Biomedical subjects

Shihua Chen

Publications and source records attributed to Shihua Chen.

7 recordsLinked to original sources

PubMed2006

Sorption and desorption behavior of benzidine in different solvent-sediment systems.

The sorption and desorption behavior of benzidine in eight solvent-sediment systems were studied using a batch method. The solvents tested included deionized water (DI), calcium chloride solution (CaCl2), sodium hydroxide solution (NaOH), acetonitrile (ACN), a mixture of acetonitrile and ammonium acetate solution (ACN-NH4OAc), methanol (MeOH), ammonium acetate solution (NH4OAc) and hydrochloric acid solution (HCl). Three sets of sorption isotherm experiments were conducted separately in these eight solvents with seven days, three weeks, and two months of contact times, respectively. The results demonstrated nonlinear benzidine sorption phenomena in all eight solvents with higher sorption affinities for sediment sites in the aqueous solvents than in the organic solvents. The results from the desorption experiments revealed that the benzidine desorption efficiencies in the solvents decreased in an order, which was approximately the reverse order of its sorption affinity. Results also suggested that hydrophobic partitioning and covalent binding processes dominated in the desorption experiments, while cation exchange process had little effect on desorption of benzidine. A three-stage model was subsequently applied to simulate the desorption data in the selected solvents of ACN, ACN-NH4OAc and NaOH, respectively. The rapidly desorbing initial fractions were about 0.13-0.20, 0.15-0.26, and 0.18-0.25 for ACN, ACN-NH4OAc and NaOH, respectively. Finally, the sorbed concentrations of benzidine in slowly and very slowly desorbing domains in the selected solvents were correlated with the maximum sorption capacities obtained from the Langmuir sorption isotherm model. The maximum sorption capacities of benzidine were found to be comparable to the amount of benzidine residing in the slowly and very slowly desorbing domains.

Adsorption↗

PubMed2006

Molecular cloning and characterization of a vacuolar H+ -pyrophosphatase gene, SsVP, from the halophyte Suaeda salsa and its overexpression increases salt and drought tolerance of Arabidopsis.

The chenopodiaceae Suaeda salsa L. is a leaf succulent euhalophyte. Shoots of the S. salsa are larger and more succulent when grown in highly saline environments. This increased growth and water uptake has been correlated with a large and specific cellular accumulation of sodium. S. salsa does not have salt glands or salt bladders on its leaves. Thus, this plant must compartmentalize the toxic Na(+) in the vacuoles. The ability to compartmentalize sodium may result from a stimulation of the proton pumps that provide the driving force for increased sodium transport into the vacuole. In this work, we isolated the cDNA of the vacuolar membrane proton-translocating inorganic pyrophosphatase (H(+) -PPase) from S. salsa. The SsVP cDNA contains an uninterrupted open reading frame of 2292 bp, coding for a polypeptide of 764 amino acids. Northern blotting analysis showed that SsVP was induced in salinity treated leaves. The activities of both the V-ATPase and the V-PPase in Arabidopsis overexpressing SsVP-2 is higher markedly than in wild-type plant under 200 mM NaCl and drought stresses. The Overexpression of SsVP can increase salt and drought tolerance of transgenic Arabidopsis.

Adaptation, Physiological↗

PubMed2005

Self-similar evolutions of parabolic, Hermite-Gaussian, and hybrid optical pulses: Universality and diversity.

Three novel types of self-similar solutions, termed parabolic, Hermite-Gaussian, and hybrid pulses, of the generalized nonlinear Schrödinger equation with varying dispersion, nonlinearity, and gain or absorption are obtained. The properties of the self-similar evolutions in various nonlinear media are confirmed by numerical simulations. Despite the diversity of their formations, these self-similar pulses exhibit many universal features which can facilitate significantly the achievement of well-defined linearly chirped output pulses from an optical fiber, an amplifier, or an absorption medium, under certain parametric conditions. The other intrinsic characteristics of each type of self-similar pulses are also discussed.

Journal Article↗

PubMed2005

Chirped self-similar solutions of a generalized nonlinear Schrödinger equation model.

Exact chirped self-similar solutions of the generalized nonlinear Schrödinger equation with varying dispersion, nonlinearity, gain or absorption, and nonlinear gain have been found. The stability of these nonlinearly chirped solutions is then demonstrated numerically by adding Gaussian white noise and by evolving from an initial chirped Gaussian pulse, respectively. It is reported that the pulse position of these chirped pulses can be precisely piloted by tailoring the dispersion profile, and that the sech-shaped solitary waves can propagate stably in the regime of beta(z)gamma(z) > 0 as well as the regime of beta(z)gamma(z) < 0 , according to the magnitude of the nonlinear chirp parameter. Our theoretical predictions are in excellent agreement with the numerical simulations.

Journal Article↗

PubMed2005

Slow desorption behavior of one highly resistant aromatic amine in Lake Macatawa, Michigan, USA, sediment.

The desorption behavior of benzidine from Lake Macatawa (Holland, MI, USA) sediment was investigated in this study using batch solvent extraction method. Seven solvents were tested as the extracting reagents: Deionized water (DI), calcium chloride in DI (CaCl2), sodium hydroxide in DI (NaOH), acetonitrile (ACN), a mixture of acetonitrile and ammonium acetate in DI (ACN-NH4OAc), methanol (MeOH), and hydrochloric acid in DI (HCl). These solvents are proposed to react with sediment-associated benzidine by different mechanisms (e.g., cation exchange, hydrophobic partitioning, and covalent binding). Three sets of sorption isotherm experiments were conducted separately in these seven solvents with a 7-d, three-week, and two-month contact time. The results demonstrated nonlinear isotherms with Freundlich 1/n values varying from 0.25 to 0.52. The desorption behavior of benzidine in the solvents was evaluated after the sorption of benzidine onto the sediment with same contact times of 7 d, three weeks, and two months. A two-stage model subsequently was applied to simulate the experimental data. The rapidly desorbing rate constants were on the order of one to two per day for ACN, ACN-NH4OAc, and NaOH solvents, and the slowly desorbing rate constants were on the order of 10(-5) to 10(-4)/d. Sequential desorption experiment demonstrated low total extraction efficiency of less than 40%. Both the observed sorption and desorption phenomena suggested that hysteresis and/or mass-transfer limited diffusion may result in the slow desorption behavior observed in this study.

Acetates↗

PubMed2004

Timing jitter of femtosecond solitons in single-mode optical fibers: a perturbation model.

On the basis of the higher-order nonlinear Schrödinger equation, an extended soliton perturbation model is proposed. The evolution equations for the soliton parameters and the resultant expressions for timing jitter are derived. Subsequently, the model is tested to be correct in the subpicosecond-femtosecond regime through direct numerical simulations of the underlying equation by using the stochastic split-step Fourier method. It is shown that the results of our numerical simulations are in excellent agreement with analytical predictions for timing jitter. It is found that the Gordon-Haus jitter for dark solitons is nearly 1/sqrt[2] of that for bright solitons, and that the Raman jitter always dominates the Gordon-Haus jitter in the femtosecond regime. In particular, the stabilities of the solitary waves are demonstrated under the Gaussian white noise. It is expected that for bright and dark solitons, the present equations of motion would find extensive applications in the high-speed communication systems more than those obtained by use of the well-known perturbation theory about the nonlinear Schrödinger equation [J. Opt. Soc. Am. B 18, 153 (2001)].

Journal Article↗

PubMed2004

Synchronizing strict-feedback chaotic system via a scalar driving signal.

We propose a systematic design procedure to synchronize a class of chaotic system in a so-called strict-feedback form based on back-stepping procedure. This approach needs only a scalar driving signal to realize synchronization no matter how many dimensions the chaotic system contains. Furthermore, the numerical simulation with Chua's chaotic circuit verifies the effectiveness of the method.

Computer Simulation↗