Broadband, unpolarized repumping and clearout light sources for Sr+^+ single-ion clocks

Future transportable optical clocks require compact and reliable light sources. Here, broadband, unpolarized repumper and state clearout sources for Sr+ single-ion optical clocks are reported. These turn-key devices require no frequency stabilization nor external modulators. They are fiber based, inexpensive, and compact. Key characteristics for clock operation are presented, including optical spectra, induced light shifts and required extinction ratios. Tests with an operating single-ion standard show a clearout efficiency of 100%. Compared to a laser-based repumper, the achievable fluorescence rates for ion detection are a few tens of per cent lower. The resulting ion kinetic temperature is 1--1.5 mK, near the Doppler limit of the ion system. Similar repumper light sources could be made for Ca+ (866 nm) and Ba+ (650 nm) using semiconductor gain media.Comment: 4 pages, 6 figure

Le rôle de la relation conjugale dans l’abus et la négligence d’enfants : vers une étude écologique

Le phénomène de Tabus et de la négligence d'enfants a toujours été répandu dans la société occidentale. Or, ce n'est que récemment que cliniciens et chercheurs se sont sérieusement penchés sur ces problèmes. Cet intérêt, sans cesse grandissant, a été suscité non seulement par le nombre impressionnant de cas signalés chaque année, mais encore par l'ampleur et la gravité des conséquences observables chez les enfants. Plusieurs professionnels intéresses par cette question ont proposé une multitude de facteurs étiologiques pour expliquer les abus et la négligence au sein d'une famille. Cependant, lorsque nous évaluons les modèles théoriques offerts (psychiatrique/psychologique, sociologique, systémique), il ressort que certains facteurs simples peuvent jouer un rôle important, comme par exemple l'histoire du développement des parents, la qualité de la relation conjugale, la relation parents-enfant, le stress et l'étendue du réseau social, mais aucun d'entre eux ne différencie parfaitement les familles abusives des familles non abusives. Il semble toutefois que ces différents facteurs explicatifs présenteraient une grande valeur s ' ils étaient considérés en interaction plutôt qu'individuellement. S'inspirant du cadre écologique de Bronfenbrenner (1977, 1979), Belsky (1980, 1984) ainsi que Cicchetti et Rizley (1981) ont d'ailleurs élaboré un modèle qui tient compte simultanément de tous ces facteurs et de leur interaction.The phenomenon of child abuse and neglect has always existed in Western society. Yet, it is only recently that clinicians and researchers have taken a serious look at these problems. This ever growing interest has come about from not only the stunning number of cases identified each year, but also by the extent and gravity of consequences observed among children. Several professionals interested by the issue have put forward a great number of etiological factors to try to explain abuse and neglect within the family unit. However, when assessing the proposed theoretical models (psychiatric/psychological, sociological, systemic), it appears that certain simple factors can play a large role, for instance the history behind parental development, the quality of marital relations, the child-parent relation, the stress and the extent of the social network, but none of these can clearly differentiate abusive families from non abusive families. It seems however that these different explicative factors would be even more valuable if they were considered in interaction rather than taken individually. Inspired by the ecological framework proposed by Bronfenbrenner (1977, 1979), Belsky (1980, 1984) as well as Cicchetti and Rizley (1981) have also developed a model that simultaneously takes into account all of these factors and their interaction

Reactivity ratio estimation for co- and terpolymerization of n-butyl acrylate, methyl methacrylate and 2-ethylhexyl acrylate

N-butyl acrylate (BA), 2-ethylhexyl acrylate (EHA) and methyl methacrylate (MMA) are commonly used as monomers in coatings, adhesives and many other applications. Our current interest is in BA/MMA/EHA terpolymer formulations for the production of pressure sensitive adhesives. For the purposes of controlling polymer adhesive performance, kinetic parameters such as the reactivity ratios, are required. Reactivity ratios for BA/MMA are available in the literature1, while that for BA/EHA and MMA/EHA are not. The bulk copolymerization reactivity ratios for BA/EHA and MMA/EHA were determined at 60 C using statistically designed free-radical polymerizations at low-conversion (\u3c10%). The estimates were then validated using high-conversion copolymerizations. These reactivity ratio estimates were used, along with the literature values for the BA/MMA system, for the prediction of BA/MMA/EHA composition in a series of high conversion bulk terpolymerizations. Please click Additional Files below to see the full abstract

A Note in the Skyrme Model with Higher Derivative Terms

Another stabilizer term is used in the classical Hamiltonian of the Skyrme Model that permits in a much simple way the generalization of the higher-order terms in the pion derivative field. Improved numerical results are obtained.Comment: Latex. Figure not include; available upon request. 7 pages, report

What Lessons it Might Teach Us! Community Engagement in HIV Research

Purpose of review Partnerships between academia and the community led to historic advances in HIV and paved the way for ongoing community engagement in research. Three decades later, we review the state of community engagement in HIV research, discuss best practices as supported by literature, explore innovations, and identify ongoing gaps in knowledge. Recent findings The community of people living with and at risk for HIV remains actively involved in the performance of HIV research. However, the extent of participation is highly variable despite long standing and established principles and guidelines of good participatory practices (GPP) and community-based participatory research (CBPR). Current literature reveals that known barriers to successful community engagement continue to exist such as power differences, and poor scientific or cultural competency literacy. Several high-quality studies share their experiences overcoming these barriers and demonstrate the potential of CBPR through reporting of qualitative and quantitative outcomes. Summary Greater time and attention should be placed on the development of community engagement in HIV research. A large body of literature, including innovative cross-cutting approaches, exists to guide and inform best practices and mitigate common barriers. However, we recognize that true growth and expansion of CBPR within HIV and in other fields will require a greater breadth of research reporting qualitative and quantitative outcomes

Experiments of Interfacial Roughening in Hele-Shaw Flows with Weak Quenched Disorder

We have studied the kinetic roughening of an oil--air interface in a forced imbibition experiment in a horizontal Hele--Shaw cell with quenched disorder. Different disorder configurations, characterized by their persistence length in the direction of growth, have been explored by varying the average interface velocity v and the gap spacing b. Through the analysis of the rms width as a function of time, we have measured a growth exponent beta ~= 0.5 that is almost independent of the experimental parameters. The analysis of the roughness exponent alpha through the power spectrum have shown different behaviors at short (alpha_1) and long (alpha_2) length scales, separated by a crossover wavenumber q_c. The values of the measured roughness exponents depend on experimental parameters, but at large velocities we obtain alpha_1 ~= 1.3 independently of the disorder configuration. The dependence of the crossover wavenumber with the experimental parameters has also been investigated, measuring q_c ~ v^{0.47} for the shortest persistence length, in agreement with theoretical predictions.Comment: 20 pages, 22 figure

Influence of wind on crop canopy reflectance measurements

Remote sensing techniques of measuring red and far-red crop canopy reflectance are frequently used to estimate crop canopy characteristics. The variability introduced in reflectance data from nonvegetative factors such as wind decreases the usefulness of the techniques. The objective of this study was to quantify and minimize the variability from wind on spectral reflectances. Red and far-red reflectances were acquired above wheat, barley, and alfalfa canopies throughout days of changing wind conditions. Periods of 312 s with little changes in irradiance values were used for the analysis. Wind had negligible effect on reflectances of a short canopy such as cut alfalfa, while it had a significant effect on reflectances from canopies with a higher vertical structure, particularly during gusty conditions. Within the windy and calm periods, extreme values of spectral reflectance differed by 60% and 12%, respectively, in the red, and by 40% and 8% in the far-red for the barley canopy. For the compact and dense canopy structure of alfalfa, these differences reached a maximum of 10% under windy conditions in both spectral regions. The plant canopy architecture, the wind conditions, and the spectral regions all affected the magnitude of the influence of wind on crop canopy spectral reflectances. The mean reflectance of a canopy overestimated the true reflectance by 2–4% while the use of the median reduced this overestimation. Sampling requirements for this sensor are evaluated, and the possibility of decreasing either the sampling rate or the sampling period is discussed