198 research outputs found
Structure Evolution of Graphene Oxide during Thermally Driven Phase Transformation: Is the Oxygen Content Really Preserved?
A mild annealing procedure was recently proposed for the scalable enhancement
of graphene oxide (GO) properties with the oxygen content preserved, which was
demonstrated to be attributed to the thermally driven phase separation. In this
work, the structure evolution of GO with mild annealing is closely
investigated. It reveals that in addition to phase separation, the
transformation of oxygen functionalities also occurs, which leads to the slight
reduction of GO membranes and furthers the enhancement of GO properties. These
results are further supported by the density functional theory based
calculations. The results also show that the amount of chemically bonded oxygen
atoms on graphene decreases gradually and we propose that the strongly
physisorbed oxygen species constrained in the holes and vacancies on GO lattice
might be responsible for the preserved oxygen content during the mild annealing
procedure. The present experimental results and calculations indicate that both
the diffusion and transformation of oxygen functional groups might play
important roles in the scalable enhancement of GO properties
Self-compression of stimulated Raman backscattering by flying focus
A novel regime of self-compression is proposed for plasma-based backward
Raman amplification(BRA) upon flying focus. By using a pumping focus moving
with a speed equal to the group velocity of stimulated Raman
backscattering(SRBS), only a short part of SRBS which does always synchronize
with the flying focus can be amplified. Due to the asymmetrical amplification,
the pulse can be directly compressed in the linear stage of BRA. Therefore,
instead of a short pulse, the Raman spontaneous or a long pulse can seed the
BRA amplifiers. The regime is supported by the 2D particle-in-cell(PIC)
simulation without a seed, presenting that the pump pulse is compressed from
26ps to 116fs, with an output amplitude comparable with the case of a
well-synchronized short seed. This method provides a significant way to
simplify the Raman amplifiers and overcome the issue of synchronization jitter
between the pump and the seed
Generation of subcycle isolated attosecond pulses by pumping ionizing gating
We present a novel approach named as pumping ionizing gating (PIG) for the
generation of isolated attosecond pulses (IAPs). In this regime, a short laser
is used to ionize a pre-existing gas grating, creating a fast-extending plasma
grating(FEPG) having an ionization front propagating with the velocity of
light. A low-intensity long counterpropagating pump pulse is then reflected by
a very narrow region of the ionization front, only where the Bragg conditions
for resonant reflection is satisfied. Consequently, the pump reflection is
confined within a sub-cycle region called PIG, and forms a wide-band coherent
IAP in combination with the frequency up-conversion effect due to the plasma
gradient. This approach results in a new scheme to generate IAPs fromlong
picosecond pump pulses. Three-dimensional (3D) simulations show that a 1.6-ps,
1-{\mu}m pump pulse can be used to generate a 330 as laser pulse with a peak
intensity approximately 33 times that of the pump and a conversion efficiency
of around 0.1%.These results highlight the potential of the PIG method for
generating IAPs with high conversion efficiency and peak intensity.Comment: It provides a new way to generate isolated attosecond pulse(IAP) by a
picosecond pump, which has a protential to boost the IAP energy to joule
leve
The Prevalence of Metabolically Healthy and Unhealthy Obesity according to Different Criteria
Objective: Obesity-related disease risks may vary depending on whether the subject has metabolically healthy obesity (MHO) or metabolically unhealthy obesity (MUO). At least 5 definitions/criteria of obesity and metabolic disorders have been documented in the literature, yielding uncertainties in a reliable international comparison of obesity phenotype prevalence. This report aims to compare differences in MHO and MUO prevalence according to the 5 most frequently used definitions. Methods: A random sample of 4,757 adults aged 35 years and older (male 51.1%) was enrolled. Obesity was defined either according to body mass index or waist circumference, and the definitions of metabolic abnormalities were derived from 5 different criteria. Results: In MHO, the highest prevalence was obtained when using the homeostasis model assessment (HOMA) criteria (13.6%), followed by the Chinese Diabetes Society (11.4%), Adult Treatment Panel III (10.3%), Wildman (5.2%), and Karelis (4.2%) criteria; however, the MUO prevalence had an opposite trend to MHO prevalence. The magnitude of differences in the age-specific prevalence of MHO and MUO varied greatly and ranked in different orders. The proportion of insulin resistance for MHO and MUO individuals differed significantly regardless of which metabolic criterion was used. Conclusion: The prevalence of MHO and MUO in the Chinese population varies according to different definitions of obesity and metabolic disorders
Suppressive Effects on the Immune Response and Protective Immunity to a JEV DNA Vaccine by Co-administration of a GM-CSF-Expressing Plasmid in Mice
As a potential cytokine adjuvant of DNA vaccines, granulocyte-macrophage colony–stimulating factor (GM-CSF) has received considerable attention due to its essential role in the recruitment of antigen-presenting cells, differentiation and maturation of dendritic cells. However, in our recent study of a Japanese encephalitis virus (JEV) DNA vaccine, co-inoculation of a GM-CSF plasmid dramatically suppressed the specific IgG response and resulted in decreased protection against JEV challenge. It is known that GM-CSF has been used in clinic to treat neutropenia for repopulating myeloid cells, and as an adjuvant in vaccine studies; it has shown various effects on the immune response. Therefore, in this study, we characterized the suppressive effects on the immune response to a JEV DNA vaccine by the co-administration of the GM-CSF-expressing plasmid and clarified the underlying mechanisms of the suppression in mice. Our results demonstrated that co-immunization with GM-CSF caused a substantial dampening of the vaccine-induced antibody responses. The suppressive effect was dose- and timing-dependent and likely related to the immunogenicity of the antigen. The suppression was associated with the induction of immature dendritic cells and the expansion of regulatory T cells but not myeloid-derived suppressor cells. Collectively, our findings not only provide valuable information for the application of GM-CSF in clinic and using as a vaccine adjuvant but also offer further insight into the understanding of the complex roles of GM-CSF
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