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{{More footnotes|date=April 2011}}{{Infobox scientist
'''Edward Nelson''' (born May 4, 1932, in [[Decatur, Georgia]]) is a professor in the Mathematics Department at [[Princeton University]].   He is known for his work on [[mathematical physics]] and [[mathematical logic]]. In mathematical logic, he is noted especially for his [[internal set theory]], and his controversial views on [[ultrafinitism]] and the [[consistency]] of [[Peano arithmetic|arithmetic]].
| name              = Edward Appleton
| image            = Appleton.jpg
| image_size        = 190px
| caption          =
| birth_name        = Edward Victor Appleton
| birth_date        = {{Birth date|1892|9|6|df=y}}
| birth_place      = [[Bradford]], [[West Yorkshire]], [[England]]
| death_date        = {{death date and age|1965|4|21|1892|9|6|df=y}}
| death_place      = [[Edinburgh]], [[Scotland]] idc
| nationality      = [[England|English]]
| field            = [[Physics]]
| workplaces        = [[Cambridge University]]</br>[[King's College London]]</br>[[Edinburgh University]]
| alma_mater        = [[Cambridge University]]
| doctoral_advisor  = <!--The PhD had only just started in Cambridge in 1919-->
| academic_advisors = [[J. J. Thomson]] </br>[[Ernest Rutherford]]
| doctoral_students =
| notable_students  = [[J. A. Ratcliffe]]</br>[[Charles Oatley]]
| known_for        = [[Ionosphere|Ionospheric Physics]]</br>[[F region|Appleton layer]]
| prizes            = {{nowrap|[[Nobel Prize in Physics]] (1947)}}
}}
 
'''Sir Edward Victor Appleton''', [[Order of the British Empire|GBE]], [[Knight Commander of the Order of the Bath|KCB]], [[Fellow of the Royal Society|FRS]] (6 September 1892 – 21 April 1965)  was an [[United Kingdom|English]] [[physicist]].<ref>{{cite web|title=Sir Edward Appleton (1892 - 1965)|url=http://www.bbc.co.uk/history/historic_figures/appleton_edward.shtml}}</ref> 
 
==Biography==
Appleton was born in [[Bradford]], [[West Yorkshire]] and educated at [[Hanson School|Hanson Grammar School]]. At the age of 18 he won a scholarship to [[St John's College, Cambridge]]. He graduated with a first class degree in Natural Sciences.
 
During the First World War he joined the [[Duke of Wellington's Regiment|West Riding Regiment]], and later transferred to the [[Royal Engineers]]. After returning from active service in [[World War I]], Appleton became assistant demonstrator in experimental physics at the [[Cavendish Laboratory]] in 1920. He was professor of physics at [[King's College London]] (1924–36) and professor of natural philosophy at [[University of Cambridge|Cambridge University]] (1936–39). From 1939 to 1949 he was secretary of the [[Department of Scientific and Industrial Research]]. Knighted in 1941, he received the 1947 [[Nobel Prize in Physics]] for his contributions to the knowledge of the [[ionosphere]], which led to the development of [[radar]].
 
From 1949 until his death in 1965, he was Principal and Vice-Chancellor of the [[University of Edinburgh]].<ref>{{cite book | first=Derek A J| last=Lister | title=Bradford's Own | year=2004 | publisher=Sutton | isbn=0-7509-3826-9}}</ref> In 1956, the BBC invited him to deliver the annual [http://www.bbc.co.uk/reithlectures Reith Lectures]. Across a series of six radio broadcasts, titled ''[http://www.bbc.co.uk/programmes/p00h9lkv Science and the Nation]'', Appleton explored the many facets of scientific activity in Britain at the time.
 
== Works ==
 
Appleton had observed that the strength of the radio signal from a transmitter on a frequency such as the medium wave band and over a path of a hundred miles or so was constant during the day but that it varied during the night. This led him to believe that it was possible that two radio signals were being received. One was traveling along the ground, and another was reflected by a layer in the upper atmosphere. The fading or variation in strength of the overall radio signal received resulted from the [[Interference (wave propagation)|interference]] pattern of the two signals.


==Career==
The existence of a reflecting atmospheric layer was not in itself a completely new idea.  Balfour Stewart had suggested the idea in the late nineteenth century to explain rhythmic changes in the earth’s magnetic field.  More recently, in 1902, [[Oliver Heaviside]] and A.E. Kennelly had suggested such a hypothesis may explain the success Marconi had in transmitting his signals across the Atlantic. Calculations had shown that natural bending of the radio waves was not sufficient to stop them from simply “shooting off” into empty space before they reached the receiver.


Nelson received his Ph.D. in 1955 from the [[University of Chicago]], where he worked with [[Irving Segal]].
Appleton thought the best place to look for evidence of the ionosphere was in the variations he believed it was causing around sunset in radio signal receptions. It was sensible to suggest these variations were due to the interference of two waves but an extra step to show that the second wave causing the interference (the first being the ground wave) was coming down from the ionosphereThe experiment he designed had two methods to show ionospheric influence and both allowed the height of the lower boundary of reflection (thus the lower boundary of the reflecting layer) to be determined.  The first method was called frequency modulation and the second was to calculate the angle of arrival of the reflected signal at the receiving aerial. 
He was a member of the [[Institute for Advanced Study]] from 1956–1959He has held a position at [[Princeton University]] from 1959 to the present, attaining the rank of professor there in 1964.
The frequency modulation method exploits the fact that there is a path difference between the ground wave and the reflected wave, meaning they travel different distances from sender to receiver.


==Early work==
Let the distance AC travelled by the ground wave be h and the distance ABC travelled by the reflected wave h’.  The path difference is:


Nelson has made contributions to the theory of infinite dimensional [[group representation]]s, the mathematical treatment of [[quantum field theory]], the use of [[stochastic process]]es in [[quantum mechanics]], and the reformulation of [[probability theory]] in terms of [[non-standard analysis]].
<math> h'-h=D  </math>


For many years he worked on [[mathematical physics]] and probability theory, and still has a residual interest in these fields, particularly in possible extensions of stochastic mechanics to [[field theory (physics)|field theory]].
The wavelength of the transmitted signal is λ . The number of wavelengths difference between the paths h and h’ is:


In 1950, Nelson formulated a popular variant of the [[four color problem]]. What is the chromatic number, denoted <math>\chi</math>, of the plane? In more detail, what is the smallest number of colors sufficient for coloring the points of the Euclidean plane in such a way that no two points of the same color are unit distance apart?<ref>p.23, Soifer, Alexander (2008); The Mathematical Coloring Book: Mathematics of Coloring and the Colorful Life of its Creators; New York: Springer. ISBN 978-0-387-74640-1</ref> We know by simple arguments that 4&nbsp;≤&nbsp;''&chi;''&nbsp;≤&nbsp;7. The problem was introduced to a wide mathematical audience by [[Martin Gardner]] in his October 1960 [[Mathematical Games]] column. The chromatic number problem, also now known as the [[Hadwiger–Nelson problem]], was also a favorite of [[Paul Erdős]], who mentioned it frequently in his problems lectures.
<math> \frac{h-h'}{\lambda}=\frac{D}{\lambda}=N  </math>


==Work on foundations==
If N is an integer number, then constructive interference will occur, this means a maximum signal will be achieved at the receiving end. If N is an integer number of half wavelengths, then destructive interference will occur and a minimum signal will be received.  Let us assume we are receiving a maximum signal for a given wavelength λ.  If we start to change λ, this is the process called frequency modulation,  N will no longer be a whole number and destructive interference will start to occur, meaning the signal will start to fade.  Now we keep changing λ until a maximum signal is once again received.  The means that for our new value  λ’, our new value N’ is an also an integer number.  If we have lengthened λ then we know that N’ is one less than N. Thus:
In recent years he has been working on mathematical logic and the foundations of mathematics. One of his goals is to extend IST ([[Internal Set Theory]]—a version of a portion of [[Abraham Robinson]]'s [[non-standard analysis]]) in a natural way to include external functions and sets, in a way that provides an external function with specified properties unless there is a finitary obstacle to its existence. Other work centers on fragments of arithmetic, studying the divide between those theories interpretable in [[Robinson arithmetic|Raphael Robinson's Arithmetic]] and those that are not; [[computational complexity theory|computational complexity]], including the problem of whether [[P = NP problem|P is equal to NP or not]]; and automated proof checking.


In September 2011, Nelson announced that his he had proved that [[Peano arithmetic]] was logically inconsistent. An error was found in the proof, and he retracted the claim.
<math> N-N'=\frac{D}{\lambda}-\frac{D}{\lambda'}=1  </math>


==Notes==
Rearranging for D gives:
{{reflist}}


==References==
<math> D=h-h'=\frac{1}{\frac{1}{\lambda}-\frac{1}{\lambda'}}  </math>
* [http://math.princeton.edu/~nelson/cv.pdf Curriculum Vitae]
 
As we know λ  and  λ’, we can calculate D.  Using the approximation that ABC is an isosceles triangle, we can use our value of D to calculate the height of the reflecting layer.  This method is a slightly simplified version of the method used by Appleton and his colleagues to work out a first value for the height of the ionosphere in 1924.  In their experiment, they used the [[BBC]] broadcasting station in [[Bournemouth]] to vary the wavelengths of its emissions after the evening programs had finished.  They installed a receiving station in Oxford to monitor the interference effects.  The receiving station had to be in [[Oxford]] as there was no suitable emitter at the right distance of about 100 km from Cambridge in those days. 
This frequency modulation method revealed that the point from which waves were being reflected was approximately 90 km.  However, it did not establish that the waves were reflected from above, indeed they may have been coming from hills somewhere between Oxford and Bournemouth.  The second method, which involved finding the angle of incidence of the reflected waves at the receiver, showed for sure that they were coming from above.  Triangulations from this angle gave results for the height of reflection compatible with the frequency modulation method.  We will not go into this method in detail because it involves fairly complex calculations using Maxwell’s electromagnetic theory.
Far from being conclusive, the success of the Oxford-Bournemouth experiment revealed a vast new field of study.  It showed that there was indeed a reflecting layer high above the earth but it also posed many new questions.  What was the constitution of this layer, how did it reflect the waves, was it the same all over the earth, why did its effects change so dramatically between day and night, did it change throughout the year?  Appleton would spend the rest of his life answering these questions.  He developed a magneto-ionic theory based on the previous work of [[Hendrik Lorentz|Lorentz]] and [[James Clerk Maxwell|Maxwell]] to model the workings of this part of the atmosphere.  Using this theory and further experiments, he showed that the so called [[Kennelly-Heaviside layer]] was heavily ionised and thus conducting.  This led to the term ionosphere.  He showed free electrons to be the ionising agents.  He discovered that the layer could be penetrated by waves above a certain frequency and that this critical frequency could be used to calculate the electron density in the layer.  However these penetrating waves would also be reflected back, but from a much higher layer.  This showed the ionosphere had a much more complex structure than first anticipated.  The lower level was labelled E – Layer, reflected longer wavelengths and was found to be at approximately 125 km.  The high level, which had much higher electron density, was labelled F – Layer and could reflect much shorter wavelengths that penetrated the lower layer.  It is situated 300 – 400 km above the earth’s surface.  It is this which is often referred to as the Appleton Layer as is responsible for enabling most long range short wave telecommunication.<ref>{{cite web |url=http://www.ieeeghn.org/wiki/index.php/Edward_V._Appleton |title=Edward V. Appleton |author=IEEE Global History Network |date=2011 |publisher=IEEE History Center |accessdate=14 July 2011}}</ref>
The magneto-ionic theory also allowed Appleton to explain the origin of the mysterious fadings heard on the radio around sunset.  During the day, the light from the sun causes the molecules in the air to become ionised even at fairly low altitudes.  At these low altitudes, the density of the air is great and thus the electron density of ionised air is very large.  Due to this heavy ionisation, there is strong absorption of electromagnetic waves caused by ‘electron friction’. Thus in transmissions over any distance, there will be no reflections as any waves apart from the one at ground level will be absorbed rather than reflected.  However, when the sun sets, the molecules slowly start to recombine with their electrons and the free electron density levels drop.  This means absorption rates diminish and waves can be reflected with sufficient strengths to be noticed, leading to the interference phenomena we have mentioned.  For these interference patterns to occur though, there must not simply be the presence of a reflected wave but a change in the reflected wave.  Otherwise the interference is constant and fadings would not be heard.  The received signal would simply be louder or softer than during the day.  This suggests the height at which reflection happens must slowly change as the sun sets.  Appleton found in fact that it increased as the sun set and then decreased as the sun rose until the reflected wave was too weak to record.  This variation is compatible with the theory that ionisation is due to the sun’s influence.  At sunset, the intensity of the sun’s radiation will be much less at the surface of the earth than it is high up in the atmosphere.  This means ionic recombination will progress slowly from lower altitudes to higher ones and therefore the height at which waves are reflected slowly increases as the sun sets.
The basic idea behind Appleton’s work is so simple that it is hard to understand at first how he devoted almost all of his scientific career to its study.  However, in the last couple of paragraphs some of the complexities of the subject have been introduced.  Like many other fields, it is one that grows in intricacy the more it is studied.    By the end of his life, ionospheric observatories had been set up all over the world to provide a global map of the reflecting layers.  Links were found to the 11 year sunspot cycle and the [[Aurora Borealis]], the magnetic storms that occur in high latitudes.  This  became particularly relevant during the second world war when the storms would lead to radio blackouts.  Thanks to Appleton’s research, the periods when these would occur could be predicted and communication could be switched to wavelengths that would be least affected.  [[RADAR]], another crucial wartime innovation, was one that came about thanks to Appleton’s work.  On a very general level, his research consisted in determining the distance of reflecting objects from radio signal transmitters.  This is exactly the idea of RADAR and the flashing dots that appear on the screen (a cathode ray tube) scanned by the circulating ‘searcher’ bar.  This system was developed partly by Appleton as a new method, called the pulse method, to make ionospheric measurements.    It was later adapted by [[Robert Watson-Watt]] to detect aeroplanes.  Nowadays, ionospheric data is important when communications with satellites are considered.  The correct frequencies for these signals must be selected so that they actually reach the satellites without being reflected or deviated before.
 
In 1974 the [[Radio Research Station|Radio and Space Research Station]] was renamed the Appleton Laboratory in honour of the man who had done so much to establish the UK as a leading force in ionospheric research, and had been involved with the station first as a researcher and then as secretary of its parent body, the Department of Scientific and Industrial Research.
 
==Legacy==
* the [[Rutherford Appleton Laboratory]]
* the [[Appleton Tower]] at the [[University of Edinburgh]]
* the [http://www.bilk.ac.uk/college/depts/science/ Appleton Science Building] at [[Bradford College (England)|Bradford College]]
* Appleton Academy, an up and coming new school, which will replace Wyke Manor School and High Fernley Primary School in the Wyke district of [[Bradford|South Bradford]]. This will be the first 'through-school' in West Yorkshire.
* The crater [[Appleton (crater)|Appleton]] on the [[Moon]] is named in his honour.
* The Appleton Layer, which is the higher atmospheric ionized layer above the E-layer
* The annual [http://www.theiet.org/events/appleton/ Appleton Lecture] at the [http://www.theiet.org/ Institute of Engineering Technology], [[Institution of Engineering and Technology|IET]].
* Likely inspiration for the pseudonym [[Victor Appleton]] – the fictitious author of the [[Tom Swift]] series of novels
* Appleton Academy in Bradford Wyke
 
== Honours and awards ==
* Fellow of the [[Royal Society]] (1927)
* Foreign Honorary Member of the [[American Academy of Arts and Sciences]] (1936)<ref name=AAAS>{{cite web|title=Book of Members, 1780–2010: Chapter A|url=http://www.amacad.org/publications/BookofMembers/ChapterA.pdf|publisher=American Academy of Arts and Sciences|accessdate=19 April 2011}}</ref>
* [[Nobel Prize in Physics]] (1947)


==See also==
==See also==
*[[Influence of non-standard analysis]]
*[[Kennelly–Heaviside layer]]
 
== References ==
{{Reflist}}
 
* {{cite encyclopedia | last=Süsskind | first=Charles | title=Appleton, Edward Victor | encyclopedia=[[Dictionary of Scientific Biography]] | volume=1 | pages=195–196  | publisher=Charles Scribner's Sons | location=New York | year=1970 | isbn=0-684-10114-9}}
* {{Cite journal|author=Appleton, EV & Ratcliffe, JA|year=1927|month=|title=On the Nature of Wireless Signal Variations I|journal=Proc, Royal Soc. Lon.}}
* {{Cite journal|author=Appleton, EV & Barnett|year=1925|month=|title=On Some direct Evidence for Downward Atmospheric Reflection Of Electric Rays|journal=Pro. Roy. Soc. Series A}}
* {{Cite journal|author=Appleton, EV|year=1932|title=Wireless Studies of the Ionosphere|journal=J. Inst. Elec. Engrs.}}
* {{Cite journal|author=Ratcliffe, JA|year=1975|title=The Early Atmospheric Investigations Of Appleton and his Colleagues|journal=Phil. Trans. Roy. Soc. Lon.}}
* {{Cite journal|year=1966|month=Nov|title=Sir Edward Appleton|journal=Biographical Memoirs of Fellows of the Royal Society|volume=12 }}
* {{Cite book|last=Appleton |first=EV |coauthors=Ratcliffe, JA|year=1929|title=The Physical Principles of Wireless|publisher=Methuen }}
* {{Cite book|last=Clark|first=Ronald|year=1971|title=Sir Edward Appleton|publisher=Pergamon Press |location=Oxford}}


==External links==
==External links==
*[http://www.math.princeton.edu/~nelson/ Edward Nelson's Homepage]
*[http://conferences.theiet.org/lectures/appleton/index.htm IET Appleton lectures]
* [http://nobelprize.org/physics/laureates/1947/index.html "Sir Edward Victor Appleton"].  ''nobelprize.org''.  Accessed October 21, 2007.  (Citation: Nobel Prize in Physics: 1947, "for his investigations of the physics of the upper atmosphere especially for the discovery of the so-called Appleton layer."  [Hyperlinked account.  Provides link to BBC ''Historic Figures'' biography.]
* [http://nobelprize.org/nobel_prizes/physics/laureates/1947/appleton-bio.html "Sir Edward Victor Appleton: Nobel Prize in Physics 1947"] – Biography from ''Nobel Lectures, Physics 1942–1962'' (Amsterdam: Elsevier Publishing Company, 1964).  [Hyperlinked in previous entry.]
* [http://www.bbc.co.uk/history/historic_figures/appleton_edward.shtml "Sir Edward Victor Appleton (1892–1965):] Appleton was an English physicist and Nobel prize winner who discovered the ionosphere."  ''Historic Figures'', ''bbc.co.uk''.  Accessed October 21, 2007.  (Photograph of Appleton c. 1935 ©). [Provides link to Nobel Foundation account, listed above.]
* [http://nobelprize.org/nobel_prizes/physics/laureates/1947/appleton-bio.html Nobelprize.org Biography]
* ''[http://www.bbc.co.uk/programmes/p00h9lkv Science and the Nation]'' The BBC [http://www.bbc.co.uk/reithlectures Reith Lectures], 1956, by Edward Appleton
 
{{s-start}}
{{s-aca}}
{{succession box | before=[[John Fraser (educator)|Sir John Fraser]]|title=[[Edinburgh University Principals|Principals of Edinburgh University]] | years=1948–1965| after=[[Michael Swann]]}}
{{s-end}}
{{Nobel Prize in Physics Laureates 1926-1950}}
{{IEEE Medal of Honor Laureates 1951-1975}}


{{Persondata <!-- Metadata: see [[Wikipedia:Persondata]]. -->
{{Persondata <!-- Metadata: see [[Wikipedia:Persondata]]. -->
| NAME              = Nelson, Edward
| NAME              = Appleton, Edward Victor
| ALTERNATIVE NAMES =
| ALTERNATIVE NAMES =  
| SHORT DESCRIPTION =
| SHORT DESCRIPTION =  
| DATE OF BIRTH    = May 4, 1932
| DATE OF BIRTH    = 6 September 1892
| PLACE OF BIRTH    =
| PLACE OF BIRTH    = [[Bradford]], [[West Yorkshire]], [[England]]
| DATE OF DEATH    =
| DATE OF DEATH    = 21 April 1965
| PLACE OF DEATH    =
| PLACE OF DEATH    = [[Edinburgh]], [[Scotland]]
}}
}}
{{DEFAULTSORT:Nelson, Edward}}
{{DEFAULTSORT:Appleton, Edward Victor}}
[[Category:1932 births]]
[[Category:1892 births]]
[[Category:Members of the United States National Academy of Sciences]]
[[Category:1965 deaths]]
[[Category:American mathematicians]]
[[Category:Academics of King's College London]]
[[Category:American logicians]]
[[Category:Academics of the University of London]]
[[Category:Set theorists]]
[[Category:Alumni of St John's College, Cambridge]]
[[Category:University of Chicago alumni]]
[[Category:Alumni of the University of Edinburgh]]
[[Category:Princeton University faculty]]
[[Category:British Nobel laureates]]
[[Category:Living people]]
[[Category:English academics]]
[[Category:Mathematical physicists]]
[[Category:English physicists]]
 
[[Category:Fellows of the Royal Society]]
[[Category:Freemasons]]
[[Category:IEEE Medal of Honor recipients]]
[[Category:Knights Grand Cross of the Order of the British Empire]]
[[Category:Nobel laureates in Physics]]
[[Category:People from Bradford]]
[[Category:Principals of the University of Edinburgh]]
[[Category:Royal Medal winners]]
[[Category:Knights Commander of the Order of the Bath]]
[[Category:Recipients of King Haakon VII's Cross of Liberty]]
[[Category:Honorary Fellows of the Royal Society of Edinburgh]]
[[Category:Fellows of the American Academy of Arts and Sciences]]
[[Category:English Nobel laureates]]


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Revision as of 17:58, 11 August 2014

Template:More footnotesTemplate:Infobox scientist

Sir Edward Victor Appleton, GBE, KCB, FRS (6 September 1892 – 21 April 1965) was an English physicist.[1]

Biography

Appleton was born in Bradford, West Yorkshire and educated at Hanson Grammar School. At the age of 18 he won a scholarship to St John's College, Cambridge. He graduated with a first class degree in Natural Sciences.

During the First World War he joined the West Riding Regiment, and later transferred to the Royal Engineers. After returning from active service in World War I, Appleton became assistant demonstrator in experimental physics at the Cavendish Laboratory in 1920. He was professor of physics at King's College London (1924–36) and professor of natural philosophy at Cambridge University (1936–39). From 1939 to 1949 he was secretary of the Department of Scientific and Industrial Research. Knighted in 1941, he received the 1947 Nobel Prize in Physics for his contributions to the knowledge of the ionosphere, which led to the development of radar.

From 1949 until his death in 1965, he was Principal and Vice-Chancellor of the University of Edinburgh.[2] In 1956, the BBC invited him to deliver the annual Reith Lectures. Across a series of six radio broadcasts, titled Science and the Nation, Appleton explored the many facets of scientific activity in Britain at the time.

Works

Appleton had observed that the strength of the radio signal from a transmitter on a frequency such as the medium wave band and over a path of a hundred miles or so was constant during the day but that it varied during the night. This led him to believe that it was possible that two radio signals were being received. One was traveling along the ground, and another was reflected by a layer in the upper atmosphere. The fading or variation in strength of the overall radio signal received resulted from the interference pattern of the two signals.

The existence of a reflecting atmospheric layer was not in itself a completely new idea. Balfour Stewart had suggested the idea in the late nineteenth century to explain rhythmic changes in the earth’s magnetic field. More recently, in 1902, Oliver Heaviside and A.E. Kennelly had suggested such a hypothesis may explain the success Marconi had in transmitting his signals across the Atlantic. Calculations had shown that natural bending of the radio waves was not sufficient to stop them from simply “shooting off” into empty space before they reached the receiver.

Appleton thought the best place to look for evidence of the ionosphere was in the variations he believed it was causing around sunset in radio signal receptions. It was sensible to suggest these variations were due to the interference of two waves but an extra step to show that the second wave causing the interference (the first being the ground wave) was coming down from the ionosphere. The experiment he designed had two methods to show ionospheric influence and both allowed the height of the lower boundary of reflection (thus the lower boundary of the reflecting layer) to be determined. The first method was called frequency modulation and the second was to calculate the angle of arrival of the reflected signal at the receiving aerial.

The frequency modulation method exploits the fact that there is a path difference between the ground wave and the reflected wave, meaning they travel different distances from sender to receiver.

Let the distance AC travelled by the ground wave be h and the distance ABC travelled by the reflected wave h’. The path difference is:

hh=D

The wavelength of the transmitted signal is λ . The number of wavelengths difference between the paths h and h’ is:

hhλ=Dλ=N

If N is an integer number, then constructive interference will occur, this means a maximum signal will be achieved at the receiving end. If N is an integer number of half wavelengths, then destructive interference will occur and a minimum signal will be received. Let us assume we are receiving a maximum signal for a given wavelength λ. If we start to change λ, this is the process called frequency modulation, N will no longer be a whole number and destructive interference will start to occur, meaning the signal will start to fade. Now we keep changing λ until a maximum signal is once again received. The means that for our new value λ’, our new value N’ is an also an integer number. If we have lengthened λ then we know that N’ is one less than N. Thus:

NN=DλDλ=1

Rearranging for D gives:

D=hh=11λ1λ

As we know λ and λ’, we can calculate D. Using the approximation that ABC is an isosceles triangle, we can use our value of D to calculate the height of the reflecting layer. This method is a slightly simplified version of the method used by Appleton and his colleagues to work out a first value for the height of the ionosphere in 1924. In their experiment, they used the BBC broadcasting station in Bournemouth to vary the wavelengths of its emissions after the evening programs had finished. They installed a receiving station in Oxford to monitor the interference effects. The receiving station had to be in Oxford as there was no suitable emitter at the right distance of about 100 km from Cambridge in those days.

This frequency modulation method revealed that the point from which waves were being reflected was approximately 90 km. However, it did not establish that the waves were reflected from above, indeed they may have been coming from hills somewhere between Oxford and Bournemouth. The second method, which involved finding the angle of incidence of the reflected waves at the receiver, showed for sure that they were coming from above. Triangulations from this angle gave results for the height of reflection compatible with the frequency modulation method. We will not go into this method in detail because it involves fairly complex calculations using Maxwell’s electromagnetic theory.

Far from being conclusive, the success of the Oxford-Bournemouth experiment revealed a vast new field of study. It showed that there was indeed a reflecting layer high above the earth but it also posed many new questions. What was the constitution of this layer, how did it reflect the waves, was it the same all over the earth, why did its effects change so dramatically between day and night, did it change throughout the year? Appleton would spend the rest of his life answering these questions. He developed a magneto-ionic theory based on the previous work of Lorentz and Maxwell to model the workings of this part of the atmosphere. Using this theory and further experiments, he showed that the so called Kennelly-Heaviside layer was heavily ionised and thus conducting. This led to the term ionosphere. He showed free electrons to be the ionising agents. He discovered that the layer could be penetrated by waves above a certain frequency and that this critical frequency could be used to calculate the electron density in the layer. However these penetrating waves would also be reflected back, but from a much higher layer. This showed the ionosphere had a much more complex structure than first anticipated. The lower level was labelled E – Layer, reflected longer wavelengths and was found to be at approximately 125 km. The high level, which had much higher electron density, was labelled F – Layer and could reflect much shorter wavelengths that penetrated the lower layer. It is situated 300 – 400 km above the earth’s surface. It is this which is often referred to as the Appleton Layer as is responsible for enabling most long range short wave telecommunication.[3]

The magneto-ionic theory also allowed Appleton to explain the origin of the mysterious fadings heard on the radio around sunset. During the day, the light from the sun causes the molecules in the air to become ionised even at fairly low altitudes. At these low altitudes, the density of the air is great and thus the electron density of ionised air is very large. Due to this heavy ionisation, there is strong absorption of electromagnetic waves caused by ‘electron friction’. Thus in transmissions over any distance, there will be no reflections as any waves apart from the one at ground level will be absorbed rather than reflected. However, when the sun sets, the molecules slowly start to recombine with their electrons and the free electron density levels drop. This means absorption rates diminish and waves can be reflected with sufficient strengths to be noticed, leading to the interference phenomena we have mentioned. For these interference patterns to occur though, there must not simply be the presence of a reflected wave but a change in the reflected wave. Otherwise the interference is constant and fadings would not be heard. The received signal would simply be louder or softer than during the day. This suggests the height at which reflection happens must slowly change as the sun sets. Appleton found in fact that it increased as the sun set and then decreased as the sun rose until the reflected wave was too weak to record. This variation is compatible with the theory that ionisation is due to the sun’s influence. At sunset, the intensity of the sun’s radiation will be much less at the surface of the earth than it is high up in the atmosphere. This means ionic recombination will progress slowly from lower altitudes to higher ones and therefore the height at which waves are reflected slowly increases as the sun sets.

The basic idea behind Appleton’s work is so simple that it is hard to understand at first how he devoted almost all of his scientific career to its study. However, in the last couple of paragraphs some of the complexities of the subject have been introduced. Like many other fields, it is one that grows in intricacy the more it is studied. By the end of his life, ionospheric observatories had been set up all over the world to provide a global map of the reflecting layers. Links were found to the 11 year sunspot cycle and the Aurora Borealis, the magnetic storms that occur in high latitudes. This became particularly relevant during the second world war when the storms would lead to radio blackouts. Thanks to Appleton’s research, the periods when these would occur could be predicted and communication could be switched to wavelengths that would be least affected. RADAR, another crucial wartime innovation, was one that came about thanks to Appleton’s work. On a very general level, his research consisted in determining the distance of reflecting objects from radio signal transmitters. This is exactly the idea of RADAR and the flashing dots that appear on the screen (a cathode ray tube) scanned by the circulating ‘searcher’ bar. This system was developed partly by Appleton as a new method, called the pulse method, to make ionospheric measurements. It was later adapted by Robert Watson-Watt to detect aeroplanes. Nowadays, ionospheric data is important when communications with satellites are considered. The correct frequencies for these signals must be selected so that they actually reach the satellites without being reflected or deviated before.

In 1974 the Radio and Space Research Station was renamed the Appleton Laboratory in honour of the man who had done so much to establish the UK as a leading force in ionospheric research, and had been involved with the station first as a researcher and then as secretary of its parent body, the Department of Scientific and Industrial Research.

Legacy

Honours and awards

See also

References

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.



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    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534

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    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
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