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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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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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27 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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66 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
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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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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
67 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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78 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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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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Magnetic field record set with a bang : Can peak magnetism last more than microseconds?

I have read a couple days ago, about the spectacular 1200T magnetic field record set by Shojiro Takeyama and his team at the University of Tokyo. Since the output peak only lasts for a couple ...
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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
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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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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
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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
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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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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
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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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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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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
26 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
51 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
74 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
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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
63 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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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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1answer
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Whats the energy spent on a push-up? [closed]

Let a human of height 1.80 m, arm length of 0.5 m and weight 80 kg do a push up. How much energy did she spend? $$ F = m \cdot a $$ $$ E = F \cdot s $$ $$ \rightarrow E = m \cdot a \cdot s,$$ where $...
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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
133 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
20 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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23 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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Effect of skin type on radiation attenuation from a nuclear source

What properties of different skin types affect attenuation of radiation from a nuclear source? Which has the most affect? This could be skin colour, age, and properties related to skin health, as ...
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1answer
35 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
117 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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How is voltage induced in polarizable electrodes by ionic current?

I'm hoping to gain a technical but still intuitive understanding -- the literature I've found is either a bit general or directly goes to derivations. When a microelectrode is placed close to a ...
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2answers
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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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Representing polypeptide in spherical polar coordinates in protein folding problem

I am trying to represent all the atoms of a protein polymer in spherical polar coordinates. However I couldn't capture the dihedral angle present in between successive polypeptide chain. How do i do ...
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1answer
22 views

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 ...
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3answers
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How does leading edge vortices LEV create lift

I'm writing a text for school about samaras, seeds that spin to create lift. The wing of some of these seeds produce leading edge vortices that somehow generates lift, but I can't properly understand ...
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Phil Anderson's Criticism of Existence of Stable Dissipative Structures

In this book chapter (1987), titled "Broken symmetry, emergent properties, dissipative structures, life," Phil Anderson and Daniel Stein criticize defining life as a dissipative structure (a ...
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2answers
60 views

Newtonian Physics vs Metabolic Equivilant (MET) calculations

I am trying to help my daughter do her physics homework. Her assignment includes calculating Calories worked off while exercising. The formula she is using is ...
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2answers
77 views

Why does yawning distort headphone music?

During deep and prolonged yawning, I noticed the music tonality is distorted: the pitch becomes slightly lower. Why?
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What's wrong with Arnold's scaling argument on jumping height?

The following question was put on hold: Is it possible to prove that an elephant and a human could jump to the same height? It reminded me of an exercise (24a) on that exact topic in Arnold's "...
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2answers
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Human body as a measuring instrument

One can easily find descriptions of human eyes and ears used for measuring phenomenons. Finding what resolution do eyes have or what frequencies can human hear is no trouble. It is also seen in scales ...
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What is a composite negative electrode?

When I was studying about ECG I came to know that there are two types of leads used to measure.I can understand about bipolar leads but in unipolar leads an active electrode and a indifferent ...
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2answers
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Vasodilation decreases blood pressure

Okay it should make sense intuitively, but Bernoulli's principle says that a higher cross sectional flow area means less velocity which means higher pressure! I also read in a related post that ...
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197 views

Number of collisions per second a water molecule is experiencing in the fluid phase at ambient conditions

I am teaching a DNA course for lay people and I want to give them an indication of the number of collision per second a water molecule experiences in pure water. Similarily, I would like to know the ...