Biomedical subjects

Jichang Wang

Publications and source records attributed to Jichang Wang.

11 recordsLinked to original sources

PubMed2006

Dynamic instabilities and mechanism of the electrochemical oxidation of thiosulfate.

The electrochemical oxidation of thiosulfate is revealed to have two distinct oscillatory regimes in both linear potential and galvanic voltammograms, where various nonlinear behaviors such as period-2, mixed-mode and quasi-periodic oscillations, and chaos are observed under potentiostatic or galvanostatic conditions. Electrochemical impedance spectroscopy and iR compensation characterization indicate that, depending on the operating conditions, the system could be either a strictly potentiostatic oscillator or an S-shaped negative differential resistance oscillator. Chronoamperometry measurements reveal that the first oscillatory process involves a single-electron transfer, whereas within the second oscillatory regime the average number of electrons transferred is around 3.8. Measurements with capillary electrophoresis and chemical methods illustrate that the oxidation products include S2O6(2-), S4O6(2-), S5O6(2-), S3O6(2-), and SO4(2-).

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PubMed2006

Spiral turbulence developed through the formation of superimposed target waves in an oscillatory reaction-diffusion medium.

An approach leading to the development of spiral turbulence is reported here in an oscillatory reaction-diffusion medium, which is through the spontaneous formation of targetlike waves near the core of a spiral wave. The newly formed target wave emerges with its own characteristic frequency and propagates on top of the original spiral wave, which eventually leads to the breakup of the spiral at a location far from the spiral center. The radius of the surviving spiral segment decreases rapidly with the bifurcation control parameter. Calculation of power spectra suggests that the meandering of the spiral tip is responsible for the onset of the superimposed target and the phase desynchronization of the superimposed target waves.

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PubMed2006

The sagittal curving osteotomy: a modified technique for advancement genioplasty.

PURPOSE: The purpose of the present study was to develop a new type of osteotomy for advancement genioplasty to decrease the incidence of neurosensory disturbance of the chin. PATIENTS AND METHOD: Forty-six patients who suffered from a slight or moderate degree of microgenia received a sagittal curving osteotomy for advancement genioplasty. Patients were followed for 1-6 months to assess the neurosensory function of the chin region by evaluating light-touch perception. The control group, 57 patients, who suffered from the same degree of microgenia, received a horizontal sliding osteotomy. They were operated on by the same surgical group and were followed for 1-33 months. RESULTS: All of the test and control patients were satisfied with the aesthetic results of the surgery. In the test group, 47 sides (51.87%) of 92 total left and right sides of chins had a transient neurosensory deficiency but none had permanent neurosensory deficiency. In the control group, 98 sides (86.84%) of 114 total chin sides had a transient neurosensory deficiency and five sides (4.43%) of 114 total chin sides had permanent neurosensory deficiency. When applied to patients who suffer from a mild or moderate degree of microgenia and have normal bite function, the sagittal curving osteotomy is a simple, safe and effective technique for advancement genioplasty. This technique can distinctively decrease the incidence of neurosensory disturbance of the chin.

Adult↗

PubMed2006

Collective reaction behavior of an oscillating system coupled with an excitable reaction.

The collective reaction behavior of limit cycles coupled to a nonoscillatory forcing is investigated experimentally and computationally. The coupled chemical system is constructed by adding 1,4-cyclohexanedione (CHD), a species which is capable of forming an oscillator with acidic bromate, into the cerium-catalyzed Belousov-Zhabotinsky reaction. Two levels of coupling exist in the system: (1) through autocatalytic reactions with bromine dioxide radicals and (2) via reactions with oxidized metal catalysts. Experiments illustrate that there is an optimum [1,4-CHD]/[cerium] ratio for inducing complex oscillations, whereas in the 1,4-CHD and malonic acid concentration phase plane two resonant ratios are observed for the onset of complex behavior. In addition, bromate, the oxidant for both suboscillators, also exhibits subtle influences on the complexity of the collective reaction behavior. The experimental observations are qualitatively reproduced with the Field-Koros-Noyes mechanism, modified to account for the coupling reactions with the 1,4-CHD-bromate system.

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PubMed2005

Thermodynamic analysis of decomposition of thiourea and thiourea oxides.

Thiourea has exhibited extremely rich dynamical behavior when being oxidized either through a chemical approach or via an electrochemical method. In this study, thermodynamic properties of thiourea and its oxides are investigated by measuring their thermogravimetry (TG), differential thermogravimetry (DTG), and differential scanning calorimetry (DSC) simultaneously. Online FT-IR measurements show that products of the thermal decomposition vary significantly with the reaction temperature. In addition to the determination of their apparent activation energy (E), preexponential factor (A), and entropy (DeltaS++), enthalpy (DeltaH++), and Gibbs energy (DeltaG++) of thermal decomposition, our investigation further illustrates that the decomposition kinetics of thiourea and thiourea oxides follows the Johnson-Mehl-Avrami Equation, f (alpha) = n(1 - alpha)[-ln(1 - alpha)](1-1/n) and G(alpha) = [-ln(1 - alpha)](1/n) with n equal to 2, 3.43, and 3, respectively.

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PubMed2005

Complex behavior in coupled bromate oscillators.

In this study, coupled bromate-oscillators constructed by adding 1,4-cyclohexanedione (1,4-CHD) to the ferroin-catalyzed Belousov-Zhabotinsky reaction are investigated in a batch reactor under anaerobic conditions. Various complex behaviors such as sequential oscillations and bursting phenomena are observed. At low concentrations of ferroin or malonic acid (MA), the development of sequential oscillations is found to depend on the ratio of [1,4-CHD]/[ferroin] and [1,4-CHD]/[MA] rather than their absolute concentrations. As the concentration of MA or ferroin was increased gradually, however, the minimum 1,4-CHD concentration required to induce complex oscillations reaches a plateau. Perturbations by light illustrate that the first oscillatory window is governed by the ferroin-MA-BZ mechanism, whereas the 1,4-CHD-bromate oscillator plays a prominent role during the non-oscillatory evolution and the second oscillatory window. Our conclusion is further supported by numerical simulations in which sequential oscillations observed in experiments are qualitatively reproduced by a modified FKN mechanism.

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PubMed2005

Stirring-controlled bifurcations in the 1,4-cyclohexanedione-bromate reaction.

We report the experimental observation that stirring in a closed 1,4-cyclohexanedione-bromate reaction can induce transitions not only between oscillatory and nonoscillatory states but also between simple and period-doubled oscillations. Notably, the transition from simple to complex oscillations occurs as a result of increasing stirring rate. When illumination was employed to characterize the importance of microfluctuations of concentrations, the threshold stirring rate for inducing a bifurcation was found to increase proportionally to the intensity of the applied light. Numerical simulations with an existing model illustrate that the experimental phenomena could be qualitatively reproduced by considering effects of mixing on diffusion-limited radical reactions, namely, the disproportion reaction of hydroquinone radicals.

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PubMed2005

Transient complex oscillations in a closed chemical system with coupled autocatalysis.

In this study, hydroquinone was introduced to the classic Belousov-Zhabotinsky (BZ) reaction to build up coupled autocatalytic feedbacks. Various complex dynamical behaviors including successive period-adding bifurcations, irregular oscillations, and frequency modulations were observed in the coupled reaction system. Not only the complexity of oscillations but also the time period during which complex oscillations persist were found to depend greatly on the initial concentration of hydroquinone, which was expected to manifest the coupling strength in the studied system. Dependence of the observed transient complex oscillations on concentrations of ferroin, sulfuric acid, bromate, and malonic acid was also characterized systematically. Numerical simulations with a modified BZ model via incorporating reactions involving hydroquinone and products of hydroquinone qualitatively reproduced the influence of hydroquinone seen in experiments.

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PubMed2005

Coexistence of two bifurcation regimes in a closed ferroin-catalyzed Belousov-Zhabotinsky reaction.

The ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction was studied in a batch reactor under anaerobic conditions and was found to evolve through two separated regimes of complex oscillations. Significantly, the two bifurcation regimes exhibited qualitatively different dependence on compositions of the reaction mixture, i.e., initial concentrations of bromate, sulfuric acid, malonic acid, and ferroin. The reaction temperature also showed opposite effects on the two bifurcation regimes, in which complexities of the first bifurcation regime were enhanced while oscillations in the second bifurcation regime became simpler as a result of decreasing temperature. Numerical simulations with a 12-variable model developed specifically for the ferroin-BZ system were able to reproduce transient complex oscillations observed in experiments. These calculations further illustrated that reactions such as ferroin and HOBr, ferroin and HBrO2, and ferriin and Br- were not essential in describing complex dynamics of the ferroin-BZ reaction.

Bromates↗

PubMed2004

Pattern formation in excitable media with concentration-dependent diffusivities.

We study a model of pattern formation in an excitable medium with concentration-dependent diffusivities. The reaction terms correspond to a two-variable Gray-Scott model in which the system has only one stable steady state. The diffusion coefficients of the two species are assumed to have a functional relationship with the concentration of the autocatalyst. A transition from self-replicating behavior to stationary spots is observed as the influence of the local autocatalyst concentration on the diffusion process increases. Notably, the transition occurs even though there is no change in the relative diffusivities of the activator and inhibitor. The observed time-independent patterns exhibit an unusual dependence on the size and geometry of an initial perturbation. Initial perturbations with a large spatial size, for example, sometimes revert to the homogeneous equilibrium state, whereas perturbations of smaller spatial extent develop into stable spots at the same parameter values.

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PubMed2003

Synchronization of spatiotemporal patterns in locally coupled excitable media.

The synchronization of two distributed Belousov-Zhabotinsky systems is experimentally and theoretically investigated. Symmetric local coupling of the systems is made possible with the use of a video camera-projector scheme. The spatial disorder of the coupled systems, with random initial configurations of spirals, gradually decreases until a final state is attained, which corresponds to a synchronized state with a single spiral in each system. The experimental observations are confirmed with numerical simulations of two identical Oregonator models with symmetric local coupling, and a systematic study reveals generalized synchronization of spiral waves. Several different types of synchronization attractors are distinguished.

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