The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?

We discuss the interpretation of the dust SED from the mid-infrared to the millimeter range of NGC 1569. The model developed by D\'esert et al. (1990) including three dust components (Polyaromatic Hydrocarbons, Very Small Grains and big grains) can explain the data using a realistic interstellar radiation field and adopting an enhanced abundance of VSGs. A simple three-temperature model is also able to reproduce the data but requires a very low dust temperature which is considered to be unlikely in this low-metallicity starburst galaxy. The high abundance of Very Small Grains might be due to large grain destruction in supernova shocks. This possibility is supported by ISO data showing that the emission at 14.3 $\mu$m, tracing VSGs, is enhanced with respect to the emission at 6.7 $\mu$m and 850 $\mu$m in regions of high star formation.Comment: 4 pages, conference proceedings paper, "The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg, 4-8 Oct. 2004, eds. C.C. Popescu & R.J. Tuffs, AIP Conf. Ser., in pres

Controlled switching of intrinsic localized modes in a 1-D antiferromagnet

Nearly steady-state locked intrinsic localized modes (ILMs) in the quasi-1d antiferromagnet (C2H5NH3)2CuCl4 are detected via four-wave mixing emission or the uniform mode absorption. Exploiting the long-time stability of these locked ILMs, repeatable nonlinear switching is observed by varying the sample temperature, and localized modes with various amplitudes are created by modulation of the microwave driver power. This steady-state ILM locking technique could be used to produce energy localization in other atomic lattices.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett. v.2 : clarifications of text and figures in response to comment

Modeling of Remote Condensing AMTEC Cells

The Alkali Metal Thermal to Electric Converter (AMTEC) is a thermally regenerated sodium concentration cell that converts heat directly into electricity without moving parts. The high efficiency of AMTEC cells is useful for power generation in space and terrestrial applications (Ivanenok et al. 1993a, 1993b). One of the advanced features proposed in current high efficiency AMTEC cell designs is remote condensing. Remote condensing occurs when the condensing surface of the cell is thermally isolated from the high temperature β“ ‐alumina solid electrolyte (BASE) tube. The parasitic heat losses are significantly reduced, thereby improving the cell efficiency. However, this configuration also increases the local Na vapor pressure (sodium concentration) on the cathode side of the BASE tube, and thus lowers the BASE tube's power output. The balance of these opposing effects is very important in optimizing system designs. This paper derives the equations necessary to calculate the vapor flow pressure drop, and compares the calculations to experimental data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87617/2/1501_1.pd

(Sub)millimetre emission from NGC 1569: an abundance of very small grains

We present new data of the dwarf galaxy NGC 1569 at 450 $\mu$m, 850 $\mu$m and 1200$\mu$m taken with SCUBA at the JCMT and the bolometer array at the IRAM 30m telescope. After including data from IRAS at 12, 25, 60 and 100 $\mu$m, we have successfully fitted the dust grain population model of D\'esert et al. (1990) to the observed midinfrared-to-millimeter spectrum. The fit requires a combination of both large and very small grains exposed to a strong radiation field as well as an enhancement of the number of very small grains relative to the number of large grains. We interpret this as the consequence of large grain destruction due to shocks in the turbulent interstellar medium of NGC 1569. The contribution of polyaromatic hydrocarbons (PAH's) is found to be negligible. Comparison of the dust emission maps with an HI map of similar resolution shows that both dust and molecular gas distributions peak close to the radio continuum maximum and at a minimum in the HI distribution. From a comparison of these three maps and assuming that the gas-to-dust mass ratio is the same everywhere, we estimate the ratio of molecular hydrogen column density to integrated CO intensity to be about 25 -- 30 times the local Galactic value. The gas-to-dust ratio is 1500 -- 2900, about an order of magnitude higher than in the Solar Neighbourhood

Targeted in vivo extracellular matrix formation promotes neovascularization in a rodent model of myocardial infarction.

BackgroundThe extracellular matrix plays an important role in tissue regeneration. We investigated whether extracellular matrix protein fragments could be targeted with antibodies to ischemically injured myocardium to promote angiogenesis and myocardial repair.Methodology/principal findingsFour peptides, 2 derived from fibronectin and 2 derived from Type IV Collagen, were assessed for in vitro and in vivo tendencies for angiogenesis. Three of the four peptides--Hep I, Hep III, RGD--were identified and shown to increase endothelial cell attachment, proliferation, migration and cell activation in vitro. By chemically conjugating these peptides to an anti-myosin heavy chain antibody, the peptides could be administered intravenously and specifically targeted to the site of the myocardial infarction. When administered into Sprague-Dawley rats that underwent ischemia-reperfusion myocardial infarction, these peptides produced statistically significantly higher levels of angiogenesis and arteriogenesis 6 weeks post treatment.Conclusions/significanceWe demonstrated that antibody-targeted ECM-derived peptides alone can be used to sufficiently alter the extracellular matrix microenvironment to induce a dramatic angiogenic response in the myocardial infarct area. Our results indicate a potentially new non-invasive strategy for repairing damaged tissue, as well as a novel tool for investigating in vivo cell biology

The IRAM-30m line survey of the Horsehead PDR: II. First detection of the l-C3H+ hydrocarbon cation

We present the first detection of the l-C3H+ hydrocarbon in the interstellar medium. The Horsehead WHISPER project, a millimeter unbiased line survey at two positions, namely the photo-dissociation region (PDR) and the nearby shielded core, revealed a consistent set of eight unidentified lines toward the PDR position. Six of them are detected with a signal-to-noise ratio from 6 to 19, while the two last ones are tentatively detected. Mostly noise appears at the same frequency toward the dense core, located less than 40" away. We simultaneously fit 1) the rotational and centrifugal distortion constants of a linear rotor, and 2) the Gaussian line shapes located at the eight predicted frequencies. The observed lines can be accurately fitted with a linear rotor model, implying a 1Sigma ground electronic state. The deduced rotational constant value is Be= 11244.9512 +/- 0.0015 MHz, close to that of l-C3H. We thus associate the lines to the l-C3H+ hydrocarbon cation, which enables us to constrain the chemistry of small hydrocarbons. A rotational diagram is then used to infer the excitation temperature and the column density. We finally compare the abundance to the results of the Meudon PDR photochemical model.Comment: 9 pages, 7 PostScript figures. Accepted for publication in Astronomy \& Astrophysics. Uses aa LaTeX macro

Low fluence UV-B as a positive regulator of photosynthesis in Arabidopsis thaliana : a thesis presented in partial fulfilment of the requirements for the degree of Doctor in Philosophy in Agriculture and Horticulture at Massey University, Palmerston North, New Zealand

Figures are re-used with permission.UV-B radiation can induce a wide range of developmental responses in plants, and magnitudes of UV-B exposure can also vary greatly. Historically, research into the effects of UV-B radiation on photosynthetic processes has often utilised high fluence rates of UV-B, which have been frequently shown to impede photosynthetic performance and induce photosystem damage. More recently, a number of studies have focused on the impact of low fluence UV-B exposure, and have found that such treatments can be beneficial to photosynthesis by upregulating photosynthetic performance. The aim of this PhD was to understand the consequences of low fluence UV-B exposure on net photosynthetic rate and underlying mechanistic responses. We characterised the photosynthetic response to 0.5 μmol m⁻² s⁻¹ of UV-B and established that net photosynthetic rate increased by 12% in wild type Arabidopsis plants at 24hrs of UV-B exposure. Through analysis of knockout lines for the UV-B photoreceptor UVR8, we determined that the photosynthesis phenotype is dependent on the presence of UVR8. To determine how low fluence UV-B exposure mediates the increase in photosynthetic rate, transcriptomic analysis via RNA-seq was undertaken. Our analysis showed that UV-B exposure results in the upregulation of photosynthesis-associated genes during the initial exposure period. The most highly upregulated genes were related to chloroplast biogenesis and synthesis of photosynthetic proteins within the chloroplast, as well as chloroplastic oxidoreductase activity. We further investigated three of these candidates: RBF1, TOC33 and TFP, and found that each of those genes plays a role in the UV-B mediated increase of photosynthetic rate at 24hrs and that the upregulation of these genes in response to UV-B exposure is regulated by UVR8. Taken together, we describe here for the first time, that low fluence UV-B increases net photosynthetic rate through UVR8-mediated upregulation of key genes, resulting in increased synthesis of chloroplastic photosynthesis-associated proteins and chloroplastic oxidoreductase activity. This further extends our knowledge of UV-B plant-response and offers further potential for exploitation of UV-B photomorphogenesis in agriculture