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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54 views

Is there a reference or a way figure out what the optimized advantage of different types of bird legs are? [on hold]

Different bird species have specific variance in the ratios between the bones in their legs. For instance, (source) some birds have a shorter femur in proportion to their tibia/fibia than in humans,...
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29 views

Bioenergetics book, biophysics

In the field of biophysics, it seems there is a subfield called "bioenergetics" about the processes of generating energy by biology. I am looking for a book to be introduced to the physics aspects of ...
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8 views

Where does the energy go that is associated with a shift in a FRET spectrum (Forster Resonance Energy Transfer)?

In the commonly used Jablonski energy diagrams, some sort of loss during resonance energy transfer is usually indicated via horizontal lines below the excited state energy of the oscillator (see for ...
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25 views

Kinetics of thermal fluctuations in liquid

I have an instinct that tells me that particles in water at temperature $T$ should be receiving and emitting "quanta" of energy of size $kT$ at a certain rate $r$. My question is: what is $r$? This ...
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1answer
230 views

Does the fluctuations-dissipation theorem hold in active matter for macroscopic physical quantities?

I am trying to understand how the fluctuation–dissipation theorem applies to active matter. I simulated a system with motors which may consume energy from the environment to move and exert force on ...
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111 views

5G networks and health concerns

Are there any peer reviewed journals on 5G networks and health concerns? I know very well that 5G radiation is of low frequency and non-ionizing and some concerns are related to the power of the ...
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31 views

Difference between coherent and incoherent energy transfer (e.g. in photosynthesis)?

Several authors distinguish between incoherent and coherent when describing the energy transfer mechanism that forms the basis for photosynthesis. (e.g. Clegg & Sener 2010 and Keren & Paltiel ...
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41 views

Can two solids, a human and a wooden desk, using only human muscular power to close the distance, actually physically touch at the atomic level? [duplicate]

If a human places their hand on a wooden desk, the sense of touch and solidity is actually provided by the repulsion effect of the electron shells of the atoms in the hand and desk giving feedback to ...
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60 views

Thermal hysteresis and its physical significance in lipid membranes?

We usually associate the phenomenon of hysteresis with memory in the system. For example, magnetic hysteresis is the basis of hard disks(if I recall it correctly). There are also electronic circuits(...
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5answers
610 views

Why we can't jump without bending our knees?

I observed it while trying to jump from my bed with my knees straightened and I failed to do it. I want to ask whether it is with all of us our it may be a medical issue with me? Why we can't jump ...
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1answer
50 views

Why does the Einstein relation hold in the derivation of the Goldman equation?

The Einstein relation $D = \mu k_B T$ is derived by assuming an equilibrium between the drift current and the diffusion current. Knowing this I would assume, that the relation is only valid under this ...
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2answers
96 views

Why do we interpret the first term of the Fokker-Planck equation as drift?

With the derivation of the Fokker-Planck equation we get: $$\frac{\partial}{\partial t}P(x,t)=-\frac{\partial}{\partial x}(A(x,t)P(x,t))+\frac{1}{2}\frac{\partial^2}{\partial x^2}(B(x,t)P(x,t))$$ We ...
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1answer
65 views

Where does the Master equation for the derivation of the Fokker-Planck equation come from?

I'm participating in an introductory course for biophysics. We briefly discussed the derivation of the Fokker-Planck equation and used the so-called Master equation as a starting point. $$ \frac{\...
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1answer
90 views

(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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24 views

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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55 views

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
45 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
48 views

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
87 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
59 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
83 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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2answers
69 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
228 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
52 views

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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2answers
186 views

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
55 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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27 views

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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14 views

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
48 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
89 views

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
331 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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20 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
242 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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211 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
46 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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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
432 views

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

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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74 views

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
82 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
22 views

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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129 views

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
99 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
23 views

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
71 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
145 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
29 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 ...