Magnetic material arrangement in oriented termites: a magnetic resonance study

Temperature dependence of the magnetic resonance is used to study the magnetic material in oriented Neocapritermes opacus (N.o.) termite, the only prey of the migratory ant Pachycondyla marginata (P.m.). A broad line in the g=2 region, associated to isolated nanoparticles shows that at least 97% of the magnetic material is in the termite’s body (abdomen + thorax). From the temperature dependence of the resonant field and from the spectral linewidths, we estimate the existence of magnetic nanoparticles 18.5 ± 0.3 nm in diameter and an effective magnetic anisotropy constant, K_eff between 2.1 and 3.2 × 10⁴ erg/cm³. A sudden change in the double integrated spectra at about 100 K for N.o. with the long body axis oriented perpendicular to the magnetic field can be attributed to the Verwey transition, and suggests an organized film-like particle system.     

Properties of blends containing two liquid crystalline polymers

Blends containing two, wholly aromatic, naphthalene-based liquid crystalline polymers (LCPs) are studied. Experimental results show that the viscosities of the resulting blends are lower than the parent LCPs over the entire shear-rate range investigated. The orientation development following capillary flow demonstrates, that over a defined blend composition range, some blends have higher orientability than the constituent polymers. This is further manifested in the tensile and flexural properties of injection-molded specimens. A detailed analysis indicates that in the composition range where synergistic effects are observed in orientation development as well as in mechanical properties, only one glass transition temperature is detected. This suggests that “miscibility” is desirable for obtaining maximum properties in these blend systems.     

PNL分子在正、负电性纳米银上的吸附取向

制备了两种不同电性的纳米银粒子的脉体,发现当邻菲罗啉分子分别吸附在这两种纳米银上时,其表面增强喇曼谱有明显的不同.在正电性纳米银上,面外弯曲模式受到增强,而在负电性纳米银上,面内伸缩模式受到增强,通过分析增强谱的差异表明,分子在这两种不同电性胶态纳米银表面上可能分别以平躺及站立方式吸附.     

Influence of particle orientation on retrieving cirrus cloud properties by use of total and polarized reflectances from satellite measurements

The influence of ice crystal orientation was investigated on retrieving cirrus optical thickness (τ) and aspect ratio of ice crystals (Q) from satellite measurements using the total and polarized reflectances at a wavelength of . We considered columnar and plate like hexagonal ice crystals whose long axes are randomly oriented in the horizontal plane (2D model) with some amplitude of oscillation expressed by a Gaussian distribution function with the standard deviation of σ.The retrieved τ and Q values significantly depend on the assumption of σ, in particular for the plate type. Furthermore, the relationship between σ and the retrieved values depends on the solar, satellite, and target geometries. In our case study, for one target area, τ value retrieved using the 2D model with σ=5° was approximately twice larger than that using the 2D model with σ=20°, while the retrieved Q value was not significantly influenced by σ. For another target area, the τ(Q) retrieved using the 2D model with σ=5° was about 1.5 (1.8) times larger than that retrieved using the 2D model with σ=20°.     

Description of the state of deformation of ethylene–tetrafluoroethylene alternating copolymer films estimated by using a model proposed in terms of orientation of crystallites within a rod

To study the deformation mechanism of ethylene–tetrafluoroethylene alternating copolymer films caused by elongation, a model relating crystal orientation to the orientation of the rods was proposed. The orientation distribution of crystallites within the rod was given as the correlation with the rod orientation. The distribution functions of a given reciprocal lattice vector of the crystal plane were derived from the two functions of the crystallites and of rods with several parameters representing the orientation of rods and the rotation of crystallites within a rod. By choosing suitable values of the parameters, the calculated functions were in good agreement with the results of X-ray diffraction experiments. From the values of the parameters to give the best fit between calculated and observed results, it turned out that the characteristic orientation of the c-axis is mainly due to the preferential orientation of the rod with respect to a stretching direction and is hardly affected by the rotation of crystallites within the rod. Using the two orientation functions concerning rods and crystallites, Hv light scattering was formulated by introducing an interparticle interference effect of the rods. The calculated results assumed the characteristic profile of the observed patterns as the superposition of broadleaf lobes and a sharp pattern of streaks. Received: 28 April 2000 Accepted: 30 September 2000     

用非偏振拉曼光谱表征聚合物的取向行为

采用非偏振激光为拉曼光源表征了聚丙烯纤维、尼龙6扁丝以及聚乙烯管材等3种取向的聚合物样品。实验表明,当入射光作用于样品的不同面(方向)时,所得到的拉曼光谱存在明显的差异。这一结果为表征聚合物取向开创了新思路,并拓宽了拉曼光谱技术的应用范围。     

Orientation relationship between α-Fe precipitate and α-Al2O3 matrix in iron-implanted sapphire

Fe ions were implanted into α-Al₂O₃ single crystals (sapphire) at room temperature and annealed in a reducing atmosphere. The orientation relationships (ORs) between α-Fe particles and sapphire matrix were investigated using transmission electron microscopy (TEM). All the α-Fe particles have the orientation relationship (OR) of (1 1 1)_α-Fe || (0 0 0 1)_sapphire and ${[1\overline{1}0]}_{\alpha \text{-Fe}}\left|\right|{[11\overline{2}0]}_{\text{sapphire}}$ with sapphire. This OR is predicted precisely by the coincidence of reciprocal lattice points (CRLP) method. The other OR of (1 1 0)_α-Fe || (0 0 0 1)_sapphire and ${[111]}_{\alpha \text{-Fe}}\left|\right|{[5\overline{1}\overline{4}0]}_{\text{sapphire}}$ reported before is confirmed by the same method to be one of the secondary preferred orientation relationships in the α-Fe/sapphire system.     

Optimal cubature on the sphere and other orientation averaging schemes

We propose an orientation averaging scheme which we call optimal cubature on the sphere to be used in light scattering computations. The cubature points are optimally arranged on the sphere to produce non-biased and fast convergence in scattering problems requiring numerical orientation averaging. We will compare performance against other possible schemes.     

Enhanced Carrier Diffusion Enables Efficient Back-Contact Perovskite Photovoltaics

Back-contact architectures offer a promising route to improve the record efficiencies of perovskite solar cells (PSCs) by eliminating parasitic light absorption. However, the performance of back-contact PSCs is limited by inadequate carrier diffusion in perovskite. Here, we report that perovskite films with a preferred out-of-plane orientation show improved carrier dynamic properties. With the addition of guanidine thiocyanate, the films exhibit carrier lifetimes and mobilities increased by 3–5 times, leading to diffusion lengths exceeding 7 μm. The enhanced carrier diffusion results from substantial suppression of nonradiative recombination and improves charge collection. Devices using such films achieve reproducible efficiencies reaching 11.2 %, among the best performances for back-contact PSCs. Our findings demonstrate the impact of carrier dynamics on back-contact PSCs and provide the basis for a new route to high-performance back-contact perovskite optoelectronic devices at low cost.     

聚乙烯在氧化铝模板中的结晶与取向行为

用多孔阳极氧化铝(AAO)模板制备了直径为200nm的聚乙烯(PE)纳米纤维,并用傅立叶变换红外光谱(FTIR)、偏光显微镜(PLM)和X-射线衍射(XRD)方法研究了PE在二维圆柱状受限条件下的结晶与取向行为.FTIR研究表明,由于模板的限制作用,PE纳米纤维的结晶度低于本体.同时,PE纳米纤维晶体的b轴平行于模板孔洞的方向取向,而a轴垂直于孔洞的方向取向.XRD结果进一步证明,在纳米孔洞中PE晶体的b轴平行于纳米孔洞方向.PLM结果表明,在结晶过程中,晶体主要是在模板与本体的界面处成核,然后晶体呈发散状向本体和纳米纤维中竞争生长.由于PE晶体的b轴是其生长速率最快的方向,在本体中形成典型的环带球晶形貌;而在二维圆柱受限条件下,只有沿孔洞方向生长的晶体才能增长,而其它生长方向则受到抑制,造成PE晶体的b轴沿孔洞方向优先取向.