Increasing nitrogen absorption and assimilation ability under mixed NO_(3)^(–)and NH_(4)^(+) supply is a driver to promote growth of maize seedlings

Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthesis rate,but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.However,whether this process depends on N absorption is unknown.Here,maize seedlings were grown hydroponically with three N forms (NO_(3)^(-)only,75/25 NO_(3)^(-)/NH_(4)^(+) and NH_(4)^(+) only).The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO_(3)^(-)supply at 0–3 d,but was higher than under sole NO_(3)^(-)supply at 6–9 d.^(15)N influx rate under mixed N supply was greater than under sole NO_(3)^(-) or NH_(4)^(+) supply at 6–9 d,although NO_(3)^(-) and NH_(4)^(+) influx under mixed N supply were reduced compared to sole NO_(3)^(-) and NH_(4)^(+) supply,respectively.qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO_(3)^(-) transporters in roots,such as ZmNRT1.1A,ZmNRT1.1B,ZmNRT1.1C,ZmNRT1.2 and ZmNRT1.3,or NH_(4)^(+) absorption transporters,such as Zm AMT1.1A,especially the latter.Furthermore,plants had higher nitrate reductase (NR)glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO_(3)^(-) supply.The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth,especially for the reduction of NO_(3)^(-) by NR reductase.This research suggested that the increased processes of NO_(3)^(-)and NH_(4)^(+) assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.

Discovery of a variable broad absorption line in the BL Lac object PKS B0138-097

We report the discovery of a broad absorption line （BAL） of - 10^4 km s^-1 in width in the previously known BL Lac object PKS 0138-097, which we tentatively identified as an Mg II BAL. This is the first detection of a BAL, which is sometimes seen in powerful quasars with high accretion rates, in a BL Lac object. The BAL was clearly detected in its spectra spanning two epochs at a high luminosity state taken in the Sloan Digital Sky Survey （SDSS）, while it disappeared in three SDSS spectra taken at a low luminosity state. The BAL and its variability pattern were also found in its historical multi-epoch spectra in the literature, but have been overlooked previously. In its high resolution radio maps, PKS 0138-097 shows a core plus a one- sided parsec-scale jet. The BAL variability can be interpreted as follows： The optical emission is dominated by the core in a high state and by the jet in a low state and the BAL material is located between the core and jet so that the BAL appears only when the core is shining. Our discovery suggests that outflows may also be produced in active galactic nuclei at a low accreting state.

Microwave absorption properties regulation and bandwidth formula of oriented Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU composite synthesized by reduction-diffusion method

As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.

方ray可解方程组与rayS^＊-阵的图论特征

给出了系数矩阵为方阵的复线性方程组为ray可解、非负ray可解及全非零ray可解等的图论特征刻画,得到了这些方程组的解的ray模式的图论表述.应用这些结论还给出了ray S*-阵和ray S-阵的图论特征刻画,及其他若干类特殊的复线性方程组的ray可解性条件.

An algorithm to resolve γ-rays from charged cosmic rays with DAMPE

The DArk Matter Particle Explorer（DAMPE）,also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.

On the intrinsic shape of the gamma-ray spectrum for Fermi blazars

The curvature of the γ-ray spectrum in blazars may reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The γ-ray spectra of Fermi blazars are normally fitted either by a single power-law（PL） or a log-normal（call Logarithmic Parabola, LP） form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3 LAC Clean Sample. We find that the γ-ray flux（100 Me V–100 Ge V） and variability index follow bimodal distributions for PL and LP blazars, where the γ-ray flux and variability index show a positive correlation. However, the distributions of γ-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of γ-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved γ-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.

INSIGHT INTO DISTILLATION/ABSORPTION COLUMNS AND FCC RISERS USING GAMMA SCANNING TECHNIQUE

This paper presents the application of gamma ray scanning technique to distillation/absorption columns and FCC risers.The flow regime transition.clear liquid height,froth height.crestliquid height over the exit weir on a V-1 type valve tray and downcomer hydraulics were investigatedusing the scanning device previously developed.The solid distribution and coke deposition were experi-mentally simulated in a FCC riser simulator by employing a three dimensional scanning device devel-oped for the present investigation.The success of this investigation should shed a light forquantifying two-phase contact phenomena in various gas liquid and gas solid two phase flow system.

Possible modulated γ-ray emission from the transitional millisecond pulsar binary PSR J1023+0038

We report the results from our analysis of Fermi Large Area Telescope （LAT） data for the transitional millisecond pulsar binary PSR J1023＋0038. The time period of the data is nearly 9 yr, and that after the source＇s transition, in June 2013 from the disk-free state to the active state of having an accretion disk, is approximately 4 yr. We identify a high-energy 〉5.5 GeV component in the source＇s spectrum in the active state, and find this component is only significantly detected in half of the orbital phase centered at the descending node （when the pulsar is moving towards the Earth）. Considering the pulsar scenario proposed for multi-frequency emission from the source, in which the pulsar is still active and a cold-relativistic pulsar wind inverse-Compton scatters the photons from the accretion disk, we discuss the origin of the high-energy component. In order to explain the observed spectrum, a power-law distribution of particles, with an index of ~3, in the pulsar wind is required, while the orbital variations are possibly due to changes in power-law index as a function of orbital phase.

Searching forγ-ray counterparts to very faint X-ray transient neutron star binaries

Very faint X-ray transients （VFXTs） are a group of X-ray binaries with low luminosities, displaying peak X-ray luminosities during their outbursts of only 1034-1036 erg s^-1. Using γ-ray data obtained with the Large Area Telescope （LAT） onboard the Fermi Gamma-Ray Space Telescope （Fermi）, we investigate their possible nature of containing rotation-powered pulsars, or more specifically being transitional millisecond pulsars （MSPs）. Among more than 40 known VFXTs, we select 12 neutron star systems. We analyze the LAT data for the fields of 12 VFXTs in the energy range 0.2-300GeV, but do not find any counterparts likely detected by Fermi. We obtain luminosity upper limits for the 12 sources. While the distances to the sources are largely uncertain, the upper limits are comparable to the luminosities of two transitional systems, PSR J1023-0038 and XSS J12270-4859. From our study, we conclude that no evidence is found at γ-rays for the suggestion that some VFXTs could contain rotation-powered MSPs （or be transitional MSP systems）.

Study of temporal and spectral characteristics of the X-ray emission from solar flares

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity ≥C class observed by the Solar X-ray Spectrometer （SOXS） during 2003-2011 are presented. We analyze the X-ray emission observed in four and three energy bands by the Si and Cadmium-Zinc-Telluride （CZT） detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation （R ~=0.2） between the rise time and the peak flux of the first peak of the flare irrespective of energy band, which is indicative of its energy-independent nature. Moreover, the magnetic field complexity of the flaring region is found to be highly anti-correlated （R = 0.61） with the rise time of the flares while positively correlated （R = 0.28） with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in 25-30keV decreases with increasing energy, suggesting conduction cooling is dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of differential emission measure （DEM） evolution is delayed by 60-360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are dependent on energy as well as the magnetic field configuration of the active region.

Possible Contribution of Mature γ-ray Pulsars to Cosmic-ray Positrons

We restudy the possible contribution of mature gamma-ray pulsars to cosmic ray positrons based on the new version of outer gap model. In this model, the inclination angle and average properties of the outer gap are taken into account, and more mature pulsars can have the outer gap and emit high energy photons. Half of the primary particles in the outer gaps will flow back toward the star surface and emit synchrotron photons, which can produce electron/positron pairs by the cascade of pair production. Some of these pairs will escape from the light cylinder and be accelerated to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves. Using a Monte Carlo method, we obtain a sample of mature gamma-ray pulsars and then calculate the production of the positrons from these pulsars. The observed excess of cosmic positrons can be well explained by this model.

Ring-Shaped Jets in Gamma-Ray Bursts

When the axis of a gamma-ray burst （GRB） does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction ζe, the magnetic energy fraction ζB^2, the width of ring △θ and the medium number density n. The overall light curve can be divided into three power-law stages, i.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet.

Gamma-ray Bursts: a Probe of Black Holes

There is strong evidence for the existence of black holes (BHs) in some X-ray binaries and in most galactic nuclei based on different types of measurement, but black holes have not been definitely identified for the lack of very firm observational evidence up to now. Because direct evidence for BHs should come from determination of strong gravitational redshift, we expect an object can fall into the region near the BH horizon where radiation can be detected. Therefore the object must be a compact star such as a neutron star (NS), and intense astrophysical processes will release highly energetic radiation that is transient and fast-varying. These characteristics may point to the observed gamma-ray bursts (GRBs). Recent observations of iron lines suggest that afterglows of GRBs show properties similar to those observed in active galactic nuclei (AGNs), implying that the GRBs may originate from intense events related to black holes. A model for GRBs and after-glows is proposed here to obtain the range of gravitational redshifts (zg) of GRBs with known cosmological redshifts. Here, we provide a new method that, with a search for high-energy emission lines (X- or -γ-rays) in GRBs, one can determine the gravitational redshift. We expect zg to be 0.5 or even larger, so we can rule out the possibility of other compact objects such as NSs, and identify the central progenitors of GRBs as black holes.

BACKGROUND RECTIFICATION AND FEATURE EXTRACTION OF IMAGE IN A SPOT WELD OF AL ALLOY X-RAY DETECTION

A primary study on Processing in X - ray inspection of spot weld for aluminum alloy spot welding,in- cluding for background simulation,acquisition of ideal binary image, and extraction and identifi- cation of defect features was presented.

Time-resolved spectral analysis of prompt emission from long gamma-ray bursts with GeV emission

We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we also use a model consisting of a black body and a power law to fit the spectra. We find that for the latter model there are indications of an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs, like （a） temperatures of the blackbodies are strongly correlated with each other, （b） fluxes in the black body components are strongly correlated with each other, （c） the temperatures of the black body trace the profile of the individual pulses of the GRBs, and （d） the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.

A statistical classification of the unassociated gamma-ray sources in the second Fermi Large Area Telescope Catalog

With the assistance of the identified/associated sources in the second Fermi Large Area Telescope （LAT） catalog, we analyze and resolve the spatial distribution and the distributions of the gamma-ray spectral and variability indices of the remaining 575 unassociated Fermi LAT sources. Consequently, it is suggested that the unassociated sources could statistically consist of Galactic supernova remnants/pulsar wind nebulae, BL Lacertae objects, fiat spectrum radio quasars and other types of active galaxies with fractions of 25%, 29%, 41% and 5%, respectively.

Gamma-ray Emission from the γ-ray-loud BL Lac Objects

Using the HST observation data of BL Lac objects by Urry et al. and γ-ray observation data, we find that there is a correlation between Fγ and Fonuclei forγ-ray-loud BL Lac objects (correlation coefficients: 7γ=0.63,p = 4.0 × 10-2), but no correlation between Fγ and Fohost, where Fonuclei and Fohost are the fluxes of nuclei and host galaxy in V-band. For 19γ-ray-loud BL Lac objects with observed spectral index in multi-wavebands, the spectral index correlations between any two bands are as follow: (1) there is a strong correlation between aγ and aK for 15 BL Lac objects(γ = 0.84,p = 3.11 × 10-4); (2) the correlation between aγ and ao for 12 BL Lac objects isγ = 0.82, p = 1.5 × 10-3; (3) there is no correlation between a7 and ax for 16 BL Lac objects. The results, together with characteristic double-humped shape of their SEDs, show that the synchrotron self-Compton mechanism might be a main mechanism for theγ-ray emission of the BL Lac objects. The electrons emitting JR and optical radiation via synchrotron are also responsible for upscattering these photons toγ-rays, and a variability in IR-optical regime should be accompanied by a change in theγ-rays.

The Relationship between the Rise Width and the Full Width of γ-ray Burst Pulses and Its Implications

We investigate the relationship between the rise width and the full width of gamma-ray burst pulses. Theoretical analysis shows that either width is proportional to Г^-2△τθ,FWHMRc/c（Г the Lorentz factor of the bulk motion, △τθ,FWHM a local pulse＇s width, Rc the radius of fireballs and c the velocity of light）. We study the relationship for four samples of observed pulses. We find： （1） merely the curvature effect could reproduce the relationship between the rise and full widths with the same slope as derived from the model of Qin et al.; （2） gamma-ray burst pulses, selected from both the short and long GRBs, follow the same sequence in the rise width vs. full width diagram, with the shorter pulses at one end; （3） all GRBs may intrinsically result from local Gaussian pulses. These features place constraints on the physical mechanism（s） for producing long and short GRBs.

On the Evolution of the Apparent Size of Gamma-Ray Burst Remnants

The remnants of two gamma-ray bursts, GRB 030329 and GRB 041227, have been resolved by Very Long Baseline Interferometry observations. The radio counterparts were observed to expand with time. These observations provide an important way to test the dynamics of the standard fireball model. We show that the observed size evolution of these two events cannot be explained by a simple jet model, rather, it can be satisfactorily explained by the two-component jet model. It strongly hints that gamma-ray burst ejecta may have complicated structures.

1，4-二苯基-6-苯基氨基-1，3，5-三嗪-2（1H）-硫酮的合成与晶体结构

目的研究1，4-二苯基-6-苯基氨基-1，3，5-三嗪-2（1H）-硫酮（分子式C2，H16N4S，相对分子质量356．44）的合成方法和其单晶结构。方法先将一定量的苄脒、氢氧化钠和N，N-二甲基甲酰胺（DMF）混合放入10ml反应器中搅拌10min，然后将一定量的苯基异硫氰酸酯加入反应器中，预搅拌20S后，在110℃温度下微波辐射（MWI）15min，高产率得到目标化合物。化合物的结构通过核磁共振氢谱（^1HNMR）、红外光谱（IR）和高分辨率气相色谱质谱（HRMS）验证，并通过X—ray单晶衍射进一步确定了产物的结构。结果合成的标题化合物C21H16N4S结构通过单晶X射线衍射分析确定，单斜晶系，空间群C2／c，a=22．94（2），b=9．5092（15），c=22．027（2）A，d=90°，D=110．473（2）°，^γ=90°，R=0．0465andwR：0．0758。分子中新形成的1，3，5-三嗪-2（1H）-硫酮环是个平面结构；它与相邻的苯环接近于共平面，二者的二面角为7．36（0．17）；而它与相邻的N一取代苯环近似于垂直，二者的二面角为85．31（0．13）。结论提供了一种1，3，5-三嗪衍生物的绿色合成方法，并经过单晶衍生确定了其分子结构及分子结构中各个六员环之间的关系。