# 4.5 Java1486-fun with java, understanding the fast fourier transform  (Page 4/14)

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## Output display of the FFT applet

A sample of the output produced by the FFT applet is shown in Figure 1 .

Figure 1. Transform of pulse with negative slope.

An examination of Figure 1 shows that the display produced by the applet contains two sections. One section is labeled f(x) and the other section islabeled F(k).

This is an interactive applet with the ability to transform the complex samples represented by f(x) into complex samples represented by F(k).Alternatively, the applet can be used to transform complex samples represented by F(k) into complex samples represented by f(x).

## Real and imaginary sections

Each section contains two boxes, one labeled Real and the other labeled Imaginary. One box contains a visual representation of a set of real samplesand the other box contains a visual representation of a set of imaginary samples.

With one exception, each sample is represented by a black circle. In each box, one of the samples is represented by an empty circle. The empty circle represents an index value of zero. Samples to the right of the sample withthe empty circle are samples at positive indices, and samples to the left of the sample with the empty circle are samples at negative indices.

## A complex sample

A pair of values, one taken from the Real box and one taken from the Imaginary box, represents a complex sample.

Any of the circles can be interactively moved up or down with the mouse. The value of each sample is represented by the distance of the correspondingcircle from the horizontal line.

When a change is made to the value of any sample belonging to either f(x) for F(k), the transformation is recomputed and the display of the otherfunction is modified accordingly. If you modify the value of a sample in f(x), the values in F(k) are automatically modified to show the Fouriertransform of f(x). If you modify the value of a sample in F(k), the values in f(x) are automatically modified to show the inverse Fourier transform ofF(k).

This is an extremely powerful interactive tool.

## Powers of two

Many and perhaps most FFT algorithms require the input series to contain a number of complex samples that is a power of two such as 2, 4, 8, 16, 32,etc. Most FFT algorithms also produce the same number of complex samples in the output as are provided in the input. The FFT algorithm used in thisapplet is no exception to those rules.

A pull-down list at the bottom of the applet lets the user specify 16, 32, or 64 complex samples for both the input and the output. All of theexamples in this module use 16 complex samples for input and output.

## Location of the origin

The applet also provides a check box that allows the user to cause the origin (the empty circle at index value zero) to either be centered or placed at the left end. The display in Figure 1 has the origin centered. Other displays that I will use later have the origin at the left end.

## Other applet controls

The other pull-down list and the button at the bottom of the applet provide other control features that don't need to be discussed here. Istrongly urge you to download this applet and experiment with it. The results can be very enlightening.

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
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