2-羟基-1-萘甲醛缩-2-萘甲酰腙对Zn2+的选择性识别

设计合成了识别Zn²⁺的荧光传感分子--2-羟基-1-萘甲醛缩-2-萘甲酰腙(3)。 通过红外光谱、核磁共振谱和质谱测试技术表征了其结构。 利用其光谱性质研究了该物质对几种过渡金属离子的识别性质,初步探讨了其结合模式。 结果表明,在乙腈介质中,受体分子3表现出对Zn²⁺良好的选择性,Zn²⁺的加入导致受体分子3的吸收光谱在435 nm处出现1新峰,其吸光度逐渐增强,同时于239、302、330、342和387 nm处观察到5个清晰的等吸收点;在516 nm处荧光增强101倍,而其它过渡金属只引起受体分子]3的荧光略微增强。 Job法实验揭示受体分子3与Zn²⁺的结合比为1∶1。     

Sub-Doppler and sub-natural narrowing of an absorption line

We experimentally demonstrate the double dark resonance windows characteristic of a four level tripod system such as the D₂ line of ⁸⁷Rb where the F_g = 1, m_g = −1, 0, 1 Zeeman sublevels form the bottom three levels and the F_e = 0 state is the upper level. Between the double dark resonance windows, a very narrow absorption resonance is observed whose line-width is shown to be sub-Doppler and sub-natural. The sharp absorptive resonance is characterized as a function of applied magnetic field and pump laser power.     

Enhanced frequency conversion of nonadiabatic pulses in a double Λ system driven by two pumps with and without carrier beams

We show that nonadiabatic, resonant amplitude- and phase-modulated pulses can be frequency converted with greater efficiency than adiabatic resonant pulses in a double Λ system, interacting with two strong cw beams on one side of the system, and a weak pulsed probe on the other. Indeed, in this double EIT (electromagnetically induced transparency) configuration, conversion efficiencies close to unity, similar to those achieved using highly detuned pulses, can be obtained using highly nonadiabatic resonant pulses. The distance at which the maximum conversion occurs is shorter than in a coherently-prepared Λ system. This counteracts the increased absorption that occurs in the double EIT configuration, so that both produce similar conversion efficiencies. The absorption experienced by matched nonadiabatic pulses in the double EIT system, at all propagation distances, can be overcome by superimposing the nonadiabatic pulses as amplitude modulations on carrier fields. Thus we demonstrate the formation of adiabatons in the double EIT system, and of diabatons in both the coherently-prepared Λ system and the double EIT system. Both the diabatons and adiabatons satisfy pulse-matching conditions. In addition, the asymptotic amplitude of the complementary amplitude modulations is proportional to the ratio of the pump to probe carrier Rabi frequencies, and is the same in each of the configurations.     

Transfer-of-coherence-enhanced stimulated emission and electromagnetically induced absorption in Zeeman split Fg-->Fe=Fg-1 atomic transitions

The probe absorption spectra in single and multiple tripod systems formed when a weak sigma polarized pump and a tunable pi polarized probe interact with a Zeeman split F(g)-->F(e)=F(g)-1 atomic transition are characterized by two interfering stimulated Raman features separated by an electromagnetically induced absorption (EIA) peak at the line center. These Raman features can appear as either sharp stimulated emission peaks or electromagnetically induced transparency windows. In the multitripod systems, the EIA and stimulated emission peaks derive from the combined effects of interference between the stimulated Raman features and transfer of coherence from the excited to ground states.     

Phase Transitions in a Highly Anisotropic Antiferromagnetic Heisenberg Toda Chain

The behavior of the antiferromagnetic spin 112 Heisenberg Toda chain is investigated in a space of interactions which include exchange anisotropy, bond alternation and Toda-like spinlattice coupling by means of coherent-state for spin. We analyse magnetically driven lattice instabilities and find that multiphase structure only occurs under the condition, of bond alternation. Three phase diagrams and tricritical points are obtained and some relevant physical properties are discussed.     

Effect of intrinsic stress gradient on the effective mode-I fracture toughness of amorphous diamond-like carbon films for MEMS

The influence of intrinsic stress gradient on the mode-I fracture of thin films with various thicknesses fabricated for Microelectromechanical Systems (MEMS) was investigated. The material system employed in this study was hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C). Uniform gauge microscale specimens with thicknesses 0.5, 1, 2.2, and 3 μm, containing mathematically sharp edge pre-cracks were tested under mode-I loading in fixed grip configuration. The effective opening mode fracture toughness, as calculated from boundary force measurements, was 4.25±0.7 MPa√m for 0.5-μm thick specimens, 4.4±0.4 MPa√m for 1-μm specimens, 3.74±0.3 MPa√m for 2.2-μm specimens, and 3.06±0.17 MPa√m for 3-μm specimens. Thus, the apparent fracture toughness decreased with increasing film thickness. Local elastic property measurements showed no substantial change as a function of film thickness, which provided evidence for the stability of the sp²/sp³ carbon binding stoichiometry in films of different thicknesses. Detailed experiments and finite element analysis pointed out that the dependence of the effective fracture toughness on specimen thickness was due to the intrinsic stress gradient developed during fabrication and post-process annealing. This stress gradient is usually unaccounted for in mode-I fracture experiments with thin films. Thicker films, fabricated from multiple thin layers, underwent annealing for extended times, which resulted in a stress gradient across their thickness. This stress gradient caused an out-of-plane curvature upon film release from its substrate and, thus, combined bending and tensile mode-I loading at the crack tip under in-plane forces. Since the bending component cannot be isolated from the applied boundary force measurements, its contribution, becoming important for thick films, remains unaccounted for in the calculation of the critical stress intensity factor, thus resulting in reduced apparent fracture toughness that varies with film thickness and curvature. It was concluded that in the presence of a stress gradient, accounting only for the average intrinsic stresses could lead in an overestimate of the fracture resistance of a brittle film. Under these considerations the material fracture toughness of ta-C, as determined from specimens with negligible curvature, is K_IC=4.4±0.4 MPa√m.     

空间频率域超声背散射参量用于骨质状况的评价*

在超声背散射骨质评价中,不同测量感兴趣区域(ROI)的超声背散射信号会有波动,致使诊断准确度降低。该文目的是研究超声背散射信号随测量区域的变化规律。采用空间扫描方法离体测量了35块骨样本,将超声背散射参数从空间域变换到空间频率域。结果表明,超声背散射参数的主要空间频率成分集中于低频部分;空间频率域超声背散射参量最大值(MASF)与骨矿密度等参数具有中高度显著相关性(R2=0.45~0.83,p0.001);空间频率域超声背散射参量衰减系数(AC)也与松质骨密度及结构特征有显著相关性(R2=0.41~0.72,p0.001)。研究表明空间频率域变换方法有助于明确超声背散射信号随测量ROI的变化规律,空间频率域的超声背散射相关新参量评价松质骨状况具有可行性。     

二氧化铈纳米球的合成

使用尿素水热法合成了均匀的二氧化铈球型纳米材料.纳米球是由纳米层以及纳米颗粒所构成的核壳结构,其平均粒径为320nm,同时表面主要暴露{111}晶面.尿素水解所产生的氨气分子为纳米球状结构的形成提供了模板,而生成的碳酸根与氢氧根离子作为铈离子的沉淀剂.使用氢气程序升温还原技术表征了氧化铈纳米球材料的氧化还原能力,同时以一氧化碳氧化为探针反应研究了其催化性能.     

The Propensity of α‐Aminoisobutyric Acid (=2‐Methylalanine; Aib) to Induce Helical Secondary Structure in an α‐Heptapeptide: A Computational Study

We present a molecular‐dynamics simulation study of an α‐heptapeptide containing an α‐aminoisobutyric acid (=2‐methylalanine; Aib) residue, Val¹‐Ala²‐Leu³‐Aib⁴‐Ile⁵‐Met⁶‐Phe⁷, and a quantum‐mechanical (QM) study of simplified models to investigate the propensity of the Aib residue to induce 3₁₀/α‐helical conformation. For comparison, we have also performed simulations of three analogues of the peptide with the Aib residue being replaced by L ‐Ala, D ‐Ala, and Gly, respectively, which provide information on the subtitution effect at C(α) (two Me groups for Aib, one for L ‐Ala and D ‐Ala, and zero for Gly). Our simulations suggest that, in MeOH, the heptapeptide hardly folds into canonical helical conformations, but appears to populate multiple conformations, i.e., C₇ and 3₁₀‐helical ones, which is in agreement with results from the QM calculations and NMR experiments. The populations of these conformations depend on the polarity of the solvent. Our study confirms that a short peptide, though with the presence of an Aib residue in the middle of the chain, does not have to fold to an α‐helical secondary structure. To generate a helical conformation for a linear peptide, several Aib residues should be present in the peptide, either sequentially or alternatively, to enhance the propensity of Aib‐containing peptides towards the helical conformation. A correction of a few of the published NMR data is reported.     

邻羟基萘甲醛缩对二甲氨基苯甲酰腙的合成及其对锌离子的识别

设计并合成了用于识别锌离子的荧光传感分子——2-羟基-1-萘甲醛缩-4-二甲氨基苯甲酰腙(1),其结构经1H NMR,IR和MS表征。利用荧光光谱研究了在乙腈中1对过渡金属离子(Zn2+,Cd2+,Cu2+,Hg2+,Pb2+和N i2+)的识别能力。结果表明:1表现出对Zn2+的良好选择性,Zn2+的加入导致1的长波长荧光增强449倍。Job曲线确定1与Zn2+形成1∶1型配合物。