Free Essay

Alkali Aggregate Reaction Phenomenon

In: Miscellaneous

Submitted By Thanu57
Words 1684
Pages 7
CHAPTER 01 – INTRODUCTION

1.1 General background

“Studying the effect of deterioration on the performance of structures is important because much of the nation’s essential infrastructure is aging. The alkali-aggregate reaction phenomenon is the cause of considerable damage to concrete structures built during the late 1920s to early 1940s” (Osama, Mohamed et.al, 2001). “Numbers of concrete structures in California, USA, was observed to develop severe cracking within a few years of their construction, although quite acceptable standards of construction and quality control of materials were employed. It was a major scientific achievement with far-reaching consequences when Stanton in 1940 was able to demonstrate the existence of alkali-aggregate reaction as an intrinsic deleterious process between the constituents of a concrete. The damage was the result of cracking throughout the concrete, manifested at the surface as extensive map cracking or pattern cracking or surface popouts and spalling. Such problems where confined mostly to certain regions of the country” (Osama, Mohamed et al., 2001). ASR was since been discovered in a number of concrete structures around the world, and has become truly a concrete durability problem with an international dimension.

Alkali Aggregate reaction (AAR) is a chemical reaction occurring between alkalis derived from Portland cement and certain aggregates which are susceptible to this reaction.

1.2 Types of reactions

AAR has been divided into two types of reaction depending on the types of minerals involved.
Alkali-Carbonate Reaction (ACR)
The Alkali-Carbonate Reaction is a chemical reaction between hydroxyl ions associated with the alkalis sodium and potassium in the cement and certain dolomitic textures in the aggregate resulting in expansion and eventually cracking of the hardened concrete.

Alkali-Silica Reaction (ASR)
It is of more concern because aggregates containing reactive silica materials are more common. In ASR, aggregates containing certain forms of silica will react with alkali hydroxide in concrete to form a gel that swells as it adsorbs water from the surrounding cement paste or the environment. These gels can swell and induce enough expansive pressure to damage concrete.
“Most of the structures severely cracked by AAR are exposed to the weather or underground in contact with damp soil. This is because for significant expansion to occur presence of moisture is essential. Apart from the moisture, High content of alkali in the concrete and reactive minerals are also essential.” (ACI Committee 221, 1998)
From the above it can be seen that AAR expansion to occur in concrete, it is necessary to have * sufficient moisture supply, * high content of alkali in concrete, and * pessimum amount of reactive minerals in aggregate.

“It is also found that, when there is sufficient moisture and alkali, maximum expansion of concrete due to AAR occurs when the content of reactive minerals in aggregate is within a sensitive region, some refer to this as "pessimum" content. Content of reactive minerals below or greater than the pessimum value, AAR expansion reduces” (Neville, 1990).

“Certain factors influence the behavior of concrete affected by AAR regardless of the type of rock or minerals. In all cases increases in expansion result from increases in available alkali, water is a requirement, and higher temperatures of exposure or accelerated curing increase expansion. However there are significant differences in behavior between different types of material. Concrete containing opal, crystobalite, tridymite and man made glasses, often expands relatively rapidly whereas the rate of expansion of concrete made with chalcedony, greywacke and related rocks is often very slow” (Gillott, 1995).

1.3 Tests methods
Numerous tests have been devised to ascertain whether a particular aggregate or concrete mix will develop alkali-silica reactivity. These tests centre on checks concerning either the aggregate alone or the concrete mix or a simplified variant of it.

Common Test Methods to assess ASR
• Petrographic Examination (ASTM C 295)
• Chemical Test (ASTM C289 – 03)
• Accelerated Mortar Bar Test (ASTM C 1260 - 05a)
• Concrete Prism Test (CPT)
• Accelerated Concrete Prism Test (ACPT)
Petrographic examination is the process of identifying the types of minerals in aggregate or concrete section by observation using microscope or other aids. This method can identify types of minerals in the aggregate and give suggestions as for whether the aggregate is potentially reactive or not. Because the uncertainties involved in the test, the method is generally used as a screening test as a part of an investigation.
Many proposed test methods using chemical analyses to identify potential reactivity of aggregate. ASTM C389-87 chemical test (ASTM 1987a), for example, evaluates aggregate reactivity by measuring the amount of dissolved silica and the reduction of alkalinity in the reaction alkali solution. (ACI Committee 221, 1998)
Accelerated Mortar Bar Test
The aggregate to be evaluated is crushed to sand size and mortar bars (25mm x 25mm x 285 mm) are made with it. After the mortar has set, the length of the bars is measured and the bars are stored, immersed in sodium hydroxide solution, at 80°C. The change in length of the bars is monitored periodically for 14 days. Expansions greater than 0.15% at 14 days are considered to be indicative of potentially deleterious expansion of the aggregate in concrete having high alkali content. This test is appropriate only for alkali-silica reactive aggregates. Although this mortar test does not exactly replicate how concrete will behave, the test is a good indicator of potential reactivity and has the great advantage of being quick.
Concrete Prism Test
The concrete prism test is applicable to both alkali-silica and alkali-carbonate reactive aggregates. The coarse aggregate is made into concrete prisms (75mm x 75mm x 275 mm). After de-molding, the length of the prisms is measured. They are then placed in sealed containers over water to maintain a humidity of over 95%. The containers are stored in an enclosure maintained at 38°C and the length of the prisms is monitored periodically for one year. Expansion greater that 0.04% at one year considered being indicative of potentially reactive aggregates.
“It should be noted that the methods that have been proposed so far have their limitations. Some succeeds in identifying reactivity for certain aggregates whereas fails for others. Therefore it is difficult to ascertain an aggregate is absolutely non-reactive using the currently available testing methods”
“The most evident manifestations of deleterious AAR in a concrete structure are map cracking, displacement of structural member due to internal expansion of the concrete, and popouts. However, these features should not be used as the only indicators in the diagnosis of AAR in the concrete structure. Cracking in concrete is essentially the result of the presence of excessive tensile stress within the concrete” (ACI Committee 221, 1998)
“The external appearance of the crack pattern in a concrete member is closely related to the stress distribution within the concrete. The distribution of strain is, among other things controlled by the location and type of reinforcement, and the structural load imposed upon the concrete. Expansion of a concrete element will tend to occur in the direction of least restraint. Cracks caused by the expansion due to AAR tend to align parallel to the direction of maximum restraint” (ACI Committee 221, 1998)
Controlling the alkali-aggregate reaction, researches tend to pay attention towards the prediction and precautionary measures. So it is necessary to develop a method that can be used for predicting the effect of alkali-aggregate reaction in an easily available way. In order to fulfill this method, we are proposing general purpose finite element package SAP2000 and computer language to predict the expansion of alkali-aggregate reaction.
1.4 Remedies

Minimizing the chances of AAR in new structures
“There are several preventative actions which will reduce the risk of occurrence of all three varieties of AAR. Most of the actions require detailed knowledge of the performance of either the cements or aggregates proposed to be used. The most recommended action is the inclusion of fly ash, so that if a potential for reaction does exist, the fly ash will mitigate its effects” ( Barry Butler,1998).
This reaction can be controlled by: * Avoiding susceptible aggregates. Local experience may show that certain types of rock contain reactive silica. Typically rock types that may be susceptible are: siliceous limestone, chert, shale, volcanic glass, synthetic glass, sandstone, opaline rocks and quartzite. River rock is also typically susceptible. * Pozzolanic admixture. By reacting with the calcium hydroxide in the cement paste, a pozzolan can lower the pH of the pore solution. Additionally, the silica contained in a pozzolan may react with the alkali in the cement. This reaction is not harmful because it essentially skips the expansive water attraction step. * Low-alkali cement. Less alkali available for reaction will limit gel formation. * Low water-cement ratio. The lower the water-cement ratio, the less permeable the concrete. Low permeability will help limit the supply of water to the alkali-silica gel.

Remedial measures in existing structures
“Remedial measures varied depending on the degree of distress and the function of the concrete. Damage may be so severe that complete replacement of the concrete is the only solution. If the expansion rate is declining and the structural effects appear small, repair may be attempted by the partial replacement of concrete, installation of improved reinforcement including steel plate adhesion, injection of resin, or cementitious material to decrease permeability, and the use of waterproof surface coatings and cutting of transverse slot by means of a diamond wire. Opening joints or cutting slots by sawing to relieve internal stresses has been the most common remedial action to keep mass-concrete structures in service. In this process, a continuous loop of wire embedded with cutting diamonds makes the desired cut.” (Gillott, 1995)

1.5 Aim
This project is aimed at developing a SAP based finite element procedure to investigate the potential of Alkali Aggregate reaction in concrete and use it to investigate the potential of AAR in a 3-D concrete structure.

1.6 Scope
Scope of the project is to predict the development of stress and deformation due to Alkali Aggregate reaction in 3-D structures by using general purpose finite element package “SAP 2000”.…...

Similar Documents

Premium Essay

The Eureka Phenomenon

...The Eureka Phenomenon uses examples throughout the story to support a certain way of dealing with a problem. The problem was when you get stuck trying to figure something out, how to get yourself back on track. Well, one of the examples used to figure out that situation was one about a king thinking that he got screwed over on the amount of gold used on his crown. The story supported the original problem, but equations were then brought into the story later on. These equations seemed to play no important role in the story in my opinion. The story talks about molecules and atoms, but I do not see the point in doing so. I believe this was just meant to make the story seem more important than what it truly is. By adding in the equation to the story, it cause confusion and makes it boring. I don’t see how using these equations help to prove the problem at the beginning of the story. The equations just seem to be added in for no reason and get the whole story off topic. The equations are just plain confusing. I may not be the best at science, but I am not the worst either, and I still don’t understand these equations. I have read over them all more than twice, and I am hopeless when it comes to trying to understand them. The story does attempt to explain the equations, but not to the level in which anyone reading the story could understand. All of the examples that have been told throughout the story, all had to do with science and equations, but why? The......

Words: 574 - Pages: 3

Premium Essay

Aggregate Demand

...specific aggregate demand determinants assumed constant when the aggregate demand curve is constructed, and that shifts the aggregate demand curve when it changes. An increase in the inflationary expectations causes an increase (rightward shift) of the aggregate curve. A decrease in the inflationary expectations causes a decrease (leftward shift) of the aggregate curve. Other notable aggregate demand determinants include interest rates, federal deficit, and the money supply. (www.amosweb.com) The expectations for inflation are that the consumers concerning future inflation. Inflationary expectations and aggregate demand work together like buyers' expectations work for market demand. When purchasing goods, the buyer looks for the lowest possible price. Expecting Higher Inflation Rates Suppose that the inflation rate has been running at a nice constant low rate for several years. Households have been able to include this specific inflation rate into their assorted plans. Now suppose that irresponsible monetary policy causes an increase in the inflation to a higher percent one year, and then continued to climb for the next several years. This would cause a major problem with the household sector and many individuals would be in trouble. The individuals would adjust their expenditures in consumption and spend more because they would realize that the house payment will be in the rise for the next couple of years. The increase in consumption expenditures will increase aggregate......

Words: 265 - Pages: 2

Free Essay

Reaction

...What is a reaction paper? Reaction or response papers are designed so that you'll consider carefully what you think or feel about something you've read or seen. Instructions Read or view whatever you've been asked to respond to read or view. While reading or viewing think about the following questions: • How do you feel about what you are reading (seeing)? • With what do you agree or disagree? • Can you identify with the situation? • What would be the best way to evaluate what you read or see? Pre-writing for Your Reaction Paper Keeping your responses to these questions in mind, complete as many statements as possible about what you read or saw. 1. I think that ____________________________________________________________________________________________________________________________________ 2. I see that ____________________________________________________________________________________________________________________________________ 3. I feel that ____________________________________________________________________________________________________________________________________ 4. It seems that ____________________________________________________________________________________________________________________________________ 5. In my opinion ____________________________________________________________________________________________________________________________________ 6. Because _______________...

Words: 361 - Pages: 2

Premium Essay

Aggregate Demand

...Unit 3 Managing the economy Steve Margetts CONTENTS Aggregate Demand (AD) Aggregate Supply Equilibrium Between Aggregate Demand And Aggregate Supply Consumption And Savings Investment Government Spending Exports and Imports Objectives Of Government Macroeconomic Policy Inflation Unemployment Economic Growth Balance of Payments Conflicts Between Macro Economic Objectives Demand Management or Supply Side? 2 4 9 11 17 25 29 31 34 50 71 80 84 87 Page 1 Unit 3 Managing the economy Steve Margetts AGGREGATE DEMAND (AD) Aggregate demand (AD) is the total demand for goods and services produced in the economy over a period of time. DEFINING AGGREGATE DEMAND Aggregate planned expenditure for goods and services in the economy = C + I + G + (X-M) C Consumers' expenditure on goods and services: This includes demand for durables & non-durable goods. I Gross Domestic Fixed Capital Formation - i.e. investment spending by companies on capital goods. Investment also includes spending on working capital such as stocks of finished goods and work in progress. G General Government Final Consumption. i.e. Government spending on publicly provided goods and services including public and merit goods. Transfer payments in the form of social security benefits (pensions, jobseekers allowance etc.) are not included as they are not a payment to a factor of production for output produced. A substantial increase in government spending would be classified as an expansionary fiscal......

Words: 24295 - Pages: 98

Premium Essay

Aggregate Demand

...Aggregate Demand and Supply Models Karen Burke ECO/372 January19, 2015 Neal Johnson Aggregate Demand and Supply Models Unemployment rates are considered an economic factor because of the effect that these rates have on the general economy. These rates affect not only individual households but communities as well, sometimes on quite a large scale. Unemployment affects demand by shifting the aggregate demand curve to the left. There are fewer consumers creating a demand for goods and services. This could also affect those who supply goods in services in that there will be less demand for that particular business and could lead to more unemployment. Unemployment shifts the aggregate supply curve to the left as well. The current U.S. unemployment rate stands at 5.60 percent as of December 2014 (tradingeconomics.com 2015). This number is down from 5.80 percent is November 2014. There are some analysts who believe that demand is responsible for causing restraints within the U.S. economy. According to Mark Thoma of MoneyWatch “This is an important debate because if the fall in unemployment is mostly structural, there's little that monetary and fiscal policy can do to help to speed the recovery. But if lack of demand is the main culprit, then replacing the lost demand through aggressive policy can help us recover faster.” (cbsnews.com 2012). Therefore it is recommended that the government keep tax rates as the currently stand. Increasing the amount of taxes paid could lead......

Words: 324 - Pages: 2

Premium Essay

Aggregate Planning

...Chapter 8: Aggregate Planning in a Supply Chain Exercise Solutions : We define a comprehensive set of decision variables that are utilized in problems 8-1 to 8-3 depending on the problem context. Decision Variables: Ht = # of workers hired in month t (t = 1,..,12) Lt = # of workers laid-off in month t (t = 1,..,12) Wt = # of workers employed in month t (t = 1,..,12) Ot = # of hours of overtime in month t (t = 1,..,12) It = # of units (000s) held in inventory at the end of month t (t = 1,..,12) Ct = # of units (000s) subcontracted in month t (t = 1,..,12) Pt = # of units (000s) produced in month t (t = 1,..,12) Parameters: Dt = # of units (000s) demanded in time period t (t = 1,…12) Problem 8-1: Minimize [pic] Subject to: Inventory constraints: [pic] [pic] Overtime constraints: [pic] Production constraints: [pic] Workforce constraints: [pic] (a) Worksheet 8.1 provides the solution to this problem and the corresponding aggregate plan. The total cost of the plan is $360,400,000. (b) If the number of overtime hours per employee were increased from 20 to 40 it would result in decreasing the total cost to $356,450,000. So, it is advantageous to do it. (c) If the number of employees is decreased to 1200 and the overtime hours per employee are held at 20 and 40 then the total costs of the plan are $363,324,000 and $357,422,000, respectively. If the number of employees is increased to 1300 and the overtime hours per......

Words: 2109 - Pages: 9

Premium Essay

Acids and Alkalis

...| 5.5 Acids and Alkalis Properties of Acids 1. Acids – sour taste 2. Turns blue litmus paper red 3. pH <7 4. corrosive 腐蚀性 5. react with metals hydrogen gas Example : Hydrochloric acid + Zinc Zinc chloride + Hydrogen | 6. Uses of Acids: a) Hydrochloric acid – clean metals, make dyes b) Citric acid – juices c) Formic acid – coagulate latex d) Benzoic acid/Acetic acid – preserve food e) Tartaric acid – bake cakes, soft drinks f) Acetic acid – vinegar g) Nitric acid – fertilizers, explosives h) Ascorbic acid – Vitamin C tablets i) Sulphuric acid – electrolytes in car batteries, fire extinguisher Properties of Alkalis 1. Alkalis – bitter taste, soapy feeling 2. Turns red litmus paper blue 3. pH >7 4. corrosive 腐蚀性 5. react with ammonium salts ammonia gas Example : Sodium hydroxide + Ammonium chloride Ammonia gas + Sodium chloride + Water | 6. Uses of Alkalis: a) Sodium hydroxide / Potassium hydroxide – soaps b) Calcium oxide – cement, slaked lime c) Ammonium hydroxide – prevent coagulation of latex d) Magnesium hydroxide – toothpaste, milk of magnesia Neutralisation 1. | Acid + Alkali Salt + Water (Neutralisation) | Example 1 : Hydrochloric acid (Acid) + Sodium Hydroxide (Alkali) Sodium chloride (Salt) + Water | Example 2 : Sulphuric acid (Acid) + Magnesium Hydroxide (Alkali) Magnesium......

Words: 798 - Pages: 4

Premium Essay

Aggregate Planning

...flow of materials  The typical manufacturer spends more than 60 percent of its total income from sales on purchased services and materials, whereas the typical service provider spends only 30 to 40 percent. 6 Inventory measures and financial measures used to monitor supply chain performance and evaluate alternative supply chain designs. Average aggregate inventory value Inventory turnover Days of supply 7  Average aggregate inventory value = the total value of all items held in inventory for a firm. AGV = (# of A items)(Value of each A)+(# of B items)(Value of each B)+…   Inventory turnover ratio: showing how many times a company's inventory is sold and replaced over a period. Inventory turnover =  Annual sales at (cost) Average aggregate inventory value Low inventory turnover means that a company has poor sales or too much inventory while high inventory turnover means strong sales performance. 8    Days of supply: It shows how many days it takes a company to sell its inventory. High value of days of supply means that the firm has a lot of inventory sitting around. Days of supply =  Average aggregate inventory value *365 days Cost of goods sold If the cost of goods sold during the year has been $1 million and the average inventory value for the year has been $100,000, then the inventory turns is 10. It takes 365/10= 36,5 days on average to cycle the whole inventory. 9  The Eagle Machine Company averaged $2 million in inventory last year,......

Words: 897 - Pages: 4

Premium Essay

Macroeconomics: Aggregate Demand and Aggregate Supply

...Aggregate Demand and Aggregate Supply Topic Question numbers 1. Aggregate demand 1-22 2. Long-run aggregate supply 23-27 3. Aggregate supply (short run) 28-63 4. Equilibrium; changes in equilibrium 64-125 5. Downward price and wage inflexibility 126-134 Consider This 135-136 Last Word 137-138 True-False 139-155 Appendix 6. AD in relation to the AE model 156-166 Multiple Choice Questions Aggregate demand Type: D Topic: 1 E: 193 MA: 193 1. The aggregate demand curve: A) is upsloping because a higher price level is necessary to make production profitable as production costs rise. B) is downsloping because production costs decline as real output increases. C) shows the amount of expenditures required to induce the production of each possible level of real output. D) shows the amount of real output that will be purchased at each possible price level. Answer: D Type: A Topic: 1 E: 194 MA: 194 2. The aggregate demand curve is: A) vertical if full employment exists. B) horizontal when there is considerable unemployment in the economy. C) downsloping because of the interest-rate, real-balances, and foreign purchases effects. D) downsloping because production costs decrease as real output rises. Answer: C Type: A Topic: 1 E: 194 MA: 194 3. The interest-rate effect suggests that: A) a decrease in the supply of money will increase interest rates and reduce interest-sensitive consumption and investment......

Words: 10057 - Pages: 41

Free Essay

Aldub Phenomenon

...Ang “ AlDub Phenomenon”ayon sa pananaw ng mga mamayan ng baranggay 409 Lergada, Manila. Pinunong Pangkat Kenneth Angelo Reyes Miyembro ng Pangkat Christian Amoguis Mary Edelyn DeLeon Marilyn Asay Jeffrey Colio Milfried Samuel Garcia Ezra Jay Polentisiya Enrico Romero Beatriz Porsuelo Bernal Kabanata I Ang Suliranin at Kaligiran Nito A. Panimula Iba’t – ibang mga telenobela at noontime show ang napanood na natin at tinangkilik. Dahil likas sa ating mga Pilipino ang manood ng mga palabas bilang panlibang o pampalipas ng oras, hindi maiwasang naihahambing natin ang ating karanasan sa mga bida o mga tauhan sa telenobelang palabas na ating napanood. Isa sa mga tinangkilik ng mga Pilipino hindi lang sa Pilipinas pati narin sa ibat-ibang panig ng mundo, ay ang Kalyeserye na AlDub sa noontime show na Eat Bulaga sa Estasyon ng GMA na pinagbibidahan ni Alden Richards bilang Alden at Maine Mendoza bilang Yaya Dub. Kinabibilangan din ito nila Jose Manalo, Wally Bayola at Paolo Balesteros bilang mga Supporting character sa serye. Nakilala si Alden Richards sa mga kanyang ginampan ang karakter bilang Jose Rizal sa Teleseryeng “Illustrado” at Pelikulang “The Road”. sa GMA Network bago maging co-host sa Eat Bulaga sa Segment na “That’s My Bae.” Samantalang si Maine Mendoza a.k.a Yaya Dub ay nagsimula bilang isang “Dubsmash Queen”. Dahil sa dami nitong Dubsmash na ini-upload sa kanyang Facebook account na naging basehan ng kanyang karakter na Yaya Dub......

Words: 1159 - Pages: 5

Premium Essay

Is-Lm, Aggregate Demand and Aggregate Supply

...Part (A) IS-LM, Aggregate Demand and Aggregate Supply Behavioral Equations, Identities, Equilibrium Conditions and List of Exogenous and Endogenous Variable The IS-LM Model is based upon six Behavioral equations, each describing the determinants of one of the macroeconomic variable considered by the model: 1. Consumption 2. Investment 3. Government spending 4. Tax revenue 5. Money demand 6. Money supply The description of the IS-LM model is completed by three key identities that are defining the links between aggregate demand, aggregate supply and the equilibrium level of income. Aggregate demand: Z = C=I=G --------------------------------1 Since firms produce as many goods and services as demanded in the economy, the aggregate supply is written as: Y=Z --------------------------------2 Combination of the equation 1 and 2 gives income identity for a closed economy Y = C + I + G. This states that in equilibrium aggregate income must be equal to aggregate demand. Exogenous variables: G: Government spending T: Tax on income M: Money supply P: Price level (fixed in the short-run) Endogenous variables: Y: Production C: Consumption I: Investments R: Interest rate Behavior Equations Y= C + I + G C= C0 + Cyd Yd –Cr r I= I0 + Ir r G= G TA = TA + Ty Y LM Behavior Equation L=M L=L0 + LyY – Lr r M=M0/P Production Function Y= Aƒ (K,N) Identities of IS C= ƒ (Y+, r –) I = ƒ (r -) G=G S=...

Words: 1811 - Pages: 8

Free Essay

Aggregate Planning

...AGGREGATE PLANNING I. Introduction A. Intermediate Planning B. The Concept of Aggregation II. The Purpose and Scope of Aggregate Planning A. Demand and Capacity B. Inputs of Aggregate Planning C. Demand and Capacity Options AGGREGATE PLANNING III. Basic Strategies for Meeting Uneven Demand IV. Techniques for Aggregate Planning A. Informal Techniques B. Mathematical Techniques V. Aggregate Planning in Services VI. Disaggregating the Aggregate Plan VII. Master Scheduling A. Inputs B. Outputs C. Stabilizing the Master Schedule AGGREGATE PLANNING DEFINITION: • Aggregate planning is intermediate-range capacity planning that typically covers a time horizon of 2 to 12 months. • It deals with translating annual business and marketing plans into a production plan for all products. • It is particularly useful for organizations that experience seasonal or other fluctuations in demand or capacity. GOAL: The goal of aggregate planning is to achieve a production plan that will effectively utilize the organization’s resources to satisfy expected demand. 3 LEVELS WHICH ORGANIZATIONS MAKE CAPACITY DECISIONS: 1. Long-term decisions - relate to product and service selection, facility size and location, equipment decisions, and layout of facilities. 2. Intermediate decisions - relate to general levels of employment, output and inventories, which in turn define the boundaries within which short-range capacity decisions must be made. 3. Short-term decisions - consists...

Words: 2428 - Pages: 10

Free Essay

Ufos Phenomenon

...then, many UFO sightings have been reported worldwide. Yet, almost all of them end up being IFOs – Identified Flying Objects, as bright planets or stars, aircraft, balloons, flares, peculiar clouds, meteors, and satellites. The remaining sightings are hard to confirm due to the lack of photographic taken, inaccurate reporting, or delusions. Some people have given evidences to support the appearance of the UFOs, arguing that there is a conspiracy to hide the truth. The paper deals with UFOs phenomenon, which is an unexplained aerial event that has happened for a long time. It discusses the evidences of UFOs’ existence and the question of whether we are not alone in this universe as well as the theories surrounding these aerial events. 2. Discussion of findings 2.1. The Evidences For centuries, the UFOs reports have been familiar with people throughout the world. According to UN (2011), it is estimated that since 1947, about 150 million people have witnessed the UFO phenomenon and most of the reports from these people are general sighting. Many picture and video have been taken and recorded to be the evidence of this unexplained aerial event, however, this type of evidence is not convincing enough and hard to confirm due to the lack of the photographic quality, technical problems and photoshop. So if UFOs exist, do they leave some physical evidence? The answer is yes, they do. The first type of physical evidence is radar evidence. With so many radar tracking......

Words: 1789 - Pages: 8

Premium Essay

Aggregate Pp

...Problems on Aggregate Production Planning 1. Planners of a company have obtained information regarding the forecasted demand of a product as follows: Period 1 2 3 4 5 6 Total Forecast 200 200 300 400 500 200 1800 Costs Regular time: $2/unit Overtime: $3/unit Subcontract: $6/unit Inventory: $1/unit Backorder: $5/unit They now want to evaluate a plan that calls for a steady rate of regular-time output, mainly using inventory to absorb the uneven demand but allowing some backlog. Overtime and subcontracting are not used because they want steady output. They intend to start with zero inventory on hand in the first period. Prepare an aggregate plan and determine its cost using the preceding information. Assume a level output rate of 300 units per period with regular time. Note that the planned inventory is zero. There are 15 workers, each can produce 20 units per period. 2. Suppose that the regular output rate drops to 290 units per period in the above problem due to an expected change in production requirements. Costs will not change. Prepare an aggregate plan and compute its total cost for each of these alternatives: a. Use overtime at a fixed rate of 20 units per period as needed. Plan an ending inventory of zero for period 6. Backlogs cannot exceed 90 units per period. b. Use subcontracting at a maximum rate of 50 units per period; the usage need not be the same in every period. Have an ending inventory of zero in the last period. Again backlogs......

Words: 1139 - Pages: 5

Premium Essay

Fishkill Phenomenon

...Fishkill Phenomenon This essay will define fishkill phenomenon and discuss its causes and effects to our environment, as well as preventive measures. Fish is the healthiest form of meat to consume.  High in antioxidants and nutritious, without the worry of saturated fat clogging up your heart, fish seems to be touted the best source of protein.  “And amongst the many kinds of fish, some are given special preference over others such as the cod and the salmon for their higher nutritional value, but there are also other types of fishes that make it to the dinner table as a staple part of the meal, and due to their availability and affordability nativity to the region makes the fish less expensive such as the milkfish in the Philippines (Angelina, 2011). Unfortunately, fishkill phenomenon occurred in the Philippines and causes massive die-off of fishes. Phenomenon, plural phenomena, come from the Latin word phænomenon, from Greek word phainomenon "that which appears or is seen" (wiki.answers.com). There are kinds of phenomena; one of those is the fishkill phenomenon, which is very familiar phenomenon in the Philippines. Fishkill phenomenon, also known as fish-die off, is a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic. Additionally, it is a phenomenon wherein a large population or species of fish die in mass extinction and resulted from poor management of water sources and contamination of rivers,......

Words: 2346 - Pages: 10