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单壳体潜艇壳体结构损伤后的屈曲分析周素莲;聂武;彭懿【摘要】针对单壳体潜艇遭受碰撞、搁浅、战时的武器命中和爆炸冲击,耐压壳体出现塑性变形但没有被击穿的损伤情况下的结构稳定性问题,利用几何缺陷薄壁圆柱壳的卡门-唐纳尔非线性应变位移关系式和变分法推导了具有初挠度的耐压壳的平衡方程和相容方程,给出了耐压壳的应力函数表达式.在只考虑几何非线性的情况下,利用里兹法得到了静水压力作用下的不同损伤程度艇体结构的载荷挠度幅值曲线和临界载荷.结果表明,与完美耐压壳体不一样,具有初挠度的耐压壳屈曲是极值点屈曲,载荷随挠度幅值增加到局部极大值后,随着挠度幅值的增大反而减小.随着损伤程度加深,即初挠度幅值的增大,耐压壳的临界压力减小,表明耐压壳的承载能力下降;同时随着损伤程度加深,极值点变得越来越不明显,极值点屈曲问题渐渐转变为强度问题.【期刊名称】《哈尔滨工程大学学报》【年(卷),期】2010(031)009【总页数】7页(P1131-1137)【关键词】单壳体;损伤;几何非线性;临界载荷;屈曲【作者】周素莲;聂武;彭懿【作者单位】哈尔滨工程大学船舶工程学院,黑龙江,哈尔滨,150001;哈尔滨工程大学船舶工程学院,黑龙江,哈尔滨,150001;哈尔滨工程大学船舶工程学院,黑龙江,哈尔滨,150001【正文语种】中文【中图分类】U674.76现代潜艇的战术使命要求其隐蔽地接近攻击目标，最大限度地发挥自己的精确打击优势，完成战斗任务，并具有耐受敌方攻击的良好性能，在受损条件下保证潜艇尽快撤出战斗，保存自己，以便修复后继续使用.由于没有外壳的保护，单壳体潜艇比双壳体潜艇更易受到损伤，如碰撞、搁浅、战时的武器命中和爆炸冲击都会导致壳体结构的破损.本文的目的在于充分考虑潜艇遭受水下爆炸攻击后，壳体出现塑性变形但没有被击穿的情况下，针对单壳体潜艇耐压壳体结构稳定性对几何尺寸和材料特性的敏感性，研究艇体的极限承载能力.从而为各系统生命力评估提供量化依据，也为艇体结构耐压性和修复性提供依据.本文研究的耐压壳仅限于纵环加筋的圆柱形壳体，因此问题实质上是圆柱壳的屈曲，受各种不同力和边界条件约束的圆柱壳非线性屈曲问题，国内外已有大量研究.国外，L.H.Donnell等［1］引入缺陷因子的概念讨论了缺陷对轴压薄壁圆柱壳屈曲的影响;Izhak Sheinman等［2］给出了几何缺陷纵环加筋圆柱壳在轴压作用下的屈曲数值解;Yamaki［3］系统地研究了受各种不同力和边界条件约束的圆柱壳的弹性屈曲等等.国内，王晓天［4］、刘涛［5］也对圆柱壳屈曲进行了多方面分析;周承倜［6］和陈铁云［7］研究了具有初始缺陷的环肋圆柱壳在均匀静水压力作用下的弹塑性屈曲等.虽然国内外对圆柱壳的屈曲有了一定的研究，但对具有初始缺陷的纵环加筋圆柱壳在均匀静水压力作用下的弹性屈曲的研究还比较少，本文就从这方面展开研究.1 坐标和挠度函数的选取图1规定了本文所采用的坐标系统:x轴沿壳体中面的母线方向，y轴沿壳体横截面的周向，为一曲线坐标，z轴沿横截面的径向，以正对圆心为正，xyz构成一正交的右手坐标系统.图1 单壳体潜艇耐压壳坐标系Fig.1 Coordinate system of mono-shell submarine pressure hull在这个坐标系下，壳体沿x向的曲率为零，沿y向的曲率为1/r，中面上的点沿坐标轴3个方向的位移分量分别用u、v、w表示，其中u沿x向称为轴向位移，v沿y向称为周向位移，w沿z向称为径向位移.潜艇舱壁的刚度很大，因此将边界条件定为简支边界条件.根据文献［8］并结合边界条件，本文应用大挠度分析方法讨论艇体损伤后的弹塑性屈曲时，取大挠度位移函数为式中:w为沿z向的径向位移，f为挠度幅值，括号内的第1项表示小挠度屈曲波形，第2项表示翘曲波形，L表示壳长.在此，假定损伤艇体初始缺陷挠度w0的波形与w相似.因此，w0的函数表达式如下:式中:f0、δ0是初挠度的幅值，可根据实际情况给定.2 具有初始挠度艇体外壳大挠度弹性屈曲分析2.1 基本假定本文的理论推导基于以下基本假设:1)薄壳很薄.厚度h与壳半径r和壳长L相比为一小量，即h/r≪1，h/L≪1.2)应变ε充分小，即ε≪1.壳体的材料是弹性的，材料各向同性，并且满足胡克定律.3)直线法假设.薄壳变形前垂直于中面的直线变形后仍为直线，且垂直于中面.z向应变εz=0.4)中面法线方向上的应力与其他方向上的应力相比可以忽略，即σz=0.5)采用唐奈尔(Donnell)简化.即忽略中面位移u、v对壳体曲率改变及扭率改变的影响.w导数的二次方与应变是同阶量，即6)位移u、v很小，壳体法向位移w与壳体厚度是同阶量，即|u|≪h，|v|≪h，|w|=0(h).2.2 基本方程2.2.1 几何方程考虑初挠度的Von Karman-Donnell中面大挠度位移方程如下:壳体中任意一点的应变与中面应变之间的关系式为2.2.2 物理方程(本构方程)认为肋骨和纵骨的变形与柱壳一致.即肋骨和纵骨的位移函数同壳体一致.2.3 内力和内力矩从潜艇外壳上取出一块dxdy大小的单元，作用在该单元上的各内力与内力矩如图2所示图2 内力与内力矩分布图Fig.2 The forces and moments on an element各内力定义如下:2.4 应变能与外力势能2.4.1 潜艇外壳应变能艇体外壳是圆柱形壳体.所以只需推导圆柱形壳体的应变能公式，就知道了艇体的变形能公式.利用弹性体应变能的一般式子，即在这里，如同在板的弯曲理论中一样，由于根据在薄壳理论中所作的直法线假设，所以应该γyz=γzx=0.此外，与应力σx和σy相比，忽略正应力σz的值，即取σz=0就得艇体外壳板的应变能的表达式如下:将式(4)、(5)代入式(13)中，并沿厚度积分得2.4.2 纵向加强筋应变能纵向加强筋位置及横剖面图如图3所示.图3 纵向加强筋位置及横剖面图Fig.3 The position and transverse section drawing of longitudinal stiffening ribs认为纵筋处于单向受力状态，如果纵筋分布足够密且大小一致，均匀分布，不考虑纵筋偏心和扭转变形时，整个艇体纵筋的应变能可以写为式中:Ix为纵筋和附连壳板惯性矩，Ax为纵筋横截面积，b为纵向加强筋间距. 2.4.3 肋骨应变能肋骨位置及横剖面图如图4所示.认为肋骨处于单向受力状态，如果肋骨分布足够密且大小一致，均匀分布，不考虑肋骨偏心和扭转变形时，整个艇体肋骨的应变能可以写为式中:Iy为肋骨和附连壳板惯性矩，Ay为肋骨横截面积，a为肋骨间距.图4 肋骨位置及横剖面图Fig.4 The position and transverse section drawing of ribs2.4.4 外力势能外力势能Vf的表达式可以写为式中为作用在壳体边界单位长度上的x向分布力，p为作用在壳体表面单位面积上的z向分布力.综上所述，艇体结构总势能Π(u，v，w)的表达式如下2.5 变分法求平衡方程和协调方程当艇体外壳处于平衡状态时，在满足边界条件的情况下，总势能Π(u，v，w)的一阶变分等于零.因此:艇体壳板应变能的变分:纵筋应变能的变分:环肋应变能的变分:外力势的变分:几何方程的变分:将式(20)～(24)代入式(19)，利用高斯定理，得到式(25)中的前一项是平衡条件，后一项是自然边界条件.显而易见，通过设置Li=0(i=1，2，3)和B=0使上式得到满足.由此得到平衡方程:式(26)中各力和力矩的表达式如下:将式(6)～(11)代入式(27)，得到其中:由式(28)中的前3个式子得到其中:现在引入应力函数.设应力函数为F(x，y)，且F(x，y)满足下列关系:变形协调方程可以通过几何方程推导，利用式(29)和挠度函数，应力函数就可以解出，具体过程如下.根据几何方程(3)，消去方程中的u、v项，并引入缺陷因子，可得到将式(29)代入式(31)，再利用应力函数F(x，y)，可得到将屈曲挠度函数式(1)代入式(32)，由参考文献［6，8-9］可解得式中:p1为周向均布压力，p2为轴向均布压力.式中各系数的表达式如下:2.6 里兹法求临界载荷假设屈曲前，即前屈曲状态，艇体外壳在均匀静水外压力p=q作用下处于无矩应力状态，那么膜应力如下:受损后的潜艇壳体，在静水外压下的总应变能VS通过下式计算:将式(28)、(29)代入式(35)中就得到受损壳体的总应变能表达式如下:利用应力函数F(x，y)和几何方程就可以解出上式:其中:根据文献［7-8，10］静水外压力做功可以分为纵向压缩力p1做功和横向压缩力p2做功，分别计算如下.为了研究外力在壳偏离其初始平衡位置时所做的功，从壳中截取单元体来研究.单元体的边长分别为dx和dy，在其纵横剖面上分别受压缩力p1和p2作用，如图5所示.图5 单元体上力的作用图Fig.5 The forces on the element1)纵向压缩力p1所做的功:2)横向压缩力P2所做的功:将w的表达式(1)代入式(38)、(39)可得外力做功的表达式为而依据计算所得的外力功和总应变能VS得总能量的表达式如下如果将f和δ均视作为未知变量.根据里兹法，将Π分别对f和δ求偏导数:3 实例计算模型数据来自于文献［10］，本文只将纵筋的位置调整为内加筋.模型为纵横加筋圆柱壳，使模型的结构形式与单壳体潜艇耐压壳的结构形式一致，其尺寸如下:壳体半径R=850 mm;壳体长度L= 500 mm;壳体厚度t=4 mm;肋骨共有11根，间距L=46mm;肋骨尺寸:S1=δ×h=6mm×21 mm= 126 mm2;纵筋位于圆柱壳内侧，共24根，沿圆周均布，间距 b=222.5 mm;纵筋尺寸，S2=δ×h= 4 mm×15 mm=60 mm2.所采用的材料常数如下:材料屈服极限均为σS=784 MPa，材料的弹性模量E=2.0×105MPa，材料的泊松比μ=0.3.将模型数据的材料参数代入式(42)中，分别计算了f0=0，0.4，0.8，1.6，2.4，3.2 mm这6种不同初挠度下的载荷值，并绘制了载荷挠度曲线.所有计算在Mahematica5.2［11］中完成，计算结果在表1和图6中列出.F是挠度幅值，q 是载荷.表1 初挠度幅值与上临界载荷Table 1 Amplitude of initial deflections and the first critical loads初挠度幅值/ mm 0 0.4 0.8 1.6 2.4 3.2上临界载荷/ MPa 6.85 6.06 5.62 4.97 4.49 －图6 载荷－挠度幅值曲线Fig.6 Load-amplitude of deflection curves4 结论1)当初挠度为零，单壳体潜艇耐压壳的临界压力大挠度解与小挠度解一致，表明完美耐压壳的临界压力可由小挠度分析得到;2)对于结构受损后的耐压壳，表现为极值点屈曲，载荷随挠度幅值增加到局部极大值后，随着挠度幅值的增大反而减小;3)随着损伤程度加深，即初挠度幅值的增大，耐压壳的临界压力减小，表明耐压壳的承载能力下降;同时随着损伤程度加深，极值点变得越来越不明显，极值点屈曲问题渐渐转变为强度问题.参考文献:【相关文献】［1］DONNELL L H，WAN C C.Effect of imperfections on buckling of thin cylinders and columns under axial compression［J］.Journal of Applied Mechanics，1950(3):72-83. ［2］SHEINMAN I，SIMITSES G J.Buckling analysis of geometrically imperfect stiffened cylinders under axial compression［J］.AIAA Journal，1976，15(3):374-382.［3］YAMAKI N.Elastic stability of circular cylindrical shells［M］.The Netherlands:Elsevier Science Publishers B.V，1984:56-74.［4］王晓天，姚文，梁超.不同纵横均匀外压作用下环肋圆柱壳稳定性分析［J］.哈尔滨工程大学学报，2007，28(10): 1079-1083.WANG Xiaotian，YAO Wen，LIANG Chao.Research on stability of ring-stiffened cylindrical shells under uniform lateral external pressures［J］.Journal of Harbin Engineering 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美国伍兹霍尔海洋研究所科研装备概览摘要：综述了伍兹霍尔海洋研究所的概况、科研设施和支撑平台，梳理了其负责运行管理的科考船、载人潜水器、水下机器人、冰下机器人、滑翔器等科研装备，对这些科研装备的技术参数、研究领域、技术能力、所从事科研任务等进行了研究、介绍和剖析。
关键词：伍兹霍尔海洋研究所，科研设施，支撑平台，载人潜水器，水下机器人1.概况美国伍兹霍尔海洋研究所（Woodshole Oceanographic Institution），简称“伍兹霍尔研究所”（WHOI），坐落于美国东海岸，位于马萨诸塞州伍兹霍尔，靠近大西洋，拥有深水良港，地理位置十分优越。
其前身是1888年在伍兹霍尔建立的海洋生物研究实验室。
1927年，美国科学院海洋学委员会开始筹建海洋研究所，根据美国科学院的建议，于1930年成立伍兹霍尔海洋研究所（以下简称“伍兹霍尔研究所”），迄今已有92年历史。
第二次世界大战期间，伍兹霍尔研究所大量接受海军任务，为反潜战、两栖登陆和其他作战任务收集了若干海洋学信息，由此改为全年工作，研究力量迅速增强，与美国政府的合作增多，其年度预算的80%来自于联邦基金和合同。
战后由国家科学基金会和海军研究署（ONR）资助。
伍兹霍尔研究所致力于海洋科学与工程研究以及海洋学科的高等教育。
设有海洋生物学、海洋化学、海洋地质学、地球物理学、物理海洋学、海洋工程 6个系/研究室。
拥有大型实验室、科学考察船、各类潜水器、电子显微镜中心和计算中心等。
1957年以后，积极参与国际海洋考察等国际海洋科学活动，研究课题广泛，涉及海洋基础学科和海洋工程各方面。
在海洋生物研究，北大西洋洋流、墨西哥湾流与西部边界流以及大涡旋的研究，深海大环流模拟等方面取得了重大成果。
1960年代末，开设颁授海洋学博士学位的研究生课程，前期课程限于自然科学，后与麻省理工学院、哈佛大学等合作增设海洋政策和管理，海洋及其资源的利用、权益和归属等方面的课程。
Astron.Astrophys.325,124–134(1997)ASTRONOMYANDASTROPHYSICSThe interstellar medium in the edge-on galaxy NGC5907Cold dust and molecular line emissionM.Dumke1,J.Braine2,3,M.Krause1,R.Zylka1,R.Wielebinski1,and M.Gu´e lin31Max-Planck-Institut f¨u r Radioastronomie,Auf dem H¨u gel69,D-53121Bonn,Germany2Observatoire de Bordeaux,URA352,CNRS/INSU,B.P.89,F-33270Floirac,France3Institut de Radioastronomie Millim´e trique,300rue de la Piscine,F-38406St.Martin d’H`e res,FranceReceived17February1997/Accepted18March1997Abstract.In this paper we present new observations of the interstellar medium in the non-interacting edge-on galaxyNGC5907.We have observed the J=2−1and J=1−0lines of the12CO molecule and radio continuum emission atλ1.2mm.The distribution of the molecular gas(as traced by CO)shows a maximum in the central region and a ring or spiral arm atr∼7kpc.Further analysis of the major axis distribution reveals evidence for an inner ring-like structure at r∼3.5kpc.Thekinematics can be described by rigid rotation in the inner part,a turnover at∼3kpc,and differential rotation with a velocityof230km/s in the outer disk.The observed continuum emission is mainly due to thermalradiation of cold dust with an average temperature of T d=18K,with a small gradient from20K to16K from the centre to theouter disk.This cold dust component is necessary to explain ourresults.The dust emission closely follows the molecular gas in thecentral region,but is also detected at large radii where no COcan be seen.In these regions the dust absorption cross sectionper H atom atλ1.2mm is estimated to beσHIλ∼4.510−27cm2, a value similar to that in the outer parts of other galaxies.From theλ1.2mm emission we estimated a molecularmass of NGC5907of0.9109M ,about50%smaller thanfrom the CO emission.By combining the CO and contin-uum data we found that the CO-H2-conversion ratio increaseswith galactocentric radius,from∼0.71020at the centre to ∼1.61020cm−2/K km s−1at r=7.5kpc.A comparison of NGC5907and other edge-on galaxies con-cerning gas distribution,central kinematics and dust propertiesis presented.Key words:galaxies:individual:NGC5907–galaxies:ISM–galaxies:kinematics and dynamics–infrared:galaxies–radio continuum:galaxies–radio lines:galaxiesSend offprint requests to:M.D.(mdumke@mpifr-bonn.mpg.de)1.IntroductionThe evolution of spiral galaxies and their properties are deter-mined by many processes.One of the most important pointsis the occurrence and time-scale of star formation,which de-pends mainly on the amount,composition,and distribution ofthe available raw material.This raw material consists of neutralgas in either atomic or molecular form.The amount of atomic hydrogen can easily be derived frommeasurements of the21cm line of HI.The mass of molecu-lar hydrogen,on the other hand,is usually determined indi-rectly by observing the lowest rotational transition of the COmolecule.The measured line intensities are converted into H2column densities using a conversion factor X=N H2/I CO(1−0). The estimated molecular mass,however,is quite uncertain be-cause X is still a matter of debate(e.g.Maloney&Black1988;Combes1991;Arimoto et al.1996).Observations of thermal dust emission at mm-wavelengthsprovide an alternative way to estimate the total mass of the in-terstellar matter of a spiral galaxy.Although this emission isdifficult to observe due to its weakness,it has several advan-tages.Firstly,at millimeter wavelengths the dust is opticallythin.Secondly,the emission scales roughly with thefirst powerof the temperature.Thirdly,at this wavelength the dust absorp-tion cross sections do not depend very much on physical dustproperties like grain size,shape,composition,and surface prop-erties(Hildebrand1983;Draine&Lee1984).And,finally,in-terstellar dust is about2orders of magnitude more abundantthan the most abundant CO molecule in normal spiral galaxies.In the last few years,the advent of multi-channel bolometerarrays has made it possible to obtain high quality maps(i.e.highangular resolution and high sensitivity)of the cold dust emissionof nearby spiral galaxies.In order to study the relation of thedust to the atomic and molecular hydrogen in a normal late-type spiral,we decided to observe the non-interacting edge-ongalaxy NGC5907.This galaxy shows a relatively low level of star formationfrom the weak infrared emission measured by IRAS(Young etM.Dumke et al.:The interstellar medium in the edge-on galaxy NGC5907125al.1989).Therefore it is–together with NGC4565observedby Neininger et al.(1996)–some kind of counterpart to themore active galaxies already observed in the radio continuumat mm-wavelengths:NGC891(Gu´e lin et al.1993),NGC3079(Braine et al.1997),NGC3627(Sievers et al.1994),NGC4631(Braine et al.1995),and M51(Gu´e lin et al.1995).NGC5907was observed in the HI-line twenty years ago andwas thefirst non-interacting galaxy where a galactic warp couldbe detected(Gu´e lin et al.1974;Sancisi1976).Former CO mea-surements(Sofue1994;Garc´ıa-Burillo&Gu´e lin1995)haveshown that this galaxy is relatively weak in CO.Although itsnearly edge-on orientation of i∼86◦.5does not allow us to ob-serve the emission of individual star forming regions or spiralarms in the disk,this inclination increases the column densityalong the line of sight to a significant and easier measurablevalue.Therefore NGC5907is a good candidate to study the ra-dial distribution of the dust and its correlation with the molecularand atomic hydrogen distributions.This will be done especiallyin comparison with the other non-interacting edge-on galaxiesmentioned above,namely NGC891and NGC4565.The latterone shows an even lower star formation activity than NGC5907and is also CO-weak,whereas NGC891contains a considerableamount of molecular gas and shows a relatively high level ofstar formation.These two galaxies are classified as Sb and Sbc,respectively,in contrast to the Sc-galaxy NGC5907.Furthermore edge-on galaxies are suitable to investigate thethickness of the gas and dust layer.Since NGC5907is lackingstrong star formation,one does not expect to detect a thick diskor halo in this galaxy because star formation and the existenceand structure of a gaseous halo seem to be directly connected(e.g.Dahlem et al.1995).In this paper we present our molecular line and bolometerobservations of NGC5907.The following section describes theobservations and the data reduction.Sect.3presents the resultswe obtained from the CO observations.In Sect.4we discussthe thermal dust emission.We estimate dust temperatures andabsorption cross sections,and compare the distribution of thecold dust with that of the atomic and molecular gas.From this weget some hints on how the CO-H2-conversion factor may vary ingalactic disks.In Sect.5the results for NGC5907are comparedwith those obtained for other edge-on galaxies,and thefinalsection gives a summary of our results and some concludingremarks.Table1lists some basic parameters of NGC5907which willbe used throughout this paper.2.Observations and data reductionThe observations presented here were all made with the30mtelescope of the Institut de Radio Astronomie Millim´e trique(IRAM),located on Pico Veleta(Spain).2.1.Molecular line observationsThe observations of the12CO(1−0)and the12CO(2−1)lineswere done in May1995and July1996.We used one3mm(two Table1.Some basic parameters of NGC5907Type Sc(de Vaucouleurs et al.1991)λ1.2mm centre:(this work)R.A.[1950]15h14m35s.7Dec.[1950]56◦30 37 .0Dynamical centre:(Garc´ıa-Burillo et al.1997)R.A.[1950]15h14m35s.5Dec.[1950]56◦30 43 .3v hel677km/s(Garc´ıa-Burillo et al.1997) Distance11Mpc(Sasaki1987)(1 corresponds to53pc)Pos.Angle155◦(Barnaby&Thronson1992)Incl.86.5◦(Garc´ıa-Burillo et al.1997)during the second observing period)and two1mm SIS receivers available at the30m telescope simultaneously.The receivers were tuned for image sideband rejections≥10dB(≥30dB at115GHz).The system temperatures were300-400K at 115GHz and500-700K at230GHz(in the T∗A scale).In the following we use main-beam line brightness temperatures T mb. These are converted from the antenna temperatures,corrected for atmospheric attenuation and rear spillover,T∗A,through T mb=T∗A/ηmb.The beam efficienciesηmb=B eff/F eff are0.73 and0.45for115and230GHz,respectively.The beamwidth was measured on Mars to be21 for the12CO(1−0)line and 11 for the12CO(2−1)line.The backends used consisted of two512×1MHz channelfilter banks,connected to one3mm and one1mm receiver,and an autocorrelator unit,connected to the other1mm receiver(and the other3mm receiver in July 1996).The observations were centered on the major axis of the galaxy.Adopting the central position from the bolometer ob-servations(given in Table1),we observed several points out toa projected radius of240 with12 spacings near the centre and24 spacings further out.Additionally we observed a few points above and below the major axis at distances of12 and24 from the plane.The observations were made by wobbling the subre-flector at a rate of0.5Hz between the source and a reference position located between±2 and±4 in azimuth(depending on the observing position and the orientation of the source).Some scans at larger radii were observed in the position-switching mode with on-and off-position located symmetrically around the center.Cold load calibrations were made every4-8minutes.During the CO observations we checked the pointing ac-curacy in two different ways.Firstly,we made pointing scans towards1641+399and1418+546every1-2hours.Sec-ondly,we measured(every∼2hours)small cuts perpendic-ular to the major axis at the center,consisting of three points at z=0 ,+12 ,and−12 ,and checked their symmetry,since the central point is expected to be strongest and the intensity of both off-axis points to be roughly equal.From these cuts and the pointing corrections made after each pointing scan we conclude that the mean pointing uncertainty is∼1 .5.The data reduction was done in a standard manner using the GILDAS software package.126M.Dumke et al.:The interstellar medium in the edge-on galaxy NGC59072.2.Bolometer observationsTheλ1.2mm observations were carried out in March1995withthe19-channel bolometer array developed at the Max-Planck-Institut f¨u r Radioastronomie,Bonn.The19channels are lo-cated in the centre and on the sides of two concentric regu-lar hexagons,with a spacing between two adjacent channels(beams)of20 .The central frequency and bandwidth of thebolometer are estimated to be245GHz and70GHz respec-tively(Gu´e lin et al.1995).For calibration purposes we haveobserved maps of Mars and Uranus during the bolometer obser-vations.These maps yielded a conversion factor from observedcounts to mJy/beam area of0.32mJy(beam area)−1count−1.The beamwidth at this frequency is∼10 .7.The continuum maps of NGC5907were observed in the Az-El coordinate system,with a scanning speed of4 /s in Azimuthwith data-acquisition every2 ,and a subscan separation of4in elevation.During the observations,the subreflector was wob-bled at2Hz in azimuth,with a beam throw of1 .The startingpoint of each subscan was shifted a few arcseconds in azimuthwith respect to the preceding one,which leads to a skewed shapeof each single coverage in the Az-El space,with two edges ofthe maps parallel to the major axis of the galaxy.This as wellas the use of different map sizes(between330 ×100 and 250 ×180 )was done in order to ensure that each subscan covers the galaxy and at least90 of blank sky on either side.We observed a total offifteen single maps of NGC5907,fivecentered on the optical centre(Barnaby&Thronson1992),theothers shifted164 along the major axis to the northwest andsoutheast,respectively.Since the optical centre and the centre oftheλ1.2mm emission(as found by our observations)differ bya few arcseconds,all offsets throughout this paper are relativeto the latter position which is given in Table1.During the bolometer observing session the pointing accu-racy was checked every1-2hours on1418+546.The pointingcorrections were always smaller than3 .The atmosphere wasrelatively stable and the sky opacity was∼0.2most of the time(always smaller than0.3).NGC5907was observed at relativelyhigh elevations(55◦-70◦)what reduces possible calibration er-rors,which are typically of the order15%.The data reduction was done with the MOPS software.Asecond order baseline wasfitted to each individual scan in az-imuth direction.Thefinal restoration was done applying the“mask-and-shift”restoring method,as outlined in the“PocketCookbook”(Zylka1996).3.Molecular gas in NGC59073.1.Observational results and kinematicsThe spectra along the major axis of the galaxy obtained duringthe molecular line observations are shown in Fig.1.The max-imum peak temperatures of∼0.33K and∼0.36K for theCO(1−0)and the(2−1)line respectively are reached near thecenter.CO is detected up to radii of more than200 (∼11kpc).A striking feature of many of the spectra(r≤80 )is thatthe observed lines contain at least two components,and thatthe Fig.1.Maps of the observed12CO(1−0)(left)and12CO(2−1)(right) major axis spectra of NGC5907,smoothed to a velocity resolution of 10.4km/s.The scale of the spectra is indicated by the small box at the bottom.Offsets are along the major axis,north is negativecentral spectrum shows a clear asymmetry.A natural explana-tion for the latter is that the location of the dynamical centre of the galaxy is not at x=0 (the centre of theλ1.2mm emission), but shifted by a few arcseconds to the northwest.This idea is also supported by the small asymmetry visible in the position-velocity diagrams(Fig.2).Garc´ıa-Burillo et al.(1997),who observed the central region of NGC5907using the Plateau de Bure interferometer,found the dynamical centre of the galaxy atα1950=15h14m35.s5,δ1950=56◦30 43. 3.This corresponds to(x,z)=(−6. 4,+1. 2)in our coordinates.They also found a small offset between the dynamical centre of the galaxy and theM.Dumke et al.:The interstellar medium in the edge-on galaxy NGC 5907127Fig. 2.Position-velocity diagram of the 12CO(1−0)(left)and the 12CO(2−1)(right)observations parallel to the major axis at z =0.Contour levels are -0.04(dashed),0.04,0.08,0.12,...,0.4K for both tran-sitions.The velocity resolution is 20km/s.The rms noise is variable along the major axis with a typical value of about 30mK for both transitions.The thick lines indicate the rotation curve as described in the text-200-100100200radius [arcsec]0204060d e p r o j e c t e d C O i n t e n s i t y [a .u .]-200-100100200x offset [arcsec]10203040I C O [K k m /s]Fig.3.a Observed (dashed line and filled black circles)and modelled (solid line)12CO(1−0)intensity distribution along the major axis of NGC 5907.The modelled distribution is obtained by a least-squares-fit and results from the line-of-sight-integrated radial distribution shown in b .b Adopted radial CO profile which leads to the major axis distribution as shown in aposition of the maximum CO intensity,which is in agreement with our results.The kinematics of NGC 5907can basically be described by rigid rotation up to a radius of ∼55 (which corresponds to ∼3kpc),followed by differential rotation with a rotational ve-locity of 230km /s.These values are relative to the systemic ve-locity of 677km /s and the dynamical centre given in Tab.1.The rotation curve follows from this work and the HI data (Caser-tano 1983)and is plotted as a thick line on the position-velocity diagrams (Fig.2).There are,however,a few deviations from this simple behaviour.A second line component is visible in the spectra near the central region (at |x |<30 ).Here the rigid (“normal”)rotation of the inner disk is accompanied by a high-velocity wing,with a much larger velocity gradient.This component is visible in the individual spectra as well as in the p -v -diagrams,and leads to a total line width of about 350km/s atthe assumed central position.It most probably results from non-circular motions due to a bar,as already suggested by Garc´ıa-Burillo &Gu´e lin (1995)and Garc´ıa-Burillo et al.(1997).3.2.Radial gas distributionThe observed major axis distribution of the CO intensity is the sum of the radial distribution and a projection effect (by which the emission at several radii is projected onto a certain position on the major axis).In order to deproject this distribution,we as-sumed a radial model function,consisting of a central Gaussian peak and two Gaussian rings,and fitted the resulting major axis distribution to the data.The existence of two ring-like struc-tures is suggested by two intensity maxima (at x ∼±60 and x ∼±120 )on either side of the centre in the p -v -diagrams.128M.Dumke et al.:The interstellar medium in the edge-on galaxy NGC5907Fig.4.Contour map of the continuum emission of NGC 5907at 245GHz,overlaid onto an optical image extracted from the Digitized Sky Survey.The beam size of 15 is indicated by the filled white circle in the lower right corner.The rms noise depends on the location in the map;on the galaxy it is about 1.5mJy/beam area,contour levels are 4,8,...,24mJy/beam area.The thin black lines indicate the λ1.2mm centre and the major axis of the galaxy as given in Table 1Additionally this distribution with two rings fits the data better than a distribution with just one ring (at r ∼120 ).The result can be seen in Fig.3.The best fit was obtained for ring radii of r 1=3.7kpc and r 2=7.0kpc and widths (FWHM)of Θpeak =4.4kpc,Θring1=1.4kpc,and Θring2=2.3kpc for the central peak and the inner and outer ring respectively.However,the outer “ring”may in fact be spiral arms seen more or less tangentially.4.Cold dust in NGC 59074.1.Observational resultsA contour map of the λ1.2mm continuum emission,overlaid onto an optical image extracted from the Digitized Sky Survey,is shown in Fig.4.This λ1.2mm-map is already smoothed to a beamsize of 15 to improve the signal-to-noise ratio.The emission is concentrated along a narrow ridge which follows closely the dusty optical disk,but is less extended,per-haps because of the sensitivity limit of our data.Although the emission is enhanced near the centre,there is no evidence for a nuclear point source.Several local maxima are visible along the major axis,but with some difference between the northern and the southern half.Whereas in the north there are three separatepeaks at projected radii of about 1 ,2 ,and 3.5,they seem to be somehow smeared out in the southern half,except the one atx ∼3 .5.In Fig.5we show the λ1.2mm continuum map,smoothed to a resolution of 21 HPBW,together with an HI total intensity map as received from Sancisi (m.),and the positions observed in the CO lines.NGC 5907is a really exemplary galaxy for the existence of galactic warps in neutral hydrogen (Sancisi 1976).It is,moreover,the first “normal”galaxy where a warp in the outer disk was observed.But in contrast to NGC 4565,another normal edge-on galaxy recently observed at λ1.2mm (Neininger et al.1996),no indication for a warp of the ther-mal dust emission can be seen (although the northernmost peak seems to be slightly shifted westwards with respect to the major axis).This may of course be due to the decreasing sensitivity at the outer edges of our dust map,which we reach at radii of ∼300 ,where the HI-warp is only marginally detected.4.2.ISM distributions along the major axisFig.6shows the distribution of the λ1.2mm continuum emis-sion along the major axis,together with the line intensities of the 12CO(1−0)and the HI emission.The spatial resolution of all three data sets is 21 ,as given by the 12CO(1−0)data.The continuum emission shows (more clearly in this plot than in the maps)the existence of two bright maxima at the end of the emission ridge (x ∼±200 )and of two less pronounced ones at x ∼±120 ,even if the southeastern one seems to be smeared out.Besides these similarities between the northern and the southern half the distribution is slightly asymmetric on smaller scales.The emission is detected up to radii of ∼250 in the south and even further,up to ∼280 ,in the northern half (with a significance of 2σ).Since there is λ1.2mm continuum emission beyond the edge of the CO disk,dust associated with the atomic component makes a significant contribution to the 1.2mm flux.The distribution of the CO line-intensities (and therefore the column densities of the molecular gas)shows also a maximum in the central region and decreases with increasing distance from the centre.Two further maxima are apparent at x ∼±120 .These features may be due to molecular rings and/or spiral arms in the inner part of the disk.The HI distribution shows a different behaviour.It has a minimum near the centre,increases at x ≤80 ,stays then roughly constant with several local peaks up to x ∼±200 ,and drops again further outwards.Hence this component is much more extended than the molecular gas in this galaxy.If we compare the dust emission with both gas phases,we find that it correlates with the molecular gas in the inner part ofM.Dumke et al.:The interstellar medium in the edge-on galaxy NGC5907129Fig.5.Contour maps of theλ1.2mm con-tinuum emission(left)and the HI line emis-sion(middle),as well as positions observed in the CO lines(right),all at the same scale and aligned in declination.The spatial reso-lution of the two maps is21 .Contour lev-els are3,7,12,18,25,33mJy/beam area for theλ1.2mm map and8,15,25,40,55, 701020atoms cm−2for the HI mapthe disk.At large radii,on the other hand,where CO is no longer detected,it seems to follow the HI emission.This result con-firms qualitatively that for NGC4565of Neininger et al.(1996). At smaller scales,wefind the two outer peaks in the dust emis-sion at x∼±200 corresponding to local maxima in the HI distribution,although there is a small displacement,especially on the southeastern side.From both CO peaks at x∼±120 only the northwestern one has a clear counterpart in the dust distribution,whereas in the southeastern half the dust emission shows just a small enhancement at this radius.4.3.Disk thicknessGarc´ıa-Burillo et al.(1997)estimated from their Plateau de Bure observations of the central region of NGC5907an inclina-tion of86.5◦and a thickness of the molecular disk of≤3 .In or-der to check if this is in agreement with our observations,wefit-ted the observed z-distribution(the averaged spectra are shown in Fig.7)with a Gaussian profiing the beamwidths given in Sect.2.1we determined a deconvolved thickness(FWHM) of the CO emission ridge of(13±5) ,somewhat thicker than in NGC4565(Neininger et al.1996).Additional off-axis ob-servations at x=60 have shown that this apparent thickness is nearly constant along the major axis.In order to estimate the extent of the atomic gas and the thermal dust emission perpen-dicular to the plane,we performed cuts along the minor axis of both maps.These lead to a mean beam deconvolved FWHM of the emission of(47±4) for the HI and(16±4) for the λ1.2mm emission.Since the galaxy is not perfectly seen edge-on,but under an inclination of i=86.5◦,a particular fraction of the off-axis emission is just projected from large radii to large z.We modelled this emission,using the radial CO profile obtained in Sect.3.2and a similar model,consisting of three rings,for the HI emission.The best agreement between model and data is found for a disk with a thickness(FWHM)of8 (which corresponds to∼400pc)for the CO and of28 (∼1.5kpc)for the HI.Both values seem to be unexpectedly large for a non-interacting spiral with only moderate star forming activity.We should note,however,that it is difficult to account for a warp in this simple modelling,and the results are very sen-sitive to the exact values of the inclination and the telescope beamwidth.Therefore,due to the large uncertainties,a thin molecular disk cannot be ruled out.4.4.Dust properties4.4.1.Non-dust contributions to the observedfluxUsing a ring integration method,we have determined the total flux density atλ1.2mm and found S1.2mm=605±55mJy.This value,however,cannot be attributed to thermal dust radiation alone.The broad band emission measured with the bolome-ter at245GHz rather consists of several components:thermal dust emission,free-free radiation,synchrotron radiation,and the CO(2−1)and some weaker lines.Since we are mainly in-terested in thefirst,we have to determine the contributions due to the other processes and to subtract them.The contribution of the12CO(2−1)line to the surface brightness measured with the bolometer can be calculated throughF line=2kν3c−3∆νbolΩbeam I CO(2−1)≈0.058I CO(2−1)(1) (with I CO(2−1)=lineT mb(12CO(2−1))dv in Kkms−1)for a bolometer bandwidth of70GHz and a beamwidth of11 for the continuum observations.With an assumed contribution of other isotopes and lines from other molecules of about10%of 12CO we estimate a totalflux density due to line contributions of S line=52±4mJy.The contribution of the continuum emission due to thermal and relativistic electrons is more difficult to determine since the130M.Dumke et al.:The interstellar medium in the edge-on galaxy NGC 5907300200100-100-200-300x offset [arcsec]010203040I C O [K k m /s ]SENW403020100I 1.2mm [mJy/b.a.]HI1.2 mmCO(1-0)Fig.6.The distribution of the 12CO(1−0)(thick dashed line,left scale)and the λ1.2mm continuum (thick solid line,right scale)along the major axis of NGC 5907.The HI distribution (thin solid line,arbi-trary units)is also shown.The spatial resolution in all three curves is 21radio continuum flux density at ν=1−10GHz originates partly in a double background source in the southern half of the galaxy (Hummel et al.1984;Dumke et al.1995).Furthermore the spectral behaviour of this background source is unknown,and the fraction of the galaxies’thermal emission is difficult to estimate.We used a total flux density of 47±5mJy at a frequency of 10.55GHz as derived by Dumke et al.(1995),a thermal fraction of 30%at this frequency and a nonthermal spectral index of −0.85which are typical for spiral galaxies (Niklas et al.1997)to calculate a value of S sync+ff =13±4mJy at 245GHz,which is about 2%of the total flux density.Besides these integrated values,we had to estimate the non-dust contributions along the major axis.The fraction of the CO lines,i.e.the line-to-continuum ratio,was calculated for each position from the CO(2−1)line following Eq.1and subtracted.Again we assumed that a fraction of 10%of the 12CO(2−1)-line stems from other lines in the bolometer band.For the free-free and synchrotron emission,we subtracted a fraction of 2%at each position,in accordance with the value estimated above.4.4.2.Dust temperaturesAfter subtracting the contributions of molecular lines and of synchrotron and free-free radiation,we determined a total flux density at 245GHz due to thermal dust emission ofS dust =540±60mJy .Including published IRAS flux densities (Young et al.1989)our observations allow to estimate color temperatures for the dust.We fitted a two-component modified Planck function to the data,using the points from 25µm to 1.2mm and under the assumption of a dust spectral index of 2(e.g.Chini et al.1986).The observed spectrum and the fitted curves (as well as their sum)are shown in Fig.8.The estimated temperatures for the two components to which we refer as cold and warm dust are 18K and 54K respectively.This result shows thatcoldFig.7.Averaged 12CO(1−0)and (2−1)spectra of the cuts through the centre.The portion of the spectra shown in each box ranges from v hel =300km /s to v hel =1000km /s and from T mb =−0.1K to T mb =0.4Kdust is necessary to explain the thermal continuum emission at λ1.2mm.The warmer dust alone which can be detected in the far-infrared by IRAS is not sufficient to account for the strong mm-emission and to explain our data.Although NGC 5907is a relatively inactive galaxy which does not show any signs of remarkable star forming activity (e.g.Dumke et al.1995),the dust emission is slightly enhanced at smaller galactocentric radii,and the dust may be somewhat warmer in this region.The FIR emission of NGC 5907was mapped by Wainscoat et al.(1987),using the IRAS CPC in-strument,at λλ50and 100µm with a resolution of 75 and 89 respectively.These maps were used to obtain spectra at different positions along the major axis of NGC 5907.We found that the temperature of the cold dust is somewhat higher in the central region (∼20K)than the value we got from the integrated flux densities,and drops to ∼16K at the outer disk.A similar de-crease is also found for other normal disk galaxies like NGC 891(Gu´e lin et al.1993),NGC 4565(Neininger et al.1996),or our Milky Way (Cox &Mezger 1989).。
江西农业大学学报2011，33（3）：0616－0621http：//xuebao．jxau．edu．cn Acta Agriculturae Universitatis Jiangxiensis E－mail：ndxb7775@sina．com7种典型挺水植物净化生活污水中氮磷的研究杨林1，伍斌2，赖发英1*，张俊3，高勇生1（1．江西农业大学国土资源与环境学院，江西南昌330045；2．江西省南昌县环保局，江西南昌330200；3．江西农业大学南昌商学院，江西南昌330045）摘要：挺水植物是构建人工湿地植被系统的主要植物类型，选取7种典型的具有一定景观效应和经济价值的挺水植物，初步研究它们对生活污水中的氮磷降解特性以及氮磷积累及其分布状况。
结果表明：美人蕉、黄菖蒲、香根草、薏苡都表现出较强的氮磷降解能力，生活污水中总氮磷的去除率与湿地植物氮磷的积累量成线性相关（P＜0．05），各植物间以及其自身的地上部分与地下部分的生物量（鲜质量）差异显著（P＜0．05），对氮磷的降解与水力停留时间成线性相关，相关系数均大于0．9，说明它们有较为稳定的氮磷吸收能力。
通过收割可以去除整个植株总氮和总磷含量的60% 80%。
关键词：人工湿地；挺水植物；生命周期；氮磷中图分类号：X173文献标志码：A文章编号：1000－2286（2011）03－0616－06Studies on Seven Typical Emerging Plants AbsorbingNitrogen and Phosphorus in Constructed Wetlands YANG Lin1，WU Bin2，LAI Fa-ying1*，ZHANG Jun3，GAO Yong-sheng1（1．College of Land Resources and Environment，JAU，Nanchang330045，China；2．Nanchang County Environmental Protection Agency，Nanchang330200，China；3．College of Nanchang Business，JAU，Nan-chang330045，China）Abstract：Emerging plants are the main types of plants for the constructed wetland vegetation system．In this test，seven typical emerging plants which have a certain landscape effect and economic value are selected to study their degradation，accumulation and distribution of nitrogen and phosphorus in constructed wetlands，which provides a theoretical backbone for the promotion of constructed wetlands．The experiment results showed that：Cannaindica，Irispseudacorus，Vetiveriazizanoides and Schoenoplectuslacustris all have a strong degradation ability of nitrogen and phosphorus，and their degradation of nitrogen and phosphorus has a linear correlation with HRT after a period of adaptation to constructed wetlands and the correlation coefficients are larger than0．9．These indicate that they have a stable absorption of nitrogen and phosphorus．The total plant uptake of nitrogen and phosphorus accounts for60%to80%of the overall nutrient removal in constructed wet-lands．Key words：wetlands；emerging plant；life cycle；nitrogen and phosphorus收稿日期：2011－12－08修回日期：2011－03－24基金项目：“十一五”国家科技支撑计划项目（2008BAD96B04）作者简介：杨林（1982—），男，硕士生，主要从事污染防治与生态修复研究，E－mail：yanglin5201234@163．com；*通讯作者：赖发英，副教授，博士，硕士生导师，E－mail：laifyjx@126．com。
782017.04军事文摘防 务 纵 览据海军技术网2017年2月8日报道，通用动力公司的巴斯钢铁造船厂向美国海军交付了新的“阿利·伯克”级导弹驱逐舰“拉斐尔·佩拉尔塔”号（DDG 115）。
该舰已顺利完成了海试和码头试验，确保了DDG 115随时可以入役。
“拉斐尔·佩拉尔塔”号是自2010年美海军重新启动该项目以来在巴斯钢铁造船厂开发的第一艘“阿利·伯克”级驱逐舰，也是通用动力公司重新启动生产后，提供给美国海军的第二艘舰艇。
新一艘“阿利·伯克”级驱逐舰USS “拉斐尔·佩拉尔塔”号交付美国海军据中国国防科技信息网2017年2月7日综合报道，AUDS反无人机系统已经达到商品化阶段，目前已服役于多个美军部队。
该系统是由英国布莱特监视系统公司、切斯动力公司和企业控制系统公司联合研发的无人机防御系统。
AUDS反无人机系统已达到商品化阶段韩国从美国采购“响尾蛇”和“幼畜”导弹据美国合众社2017年2月2日报道，美国批准向韩国出售“响尾蛇”和“幼畜”导弹。
据负责管理对外军售项目的美国国防安全合作署向国会报告，两份合同总值1.4亿美元。
雷声公司是两份合同的主要承包商。
据中国国防科技信息网2017年2月4日报道，罗马尼亚同通用动力公司欧洲地面系统部签订第五批“食人鱼”III型8×8轮式装甲车合同。
首批装甲车早在2007年就已开始交付。
该合同于2016年12月30日正式签署，合同内容包括升级在罗马尼亚武装部队服役的轮式装甲车。
瑞士“食人鱼”轮式装甲车由瑞士莫瓦格公司研制。
目前已成为国际军贸市场上的热门产品，长盛不衰。
除罗马尼亚采购外，欧洲、非洲、澳洲、北美和南美洲等多个国家采购了“食人鱼”。
罗马尼亚继续进口“食人鱼”轮式装甲车美国海军升级气象预报与作战管理系统据军事宇航2017年2月6日报道，雷声公司作战管理专家表示将升级美海军气象预报与嵌入式计算系统，辅助指挥官规划、执行作战，免受不利天气条件影响。
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资料图：1959年12月5日进入现役的美国海军SSN-584海龙号攻击型核潜艇1950年8月，美国总统杜鲁门签署了建造第一艘核潜艇的正式文件，并将其命名为“鹦鹉螺”号。
1951年8月20日，电船分公司签订了“鹦鹉螺”号的建造合同，1952年6月14日开工。
1953年9月15日，第2艘核潜艇“海狼”号也在电船分公司开工建造。
当这两艘核潜艇尚未服役时，1955财政年度，4艘排水量较小且造价较低的鳐鱼(Skate)攻击型核潜艇项目获批。
批量建造组建成军“鹦鹉螺”号和“海狼”号只能算是美国海军名义上的第一批核潜艇，因其带有浓厚的试验性质，主要技术关键是解决反应堆上艇的问题，艇体线型是第二位的问题。
因此，这两艘核潜艇的排水量都显得过大，线型也不够光顺。
而紧跟其后建造的鳐鱼级就要妥善解决反应堆与艇体进一步协调的问题，使其真正成为可以部署在第一线的作战潜艇。
首先想到的是，将新艇的主尺度和排水量缩小到与刺尾鱼级常规动力潜艇相当的程度。
刺尾鱼级是美国战后建造的第一批常规动力潜艇，主尺度为81.99 x 8.23×5.18米.水面排水量1800吨，水下排水量2400吨。
鳐鱼级还在方案论证初始期，“鹦鹉螺”号和“海狼”号止建着，核潜艇水下高速产生的巨大影响是在其后的实践中得以验证的。
因而当时的鳐鱼级的设计理念，只能建立在二战的经验上，简言之为：把刺尾鱼级所具有的水下航速与核动力的无限水下续航力结合起来，鳐鱼级的主要战术技术性能指标就被定位存这种程度上。
1954年确定的鳐鱼级水下排水量大约为2500吨，总长度为73.2米，宽度为8.7米，水下最高航速为18节。
考虑到要批量建造，基本设计方案出台后，反复进行了多次讨论和修改。
直到1955年，首制艇开工建造前，主尺度和备种状态的排水量才最后确定下来。
鳐鱼级的最终主尺度为81.7×7.9×6.1米，水而排水量为2552吨，水下排水量为2851吨，仍采用常规动力艇型。
a r X i v :a s t r o -p h /9806395v 1 30 J u n 1998Ring structure and warp of NGC 5907–Interaction with dwarf galaxies 1Zhaohui Shang,2,3,4Zhongyuan Zheng,2,4Elias Brinks,5Jiansheng Chen,2,4David Burstein,6Hongjun Su,2Yong-IK Byun,7Licai Deng,2,4Zugan Deng,4,8Xiaohui Fan,2,9Zhaoji Jiang,2,4Yong Li,6Weipeng Lin,2,4Feng Ma 3Wei-hsin Sun,7Beverley Wills,3Rogier A.Windhorst,6Hong Wu,2,4Xiaoyang Xia,4,10Wen Xu,2,6Suijian Xue,2,4Haojing Yan,2,6Xu Zhou,2,4Jin Zhu,2,4and Zhenlong Zou,2,4ABSTRACTThe edge-on,nearby spiral galaxy NGC 5907has long been used as the prototype of a “non-interacting”warped galaxy.We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture.First,a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy.The ring is elliptical in shape with the center of NGC 5907close to one of the ring’s foci.This suggests the ring material is in orbit around NGC 5907.No gaseous component to the ring has been detected either with deep H αimages or in Very Large Array (VLA)HI 21–cm line maps.The visible material in the ring has an integrated luminosity ≤108L ⊙and its brightest part has a color R–I ∼0.9.All of these properties are consistent with the ring being a tidally-disrupted dwarf spheroidal galaxy.Second,we find that NGC 5907has a dwarf companion galaxy,PGC 54419,projected to be only 36.9kpc from the center of NGC 5907,close in radial velocity (∆V =45km s −1)to the giant spiral galaxy.This dwarf is seen at the tip of the HI warp and in the direction of the warp.Hence,NGC 5907can no longer be considered “non-interacting,”but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies.These results,coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies,suggest that tidal interaction with companions,even if containing a mere 1%of the mass of the parent galaxy,might be sufficient to excite the warps found in the disks of many large spiral galaxies.Subject headings:galaxies:individual(NGC5907,PGC054419)–galaxies:interactions –galaxies:photometry–galaxies:spiral–radio lines:galaxies1.IntroductionNGC5907is an edge-on spiral galaxy,large in an-gular size,with a well-known warp both in its HI gas (Sancisi1976;see also below)and in its optical disk (Sasaki1987;Morrison,Boroson,&Harding1994; Zheng et al.1998).As such,it has been a popu-lar galaxy in which to study the vertical luminosity distribution in a spiral galaxy,not only in the opti-cal(Morrison,Boroson,&Harding1994;Sackett et al.1994;Lequeux et al.1996;Lequeux et al.1998; Zheng et al.1998),but also in the infrared(Rudy et al.1997).Much of the recent interest on NGC5907 was stimulated by the announcement by Sackett et al. of the detection of a faint halo around it,sufficient to supply the halo mass of this galaxy.We present here deep optical images and new VLA HI maps of NGC5907that are used to reassess the origin of the warp in this galaxy.In a separate paper (Zheng et al.1998),we will use these same data to study the halo of NGC5907in detail.2.ObservationsOptical observations of NGC5907were made as part of the Beijing-Arizona-Taipei-Connecticut(BATC) Color Survey of the Sky(cf.Fan et al.1996).This survey uses the Beijing Astronomical Observatory (BAO)0.6/0.9m Schmidt telescope equipped with a 2048×2048Ford CCD and a custom-designed set of15intermediate-bandfilters to do spectrophotom-etry for specific1deg2regions of the northern sky. NGC5907is in the center of one of these regions and,given the great interest in its low surface bright-ness properties,we obtained long integrations of it in two BATCfilters:central wavelength6660˚A,band-width480˚A(m6660)and central wavelength8020˚A, bandwidth260˚A(m8020).The CCD subtends58′×58′(1.71′′/pixel)in the focal plane of the BAO Schmidt.Out of43hours of actual observation of NGC5907at6660˚A,we select the84best images for analysis with a total exposure time of26.17hours(Zheng et al.1998).The telescope was centered at slightly different positions for these images for greater reliability offlat-fielding.Figure1 shows the inner part of the combined BATC m6660 image with low surface brightness features empha-sized.We also obtained21hours of integration with the8020˚Afilter,of which the best16.7hours were used.By directly comparing with standard broad-band photometry of NGC5907(Morrison,Boroson,&Harding1994;Rudy et al.1997),we obtain the transformation between our two bands and R and I bands(Zheng et al.1998).Within an error of0.5mag arcsec−2,our limiting magnitudes correspond to28.6 and26.9mag arcsec−2in R and I,respectively.As is evident from Figure1,a luminous ring en-compasses this galaxy.The part of this ring closest to NGC5907can be seen faintly in Figure3of Mor-rison et al.(1994).In separate papers(Zheng et al. 1998;Chen et al.1998),we detail the data taking and data reduction processes that permit us to reli-ably investigate low surface brightness features on our images.For the present paper,we present Figure1as evidence that we can reliablyflatfield large portions of our images to very faint surface brightnesses.We have also used the McDonald Observatory 0.76m telescope(field of view46′×46′with a2048×2048CCD)to obtain broad band R(4.5hours)and 30˚A–wide Hα(7.5hours)and[OIII](2.5hours)im-ages of NGC5907.The narrow bandfilters are of suf-ficient width to cover gas emission from zero velocity to well past the667km s−1heliocentric recession ve-locity of NGC5907.The ring clearly appears in the 0.76m R images(ruling out ghost images on Schmidt plates as a possible source),but does not appear in either narrow band image(the exposures of which are too short to see the ring in just the faint continuum), confirming previous Hαobservations(Rand1996).In order to understand the distribution of neutral hydrogen gas around NGC5907,21cm HI line obser-vations were obtained with the VLA in its modified C–array(one antenna each from the middle of the East and West arm having been moved inward to im-prove coverage of the inner portion of the uv–plane). We employed spectral line mode4,in which the two independently tunable passbands are used to cover a total velocity range of around1000km s−1,centered on667km s−1and with a velocity resolution of20 km s−1.To optimize sensitivity,both right and left hand polarized emission are recorded.At21cm,thefield of view of the VLA is about32′, large enough to include the area of interest.As our aim was to go as deep as possible,naturally weighted maps were made,leading to a synthesized beam of 18′′,sufficient to resolve the ring.The total integra-tion time of6hours results in a1σnoise level of0.23 mJy beam−1.This translates to a column density of 9×1019atom cm−2assuming a3σdetection in two adjacent channels.The resulting HI map,superim-posed on our optical image of NGC5907,is shownin Figure2.The observations confirm the impressive warp reported earlier by Sancisi(1976).On the other hand,within the quoted sensitivity limits no HI was found to coincide with the optical ring.3.The RingThe possible physical interpretations of this ring are either Galactic in origin—“cirrus,”planetary nebula or supernova remnant—or physically asso-ciated with NGC5907.Examination of the whole BATCfield of view(only1/4of which is shown in Fig-ure1)shows no other evidence of ring-like structures near NGC5907.In addition,the Burstein–Heiles (1978)predicted reddening for this galaxy is only E(B–V)=0.003.These two facts make it unlikely that this ring is an artifact due to Galactic“cirrus.”If the ring has a Galactic origin,its ionized gas should easily have been detected on our narrow bandfilter images.In addition,from our images we measure the m6660−m8020color to be0.7±0.3mag arcsec−2,of the brightest part of the ring(26.8±0.1m6660arcsec−2). This corresponds to an R–I color of0.9±0.4based on our transformation to broad-band photometry,cer-tainly not the color of a planetary nebula.These ob-servations,together with the fact that thefield is at high Galactic latitude(b=+51◦),make it highly unlikely that this ring could be a Galactic super-nova remnant or a planetary nebula.While we can not completely rule out the possibility that this is a planetary nebula,it would have to be relatively close (within1kpc),very old and cold,with little ionized gas.Alternatively,the ring is physically associated with NGC5907.To test this hypothesis we derived the lu-minosity distribution along the ring andfitted it with an ellipse(Figure3).Wefind that it is almost per-fectly elliptical in shape.Within the errors,the center of the galaxy falls on the ring’s major axis,and is close to one of its foci,as should be the case if the mate-rial in the ring is in orbit around NGC5907.The separation of1.4′between the focus and the center of NGC5907implies an orbit inclination of45◦and in-trinsic ring dimensions of13.4′×10.3′and eccentricity 0.63.The major axis size is the same as the optical di-ameter of NGC5907itself,43kpc at an assumed distance of11Mpc(using H0=75km s−1Mpc−1). Thus,based both on the lack of a plausible alterna-tive and a plausible orbital interpretation of the ring,our conclusion is that the ring is physically associated with NGC5907.How bright is the ring?Fan et al.(1996)showed that we canflatfield BATC images to<1%accuracy (see also Zheng et al.1998),and photometrically cali-brate them to1–2%absolute accuracy usingflux stan-dard stars(Oke&Gunn1983).Our images yield an average sky brightnesses of21.25mag arcsec−2at 6660˚A and19.91mag arcsec−2at8020˚A,respectively (on the A B standard system of Oke&Gunn1983). We get m6660≥14.7for the ring by taking the aver-age surface brightness for the part of the ring we can see and assuming a complete ring of similar surface brightness.In contrast,by replacing all foreground stars with the mean value of surrounding background,wefind that NGC5907itself has m6660≈9.9to a surface brightness of27m6660arcsec−2.From our VLA ob-servations we obtain a rotation velocity of205km s−1 and an outer HI radius of7.5′(25kpc),giving a dy-namical mass of1.9×1011M⊙.Based on these measurements,the luminosity of the ring is≤1.2%that of the galaxy,or an absolute 6660˚A luminosity of≤108L⊙.While it is evident the ring is not of uniform surface brightness,this upper limit is comparable to the luminosity estimated for the Sagittarius dwarf galaxy,recently found to be in the process of tidal disruption by our own Galaxy (Ibata,Gilmore&Irwin1994.)The R–I color of∼0.9of the brightest part of the ring suggests that the optical emission is mostly from late-type stars.The lack of detection of gas in the ring,either in the VLA21cm map or the Hαand O[III]images, suggests that gas is a minor constituent of this ring. For example,suppose the pre-tidally-distorted dwarf galaxy originally had an equal amount of gas asso-ciated with it as stars(a reasonable assumption for low–mass,dIrr galaxies),or∼108M⊙.If we dis-tribute this gas evenly along the ring,we would ex-pect a column density of4×1019atom cm−2,close to our detection limit.Only modest clumping would be sufficient for us to detect this gas,which we do not see (cf.Figure2).We thus conclude that the ring con-sists mostly of stars,in agreement with its measured R–I color.4.PGC54419and the WarpOur VLA map clearly shows the well-known warped HI disk of NGC5907(e.g.,Sancisi1976)extendingfar beyond the optical disk.Because of the absenceof any nearby galaxy candidate,NGC5907has long been considered a prime example(Sancisi1976)of a non–interacting galaxy with an HI warp.However, our VLA map reveals that the object PGC54419, which was once considered a background object,hasa radial velocity of712.0±1.5km s−1,or only45 km s−1from that of the main galaxy.It thereforeis a dwarf companion at a projected distance of36.9 kpc(∼11.5′)from the nucleus of NGC5907.It is located near the northern tip and in the direction of the warp,at some3.7′(12kpc)in projection to the west.PGC54419is likely closer to NGC5907than the Magellanic Clouds are to the Milky Way.We obtain m6660=15.34±0.02and m8020= 15.33±0.02for PGC54419,with m6660−m8020= 0.01±0.03(R–I∼0.2).From Fan et al.(1996),we estimate its V mag to be essentially the same as itsm6660mag,or V=15.34.The angular size of PGC 54419is54.6′′×31.4′′(2.9×1.7kpc),yielding an in-clination of56.6◦(based on an intrinsic axial ratio of 0.2).From the VLA data we observe an HI profile with full width at20%maximum of88km s−1,giv-ing an inclination-corrected rotation velocity of53kms−1.From this,we measure the mass of PGC54419tobe9.5×108M⊙(0.5%the mass of NGC5907),and its mass-to-light ratio to be12in solar units.From the VLA HI profile we measure an HI mass of3.6×107M⊙for this galaxy.In all of its measured characteristics, PGC54419is a dwarf irregular galaxy(cf.Roberts& Haynes;and is likely misclassified as a spiral galaxy; see Paturel1989).It is of interest to understand why PGC54419was not previously detected in HI by Sancisi(1976).The object measures,in the channel map at715km s−1in which it is most clearly seen,about30′′×12′′(ata position angle of∼65◦)and has an integratedflux density of14±2mJy.Once smoothed to the resolu-tion obtained by Sancisi(51′′×61′′)the source has become unresolved and itsflux density corresponds to 2.6Kelvin,or less than4σin Sancisi’s maps.The sig-nal in neighbouring channels falls well below3σwhich explains why it was not detected in the Westerbork data.5.DiscussionWe propose that the ring around NGC5907was once a dwarf spheroidal galaxy in orbit around NGC5907, now tidally-disrupted by its interaction with the larger galaxy.A nearby(at36.9kpc projected distance) dwarf irregular galaxy is suggestively situated right at the end of the more prominent warp in NGC5907 (Figure2).At the very least,NGC5907is no longer a“non-interacting”galaxy with an HI warp.Low surface brightness,ring–like structures may be common around galaxies,as few nearby galaxies have been probed as deeply as NGC5907.Even our own galaxy is tidally interacting with its entourage of dwarf galaxies(e.g.the Sagitarrius dwarf;Magellanic stream)and is a likely candidate for such a ring-like feature in the future(cf.Johnston,Spergel&Hern-quist1995).Indeed,models by Johnston et al.(1995) show that such a ring could exist from the tidal dis-ruption of a dwarf galaxy in much the form we see it around NGC5907.A dwarf spheroidal galaxy would have low velocity dispersion(cf.Bender,Burstein& Faber1992),so its tidal debris would tend to produce a coherent stream.The stream would tend to bunch up at apogalacticon,which is near where we see the highest surface brightness in the NGC5907ring.The models of Johnston et al.indicate that such rings can persist for∼2dynamical time scales,or∼1billion years in the case of NGC5907(rotation velocity of 205km s−1from our HI data).The situation is not as clear with regards to how the ring and PGC54419are related to the HI warp in NGC5907.The ring and dwarf galaxy combined have∼1%of the luminosity of NGC5907,and likely a similar percentage of its mass.On the one hand, Weinberg(1995)points out that,in the case of the LMC and the Galaxy,a dynamically active halo acts to amplify the tidal warping effect of a small galaxy on the disk of a much larger galaxy,through distor-tion of the halo of the larger parent galaxy.On the other hand,the LMC is10%of the mass of the Milky Way,while the ring and dwarf are much smaller com-pared to NGC5907.It remains to be seen whether realistic models of tidal interactions of outer HI disks with small companion dwarf galaxies can produce the warps,both HI and optical seen in NGC5907.Related to this issue is that detailed investigation of the HI map shows that the vertical distribution of HI is not symmetric on both sides near the central region of the galaxy.On the side of the ring there are weak HI features just above3σlevel,as may result from tidal interaction between the ring material and the disk.Deeper VLA maps of this galaxy will be needed to confirm this feature.Finally,it is well-known that dwarf galaxies tendto group around giant spiral galaxies.Such is cer-tainly the case for the Milky Way and M31in the Local Group(e.g.Grebel1997).The study of Zarit-sky et al.(1997)shows the same to be true around most giant spiral galaxies,even“isolated”giant spi-rals.While it would be very hard to show that a galaxy did not have dwarf companions,given their low surface brightnesses,it is also equally hard to show that all galaxies have them.Only by taking a deep look at the environments around“isolated”spiral galaxies with warped disks can this issue be resolved.6.AcknowledgmentsWe thank McDonald Observatory for supporting part of the observations and data reductions,David Spergel for a helpful conversation,the VLA person-nel for efficient service,and the anonymous referee for helpful comments.This research is supported in part by the Chinese National Natural Science Foundation (CNNSF)and by the U.S.National Science Founda-tion(NSF Grant INT-93-01805).REFERENCESAaronson,M.1983,ApJ,266,L11Bender,R.,Burstein,D.&Faber,S.M.1992,ApJ, 399,462Burstein,D.&Heiles,C.1984,ApJ,54,33 Chen,J.et al.1998,AJ,submittedde Vaucouleurs,G.,de Vaucouleurs, A.,Corwin,H.C.G.,Jr.,Buta,R.J.,Paturel,G.&Fouqu´e,P.1991,Third Reference Catalog of Bright Galaxies (Springer-Verlag:New York)Faber,S.M.&Lin,D.1983,ApJ,266,L17Fan,X.et al.1996,AJ,112,628Grebel,E.K.1997,Rev Mod Astr,10,29Ibata,R.A.,Gilmore,G.&Irwin,M.J.1994,Nature, 370,194Johnston,K.V.,Spergel,D.N.&Hernquist,L.1995, ApJ,451,598Lequeux,J.,Fort,B.,Dantel-Fort,M.,Cuillandre, J.-C.&Mellier,Y.1996,A&A,321,L1Lequeux,J.,Combes,F.,Dantel-Fort,M.,Cuillandre, J.-C.,Fort,B.&Mellier,Y.1998,A&A,(in press)Morrison,H.,Boroson,T.&Harding,P.1994,AJ, 108,1191Oke,J.B.&Gunn,J.E.1983,ApJ,266,713Paturel,G.,Fouqu´e,P.,Bottinelli,L.&Gouguen-heim,L.1989,Catalogue of Principal Galaxies (Observatoire de Lyon)Rand,R.1996,ApJ,462,712Roberts,M.S.&Haynes,M.P.1994,ARA&A,32,115Rudy,R.J.,Woodward,C.E.,Hodge,T.,Fairfield, S.W.&Harker,D.E.1997,Nature,387,159 Sackett,P.D.,Morrison,H.L.,Harding P.&Boro-son,T.A.1994,Nature,370,441Sancisi,R.1976,A&A,53,159Sasaki,T.1987,PASJ,39,849Weinberg,M.1995,ApJ,455,L31Zheng,Z.et al.1998,(in preparation)Zaritsky,D.,Smith,R.,Frenk,C.&White,S.D.M.1997,ApJ,478,39Fig. 1.—This is the combined26.17hour BAO Schmidt image of a28′×28′subfield of our58′×58′image,centered around NGC5907taken through the6660˚A BATCfilter.All foreground stars,other galaxies(including PGC54419)and the dust lane of NGC5907have been blanked.This permits display-ing a range of grey levels to enhance the faintest sur-face brightness features in this galaxy.The inset di-agram shows the shape of the ring and its relative orientation with respect toNGC5907.Fig.2.—The integrated intensity map of21cm emis-sion as derived from our6hour VLA observation, superimposed on our m6660image,of size25′×25′. The21cm contours are0.69(3σ),4.0,12.5,22.5,75 mJy beam−1(1mJy beam−1=1.85Kelvin).The beamwidth is18′′.Note the discovery of HI at a sim-ilar velocity as NGC5907in the dwarf galaxy PGC 54419offto the upper right.Fig.3.—The peak brightness distribution along the ring and thefitted ellipse.Only the clear part of the ring is measured.Major axis is13.4′;minor axis,7.3′with eccentricity of0.84.The small dot is the center of NGC5907,while the open circle shows the focus of the ring nearest the galaxy nucleus.The radius of this circle(10pixels)indicates the position error of the focus location.Also shown is the major axis of the ring.。
