| 1. |
- Beal, Jacob, et al.
(författare)
-
Robust estimation of bacterial cell count from optical density
- 2020
-
Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
-
Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
|
|
| 2. |
- Cheng, Yu, et al.
(författare)
-
Star Formation in a Strongly Magnetized Cloud
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 916:2
-
Tidskriftsartikel (refereegranskat)abstract
- We study star formation in the Center Ridge 1 (CR1) clump in the Vela C giant molecular cloud, selected as a high column density region that shows the lowest level of dust continuum polarization-angle dispersion, likely indicating that the magnetic field is relatively strong. We observe the source with the Atacama Large Millimeter/submillimeter Array 7 m array at 1.05 and 1.3 mm wavelengths, which enable measurements of dust temperature, core mass, and astrochemical deuteration. A relatively modest number of 11 dense cores are identified via their dust continuum emission, with masses spanning from 0.17-6.7 M-circle dot. Overall CR1 has a relatively low compact dense gas fraction compared with other typical clouds with similar column densities, which may be a result of the strong magnetic field and/or the very early evolutionary stage of this region. The deuteration ratios, D-frac, of the cores, measured with N2H+(3-2) and N2D+(3-2) lines, span from 0.011-0.85, with the latter being one of the highest values yet detected. The level of deuteration appears to decrease with evolution from prestellar to protostellar phase. A linear filament, running approximately parallel with the large scale magnetic field orientation, is seen connecting the two most massive cores, each having CO bipolar outflows aligned orthogonally to the filament. The filament contains the most deuterated core, likely to be prestellar and located midway between the protostars. The observations permit measurement of the full deuteration structure of the filament along its length, which we present. We also discuss the kinematics and dynamics of this structure, as well as of the dense core population.
|
|
