Quantum Vacuum Experiments Using High Intensity Lasers

The quantum vacuum constitutes a fascinating medium of study, in particular since near-future laser facilities will be able to probe the nonlinear nature of this vacuum. There has been a large number of proposed tests of the low-energy, high intensity regime of quantum electrodynamics (QED) where the nonlinear aspects of the electromagnetic vacuum comes into play, and we will here give a short description of some of these. Such studies can shed light, not only on the validity of QED, but also on certain aspects of nonperturbative effects, and thus also give insights for quantum field theories in general.Comment: 9 pages, 8 figur

The Negative Impacts of COVID-19 Containment Measures on South African Families - Overview and Recommendations

The World Health Organization (WHO) reported various pneumonia cases (‘Coronavirus Disease 2019’ [COVID-19]) on 31 December 2019 in Wuhan City, China, which has spread to many countries, including South Africa. In response to this, the President of South Africa declared a state of national disaster on 15th March 2020, followed by introducing various COVID-19 containment measures to minimize the spread of the virus. This paper examines the negative impacts that COVID-19 containment measures may have had on the family as a unit of society and furthermore provides recommendations to mitigate the impacts of these measures. It can be concluded that COVID-19 containment measures, specifically the lockdown restrictions, would yield both short-term and long-term impacts on proper family functioning. Several families in South Africa have been impacted financially due to the closure of business which led to the temporary/ permanent unemployment of some breadwinners in the families. This also has had a cascading impact on the food security of families and their ability to afford other basic necessities. Distress as a result of financial challenges or failure to provide for the family alongside spending much time locked down together as a family has also led to violence in the family. This was further exacerbated by the fact that the victims were stuck with the abusers and some could not report or find help due to the restricted movements. Furthermore, since most institutions predominantly moved learning online, results indicated that the lockdown restrictions affected the ability of some individuals especially those from poor families to access formal education during the period due to the lack of digital devices and internet facilities. In order to mitigate the impacts of the COVID-19 containment measures on the family, there is a need for collaborative efforts at intrapersonal, interpersonal, institutional, community and policy levels using the ecological framework

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behavior, and is one of only a few FSRQs detected at very high energy (VHE, E >100 GeV) -rays. VHE -ray observations with H.E.S.S. and MAGIC during late May and early June 2016 resulted in the detection of an unprecedented flare, which reveals for the first time VHE -ray intranight variability in this source. While a common variability timescale of 1.5 hr is found, there is a significant deviation near the end of the flare with a timescale of ∼ 20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, curvature is detected in the VHE -ray spectrum of PKS 1510-089, which is fully explained through absorption by the extragalactic background light. Optical R-band observations with ATOM reveal a counterpart of the -ray flare, even though the detailed flux evolution differs from the VHE lightcurve. Interestingly, a steep flux decrease is observed at the same time as the cessation of the VHE flare. In the high energy (HE, E >100 MeV) -ray band only a moderate flux increase is observed with Fermi-LAT, while the HE -ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the -ray spectrum indicates that the emission region is located outside of the BLR. Radio VLBI observations reveal a fast moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located ∼ 50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this correlation is indeed true, VHE rays have been produced far down the jet where turbulent plasma crosses a standing shock.Accepted manuscrip

Sur la variation du module du quartz en fonction de la température. II. Températures inférieures à la température ordinaire

Comme suite à un précédent article nous donnons ici les valeurs du module piézoélectrique du quartz pour des températures, comprises entre + 23° C et - 60° C. Les valeurs trouvées montrent que le module reste constant entre + 20° et 0° C, puis décroit sensiblement linéairement entre 0° et - 60°. Dans cet intervalle de température la variation constatée pour le module est de 5,8 pour 100