2,027 research outputs found
Total Nuclear Reaction Cross Section Induced by Halo Nuclei and Stable Nuclei
We develop the method for the calculation of the total reaction cross
sections induced by the halo nuclei and stable nuclei. This approach is based
on the Glauber theory, which is valid for nuclear reactions at high energy. It
is extended for nuclear reactions at low energy and intermediate energy by
including both the quantum correction and Coulomb correction under the
assumption of the effective nuclear density distribution. The calculated
results of the total reaction cross section induced by stable nuclei agree well
with the 30 experimental data within 10 percent accuracy.The comparison between
the numerical results and the 20 experimental data for the total nuclear
reaction cross section induced by the neutron halo nuclei and the proton halo
nuclei indicates a satisfactory agreement after considering the halo structure
of these nuclei, which implies the quite different mean fields for the nuclear
reactions induced by halo nuclei and stable nuclei. The halo nucleon
distributions and the root mean square radii of these nuclei can be extracted
from above comparison based on the improved Glauber model, which indicate
clearly the halo structures of these nuclei. Especially, it is clear to see
that the medium correction of the nucleon-nucleon collision has little effect
on the total reaction cross sections induced by the halo nuclei due to the very
weak binding and the very extended density distribution.Comment: 15 pages,2 figures. Communucations in Theoretical Physics, (2003) in
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Excitonic energy transfer in light-harvesting complexes in purple bacteria
Two distinct approaches, the Frenkel-Dirac time-dependent variation and the
Haken-Strobl model, are adopted to study energy transfer dynamics in
single-ring and double-ring light-harvesting systems in purple bacteria. It is
found that inclusion of long-range dipolar interactions in the two methods
results in significant increases in intra- or inter-ring exciton transfer
efficiency. The dependence of exciton transfer efficiency on trapping positions
on single rings of LH2 (B850) and LH1 is similar to that in toy models with
nearest-neighbor coupling only. However, owing to the symmetry breaking caused
by the dimerization of BChls and dipolar couplings, such dependence has been
largely suppressed. In the studies of coupled-ring systems, both methods reveal
interesting role of dipolar interaction in increasing energy transfer
efficiency by introducing multiple intra/inter-ring transfer paths.
Importantly, the time scale (~4ps) of inter-ring exciton transfer obtained from
polaron dynamics is in good agreement with previous studies. In a double-ring
LH2 system, dipole-induced symmetry breaking leads to global minima and local
minima of the average trapping time when there is a finite value of non-zero
dephasing rate, suggesting that environment plays a role in preserving quantum
coherent energy transfer. In contrast, dephasing comes into play only when the
perfect cylindrical symmetry in the hypothetic system is broken. This study has
revealed that dipolar interaction between chromophores may play an important
part in the high energy transfer efficiency in the LH2 system and many other
natural photosynthetic systems.Comment: 14 pages 9 figure
Estimating Allele Frequency from Next-Generation Sequencing of Pooled Mitochondrial DNA Samples
Background: Both common and rare mitochondrial DNA (mtDNA) variants may contribute to genetic susceptibility to some complex human diseases. Understanding of the role of mtDNA variants will provide valuable insights into the etiology of these diseases. However, to date, there have not been any large-scale, genome-wide association studies of complete mtDNA variants and disease risk. One reason for this might be the substantial cost of sequencing the large number of samples required for genetic epidemiology studies. Next-generation sequencing of pooled mtDNA samples will dramatically reduce the cost of such studies and may represent an appealing approach for large-scale genetic epidemiology studies. However, the performance of the different designs of sequencing pooled mtDNA has not been evaluated. Methods: We examined the approach of sequencing pooled mtDNA of multiple individuals for estimating allele frequency using the Illumina genome analyzer (GA) II sequencing system. In this study the pool included mtDNA samples of 20 subjects that had been sequenced previously using Sanger sequencing. Each pool was replicated once to assess variation of the sequencing error between pools. To reduce such variation, barcoding was used for sequencing different pools in the same lane of the flow cell. To evaluate the effect of different pooling strategies pooling was done at both the pre- and post-PCR amplification step. Results: The sequencing error rate was close to that expected based on the Phred score. When only reads with Phredāā„ā20 were considered, the average error rate was about 0.3%. However, there was significant variation of the base-calling errors for different types of bases or at different loci. Using the results of the Sanger sequencing as the standard, the sensitivity of single nucleotide polymorphism detection with post-PCR pooling (about 99%) was higher than that of the pre-PCR pooling (about 82%), while the two approaches had similar specificity (about 99%). Among a total of 298 variants in the sample, the allele frequencies of 293 variants (98%) were correctly estimated with post-PCR pooling, the correlation between the estimated and the true allele frequencies being >0.99, while only 206 allele frequencies (69%) were correctly estimated in the pre-PCR pooling, the correlation being 0.89. Conclusion: Sequencing of mtDNA pooled after PCR amplification is a viable tool for screening mitochondrial variants potentially related to human diseases
Korean Red Ginseng protects dopaminergic neurons by suppressing the cleavage of p35 to p25 in a Parkinson's disease mouse model
AbstractBackgroundGinseng is known to have antiapoptotic, anti-inflammatory, and antioxidant effects. The present study investigated a possible role of Korean Red Ginseng (KRG) in suppressing dopaminergic neuronal cell death and the cleavage of p35 to p25 in the substantia nigra (SN) and striatum (ST) using a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease mouse model.MethodsTen-week-old male C57BL/6 mice were injected intraperitoneally with 30Ā mg/kg of MPTP at 24-h intervals for 5Ā d, and then administered KRG (1Ā mg/kg, 10Ā mg/kg, or 100Ā mg/kg) once a day for 12 consecutive days from the first injection. Pole tests were performed to assess the motor function of the mice, dopaminergic neuronal survival in the SN and ST was evaluated using tyrosine hydroxylase-immunohistochemistry, and the expressions of cyclin-dependent kinase 5 (Cdk5), p35, and p25 in the SN and ST were measured using Western blotting.ResultsMPTP administration caused behavioral impairment, dopaminergic neuronal death, increased Cdk5 and p25 expression, and decreased p35 expression in the nigrostriatal system of mice, whereas KRG dose-dependently alleviated these MPTP-induced changes.ConclusionThese results indicate that KRG can inhibit MPTP-induced dopaminergic neuronal death and suppress the cleavage of p35 to p25 in the SN and the ST, suggesting a possible role for KRG in the treatment of Parkinson's disease
Collision-induced C_60 rovibrational relaxation probed by state-resolved nonlinear spectroscopy
Quantum state-resolved spectroscopy was recently achieved for C60 molecules
when cooled by buffer gas collisions and probed with a midinfrared frequency
comb. This rovibrational quantum state resolution for the largest molecule on
record is facilitated by the remarkable symmetry and rigidity of C60, which
also present new opportunities and challenges to explore energy transfer
between quantum states in this many-atom system. Here we combine state-specific
optical pumping, buffer gas collisions, and ultrasensitive intracavity
nonlinear spectroscopy to initiate and probe the rotation-vibration energy
transfer and relaxation. This approach provides the first detailed
characterization of C60 collisional energy transfer for a variety of collision
partners, and determines the rotational and vibrational inelastic collision
cross sections. These results compare well with our theoretical modeling of the
collisions, and establish a route towards quantum state control of a new class
of unprecedentedly large molecules
TonEBP suppresses IL-10-mediated immunomodulation
TonEBP is a key transcriptional activator of M1 phenotype in macrophage, and its high expression is associated with many inflammatory diseases. During the progression of the inflammatory responses, the M1 to M2 phenotypic switch enables the dual role of macrophages in controlling the initiation and resolution of inflammation. Here we report that in human and mouse M1 macrophages TonEBP suppresses IL-10 expression and M2 phenotype. TonEBP knockdown promoted the transcription of the IL-10 gene by enhancing chromatin accessibility and Sp1 recruitment to its promoter. The enhanced expression of M2 genes by TonEBP knockdown was abrogated by antagonism of IL-10 by either neutralizing antibodies or siRNA-mediated silencing. In addition, pharmacological suppression of TonEBP leads to similar upregulation of IL-10 and M2 genes. Thus, TonEBP suppresses M2 phenotype via downregulation of the IL-10 in M1 macrophagesope
Interface-tuned epoxy/clay nanocomposites
Though interface has been known for a critical role in determining the properties of conventional composites, its role in polymer nanocomposites is still fragmented and in its infancy. This study synthesized a series of epoxy/clay nanocomposites with different interface strength by using three types of modiļ¬ers: ethanolamine (denoted ETH), Jeffamineļæ½ M2070 (M27) and Jeffamineļæ½ XTJ502 (XTJ). XTJ created a strong interface between clay layers and matrix because it bridged the layers with matrix by a chemical reaction as proved by Fourier transform infrared spectroscopy; M27 produced an interme-diate interface strength due to the molecular entanglement between grafted M27 chains and matrix molecules; the interface made by ETH was weak because neither chemical bridging nor molecular entanglement was involved. The studies of mechanical and thermal properties and morphology at a wide range of magniļ¬cation show that the strong interface promoted the highest level of exfoliation and dispersion of clay layers, and achieved the most increment in Youngās modulus, fracture toughness and glass transition temperature (Tg) of matrix. With w1.3 wt% clay, the critical strain energy release rate G1c of neat epoxy improved from 179.0 to 384.7 J/m, 115% improvement and Tg enhanced from 93.7 to 99.
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