Interplay between random laser performance and self-frequency conversions in NdxY1.00−xAl3(BO3)4 nanocrystals powders

Random Laser emission at 1.06 μm, self-second-harmonic generation at 0.53 μm and self-sum-frequency generation at 0.46 μm were investigated in Nd_xY_1.00−xAl₃(BO₃)₄ nanocrystalline powders, for 0.05 ⩽ x ⩽ 1.00, excited by a pulsed laser operating at 808 nm, focusing on the interplay between the RL performance and the second-order nonlinear processes. The RL performance, characterized by a figure-of-merit relating the laser slope efficiency and the excitation pulse energy threshold, improved as x increased up to 1.00 while the efficiency of the self-frequency conversion processes reduced for increasing x because of distortions introduced in the crystalline structure of the grains. The RL wavelength was also dependent on the Nd³⁺ concentration and presented a redshift from 1061.9 nm to 1063.5 nm for increasing values of x.     

Colour shift and mechanism investigation on the PMMA diffuser used in LED-based luminaires

PMMA material is widely used in LED-based luminaires due to several advantages such as excellent optical transparency, durability against radiation, surface hardness (scratch free), rigidity and strength and can be completely recycled. However, few studies have been reported on the colour shift and failure mechanisms caused by this type of material. This paper experimentally investigated PMMA materials with different aging conditions. The following conclusions could be drawn. (1) Discolouration was not observed for any sample subjected to aging of 85 °C for 5000 h, or with additional blue light irradiation for 5000 h, or with additional humidity of 85%RH for 5000 h, or even with aging of 100 °C for 3000 h. (2) The specimen subjected to aging of 150 °C for 360 h has a surface discoloration and has a significant wavelength dependent degradation in the transmission spectrum caused by oxidation. The specimen with aging of 100 °C for 3000 h has a less oxidation, although no significant transmission spectrum reduction was observed. (3) Using such aged specimen as a diffuser mounted on a LED-based luminaire, the radiant flux peak intensity in the blue light area has a more severe reduction than that in the yellow light area, which results in a reduction of the radiant flux intensity ratio of blue light to yellow light and hence induces the colour shift to yellow. The colour shift investigated is 0.005, very close to the general failure criterion of 0.007, while the lumen decay is 10.2%, far less than the failure criterion of 30%.     

Experimental evidence of structural evolution for TiB2 microcrystal under externally high stresses

The morphology evolution and defect structure of TiB₂ microcrystals treated under high stresses were analyzed using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results show that hexagonal TiB₂ with large particle size gradually evolved to flowerlike TiB₂ with small particle size under high stresses. The evolution process is mainly determined by the preferential cleavage of TiB₂ microcrystal, and the presence of multiple lamellar nanotwin and edge dislocation directly provides some evidence of plastic deformation and structural evolution. For clarity, a possible model is suggested based on the HTREM observation and the natural properties of TiB₂ materials to explain the process mechanism.     

Enhanced magnetodielectric properties of Co2Z ferrite ceramics for ultrahigh frequency applications achieved via Cr3+ ion doping

Phase formation, microstructure, magnetic properties, and dielectric properties of Ba_1.5Sr_1.5Co₂Fe₍₂₃−_x)Cr_xO₄₁ (0.0 ≤ x ≤ 1.0) ceramics, in which Fe³⁺ ions were substituted by Cr³⁺ ions, were systematically investigated. X-ray diffraction results reveal that Z-type hexagonal ferrite was formed by sintering at 1250 °C, and Cr³⁺ ions successfully enter lattice without destroying crystal structure. Analysis of the microstructure reveals that Cr³⁺ ion doping has significant effect on crystal micromorphology. Samples with x = 0.4 have the most homogeneous micromorphology and the highest sintering density of 5.12 g/cm³. In addition, under the influence of external magnetic field, all samples exhibit typical soft magnetic character and hysteresis characteristics, with saturation magnetization up to 63.86 emu/g (x = 0.6). Particularly, compared with undoped sample, Cr-doped samples have outstanding magnetic–dielectric properties. Firstly, with increasing Cr³⁺ amount, real part of the permeability (μ′) reaches the maximum value of 10.70 at x = 0.4, while cutoff frequency exceeds 2 GHz, and Snoek constant reaches ∼19.50 GHz. Furthermore, due to more homogeneous microstructure, samples with x = 0.4 have low magnetic loss and can maintain high quality factor (Q) over a broad frequency range. Moreover, real part of the permittivity (ε′) reaches the maximum value of 16.90 at x = 0.6, and dielectric loss remains lower than 0.013 for frequencies below 0.7 GHz. Consequently, magnetic–dielectric materials prepared in this work are expected to have extensive application prospects for ultrahigh-frequency devices.     

The effect of tool heating arrangement on fibre material forming

In this paper, a new heating arrangement has been developed for improving the performance of paperboard forming process. Problem areas of current heating methods were identified by analyzing several forming moulds used for tray production in packaging industry. This analysis was used as basis for design process of the new and more advanced mould. The new process utilizes oil to distribute heat evenly in the mould resulting in reduced process parameter adjustment during production. The versatility of the improved design manifests in less variance in outer dimension of trays and reduced volume of rejects.     

新型SPECT/MRI双模态显像剂SPION-DMSA-RGD-~(99)Tc~m的合成与生物评价

为制备纳米材料SPION-DMSA-RGD及其标记物SPION-DMSA-RGD-99 Tcm,探讨该标记物作为SPECT/MRI双模态显像剂的可能性,在水溶性纳米颗粒SPION-DMSA上连接c(RGDfC),得到了SPION-DMSA-RGD,并进行了结构表征。用99 Tcm对SPION-DMSA-RGD进行标记,并对该标记物进行了正常鼠和荷U87MG人脑神经胶质瘤裸鼠的生物分布研究,及荷U87MG人脑神经胶质瘤裸鼠的MRI和SPECT显像研究。研究结果表明,SPION-DMSA-RGD具有超顺磁性,99 Tcm标记率约为98%。正常鼠和荷U87MG人脑神经胶质瘤裸鼠的生物分布结果表明,SPION-DMSA-RGD-99 Tcm在血液中清除较快,在肝脏中摄取较高,在肿瘤中有摄取。荷U87MG人脑神经胶质瘤裸鼠的MRI和SPECT显像结果表明,SPION-DMSA-RGD和SPION-DMSA-RGD-99 Tcm的肿瘤主动靶向作用明显。以上结果提示,对于荷U87MG人脑神经胶质瘤裸鼠,SPION-DMSA-RGD-99 Tc m是一种SPECT/MRI双模态显像剂。     

3-羟基-4-吡啶酮类螯合剂在镓放射性药物中的 研究进展及展望

目前，在肿瘤等重大疾病的早期诊断中，PET/CT（或PET/MRI）是灵敏度最高、分辨率最好的医学影像手段。PET/CT（或PET/MRI）依赖于PET药物，很大程度上依赖于¹⁸F PET药物。然而，随着世界上第一个⁶⁸Ga药物（⁶⁸Ga-DOTATATE）获得美国FDA批准进入市场，⁶⁸Ga及其药物的研究正受到越来越多的关注。本文首先介绍了镓的基本核性质和化学性质，然后提出了金属双功能螯合剂的设计要求，并讨论了一些常用镓螯合剂的优缺点。由于3-羟基-4-吡啶酮基团对三价镓离子具有高的亲和力和选择性，因此，特别重点关注了3-羟基-4-吡啶酮多齿螯合剂在镓放射性药物中的最新研究进展。最后，还对3-羟基-4-吡啶酮多齿螯合剂在镓放射性药物中的应用前景进行了展望。     

正电子核素标记奥曲肽类似物的研究进展

奥曲肽是一种人工合成的含有8个氨基酸的生长抑素类似物,与生长抑素受体(SSTR)能够高特异性地结合。肿瘤细胞组织上常有一些生长抑素受体的过度表达,因此,应用正电子核素标记的奥曲肽及其类似物作为肿瘤示踪剂,对生长抑素受体阳性肿瘤进行诊断与治疗具有潜在的重要的临床意义。本文就正电子核素标记的奥曲肽类似物的研究现状进行综述。     

全钢载重子午线轮胎过渡层的辐射预硫化及组胎后性能研究

以天然橡胶为基材作为全钢载重子午线轮胎的过渡层,在0 60 kGy吸收剂量范围内,采用电子束辐照技术对其进行辐射预硫化研究,结果表明,过渡层的格林强度随吸收剂量增加,吸收剂量60 kGy时,胶料的格林强度增幅可达300%;低吸收剂量时,胶料的粘度增加较快,之后吸收剂量虽有增加,但粘度变化不大;辐射预硫化与未辐射预硫化的过渡层相比,热硫化后的力学性能相差不大;过渡层减薄1 mm后,单胎质量平均减少1.5 kg而不影响轮胎的主要性能。     

Radiation pre-vulcanization effect on properties of the truck tyre＇s transition layer and the truck tyre

In this paper,the natural rubber is chosen as the main constituents for the transition layer of all-steel load radial tyre,which is pre-vulcanized by 500-keV E-beam irradiation of up to 60 kGy.The results show that the green strength of transitional layer increases with the dose,reaching four times as much as the control(without irradiation) at 60 kGy.The final mechanical properties do not differ significantly from those of the control except that the aging and fatigue performance increased.However,thickness of the natural rubber transitional layer for an average single tyre can be reduced by 1 mm(or 1.5 kg) without obvious adverse effect on tyre performance.