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Biomedical subjects

H Walther

Publications and source records attributed to H Walther.

At least 37 records · Page 2Linked to original sources

Above-threshold ionization by an elliptically polarized field: interplay between electronic quantum trajectories

Measurements of energy-resolved angular distributions of electrons generated in above-threshold ionization of rare gases in a field with elliptical polarization are presented, with emphasis on the high-energy part of the spectra. The data show a second plateau at a specific angle with respect to the large component of the laser field. The results are compared to a calculation based on a strong-field rescattering approximation. This is interpreted in terms of the superposition of quantum trajectories. The second plateau is associated with the interference of electrons that do and that do not rescatter.

Journal Article↗

Preparing pure photon number states of the radiation field

The quantum mechanical description of a radiation field is based on states that are characterized by the number of photons in a particular mode; the most basic quantum states are those with fixed photon number, usually referred to as number (or Fock) states. Although Fock states of vibrational motion can be observed readily in ion traps, number states of the radiation field are very fragile and difficult to produce and maintain. Single photons in multi-mode fields have been generated using the technique of photon pairs. But in order to generate these states in a cavity, the mode in question must have minimal losses; moreover, additional sources of photon number fluctuations, such as the thermal field, must be eliminated. Here we observe the build-up of number states in a high-Q cavity, by investigating the interaction dynamics of a probe atom with the field. We employ a dynamical method of number state preparation that involves state reduction of highly excited atoms in a cavity, with a photon lifetime as high as 0.2 seconds. (This set-up is usually known as the one-atom maser or 'micromaser'.) Pure states containing up to two photons are measured unambiguously.

Journal Article↗

Atmospheric heat exchange of the human being, bioclimate assessments, mortality and thermal stress.

In epidemiological investigations of the impact of the atmospheric environment on mortality usually only air temperature, in addition to sometimes relative humidity, are used, although it is generally known that the heat exchange conditions of the human body also depend on water vapour pressure, wind velocity, and short- and long-wave radiation. The state-of-the-art approach to this problem is the application of complete heat budget models which allow thermophysiologically significant assessments of the above-mentioned meteorological variables taking metabolic rate and isolation of clothing into account. The application of such a model to 30-year mortality data of Baden-Württemberg (SW-Germany) shows, in winter, increasing daily mortality rate with decreasing "perceived temperature." (a term which relates temperature to a fixed standard condition). A sudden warming during a cold period also results in an increase in mortality, a certain contradiction which has not yet been able to be explained. During cold spells a marked increase in mortality with a delay of 3 days can be observed. Above normal values last for about 4 weeks and will then be partially compensated by an "undershot". Generally the explanation of variance in winter is distinctly lower than in summer, probably because in winter there is rarely direct exposure to outdoor conditions. The degree of cold stress is likely to serve only as an indicator for indoor conditions which promote infectious diseases.

Body Temperature Regulation↗

Generation of multiple-charged optical vortex solitons in a saturable nonlinear medium.

Multiply charged optical vortex solitons (OVS) (m=1,...,4) are generated in a thermal nonlinear medium with saturation. The respective soliton constants are found to be linearly proportional to the topological charges. Special attention is paid to the modulational instability, which is effectively suppressed by a moderate saturation but still remains an increasing function of the topological charge. For the particular experimental conditions, the recorded OVS profiles are found to be in good qualitative agreement with the numerical stationary solutions of the generalized nonlinear Schrödinger equation.

Journal Article↗

Modulational instability of multiple-charged optical vortex solitons under saturation of the nonlinearity.

We present a linear analysis and numerical simulations of the instability of optical vortex solitons (OVSs) of arbitrary topological charge. They show a rich variety of instability scenarios depending on the type of perturbation. The saturation of the nonlinearity is shown to be able to slow down the decay of multiple charged dark beams at an intermediate evolution stage and to prevent their ultimate decay into charge-1 OVSs. This concept is experimentally verified by the observation of a partial decay of a triple-charged OV beam and by comparing this dynamic with the behavior of OV beams of topological charges m=1, 2, 3, and 4.

Journal Article↗

Development of a regional cohort of very-low-birthweight children at six years: cognitive abilities are associated with neurological disability and social background.

The authors studied the intelligence, memory, visuomotor skills and la nguage of 298 six-year-old children with very low birthweight (VLBW) (less that 1500g). Of 591 VLBW childern born July 1983 to June 1986 within 50km of the centre of Hamburg, Germany, 330 were traceable at age six years and 298 of these were seen by a neuropaediatrician and a psychologist; the other 19 were too severely disabled for psychological assessment with the standardized tests used. The mean memory performance of VLBW children at age six years was below the standard mean in all diagnostic and socio-economic subgroups. As expected, visuomotor development was clearly influenced by neurological but not socio-economic status. Intelligence and language skills were much more closely related to socio-economic background that to neurological morbidity. However, VLBW children with hyperactivity, clumsiness or cerebral palsy differed significantly in intelligence and visuomotor performance from those without neurological symptoms.

Cerebral Palsy↗

[Leiomyosarcoma of the stomach].

A 35-year old woman showed gastrointestinal bleeding right after normal pregnancy. With endoscopy of the GI-tract with biopsy, ultrasound, conventional radiology of the stomach and computed tomography a gastric leiomyoma was diagnosed. After en-bloc resection of tumor, part of the stomach and spleen, histologic examination and size of tumor changed diagnosis in gastric leiomyosarcoma. Patient died 15 month postoperatively on systemic metastasis. Case report and review of the literature show difficulties in diagnosis and prognosis of gastric leiomyosarcoma.

Adult↗

A hydrophilic omega-loop (Tyr181 to Tyr188) in the nonsubstrate binding area of HIV-1 reverse transcriptase.

Using the molecular "cloud" of the HIV-1 reverse transcriptase (RT) as starting point, the peptide backbone of the polymerase subunit was visualized by molecular modelling. Then, the two subregions 98-106 and 179-190 of the allosteric area were "isolated". From the latter subregion, the Tyr181 to Tyr188 segment containing two amino acids (Asp185, Asp186) of the catalytic aspartyl triad and two amino acids (Tyr181, Tyr188) of the nonnucleoside RT inhibitor (NNRTI) binding sites, was excised. It was shown that the segment has a omega-like loop configuration which is highly hydrophilic. The two phenolic side chains of Tyr181 and Tyr188 represent the lipophilic "horizontal axes" of the omega-loop shape. The relative rigidity of the omega-loop is mainly based on a hydrogen bond between the peptide CO of Tyr181 and the peptide NH of Tyr188. Solvation in water increases the number of intramolecular hydrogen bonds. Therefore, desolvation is one of the conditions of binding with NNRTIs. Site-directed mutagenesis affects the hydrophilicity of the omega-loop while steric features are less influenced.

Binding Sites↗