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21.
(±) Sarkomycin ethyl ester has been prepared in four steps from ethyl acrylate. 相似文献
22.
LUO SHENGWU; AHMED SHAHEEN; ZRIBI MOHAMED 《IMA Journal of Mathematical Control and Information》1997,14(3):225-253
A redundant robot has more degrees of freedom than those neededto position the Robert end-effector uniquely. In a usual robotictask, only end-effector position trajectory is specified. Thejoint position trajectory is unknown, and it must be selectedfrom a self-motion manifold for a specified end-effector. Inmany situations, the robot dynamic parameters such as the linkmass, inertia, and joint viscous friction are unknown. The lackof knowledge of the joint trajectory and the dynamic parametersmake it difficult to control redundant robots. In this paper we show, through careful formulation of the problem,that the adaptative control of redundant robots can be addressedas a reference-velocity traking problem in the joint space.A control law ensures bounded estimation of the unknown dynamicparameters of the robot, and the convergence to zero of thevelocity traking error is derived. To ensure the joint motionon the self-motion manifold remains bounded, a homeomorphictransformation is found. This transformation decomposes thedynamics of the velocity tracking error into a cascade systemconsisting of the dynamics in the end-effector error coordinatesand the dynamics on the self-motion manifold. The dynamics onthe self-motion manifold is shown to be related to the conceptof zero dynamics. In the shown that, if the reference jointtrajectory is selected to optimize a certain type of objectivefunction, then stable dynamics on the self-motion manifold result.This ensures the overall stability of the adaptive system. Detailedsimulations are given to test the theoretical developments.The proposed adaptive scheme does not require measurements ofthe joint acceleration or the inversion of the inertia matrixof the robot. 相似文献
23.
R. Ben Hassen A. Ben Salah A. Kallel A. Daoud J. Jaud 《Journal of chemical crystallography》2002,32(11):427-430
CH3NH3CdBr3 crystallizes in the space group Ccm21, a = 13.693(1) Å, b = 7.906(1) Å, c = 6.886(1) Å, V = 745.46(15) Å3, Z = 4, D
x
= 3.42 Mg m–3. The structure of the title compound is one-dimensional consisting of infinite chains made of face sharing CdBr6 octahedra. The methylammonium groups are situated in the space between chains. The cations and anions are joined by hydrogen bonding. 相似文献
24.
MOHAMED SAÏDI 《Compositio Mathematica》1997,107(3):319-338
Let R be a discrete complete valuation ring, with algebraically closedresidue field. Let X be a semi-stable R-curve, with smooth generic fibre. In this paper we study tame coverings of X. 相似文献
25.
Amino acid and peptide esters protected by the PChd group can be deprotected cathodically under mild conditions. 相似文献
26.
Kamoun F Fguira IB Hassen NB Mejdoub H Lereclus D Jaoua S 《Applied biochemistry and biotechnology》2011,165(1):300-314
This study reports on the identification, characterization and purification of a new bacteriocin, named Bacthuricin F103,
from a Bacillus thuringiensis strain BUPM103. Bacthuricin F103 production began in the early exponential phase and reached a maximum in the middle of the
same phase. Two chromatographic methods based on high performance liquid chromatography and fast protein liquid chromatography
systems were used to purify Bacthuricin F103. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed that this
bacteriocin had a molecular weight of approximately 11 kDa. It also showed a wide range of thermostability of up to 80 °C
for 60 min and a broad spectrum of antimicrobial activity over a pH range of 3.0–10.0. This bacteriocin was noted, and for
the first time, to exhibit potent antimicrobial activity against Agrobacterium subsp. strains, the major causal agents of crown gall disease in tomato and vineyard crops, and against several challenging
organisms in food, such as Listeria monocytogenes and Bacillus cereus. Complete killing with immediate impact on cells was observed within a short period of time. The sequence obtained for Bacthuricin
F103 by direct N-terminal sequencing shared considerable homology with hemolysin. Bacthuricin F103 was noted to act through
the depletion of intracellular ions, which suggest that the cell membrane was a possible target to Bacthuricin F103. 相似文献
27.
An easy regio‐ and stereoselective synthesis of new nitrogenous molecules 2a–e was successfully realized via an effective coupling reaction of diethyl (E)‐1‐(bromomethyl)‐2‐cyanovinylphosphonate 1 with various secondary amines in methanol. Hence, the use of less and more bulky secondary amines gives rise, respectively, to the successive (SN2′) substitution–isomerization and (SN2) substitution derivatives 2a–c and 2d–e . Moreover, the addition of tertiary amines to 1 in the same reaction conditions, leads exclusively to the rearranged vinyl ether 3 in good yields. 相似文献
28.
Vito VeceKhadija Ben Hadj Hassen Sylvain Antoniotti Elisabet Duñach 《Tetrahedron letters》2012,53(38):5102-5105
We described herein a Sn(NTf2)4-catalysed cyclisation of gem-(dialkoxymethyl)-1,6-dienes and derivatives where cyclohexane or tetrahydrofuran rings are formed following either a 6-enexo-endo-trig process or a 5-exo-trig process, respectively, depending on substitution patterns. The latter process features an unusual dealkylative ether cyclisation, triggered by the strong Lewis acid character of the tin(IV) triflimidate catalyst. 相似文献
29.
30.
Algebraic decay and variable speeds in wavefront solutions of a scalar reaction-diffusion equation 总被引:1,自引:0,他引:1
Wavefront solutions of scalar reaction-diffusion equations havebeen intensively studied for many years. There are two basiccases, typified by quadratic and cubic kinetics. An intermediatecase is considered in this paper, namely, ul = uxx + u2(1 u). It is shown that there is a unique travelling-wave solution,with a speed 1/2, for which the decay to zero ahead of the waveis exponential with x. Moreover, numerical evidence is presentedwhich suggests that initial conditions with such exponentialdecay evolve to this travelling-wave solution, independentlyof the half-life of the initial decay. It is then shown thatfor all speeds greater than 1/2 there is also a travelling-wavesolution, but that these faster waves decay to zero algebraically,in proportion to 1/x. The numerical evidence suggests that initialconditions with such a decay rate evolve to one of these fasterwaves; the particular speed depends in a simple way on the detailsof the initial condition. Finally, initial conditions decayingalgebraically for a power law other than 1/x are considered.It is shown numerically that such initial conditions evolveeither to an algebraically decaying travelling wave, or in somecases to a wavefront whose shape and speed vary as a functionof time. This variation is monotonic and can be quite pronounced,and the speed is a function of u as well as of time. Using asimple linearization argument, an approximate formula is derivedfor the wave speed which compares extremely well with the numericalresults. Finally, the extension of the results to the more generalcase of ul = uxx + um(1 u), with m > 1, is discussed. 相似文献