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Biomedical subjects

K P Schmidt

Publications and source records attributed to K P Schmidt.

17 recordsLinked to original sources
PubMed2004

Unifying magnons and triplons in stripe-ordered cuprate superconductors.

Based on a two-dimensional model of coupled two-leg spin ladders, we derive a unified picture of recent neutron scattering data of stripe-ordered La15/8Ba1/8CuO4, namely, of the low-energy magnons around the superstructure satellites and of the triplon excitations at higher energies. The resonance peak at the antiferromagnetic wave vector Q(AF) in the stripe-ordered phase corresponds to a saddle point in the dispersion of the magnetic excitations. Quantitative agreement with the neutron data is obtained for J=130-160 meV and Jcyc/J=0.2-0.25.

Journal Article↗
PubMed2003

Charge-order-induced sharp Raman peak in Sr14Cu24O41.

In the two-leg S=1/2 ladders of Sr14Cu24O41, a modulation of the exchange coupling arises from the charge order within the other structural element, the CuO2 chains. In general, breaking transla-tional invariance by modulation causes gaps within the dispersion of elementary excitations. We show that the gap induced by the charge order can drastically change the magnetic Raman spectrum, leading to the sharp peak observed in Sr14Cu24O41. This sharp Raman line gives insight into the charge-order periodicity and hence into the distribution of carriers. The much broader spectrum of La6Ca8Cu24O41 reflects the response of an undoped ladder in the absence of charge order.

Journal Article↗
PubMed2001

Fractional and integer excitations in quantum antiferromagnetic spin 1/2 ladders.

Spectral densities are computed in unprecedented detail for quantum antiferromagnetic spin 1/2 two-leg ladders. These results were obtained due to a major methodical advance achieved by optimally chosen unitary transformations. The approach is based on dressed integer excitations. Considerable weight is found at high energies in the two-particle sector. Precursors of fractional spinon physics occur supporting the conclusion that there is no necessity to resort to fractional excitations in order to describe features at higher energies.

Journal Article↗
PubMed2001

Observation of two-magnon bound states in the two-leg ladders of (Ca,La)(14)Cu(24)O(41).

Phonon-assisted two-magnon absorption is studied in the spin- 1/2 two-leg ladders of (Ca,La)(14)Cu(24)O(41) for E parallel c (legs) and E parallel a (rungs). We verify the theoretically predicted existence of two-magnon singlet bound states, which give rise to peaks at approximately equal to 2140 and 2800 cm(-1). The two-magnon continuum is observed at approximately equal to 4000 cm(-1). Two different theoretical approaches (Jordan-Wigner fermions and perturbation theory) describe the data very well for J parallel approximately equal to 1020-1100 cm(-1), J parallel/J perpendicular approximately equal to 1-1.2. At high energies, the magnetic contribution to sigma(omega) is strikingly similar in the ladders and in the undoped high-T(c) cuprates, which emphasizes the importance of strong quantum fluctuations in the latter.

Journal Article↗
PubMed1990

[Initial experiences with radiation planning of combined teletherapy and brachytherapy of gynecologic tumors using CT tomograms].

Dose distributions of a combination from telecobalt-arc-therapy and afterloading-therapy for radiation therapy of gynecological cancers were calculated, using a computer program developed in our institute. Taking as a basis CT-scans the bone structures were taken into consideration like inhomogeneities. Conclusions about the individual dose on sensitive organs into the irradiated area like bladder and rectum become possible. The influence of changing parameters such like distance of axis of arc-therapy can be shown clearly.

Brachytherapy↗
PubMed1989

[Localization technic and positioning methodology in afterloading therapy].

For use in afterloading therapy there was constructed a special combination consisting of X-ray multiplier and a gynaecological table. Because of the constant magnification of radiographs topometric examinations became easier. Examining the displacement of points of interest when the patient is restored from a lithotomic position into a position with stretched legs we concluded that from the point of view of treatment planning it will be necessary to carry out afterloading irradiation with stretched legs like in the teletherapy. Only in such a way it is possible to calculate a common dose distribution of teletherapy and afterloading therapy.

Brachytherapy↗
PubMed1978

[Iron determination by carbon rod atomizer (author's transl)].

A method is described for direct analysis of iron in proteins. The organic and inorganic matrices can be removed during the ashing step. The results obtained with simple aqueous standards were confirmed for all determinations by the standard addition method. The interpretation of the results by means of regression analysis showed, in dependence on the biological material (Haemoglobin, suspension of Microsomes, Cytochrome P 450), relative standard deviations between 4 and 20%.

Animals↗