Multi-residues analysis of pre-emergence herbicides in fluvial sediments : application to the mid-Garonne River

Contamination of man and ecosystems by pesticides has become a major environmental concern. Whereas many studies exist on contamination from agriculture, the effects of urban sources are usually omitted. Fluvial sediment is a complex matrix of pollutants but little is known of its recent herbicide content. This study proposes a method for a fast and reliable analysis of herbicides by employing the accelerated solvent extractor (ASE). The aim of the study is to show the impact of a major town (Toulouse) on the herbicide content in the river. In this study, three herbicide families (i.e. s-triazine, substituted ureas and anilides) were analysed in fluvial sediment fractions at 11 sampling sites along the mid-Garonne River and its tributaries. River water contamination by herbicides is minor, except for at three sites located in urban areas. Among the herbicidal families studied, urban and suburban areas are distinguished from rural areas and were found to be the most contaminated sites during the study period, a winter low-water event. The herbicide content of the coarse sediment fractions is about one third of that found in the fine fractions and usually ignored. The distribution of pesticide concentrations across the whole range of particle sizes was investigated to clarify the role of plant remains on the significant accumulation in the coarse fractions

Molecular fluorine chemistry in the early Universe

Some models of Big Bang nucleosynthesis suggest that very high baryon density regions were formed in the early Universe, and generated the production of heavy elements other than lithium such as fluorine F. We present a comprehensive chemistry of fluorine in the post-recombination epoch. Calculation of F, F- and HF abundances, as a function of redshift z, are carried out. The main result is that the chemical conditions in the early Universe can lead to the formation of HF. The final abundance of the diatomic molecule HF is predicted to be close to 3.75 10(-17) when the initial abundance of neutral fluorine F is 10(-15). These results indicate that molecules of fluorine HF were already present during the dark age. This could have implications on the evolution of proto-objects and on the anisotropies of cosmic microwave background radiation. Hydride of fluorine HF may affect enhancement of the emission line intensity from the proto-objects and could produce spectral-spatial fluctuations.Comment: Accepted in Astronomy and Astrophysics, 7 pages, 2 figure

Primordial magnetic field and spectral distortion of cosmic background radiation

The role played by a primordial magnetic field during the pre-recombination epoch is analysed through the cyclotron radiation (due to the free electrons) it might produce in the primordial plasma. We discuss the constraint implied by the measurement or lack thereof COBE on this primordial field.Comment: to appear in International Journal of Mod. Phy

The distribution of two-dimensional eccentricity of Sunyaev-Zeldovich Effect and X-ray surface brightness profiles

With the triaxial density profile of dark matter halos and the corresponding equilibrium gas distribution, we derive two-dimensional Sunyaev-Zeldovich (SZ) effect and X-ray surface brightness profiles for clusters of galaxies. It is found that the contour map of these observables can be well approximated by a series of concentric ellipses with scale-dependent eccentricities. The statistical distribution of their eccentricities (or equivalently axial ratios) is analyzed by taking into account the orientation of clusters with respect to the line of sight and the distribution of the axial ratios and the concentration parameters of dark matter halos. For clusters of mass $10^{13}h^{-1}{M}_{\odot}$ at redshift $z=0$, the axial ratio is peaked at $\eta \sim 0.9$ for both SZ and X-ray profiles. For larger clusters, the deviation from circular distributions is more apparent, with $\eta$ peaked at $\eta \sim 0.85$ for $M=10^{15}h^{-1}{M}_{\odot}$. To be more close to observations, we further study the axial-ratio distribution for mass-limited cluster samples with the number distribution of clusters at different redshifts described by a modified Press-Schechter model. For a mass limit of value $M_{lim}=10^{14}h^{-1}{M}_{\odot}$, the average axial ratio is $\sim 0.84$ with a tail extended to $\eta \sim 0.6$. With fast advance of high quality imaging observations of both SZ effect and X-ray emissions, our analyses provide a useful way to probe cluster halo profiles and therefore to test theoretical halo-formation models.Comment: 28 pages, 6 figures. Accepted for publication in the Astrophysical Journa

Herbicide accumulation and evolution in reservoir sediments

The aim of the present study was to understand the effect of reservoir configurations on sediment pesticide fate. Two dams were selected on the River Garonne, in southwest France: Carbonne and Golfech, both with reservoirs subject to accumulation of herbicide-contaminated sediment. They are situated upstream and downstream respectively of an agricultural and urban area: the Mid-Garonne. The results presented include pesticide concentrations and C/N ratios in the smaller sediment particles (b2 mm) and values of oxygenation and herbicide concentrations in the water. The dynamic behaviour of sediment in the reservoirs is discussed. The present study shows that the theoretical lifespan (weak remanence in vitro) and the results actually observed in the sediment are conflicting. Pesticide contamination in Carbonne indicates conservation, even accumulation, of herbicide molecules while in Golfech transformation processes clearly dominate. The hydromorphological position of Golfech reservoir, i.e. located at the junction of two rivers with contrasting hydrological regimes and very different oxygenation conditions, leads to accelerated pesticide desorption or degradation. Unfortunately, this configuration is rare

Reference normal values and design of a vision screening for 4 to 5 years old preschoolers

A vision screening program for preschool children of 4-5 years old was designed and analyzed. Information of the prevalence of ocular conditions among preschool children was obtained. The vision health of a group of 127 children was evaluated by a comprehensive examination in their own school. If a child failed one or more screening tests, he was referred to the ophthalmologist. Of the children screened in this study, 61% passed distance visual acuity and retinoscopy tests, 17% were referred to the ophthalmologist and 22% will be annually monitoring. Values of monocular/binocular acuity worse than 0.5/0.6 are too poor for 4 years old children, whereas these limits increase up to 0.6/0.8 for 5 years old children. In conclusion, the prevalence of undetected vision problems in preschool children has been clearly demonstrated. Vision screening programs in schools are highly recommended. Nevertheless, coordination among professionals conducting screening, school personnel and parents are needed to reach high levels of success. The results of this study validate an easy and fast battery of tests. The vision screening has been highly reliable because reference normal values have been defined by analyzing statistically the results of these tests. Se diseñó y analizó un screening visual en preescolares de 4-5 años de edad. Se obtuvo información de la prevalencia de las condiciones oculares entre estos preescolares. Se evaluó la salud visual de un grupo de 127 niños con un examen completo en su propia escuela. Si el niño fallaba uno o más test era referido al oftalmólogo. De los niños revisados en el estudio, el 61% superó los test de agudeza visual y retinoscopía, al 17% se le refirió al oftalmólogo y el 22% será controlado anualmente. Valores de agudeza monocular/binocular peores de 0.5/0.6 son demasiado bajos para niños de 4 años de edad, mientras que estos límites se incrementan a 0.6/0.8 para niños de 5 años. En conclusión, la prevalencia de problemas de visión sin detectar en niños preescolares ha sido claramente demostrada. Sin embargo, es necesaria la coordinación entre profesionales que realicen el screening, personal del colegio y padres para alcanzar niveles altos de éxito. Los resultados de este estudio validan una batería rápida de test. El screening visual ha sido altamente fiable porque los valores normales de referencia han sido definidos analizando estadísticamente los resultados de estos tests

Compressed sensing imaging techniques for radio interferometry

Radio interferometry probes astrophysical signals through incomplete and noisy Fourier measurements. The theory of compressed sensing demonstrates that such measurements may actually suffice for accurate reconstruction of sparse or compressible signals. We propose new generic imaging techniques based on convex optimization for global minimization problems defined in this context. The versatility of the framework notably allows introduction of specific prior information on the signals, which offers the possibility of significant improvements of reconstruction relative to the standard local matching pursuit algorithm CLEAN used in radio astronomy. We illustrate the potential of the approach by studying reconstruction performances on simulations of two different kinds of signals observed with very generic interferometric configurations. The first kind is an intensity field of compact astrophysical objects. The second kind is the imprint of cosmic strings in the temperature field of the cosmic microwave background radiation, of particular interest for cosmolog

Urban Impact on Selected Pre-Emergence Herbicides in Sediment cores

In order to determine if pre-emergence herbicide pollutant source, mixing with many others from residential and industrial activities, has an effect on pollutant degradation, three sediment cores were sampled in appropriate sites of the Garonne river near the city of Toulouse: two in rural surroundings, one upstream and one downstream from the urban area away from its influence, and one downtown close to Toulouse. Atrazine and DEA were analysed and, using DAR pesticide/metabolite ratio, an inferior metabolisation ratio was highlighted in the urban sediment compared to the rural ones, regardless of sedimentation rate, organic carbon content, topography or differences in the intensity of surrounding activities between rural cores

Evaluation of morphological changes produced by orifice opener systems using computerized tomography (CT)

Objectives: To evaluate modifications in root canal morphology following instrumentation with orifice openers using Computerized Tomography (CT). Study design: Experimental in vitro study. A preoperative CT was performed on 49 molars to measure the root canal cross-sections. After preparing the canals with 6 different nickel-titanium (Ni-Ti) rotary system orifice opener type instruments and Gates Glidden burs, a further CT was made and compared with the preoperative one. Kruskal-Wallis and ANOVA statistical analysis were used. Results: Gates Glidden burs were significantly more aggressive in the coronal portion of the canals, although all the instruments removed more dental tissue in the most coronal of the sections studied. Bucco-lingual diameters were modified more than the mesio-distal ones. The stainless steel instruments used lead to greater modifications being required in the canals than those made of nickel-titanium. The ProFile system instruments were observed to be those that caused the least amount of change. Conclusions: Stainless steel burs are more aggressive than new orifice openers without significant differences observed between Ni-Ti instrument

The First Stars

We review recent theoretical results on the formation of the first stars in the universe, and emphasize related open questions. In particular, we discuss the initial conditions for Population III star formation, as given by variants of the cold dark matter cosmology. Numerical simulations have investigated the collapse and the fragmentation of metal-free gas, showing that the first stars were predominantly very massive. The exact determination of the stellar masses, and the precise form of the primordial initial mass function, is still hampered by our limited understanding of the accretion physics and the protostellar feedback effects. We address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars, to the familiar mode dominated by low mass stars, at later times. We show how complementary observations, both at high redshifts and in our local cosmic neighborhood, can be utilized to probe the first epoch of star formation.Comment: 38 pages, 10 figures, draft version for 2004 Annual Reviews of Astronomy and Astrophysics, high-resolution version available at http://cfa-www.harvard.edu/~vbromm