New York 1939-1940 - Trylon and Perisphere :: Architecture History

New York 1939-1940 - Trylon and Perisphere As the 1939 New York World's Fair was divided into many different thematic zones, its planners wanted a central symbol for this event. The original idea was to have a theme center, with twin 250 feet towers and a semicircular hall to display dioramas. Wallace K. Harrison, a prominent New York architect of the Harrison Fouilhoux firm, was selected to design the theme center in November 1936. Harrison wanted a design that would represent a new architecture concept. In his own words, "we found ourselves constantly referring to the domes and campaniles of Venice, perhaps because the flat country and water of the Fair grounds are very like that of the site of Venice and in addition the sky color of New York is practically the same." (Newhouse,82) The idea of a large dome was a starting point for all further designs, and many different ideas were initially developed. There were plans to use a sphere that was suspended by steel cables, giving it a light, airy feel as well as a large balloon , anchored by steel cables and accessible by elevator. A spherical design was not a new idea, however. An earlier example of such a design was proposed by Etienne-Louis Boullà ©e in his project for Newton's Cenotaph in 1783, featuring a huge sphere at the center. In the end a design that featured a sphere 200 feet in diameter raised on pillars was selected. Despite its huge dimensions, with a 200-foot diameter, it was hard to grasp the exact scale of the sphere. Harrison and his design team finally came up with the idea of using a tall spike to frame the sphere, but there was still the problem of placing the two in relation with each other. They found inspiration from drawings by a Soviet constructivist architect named Jacob Tchernikhov, which represented two large spheres connected to a tall spike by way of a ramp. The final design had emerged. It included the Perisphere, a 200 foot spherical exhibit building, the Trylon, a 700 foot tall three sided obelisk, and the Helicline , a 950 foot circular ramp which connected the two and allowed visitors to exit. However the final dimensions of the building was reduced from the original values to a 180 foot sphere and a 610 foot spike due to budget limitations, which threw off the carefully calculated proportions. The Perisphere was elevated from the ground by five steel pillars, and rested over a large reflecting pool.

Language as a badge of identity Essay

Language is used every day to communicate with one another but beneath that conversation lies another message. The speaker’s use of language gives listeners insight as to who they are, like a badge of identity on their chest. Australian English’s unique phonology and lexicon is recognised globally and distinguishes it from other accents, giving the speaker a clear national identity. Ethno-lects are spoken by a specific group of people who have the same cultural background. These â€Å"ethno-lects† not only help express an individual’s identity and separate themselves from the rest, but also assist in bringing together speakers from similar backgrounds; much like a football jersey. Text speak is constantly evolving as lexemes are taking on new changes. Many teenagers and younger children have begun to adopt this in an attempt to identify with others and fit in. Through language, we can get a glimpse of a person’s identity but they can use the same me dium to change that identity as well. Australian English is unlike other Englishes in many different aspects, especially phonetically morphologically and semantically. Phonology plays a great role in national identity as it is what creates different accents. The broad, ocker Australian accent with its trademark nasal, flattened vowels is one of the key elements of Australian linguistics that sets it apart from the rest of the world. Diphthongs in lexemes like â€Å"high† are more rounded, resulting in /hoÉ ª/. Phonetic features such as these are easily identified as Australian. Slang is another feature of Australian English that sets it apart from others. Replacing suffixes with vowels is a good example of this. â€Å"Afternoon† becomes â€Å"arvo†, names like â€Å"Barry† becomes â€Å"Bazza† and by replacing the last element with an ‘-o’, the adjective â€Å"povo† has undergone a word class shift from the noun â€Å"poverty†. Popular culture has also influe nced Australian English, with ABC television series J’amie, Private School girl introducing a semantic and word class shift of ‘quiche’ (a noun meaning a savoury open-faced pastry) to an adjective to describe an attractive individual. Australia’s linguistic innovation displays individuality and opposes claims that slang is borrowed from America.  Australian English shows both national pride and identity. Teenagers are at the age when they are starting to establish their identity. Neologisms are created by teenagers to claim a different identity from that of children or adults. As adults become more familiar with these lexemes and their use, teenagers abandon them or alter the semantics and use to maintain a linguistic barrier. A good example of this is the well-known acronym â€Å"lol† which stands for Laugh Out Loud. As more adults become aware of this lexical item and start to include it in their daily texts, teenagers have brought it into speech as an exclamatory and discourse particle. The case of the letters now also alters the semantics; when typed in lower-case, â€Å"lol† is sarcastic whilst â€Å"LOL† in capital letters shows true amusement. It is evident that this constant changing of terms by teenagers is a sign of rebellion and an effort to keep a linguistic barrier between themselves and adults, thus maintaining a separate identity. The malleability of the lexicon is taken advantage of by teenagers to form a linguistic barrier between themselves and unwanted people such as adults and other teenagers who don’t belong in their group. Thus, a unique identity is maintained. While teenagers are constantly seeking to separate themselves from children and adults, they are also pressured to conform to the teenage group. Acronyms such as â€Å"idek† (I don’t even know) and â€Å"tbh† (to be honest) are now frequently used lexicon in a teenager’s text vocabulary due to connotations of â€Å"cool† and â€Å"modern† being associated with them. Similarly, whatever was once popular amongst a teenager’s discourse. In time, it was shortened to â€Å"whatevs† and this trend spread quickly amongst them as a result of peer pressure and the need to be fashionable. Professor Steven Pinker suggests the reason for this is because â€Å"the coolest kids decide to talk that way and it spreads like wildfire†. Individuals who wish to associate with others who sit higher on the â€Å"social pyramid† will pick up their speech habits and wear it as a new badge of identity. Having their own exclusive vocabulary allows teenagers to relate to each other and share the same identity, giving them a sense of belonging to a group. Language can be worn as a badge of identity, giving speakers national,  interpersonal and intrapersonal identity. The phonology of Australian English gives the speaker a distinct accent and, paired along with its unique slang, makes it identifiable across the globe. In order to separate themselves from adults and children, teenagers build a linguistic barrier by creating neologisms and maintaining that barrier by constantly altering lexicon to avoid adults becoming too familiar with them. On the other hand, inside the teenage group is a drive to conform and use similar language in an attempt to fit in with peers and to have a sense of belonging. Language is used as a badge of identity regardless of what that identity is. Bibliography Das, S, 2005. Struth! Someone’s nicked me Strine. The Age, 29 January. 34. Seaton, M, 2001. Word Up. Guardian, 21 September. 46.

Indian Removal Act Essay

Known as having adopted an Indian child as his son, Andrew Jackson was quite fond of the Indian race; however, with pressure to expand westward, he needed to transfer the Indians farther west and soon became their worst enemy. Andrew Jackson’s Indian Policy was to move the Indians westward as peacefully as possible, for the tribes that stayed in the East Coast were annihilated. Also, moving them West will help them live longer, and there is a fair exchange for the tribes moving. Another important component is the gain of Western lands and the addition of American power; this will add on to America’s size and increase America’s authority. Jackson validates his actions by saying he will pay for the land the Indians inhabit, pay for their long journey West, also known as the Trail of Tears, and support them a little while their settling in. President Jackson also said if they move west, they will enjoy sovereignty forever. Jackson made the point that with the Indians gone there will be less conflict between them and state governments, it will allow for prosperous populations and cities to flourish, and the free land will add another line of defense for America. President Jackson’s attitude toward the Indians in his speech reveals that he wants the Indians gone so America can gain land and grow stronger. He uses words like â€Å"Red Men† and â€Å"Savages† to describe them, so they seem like outcasts. He makes it sounds like the Indians are a nuisance and if they move, they will prosper as a people. Jackson says, â€Å"†¦perhaps cause them gradually†¦to cast off their savage habits and become an interesting, civilized, and Christian community.† Overall, Jackson wants the Indians gone for his own benefit. He refers to them as uncivilized, uninteresting, and having savage habits, and was proving that he is just looking for a gain for his country, not the native people who have lived there forever.

Academy of Classical Homeopathy Essays

Academy of Classical Homeopathy Essays Academy of Classical Homeopathy Paper Academy of Classical Homeopathy Paper Essay Topic: Classical The whole definition of health, as summarized by the International Academy of Classical Homeopathy based on the book entitled, â€Å"A New Model for Health and Disease† states. â€Å"Health is freedom from pain in the physical body, a state of well being; freedom from passion on the emotional plane, resulting in a dynamic state of serenity and calm; and freedom from selfishness in the mental sphere, having as a result total unification with Truth† (International Academy of Classical Homeopathy, 2007). I truly believe that the above definition summarizes the complete definition of health and I agree with what is stated above. Good health cannot be characterized by a single component as our health is constituted by the physical, spiritual and mental components and an imbalance in either of these would disturb the rest thereby making the definition of health incomplete. An inner peace through love and wisdom that is attained only in the absence of selfishness and acknowledging the truth can lead to a true health as selfishness is an impurity that should be cleansed from hearts. This is similar to the cause-and-effect relationship. If you think well, you will be good and if you are ill-thinking, you will be bad. Emotional stance of health should be taken into account as our health depends on it. Spiritually, we acknowledge the truth if the emotion of selfishness or greediness is cleansed from the heart†¦ RESPONSE: The views of WHO are similar to what I have stated above. A healthy lifestyle is truly the need for good health but today, spiritual accounts on the maintenance of good health is also growing popular due to its known effect on the confidence level of a person. It is possible for the person to be mentally, physically and socially well but on a spiritual level, it is like liberating yourself from all kinds of unethical worldly acts and feelings and stepping into a new dimension of love. Health is never a compromised issue so I believe the spiritual stance in the definition of health makes a big difference†¦

26 Great Alternatives to ACT Practice Tests

26 Great Alternatives to ACT Practice Tests SAT / ACT Prep Online Guides and Tips To completely prepare for the ACT, you must spend time taking official ACT testsin the same conditions that you’ll face on the day of the real thing. But what if you’re stuck on a concept that you just can’t seem to quite wrap your head around? Or what if you gone through many of the available practice tests already, but still would like to keep working on your skills? The great news is that there are many otherways to effectively study the concepts being tested on the ACT! In this article, I’ll talk about what alternative practice ACT resources are good for, and how to use them bestwhen preparing for the test. Then, I’ll also go through the ACT section by section and lay out all the availablealternative resources. By the end of this post, you'll have a huge stock of extra practice material to help you prep for the ACT. How Do You Use Alternative Practice Resources? What do I mean by "alternative" resources? Basically, any test preparation material that isn't the official ACT practice tests that are released by ACT. Getting good at taking the ACT is a combination of three things. First, you have tounderstand the basic content being tested. For instance, you have to have mastered algebra concepts forthe math section and grammar nuances forthe English section. Second, you have to know how to apply this content to solving problems and answering questions. For example, you must know which punctuation rule applies when, and which math formula goes with which calculation. Third, you have to be very comfortable with the test itself. In other words, the format, pacing, time pressure, and having built up enough stamina for this very long test should be second nature from repeated practice. Now, it's 100% true that the only way to master the last of these three things is through taking official ACT practice tests in test day conditions. Nothing can give you that day-of-test confidence like having gone through it a bunch of times already. However,learning content does not necessarily have to come from ACT materials! In fact, it’s good to be exposed to the same concepts presented in many different ways to really cement your understanding of how they work. This means that alternative resources that aren't necessarily specifically designed for ACT practice are actually a great way to boostconceptmastery. Alternative Study Resources for Each ACT Section Now letsgo through each of the ACT test sections one by one, and discuss ways to study for them other than usingtheoffical ACT practice question sets and tests released by ACT. Math Before diving into study alternatives, let's first go over what concepts are tested on the ACT Math section. Not surprisingly, it's the math you've been learning in school: Pre-algebra Algebra Geometry Trigonometry Alternative Study Resources for ACT Math Your school math textbooks or an online math textbook like theKhan Academy. These resources are great forexplaining difficult concepts, formulas, and theorems, and potentially for doing some of the non-multiple choice problems. Online ACT-style math questions. It's true that other companies generallyaren't that good at reproducing actual ACT questions. Still, third-party question banks can be helpful for some extra work attacking your math weaknesses. We've combed through them all to bring you anoverview of the best question bank websites. Math sections from the new post-2016 SAT. The new SAT math section is much more like the ACT, since itnow includes trigonometry questions and gives only 4 answer choices per question. This means that practice SAT questionsa great way to get in some more multiple choice practice. But, you're best off treating SAT math sections the same way you would treat question banks from other companies: their wording and format also don't reproduce those on the ACT. ACT Math review books.These will go over the key concepts you have to know to do well on ACT Math, and explain how the ACT will test them. To make your life easier, we’ve put togethera guide to the best ACT study booksout there. PrepScholar’s ACT Math guides.Our section on everything to do with ACT Math has some of the best researched and most detailed information you'll find anywhere. Some especially helpful guides include: All about math formulas.ACT won’t provide you with formulas, so you have to have the most commonly used ones down cold. Sounds stressful, but we can help! Readthrough our guide to the 31 math formulas you must knowcoupled with ourexplanation for how to actually use those formulasto get the full scoop on what you have to know. It's nice how1+2*3 is mixed into the infinity/pi/square root of 2 morass there. Looks like kindergarten and 10th grade are sharing the math room again. English This section will test your knowledge of how the English language works by asking you passage-based questions on the rules that apply to formal writing. There are two main types of questions: usage and mechanics (punctuation, grammar, and sentence structure) rhetorical skills (writing strategies, logic, paragraph and passage structure, and style) Alternative Study Resources for ACT English Grammar guides. There's just no way around it: knowing grammar and punctuation rules is critical for this section of the test. In order to learn the best grammar practices, go back toany textbooks you may have used inEnglish class. I also recommendthat youscroll through Erica Meltzer's Critical Reader blog for her helpful posts on ACT English, and read our complete guide to ACT grammar rules. Writing sectionsfrom the new post-2016 SAT.After its major overhaul, the new SAT will much more closely resemble the ACT. This means that you can use new SAT questions to drill your understanding of grammar and sentence structure. In particular, seek out practice questions from the Writing portion of the Writing Literature section from the post-2016SAT. "Improving Paragraphs"questions from the pre-2016 SAT. The old version of the SAT offers one useful type of question for studying for the ACT. Part of the old SAT Writing section was devoted to Improving Paragraphs: questions about grammar and punctuation in the context of a passage, rather than an isolated sentence. These are fairly similar to the questions you'll encounter on ACT English. But be careful to avoid the other questions in that section, because they are simply too far removed from what you have to be able to do well on the ACT. Read, read, read. Read widely, read challenging material, and particularly read nonfiction. The more you read complex writing, the more the nuances of grammar and structure will embed themselves in your mind, the more familiar you will be with elevated vocabulary, and the more you will learn how an author uses logic and rhetoric to get a point across. I recommend slowly digestingand really trying to understand a few articles a week from Grantland, The Atlantic, or Slate. If you have access to a subscription, you can also read the New York Times. PrepScholar's ACT English guides.We've worked hard to bring you as much helpful information about ACT English as possible. Some especiallyusefulguides include: Strategy.Part of doing well on the test is using a great approach to attack each section. We've analyzed and compiled 9 different key tactics for ACT English. All about grammar, syntax, and diction. We have broken down the complicated rules that you need to know into manageable chunks like: common word choice errors, the relative formality of the language on the ACT, and how to deal with shifting verb tenses. Maybe ACT English should actually test your relative English-ness. I think I could ace the tea test, especially if cucumber sandwiches were involved. Reading This portion of ACT tests your reading comprehension abilities. Let's once again start with a quick overview ofwhat's actually coveredon the ACT Reading section: 4 sections of passages from different genres (fiction, or nonfiction from the humanities, social studies, or natural sciences) questions ask you tocompare and contrast ideas, extract information, generalize from narrowly focused facts, and explain vocabulary in context Alternative Study Resources for ACT Reading Vocabulary guides. The ACT does not test vocabulary by itself, by you will see many complex words in context so if this is a challenging area for you then it will be helpful to see some guides to commonly occurring vocabulary. Check out resources like our free set of 200 flashcards and our guideto the vocabulary commonly used on the ACT vocabulary. Readingsectionsfrom the new post-2016 SAT. The redesignedSAT now has a section that also tests reading comprehension by asking questions about provided passages. Looking at these would be a good way to get in some extra practice. When studying, seek out passage-based questions from the Reading portion of the Writing Literature section. Passage-based reading questions from the old SAT.On the pre-2016 SAT, there were a few sections that could help with preparing for ACT Reading. Look for the parts of the Critical Reading section that feature multiple-choice questions based on provided passages. These won't be exactly like the ones on the ACT, but they can help you practice context-based questions. GRE Reading Comprehension questions. The Verbal Reasoning section of the GRE has a number of passage-based Reading Comprehension questions. It's true that these are pitched at a higher level than the ones you'll see on the ACT because the GRE is meant for college students heading to grad school. But if you are a student who is consistently getting medium- to high-scores on practice tests, you can use the GRE to challenge yourself. AP Language and AP Literature multiple choice section questions.Both of these AP test feature portions with passage-based multiple-choice question that test reading comprehensionandyour understanding of logic and structure. They are pitched at a higher level than the ACT, but if you do well on these, you’ll be fine on the ACTas well. Reading widely will also really help here. The test wants to measure how you are at understanding information being presented in written form, and how much you can tell about the way authors structure arguments. Try making time for weekly explorations of Reasonor The Root.On the paid subscription side, you can't go wrong with The New Yorker. PrepScholar’s ACT Reading guides.Let us guide you through some of the trickier parts of what you have to know to ace this part of the test. Some particularlyhelpful guides: Dissecting the test. We describe the4 types of ACT Reading passages you should know, give you some pointers onthe best way to read ACT passages, and enumerate every single type of question you're going to encounter. Her hair is fromPippi Longstocking, her book is The Little Prince, and her candy is Turkish delights from The Lion, The Witch, and the Wardrobe?! Pick a fandom, already, will you! Science Unlike its name suggests, this section relies more on your ability to understand visually presented data then on your knowledge of hard sciences. A quick refresher on what's tested on the ACT science section: paragraphs with visually presented data you’ll have to interpret descriptions ofexperiments that you’ll have to evaluate and analyze a set of two or more alternate theories or hypotheses that you’ll have to compare and contrast concepts from Biology, Chemistry, Physics, Astronomy, and Geology Alternative Study Resources for ACT Science Basic science guides.The test is almost exclusively focused on your ability to comprehend passages about science that are written for a non-scientist audience. Nevertheless, you will find it helpful to be familiar with some of the more basic concepts from biology, chemistry, physics, and math. We have put together an explanation of thescience you actually have to know for the ACT. If you need to re-familiarize yourself, go back to your high school textbooks, or use an online version (again, I likeKhan Academy). ACT Prep books.Many of these will give you tips and tricks on dealing with this portion of the test. Our guideto the best ACT books for intense study saves you from having to navigate the hundreds out there. Readingsectionsfrom the new post-2016 SAT.The redesigned SAT has somepassage-based reading comprehension questions based on scientific passages in the Reading portion of the Writing and Literature section. These are very similar to what you will encounter on the ACT science section because they also ask you to draw conclusions about graphs, charts, and tables, as well as passages describing a scientific process, theory or experiment., so you can seek those out. Make sure you look only at test prep designed for the post-2016 SAT. Popular science articles. You don’t need to dig out scholarly journals, but you should spend time reading scientific nonfiction intended for lay readers. It’ll give you familiarity with how data can be presented graphically through charts, graphs, and tables. My favorites areWired, FiveThirtyEight,Scientific American, andNature. If you can access a subscription, read The Economist or the magazine Science. PrepScholar’s ACT Science guides. Some especially helpful guides: Strategy. Check out our suggestions for attacking this section and tips to keep in mind while taking the test. All about the question types. We can explainthe 3 types of ACT Science passagesyou'll encounter, along with how todeal with questions about interpreting experiments, how to handle questions about experiment design, what to make of questions about trends, and finally, how to approach the conflicting viewpoints part of the section. How much science do you need to know to play Fruit Ninjain space? Writing The essay section was dramatically changed in 2015 to more closely align the test with Common Core standards and the kind of writing you'll do in college, so make sure you're familar with the updated format: You'll be asked to write an essay on a controversial topic, including information and analysis from 3different presented perspectives. You also need to explain your own point of view. Alternative study resources for ACT Writing: Guides to the standard 5-paragraph essay. This is our recommended structure for the ACT essay. For many explanations of how a 5 paragraph essay works, search for â€Å"5-paragraph essay,† or readour guide to ACT format and essay templates. Staying well informed. The essay will ask you to present evidence to back up your thinking. The best places to draw that evidence from? Current events, historical events, and incidents from your own life. So read newspapers, listen to NPR, and download podcasts like Planet Money, RadioLab, and On the Media. Excellent essays written by others. Reading well-written essays can help you understand how essays work and how authors structure arguments and ideas. You may even pick up some helpful ideas for your own writing as well! One great source of excellent short essays is The Electric Typewriter. PrepScholar’s ACT Writing guides.We've put together some helpful advice on tackling the ACT essay. Great guides include: All about the essay. We lay out a step by step explanation ofhow to write an ACT essay, and also give you ourcomplete guide to ACT Writing prompts. If I were an ACT writing grader, I would totally give super bonus points for any essays written in Aztec pictographs. The Bottom Line So what should you take away from this article? Studying content and concepts for the ACT can be done really effectively through resources not designed for test prep, andnd there are many of these kinds of resources! There are enough similarities between ACT and the SAT that you can use certain sections of both the old and new SAT as extra study materials for the ACT. Reading widely, reading often, and reading for meaning will help you on almost all of the different ACT sections you'll face the day of the test. What’s Next? Stuck trying to motivate yourself to get started studying? We hear you. Here’s our advice on how to beat the urge to procrastinate and how to give yourself the gift of properly structuring your study time. If you’re in the middle of studying for the ACT, we have alist of 21 tips you should not miss out on and15 ways to really boost your ACT score. We also have a general ACT prep guide. Unsure what your ACT target score should be? We explainwhat score you need to get into your target college, and give you some pointers on figuring outwhat’s a good ACT score for you. Want to improve your ACT score by 4 points?We have the industry's leading ACT prep program. Built by Harvard grads and ACT full scorers, the program learns your strengths and weaknesses through advanced statistics, then customizes your prep program to you so you get the most effective prep possible. Check out our 5-day free trial today:

Nanotechnology Applications Essay Example | Topics and Well Written Essays - 500 words

Nanotechnology Applications - Essay Example The rapid advancement in the field of nanotechnology calls for advance knowledge and research in its applications as well as the associated risks. Nanotechnology is currently the center fold of research and study. In consequence, the technology is rapidly growing in terms of advancements. The technology has immense potential for producing innovations and improvements in a variety of area in life; faster and smaller devices; increased product life cycle; mitigated use of harmful and scarce resources; improved health treatment, and faster, cleaner and safer manufacturing (Langwith, 2009). Nanotechnology entails the manipulation of matter at an atomic or molecular level with the aim of manufacturing novel devices and materials with new astonishing properties. The technology is not new rather it is the combination of knowledge from the amalgamation of multiple scientific disciplines to transform materials at the nano-scale. The research and studies done on the application of quantum mechanics enables nanotechnology to be revolutionary and innovative at the same time. It has been discovered that there is a momentous changes in the performance of matter when its surface area to volume ratio is dramatically increased. The behavior of materials is currently under the control of quantum physics instead of classical physics. For this reason, nano-structured material poses more favorable properties and abilities than the bulk material version. Polymers are considered insulators in their bulk form but nanotechnology transforms them into semiconductor at nanoscale (Langwith, 2009). Medicine: In medicine, nanotechnology has been employed to develop nano-particles capable of delivering drugs to the diseased cell. The machinery has also aided in the manufacture of bio-compatible materials which are used to make medical implants. The production of stents is significant in preventing artery blockage. Engineering: The

Air Pollution Research Paper Example | Topics and Well Written Essays - 750 words

Air Pollution - Research Paper Example Both humans as well as the nature have been held responsible for the emission of pollutants in the air. The emission of these pollutants is the reason behind the occurrence of air pollution. Various human activities have been found to heavily contribute to the increase in air pollution.One of the human activities that are constantly increasing the levels of air pollution is the emission of harmful gasses from organizations that produce goods to satisfy human needs. The most common form of air pollutants that is emitted by the industries includes carbon monoxide as well as other chemicals. Another reason due to which pollutants are released in air is the burning down of fossil fuels through airplanes as well as automobiles. Individuals try to keep their homes as well as crops free from insects and pests with the assistance of pesticides and other clearing products and these products release harmful chemicals that result in air pollution. According to Jacoby, the vehicles that travel o n road account for more than 90% of the carbon dioxide.Those who are harming the environment are those who are being negatively impacted by their own actions. Air pollution has been found to be negatively impacting all living things including plants, animals as well as hum beings. Air pollution has been found to result in impacting human health in a negative manner and these effects are both long term as well as short term. The level of impact is directly correlated with the level and length of time an individual is being exposed to these pollutants