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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Prismatic Beams: Problem Solving01:15

Prismatic Beams: Problem Solving

In the design of a supported timber beam subjected to a distributed load, both the beam's physical dimensions and the timber's characteristics, such as its grade and species, are critical. These factors determine the allowable stress values, which are crucial for calculating the necessary beam depth to ensure structural integrity and safety.
The design begins with analyzing the beam as a free body to identify moments and force balances, thereby determining support reactions. Next, the designer...

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Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light
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Nonlinear prism coupling with nonlocality.

G Vitrant, R Reinisch, J C Paumier

    Optics Letters
    |September 16, 2009
    PubMed
    Summary
    This summary is machine-generated.

    Researchers studied prism coupling in nonlinear waveguides with diffusive nonlinearities. They found that nonlocal nonlinearity leads to bistability, with a threshold dependent on diffusion length and angular detuning.

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    Area of Science:

    • Nonlinear optics
    • Waveguide theory
    • Condensed matter physics

    Background:

    • Nonlinear waveguides are crucial for optical devices.
    • Diffusive nonlinearities, like thermal effects, introduce nonlocal behavior.
    • Understanding beam coupling in these systems is essential for device design.

    Purpose of the Study:

    • To investigate prism coupling of finite-width beams into nonlinear waveguides with diffusive nonlinearities.
    • To analyze the impact of nonlocal nonlinearity on waveguide behavior.
    • To determine the relationship between diffusion length, angular detuning, and bistability.

    Main Methods:

    • Numerical calculation of prism coupling characteristics.
    • Inclusion of a one-dimensional diffusion equation to model nonlocal nonlinearity.
    • Analysis of longitudinal feedback effects.

    Main Results:

    • Prism coupling in nonlinear waveguides with diffusive nonlinearities exhibits bistability.
    • The observed bistability arises from longitudinal feedback due to nonlocal nonlinearity.
    • The threshold for minimum diffusion length is inversely proportional to angular detuning.

    Conclusions:

    • Nonlocal nonlinearity significantly influences beam coupling in waveguides.
    • Bistability is a key characteristic of such systems.
    • Control over diffusion length and angular detuning can manage waveguide behavior.