Understanding and Using Cyclic. Redundancy Checks 01

The study of the properties of metalcomplexesMetal complexes are compounds formed by metal ions and ligands. They have unique properties that make them important in various fields like medicine, material science, nanotechnology, and environmental studies. Understanding the properties of metal complexes is crucial for designing new compounds with specific functions. In this article, we will discuss the important properties of metal complexes and their applications.Ligand Exchange ReactionsLigand exchange reactions are the most important properties of metal complexes. In these reactions, a ligand replaces another ligand from the metal ion, which results in the formation of a new complex. The rate of the ligand exchange reaction depends on the steric and electronic factors. Steric factors such as the size of the ligand and the geometry of the metal complex affect the rate of the reaction. Electronic factors such as the charge and the electronegativity of the ligand also play a crucial role.Applications: Ligand exchange reactions are important in catalysis and bioinorganic chemistry. Many catalysts use metal complexes because of their ability to undergo ligand exchange reactions. In bioinorganic chemistry, metal complexes play a crucial role in the transport and storage of metals in the body.Redox PropertiesRedox properties refer to the ability of a metal complex to undergo oxidation-reduction reactions. In these reactions, the metal ion changes its oxidation state, resulting in the formation of a new complex. The redox potential of a metal complex depends on the ligands and the metal ion. The presence of strong field ligands like cyanide and carbon monoxide increases the redox potential of the metal complex.Applications: Redox properties of metal complexes are important in electrochemistry and catalysis. In electrochemistry, metal complexes are used as mediators in the redoxreactions. In catalysis, many reactions are driven by the redox properties of metal complexes.Optical PropertiesOptical properties refer to the ability of a metal complex to exhibit color and luminescence. The color of a metal complex depends on the nature of the ligands and the metal ion. The presence of d-orbitals in the metal ion gives rise to the color of the complex. The luminescence of a metal complex depends on the energy gap between the ground and excited states.Applications: Optical properties of metal complexes are important in materials science, biology, and medicine. In materials science, metal complexes are used as dyes, pigments, and sensors. In biology, metal complexes are used as probes to study biological processes. In medicine, metal complexes are used as imaging agents and anticancer drugs.Structural PropertiesStructural properties refer to the geometry and bonding of a metal complex. The geometry of a metal complex is determined by the coordination number, the ligands, and the metal ion. The bonding in a metal complex can be classified as covalent, ionic, and dative.Applications: Structural properties of metal complexes are important in catalysis, material science, and environmental studies. In catalysis, the geometry and bonding of metal complexes determine their catalytic activity. In material science, the structure of metal complexes determines their thermal stability and mechanical properties. In environmental studies, the structure of metal complexes plays a crucial role in their toxicology and biodegradation.In conclusion, the study of the properties of metal complexes is crucial for their understanding and applications. The properties of metal complexes like ligand exchange reactions, redox properties, optical properties, and structural properties make them important in various fields like medicine, material science, nanotechnology, andenvironmental studies. Further research in this field will lead to the development of new compounds with specific functions.。

用C语言实现CRC校验计算在编写数据传输程序时，数据容错是一个非常重要的问题。

循环冗余位校验（Cyclicl Redundncy Check英文简称CRC）是目前运用非常广泛的一种数据容错方法，在数据传输，数据压缩等领域运用极其广泛。

CRC的实现分为硬件和软件两种方法，其中软件实现的关键在于计算速度。

如果单纯模拟硬件实现方法，则计算速度较慢。

笔者在编制一个数据通讯软件中，运用了一种新颖的查表法计算CRC，速度很快，效果极佳。

首先介绍其原理，如果每次参与CRC计算的信息为一个字节，该信息字节加到16位的累加器中去时，只有累加器的高8位或低8位与信息字节相互作用（异或），相互作用（异或）的结果记为组合值，那么累加器中的新值等于组合值加上（按模2异或）累加器中未改变的那一半即为新的CRC值。

组合值只有256种可能，因此可利用硬件模拟算法先算好它们的CRC值预先填入一张表中，该表的每一单元对应相对值的CRC。

这样就可以通过查表法来计算CRC值，以便大大提高CRC运算的速度。

下面给出用Ｃ语言编制的计算程序。

首先将CRC生成多项式及CRC值表定义为一个头文件CRC.H：#define CRC_CCITT 0x1021 //CCITT多项式#define REV_CCITT 0x8408 //反转CCITT多项式#define CRC16 0x8005 //CRC16多项式#define REV_CRC16 0x001 //反转CRC16多项式unsigned short crc_tble[256];//CRC值表注：16位CCITT多项式（X16 +X12 +X5 +1）和16位CRC16多项式（X16 +X15 +X2+1）为两种最常用的CRC多项式。

反转多项式是指在数据通讯时，信息字节先传送或接收低位字节，如重新排位影响CRC计算速度，故设反转多项式。

造表和查表法CRC计算函数。

#include crc.hvoid mk_crctble(unsigned short genpoly){unsigned short crc_tble[256];unsigned short ccnum=0;unsigned short i,j,k;for(i=0,k=0;i<256;i++,k++){i<<=8;for(j=8;j>0;j ){if((i^ccnum)&0x8000) ccnum=(ccnum<<=1)^genpoly;else ccnum<<=1;i<<=1;crc_tble[k]=ccnum;}}void crc_updte(unsigned short dt,unsigned short ccnum)ccnum=(ccnum<<=8)^crc_tble[(ccnum>>8)^dt];}}注：genpoly为CRC多项式，ccnum为累加器值（即为新的CRC值），dt为参与CRC计算的信息。

2021高考英语二轮专题复习阅读理解环境保护类提分训练（2021年真题集锦，含解析）新人教版(2020·大纲版全国卷·E)The oldest and most common source(来源)of renewable energy known to man,biomass is one of the most important forms of energy production in the United States and such a wide variety of biomass materials is everywhere—from trees and grasses to agricultural and city-life wastes—biomass promises to play a continuing role in providing power and heat for millions of people around the world.According to the Union of Concerned Scientists(UCS),biomass is a kind of renewable energy source that produces no carbon dioxide(二氧化碳),because the energy it contains comes from the plant matter is burned,it gives off the sun’s this way,biomass serves as a sort of natural battery(电池)for storing the sun’s long as biomass is produced continuously—with only as much grown as is used—the “battery”lasts forever.According to the Energy Information Administration, biomass has been one of the leading renewable energy sources in the United States for several years running through 2007, making up between and percent of the nation’s total electricity 2008—although the numbers aren’t all in yet—wind power probably took over first place because of the rapid development of wind farms across the country.Producing power from biomass helps reduce some 11 million tons of carbon dioxide each homeowners also try to make their own heat by using biomass practice may save homeowners’money, but it also produces a lot of pollution. So, the best way is to encourage power plants to use it.【文章大意】本文要紧介绍了biomass(生物能)将为世界上成千上万的人们提供能源和热量。

小学上册英语第4单元暑期作业英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The cake is _______ (delicious) and sweet.2.I enjoy visiting ________ (亲戚) during the holidays.3.In which direction does the sun rise?A. NorthB. SouthC. EastD. WestC4.What do you call a drawing made using a pencil?A. PaintingB. SketchC. SculptureD. IllustrationB5.I enjoy listening to ________ (音乐) in my free time.6. A __________ is known for its long ears and strong legs.7.She helps her mom in the ___. (kitchen)8. A ______ is a type of fungus that can grow on trees.9.My sister is a great __________. (歌手)10.The study of Earth's geology is essential for understanding ______.11.What do you wear on your feet?A. HatB. ShoesC. GlovesD. Scarf12. Fire of London happened in ________ (1666). The Grea13.What is the name of the dog in "The Wizard of Oz"?A. TotoB. SnoopyC. PlutoD. BrianA14.Plants can grow in both _______ and dry conditions.15.The __________ was the first civilization in Mesopotamia.16.What do we call a person who studies paleontology?A. PaleontologistB. ArchaeologistC. GeologistD. Anthropologist17.My uncle is a fantastic ____ (chef).18.What do we call the leader of a country?A. PresidentB. KingC. MayorD. GovernorA19.How many wheels does a bicycle have?A. 2B. 3C. 4D. 5A20.What is the name of the famous bear from the jungle?A. BalooB. PaddingtonC. YogiD. WinnieA21.Pressure can affect the ________ of gases.22.__________ (微量元素) are necessary for health in small amounts.23. A chemical reaction can be fast or ______.24._____ (herbal) teas are soothing.25.I have a _____ (new/old) bicycle.26.The parakeet enjoys playing with ________________ (其他鸟).27.What do we call a doctor who takes care of teeth?A. PhysicianB. DentistC. ChiropractorD. SurgeonB28.What is the opposite of big?A. SmallB. LargeC. HugeD. Tall29.We have a ______ (丰富的) curriculum that includes arts and sciences.30.The _____ shows the positions of planets in the sky.31.The Earth's crust can vary in composition depending on the ______.32.He plays ______ (soccer) every Saturday.33.River flows northward through _____ (埃及). The Nile34.The reaction between an acid and a metal produces ______.35.What is the name of the famous American author known for "The Grapes of Wrath"?A. John SteinbeckB. Ernest HemingwayC. F. Scott FitzgeraldD. Mark TwainA36. A ______ is a method for analyzing substances.37. A _______ is a solution that has reached its maximum solute concentration.38.The first recorded civilization was the ______ (美索不达米亚).39.The boy has a new ________.40. A _______ provides food and shelter for animals.41.The bear catches fish in the ____.42.The _____ (小羊) bleats softly as it grazes in the field. 小羊在田野里吃草时轻声叫唤。

CQUniversityUnit 3: Understanding matter - atoms and moleculesCase study (4)Objectives (5)What is matter? (6)The Particle theory (6)States of matter (7)Chemical and physical changes (9)Classification of matter (11)Homogeneous matter (11)Heterogeneous mixtures (11)Special types of mixtures (12)Building blocks of matter (14)Elements (14)Atoms (15)Isotopes (17)Electron orbitals - energy levels and valence electrons (18)Ions (19)Molecules (20)Bonding (22)Ionic bonding (22)Covalent bonding (23)Rules to predict which type of bonding will occur (24)Multiple bonds (25)Cyclic bonding (26)Aromatic bonding (27)Hydrogen bonding (27)Unit 3: Understanding matter – atoms and molecules Page 3-2Chemical reactions (29)Energy of reactions (31)Catalysts (32)Enzymes – catalysts in the body (33)Measuring atoms and molecules – the mole (35)Mass – mole conversions. (36)Solutions (38)Dilutions (41)Calculating dilution factors (42)Preparing diluted solutions (43)Electrolytes (44)Acids and Bases (46)What is meant by pH? (48)Acid-base neutralisation (49)Buffers (49)Organic compounds (51)Biomolecules (52)Carbohydrates (55)Lipids (55)Amino acids and proteins (56)Bibliography (57)Unit 3: Understanding matter – atoms and molecules Page 3-3Unit 3: Understanding matter - atoms and molecules Case studyFiona presented at outpatients with symptoms of extreme lethargy, rapid breathing and abdominal pain. After an initial consultation it was revealed that Fiona suffers from insulin dependent diabetes mellitus and had missed taking her last insulin dose. Blood tests show a pH of 7.32 along with high concentrations of the electrolyte potassium and elevated glucose, ketones and lactic acid levels. Urine pH was very low at 4.3. These results along with an electrocardiograph showed erratic heart muscle activity confirmed that Fiona was in a state of metabolic acidosis and may be at risk of going into a coma.Immediate treatment for Fiona was administration of 10 mL of 10% calcium gluconate to reduce cardiac muscle excitability along with insulin and 50 mL 50% glucose. To help her breathing, Fiona was given ventolin.Once stabilised Fiona will need to take regular doses of insulin and maintain a healthy diet comprising of approximately 50% carbohydrates, 15% protein, less than 10% unsaturated fats, limited sugar and salt intake. Cholesterol should be maintained at or below 5.0 mmol/L and blood glucose (after fasting) to be 4.7 mmol/L.Understanding Fiona’s case:The chemistry involved in Fiona’s case requires an understanding of concentrations, acids, bases and buffers, chemical reactions, enzymes and types of biomolecules such as proteins.It is hoped that through studying this unit you will appreciate that the human body is made up of an array of molecules and that the body functions through a series of chemical reactions. When the body is unable to maintain a healthy state, treatment often includes the administration of medications at appropriate doses.Unit 3: Understanding matter – atoms and molecules Page 3-4ObjectivesOn completion of this section you should be able to:•name and describe the states of matter•use the particle theory to discuss matter•distinguish between chemical and physical changes•classify matter into pure substances and mixtures•describe an atom and its structure using terms such as nucleus, proton, neutron and electron •explain the meaning of the terms atomic number, mass number, isotopes and atomic weight •discuss why atoms bond to form molecules•explain what is meant by a molecular formula•explain aspects of chemical reactions such as reversibility, heat of reaction, role of catalysts and enzymes•define the terms solution, solute, solvent and solubility•describe what is meant by the term concentration and explain its importance in relation to the reporting of test results from clinical pathology laboratories•perform dilution calculations using a simple formula•define the terms electrolyte and non-electrolyte•define the terms acid, base and buffer•describe the pH scale of acidity•explain the difference between organic and inorganic compounds•name some biomolecules present in the body.Unit 3: Understanding matter – atoms and molecules Page 3-5What is matter?Matter is defined as being anything that occupies space and has mass. Mass is a measure of the amount of matter that an object contains. For example, a golf ball has more mass than a table tennis ball, and therefore contains more matter.But what does matter consist of?Before answering this question you are invited to perform the following mini-practical and reflect on possible explanations for the observations that you make.Mini-practical 3-1: Diffusion - Perfumes, dyes in waterEquipment: You will need some food colouring and a glass of water1.Recall how perfumes, nasty smells and nice food odours spread quickly in air.2.Place a couple of drops of food colouring in a glass of water and observe how the dye moves.3.Can you explain your observations?… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …What is happening? The spread of odours and colours suggests outward movement of particles from a concentrated source.Consider what happens when you mix a bucket of sand and a bucket of gravel. The combined mix does not equate to 2 buckets. On a micro scale this phenomenon can be observed using methanol and water. Mixing ½ a cup of water with ½ a cup of methanol results in a total volume of less than 1 cup. This observation is best explained by assuming that particles of water and methanol fit between each other.The particle theoryThe observations made in these mini-practicals suggest very strongly that matter is composed of particles. The particle theory is an accepted scientific theory that is used to explain many phenomena.The particle theory states that:•Matter is composed of particles.•Particles of matter are in constant random motion.•The speed at which particles move increases with increasing temperatures.•Particles of matter are held together by electrostatic forces.•Empty spaces exist between the particles of matter.Unit 3: Understanding matter – atoms and molecules Page 3-6All matter is composed of very small particles, called atoms (or groups of atoms called molecules). The distance particles are apart and the forces of attraction between the particles determine the form or state that the matter exists in.States of matterMatter exists in three different physical states. These physical states of matter are: solid, liquid and gas. If the particles of matter are strongly attracted to each other and held close together, it is in the solid state. When the forces of attraction are reduced but particles are still held closely together, matter is in the liquid state. If the distance between the particles is large and forces of attraction are negligible matter takes a gaseous form.Consider what happens when a corn kernel is heated in oil and forms popcorn. As the kernel is heated, the particles of moisture inside gain energy and the liquid changes to gas. The pressure inside the kernel increases to a point where the kernel ruptures. The starch and proteins in the kernel also expand and the texture becomes like airy foam. Refer to figure 3-1.Figure 3-1: Corn kernel and popped popcornAlthough there are three physical states of matter, it is important to realise that chemical substances are unchanged in these physical states. The only difference between them is in how closely they are packed together (the density of the substance which is the ratio of mass to volume) and in how rapidly these molecules are moving (their kinetic energy).Table 3-1 summarises the important characteristics of the three states of matter.Unit 3: Understanding matter – atoms and molecules Page 3-7Table 3-1: The three states of matter—solids, liquids and gasesthe particles are already packed together, aSolidsolid is not easily compressed.shape of a container (e.g., milk, blood,water)Particles in a liquid although held closelytogether are able to move past each other,allowing the liquid to flow. Like solids,liquids cannot be easily compressed.Gas Matter that takes both the shape and thevolume of its container.In the gas state particles of matter are at agreat distance apart and have negligibleforces of attraction between each other.This allows gases to expand without limit tofill any space and also explains why gasesare easily compressed. (e.g., oxygen)(Adapted from Hickman & Caon, 1995.)Matter can be transformed from one state to another by adding or removing energy in the form of heat. When a solid becomes a liquid it is said to melt and the temperature at which this happens is the melting point. When a liquid reaches boiling point, it transforms to a gas. This process is known as evaporation. As heat is removed, a gas turns to liquid and is said to condense. As more heat is removed and the liquid turns to a solid we say it freezes.Consider the process of evaporation. As heat is added to a liquid, the particles or molecules gain more energy and are able to move faster and further apart until they are able to overcome the forces of attraction that hold them together. When this occurs, the state of matter is that of a gas.Unit 3: Understanding matter – atoms and molecules Page 3-8The processes involved in change of state of matter are summarised in Figure 3-2.Melting EvaporationSOLID LIQUID GASFreezing CondensationFigure 3-2: Processes of change of state of matterChemical and physical changesThe change that occurs as matter changes state between solid, liquid and gas are physical changes. In physical changes no new substance is formed since the substance is the same, it just has different physical properties.A chemical change occurs when new substances are formed that have different properties and composition to the original material. Some indicators of a chemical change occurring is a change in colour, formation of gas, production of heat.So as to witness chemical and physical changes first hand you might like to perform the following tasks. Identify each task as being an example of either a physical or chemical change and suggest on a particle level what may be occurring.Mini-practical 3-2: Chemical and physical changesEquipment: You will need an egg, vinegar, a thermometer and a glass of hot water.1.Place an egg into a container of vinegar and leave for 48 hours. Observe any changes thatmay occur to the appearance and feel of the shell.… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …What is happening? The composition of the egg shell has changed chemically. The calcium carbonate in the egg shell has reacted with the acetic acid in the vinegar. This chemical reaction results in the removal of calcium from the egg shell making it go soft, or even disappear. Unit 3: Understanding matter – atoms and molecules Page 3-92.Place a (non digital) thermometer into a glass of hot water and observe any changes that areseen in the thermometer’s mercury or alcohol level over 2 hours.… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …What is happening? The mercury/alcohol level changes as a result of the temperature change of the water. When the water is hot, the particles of mercury/alcohol have greater energy and are able to move faster and at a greater distance apart. As the water cools, mercury/alcohol particles have less energy and so move closer together. The physical change in the mercury/alcoholallows it to be used effectively as an indicator of temperature in the thermometer.Activity 3-1Indicate in the following table whether the occurrences are physical or chemical changes.Occurrence Physical or chemicalExplanationchange?Melting iceBurning paperRusting ironTearing paperBreaking glassBoiling waterBleaching a stainFermenting grapesUnit 3: Understanding matter – atoms and molecules Page 3-10Classification of matterSome materials are composed of numerous types of matter (variable composition), while others consist of a single type of matter (constant composition).Homogeneous matterWhen matter has a constant or uniform composition, it is homogeneous. Homogenous matter has only one phase, each portion of the sample being identical in composition, resulting in the sample having the same composition throughout. Homogeneous matter can be either a homogeneous mixture (such as a solution where the solid is completely dissolved in the liquid as in a teaspoon of sugar in a cup of tea) or a pure substance (such as gold).Some other examples of homogenous mixtures include:•Salt water – a single phase, uniform mixture of salt dissolved in water.• A piece of steel – a single phase, uniform mixture of different metals forming an alloy.• A solution of bleach - a single phase, uniform mixture of hydrogen peroxide in water. Homogeneous mixtures can be separated by physical processes into pure substances.Pure substances are composed of elements or compounds. The smallest unit or particle of matter is the atom. Elements contain only one type of atom while compounds contain two or more types of atoms in fixed proportions. Pure substances cannot be broken down into smaller units by physical methods. Compounds can only be separated into elements by chemical methods. Heterogeneous mixturesWhen matter has variable composition it is a heterogeneous mixture. The components of a heterogeneous mixture are easily separated and have different properties. A heterogeneous mixture is composed of mixed or multiple phases. Heterogeneous mixtures can be separated by physical processes into homogeneous matter.Fruit salad is a good example of a heterogeneous mixture – it is composed of many different and distinguishable solid phases. Fruit salad can be separated into apples, grapes and strawberries etc. by hand.Some other examples of heterogeneous mixtures include:•The sand at the beach – composed of different solid phases as many different coloured sand particles can be observed.•Soft drink – composed of a gas and liquid phase as bubbles of carbon dioxide are present in the drink.•Blood – composed of different liquid phases since the components of blood are red and white blood cells, platelets and plasma which are easily separated when left to stand or whencentrifuged (spun at high speed).Unit 3: Understanding matter – atoms and molecules Page 3-11Activity 3-2Classify the following as either homogenous or heterogeneous mixtures:ExplanationMixture Homogeneous orheterogeneous?JellyAir when clouds are presentAir in a roomSalad dressing of vinegar andoilSpecial types of mixturesColloids and emulsions are names given to particular types of homogeneous mixtures. Remember a homogeneous mixture appears to have the same composition throughout since the particle sizes are too small to be seen. Colloids are mixtures where one substance is evenly dispersed throughout another. There are many examples, including gas/liquid colloids such as fog, or aerosol sprays; solid/gas colloids such as whipped cream or liquid/liquid colloids such as hand cream or homogenised milk. Liquid/liquid colloids are given a special name of emulsion.A suspension is a particular type of heterogeneous mixture, since it has large particles that settle out on standing. An example of a suspension is a preparation of the antibiotic, amoxicillin or augmentin, in water where the active ingredient is mixed with water but does not dissolve, rather remains as a suspended solid: this is why it is important to shake these medicines thoroughly before measuring a dose.Figure 3-3 provides a summary of information regarding the classification of matter.Unit 3: Understanding matter – atoms and molecules Page 3-12Figure 3-3: Classification of matterUnit 3: Understanding matter – atoms and molecules Page 3-13Unit 3: Understanding matter – atoms and molecules Page 3-14Building bl ocks of matterElementsAs mentioned previously, the elements are pure substances containing only one type of atom. Many atoms of the element need to be grouped together before macroscopic properties of the element are evident (e.g. lustre of metals). Elements cannot be broken down into simpler substances by chemicalmethods. There are approximately 92 naturally occurring elements and a number of synthetic ones. Many elements will be familiar to you, for example gold, silver, iron and carbon. All of the elements are listed systematically in the Periodic Table. A copy of the Periodic Table of the Elements is provided in Figure 3-4.Figure 3-4: The Periodic Table of the Elements (Adapted from Timberlake 1992)Consider the layout of the periodic table. The horizontal rows of the periodic table are calledperiods (or rows ). There are seven periods. And the vertical columns are called groups . There are 18 groups.The Periodic Table is designed so as to group elements with similar properties together. Thisgrouping system simplifies a study of the elements since knowledge of a particular group rather than every element (118 of them!) is usually all that is needed to predict the chemistry of the element. For example the chemical behaviour of the elements in group 1A (the alkali metals) with the exception of hydrogen, is very similar. Other groups that should be noted are group 2A (the alkaline earth metals), group7A (the halogens) and group 8A the noble gases. Note also that there is a zig zag black line going from the top left to bottom right of the periodic table. Elements on the left of this line (except for hydrogen) ar e metals , while those to the right of the line are non-metals . With theexception of aluminium, those elements located beside the stepped line are metalloids, which have some properties of both metals and nonmetals.You will notice that the names for the elements listed in the Periodic Table have been abbreviated using a form of shorthand notation. Elements are abbreviated using any of the following: •the first letter (e.g. hydrogen = H),•the first two letters (e.g. helium = He)•the first letter and another letter of the element name (e.g. chlorine = Cl) or•letters based on the Latin names of the element (e.g. potassium = K from the latin, Kalium) Table 3-2, provided for your interest only, presents the elements that are essential for the body to function.Table 3-2: Essential elements for the bodySymbolName of element Symbol Elements necessaryin trace amountsCarbon C Chlorine ClHydrogen H Cobalt CoOxygen O Fluorine FNitrogen N Iodine IIron Fe Magnesium MgCalcium Ca zinc ZnPhosphorus P Copper CuPotassium K Selenium SeSodium Na Manganese MnSulphur S Molybdenum MoAdapted from Strobe, 2008.AtomsThe smallest unit of an element is the atom. If an atom is split (as in a nuclear reactor) that atom no longer exists – different atoms are formed. The atom is made up of a central, extremely dense nucleus which is surrounded by a cloud of rapidly moving, extremely small electrons. The nucleus contains two types of particles, the proton and the neutron. (A representation of an atom is given in Figure 3-5). The electrons move around the nucleus at a larger distance and at high speed creating an electron cloud. This cloud can be likened to the appearance of the spinning blades of a helicopter. When the rotor is spinning, the two blades appear as if they occupy a circular cloud around the rotor. Electrons move in paths called electron energy shells or electron orbitals.Unit 3: Understanding matter – atoms and molecules Page 3-15Unit 3: Understanding matter – atoms and moleculesPage 3-16Figure 3-5: The arrangement of the subatomic particles in an atom.All of the subatomic particles are extremely small compared to the things you see around you.Because the mass of a subatomic particle is so minute, chemists find it convenient to use a very small unit of mass called an atomic mass unit (amu). A single proton and a single neutron each have a mass of 1 amu. Since the electron is so small and light, its mass is usually ignored in atomic mass calculations.The electron is much lighter than either the proton or neutron (approximately 2000 electrons equal the weight of one proton). Table 3-3, summarises some of the information known about the subatomic particles. (Note the use of scientific notation to write the mass of each particle.)The proton is positively charged, the electron, negatively charged and the neutron has no charge. All atoms are electrically neutral as they contain the same number of protons as electrons. Table 3-3: Characteristics of the subatomic particles in atomsSubatomic particle Electrical charge (relative values)Particle mass Atomic mass units (amu) Location in atomProton +1 1.67263 × 10-24 g 1.00728 Inside nucleus Neutron 0 1.67494 × 10-24 g 1.00867 Inside nucleus Electron–19.10939 × 10-28 g5.48580 × 10-4Outside nucleusAdapted from Gilbert, Kirss & Davies , 2004.Atoms of each element are identified by the number of protons present in the nucleus. The number of protons in a nucleus of an atom is defined by the atomic number . Different atoms have different atomic numbers. For example any atom with 1 proton will be a hydrogen atom, any atom with 2 protons will be a helium atom and any atom with 6 protons will be a carbon atom. Since atoms are neutral, the atomic number is also equivalent to the number of electrons.Another number which identifies an atom is the mass number . The mass number indicates the mass of the atom. Since the mass is due to protons and neutrons, it is possible to calculate the number of neutrons present in an atom by subtracting the atomic number (number of protons) from the mass number (number of protons and neutrons).Consider some examples of using atomic and mass numbers to determine the number of protons, neutrons and electrons in an atom:•Hydrogen has an atomic number of 1. This means that an atom of hydrogen has 1 proton and1 electron. The mass number of hydrogen is also 1 which indicates that hydrogen does nothave any neutrons.•Helium has an atomic number of 2, and therefore each helium atom contains 2 protons and 2 electrons. Since helium has a mass number of 4, there must also be 2 neutrons present.•An atom of potassium with an atomic number of 19 and mass number of 39 has 19 protons and 19 electrons (inferred from the atomic number) and 20 neutrons, (calculated bysubtracting atomic number from mass number, i.e. 39 – 19=20).The Periodic Table is arranged so that the atomic numbers increase from left to right across the table, and from top to bottom down the table.Activity 3-3Complete the following table:Atom Atomicnumber Mass number Number ofprotonsNumber ofelectronsNumber ofneutronsCarbon 6 6Sulfur 16 16 Fluorine 9 19Oxygen 16 8Sodium 11 23IsotopesAtoms of the same element always have the same number of protons present in the nucleus, however not all atoms of the same element have the same number of neutrons.Isotopes are atoms of the same element that have different numbers of neutrons. The atomic numbers of the isotopes are the same, but their mass numbers are different. When we are talking about isotopes we say the name of the element and then the mass number, e.g. carbon 13. When we write isotopes, the shorthand convention is to place the mass number as a superscript in front of the symbol, e.g. 13C. or it can also be written 136C, with both mass number and atomic numbers indicated.Most of the elements occur in nature as mixtures of isotopes. However, many isotopes are unstable. Indeed, some are radioactive and are continuously decomposing to form other elements. Of the seven known isotopes of carbon, only two, carbon-12 and carbon-13 are stable. You may have heard of carbon dating, which analyses the amount of carbon-14 present in carbon containing specimens. Other isotopes are used in radiation therapy. Unit 5 will introduce applications of radiation in medicine.Unit 3: Understanding matter – atoms and molecules Page 3-17Electron orbitals - energy levels and valence electronsThe chemical behaviour of an element is determined by its electronic configuration – i.e. how electrons are arranged around the nucleus of the atom.The cloud of electrons that surrounds the nucleus has electrons arranged in a series of seven discrete energy levels or orbitals. Orbitals closest to the nucleus have the lowest energy. Each energy level holds a different number of electrons. The maximum number of electrons in the first three energy levels is shown in the Table 3-4.Table 3-4: Electrons in first three energy levelsElectron energy level Maximum number of electrons1 22 83 18For the first 18 elements in the Periodic Table, energy levels tend to be filled with electrons consecutively. This means that 2 electrons enter the first energy level before any electrons enter the second energy level. Similarly, 8 electrons enter the second energy level before electrons begin to enter the third energy level. Note that so far a total of 10 electrons have been accounted for, so the next 8 electrons will enter the3rd energy level.The electrons in the outer energy level are referred to as valence electrons. These valence electrons have an important role in determining the chemical properties of the element.Activity 3-4a)Using the information from the Periodic Table (Atomic number) and the maximum number ofelectrons allowed in the first 3 energy levels, complete the following table by predicting how many valence electrons the following elements have.Element Atomic number Number of electronsNumber of valence electronsFluorineCarbonOxygenChlorineHydrogenNeonSodiumSulfurUnit 3: Understanding matter – atoms and molecules Page 3-18b)Of the elements in this table, there are three pairs, each pair belonging to a different group of thePeriodic Table. Can you identify the three pairs and name the group that each pair belongs to?… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …c)Do you notice a trend with the number of valence electrons for elements in the same group of thePeriodic Table?… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …… … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … … …… … …IonsAtoms may lose or gain valence electrons in order to attain the electronic configuration of a noble gas. If electrons are gained, the atom becomes negatively charged, and if electrons are lost, the atom becomes positively charged. These charged species are called ions. Positive ions are referred to as cations while negative ions are referred to as anions.Whether an atom forms an anion or cation is dependant on their relevant position in the Periodic Table. Metals (elements positioned on the left hand side of the stepped line) tend to lose electrons and become positively charged ions or cations. Non-metals (those elements positioned on the right hand side of the stepped line) tend to gain electrons and become negatively charged ions or anions.Following these guidelines you will notice that the gain or loss of electrons is kept at a minimum. Activity 3-5Using the position in the Periodic Table and the number of valence electrons for each of the elements in Activity 3-4, predict what type of ion will form and the number of charges on it.ElementPosition inPeriodic Table(metal/non-metal?)Number ofvalenceelectronsAnion orcation?Number ofcharges on theionFluorineOxygenChlorineHydrogenNeonSodiumSulfurUnit 3: Understanding matter – atoms and molecules Page 3-19。

Understanding the Science of Frictionand WearFriction and wear are an inseparable part of our lives. Everywhere we go, we encounter friction and wear in some form or the other. From the wheels of our vehicles to the zippers on our clothes, friction is always at play. But what is friction, and how does it work? How does friction affect the wear and tear of our belongings, and how can we prevent or reduce it? In this article, we will explore the science of friction and wear and try to answer these questions.What is Friction?Friction is a force that opposes motion between two surfaces that are in contact with each other. It is caused by the roughness of the surfaces and the interlocking of their microscopic bumps and ridges. When we try to slide one surface over another, the bumps and ridges of the surfaces get entangled, creating resistance that opposes the motion. This resistance is called friction.Friction can be either static or kinetic. Static friction is the force that must be overcome to start an object moving. Kinetic friction is the force that opposes the motion of a moving object. The amount of friction depends on the materials of the surfaces in contact, the surface area, and the force pressing the surfaces together. The roughness of the surfaces also plays a significant role in determining friction.How Does Friction Affect Wear?Friction and wear are closely related. When two surfaces rub against each other, friction causes some of the material to wear away. This wear can be in the form of abrasion, adhesion, or fatigue. Abrasion occurs when the rough surfaces of the materials rub against each other, causing small pieces of material to break away. Adhesion occurs when the surfaces stick together and then tear apart, causing material to be transferredfrom one surface to the other. Fatigue wear occurs when repeated cycles of loading and unloading cause cracks to form in the material, leading to surface damage or even failure.Wear can be minimized by reducing friction. This can be achieved through lubrication, the use of harder materials, or by smoothing the surfaces. Lubrication involves placing a substance, such as oil or grease, between the surfaces to reduce the friction. Using harder materials can reduce the wear and tear of the surfaces, as the harder material is less susceptible to abrasion or adhesion. Smoothing the surfaces can reduce the roughness of the surface, reducing the contact area and thus, reducing friction.ConclusionFriction and wear are natural phenomena that occur whenever two surfaces are in contact. Understanding the science of friction and wear can help us to prevent or reduce the wear and tear of our belongings. It can also help us to design better products that are more efficient, safer, and longer-lasting. As we continue to explore the properties of materials and the science of friction, we can look forward to a future with less friction and more wear-resistant materials.。

小学上册英语第5单元综合卷(有答案)英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.What do we call the process of a caterpillar turning into a butterfly?A. MetamorphosisB. EvolutionC. TransformationD. Development 答案: A. Metamorphosis2.Helium was first discovered in the ______ spectrum.3.The capital of Indonesia is _______.4. A ____ has large, flapping ears and can hear very well.5.What do we call the stars and planets in the sky?A. UniverseB. Solar SystemC. GalaxyD. Atmosphere答案: A6.The _______ (The fall of the Berlin Wall) marked the end of Communist control in Eastern Europe.7.My friend is very ________.8.When it snows, I enjoy making __________ with my friends. (雪人)9.What is the main purpose of a refrigerator?A. To heat foodB. To cool foodC. To cook foodD. To freeze food答案: B10. A _____ (植物研究合作) can lead to groundbreaking discoveries.11.The __________ is a natural wonder located in the United States. (黄石公园)12.Turtles can live for a ______ (很长的时间).13.My brother is __________ (富有想象力).14. A ____(mixed-use development) combines residential and commercial spaces.15.What is the name of the famous ancient ruins in Mexico?A. TeotihuacanB. Machu PicchuC. Angkor WatD. Petra答案: A16.We visit the ______ (自然史博物馆) to learn about fossils.17.The discovery of ________ changed the course of history.18. A dolphin leaps gracefully out of the _______ and splashes down again.19.I enjoy playing ________ with my family.20.I like to ___ (play/watch) games.21.What do we call a young female goat?A. KidB. CalfC. LambD. Foal答案:A.Kid22.My friend is __________ (聪明绝顶).23.The _______ can change its shape with the seasons.24.The _____ (养分) in the soil is vital for plant health.25.What is the term for a young goat?A. CalfB. KidC. LambD. Foal答案: B26.An electric motor converts electrical energy into _______ energy.27.Animals that have scales are typically __________.28.The capital of Bonaire is __________.29.My favorite animal is a ______ (dolphin).30. A __________ is a reaction that involves a change in temperature.31.The first successful cloning of a mammal was of _____.32.I like to go ________ (爬山) with my friends.33.The ______ (小鸟) builds a nest for its eggs.34.My _____ (仓鼠) runs on its wheel.35.The ______ helps us learn about communication.36.The painting is very ___ (colorful).37.I often visit my ____.38.I can see a ______ in the sky. (bird)39. A strong acid has a pH less than ______.40.The atomic number of an element tells you the number of _____ (protons) it has.41.What do we call the part of the brain that controls balance?A. CerebellumB. CerebrumC. BrainstemD. Cortex答案:A42.The __________ is a famous natural landmark in the United States. (黄石公园)43.The capital of Ecuador is __________.44.The iguana is often seen basking in the ______ (阳光).45.The __________ (农业) is important for our economy.46.The ______ (小龙) is a mythical creature often found in ______ (故事).47.What is the term for a baby capybara?A. PupB. KitC. CalfD. Hatchling答案:c48.The fish swims in the ___. (water)49.The chemical formula for calcium chloride is ______.50.The ancient Romans practiced ________ (宗教多元).51.I want to _____ (go/stay) at home.52.The speed of light is very ______.53.What do we call a baby dog?A. KittenB. PuppyC. CalfD. Chick答案:B54.The chemical formula for yttrium oxide is _____.55.The Earth's surface is shaped by both climatic and ______ factors.56.Understanding plant _____ (结构) helps in gardening.57.The _____ (spoon) is shiny.58.The _____ (温带雨林) hosts a variety of plant species.59.The balloon is ______ (floating) in the air.60.The river is ______ (calm) and clear.61. A solution with a pH of contains more ______ than a solution with a pH of .62. A ____ is a large animal that can be trained to work.ets are made of ice, dust, and ______.64.__________ are used in the beauty industry for skincare.65.The _____ is a phenomenon where the moon blocks the sun.66.My cat enjoys the warmth of the _______ (阳光).67.The __________ is important for keeping bones strong.68.The __________ is the area of land between two rivers.69.The __________ (历史的深度剖析) reveals nuances.70.Certain plants can ______ (提供) habitat for endangered species.71. A _______ can measure the amount of energy consumed by a device.72.The ________ was a significant treaty that fostered diplomatic relations.73.The chemical symbol for silver is ________.74.I like to draw pictures of my ________ (玩具名) and imagine their adventures.75.I share my toys with my ______. (我和我的______分享玩具。

Curiosity is a rover designed by NASA to explore the Gale Crater on Mars,which is believed to be the source of a vast lake that once existed on the planet.This mission aims to investigate the planets climate and geology,as well as search for signs of ancient life.Launched in November2011,Curiosity landed on Mars in August2012.It is equipped with a variety of scientific instruments to study the Martian surface and atmosphere.One of its key instruments is the Mars Hand Lens Imager MAHLI,which captures highresolution images of the rovers surroundings.The rover has discovered evidence of an ancient riverbed and lakebed,suggesting that Mars once had liquid water.This is significant because water is considered a key ingredient for life.Curiosity has also found organic molecules,which are the building blocks of life,in Martian rocks.Curiosity has also measured the Martian atmosphere and found it to be composed mainly of carbon dioxide,with traces of other gases.The rover has also detected methane,a gas that can be produced by geological or biological processes.In addition to its scientific mission,Curiosity has also captured stunning images of the Martian landscape.The rover has sent back panoramic views of the Gale Crater,showing its rugged terrain and the towering Mount Sharp in the distance.Despite facing technical challenges and harsh conditions on Mars,Curiosity has exceeded its expected lifespan and continues to explore the Red Planet.It has provided valuable insights into Mars past and present,and has inspired further exploration of our neighboring planet.In conclusion,the Curiosity rovers mission to explore the source of Mars ancient lake has been a remarkable success.It has expanded our understanding of the planets history and potential for life,and has paved the way for future Mars missions.。