排序方式: 共有199条查询结果,搜索用时 15 毫秒
41.
Karl Lundengård Jonas Österberg Sergei Silvestrov 《Methodology and Computing in Applied Probability》2018,20(4):1417-1428
The value of the Vandermonde determinant is optimized over various surfaces, including the sphere, ellipsoid and torus. Lagrange multipliers are used to find a system of polynomial equations which give the local extreme points in its solutions. Using Gröbner basis and other techniques the extreme points are given either explicitly or as roots of polynomials in one variable. The behavior of the Vandermonde determinant is also presented visually in some interesting cases. 相似文献
42.
Tetrakis(selenodiazole)porphyrazine and its vanadyl (VO2+) complex have been prepared and characterized by FT-IR, UV–vis, and MALDI-MS. The magnetic properties of the complex have
been investigated by EPR spectroscopy. 相似文献
43.
Tero Taipale Monika Österberg Antti Nykänen Janne Ruokolainen Janne Laine 《Cellulose (London, England)》2010,17(5):1005-1020
Different types of microfibrillated cellulose (MFC) and fines suspensions were produced, characterized, and then added to
a papermaking pulp suspension. High and medium molar mass cationic polyelectrolytes were used as fixatives. The drainage behavior
of the pulp suspensions with additives were evaluated against the strength properties of hand sheets made thereof. The effects
of salt concentration, pH, fixative type, dosage and type of fibrillar material on drainage were examined. All the MFC and
fines samples produced had clearly different properties due to their dissimilar production methods, and they also introduced
specific responses on the measured drainage and paper strength. Generally, the addition of MFC decreased the drainage rate
of pulp suspension and increased the strength of paper. However, it was shown that by optimum selection of materials and process
conditions an enhancement of the strength properties could be achieved without simultaneously deteriorating the drainage. 相似文献
44.
In this study, we work on the traveling salesperson problems and bottleneck traveling salesperson problems that have special
matrix structures and lead to polynomially solvable cases. We extend the problems to multiple objectives and investigate the
properties of the nondominated points. We develop a pseudo-polynomial time algorithm to find a nondominated point for any
number of objectives. Finally, we propose an approach to generate all nondominated points for the biobjective case. 相似文献
45.
Carbonyl-metal (M:Cr, Mo, W) derivatives of 4-substituted pyridines [4-methylpyridine (4-mp), 4-tert-butylpyridine (4-tbp)
and 4-dimethylaminopyridine (4-dmap)] where the metal center is bonded to the nitrogen atom of the substituted pyridine ring
are described. The organometallic complexes, M(CO)5L, were synthesized by either the direct reaction of the metal hexacarbonyls or by the thermal substitution of M(CO)5(THF) with the pyridine ligands; 4-methylpyridine (1), 4-tert-butylpyridine (2), 4-dimethylaminopyridine (3). The reported complexes were purified by column chromatography and recrystallization. The complexes were all characterized
in solution by elemental analysis, MS, ir , 1H-nmr and 13C-nmr spectroscopies. 相似文献
46.
Chemical polymerization of acrylamide at room temperature was examined by using thioglycolic acid-cerium (IV) sulfate and
thioglycolic acid-KMnO4 redox systems in acid aqueous medium. Water soluble polyacrylamides containing thioglycolic acid end groups were synthesized.
The effects of the molar ratio of acrylamide to Ce(IV) n
AAm
/n
Ce(IV)
, the polymerization time, the temperature, the monomer concentration, the molar ratio of cerium (IV) sulfate to thioglycolic
acid and the concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. Lower molar ratios
of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight
of polymer. The increase of reaction temperature from 20 to 70°C resulted in a decrease in the yield but generally resulted
in a constant value for the molecular weight of polymer. With increasing polymerization time, the yield and molecular weight
of polymer did not change substantially. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions respectively in the
polymerization reaction. The existence of Ce(III) ion bound to polymer was investigated by UV-visible spectrophotometry and
fluoresce measurements. The amount of Mn(II) incorporated into the polymer was determined using graphite furnace atomic absorption
spectrometry. The mechanism of this phenomenon is discussed. 相似文献
47.
Barbara M. Casari Elisabeth Öberg Vratislav Langer 《Journal of chemical crystallography》2007,37(2):135-140
Synthesis and crystal structure of a trichromium(VI) decaoxide compound, α–(NH4)2Cr3O10, is reported. The crystal structure has been determined from three dimensional X-ray data collected at low temperature, 173 K.
The structure is isomorphous with its Rb and Cs trichromate analogues, orthorhombic, space group Pbca, with a = 11.2558(3), b = 9.3193(3), c = 18.9819(5) ? and Z = 8. The title compound is composed of discrete [Cr3O10]2– chains held together by the counter ion charge and a hydrogen bonding network. The different conformations adopted by trichromate
anion within its ammonium, alkali and organic salts are discussed. 相似文献
48.
Summary We introduce the concepts of γ-semi-open set, γs-set, γs-set, generalized γs-set, generalized γs-set, semi-T1γspace and semi-R0γspace by using γ-open-sets. 相似文献
49.
İ K Altınel S Özekici O Feyziog̃lu 《The Journal of the Operational Research Society》2001,52(8):937-944
We consider the component testing problem of a device that is designed to perform a mission consisting of a sequence of stages. Once a stage is over, the device is overhauled to replace all failed components before the next stage starts to improve mission reliability. The components fail exponentially where the failure rate depends on the stage of the mission. The reliability structure of the device involves a series connection of redundant subsystems. The optimal component testing problem is formulated as a semi-infinite linear programme. We present an algorithmic procedure to compute optimal test times based on the column generation technique, and illustrate it with numerical results. 相似文献
50.
A similarity analysis was performed to investigate the laminar boundary-layer flow in the presence of a transverse magnetic
field over a down-pointing and spinning cone with mixed thermal boundary conditions. Boundary layer velocity and temperature
profiles were determined numerically for various values of the magnetic and spin parameters and the Prandtl number. The spin
of the cone compresses the velocity profiles towards the surface by inducing an upward flow and decreases the surface temperature.
The magnetic field suppresses the velocity profiles and increases the surface temperature. A transformation relating the similarity
solutions of the boundary-layer velocity and temperature profiles associated with different values of the mixed thermal boundary
condition parameter was obtained. 相似文献