8,495 research outputs found
ISM properties in hydrodynamic galaxy simulations: Turbulence cascades, cloud formation, role of gravity and feedback
We study the properties of ISM substructure and turbulence in hydrodynamic
(AMR) galaxy simulations with resolutions up to 0.8 pc and 5x10^3 Msun. We
analyse the power spectrum of the density distribution, and various components
of the velocity field. We show that the disk thickness is about the average
Jeans scale length, and is mainly regulated by gravitational instabilities.
From this scale of energy injection, a turbulence cascade towards small-scale
is observed, with almost isotropic small-scale motions. On scales larger than
the disk thickness, density waves are observed, but there is also a full range
of substructures with chaotic and strongly non-isotropic gas velocity
dispersions. The power spectrum of vorticity in an LMC-sized model suggests
that an inverse cascade of turbulence might be present, although energy input
over a wide range of scales in the coupled gaseous+stellar fluid could also
explain this quasi-2D regime on scales larger than the disk scale height.
Similar regimes of gas turbulence are also found in massive high-redshift disks
with high gas fractions. Disk properties and ISM turbulence appear to be mainly
regulated by gravitational processes, both on large scales and inside dense
clouds. Star formation feedback is however essential to maintain the ISM in a
steady state by balancing a systematic gas dissipation into dense and small
clumps. Our galaxy simulations employ a thermal model based on a barotropic
Equation of State (EoS) aimed at modelling the equilibrium of gas between
various heating and cooling processes. Denser gas is typically colder in this
approach, which is shown to correctly reproduce the density structures of a
star-forming, turbulent, unstable and cloudy ISM down to scales of a few
parsecs.Comment: MNRAS in pres
Comparative transcriptomics reveals key differences in the response to milk oligosaccharides of infant gut-associated bifidobacteria.
Breast milk enhances the predominance of Bifidobacterium species in the infant gut, probably due to its large concentration of human milk oligosaccharides (HMO). Here we screened infant-gut isolates of Bifidobacterium longum subsp. infantis and Bifidobacterium bifidum using individual HMO, and compared the global transcriptomes of representative isolates on major HMO by RNA-seq. While B. infantis displayed homogeneous HMO-utilization patterns, B. bifidum were more diverse and some strains did not use fucosyllactose (FL) or sialyllactose (SL). Transcriptomes of B. bifidum SC555 and B. infantis ATCC 15697 showed that utilization of pooled HMO is similar to neutral HMO, while transcriptomes for growth on FL were more similar to lactose than HMO in B. bifidum. Genes linked to HMO-utilization were upregulated by neutral HMO and SL, but not by FL in both species. In contrast, FL induced the expression of alternative gene clusters in B. infantis. Results also suggest that B. bifidum SC555 does not utilize fucose or sialic acid from HMO. Surprisingly, expression of orthologous genes differed between both bifidobacteria even when grown on identical substrates. This study highlights two major strategies found in Bifidobacterium species to process HMO, and presents detailed information on the close relationship between HMO and infant-gut bifidobacteria
Carbon turnover in the water-soluble protein of the adult human lens.
PurposeHuman eye lenses contain cells that persist from embryonic development. These unique, highly specialized fiber cells located at the core (nucleus) of the lens undergo pseudo-apoptosis to become devoid of cell nuclei and most organelles. Ostensibly lacking in protein transcriptional capabilities, it is currently believed that these nuclear fiber cells owe their extreme longevity to the perseverance of highly stable and densely packed crystallin proteins. Maintaining the structural and functional integrity of lenticular proteins is necessary to sustain cellular transparency and proper vision, yet the means by which the lens actually copes with a lifetime of oxidative stress, seemingly without any capacity for protein turnover and repair, is not completely understood. Although many years of research have been predicated upon the assumption that there is no protein turnover or renewal in nuclear fiber cells, we investigated whether or not different protein fractions possess protein of different ages by using the (14)C bomb pulse.MethodsAdult human lenses were concentrically dissected by gently removing the cell layers in water or shaving to the nucleus with a curved micrometer-controlled blade. The cells were lysed, and the proteins were separated into water-soluble and water-insoluble fractions. The small molecules were removed using 3 kDa spin filters. The (14)C/C was measured in paired protein fractions by accelerator mass spectrometry, and an average age for the material within the sample was assigned using the (14)C bomb pulse.ResultsThe water-insoluble fractions possessed (14)C/C ratios consistent with the age of the cells. In all cases, the water-soluble fractions contained carbon that was younger than the paired water-insoluble fraction.ConclusionsAs the first direct evidence of carbon turnover in protein from adult human nuclear fiber cells, this discovery supports the emerging view of the lens nucleus as a dynamic system capable of maintaining homeostasis in part due to intricate protein transport mechanisms and possibly protein repair. This finding implies that the lens plays an active role in the aversion of age-related nuclear (ARN) cataract
The HI Chronicles of LITTLE THINGS BCDs II: The Origin of IC 10's HI Structure
In this paper we analyze Very Large Array (VLA) telescope and Green Bank
Telescope (GBT) atomic hydrogen (HI) data for the LITTLE THINGS(1) blue compact
dwarf galaxy IC 10. The VLA data allow us to study the detailed HI kinematics
and morphology of IC 10 at high resolution while the GBT data allow us to
search the surrounding area at high sensitivity for tenuous HI. IC 10's HI
appears highly disturbed in both the VLA and GBT HI maps with a kinematically
distinct northern HI extension, a kinematically distinct southern plume, and
several spurs in the VLA data that do not follow the general kinematics of the
main disk. We discuss three possible origins of its HI structure and kinematics
in detail: a current interaction with a nearby companion, an advanced merger,
and accretion of intergalactic medium. We find that IC 10 is most likely an
advanced merger or a galaxy undergoing accretion.
1:Local Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy
Survey; https://science.nrao.edu/science/surveys/littlethingsComment: 36 pages, 17 figures, accepted for publication in The Astronomical
Journa
Very high-current-density Nb/AlN/Nb tunnel junctions for low-noise submillimeter mixers
We have fabricated and tested submillimeter-wave superconductor–insulator–superconductor (SIS) mixers using very high-current-density Nb/AlN/Nb tunnel junctions (Jc[approximate]30 kA cm–2). The junctions have low-resistance-area products (RNA[approximate]5.6 Omega µm2), good subgap-to-normal resistance ratios Rsg/RN[approximate]10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that omegaRNC = 1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlOx/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected double-sideband receiver noise temperature of TRX = 110 K at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing rf loss in the tuning circuits
A copula model of wind turbine performance
The conventional means of assessing the performance of a wind turbine is through consideration of its power curve which provides the relationship between power output and measured wind speed. In this paper it is shown how the joint probability distribution of power and wind speed can be learned from data, rather than from examination of the implied function of the two variables. Such an approach incorporates measures of uncertainty into performance estimates, allows inter-plant performance comparison, and could be used to simulate plant operation via sampling. A preliminary model is formulated and fitted to operational data as an illustration
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