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. C

    Comp Sci Validating Braces Placement for Expression Evaluation

    Here's what I've done: Mentor note: replaced icode tags with code=python and \code pair. def valid_braces_placement(s, L): if len(L)==0: return False string = '' for element in L: string = string + str(element) D = ['+','-','*'] return...
  2. G

    To find the modulus of elasticity of a light elastic string

    Could I please ask for help with the following question? Four uniform rods of equal length l and weight w are freely jointed to form a framework ABCD. The joints A and C are connected by a light elastic string of natural length a. The framework is freely suspended from A and takes up the shape...
  3. R

    Fourier series, periodic function for a string free at each end

    From the statement above, since the ring is massless, there's no force acting vertically on the rings. Thus, the slope is null. ##\frac{\partial y(0,0)}{\partial x} = \frac{\partial y(L,0)}{\partial x} = 0## ##\frac{\partial y(0,0)}{\partial x} = A\frac{2 \pi}{L}cos(\frac{2 \pi 0}{L}) =...
  4. DonFromPgh

    I String Basics question from an ABJECT ignoramus

    I know this will demonstrate how ignorant I am about the current state of string an brane theory, but I have a question that I don't think I could find the answer in current discussions. Please don't be too harsh. A string has to come in one of only a few "types": Closed - the string is...
  5. Z

    Mass matters for standing waves on a string?

    The question is to explain the equation of motion of the red ball. The string is massless and a small ball of mass m is attached to the string halfway. I just assumed the mass of the string is the same as the mass of the ball and explained the equation A cos(Wt) by defining the terms. I'm not...
  6. S

    Intermediate Value Theorem Problem on a String

    Preceding Problem. Let ##y=f(x)## be a continuous function defined on a closed interval ##[0, b]## with the property that ##0 < f(x) < b## for all ##x## in ##[0, b]##. Show that there exist a point ##c## in ##[0, b]## with the property that ##f(c) = c##. This problem can be solved by letting...
  7. R

    How to find the amplitude of oscillations of a string with 5 beads?

    Hi, First of all, I'm wondering if a beaded string is the right term? I have to find the amplitude of the modes 2 and 3 for a string with 5 beads. In my book I have $$A_n = sin(\kappa p)$$ or $$A_n = cos(\kappa p) $$ it depends if the string is fixed or not I guess. where $$\kappa = \frac{n\pi...
  8. topsquark

    Quantum Looking for a good String Theory text

    (Sorry about writing a book! But I felt more information was the better mistake.) Okay, here's the deal. I have been teaching myself Physics and Math beyond my MS in QFT. I have been doing this for the last 20 or so years and I've gotten reasonably decent at it but String Theory is a bit...
  9. TheHeraclitus

    I String theory in 4 dimensions?

    Non-critical string theory, on Wikipedia it says: Has it been experimentally disproven or are other reasons for its apparent obscurity?
  10. T

    Circular motion of a mass on a string on an inclined plane

    (I drew motion in the opposite direction so the object would rotate trigonometrically but it should be the same thing) I have just finished the Kinetic Energy and Work chapter in my course and this is the last problem from the problem set. I have not worked many problems with the Work-Kinetic...
  11. TheHeraclitus

    I Is Supersymmetry required by String theory?

    From what I understood Supersymmetry means there are more particles than we currently know about and they are predicted by (some/all, I do not know) versions of String theory. Is it so important to String theory or can it work without SUSY? Thank you!
  12. TheHeraclitus

    I Bohmian mechanics and String theory

    Is it easy to combine them or impossible? Is there a tension due to the non-locality found in Bohmian mechanics? Thank you!
  13. P

    Two Pulleys, two weights and a string

  14. S

    Nobel laureates for and against string theory?

    According to Michio Kaku, Nobel laureates have taken both sides towards string theory since some of them accept it and some of them reject it, as he says here (https://www.snowboundbooks.com/book/9780385542746): “Kaku also explains the intense controversy swirling around this theory, with...
  15. nmsurobert

    B LED light and guitar string (strobe light effect)

    I've trying to explain this to myself but I know I'm missing something. I tuned the low E string to B. The frequency of that note is about 62 Hz. When I play that note under the led lights in my backyard I can see the string oscillate back and forth. After doing some reading, the LED light...
  16. S

    Tension of string acting on stone moving in horizontal circular motion

    Is it possible for the stone to move in horizontal circular motion just like in the picture? I try to draw the free body diagram of the stone and there are two forces acting on the stone, its weight (directed downwards) and the tension of the string (directed to the left). The tension will...
  17. LCSphysicist

    Can Laplace Transforms be Applied to Finite Intervals?

    "Consider a string of length L that is connected at both ends to supports and is subjected to a load (external force per unit length) of f(x). Find the displcament u" https://i.stack.imgur.com/yVIDG.png We need to solve this: $$Tu_{xx} = f(x)$$ subject to $$u(0)=u(L)=0$$ But i don't understand...
  18. Mcmenhweilleisi

    Equilibrium with the string in the center exactly horizontal

  19. M

    A New string formulae for Higgs mass and cosmological constant

    https://arxiv.org/abs/2106.04622 Calculating the Higgs Mass in String Theory Steven Abel, Keith R. Dienes [Submitted on 8 Jun 2021] There are at least two properties of the Higgs mass one might hope to explain with such a fundamental calculation: its criticality, and its participation in...
  20. S

    Nobel laureates supporting string theory?

    Are there any living Nobel laureates in physics (apart from David Gross, François Englert and perhaps Gerard 't Hooft and Steven Weinberg) who have made research in string theory or at least find it attractive?
  21. D

    A BRST operator Q in string theory and string field theory

    In string theory, physical states satisfy QBΨ = 0, where QB is the BRST operator. This equation of motion can be obtained from an action S = ∫ QBΨ*Ψ + Ψ*Ψ*Ψ There is a gauge invariance under δΨ = QBΛ. what is the framework in which the role of the BRST operator QB is understood in open string...
  22. Chestermiller

    Time Average Value of Pendulum String Tension

    Another member and I, in private conversations, have been discussing the time average tension in a pendulum string. He has done a numerical analysis of the problem, and his calculations indicate that the time average tension is less than mg. I have analyzed the problem analytically by...
  23. keo

    Mips count characters in string

    Summary:: Count characterers in a string and display it in hexadecimal [New user has been reminded to show their work on schoolwork problems] Hi, how can I do this in MIPS? Given a string of characters, the program has to count the number of characters in the string, and display it in...
  24. Z

    I Longitudinal waves on a string

    Good day to everyone, I kindly ask for your help. My question is: "Does a string have to be under tension, to transmit longitudinal waves? Why is it so?" I have trouble finding relevant scientific articles regarding the question and for reasearching "longitudinal waves on a string". If anyone...
  25. E

    A Conservation of energy for stationary particle attached to string

    I was going to put this in the homework forums, but on second thoughts it's more conceptual so perhaps here is better. It's about problem 4, chapter 6 of Wald. Part (a) is fine, $$u^a \nabla_a u^b = \frac{\xi^a}{(-\xi^c \xi_c)^{1/2}} \left( \frac{\nabla_a \xi^b}{(-\xi^c \xi_c)^{1/2}} +...
  26. E

    Other Should I give up string theory due to its job prospects?

    I'm currently a fresh grad student in theoretical physics, and I'm still deciding to choose which research group to join. My current understanding (maybe I'm wrong) is the PhD theme pretty much determines the topic for future post-doc research so I kinda need to choose very carefully. I'm...
  27. P

    If I pull a pulley, what is the tension in the string around it?

    I assumed that each of the masses attached to the string would be pulled with a force F, instead of F/2, which appears to be the correct value. Why is it F/2? I suspect the fact that the pulley is "weightless" has something to do with the F/2 value. What is it? Thank you.
  28. J

    Equilibrium: Mass on an inclined plane held by a string, find the tension

    6.2(9.8)=60.8 (incorrect) 46.2cos40.4= 35.2 (incorrect)
  29. D

    I Does string theory falsify the theory of special relativity?

    Hello, I am spending time learning more about the theory of special relativity and string theory. One of the things that I have read about string theory is that it includes other dimensions in relation to space (space has 9 dimensions in string theory, supposedly). However, from what I...
  30. S

    I Brane cosmology without string theory?

    There are several models of brane cosmology (https://en.wikipedia.org/wiki/Brane_cosmology) and several physicists working in this field (e.g Lisa Randall and Raman Sundrum), but as you will notice, apparently they are all directly related to string theory. This has several consequences, for...
  31. S

    A String Theory in N dimensions?

    String Theory and related theories like M Theory have strong constraints in the number of dimensions where they can be formulated (for example, in the case of M theory, it is only allowed in 11D or in the case of bosonic string theory is only allowed in 26D. Since string theory and related...
  32. J

    I Movement of a guitar string at relativistic speeds

    Hey! I'm and undergrad in the third year of my applied physics program. I'm taking a course in Special Relativity, and due to Corona the exam has been replaced by a pretty free project where we delve deeply into a topic related to the course. I'm interested in music, so my professor suggested I...
  33. sahilmm15

    A classic string and pulley problem

    I tried hard but was not able to make progress. Problem no 33.
  34. D

    High Energy String Theory Books: Intro & Advanced Level | GSW, Polchinski, McMahon, Becker

    Some good introductory string theory books that I know are GSW Polchinski McMahon Becker What are the good books at a more advanced level? Are there any such books, or do I have to dig it out of the research papers? There is a set of books called "mirror symmetry" and "dirichlet branes and...
  35. A

    Conical Pendulum with varying string length

    Consider a conical pendulum like that shown in the figure. A ball of mass, m, attached to a string of length, L, is rotating in a circle of radius, r, with angular velocity, ω. The faster we spin the ball (i.e., the greater the ω), the greater the angle, θ, will be, and thus, the smaller the...
  36. S

    A Different symmetries or no symmetries in string theory?

    I was reading the book "A Fortunate Universe" by Geraint Lewis and Luke Barnes and something caught my attention: At page 195 the authors say that universes with different symmetries could be modeled and they would have dramatic results like having different conservation laws. I asked Mr...
  37. Bancrates

    A What is the Best Resource for Learning String Theory as a Side Project?

    I've completed my PhD and am leaving the field to take up a career elsewhere, however I'm interested in developing my knowledge of string theory as a (potentially lifelong) side project. I have a solid understanding of GR and some extensions (my PhD was in relativistic effects in cosmology, and...
  38. T

    Moment of Inertia with pulley and two masses on a string (iWTSE.org)

    Note: the working (taken from iWTSE website) refers to inertia as the symbol ‘J’ (in-case there was any confusion).I found equations of motion for mass m and 2m which were ‘T1 = ma + mg’ and ‘T2 = 2mg – 2ma’, respectively. I know they are connected particles with the same acceleration ‘a’.I have...
  39. Vivek98phyboy

    Reflection of inverted waves to form a standing wave

    Standing waves in a string fixed at one end is formed by incoming and reflected waves. If reflected waves are 180° out of phase with incoming wave, how could they combine to give an oscillating wave? Shouldn't it be completely destructive interference all the time across the whole length of string?
  40. K

    How will the pitch of a string change when I stretch it? (sound)

    I was trying to search but found no results. Is there a way to calculate how frequency will change if I stretch a string by certain amount (0.14 mm in my case)? I found out I can measure its frequency once stretched, but no results as of how to estimate new frequency ahead of the time. I know a...
  41. W

    B Difference between an Einstein frame and a String frame?

    I have listening to talks come across the terms"Einstein frame" and "String frame" but am not at all clear what they mean. Can anyone give a layman's explanation as to what is theses phrases mean in the context of cosmology ?
  42. Demystifier

    A Can String Theory Finally Win a Nobel Prize?

    Given that Penrose now got the Nobel prize for a theory that is almost impossible to verify experimentally in a near future (that is, for theorems that predict singularities inside black holes), does it mean that now string theory can also get a Nobel prize? (If so, Witten and Schwarz would be...
  43. Redbelly98

    Insights Intro to Physically Reasonable Waves on a String

    Continue reading...
  44. A

    Comp Sci Problem with this Java string program

    Summary:: I'm having problem with this source code.we need to find the frequency of the number of words beginning with an UPPERCASE Alphabet in a sentence. The data members and member method must be according to the question given in the document. though i could compile it but it's giving...
  45. LCSphysicist

    Standing waves on a string -- Find the difference of phases

    The immediate thing i did here is ## \Delta \varphi = k(\Delta x) ## Interesting enough for a topic, if you use this equation you end up wrong like me, the answer is not D. Not sure what is the problem.
  46. A

    Comp Sci How to Structure Java String Code in a Static Main Method?

    here the class name is test153 sent is the sentence entered l is the length of the sentence w is the variable storing each word temporarily before printing.
  47. Iliody

    A Sum over backgrounds in String Theory

    Usually, I saw that string theory (perturbative, or matrix models) are made in a fixed background. Even if you consider that the metric is quantized and etc. there is an apparent physically motivated need for making a sum over topologies (manifolds, conifolds, orbifolds, and etc), for example...
  48. Y

    Please help with a problem displaying a string using pointers

    Hi I wrote a program to copy an array of C-String into dynamic memory in the function using pointers. I think I did it right, but I cannot display without garbage at the end of the string. //10.9 function copy C-String using pointer #include <iostream> using namespace std; void strCopy(char**...
  49. LCSphysicist

    A traveling wave on an infinite string, find the intensity

    The answer is about 40 Watts, but i am really not getting it: <Pot> = 0.5((pλ)(ωA)²)v p density linar λ wavelength ω angular frequency A amplitude v phase speed Why is this wrong? (I already tried too by <Pot> = Z*(ωA)²/2) Z is impedance
  50. Hamiltonian

    Does the tension in a string act on the body to which the pulley is attached?

    The normal reaction from the ground and from block m, the force of gravity are the forces I feel should act on the wedge but since the wedge is a perfectly rigid body and the pulley(which is massless) is attached to it so will tension also act on the wedge as well?
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