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Biomedical subjects

G Grubel

Publications and source records attributed to G Grubel.

13 recordsLinked to original sources
PubMed2000

Complex dynamic behavior of fluctuating smectic- A films as studied by scattering with coherent X-rays

Coherent dynamic x-ray scattering has been used to study the thermally excited layer fluctuations in freely suspended smectic films of the compound 4O.8. Using 8-keV x rays and films with a thickness around 0.3 &mgr;m we resolve relaxation times down to a few &mgr;s. A combination of damped and oscillatory behavior is observed for the layer undulations, which can be attributed to inertial effects. These are due to the surface contribution to the free energy which cannot be disregarded for thin films.

Journal Article↗
PubMed2000

Critical adsorption and dimensional crossover in epitaxial FeCo films

The critical behavior of thin FeCo films grown on MgO has been studied using phase-sensitive synchrotron x-ray diffraction. These studies unravel several novel features of criticality in thin films, as the simultaneous appearance of the 3D-2D crossover and the truncation of the correlation length normal to the film at approximately 1/3 of the film thickness. Above the critical temperature of the film we observe a pronounced pinning of the order parameter at the MgO-FeCo interface, which indicates a novel critical adsorption behavior.

Journal Article↗
PubMed2000

Magnetic splitting of valence states in ferromagnetic and antiferromagnetic lanthanide metals

The magnetic splitting of Delta(2) valence states in the heavy lanthanide metals Gd, Tb, Dy, and Ho was studied in epitaxial films by angle-resolved photoemission, revealing an essentially Stoner-like temperature dependence in all cases. It scales linearly with the 4f spin moment, even in the case of the helical antiferromagnet Ho. Such a behavior can be explained by a substantial localization of the corresponding wave function in the c direction. The helical magnetic structure was confirmed for the thin Ho films by in situ resonant magnetic x-ray diffraction.

Journal Article↗
PubMed2000

Photon correlation spectroscopy: X rays versus visible light

We have performed combined dynamic light scattering (DLS) and dynamic x-ray scattering (DXS) experiments on dense colloidal suspensions. The intermediate scattering functions obtained with these two techniques are compared directly. In the case of optically index matched samples, the comparison demonstrates that DXS yields accurate and reliable results. It is shown that the hydrodynamic interaction H(q) can be determined experimentally, without taking recourse to any theoretical model, by combining DXS and DLS. The combination of the two methods probes the dynamics over more than one decade in scattering vector. Experiments on optically opaque samples, where DLS fails, demonstrate the necessity to use x rays in these systems.

Journal Article↗
PubMed1995

Malignant melanotic neuroectodermal tumor of infancy.

A 2-month-old boy underwent surgery for removal of a right temporal melanotic neuroectodermal tumor of infancy (MNTI). Histologically the tumor tissue showed signs of malignancy. The child was reexamined several times up to the age of 5 years. Neuroradiological evaluation showed no evidence of tumor recurrence or metastases. No resulting handicap was observed during neurological and psychological follow-up examination at the age of 5 years. Our findings confirm that surgical removal as the therapy of choice provides an excellent prognosis for this kind of tumor in spite of its histologically malignant appearance.

Brain↗
PubMed1984

Long-term follow-up of children with craniopharyngioma.

Management of craniopharyngiomas is still controversial. 28 children with this tumor were studied. GH deficiency was present in 22 patients following surgery, 10 of these GH-lacking patients had normal or accelerated growth (usually associated with rapid weight gain) postoperatively. Somatomedin levels were normal in three of six normally growing patients. After craniotomy their basal and TRH-stimulated prolactin levels were in the normal range, but their insulin secretion was markedly increased. Postoperatively there was a significant correlation between peak insulin levels following arginine infusion and growth velocity in all patients. Complete tumor removal could be performed in 28% of our patients. Altogether 36% of all patients had at least one tumor recurrence. Recent literature with the addition of our series showed tumor recurrence in 22% of patients with "total" tumor excision and in 72% of patients with partial tumor removal. Radiotherapy seems to be capable of destroying craniopharyngioma tissue. The recurrence rate was only 26% in patients with subtotal excision plus radiotherapy. Unless radical tumor removal can be attempted with safety, subtotal tumor removal plus radiotherapy appears to be the treatment of choice for craniopharyngioma.

Adolescent↗
PubMed1983

Factors influencing peripheral nerve suture results.

Besides the surgical treatment, other factors do greatly influence the results following peripheral nerve suture. On the basis of our own findings in more than 80 patients, we analyze those factors, the exclusion of which prevents a satisfactory comparison between the different results in peripheral nerve suturing, as well as a valid discussion of their implications.

Adolescent↗
PubMed1977

[CSF-rhinorrhea due to removal of an acoustic neuroma (author's transl)].

After removal of an acoustic neuroma by the suboccipital route cerebrospinal fluid rhinorrhea was observed. This procedure was complicated by meningitis and pneumatocephalus. Finally, after one neurosurgical and four otosurgical interventions, the cerebrospinal fluid leak was identified in the membrane of the round window. It was plugged with a fascial graft.

Adult↗