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212822 results in Engineering

Page 220 of 10642

  • 4 - Convolutional Codes

  • William E. Ryan, Zeta Associates, Shu Lin, University of California, Davis, Stephen G. Wilson, University of Virginia
  • Book:
    Channel Codes
    Published online:
    06 March 2025
    Print publication:
    21 November 2024, pp 166-234

  • Summary

    Channel coding lies at the heart of digital communication and data storage. Fully updated to include current innovations in the field, including a new chapter on polar codes, this detailed introduction describes the core theory of channel coding, decoding algorithms, implementation details, and performance analyses. This edition includes over 50 new end-of-chapter problems to challenge students and numerous new figures and examples throughout.

    The authors emphasize a practical approach and clearly present information on modern channel codes, including polar, turbo, and low-density parity-check (LDPC) codes, as well as detailed coverage of BCH codes, Reed–Solomon codes, convolutional codes, finite geometry codes, and product codes for error correction, providing a one-stop resource for both classical and modern coding techniques.

    Assuming no prior knowledge in the field of channel coding, the opening chapters begin with basic theory to introduce newcomers to the subject. Later chapters then begin with classical codes, continue with modern codes, and extend to advanced topics such as code ensemble performance analyses and algebraic LDPC code design.

    • 300 varied and stimulating end-of-chapter problems test and enhance learning, making this an essential resource for students and practitioners alike.

    • Provides a one-stop resource for both classical and modern coding techniques.

    • Starts with the basic theory before moving on to advanced topics, making it perfect for newcomers to the field of channel coding.

    • 180 worked examples guide students through the practical application of the theory.

  • 5 - Low-Density Parity-Check Codes

  • William E. Ryan, Zeta Associates, Shu Lin, University of California, Davis, Stephen G. Wilson, University of Virginia
  • Book:
    Channel Codes
    Published online:
    06 March 2025
    Print publication:
    21 November 2024, pp 235-280

  • Summary

    Channel coding lies at the heart of digital communication and data storage. Fully updated to include current innovations in the field, including a new chapter on polar codes, this detailed introduction describes the core theory of channel coding, decoding algorithms, implementation details, and performance analyses. This edition includes over 50 new end-of-chapter problems to challenge students and numerous new figures and examples throughout.

    The authors emphasize a practical approach and clearly present information on modern channel codes, including polar, turbo, and low-density parity-check (LDPC) codes, as well as detailed coverage of BCH codes, Reed–Solomon codes, convolutional codes, finite geometry codes, and product codes for error correction, providing a one-stop resource for both classical and modern coding techniques.

    Assuming no prior knowledge in the field of channel coding, the opening chapters begin with basic theory to introduce newcomers to the subject. Later chapters then begin with classical codes, continue with modern codes, and extend to advanced topics such as code ensemble performance analyses and algebraic LDPC code design.

    • 300 varied and stimulating end-of-chapter problems test and enhance learning, making this an essential resource for students and practitioners alike.

    • Provides a one-stop resource for both classical and modern coding techniques.

    • Starts with the basic theory before moving on to advanced topics, making it perfect for newcomers to the field of channel coding.

    • 180 worked examples guide students through the practical application of the theory.

  • 7 - Turbo Codes

  • William E. Ryan, Zeta Associates, Shu Lin, University of California, Davis, Stephen G. Wilson, University of Virginia
  • Book:
    Channel Codes
    Published online:
    06 March 2025
    Print publication:
    21 November 2024, pp 322-364

  • Summary

    Channel coding lies at the heart of digital communication and data storage. Fully updated to include current innovations in the field, including a new chapter on polar codes, this detailed introduction describes the core theory of channel coding, decoding algorithms, implementation details, and performance analyses. This edition includes over 50 new end-of-chapter problems to challenge students and numerous new figures and examples throughout.

    The authors emphasize a practical approach and clearly present information on modern channel codes, including polar, turbo, and low-density parity-check (LDPC) codes, as well as detailed coverage of BCH codes, Reed–Solomon codes, convolutional codes, finite geometry codes, and product codes for error correction, providing a one-stop resource for both classical and modern coding techniques.

    Assuming no prior knowledge in the field of channel coding, the opening chapters begin with basic theory to introduce newcomers to the subject. Later chapters then begin with classical codes, continue with modern codes, and extend to advanced topics such as code ensemble performance analyses and algebraic LDPC code design.

    • 300 varied and stimulating end-of-chapter problems test and enhance learning, making this an essential resource for students and practitioners alike.

    • Provides a one-stop resource for both classical and modern coding techniques.

    • Starts with the basic theory before moving on to advanced topics, making it perfect for newcomers to the field of channel coding.

    • 180 worked examples guide students through the practical application of the theory.

  • Acoustic interaction of a finite body in a rarefied gas: does sound reciprocity hold at non-continuum conditions?

  • A. Manela, Y. Ben-Ami
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A105
    • Article
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  • We study the effect of gas rarefaction on the interaction of small thermodynamic non-uniformities with a finite body. Considering a two-dimensional set-up, the initial system state is modelled as slight perturbations over its uniform density and temperature fields, prescribed in the vicinity of a thin plate. The problem is analysed in the collisionless limit and complemented by direct simulation Monte Carlo computations to cover the entire range of gas rarefaction rates. The high-Knudsen ‘sink-like’ and ‘source-like’ propagation patterns observed in the density- and temperature-driven set-ups, respectively, are discussed, together with the impact of specular (smooth) and diffuse (isothermal) wall reflections. At highly rarefied conditions, the solid body obstructs part of the gas domain, preventing the propagation of acoustic disturbances therein. With decreasing gas rarefaction, the acoustic field penetrates the obscured area via the effect of molecular collisions. Inspecting the near-field description, the propagation of flow disturbances along the plate surface is examined, and the acoustic force on the body is computed. In the thermally excited case, both normal- and shear-force components change sign at late times, attracting the plate towards the initial perturbation location. With reducing gas rarefaction, the shear force diminishes while the normal force sharply increases due to the decrease in signal decay. Finally, we apply the analysis to study the impact of gas rarefaction on acoustic reciprocity. Notably, acoustic reciprocity does not hold at non-continuum conditions over non-specular surfaces, where boundary reflections propagate in the presence of few molecular collisions, insufficient to retain reciprocal symmetry.

  • 10 - Polar Codes

  • William E. Ryan, Zeta Associates, Shu Lin, University of California, Davis, Stephen G. Wilson, University of Virginia
  • Book:
    Channel Codes
    Published online:
    06 March 2025
    Print publication:
    21 November 2024, pp 454-510

  • Summary

    Channel coding lies at the heart of digital communication and data storage. Fully updated to include current innovations in the field, including a new chapter on polar codes, this detailed introduction describes the core theory of channel coding, decoding algorithms, implementation details, and performance analyses. This edition includes over 50 new end-of-chapter problems to challenge students and numerous new figures and examples throughout.

    The authors emphasize a practical approach and clearly present information on modern channel codes, including polar, turbo, and low-density parity-check (LDPC) codes, as well as detailed coverage of BCH codes, Reed–Solomon codes, convolutional codes, finite geometry codes, and product codes for error correction, providing a one-stop resource for both classical and modern coding techniques.

    Assuming no prior knowledge in the field of channel coding, the opening chapters begin with basic theory to introduce newcomers to the subject. Later chapters then begin with classical codes, continue with modern codes, and extend to advanced topics such as code ensemble performance analyses and algebraic LDPC code design.

    • 300 varied and stimulating end-of-chapter problems test and enhance learning, making this an essential resource for students and practitioners alike.

    • Provides a one-stop resource for both classical and modern coding techniques.

    • Starts with the basic theory before moving on to advanced topics, making it perfect for newcomers to the field of channel coding.

    • 180 worked examples guide students through the practical application of the theory.

  • Linear dynamics in turbulent stratified plane Poiseuille flow

  • C.J. Lloyd, R.M. Dorrell
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A104
    • Article
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      • Open access
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  • We investigate a turbulent stratified plane Poiseuille flow using linear models and nonlinear simulations. We propose the first complete explanation for the prolific and coherent backward (BWs)- and forward-propagating waves (FWs), which have been observed in these flows. We demonstrate a significant presence of oblique waves in the channel core, particularly for the FWs. Critically, we show that neglect of spanwise structure leads to a distorted dispersion relation due to its strong dependence on the angle of obliquity. Interestingly, solutions to the Taylor–Goldstein equations show that wave dynamics is strongly dependent on shear, with only a weak dependence on buoyancy for the BWs at low and order-one wavenumbers, when the wavenumber is scaled by the channel half-height. As the wavenumber increases, waves transition from a shear-dominated regime to a buoyancy-dominated regime, with their dispersion relation tending towards that of idealised internal waves subject to a shear-free and constant-buoyancy-gradient flow, with a characteristic velocity and buoyancy frequency corresponding to respective centreline values in the channel. Finally, we show that the dominance of the BWs arises due to the external forcing of the system, whereby turbulent fluid ejected into the core has a lower momentum when compared with the local flow, therefore preferentially generating BWs in the channel. Qualitatively, channel-core dynamics can be reproduced with low-momentum forcing to a velocity profile with a velocity maximum and a corresponding negative second derivative intersecting a region of strong buoyancy gradient. This structure is inherent to a wide variety of jet-like environmental, atmospheric and industrial flows, suggesting that BWs are a critical control on dynamics of such flows.

  • 8 - Ensemble Enumerators for Turbo and LDPC Codes

  • William E. Ryan, Zeta Associates, Shu Lin, University of California, Davis, Stephen G. Wilson, University of Virginia
  • Book:
    Channel Codes
    Published online:
    06 March 2025
    Print publication:
    21 November 2024, pp 365-409

  • Summary

    Channel coding lies at the heart of digital communication and data storage. Fully updated to include current innovations in the field, including a new chapter on polar codes, this detailed introduction describes the core theory of channel coding, decoding algorithms, implementation details, and performance analyses. This edition includes over 50 new end-of-chapter problems to challenge students and numerous new figures and examples throughout.

    The authors emphasize a practical approach and clearly present information on modern channel codes, including polar, turbo, and low-density parity-check (LDPC) codes, as well as detailed coverage of BCH codes, Reed–Solomon codes, convolutional codes, finite geometry codes, and product codes for error correction, providing a one-stop resource for both classical and modern coding techniques.

    Assuming no prior knowledge in the field of channel coding, the opening chapters begin with basic theory to introduce newcomers to the subject. Later chapters then begin with classical codes, continue with modern codes, and extend to advanced topics such as code ensemble performance analyses and algebraic LDPC code design.

    • 300 varied and stimulating end-of-chapter problems test and enhance learning, making this an essential resource for students and practitioners alike.

    • Provides a one-stop resource for both classical and modern coding techniques.

    • Starts with the basic theory before moving on to advanced topics, making it perfect for newcomers to the field of channel coding.

    • 180 worked examples guide students through the practical application of the theory.

  • Classifications and scaling of generic shaped, steady and unsteady water bells formed by a jet impinging onto a vial

  • Javed Mohd, Amar Yadav, Debopam Das
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A96
    • Article
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      • Open access
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  • We present the results of a combined experimental and theoretical investigation of different fluid sheet structures formed during the impingement of a laminar liquid jet on a vial, with a slightly larger diameter than the jet and filled with the same liquid. The present set-up produces all diverse fluid sheet structures, unlike previous experiments that required a deflector disk resulting in no-slip and no-penetration boundary conditions. The water sheet structures are classified into four regimes; regime I: pre-sheet; regime II: puffing, characterized by the periodic formation and destruction of the upward-rising water sheet, an interesting observation not reported earlier; regime III, steady upward, inverted umbrella-like sheet structures; and regime IV, the formation of downward, umbrella-like sheet structures, which can be either open or closed, classically referred to as ‘water bells’. The water sheet structures observed are governed by the non-dimensional parameters: the ratio of vial diameter to the jet diameter at impact ($X$), the capillary number ($Ca$), the Weber number ($We$) and the Froude number ($Fr$). The parametric spaces $X-Ca$, $X-We$ and $X-Fr$ exhibit the demarcation of the four regimes. A semi-empirical expression for the ejection angle of the liquid sheet, primarily responsible for different shapes, is derived in a control volume that provides a theoretical basis for the identified regime diagrams. The puffing water bells in regime II are found to be quasi-steady as the experimental trajectories are in good agreement with the steady-state theory. The rise time of puffing water bells that determines the puffing frequency has been modelled.

  • Atomisation of an acoustically levitated droplet: experimental observations of myriad complex phenomena

  • S.K. Saroj, R.M. Thaokar
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A89
    • Article
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  • We report the dynamics of a droplet levitated in a multi-emitter, single-axis acoustic levitator. The deformation and atomisation behaviour of the droplet in the acoustic field displays myriad complex phenomena, in a series of events. These include the primary breakup of the droplet, wherein it exhibits stable levitation, deformation, sheet formation and equatorial atomisation, followed by its secondary breakup, which could be of various types such as umbrella, bag, bubble or multi-stage breakup. A large number of tiny atomised droplets, formed as a result of the primary and secondary breakup, can remain levitated in the acoustic levitator and exhibit aggregation and coalescence. The visualisation of the interfacial instabilities on the surface of the liquid sheet using both side- and top-view imaging is presented. An approximate size distribution of the atomised droplets is also provided. The stable levitation of the droplet is due to a balance of acoustic and gravitational forces while the resulting ellipsoidal shape of the droplet is a consequence of the balance of the deforming acoustic force and the restoring capillary force. Stronger acoustic forces can no longer be balanced by capillary forces, resulting in a highly flattened droplet, with a thin liquid sheet at the edge (equatorial region). The thinning of the sheet is caused by the differential acceleration induced by the increasing pressure difference between the poles and the equator as the sheet deforms. When the sheet thickness reduces to of the order of a few microns, Faraday waves develop at the thinnest region (preceding the rim), which causes the generation of tiny-sized droplets that are ejected perpendicular to the sheet. The corresponding hole formation results in a perforated sheet that causes the detachment of the annular rim, which breaks due to Rayleigh–Plateau (RP) instability. The radial ligaments generated in the sheet, possibly due to Rayleigh–Taylor (RT) instability, break into droplets of different sizes. The secondary breakup exhibits Weber number dependency and includes umbrella, bag, bubble or multi-stage types, ultimately resulting in the complete atomisation of the droplets. Both the primary and the secondary breakup of the droplet involve interfacial instabilities such as Faraday, Kelvin–Helmholtz, RT and RP and are well supported by visual evidence.

  • Upper bound of heat flux in an anelastic model for Rayleigh–Bénard convection

  • T. Alboussière, Y. Ricard, S. Labrosse
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A94
    • Article
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      • Open access
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  • Bounds on heat transfer have been the subject of previous studies concerning convection in the Boussinesq approximation: in the Rayleigh–Bénard configuration, the first result obtained by Howard (J. Fluid Mech., vol. 17, issue 3, 1963, pp. 405–432) states that the dimensionless heat flux $\textit {Nu}$ carried out by convection is such that $\textit {Nu} < (3/64 \ Ra)^{1/2}$ for large values of the Rayleigh number $Ra$, independently of the Prandtl number $Pr$. This is still the best-known upper bound, only with the prefactor improved to $\textit {Nu} -1 < 0.02634 \ Ra^{1/2}$ by Plasting & Kerswell (J. Fluid Mech., vol. 477, 2003, pp. 363–379). In the present paper, this result is extended to compressible convection. An upper bound is obtained for the anelastic liquid approximation, which is similar to an anelastic model used in astrophysics based on a turbulent diffusivity for entropy. The anelastic bound is still scaling as $Ra^{1/2}$, independently of $Pr$, but depends on the dissipation number $\mathcal {D}$ and on the equation of state. For monatomic gases and large Rayleigh numbers, the bound is $\textit {Nu} < 25.8\, Ra^{{1}/{2}} / (1-\mathcal {D}/2 )^{{5}/{2}}$.

  • Flows over a spinning disc at incidence

  • Abdullah M. Kuraan, Ömer Savaş
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A95
    • Article
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      • Open access
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  • Flows over a disc are studied in a wind tunnel over incidence angles between $0^\circ \text { and }36^\circ$, a Reynolds number of $2.7 \times 10^4$ and rotational speed ratios of $0\unicode{x2013}10$. Smoke-wire visualization, particle image velocimetry and hot-film anemometry are employed. Two vortex shedding modes originating from the upstream surface of the disc are observed. The first is dominant at incidence angles up to ${\sim }21^\circ$. Beyond $21^\circ$, the second mode dominates. It appears as a soliton on the vortices and has a shedding frequency nearly twice that of the first at the highest incidence angle. The Strouhal number monotonically increases with incidence angle from approximately 0.2 to 0.4. Spectral analysis of the hot-film measurements confirms the findings from flow visualization experiments. Flows over the spinning disc generally mimic the stationary disc flows; however, centrifugal forces lead to cross-stream instability features that may be attributed to spiral wave instabilities intrinsic to the boundary layers in rotating flows. Velocity measurements are used to construct streamline patterns to compare with the smoke streaklines. The unsteadiness of the flows results in large variances. Mean strain rates are extracted from velocity data, where the fixed disc case at normal incidence compares well with theoretical predictions. The unsteady boundary layer thickness over the fixed disc, however, is approximately twice that predicted by theory for steady flow, stemming from the dominance of large unsteady vortices. Limited comparisons are made of the Strouhal numbers from experiments and numerical calculations in the literature.

  • 1 - Introductory Concepts

  • Stelios Rigopoulos, Imperial College London
  • Book:
    Population Balance of Particles in Flows
    Published online:
    14 November 2024
    Print publication:
    21 November 2024, pp 1-23

  • Summary

    The population balance is introduced as an approach for modelling problems involving a population of particles with a distribution of one or more properties. Numerous applications are identified. The general methodology of applying the population balance in four basic steps is introduced. Basic concepts such as distributions, choice of distributed variables, kinetic and transport processes and the coupling of the population balance with fluid dynamics, are also introduced.

  • The 2.5-dimensional turbulence in shear-thinning jets

  • Christian Amor, Giovanni Soligo, Andrea Mazzino, Marco E. Rosti
  • Journal:
    Journal of Fluid Mechanics / Volume 999 / 25 November 2024
    Published online by Cambridge University Press:
    21 November 2024, A102
    • Article
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  • The dimensional transition in turbulent jets of a shear-thinning fluid is studied via direct numerical simulations. Our findings reveal that under vertical confinement, the flow exhibits a unique mixed-dimensional (or 2.5-dimensional) state, where large-scale two-dimensional and small-scale three-dimensional structures coexist. This transition from three-dimensional turbulence near the inlet to two-dimensional dynamics downstream is dictated by the level of confinement: weak confinement guarantees turbulence to remain three-dimensional, whereas strong confinement forces the transition to two dimensions; the mixed-dimensional state is observed for moderate confinement and it emerges as soon as flow scales are larger than the vertical length. In this scenario, we observed that the mixed-dimensional state is an overall more energetic state, and it shows a multi-cascade process, where the direct cascade of energy at small scales and the direct cascade of enstrophy at large scales coexist. The results provide insights into the complex dynamics of confined turbulent flows, relevant in both natural and industrial settings.

  • 2 - Technology and Cancer in the Twenty-First Century

  • Nirmala Ramanujam, Duke University, North Carolina, Brian Crouch, Duke University, North Carolina
  • Book:
    Biomedical Engineering for Global Health
    Published online:
    20 December 2024
    Print publication:
    21 November 2024, pp 31-73

  • Summary

    Explore the fundamentals of biomedical engineering technologies with this thought-provoking introduction, framed around modern-day global cancer inequities. Connecting engineering principles to real-world global health scenarios, this textbook introduces major technological advances in cancer care through the lens of global health inequity, discusses how promising new technologies can address this inequity, and demonstrates how novel medical technologies are adopted for real-world clinical use. It includes modular chapters designed to enable a flexible pathway through the material for students from a wide range of backgrounds; boxed discussion of contemporary issues in engineering for global health, encouraging students to explore ethical questions related to science and society; supplementary lab modules for hands-on experience in translating engineering principles into healthcare solutions; and over 200 end-of-chapter problems targeting multiple learning outcomes to solidify student understanding. Designed to equip students with all the critical, technical, and ethical knowledge they need to excel, this is the ideal introduction for students in biomedical engineering and global health.

  • 10 - The Evolution of Healthcare in the Twenty-First Century

  • Nirmala Ramanujam, Duke University, North Carolina, Brian Crouch, Duke University, North Carolina
  • Book:
    Biomedical Engineering for Global Health
    Published online:
    20 December 2024
    Print publication:
    21 November 2024, pp 344-368

  • Summary

    Explore the fundamentals of biomedical engineering technologies with this thought-provoking introduction, framed around modern-day global cancer inequities. Connecting engineering principles to real-world global health scenarios, this textbook introduces major technological advances in cancer care through the lens of global health inequity, discusses how promising new technologies can address this inequity, and demonstrates how novel medical technologies are adopted for real-world clinical use. It includes modular chapters designed to enable a flexible pathway through the material for students from a wide range of backgrounds; boxed discussion of contemporary issues in engineering for global health, encouraging students to explore ethical questions related to science and society; supplementary lab modules for hands-on experience in translating engineering principles into healthcare solutions; and over 200 end-of-chapter problems targeting multiple learning outcomes to solidify student understanding. Designed to equip students with all the critical, technical, and ethical knowledge they need to excel, this is the ideal introduction for students in biomedical engineering and global health.

  • 7 - From Technology to Translation

  • Nirmala Ramanujam, Duke University, North Carolina, Brian Crouch, Duke University, North Carolina
  • Book:
    Biomedical Engineering for Global Health
    Published online:
    20 December 2024
    Print publication:
    21 November 2024, pp 219-264

  • Summary

    Explore the fundamentals of biomedical engineering technologies with this thought-provoking introduction, framed around modern-day global cancer inequities. Connecting engineering principles to real-world global health scenarios, this textbook introduces major technological advances in cancer care through the lens of global health inequity, discusses how promising new technologies can address this inequity, and demonstrates how novel medical technologies are adopted for real-world clinical use. It includes modular chapters designed to enable a flexible pathway through the material for students from a wide range of backgrounds; boxed discussion of contemporary issues in engineering for global health, encouraging students to explore ethical questions related to science and society; supplementary lab modules for hands-on experience in translating engineering principles into healthcare solutions; and over 200 end-of-chapter problems targeting multiple learning outcomes to solidify student understanding. Designed to equip students with all the critical, technical, and ethical knowledge they need to excel, this is the ideal introduction for students in biomedical engineering and global health.

Page 220 of 10642