Things Fall Apart 6 Essay Example For Students

Things Fall Apart 6 Essay Things Fall Apart EssayThe book Things Fall Apart by Chinua Achebe definitely has a fitting title. It explains how two cultures with different ideas and beliefs can clash and be intolerant towards one another. Most of the theme is developed through the plot of the story and through a man and his struggle against fear and anger (the main character, Okonkwo). Throughout the book he tries to resolve the problems that develop all around him and within himself. As the story progresses, conflict overwhelms him and leads to his downfall and the downfall of the Ibo culture. One part of the book that shows how the title is developed is when Okonkwos character is introduced and explained to the reader. The author tells how he is shameful of his father and that he is belligerent and cold-hearted. Pointing out these flaws in Okonkwos character seems to foreshadow his downfall. Since Okonkwo probably represents the intolerant culture;, that cultures downfall is also foreshadowed. Later more obvious instances occur. Okonkwo kills Ikemefuna, who is like a son to him. His decision of killing the boy is definitely unreasonable, and he only acts on what he was told was right. Just like the rest of the clan he follows these customs that seem immoral and unjust to other cultures. We will write a custom essay on Things Fall Apart 6 specifically for you for only $16.38 $13.9/page Order now In another part of the story, Okonkwo is banished from his fatherland. This incident is the first where he is punished greatly for his actions. It marks a turning point in Okonkwos downfall, and therefore the downfall of the traditional culture that he stands for. His hopes and aspirations are almost forgotten while he is away from Umuofia, and he desperately tries to regain his status when he returns. During this period of time, Okonkwo also discovers that his son has converted to his enemys ways and beliefs. He abandons his son, and doesnt want to be his father any longer. This shows that his relationships with family and other people are beginning to fall apart;. The most obvious development of the theme and title takes place at the end of the book, when the final clash of cultures occurs. Perhaps it is more of a clash between Okonkwo and the new culture, since the rest of the clan seems to have deserted him. When the Christians finally take over; the clan, Okonkwo is dead and the traditional Ibo culture has fallen apart. This incident is the final conflict between the two cultures, and its the best example of what can happen to a society if its people are ignorant about others beliefs and untrue to their own.

Two Ways of Communication

Two Ways of Communication Communication is an essential part of human life. People have been created as social units and they are unable to live too long far from other human beings. During the centuries people used face-to-face type of communication with personal presence. The situation has changed with the development of the innovative technologies which has changed the style of communication.Advertising We will write a custom essay sample on Two Ways of Communication specifically for you for only $16.05 $11/page Learn More Now people can communicate without seeing each other or using the technologies to seeing the opponent but without being too close. Thus, nowadays people can experience both advantages and disadvantages of the modern technologies. Therefore the communication has become absolutely different, it is important to consider the advantages and disadvantages of modern technology and face-to-face communication. It is obvious that the face-to-face communication is consider ed to be preferable for more people than the modern technology one. One of the main advantages of the face-to-face contact is the possibility to have a personal contact. People can shake hands and this is really important. Touch contact is important in communication as it gives an opportunity to feel a person better. Face-to-face contact gives more chances to understand a person correctly as while communication we pay much attention to mimics and gestures. However, one of the main disadvantages of the face to face contact is the inability to see the person immediately when one needs it, especially when the opponents or on different continents. The supporters of the modern technology communication do not have such problems as they are able to use different means for communication and be in touch any time and at any place they need. However, those who communicate over the telephone are unable to see the face of the opponent, to check his/her face impression and gestures which are usua lly important while discussing the problem. The communication via e-mails is even more complicated and hidden as people are unable even to understand the intonation of the voice. There are different ways for communication via web camera and many people consider it as the substitute of the face-to-face communication. However, this is not true as using the web camera people can see each other, but they are unable to feel each other which is really important. Still, the main advantage of the modern technology communication remains unchanged and it is considered as a strong argument in favor of this means.Advertising Looking for essay on communication strategies? Let's see if we can help you! Get your first paper with 15% OFF Learn More Conducting a comparison and contrast analysis of the advantages and disadvantages of face-to-face and modern technology communication, it is possible to stress that each type should be used in accordance of the appropriateness of the situation. Thus, the emergency cases should be considered with the help of the modern technology communication as well as those when the situation doe not allow personal presence (for example, when relatives live far from you and you want to communicate with them). However, the serious business problems and other life conflicts or happy moments should be solved and supported only with face-to-face communication and personal presence. It is obvious that running business, those managers who deal with clients in their cabinet with the personal presence have more chances to succeed. In conclusion, it should be stated that each type of communication, either face-to-face or with the use of the modern technology should be used in an appropriate situation. Only in this case communication is going to be successful and pleasant for both opponents.

A Guide to Power Relationships in The Tempest

A Guide to Power Relationships in The Tempest The Tempest includes elements of both tragedy and comedy. It was written around 1610 and its generally considered Shakespeares final play as well as the last of his romance plays. The story is set on a remote island, where Prospero, the rightful Duke of Milan, schemes to restore his daughter Miranda to her proper place using manipulation and illusion. He conjures up a stormthe aptly named tempestto lure his power-hungry brother Antonio and the conspiring King Alonso to the island. In The Tempest, power and control are dominant themes. Many of the characters are locked into a power struggle for their freedom and for control of the island, forcing some characters (both good and evil) to abuse their power. For example: Prospero enslaves and treats Caliban badly.Antonio and Sebastian plot to kill Alonso.Antonio and Alonso aim to get rid of Prospero. The Tempest: Power Relationships In order to demonstrate power relationships in The Tempest, Shakespeare plays with master/servant relationships. For example, in the story Prospero is master to Ariel and Caliban although Prospero conducts each of these relationships differently, both Ariel and Caliban are acutely aware of their subservience. This leads Caliban to challenge Prospero’s control by taking on Stefano as his new master. However, in trying to escape one power relationship, Caliban quickly creates another when he persuades Stefano to murder Prospero by promising that he can marry Miranda and rule the island. Power relationships are inescapable in the play. Indeed, when Gonzalo envisages an equal world with no sovereignty, he is mocked. Sebastian reminds him that he would still be king and would therefore still have power – even if he did not exercise it. The Tempest: Colonization Many of the characters compete for colonial control of the island – a reflection of England’s colonial expansion in Shakespeare’s time. Sycorax, the original colonizer, came from Algiers with her son Caliban and reportedly performed evil deeds. When Prospero arrived on the island he enslaved its inhabitants and the power struggle for colonial control began - in turn raising issues of fairness in The Tempest Each character has a plan for the island if they were in charge: Caliban wants to â€Å"people the isle with Calibans, Stefano plans to murder his way into power, and Gonzalo imagines an idyllic mutually controlled society. Ironically, Gonzalo is one of the few characters in the play who is honest, loyal and kind throughout – in other words: a potential king. Shakespeare calls into question the right to rule by debating which qualities a good ruler should possess – and each of the characters with colonial ambitions embodies a particular aspect of the debate: Prospero: embodies the all-controlling, omnipresent rulerGonzalo: embodies the utopian visionaryCaliban: embodies the rightful native ruler Ultimately, Miranda and Ferdinand take control of the island, but what sort of rulers will they make? The audience is asked to question their suitability: Are they too weak to rule after we have seen them manipulated by Prospero and Alonso?

Technological, Designs & Art Developments Assignment

Technological, Designs & Art Developments - Assignment Example Art is an aspect that is intertwined with culture and traditions and as culture and traditions changed towards civilization so did art. Significant inventions in history changed the approached towards art as artists sought to embrace emerging technologies to be able to portray their art more effectively while at the same time improving on aesthetics. According to Kleiner (2010), developments in art have always occurred roughly during similar periods in history as developments in other fields such as science, philosophy and politics. Therefore, the general realization is that art is an aspect that is intertwined with developments in other areas due to the need for artists to respond to these developments either by critiquing or seeking to highlight important aspects of these developments. The following timeline project will conduct an analysis on the developments in art and design from the 15th to the 20th century with a specific emphasis on four genres. The four genres of focus will be sculptures, drawings, paintings and architecture. The timeline has revealed that art was significantly influenced by historical periods and advancements in the fields of science, politics and philosophy. Moving from the Gothic era to the modernism era, there is the realization that art is a significant part of the society and that art responds to societal changes. During the Gothic era when the Catholic Church significantly influenced most aspects of life, art basically responded to this influence by concentrating on religious designs. The renaissance art on the other hand sought detachment from the church and sculptures could be evident in streets. Baroque art was significant in introducing the use of oil paints. During the enlightenment era, the Catholic Church sought to regain its popularity through art but in vain due to the protestant influences. The Romantic era depicted art not as it is but as it ought to be with regard

Read the three articles in the instructions . Then, write three Assignment

Read the three articles in the instructions . Then, write three synopsis of the work - Assignment Example uses direct communication). He comments that the concepts of high-context and low-context cultures and polychronic (i.e. multitasking) versus monochronic time (i.e. one thing at a time) orientation are useful, but ambiguous. The next theory comes from Hofstede’s cultural dimensions. These dimensions pertain to: power distance, individualism /collectivism, masculinity/femininity and uncertainty avoidance (Dahl 12). Dahl commends the model for its simplicity and widespread application on different cultural interactions. Dahl also explains Trompenaars and Hampden-Turner’s seven value orientations. These orientations are: universalism versus particularism; communitarianism versus individualism; neutral versus emotional; defuse versus specific cultures; achievement versus ascription; human-time relationship and; human-nature relationship (Dahl 14). Dahl explains the connections between these orientations and other intercultural theories. In addition, Dahl describes Shalom Schwartz’s Schwartz Value Inventory (SVI). SVI has two categories: individual-level analysis and cultural-level analysis. Dahl concludes that there is no one theory of cultural dimensions. In the article, â€Å"What Do Employers Really Want? Top Skills and Values Employers Seek from Job-Seekers,† Randall S. Hansen and Katharine Hansen discuss the major skills and values that employers desire from their employees. They want to help job-seekers become more employable for target employers by explaining these skills and values and how the latter can appear in resumes, cover letters, and interviews. Hansen and Hansen discuss that the top main skills that employers want from employees are: communication skills, analytical/research skills, technical literacy, flexibility, interpersonal abilities, leadership and management skills, multicultural sensitivity, planning and organizing skills, problem-solving/reasoning/creativity skills, and teamwork

The Corrosion Of Metals Engineering Essay

The Corrosion Of Metals Engineering Essay Each year, billions of dollars are spent on repairing and preventing the damage of metal parts caused by corrosion, the electrochemical deterioration of metals. The majority of metallic materials in a practical context are generally exposed to corrosion in both atmospheric and aqueous environments. Metallic corrosion has become a global problem which has negatively affected the industrialised society; hence why it has been studied in such comprehension since the beginning of the industrial revolution in the late eighteenth century. Corrosion also affects the average daily life both directly, as it affects the commonly used service possessions and indirectly, as producers and suppliers of goods and services incur corrosion costs, which they pass on to consumers. (ASM International, 2012). The effects of corrosion are distinctively recognized on automobile parts, charcoal grills and metal tools all of which will have a depleted efficiency once corroded. This corrosion may result in con tamination which then poses health risks. For example, the pollution due to escaping product from corroded equipment or due to a corrosion product itself. As a result of these consequences, corrosion prevention has been studied in great depth. Corrosion of various metals may be prevented by applying a coating of paint, lacquer, grease of a less active metal to keep out air and moisture. These coatings will continue to suppress the effects of coating so long as they stay intact. Examples of metals that are heavily protected in the industrial world are iron and aluminium. Vast quantities of the ores or each metal are mined and processed each year using large scale chemical reactions to produce metals of the purity required for their end use. For this report, the chemistry involved in the corrosion of both iron and aluminium will be researched as well as the methods employed to prevent their corrosion. Justification as to why corrosion happens will be explained with reference to physic al and chemical properties, electrochemistry, equilibrium, rates of reaction, enthalpy and solubility at every point where it is appropriate. Before explaining why corrosion happens, it is important to define corrosion in terms of electrochemical processes. An electrochemical reaction is defined as a chemical reaction involving the transfer of electrons through redox. Corrosion is a broad and complex subject that can be examined in three different categories; electrochemical corrosion, galvanic corrosion and electrolytic corrosion. In all forms of corrosion, three components must be present an anode, a cathode, a metallic path for electrons to flow through, and an electrolyte for the ions to flow through. Both the anode and the cathode must be in contact with the electrolyte to allow the ions to flow. As well as this, oxygen and hydrogen must also be available, either directly or as a result of chemical action and the resultant dissociation of water into its two constituents. In this report, electrochemical will be investigated in terms of its spontaneous nature and self-sustainability. Firstly, spontaneity is dependent on the sign of free energy. Gibbs free energy can be defined by the following equation:; where is the enthalpy, is entropy and is the temperature in kelvins. When is negative, the reaction will occur spontaneously (Zhang, H. 2012). For this to occur the entropy must increase and the enthalpy must decrease. This can be proven as a system of spontaneity aims towards disorder which directly coincides with entropy. Also, the change in enthalpy must be negative as thermal energy will be released from the energy stored within chemical bonds in a spontaneous system. Furthermore, in this electrochemical procedure, the negative electrode is the cathode and the positive electrode is the anode. Note that metals are used as they are good conductors of electric current due to the specific ionic bonding which then allows the electrons to be delocalized and move relatively freely. When these two electrodes are connected by a wire, free electrons flow through the wire from the anode to the cathode forming an electric current. Both the anode and cathode are submerged in separate substances respective to the elements of both electrodes from which the positive ions are attracted to the anode and the negative electrons are attracted to the cathode. The anode atoms are being oxidised as they are losing electrons and forming positive ions which then dissolves into solution. This results in a loss of overall quantity of zinc metal. In practical terms, this could be considered the pitting of the corrosion process which can be defined as a form of extremely local ized corrosion that leads to the creation of small holes in the metal (ASM International, 1987). Electrons formed at the anode travel to the cathode where they combine with the positive ions in solution to turn into the respective metal. Therefore the cathodic ions in solution are being reduced as they are gaining electrons. This production of extra cathode metal can be compared with rust which is a reddish- or yellowish-brown flaky coating of iron oxide that is formed on a metal by redox reactions. With just this in mind, the electric current would flow for only a limited time as the anode would have a build-up of positive ions being formed. While at the cathode increased amounts of electrons are being pumped into it. The result is an excessive positive charge that builds up at the anode that attracts electrons (negative) and prevents them moving away. While at the cathode the negative build up repels the electrons. As a consequence of this build-up of charge, no electron flow occurs and the cell eventually fails (Dynamic Science, 2012). Note that a solution cannot have a full charge and only a partial charge. To negate this issue, a salt bridge is used which contains ions that complete the circuit by moving freely from the bridge to the half cells. The substance that is placed into the salt bridge is usually an inert electrolyte whose ions are neither involved in any electrochemical change nor do they react chemically with the electrolytes in the two half-cells (IIT, 2012). As well as completing the circuit, it ensures that the charge between the two half cells remains electrically neutral. It does this by passing negative ions into the anodic half-cell where there shall be an accumulation of extra positive ions due to oxidation resulting in a slightly positive charge. Similarly, an accumulation of negative ions will exist in the cathodic half-cell due to the deposition of positive ions by reduction. Electrical neutralization is once again achieved by the salt bridge providing positive ions to the cathodic substance. Thus, the salt bridge maintains electrical neutrality. IRON CORROSION Only a few metals, such as copper, gold and platinum occur naturally in their elemental forms. Most metals occur in nature as oxides in ores, combined with some unusable metal like clay or silica. Ores must be processed to get the pure metals out of them, and there are nearly as many different processes for this purpose as there are metals. The process, as well as the elements present, greatly influences the properties of the metal. An important characteristic of metals is the extremely significant effect that very small amounts of other elements can have upon their properties. The huge difference in properties resulting from a small amount of carbon allowed with iron to make steel is an example of this. Taking into consideration the amount of iron that is used globally, the effect of corrosion on iron alone requires millions of dollars each year. The problem with iron as well as many other metals is that the oxide formed by oxidation does not firmly adhere to the surface of the meta l and flakes off easily causing pitting (KKC, 2012). Extensive pitting eventually causes structural weakness and disintegration of the metal. The iron oxide acts as a sacrificial anode which is a stronger reducing agent than iron that is oxides instead of the protected metal. Therefore it can be said that it acts as the anode. Since the oxide does not firmly adhere, it does little to protect the iron metal. As mentioned, iron in contact with moisture and air (oxygen) is corroded by a redox reaction. The anode reaction can be expressed as an oxidation of iron atoms: Both water and oxygen are required for the next sequence of reactions. The iron ions are further oxidized to form ferric ions (iron ) ions. This can be written as: These electrons are then conducted through the metal and are used to reduce atmospheric oxygen to hydroxide at another region of the iron. Therefore the cathodic reaction is: Considering that iron atoms dissolve at the anodic sides to form pits and ions which diffuse toward the cathodic sites; ions are formed at cathodic sites diffuse toward the anodic sites. Iron (II) hydroxide forms in a random location between the cathode and the anode which is then oxidised by atmospheric oxygen to iron (III) hydroxide. This can be expressed by: From here, the iron (III) hydroxide is then gradually converted to rust otherwise known as hydrated iron (III) oxide: ; Where generally equals 3. The formation of rust does not have a designated position as it can occur at random away from the actual pitting or corrosion of iron. A possible explanation of this is that the electrons produced in the initial oxidation of iron be electrically conducted through the metal and the iron ions can diffuse through the water layer to another position on the metal surface which is available to the atmospheric oxygen (KKC, 2012). Also, points of stress, such as where the piece of metal has been shaped, are more active than unstressed regions and thus act as anodic sites. The electric current between the anodic and cathodic sites is completed by ion migration; thus, the presence of electrolytes increases the rate of corrosion by hastening this mitigation. Therefore it is evident that the corrosion of iron can be directly related to a voltaic cell and can both be defined as electrochemical cells due to their spontaneous nature. ALUMINIUM CORROSION Similar to Iron, aluminium is also susceptible to electrochemical corrosion when exposed to moister. Aluminium, both in its pure state and allow, is truly a remarkable metal as it is light, tough, strong and readily worked by all common processes. Unlike iron however, It has excellent resistant to corrosion in the marine environment, and it requires little maintenance. The fundamental reactions of the corrosion of aluminium in aqueous medium have been the subject of many studies. In simplified terms, the oxidation of aluminium in water proceeds according to the equation (ELSIVIER, 2012): This specific reaction is balanced by a simultaneous reduction reaction, similar to iron, in ions available in the solution which then consumes the oxidised electrons. In an aqueous solution such as fresh water, seawater or moisture, thermodynamic considerations can be used to represent only two possible reduction reactions that can occur. The other occurring reaction is the reduction of oxygen dissolved in the moisture: Quite similar to the corrosion of iron, the aluminium atoms dissolve at the anodic sites to once again form pits and which diffuse toward the cathodic sites while ions are formed at the cathodic sites and diffuse toward the anodic sites. Therefore: ; Where generally equals 3. Although aluminium is still susceptible to corrosion, the metal itself is very resistive. Aluminium alloys generally have excellent resistance to atmospheric corrosion; require no protective coatings or maintenance beyond cleaning, which aids greatly in preventing unsightly pitting where dirt or salt accumulate. When aluminium is exposed to oxygen, it forms an oxide surface film that protects it from corrosive attack. The oxide acts as a sacrificial anode which is a stronger reducing agent than aluminium. It is then oxidised instead of the protected aluminium metal, serving as the anode. For the most part, damage due to atmospheric corrosion is pretty much limited to fairly slightly pitting of the surface with no significant loss of material or strength. Duration of exposure is an important consideration in aluminium allows, the rate of corrosion decreases with time to a low steady rate regardless of the type of allow or the specific environment. Thus corrosion of both aluminium and iron can both be defined as electrochemical processes which are similar in nature but have different protection potentials. PROTECTION METHODS Corrosion avoidance begins in the design process. Although corrosion concerns may ultimately reduce structural integrity, they should be a consideration to decrease money loss. Good maintenance practices are another way of avoiding corrosion, such as rinsing away salt water or avoid standing water. Corrosion protection systems, for the most part, are designed to control corrosion, not necessarily eliminate it. The primary goal is to reduce the rate of corrosion by having the smallest possible current. Current is defined as the flow of charge, or electrons, per time through a conductor hence. Since corrosion is the movement of electrons through redox, it can be quantified using this equation which represents the corrosion reaction per time or the corrosion rate. To do this, two efficient protection methods are available: cathodic protection systems and coatings. All cathodic protection schemes operate on the basis of the voltaic corrosion process, so like voltaic corrosion; cathodic protection systems require an anode, a cathode, an electrical connection and an electrolyte. Cathodic protection will not reduce the corrosion rate if any of these four things are missing. The basis of this protection method depends on the difference in corrosion potentials between the two metals immersed in the same electrolyte. This causes electrons to flow from the metal with the higher activity and negative potential (anode) to the metal with less activity and negative potential (cathode). This flow of electrons continues until the two metals are at the same potential, that is, there is equilibrium between the voltages. Electrode potential is a measure of the tendency for a material to be reduced e.g. accepts electrons. Also, activity is a measure of how easily a metal will give up electrons. Thus, the more active a metal is, the more negative the electrode p otential. This principle, directly relates to the two types of cathodic protection systems: sacrificial anode systems called passive protection and impressed current systems also known as active protection. Sacrificial anode systems are simple, require little but regular maintenance, and have low installation costs. We intentionally add a metal to the circuit to supply the electrons to the cathode. When metals are in a voltaic couple, the difference in there negative potentials causes the anodic metal to corrode and release metallic ions into the electrolyte. The more negativity in the corrosion potential means it will be a stronger reducing agent and will more readily give away electrons thus corroding first. Since the more negative metal in the closed circuit corrodes first, we can control corrosion by simply adding to the circuit a metal that possess two necessary characteristics: a corrosion potential more negative than the metal that is being protected, it is expendable which is not essential to the operation of any particular system. Therefore when a metal possessing these characteristics is made the anode, corrosion is controlled. The impressed-current type of cathodic protection system depends on an external source of direct current. Alternating current cannot be used since the protected metal would likewise be alternating, between anodic and cathodic. Basically, the anode is immersed in the electrolyte is connected to one side of a DC power supply and the metal to be protected is connected to the other side. The voltaic current flow is detected and measure against a reference electrode. If unfavourable, current flow is adjusted automatically by the power supply control system to compensate. Due to the high currents involved in many seawater systems, it is not uncommon to use impressed current systems in marine situations. Impressed current systems use anodes (ICCP anode) of a type that are not easily dissolved into metallic ions, but rather sustain an alternative reaction, oxidization of the dissolved chloride ions (Deepwater, 2012). Advantages of this cathodic protection are that they can develop so much higher voltages than sacrificial anode systems, so they can either push current through lower conductivity electrolytes or through longer distances. Disadvantages include the possibility of over protecting certain metals. This can cause hydrogen embrittlement in high strength steels. In aluminium specifically, accelerated corrosion can occur of the very structure that is being protected. Therefore it is evident that this form of cathodic protection, although more complex, poses some reliable advantages as well as some detrimental disadvantages.

Compaction of Concrete

Consolidation of plastic concrete is termed as compaction. In the process of compaction, efforts are only directed to reduce the voids in the compacted concrete. Compaction of concrete can be done either manually or mechanically. When it is done manually it is called hand compaction or tamping, and in second case it is termed as machine compaction. ?Hand compaction: Hand compaction is done with the help of steel tamping rods, or timber screeds. Marrow and deep members are compacted with tamping rods. Thin slabs and floors are tamped with the help of screeds.Compaction should be done in layers of 30 cm for mass concrete and 15 cm for reinforced concrete. Companction should be carried out for such a time that a layer of mortar starts appearing at the compacted surface. Excessive compaction and under compaction both are harmful for concrete. Due to excessive compaction, C. A. particles sink to the bottom and cement and F. A. mortar appears at the top. This makes concrete structure heter ogeneous, and hence affects strength. This method of curing is adopted in the case of precast members.It has been noticed that by keeping the wet conditions, if temperature is increased, the rate of increase of strength also increases. This enables concrete to acquire its full strength within short period and hence, curing is also finished within short period. ?Machine compaction: Machine or mechanical compaction of concrete is done with the help of vibrators. Vibrators produce vibrations which when transmitted to plastic concrete make it to flow and affect compaction. The air bubbles are forced out of concrete due to vibrations. Over vibration should not be allowed, otherwise C.A. particles will concentrate at the lower layers and mortar will come to the surface. There are three types of vibrators in most common use: †¢Internal vibrator: This vibrator is also known as immersion, poker, or needle vibrator. It consists of a power unit and a long flexible tube at the end of which a vibrating head is attached. This vibrator develops about 7000 vibrations per minute. Wherever, compaction is to be done, the vibrating head is inserted in the concrete. This vibrator is very useful for compaction of mass concrete. †¢Form vibrator: This vibrator is clamped to he form-work and imparts vibrations to the concrete through form-work. This vibrator is used only if the use of internal vibrator is not practicable as in the case of thin and congested situations. It is also called external vibrator. †¢Surface vibrator: It is also named as screed or pan vibrator. It is clamped to the screed, it Imparts vibration to the concrete from the surface when screeding operation of the concrete is carried out. It is effective only for depths of about 20 cm and hence useful for thin horizontal surface such as pavements. Compaction of Concrete Consolidation of plastic concrete is termed as compaction. In the process of compaction, efforts are only directed to reduce the voids in the compacted concrete. Compaction of concrete can be done either manually or mechanically. When it is done manually it is called hand compaction or tamping, and in second case it is termed as machine compaction. ?Hand compaction: Hand compaction is done with the help of steel tamping rods, or timber screeds. Marrow and deep members are compacted with tamping rods. Thin slabs and floors are tamped with the help of screeds.Compaction should be done in layers of 30 cm for mass concrete and 15 cm for reinforced concrete. Companction should be carried out for such a time that a layer of mortar starts appearing at the compacted surface. Excessive compaction and under compaction both are harmful for concrete. Due to excessive compaction, C. A. particles sink to the bottom and cement and F. A. mortar appears at the top. This makes concrete structure heter ogeneous, and hence affects strength. This method of curing is adopted in the case of precast members.It has been noticed that by keeping the wet conditions, if temperature is increased, the rate of increase of strength also increases. This enables concrete to acquire its full strength within short period and hence, curing is also finished within short period. ?Machine compaction: Machine or mechanical compaction of concrete is done with the help of vibrators. Vibrators produce vibrations which when transmitted to plastic concrete make it to flow and affect compaction. The air bubbles are forced out of concrete due to vibrations. Over vibration should not be allowed, otherwise C.A. particles will concentrate at the lower layers and mortar will come to the surface. There are three types of vibrators in most common use: †¢Internal vibrator: This vibrator is also known as immersion, poker, or needle vibrator. It consists of a power unit and a long flexible tube at the end of which a vibrating head is attached. This vibrator develops about 7000 vibrations per minute. Wherever, compaction is to be done, the vibrating head is inserted in the concrete. This vibrator is very useful for compaction of mass concrete. †¢Form vibrator: This vibrator is clamped to he form-work and imparts vibrations to the concrete through form-work. This vibrator is used only if the use of internal vibrator is not practicable as in the case of thin and congested situations. It is also called external vibrator. †¢Surface vibrator: It is also named as screed or pan vibrator. It is clamped to the screed, it Imparts vibration to the concrete from the surface when screeding operation of the concrete is carried out. It is effective only for depths of about 20 cm and hence useful for thin horizontal surface such as pavements.