upon other dimensions, which makes it difficult to objectively assess these dimensions. This research utilizes a product perspective of information and applies Six-Sigma methodology to assess information quality. It describes a case study of a Korean manufacturing organization where analytical hierarchy process and quality function deployment was utilized to determine the mutual relationships of information quality dimensions and critical to information quality factors.<br /

Evaluation of reference genes in mouse preimplantation embryos for gene expression studies using real-time quantitative RT-PCR (RT-qPCR)

BACKGROUND: Real-time quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) is the most sensitive, and valuable technique for rare mRNA detection. However, the expression profiles of reference genes under different experimental conditions, such as different mouse strains, developmental stage, and culture conditions have been poorly studied. RESULTS: mRNA stability of the actb, gapdh, sdha, ablim, ywhaz, sptbn, h2afz, tgfb1, 18 s and wrnip genes was analyzed. Using the NormFinder program, the most stable genes are as follows: h2afz for the B6D2F-1 and C57BL/6 strains; sptbn for ICR; h2afz for KOSOM and CZB cultures of B6D2F-1 and C57BL/6 strain-derived embryos; wrnip for M16 culture of B6D2F-1 and C57BL/6 strain-derived embryos; ywhaz, tgfb1, 18 s, 18 s, ywhaz, and h2afz for zygote, 2-cell, 4-cell, 8-cell, molular, and blastocyst embryonic stages cultured in KSOM medium, respectively; h2afz, wrnip, wrnip, h2afz, ywhaz, and ablim for zygote, 2-cell, 4-cell, 8-cell, molular, and blastocyst stage embryos cultured in CZB medium, respectively; 18 s, h2afz, h2afz, actb, h2afz, and wrnip for zygote, 2-cell, 4-cell, 8-cell, molular, and blastocyst stage embryos cultured in M16 medium, respectively. CONCLUSIONS: These results demonstrated that candidate reference genes for normalization of target gene expression using RT-qPCR should be selected according to mouse strains, developmental stage, and culture conditions. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/1756-0500-7-675) contains supplementary material, which is available to authorized users

Deficiency of peroxiredoxin 2 exacerbates angiotensin II-induced abdominal aortic aneurysm

Abdominal aortic aneurysm: Potential enzyme biomarker identified An enzyme with antioxidant properties may provide a biomarker and therapeutic agent to help treat abdominal aortic aneurysm (AAA). AAA involves the structural deterioration of the aorta through chronic inflammation and oxidative stress, and can trigger life-threatening artery rupture. An antioxidant enzyme called peroxiredoxin 2 (PRDX2) is increased in patients with ruptures, but whether its role in AAA is beneficial or detrimental is unclear. Goo Taeg Oh at the Ewha Womans University in Seoul, Jong-Gil Park at the Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea, and co-workers examined the effect of PRDX2 on AAA progression. PRDX2 suppressed structural damage in mice, limiting artery dilation and protein degradation. Loss of PRDX2 accelerated AAA development. Measuring levels of PRDX2 may indicate AAA severity in patients, while boosting the enzyme could repair aortic damage