Annealing behavior of gel‐spun polyethylene fibers at temperatures lower than needed for significant shrinkage

The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003     

抗坏血酸-铁(Ⅱ)络合反应在薄层色谱板上的吸收光谱

本文利用薄层色谱板上吸收光谱研究了抗坏血酸与铁（Ⅱ）离子在不同pH值和不同配比溶液中络合反应情况，并对抗坏血酿-铁（Ⅱ）螯合物的结构进行了探讨。     

Anisotropy in Shape and Ligand‐Conjugation of Hybrid Nanoparticulates Manipulates the Mode of Bio–Nano Interaction and Its Outcome

In an attempt to manipulate the biological features of nanomaterials via both anisotropic shape and ligand modification, four types of nanoparticulates with good morphological stability are designed and engineered, including hybrid nanospheres, nanodiscs, and nanodiscs with edge modification or plane modification of octa‐arginine (R8) sequence. It is found that the R8 modification anisotropy can trigger huge differences in the endocytosis, intracellular trafficking, and even tissue penetration of nanoparticulates. From plane modification to edge modification of R8, the maximum increase in cell uptake is up to 17‐fold, which is much more significant than shape anisotropy alone. On the other hand, six types of different cell lines are investigated to simulate biological microenvironment. It is demonstrated that the maximum difference in cell uptake among six cell lines is 12‐fold. Three main driving forces are found to contribute to such bio–nano interactions. Based on the findings of this study, it seems possible to manipulate the biointeraction mode of nanomaterials and its output by regulating their anisotropy in both shape and ligand modification.     

Fast-scan chip-calorimeter measurement on the melting behaviors of melt-crystallized syndiotactic polystyrene

We employed fast-scan chip-calorimeter (FSC) measurement (Flash DSC1) to study the melting of syndiotactic polystyrene after melt-crystallized at various cooling rates as well as after isothermally crystallized at various high temperatures. We attributed the observed double melting peak to a melting-recrystallization process of beta-form crystals upon heating, as evidenced by their variations with different cooling and heating rates. Our experiments demonstrated the advantages of FSC techniques in the investigation of crystallization and melting behaviors of polymer materials.     

Aromatic Nitrogen Mustard‐Based Prodrugs: Activity,Selectivity, and the Mechanism of DNA Cross‐Linking

Three novel H₂O₂‐activated aromatic nitrogen mustard prodrugs ( 6 – 8 ) are reported. These compounds contain a DNA alkylating agent connected to a H₂O₂‐responsive trigger by different electron‐withdrawing linkers so that they are inactive towards DNA but can be triggered by H₂O₂ to release active species. The activity and selectivity of these compounds towards DNA were investigated by measuring DNA interstrand cross‐link (ICL) formation in the presence or absence of H₂O₂. An electron‐withdrawing linker unit, such as a quaternary ammonia salt ( 6 ), a carboxyamide ( 7 ), and a carbonate group ( 8 ), is sufficient to deactivate the aromatic nitrogen mustard resulting in less than 1.5 % cross‐linking formation. However, H₂O₂ can restore the activity of the effectors by converting a withdrawing group to a donating group, therefore increasing the cross‐linking efficiency (>20 %). The stability and reaction sites of the ICL products were determined, which revealed that alkylation induced by 7 and 8 not only occurred at the purine sites but also at the pyrimidine site. For the first time, we isolated and characterized the monomer adducts formed between the canonical nucleosides and the aromatic nitrogen mustard ( 15 ) which supported that nitrogen mustards reacted with dG, dA, and dC. The activation mechanism was studied by NMR spectroscopic analysis. An in vitro cytotoxicity assay demonstrated that compound 7 with a carboxyamide linker dramatically inhibited the growth of various cancer cells with a GI₅₀ of less than 1 μM , whereas compound 6 with a charged linker did not show any obvious toxicity in all cell lines tested. These data indicated that a neutral carboxyamide linker is preferable for developing nitrogen mustard prodrugs. Our results showed that 7 is a potent anticancer prodrug that can serve as a model compound for further development. We believe these novel aromatic nitrogen mustards will inspire further and effective applications.     

LaMgAl11O19:Co2+被动调Q铒玻璃激光器研究

综述了被动调Q铒玻璃激光器的发展概况,推导了被动调Q铒玻璃激光器输出脉冲能量、脉宽的解析表达式,数值模拟了腔内损耗与输出脉冲能量、脉宽及峰值功率的关系以及输出脉冲能量与输入抽运能量的关系.设计了一台LaMgAl11O19:Co2 被动调Q铒玻璃激光器,实验验证了数值模拟分析结果.结果表明,腔内损耗增加将导致输出脉冲能量下降,脉宽变大,从而峰值功率降低.输入能量低于12 J时,输出只有单脉冲,当输入能量大于12 J时,输出会出现双脉冲.在8 J的电输入下,获得了峰值功率50 kW,2.7 mJ的1.535 tm激光输出.最后讨论了提高单脉冲能量的方法.     

Synthesis of narrow bandwidth flat-top ns pulse with multi-ultra-short pulses

Making use of the spectral narrowing of ultra-short pulses subject to amplification in the gain bandwidth media, a multi-ultra-short pulse coherent synthesizer (MUSPCS) developed from the traditional regenerative amplifier is proposed, and its operational principle is described. In the small signal gain regime, the theoretical analysis and numerical simulation on the MUSPCS have been made. The simulation results show that the narrow bandwidth flat-top long pulse can be composed if the parameters were controlled carefully.     

Correct determination of TE and TM cutoff wavenumbers intransmission lines with circular outer conductors and eccentric circularinner conductors

The cutoff wavenumbers of TE and TM modes (higher order modes) in transmission lines with circular outer conductors and eccentric circular inner conductors are carefully evaluated. The correctness of Kuttler's bounds is confirmed and the reason why some of the values obtained lie outside the bounds and why some of the modes could not be found in the work of A. Vishen et al. (1986) is given. A reliable technique for accurately determining the roots of an analytical function is proposed for finding cutoff wavenumbers in such a way as to avoid missing any modes     

A Novel UWB Antenna with Small Side-Leakage

A successful design for a UWB (ultra-wideband antennas) antenna based on NRD-guide (nonradiative dielectric waveguide) with small side-leakage is presented. The rule of the theoretical selection of its parameters, if NRD-guide is used as the UWB antennas, is studied firstly, then the temporal propagation characteristics of the NRD-guide and the radiation characteristics for an tapered open-ended NRD-guide are calculated by FDTD (finite-difference time-domain) method.