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Biomedical subjects

A J Liu

Publications and source records attributed to A J Liu.

At least 19 recordsLinked to original sources
PubMed2004

Statistical mechanics of a gas-fluidized particle.

Characterization of the microscopic fluctuations in systems that are far from equilibrium is crucial for understanding the macroscopic response. One approach is to use an 'effective temperature'--such a quantity has been invoked for chaotic fluids, spin glasses, glasses and colloids, as well as non-thermal systems such as flowing granular materials and foams. We therefore ask to what extent the concept of effective temperature is valid. Here we investigate this question experimentally in a simple system consisting of a sphere placed on a fine screen in an upward flow of gas; the sphere rolls because of the turbulence it generates in the gas stream. In contrast to many-particle systems, in which it is difficult to measure and predict fluctuations, our system has no particle-particle interactions and its dynamics can be captured fully by video imaging. Surprisingly, we find that the sphere behaves exactly like a harmonically bound brownian particle. The random driving force and frequency-dependent drag satisfy the fluctuation-dissipation relation, a cornerstone of statistical mechanics. The statistical mechanics of near-equilibrium systems is therefore unexpectedly useful for studying at least some classes of systems that are driven far from equilibrium.

Journal Article↗
PubMed2001

Elastically driven linker aggregation between two semiflexible polyelectrolytes.

The behavior of mobile linkers connecting two semiflexible charged polymers, such as polyvalent counterions connecting DNA or F-actin chains, is studied theoretically. The chain bending rigidity induces an effective repulsion between linkers at large distances while the interchain electrostatic repulsion leads to an effective short-range interlinker attraction. We find a rounded phase transition from a dilute linker gas where the chains form large loops between linkers to a dense disordered linker fluid connecting parallel chains. The onset of chain pairing occurs within the rounded transition.

Actins↗
PubMed2001

Effect of nonzero chain diameter on "DNA" condensation.

We present a simple model to investigate the effect of chain diameter on multivalent-counterion-induced attractions between two charged chains. In our minimal model, the chains are rigid rods of diameter D with a uniform charge density on the surface, and the counterions are point ions. As a function of the separation between two rods, we find a repulsive barrier in the free energy whose height increases with D. We have also explored the effect of counterion valency Z on the interaction. For parameters characteristic of DNA, we find that a minimum valency of Z=3 is required to produce condensation. We also find that the shape of the potential is fairly insensitive to Z for Z>/=3. These results are consistent with experimental observations of DNA condensation.

Biophysical Phenomena↗
PubMed2001

Serotyping and antimicrobial susceptibility of group B Streptococcus over an eight-year period in southern Taiwan.

The increase in penicillin resistance among pneumococci and viridans streptococci and the development of serotype-specific conjugate vaccine have increased the need for knowledge of the antimicrobial susceptibility and the capsular serotypes of group B streptococci. Over an 8-year period, 351 group B streptococcal isolates from southern Taiwan were tested for antimicrobial susceptibility and serotype determination. Eighty-seven percent of the isolates were typeable. Types III (28.5%) and V (27.1%) were the most common serotypes. The occurrence of type V isolates increased with age, while that of type III isolates decreased with age, showing a predominance in children less than 1 year of age. Of 118 isolates from cases of invasive infection, types Ia, Ib, II, III, IV, and V accounted for 12.7, 11.9, 0.8, 33, 1.7, and 26.3%, respectively. Using the agar dilution method, all isolates were found to be susceptible to penicillin, cefotaxime, and vancomycin, 99.4% to ofloxacin, 78.1% to chloramphenicol, 63.2% to azithromycin, 62.6% to erythromycin, 57.3% to clindamycin, and 2.8% to tetracycline. Chloramphenicol resistance was associated with type III isolates (59 of 100, 59%) and erythromycin and azithromycin resistance with type Ib isolates (25 of 33 176%], and 21 of 33 [64%], respectively). Thus, 72% of the isolates from invasive infections were serotype III, V, or Ia, and penicillin remains the drug of choice for treatment or prophylaxis of group B streptococcal infections in southern Taiwan, despite the high prevalence of penicillin resistance among Streptococcus pneumoniae and viridans streptococci.

Adolescent↗
PubMed2001

[Expression of glucose transporter-1 in endometrial hyperplasia and well-differentiated endometrioid adenocarcinoma].

OBJECTIVE: To investigate the expression of glucose transporter-1 (GLUT1) in endometrial hyperplasia and well-differentiated endometrioid adenocarcinomas. METHODS: Sixty formalin fixed, paraffin-embedded sections of various endometrial hyperplasia and well-differentiated endometrioid adenocarcinomas were immunostained with rabbit anti-GLUT1 antibody using streptavidin-biotin method. RESULTS: Two of 12 simple hyperplasia and one of seven complex hyperplasia without atypia were focally positive in metaplastic epithelia. All complex atypical hyperplasia showed positive in varied degree, and 26 among 28 cases of adenocarcinoma were stained positively. CONCLUSIONS: Overexpression of GLUT1 is a consistent feature of atypical hyperplasia and adenocarcinoma. GLUT1 immunostaining is found to be helpful in distinguishing hyperplasia with atypia from those without atypia.

Adenocarcinoma↗
PubMed1999

Statistics of shear-induced rearrangements in a two-dimensional model foam.

Under steady shear, a foam relaxes stress through intermittent rearrangements of bubbles accompanied by sudden drops in the stored elastic energy. We use a simple model of foam that incorporates both elasticity and dissipation to study the statistics of bubble rearrangements in terms of energy drops, the number of nearest neighbor changes, and the rate of neighbor-switching (T1) events. We do this for a two-dimensional system as a function of system size, shear rate, dissipation mechanism, and gas area fraction. We find that for dry foams, there is a well-defined quasistatic limit at low shear rates where localized rearrangements occur at a constant rate per unit strain, independent of both system size and dissipation mechanism. These results are in good qualitative agreement with experiments on two-dimensional and three-dimensional foams. In contrast, we find for progessively wetter foams that the event size distribution broadens into a power law that is cut off only by system size. This is consistent with criticality at the melting transition.

Journal Article↗
PubMed1999

Counterion-mediated, non-pairwise-additive attractions in bundles of like-charged rods.

Stiff polyelectrolyte chains, such as DNA, can attract each other in solution even though they have the same sign of charge. The attractions are mediated by multivalent counterions, which lead to an effective interaction at the two-chain level that is attractive at short range and repulsive at long range. However, the effective interchain interactions are not pairwise additive. We present a formulation that allows theoretical treatment of the many-chain problem without assuming pairwise additivity. We show that a bundle of chains held together by counterion-mediated attractions can be described in terms of a bulk and surface free energy, and discuss the temperature dependence of the attraction.

DNA↗
PubMed1999

Effect of ordering on spinodal decomposition of liquid-crystal/polymer mixtures.

Partially phase-separated liquid-crystal/polymer dispersions display highly fibrillar domain morphologies that are dramatically different from the typical structures found in isotropic mixtures. To explain this, we numerically explore the coupling between phase ordering and phase-separation kinetics in model two-dimensional fluid mixtures phase separating into a nematic phase, rich in liquid crystal, coexisting with an isotropic phase, rich in polymer. We find that phase ordering can lead to fibrillar networks of the minority polymer-rich phase.

Journal Article↗
PubMed1999

Rickettsia helvetica in Ixodes ricinus ticks in Sweden.

In the present study further characterization of the amplified sequence of the citrate synthase gene of the spotted fever group Rickettsia isolated from Ixodes ricinus ticks in Sweden showed that it has 100% homology with the deposited sequence of the citrate synthase gene of Rickettsia helvetica. The restriction fragment length polymorphism (RFLP) pattern of an amplified 382-bp product of the citrate synthase sequence, defined by primers RpCS877 and RpCS1258, yielded fragments for our isolate that could be visualized as a double band that migrated at approximately 44 bp, another double band at 85 bp, and a single band at nearly 120 bp after digestion with the restriction enzyme AluI. When calculating a theoretical PCR-RFLP pattern of the sequence of the citrate synthase gene of R. helvetica from the known positions where the AluI enzyme cuts, we arrived at the same pattern that was obtained for our isolate, a pattern distinctly different from the previously published PCR-RFLP pattern for R. helvetica. Investigation of 125 living I. ricinus ticks showed a higher prevalence of rickettsial DNA in these ticks than we had found in an earlier study. Rickettsial DNA was detected by amplification of the 16S rRNA gene, for which a seminested primer system consisting of two oligonucleotide primer pairs was used. Of the 125 ticks, some were pooled, giving a total of 82 tick samples, of which 20 were found to be positive for the rickettsial DNA gene investigated. When considering the fact that some of the positive samples were pooled, the minimum possible prevalence in these ticks was 20 of 125 (16%) and the maximum possible prevalence was 46 of 125 (36.8%). These prevalence estimates conform to those of other studies of spotted fever group rickettsiae in hard ticks in Europe.

Animals↗
PubMed1991

20-[18F]fluoromibolerone, a positron-emitting radiotracer for androgen receptors: synthesis and tissue distribution studies.

To develop an androgen receptor-based, positron-emitting imaging agent for prostate tumors, we have prepared 20-fluoromibolerone (F-Mib) and evaluated its tissue distribution. This compound was synthesized in eight steps from 7 alpha-methyl-19-nortestosterone, with fluorine introduced in the penultimate step by fluoride ion displacement on a spirocyclic sulfate. Fluoromibolerone was obtained in 9%-19% radiochemical yield (decay corrected), at 1.5 hr after bombardment, with an effective specific activity of 217-283 Ci/mmol. The relative binding affinity of F-Mib is 53 (versus R1881 = 100 or mibolerone = 118). In tissue distribution studies in diethylstilbestrol-treated male rats, 18F-Mib demonstrates high target/tissue uptake efficiency and selectivity: the prostate uptake at 0.5 hr and 4 hr is 1.0%-1.3% injected dose/gram tissue (ID/g) and 0.5%-0.6% ID/g, respectively; the prostate-to-blood and the prostate-to-muscle (non-target) ratios are both ca. 4 at 0.5 hr, and increase to ca. 12 by 4 hr after injection. The observed distribution of 18F-Mib suggests that it may be useful for in vivo imaging of prostatic tumors in man by positron emission tomography.

Animals↗
PubMed1986

Venous outflow obstruction in myocutaneous flaps: changes in microcirculation detected by the perfusion fluorometer and laser Doppler.

The effects of venous occlusion on the perfusion of porcine myocutaneous groin flaps were studied by means of the laser Doppler and the dermofluorometer. A consistent decrease in fluorometer readings following venous clamping with rebound to original or greater levels after unclamping was noted. A similar pattern was noted in laser Doppler studies. However, flow as measured by the Doppler remained significant (greater than 100 mV) even with venous outflow occlusion. It is hypothesized that the Doppler is more prone than the dermofluorometer to reflect non-nutritive flow in the flap during the early period following flap construction and, therefore, may be less accurate in the evaluation of actual flap microperfusion. The fluorometer was determined to be the more desirable instrument in monitoring the microcirculatory status of myocutaneous flaps during the immediate period after flap elevation and transposition.

Animals↗