What is String: Definition and 1000 Discussions

In molecular biology, STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) is a biological database and web resource of known and predicted protein–protein interactions.
The STRING database contains information from numerous sources, including experimental data, computational prediction methods and public text collections. It is freely accessible and it is regularly updated. The resource also serves to highlight functional enrichments in user-provided lists of proteins, using a number of functional classification systems such as GO, Pfam and KEGG. The latest version 11b contains information on about 24,5 million proteins from more than 5000 organisms. STRING has been developed by a consortium of academic institutions including CPR, EMBL, KU, SIB, TUD and UZH.

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  1. Demystifier

    A Negative cosmological constant from string theory

    Allegedly, string theory (in it's simplest form) predicts that cosmological constant must be negative (or zero). Can someone explain where does this result come from? A reference would also be welcome.
  2. prakhargupta3301

    What is the tension in string?

    Homework Statement We have to find T1 and T2 From right to left objects are: A B C Homework Equations F=ma The Attempt at a Solution Okay. So I found acceleration of whole system: F=ma 200N= (20+10+5)*a 200/35=a a= 40/7 ms-2 Now, finding T1 is fairly simple: f=ma T1=5*(40/7) T1=200/7 Newtons...
  3. Sophrosyne

    B Reconciling QM with string theory

    I am trying to read about and understand string theory. But in trying to understand how it reconciles with the world of quantum field theory and quantum mechanics, I am getting a little confused. How does the string move through and propagate through the quantum field? Does string theory...
  4. M

    A Why does a guitar string "beat" as if it is out of phase?

    I am working on synthesis modelling of guitars, and I have managed to capture most elements of the guitar well so far. Something I am struggling to understand is why a guitar string has a natural "beating" sound to it, meaning it sounds as if it is ebbing and flowing slowly as it vibrates. To...
  5. E

    A Why Haven't We Observed Heavy Particles from Massive String Theory in Real Life?

    Am I understanding it correctly that if you keep acting with an internal 2-dimensional creation operator on a string you will get heavier and heavier particle from the 11-dimensional (26 dimensional) point of view? If so, how come we haven't observed those particles in the real life? Is it...
  6. K

    Unfingered Guitar String Vibration Frequency: 627 Hz

    Homework Statement When unfingered, a string on a guitar vibrates at 627 Hz. What frequency will the string produce when fingered one third of the way from the end, that is only two thirds of the string can vibrate? Homework EquationsThe Attempt at a Solution I am not too sure what equations...
  7. J

    Finding the tension of a rope given the mass of a pulley

    Homework Statement mass of pulley is 8 kg Homework Equations m1a=T m2g-T=m2a The Attempt at a Solution I solved question with neglecting mass of pulley but should I?
  8. Mutatis

    How can I find the wave equation u(x,t) of a string

    Find the wave equation U(x,t) of a vibrating string with linear density d, tension p, initial velocity zero, weight L and initial displacement U0(x) = a1*sin(2*pi*x/L)+a2*sin(4*pi*x/L). Guys, please help me with this task. I did the following procedure: The U(x,t) solution must me a sum of...
  9. B

    Tension in the string of a simple pendulum

    Homework Statement Is the tension in the string of a pendulum, when averaged over time, larger or smaller than the weight of the pendulum? Quantify your answer. You may also assume that the angular amplitude of the oscillations is small. Homework Equations For tension ##T##, angular...
  10. HappyFlower

    A small mass m hangs from a thing string and can swing....

    Homework Statement a small mass m hangs from a thing string can swing like a pendulum. You attach it above the window of your car as shown in the figure. When the car is at rest the string hangs vertically. What angle does the string make? a) when the car accelerates 1.20m/s^2 b)when the car...
  11. R

    I Clarification for a standing wave on a string equation

    Hello, Came across https://drive.google.com/file/d/1bpB7BcVf1yQLiwg9quAn2vlhu8-i6Zy_/view and I'm not sure about one thing For the 2 parts of the equation with sin, is it: 1. [...sin(kx)]sin(wt) or is it: 2. [...sin(k)*x]sin(w)*t Thank you -DR
  12. Suyash Singh

    Falling solid cylinder with string

    Homework Statement Homework Equations m:mass of solid cylinder T: tension in string w:angular velocity The Attempt at a Solution m(g-a)=T mg-ma=T a=v^2/r=w^2r now what?
  13. D

    B Showing/proving a physical relationship

    I derived a relationship between frequency and tension of a string, accounting for tension's effect in the linear density of the string. So in a nutshell, the equation is more complicated and is in the form of f^2=aT^2+bT (f is frequency, T is tension, ab are constants involving the control...
  14. D

    Tension and frequency of a vibrating violin string

    1. The problem statement, all variables, and given/known data So I'm doing an IB extended essay on the relationship between frequency and tension of a violin string. As you apply more tension to the string (using weights and pulley), the frequency will be higher, as shown below. There's not too...
  15. T

    Propagation of transverse pulse on a string

    Homework Statement A horizontal string at tension T is tapped at the midpoint to create a small transverse pulse. What happens to the pulse as time passes? If the pulse is instead created at a point other than the midpoint, what happens to it? Neglect damping. Homework Equations Speed of...
  16. CessnaTexan

    I Definition of "info" as it pertains to string theory

    Hello, everyone! I am a lover of physics, specifically that of the quantum type. The very specific question I have is the exact scientific definition of "information" pertaining to string theory. Any insight is good insight!
  17. P

    When and where do two transverse waves on strings overtake each other?

    Homework Statement Two long strings P and Q ,each having linear mass density 1.2 x 10^-2 are stretched by a different tension 4.8 N and 7.5 N respectively and are kept parallel to each other with their left ends at x=0.Wave pulses are produced on the strings at t=0 on string P and at t=20ms at...
  18. Phantoful

    Bead on a string, find y(x) if horizontal velocity is const.

    Homework Statement Homework Equations K = (1/2)mv2 U = mgh W=Fd Integration/Calculus The Attempt at a Solution I'm not sure what I should be doing for this question, if height changes how is it possible that velocity stays the same, according to the conservation of energy (frictionless wire)...
  19. cromata

    I Boundary conditions of a forced oscillator (string)

    -If we have string of length L that has fixed ends, then we can easily find frequencies with which this string can oscillate: We just need to solve wave equation: ∂2y/∂x2=1/c2*∂2∂t2 (c is determined by strings properties (linear density and tension), with Dirichlet boundary conditions...
  20. thebosonbreaker

    Resolving forces involving an elastic string

    Homework Statement A light elastic string of natural length 0.3m has one end fixed to a point on a ceiling. To the other end of the string is attached a particle of mass M. When the particle is hanging in equilibrium, the length of the string is 0.4m. (a) Determine, in terms of M and g (take g...
  21. O

    Faster than the speed of light (pulling on a string)?

    If you were to connect a string from one star to another (assuming everything remains still), and then you were to pull one side of the string towards you, the other would be pulled immediately, thus the "communication" between the two edges is technically faster than the speed of light? Does...
  22. Tibriel

    Tension in a string holding a spinning object

    Homework Statement You spin a 1.20 kg mass at the end of a 1.10 m string. The tangential velocity is 13 m/s. What is the tension in the string? Homework Equations x = angle string makes to the vertical L = string length r = L*sin(x) T*cos(x) = mg (because the sum of the vertical forces has...
  23. A

    MHB Can You Define the Recursive Equation for Strings of 1s and 2s with 3 Mod 4 1s?

    If $K$ is the set of strings of 1s and 2s with the number of 1s $\equiv3\bmod4$ and with any amount of $2$s, find a recursive definition of $K$. For example, $1112112121$. I'm in need of some hints. The string can be empty, have no 1's or have 1's equivalent to 3 mod 4...
  24. Spinnor

    I Can String Theory Explain the Energy Density of Empty Space?

    So if string theory is to be correct it must be able to come up with the observed value for the energy density of empty space which is pretty close to zero? A naive understanding of the compact spaces of string theory tells me that an "energy audit" of the highly curved compact manifolds of...
  25. HydroMarioUSA

    Newton's 3rd Law (Pulleys - 1)

    Hi, I'm new here. Could someone provide some guidance on how to start this problem?
  26. S

    Frequency of Wave on a Guitar String HW

    Homework Statement When a guitar string is stretched to have a tension T, it produces a frequency f. You change the tension by a very small amount ∆T . Show that the new frequency of the guitar string is fnew = f ( 1 + (delta T)/2T) For example, a guitar string has tension T = 10N and...
  27. P

    Finding the period of a pendulum witha string that has mass

    1. The problem statement, all variables and gihttps://www.physicsforums.com/attachments/218400 ven/known data Assuming the string from a simple pendulum did not have negligible mass and the pendulum bob was not a point mass, then determine an expression for the period of a single small-amplitude...
  28. I

    Schools String theory school recommendation: UC Davis, UIUC or other

    I'm currently applying for grad schools in string theory with an interest in AdS/CFT but am open to fundamental formalisms in string theory. I was trying to decide on a few universities to apply to. I am currently considering University of California Davis and University of Illinois Urbana...
  29. Spinnor

    B String theory, Calabi–Yau manifolds, complex dimensions

    So in string theory at each point of Minkowski spacetime we might have a 3 dimensional compact complex Calabi–Yau manifold? We can have curved compact spaces without complex numbers I assume, what is interesting or special about complex compact spaces? Thanks!
  30. Spinnor

    I Open string end points, their motion in spacetime

    I have some questions and refer you to the image below the caption of which states, "D-branes may be of exceptional importance in the explanation of elementary particles of the Standard Model. However, it still remains to find a solid connection between the M-theory and the Standard Model."...
  31. B

    Exploring String Theory: Recommended Books and Critiques

    What are the books that speak about string theory you would suggest me? And the book against this theory? (I'm an undergraduate physics student) Thanks!
  32. binbagsss

    Polyakov action, reparameterisation q, string theory

    Homework Statement i am stuck on part d , see below Homework Equations parts a to c are fine polyakov action: ## \frac{1}{2} \int \frac{1}{e(t)} \frac{dX^u}{dt}\frac{dX_u}{dt}-m^2 e(t) dt ## EoM of ##e(t)##: ##\frac{-1}{(e(t))^2} \frac{dX^u}{dt}\frac{dX_u}{dt}-m^2=0## [1]you plug the EoM...
  33. K

    Circular motion, string and ball in a horizontal circle

    A mass m = 0.15 kg is attached to a massless string and rotates at constant speed v = 4 m/s in a horizontal circle of radius 2 m. The tension T (in N) in the string is: (a) 1.1 (b) 1.9 (c) 2.4 (d) 3.3 (e) 4.9 I would assume that first I calculate the centripetal acceleration by using v^2/r =...
  34. C

    String with masses on either end being pulled from the center

    Homework Statement Two equal 1 kg masses are connected by a light 1.6 m string on a flat frictionless surface. A 2 N force is applied to the midpoint of the string which causes the system to accelerate in the positive x-direction. After 1.5 seconds, the rope makes an angle of 55° with the...
  35. T

    Wave equation, taut string hit with hammer

    Homework Statement A string of length L is fixed at both ends ##u(0,L)=u(L,t)=0## The string is struck in the middle with a hammer of width a, leading to an intial condtion ##u(x,0)=0## and $$U_t(x,0)=v_0 $$ for $$\frac{l}{2}-\frac{a}{2} \leq x \leq \frac{l}{2}+\frac{a}{2} $$ and...
  36. A

    How to calculate the speed of an object attached to a string

    Homework Statement The question and the known/given variables are on the image in part 3. The question says that a 20-g bead is attached to a light 120 cm-long string. Now in my mind the bead will travel in a circular path if it is pushed really hard. So Isn't the length of the string, 120 cm...
  37. axer

    I What's the restoring force, if there's a mass on a string.

    Hello, I'm finding difficulties understanding the logic behind the multiple choice answers and the exams are near(finals! :)) What's the restoring force, if there's a mass on a string? mg m m/g – m – mg I know F=-kx and that F=weight and weight=mg. But i don't know which answer is the correct,
  38. K

    A Are String Theory physicists violating the Scientific Method

    The Scientific Method says that if a theory disagrees with observations, it has been falsified (according to Karl Popper). String theory predicts that spacetime is 10-D, but it is observed to be 4-D. This is a wrong prediction by the theory. So string theory is falsified. String theorists then...
  39. A

    A String Vacua and Particle Interactions

    I've been doing a little bit of reading on string theory, and the very large number of string vacua that are possible (i.e., perhaps 10^500 or more). One thing that is not clear to me is exactly what constitutes a 'vacuum' in string theory. In QFT theory, the vacuum is defined as the state with...
  40. K

    I String theory on complex spacetime, twistor string

    bosonic string theory requires 26 dimensions superstring theory requires 10, 9 spatial 1 dimension of time Witten has researched twistor string theory has there been any serious research with (super) string theory written on 4 complex -valued dimensions of spacetime? the additional dimensions...
  41. Z

    Calculating Mass of a Vibrating String Using Known Quantities

    Homework Statement A second harmonic standing wave has the known quantities of Amplitude (max y at antinode) A, maximum velocity (y=0 at antinode) v, string length L, tension in the string T. Given that we know that it is second harmonic, we can assume that λ = L How can one determine the...
  42. binbagsss

    String Theory, Number Operator , Mass of States

    Homework Statement I have the following definition of the space-time coordinates Homework Equations Working in a certain gauge we can also do: From which we can find: Where ##N_{lc} ## sums over the transverse oscillation modes only. The Attempt at a Solution [/B] MY QUESTION: I...
  43. L

    Tension in a String: Explaining P=T+25 N vs P+T=125

    Homework Statement Homework Equations Ook, so I'm really bad at physics, and i need someone to help explain why the answer is P=T+25 N I thought it is P+T = 125 The Attempt at a Solution Since the system is in constant velocity, then Fnet = 0 so that P + T + W = 0 Why isn't it P + T + 125...
  44. T

    Tension required to tune a string to the note of ##E_2##

    Homework Statement State the boundary condition which must be met at a point where the string of question 2 is fixed. Hence find the real standing wave solutions to the wave equation, and determine the allowed oscillation frequencies, when such a string of length ##L## is fixed at its ends...
  45. J

    What is the largest pulling force before the string breaks?

    Homework Statement A person pulls three crates over a smooth horizontal floor at an angle of 34 degrees to the horizontal. The crates are connected to each other by identical horizontal strings A and B, each of which can support a maximum tension of 38.0 N before breaking. What is the...
  46. M

    MHB Statics for rod attached to string

    could someone please explain to me why there is no relative force at point a where the rod ab is attached to a thanks
  47. parshyaa

    A few questions related to tension in a string

    Its getting hard for me to deal with the problems related to tension and reason behind this is not clear understanding of the concept so i have few questions on this. What causes tension in a rope/string(i think its related to electromagnetism, but i am not getting the clear idea behind this)...
  48. D

    S.H.M of the midpoint of a guitar string

    Hi guys, I would be grateful if you could help me out with this problem, I've worked though it myself, but my answer to part c is very large, which is making me doubt my answer, and in turn making me doubt my answer to part b Homework Statement The midpoint of a guitar string executes s.h.m...
  49. Spinnor

    B Branes, gluons, time reversal, and string theory.

    So a gluon in string theory may be an open string whose ends live on one or two branes? These strings have an orientation along the string? Does the orientation change direction if we reverse time, some where I thought I read that one can think of a flow along the string so if you reverse...
  50. Rodrigo Schmidt

    Why does the pulse related to the inverted phase travel to the right?

    So I'm having a introductory study on waves and there's something that i can't understand when dealing with reflections on a fixed end. We have the general solution for the wave equation: ## y(x,t)=f(x-vt)+g(x+vt)## Supposing that the fixed point is in the origin we have the boundary condition...
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