2,377 research outputs found
Standard map in magnetized relativistic systems: fixed points and regular acceleration
We investigate the concept of a standard map for the interaction of
relativistic particles and electrostatic waves of arbitrary amplitudes, under
the action of external magnetic fields. The map is adequate for physical
settings where waves and particles interact impulsively, and allows for a
series of analytical result to be exactly obtained. Unlike the traditional form
of the standard map, the present map is nonlinear in the wave amplitude and
displays a series of peculiar properties. Among these properties we discuss the
relation involving fixed points of the maps and accelerator regimes.Comment: Work to appear in Phys. Rev. E. 2 figure
Local magnetic anisotropy in BaFeAs: a polarized inelastic neutron scattering study
The anisotropy of the magnetic excitations in BaFeAs was studied by
polarized inelastic neutron scattering which allows one to separate the
components of the magnetic response. Despite the in-plane orientation of the
static ordered moment we find the in-plane polarized magnons to exhibit a
larger gap than the out-of-plane polarized ones indicating very strong
single-ion anisotropy within the layers. It costs more energy to rotate a spin
within the orthorhombic {\it a-b} plane than rotating it perpendicular to the
FeAs layers.Comment: 4 pages, 4 figure
ALTERED SYMPATHETIC CONTROL OF NUTRIENT MOBILIZATION DURING PHYSICAL EXERCISE AFTER LESIONS IN THE VMH
To study the impact of obesity on sympathetic nervous regulation of nutrient mobilization, obese rats and lean controls were subjected to physical exercise. Male Wistar rats, rendered obese by bilateral electrolytic lesions of the ventromedial hypothalamus (VMH) were subjected to 15 min swimming. Permanent cardiac catheters allowed frequent blood sampling. At rest, glucose, free fatty acids (FFA), and insulin concentrations were elevated in the obese animals, whereas catecholamine levels were similar in both groups. During exercise, glucose concentrations reached higher values in the lesioned rats, whereas these animals did not display the normal FFA increment. Plasma insulin concentrations were suppressed in both groups, and the rate of suppression was very similar when expressed as percentage change from resting levels. There was no difference in plasma epinephrine responses during swimming, but the increase in norepinephrine was diminished in the obese animals. The results suggest that obesity after VMH lesion leads to reduced stimulation of lipolysis by norepinephrine and a predominant mobilization of glucose during exercise, both favoring glucose utilization and the accumulation of fat
Overfeeding, Autonomic Regulation and Metabolic Consequences
The autonomic nervous system plays an important role in the regulation of body processes in health and disease. Overfeeding and obesity (a disproportional increase of the fat mass of the body) are often accompanied by alterations in both sympathetic and parasympathetic autonomic functions. The overfeeding-induced changes in autonomic outflow occur with typical symptoms such as adiposity and hyperinsulinemia. There might be a causal relationship between autonomic disturbances and the consequences of overfeeding and obesity. Therefore studies were designed to investigate autonomic functioning in experimentally and genetically hyperphagic rats. Special emphasis was given to the processes that are involved in the regulation of peripheral energy substrate homeostasis. The data revealed that overfeeding is accompanied by increased parasympathetic outflow. Typical indices of vagal activity (such as the cephalic insulin release during food ingestion) were increased in all our rat models for hyperphagia. Overfeeding was also accompanied by increased sympathetic tone, reflected by enhanced baseline plasma norepinephrine (NE) levels in both VMH-lesioned animals and rats rendered obese by hyperalimentation. Plasma levels of NE during exercise were, however, reduced in these two groups of animals. This diminished increase in the exercise-induced NE outflow could be normalized by prior food deprivation. It was concluded from these experiments that overfeeding is associated with increased parasympathetic and sympathetic tone. In models for hyperphagia that display a continuously elevated nutrient intake such as the VMH-lesioned and the overfed rat, this increased sympathetic tone was accompanied by a diminished NE response to exercise. This attenuated outflow of NE was directly related to the size of the fat reserves, indicating that the feedback mechanism from the periphery to the central nervous system is altered in the overfed state.
Experimentally exploring compressed sensing quantum tomography
In the light of the progress in quantum technologies, the task of verifying
the correct functioning of processes and obtaining accurate tomographic
information about quantum states becomes increasingly important. Compressed
sensing, a machinery derived from the theory of signal processing, has emerged
as a feasible tool to perform robust and significantly more resource-economical
quantum state tomography for intermediate-sized quantum systems. In this work,
we provide a comprehensive analysis of compressed sensing tomography in the
regime in which tomographically complete data is available with reliable
statistics from experimental observations of a multi-mode photonic
architecture. Due to the fact that the data is known with high statistical
significance, we are in a position to systematically explore the quality of
reconstruction depending on the number of employed measurement settings,
randomly selected from the complete set of data, and on different model
assumptions. We present and test a complete prescription to perform efficient
compressed sensing and are able to reliably use notions of model selection and
cross-validation to account for experimental imperfections and finite counting
statistics. Thus, we establish compressed sensing as an effective tool for
quantum state tomography, specifically suited for photonic systems.Comment: 12 pages, 5 figure
Incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering
We present an inelastic neutron scattering study on single-crystalline LiFeAs
devoted to the characterization of the incommensurate antiferromagnetic
fluctuations at . Time-of-flight
measurements show the presence of these magnetic fluctuations up to an energy
transfer of 60 meV, while polarized neutrons in combination with longitudinal
polarization analysis on a triple-axis spectrometer prove the pure magnetic
origin of this signal. The normalization of the magnetic scattering to an
absolute scale yields that magnetic fluctuations in LiFeAs are by a factor
eight weaker than the resonance signal in nearly optimally Co-doped
BaFeAs, although a factor two is recovered due to the split peaks owing
to the incommensurability. The longitudinal polarization analysis indicates
weak spin space anisotropy with slightly stronger out-of-plane component
between 6 and 12 meV. Furthermore, our data suggest a fine structure of the
magnetic signal most likely arising from superposing nesting vectors.Comment: 9 pages, 8 figure
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