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Biomedical subjects

H W Schumacher

Publications and source records attributed to H W Schumacher.

8 recordsLinked to original sources
PubMed2003

Quasiballistic magnetization reversal.

We demonstrate a quasiballistic switching of the magnetization in a microscopic magnetoresistive memory cell. By means of time resolved magnetotransport, we follow the large angle precession of the free layer magnetization of a spin valve cell upon application of transverse magnetic field pulses. Stopping the field pulse after a 180 degrees precession rotation leads to magnetization reversal with reversal times as short as 165 ps. This switching mode represents the fundamental ultrafast limit of field induced magnetization reversal.

Journal Article↗
PubMed2003

Phase coherent precessional magnetization reversal in microscopic spin valve elements.

We evidence multiple coherent precessional magnetization reversal in microscopic spin valves. Stable, reversible, and highly efficient magnetization switching is triggered by transverse field pulses as short as 140 ps with energies down to 15 pJ. At high fields a phase coherent reversal is found revealing periodic transitions from switching to nonswitching under variation of pulse parameters. At the low field limit the existence of a relaxation dominated regime is established allowing switching by pulse amplitudes below the quasistatic switching threshold.

Journal Article↗
PubMed2001

Magnetoresistance anisotropy in Si /SiGe in tilted magnetic fields: experimental evidence for a stripe-phase formation.

We observe pronounced transport anisotropies in magnetotransport experiments performed in the two-dimensional electron system of a Si/SiGe heterostructure. They occur when an in-plane field is used to tune two Landau levels with opposite spin to energetic coincidence. The observed anisotropies disappear drastically for temperatures above 1 K. We propose that our experimental findings may be caused by the formation of a unidirectional stripe phase oriented perpendicular to the in-plane field.

Journal Article↗
PubMed1997

[Paraganglioma of the cauda equina].

We report on a case of paraganglioma of the cauda equina in a 48-year-old man. These slow-growing, mostly benign and encapsulated intradural-extramedullar tumours are clinically characterized by lumbago, paraesthesia and motor deficits as well as occasionally by incontinence. Paragangliomas of the cauda equina show monomorphous (main) cells arranged in a typical cell cluster pattern, demonstrating a lobular architecture and a fine net of connective tissue formed by so-called sustentacular cells; some tumours show focal ganglionic differentiation. Because of their morphological similarity to the more common ependymomas, paragangliomas of the cauda equina are sometimes misdiagnosed so that their incidence is likely to be higher than previously estimated. Immunohistochemistry findings are positive for neuron-specific enolase, chromogranin and other neuronal markers as well as neuropeptides (main cells) and S-100 protein (sustentacular cells) while widely lacking reactivity for GFAP. Paragangliomas of the cauda equina represent a rare entity, of which only 80 cases have been described in the literature. Because they only occur sporadically, they are often not included in the differential diagnosis of mass lesions of the region of the cauda equina.

Biomarkers↗
PubMed1991

Effect of stable xenon on regional cerebral blood flow and the electroencephalogram in normal volunteers.

We evaluated the effects of breathing 35% stable xenon in 65% oxygen on regional cerebral blood flow and the electroencephalogram in 20 normal volunteers. We measured blood flow in 32 brain regions over both hemispheres with the xenon-133 intravenous injection technique in two protocols. In the first protocol (n = 10), a baseline study was followed by a second study during 5 minutes of breathing stable xenon; in the other protocol (n = 8), the baseline study was followed by a second study after 5 minutes of breathing stable xenon. Two volunteers were excluded due to excessive movements during the inhalation of stable xenon. Some of the remaining 18 volunteers had varying alterations of consciousness accompanied by electroencephalogram changes. After stable xenon inhalation the electroencephalogram returned to normal within 2-3 minutes. During stable xenon inhalation mean +/- SD PECO2 dropped significantly from 39.4 +/- 4.4 to 33.3 +/- 5.4 mm Hg in the first protocol and from 39.4 +/- 2.6 to 34.8 +/- 4.1 mm Hg in the second protocol due to hyperventilation in 13 volunteers. Mean regional cerebral blood flow increased significantly by 13.5-25.4% without correction for PECO2. In the first protocol regional cerebral blood flow increased by greater than 12% in 11-14 (depending on the flow parameter) of the 20 hemispheres. In the second protocol regional cerebral blood flow increased by greater than 12% in 9-13 of the 16 hemispheres. We conclude that cautious interpretation is necessary in the assessment of regional cerebral blood flow with 35% xenon-enhanced computed tomography.

Adult↗
PubMed1988

Pseudomeningocele of the lumbar spine.

A patient with a lumbar pseudomeningocele after intervertebral disc surgery is reported and the findings of computed tomography and magnetic resonance imaging are described.

Adult↗
PubMedDate not supplied

Effect of stable xenon in room air on regional cerebral blood flow and electroencephalogram in normal baboons.

Measurement of regional cerebral blood flow (rCBF) was performed in 6 healthy baboons during ventilation with 35% stable xenon in artificial air. rCBF was measured with the intraarterial xenon-133 method. EEG was recorded continuously. All CBF areas of interest over one hemisphere reacted in the same way. Mean flow increased during short-term exposure to stable xenon and decreased if stable xenon inhalation was continued for at least 24 minutes. EEG showed a decrease of alpha- and beta-wave patterns a short time after the start of stable xenon inhalation without further changes over the period when rCBF finally decreased. CO2 reactivity increased in most animals, and autoregulation to mild arterial hypotension was significantly impaired with increased flow. It is concluded that 35% stable xenon in artificial air increases rCBF after short-term exposure and decreases rCBF after longer exposure. EEG changes were noted after short-term exposure. rCBF and EEG recovered rapidly after the end of stable xenon inhalation.

Administration, Inhalation↗