Conventional Dynamic Method Research Articles

The kinetics of solid‐state reactions toward consensus, Part 2: Fitting kinetics data in dynamic conventional thermal analysis

AbstractThis paper is the second part of a review of some of the controversial kinetic aspects of conventional thermal analysis (TA). In this part the physico‐geometric kinetics for the solid‐state reactions were examined. The main problems discussed are (1) problems in fitting kinetics data: the identification of the f (α) function, (2) the suitability of conventional dynamic methods of TA, and (3) the complex reactions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 193–208, 2002; DOI 10.1002/kin.10028

会合性高分子水溶液の高周波数領域における粘弾性特性

High frequency viscoelasticity of an aqueous solution of associating polymer was directly measured. Viscoelasticity of the solution was determined at frequencies 10-1-102 rad s-1 with a conventional dynamic measurement method and at frequencies 10-2-104 rad s-1 with pulse strain method and surface loading method. The viscoelastic behavior of the solution was close to that of the Maxwell model in a range of polymer concentration 2-5wt%. Relaxation time τ and modulus G were determined by fitting data to the Maxwell model. The value of G increased with polymer concentration, while τ was independent of polymer concentration. These results were in good agreement with the prediction of Tanaka's theory.

Rheological Properties and Interparticle Force in Aqueous Suspensions of Resin Particles with/without Associating Polymers.

Rheological properties of aqueous suspensions and rheometry for viscoelastic measurements over a wide range of frequency were investigated. The raised cosine pulse method for the measurements was improved by using rectangular pulse strain including high-frequency Fourier components. For further extension of the frequency range, a new rheometer was also developed on the basis of the surface loading method. These methods as well as a conventional dynamic method were utilized to determine rheological properties of aqueous solutions of an end-associating polymer (suspending media for resin particles). The relaxation behavior of these solutions was in good agreement with predictions of the Tanaka theory for transient networks. Aqueous suspensions of poly(acryl-co-styrene)(AS) particles with radius a0=45nm showed linear viscoelastic relaxation behavior, and the time-volume fraction superposition was found to be valid. In the linear regime, AS particles behaved as the Brownian hard particles having an effective radius aeff = a0 + ξ with ξ being a thickness of the electric double layer, and the dependence of their zero-shear viscosity η0 on an effective volume fraction φeff (= {aeff /a0}3 φ ) agreed with the dependence of η0 of ideal silica suspensions on the bare volume fraction φ . In the range of φeff < φ m (φ m ; random close packing volume fraction), η0 was well described by the Brady theory for Brownian particles. In the range of φeff > 0.6, a repulsive force due to overlapping electric double layers also contributed to the viscoelastic behavior of AS suspensions. In aqueous suspensions of polystyrene (PS) particles, flocculation and sedimentation of PS particles occurred on addition of a small amount of the associating polymer. Analysis of the polymer conformation at the particle surface suggested that the polymers formed interparticle bridges thereby inducing of the flocculation and sedimentation.

A study of the display pixel-based focusing method in ultrasound imaging.

This paper presents a new beamforming technique, in which ultrasound waves are focused at the display pixels on the Cartesian coordinates, rather than sampling points located on the uniformly-separated scanlines on either the polar or Cartesian coordinates. Consequently, this method does not require a digital scan converter (DSC) and therefore completely eliminates the distortions due to the DSC. A new imaging system based on the proposed method is also presented, which is advantageous over conventional systems in hardware complexity, especially when high-density imaging is required. The new method can also be used effectively to achieve high frame rates for real-time 3D imaging and cardiac applications. To verify the proposed method, we modified a commercial ultrasound scanner and performed experiments with a 3.5 MHz convex array and a 7.5 MHz linear array. The experimental results with in vivo and in vitro data show that the proposed technique provides much smoother and finer images than the conventional dynamic focusing methods.

A dynamicaltechnique for measuring the gravitational quadrupole coupling of the STEPand µSCOPE experimental test masses

This paper describes a new method for determining the suitability of `testmasses' for use in exceptionally sensitive spaceborne experiments fortesting the equivalence principle, such as STEP and µSCOPE. It isaimed at measuring the size of the gravitational quadrupolar coupling oftest masses. Conventional dynamical methods measure principal momentsof inertia separately, and then difference them. The technique proposedhere measures directly any moment of inertia imbalance of the mass undertest, by spinning it at low frequency (a few hertz) about a vertical axisthrough its centre of mass. Any mass quadrupolar moment then results ina torque on the body about a horizontal axis. In order to quantify thequadrupolar coupling either this torque may be measured directly, or thetest mass may be allowed to perform low-frequency oscillations. Somepractical limitations of the technique are discussed.

Lobe dynamics applied to barotropic Rossby-wave breaking

We applied the methods of lobe dynamics to the problem of transport across the edge of a barotropic vortex patch. The model used captures the essential dynamics of filament shedding in the wintertime stratospheric polar vortex. Two approaches were adopted for the problem: (1) the dominant periodic component of the vortical flow was identified and conventional lobe dynamics methods for periodic dynamical systems were applied to it; (2) the full aperiodic, dynamically consistent flow was retained and a modified brand of lobe dynamics was used to quantify the transport. Our results show that in the periodic case, much reversible transport occurs across the lobe dynamical boundary due to overlapping intruding and extruding lobes. In the aperiodic case, a small amount of intrusion was noted, contrary to the well-established fact that potential vorticity shedding in barotropic vortices is uniquely outwards. In our discussion, we argue that while lobe dynamics provides a rigorous framework for quantifying transport across the lobe dynamical boundary, this boundary may not be appropriate for quantifying transport across internal transport barriers, such as the stratospheric polar vortex edge.

Comparison of experimental methods for determination of the volumetric mass transfer coefficient in fermentation processes

Mass transfer in bioreactors has been examined. In the present work, dynamic methods are used for the determination of K L a values for water, model media and a fermentation broth (Candida utilis) in an airlift reactor. The conventional dynamic method is applied at the end of the microbial process in order to avoid an alteration in the metabolism of the microorganisms. New dynamic methods are used to determine K L a in an airlift reactor during the microbial growth of Candida utilis on glucose. One of the methods is based on the continuous measurement of carbon dioxide production while the other method is based on the relationship between the oxygen transfer and biomass growth rates. These methods of determining K L a does not interfere with the microorganisms action. A theoretical mass transfer model has been used for K L a estimation for the systems described above. Some differences between calculated and measured values are found for fermentation processes due to the model is developed for two-phase air-water systems. Nevertheless, the average deviation between the predicted values and those obtained from the relationship between oxygen transfer and biomass production rates are lower than 25% in any case.

A modified dynamic inelastic analysis of tall buildings considering changes of dynamic characteristics

Pushover analysis is commonly used to evaluate the inelastic ultimate capacity of structures. However, pushover analysis is carried out based on constant distributions throughout the incremental analysis, which cannot capture the variation in the acceleration profile due to inelastic behavior. For this reason, when plastic hinges form in structure, constant distributions of lateral forces cannot be used any longer. Conventional dynamic inelastic method by time-history analysis can be used for specific earthquakes to consider the changes in the distribution of lateral forces. This alternative approach, however, is not practical due to the volume of calculations required. In this study, MOdified Dynamic Inelastic Analysis (MODIA) is introduced to capture a distribution proportional to changing mode shapes affected by the change of stiffness. In this method, as a structure enters into the inelastic range, the distribution of lateral forces is changed according to the mode shapes of structure. The efficiency of the proposed method is verified by comparing the results from DRAIN. A 7-story moment resisting frame and a 36-story existing structure were analysed by both methods. The comparison showed a good agreement. The story shear–drift relationship, base shear, drift, ductility and overturning moment for the structures are also evaluated. Copyright © 1999 John Wiley & Sons, Ltd.

A modified dynamic inelastic analysis of tall buildings considering changes of dynamic characteristics

Pushover analysis is commonly used to evaluate the inelastic ultimate capacity of structures. However, pushover analysis is carried out based on constant distributions throughout the incremental analysis, which cannot capture the variation in the acceleration profile due to inelastic behavior. For this reason, when plastic hinges form in structure, constant distributions of lateral forces cannot be used any longer. Conventional dynamic inelastic method by time-history analysis can be used for specific earthquakes to consider the changes in the distribution of lateral forces. This alternative approach, however, is not practical due to the volume of calculations required. In this study, MOdified Dynamic Inelastic Analysis (MODIA) is introduced to capture a distribution proportional to changing mode shapes affected by the change of stiffness. In this method, as a structure enters into the inelastic range, the distribution of lateral forces is changed according to the mode shapes of structure. The efficiency of the proposed method is verified by comparing the results from DRAIN. A 7-story moment resisting frame and a 36-story existing structure were analysed by both methods. The comparison showed a good agreement. The story shear–drift relationship, base shear, drift, ductility and overturning moment for the structures are also evaluated. Copyright © 1999 John Wiley & Sons, Ltd.

Proposal for an impulse response evaluation method for force transducers

A method for evaluating the dynamic characteristics of force transducers in impact detection is proposed. In this method a mass is made to collide with a force transducer and the impulse, i.e. the time integration of the impact force, is measured highly accurately as a change in momentum of the mass. To realize linear motion with a sufficiently low friction acting on the mass, the pneumatic linear bearing `Air-Slide' is used, and the velocity of the mass, the moving part of the bearing, is measured using an optical interferometer. This method will be effective for evaluating the dynamic characteristics and the uncertainties of force transducers in impact detection, and evaluating the uncertainty in applying the results of other conventional dynamic calibration methods to impact detection. The relative combined standard uncertainty in the measurement of the impulse acting on a force transducer by this method is estimated to be less than .

Microcracks, spall and fracture in glass: A study using short pulsed laser shock waves

This work reports our meso mechanical study of microcrack behavior, especially the process leading from microcracking to macro failure. Using laser loading with a duration on the order of nanoseconds, spallation in a cylindrical geometry was achieved in soda-lime glass at the microcrack evolution stage. Laser induced shock waves were used to conduct crack initiation experiments for the first time. The specimens were examined after experiments and were compared with those loaded by conventional static and dynamic methods. A meso scale failure model of nucleation, growth, and percolation (NGP) is suggested based on the experiments. The NGP model is characterized by a randomly generated microcrack field and by simultaneous percolation statistics in time iteration. In most existing damage models, the statistical average of microcracks over a finite space is required in order to evaluate the damage variables. This procedure is not necessary in the NGP model. We show that the connection of microcracks can be very complicated, possibly a self-organized process.

Melting of corundum using conventional and two-phase molecular dynamic simulation method

The melting curve of corundum is calculated by using two approaches: the first one is conventional and the second one is two-phase molecular dynamics method both utilizing the same pairwise interatomic potential developed earlier on. The melting curve obtained by the two-phase simulation method is in agreement with the existing experimental data up to 25 GPa. A comparison of melting curves obtained by a two-phase simulation method and a conventional molecular dynamic method in NPT ensemble demonstrates a substantial overestimation of melting temperatures when applying conventional molecular dynamic technique. The inaccuracy of the conventional method increases with increasing pressure and, in the case of corundum, changes from about 300 K at 1 bar to about 1000 K at 1 Mbar.

Measurement of the microhardness and young's modulus of human enamel and dentine using an indentation technique

Conventional quasi-static and dynamic test methods have a number of limitations when used to measure the mechanical properties of enamel and dentine. These are due to the complex structure of the material and the small specimen size. In this investigation, a microindentation technique was used to measure the hardness and Young's modulus of human enamel and dentine and any variations with location. Freshly extracted molar teeth were sectioned, and the cut surfaces were ground and polished progressively to 1 μm. The polished surfaces were indented at different distances from the surface and amelodentinal junction with a Knoop indentor. Measurements of the length of the long indentation diagonal were used to calculate a value for hardness. It has been shown that the a-value for Young's modulus of a material can be calculated by comparing the ratio of the long and short diagonals on an indented specimen with the actual ratio of the indentor as any changes will be due to elastic recovery in the specimen. Values obtained for the Knoop hardness of enamel and dentine were in good agreement with those of other workers. It was also possible to show that there was a decrease in hardness with depth from the surface in enamel. The hardness of dentine increased with distance from the amelodentinal junction. Values for Young's modulus for dentine were in good agreement with those of other workers, and there was an increase in modulus with depth from the amelodentinal junction from 8.7 to 11.2 GNm −2. Values for Young's modulus of enamel were not as easy to calculate because of surface- and subsurface damage.

Use of the homotopy method for excitation control of generators for multimachine power system

AbstractIt is important to consider the stabilization problem for a large‐scale power system. This paper uses a dynamic compensator based on observer theory such that desired poles are placed for a closed‐loop multimachine power system. Since the system dimension is large, it is difficult to apply a conventional dynamic compensator method to an excitation control problem for a multimachine power system.The homotopy method is introduced to solve fundamental nonlinear equations which are required for observer synthesis. To show the effectiveness of the proposed method an excitation control of generators for a multimachine power system is considered. From the simulation result, it is shown that the present method is useful in stabilizing a multimachine power system.

Comparison of inactivation and conformational changes of aminoacylase during guanidinium chloride denaturation

The inactivation and unfolding of aminoacylase (EC 3.5.1.14) during denaturation by different concentrations of guanidinium chloride (GuHCl) have been compared. A marked decrease in enzyme activity is already evident at low GuHCl concentrations before significant unfolding of the enzyme molecule, as monitored by fluorescence, ultraviolet difference absorption and CD measurement. The kinetic theory of the substrate reaction during irreversible inhibition of enzyme activity previously described by Tsou has been applied to a study on the kinetics of the course of inactivation of aminoacylase during denaturation by GuHCl. The inactivation rate constants of free enzyme and substrate-enzyme complex were determined by Tsou's method. The inactivation reaction kinetics were found to be a monophasic first-order reaction. The kinetics of the unfolding were a bisphasic process consisting of two first-order reactions. At lower GuHCl concentration (< 1.0 M), the enzyme activity was stripped at a high rate whereas its conformation was only slightly affected. At 1.0 M GuHCl, the inactivation rate of the enzyme was much faster than the unfolding rate. At higher GuHCl concentrations (> 1.0 M), the inactivation rate was too fast to be measured by conventional dynamic methods, whereas the unfolding remained as a bisphasic process with the fast reaction accruing very fast and the slow reaction occurring at a measurable rate. The results suggest that active sites of aminoacylase containing Zn 2+ ions are situated in a limited region of the enzyme molecule that is more fragile to denaturants than the protein as a whole.

Dynamic Ultrasound-Based Fetal Assessment: The Fetal Biophysical Profile Score

The advent of ultrasound fetal imaging and the evolution of dynamic imaging (real-time) methods have opened great new vistas in which fetal responses can be monitored with remarkable precision and clarity. Contained within this new wealth of information may lie the key to direct determination of the fetus at risk for death or injury in utero. Consideration of fetal activities so plainly recognized by conventional dynamic ultrasound methods and an assessment of fetal environment appear to be integral parts of this process. It is reasonable to assume that composite assessment by the dynamic ultrasound-based PBS will remain a valuable adjunct in caring for the high-risk fetus.

Application of pulse strain as a method of viscoelastic measurement

Pulse Strain Method for viscoelastic measurements is presented, which is based on the Raised Cosine Pulse Method (RCP Method). According to the RCP Method, frequency dependence of complex shear modulus is given by the Fourier transform of shear stress as the response to a pulse strain of cosine type. However, frequency range of observation is limited to only 1 or 2 decades in lower region of fundamental frequency of applied pulse strain. To expand the frequency range, we have modified the RCP Method using Rectangular Pulse Strain, which includes high‐frequency components (RAP Method). Comparison among the RCP Method, RAP Method and conventional dynamic methods was made on a 20% polystyrene solution in diethylphthalate. In the case of the RAP Method, frequency range was expanded to higher frequencies of fundamental frequency of applied pulse strain compared with the RCP Method. Computer simulation of Pulse Strain Method was made to know the requirements for further expansion of frequency range. The shear stress as the response to pulse strain was calculated for a Maxwell model using the Boltzmann superposition principle, and then complex shear modulus was calculated from Fourier transform of pulse strain and shear stress. The obtained shear modulus from simulation was compared with the theoretical value. It has been shown that resolution and response time of a torque transducer are important to make the best use of Pulse Strain Method. The requirements for a torque transducer are as follows, resolution is 1/10000, and response time is 0.1 ms.

Application of Pulse Strain as a Method of Viscoelastic Measurement

Pulse Strain Method for viscoelastic measurements is presented, which is based on the Raised Cosine Pulse Method (RCP Method). According to the RCP Method, frequency dependence of complex shear modulus is given by the Fourier transform of shear stress as the response to a pulse strain of cosine type. However, frequency range of observation is limited to only 1 or 2 decades in lower region of fundamental frequency of applied pulse strain. To expand the frequency range, we have modified the RCP Method using Rectangular Pulse Strain, which includes high‐frequency components (RAP Method). Comparison among the RCP Method, RAP Method and conventional dynamic methods was made on a 20% polystyrene solution in diethylphthalate. In the case of the RAP Method, frequency range was expanded to higher frequencies of fundamental frequency of applied pulse strain compared with the RCP Method. Computer simulation of Pulse Strain Method was made to know the requirements for further expansion of frequency range. The shear s...

Direct dynamic kLa measurement in viscous fermentation broths - the residual gas hold-up problem

Dynamic measurement of the volumetric oxygen transfer coefficient k L a and oxygen uptake rate OUR in viscous fermentation broths is distorted by a hold-up of small bubbles with very long residence times; these bubbles interact with the liquid and amplify the apparent capacity of the liquid for oxygen. Experimental results reveal that extremely large errors affect the apparent values of k L a and OUR as determined by conventional dynamic methods in respiring broths. Theory predicts that a simple correction procedure is applicable, if the residual gas hold-up of small bubbles is approximately permanent in the time scale of the dynamic experiment and if equilibrium with the liquid may be accepted. Experiments with a mycelial fermentation broth confirm the theoretical correction of measurements affected by up to a 400% error. Simulations suggest that the size of small bubbles consistent with the applicability of the correction procedure in this case was diameter d B⩽10 −5 m. Residual gas hold-up was stable enough to be measured by a centrifugation technique.

Phenolic triazine (PT) resins. II: Cure characterization by dynamic melt rheology and its comparison to DSC

AbstractA new approach involving dynamic melt rheology i.e. dynamic mechanical analysis in a molten inert matrix, is presented for studying the cure of thermoset resins. The degree of cure by dynamic melt rheology has been correlated with that from differential scanning calorimetry, DSC (correlation coefficient = 0.87) and the lack of an excellent correlation is attributed to the uncertainties with the DSC method at higher cure levels. A kinetic expression with appropriate constants, “E, A, and n” from our new approach is presented for predicting the time‐temperature dependence of the degree of cure. Advantages of dynamic melt rheology are discussed in relationship to conventional dynamic mechanical and DSC methods.