Extreme deuterium enrichment in stratospheric hydrogen and the global atmospheric budget of H_2

Molecular hydrogen (H_2) is the second most abundant trace gas in the atmosphere after methane (CH_4). In the troposphere, the D/H ratio of H_2 is enriched by 120‰ relative to the world's oceans. This cannot be explained by the sources of H_2 for which the D/H ratio has been measured to date (for example, fossil fuels and biomass burning). But the isotopic composition of H_2 from its single largest source—the photochemical oxidation of methane—has yet to be determined. Here we show that the D/H ratio of stratospheric H2 develops enrichments greater than 440‰, the most extreme D/H enrichment observed in a terrestrial material. We estimate the D/H ratio of H_2 produced from CH_4 in the stratosphere, where production is isolated from the influences of non-photochemical sources and sinks, showing that the chain of reactions producing H_2 from CH_4 concentrates D in the product H_2. This enrichment, which we estimate is similar on a global average in the troposphere, contributes substantially to the D/H ratio of tropospheric H_2

Finite temperature quantum simulation of stabilizer Hamiltonians

We present a scheme for robust finite temperature quantum simulation of stabilizer Hamiltonians. The scheme is designed for realization in a physical system consisting of a finite set of neutral atoms trapped in an addressable optical lattice that are controllable via 1- and 2-body operations together with dissipative 1-body operations such as optical pumping. We show that these minimal physical constraints suffice for design of a quantum simulation scheme for any stabilizer Hamiltonian at either finite or zero temperature. We demonstrate the approach with application to the abelian and non-abelian toric codes.Comment: 13 pages, 2 figure

Instantons and Yang-Mills Flows on Coset Spaces

We consider the Yang-Mills flow equations on a reductive coset space G/H and the Yang-Mills equations on the manifold R x G/H. On nonsymmetric coset spaces G/H one can introduce geometric fluxes identified with the torsion of the spin connection. The condition of G-equivariance imposed on the gauge fields reduces the Yang-Mills equations to phi^4-kink equations on R. Depending on the boundary conditions and torsion, we obtain solutions to the Yang-Mills equations describing instantons, chains of instanton-anti-instanton pairs or modifications of gauge bundles. For Lorentzian signature on R x G/H, dyon-type configurations are constructed as well. We also present explicit solutions to the Yang-Mills flow equations and compare them with the Yang-Mills solutions on R x G/H.Comment: 1+12 page

Comparison of Vaginal Hysterectomy Techniques and Interventions for Benign Indications: A Systematic Review

OBJECTIVE: To create evidence-based clinical practice guidelines based on a systematic review of published literature regarding the risks and benefits of available preoperative, intraoperative, and postoperative technical steps and interventions at the time of vaginal hysterectomy for benign indications. DATA SOURCES: We systematically searched the literature to identify studies that compared technical steps or interventions during the preoperative, intraoperative, and postoperative periods surrounding vaginal hysterectomy. We searched MEDLINE, Cochrane Central Register of Controlled Trials, Health Technology Assessments, and ClinicalTrials.gov from their inception until April 10, 2016, using the MeSH term "Hysterectomy, Vaginal" and associated text words. We included comparative studies, single-group studies, and systematic reviews published in English. METHODS OF STUDY SELECTION: We double-screened 4,250 abstracts, identifying 60 eligible studies. Discrepancies were adjudicated by a third reviewer. We followed standard systematic review methodology and the Grades for Recommendation, Assessment, Development and Evaluation approach to evaluate the evidence and generate guideline recommendations. TABULATION, INTEGRATION, AND RESULTS: Because of limited literature, only 16 perioperative risks, technical steps, and interventions were identified: obesity, large uteri, prior surgery, gonadotropin-releasing hormone agonists, vaginal antisepsis, bilateral salpingo-oophorectomy, morcellation, apical closure, uterine sealers, hemostatic injectants, hot cone, retractor, cystoscopy, vaginal packing, bladder management, and accustimulation. We organized and reported these as four domains: patient selection, preoperative, intraoperative, and postoperative. We did not identify any patient characteristics precluding a vaginal approach; chlorhexidine or povidone is appropriate for vaginal antisepsis; vasopressin decreases blood loss by 130 cc; tissue-sealing devices decrease blood loss by 44 cc and operative time by 15 minutes with uncertain complication implications; vertical cuff closure results in 1-cm increased vaginal length; either peritoneum or epithelium can be used for colpotomy closure; and routine vaginal packing is not advised. CONCLUSION: Minimal data exist to guide surgeons with respect to planning and performing a vaginal hysterectomy. This study identifies available information and future areas for investigation

Converting simulated total dry matter to fresh marketable yield for field vegetables at a range of nitrogen supply levels

Simultaneous analysis of economic and environmental performance of horticultural crop production requires qualified assumptions on the effect of management options, and particularly of nitrogen (N) fertilisation, on the net returns of the farm. Dynamic soil-plant-environment simulation models for agro-ecosystems are frequently applied to predict crop yield, generally as dry matter per area, and the environmental impact of production. Economic analysis requires conversion of yields to fresh marketable weight, which is not easy to calculate for vegetables, since different species have different properties and special market requirements. Furthermore, the marketable part of many vegetables is dependent on N availability during growth, which may lead to complete crop failure under sub-optimal N supply in tightly calculated N fertiliser regimes or low-input systems. In this paper we present two methods for converting simulated total dry matter to marketable fresh matter yield for various vegetables and European growth conditions, taking into consideration the effect of N supply: (i) a regression based function for vegetables sold as bulk or bunching ware and (ii) a population approach for piecewise sold row crops. For both methods, to be used in the context of a dynamic simulation model, parameter values were compiled from a literature survey. Implemented in such a model, both algorithms were tested against experimental field data, yielding an Index of Agreement of 0.80 for the regression strategy and 0.90 for the population strategy. Furthermore, the population strategy was capable of reflecting rather well the effect of crop spacing on yield and the effect of N supply on product grading

Yang-Mills instantons and dyons on homogeneous G_2-manifolds

We consider Lie G-valued Yang-Mills fields on the space R x G/H, where G/H is a compact nearly K"ahler six-dimensional homogeneous space, and the manifold R x G/H carries a G_2-structure. After imposing a general G-invariance condition, Yang-Mills theory with torsion on R x G/H is reduced to Newtonian mechanics of a particle moving in R^6, R^4 or R^2 under the influence of an inverted double-well-type potential for the cases G/H = SU(3)/U(1)xU(1), Sp(2)/Sp(1)xU(1) or G_2/SU(3), respectively. We analyze all critical points and present analytical and numerical kink- and bounce-type solutions, which yield G-invariant instanton configurations on those cosets. Periodic solutions on S^1 x G/H and dyons on iR x G/H are also given.Comment: 1+26 pages, 14 figures, 6 miniplot

Tuning strategy for Curie-temperature enhancement in the van der Waals magnet Mn_1+xSb_2−xTe₄

The van-der-Waals antiferromagnetic topological insulator MnBi2Te4 is one of the few materials that realize the sought-after quantum anomalous Hall (QAH) state and quantized surface charge transport. To assess the relevance of its isostructural analog MnSb2Te4 as a potential QAH candidate, the roles of Mn/Sb site mixing and cationic vacancies need to be clarified. Recent findings have shown that non-stoichiometry in Mn1±xSb2∓xTe4 is an efficient tuning knob to achieve a net spin-polarized state and to raise the magnetic ordering temperature well above that of MnBi2Te4. Here, we report the crystal structure, the bulk and the surface magnetism of two new Mn1+xSb2−xTe4 samples: Mn1.08Sb1.92Te4(x ≈ 0.1) with TC = 44 K, and Mn2.01Sb1.19Te4(x ≈ 1.0) with the record TC = 58 K. We quantify the site mixing comprehensively by combining various structural probes on powders and single crystals, and then employ bulk, local (electron spin resonance), and spectroscopic (x-ray magnetic circular dichroism) probes to connect these insights to the magnetism of these materials. We demonstrate that Mn over-stoichiometry up to x = 1.0, in combination with a particular Mn/Sb intermixing pattern and the increasingly three-dimensional character of the magnetic order, push the TC upwards. The tendency towards more robust ferromagnetism mediated by stronger interlayer exchange in Mn1+xSb2−xTe4 upon increasing x is confirmed by bulk magnetometry and by a series of density-functional-theory calculations of model structures with varying intermixing.</p

Enabling HCCI modeling: The RIOT/CMCS Web Service for Automatic Reaction Mechanism Reduction

New approaches are being developed to facilitate multidisciplinary collaborative research of Homogeneous Charge Compression Ignition (HCCI) combustion processes. In this paper, collaborative sharing of the Range Identification and Optimization Toolkit (RIOT) and related data and models is discussed. RIOT is a developmental approach to reduce the computational complexity of detailed chemical kinetic mechanisms, enabling their use in modeling kinetically-controlled combustion applications such as HCCI. These approaches are being developed and piloted as a part of the Collaboratory for Multiscale Chemical Sciences (CMCS) project. The capabilities of the RIOT code are shared through a portlet in the CMCS portal that allows easy specification and processing of RIOT inputs, remote execution of RIOT, tracking of data pedigree and translation of RIOT outputs (such as the reduced model) to a table view and to the commonly-used CHEMKIN mechanism format. The reduced model is thus immediately ready to be used for more efficient simulation of the chemically reacting system of interest. This effort is motivated by the need to improve computational efficiency in modeling HCCI systems. Preliminary use of the web service to obtain reduced models for this application has yielded computational speedup factors of up to 20 as presented in this paper