What is Membrane: Definition and 167 Discussions

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.

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  1. Esref AHMETOGLU

    HVAC Pressure tank bladder replacement

    How did you find PF?: by searching If I have an old 5000 lt pressure tank and as I see it needs a change of its membrane (Bludder) what is the recommendation that must be followed and also what is the volume ratio between the membrane before using and after testing or working situations
  2. somasimple

    Medical Is there a contradiction between growth and membrane potential?

    Hello everyone, All living things have a growth cycle in which they gain mass and volume. These elements are obviously and undoubtedly taken from the environment in which these creatures live. Therefore, it is undeniable that the amount of potassium, for example, in the body increases during...
  3. C

    How does soap water membrane thickness affect surface tension?

    1.If the thickness of soap water surface decrease, whereas the concentration remain the same, how will the surface tension change? 2. If the membrane of soap water start to evaporate, its thickness become thinner and it’s concentration increase, How will the surface tension change? Thank you!
  4. red65

    Medical Why do we say basolateral membrane and not basal?

    Hello everyone, I am studying the physiology of the kidneys and in all of the textbooks they say basolateral membrane referring to the basal membrane, does anyone know why we don't just say basal membrane?
  5. J

    A Can Membrane Field Theory Elucidate M-Theory?

    Hey guys, I just wanted to know if you think that a membrane field theory could ellucidate the non-perturbative framework of M-theory? Let me specify and explain what I mean by that: String field theory was intoduced to study the non-perturbative regime of string theory and some achievements in...
  6. W

    MHB Neuronal Dynamics Passive membrane equation

    Hi guys, I am able to solve dif equation of passive membrane model. But later, author says following instructions to integrate first model. Even though I can solve the dif equation of model, I couldn't achieve the solution. Could you help me pls. Best regards.
  7. J

    Membrane potential explained: Nernst potential

    Good evening, I got a seriously problem at understanding the membrane potential for ions in a cell. Particulary, i don't understand the case for example for ions with a charge of 2 or higher. I take a look on two scenarios: If you got an ion like calium and got a concentration ratio of 1:10...
  8. S

    Aluminium anodizing pore membrane

    When anodizing aluminium (or Titanium) a dense hexagonal pattern of microscopic pores is formed, and you can get a pretty high aspect ratio with them. But the illustrations always show the oxide layer with pores on top of a pure aluminium layer. But can you oxidize a thin sheet of material so...
  9. A

    Oscillation of a drumhead membrane

    My attempt, Considering that it jumps in the maximum compression position: $$\frac{kA^2}{2} = mg(H+A)$$ replacing k / m with w ^ 2 : $$A^2 w^2-2gA-2gH=0$$ Solving the second degree equation: $$A=\frac{2g+\sqrt{4g^2+8gHw^2}}{2w^2}$$ But the answer is...
  10. E

    I 4 spaceships are pulling a membrane through an asteroid belt

    Given 4 spaceships are pulling an elastic rubber membrane with constant speed and slow velocity into an asteroid belt. - In that way, that they all start in empty space and have a constant low speed of say 50km/h as they reach the belt. - The four edges of the membrane are tied to one of the...
  11. C

    Max velocity of a vibrating loud speaker membrane given sound intensity

    My attempt: p and T allows us to calculate ##Z=402 \frac{kg}{sm^2}## using ## Z=p*\sqrt(\frac{\gamma*M}{R*T})## . The sound intensity level at 10 meters allows us to calculate the intensity at 10 meters to be I=10``````^{-7} W/m^2 using ##50 = 10*log(I/I_0)##. Then, using the formula...
  12. LCSphysicist

    Permeable membrane and entropy

    Actually i am trying to see what the first equation to the entropy means, maybe N1 remets to the part 1 (the left suppose) of the system? (or the molecules type 1?) I am not sure about the equations i will do below, probably it will be wrong, anyway. ∂S/∂U1 = 1/T1 = 3NR/2U1 Okay, it will give...
  13. TytoAlba95

    Biology MCQ- Insertion of a protein into a liposome membrane

    Please give me clues as to how to solve this question. The answer provided is (c).
  14. calvinrose

    B Kill drum head overtones without anything touching the drum head

    Hi All, I considered filing a patent for this invention, but instead decided to publish it so people could use it to advance the state-of-the-art in drums. You don't need to add tape or pillows to your drum heads to muffle the overtones. Using tape or pillows also kills the strike of the...
  15. ContagiousKnowledge

    Normal modes of a rectangular elastic membrane

    Let's try inputting a solution of the following form into the two-dimensional wave equation: $$ \psi(x, y, t) = X(x)Y(y)T(t) $$ Solving using the method of separation of variables yields $$ \frac {v^2} {X(x)} \frac {\partial^2 X(x)} {\partial x^2} + \frac {v^2} {Y(y)} \frac {\partial^2 Y(y)}...
  16. PGaccount

    A Understanding Membrane Theory: Main Concepts & Beautiful GI Results

    what are the main concepts of membrane theory? the most beautiful possible giresults. g → 1/g where g is the coupling constant ive read that this transformation changes a dirichlet membrane into fundamental strings. does this have something to do with evaporation of black holes?
  17. S

    Light testing for leaks in a thin metallic membrane

    We have a small (15 X 25mm), thin membrane (0.03mm thick) that we currently inspect for pinholes and small cracks manually by backlighting and inspecting under magnification, one at a time. Does anyone know of an instrument that can do this inspection for us, with a high degree of accuracy?
  18. dykuma

    Calculate the sag (deflection) of a membrane

    Homework Statement Not sure if this is the appropriate place to ask this question, but I didn't know where else to ask. Anyway. Let's assume that I have a film (or membrane) material that is stretched over some boundary, (lets assume a thin hollow cylinder). Then some constant force is...
  19. K

    I Resonant frequencies of a membrane, dependance on Young's modulus?

    Hello, natural frequencies of (circular) membrane are expressed in every textbook as: where is the m-th positive root of the Bessel Function of the first kind of order n. For m=1, n=0: ξmn = 2,405. represents the radius of membrane, and is the velocity of wave propagation...
  20. A

    Cell and membrane volume physics

    Homework Statement A typical human cell is approximately 10 μm in diameter and enclosed by a membrane that is 4.2 nm thick. To simplify the calculations, model the cell as a sphere. 1) What is the volume of cell? (in μm^3) 2) What is the volume of cell membrane? (in μm^3) 3) Percent cell volume...
  21. K

    A Natural frequencies of simplified tympanic membrane model

    I am trying to anallytically determine natural frequencies ƒ of the tympanic membrane. I am using 2D sectorial annulus membrane as a simplified model of tympanic membrane according to following picture The parameters that i want to use are following: THICKNESS = 0,1 mm The natural...
  22. S

    Eigenvalue problem -- Elastic deformation of a membrane

    Homework Statement An elastic membrane in the x1x2-plane with boundary circle x1^2 + x2^2 = 1 is stretched so that point P(x1,x2) goes over into point Q(y1,y2) such that y = Ax with A = 3/2* [2 1 ; 1 2] find the principal directions and the corresponding factors of extension or contraction of...
  23. M

    A Calculating decay rates for modes of a circular membrane

    I am trying to solve for the theoretical relative decay rates of the various (m,n) modes of an ideal circular membrane, if that membrane is excited momentarily by an impulse or deformation. I would ideally like the decays of the (m,n) modes in dB/s. Imagine a simple isolated drum head being...
  24. BillTre

    Membrane Channels Involved in Electrosensitivity

    This little industry news article walks through how some researchers identified the channel proteins underlying a skate's (similar to a ray) electrosensitivity, which allows it to find prey buried in sand or otherwise obscured (heartbeats make weak electrical signals the animals can detect)...
  25. Xezlec

    A How to simulate a membrane in a (2D) fluid?

    I wasn't sure whether to post this in here or in computer programming, since it touches on both. I have a personal project that is based on a 2-dimensional finite-element fluid simulation (which already works just fine) but needs to be able to simulate an elastic membrane stretched across a...
  26. W

    Pressure between a membrane and a solid body

    I would like to understand this a bit better, so I am looking for a reference to refer to and not necessarily an explanation in a reply. I have a non-porous membrane of a compressible material wrapped around a solid body. I then draw out the air between the membrane and the solid body. I want...
  27. D

    Getting rid of fuel cell / flow battery membrane

    I am aware of laminar flow but would like to look for some other ways. Is it possible to block ions from flowing in the "wrong" direction by applying a magnetic field to the electrolyte and let neutral molecules pass through?
  28. Z

    A Gas diffusion through a semi permeable membrane

    Say I have a small solid polymer container filled with gas A. The walls of the container are semi-permeable, so gas A on inside can't get through/out. On the outside, gas B at atmospheric pressure, which can migrate through the membranes of container. Pressure inside the container is 0,6 bar...
  29. M

    I Modal frequencies of a vibrating circular membrane? (DRUM)

    I am in the process of trying to develop a modal drum synth. I have the following graphics as references for the frequencies of some of the first modes relative to the fundamental: This is a good start. But I want to be able to model more modes than just that. What is the formula required...
  30. Spinnor

    I Harmonically forcing a drum membrane -- are the waves isotropic?

    Suppose I apply a pair of equal and opposite harmonically varying forces perpendicular to an infinite drum membrane. Consider the following forcing functions at two nearby points,(x=0,y=a) and (x=0,y=-a), separated by a distance 2a, F(t,0,a) = Acos(ωt), F(t,0,-a) = -Acos(ωt) Let the forcing...
  31. M

    Electrical processes through a membrane - active transport

    Homework Statement [/B] I am given the configuration below of a membrane and it is said that Na+ ions are transported actively through transporters from the inside to the outside. The J_Na_a seen below is the active current density of the Na ions and it is constant. Vm is the potential...
  32. R

    How does a hollow fiber membrane work to filter water?

    What is the process? And can/cannot it filter out?
  33. louisnach

    Vibration membrane exercice physics

    Homework Statement We have a square membrane and a circular membrane, both fixed from the edges. They are made of the same material with a surface mass σ , and their surface tension is T. We want to tune the lowest eigenfrequency (the fundamental frequency) of both membranes to the same...
  34. Buzz Bloom

    What are the lipids on the double membrane of a eukaryote cell's nucleus?

    Various sources describe the origin of the eukaryotes as occurring when a bacterial cell ingested an archaea cell, which then symbiotically became the nucleus of the created cell, and which was then the LUCA (Latest Universal Common Ancestor) of all the eukaryotes. The cell membranes of the...
  35. R

    Are there two or three types of membrane proteins?

    Most sources I've read state that there are two types of membrane proteins: integral and peripheral. However, my lecturer has been saying there is a third type: lipid anchoring. Doing a search online, I've found many sources say that there are only two types, whilst others say there are three...
  36. F

    3d printing neuron with membrane potential

    Is it possible to 3d print a neuronal structure with a different material than neurons that would work just like a neuron with membrane potential?
  37. J

    Drum Resonance Physics: Understanding How Tunings Affect Frequency

    Hello, I have recently picked up drumming and the topic of tuning has peaked my interest. I have gone over numerous sources (academic theses, Wikipedia, HyperPhysics, etc.) trying to piece together what is occurring when drums (right now tom with two heads, batter and resonant, are of most...
  38. P

    Calculating Membrane Deflection of Clamped Rectangle

    Hi, I have a rectangular membrane (material: laminated aluminum like food packaging). The membrane is clamped around perimeter. From one side I have uniform (gas) pressure. The membrane is constrained from another side with rigid plate and, hence, do not deflect. But I can measure force that...
  39. M

    How Can Membrane Filter Presses Be Produced Locally in Iran?

    Hi.i am reza from iran. really i don't know how many membrane have been introduced and what kind of it have being discussed here.but anyway ask my question and hope to get useful answers. in membrane filter press the filter press producers importing membrane from china. no one and no company...
  40. Y

    Why membrane for distillation has to be hydrophobic

    I have a question about membrane distillation. I have read the following from a review paper about membrane distillation: The membrane distillation should be applied for membrane operations having the following characteristics: - The membrane should be porous. - The membrane should not be...
  41. M

    Membrane Measuring: Light Pipe & Diode Tech

    Hi! I found a nice thing via google for a measuring forces by using a light pipe. The light gets coupled into a light pipe and the amount of light is measured by a diode (http://www.dr-iguana.com/prj_LightPipe/). I think you can also use such a device for measuring the deflection of a membrane...
  42. Chrono G. Xay

    Attempting to Predict Tension on a Circular Membrane

    I have been wanting to write an equation which predicts the tension on a circular membrane (AKA drumhead). However, I'm not sure that my answer is on the right kind of track, if it's even correct. As for the procedures I took, first I started with the equation for tension on a string, which I...
  43. R

    Equation linking superstring vibration with mass?

    Is there an existing equation, or set of equations, that directly links the specific vibration of a superstring filament with the resultant particle mass? A brief explanation of any mathematics would be helpful. Thank you.
  44. gfd43tg

    Membrane separations experimental set up

    Hello, I will be doing an experiment to separate N2 from O2 in air using membrane separations. I need to write my own experimental procedure to find the objectives of the experiment. Here is our experimental set up I'm trying to figure out how to do objective i. I need to figure out the...
  45. nedallica

    Membrane Polarization: Best Source for Understanding Effect in Rocks

    What is the best source for understanding the membrane polarization effect in rocks??
  46. gracy

    Single Membrane / Double membrane /no membrane?

    Nucleus - Double membrane Nucleolus- no membrane Chromatin- no membrane Nuclear Envelope - Double membrane Smooth/Rough Endoplasmic Reticulum -single Membrane Golgi Body- single Membrane Central Vacuole- single Membrane Lysosomes - single Membrane Chloroplasts - Double membrane Mitochondria...
  47. gracy

    Is nuclear membrane organelle?

    I am quoting from wikipedia https://en.wikipedia.org/wiki/Endomembrane_system "In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes and the cell membrane." From this question arises...
  48. S

    What is the optimal shape of a membrane on a rectangle under pressure?

    Homework Statement This is not a homework or anything similar, but it is a problem I am trying to solve and I don't know how to start. I do know, that the most stable structure in 3D is a sphere - that is the reason why the drops are in a spherical shape. But now imagine a rectangle and...
  49. S

    Switchable Porosity: Can Microporous Materials Be Controlled?

    Is it possible to switch the porosity of any microporous material by external stimuli (eg. optical, pressure or electrical ). I'm trying to imagine something akin to an "Artificial Stomata" where the pore opening & closing Can be externally controlled. I'd be very thankful if someone could...