Biomedical subjects

Hai Qian

Publications and source records attributed to Hai Qian.

6 recordsLinked to original sources

PubMed2006

Pharmacology of N-, L-, and B-subtypes of nematode nAChR resolved at the single-channel level in Ascaris suum.

Pharmacological experiments on Ascaris suum have demonstrated the presence of three (N-, L-, and B-) subtypes of cholinergic receptor mediating contraction of body wall muscle in parasitic nematodes. In the present study, these ionotropic acetylcholine (ACh) receptors (nAChRs) were activated by levamisole and bephenium under patch-clamp conditions and competitively antagonized by paraherquamide and 2-desoxoparaherquamide. A number of recordings exhibited three separate current amplitude levels, indicating the presence of small, intermediate, and large conductance subtypes of receptor. The mean conductance of the small conductance subtype, G25, was 22 +/- 1 pS; the intermediate conductance channel, G35, was 33 +/- 1 pS; and the large conductance channel, G45, was 45 +/- 1 pS. The small channel was not antagonized significantly by paraherquamide and was identified as the N-subtype. The intermediate channel was preferentially activated by levamisole rather than bephenium and antagonized by paraherquamide: the intermediate channel was identified as the L-subtype. The large conductance channel was preferentially activated by bephenium, antagonized more by 2-desoxoparaherquamde than by paraherquamide and was identified as the B-subtype. These observations reveal that the three channel subtypes have different selectivity for cholinergic anthelmintics. The different selectivity of these compounds should be considered when dealing with drug resistant infections.

Animals↗

PubMed2006

Growth of order in an anisotropic Swift-Hohenberg model.

We have studied the ordering kinetics of a two-dimensional anisotropic Swift-Hohenberg (SH) model numerically. The defect structure for this model is simpler than for the isotropic SH model. One finds only dislocations in the aligned ordering striped system. The motion of these point defects is strongly influenced by the anisotropic nature of the system. We developed accurate numerical methods for following the trajectories of dislocations. This allows us to carry out a detailed statistical analysis of the dynamics of the dislocations. The average speeds for the motion of the dislocations in the two orthogonal directions obey power laws in time with different amplitudes but the same exponents. The position and velocity distribution functions are only weakly anisotropic.

Journal Article↗

PubMed2004

Vortex kinetics of conserved and nonconserved On models.

We study the motion of vortices in the conserved and nonconserved phase-ordering models. We give an analytical method for computing the speed and position distribution functions for pairs of annihilating point vortices based on heuristic scaling arguments. In the nonconserved case this method produces a speed distribution function consistent with previous analytic results. As two special examples, we simulate numerically the conserved and nonconserved O(2) model in two-dimensional space. The numerical results for the nonconserved case are consistent with the theoretical predictions. The speed distribution of the vortices in the conserved case is measured. Our theory produces a distribution function with the correct large speed tail but does not accurately describe the numerical data at small speeds. The position distribution functions for both models are measured and we find good agreement with our analytic results. We are also able to extend this method to models with a scalar order parameter.

Journal Article↗

PubMed2004

Model for striped growth.

We introduce a model for describing the defected growth of striped patterns. This model, while roughly related to the Swift-Hohenberg model, generates a quite different mixture of defects during phase ordering. We find two characteristic lengths in the system: the scaling length L(t), and the average width of the domain walls. The growth law exponent is larger than the value of 1/2 found in typical point defect systems.

Journal Article↗

PubMed2003

Vortex dynamics in a coarsening two-dimensional XY model.

The vortex velocity distribution function for a two-dimensional coarsening nonconserved O(2) time-dependent Ginzburg-Landau model is determined numerically and compared to theoretical predictions. In agreement with these predictions the distribution function scales with the average vortex speed which is inversely proportional to t(x), where t is the time after the quench and x is near 1/2. We find the entire curve, including a large speed algebraic tail, in good agreement with the theory.

Journal Article↗

PubMed2003

Defect structures in the growth kinetics of the Swift-Hohenberg model.

The growth of striped order resulting from a quench of the two-dimensional Swift-Hohenberg model is studied in the regime of a small control parameter and quenches to zero temperature. We introduce an algorithm for finding and identifying the disordering defects (dislocations, disclinations, and grain boundaries) at a given time. We can track their trajectories separately. We find that the coarsening of the defects and lowering of the effective free energy in the system are governed by a growth law L(t) approximately t(x) with an exponent x near 1/3. We obtain scaling for the correlations of the nematic order parameter with the same growth law. The scaling for the order parameter structure factor is governed, as found by others, by a growth law with an exponent smaller than x and near to 1/4. By comparing two systems with different sizes, we clarify the finite-size effect. We find that the system has a very low density of disclinations compared to that for dislocations and fraction of points in grain boundaries. We also measure the speed distributions of the defects at different times and find that they all have power-law tails and the average speed decreases as a power law.

Journal Article↗