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Quantum dots (QDs) are recognized as the excellent fluorescence and photochemical materials to be applied in bioimaging, biomedical, and solar cell fields. Biosynthesized QDs (bio-QDs) have attracted attention due to their simple, eco-friendly, and excellent biocompatible traits. Moreover, bio-QDs could not be replaced by chemically fabricated QDs in many fields. Bio-QDs synthesized by different microorganisms have diverse characteristics. In this work, the biosynthesis of QDs by Tetrahymena pyriformis, a typical protozoa in aquatic environments, was achieved for the first time. The synthesized materials by T. pyriformis emitted yellow fluorescence and had an average diameter of 8.27 ± 0.77 nm. Spectral characterization results demonstrated that the synthesized QDs were CdS1-XSeX. Meanwhile, the fluorescence intensities of the synthesized bio-QDs showed a linear relationship with Cd2+ dosage ranging from 20 to 80 μM. The fluorescence enhancement of the synthesized QDs was highly selective to Cd2+ compared to other metal ions. The bio-QDs were demonstrated to have a great potential to be applied for Cd2+ detection. This work provides valuable information about the transformation of heavy metal ions in protozoan and is useful to accelerate the applications of the synthesized QDs. [ABSTRACT FROM AUTHOR]

Iron reduction mediated by Fe(III)-reducing bacteria (FeRB) occurs in aqueous environments and plays an essential role in removing contaminates in polluted freshwater lakes. Two model FeRB species, Shewanella and Geobacter, have been intensively studied because of their functions in bioremediation, iron reduction, and bioelectricity production. However, the abundance and community diversity of Shewanella and Geobacter in eutrophic freshwater lakes remain largely unknown. In this work, the distribution, abundance and biodiversity of Shewanella, Geobacter and other FeRB in the sediments of a heavily polluted lake, Chaohu Lake, China, across four successive seasons were investigated. Shewanella, Geobacter, and other FeRB were found to be widely distributed in the sediment of this heavily eutrophic lake. Geobacter was abundant with at least one order of magnitude more than Shewanella in cold seasons. Three Shewanella-related operational taxonomic units were detected and sixty one Geobacter-related operational taxonomic units were grouped into three phylogenetic clades. Thiobacillus, Desulfuromonas and Geobacter were identified as the main members of FeRB in the lake sediments. Interestingly, nutrients like carbon, nitrogen, and phosphorus were found to be the key factors governing the abundance and diversity of FeRB. Total FeRB, as well as Geobacter and Shewanella, were more abundant in the heavily eutrophic zone than those in the lightly eutrophic zone. The abundance and diversity of FeRB in the sediments of freshwater lakes were highly related with the degree of eutrophication, which imply that FeRB might have a great potential in alleviating the eutrophication and contamination in aqueous environments. [ABSTRACT FROM AUTHOR]

Plants encounter a variety of stresses in natural environments. One-year-old pot-grown trees of pear ( Pyrus pyrifolia Nakai cv. Cuiguan and Wonhwang) were exposed to two heat stress regimes. Under constant short-term heat stress, chloroplasts and mitochondria were visibly damaged. Relative chlorophyll content and maximum photochemical efficiency of photosystem II were significantly decreased, which indicated that the leaf photosynthetic capability declined. Under chronic heat stress, mesophyll cell ultrastructure was not obviously damaged, but leaf photosynthetic capability was still restrained. As chronic heat stress was a simulation of the natural environment in summer, further study of the responses under this stress regime was undertaken. Ascorbate peroxidase (APX) activity was increased in ‘Cuiguan’, but not in ‘Wonhwang’. Inducible expression of PpAPX genes in the cytoplasm, chloroplasts and peroxisomes was consistent with increased APX activity in ‘Cuiguan’, whereas only weak induction of PpAPX genes was observed in ‘Wonhwang’. The isoenzymes cytosolic APX1 (cAPX1) and stromal APX (sAPX) were confirmed to be localized in the cytoplasm and chloroplasts, respectively. [ABSTRACT FROM AUTHOR]

We study the effects of microscopic dynamics of electrons on the intersubband optical absorption in terahertz lasers based on optically pumped quantum wells (THz-OPQW). The ensemble Monte Carlo method is used to include different electron scattering mechanisms in the calculation, so that the dependence of intersubband absorption lineshape on microscopic dynamics of electrons can be easily investigated. We find that electron-electron scattering is the dominant factor to determine the absorption linewidth. The real distributions of hot electrons are included to study the temporal changes of the spectra lineshape. Our findings show that the dependence of spectral lineshape on electron population essentially results from the electron scattering and the non-Fermi electron energy distribution. [ABSTRACT FROM AUTHOR]

The spatio-temporal distributions of photo-Dember fields on the semiconductor surface of InAs and the pump wavelength-dependent dynamics of THz radiation from this semiconductor have been investigated with the method of ensemble Monte Carlo Simulation. Our simulations not only confirm the experimental results [P. Gu et al., J. Appl. Phys. 91, 5533(2002)] that the pump wavelength-dependent feature of THz pulse amplitudes for InAs is completely different with that for GaAs, but also point out that the corresponding mechanism is the characteristics of photo-Dember fields. [ABSTRACT FROM AUTHOR]

In this paper, we have numerically analyzed the ultrafast change of local fields on the surfaces of a large-aperture photoconducting (LA-PC) antenna with GaAs and GaAs: As+ substrates. We find that the ultrafast screening of photogenerated carriers to the externally applied electric field has different effects on the saturation of THz radiation as the function of the laser fluence in the near and far field, respectively. Both screening effect of photocarriers and radiation effect are important in forming the saturation phenomena in the case of near field. But in far field, only the radiation effect is important. [ABSTRACT FROM AUTHOR]

In this paper the THz radiation dynamics of InSb and InAs, two typical narrow band semiconductors, was investigated using the ensemble Monte Carlo method. Our simulations indicated that the single mechanism of current surge only can result in small difference of THz emission efficiency for InSb and InAs. The great advantage of InAs over InSb in THz emission efficiency that was found in a published work is possibly due to the mechanism of optical rectification. In addition, under low excitation level, we found the emission efficiency of InSb is advantage over that of InAs, but under high excitation level, the result is reversed. On the other hand, through the Fourier transforms of temporal THz waveforms we found that the main frequency of THz pulses from InAs is always higher than that of InSb. [ABSTRACT FROM AUTHOR]