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C C Han

Publications and source records attributed to C C Han.

10 recordsLinked to original sources
PubMed2004

Shear-induced structure in polymer-clay nanocomposite solutions.

The equilibrium structure and shear response of model polymer-clay nanocomposite gels are measured using X-ray scattering, light scattering, optical microscopy, and rheometry. The suspensions form physical gels via the "bridging" of neighboring colloidal clay platelets by the polymer, with reversible adsorption of polymer segments onto the clay surface providing a short-range attractive force. As the flow disrupts this transient network, coupling between composition and stress leads to the formation of a macroscopic domain pattern, while the clay platelets orient with their surface normal parallel to the direction of vorticity. We discuss the shear-induced structure, steady-shear rheology, and oscillatory-shear response of these dynamic networks, and we offer a physical explanation for the mesoscale shear response. In contrast to flow-induced "banding" transitions, no stress plateau is observed in the region where macroscopic phase separation occurs. The observed platelet orientation is different from that reported for polymer-melt clay nanocomposites, which we attribute to effects associated with macroscopic phase separation under shear flow.

Journal Article↗
PubMed2003

Early-stage compositional segregation in polymer-blend films.

The existence of a transient period during the surface enrichment of a binary polymer blend by one of its components has been suggested by previous theoretical and experimental studies as well as computer simulations. Taking advantage of the high depth resolution of neutron reflectivity and the slow dynamics of polymers near their glass transition, we investigate this early-stage surface compositional enrichment in a phase separating polymer blend for the first time. Two stages of surface enrichment layer growth are observed. A rapid local surface enrichment at the chain segmental level occurs first, followed by a slower growth of a diffuse layer having a scale on the order of the bulk correlation length and the radius of gyration of the surface enriching polymer chains.

Journal Article↗
PubMed2003

FIGO stage 1B2 cervical carcinoma--the KK Women's and Children's Hospital experience.

INTRODUCTION: The objectives of this review were to document the surgico-pathological characteristics of surgically resected FIGO stage 1B2 cervical carcinoma and to review our overall experience with this disease. MATERIALS AND METHODS: This is a retrospective review of 35 patients diagnosed and treated from September 1990 to November 2001. RESULTS: The median age was 42 years and the mean tumour diameter was 5.1 cm. Majority were squamous cell carcinomas (65.7%), 28.6% were adenocarcinomas and 5.7% were adeno-squamous carcinomas. The primary treatment comprised radical surgery in 77.1%, radiotherapy in 20% and neoadjuvant chemotherapy followed by radical surgery and adjuvant radiotherapy in 2.9%. Significant surgico-pathological features noted were deep stromal invasion (66.7%), lympho-vascular space invasion (55.6%), parametrial involvement (22.2%), positive margins (3.7%) and pelvic node metastases (33.3%). Postoperative radiation was given to 92.6% of the patients who underwent primary surgery, of whom 29% received concurrent chemotherapy. Radiation toxicity was mild with no grade 3 or 4 toxicity documented. For the patients who had surgery, the recurRence rate was 14.8% (11.1% pelvic and 3.7% distant) and the survival rate was 88.9%. For those who had primary radiation, the rate of persistent disease was 28.6%, the distant recurrence rate was 28.6% and the survival rate was 57.1%. CONCLUSION: FIGO stage 1B2 cervical carcinomas are associated with significant rates of adverse surgico-pathological features. The ideal primary treatment is yet to be established and should be determined by prospective randomised trials.

Adult↗
PubMed2002

Optical detection and charge-state analysis of MALDI-generated particles with molecular masses larger than 5 MDa.

Charged polystyrene nanoparticles are generated by matrix-assisted laser desorption/ionization (MALDI) and detected by laser-induced fluorescence (LIF) in a quadrupole ion trap. Employing the LIF technique, observations of individual fluorescent nanospheres (27 nm in diameter and containing 180 fluorescein dye equivalents) have been achieved with an average signal-to-noise ratio of approximately 10. With the trap operating at a frequency around 5 kHz, charge state analysis of the particles reveals that the number of charges carried by the spheres is between 1 and 10. It suggests a mass-to-charge ratio (m/z) in the range of 10(5)-10(6) for the MALDI-generated particles. To effectively trap such large particles (m > 5 MDa), damping of the particles' motions by using approximately 50 mTorr He buffer gas is absolutely required. Similar findings are obtained for particles with a nominal size of 1 microm in diameter, demonstrating that production of charged particles with a molecular mass as high as 10(12) Da is possible using the MALDI technique.

Fluorescent Dyes↗
PubMed2000

A view of dynamics changes in the molten globule-native folding step by quasielastic neutron scattering.

In order to understand the changes in protein dynamics that occur in the final stages of protein folding, we have used neutron scattering to probe the differences between a protein in its folded state and the molten globule states. The internal dynamics of bovine alpha-lactalbumin (BLA) and its molten globules (MBLA) have been examined using incoherent, quasielastic neutron scattering (IQNS). The IQNS results show length scale dependent, pico-second dynamics changes on length scales from 3.3 to 60 A studied. On shorter-length scales, the non-exchangeable protons undergo jump motions over potential barriers, as those involved in side-chain rotamer changes. The mean potential barrier to local jump motions is higher in BLA than in MBLA, as might be expected. On longer length scales, the protons undergo spatially restricted diffusive motions with the diffusive motions being more restricted in BLA than in MBLA. Both BLA and MBLA have similar mean square amplitudes of high frequency motions comparable to the chemical bond vibrational motions. Bond vibrational motions thus do not change significantly upon folding. Interestingly, the quasielastic scattering intensities show pronounced maxima for both BLA and MBLA, suggesting that "clusters" of atoms are moving collectively within the proteins on picosecond time scales. The correlation length, or "the cluster size", of such atom clusters moving collectively is dramatically reduced in the molten globules with the correlation length being 6.9 A in MBLA shorter than that of 18 A in BLA. Such collective motions may be important for the stability of the folded state, and may influence the protein folding pathways from the molten globules.

Animals↗
PubMed2000

Characterizing the transmission properties of an ion funnel.

The characteristic features of ion transmission properties in a radio-frequency (RF) electric-field driven ion funnel using the SIMION ion trajectory simulation package is presented. A user program applying the Douglas ion-neutral collisional drag coefficient model is incorporated to properly account for the ion focusing and transport effect of the background gas under the effect of the driving RF and a superimposed DC field. The simulated m/z transmission window compares favorably with the experimental results reported by Smith et al. RF amplitude and pressure dependence of experimentally observed m/z transmission windows are also examined, and an approximated effective potential model based on Gerlich's equation is proposed to interpret the low-m/z cutoff behavior. A modified ion funnel configuration is described.

Journal Article↗
PubMed1999

Identification of Enterobacteriaceae bacteria by direct matrix-assisted laser desorptiom/ionization mass spectrometric analysis of whole cells.

Several members of Enterobacteriaceas were analyzed by matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometry (TOFMS). Characteristic mass spectral peaks and patterns were observed in the mass range of 2 to 20 kDa. The mass peaks reported to be reproducibly observed by previous researchers, which were claimed to serve as species/strain-specific biomarkers, are consistently observed in our current study. Despite the high degree of similarity found in the MALDI mass spectra within the enteric bacteria, minor yet notable differences existed to allow their differentiation. Five spectral peaks at m/z 4364, 5380, 6384, 6856, and 9540, generated reproducibly for each genus studied here, are assigned as family-specific biomarkers for the Family Enterobacteriaceae. The mass peaks at m/z 7324, 7724, 9136, and 9253 are assigned as genus-specific biomarkers for Salmonella. Some unique biomarkers characterizing the species and strains of E. coli are also presented.

Biomarkers↗
PubMed1997

Characterization of a partially structured state in an all-beta-sheet protein.

Cardiotoxin analogue III (CTX III) is a low-molecular-mass all-beta-sheet protein isolated from the Taiwan cobra (Naja naja atra) venom. A stable partially structured state similar to the "molten globule' state has been identified for CTX III in a 3% (w/v) solution of 2,2,2-trichloroacetic acid at 298 K. This stable state has been structurally characterized using a variety of techniques such as CD, 1-anilinonaphthalene-8-sulphonate fluorescence binding, Fourier transform IR and two-dimensional NMR spectroscopy techniques. Direct assignment of the homonuclear two-dimensional NMR spectra of the protein in 3% trichloroacetic acid showed that drastic structural perturbation had not taken place in the protein and that the 'intermediate' state retained a significant portion of the native secondary-structural interactions. It is found that about 65% of the native beta-sheet structural contacts are maintained in the partially structured state of CTX III in 3% trichloroacetic acid.

Circular Dichroism↗
PubMed1995

Riboflavin-deficient chicken embryos: hypoglycemia without dicarboxylic aciduria.

Chicken embryos in eggs laid by hens that are genetically unable to deposit riboflavin into their eggs die on or about the 13th day of incubation. We show that these riboflavin-deficient embryos grow normally until the day of death and that their heart rate is normal to within an hour of death. The embryos have symptoms of impaired fatty acid oxidation, including decreased activity of FAD-dependent medium-chain acyl CoA dehydrogenase in liver and heart along with a significant accumulation of intermediates of fatty acid oxidation (C10, C12, and C14 acids). Unlike riboflavin-deficient mammals, the embryos do not accumulate dicarboxylic acids derived from omega-oxidation of fatty acids. Blood glucose is near normal on day 10 but declines to undetectable levels by the time of death. Allantoic fluid from the riboflavin-deficient embryos of 11 days or older contains more lactate than 3-hydroxybutyrate, while in normal embryos the reverse is true. No appreciable amounts of glycine-conjugated acids were found. We conclude that the major and perhaps primary pathological effect of riboflavin deficiency in chicken embryos is the impairment of fatty acid beta-oxidation, and that the subsequent depletion of limited carbohydrate reserves leads to sudden death.

Animals↗