A Numerical Method for General Relativistic Magnetohydrodynamics

This paper describes the development and testing of a general relativistic magnetohydrodynamic (GRMHD) code to study ideal MHD in the fixed background of a Kerr black hole. The code is a direct extension of the hydrodynamic code of Hawley, Smarr, and Wilson, and uses Evans and Hawley constrained transport (CT) to evolve the magnetic fields. Two categories of test cases were undertaken. A one dimensional version of the code (Minkowski metric) was used to verify code performance in the special relativistic limit. The tests include Alfv\'en wave propagation, fast and slow magnetosonic shocks, rarefaction waves, and both relativistic and non-relativistic shock tubes. A series of one- and two-dimensional tests were also carried out in the Kerr metric: magnetized Bondi inflow, a magnetized inflow test due to Gammie, and two-dimensional magnetized constant-$l$ tori that are subject to the magnetorotational instability.Comment: 37 pages, 14 figures, submitted to ApJ. Animations can be viewed at http://www.astro.virginia.edu/~jd5v/grmhd/grmhd.htm

The effects of exclusive versus non-exclusive breastfeeding on specific infant morbidities in Conakry

Background:This study examines the effect of exclusive versus non-exclusive breastfeeding on specific infant morbidities from birth to nine months, in Conakry (Guinea). Methods:A cross-sectional study was conducted on 1,167 mother-infant pairs who visited one of 20 immunization centres in Conakry for vaccination between the 45th and 270th days of the child’s life. Two data sources were used: the infant health book and an orally administered questionnaire completed with the mother. Data analyses included univariate cross-tabulations and multivariate logistic regression models to estimate the effect of breastfeeding on infant morbidity. Results:Exclusive breastfeeding decreased with the infant’s age. At six months of age, the proportion of infants who were exclusively breastfed was only 15.5%. After adjusting for the infant’s age, and the interaction between the type of breastfeeding and the infant’s age, exclusive breastfeeding significantly protected the infants against many of the studied morbidities (OR: 0.28, CI: 0.15-0.51) and specifically against diarrhoea (OR: 0.38; 95% CI: 0.17 – 0.86), respiratory infections (OR: 0.27; 95% CI: 0.14 – 0.50), and low growth rate (OR: 0.11; 95% CI: 0.02 – 0.46), but not for otitis, urinary infection, or meningitis. Conclusion:This investigation confirmed the protective effects of exclusive breastfeeding on some specific infant’s morbidities during the first nine months of life. The results of this study are of great importance for the development of an information program designed to encourage the exclusive breastfeeding among the mothers of Conakry, Guinea

On the multiplicity of the O-star Cyg OB2 #8A and its contribution to the gamma-ray source 3EG J2033+4118

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6 + O5.5 binary system with a period of about 21.9 d. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to gamma-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative gamma-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+4118.Comment: 8 pages, 4 figures, conference on "The Multiwavelength Approach to Gamma-Ray Sources", to appear in Ap&S

New near-IR observations of mesospheric CO2 and H2O clouds on Mars

Carbon dioxide clouds, which are speculated by models on solar and extra-solar planets, have been recently observed near the equator of Mars. The most comprehensive identification of Martian CO2 ice clouds has been obtained by the near-IR imaging spectrometer OMEGA. CRISM, a similar instrument with a higher spatial resolution, cannot detect these clouds with the same method due to its shorter wavelength range. Here we present a new method to detect CO2 clouds using near-IR data based on the comparison of H2O and CO2 ice spectral properties. The spatial and seasonal distributions of 54 CRISM observations containing CO2 clouds are reported, in addition to 17 new OMEGA observations. CRISM CO2 clouds are characterized by grain size in the 0.5-2\mum range and optical depths lower than 0.3. The distributions of CO2 clouds inferred from OMEGA and CRISM are consistent with each other and match at first order the distribution of high altitude (>60km) clouds derived from previous studies. At second order, discrepancies are observed. We report the identification of H2O clouds extending up to 80 km altitude, which could explain part of these discrepancies: both CO2 and H2O clouds can exist at high, mesospheric altitudes. CRISM observations of afternoon CO2 clouds display morphologies resembling terrestrial cirrus, which generalizes a previous result to the whole equatorial clouds season. Finally, we show that morning OMEGA observations have been previously misinterpreted as evidence for cumuliform, and hence potentially convective, CO2 clouds.Comment: Vincendon, M., C. Pilorget, B. Gondet, S. Murchie, and J.-P. Bibring (2011), New near-IR observations of mesospheric CO2 and H2O clouds on Mars, J. Geophys. Res., 116, E00J0

Family Farming Systems in Northern Central Cameroon: Challenges and Prospects for Food Security

If family farming is supported, it can serve as a foundation for growth and food security. One of Cameroon's biggest development challenges is still food insecurity. Therefore, the purpose of this study was to investigate the situation and key determinants of food security in the northern forest-savanna transition zone of the Central Cameroon Region. To do this, 180 family farmers from Mbangassina, Ntui, Batchenga, and Obala participated in a survey and field observations (January-March 2020; March-May 2021, and July-September 2021). According to this survey and these findings, the useful agricultural area is 4.55 ± 0.21 hectares. Cocoa, yam, cassava, maize, plantain, sweet potato, and peanut are the principal crops mentioned. With a mixed workforce, the vast majority of agricultural work is performed manually (machetes, daba, etc). (Family and external). Seven significant challenges face family farming in these areas: poor market organization, bad road/track conditions, a lack of inputs, seasonal uncertainties/rainfall deficits, challenging access to irrigation, unstable land tenure, challenging access to credit, and challenging access to agricultural equipment. Each community faces unique challenges. The family agricultural industry, which these people rely on for their food security, needs to be saved to overcome these obstacles. According to the findings, expanding access to financial and commercial services will help agricultural operations in the study area increase food security. This will be in line with initiatives made by both governmental and non-governmental organizations to advance agricultural technologies as a way to address the issue of food insecurity

Family Farming Systems in Northern Central Cameroon: Challenges and Prospects for Food Security

If family farming is supported, it can serve as a foundation for growth and food security. One of Cameroon's biggest development challenges is still food insecurity. Therefore, the purpose of this study was to investigate the situation and key determinants of food security in the northern forest-savanna transition zone of the Central Cameroon Region. To do this, 180 family farmers from Mbangassina, Ntui, Batchenga, and Obala participated in a survey and field observations (January-March 2020; March-May 2021, and July-September 2021). According to this survey and these findings, the useful agricultural area is 4.55 ± 0.21 hectares. Cocoa, yam, cassava, maize, plantain, sweet potato, and peanut are the principal crops mentioned. With a mixed workforce, the vast majority of agricultural work is performed manually (machetes, daba, etc). (Family and external). Seven significant challenges face family farming in these areas: poor market organization, bad road/track conditions, a lack of inputs, seasonal uncertainties/rainfall deficits, challenging access to irrigation, unstable land tenure, challenging access to credit, and challenging access to agricultural equipment. Each community faces unique challenges. The family agricultural industry, which these people rely on for their food security, needs to be saved to overcome these obstacles. According to the findings, expanding access to financial and commercial services will help agricultural operations in the study area increase food security. This will be in line with initiatives made by both governmental and non-governmental organizations to advance agricultural technologies as a way to address the issue of food insecurity

Family Farming Systems in Northern Central Cameroon: Challenges and Prospects for Food Security

If family farming is supported, it can serve as a foundation for growth and food security. One of Cameroon's biggest development challenges is still food insecurity. Therefore, the purpose of this study was to investigate the situation and key determinants of food security in the northern forest-savanna transition zone of the Central Cameroon Region. To do this, 180 family farmers from Mbangassina, Ntui, Batchenga, and Obala participated in a survey and field observations (January-March 2020; March-May 2021, and July-September 2021). According to this survey and these findings, the useful agricultural area is 4.55 ± 0.21 hectares. Cocoa, yam, cassava, maize, plantain, sweet potato, and peanut are the principal crops mentioned. With a mixed workforce, the vast majority of agricultural work is performed manually (machetes, daba, etc). (Family and external). Seven significant challenges face family farming in these areas: poor market organization, bad road/track conditions, a lack of inputs, seasonal uncertainties/rainfall deficits, challenging access to irrigation, unstable land tenure, challenging access to credit, and challenging access to agricultural equipment. Each community faces unique challenges. The family agricultural industry, which these people rely on for their food security, needs to be saved to overcome these obstacles. According to the findings, expanding access to financial and commercial services will help agricultural operations in the study area increase food security. This will be in line with initiatives made by both governmental and non-governmental organizations to advance agricultural technologies as a way to address the issue of food insecurity

Family Farming Systems in Northern Central Cameroon: Challenges and Prospects for Food Security

If family farming is supported, it can serve as a foundation for growth and food security. One of Cameroon's biggest development challenges is still food insecurity. Therefore, the purpose of this study was to investigate the situation and key determinants of food security in the northern forest-savanna transition zone of the Central Cameroon Region. To do this, 180 family farmers from Mbangassina, Ntui, Batchenga, and Obala participated in a survey and field observations (January-March 2020; March-May 2021, and July-September 2021). According to this survey and these findings, the useful agricultural area is 4.55 ± 0.21 hectares. Cocoa, yam, cassava, maize, plantain, sweet potato, and peanut are the principal crops mentioned. With a mixed workforce, the vast majority of agricultural work is performed manually (machetes, daba, etc). (Family and external). Seven significant challenges face family farming in these areas: poor market organization, bad road/track conditions, a lack of inputs, seasonal uncertainties/rainfall deficits, challenging access to irrigation, unstable land tenure, challenging access to credit, and challenging access to agricultural equipment. Each community faces unique challenges. The family agricultural industry, which these people rely on for their food security, needs to be saved to overcome these obstacles. According to the findings, expanding access to financial and commercial services will help agricultural operations in the study area increase food security. This will be in line with initiatives made by both governmental and non-governmental organizations to advance agricultural technologies as a way to address the issue of food insecurity

Advertising Bans and the Substitutability of Online and Offline Advertising

The authors examine whether the growth of the Internet has reduced the effectiveness of government regulation of advertising. They combine nonexperimental variation in local regulation of offline alcohol advertising with data from field tests that randomized exposure to online advertising for 275 different online advertising campaigns to 61,580 people. The results show that people are 8% less likely to say that they will purchase an alcoholic beverage in states that have alcohol advertising bans compared with states that do not. For consumers exposed to online advertising, this gap narrows to 3%. There are similar effects for four changes in local offline alcohol advertising restrictions when advertising effectiveness is observed both before and after the change. The effect of online advertising is disproportionately high for new products and for products with low awareness in places that have bans. This suggests that online advertising could reduce the effectiveness of attempts to regulate offline advertising channels because online advertising substitutes for (rather than complements) offline advertising.Google (Firm)WPP (Firm

Electrically tunable solid-state silicon nanopore ion filter

We show that a nanopore in a silicon membrane connected to a voltage source can be used as an electrically tunable ion filter. By applying a voltage between the heavily doped semiconductor and the electrolyte, it is possible to invert the ion population inside the nanopore and vary the conductance for both cations and anions in order to achieve selective conduction of ions even in the presence of significant surface charges in the membrane. Our model based on the solution of the Poisson equation and linear transport theory indicates that in narrow nanopores substantial gain can be achieved by controlling electrically the width of the charge double layer