A bipolar outflow from the massive protostellar core W51e2-E

We present high resolution images of the bipolar outflow from W51e2, which are produced from the Submillimeter Array archival data observed for CO(3-2) and HCN(4-3) lines with angular resolutions of 0.8" x 0.6" and 0.3" x 0.2", respectively. The images show that the powerful outflow originates from the protostellar core W51e2-E rather than from the ultracompact HII region W51e2-W. The kinematic timescale of the outflow from W51e2-E is about 1000 yr, younger than the age (~5000 yr) of the ultracompact HII region W51e2-W. A large mass loss rate of ~1 x 10^{-3} M_sun yr^{-1} and a high mechanical power of 120 L_sun are inferred, suggesting that an O star or a cluster of B stars are forming in W51e2-E. The observed outflow activity along with the inferred large accretion rate indicates that at present W51e2-E is in a rapid phase of star formation.Comment: 5 pages, 2 figures, 1 table, accepted for publication in ApJL. v2: some typos correcte

Magnetic structure of our Galaxy: A review of observations

The magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of uG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.Comment: 10+1 pages. Invited Review for IAU Symp.259: Cosmic Magnetic Fields: From Planets, to Stars and Galaxies (Tenerife, Spain. Nov.3-7, 2009). K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman (eds.

AXPs & SGRs: Magnetar or Quarctar?

The concept of a "magnetar" was proposed mainly because of two factors. First, the X-ray luminosity of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Ray Repeaters (SGRs) is larger than the rotational energy loss rate, and second, the magnetic field strength calculated from "normal method" is super strong. It is proposed that the radiation energy of magnetar comes from its magnetic fields. Here it is argued that the magnetic field strength calculated through the normal method is incorrect when X-ray luminosity is larger than rotational energy loss rate, because the wind braking is not taken into account. Besides, the "anti-magnetar" and some other X-ray and radio observations are difficult to understand with a magnetar model. Instead of the magnetar, we propose a "quarctar", which is a crusted quark star in an accretion disk, to explain the observations. In this model, the persistent X-ray emission, burst luminosity, spectrum of AXPs and SGRs can be understood naturally. The radio-emitting AXPs, which are challenging the magnetar, can also be explained by the quarctar model.Comment: Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and Opportunities after 80 years", J. van Leeuwen (ed.); 3 pages, 1 figur

Experimental investigation performance and emission of hydrotreated pyrolysis oil in a heavy-duty engine with EGR

Drop-in biofuels can play an important role in the transition from fossil-based fuels to carbon-neutral energy carriers. This work focuses on performance and emission of hydrotreated pyrolysis oil (HPO) for heavy-duty (HD) engines application. The HPO is blended with marine gas oil (MGO) in various mass ratios and tested both in combustion research unit (CRU) and engine facilities. Typical cruise speeds and multiple loads are selected in the heavy-duty engine tests. Both inlet temperature and EGR rate are varied to investigate the effects of control parameters on HPO. The results reveal that HPO present lower reactivity than MGO and diesel under CRU condition. It can function as a drop-in fuel without any modification to the engine and no recalibration was required. Specifically, key combustion phases are noticed to be identical. The engine can run smoothly and safely at 50% blend ratio with 1% reduction on net indicated efficiency (NIE) and 0.002 g/kWh particulate matter emissions (PM). At low load, the NOx emissions decrease to 1 g/kWh at 40% EGR, yet 1% decrease of NIE is shown. While all fuels yield more NOx but less PM emissions as the increase of inlet temperature. Inlet heating does decrease the NIE by 1%.</p

Ignition and combustion characteristics of hydrotreated pyrolysis oil in a combustion research unit

Biomass-derived fuels are promising in reducing life-cycle CO2 emissions and achieving the goal of sustainable mobility in the future. This work investigates the ignition behavior and combustion process of hydrotreated pyrolysis oil (HPO) derived from various biomass resources. They are tested in a combustion research unit based on constant volume combustion technology, which imitates the ignition behavior in compression ignition engines. Various conditions are tested and HPO are benchmarked with commericially avalable biofuels and fossile fuels: hydrotreated vegetable oil (HVO) and fatty acid methyl ester (FAME), diesel, and marine gas oil. The results showed that the igntiion delay time follows an order of folloing: HPO &gt; diesel-like fuels &gt; HVO. Both the biomass type and after-treatment have a small influence on the ignition delay of HPO. Two combustion regimes are observed at different chamber temperature range. It also revealed that blending HPO into HVO can extend the ignition delay of HVO. And ignition delay of HVO/HPO increases as the HPO blend ratio increases. At 75 vol% HPO blend ratio, the HPO/HVO blend shows identical ignition and combustion behavior as diesel. In addition, the viscosity of HPO/HVO blends and diesel are also quite similar. The results indicated the possibility of using 100% bio-fuel in a modern marine engine to provide power to future mobility.</p

Multi-Resolution LSTM-Based Prediction Model for Remaining Useful Life of Aero-Engine

Abstract Aircraft is an important means of travel and the most convenient and fast vehicle in long-distance transportation. The aircraft engine is one of the most critical parts of an aircraft, and its reliability and safety are extremely important. In this article, we consider that the operating conditions of aero-engines are complex and changeable, and a multi-resolution long short-term memory (MR-LSTM) model is proposed. The model can effectively predict the remaining useful life (RUL) of an aero-engine, which is a priority issue within the Prognostics and Health Management (PHM) framework - and thus it can support maintenance decisions. Sequences with multiple temporal resolutions are generated by a reconstruction of the decomposed wavelets. A two-layer LSTM model is then designed: 1) the first layer LSTM is used to learn attention at different time resolutions as well as to generate an integrated historical representation; 2) the second layer LSTM is used to learn the long and short-term time dependencies in the integrated historical representation. Experimental evaluations using the C-MAPSS datasets (FD002 and FD004) and the N-CMAPSS dataset showed that compared to other state-of-the-art RUL prediction methods, the FD002 sub-dataset showed a 12.1% reduction in RMSE and a 3.8% reduction in Score; the FD004 sub-dataset showed a 21.8% reduction in RMSE and a decreased by 62.1%; the RMSE of the N-CMAPSS dataset decreased by at most 25.8%.Abstract Aircraft is an important means of travel and the most convenient and fast vehicle in long-distance transportation. The aircraft engine is one of the most critical parts of an aircraft, and its reliability and safety are extremely important. In this article, we consider that the operating conditions of aero-engines are complex and changeable, and a multi-resolution long short-term memory (MR-LSTM) model is proposed. The model can effectively predict the remaining useful life (RUL) of an aero-engine, which is a priority issue within the Prognostics and Health Management (PHM) framework - and thus it can support maintenance decisions. Sequences with multiple temporal resolutions are generated by a reconstruction of the decomposed wavelets. A two-layer LSTM model is then designed: 1) the first layer LSTM is used to learn attention at different time resolutions as well as to generate an integrated historical representation; 2) the second layer LSTM is used to learn the long and short-term time dependencies in the integrated historical representation. Experimental evaluations using the C-MAPSS datasets (FD002 and FD004) and the N-CMAPSS dataset showed that compared to other state-of-the-art RUL prediction methods, the FD002 sub-dataset showed a 12.1% reduction in RMSE and a 3.8% reduction in Score; the FD004 sub-dataset showed a 21.8% reduction in RMSE and a decreased by 62.1%; the RMSE of the N-CMAPSS dataset decreased by at most 25.8%