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Biomedical subjects

K M Ho

Publications and source records attributed to K M Ho.

At least 19 recordsLinked to original sources
PubMed2006

Oxidation pattern of small silicon oxide clusters: structures and stability of Si6On (n = 1-12).

We have performed systematic ab initio calculations to study the structures and stability of Si(6)O(n)() clusters (n = 1-12) in order to understand the oxidation process in silicon systems. Our calculation results show that oxidation pattern of the small silicon cluster, with continuous addition of O atoms, extends from one side to the entire Si cluster. Si atoms are found to be separated from the pure Si cluster one-by-one by insertion of oxygen into the Si-O bonds. From fragmentation energy analyses, it is found that the Si-rich clusters usually dissociate into a smaller pure Si clusters (Si(5), Si(4), Si(3), or Si(2)), plus oxide fragments such as SiO, Si(2)O(2), Si(3)O(3), Si(3)O(4), and Si(4)O(5). We have also studied the structures of the ionic Si(6)O(n)(+/-) (n = 1-12) clusters and found that most of ionic clusters have different lowest-energy structures in comparison with the neutral clusters. Our calculation results suggest that transformation Si(6)O(n)+(a) + O --> Si(6)O(n+1)+(a) should be easier.

Journal Article↗
PubMed2006

Quantum size effect on the diffusion barriers and growth morphology of Pb/Si(111).

An intriguing growth morphology of Pb islands on a Si(111) surface is observed in our STM experiments: the growth of a Pb layer on Pb islands with unstable heights starts from the periphery and moves towards the center, while the nucleation of the next layer on stable Pb islands starts away from the periphery. Using first-principles total energy calculations, we have studied the diffusion barriers of Pb adatoms on a freestanding Pb(111) film as a function of film thickness. The diffusion barriers are found to be very low (<60 meV), and a bi-layer oscillation due to the quantum size effect (QSE) is observed, with a lower barrier on the odd-layered, relatively unstable Pb films. The diffusion barrier difference between the odd- and even-layered film is as large as 40 meV. The observed unusual growth can be attributed to this big difference in the diffusion barriers due to QSE.

Journal Article↗
PubMed2006

Dynamics of the trimeric AcrB transporter protein inferred from a B-factor analysis of the crystal structure.

The Escherichia coli AcrB multidrug transporter recognizes a wide range of toxic chemicals and actively extrudes them from cells. The molecular basis of multidrug transport in AcrB remains unknown. Herein, we describe normal mode analyses to study important regions for drug recognition and extrusion in this transporter. Based on the X-ray structure of AcrB, an elastic network model has been able to correct errors arising from crystal imperfection in the experimental B-factors. The results allow us to understand the functional dynamics of this membrane protein. It is expected that this technique can be applied to other membrane proteins with known structures.

Crystallography↗
PubMed2005

Characterization of contamination in and toxicities of a shipyard area in Hong Kong.

This is the first integrated study on the contaminant characterization and toxicities of a shipyard area. This site in Hong Kong contained 3.6-33.4 mg kg(-1) dichlorodiphenyltrichloroethane and 5-79 g kg(-1) oil and grease. Other pollutants exceeding the Dutch intervention values were total polyaromatic hydrocarbons, total petroleum hydrocarbons, and metals Cu, Pb and Zn. These pollutants persisted partially owing to the poor fertility with <125 mg N kg(-1) and <530 mg P kg(-1) typical of coastal soil. Sediments collected within 100 m also showed contamination exceeding the China and Hong Kong intervention levels. The shipyard soil killed two bacteria Pseudomonas stutzeri and Acinetobacter sp. isolated from a clean coastal soil, inhibited germination of three exogenous plants Triticum aestivum, Brassica chinense and Lolium perenne, and inhibited proliferation of three indigenous bacteria: Methylobacterium sp., Pseudomonas aeruginosa and Bacillus cereus. Thus, ex situ remediation was needed.

Bacteria↗
PubMed2005

Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers.

Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers are investigated by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. It is observed in the TBMD simulations that two single vacancies coalesce into a 5-8-5 double vacancy at the temperature of 3000 K, and it is further reconstructed into a new defect structure, the 555-777 defect, by the Stone-Wales type transformation at higher temperatures. First principles calculations confirm that the 555-777 defect is energetically much more stable than two separated single vacancies, and the energy of the 555-777 defect is also slightly lower than that of the 5-8-5 double vacancy. In TBMD simulation, it is also found that the four single vacancies reconstruct into two collective 555-777 defects which is the unit for the hexagonal haeckelite structure proposed by Terrones et al. [Phys. Rev. Lett. 84, 1716 (2000)].

Journal Article↗
PubMed2005

Structure and stability of oxygen adsorption on Si(n) (n = 5-10) clusters.

The structures, binding energies, and electronic properties of one oxygen atom (O) and two oxygen atoms (2O) adsorption on silicon clusters Si(n) with n ranging from 5 to 10 are studied systematically by ab initio calculations. Twelve stable structures are obtained, two of which are in agreement with those reported in previous literature and the others are new structures that have not been proposed before. Further investigations on the fragmentations of Si(n)O and Si(n)O2 (n = 5-10) clusters indicate that the pathways Si(n)O --> Si(n-1) + SiO and Si(n)O2 --> Si(n-2) + Si2O2 are most favorable from thermodynamic viewpoint. Among the studied silicon oxide clusters, Si8O, Si9O, Si5O2 and Si8O2 correspond to large adsorption energies of silicon clusters with respect to O or 2O, while Si8O, with the smallest dissociation energy, has a tendency to separate into Si7 + SiO. Using the recently developed quasi-atomic minimal-basis-orbital method, we have also calculated the unsaturated valences of the neutral Si(n) clusters. Our calculation results show that the Si atoms which have the largest unsaturated valences are more attractive to O atom. Placing O atom right around the Si atoms with the largest unsaturated valences usually leads to stable structures of the silicon oxide clusters.

Adsorption↗
PubMed2005

Ab initio molecular dynamics simulation of liquid Al88Si12 alloys.

First-principles molecular dynamics simulations are carried out to study the structures, dynamics, and electronic properties of liquid Al88Si12 in the temperature ranging from 898 to 1298 K. The temperature dependence of static structure factors, pair correlation functions, and electronic density-of-states are investigated. The structural properties obtained from the simulations are in good agreement with the x-ray diffraction experimental results.

Journal Article↗
PubMed2005

Use of intrathecal neostigmine as an adjunct to other spinal medications in perioperative and peripartum analgesia: a meta-analysis.

Intrathecal neostigmine has been used as an adjunct to intrathecal local anaesthetic or opioid to prolong regional analgesia and improve haemodynamic stability, with variable results. This meta-analysis aims to evaluate the effectiveness and side-effects of intrathecal neostigmine in the perioperative and peripartum settings. The literature search was based on Cochrane Controlled Trials Register, EMBASE and MEDLINE (from 1966 to 14 November 2003) databases. Volunteer and animal studies were excluded. We identified 26 studies and 19 were considered suitable for detailed data extraction. Intrathecal neostigmine increased the incidence of nausea and vomiting (OR 5.0, 95% CI: 3.4 to 7.3; P<0.00001), bradycardia requiring intravenous atropine (OR 2.7, 95% CI: 1.4 to 5.4; P=0.005), and anxiety, agitation, or restlessness (OR 10.3, 95% CI: 3.7 to 28.9; P=0.00001). It improved the overall 24 hour VAS score (-1.4 VAS pain score, 95% CI: -1.7 to -1.2, P<0.00001), delayed the time of first request for rescue analgesia (168 min, 95% CI: 125 to 211; P<0.00001), and reduced the total number of rescue injections of nonsteroidal anti-inflammatory drug within the first 24 hours (-0.8, 95% CI: -1.1 to -0.4; P=0. 00001). It did not affect the duration of motor blockade (3.5 min, 95% CI: -1.5 to 8.6; P=0.17) or the total amount of ephedrine required (-0.4 mg, 95% CI: -1.5 to 0.7; P=0.5). Adding intrathecal neostigmine to other spinal medications improves perioperative and peripartum analgesia marginally when compared with placebo. It is associated with significant side-effects and the disadvantages outweigh the minor improvement in analgesia achieved.

Adjuvants, Anesthesia↗
PubMed2004

Effect of chain connectivity on the structure of Lennard-Jones liquid and its implicationon statistical potentials for protein folding.

Statistical contact potentials and bead-spring models have been widely used for computational studies of protein folding. However, there has been speculation that systematic error may arise in the contact energy calculations when the statistical potentials are deduced under the assumption that the chain connectivity in proteins can be ignored. To address this issue, we have performed molecular-dynamics simulations to study the structure and dynamics of a simple liquid system in which the beads are either connected or unconnected with springs. Results from the present study provide useful information for assessing the accuracy of the statistical potentials for protein structure simulations.

Base Sequence↗
PubMed2004

Molecule intrinsic minimal basis sets. I. Exact resolution of ab initio optimized molecular orbitals in terms of deformed atomic minimal-basis orbitals.

A method is presented for expressing the occupied self-consistent-field (SCF) orbitals of a molecule exactly in terms of chemically deformed atomic minimal-basis-set orbitals that deviate as little as possible from free-atom SCF minimal-basis orbitals. The molecular orbitals referred to are the exact SCF orbitals, the free-atom orbitals referred to are the exact atomic SCF orbitals, and the formulation of the deformed "quasiatomic minimal-basis-sets" is independent of the calculational atomic orbital basis used. The resulting resolution of molecular orbitals in terms of quasiatomic minimal basis set orbitals is therefore intrinsic to the exact molecular wave functions. The deformations are analyzed in terms of interatomic contributions. The Mulliken population analysis is formulated in terms of the quasiatomic minimal-basis orbitals. In the virtual SCF orbital space the method leads to a quantitative ab initio formulation of the qualitative model of virtual valence orbitals, which are useful for calculating electron correlation and the interpretation of reactions. The method is applicable to Kohn-Sham density functional theory orbitals and is easily generalized to valence MCSCF orbitals.

Journal Article↗
PubMed2004

Molecule intrinsic minimal basis sets. II. Bonding analyses for Si4H6 and Si2 to Si10.

The method, introduced in the preceding paper, for recasting molecular self-consistent field (SCF) or density functional theory (DFT) orbitals in terms of intrinsic minimal bases of quasiatomic orbitals, which differ only little from the optimal free-atom minimal-basis orbitals, is used to elucidate the bonding in several silicon clusters. The applications show that the quasiatomic orbitals deviate from the minimal-basis SCF orbitals of the free atoms by only very small deformations and that the latter arise mainly from bonded neighbor atoms. The Mulliken population analysis in terms of the quasiatomic minimal-basis orbitals leads to a quantum mechanical interpretation of small-ring strain in terms of antibonding encroachments of localized molecular-orbitals and identifies the origin of the bond-stretch isomerization in Si4H6. In the virtual SCF/DFT orbital space, the method places the qualitative notion of virtual valence orbitals on a firm basis and provides an unambiguous ab initio identification of the frontier orbitals.

Journal Article↗
PubMed2004

A simple maneuver to replace dislodged laparoscopic port.

Inadvertent dislodgment of laparoscopic port can occur despite preventive measures. We describe a simple maneuver to replace a dislodged port using a palpation probe. The principle is analogous to that of using a laparoscopic grasping forceps. It is easy to perform, quick, reliable, safe, and particularly useful for the laparoscopists in training.

Humans↗
PubMed2004

Fatal systemic air embolism during endoscopic retrograde cholangio-pancreatography.

Air embolism is a rare complication of gastrointestinal endoscopy. We present a 56-year-old male who developed both venous and systemic arterial air embolism during an endoscopic retrograde cholangiopancreatogram. Despite early treatment based on clinical diagnosis and confirmation by transthoracic echocardiography, the patient died as a result of severe cerebral ischaemia. Risk factors associated with air embolism in gastrointestinal endoscopic procedures include situations where the mucosa is not intact or where high pressures are generated in the lumen of the gastrointestinal tract. Clinical diagnosis of air embolism during endoscopy is difficult and urgent echocardiography is the investigation of choice. Treatment is largely supportive but hyperbaric oxygen therapy should be considered in any severe cases, especially if neurological injury is present.

Cholangiopancreatography, Endoscopic Retrograde↗