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Two aspects of the stand-off sensing technique (Kocharovsky et al. Proc. Natl Acad. Sci. 2005, 102, 7806-7811) were demonstrated using a femtosecond laser system and an organic dye. First, three cells of a solution of Rhodamine B dye in ethanol were pumped with a single wavelength. Amplification of the light generated by two-photon absorption occurred when the pulses were overlapped temporally, in a direction opposite to that of the pump laser beam. Second, the dispersion of the dye solution permitted two pulses of different wavelength to overlap at a specified location in the solution. The overlapped pulses generated light as the result of two-photon absorption in both the forward and backward directions, relative to that of the pump laser beam. [ABSTRACT FROM AUTHOR]

The quantum fluctuations of optical beams are highly correlated in electromagnetically induced transparency (EIT). The intensity fluctuations are enhanced by conversion of phase noise to intensity noise in atomic vapour. We have studied spectra of intensity fluctuations in dense rubidium vapour for different laser beam powers. Observed excess noise spectrum is broader than EIT window at the same optical power. Both spectral widths are proportional to the laser beam intensity. By using signal subtraction scheme we can reduce amplitude of the fluctuations to close the photonic short noise level. This result confirms the high degrees of intensity correlations and can be used to improve quality of optical atomic clocks. [ABSTRACT FROM AUTHOR]

In total, 170 strains of thermophilic bacteria were isolated from deep-sea hydrothermal fields in the Pacific Ocean and a hot spring in Xiamen of China. To facilitate the identification of thermophilic strains, sodium dodecyl sulfate – polyacrylamide gel electrophoresis (SDS–PAGE) of whole-cell proteins of these strains was first performed. The results showed that there exist four different protein patterns, indicating that the 170 strains might belong to four species or genera. The RAPD (random amplified polymorphic DNA) profiles of nine representative strains were consistent with those of SDS–PAGE. To further identify the species of the nine strains, their 16S rDNA sequences were analyzed. The results showed that the nine strains fell into four species of three genera, which was the same as revealed by SDS–PAGE. Therefore, SDS–PAGE of whole-cell proteins could be used as a rapid and simple method for the discrimination of thermophilic bacteria as the first step of species identification. [ABSTRACT FROM AUTHOR]

Vineyard soil microbial communities potentially mediate grapevine growth, grape production as well as wine terroir. Simultaneously assessing shifts of microbial community composition at the intra-vineyard scale allows us to decouple correlations among environmental variables, thus providing insights into vineyard management. Here we investigated bacterial and fungal community compositions and their relationships with edaphic properties in soils collected from a commercial vineyard at four different soil depths (0–5, 5–10, 10–20, and 20–40 cm). Soil organic carbon (SOC) content, invertase activity and phosphatase activity decreased along depth gradient in the 0–20 cm soil fraction (P < 0.001). The soil bacterial biomass and α-diversity were significantly higher than those of fungi (P ≤ 0.001). Statistical analyses revealed that SOC content, pH, C/N ratio and total phosphorus (TP) were significant determinants of soil bacterial (R = 0.494, P = 0.001) and fungal (R = 0.443, P = 0.001) community structure. The abundance of dominated bacterial phyla (Proteobacteria, Acidobacteria and Actinobacteria) and fungal phyla (Ascomycota, Zygomycota and Basidiomycota) slightly varied among all soil samples. Genus Lactococcus, which comprised 2.72% of the soil bacterial community, showed increasing pattern with depth. Importantly, Candidatus Nitrososphaera, Monographella and Fusarium were also detected with high abundances in soil samples, indicating their ecological function in soil nitrogen cycle and the potential risk in grapevine disease. Overall, this work detected the intra-vineyard variation of bacterial and fungal communities and their relationships with soil characteristics, which was beneficial to vineyard soil management and grapevine disease prevention.

Riemerella anatipestifer (R. anatipestifer) is one of the most important pathogens in ducks. The bacteria causes acute or chronic septicemia characterized by fibrinous pericarditis and meningitis. The R. anatipestifer genome encodes multiple iron/hemin-uptake systems that facilitate adaptation to iron-limited host environments. These systems include several TonB-dependent transporters and three TonB proteins responsible for energy transduction. These three tonB genes are present in all the R. anatipestifer genomes sequenced so far. Two of these genes are contained within the exbB-exbD-tonB1 and exbB-exbD-exbD-tonB2 operons. The third, tonB3, forms a monocistronic transcription unit. The inability to recover derivatives deleted for this gene suggests its product is essential for R. anatipestifer growth. Here, we show that deletion of tonB1 had no effect on hemin uptake of R. anatipestifer, though disruption of tonB2 strongly decreases hemin uptake, and disruption of both tonB1 and tonB2 abolishes the transport of exogenously added hemin. The ability of R. anatipestifer to grow on iron-depleted medium is decreased by tonB2 but not tonB1 disruption. When expressed in an E. coli model strain, the TonB1 complex, TonB2 complex, and TonB3 protein from R. anatipestifer cannot energize heterologous hemin transporters. Further, only the TonB1 complex can energize a R. anatipestifer hemin transporter when co-expressed in an E. coli model strain.

We study the dipole-dipole spectral broadening of a resonance line at high atomic densities when the self-broadening dominates. The selective reflection spectrum of a weak probe beam from the interface of the cell window and rubidium vapour is recorded in the presence of a far-detuned pump beam. The excitation due to the pump reduces the self-broadening. We found that the self-broadening reduction dependence on the pump power is atomic density independent. These results provide experimental evidence for the disordered exciton based theory of self-broadening, and can be useful for the description of the interaction of a strong optical field with a dense resonance medium. [ABSTRACT FROM AUTHOR]

We study an asymmetric double InGaAs quantum well using optical two-dimensional coherent spectroscopy. The collection of zero-quantum, one-quantum, and two-quantum two-dimensional spectra provides a unique and comprehensive picture of the double well coherent optical response. Coherent and incoherent contributions to the coupling between the two quantum well excitons are clearly separated. An excellent agreement with density matrix calculations reveals that coherent interwell coupling originates from many-body interactions. [ABSTRACT FROM AUTHOR]

The homogeneous and inhomogeneous linewidths of the heavy-hole exciton resonance in a (110)-oriented GaAs multiple-quantum-well sample are measured using optical two-dimensional Fourier transform spectroscopy. By probing the optical nonlinear response for polarization along the in-plane crystal axes [110] and [110], we measure different homogeneous linewidths for the two orthogonal directions. This difference is found to be due to anisotropic excitation-induced dephasing, caused by a crystal-axis-dependent absorption coefficient. The extrapolated zero-excitation density homogeneous linewidth exhibits an activation-like temperature dependence. We find that the homogeneous linewidth extrapolated to zero excitation density and temperature is ∼34 μeV, while the inhomogeneous linewidth is 1.9 meV for both polarizations. [ABSTRACT FROM AUTHOR]

Exciton transport in nanomaterials is sensitive to fluctuations in the confinement potential that are intrinsic to heterogeneous solid-state systems. Redistribution of exciton population manifests as spectral diffusion in which the exciton energy shifts. It is generally assumed that increase or decrease in the exciton energy are equally probable. We show that this assumption is not necessarily valid using two-dimensional coherent spectroscopy on a disordered GaAs quantum well. High-energy excitons relax into lower-energy localized states over a time scale of tens of picoseconds at low sample temperatures (~5K). A transition to uniform spectral diffusion of excitons is observed as the temperature is increased to ~20K. Numerical simulations reveal the contribution of exciton-phonon interactions to spectral diffusion of excitons. These results provide a perspective on the process of dynamic localization and the effect of the correlation length of disorder on spectral diffusion of excitons. [ABSTRACT FROM AUTHOR]

Charged excitons called trions play an important role in the fundamental valley dynamics in newly emerging two-dimensional semiconductor materials. We use ultrafast pump-probe spectroscopy to study the valley trion dynamics in a MoSe2 monolayer grown by using chemical vapor deposition. The dynamics displays an ultrafast trion formation followed by a nonexponential decay. The measurements at different pump fluences show that the trion decay dynamics becomes slower as the excitation density increases. The observed trion dynamics and the associated density dependence are a result of the trapping by two defect states as being the dominating decay mechanism. The simulation based on a set of rate equations reproduces the experimental data for different pump fluences. Our results reveal the important trion dynamics and identify the trapping by defect states as the primary trion decay mechanism in monolayer MoSe2 under the excitation densities used in our experiment. [ABSTRACT FROM AUTHOR]