Classical simulation of noninteracting-fermion quantum circuits

We show that a class of quantum computations that was recently shown to be efficiently simulatable on a classical computer by Valiant corresponds to a physical model of noninteracting fermions in one dimension. We give an alternative proof of his result using the language of fermions and extend the result to noninteracting fermions with arbitrary pairwise interactions, where gates can be conditioned on outcomes of complete von Neumann measurements in the computational basis on other fermionic modes in the circuit. This last result is in remarkable contrast with the case of noninteracting bosons where universal quantum computation can be achieved by allowing gates to be conditioned on classical bits (quant-ph/0006088).Comment: 26 pages, 1 figure, uses wick.sty; references added to recent results by E. Knil

Nitrous oxide fluxes and nitrogen cycling along a pasture chronosequence in Central Amazonia, Brazil

International audienceWe studied nitrous oxide (N2O) fluxes and soil nitrogen (N) cycling following forest conversion to pasture in the central Amazon near Santarém, Pará, Brazil. Two undisturbed forest sites and 27 pasture sites of 0.5 to 60 years were sampled once each during wet and dry seasons. In addition to soil-atmosphere fluxes of N2O we measured 27 soil chemical, soil microbiological and soil physical variables. Soil N2O fluxes were higher in the wet season than in the dry season. Fluxes of N2O from forest soils always exceeded fluxes from pasture soils and showed no consistent trend with pasture age. At our forest sites, nitrate was the dominant form of inorganic N both during wet and dry season. At our pasture sites nitrate generally dominated the inorganic N pools during the wet season and ammonium dominated during the dry season. Net mineralization and nitrification rates displayed large variations. During the dry season net immobilization of N was observed in some pastures. Compared to forest sites, young pasture sites (?2 years) had low microbial biomass N and protease activities. Protease activity and microbial biomass N peaked in pastures of intermediate age (4 to 8 years) followed by consistently lower values in older pasture (10 to 60 years). The C/N ratio of litter was low at the forest sites (~25) and rapidly increased with pasture age reaching values of 60-70 at pastures of 15 years and older. Nitrous oxide emissions at our sites were controlled by C and N availability and soil aeration. Fluxes of N2O were negatively correlated to leaf litter C/N ratio, NH4+-N and the ratio of NO3--N to the sum of NO3--N + NH4+-N (indicators of N availability), and methane fluxes and bulk density (indicators of soil aeration status) during the wet season. During the dry season fluxes of N2O were positively correlated to microbial biomass N, ?-glucosidase activity, total inorganic N stocks and NH4+-N. In our study region, pastures of all age emitted less N2O than old-growth forests, because of a progressive decline in N availability with pasture age combined with strongly anaerobic conditions in some pastures during the wet season

Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: I. Magnetospheric Flow at Different Theta

We present results of fully three-dimensional MHD simulations of disk accretion to a rotating magnetized star with its dipole moment inclined at an angle Theta to the rotation axis of the disk. We observed that matter accretes from the disk to a star in two or several streams depending on Theta. Streams may precess around the star at small Theta. The inner regions of the disk are warped. The warping is due to the tendency of matter to co-rotate with inclined magnetosphere. The accreting matter brings positive angular momentum to the (slowly rotating) star tending to spin it up. The corresponding torque N_z depends only weakly on Theta. The angular momentum flux to the star is transported predominantly by the magnetic field; the matter component contributes < 1 % of the total flux. Results of simulations are important for understanding the nature of classical T Tauri stars, cataclysmic variables, and X-ray pulsars.Comment: 26 pages, 22 figures, LaTeX, macros: emulapj.sty, avi simulations are available at http://www.astro.cornell.edu/us-rus/inclined.ht

Influence of human impact and bedrock differences on the vegetational history of the Insubrian Southern Alps

Vegetation history for the study region is reconstructed on the basis of pollen, charcoal and AMS14C investigations of lake sediments from Lago del Segrino (calcareous bedrock) and Lago di Muzzano (siliceous bedrock). Late-glacial forests were characterised byBetula andPinus sylvestris. At the beginning of the Holocene they were replaced by temperate continental forest and shrub communities. A special type of temperate lowland forest, withAbies alba as the most important tree, was present in the period 8300 to 4500 B.P. Subsequently,Fagus, Quercus andAlnus glutinosa were the main forest components andA. alba ceased to be of importance.Castanea sativa andJuglans regia were probably introduced after forest clearance by fire during the first century A.D. On soils derived from siliceous bedrock,C. sativa was already dominant at ca. A.D. 200 (A.D. dates are in calendar years). In limestone areas, however,C. sativa failed to achieve a dominant role. After the introduction ofC. sativa, the main trees were initially oak (Quercus spp.) and later the walnut (Juglans regia). Ostrya carpinifolia became the dominant tree around Lago del Segrino only in the last 100-200 years though it had spread into the area at ca. 5000 cal. B.C. This recent expansion ofOstrya is confirmed at other sites and appears to be controlled by human disturbances involving especially clearance. It is argued that these forests should not be regarded as climax communities. It is suggested that under undisturbed succession they would develop into mixed deciduous forests consisting ofFraxinus excelsior, Tilia, Ulmus, Quercus andAce

A Secondary Analysis of a Randomized Clinical Trial

This work is licensed under a Creative Commons Attribution 4.0 International License.Importance The blood pressure–lowering property of docosahexaenoic acid (DHA) in children and adults is known, and an observational study from the Netherlands has linked higher intrauterine DHA exposure to lower childhood blood pressure. However, the association of prenatal intake of DHA supplement with childhood blood pressure has not been evaluated in randomized clinical trials. Objective To determine the effect of DHA supplementation during pregnancy on childhood blood pressure. Design, Setting, and Participants This prespecified secondary analysis of the Kansas University DHA Outcome Study (KUDOS), a phase 3, double-blind, randomized, placebo-controlled clinical trial was conducted at several local hospitals in the Kansas City, Kansas, metropolitan area. Pregnant women (n = 350) were enrolled in the KUDOS trial between January 10, 2006, and November 17, 2009, and were followed up until their children were 18 months of age. During pregnancy, the women received either 3 capsules per day of placebo or 600 mg per day of DHA from a mean (SD) of 14.5 (3.7) weeks’ (all before 20 weeks) gestation until birth. The parents of 190 children consented to additional follow-up of their children until 6 years, which ended April 29, 2016. Study personnel involved in testing were blind to the randomization until all children had completed the trial. Data analysis was performed from May 23, 2017, to July 10, 2018. Interventions Pregnant women were assigned to either 600 mg per day of DHA or a placebo that was half soy and half corn oil. Both placebo and DHA were provided in 3 capsules per day. Main Outcomes and Measures Childhood blood pressure was a planned secondary outcome of a study powered to measure cognitive development. The hypothesis was that DHA would lower blood pressure prior to data analysis. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured at 4, 4.5, 5, 5.5, and 6 years and were analyzed for possible covariates using mixed models to generate a final model. Results In total, 171 children (88 [51.5%] female) were included in this analysis. Of these children, 89 (52.0%) were randomized to the DHA group and 82 (47.9%) to the placebo group. A statistically significant interaction was found between treatment (placebo or DHA) and child weight status (5-year body mass index ≤85th or >85th percentile) for both SBP and DBP. Children who were overweight or obese whose mothers received placebo during pregnancy had higher SBP and DBP compared with children who were overweight or obese whose mothers received DHA (mean [SE] SBP, 104.28 [1.37] mm Hg vs 100.34 [1.02] mm Hg; DBP, 64.7 [1.23] mm Hg vs 59.76 [0.91] mm Hg). No differences in the SBP and DBP were found between children who were overweight or obese whose mothers received DHA and children who were not overweight or obese. In the mixed model analysis, the child’s age at blood pressure measurement and the maternal prepregnancy body mass index were the only other statistically significant variables (child age, SBP: F = 7.385; P = .001; DBP: F = 7.39; P = .001; prepregnancy BMI, SBP: r = 0.284; P = .001; DBP: r = 0.216; P = .01). Conclusions and Relevance Maternal docosahexaenoic acid intake during pregnancy appeared to mitigate the association between childhood overweight condition or obesity and blood pressure

The Physical Principles of Quantum Mechanics. A critical review

The standard presentation of the principles of quantum mechanics is critically reviewed both from the experimental/operational point and with respect to the request of mathematical consistency and logical economy. A simpler and more physically motivated formulation is discussed. The existence of non commuting observables, which characterizes quantum mechanics with respect to classical mechanics, is related to operationally testable complementarity relations, rather than to uncertainty relations. The drawbacks of Dirac argument for canonical quantization are avoided by a more geometrical approach.Comment: Bibliography and section 2.1 slightly improve

Exact spinor-scalar bound states in a QFT with scalar interactions

We study two-particle systems in a model quantum field theory, in which scalar particles and spinor particles interact via a mediating scalar field. The Lagrangian of the model is reformulated by using covariant Green's functions to solve for the mediating field in terms of the particle fields. This results in a Hamiltonian in which the mediating-field propagator appears directly in the interaction term. It is shown that exact two-particle eigenstates of the Hamiltonian can be determined. The resulting relativistic fermion-boson equation is shown to have Dirac and Klein-Gordon one-particle limits. Analytic solutions for the bound state energy spectrum are obtained for the case of massless mediating fields.Comment: 12 pages, RevTeX, 1 figur