考虑制动力影响的大型客车舒适性分析

利用有限元法和动力平衡原理,建立了具有层间接触的沥青路面和13个自由度的大型客车人体三维模型。以不平顺作为激励,随机模拟车流分布,在不同制动情况下,从时域和频域两方面分析人-车-路耦合振动下车辆和人体的动力响应。时域分析采用客观评价标准和主观烦恼率相结合的方法,频域分析考虑人体共振、人的心理和生理因素。结果表明:随着制动力增大,人体的竖向加速度幅值不变,俯仰、侧倾加速度幅值都增大,但是俯仰加速度增幅远大于侧倾加速度的情况,人的舒适性变差,烦恼率增高;在紧急制动时,主频段对人体共振、心理和生理产生的影响很小,但是次主频段与人体某些器官固有频段重合,对人体共振、心理和生理产生的影响是不容忽视的。     

某型电动飞机螺旋桨振动特性实验研究

某型电动飞机采用螺旋桨产生拉力,为了防止螺旋桨工作时共振,利用ES-2-150振动实验系统进行了两叶木质螺旋桨和碳纤维螺旋桨的振动特性实验,采用谐振搜索与驻留方法测量出木质螺旋桨的第一阶固有频率为36.07Hz,碳纤维螺旋桨的第一阶固有频率为73.58Hz。螺旋桨爬升状态转频为39Hz,这与木质螺旋桨的第一阶固有频率非常接近,导致木质螺旋桨在爬升状态出现比较严重的振动故障。因此,某型电动飞机最终选择两叶碳纤维螺旋桨作为其拉力产生装置。     

群集建筑中大跨裙摆屋盖风荷载特性的数值模拟研究

以苏州太平金融大厦为工程背景,针对其大跨裙摆屋盖的风荷载作用,首先采用RNG k-ε模型模拟分析了其平均风压分布规律,以及风向变化对屋盖表面风荷载体型系数的影响;其次,引入干扰因子IF,探讨了周边建筑对大跨裙摆屋盖风荷载的气动干扰作用。结果表明:0°风向下,走廊上方屋盖两侧区域出现“上吸下顶”的叠加作用;90°风向下屋盖北侧飘带末端区域受到狭道风效应出现正压集中现象;风向变化对大跨裙摆屋盖的风荷载体型系数分布影响较大;且周围建筑物对大跨裙摆屋盖的气动干扰效应明显,主要表现为风压“遮挡效应”,而局部区域表现为风压“放大效应”。     

螺栓松动边界下纤维增强复合薄板的振动测试方法

提出了基于预埋压力传感器的量化测试方法,研究了螺栓松动边界对纤维增强复合薄板振动特性的影响。首先,自主设计并开发了带有预埋压力传感器的螺栓松动边界下复合薄板的振动测试系统,并详细介绍了系统各个部件的组成和功能;然后,归纳出一套合理、规范的松动边界下复合薄板的振动测试流程,并对HF10碳纤维/树脂复合薄板进行了实际测试。结果表明:随着螺栓松动程度的不断增加,复合薄板的固有频率逐渐降低,模态振型的节线位置也发生了不同程度的变化,但其阻尼结果呈现先增大后减小的趋势;而共振和非共振响应呈现先减小后增大的趋势。     

Controllable Preparation of Plasmonic Gold Nanostars for Enhanced Photothermal and SERS Effects

Gold nanostars(Au NSs) are asymmetric anisotropic nanomaterials with sharp edge structure. As a promising branched nanomaterial, Au NS has excellent plasmonic absorption and scattering properties. In order to tune the plasmonic photothermal and surface-enhanced Raman scattering(SERS) activity of Au NSs to obtain the desired characteristics, the effects of reagents on the local surface plasmon resonance(LSPR) bands of Au NSs were studied and the morphology and size were regulated. Nanoparticles with different sharp edges were synthesized to make their local plasmon resonance mode tunable in the visible and near-infrared region. The effects of the number and sharpness of different tips under the control of AgNO₃ on the photothermal response of Au NSs and the SERS activity and their mechanism were discussed in detail. The results show that as the length of the branch tip becomes longer and the sharpness increases, the plasmonic photothermal effect of Au NSs is strengthened, and the photothermal conversion efficiency is the highest up to 40% when the length of Au NSs is the longest. Au NSs with high SERS activity are used for the Raman detection substrate. Based on this property, the quantitative detection of the pesticide thiram is achieved.     

粉末晶体(ZrO2)x(Bi2O3)1-x(x=1.0, 0.97) 晶体结构分析

为了确定ZrO2和(ZrO2)0.97(Bi2O3)0.03的晶体结构和原子热振动各向同性温度因子B，对该粉末晶体进行X射线衍射实验，建立了晶体结构模型，进行晶体结构分析。首先，采用共沉淀法和高温固相烧结法制备了纳米氧化锆ZrO2和(ZrO2)0.97(Bi2O3)0.03粉末晶体，接着，使用X射线测试仪对两种样品进行了衍射实验（XRD），利用Rietveld 精修方法的 RIETAN-2000程序对所得实验结果进行了晶体结构分析，获得了晶体结构参量和原子热振动各向同性温度因子B。通过Maximum Entropy Method（MEM）解析得到了粉末晶体(ZrO2)x(Bi2O3)1-x(x=1.0，0.97)的等高电子密度分布可视化图谱。结果表明，(ZrO2)0.97(Bi2O3)0.03的晶胞体积比ZrO2的晶胞体积大分别为140.6850 Å3和140.5637Å3；ZrO2晶体的原子热振动各向同性温度因子B(Zr)、BO(1)、BO(2)和 B（Bi）分别为0.690、0.269、 0.178 和 0 Å2，(ZrO2)0.97(Bi2O3)0.03晶体的分别为0.460 、0.583 、0.121 和0.581 Å2。 确定了(ZrO2)0.97(Bi2O3)0.03的晶体结构属于单斜晶系，实现了等高电子密度分布三维（3D）和二维（2D）的可视化，进一步确定了晶体结构和原子位置。     

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

Orthorhombic La_0.7-xEu_xCa_0.3MnO₃ samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm³ prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (T_C) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around T_C reaches the maximum (|ΔS_max|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔS_max| values are about 5.88, 4.93, and 4.71 J/kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔS_max| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around T_C have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La_0.7Ca_0.3MnO₃ materials for magnetic refrigeration below room temperature.     

Influence of spin–orbit interaction,Zeeman effect and light polarisation on the electronic and optical properties of pseudo-elliptic quantum rings under magnetic field

ABSTRACT

We theoretically investigated the influences of the magnetic field and light polarisation on the electronic and optical properties of a GaAs/GaAlAs pseudo-elliptic quantum ring, modelled by an outer ellipsis and an inner circle, in the presence of the Rashba and Dresselhaus spin–orbit interactions and Zeeman effect. We show that Aharonov-Bohm oscillations of the energy spectrum are not affected by the presence of the Zeeman effect alone but, in the presence of Rashba and Dresselhaus spin–orbit couplings, the periodicity of certain levels becomes hardly definite. The Zeeman effect generally enhances/diminishes the separation levels produced by Rashba/Dresselhaus interactions (SOI) and when both types of SOI are considered, the effect depends on their relative strength. The magnetic field can trigger spin-flip for each type of spin–orbit interaction and Zeeman effect or their combination through anticrossings in the energy spectra. Our results reveal that the absorption spectra are very sensitive to the magnetic field and light polarisation. For all polarisations considered, the magnetic field increment leads to the redshift or blueshift of some particular peaks (an effect of this ring geometry) and a better separation of the peaks. The x-polarised light determines spectra with many small, but separated peaks while the circular polarised light leads to spectra with large peaks of high amplitude.     

Preparation of sonoactivated TiO2-DVDMS nanocomposite for enhanced antibacterial activity

Titanium dioxide (TiO₂) nanoparticle has good photo-/sono-catalytic features, the reunion of this particle in solution-phase generally limits the extensive biomedical application. In the present study, the aggregation of TiO₂ nanoparticles was alleviated by facile fabrication under different pH conditions. A novel TiO₂ nanocomposite was further synthesized by properly conjugation with trace amount of DVDMS sensitizer (named DFT). The characterization, sonoactivity, as well as the antibacterial efficiency were specially evaluated. The results showed that the sonochemical activity of DFT was greatly improved as compared with the simple surface modification of TiO₂ (F-TiO₂) and free DVDMS, regarding to the hydroxyl radicals and singlet oxygen yields using the same ultrasound exposure. Moreover, ultrasonic stimulation of DFT exhibited excellent bacterial eradication, with up to 92.41% of killing efficiency in S. aureus. The flow cytometry analysis indicated an increased intracellular ROS and membrane disturbance by combination of DFT and ultrasound. The findings suggest that the proper fabrication and DVDMS incorporation greatly improved the sonocatalytic process of TiO₂, and the ultrasound based biomedical applications of DFT deserve future deep investigation.