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Cole–Cole Equation
The Cole–Cole equation is a relaxation model that is often used to describe dielectric relaxation in polymers. It is given by the equation : \varepsilon^*(\omega) = \varepsilon_\infty + \frac where \varepsilon^* is the complex dielectric constant, \varepsilon_s and \varepsilon_\infty are the "static" and "infinite frequency" dielectric constants, \omega is the angular frequency and \tau is a time constant. The exponent parameter \alpha, which takes a value between 0 and 1, allows the description of different spectral shapes. When \alpha=0, the Cole-Cole model reduces to the Debye model. When \alpha>0, the relaxation is ''stretched''. That is, it extends over a wider range on a logarithmic \omega scale than Debye relaxation. The separation of the complex dielectric constant \varepsilon(\omega) was reported in the original paper by Kenneth Stewart Cole and Robert Hugh Cole as follows: \varepsilon' = \varepsilon_\infty+ (\varepsilon_s-\varepsilon_\infty)\frac \varepsilon''= ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relaxation (physics)
In the physical sciences, relaxation usually means the return of a perturbed system into equilibrium. Each relaxation process can be categorized by a relaxation time τ. The simplest theoretical description of relaxation as function of time ''t'' is an exponential law (exponential decay A quantity is subject to exponential decay if it decreases at a rate proportional to its current value. Symbolically, this process can be expressed by the following differential equation, where is the quantity and (lambda) is a positive rate ...). In simple linear systems Mechanics: Damped unforced oscillator Let the homogeneous differential equation: :m\frac+\gamma\frac+ky=0 model damped harmonic oscillator, damped unforced oscillations of a weight on a spring. The displacement will then be of the form y(t) = A e^ \cos(\mu t - \delta). The constant T (=2m/\gamma) is called the relaxation time of the system and the constant μ is the quasi-frequency. Electronics: RC circuit In an RC ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dielectric Relaxation
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor, because they have no loosely bound, or free, electrons that may drift through the material, but instead they shift, only slightly, from their average equilibrium positions, causing dielectric polarisation. Because of dielectric polarisation, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field (for example, if the field is moving parallel to the positive ''x'' axis, the negative charges will shift in the negative ''x'' direction). This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarise ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compounds, produces unique physical properties including toughness, high elasticity, viscoelasticity, and a tendency to form amorphous and semicrystalline structures rather than crystals. The term "polymer" derives from the Greek word πολύς (''polus'', meaning "many, much") and μέρος (''meros'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dielectric Constant
The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field. Permittivity is a material's property that affects the Coulomb force between two point charges in the material. Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum. Likewise, relative permittivity is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has vacuum as its dielectric. Relative permittivity is also commonly known as the dielectric constant, a term still used but deprecated by standards organizations in engineering as well as in chemistry. Definition Relative permittivity is typically denoted as (sometimes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angular Frequency
In physics, angular frequency "''ω''" (also referred to by the terms angular speed, circular frequency, orbital frequency, radian frequency, and pulsatance) is a scalar measure of rotation rate. It refers to the angular displacement per unit time (for example, in rotation) or the rate of change of the phase of a sinusoidal waveform (for example, in oscillations and waves), or as the rate of change of the argument of the sine function. Angular frequency (or angular speed) is the magnitude of the pseudovector quantity angular velocity.(UP1) One turn is equal to 2''π'' radians, hence \omega = \frac = , where: *''ω'' is the angular frequency (unit: radians per second), *''T'' is the period (unit: seconds), *''f'' is the ordinary frequency (unit: hertz) (sometimes ''ν''). Units In SI units, angular frequency is normally presented in radians per second, even when it does not express a rotational value. The unit hertz (Hz) is dimensionally equivalent, but by convention it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dielectric
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor, because they have no loosely bound, or free, electrons that may drift through the material, but instead they shift, only slightly, from their average equilibrium positions, causing dielectric polarisation. Because of dielectric polarisation, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field (for example, if the field is moving parallel to the positive ''x'' axis, the negative charges will shift in the negative ''x'' direction). This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polaris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kenneth Stewart Cole
Kenneth Stewart Cole (July 10, 1900 – April 18, 1984) was an American biophysicist described by his peers as "a pioneer in the application of physical science to biology". Cole was awarded the National Medal of Science in 1967. Biography He was born on July 10, 1900 in Ithaca, New York to Charles Nelson Cole, an instructor in Latin at Cornell University and Mabel Stewart. Kenneth had a younger brother, , with whom he remained very close throughout his life despite a large difference in age; they were joint authors of four papers published between 1936 and 1942. In 1902 the family moved to Oberlin, Ohio, when his father took a post at Oberlin College. His father would later become the Dean. Kenneth's mother was, and Cole graduated from Oberlin College in 1922 and received a Ph.D. in physics with Floyd K. Richtmyer from Cornell University in 1926. He spent summers working at the General Electric laboratory in Schenectady, New York. In 1932, Cole married Elizabeth Evans Roberts, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Havriliak–Negami Relaxation
The Havriliak–Negami relaxation is an empirical modification of the Debye relaxation model in electromagnetism. Unlike the Debye model, the Havriliak–Negami relaxation accounts for the asymmetry and broadness of the dielectric dispersion curve. The model was first used to describe the dielectric relaxation of some polymers, by adding two exponential parameters to the Debye equation: : \hat(\omega) = \varepsilon_ + \frac, where \varepsilon_ is the permittivity at the high frequency limit, \Delta\varepsilon = \varepsilon_-\varepsilon_ where \varepsilon_ is the static, low frequency permittivity, and \tau is the characteristic relaxation time of the medium. The exponents \alpha and \beta describe the asymmetry and broadness of the corresponding spectra. Depending on application, the Fourier transform of the stretched exponential function can be a viable alternative that has one parameter less. For \beta = 1 the Havriliak–Negami equation reduces to the Cole–Cole equation, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
