24 research outputs found
Three photon absorption in ZnO and ZnS crystals
We report a systematic investigation of both three-photon absorption
(3PA)spectra and wavelength dispersions of Kerr-type nonlinear refraction in
wide-gap semiconductors. The Z-scan measurements are recorded for both ZnO and
ZnS with femtosecond laser pulses. While the wavelength dispersions of the Kerr
nonlinearity are in agreement with a two-band model, the wavelength dependences
of the 3PA are found to be given by (3Ephoton/Eg-1)5/2(3Ephoton/Eg)-9. We also
evaluate higher-order nonlinear optical effects including the fifth-order
instantaneous nonlinear refraction associated with virtual three-photon
transitions, and effectively seventh-order nonlinear processes induced by
three-photon-excited free charge carriers. These higher-order nonlinear effects
are insignificant with laser excitation irradiances up to 40 GW/cm2. Both
pump-probe measurements and three-photon figures of merits demonstrate that ZnO
and ZnS should be a promising candidate for optical switching applications at
telecommunication wavelengths.Comment: 13 pages, 7 figure
Multi-photon excitation and relaxation in colloidal semiconductor quantum dots
Ph.DDOCTOR OF PHILOSOPH
Residential exposure to 50 Hz magnetic fields and the association with miscarriage risk: a 2-year prospective cohort study.
OBJECTIVE: The hypothesis of whether exposure to extremely low-frequency magnetic fields (ELF-MF) may increase miscarriage risk is controversial. A 2-year prospective cohort study was designed to study the association between exposure to 50 Hz magnetic fields (MF) and the miscarriage risk for women residing in the area of the Pearl-River Delta of China. METHOD: Two towns with densely distributed power supply constructions were selected as the study sites. From 2010 to 2012, 552 women in the region who were at approximately 8 weeks of gestation or who planned to have a baby within 1 year were selected as candidate subjects. Exposure to MF was estimated by measurements at their front doors and in the alley in front of the subjects' houses. The average exposure level was used as a cutoff point to define the exposed group. Clinical miscarriage was diagnosed by local obstetricians. Staffs from the local population and family planning service stations were responsible for the follow-up interviews every 2 months. RESULTS: Four hundred and thirteen pregnant women were selected for the cohort study. The average residential exposure to MF was 0.099 µT. No significantly increased risk of miscarriage was found to be associated with the average front-door exposure (p>0.05). However, miscarriage risk was found to be significantly associated with maximum alley exposure (p=0.001). The relative risk (RR) of miscarriage from maximum alley exposure was 2.35 (95% C.I.: 1.18-4.71). In addition, Cox regression analysis showed that the adjusted hazard ratio of maximum alley exposure for miscarriage was 1.72 (95% C.I.:1.10-2.69). CONCLUSION: Although the miscarriage incidence was shown to be positively associated with the maximum alley MF exposure, the association between miscarriage risk and the exposure to MF was not confirmed in the study. The results of this study are of interest concerning MF exposure assessment and pregnancy outcomes
Assessment of sulfamethoxazole toxicity to marine mussels (Mytilus galloprovincialis): Combine p38-MAPK signaling pathway modulation with histopathological alterations
Sulfamethoxazole (SMX), is a ubiquitous antibiotic in the aquatic environment and received concerns on its health hazards, especially its sub-lethal effects on non-target organisms which were remained largely unknown. In the present study, in order to investigate SMX induced tissue damages and reveal underlying mechanisms, marine mussels, Mytilus galloprovincialis were challenged to SMX series (0.5, 50 and 500 μg/L) for six-days followed by six-day-recovery. Comprehensive histopathological alteration (including qualitative, semi-quantitative and quantitative indices), together with transcriptional and (post-) translational responses of key factors (p38, NFκB and p53) in the p38-MAPK signaling pathway were analyzed in gills and digestive glands. Tissue-specific responses were clearly investigated with gills showing more prompt responses and digestive glands showing higher tolerance to SMX. The histopathology showed that SMX triggered inflammatory damages in both tissues and quantitative analysis revealed more significant responses, suggesting its potential as a valuable health indicator. SMX activated expressions of p38, NFκB and p53 at transcriptional and (post-) translational levels, especially after exposed to low level SMX, evidenced by p38 coupled with NFκB/p53 regulation on immunity defense in mussels. Less induction of targeted molecules under severe SMX exposure indicated such signaling transduction may not be efficient enough and can result in inflammatory damages. Taken together, this study expanded the understanding of aquatic SMX induced health risk in marine mussels and the underlying regulation mechanism through p38 signaling transduction
Artificial Peroxidase/Oxidase Multiple Enzyme System Based on Supramolecular Hydrogel and Its Application as a Biocatalyst for Cascade Reactions
Inspired by delicate structures and
multiple functions of natural multiple enzyme architectures such as
peroxisomes, we constructed an artificial multiple enzyme system by
coencapsulation of glucose oxidases (GOx) and artificial peroxidases
in a supramolecular hydrogel. The artificial peroxidase was a functional
complex micelle, which was prepared by the self-assembly of diblock
copolymer and hemin. Compared with catalase or horseradish peroxidase
(HRP), the functional micelle exhibited comparable activity and better
stability, which provided more advantages in constructing a multienzyme
with a proper oxidase. The hydrogel containing the two catalytic centers
was further used as a catalyst for green oxidation of glucose, which
was a typical cascade reaction. Glucose was oxidized by oxygen (O<sub>2</sub>) via the GOx-mediated reaction, producing toxic intermediate
hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>). The produced H<sub>2</sub>O<sub>2</sub> further oxidized peroxidase substrates catalyzed
by hemin-micelles. By regulating the diffusion modes of the enzymes
and substrates, the artificial multienzyme based on hydrogel could
successfully activate the cascade reaction, which the soluble enzyme
mixture could not achieve. The hydrogel, just like a protective covering,
protected oxidases and micelles from inactivation via toxic intermediates
and environmental changes. The artificial multienzyme could efficiently
achieve the oxidation task along with effectively eliminating the
toxic intermediates. In this way, this system possesses great potentials
for glucose detection and green oxidation of a series of substrates
related to biological processes
Association between Miscarriage and Exposure to Risk Factors.
<p>Note: β, regression coefficient; SE, standard error; exposure to 50 Hz MF in the Cox regression is the measured values at the front door or in the alley in front of the subjects’ houses. Multivariate analysis was conducted using Cox regression analysis; <b><sup><i>a</i></sup></b>, the front door MF exposure was retained in the model.</p
Miscarriage Incidence of the Subjects.
<p>Note: CI, cumulative incidence; ID, incidence density; PY, person year*, tested by chi-square, p<0.05.</p