504 research outputs found
Performance Analysis of Adaptive GPS Signal Detection in Urban Interference Environment using the Monte Carlo Approach
Long-range correlation energies calculations for electronic systems
A simple formula for correlation energy of the electron systems
is obtained under an approximation for the electron-electron interactions. This
formula is related directly to square of the bond order matrix and the
nearest-neighbor Coulomb electron-electron interaction. The influence of the
correlation energy on the band energy gap is discussed. The values of the
correlation energy for polyacetylene (PA) are calculated and can be compared
with those for PA obtained by other methods, including method.Comment: Preprint, Latex file, 9 pages, 1 Postscript figur
On the state dependency of fast feedback processes in (palaeo) climate sensitivity
Palaeo data have been frequently used to determine the equilibrium (Charney)
climate sensitivity , and - if slow feedback processes (e.g. land
ice-albedo) are adequately taken into account - they indicate a similar range
as estimates based on instrumental data and climate model results. Most studies
implicitly assume the (fast) feedback processes to be independent of the
background climate state, e.g., equally strong during warm and cold periods.
Here we assess the dependency of the fast feedback processes on the background
climate state using data of the last 800 kyr and a conceptual climate model for
interpretation. Applying a new method to account for background state
dependency, we find K(Wm) using the latest LGM
temperature reconstruction and significantly lower climate sensitivity during
glacial climates. Due to uncertainties in reconstructing the LGM temperature
anomaly, is estimated in the range K(Wm).Comment: submitted to Geophysical Research Letter
Reduced Plasticity in Coupling Strength in the Aging SCN Clock as Revealed by Kuramoto Modeling
Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand
The last interglacial (LIG; ~130 to ~118 thousand years ago, ka) was the last time global sea level rose well above the present level. Greenland Ice Sheet (GrIS) contributions were insufficient to explain the highstand, so that substantial Antarctic Ice Sheet (AIS) reduction is implied. However, the nature and drivers of GrIS and AIS reductions remain enigmatic, even though they may be critical for understanding future sea-level rise. Here we complement existing records with new data, and reveal that the LIG contained an AIS-derived highstand from ~129.5 to ~125 ka, a lowstand centred on 125–124 ka, and joint AIS + GrIS contributions from ~123.5 to ~118 ka. Moreover, a dual substructure within the first highstand suggests temporal variability in the AIS contributions. Implied rates of sea-level rise are high (up to several meters per century; m c−1), and lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations
Phase Shifting Capacity of the Circadian Pacemaker Determined by the SCN Neuronal Network Organization
In mammals, a major circadian pacemaker that drives daily rhythms is located in the suprachiasmatic nuclei (SCN), at the base of the hypothalamus. The SCN receive direct light input via the retino-hypothalamic tract. Light during the early night induces phase delays of circadian rhythms while during the late night it leads to phase advances. The effects of light on the circadian system are strongly dependent on the photoperiod to which animals are exposed. An explanation for this phenomenon is currently lacking.We recorded running wheel activity in C57 mice and observed large amplitude phase shifts in short photoperiods and small shifts in long photoperiods. We investigated whether these different light responses under short and long days are expressed within the SCN by electrophysiological recordings of electrical impulse frequency in SCN slices. Application of N-methyl-D-aspartate (NMDA) induced sustained increments in electrical activity that were not significantly different in the slices from long and short photoperiods. These responses led to large phase shifts in slices from short days and small phase shifts in slices from long days. An analysis of neuronal subpopulation activity revealed that in short days the amplitude of the rhythm was larger than in long days.The data indicate that the photoperiodic dependent phase responses are intrinsic to the SCN. In contrast to earlier predictions from limit cycle theory, we observed large phase shifting responses in high amplitude rhythms in slices from short days, and small shifts in low amplitude rhythms in slices from long days. We conclude that the photoperiodic dependent phase responses are determined by the SCN and propose that synchronization among SCN neurons enhances the phase shifting capacity of the circadian system
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