| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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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.
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| 2. |
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| 3. |
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| 4. |
- Li, Hong-Kou, et al.
(författare)
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A PIXE System for Routine Longitudinal Scanning of Single Hair Strands
- 1984
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 3:1-3, s. 347-351
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Tidskriftsartikel (refereegranskat)abstract
- This article describes a PIXE system designed and constructed for routine longitudinal scanning of single hair strands. In constructing a PIXE system for trace elemental scans of single hair strands on a routine basis, a fairly intense beam has to be used but the heating damage must be kept to a minimum. The experimental conditions (charge integration, beam homogeneity etc.) have to be carefully controlled in order to give accurate PIXE results. The geometrical thickness of the hair at each point of the scan has to be determined and a qualitative knowledge of the elemental distribution over the cross section of the hair has to be provided for a proper interpretation of the PIXE results. In the present PIXE system the geometrical thickness of a hair strand at each point along the scan is determined by counting the number of backscattered protons simultaneously with the PIXE analysis, and a qualitative knowledge of the elemental distribution over the cross section of the hair is obtained through bombarding the hair at particular points with different proton energies.
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| 5. |
- Li, Hong-Kou, et al.
(författare)
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A Quantative Basis for Hair Analysis Using PIXE
- 1985
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 12:2, s. 248-256
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Tidskriftsartikel (refereegranskat)abstract
- The PIXE technique offers the possibility of scanning a single hair strand longitudinally with a millimetre proton beam for trace elements. However, the accuracy of the method has been questioned since the quantification of the mass concentration has been a serious problem. In this paper a specific beam-hair-detector geometry is assumed, and the correction factor accounting for the proton energy loss and the X-ray absorption in a regular hair is calculated. 43 hair segments from 8 individuals, ranging from 45 to 110 μm in in diameter were analyzed giving a mean value of 4.32% (standard deviation 0.25%) for sulphur, and a mean value of 149 ppm (standard deviation 35 ppm) for zinc. It is shown that the correction is important not only for the determination of the absolute elemental concentrations but also for the determination of their relative longitudinal distributions. The secondary corrections accounting for the inhomogeneous elemental distribution over the cross section and the irregular shape and/or the differing mass density of a hair are also calculated. It is concluded that the accuracy and precision of the PIXE method does not become considerably lower when it is applied to single hair strands, and accuracy and precision below 10% may be reached by implementing the procedure described.
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| 6. |
- Li, Hong-Kou, et al.
(författare)
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Rutherford Backscattering - A Tool for Quantification of the Results of PIXE Analysis of Single Hair Strands
- 1985
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. - 0168-583X. ; 12:2, s. 265-268
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Tidskriftsartikel (refereegranskat)abstract
- As shown in a companion paper the geometrical diameter of a hair strand is an important parameter for quantification of its trace element content after PIXE analysis. By analysing Rutherford backscattered protons simultaneously with PIXE analysis a reliable estimate of the hair diameter can be obtained. In this work the hypothesis that there exists a linearity between the geometrical diameter and the number of backscattered protons in a certain energy interval is developed, discussed and experimentally verified.
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| 7. |
- Pallon, Jan, et al.
(författare)
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Metodik för snabba multielementanalyser av biologiskt material
- 1984
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Avsikten med detta projekt har varit att utveckla väl fungerande rutiner för PIXE-analys av biologiska prov med anknytning till exponering i arbetsmiljösituationer. Kravet på metoderna är att de tillvaratar PIXE-metodens fördelar (multielementanalys, små prov, snabb analys, låga detektionsgränser) och samtidigt förändrar eller förstör så lite som möjligt av den information som finns i de ursprungliga biologiska proven under de behandlingssteg som är nödvändiga före analysen. Ett antal standardrutiner har utvecklats med vilka man kan hantera prov som blod, lever, njure och liknande. Direkt analys av enskilda hårstrån och nagelprov kan göras utan förbehandling. Avsikten är att dessa vävnader till viss del skall tjäna som personliga monitorer för exponering,. För detta ändamål, liksom för studier av elementprofiler i hud har även protonmikrostråleteknik utnyttjats. Försök med selektiv koncentrering av vissa ämnen i urin liksom separation av serumproteiner har gjorts. Avsikten med det sistnämnda är att finna om metallbindande protein kan användas som exponeringsindikator. I det följande redogörs kortfattat för principerna, de olika prepareringsmetoderna och vilka provtyper de tillämpats på. De hänvisningar till figurer som görs syftar till figurer i slutet av rapporten.
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| 8. |
- Sada, Y., et al.
(författare)
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Structure near the K- + p + p threshold in the in-flight 3He(K-, Λp)n reaction
- 2016
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Ingår i: Progress of Theoretical and Experimental Physics. - : Oxford University Press (OUP). - 2050-3911. ; 2016:5
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Tidskriftsartikel (refereegranskat)abstract
- To search for an S = -1 di-baryonic state which decays toΛp, the 3He(K-,Λp)nmissing reaction was studied at 1.0 GeV/c. Unobserved neutrons were kinematically identified from the missing mass MX of the 3He (K-,Λp) X reaction in order to have a large acceptance for the Λpn final state. The observed Λpn events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three-nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the Λp. To account for the observed peak structure, the simplest S-wave polewas assumed to exist in the reaction channel, having a Breit-Wigner formin energy and with a Gaussian form factor. A minimum X2 method was applied to deduce its mass, MX = 2355+6 -8 (stat.) ±12 (syst.)MeV/c2, and decay width, γX = 110+19 -17 (stat.) ±27 (syst.)MeV/c2, respectively. The form factor parameter QX ∼ 400MeV/c implies that the range of the interaction is about 0.5 fm.
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