White matter maturation in the brains of Long Evans shaker myelin mutant rats by ex-vivo QSI and DTI

The brains of Long Evans shaker (les) rats, a model of dysmyelination, and their age- matched controls were studied by ex-vivo q-space diffusion imaging (QSI) and diffusion tensor imaging (DTI). The QSI and DTI indices were computed from the same acquisition. The les and the control brains were studied at different stages of maturation and disease progression. The mean displacement, the probability for zero displacement and kurtosis were computed from QSI data while the fractional anisotropy (FA) and the eigenvalues were computed from DTI. It was found that all QSI indices detect the les pathology, at all stages of maturation, while only some of the DTI indices could detect the les pathology. The QSI mean displacement was larger in the les group as compared with their age-matched controls while the probability for zero displacement and the kurtosis were both lower all indicating higher degree of restriction in the control brains. Since all the DTI eigenvalues were higher in the les brains as compared to controls, the less efficient DTI measure for discerning the les pathology was found to be the FA. Clearly, the most sensitive DTI parameter to the les pathology is λ₃, i.e. the minimal diffusivity. Since the QSI and DTI data were obtained from the same acquisition, despite the somewhat higher SNR of the QSI data compared to the DTI data, it seems that the higher diagnostic capacity of the QSI data in this experimental model of dysmyelination, originates mainly from the higher diffusing weighting of the QSI data.     

Influence of steady background gradients on the accuracy of molecular diffusion anisotropy measurements

Spatial susceptibility variations of body components lead to local gradients of the static magnetic field. Effects of such background gradients on fractional diffusion anisotropy (FA) measurements on whole-body magnetic resonance units operating at 1.5, 3.0 and 7.0 T were analyzed theoretically and experimentally. Analytical expressions were derived for the cases of diffusion occurring in isotropic media and in tissues with cylindrical symmetry (e.g., white matter tracts or skeletal musculature). Typical magnitudes of background gradient strengths were estimated from in vivo and in vitro measurements with B0 field mapping sequences. Additionally, numerical simulations of magnetic field distributions and resulting field gradients were performed considering tissue-air interfaces in simplified geometrical arrangements. For media with isotropic diffusion, both measurements and analytical calculations showed increasing FA inaccuracy with stronger coupling between diffusion-encoding and background gradients. For cylindrical symmetry, FA values were estimated for a standard diffusion tensor imaging protocol in a realistic scenario. At 1 mm distance from a water-air interface, susceptibility-related background gradients amount to approximately 9 mT/m at 7 T and lead to a relative error of the measured FA of up to 48%. The error in the anisotropy assessment rises considerably with increasing field strength and must be taken into account especially for experimental and clinical studies on modern high-field systems.     

Effect of microstructure on the coercivity of HDDR Nd-Fe-B permanent magnetic alloy

The effect of the grain boundary microstructure on the anisotropy and coercivity was investigated in an HDDR Nd-Fe-B permanent magnetic alloy. Considering the special microstructure of its magnetic powder grain, an anisotropic theoretical model influenced simultaneously by the structure defect at the grain boundary and the exchange coupling interaction was put forward. The variations of the structure defect factors based on the nucleation and pinning mechanism with 2r ₀/lex (where r ₀ and lex are the defect thickness and the length of exchange coupling, respectively) were calculated. The results show that the coercivity mechanism of an HDDR Nd-Fe-B permanent magnetic alloy is greatly related to its microstructure defect at the grain boundary. For a fixed lex, when 2r ₀/lex < 1.67, the coercivity is controlled by the pinning mechanism; when 2r ₀/lex > 1.67, it is determined by the nucleation mechanism. The coercivity reaches the maximum when 2r ₀/lex = 1.67. The calculation result is consistent well with the experimental result given by Morimoto et al. Supported by the National Natural Science Foundation of China (Grant No. 50671055)     

Study on the binding of 2,3-diazabicyclo[2.2.2]oct-2-ene with bovine serum albumin by fluorescence spectroscopy

The interaction of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) with bovine serum albumin (BSA) has been studied using absorption and steady state fluorescence techniques. Fluorescence spectrum of BSA (λ_exi=280 nm) in the presence of DBO clearly shows that DBO acts as a quencher. The number of binding sites ‘n’ and apparent binding constant ‘K’ were measured by Stern-Volmer equation. Synchronous fluorescence and absorption spectra were used to study protein conformation. The interaction between DBO and BSA is consistent with static quenching and the conformational changes of BSA observed.     

Blended polyethylene terephthalate and polyethylene naphthalate polymers for scintillation base substrates

Polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are both good candidates for use as scintillation base substrates. One advantage is their relatively high density of 1.33 g cm⁻³. To enhance their relative strengths and to mitigate their weaknesses, we blended PET and PEN 1:1 by weight and found that the overall characteristics are improved. The wavelength at maximum emission was 415 nm, the refractive index was 1.61, and the light yield was 0.85 times that of PEN. These results increase the available options for base materials to be used as scintillators.     

Ultrafast photo-induced turning of magnetization and its relaxation dynamics in GaMnAs

We report that,by linearly polarized pumping of different wavelengths,Kerr transients appear at zero magnetic field only in the case when GaMnAs samples are initialized at 3 K by first applying a 0.8 Tesla field and then returning to zero field.We find that,instead of magnetization precession,the near-band gap excitation induces a coherent out-of-plane turning of magnetization,which shows very long relaxation dynamics with no precession.When photon energy increases,the peak value of the Kerr transient incre...     

Long-Lived Luminescent Re(I) Complexes Containing cis-Carbonyl and Bidentate Phosphine Ligands

Highly emissive Re(I) complexes, hydrophobic cis-Re(CO)₂(c-dppene)(dpphen) and water-soluble cis-Re(CO)₂(c-dppene)(SO₃-dpphen) with a negative charge, were synthesized [where c-dppene is cis-(bis(diphenylphosphino)ethylene, dpphen is 4,7-diphenyl-1,10-phenanthroline, and SO₃-dpphen is its disulfonate derivative]. These Re(I) complexes have significantly higher molar absorption in the 350- to 490-nm region compared to their tricarbonyl Re(I) counterparts and their emission spectra are similar to those of Ru(II) polypyridyl complexes. The luminescence lifetimes of these Re(I) complexes approach 10 s in the absence of oxygen in both aqueous and less polar solvents. The complexes have limiting anisotropy values exceeding 0.3. As both ligands, the diimine and the bidentate phosphine, can be modified by adding different substituents, it should be possible to make cis-Re(CO)₂(diimine)(P-P) derivatives which are capable of labeling biomacromolecules for biochemical and biophysical studies.     

新开花粉蛋白的盐酸胍去折叠过程

本文利用荧光光谱和园二色光谱了新开花粉蛋白的盐酸胍去折叠过程。结果显示：新开花粉蛋白的盐酸胍去折叠是一个只包含天然蛋白和变性终态的二态过程,与已经报道的天花粉蛋白的盐酸胍去折叠的过程不同。     

Luminescence enhancement in (Nd+Ce) doped SiO2 : Al2O3 sol–gel glasses

An enhancement in NIR luminescence from Nd³⁺-doped Ce³⁺ co-doped SiO₂+Al₂O₃ sol–gel glasses has been observed. The lasing transition (⁴F_3/2→⁴I_11/2) at 1072 nm from the dual rare-earth Nd³⁺+Ce³⁺-doped glasses has shown an emission strength of about five times that of the single rare-earth ion Nd³⁺-doped glass. From the measurement of lifetimes of the transition at 1072 nm, the transfer rate (W_tr), critical distance (R₀) and energy transfer efficiency (η) of the neodymium glasses have been calculated.     

消癌平诱导人肺腺癌(ASTC-a-1)细胞内caspase-3活化的荧光光谱分析

采用CCK-8技术检测发现传统中药消癌平（XAP）对人肺腺癌（ASTC-a-1）细胞的增殖活性具有显著的抑制作用。利用共聚焦扫描荧光显微成像、荧光共振能量转移（FRET）及其受体光漂白技术证实了基于FRET技术构建的SCAT3质粒在ASTC-a-1细胞中的稳定表达。将消癌平加入细胞培养液中培育细胞,并在不同的时间检测活细胞内SCAT3的荧光发射光谱,从而监测细胞中caspase-3的活化状态。实验结果表明：(1)消癌平可以有效抑制人肺腺癌（ASTC-a-1）细胞的增殖活性并诱导细胞的死亡,消癌平对细胞的抑制作用具有剂量依赖性。(2)消癌平处理细胞72 h后,细胞内大量的SCAT3被切割,表明细胞内caspase-3的活化水平明显升高。(3)将含消癌平的细胞培养液与细胞共同培养24 h,然后采用没有消癌平的细胞培养液培养细胞48和72 h后,细胞内SCAT3的光谱没有明显改变,表明消癌平作用细胞24 h内没有显著激活细胞内的caspase-3。