# 0.3 Modelling corruption  (Page 7/11)

 Page 7 / 11
$w\left(t\right)=\frac{A}{2j}\left[{e}^{j2\pi {f}_{0}t},-,{e}^{-j2\pi {f}_{0}t}\right].$

Applying the linearity property [link] and the result of Exercise  [link] gives

$\begin{array}{ccc}\hfill \mathcal{F}\left\{w\left(t\right)\right\}& =& \frac{A}{2j}\left[\mathcal{F},\left\{{e}^{j2\pi {f}_{0}t}\right\},-,\mathcal{F},\left\{{e}^{-j2\pi {f}_{0}t}\right\}\right]\hfill \\ & =& j\frac{A}{2}\left[-,\delta ,\left(f-{f}_{0}\right),+,\delta ,\left(f+{f}_{0}\right)\right].\hfill \end{array}$

Thus, the spectrum of a sine wave is a pair of $\delta$ functions with opposite signs, located symmetrically about zero frequency. The corresponding magnitude spectrum,shown in [link] , is at the heart of one importantinterpretation of the Fourier transform: it shows the frequency content of any signal by displayingwhich frequencies are present (and which frequencies are absent) from the waveform. For example, [link] (a) shows the magnitude spectrum $W\left(f\right)$ of a real-valued signal $w\left(t\right)$ . This can be interpreted as saying that $w\left(t\right)$ contains (or is made up of) “all the frequencies” up to $B$ Hz, and that it contains no sinusoids with higher frequency. Similarly,the modulated signal $s\left(t\right)$ in [link] (b) contains all positive frequencies between ${f}_{c}-B$ and ${f}_{c}+B$ , and no others.

Note that the Fourier transform in [link] is purely imaginary, as it must be because $w\left(t\right)$ is odd (see  [link] ). The phase spectrum is a flat line at $-{90}^{\circ }$ because of the factor  $j$ .

What is the magnitude spectrum of $\mathrm{sin}\left(2\pi {f}_{0}t+\theta \right)$ ? Hint: Use the frequency shift property [link] . Show that the spectrum of $\mathrm{cos}\left(2\pi {f}_{0}t\right)$ is $\frac{1}{2}\left(\delta \left(f-{f}_{0}\right)+\delta \left(f+{f}_{0}\right)\right)$ . Compare this analytical result to the numerical resultsfrom Exercise  [link] .

Let ${w}_{i}\left(t\right)={a}_{i}\mathrm{sin}\left(2\pi {f}_{i}t\right)$ for $i=1,2,3$ . Without doing any calculations, write down the spectrum of $v\left(t\right)={w}_{1}\left(t\right)+{w}_{2}\left(t\right)+{w}_{3}\left(t\right)$ . Hint: Use linearity. Graph the magnitude spectrum of $v\left(t\right)$ in the same manner as in [link] . Verify your results with a simulation mimicking that in  [link] .

Let $W\left(f\right)=\mathrm{sin}\left(2\pi f{t}_{0}\right)$ . What is the corresponding time function?

## Convolution in time: it's what linear systems do

Suppose that a system has impulse response $h\left(t\right)$ , and that the input consists of a sum of three impulses occurring at times ${t}_{0}$ , ${t}_{1}$ , and ${t}_{2}$ , with amplitudes ${a}_{0}$ , ${a}_{1}$ , and ${a}_{2}$ (for example, the signal $w\left(t\right)$ of [link] ). By linearity of the Fourier transform, property [link] , the output is a superpositionof the outputs due to each of the input pulses. The output due to the first impulse is ${a}_{0}h\left(t-{t}_{0}\right)$ , which is the impulse response scaled by the size of the input and shifted to beginwhen the first input pulse arrives. Similarly, the outputs to the second and thirdinput impulses are ${a}_{1}h\left(t-{t}_{1}\right)$ and ${a}_{2}h\left(t-{t}_{2}\right)$ , respectively, and the complete output is the sum ${a}_{0}h\left(t-{t}_{0}\right)+{a}_{1}h\left(t-{t}_{1}\right)+{a}_{2}h\left(t-{t}_{2}\right)$ .

Now suppose that the input is a continuous function $x\left(t\right)$ . At any time instant $\lambda$ , the input can be thought of as consisting of an impulse scaled by the amplitude $x\left(\lambda \right)$ , and the corresponding output will be $x\left(\lambda \right)h\left(t-\lambda \right)$ , which is the impulse response scaled by thesize of the input and shifted to begin at time $\lambda$ . The complete output is then given by integrating over all $\lambda$

$y\left(t\right)={\int }_{-\infty }^{\infty }x\left(\lambda \right)h\left(t-\lambda \right)d\lambda \equiv x\left(t\right)*h\left(t\right).$

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
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
how did you get the value of 2000N.What calculations are needed to arrive at it
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