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Questions tagged [biophysics]

The use of methods from the physical sciences to aid in the study of biological systems. Note that biophysics questions are only allowed if they are mainly about physics.

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(Why) does wet air contain more oxygen?

I've heard the fact wet air contains more oxygen is the reason experts recommend to humidify the air. Intuitively, I'd say wet air should contain water of a greater density and thus, make less space ...
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For which energetic reasons are ions blocked by cell membranes?

The permeability of cell membranes is given by the following diagram from the book "Biochemistry": The reason that ions get blocked can be explained chemically: The ions favor interactions with the ...
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How do gaseous molecules arrange themselves in liquids when they are “dissolved”?

To provide some context, I am trying to understand in better detail how oxygen from the lungs passes through a membrane and enters the vasculature in order to be transported via blood. I have ...
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1answer
29 views

What is the link between the meaning of excluded volume and its mathematical derivation?

When we examine real polymer chains we have to consider the interactions between single monomers. Therefore we consider a Lennard-Jones-like potential for bringing two monomers together and calculate ...
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1answer
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If you get punched, is it better to be lighter or heavier?

I've seen people argue that lighter people can take a punch better because they can "go with it" better. This seems plausible to me, but is it really true? One reason why it seems plausible is that ...
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3answers
82 views

When does the retina fail to recognize images of two closely separated points as distinct?

Our eye is a lens and lenses have a resolving power. The resolving power of a lens, physically speaking, is related to how good two closely separated points A and B can be distinguished as separate. ...
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1answer
39 views

Diffusion equation with external forces

I am given the diffusion equation including the external forces as follows: $$\frac{\partial c}{\partial t} = D\frac{\partial^2 c}{\partial x^2} - \frac{F}{\gamma} \frac{\partial c}{\partial x}$$ ...
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1answer
78 views

How can sunlight cause skin cancer? [closed]

If the atmosphere absorbs the UV wavelengths, then what’s left is visible, IR and maybe a really small amount of UV that transmits it’s way to earth. IR and visible are non ionising, so is it the case ...
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67 views

Calculate heat production rates in well-mixed batch fermenter

I have a formula to calculate the heat production rates in well-mixed batch fermenter: $$V * c_p * \rho * \frac{dT_j}{dt} = F * c_p * \rho * (T_0 - T_j) + U * A * (T_R - T_j) + r_Q * V$$ U [kJ/($m^2$ ...
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3answers
195 views

Can radio waves be harmful to us?

I was studying about Microwaves and their action on water molecules in heating up the food. This all is probably due to Microwaves have wavelength such that it can be absorbed by water molecules (am i ...
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4answers
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Could quantum mechanics be necessary to analyze some biology scenarios?

As an example, we could talk about a neuron cell in brain, with a size of $1 \mu m$ (=$10^{-6}$ m), being the distance between one neuron and next one in a synaptic connection of around 40 nm (=$40 \...
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2answers
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Ought we say 'body mass', rather than 'body weight'?

I'm asking in the context of medicine, where you're "massed" (or is it "weighted"?) on a scale. This answer beneath insinuates that 'mass' may be the preferred term, but it doesn't outwardly clarify ...
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Why does a person carry more weight when sitting down?

Today, while shopping for a chair at a shopping mall, I saw this poster regarding the amount of weight a person is carrying when doing various activities. When standing upright, one carries 100% of ...
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1answer
47 views

Physics of Neuroscience - Action potential

I am confused about how to understand action potential in the context of physics. Are action potential and potential difference synonymous? If so why is it stated that an action potential 'travels' ...
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How are fluid membranes stretchable?

The Poisson's ratio of fluid lipid membranes is exactly $\nu=0.5$, because fluids can flow. As answered in this question, under the assumption of a finite bulk modulus $K$, this is the value of $\nu$ ...
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Statistical model for local polymer concentration

I'm trying to describe the local constraining of two points located on a 2-part DNA polymer (double and single stranded), with respect to one fixed end. See the schematic below: Here I would like to ...
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1answer
38 views

Electronic band structure of proteins

Proteins are a class of macromolecules. What range of electronic band structure do These have? Are These more like semiconductors? Or like insulators? How high is the typical Fermi Level for Proteins? ...
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1answer
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Does the human brain emit ULF waves?

In the book The Electric Universe by David Bodanis, the author writes that "invisible waves stream out of from our brains with a wavelength of about 200 miles". Is it true that the brain produces ULF ...
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2answers
209 views

Relationship between blood pressure and cross sectional area of blood vessel

What is the reason why blood pressure and a larger cross sectional area of blood vessel cause a lower blood pressure and vice versa? This question is related to another question I found here. The ...
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0answers
19 views

Frequency domain theory for absorption and scattering tomography

TL, DR: in the theory absorption and scattering tomography it is possible to obtain a formula for the field in a detector point once it is known the position of the source and the inhomogeneities of ...
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1answer
194 views

Electric potentials around the heart. What and How does the EKG measure?

Recently I've been having trouble understanding how(and even what) the EKG measures and have not been able to find a satisfactory response. The health science forums haven't been much help and I ...
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0answers
154 views

A question on $\pi=iCRT$

I was given this pretty basic question about the osmotic pressure: 1) At 25$^{\circ}$C what osmotic pressure would develop across a membrane permeable to water but not starch if there was 300 mM ...
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5answers
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If two sound waves that are different frequencies create beats that occur several hundred times per second, can you hear this effect as its own tone?

If you have multiple waves of different frequencies, the interference from the different waves cause "beats". (Animation from https://en.wikipedia.org/wiki/Group_velocity) Let's say that a green dot ...
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3answers
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Humans have an average energy budget of $100$ Watts, but the power radiated from the body is $1000$ Watts?

On average a human consumes around $2000$ kilocalories per day. This converts to roughly $2000000$ calories / $86400$ seconds or around $100$ joules / second giving roughly $100$ watts. But if you ...
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1answer
44 views

DNA - optical response and fluorescence

I am curious about the state of affairs with the DNA fluorescence. I know that there was some initiative in physics community in 1980's and 1990's, but some authors question even whether DNA molecules ...
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0answers
22 views

Laser light radiation interactions with biological tissues?

I was wondering what are the interaction between light generated by a laser source and biological tissues (e.g. human skin) in terms of geometric optics. I suppose from my studies that a part of the ...
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1answer
42 views

about the muscle's tension's variables

I'm reading the paper "The Problem of the Interrelation of Coordination and Localization", which is written by N. Bernstein. The paper says, The degree of tension of a muscle is a function, in the ...
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2answers
288 views

Why might Roger Penrose argue that Godel's incompleteness theorem(s) suggest that consciousness is non-algorithmic?

This past March, when I called Penrose in Oxford, he explained that his interest in consciousness goes back to his discovery of Gödel’s incompleteness theorem while he was a graduate student at ...
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0answers
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Introductory Electricity and Magnetism Textbook for Biology and Biophysics

My research advisor will be teaching a new course at my university on Electricity and Magnetism for Biophysics and Biology students. This is the first course the students would be taking in E&M. ...
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2answers
75 views

Physical mechanism by which the body removes weight during long-term human weight loss [duplicate]

I'm trying to confirm the method by which the body physically loses weight during "long-term" weight loss. I'm specifying "long-term" here because obviously there are lots of ways to temporarily lose ...
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0answers
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What are good references for learning Biophysics at the graduate level for a biochemist/experimental molecular biologist?

I recently started graduate school in the fields of molecular biology and genetics. Over the past few months I have been gaining a strong interest in mechanotransduction and tissue engineering. While ...
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0answers
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Do symmetric angular velocities lead to symmetric axis of rotation observed in a fixed frame?

It has been observed that some insects with relatively small stroke amplitudes (such as mosquitos) take advantage of a translating axis of rotation to generate lift where insects with larger stroke ...
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1answer
61 views

Compton scattering and X-ray Imaging

Is there any importance to having Compton scattering in x-ray imaging. I ask this because most books that I have read talk about reducing the effect through anti-scatter grids, as Compton scattering ...
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1answer
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Photomulitplyer Tubes and NaI(TI) crystals in Gamma Camera, Energy and spatial resolution

I am trying to understand how the PM tubes and NaI(TI) crystals are used for the energy and spatial resolution. I understand the principle behind how the crystals and PMT work, but very confused to ...
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2answers
63 views

Changin the optical depth (axial resoltuion) on an Optical Cohernce Tomagrpahy system

So the axial resolution in a OCT system is given by: $$I_c=\frac{4ln2}{\pi}\frac{\lambda^2}{\Delta \lambda}$$ My question what would you do to say increase the axial resolution, and how would it ...
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1answer
101 views

Motion of head during sneezing

When we sneeze, our head moves forward. However since the air from our mouth moves forward with a high velocity, shouldn't the head should recoil backwards (like a gun, to conserve the momentum) ...
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1answer
27 views

Adjusting dose rate, Image quality, X-ray Flurocopy

When adjusting the dose rate, in this procedure from either film or detector the image quality would become poor due to less photons being transmitted via the x-ray tube. How many ways with respect ...
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1answer
101 views

CT scan advantages and disadvanatges Vs General Radiology

So recently I have been looking at how CT scans work and the disadvantage and advantages they have compare to general radiology techniques, but this has brought up some questions. My question refers ...
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0answers
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Why are moderators here blocking clear answers to questions? [closed]

I presented a very insightful answer to a question about breaking molecular bonds via electromagnetism. I put a great deal of time and effort into including diagrams and a 3-d perspective of the ...
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0answers
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Coordinates of all the atoms in protein molecule for the given Ramachandran angles for all the peptides

How to determine coordinates of all the atoms when ramachandran angles are given ? Can someone suggest some references to determine all the coordinates for the given Ramachandran angles ?
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2answers
226 views

Depth of field of the human eye

When reading about the basics of photography and the physics involved, I learned about  depth of field. Long story short, the message is that with a smaller aperture, the length of the depth of field ...
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1answer
28 views

What construction materials could enable a capillary effect to raise water?

Are there materials (possibly in research stage) which are investigated as replacement for piping and pumping systems in construction work to transport water from the ground to elevated floors in ...
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0answers
31 views

Does a Conical Intersection imply that the HOMO-LUMO gap in a molecule is very small?

I came across some notes in which the author swiftly made this comment, that if there's always a large gap between the HOMO and the LUMO along a chemical reaction ("large" can mean at least bigger ...
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1answer
28 views

Formation of patterns in instabilities according to the wavelength of instability

Do the wavelengths of the instability have an influence on the type of patterns that we are going to get? Meaning for example in 2D, if the unstable wavelengths are small with respect to the size of ...
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1answer
39 views

A thought experiment regarding a unidirectionally permeable membrane

Imagine a container containing a solution with a solute, X, evenly distributed within it. Say we could engineer a membrane to split the container that only allows particles of X from say, left to ...
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3answers
161 views

Why can I see the glow from my TV remote's LED if it is supposed to emit in the infrared?

The TV remote light emissions being >700nm are supposed to be invisible right? Same goes for proximity sensor on phone and laser focus on phone's back camera. But how could, me and 3 more people I ...
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2answers
43 views

What is the enviroment in which water will come out of an ice fishing hole?

I have watched some videos on YouTube of people cutting holes in ice and water not just finding equilibrium in the hole, but water actually coming out of the hole along with many fish. There has to be ...
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1answer
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Multi-stability potential is suitable for interdisciplinary branches of science?

The potential function $V(x) = c(x-a)^2(x-b)^2$ with constants $a,b,c$ and some variable $x$ has two minima: One at $x=a$ and another at $x=b$. When plugging this potential function in Newton's ...
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1answer
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does second harmonic generation (SHG) take place in amorphous materials or disordered molecular assembly?

A review paper claims that SHG can take place in biological samples, that is when the endogenous molecules assemble themselves reasonably in order, such as collagen fibril in connective tissues. I ...
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1answer
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Can we calculate moment of Inertia of the picture given below? [closed]

So one half of this picture is formed of a broad , more or less Triangular bony plate , called scapulo-coracoid and a small clavicle bone. I m interested in biomimcry and I want to know the hidden ...