The Experts below are selected from a list of 57 Experts worldwide ranked by ideXlab platform

Daniel J. Gershman - One of the best experts on this subject based on the ideXlab platform.

  • Energy Conversion Within Current Sheets in the Earth's Quasi‐Parallel Magnetosheath
    Geophysical Research Letters, 2021
    Co-Authors: Steven J. Schwartz, Harald Kucharek, Charles J. Farrugia, K. J. Trattner, Imogen Gingell, Robert Ergun, Robert J. Strangeway, Daniel J. Gershman
    Abstract:

    Shock waves in collisionless plasmas rely on kinetic processes to convert the primary Incident bulk flow Energy into thermal Energy. That conversion is initiated within a thin transition layer but may continue well into the downstream region. At the Earth's bow shock, the region downstream of shock locations where the interplanetary magnetic field is nearly parallel to the shock normal is highly turbulent. We study the distribution of thin current events in this magnetosheath. Quantification of the Energy dissipation rate made by the Magnetospheric Multiscale spacecraft shows that these isolated intense currents are distributed uniformly throughout the magnetosheath and convert a significant fraction (5%–11%) of the Energy Flux Incident at the bow shock.

David H. Wolpert - One of the best experts on this subject based on the ideXlab platform.

  • Extending Landauer’s bound from bit erasure to arbitrary computation
    Bulletin of the American Physical Society, 2017
    Co-Authors: David H. Wolpert
    Abstract:

    Recent analyses have calculated the minimal thermodynamic work required to perform a computation pi when two conditions hold: the output of pi is independent of its input (e.g., as in bit erasure); we use a physical computer C to implement pi that is specially tailored to the environment of C, i.e., to the precise distribution over C's inputs, P_0. First I extend these analyses to calculate the work required even if the output of pi depends on its input, and even if C is not used with the distribution P_0 it was tailored for. Next I show that if C will be re-used, then the minimal work to run it depends only on the logical computation pi, independent of the physical details of C. This establishes a formal identity between the thermodynamics of (re-usable) computers and theoretical computer science. I use this identity to prove that the minimal work required to compute a bit string sigma on a "general purpose computer" rather than a special purpose one, i.e., on a universal Turing machine U, is k_BT ln(2) times the sum of three terms: The Kolmogorov complexity of sigma, log of the Bernoulli measure of the set of strings that compute sigma, and log of the halting probability of U. I also prove that using C with a distribution over environments results in an unavoidable increase in the work required to run the computer, even if it is tailored to the distribution over environments. I end by using these results to relate the free Energy Flux Incident on an organism / robot / biosphere to the maximal amount of computation that the organism / robot / biosphere can do per unit time.

  • Minimal work required for arbitrary computation
    arXiv: Statistical Mechanics, 2015
    Co-Authors: David H. Wolpert
    Abstract:

    Recent studies have analyzed the minimal thermodynamic work required for a given logical map to be implemented on any physical system. These studies have focused on maps whose output does not depend on the input, e.g., bit erasure in a digital computer. In addition, they have considered physical systems whose design varies depending on the distribution of inputs to the map. However very often we are interested in implementing a map whose output depends on its input. In addition, we often want our system to implement the same map even if the system's environment changes, so that the distribution over map inputs changes. Here I introduce a thermodynamic engine that satisfies both of these desiderata. I then calculate how much work it requires, deriving an additive correction to the "generalized Landauer bound" of previous studies. I also calculate the Bayes-optimal engine for any given distribution over environments. I end with a short discussion on how these results relate the free Energy Flux Incident on an organism / robot / biosphere to the maximal amount of (noisy) computation that the organism / robot / biosphere can do per unit time.

  • Extending Landauer's Bound from Bit Erasure to Arbitrary Computation
    arXiv: Statistical Mechanics, 2015
    Co-Authors: David H. Wolpert
    Abstract:

    Recent analyses have calculated the minimal thermodynamic work required to perform a computation pi when two conditions hold: the output of pi is independent of its input (e.g., as in bit erasure); we use a physical computer C to implement pi that is specially tailored to the environment of C, i.e., to the precise distribution over C's inputs, P_0. First I extend these analyses to calculate the work required even if the output of pi depends on its input, and even if C is not used with the distribution P_0 it was tailored for. Next I show that if C will be re-used, then the minimal work to run it depends only on the logical computation pi, independent of the physical details of C. This establishes a formal identity between the thermodynamics of (re-usable) computers and theoretical computer science. I use this identity to prove that the minimal work required to compute a bit string sigma on a "general purpose computer" rather than a special purpose one, i.e., on a universal Turing machine U, is k_BT ln(2) times the sum of three terms: The Kolmogorov complexity of sigma, log of the Bernoulli measure of the set of strings that compute sigma, and log of the halting probability of U. I also prove that using C with a distribution over environments results in an unavoidable increase in the work required to run the computer, even if it is tailored to the distribution over environments. I end by using these results to relate the free Energy Flux Incident on an organism / robot / biosphere to the maximal amount of computation that the organism / robot / biosphere can do per unit time.

  • Extending Landauer's Bound to Arbitrary Computation
    2015
    Co-Authors: David H. Wolpert
    Abstract:

    Recent analyses have calculated the minimal thermodynamic work required to perform a computation pi when two conditions hold: the output of pi is independent of its input (e.g., as in bit erasure); we use a physical computer C to implement pi that is specially tailored to the environment of C, i.e., to the precise distribution over C's inputs, P_0. First I extend these analyses to calculate the work required even if the output of pi depends on its input, and even if C is not used with the distribution P_0 it was tailored for. Next I show that if C will be re-used, then the minimal work to run it depends only on the logical computation pi, independent of the physical details of C. This establishes a formal identity between the thermodynamics of (re-usable) computers and theoretical computer science. I use this identity to prove that the minimal work required to compute a bit string sigma on a "general purpose computer" rather than a special purpose one, i.e., on a universal Turing machine U, is k_BT ln(2) times the sum of three terms: The Kolmogorov complexity of sigma, log of the Bernoulli measure of the set of strings that compute sigma, and log of the halting probability of U. I also prove that using C with a distribution over environments results in an unavoidable increase in the work required to run the computer, even if it is tailored to the distribution over environments. I end by using these results to relate the free Energy Flux Incident on an organism / robot / biosphere to the maximal amount of computation that the organism / robot / biosphere can do per unit time.

M Papini - One of the best experts on this subject based on the ideXlab platform.

  • the effect of inter particle collisions in erosive streams on the distribution of Energy Flux Incident to a flat surface
    Tribology International, 2004
    Co-Authors: C Gomesferreira, D Ciampini, M Papini
    Abstract:

    Abstract The effect of interference between Incident spheres in a stream, and those rebounding from a flat surface on the distribution of Incident Energy Flux to the surface was determined for a typical erosion testing apparatus using a previously described computer simulation. A dimensional analysis allowed for presentation of the results in a generalized format, so that they could be used to assess interference effects under varying input parameters. Under conditions in which less than 50% of the Incident particles underwent inter-particle collisions, expressions describing the impact velocity, the striking angle and the spatial distribution of impacting particles were derived as a function of process parameters. Compared to the no-interference case, the Incident Energy Flux was found to significantly decrease near the center of the impacting stream, but increase far from the centre, when Incident parameters that tended to reduce the space between particles in the Incident stream were varied. Implications for erosion test ing and expected initial erosion profile were discussed.

Steven J. Schwartz - One of the best experts on this subject based on the ideXlab platform.

  • Energy Conversion Within Current Sheets in the Earth's Quasi‐Parallel Magnetosheath
    Geophysical Research Letters, 2021
    Co-Authors: Steven J. Schwartz, Harald Kucharek, Charles J. Farrugia, K. J. Trattner, Imogen Gingell, Robert Ergun, Robert J. Strangeway, Daniel J. Gershman
    Abstract:

    Shock waves in collisionless plasmas rely on kinetic processes to convert the primary Incident bulk flow Energy into thermal Energy. That conversion is initiated within a thin transition layer but may continue well into the downstream region. At the Earth's bow shock, the region downstream of shock locations where the interplanetary magnetic field is nearly parallel to the shock normal is highly turbulent. We study the distribution of thin current events in this magnetosheath. Quantification of the Energy dissipation rate made by the Magnetospheric Multiscale spacecraft shows that these isolated intense currents are distributed uniformly throughout the magnetosheath and convert a significant fraction (5%–11%) of the Energy Flux Incident at the bow shock.

C Gomesferreira - One of the best experts on this subject based on the ideXlab platform.

  • the effect of inter particle collisions in erosive streams on the distribution of Energy Flux Incident to a flat surface
    Tribology International, 2004
    Co-Authors: C Gomesferreira, D Ciampini, M Papini
    Abstract:

    Abstract The effect of interference between Incident spheres in a stream, and those rebounding from a flat surface on the distribution of Incident Energy Flux to the surface was determined for a typical erosion testing apparatus using a previously described computer simulation. A dimensional analysis allowed for presentation of the results in a generalized format, so that they could be used to assess interference effects under varying input parameters. Under conditions in which less than 50% of the Incident particles underwent inter-particle collisions, expressions describing the impact velocity, the striking angle and the spatial distribution of impacting particles were derived as a function of process parameters. Compared to the no-interference case, the Incident Energy Flux was found to significantly decrease near the center of the impacting stream, but increase far from the centre, when Incident parameters that tended to reduce the space between particles in the Incident stream were varied. Implications for erosion test ing and expected initial erosion profile were discussed.