Closed-loop expressions of minimum energy control for single-inputlinear digital systems

Closed-loop expressions for the minimum energy control of a single-input linear digital system are described. They are obtained by two different methods. The optimal inputs are given by state feedback with the bounded variable gains. The gains are independent of the initial state of the system     

Simplified expressions for the near fields of a magnetic frill current

The simplified expressions for the electromagnetic field of the near zone from the magnetic frill are derived. In these formulas,E_{rho}andH_{phi}are expressed as a single integration of the complete elliptical integrals of the first and second kinds. Furthermore the closed form ofE_{z}is obtained approximately. Their accuracy is checked numerically by comparing with Tsai's, and significant improvement in efficiencies is obtained.     

Microporous carbons prepared from cationic surfactant-resorcinol/formaldehyde composites

Microporous carbons have been synthesized by the carbonization of cationic surfactant-resorcinol/formaldehyde (RF) composites, which were themselves formed by electrostatic organic-organic interaction. The porous structure produced by the decomposition of the surfactant plays an important role for the gasification of the RF polymer at higher temperatures. The pore size of the carbon prepared from tetrapropylammonium bromide (TPAB)-RF, cetyltrimethylammonium bromide (C₁₆TAB)-RF and decyltrimethylammonium bromide (C₁₀TAB)-RF mixtures can be estimated as 0.53 nm from the Horvath-Kawazoe method using N₂ adsorption isotherms. Their pore size distributions were very narrow, showing that the microporous carbons derived from surfactant-RF mixture may have promise as adsorbents and membrane materials.     

柿叶多酚的提取及体外生物活性的研究

利用水以及不同体积百分比(20%、40%、60%、80%和100%)的甲醇、乙醇、丙酮时柿(Diospyros kaki cv.Mopan)叶中的多酚物质进行提取,提取率最高的不同溶剂提取物采用HP-20大孔树脂进行纯化,分别得到了水提取物(WE)、甲醇提取物(ME)、乙醇提取物(EE)和丙酮提取物(AE),并时不同提取物的体外抗氧化活性、胶原酶和酪氨酸酶抑制活性进行了分析和比较.结果表明.柿叶中的多酚含量相于27.4±0.21mg GA/g(干重).采用体积分数为60%的丙酮溶液提取柿叶多酚时.柿叶多酚的提取率最高,为74.3%±2.3%.60%丙酮提取物对1,1-二苯基-2-苦基苯肼(DPPH)自由基的清除能力最高,达O.27±0.02μmol Trolox/mg,对胶原酶和酪氨酸酶也具有较高的抑制活性,IC50值分别为92.8 4-2.9μg/mL和185.4±5.3μg/mL.     

Quantification of wear,strain and heat energy consumption rates for sliding steel ball against diamond-like carbon coatings

Abstract

In this work, we evaluated the different energy consumption rates associated with the total frictional energy for a ball sliding on a flat surface. The energy generated by the sliding two bodies in contact is dissipated into the materials in various forms. The wear consumption energy for a steel ball against a diamond-like carbon surface was evaluated by the wear coefficient of the wear volume–energy input equation. The strain energy generated in the steel ball as a result of being made to slide under a certain load was calculated using the Hertzian theory. The chemical reaction energy was estimated based on iron oxidation. Finally, the frictional energy dissipated as heat was obtained by subtracting the wear and the strain energies from the total frictional energy.     

Preparation and Luminescence Spectra of Calcium- and Rare-Earth (R = Eu, Tb, and Pr)-Codoped α-SiAlON Ceramics

Rare-earth-doped oxynitride or nitride compounds have been reported to be luminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, we report the photoluminescence (PL) spectra of europium-, terbium-, and praseodymium-doped Ca-α-SiAlON ceramics. The highly dense ceramics were prepared by hot pressing at 1750°C for 1 h under 20 MPa in a nitrogen atmosphere. Europium-doped Ca-α-SiAlON displayed a single broad emission band peaking at λ= 550–590 nm depending on the europium concentration. The emission bands in the spectra of europium-doped Ca-α-SiAlONs were assigned to the allowed transition of Eu²⁺ from the lowest crystal field component of 4 f ⁶5 d to ⁸S_7/2 (4 f ⁷) ground-state level. The emission spectra of terbium- and praseodymium-doped Ca-α-SiAlON ceramics both consisted of several sharp lines, which were attributed to the ⁵D₄→⁷F _j ( j = 3, 4, 5, 6) transitions of Tb³⁺ and ³P₀→³H _j ( j = 3, 4, 5) transitions of Pr³⁺, respectively. In particular, the terbium-doped α-SiAlON ceramics showed a strong green emission among these phosphors.     

Experimental investigation of melt pool behaviour during selective laser melting by high speed imaging

Melt pool behaviour and the characteristics of the surrounding metal powder during selective laser melting (SLM) are captured using high-speed imaging, and the influence of the substrate temperature and the line building sequence on the formation of the built structure and the generation of spatter particles is experimentally investigated. The results indicate that the substrate temperature has a measurable effect on the formation of droplets and the generation of spatter particles, while the volume specific energy density of the process was the principal factor affecting the built structure.     

Inhibition of carbon fiber growth from naphthalene with halogens

The influence of HCl, Cl₂, Br₂ and I₂ on the vapor phase growth of carbon fibers from naphthalene was examined at 1100°C with the expectation of a promotive effect similar to H₂S. However, these halogen additives were found not to catalyse but to inhibit the growth. Employment of 1-chloronaphthalene as the source material also resulted in the remarkable suppression of fiber formation. The fibers obtained in the presence of the halogens exhibited highly pockmarked surfaces, due to deposition of soot-like carbon. In addition, the deposition was preferential at the growing end of the fiber, so that the diameter became thick progressively from root to tip. From these observations, the inhibition of the fiber growth with halogens was attributed to the accelerated decomposition of naphthalene into soot-like carbon.     

Influence of water vapor on the reduction of cuprous chloride to copper microfibers

Reduction of cuprous chloride has been examined in various atmospheres, mostly at 600°C, to produce copper microfibers that can be applied as a filler for electromagnetic interference shielding and electron conductive paste composites. The reduction with hydrogen resulted in formation of a large amount of copper films, but fine particles and short filaments were obtained when carbon black was mixed into the raw material. The most promising copper microfibers with dimensions of several mm length and 1–10 m thickness could be produced with the system CuCl — C — H₂O using argon as a carrier gas, where H₂ and CO formed then probably reduced the vaporized CuCl molecules. Introduction of hydrogen gas into this system increased the yield of copper microfibers, though they became more bent, curved and kinked in shape. However, the morphology of the microfibers is still acceptable as a filler.