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Biomedical subjects

M J Padgett

Publications and source records attributed to M J Padgett.

10 recordsLinked to original sources
PubMed2006

Multipoint holographic optical velocimetry in microfluidic systems.

We show how holographic optical trapping can be used for the multipoint measurement of fluid flow in microscopic geometries. An array of microprobes can be simultaneously trapped and used to map out the fluid flow in a microfluidic device. The optical traps are alternately turned on and off such that the probe particles are displaced by the flow of the surrounding fluid and then retrapped. The particles' displacements are monitored by digital video microscopy and directly converted into velocity field values. This technique enables the measurement of a two-dimensional flow field at points arbitrarily distributed in a three-dimensional volume. The validity of the technique is demonstrated for the case of the flow around a spinning sphere and the flow at the outlet of a microchannel.

Journal Article↗
PubMed2005

Application of laser spectroscopy for measurement of exhaled ethane in patients with lung cancer.

There is increasing interest in ethane (C(2)H(6)) in exhaled breath as a non-invasive marker of oxidative stress (OS) and thereby a potential indicator of disease. However, the lack of real-time measurement techniques has limited progress in the field. Here we report on a novel Tunable Diode Laser Spectrometer (TDLS) applied to the analysis of exhaled ethane in patients with lung cancer. The patient group (n=52) comprised randomly selected patients presenting at a respiratory clinic. Of these, a sub-group (n=12) was subsequently diagnosed with lung cancer. An age-matched group (n=12) corresponding to the lung cancer group was taken from a larger control group of healthy adults (n=58). The concentration of ethane in a single exhaled breath sample collected from all subjects was later measured using the TDLS. This technique is capable of real-time analysis of samples with accuracy 0.1 parts per billion (ppb), over 10 times less than typical ambient levels in the northern hemisphere. After correcting for ambient background, ethane in the control group (26% smokers) ranged from 0 to 10.54 ppb (median of 1.9 ppb) while ethane in the lung cancer patients (42% smokers) ranged from 0 to 7.6 ppb (median of 0.7 ppb). Ethane among the non-lung cancer patients presenting for investigation of respiratory disease ranged from 0 to 25 ppb (median 1.45 ppb). We conclude that, while the TDLS proved effective for accurate and rapid sample analysis, there was no significant difference in exhaled ethane among any of the subject groups. Comments are made on the suitability of the technique for monitoring applications.

Aged↗
PubMed2004

Three-dimensional optical trapping of partially silvered silica microparticles.

We demonstrate three-dimensional trapping of micrometer-diameter silica particles, partially coated with silver, within conventional optical tweezers. Although metallic particles are usually repelled from the beam focus by the scattering force, we show that transparent spheres partially coated with silver can be trapped with efficiencies comparable with dielectric particles. The trapping characteristics of these particles are examined as a function of metallic coverage, and the application of these particles to surface-enhanced resonance Raman scattering is investigated.

Coated Materials, Biocompatible↗
PubMed2003

Observation of the transfer of the local angular momentum density of a multiringed light beam to an optically trapped particle.

We observe the spinning and orbital motion of a microscopic particle trapped within a multiringed light beam that arises from the transfer of the spin and orbital components of the light's angular momentum. The two rotation rates are measured as a function of the distance between the particle and the axis of the trapping beam. The radial dependence of these observations is found to be in close agreement with the accepted theory.

Journal Article↗
PubMed2002

Construction of a database of benzene biological monitoring.

Biological monitoring of occupational exposure to benzene has been conducted in the petroleum, steel and chemical industries. The urinary benzene-specific biomarker, S-phenylmercapturic acid (PMA), was quantified in post-shift samples using a sensitive enzyme-linked immunosorbent assay (ELISA) and expressed as a function of urinary creatinine concentration. The assay, based on a PMA-specific antiserum, is sufficiently sensitive to measure PMA levels in non-occupationally exposed control subjects. The assay delivers batch results in a timely manner which may be as short as 3 h. Samples were analysed from groups of workers engaged in coke oven combustion processes, petroleum refining and decontamination of a benzene land spill. The construction of a database of results provides an index of benzene uptake as a consequence of the respective work processes and tasks and readily enables benchmarking exercises aimed at comparing degrees of exposure across segments of industry.

Acetylcysteine↗
PubMed2002

Intrinsic and extrinsic nature of the orbital angular momentum of a light beam.

We explain that, unlike the spin angular momentum of a light beam which is always intrinsic, the orbital angular momentum may be either extrinsic or intrinsic. Numerical calculations of both spin and orbital angular momentum are confirmed by means of experiments with particles trapped off axis in optical tweezers, where the size of the particle means it interacts with only a fraction of the beam profile. Orbital angular momentum is intrinsic only when the interaction with matter is about an axis where there is no net transverse momentum.

Journal Article↗
PubMed2001

Mueller matrix error correction for a fringe-free interferometry system.

We present an automated surface profiling system based on a shearing interferometer, in which precise measurement of the polarization states eliminates fringe ambiguity. A full error correction based on Mueller matrices allows comparatively inaccurate but rapidly switchable liquid-crystal wave plates to be used, enabling unambiguous profile information to be obtained in real time.

Journal Article↗
PubMed2000

Monitor-outside-a-monitor effect and self-similar fractal structure in the eigenmodes of unstable optical resonators.

A novel mechanism is proposed for the generation of self-similar structure over a limited range of length scales. Our mechanism, which we call the monitor-outside-a-monitor effect, comprises repeated magnification and addition of small-scale structure. We invoke this mechanism to explain recent observations of fractal structure in the eigenmodes of unstable optical resonators [G. P. Karman et al., Nature (London) 402, 138 (1999)].

Journal Article↗
PubMedDate not supplied

Fractals in pixellated video feedback.

Video feedback occurs whenever a video camera is directed at a screen displaying the image currently being recorded by the camera. It can be observed in everyday situations, for example at sporting events when a stadium's display screen comes into the camera's view. Here we consider how this simple physical process is affected by the fact that monitors are pixel-based, and show that it can result in stationary fractal patterns such as von-Koch snowflakes and Sierpinski gaskets.

Journal Article↗