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Biomedical subjects

A Richter

Publications and source records attributed to A Richter.

At least 55 records · Page 3Linked to original sources
PubMed2004

First experimental evidence for quantum echoes in scattering systems.

A self-pulsing effect termed quantum echoes has been observed in experiments with an open superconducting and a normal conducting microwave billiard whose geometry provides soft chaos, i.e., a mixed phase space portrait with a large stable island. For such systems a periodic response to an incoming pulse has been predicted. Its period has been associated with the degree of development of a horseshoe describing the topology of the classical dynamics. The experiments confirm this picture and reveal the topological information.

Journal Article↗
PubMed2004

Fine structure in the energy region of the isoscalar giant quadrupole resonance: characteristic scales from a wavelet analysis.

Fine structure in the energy region of the isoscalar giant quadrupole resonance in nuclei is observed in high-resolution proton scattering experiments at iThemba LABS over a wide mass range. A novel method based on wavelet transforms is introduced for the extraction of scales characterizing the fine structure. A comparison with microscopic model calculations including two-particle two-hole (2p2h) degrees of freedom identifies the coupling to surface vibrations as the main source of the observed scales. A generic pattern is also found for the stochastic coupling to the background of the more complex states.

Journal Article↗
PubMed2004

Altered expression of preproenkephalin and prodynorphin mRNA in a genetic model of paroxysmal dystonia.

The dtsz mutant hamster represents a model of primary paroxysmal dystonia, in which dystonic episodes occur in response to stress. Previous examinations demonstrated striatal dysfunctions in dtsz hamsters. In the present study, in situ hybridization was used to examine preproenkephalin and prodynorphin expression as potential indices of imbalances between the striatopallidal and striatonigral pathways. Brain analyses were performed in dtsz hamsters under basal conditions, i.e., in the absence of dystonia, as well as mutant hamsters that exhibited severe stress-induced dystonic attacks immediately prior to sacrifice. In the striatum the basal expression of prodynorphin tended to be higher, while that of preproenkephalin tended to be lower in mutant hamsters in comparison to non-dystonic control hamsters. Significant basal changes were restricted to higher levels of prodynorphin in the ventrolateral striatum and lower prodynorphin and preproenkephalin mRNA expression in the hippocampus and/or in subregions of the hypothalamus. After stressful stimulation, the neuropeptides increased in several regions in both animals groups. In comparison to stimulated control hamsters, a significantly lower prodynorphin expression was found in several limbic areas of stimulated mutant hamsters during the manifestation of dystonia, while preproenkephalin mRNA was significantly lower in the anterior and dorsal striatal subregions and in nucleus accumbens. Since changes in the expression of these opioid peptides have been suggested to be related to abnormal dopaminergic activity, the present findings may reflect disturbances in striatal dopaminergic systems, and also in limbic structures in the dtsz mutant, particularly during the expression of dystonia.

Analysis of Variance↗
PubMed2004

Encircling an exceptional point.

We calculate analytically the geometric phases that the eigenvectors of a parametric dissipative two-state system described by a complex symmetric Hamiltonian pick up when an exceptional point (EP) is encircled. An EP is a parameter setting where the two eigenvalues and the corresponding eigenvectors of the Hamiltonian coalesce. We show that it can be encircled on a path along which the eigenvectors remain approximately real and discuss a microwave cavity experiment, where such an encircling of an EP was realized. Since the wave functions remain approximately real, they could be reconstructed from the nodal lines of the recorded spatial intensity distributions of the electric fields inside the resonator. We measured the geometric phases that occur when an EP is encircled four times and thus confirmed that for our system an EP is a branch point of fourth order.

Journal Article↗
PubMed2004

[Shared decision making (SDM) with chronic pain patients. The patient as a partner in the medical decision making process].

Fibromyalgia syndrome (FMS) is an exemplary condition of chronic widespread pain that is difficult to control and often leads to frustration and resignation on the part of both the patient and the doctor. Shared decision making (SDM) could be a means to facilitate doctor-patient interaction and might therefore influence therapeutic decisions taken. We conducted a prospective study to evaluate the effects of SDM with FMS patients. We developed a communication train-ing program for physicians and a computer-based information tool on FMS for patients. The study included 133 FMS patients. Intervention group I (IG I) was treated by communication-trained doctors and had access to a computer-based information tool on FMS,intervention group II (IG II) was treated by standard doctors and received the information tool, and the control group (CG) was treated by standard doctors and got no additional information. All three groups we-re offered the same evidence-based treatment options for FMS. Patients of the IGs were more willing to become involved in exercise, to enroll in integrated group therapy for FMS patients (IGTF), and to take analgesics. Patients of the CG preferred anti-depressants. More patients from IG II and CG opted for relaxation techniques. Patients in IG I and IG II choose significantly more therapeutic options than patients in the CG. SDM is one means to increase FMS patients' readiness for treatment. Especially the element of providing sufficient medical information seems to account for this effect. The readiness to enroll in physical activities, to take analgesics, and to participate in psychotherapeutic elements was most likely to be raised through SDM.

Adult↗
PubMed2004

[Preoperative imaging as the basis for image-guided neurosurgery].

With the progressive development of soft- and hardware, the acceptance of image-guided neurosurgery has increased dramatically. Additional image data are required to analyze the nature and the dimensions of pathological processes and the surrounding tissue. In this context, fMRI, SPECT, PET, as well as special modalities of CT and MR imaging, are routinely used. Secondary post-processing options are used to detect intracerebral lesions as well as adjacent functional eloquent regions in the parenchymatous organ pre- and intraoperatively. The integration of different image information guarantees the precise planning and realization of surgical maneuvers. The segmentation of interesting structures and risk structures, as well as their implementation in the neuronavigation systems, help to avoid additional intraoperative traumatization and offer a higher level of safety and precision. In this article the value and limitations of presurgical imaging will be discussed.

Brain↗
PubMed2004

Chlamydia pneumoniae IgG and the severity of coronary atherosclerosis.

BACKGROUND: The aim of this study was to compare Chlamydia pneumoniae IgG and the extent of coronary atherosclerosis. METHODS: We investigated 92 patients with stable angina pectoris who underwent coronary angiography to assess chest pain. Before angiography, C. pneumoniae IgG was analyzed. The number of major coronary arteries (1-3) having at least one diameter narrowing (>/=50%) stenosis was determined. The patients were divided into two groups of equal size, according to C. pneumoniae IgG levels. One group included individuals with C. pneumoniae IgG levels exceeding 46 enzyme-immuno-units (EIU)/L and the other consisted of subjects with IgG concentrations below 46 EIU/L. RESULTS: Subjects with higher antibody concentrations had a more severe disease. The number of diseased arteries was 2.1+/-0.8 (S.D.) and 1.4+/-0.6 (S.D.) for the two groups, respectively. The difference is highly significant (p<0.0001). CONCLUSIONS: This study suggests a causative relationship between C. pneumoniae IgG and the degree of coronary atherosclerosis. It does not, however, prove causality.

Journal Article↗
PubMed2004

C2 blood concentrations of orally administered cyclosporine in pediatric liver graft recipients with a body weight below 10 kg.

Pharmacokinetic studies in adult and pediatric liver transplant recipients have shown that the C(2) monitoring is superior to the traditional determination of CsA trough levels (C(0)) as an estimate of CsA exposure. However, target reference values for C(2) in very small infants have not been established yet. The objective of our study was to assess the distribution of C(2) levels in the first week following Ltx and to analyze enteral absorption of CsA for this group of patients. We documented CsA C(0) and C(2) levels in 25 infants with a body weight below 10 kg (median 6.8 kg; range 3.0-9.8 kg) in the first 7 days after Ltx. The infants had a median age at transplantation of 7 months (range 0.3-20.0 months). The underlying diagnoses were biliary atresia (n = 17), acute liver failure (n = 4), metabolic disease (n = 4). All children received CsA microemulsion (Neoral, initial 10 mg/kg/day), prednisolone, and two single doses of basiliximab as immunosuppressive drugs. The mean C(0) and C(2) levels were as follows: day 1: C(0) 77.0 +/- 39.6, C(2) 340.5 +/- 140.0 ng/mL; day 2: C(0) 135.5 +/- 53.2, C(2) 467.0 +/- 168.2 ng/mL; day 3: C(0) 146.5 +/- 70.8, C(2) 519.0 +/- 219.1 ng/mL; day 4: C(0) 168.5 +/- 55.1, C(2) 570.0 +/- 163.7 ng/mL; day 5: C(0) 156.5 +/- 38.0, C(2) 612.0 +/- 132.4 ng/mL; day 6: C(0) 177.0 +/- 41.1, C(2) 606.0 +/- 149.2 ng/mL; day 7: C(0) 174.0 +/- 27.2, C(2) 622.0 +/- 98.8 ng/mL (r = 0.82, p < 0.05). This analysis demonstrates that there is a good enteral absorption of CsA in very small children post-Ltx in the early post-operative period. Based on the C(2) levels achieved, we conclude that there is a good correlation between C(0) and C(2) levels even in very small infants.

Administration, Oral↗
PubMed2004

Cavernous malformations--navigational supported surgery.

OBJECTIVE: Navigational supported surgery of intracranial lesions is expected to be associated with a lower rate of brain traumatization as well as an avoidance of additional neurological deficits and surgical morbidity. In our study we used the computer-assisted image guidance for resection of cerebral cavernous malformations. METHODS: In all patients the planning procedure for the following image-guided surgery was realized using preoperative MRl data sets and a neuronavigation system (STP 4.0, SNN). In cases in which the cavernoma was situated near functional eloquent regions, functional MR images were fused preoperatively. RESULTS: During the last 24 months, 21 patients were surgically treated for cerebral cavernoma. No patient was operated twice. The mean size of cavernoma was 18.3 mm, ranging from 5 to 60 mm, the mean distance between cortical surface and cavernoma was 26 mm, ranging from 5 to 50 mm. The surgical procedure lasted in the median 180 min. All patients showed an identical or better neurological outcome. CONCLUSIONS: Neuronavigation allows an accurate definition of the intraoperative target, a correct approach and a safe surgery. With the help of neuronavigation the surgical approach and the extirpation of cavernous malformations were realized in a comfortable and safe way and allowed a minimization of tissue manipulation.

Adolescent↗
PubMed2004

Expression of ErbB receptors and mucins in the airways of long term current smokers.

BACKGROUND: Airway epithelial goblet cell hyperplasia is known to occur in chronic smokers. Although the epidermal growth factor receptor has been implicated in this process, neither ErbB receptor expression nor the mucosecretory phenotype of the epithelium have been characterised in current smokers. METHODS: Bronchial biopsies obtained from non-smokers (n = 10) and current smokers, with or without chronic obstructive pulmonary disease (n = 51), were examined immunohistochemically to measure the expression of epidermal growth factor receptor, ErbB2, ErbB3, ErbB4 and mucin subtypes (MUC2, MUC5AC and MUC5B) in the bronchial epithelium. The results were correlated with neutrophil counts measured in the airway wall and induced sputum. RESULTS: Epidermal growth factor receptor, ErbB3 and MUC5AC expression, in addition to PAS staining, were significantly increased in all smokers compared with non-smokers, irrespective of the presence of chronic obstructive pulmonary disease. MUC5AC expression was significantly associated with both PAS staining and ErbB3 expression; no correlation was observed between either mucin or ErbB receptor expression and neutrophil counts. CONCLUSIONS: The results suggest that long term current smoking induces enhanced epidermal growth factor receptor, ErbB3, and MUC5AC expression in vivo; these increases are not associated with the presence of neutrophilic inflammation. ErbB receptors may contribute to epithelial responses to cigarette smoke.

Bronchi↗
PubMed2004

[The compatibility of ronidazol in racing pigeons in a controlled clinical study].

Ronidazol is often used in racing pigeons for the treatment of Trichomonas infections and diseases. Therefore, in this study, the compatibility of the drug was examined by oral application over 7 days. For this purpose a randomized blind study was performed using four different groups (control group, 10 mg = therapy-group, 20 mg = double-dose-group and 40 mg = high-dose-group) of pigeons (Columba livia f. domestica) with 6 male and 6 female birds each. All birds were clinically healthy and between 6 and 12 weeks of age. The application of ronidazol at a dose of 10 mg/racing pigeon did show no side-effect within the duration of the study, e.g. no influence could be seen on clinical, haematological, blood-chemical and pathological parameters. Low-to middle-grade clinical alterations of the gastro-intestinal tract occurred in the high-dose group at day 6 and 7 of the application of the drug. Therefore a fourfold overdosing of ronidazol should be avoided.

Administration, Oral↗
PubMed2003

The t+n+n system and 5H.

The one-proton knockout channel from 6He (240 MeV/u) impinging on a carbon target has been investigated. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure, peaked at 3 MeV above the t+2n threshold, is observed in the t+n+n-relative energy spectrum. It is shown that this structure is mainly due to a I(pi)=1/2(+) resonance as expected for the 5H ground state, and from the observed angular and energy correlations, being used for the first time in 5H studies, that the neutrons to a large extent occupy the p shell.

Journal Article↗
PubMed2003

Investigation into the ability of roots of the poikilohydric plant Craterostigma plantagineum to survive dehydration stress.

The ability of the root system of the poikilohydric plant Craterostigma plantagineum to survive dehydration was investigated. The data presented here reveal that the root system is capable of surviving dehydration, but shortly after rehydration the root system senesces. Two weeks after rehydration the growth of a complete new root system is initiated. During dehydration sucrose accumulates from 36 to a maximum of 111 micromol g-1 DW in the roots. It is suggested that the accumulation of sucrose protects the root system during dehydration. There are major stores of stachyose in the roots of Craterostigma (making up over 40% of the dry weight of the tissue) and during dehydration these stores are metabolized. It is suggested that these stachyose stores act as carbohydrate reserves for the synthesis of sucrose. However, over 350 micromol g-1 DW stachyose is metabolized in the roots, which is well in excess of that required for the accumulation of sucrose observed. It is likely that the stachyose reserves in the root system are translocated to other regions of the plant to support carbohydrate metabolism during dehydration of the tissue. During rehydration, the stachyose reserves return to their original level within 96 h. There is no change in the elevated sucrose content of the roots over this period. Thus the roots maintain the protective properties of sucrose much longer than they are needed. The maintenance of high sucrose contents in rehydrating roots is discussed as a possible survival strategy against recurrent desiccation events.

Carbohydrate Metabolism↗
PubMed2003

R-matrix theory of driven electromagnetic cavities.

The resonances of cylindrical symmetric microwave cavities are analyzed in R-matrix theory, which transforms the input channel conditions to the output channels. Single and interfering double resonances are studied and compared with experimental results obtained with superconducting microwave cavities. Because of the equivalence of the two-dimensional Helmholtz and the stationary Schrödinger equations, the results give insight into the resonance structure of regular and chaotic quantum billiards.

Journal Article↗
PubMed2003

Observation of a chiral state in a microwave cavity.

A microwave experiment has been realized to measure the phase difference of the oscillating electric field at two points inside the cavity. The technique has been applied to a dissipative resonator which exhibits a singularity-called exceptional point-in its eigenvalue and eigenvector spectrum. At the singularity, two modes coalesce with a phase difference of pi/2. We conclude that the state excited at the singularity has a definitive chirality.

Journal Article↗
PubMed2003

Phase shift experiments identifying Kramers doublets in a chaotic superconducting microwave billiard of threefold symmetry.

The spectral properties of a two-dimensional microwave billiard showing threefold symmetry have been studied with a new experimental technique. This method is based on the behavior of the eigenmodes under variation of a phase shift between two input channels, which strongly depends on the symmetries of the eigenfunctions. Thereby a complete set of 108 Kramers doublets has been identified by a simple and purely experimental method. This set clearly shows Gaussian unitary ensemble statistics, although the system is time-reversal invariant.

Journal Article↗