Ferromagnetic resonance in periodic particle arrays

We report measurements of the ferromagnetic resonance (FMR) spectra of arrays of submicron size periodic particle arrays of permalloy produced by electron-beam lithography. In contrast to plane ferromagnetic films, the spectra of the arrays show a number of additional resonance peaks, whose position depends strongly on the orientation of the external magnetic field and the interparticle interaction. Time-dependent micromagnetic simulation of the ac response show that these peaks are associated with coupled exchange and dipolar spin wave modesComment: 4 pages, 4 figure

A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood

Full space velocities are computed for a sample of 130 nearby RR Lyrae variables using both ground-based and Hipparcos proper motions. In many cases proper motions from multiple sources have been averaged to produce a significant improvement in the transverse space velocity errors. In most cases, this exceeds the accuracy of Hipparcos proper motions alone. The velocity ellipsoids computed for halo and thick disk samples are in agreement with previous studies. No distinct sample of thin disk RR Lyraes has been isolated but there is kinematic evidence for some thin disk stars in our thick disk samples. A sample of 21 stars with [Fe/H] < -1.0 and disk-like kinematics have been isolated. It is concluded from their kinematics and spatial distribution that these stars represent a sample of RR Lyraes in the metal weak tail of the thick disk. In the halo samples the distribution of V velocities is not gaussian, even when the metal weak thick disk stars are removed. Also, a plot of U and W velocities as a function of V velocity for the kinematically unbiased halo sample shows some curious structure. The cause of these kinematic anomalies is not clear. In addition, systematic changes to the distance scale within the range of currently accepted values of Mv(RR) are shown to significantly change the calculated halo kinematics. Fainter values of Mv(RR), such as those obtained by statistical parallax (~ 0.60 to 0.70 at [Fe/H]=-1.9), result in local halo kinematics similar to those reported in independent studies of halo kinematics, while brighter values of Mv(RR), such as those obtained through recent analysis of Hipparcos subdwarf parallaxes (~ 0.30 to 0.40 at [Fe/H]=-1.9), result in a halo with retrograde rotation and significantly enlarged velocity dispersions.Comment: 40 pages (including tables), 7 PostScript figures, accepted for publication in the Astronomical Journa

Acceleration Schemes for Ab-Initio Molecular Dynamics and Electronic Structure Calculations

We study the convergence and the stability of fictitious dynamical methods for electrons. First, we show that a particular damped second-order dynamics has a much faster rate of convergence to the ground-state than first-order steepest descent algorithms while retaining their numerical cost per time step. Our damped dynamics has efficiency comparable to that of conjugate gradient methods in typical electronic minimization problems. Then, we analyse the factors that limit the size of the integration time step in approaches based on plane-wave expansions. The maximum allowed time step is dictated by the highest frequency components of the fictitious electronic dynamics. These can result either from the large wavevector components of the kinetic energy or from the small wavevector components of the Coulomb potential giving rise to the so called {\it charge sloshing} problem. We show how to eliminate large wavevector instabilities by adopting a preconditioning scheme that is implemented here for the first-time in the context of Car-Parrinello ab-initio molecular dynamics simulations of the ionic motion. We also show how to solve the charge-sloshing problem when this is present. We substantiate our theoretical analysis with numerical tests on a number of different silicon and carbon systems having both insulating and metallic character.Comment: RevTex, 9 figures available upon request, to appear in Phys. Rev.

Localization in non-chiral network models for two-dimensional disordered wave mechanical systems

Scattering theoretical network models for general coherent wave mechanical systems with quenched disorder are investigated. We focus on universality classes for two dimensional systems with no preferred orientation: Systems of spinless waves undergoing scattering events with broken or unbroken time reversal symmetry and systems of spin 1/2 waves with time reversal symmetric scattering. The phase diagram in the parameter space of scattering strengths is determined. The model breaking time reversal symmetry contains the critical point of quantum Hall systems but, like the model with unbroken time reversal symmetry, only one attractive fixed point, namely that of strong localization. Multifractal exponents and quasi-one-dimensional localization lengths are calculated numerically and found to be related by conformal invariance. Furthermore, they agree quantitatively with theoretical predictions. For non-vanishing spin scattering strength the spin 1/2 systems show localization-delocalization transitions.Comment: 4 pages, REVTeX, 4 figures (postscript

Relationship between Prenatal or Postnatal Exposure to Pesticides and Obesity: A Systematic Review

In recent years, the worldwide prevalence of overweight and obesity among adults and children has dramatically increased. The conventional model regarding the onset of obesity is based on an imbalance between energy intake and expenditure. However, other possible environmental factors involved, such as the exposure to chemicals like pesticides, cannot be discarded. These compounds could act as endocrine-disrupting chemicals (EDC) that may interfere with hormone activity related to several mechanisms involved in body weight control. The main objective of this study was to systematically review the data provided in the scientific literature for a possible association between prenatal and postnatal exposure to pesticides and obesity in offspring. A total of 25 human and 9 animal studies were analyzed. The prenatal, perinatal, and postnatal exposure to organophosphate, organochlorine, pyrethroid, neonicotinoid, and carbamate, as well as a combined pesticide exposure was reviewed. This systematic review reveals that the effects of pesticide exposure on body weight are mostly inconclusive, finding conflicting results in both humans and experimental animals. The outcomes reviewed are dependent on many factors, including dosage and route of administration, species, sex, and treatment duration. More research is needed to effectively evaluate the impact of the combined effects of different pesticides on human health.This study was supported by grants from the Spanish Government (Ministerio de Economía y Competitividad and Instituto Mixto de Investigación-Escuela Nacional de Sanidad (IMIENS)) and the Fondo Europeo de Desarrollo Regional (MINECO-FEDER) Grant numbers: PSI2017-90806-REDT, PSI2017-83038-P, PSI2017-83893-R, PSI2017-86396-P, PSI2017-86847-C2-2-R MINECO-FEDER, and IMIENS: PIC-IMIENS-2018-003.S

Exponential increase of plastic burial in mangrove sediments as a major plastic sink

© 2020 The Authors. Sequestration of plastics in sediments is considered the ultimate sink of marine plastic pollution that would justify unexpectedly low loads found in surface waters. Here, we demonstrate that mangroves, generally supporting high sediment accretion rates, efficiently sequester plastics in their sediments. To this end, we extracted microplastics from dated sediment cores of the Red Sea and Arabian Gulf mangrove (Avicennia marina) forests along the Saudi Arabian coast. We found that microplastics \u3c0.5 mm dominated in mangrove sediments, helping explain their scarcity, in surface waters. We estimate that 50 ± 30 and 110 ± 80 metric tons of plastic may have been buried since the 1930s in mangrove sediments across the Red Sea and the Arabian Gulf, respectively. We observed an exponential increase in the plastic burial rate (8.5 ± 1.2% year-1) since the 1950s in line with the global plastic production increase, confirming mangrove sediments as long-term sinks for plastics

ALMA images the many faces of the NGC 1068 torus and its surroundings

Aims. We investigate the fueling and the feedback of nuclear activity in the nearby (D = 14 Mpc) Seyfert 2 barred galaxy NGC 1068 by studying the distribution and kinematics of molecular gas in the torus and its connections to the host galaxy disk. Methods.We used the Atacama Large Millimeter Array (ALMA ) to image the emission of a set of molecular gas tracers in the circumnuclear disk (CND) and the torus of the galaxy using the CO(2-1), CO(3-2), and HCO+(4-3) lines and their underlying continuum emission with high spatial resolutions (0:0300 0:0900 \u27 26 pc). These transitions, which span a wide range of physical conditions of molecular gas (n(H2) 103107 cm3), are instrumental in revealing the density radial stratification and the complex kinematics of the gas in the torus and its surroundings. Results. The ALMA images resolve the CND as an asymmetric ringed disk of D \u27 400 pc in size and \u271:4 108 M in mass. The CND shows a marked deficit of molecular gas in its central \u27130 pc region. The inner edge of the ring is associated with the presence of edge-brightened arcs of NIR polarized emission, which are identified with the current working surface of the ionized wind of the active galactic nucleus (AGN). ALMA proves the existence of an elongated molecular disk/torus in NGC 1068 of Mgas torus \u27 3 105 M, which extends over a large range of spatial scales D \u27 1030 pc around the central engine. The new observations evidence the density radial stratification of the torus: the HCO+(4-3) torus, with a full size DHCO+(43) = 11 0:6 pc, is a factor of between two and three smaller than its CO(2-1) and CO(3-2) counterparts, which have full sizes of DCO(32) = 26 0:6 pc and DCO(21) = 28 0:6 pc, respectively. This result brings into light the many faces of the molecular torus. The torus is connected to the CND through a network of molecular gas streamers detected inside the CND ring. The kinematics of molecular gas show strong departures from circular motions in the torus, the gas streamers, and the CND ring. These velocity field distortions are interconnected and are part of a 3D outflow that reflects the eects of AGN feedback on the kinematics of molecular gas across a wide range of spatial scales around the central engine. In particular, we estimate through modeling that a significant fraction of the gas inside the torus (\u270:40:6 Mgas torus) and a comparable amount of mass along the gas streamers are outflowing. However, the bulk of the mass, momentum, and energy of the molecular outflow of NGC 1068 is contained at larger radii in the CND region, where the AGN wind and the radio jet are currently pushing the gas assembled at the Inner Lindblad Resonance (ILR) ring of the nuclear stellar bar. Conclusions. In our favored scenario a wide-angle AGN wind launched from the accretion disk of NGC1068 is currently impacting a sizable fraction of the gas inside the torus. However, a large gas reservoir (\u271:21:8 105 M), which lies close to the equatorial plane of the torus, remains unaected by the feedback of the AGN wind and can therefore continue fueling the AGN for at least \u2714 Myr. Nevertheless, AGN fueling currently seems thwarted on intermediate scales (15 pc r 50 pc)

Impact of COVID-19 on quality of life in Peruvian older adults: construct validity, reliability and invariance of the COV19-Impact on Quality of Life (COV19-QoL) measurement

The aim of the present study was to translate into Spanish and evaluate the psychometric evidence of the Impact on Quality of Life (COV19-QoL) applied to a sample of Peruvian older adults (N = 298; 58.1% women, 41.9% men, mean age 65.34 years [SD = 11.33]). The study used techniques from the Classical Test Theory (CTT) and Item Response Theory (IRT). The findings confirmed the single factor structure of the COV19-QoL, high internal consistency reliability, measurement invariance by gender, and all items demonstrated adequate discrimination and difficulty indices. In this sense, the items allow adequate discrimination between low, medium and high levels of the impact of the COVID-19 pandemic on quality of life. In addition, a greater perceived impact of the pandemic on quality of life is necessary to answer the higher response options of the COV19-QoL. In conclusion, the COV19-QoL is a valid measurement scale of the impact of the COVID-19 pandemic on the quality of life of Peruvian older adults

Influence of Polymorphisms Involved in Platelet Activation and Inflammatory Response on Aspirin-Related Upper Gastrointestinal Bleeding: A Case-Control Study

Background: Despite the wide benefits of aspirin and its cost-effectiveness, aspirin prescriptions have been reduced due to idiosyncratic responses in susceptible individuals. Low-dose aspirin and single-nucleotide polymorphisms (SNPs) are independently associated with increased risk of gastrointestinal hemorrhage; however, to-date, no studies investigated the SNP-aspirin interaction effect on upper gastrointestinal hemorrhage (UGIH). Therefore, we aimed to evaluate the role of 25 SNPs in multiple genes involved in platelet activation, angiogenesis and inflammatory response in aspirin-related UGIH. Methods: A multicenter, full case-control study was conducted in patients exposed and unexposed to aspirin. Three hundred twenty-six cases diagnosed with UGIH were matched with 748 controls (1:3) by age, gender, health center, and recruitment date. Only adults of European origin were included. Participants were stratified by aspirin exposure and genotype [(Aspirin(-), wild-type), (Aspirin(+), wild-type), (Aspirin(+), genetic variation), (Aspirin(-), genetic variation)]. For each SNP, the Odds Ratio of UGIH and their 95% confidence intervals were estimated in each subgroup by using the generalized linear mixed models for dependent binomial variables. SNP-aspirin interaction effect was estimated through Relative Excess Risk due to Interaction (RERI) measures. Results: We observed two categories of SNPs that might modify the risk magnitude of UGIH in aspirin consumers. Seven SNPs (rs1387180 A > G, rs2238631 T > C, rs1799964 T > C, rs5050 T > C/T > G, rs689466 T > C, rs1799983 T > A/T > G, and rs7756935 C > A) were "positive modifiers" associated with an excess of risk from aspirin exposure and carrying that genetic variation (1.75 T, rs1131882 G > A, rs4311994 C > T, rs10120688 G > A, rs4251961 T > C, rs3778355 G > C, rs1330344 C > T, rs5275 A > G/A > T, and rs3779647 C > T) were "negative modifiers" and associated with a reduced risk in aspirin users (-2.74 </= RERI </= -0.95). Conclusion: This preliminary study suggests that polymorphisms in genes involved in platelets activity, angiogenesis and inflammatory response might modify the risk of aspirin-related UGIH. Further studies with larger sample size and in different populations are needed to confirm our findings. If confirmed, this might have great impact on public health, thanks to aspirin's prophylactic properties in diseases of high incidence and severity

Payments for ecosystem services in the tropics: a closer look at effectiveness and equity

We undertake a review of academic literature that examines the effectiveness and equity-related performance of PES initiatives targeting biodiversity conservation in tropical and sub-tropical countries. We investigate the key features of such analyses as regards their analytical and methodological approach and we identify emerging lessons from PES practice, leading to a new suggested research agenda. Our results indicate that analyses of PES effectiveness have to date focused on either ecosystem service provision or habitat proxies, with only half of them making explicit assessment of additionality and most describing that payments have been beneficial for land cover and biodiversity. Studies evaluating the impact of PES on livelihoods suggest more negative outcomes, with an uneven treatment of the procedural and distributive considerations of scheme design and payment distribution, and a large heterogeneity of evaluative frameworks. We propose an agenda for future PES research based on the emerging interest in assessing environmental outcomes more rigorously and documenting social impacts in a more comparative and contextually situated form