Molecular cooling in the diffuse interstellar medium

We use a simple one-zone model of the thermal and chemical evolution of interstellar gas to study whether molecular hydrogen (H2) is ever an important coolant of the warm, diffuse interstellar medium (ISM). We demonstrate that at solar metallicity, H2 cooling is unimportant and the thermal evolution of the ISM is dominated by metal line cooling. At metallicities below 0.1 Z_solar, however, metal line cooling of low density gas quickly becomes unimportant and H2 can become the dominant coolant, even though its abundance in the gas remains small. We investigate the conditions required in order for H2 to dominate, and show that it provides significant cooling only when the ratio of the interstellar radiation field strength to the gas density is small. Finally, we demonstrate that our results are insensitive to changes in the initial fractional ionization of the gas or to uncertainties in the nature of the dust present in the low-metallicity ISM.Comment: 13 pages, 6 figures. Minor changes to match version accepted by MNRA

Approximations for modelling CO chemistry in GMCs: a comparison of approaches

We examine several different simplified approaches for modelling the chemistry of CO in three-dimensional numerical simulations of turbulent molecular clouds. We compare the different models both by looking at the behaviour of integrated quantities such as the mean CO fraction or the cloud-averaged CO-to-H2 conversion factor, and also by studying the detailed distribution of CO as a function of gas density and visual extinction. In addition, we examine the extent to which the density and temperature distributions depend on our choice of chemical model. We find that all of the models predict the same density PDF and also agree very well on the form of the temperature PDF for temperatures T > 30 K, although at lower temperatures, some differences become apparent. All of the models also predict the same CO-to-H2 conversion factor, to within a factor of a few. However, when we look more closely at the details of the CO distribution, we find larger differences. The more complex models tend to produce less CO and more atomic carbon than the simpler models, suggesting that the C/CO ratio may be a useful observational tool for determining which model best fits the observational data. Nevertheless, the fact that these chemical differences do not appear to have a strong effect on the density or temperature distributions of the gas suggests that the dynamical behaviour of the molecular clouds on large scales is not particularly sensitive to how accurately the small-scale chemistry is modelled.Comment: 18 pages, 10 figures. Minor revisions, including the addition of a comparison of simulated and observed C/CO ratios. Accepted by MNRA

Heat transfer in a compact tubular heat exchanger with helium gas at 3.5 MPa

A compact heat exchanger was constructed consisting of circular tubes in parallel brazed to a grooved base plate. This tube specimen heat exchanger was tested in an apparatus which radiatively heated the specimen on one side at a heat flux of up to 54 W/sq cm, and cooled the specimen with helium gas at 3.5 MPa and Reynolds numbers of 3000 to 35,000. The measured friction factor of the tube specimen was lower than that of a circular tube with fully developed turbulent flow, although the uncertainty was high due to entrance and exit losses. The measured Nusselt number, when modified to account for differences in fluid properties between the wall and the cooling fluid, agreed with past correlations for fully developed turbulent flow in circular tubes

Identifying the transporters of different flavonoids in plants

We recently identified a new component of flavonoid transport pathways in Arabidopsis. The MATE protein FFT (Flower Flavonoid Transporter) is primarily found in guard cells and seedling roots, and mutation of the transporter results in floral and growth phenotypes. The nature of FFT’s substrate requires further exploration but our data suggest that it is a kaempferol diglucoside. Here we discuss potential partner H+-ATPases and possible redundancy among the close homologues within the large Arabidopsis MATE family

Design, development and delivery of one /1/ breadboard and three /3/ production units of a 75 VA integrated static inverter Monthly progress report no. 11, Mar. 1966

Breadboard model development of integrated static inverte

Design, development and delivery of one /1/ breadboard and three /3/ production units of a 75 VA integrated static inverter Monthly report no. 15

Flip-flop arrays, power transistors, epitaxial stress, and other technological developments in integrated static inverter progra

Empirical modelling and simulation of transmission loss between wireless sensor nodes in gas turbine engines

Transmission loss measurements between a grid of hypothetical WSN node locations on the surface of a gas turbine engine are reported for eight frequencies at 1 GHz intervals in the frequency range 3.0 to 11.0 GHz. An empirical transmission loss model is derived from the measurements. The model is incorporated into an existing system channel model implemented using Simulink as part of a wider project concerning the development of WSNs for the testing and condition monitoring of gas turbine engines