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我国目前拥有全球各种陨石数据库除了相关科研单位就只有湖南中历收藏品鉴定中心。
由于缺乏大气层的保护，月球曾经历了强烈的撞击作用，月表留下的大量撞击坑就是最直接的证据。
因此，绝大部分月球陨石都是碎屑岩，只有少部分月球陨石保留了未碎裂的结晶结构。
Miller Ｒange(MIL)05035 陨石搜寻项目组(ANSMET) 于2005 年底在南极米勒山区收集到的，属于非常珍贵的具有粗粒结晶结构的月海玄武岩。
根据国际陨石数据库(Meteoritical Bulletin Database)的统计，截至2013 年7 月31 日，地球上共发现月球陨石165 个，其中仅有25 块属于未碎裂的月球陨石，代表了10 次月球溅射作用，这些月球陨石均为玄武岩或辉长岩。
根据岩石学特征研究，这些未碎裂玄武岩质月球陨石具有如下特征。
(1)矿物组合存在明显的相似性，主要矿物为辉石、斜长石和橄榄石等，此外还含有石英、钛铁矿、尖晶石、磷灰石和锆石等矿物，岩性都为玄武岩质。
(2)结构上存在明显相似性，主要为次辉绿结构和辉长结构，在矿物结晶粒度上有一定变化，从细粒至中粗粒不等，少数陨石中矿物颗粒粗大，如Asuka-881757 和本次研究的MIL05035。
(3)与地球上的玄武岩和辉长岩相比有明显成分差异，辉石以单斜辉石为主，具有明显的成分环带，富铁钙贫镁，斜长石富钙，有些如NWA4734、Dhofar287 和Asuka881757 等陨石中斜长石具有明显的成分环带，橄榄石富铁贫镁。
(4)所有这些陨石都具有强烈的冲击变质特征，如斜长石的熔长石化，冲击熔脉发育等。
MIL05035 的岩石学矿物学特征具有该类型月球陨石的一般特征，因此该陨石具有开展月海玄武岩研究的普遍科学意义。
另外，月海玄武岩岩浆活动时间主要在43. 5 亿年Terada et al. ，2007) 至28 亿年前之间(Fernandes et al. ，2005; Borg et al. ，2007)。
坦桑尼亚马拉绿岩带金矿床地质特征李俊生;白德胜;卫建征;王滑冰;白文杰【摘要】马拉绿岩带是坦桑尼亚太古宇绿岩带金成矿带的重要组成部分,研究区域金矿床类型、分布及矿床特征,总结成矿控矿规律对找矿工作具有重要意义.该区域金矿床类型分为构造蚀变岩型、含金石英脉型、层控型金矿床以及早期人工采矿形成的尾矿.构造蚀变岩型、含金石英脉型金矿床集中分布于绿岩带中的北西向、北东向断裂构造(韧性剪切带)及其交汇处,层控型金矿床主要赋存于中基性火山沉积岩、条带状铁建造中.矿体呈脉状、透镜状,品位、厚度变化较大,矿体规模大小不一.金矿石类型主要是蚀变岩型、石英脉型.尼安萨群的基性火山岩、BIF为金的“初始矿源层”,岩石经历了韧性-脆性变形,在岩浆侵入活动中,Au等成矿元素活化、迁移,并在上述构造有利部位富集成矿.【期刊名称】《矿产勘查》【年(卷),期】2018(009)005【总页数】8页(P977-984)【关键词】坦桑尼亚;马拉绿岩带;金矿床;地质特征【作者】李俊生;白德胜;卫建征;王滑冰;白文杰【作者单位】河南省地矿局第二地质矿产调查院,郑州450001;河南省地矿局第二地质矿产调查院,郑州450001;河南省地矿局第二地质矿产调查院,郑州450001;河南省地矿局第二地质矿产调查院,郑州450001;南方科技大学,深圳518055【正文语种】中文【中图分类】P618.51绿岩带，通常由大量枕状镁铁质(少量超镁铁质)岩、长英质火山岩和喷气岩石组成，绿岩带型金矿床是在绿岩带形成、演化及改造过程中形成的一系列金矿床的总称(沈保丰等，1997),是世界重要的金矿床类型。
资料统计，全世界范围内绿岩带型金矿金的产量约占55%(Keays,1982)，加拿大绿岩型金矿产量高达92% (Shank, 1974)，澳洲、非洲、印度和斯堪地纳维亚的金矿也大部分采自绿岩带。
绿岩带型金矿床占有极其重要的地位，甚至有“没有绿岩带就没有金矿”的说法(周作侠，1991)。
ASTMD1654-2008测试标准一、概述ASTMD1654-2008是一项广泛应用于材料测试领域的标准测试方法。
该标准旨在为测试人员提供一种可靠、准确、重现性好的测试流程，以评估材料的性能和特性。
ASTMD1654-2008测试标准适用于各种材料，包括金属、塑料、橡胶、陶瓷等，可用于材料的质量控制、产品设计以及研发过程中的材料分析等领域。
二、测试标准的范围ASTMD1654-2008测试标准主要包括以下几个方面的内容：1. 测试样品的准备：测试标准规定了测试样品的准备方法，包括样品的制备尺寸、表面处理以及必要的加工工艺等。
2. 材料的试验：测试标准要求对测试样品进行相应的力学性能测试，包括拉伸强度、屈服强度、延伸率等指标的测定，以评估材料的强度和变形性能。
3. 材料的物理性能测试：标准要求对测试样品进行密度、硬度、热膨胀系数等物理性能参数的测定，以评估材料的物理特性。
4. 性能参数的计算：标准要求根据测试数据，计算材料的力学性能指标、物理性能参数等，以便进行材料性能的准确评估。
5. 测试结果的报告：标准要求对测试结果进行准确记录和报告，包括测试条件、测试方法、测试数据等信息的详细说明。
这些内容的规定和要求，为测试人员提供了一种操作流程，以确保测试过程的准确性和可重复性，为不同材料的性能评估提供了统一的标准依据。
三、测试标准的意义和作用ASTMD1654-2008测试标准具有以下几个方面的意义和作用：1. 推动材料测试技术的发展：测试标准提供了一种可靠的测试方法，促进了材料测试技术的发展和提高，推动了材料科学研究的进步。
2. 促进产品质量的提高：通过对材料进行准确、全面的性能评估，可以有效指导产品设计和生产过程中的材料选择和质量控制工作，提高产品的质量和性能。
3. 促进材料行业的发展：测试标准的制定与实施，促进了材料行业的标准化和规范化发展，提高了材料产品的市场竞争力和整体水平。
4. 为材料研发提供技术支撑：测试标准为材料的研发提供了技术支撑和科学依据，为材料的新品种、新配方和新工艺的开发提供了可靠的测试手段。
三聚氰胺系列阻燃剂的改性研究进展池华春【摘要】Based on the analysis of the research status quo of MCA and MP flame retardant, MCA particle surface was modified with the organic matter and the inorganic matter, control of MCA macromolecular conformation, improved the dispersibility and reduce the water absorbability of MP flame retardant in other material.It was pointed out that the development trend and research direction of melamine flame retardant was focused on improving the flame retardant effect and mechanical properties of flame retardant materials, improved the flame retardancy and dispersibility, and was mixed with other flame retardant, etc.%通过对三聚氰胺氰脲酸盐阻燃剂在颗粒有机包覆改性、颗粒表面无机改性和分子结构改性等研究方向和进展的综述，和解决三聚氰胺磷酸盐类阻燃剂在阻燃材料中各组分分配不均，吸潮等缺点的研究进展综述。
总结提出了三聚氰胺系列阻燃剂的研究方向应集中在提高阻燃材料的阻燃效果和力学性能，提高提高阻燃性和分散性以及通过与其它协效阻燃成分进行复配等方面，满足目前市场不同材料对阻燃剂的性能要求。
外泌体在肺癌诊断中的应用研究郝昱徐兴祥肺癌是全世界发病率和病死率最高的恶性肿瘤,一直威胁着人类的健康，四分之一的癌症死亡是肺癌，大多数肺癌确诊时已是晚期阶段,5年相对生存率仅有大约16%-19%［1］o肺癌的传统治疗方法是基于组织活检中癌细胞的组织病理学分析，但因为其有创性，患者需要承担较大的风险，因此，寻找有效的肺癌早期筛查手段已成为一个亟待解决的问题。
外泌体作为液体活检其中的一种成分，因其获取的非侵入性、可重复性、成本低等优点用于诊断肺癌已经成为一个研究热点话题［2-3］o目前已经有研究表明，外泌体在肺癌发生发展的肿瘤微环境、肺癌的侵袭和转移、免疫调节、参与放化疗抵抗中，分别都发挥着重要作用。
尤其是外泌体所含的蛋白质、miRNA等成分已经研究证实对于肺癌的早期诊断有重要价值，具有作为新的早期诊断标记物的潜力。
本文主要将从外泌体作为液体活检标记物在肺癌中的生物学作用与应用于肺癌方面进行综述。
外泌体概述在人体的多种体液中都能够发现外泌体的存在，例如脑脊液、唾液、胸腔积液、乳汁、腹水、血液、精液、尿液等。
外泌体来源于晚期的内吞体,又称为多囊泡体，（muldvesicular bodies,MVB）,是体内活细胞通过内吞-融合-外排等一系列生物学过程而形成的具有脂质双层膜结构的多囊泡体，它们的直径大约在30〜100n叫密度在1.13〜1.19y/ml。
外泌体的生物成分中含有蛋白质、核酸（DNA、mR- NA、miRNA、其他非编码RNA）、脂质等［4'5］。
外泌体最初是在1987年,Johnstone等人在研究网织红细胞成熟的过程中，对绵羊红细胞上清液进行超速离心时发现的［6］o最初人们认为外泌体是细胞丢弃的“垃圾”，在1995年Raposa等人发现被EB病毒感染的B淋巴细胞释放的外泌体携带了适应性免疫应答所需要的膜结合分子［7］o从而发现外泌doi:10.3969/j.imn.1009-6663.2021.07.026作者单位*225000江苏扬州,苏北人民医院呼吸与危重症医学科通信作者:徐兴祥,E-mail：xux63U 体可能具有改变细胞外微环境、呈递抗原、刺激T 细胞增殖、诱导机体免疫反应等功能！一、外泌体的生物发生外泌体生物发生最重要的一个机制是ESCRT 依赖机制,ESCRT是由四种蛋白质复合物和辅助蛋白质组成（ESCRT-0、ESCRT--ESCRTT g ESCRT A ll 和Vps4）o这一机制的过程包括从内芽形成细胞内小体，到多泡小体的产生，到多泡小体的融合成有质膜的细胞体，然后将外泌体释放到胞外［8］。
CHEMICAL INDUSTRY AND ENGINEERING PROGRESS 2016年第35卷第11期·3392·化 工 进 展硅烷流化床制备粒状多晶硅的研究进展田博，黄国强（天津大学化工学院，天津 300072）摘要：硅烷流化床生产粒状多晶硅的技术具有节能、高效、环境友好等优点，是生产太阳能级多晶硅的首选工艺技术，但国内对于该工艺技术的研究仍处于起步阶段。
本文简介了硅烷流化床的基本原理，包括操作原理和反应模型，并讨论了温度、硅烷分压、颗粒尺寸以及流化速度等反应条件对硅烷流化床内流动稳定性和硅粉尘产生的影响。
根据发展硅烷流化床所面临的热壁沉积、产生硅粉尘、加热方式的选择、硅晶种的获得、气体分布方式的控制以及产品纯度的控制等技术挑战，分析了不同的流化床设计对这些技术挑战的解决方案，指出了不同的流化床设计的优缺点与工业应用前景。
讨论了硅烷流化床的CFD 模拟与一般的流态化模拟的区别，并回顾了相关的研究工作。
最后指明了对硅烷流化床技术的研究应从优化反应条件、改善反应器设计以及完善多尺度模拟硅烷流化床的模型三个方面着手。
关键词：流化床；热解；团聚；粒状多晶硅；硅粉尘；计算流体力学中图分类号：TQ 127.2 文献标志码：A 文章编号：1000–6613（2016）11–3392–08 DOI ：10.16085/j.issn.1000-6613.2016.11.002Research progress on preparation of granular polysilicon by fluidized-bedsilane pyrolysisTIAN Bo ，HUANG Guoqiang（School of Chemical Engineering and Technology ，Tianjin University ，Tianjin 300072，China ）Abstract ：As energy-efficient ，high-performance and environment-friendly method the fluidized-bed silane pyrolysis makes its potential to become the dominating way for production of granular polysilicon ，while the domestic research on this process is still in its infancy. The review starts with a brief induction of the basic principle of fluidized-bed silane pyrolysis ，including the operating principle and the reaction model ，and discusses the effects of temperature ，silane concentration ，particle size and gas flow rate on stable fluidization and fines formation. Developing the technology of fluidized-bed silane pyrolysis faces many technical challenges ，such as fines formation ，unwanted depositions on internals ，heating and temperature control ，seed particles generation ，gas distribution and quality. The advantages and disadvantages of solutions of these technical challenges are summarized by analyzing different fluidized-bed reactor designs and the industrial application prospects of these solutions are pointed out. The difference between the CFD simulation of the fluidized-bed silane pyrolysis and the general fluidization is discussed and related researches are reviewed. Finally ，the review proposes that the domestic research on fluidized-bed silane pyrolysis should put emphasis on optimizing the reaction conditions ，improving fluidized-bed designs and completing the multi-scale model of fluidized-bed silane pyrolysis.***************.cn 。
E VA A L CÓN A N D M A R I A P I L A R S AF O N T J O R DÀPRAGMATIC AWARENESS IN SECOND LANGUAGEACQUISITIONI N T R O D U C T I O NPragmatic awareness is the conscious,reflective,explicit knowledge about pragmatics.It thus involves knowledge of those rules and conventions underlying appropriate language use in particular com-municative situations and on the part of members of specific speech communities.Following an educational perspective,we deal with prag-matic awareness in relation to the construct of communicative compe-tence,and we consider research on the role of awareness in pragmatic learning.First,pragmatic competence is introduced as part of the over-all framework of communication.Second,we raise the need to focus on pragmatics including pragmalinguistic and sociopragmatic aware-ness.Third,a review on research dealing with learners’pragmatic awareness is provided.Finally,some future directions deriving from the previous subsections are briefly mentioned.E A R LY D E V E L O P M E N T SThe notion of communicative competence originated from those criti-cisms raised by the Chomskyan notion of linguistic competence (1965).Scholars of differentfields,namely those of linguistics,psy-chology,sociology and anthropology,argued against the absence of aspects related to language use in the concept of linguistic competence, as it merely accounted for an ideal grammatical knowledge shared by native speakers of a given language.Hymes(1972)first suggested the substitution of Chomsky’s linguistic competence into a wider con-cept,that of communicative competence,which would also include social and referential aspects of the language.Nevertheless,the term communicative competence may involve much more than the mere extension of linguistic competence.According to Cenoz(1996),it also implies a qualitative change and a distinct approach to the study of lan-guage use,since communicative competence is a dynamic concept that depends on the interlocutors’negotiation of meaning.The construct of communicative competence has been particularly influential in thefield of language learning as it bears a direct relation-ship with the communicative approach to language teaching.For this J.Cenoz and N.H.Hornberger(eds),Encyclopedia of Language and Education,2nd Edition,Volume6:Knowledge about Language,193–204.#2008Springer Science+Business Media LLC.194 E.A L CÓN A N D M.P.S A F O N T J O R DÀreason,different scholars in thefield of applied linguistics have attempted to describe that construct by identifying various components that would constitute a whole model for the study of learners’communi-cative competence.One of the most representative and significant mod-els that have arisen within thefield of applied linguistics is that of Bachman(1990)as it was thefirst explicitly identified pragmatics as one of the two major components of communicative competence.Bachman (1990)distinguishes between organisational and pragmatic competence. On the one hand,organisational competence refers to those abilities taking part in the production and identification of grammatical and ungrammatical sentences,and also in understanding their meaning and in ordering them to form texts.These abilities are sub-divided into gram-matical and textual competence.On the other hand,pragmatic compe-tence is understood as dealing with the relationship between utterances and the acts performed through these utterances as well as with the features of the context that promote appropriate language use.The rela-tionship between utterances and acts concerns the illocutionary force, whereas the context involves those sociolinguistic conventions taking part in using the language.The illocutionary competence is defined in terms of Searle’s speech acts(1969)and Halliday’s language functions (1973),since it involves the relationship between the utterances and speakers’intentions specified in them.In addition,the sociolinguistic competence refers to sensitivity to differences in variety,register and to the ability of interpreting cultural references.Bachman’s model(1990)points out the idea that communicative com-petence can not only be achieved by improving learners’grammatical knowledge,but it also concerns the development of other competencies such as the textual and pragmatic ones.From this point of view,prag-matics has become a common target in the language classroom,as illustrated by current proposals(Bardovi-Harlig and Mahan-Taylor, 2003).In those proposals,most suggestions and lessons for pragmatic instruction focus on routines as part of the pragmalinguistic compo-nent that constitutes pragmatic competence.Hence,wefind lesson plans for teaching how to make requests(Mach and Ridder,2003; Yuan,2003),others dealing with refusals(Kondo,2003),apologies (Bardovi-Harlig and Mahan-Taylor,2003)or complaints(Reynolds, 2003).Yet few proposals consider a sociopragmatic perspective in foreign/second language teaching,thus presenting a partial view of the pragmatic component.However,the literature on inter language pragmatics(ILP),by referring to pragmatic awareness as learners’conscious and explicit knowledge about pragmatics,has pointed out that both pragmalinguis-tic and sociopragmatic aspects should be included.For instance, Safont(2005)suggests that unless students are provided with socio-cultural and sociolinguistic information,their difficulty to understandP R A G M AT I C AWA R E N E S S195 politeness issues affecting the use of the target language will increase. This has raised the need for focusing on pragmatic awareness and pro-duction in the language classroom.Pragmatic awareness might beachieved by fostering learners’connections between their previous pragmalinguistic knowledge(both in their L1and the TL)and newpragmatic information they may be provided with.In addition,prag-matic production should focus on appropriateness,thus paying atten-tion to both propositional content,on the one hand,and culturaleffects on the other.M A J O R C O N T R I B U T I O N SAnalysing language use in context has provided language teachers andlearners with a research-based understanding of the language forms and functions that are appropriate to the many contexts in which a languagemay be used.From this perspective,research in cross-cultural and ILPhas provided information on the interactive norms in different lan-guages and cultures.Cross-cultural studies with a focus on speakers’pragmatic performance aim to determine whether the same speech actcan be found in different cultures,and if so,to what extent it is per-formed.Likewise,explanations that account for those differences areprovided.Among them,pragmatic transfer at the level of formal,semantic and speakers’perception of contextual factors seems to explain some of the differences between L1and L2speakers’use ofthe language.In addition to transfer,learning effects,which may beof a formal or informal nature have been reported to cause a deviation from the target language norm.Examples of types of learning effectsinclude overgeneralization,hypercorrection,or responses that do notreflect reality.Research from an inter language perspective takes into accountacquisitional rather than contrastive issues,as is the case of cross-cultural perspectives stated earlier.Barron’s(2003)study follows this acquisitional perspective in inter language development.Barron’s(2003,p.10)definition of pragmatic competence states that it involves ‘knowledge of the linguistic resources available in a given language for realising particular illocutions,knowledge of the sequential aspectsof speech acts and knowledge of the appropriate contextual use of theparticular languages linguistic resources’.In the same line,Bachman (1990)and Thomas(1983)account for the realisation of speech acts in which they distinguish between pragmalinguistic and socio-pragmatic components.Hence,while dealing with pragmatics they sug-gest that not only routines and forms specific to particular pragmatic realisations should be considered,but also the context of use.Most studies to date(see contributions to Rose and Kasper’s volume, 2001and Kasper and Rose,1999)have focussed on the former196 E.A L CÓN A N D M.P.S A F O N T J O R DÀcomponent,that is,routines and pragmalinguistic realisations.A wide amount of studies now exist with a focus on request realisations (Hassall,1997;Li,2000;Rose,2000,among many others).Other speech acts that have received some attention on the part of scholars may be refusals(Félix-Brasdefer,2004),compliments(Rose and Ng, 2001)and apologies(Trosborg,1995).We may alsofind exceptional studies in which sociopragmatic factors have been dealt with,but they usually refer to descriptions of situations presented to learners so that they acknowledge the most appropriate routine(Lorenzo-Dus,2001). However,it seems as argued by Kasper(2000),that the sociopragmatic component has received less attention in ILP.The relevance of the sociopragmatic view in L2pragmatic develop-ment is also put forward by Jung(2002).The author states that L2 pragmatic acquisition should be studied from both the psycholinguistic perspective of the learner that has traditionally paid attention to vari-ables such as proficiency level,or the type of task(among others), and the socio cultural perspective,which emphasises the need to analyse sociopragmatic development just as pragmalinguistic develop-ment has been investigated(Barron,2003;Kasper and Rose,2002). Bou-Franch and Garcés-Conejos(2003)acknowledge such need in their proposal for teaching linguistic politeness.The authors particu-larly focus on avoiding sociopragmatic failure in the language classroom.Sociopragmatics is here understood as related to‘our knowledge,beliefs and perceptions of socially adequate linguistic behaviour’(see Bou-Franch and Garcés-Conejos,2003,p.2).On that account,these authors’proposal is based on Brown and Levinson’s (1987)politeness variables—namely those of power,distance and ranking of imposition—and Scollon and Scollon’s(1995)suggested politeness systems.Scollon and Scollon(1995)identify three main politeness frameworks on the basis of face relationships.The former one,also named deference politeness system,relates to those relations where there are no power differences,but there is social distance(e.g. colleagues at work).The second system refers to solidarity politeness, where there are no power differences or social distance(e.g.family members).Finally,the third system relates to hierarchical politeness, where there are power differences and social distance(e.g.boss and employee).Although Scollon and Scollon’s(1995)proposed politeness systems have been criticised for including a simplistic view of human communication(see Bou-Franch and Garcés-Conejos,2003),it may serve as a point of departure for research in sociopragmatic develop-ment.In fact,these politeness systems may be employed to test the effect of instruction in sociopragmatic development,just as speech act routines and linguistic realisations have been used in testing the acquisition of pragmalinguistic aspects.P R A G M AT I C AWA R E N E S S197 Second language pragmatics learning is also L2culture learning(see also Fenner,Cultural Awareness in the Foreign Language Classroom,V olume6).This may imply learners’modification of their own worldview,thus including attitudes and ethnolinguistic variation while ac-quiring foreign/second language pragmatics.In fact,as suggested byThomas(1995)and Jung(2002),one’s own linguistic and culturalidentity is usually best acknowledged when being confronted with a different reality.From this perspective,awareness is probably thefirststep to the earlier quoted shift as it would involve knowledge of thesepoliteness systems.Research on learners’pragmatic awareness may in turn provide us with suitable information on those needs and difficulties,which also relate to their language learning process.As stated by various scholars,learners’pragmatic awareness mani-fested in their ability to recognise and identify speech act types is lim-ited.For instance,Kasper’s(1984)investigation of the pragmaticcomprehension of German-speaking English learners,suggested that failure to comprehend the illocutionary force of speech acts could beexplained by learners’inability to produce those illocutionary devicesin non-conventional indirect speech acts.In addition,the effect of pro-ficiency on language learners’pragmatic awareness has been examined by Koike(1996),Cook and Liddicoat(2002)and García(2004).Koike(1996)found that the more proficient participant could recognise speech act type and understand the illocutionary force of the utterance better than less proficient participants.Similarly,Cook and Liddicoat’s (2002)study reveals that there is a proficiency effect for interpreting request speech acts at different levels of directness.In the same line, García(2004)shows that there are proficiency-related differences in the identification of speech acts.However,the author suggests that con-textual knowledge and linguistic ability should be viewed as comple-menting variables that interact with each other in the comprehension of indirect speech acts.In addition,it is suggested that by examining L2learners’pragmatic awareness we can infer learners’pragmatic comprehension,and we might also discover linguistic factors that con-tribute to comprehension as well as to enhance the provision of those conditions for understanding pragmatic meanings.This is particularly relevant in second language learning,since in contrast to native speak-ers,who may not need to recognise speech act type consciously,second language learners’attention to pragmatic issues seems to play a role in developing pragmatic competence.The fact that second language learners need to recognise speech act conventions in a conscious way may determine the importance of pragmatic comprehension in the lan-guage classroom.Yet,awareness understood as conscious pragmatic knowledge would not only refer to comprehension but also to produc-tion as long as both involve some degree of consciousness.198 E.A L CÓN A N D M.P.S A F O N T J O R DÀW O R K I N P R O G R E S SCurrent research has been motivated by an attempt to establish a more direct link between thefields of ILP research and SLA studies,which address learners’development of pragmatics(Kasper and Rose,2002). From this perspective,studies have been conducted to address whether the instructional contexts provides opportunities for pragmatic learn-ing.Furthermore,the teachability hypothesis in the pragmatic realm has been tested in several studies.In relation to the conditions offered in second and foreign language learning contexts to develop pragmatic competence,Bardovi-Harlig and Hartford(1996)illustrate how the input offered to learners in academic contexts may not result in prag-matic learning.The authors point out that in an ESL context the sug-gestions made were status-bound,and as a consequence they could not serve as direct models for the learner.In this line,Nikula’s(2002) study also focuses on how pragmatic awareness is reflected in the use of modifying elements of talk by two non-native speakers(NNSs)in EFL and content-based classrooms.Findings of this study reveal a ten-dency towards directness in teachers’performance,which is explained in terms of the constraints of the classroom and the teacher’s status compared to that of students.In addition,Rose(1999)claims that large classes,limited contact hours and little opportunity for intercultural communication are some of the features of the EFL context that hinder pragmatic learning.Apart from the analysis of the input,other studies have examined if textbooks present pragmatically accurate models for learners(Bardovi-Harlig,1996;Crandall and Basturkmen,2004; Vellenga,2004).Results of these studies have showed that the way speech acts or conversational functions are considered in textbooks is not adequate.Bardovi-Harlig(1996)showed that textbooks do not often present a particular speech act or language function at all,and very often when they do,it may not reflect authentic language use. Finally,according to Vellenga(2004),textbooks do not include suffi-cient metapragmatic explanations to facilitate learners’awareness of pragmatic issues.As a consequence of the difficulties mentioned earlier to develop pragmatic competence in language learning contexts,several investiga-tions draw on Schmidt’s(1993,2001)noticing hypothesis to address awareness-raising as an approach to the teaching of pragmatics(see also Robinson,Attention and Awareness,V olume6).First,the use of authentic audiovisual input has received special attention as a way to foster learners’pragmatic knowledge;being that knowledge conscious it would then refer to pragmatic awareness.Audiovisual input(the use of video,films and TV)has been stated to be useful to address knowl-edge of a pragmatic system,and knowledge of its appropriate use.P R A G M AT I C AWA R E N E S S199 The studies conducted by Rose(2000),Grant and Starks(2001), Washburn(2001)and Alcón(2005)were motivated by the assumption that both pragmalinguistic and sociopragmatic awareness are particu-larly difficult for those studying in an EFL context.From this perspec-tive,the authors claim that authentic audiovisual input provides ample opportunities to address all aspects of language use in a variety of contexts.Besides,as quoted by Rose(2000),audiovisual materialfirst offers language teachers the possibility of choosing the richest and most suitable segments,analyse them in full,and design software to allow learners to access pragmatic aspects as needed.Secondly,it may be useful to expose learners to the pragmatic aspects of the target language.Thirdly,pragmatic judgment tasks can be based on audiovi-sual discourse analysis and prepare learners for communication in new cultural settings.This last aspect takes into account the issue of task design and task implementation,which in turn is related to research focussing on the effect of instruction on learners’noticing of pragmatic target features.As pointed out in various studies on pragmatic instructional inter-vention(House and Kasper,1981;House,1996;Rose and Ng,2001, Takahashi,2001),explicit metapragmatic instruction seems to be more effective than implicit teaching.However,more recently,research has focussed on the effect of implicit instruction for pragmatic learning fol-lowing a focus on form approach.Taking into account that a higher level of awareness can be achieved by manipulating input,the studies conducted by Fukuya,Reeve,Gisi and Christianson(1998),Fukuya and Clark(2001),Martínez-Flor(2004)and Alcón(2005)aim to prove whether learners’intake of pragmatic target forms can be enhanced even in implicit conditions.Fukuya,Reeve,Gisi and Christianson (1998)implemented recasts as implicit feedback on learners’produc-tion of requests.Results of the study did not support the hypothesis that this implicit feedback would result efficient in comparison to the group that received explicit instruction on the sociopragmatic factors that affected appropriateness of requests in different situations.In a similar vein,the studies conducted by Fukuya and Clark(2001)and Martínez-Flor(2004)used input enhancement techniques to draw learn-ers’attention to the target features.In Fukuya and Clark’s(2001) study,findings from the three groups’performance(i.e.focus on forms, focus on form and control group)did not reveal significant differences on learners’pragmatic ability.The authors claimed that a different operationalisation of the input enhancement may have involved differ-ences as far as potential of saliency is concerned.To their explanation, it could be added Izumi’s(2002)suggestion of using a combination of implicit techniques to help learners notice the target features. In line with Izumi(2002),Martínez-Flor(2004)used a combination200 E.A L CÓN A N D M.P.S A F O N T J O R DÀof implicit techniques to analyse the effect of explicit and implicit teaching on the speech act of suggestion.Results of her study demon-strated that both implicit and explicit instructional treatment groups outperformed the control group in awareness and production of the speech act of suggesting.Alcon’s(2005)study also showed an advan-tage of explicit and implicit instructed learners over uninstructed ones in their awareness and production of requests.However,the author indicates the need to consider the delayed effect of explicit and implicit teaching on pragmatic learning in future research.P R O B L E M S A N D D I F F I C U LT I E S:F U T U R ED I RE C T I O N SThe research mentioned earlier is based on the assumption that aware-ness is related to acquisition of pragmatic competence.From a cogni-tive perspective,research on pragmatic awareness and language learning is based on one of the tenets of SLA theory that claims that attention to input determines intake.Thus,drawing on Schmidt’s theo-retical framework(1993)which points out the need to implement ped-agogical intervention on pragmatic issues,most of the studies on pragmatic awareness and language learning address learners’noticing of L2features as a requirement for further second language develop-ment.However,although it is possible that Doughty’s(2001)micro-processes,which potentially contribute to learning-selective attention and cognitive comparison,may be activated through direct and indirect pragmatic consciousness raising instruction,it is not clear the extent to which awareness is sufficient to gain absolute proficiency at the prag-matic level.According to Schmidt(1993),the noticing hypothesis pos-tulates two levels of awareness:at the level of noticing(referring to the targets without mentioning any rules)and awareness at the level of understanding(referring to the explicit formulation of rules).However, since it is hypothesised that even awareness at the level of understand-ing may be insufficient to gain absolute proficiency(Gass,Svetics and Lemelin,2003;Rosa and Leow,2004),the noticing hypothesis may be further examined in empirical studies at the pragmatic realm.To do that,first it should be tested empirically.For instance,it needs to be tested whether Tomlin and Vila’s(1994)functions of attention(alert-ness,orientation and detection)are separable,or,as suggested by Simard and Wong(2001),they are activated at the same time in processing pragmatic information.In addition,and related to research conducted in cognitive psychology,a different operationalisation of awareness may be needed in ILP research.While in cognitive psychol-ogy awareness is usually linked to the ability to verbally report aP R A G M AT I C AWA R E N E S S201 subjective experience(Schmidt,2001;Tomlin and Vila,1994),most SLA studies dealing with the role of instructional techniques to draw learners’attention to formal aspects of the input,assess what is attended to by means of post-exposure tasks(Fotos,1993).Following this procedure to measure awareness,most studies point to an indirect evidence on the role played by attention and awareness on pragmatic language learning,but more direct assessment of attention and aware-ness,for instance by using think-aloud protocols,should be included in further research.Secondly,considering Izumi’s(2002)suggestion of using a combination of implicit techniques to help learners notice the target features,input enhancement of pragmalinguistic and socio-pragmatic factors,together with other techniques such as positive feed-back,need to be examined to shed light on how they help implicit instructed learners to pay attention to pragmatic features of the lan-guage.Thirdly,since the effect of instructional treatments has been proved effective for pragmatic awareness,the delayed effect that prag-matic awareness(both at the level of noticing and understanding)may have on learners’pragmatic learning should be addressed in the future. Likewise,in line with Takahashi(2005)and Safont(2005),further studies that examine to what extend pragmatic awareness is related to learners’individual variables are desirable.In relation to the pedagogical insights which are likely to be drawn from research on pragmatic awareness,it should be pointed out that, in line with second language acquisition research,the focus is not to transform results into pedagogical ideas.Nevertheless,some implica-tions can be drawn.First,due to the limitations involved in classroom discourse and in textbooks presentation of pragmatic issues,more valid data can be obtained from authentic audiovisual input,and awareness and comprehension of different pragmatic meanings can be achieved by drawing attention to the linguistic forms and the sociopragmatic variables of selected speech events.Thus,a possibility would be designing material that combines the different speech acts taxonomies of linguistic formulations,and the actual face relations described in terms of different politeness systems.See Also:Anne-Brit Fenner:Cultural Awareness in the Foreign Language Classroom(Volume6);Peter Robinson:Attention and Awareness(Volume6)REFERENCESAlcón,E.:2005,‘Does instruction work for learning pragmatics in the EFL context?’, System3,417–435.202 E.A L CÓN A N D M.P.S A F O N T J O R DÀBachman,L.F.:1990,Fundamental Considerations in Language Testing,Oxford University Press,Oxford.Bardovi-Harlig,K.and Hartford,B.S.:1996,‘Input in an institutional setting’,Studies in Second Language Acquisition18,171–190.Bardovi-Harlig,K.and Mahan-Taylor,R.:2003,Teaching Pragmatics,US Depart-ment of State Office of English Language Programs,Washington,DC. Barron, A.:2003,Acquisition in Interlanguage Pragmatics’,John Benjamins, Amsterdam.Bou-Franch P.and Garcés-Conejos,P.:2003,‘Teaching linguistic politeness:A method-ological proposal,IRAL41,1–22.Brown,P.and Levinson,S.C.:1987,Politeness:Some Universals in Language Usage, Cambridge University Press,Cambridge.Cenoz,J.:1996.‘La competencia comunicativa:Su origen y componentes’,in J.Cenoz and F.Valencia(eds.),La Competencia Pragmática:Elementos Lingüísti-cos y Psicosociales,Servicio Editorial de la Universidad del País Vasco,Bilbao. Chomsky,N.:1965,Aspects of the Theory of Syntax,MIT Press,Cambridge,Mass. Cook,M.and Liddicoat,A.J.:2002,‘The development of comprehension in interlan-guage pragmatics:The case of request strategies in English’,Australian Review of Applied Linguistics25,19–39.Crandall,E.and Basturkmen,H.:2004,‘Evaluating pragmatics—focused materials’, ELT Journal58(1),38–49.Doughty,C.:2001,‘Cognitive underpinnings of focus on form’,in P.Robinson(ed.), Cognition and Second Language Instruction,Cambridge University Press, Cambridge,206–257.Félix-Brasdefer,J.J.:2004,‘Interlanguage refusals:Linguistic politeness and length of residence in the target community’,Language Learning54(4),587–653. Fotos,S.:1993,‘Consciousness-raising and noticing through focus on form:Grammar task performance versus formal instruction’,Applied Linguistics14,385–407. Fukuya,Y.J.and Clark,M.K.:2001,‘A comparison of input enhancement and explicit instruction of mitigators’,in L.Bouton(ed.),Pragmatics and Language Learning, V olume10,Division of English as an International Language Intensive English Institute,University of Illinois at Urbana-Champaign,111–130,Urbana,IL. Fukuya,Y.J.,Reeve,M.,Gisi,J.,and Christianson,M.:1998,‘Does focus on form work for teaching sociopragmatics?’,Paper presented at the12th International Conference on Pragmatics and Language Learning,University of Illinois at Urbana-Champaign,Urbana,IL(ERIC Document Reproduction Service No.ED 452736).García,P.:2004,‘Pragmatic comprehension of high and low level language learners’, Teaching English as a Second or Foreign Language8,1–10.Gass,S.,Svetics,I.,and Lemelin,S.:2003,‘Differential effects of attention’, Language Learning53(3),495–543.Grant,L.and Starks,D.:2001,‘Screening appropriate teaching materials’,Closings from textbooks and television soap operas,International Review of Applied Linguistics39,39–50.Halliday,M.:1973,Explorations in the Functions of Language,Edward Arnold,London. Hassall,T.J.:1997,Requests by Australian Learners of Indonesian’,Unpublished doctoral dissertation,Australian National University,Canberra.House,J.:1996,‘Developing pragmaticfluency in English as a foreign language’, Studies in Second Language Acquisition18,225–253.House,J.and Kasper,G.:1981,‘Zur rolle der kognition in kommunikationskursen’, Die Neueren Sprachen80,42–55.Hymes,D.:1972,‘On communicative competence’,in B.J.Pride and J.Holmes(eds.), Sociolinguistics,Penguin,Harmondsworth.。
Mesoscale simulations of a dart penetrating sandJ.P.Borg a ,*,T.J.Vogler ba Department of Mechanical Engineering,Marquette University,Milwaukee,WI 53233,USA bSandia National Laboratories,M.S.1181,Albuquerque,NM 87185,USAa r t i c l e i n f oArticle history:Received 7May 2007Accepted 6June 2008Available online 3August 2008Keywords:Mesoscale simulations Porous compaction Penetration dynamics Sanda b s t r a c tHistorically,hydrodynamic calculations have utilized continuum constitutive models to simulate the coupled dynamic response of a solid projectile penetrating a heterogeneous target system such as concrete,foam or a granular porous medium.Continuum models fail to capture the complicated grain level response within the heterogeneous target which can result in asymmetric loading of the projectile leading to variations in projectile performance.These grain level effects can be crucial to predicting the penetration depth or overall effectiveness of the projectile.In order to assess the possibility of using mesoscale simulations to resolve the grain level dynamics,hydrodynamic simulations were performed for an 11.4cm long,0.9cm diameter dart penetrating a bed of porous granular dry sand with an initial velocity of 366m/s.Simulations were performed using the Eulerian hydrocode CTH in a two-dimensional planar configuration.The goal of the mesoscale simulations is to determine the viability of using these techniques as an alternative to continuum models and to assess the effects of grain level variability such as anisotropic material distributions and variations in the dynamic yield and fracture strength.The results indicate that variations in the size distribution of aggregate added and the fracture strength of the sand system can have a significant effect on penetration performance of the dart;whereas variations in the dynamic strength of the sand had little effect on the dart penetration.Ó2008Elsevier Ltd.All rights reserved.1.IntroductionThe penetration dynamics of a projectile fired into a heteroge-neous target have long been of interest and remain an active research area.Experimental investigations have demonstrated a wide variety of behaviors of a solid projectile against various heterogeneous materials such as soil [1–4],sand [5–8],concrete [9–12],and a variety of laminated and/or composite materials.Recent experiments [13]were conducted in order to assess the variability in performance associated with a brass rod (3.2mm diameter and 7.6cm long)traveling at approximately 40m/s into a large container of dry Ottawa sand (0.45–0.55mm effective diameter,average bulk density:1.56g/cm 3).The rod did not deviate from its initial straight-line trajectory throughout the penetration event and was recovered without apparent visual damage.The average penetration depth was 20.5cm or approximately three rod lengths.However,as larger aggregates were mixed with the sand the penetration depth was greatly reduced.In the extreme,course aggregate with a characteristic length of 0.95cm (sieved:passed 1.27cm,retained 0.95cm)was added to the fine sand ata volumetric ratio of one part aggregate to four parts sand,the penetration depths were reduce to less than a rod length.The addition of heterogeneity,i.e.the inclusion of a large variety of length scales,greatly affected the performance characteristics of the projectile.In similar experiments the performance of a projec-tile demonstrated sensitivity to other system characteristics such as boundary condition [5],obliquity and projectile nose profiles [6,14].Thus large scale dart behavior,such as penetration depth or devi-ation from the shot line trajectory,is sensitive to small scale vari-ations within the test.Penetration experiments have led to a wide variety of modeling techniques in order to predict various aspects of a projectile’s performance.Modeling techniques can be distinguished as falling into one of three categories:empirical,approximate analytical or numerical.Reviews of empirical and approximate methods can be found in Zukas,et al.[15]and Orphal [16].One of the early approximate approaches to characterize the performance of ballistic projectile against a heterogeneous target was performed by Robins in 1742[17],in which a bulk kinetic energy approach was applied to the ballistic energy delivered to a wood pendulum system.After calibration,the model successfully predicted the variation in depth of penetration.Similarly,hydrodynamic approximations have successfully been used to predict a wide variety of projectile–target configurations [18],including materials*Corresponding author.Tel.:þ14142887519;fax:þ14142887790.E-mail address:john.borg@ (J.P.Borg).Contents lists available at ScienceDirectInternational Journal of Impact Engineeringjournal home page:/locate/ijimpeng0734-743X/$–see front matter Ó2008Elsevier Ltd.All rights reserved.doi:10.1016/j.ijimpeng.2008.07.064International Journal of Impact Engineering 35(2008)1435–1440with porosity[19].This bulk modeling approach continues to evolve,with the addition of strength,friction,inertia and projectile erosion models,into several widely used predictive tools.With the evolution of numeric methods,the penetration dynamics have been solved utilizing hydrocodes[20,21].Within this framework,complex target and projectile geometries,such as obliquity,multi-layered materials,can be readily analyzed.In addition,phenomenology such as material strength modeling, including strain-hardening or spall,and complex equations of state, which include such effects as thermal softening and phase change, can readily be incorporated to enhance the range of complexity of the simulation.However,in a continuum approach the heteroge-neous materials are treated as a bulk material which requires an additional model such as P-a[22],P-l[23]or work hardening models with time and temperature-independent properties(i.e. Drucker–Prager or CAP)[24].These constitutive models are formulated using a continuum assumption,thus phenomenology such as material anisotropy,void collapse and internal heating, grain contact and fracture is lost.Although homogeneous continuum level models for soils are able to capture the bulk shock loading and penetration performance if properly calibrated,they are unable to resolve heterogeneous variations in the sand,such as particle size and shape distribution,and variations of constituents, all of which can account for large variations observed in dart performance experiments.In addition,continuum level modeling often requires bulk parameters which are not known a priori;this isespecially true for new materials or for variations in distention.As an alternative to continuum level modeling,the focus of this paper is to study the penetration dynamics of a dart into a porous granular sand system utilizing high resolution mesoscale compu-tational techniques where the dynamics of individual sand grains are resolved.All of the calculations presented here were performed utilizing the hydrocode CTH[25].Of particular interest is comparing the penetration dynamics with regards to several different porous sand systems and assessing the sensitivity of the penetration event to variations in underlying material properties. Mesoscale techniques more accurately represent the variations in material distribution and grain level response of the medium to the impact loading as compared to continuum models.They have an additional advantage in that there are no continuum level model parameters to be specified;all material constants can be obtained from the underlying material properties.The disadvantage of mesoscale simulations is the considerable increase in computa-tional cost.Also,because material interfaces are not resolved within CTH,this hydrocode may not be completely ideal for this application since it lacks realistic fracture,grain on grain contact dynamics and material interface tracking.This inability to model grain fracture might represent a significant deficiency since frac-ture may play an important role in the penetration process. However,similar mesoscale simulations have been successfully used to describe a variety of problems involving the shock compaction of porous granular materials such as equation of state development[26–29]and energetic materials[30–33].Curran demonstrated that a meso-mechanical shear-strength model can accurately describe the microscopicflow around the tip of a long-rod projectile penetrating ceramic armor[34].putational setup2.1.Dart projectileA schematic of the dart used in these simulations is presented in Fig.1.The main body of the dart is0.90cm(0.35inch)in diameter and11.43cm(4.5inch)long and has a total mass of49.9g.The dart has threefins which are not included in the simulations in order to maintain a two-dimensional planar configuration.The main body of the dart is constructed of aluminum and the nose,i.e.standoff pin,is a tungsten right circular cylinder.The front third of the dart contains a pin ignition and delay system and the back two thirds is filled with plastic bonded explosive(PBX).The design of the dart includes a1.5cm long cavity starting2.8cm from the nose,which is an integral part of the ignition delay system.The dart impacts the sand target at a right angle normal impact orientation traveling 366m/s(w1200ft/s).2.2.Sand system:semi-infinite targetTwo basic sand systems were used in this study:fine sand and a mixture offine sand and pea gravel.Thefine sand configuration was composed of224m m diameter(60mesh sieve)solid circular grains with a volume fraction packing density of0.55(i.e.45% porosity),which resulted in a bulk density of 1.55g/cm3.The mixture sand configuration is identical to thefine sand configura-tion except larger aggregate(pea gravel)with a diameter of 0.165cm was added.The mixing was constrained such that the mixture had the same bulk density as thefine configuration.In order to construct the two-dimensional material distribution for thefine sand which is representative of the random distribution of smooth spherical particles,a numeric procedure forfilling the computational domain was developed which simulates particle flow during pouring[29].This procedure produces a randomly distributed material realization of particles which may or may not be touching their nearest neighbor.In order to construct the mixed sand configuration,larger aggregate is randomly superimposed into the computational geometry of thefine sand configuration. Thefind sand spacing was perturbed in order to keep the bulk density constant for the two realizations.Fig.2presents two enlarged images of thefind sand and mixed configurations, respectively.2.3.Material propertiesMaterial constants utilized for these calculations are listed in Table1.The material properties of thefine sand and pea gravel are based on Ottawa sand[35]which is99.8%pure crystallinesiliconFig.1.Dart configuration.J.P.Borg,T.J.Vogler/International Journal of Impact Engineering35(2008)1435–1440 1436dioxide,i.e.quartz.A Mie–Gru¨neisen equation of state [36]was used for all of the materials included in these calculations.The quartz utilized a perfectly elastic–plastic strength model whereas the PBX was modeled as inert and hydrodynamic,i.e.zero shear strength.The rest of the materials utilized a Johnson–Cook visco-plastic strength model [37,38].Quartz has famously demonstrated a rich variety of behaviors as a result of shock loading,including phase transitions,material property variability due to driving pressure and sample thickness [39–42].In addition,crystalline quartz contains variability as a result of crystallographic orientation.Thus some care must be taken to insure the parameters selected for the sand corresponded to the range of loading induced by the dart.The individual sand grains were modeled as homogeneous single crystalline a -quartz.Given the nature of the Eulerian calculations,the crystallographic orientation of individual grains is not resolved,thus non-isotropic grain properties were averaged.For example,the zero pressure shock speed and the Hugoniot slope reported in Table 1for a -quartz were obtained by averaging x ,y and z cut data [39].It has been shown that the dynamic strength of quartz varies with respect to the orientation of the crystalline structure and the loading ampli-tude [40],where estimates of the Hugoniot elastic limit (HEL)for x and y cut axes are 5.5–8.5GPa and 10–15GPa for the z axis [39].Hydrostatic data indicate that the lower limit is closer to 2.3GPa[41].An initial averaged HEL of 8.8GPa was used but was varied in order to assess the effect of dynamic strength on the performance of the dart.The remaining material properties were obtained from a variety of sources [39,43–47].3.ResultsInitially simulations were performed using a coarse mesh of approximately one computational cell per sand grain.The resolu-tion was increased to three computational cells per sand grain and finally increased again to seven cells per sand grain.The higher resolution was necessary to capture the grain strength.3.1.Variations in sand systemsFig.3presents a side-by-side comparison of the dart penetrating the fine and mixed sand systems,where the contours represent pressure.Two events occur early in the engagement that signifi-cantly influences the overall projectile penetration:asymmetric loading of the dart nose and the dart structural failure near the time delay primer cavity.Comparisons between the two engagements reveal a more significant asymmetric loading near the nose for the dart pene-trating the mixed sand system as compared to the dart penetrating the fine sand.This asymmetric loading results from the almost immediate interaction with larger aggregate near the nose as seen in Fig.2.As a result,the medium aggregate sustains and transmits higher stress causing a more rapid drop in particle velocity through the front section of the dart.The transmitted stress is greatly attenuated through the dart cavity section,thus the rear two thirds of the dart does not decelerate as rapidly as compared to the front third of the dart.The overall result is a collapse in the cavity section as the rear two thirds of the dart drives down through the cavity and into the front third of the dart.The resulting failure of the dart body near the delay primer cavity,a structurally weak point in the dart construction,causes the dart body casing to jet downward.These two coupled events,asymmetric loading and case failure,lead to obliquity in the nose section,a decrease in performance,and catastrophic failure of the dart.With respect to the fine grain sand,there is asymmetric loading of the dart,but the asymmetric loading of the dart does not cause significant nose obliquity.These results were repeated using a second randomly generated fine grain sand system;thus these results appear to be geometrically independent for the same grain sizedistribution.Fig.2.Material distribution and initial conditions utilized in thesimulations.Table 1Johnson–Cook visco-plastic model constants.J.P.Borg,T.J.Vogler /International Journal of Impact Engineering 35(2008)1435–14401437Fig.4presents a plot of the penetration velocity measured at the nose comparing dart performance in the fine and mixed sand.In the fine sand the dart remains aligned with the shot line and undergoes a 33%reduction in penetration velocity.Over the same time period,the dart penetrating the mixed sand tilts off axis and undergoes a 38%reduction in penetration velocity.3.2.Variations in material parametersIn order to investigate the sensitivity in the dart’s performance as related to select sand properties,the dynamic fracture and yield strength were varied.Additional simulations were performed in which the yield strength of the sand was varied from 5.0GPa to 8.8GPa.This increase in dynamic strength corresponds to the variation in average strength reported from experiments [38].This change had no perceptible change in the performance of the dart.The performance of the dart demonstrated a great deal of sensitivity to the fracture strength of the sand.It has been reported that the dynamic fracture strength (i.e.spall strength)of x-cut crystalline quarts is approximately 1GPa when the material has been loaded below the HEL.However,once the material loading has exceeded the HEL the dynamic fracture strength drops to near zero [48].In order to assess this effect on the dart penetration the fracture strength was increased from 44MPa to 440MPa.In so doing,near catastrophic failure of the dart resulted and the penetration depth of the dart was greatly reduced.Allen et al.[5]noted that the projectile left ‘‘a trail of powdered quartz in its wake’’;this trail was used to determine the projectile trajectory.The powdered quartz also indicates the sand grains failed as a result of the penetration event.The fracture strength of the grain is related to failure under tensile loading.Thus the failure in the sand grains as a result of tensile loading is a key component of the dartperformance.Fig.3.A comparison of dart penetration and the resulting shock propagation through either fine grain sand or fine grain sand with larger particulate for the medium resolution mesh.Color indicates shock front.J.P.Borg,T.J.Vogler /International Journal of Impact Engineering 35(2008)1435–144014384.DiscussionGiven the geometry of the dart and the existence of the cavity in the structure,the dart catastrophically fails early in the penetration for a target with a distribution in sand grain size.It seems unlikely that the addition of such a small scale aggregate would have as a dramatic effect on a solid projectile.These possibilities will be explored in future work.For the right conditions,the total pene-tration of the dart could exceed five initial lengths.Thus the total penetration of the dart could be on the order of a half a meter.The computational requirements of performing an Eulerian mesoscale simulation in which there are seven cells per grain for over half a meter in sand depth would exceed the computational resource available.Numeric techniques such as adaptive mesh refinement,moving meshes,could be used to reduce computational load.These techniques will be pursued in future work.5.ConclusionThe calculations presented indicate that mesoscale simulations can be used to investigate not only the bulk response of a projectile penetrating a heterogeneous target material but also the effect of 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