Search PubMed⌕ Search

Biomedical subjects

K M Chan

Publications and source records attributed to K M Chan.

At least 73 records · Page 4Linked to original sources
PubMed2001

Search for heavy particles decaying into electron-positron pairs in pp collisions.

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

Journal Article↗
PubMed2001

Quasi-model-independent search for new high p(T) physics at D0.

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p(T) physics in approximately 100 pb(-1) of pp collisions at square root of (s) = 1.8 TeV collected by the D0 experiment during 1992-1996 at the Fermilab Tevatron. We systematically analyze many exclusive final states and demonstrate sensitivity to a variety of models predicting new phenomena at the electroweak scale. No evidence of new high p(T) physics is observed.

Journal Article↗
PubMed2001

Ratio of jet cross sections at square root of s = 630 GeV and 1800 GeV.

The D0 Collaboration has measured the inclusive jet cross section in barpp collisions at square root of s = 630 GeV. The results for pseudorapidities (eta)<0.5 are combined with our previous results at square root of s = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute magnitude, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

Journal Article↗
PubMed2001

Parvalbumin expression is downregulated in rat fast-twitch skeletal muscles during aging.

In this study, the protein expression profile of extensor digitorum longous (EDL) and Soleus (SOL) muscles, representing fast- and slow-twitch skeletal muscles, respectively, was established using high resolution two-dimensional electrophoresis (2-DE). One protein spot was found uniquely expressed in EDL muscle. N-terminal sequence analysis identified the protein as parvalbumin. Parvalbumin is a high affinity calcium binding protein that regulates muscle contraction and relaxation. Our experiments revealed that parvalbumin expression in EDL muscle was down-regulated during aging. In addition, high-intensity exercise could reverse this age-related change. Soleus muscles do not normally express parvalbumin, but high-intensity exercise could ectopically induce its expression in both young and old SOL muscles. We have also confirmed our 2-DE findings by immunohistochemistry on muscle sections. Our results suggest that high-intensity training could be used to improve muscle functions during aging because parvalbumin play an important role in regulating skeletal muscle contraction and relaxation.

Aging↗
PubMed2001

Ratios of multijet Cross Sections in p p collisions at radical(s) = 1.8 TeV.

We report on a study of the ratio of inclusive three-jet to inclusive two-jet production cross sections as a function of total transverse energy in p&pmacr; collisions at a center-of-mass energy sqrt[s] = 1.8 TeV, using data collected with the D0 detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are used to deduce preferred renormalization scales in perturbative O(alpha(3)(s)) QCD calculations in modeling soft-jet emission.

Journal Article↗
PubMed2001

Inclusive jet production in pp(macro) collisions.

We report a new measurement of the pseudorapidity (eta) and transverse-energy ( E(T)) dependence of the inclusive jet production cross section in pp(macro) collisions at square root of s = 1.8 TeV using 95 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron. The differential cross section d(2)sigma/(dE(T)d eta) is presented up to eta = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.

Journal Article↗
PubMed2001

Search for large extra dimensions in dielectron and diphoton production.

We report a search for effects of large extra spatial dimensions in pp collisions at a center-of-mass energy of 1.8 TeV with the D0 detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% C.L. on the effective Planck scale between 1.0 and 1.4 TeV for several formalisms and numbers of extra dimensions.

Journal Article↗
PubMed2001

Contractile properties of human motor units in health, aging, and disease.

The primary function of skeletal muscle is to produce force for postural control and movement. Although the contractile properties of the whole muscle are useful functional indicators, they do not accurately reflect the heterogeneity of the constituent motor units (MUs) and their changes in health and disease. However, data on the contractile properties of human MUs, in comparison to other animal species, are relatively sparse. This, in part, is due to greater methodological challenges of in vivo studies of MUs in the human. The purpose of this review is to critically appraise the methods used in humans; to describe the normative data from different muscle groups; to discuss differences between data from healthy humans and other animal species; and, last, to characterize changes of the MU contractile properties in aging, disease, and in response to intervention. Because the spike-triggered averaging technique can only be used to study the twitch properties, other methods were subsequently developed to measure a wider range of contractile properties. Although there is general agreement between human data and those from other animal species, major differences do exist. Potential reasons for these discrepancies include true biological differences, but differences in the techniques used may also be responsible. Although limited, measurement of MU contractile properties in humans has provided insight into the changes associated with aging and motoneuronal diseases and provides a means of gauging their adaptive capacity for training and immobilization.

Aging↗
PubMed2001

Intra-articular hyaluronic acid following knee immobilisation for 6 weeks in rabbits.

Thirty-two mature female New Zealand White rabbits were immobilised in an aluminium splint on one knee, using the contralateral non-treated knee as control. After 6 weeks the splints were removed and the rabbits allowed unrestricted movement. On a random basis, 16 rabbits were given an intra-articular injection of 5 mg in 0.5 ml of hyaluronic acid (HA) in the knee of the immobilised hindlimb at weekly intervals for 6 weeks, starting 1 week after the joint had been remobilised, for a total of six injections. In the other 16 rabbits no further intervention was conducted. At the end of the experiment the rabbits were killed, the area of degenerated joint surface of the distal femur, and water and proteoglycan content were measured, and the articular cartilage stained with haematoxylin and eosin and safranin O. Remobilisation without HA administration resulted in a significantly larger degenerated joint surface area. By the end of the experiment both remobilisation and remobilisation and intra-articular HA injections had produced a greater but non-significant water cartilage content compared to the control side. The average cartilage glycosaminoglycan content of the remobilisation and intra-articular HA injection group was significantly greater than in the remobilisation group. In conclusion, in the rabbits with one knee immobilised for 6 weeks, 6 weeks of remobilisation alone are not sufficient to recover from the moderate articular surface changes produced, and the intra-articular administration of HA may produce a morphologically and biochemically more normal cartilage. More extensive animal and human studies should be performed before the routine use of intra-articular administration of HA following musculoskeletal injuries that required immobilisation can be recommended.

Animals↗
PubMed2001

Bronchogenic carcinoma in lung transplant recipients.

Although lung transplant recipients have a higher prevalence of non-melanoma skin cancers and lymphoma than the general population, the same has not been noted for bronchogenic carcinoma. If an increased prevalence of bronchogenic carcinoma exists, contributing factors may include the high rate of previous tobacco use in this population and/or the chronic immunosuppression used to prevent allograft rejection. With time, the incidence of bronchogenic carcinoma in the lung transplant population is likely to parallel the increasing longevity and number of transplanted individuals. We describe 2 cases of bronchogenic carcinoma in lung transplant recipients that demonstrate the morbidity associated with the discovery or development of bronchogenic carcinoma in this population.

Adenocarcinoma↗
PubMed2001

Characterization of AFMP1: a novel target for serodiagnosis of aspergillosis.

We cloned the AFMP1 gene, which encodes the first antigenic cell wall galactomannoprotein in Aspergillus fumigatus. AFMP1 codes for a protein, Afmp1p, of 284 amino acid residues, with a few sequence features that are present in Mp1p, the antigenic cell wall mannoprotein in Penicillium marneffei that we described previously, as well as several other cell wall proteins of Saccharomyces cerevisiae and Candida albicans. It contains a serine- and threonine-rich region for O glycosylation, a signal peptide, and a putative glycosylphosphatidyl inositol attachment signal sequence. Specific anti-Afmp1p antibody was generated with recombinant Afmp1p protein purified from Escherichia coli to allow further characterization of Afmp1p. Afmp1p has a high affinity for Galanthus nivalis agglutinin, a characteristic indicative of a mannoprotein. Furthermore, it was recognized by a rat monoclonal antibody against the galactofuran side chain of galactomannan, indicating that it is a galactomannoprotein. Ultrastructural analysis by immunogold staining indicated that Afmp1p is present in the cell walls of the hyphae and conidia of A. fumigatus. Finally, it was observed that patients with aspergilloma and invasive aspergillosis due to A. fumigatus develop a specific antibody response against Afmp1p. This suggested that the recombinant protein and its antibody may be useful for serodiagnosis in patients with aspergilloma or invasive aspergillosis, and the protein may represent a good cell surface target for host humoral immunity.

Amino Acid Sequence↗
PubMed2001

Tai chi: physiological characteristics and beneficial effects on health.

OBJECTIVES: To assess the characteristic effects of Tai Chi Chuan (TCC) exercise on metabolism and cardiorespiratory response, and to measure its effect on cardiorespiratory function, mental control, immune capacity, and the prevention of falls in elderly people. DESIGN: A review of controlled experimental studies and clinical trials designed with one of two aims: either to assess physiological responses during the performance of TCC or to assess the impact of this exercise on general health and fitness. MAIN OUTCOME MEASURES: Metabolic rate, heart rate, blood pressure, ventilation, maximal oxygen uptake (VO(2)MAX), immune capacity, falls, and fall related factors. SUBJECTS: A total of 2216 men and women. RESULTS: Under review were 31 original studies, published in Chinese or English journals, that met the criteria for inclusion. Most of the papers written in Chinese had not been introduced into the Western literature. Nine of these studies showed that TCC can be classified as moderate exercise, as its does not demand more than 55% of maximal oxygen intake. When this form of exercise and others conducted at equal intensity were compared, TCC showed a significantly lower ventilatory equivalent (VE/VO(2)MAX). Evidence provided by cross sectional and longitudinal studies suggests that TCC exercise has beneficial effects on cardiorespiratory and musculoskeletal function, posture control capacity, and the reduction of falls experienced by the elderly. CONCLUSIONS: TCC is a moderate intensity exercise that is beneficial to cardiorespiratory function, immune capacity, mental control, flexibility, and balance control; it improves muscle strength and reduces the risk of falls in the elderly.

Accidental Falls↗
PubMed2001

Treatment of painful osteoarthritis of the knee with hyaluronic acid. Results of a multicenter Asian study.

Hyaluronic acid is a component of synovial fluid, in osteoarthritis (OA) and shows a change of property of hyaluronic acid especially its viscoelasticity causing degradation of the cartilage. Injection of hyaluronic acid into OA of the knee (Hyalgan 2 ml/wk for 4 doses) in international multicentres gave dramatic responses: decreased pain, increased mobility of the joint after 49 days of injections compared to a placebo (2 ml of normal saline) p<0.01.

Aged↗
PubMed2000

Measurement of the W-->taunu production cross section in pp collisions at square root s=1.8 TeV.

We report on a measurement of sigma(pp-->W+X)B(W-->taunu) in pp collisions at sqrt[s]=1.8 TeV at the Fermilab Tevatron. The measurement is based on an integrated luminosity (lum) of 18 pb-1 of data collected with the D0 detector during 1994-1995. We find that sigma(pp-->W+X)B(W-->taunu)=2.22+/-0.09 (stat)+/-0. 10 (syst)+/-0.10 (lum) nb. Lepton universality predicts that the ratio of the tau and electron electroweak charged current couplings to the W boson, gWtau/gWe, be unity. We find gWtau/gWe=0.980+/-0.031, in agreement with lepton universality.

Journal Article↗
PubMed2000

Probing Balitsky-Fadin-Kuraev-Lipatov dynamics in the dijet cross section at large rapidity intervals in pp collisions at sqrt[s]=1800 and 630 GeV.

Inclusive dijet production at large pseudorapidity intervals (Deltaeta) between the two jets has been suggested as a regime for observing Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics. We have measured the dijet cross section for large Deltaeta in pp collisions at sqrt[s]=1800 and 630 GeV using the D0 detector. The partonic cross section increases strongly with the size of Deltaeta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of alphaBFKL(20 GeV)=1.65+/-0.07.

Journal Article↗