Review on possible gravitational anomalies

This is an updated introductory review of 2 possible gravitational anomalies that has attracted part of the Scientific community: the Allais effect that occur during solar eclipses, and the Pioneer 10 spacecraft anomaly, experimented also by Pioneer 11 and Ulysses spacecrafts. It seems that, to date, no satisfactory conventional explanation exist to these phenomena, and this suggests that possible new physics will be needed to account for them. The main purpose of this review is to announce 3 other new measurements that will be carried on during the 2005 solar eclipses in Panama and Colombia (Apr. 8) and in Portugal (Oct.15).Comment: Published in 'Journal of Physics: Conferences Series of the American Institute of Physics'. Contribution for the VI Mexican School on Gravitation and Mathematical Physics "Approaches to Quantum Gravity" (Playa del Carmen, Quintana Roo, Mexico, Nov. 21-27, 2004). Updates to this information will be posted in http://www.lsc-group.phys.uwm.edu/~xavier.amador/anomalies.htm

Experimental and numerical characterization of anisotropic damage evolution of forged Al6061-T6 alloy

AbstractAluminum alloy 6061-T6 (Al-Mg-Si) has been selected as the material of the vessel for the construction of Jules-Horowitz material testing reactor. Fracture mechanism of this alloy has been investigated using mechanical testing of smooth and notched tensile specimens loaded in different directions. A strong anisotropic fracture behavior has been observed. Microstructural studies using tomography and image analysis have shown a presence of anisotropic distributed coarse precipitates which is the key microstructural feature affecting the damage evolution. These observations were complemented by investigations on fractured tensile samples. A damage scenario of anisotropic growth and coalescence of voids is proposed to explain the fracture behavior associated with the distribution of precipitates. A GTN (Gurson-Tvergaard-Needleman) damage model is used to simulate this scenario and to predict damage evolution

Conceptualising Higher Education and the Public Good in Ghana, Kenya, Nigeria, and South Africa

Higher education has been the object of policy attention in sub-Saharan Africa in recent years. It has been seen as key to unlocking the potential of the youth bulge, responding to the demands of a growing middle class and to transforming commodities-based economies into knowledge societies (World Bank 2009; Cloete, Maassen & Bailey 2015; Chuks, 2017). Yet despite significant expansions of enrolment – including widening participation by women, major barriers to access exist, reflecting inequalities based on class, gender, geographical location, ethnicity, religion, language and disability (AAI 2015; Morley & Lugg 2009; Morley & Croft, 2011). There are quality challenges in relation to teaching and learning, research, and governance. While some comment on a ’renaissance in African higher education’ (Higgs, 2016), and others on the effects and framings of colonial epistemicides (Nyamnjoh, 2012) key questions abound about relevance and power relations highlighting the need to decolonise the curriculum, structure, organisation and cultures of universities. The student protests in South Africa from 2015 highlighted problems of access and funding, but these are not isolated events. They expose an unresolved colonial legacy in these higher education systems. These processes raise questions not only of the public good relevance of higher education - beyond the obvious advantages conferred on those who manage to go to these institutions – but also of how higher education and its relationship with society may be conceptualised given these contexts (Lebeau and Milla, 2008; Mamdani, 2017). An overarching question is who is defining the public good and how? While many of the above issues are global e.g. universities throughout Latin America, Australasia, Asia and Europe are involved in similar debates and protests, this paper explores the relationship between higher education and the public good in the sub- Saharan African context through a consideration of some connections and disconnections. There appear to be two distinct ways in which higher education and the public good have been conceptualised are discussed. Firstly, higher education can be portrayed as instrumental in shaping a version of the public good where its qualifications, knowledge production, innovation, development of the professional classes, and expertise are perceived to lead to particular manifestations of public good, delineated as economic, social, political or cultural (McMahon 2009; Stiglitz 1999). The key arguments that underpin this conceptual framing speak to different levels of the public good, whether individual and community levels or the provision of ‘global public goods’ (Marginson 2007; 2013; Menashy 2009). However, a contrasting set of arguments portray the relationship between higher education and the public good as an intrinsic one, where the intellectual, physical and cultural experiences enabled through higher education express and enact the public good e.g. prejudice reduction, democratisation, critical thinking, active citizenship (Singh 2001; Calhoun 2006; Leibowitz, 2013; Marginson, 2011; Locatelli, 2017). Important here are considerations of the historical conjuncture that shapes experiences of higher education at a particular time and what these may mean. In considering the connections and disjunctures between these two formulations and the way writings on higher education in contemporary Africa have engaged with this debate, the paper makes an argument for discussing the importance of processes that link instrumental and intrinsic visions of higher education and the public good. The analysis of these from a rigorous review of literature leads to a delineation of some different views of time, space and evaluation. The paper argues that these contestations need to be read contextually. Higher education in sub-Saharan Africa has moved through phases, from the establishment of flagship national universities in the post-independence period for state bureaucracy formation (Teferra, 2017), to the emergence of developmental universities with a commitment to indigenising knowledge and benefiting marginalised populations, through more recent tendencies towards the marketisation of public institutions and the significant growth of the private sector (Assié-Lumumba & CODESRIA 2006; ADEA & AAU 2004; Coleman 1986; Mamdani, 2007; McCowan 2016). Appreciating these contextual factors in shaping the role and functioning of higher education and thus its relationship to the public good is a central theme in our analysis. We suggest that mainstream conceptualisations of higher education and the public good are underpinned by particular understandings of the nature and form of higher education and how knowledge is acquired, developed and disseminated – orientations that may be very far from the reality of highly unequal, socially stratified, and politically complex societies within which higher education is deeply embedded. Thus a reconceptualisation of the public is required by these contexts and some challenge to conceptualisations of the private, given the strong obligations of individuals to extended families, and the sharing of the benefits of higher education amongst their communities of origin. The paper concludes with a consideration of what may be important in conceptualising higher education and the public good in the African context and the value of such thinking for broader debates on the role of higher education

Flux tube delocalization at the deconfinement point

We study the behaviour of the flux tube thickness in the vicinity of the deconfinement transition. We show, using effective string methods, that in this regime the square width increases linearly and not logarithmically with the interquark distance. The amplitude of this linear growth is an increasing function of the temperature and diverges as the deconfinement transition is approached from below. These predictions are in good agreement with a set of simulations performed in the 3d gauge Ising model.Comment: 16 pages, 1 figure. Revised version, with an improved discussion of the dimensional reduction approach. Accepted for publication in JHE

Via Hexagons to Squares in Ferrofluids: Experiments on Hysteretic Surface Transformations under Variation of the Normal Magnetic Field

We report on different surface patterns on magnetic liquids following the Rosensweig instability. We compare the bifurcation from the flat surface to a hexagonal array of spikes with the transition to squares at higher fields. From a radioscopic mapping of the surface topography we extract amplitudes and wavelengths. For the hexagon--square transition, which is complex because of coexisting domains, we tailor a set of order parameters like peak--to--peak distance, circularity, angular correlation function and pattern specific amplitudes from Fourier space. These measures enable us to quantify the smooth hysteretic transition. Voronoi diagrams indicate a pinning of the domains. Thus the smoothness of the transition is roughness on a small scale.Comment: 17 pages, 14 figure

Linear broadening of the confining string in Yang-Mills theory at low temperature

The logarithmic broadening predicted by the systematic low-energy effective field theory for the confining string has recently been verified in numerical simulations of (2+1)-d SU(2) lattice Yang-Mills theory at zero temperature. The same effective theory predicts linear broadening of the string at low non-zero temperature. In this paper, we verify this prediction by comparison with very precise Monte Carlo data. The comparison involves no additional adjustable parameters, because the low-energy constants of the effective theory have already been fixed at zero temperature. It yields very good agreement between the underlying Yang-Mills theory and the effective string theory.Comment: 10 pages, 3 figures. Version published in JHEP; improved figures 1 and

A new approach to the study of effective string corrections in LGTs

We propose a new approach to the study of the interquark potential in Lattice Gauge Theories. Instead of looking at the expectation value of Polyakov loop correlators we study the modifications induced in the chromoelectric flux by the presence of the Polyakov loops. In abelian LGTs, thanks to duality, this study can be performed in a very efficient way, allowing to reach high precision at a reasonable CPU cost. The major advantage of this strategy is that it allows to eliminate the dominant effective string correction to the interquark potential (the Luscher term) thus giving an unique opportunity to test higher order corrections. Performing a set of simulations in the 3d gauge Ising model we were thus able to precisely identify and measure both the quartic and the sextic effective string corrections to the interquark potential. While the quartic term perfectly agrees with the Nambu-Goto one the sextic term is definitely different. Our result seems to disagree with the recent proof of the universality of the sextic correction. We discuss a few possible explanations of this disagreement.Comment: 22 pages, 5 figures. Comment added in the last sectio

Lattice potentials and fermions in holographic non Fermi-liquids: hybridizing local quantum criticality

We study lattice effects in strongly coupled systems of fermions at a finite density described by a holographic dual consisting of fermions in Anti-de-Sitter space in the presence of a Reissner-Nordstrom black hole. The lattice effect is encoded by a periodic modulation of the chemical potential with a wavelength of order of the intrinsic length scales of the system. This corresponds with a highly complicated "band structure" problem in AdS, which we only manage to solve in the weak potential limit. The "domain wall" fermions in AdS encoding for the Fermi surfaces in the boundary field theory diffract as usually against the periodic lattice, giving rise to band gaps. However, the deep infrared of the field theory as encoded by the near horizon AdS2 geometry in the bulk reacts in a surprising way to the weak potential. The hybridization of the fermions bulk dualizes into a linear combination of CFT1 "local quantum critical" propagators in the bulk, characterized by momentum dependent exponents displaced by lattice Umklapp vectors. This has the consequence that the metals showing quasi-Fermi surfaces cannot be localized in band insulators. In the AdS2 metal regime, where the conformal dimension of the fermionic operator is large and no Fermi surfaces are present at low T/\mu, the lattice gives rise to a characteristic dependence of the energy scaling as a function of momentum. We predict crossovers from a high energy standard momentum AdS2 scaling to a low energy regime where exponents found associated with momenta "backscattered" to a lower Brillioun zone in the extended zone scheme. We comment on how these findings can be used as a unique fingerprint for the detection of AdS2 like "pseudogap metals" in the laboratory.Comment: 42 pages, 5 figures; v2, minor correction, to appear in JHE

On higher derivative gravity, c-theorems and cosmology

We consider higher derivative gravity lagrangians in 3 and 4 dimensions, which admit simple c-theorems, including upto six derivative curvature invariants. Following a suggestion by Myers, these lagrangians are restricted such that the fluctuations around (anti) de Sitter spaces have second order linearized equations of motion. We study c-theorems both in the context of AdS/CFT and cosmology. In the context of cosmology, the monotonic function is the entropy defined on the apparent horizon through Wald's formula. Exact black hole solutions which are asymptotically (anti) de Sitter are presented. An interesting lower bound for entropy is found in de Sitter space. Some aspects of cosmology in both D=3 and D=4 are discussed.Comment: 23 pages, v3: clarifications added, references adde