12,217 research outputs found
Influence of Nd on the magnetic properties of Nd1-xCaxMnO3
The role played by the Nd ions in the magnetic properties of Nd0.5Ca0.5MnO3
and Nd0.7Ca0.3MnO3 is studied using static magnetization, neutron diffraction
and high frequency (9.4-475GHz) Electron Spin Resonance. We show that the Nd
ions are weakly coupled to the Mn ions via ferromagnetic exchange and are
responsible for the peculiar ferromagnetic resonance observed in the FM phase
of both compounds (ground state below 120K for x=0.3, high field state for
x=0.5). We then use ESR to look for magnetic phase separation in the low field,
CO phase of Nd0.5Ca0.5MnO3. We show that there is no trace of the FM phase
imbedded in the CO phase, contrary to what is observed in La0.5Ca0.5MnO3 or
Pr0.5Sr0.5MnO3.Comment: to be published in phys.Rev.B as a Rapid Com
Conception et realisation d 'un ordinateur analogique tout optique de type 'reservoir' a l 'aide d'une cavite optique lineaire passive fonctionnant en lumiere coherente
Search for anisotropic effects of hcp solid helium on optical lines of cesium impurities
The anisotropic effect of a hcp 4He solid matrix on cesium atoms has been
proposed as a tool to reveal the parity violating anapole moment of its
nucleus. It should also result in splitting the D2 optical excitation line in a
way depending on the light polarization. An experimental investigation has been
set up using oriented hcp helium crystals in which cesium metal grains are
embedded. Atoms are created by laser sputtering from this grains. Optical
absorption spectra of the D2 line have been recorded in the temperature range
of 1.0 to 1.4 K at liquid/solid coexistence pressure by monitoring the
fluorescence on the D2 line at 950 nm. No significant effect of the light
polarization has been found, suggesting a statistically isotropic disordered
solid environment for the cesium atoms.Comment: The original publication will be available at
http://www.springerlink.co
Impact of ocean acidification on marine organisms-unifying principles and new paradigms
This special issue combines original research with seminal reviews of the biological impact of ocean acidification. The ten contributions cover a wide range of topics from chemical and biological responses to increased CO2 and decreased pH to socio-economical sensitivities and adaptation options. Overall, this special issue also highlights the key knowledge gaps and future challenges. These include the need to develop research strategy and experiments that factor in evolution, incorporate natural variability in physical conditions (e.g.; pH, temperature, oxygen, food quality and quantity) and ecological interactions. The research presented in this special issue demonstrates the need to study more habitats (e.g.; coastal, deep sea) and prioritize species of ecological or economic significance
Drug Predictive Cues Activate Aversion-Sensitive Striatal Neurons That Encode Drug Seeking
Drug-associated cues have profound effects on an addictâs emotional state and drug-seeking behavior. Although this influence must involve the motivational neural system that initiates and encodes the drug-seeking act, surprisingly little is known about the nature of such physiological events and their motivational consequences. Three experiments investigated the effect of a cocaine-predictive stimulus on dopamine signaling, neuronal activity, and reinstatement of cocaine seeking. In all experiments, rats were divided into two groups (paired and unpaired), and trained to self-administer cocaine in the presence of a tone that signaled the immediate availability of the drug. For rats in the paired group, self-administration sessions were preceded by a taste cue that signaled delayed drug availability. Assessments of hedonic responses indicated that this delay cue became aversive during training. Both the self-administration behavior and the immediate cue were subsequently extinguished in the absence of cocaine. After extinction of self-administration behavior, the presentation of the aversive delay cue reinstated drug seeking. In vivo electrophysiology and voltammetry recordings in the nucleus accumbens measured the neural responses to both the delay and immediate drug cues after extinction. Interestingly, the presentation of the delay cue simultaneously decreased dopamine signaling and increased excitatory encoding of the immediate cue. Most importantly, the delay cue selectively enhanced the baseline activity of neurons that would later encode drug seeking. Together these observations reveal how cocaine cues can modulate not only affective state, but also the neurochemical and downstream neurophysiological environment of striatal circuits in a manner that promotes drug seeking
Effect of trap symmetry and atom-atom interactions on a trapped atom interferometer with internal state labelling
In this paper, we study the dynamics of a trapped atom interferometer with
internal state labelling in the presence of interactions. We consider two
situations: an atomic clock in which the internal states remain superposed, and
an inertial sensor configuration in which they are separated. From the average
spin evolution, we deduce the fringe contrast and the phase-shift. In the clock
configuration, we recover the well-known identical spin rotation effect (ISRE)
which can significantly increase the spin coherence time. We also find that the
magnitude of the effect depends on the trap geometry in a way that is
consistent with our recent experimental results in a clock configuration [M.
Dupont-Nivet, and al., New J. Phys., 20, 043051 (2018)], where ISRE was not
observed. In the case of an inertial sensor, we show that despite the spatial
separation it is still possible to increase the coherence time by using mean
field interactions to counteract asymmetries of the trapping potential.Comment: 18 pages, 5 figure
Superpotentials for M-theory on a G_2 holonomy manifold and Triality symmetry
For -theory on the holonomy manifold given by the cone on {\bf
S^3}\x {\bf S^3} we consider the superpotential generated by membrane
instantons and study its transformations properties, especially under monodromy
transformations and triality symmetry. We find that the latter symmetry is,
essentially, even a symmetry of the superpotential. As in Seiberg/Witten
theory, where a flat bundle given by the periods of an universal elliptic curve
over the -plane occurs, here a flat bundle related to the Heisenberg group
appears and the relevant universal object over the moduli space is related to
hyperbolic geometry.Comment: 58 pages, latex; references adde
Mine burial in the seabed of high-turbidity area (Belgian coastal zone): findings from a first experiment
Suspended particulate matter; particle size distribution; statistical handling; coastal turbidity maximum; wind impact; seabed variations The seabed of the North Sea is covered with ammunition dating back from World Wars I and II. With increasing human interference (e.g. fisheries, aggregate extraction, harbour related activities), it forms a threat to the safety at sea. In this study, test mines were deployed on a sandy seabed for three months to investigate mine burial processes as a function of hydrodynamic and meteorological conditions. The mine experiment was conducted in a shallow (9 m), macrotidal environment characterized by highly turbid waters (yearly and depth-averaged suspended particulate matter concentration of 100 mg l-1). Results showed some variability of the overall mine burial, which corresponded with scouring processes induced by a (sub-) tidal forcing mechanism. The main burial events however were linked to storm-related scouring processes, and subsequent mine roll into the resulting pit. Two storms affecting the mines during the 3-month experiment resulted in enduring increases in burial volume to 60% and 80%, respectively. More cyclic and ephemeral burial and exposure events appear to be linked to the local hydrodynamic regime. During slack tides, suspended sediment settles on the seabed, increasing the burial volume. In between slack tides, sediment is re-suspended, decreasing the burial volume. The temporal pattern of this never reported burial mechanism, as measured optically, mimics the cyclicity of the suspended sediment concentration as recorded by ultrasonic signals at a nearby benthic observatory. Given the similarity in response signals at the two sites, we hypothesize that the formation of high-concentrated mud suspensions (HCMS) is a mechanism causing short-term burial and exposure of mines. This short-term burial and exposure increase the chance that mines are âmissedâ during tracking surveys. Test mines contribute to our understanding of the settling and erosion of HCMS, and thus shed a light on generic sedimentary processes
- âŠ