Biomedical subjects

B Gompf

Publications and source records attributed to B Gompf.

5 recordsLinked to original sources

PubMed2002

Microspectroscopy and imaging in the THz range using coherent CW radiation.

A novel THz near-field spectrometer is presented which allows the performance of biological and medical studies with high spectral resolution combined with a spatial resolution down to lambda/100. In the setup an aperture much smaller than the used wavelength is placed in the beam very close to the sample. The sample is probed by the evanescent wave behind the aperture. The distance is measured extremely accurately by a confocal microscope. We use monochromatic sources which provide powerful coherent cw radiation tuneable from 50 GHz up to 1.5 THz. Transmission and reflection experiments can be performed which enable us to study solids and molecules in aqueous solution. Examples for spectroscopic investigations on biological tissues are presented.

Adipose Tissue↗

PubMed2000

Does water vapor prevent upscaling sonoluminescence?

Experimental results for single-bubble sonoluminescence of air bubbles at very low frequency f = 7.1 kHz are presented: In contrast to the predictions of a recent model [S. Hilgenfeldt and D. Lohse, Phys. Rev. Lett. 82, 1036 (1999)], the bubbles are only as bright (10(4)-10(5) photons per pulse) and the pulses as long (approximately 150 ps) as at f = 20 kHz. We can theoretically account for this effect by incorporating water vapor into the model: During the rapid bubble collapse a large amount of water vapor is trapped inside the bubble, resulting in an increased heat capacity and hence lower temperatures, i.e., hindering upscaling. At this low frequency water vapor also dominates the light emission process.

Journal Article↗

PubMed2000

Microimplosions: cavitation collapse and shock wave emission on a nanosecond time scale

A streak camera with high spatial and temporal resolution was used for imaging the dynamics of the violent collapse in single-bubble sonoluminescence. The high pressure in the last phase of the bubble collapse leads to the emission of a shock wave, which is launched with a shock velocity of almost 4000 m/s. The shock amplitude decays much faster than approximately 1/r. From the strongly nonlinear propagation the pressure in the vicinity of the bubble can be calculated to be in the range of 40-60 kbar.

Journal Article↗

PubMed2000

Mie scattering from a sonoluminescing bubble with high spatial and temporal resolution

The dynamics of a single-air bubble trapped in a resonant sound field in water has been characterized by Mie scattering and a Streak camera with high spatial and temporal resolution. The streak images show that in the endphase of the cavitation collapse the scattered light intensity is no function of the bubble radius anymore. In the last nanoseconds around minimum bubble radius most of the light is scattered at the highly compressed water surrounding the bubble and not at the bubble wall. This leads to a minimum in the scattered light intensity about 700 ps before the sonoluminescence pulse is emitted. And neglecting this changes leads to a strong overestimation of the bubble-wall velocity. In the reexpansion phase the high spatial resolution of the streak camera allows one to distinguish between the light scattered at the bubble wall and the light scattered at the outgoing shock wave.

Journal Article↗

PubMed1984

Quantification of postural sway in normals and patients with cerebellar diseases.

Posturography was performed in 41 patients with cerebellar diseases by means of a force measuring platform using an on-line computer program which calculated sway path, sway area, antero-posterior and lateral sway components and the amount of visual stabilization. Postural ataxia was quantitatively studied in 8 patients with spinal ataxia (Friedreich's), 6 patients with vestibulocerebellar lesions, 11 patients with anterior lobe atrophy, 7 patients with hemispheral cerebellar lesions, and 9 patients with a disease affecting all parts of the cerebellum. Patients with lesions of the cerebellar hemispheres could not be separated from normals by means of posturography. Lesions of the spino-cerebellar afferents (Friedreich' ataxia) caused an omnidirectional low frequency sway with preserved visual stabilization. Patients with anterior lobe atrophy showed a predominant antero-posterior sway, often with a spontaneous high frequency body tremor around 3 Hz. Vestibulo-cerebellar lesions exhibited omnidirectional low frequency sway poorly stabilized by vision. Quantitative posturography helps to localize cerebellar lesions and allows for quantitative follow-up studies of cerebellar diseases.

Adult↗