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Biomedical subjects

K Prokes

Publications and source records attributed to K Prokes.

At least 19 recordsLinked to original sources
PubMed2005

Novel coexistence of superconductivity with two distinct magnetic orders.

The heavy fermion system exhibits properties that range from an incommensurate antiferromagnet for small to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of and a new, commensurate antiferromagnetism that orders separately. The coexistence of -electron superconductivity with two distinct -electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.

Journal Article↗
PubMed2005

Helimagnetism of Fe: high pressure study of an Y2Fe17 single crystal.

In this Letter we present direct observation of the Fe helimagnetism in an Y2Fe17 single crystal under pressure. Combined neutron diffraction and magnetization measurements under pressure showed that the collinear ferromagnetic phase of Y2Fe17 is substituted by the pressure induced helical incommensurate phases. The complex pressure-temperature-field behavior of the pressure induced helical magnetic phases is attributed to intrinsic properties of the iron sublattice that gives a valuable contribution to the discussion about dominating theoretical models of magnetism in gamma-Fe.

Journal Article↗
PubMed2003

Inflection point in the magnetic field dependence of the ordered moment of URu2Si2 observed by neutron scattering in fields up to 17 T.

We have measured the magnetic field dependence of the ordered antiferromagnetic moment and the magnetic excitations in the heavy-fermion superconductor URu2Si2 for fields up to 17 T applied along the tetragonal c axis, using neutron scattering. The decrease of the magnetic intensity of the tiny moment with increasing field does not follow a simple power law, but shows a clear inflection point, indicating that the moment disappears first at the metamagnetic transition at approximately 40 T. This suggests that the moment m is connected to a hidden order parameter psi which belongs to the same irreducible representation breaking time-reversal symmetry. The magnetic excitation gap at the antiferromagnetic zone center Q = (1,0,0) increases continuously with increasing field, while that at Q = (1.4,0,0) is nearly constant. This field dependence is opposite to that of the gap extracted from specific-heat data.

Journal Article↗
PubMed2001

Inactivation of individual cells by divers ions at different LET values.

A new formula linking the shape of survival curve to the inactivation probabilities after different numbers of cell hits has been derived. It has been used in analyzing recent experimental data obtained with monolayer cells irradiated at definite values of LET (in different parts of Bragg peaks). The new approach allows not only deriving the values of inactivation probabilities at given LET values; unexpected consequences seem to follow especially for inactivation characteristics of carbon ions in different parts of the Bragg peak, too.

Animals↗
PubMed2000

Neutron scattering study of the field-induced soliton lattice in CuGeO3

CuGeO3 undergoes a transition from a spin-Peierls phase to an incommensurate phase at a critical field of H(c) approximately 12.5 T. In the high-field phase a lattice of solitons forms, with both structural and magnetic components, and these have been studied using neutron scattering techniques. Our results provide direct evidence for a long-ranged magnetic soliton structure which has both staggered and uniform magnetizations with amplitudes that are broadly in accord with theoretical estimates. The magnetic soliton width gamma(m) and the field dependence of the incommensurability deltak(SP) are found to agree well with theoretical predictions.

Journal Article↗
PubMed1996

Perspectives of tumour radiotherapy in the Czech Republic and "Oncology 2000" Foundation.

The incidence of tumours has still an increasing tendency. A great effort is being devoted to prevention as well as to improving early diagnosis and treatment. It is the radiotherapy which seems to bring new treatment possibilities at the present. Its goal consists in destroying all tumour cells in the target volume while all normal cells being damaged unsubstantially only. That is being achieved with standard available means only with rather great difficulties. However, in the last time two radiotherapy methods have been developed which are based on the use of the so called hadrons (i.e. particles exhibiting strong mutual interactions) and come nearer to the mentioned ideal goal of any tumour therapy. The first method consists in the application of beams of charged hadrons having a suitable characteristic of energy transfer; the most energy being transferred to the matter in the end of hadron tracks. Thus, by a suitable choice of initial energy of beam particles this maximum may lie in a tumour volume, while all other tissues obtain a smaller dose, the difference being greater when a multiple-field technique is used. The other approach (neutron capture therapy-NCT) makes use of epithermal (or thermal) neutrons captured by special isotopes accumulated in tumour cells with the help of suitable chemical carriers. Both the methods are now being introduced into clinical use in many countries. The "Oncology 2000" Foundation was grounded to introduce these methods into clinical use also in the Czech Republic. It proceeds with activities started by an interdisciplinary group of specialists formed approximately 20 years ago and having prepared some necessary conditions. As to the NCT a corresponding facility is now being finished and clinical tests are expected to be started in 1997. The main attention is now devoted to building up an oncology center based on the use of hadron beams.

Czech Republic↗
PubMed1990

Application of a semi-phenomenological model to experimental data of radiation induced pneumopathy in pigs.

A semi-phenomenological model has been derived, which describes the inactivation effect on individual cells by survival curves. This model is applied to experimental data of pneumopathy in pigs. The corresponding survival curves as well as the relations between cell survival and complication probability are calculated and discussed. Furthermore, dose-response curves for single dose irradiation and different fractionation schemes are derived. The comparison between the response curve for single dose irradiation and similar curves from the literature shows a good agreement.

Animals↗
PubMed1988

Mathematical models of cumulative effect and optimization of fractionation regimes.

Different (most known) mathematical models are shortly described and basic assumptions the individual models are based on are discussed and critically examined. Advantages and shortages of individual models are mentioned. A semiphenomenological model is then used to demonstrate some possibilities how to make use of the mathematical models in attempts of optimizing the fractionation approaches in individual cases.

Dose-Response Relationship, Radiation↗
PubMed1984

The mutagenic activity of aflatoxin B1 in the Cricetulus griseus hamster and Macaca mulatta monkey.

Chromosome aberrations were scored in bone marrow cells of Cricetulus griseus hamsters and Macaca mulatta monkeys given a single i.p. injection of aflatoxin B1 (AFB1). The mutagenic activity of AFB1 was assessed by the percentage of cells bearing aberrations and by the total frequency of chromosome and chromatid breaks. Chinese hamsters were treated with five different doses of AFB1 ranging from 1 microgram to 5 mg/kg (LD50/30 = 12.2 mg/kg) and the aberration yields at each AFB1 dose level tested were determined at 24 h intervals for 5 consecutive days. Compared to controls the increase in the two types of chromosome abnormalities was significant in all tests. At 5 mg/kg of AFB1 the tests were carried out over a period of 92 days to assure the analysis of aberration yields with time. All chromosome aberration assays conducted during this period showed significant increases in the frequencies of aberrant cells and chromosome and chromatid breaks in comparison to controls. Macaque monkeys were treated in the same fashion using 0.1 and 1.0 mg/kg of AFB1 and the dynamics of chromosome aberration yields was analyzed for a period of 730 days. Similarly as in the case of Chinese hamsters the percentage of cells with aberrations and the frequency of chromosome and chromatid breaks were always higher in this period than the control value. Long-term aberration yield data obtained experimentally were expressed in the form of analytical curves which allowed to establish the time when the yields of aberrant cells reached their maxima and when they returned to the control level. In both animal species tested the courses of analytical curves had a similar dynamics. Factors that might be responsible for a long-term persistence and relatively great fluctuations of the chromosome aberration yields encountered after a single injection of AFB1 are discussed in detail.

Aflatoxin B1↗