116897797
What Happens When the Geomagnetic Field Reverses
During geomagnetic field reversals the radiation belt high-energy proton populations become depleted. Their energy spectra become softer, with the trapped particles of highest energies being lost first, and eventually recovering after a field reversal. The radiation belts rebuild in a dynamical way with the energy spectra flattening on the average during the course of many millennia, but without ever reaching complete steady state equilibrium between successive geomagnetic storm events determined by southward turnings of the IMF orientation. Considering that the entry of galactic cosmic rays and the solar energetic particles with energies above a given threshold are strongly controlled by the intensity of the northward component of the interplanetary magnetic field, we speculate that at earlier epochs when the geomagnetic dipole was reversed, the entry of these energetic particles into the geomagnetic field was facilitated when the interplanetary magnetic field was directed northward. Unlike in other complementary work where intensive numerical simulations have been used, our demonstration is based on a simple analytical extension of Stormer's theory. The access of GCR and SEP beyond geomagnetic cut-off latitudes is enhanced during epochs when the Earth's magnetic dipole is reduced, as already demonstrated earlier.
118184102
Determination of coronal temperatures from electron density profiles
The most popular method for determining coronal temperatures is the scale-height-method (shm). It is based on electron density profiles inferred from White Light (WL) brightness measurements of the corona during solar eclipses. This method has been applied to several published coronal electron density models. The calculated temperature distributions reach a maximum at r > 1.3 RS, and therefore do not satisfy one of the conditions for applying the shm method. Another method is the hydrostatic equilibrium method (hst), which enables coronal temperature distributions to be determined, providing solutions to the hydrostatic equilibrium equation. The temperature maximas using the hst method are almost equal to those obtained using the shm method, but the temperature peak is always at significantly lower altitude when the hst-method is used than when the shm-method is used. A third and more recently developed method, dyn, can be used for the same published electron density profiles. The temperature distributions obtained using the dyn method are regular solutions of the hydrodynamic equations. They depend on the expansion velocity of the coronal plasma considered as a free input parameter in the calculations. At the base of the solar corona, where the coronal bulk velocity is small (subsonic), the dyn and hst methods give similar temperature values. Larger differences are found at higher altitudes where the expansion velocity approaches and exceeds the velocity of sound. This paper shows also the effects of the flow tube geometry and ion temperatures on the electron temperature distributions. The dyn method is a generalization of the hst method, where the electron temperature distribution tends to zero at infinite radial distances. It is a new diagnostic tool for determining from WL coronal observations the range of radial distances where the coronal heating rate is at its maximum.
118502743
VLT/NACO near-infrared imaging and spectroscopy of N88A in the SMC
Aims. We present near-infrared imaging and spectroscopic high spatial resolution observations of the SMC region N88 containing the bright, excited, extincted and compact H II region N88A of the size of about 1 pc. Methods. To investigate its stellar content and reddening, N88 was observed using spectroscopy and imagery in the JHKs- and L � -band at a spatial resolution of ∼0.1−0.3 �� , using the VLT UT4 equipped with the NAOS adaptive optics system. In an attempt to establish if the origin of the infra-red (IR) excess is due to bright nebulosity, circumstellar material and/or local dust, we used K sv s. J − K color−magnitude (CM) and JHK color−color (CC) diagrams, as well as Limagery. Results. Our IR-data reveal in the N88 area an IR-excess fraction of ≥30 per cent of the detected stars as well as an unprecedently detailed morphology of N88A. It consists of an embedded cluster of ∼3.5 �� (∼1 pc) in diameter of at least thirteen resolved stars superposed with an unusual bright continuum centered on a very bright star. The four brightest stars in this cluster lie red-ward of H − K ≥ 0.45 mag and could be classified as young stellar object (YSO) candidates. Four other probable YSO candidates are also detected in N88 along a north-south bow-shaped thin H2 filament at ∼7 �� east of the young central bright star. This star, which we assume to be the main exciting source, could also be complex. At 0.2 �� east of this star, a heavily embedded core is detected in the L � -band. This core with L � ∼ 14 mag and L � − K ≥ 4.5 mag could be a massive class I protostar candidate. The 2.12 μ mH 2 image of N88A resembles a shell of a diameter of ∼3 �� (∼0.9 pc) centered on the bright star. This shell consists of three bright components, of which the brightest one superposes the ionization front. The line ratios of H2 2− 1S (1) and 1−0 S(0) relative to 1−0 S(1), as well as the presence of high v lines, are indicative of photodissociation regions, rather than shocks.
15641163
Highlights of Accelerator Activities in France on behalf of the Accelerator Division of the French Physics Society
The French Physics Society is an association the purpose of which is to promote physics and physicists. In this context, the accelerator physics and associated technology division is in charge of the promotion of accelerator activities in France. This paper presents the missions and actions of the division, highlighting those concerning young scientists. A brief presentation of the laboratories, institutes or facilities who are the main actors in the field will then be given. Significant projects which are underway or planned will be described, including medical applications. The major contribution of France to international projects will then be introduced. Finally the cultural and technical relations between industry and laboratories will be discussed.
59398810
Optical and infrared observations of the young SMC “ blob ” N 26 and its environment ?
1 LERMA, UMR 8112 du CNRS, Observatoire de Paris, 92195 Meudon, France e-mail: gerard.testor@obspm.fr 2 Department of Astronomy, University of Virginia , PO Box 400325, Charlottesville, VA 22904, USA 3 Max-Planck-Institut fur Radioastronomie, D-53121 Bonn, Germany 4 Université de Cergy-Pontoise, 95031 Cergy Cedex, France 5 The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA 6 Space Science Institute, 4750 Walnut St. Suite 205, Boulder, CO 80301, USA
56163569
IPHI, the Saclay high-intensity proton injector project
High-power accelerators are being studied for several projects based on high-flux neutron sources driven by proton or deuteron beams. Since the front end is the most critical part of such accelerators, it has been decided to build a high-intensity proton injector (IPHI) designed to accelerate a CW 100 mA beam up to 11 MeV. The aim is to validate design codes, test technical choices, demonstrate operational reliability and measure the beam parameters in order to optimize the high-energy part of the accelerator. The design chosen for IPHI (ECR source, RFQ, DTL and diagnostic line) and the construction schedule are presented.