Skeleton as a probe of the cosmic web: the 2D case

We discuss the skeleton as a probe of the filamentary structures of a 2D random field. It can be defined for a smooth field as the ensemble of pairs of field lines departing from saddle points, initially aligned with the major axis of local curvature and connecting them to local maxima. This definition is thus non local and makes analytical predictions difficult, so we propose a local approximation: the local skeleton is given by the set of points where the gradient is aligned with the local curvature major axis and where the second component of the local curvature is negative. We perform a statistical analysis of the length of the total local skeleton, chosen for simplicity as the set of all points of space where the gradient is either parallel or orthogonal to the main curvature axis. In all our numerical experiments, which include Gaussian and various non Gaussian realizations such as \chi^2 fields and Zel'dovich maps, the differential length is found within a normalization factor to be very close to the probability distribution function of the smoothed field. This is in fact explicitly demonstrated in the Gaussian case. This result might be discouraging for using the skeleton as a probe of non Gausiannity, but our analyses assume that the total length of the skeleton is a free, adjustable parameter. This total length could in fact be used to constrain cosmological models, in CMB maps but also in 3D galaxy catalogs, where it estimates the total length of filaments in the Universe. Making the link with other works, we also show how the skeleton can be used to study the dynamics of large scale structure.Comment: 15 pages, 11 figures, submitted to MNRA

The influence of tillage practice and dissolved organic carbon on the soil sorption and desorption of fluometuron and norflurazon

Fluometuron (FLMT) and norflurazon (NORF) are preemergence herbicides applied to cotton in the southeastern U.S. Residual levels of both herbicides have been detected in soils long after application, potentially posing risks to subsequent crops and groundwater resources. Herbicide sorption is an important mechanism influencing their fate and behavior. Sorption by soil organic matter (SOM), which is influenced by tillage practice, is the dominant mechanism by which herbicides are removed from the aqueous phase. Dissolved organic carbon (DOC) concentrations greater than 100 mg L-1 have been shown to reduce the sorption of some trace organic compounds in soil systems. The objectives of this study were to 1) determine the effect of tillage, (SOM content) on the sorption and desorption of FLMT and NORF, 2) determine the effect of DOC source (poultry litter, dairy manure, and no-till (NT) surface soil) and concentration on the sorption of FLMT and NORF, and 3) examine the effect of NT DOC on subsoil sorption of FLMT and NORF. Sorption of FLMT and NORF to NT and conventional tillage (CT) managed surface soil and subsoil [Lexington silty loam (fine-silty, mixed, thermic, Typic Paleudalf)] was characterized using batch sorption isotherms. Herbicide sorption experiments were conducted in the presence and absence of DOC extracted from poultry litter, dairy manure and NT surface soil. Desorption of FLMT and NORF was analyzed in the absence of DOC, with DOC in the desorption solution only, and with DOC in both the sorption and desorption systems. Dissolved organic carbon was extracted from poultry litter, dairy manure, and NT surface soil. The DOC extracts were analyzed for organic carbon content. The E4/E6 ratio and gel permeation chromatography were employed to characterize the DOC extracts. The increased SOM content of NT soil enhanced the sorption of FLMT and NORF. The retention of FLMT and NORF by Lexington silt loam soil decreases in the following order: NT \u3e CT \u3e subsoil. Herbicide sorption conformed to the L-curve and C-curve isotherms, with the C-curve being more representative of sorption by the high organic carbon, NT surface soil. Sorption of FLMT and NORF was generally reduced with DOC in the sorption equilibration solution, regardless of source or concentration. The greatest reduction in FLMT and NORF sorption occurred in the presence of poultry DOC. Dairy DOC ranked second in decreasing the amount of herbicide sorbed, followed by NT DOC. Spectroscopie E4/E6 ratios of the DOC molecules indicate that the poultry, dairy, and NT DOC extracts are composed of predominately low molecular weight compounds. According to gel chromatography, poultry DOC had the greatest distribution of large DOC molecules, while dairy DOC had a significant distribution of both smaller and larger molecules. No-till DOC was composed of a single size distribution of molecules, close in size to FLMT and NORF. The spectroseopic characterization of the DOC molecules coupled with the sorption results suggests that the large DOC molecules were responsible for the reduced sorption of the herbicides. The concentration of DOC in the sorption systems also influenced the sorption of FLMT and NORF. In general, sorption decreased with increasing DOC concentration. Recent literature suggests that DOC concentrations below 100 mg DOC L-1 do not effect the sorption of the herbicides. However, this study shows that DOC concentrations as low as 75 and to a lesser extent, 37.5 mg L-1 result in reduced herbicide sorption. The aqueous association of herbicide with DOC can be quantified by the KDOC. Solid SOM is known to be at least twice as effective a sorbent for herbicides compared to soluble DOC. Therefore, SOM should exert a much greater influence on the sorption of FLMT and NORP. The organic carbon normalized distribution coefficients (KOC values) indicate the contribution of SOM to organic compound sorption. Computed KDOC values greatly exceeded the KOC values calculated in this study. Thus, DOC complexation of the herbicides in solution is improbable in these systems. Reduced herbicide retention in the presence of DOC may result from competition between the herbicide and DOC molecules for limited sorption sites is at work in these systems. Conversely, DOC may coat the soil surfaces and present a hydrophobic surface that forces the herbicides to remain in aqueous solution. Desorption of FLMT and NORF was hysteretic in all soils. Hysteresis was greater with NORF, compared to FLMT. No effect of SOM content on desorption hysteresis was evident. Desorption of FLMT and NORF from soil was enhanced with the addition of DOC to the soil systems. Poultry DOC enhanced desorption the greatest followed by dairy and NT DOC, respectively. The addition of DOC at the desorption step appeared to reverse herbicide sorption when compared with the no-DOC isotherm. However, the addition of DOC at the desorption step changed the chemistry of the system. Thus, desorption should revert to a DOC sorption isotherm. Some poultry DOC isotherms showed reversible herbicide sorption. However, in general, desorption was incomplete with DOC in the desorption solution only. In systems with DOC concentrations greater than 20 mg L-1, desorption reversibility was approached with equilibration time. However, in systems with 10 mg DOC L-1, desorption became more hysteretic with equilibration time. Thus, a threshold concentration of DOC (regardless of source) exists between 20 and 10 mg DOC L-1, influencing the sorption and desorption of the herbicides. Desorption of FLMT and NORP sorbed in the presence of DOC, occurred at a much faster rate than in the systems where DOC was absent during sorption. Poultry DOC promoted the greatest decrease in sorption and the greatest desorption, followed by dairy and NT DOC. The desorption of FLMT and NORP from SUB soil with 1150 mg poultry DOC L-1 in the desorption solution resulted in less herbicide sorption than at the onset of the desorption process, with only 920 mg poultry DOC L-1 in the sorption system. Perhaps, the desorption of herbicides in the presence of 1150 mg poultry DOC L-1 followed an sorption isotherm consistent with the presence of 1150 mg poultry DOC L-1 in the sorption solution. Dairy DOC facilitated the desorption of FLMT and NORP adsorbed in the presence of lesser concentrations of dairy DOC. Similarly, NT DOC resulted in less sorption of FLMT and NORP, and greater desorption of the herbicides. The greater SOM content of no-till systems results in greater sorption of FLMT and NORP. The addition of DOC to the systems results in reduced sorption of the herbicides. Desorption of FLMT and NORP exhibits hysteresis without added DOC. However, DOC concentrations greater than 10 mg L-1 enhance the desorption of FLMT and NORP from soil

Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices

Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker of two structures formed in CaCuO2 at the interface with SrTiO3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation

Effect of Al doping on the optical phonon spectrum in Mg(1-x)Al(x)B(2)

Raman and infrared absorption spectra of Mg(1-x)Al(x)B(2) have been collected for 0<x<0.5 in the spectral range of optical phonons. The x-dependence of the peak frequency, the width and the intensity of the observed Raman lines has been carefully analized. A peculiar x-dependence of the optical modes is pointed out for two different Al doping ranges. In particular the onset of the high-doping structural phase previously observed in diffraction measurements is marked by the appearence of new spectral components at high frequencies. A connection between the whole of our results and the observed suppression of superconductivity in the high doping region is established

Optical conductivity of CuO_2 infinite-layer films

The infrared conductivity of CaCuO_2, SrCuO_{2-y}, and Sr_{0.85}Nd_{0.15}CuO_2 infinite-layer films is obtained from reflectivity measurements by taking into account the substrate contribution. SrCuO_{2-y} and Sr_{0.85}Nd_{0.15}CuO_2 exhibit extra-phonon modes and structured bands in the midinfrared, not found in stoichiometric CaCuO_2. These features mirror those observed in the perovskitic cuprates, thus showing that the polaronic properties of high-T_c superconductors are intrinsic to the CuO_2 planes.Comment: File latex, 5 p. incl. 4 fig. in epsf. Submitted to Solid State Com

Far infrared properties of the rare-earth scandate DyScO3

We present reflectance measurements in the infrared region on a single crystal the rare earth scandate DyScO3. Measurements performed between room temperature and 10 K allow to determine the frequency of the infrared-active phonons, never investigated experimentally, and to get information on their temperature dependence. A comparison with the phonon peak frequency resulting from ab-initio computations is also provided. We finally report detailed data on the frequency dependence of the complex refractive index of DyScO3 in the terahertz region, which is important in the analysis of terahertz measurements on thin films deposited on DyScO3

The changing characteristics of patients with chronic hepatitis C prescribed direct acting antiviral medicines in general practice since listing of the medicines on the Australian Pharmaceutical Benefits Scheme

Background and Aim: The primary objective of this study was to determine whether the characteristics of patients prescribed direct acting antiviral (DAA) medicines have changed since initial listing of the medicines on the Australian Pharmaceutical Benefits Scheme (PBS). Methods: A cross-sectional study was conducted using data from MedicineInsight, an Australian database of general practice electronic health records, from March 2016 to August 2018. We compared sociodemographic, comorbidity, and clinical characteristics of patients aged at least 18 years who were prescribed at least one DAA in the first 4 months of PBS listing in 2016 with those prescribed at least one DAA in 2018. Results: There were 2251 eligible adult patients prescribed a DAA during the study period, 62% were men and 59% were aged 50 years and older. Patients prescribed DAA medicines initially were older (aged ≥50 years: 67.9% vs 49.3%; P 1 (20.4% vs 8.9%; P < 0.001) than those prescribed DAA medicines in 2018. A greater proportion of patients in regional/remote (46.5% vs 35.6%; P < 0.001) and socioeconomically disadvantaged areas (44.4% vs 34.5%; P = 0.003) accessed treatment in 2018 compared with 2016. Conclusions: Despite evidence of decreasing uptake of DAA medicines across Australia, this study indicates broadened uptake among younger age groups and those residing in regional/remote and socioeconomically disadvantaged areas since 2016. While uptake of DAA medicines in some population subgroups appears to have improved, continuous efforts to improve uptake across the Australian population are essential