Super- and Sub-critical Regions in Shocks driven by Radio-Loud and Radio-Quiet CMEs

White-light coronagraphic images of Coronal Mass Ejections (CMEs) observed by SOHO/LASCO C2 have been used to estimate the density jump along the whole front of two CME-driven shocks. The two events are different in that the first one was a "radio-loud" fast CME, while the second one was a "radio quiet" slow CME. From the compression ratios inferred along the shock fronts, we estimated the Alfv\'en Mach numbers for the general case of an oblique shock. It turns out that the "radio-loud" CME shock is initially super-critical around the shock center, while later on the whole shock becomes sub-critical. On the contrary, the shock associated with the "radio-quiet" CME is sub-critical at all times. This suggests that CME-driven shocks could be efficient particle accelerators at the shock nose only at the initiation phases of the event, if and when the shock is super-critical, while at later times they lose their energy and the capability to accelerate high energetic particles.Comment: 7 pages, 5 figures. In press on the "Journal of Advanced Research", Cairo University Pres

Influence of projection effects on the observed differential rotation rate in the UV corona

Following previous investigations by Giordano and Mancuso [1] and Mancuso and Giordano [2, 3] on the differential rotation of the solar corona as obtained through the analysis of the intensity time series of the O VI 1032 Ang. spectral line observed by the UVCS/SOHO telescope during solar cycle 23, we analysed the possible influence of projection effects of extended coronal structures on the observed differential rotation rate in the ultraviolet corona. Through a simple geometrical model, we found that, especially at higher latitudes, the differential rotation may be less rigid than observed, since features at higher latitudes could be actually linked to much lower coronal structures due to projection effects. At solar maximum, the latitudinal rigidity of the UV corona, with respect to the differential rotating photosphere, has thus to be considered as an upper limit of the possible rigidity. At solar minimum and near the equatorial region throughout the solar cycle, projection effects are negligible.Comment: In press on Journal of Advanced Researc

The New African Law: Beyond the Difference Between Common Law and Civil Law

The current investments into African countries are limited as a result of the judicial and juridical insecurity. As such, there is a strong need to rebuild the respective legal systems in order to enhance investors\u27 reliance and to further attract foreign investment. The idea of the unification of African laws has been considered as the only solution to eliminate obstacles to development amounting from the judicial differences among the varying African nations. Such a change would give the countries joining the process of regional integration the opportunity to assert their interests in a stronger and more confident manner within the international arena

The New African Law: Beyond the Difference Between Common Law and Civil Law

The current investments into African countries are limited as a result of the judicial and juridical insecurity. As such, there is a strong need to rebuild the respective legal systems in order to enhance investors\u27 reliance and to further attract foreign investment. The idea of the unification of African laws has been considered as the only solution to eliminate obstacles to development amounting from the judicial differences among the varying African nations. Such a change would give the countries joining the process of regional integration the opportunity to assert their interests in a stronger and more confident manner within the international arena

Trends on the Harmonization of Contract Law in Africa

Taking into consideration both the need for domestic legal reform in commercial matters and the importance of promoting harmonized commercial solutions for Africa, in this paper I first review the concept of legal harmonization in general and with particular reference to the situation in Africa. I then provide an overview of OHADA and COMESA, the two main initiatives of regional integration in Africa having implications in the harmonization of commercial law in general, and in the law of contract in particular. I conclude by affirming the interest of further exploring the possibilities related to the harmonization/uniformization of the law of contracts in Africa to enhance the opportunities for the development on this continent

China in Africa and the Law

This paper is based on the enormous amount of Chinese investments in Africa, with the objective of considering the legal aspects involved therein. Under international business law, commercial relations are usually ruled according to the law of the country hosting the investment. This paper will examine the challenges presented by Chinese investments in Africa given that the systems of business law in Africa are generally out of date and enforcement mechanisms under Western rule of law standards are often far from the reality. This observation is accompanied by the fact that there is presently a wide movement towards legal integration in Africa, and that many African states are already involved in, or considering, legal integration. For several reasons, business law is the area of most interest in the phenomenon of legal integration in Africa. Business law is currently one of the least addressed areas of native African law. Concurrently, it is the area where up-to-date, user-friendly rules are most necessary. The need for effective legal rules and enforcement in African business law are due to its impact on foreign investors. This paper will discuss what is “legal” in the context of trade relations between China and Africa. The paper will also analyze the legal aspects of business relationships between China and Africa and assess the state of legal cooperation among them, with particular focus on the possibility for future developments. Cite as: 18 Annl. Survey Int\u27l. Comp. L. 243 (2012)

Plasma properties from the multi-wavelength analysis of the November 1st 2003 CME/shock event

The analysis of the spectral properties and dynamic evolution of a CME/shock event observed on November 1st 2003 in white-light by the LASCO coronagraph and in the ultraviolet by the UVCS instrument operating aboard SOHO, has been performed to compute the properties of some important plasma parameters in the middle corona below about 2 solar radii. Simultaneous observations obtained with the MLSO/Mk4 white-light coronagraph, providing both the early evolution of the CME expansion in the corona and the pre-shock electron density profile along the CME front, were also used to study this event. By combining the above information with the analysis of the metric type II radio emission detected by ground-based radio spectrographs, we finally derive estimates of the values of the local Alfv\'en speed and magnetic field strength in the solar corona.Comment: In press Journal of Advanced Research, Cairo University. Production and hosting by Elsevier B.

Coronal Rotation at Solar Minimum from UV Observations

UVCS/SOHO observations have been analyzed to reconstruct intensity time series of the O VI 1032 A and H 11216 A spectral lines at different coronal heliolatitudes from 1.5 to 3.0 solar radii from Sun center. Evidence was found for coronal differential rotation that differs significantly from that of the photospheric plasma. The study of the latitudinal variation shows that the UV corona decelerates toward the photospheric rates from the equator up to the poleward boundary 2 of the midlatitude streamers, reaching a peak of 28.16+/-0.20 days around +30 from the equator at 1.5 solar radii, while a less evident peak is observed in the northern hemisphere. This result suggests a real north-south rotational asymmetry as a consequence of different activity and weak coupling between the magnetic fields of the two hemispheres. The study of the radial rotation profiles shows that the corona is rotating almost rigidly with height

UV AND RADIO OBSERVATIONS OF THE CORONAL SHOCK ASSOCIATED WITH THE 2002 JULY 23 CORONAL MASS EJECTION EVENT

We report on the analysis of a fast coronal mass ejection (CME)-driven shock observed on 2002 July 23 with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO). The CME was first detected in white light by the Large Angle and Spectrometric Coronagraph Experiment (LASCO), and shock-associated type II metric emission was recorded by several ground-based radio spectrographs. The evolution of the excess broadening of the O VI λ1032 line profiles observed by UVCS at 1.63 R☉ is consistent with the passage of a CME-driven shock surface enveloping a bubble-type, conically expanding CME, and its dynamics is found to be well associated with the complex, multiple type II radio emission detected in the metric band. Our results suggest that there might be a deficiency of ion heating in the present event with respect to what was observed in previous CME shocks detected by UVCS, and that this paucity might be attributed to different local plasma conditions, such as higher ambient coronal plasma β. We conclude that plasma β could be an important parameter in determining the effect of ion heating at collisionless shock fronts in the solar corona