一般增长曲线模型参数阵的BLU估计

考虑一般增长曲线模型：Ｙ＝Ｘ１ＢＸ２＋εＥ（Ｖｅｃ（ε））＝０Ｖ（Ｖｅｃ（ε））＝σ２ＶＩｎ（Ｖ０）本文对任一可估函数ＫＢＬ给出了它的ＢＬＵ估计（最佳线性无偏估计），并得到了方差σ２的一个无偏估计．     

Synthesis,growth and characterization of non-linear optical material: l-Tryptophan p-nitrophenol (LTPNP) single crystal

A new nonlinear optical organic crystal l-tryptophan p-nitrophenol (LTPNP) of dimension 19 mm × 2 mm × 1.5 mm has been grown from an aqueous solution for the first time by slow evaporation technique at ambient temperature. The crystal structure of LTPNP was confirmed by single crystal X-ray diffraction. LTPNP crystallizes in non-centrosymmetric monoclinic system with space group P₂₁. The recorded FTIR spectrum confirms the presence of various functional groups in the grown crystal and confirms the formation of LTPNP. Thermal stability and melting temperature of the LTPNP crystal were identified from TG/DTA analysis. The optical absorption study confirms the suitability of the crystal for device applications. LTPNP exhibits SHG efficiency over 1.7 orders of magnitude higher than that of urea and 4 orders of magnitude higher than that of KDP.     

Synthesis and Characterization of Titanium-doped Ordered Mesoporous Alumina

Titanium-doped ordered mesoporous alumina with specific structural properties has been prepared by the evaporation induced self-assembly sol-gel method. The results show that the doped titanium helps to stabilize the ordered mesoporous alumina material without influencing the ordered mesoporosity. The textural properties of the obtained sample are related to the amount of doped titanium. When the molar ratio of aluminum to titanium(n(Al)/n(Ti)) is controlled as 10.2, the titanium-doped ordered mesoporous alumina exhibits high surface area(up to 218 m2 g-1), large pore volume(0.42 cm3 g-1) and narrow pore diameter(6.1 nm) after treating at 900 ℃, showing high thermal stability. Moreover, the obtained sample calcined at 900 ℃ still maintains ordered mesoporous structure and exhibits high thermal stability.     

Seed‐Mediated Synthesis of Gold Tetrahedra in High Purity and with Tunable,Well‐Controlled Sizes

We report a facile synthesis of Au tetrahedra in high purity and with tunable, well‐controlled sizes via seed‐mediated growth. The success of this synthesis relies on the use of single‐crystal, spherical Au nanocrystals as the seeds and manipulation of the reaction kinetics to induce an unsymmetrical growth pattern for the seeds. In particular, the dropwise addition of a precursor solution with a syringe pump, assisted by cetyltrimethylammonium chloride and bromide at appropriate concentrations, was found to be critical to the formation of Au tetrahedra in high purity. Their sizes could be readily tuned in the range of 30–60 nm by simply varying the amount of precursor added to the reaction solution. The current strategy not only enables the synthesis of Au tetrahedra with tunable and controlled sizes but also provides a facile and versatile approach to reducing the symmetry of nanocrystals made of a face‐centered cubic lattice.     

Controllable synthesis,characterization,and growth mechanism of hollow Zn_x Cd_(1-x) S spheres generated by a one-step thermal evaporation method

Novel hollow ZnxCdl xS spheres that are uniform in size are synthesized through the one-step thermal evaporation of a mixture of Zn and CdS powder. From an X-ray diffraction （XRD） study, the hexagonal wurtzite phase of ZnxCdl_xS is verified, and the Zn mole fraction （x） is determined to be 0.09. According to the experimental results, we propose a mechanism for the growth of Zn0.09Cd0.91S hollow spheres. The results of the cathodoluminescence investigation indicate uniform Zn, Cd, and S distribution of alloyed Zn0.09Cd0.91S, instead of separate CdS, ZnS, or nanocrystals of a core- shell structure. To the best of our knowledge, the fabrication of ZnxCd1-xS hollow spheres of this kind by one-step thermal evaporation has never been reported. This work would present a new method of growing and applying hollow spheres on Si substrates, and the discovery of the Zn0.09Cd0.91S hollow spheres would make the investigation of ZnxCd1-xS micro/nanostructures more interesting and intriguing.     

Multiple Regulation Effects of Ammonium Acetate on ZnO Growth Process in Chemical Bath Deposition

Chemical bath deposition method has been used to synthesize a variety of ZnO morphology structures. However, the specificity and interaction of acetate and ammonium ions with ZnO crystal during the growth process remain elusive. This study contributes to understand the roles of ammonium acetate on the growth mechanism of ZnO in Zn(NO₃)₂-HMTA system. The growth process indicates that the nucleation experienced Zn²⁺-layered basic zinc salts (LBZs)-ZnO process, while the self-assembled unit changed from urchin-shaped, rod-shaped to a fully coupled twin-shaped structure with increasing ammonium acetate concentration. Ammonium acetate dominates the growth process by combing the ligand-ligand interaction of acetate ions binding to the same Zn-rich (0001) polar surface and ammonium ions regulating hexamethylenetetramine (HMTA) hydrolysis. Relatively regular hexagonal wurtzite structure and a dissolve-renucleation-regrowth process which retains the twin-shaped template and renucleates at the same position are observed at ∼10 mM ammonium acetate. Photoelectrochemistry (PEC) measurements show that the uniform hexagonal ZnO rods (Y-10, the sample named as Y-x (x represents x mM ammonium acetate, herein, x is 10 mM)) have a maximum photocurrent density of 1.54 mA cm⁻² at 1.23 V (vs. RHE), much higher than that of the dumbbell-shaped ZnO rods (Y-50, 0.20 mA cm⁻²) at the same voltage. These results provide a further explanation of morphology regulation mechanisms on ZnO synthesis processes and pave the road for more practical applications.     

The use of relative residues in fitting experimental data: an example from fluid mechanics

A curve fitting model is presented which minimizes the sum of squares of relative residues and expressions for the fit coefficients and their respective errors are derived. The new model is compared to the normal least squares model, using as an example the Reynolds number-drag coefficient data for a sphere. The results show that the best fit was obtained with the new model, indicating it may provide a useful tool for data analysis.     

Determination of crack growth kinetics in non-reinforced semi-crystalline thermoplastics using the linear elastic fracture mechanics (LEFM) approach

The aim of this study was to find a satisfactory method to characterize the fatigue crack growth behavior of non-reinforced, semi-crystalline thermoplastic polymers using linear elastic fracture mechanics (LEFM). For this, crack growth curves (crack length versus cycle number) as well as crack growth kinetics curves (crack growth rate da/dN versus amplitude stress intensity factor ΔK) had to be generated. As methods suggested by ISO 15850 and ASTM E 647-11 failed to provide satisfactory results for the crack growth curves, a more advanced method was searched for and finally found in the literature. Regarding the crack growth kinetics curve, the idea of the calculation was based on methods recommended in ISO 15850 and ASTM E 647-11. However, these methods had to be considerably modified and improved in order to get accurate results with little scatter. The whole methodology was developed and verified with fatigue crack growth tests on two semi-crystalline thermoplastics (polyoxymethylene POM and polyetheretherketone PEEK).     

Single crystal synthesis and magnetism of the BaLn2O4 family (Ln = lanthanide)

The series of compounds in the BaLn₂O₄ family (Ln = La–Lu, Y) has been synthesized for the first time in single crystalline form, using a molten metal flux. The series crystallizes in the CaV₂O₄ structure type with primitive orthorhombic symmetry (space group Pnma, #62), and a complete structural study of atomic positions, bonds, angles, and distortions across the lanthanide series is presented. With the exception of the Y, La, Eu, and Lu members, magnetic susceptibility measurements were performed between 2 K and 300 K. BaCe₂O₄ and BaYb₂O₄ display large crystal fields effects and suppression of magnetic ordering. All compounds show signs of magnetic frustration due to the trigonal arrangements of the trivalent lanthanide cations in the structure.