Search results for "Isothermal"

1989

Heat of crystallization significantly slows down polymer cooling and thus pressure drop increase during mould filling with thermoplastic crystalline polymers. If a correction of thermal diffusivity can account for such a cooling slow down at least as far as the effect on pressure drop is concerned, the use of nonisothermal crystallization kinetics may be avoided in the simulation of mould filling. A procedure to identify such a correction is outlined in this work. Pressure drop values during cavity filling calculated by using a corrected thermal diffusivity in the model proposed by Lord and Williams favourably compare with literature data taken with polypropylene and polyethylene resins. Be…

Allosteric Models for Multimeric Proteins:  Oxygen-Linked Effector Binding in Hemocyanin

2005

In many crustaceans, changing concentrations of several low molecular weight compounds modulates hemocyanin oxygen binding, resulting in lower or higher oxygen affinities of the pigment. The nonphysiological effector caffeine and the physiological modulator urate, the latter accumulating in the hemolymph of the lobster Homarus vulgaris during hypoxia, increase hemocyanin oxygen affinity and decrease cooperativity of oxygen binding. To derive a model that describes the mechanism of allosteric interaction between hemocyanin and oxygen in the presence of urate or caffeine, studies of oxygen, urate, and caffeine binding to hemocyanin were performed. Exposure of lobster hemocyanin to various pH …

Non-isothermal crystallization kinetics of PET

2000

The crystallization kinetics of poly(ethylene terephthalate) was studied using constant cooling rate, isothermal and quenching experiments. A non-isothermal crystallization kinetics equation based on a single mechanism was used to analyze the data. Different mechanisms of crystallization at low, intermediate, and high cooling rates were hypothesized based on deviation of the experimental data from the single mechanism model.

Structure development in poly(ethylene terephthalate) quenched from the melt at high cooling rates: X-ray scattering and microhardness study

2000

The structure and microhardness of poly(ethylene terephthalate) (PET) cooled from the melt, using a wide range of cooling rates, was studied. PET thin films rapidly cooled from the melt (cooling rates larger than 5°C/s) show a continuous variation of structure and properties depending on cooling rate. Results highlight differences in the micro-mechanical properties of the glass suggesting the occurrence of amorphous structures with different degrees of internal chain ordering. The comparative X-ray scattering study of two glassy PET samples (7500 and 17°C/s) reveals the occurrence of frozen-in electron density states giving rise to an excess of scattering for the amorphous sample solidified…

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

2020

Crown ethers are common building blocks in supramolecular chemistry and are frequently applied as cation sensors or as subunits in synthetic molecular machines. Developing switchable and specifically designed crown ethers enables the implementation of function into molecular assemblies. Seven tailor-made redox-active crown ethers incorporating tetrathiafulvalene (TTF) or naphthalene diimide (NDI) as redox-switchable building blocks are described with regard to their potential to form redox-switchable rotaxanes. A combination of isothermal titration calorimetry and voltammetric techniques reveals correlations between the binding energies and redox-switching properties of the corresponding ps…

Evaluation of multivalency as an organization principle for the efficient synthesis of doubly and triply threaded amide rotaxanes

2014

Mono-, di- and trivalent pseudorotaxanes with tetralactam macrocycle hosts and axles containing diamide binding stations as the guests have been synthesised. Their threading behaviour was analyzed in detail by NMR experiments and isothermal titration calorimetry. An X-ray crystal structure of the monovalent pseudorotaxane confirms the binding motif. Double mutant cycle analysis provides the effective molarities and insight into the chelate cooperativity of multivalent binding. While the second binding event in a trivalent pseudorotaxane exhibits a slightly positive cooperativity, the third binding is nearly non-cooperative. Nevertheless, the enhanced binding affinities resulting from the mu…

Control of a Non-isothermal CSTR by Type-2 Fuzzy Logic Controllers

2009

The paper describes the application of a type-2 fuzzy logic controller (FLC) to a non-isothermal continuous stirred tank reactor (CSTR) characterized by the presence of saddle node and Hopf bifurcations. Its performance is compared with a type-1 fuzzy logic controller performance. A full analysis of the uncontrolled CSTR dynamic was carried out and used for the feedback-feedforward fuzzy controllers development. Simulation results confirm the effectiveness and the robustness of the type-2 FLCs which outperform their type-1 counterparts, particularly when uncertainties are present in the system.

Control of a non-isothermal continuous stirred tank reactor by a feedback–feedforward structure using type-2 fuzzy logic controllers

2011

A control system that uses type-2 fuzzy logic controllers (FLC) is proposed for the control of a non-isothermal continuous stirred tank reactor (CSTR), where a first order irreversible reaction occurs and that is characterized by the presence of bifurcations. Bifurcations due to parameter variations can bring the reactor to instability or create new working conditions which although stable are unacceptable. An extensive analysis of the uncontrolled CSTR dynamics was carried out and used for the choice of the control configuration and the development of controllers. In addition to a feedback controller, the introduction of a feedforward control loop was required to maintain effective control…

Molecular mechanism of T-cell protein tyrosine phosphatase (TCPTP) activation by mitoxantrone.

2013

T-cell protein tyrosine phosphatase (TCPTP) is a ubiquitously expressed non-receptor protein tyrosine phosphatase. It is involved in the negative regulation of many cellular signaling pathways. Thus, activation of TCPTP could have important therapeutic applications in diseases such as cancer and inflammation. We have previously shown that the α-cytoplasmic tail of integrin α1β1 directly binds and activates TCPTP. In addition, we have identified in a large-scale high-throughput screen six small molecules that activate TCPTP. These small molecule activators include mitoxantrone and spermidine. In this study, we have investigated the molecular mechanism behind agonist-induced TCPTP activation.…

Effect of heat activation and inactivation conditions on germination and thermal resistance parameters of Bacillus cereus spores.

2001

The effect of isothermal and non-isothermal heat activation on germination and thermoresistance of two strains of Bacillus cereus spores was studied. Results indicated that the germination after isothermal activation was lower than after non-isothermal heating. The activation rate affected the z value, which increased with faster heating rates. For each temperature and inactivation rate, the non-isothermal activation at rate of 2 degrees C/min resulted in larger D values (D90 = 4.70 min) than isothermal activation (D90 = 4.04 min). The two mathematical equations used to analyse non-isothermal data produced similar predicted D and z values, nevertheless the Hayakawa equation modified in this…