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DC magnetic relaxation measurements in HgBa2CuO4 single crystals are analyzed nearby the fishtail line. It is found that in this case, it is not necessary to introduce any crossover from plastic creep to elastic creep models at the fishtail line. This type of fishtail effect comes only from a competition between a critical current at low temperature which increases versus field and the activation energy, which decreases versus field. According to the doping level of the compound, the fishtail effect can be observed or not, without any correlation with a vortex phase transition. Moreover, in this type of fishtail effect, there is no history effects as recently observed in YBaCu2O3 by the partial magnetization loop technique, suggesting that the transition from plastic to elastic flow is here hidden by the disorder of these materials.

To investigate the existence of a splay effect in Bi2Sr2CaCu2O8 (Bi-2212), vortex pinning has been studied in different configurations of strongly inclined columnar defects (75 ° from the c axis), installed by heavy-ion irradiation. It is shown that the symmetry of the track setting with respect to the field direction is a more influent parameter than the presence of a dispersion in the track directions. We claim that the enhanced pinning efficiency which is observed in some splayed configurations of columnar defects in Bi-2212 can be interpreted without invoking a splay effect.

An extensive study of small angle neutron scattering was performed in twinned YBa2Cu3O7 crystals in its superconducting state as a function of the angle \(\) between the c-axis of the crystal and the magnetic field. The half of the twin boundaries are oriented in the horizontal plane, which also contains the neutron beam and the magnetic field. Two different diffraction patterns are studied as a function of \(\) at 5 K and B = 0.5 T, one along the c-axis of the crystal, the other one along the applied field. These variations are interpreted in the model of accommodation of the vortices on the twin planes by zigzagging from these planes to the ab-planes of the crystal, in order to minimize their energy.

Pinning properties of (Bi/Pb)-2223 textured ceramics have been improved by 6 GeV Pb ions irradiation. Two samples were irradiated at fluencesφt=5 × 1010 ions/cm2 and 2 × 1011 ions/cm2, respectively. The magnetic irreversibility is clearly improved in the intermediate range of temperature: (30–35) K

The systematic study of the manganese perovskite Nd0.7Ca0.3−xSrxMnO3−δ has allowed colossal magnetoresistance effects (CMR) with resistance ratios (RR), RB=0/RB=5T, up to 104 at 60 K in a field of 5 tesla to be evidenced. The influence of the mean size of the interpolated cation (Nd, Ca, Sr), on the magnitude of the RR ratios, has been demonstrated for the first time: RR goes through a maximum for a particular value of the mean radius of the interpolated cation. This effect seems to be correlated with the evolution of the cell volume that exhibits a singular point around x=0.085. A second important feature deals with the irreversibility of the CMR effect at low temperature that decreases as T increases and disappears at Tmax. It is also remarkable that for ρ(T) curves characterized by a maximum, Tmax not only increases as the size of the interpolated cation increases, but also as the magnitude of the applied magnetic field increases.

Transition metal oxides belong to the class of iono-covalent materials in which electrons are, to first order, localized in tight metal-oxygen bonds. They appear to be quite different from classical metals in which electrons are assumed to be delocalized in a free electron gas. Nevertheless, due to exchange interactions and hybridization of atomic orbitals, oxides exhibit many interesting physical properties like magnetic ordering and various electron transport properties that extend from wide gap insulators to narrow band conductors and high-temperature superconducting (HTS) superconductors. This class of materials appears well-suited to the study of the damage induced by heavy ion irradiation and its consequence on physical properties like electrical resistivity.In this article, we will describe the results of heavy ion irradiations in magnetic oxides, exhibiting a wide palette of electron transport properties from insulators to metals through hopping semiconductors and in HTS copper oxides that are narrow-band metals aboveTc. We will show that heavy ion irradiation, in addition to disordering matter, can induce changes in some physical properties like magnetic ordering and orientation of magnetic fields, and can produce large increases of the critical current. To account for these results, the thermal spike model will be considered as a possible way to understand the damage creation in iono-covalent compounds.

The exploration of the magnetic and transport properties of four series of manganese perovskites, Pr0.7Ca0.34−xAxMnO3−δ (A=Sr, Ba), Pr0.7−xLaxCa0.3 MnO3−δ and Pr0.66Ca0.34−xSrxMnO3−δ has allowed four phases with colossal magnetoresistive (CMR) properties to be isolated: Pr0.7Ca0.25Sr0.025MnO3−δ and Pr0.66Ca0.26Sr0.08MnO3−δ that exhibit a variation of resistance of 2.5. 107% and 109% at μ0 H=5 T for T=88 K and 50 K respectively, Pr0.58La0.12Ca0.3 MnO3−δ that exhibits a variation of 6.106% for μ0 H=5 T at T=80 K and Pr0.7Ba0.025Ca0.275MnO3−δ for which a resistance variation of 5.109%, at T=50 K, for μ0 H=5 T is evidenced. for each compound of this series except the barium phase, one observes that the temperature Tmax, which corresponds to the resistance maximum on the R(T) curves in zero magnetic field, increases dramatically as the mean size of the interpolated cations increases, and that the CMR effect correlatively decreases dramatically. The comparison of the two series Pr0.7Ca0.3−xSrxMnO3−δ and Pr0.66Ca0.34−xSrxMnO3−δ shows also the crucial role of the hole carrier density: for a same mean ionic radius of the interpolated cation Tmax is decreased of about 50 K by introducing 0.034 hole per Mn mole.

Splayed configurations of columnar defects with different characteristic angles θi relative to the $$\vec c$$ have been achieved in single crystals of YBCO, (Tl,Bi)-1212 and Bi-2212. An increased pinning efficiency consistents with the splayed model of Hwa et al, has been observed with θi=10° for YBCO and (Tl,Bi)-1212. For the more anisotropic compound Bi-2212, higher angles up to θi=75° are necessary to obtain the same result, but these last results are more delicate to interpret.

In 4 Adelie penguins, thermodes were implanted in the rostral brain stem. Two animals were additionally equipped with spinal canal thermodes. At thermoneutral (+8 to +16 degrees C) and cold (-18 to -22 degrees C) ambient conditions, the effects of hypothalamic heating and cooling on the surface temperature of one flipper (skin blood flow), oxygen consumption (metabolic heat production) and esophageal (core) temperature were observed in the conscious animals.- Heating the rostral brain stem induced heat defence responses: Heat production was reduced in the cold and skin vasodilatation was evoked at thermoneutral ambient conditions. As a rule, core temperature fell during rostral brain stem heating.- Cooling the rostral brain stem did not induce clear-cut cold defence responses. On the contrary, strong cooling at thermo-neutral ambient conditions induced vasodilation in the skin. In the cold, even slight degrees of rostral brain stem cooling decreased metabolic heat production. As a rule, core temperature fell when the rostral brain stem was cooled.- It is concluded from the results that thermosensitive structures in the stimulated section of the rostral brain stem of the Adelie penguin contribute to the central temperature signal input in the range of normal to elevated core temperatures. These hypothalamic warm signals appear to be at least as effective as spinal warm signals in controlling skin blood flow and metabolic heat production. The inhibition of ongoing thermoregulatory effector activity by rostral brain stem cooling suggests positive temperature coefficients of the integrative and/or efferent neurons in the hypothalamic temperature regulation center of the Adelie penguin.

In den vorliegenden Untersuchungen sollte die Frage eines sogenannten Filtrationsodems im Rahmen einer cerebralen Vasoparalyse und/oder einer arteriellen Hypertension geklart werden. Bei Gruppen von Hunden wurde in Chloralose-Urethan-Narkose eine cerebrale Vasoparalyse durch Hyperkapnie (PaCO2 um 150 mm Hg) und Hypoxamie (PaO2 40–60 mm Hg), eine arterielle Hypertension sowie eine Kombination von Vasoparalyse und arterieller Hypertension erzeugt. Unter den Bedingungen einer Vasoparalyse und Hypertension kommt es zu einem erheblichen Abfall des cerebrovascularen Widerstandes, wahrend der venose Widerstand geringgradig ansteigt. Die Folge ist eine Zunahme der Hirndurchblutung, eine Zunahme des intrakraniellen Druckes sowie eine Druckzunahme im postcapillaren Bereich (SSWP und CSP). Ein Hirnodem in verschiedenen Hirnarealen konnte bei alleiniger Vasoparalyse bei intakter Blut-Hirn-Schranke nicht nachgewiesen werden, selbst wenn der arterielle Blutdruck mehr als 90 min uber 180 mm Hg lag. Erst wenn neben der Vasoparalyse die arterielle Hypertension langer als 90 min uber 220 mm Hg bestand, konnte eine statistisch signifikante Zunahme des Wassergehaltes in der weisen Substanz gefunden werden. Unabhangig davon fanden sich in der Hirnrinde nach arterieller Hypertension wie auch nach Hypertension und Vasoparalyse punktformige Evans-Blau-Extravasate, welche eine Schadigung der Blut-Hirn-Schranke anzeigen. In diesen blaugefarbten, punktformigen Arealen lag der Wassergehalt deutlich uber der Norm. Aus den Ergebnissen wird geschlossen, das die Vasoparalyse allein nicht in der Lage ist, ein Hirnodem uber den erhohten hydrostatischen Druckgradienten zwischen Intravasalraum und Extracellularraum zu erzeugen. Erst wenn sich zu der Vasoparalyse eine starkere arterielle Hypertension addiert, findet sich in den Arealen der weisen Substanz ein solches Odem. Die akute Hypertension selbst ist aber in der Lage, in der Hirnrinde fokale Storungen der Blut-Hirn-Schranke auszulosen. Das von mehreren Autoren bei den klinischen Zustanden von Vasoparalyse beschriebene „brain swelling“ kann demnach nicht bzw. nicht allein auf Hirnodem zuruckgefuhrt werden, sondern ist meist durch das erhohte Blutvolumen zu erklaren. Die klinischen Konsequenzen dieser Befunde werden diskutiert.

In 6 Adelie penguins, thermodes were implanted in the cervical and upper thoracic spinal canal. At thermoneutral (+8 to +16 degrees C) and cold (-18 to -22 degrees C) ambient conditions, the effects of spinal canal heating and cooling on the surface temperature of one flipper (skin blood flow), oxygen consumption (metabolic heat production) and esophageal (core) temperature were observed in the conscious animals.- At thermoneutral ambient conditions, spinal cord cooling reduced and spinal heating increased skin blood flow. Only very strong spinal cooling induced small increases of oxygen consumption, while spinal heating had no effect at all. The relation between spinal canal temperature and metabolic heat production at thermoneutral ambient conditions could be described by a linear regression with a slope of -0.05 W. KG-1 . DEGREES C-1. -At cold ambient conditions, the skin vessels of the flippers were permanently constricted and an increase of metabolic heat production by 5-50% of the resting rate developed within 1-3 h of cold exposure. Spinal cord cooling augmented metabolic heat production. Spinal heating reduced heat production but did not release skin vasoconstriction even at high stimulus intensities. The relation between spinal canal temperature and metabolic heat production in the cold could be described by a linear regression with a slope of -0,52 W. kg-1 . degrees C-1. -It is concluded that temperature sensors with specific functions in temperature regulation are located in the spinal cord of the Adelie penguin. These sensors contribute to the central temperature signal input in the hypothermic and hyperthermic ranges of core temperature. The peripheral thermal conditions strongly influence the responsiveness of the various thermoregulatory effectors to the spinal thermal stimulus.

Ducks were chronically implanted with thermodes in the POAH region, the lower brainstem or the vertebral canal. At thermoneutral conditions, lowering the temperature of the spinal cord (Tvc) or the lower brainstem (Tmb) stimulated metabolic heat production (M) with a subsequent rise of core temperature (Tc). Lowering the temperature of the POAH region (Thy) induced a fall of Tc due to paradoxical activation of heat defence and, thus, induced slight to moderate general hypothermia depending on the cooling intensity. When Thy was normalized, the hypothermia temporarily stimulated metabolic heat production until Tc was normalized. Cold sensitivity of the entire body, as revealed by the metabolic response to the hypothermia induced by preceding POAH cooling, and cold sensitivity of the spinal cord and the lower brainstem, as revealed by the metabolic response to local cooling, were quantified by calculating the quotient δM/δT from the maximum metabolic response and the experimentally induced drop of Tc, Tmb and Tvc. With lower brainstem cooling δM/δTmbdid not exceed −0.4 W/(kg · ‡C). With spinal cord cooling, δM/δTvc did not exceed −0.6 W/(kg · ‡C). The mean value of δM/δTc after hypothermia induced by POAH cooling was −4.02 W/(kg · ‡C). The results indicate that the cold sensitivity residing in the CNS of ducks represents only a small fraction of the entire cold sensitivity of the body.

Coherent inelastic neutron scattering results on the second-stage graphite intercalation compound C8Br are presented. Phonons polarized along the c-axis and in the basal plane were observed. A phenomenological Born-von Kármán force constant model with non-axial symmetry is used with parameters adjusted in agreement with the results. Several specific points of the phonon spectrum which are outside of the limits of the model are discussed.

We have measured the temperature and the magnetization of singlecrystalline YBaCuO samples in a variable magnetic field under quasi adiabatic conditions. By varying the sweep rate of the field, the thermal link to the bath, the size of the sample, the critical temperature and the sample temperature, we have measured the time dependence of the vortex relaxation (the penetration of the critical state, flux jumps, and the instability regime). This magnetothermal instability controls the value of the effective critical current.

Results of de Haas van Alphen effect study on second-stage bromine graphite intercalation compound C14 Br are presented together with a two dimensional model of electronic structure and Fermi surface. The results are characterized by a mixing of de Haas-van Alphen frequencies. The nature of the coupling mechanisms between orbits is discussed. It is shown that the two dimensional Fermi surface of C14 Br contains nested parallel parts which can stabilize charge density waves. A comparison between the nesting vectors of this Fermi surface and the satellites and diffuse streaks found in structural studies shows a fair agreement between both.