Robust estimation of bacterial cell count from optical density

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

A study of the structural properties of SiC and GaN surfaces and theirinterfaces by first principle total energy calculation

published_or_final_versionPhysicsDoctoralDoctor of Philosoph

Tunable Band Alignment in the Arsenene/WS₂ Heterostructure by Applying Electric Field and Strain

Arsenene has received considerable attention because of its unique optoelectronic and nanoelectronic properties. Nevertheless, the research on van der Waals (vdW) heterojunctions based on arsenene has just begun, which hinders the application of arsenene in the optoelectronic and nanoelectronic fields. Here, we systemically predict the stability and electronic structures of the arsenene/WS2 vdW heterojunction based on first-principles calculations, considering the stacking pattern, electric field, and strain effects. We found that the arsenene/WS2 heterostructure possesses a type-II band alignment. Moreover, the electric field can effectively tune both the band gap and the band alignment type. Additionally, the band gap could be tuned effectively by strain, while the band alignment type is robust under strain. Our study opens up a new avenue for the application of ultrathin arsenene-based vdW heterostructures in future nano- and optoelectronics applications. Our study demonstrates that the arsenene/WS2 heterostructure offers a candidate material for optoelectronic and nanoelectronic devices

First-principles study of Sr adsorption on InN (0001)

Structures of Sr adsorbed on InN (0001) surfaces are theoretically investigated by first-principles calculations. The adsorption energies of Sr on InN (0001) decrease with decreasing Sr coverage. An InN (0001)-(2×2) surface structure covered by a 1/4 monolayer of Sr at the T4 sites may be the most energetically favourable. Sr atoms may substitute indium atoms, or accumulate at the voids inside InN films. The interstitial Sr defects may act as a potential source of compensation for the p-type behaviour of Sr-doped InN at the surface

Modulation of electronic and optical properties of BlueP/MoSSe heterostructures via biaxial strain and vertical electric field

Constructing van der Waals heterostructures (vdWHs) is an efficient approach for enhancing the desirable properties of two-dimensional (2D) materials and greatly expanding the range of applications of the original monolayer materials. The structure, stability, electronic and optical properties of BlueP/MoSSe heterostructures are explored by density functional theory (DFT) calculations. The different configurations of BlueP/MoSSe vdWHs are all indirect bandgap semiconductors and have similar energy band structures, with the bandgap of about 1.0 eV under the PBE method. The bandgap of the A3 (B3) configuration calculated with HSE06 method is 1.608 (1.377) eV. The A3 configuration exhibits type-II band alignment while the B3 configuration shows type-I band alignment, both of which have high stability. The bandgap and band edge of A3 (B3) configuration can be modulated effectively by biaxial strain and vertical electric field (Efield). The BlueP/MoSSe vdWHs have broader absorption range and higher absorption intensity than their monolayers. The optical absorption intensity of heterostructures is gradually improved with increasing compressive strain, and the optical absorption spectrum is red-shifted under tensile strain. We hope that our findings will provide meaningful theoretical guidance for the preparation and potential application of BlueP/MoSSe vdWHs

Tuning electronic and optical properties of BlueP/MoSe2 van der Waals heterostructures by strain and external electric field

Van der Waals heterostructures (vdWHs) have recently attracted much attention owing to their excellent physicochemical properties and extensive application prospects. The structural, electronic and optical properties of BlueP/MoSe2 vdWHs are systematically investigated based on the first-principles calculations. The BlueP/MoSe2 vdWHs are indirect band gap semiconductors with type II band alignment. Biaxial strain and external electric field (Efield) can effectively modulate the electronic and optical properties of the heterostructures. The biaxial strain and Efield not only can induce a transition of the semiconductors from type Ⅱ to type I band alignment, but also can achieve the semiconductor–metal transition. The band gap values of heterostructures show linear variation, while the characteristic of the indirect band gap is not changed under the Efield. Tensile strain can induce the red shift and the compressive strain cause the blue shift of the heterostructures. The work provides theoretical guidance for design of the photovoltaic materials and photoelectric devices

Stability, electronic and magnetic properties of Co-anchored on graphene sheets towards S, SH and H

The adsorption behaviors of H2S and its intermediates (SH and S) on Co anchored graphene sheets (Co-graphene) are investigated using first-principles calculations based density functional theory. It is found that the adsorbed SH and S species on the Co-graphene sheets are more stable than that of the H2S molecule. Besides, the chemisorbed SH and S species on the Co-graphene can lead to dramatic changes in the electronic structure and magnetic property by the occurring charge transfer. The electronic transport behaviors of Co-graphene nanosheets indicate that the chemical sensors construct with the materials could exhibit high sensitivity for detecting SH and S species. Therefore, these results provide valuable guidance on designing graphene-based gas sensors

Geometric stability and adsorption property of hydroxyl group on graphene sheets

<div><p></p><p>The stable geometrics and adsorption behaviors of hydroxyl (OH) groups on graphene sheets are investigated using the first-principles calculations. The single hydroxyl adatom has small adsorption energy and diffusion barrier on pristine graphene. The binding strength of the hydroxyl group increases with the coverage, and the aggregations of the hydroxyl groups reduce the structural bucking of graphene sheet. On the graphene with single vacancy (SV-graphene), the large trapping zones mean the adsorbed OH would be easily trapped at the vacancy site. The hydroxyl groups prefer to aggregate on graphene surfaces and form the water molecule, leaving the epoxy group on pristine graphene or oxygen dopant in SV-graphene, which is used to constitute the structural model of oxidized graphene. These results would provide us a useful reference to understand the atomic structure and adsorption property of functional groups on graphene sheets.</p></div

Magnetic modification of transition-metal-atom–adsorbed blue phosphorus monolayer: A first-principles study

Based on density functional theory, we systematically studied the electronic and magnetic properties of transition metal (TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni and Cu atoms) adsorbed on blue phosphorus monolayer by using first-principles calculations. In addition to Ni atoms, the adsorption of Sc, Ti, V, Cr, Mn, Fe, Co and Cu atoms can produce magnetic moments on the blue phosphorus monolayer. The source of the magnetic moment is determined by the $p\text{-}d$ hybridization mechanism between the TM atoms and the blue phosphorus monolayer. We also studied the effect of biaxial strain on the magnetism of the blue phosphorus adsorption system. The results show that the magnetic moments of the Ti, V and Cu atoms adsorbed blue phosphorus monolayers are rather sensitive to the strain, and other TM atoms adsorbed blue phosphorus systems will not be affected by the strain. Therefore, blue phosphorus has broad application prospects in nanoelectronics and spintronic devices