Biomedical subjects

H B Chan

Publications and source records attributed to H B Chan.

10 recordsLinked to original sources

PubMed2006

Supernarrow spectral peaks near a kinetic phase transition in a driven nonlinear micromechanical oscillator.

We measure the spectral densities of fluctuations of an underdamped nonlinear micromechanical oscillator. By applying a sufficiently large periodic excitation, two stable dynamical states are obtained within a particular range of driving frequency. White noise is injected into the excitation, allowing the system to overcome the activation barrier and switch between the two states. While the oscillator predominately resides in one of the two states for most frequencies, a narrow range of frequencies exist where the occupations of the two states are approximately equal. At these frequencies, the oscillator undergoes a kinetic phase transition that resembles the phase transition of thermal equilibrium systems. We observe a supernarrow peak in the spectral densities of fluctuations of the oscillator. This peak is centered at the excitation frequency and arises as a result of noise-induced transitions between the two dynamical states.

Journal Article↗

PubMed2006

Optical transmission through double-layer metallic subwavelength slit arrays.

We present measurements of transmission of infrared radiation through double-layer metallic grating structures. Each metal layer contains an array of subwavelength slits and supports transmission resonance in the absence of the other layer. The two metal layers are fabricated in close proximity to allow coupling of the evanescent field on individual layers. The transmission of the double layer is found to be surprisingly large at particular wavelengths, even when no direct line of sight exists through the structure as a result of the lateral shifts between the two layers. We perform numerical simulations using rigorous coupled wave analysis to explain the strong dependence of the peak transmission on the lateral shift between the metal layers.

Journal Article↗

PubMed2006

Ex-utero intrapartum treatment: a controlled approach to the management of anticipated airway problems in the newborn.

Airway problems in an unborn foetus that may cause obstruction can be safely managed using an ex-utero intrapartum technique. Advanced technology now allows many congenital airway problems to be diagnosed in the prenatal period. Careful prenatal planning of an ex-utero intrapartum treatment allows safe airway control while the foetus remains on uteroplacental support. It avoids the need for emergent intervention of an acutely obstructed airway in a neonate that often has disastrous consequences.

Adult↗

PubMed2003

Desbuquois syndrome: clinical and radiological report of the first two Chinese cases from a consanguineous family.

Two siblings from China have been observed with severe short stature of prenatal onset and developmental delay. The radiographic features were characteristic of Desbuquois syndrome. The association of a genetic skeletal dysplasia and developmental delay is a relatively rare combination, although this syndrome is readily diagnosable from its distinctive radiographic features.

Abnormalities, Multiple↗

PubMed2001

Nonlinear micromechanical Casimir oscillator.

The Casimir force between uncharged metallic surfaces originates from quantum-mechanical zero-point fluctuations of the electromagnetic field. We demonstrate that this quantum electrodynamical effect has a profound influence on the oscillatory behavior of microstructures when surfaces are in close proximity (< or =100 nm). Frequency shifts, hysteretic behavior, and bistability caused by the Casimir force are observed in the frequency response of a periodically driven micromachined torsional oscillator.

Journal Article↗

PubMed2001

Quantum mechanical actuation of microelectromechanical systems by the Casimir force.

The Casimir force is the attraction between uncharged metallic surfaces as a result of quantum mechanical vacuum fluctuations of the electromagnetic field. We demonstrate the Casimir effect in microelectromechanical systems using a micromachined torsional device. Attraction between a polysilicon plate and a spherical metallic surface results in a torque that rotates the plate about two thin torsional rods. The dependence of the rotation angle on the separation between the surfaces is in agreement with calculations of the Casimir force. Our results show that quantum electrodynamical effects play a significant role in such microelectromechanical systems when the separation between components is in the nanometer range.

Journal Article↗

PubMed1999

Early onset of hypernatraemic dehydration and fever in exclusively breast-fed infants.

Five cases of moderately severe hypernatraemic dehydration were identified within a 5-month period between two regional hospitals in Hong Kong. Unlike previous reported cases, these exclusively breast-fed infants presented with the unusual triad of fever, absence of overt signs of dehydration and within the first week of life. Three of the cases also had high serum bilirubin concentrations at presentation. The fever subsided quickly and the serum bilirubin concentration fell rapidly within a few hours of rehydration. All infants made an uneventful recovery without permanent neurological sequelae. Fever, presumably secondary to dehydration, is an useful early warning sign. These cases emphasize the importance of early and regular measurement of bodyweight in exclusively breast-fed infants so that prompt identification of affected cases may prevent potentially detrimental complications.

Age of Onset↗

PubMed1997

Report on anti-Dib encountered in two Hong Kong Chinese.

Two cases of anti-Dib, a rarely encountered antibody, were identified in serum samples referred by hospital blood banks during the past 13 months. Case 1 is a 41-year-old female who required blood for elective surgery. Case 2 is a premature infant suffering from mild neonatal jaundice on day 2 after birth. The anti-Dib in both cases exhibited marked dosage effect. The titer/score against Di(a+b+) and Di(a-b+) red blood cells (RBCs) in case 1 was 8/10 and 32/32, respectively, and in case 2, 4/18 and 32/46. The monocyte monolayer assay (MMA) also gave a similar pattern of results, being l5 percent and 100 percent reactive when tested with Di(a+b+) and Di(a-b+) RBCs in case 1, and 0.4 percent (within normal range) and l4.4 percent in case 2. The patient in case 1 underwent her operation without blood transfusion. The infant in case 2 was treated by phototherapy and subsequently recovered without the need for exchange transfusion.

Journal Article↗

PubMedDate not supplied

Alteration of nuclear matrix protein composition of neuroblastoma cells after arsenic trioxide treatment.

The aims of the present study were to assess the effects of arsenic trioxide on the nuclear matrix protein profiles of mouse neuroblastoma cells. Arsenic trioxide induces apoptosis of acute promyelocytic leukemia cells. Our results demonstrated that 2 microM As2O3 could significantly inhibit the growth of Neuro-2a cells. As early as 24 hours after As2O3 treatment, we began to observe the alteration of nuclear matrix proteins and apoptosis in tumor cells by TUNEL assay but not by DNA ladder. An increase expression of Hsc in nuclear matrix proteins of 2 microM As2O3 treated cells was also noted. Our results also showed that before a mass range of apoptosis occurred, the composition of nuclear matrix proteins had altered. Hence the alteration of nuclear matrix proteins, such as increased expression of Hsc, may be a sensitive indicator for the detection of early apoptosis.

Animals↗

PubMedDate not supplied

The effect of arsenic trioxide on the expression of Hsc and HNF4 in nuclear matrix proteins in HepG2 cells.

Anticancer agents interfere with the proliferation and survival of tumor cells by a variety of mechanisms. An important factor in the development of a cytotoxic effect by certain anticancer agents is the localization of drug-induced lesions within the cell nucleus. Drug-target interactions at the level of nuclear matrix (NM) may be critical events in the induction of cell death by some of these agents. Arsenic trioxide (As2O3) was identified as a very potent anti-leukemic agent by inducing apoptosis. The present study shows that As2O3 significantly inhibits the growth of hepatoblastoma cell line, HepG2, changes the composition of nuclear matrix proteins and reduces the expression of Hsc 70 and HNF4 in HepG2, which in turn initiate a cascade of events that compromise multiple nuclear functions and, ultimately, cell survival.

Antigens, Nuclear↗