New compounds with a Y2ReB6 type structure

The Ln’Mo’MB ternary systems (where Ln is Tm, Yb, Lu) are studied by means if X-ray analysis. New compounds of the Y2ReB6 structure type (space group Pbam) were found: Tm₂MoB₆ (a=0.9210(2), b=1.1409(1), c=0.35983(6) nm), Yb₂MoB₆ (a=0.9068(3), b=1.1394(3), c=0.3588(1) nm), Lu₂MoB₆ (a=0.9031(4), b=1.1364(3), c=0.35526(9) nm); the atomic factors of the last structure are refined up to R=0.068. Lattice parameters for the known boride Er₂MoB₆ are refined: a=0.925492), b=1.1449(3), c=0.36065(6) nm. The smoothly decreasing lattice parameters and unit cell volumes in the series Ln₂MoB₆ (Ln is Er, Tm, Yb, Lu) point to the trivalent state of the rare earth atoms (REM).     

Crystal structure of Ni4Ge0.33P1.17

The structure of the compound Ni₄Ge_0.33P_1.17, whose composition was earlier tentatively determined as ∼Ni₆GeP, was refined from single-crystal x-ray diffraction data (triclinic symmetry, new structure type). The positional and thermal parameters, site occupancies, coordination polyhedra, and bond distances were determined.     

激光微熔覆沉积成形工艺参数对沉积组织的影响

通过改变激光微熔覆沉积制造过程中的激光功率和扫描速度,研究了成形工艺参数对TC4合金组织和显微硬度的影响。结果表明：激光微熔覆沉积组织可以为贯穿整个熔覆层的外延生长的柱状晶,也可能下部晶粒延续着前一层的柱状晶生长,最上部为快速凝固的枝晶薄层。宏观上存在明暗两个组织区域,当P/V值小于40 W?s?mm-1时,成形试样的显微组织顶部区域为明区,下部为暗区。两个区域的组织都为细长针状马氏体,明区组织更细密。同时,明区的硬度要比暗区高,并且随着激光功率的增加或扫描速度的减小,顶部明区的宽度增加,而明区和暗区的硬度都呈下降趋势。反之为暗区在上,明区在下。此时,明区的组织仍然是细针状的马氏体组织。暗区是由于发生了固溶时效处理,细针状马氏体组织粗化,同时暗区的硬度要高于明区的硬度。     

Electrophoretic Determination of Symmetric and Asymmetric Dimethylarginine in Human Blood Plasma with Whole Capillary Sample Injection

Asymmetric and symmetric dimethylarginines are toxic non-coded amino acids. They are formed by post-translational modifications and play multifunctional roles in some human diseases. Their determination in human blood plasma is performed using capillary electrophoresis with contactless conductivity detection. The separations are performed in a capillary covered with covalently bonded PAMAPTAC polymer, which generates anionic electroosmotic flow and the separation takes place in the counter-current regime. The background electrolyte is a 750 mM aqueous solution of acetic acid with pH 2.45. The plasma samples for analysis are treated by the addition of acetonitrile and injected into the capillary in a large volume, reaching 94.5% of the total volume of the capillary, and subsequently subjected to electrophoretic stacking. The attained LODs are 16 nm for ADMA and 22 nM for SDMA. The electrophoretic resolution of both isomers has a value of 5.3. The developed method is sufficiently sensitive for the determination of plasmatic levels of ADMA and SDMA. The determination does not require derivatization and the individual steps in the electrophoretic stacking are fully automated. The determined plasmatic levels for healthy individuals vary in the range 0.36–0.62 µM for ADMA and 0.32–0.70 µM for SDMA.     

气相爆轰法制备球形铜纳米粒子及其形成机理

本文以氢氧混合气体为爆炸源,乙酰丙酮铜(II)为前驱体,采用操作简单、高效的气相爆轰方式合成了类球形的铜纳米晶颗粒。进一步采用XRD、TEM、SAED和EDX对所获得产物的形貌特征、物相组成和微观结构进行了表征和分析。同时为了预测气相爆轰流场中铜纳米颗粒的生长特性,将Kruis模型引入气体爆轰反应程序中。研究结果表明：实验合成的类球型FCC结构纳米铜晶体分散性良好,平均粒径在24 nm左右且纳米铜晶体外包覆了1nm左右的较薄石墨层。基于Kruis模型对球形铜纳米粒子的生长特性预测结果与实验数据吻合较好,为可控合成铜纳米粒子提供了可靠的理论指导。     

X-ray studies on phase equilibria in {Tm, Lu} - W - B ternary systems at 1070 K

Isothermal sections at 1070 K have been constructed by x-ray diffraction applied to the phase diagrams in the Tm - W - B and Lu - W - B systems. The solubility of “WB₂” in TmB₂ is low, while that in LuB₂ attains 0.15 molar fraction (lattice parameters of the (Lu, W) B₂ phase with a limiting composition and having the AlB₂ structure a=0.31772(6), c=0.35804(9) nm). The distinct boride reported previously Tm₃WB₇ is confirmed (Er₃CrB₇ structure type). New ternary compounds have been identified and examined by powder method (DRON-3M diffractometer): TmWB₄ (space group Pbam, structure type YCrB₄, a=0.59989(2), b=1.15866(4), c=0.35821(1) nm, N_hkl=157, R=0.0796) and Lu₂WB₆ (Pbam, structure type Y₂ReB₆, a=0.91339(4), b=1.14865(5), c=0.35124(2) nm, N_hkl=408, R=0.0981). Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 43–48, May–June, 2000.     

On cavities in thermally spheroidized powder particles

A melted spherical particle begins to solidify on cooling, and the radius of the first thin solid layer is approximately equal to the radius of the melted particle. Since the density of the solid phase is higher than that of the liquid one, porosity forms inside the sphere during further solidification. The pressure in the remaining melted material may decrease considerably. The requirement for a pressure balance implies that a relationship for the pore radius can be derived. The pore arises as a bubble in a boiling liquid. The bubble stability and its minimum radius are derived, as well as conditions for its formation. It is shown that, at most, one bubble can occur in the particle. Analytical results are applied to the case of alumina particles, and the growing process of the cavity is simulated. Craters found on some spheroidized particles stem from asymmetry of the solid shell formation and the simultaneous action of the atmospheric pressure. The practical importance of this effect is that additional porosity may be formed in thermal spray products.     

Effect of Chitosan-Coated Alginate Microspheres on the Permeability of Caco-2 Cell Monolayers

ABSTRACT

Alginate microspheres were prepared by emulsification/internal gelation and coated with chitosan. The ability of chitosan-coated alginate microspheres to increase the paracellular transport across Caco-2 cell monolayers was evaluated in comparison to uncoated microspheres and chitosan solutions. Transport studies were performed by using a permeability marker, Lucifer Yellow (LY), and by measuring the transepithelial electric resistance (TEER) variations. Furthermore, the occurrence of cytotoxic effects was assessed by evaluating neutral red uptake in viable cells and lactate dehydrogenase (LDH) release from damaged cells. A 3-fold increase on LY permeability was obtained for coated microspheres when compared to chitosan solutions. TEER variations were in agreement with permeability results. Chitosan solutions exhibited a dose-dependent toxicity, but coated microspheres did not decrease the viability of cells. Chitosan-coated alginate microspheres have potential to be used as carriers of poorly absorbable hydrophilic drugs to the intestinal epithelia and possibly increase their oral bioavailability.