PubMed Health⌕ Search

Biomedical subjects

R Simon

Publications and source records attributed to R Simon.

At least 109 records · Page 6Linked to original sources
PubMed2000

Effect of holes and vortices on beam quality.

The effect of a vortex on the invariant quality factors of a light beam is studied. It is shown that a vortex degrades beam quality. The beam intensity at the eye of the vortex necessarily vanishes, creating a hole in the intensity distribution. The degradation in the beam quality is shown to be due partly to the vortex phase and partly to the hole. The results are illustrated graphically. An important inequality to be obeyed by the beam-quality parameters is exhibited.

Light↗
PubMed2000

Structure of the set of paraxial optical systems.

The set of paraxial optical systems is the manifold of the group of symplectic matrices. The structure of this group is nontrivial: It is not simply connected and is not of an exponential type. Our analysis clarifies the origin of the metaplectic phase and the inherent limitations for optical map fractionalization. We describe, for the first time to our knowledge, an image girator and a cross girator whose geometric and wave implementations are of interest.

Lenses↗
PubMed2000

Fractional Fourier transforms in two dimensions.

We analyze the fractionalization of the Fourier transform (FT), starting from the minimal premise that repeated application of the fractional Fourier transform (FrFT) a sufficient number of times should give back the FT. There is a qualitative increase in the richness of the solution manifold, from U(1) (the circle S1) in the one-dimensional case to U(2) (the four-parameter group of 2 x 2 unitary matrices) in the two-dimensional case [rather than simply U(1) x U(1)]. Our treatment clarifies the situation in the N-dimensional case. The parameterization of this manifold (a fiber bundle) is accomplished through two powers running over the torus T2 = S1 x S1 and two parameters running over the Fourier sphere S2. We detail the spectral representation of the FrFT: The eigenvalues are shown to depend only on the T2 coordinates; the eigenfunctions, only on the S2 coordinates. FrFT's corresponding to special points on the Fourier sphere have for eigenfunctions the Hermite-Gaussian beams and the Laguerre-Gaussian beams, while those corresponding to generic points are SU(2)-coherent states of these beams. Thus the integral transform produced by every Sp(4, R) first-order system is essentially a FrFT.

Journal Article↗
PubMed2000

Optical phase space, Wigner representation, and invariant quality parameters.

Wigner's quasi probability and related functional and operator methods of quantum mechanics have recently played an important role in optics. We present an account of some of these developments. The symmetry structures underlying the ray and wave approaches to paraxial optics are explored in some detail, and the manner in which the Wigner phase-space representation captures the merits of both approaches is brought out. A fairly self-contained analysis of the second or intensity moments of general astigmatic partially coherent beams and of their behavior under transmission through astigmatic first-order optical systems is presented. Geometric representations of the intensity moments that render the quality parameters or polynomial invariants manifest are discussed, and the role of the optical uncertainty principle in assigning unbeatable physical bounds for these invariants is stressed. Measurement of the ten intensity moments of an astigmatic partially coherent beam is considered.

Journal Article↗
PubMed2000

Patterns of chromosomal imbalances in muscle invasive bladder cancer.

Cytogenetic investigations of bladder cancer suggested that development and progression is characterized by specific chromosomal aberrations. In order to identify genetic changes linked to muscle invasive tumors and metastatic growth we analyzed 67 bladder carcinomas (30 pT1 and 37 pT2-4) by means of comparative genomic hybridization (CGH). The most frequent changes were gains of chromosome 1q (54%), 8q (54%), 17q (49%), 2p (30%), 12 (30%), 5p (25%), 3q (24%) and 6p (24%) as well as losses of 11p (43%), 8p (42%), 9p (36%), 11q (34%), 2q, 4q, 5q (30% each), 9q (27%) and 10q (27%). Previously not described amplifications were found at 5p11-p13, 7q21-q31, 9p24 and 17q24-q25. Gains of 3q, 7p, and 18p were markedly more frequent in pT2-4 in comparison to pT1 carcinomas but the difference did not reach statistical significance. Non-metastatic tumors showed more aberrations on average than metastatic carcinomas, although no particular change was found to be predominating in either group. Our data confirm previous findings of strong genetic similarities between minimally and deeply invasive bladder carcinomas but argue for differences between metastatic and non-metastatic disease.

Carcinoma, Transitional Cell↗
PubMed2000

Autonomy and relatedness in the development of anorexia nervosa: a clinical case series using grounded theory.

The authors propose a prototype for the development of anorexia nervosa on the basis of a series of clinical interviews with 11 women with this disorder. Grounded Theory analysis of the narrative data-generated themes suggested the following prototype: Women with the personality characteristics of compliance and perfectionism who are encouraged by families and culture to substitute others' needs for their own are at greater risk for anorexia nervosa during periods of developmental stress. This proposal is considered from the perspective of psychodynamic, cognitive, and family systems viewpoints as well as attachment theory and feminist models of the development of women. The authors suggest that narrative research contributes substantially to clinical understanding by capturing the intricate details of a phenomenon or the richness of a lived life. Nevertheless, there is a need for further quantitative research to test the specificity and generalizability of this prototype.

Adolescent↗
PubMed2000

Chromosome abnormalities in ovarian adenocarcinoma: III. Using breakpoint data to infer and test mathematical models for oncogenesis.

Cancer geneticists seek to identify genetic changes in tumor cells and to relate the genetic changes to tumor development. Because single changes can disrupt the cell cycle and promote other genetic changes, it is extremely hard to distinguish cause from effect. In this article we illustrate how 7 techniques from statistics, theoretical computer science, and phylogenetics can be used to infer and test possible models of tumor progression from single genome-wide descriptions of aberrations in a large sample of tumors. Specifically, we propose 4 tree models for tumor progression inferred from the large ovarian cancer data set described in the first 2 articles in this series. The models are derived from 2 different methods to select the non-random genetic aberrations and 2 different methods to infer the trees, given a set of events. Various aspects of the tree models are tested and extended by 5 methods: overall tests of independence, likelihood ratio tests, principal components analysis, directed acyclic graph modeling, and Bayesian survival analysis. All our methods lead to strikingly consistent conclusions about chromosomal breakpoints in ovarian adenocarcinoma, including (1) the non-random breakpoints in ovarian adenocarcinoma do not occur independently; (2) breakpoints in regions 1p3 and 11p1 are important early events and distinguish a class of tumors associated with poor prognosis; and (3) breakpoints in 1p1, 3p1, and 1q2 distinguish a class of ovarian tumors, and the breaks at 1p1 and 3p1 are associated with poor prognosis.

Adenocarcinoma↗
PubMed1999

Exercise-induced myocardial ischemia in isolated coronary artery ectasias and aneurysms ("dilated coronopathy").

OBJECTIVES: The purpose of our study was to evaluate the clinical significance of isolated coronary artery ectasias or aneurysms (CEA). BACKGROUND: It has been postulated that altered coronary blood flow in CEA predisposes patients to the development of myocardial ischemia (CI) and infarction. METHODS: Sixty-seven patients with bilateral nonobstructive CEA without associated cardiac defects ("dilated coronaropathy") were derived from 16,341 cardiac catheterizations between 1986 and 1997. Ectasias were defined as luminal dilation of 1.5- to 2.0-fold, aneurysms of >2.0-fold of normal limits. Eleven of 25 patients presented with myocardial infarction due to an occlusion of the infarct vessel. In 42 patients without infarction (study group), exercise-induced CI was investigated. RESULTS: A corresponding CI was documented in 32 of 42 patients in a coronary sinus lactate study (reduced lactate extraction 5.6 +/- 4.1%) and in 29 of 40 patients in an ergometry (0.25 +/- 0.06 mV ST depressions). The results differed significantly from a control group of 29 patients without heart disease (p < 0.001). Nitroglycerin (0.8 mg) provoked a further significant deterioration of CI in the 32 of 42 developing a frank cardiac lactate production (-2.6 +/- 6.8%, p < 0.001). The metabolic extent of CI was significantly correlated to the coronary diameters of the proximal and middle segments of left anterior descending artery and the middle segment of left circumflex artery (r = 0.87, p < 0.001). Stigmata of an impaired coronary blood flow such as delayed antegrade filling, segmental backflow phenomenon and local deposition of dye were found significantly more often with increasing coronary diameters (p < 0.04). CONCLUSIONS: "Dilated coronaropathy" is an entity of nonobstructive, ischemic coronary artery disease. Nitroglycerin is of no therapeutic benefit but leads to an aggravation of exercise-induced CI.

Coronary Aneurysm↗
PubMed1999

[Coach-class thrombosis--a potential risk for long distance-travelers].

Prolonged non-stop flights imply the hazard of thromboses in the deep veins of the leg. Since more than a billion passengers each year travel by air, the economy class syndrome (coach class thrombosis) has become a rather frequent complication among travellers. For various reasons it is difficult to investigate the economy class syndrome in a methodological way. Therefore, we approached the subject of travellers' thrombosis by using standardised questionnaires and, using this method, we reviewed 121 patients with traveller's thromboses and its complications (50 males, 71 females, mean age 55 years). Seventy-seven patients of this sample suffered from deep venous thromboses, 39 suffered from pulmonary embolism as a consequence of manifest thromboses and 4 were found to have "isolated" pulmonary embolism. The journeys had a mean duration of 12 hours and the first symptoms were observed 3.1 days after the migration. Specific risk factors for thrombosis were identified in no more than 41 patients. Based on our data, a Consensus Conference on travellers' thrombosis was held in 1995, in which the diagnosis, prophylaxis and treatment of deep vein thrombosis associated with migration were investigated and established.

Adolescent↗
PubMed1999

Signaling of cell fate decisions by CLAVATA3 in Arabidopsis shoot meristems.

In higher plants, organogenesis occurs continuously from self-renewing apical meristems. Arabidopsis thaliana plants with loss-of-function mutations in the CLAVATA (CLV1, 2, and 3) genes have enlarged meristems and generate extra floral organs. Genetic analysis indicates that CLV1, which encodes a receptor kinase, acts with CLV3 to control the balance between meristem cell proliferation and differentiation. CLV3 encodes a small, predicted extracellular protein. CLV3 acts nonautonomously in meristems and is expressed at the meristem surface overlying the CLV1 domain. These proteins may act as a ligand-receptor pair in a signal transduction pathway, coordinating growth between adjacent meristematic regions.

Amino Acid Sequence↗
PubMed1999

Comparative genomic hybridization of ductal carcinoma in situ of the breast-evidence of multiple genetic pathways.

There is strong evidence that ductal carcinoma in situ (DCIS) represents a precursor lesion of invasive breast cancer. In order to analyse specific chromosomal alterations of DCIS, 38 paraffin-embedded specimens of DCIS and six associated invasive carcinomas were examined by means of comparative genomic hybridization (CGH). Losses of 16q material were seen almost exclusively in well- and intermediately-differentiated DCIS. These two subgroups differed in the average number of genetic imbalances, 2.5 and 5.5 respectively. Additionally, a higher frequency of gains of 1q and losses of 11q material was seen in intermediately-differentiated in contrast to well-differentiated DCIS. Poorly-differentiated DCIS displayed a higher frequency of amplifications (17q12, 11q13) and a higher average rate of genetic imbalances (7.1). Analysis of adjacent invasive breast carcinoma revealed a genetic pattern almost identical to the one seen in the DCIS counterpart. These data characterize DCIS as a genetically far-advanced, heterogeneous lesion and as a direct precursor of invasive breast cancer.

Breast Neoplasms↗
PubMed1999

Different genetic pathways in the evolution of invasive breast cancer are associated with distinct morphological subtypes.

Invasive breast cancer shows a wide range of morphological differentiation, associated with differences in prognosis, but as yet, the underlying genetic mechanisms cannot be accounted for. In order to establish a model of the possible progression from the different subtypes of ductal carcinoma in situ (DCIS) to invasive breast cancer, 77 selected cases of invasive breast cancer representing distinct morphological subtypes were investigated by means of comparative genomic hybridization (CGH). There was a high degree of genetic homology between tubular and tubulo-lobular carcinoma and well-differentiated DCIS, and between ductal invasive carcinoma G3 and poorly differentiated DCIS. Highly differentiated invasive breast cancers were characterized by a loss of 16q and a low average number of aberrations per case. In high-grade tumours, losses of this chromosomal region were seen with a much lower frequency in cases with evidence of an aneuploid tumour status. These data demonstrate the close genetic similarity of well-, intermediately, and poorly differentiated DCIS and distinct morphological types of invasive breast carcinoma, providing further evidence that DCIS is a direct precursor lesion of invasive breast cancer and that various evolutionary genetic pathways exist.

Adenocarcinoma↗
PubMed1999

Interactions of hydroxy-s-triazines with sodium dodecyl sulfate-micelles investigated by micellar capillary electrophoresis.

The electrophoretic behavior of fourteen 4,6-diamino-s-triazines was investigated in the presence of an anionic surfactant (sodium dodecyl sulfate, SDS) using micellar capillary electrophoresis (MCE). The measurements were performed at the pH of zero charge of the hydroxytriazines and the existence of strong ionic and H-bond interactions of hydroxy-s-triazine species with the anionic micelles could be shown. Their migration behavior was compared to the n-octanol-water partition coefficients (log Kow) measured with reverse-phase HPLC and calculated with different fragment contribution methods. A partition model was proposed to understand the interactions of the three major hydroxy-s-triazine species: cationic, anionic and neutral (presenting enol and keto forms) with the charged SDS micelles taken as model for charged natural polyelectrolytes like humic substances. These results strongly indicate that hydroxy-striazines are polarized in the presence of the charged micelles and that they are essentially present in their keto form in the micellar phase (and enol form in the water phase), confirming previous studies suggesting the presence of zwitterionic resonance structures at a neutral pH around their isoelectric point.

Algorithms↗
PubMed1999

The ARTS study (Arterial Revascularization Therapies Study).

The rising costs of health care have forced policy makers to make choices, and new treatments are increasingly assessed in terms of the balance between additional costs and additional effects. The recent recognition that stenting has a major and long-lasting effect enhancing balloon PTCA procedure has made it imperative to compare in patients with multivessel disease the standard surgical procedure with multiple stenting in a large scale multinational and multicentre approach (19 countries, 68 sites). Selection and inclusion of patients is based on a consensus of the cardiac surgeon and interventional cardiologist on equal 'treatability' of patients by both techniques with analysis of clinical follow-up (event-free survival) on the short (30 day), medium (1 year), and long-term (3 and 5 year) with analysis of cost-effectiveness and quality of life (EuroQol and SF-36). Of the entire trial, the primary null hypothesis which needs to be rejected is that there will be no difference in event-free survival or effectiveness (E), at 1 year and also that the direct and indirect costs (C) per event-free year are not different between surgery or stenting. For this to become significant with a power of 90% one needs 1200 patients. Between April 97 and June 98, 1205 patients have been randomized with a monthly recruitment of 83 patients. Expected costs, effects and cost-effectiveness ratio (CE ratio) are: Stent high costs 2 VDStent high costs 3 VDStent low costs 2 VDStent low costs 3 VDCABG costs (C)$19.297$24.566$16.638$20.456$21.350 effects (E)81%81%81%81%88% CE ratio$23.876$30.397$20.586$25.322$24.348 Clinically, stenting is not expected to be more effective than CABG, but should be cost effective in both the 2- and 3-VD group when using the lower cost estimate and in the 2 VD group when using the higher cost assumptions.

Angioplasty, Balloon, Coronary↗
PubMed1999

[In Process Citation]

To optimise the microsurgical training in our clinic we organized a permanent possibility to practice microsurgical techniques of vascular anastomosis. This includes step-wise education by means of plastic materials, human placenta and the rat model. The most important role in this concept is played by the placenta. It supplies a realistic simulation of different in vivo situations concerning microvascular anastomosis. As to availability, handling and costs the placenta is superior to animal models and has replaced them almost completely in our educational concept.

Journal Article↗
PubMed1999

[Determination of torsion angle after shaft fractures of the lower extremity--clinical relevance and measurement techniques].

In the treatment of femoral and tibial fractures the frontal and sagittal planes are controlled and documented by conventional X-ray films. Computed tomography permits exact measurement of the coronal plane. Between June 1993 and December 1997, 161 computed tomographic measurements of femoral torsion and 55 of tibial torsion after shaft fracture were carried out. The results were analyzed in a clinical study. A CT examination was carried out if the clinical examination aroused suspicion of a difference in torsion. 28.5% of the patients examined with femoral fractures and 23.8% of those with tibial fractures and torsion differences of more than 20 degrees. Between June 1993 and June 1997, 30 corrective derotating osteotomies of the femur and 9 of the tibia were carried out. The average preoperative difference of torsion of the femur was 29 degrees and of the tibia 25 degrees. After the operation the average femur difference was 7 degrees and of the lower leg 6.5 degrees, which are inside normal physiological limits. The osteotomies were carried out in the metaphysis near the fracture. Additional corrections in other planes were necessary on the femur in 27% and on the lower leg in 46%. With the aim of avoiding torsion differences, or at least to recognize them at an early stage, CT measurements of torsion after osteosythetic treatment of fresh unilateral femur-shaft fractures were carried out in 49 patients between October 1996 and December 1997. The torsion measurements during the operations had to be carried out clinically. No sufficiently exact method of measurement is available in the operating room. Three patients with increased differences of 28 degrees, 26 degrees or 19 degrees had their osteosyntheses corrected. The measurements after correction were inside the normal spread.

Adult↗