Relativistic positioning: four-dimensional numerical approach in Minkowski space-time

We simulate the satellite constellations of two Global Navigation Satellite Systems: Galileo (EU) and GPS (USA). Satellite motions are described in the Schwarzschild space-time produced by an idealized spherically symmetric non rotating Earth. The trajectories are then circumferences centered at the same point as Earth. Photon motions are described in Minkowski space-time, where there is a well known relation, Coll, Ferrando & Morales-Lladosa (2010), between the emission and inertial coordinates of any event. Here, this relation is implemented in a numerical code, which is tested and applied. The first application is a detailed numerical four-dimensional analysis of the so-called emission coordinate region and co-region. In a second application, a GPS (Galileo) satellite is considered as the receiver and its emission coordinates are given by four Galileo (GPS) satellites. The bifurcation problem (double localization) in the positioning of the receiver satellite is then pointed out and discussed in detail.Comment: 16 pages, 9 figures, published (online) in Astrophys. Space Sc

Positioning systems in Minkowski space-time: from emission to inertial coordinates

The coordinate transformation between emission coordinates and inertial coordinates in Minkowski space-time is obtained for arbitrary configurations of the emitters. It appears that a positioning system always generates two different coordinate domains, namely, the front and the back emission coordinate domains. For both domains, the corresponding covariant expression of the transformation is explicitly given in terms of the emitter world-lines. This task requires the notion of orientation of an emitter configuration. The orientation is shown to be computable from the emission coordinates for the users of a `central' region of the front emission coordinate domain. Other space-time regions associated with the emission coordinates are also outlined.Comment: 20 pages; 1 figur

International response to the HIV/AIDS epidemic: planning for success.

More assertive political leadership in the global response to AIDS in both poor and rich countries culminated in June 2001 at the UN General Assembly Special Session on AIDS. Delegates made important commitments there, and endorsed a global strategy framework for shifting the dynamics of the epidemic by simultaneously reducing risk, vulnerability and impact. This points the way to achievable progress in the fight against HIV/AIDS. Evidence of success in tackling the spread of AIDS comes from diverse programme areas, including work with sex workers and clients, injecting drug users, and young people. It also comes from diverse countries, including India, the Russian Federation, Senegal, Thailand, the United Republic of Tanzania, and Zambia. Their common feature is the combination of focused approaches with attention to the societywide context within which risk occurs. Similarly, building synergies between prevention and care has underpinned success in Brazil and holds great potential for sub-Saharan Africa, where 90% reductions have been achieved in the prices at which antiretroviral drugs are available. Success also involves overcoming stigma, which undermines community action and blocks access to services. Work against stigma and discrimination has been effectively carried out in both health sector and occupational settings. Accompanying attention to the conditions for success against HIV/AIDS is global consensus on the need for additional resources. The detailed estimate of required AIDS spending in low- and middle-income countries is US$9.2 billion annually, compared to the$ 2 billion currently spent. Additional spending should be mobilized by the new global fund to fight AIDS, tuberculosis and malaria, but needs to be joined by additional government and private efforts within countries, including from debt relief. Commitment and capacity to scale up HIV prevention and care have never been stronger. The moment must be seized to prevent a global catastrophe

DAMA detection claim is still compatible with all other DM searches

We show that the annual modulation signal observed by DAMA can be reconciled with all other negative results from dark matter searches with a conventional halo model for particle masses around 5 to 9 GeV. We also show which particular dark matter stream could produce the DAMA signal.Comment: Talk given at TAUP2005, Sept. 10-14 2005, Zaragoza (Spain). 3 pages, 4 figure

On the degrees of freedom of a semi-Riemannian metric

A semi-Riemannian metric in a n-manifold has n(n-1)/2 degrees of freedom, i.e. as many as the number of components of a differential 2-form. We prove that any semi-Riemannian metric can be obtained as a deformation of a constant curvature metric, this deformation being parametrized by a 2-for

Presidents and the Campus Mental Health Crisis: Challenges, Options, and Strategy

The COVID-19 pandemic has impacted every institution of higher education differently. It is recognized that a return to pre-pandemic institutional life is no longer possible. Presidential leadership is being required to reposition the institution to face this new era. One of the most vexing results of the pandemic is the emergence of student, faculty and staff mental health and wellness as a priority issue. Upon examination, the campus mental health crisis encompasses most aspects of campus life. The purpose of this review is threefold: 1) to illuminate the impact of campus mental health and wellness issues 2) to outline institutional challenges and options, and 3) to propose a set of strategic actions for presidential leadership to respond to the campus mental health crisis

A physical application of Kerr-Schild groups

The present work deals with the search of useful physical applications of some generalized groups of metric transformations. We put forward different proposals and focus our attention on the implementation of one of them. Particularly, the results show how one can control very efficiently the kind of spacetimes related by a Generalized Kerr-Schild (GKS) Ansatz through Kerr-Schild groups. Finally a preliminar study regarding other generalized groups of metric transformations is undertaken which is aimed at giving some hints in new Ans\"atze to finding useful solutions to Einstein's equations.Comment: 18 page

Education Deans: Challenges and Stress

Abstract: This study explored issues facing deans within higher education, specifically deans of doctoral granting schools/colleges of education. The study explored key challenges/issues and related stress education deans experience at research universities

Modeling of the general circulation with the LMD-AOPP-IAA GCM: Update on model design and comparison with observations

The LMD-AOPP GCM is developed conjointly by LMD in Paris and AOPP in Oxford, with the collaboration of IAA in Granada for the physical processes specific to the upper atmosphere. The collaboration between the two teams is based on the use of two different dynamical core (gridpoint at LMD, spectral at AOPP), which allow us to estimate the likely uncertainty arising from certain types of modeling errors. Similarly, we use different schemes to compute tracer transport, etc. The work has benefited from support from ESA (since 1995) and CNES (since 2000). Within that context, the GCMs are used to produce a Martian climate 'database' which is used by more than 30 teams around the world for mission design and scientific studies (see Bingham et al., this issue and Lewis et al., 1999). The baseline version of the GCM is described in detail in Forget et al. (1999). Here we describe the recent improvement and design changes since this publication. Compared to this previous version, the new GCM covers a wider range of altitude, from 0 to 120km in the vertical, it uses improved topography and thermal inertia surface maps from Mars Global Surveyor (MGS), and includes a new 'dust scenario' to describe the distribution of airborne dust in the atmosphere