A study of some 1-alkyl-2,3-dihydroimidazo[1,2-a]benzimidazoles

A series of 1-alkyl-7-nitro (and 7-amino)-2,3-dihydroimidazo[1,2-α]benzimidazoles has been prepared. Similarly, a series of 1-alkyl-2,3-dihydroimidazo[1,2-α]benzimidazoles has been prepared. The prototropic tautomerism of this system has been studied. The site of electrophilic attack (alkylation) has been examined. 1-Alkylation takes place under strongly basic conditions and 9-alkylation occurs under neutral conditions.     

Band effects and the dipole interaction between two adatoms on a metal surface

The contribution of band effects to the adatom interaction energy is investigated to second order in perturbation theory. These are found to bring an important correction to the dipole law derived recently by Kohn and Lau.     

Time's arrow in an oscillating universe

In view of the time-symmetric nature of the laws of physics, time asymmetry in the universe must arise from “initial” conditions. A fully time-symmetric oscillating model is presented which exists in a highly compressed, highly ordered state att=0 and evolves forward, in the thermodynamic sense, as ∣t ∣ increases. This model offers the possibility of accounting for several fundamental and puzzling aspects of our universe, including matter-antimatter asymmetry, the large entropy per baryon, primordial density enhancements sufficient to form galaxies, and large-scale homogeneity.     

Perturbations of subalgebras of type II1 factors

In this paper we consider two von Neumann subalgebras and of a type II₁ factor . For a map φ on , we define

     

Natural product based inhibitors of the thioredoxin-thioredoxin reductase system

Spiroketal naphthodecalins are readily assembled by Barton's base mediated Ullmann binaphthyl ether coupling, Dakin reactions and hypervalent iodine spirocyclization. The core structures can be further diversified by enone addition and Stille coupling reactions. Nanomolar inhibitors for the Trx/TrxR redox control system were prepared by this approach and compared to series of natural product isolates. Cytotoxicity in MCF-7 cell assays ranged from an IC50 of 1.6 to >100 microM.     

Structural complexity in gallium under high pressure: relation to alkali elements

Ga-II, the stable phase of Ga between 2 and 10 GPa at room temperature, is shown to have a complex 104-atom orthorhombic structure. A new phase, Ga-V, is found between 10 and 14 GPa, with a rhombohedral hR6 structure. Ga-II has a modulated layer structure like those recently reported for Rb-III and Cs-III, with similar 8- and 10-atom a-b layers stacked along the c axis in the sequence 8-10-8-8-10-8-8-10-8-8-10-8. The cI16 structure of Li and Na can be understood as a stacking of very similar 8-atom layers. It is suggested that a Hume-Rothery mechanism contributes to the occurrence of these complex structures in such different metals.     

The effect of a concurrent cognitive task on cortical potentials evoked by unpredictable balance perturbations

Background  

Although previous studies suggest that postural control requires attention and other cognitive resources, the central mechanisms responsible for this relationship remain unclear. To address this issue, we examined the effects of altered attention on cortical activity and postural responses following mechanical perturbations to upright stance. We hypothesized that cortical activity would be attenuated but not delayed when mechanical perturbations were applied during a concurrent performance of a cognitive task (i.e. when attention was directed away from the perturbation). We also hypothesized that these cortical changes would be accompanied by alterations in the postural response, as evidenced by increases in the magnitude of anteroposterior (AP) centre of pressure (COP) peak displacements and tibialis anterior (TA) muscle activity. Healthy young adults (n = 7) were instructed to continuously track (cognitive task) or not track (control task) a randomly moving visual target using a hand-held joystick. During each of these conditions, unpredictable translations of a moving floor evoked cortical and postural responses. Scalp-recorded cortical activity, COP, and TA electromyographic (EMG) measures were collected.     

Studies on pyridazine azide cyclisation reactions

Reaction of sodium azide with 4-methyl-3,5,6-tribromopyridazine results in the formation of 3,5,6-triazide intermediate which could cyclise to give two possible bicyclic products while ab initio calculations show that the formation of a tricyclic compound is extremely energetically unfavourable. However, experimentally, only one major product is isolated. The structure of this unstable product has been conclusively established by X-ray crystallography as 3,5-diazido-4-methyl[1,5-b]tetrazolopyridazine confirming theoretical predictions.     

Effect of polymer surface activity on cavitation nuclei stability against dissolution

The persistence of acoustic cavitation in a pulsed wave ultrasound regime depends upon the ability of cavitation nuclei, i.e., bubbles, to survive the off time between pulses. Due to the dependence of bubble dissolution on surface tension, surface-active agents may affect the stability of bubbles against dissolution. In this study, measurements of bubble dissolution rates in solutions of the surface-active polymer poly(propyl acrylic acid) (PPAA) were conducted to test this premise. The surface activity of PPAA varies with solution pH and concentration of dissolved polymer molecules. The surface tension of PPAA solutions (55-72 dynes/cm) that associated with the polymer surface activity was measured using the Wilhelmy plate technique. Samples of these polymer solutions then were exposed to 1.1 MHz high intensity focused ultrasound, and the dissolution of bubbles created by inertial cavitation was monitored using an active cavitation detection scheme. Analysis of the pulse echo data demonstrated that bubble dissolution time was inversely proportional to the surface tension of the solution. Finally, comparison of the experimental results with dissolution times computed from the Epstein-Plesset equation suggests that the radii of residual bubbles from inertial cavitation increase as the surface tension decreases.     

Noise spectroscopy and interlayer phase coherence in bilayer quantum Hall systems

Bilayer quantum Hall systems develop strong interlayer phase coherence when the distance between layers is comparable to the typical distance between electrons within a layer. The phase-coherent state has until now been investigated primarily via transport measurements. We argue here that interlayer current and charge-imbalance noise studies in these systems will be able to address some of the key experimental questions. We show that the characteristic frequency of current noise is that of the zero wave vector collective mode, which is sensitive to the degree of order in the system. Local electric potential noise measured in a plane above the bilayer system, on the other hand, is sensitive to finite-wave-vector collective modes and, hence, to the soft-magnetoroton picture of the order-disorder phase transition.