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Biomedical subjects

W D Lee

Publications and source records attributed to W D Lee.

9 recordsLinked to original sources
PubMed2003

Observation of anomalous momentum transport in tokamak plasmas with no momentum input.

Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas through analysis of the time evolution of core impurity toroidal rotation velocity profiles. Following the L-mode to EDA (enhanced D(alpha)) H-mode transition, the ensuing cocurrent toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core. The steady state toroidal rotation velocity profiles are relatively flat and the momentum transport can be simulated with a simple diffusion model. Velocity profiles during edge localized mode free (ELM-free) H-modes are centrally peaked, which suggests the addition of inward momentum convection. In all operating regimes the observed momentum diffusivities are much larger than the neoclassical values.

Journal Article↗
PubMed2001

An optical clock based on a single trapped 199Hg+ ion.

Microwave atomic clocks have been the de facto standards for precision time and frequency metrology over the past 50 years, finding widespread use in basic scientific studies, communications, and navigation. However, with its higher operating frequency, an atomic clock based on an optical transition can be much more stable. We demonstrate an all-optical atomic clock referenced to the 1.064-petahertz transition of a single trapped 199Hg+ ion. A clockwork based on a mode-locked femtosecond laser provides output pulses at a 1-gigahertz rate that are phase-coherently locked to the optical frequency. By comparison to a laser-cooled calcium optical standard, an upper limit for the fractional frequency instability of 7 x 10(-15) is measured in 1 second of averaging-a value substantially better than that of the world's best microwave atomic clocks.

Journal Article↗
PubMed2001

Absolute frequency measurements of the Hg+ and Ca optical clock transitions with a femtosecond laser.

The frequency comb created by a femtosecond mode-locked laser and a microstructured fiber is used to phase coherently measure the frequencies of both the Hg+ and Ca optical standards with respect to the SI second. We find the transition frequencies to be f(Hg) = 1 064 721 609 899 143(10) Hz and f(Ca) = 455 986 240 494 158(26) Hz, respectively. In addition to the unprecedented precision demonstrated here, this work is the precursor to all-optical atomic clocks based on the Hg+ and Ca standards. Furthermore, when combined with previous measurements, we find no time variations of these atomic frequencies within the uncertainties of the absolute value of( partial differential f(Ca)/ partial differential t)/f(Ca) < or =8 x 10(-14) yr(-1) and the absolute value of(partial differential f(Hg)/ partial differential t)/f(Hg) < or =30 x 10(-14) yr(-1).

Journal Article↗
PubMed2000

Tilmicosin induces apoptosis in bovine peripheral neutrophils in the presence or in the absence of Pasteurella haemolytica and promotes neutrophil phagocytosis by macrophages.

Pathogen virulence factors and inflammation are responsible for tissue injury associated with respiratory failure in bacterial pneumonia, as seen in the bovine lung infected with Pasteurella haemolytica. Tilmicosin is a macrolide antibiotic used for the treatment of bovine bacterial pneumonia. Recent evidence suggests that tilmicosin-induced neutrophil apoptosis may have anti-inflammatory effects. Using bovine leukocytes, we sought to define whether live P. haemolytica affected tilmicosin-induced neutrophil apoptosis, assessed the proapoptotic effects of tilmicosin in comparison with other drugs, and characterized its impact on phagocytic uptake of neutrophils by macrophages. Induction of apoptosis in the presence or absence of P. haemolytica was assessed by using an enzyme-linked immunosorbent assay for apoptotic nucleosomes. In addition, fluorescent annexin-V staining identified externalized phosphatidylserine in neutrophils treated with tilmicosin, penicillin, ceftiofur, oxytetracycline, or dexamethasone. Neutrophil membrane integrity was assessed by using propidium iodide and trypan blue exclusion. As phagocytic clearance of apoptotic neutrophils by macrophages contributes to the resolution of inflammation, phagocytosis of tilmicosin-treated neutrophils by esterase-positive cultured bovine macrophages was assessed with light microscopy and transmission electron microscopy. Unlike bovine neutrophils treated with penicillin, ceftiofur, oxytetracycline, or dexamethasone, neutrophils exposed to tilmicosin became apoptotic, regardless of the presence or absence of P. haemolytica. Tilmicosin-treated apoptotic neutrophils were phagocytosed at a significantly greater rate by bovine macrophages than were control neutrophils. In conclusion, tilmicosin-induced neutrophil apoptosis occurs regardless of the presence or absence of live P. haemolytica, exhibits at least some degree of drug specificity, and promotes phagocytic clearance of the dying inflammatory cells.

Animals↗
PubMed1992

[The detection of an early glomerular filtration rate change of spinal cord injury patients by renal scan].

A Technetium-99m DTPA computer-assisted renal scan and CCR studies were performed on 35 spinal cord injured patients who had been hospitalized in the rehabilitation ward of Kaohsiung Medical College Hospital for less than 6 months during the period of August 1988 to March 1990. For each patient, the glomerular filtration rate (GFR), the effective renal plasma flow (ERPF), and the filtration fraction (FF) were obtained by a renal scan. CCR was measured by conventional procedure and was corrected with body length, body weight and body surface. Least square fit linear regression analysis revealed the best correlation between GFR and CCR. Based on GFR values the renal function was classified into four grades from normal to severe damage and the change of renal function was analyzed using four corresponding factors. The results showed that the ratio of GFR impairment in early spinal injury is 48.6% (mostly mild impairment). There are not significant differences between levels of lesion, severity of injury or successfulness of bladder training by Fisher's exact test. Renal function deteriorated proportionally with age and most of those patients having the worst renal function belonged to an old age group. Thus age is also one of the major factors in renal function impairment. Single kidney function impairment was noted in two patients whose total GFR or CCR were in the normal range, which implied the characteristic of early detection of renal dysfunction by renal scan.

Adult↗
PubMed1986

Computer sleep stage scoring--an expert system approach.

This paper describes the application of the expert system concept to sleep stage scoring and is aimed at managing the large variability found in such records. The primary computational burden, sleep parameter calculation, can be relieved by recognizing major classes of recordings or 'somnotypes' having internally consistent sleep parameters for each class but significant differences between classes. The initiation and evolution of somnotypes so as to maintain accuracy while introducing a variety of sleep recordings is treated. The technique is demonstrated on seven all-night recordings resulting in 89.6% accuracy for about 5000 pages of data.

Computers↗