4,375 research outputs found

    Galactic Populations of Ultracompact Binaries

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    Recent RXTE and Chandra discoveries of low mass X-ray binaries with ultra-short orbital periods have initiated theoretical work on the origins of these peculiar systems. Using the StarTrack population synthesis code the formation and evolution of X-ray ultracompact binaries (UCBs) in the Galactic field are analyzed. The relative number of UCBs with a neutron star or a black hole accretor populating our Galaxy is predicted. Our results demonstrate that standard evolutionary scenarios involving primordial binaries can be sufficient to produce the UCBs in the Galactic field without requiring additional processes associated with the dense stellar environments in the cores of globular clusters. In contrast to previous studies we find that the majority of the immediate progenitors of these systems consist of a hydrogen exhausted donor with an ONeMg white dwarf. The evolution of these systems leads to the accretion induced collapse of the white dwarf to a neutron star, which can play an important role in the formation of a majority of Galactic UCBs. We predict that with an increase in the number of X-ray active UCBs hosting neutron stars by an order of magnitude, a system with a black hole accretor may be found.Comment: 9 pages, 2 figures, Astrophysical Journal, accepted (significant additions

    Modeling impacts of farming management alternatives on CO2, CH4, and N2O emissions: A case study for water management of rice agriculture of China

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    Since the early 1980s, water management of rice paddies in China has changed substantially, with midseason drainage gradually replacing continuous flooding. This has provided an opportunity to estimate how a management alternative impacts greenhouse gas emissions at a large regional scale. We integrated a process-based model, DNDC, with a GIS database of paddy area, soil properties, and management factors. We simulated soil carbon sequestration (or net CO2 emission) and CH4 and N2O emissions from China\u27s rice paddies (30 million ha), based on 1990 climate and management conditions, with two water management scenarios: continuous flooding and midseason drainage. The results indicated that this change in water management has reduced aggregate CH4 emissions about 40%, or 5 Tg CH4 yr−1, roughly 5–10% of total global methane emissions from rice paddies. The mitigating effect of midseason drainage on CH4 flux was highly uneven across the country; the highest flux reductions (\u3e200 kg CH4-C ha−1 yr−1) were in Hainan, Sichuan, Hubei, and Guangdong provinces, with warmer weather and multiple-cropping rice systems. The smallest flux reductions (\u3c25 kg CH4-C ha−1 yr−1) occurred in Tianjin, Hebei, Ningxia, Liaoning, and Gansu Provinces, with relatively cool weather and single cropping systems. Shifting water management from continuous flooding to midseason drainage increased N2O emissions from Chinese rice paddies by 0.15 Tg N yr−1 (∼50% increase). This offset a large fraction of the greenhouse gas radiative forcing benefit gained by the decrease in CH4 emissions. Midseason drainage-induced N2O fluxes were high (\u3e8.0 kg N/ha) in Jilin, Liaoning, Heilongjiang, and Xinjiang provinces, where the paddy soils contained relatively high organic matter. Shifting water management from continuous flooding to midseason drainage reduced total net CO2emissions by 0.65 Tg CO2-C yr−1, which made a relatively small contribution to the net climate impact due to the low radiative potential of CO2. The change in water management had very different effects on net greenhouse gas mitigation when implemented across climatic zones, soil types, or cropping systems. Maximum CH4 reductions and minimum N2O increases were obtained when the mid-season draining was applied to rice paddies with warm weather, high soil clay content, and low soil organic matter content, for example, Sichuan, Hubei, Hunan, Guangdong, Guangxi, Anhui, and Jiangsu provinces, which have 60% of China\u27s rice paddies and produce 65% of China\u27s rice harvest

    Reduced methane emissions from large-scale changes in water management of China’s rice paddies during 1980-2000

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    Decreased methane emissions from paddy rice may have contributed to the decline in the rate of increase of global atmospheric methane (CH4) concentration over the last 20 years. In China, midseason paddy drainage, which reduces growing season CH4 fluxes, was first implemented in the early 1980s, and has gradually replaced continuous flooding in much of the paddy area. We constructed a regional prediction for China\u27s rice paddy methane emissions using the DNDC biogeochemical model. Results of continuous flooding and midseason drainage simulations for all paddy fields in China were combined with regional scenarios for the timing of the transition from continuous flooding to predominantly mid-season drainage to generate estimates of total methane flux for 1980–2000. CH4 emissions from China\u27s paddy fields were reduced over that period by ∼5 Tg CH4 yr−1

    Solid-state electric double layer capacitors for ac line-filtering

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    Ultra-fast solid electric double layer capacitors (EDLCs) have been developed in both sandwich and planar interdigitated configurations using vertically-oriented graphene nanosheet (VOGN) electrodes with a hydroxide ion-conducting tetraethylammonium hydroxide (TEAOH)-polyvinyl alcohol (PVA) polymer electrolyte. These solid-state EDLCs could be scanned at a rate of 1000 Vs(-1) in cyclic voltammetry and demonstrated response times of less than 1 ms. They retained high performance over 18 months of shelf storage and after 100,000 charge/discharge cycles with limited packaging, demonstrating the high stability of TEAOH-PVA electrolyte. The solid-state capacitors are capable of performing at elevated temperatures and have demonstrated a response time of 0.35 ms at 90 degrees C. Given their ultra-fast rate capability, excellent shelf-life and cycle life, and excellent temperature stability, these solid-state EDLCs are promising smaller and lighter alternatives to the bulky electrolytic capacitors now used for ac line-filtering. (C) 2016 Elsevier B.V. All rights reserved

    A cusp electron gun for millimeter wave gyrodevices

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    The experimental results of a thermionic cusp electron gun, to drive millimeter and submillimeter wave harmonic gyrodevices, are reported in this paper. Using a "smooth" magnetic field reversal formed by two coils this gun generated an annular-shaped, axis-encircling electron beam with 1.5 A current, and an adjustable velocity ratio alpha of up to 1.56 at a beam voltage of 40 kV. The beam cross-sectional shape and transported beam current were measured by a witness plate technique and Faraday cup, respectively. These measured results were found to be in excellent agreement with the simulated results using the three-dimensional code MAGIC

    Integrated IMU and radiolocation-based navigation using a Rao-Blackwellized particle filter

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    In this paper, we develop a cooperative IMU/radio-location-based navigation system, where each node tracks the location not only based on its own measurements, but also via collaboration with neighbor nodes. The key problem is to design a nonlinear filter to fuse IMU and radiolocation information. We apply the Rao-Blackwellization method by using a particle filter and parallel Kalman filters for the estimation of orientation and other states (i.e., position, velocity, etc.), respectively. The proposed method significantly outperforms the extended Kalman filter (EKF) in the set of simulations here.National Science Foundation (U.S.) (Grant ECCS-0901034)United States. Office of Naval Research (Grant N00014-11-1-0397)Defense University Research Instrumentation Program (U.S.) (Grant N00014-08-1-0826)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie

    A smartphone localization algorithm using RSSI and inertial sensor measurement fusion

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    Indoor navigation using the existing wireless infrastructure and mobile devices is a very active research area. The major challenge is to leverage the extensive smartphone sensor suite to achieve location tracking with high accuracy. In this paper, we develop a navigation algorithm which fuses the WiFi received signal strength indicator (RSSI) and smartphone inertial sensor measurements. A sequential Monte Carlo filter is developed for inertial sensor based tracking, and a radiolocation algorithm is developed to infer mobile location based on RSSI measurements. The simulation results show that the proposed algorithm significantly outperforms the extended Kalman filter (EKF), and achieves competitive location accuracy compared with the round trip time (RTT) based ultra-wideband (UWB) system.National Science Foundation (U.S.) (Grant ECCS-0901034)United States. Office of Naval Research (Grant N00014-11-1-0397)Defense University Research Instrumentation Program (U.S.) (Grant N00014-08-1-0826)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie

    Molecular Motions of the Outer Ring of Charge of the Sodium Channel: Do They Couple to Slow Inactivation?

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    In contrast to fast inactivation, the molecular basis of sodium (Na) channel slow inactivation is poorly understood. It has been suggested that structural rearrangements in the outer pore mediate slow inactivation of Na channels similar to C-type inactivation in potassium (K) channels. We probed the role of the outer ring of charge in inactivation gating by paired cysteine mutagenesis in the rat skeletal muscle Na channel (rNav1.4). The outer charged ring residues were substituted with cysteine, paired with cysteine mutants at other positions in the external pore, and coexpressed with rat brain β1 in Xenopus oocytes. Dithiolthreitol (DTT) markedly increased the current in E403C+E758C double mutant, indicating the spontaneous formation of a disulfide bond and proximity of the α carbons of these residues of no more than 7 Å. The redox catalyst Cu(II) (1,10-phenanthroline)3 (Cu(phe)3) reduced the peak current of double mutants (E403C+E758C, E403C+D1241C, E403C+D1532C, and D1241C+D1532C) at a rate proportional to the stimulation frequency. Voltage protocols that favored occupancy of slow inactivation states completely prevented Cu(phe)3 modification of outer charged ring paired mutants E403C+E758C, E403C+D1241C, and E403C+D1532C. In contrast, voltage protocols that favored slow inactivation did not prevent Cu(phe)3 modification of other double mutants such as E403C+W756C, E403C+W1239C, and E403C+W1531C. Our data suggest that slow inactivation of the Na channel is associated with a structural rearrangement of the outer ring of charge
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