# 4.10 Frequency domain problems  (Page 4/6)

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## Circuits filter!

A unit-amplitude pulse with duration of one second serves as the input to an RC-circuit having transfer function $H(f)=\frac{i\times 2\pi f}{4+i\times 2\pi f}$

1. How would you categorize this transfer function: lowpass, highpass, bandpass, other?
2. Find a circuit that corresponds to this transfer function.
3. Find an expression for the filter's output.

## Reverberation

Reverberation corresponds to adding to a signal its delayed version.

1. Assuming $\tau$ represents the delay, what is the input-output relation for a reverberation system? Is the systemlinear and time-invariant? If so, find the transfer function; if not, what linearity or time-invariancecriterion does reverberation violate.
2. A music group known as the ROwls is having trouble selling its recordings. The record company'sengineer gets the idea of applying different delay to the low and high frequencies and adding theresult to create a new musical effect. Thus, the ROwls' audio would be separated into two parts (oneless than the frequency ${f}_{0}$ , the other greater than ${f}_{0}$ ), these would be delayed by ${\tau }_{l}$ and ${\tau }_{h}$ respectively, and the resulting signals added. Drawa block diagram for this new audio processing system, showing its various components.
3. How does the magnitude of the system's transfer function depend on the two delays?

## Echoes in telephone systems

A frequently encountered problem in telephones is echo. Here, because of acoustic coupling between the ear pieceand microphone in the handset, what you hear is also sent to the person talking. That person thus not onlyhears you, but also hears her own speech delayed (because of propagation delay over the telephonenetwork) and attenuated (the acoustic coupling gain is less than one). Furthermore, the same problem appliesto you as well: The acoustic coupling occurs in her handset as well as yours.

1. Develop a block diagram that describes this situation.
2. Find the transfer function between your voice and what the listener hears.
3. Each telephone contains a system for reducing echoes using electrical means. What simple system couldnull the echoes?

## Effective drug delivery

In most patients, it takes time for the concentration of an administered drug to achieve a constant level in the blood stream. Typically, if the drug concentration in the patient's intravenous line is ${C}_{d}u(t)$ , the concentration in the patient's blood stream is ${C}_{p}(1-e^{-(at)})u(t)$ .

1. Assuming the relationship between drug concentration in the patient's drug and the delivered concentration can be described as a linear, time-invariant system, what is the transfer function?
2. Sometimes, the drug delivery system goes awry and delivers drugs with little control. What would the patient's drug concentration be if the delivered concentration were a ramp?More precisely, if it were ${C}_{d}tu(t)$ ?
3. A clever doctor wants to have the flexibility to slow down or speed up the patient's drug concentration. In other words, the concentration is to be ${C}_{p}(1-e^{-(bt)})u(t)$ , with $b$ bigger or smaller than $a$ . How should the delivered drug concentration signal be changed to achieve this concentration profile?

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