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magazine article英语作文全文共10篇示例，供读者参考篇1Hey guys, do you know what a magazine article is? It's like a cool story that you can read in a magazine. And guess what? Today, I'm going to write my very own magazine article!The article I'm going to write is about my favorite subject in school, which is science. Science is so awesome because you get to learn all about how things work in the world. I love doing experiments and seeing how things react. It's like magic, but with a scientific explanation!One of the coolest experiments we did in science class was making a volcano erupt. We mixed baking soda, vinegar, and food coloring together and watched as the mixture bubbled up and overflowed, just like a real volcano. It was messy, but so much fun!Another fun experiment we did was making a homemade compass using a magnet and a paper clip. We learned all about how the Earth's magnetic field works and how a compass can help you find your way. It was like being a real explorer!I also love learning about animals in science class. Did you know that some animals can camouflage themselves to blend in with their surroundings? It's like they have superpowers! We even did a project where we had to create our own animal with special adaptations to survive in different environments.Science is so cool because you get to ask questions, make predictions, and test your ideas. It's like being a detective, trying to solve a mystery. I can't wait to learn more about science and discover all the amazing things in the world. Science rocks!So that's my magazine article about why science is my favorite subject in school. I hope you enjoyed reading it as much as I enjoyed writing it. Stay curious and keep exploring the world around you. Who knows, maybe you'll discover something amazing too! Thanks for reading, guys! See you in the next article!篇2Hello everyone! Today I want to share with you some tips on writing a magazine article. It might sound a bit boring, but trust me, it's actually really fun! So let's get started.First of all, think about what you want to write about. It could be something you're passionate about, like sports, animals, oreven your favorite video game. The key is to write about something you enjoy, so that you can share your enthusiasm with your readers.Next, do some research on your topic. This will help you gather information and facts to make your article more interesting and informative. You can search online, read books, or even interview experts to get more insights on the subject.Once you have collected all the information you need, it's time to start writing. Remember to keep your language simple and easy to understand. You don't want your readers to get confused or bored, so use clear and concise sentences.Don't forget to include some catchy headlines and subheadings to grab your readers' attention. And don't be afraid to add some fun facts, quotes, or even personal anecdotes to make your article more engaging.Finally, make sure to proofread your article before submitting it. Check for any spelling or grammar mistakes, and make sure your ideas flow smoothly from one paragraph to the next.So there you have it, some tips on writing a magazine article in a fun and engaging way. Remember to have fun with your writing and let your creativity shine through. Happy writing!篇3Title: The Amazing World of AnimalsHey everyone! Do you like animals? I bet you do! Animals are so cool and interesting. There are all kinds of animals out there, big ones, small ones, fluffy ones, scaly ones, and everything in between. In this article, we are going to explore the amazing world of animals and learn some fun facts about them.First up, let's talk about elephants. Did you know that elephants are the largest land animals in the world? They are really big and strong! Elephants also have big ears that they use to cool themselves down. How cool is that?Next, let's talk about dolphins. Dolphins are super smart and friendly animals. They love to swim and play in the ocean. Did you know that dolphins communicate with each other using clicks and whistles? They are like the chatterboxes of the sea!Moving on to lions. Lions are the kings of the jungle. They have big manes and loud roars. Lions are also known for living ingroups called prides. The females do most of the hunting while the males protect the pride. Teamwork makes the dream work!Now, let's talk about penguins. Penguins are so cute and funny. They waddle around on land and swim like little rockets in the water. Did you know that penguins have a special gland near their eyes that helps them drink saltwater? It's like having your own built-in purifier!Last but not least, let's talk about butterflies. Butterflies are beautiful insects with colorful wings. They go through a process called metamorphosis where they transform from a caterpillar to a butterfly. Isn't that amazing?So there you have it, some fun facts about the amazing world of animals. Animals are incredible creatures that deserve our love and respect. Let's continue to learn about them and protect them so that they can thrive for generations to come. See you next time!篇4Title: My Favorite ThingsHey guys! I want to talk about some of my favorite things in this article. I hope you enjoy reading it as much as I enjoy writing it!First off, I want to talk about my favorite food - pizza! Who doesn't love pizza, right? I love all kinds of pizza - pepperoni, cheese, veggie, you name it! It's so delicious and I could eat it every day if my mom let me.Next, let's talk about my favorite TV show. I absolutely love watching cartoons, especially ones with superheroes. My favorite show right now is "The Amazing Adventures of Super Kid". It's about a kid who has superpowers and saves the day. It's so cool and I wish I could be just like him!Now, let's move on to my favorite hobby - drawing. I love to draw and color pictures of my favorite cartoon characters. It's so much fun and I can spend hours doing it. I even have a whole collection of drawings hanging on my wall.Another thing I love is playing outside with my friends. We play games like tag, hide and seek, and soccer. It's so much fun running around and laughing together. I always have a blast when I'm hanging out with my friends.Last but not least, I want to talk about my favorite subject in school - art class! I love art class because I get to be creative and make all kinds of cool things. It's so much fun painting, sculpting, and drawing in art class. I always look forward to it every week.Well, those are some of my favorite things. I hope you enjoyed reading about them. What are some of your favorite things? Let me know in the comments below! Thanks for reading!篇5Title: My Favorite MagazineHey guys! Today I want to talk about my favorite magazine. It's called "Science Explorer" and it's super cool! I love reading it because it's all about science and nature, which are two of my favorite things.One of the reasons I love "Science Explorer" is because it has really cool articles about animals. I love learning about different animals and their habitats. Did you know that there are animals that can change colors to blend in with their surroundings? How cool is that! I also love reading about new species that scientists discover. It's so exciting to learn about all the amazing creatures that share our planet.Another thing I love about "Science Explorer" is the experiments and activities they have in each issue. They have simple and fun experiments that you can try at home with materials you probably already have. My favorite experiment so far was making a volcano out of baking soda and vinegar. It was so cool to see the volcano "erupt" and fizz everywhere. I felt like a real scientist!"Science Explorer" also has really great illustrations and pictures that make learning about science even more fun. The photos are so colorful and detailed, and they help me understand the articles better. I love looking at the pictures of animals in their natural habitats, or seeing diagrams of how things work. It's like having a visual learning experience!In conclusion, "Science Explorer" is my favorite magazine because it's all about science and nature, which are things I love.I enjoy reading about animals, doing the experiments, and looking at the cool pictures. It makes learning about science fun and exciting, and I can't wait for the next issue to come out!That's all for now, my fellow science explorers. Remember to keep reading and exploring the world around you. Bye for now!篇6Title: Let's Talk about Magazines!Hey guys! Have you ever read a magazine before? Magazines are so cool and fun to read! Today, I want to talk to you about why magazines are awesome and why you should give them a try.First of all, magazines are full of interesting information. You can learn about all kinds of stuff like animals, sports, fashion, and so much more! There are articles, photos, and even games in magazines. It's like a whole world of fun and knowledge inside one little book.Secondly, magazines are great for improving your reading skills. When you read a magazine, you get to practice reading different kinds of texts like stories, interviews, and news articles. It's a fun way to become a better reader and learn new words.Another cool thing about magazines is that they are easy to carry around. You can take a magazine with you wherever you go, whether it's to school, the park, or even on a road trip. It's a great way to pass the time and keep yourself entertained.Lastly, magazines are a great way to relax and unwind. After a long day at school or on the weekends, you can curl up with amagazine and just chill out. It's a nice way to escape from the real world for a little bit and just enjoy some good reading time.So, what are you waiting for? Go pick up a magazine and give it a try! You might just discover a new favorite hobby. Trust me, magazines are awesome!篇7Title: My Favorite Magazine - The Cool Kids GazetteHi everyone! Today I want to tell you about my favorite magazine called The Cool Kids Gazette. It's the best magazine ever because it has so many fun and interesting articles for kids like me to read.One of the things I like about The Cool Kids Gazette is the comics section. The comics are so funny and they always make me laugh. My favorite comic strip is about a superhero kid who saves the day with his superpowers. It's so awesome!Another thing I love about the magazine is the science experiments. They have cool experiments that you can do at home with everyday items. I tried making a volcano with baking soda and vinegar once, and it was so cool to see it erupt like a real volcano!The Cool Kids Gazette also has stories about kids who are doing amazing things. Like one time, I read about a girl who had her own pet-sitting business and she was only nine years old! It's so inspiring to see other kids doing big things.The magazine also has a section where kids can write in and share their own stories and drawings. I once sent in a drawing of my pet dog and they published it in the magazine. It made me feel really proud to see my artwork in print!Overall, The Cool Kids Gazette is a super awesome magazine that all kids should read. It's fun, informative, and it makes me feel like I'm part of a cool community of kids who love to read and learn new things. If you haven't checked it out yet, you definitely should!篇8Hey guys! Today I want to talk to you all about something super cool - magazines! Have you ever read a magazine before? They're like books, but with lots of pictures and fun articles to read.Magazines come in all different types, like fashion magazines, sports magazines, and even magazines about animals! You can learn all sorts of interesting things from readingmagazines. For example, did you know that elephants can communicate with each other using sounds that are too low for humans to hear? How cool is that!One of the best things about magazines is that they are always changing. Each month, new issues come out with fresh stories and updates on the latest trends. It's like getting a present in the mail every time a new magazine arrives!Another awesome thing about magazines is that they are full of fun activities and puzzles to do. You can test your brain power with crossword puzzles, word searches, and even riddles. It's a great way to keep your brain sharp and have fun at the same time.So the next time you see a magazine at the store or in your library, be sure to pick it up and give it a read. You never know what new and exciting things you might learn from the pages inside. Happy reading, everyone!篇9A Magazine ArticleHello everyone! I'm excited to share with you all about the latest happenings in our school in this magazine article. So, let's get started!First of all, let me tell you about the fun sports day we had last week. We had so many exciting games and races to participate in, like the sack race, three-legged race, andtug-of-war. It was so much fun cheering on our friends and competing in the games. I even won a medal in the egg and spoon race! It was a fantastic day filled with laughter and happy memories.Next, I want to talk about the school talent show that we had last month. There were so many talented students who showcased their amazing skills, like singing, dancing, and playing musical instruments. I was amazed by how talented everyone was! I performed a magic trick with my friends, and we got a huge round of applause from the audience. It was such a great experience to be on stage and share our talents with our schoolmates.In other news, our school recently had a charity drive to help those in need. We collected donations of clothes, toys, and books to give to a local charity organization. It was heartwarming to see how generous everyone was in donating items to helpothers. I felt proud to be a part of such a caring and compassionate school community.Lastly, I want to share about the upcoming school field trip we are going on next month. We are going to visit a farm to learn about animals and agriculture. I'm so excited to see the cows, chickens, and pigs up close and maybe even milk a cow! It will be a fun and educational trip, and I can't wait to go on this adventure with my classmates.That's all for now, folks! I hope you enjoyed reading about all the exciting events happening in our school. Stay tuned for more updates in the next issue of our school magazine. Thanks for reading!Yours truly,[Your Name]篇10Title: The Best Magazine Ever!Hey guys, have you heard about the latest magazine that everyone is talking about? It's called "Super Kids Magazine" and it's seriously the best magazine ever!First of all, the magazine is packed full of awesome stories, fun facts, and cool activities that will keep you entertained for hours. From silly jokes to interesting articles about animals and nature, there's something for everyone in every issue.But that's not all! "Super Kids Magazine" also features interviews with famous athletes, scientists, and even superheroes. You can learn all about their amazing adventures and how they became so successful. It's super inspiring!And the best part? The magazine also has a section where readers can submit their own stories, drawings, and jokes. How cool is that? You could have your own work published in a real magazine!So, if you're looking for the ultimate source of fun and knowledge, be sure to check out "Super Kids Magazine." It's the perfect way to spend a lazy afternoon or a rainy day. Trust me, you won't be disappointed!Pick up a copy today and join the thousands of kids who are already loving this awesome magazine. You won't regret it!。

Elsevier ScienceDirect(SD)荷兰Elsevier Science 出版集团出版的期刊是世界上公认的高质量学术期刊，其中大部分期刊被S CI、SSCI、EI所收录。

目前其SDOS（Science Direct Onsite）网络全文数据库包括1995年以来Es evier Science 出版的1800余种高品质全文学术期刊，涵盖了生命科学、计算机科学、工程、环境科学、农业和生物科学、数学、经济、商业、管理、社会科学、艺术和人文科学等23个学科领域。

SD收录的图书不在图书馆购买范围之内，因此不能阅读、下载SD的图书。

Web of Science数据库Web of Science是美国Thomson Scientific（汤姆森科技信息集团）基于WEB开发的产品，是大型综合性、多学科、核心期刊引文索引数据库，包括三大引文数据库（科学引文索引（Science Citation Index，简称SCI）、社会科学引文索引（Social Sciences Citation Index，简称SSCI）和艺术与人文科学引文索引（Arts & Humanities Citation Index，简称A&HCI））和两个化学信息事实型数据库(C urrent Chemical Reactions，简称CCR和Index Chemicus，简称IC)，以及科学引文检索扩展版（S cience Ciation Index Expanded,SCIE）、科技会议文献引文索引（Conference Proceedings Citation Index-Science,CPCI-S）和社会科学以及人文科学会议文献引文索引（Conference Proceedings Ci tation index-Social Science&Humannalities,CPCI-SSH）三个引文数据库，以ISI Web of Knowledge作为检索平台。

英文作文articleTitle: The Impact of Technology on Education。

In today's rapidly evolving world, technology plays an increasingly significant role in every aspect of our lives, including education. The integration of technology into education has brought about both positive and negative impacts, shaping the way students learn and educators teach. This article explores the various ways in which technology influences education and discusses its implications for the future.First and foremost, technology has revolutionized the way information is accessed and disseminated. With the internet and digital devices, students now have access to a vast amount of information at their fingertips. They can easily conduct research, explore diverse perspectives, and engage with multimedia resources to enhance their learning experience. This accessibility to information has democratized education, breaking down barriers to learningand empowering students from all backgrounds to pursue knowledge.Moreover, technology has transformed the traditional classroom environment. Interactive whiteboards, educational apps, and online platforms have become commonplace, providing educators with tools to create dynamic and engaging lessons. These digital resources cater todifferent learning styles and allow for personalized instruction, enabling students to learn at their own pace and according to their individual needs. Additionally, technology facilitates collaboration among students through online forums, video conferencing, and shared documents, fostering a sense of community and enhancing communication skills.Furthermore, technology has opened up new avenues for creativity and innovation in education. Students can now utilize multimedia tools to express their ideas, create multimedia presentations, and develop digital projects. Virtual reality (VR) and augmented reality (AR) technologies offer immersive learning experiences, allowingstudents to explore virtual environments and simulate real-world scenarios. These innovative approaches not only make learning more engaging but also cultivate critical thinking, problem-solving, and digital literacy skills essential for success in the 21st century.However, despite its numerous benefits, the widespread use of technology in education also poses challenges and concerns. One major issue is the digital divide, whichrefers to the gap between those who have access to technology and those who do not. Socioeconomic disparities and inadequate infrastructure can hinder access to digital devices and high-speed internet, depriving certain students of the opportunities afforded by technology. Bridging this divide requires concerted efforts from policymakers, educators, and technology providers to ensure equitable access to technology for all students.Additionally, the overreliance on technology in education raises concerns about its potential drawbacks. Excessive screen time and digital distractions can impede students' focus and concentration, leading to decreasedacademic performance and impaired social skills. Moreover, the proliferation of online resources raises questions about the quality and credibility of information available to students. Educators must teach students how tocritically evaluate sources and discern fact from fiction in an age of information overload.In conclusion, technology has undoubtedly reshaped the landscape of education, offering unprecedentedopportunities for learning and innovation. From enhancing access to information to fostering collaboration and creativity, technology has the potential to revolutionize education for the better. However, realizing this potential requires addressing challenges such as the digital divide and mitigating the risks associated with overreliance on technology. By harnessing the power of technology responsibly, educators can empower students to thrive in a digital age and prepare them for the challenges of the future.。

Section DⅠ. Material analysis本课是第二单元第一话题的第四课时，主活动是1a和Project。

通过Grammar 来巩固总结一般过去时和现在完成时的区别，通过Functions 来复习重要的表达法。

1a按照“总—分—总”的模式分别介绍了各种污染的成因及危害。

通过完成文章后的表格，训练和提高学生获取信息的能力。

教师还可以利用表格内容，引导学生整合信息复述课文，巩固课文内容。

1b属于同义转换练习。

Project部分培养学生动手动脑的能力，让学生运用收集的信息和所学知识，通过墙报的形式来宣传污染带来的危害，让更多的人关注环境污染，树立环保意识，增强人们的忧患意识和社会责任感。

Ⅱ.Teaching aims1.Knowledge aims：掌握本课的重点词汇和短语。

总结一般过去时和现在完成时的区别；复习本话题的重点表达法。

2.Skill aims:能读懂与环境污染问题有关的文章。

能根据关键词复述课文。

3. Emotional aims: (optional)通过了解各种污染带来的危害，帮助学生树立环保意识，爱护环境，保护地球。

14.Culture awareness: (optional)通过学习，引导学生了解环境污染对人类健康有巨大的危害，不同种类的污染体现在不同的方面。

Ⅲ. The key points and difficult points1. Key points:Words and phrases: coal, create, blood, planet, in many ways, with the development of industry, high blood pressure Grammar: the differences between the simple past and present perfect2. Difficult points：能根据关键词复述课文。

research article 中各部分的内容和作用
在Research Article中，通常包含以下几个部分，这些部分各自具有其特定的内容与作用：
1. 摘要（Abstract）：摘要部分通常简明扼要地概括了研究的主要内容、方法、结果和结论。

它为读者提供了关于研究的快速概览，帮助读者决定是否需要进一步阅读整篇文章。

2. 引言（Introduction）：引言部分详细介绍了研究的背景和目的，为理解后续的研究内容提供了背景信息。

它解释了为什么这个研究是重要的，以及预期的研究结果如何影响该领域的知识。

3. 方法（Methods）：这一部分详细描述了用于收集数据或执行实验的程序和过程。

它确保其他研究人员能够复制并验证研究结果。

4. 结果（Results）：结果部分呈现了通过研究获得的数据。

这些数据通常以图表、表格等形式呈现，以便读者可以直观地理解。

5. 讨论（Discussion）：在讨论部分，研究人员会解释研究结果的含义，将其与之前的研究进行比较，并探讨可能的解释和局限性。

此外，他们通常也会提出对未来研究的建议。

6. 结论（Conclusion）：结论部分总结了研究的主要发现，并强调这些发现对领域的影响和贡献。

它也指出了研究的局限性和未来可能的研究方向。

以上是Research Article中常见的各个部分的内容和作用。

具体组成部分可能会根据研究领域和期刊的要求有所不同。

在撰写Research Article时，遵循期刊的格式和结构要求是非常重要的。

Effect of shearing on crystallization behavior ofpoly(ethylene naphthalate)W.J.Yoon,H.S.Myung,B.C.Kim,S.S.Im *Department of Textile Engineering,Hanyang University,Haengdang,Seongdong,Seoul 133-791,South KoreaReceived 11August 1999;received in revised form 24September 1999;accepted 30September 1999AbstractThe effect of shear history on the isothermal crystallization behavior of poly(ethylene naphthalate)(PEN)was investigated by rheological and morphological measurements.Time sweep measurements of storage modulus (G H )and dynamic viscosity (h H )were carried out on the molten PEN by Advanced Rheometric Expansion System (ARES)in the parallel-plate geometry at several different temperatures and frequencies,followed by structural analysis by differential scanning calorimeter (DSC),X-ray diffractometer,and polarizing microscopy for the shear-induced crystallized PEN specimens in the ARES measurements.The rate of isothermal crystallization of PEN was notably affected by temperature,while the shear rate has an important effect on the structures of the resultant crystals.At a constant shear rate,the rate of crystallization by shear-induced structuring mechanism was increased with lowering temperature over the temperature range 230–250ЊC.The rate of crystallization was increased with increasing shear rate at a given temperature.An increase in shear rate increased both nucleation and number of crystallites.Further,it increased the content of the a -form crystal in the specimen.On the other hand,lower shear rate offered more favorable conditions for forming the b -form crystal.DSC analysis exhibited that the b -form crystal had higher melting temperature (T m )than the a -form crystal.The wide angle X-ray diffraction (WAXD)patterns also ascertained that higher content of the a -form crystal was produced in the PEN specimen crystallized at higher frequency.᭧2000Elsevier Science Ltd.All rights reserved.Keywords :Poly(ethylene naphthalate);Rheology;Shear-induced crystallization1.IntroductionShear-induced structural changes in polymeric materials take an increasing interest in the field of polymer proces-sing.In real polymer processing very complex deformation histories are involved,which can influence ultimate proper-ties of plastics.Recent advances in experimental techniques that allow in situ measurements of materials under deforma-tion have escalated research in this subject area.It has been known for a long time that flow stress have accelerating effect on the crystallization of semi-crystalline polymers [1–6].It is supposed that the application of a shear stress to a polymer melt should lead to formation of orientation and reduce the entropy of the melt,which results in a higher melting temperature and,hence,lead to an increased super-cooling [3,7].Several experiments have been described in the literature where attempts were made to quantify the shear stress-induced crystallization in molten semi-crystal-line polymers such as polypropylene [3,8,9],polyethylene oxide [10],polypropylene [11–13],and polybutene-1[3,14].Some investigators used rotational viscometers andmeasured either the volume change [15]or the number of nuclei formed during shearing [11,14].The polymers enum-erated above are apt to process because of low melting point and viscosity.On the other hand,PEN has good thermal and mechanical properties and is being used as engineering plastics.PEN is reported to have two different triclinic crystalline structures,a -form and b -form crystals.Of two crystal forms,the b -form crystal is known to be more stable than the a -form.The effect of crystallization temperature on the resultant crystal structure is well recognized;lower temperature favors formation of the a -form crystal.The critical temperature is reported about 230ЊC.However,the effect of shear history on the crystal structure of PEN has not been reported.In this study,the shear-induced crystallization behavior of PEN was investigated on the rheological basis.The effect of shear history on the crystalline structure was also discussed in terms of thermal and morphological properties.2.Experimental 2.1.MaterialThe PEN tested was a commercially available gradePolymer 41(2000)4933–49420032-3861/00/$-see front matter ᭧2000Elsevier Science Ltd.All rights reserved.PII:S0032-3861(99)00703-X*Corresponding author.Tel.:ϩ82-2-2292-0495;fax:ϩ82-2-2297-5859.E-mail address:imss007@email.hanyang.ac.kr (S.S.Im).supplied by Kolon Group in South Korea.The inherent viscosity,0.344dl/g was determined in a mixture of trifluoroacetic acid and chloroform (1/3v/v%)with an Ubbelohde viscometer at 25^0:1ЊC :The polymer was dried in a vacuum oven at 120ЊC for 24h prior to use.2.2.Measurement of physical propertiesThe dynamic rheological properties were measured by ARES (Rheometric Scientifics)in the parallel plate geome-try.The plate diameter was 12.5mm,strain level was 5%,and gap between the plates was 1mm.The PEN chips were melted at 300ЊC.The initial gap was set to a value equiva-lent to final gap plus 50m m.The excess sample squeezed out by reducing the gap was carefully trimmed off.The value was reset to the final gap value,1mm.To remove the residual stress the newly set PEN specimen was relaxed for about 5min at the temperature in nitrogen atmosphere,then cooled to the predetermined temperature for rheologi-cal measurements.A time-sweep experiment was continued for the specimen till the G H reached the ceiling value of the apparatus.After ARES measurement,the molten PEN sample was detached from the plates for measuring other properties such as thermal and morphological properties by DSC,X-ray diffractometer and polarizing optical micro-scopy.Thermal properties were measured by Perkin–Elmer DSC-7over the temperature 50–300ЊC at the heating rate of 10ЊC/min under nitrogen purge.The isothermalcrystallization experiment was performed by two different methods.Firstly,the PEN sample was heated to 300ЊC at the heating rate of 200ЊC/min,and held for about 5min,then they were cooled to the preset temperature to bring about the isothermal crystallization for same time required in ARES experiment.Secondly,the PEN chips were melted at 300ЊC between two slide glasses for 5min on the hot stage.They were moved to an oil bath very quickly and isothermally crystallized at 230,240,and 250ЊC for 4,10,and 24h,respectively.Wide angle X-ray diffraction patterns of the isothermally crystallized PEN specimen in the oil bath and ARES were obtained by X-ray diffractometer (Rigaku Denki)with Ni-filtered CuK a radiation at 35kV and 35mA.Morphology of quiescent and shear-induced crystallized PEN specimen was observed by polarized microscopy (Nikon HFX-IIA).The spherulite structure was observed by microtoming the specimen.3.Results and discussionIn the plot of G H and h H versus time at a given frequency for a polymer,the two parameters may give information on the change in physicochemical properties of the polymer.For thermally sensitive polymer melts,an irreversible decrease of viscosity with time at a constant shear rate suggests the possibility of thermal degradation of polymer molecules,whereas an irreversible increase of viscosityW.J.Yoon et al./Polymer 41(2000)4933–49424934Fig.1.Variation of G H with time for PEN melt at 240ЊC at three different frequencies.with time indicates the possibility of chemical crosslinkingbetween polymer molecules.Both thermal degradation andchemical crosslinking show irreversibility in the rheologicalresponses.On the other hand,a reversible change in G H and h H with time at a constant frequency may be caused by changing in the physical state of the polymer melts.A typi-cal example of the physical change is the isothermal crystal-lization.As the crystallites grow to larger sized spheruliteswithin the PEN melt through nucleation and growth,thehomogeneous melt system changes to the heterogeneoussystem.Thus the G H and h H increase with the crystallization time.Figs.1and2show the variation of the G H and h H of PEN melt with time at240ЊC at three different shear rates(1,3, and5rad/s).At the early stage of experiment,both G H and h H are increased slowly,indicating an induction time for crystallization.The induction period is the stage when randomly entangled polymer chains transform to the regular aligned lattice.Because of topological obstruction of such entanglements,the polymer crystallization is extremely slow[16].However,an abrupt increase of both parameters follows in some minutes.This phenomenon can be ascribed to the formation of tiny crystals so-called crystallites prob-ably due to shear-induced crystallization.It can be easily imagined that the homogeneous PEN melt changes to a suspension system with proceeding crystallization,in which numerous crystallites are dispersed in the homo-geneous molten polymer matrix.The viscosity increases due to increasing the volume fraction of dispersed crystal-lites with progressing crystallization,which is also reportedby others[7,9,11,14,17].The ceiling value of G H is the same regardless of frequen-cies and temperatures whenfinishing crystallization asshown in Fig.1.On the other hand,the ceiling value of h H is gradually decreased with increasing the applied frequency as shown in Fig.2.This is attributable to pseudo-plasticity.That is,the heterogeneous system is expected toshow yield behavior[18].At low shear rates the hetero-geneous systems exhibit very high viscosity,and almostunbounded viscosity at zero shear rate.The viscosity,however,is rapidly decreased if the shear rate exceeds acritical value.Consequently,the ceiling viscosity at1rad/sis greater than at5rad/s.In addition,the ceiling value of h H shows a gradual decrease with time after having reached maximum as shown in Fig.2,which is more noticeable at the higher frequency.The gradual decrease of h H seems to result from the restructuring of the heterogeneous systems. That is,the viscosity is decreased with shearing on account of destruction of the orderedfiller particle structure.The destruction of the pseudostructure offiller particles is increased as shear rate is increased.Fig.2reflects this.It is also noted in Figs.1and2that the induction time forcrystallization is decreased as frequency is increased.Anapplication of shear stress to a polymer melt would giverise to two characteristic responses,orientation and slippageof polymer molecules.They are associated with theW.J.Yoon et al./Polymer41(2000)4933–49424935Fig.2.Variation of h H with time for PEN melt at240ЊC at three different frequencies.W.J.Yoon et al./Polymer41(2000)4933–49424936Fig.3.Variation of G H(A)and h H(B)for PEN melt at3rad/s at three different temperatures.W.J.Yoon et al./Polymer41(2000)4933–49424937Fig.4.DSC thermograms of PEN isothermally crystallized at(A)230ЊC,(B)240ЊC and(C)250ЊC at various frequencies.macroscopic phenomena of elasticity and flow,respectively.That is,the oriented polymer molecule has fewer possible conformations than the unoriented one,which results in lower entropy.At the melting temperature,the free energy of the crystal equals the free energy of the melt as written by [3]T mD H f D S f H m ϪH cS m ϪS c1Hence,for an oriented melt,the ensuing reduction in entropy raises T m .Further,it increases the degree of super-cooling,accelerating the rate of crystallization.In general,higher shear rate gives better chance for orientation.Con-sequently,the induction time for cystallization is decreased with increasing shear rate.In Fig.3(A)and (B)shows that the annealing temperaturehas a profound effect on the nucleation and crystallization mechanism of PEN melts.The increase of G H and h H with annealing time represents the extent of crystallization of the melts with annealing time.Fig.3suggests that the number and growth rate of the nucleated crystallites is greater at 230ЊC than at 250ЊC.That is,both nucleation density and growth rate of crystallites are diminished with raising the annealing temperature.This stands to reason because the maximum rate of the homogeneous crystallization of PEN melts is observed in the vicinity of 215ЊC.The viscosity behavior of the PEN melt with crystalliza-tion in Fig.3may be accounted for by adopting the Mooney equation in a qualitative manner [19].ln h =h 1K E F 21ϪF 2=F m2W.J.Yoon et al./Polymer 41(2000)4933–49424938Fig.4.(continued )Table 1The values of T m H and T m HH of PEN with frequency (230,240and 250indicate temperature.(a)and (b)indicate v 0 a and v 0 b ;respectively (see Fig.6).1,3and 5indicate frequencyT m HT m HH T m HT m HH T m HT m HH PEN230(a)259.2272.1PEN240(a)266.7PEN250(a)270.1PEN230(b)264.1270.9PEN240(b)272.1PEN250(b)280.1PEN2301255.6270.3PEN2401259.3269.3PEN2501269.1PEN2303256.0270.0PEN2403261.9268.7PEN2503270.4PEN2305256.2269.7PEN2405263.6268.0PEN2505270.7F m true volume of fillerapparent volume occupied by the filler3 in which h is the viscosity of the suspension,h l is the viscosity of the suspending medium,f2is the volume frac-tion of thefiller,f m is the maximum volume fraction that thefiller can have,and K E is the Einstein coefficient,whose value is known to be2.5for the dispersed sphericalfiller.W.J.Yoon et al./Polymer41(2000)4933–49424939Fig.5.WAXD patterns of PEN isothermally crystallized at(A)230ЊC,(B)240ЊC and(C)250ЊC at various frequencies.Referring to the Mooney equation,the crystallization patterns of PEN melts at 230ЊC and at 250ЊC are distinc-tively different from each other.The Mooney equation predicts that the degree of increasing the suspension visc-osity with increasing f 2is greatly increased if the spheres form aggregates because the aggregation of spheres (spheru-litic crystallites or crystals in this study)increases the appar-ent filler volume fraction.That is,the immobile portions (homogeneous molten PEN matrix in this study)caged by aggregated spheres also act as filler portion.On this assump-tion,it may be suggested that an application of higher shear rate during isothermal crystallization tends to increase the heterogeneous crystallization characteristics.Hence,the higher nucleation density and higher growth rate of the nucleated crystallites is obtained at higher frequency,and the resultant is more abundant with less stable a -form crys-tals (this will be discussed later in detail).The melt endotherms of quiescently and shear-induced crystallized PEN were shown in Fig.4and the correspond-ing peak temperatures are listed in Table 1.The double melting endotherm behavior is displayed during heating the PEN sample in the DSC cell.In the melting process of the shear-induced crystallized PEN sample,three endother-mic peaks are identified;a broad endotherm,a low endotherm (T m H ),and a high endotherm (T m HH )as shown in Fig.4.The broad endotherm might be due to the thermal history during cooling and reheating,and both low and high endotherms are due to the melting of original lamella and recrystallized one,respectively.These results well coincide with the results of Zachman et al.[20]:(1)no change of crystal modification is observed during DSC scanning;(2)the double melting behavior of PEN is due to the mechan-ism based on melting and recrystallization;(3)the b -form crystal has the T m higher than the a -form crystal by 2ЊC;and (4)the peaks of two forms of crystal are not separated in DSC thermogramsIn Fig.4(A)–(C)v 0rad =s indicates quiescent crystal-lization.(A)indicates that the PEN sample was crystallized at 230,240,and 250ЊC for the same time that required in the ARES experiments,and (B)expresses the PEN sample crys-tallized in an oil bath at the same temperature as in (A)for the time long enough to fully crystallize.Since the crystal-lization time in (A)is much shorter than in (B),an exother-mic peak is observed in the thermogram (A)at around 205ЊC.The v 0rad =s (b)curves in Fig.4(B)show a single melting peak.The T m shifts to higher temperature and peak width gets narrower as the crystallization time and tempera-ture are increased.This is attributable to the increased perfectness of the resultant crystal structure,which is observed more clearly when the sample is crystallized at higher temperature as can be seen in Fig.4(C).Only the b -form crystal exists when the sample is isothermally crys-tallized at 250ЊC after having melted at 300ЊC.This result matches well with the X-ray data.As mentioned the T m of the b -form crystal is higher than the a -form crystal by 2–4ЊC.It has been known that PEN has two different triclinic crystal structures.Buchner et al.reported that crystalW.J.Yoon et al./Polymer 41(2000)4933–49424940Fig.5.(continued )structures are influenced by both melting and isothermal crystallization temperature.They observed that the b -form crystal appeared mainly when PEN was isothermally crys-tallized above 230ЊC quiescently and the a -form crystal did below 230ЊC after having melted at 300ЊC [20].Fig.5presents WAXD patterns of PEN specimens shear-inducedcrystallized at (A)230ЊC,(B)240ЊC,(C)250ЊC at several frequencies.In Fig.5(A)the WAXD patterns for v 0rad =s shows diffraction peaks at 15.6and 23.3Њwhich correspond to (010)and (100)plane of the a -form crystal,respectively.The intensity of these peaks has a tendency to increase with increasing frequency.It means that the appli-cation of shear promotes the formation of the a -form crystal and the increase of frequency increases the content of the a -form crystal.In Fig.5(B)the (010)plane peak of the a -form crystal is smaller than that of the sample crystallized at 230ЊC in Fig.5(A)for v 0rad =s :However,the plane peak is increased with increasing frequency.In the case of the (100)plane peak,a shoulder appears at v 0rad =s :As frequency increases,the intensity of the plane peak standing for the a -form crystal shows tendency to increase.Particu-larly,for v 0rad =s in Fig.5(C)any plane peak of the a -form crystal is not observed,which is consistent with the results reported by Buchner et al.[20].The (010)and (100)plane peaks appear simultaneously,and keep on growing with increasing frequency.In addition,all diffraction peaks of Fig.5shift to lower angle when frequency is increased.This suggests that there is deformation in the crystal struc-tures as well.Thus,this X-ray trace of the sample is similar to those of Fig.5(A)and (B),suggesting similarity in the crystallization behavior at 230–250ЊC.In general,the b -form crystal is thermodynamically more stable but more difficult to nucleate than the a -form crystal and the form of the crystal is largely determined by kinetic factors during crystallization such as the rate of nucleation and spherulite growth [21].In the case of the a -form crystal,one chain passes through the unit cell and the chains in the crystal are extended.In the case of the b -form crystal,however,four chains pass through the unit cell and the chains in the crystal are not completely extended.When the polymer is sheared,the number of crystallites increases with shear rate,representing faster nucleation.Wolkowicz [14]mentioned that the number of crystallites increased exponentially with time at all shear rates.Also,this can be confirmed in Fig.6,which indicates that nuclea-tion becomes increasingly profuse with increasing frequency until the crystalline structure formed is no longer distinguishable with a microscope [3,22].Hence,the content of the a -form crystal in the speci-men increases with frequency because the a -form crys-tal is apt to nucleate due to fast nucleation.Consequently,the resultant a -form crystal is thermody-namically less stable than the b -form crystal because of much reduced entropy by molecular orientation under high shear force.References[1]Hill MJ,Keller A.J Macromol Sci (Phys)1969;B3(1):153.[2]Andrews EH.J Polym Sci 1966;A-2(4):663.[3]Haas TW,Maxwell B.Polym Eng Sci 1969;9:226.W.J.Yoon et al./Polymer 41(2000)4933–49424941(B)(A)(C)Fig.6.Polarizing optical micrographs of PEN crystallized at 240ЊC (A)v 0;(B)v 1;and (C)v 5:[4]Pennings AJ,van der Mark JMAA,Booj HC.kolloid Z v Z Polym1970;236:99.[5]Mackley MR,Keller A.Polymer1973;14:16.[6]Peterlin A.Polym Eng Sci1976;16:126.[7]Kobayashi K,Nagasawa T.J Macromol Sci(Phys)1970;B4:331.[8]Lagasse RR,Maxwell B.Polym Eng Sci1976;16:189.[9]Titomanlio G,Brucato V.Plastics Processing Society,The TenthAnnual Meeting,Akron,OH,1965,p.93.[10]Ulrich RD,Price FP.J Appl Polym Sci1976;14:401.[11]Eder G,Janeschizt-Kriehl H,Liedauer S.Progr Polym Sci1989;15:629.[12]Liedauer S,et al.Int Polym Proc VIII1993;3:236–44.[13]Moitzi J,Skallcky P.Polymer1993;34:3168.[14]Wolkowicz MD.J Polym Sci:Polym Symp1978;63:365.[15]Sherwood CH,Price FP,Stein RS.J Polym Sci;Polym Symp1977;63:77.[16]Imai M,et al.Phys.Rev.1995;B52:12696.[17]Kim JG,Park HJ,Lee JW.Korean J Rheol1997;4:174.[18]Carreau PJ,De Kee DCR,Chhabra RP.Rheology of polymericsystems,New York:Hanser,1997.[19]Nielsen LE.Polymer rheology,New York:Marcel Dekker,1977.[20]Buchner S,Wiswe D,Zachman HG.Polymer1989;30:480.[21]Zachman HG,Wiswe D,Riekel C.Macromol Chem Suppl1985;12:175.[22]Kim SP,Kim SC.Polym Eng Sci1993;33:83.W.J.Yoon et al./Polymer41(2000)4933–4942 4942。

Computational noteElectronic dipole polarizabilities of polychlorinated dibenzofurans and semiempirical PM6level performanceAndrea Alparone,Vito Librando *Research Centre for Analysis,Monitoring and Minimization Methods of Environmental Risk,Department of Chemistry,University of Catania,viale A.Doria 8,Catania I-95125,ItalyPolychlorinated dibenzofurans (PCDFs)are widespread and per-sistent environmental contaminants [1].Electronic dipole polariz-abilities (a )of PCDFs were previously computed at the B3LYP level with cc-pVDZ,6-31G Ãand 6-31G ÃÃbasis sets in order to elucidate the effect of the substituent position on the congener specific tox-icity [2,3]and aqueous solubility [4].Recently,semiempirical PM6method [5]has been implemented in MOPAC 2007package [6],giving satisfactory estimates of molecular properties such as heats of formation [5]and electronic a values [7,8].This work is principally concerned on the validation of the PM6method in the determination of a values,focusing attention on DF and the 135PCDF congeners (Fig.S1of the Supporting Material).Static a ij (i,j =x ,y ,z )components were calculated at the AM1,PM3and PM6levels.Additionally,we computed a ij values for DF and its octacloro substituted congener at the HF,MP2and PBE0levels with aug-cc-pVDZ basis set on the B3LYP/6-31G ÃÃgeometry.Present computations were performed with MOPAC 2007[6]and PC GAMESS [9,10]programs.Calculated average polarizability,h a i ¼1=3ða xx þa yy þa zz Þ,and polarizability anisotropy,D a ¼f 1½ða xx Àa yy Þ2þða xx Àa zz Þ2þða yy Àa zz Þ2þ6ða 2xy þa 2xz þa 2yz Þ g 1=2,are given in Tables S1–S3of the Supporting Material.The results show that PM6is noticeably superior to both the commonly em-ployed semiempirical AM1and PM3methods,reproducing the PBE0/aug-cc-pVDZ (and also MP2/aug-cc-pVDZ)h a i values of DF and 1,2,3,4,5,6,7,8-OCDF within 5a.u.(2–3%)and D a data within 8–11a.u.(3–8%),geometrical effects (PM6vs.B3LYP/6-31G ÃÃ)being almost negligible.Note that the corresponding deviations for h a i obtained using the AM1,PM3and B3LYP/6-31G ÃÃ[3]data are substantially larger,being 36–94a.u.(25–34%),41–76a.u.(27–28%),24–47a.u.(16–17%),respectively,while those for D a are 22–25a.u.(9–20%),16–43a.u.(12–18%)and 11–14a.u.(4–11%),respectively.However,least-mean squared fitting linear relationships between the semiempirical and B3LYP/6-31G ÃÃh a i and D a data (See Figs.S2and S3of the Supporting Material)aresatisfactory (r 2=0.97–1.00).As can be appreciated from Figs.S4and S5of the Supporting Material,on passing from PM6to AM1(PM3),h a i and D a values decrease and increase by 21–33%(26–28%)and 13–31%(19–23%),respectively.These discrepancies are principally originated from differences in the out of the plane polarizability component.Due to its relatively low computational cost and good accuracy,PM6is a promising method for the predic-tion of a of large p -conjugated systems and is particularly indi-cated for QSPR studies.AcknowledgementWork partially supported by MIUR,Rome.Appendix A.Supplementary dataSupplementary data associated with this article can be found,in the online version,at doi:10.1016/j.theochem.2008.09.023.References[1]S.Safe,Crit.Rev.Toxicol.21(1990)51.[2]S.Hirokawa,T.Imasaka,T.Imasaka,Chem.Res.Toxicol.18(2005)232.[3]C.Gu,X.Jiang,X.Ju,G.Yu,Y.Bian,Chemosphere 67(2007)1325.[4]G.Yang,X.Zhang,Z.Wang,H.Liu,X.Ju,J.Mol.Struct.(Theochem)766(2006)25.[5]J.J.P.Stewart,J.Mol.Model.13(2007)1173.[6]J.J.P.Stewart,MOPAC 2007,Stewart Computational Chemistry,Colorado Springs,CO,USA,[7]T.Puzyn,N.Suzuki,M.Haranczyk,J.Rak,J.Chem.Inf.Model.48(2008)1174.[8]A.Alparone,V.Librando,Z.Minniti,Chem.Phys.Lett.460(2008)151.[9]M.W.Schmidt,K.K.Baldridge,J.A.Boatz,S.T.Elbert,M.S.Gordon,J.H.Jensen,S.Koseki,N.Matsunaga,K.A.Nguyen,S.J.Su,T.L.Windus,M.Dupuis,J.A.Montgomery,put.Chem.14(1993)1347.[10]A.A.Granovsky,PC GAMESS version 7.0,Available from:<http://classic.chem.msu.su/gran/gamess/index.html/>.0166-1280/$-see front matter Ó2008Elsevier B.V.All rights reserved.doi:10.1016/j.theochem.2008.09.023*Corresponding author.Tel.:+39957385201;fax:+3995580138.E-mail address:vlibrando@unict.it (V.Librando).Journal of Molecular Structure:THEOCHEM 894(2009)128Contents lists available at ScienceDirectJournal of Molecular Structure:THEOCHEMj o ur na l h o me pa ge :w w w.e ls e v ie r.c o m/lo c a t e/t he o c hem。

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Copper(II)tetrafluoroborate as a novel and highly efficientcatalyst for acetal formationRaj Kumar and Asit K.Chakraborti *Department of Medicinal Chemistry,National Institute of Pharmaceutical Education and Research (NIPER),S ector 67,S .A.S .Nagar,Punjab 160062,IndiaReceived 24July 2005;revised 23September 2005;accepted 28September 2005Available online 11October 2005Dedicated to Professor Mark S.CushmanAbstract—Commercially available copper(II)tetrafluoroborate hydrate has been found to be a highly efficient catalyst for dimethyl/diethyl acetal formation in high yields from aldehydes and ketones by reaction with trimethyl/triethyl orthoformate at room tem-perature and in short period.Acetalisation was carried out under solvent-free conditions with electrophilic aldehydes/ketones.For weakly electrophilic aldehydes/ketones (e.g.,benzaldehyde,cinnamaldehyde and acetophenone)and for aldehydes having a substi-tuent that can coordinate with the catalyst,the corresponding alcohol was used as solvent.Ó2005Elsevier Ltd.All rights reserved.1.IntroductionProtection of aldehyde and ketone carbonyl groups is a frequently desired exercise in organic synthesis as it is often necessary to carry out a reaction on a multifunc-tional substrate without affecting an aldehyde/ketone group.One convenient method of protecting aldehydes and ketones is to convert them into the corresponding acetals.1Acetalisation can be achieved by treatment with alcohols in the presence of a protic 1,2or Lewis 1,3acid catalyst.A common regimen for acetal formation is protic 1,4or Lewis 1,5acid catalysed reaction of alde-hydes and ketones with trialkyl orthoformates.Other methods use MeOH–PhSO 2NHOH–MeONa,1b alkoxy-silanes in the presence of TMSOTf,1b (EtO)3CH–DDQ–EtOH 6and CAN–Na 2CO 3–ROH.7However,these methods have one or more drawbacks such as long reaction times,high temperatures,use of costly re-agents/catalysts,use of additional reagents,requirement of special efforts for catalyst preparation,requirement of stoichiometric amount of the catalysts,the need to use special apparatus and moderate yields and side reac-tions.Thus,the development of an improved method is still desirable.2.Results and discussionsWhen designing a new method,we realised that the use of trialkyl orthoformates as the acetalisation agent in the presence of a suitable transition metal catalyst should constitute a better procedure operable under mild conditions.The efficiency of the method would depend upon the coordination property of the metal catalyst to activate trialkyl orthoformate and/or the carbonyl substrate.Recently,we have reported that copper(II)tetrafluoroborate is an excellent catalyst for electrophilic activation during acylation,8diacetate for-mation 9and thia-Michael addition 10reactions.In this report,we disclose a highly efficient acetal formation reaction catalysed by copper(II)tetrafluoroborate (Scheme 1).Various aldehydes and ketones were treated with tri-methyl orthoformate in the presence of Cu(BF 4)2Æx H 2O0040-4039/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.tetlet.2005.09.168Keywords :Dimethyl acetals;Diethyl acetals;Aldehydes;Ketones;Copper(II)tetrafluoroborate hydrate;Catalyst;Trimethyl orthofor-mate;Triethyl orthoformate.*Corresponding author.Tel.:+9101722214682686;fax:+9101722214692;e-mail:akchakraborti@niper.ac.in(1mol %)at $25–30°C under neat conditions.The reactions were monitored by IR and GCMS and the optimum results are provided in Table 1.Substituted benzaldehydes with Me,Cl,Br,NO 2and OCOPh groups (entries 1–7),1-naphthaldehyde (entry 8),9-anthraldehyde (entry 9),aryl alkyl aldehydes (entries 10and 11)and saturated cyclic ketones (entries 12and 13)afforded excellent results after 2–15min.The reac-tions could also be monitored visually:immediately after the addition of the catalyst to the mixture of alde-hyde and trimethyl orthoformate an exothermic reaction takes place and the reaction mixture becomes homoge-neous (for solid aldehydes)indicating completion of ace-tal formation.In the case of 9-anthraldehyde,as the product was solid,a small excess (3equiv)of trimethyl orthoformate was required.In the cases of benzaldehyde,cinnamaldehyde,aceto-phenone and aldehydes bearing substituents that are capable of coordinating with the metal ion,the acetalformation was slow under neat conditions.However,in these cases,the reactions proceeded well using MeOH as solvent affording excellent yields (Table 2).The phenyl/styryl groups in benzaldehyde,cinnamalde-hyde and acetophenone made aldehyde/ketone carbonyl less electrophilic due to resonance and inhibited the effective formation of coordinate bonds with the cata-lyst.For aldehydes bearing substituents that can coordi-nate with the metal cation (e.g.,OR,F,CN,NMe 2,etc.)no effective activation of trimethyl orthoformate by the metal salt took place and acetal formation was retarded.The moderate yield obtained with 4-dimethylamino-benzaldehyde after 12h (Table 2,entry 6)supported the role of a coordinating effect of the substituent in influencing acetal parison of acetal for-mation from 4-methylbenzaldehyde,4-chlorobenzalde-hyde and 4-nitrobenzaldehyde (Table 1,entries 1–3)with those from 4-methoxybenzaldehyde,4-fluorobenz-aldehyde and 4-cyanobenzaldehyde (Table 2,entries 2–4),respectively,highlighted the coordinating effect of the substituents in the latter cases.The role of MeOH may be explained by the fact that initial reaction ofTable 2.Cu(BF 4)2Æx H 2O catalysed dimethyl acetal formation from aldehydes/ketones in dry MeOH aEntryAldehyde/ketone Time (min)Yield (%)b ,cCHO1R =H 593d 2R =F 10953R =CN 10924R =OMe 20915R =NMe 212h58CHOO R6R =Me 30887R =c -C 5H 910928CHOPh20919O308510S 2082O111.5h 96aThe aldehyde/ketone (2.5mmol)in dry methanol (1mL)was treated with CH(OMe)3(2.0equiv)in the presence of Cu(BF 4)2Æx H 2O (1mol %)at room temperature ($25–30°C).bIsolated yield of the corresponding acetal.cThe products were characterised by IR and NMR.dA 36%yield was obtained on carrying out the reaction under neat conditions.Table 1.Cu(BF 4)2Æx H 2O catalysed dimethyl acetal formation from aldehydes/ketones under solvent-free conditions aEntryAldehyde/ketone Time (min)Yield (%)b ,cCHO3R 1R 21R 1=R 2=H;R 3=Me 5922R 1=R 2=H;R 3=Cl 5903R 1=R 2=H;R 3=NO 23924R 1=R 2=H;R 3=OCOPh 5915R 1=Br;R 2=R 3=H 5886R 1=Cl;R 2=R 3=H 5907R 1=R 3=H;R 2=NO 28928CHO15859CHO1582d10Ph CHO 28511CHOPh38612O57813O295aThe aldehyde/ketone (2.5mmol)was treated with CH(OMe)3(2.0equiv)in the presence of Cu(BF 4)2Æx H 2O (1mol %)at room temperature ($25–30°C)under neat conditions.bIsolated yield of the corresponding acetal.cThe products were characterised by IR,NMR.dThe reaction was carried out using 3equiv of CH (OMe)3.8320R.Kumar,A.K.Chakraborti /Tetrahedron Letters 46(2005)8319–8323aldehyde with MeOH leads to the formation of a hemi-acetal,which undergoes nucleophilic attack on trimethyl orthoformate complexed with Cu(BF 4)2Æx H 2O and results in acetal formation.4Since there are limited reports for diethyl acetal forma-tion,3e,f,4,5c–e,gwe planned to evaluate the catalytic effi-ciency of Cu(BF 4)2Æx H 2O during the reaction of a few representative aldehydes and ketones with triethyl orthoformate (Table 3).Excellent results were obtained in each case.As observed in the case of dimethyl acetal formation,the reactions of benzaldehyde,cinnamaldehyde and aceto-phenone required dry EtOH as solvent for diethyl acetal formation.A comparison of the results of entries 1and 6(Table 2)prompted us to study selective acetal formation during intermolecular competition between benzaldehyde 1and 4-dimethylaminobenzaldehyde 2.Thus,a mixture of 1(2.5mmol)and 2(2.5mmol)in dry MeOH (1mL)was treated with trimethyl orthoformate (5mmol)in the presence of Cu(BF 4)2Æx H 2O (1mol %)for 5min at room temperature (Scheme 2).Excellent selectivity was observed,(dimethoxymethyl)benzene 3and 4-(dimethoxymethyl)-N ,N -dimethylaniline 4were formed in a ratio of 88:12(NMR).Similarly,the differ-ence in the rate of reaction of 1and acetophenone 5(Table 2,compare the results of entries 1and 11)encouraged us to study the selectivity of acetal forma-tion during inter-and intramolecular competition stud-ies involving aldehyde and ketone carbonyl groups.Thereaction of 1(2.5mmol)and 5(2.5mmol)with trimethyl orthoformate (5mmol)in dry MeOH (1mL)in the pres-ence of Cu(BF 4)2Æx H 2O (1mol %)at room temperature for 5min (Scheme 2)resulted in the formation of 3and 2,2-dimethoxy-1-phenylethane 6in a ratio of 86:14(NMR).The reaction of 4-acetylbenzaldehyde 7(2.5mmol)with trimethyl orthoformate (5mmol)in MeOH (1mL)in the presence of Cu(BF 4)2Æx H 2O (1mol %)for 5min at room temperature resulted in the formation of 4-(dimethoxymethyl)acetophenone 8and 2,2-dimethoxy-(40-dimethoxymethyl)-1-phenyl-ethane 9in a ratio of 77:23(GCMS).3.ConclusionsWe have described herein the use of Cu(BF 4)2Æx H 2O as ahighly efficient and reusable catalyst for dimethyl and diethyl acetal formation at room temperature.The advantages include,(i)the use of a cheap,easy to handle and commercially available catalyst,(ii)room tempera-ture reaction conditions,(iii)short reaction times,(iv)high yields and (v)excellent chemoselectivity.4.Experimental4.1.Typical procedure for acetal formation under neat conditionsTo a magnetically stirred mixture of 4-methylbenzalde-hyde (0.3g, 2.5mmol)and trimethyl orthoformate (0.53g,5mmol),Cu(BF 4)2Æx H 2O (6.0mg,0.025mmol,1mol %)was added and the mixture was stirred at 25–30°C until completion of the reaction (5min,TLC,IR).The mixture was diluted with saturated aq NaHCO 3(10mL)and extracted with EtOAc (3·10mL).TheTable 3.Cu(BF 4)2Æx H 2O catalysed diethyl acetal formation from aldehydes and ketones aEntryAldehyde/ketone Time (min)Yield (%)b ,cCHO1R =H 1093d 2R =Me 3953R =NO 25954CHO Ph 10925CHOPh 380d6O375The aldehyde/ketone (1equiv)was treated with CH(OEt)3(2.0equiv)in the presence of Cu(BF 4)2Æx H 2O (1mol %)at rt ($25–30°C)in the absence of solvent (except for entries 1,5and 7).bIsolated yield of the corresponding acetal.cThe products were characterised by IR,NMR.dThe reaction was carried out in dry ethanol (1mL).R.Kumar,A.K.Chakraborti /Tetrahedron Letters 46(2005)8319–83238321combined EtOAc extracts were washed with water(2·10mL),dried(Na2SO4)and concentrated under reduced pressure to afford4-(dimethoxy)methylbenzene(colour-less oil,0.415g,92%,entry1,Table1),IR(neat):2936, 2828,1618,1447,1353,1201,1105,1054,912, 807cmÀ1;1H NMR(300MHz,CDCl3):d=2.33(s, 3H),3.30(s,6H),5.35(s,1H),7.15(d,2H,J=7.6Hz), 7.32(d,2H,J=7.6Hz);13C NMR(75MHz,CDCl3): d=21.2,52.53,103.16,126.56,128.81,135.13,138.06, identical with an authentic sample.5e5.Representative experimental procedure for acetalformation in the presence of solventTo a magnetically stirred mixture of4-cyanobenzalde-hyde(0.327g, 2.5mmol)and trimethyl orthoformate (0.53g,5mmol)in dry MeOH(1mL),Cu(BF4)2Æx H2O (6.0mg,0.025mmol,1mol%)was added and the mix-ture was stirred at25–30°C until completion of the reac-tion(10min,TLC,IR).The reaction mixture was diluted with saturated aq NaHCO3(10mL)and extracted with EtOAc(3·10mL).The combined EtOAc extracts were washed with water(2·10mL), dried(Na2SO4)and concentrated under reduced pres-sure to afford pure4-(cyano)dimethoxymethylbenzene (colourless oil,0.407g,92%,entry3,Table2),IR(neat): 2938,2832,2229,1353,1209,1101,1057,988,822, 556cmÀ1;1H NMR(300MHz,CDCl3):d=3.32(s, 6H),5.43(s,1H),7.50(d,2H,J=8.3H z),7.68(d, 2H,J=8.3H z);13C NMR(75MHz,CDCl3): d=52.56,101.62,112.14,118.52,127.45,131.91, 143.10,identical with an authentic sample.2cThe remaining reactions were carried out following these general procedures.On each occasion,the spectral data(IR,1H NMR and13C NMR)of the prepared known compounds were found to be identical with those reported in the literature.The following compounds had not been reported.2-(Bromo)dimethoxymethylbenzene(Table1,entry5): IR(neat):2933,2829,1468,1364,1204,1103,1057, 980,755cmÀ1.1H NMR(300MHz,CDCl3):d=3.35 (s,6H),5.55(s,1H),7.14(t,1H,J=7.5Hz),7.28(t, 1H,J=7.5Hz),7.52(d,1H,J=7.6Hz),7.59(d,1H, J=7.6Hz).13C NMR(75MHz,CDCl3):d=53.57, 102.71,122.75,126.92,128.18,129.84,132.66,136.68. Anal.Calcd for C9H11BrO2:C,46.78;H,4.80.Found. C,46.80;H, 4.82.2-(Chloro)dimethoxymethylbenzene (Table1,entry6):IR(neat):2934,2830,1366,1201, 1107,1058,981,756cmÀ1.1H NMR(300MHz, CDCl3):d=3.37(s,6H),5.62(s,1H),7.22–7.29(m, 2H),7.33–7.36(m,1H),7.60–7.63(m,1H).13C NMR (75MHz,CDCl3):d=53.68,100.86,126.45,128.02, 129.50,129.65,133.11,135.28.Anal.Calcd for C9H11ClO2:C,57.92;H, 5.94.Found.C,57.91;H, 5.97.9-Dimethoxymethylanthracene(Table1,entry9): Mp:107–108°C IR(KBr):2932,1448,1186,1105, 1066,891,740cmÀ1.1H NMR(300MHz,CDCl3): d=3.50(s,6H),6.53(s,1H),7.38–7.61(m,4H),7.93 (d,2H,J=8.4Hz),8.39(s,1H),8.68(d,2H, J=8.4Hz).13C NMR(75MHz,CDCl3):d=53.68,100.86,126.45,128.02,129.50,129.65,133.11,135.28. Anal.Calcd for C17H16O2:C,80.93;H,6.39.Found. C,80.96;H,6.41.3,4-(Dimethoxy)dimethoxymethylbenz-ene(Table2,entry6):IR(neat):2937,2832,1607, 1594,1414,1259,1194,1136,1102,990,863,863,795, 762cmÀ1.1H NMR(300MHz,CDCl3):d=3.32(s, 6H),3.88(s,3H),3.90(s,3H),5.33(s,1H),6.84–6.97 (m,1H), 6.98–6.99(m,2H).13C NMR(75MHz, CDCl3):d=52.34,55.53,102.86,109.33,110.40, 119.00,126.48,130.61,148.64.Anal.Calcd for C11H16O4C,62.25;H,7.60.Found.C,62.23;H,7.63. 4-Cyclopentyloxy-3-methoxy dimethoxymethylbenzene (Table2,entry7):IR(neat):2954,2829,1607,1510, 1351,1264,1160,1102,1053,988,862,804cmÀ1.1H NMR(300MHz,CDCl3):d=1.57–1.61(m,2H), 1.79–1.97(m,6H),3.32(s,6H),3.85(s,3H),4.73–4.79 (m,1H),5.31(s,1H),6.84(d,1H,J=8.1Hz),6.93–6.97(m,2H).13C NMR(75MHz,CDCl3):d=24.03, 32.77,52.75,55.95,80.32,103.29,110.10,114.16, 119.07,130.54,147.73,149.81.Anal.Calcd for C15H22O4:C,67.64;H,8.33.Found.C,67.63;H,8.35.Supplementary dataSupplementary data associated with this article can be found,in the online version,at doi:10.1016/j.tetlet. 2005.09.168.References and notes1.(a)Meskens,F.A.J.Synthesis1981,501–521;(b)Greene,T.W.;Wuts,P.G.M.In Protecting Groups in Organic Synthesis,3rd ed.;John Wiley and Sons:New York,1999.2.p TsOH-MgSO4:(a)Lu,T.-J.;Yang,J.-F.;Sheu,L.-J.J.Org.Chem.1995,60,2931–2934;p TsOH under microwave heating:(b)Pe´rio, B.;Dozias,M.-J.;Jacquault,P.;Hamelin,J.Tetrahedron Lett.1997,38,7867–7870;Polymer-supported acid catalysts in an electroosmotic flow reactor:(c)Wiles, C.;Watts,P.;Haswell,S.J.Tetrahedron2005,61,5209–5217.3.Montmorillonite K-10:(a)Li,T.-S.;Li,S.-H.;Li,J.-T.;Li,H.-Z.J.Chem.Res.(S)1997,26–27;I2under microwaveheating:(b)Kalita, D.J.;Borah,R.;Sarma,J. C.Tetrahedron Lett.1998,39,4573–4574;MCM-41:(c) Tanaka,Y.;Sawamura,N.;Iwamoto,M.Tetrahedron Lett.1998,39,9457–9460;I2:(d)Basu,M.K.;Samajdar, S.;Becker,F.F.;Banik,B.K.Synlett2002,319–321;CoCl2:(e)Velusamy,S.;Punniyamurthy,T.Tetrahedron Lett.2004,45,4917–4920;RuCl3:(f)De,S.K.;Gibbs, R.A.Tetrahedron Lett.2004,45,8141–8144.4.TBATB:Gopinath,R.;Haque,S.J.;Patel,.Chem.2002,67,5842–5845.5.Rh(II)triphos:(a)Ott,J.;Tombo,G.M.R.;Schmid,B.;Venanzi,L.M.;Wang,G.;Ward,T.R.Tetrahedron Lett.1989,30,6151–6154;TiCl4:(b)Clerici,A.;Pastori,N.;Porta,O.Tetrahedron1998,54,15679–15690;ZrCl4:(c) Firouzabadi,H.;Iranpoor,N.;Karimi,B.Synlett1999, 321–323;NBS:(d)Karimi,B.;Seradj,H.;Ebrahimian,G.-R.Synlett1999,1456–1458;Bi(OTf)3:(e)Leonard,N.M.;Oswald,M.C.;Freiberg,D.A.;Nattier,B.A.;Smith,R.C.;Mohan,.Chem.2002,67,5202–5207;B10H14:(f)Lee,S.H.;Lee,J.H.;Yoon,C.M.Tetrahedron Lett.2002,43,2699–2703;LiBF4:(g)Hamada,N.;Kazahaya,K.;Shimizu,H.;Sato,T.Synlett2004,1074–8322R.Kumar,A.K.Chakraborti/Tetrahedron Letters46(2005)8319–83231076;InCl3:(h)Ranu,B.C.;Jana,R.;Samanta,S.Adv.S ynth.Catal.2004,346,446–450.6.Karimi, B.;Ashtiani, A.M.Chem.Lett.1999,1199–1200.7.Nair,V.;Rajan,R.;Balagopal,L.;Nair,L.G.;Ros,S.;Mohanan,K.Indian J.Chem.2005,44B,141–143.8.Chakraborti,A.K.;Gulhane,R.;Shivani Synthesis2004,111–115.9.Chakraborti,A.K.;Thilagavathi,R.;Kumar,R.Synthe-sis2004,831–833.10.Garg,S.K.;Kumar,R.;Chakraborti,A.K.TetrahedronLett.2005,46,1721–1724.R.Kumar,A.K.Chakraborti/Tetrahedron Letters46(2005)8319–83238323。

如何收集媒体资料英语作文Title: Effective Strategies for Collecting Media Materials。

In today's digital age, gathering media materials has become an essential skill for many individuals, whether they are students conducting research, journalists seeking information, or professionals compiling data for presentations. This essay explores various effective strategies for collecting media materials, encompassing both traditional and digital methods.1. Utilizing Online Databases and Archives:Online databases and archives provide a vast repository of media materials accessible with just a few clicks. Platforms like Google Scholar, JSTOR, and ProQuest offer a wide range of academic journals, articles, and research papers. Additionally, specialized archives such as the Library of Congress Digital Collections or the BritishLibrary's Online Catalog can be invaluable resources for historical media materials.2. Social Media Monitoring:Social media platforms have emerged as powerful sources of real-time information and media content. Monitoring hashtags, trends, and relevant accounts on platforms like Twitter, Instagram, and Facebook can yield valuable insights and media materials related to specific topics or events. Tools like Hootsuite or TweetDeck facilitate efficient social media monitoring by organizing feeds and notifications.3. RSS Feeds and Aggregators:RSS (Really Simple Syndication) feeds allow users to subscribe to content from their favorite websites, blogs, or news outlets. By aggregating multiple RSS feeds using platforms like Feedly or Flipboard, individuals can streamline the process of collecting media materials tailored to their interests. This method ensures a constantinflux of relevant content without the need for manual searching.4. Engaging with Online Communities and Forums:Online communities and forums centered around specific interests or industries often serve as hubs for sharing media materials and information. Participating in discussions, asking questions, and networking within these communities can lead to valuable media resources and insights shared by fellow members. Platforms like Reddit, Quora, and specialized forums cater to a wide range of topics and fields.5. Content Curation Tools:Content curation tools such as Pocket, Instapaper, or Evernote enable users to save, organize, and annotate media materials for future reference. These tools often include features like tagging, categorization, and offline access, allowing for efficient management of a diverse range of media content across devices.6. Traditional Media Sources:Despite the digital revolution, traditional media sources such as newspapers, magazines, and television continue to provide valuable media materials. Subscribing to print or digital editions of reputable publications, accessing online archives of newspapers, or watching relevant television programs can offer unique perspectives and insights not found elsewhere.7. Interviews and Surveys:Conducting interviews or surveys with experts, professionals, or individuals with firsthand experience can yield valuable media materials, including quotes, testimonials, and personal accounts. These primary sources add depth and authenticity to research or journalistic endeavors, providing unique perspectives and insights that complement secondary sources.8. Open Access Repositories and Creative CommonsResources:Open access repositories and platforms like Wikimedia Commons, Creative Commons, and Open Culture offer a wealth of media materials, including images, videos, audio recordings, and educational resources. These resources are often available for reuse, remixing, and redistribution under open licenses, making them valuable assets for various projects and presentations.In conclusion, the effective collection of media materials encompasses a diverse array of strategies, ranging from digital tools and online platforms to traditional sources and interpersonal interactions. By leveraging these strategies intelligently and ethically, individuals can access a wealth of media content to enhance their research, reporting, and creative endeavors.。

igcse英语article范文The IGCSE English examination is a challenging yet rewarding experience for students seeking to demonstrate their proficiency in the English language. As an international qualification recognized globally, the IGCSE English exam assesses a range of essential skills, including reading comprehension, writing, and language use. Preparing for this examination requires a comprehensive understanding of the assessment criteria and a dedication to honing one's abilities in various aspects of the English language.One of the key components of the IGCSE English exam is the article writing task. This genre of writing is designed to test a student's ability to effectively communicate ideas, express opinions, and engage the reader. The article format allows students to showcase their creativity, organizational skills, and command of the English language.When approaching the article writing task, it is essential to understand the specific requirements and expectations outlined by the exam board. The IGCSE English syllabus typically specifies thelength, format, and content guidelines for the article. Students must be mindful of these parameters and ensure that their writing adheres to the prescribed structure.The opening paragraph of the article is crucial in capturing the reader's attention and setting the tone for the entire piece. It should introduce the central theme or focus of the article, providing a clear and concise overview of the main ideas to be explored. Effective use of hooks, such as thought-provoking questions or intriguing statements, can help draw the reader in and encourage them to continue reading.Following the introduction, the body paragraphs of the article should delve deeper into the chosen topic, presenting a logical and well-structured argument or discussion. Each paragraph should have a clear topic sentence that guides the reader through the progression of ideas. The use of supporting evidence, examples, and relevant facts can strengthen the overall persuasiveness and credibility of the article.Effective article writing also requires a strong command of language and a keen eye for detail. Students should strive to use a diverse vocabulary, employ various sentence structures, and maintain a cohesive and coherent flow throughout the piece. Attention to grammar, spelling, and punctuation is essential to ensure the articleis polished and professional in its presentation.One of the hallmarks of a well-written IGCSE English article is the ability to present a balanced and objective perspective on the chosen topic. While students are encouraged to express their own opinions and viewpoints, they should also acknowledge and address alternative perspectives or counterarguments. This demonstrates a nuanced understanding of the subject matter and a willingness to engage in critical thinking.In addition to the content and language proficiency, the IGCSE English article writing task also requires students to consider the intended audience and the appropriate tone and style for the piece. The article should be tailored to the specific needs and expectations of the reader, whether it be a general public audience or a more specialized readership.Effective article writing also involves the skillful use of organizational techniques, such as the incorporation of headings, subheadings, and transitional phrases. These elements help to guide the reader through the article, ensuring a clear and logical flow of ideas. Additionally, the use of relevant and engaging visuals, such as images or infographics, can enhance the overall presentation and appeal of the article.Throughout the writing process, students should engage in a cycle of drafting, revising, and editing to refine their work. This iterative approach allows for the identification and correction of any errors or weaknesses, as well as the opportunity to enhance the overall quality and coherence of the article.Ultimately, the IGCSE English article writing task is a valuable opportunity for students to showcase their language proficiency, critical thinking skills, and ability to communicate effectively in written form. By understanding the expectations of the exam and dedicating time to honing their writing abilities, students can approach this component of the IGCSE English examination with confidence and a strong foundation for success.。

常见SD大鼠神经病理性疼痛模型研究本文旨在总结常见SD大鼠神经病理性疼痛模型优缺点，为NP研究者提供模型选择参考。

目前主流NP模型主要可分CCI、SNI、SNL、CCD模型四大类。

四大类根据不同疾病的研究需要分不同小类，具体文中细述。

Abstract：This article aims to summarize the advantages and disadvantages of the common neuropathic pain model of SD rats and to provide a reference for NP researchers to choose the model.The current mainstream NP model can be divided into CCI，SNI，SNL，CCD model four categories.Four major categories according to different diseases need to be divided into different sub-categories，specific details of the article.Key words：NP；CCI；SNI；SNL；CCD2011年国际疼痛研究学会对神经病理性疼痛定义：神经病理性疼痛是由于躯体感觉系统的损伤或疾病所引起的疼痛[1]。

这病变原因可是创伤、压迫、感染、肿瘤、药物毒性或自身免疫性疾病等。

SD大鼠坐骨神经病理性疼痛模型主要有CCI、SNI、SNL、CCD四大类，CCI衍生出bCCI、iCCI、分级坐骨神经缩窄模型，SNI衍生出mSNI，与SNL类似有pSNL和L5 VRT，CCD模型暂只有一种。

1 NP模型分类1.1 CCI 慢性坐骨神经缩窄性损伤CCI模型[2]：备皮暴露神经，松扎坐骨神经主干4处，逐层缝合。

成功标志：术后大鼠跛行，足呈轻度外翻状，出现舔舐、悬空等痛行为学表现，并呈现持续的疼痛状态。

生物多样性数据论文发表趋势分析和被引用次数等指标，以期基于实证数据揭示数据论文的发表趋势。

1 资料来源与研究方法。

1.1 研究对象。

本研究主要关注发表生物多样性相关数据论文的两本代表性数据期刊Biodiversity Data Journal（BDJ）和Scientific Data （SD）。

BDJ自2021年9月16日开始出版，旨在基于同行评审的学术出版模式，快速发表生物多样性数据。

BDJ发表的文章类型主要包括Data Paper （数据论文）、Taxonomic Paper （分类论文）、General Article （综合论文）、Software De-scription （软件描述）、Species Inventory （物种目录）、Interactive Key （交互式检索表）等。

BDJ要求所有基于原始数据的论文以符合规范的形式共享数据，因此虽然有文章类型的人为划分，它们（除SoftwareDescription外）的区别更多的只是所共享数据的类型和多少，实际上都属于数据论文的范畴。

BDJ发表的文章涉及物种分类和标本信息、生物区系数据库、植被组成、形态特征、鸣声记录、DNA条形码等多种生物多样性数据类型。

SD自2021年3月11日开始出版，作为自然出版集团力推的综合性数据期刊，主要发表具有重要科学价值、数据量大的原始数据集及其分析（Data Descriptor），面向众多科学领域。

本研究期望基于对BDJ的分析揭示生物多样性数据论文的发表和使用趋势，对SD的分析则可以从更广泛的角度揭示数据论文的发表情况，因此未单独提取生物多样性相关领域文章。

1.2 数据收集。

BDJ和SD均为在线出版期刊，本研究的数据主要基于两本期刊网站提供的文献计量指标，收集了两本期刊自创刊截止到2021年6月17日的文献信息。

BDJ 文章信息包括每篇文章的出版时间、文章类型、涉及生物类群、作者国别、文章内容、浏览量等6个方面； SD文章信息包括每篇文章的出版时间、文章类型、浏览量、引用量等4个指标。