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Biomedical subjects

R S Simon

Publications and source records attributed to R S Simon.

At least 19 recordsLinked to original sources
PubMed2003

Exclusive measurement of coherent proton-deuteron bremsstrahlung.

For the first time a high-precision proton-deuteron bremsstrahlung experiment has been performed in which all the different exit channels have been distinguished separately. High-precision cross sections and analyzing powers in one of the outgoing channels, namely, the coherent bremsstrahlung with a proton and a deuteron in the final state, are presented at 190 MeV incoming proton beam energy and are compared to calculations based on the low-energy theorem. The results of the calculations vary considerably calling for a fully microscopic calculation. However, using a recipe including the initial- and final-state interactions, the predictions come close to the data.

Journal Article↗
PubMed2002

Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions.

Photon energy spectra up to the kinematic limit have been measured in 190 MeV proton reactions with light and heavy nuclei to investigate the influence of the multiple-scattering process on the photon production. Relative to the predictions of models based on a quasifree production mechanism, a strong suppression of bremsstrahlung is observed in the low-energy region of the photon spectrum. We attribute this effect to the interference of photon amplitudes due to multiple scattering of nucleons in the nuclear medium.

Journal Article↗
PubMed1988

Genetic analysis of in vivo-selected viral variants causing chronic infection: importance of mutation in the L RNA segment of lymphocytic choriomeningitis virus.

Viral variants with different biological properties are present in the central nervous systems (CNS) and lymphoid tissues of mice persistently infected with lymphocytic choriomeningitis virus (LCMV). Viral isolates from the CNS are similar to the original Armstrong LCMV strain and induce potent virus-specific T-cell responses in adult mice, and the infection is rapidly cleared. In contrast, LCMV isolates derived from spleens of carrier mice cause persistent infections in adult mice. This chronic infection is associated with low levels of antiviral T-cell responses. In this study, we genetically characterized two independently derived spleen variants by making recombinants (reassortants) between the spleen isolates and wild-type (wt) LCMV and showed that the ability to persist in adult mice and the associated suppression of T-cell responses segregates with the large (L) RNA segment. In addition, we analyzed a revertant (isolated from the CNS) derived from one of the spleen variants. By comparing the biological properties of three reassortants that contained the same S segment but had the L segment of either the original wt Armstrong LCMV, the spleen variant derived from it, or the CNS revertant derived from the spleen variant, we were able to show unequivocally that biologically relevant mutations occurred in the L segment not only during generation of the spleen variant from wt LCMV but also in reversion of the spleen variant to the wt phenotype. Thus, our results showed that (i) genetic alterations in the L genomic segment were involved in organ-specific selection of viral variants, and (ii) these mutations profoundly affected the ability of LCMV to cause chronic infections in adult mice.

Animals↗
PubMed1980

Clinical, chemical, and CT evaluation of short-term and long-term antiedema therapy with dexamethasone and diuretics.

Three independent methods were used to quantify the therapeutic effect on peritumoral brain edema with respect to different forms of treatment (dexamethasone, furosemide, and their combination with different dosages and different periods of treatment). 1. The neurological deficit evaluated by frequency distribution analysis showed an improvement in nearly all cases. In a few cases the initial improvement was followed by a secondary deterioration. The various symptoms showed significant differences in regression with regard to the extent of the reduced deficit as well as the time dependence. 2. With a certain delay (compared to item 1), diminution of brain edema was detected by CT follow-up. The effect of dexamethasone and the combination with furosemide differed depending on the nature of the brain tumor. 3. Compared to the untreated patients, the water content was reduced by nearly 3% following dexamethasone treatment 4 x 4 mg for 4 to 6 days. Following dexamethasone/furosemide therapy for 4 to 6 days, it was reduced by about 4.5%. The result of long-term therapy with dexamethasone alone was similar. The sodium content changed parallel to the water content. Dexamethasone and dexamethasone/furosemide was most effective in patients with glioblastoma, where the water content decreased by nearly 6%. The data presented suggest that preoperative antiedema treatment with dexamethasone is necessary for several days or a few weeks in some cases. The period of treatment can be reduced significantly by dexamethasone/furosemide or extremely high doses of dexamethasone. On the other hand, the results of follow-up scoring of the neurological situation show that the optimal time of pretreatment must be limited with respect to the individual case. The therapeutic results presented allow inferences to be made concerning pathophysiology of the resolution of brain edema.

Brain Chemistry↗
PubMed1978

CT of the base of the skull.

A systematic study of the structures of the base of the skull was performed with CT. The findings in 141 pathological cases are described. The value and some limitations of this kind of investigation are described and discussed. A comparison with conventional tomography is made.

Brain↗
PubMed1977

Angiography in vascular malformations of the face.

While angiography has been established as a useful procedure in evaluating vascular malformations of the face, the role of selective catheterization has not been stressed. Five patients with either capillary-cavernous hemangiomas or arteriovenous racemose hemangiomas were selected to illustrate the angiographic features of vascular malformations of the face as well as problems in angiographic evaluation and therapeutic techniques. Angiographic studies were valuable in establishing the extent and type of hemangioma, its blood supply and drainage, and associated intraorbital or intracranial extensions. We believe that selective catheterization is essential in preoperative evaluation of facial hemoangiomas, particularly in detecting unsuspected intracranial involvement.

Adult↗
PubMed1977

Failure to induce tolerance to mechlorethamine hydrochloride.

In view of the contradictory results reported in the literature regarding induction of specific immunologic tolerance to mechlorethamine hydrochloride (HN2), the problem was reinvestigated using a "tolerogenic" schedule that had been reported to be effective. Mechlorethamine hydrochloride, 200 microgram, intravenously, was given weekly for five weeks before beginning topical therapy with it. In the test group, five of 13 patients (11 with mycosis fungoides and two with psoriasis) became contact sensitized to mechlorethamine. In another patient, what was probably a contact urticarial reaction developed. In the control group, five of 13 patients (12 with mycosis fungoides, one with parapsoriasis) became contact sensitized to mechlorethamine. Thus, 38% of the patients in both groups became contact sensitized to mechlorethamine. It is concluded that this tolerogenic schedule, just as others previously tried, was not effective in inducing specific tolerance to mechlorethamine.

Dermatitis, Contact↗
PubMed1976

A radioanatomical study of the choroid plexus of the fourth ventricle.

A radioanatomical study of the plexus of the 4th ventricle has shown it to be clearly visible in about 35% of the lateral vertebral angiograms. With tumors of the posterior fossa the plexus is often not recognizable, perhaps because it is compressed. If filled, better information about the localization of tumors can be obtained.

Brain Neoplasms↗
PubMed1976

[Radiogenic carotid stenosis. The problem of radiation induced arterio-sclerosis (author's transl)].

Amongst late radiation damage, lesions of the cerebral arteries are relatively rare. The relationship between the radiation and arterio-sclerosis is discussed in connection with a 63-year old female patient with an atheromatous carotid stenosis; at the age of 5 years she received high dose rate radiation for cervical node tuberculosis. From animal experiments and an increasing number of human observations, it is concluded that radiation may be a predisposing and accelerating local factor in the formation of arterio-sclerosis. Amongst the recognised cases of radiogenic carotid stenosis or occlusion, the latent period averages 30 (9-57) years.

Aortography↗