437 research outputs found
Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse
The search for binarity in AGB stars is of critical importance for our
understanding of how planetary nebulae acquire the dazzling variety of
aspherical shapes which characterises this class. However, detecting binary
companions in such stars has been severely hampered due to their extreme
luminosities and pulsations. We have carried out a small imaging survey of AGB
stars in ultraviolet light (using GALEX) where these cool objects are very
faint, in order to search for hotter companions. We report the discovery of
significant far-ultraviolet excesses towards nine of these stars. The
far-ultraviolet excess most likely results either directly from the presence of
a hot binary companion, or indirectly from a hot accretion disk around the
companion.Comment: revised for Astrophysical Journa
The TFAM-to-mtDNA ratio defines inner-cellular nucleoid populations with distinct activity levels
In human cells, generally a single mitochondrial DNA (mtDNA) is compacted into a nucleoprotein complex denoted the nucleoid. Each cell contains hundreds of nucleoids, which tend to cluster into small groups. It is unknown whether all nucleoids are equally involved in mtDNA replication and transcription or whether distinct nucleoid subpopulations exist. Here, we use multi-color STED super-resolution microscopy to determine the activity of individual nucleoids in primary human cells. We demonstrate that only a minority of all nucleoids are active. Active nucleoids are physically larger and tend to be involved in both replication and transcription. Inactivity correlates with a high ratio of the mitochondrial transcription factor A (TFAM) to the mtDNA of the individual nucleoid, suggesting that TFAM-induced nucleoid compaction regulates nucleoid replication and transcription activity in vivo. We propose that the stable population of highly compacted inactive nucleoids represents a storage pool of mtDNAs with a lower mutational load
Campus Vol 1 N 3
Todd, George. The Valentine . Prose. 2.
Fanslow, Ellen. Campus Canines . Prose. 3.
Anonymous. Spring Glimpses on Campus . Picture. 4.
Anonymous. Casual Corners . Prose. 6.
Welch, Vera. Death is Not Sad . Poem. 7.
Welch, Vera. I Do Not Love You . Poem. 7.
Taylor, Louis. Clouds . Poem. 7.
Dancy, Betty Jane. Pray Tell Me M\u27 Lord . Poem. 7.
Dancy, Betty Jane. Really Our Friendship is Perfect . Poem. 7.
Dancy, Betty Jane. You Say You Love Me For My Faith . Poem. 7.
B.Z. The Mountain . Poem. 7.
Findeisen, Robert. Do You Want to Be A Doctor? Cartoon. 8.
Thomas, John C. Campus Kaleidoscope . Prose. 10.
Harman, Betty. Sororities: The Way We See \u27Em . Prose. 12.
Marshall, James. Dischargee . Poem. 14.
Marshall, James. Suggestions to Dali . Poem. 14.
Marshall, James. Sonnet Modern, In G Minor . Poem. 14.
Marshall, James. The Request . Poem. 15.
Dancy, Betty Jane. My Mother Always Bade Me Beware . Poem. 15.
Anonymous. On the Cuff . Prose. 16
Fast, inexpensive, and reliable HPLC method to determine monomer fractions in poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
The determination of the monomer fractions in polyhydroxyalkanoates is of great importance for research on microbial-produced plastic material. The development of new process designs, the validation of mathematical models, and intelligent control strategies for production depend enormously on the correctness of the analyzed monomer fractions. Most of the available detection methods focus on the determination of the monomer fractions of the homopolymer poly(3-hydroxybutyrate). Only a few can analyze the monomer content in copolymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate), which usually require expensive measuring devices, a high preparation time or the use of environmentally harmful halogenated solvents such as chloroform or dichloromethane. This work presents a fast, simple, and inexpensive method for the analysis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with high-performance liquid chromatography. Samples from a bioreactor experiment for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with Cupriavidus necator H16 were examined regarding their monomer content using the new method and gas chromatography analysis, one of the most frequently used methods in literature. The results from our new method were validated using gas chromatography measurements and show excellent agreement. Key points ∙ The presented HPLC method is an inexpensive, fast and environmentally friendly alternative to existing methods for quantification of monomeric composition of PHBV. ∙ Validation with state of the art GC measurement exhibits excellent agreement over a broad range of PHBV monomer fractions
Enhanced incorporation of subnanometer tags into cellular proteins for fluorescence nanoscopy via optimized genetic code expansion
With few-nanometer resolution recently achieved by a new generation of fluorescence nanoscopes (MINFLUX and MINSTED), the size of the tags used to label proteins will increasingly limit the ability to dissect nanoscopic biological structures. Bioorthogonal (click) chemical groups are powerful tools for the specific detection of biomolecules. Through the introduction of an engineered aminoacyl–tRNA synthetase/tRNA pair (tRNA: transfer ribonucleic acid), genetic code expansion allows for the site-specific introduction of amino acids with “clickable” side chains into proteins of interest. Welldefined label positions and the subnanometer scale of the protein modification provide unique advantages over other labeling approaches for imaging at molecular-scale resolution. We report that, by pairing a new N-terminally optimized pyrrolysyl–tRNA synthetase (chPylRS2020) with a previously engineered orthogonal tRNA, clickable amino acids are incorporated with improved efficiency into bacteria and into mammalian cells. The resulting enhanced genetic code expansion machinery was used to label β-actin in U2OS cell filopodia for MINFLUX imaging with minimal separation of fluorophores from the protein backbone. Selected data were found to be consistent with previously reported high-resolution information from cryoelectron tomography about the cross-sectional filament bundling architecture. Our study underscores the need for further improvements to the degree of labeling with minimal-offset methods in order to fully exploit molecularscale optical three-dimensional resolution
Interpretation of High-Dimensional Linear Regression: Effects of Nullspace and Regularization Demonstrated on Battery Data
High-dimensional linear regression is important in many scientific fields.
This article considers discrete measured data of underlying smooth latent
processes, as is often obtained from chemical or biological systems.
Interpretation in high dimensions is challenging because the nullspace and its
interplay with regularization shapes regression coefficients. The data's
nullspace contains all coefficients that satisfy , thus
allowing very different coefficients to yield identical predictions. We
developed an optimization formulation to compare regression coefficients and
coefficients obtained by physical engineering knowledge to understand which
part of the coefficient differences are close to the nullspace. This nullspace
method is tested on a synthetic example and lithium-ion battery data. The case
studies show that regularization and z-scoring are design choices that, if
chosen corresponding to prior physical knowledge, lead to interpretable
regression results. Otherwise, the combination of the nullspace and
regularization hinders interpretability and can make it impossible to obtain
regression coefficients close to the true coefficients when there is a true
underlying linear model. Furthermore, we demonstrate that regression methods
that do not produce coefficients orthogonal to the nullspace, such as fused
lasso, can improve interpretability. In conclusion, the insights gained from
the nullspace perspective help to make informed design choices for building
regression models on high-dimensional data and reasoning about potential
underlying linear models, which are important for system optimization and
improving scientific understanding.Comment: Manuscript: 14 pages, 7 figures; Supplementary Information: 4 pages,
2 figures; Code available: https://github.com/JoachimSchaeffer/HDRegAnalytic
Planets Around Low-Mass Stars (PALMS). II. A Low-Mass Companion to the Young M Dwarf GJ 3629 Separated By 0.2"
We present the discovery of a 0.2" companion to the young M dwarf GJ 3629 as
part of our high contrast adaptive optics imaging search for giant planets
around low-mass stars with the Keck-II and Subaru telescopes. Two epochs of
imaging confirm the pair is co-moving and reveal signs of orbital motion. The
primary exhibits saturated X-ray emission, which together with its UV
photometry from GALEX point to an age younger than ~300 Myr. At these ages the
companion lies below the hydrogen burning limit with a model-dependent mass of
46 +/- 16 Mjup based on the system's photometric distance of 22 +/- 3 pc.
Resolved YJHK photometry of the pair indicates a spectral type of M7 +/- 2 for
GJ 3629 B. With a projected separation of 4.4 +/- 0.6 AU and an estimated
orbital period of 21 +/- 5 yr, GJ 3629 AB is likely to yield a dynamical mass
in the next several years, making it one of only a handful of brown dwarfs to
have a measured mass and an age constrained from the stellar primary.Comment: Accepted for publication in Ap
Searching for Young M Dwarfs with GALEX
The census of young moving groups in the solar neighborhood is significantly
incomplete in the low-mass regime. We have developed a new selection process to
find these missing members based on the GALEX All-Sky Imaging Survey. For stars
with spectral types >K5 and younger than 300~Myr, we show that near-UV and
far-UV emission is greatly enhanced above the quiescent photosphere, analogous
to the enhanced X-ray emission of young low-mass stars seen by ROSAT but
detectable to much larger distances with GALEX. By combining GALEX data with
optical (HST Guide Star Catalog) and near-IR (2MASS) photometry, we identified
an initial sample of 34 young M dwarf candidates in a 1000 sq.~deg.~region
around the 10-Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30
of these found 16 which had H_alpha in emission, which were then followed-up at
high resolution to search for spectroscopic evidence of youth and to measure
radial velocities. Four objects have low surface gravities, photometric
distances and space motions consistent with TWA, but the non-detection of Li
indicates they may be too old to belong to this moving group. One object (M3.5,
93 pc) appears to be the first known accreting low-mass member of the 15~Myr
Lower Centaurus Crux OB association. Two objects exhibit all the
characteristics of the known TWA members, and thus we designate them as TWA 31
(M4.2, 110 pc) and TWA 32 (M6.3, 53 pc). TWA 31 shows extremely broad (447
km/s) H_alpha emission, making it the sixth member of TWA found to have ongoing
accretion. TWA 32 is resolved into a 0.6" binary in Keck laser guide star
adaptive optics imaging. Our search should be sensitive down to spectral types
of at least M4-M5 in TWA and thus the small numbers of new member is puzzling.
This may indicate TWA has an atypical mass function or that the presence of Li
may be too restrictive a criteria for selecting young low-mass stars.Comment: Accepted to Ap
Aerosol Mixing State: Measurements, Modeling, and Impacts
Atmospheric aerosols are complex mixtures of different chemical species, and individual particles exist in many different shapes and morphologies. Together, these characteristics contribute to the aerosol mixing state. This review provides an overview of measurement techniques to probe aerosol mixing state, discusses how aerosol mixing state is represented in atmospheric models at different scales, and synthesizes our knowledge of aerosol mixing state’s impact on climate‐relevant properties, such as cloud condensation and ice nucleating particle concentrations, and aerosol optical properties. We present these findings within a framework that defines aerosol mixing state along with appropriate mixing state metrics to quantify it. Future research directions are identified, with a focus on the need for integrating mixing state measurements and modeling.Key PointsWe define aerosol mixing state and connect it to the physicochemical properties of aerosol particlesWe discuss existing measurements and models to understand chemical and physicochemical mixing stateWe explain the connection between aerosol mixing state and climate‐relevant aerosol propertiesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150540/1/rog20184_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150540/2/rog20184.pd
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