Computational roles for dopamine in behavioural control

Neuromodulators such as dopamine have a central role in cognitive disorders. In the past decade, biological findings on dopamine function have been infused with concepts taken from computational theories of reinforcement learning. These more abstract approaches have now been applied to describe the biological algorithms at play in our brains when we form value judgements and make choices. The application of such quantitative models has opened up new fields, ripe for attack by young synthesizers and theoreticians.     

C*-Algebras with Dense Nilpotent Subalgebras

In a beautiful result, Herrero (D. A. Herrero, ‘Normallimits of nilpotent operators’, Indiana Univ. Math. J.23 (1973/74) 1097–1108) showed that a normal operatoron l² lies in the closure of the set of nilpotent operatorsif and only if its spectrum is connected and contains zero.In the quest for an automatic continuity result for algebrahomomorphisms between C* -algebras, Dales showed that, if adiscontinuous algebra homomorphism : A u exists between C*-algebrasA and u, and if (A) is dense in u, then there is a C*-algebrau₂ with a dense subalgebra N u² such that every x N is quasinilpotent(see p. 685 of H. G. Dales, Banach algebras and automatic continuity,London Mathematical Society Monographs 24, Oxford UniversityPress, 2001). (A discontinuous homomorphism ₂: A₂ u₂ can bedefined with the same basic properties as , but the revisedtarget space u₂ has a dense subalgebra consisting of quasinilpotentelements.) As remarked by Dales, no such C*-algebra was thenknown; but here we present one. Indeed, using the full powerof Herrero's result, one may arrange that every x N is nilpotent.The C*-algebra is constructed in a ‘neat’ way; itis most naturally constructed as a non-separable, concrete C*-algebraof operators on a separable Hilbert space K but one can arrangethat the algebra u itself be separable if desired. 2000 MathematicsSubject Classification 47C15, 46H40 (primary), 47A10, 46L06,46L05, 46H35 (secondary).     

模糊滑动控制的一般方法(英文)

陈述了一种新的模糊逻辑控制方法,它可消除滑动控制所固有的抖动问题。方法的推导是将多开关滑动控制问题简化成等效的单开关问题。控制规律显示它是一种模糊滑动控制的一般方法。文献中的其他方法可由此法导出。模糊推理规则由两个输入变量组成。第一个输入变量是系统状态到所预定的状态空间中的超平面之间的方向距离;第二个输入变量的选择可根据应用而定,例如方向距离的导数、控制设计者所感兴趣的特定变量,或者某些状态变量的加权之和。这个新方法易于在高阶系统中实现,并且可以直接而明确地控制系统的动态过程。它消除了滑动控制和经典模糊滑动控制中的抖动问题。此外。新方法比其他类似方法的控制要简单。稳定性和性能分析显示了此法的有效性。此法已用于一带有典型驱动和反馈传感器的工业直流电机的位置控制之中。     

BA和激素对‘Bonny Best’试管番茄愈伤组织形态发生的影响

用’Bonny Best’番茄品种的子叶和下胚轴作为外植体,在MS附加不同水平和比率的BA和2,4—D(或NAA)或IAA的培养基中,愈伤组织形态发生的情况是不同的。MS+BA4.44μM+2,4-D10μM(子叶),MS+BA0.44-4.44μM+2,4-D1—5μM(下胚轴)使外值体产生淡黄色疏松的愈伤组织,而且生长迅速。若2,4-D浓度低于5μM(子叶)或高于5μM(下胚轴)时,外植体形成白色紧密的愈伤组织,而且生长缓慢,固定2,4-D的浓度,BA浓度由高到低,所形成的愈伤组织的结构由紧密向疏松变化。愈伤组织的液体培养中也出现了类似现象。把愈伤组织转移到生茎培养基中,白色紧密的愈伤组织形成茎较为容易,培养21天后,茎的分化即开始。而疏松的愈伤组织的形态发生则经过了黄色疏松、深褐色胶状到白色紧密的变化。茎的分化出现较晚。愈伤组织培养时生长调节剂的水平对茎的分化有着直接的影响。较高水平的BA(22.2—44.4μM)+NAA10-40μM有利于茎的分化。把子叶和下胚轴切段培养在MS+BA22.2-44.4μM+IAA1-5μM的生茎培养基上,24—60天后,70％以上的外植体正常分化并伸长成茎,生枝率每个切段为3—4个。转移到MS培养基上,形成正常的带根幼苗。把下胚轴切段直接培养在没有激素的MS培养基上,三周后,45.8％的下胚轴形成正常幼苗,出枝率为1.0。把这些幼苗移栽到温室     

Sloping convection: A paradigm for large-scale waves and eddies in planetary atmospheres?

In laboratory studies and associated theoretical and numerical work covering a very wide range of conditions (as specified by the key dimensionless parameters of the systems used) the phenomenon of sloping convection in rotating fluids can manifest itself in one of several spatial forms (waves, closed eddies, and combinations thereof), but all with strong local gradients (fronts, jet streams) and exhibiting various types of temporal behavior [steady, periodic vacillation, aperiodic (geostrophic) turbulence]. These general properties were first discovered in cylindrical (annular) systems, but they do not depend critically on geometry; differences between spherical and cylindrical systems are largely to be found in quantitative details. In all cases, the raison d'e tre of sloping convection is horizontal advective transfer, a process accompanied by upward advective heat transfer, which affects and may control vertical potential density gradients. It has been argued that sloping convection is the basic dynamical process underlying a wide variety of large-scale flow phenomena seen in planetary atmospheres (e.g., irregular waves in the Earth's atmosphere, regular waves in the Martian atmosphere, the Jovian Great Red Spot and other long-lived eddies seen in the atmospheres of the giant planets). In this review the extent to which this paradigm is upheld in the atmospheres of the major planets by recent work is discussed.     

Simple high-performance liquid chromatographic method for the determination of medroxyprogesterone acetate in human plasma

The high-performance liquid chromatographic (HPLC) method was developed as a simple, reliable alternative to available methods for measuring plasma concentrations of medroxyprogesterone acetate (MPA). The HPLC method has been successfully automated and is suitable for the rapid, inexpensive analysis of large batches of plasma samples. The best approach involves a solvent extraction followed by HPLC separation and analysis. MPA can be efficiently extracted, at all pH values, by nonpolar solvents. The Spherisorb 5-ODS2 HPLC column provides excellent separation of MPA from endogenous steroids of similar structure and from extraneous plasma blank peaks. A batch of 30-40 samples can be prepared by HPLC analysis in 2-3 hours, with a chromatographic run time of 10 minutes/sample. Calibration curves between 5-250 ng/ml show a good correlation between peak height ratio and MPA concentration, even at low levels. Plasma concentrations of MPA in patients receiving 1 g/day were between 12.6-270 ng/ml in this study, suggesting that the sensitivity of this method, 10 ng/ml, is sufficient for monitoring therapeutic concentrations of MPA. The results show a wide individual variation in plasma concentrations following similar dosing schedules--a finding reported by other workers.     

Synthesis of a 1,8-naphthyridin-5-one derivative via an intramolecular 1,3-dipolar cycloaddition reaction

Synthesis of a 1,8-naphthyridin-5-one derivative [(5,6,7,8-tetrahydro-(3-chloro-6-hydroxymethyl-8-methyl)-1,8-naphthyridin-5-one (9) ] is described starting from 2-chloronicotinic acid using an intramolecular 1,3-dipolar cycloaddition reaction as the key step.     

Kinetics and Mechanism of the Ferrate Oxidation of Thiosulfate and Other Sulfur-Containing Species

The kinetics of the reaction of ferrate, FeO(4)(2-), with several sulfur-containing species in aqueous media have been investigated, and the results are reported. It was found that, when the reductant is in excess, ferrate rapidly oxidizes thiosulfate to sulfite, benzenesulfinate to benzenesulfonate, methionine to its corresponding sulfoxide, and dimethyl sulfoxide to dimethyl sulfone. The rate law for each reaction is first order with respect to each reactant and first order with respect to the hydrogen ion concentration. A mechanism for each oxidation reaction is discussed.