# 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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### Question on height of a jump in terms of Power (from WPE chapter, JEE level) [closed]

This is an interesting question I came about and I am not sure how to proceed. I used the equation P = Work done/time $\rightarrow P = \frac{1}{2t} mv^2$. I then multiplied by s on both sides and got: ...
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### If we have a beam of photons and a beam of protons with the same energy, which one will get further inside the human body?

If we have a beam of photons (high energy X-ray) and a beam of protons both with the same energy, which one will get further inside the human body and why? Can this be explaind due to LET (Linear ...
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### Why does Near Infrared (NIR) light allow deeper imaging in biological tissue in Multiphoton Microscopy?

I have been reading this paper on multiphoton microscopy (https://www.nature.com/articles/nphoton.an.2010.2) and I am very confused about something. Here is a quote from the paper: "The NIR ...
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1 vote
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### Question regarding notation

In the paper Inverse statistical problems: from the inverse Ising problem to data science for equation (51), the authors state, "This yields equations which determine the values $m^{MF}_i$ of the ...
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### Understanding the transfer matrix for a 1D Ising Model

I apologize in advanced for how trivial this question will come to many of you. I am in fact not a Mathematician nor physicist, just a math friendly Biologist who needs to understand the transfer ...
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### What is the relation between the torque generated by the flagellar motor and the torque acted on the flagellar and cell body?

I was reading a lecture slide on modeling the motion of E. Coli and came into this set of equations. The equations are given assuming the bacterium is in constant straight motion so no net force and ...
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### Mean squared displacement of a particle on a biased random walk [closed]

Given a particle on a 1-D random walk with some drift velocity $\nu_d = \frac{\Delta x_d}{\Delta t}$, the position in at some time step j is given by $$x_j=x_{j-1}+k_j L + \Delta x_d$$ where $L$ is ...
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### Surface Isotropic and Shear Stress [duplicate]

I am going over a 1987 biomechanics paper looking at surface shear stress in a biological membrane, which behaves analogous to a liquid in the plane of the membrane (see image/sketch below). The ...
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### Why are systems operating far from equilibrium more efficient?

In many (biological and living systems) physics courses I encountered the notion that systems operating far from equilibrium are related with more efficiency with regard to their specific tasks. One ...
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### Back-of-the-envelope estimate of thermodynamic cost of food absorbtion from first principles

Just out of curiosity, I'm trying to get a sense of the order-of-magnitude theoretical thermodynamic cost of food absorbtion. I'm thinking of food absorption as "move nutrients in newly consumed ...
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### Do vibrational frequencies produced from sound pass through your entire body? from one side to another? [closed]

when there is a noise by me, i feel the vibration on my skin from the direction it’s coming, it moves into my body. a wall of what sound would feel like passing through me. i perceive it as container ...
1 vote
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### Biophysics intro resource recommendation for a math stat PhD

(Question has been edited for specificity based on feedback. I followed the guidelines StackExchange recommended to me: Are resource recommendations allowed?) Within biophysics, I'm looking to build ...
5k views

### Why does an MRI machine or other EMP generating machine not damage humans, but it will fry computers?

A sufficiently strong electromagnetic pulse can/will destroy smartphones and computers. I know somebody who went into MRI machine and forgot a Visa credit card in his pocket. The card was toast and he ...
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### What takes more energy? Walking up stairs or ramp over the same height?

Often when we go hiking, we encounter two kinds of paths whenever we have to cover elevation. We either go up via stairs or via walking up a ramp. Sometimes both are available side to side. And it's ...
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### Functionalizing iron oxide nanoparticles for antimicrobial activity [closed]

I'm working on my thesis which is about synthesis of iron oxide nanoparticles from a plant leaf extract and testing the particles activity on bacteria to measure their toxicity towards it. The thing ...
1 vote
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### Why is water bright in a T2 weighted image?

I am new to study MRI. Please understand if some terminologies I use are wrong. This might be a silly question, but I wonder why water is bright in a T2 weighted image. T2 relaxation is also called ...
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### Why does vitrification cause less damage to biological tissue than freezing does?

Long-duration cryopreservation of biological tissue (most often semen, egg cells, or fertilized embryos) is typically done at 77 K, since the samples can be easily kept at that temperature by ...
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### How does safe fall distance scale with the size of an animal?

An animal has a maximum safe fall distance, the distance it can fall without getting hurt. If you take an animal and a similar animal twice as large, what would we expect to hold about the maximum ...
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### Why does a centrifuge cause blood to be pushed downwards in the human body?

Good evening all, I recently watched this YouTube video about a centrifuge by Tom Scott (https://www.youtube.com/watch?v=DMKcO-T5Y4o). Around the 2:30 mark, it is said that blood will be 'pushed ...
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### Why does UV light feel warm on my skin? Whereas infrared light heats up space around me plus my skin?

Noticed something weird today. I have an infrared space heater that is pretty good at heating up my desk at work (as well as my skin obviously). I also have a UV flashlight. I noticed the UV ...
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### What would a hypothetical lifeform in a universe with no electromagnetism look like? [closed]

I was watching an amazing Arvin Ash video in which he explained the purpose of light and speculated that life could possibly exist if the universe did not have the electromagnetic force but just ...
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### Quantitatively, how much would radiation levels increase without the geomagnetic field?

Many, many popular science articles claim that if the Earth didn't have a magnetic field, then the much higher concentration of cosmic rays that reached the surface would cause health damage to humans....
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### What causes blood flow to become turbulent after a constriction?

If a blood vessel is narrowed from the middle, the blood flow turns turbulent (see image below). Why does this happen? Does it have to do with Reynolds number becoming high because velocity has ...
1 vote
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### What Continued Upwards Momentum Has to Do with Vortex in Bee Wings?

In this answer to how bumblebees fly, it says that The wing motion has a sort of double lift feature. By twisting her wings over at the end of each down stroke, the upward momentum is never lost. ...
255 views

### Under what conditions is mean square displacement $\text{MSD}(t)=4Dt+v^2t^2$ a valid asymmetric random walk model?

I am reading the paper Actin dynamics drive microvillar motility and clustering during brush border assembly by Meenderink et al. (2019). In this paper, the authors fit the mean square displacement (...
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### Why is it important to release energy as quickly as possible to perform a vertical jump?

Let's assume that we create this mechanism, where we must decide if the actuating cylinders are double-acting hydraulic or pneumatic with a spring inside. the goal is for the mechanism to suddenly ...
1 vote
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### Choice and Energy [closed]

Does the action of making a choice expend energy? If any conscious choice is predetermined, it must always be taken towards a greater entropy state, which means it must somehow "know" ahead ...
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### Where do beta particles go after being emitted from the nucleus?

What high-school taught me: In beta radiation, beta particles are lone electrons that are emitted from the nucleus at high speeds after a neutron decays into a proton and an electron. Beta radiation ...
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### Can you perfectly control electric currents' behavior in anisotropic media?

I'm an undergrad who is learning recently about anisotropy w.r.t. E&M. I understand that in anisotropic media the behavior of electric currents and other E&M aspects can be very unpredictable ...
1 vote
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### Electronic tunneling between two states

I am reading Steering Electrons on Moving Pathways (Beratan et al. 2009) which is about electron tunneling in biomolecules, and specifically the processes via which an electron can move from an ...
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### How often does a molecular machine run in reverse?

I was reading the Wikipedia article on Stochastic thermodynamics, and came across this statement in the overview: When a microscopic machine (e.g. a MEM) performs useful work it generates heat and ...
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### What is the hydrodynamic interaction (Oseen kernel)?

I am reading through the paper "Dynamics of Membranes Driven by Actin Polymerization" by Nir S. Gov and Ajay Gopinathan. In this paper, the authors develop a PDE model to explore the ...
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### Is a worm-like-chain purely entropic?

I consider a worm-like chain with the Hamiltonian given by: $$H(L)=\frac{\kappa}{2}\int_{0}^{L}ds\left(\frac{\partial\vec{t}}{\partial s}\right)^2$$ where $\kappa$ is the ...
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### Elucidation needed in protein dynamics

I'm reading some papers about protein dynamic, stability and energy landscape. Switching from paper to paper I'm encountering different term used for talking about protein movements, for example: α- ...
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### In an open quantum system, what is the justification for using a harmonic oscillator bath to represent the molecular environment in a solvent?

The Caldeira-leggett (CL) model is sometimes used to describe quantum mechanical effects in a system (like a biomolecule) immersed in a solvent. The Hamiltonian of the CL model consists of an ...
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### How to understand radiation dose and dose-area-product?

I am learning about radiation protection measures and am confused about the idea behind certain measures and practices, and I hope somebody can help me. Dose definition and Gy The absorbed dose is ...
1 vote
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### Radical pair mechanism in photosynthesis

I am aware that in Photosystem II of the chloroplast, there sometimes forms a spin-correlated radical pair of electrons whose spins precess around the effective magnetic field for several nanoseconds (...
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### Does the human brain use random number generators? [duplicate]

Neurons fire depending on the impulses they get from other neurons. This seems to be 'deterministic'. However, sometimes it might be useful to use random processes instead. Does the human brain have ...
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If I exercise by weightlifting, I can "burn calories". The way I understand the process is as follows: when I'm moving the weight up, the energy from chemical bonds turns into potential ...
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### Generation of order on the Earth

I learnt in a course on Biological Physics that it is possible to generate order without violating the second law of thermodynamics. This can be done if "high quality" energy is delivered to ...
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### An invitation to brownian traps to capture or destroy viruses and bacteria

I'm interested for general feedback about modern brownian traps for viruses and bacteria. In my rememberings a related reference is a column added to the article in Spanish [1] (I don't remember well ...
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### With blast injuries, how much of the damage is from rapid decompression? [closed]

If a person or creature suffers a high explosive or low explosive blast, how much of their injuries will be due to the sudden decompression immediately after the shockwave? Sudden decompression can ...
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### How can we define a "free energy" for a protein configuration?

In my naive understanding, a free energy (either Gibbs $G$ or Helmholtz free enrgy $F$) is a property defined for an ensemble of microstates under certrain circumstances. (NPT or NVT) But I often see ...
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### Conflicting result for velocity and radius in physiology

My problem is that we say V = Q/A (V velocity, Q flow, and A area of pipe) in haemodynamics. Based on this formula, the velocity ​​is inversely related to the second power of the radius. Combining ...
1 vote
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### Why must all reactions be reversible according to thermodynamics?

I am reading the book "Models of Calcium Signalling" by Dupont et al., and on pages 31-32 the statement is made with regard to some previously written chemical reaction equations We have ...
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### Can humans feel artificial light? [closed]

I know humans can feel sunlight - even blindfolded, it's easy to tell if one is in the noon sun or indoors. However, I don't know about artificial light. Can humans feel sufficiently harsh artificial ...
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### Voltage propagation in neurons

Context In the classical theory of passive neurons (where the non linear action potential is not excited), the voltage is successfully described by cable theory. The axon is modeled as a series of (...
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### The *compressive* strength of spider silk

There's plenty of information about the tensile strength, density, energy density, ductility, etc. of spider silk. However, I personally cannot find any figures in regards to the compressive strength ...
1 vote
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### Modeling the Effect of Magnetic Induction on Single Neurons

In this paper, the authors suggest a potential mechanism for magnetoreception in birds: as the Earth's magnetic field (taken to be homogeneous over sufficiently small spatial scales) passes through ...
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