| 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. |
- Karpus, V., et al.
(författare)
-
Coordination-induced structure of the Mg 2p core level in i-ZnMgR quasicrystals
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:15
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed analysis of Mg 2p photoemission (PE) spectra in icosahedral ZnMgR (R=Y, Ho, Er) quasicrystals and in the crystalline Zn2Mg Laves phase. Synchrotron-radiation PE measurements were performed on in situ cleaved single-grain samples at 10(-10) mbar pressure and low, 90-150 K, temperature. The analysis of Mg 2p PE spectra in Zn2Mg reveals a surface shift of the core level of -0.12 eV. The Mg 2p PE spectra in i-ZnMgR quasicrystals are essentially broadened as compared to spectra in Zn2Mg Laves phase. The effect is due to the coordination-induced structure of the Mg 2p levels. Different local surroundings of Mg atoms in quasicrystals induce both different shifts of the Mg 2p level and splittings of its spin-orbit components. The local coordination potential at different Mg sites in the quasicrystalline lattice is calculated on the basis of the face-centered icosahedral ZnMgY atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts calculated are spread within an interval of about 0.3 eV, while the splittings of the 2p(3/2) component are of the order of 1-10 meV. The simulated theoretical Mg 2p PE spectra of fci-ZnMgR quasicrystals perfectly fit the experimental data.
|
|
| 3. |
- Karpus, V., et al.
(författare)
-
Interband optical transitions of Zn
- 2016
-
Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 253:3, s. 419-428
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental results of an optical study of single-crystal zinc are presented. Components of the Zn dielectric function tensor were measured by spectroscopic ellipsometry in the 0.1-5 eV spectral range. In the NIR-VIS range, the dielectric function spectra show two clearly resolved, polarization-dependent optical features located at about 1 and 1.7 eV. The optical features were analyzed in a framework of parallel-band optical transitions. The performed theoretical calculations of the optical conductivity spectra well reproduce the experimental data with respect to positions, intensities, and polarization dependencies of the observed interband absorption peaks. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
|
|
| 4. |
- Karpus, V., et al.
(författare)
-
Mg 2p shallow core-level and local atomic structure of i-ZnMgRE quasicrystals
- 2006
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:15, s. 5411-5414
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed analysis of the Mg 2p shallow core-levels measured on icosahedral single-grain ZnMgY, ZnMgHo, and ZnMgEr quasicrystals during a photoelectron microscopy study. The synchrotron radiation photoemission measurements were performed on in situ cleaved samples at a pressure of 10(-10) mbar and at low temperature, typically 90-150 K. The Mg 2p photoemission lines are essentially broadened as compared to those of the Mg 2p spin-orbit doublet recorded on the Zn2Mg crystalline Laves phase. The broadening is associated to the coordination shifts of the Mg 2p level due to the inequivalent magnesium sites in the quasicrystalline lattice. The coordination shifts are calculated on the basis of i-ZnMg(Ho, Y) atomic structure data, recently determined from the pair distribution function analysis. The coordination shifts obtained are up to 0.2 eV. The Mg 2p experimental spectral intensity is nicely reproduced by a superposition of coordination-shifted Mg 2p spin-orbit doublets.
|
|
| 5. |
|
|
| 6. |
- Karpus, V, et al.
(författare)
-
Optical spectroscopy and electronic structure of the face-centered icosahedral quasicrystals Zn-Mg-R (R=Y, Ho, Er)
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 88:9
-
Tidskriftsartikel (refereegranskat)abstract
- Results of optical spectroscopy studies of the face-centered icosahedral (fci) single-grain Zn-Mg-Y, Zn-Mg-Ho, and Zn-Mg-Er quasicrystals (QCs) are presented. The dielectric function of the QCs was measured in the 0.01–6 eV spectral range by IR-UV spectroscopic ellipsometry and far infrared reflection spectroscopy techniques. A theoretical scheme of optical conductivity calculations is extended to account for the Fermi level positions within and below a pseudogap. The model of the QC electron energy spectrum, based on a band structure hypothesis, is suggested, which treats the electronic subsystem as a nearly free electron gas affected by intersections of the Fermi surface with several families of Bragg planes. The experimental optical spectra are reproduced in detail by theoretical calculations carried out within the framework of the model. The parameters of the electron energy spectrum deduced from an analysis of optical data are close to those previously determined in an analysis of fci Zn-Mg-R valence band photoemission spectra.
|
|
| 7. |
- Karpus, V., et al.
(författare)
-
Photoemission spectroscopy study of si-ZnMgHo quasicrystals
- 2008
-
Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 30:5, s. 690-692
-
Tidskriftsartikel (refereegranskat)abstract
- The results of photoemission spectroscopy of the simple-icosahedral single-grain ZnMgHo quasicrystals are presented. Synchrotron radiation photoemission measurements were performed on in situ cleaved samples at 10(-10) mbar pressure and low, 160 K, temperature. The valence band photoemission spectra measured reveal a simple metal type valence band with a distinct Fermi edge and a sharp pseudogap feature, which originates from the van Hove singularities in the density of states. The photoemission spectra of the Mg 2p core level show the coordination shifts of Mg 2p, spin-orbit doublet due to inequivalent Mg sites in the quasicrystalline lattice.
|
|
| 8. |
- Suchodolskis, A., et al.
(författare)
-
Indication of van Hove singularities in the density of states of ZnMg(Y,Ho) quasicrystals
- 2003
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:5
-
Tidskriftsartikel (refereegranskat)abstract
- We present a low-temperature synchrotron-radiation photoelectron microspectroscopy study of the valence bands of single-grain icosahedral ZnMgY and ZnMgHo quasicrystals. Their valence band photoemission spectra reveal in both cases a simple metal-type behavior with a clear metallic Fermi edge and a sharp pseudogap feature: the spectral intensity exhibits a maximum at approximate to0.7 eV below the chemical potential and a subsequent decrease as the Fermi level is approached. The analysis of the pseudogap feature, based on the band-structure hypothesis, shows that it corresponds to the van Hove singularities in the density of states (DOS), which originate from the intersections of the isoenergetic surface with the 222100 and 311111 Bragg planes. The reconstructed density of states agrees in general trends with the theoretical first-principles DOS of hexagonal ZnMgY approximants, and correctly reproduces the experimental value of i-ZnMgY electronic specific-heat coefficient.
|
|
| 9. |
- Suchodolskis, A., et al.
(författare)
-
Photoemission and optical spectroscopy of i-ZnMgEr quasicrystal
- 2005
-
Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 107:2, s. 412-419
-
Tidskriftsartikel (refereegranskat)abstract
- The results of photoemission and optical studies of icosahedral single-grain ZnMgEr quasicrystals are presented. Synchrotron radiation photoemission measurements were performed on in situ cleaved samples at 10(-10) mbar pressure and low, 140-150 K temperature. The valence band photoemission spectra measured reveal a simple metal-type valence band of icosahedral ZnMgEr with a distinct Fermi edge cut-off and with a sharp pseudogap feature. The photoemission spectra of shallow Mg 2p and Zn 3d core levels indicate a coordination shift of Mg 2p spin-orbit doublet and an oscillating dependence of Zn 3d photoemission line components on the photon energy within the hv = 20-160 eV range investigated. The optical response of icosahedral ZnMgEr, a dispersion of the dielectric function, was measured by the spectroscopic ellipsometry technique in the 0.5-5.0 eV spectral range. The optical spectra of the quasicrystal indicate the Drude-type optical response superimposed with a peak of interband optical transitions. The interband optical transitions can be modelled with the pseudogap parameters which agree with those deduced in an analysis of the photoemission valence band spectra.
|
|
| 10. |
- Suchodolskis, Arturas, et al.
(författare)
-
Photoemission studies of Mg and Rb layers on Zn(0001)
- 2004
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 137-40, s. 189-192
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the clean Zn(0 0 0 1) surface is studied by angle resolved photoemission. An earlier detected surface state at the surface Brillouin zone centre is confirmed and a new surface state is found at the surface Brilluoin zone boundary. The surface electronic structure of Zn is found to be similar to the that of Cd. Evaporation of thin films of Mg and Rb onto the Zn(0 0 0 1) surface quenches the emission from both surface states and reduces the intensity of the bulk related structures.
|
|
