A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes (outer coverings of cells or organelles that allow passage of certain constituents); nuclear membranes, which cover a cell nucleus; and tissue membranes, such as mucosae and serosae. Synthetic membranes are made by humans for use in laboratories and industry (such as chemical plants).
This concept of a membrane has been known since the eighteenth century but was used little outside of the laboratory until the end of World War II. Drinking water supplies in Europe had been compromised by the war and membrane filters were used to test for water safety. However, due to the lack of reliability, slow operation, reduced selectivity and elevated costs, membranes were not widely exploited. The first use of membranes on a large scale was with micro-filtration and ultra-filtration technologies. Since the 1980s, these separation processes, along with electrodialysis, are employed in large plants and, today, several experienced companies serve the market.The degree of selectivity of a membrane depends on the membrane pore size. Depending on the pore size, they can be classified as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes. Membranes can also be of various thickness, with homogeneous or heterogeneous structure. Membranes can be neutral or charged, and particle transport can be active or passive. The latter can be facilitated by pressure, concentration, chemical or electrical gradients of the membrane process. Membranes can be generally classified into synthetic membranes and biological membranes.
I believe I know the answer to this question; I need an expert to verify it for me.
I work for a company that makes latex balloons. The people that have been here for a long time insist that if one is putting a small (5" balloon) filled with helium inside a larger (30") balloon then one must...
Homework Statement
A string is sewn in a 2D membrane. What is the amplitude of the reflected wave? All the parameters you need in order to get to the result are known.
Homework EquationsThe Attempt at a Solution
Ok, so we have a 2D membrane, with a string at ##x=0## along the the ##y## axis...
Homework Statement
Find stationary state of a circular membrane, on which a coin is put.
Homework EquationsThe Attempt at a Solution
I am not sure about the second boundary condition, so if any of you has the time, please check the following solution:
$$u_{tt}=c^2\nabla ^2u+\rho g$$ Where...
Hello,
Suppose sinosodial AC and pulsed DC magnetic fields with equal rms are applied on animal cells in the presence of magnetic nanoparticles. For the mean field strengths to be equal, the peak value of the square wave (with 50% duty cycles) must be sqrt. 2, which means that the maxiumum...
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I am chemist. and I prepare ionic membrane and placed in a home made acrylic cell containing 0.1M NaCl separated into two portions by ionic membrane. I applied DC voltage of 9.6V (using 9V battery). Using multi-meter the measured DC voltage in water was 4.45V. The distance...
Hello to all. I'm building a prototype of a portable air compressor system. I would like to place a membrane just after the tank drain that would allow the liquid water (condensate) to pass through into a canister. This membrane would allow the water to pass through by gravity. When the portable...
During a synapse, a synaptic vesicle fuses with the presynaptic membrane releasing whatever neurotransmitters it contains. Neurotransmitters are then taken in through transport proteins during re-uptake. Stimulation occurs on a regular basis for some neurons and since the neurotransmitters are...
Hi all - I'm preparing a presentation that includes circuit diagram stuff, and it's been a very long time since I've done any of that.
For this circuit, http://alford.bios.uic.edu/Images/586%20images/circuit%20model (i.e. a circuit model of an isolated patch of cell membrane), I read that...
Hello,
As of this moment I am trying to get in the process of writing an Extended Essay on Chladni Plates, more specifically on a circular vibrating membrane with free ends. To begin with I thought the concept could be simplified to such an extent where I could take a cross-section of the plate...
I am working on a design of a spherical dome.
I tried to understand membrane theory with no success.Can anyone please help me with an clear explanation to derivation of membrane theory of shells.
Hi.
Can you do a computer simulation of a membrane with a standing wave(s)/node(s) with a shape of a cube or cone?
It is possible on a string so why not on a membrane.
Can you do a computer simulation of a spherical membrane with a standing wave(s)/node(s) with a shape of a cube or cone...
So the equation to obtain the frequency of the modes of a square membrane is something like
ω m,n = ∏ [(m/a)^2 + (n/b)^2]^(1/2)
This equation can be used to get the frequency for Modes such as (2,1) and (1,2). How do I get the frequency for such modes as (2,1)+(1,2) and (2,1)-(1,2) ...
I need to know a realistic minimum biaxial tension per unit length - in N/m - for the surface of a membrane which is 27.4 mm square - with surface density 0.0912 kg/m^2 - so that it could be vertical and remain tense so that mode shapes due incoming acoustic energy would remain intact (if the...
I'm learning about a very basic model neuron, in which only potassium and chloride is permeable.
Why is it that when the extracellular concentration of potassium is increased, the neuron become depolarized, whereas when extracellular concentration of chloride is reduced, the neural membrane...
I've just got a quick question that hopefully someone can answer.
My question is - why does the membrane in COMSOL vibrate without you telling it to?
Here are some specifics if required...
In COMSOL here are my setup details: -
Physics: (3D) Structural mechanics - Membrane
Study...
Homework Statement
I'm following a procedure in a particular paper as part of my Masters project. The paper is called 'Theoretical investigation of the sound attenuation of membrane-type acoustic metamaterials - Y Zhang, J Wen, Y Xiao, X Wen and J Wang (2012)' and can be seen...
I keep coming across the word apical and basolateral membrane in my study of plasma membranes of cells. I am wondering if the apical membrane is towards the inside of the cell (cytoplasm) or towards the outside ?
I have heard that nobody really knows how many receptors are placed on E.Coli cell membrane. Of course we know the general types of the proteins incorporated in membrane (Carrier proteins, Na+/K+-ATPase, various transporters, Ion channels) but I need to know the exact number of types and exact...
Appreciated experts,
I want to model the inflation of a thin and isotropic circular plastic membrane clamped by a ring. I need to determine the maximum deflection at the pole, stresses, strain, etc..., as a function of the applied pressure difference. The large deflection range complicates it...
Homework Statement
An inflatable membrane is filled with an ideal gas at a pressure of 0.3 bar gauge. The gas is at 40 deg C and the volume of the membrane is 100m^3.
The membrane is constrained on all sides and bottom, and a force of F acts on the top of the membrane.
The material the...
So if we have an ion, say Cl- in solution, and we have a membrane immersed into the solution.
Apparently there is a method in which any ion, of any charge is inhibited from crossing the membrane because it induces the same charge as itself on the membrane.
This is called dielectric...
Hello everyone,
Lets say there is a membrane, which has a channel for the solute(eg sodium) and another channel for water
Now if I have a hypertonic (more sodium) solution in side A, and hypotonic (less sodium) solution in side B. Which way would water go?
* I'm very confused here...
The surface of any liquid behave like a stretched membrane. Is it because of surface tension or all the possible forces acting on a liquid molecule at the surface? I asked this question because if the furface behaves stretched because of surface tension then it means that the forces making the...
Homework Statement
Is it possible to find a solution to the wave equation on a circular membrane such that the shape remains constant, but rotates at a fixed rate in the angular direction?
Homework Equations
The Attempt at a Solution
I've tried separating variables, and assuming...
In membrane potential determination of a cell, the Goldman Hodgkin Katz equation says the contribution of an ion to diffusion potential is dependent on its membrane permeability.
So in case an ion, one that has a zero permeability, is present outside the cell, using the equation , one will get...
http://www.vibsys.put.poznan.pl/journal/2010-24/noga-2.pdf
Equations (9) leads to (11).
How from R boundary condition do we end up with the equation in (11)?
My (probably misguided) intuition says the following :
'Take a closed loop of wire and bend it into any arbitrary shape so that it lies flat on a table. stretch a membrane over it (i.e. a soap membrane say). Then, I should be able to vibrate it at just the right frequency to generate (at least)...
Homework Statement
I must find the oscillations of a circular membrane (drum-like).
1)With the boundary condition that the membrane is fixed at r=a.
2)That the membrane is free.
Homework Equations
The wave equation \frac{\partial ^2 u }{\partial t^2 } - c^2 \triangle u =0...
hello world long time no see..actually I've been very confused with this resting membrane potential I've sooo many questions but i'll only ask one question for now .at rest the membrane of nerve cell is permeable to potassium , potassium goes outside the cell along its concentration gradient...
Hey everybody,
I'm trying to figure out what the vibration modes of a circular membrane would look like if we put some sound through it.
As you may know does a circular membrane with clamped edges at radius a behave according to the wave equation.
The general solution thereof has the form...
Is there any reason,resting membrane potential is cca -70mV?because teacher asked us today,and it was not enough for him to say,that it is due concentrations of ions...What is the reason of this value?
Thanks
Hi guys,
I am in need of a 'one-sided' membrane.
Basically, something like a bad damp proofing membrane. Allow me to explain:
A membrane which will allow water to pass through one-way (at a fast rate - this is where it differs from the damp proof membrane you can buy in the diy shop)...
Homework Statement
I'm trying to solve the vibrations of a rectangular membrane with a rectangular hole inside. Both the inner and outer edges are fixed. I know i have to use the wave equation, but how do i write the boundary conditions in orden to incluye the hole? Any ideas?
F.Y.I. I...
I have a sphere of radius 4.8mm surrounded by a membrane .2 mm that has a drug in the inner sphere and is diffusing out through the membrane. I know the saturation concentration, the partition coefficient and diffusivity of the drug. I also know that the concentration outside of the membrane is...
Hi,
Was wondering if I could get some help with part b of this question?
I've attached the question and my attempt in the pictures as there was a lot of data and writing, so thought this would be the easiest way.
With my attempt I think I'm missing something pretty obvious, but I'm drawing...
Hi. I am currently doing an experiment regarding to the factors affecting beet root cell membrane. Some of them are pH (2,4,6,8,10) , Ethanol (1%, 25%, 50%) and Detergent(1%, 5%). I've seen that different pH, different concentration in ethanol and detergent each has different results in both...
Hi, I am solving the diffusion equation using explicit finite difference to model the diffusion of an analyte through a membrane. I am interested in the concentration of the analyte on the other side vs time elapsed. On one side of the membrane is an initial concentration, which I am...
The ribosomes have a membrane to prevent damage of the cell from the enzyme. but why are the cells not damaged when the enzymes are digesting unwanted structures, since the enzymes have to be released to digest unwanted structures.
Homework Statement
Are phospholipids cholesterol?Because in one book it says that ' cholesterol molecules, like phospholipids'. I am a little bit confused.
Homework Equations
The Attempt at a Solution
Hello!
Electric force is inversely proportional to the dielectric constant. In a textbook, this is said to be forty-fold greater for water than the phospholipid membrane. As such, ions are unlikely to cross the plasmamembrane. I assume this has something to do with preferring to stay in...
Hi,
Please can anyone help me here?
Consider the link below;
http://online.physics.uiuc.edu/courses/phys193/Lecture_Notes/P193_Lect4_Ch4_Part2.pdf
I'm just trying to qualitatively undestand the pictures in the above link.
Consider Page 2 of 18
Now, consider figure 3.6...
I've just finished reading through the generally well-written Wikipedia article on membrane potential:
http://en.wikipedia.org/wiki/Membrane_potential
I found almost everything to be clear, but one question is nagging at me. Why do changes in membrane permeability directly affect membrane...
Hi PS users,
I am trying to explain to some students why, when you inject a neurone with a constant current intracellularly, the membrane potential charges linearly, until the injected current is removed, at which point the membrane potential becomes flat.
To put this in circuitry terms...
Homework Statement
An analysis of proteins in plasma membranes would reveal that:
they are all enzymes.
they are immobile in the bilayer.
they are entirely non-polar molecules.
they are formed from nitrogenous bases linked together by peptide bonds.
they are built by the same...
Finkelstein's "unidirectional membrane" paper
The "unidirectional membrane" interpretation of black-hole event horizons originated with this paper:
Finkelstein, Phys. Rev. 110, 965–967 (1958), "Past-Future Asymmetry of the Gravitational Field of a Point Particle," downloadable from his web...
Homework Statement
We will deal here with a certain identified synapse in the CNS of the mooncalf (Bos lunaris). The post synaptic cell has voltage-sensitive channels like the squid axon-- a rapidly depolarizing, inactivating channel which conducts only sodium ions, and a slowly depolarizing...
I'm about to build a plate reverb and I have some thought, or questions about the plate. The set-up is as follows:
A rectangular plate, firmly tensioned in the corners.
A forced motion entered.
2 or more pick-ups, piezo style.
I'd like to know how the plate, it would be thickness...