Occurrence of fragmentation during compression of pellets prepared from a 4 to 1 mixture of dicalcium phosphate dihydrate and microcrystalline cellulose

The occurrence of pellet fragmentation during the compression of pellets prepared mainly from a hard pharmaceutical filler material was investigated. The pellets consisted of 4 parts dicalcium phosphate dihydrate (generally considered as a hard material) to 1 part microcrystalline cellulose (used as a pellet forming material). Pellets of two porosities, 36% and 55%, were prepared. Compacts formed at 100 MPa applied pressure were fractured and the fracture surfaces were then visually examined. Lubricated pellets were also compacted in order to obtain tablets which could be easily deaggregated. Pellets retrieved from deaggregated tablets were compared with uncompacted pellets with respect to size and fracture resistance. The results showed that many pellets exposed in the tablet fracture surface were fractured, especially those with higher porosity. However, the lubricated pellets retrieved from deaggregated tablets were similar in size to the uncompacted pellets, i.e. fragmentation of these pellets was minimal. Furthermore, these retrieved pellets were more resistant to fracture than the original uncompacted pellets, indicating that the formation of cracks or flaws in the pellets during compaction was also minimal. It was thus concluded that deformation and probably densification, and not fragmentation, was the dominant compression mechanisms of this pellet formulation.     

Dissolution behavior and bioavailability of phenytoin from a ground mixture with microcrystalline cellulose

The ground mixture of phenytoin and microcrystalline cellulose was prepared by grinding in a vibrational ball mill. The X-ray diffraction patterns indicated the amorphous nature of the ground mixture. Comparative studies were made concerning the in vitro dissolution and in vivo absorption of fine phenytoin powder, phenytoin sodium powder, and the ground mixture. The ground mixture showed a greater dissolution rate than the fine powder and attained supersaturation in the pharmacopeial disintegration media at pH 1.2 and 7.4. In vivo absorption studies of each preparation were carried out in five subjects, using a crossover design, by measuring the urinary excretion rate of a main metabolite, 5-(p-hydroxyphenyl)-5-phenylhydantoin. The blood levels of phenytoin and the corresponding urinary excretion patterns of the metabolite were determined in two subjects. The ground mixtures significantly improved the bioavailability of phenytoin. The drug was completely and rapidly absorbed after oral administration of the ground mixture. The vibrational ball milling technique for a poorly water-soluble drug with microcrystalline cellulose provides a promising way of improving the in vivo drug absorption.     

Propofol and thiopental in a 1:1 volume mixture is chemically stable

Propofol and thiopental have been used clinically in combination for induction of anesthesia. Studies suggest that this mixture has synergistic activity, recovery characteristics similar to propofol alone, and bactericidal effects on multiple organisms. It may therefore be both clinically useful and cost-effective. In this study, we examined the chemical stability of this mixture. We used high-performance liquid chromatography to quantify the concentration of both propofol and thiopental in a given sample. This technique allows the detection of loss in total drug mass and of the appearance of breakdown products resulting from drug interaction. Ten samples of a 1:1 mixture by volume were prepared and assayed at Time 0 and Days 1, 3, and 7. Half the samples were incubated at 23 degrees C and the rest were stored at 4 degrees C. Other mixtures were assayed before and after filtration at Time 0 and Days 1 and 7 after storage at 23 degrees C. The assay was able to measure accurately the quantity of drug present in the samples. There was no significant decrease in the quantities of either propofol or thiopental in the mixture over the 7-day period. We conclude that the 1:1 volume mixture of propofol and thiopental is chemically stable for 1 wk at room temperature. Implications: A mixture of propofol and thiopental has been used to induce anesthesia. We investigated the chemical stability of this mixture using high-performance liquid chromatography and found it to be stable for at least 24 h.     

模具润滑温压成形法制作的高密度铁基烧结体的磁性与组织

烧结铁是一种好的软磁材料,但其磁通密度比铸造材料的低。低的磁通密度是由于密度低所引起的。本研究开发了一种温压与硬脂酸锂模壁润滑技术(WC-DWL)。使用该技术,得到了密度非常高的成形体。纯铁粉在1176MPa的压力下成形,经1523K烧结后的性能如下:密度=7.76Mg/m3,μm=5300,B160=1.16T,B240=1.28T,B400=1.40T,B2k=1.60T,bHc=110A/m。一些烧结铁表现出各向异性的变化与组织,这导致异常晶粒长大到长度为数毫米。这种异常长大在试样成形密度较高时更为明显。     

压制方式对锆钛酸铅压电陶瓷密度及性能影响的研究

将低电压电磁成形引入陶瓷粉末成形,以锆钛酸铅(PZT)粉末为研究对象,采用间接加工方式对其进行低电压电磁压制.结果表明,相比于模压成形,通过选择放电参数,低电压电磁压制能提高PZT陶瓷压坯密度并改善陶瓷体的烧结性能.密度测试结果表明,经电磁压制后烧结的PZT制品密度较高.通过电性能参数测试,经电磁压制后烧结的PZT制品压电常数、相对介电常数、机电耦合系数均较高,介质损耗较低.     

Theory and technology of article forming features of the density distribution with axial compression of porous articles bounded by compaction surfaces inclined towards the compaction direction. Numerical analysis

The stressed state of porous preforms that have surfaces inclined towards the compaction axis is considered. Relationships from plasticity theory for a porous body are used. Solutions of the corresponding boundary-value problem are effected using the finite element method. The moulding of powder preforms whose initial properties are not distributed uniformly is studied on the example of two-layer preforms. It is assumed that the interface is parallel to the top and bottom punch surfaces. Compaction of the less strong layer occurs more intensely. The interface moves towards the less strong layer during forming. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6(395), pp. 43–52, May–June, 1997.     

Analysis of the biological characteristics of primary HIV-1 isolates using the main components method

1-18 months old Norwegian-Sami girls from Karasjok/Katokeino were compared with girls from Falk?ping in Sweden. All Karasjok/Kautokeino children were breastfed, usually until 1 year of age. Only a few developed a dummy- or fingersucking habit. They started eating porridge at 4-5 months of age. At about half a year of age they were fed dark, hard chewing bread to gnaw at. Cut and pulped adult food was introduced during the end of the first year of life. In almost all cases the children had dried reindeer meat to gnaw at. They were mostly fed by spoon and drank from a cup. The Falk?ping girls, on the other hand, were not so often breastfed and for a shorter time. They usually became dummysuckers. The Falk?ping girls got almost all their nutrition during the first one or two years by sucking or eating food with little chewing resistance. The differences in sucking and chewing behavior could influence on the transversal development of the jaws.     

Dynamic compaction of titanium aluminides by explosively generated shock waves: Microstructure and mechanical properties

A detailed microstructural analysis and evaluation of the mechanical properties of titanium aluminides consolidated by novel shock processes^[13] are presented. Successful consolidation was obtained and was evidenced by strong bonding between individual particles. Additions of Nb and Ti and Al elemental powders resulted in enhanced interparticle bonding through intense plastic deformation of Nb and shock-induced reactions between Ti and Al. Rapid cooling of interparticle molten layers yielded amorphous Ti-Al alloys; this interparticle melting and rapid cooling are a unique feature of shock processing. Embrittlement of individual particles of Ti₃Al-based alloy after exposure to 550 °C and 750 °C was observed. There is evidence of phase transformation after preheating the powder, and this fact can explain the high density of cracks obtained with this alloy after high-temperature shock consolidation. Mechanical properties of the Ti₃Al-based alloy were determined at room temperature and the fracture modes were studied. The microstructural observations are correlated with the mechanical properties.     

Investigation of a discus-milling process using a powder mixture of Al and TiO2

In this study, a powder mixture of Al and TiO₂ was employed to investigate the milling process in a discus mill. In this first report on this novel mechanical mill, several variables, including the milling time and powder charge and their effects on the microstructural evolution of powder particles, are monitored and studied. The study reveals that the dominant parameters of the milling process are the milling time and the starting powder charge, similar to the other high-energy ball-milling processes. The longer the milling time and the smaller the starting powder charge, the more homogeneous the mixing and the finer the microstructure of the powder particles. The reaction between Al and TiO₂ was not observed with a milling period as long as 6 hours, for the present materials. However, the reaction between Al and TiO₂, during the subsequent heat treatment, is influenced by the milling condition. The powders with the longer milling times and finer mixing microstructures also form a finer microstructure, after the reaction between Al and TiO₂ during heat treatment. The methods for achieving an optimal milling efficiency for the Al-TiO₂ system are discussed.     

Thixotropic properties of multi-functional binder and compaction behaviour of the low alloyed binder-treated powder

A new multi-functional binder with adhesive and lubricant effect was designed, and the thixotropic properties of the binder components and the resulting binder, the adhesive effect and compaction behaviour of the binder-treated powder were investigated. The results demonstrate that the thixotropic components in the binder are polyethylene wax and microcrystalline wax. With the increase of polyethylene wax content, the critical solid–liquid shear stress of binders decreases gradually. The main lubrication components in the low-pressure and high-pressure stages during the compaction process are found to be polyethylene wax and microcrystalline wax, respectively. The fine metal or graphite additives are effectively bonded on the surface of iron particles and filled in the pits. The green density reaches 7.25?g?cm^?3 at 600?MPa when the content of polyethylene wax is 30%. From 400 to 750?MPa, the content of polyethylene wax corresponding to the minimum ejection pressure decreases from 20 to 0%.     

Solid solution decomposition mechanisms in as-cast and microcrystalline Al-Sc alloys: IV. Effect of the decomposition of a solid solution on the mechanical properties of the alloys

The effect of the decomposition of the solid solution in Al-X wt % Mg-0.22 wt % Sc-0.15 wt % Zr (X = 0, 1.5, 4.5 wt %) alloys on their mechanical properties in the as-cast and microcrystalline (MC) states is studied. The contribution of the particles that precipitate during the decomposition to the mechanical properties of the as-cast and MC alloys is determined. For this purpose, the dependences of the volume fraction and the size of the particles precipitating during the decomposition on the annealing time and temperature and the magnesium content in the as-cast and MC alloys are calculated. An additional contribution to the hardening of the MC alloys is shown to be related to the internal stress fields created by the defects that accumulate at the disperse particles distributed in grain boundaries during grain-boundary migration. The calculated macroelasticity limits in the as-cast and MC alloys are compared with the experimental data.     

Computer model for a multicomponent slag-forming mixture melt: Relation between its atomic structure and physicochemical properties

Experimental data on the density are used to perform molecular dynamics simulation (for the first time) of the multicomponent melt of a commercial slag-forming SiO₂-CaO-Al₂O₃-MgO-CaF₂-Na₂O-K₂O-FeO mixture using an ionic bond model. The simulation results are discussed and compared to available experimental and calculated data. The developed model exhibits a weak temperature dependence of the melt structure. A high diffusion mobility of fluorine ions and alkali metal ions as compared to other elements is revealed.     

Study of casting and mechanical properties of the AK8L alloy in castings fabricated using printed molds made of the ZCAST mixture

Due to the lack of information about the casting and mechanical properties of the AK8l alloy during casting into printed molds made of the ZCast mixture, studies on determining its fluidity, shrinkage, and mechanical properties, as well as on increasing the relative elongation of this alloy by means of optimizing its chemical composition, have been performed. It is shown that the method of casting into a printed mold made of the ZCast mixture can be effectively used in obtaining castings for critical applications from the AK8l alloy, especially at the stage of preparing cast products for production.     

Arabidopsis NPH1: a flavoprotein with the properties of a photoreceptor for phototropism

The NPH1 gene of Arabidopsis thaliana encodes a 120-kilodalton serine-threonine protein kinase hypothesized to function as a photoreceptor for phototropism. When expressed in insect cells, the NPH1 protein is phosphorylated in response to blue light irradiation. The biochemical and photochemical properties of the photosensitive protein reflect those of the native protein in microsomal membranes. Recombinant NPH1 noncovalently binds flavin mononucleotide, a likely chromophore for light-dependent autophosphorylation. The fluorescence excitation spectrum of the recombinant protein is similar to the action spectrum for phototropism, consistent with the conclusion that NPH1 is an autophosphorylating flavoprotein photoreceptor mediating phototropic responses in higher plants.     

纤维素及其衍生物对金属离子吸附性能的研究进展

纤维素衍生物的吸附性主要是通过对金属离子选择性吸收而体现出来的,文中针对纤维素及其衍生物能够吸附不同的金属离子的性能,综述了近十几年来纤维素及其衍生物对黑色金属离子,轻金属离子和重金属离子的吸附状况和应用情况,简单总结了纤维素衍生物金属离子吸附剂的再生利用,展望了纤维素衍生物金属离子吸附剂在其他方面应用的良好前景.