We present ground-based and Swift photometric and spectroscopic observations of the candidate tidal disruption event (TDE) ASASSN-14li, found at the centre of PGC 043234 (d ... 90 Mpc) by the All-Sky ...Automated Survey for SuperNovae (ASAS-SN). The source had a peak bolometric luminosity of ... and a total integrated energy of ... erg radiated over the ~6 months of observations presented. The UV/optical emission of the source is well fitted by a blackbody with roughly constant temperature of T ... 35,000 K, while the luminosity declines by roughly a factor of 16 over this time. The optical/UV luminosity decline is broadly consistent with an exponential decline, ..., with t0 ... 60 d. ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the optical and UV emission but declining at a slower rate, and the X-ray emission now dominates. Spectra of the source show broad Balmer and helium lines in emission as well as strong blue continuum emission at all epochs. We use the discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by ASAS-SN, finding an average rate of ... per galaxy with a 90 per cent confidence interval of ... per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia supernovae in 2014, a rate that is much higher than that of other surveys. (ProQuest: ... denotes formulae/symbols omitted.)
In this study, a novel cobalt-free Fe40Mn20Cr20Ni20 (at.%) medium-entropy alloy (MEA) with low cost is purposively designed. The partially recrystallized microstructure was introduced into the ...single-phase FeMnCrNi MEA via thermo-mechanical processing. Surprisingly, the present MEA displays ultrahigh yield and ultimate tensile strengths of 1.2 and 1.34 GPa, respectively, and large ductility with a uniform elongation of 22% at 77 K. This is mainly due to the accumulation and entanglement of a large number of dislocations and the activation of deformation twins at 77 K.
•A novel cobalt-free Fe40Mn20Cr20Ni20 medium-entropy alloy with low cost is purposively designed.•The present medium-entropy alloy displays ultrahigh yielding and ultimate tensile strengths of 1.2 and 1.34 GPa, respectively, and good ductility with a uniform elongation of 22% at 77 K.•Compared with many other advanced alloys, the present MEA has outstanding advantages in the mechanical performances at 77 K and the cost of raw materials for the preparation.
Base station (BS) sleeping is an effective way to improve the energy-efficiency of cellular networks. However, it may bring extra user-perceived delay. We conduct a theoretical study into the impact ...of BS sleeping on both energy-efficiency and user-perceived delay. We consider hysteresis sleep and three typical wake-up schemes, namely single sleep, multiple sleep, and N-limited schemes. We model the system as an M/G/1 vacation queue, which captures the setup time, the mode-changing cost, as well as the counting or detection cost during the sleep mode. Closed-form expressions for the average power and the Laplace-Stieltjes transform of delay distribution are obtained. The impacts of system parameters on these expressions are analyzed. We then formulate an optimization problem to design delay-constrained energy-optimal BS sleeping policies. We show that the optimal solutions possess a special structure, thereby allowing us to obtain them explicitly or numerically by simple bisection search. In addition, the relationship between the optimal power consumption and the mean delay constraint is analyzed, so as to answer the fundamental question: how much energy can be saved by trading off a certain amount of delay? It is shown that this optimal relationship is linear only when the delay constraint is lower than a threshold. Numerical studies are also conducted, where the impact of detection or counting cost during the sleep mode is explored, and the delay distribution under the optimal policy is obtained.
The first known magnetic mineral, magnetite, has unusual properties, which have fascinated mankind for centuries; it undergoes the Verwey transition around 120 K with an abrupt change in structure ...and electrical conductivity. The mechanism of the Verwey transition, however, remains contentious. Here we use resonant inelastic X-ray scattering over a wide temperature range across the Verwey transition to identify and separate out the magnetic excitations derived from nominal Fe
and Fe
states. Comparison of the experimental results with crystal-field multiplet calculations shows that the spin-orbital dd excitons of the Fe
sites arise from a tetragonal Jahn-Teller active polaronic distortion of the Fe
O
octahedra. These low-energy excitations, which get weakened for temperatures above 350 K but persist at least up to 550 K, are distinct from optical excitations and are best explained as magnetic polarons.
Coupled magmatic and tectonic activity plays an important role in high-temperature hydrothermal circulation at mid-ocean ridges. The circulation patterns for such systems have been elucidated by ...microearthquakes and geochemical data over a broad spectrum of spreading rates, but such data have not been generally available for ultra-slow spreading ridges. Here we report new geophysical and fluid geochemical data for high-temperature active hydrothermal venting at Dragon Horn area (49.7°E) on the Southwest Indian Ridge. Twin detachment faults penetrating to the depth of 13 ± 2 km below the seafloor were identified based on the microearthquakes. The geochemical composition of the hydrothermal fluids suggests a long reaction path involving both mafic and ultramafic lithologies. Combined with numerical simulations, our results demonstrate that these hydrothermal fluids could circulate ~ 6 km deeper than the Moho boundary and to much greater depths than those at Trans-Atlantic Geotraverse and Logachev-1 hydrothermal fields on the Mid-Atlantic Ridge.
Summary
Multi‐parent advanced generation inter‐cross (MAGIC) populations are an emerging type of resource for dissecting the genetic structure of traits and improving breeding populations. We ...developed a MAGIC population for cowpea (Vigna unguiculata L. Walp.) from eight founder parents. These founders were genetically diverse and carried many abiotic and biotic stress resistance, seed quality and agronomic traits relevant to cowpea improvement in the United States and sub‐Saharan Africa, where cowpea is vitally important in the human diet and local economies. The eight parents were inter‐crossed using structured matings to ensure that the population would have balanced representation from each parent, followed by single‐seed descent, resulting in 305 F8 recombinant inbred lines each carrying a mosaic of genome blocks contributed by all founders. This was confirmed by single nucleotide polymorphism genotyping with the Illumina Cowpea Consortium Array. These lines were on average 99.74% homozygous but also diverse in agronomic traits across environments. Quantitative trait loci (QTLs) were identified for several parental traits. Loci with major effects on photoperiod sensitivity and seed size were also verified by biparental genetic mapping. The recombination events were concentrated in telomeric regions. Due to its broad genetic base, this cowpea MAGIC population promises breakthroughs in genetic gain, QTL and gene discovery, enhancement of breeding populations and, for some lines, direct releases as new varieties.
Significance Statement
This paper reports the development and analysis of a multi‐parent population of the warm‐season legume cowpea, a crop of vital importance in global food security, providing a foundation for breakthroughs in genetic gain and quantitative trait locus (QTL) discovery. In particular, the QTL detected for photoperiod sensitivity will further our understanding of the genetics of flowering time in the photoperiod‐sensitive cowpea and related species.
The genomic loci associated with B cell differentiation that are subject to transcriptional and epigenetic regulation in vivo are not well defined, leaving a gap in our understanding of the ...development of humoral immune responses. Here, using an in vivo T cell independent B cell differentiation model, we define a cellular division-dependent cis-regulatory element road map using ATAC-seq. Chromatin accessibility changes correlate with gene expression and reveal the reprogramming of transcriptional networks and the genes they regulate at specific cell divisions. A subset of genes in naive B cells display accessible promoters in the absence of transcription and are marked by H3K27me3, an EZH2 catalyzed repressive modification. Such genes encode regulators of cell division and metabolism and include the essential plasma cell transcription factor Blimp-1. Chemical inhibition of EZH2 results in enhanced plasma cell formation, increased expression of the above gene set, and premature expression of Blimp-1 ex vivo. These data provide insights into cell-division coupled epigenetic and transcriptional processes that program plasma cells.
In networked cyber-physical systems, the inter-delivery time of data packets becomes an important quantity of interest. However, providing a guarantee that the inter-delivery times of the packets are ..."small enough" becomes a difficult task in such systems due to the unreliable communication medium and limited network resources. We design scheduling policies that meet the inter-delivery time requirements of multiple clients connected over wireless channels. We formulate the problem as an infinite-state risk-sensitive Markov decision process, where large exceedances of inter-delivery times for different clients over their design thresholds are severely penalized. We reduce the infinite-state problem to an equivalent finite-state problem and establish the existence of a stationary optimal policy and an algorithm for computing it in a finite number of steps. However, its computational complexity makes it intractable when the number of clients is of the order of 100 or so that is found in applications such as in-vehicle networks. To design computationally efficient optimal policies, we, therefore, develop a theory based on the high reliability asymptotic scenario, in which the channel reliability probabilities are close to one. We thereby obtain an algorithm of relatively low computational complexity for determining an asymptotically optimal policy. To address the remaining case when the channels are not relatively reliable, we design index-based policies for the risk sensitive case, which extends key ideas for index policies in risk-neutral multi-armed bandit problems. Simulation results are provided to show the effectiveness of our policies.
The nitrided layer on Ni45(CoCrFe)40(AlTi)15 high-entropy alloys (HEAs) was prepared by plasma nitriding. The microstructure, hardness, the effect of temperature on the tribological properties and ...adhesive strength of the nitride layer were investigated. The results revealed that the as-cast alloy was composed of a single FCC phase, and the hardness measured by nano-indentation was 8.8 GPa. After nitriding, the hard phases, such as AlN, CrN, Fe3N, and TiN, appeared, the surface hardness was increased to 14.9 GPa, and the hardness distribution of the cross section of the nitrided layer was uniform. Moreover, the scratch test showed that the nitrided layer had good bonding properties with the substrate. The friction coefficient and the wear rate were significantly reduced, compared to the as-cast alloys due to the generation of unique nitride particles on the surface of the nitrided alloys. At low temperatures, the friction mechanism of as-cast and nitrided alloys was dominated by the adhesive wear and abrasive wear. Subsequently, the friction mechanism was changed to the oxidative wear and delamination wear with increasing the temperature.
Display omitted
•Hard particles of AlN, CrN, Fe4N, and TiN phases were produced after nitriding.•The surface hardness of HEAs increased from 8.8 GPa to 14.9 GPa after nitriding.•The thickness of the nitrided layer on Ni45(FeCoCr)40(AlTi)15 HEAs was 11.5 μm.•The wear resistance of nitrided HEAs was superior than that of as-cast HEAs.•Oxidative behavior played a dominant role in high wear resistance of HEAs.
A three-dimensional mathematical model of the combustion of pulverized coal and coke is developed. The model is applied to the region of lance-blowpipe-tuyere-raceway-coke bed to simulate in-furnace ...phenomena of pulverized coal injection in an ironmaking blast furnace. The model integrates not only pulverized coal combustion model in the blowpipe-tuyere-raceway-coke bed but also coke combustion model in the coke bed. The model is validated against the measurements under different conditions. The comprehensive in-furnace phenomena are investigated in the raceway and coke bed, in terms of flow, temperature, gas composition, and coal burning characteristics. The underlying mechanisms for the in-furnace phenomena are also analysed. The simulation results indicate that it is important to include recirculation region in the raceway and the coke bed reactions for better understanding in-furnace phenomena. The model provides a cost-effective tool for understanding and optimizing the in-furnace flow-thermo-chemical characteristics of the PCI operation in full-scale blast furnaces.
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