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81.
Kannan S Wesley SD Ruba A Rajalakshmi AR Kumaragurubaran K 《Natural product research》2007,21(5):469-472
To meet the strong demand of colchicine an attempt is made to optimize the solvent system for isolation of colchicine. Gloriosa superba dried seed powder was extracted by using different solvents. Maximum yield of colchicine was obtained when extracted with water and alcohol in the ratio of 50 : 50. 相似文献
82.
Group theory can be used to model and synthesize the neighborhood of Traveling Salesman tours reachable through k-OPT exchanges. A primary concept is that a dihedral group action partitions the sets of cut arcs so that k-OPT exchanges of orbital elements are conjugate. Also presented is a method to produce all k-OPT exchanges for a given set of cut arcs. 相似文献
83.
Wesley R. Burghardt 《Journal of Polymer Science.Polymer Physics》1999,37(7):617-617
84.
Chunbiao Li J. C. Sprott Wesley Thio 《Journal of Experimental and Theoretical Physics》2014,118(3):494-500
A hyperchaotic system with an infinite line of equilibrium points is described. A criterion is proposed for quantifying the hyperchaos, and the position in the three-dimensional parameter space where the hyperchaos is largest is determined. In the vicinity of this point, different dynamics are observed including periodicity, quasi-periodicity, chaos, and hyperchaos. Under some conditions, the system has a unique bistable behavior, characterized by a symmetric pair of coexisting limit cycles that undergo period doubling, forming a symmetric pair of strange attractors that merge into a single symmetric chaotic attractor that then becomes hyperchaotic. The system was implemented as an electronic circuit whose behavior confirms the numerical predictions. 相似文献
85.
86.
Louis T. Weinstock C. J. Wesley Wiegand C. C. Cheng 《Journal of heterocyclic chemistry》1977,14(7):1261-1262
1,5-Dideazariboflavin, an analog of riboflavin containing the original conjugated double bond system between positions 1 and 5, was synthesized by the condensation of 4,5-dimethyl- N-ribitylanthranilaldehyde and the sodium salt of 2,4,6-piperidinetrione. 相似文献
87.
Wesley H. Monillas Glenn P. A. Yap Klaus H. Theopold 《Journal of chemical crystallography》2011,41(3):415-418
Abstract
The complex (bis(2,6-diisopropylphenyl)pentane-2,4-ketiminato)(9,10-dihydro-9,10-(ethenediolato)anthracene)(tetrahydrofuran)chromium(III) (1) has been synthesized and structurally characterized. Complex 1 crystallizes in the spacegroup Cc with the crystal cell parameters a = 22.285 (3) ?, b = 9.3317 (13) ?, c = 40.782 (6) ?, β = 99.338 (3)°, V = 8369 (2) ?3, and Z = 8. Two symmetry unique complex molecules were located in the asymmetric unit making Z′ = 2. The chromium atoms display square pyramidal coordination with THF located in the axial position. The previously neutral α-diketone moiety has been reduced by two electrons to an enediolate group with a corresponding increase of oxidation state of the chromium center. 相似文献88.
William D. Banks Derrick N. Hart Pieter Moree C. Wesley Nevans 《Monatshefte für Mathematik》2009,157(4):303-322
In 1984, G. Robin proved that the Riemann hypothesis is true if and only if the Robin inequality σ(n) < e
γ
n log log n holds for every integer n > 5040, where σ(n) is the sum of divisors function, and γ is the Euler–Mascheroni constant. We exhibit a broad class of subsets of the natural numbers such that the Robin inequality holds for all but finitely many . As a special case, we determine the finitely many numbers of the form n = a
2 + b
2 that do not satisfy the Robin inequality. In fact, we prove our assertions with the Nicolas inequality n/φ(n) < e
γ
log log n; since σ(n)/n < n/φ(n) for n > 1 our results for the Robin inequality follow at once.
相似文献
89.
William D. Banks Derrick N. Hart Pieter Moree C. Wesley Nevans 《Monatshefte für Mathematik》2009,1(1):303-322
In 1984, G. Robin proved that the Riemann hypothesis is true if and only if the Robin inequality σ(n) < e
γ
n log log n holds for every integer n > 5040, where σ(n) is the sum of divisors function, and γ is the Euler–Mascheroni constant. We exhibit a broad class of subsets S{\mathcal {S}} of the natural numbers such that the Robin inequality holds for all but finitely many n ? S{n \in \mathcal {S}} . As a special case, we determine the finitely many numbers of the form n = a
2 + b
2 that do not satisfy the Robin inequality. In fact, we prove our assertions with the Nicolas inequality n/φ(n) < e
γ
log log n; since σ(n)/n < n/φ(n) for n > 1 our results for the Robin inequality follow at once. 相似文献
90.
A number of subtle and confusing issues are addressed concerning large amplitude motion (LAM) coordinates (chi) for internal molecular motions, using the methyl rotation in acetaldehyde (CH(3)CHO) as a model problem. If the LAM coordinate is chosen to be one of the H-C-C-O dihedral angles rho(1), rho(2), or rho(3), it lacks the required 2pi3 periodicity, and its use is thus undesirable. An excellent local internal coordinate for this model problem is tau(3)=13(rho(1)+rho(2)+rho(3)-2pi). A similarly good but nonlocal coordinate for the adiabatic approximation of internal rotation is provided by the intrinsic reaction coordinate s. Comparison of the mass-independent V(0)(tau(3)) and the mass-dependent V(0)(s) internal rotation curves shows that the two are virtually identical for the parent isotopolog of acetaldehyde. A unified internal coordinate projection scheme for determining complementary vibrational frequencies and subsequently V(ZPVE)(chi) along a path for LAM has been formulated, where V(ZPVE)(chi) is the zero-point vibrational energy correction to the internal rotation curve. In addition to its simplicity, the projection scheme developed for a distinguished reaction path generated by constrained optimizations is appealing because the vibrational frequencies along the LAM path are invariant to chemically meaningful choices of the internal coordinates for the complementary modes. 相似文献