Surface effects in alkali-halide crystals resulting from irradiation by x-rays

Absorption spectrum of alkali halide crystals before and after radiation exposur

Regulation of Skeletal Muscle Insulin Action and Fatty Acid Trafficking with Obesity and Exercise

Altered skeletal muscle fat metabolism is linked to changes in skeletal muscle insulin sensitivity. Whereby the accumulation of bioactive signaling lipids (i.e., diacylglycerols and ceramides) within skeletal muscle are negatively associated with insulin sensitivity and the exercise-induced changes to fatty acid trafficking are related to improved skeletal muscle insulin action. However, the mechanisms that contribute to these observations remain to be completely elucidated. The overall aim of this dissertation was to investigate potential underlying mechanisms that contribute to altered skeletal muscle fat metabolism and/or insulin sensitivity in response to lipid/obesity-induced insulin resistance, exercise training, and a single session of exercise. The primary mechanisms of focus were the role of skeletal muscle Ras-related C3 botulinum toxin substrate 1 (Rac1) in insulin- and exercise-stimulated glucose regulation and the contribution of long-chain acyl-coenzyme a synthetases (ACSL) to skeletal muscle fat metabolism. Rac1 is required for normal insulin-stimulated glucose transporter 4 (GLUT4) translocation and evidence suggest it may be negatively regulated by lipids. Therefore, the primary aim of my second chapter was to investigate the potential role for diacylglycerols and ceramides as negative regulators on insulin-stimulated Rac1 activation. Cultured muscle cells were treated overnight with or without fatty acids, one of which is known to induced insulin resistance (i.e., palmitate). Overnight fatty acid treatments were followed by a time course approach to measure insulin-stimulated Rac1 activation (GTP-binding), other components of insulin signaling, and functional output measure of insulin action, GLUT4 translocation. Overnight palmitate treatment resulted accumulation of diacylglycerols and ceramides and almost complete ablation of insulin-stimulated GLUT4 translocation. However, impaired GLUT4 translocation occurred independent of changes to insulin-stimulated Rac1-GTP binding. Phosphorylation of a Rac1 downstream effector protein p21-activated kinase (PAK) was blunted by palmitate treatment as was Akt phosphorylation, which stimulates GLUT4 translocation independent of Rac1. Collectively, we interpret our findings to indicate that palmitate-induced down regulation of PAK1 activation and GLUT4 translocation occur independent to insulin-stimulated Rac1-GTP binding. Evidence suggest ACSLs may regulate fat oxidation and fat storage within skeletal muscle. Whereby specific skeletal muscle isoform ACSL1 is suggested to contribute to fat oxidation and ACSL6 may play a role in fat storage. However, it is unknown if ACSLs are regulated by diet-induced obesity and/or aerobic exercise training. The primary aims of my third chapter were to investigate skeletal muscle ACSL isoform protein expression following high fat diet (HFD)-induced obesity and aerobic exercise training, and determine potential roles for ACSL1 and 6 with measures of fat metabolism in mice. In mouse gastrocnemius muscle, protein abundance for 4 of the 5 known ACSL isoforms was detected. HFD-induced obesity resulted in a non-significant increase in ACSL1, significantly greater ASCL6, and no change in ACSL4 or ACSL5. Aerobic exercise training resulted in decreased ACSL4 protein abundance, greater ACSL6, and no changes in ACSL1 or ACSL5. Skeletal muscle ACSL1 protein abundance was not related to measures of whole-body fat oxidation at rest, whereas ACSL6 was positively associated with intramyocellular lipid content. Taken together, we interpret our findings to demonstrate ACSLs undergo isoform specific regulation by diet and exercise and ACSL6 may be a regulator of skeletal muscle fat storage. Model systems implicate ACSLs as key regulators of skeletal muscle fat oxidation and fat storage; however, such roles remain underexplored in humans. The primary aims of my fourth chapter were to determine the protein expression of ACSL isoforms in skeletal muscle at rest and in response to acute exercise, and identify relationships between skeletal muscle ACSLs and measures of fat metabolism. In vastus lateralis biopsy samples collected from relatively lean sedentary adults, protein abundance for 4 of 5 known ACSL isoforms was detected. ACSL isoforms were largely unaltered by acute exercise aside from a transient increase in ACSL5 15 minutes post-exercise which returned to resting levels by 120 minutes. Skeletal muscle ACSL1 was not related to measures of resting whole-body fat oxidation. ACSL1 did tend to be positively related to whole-body fat oxidation during exercise, when skeletal muscle a major determinant of whole-body substrate oxidation. Skeletal muscle ACSL6 was positively related to skeletal muscle triacylglycerol concentration suggesting a role in the regulation of fat storage. We interpret our findings to indicate the protein abundance for ACSLs undergo isoform specific regulation by acute exercise and provide further evidence for their role in skeletal muscle fat metabolism in humans. A single session of exercise improves insulin sensitivity in most adults. Rac1 facilitates GLUT4 translocation and is activated by both insulin and exercise (i.e., mechanical stress). However, it is unknown whether insulin-stimulated Rac1 activation is further enhanced by prior exercise. The primary aims of my fifth chapter were to determine the effects of previous exercise on insulin sensitivity, Rac1 signaling, and other components of insulin signaling in the hours after exercise in relatively lean sedentary adults. A single session of moderate-intensity exercise improved measures of whole-body insulin sensitivity. Observed improvements in insulin sensitivity occurred independent of enhanced insulin-stimulated Rac1 activation, phosphorylation of its downstream effector protein PAK, or insulin-stimulated Akt activation post-exercise. Exercise induces activation of AMPK and its downstream effector protein TBC1D1 and contribute to glucose uptake in the hours after exercise. AMPK-specific activation of TBC1D1 was increased 15 minutes post-exercise and remained elevated at 180 minutes compared with basal measures and the rest trial, which closely coincided with when measures of insulin sensitivity during the steady state of the hyperinsulinemic-euglycemic clamp (i.e., 270-300 minutes post-exercise). Collectively, we interpret our results to suggest the mechanisms independent of insulin-stimulated Rac1 signaling such as TBC1D1 may contribute to the insulin sensitizing effects of exercise. This collection of studies indicate that lipid-induced insulin resistance occurs independent to impairments in insulin-stimulated Rac1 activation. Skeletal muscle ACSLs are related to measures of fat metabolism in mice and humans and demonstrate isoform specific regulation by diet-induced obesity and aerobic exercise training in mice, but are largely unaltered by acute exercise in humans. These isoform specific changes in ACSL protein abundance may contribute to the altered skeletal muscle fat metabolism with diet-induced obesity and/or aerobic exercise training. Lastly, the insulin sensitizing effects occur independent to enhanced insulin-stimulated activation of Rac1 post-exercise

A Widespread, Clumpy Starburst in the Isolated Ongoing Dwarf Galaxy Merger dm1647+21

Interactions between pairs of isolated dwarf galaxies provide a critical window into low-mass hierarchical, gas-dominated galaxy assembly and the buildup of stellar mass in low-metallicity systems. We present the first VLT/MUSE optical IFU observations of the interacting dwarf pair dm1647+21, selected from the TiNy Titans survey. The H$\alpha$ emission is widespread and corresponds to a total unobscured star formation rate (SFR) of 0.44 M$_{\odot}$ yr$^{-1}$, 2.7 times higher than the SFR inferred from SDSS data. The implied specific SFR (sSFR) for the system is elevated by more than an order of magnitude above non-interacting dwarfs in the same mass range. This increase is dominated by the lower-mass galaxy, which has a sSFR enhancement of $>$ 50. Examining the spatially-resolved maps of classic optical line diagnostics, we find the ISM excitation can be fully explained by star formation. The velocity field of the ionized gas is not consistent with simple rotation. Dynamical simulations indicate that the irregular velocity field and the stellar structure is consistent with the identification of this system as an ongoing interaction between two dwarf galaxies. The widespread, clumpy enhancements in star formation in this system point to important differences in the effect of mergers on dwarf galaxies, compared to massive galaxies: rather than the funneling of gas to the nucleus and giving rise to a nuclear starburst, starbursts in low-mass galaxy mergers may be triggered by large-scale ISM compression, and thus be more distributed.Comment: Accepted for publication in ApJ. 11 pages, 5 figures, 1 table. Figures slightly degraded to meet arXiv size restrictions. For more information about TiNy Titans see https://lavinia.as.arizona.edu/~tinytitans

Infrared luminosities and aromatic features in the 24 μm flux-limited sample of 5muses

We study a 24 μm selected sample of 330 galaxies observed with the infrared spectrograph for the 5 mJy Unbiased Spitzer Extragalactic Survey. We estimate accurate total infrared luminosities by combining mid-IR spectroscopy and mid-to-far infrared photometry, and by utilizing newempirical spectral templates from Spitzer data. The infrared luminosities of this sample range mostly from 10^9 L_⊙ to 10^(13.5) L_⊙,with 83% in the range 10^(10) L_⊙ < L_(IR) < 10^(12) L_⊙. The redshifts range from 0.008 to 4.27, with a median of 0.144. The equivalent widths of the 6.2 μm aromatic feature have a bimodal distribution, probably related to selection effects. We use the 6.2μm polycyclic aromatic hydrocarbon equivalent width (PAH EW) to classify our objects as starburst (SB)-dominated (44%), SB-AGN composite (22%), and active galactic nucleus (AGN)-dominated (34%). The high EW objects (SB-dominated) tend to have steeper mid-IR to far-IR spectral slopes and lower L_(IR) and redshifts. The low EW objects (AGN-dominated) tend to have less steep spectral slopes and higher L_(IR) and redshifts. This dichotomy leads to a gross correlation between EW and slope, which does not hold within either group. AGN-dominated sources tend to have lower log(L_(PAH7.7 μm)/L_(PAH11.3 μm)) ratios than star-forming galaxies, possibly due to preferential destruction of the smaller aromatics by the AGN. The log(L_(PAH7.7 μm)/L_(PAH11.3 μm)) ratios for star-forming galaxies are lower in our sample than the ratios measured from the nuclear spectra of nearby normal galaxies, most probably indicating a difference in the ionization state or grain size distribution between the nuclear regions and the entire galaxy. Finally, we provide a calibration relating the monochromatic continuum or aromatic feature luminosity to L_(IR) for different types of objects

Star-forming Clumps in Local Luminous Infrared Galaxies

We present HST narrowband near-infrared imaging of Paα and Paβ emission of 48 local luminous infrared galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey. These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extranuclear clumps) and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs the star-forming clumps have radii ranging from ~90 to 900 pc and star formation rates (SFRs) of ~1 × 10⁻³ to 10 M⊙ yr⁻¹, with median values for extranuclear clumps of 170 pc and 0.03 M⊙ yr⁻¹. The detected star-forming clumps are young, with a median stellar age of 8.7 Myr, and have a median stellar mass of 5 × 10⁵ M ⊙. The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at z = 1–3. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10% to 90%. If local LIRGs are similar to these simulated galaxies, we expect that future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs

New Probable Dwarf Galaxies in Northern Groups of the Local Supercluster

We have searched for nearby dwarf galaxies in 27 northern groups with characteristic distances 8-15 Mpc based on the Second Palomar Sky Survey prints. In a total area of about 2000 square degrees, we have found 90 low-surface-brightness objects, more than 60% of which are absent from known catalogs and lists. We have classified most of these objects (~80%) as irregular dwarf systems. The first 21-cm line observations of the new objects with the 100-m Effelsberg radio telescope showed that the typical linear diameters (1-2 kpc), internal motions (30 km/s), and hydrogen masses (~2*10^7M_sun) galaxies correspond to those expected for the dwarf population of nearby groups.Comment: 8 pages, 1 fugur

A controlled study of cold dust content in galaxies from z=0−2z=0-2

At $z=1-3$, the formation of new stars is dominated by dusty galaxies whose far-IR emission indicates they contain colder dust than local galaxies of a similar luminosity. We explore the reasons for the evolving IR emission of similar galaxies over cosmic time using: 1) Local galaxies from GOALS $(L_{\rm IR}=10^{11}-10^{12}\,L_\odot)$; 2) Galaxies at $z\sim0.1-0.5$ from the 5MUSES ($L_{\rm IR}=10^{10}-10^{12}\,L_\odot$); 3) IR luminous galaxies spanning $z=0.5-3$ from GOODS and Spitzer xFLS ($L_{\rm IR}>10^{11}\,L_\odot$). All samples have Spitzer mid-IR spectra, and Herschel and ground-based submillimeter imaging covering the full IR spectral energy distribution, allowing us to robustly measure $L_{\rm IR}^{\rm\scriptscriptstyle SF}$, $T_{\rm dust}$, and $M_{\rm dust}$ for every galaxy. Despite similar infrared luminosities, $z>0.5$ dusty star forming galaxies have a factor of 5 higher dust masses and 5K colder temperatures. The increase in dust mass is linked with an increase in the gas fractions with redshift, and we do not observe a similar increase in stellar mass or star formation efficiency. $L_{160}^{\rm\scriptscriptstyle SF}/L_{70}^{\rm\scriptscriptstyle SF}$, a proxy for $T_{\rm dust}$, is strongly correlated with $L_{\rm IR}^{\rm\scriptscriptstyle SF}/M_{\rm dust}$ independently of redshift. We measure merger classification and galaxy size for a subsample, and there is no obvious correlation between these parameters and $L_{\rm IR}^{\rm \scriptscriptstyle SF}/M_{\rm dust}$ or $L_{160}^{\rm\scriptscriptstyle SF}/L_{70}^{\rm\scriptscriptstyle SF}$. In dusty star forming galaxies, the change in $L_{\rm IR}^{\rm\scriptscriptstyle SF}/M_{\rm dust}$ can fully account for the observed colder dust temperatures, suggesting that any change in the spatial extent of the interstellar medium is a second order effect.Comment: Accepted for publication in ApJ. 21 pages, 11 figure

A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High Resolution Measurements of the Radio Continuum

We present Very Large Array observations of the 33 GHz radio continuum emission from 22 local ultraluminous and luminous infrared (IR) galaxies (U/LIRGs). These observations have spatial (angular) resolutions of 30--720 pc (0.07"-0.67") in a part of the spectrum that is likely to be optically thin. This allows us to estimate the size of the energetically dominant regions. We find half-light radii from 30 pc to 1.7 kpc. The 33 GHz flux density correlates well with the IR emission, and we take these sizes as indicative of the size of the region that produces most of the energy. Combining our 33 GHz sizes with unresolved measurements, we estimate the IR luminosity and star formation rate per area, and the molecular gas surface and volume densities. These quantities span a wide range (4 dex) and include some of the highest values measured for any galaxy (e.g., $\mathrm{\Sigma_{SFR}^{33GHz} \leq 10^{4.1} M_{\odot} yr^{-1} kpc^{-2}}$). At least $13$ sources appear Compton thick ($\mathrm{N_{H}^{33GHz} \geq 10^{24} cm^{-2}}$). Consistent with previous work, contrasting these data with observations of normal disk galaxies suggests a nonlinear and likely multi-valued relation between SFR and molecular gas surface density, though this result depends on the adopted CO-to-H$_{2}$ conversion factor and the assumption that our 33 GHz sizes apply to the gas. 11 sources appear to exceed the luminosity surface density predicted for starbursts supported by radiation pressure and supernovae feedback, however we note the need for more detailed observations of the inner disk structure. U/LIRGs with higher surface brightness exhibit stronger [{\sc Cii}] 158$\mu$m deficits, consistent with the suggestion that high energy densities drive this phenomenon.Comment: 32 pages, 11 figures, 7 tables. Accepted for publication in Ap