Thermodynamic evidence for valley-dependent density of states in bulk bismuth

Electron-like carriers in bismuth are described by the Dirac Hamiltonian, with a band mass becoming a thousandth of the bare electron mass along one crystalline axis. The existence of three anisotropic valleys offers electrons an additional degree of freedom, a subject of recent attention. Here, we map the Landau spectrum by angle-resolved magnetostriction, and quantify the carrier number in each valley: while the electron valleys keep identical spectra, they substantially differ in their density of states at the Fermi level. Thus, the electron fluid does not keep the rotational symmetry of the lattice at low temperature and high magnetic field, even in the absence of internal strain. This effect, reminiscent of the Coulomb pseudo-gap in localized electronic states, affects only electrons in the immediate vicinity of the Fermi level. It presents the most striking departure from the non-interacting picture of electrons in bulk bismuth.Comment: 6 pages, 3 Figure

Syndrome D’aniridie Associé À La Dermatite Atopique: À Propos D’un Cas

Aniridia syndrome is a genetic anomaly affecting all ocular structures; it is transmitted by an autosomal dominant mode. In its isolated form aniridia is characterized by a hypoplasia of the iris frequently associated with other ocular anomalies. It the syndromic form it is associated to other systemic abnormalities. Authors are here reporting a case of aniridia associating: a corneal pannus, total aniridia, lens ectopia, and cataract found in a 14 years old girl. She also presented an atopic background with a positive family history of atopia. She is issued from a first degree consanguineous marriage. The management was multidisciplinary. In ophthalmology she underwent an intra-capsular extraction of the lens in both eyes with no intra-ocular lens implantation. Dermatological management was treatment of cuteanous lesions with emollients, corticoids and antihistamines drugs and ointments

Human resources for primary health care in sub-Saharan Africa: progress or stagnation?

BACKGROUND: The World Health Organization defines a "critical shortage" of health workers as being fewer than 2.28 health workers per 1000 population and failing to attain 80% coverage for deliveries by skilled birth attendants. We aimed to quantify the number of health workers in five African countries and the proportion of these currently working in primary health care facilities, to compare this to estimates of numbers needed and to assess how the situation has changed in recent years. METHODS: This study is a review of published and unpublished "grey" literature on human resources for health in five disparate countries: Mali, Sudan, Uganda, Botswana and South Africa. RESULTS: Health worker density has increased steadily since 2000 in South Africa and Botswana which already meet WHO targets but has not significantly increased since 2004 in Sudan, Mali and Uganda which have a critical shortage of health workers. In all five countries, a minority of doctors, nurses and midwives are working in primary health care, and shortages of qualified staff are greatest in rural areas. In Uganda, shortages are greater in primary health care settings than at higher levels. In Mali, few community health centres have a midwife or a doctor. Even South Africa has a shortage of doctors in primary health care in poorer districts. Although most countries recognize village health workers, traditional healers and traditional birth attendants, there are insufficient data on their numbers. CONCLUSION: There is an "inverse primary health care law" in the countries studied: staffing is inversely related to poverty and level of need, and health worker density is not increasing in the lowest income countries. Unless there is money to recruit and retain staff in these areas, training programmes will not improve health worker density because the trained staff will simply leave to work elsewhere. Information systems need to be improved in a way that informs policy on the health workforce. It may be possible to use existing resources more cost-effectively by involving skilled staff to supervise and support lower level health care workers who currently provide the front line of primary health care in most of Africa

Zooming on the Quantum Critical Point in Nd-LSCO

Recent studies of the high-Tc superconductor La_(1.6-x)Nd_(0.4)Sr_(x)CuO_(4) (Nd-LSCO) have found a linear-T in-plane resistivity rho_(ab) and a logarithmic temperature dependence of the thermopower S / T at a hole doping p = 0.24, and a Fermi-surface reconstruction just below p = 0.24 [1, 2]. These are typical signatures of a quantum critical point (QCP). Here we report data on the c-axis resistivity rho_(c)(T) of Nd-LSCO measured as a function of temperature near this QCP, in a magnetic field large enough to entirely suppress superconductivity. Like rho_(ab), rho_(c) shows an upturn at low temperature, a signature of Fermi surface reconstruction caused by stripe order. Tracking the height of the upturn as it decreases with doping enables us to pin down the precise location of the QCP where stripe order ends, at p* = 0.235 +- 0.005. We propose that the temperature T_(rho) below which the upturn begins marks the onset of the pseudogap phase, found to be roughly twice as high as the stripe ordering temperature in this material.Comment: Submitted for the Proceedings of the M2S-IX Conference (Tokyo, September 2009

Understanding the needs of Mena public transport customers: culture of service and gender responsive recommendations

Fast population growth, urban sprawl and the raise in households’ motorization observed in all major cities of the Middle-East and North-Africa (MENA) region, are constantly challenging public transport providers who seek to handle efficiently the continuously rising travel demand. Most of the MENA cities suffer from traffic congestion that not only impacts the quality of life of MENA citizens, but also their access to job opportunities, health services, and social and political participation. Alongside the development of public transport network, it is crucial to encourage urban dwellers to reduce their dependence on personal cars, use public transport, and develop soft mobility skills. Therefore, operators and service providers need to define customer-centric strategy and build a culture of service excellence in line with their customers’expectations. In cooperation with academic partners, the UITP MENA Centre for Transport Excellence launched the User-Oriented Public Transport research project with the aim to understand the perceptions of female and male users and non-users about public transport services in five MENA cities: Algiers, Amman, Beirut, Casablanca and Muscat. The methodological framework was built around the five dimensions of the user’s needs pyramid: safety, security, ease-to-use, comfort and experience. Based on the quantitative analysis of data collected from 984 respondents and the qualitative analysis of 49 women’s testimonies collected during the focus groups, recommendations were made to encourage culture of service and gender mainstreaming in public transport development in the region

Towards a consistent picture for quasi-1D organic superconductors

The electrical resistivity of the quasi-1D organic superconductor (TMTSF)2PF6 was recently measured at low temperature from the critical pressure needed to suppress the spin-density-wave state up to a pressure where superconductivity has almost disappeared. This data revealed a direct correlation between the onset of superconductivity at Tc and the strength of a non-Fermi-liquid linear term in the normal-state resistivity, going as r(T) = r0 + AT + BT2 at low temperature, so that A goes to 0 as Tc goes to 0. Here we show that the contribution of low-frequency antiferromagnetic fluctuations to the spin-lattice relaxation rate is also correlated with this non-Fermi-liquid term AT in the resistivity. These correlations suggest that anomalous scattering and pairing have a common origin, both rooted in the low-frequency antiferromagnetic fluctuations measured by NMR. A similar situation may also prevail in the recently-discovered iron-pnictide superconductors.Comment: ISCOM'09 proceedings to be published in Physica

Lifshitz critical point in the cuprate superconductor YBa2Cu3Oy from high-field Hall effect measurements

The Hall coefficient R_H of the cuprate superconductor YBa2Cu3Oy was measured in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152, in the underdoped regime. In fields large enough to suppress superconductivity, R_H(T) is seen to go from positive at high temperature to negative at low temperature, for p > 0.08. This change of sign is attributed to the emergence of an electron pocket in the Fermi surface at low temperature. At p < 0.08, the normal-state R_H(T) remains positive at all temperatures, increasing monotonically as T \to 0. We attribute the change of behaviour across p = 0.08 to a Lifshitz transition, namely a change in Fermi-surface topology occurring at a critical concentration p_L = 0.08, where the electron pocket vanishes. The loss of the high-mobility electron pocket across p_L coincides with a ten-fold drop in the conductivity at low temperature, revealed in measurements of the electrical resistivity $\rho$ at high fields, showing that the so-called metal-insulator crossover of cuprates is in fact driven by a Lifshitz transition. It also coincides with a jump in the in-plane anisotropy of $\rho$, showing that without its electron pocket the Fermi surface must have strong two-fold in-plane anisotropy. These findings are consistent with a Fermi-surface reconstruction caused by a unidirectional spin-density wave or stripe order.Comment: 16 pages, 13 figures, see associated Viewpoint: M. Vojta, Physics 4, 12 (2011

Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor

The nature of the pseudogap phase is a central problem in the quest to understand high-Tc cuprate superconductors. A fundamental question is what symmetries are broken when that phase sets in below a temperature T*. There is evidence from both polarized neutron diffraction and polar Kerr effect measurements that time- reversal symmetry is broken, but at temperatures that differ significantly. Broken rotational symmetry was detected by both resistivity and inelastic neutron scattering at low doping and by scanning tunnelling spectroscopy at low temperature, but with no clear connection to T*. Here we report the observation of a large in-plane anisotropy of the Nernst effect in YBa2Cu3Oy that sets in precisely at T*, throughout the doping phase diagram. We show that the CuO chains of the orthorhombic lattice are not responsible for this anisotropy, which is therefore an intrinsic property of the CuO2 planes. We conclude that the pseudogap phase is an electronic state which strongly breaks four-fold rotational symmetry. This narrows the range of possible states considerably, pointing to stripe or nematic orders.Comment: Published version. Journal reference and DOI adde