Thermal isomerizations of protonated bicyclo[3.1.0]hexenones

1988 ◽  
Vol 66 (6) ◽  
pp. 1350-1354 ◽  
Author(s):  
Ronald F. Childs ◽  
Baha E. George
Keyword(s):  
Rate Constants ◽  
Ring Opening ◽  
Strong Acid ◽  
Activation Energies ◽  
Thermal Isomerization ◽  
The Other ◽  
Triflic Acid ◽  
Wide Range

The thermal isomerization of a wide range of protonated methyl substituted bicyclo[3.1.0]hex-3-en-2-ones to protonated phenols has been examined using triflic acid as a strong acid solvent. The rate constants and activation energies of these isomerizations have been determined. The barriers to the isomerizations were shown to be dependent on the number and position of the methyl substituents. The results show that three different mechanisms are needed to account for these isomerizations, two of which involve a preliminary circumambulatory rearrangement prior to ring opening and the other process involving a direct ring opening of the initial protonated bicyclohexenone to give an intermediate meta-protonated phenol.

scholarly journals Rate constants rather than biochemical mechanism determine behaviour of genetic clocks

2008 ◽  
Vol 5 (suppl_1) ◽  
Author(s):  
Emery Conrad ◽  
Avraham E Mayo ◽  
Alexander J Ninfa ◽  
Daniel B Forger
Keyword(s):  
Transcription Regulation ◽  
Negative Feedback ◽  
Rate Constants ◽  
The Other ◽  
Type I ◽  
Type Ii ◽  
Biochemical Mechanism ◽  
Wide Range ◽  
Negative Feedbacks ◽  
Positive And Negative Feedbacks

Many biological systems contain both positive and negative feedbacks. These are often classified as resonators or integrators. Resonators respond preferentially to oscillating signals of a particular frequency. Integrators, on the other hand, accumulate a response to signals. Computational neuroscientists often refer to neurons showing integrator properties as type I neurons and those showing resonator properties as type II neurons. Guantes & Poyatos have shown that type I or type II behaviour can be seen in genetic clocks. They argue that when negative feedback occurs through transcription regulation and post-translationally, genetic clocks act as integrators and resonators, respectively. Here we show that either behaviour can be seen with either design and in a wide range of genetic clocks. This highlights the importance of parameters rather than biochemical mechanism in determining the system behaviour.

THE REACTION OF 2,2-DIPHENYL-1-PICRYLHYDRAZYL WITH SECONDARY AMINES

1958 ◽  
Vol 36 (12) ◽  
pp. 1729-1734 ◽  
Author(s):  
J. E. Hazell ◽  
K. E. Russell
Keyword(s):  
Secondary Amine ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Major Product ◽  
The Other ◽  
Secondary Amines ◽  
First Order ◽  
Kinetics Of

The reaction of DPPH (2,2-diphenyl-1-picrylhydrazyl) with N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, diphenylamine, and methylaniline has been studied and has been shown to be primarily a hydrogen abstraction process. Two moles DPPH react with 1–1.15 moles secondary amine to give 1.7–1.8 moles 2,2-diphenyl-1-picrylhydrazine and further products.The reaction between DPPH and N-phenyl-1-naphthylamine is first order with respect to each reactant. The reaction of DPPH with the other amines is retarded by the major product 2,2-diphenyl-1-picrylhydrazine and the kinetics of the over-all reaction are complex. However second-order rate constants and activation energies have been obtained using initial rates of reaction. Possible reaction mechanisms are discussed.

Kinetics of esterification of diisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (8) ◽  
pp. 2099-2104
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Differential Equations ◽  
Rate Constants ◽  
Activation Energies ◽  
The Other ◽  
Kinetics Of

The title liquid-phase isothermal esterification kinetics have been measured in the temperature intervals of 110-125 and 110-160 °C for 2,4- and 2,6-diisopropylphenols, resp. The values measured have been used to calculate the rate constants of the respective three steps and to determine the activation energies. 2,6-Diisopropylphenol has been found to react only to the first degree, and the rate constants of the other two reaction steps (k2, k3) were only calculated from the differential equations given by means of a computer.

Studies of the Vulcanization of Elastomers. VIII. The Vulcanization of Synthetic Rubbers with Thiuram Disulfides (1)

1957 ◽  
Vol 30 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint
Keyword(s):  
Natural Rubber ◽  
Quantitative Study ◽  
Rate Constants ◽  
Activation Energies ◽  
First Order ◽  
Wide Range ◽  
Tetraethylthiuram Disulfide

Abstract The vulcanization of Buna S-3 by tetraethylthiuram disulfide is reported. A quantitative study of the transformation reactions led to the following results. (1) Using tetraethylthiuram disulfide as representative of the class, it was found that two thirds of it undergoes transformation to zinc dithiocarbamate during the vulcanization of Buna S-3, independent of the temperature. (2) Both the decrease of thiuram disulfide and increase of dithiocarbamate are first-order reactions within a wide range of the transformation. (3) The rate constants of the decrease of thiuram and of the increase of dithiocarbamate are a little less than a tenth power greater than for the vulcanization of natural rubber. This is possibly explainable by the different structure of the allyl units in Buna S-3. (4) The activation energies of the decrease of thiuram as well as the increase of dithiocarbamate are nearly the same and are greater than for the vulcanization of natural rubber.

Simulation and Verification for Sulfur Accelerated Vulcanization of Gum Natural Rubber Compound

2002 ◽  
Vol 75 (2) ◽  
pp. 287-297 ◽  
Author(s):  
Ru-liang Fan ◽  
Yong Zhang ◽  
Chen Huang ◽  
Peng Gong ◽  
Yin-xi Zhang
Keyword(s):  
Natural Rubber ◽  
Rate Constants ◽  
Arrhenius Equation ◽  
Kinetic Scheme ◽  
Activation Energies ◽  
Simulation Process ◽  
Swelling Equilibrium ◽  
Wide Range ◽  
Different Temperatures ◽  
Good Agreement

Abstract A simplified and realistic kinetic scheme was proposed for the cure reversion mechanism of accelerated sulfur vulcanization for gum natural rubber (NR) compounds. The vulcametric curves at different temperatures were simulated from curing to overcuring periods by using a kinetic approach. The different rate constants and activation energies were calculated from the simulation process. The simulated results showed a good agreement with isothermal vulcametric data over a wide range of temperatures and showed that the relationships between the rate constants and the cure temperatures were in accordance with the Arrhenius Equation. The activation energies (Ea1, Ea2, and Ea3) of the formation, desulfurization and decomposition of polysulfidic crosslink obtained from Arrhenius plots were 79.5,102.6 and 138.8 kJ/mol, respectively. The experimentally measured crosslink densities determined by using swelling equilibrium and chemical probe techniques agreed with the simulated vulcametric curves to some extent.

2D Color-Intensity Representation of Ultrasonic Thickness Gauge Measurements

2020 ◽  
pp. 1192-1198
Author(s):  
M.S. Mohammad ◽  
Tibebe Tesfaye ◽  
Kim Ki-Seong
Keyword(s):  
Cost Effective ◽  
The Other ◽  
Thickness Gauge ◽  
Color Intensity ◽  
Digital Readout ◽  
Flat Surfaces ◽  
Video Cameras ◽  
Wide Range ◽  
Cost Effective Alternative ◽  
Ultrasonic Thickness

Ultrasonic thickness gauges are easy to operate and reliable, and can be used to measure a wide range of thicknesses and inspect all engineering materials. Supplementing the simple ultrasonic thickness gauges that present results in either a digital readout or as an A-scan with systems that enable correlating the measured values to their positions on the inspected surface to produce a two-dimensional (2D) thickness representation can extend their benefits and provide a cost-effective alternative to expensive advanced C-scan machines. In previous work, the authors introduced a system for the positioning and mapping of the values measured by the ultrasonic thickness gauges and flaw detectors (Tesfaye et al. 2019). The system is an alternative to the systems that use mechanical scanners, encoders, and sophisticated UT machines. It used a camera to record the probe’s movement and a projected laser grid obtained by a laser pattern generator to locate the probe on the inspected surface. In this paper, a novel system is proposed to be applied to flat surfaces, in addition to overcoming the other limitations posed due to the use of the laser projection. The proposed system uses two video cameras, one to monitor the probe’s movement on the inspected surface and the other to capture the corresponding digital readout of the thickness gauge. The acquired images of the probe’s position and thickness gauge readout are processed to plot the measured data in a 2D color-coded map. The system is meant to be simpler and more effective than the previous development.

p-Sulfonic acid calix[n]arene catalyzed synthesis of bioactive heterocycles: A review

2020 ◽  
Vol 24 ◽  
Author(s):  
Bubun Banerjee ◽  
Gurpreet Kaur ◽  
Navdeep Kaur
Keyword(s):  
Supramolecular Chemistry ◽  
Sulfonic Acid ◽  
Catalytic Efficiency ◽  
The Other ◽  
Reaction Conditions ◽  
Metal Free ◽  
Bioactive Scaffolds ◽  
Wide Range ◽  
Efficient Alternative ◽  
Bioactive Heterocycles

: Metal-free organocatalysts are becoming an important tool for the sustainable developments of various bioactive heterocycles. On the other hand, during last two decades, calix[n]arenes have been gaining considerable attention due to their wide range of applicability in the field of supramolecular chemistry. Recently, sulfonic acid functionalized calix[n] arenes are being employed as an efficient alternative catalyst for the synthesis of various bioactive scaffolds. In this review we have summarized the catalytic efficiency of p-sulfonic acid calix[n]arenes for the synthesis of diverse biologically promising scaffolds under various reaction conditions. There is no such review available in the literature showing the catalytic applicability of p-sulfonic acid calix[n]arenes. Therefore, we strongly believe that this review will surely attract those researchers who are interested about this fascinating organocatalyst.

Kinetics of esterification of monoisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (5) ◽  
pp. 1311-1317
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Reaction Rates ◽  
Activation Energies ◽  
The Individual ◽  
Kinetics Of

The kinetics of liquid-phase isothermal esterification of POCl3 with 2-isopropylphenol and 4-isopropylphenol have been studied within the temperature intervals of 110 to 130 and 90 to 110 °C, respectively. The rate constants and activation energies of the individual steps of this three-step reaction have been calculated from the values measured. The reaction rates of the two isomers markedly differ: at 110 °C 4-isopropylphenol reacts faster by the factors of about 7 and 20 for k1 and k3, respectively. This finding can be utilized in preparation of mixed triaryl phosphates, since the alkylation mixture after reaction of phenol with propene contains an excess of 2-isopropylphenol over 4-isopropylphenol.

scholarly journals Density Guarantee on Finding Multiple Subgraphs and Subtensors

2021 ◽  
Vol 15 (5) ◽  
pp. 1-32
Author(s):  
Quang-huy Duong ◽  
Heri Ramampiaro ◽  
Kjetil Nørvåg ◽  
Thu-lan Dam
Keyword(s):  
Lower Bound ◽  
State Of The Art ◽  
The State ◽  
The Other ◽  
Exact Methods ◽  
Practical Solution ◽  
Novel Approach ◽  
Wide Range ◽  
Real World Datasets ◽  
Tensor Data

Dense subregion (subgraph & subtensor) detection is a well-studied area, with a wide range of applications, and numerous efficient approaches and algorithms have been proposed. Approximation approaches are commonly used for detecting dense subregions due to the complexity of the exact methods. Existing algorithms are generally efficient for dense subtensor and subgraph detection, and can perform well in many applications. However, most of the existing works utilize the state-or-the-art greedy 2-approximation algorithm to capably provide solutions with a loose theoretical density guarantee. The main drawback of most of these algorithms is that they can estimate only one subtensor, or subgraph, at a time, with a low guarantee on its density. While some methods can, on the other hand, estimate multiple subtensors, they can give a guarantee on the density with respect to the input tensor for the first estimated subsensor only. We address these drawbacks by providing both theoretical and practical solution for estimating multiple dense subtensors in tensor data and giving a higher lower bound of the density. In particular, we guarantee and prove a higher bound of the lower-bound density of the estimated subgraph and subtensors. We also propose a novel approach to show that there are multiple dense subtensors with a guarantee on its density that is greater than the lower bound used in the state-of-the-art algorithms. We evaluate our approach with extensive experiments on several real-world datasets, which demonstrates its efficiency and feasibility.

scholarly journals Grasp to See—Object Classification Using Flexion Glove with Support Vector Machine

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1461
Author(s):  
Shun-Hsin Yu ◽  
Jen-Shuo Chang ◽  
Chia-Hung Dylan Tsai
Keyword(s):  
Support Vector Machine ◽  
Daily Life ◽  
Object Classification ◽  
Target Object ◽  
The Other ◽  
Support Vector ◽  
Wide Range ◽  
Dark Space ◽  
Flex Sensors ◽  
Shape And Size

This paper proposes an object classification method using a flexion glove and machine learning. The classification is performed based on the information obtained from a single grasp on a target object. The flexion glove is developed with five flex sensors mounted on five finger sleeves, and is used for measuring the flexion of individual fingers while grasping an object. Flexion signals are divided into three phases, and they are the phases of picking, holding and releasing, respectively. Grasping features are extracted from the phase of holding for training the support vector machine. Two sets of objects are prepared for the classification test. One is printed-object set and the other is daily-life object set. The printed-object set is for investigating the patterns of grasping with specified shape and size, while the daily-life object set includes nine objects randomly chosen from daily life for demonstrating that the proposed method can be used to identify a wide range of objects. According to the results, the accuracy of the classifications are achieved 95.56% and 88.89% for the sets of printed objects and daily-life objects, respectively. A flexion glove which can perform object classification is successfully developed in this work and is aimed at potential grasp-to-see applications, such as visual impairment aid and recognition in dark space.

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