Third Power Of Time Research Articles

Phenomenological Inferences on the Kinetics of a Mechanically Activated Knoevenagel Condensation: Understanding the "Snowball" Kinetic Effect in Ball Milling.

We focus on understanding the kinetics of a mechanically activated Knoevenagel condensation conducted in a ball mill, that is characterized by sigmoidal kinetics and the formation of a rubber-like cohesive intermediate state coating the milling ball. The previously described experimental findings are explained using a phenomenological kinetic model. It is assumed that reactants transform into products already at the very first collision of the ball with the wall of the jar. The portion of reactants that are transformed into products during each oscillation is taken to be a fraction of the amount of material that is trapped between the ball and the wall of the jar. This quantity is greater when the reaction mixture transforms from its initial powder form to the rubber-like cohesive coating on the ball. Further, the amount of reactants processed in each collision varies proportionally with the total area of the layer coating the ball. The total area of this coating layer is predicted to vary with the third power of time, thus accounting for the observed dramatic increase of the reaction rate. Supporting experiments, performed using a polyvinyl acetate adhesive as a nonreactive but cohesive material, confirm that the coating around the ball grows with the third power of time.

Activation and co-ordination of InsP3-mediated elementary Ca2+ events during global Ca2+ signals in Xenopus oocytes.

1. The activation of elementary calcium release events ('puffs') and their co-ordination to generate calcium waves was studied in Xenopus oocytes by confocal linescan imaging together with photorelease of inositol 1,4,5-trisphosphate (InsP3) from a caged precursor. 2. Weak photolysis flashes evoked no responses or isolated calcium puffs, whereas flashes of increasing strength evoked more frequent puffs, often occurring in flurries as abortive waves, and then a near-simultaneous calcium liberation originating at multiple sites. The numbers of sites activated increased initially as about the fourth power of photoreleased [InsP3]. 3. Following repeated, identical photolysis flashes, puffs arose after stochastically varying latencies of a few hundred milliseconds to several seconds. The cumulative number of events initially increased as about the third power of time. No rise in free [Ca2+] was detected preceding the puffs, suggesting that this co-operativity arises through binding of multiple InsP3 molecules, rather than through calcium feedback. 4. The mean latency to onset of calcium liberation shortened as about the square of the flash strength, and the dispersion in latencies between events reduced correspondingly. 5. Weak stimuli often evoked coupled puffs involving adjacent sites, and stronger flashes evoked saltatory calcium waves, propagating with non-constant velocity. During waves, [Ca2+] rose slowly between puff sites, but more abruptly at active sites following an initial diffusive rise in calcium. 6. Initial rates of rise of local [Ca2+] at release sites were similar during puffs and release induced by much (> 10-fold) greater [InsP3]. In contrast, macroscopic calcium measurements averaged over the scan line showed a graded dependence of rate of calcium liberation upon [InsP3], due to recruitment of additional sites and decreasing dispersion in activation latencies. 7. We conclude that the initiation of calcium liberation depends co-operatively upon [InsP3] whereas the subsequent regenerative increase in calcium flux depends upon local calcium feedback and is largely independent of [InsP3]. Wave propagation is consistent with the diffusive spread of calcium evoking regenerative liberation at heterogeneous discrete sites, the sensitivity of which is primed by InsP3.

Allometry and cirque evolution

Research Article| September 01, 1981 Allometry and cirque evolution GREG A. OLYPHANT GREG A. OLYPHANT 1Department of Geography, Indiana University, Bloomington, Indiana 47405 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1981) 92 (9): 679–685. https://doi.org/10.1130/0016-7606(1981)92<679:AACE>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GREG A. OLYPHANT; Allometry and cirque evolution. GSA Bulletin 1981;; 92 (9): 679–685. doi: https://doi.org/10.1130/0016-7606(1981)92<679:AACE>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A deductive analysis of the processes responsible for cirque formation leads to a model that describes cirque development through time. In this model, cirque volumes increase as the third power of time, although observed variations in cirque size also reflect pre-glacial erosion, as well as the average rate of surface recession/lowering.The deductive findings are extended via analysis of 23 cirques from a part of the Sangre de Cristo Mountains, south-central Colorado. The assumption that glacier-occupance times are proportionately adjusted to topoclimatic situation leads to the conclusion that average rates of cirque erosion exhibit at least a fourfold (possibly as much as an order of magnitude) range within a given massif. The notion that cirque-development rates depend on bed-rock resistance is supported by a statistically significant inverse relationship between estimated erosion coefficients and average bed-rock joint spacing.Allometric analysis of a 15-cirque subsample (the cirques were chosen because they exhibit similar erosion susceptibility) lends credence to the hypothesis that headwall recession has been more rapid than cirque-floor lowering within the study area. However, allometric enlargement cannot by itself account for observed values for the ratio cirque length:cirque depth. The results imply that pre-glacial topography strongly influences observed variability in glacial morphometry. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chemical analysis of DNA alterations IV. Reactions of oligodeoxynucleotides with monofunctional alkylating agents leading to backbone breakage

The mechanisms leading to inactivating DNA alterations by the monofunctional alkylating agents methyl and ethyl methane sulfonate have been studied using oligodeoxythymidylic and oligodeoxyadenylic acids of different chain length as well as mononucleotides and their components. Thymine did not react and deoxythymidylic acid was alkylated exclusively at the phosphate group, about twice as fast as guanine at the 7-position. The alkylation of oligodeoxythymidylic acids produced products, separated by chromatography, which proved the existence of triester breakage. During alkylation of dGMP and dAMP, the amount of free alkylated guanine and adenine both increased with the square of time, which shows a two-step reaction of first alkylation and then depurination. The identification of certain reaction products (dAMP) of oligodeoxyadenylic acid furthermore proved the existence of a small but significant amount of backbone breakage which accompanied alkylation at neutral pH. A quantitative evaluation of the results concluded that triester breakage and depurination of DNA should occur with about equal frequency, both increasing with the square of the time during treatment and linearly afterwards. In contrast, backbone breakage caused by depurination should increase with the third power of time during treatment and with the square of the time afterwards. The results are significant for the explanation of the effects of deoxyribonucleases or repair mechanisms on alkylated DNA.

Effect of Limited Wordlength on Satellite Prediction Accuracy

Round-off error accumulation in numerical integration of the equations of motion in an inverse square field has been studied for approximately circular orbits. The second order equations of motion in Cowell formulation were assumed to be integrated with a one-step method of arbitrary order after reduction to a first order system. Analytical expressions for the first two statistical moments of the accumulated error in one position component have been derived via the adjoint method for particular classes of fixed and floating point arithmetics. The error mean increases linearily or quadratically with time dependent on the mechanization of the ADD-instruction regardless of number system (sign-magnitude or two’s complement) and method of scaling (fixed or floating point). The error variance increases with third power of time.

Smooth power control for high current furnaces

A method is described whereby the temperature of resistances furnaces operating with currents of 500 to 2000 A can be adjusted continuously and smoothly. The furnace power is supplied from a saturable reactor, the output of which is controlled by a manually operated or motor driven auto-transformer in series with a rectifier. The system described will provide power output voltage supplies which vary as the first, second or third power of time, in response to impulses from a thermocouple or total radiation pyrometer.

Kinetics of crystallization of isotactic polypropylene between 120 and 160°C.

AbstractPhysical changes which accompany the crystallization of isotactic polypropylenes have been observed by dilatometry and optical microscopy at temperatures between 120 and 160°C. Samples were fused at 220°C. and then held at a predetermined crystallization temperature for times ranging up to many hours. Rate constants for the crystallization were calculated from volume changes and from measurements of radial growth of spherulites. Polypropylenes from different sources exhibited quite different concentrations of spherulites and growth rates. Crystallization appears to proceed, at least at the higher temperatures, by spherical growth from a fixed number of nuclei, apparently arising from foreign matter in the polymer. With decreasing temperature, the number of nuclei (hence also the number of spherulites) increases, since apparently the conditions for nucleation become less critical. The crystallization follows the kinetics of a nucleation‐controlled process according to an Avrami equation, ‐log (1 ‐ ΔV / ΔV ∞) = kt3. Deviations from the third power of time at the lower temperatures may be the result of a secondary ordering process, slower than the primary crystallization.