Tetrabromobutatriene: completing the perhalocumulene series

[structure: see text] Tetrabromobutatriene, C(4)Br(4), can be prepared directly from dibromobutadiyne by reaction with Br(2) at -25 degrees C in concentrated hexanes solution. The cumulene precipitates out of the reaction mixture as a yellow powder. Under palladium-catalyzed coupling conditions, C(4)Br(4) can undergo allylic rearrangement, giving a mixture of products, including some with butenyne backbones. However, in furan solution, C(4)Br(4) reacts cleanly at its central double bond to give the furan Diels-Alder adduct. Under Suzuki conditions, this adduct reacts at the furan double bond rather than at bromide.     

The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals,Mirounga angustirostris

Changes in the diving behavior of individual free-ranging juvenile northern elephant seals, Mirounga angustirostris, exposed to the acoustic thermometry of the ocean climate (ATOC) sound source were examined using data loggers. Data loggers were attached to the animals and measured swim speed, maximum depth of dive, dive duration, surface interval, descent and ascent rate, and descent and ascent angle along with sound pressure level (SPL). The ATOC sound source was at a depth of 939 m and transmitted at 195 dB re: 1 microPa at 1 m centered at 75 Hz with a 37.5-Hz bandwidth. Sound pressure levels (SPL) measured at the seal during transmissions averaged 128 dB and ranged from 118 to 137 dB re: 1 microPa for the 60-90 Hz band, in comparison to ambient levels of 87-107 dB within this band. In no case did an animal end its dive or show any other obvious change in behavior upon exposure to the ATOC sound. Subtle changes in diving behavior were detected, however. During exposure, deviations in descent rate were greater than 1 s.d. of the control mean in 9 of 14 seals. Dive depth increased and descent velocity increased in three animals, ascent velocity decreased in two animals, ascent rate increased in one animal and decreased in another, and dive duration decreased in only one animal. There was a highly significant positive correlation between SPL and descent rate. The biological significance of these subtle changes is likely to be minimal. This is the first study to quantify behavioral responses of an animal underwater with simultaneous measurements of SPL of anthropogenic sounds recorded at the animal.     

Precursor film controlled wetting of Pb on Cu

Wetting in a system where the kinetics of drop spreading are controlled by the rate of formation of a precursor film is modeled for the first time at the atomistic scale. Molecular dynamics simulations of Pb(l) wetting Cu(111) and Cu(100) show that a precursor film of atomic thickness evolves and spreads diffusively. This precursor film spreads significantly faster on Cu(111) than on Cu(100). For Cu(100), the kinetics of drop spreading are dramatically decreased by slow advancement of the precursor film. Slow precursor film kinetics on Cu(100) are partly due to the formation of a surface alloy at the solid-liquid interface which does not occur on Cu(111).     

Polyclonal-based ELISA for the identification of cyclohexanedione analogs that inhibit maize acetyl coenzyme-A carboxylase

Cyclohexanedione herbicides inhibit monocotyledonous acetyl coenzyme-A carboxylase (ACCase; E.C. 6.4.1.2.), which catalyzes the first committed step in fatty acid biosynthesis. Although the target site has been identified, little is known about the mechanisms involved in herbicide binding. An immunological study was undertaken to create a model to better characterize the herbicide-enzyme interaction. Cyclohexanedione-specific antiserum was raised in New Zealand white rabbits by immunizing them with a cyclohexanedione analog-bovine serum albumin conjugate. Two indirect enzyme-linked immunosorbent assays (ELISA) were developed using 2 different cyclohexanedione analogs conjugated to ovalbumin as coating conjugates. Nineteen cyclohexanedione analogs, 13 active ACCase inhibitors, and 6 inactive analogs were tested for their ability to compete with both coating conjugates for antiserum binding. All active ACCase inhibitors were observed to compete with both coating conjugates, whereas all inactive analogs failed to compete with at least one coating conjugate. On the basis of these results, the immunological model could be used to distinguish all active ACCase inhibitors from inactive analogs using the 2 ELISAs sequentially.     

Observation of diffractive b-quark production at the fermilab tevatron

We report a measurement of the fraction of b quarks produced diffractively in &pmacr;p collisions at sqrt[s] = 1.8 TeV. Diffraction is identified by the absence of particles in a forward pseudorapidity region. From events with an electron of transverse momentum 9.5相似文献   

Diffractive dijets with a leading antiproton in &pmacr;p collisions at sqrt

We report results from a study of events with a leading antiproton of beam momentum fraction 0.9057 GeV. Using the dijet events, we evaluate the diffractive structure function of the antiproton and compare it with expectations based on results obtained in diffractive deep inelastic scattering experiments at the DESY ep collider HERA.     

Effect of temperature on rectified diffusion during ultrasound-induced heating

Experimental observations of delayed-onset cavitation during ultrasound insonation have been suggested as being caused by a change in the size distribution of the bubble population due to rectified diffusion. To investigate this hypothesis, a single bubble model is used here to explore the effect of heating and the subsequent elevated temperatures on the rectified diffusion process. Numerical solution of the model, which includes the temperature dependences of seven relevant physical parameters, allows quantification of the change in the pressure threshold for rectified diffusion, as well as the importance of the bulk liquid saturation concentration in determining bubble evolution. Although elevated temperatures and liquid supersaturation reduce the rectified diffusion threshold, it remains coincident with the inertial cavitation thresholds at submicron bubble sizes at all temperatures. This observation suggests that changes in the nucleation environment, rather than bubble growth due to rectified diffusion, is a more likely cause of delayed-onset cavitation events.