CHLORINE (PREPARATION, PROPERTIES AND USES)

CHLORINE

Chlorine is the most important element of all halogens. It was discovered by Scheede in 1774 when he heated some concentrated hydrochloric acid with manganese (IV) oxide. The gas was named Chlorine in 1810 by Davy from the Greek word ‘Chloros’ meaning greenish yellow.

Laboratory Preparation of Chlorine

Chlorine is generally prepared in the laboratory by the oxidation of concentrated hydrochloric acid (HCl). The two common oxidising agents that can be used are manganese (IV) oxide (MnO₂) and potassium tetraoxomanganate (VII) acid (KMnO₄).

Industrial Preparation of Chlorine

Chlorine is prepared or manufactured industrially by the electrolysis of:

·        Brine

·         Chlorides of molten sodium, magnesium and calcium. The chlorine is then liquefied and stored under pressure in steel cylinders.

Physical Properties of Chlorine

a. Chlorine is a greenish-yellow gas with choking, unpleasant, irritating smell

b. It is denser than air

c. It is moderately soluble in water

d. It is easily liquefied under pressure

e. Chlorine is a poisonous gas. If inhaled to a very small extent, it can damage the mucous lining of the lungs.

Chemical Properties of Chlorine

Chlorine combines directly with most other elements to form chlorides. It reacts directly with metals and non-metals to form metallic and non-metallic chlorides.

a. Reactions with metals: metals react readily with chlorine especially when heated to form their chlorides. Example;

   2Na_(s) + Cl₂ → 2NaCl_(s)

   Mg_(s) + Cl_2(g)  → MgCl₂

b. Reaction with non-metals: with the exception of oxygen, carbon, nitrogen and noble gases, all other non-metals burn in chlorine to produce the corresponding chlorides. Examples include burning of phosphorous in chlorine to produce a mixture of phosphorous (V) chloride and phosphorous (III) chloride.

  2P + 3Cl₂ → 2PCl₃

  2P + 5Cl₂ → 2PCl₅

c. Chlorine as an oxidizing agent: chlorine readily removes hydrogen from its compound to form hydrogen chloride. Chlorine behaves as an oxidizing agent by removing hydrogen from compounds like ammonia, hydrogen sulphide, hydrocarbons, iron (II) chloride and trioxosulphate ((IV) ion.

d. Reaction with alkalis: chlorine forms a pale yellow solution of sodium oxochlorate (I) when passed into a cold sodium hydroxide solution.

NaOH_(aq) + Cl_2(g) → NaCl_(aq) + NaClO_(aq) + H₂O_(l)

e. As a bleaching agent: chlorine is a common bleaching agent. It bleaches most dyes and inks in the presence of water

  HOCl_(aq) + HCl_(aq) → [O] Dye + [O] → (Dye + O)

Uses of Chlorine

a. Chlorine is used as a bleaching agent for cotton, linen and wood- pulp.

b. It is used in the sterilization of water for domestic and industrial use

c. Chlorine is used in the manufacture of important organic solvents such as trichloromethane (CHCl₃), trichloroethene (C₂HCl₃) and trichloro ethanal (CCl₃. CHO).

d. It is used in the manufacture of plastic, poly(chloroethene) known as PVC and synthetic rubber

e. It is used in the manufacture of hydrochloric acid and domestic antiseptic such as acidified sodium oxochlorate (1) solution. 

OXYGEN (PREPARATION, PROPERTIES AND ITS USES)

OXYGEN

Oxygen is the most abundant element in the earth and its outer crust. Oxygen was discovered by Scheede in 1772 and Priestly in 1774 rediscovered it. Oxygen occurs in nature in both free and combined states, much combined oxygen are found in minerals like clay, limestone and sand. This also occurs in form of water, many metallic and non-metallic oxides.

PREPARATION OF OXYGEN
There are many ways of preparing oxygen both in the laboratory and industrially.
Laboratory Preparation of Oxygen
There are two ways of preparing oxygen in the laboratory:
1. Thermal decomposition of pottassium trioxochlorate (V). This is done by heating pottassium trioxochlorate (V), which decomposes to release all its oxygen. Manganese (IV) oxide acts as catalyst which makes the reaction to occur at a lower temperature and at much faster rate;

2KClO_3(S) → KCl_(S) + 3O_{2 (g)}

2. Decomposition of hydrogen peroxide: this is the most convenient method for the preparation of oxygen. It requires no heat. Hydrogen peroxide decomposes readily in the presence of manganese (IV) oxide as catalyst to liberate oxygen;

2H₂O_2(aq)  → 2H₂O_(l)  + O_{2 (g)}

Hydrogen peroxide also reacts with acidified pottassium tetraoxomaganate (VII) solution in cold water to produce oxygen. This is an oxidation-reduction  reaction;

5H₂O_2(aq) + 2KMnO_{4 (aq)} + 3H₂SO₄ → K₂SO₄ (aq) + 2MnSO₄ (aq) +8H₂O(l) + 5O₂(g)

This method is highly recommended for use in school laboratories because it is safe and efficient. Other methods include, thermal decomposition of oxides such as mercury, silver, lead and reaction of sodium peroxide with water;

2HgO(s) → 2Hg(l) + O₂(g)

2Ag₂O(s) → 4Ag(s) + O₂(g)

PbO₂(s) → Pb(s) + O₂(g)

2Na₂O₂(s) + 2H₂O(l) → 4NaOH(aq) + O₂(g)

Physical Properties of Oxygen
1. Pure oxygen is a colorless, odorless and tasteless gas.
2. It is neutral to litmus paper.
3. It is slightly soluble in water.
4. Its density is about the same as that of air. 

Chemical Properties of Oxygen

Oxygen gas supports combustion of many substances. Metals, except mercury, silver and gold react with oxygen to form basic oxides. Examples:

4Na(s) + O₂(g) → 2Na₂O(s)

4K(s) + O₂(g) → 2K₂O(s)

2Ca(s) + O₂(g) → 2CaO

Non-metals like sulphur, carbon and phosphorous burn in oxygen to form acidic oxides which are also known as acid anhydrides, as they dissolve in water to form acids. Examples;

S(s) → O₂(g) → SO₂(g) → H₂SO₂(aq)

P₄(s) + 3O₂(g) → P₄O₄(s) → 4H₃PO₃(aq)

C(s) + O₂(s) → H₂CO₃(aq)

Hydrocarbons burn in oxygen to form carbon(IV) oxide and water

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

The oxygen we breathe in, oxidizes the carbonhydrate we eat to release energy

C₆H₁₂O₆(s) → 6CO₂(g) + 6H₂O(g) + Energy

Uses of Oxygen

1. Oxygen from air is breathed in by animals. In hospitals, pure oxygen is given to patients suffering from respiratory complaints.

2. Oxygen is used in industries for the production of oxygen-hydrogen blow pipe and oxy-ethyne flame.

3. Oxygen is also used in the manufacture of important chemical compounds like  tetraoxosulphate (VI) acid,  trioxonitrate (V) acid and ethanoic acid.

4. Oxygen is used in making steel for the removal of carbon, sulphur and phosphorous impurities.

5. Liquid oxygen and fuel are used as propellant for space rockets.

HOW TO CHECK SBRS-ABU 2017 ENTRANCE EXAMINATION RESULTS

The Ahmadu Bello University, School of Basic and Remedial Studies, Funtua wishes to inform all applicants who wrote the pre-entrance examination for the 2017/2018 academic session that the results are out online.

Candidates are to check their 2017 SBRS Remedial results by following the below steps:

1. Visit the SBRS results checking portal http://www.sbrsabu.org/result/results.html
2. Enter your Registration Number: (e.g.: R16S10001) and Pin Number in the spaces provided.
3. Click on "Check Result" to view your result.

ALKENES, ALKYNES AND AROMATIC COMPOUNDS

ASSIGNMENT
QUESTION: Give the physical, chemical and uses of the following.
A. Alkene
B. Alkyne
C. Aromatic compounds


ANSWERS
1. Alkene
Physical properties
a. Physical state:  Ethene, propene, and butane exist as colourless gases. Members of the 5 or more carbons such as pentene, hexane, and heptene are liquid, and members of the 15 carbons or more are solids.
b. Density: Alkenes are lighter than water and are insoluble in water due to their non-polar characteristics. Alkenes are only soluble in nonpolar solvents.
c. Solubility:  Alkenes are virtually insoluble in water, but dissolve in organic solvents. The reasons for this are exactly the same as for the alkanes.
d. Boiling points: The boiling point of each alkene is very similar to that of the alkane with the same number of carbon atoms. Ethene, propene and the various butenes are gases at room temperatures. All the rest that you are likely to come across are liquid. Boiling points of alkenes depends on low molecular mass (chain length). The more intermolecular mass is added, then the higher the boiling point. Intermolecular forces of alkenes get stronger with increase in the size of the molecules.
e. Melting points: melting points of alkenes depends on the packaging of the molecules. Alkenes have similar melting points to that of alkanes, however in cis isomers molecules are package in a u-bending shape, therefore, will display lower melting points to that of the trans isomers.
f. Polarity: chemical structure and functional groups can affect the polarity of alkenes compounds. The sp2 carbon is much more electron-withdrawing than the sp3 hybridized orbitals, therefore, creates a weak dipole alone the substituent alkenly carbon bond. The two individual dipoles together form a net molecular dipole. In trans-substituted alkenes there is a net dipole, therefore contributing to higher boiling in cis-isomer than trans-isomer.
Alkenes Chemical Properties
Although the double bond between two carbon atoms is stronger link than a single bond, it is not twice as strong, (i.e. the second bond formed between the carbon atoms is weaker than the first). Thus, the second bond is more vulnerable to attack by suitable reagents, even under fairly mild conditions. Thus, the reaction of this second bond tends to be addition reactions, where the unsaturated carbon atoms become saturated. The alkenes are much more reactive than alkanes.
Combustion of Alkenes
The alkenes are highly flammable and burn readily in air, forming carbon dioxide and water,. For example, ethene burns as follows:


C2H4   +   3 O2   ==>   2 CO2   +   2 H2O      
Addition Reactions across the Double Bond
Because the alkenes are unsaturated hydrocarbons, their most important reactions are addition reactions across the double bond.
The alkenes are readily oxidised by potassium permanganate to form glycols. For example, ethene is oxidised to ethylene glycol.


3 H2C=CH2   +   2 KMnO4   +   4 H2O    

==>     2MnO2  +  2KOH   +   CH2OHCH2OH

Ethylene Glycol
During the oxidation of alkenes, the purple colour of the permanganate solution disappears and the reaction constitutes a test, known as Baeyer's Test, to detect unsaturation in any compound.
Addition of Hydrogen
The alkenes are readily reduced by the addition of hydrogen across the double bond to form alkanes (i.e. reduction of alkenes). For example, when alkenes are passed over a nickel catalyst at 150oC, the alkene is reduced to an alkane.


H2C=CH2   +   H2      ==>     CH3CH3

Ethene                                       Ethane
Addition of Halogen
Halogens readily add across the double bond of the alkenes to form dihalides

H2C=CH2   +   Cl2       ==>     CH2ClCH2Cl    

Ethene                          DiChloroEthane
H2C=CH2 + Br2 ==> H2Br CH2Br
Ethene DiBromoEthane
The decolourisation of bromine is a second test for an unsaturated organic compound.
Addition of Hydrogen Halide
Hydrogen halides readily add across the double bond of the alkenes to form alkyl halides the reactivity of ethene, with the halogen acids is in the order


HI >> HBr > HCl    
Thus, ethene reacts readily with hydrogen iodide and with hydrogen bromide at room temperature to form ethyl iodide and ethyl bromide, respectively.

H2C=CH2     +    HI      ==>     CH3CH2I
Ethyl Iodide  
With ethene, the hydrogen atom of the halogen acids can add to either carbon atom to yield bromoethane.
However, with higher members of the ethene series, the orientation of the addition of asymmetric molecules across the double bond is governed by the Markownikoff Rule.
Addition of Water
Water can add across the double bond of the alkenes to form aliphatic alcohols. This is hydration reaction is catalysed under a number of different conditions.
When ethylene and steam are heated (i.e. at 300oC) under high pressure (i.e. at 70 atm.) in the presence of a catalyst (i.e. phosphoric acid, on a silica support), ethanol is formed.
H2C=CH2   +   H2O       ==>     C2H5OH
Reaction with Sulphuric Acid
Similarly, fuming sulphuric acid absorbs ethylene at room temperature to form ethyl hydrogen sulphate, with much evolution of heat.
C2H4   +   H2SO4 ==>     C2H5.HSO4      
If this is treated with water and warmed, ethanol is formed.  
C2H5.HSO4   +   H2O     =heat=>     C2H5OH + H2SO4        
Polymerisation Reactions due to the Double Bond
When ethylene is heated under great pressure in the presence of a catalyst a large number of the molecules combine to form polythene, (C2H4)n, (i.e. Polyethylene). This particular kind of reaction is called an addition polymerisation and the mechanism by which it takes place is a reaction is a free radical chain reaction. The overall reaction is

  n (C2H4)         ==>             (C2H4)n
Ethene                          Polythene
Uses of alkenes
 Alkenes are extremely important in the manufacture of plastics. All plastics are in some way related to alkenes. The names of some plastics (Polythene or Poly Ethene, Polypropene), relate to their alkene partners. Plastics are used for all kinds of tasks, from packaging and wrapping, to clothing and outdoor apparel.
 Lower alkenes are used as fuel and illuminant. These may be obtained by the cracking of kerosene or petrol.
 For the manufacture of a wide variety of polymers, e.g., polyethene, polyvinylchloride (PVC) and Teflon etc.
 As raw materials for the manufacture of industrial Chemicals such as alcohols, aldehydes, and etc.
 Besides, alkenes also used for artificial ripening of fruits, as a general anesthetic, for making poisonous mustard gas (War gas) and ethylene-oxygen flame.
2. ALKYNES
Physical properties of alkynes
Physical state
The first three members (ethyne, propyne and butyne) are colourless and odourless gases. Due to the presence of phosphine as an impurity ethyne (acetylene) has garlic smell. The next eight members are liquids, and higher members are solids under normal conditions of temperature and pressure.
Solubility
Alkynes are insoluble in water, but are fairly soluble in organic solvents such as, alcohol, ether, acetone etc.
Melting and boiling points
The melting and boiling points of alkynes increase with molecular mass. Melting boiling points of some alkynes are,
Ethyne/acetylene (CH º CH), - 83oC or 190 K
Propyne (CH3-CºCH), - 27oC or 246 K
1 - Butane (CH3-CH2-CºCH), 8oC or 281 K
2 - Butane (CH3-CºC-CH3), 29oC or 302 K
1 - Pentyne (CH3-CH2-CH2-CºCH) 48oC or 321 K
2 - Pentyne (CH3-CºC-CH2-CH3) 55oC or 328 K
Chemical properties of alkynes
Alkynes contain a triple bond ( ). A triple bond has one and two bonds.
Some characteristic reactions of alkynes are,
Combustion
Alkynes burns in air or oxygen with smoky flame.

Electrophilic addition reactions
Carbon-carbon triple bond, C=C, is a combination of one and two bonds. Alkynes give electrophilic addition reactions as they show reactivity due to the presence of bonds. This property is similar to alkenes but alkynes are less reactive than alkenes towards electrophilic addition reactions due to the compact CC electron cloud. Some typical electrophilic addition reactions given by alkynes are:
Addition of hydrogen
An alkyne reacts with hydrogen in the presence of catalyst (Pt or Ni) at 250°C, first forming alkenes and finally alkane.

For example, ethyne gives ethane in two steps.

Ethyne etheneethane
Ethane is obtained in good yields if hydrogenation is done with a calculated amount of hydrogen in the presence of palladium or barium sulphate.
Propyne gives,


Addition of halogens
Alkynes react with halogens (Cl2 or Br2) in the dark, forming dihaloalkenes first and finally tetrahaloalkanes. The reaction gets accelerated in the presence of light or halogen carriers.
RCCH                   RCX=CHX     RCX2CX2
alkyne dihaloalkene tetrahaloalkane
For example, ethyne (acetylene) with chlorine gives,


The order of reactivity is Cl2 > Br2 > I2.
Addition of halogen acids
Alkynes react with halogen acids according to the Markownikoff's rule i.e. the carbon atom carrying the least number of hydrogen atoms will have the negative part of the addendum attached to it.

For example, ethyne (acetylene) with HBr gives,

Addition of hypochlorous acid
Alkynes react with hypochlorous acid according to the Markownikoff's rule.

For example, ethyne with HOCl gives,

Dichloroethanal
In the presence of peroxides the addition of HBr takes place according to the anti-MarkowniKoff's rule.
Addition of sulphuric acid
Alkynes add up two molecules of sulphuric acid. For example, ethyne gives

Nucleophilic addition reactions
Alkynes also give the following nucleophilic addition reactions.
Addition of water
In the presence of sulphuric acid (42%) and 1 % mercuric sulphate at 60°C, alkynes add on one water molecule to give aldehydes or ketones. For example,

Alkyne ketone
Ethyne gives ethanal and propyne gives acetone.

ethyne (acetylene) ethanal (acetaldehyde)


Addition of HCN
Alkynes add one molecule of HCN in the presence of Ba(CN)2. For example,

Ethyne gives

ethyne vinyl cyanide

Addition of ozone
Ozone adds up across the triple bond to give ozonides. After hydrolysis, ozonides give diketones and carboxylic acids.

Ethyne gives glyoxal and formic acid,

glyoxal formic acid

Substitution reactions
Due to their acidic nature, alkynes form metallic salts called alkynides e.g., sodium, silver and copper(ous) salts. Examples are,


Acidic hydrogen in 1-alkynes
Hydrogen atoms in ethyne and 1-alkynes, linked to the carbon atom having a triple bond on it, are acidic in nature. For example, ethyne (acetylene) is a weak acid: weaker than water but stronger than ammonia. This may be explained as follows:
The -electrons are more weakly bound than electrons. Thus, in those compounds containing carbon-carbon double or triple bonds, the electron density around such carbon atoms will be lesser than the carbon atoms linked only through bonds. Thus, electronegativity of differently hybridized carbon atoms will follow the order,sp > sp2 > sp3
i.e., the electronegativity will increase with the s character in the hybrid orbitals. This increase in the electronegativity of an alkyne carbon, (relative to the carbon atoms in alkenes and alkanes) will polarize the C-H electron bond towards carbon and facilitate the release of proton(s). Accordingly the acid strength of hydrogens will follow the order, Alkynes > Alkenes > Alkanes.
The stabilities of the anion left after the removal of proton, i.e. carbanions follow the order,
RC C- > RCH = CH- > R-CH2-CH2-
Thus, the acid strength follows the order, HC CH > H2C = CH2 > H3C-CH3
Compared to the organic acids e.g...Ethanoic acid (CH3OOH), ethyne is about 1020 time less acidic, while ethane is 1040 times less acidic.
Polymerization
On heating alkynes undergo polymerization in the presence of catalyst. The nature of products depends upon the conditions. For example,
• When ethyne (acetylene) is passed through a hot copper tube, it polymerizes to benzene.

ethyne benzene benzene
• When passed through a solution of cuprous chloride in ammonium chloride, ethyne undergoes linear polymerization.
• Vinyl acetylene with hydrogen chloride gives chloroprene (2-chlorobuta-1,3-diene), which readily polymerizes to give neoprene (a synthetic rubber)

Oxidation
Oxidation of alkynes gives mono or dicarboxylic acids.
For example,
• Alkaline KMnO4 oxidises ethyne to oxalic acid.
Oxalic acid (ethanedioic acid)
• With chromic acid, ethyne gives acetic acid.
Ethyneethanoic acid (acetylene) (acetic acid)
Homologues of ethyne on oxidation with alkaline KMnO4 give mixture of acids. During oxidation, rupture takes place at the triple bond.

3. AROMATIC COMPOUNDS

Physical properties of aromatic compounds
 Non polar
 good industrial solvents for other non polar compounds
 Insoluble in water
 liquid at room temperature

Chemical properties of aromatic compounds
 They undergo electrophilic substitution reactions.
 They undergo mono substitution of derivatives of benzene.
 They undergo addition reactions under drastic condition.
 They undergo side-chain substitution reaction.
 They undergo oxidation reaction.

USES OF AROMATIC COMPOUNDS
 They occur naturally in compounds like DNA and within some amino acid that make up protein and chlorophyll.
 They make up the heme groups which helps the blood cells carry oxygen.
 They are the spicy compounds in hot pepper, ginger and other black compounds
 Health: aromatic compounds are used in drugs formation and purifications
 Automotives: car bodies, bumpers, lightening, dashboard, seat, upholstery, fuel system, bonnets are made from products derived from aromatic compounds.
 Clothing: aromatic compounds are used in textile industry for manufacturing of clothes.
 Sports equipments: aromatic compounds are used in the productions of sport equipments e.g football, swim suits etc


REFERENCES
1. Vollhardt, K,P.C & shore, N. (2007). Organic chemistry  (5th ED) new York: W.H freemen (453-454)
2. Vollhardt, K,P.C & shore, N. (2007). Organic chemistry: study guide and solution Manuel (5th ED.). new York: W.H Freeman (200-202)
3. https://www.ucc.ie/academic/chem/dolchem/html/dict/alkenes.html

CORROSION OF METALS

           CORROSION CHEMISTRY
Corrosion refers to the loss or conversion into other insoluble compounds of a surface layer of a solid in contact with a fluid. Corrosion can also be defined as the deterioration of metals by an electrochemical process. The economic damage of corrosion causes a lot of tremendous economic damage to building, bridges, ships, cars, equipment and metallurgical plants, river and sea vessel, underground pipelines and other structures. Examples of corrosion are;
• Formation of rust on iron, oxygen gas and water must be present for iron to rust                            Fe  → Fe2+ + 2e- , 4Fe2+ (aq) + O2 (g) + (4+2x) H2O → 2Fe2O3. X H2O + 8H2+(aq)
• Coinage metal such as copper and silver also corrode but much slowly                                                Cu(s) →Cu2+(aq) + 2e-,        Ag(s) → Ag+(aq) + e-
• Deterioration of copper and brass
• Tarnish on silver
Aluminium is another metal which corrode. Aluminium has a much greater tendency to oxides than iron does because aluminium has a more negative standard reduction potential than iron, base on this fact, we expect to see air plane slowly corrode away in rainstorms and soda cans transform into piles of corroded aluminium. This process do not occur because the layer of insoluble aluminium oxide Al2O3 that forms on its surface when the metal is exposed to air serves to protect the aluminium underneath from further corrosion.
           Electrochemical Methods of Preventing Corrosion
The electrochemical methods of avoiding corrosion are:
• Application of external voltage or current or use of a sacrificial anode to set the voltage of the material in the passive zone (anodic protection) or at a sufficiently negative potential such that the rate of corrosion is slow (cathodic protection).
• Removal of the reducible and aggressive species in solution e.g increase of pH, removal of hydrogen or in humid atmospheres and reduction of humidity.
• Avoidance of bimetallic contacts where this can lead to enhanced corrosion.
• Avoidance of mechanical stress
• Selection of a bulk material with high corrosion resistance
• Coating of metal with a suitable, sufficiently thick and homogenous protective film, example oxide and paint
The fundamental electrochemical processes that occur during formation of rust on iron are;
Oxygen gas and water must be present for iron to rust. A region of the metal surface serves as the anode, where oxidation half reaction occurs; Fe  → Fe2+ + 2e-, the electrons given up by ions to reduce atmospheric oxygen to water at the cathode. Half reaction at the cathode is                          O2(g) +4H+ + 4e- → 2H2O(l), the overall reaction is  2Fe(s) + O2(g) + 4H+(aq)  → 2Fe2+(aq) + 2H2O       the reaction occurs in acidic medium, the H+ are supplied by the reaction of atmospheric carbon dioxide with water to form carbonic acids.
CO2 + H2O → H2CO3 (carbonic acid)

Fe2+ ions formed at the anode are further oxidised by oxygen
4Fe2+(aq) + O2(g) + (4 + 2x)H2O   → 2Fe2O3.xH2O + 8H+(aq)
The chemical formula of the substance referred to as rust is Fe2O3.XH2O
Other various ways of preventing rust metals are:
• Barrier protection: in this method a barrier film is introduced between iron and atmospheric oxygen and moisture. Barrier protection can be achieved by one of the following ways: by painting the surface, by coating the surface with a thin film of oil or grease and by electroplating iron with some non-corrosive metal such as nickel, chromium, copper e.t.c.
• Sacrificial protection: in this method surface of iron is covered with layer of more active like zinc. This active metal loses electrons (undergoes oxidation) in preference to iron and hence, prevents the rusting of iron. Zinc metal is generally used for protecting iron and the process is called Galvanization. Zinc, magnesium and aluminium powder dissolved in paints can also be applied as protective layers.
• Use of anti-rust solutions: the alkaline phosphate and alkaline chromate solutions act as anti-rust solutions. When iron articles are dipped into a boiling and strongly alkaline solution of sodium phosphate, a protective insoluble film of iron phosphate is formed on them. The film protects the article from rusting.

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PhD /MSc INTERNATIONAL SCHOLARSHIP OPPORTUNITIES

PhD/MSc Scholarship, WENS Lab, KIT, South Korea, Spring 2018

Kumoh National Institute of Technology (KIT) is offering graduate scholarship within the Wireless and Emerging Network System (WENS) Laboratory. Applicants must have a strong background on

1. computer network, wired/wireless communications, communication engineering, and embedded system or

2. signal processing, image processing, and programing such as MATLAB, C/C++/C#, etc.

Those who have knowledge and publications related to "5G and Future Radio Access" such as NOMA, FTN, waveform shaping, massive MIMO, index modulation, and etc. will get more plus points. 

Scholarship includes full tuition fees until graduation, Medical Insurance and monthly stipend.

▶ Who can apply?  - Candidates from all nationalities can apply for the scholarship.

▶ Application deadline  - 30th Nov. 2017

▶ Prerequisites

- Bachelor / Master Degree in engineering (Electrical, Electronics, Telecommunication, or Computer Engineering/Science)

- CGPA >= 3.3/4.0  - IELTS >= 6.0, TOEFL IBT>= 85, PBT>= 570, CBT>=230, TOEIC >= 750   

▶ Required documents

- Curriculum Vitae

- Formal English score certificate (within 2 years)

- Transcripts etc

Kindly fill your online application form at the below mentioned link and submit the required documents.

http://wens.re.kr/xe/application/

For any queries, send us email at labwens@gmail.com 

Eligibility

- Bachelor / Master Degree in engineering (Electrical, Electronics, Telecommunication, or Computer Engineering/Science)

- CGPA >= 3.3/4.0  - IELTS >= 6.0, TOEFL IBT>= 85, PBT>= 570, CBT>=230, TOEIC >= 750

Benefits

Scholarship includes full tuition fees until graduation, Medical Insurance and monthly stipend.

Application

Kindly fill your online application form at the below mentioned link and submit the required documents.

http://wens.re.kr/xe/application/

EDUFI FELLOWSHIPS PROGRAMME (BENCHWORK OPPORTUNITY FOR MASTERS AND PhD STUDENTS)

EDUFI FELLOWSHIPS

The EDUFI Fellowships programme is open to young Doctoral 

level students and researchers from all countries and from 

all academic fields. Master's level studies or post-doctoral

 studies/research are not supported in the programme.

The primary target group in the EDUFI Fellowship programme are such Doctoral level students who will be doing their Doctorate (or Double Doctorate) at a Finnish university. Visiting Doctoral-level students and researchers who are doing their Doctorate degree at some foreign university can also be considered eligible, provided that the motivation letter of the hosting Finnish university department presents exceptionally good grounds for such an application.

The programme is open for candidates of all foreign nationalities. However, when decisions on scholarship are made, emphasis is given to applicants from Russia, China, India, Chile, Brazil and North America.

The scholarship period may vary from 3 to 12 months. The monthly allowance is 1500 euros. The scholarship is intended to cover living expenses in Finland for a single person. No additional allowance for housing is paid. Expenses due to international travel to and from Finland are not covered by the programme.

NB: the EDUFI Fellowship is a start-up grant rather than a full degree scholarship, so if you for example receive an EDUFI Fellowship for 12 months, after that period you should seek other sources of funding for the remaining period of your studies/research.

If you are already residing in Finland, please note that the Doctoral students/researchers for whom the Finnish universities can apply for an EDUFI Fellowship should not have resided in Finland for more than one (1) year prior to submitting an EDUFI Fellowship application. If you have resided in Finland longer than that, please refer to the section Other sources of funding.

HOW TO APPLY

The prerequisite for applying is that the visiting researcher must have established contacts with a Finnish host university - please see the section Doctoral Admissions for further information (you'll find links to the universities' Doctoral Admissions pages there). You are also advised to visit the Finnish universities' own websites for detailed information on the Doctoral level study and research options the universities offer.

If a Finnish university is willing to host you, then the Finnish university department wishing to host you can apply for the EDUFI Fellowship on your behalf. That is, only the hosting Finnish university can act as an 'applicant' in the EDUFI Fellowship programme.

The application form for the EDUFI Fellowship can be downloaded below. Additionally, the following attachments are required for a EDUFI Fellowship application:

• A motivation letter from the applicant (the hosting university), max 1 page
• Complete CV of the scholarship candidate
• Research plan (3-5 pages)

Two printed and signed copies of the application with required attachments should be submitted to the following address: Finnish National Agency for Education (EDUFI), PO Box 380, 00531 Helsinki. Please mark the envelope with “EDUFI Fellowships”.

WHEN TO APPLY

There are no annual application deadlines in the EDUFI Fellowship programme. Applications may be considered at all times. However, applications should be submitted at least 5 months before the intended scholarship period. Decisions will be made within approximately 3 months after receipt of application.

APPLICATION FORM AND DETAILED INSTRUCTIONS

A detailed set of guidelines for a EDUFI Fellowship application is provided (in English) alongside the downloadable application form, see the link below.

EDUFI Fellowship application form and instructions

EQUIPMENTS AND DEVICES USED FOR ENVIRONMENTAL MONITORING AND POLLUTION CONTROL

Equipments and Devices for Environmental Monitoring and Pollution Control
Pollution control devices include:
• Dust collection system
• Baghouse
• Cyclones
• Electrostatic precipitators
• Scrubbers
• Spray tower
• Sewage treatment
• Vapour recovering systems
Separators are devices that are used to control particulate matters. Particulate matters are common pollutants present in the emission of an industry. They have applications in the emission of an industry and in mechanical operation for dust control such as pulverizing, grinding, blending, wood work and other dusty operations e.t.c.
There three types of devices which are commonly used as internal separators, they are:
• Gravitational settling chambers
• Cyclone separators
• Baghouse filter (cloth screen or fabric filters)
Gravitational settling chambers
They are used to separate larger particles size greater than 50 microns. A stream of dust laden gas is passed into the settling chambers where the velocity of the gas is suddenly reduced as a result of the dust particles that settle down and it is collected through a hopper at the bottom. The collection efficiency of the settling chambers can be increased by installing a series of settling chambers in parallel.
Advantages of gravitational settling chambers
• It is cheaper to maintain and install
• It has low energy consumption
• It is very easy to maintain
• Very simple technology is required
• Ensures dry and continuous disposal of solid particles.

Disadvantages of gravitational settling chambers
• It requires large space for installation
• It is not highly efficient

Cyclonic Separators
Cyclonic separation is a method of removing particulates from air, gas or liquid stream without the use of filters through vortex separation. Rotational effects and gravity is used to separate mixture of solid and liquid. A high speed rotating (air) flow is established within a cylindrical or conical container called Cyclone. Air flow in a helical pattern beginning from the top of the cyclone and ending at the bottom of the cyclone, before exiting the cyclone. Large particles fall to the bottom of the cyclone where they can be removed. As the rotating flow moves towards the narrow end of the cyclone, the rotational radius of the stream is reduced, separating smaller particles.  Large scale cyclones are used in sawmills to remove sawdust from extracted air. Cyclones are also used in oil refineries to separate oil from gases.
Advantage of Cyclonic Separators
• Simple technology
• Low cost maintenance
• High efficiency
• It is easy to maintain
• Low energy consumption
Disadvantages of Cyclonic Separators
• It cannot collect particles between 5-10 microns effectively
• Equipment can be subjected to severe corrosion and abrasion.


Fabric Filters (Baghouse or Cloth Screen Filter)
These are devices by which gas is purified through various filtering cloths (cotton wool, chemical filters) or fabric filters. A typical baghouse fiter consist of tabular bag or an envelope mounted in a manner that the particle laden gas passing through the filter get deposited on the inside surface of the bags which are dusted by shaking at regular interval. The dusts are collected in a hopper at the bottom. Bag filters have high efficiency but the filters are required to be cleared and changed at regular intervals. Baghouse filter can be used to remove particulates out of air and gas release from commercial processes or combustion from electricity generation power plants, steel mill, pharmaceutical industries, food manufacturers and chemical industries use baghouse to control emission.
Advantages of Fabric Filters (Baghouse or Cloth Screen Filter)
• High collection efficiency for particles of all sizes, especially those smaller than 10 microns in size
• Simple construction and operation
• Low energy consumption
• Dry disposal of collected materials.
Disadvantages of Fabric Filters (Baghouse or Cloth Screen Filter)
• It is difficult to maintain
• The equipment is usually large, therefore occupying a lot of space.
POLLUTION CONTROL PRACTICES
Pollution control practices include: recycling, regulation, restriction, reusing, reducing, preventing, composting, recovery, mitigation e.t.c.
RECYCLING
Recycling is the process of using waste material to form a new product to prevent waste of potential useful materials. Recycling is also the collection of a product by the public and return of this material to the industrial sector. Examples of recycling are the collection of newspapers and aluminium cans by the individuals and their eventual return to paper manufacturers them and sell to members of the public. The recycling process requires the participation of the public, since the public must perform the separation step.
Regulation
Regulation is the process of enacting laws or rules to protect the environment from adverse effect of pollution. Many nations enact legislation to regulate various types of pollution as well as to mitigate adverse effects of pollution. The purpose of environmental regulations on pollution control is set to maximum levels of the pollutants to be released into the environment and to prosecute offenders of pollution control laws. Regulation helps in environmental monitoring.
Development of New Technologies for Pollution Control
In this age and time, science and technology are advancing at an alarming rate. The rapid development of science and technology brings considerate benefits to human beings, but it also brings environmental pollution and energy shortage. With advances in technology to exploit more energy (including fossil, fuel, coal, natural gas and so on) to meet the demand of the growing population. The more population we have, the more energy we need. With the expansion of industrialization, requirement for energy worldwide has increased. We have a great need for energy because of rapid growth of our economy.
Environmental pollution can be reduced by green technology, renewable and clean energy such as solar energy to solve energy crisis. But these new technologies need a large amount for investment, research and development. Most countries cannot afford it. Therefore these methods are infeasible in the short term e.g of new technology is nano-porous fibres, it traps carbon dioxide and other pollutants so they can be removed and recycled back into the production process.
GIS for Pollution Detection
Geographical information system (GIS) was established in 1960 in Canada from Canadian information system, it was implemented in 1964 by Tomhinson. It gained awareness in 1980. The use, training and popularity of GIS grew in 1980. GIS is a system for capturing, storing, checking, manipulating, analysis and displaying of data that are spatially referenced to the earth. GIS can also be defined as computer based set of procedures used to store and manipulate geographical data. GIS is an information technology and advanced technique of investigation.
GIS is used by environmental researchers, urban management, business world, government and non-governmental programmes e.t.c. GIS can be applied in environmental planning and monitoring in conservation area planning, land use planning, air quality monitoring and water quality monitoring e.t.c.
AIR SAMPLER
Air sampling devices are used to detect smoke, particulates and gases. The equipment used, selected and its siting is determined by the problem being studied and the purpose to be served. Monitoring instruments for measurement of pollution include:
Pollutants                                     Measurement Method
Carbon monoxide (CO)                gas chromatography, non-dispersive infra-red, spectrophotometry
Sulphur dioxide                             ultraviolet pulsed fluorescence, flame photometric dilution or                                                                         permeation tube calibrators
Ozone ultraviolet spectrophotometer, gas phase, chemiluminiscence, gas
Phase titration (GPT), calibrators
Nitrogen dioxide chemiluminiscence, permeation or GPT calibrators
Lead (Pb) high volume sampler and atomic absorption analysis
Suspend particulate matter high volume sampler and weight determination
Hydrocarbons   flame ionization and gas chromatography, calibration with methane
             gas tank.


Environmental Monitoring Laboratories
Environmental monitoring laboratories are laboratory that deals with measurement, sampling, analysis, observation and evaluation of pollution levels in air, water, soil, food and living organisms in an environment.
Environmental monitoring provides pollution information and data.
Environmental monitoring could make one predict the possible hazards that will be generated in future.
Environmental monitoring laboratories sees to the level at which industries or polluters comply with laid standards.
Environmental monitoring guide environmental impact assessment procedures, it also gives useful advice and suggestion to industries on how to manage their waste.

ASSESSMENT OF MOBOGUNJE'S SYSTEM APPROACH TO A THEORY OF RURAL-URBAN MIGRATION

                   MIGRATION
Introduction:
“Man is a mobile creature, capable of enquiring, susceptible to suggestion, and endowed with imagination and initiative. This explains why, having conceived with the notion that his wants might be satisfied elsewhere, he may decide not merely on going there but also on the means by which his can be achieved.”
The word ‘migration’ is derived from the Latin word ‘migrate’, which means to change one’s residence. The Encyclopedia Americana defines the term as a co-ordinated voluntary movement of a considerable number of people from an accustomed habitat to a new one. The International Encyclopedia of Social Sciences has defined it as the relatively permanent movement of persons over a significant distance. In International Encyclopedia of Population, ‘migration’ is defined as a geographical mobility that involves a change of usual residence between defined political or statistical areas or between residence areas of different types.
Migration is one of the distinguishing features of human beings that has been occurring since it started from the very beginning of man’s appearance in this universe. Though human mobility was the characteristic of even the stone age man, the rapidity of industrialisation and urbanisation of the modern age has given it big push and with the development of modern means of transport and communication, thousands of people in each country –especially from the third world - started to leave their usual abode in search of new jobs and fresh opportunities.
Migration is one of the causes of social change and it is one of the three basic reasons of demographic change, the other two being birth and death. “Migration is a two – way process; it is a response to economic and social change and equally it is a catalyst to change for those areas gaining and losing migrants.”A large number of studies have come out regarding migration analysis. Due to different approaches and methodologies used by each investigator and also by varied purposes and perspectives in their analysis the whole migration literature itself has become highly complex.
Volume of migration
1). The volume of migration within a territory varies with the degree of diversity of areas included in that territory.
2). The volume of migration varies with the diversity of people.
3). The volume of migration is related to the difficulty of surmounting the intervening obstacles.
4). The volume of migration varies with fluctuations in the economy.
5). Unless severe checks are imposed, both volume and rate of migration tend to increase with time.
Stream and Counter stream
1) Migration tends to take place largely within well-defined streams (e.g. From rural areas to nearby towns and towards major cities).
2) For every migration stream a counter stream develops (may be because of disappearance of positive factors at origin or acquisition of new skills or wealth at destination).
3) The efficiency of stream and counter stream tends to be low if origin and destination are similar.
4) The efficiency of migration stream will be higher if the intervening obstacles are great.
5) The efficiency of migration stream varies with economic conditions, being high in prosperous times and low in times of depression.


Characteristics of Migrants
1) Migration is selective which simply means that migrants are not a random sample of the population at origin.
2) Migrants responding primarily to plus factors at destination tend to be positively selected ( e.g. Highly educated).
3) Migrants responding primarily to minus factors at origin tend to be negatively selected; or when the minus factors are overwhelming the entire population groups, they may not be selected at all.
4) The degree of positive selection increases with the difficulty of intervening obstacles  e.g. The voyage of the Europeans to North Americas in the 17th and 18th c eliminated many of the weak.
5) The characteristics of migrants tend to be intermediate between the characteristics of population at origin and the population at destination.
System Approach
Some have conceived migration as a system in which migration is viewed as circular inter – dependent and self – modifying system in which the effects of changes in one part has a ripple effect through the whole system.
Mabogunje, after his study of rural – urban migration in Africa has presented a paper ‘A System Approach to a Theory of Rural – urban Mgration’ (1970). According to him migration system is made up of three basic element; Firstly, the migrant who is urged to leave the rural sector by incentives from the surroundings. Secondly, there are certain institutions that control and direct the degree of migration flow. Thirdly, various social, economic and political forces which play major role in he process. Although Mabogunje’s study is concerned with rural – urban migration in Africa, the conceptualisation has a wider application.


Systems Approach to a Theory of Rural-Urban Migration
In the growing literature on the study of migration, two theoretical issues have attracted the greatest attention, namely, why people migrate and how far they move. A simple model for explaining the reasons why people move has been formulated in terms of the “pull- push” hypothesis [Id, 191. This has been elaborated variously to take account of internal migration movements of the rural-rural, rural- urban, or urban-urban types and international migrations. The issue of how far people move has, in turn, given rise to the formulation of a surprisingly large number of models of varying degrees of statistical or mathematical sophistication.
Rural-urban migration also represents an essentially spatial con- comitant of the economic development of a region. Indeed, it has been suggested that one of the basic goals of economic development is to reverse the situation wherein 85 per cent of the population is in agriculture and lives in rural areas while only about 15 per cent is in non-agricultural activities and lives in the cities [lQ]. Rural-urban migration represents the spatial flow component of such a reversal. It is a complex phenomenon which involves not only the migrants but also a number of institutional agencies, and it gives rise to significant and highly varied adjustments everywhere in a region.
It can be argued with a great deal of justification that few of the theoretical models provided so far have considered migrations, espe- cially rural-urban migration, as a spatial process whose dynamics and spatial impact must form part of any comprehensive understanding of the phenomenon. It is the main contention of this paper that such an understanding can best be achieved within the framework of General Systems Theory [50]. This approach demands that a particular com- plex of variables be recognized as a system possessing certain proper- ties which are common to many other systems. It has the fundamental advantage of providing a conceptual framework within which a whole range of questions relevant to an understanding of the structure and operation of other systems can be asked of the particular phenomenon under study. In this way, new insights are provided into old problems and new relationships whose existence may not have been appreciated previously are uncovered. In this paper no attempt is made to define major components and relationships in a formal, mathematical manner. The emphwis here is on a verbal analysis of the ways in which the system operates. This, it is hoped, will enable us to identify areas where present knowledge is fragmentary and where future re- search may be concentrated with some profit.


Defining the System of Rural-Urban Migration
A system may be defined as a complex of interacting elements, together with their attributes and relationships [ll]. One of the major tasks in conceptualizing a phenomenon as a system, therefore, is to identify the basic interacting elements, their attributes, and their relationships. Once this is done, it soon becomes obvious that the system operates not in a void but in a special environment. For any given system, this environment comprises “the set of all objects a change in whose attributes affects the system, and also those objects whose attributes are changed by the behaviour of the system”. Thus, a system with its environment constitutes the universe of phenomena which is of interest in a given context.
It can be shown theoretically that areas with isolated and self- sufficient villages such as were found in many parts of Africa until recently, are not likely to experience rural-urban migration, since, in any case there would be hardly any cities in such areas. The fact that today such movements characterize many parts of the continent and are lately assuming spectacular proportions means that rural areas are in general no longer isolated or self-sufficient. It is therefore relevant to ask: what forces have contributed and continue to con- tribute to the decline in these conditions of isolation and self-sufficiency in the rural areas? They are, in the main, forces set in motion by increasing economic development. In most African countries, this was brought about initially by the colonial administrations and further reinforced in recent years by the activities of the new African governments. Decreasing isolation means not only improvement in transportation and communication links but also greater integration of the rural economy into a national economy. Such integration makes the rural economy more responsive to changes in wages and prices, consumer preferences, and the overall demand pattern within the country.
Within the systems framework, attention is focussed not only on the migrant but also on the various institutions (sub-systems) and the social, economic, and other relationships (adjustment mechanisms) which are an integral part of the process of the migrant’s transformation. The two most important sub-systems are the rural and the urban control sub-systems. A control sub-system is one which oversees the operation of the general system and determines when and how to increase or decrease the amount of flow in the system. A simple example is provided by the thermostat which controls the amount of heat that flows within a given area. If we accept the existence of control sub-systems in this type of migration movement, the problem then is to identify which institutions operate in this manner both in the rural and the urban areas.
In the rural areas, a true control sub-system would, of course, be the family, both nuclear and extended. In the first place, it is the family that holds back potential migrants until they are old enough to under- take the move. Even when they are of an age to move, the family still acts as a control sub-system in many ways. In some places, it enables members of both sexes to move out; in others, members of one sex tend to get away more easily than those of the other. Where the potential migrant is married, the issue of whether he can move alone or with his wife and children may depend on the customary role of the sexes in agricultural activities, the age at which marriage is encouraged, and the circumstances and age at which a young man may expect to be economically independent of his parents. More important as a control mechanism is the relation of family members to the family land, especially as this relation is expressed through the lineage system and the inheritance law. An inheritance law that encourages most of the land to go into the hands of the first child (the primogeniture rule) will tend to stimulate more migration of the other children [d] compared to one based on the equality of access (partible inheritance rule) by all the children. In either case, the size of the farmland, the nature of the major agricultural products, and the prevailing prices for these would also be of decisive significance.
Apart from the family, the village community itself may act as a control sub-system. Its controlling role is not often direct but is obvious in either a positive or negative way in the various activities which it sponsors or encourages. Thus, a village community which attempts to improve its economic conditions, for instance, through co-operative farming or marketing, may discourage, at least in the short-run, permanent migration. On the other hand, a village com- munity which puts emphasis on social betterment, for example, through education, may inadvertently stimulate migration to the city through training the younger generation to be more enlightened and more highly motivated. A pertinent aspect of the study of rural-urban migration is thus to assess how different rural communities react to migration away from the village. Such assessment should involve more than the opinion survey of the older generations. It should include an investigation of village activities and administration, and of the degree of cohesiveness in the community.
The Energy Concept in Systems Analysis
A system comprises not only matter (the migrant, the institutions, and the various organizations mentioned) but also energy. In the physical sense, energy is simply the capacity of a given body to do work. It can be expressed in a number of ways, but two forms of it are relevant here. There is “potential energy’’ which is the body’s power of doing work by virtue of stresses resulting from its relation either with its environment or with other bodies. The second form is “kinetic energy” which is the capacity of a body to do work by virtue of its own motion or activity. In a theory of rural-urban migration, potential energy can be likened to the stimuli acting on the rural individual to move. What is the nature of these stimuli? As pointed out earlier, a number of studies have tried to identify why people migrate and have come up with a variety of answers generally subsumed under the push-and-pull hypothesis. This suggests that people migrate from rural areas to the cities because of one of two general causes: overpopulation and environmental deterioration in the rural areas (the push factor) or the allurement or attraction of the city (the pull factor or the so-called “bright-light theory”). The push factor, it is claimed, explains migrations directed to earning extra income to pay the annual tax or to take a new bride or to buy a few manufactured articles or to escape oppressive local mores. The pull factor, on the other hand, explains migrations undertaken as a modern form of initiation ceremony to adult status or as the basis for later receiving preferential admiration of the village girls or as the product simply of an intense curiosity about the city. These explanations, to the extent that they have any theoretical validity at all, are relevant only at the aggregate level.
Relation Between a System and its Environment
Systems can be classified into three categories depending on the relationship they maintain with their environment; first, the isolated systems which exchange neither “matter” nor “energy” with their environment; second, the closed systems which exchange “energy” but not “matter”; third, the open systems which exchange both “energy” and ‘(matter.” The distinction between the categories, however, is largely one of scale and depends on which elements are regarded as belonging to the system and which to the environment. Thus, if the scale was to be reduced significantly, an open system could become an isolated system. Given the system in Figure 1, it can be seen that rural-urban migration is an open system involving not only an exchange of energy but. also of matter (in this case, persons) with the environment.
CONCLUSION
Rural-Urban migration is a circular, interdependent, progressively complex, and self modifying system in which the effect of changes in one par can be traced through the whole system. Rural-Urban migration is a continuous process, occurring in most countries all the time though at different levels of complexity. Migration systems link people, families, and communities over space in what today might be called transnational or translocal communities. This results in a geographical structuring and clustering of migration flows, which is far from a ‘random state’. By advancing the systems approach, Mabogunje is concerned with recognizing migration as a process with feedback mechanisms that change the future patterns of migration. He applies the systems approach to rural–urban migration within the African continent as a way of explaining why and how a rural migrant becomes a permanent urban dweller.

REFERENCE
Beajeau – Garnier,  Geography of Population (Longman, London, 1966), p.171.
 Encyclopaedia Americana, Vol. 19 (America Corporation, New York, 1969), p.48.
International Encyclopaedia of the Social Sciences, Vol.10 (Macmillan and Free Press, 1968), p.286.
  Internatioonal Encyclopaedia of Population, Vol. 2 (The Free Press, New York, 1982), p.448.
C.J.Lewis,  Human Migration: A Geographical perspective  (Croom Helm, London and Canberra, 1982), p.1.
See W. Farr, ‘Birth places of the people and the laws of migration’, Geographical Magazine, 3 (London, 1876), p.35- 37.
“Wage Labour and African Population Movements in CentraI Africa,’’ in Essays on African Population, ed. K. M. Barbour & R. M. Prothero. New York, 1962. P. 232.
 MORRILL, R. L. “Migration and the Spread and Growth of Urban Settlement,” Lund Studies in Geography, Ser. B, 26 (1965).
HALL, A. D. and R. E. FAGEN. “Definition of System,’’ General Systems Yearbook, 1 (1956), 18.
 LEWIS, W. A. Theory of Economic Growth. London, 1955. P. 333.
VON BERTALANFFLY. , “An Outline of General System Theory,” British Journal of the Philosophy of Science, 1 (1950), 134-165; - . “General System Theory,” General Systems Yearbook, 1 (1956), 1-10; -. “General System Theory-a Critical Review,” General Systems Year-book, 7 (1962), 1-20.
Mabogunje, A. L. (1970) ‘Systems approach to a theory of rural urban migration’, Geo- graphical Analysis, 2(1): 1-18.