698 research outputs found
Long-period intensity pulsations in the solar corona during activity cycle 23
We report on the detection (10 \sigma) of 917 events of long-period (3 to 16
hours) intensity pulsations in the 19.5 nm passband of the SOHO Extreme
ultraviolet Imaging Telescope. The data set spans from January 1997 to July
2010, i.e the entire solar cycle 23 and the beginning of cycle 24. The events
can last for up to six days and have relative amplitudes up to 100%. About half
of the events (54%) are found to happen in active regions, and 50% of these
have been visually associated with coronal loops. The remaining 46% are
localized in the quiet Sun. We performed a comprehensive analysis of the
possible instrumental artifacts and we conclude that the observed signal is of
solar origin. We discuss several scenarios which could explain the main
characteristics of the active region events. The long periods and the
amplitudes observed rule out any explanation in terms of magnetohydrodynamic
waves. Thermal nonequilibrium could produce the right periods, but it fails to
explain all the observed properties of coronal loops and the spatial coherence
of the events. We propose that moderate temporal variations of the heating term
in the energy equation, so as to avoid a thermal nonequilibrium state, could be
sufficient to explain those long-period intensity pulsations. The large number
of detections suggests that these pulsations are common in active regions. This
would imply that the measurement of their properties could provide new
constraints on the heating mechanisms of coronal loops.Comment: 10 pages, 4 figure
Heureuse influence de l’introduction de vitamines dans la nourriture des Cobayes élevés pour usage de laboratoire
Tison F. Heureuse influence de l’introduction de vitamines dans la nourriture des Cobayes élevés pour usage de laboratoire. In: Bulletin de l'Académie Vétérinaire de France tome 103 n°2, 1950. pp. 139-142
Homothetic Wyman Spacetimes
The time-dependent, spherically symmetric, Wyman sector of the Unified Field
Theory is shown to be equivalent to a self-gravitating scalar field with a
positive-definite, repulsive self-interaction potential. A homothetic symmetry
is imposed on the fundamental tensor, and the resulting autonomous system is
numerically integrated. Near the critical point (between the collapsing and
non-collapsing spacetimes) the system displays an approximately periodic
alternation between collapsing and dispersive epochs.Comment: 15 pages with 6 figures; requires amsart, amssymb, amsmath, graphicx;
formatted for publication in Int. J. Mod. Phys.
Truly unentangled photon pairs without spectral filtering
We demonstrate that an integrated silicon microring resonator is capable of
efficiently producing photon pairs that are completely unentangled; such pairs
are a key component of heralded single photon sources. A dual-channel
interferometric coupling scheme can be used to independently tune the quality
factors associated with the pump and signal and idler modes, yielding a
biphoton wavefunction with Schmidt number arbitrarily close to unity. This will
permit the generation of heralded single photon states with unit purity.Comment: 5 pages, 3 figure
Linearisation Instabilities of the Massive Nonsymmetric Gravitational Theory
The massive nonsymmetric gravitational theory is shown to posses a
linearisation instability at purely GR field configurations, disallowing the
use of the linear approximation in these situations. It is also shown that
arbitrarily small antisymmetric sector Cauchy data leads to singular evolution
unless an ad hoc condition is imposed on the initial data hypersurface.Comment: 14 pages, IOP style for submission to CQG. Minor changes and
additional background material adde
Sea ice <i>p</i>CO<sub>2</sub> dynamics and air-ice CO<sub>2</sub> fluxes during the Sea Ice Mass Balance in the Antarctic (SIMBA) experiment - Bellingshausen Sea, Antarctica
Temporal evolution of pCO2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows physical and thermodynamic processes controls the CO2 system in the ice. During the survey, cyclical warming and cooling strongly influenced the physical, chemical, and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We show that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (TCO2), and in situ brine and bulk ice CO2 partial pressures (pCO2). Thicker snow covers reduced the amplitude of these changes: snow cover influences the sea ice carbonate system by modulating the temperature and therefore the salinity of the sea ice cover. Results indicate that pCO2 was undersaturated with respect to the atmosphere both in the in situ bulk ice (from 10 to 193 µatm) and brine (from 65 to 293 µatm), causing the sea ice to act as a sink for atmospheric CO2 (up to 2.9 mmol m-2 d-1), despite supersaturation of the underlying seawater (up to 462 µatm)
- …