[en] The authors report an X-ray scattering study of the tetragonal to orthorhombic (T-O) transition in the high T/sub c/ superconductor La/sub 2-x/Sr/sub x/CuO/sub 4/. For x = 0.12 a detailed single crystal study reveals a T-O transition at T/sub T-O/ = 215 +- 5 K with nearly isotropic precursor diffuse scattering up to room temperature. Additional powder data constructs a temperature - Sr concentration phase diagram of the T-O transition. It shows clearly that superconductivity coexists with the O distortion in a broad Sr concentration range. The highest T/sub c/ values are observed either in the O phase or close to the T-O phase boundary

[en] This review covers the structural instabilities of the molybdenum bronzes A_xMo_yO_z, where A is a monovalent metal, and of the Molybdenum oxides Mo_nO_3n-1. Two families of Mo bronzes are considered: A_0.3MoO₃ with A= K, Rb, or Tl ( the blue bronzes), and A_0.9Mo₆O₁₇ with A= K, Na, Tl or Li (the purple bronzes). First some basic features of the charge-density wave instability and periodic lattice distortion of low dimensional conductors are recalled. Then their manifestation in the 1D case (blue bronzes) and 2D case (purple bronzes and Mo oxides are detailed. (H.W.). 123 refs.; 31 figs.; 2 tabs

[en] The high-temperature tetragonal to low-temperature orthorhombic phase transition of La_1.88Sr_0.12CuO₄ has been studied by single-crystal X-ray diffraction and diffuse scattering. The temperature dependence of superstructure reflections below T_T-O=215 K, precursor diffuse scattering above T_T-O and the orthorhombic lattice parameter distortion is reported. Supplementary powder diffraction data allow to construct the structural phase diagram in the Sr concentration range 0≤X≤0.12. It shosw that suppression of the orthorhombic distortion by Sr substitution is not a necessary condition for the occurrence of superconductivity

[en] The full text of the publication follows. Most of what is known in radiobiology of radiation therapy has been determined in experiments using conventional external beam radiotherapy (CEBR). However, targeted radiotherapy and radioimmunotherapy (RIT) in particular, differ in many ways from CEBR. First, while CEBR mostly use energetic photons, RIT relies on the use of vectors specifically directed against tumor cells or their microenvironment, and labeled with radioisotopes. Radioisotopes may decay by emitting helium nuclei, energetic or non energetic electrons, that may be associated or not to X or γ-rays. The path length in biological materials of the emitted particles ranges from few nm to several mm and is straightly correlated with energy and linear energy transfer (LET). Finally, targeted cell may be exposed to self- and cross-fire irradiation and to both low- and high-LET radiation. These physical characteristics make that highly heterogeneous doses are delivered at the cellular level or at the level of the tumor burden. Therefore, the correlation between the biological endpoints and the absorbed irradiation dose must be investigated carefully and sophisticated dosimetric approaches are required. RIT is also featured by extended exposure delivered at very low dose rate (LDR) (<1 Gy/h vs 60 Gy/h for CEBR) and declining progressively. Such a LDR provides a window of opportunity for the cell to repair radiation-induced damage and to proliferate. However, experimental data showed that tumor cells are more sensitive to LDR than to HDR for final equivalent irradiation doses. Cell death might involve mostly apoptosis for hematological malignancies and mitotic death for solid tumors. Death would be due to a single hit killing phenomenon and might involve G2/M cell cycle arrest. Since bystander effect is essentially a low dose phenomenon observed after CEBR, it plays a significant role in RIT. Therefore, it might compensate for heterogeneous distribution of radiolabeled vectors within tumor burden and could be complementary to cross-fire irradiation in producing additional cell kill. (author)

[en] We report an X-ray diffuse scattering study of the CDW (charge density waves) fluctuations in strongly irradiated TTF-TCNQ. The 2 ksub(F) and 4 ksub(F) CDW become onedimensional for 5.0 mol % of introduced defects, even at the lowest temperature (28 K). At the concentration level of 15 mol % the 2 ksub(F) anomaly disappears, while a temperature independent 4 ksub(F) distortion is stabilized. These results are compared with those for the alloy TTFsub(0.97)TSFsub(0.03)TCNQ and for TMTSF-DMTCNQ

[en] Radiobiological studies have shown for some time that the effects of ionising radiation on cells are mainly explained by modification of the DNA. Numerous studies over the past 50 years have accumulated clear evidence of the cause-effect relationship between damage to DNA and the cytotoxic and mutagenic effects of ionising radiation. However, the path from irradiation of the cells to the induction of biological effects comprises several complex steps. The first step involves interactions between the radiation and the cellular environment. These consist of physical and chemical reactions which produce ions, excited molecules and radical species. Excitations and ionisations are complete in about 10^-15 s, and are followed by a chemical thermal equilibrium of the species produced within 10^-12 s. These species then diffuse from their site of production and provoke alterations to a variety of cellular components. This damage is detected by cellular surveillance systems, which in turn activate signalling cascades, gene transcription and enzyme recruitment, which participate in the cellular response. In most cases, cell cycle arrest occurs, allowing, according to the biological relevance of the DNA damage, either a process of DNA repair or programmed cell death (apoptosis). The accuracy of the DNA repair which is performed depends on the complexity of the DNA lesion and on the DNA repair machinery fidelity itself. Improper DNA repair can lead to mutation, chromosome aberration, genetic instability, oncogenic transformation and, ultimately, cell death. (orig.)

[en] This paper reports elastic and inelastic neutron-scattering studies on a incommensurate linear-chain mercury compound. The one-dimensional phonon dispersion curse associated with the randomly phased linear Hg chains has been measured at room temperature. A transition, at 120 K, from a randomly phased interchain structure to a ''phase-ordered'' structure has been found and characterized

[en] NMR and EPR measurements in VO₂ under uniaxial stress in the 110/subR/ direction lead to a phase diagram entirely similar to that obtained in V/sub 1 - x/ Cr/sub x/ 0₂ alloys. Two intermediate phases M₂ and T are observed, and, as established for V/sub 1 - x/ Cr/sub x/ 0₂, correspond to linear Heisenberg chains of spin 1/2 (M₂ phase) on one V sublattice. These chains undergo a progressive dimerization in the T phase as the temperature is lowered

[en] Elastic-neutron-scattering experiments performed on the linear-chain mercury compound Hg/sub 3-delta/AsF₆ are presented. On cooling, a progressive phase ordering between the Hg chains, randomly phased at room temperature, has been found and characterized. Short-range order gradually builds up, with transverse coherence lengths of a few lattice constants, as a result of parallel chain-chain interactions. At 120 K, the competing orthogonal chain-chain interaction leads to three-dimensional order and a phase-ordering phase transition. The three-dimensional low-temperature phase is accompanied by an incommensurate modulation of the Hg chains indicating an interaction with the host lattice

[en] This contribution is a tribute to Andre Guinier and to the scientific school he created. We show how his thesis work allowed one to develop new X-ray scattering techniques of investigation of matter both at small and large scattering Bragg angles. In parallel to his pioneering experimental work, A.Guinier introduced a well-adapted formalism allowing a precise characterization of various types of local order in the matter. These findings, which have been extended by his own students, have seed an 'X-ray scattering' school of international reputation, which remains very active today. Here, we cover in detail the birth of this school from 1940 to 1980. Then, we outline the evolution of researches of the team he founded at the 'Laboratoire de physique des solides - LPS' of Paris-Sud University until the beginning of the 21. century, when investigations using synchrotron radiation have revolutionized the study of the structure of the matter. (authors)