检索结果-南通市图书馆

The X-ray nature of the nucleus in Seyfert 2 galaxy NGC 7590

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2012年第9期12卷 1247-1254页

作者： Xin-Wen Shu jun-xian wang Teng LiuI and Wei Zheng CAS Key Laboratory for Research in Galaxies and Cosmology Department of AstronomyUniversity of Science and Technology of China Hefei 230026 China xwshu @*** Department of Physics and Astronomy The Johns Hopkins University Baltimore MD 21218USA

We present the results of the Chandra high-resolution observation of the Seyfert 2 galaxy NGC 7590. This object was reported to show no X-ray absorption in the low-spatial resolution ASCA data. The XMM-Newton observations show that the X-ray emission of NGC 7590 is dominated by an off-nuclear ultra-luminous X- ray source (ULX) and extended emissions from the host galaxy, and the nucleus is rather weak, likely hosting a Compton-thick AGN. Our recent Chandra observation of NGC 7590 enables us to effectively remove the X-ray contamination from the ULX and the extended component. The nuclear source remains undetected at the flux level of ～ 4 × 10-15 erg cm-2 s-1. Although not detected, the Chandra data give a 2- 10 keV flux upper limit of ～ 6.1 × 10-15 erg cm-2 s-1 (at a 3σ level), a factor of three less than the XMM-Newton value, strongly supporting the Compton-thick nature of the nucleus. In addition, we detected five off-nuclear X-ray point sources within the galaxy's D25 ellipse, all with 2 - 10 keV luminosity above 2×1038 erg s-1 (assuming the distance of NGC 7590). In particular, the ULX previously identified by ROSAT data is resolved by Chandra into two distinct X-ray sources. Our analysis highlights the importance of high spatial resolution images in discovering and studying ULXs.

关键词： galaxies: active — galaxies: individual (NGC 7590) — galaxies: nuclei — X-rays: galaxies

Study on the thermally induced spindle angular errors of a five-axis CNC machine tool

在线全文

学校读者我要写书评

暂无评论

Advances in Manufacturing 2023年第1期11卷 75-92页

作者： Ji Peng Ming Yin Li Cao Luo-Feng Xie xian-jun wang Guo-Fu Yin School of Mechanical Engineering Sichuan UniversityChengdu610065People’s Republic of China

Thermally induced spindle angular errors of a machine tool are important factors that affect the machining accuracy of *** is critical to develop models with good generalization abilities to control these angular thermal ***,the current studies mainly focus on the modeling of linear thermal errors,and an angular thermal error model applicable to different working conditions has rarely been ***,the formation mechanism of the angular thermal error remains to be *** this study,an analytical modeling method was proposed by analyzing the formation and propagation chain of the spindle angular thermal errors of a five-axis computer numerical control(CNC)machine *** effects of the machine tool structure and position were considered in the modeling *** angular thermal error equations were obtained by analyzing the spatial thermoelastic deformation *** analytical model of the spindle angular thermal error was established based on the geometric relation between thermal *** model parameters were identified using the trust region least squares *** results showed that the proposed analytical model exhibited good generalization ability in predicting spindle pitch angular thermal errors under different working conditions with variable spindle rotational speeds,spindle positions,and environmental temperatures in different *** average mean absolute error(MAE),root mean square error(RMSE)and R2 in twelve different experiments were 4.7μrad,5.6μrad and 0.95,*** study provides an effective method for revealing the formation mechanism and controlling the spindle angular thermal errors of a CNC machine tool.

关键词： Machine tool Angular thermal errors Thermal error modeling Analytical model

The study of Seyfert 2 galaxies with and without infrared broad lines

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2010年第5期10卷 427-437页

作者： Hong-Bing Cai Xin-Wen Shu Zhen-Ya Zheng jun-xian wang CAS Key Laboratory for Research in Galaxies and Cosmology Department of AstronomyUniversity of Science and Technology of China Hefei 230026 China National Time Service Center CAS Xi＇an 710600 China

From the literature, we construct a sample of 25 Seyfert 2 galaxies （S2s）with a broad line region （BLR） detected in near infrared （NIR） spectroscopy and 29with NIR BLRs which were not detected. We find no significant difference betweenthe nuclei luminosity （extinction-corrected [OIII] 5007） and infrared color f 60/f25between the two populations, suggesting that the non-detections of NIR BLRs couldnot be due to low AGN luminosity or contamination from the host galaxy. As ex-pected, we find significantly lower X-ray obscurations in Seyfert 2s with NIR BLRdetection, supporting the unification scheme. However, such a scheme was challengedby the detection of NIR BLRs in heavily X-ray obscured sources, especially in sixof them with Compton-thick X-ray obscuration. The discrepancy could be solved bythe clumpy torus model and we propose a toy model demonstrating that IR-thin X-ray-thick S2s could be viewed at intermediate inclinations and compared with thoseIR-thick X-ray-thick S2s. We note that two of the IR-thin X-ray-thick S2s （NGC 1386and NGC 7674） experienced X-ray transitions, i.e. from Compton-thin to Compton-thick appearance or vice versa based on previous X-ray observations, suggesting thatX-ray transitions could be common in this special class of objects.

关键词： galaxies: active — galaxies: Seyfert — infrared: galaxies

More than softer-when-brighter: The X-ray powerlaw spectral variability in NGC 4051

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2020年第12期63卷 102-112页

作者： Yun-Jing Wu jun-xian wang Zhen-Yi Cai Jia-Lai Kang Teng Liu Zheng Cai CAS Key Laboratory for Research in Galaxies and Cosmology Department of AstronomyUniversity of Science and Technology of ChinaHefei 230026China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China Department of Astronomy Tsinghua UniversityBeijing 100084China Max-Planck-Institut für Extraterrestrische Physik Garching bei Munchen D-85748Germany

The powerlaw X-ray spectra of active galactic nuclei at moderate to high accretion rates normally appear softer when they brighten,for which the underlying mechanisms are yet *** XMM-Newton observations and excluding photons<2 keV to avoid contamination from the soft excess,in this work we scrutinize the powerlaw spectral variability of NCG 4051 from two new *** first find that a best-fit"softer-when-brighter"relation is statistically insufficient to explain the observed spectral variabilities,and intervals deviated from the empirical relation are clearly visible in the light curve of 2-4 ke V/4-10 keV count rate *** deviations are seen not only between but also within individual XMM-Newton exposures,consistent with random variations of the corona geometry or inner structure(with timescales as short as^1 ks),in addition to those behind the smooth"softer-when-brighter"*** further find the"softer-when-brighter"trend gradually weakens with the decreasing timescale(from^100 ks down to 0.5 ks).These findings indicate that the powerlaw spectral slope is not solely determined by its *** propose a two-tier geometry,including flares/nano-flares on top of the inner disc and an embedding extended corona(heated by the flares,in analogy to solar corona)to explain the observations together with other observational clues in *** spectral variabilities could be due to individual flares/nano-flares,while slow ones are driven by the variations in the global activity of inner disc region(akin to the variation of solar activity,but not the accretion rate)accompanied with heating/cooling and inflation/contraction of the extended corona.

关键词： active galaxies X-ray Seyfert galaxies

Selenocysteine antagonizes oxygen glucose deprivation-induced damage to hippocampal neurons

在线全文

学校读者我要写书评

暂无评论

Neural Regeneration Research 2018年第8期13卷 1433-1439页

作者： xian-jun wang Mei-Hong wang Xiao-Ting Fu Ya-jun Hou wang Chen Da-Chen Tian Su-Yun Bai Xiao-Yan Fu Department of Neurology People's Hospital of Linyi Linyi Shandong Province China Department of Neurology People's Hospital of Yishui Linyi Shandong Province China School of Basic Medicine Taishan Medical University Taian Shandong Province China

Designing and/or searching for novel antioxidants against oxygen glucose effective strategy for the treatment of human isdlemic stroke. Selenium is deprivation （OGD）-induced oxidative damage represents an an essential trace dement, which is beneficial in the chemo- prevention and chemotherapy of cerebral ischemic stroke. The underlying mechanisms for its therapeutic effects, however, are not well documented. Selenocysteine （SeC） is a selenium-containing amino acid with neuroprotective potential. Studies have shown that SeC can reduce irradiation-induced DNA apoptosis by reducing DNA damage. In this study, the in vitro protective potential and mechanism of action of SeC against OGD-induced apoptosis and neurotoxicity were evaluated in HT22 mouse hippocampal neurons. We cultured HT22 cells in a glucose-free medium containing 2 mM Na2S402, which formed an OGD environment, for 90 minutes. Findings from MTT, flow cytometry and TUNEL staining showed obvious cytotoxicity and apoptosis in HT22 cells in the OGD condition. The activation of Caspa se-7 and Caspase-9 further revealed that OGD-induced apoptosis of HT22 cells was mainly achieved by triggering a mitochondrial-medi- ated pathway. Moreover, the OGD condition also induced serious DNA damage through the accumulation of reactive oxygen species and superoxide anions. However, SeC pre-treatment for 6 hours effectively inhibited OGD-induced cytotoxicity and apoptosis in HT22 cells by inhibiting reactive oxygen species-mediated oxidative damage. Our findings provide evidence that SeC has the potential to suppress OGD-induced oxidative damage and apoptosis in hippocampal neurons.

关键词： selenium selenocysteine ischemic stroke oxygen glucose deprivation hippocampal neuron mitochondria reaction oxygen species superoxide anion oxidative damage apoptosis

The feasibility and flexibility of selecting quasars by variability using ensemble machine learning algorithms

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2021年第4期21卷 271-281页

作者： Da-Ming Yang Zhang-Liang Xie jun-xian wang CAS Key Laboratory for Researches in Galaxies and Cosmology University of Science and Technology of ChinaChinese Academy of SciencesHefei 230026China

In this work,we train three decision-tree based ensemble machine learning algorithms(Random Forest Classifier,Adaptive Boosting and Gradient Boosting Decision Tree respectively)to study quasar selection in the variable source catalog in SDSS Stripe *** build training and test samples(both containing 1:1 of quasars and stars)using the spectroscopic confirmed sources in SDSS DR14(including8330 quasars and 3966 stars).We find that when trained with variation parameters alone,all three models can select quasars with similarly and remarkably high precision and completeness(~98.5%and 97.5%),even better than trained with SDSS colors alone(~97.2%and 96.5%),consistent with previous *** applying the trained models on the variable sources without spectroscopic identifications,we estimate the spectroscopically confirmed quasar sample in Stripe 82 variable source catalog is~93%complete(95%for mi<19.0).Using the Random Forest Classifier we derive the relative importance of the observational features utilized for *** further show that even using one-or two-year time domain observations,variability-based quasar selection could still be highly efficient.

关键词： quasars:general catalogs methods:data analysis

Therapy-induced senescent tumor cells in cancer relapse

在线全文

学校读者我要写书评

暂无评论

Journal of the National Cancer Center 2023年第4期3卷 273-278页

作者： Ke-Xin Song jun-xian wang De Huang Department of General Surgery The First Affiliated Hospital of USTCDivision of Life Sciences and MedicineUniversity of Science and Technology of ChinaHefeiChina Anhui Province Key Laboratory of Hepatopancreatobiliary Surgery HefeiChina School of Basic Medical Sciences Division of Life Sciences and MedicineUniversity of Science and Technology of ChinaHefeiChina

Cellular senescence is characterized by a generally irreversible cell cycle arrest and the secretion of bioactive factors known as the senescence-associated secretory phenotype(SASP).In an oncogenic context,senescence is considered a tumor suppressive mechanism as it prevents cell proliferation and inhibits the progression from pre-malignant to malignant ***,recent studies have demonstrated that senescent tumor cells,which could spontaneously exist within cancer tissues or arise in response to various cancer interventions(the so-called therapy-induced senescence,TIS),can acquire pro-tumorigenic properties and are capable of driving local and metastatic *** highlights the complex and multifaceted nature of cellular senescence in cancer ***,we summarize the current knowledge of the pathological function of therapy-induced senescent tumor cells and discuss possible mechanisms by which tumor cell senescence contributes to cancer *** also discuss implications for future studies toward targeting these less appreciated cells.

关键词： Cancer therapy Tumor cell senescence Relapse

Double-edged effect of sodium citrate in Nile tilapia(Oreochromis niloticus):Promoting lipid and protein deposition *** hyperglycemia and insulin resistance

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Animal Nutrition 2023年第3期14卷 303-314页

作者： jun-xian wang Fang Qiao Mei-Ling Zhang Li-Qiao Chen Zhen-Yu Du Yuan Luo Laboratory of Aquaculture Nutrition and Environmental Health(LANEH) School of Life SciencesEast China Normal UniversityShanghaiChina

Citrate is an essential substrate for energy metabolism that plays critical roles in regulating glucose and lipid metabolic ***,the action of citrate in regulating nutrient metabolism in fish remains poorly ***,we investigated the effects of dietary sodium citrate on growth performance and systematic energy metabolism in juvenile Nile tilapia(Oreochromis niloticus).A total of 270Nile tilapia(2.81±0.01 g)were randomly divided into three groups(3 replicates per group,30 fish per replicate)and fed with control diet(35%protein and 6%lipid),2%and 4%sodium citrate diets,respectively,for 8 *** results showed that sodium citrate exhibited no effect on growth performance(P>0.05).The whole-body crude protein,serum triglyceride and hepatic glycogen contents were significantly increased in the 4%sodium citrate group(P0.05).The 4%sodium citrate treatment significantly increased the serum glucose and insulin levels at the end of feeding trial and also in the glucose tolerance test(P<0.05).The 4%sodium citrate significantly enhanced the hepatic phosphofructokinase activity and inhibited the expression of pyruvate dehydrogenase kinase isozyme 2 and phosphor-pyruvate dehydrogenase E1 component subunit alpha proteins(P<0.05).Additionally,the 4%sodium citrate significantly increased hepatic triglyceride and acetyl-Co A levels,while the expressions of carnitine palmitoyl transferase 1a protein were significantly down-regulated by the 4%sodium citrate(P<0.05).Besides,the 4%sodium citrate induced crude protein deposition in muscle by activating m TOR signaling and inhibiting AMPK signaling(P<0.05).Furthermore,the 4%sodium citrate significantly suppressed serum aspartate aminotransferase and alanine aminotransferase activities,along with the lowered expression of pro-inflammatory genes,such as nfκb,tnfa and il8(P<0.05).Although the 4%sodium citrate significantly increased phosphor-nuclear factor-k B p65 prote

关键词： Sodium citrate Lipid and protein deposition Insulin resistance Nile tilapia

Intermediate-mass black holes in Green pea galaxies(IMBH-GP)I:A candidate sample from LAMOST and SDSS

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2024年第10期67卷 147-161页

作者： Ruqiu Lin Zhen-Ya Zheng Fang-Ting Yuan jun-xian wang Chunyan Jiang Ning Jiang Lingzhi wang Linhua Jiang xiang Ji Shuairu Zhu Xiaodan Fu Key Laboratory for Research in Galaxies and Cosmology Shanghai Astronomical ObservatoryChinese Academy of SciencesShanghai 200030China School of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China CAS Key Laboratory for Research in Galaxies and Cosmology Department of AstronomyUniversity of Science and Technology of ChinaHefei 230026China Chinese Academy of Sciences South America Center for Astronomy(CASSACA) National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China CAS Key Laboratory of Optical Astronomy National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy School of PhysicsPeking UniversityBeijing 100871China

The scaling relation of central massive black holes(M_(BH)s)and their host galaxies is well-studied for supermassive BHs(SM_(BH)s,M_(BH)≥10^(6)M_(⊙)).However,this relation has large uncertainties in the mass range of the intermediate-mass BHs(IM_(BH)s,M_(BH)~10^(3)-10^(6)M_(⊙)).Since Green pea(GP)galaxies are luminous compact dwarf galaxies,which may be likely to host less massive SM_(BH)s or even IM_(BH)s,we systematically search for M_(BH)s in a large sample of 2190 GP galaxies at z<0.4,selected from LAMOST and SDSS spectroscopic ***,we report a newly discovered sample of 59 M_(BH) candidates with broad Hα*** sample has a median stellar mass of 108.83±0.11M_(⊙)and hosts M_(BH)s with single-epoch virial masses ranging from M_(BH)~10^(4.7)to 10^(8.5)M_(⊙)(median 105.85±0.64M_(⊙)).Among the 59 M_(BH) candidates,36 have black hole masses M_(BH)≤10^(6)M_(⊙)(IM_(BH) candidates),one of which even has M_(BH)■10^(5)M_(⊙).We find that the M_(BH)-M_(*)relation of our M_(BH) sample is consistent with the M_(BH)-M_(bulge)relation for SM_(BH)s,while is above the M_(BH)-M_(*)relation for M_(BH)s in dwarf galaxies in the same mass ***,we show that 25 M_(BH) candidates,including 4 IM_(BH) candidates,have additional evidence of black hole activities,assessed through various methods such as the broad-line width,BPT diagram,mid-infrared color,X-ray luminosity,and radio *** studies show that it is very promising to find IM_(BH)s in GP galaxies,and the BH sample so obtained enables us to probe the connection between the M_(BH)s and compact dwarf galaxies in the low-redshift Universe.

关键词： SMBHs IMBHs Green pea galaxies compact dwarf galaxies